Mohammad Rehan

This study examines point and non-point sources of air pollution and particulate matter and their associated socioeconomic and health impacts in South Asian countries, primarily India, China, and Pakistan. The legislative frameworks, policy gaps, and targeted solutions are also scrutinized. The major cities in these countries have surpassed the permissible limits defined by WHO for sulfur dioxide, carbon monoxide, particulate matter, and nitrogen dioxide. As a result, they are facing widespread health problems, disabilities, and causalities at extreme events. Populations in these countries are comparatively more prone to air pollution effects because they spend more time in the open air, increasing their likelihood of exposure to air pollutants. The elevated level of air pollutants and their long-term exposure increases the susceptibility to several chronic/acute diseases, i.e., obstructive pulmonary diseases, acute respiratory distress, chronic bronchitis, and emphysema. More in-depth spatial-temporal air pollution monitoring studies in China, India, and Pakistan are recommended. The study findings suggest that policymakers at the local, national, and regional levels should devise targeted policies by considering all the relevant parameters, including the country's economic status, local meteorological conditions, industrial interests, public lifestyle, and national literacy rate. This approach will also help design and implement more efficient policies which are less likely to fail when brought into practice.

The organic Rankine cycle (ORC) has recently emerged as a practical approach for generating electricity from low-to-high-temperature waste industrial streams. Several ORC-based waste heat utilization plants are already operational; however, improving plant cost-effectiveness and competitiveness is challenging. The use of thermally efficient and cost-competitive working fluids (WFs) improves the overall efficiency and economics of ORC systems. This study evaluates ORC systems, facilitated by biogas combustion flue gases, using n-butanol, i-butanol, and methylcyclohexane, as WFs technically and economically, from a process system engineering perspective. Furthermore, the performance of the aforementioned WFs is compared with that of toluene, a well-known WF, and it is concluded that i-butanol and n-butanol are the most competitive alternatives in terms of work output, exergy efficiency, thermal efficiency, total annual cost, and annual profit. Moreover, the i-butanol and n-butanol-based ORC systems yielded 24.4 and 23.4% more power, respectively, than the toluene-based ORC system; in addition, they exhibited competitive thermal (18.4 and 18.3%, respectively) and exergy efficiencies (38 and 37.7%, respectively). Moreover, economically, i-butanol and n-butanol showed the potential of generating 48.7 and 46% more profit than that of toluene. Therefore, this study concludes that i-butanol and n-butanol are promising WFs for high-temperature ORC systems, and their technical and economic performance compares with that of toluene. The findings of this study will lead to energy efficient ORC systems for generating power.

Fabrication of superior and cost-effective cathodic materials is vital in manufacturing sustainable microbial electrolysis cells (MECs) for biofuels production. In the present study, a novel manganese dioxide (MnO 2) coated felt cathode (Mn/CF) has been developed for MECs using electrodeposition method via potentiostat. MnO 2 is considered to encourage exogenous electron exchange and, in this way, improves the reduction of carbon dioxide (CO 2). MnO 2 , as a cathodic catalyst, enhances the rate of biofuel production, electron transfer, and significantly reduces the cost of MECs. A maximum stabilized current density of 3.70 ± 0.5 mA/m 2 was obtained in case of MnO 2-coated Mn/CF based MEC, which was more than double the non-coated carbon felt (CF) cathode (1.70 ± 0.5 mA/m 2). The dual chamber Mn/CF-MEC achieved the highest production rate of acetic acid (37.9 mmol/L) that was significantly higher (43.0%) in comparison to the non-coated CF-MEC. The cyclic voltammograms further verified the substantial enhancement in the electron transfer between the MnO 2 coated cathode and microbes. The obtained results demonstrate that MnO 2 interacted electrochemically with microbial cells and enhanced the extracellular electron transfer, therefore validating its potential role in biofuel production. The MnO 2 coated CF further offered higher electrode surface area and better electron transfer efficiency, suggesting its applicability in the large-scale MECs.

The world is facing severe environmental challenges, including increasing consumption of fossil-based energy and its consequent devastative impact, i.e. global warming and climate change. Biofuels are promising alternatives to fossil fuels with tremendous environmental and socio-economic benefits. There has been a considerable deal of research and development carried out on the production of biofuels in the last 2 decades. However, there is still a huge potential for achieving more cost-effective and efficient biofuel production processes through the application of nanotechnology. The exceptional properties of nanomaterials (nanocatalysts) such as high surface area, catalytic performance, crystallinity, durability, energy storage capacity, etc. offer great potential for optimizing biofuel production systems. Nanocatalysts could also serve recovery, reusability, and recycling purposes.

Black liquor (BL) rich phenolic and complex compounds is generated from pulp and paper mill manufacturing processes which should be treated before reaching the environment. The potential of achieving several sustainable development goals (SDGs) by recovering energy and valuable by-products from BL was extensively investigated. Results revealed that under a dark-fermentation process, the organic content in BL was effectively bio-degraded by anaerobes to achieve a hydrogen yield (HY) of 0.62 ± 0.04 mol/mol glucose. Fortunately, the HY was significantly increased up to 1.41 ± 0.13 mol/mol glucose by immobilizing the anaerobes onto magnetite nanoparticles (MN). α-amylase, xylanase, CM-cellulase, polygalacturinase, and protease enzymes activities were increased by 2.3, 23.7, 2.7, 26.8, and 31.1 folds with supplementation of MN. Moreover, the conversion efficiencies of protein and carbohydrate were improved by values of 36 and 113.3% and total phenolic compounds (TPC) were enhanced by 23.5% compared with the control test. Electron-equivalent and COD mass balances were estimated to comprehensively describe the effect of Mn supplementation on the HY performance and fermentation pathways. Digestate generated from the fermentation process was utilized to produce biochar, having C (58.2%), O (32.4%), Na (4.7%), and P (1.1%). The study outputs were interlinked to bio-energy generation, pollution minimization, biochar as a soil amendment, nanoparticles and paper manufacturing industrialization, meeting environmental, economic, and social related SDGs.

The articles published in this special issue focus on recent developments in sustainable waste-to-energy systems and waste management practices and highlight the critical challenges and potential solutions. The editorial paper aims to give a brief overview of the key findings and future perspectives proposed in these 25 selected papers. It is worth noting that although the articles presented in this special issue covered a wider range of topics, they are categorized into five categories. These include the latest developments in 1) waste-to-energy technologies, 2) biofuels and bioenergy, 3) waste valorization, 4) emerging renewable and sustainable energy systems, and finally, 5) biorefineries and circular economy.

The global demand for clean products obtained from biobased resources has increased significantly with the rapid growth of the world's population. In this context, microbially-produced compounds are highly attractive for their safety, reliability, being environment friendly and sustainability. Nevertheless, the cost of the carbon sources required for such approaches accounts for greater than 60% of the total expenses, which further limits the scaling up of industries. In recent years, algae have been used in numerous industrial areas because of their rapid growth rate, easy cultivation, ubiquity and survival in harsh conditions. Over the past decade, notable advances have been observed in the extraction of high-value compounds from algae biomass (ABs). However, few studies have investigated ABs as green substrates for microbial conversion into value-added products. This review presents the potential of ABs as the substrates for microbial growth to produce industrially-important products, which sheds light on the importance of the symbiotic relationship between ABs and microbial species. Moreover, the successful algal-bacterial gene transformation paves the way for accommodating green technology advancements. With the escalated need for natural pigments, biosurfactants, natural plastics and biofuels, ABs have been new resources for microbial biosynthesis of these value-added products, resolving the problem of high carbon consumption. In this review, the fermentative routes, process conditions, and accessibility of sugars are discussed, together with the related metabolic pathways and involved genes. To conclude, the full potential of ABs needs to be explored to support microbial green factories, producing novel bioactive compounds to meet global needs.

The sustainable and ecological economic growth of a country is associated with its economic progress and the advancement of its bioenergy sector. Biowaste can be used to produce bioenergy and is increasingly being recognized as a promising resource for filling the energy gap. However, in developing countries, biowaste-to-energy techniques are relatively immature owing to economic and technological crises, forcing these countries to export cheap biowaste and obtain expensive energy imports. In this study, country-wise export data of potential biowaste materials were gathered, assessed, and filtered according to the feasibility of bioenergy generation. Five developing countries (Argentina, Brazil, India, Thailand, and Ukraine) were selected for the economic assessment on the basis of the export value and revealed comparative advantage (RCA). Argentina has the most exports (10.3 billion USD), with six biowaste products having RCA > 1. The product space model (PSM) was employed to evaluate the income potential of biowaste country-level sophistication, and a suitable economic policy was proposed according to PSM indicators. All the considered biowastes have low income potential. Thailand has the highest country-level sophistication, followed by India, Brazil, Ukraine, and Argentina. However, according to the PSM, the EXPY values exhibit growth only for India (15.4%) and Thailand (5.7%); for the remaining countries, they decline. On the PSM industrial policy map, India, Thailand, and Ukraine lie in ample space, while Brazil and Argentine are in a “parsimonious industrial policy” region. Moreover, a comparison between bioenergy and current exports ensures that the implementation of suggested industrial policies can enhance energy-production capabilities through export diversification and assist countries in achieving their projected gross domestic products.

Investment in biofuels, as sustainable alternatives for fossil fuels, has gained momentum over the last decade due to the global environmental and health concerns regarding fossil fuel consumption. Hence, effective management of biofuel supply chain (BSC) components, including biomass feedstock production, biomass logistics, biofuel production in biorefineries, and biofuel distribution to consumers, is crucial in transitioning towards a low-carbon and circular economy (CE). The present study aims to render an inclusive knowledge map of the BSC-related scientific production. In this vein, a systematic review, supported by a keywords co-occurrence analysis and qualitative content analysis, was carried out on a total of 1,975 peer-reviewed journal articles in the target literature. The analysis revealed four major research hotspots in the BSC literature, namely (1) biomass-to-biofuel supply chain design and planning, (2) environmental impacts of biofuel production, (3) biomass to bioenergy, and (4) techno-economic analysis of biofuel production. Besides, the findings showed that the following subject areas of research in the BSC research community have recently attracted more attention: (i) global warming and climate change mitigation, (ii) development of the third-generation biofuels produced from algal biomass, which has recently gained momentum in the CE debate, and (iii) government incentives, pricing, and subsidizing policies. The provided insights shed light on the understanding of researchers, stakeholders, and policy-makers involved in the sustainable energy sector by outlining the main research backgrounds, developments, and tendencies within the BSC arena. Looking at the provided knowledge map, potential research directions in BSCs towards implementing the CE model, including (i) integrative policy convergence at macro, meso, and micro levels, and (ii) industrializing algae-based biofuel production towards the CE transition, were proposed.

This study aims to examine the potential of non-edible seed oil (Cucumis melo var. agrestis), seed oil content 29.1%, FFA 0.64 (mg KOH/g) for biodiesel production via nanocatalyst. The catalyst was characterized using X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The maximum biodiesel yield (93%) was attained under optimized conditions, i.e., 9:1 methanol to oil molar ratio, 2 wt% catalyst (MgO) at 60°C. The synthesized biodiesel yield was optimized through response surface technology via Box Behnken design (BBD). Biodiesel was characterized by advanced analytical techniques, including gas chromatography and mass spectroscopy, FTIR, and nuclear magnetic resonance (NMR). Fuel properties of synthesized biodiesel, including density (0.800 kg/L), K. viscosity @ 40°C (4.23 cSt), cloud point −12°C, pour point −7°C, sulfur content (0.0001%), flash point (73.5°C), total acid no (0.167 mg KOH/g) were found in lines with international standard of American Society of Testing Materials (ASTM). Cucumis melo var. agrestic seed oil and nano MgO catalyst appeared as economical, sustainable, and feasible candidates to overcome global energy glitches and environmental issues. The study findings involving unpalatable seed oil will be a promising step toward non-food biomass biorefinery.

As the global population and economy grow, so does the energy demand. Over-reliance on non-renewable resources leads to depletion and price spikes, making renewable alternatives necessary. Biodiesel is an eco-friendly and non-toxic fuel that closely resembles traditional fossil fuels. It is produced from various sources, including animal fat, palm oil, and non-edible plant oil. Biodiesel releases fewer harmful air pollutants and greenhouse gases than fossil fuels and is simpler to manage. Despite these advantages, it cannot replace traditional diesel fuel on a large scale. This overview summarizes biodiesel production, explaining the different types of feedstock utilized and their benefits and drawbacks. Various biodiesel production methodologies are discussed. The primary objective of this article is to inform engineers, industrialists, and researchers involved in waste biodiesel, as well as to highlight waste biodiesel as a potential substitute for fossil fuels. This review article discusses the nanoadditives in biodiesel and applications of internet of things, artificial intelligence, and machine learning in biofuel. This review shows that nano-additives can potentially improve biodiesel fuel properties, favorable economic and policy environments promoting biodiesel production, and internet of things, artificial intelligence, and machine learning technologies optimize the biodiesel production processes. These advances can help promote biodiesel as a cleaner, renewable energy source, lowering the consumption of fossil fuels. It also suggests further biofuel development by improving efficiency, expanding feedstock options, creating policy support, developing infrastructure, and increasing public awareness.

The current study analyzed the high heating values (HHVs) of various waste biomass materials intending to the effective management and more sustainable consumption of waste as clean energy source. Various biomass waste samples including date leaves, date branches, coconut leaves, grass, cooked macaroni, salad, fruit and vegetable peels, vegetable scraps, cooked food waste, paper waste, tea waste, and cardboard were characterized for proximate analysis. The results revealed that all the waste biomass were rich in organic matter (OM). The total OM for all waste biomass ranged from 79.39% to 98.17%. Likewise, the results showed that all the waste biomass resulted in lower ash content and high fixed carbon content associated with high fuel quality. Based on proximate analysis, various empirical equations (HHV=28.296-0.2887(A)-656.2/VM, HHV=18.297-0.4128(A)+35.8/FC and HHV=22.3418-0.1136(FC)-0.3983(A)) have been tested to predict HHVs. It was observed that the heterogeneous nature of various biomass waste considerably affects the HHVs and hence has different fuel characteristics. Similarly, the HHVs of waste biomass were also determined experimentally using the bomb calorimeter, and it was observed that among all the selected waste biomass, the highest HHVs (21.19 MJ kg − 1) resulted in cooked food waste followed by cooked macaroni (20.25 MJ kg − 1). The comparison revealed that experimental HHVs for the selected waste biomass were slightly deviated from the predicted HHVs. Based on HHVs, various thermochemical and biochemical technologies were critically overviewed to assess the suitability of waste biomass to energy products. It has been emphasized that valorizing waste-to-energy technologies provides the dual benefits of sustainable management and production of cleaner energy to reduce fossil fuels dependency. However, the key bottleneck in commercializing waste-to-energy systems requires proper waste collection, sorting, and continuous feedstock supply. Moreover, related stakeholders should be involved in designing and executing the decision-making process to facilitate the global recognition of waste biorefinery concept.

Waste-to-energy (WTE) production is one of the sustainable solutions to fulfill energy demands and minimize the environmental problems associated with waste landfilling. This work investigates the biogas production and methane (CH4) enrichment for anaerobic digestion (AD) of fruit and vegetable waste (FVW). The effect of pH and temperature were studied using a lab scale batch anaerobic digester. The raw biogas was pebbled through water, NaOH, Ca(OH)2 and triethanolamine (TEA) for biogas purification and CH4 enrichment. The results showed that mixed fruit waste (MFW) provides 10 % more biogas yield than mixed fruit vegetable waste (MFVW). The maximum biogas yield of 0.030 (g/g volatile solids) was achieved at thermophilic temperature (TT). The optimum pH range under mesophilic temperature (MT) and TT condition was in between 8.3 - 8.8. The use of NaOH, Ca(OH)2 and TEA increased CH4 enrichment upto 5 %, 9 % and 7 %. Biogas having 71 % CH4 contents with 28 % reduced CO2 and 150 ppm H2S was produced using Ca(OH)2.

Municipal Solid Waste (MSW) management is a chronic environmental problem in most of the developing countries, including the Kingdom of Saudi Arabia (KSA). The concept of Waste-to-Energy (WTE) is known as one of the several technologies capable of benefiting a society, which desires to reduce fossil-fuel addiction. Currently, there is no WTE facility existing in the KSA. The MSW is collected and disposed in landfills untreated. A substantial increase in the population by 3.4 %/y over the last 35 y coupled with urbanization and raised living standards have resulted in high generation rate of MSW. In 2014, about 15.3 Mt of MSW was generated in KSA. The food and plastic waste are the two main waste streams, which covers 70 % of the total MSW. The waste is highly organic (up to 72 %) in nature and food waste covers 50.6 % of it. An estimated electricity potential of 2.99 TWh can be generated annually, if all of the food waste is utilized in anaerobic digestion (AD) facilities. Similarly, 1.03 and 1.55 TWh electricity can be produced annually if all of the plastics and other mixed waste are processed in the pyrolysis and refuse derived fuel (RDF) technologies respectively. The aim of this paper is to review the prospective WTE technologies in Saudi Arabia. However, the real selection of the conversion technologies will be done in conjunction with the fieldwork on waste characterization and laboratory examination of selected technologies and further socioeconomic and environmental evaluations.

The increasing population, urbanization and industrial growth are causing serious environmental challenges including air pollution worldwide. According to WHO, the indoor and outdoor air pollution exposure has caused around 7 million deaths globally only in 2012. The major air pollution sources include transportation and petrochemical based industry. Motor vehicle repair workshops (MVRW) pose many environmental as well as occupational health challenges. Workers safety and protection at workplace has been a great concern for employees, employers, governments and the entire society for years. This review article highlights the prominent air pollutants and health and safety challenges at MVRW. Many scientific articles studying pollutants that are detrimental to health e.g. benzene, PAHs, VOCs, heavy metals, PM, NO x and SO x are reviewed here. The national and international environmental legislations and health and safety standards by Occupational Safety and Health Administration (OSHA), US Environmental Protection Agency (USEPA) and Presidency of Meteorology and Environment (PME) Saudi Arabia have been mentioned and compared for air quality both outdoor and in occupational environment. Latest developments in ambient air pollution monitoring and occupational personals health risk assessment methods and strategies have also been reviewed coherently, including the prominent physical, chemical, biological, musculoskeletal and accidental safety hazards at MVRW. The current environmental challenges and perspectives for Saudi Arabia in terms of both ambient air pollution as well as in occupational settings are also discussed. The review ends with identifying gaps and limitations in monitoring and legislation in the subject area, and suggesting the way forward for Saudi Arabia including further research and development needed in the subject area.

An industrial-scale molasses-based bioethanol production system was modeled and studied by conducting exergy, exergoeconomic, and exergoenvironmental analyses. The entire process was represented by a control volume, and its exergoeconomic and exergoenvironmental parameters were determined using the specific exergy costing (SPECO) approach. These exergy-based analyses were carried out to measure the overall exergy dissi-pation, cost, and environmental impact of the bioethanol production process based on actual operational ther-modynamic, economic, and environmental data. Natural gas showed the highest contribution to the total input exergy (61.1%) and total environmental impact rate (56.6%) of the process, while the highest contribution to its total cost rate (75.7%) was from molasses. The exergetic efficiency determined for the process was 35.9%, while the exergy dissipation accounted for 60.8% of its total input exergy. The unit exergoeconomic costs of the fuel and product were determined to be 6.2 and 20.9 USD/GJ, while the unit exergoenvironmental impacts of the fuel and product were 15.5 and 31.5 mPts/GJ, respectively. The exergoeconomic factor of the process was found to be 29.4%, while the exergoenvironmental factor was 0.74%. Overall, natural gas consumption was the most significant exergetic hotspot of the process, and hence more exergetically-sustainable alternatives should be considered to improve the process. Low-cost waste feedstocks need to be utilized to improve the economic viability of the process.

The rapid depletion of fossil fuel resources and climatic changes has triggered the researchers' attention to find an alternative and renewable energy source. Thus, biodiesel has been recognized as a potential alternative to petrodiesel for its biodegradability, non-toxicity, and environment-friendly attributes. In this study, an efficient and recyclable Cu-Ni doped ZrO 2 catalyst was synthesized and used to produce biodiesel from a novel non-edible caper (Capparis spinosa L.) seed oil. The synthesized catalyst was characterized by x-ray diffraction, fourier-transform infrared spectroscopy, scanning electron microscopy, and energy dispersive x-ray analysis. The catalyst was reused in four consecutive transesterification reactions without losing any significant catalytic efficiency. Transesterification reaction conditions were optimized via response surface methodology based on Box-Behnken design for predicting optimum biodiesel yields by drawing 3D surface plots. Maximum biodiesel yield of 90.2% was obtained under optimal operating conditions of 1:6 M ratio of oil to methanol, reaction temperature of 70 • C, reaction time of 1.5 h, and 2.5% catalyst loading. Fourier-transform infrared spectroscopy, gas chromatography mass spectrometry, and nuclear magnetic resonance (1 H and 13 C) analysis confirmed the high quality of biodiesel produced from non-edible caper (Capparis spinosa L.) seed oil. The fuel properties of the produced biodiesel were also found, such as kinematic viscosity (4.17 cS T), density (0.8312 kg/L), flash point (72 • C), acid no (0.21 mgKOH/g) and sulphur content (0.00042 wt%). These properties were matched and are in close agreement with the International Biodiesel Standards of European Union (EU-14214), China GB/T 20,828 (2007), and American (ASTM6751). Thus, non-edible Capparis spinosa L. seed oil and Cu-Ni doped ZrO 2 catalyst appeared to be highly active, stable, and cheap candidates to boost the future biodiesel industry.

The poly deep eutectic solvents (PDESs), a potential substituent to ionic liquids, have emerged as relatively new material and have been successfully applied in catalysis, nanotechnology, and, more importantly, in gas separation. Herein, the PDESs were incorporated for the first time in the CO 2 capturing membranes to exploit their inherent advantages in the acid gas capture. The PDESs were synthesized by mixing choline chloride (hydrogen bond acceptor-HBA) and two hydrogen bond donors-HBDs (polyacrylic acid and polyacrylamide) separately in different molar ratios. The physical changes of the resulting homogeneous mixture along with the Fourier Transform Infrared confirmed the successful synthesis of the PDESs. Afterward, these PDESs were impregnated into microporous polyvinylidene fluoride (PVDF) membrane support to fabricate supported liquid membranes (SLMs). The gas performance of the prepared PDES-SLMs was tested under pure and mixed-gas conditions for CO 2 , CH 4 , and N 2. The PDES-SLMs showed a significantly high CO 2 / CH 4 and CO 2 /N 2 selectivities of the order of 55.5 and 60, respectively. To evaluate their practical implication, the SLMs were investigated systematically under different operating conditions such as choline content, temperature, volume fraction of the CO 2 in the feed, and the activation energy required for CO 2 capture. The synthesized SLMs showed exceptional results in both permeability and selectivity viewpoint. The remarkable SLMs gas performance can be ascribed to the basicity, molar free volume, and the H-bonding strength of the synthesized PDESs. The green potential, low cost, and the promising gas separation performance make theses PDESs a favorable alternative to the competing PILs in capturing the greenhouse acid gases.

Forest harvesting activities on peatlands have long been associated with nutrient leaching and deterioration of downstream water quality. This study aims to assess the effect of grass seeding practice on harvested blanket peatlands to immobilize N and reduce its export to water courses. First, a plot-scale field experiment was conducted by seeding with two grass species (Holcus lanatus and Agrostis capillaris) to study the N uptake potential from a harvested area. Secondly, a simulated rainfall experiment was conducted to study the effect of these grasses on reducing N leaching from surface peat using laboratory flume approach. In the end, the role of seeded grasses in removing N from nutrient-rich throughflow water was assessed using simulated overland flow experiment. The results showed that the seeded grasses had the potential to uptake over 30 kg ha −1 of N in the first year after seeding on harvested peatlands, whereas it takes over 2.5 years to establish the same level of N uptake by natural re-vegetation (non-grassed). In the simulated rainfall experiment, the inorganic N (NH 4 +-N and NO 3 −-N) leaching in surface runoff from grassed flumes was 72% lower (453 mg m −2) than non-grassed flumes (1643 mg m −2). In the simulated overland flow experiment , the N retention by grassed flumes was significantly higher (98%) as compared to non-grassed flumes (70%) in the simulated overland flow experiment. Comparatively higher concentrations of NH 4 +-N and NO 3 −-N in soil porewaters of non-grassed flumes suggest that this N retention by non-grassed flumes is less sustainable and is likely to be leached in runoff in subsequent flow events. The results from all three experiments in this study suggest that seeded grasses are a major sink of N on harvested blanket peatland forests. Immobilization of N onsite using the grass seeding and mini-buffer practice could be an efficient and a feasible mean of reducing N export from harvested blanket peatland forests in order to protect the sensitive water courses. However, the sustainability of retention and immobilization of N by grasses needs to be studied further in long-term field-scale experiments on multiple peatland sites.

This study focused on producing high quality and yield of biodiesel from novel non-edible seed oil of abundantly available wild Raphnus raphanistrum L. using an efficient, recyclable and eco-friendly copper modified mont-morillonite (MMT) clay catalyst. The maximum biodiesel yield of 83% was obtained by base catalyzed trans-esterification process under optimum operating conditions of methanol to oil ratio of 15:1, reaction temperature of 150 • C, reaction time of 5 h and catalyst loading of 3.5%. The synthesized catalyst and biodiesel were characterized for their structural features and chemical compositions using various state-of-the-art techniques, including x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance (1 H, 13 C) and gas chromatography-mass spectroscopy. The fuel properties of the biodiesel were estimated including kinematic viscosity (4.36 cSt), density (0.8312 kg/ L), flash point (72 • C), acid value (0.172 mgKOH/g) and sulphur content (0.0002 wt.%). These properties were compared and found in good agreement with the International Biodiesel Standards of American (ASTM-951, 6751), European Committee (EN-14214) and China GB/T 20828 (2007). The catalyst was re-used in five consecutive transesterification reactions without losing much catalytic efficiency. Overall, non-edible Raphnus raphanistrum L.. seed oil and Cu doped MMT clay catalyst appeared to be highly active, stable, and cheap contenders for future biofuel industry. However, detailed life cycle assessment (LCA) studies of Raphnus raphanistrum L. seed oil biodiesel are highly recommended to assess the technical, ecological, social and economic challenges.

This paper critically reviews the current status of utilization of municipal solid waste and biomass blends for energy and resources recovery together with identifying the opportunities for future development in technological equipment and physicochemical waste compositions involved in such complex processes. Among numerous thermochemical conversion techniques, gasification of municipal solid waste with different biomass blends has unveiled as an auspicious technology to develop a sustainable waste management system that would substantially reduce pollution and maximize energy and materials recovery. Municipal solid wastes and biomass have different properties and elemental compositions and are abundantly available. These materials have the potential to produce various types of value-added products in terms of energy and chemicals through the gasification process. Recently, hybrid systems have been introduced with simple gasification technologies in terms of fuel oxidation system, plasma torch, or some biochemical conversion systems to enhance the process efficiency, energy, economics, quality, the yield of syngas, and to alter the composition of gaseous products. Consequently, gasification of biomass and waste would be the most suitable option to reduce toxic elements and harmful gases for the surroundings. For instant, ecological influence is not the real issue for limitation of biomass and waste gasification development, while a feasible economic return could appeal to investors and initiate its commercialization. Energy and resource recovery is assessed as an integrated approach to overcoming limitations. Also, techno-economic and environmental impact, life cycle assessment, and their implications are discussed in detail. Key bottlenecks that need urgent attention to facilitate global recognition of hybrid technology are highlighted.

Although currently microalgae biomass is not considered as a sustainable feedstock for biofuel production, future developments of microalgae cultivation and harvest could make the commercial application of such fast-growing photosynthetic biomass economically and environmentally feasible. This article aims at reviewing thermochemical conversion of microalgae into bio-crude oil through pyrolysis and hydrothermal liquefaction technologies. Subsequently, possible solutions to overcome the constraints to achieve the sustainable conversion of microalgae biomass are discussed in detail. The drawbacks of bio-crude oil as a transportation fuel and the technologies required for its upgrading are highlighted. Currently, microalgae-derived bio-crude oil is inferior to biodiesel and diesel in terms of quality, thus cannot be used as a transportation or jet fuel. It requires catalytic upgrading steps and further processing, including durable and cost-effective catalysts with strong regenerative capabilities.

This study critically reviews the recent developments and future opportunities pertinent to the conversion of CO 2 as a potent greenhouse gas (GHG) to fuels and valuable products. CO 2 emissions have reached an alarming level of around 410 ppm and have become the primary driver of global warming and climate change leading to devastating events such as droughts, hurricanes, torrential rains, floods, tornados and wildfires across the world. These events are responsible for thousands of deaths and have adversely affected the economic development of many countries, loss of billions of dollars, across the globe. One of the promising choices to tackle this issue is carbon sequestration by pre-and post-combustion processes and oxyfuel combustion. The captured CO 2 can be converted into fuels and valuable products, including methanol, dimethyl ether (DME), and methane (CH 4). The efficient use of the sequestered CO 2 for the desalinization might be critical in overcoming water scarcity and energy issues in developing countries. Using the sequestered CO 2 to produce algae in combination with waste-water, and producing biofuels is among the promising strategies. Many methods, like direct combustion, fermentation, transesterification, pyrolysis, anaerobic digestion (AD), and gasification, can be used for the conversion of algae into biofuel. Direct air capturing (DAC) is another productive technique for absorbing CO 2 from the atmosphere and converting it into various useful energy resources like CH 4. These methods can effectively tackle the issues of climate change, water security, and energy crises. However, future research is required to make these conversion methods cost-effective and commercially applicable.

The current study examines the efficiency of double metals (Cd and Mn) impregnated montmorillonite clay (Cd-Mn-Mmt) catalyst for the cleaner synthesis of biodiesel from novel non-edible seed oil of Prunus Cerasoides D. Don. (seed oil content 54.5%, and FFA content 0.45 mg KOH/g). X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and Fourier Transform Infrared Radiation Spectroscopy (FTIR) were used for characterizing the newly synthesized catalyst. The highest (85%) fatty acid methyl ester yield (FAME) of Prunus Cerasoides D. Don. biodiesel was obtained at optimized transesterification reaction conditions; 5 h of reaction time at 120 °C, 12:1 M ratio of methanol to oil and 4% catalyst loading. Synthesized biodiesel was further characterized via FTIR, Gas Chromatography/Mass spectroscopy (GC/MS), and Nuclear magnetic resonance (NMR (1 H, 13 C)). Additionally, the determined fuel properties, such as density (0.8612 kg/ L), kinematic viscosity (4.11 mm 2 /s), flash point (73 °C), cloud point (−9 °C) and pour point (−10 °C), of synthesized biodiesel, agreed with International Standards of China GB/T 20828 (2007), American (ASTM-951, 6751) and European Union (EU-14214). Pseudo-first-order kinetics fitted well with the experimental data (R 2 = 0.9172). The study findings recommended that the modified montmorillonite clay catalyst is a cleaner, cheaper, and easy to use along with high stability and catalytic performance in the transesterification process.

Anaerobic digestion (AD) is a sustainable wastewater treatment technology which facilitates energy, nutrient, and water recovery from organic wastes. The agricultural and industrial wastes are suitable substrates for the AD, as they contain a high level of biodegradable compounds. The aim of this study was to examine the AD of three different concentrations of phenol (100, 200, and 300 mg/L) containing wastewater with and without co-substrate (acetate) at four different temperatures (25, 35, 45, and 55 °C) to produce methane (CH 4)-enriched biogas. It was observed that the chemical oxygen demand (COD) and phenol removal efficiencies of up to 76% and 72%, respectively, were achieved. The CH 4 generation was found higher in anaerobic batch reactors (ABRs) using acetate as co-substrate, with the highest yield of 189.1 μL CH 4 from 500 μL sample injected, obtained using 200 mg/L of phenol at 35 °C. The results revealed that the performance of ABR in terms of degradation efficiency, COD removal, and biogas generation was highest at 35 °C followed by 55, 45, and 25 °C indicating 35 °C to be the optimum temperature for AD of phenolic wastewater with maximum energy recovery. Scanning electron microscopy (SEM) revealed that the morphology of the anaerobic sludge depends greatly on the temperature at which the system is maintained which in turn affects the performance and degradation of toxic contaminants like phenol. It was observed that the anaerobic sludge maintained at 35 °C showed uniform channels leading to higher permeability through enhanced mass transfer to achieve higher degradation rates. However, the denser sludge as in the case of 55 °C showed lesser permeability leading to limited transfer and thus reduced treatment. Quantitative real-time PCR (qPCR) analysis revealed a more noteworthy change in the population of the microbial communities due to temperature than the presence of phenol with the methanogens being the dominating species at 35 °C. The findings suggest that the planned operation of the ABR could be a promising choice for CH 4-enriched biogas and COD removal from phenolic wastewater.

articles presented in VSI highlight the recent developments in waste valorisation for the recovery of energy, fuels and value-added products. They also cover the primary hurdles and potential solutions moving towards more sustainable society. This editorial not only presents the overall summary of the extended research papers from NAXOS 2018, but also provides an overview of the current trends and developments in the fields of waste management, waste valor-ization, and energy production systems. The articles published in this VSI cover a wide range of topics, including energy recovery from waste, waste to energy technologies, sustainable energy systems, anaerobic digestion, thermal arc plasma gasification, microalgal-based biorefinery, waste management, modelling of advanced gasification systems, waste valorization, and microbial fuel cell technology. 10 manuscripts, out of total 21 extended mansucripts invited, were accepted for publication in the Applied Energy Journal through peer review process conducted by the expert reviewers in the relevant fields with the aid of the guest editors.

Sustainability in power generation mainly depends on the transition from fossils to sustainable energy resources. Biomass from the crop residue has huge potential for renewable power generation, but it is still not utilized to its full potential. This study presents a comprehensive methodology to evaluate and forecast the current and future availability of selective crop residue to generate renewable energy. A forecast model incorporating historical trends in the crop yield has been developed in MATLAB and implemented for crop residue based biomass resource assessment of five primary crops (wheat straw, rice husk, rice straw, cotton straw, corn stover, and bagasse) in order to estimate the energy generation potential for Pakistan from 2018 till 2035. It was found that about 40 million tonnes of crop residue was available in Pakistan for power generation in the year 2018 considering a residue removal (availability) factor of 50%. This translates to an estimated potential of about 11,000 MW of electricity generation capacity using crop residue derived biomass for 2018. This capacity is predicted to gradually increase up to 16,000 MW by the year 2035 based on the trends in the growth of crop production since 2001. The suitability of a potential region for the installation of 100 MW biomass-fired power plants was also assessed by calculating crop residue density and an equivalent collection radius (R e) of 50 km (km). Punjab province of Pakistan, being an agricultural province, with relatively better road infrastructure can sustain crop residue based power plants of up to 7000 MW cumulative capacity at various locations. The challenges , such as economic, logistics, regulatory and political barriers, in generating renewable energy from biomass along with their potential solutions were also discussed. The study also provides a baseline for future research to evaluate and forecast the growth in bio-power generation potential of any biomass resource in a region based on crop yield and area of the region.

This editorial prepared for Renewable and Sustainable Energy Reviews as a Virtual Special Issue overviews the research work presented at the NAXOS 2018 6th International Conference on Sustainable Solid Waste Management, held from the 13th June to 16th June 2018 in Naxos Island, Greece. The research work published in this Virtual Special Issue is focused not only on the recent advances in the areas of renewable and sustainable energy systems, but also highlights the key issues and challenges faced with potential solutions and way forward. This editorial summarises the review and original research articles from NAXOS 2018, as well as providing a comprehensive overview of the current trends in the field of renewable and sustainable energy systems. The articles published in this Virtual Special Issue cover a wide range of energy-related topics, including biofuels and bioenergy, biorefineries, wind energy, energy sustainability, biomass, waste to energy technologies, life cycle assessment study, energy and materials recovery from waste and integrated waste management techniques. A total of 29 extended manuscripts were invited, 19 of which were accepted for publication in Renewable and Sustainable Energy Reviews after vigorous review process carried out by expert reviewers in the field with the help of guest editors.

Waste-to-valuable products are being considered as one of the best solutions to convert the waste biomass into green and environment-friendly products. The wide utilization of waste biomass as a potential source of fuels, power, recycled materials, and valuable chemicals is well recognized globally. The waste driven fuels are used in all sectors of society for production of electricity, transport fuel, heating and cooling source, and in industrial processes. These fuels not only solve the waste disposal issues but also generate enormous economic and environmental benefits. They are promising alternatives due to their renewable, sustainable and eco-friendly features. However, there are multiple challenges in conversion and efficient utilization of waste biomass into sustainable energy and fuels. The purpose of the special issue, titled "Waste Biomass Utilization for Value-added Green Products" is to focus on the best possible ways to convert the waste biomass into value added and renewable products with an ambition to highlight the recent trends targeting the challenges and opportunities in this area. Renowned researchers have accepted our invitation to contribute their articles on the below subtopics; Conversion/Utilization of Waste Biomass Feedstocks into Fuels: The aspects of discovery and utilization of different waste biomass feedstocks for generation of various fuels. The examples of such waste biomass to fuels systems include the bio-alcohols, biodiesel, biogas, biohydrogen, and pyrolysis oils. The issue will cover a wide range of feedstock and conventional and new production methods including the challenges and prospects. In the last few decades, due to the ever-increasing exploitation of fossil fuels, there is a significant emphasis and demand on exploring and developing alternative, cost-effective, and non-food feedstocks or waste biomass sources for producing fuels and value-added products. Therefore, authors are expected to submit high-quality papers on this subtopic that will serve as a great contribution to this demanding area. Micro-Algae and Macro-Algae Based Biofuels: In the last few decades, there has been tremendous research on the utilization of micro and macro algae for biofuels production and increasing the process efficiency and quality of the products. Despite all these efforts and investment, there remain many challenges and scope for improvement in this area before potential commercialization of this technology worldwide. The authors are expected to not only highlight and discuss these areas but also give solutions and their recommendation for overall process optimization. Multiple benefits are sought through these processes including bio-waste treatment, production of clean fuels and CO 2 capturing for huge environmental and economic benefits. Contributions under this subtopic would be preferred covering both the scientific and engineering aspects of algae biofuels. Development of Advanced Catalysts for Biofuels: The role of catalysts is critical not only in the conversion process of biofuels systems but also in making the overall process more efficient, less energy intensive and economically feasible. However, the primary challenge with the use of catalysts is the high cost. Recently, waste biomass-based catalysts such as biochar and natural minerals like natural zeolite are utilized instead of costly commercial catalysts. Therefore, this subtopic would cover how such cheap and effective catalysts could be developed for various biofuels systems such as transesterification (biodiesel), anaerobic digestion (biogas), fermentation (bio-alcohols) and bio-hydrogen. State-of-the-art Cost-Effective Bioenergy Production Technologies: This subtopic would cover the state-of-the-art and cost-effective bioenergy production technologies such as pyrolysis, supercritical water reforming, gasification, anaerobic digestion, torrefaction, and liquid phase processing. Currently, one of the most limiting factors of bioenergy production technologies is the high capital/ operational cost or low profitability. New ideas and paradigm will be gathered to contribute to solving this issue through this special issue. A primary emphasis will be given to such contributions, covering the scientific aspects of process and products chemistry. Use of Waste and Non-profitable Natural Resources for Optimization of Biofuel Production: This subtopic would cover the utilization of waste and non-profitable natural resources such as lands, water, and biochar, natural minerals in optimizing the first and second generation biofuels such as bioalcohols (ethanol or methanol), biomethanation and biodiesel.

This paper aims to examine the influence of various catalysts on biodiesel production, especially from non-food feedstocks with an ambition to optimize the catalytic biodiesel production. Homogenous acid catalysts are mainly used in biodiesel production, but they cannot be recovered and demand costly fuel purification as being corrosive. Similarly, enzyme catalysts are expensive in industrial-scale production of biodiesel. However, heterogeneous catalysts simplify the easy separation of product and by-products from the catalyst along with catalyst reusability and reduction of waste. Solid acid and base catalysts offer more advantages due to their non-toxicity, high surface area, reusability, higher stability, and the simplicity of purification. Solid base catalysts yield better activity than solid acid catalysts, however, they cannot esterify large amounts of free fatty acids (FFAs) in non-food feedstocks. The solid acid catalysts have the added advantages of being more tolerant to high amounts of FFAs and being able to simultaneously esterify FFAs and transesterify triglycerides in cheap feedstocks like waste cooking oil. Recently, an array of inorganic, organic and polymeric solid acid and nanomaterial-based catalysts have been developed using cheap feedstocks. However, the issues of low reactivity, small pore sizes, low stabilities, long reaction times, and high reaction temperatures still need to be solved. The developments of producing efficient, cheap, durable, and stable solid acid and nanomaterial-based catalysts have been critically reviewed in this study. Furthermore, the challenges and future perspectives of production of biodiesel and its industry growth have also been discussed.

Fabrication of superior and cost-effective cathodic materials is vital in manufacturing sustainable microbial electrolysis cells (MECs) for biofuels production. In the present study, a novel manganese dioxide (MnO2) coated felt cathode (Mn/CF) has been developed for MECs using electrodeposition method via potentiostat. MnO2 is considered to encourage exogenous electron exchange and, in this way, improves the reduction of carbon dioxide (CO2). MnO2, as a cathodic catalyst, enhances the rate of biofuel production, electron transfer, and significantly reduces the cost of MECs. A maximum stabilized current density of 3.70 ± 0.5 mA/m2 was obtained in case of MnO2-coated Mn/CF based MEC, which was more than double the non-coated carbon felt (CF) cathode (1.70 ± 0.5 mA/m2). The dual chamber Mn/CF-MEC achieved the highest production rate of acetic acid (37.9 mmol/L) that was significantly higher (43.0%) in comparison to the non-coated CF-MEC. The cyclic voltammograms further verified the substantial enhancement in the electron transfer between the MnO2 coated
cathode and microbes. The obtained results demonstrate that MnO2 interacted electrochemically with microbial cells and enhanced the extracellular electron transfer, therefore validating its potential role in biofuel production. The MnO2 coated CF further offered higher electrode surface area and better electron transfer efficiency, suggesting its applicability in the large-scale MECs.

Energy recovery from waste resources holds a significant role in the sustainable waste management hierarchy to support the concept of circular economies and to mitigate the challenges of waste
originated problems of sanitation, environment, and public health. Today, waste disposal to landfills is the most widely used methodology, particularly in developing countries, because of limited budgets and lack of efficient infrastructure and facilities to maintain efficient and practical
global standards. As a consequence, the dump-sites or non-sanitary landfills have become the significant sources of greenhouse gases emissions, soil and water contamination, unpleasant odors,
leachate, and disease spreading vectors, flies, and rodents. However, waste can be a potential source of energy, fuels, and value-added products, if appropriately and wisely managed.
This Frontiers Research Topic was designed to collect new advancements and discoveries on the development of emerging waste-to-energy technologies, practical implementation, and lessons
learned from sustainable waste management practices under waste biorefinery concept (Figure 1), which will accelerate the growth of circular economies in the world. This Frontiers Research Topic
has attracted and compiled 13 top quality research and review articles. The articles have been written by researchers and academics working in institutions at different countries across the world including Germany, Netherlands, Greece, South Korea, Japan, Hong Kong, Saudi Arabia, Pakistan, Indonesia, Malaysia, Iran, and India. The editorial team of this research topic is very grateful to all the authors for their excellent contributions and making the research topic successful.

This study aims to examine the potential of natural clay mineral from the southern part of Saudi Arabia as an effective adsorbent material for the removal of heavy metal ions of cadmium (Cd) and nickel (Ni) from aqueous solutions. The SEM analysis showed that clay particles had mixed shapes such as elongated rod-like and rectangular shape having rough corners with larger particles of 2-8 µm in size and smaller particles in the sub-micron size range. X-ray diffraction data revealed that clay particles had a good crystalline structure and composed of a mixture of various minerals including feldspar, illite, quartz, calcite, and gypsum. The BET surface area was found to be 35 ± 1 m 2 /g and the average pore size and pore volume of 6.5 ± 0.5 nm and 5.7e-02 cc/g, respectively. The X-ray fluorescence analysis of clay showed main compounds of SiO 2 (47.33%), Al 2 O 3 (18.14%), Fe 2 O 3 (15.89%) with many others such as CaO, MgO, TiO 2 , and K 2 O in minor quantities. It was found that 1.2 g of clay removed up to 99.5% of Ni and 97.5% of Cd from 40 ppm aqueous solutions. The metal removal efficiencies were increased from around 95% up to 99% by increasing the pH of aque-ous solutions from 4 to 11. The adsorption of Ni and Cd ions on Saudi clay was relatively fast, and up to 97% of ions were removed from solution within 45 min. The SEM-EDX and BET analysis for recycled clays further confirmed that the metal ions were removed from water through adsorption onto the clay. The experimental data fitted well with Langmuir and Freundlich isotherms. The maximum adsorption capacity of clay for Cd and Ni from isotherms was found to be 3.3 and 2.7 mg/g respectively. The findings of this study confirm the potential role of Saudi natural clay in wastewater treatment processes as a cheap, environment-friendly and safe natural adsorbent material.

India has emerged as a key player with a high potential to develop a biomass and biobased economy due to its large geographic size and the massive amounts of agricultural and non agricultural biomass produced. India has joined hands with Europe to synchronize its efforts to create
and facilitate the development of a biobased economy in this country. This paper aims to examine common research and development actions between the European Union (EU) and India to facilitate the development of these biobased economies. As a base, a thorough study has been performed considering the biomass potential and current status of the bioeconomy in both the EU and India based on the distillation of a series of 80 potential recommendations. The recommendations were grouped into four major categories: (1) biomass production, (2) by-products/
waste, (3) biorefineries and (4) policy, market, and value-added products. A questionnaire was designed and distributed to key stakeholders belonging to: academia, industry, and policymakers in both India and the EU. A total of 231 responses were received and analyzed, based on
the key recommendations made for the essential research and development topics that are of prime importance to develop biobased economies in both the EU and India. The findings of this study suggest recognizing the value-added contributions made by biobased products such as: food, feed, valuable materials and chemicals in both regions. It is important to reduce the overall process costs and minimize the environmental impacts of such a biobased economy.

Although currently microalgae biomass is not considered as a sustainable feedstock for biofuel production, future developments of microalgae cultivation and harvest could make the commercial application of such fastgrowing photosynthetic biomass economically and environmentally feasible. This article aims at reviewing
thermochemical conversion of microalgae into bio-crude oil through pyrolysis and hydrothermal liquefaction technologies. Subsequently, possible solutions to overcome the constraints to achieve the sustainable conversion of microalgae biomass are discussed in detail. The drawbacks of bio-crude oil as a transportation fuel and the
technologies required for its upgrading are highlighted. Currently, microalgae-derived bio-crude oil is inferior to biodiesel and diesel in terms of quality, thus cannot be used as a transportation or jet fuel. It requires catalytic upgrading steps and further processing, including durable and cost-effective catalysts with strong regenerative
capabilities.

The current study examines the efficiency of double metals (Cd and Mn) impregnated montmorillonite clay (Cd-Mn-Mmt) catalyst for the cleaner synthesis of biodiesel from novel non-edible seed oil of Prunus Cerasoides D. Don. (seed oil content 54.5%, and FFA content 0.45 mg KOH/g). X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and Fourier Transform Infrared Radiation Spectroscopy (FTIR) were used for characterizing the newly synthesized catalyst. The highest (85%) fatty acid methyl ester yield (FAME) of Prunus Cerasoides D. Don. biodiesel was obtained at optimized transesterification reaction conditions; 5 h of reaction time at 120 °C, 12:1 M ratio of methanol to oil and 4% catalyst loading. Synthesized biodiesel was further characterized via FTIR, Gas Chromatography/Mass spectroscopy (GC/MS), and Nuclear magnetic resonance (NMR (1 H, 13 C)). Additionally, the determined fuel properties, such as density (0.8612 kg/ L), kinematic viscosity (4.11 mm 2 /s), flash point (73 °C), cloud point (−9 °C) and pour point (−10 °C), of synthesized biodiesel, agreed with International Standards of China GB/T 20828 (2007), American (ASTM-951, 6751) and European Union (EU-14214). Pseudo-first-order kinetics fitted well with the experimental data (R 2 = 0.9172). The study findings recommended that the modified montmorillonite clay catalyst is a cleaner, cheaper, and easy to use along with high stability and catalytic performance in the transesterification process.

This work highlights how the treatment of ZSM-5 (parent Zeolite Socony Mobil-5, Si/Al = 23) with different surfactant templates and alkaline solution, improved the catalytic performance in the Friedel-Crafts acylation of anisole with a propionic anhydride to obtain p-methoxypropiophenone. The modified microporous to mesoporous zeolite catalysts were characterized using different analytical techniques, including X-ray diffraction (XRD), nitrogen porosimetry, Fourier-transform infrared spectroscopy (FT-IR), temperature-programmed desorption (ammonia-TPD) and field emission scanning electron microscopy (FE-SEM) to analyze the crystallographic structure, surface acidity, surface area, porosity, morphology, and particle size. The results showed that the formed mesoporous zeolite by NaOH solution had smaller mesopores (ca. 3.7 nm) as compared to the mesoporous zeolites obtained by surfactant templates, such as, CTAB (ca. 14.9 nm), TPAOH (ca. 11.1 nm) and mixture of CTAB/TPAOH (ca. 15.2 nm). The catalytic acylation reaction was conducted in a batch glass reactor at various temperatures and the products were analyzed using off-line gas chromatography-mass spectrometry (GC-MS). It was found that the activity of treated ZSM-5 with mixed surfactant templates (CTAB/TPAOH) exhibited enhanced selectivity towards the main product (p-methoxypropiophenone) by a factor 1.7 or higher than unmodified ZSM-5 due to its increased surface area by 1.5 times and enhanced acid sites.

This paper for the first time aims to valorize the environmental and economic values of electronic waste recycling for member states of the Gulf Cooperation Council (GCC) from the year 2018 up to 2040. GCC countries have a unique situation due to the significant economic growth with the resulting urbanization and population growth accompanied by high standards of living that in turn increase all types of waste. A direct link among the living standards and quantity of electronic waste production is observed in the GCC states. The annual growth of electronic waste in GCC is 3-5% while the current estimated electronic waste generation exceeds 52.2 million metric tonnes (Mt). In 2018, GCC states generated 857 kilotonnes (kt) electronic waste that would be 1.094 Mt by 2040. KSA, among the GCC states, generated the highest amount of electronic waste (533 kt) in 2018 that would be 675 kt by 2040. GCC countries are on the right track of developing policies and regulations for managing electronic waste. However, more efforts are required to ensure the implementation of these regulations. The findings of this study would be a base for the future studies in the electronic waste sector in the GCC region and a novel initiative for GCC to develop a unified free zone for the electronic waste recycling that will meet the local, regional, and international standards and regulations. This unified GCC initiative has substantial economic and environmental benefits for the region.

Pyrolysis based biorefineries have great potential to convert waste such as plastic and biomass waste into energy and other valuable products, to achieve maximum economic and environmental benefits. In this study, the catalytic pyrolysis of different types of plastics wastes (PS, PE, PP, and PET) as single or mixed in different ratios, in the presence of modified natural zeolite (NZ) catalysts, in a small pilot scale pyrolysis reactor was carried out. The NZ was modified by thermal activation (TA-NZ) at 550 • C and acid activation (AA-NZ) with HNO 3 , to enhance its catalytic properties. The catalytic pyrolysis of PS produced a higher liquid oil (70 and 60%) than PP (40 and 54%) and PE (40 and 42%), using TA-NZ and AA-NZ catalysts, respectively. The gas chromatography-mass spectrometry (GC-MS) analysis of oil showed a mixture of aromatics, aliphatic and other hydrocarbon compounds. The TA-NZ and AA-NZ catalysts showed a different effect on the wt% of catalytic pyrolysis products and liquid oil chemical compositions, with AA-NZ showing higher catalytic activity than TA-NZ. FT-IR results showed clear peaks of aromatic compounds in all liquid oil samples with some peaks of alkanes that further confirmed the GC-MS results. The liquid oil has a high heating value (HHV) range of 41.7-44.2 MJ/kg, close to conventional diesel. Therefore, it has the potential to be used as an alternative source of energy and as transportation fuel after refining/blending with conventional fuels.

The present study aims to investigate the thermal and catalytic pyrolysis of CD case wastes over natural zeolite catalyst. The effect of temperature and catalyst on product yields have been investigated for each condition. The thermal pyrolysis experiments were carried out at the reactor temperature of 400, 450, and 500°C. Furthermore, the effect of natural zeolite (NZ) catalyst on pyrolysis products was also studied at various catalyst to feedstock ratio. The results showed that the temperature and catalyst affected the products yield and liquid composition. CD case pyrolysis produced highest liquid fraction at the temperature of 450°C. Furthermore an estimated 5.74 kW of electricity can be generated by pyrolysis oil produced from CD case wastes at a recycling site in Yogyakarta city, Indonesia.

The quest for a sustainable environment and combating global warming, carbon capture, and storage (CCS) has become the primary resort. A complete shift from non-renewable resources to renewable resources is currently impossible due to its major share in energy generation; making CCS an imperative need of the time. This study, therefore, aims to examine the reckoning of carbon dioxide (CO2), measurement methods, and its efficient capture and storage technologies with an ambition to combat global warming and achieve environmental sustainability. Conventionally, physical, geological and biological proxies are used to measure CO 2. The recent methods for CO 2 analyses are spectrometry, electrochemical gas sensors, and gas chromatography. Various procedures such as pre, post, and oxyfuel combustion, and use of algae, biochar, and charcoal are the promising ways for CO2 sequestration. However, the efficient implementation of CCS lies in the application of nano-technology that, in the future, could provide a better condition for the environment and economic outlooks. The captured carbon can be stored in the earth crust for trillions of years, but its leakage during storage can raise many issues including its emissions in the atmosphere and soil acidification. Therefore, global and collective efforts are required to explore, optimize and implement new techniques for CCS to achieve high environmental sustainability and combat the issues of global warming.

The increasing concentration of carbon dioxide (CO2) in the atmosphere is a primary global environmental concern due to its detrimental impacts on climate change. A significant reduction in CO2 generation together with its capture and storage is an imperative need of the time. CO2 can be captured from power plants and other industries through various methods such as absorption, adsorption, membranes, physical and biological separation techniques. The most widely used systems are solvent based CO2 absorption method. The aim of this study was to analyze the effect of various random and structured packing materials in absorption column on CO2 removing efficiency. Aspen plus was used to develop the CO2 capture model for different packing materials with Monoethanolamine (MEA) solvent in order to optimize the system. It was found that the lowest re-boiler duty of 3,444 kJ/KgCO2 yield the highest rich CO2 loading of 0.475 (mole CO2/mole MEA) by using the BX type of structured packing having the highest surface area. The surface area of the different packing materials were inversely proportional to the temperature profiles along the column. Furthermore, the packing materials with higher surface areas yielded higher CO2 loading profiles and vice versa. The findings of this study and recommendation would help further research on optimization of solvent-based CO2 capturing technologies.

The octane enhancement of light straight run naphtha is one of the significant solid acid catalyzed processes in the modern oil refineries due to limitations of benzene, aromatics, and olefin content in gasoline. This paper aims to examine the role of various catalysts that are being utilized for the isomerization of light naphtha with an ambition to give an insight into the reaction mechanism at the active catalyst sites, and the effect of various contaminants on catalyst activity. In addition, different technologies used for isomerization process are evaluated and compared by different process parameters.

Bio-electrochemical degradation of pentachlorophenol was carried out in single as well as dual chambered microbial fuel cell (MFC) with simultaneous production of electricity. The maximum cell potential was recorded to be 787 and 1021 mV in single and dual chambered systems respectively. The results presented nearly 66 and 89% COD removal in single and dual chambered systems with corresponding power densities of 872.7 and 1468.85 mW m À2 respectively. The highest coulombic efficiency for single and dual chambered counterparts was found to be 33.9% and 58.55%. GC-MS data revealed that pentachlorophenol was more effectively degraded under aerobic conditions in dual-chambered MFC. Real-time polymerase chain reaction showed the dominance of exoelectrogenic Geobacter in the two reactor systems with a slightly higher concentration in the dual-chambered system. The findings of this work suggested that the aerobic treatment of pentachlorophenol in cathodic compartment of dual chambered MFC is better than its anaerobic treatment in single chambered MFC in terms of chemical oxygen demand (COD) removal and output power density.

The biofuel industry is rapidly growing with a promising role in producing renewable energy and tackling climate change. Nanotechnology has tremendous potential to achieve cost-effective and process-efficient biofuel industry. Various nanomaterials have been developed with unique properties for enhanced biofuel production/utilization. The way forward is to develop nanotechnology-based biofuel systems at industrial scale.

This study aims to examine the potential substitute natural gas (SNG) production by integrating black liquor gasification (BLG) island with a small wheat straw-based non-wood pulp mills (NPM), which do not employ the black liquor recovery cycle. For such integration, it is important to first build knowledge on expected improvements
in an overall integrated non-wood pulp mill energy system using the key performance indicators. O2-blown circulating fluidized bed (CFB) gasification with direct causticization is integrated with a reference small NPM to evaluate the overall performance. A detailed economic analysis is performed together with a sensitivity analysis based on variations in the rate of return due to varying biomass price, total capital investment, and natural gas prices. The quantitive results showed considerable SNG production but significantly reduced electricity
production. There is a substantial CO2 abatement potential combining CO2 capture and CO2 mitigation from SNG use replacing compressed natural gas (CNG) or gasoline. The economic performance through sensitivity analysis reflects significant dependency on both substitute natural gas production and natural gas market price. Furthermore, the solutions to address the challenges and barriers for the successful commercial implementation of BLG based polygeneration system at small NPMs are discussed. The system performance and discussion on the real application of integrated system presented in this article form a vital literature source for future use by large number of small non-wood pulp industries.

This study aims to (1) convert agricultural waste to biochar through pyrolysis, (2) examine its physiochemical characteristics, and (3) investigate its potential role as fuel and catalyst in energy recovery technologies. The produced biochars at 250, 350, and 450 °C showed a wide range of mineralogical composition, high porosity, and thermal stability, and alkaline pH that make biochar suitable for improving the processes of energy recovery technologies such as anaerobic digestion (AD), transesterification and pyrolysis. The alkaline pH of biochars can neutralize the acidic condition and increase the digestibility of the feedstock in AD process for enhanced methane (CH4) production. Biochar favors the transesterification process for biodiesel production due to products separation and high stability under basic and acidic conditions. In pyrolysis process, biochar can act as a catalyst to increase the degradation rates of plastic or biomass wastes or can be used as an adsorbent material during the post-treatment to improve the quality of the liquid oil. The high heating values (HHV) of biochars produced at 250, 350 and 450 °C were 24, 23.64 and 23.08 MJ kg-1. This characteristic of biochar along with the high tendency of slagging indicate that biochar could be used itself as a source of energy. Biochar can also act as a promising low-cost adsorbent for capturing carbon dioxide (CO2) due to its highly porous structure and sorptive capacity and subsequently the conversion of absorbed CO2 to fuel. Research is yet required on the application of biochar in pyrolysis and capturing and catalyzing the conversion reactions of CO2 to fuels.

This study aims to examine the effect of various advanced catalysts on tire waste pyrolysis oil using a small pilot-scale pyrolysis reactor with a capacity of 20 L. The catalytic pyrolysis with activated alumina (Al2O3) catalyst produced maximum liquid oil (32 wt.%) followed by activated calcium hydroxide (Ca(OH)2) (26 wt.%), natural zeolite (22 wt.%) and zeolite (H-SDUSY) (14 wt.%) catalysts, whereas liquid oil yield of 40% was obtained without catalyst. The gas chromatography-mass spectrometry results confirmed the pyrolysis liquid oil produced without catalyst consist of up to 93.3% of mixed aromatic compounds. The use of catalysts decreased the concentration of aromatic compounds in liquid oil down to 60.9% with activated calcium hydroxide, 71.0% with natural zeolite, 84.6% with activated alumina, except for synthetic zeolite producing 93.7% aromatic compounds. The Fourier-transform infrared spectroscopy data revealed that the mixture of aromatic and aliphatic hydrocarbon compounds were found in all liquid oil samples, which further confirmed the gas chromatography results. The characteristics of pyrolysis liquid oil had viscosity (1.9 cSt), density (0.9 g/cm3), pour point (-2 °C) and flash point (27 °C), similar to conventional diesel. The liquid oil had higher heating values, key feature of a fuel, in the range of 42-43.5 MJ/kg that is same to conventional diesel (42.7 MJ/kg). However, liquid oil requires post-treatments, including refining and blending with conventional diesel to be used as a transport fuel, source of energy and value-added chemicals.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract In the Kingdom of Saudi Arabia (KSA), millions of worshippers come from across the globe to perform religious rituals of Pilgrimage (Hajj) and Umrah. Madinah-tul-Munawara is one of the holiest city, where pilgrims come after performing rituals in Makkah. In this city, most of the collected municipal solid waste (MSW) is disposed of in the landfills after a partial recycling of paper, cardboard, and metals (~10-20% of total MSW). The Saudi's government has recently launched a new policy of Vision 2030, which outlined the safeguard of local environment through increased efficiency of waste recycling and management, pollution prevention strategies and generating renewable energy from indigenous sources, including the waste. Currently, the recycling practices in KSA are mainly regulated by an informal sector through waste pickers or waste scavengers. This has led to the need of recycling schemes, especially in the holiest cities of Makkah and Madinah through a public-private partnership (PPP). Huge amounts of energy can be conserved, that would otherwise be spent on raw material extraction, transportation, and manufacturing of materials, through recycling into the same materials. Around 10,009 TJ of energy can be saved through recycling of 24.21% of MSW in Madinah city, including glass, metals, aluminum, cardboard, and paper. It is estimated that around 10,200 tons of methane (CH4) emissions and 254,600 Mt.CO2 eq. of global warming potential (GWP) can also be saved. In addition, carbon credit revenue of US $5.92 million, and landfill diversion worth of US $32.78 million can be achieved with a net revenue of US $49.01 million every year only by recycling 24.21% of MSW in Madinah city. The waste recycling doesn't require high technical skills and labor, and complicated technologies for large-scale implementation, and therefore, can be implemented easily in the holiest cities of Makkah and Madinah to achieve multiple economic and environmental benefits. Abstract In the Kingdom of Saudi Arabia (KSA), millions of worshippers come from across the globe to perform religious rituals of Pilgrimage (Hajj) and Umrah. Madinah-tul-Munawara is one of the holiest city, where pilgrims come after performing rituals in Makkah. In this city, most of the collected municipal solid waste (MSW) is disposed of in the landfills after a partial recycling of paper, cardboard, and metals (~10-20% of total MSW). The Saudi's government has recently launched a new policy of Vision 2030, which outlined the safeguard of local environment through increased efficiency of waste recycling and management, pollution prevention strategies and generating renewable energy from indigenous sources, including the waste. Currently, the recycling practices in KSA are mainly regulated by an informal sector through waste pickers or waste scavengers. This has led to the need of recycling schemes, especially in the holiest cities of Makkah and Madinah through a public-private partnership (PPP). Huge amounts of energy can be conserved, that would otherwise be spent on raw material extraction, transportation, and manufacturing of materials, through recycling into the same materials. Around 10,009 TJ of energy can be saved through recycling of 24.21% of MSW in Madinah city, including glass, metals, aluminum, cardboard, and paper. It is estimated that around 10,200 tons of methane (CH4) emissions and 254,600 Mt.CO2 eq. of global warming potential (GWP) can also be saved. In addition, carbon credit revenue of US $5.92 million, and landfill diversion worth of US $32.78 million can be achieved with a net revenue of US $49.01 million every year only by recycling 24.21% of MSW in Madinah city. The waste recycling doesn't require high technical skills and labor, and complicated technologies for large-scale implementation, and therefore, can be implemented easily in the holiest cities of Makkah and Madinah to achieve multiple economic and environmental benefits.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract It has been globally recognized as necessary to reduce greenhouse gas (GHG) emissions for mitigating the adverse effects of global warming on earth. Carbon dioxide (CO2) capture and storage (CCS) technologies can play a critical role to achieve these reductions. Current CCS technologies use several different approaches including adsorption, membrane separation, physical and chemical absorption to separate CO2 from flue gases. This study aims to evaluate the performance and energy savings of CO2 capture system based on chemical absorption by installing an intercooler in the system. Monoethanolamine (MEA) was used as the absorption solvent and Aspen HYSYS (ver. 9) was used to simulate the CO2 capturing model. The positioning of the intercooler was studied in 10 different cases and compared with the base case 0 without intercooling. It was found that the installation of the intercooler improved the overall efficiency of CO2 recovery in the designed system for all 1-10 cases. Intercooler case 9 was found to be the best case in providing the highest recovery of CO2 (92.68%), together with MEA solvent savings of 2.51%. Furthermore, energy savings of 16 GJ/h was estimated from the absorber column alone, that would increase many folds for the entire CO2 capture plant. The intercooling system, thus showed improved CO2 recovery performance and potential of significant savings in MEA solvent loading and energy requirements, essential for the development of economical and optimized CO2 capturing technology.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract This study aims to examine the economic and environmental benefits of recovered paper and potential contribution of the recovered paper to the Kingdom of Saudi Arabia (KSA) Vision 2030. The Vision 2030 is an inclusive development policy, recently launched, with the objectives to build the best future for the country. The Vision 2030 is based on three ambitious goals: making the country a vibrant society, a thriving economy and an ambitious nation. It is estimated that by 2030, 5.05 million ton of waste paper would be recovered in the country. About 11.3 billion SAR (US $3.01 billion) would be added to the country's GDP and would create about 16,536 new jobs if the recovered paper industry is built in the country. Moreover, a net environmental benefit of 9.6 million crude barrel oil savings and 4.5 million ton of CO2 savings from GHG emissions could be achieved by 2030 only from the paper waste recovery in the country. The potential benefits of paper waste recycling in KSA highlight the needs of effective measures to optimize the economic and environmental opportunities inherited in the waste paper industry. These measures should focus on capitalizing the local waste paper processing industry, restrict the export of raw waste paper materials, and enhance the waste paper collection process and quantity.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract This study aims to examine the nonsterilized fermentation conditions for coproduction of pectinases and lipase enzymes using several fruit wastes as an energy source. Thermophilic fungal strain, Penicillium expansum CMI 39671 was used as a fermenting strain. The effect of process conditions including; nitrogen sources, pH, temperature, time and moisture contents, on the production of both enzymes were studied. The highest activities of pectinase and lipase (2817, 1870 U/g dry substrate) enzymes were found with orange peel feedstock, whereas the lowest activities of 1662 U/g and 1266 U/g were found with banana peel and papaya peel feedstocks respectively. Overall, pectinase showed higher enzymatic activities than lipase enzymes, both having similar increasing and decreasing trends, at all studied conditions. The optimum process conditions of peptone as a nitrogen source, pH 7, 40°C, 5 days and 70% moisture contents, were found to show highest enzymatic activities for both enzymes. The orange peel feedstock showed no significant difference in both enzymes' activities at sterilized and nonnotarized process conditions. Pectinase and lipase enzymes showed (13791 U/g) and (8114 U/g) for sterilized and (14091 U/g) and (8324 U/g) for nonnotarized process conditions respectively. In addition, the fungal strains also produce bacteriocin-like compounds that could inhibit microbial growth. These findings will help to design and develop robust, cost-effective and less energy intensive enzyme production processes and consequently an efficient fruit waste to energy system through open fermentation. Abstract This study aims to examine the nonsterilized fermentation conditions for coproduction of pectinases and lipase enzymes using several fruit wastes as an energy source. Thermophilic fungal strain, Penicillium expansum CMI 39671 was used as a fermenting strain. The effect of process conditions including; nitrogen sources, pH, temperature, time and moisture contents, on the production of both enzymes were studied. The highest activities of pectinase and lipase (2817, 1870 U/g dry substrate) enzymes were found with orange peel feedstock, whereas the lowest activities of 1662 U/g and 1266 U/g were found with banana peel and papaya peel feedstocks respectively. Overall, pectinase showed higher enzymatic activities than lipase enzymes, both having similar increasing and decreasing trends, at all studied conditions. The optimum process conditions of peptone as a nitrogen source, pH 7, 40°C, 5 days and 70% moisture contents, were found to show highest enzymatic activities for both enzymes. The orange peel feedstock showed no significant difference in both enzymes' activities at sterilized and nonnotarized process conditions. Pectinase and lipase enzymes showed (13791 U/g) and (8114 U/g) for sterilized and (14091 U/g) and (8324 U/g) for nonnotarized process conditions respectively. In addition, the fungal strains also produce bacteriocin-like compounds that could inhibit microbial growth. These findings will help to design and develop robust, cost-effective and less energy intensive enzyme production processes and consequently an efficient fruit waste to energy system through open fermentation.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract Pulp mills without black liquor recovery cycle could play a major role in employing black liquor gasification (BLG) to produce transport fuels. In conventional chemical pulp mills, black liquor is burnt in recovery boilers to generate steam and electricity to meet energy demands. The inorganic chemicals are reused for the digestion process. However, the energy content and inorganic chemicals are not recovered in small scale pulp mills especially in the developing countries which do not employ recovery cycle. This study investigates the potential of synthetic natural gas (SNG) production by integrating BLG island with a reference pulp mill without chemical recovery cycle. The improvements in overall energy efficiency are evaluated using performance indicators such as biofuel production potential, integrated system's efficiency, and energy ratios. The oxygen-blown circulating fluidized bed (CFB) gasification with direct causticization is integrated with reference pulp mill. The results showed considerable SNG production without external biomass import. However to compensate total electricity deficit, the electricity will be imported from the grid. There is a substantial CO 2 abatement potential of combining CO 2 capture using seloxol absorption, and CO 2 mitigation from SNG by replacing gasoline.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract The fossil fuels accomplish almost 80% of the world energy needs. The ever increasing exploitation of fossil fuels has led to environmental pollution, global climate change and health problems to living beings. Hence to meet the needs of the future energy and to mitigate the environmental pollution, it is critical to look for the alternate fuels. Global energy infrastructure in the future is believed to be accomplished by the energy generated from the low-cost renewable resources. Algae biomass has emerged as a promising biofuel source, as microalgae-based biofuels are biodegradable, renewable, and eco-friendly in comparison to fossil driven fuels. This study aims to examine the importance of microalgae as an alternative renewable energy source and evaluate the key challenges in the production of microalgae biofuel.

Biogas potential was explored for animal manure, wheat straw, food waste and rice straw. Batch experiments were performed at a laboratory scale using potential biomethane assays (BMP) for a period of 50 days. The biogas yield was observed higher when using rice straw (0.40 m3/kg VSadded) as a substrate, as compared to wheat straw (0.33 m3/kg VSadded) and animal manure (0.30 m3/kg VSadded) substrates. Around 10% of biogas was produced in the initial phase of 4 days for manure, wheat straw, and rice straw feedstocks. During the middle phase of 30 days for these feedstocks, 65 – 80% of biogas was produced. Less than 20% of biogas was produced during the final phase of last 16 days of the experiment. The biogas production from food waste was found lowest (0.02 m3/kg VSadded) among all substrates. Therefore, the anaerobic digestion (AD) of both food waste and animal manure is more suited in co-digestion fashion than mono-digestion.

The Gulf Cooperation Countries (GCC) consistently rank among the top 10% of per capita waste producers in the world. Collectively around 120 million tons of waste is produced annually in GCC; 55% construction and demolition (C&D) waste, 20% municipal solid waste (MSW), 18% industrial waste, and 7% hazardous waste. Like other GCC nations, the Kingdom of Saudi Arabia (KSA) generates massive amounts of MSW, C&D waste, and industrial waste. This study aims to examine 81 construction companies in the Eastern Province of KSA to determine which factors critically affect the sustainable management of C&D waste in the country. Only 39.5% of the companies studied had a pollution control plan for their projects. It was also found that only 13.6% of C&D waste is recycled and reused every year, whereas the remaining 86.4% C&D waste eventually goes to the landfills. Most of the C&D waste in the country is a promising source of potential recyclable construction materials such as gravel from debris, metals, and sand. This would not only fulfill the requirements of gravel and metal production of the KSA but also solve the waste disposal issues along with generating huge economic benefits. However, to accomplish the goal of sustainable construction waste management, it is critical to underline the various factors that might impact the construction waste management practices in the country. Keywords Construction and demolition (C&D) waste · Municipal solid waste (MSW) · Waste recycling · Landfill sites · Sustainable construction material

This study presents a preliminary assessment of biodiesel production from waste sources available in the Kingdom of Saudi Arabia (KSA) for energy generation and solution for waste disposal issues. A case study was developed under three different scenarios: (S1) KSA population only in 2017, (S2) KSA population and pilgrims in 2017, and (S3) KSA population and pilgrims by 2030 using the fat fraction of the municipal solid waste. It was estimated that S1, S2, and S3 scenarios could produce around 1.08, 1.10 and 1.41 million tons of biodiesel with the energy potential of 43423, 43949 and 56493 TJ respectively. Furthermore, annual savings of US $55.89, 56.56 and 72.71 million can be generated from landfill diversion of food waste and added to the country's economy. However, there are challenges in commercialization of waste to biodiesel facilities in KSA, including waste collection and separation, impurities, reactor design and biodiesel quality.

A low-cost novel carbon-metal double layered oxides (C/MnCuAl-LDOs) nano-adsorbent was synthesized by co-precipitation, for the adsorption of Congo red (CR), using modified carbon derived from pyrolysis of polystyrene (PS) plastic waste. The synthesized C/MnCuAl-LDOs has a crystalline structure with a high surface area of 60.43 m²/g and pore size of 99.85 Å. Adsorption of CR using all prepared adsorbents from aqueous solution under equilibrium and kinetic conditions were evaluated against different values of the pH (4-10), initial CR concentrations (25-250 mg/g), contact time (0-310 min) and temperature (30-50°C). The obtained results revealed that C/MnCuAl-LDOs showed maximum adsorption capacity for CR among all the used adsorbents. The optimum equilibrium time was 180 min, whereas acidic medium (pH 4.5) favored the maximum adsorption of CR up to 317.2 mg/g on C/MnCuAl- LDOs. The adsorption kinetics followed the pseudo-second-order model, whereas Freundlich adsorption isotherm fitted best to obtained data in comparison to Langmuir adsorption isotherm. The results suggested that C/MnCuAl-LDOs is an efficient material for the removal of organic pollutants from the wastewater.

This study aims to examine the catalytic pyrolysis of various plastic wastes in the presence of natural and synthetic zeolite catalysts. A small pilot scale reactor was commissioned to carry out the catalytic pyrolysis of polystyrene (PS), polypropylene (PP), polyethylene (PE) and their mixtures in different ratios at 450 °C and 75 min. PS plastic waste resulted in the highest liquid oil yield of 54% using natural zeolite and 50% using synthetic zeolite catalysts. Mixing of PS with other plastic wastes lowered the liquid oil yield whereas all mixtures of PP and PE resulted in higher liquid oil yield than the individual plastic feed-stocks using both catalysts. The GC–MS analysis revealed that the pyrolysis liquid oils from all samples mainly consisted of aromatic hydrocarbons with a few aliphatic hydrocarbon compounds. The types and amounts of different compounds present in liquid oils vary with some common compounds such as styr-ene, ethylbenzene, benzene, azulene, naphthalene, and toluene. The FT-IR data also confirmed that liquid oil contained mostly aromatic compounds with some alkanes, alkenes and small amounts of phenol group. The produced liquid oils have high heating values (HHV) of 40.2–45 MJ/kg, which are similar to conventional diesel. The liquid oil has potential to be used as an alternative source of energy or fuel production.

This paper aims to examine the potential of waste biorefineries in developing countries as a solution to current waste disposal problems and as facilities to produce fuels, power, heat, and value-added products. The waste in developing countries represents a significant source of biomass, recycled materials, chemicals, energy, and revenue if wisely managed and used as a potential feedstock in various biorefinery technologies such as fermentation, anaerobic digestion (AD), pyrolysis, incineration, and gasification. However, the selection or integration of biorefinery technologies in any developing country should be based on its waste characterization. Waste biorefineries if developed in developing countries could provide energy generation, land savings, new businesses and consequent job creation, savings of landfills costs, GHG emissions reduction, and savings of natural resources of land, soil, and groundwater. The challenges in route to successful implementation of biorefinery concept in the developing countries are also presented using life cycle assessment (LCA) studies.

Sorghum Bagasse in recent years has emerged as a promising feedstock for production of biofuels and value-added products following various biological conversion pathways. However, adequate conservation is critical for utilising Sorghum Bagasse as a feedstock for fuel production around the year in bioenergy plants. Therefore, this study aims to examine the pressure drop as a function of airflow velocity and construct Shedd's curves for energy Sorghum Bagasse. The ambition was to facilitate large-scale drying systems for biomass conservation. The Bagasse was prepared by extracting the juice from the harvested sorghum and passing through a juicing machine. Afterwards, it was manually chopped and stored on a wooden platform having 2.44 m2 area in a 55-gallon drum at a depth of 0.57 m. The airflow velocities (0.24–1.32 ms−1) caused a pressure drop (9.96–346.23 Pa) across the empty drum. The different pressure drop in the drum containing Sorghum Bagasse (19.92–263.25 Pa) was due to various airflow velocities (0.043–0.799 ms−1). Pressure drop was further increased with increasing airflow velocity, and it was found in line with the values of pressure drop for ear and shelled corn, as reported in ASABE standards. Shedd's curves for Sorghum Bagasse samples were developed, as these curves can be used for designing large-scale aeration systems for chopped energy sorghum. The whole production chain of biofuel by conserving biomass can be improved by the findings of this work, thus allowing the biomass to be used more economically around the year in bioenergy plants.

This study aims to examine the effect of different co-substrates on the anaerobic degradation of pentachlorophenol (PCP) with simultaneous production of biogas. Acetate and glucose were added as co-substrates to monitor and compare the methanogenic reaction during PCP degradation. During the experiment, a chemical oxygen demand (COD) removal efficiency of 80% was achieved. Methane (CH4) production was higher in glucose-fed anaerobic reactors with the highest amount of CH4 (303.3 µL) produced at 200 ppm of PCP. Scanning electron microscopy (SEM) demonstrates the high porous structure of anaerobic sludge with uniform channels confirming better mass transfer and high PCP removal. Quantitative real-time PCR (qPCR) revealed that methanogens were the dominating species while some sulfate reducing bacteria (SRBs) were also found in the reactors. The study shows that strategic operation of the anaerobic reactor can be a feasible option for efficient degradation of complex substrates like PCP along with the production of biogas.

In the Kingdom of Saudi Arabia (KSA), millions of Muslims come to perform Pilgrimage every year. Around one million ton of municipal solid waste (MSW) is generated in Makkah city annually. The collected MSW is disposed of in the landfills without any treatment or energy recovery. As a result, greenhouse gas (GHG) emissions and contamination of the soil and water bodies along with leachate and odors are occurring in waste disposal vicini-ties. The composition of MSW shows that food waste is the largest waste stream (up to 51%) of the total generated MSW. About 13% of the food waste consists of fat content that is equivalent to about 64 thousand tons per year. This study aims to estimate the production potential of biodiesel first time in Makkah city from fat/oil fractions of MSW and highlight its economic and environmental benefits. It has been estimated that 62.53, 117.15 and 6.38 thousand tons of biodiesel, meat and bone meal (MBM) and glycerol respectively could be produced in 2014. A total electricity potential of 852 Gigawatt hour (GWh) from all three sources based on their energy contents, Higher Heating Value (HHV) of 40.17, 18.33 and 19 MJ/kg, was estimated for 2014 that will increase up to 1777 GWh in 2050. The cumulative net savings from landfill waste diversion (256 to 533 million Saudi Riyal (SAR)), carbon credits (46 to 96 million SAR), fuel savings (146 to 303 million SAR) and electricity generation (273 to 569 million SAR) have a potential to add a total net revenue of 611 to 1274 million SAR every year to the Saudi economy, from 2014 to 2050 respectively. However, further studies including real-time data about annual slaughtering activities and the amount of waste generation and its management are critical to decide optimum waste management practices based on life cycle assessment (LCA) and life cycle costing (LCC) methodologies.

The Kingdom of Saudi Arabia (KSA) is situated in an arid region and faces a chronic challenge to meet its increasing water demand. Riyadh is the capital of KSA and home to about six million people. The water demand is mostly met by groundwater resources (up to 48%), while the desalination plants cover the rest of the water supply requirements. There is a potential risk of a significant gap in water demand–supply due to the retirement of old desalination plants. This study, therefore, developed a probabilistic model to forecast desalinated water demand in Riyadh for domestic purposes up to the year 2040 based on three scenarios: low growth, the most likely (mean), and high growth scenario. The results showed that an investment of about US$6.24, 11.59, and 16.04 billion is required to meet the future domestic water demand of the city for the next 25 years based on low, mean, and high growth scenarios, respectively. Moreover, a strong commitment to public–private partnership is required to remove the fiscal budget burden related to the desalination along with public awareness campaigns to reduce per capita water consumption, upgrading the water tariff system and using renewable energy to run desalination plants.

This paper aims to determine the waste-to-energy (WTE) and recycling
value of municipal solid waste (MSW) for developing an integrated solid
waste management (ISWM) system for Lahore, the second largest city in
Pakistan. The overall generated waste in Lahore contains 58% organic
waste, 25% recyclables, and 17% others. The recyclable materials including glass, paper, and plastic are generating US$ 15.3 million per year mostly by informal sector. An estimated production of 0.45 m3 CH4/kg volatile solids with total energy value of 8747.3 TJ or 2.43 TWh can be achieved if the total organic waste stream (0.57 million ton/year) dumped at Saggian landfill site is processed using anaerobic digestion technology. The estimated refused derived fuel (RDF) value for MSW, excluding metals, glass, and other inorganic waste is about 7.71 MJ/kg with total energy potential of 6191.13 TJ or 1.72 TWh/year. The presence of high volatile organic carbon and fixed carbon in textile and paper-related waste confirmed their suitability for incineration process. A significant reduction in the final volume of waste reaching to landfill can be achieved if these WTE technologies and recycling practices are in place. This will make a premise for ISWM system in Lahore based on reduce, reuse, recycle, and recovery principles. The recovered
materials and energy will not only generate revenue to fund waste management activities in Lahore, but also protect the River Ravi from waste pollution.

In recent years, attention has been given to obtaining methane gas from natural gas hydrates (NGHs) sediment; but its production, economics, and safety are still far away from being commercially viable for many years, and so more research is needed. NGHs are nonstoichiometric crystalline solid compounds that form from mixtures of water molecules and light weight natural gases such as methane, ethane, propane, and carbon dioxide. They are formed in specific thermodynamic conditions, low temperatures (5–15°C) and high pressures (2–3 MPa), and are found in (a) onshore polar regions beneath permafrost and (b) offshore deep-sea sediments. Methane, NG, is the cleanest fossil fuel and its huge amounts in NGHs have carbon quantities more than double of all fossil fuels. The methods that have been proposed for NG extraction from NGHs include: (a) depressurization, (b) thermal stimulation, and (c) chemical inhibitor injections. The authors review the potential of methane gas from NGHs as an unconventional source of future energy. The formation of NGHs as well as extraction of methane from NGHs coupled with technical and environmental challenges are also addressed.

This paper aims to investigate the effect of temperature and reaction time on the yield and quality of liquid oil produced from a pyrolysis process. Polystyrene (PS) type plastic waste was used as a feedstock in a small pilot scale batch pyrolysis reactor. At 400 °C with a reaction time of 75 min, the gas yield was 8% by mass, the char yield was 16% by mass, while the liquid oil yield was 76% by mass. Raising the temperature to 450 °C increased the gas production to 13% by mass, reduced the char production to 6.2% and increased the liquid oil yield to 80.8% by mass. The optimum temperature and reaction time was found to be 450 °C and 75 min. The liquid oil at optimum conditions had a dynamic viscosity of 1.77 mPa s, kinematic viscosity of 1.92 cSt, a density of 0.92 g/cm 3 , a pour point of À60 °C, a freezing point of À64 °C, a flash point of 30.2 °C and a high heating value (HHV) of 41.6 MJ/kg this is similar to conventional diesel. The gas chromatography with mass spectrophotometry (GC–MS) analysis showed that liquid oil contains mainly styrene (48%), toluene (26%) and ethyl-benzene (21%) compounds.

This paper aims to examine the effect of different plastic waste types such as polystyrene (PS), poly-ethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) on the yield and quality of produced liquid oil from the pyrolysis process. A small pilot scale pyrolysis reactor was commissioned for this purpose, and operated at optimum temperature and retention time of 450 C and 75 min respectively. PS plastic waste showed maximum production of liquid oil (80.8%) along with least production of gases (13%) and char (6.2%) in comparison to other plastic types. Liquid oils from all plastic types contained mostly aromatic compounds with some alkanes and alkenes. Liquid oil from PS pyrolysis contained styrene (48.3%), ethylbenzene (21.2%) and toluene (25.6%). Pyrolysis liquid oils found to have ranges of dynamic viscosity (1.77e1.90 mPa s), kinematic viscosity (1.92e2.09 cSt), density (0.91e0.92 g/ cm 3), pour point (À11(-60 C)), freezing point (À15-(-65 C)), flash point (28.1e30.2 C) and high heating value (HHV) (41.4e41.8 MJ/kg) similar to conventional diesel, thus have potential as an alternative energy source for electricity generation. Upgrading of liquid oil using different post-treatment methods such as distillation, refining and blending with conventional diesel is required to make it suitable as a transport fuel due to presence of high aromatic compounds. The recovery of aromatic compounds especially styrene from pyrolysis oil can be a potential source of precursor chemical in industries for polymerization of styrene monomers.

KSA is the world's third largest per capita water user country. 1.17 (domestic), 0.38 (industrial) billion m 3 /year wastewater is generated in KSA. 612, 767 MW electricity can be produced for years 2025, 2035 from wastewater by MEC. Net 508, 637 MW electricity for years 2025 and 2035 can be added to national grid. MEC technology can achieve 25.6% of KSA 3G W electricity from waste target by 2035. Keywords: Microbial electrolysis cell (MEC) Hydrogen (H 2) energy Urban wastewater Waste-to-energy (WTE) Wastewater treatment plant a b s t r a c t This paper reviews the status of microbial electrolysis cells (MEC) as a mean for hydrogen (H 2) production and urban wastewater treatment method. A case study of the Kingdom of Saudi Arabia (KSA) under MEC concept was developed. KSA is the world's third largest per capita water user country with no lakes and rivers. Every year, around 1.17 and 0.38 billion m 3 of domestic and industrial wastewater is generated respectively. The KSA government is seeking sustainable solutions for wastewater treatment and waste-to-energy (WTE) production to bridge the ever increasing water and energy demand-supply gap. However, there is no WTE facility exists to convert the wastewater into energy. Moreover, the potential of wastewater is not examined as an energy recovery substrate. This study, for the first time, estimated that a total electricity of 434 MWe can be produced in 2015 from the KSA's wastewater if MEC technology is employed. Similarly, an estimated total electricity of 612 and 767 MWe can be produced for the years 2025 and 2035 from the domestic and industrial wastewater by using MEC technology. A surplus electricity of 508 and 637 MWe for the years 2025 and 2035 respectively can be added to the national grid after fulfilling the energy requirement of MEC wastewater treatment plants. Collectively, MEC will contribute 20.4% and 25.6% share of the KSA government's WTE target of 3 GW in 2025 and 2035 respectively. A number of challenges in MEC such as ohmic and concentration losses, saturation kinetics and competing reactions that lower the H 2 production are discussed with their potential solutions including, the improvements in MEC design and the use of appropriate electrolytes, antibiotics and air or oxygen.

The aim of this study was to determine the quality and applications of liquid oil produced by thermal and catalytic pyrolysis of polystyrene (PS) plastic waste by using a small pilot scale pyrolysis reactor. Thermal pyrolysis produced maximum liquid oil (80.8%) with gases (13%) and char (6.2%), while catalytic pyrolysis using synthetic and natural zeolite decreased the liquid oil yield (52%) with an increase in gases (17.7%) and char (30.1%) production. The lower yield but improved quality of liquid oil through catalytic pyrolysis are due to catalytic features of zeolites such as microporous structure and high BET surface area. The liquid oils, both from thermal and catalytic pyrolysis consist of around 99% aromatic hydrocarbons, as further confirmed by GC-MS results. FT-IR analysis further showed chemical bonding and functional groups of mostly aromatic hydrocarbons, which is consistent with GC-MS results. The produced liquid oils can be suitable for energy generation and heating purposes after the removal of acid, solid residues and contaminants. Further upgrading of liquid oil and blending with diesel is required for its potential use as a transport fuel.

This paper reviews the progress and challenges of the catalytic pyrolysis of plastic waste along with future perspectives in comparison to thermal pyrolysis. The factors affecting the catalytic pyrolysis process such as the temperature, retention time, feedstock composition and the use of catalyst were evaluated in detail to improve the process of catalytic pyrolysis. Pyrolysis can be carried out via thermal or catalytic routes. Thermal pyrolysis produces low quality liquid oil and requires both a high temperature and retention time. In order to overcome these issues, catalytic pyrolysis of plastic waste has emerged with the use of a catalyst. It has the potential to convert 70–80% of plastic waste into liquid oil that has similar characteristics to conventional diesel fuel; such as the high heating value (HHV) of 38–45.86 MJ/kg, a density of 0.77–0.84 g/cm 3 , a viscosity of 1.74–2.5 mm 2 /s, a kinematic viscosity of 1.1–2.27 cSt, a pour point of (−9) to (−67) • C, a boiling point of 68–352 • C, and a flash point of 26.1–48 • C. Thus the liquid oil from catalytic pyrolysis is of higher quality and can be used in several energy-related applications such as electricity generation, transport fuel and heating source. Moreover, process by-products such as char has the potential to be used as an adsorbent material for the removal of heavy metals, pollutants and odor from wastewater and polluted air, while the produced gases have the potential to be used as energy carriers. Despite all the potential advantages of the catalytic pyrolysis, some limitations such as high parasitic energy demand, catalyst costs and less reuse of catalyst are still remaining. The recommended solutions for these challenges include exploration of cheaper catalysts, catalyst regeneration and overall process optimization.

Wax deposition is one of the chronic problems in the petroleum industry.
The various crude oils present in the world contain wax contents of up to
32.5%. Paraffinwaxes consist of straight chain saturated hydrocarbons with carbons atoms ranging fromC18 to C36. Paraffin wax consists mostly with normal paraffin content (80–90%), while, the rest consists of branched paraffins (isoparaffins) and cycloparaffins. The sources of higher molecular weight waxes in oils have not yet been proven and are under exploration. Waxes may precipitate as the temperature decreases and a solid phase may arise due to their low solubility. For instance, paraffinic waxes can precipitate out when temperature decreases during oil production, transportation through pipelines, and oil storage. The process of solvent dewaxing is used to remove wax from either distillate or residual feedstocks at any stage in the refining process. The solvents
used, methyl-ethyl ketone and toluene, can then be separated from dewaxed oil filtrate stream by membrane process and recycled back to be used again in solvent dewaxing process.

The current study aims to determine the dust-borne lead (Pb) levels into outdoor dust, which were collected from the areas nearby the cities/districts of Islamabad and Swat in Pakistan. In general dust samples from all land use settings (industrial, urban and rural) showed significantly higher (p < 0.05) Pb-levels (median, ppm) from Islamabad (110, 52, 24) than those of Swat district (75, 37, 21), respectively. Index of Geo-accumulation (I geo values) indicated that industrial and urban areas of both sites were highly polluted due to severe anthropogenic influence, whereas the rural areas were in most parts unpolluted and where moderately polluted, this was mainly due to geological factors and short and/or long distance atmospheric deposition from surrounding polluted areas. According to the calculated chemical daily intake (mg/kg-day) values, dust ingestion is one of the major routes of human exposure for lead. Hazard Index (HI) values, calculated for both adult and children populations, were above unity in industrial and urban areas, indicating serious health risks especially to the children populations.

This paper reviews the global status of waste to energy (WTE) technologies as a mean for renewable energy production and municipal solid waste (MSW) disposal method. A case study of the Kingdom of Saudi Arabia (KSA) under this concept was developed. The WTE opportunities in the KSA is undertaken in the context of two scenarios: (1) incineration and (2) refuse derived fuel (RDF) along with bio-methanation from 2012 to 2035. Biomethanation technology can proved to be the most suitable WTE technology for KSA due to (a) availability of high food waste volume (37% of total MSW) that can be used as a feedstock, (b) higher efficiency (25–30%) and (c) lowest annual capital ($0.1–0.14/ton) and operational cost. However, the need for large space for continuous operation might increase operational cost. The RDF has an advantage over incineration due to (a) less annual capital ($7.5–11.3/ton) and (b) operational cost ($0.3–0.55/ton), but the high labor skills requirements will most probably be a limitation, if appropriate training and related infrastructure are not scheduled to be included as a prerequisite. The incineration technology also proves to be an efficient solution with a relatively higher efficiency (25%) and lower operational cost ($1.5–2.5/ton). However, the need for treatment of air and waterborne pollutants and ash within the incineration facility can be the limiting factors for the development of this technology in KSA. In 2012, the power generation potential for KSA was estimated at 671 MW and 319.4 MW from incineration and RDF with biomethanation scenarios respectively, which was forecasted to reach upto 1447 MW and 699.76 MW for both scenarios respectively by 2035. Therefore, WTE technologies, could make a substantial contribution to the renewable energy production in KSA as well as alleviating the cost of landfilling and its associated environmental impacts. However, the decision to select between the two scenarios requires further in-depth financial, technical and environmental analysis using life cycle assessment (LCA) tool.

ABSTRACT The energy consumption in Saudi Arabia has increased significantly in recent years due to a rapidly growing population and economic development. The current peak demand of electrcity is 55 GW and it is projected to become 120 GW in the year 2032. Fossil fuels are the only choice to meet the energy requirements. The government plans to double its energy generating capacity by 2020, of which around 85% will come from renewable resources. Natural zeolites are found abundantly in Saudi Arabia and have a significant role in the energy generation applications. Natural zeolites samples have been collected from the Jabal Shama occurrence near Jeddah city. All of the samples showed the standard zeolite group of alumina-silicate minerals with the presence of other elements such as Na, Mg and K etc. A highly crystalline structure is found in natural zeolites, which is critical when using in the energy applications as a process catalyst. However, there is a need of special milling and purification process to achieve homogeneous particle morphology and sizes in a range of sub-micron to nano-meter without impurities. This will significantly increase the surface area and pore volume of natural zeolites, thus improving their properties as a process catalyst and optimizer. The aim of this paper is to investigate the potential and utilization of naturally occurring zeolites in Saudi Arabia for pyrolysis of waste plastic to fuel oil.