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Wastewater treatments such as forward osmosis (FO) can be widely applied to separate or the reject substances from secondary treated effluents. Experimental studies have investigated the influence of membrane fouling and operating... more
Wastewater treatments such as forward osmosis (FO) can be widely applied to separate or the reject substances from secondary treated effluents. Experimental studies have investigated the influence of membrane fouling and operating conditions. The performance of FO is affected by membrane fouling characteristics, composition of the feed solution and operating conditions. The experiments were performed using an osmotic membrane (FO-4040) to investigate the influences of operating conditions on water flux and reverse salt selectivity. The surfactant content, cross-flow velocity, and pH of the feed solution were systematically investigated for their effects on FO performance. The results showed that higher cross-flow velocities, increase of the pH of the feed solution, and adding surfactant into the feed solution yielded higher water fluxes. Reverse salt selectivity also increased after adding a surfactant to the feed solution but showed no significant increase at higher surfactant conc...
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A new guideline with atomic force microscopy (AFM) to select the effective extraction method for extracellular polymeric substances (EPS), was proposed and validated by ‘classical’ biochemical ways. The classical biochemical guidelines... more
A new guideline with atomic force microscopy (AFM) to select the effective extraction method for extracellular polymeric substances (EPS), was proposed and validated by ‘classical’ biochemical ways. The classical biochemical guidelines showed that efficiencies of four extraction methods were comparable regardless of different microbial species and the extraction using NaOH or FormaldehydeNaOH was the best. The efficiencies of extraction were further investigated using AFM by analyzing interaction forces between bio-probe, which a single cell of S. cerevisiae was attached at the end of the cantilever, and flat surface. Interaction forces fitted with steric model showed the thickness of residual polymer layer had good agreement with biochemical results. The comparison of results from two guidelines explained the basic mechanisms of extraction methods.
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Although a powdered form of hydroxyapatite (p-HdA) has been studied for the adsorption of heavy metals that contaminate the restoration sites of decommissioned nuclear power plants, most of the studies are limited in the laboratory due to... more
Although a powdered form of hydroxyapatite (p-HdA) has been studied for the adsorption of heavy metals that contaminate the restoration sites of decommissioned nuclear power plants, most of the studies are limited in the laboratory due to the head loss and post-separation in practical applications. Herein, we fabricated a porous bead form of HdA (b-HdA) as a novel adsorbent for removing radionuclides from aqueous environments via a facile synthesis by mixing the p-HdA precursor and polyvinyl butyral (PVB) as a binder and added a sintering process for the final production of a porous structure. The spherical b-HdA with an approximate diameter of 2.0 mm was successfully fabricated. The effectiveness of the b-HdA at removing Co(II) was investigated via the adsorption equilibrium at various experimental temperatures. The b-HdA exhibited the adsorption capacity for Co(II) ions with a maximum of 7.73 and 11.35 mg/g at 293 K and 313 K, respectively. The experimental kinetic data were well ...
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In this study, the weighted mass of standard molecular weight compounds (SMWC) was adopted to improve the accuracy of molecular weight distribution measured by the gel permeation chromatography (GPC). To evaluate the impact of SMWC... more
In this study, the weighted mass of standard molecular weight compounds (SMWC) was adopted to improve the accuracy of molecular weight distribution measured by the gel permeation chromatography (GPC). To evaluate the impact of SMWC compositions, the mixture prepared by constant, linear-weighted, and polynomial-weighted SMWC (3 g/L total) was used for the calibration of GPC, and results were confirmed with typical membrane-based size-exclusion experiments. The results obtained by GPC analysis revealed that the composition of SMWC in the feed significantly altered the final molecular weight cut-off (MWCO) of same membranes, and the polynomial-weighted SMWC provided the best match with the result of MWCO measured by the single-compound rejection experiment due to the enhanced signal intensity at the higher molecular weight compounds (>20,000 Da). Consequently, the preparation of SMWC in the polynomial manner should be suggested during the calibration and MWCO measurements of membran...
The production of biogas was promoted via direct interspecies electron transfer (DIET) by employing electro-conductive carbon-nanotube hollow-fiber media (CHM) in anaerobic digestion. Experimental results showed a positive effect of CHM... more
The production of biogas was promoted via direct interspecies electron transfer (DIET) by employing electro-conductive carbon-nanotube hollow-fiber media (CHM) in anaerobic digestion. Experimental results showed a positive effect of CHM presence on CH4 productivity with 34% higher CH4 production rate than that of in the presence of non-electroconductive polymeric hollow fiber media. An increased CH4 production rate was due to the shift in the microbiome with more abundant Pelobacter (10.0%), Geobacter (6.9%), and Methanosaeta (15.7%), which play key roles in promoting CH4 production via syntrophic metabolism associated with DIET. Microscopic morphology analysis, using confocal laser scanning microscopy and scanning electron microscopy, exhibited that several living cells were attached with electro-conductive pili on the CHM surface, thereby facilitated electron transport between microbial cells.
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Abstract The commercialization of sustainable 3D printing technology changed the face of manufacturing with its precise and uniform sustainable fabrication. Therefore, like other fields of science, research related to water treatment... more
Abstract The commercialization of sustainable 3D printing technology changed the face of manufacturing with its precise and uniform sustainable fabrication. Therefore, like other fields of science, research related to water treatment membranes has adopted this technology successfully, preventing the waste of huge amounts of solvents and thus reducing the high carbon emissions caused by fabrication. Currently, critical research is being conducted in relation to the membrane modules and the fabrication of the membranes themselves. The module studies focus primarily on spacer production and the membrane studies are mostly concerned with the membrane surface. The membrane surface research has successfully adapted inkjet printing for enhanced surface properties for high selectivity and fouling resistance through the printing of nano-materials on the membranes’ surfaces. Recently, 3D printing of the polymer membrane support or 3D printing-based interfacial polymerization has also been introduced into water treatment technologies. Since fouling resistance, selectivity and water permeability are the critical factors, many of the parameters can be controlled by the assistance of bespoke and precise 3D printing fabrication. In this study, we examine key aspects of technology which may shed light on future studies regarding 3D printed water treatment membranes and we review the critical developments to date.
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Various pretreatment methods have been combined and employed for maximizing the solubilization of waste-activated sludge (WAS). However, the question “by changing the series of applied combined pretreatments (CPs), can the solubilization... more
Various pretreatment methods have been combined and employed for maximizing the solubilization of waste-activated sludge (WAS). However, the question “by changing the series of applied combined pretreatments (CPs), can the solubilization efficiency of WAS be affected?” has never been addressed. In this study, firstly, thermal (T), alkaline (A), and ultrasonic (U) pretreatments were individually applied at broad strengths (T = 80–120 °C for 30 min, A = pH 9–12, and U = 5–60 min at 300 W). Then, pretreatment conditions that caused similar solubilization (13.0%) (120 °C, pH 11, and 30 min for T, A, and U, respectively), were adopted for CP with reverse sequences of T&A, U&A, and T&U. A similar disintegration degree was observed in U→A and A→U, while a meaningful difference was found in T&A and T&U: T→A (28.3%), A→T (42.9%), T→U (22.9%), and U→T (27.1%). The difference in pretreatment series also affected the characteristics of soluble matters, which was analyzed by excitation emission ...
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Livestock wastewater effluent generated after the anaerobic treatment process contains the considerable amount of color-causing organic matter. In this study, a quantitative comparison of three carbon-based adsorbents included granular... more
Livestock wastewater effluent generated after the anaerobic treatment process contains the considerable amount of color-causing organic matter. In this study, a quantitative comparison of three carbon-based adsorbents included granular activated carbon (GAC), expanded graphite (EG), and multi-walled carbon nanotubes (MWNTs) was carried out for the potential application to the removal of color substances, and their mechanism was proposed. Although GAC showed the highest specific dissolved organic carbon (DOC) adsorption capacity, the color removal efficiency was the smallest among three adsorbents. The selective color removal ratios of EG and MWNTs reached 22.7 ± 0.1 PtCo/mg-DOC-removed and 21.2 ± 0.1 PtCo/mg-DOC-removed, respectively, while that of GAC was only 12.3 ± 0.1 PtCo/mg-DOC-removed. The selective adsorption of color substances by graphene-based carbon materials was due to the aromatic π – π interaction between organic matter and the hexagonal carbon lattice of graphene. The analysis of molecular weight distribution also confirmed that the exposed surface area and macro-pores were responsible for the adsorption of high molecular weight color substances. The chemical regeneration of three adsorbents was examined using 1% NaOCl solution and MWNTs showed almost complete recovery of the initial color removal capacity. In conclusion, MWNTs were the most suitable carbon nanomaterial for the selective color removal from livestock wastewater effluent.
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Abstract Fatty acids (FA) from organic wastes are environmentally friendly raw materials with high economic value ranging from fuels to oleo-chemicals for growing diversity of products. In this study, expanded graphite (EG) and isopropyl... more
Abstract Fatty acids (FA) from organic wastes are environmentally friendly raw materials with high economic value ranging from fuels to oleo-chemicals for growing diversity of products. In this study, expanded graphite (EG) and isopropyl alcohol have been used to adsorb and concentrate the low content of FA in aqueous solution to replace the existing solid-phase extraction methods. The results showed that the maximum adsorption capacity of EG was more than 8.2 g-FA/g due to the inter-latticed structure of graphene sheets, and subsequent coalescence of FA droplets. The extraction efficiency of isopropyl alcohol was always higher than those of dichloromethane and ethanol for the recovery of absorbed FA due to the lower surface tension and higher miscibility with water. After 5 times of recycle, although the specific FA adsorption was decreased 42% of raw EG, extraction efficiencies by isopropyl alcohol were not changed. In conclusion, our study suggested that the EG and isopropyl alcohol could achieve the efficient and environmentally friendly harvesting of low concentration of FA in aqueous solutions during the biological conversion of organic matters in food waste.
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In this study, expanded graphite (EG) was decorated with manganese oxide nanoparticles (MONPs) by the hydrothermal method, and the newly formed composite (MONPs-EG) was applied as adsorbent for the removal of heavy metals from aqueous... more
In this study, expanded graphite (EG) was decorated with manganese oxide nanoparticles (MONPs) by the hydrothermal method, and the newly formed composite (MONPs-EG) was applied as adsorbent for the removal of heavy metals from aqueous solutions. The comparative and competitive adsorption of Pb2+ and Ni2+ (0.01–1.00 mM) on MONPs-EG was investigated. Data from isothermal adsorption of single and binary systems suggested that both Pb2+ and Ni2+ were well described by the Langmuir isotherm, and the maximum adsorption capacities at 298 K were calculated at 0.278 and 0.113 mmol/g for Pb2+ and Ni2+, respectively. In binary systems, a dramatic decrease in adsorption capacity of Ni2+ was observed, while the adsorption capacity of Pb2+ was almost stable, indicating the favorable adsorption of Pb2+ over Ni2+ onto the prepared adsorbent. Kinetics studies of single and binary systems showed that a pseudo-second order model could explain the adsorption processes well. Thermodynamic analysis resul...
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Abstract Electrochemical CO2 reduction (CO2RR) has received much attention for its ability to generate value-added chemicals from a molecule that would otherwise be a waste end-product. Numerous studies have emerged in the past decades,... more
Abstract Electrochemical CO2 reduction (CO2RR) has received much attention for its ability to generate value-added chemicals from a molecule that would otherwise be a waste end-product. Numerous studies have emerged in the past decades, but the renewable and sustainable carbon-neutral CO2 reduction process is yet to be industrialized. Here, we review the progress and bottlenecks of the electrochemical CO2 reduction technologies over the past 15 years (2004–2018) to examine whether CO2RR process is to be applicable in a large-scale. Although the techno-economic analysis and pilot plants based on liquid-phase electrolysis have shown some positive results, current densities of the liquid-phase electrochemical CO2 reduction are well below what techno-economic analyzes have projected due to its intrinsic limitations of solubility. On the other hand, the gas-phase electrolysis of CO2 has shown superior performance parameters compared to the liquid-phase electrolysis, especially in the current densities, showing commercial viability although its techno-economic analysis is yet to be performed. Herein, we offer some perspectives and guidelines where future research in CO2 electrolysis should aim. Based on the performance parameters obtained from the lab-scale gas-phase reactions, we believe that the current negative outlooks towards the industrial feasibility of the CO2 electrolysis system could turn to positive views.
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In this research, ceramic nanofiltration (NF) membranes were prepared by depositing alumina-zirconia (Al-Zr) nanoparticles into the pores of ceramic ultrafiltration (UF) membranes for the removal of radioactive uranium in an aquatic... more
In this research, ceramic nanofiltration (NF) membranes were prepared by depositing alumina-zirconia (Al-Zr) nanoparticles into the pores of ceramic ultrafiltration (UF) membranes for the removal of radioactive uranium in an aquatic system. The modified ceramic membranes showed NF membrane performance with around 1,000 Da molecular weight cut-off (MWCO) and 58% CaCl2 rejection. The removal efficiencies of uranium species by these successfully modified ceramic NF membranes exhibited differences depending on the pH conditions (pH 5.0, 7.4, and 10.0), and achieved the highest rejection of 91% at pH 7.4. This behavior is due to the dominant aqueous species of uranium in pH 7.4, (UO2)2CO3(OH3)−, which has the largest molecular weight among the conditions and the negatively charged species having electrostatic attraction to the positively charged ceramic NF membranes. The ceramic NF membrane prepared here is expected to be feasible in the advanced water treatment process to remove radioac...
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Abstract Biofouling on a thin film composite (TFC) membrane is one of the most serious obstacles during the operation of reverse osmosis (RO) processes. In this study, chlorhexidine (CH) was immobilized as a novel non-oxidizing chemical... more
Abstract Biofouling on a thin film composite (TFC) membrane is one of the most serious obstacles during the operation of reverse osmosis (RO) processes. In this study, chlorhexidine (CH) was immobilized as a novel non-oxidizing chemical on a RO membrane surface with glutaraldehyde (GA) as a cross-linking agent. The analysis of the membrane surface showed that CH was successfully immobilized with a molecular layer-by-layer technique seen by the increase of Cl and methylene peaks from the XPS and FT-IR, respectively. From the static biofilm growth tests using drip-flow cells, CH immobilized membranes exhibited a high anti-bacterial potential, and the CH bi-layered (CHBL) membrane showed a better anti-biofouling ability than that of the CH mono-layered (CHML) membrane due to the complete coverage of CH on the RO membrane surface. The retardation of biofilm formation and the higher physical cleaning efficiency of the CHML and CHBL membranes were introduced by direct inactivation of the attached bacteria as well as a decreased secretion of biofilm building materials such as exocellular polymeric substances (EPS).
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The anaerobic co-digestion of sewage sludge and other organic waste is an attractive method for both waste treatment and biogas production. In this study, we examined the optimal substrate mixing ratio in co-digestion of sewage sludge,... more
The anaerobic co-digestion of sewage sludge and other organic waste is an attractive method for both waste treatment and biogas production. In this study, we examined the optimal substrate mixing ratio in co-digestion of sewage sludge, swine waste, and food waste using the response surface methodology. The single digestion of sewage sludge produced 138 mL CH 4 /g total solids (TS) with 35% chemical oxygen demand removal. The co-digestion with food waste and swine waste increased the methane yield to 294 mL/g TS under the optimal mixing ratio of 1:0.39:1 (sewage sludge:food waste:swine waste). The statistical analysis of the experimental data indicated a synergistic effect in the mixing of food waste and swine waste. This study showed that co-digestion of the organic wastes would be a feasible and economic approach to retrofit conventional anaerobic digesters.
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For the use of biologically produced H, removal of CO is an indispensable process. Unlike conventional CO removal methods, this study proposed a self-generated high-pressure dark fermentation (HPDF) process as a novel strategy for... more
For the use of biologically produced H, removal of CO is an indispensable process. Unlike conventional CO removal methods, this study proposed a self-generated high-pressure dark fermentation (HPDF) process as a novel strategy for directly producing high-calorific bio-H. The pressure was automatically increased by self-generated gas, while the maximum pressure inside fermenter was restricted to 1, 3, 5, 7, and 10 bar in a batch operation. As the pressure increased from 1 to 10 bar, the H content increased from 55% to 80%, whereas the H yield decreased from 1.5 to 0.9 mol H/mol hexose. The highest H content of 80% was obtained at both of 7 and 10 bars. Increased lactate production with increased abundance of lactic acid bacteria was observed at high-pressure. Despite the lower H yields at high-pressure conditions, HPDF was found to be economically beneficial for obtaining high-calorific bio-H owing to the low CO removal cost.
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Abstract To investigate the characteristics of hydrogenotrophic methanogenic (HM, 4H 2 + CO 2 → CH 4 + 2H 2 O) mixed cultures, continuous stirred-tank reactors (CSTRs) were operated at various H 2 loading rates (HLR, 2.8–14.0 m 3 H 2 /m... more
Abstract To investigate the characteristics of hydrogenotrophic methanogenic (HM, 4H 2 + CO 2 → CH 4 + 2H 2 O) mixed cultures, continuous stirred-tank reactors (CSTRs) were operated at various H 2 loading rates (HLR, 2.8–14.0 m 3 H 2 /m 3 /d) and hydraulic retention times (HRTs, 5–30 d). The feeding gas was composed of H 2 /CO 2 (80:20 on volume basis), and HRT was controlled by the continuous pumping of a nutrient medium. At a fixed HLR of 4 kg COD/m 3 /d (1 kg COD = 1.4 m 3 H 2 ), complete H 2 conversion to CH 4 (> 98% on a COD basis) was observed up to the HRT decrease to 6 d. However, at HRT 5 d, the H 2 conversion gradually decreased, reaching 30% within 30 d, and the H 2 content in the head space increased to 70%, which triggered the production of acetate with an increased concentration to 3 g COD/L. When the HLR was increased at a fixed HRT of 10 d, the maximum CH 4 production rate of 2.75 m 3 CH 4 /m 3 /d was achieved at 8 kg COD/m 3 /d. A kinetic analysis conducted using the Monod equation showed that HM cultures had a maximum specific growth rate of 0.18 d −1 and a half-saturation coefficient of 1.73 g COD/L. Though, successful hydrogenotrophic CH 4 conversion was achieved, the broth contained soluble microbial products (SMPs) at a concentration of 80–250 mg/L, which exceeded the effluent regulation standard. Most of the organic matters in SMPs consisted of humic-like and fulvic-like organic matters with a low molecular weight (
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Abstract Biomethanation by hydrogenotrophic methanogens has been proven as a potential process for managing renewable power intermittency and upgrading biogas. The present work aimed to enrich hydrogenotrophic methanogens under different... more
Abstract Biomethanation by hydrogenotrophic methanogens has been proven as a potential process for managing renewable power intermittency and upgrading biogas. The present work aimed to enrich hydrogenotrophic methanogens under different mixing conditions (gas recycle vs. mechanical mixing) and temperatures (mesophilic vs. thermophilic conditions) for biogas upgrading. The synthetic gas (H2:CO2 = 4:1) was fed to the reactor bottom at a hydrogen injection rate (HIR) of 1.6 L H2 L−1 d−1. The gas recycle (100 L L−1 d−1) under thermophilic condition was found to be the most effective, reaching over 96% H2 conversion to CH4 within 15 d of operation. Archaea community analysis performed by 454 pyrosequencing showed that the sequence of Methanosaeta sp. decreased while obligate-hydrogenotrophic methanogens increased: Methanoculleus chikugoensis (19.5%) and Methanothermococcus thermolithotrophicus (28.1%) under mesophilic and thermophilic condition, respectively. To the thermophilic enriched culture, the biogas produced from an up-flow anaerobic sludge blanket reactor with additional hydrogen (four times of CO2) was fed at various HIRs for 200 d. As HIR increased, H2 consumption rate also increased with CO2 removal contained in the biogas. Up to an HIR increase to 19.2 L H2 L−1 d−1, the high calorific biomethane (96% of CH4) could be obtained at gas recycle rate of 200 L L−1 d−1.
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AbstractIn this study, we evaluated the efficiencies of chemical cleaning agents for the removal of foulant and related the changes of membrane surface properties to the flux recovery in forward osmosis (FO) membrane process. Commercially... more
AbstractIn this study, we evaluated the efficiencies of chemical cleaning agents for the removal of foulant and related the changes of membrane surface properties to the flux recovery in forward osmosis (FO) membrane process. Commercially available chemical cleaning agents were added and processed according to the protocols of reverse osmosis (RO) membrane processes into two steps—acid treatment, then base treatment, and the flux recovery and membrane surface properties were tested in FO mode. The flux of the fouled membrane was only 23% of initial water flux tested in FO mode, and the addition of cleaning chemicals could improve the water flux to be 65 and 83% of initial water flux after each step, respectively. The reverse flux selectivity of fouled membrane was increased up to 61 and 86% after each cleaning steps due to the decrease in the concentration polarization inside the layer. The removal of biofouling layer during each cleaning step was demonstrated by scanning electron microscopy (SEM) and FT-...
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AbstractThe impact of feed ionic concentration in the presence of organic and colloidal foulant on osmotically driven membrane processes (ODMPs) was demonstrated. The normalized flux of ODMPs was significantly decresed in both DI and... more
AbstractThe impact of feed ionic concentration in the presence of organic and colloidal foulant on osmotically driven membrane processes (ODMPs) was demonstrated. The normalized flux of ODMPs was significantly decresed in both DI and 10 mM NaCl feed solution when the feed solution contained colloidal particles as foulants due to the deposition of colloidal particles on the membrane surface. The deposited colloidal particles strongly promoted cake-enhanced osmotic pressure near the surface of the membrane. In contrast, the normalized flux of ODMPs was slightly increased when humic acids (HA) were added as the organic foulant into the feed solution. The attachment of HA molecules changed the membrane surface conducting it more hydrophilic, and induced a stronger diffusion of water molecules into the membrane active layer. As a result, both the increased feed ionic strength and deposited colloidal fouling did not significantly alter the reversal salt selectivity of the ODMPs, while the reversal salt selectiv...
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ABSTRACT In this study, adsorption characteristics of expanded graphite (EG) were investigated by a series of batch adsorption tests using p-Xylene as a model volatile organic compounds (VOCs). After acid treatment, graphite were expanded... more
ABSTRACT In this study, adsorption characteristics of expanded graphite (EG) were investigated by a series of batch adsorption tests using p-Xylene as a model volatile organic compounds (VOCs). After acid treatment, graphite were expanded at various temperature from to for one minute. The optimal temperature was , where the expansion ratio reached 195 times of original volume. The BET specific surface area of EG was , which was only 1/10 of granular activated carbon (GAC), however the adsorption of p-Xylene by EG was almost completed within 5 minutes while that of GAC continued for 7 days because the majority of pores of EG was consisted with meso- and macro-pores. According to the Langmuir isotherm analysis, the maximum specific adsorption of p-Xylene onto EG was 24.0 mg/L with the adsorption constant of 7.94. In conclusion, the adsorption capacity of EG was much less than that of GAC due to the significantly lower specific surface area, but the first order kinetic constant was more than 500 times larger than GAC. Overall, EG might be effective where the fast adsorption is required.
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Abstract: Nitrate in the anaerobic condition was supposed to be reduced to ammonia (ammonification). But recent researches showed that denitrification was possible according to kinds of substrate and COD/NO 3-N ratio in the anaerobic... more
Abstract: Nitrate in the anaerobic condition was supposed to be reduced to ammonia (ammonification). But recent researches showed that denitrification was possible according to kinds of substrate and COD/NO 3-N ratio in the anaerobic condition. Denitrification was ...