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Water, Volume 13, Issue 9 (May-1 2021) – 195 articles

Cover Story (view full-size image): The high visual quality of lakes supports aesthetic and recreational experiences. This study assessed people’s preferences regarding visual characteristics of mountain lakes. We used a photo-based questionnaire including different picture sets related to water clarity, water colour, presence of algae, lake shore, and surrounding land cover. Our results indicate a strong preference for blue and clear water without algae. Most preferred were large rocks at the lake shore and forest around the lake. This study also exemplifies the quantification of aesthetic value for four selected study lakes in the European Alps, integrating the results with spatial and limnological data. View this paper
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37 pages, 380 KiB  
Review
A Comprehensive Review on Membrane Fouling: Mathematical Modelling, Prediction, Diagnosis, and Mitigation
by Nour AlSawaftah, Waad Abuwatfa, Naif Darwish and Ghaleb Husseini
Water 2021, 13(9), 1327; https://doi.org/10.3390/w13091327 - 11 May 2021
Cited by 156 | Viewed by 18368
Abstract
Membrane-based separation has gained increased popularity over the past few decades, particularly reverse osmosis (RO). A major impediment to the improved performance of membrane separation processes, in general, is membrane fouling. Fouling has detrimental effects on the membrane’s performance and integrity, as the [...] Read more.
Membrane-based separation has gained increased popularity over the past few decades, particularly reverse osmosis (RO). A major impediment to the improved performance of membrane separation processes, in general, is membrane fouling. Fouling has detrimental effects on the membrane’s performance and integrity, as the deposition and accumulation of foulants on its surface and/or within its pores leads to a decline in the permeate flux, deterioration of selectivity, and permeability, as well as a significantly reduced lifespan. Several factors influence the fouling-propensity of a membrane, such as surface morphology, roughness, hydrophobicity, and material of fabrication. Generally, fouling can be categorized into particulate, organic, inorganic, and biofouling. Efficient prediction techniques and diagnostics are integral for strategizing control, management, and mitigation interventions to minimize the damage of fouling occurrences in the membranes. To improve the antifouling characteristics of RO membranes, surface enhancements by different chemical and physical means have been extensively sought after. Moreover, research efforts have been directed towards synthesizing membranes using novel materials that would improve their antifouling performance. This paper presents a review of the different membrane fouling types, fouling-inducing factors, predictive methods, diagnostic techniques, and mitigation strategies, with a special focus on RO membrane fouling. Full article
(This article belongs to the Section Water and One Health)
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21 pages, 3689 KiB  
Article
Systematic Design, Optimization, and Sustainability Assessment for Generation of Efficient Wastewater Treatment Networks
by Emmanuel A. Aboagye, Sean M. Burnham, James Dailey, Rohan Zia, Carley Tran, Maya Desai and Kirti M. Yenkie
Water 2021, 13(9), 1326; https://doi.org/10.3390/w13091326 - 10 May 2021
Cited by 13 | Viewed by 4282
Abstract
Due to population growth and economic development, there has been an increase in global wastewater (WW) generation footprint. There are different technologies associated with the wastewater treatment (WWT) process. The challenge is to select technologies that minimize the cost of treatment, as well [...] Read more.
Due to population growth and economic development, there has been an increase in global wastewater (WW) generation footprint. There are different technologies associated with the wastewater treatment (WWT) process. The challenge is to select technologies that minimize the cost of treatment, as well as meet purity requirements. Further, there is a need to integrate sustainability analysis to facilitate a holistic decision. With the application of systems engineering, sustainable and cost-effective solutions can be achieved. In this work, we apply systems engineering to generate a sustainable and cost-effective solution. A superstructure was generated by categorizing technologies into four treatment stages. After modeling all functional equations for each technology, an optimization problem was formulated to determine the best path for the treatment process. Mixed-integer non-linear programming (MINLP), which implements a 0–1 binary integer constraint for active/inactive technologies at each stage was used. Sustainability analysis was performed for each representative case study (municipal and pharmaceutical WWT) using the sustainable process index (SPI). The total cost of municipal WWT is 1.92 USD/m3, while that for the pharmaceutical WWT is 3.44 USD/m3. With the treatment of WW, there is a reduction of over 90% ecological burden based on the SPI metric. Full article
(This article belongs to the Section Wastewater Treatment and Reuse)
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<p>The three major types of categories for WWT.</p> Full article ">Figure 2
<p>Stage-wise WWT and some typical technologies. Technologies are classified based on their efficiencies, driving force for separation, and type of contaminant removal.</p> Full article ">Figure 3
<p>Overall superstructure for WW treatment. The treatment technologies are flocculation (Flc), sedimentation (Sdm), filtration (Ftt), adsorption (Ads), activated sludge (Asl), rotating biological containers (Rbc), disinfection (Dis), membrane bioreactor (Mbrt), advanced oxidation processes (Aop), bleaching (Blc), and membrane processes (Mbr). Bypass (Byp 1,2,3,4) streams become active if a stage does not apply to the treatment process.</p> Full article ">Figure 4
<p>Optimal path selected for municipal WWT through GAMS. Flocculation (Flc), sedimentation (Sdm), adsorption (Ads), and bleaching (Blc) are the selected technologies. The tertiary stage contributes a percentage of 45.03% to the total cost, followed by the pretreatment, secondary, and primary stages, respectively.</p> Full article ">Figure 5
<p>Percentage stage-wise cost for municipal WWT. TC is the total treatment cost. It can be noted that the material cost contributes the highest cost to the total treatment cost. Therefore, other alternatives can be used to lower the cost contribution of the materials.</p> Full article ">Figure 6
<p>Optimal network path and cost distribution for pharmaceutical WWT case study. Selected technologies are flocculation (Flc), filtration (granular) (Ftt), and adsorption (Ads).</p> Full article ">Figure 7
<p>Percentage distribution of the various cost categories for pharmaceutical WWT case study. Other costs from the primary stage dominated the overall cost of treatment.</p> Full article ">Figure 8
<p>Sustainable process index (SPI) for the various scenarios. (MWWT = municipal wastewater treatment; DDMWW = direct disposal of municipal wastewater; PWWT = pharmaceutical wastewater treatment; DDPWW = direct disposal of pharmaceutical wastewater).</p> Full article ">
22 pages, 3514 KiB  
Article
Linking Microbial Functioning and Trophic Pathways to Ecological Status in a Coastal Mediterranean Ecosystem
by Franco Decembrini, Carmela Caroppo, Gabriella Caruso and Alessandro Bergamasco
Water 2021, 13(9), 1325; https://doi.org/10.3390/w13091325 - 10 May 2021
Cited by 9 | Viewed by 3161
Abstract
Coastal marine ecosystems host complex microbial communities whose composition and metabolism are influenced by continental inputs and mesoscale properties of seawater masses. The identifying traits of the phytoplankton and bacteria such as biomass, size, shape and their metabolism related to organic matter production [...] Read more.
Coastal marine ecosystems host complex microbial communities whose composition and metabolism are influenced by continental inputs and mesoscale properties of seawater masses. The identifying traits of the phytoplankton and bacteria such as biomass, size, shape and their metabolism related to organic matter production and degradation, recognized as indicators of the functioning of an ecosystem, were observed in the Gulf of Manfredonia (South Adriatic Sea, Italy) in late spring. This Gulf area is characterized by terrestrial inputs and mesoscale circulation influence such as coastal waters flowing southward from the North Adriatic and offshore waters interested by the Ionian Sea. Water samples were grouped in clusters (Coastal, Intermediate, Offshore and Deep Systems) according to the water column properties. Phytoplankton community biomass and composition, autotrophic and total prokaryotic abundances and microbial metabolism such as enzyme activity rates and prokaryotic heterotrophic production were analyzed to elucidate the trophic pathways with the objective to infer on the ecosystem status. As expected, size-fractionated phytoplankton biomass and production showed greater concentration in coastal waters with prevalence of the largest fractions (micro- and nano-) supported by the diatoms. Conversely, lower biomass and production were measured in all off-shore waters, mainly sustained by smallest fractions (nano-sized phytoflagellates and picophytoplankton). Total and autotrophic prokaryotic abundance decreased from coastal to offshore stations, inversely with respect to cell volume. Prokaryotic heterotrophic production was just below 50% compared to that of phytoplankton in all waters, evidencing an active biomass synthesis. High alkaline phosphatase and leucine aminopeptidase in coastal and offshore waters suggested the quick regeneration of Phosphorus and protein decomposition, respectively. Different levels of phytoplankton-bacteria association might provide a tool to define the ecological status of the studied system in the observed period; an approach to ecosystem assessment exportable to other coastal systems is proposed. Full article
(This article belongs to the Special Issue Advances in Water Quality Monitoring and Assessment in Marine and Coastal Regions)
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<p>Location of sampling stations in the Gulf of Manfredonia (South Adriatic Sea). The continuous arrows show the paths of the main currents: the Adriatic Surface Water (ASW) characterized by relatively low salinity due to riverine inputs flows geostrophically South-Eastward along the Italian coast and is called Western Adriatic Current (WAC); in the lee side of the Gargano promontory, a slow anticyclonic recirculation cell is induced in the Gulf. The Adriatic Deep Water (ADW, indicated by dashed arrows) forms in winter due to open convection mechanisms and spills deeper through the shelf canyons. Ionian Surface Water (ISW) enters the basin along the Albanian coast as Eastern Adriatic Current (EAC) and form the South Adriatic Gyre (SAG) [<a href="#B23-water-13-01325" class="html-bibr">23</a>,<a href="#B24-water-13-01325" class="html-bibr">24</a>,<a href="#B25-water-13-01325" class="html-bibr">25</a>,<a href="#B26-water-13-01325" class="html-bibr">26</a>,<a href="#B27-water-13-01325" class="html-bibr">27</a>].</p> Full article ">Figure 2
<p>(<b>a</b>) Temperature (°C)/Salinity (T/S) diagram of CTD measurements and samples bounding in assigned clusters (Coastal (CS), Offshore (OS), Intermediate (IS) and the Deep (DS) Systems) according to the salinity and depth; (<b>b</b>) vertical section of fluorescence from chl<span class="html-italic">a</span> along the central transect in the Gulf area.</p> Full article ">Figure 3
<p>Boxplots of the Assimilation Number (AN, μgC h<sup>−1</sup>/μg- chl<span class="html-italic">a</span>) of total and size-fractionated (micro-, nano- and pico) phytoplankton in the Coastal (CS), Offshore (OS) and Intermediate (IS) in the Gulf area.</p> Full article ">Figure 4
<p>Boxplots of autotrophic (PPA) and total (PPT) prokaryotic community in the Coastal (CS), Offshore (OS), Intermediate (IS) and Deep (DS) Systems in the Gulf area.</p> Full article ">Figure 5
<p>(<b>a</b>) Boxplot of total phytoplankton in the Coastal (CS), Intermediate (IS), Offshore (OS) and Deep (DS) Systems in the Gulf area; (<b>b</b>) Relative percentages of the four most abundant phytoplankton species (&gt;15%) in the three Systems in the Gulf area.</p> Full article ">Figure 6
<p>Non-metric multidimensional scaling (nMDS) ordination plot of the phytoplankton species abundances collected in the Coastal (CS), Intermediate (OS) and Offshore (OS) Systems. The groups identified by the green line are obtained by overlaying the cluster analysis performed on the same matrix at similarity level of 33%. Note that the station 43 (four red triangles: 0, 25, 35 and 45 m) identifies the inflow waters from the Northern Adriatic Sea.</p> Full article ">Figure 7
<p>Simplified model of the standing stocks and metabolic processes (production and decomposition) mediated by microbial assemblages in the Coastal and Offshore Systems in the Gulf of Manfredonia in late spring period. The model shows the pools, in terms of relative concentration or abundance, of nutrients (P, DIN, Si) and autotrophic (size-fractionated chl<span class="html-italic">a</span> and phaeo, PPA and large phytoplankton main groups) and heterotrophic PPH (size-fractionated morphotypes as cocci and rods) compartments. Arrows indicate: (1) the Carbon fluxes through the autotrophic size-fractionated primary production (PP, in yellow) and the prokaryotic heterotrophic production (PHP, in orange); (2) Carbon and Phosphorus fluxes mobilized by microbes through enzymatic activities (a-Glu in red, b-Glu in blue, AP in light blue and LAP in green). Histogram/arrow widths are proportional to the total magnitude of each pool/flux. The grazing index (Gi = phaeo/(phaeo + chl<span class="html-italic">a</span>) [<a href="#B34-water-13-01325" class="html-bibr">34</a>,<a href="#B55-water-13-01325" class="html-bibr">55</a>] as the chl<span class="html-italic">a</span> potentially exported from the System is shown in dark orange. Red/White rightward arrows indicate the biogenic-C fate in the <span class="html-italic">continuum</span> trophic pathway. Overall, the multivorous pathway prevails, even if the maximum value of CS points towards the herbivorous pathway. The Organic Matter (dissolved and particulate) pool (in grey) as well as the role of the eukaryotic organisms or predators of higher trophic levels in the decomposition/remineralization processes were not estimated.</p> Full article ">
35 pages, 6786 KiB  
Article
A Holistic Framework for Evaluating Adaptation Approaches to Coastal Hazards and Sea Level Rise: A Case Study from Imperial Beach, California
by David Revell, Phil King, Jeff Giliam, Juliano Calil, Sarah Jenkins, Chris Helmer, Jim Nakagawa, Alex Snyder, Joe Ellis and Matt Jamieson
Water 2021, 13(9), 1324; https://doi.org/10.3390/w13091324 - 10 May 2021
Cited by 7 | Viewed by 5636
Abstract
Sea level rise increases community risks from erosion, wave flooding, and tides. Current management typically protects existing development and infrastructure with coastal armoring. These practices ignore long-term impacts to public trust coastal recreation and natural ecosystems. This adaptation framework models physical responses to [...] Read more.
Sea level rise increases community risks from erosion, wave flooding, and tides. Current management typically protects existing development and infrastructure with coastal armoring. These practices ignore long-term impacts to public trust coastal recreation and natural ecosystems. This adaptation framework models physical responses to the public beach and private upland for each adaptation strategy over time, linking physical changes in widths to damages, economic costs, and benefits from beach recreation and nature using low-lying Imperial Beach, California, as a case study. Available coastal hazard models identified community vulnerabilities, and local risk communication engagement prioritized five adaptation approaches—armoring, nourishment, living shorelines, groins, and managed retreat. This framework innovates using replacement cost as a proxy for ecosystem services normally not valued and examines a managed retreat policy approach using a public buyout and rent-back option. Specific methods and economic values used in the analysis need more research and innovation, but the framework provides a scalable methodology to guide coastal adaptation planning everywhere. Case study results suggest that coastal armoring provides the least public benefits over time. Living shoreline approaches show greater public benefits, while managed retreat, implemented sooner, provides the best long-term adaptation strategy to protect community identity and public trust resources. Full article
(This article belongs to the Special Issue Adaptation to Coastal Climate Change and Sea-Level Rise)
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<p>Adaptation framework process including Phase One (Vulnerability Assessment) and Phase Two (Analysis of Adaptation Alternatives).</p> Full article ">Figure 2
<p>Case Study site of Imperial Beach in California, USA. Coastal hazard extents combined USGS CoSMoS 1.0, 3.0 Preliminary, and Department of Defense—SPAWAR.</p> Full article ">Figure 3
<p>Impact of coastal armoring on public beach—with sand following nourishment (<b>left</b>), and without sand (<b>right</b>). Photo: J. Nakagawa.</p> Full article ">Figure 4
<p>Coastal hazards (<b>a</b>) wave flooding, (<b>b</b>) coastal erosion, (<b>c</b>) tidal inundation.</p> Full article ">Figure 5
<p>Conceptual model of physical upland and beach widths tracked as a result of adaptation strategy implementation over time. For this case study, developed and yard were considered as upland. The revetment in this figure was the adaptation project, while the beach, and intertidal were considered as the beach width.</p> Full article ">Figure 6
<p>Shoreline change rates for 159-year historical time period. Erosion hot spots shown in red. Green is accretion. Grey is within the range of uncertainty.</p> Full article ">Figure 7
<p>Losses and damages for private development from each of the coastal hazards through time.</p> Full article ">Figure 8
<p>(<b>A</b>) Evolution of the armoring adaptation strategy, showing a small increase in usable beach as the existing revetments are replaced with vertical seawalls, then the loss of dry and eventually intertidal sand beaches over time. (<b>B</b>) Dry sand beach width over time with armoring (wide vs. narrow beach) (Ba top plot); upland width over time with armoring (wide vs. narrow beach) (Bb bottom plot).</p> Full article ">Figure 9
<p>(<b>A</b>) Evolution of the beach nourishment strategy over time. Example does not illustrate the shortening time between nourishment cycles as sea level rises. (<b>B</b>) Dry sand beach width over time with armoring (wide vs. narrow beach) (Ba top plot); upland width over time with armoring (wide vs. narrow beach) (Bb bottom plot).</p> Full article ">Figure 10
<p>(<b>A</b>) Evolution of the living cobble and dune shoreline strategy over time. Example does not illustrate the shortening time between nourishment cycles as sea level rises. (<b>B</b>) Dry sand beach width over time with armoring (wide vs. narrow beach) (Ba top plot); upland width over time with armoring (wide vs. narrow beach) (Bb bottom plot).</p> Full article ">Figure 11
<p>(<b>A</b>) Sand retention with groins adaptation strategy over time. (<b>B</b>) Dry sand beach width over time with armoring (wide vs. narrow beach) (Ba top plot); upland width over time with armoring (wide vs. narrow beach) (Bb bottom plot).</p> Full article ">Figure 12
<p>(<b>A</b>) Managed retreat adaptation follows removal of existing coastal armoring in 2030, with coastal erosion damaging private property while allowing beaches to migrate inland and maintain their public recreation and natural values. (<b>B</b>) Dry sand beach width over time with armoring (wide vs. narrow beach) (Ba top plot); upland width over time with armoring (wide vs. narrow beach) (Bb bottom plot).</p> Full article ">Figure 13
<p>Length of time for rent to pay back the property value.</p> Full article ">Figure 14
<p>Estimated (local) sales tax and transient occupancy tax revenues for different scenarios.</p> Full article ">Figure 15
<p>Ecological value of beaches in Imperial Beach using the upland vs. beach width framework coupled with a replacement valuation.</p> Full article ">Figure 16
<p>Net benefits of the selected adaptation alternatives over time for both a narrow beach (<b>left</b>) and a wide beach (<b>right</b>).</p> Full article ">
16 pages, 16365 KiB  
Article
GIS-Based Spatiotemporal Mapping of Groundwater Potability and Palatability Indices in Arid and Semi-Arid Areas
by Tariq Judeh, Hanbing Bian and Isam Shahrour
Water 2021, 13(9), 1323; https://doi.org/10.3390/w13091323 - 10 May 2021
Cited by 14 | Viewed by 3399
Abstract
This paper aims to assess groundwater potability and palatability in the West Bank, Palestine. It combines the adjusted weighted arithmetic water quality index method (AWAWQIM), a close-ended questionnaire, and step-wise assessment ratio analysis (SWARA) to develop groundwater potability (PoGWQI) and palatability (PaGWQI) indices. [...] Read more.
This paper aims to assess groundwater potability and palatability in the West Bank, Palestine. It combines the adjusted weighted arithmetic water quality index method (AWAWQIM), a close-ended questionnaire, and step-wise assessment ratio analysis (SWARA) to develop groundwater potability (PoGWQI) and palatability (PaGWQI) indices. Both a geographic information system (GIS) and the kriging interpolation method (KIM) are employed to create spatiotemporal mapping of PoGWQI and PaGWQI. The research is based on data from 79 wells, which were provided by the Palestinian Water Authority (PWA). Data include fecal coliform (FC), nitrate (NO3), pH, chloride (Cl), sulfate (SO4), bicarbonate (HCO3), total dissolved solids (TDS), turbidity, and hardness. Results indicate that 2% and 5% of water samples were unpotable and unpalatable, respectively. Unpotable samples were found in areas with poor sewer networks and intensive use of agrochemicals. All groundwater samples (100%) in the eastern part of the West Bank were unpalatable because of seawater intrusion. Unconfined aquifers were more vulnerable to potability and palatability contamination. It was noticed that PoGWQI is sensitive to FC and NO3, while PaGWQI is sensitive to HCO3, TDS, and Cl. Consequently, these quality parameters should be monitored well. The proposed method is of great interest to water decision-makers in Palestine for establishing strategies to protect water resources. Full article
(This article belongs to the Section Water Quality and Contamination)
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<p>Overall methodological framework.</p> Full article ">Figure 2
<p>Development of potability and palatability groundwater quality indexes (PoGWQI and PaGWQI).</p> Full article ">Figure 3
<p>Regional location of the West Bank.</p> Full article ">Figure 4
<p>PoGWQGs and PaGWQGs in the West Bank.</p> Full article ">Figure 5
<p>Un-potability rate over four contaminated groundwater wells in the West Bank.</p> Full article ">Figure 6
<p>Spatiotemporal mapping of PoGWQI and PaGWQI in the West Bank between 2001 and 2016.</p> Full article ">Figure 7
<p>PoGWQGs and PaGWQGs cross the West Bank governorates.</p> Full article ">Figure 8
<p>Sensitivity analysis of PoGWQI and PaGWQI.</p> Full article ">Figure 9
<p>Factors affecting PoGWQI and PaGWQI in the West Bank.</p> Full article ">Figure 10
<p>Relative importance analysis for the main factors affecting PoGWQI and PaGWQI.</p> Full article ">
11 pages, 12570 KiB  
Article
A Predictive Model for Estimating Damage from Wind Waves during Coastal Storms
by Yeon Moon Choo, Kun Hak Chun, Hae Seong Jeon and Sang Bo Sim
Water 2021, 13(9), 1322; https://doi.org/10.3390/w13091322 - 10 May 2021
Cited by 3 | Viewed by 2271
Abstract
In recent years, climate abnormalities have been observed globally. Consequently, the scale and size of natural disasters, such as typhoons, wind wave, heavy snow, downpours, and storms, have increased. However, compared to other disasters, predicting the timing, location and severity of damages associated [...] Read more.
In recent years, climate abnormalities have been observed globally. Consequently, the scale and size of natural disasters, such as typhoons, wind wave, heavy snow, downpours, and storms, have increased. However, compared to other disasters, predicting the timing, location and severity of damages associated with typhoons and other extreme wind wave events is difficult. Accurately predicting the damage extent can reduce the damage scale by facilitating a speedy response. Therefore, in this study, a model to estimate the cost of damages associated with wind waves and their impacts during coastal storms was developed for the Republic of Korea. The history of wind wave and typhoon damages for coastal areas in Korea was collected from the disaster annual report (1991–2020), and the damage cost was converted such that it reflected the inflation rate as in 2020. Furthermore, data on ocean meteorological factors were collected for the events of wind wave and typhoon damages. Using logistic and linear regression, a wind wave damage prediction model reflecting the coastal regional characteristics based on 74 regions nationwide was developed. This prediction model enabled damage forecasting and can be utilized for improving the law and policy in disaster management. Full article
(This article belongs to the Special Issue Coastal Hazards Management)
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<p>Precedure to Develop Wind Wave Damage Amount Prediction Model.</p> Full article ">Figure 2
<p>Study Area.</p> Full article ">Figure 3
<p>k-fold Cross-validation.</p> Full article ">Figure 4
<p>Evaluating Group Classification Model with ROC-Curve.</p> Full article ">
13 pages, 1438 KiB  
Article
Assessing Progress towards Sustainable Development Goals through Nexus Planning
by Tafadzwanashe Mabhaudhi, Luxon Nhamo, Tendai P. Chibarabada, Goden Mabaya, Sylvester Mpandeli, Stanley Liphadzi, Aidan Senzanje, Dhesigen Naidoo, Albert T. Modi and Pauline P. Chivenge
Water 2021, 13(9), 1321; https://doi.org/10.3390/w13091321 - 10 May 2021
Cited by 25 | Viewed by 6826
Abstract
Sustainable Development Goals (SDGs) acknowledge the inter-linkages between human wellbeing, economic prosperity, and a healthy environment and, hence, are associated with a wide range of topical issues that include the securities of water, energy and food resources, poverty eradication, economic development, climate change, [...] Read more.
Sustainable Development Goals (SDGs) acknowledge the inter-linkages between human wellbeing, economic prosperity, and a healthy environment and, hence, are associated with a wide range of topical issues that include the securities of water, energy and food resources, poverty eradication, economic development, climate change, health, among others. As SDGs are assessed through targets to be achieved by 2030 and monitored through measurable indicators, this study applied the nexus planning model to monitor and evaluate progress towards SDGs using South Africa as a case study. The study highlighted pathways to ensure socio-ecological sustainability and environmental health by establishing the connectivity between SDGs and nexus approaches. The linkages between SDGs and nexus planning facilitated the sustainable management of resources in an integrated manner. They addressed the cross-sectoral synergies, value-addition, and trade-offs within interlinked sectors. The connectedness of current challenges facing humankind (climate change, rapid urbanisation, migration, and the emergence of novel infectious diseases) require transformative approaches that address these cross-cutting challenges holistically. Managing the intricate relationships between distinct but interconnected sectors through nexus planning has provided decision support tools to formulate coherent strategies that drive resilience and sustainability. The established linkages between nexus planning and SDGs have strengthened cross-sectoral collaboration and unpacked measures for cooperative governance and management through evidence-based interventions. As food production, water provision, and energy accessibility are the major socio-economic and environmental issues currently attracting global attention; the methodology promotes attaining sustainability by 2030. Full article
(This article belongs to the Special Issue Management of Water-Energy-Food Security Nexus)
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<p>A conceptual framework linking nexus processes with Sustainable Development Goals (SDGs)<b>.</b></p> Full article ">Figure 2
<p>Quantitative relationships between the indicators representing the WEF nexus (<b>a</b>) and the WHEN nexus (<b>b</b>) in South Africa in 2015.</p> Full article ">Figure 3
<p>Changes in WEF nexus indicators between 2015 and 2018. The comparison is necessary to assess progress towards SDGs.</p> Full article ">
23 pages, 6789 KiB  
Article
Structure and Dynamics of Interfacial Water on Muscovite Surface under Different Temperature Conditions (298 K to 673 K): Molecular Dynamics Investigation
by Masashige Shiga, Masaatsu Aichi, Masao Sorai and Tetsuya Morishita
Water 2021, 13(9), 1320; https://doi.org/10.3390/w13091320 - 9 May 2021
Cited by 8 | Viewed by 3278
Abstract
We performed molecular dynamics (MD) simulations to study structure, stability, and dynamics of the water adsorption layer on muscovite mica at several temperatures (from 298 K to 673 K) and pressures (0.1 MPa, 10 MPa, and 50 MPa). We studied the structure of [...] Read more.
We performed molecular dynamics (MD) simulations to study structure, stability, and dynamics of the water adsorption layer on muscovite mica at several temperatures (from 298 K to 673 K) and pressures (0.1 MPa, 10 MPa, and 50 MPa). We studied the structure of the adsorption layers with three characteristic peaks of density and orientation of H2O molecules in one-dimensional and two-dimensional profiles. The results show that the water adsorption layers become less structured and more mobile as the temperature increases. We also found the first and the second layers are less diffusive than the third one, and the difference of diffusivity gets unclear as the temperature increases. Finally, we discuss implications to hydration forces and wettability, which are significant interfacial properties of the multiphase fluids system such as water/gas/mineral systems, from the viewpoint of water adsorption film with nanometer thickness. Full article
(This article belongs to the Section Water Quality and Contamination)
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<p>A snapshot of the initial state of the calculation system (H<sub>2</sub>O/muscovite system). The area outside the blue line is the area duplicated by the periodic boundary conditions. Each atom is colored differently—oxygen: red; hydrogen: white; aluminum: cyan; silicon: yellow; potassium: orange.</p> Full article ">Figure 2
<p>Schematic image of muscovite structure (<b>a</b>) XY view (<b>b</b>,<b>c</b>) XZ views of the surface (<b>d</b>) K<sup>+</sup>-site (yellow: Si, blue: Al, red: O, white: H, orange: K).</p> Full article ">Figure 3
<p>Density profiles of H<sub>2</sub>O molecules vs. distance from the muscovite surface.</p> Full article ">Figure 4
<p>2D normalized density maps of O and H atoms of H<sub>2</sub>O molecules at (<b>a</b>) the first layer, (<b>b</b>) the second layer, and (<b>c</b>) the third layer; the lattice on the map is from <a href="#app1-water-13-01320" class="html-app">Figure S6</a> in <a href="#app1-water-13-01320" class="html-app">Supplementary Materials</a>.</p> Full article ">Figure 5
<p>Snapshots of the muscovite surface, K<sup>+</sup>, and H<sub>2</sub>O molecules.</p> Full article ">Figure 6
<p>Normalized density profiles of O, H, and K<sup>+</sup> on K<sup>+</sup>-site and o-site.</p> Full article ">Figure 7
<p>Definition of the orientation angle of H<sub>2</sub>O.</p> Full article ">Figure 8
<p>Profiles of the orientation angle <math display="inline"><semantics> <mi>θ</mi> </semantics></math> of H<sub>2</sub>O molecules from the muscovite surface at (<b>a</b>) 0.1 MPa (<b>b</b>) 10 MPa (<b>c</b>) 50 MPa; a snapshot of a H<sub>2</sub>O molecule at each of three extreme values of <math display="inline"><semantics> <mi>θ</mi> </semantics></math> is shown.</p> Full article ">Figure 9
<p>2D Maps of the orientation angle <math display="inline"><semantics> <mi>θ</mi> </semantics></math> at 50 MPa; the lattice on the map is from <a href="#app1-water-13-01320" class="html-app">Figure S6</a> in <a href="#app1-water-13-01320" class="html-app">Supplementary Materials</a>.</p> Full article ">Figure 9 Cont.
<p>2D Maps of the orientation angle <math display="inline"><semantics> <mi>θ</mi> </semantics></math> at 50 MPa; the lattice on the map is from <a href="#app1-water-13-01320" class="html-app">Figure S6</a> in <a href="#app1-water-13-01320" class="html-app">Supplementary Materials</a>.</p> Full article ">Figure 10
<p>Profiles of the orientation angle <math display="inline"><semantics> <mi>θ</mi> </semantics></math> on K<sup>+</sup>-site (red) and o-site (green).</p> Full article ">Figure 10 Cont.
<p>Profiles of the orientation angle <math display="inline"><semantics> <mi>θ</mi> </semantics></math> on K<sup>+</sup>-site (red) and o-site (green).</p> Full article ">Figure 11
<p>Distributions of <math display="inline"><semantics> <mrow> <mi>c</mi> <mi>o</mi> <mi>s</mi> <mi>θ</mi> </mrow> </semantics></math> at (<b>a</b>) the first layer, (<b>b</b>) the second layer, (<b>c</b>) the third layer, and (<b>d</b>) bulk region (2.0 nm &lt; <span class="html-italic">d</span> &lt; 3.0 nm). Each pressure condition is 50 MPa.</p> Full article ">Figure 12
<p>The number of hydrogen bonding per H<sub>2</sub>O molecule vs distance from muscovite surface.</p> Full article ">Figure 13
<p>The normalized self-diffusion coefficient of H<sub>2</sub>O molecules <math display="inline"><semantics> <mrow> <msup> <mi>D</mi> <mo>*</mo> </msup> <msub> <mrow/> <mi>f</mi> </msub> <mfenced> <mi>d</mi> </mfenced> </mrow> </semantics></math> vs distance from the muscovite surface.</p> Full article ">Figure 14
<p>Schematic image of the thin film with two different thicknesses (thinner: <math display="inline"><semantics> <mrow> <msub> <mi>h</mi> <mn>1</mn> </msub> </mrow> </semantics></math>; thicker: <math display="inline"><semantics> <mrow> <msub> <mi>h</mi> <mn>2</mn> </msub> </mrow> </semantics></math>) in the gas/water/mineral system.</p> Full article ">
23 pages, 4510 KiB  
Article
Combined Dispatching of Hydropower and Wind Power Based on the Hedging Theory
by Kaoshe Zhang, Mengyan Xie, Gang Zhang, Tuo Xie, Xin Li and Xin He
Water 2021, 13(9), 1319; https://doi.org/10.3390/w13091319 - 9 May 2021
Viewed by 2338
Abstract
In order to improve the utilization rate of water resources in the flood season of the reservoir effectively and promote wind power consumption, this paper proposes an optimization model for the combined dispatching of wind power and hydropower based on the hedging theory. [...] Read more.
In order to improve the utilization rate of water resources in the flood season of the reservoir effectively and promote wind power consumption, this paper proposes an optimization model for the combined dispatching of wind power and hydropower based on the hedging theory. First, the conflicting relationship between the water storage benefits of hydropower stations, flood control risks, and the joint output of hydropower and wind power in joint dispatching is studied. The introduction of hedging theory divides the combined dispatching of wind power and hydropower into a two-stage dispatching problem including the decision-making stage and the remaining stage; Second, considering the uncertainty of water forecasting and wind power forecasting, a multi-objective optimal dispatching model of hydropower and wind power based on hedging theory is constructed. This model aims to minimize flood control risks, maximize water storage benefits, and minimize wind power and hydropower combined power output volatility. Finally, the non-dominated sorting genetic algorithm (NSGA2) is used to solve the specific examples. The results show that the model built in the article controls the flood control risk at each time period not to be higher than 1.63 × 10−3 (the flood control standard corresponding to the flood control risk in 50 years is 0.006). Additionally, the water level of the reservoir increased from the flood limit water level (583.00 m) to 583.70 m. It greatly increases the water storage capacity and effectively improves the utilization rate of water resources. At the same time, the optimized scheduling scheme reduced the peak-valley difference of joint output from 125.00 MW to 35.66 MW, and the peak-valley difference was greatly reduced. It effectively improves the volatility of wind power. The validity of the model is verified, and the obtained scheme can provide decision-making for the joint dispatch scheme of hydropower and wind power. Full article
(This article belongs to the Special Issue Advances and Challenges in Hydropower)
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<p>Standard Operation Policy and Hedging Rules.</p> Full article ">Figure 2
<p>Multi-objective hedging relationship in the joint dispatch of hydropower and wind power.</p> Full article ">Figure 3
<p>Schematic diagram of rolling forecast.</p> Full article ">Figure 4
<p>Two-stage decision diagram for joint dispatch of hydropower and wind power.</p> Full article ">Figure 5
<p>The process of using NSGA2 algorithm to solve the joint dispatching model.</p> Full article ">Figure 6
<p>(<b>a</b>) Water level-storage capacity curve; (<b>b</b>) Discharge flow-water level curve.</p> Full article ">Figure 7
<p>Interval Prediction of Wind Power.</p> Full article ">Figure 8
<p>(<b>a</b>) Relationship between actual inbound flow and forecasted flow; (<b>b</b>) Relationship between actual inbound flow and relative error.</p> Full article ">Figure 9
<p>The relationship between the maximum increase in storage capacity, acceptable risk, and forecast uncertainty.</p> Full article ">Figure 10
<p>Pareto frontier for multi-objective hedging. (<b>a</b>) Pareto frontier with three goals for hedging; (<b>b</b>) Pareto frontier of Goal 1 and Goal 2.</p> Full article ">Figure 11
<p>Comparison of joint dispatching results. (<b>a</b>) Joint dispatch of hydropower and wind power based on hedging theory; (<b>b</b>) Conventional hydropower and wind power joint dispatch.</p> Full article ">Figure 12
<p>Comparison of joint output volatility under the two schemes.</p> Full article ">Figure 13
<p>Comparison of water storage process of joint dispatch schemes. (<b>a</b>) Water storage process based on the hedging theory scheme; (<b>b</b>) Conventional water storage process.</p> Full article ">Figure 14
<p>Comparison of water storage changes in hydropower and wind power joint dispatch schemes. (<b>a</b>) Water storage change based on the hedging theory scheme; (<b>b</b>) Water storage change of conventional schemes.</p> Full article ">Figure 15
<p>Water storage capacity during the hedge period 9–12.</p> Full article ">Figure 16
<p>Water storage change process without hedging rules.</p> Full article ">Figure 17
<p>Water storage change process without hedging rules.</p> Full article ">
24 pages, 4405 KiB  
Article
An Improved Inexact Two-Stage Stochastic with Downside Risk-Control Programming Model for Water Resource Allocation under the Dual Constraints of Water Pollution and Water Scarcity in Northern China
by Chong Meng, Wei Li, Runhe Cheng and Siyang Zhou
Water 2021, 13(9), 1318; https://doi.org/10.3390/w13091318 - 9 May 2021
Cited by 8 | Viewed by 2257
Abstract
Water resource allocation aimed at sustainable watershed development suffers from prominent challenges such as water pollution and scarcity, especially in water-deprived regions. Based on analysis of water quality, use, and sectoral demands during the planning period in the Fenhe River Basin, an improved [...] Read more.
Water resource allocation aimed at sustainable watershed development suffers from prominent challenges such as water pollution and scarcity, especially in water-deprived regions. Based on analysis of water quality, use, and sectoral demands during the planning period in the Fenhe River Basin, an improved inexact two-stage stochastic programming model with downside risk control was built for optimal resource allocations for the four primary sectors (industry, domestic use, agriculture, and the environment) in the basin. The principal constraints are river water quality and available water resources under the three hydrological scenarios (low, medium, and high). The results show that industrial, domestic, and agricultural water use in the middle and lower reaches were significantly reduced by requiring improved water quality; agriculture suffered the greatest water shortage and risk. As the level of risk control improved, the comprehensive watershed benefits and agricultural risks were gradually reduced. Improving water reuse significantly reduces the risk and increases the benefits. The model can effectively manage rational water allocations under the dual constraints of water quality and quantity, meanwhile alleviating water competition caused by different water benefits to provide support for coordinating the improvement of water quality and socio-economic development in the basin. Full article
(This article belongs to the Section Water Resources Management, Policy and Governance)
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<p>Framework for the inexact downside risk control and two-stage stochastic programming model.</p> Full article ">Figure 2
<p>Geographical position and study area of the Fenhe River Basin.</p> Full article ">Figure 3
<p>Downside risks in the Fenhe River Basin at different risk levels.</p> Full article ">Figure 4
<p>Water compensation for the Fenhe River Basin.</p> Full article ">Figure 5
<p>Water compensation by region in the Fenhe River Basin in period 1.</p> Full article ">Figure 6
<p>Water compensation by region in the Fenhe River Basin in period 2.</p> Full article ">Figure 7
<p>Water compensation by region in the Fenhe River Basin in period 3.</p> Full article ">Figure 8
<p>Water resource deficit by region in the Fenhe River Basin in period 1.</p> Full article ">Figure 9
<p>Water resource deficit by region in the Fenhe River Basin in period 2.</p> Full article ">Figure 10
<p>Water resource deficits by region in the Fenhe River Basin in period 3.</p> Full article ">Figure 11
<p>Reused water resources by region in the Fenhe River Basin in period 1.</p> Full article ">Figure 12
<p>Reused water resources by region in the Fenhe River Basin in period 2.</p> Full article ">Figure 13
<p>Reused water resources for by region in the Fenhe River Basin in period 3.</p> Full article ">Figure 14
<p>Water resource deficits in the Fenhe River Basin by scenario.</p> Full article ">Figure 14 Cont.
<p>Water resource deficits in the Fenhe River Basin by scenario.</p> Full article ">Figure 15
<p>Reuse water resources in the Fenhe River Basin by scenario.</p> Full article ">Figure 15 Cont.
<p>Reuse water resources in the Fenhe River Basin by scenario.</p> Full article ">Figure 16
<p>Water compensation in the Fenhe River Basin under different scenarios.</p> Full article ">
12 pages, 2547 KiB  
Article
Design, Scaling, and Development of Biofilters with E crassipes for Treatment of Water Contaminated with Cr (VI)
by Uriel Fernando Carreño Sayago
Water 2021, 13(9), 1317; https://doi.org/10.3390/w13091317 - 8 May 2021
Cited by 8 | Viewed by 3142
Abstract
The heavy metal water treatment process is the subject of worldwide research. Chromium (VI) is a heavy metal that is very dangerous to humans due to it being able to alter genetic material and cause cancer. Cellulose is an interesting material for removing [...] Read more.
The heavy metal water treatment process is the subject of worldwide research. Chromium (VI) is a heavy metal that is very dangerous to humans due to it being able to alter genetic material and cause cancer. Cellulose is an interesting material for removing heavy metals, and excellent removals have been achieved in many experiments at the laboratory scale. However, scaling these processes to polluting industries is not easy. The objective of this research is to design, scale, and test a biofilter with biomass of E crassipes transformed with iron for treatment of water contaminated with Cr (VI). The biomasses of E crassipes (EC) and E crassipes with iron (EC + Fe) were evaluated at the batch laboratory scale to determine the adsorption capacities through Langmuir isotherms. With these capacities, a mass balance was formulated, obtaining the design equation to build a biofilter at the pilot scale and providing the required amount of biomass from (EC) and (EC + Fe) for the adequate treatment of the Cr (VI) present in the water. The mass, as suggested by the relevant equations, for the greatest concentration of Cr (VI) of 500 mg/L was 42 g together with a flow rate of 10 mL/min for the biomass of (EC + Fe); for the biomass of (EC), the suggested model for the treatment of the greatest Cr (VI) concentration of 500 mg/L was 64 g of biomass together with a flow rate of 10 mL/min. We conclude that the two pilot-scale treatment systems were consistent with the Cr (VI) removal process and that the equation for the design was adequate. Full article
(This article belongs to the Special Issue Advanced Technologies in Wastewater Treatment)
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<p>Representation of the filter model in the Cr (VI) treatment process—mathematical model of input, output and internal adsorption.</p> Full article ">Figure 2
<p>(EC) removal percentages.</p> Full article ">Figure 3
<p>(EC + Fe) removal efficiency.</p> Full article ">Figure 4
<p>Langmuir isotherm EC.</p> Full article ">Figure 5
<p>Langmuir isotherms (EC + Fe).</p> Full article ">Figure 6
<p>Biofilters used in the adsorption process: E <span class="html-italic">crassipes</span> (EC) (<b>a</b>); E <span class="html-italic">crassipes</span> with iron (EC + Fe) (<b>b</b>).</p> Full article ">Figure 7
<p>(EC) and (EC + Fe) removal percentages: Biofiliters EC (<b>a</b>); Biofilters EC + Fe (<b>b</b>).</p> Full article ">
17 pages, 2658 KiB  
Article
Promotion of Growth and Physiological Characteristics in Water-Stressed Triticum aestivum in Relation to Foliar-Application of Salicylic Acid
by Abida Parveen, Muhammad Arslan Ashraf, Iqbal Hussain, Shagufta Perveen, Rizwan Rasheed, Qaisar Mahmood, Shahid Hussain, Allah Ditta, Abeer Hashem, Al-Bandari Fahad Al-Arjani, Abdulaziz A. Alqarawi and Elsayed Fathi Abd Allah
Water 2021, 13(9), 1316; https://doi.org/10.3390/w13091316 - 8 May 2021
Cited by 27 | Viewed by 4362
Abstract
The present work reports the assessment of the effectiveness of a foliar-spray of salicylic acid (SA) on growth attributes, biochemical characteristics, antioxidant activities and osmolytes accumulation in wheat grown under control (100% field capacity) and water stressed (60% field capacity) conditions. The total [...] Read more.
The present work reports the assessment of the effectiveness of a foliar-spray of salicylic acid (SA) on growth attributes, biochemical characteristics, antioxidant activities and osmolytes accumulation in wheat grown under control (100% field capacity) and water stressed (60% field capacity) conditions. The total available water (TAW), calculated for a rooting depth of 1.65 m was 8.45 inches and readily available water (RAW), considering a depletion factor of 0.55, was 4.65 inches. The water contents corresponding to 100 and 60% field capacity were 5.70 and 1.66 inches, respectively. For this purpose, seeds of two wheat cultivars (Fsd-2008 and S-24) were grown in pots subjected to water stress. Water stress at 60% field capacity markedly reduced the growth attributes, photosynthetic pigments, total soluble proteins (TSP) and total phenolic contents (TPC) compared with control. However, cv. Fsd-2008 was recorded as strongly drought-tolerant and performed better compared to cv. S-24, which was moderately drought tolerant. However, water stress enhanced the contents of malondialdehyde (MDA), hydrogen peroxide (H2O2) and membrane electrolyte leakage (EL) and modulated the activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as accumulation of ascorbic acid (AsA), proline (Pro) and glycine betaine (GB) contents. Foliar-spray with salicylic acid (SA; 0, 3 mM and 6 mM) effectively mitigated the adverse effects of water stress on both cultivars. SA application at 6 mM enhanced the shoot and root length, as well as their fresh and dry weights, and improved photosynthetic pigments. SA foliage application further enhanced the activities of antioxidant enzymes (SOD, POD, and CAT) and nonenzymatic antioxidants such as ascorbic acid and phenolics contents. However, foliar-spray of SA reduced MDA, H2O2 and membrane permeability in both cultivars under stress conditions. The results of the present study suggest that foliar-spray of salicylic acid was effective in increasing the tolerance of wheat plants under drought stress in terms of growth attributes, antioxidant defense mechanisms, accumulation of osmolytes, and by reducing membrane lipid peroxidation. Full article
(This article belongs to the Section Water, Agriculture and Aquaculture)
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<p>Effect of foliar-application of salicylic acid on (<b>A</b>) shoot length, (<b>B</b>) root length, (<b>C</b>) shoot fresh weight, (<b>D</b>) scheme 0., FSD-2008 (<b>E</b>) and SD-24 (<b>F</b>) Error bars above the means indicate standard errors (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 1 Cont.
<p>Effect of foliar-application of salicylic acid on (<b>A</b>) shoot length, (<b>B</b>) root length, (<b>C</b>) shoot fresh weight, (<b>D</b>) scheme 0., FSD-2008 (<b>E</b>) and SD-24 (<b>F</b>) Error bars above the means indicate standard errors (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 2
<p>Effect of foliar-application of salicylic acid on (<b>A</b>) chlorophyll a, (<b>B</b>) chlorophyll b, (<b>C</b>) carotenoids, (<b>D</b>) proline, (<b>E</b>) total soluble sugar contents, (<b>F</b>) glycine betaine contents in two wheat cultivars under water-stress conditions. Means with the same letter (S) do not differ significantly at <span class="html-italic">p</span> ≤ 0.05. Error bars above the means indicate standard error (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 2 Cont.
<p>Effect of foliar-application of salicylic acid on (<b>A</b>) chlorophyll a, (<b>B</b>) chlorophyll b, (<b>C</b>) carotenoids, (<b>D</b>) proline, (<b>E</b>) total soluble sugar contents, (<b>F</b>) glycine betaine contents in two wheat cultivars under water-stress conditions. Means with the same letter (S) do not differ significantly at <span class="html-italic">p</span> ≤ 0.05. Error bars above the means indicate standard error (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 3
<p>Effect of foliar application of salicylic acid on (<b>A</b>) catalase, (<b>B</b>) superoxide dismutase, (<b>C</b>) peroxidase, (<b>D</b>) malondialdehyde, (<b>E</b>) hydrogen peroxide, (<b>F</b>) relative membrane permeability, (<b>G</b>) total phenolics, (<b>H</b>) ascorbic acid contents, in two wheat cultivars under water-stress conditions. Means with the same letter (S) do not differ significantly at <span class="html-italic">p</span> ≤ 0.05. Error bars above the means indicate standard error (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 3 Cont.
<p>Effect of foliar application of salicylic acid on (<b>A</b>) catalase, (<b>B</b>) superoxide dismutase, (<b>C</b>) peroxidase, (<b>D</b>) malondialdehyde, (<b>E</b>) hydrogen peroxide, (<b>F</b>) relative membrane permeability, (<b>G</b>) total phenolics, (<b>H</b>) ascorbic acid contents, in two wheat cultivars under water-stress conditions. Means with the same letter (S) do not differ significantly at <span class="html-italic">p</span> ≤ 0.05. Error bars above the means indicate standard error (<span class="html-italic">n</span> = 3).</p> Full article ">
10 pages, 4913 KiB  
Article
Effect of Salinity on UVA-Vis Light Driven Photo-Fenton Process at Acidic and Circumneutral pH
by Iván Vallés, Lucas Santos-Juanes, Ana M. Amat, Javier Moreno-Andrés and Antonio Arques
Water 2021, 13(9), 1315; https://doi.org/10.3390/w13091315 - 8 May 2021
Cited by 16 | Viewed by 2704
Abstract
In the present work, the treatment of a mixture of six emerging pollutants (acetamiprid, acetaminophen, caffeine, amoxicillin, clofibric acid and carbamazepine) by means of photo-Fenton process has been studied, using simulated sunlight as an irradiation source. Removal of these pollutants has been investigated [...] Read more.
In the present work, the treatment of a mixture of six emerging pollutants (acetamiprid, acetaminophen, caffeine, amoxicillin, clofibric acid and carbamazepine) by means of photo-Fenton process has been studied, using simulated sunlight as an irradiation source. Removal of these pollutants has been investigated in three different aqueous matrices distinguished by the amount of chlorides (distilled water, 1 g L−1 of NaCl and 30 g L−1 of NaCl) at a pH of 2.8 and 5.0. Interestingly, the presence of 1 g L−1 was able to slightly accelerate the pollutants removal at pH = 5, although the reverse was true at pH = 2.8. This is attributed to the pH-dependent interference of chlorides on photo-Fenton process, that is more acute in an acidic medium. As a matter of fact, the fastest reaction was obtained at pH = 3.5, in agreement with literature results. Monitoring of hydrogen peroxide consumption and iron in solution indicates that interference with chlorides is due to changes in the interaction between iron and the peroxide, rather than a scavenging effect of chloride for hydroxyl radicals. Experiments were also carried out with real seawater and showed higher inhibition than in the NaCl experiments, probably due to the effect of different dissolved salts present in natural water. Full article
(This article belongs to the Special Issue Wastewater Treatment by Using the Photocatalysis)
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<p>Scheme of the 6 different contaminants of emerging concern employed in this work as target pollutants.</p> Full article ">Figure 2
<p>Photo-Fenton treatment of a mixture of pollutants at pH 5 in solutions containing different concentrations of salt: (<b>A</b>). DW, (<b>B</b>). LSW and (<b>C</b>). HSW. Plot of the relative concentration of each pollutant vs. time: (◆) amoxicillin, (⁃) acetaminophen, (■) acetamiprid, (<b>○</b>) clofibric acid, (<b>✖</b>) caffeine, (▲) carbamazepine.</p> Full article ">Figure 3
<p>Photo-Fenton treatment of a mixture of pollutants at pH = 5 under different conditions: DW (◆), LSW (■) and HSW (▲). Results obtained for Fenton (●) and photolysis (<b>○</b>) in DW are also given for comparison. Plots of the relative amount of the total concentration of emerging pollutants, ΣCECs (C/C<sub>0</sub>) vs. time are given.</p> Full article ">Figure 4
<p>Photo-Fenton treatment of a mixture of pollutants at pH = 2.8 under different conditions: DW (◆), LSW (■), and HSW (▲). Plots of the relative amount of the total concentration of emerging pollutants, ΣCECs (C/C<sub>0</sub>) vs. time are given.</p> Full article ">Figure 5
<p>Photo-Fenton treatment of a mixture of pollutants in LSW at three different pH values: 2.8 (◆), 3.5 (●), and 5.0 (▲). Plot of the ΣCEC/ΣCEC<sub>0</sub> vs. time.</p> Full article ">Figure 6
<p>Photo-Fenton treatment of a mixture of pollutants at (<b>A</b>). pH 2.8 and (<b>B</b>). pH 5 in different aqueous matrices DW (◆), DSW (■), LSW (▢), SW (▲) and HSW (△). Plot of the ΣCEC/ΣCEC<sub>0</sub> vs. time.</p> Full article ">
19 pages, 3713 KiB  
Article
Predicting Tropical Monsoon Hydrology Using CFSR and CMADS Data over the Cau River Basin in Vietnam
by Duy Minh Dao, Jianzhong Lu, Xiaoling Chen, Sameh A. Kantoush, Doan Van Binh, Phamchimai Phan and Nguyen Xuan Tung
Water 2021, 13(9), 1314; https://doi.org/10.3390/w13091314 - 8 May 2021
Cited by 11 | Viewed by 3605
Abstract
To improve knowledge of this matter, the potential application of two gridded meteorological products (GMPs), the China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS) and Climate Forecast System Reanalysis (CFSR), are compared for the first time with data from ground-based meteorological [...] Read more.
To improve knowledge of this matter, the potential application of two gridded meteorological products (GMPs), the China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS) and Climate Forecast System Reanalysis (CFSR), are compared for the first time with data from ground-based meteorological stations over 6 years, from 2008 to 2013, over the Cau River basin (CRB), northern Vietnam. Statistical indicators and the Soil and Water Assessment Tool (SWAT) model are employed to investigate the hydrological performances of the GMPs against the data of 17 rain gauges distributed across the CRB. The results show that there are strong correlations between the temperature reanalysis products in both CMADS and CFSR and those obtained from the ground-based observations (the correlation coefficients range from 0.92 to 0.97). The CFSR data overestimate precipitation (percentage bias approximately 99%) at both daily and monthly scales, whereas the CMADS product performs better, with obvious differences (compared to the ground-based observations) in high-terrain areas. Regarding the simulated river flows, CFSR-SWAT produced “unsatisfactory”, while CMADS-SWAT (R2 > 0.76 and NSE > 0.78) performs better than CFSR-SWAT on the monthly scale. This assessment of the applicative potential of GMPs, especially CMADS, may further provide an additional rapid alternative for water resource research and management in basins with similar hydro-meteorological conditions. Full article
(This article belongs to the Special Issue Water and the Ecosphere in the Anthropocene)
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<p>Map of the Cau River basin: (<b>a</b>) location, digital elevation model (DEM), river systems, ground-based meteorological station (GMS) and hydrological station; (<b>b</b>) land use map.</p> Full article ">Figure 2
<p>Box plots of daily maximum (<b>a</b>–<b>d</b>) and minimum (<b>e</b>–<b>h</b>) temperatures from CFSR and CMADS at the Bac Kan, Dinh Hoa, Thai Nguyen and Bac Ninh meteorological stations.</p> Full article ">Figure 3
<p>Spatial distributions of the correlation coefficient (CC) on the daily (<b>a</b>,<b>b</b>) and monthly (<b>c</b>,<b>d</b>) scales and of MAE (mm/month) (<b>e</b>,<b>f</b>) and PBIAS (%) (<b>g</b>,<b>h</b>) on the monthly scale in the Cau River basin over the period from 2008–2013.</p> Full article ">Figure 4
<p>Occurrence frequencies (<b>a</b>) and relative contributions (<b>b</b>) of daily-scale rainfall thresholds obtained from the CFSR, CMADS and GMS data for the period 2008–2013.</p> Full article ">Figure 5
<p>Number of days when hot weather occurred in the period 2008–2013.</p> Full article ">Figure 6
<p>Observed streamflow and simulations performed using the GMS-, CFSR-, and CMADS-driven models at the daily scale over the CRB.</p> Full article ">Figure 7
<p>Observed streamflow and simulations obtained using the GMS-, CFSR-, and CMADS-driven models at the monthly scale over the CRB.</p> Full article ">
20 pages, 3596 KiB  
Review
A Review of SWAT Model Application in Africa
by George Akoko, Tu Hoang Le, Takashi Gomi and Tasuku Kato
Water 2021, 13(9), 1313; https://doi.org/10.3390/w13091313 - 8 May 2021
Cited by 120 | Viewed by 13715
Abstract
The soil and water assessment tool (SWAT) is a well-known hydrological modeling tool that has been applied in various hydrologic and environmental simulations. A total of 206 studies over a 15-year period (2005–2019) were identified from various peer-reviewed scientific journals listed on the [...] Read more.
The soil and water assessment tool (SWAT) is a well-known hydrological modeling tool that has been applied in various hydrologic and environmental simulations. A total of 206 studies over a 15-year period (2005–2019) were identified from various peer-reviewed scientific journals listed on the SWAT website database, which is supported by the Centre for Agricultural and Rural Development (CARD). These studies were categorized into five areas, namely applications considering: water resources and streamflow, erosion and sedimentation, land-use management and agricultural-related contexts, climate-change contexts, and model parameterization and dataset inputs. Water resources studies were applied to understand hydrological processes and responses in various river basins. Land-use and agriculture-related context studies mainly analyzed impacts and mitigation measures on the environment and provided insights into better environmental management. Erosion and sedimentation studies using the SWAT model were done to quantify sediment yield and evaluate soil conservation measures. Climate-change context studies mainly demonstrated streamflow sensitivity to weather changes. The model parameterization studies highlighted parameter selection in streamflow analysis, model improvements, and basin scale calibrations. Dataset inputs mainly compared simulations with rain-gauge and global rainfall data sources. The challenges and advantages of the SWAT model’s applications, which range from data availability and prediction uncertainties to the model’s capability in various applications, are highlighted. Discussions on considerations for future simulations such as data sharing, and potential for better future analysis are also highlighted. Increased efforts in local data availability and a multidimensional approach in future simulations are recommended. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Methodological approach of the papers reviewed.</p> Full article ">Figure 2
<p>Relative distribution of reviewed papers by countries in Africa.</p> Full article ">Figure 3
<p>Number of papers by year, watershed distribution by area, and number of papers by index.</p> Full article ">Figure 4
<p>Application areas for studies reviewed considering water resources and streamflow simulations in Africa.</p> Full article ">Figure 5
<p>Application areas for studies reviewed considering erosion and sedimentation-related studies in Africa.</p> Full article ">Figure 6
<p>Applications considering a climate context.</p> Full article ">Figure 7
<p>Applications considering model parameterization and dataset inputs.</p> Full article ">
18 pages, 2595 KiB  
Article
Micropollutants in Urban Stormwater Runoff of Different Land Uses
by Daniel Wicke, Andreas Matzinger, Hauke Sonnenberg, Nicolas Caradot, Rabea-Luisa Schubert, Robert Dick, Bernd Heinzmann, Uwe Dünnbier, Dörthe von Seggern and Pascale Rouault
Water 2021, 13(9), 1312; https://doi.org/10.3390/w13091312 - 7 May 2021
Cited by 36 | Viewed by 7182
Abstract
The main aim of this study was a survey of micropollutants in stormwater runoff of Berlin (Germany) and its dependence on land-use types. In a one-year monitoring program, event mean concentrations were measured for a set of 106 parameters, including 85 organic micropollutants [...] Read more.
The main aim of this study was a survey of micropollutants in stormwater runoff of Berlin (Germany) and its dependence on land-use types. In a one-year monitoring program, event mean concentrations were measured for a set of 106 parameters, including 85 organic micropollutants (e.g., flame retardants, phthalates, pesticides/biocides, polycyclic aromatic hydrocarbons (PAH)), heavy metals and standard parameters. Monitoring points were selected in five catchments of different urban land-use types, and at one urban river. We detected 77 of the 106 parameters at least once in stormwater runoff of the investigated catchment types. On average, stormwater runoff contained a mix of 24 µg L−1 organic micropollutants and 1.3 mg L−1 heavy metals. For organic micropollutants, concentrations were highest in all catchments for the plasticizer diisodecyl phthalate. Concentrations of all but five parameters showed significant differences among the five land-use types. While major roads were the dominant source of traffic-related substances such as PAH, each of the other land-use types showed the highest concentrations for some substances (e.g., flame retardants in commercial area, pesticides in catchment dominated by one family homes). Comparison with environmental quality standards (EQS) for surface waters shows that 13 micropollutants in stormwater runoff and 8 micropollutants in the receiving river exceeded German quality standards for receiving surface waters during storm events, highlighting the relevance of stormwater inputs for urban surface waters. Full article
(This article belongs to the Special Issue Research on Urban Runoff Pollution)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Land-use types and location of monitoring catchments in Berlin (Pictures © Google 2015, Geobasis-DE/BKG).</p> Full article ">Figure 2
<p>Comparison of means (black line) and 95% interval (grey area between 2.5% and 97.5% quantiles) with literature values on stormwater runoff in separated sewer systems.</p> Full article ">Figure 3
<p>Concentration boxplots of micropollutant groups (sum of all micropollutants per group, see <a href="#water-13-01312-t003" class="html-table">Table 3</a>) in stormwater of all 5 catchment types. Boxes show 25% and 75% quantiles with median as thick line, whiskers show 5%/95% quantiles, n is number of samples.</p> Full article ">Figure 4
<p>Concentration boxplots of selected biocides/pesticides (<b>a</b>) and DEHP, PAH and nicotine (<b>b</b>) by catchment type (OLD—old building areas, NEW—high-rise newer buildings, OFH—one-family houses, STR—streets &gt;7500 vehicles/d, COM—commercial areas). Whiskers show 5%/95% quantiles.</p> Full article ">Figure 5
<p>Concentrations of selected substances during storm events (boxplots) and dry weather (open circles) in the urban river Panke. Whiskers show minimal and maximal values.</p> Full article ">
23 pages, 10265 KiB  
Article
A Novel Hybrid Approach Based on Cellular Automata and a Digital Elevation Model for Rapid Flood Assessment
by Obaja Triputera Wijaya and Tsun-Hua Yang
Water 2021, 13(9), 1311; https://doi.org/10.3390/w13091311 - 7 May 2021
Cited by 13 | Viewed by 4065
Abstract
An efficient inundation model is necessary for emergency flood responses during storm events. Cellular automata (CA)-based flood models have been proven to produce rapid results while maintaining a certain degree of accuracy. However, the need for computational resources dramatically increases when the number [...] Read more.
An efficient inundation model is necessary for emergency flood responses during storm events. Cellular automata (CA)-based flood models have been proven to produce rapid results while maintaining a certain degree of accuracy. However, the need for computational resources dramatically increases when the number of grid cells increases. Digital elevation model (DEM)-based models generate results even faster, but the simplified governing equations within the models fail to reflect temporal flood evolution. To achieve rapid flood modeling while maintaining model simplicity, a novel two-dimensional hybrid inundation model (HIM) was developed by combining the CA- and DEM-based concepts. Given the temporal flood evolution generated by the CA concept, final finer-scale predictions were obtained by applying the DEM-based concept. The performance of this model was compared to those of widely used, physically based hydraulic models using three UK Environment Agency (EA) benchmark test cases. The HIM yielded consistent prediction results but was faster than the CA-based model. Finally, a comparison was made against flood observations, and the overall root mean squared error (RMSE) for flood depth was 0.388–0.400 m. Considering the uncertainty in the observed flood depths, the HIM shows promising potential to serve as an intermediate tool for emergency response in practical cases. Full article
(This article belongs to the Special Issue New Paradigms in Flood Hazard and Risk Management)
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<p>Flowchart of the HIM.</p> Full article ">Figure 2
<p>Pseudocode for calculating velocity by using the Numpy function library. Python functions are shown in blue, and comments are shown in green.</p> Full article ">Figure 3
<p>IZ illustration. The block of cells on the left (<b>a</b>) represents the coarse grid used by the CA-4D model. Each coarse grid cell acts as an IZ for the finer grid (<b>b</b>) used by the D-Flat model.</p> Full article ">Figure 4
<p>Pseudocode for distributing the water volume within the coarse grid cells to the finer grid cells. The IZ parameter refers to the ground elevation within the IZ.</p> Full article ">Figure 5
<p>(<b>a</b>) EAT2 domain with contour lines every 0.05 m (<b>b</b>) Inflow from the northwest point (x, y = 0 m, 2000 m).</p> Full article ">Figure 6
<p>Temporal variation in the water level for EAT2 at points 1, 2, 3, and 4; comparison among the CA-4D, HIM, TUFLOW, and LISFLOOD-FP models. (<b>a</b>) simulated water level at point 1; (<b>b</b>) simulated water level at point 2; (<b>c</b>) simulated water level at point 3; (<b>d</b>) simulated water level at point 4.</p> Full article ">Figure 7
<p>EAT2: predicted water depth at 48 h by (<b>a</b>) the CA-4D model with 20 m resolution and (<b>b</b>) the HIM.</p> Full article ">Figure 8
<p>(<b>a</b>) EAT4 domain with 6 outpoints taken from Néelz and Pender [<a href="#B38-water-13-01311" class="html-bibr">38</a>] (<b>b</b>) Inflow hydrograph at the central-west point (x, y = 0 m, 1000 m).</p> Full article ">Figure 9
<p>Temporal variation in water level for EAT4 at points 1, 3, 5, and 6; comparison among the CA-4D, HIM, TUFLOW, and LISFLOOD-FP models; (<b>a</b>) simulated water level at point 1; (<b>b</b>) simulated water level at point 3; (<b>c</b>) simulated water level at point 5; (<b>d</b>) simulated water level at point 6.</p> Full article ">Figure 10
<p>EAT4: comparison of flood extents at t = 1 h (<b>first row</b>) and at t = 3 h (<b>second row</b>).</p> Full article ">Figure 11
<p>Cross-section of depths along the line y = 1000 m at t = 1 h.</p> Full article ">Figure 12
<p>EAT8A rainfall event (<b>a</b>) and surcharge flow (<b>b</b>).</p> Full article ">Figure 13
<p>EAT8A domain in which the area inside the black solid lines is considered the road.</p> Full article ">Figure 14
<p>Temporal variation in water level for EAT8A at points 1, 2, 3, and 6; comparison among the CA-4D, HIM, TUFLOW, and LISFLOOD-FP models; (<b>a</b>) simulated water level at point 1; (<b>b</b>) simulated water level at point 2; (<b>c</b>) simulated water level at point 3; (<b>d</b>) simulated water level at point 6.</p> Full article ">Figure 15
<p>Flood extents produced by the HIM (left column) and CA-4D (right column) at t = 1800 s (first row) and t = 18,000 s (second row); (<b>a</b>) the result of HIM at t = 1800 s; (<b>b</b>) the result of CA-4D at t = 1800 s; (<b>c</b>) the result of HIM at t = 18,000 s; (<b>d</b>) the result of CA-4D at t = 18,000 s.</p> Full article ">Figure 16
<p>Rainfall distribution in Chiayi County on 23–24 August 2018.</p> Full article ">Figure 17
<p>Maximum flood extent of the (<b>a</b>) Chiayi County DEM and observation points (red dots), (<b>b</b>) C25 m and (<b>c</b>) C40 m.</p> Full article ">
18 pages, 42359 KiB  
Article
Joint Gravity and Seismic Reflection Methods to Characterize the Deep Aquifers in Arid Ain El Beidha Plain (Central Tunisia, North Africa)
by Hajer Azaiez, Hakim Gabtni and Mourad Bédir
Water 2021, 13(9), 1310; https://doi.org/10.3390/w13091310 - 7 May 2021
Cited by 13 | Viewed by 3842
Abstract
Electric resistivity sounding and tomography, as well as electromagnetic sounding, are the classical methods frequently used for hydrogeological studies. In this work, we propose the development and implementation of an original integrated approach using the unconventional hydro–geophysical methods of gravity and seismic reflection [...] Read more.
Electric resistivity sounding and tomography, as well as electromagnetic sounding, are the classical methods frequently used for hydrogeological studies. In this work, we propose the development and implementation of an original integrated approach using the unconventional hydro–geophysical methods of gravity and seismic reflection for the fast, large–scale characterization of hydrogeological potential using the Ain El Beidha plain (central Tunisia) as an analogue. Extending the values of vintage petroleum seismic reflection profiles and gravity data, in conjunction with available geological and hydrogeological information, we performed an advanced analysis to characterize the geometry of deep tertiary (Oligocene and Eocene) aquifers in this arid area. Residual and tilt angle gravity maps revealed that most gravity anomalies have a short wavelength. The study area was mainly composed of three major areas: the Oued Ben Zitoun and Ain El Beidha basins, which are both related to negative gravity trends corresponding to low–density subsiding depocenters. These basins are separated by an important NE–SW trend called “El Gonna–J. El Mguataa–Kroumet Zemla” gravity high. Evaluation of the superposition of detected lineaments and Euler deconvolution solutions’ maps showed several NE–SW and N–S relay system faults. The 3D density inversion model using a lateral and vertical cutting plane suggested the presence of two different tectonic styles (thin VS thick). Results from the gravity analysis were in concordance with the seismic analysis. The deep Oligocene and Eocene seismic horizons were calibrated to the hydraulic wells and surrounding outcrops. Oligocene and Eocene geological reservoirs appear very fractured and compartmented. The faulting network also plays an important role in enhancing groundwater recharge process of the Oligocene and Eocene aquifers. Finally, generated isochron maps provided an excellent opportunity to develop future comprehensive exploration surveys over smaller and more favorable areas’ sub–basins. Full article
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<p>(<b>A</b>). Regional situation of Tunisia. (<b>B</b>) Geological and hydrogeological setting of the Ain El Beidha plain located in central Tunisia (Geological data adapted from [<a href="#B11-water-13-01310" class="html-bibr">11</a>,<a href="#B20-water-13-01310" class="html-bibr">20</a>] UTM projection WGS84 N32. (1) Quaternary and Mio–Plio–Quaternary. (2) Miocene (Sbiba graben). (3) Miocene (Ain El Beidha plain). (4) Oligocene. (5) Eocene. (6) Upper Cretaceous. (7) Lower Cretaceous. (8) Triassic. (9) Major mapped faults. (10) Dip. (11) River. (12) Boreholes. (13) Seismic line. (14) L1 and L2 seismic lines. (15) Limit of 1km*1km used gravity survey. (16) Hydrogeological well correlation. (17) Groundwater flow direction. (Adopted from [<a href="#B19-water-13-01310" class="html-bibr">19</a>]). (18) Position of the picture. (<b>C</b>) General view of the Ain El Beidha plain.</p> Full article ">Figure 2
<p>Lithostratigraphic column of the tertiary series in the Ain El Beidha plain (adapted from the J. Touila tertiary series description [<a href="#B17-water-13-01310" class="html-bibr">17</a>]) and associated hydrogeological systems. (1) Clay. (2) Sandy clay. (3) Sand. (4) Sandstones. (5) Clayey sand. (6) Sand and clay alternances. (7) consolidated and fossilized Sandstones. (8) Siliciclastic deposits. (9) Dolomites. (10) Limestones.</p> Full article ">Figure 3
<p>Hydrogeological wells correlation crossing the Ain El Beidha plain. (1) Quaternary and Mio–Plio–Quaternary. (2) Miocene (Ain El Beidha plain). (3) Oligocene. (4) Upper Eocene. (5) Lower Eocene. (6) Fault. (7) Water table level. GL: groundwater level. S: salinity. WF: water flow.</p> Full article ">Figure 4
<p>Interpreted Bouguer gravity map of the Ain El Beidha plain. (1) Limits of the major gravity anomalies.</p> Full article ">Figure 5
<p>Interpreted residual gravity map of the Ain El Beidha plain. (1) Limits of major gravity anomalies. (2) Major positive gravity anomaly axis. (3) Major negative gravity anomaly axis. (4) Northern and southern limits of the Ain El Beidha plain.</p> Full article ">Figure 6
<p>Interpreted tilt angle map of the Ain El Beidha plain. (1) Major positive gravity anomaly axis. (2) Major negative gravity anomaly axis. (3) Northern and southern limits of the Ain El Beidha plain.</p> Full article ">Figure 7
<p>Interpreted magnitude of horizontal gravity gradient map of the Ain El Beidha plain. (1) Lineaments.</p> Full article ">Figure 8
<p>Detailed lineament map of the Ain El Beidha plain. deduced from the SED filter and Euler deconvolution solution results. Depth to source estimation was performed using a structural index of 0, a window size of 10*10, and a maximum percentage of depth tolerance of 15%. (1) Major positive gravity anomaly axis. (2) Major negative gravity anomaly axis. (3) Northern and southern limits of the Ain El Beidha plain. (4) Major fault/discontinuity corridors.</p> Full article ">Figure 9
<p>Interpreted 3D density inversion model using the lateral cutting plane of the Ain El Beidha plain. (<b>A</b>) Lateral cutting across El Gonna and Touila structures. (<b>B</b>) Lateral cutting across Oued Ben Zitoun, Kroumet Zemla and Ain El Beidha. (<b>C</b>) Lateral cutting across southern Trozza Mountain, northern Oued Ben Zitoun syncline and northern Kroumet Zemla fold. (<b>D</b>) Lateral cutting across Trozza Mountain and northern Ain El Beidha plain.</p> Full article ">Figure 10
<p>Interpreted seismic reflection profile L1. (1) Top. Oligocene. (2) Top. Eocene. (3) Top. Upper Cretaceous. (4) Major fault.</p> Full article ">Figure 11
<p>Interpreted seismic reflection profile L2. (1) Top. Oligocene. (2) Top. Eocene. (3) Top. Upper Cretaceous. (4) Major fault.</p> Full article ">Figure 12
<p>Isochron map of the top of the Oligocene aquifer. (1) Major positive gravity anomaly axis. (3) Major negative gravity anomaly axis. (4) Northern and southern limits of the Ain El Beidha plain. (4) Major fault/discontinuity corridors.</p> Full article ">Figure 13
<p>Isochron map of the top of the Eocene aquifer. (1) Major positive gravity anomaly axis. (3) Major negative gravity anomaly axis. (4) Northern and southern limits of the Ain El Beidha plain. (4) Major fault/discontinuity corridors.</p> Full article ">Figure 14
<p>Thickness TWT map of the Oligocene aquifer. (1) Major positive gravity anomaly axis. (3) Major negative gravity anomaly axis. (4) Northern and southern limits of the Ain El Beidha plain. (4) Major fault/discontinuity corridors.</p> Full article ">
3 pages, 188 KiB  
Editorial
Advanced Oxidation Processes for Water and Wastewater Treatment
by Marco S. Lucas, José A. Peres and Gianluca Li Puma
Water 2021, 13(9), 1309; https://doi.org/10.3390/w13091309 - 7 May 2021
Cited by 8 | Viewed by 5051
Abstract
Technical and scientific developments have facilitated an increase in human life expectancy and quality, which is reflected in a large growth of global population [...] Full article
(This article belongs to the Special Issue Advanced Oxidation Processes for Water and Wastewater Treatment)
17 pages, 4269 KiB  
Article
A Medium and Long-Term Runoff Forecast Method Based on Massive Meteorological Data and Machine Learning Algorithms
by Yujie Li, Jing Wei, Dong Wang, Bo Li, Huaping Huang, Bin Xu and Yueping Xu
Water 2021, 13(9), 1308; https://doi.org/10.3390/w13091308 - 7 May 2021
Cited by 16 | Viewed by 3880
Abstract
Accurate and reliable predictors selection and model construction are the key to medium and long-term runoff forecast. In this study, 130 climate indexes are utilized as the primary forecast factors. Partial Mutual Information (PMI), Recursive Feature Elimination (RFE) and Classification and Regression Tree [...] Read more.
Accurate and reliable predictors selection and model construction are the key to medium and long-term runoff forecast. In this study, 130 climate indexes are utilized as the primary forecast factors. Partial Mutual Information (PMI), Recursive Feature Elimination (RFE) and Classification and Regression Tree (CART) are respectively employed as the typical algorithms of Filter, Wrapper and Embedded based on Feature Selection (FS) to obtain three final forecast schemes. Random Forest (RF) and Extreme Gradient Boosting (XGB) are respectively constructed as the representative models of Bagging and Boosting based on Ensemble Learning (EL) to realize the forecast of the three types of forecast lead time which contains monthly, seasonal and annual runoff sequences of the Three Gorges Reservoir in the Yangtze River Basin. This study aims to summarize and compare the applicability and accuracy of different FS methods and EL models in medium and long-term runoff forecast. The results show the following: (1) RFE method shows the best forecast performance in all different models and different forecast lead time. (2) RF and XGB models are suitable for medium and long-term runoff forecast but XGB presents the better forecast skills both in calibration and validation. (3) With the increase of the runoff magnitudes, the accuracy and reliability of forecast are improved. However, it is still difficult to establish accurate and reliable forecasts only large-scale climate indexes used. We conclude that the theoretical framework based on Machine Learning could be useful to water managers who focus on medium and long-term runoff forecast. Full article
(This article belongs to the Special Issue Using Statistical and Machine Learning Algorithms for Big Data Applications in Hydrology)
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<p>Flow chart of Bagging algorithm.</p> Full article ">Figure 2
<p>Flow chart of Boosting algorithm.</p> Full article ">Figure 3
<p>Scatterplots of monthly observed and simulated runoff sequences estimated from (<b>a</b>) RF and (<b>b</b>) XGB model in calibration. The orange line represents 1:1 line which means a perfect fitness. The vertical axis is the observed runoff value and the horizontal axis is the simulated runoff value.</p> Full article ">Figure 4
<p>Heatmaps plots of monthly observed and simulated runoff sequences estimated from RF and XGB model in validation. The legend is set to +50% at the maximum and −50% at the minimum of all the heatmaps and the lighter the color, the smaller the absolute value of the RE.</p> Full article ">Figure 5
<p>Letter-value plots of monthly observed and simulated runoff sequences estimated from RF and XGB model of Scheme A, B, C in validation. 1-A means the result of using Scheme A as predictors in Jan and others have an analogous meaning. The vertical axis is the observed runoff value, and the horizontal axis is the simulated runoff value.</p> Full article ">Figure 5 Cont.
<p>Letter-value plots of monthly observed and simulated runoff sequences estimated from RF and XGB model of Scheme A, B, C in validation. 1-A means the result of using Scheme A as predictors in Jan and others have an analogous meaning. The vertical axis is the observed runoff value, and the horizontal axis is the simulated runoff value.</p> Full article ">Figure 6
<p>Scatterplots of seasonal observed and simulated runoff sequences estimated from (<b>a</b>) RF and (<b>b</b>) XGB model in calibration. The orange line represents 1:1 line which means a perfect fitness. The vertical axis is the observed runoff value, and the horizontal axis is the simulated runoff value.</p> Full article ">Figure 7
<p>Heatmaps plots of seasonal observed and simulated runoff sequences estimated from RF and XGB model in validation. The legend is set to +50% at the maximum and −50% at the minimum of all the heatmaps and the lighter the color, the smaller the absolute value of the RE. S1_A means the result of using Scheme A as predictors in first season and others have an analogous meaning.</p> Full article ">Figure 8
<p>Scatterplots of annual observed and simulated runoff sequences estimated from (<b>a</b>) RF and (<b>b</b>) XGB model in calibration. The orange line represents 1:1 line which means a perfect fitness. The vertical axis is the observed runoff value and the horizontal axis is the simulated runoff value.</p> Full article ">Figure 9
<p>Bar plots of RE of annual observed and simulated runoff sequences estimated from (<b>a</b>) RF and (<b>b</b>) XGB model in validation. Blue, green and red respectively represent the result of Scheme A, B and C.</p> Full article ">
11 pages, 3812 KiB  
Article
Remote Sensing Investigation of the Offset Effect between Reservoir Impoundment and Glacier Meltwater Supply in Tibetan Highland Catchment
by Jingying Zhu, Chunqiao Song, Linghong Ke, Kai Liu and Tan Chen
Water 2021, 13(9), 1307; https://doi.org/10.3390/w13091307 - 7 May 2021
Cited by 4 | Viewed by 2181
Abstract
This article presents multi-source remote sensing measurements to quantify the water impoundment and regulation of the Zhikong Reservoir (ZKR) and Pangduo Reservoir (PDR), together with the estimation of the glacier mass balance to explore whether the increased glacier meltwater supply can buffer the [...] Read more.
This article presents multi-source remote sensing measurements to quantify the water impoundment and regulation of the Zhikong Reservoir (ZKR) and Pangduo Reservoir (PDR), together with the estimation of the glacier mass balance to explore whether the increased glacier meltwater supply can buffer the influences of the reservoir impoundment to some degree in the Tibetan highland catchment. The ZKR and PDR are two reservoirs constructed on the upper Lhasa River that originate from the Nyainqentanglha glaciers in the remote headwater in the Tibetan Plateau (TP) and lacks historical in situ hydrological observations in the long term. Therefore, the Joint Research Center (JRC) Global Surface Water dataset (GSW), and the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) data were used for estimating the total amount of water storage of the two reservoirs, and the SRTM and TanDEM-X DEMs were used for estimating the glacier mass balance. The result shows that the total amount of water impounded by reservoirs is 0.76 Gt, roughly 54% of their design capacities. The mass balance of the glaciers is estimated by comparing the elevation changes between the SRTM and TanDEM-X DEMs. The glaciers in this region melt at an average rate of 0.09 ± 0.02 Gt·year−1 from 2000 to circa 2013, and the impounded water of these reservoirs is comparable to the amount of glacier-fed meltwater in eight years. Full article
(This article belongs to the Special Issue Understanding Surface Water Dynamics Based on Multisource Remote Sensing Data)
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<p>Overview of the Lhasa River basin and the location and main hydrological elements (DEM) of the study area.</p> Full article ">Figure 2
<p>The distribution of elevation differences (dh) between the TanDEM-X and SRTM DEMs in relation to the aspect (<b>a</b>) and elevation (<b>b</b>) before and after systemic bias correction.</p> Full article ">Figure 3
<p>Multiyear averaged monthly water level, storage, and storage change of the PDR (2014–2018) and the ZKR (2007–2018), respectively. The dashed lines of the water level and water storage are the designed normal water level and the corresponding water storage. The month of December for the PDR is omitted because of a lack of valid observations in the GSW datasets.</p> Full article ">Figure 4
<p>Changes in (<b>a</b>) the annual elevation and (<b>b</b>) the annual glacier elevation in the study area, and (<b>c</b>,<b>d</b>) the glacier elevation changes in relation to the elevation (m a.s.l.) derived from differentiating the TanDEM-X and SRTM. Statistics are grouped in a 100-m elevation bin.</p> Full article ">Figure 5
<p>Bathymetry of the PDR and ZKR; the 3D topographic map of the PDR and ZKR.</p> Full article ">Figure 6
<p>(<b>a</b>) Monthly surface runoff and (<b>b</b>) SWE derived from Noah, VIC, and CLM and their average upstream basin values from 2007 to 2018.</p> Full article ">
16 pages, 783 KiB  
Article
Sewage Sludge Compared with Other Substrates in the Inoculation, Growth, and Tolerance to Water Stress of Samanea saman
by Gustavo Wyse Abaurre, Jorge Makhlouta Alonso, Orivaldo José Saggin Júnior and Sergio Miana de Faria
Water 2021, 13(9), 1306; https://doi.org/10.3390/w13091306 - 7 May 2021
Cited by 3 | Viewed by 2336
Abstract
This study evaluated the initial growth and tolerance to water stress after planting Samanea saman seedlings produced with different substrates and inoculation patterns. The experiment used a factorial design (3 × 3), with three substrates: standard (67% subsoil + 33% cattle manure), a [...] Read more.
This study evaluated the initial growth and tolerance to water stress after planting Samanea saman seedlings produced with different substrates and inoculation patterns. The experiment used a factorial design (3 × 3), with three substrates: standard (67% subsoil + 33% cattle manure), a commercial substrate (composed mainly of peat), and treated sewage sludge; and three inoculation patterns: control (no inoculation), fertilized (no inoculation + chemical fertilization), and inoculation with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi. The seedlings were planted in plastic pots inside a greenhouse. They received irrigation after planting and were submitted to water deficit for 35 days, followed by rehydration for 31 days. The inoculation promoted higher height and biomass for seedlings produced in the standard substrate. In the sludge, the roots biomass decreased when fertilized or inoculated. Seedlings grown in sludge showed higher height and biomass before planting and at the end of the experiment. Although, after rehydration, the height increment was similar for the sludge and the standard substrate. Seedlings grown with the commercial substrate are not recommended for planting sites subjected to water deficit. The standard substrate with inoculation and the sludge without inoculation or fertilization produced seedlings that showed better recovery and growth after water deficit. Full article
(This article belongs to the Special Issue Management and Reuse of Sewage Sludge from Wastewater Treatment)
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<p>Root dry mass (RDM) and shoot dry mass (SDM) of <span class="html-italic">Samanea saman</span> plants, in which seedlings were produced with different inoculation patterns and substrates. Equal lower-case letters for inoculation patterns (<b>a</b>) and equal upper-case letters for substrate (<b>b</b>) do not differ from each other by Scott-Knott test at 5% of probability. Letters inside the black bars refer to seedlings’ dry mass before planting (CV = 7.2 and 10.2% respectively for SDM and RDM), inside white bars to their increment during the 66 days of the experiment (CV = 23.2 and 17.2% respectively for SDM and RDM), and out of the bars for the total dry mass at 66 after planting (CV = 12.1 and 9.1% respectively for SDM and RDM). Inoculation treatments: NFB + AMF (seedlings inoculated with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi); PC = positive control (non-inoculated seedlings fertilized with 111 mg of N, 16 mg of P<sub>2</sub>O<sub>5</sub>, and 51 mg of K<sub>2</sub>O); C = control (no inoculation and no fertilization). Substrate treatments: sludge (sewage sludge from the Ilha do Governador WWTP, provided by CEDAE); commercial (commercial substrate composed mainly of sphagnum peat plus vermiculite and carbonized rice husk); standard (67% clay subsoil plus 33% of cattle manure).</p> Full article ">Figure 1 Cont.
<p>Root dry mass (RDM) and shoot dry mass (SDM) of <span class="html-italic">Samanea saman</span> plants, in which seedlings were produced with different inoculation patterns and substrates. Equal lower-case letters for inoculation patterns (<b>a</b>) and equal upper-case letters for substrate (<b>b</b>) do not differ from each other by Scott-Knott test at 5% of probability. Letters inside the black bars refer to seedlings’ dry mass before planting (CV = 7.2 and 10.2% respectively for SDM and RDM), inside white bars to their increment during the 66 days of the experiment (CV = 23.2 and 17.2% respectively for SDM and RDM), and out of the bars for the total dry mass at 66 after planting (CV = 12.1 and 9.1% respectively for SDM and RDM). Inoculation treatments: NFB + AMF (seedlings inoculated with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi); PC = positive control (non-inoculated seedlings fertilized with 111 mg of N, 16 mg of P<sub>2</sub>O<sub>5</sub>, and 51 mg of K<sub>2</sub>O); C = control (no inoculation and no fertilization). Substrate treatments: sludge (sewage sludge from the Ilha do Governador WWTP, provided by CEDAE); commercial (commercial substrate composed mainly of sphagnum peat plus vermiculite and carbonized rice husk); standard (67% clay subsoil plus 33% of cattle manure).</p> Full article ">
16 pages, 18505 KiB  
Article
A Sentinel-2 Image-Based Irrigation Advisory Service: Cases for Tea Plantations
by Yi-Ping Wang, Chien-Teh Chen, Yao-Chuan Tsai and Yuan Shen
Water 2021, 13(9), 1305; https://doi.org/10.3390/w13091305 - 7 May 2021
Cited by 5 | Viewed by 2611
Abstract
In this study, we aim to develop an inexpensive site-specific irrigation advisory service for resolving disadvantages related to using immobile soil moisture sensors and to the differences in irrigation needs of different tea plantations affected by variabilities in cultivars, plant ages, soil heterogeneity, [...] Read more.
In this study, we aim to develop an inexpensive site-specific irrigation advisory service for resolving disadvantages related to using immobile soil moisture sensors and to the differences in irrigation needs of different tea plantations affected by variabilities in cultivars, plant ages, soil heterogeneity, and management practices. In the paper, we present methodologies to retrieve two biophysical variables, surface soil water content and canopy water content of tea trees from Sentinel-2 (S2) (European Space Agency, Paris, France) images and consider their association with crop water availability status to be used for making decisions to send an alert level. Precipitation records are used as auxiliary information to assist in determining or modifying the alert level. Once the site-specific alert level for each target plantation is determined, it is sent to the corresponding farmer through text messaging. All the processes that make up the service, from downloading an S2 image from the web to alert level text messaging, are automated and can be completed before 7:30 a.m. the next day after an S2 image was taken. Therefore, the service is operated cyclically, and corresponds to the five-day revisit period of S2, but one day behind the S2 image acquisition date. However, it should be noted that the amount of irrigation water required for each site-specific plantation has not yet been estimated because of the complexities involved. Instead, a single irrigation rate (300 t ha−1) per irrigation event is recommended. The service is now available to over 20 tea plantations in the Mingjian Township, the largest tea producing region in Taiwan, free of charge since September 2020. This operational application is expected to save expenditures on buying irrigation water and induce deeper root systems by decreasing the frequency of insufficient irrigation commonly employed by local farmers. Full article
(This article belongs to the Special Issue Contributions of Remote Sensing to Hydrologic Flux Quantification)
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<p>Schematics showing the two-tiered approach used in developing the irrigation advisory service. Abbreviations used are explained in the text.</p> Full article ">Figure 2
<p>Changes in soil water content (SWC) at 15 and 30 cm depths measured by volumetric soil moisture sensors and SWC retrieved from Sentinel-2 (S2) images.</p> Full article ">Figure 3
<p>Relationships between SWC and NDWI (<b>A</b>) and accumulated frequency distributions of SWC (<b>B</b>) and NDWI (<b>C</b>).</p> Full article ">Figure 4
<p>Changes in (<b>A</b>) soil water content (SWC); (<b>B</b>) normalized difference water index (NDWI); (<b>C</b>) crop water availability index (CWAI); (<b>D</b>) modified soil-adjusted vegetation index (MSAVI), at three ground data collecting plantations from 2018 to 2020.</p> Full article ">Figure 5
<p>Spatiotemporal maps of SWC, NDWI, CWAI, and MSAV for three ground data collecting plantations (F1, F2, and F3) from September to December 2020 and corresponding aerial image. Scales of SWC and NDVI correspond to the four levels classified by the thresholds specified in <a href="#water-13-01305-t001" class="html-table">Table 1</a> (1, the driest and 4, the wettest). The aerial image on 6 October 2020 was taken by a Phantom 4 Pro (DJI Science and Technology Co., Ltd., Shenzhen, China) and the orthomosaic was generated by Pix4Dmapper (Pix4D Inc., San Francisco, CA, USA).</p> Full article ">
18 pages, 4872 KiB  
Article
Optimising the Workflow for Fish Detection in DIDSON (Dual-Frequency IDentification SONar) Data with the Use of Optical Flow and a Genetic Algorithm
by Triantafyllia-Maria Perivolioti, Michal Tušer, Dimitrios Terzopoulos, Stefanos P. Sgardelis and Ioannis Antoniou
Water 2021, 13(9), 1304; https://doi.org/10.3390/w13091304 - 7 May 2021
Cited by 6 | Viewed by 2804
Abstract
DIDSON acoustic cameras provide a way to collect temporally dense, high-resolution imaging data, similar to videos. Detection of fish targets on those videos takes place in a manual or semi-automated manner, typically assisted by specialised software. Exploiting the visual nature of the recordings, [...] Read more.
DIDSON acoustic cameras provide a way to collect temporally dense, high-resolution imaging data, similar to videos. Detection of fish targets on those videos takes place in a manual or semi-automated manner, typically assisted by specialised software. Exploiting the visual nature of the recordings, tools and techniques from the field of computer vision can be applied in order to facilitate the relatively involved workflows. Furthermore, machine learning techniques can be used to minimise user intervention and optimise for specific detection and tracking scenarios. This study explored the feasibility of combining optical flow with a genetic algorithm, with the aim of automating motion detection and optimising target-to-background segmentation (masking) under custom criteria, expressed in terms of the result. A 1000-frame video sequence sample with sparse, smoothly moving targets, reconstructed from a 125 s DIDSON recording, was analysed under two distinct scenarios, and an elementary detection method was used to assess and compare the resulting foreground (target) masks. The results indicate a high sensitivity to motion, as well as to the visual characteristics of targets, with the resulting foreground masks generally capturing fish targets on the majority of frames, potentially with small gaps of undetected targets, lasting for no more than a few frames. Despite the high computational overhead, implementation refinements could increase computational feasibility, while an extension of the algorithms, in order to include the steps of target detection and tracking, could further improve automation and potentially provide an efficient tool for the automated preliminary assessment of voluminous DIDSON data recordings. Full article
(This article belongs to the Special Issue Water Resources Management: Advances in Machine Learning Approaches)
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<p>The site studied for monitoring fish upstream migration was located on the Vltava River, Czech Republic, approximately 2 km upstream off the Lipno reservoir (<b>upper</b> enlargement) and the DIDSON acoustic camera was placed on the right bank of the river (<b>lower</b> enlargement).</p> Full article ">Figure 2
<p>Flow chart depicting the proposed procedure for fish-target mask extraction from raw DIDSON data, i.e., the data pre-processing step and the iterative part, which utilizes the optical flow calculation and a genetic algorithm to extract an optimal foreground mask for subsequent target detections.</p> Full article ">Figure 3
<p>A conversion diagram of a real-world ensonified field-of-view to a digital image sequence representation.</p> Full article ">Figure 4
<p>A comparison of histograms, from the entire image frame to a small region encompassing an identified target object (pixel values with intensity equal to 0 are excluded from the calculations).</p> Full article ">Figure 5
<p>Evolution of the mean and average penalty per generation along a run of 5 iterations, using a penalty function of the average mask pixel count per frame.</p> Full article ">Figure 6
<p>Evolution of the mean and average penalty per generation for a run of 5 iterations, using a penalty function assigning a significant penalty to very large objects (&gt;5000 px) and a size-dependent penalty to very small objects.</p> Full article ">Figure 7
<p>Scenario 33–14 threshold distribution histogram, indicating the most frequent pixel intensity thresholds of 17 and 18.</p> Full article ">Figure 8
<p>Sample frame subsequence displaying the optical flow determined velocity magnitudes mapped as normalized values between 0–255. Whiter shades represent larger velocity magnitudes, hence, more intense motion.</p> Full article ">Figure 9
<p>Sample frame subsequence displaying the determined mask superimposed on the original corresponding video frames. White represents masked areas.</p> Full article ">Figure 10
<p>Sample frame of the final resulting target mask, displayed for three different parameter choices for the filter size <span class="html-italic">s<sub>f</sub></span> and neighbourhood size <span class="html-italic">s<sub>n</sub></span> (displayed beneath each frame in the form <span class="html-italic">s<sub>f</sub></span>–<span class="html-italic">s<sub>n</sub></span>).</p> Full article ">Figure 11
<p>Layout for the manual target detection (left) and comparison to automatic criteria-based (50 px &lt; object area &lt; 350 px) target detection (right) result. Total detections, total correct detections and total misdetections were counted.</p> Full article ">Figure 12
<p>Classified per-frame target detection success rate—Comparison between scenarios.</p> Full article ">Figure 13
<p>Classified per-frame target misdetections—Comparison between scenarios.</p> Full article ">
26 pages, 9638 KiB  
Article
Analysis of Seepage Characteristics of a Foundation Pit with Horizontal Waterproof Curtain in Highly Permeable Strata
by Chenghua Shi, Xiaohe Sun, Shengli Liu, Chengyong Cao, Linghui Liu and Mingfeng Lei
Water 2021, 13(9), 1303; https://doi.org/10.3390/w13091303 - 6 May 2021
Cited by 9 | Viewed by 4930
Abstract
At present, jet-grouted horizontal waterproof curtain reinforcement has become an essential method for deep foundation pit groundwater control. However, there is still a lack of an effective theoretical calculation method for horizontal waterproof curtain reinforcement, and there is little research on the seepage [...] Read more.
At present, jet-grouted horizontal waterproof curtain reinforcement has become an essential method for deep foundation pit groundwater control. However, there is still a lack of an effective theoretical calculation method for horizontal waterproof curtain reinforcement, and there is little research on the seepage laws of foundation pits under different horizontal waterproof curtain conditions. Based on Darcy’s seepage theory, theoretical analysis models of deep foundation pit seepage were established considering the effect of a horizontal curtain in a highly permeable formation. Through the established models, the calculation method of the water inflow and the water pressure under the condition of a horizontal curtain was derived. Then through indoor tests, the reliability of the theoretical calculation method was verified. Furthermore, the established theoretical calculation method is used to analyze the influence of various factors on the water inflow and the water pressure, such as the ratio of hydraulic conductivity of the horizontal curtain to surrounding soil, thickness, and reinforcement position of the horizontal curtain. It is found that the hydraulic conductivity ratio has the most significant influence on the seepage characteristics of the foundation pit. Finally, the design method was applied to an example of the horizontal waterproof curtain of the foundation pit, which is located at Juyuanzhou Station in Fuzhou (China). The water inflow per unit area is 0.36 m3/d in the foundation pit, and this implies that the design method of the horizontal waterproof curtain applied for the excavation case is good and meets the requirements of design and safety. Full article
(This article belongs to the Special Issue Modeling of Flow and Transport in Saturated and Unsaturated Porous Media)
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<p>The schematic diagram for seepage calculation of horizontal waterproof curtain of foundation pit under the action of phreatic in homogeneous strata. (<span class="html-italic">w</span> the width of the pit; <span class="html-italic">h</span> water head height; <span class="html-italic">l</span> length of the seepage path; <span class="html-italic">L</span> the length of the seepage path outside the pit; <span class="html-italic">k</span> hydraulic conductivity).</p> Full article ">Figure 2
<p>Schematic diagram for seepage calculation of horizontal waterproof curtain of foundation pit under the action of phreatic water in multiple strata. (<span class="html-italic">h</span> water head height; <span class="html-italic">k</span> hydraulic conductivity; <span class="html-italic">l</span> the length of the seepage path).</p> Full article ">Figure 3
<p>Schematic diagram for seepage calculation of horizontal waterproof curtain of foundation pit under the action of artesian water. (<span class="html-italic">h</span> water head height; <span class="html-italic">l</span> the length of the seepage path; <span class="html-italic">k</span> hydraulic conductivity; <span class="html-italic">w</span> width of the pit; <span class="html-italic">p</span> water pressure at the bottom of the diaphragm wall).</p> Full article ">Figure 4
<p>Schematic diagram of test model box. (<span class="html-italic">z</span> the thickness of the curtain; <span class="html-italic">y</span> the distance between the curtain and the top surface of the fill).</p> Full article ">Figure 5
<p>Comparison curves of pit water inflow with different parameters. (<b>a</b>) influence of hydraulic conductivity ratio on water inflow; (<b>b</b>) influence of curtain’s thickness on water inflow; (<b>c</b>) influence of curtain’s position on water inflow.</p> Full article ">Figure 6
<p>Comparison curves of water head height with different parameters. (<b>a</b>) influence of hydraulic conductivity ratio on water pressure; (<b>b</b>) influence of curtain’s thickness on water pressure; (<b>c</b>) influence of curtain’s position on water pressure.</p> Full article ">Figure 7
<p>Diagram of water line.</p> Full article ">Figure 8
<p>Simplified model diagram of a foundation pit. (<span class="html-italic">H</span> the height difference between the water level outside the pit and the bottom of the pit; <span class="html-italic">l</span> the length of the seepage path; <span class="html-italic">z</span> the thickness of the curtain).</p> Full article ">Figure 9
<p>Variation of water head under different hydraulic conductivity ratios.</p> Full article ">Figure 10
<p>Variation of water inflow with different hydraulic conductivity ratios.</p> Full article ">Figure 11
<p>Variation of bottom water head with different thickness.</p> Full article ">Figure 12
<p>Variation of water inflow with different thickness.</p> Full article ">Figure 13
<p>Variation of the water pressure with different positions.</p> Full article ">Figure 14
<p>Variation of water inflow with different positions.</p> Full article ">Figure 15
<p>Multi-aquifer calculation model diagram. (<span class="html-italic">z</span> the thickness of the curtain; <span class="html-italic">y</span> the distance between the curtain’s bottom and the diaphragm wall’s bottom).</p> Full article ">Figure 16
<p>Effect of hydraulic conductivity ratio on result.</p> Full article ">Figure 17
<p>The effect of the thickness of horizontal curtain on water inflow.</p> Full article ">Figure 18
<p>Position sketch of both horizontal curtain and impermeable layer. (<span class="html-italic">y</span> the distance between the curtain’s bottom and the diaphragm wall’s bottom).</p> Full article ">Figure 19
<p>The effect of curtain position on result diagram.</p> Full article ">Figure 20
<p>Station location.</p> Full article ">Figure 21
<p>Station plan and surrounding environment.</p> Full article ">Figure 22
<p>The diagram of the geological section and partition of the cut-off wall.</p> Full article ">Figure 23
<p>The cross section of the station.</p> Full article ">Figure 24
<p>Change graph of water inflow with hydraulic conductivity.</p> Full article ">Figure 25
<p>Change graph of water pressure with hydraulic conductivity.</p> Full article ">Figure 26
<p>Pumping and observation wells distribution. (JS pumping wells; SW observation wells; GB pumping and observation wells).</p> Full article ">Figure 27
<p>Water depth and water inflow in No.1 pit. (JS pumping wells; SW observation wells; <span class="html-italic">Q</span>1 the water inflow inside the No. 1 pit).</p> Full article ">
18 pages, 4139 KiB  
Article
Interactions of Solitary Wave with a Submerged Step: Experiments and Simulations
by Wei-Ting Chao, Shin-Jye Liang, Chih-Chieh Young and Chao-Lung Ting
Water 2021, 13(9), 1302; https://doi.org/10.3390/w13091302 - 6 May 2021
Cited by 1 | Viewed by 2590
Abstract
A series of experiments exploring the propagation of a solitary wave over a submerged step were performed using a flow-field visualization measurement system, an image-connection technique as well as model simulations. The experimental data were used to validate a one-layer finite-element non-hydrostatic model [...] Read more.
A series of experiments exploring the propagation of a solitary wave over a submerged step were performed using a flow-field visualization measurement system, an image-connection technique as well as model simulations. The experimental data were used to validate a one-layer finite-element non-hydrostatic model and a multi-layer finite-difference non-hydrostatic σ model for various submerged step configurations and wave conditions—combinations of step height ratios d/h, width ratios B/h and solitary wave height ratios H/h, where d denotes the step height, B the step width, H the solitary wave height, and h the still water depth. The main differences between the numerical results and the experimental data are highlighted. The effect of the height and width of the submerged step as well as the wave height of the solitary wave are quantified in terms of reflection (R), transmission (T), and energy dissipation (D). Through a series of numerical experiments, an optimal combination of the height ratio d/h, width ratio B/h, and solitary wave height ratio H/h for breakwater design for coastal protection is suggested. Full article
(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)
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<p>Illustration of setup of (<b>a</b>) experiments and (<b>b</b>) model simulations.</p> Full article ">Figure 2
<p>(<b>a</b>) Snapshot of the free surface and (<b>b</b>) 2D spatial-temporal results of the waveforms of experimental results of Case 06 after post-processing.</p> Full article ">Figure 3
<p>Comparison of approximations with computed results of a propagating solitary wave in a flat channel at <span class="html-italic">t</span> = 5 and 10 s: (<b>a</b>) horizontal velocity, (<b>b</b>) vertical velocity, and (<b>c</b>) dynamic pressure, respectively (circles denote analytical solution; black lines denote FD model results; green lines denote FE model results).</p> Full article ">Figure 4
<p>Comparison of free-surface of experiment with model result for a propagating solitary wave in a flat channel at various time instances (circles denote experimental data; black lines denote FD model results; green lines denote FE model results).</p> Full article ">Figure 5
<p>Snapshots of the wave profiles at <span class="html-italic">t</span> = 2, 4, 6, and 8 s (from bottom to top): (<b>a</b>) Case 01, <span class="html-italic">d</span>/<span class="html-italic">h</span> of 0.5 and (<b>b</b>) Case 03, <span class="html-italic">d</span>/<span class="html-italic">h</span> of 0.7 (circles denote experimental data; black lines denote FD results; grey lines denote FE results).</p> Full article ">Figure 5 Cont.
<p>Snapshots of the wave profiles at <span class="html-italic">t</span> = 2, 4, 6, and 8 s (from bottom to top): (<b>a</b>) Case 01, <span class="html-italic">d</span>/<span class="html-italic">h</span> of 0.5 and (<b>b</b>) Case 03, <span class="html-italic">d</span>/<span class="html-italic">h</span> of 0.7 (circles denote experimental data; black lines denote FD results; grey lines denote FE results).</p> Full article ">Figure 6
<p>Relation of (<b>a</b>) reflection (<b>b</b>) transmission and (<b>c</b>) dissipation coefficient with step height for the solitary wave over a submerged step with step widths <span class="html-italic">B/h</span> = 10 and 20 (red squares denote experimental results with <span class="html-italic">B/h</span> = 10 and red triangles denote experimental results with <span class="html-italic">B/h</span> = 20; black squares denote FD model results with <span class="html-italic">B/h</span> = 10 and black triangles denote FD model results with <span class="html-italic">B/h</span> = 20; green squares denote FE model results with <span class="html-italic">B/h</span> = 10 and green triangles denote FE model results with <span class="html-italic">B/h</span> = 20, respectively).</p> Full article ">Figure 7
<p>Comparison of the free surface at <span class="html-italic">t</span> = (<b>a</b>) 4 s and (<b>b</b>) 12 s for <span class="html-italic">B/h</span> values of 10, 30, and 50 (black lines: FD model results; green lines: FE model results; the black thick line indicates the position of the submerged step).</p> Full article ">Figure 8
<p>Relation of (<b>a</b>) reflection (<b>b</b>) transmission and (<b>c</b>) dissipation coefficient with the step width ratio (<span class="html-italic">B/h</span>) for the solitary wave over a submerged step with step heights <span class="html-italic">d/h</span> of 0.5 and 0.7 (red and filled squares denote experimental results with a <span class="html-italic">d/h</span> of 0.5 and 0.7; black and filled squares represent FD model results with a <span class="html-italic">d/h</span> of 0.5 and 0.7; green and filled squares denote FE model results with a <span class="html-italic">d/h</span> of 0.5 and 0.7, respectively).</p> Full article ">Figure 9
<p>Snapshots of the wave profiles from bottom to top at <span class="html-italic">t</span> = 2, 4, 6, and 8 s (red circles and dashed lines denote <span class="html-italic">H/h</span> values of 0.09 and 0.13 for the experimental data; black dashed and solid lines denote <span class="html-italic">H/h</span> values of 0.09 and 0.13 for the FD model; grey dashed and solid lines denote <span class="html-italic">H/h</span> values of 0.09 and 0.13 for the FE model).</p> Full article ">Figure 10
<p>A parameter study of the relation of the dissipation coefficient <span class="html-italic">D</span> with the combined parameters of <span class="html-italic">d/h</span>, <span class="html-italic">B/h,</span> and <span class="html-italic">H/h</span> (the black line denotes the optimal regression; black and green circles denote FD and FE model results, respectively).</p> Full article ">
11 pages, 1450 KiB  
Article
Effects of Infiltration Amounts on Preferential Flow Characteristics and Solute Transport in the Protection Forest Soil of Southwestern China
by Mingfeng Li, Jingjing Yao, Ru Yan and Jinhua Cheng
Water 2021, 13(9), 1301; https://doi.org/10.3390/w13091301 - 6 May 2021
Cited by 18 | Viewed by 3058
Abstract
Preferential flow has an important role as it strongly influences solute transport in forest soil. The quick passage of water and solutes through preferential flow paths without soil absorption results in considerable water loss and groundwater pollution. However, preferential flow and solute transport [...] Read more.
Preferential flow has an important role as it strongly influences solute transport in forest soil. The quick passage of water and solutes through preferential flow paths without soil absorption results in considerable water loss and groundwater pollution. However, preferential flow and solute transport under different infiltration volumes in southwestern China remain unclear. Three plots, named P20, P40 and P60, were subjected to precipitation amounts of 20, 40 and 60 mm, respectively, to investigate preferential flow and solute transport characteristics via field multiple-tracer experiments. Stained soils were collected to measure Br− and NO3− concentrations. This study demonstrated that precipitation could promote dye tracer infiltration into deep soils. The dye tracer reached the maximum depth of 40 cm in P60. Dye coverage generally reduced with greater depth, and sharp reductions were observed at the boundary of matrix flow and preferential flow. Dye coverage peaked at the soil depth of 15 cm in P40. This result demonstrated that lateral infiltration was enhanced. The long and narrow dye coverage pattern observed in P60 indicated the occurrence of macropore flow. Br− and NO3− were found at each soil depth where preferential flow had moved. Increasing precipitation amounts increased Br− and NO3− concentration and promoted solute movement into deep soil layers. Solute concentration peaked at near the end of the preferential flow path and when preferential flow underwent lateral movement. These results indicated that the infiltration volume and transport capacity of preferential flow had important effects on the distribution of Br− and NO3− concentrations. The results of this study could help expand our understanding of the effects of preferential flow on solute transport and provide some suggestions for protection forest management in southwestern China. Full article
(This article belongs to the Special Issue Soil Water Erosion)
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<p>Diagram of the experimental set-up for multiple-tracer experiments.</p> Full article ">Figure 2
<p>Images showing vertical slices from the dye-stained soil profiles and average dye coverage of vertical slices with depth under different water amounts: (<b>a</b>) 20, (<b>b</b>) 40 and (<b>c</b>) 60 mm.</p> Full article ">Figure 3
<p>Changes in Br<sup>−</sup> concentration with soil depth.</p> Full article ">Figure 4
<p>Changes in NO<sub>3</sub><sup>−</sup> concentration with soil depth.</p> Full article ">
16 pages, 2354 KiB  
Article
Evaluation of Subsurface Drip Irrigation Designs in a Soil Profile with a Capillary Barrier
by Koichi Noguchi, Hirotaka Saito, Reskiana Saefuddin and Jiří Šimůnek
Water 2021, 13(9), 1300; https://doi.org/10.3390/w13091300 - 6 May 2021
Cited by 7 | Viewed by 4446
Abstract
Enhanced water use efficiency (WUE) is the key to sustainable agriculture in arid regions. The installation of capillary barriers (CB) has been suggested as one of the potential solutions. CB effects are observed between two soil layers with distinctly different soil hydraulic properties. [...] Read more.
Enhanced water use efficiency (WUE) is the key to sustainable agriculture in arid regions. The installation of capillary barriers (CB) has been suggested as one of the potential solutions. CB effects are observed between two soil layers with distinctly different soil hydraulic properties. A CB helps retain water in the upper, relatively fine-textured soil layer, suppressing water losses by deep drainage. However, retaining water in a shallow surface layer also intensifies water loss by evaporation. The use of subsurface drip irrigation (SDI) with a CB may prevent such water loss. This study evaluated the performance of SDI in a soil profile with a CB using a pot experiment and numerical analysis with the HYDRUS (2D/3D) software package. The ring-shaped emitter was selected for the SDI system for its low capital expenditures (CapEx) and maintenance. Strawberry was selected as a model plant. The results indicated that the proposed SDI system with a CB was effective in terms of WUE. The numerical analysis revealed that the CB’s depth influences the system’s water balance more than the ring-shaped emitter’s installation depth. While the CB’s shallow installation led to more root water uptake by the strawberry and less water loss by deep drainage, it induced more water loss by evaporation. Full article
(This article belongs to the Special Issue Development and Application of Subsurface Irrigation Techniques)
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<p>Configuration of the ring-shaped emitter (adapted from Saefuddin et al. [<a href="#B20-water-13-01300" class="html-bibr">20</a>]).</p> Full article ">Figure 2
<p>(<b>a</b>) A vertical cross-section and (<b>b</b>) top view of the setup of the pot experiment. Red points S1–S6 show the positions of the soil moisture sensors. Points P1–P4 show the horizontal positions where soil samples were collected at the end of the experiment.</p> Full article ">Figure 3
<p>The simulation domain of the HYDRUS (2D/3D). The depths of the ring-shaped emitter and CB were varied.</p> Full article ">Figure 4
<p>Soil water dynamics in the pot experiment. S1–S6 indicate soil water contents measured using the soil moisture sensors in the pot experiment, while Obs1–Obs6 show corresponding soil water contents simulated by HYDRUS (2D/3D) using the optimized soil hydraulic parameters.</p> Full article ">Figure 5
<p>Cumulative RWU expressed as a fraction of AW during the 28-day simulations when the ring-shaped emitter and CB are at different depths. The results for different ring-shaped emitter depths (10, 20, 30, and 40 cm) are shown using lines of different colors.</p> Full article ">Figure 6
<p>Cumulative evaporation expressed as a fraction of AW during the 28-day simulations when the ring-shaped emitter and CB are at different depths. The results for different ring-shaped emitter depths (10, 20, 30, and 40 cm) are shown using lines of different colors.</p> Full article ">Figure 7
<p>Cumulative deep drainage expressed as a fraction of AW during the 28-day simulations when the ring-Scheme 10, 20, 30, and 40 cm) are shown using lines of different colors.</p> Full article ">
16 pages, 5001 KiB  
Article
Relationship between Upstream Swimming Behaviors of Juvenile Grass Carp and Characteristic Hydraulic Conditions of a Vertical Slot Fishway
by Ping Cao, Xiangpeng Mu, Xiang Li, Baoligao Baiyin, Xiuying Wang and Wanyue Zhen
Water 2021, 13(9), 1299; https://doi.org/10.3390/w13091299 - 6 May 2021
Cited by 11 | Viewed by 2750
Abstract
The successful fish upstream movement through a dam/gate is closely associated with the hydraulic conditions of a fishway. To improve the passage efficiency, this study investigated the upstream swimming behaviors of juvenile grass carp, a representative fish of four major Chinese carps, under [...] Read more.
The successful fish upstream movement through a dam/gate is closely associated with the hydraulic conditions of a fishway. To improve the passage efficiency, this study investigated the upstream swimming behaviors of juvenile grass carp, a representative fish of four major Chinese carps, under characteristic hydraulic conditions of a designed vertical slot fishway model. The impacts of different discharges and baffle lead angles on the successful movement of test fish were analyzed, and the selection of the movement trajectory was studied through overlay of their upstream swimming trajectories on the water flow field resulting from numerical modeling. We found that under the same discharge, the percentage of successful test fish movement with a lead angle of 45° was higher than 60° and 30°. Within a fixed lead angle, the higher the discharge, the lower the percentage of successful movement. During upstream movement, the test fish had a preferred water velocity of 0.01–0.45 m/s in the pool, and avoided areas where the turbulence kinetic energy (TKE) was greater than 0.012 m2/s2. These results provide a basis for the hydraulic design of vertical slot fishways and a reference for studying swimming behaviors of other fish species. Full article
(This article belongs to the Special Issue Fish Passage at Hydropower Dams)
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<p>Illustration of vertical slot fishway model. (<b>a</b>) Top view. (<b>b</b>) Front view. (<b>c</b>) Water velocity measurement points (which are in a plane parallel to 60 and 60 mm from the bottom) in observation zone (Pool 4, the black dots indicate Line 10).</p> Full article ">Figure 2
<p>Illustration of the fishway model of various baffle lead angles and corresponding recirculation zones (the RZ denotes the recirculation zone; the blue line denotes the vertical slot. (<b>a</b>–<b>c</b>) are fishways with lead angles of 30°, 45°, and 60°, respectively).</p> Full article ">Figure 3
<p>Comparison between measured and simulated water velocities and turbulent kinetic energies of measurement points at Line 10 in observation zone (lead angle = 60°, Q = 0.011 m<sup>3</sup>/s. (<b>a</b>) Water velocity, (<b>b</b>) Turbulent kinetic energy).</p> Full article ">Figure 4
<p>Overlay chart of upstream movement trajectories of test fish with water velocity field in observation zone. (Discharges of the left, middle, and right columns are 0.011, 0.025, 0.041 m<sup>3</sup>/s, respectively. (<b>a</b>–<b>c</b>) are fishways with lead angles of 30°, 45°, and 60°, respectively).</p> Full article ">Figure 5
<p>Overlay chart of upstream movement trajectories of test fish with turbulent kinetic energy field in observation zone. (Discharges of the left, middle, and right columns are 0.011, 0.025, 0.041 m<sup>3</sup>/s, respectively. (<b>a</b>–<b>c</b>) are fishways with lead angles of 30°, 45°, and 60°, respectively).</p> Full article ">Figure 5 Cont.
<p>Overlay chart of upstream movement trajectories of test fish with turbulent kinetic energy field in observation zone. (Discharges of the left, middle, and right columns are 0.011, 0.025, 0.041 m<sup>3</sup>/s, respectively. (<b>a</b>–<b>c</b>) are fishways with lead angles of 30°, 45°, and 60°, respectively).</p> Full article ">Figure 6
<p>Trajectory ranges of test fish through observation zone.</p> Full article ">Figure 7
<p>Water velocity and turbulent kinetic energy distributions on upstream movement trajectories of 16 representative test fish. (In (<b>a</b>,<b>b</b>), F1, F2, …, F16 indicate the 16 representative test fish; the blue dots indicate fish upstream movement trajectories along Trajectory range 2, while the black dots indicate those along Trajectory range 1; the red lines are the mean values of water velocity and turbulent kinetic energy; in (<b>c</b>,<b>d</b>), red, blue and black, indicate low, medium, and large discharges).</p> Full article ">Figure 7 Cont.
<p>Water velocity and turbulent kinetic energy distributions on upstream movement trajectories of 16 representative test fish. (In (<b>a</b>,<b>b</b>), F1, F2, …, F16 indicate the 16 representative test fish; the blue dots indicate fish upstream movement trajectories along Trajectory range 2, while the black dots indicate those along Trajectory range 1; the red lines are the mean values of water velocity and turbulent kinetic energy; in (<b>c</b>,<b>d</b>), red, blue and black, indicate low, medium, and large discharges).</p> Full article ">Figure 8
<p>Distribution diagram of fields of water velocity (m/s) and turbulent kinetic energy (m<sup>2</sup>/s<sup>2</sup>) at vertical slot. (lead angle = 45°, the left side of each subfigure shows the long baffle side, and the right side shows the short baffle side. (<b>a</b>,<b>c</b>,<b>e</b>) are water velocity field under the discharge of 0.011, 0.025, 0.041 m<sup>3</sup>/s, respectively. (<b>b</b>,<b>d</b>,<b>f</b>) are TKE field under the discharge of 0.011, 0.025, 0.041 m<sup>3</sup>/s, respectively).</p> Full article ">Figure 8 Cont.
<p>Distribution diagram of fields of water velocity (m/s) and turbulent kinetic energy (m<sup>2</sup>/s<sup>2</sup>) at vertical slot. (lead angle = 45°, the left side of each subfigure shows the long baffle side, and the right side shows the short baffle side. (<b>a</b>,<b>c</b>,<b>e</b>) are water velocity field under the discharge of 0.011, 0.025, 0.041 m<sup>3</sup>/s, respectively. (<b>b</b>,<b>d</b>,<b>f</b>) are TKE field under the discharge of 0.011, 0.025, 0.041 m<sup>3</sup>/s, respectively).</p> Full article ">
14 pages, 3337 KiB  
Article
Characteristics of Ultrasonically Enhanced Low-Temperature Thermal Regeneration of Powdered Activated Carbon: A Case Study of Acetone and Aniline
by Dan Zheng, Zhiwei Zhou, Rui Yu and Menghu Wang
Water 2021, 13(9), 1298; https://doi.org/10.3390/w13091298 - 6 May 2021
Cited by 3 | Viewed by 2094
Abstract
Effective regeneration of powdered activated carbon (PAC) is the key to reduce the operating cost of the PAC in wastewater treatment processes. In this study, volatile acetone and semi-volatile aniline were selected to investigate the regeneration characteristics of ultrasonically enhanced low-temperature thermal process. [...] Read more.
Effective regeneration of powdered activated carbon (PAC) is the key to reduce the operating cost of the PAC in wastewater treatment processes. In this study, volatile acetone and semi-volatile aniline were selected to investigate the regeneration characteristics of ultrasonically enhanced low-temperature thermal process. The results showed that the regeneration efficiency of the PAC that had adsorbed aniline or acetone increased with the increase in ultrasonic power, and optimal value of frequency and regeneration times were determined. The concentration and properties of organic solvents had a significant influence on the ultrasonic regeneration process. With the increase in heating temperature and regeneration time, the regeneration efficiency increased, but the loss of mass of the saturated PAC increased noticeably. With the combination of ultrasonic treatment in a solvent with low temperature heating, the PAC regeneration efficiency was successfully improved, and the PAC mass loss rate was noticeably reduced. The microjet, shock wave, and cavitation effects produced by ultrasonic treatment restored the specific surface area of the PAC, expanded its mesopore volume, and increased the pore diameter. A reasonable selection of the regeneration solution and optimization of the ultrasonic treatment conditions could create favorable conditions for subsequent low temperature thermal regeneration. Full article
(This article belongs to the Section Wastewater Treatment and Reuse)
►▼ Show Figures

Figure 1

Figure 1
<p>Factors affecting ultrasonic regeneration efficiency. (<b>a</b>) Power (frequency of 40 kHz, time of 180 min). (<b>b</b>) Frequency (power of 180 W, time of 180 min). (<b>c</b>) Time (frequency of 40 kHz, power of 180 W). (<b>d</b>) Effect of pH (3, 5, 7, 9, 11) on the regeneration efficiency (power of 180 W, frequency of 40 kHz, time of 180 min).</p> Full article ">Figure 2
<p>Effect of organic solvent and concentration on ultrasonic regeneration efficiency. Ultrasound power of 180 W, frequency of 40 kHz, time of 180 min. (<b>a</b>) Influence of methanol concentration. (<b>b</b>) Influence of ethanol concentration.</p> Full article ">Figure 3
<p>Effect of temperature and process time on low-temperature thermal regeneration efficiency. (<b>a</b>) Influence of temperature, time of 30 min. (<b>b</b>) Influence of time, temperature of 200 °C.</p> Full article ">Figure 4
<p>Regeneration efficiency of the combined method of an ultrasonic pretreatment with 50% aqueous solutions an organic solvent (ethanol (EtOH) or methanol (MeOH)) followed by low-temperature heating (A1: thermal regeneration, 200 °C, 15 min, A2: ultrasonic/ethanol–thermal regeneration, 200 °C, 15 min, A3: thermal regeneration, 200 °C, 40 min, B1: thermal regeneration, 150 °C, 30 min, B2: ultrasonic/methanol-thermal regeneration, 150 °C, 30 min, B3: thermal regeneration, 200 °C, 30 min).</p> Full article ">Figure 5
<p>N2 adsorption–desorption isotherms of the PAC before and after regeneration. (<b>a</b>) Unused PAC. (<b>b</b>) PAC saturated with adsorbed aniline. (<b>c</b>) PAC regenerated by ultrasonic treatment. (<b>d</b>) PAC regenerated by ultrasonic treatment in ethanol. (<b>e</b>) Thermally regenerated PAC. (<b>f</b>) PAC treated by the combined regeneration process.</p> Full article ">Figure 5 Cont.
<p>N2 adsorption–desorption isotherms of the PAC before and after regeneration. (<b>a</b>) Unused PAC. (<b>b</b>) PAC saturated with adsorbed aniline. (<b>c</b>) PAC regenerated by ultrasonic treatment. (<b>d</b>) PAC regenerated by ultrasonic treatment in ethanol. (<b>e</b>) Thermally regenerated PAC. (<b>f</b>) PAC treated by the combined regeneration process.</p> Full article ">Figure 6
<p>SEM of the PAC before and after different treatments. (<b>a</b>) Unused PAC. (<b>b</b>) PAC saturated with adsorbed aniline. (<b>c</b>) PAC regenerated by ultrasonic treatment. (<b>d</b>) PAC regenerated by ultrasonic treatment in ethanol. (<b>e</b>) Thermally regenerated PAC. (<b>f</b>) PAC treated by the combined regeneration process.</p> Full article ">Figure 6 Cont.
<p>SEM of the PAC before and after different treatments. (<b>a</b>) Unused PAC. (<b>b</b>) PAC saturated with adsorbed aniline. (<b>c</b>) PAC regenerated by ultrasonic treatment. (<b>d</b>) PAC regenerated by ultrasonic treatment in ethanol. (<b>e</b>) Thermally regenerated PAC. (<b>f</b>) PAC treated by the combined regeneration process.</p> Full article ">Figure 7
<p>Degradation efficiency of aniline by ultrasonic cavitation.</p> Full article ">
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