Dr. Abdul-Sattar Nizami

This study aims to evaluate the environmental and economic performance of biodiesel production from mixed vegetable oil waste using the life cycle assessment (LCA) model. Due to its huge potential, Pakistan is taken as a case study. It produces 468,842 tons of vegetable oil waste
annually. As no biodiesel production plant exists to process it, the environmental performance of biodiesel prototypes has not been investigated. Therefore, the current study is conducted to
support the design of a plant to produce biodiesel from mixed oil waste..............

The solid waste management (SWM) system is in a transitional phase in developing economies, and local municipalities and waste management companies are stepping toward integrating a waste treatment approach in the scheme of waste handling. However, there is an urgent need to explore cost-effective techniques, models, and potential revenue streams to sustain the state-run waste sector self-sufficiently. The proposed SWM model aims to support the local waste sector in Islamabad, the capital city of Pakistan, with 100% service area coverage to attain environmental and economic sustainability by defining dedicated waste collection streams to ensure quality material recovery under a cost-effective approach and modality. The innovative approach is applied to allocate the tonnage to various streams as per the city's current land use plan. The estimated/cost of the cleanliness services will be USD13.1 million per annum with an estimated per ton cost of USD 23. The establishment of the proposed material recovery facility (MRF) will process about 500 t/d of waste to produce 45 t/ d compost and recover 130 t/d of recyclables. The environmentally friendly model saves 2.4 million tons of CO 2eq/month from composting and recycling. The average economic potential from MRF and debris-crushing plants, including environmental benefit value, is calculated as USD 3.97 million annually. Recovery of services fee (70%) for various collection streams based on city land use and socioeconomic conditions will generate revenue of USD 7.33 million annually. The total revenue will be USD 11.31 million (86% of total annual expenditures) to track the sector's self-sufficiency. To successfully reach the Sustainable Development Goals (SDGs) and Nationally Determined Contributions (NDCs), engaging the private sector from environmentally advanced economies to collaborate in the waste sector to enhance local technical capabilities is recommended.

Sustainable socio-economic development largely depends on the sustainability of the energy supply from economic, environmental, and public health perspectives. Fossil fuel combustion only meets the first element of this equation and is hence rendered unsustainable. Biofuels are advantageous from a public health perspective, but their environmental and economic sustainability might be questioned considering the conflicts surrounding their feedstocks, including land use change and fuel vs. food conflict. Therefore, it is imperative to put more effort into addressing the downsides of biofuel production using advanced technologies, such as nanotechnology. In light of that, this review strives to scrutinize the latest developments in the application of nanotechnology in producing biodiesel, a promising alternative to fossil diesel with proven environmental and health benefits. The main focus is placed on nanotechnology applications in the feedstock production stage. First, the latest findings concerning the application of nanomaterials as nanofertilizers and nanopesticides to improve the performance of oil crops are presented and critically discussed. Then, the most promising results reported recently on applying nanotechnology to boost biomass and oil production by microalgae and facilitating microalgae harvesting are reviewed and mechanistically explained. Finally, the promises held by nanomaterials to enhance animal fat production in livestock, poultry, and aquaculture systems are elaborated. Despite the favorable features of using nanotechnology in biodiesel feedstock production, the presence of nanoparticles in living systems is also associated with important health and environmental challenges, which are critically covered and discussed in this work.

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.

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.

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.

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.

Municipal solid waste management (MSWM) is a critical administrative, environmental and financial issue in low-income countries, such as Pakistan, where waste collection efficiency is less than 75% in all urban areas, except Lahore. Therefore, it is pertinent to develop practical decisionmaking tools to enhance waste collection efficiency by local municipalities and waste management companies (WMCs). A tool/calculator, holistically measure analyze forecast honestly (HMAFH), is
proposed for waste collection in urban areas based on the lessons learned. The tool was developed considering local conditions, i.e., business environment, socio-economic and cultural dynamics, city
infrastructure and stakeholders’ desires. It is flexible to various proposed waste collection modes, with heterogeneous fleet choices, and it presents an opportunity to integrate collection with a material recovery facility (MRF) or direct haulage to the disposal site. The HMAFH was tested successfully in the Lahore district. Based on the proposed scenarios, the result shows a material recovery of up to 33% by defining dedicated waste collection streams with a 26% saving on fuel. The proposed interventions
can prove to be a defining step toward building a circular economy (CE) that allows the integration of treatment options with economic potential to account for 35% of the current operating expenditures and a reduction in greenhouse gases (GHGs) emission, i.e., 1,604,019 tons of CO2-eq./annum.

The Solid Waste Management (SWM) sector is given a low-priority by the Pakistani Government, with the climate change agenda of Sustainable Development Goals (SDGs) being a priority-3 only, similar to other developing countries. Although sustained efforts have been made
during the last decade to strengthen the SWM sector, all actions were focused on manual sweeping and waste collection without integrating waste treatment and disposal options. In this respect, the current model of SWM in the country was analyzed for efficient future planning to strengthen the sector waste management regime in line with the targets of Nationally Determined Contributors (NDCs) and SDGs. An assessment of the SWM sector was performed in eleven major cities of Pakistan, applying Waste-aware benchmarking indicators as strategic tools. The current study highlights the strengths and weaknesses of concerned local municipalities andWaste Management Companies (WMCs) along with interventions to reduce Greenhouse Gases (GHGs) emission targets
by 2030. Proposed interventions from the environment and economy perspective will generate revenue to cater for up to 29% of the operational costs, and this will be an important step towards 100% self-sufficiency in the SWM sector.

Solid Waste Management (SWM) is a technical subject which requires comprehensive planning, execution, and effective operational monitoring under cost-effective modes compatible with environmentally sound technologies. The policymakers made some enormous efforts for
the sustainability of this sector as well as setting a benchmark for other municipalities and Waste Management Companies (WMCs) in the country. Provincial Government prioritizes its focus on SWM, i.e., waste collection, transportation, treatment, and final disposal. The waste management
sector in Lahore has achieved sustainability in waste collection and haulage components by gaining experience from international outsourcing and, now, sharing its knowledge with other municipalities to strengthen the sector in the country. Lahore has emerged with the highest collection efficiency (84%) in SAARC countries and placed fifth in rank in comparison to 54 low–middle-income countries/cities worldwide. The sectorial interventions in Lahore reveal an aspiration for the sustainability of the
SWM sector in Pakistan. However, there is an urgent need to focus and invest in waste-related infrastructure development, i.e., permanent/mobile transfer stations, semi-underground containers for commercial and planned areas, material recovery facilities (MRF), and landfill. Environmental and economic sustainability in this sector can be achieved through public–private partnership (PPP) modality in compost, anaerobic digestion, recycling, and refuse-derived fuel (RDF) as it is a more
feasible option to strengthen the industry in the country.

With raising concerns around the usage of fossil fuels and increasing waste there is an increased focus on finding alternate sources of energy to protect the environment as well as for sustainable development. Biomass waste has emerged as the new feedstock to produce renewable energy that can help in tackling climate changes and reduce dependence on traditional energy sources. Bioenergy production using wastes as feedstocks is an environmentally friendly and cost-effective process. However, deriving bioenergy from biomass waste streams requires pretreatment and/or innovative valorization strategies before being used as a feedstock in various conversion techniques such as thermo-chemical or biological processes. Most techniques require the application of heat to break down complex polymeric structures in the biowaste and make it more susceptible to hydrolysis. There is an increased focus on microwave heating as an alternative to conventional heating due to its various advantages such as speed, energy requirement and uniformity of heat dispersion. This review dives into a few of these aspects of microwaves and explores the application of microwaves as a standalone pretreatment technique as well as a co-pretreatment technique to enhance the performance of other thermo-chemical pretreatments. It also brings forward few of the challenges associated with the usage of microwaves and future research directions on tackling them.

Amidst the exponential industrialization and global economy, the textile sector has been considered a grave concern worldwide in terms of effluent discharge, and high-water consumption that ultimately causes water pollution. Conventional treatment technologies have over 100 times more water footprint, high capital cost, time-intensive, high material usage, land issue, high infrastructure, and manpower consumption than the advanced oxidation processes. The current study primarily examines the most sustainable approach for treating textile dye-bath effluents through combined physical and advanced oxidation technologies, providing a comprehensive literature survey about treatment techniques. First, it explores the physical treatment processes with electrocoagulation, dissolved air flotation, lamella clarifier, and reverse osmosis stages. Secondly, the advanced oxidation processes (AOPs) such as ozonation, direct photolysis (UV), UV/H 2 O 2 , UV/H 2 O 2 /O 3 , Fenton, and photo-Fenton system are also individually discussed, which showed significant results in the treatment efficiency. Particularly, the integrated electrocoagulation process and AOPs are also ameliorated, which achieved the best eco-friendly treatment, time-effective, and reduce area footprint provided by numerous studies. The AOPs are required for almost 30 min for the treatment, whereas the biological treatment takes 24-72 h, which resultantly minimizes 25 times area footprint, minimum electricity consumption, and high removal efficiency. Lastly, cost estimation and policy formulation of the effluent treatment plants at the national level are also demonstrated to prevent the toxicity of treatment practices in textile industries. Overall, the current investigation of integrated treatment technologies illustrated a promising alternative and environmental-friendly area footprint, which could be readily promulgated towards the sustainable treatment and reuse of textile dye-bath effluents.

This study aims to evaluate municipal landfill sites' operational and financial viability, waste amount and characterization, primary and secondary collection systems, revenue generation from MSW, vehicle routing, and age of landfill sites located in Akhtarabad, Sahiwal Division. Three operational and financial models were developed to calculate cost/ton value based on obtained data. The obtained results indicate that the cost/ton values for models are the following: 20.01 USD for Model-1, 8.96 USD Model-2, and Model-3 is about 10.23 USD. The waste characterization represented waste consisting of compostable (57%), recyclable (10%), Refuse Derived Fuel (RDF) (12%), earth fill (20%), and disposable material (1%). Revenue/ ton of municipal solid waste was about 19.47 USD, and according to cost-benefit analysis, the cost of Model-1 was higher than the benefit. In contrast, the costs of Model-2 and Model-3 were found to be lower than the revenue/ton. However, the waste collection efficiency of Model-1 was greater than both remaining models. The study concluded that utilizing all generated waste, only 21% of waste is dumped at the landfill site. It will reduce the area required for landfill sites from 431437 to 90602 m 2 for the next 10 years and increase the age of landfill sites by over 20 years. It is recommended that the reuse of municipal solid waste and implementation of the no waste to landfill model would surely save money, land, and fuel, and it will also increase the age of landfill sites.

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.

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.

Biogas has emerged as an alternative renewable fuel to natural gas. However, the presence of trace contaminants and large quantities of CO 2 in biogas necessitates its purification and upgrading to increase its calorific value. Different technologies have been developed to upgrade biogas to biomethane. Among these, chemical absorption is commonly employed due to its high process efficiency and less solvent requirement due to high selectivity compared to physical absorption. However, the chemical decomposition of amine-based solvents, toxicological impact, high plant maintenance costs, high enthalpy of reaction, and corrosivity associated with chemical absorption limit its large-scale application. Recently, ionic liquids (ILs) have garnered attention as alternative absorption media to conventional solvents. ILs have a high CO 2 uptake, thermal stability, and negligible vapor pressure. Recent process simulation studies featuring ILs as solvents for biogas upgrading reveal the suitability of these approaches as alternatives to laborious experimental work to assess the practical, technical, and economic viability of ILs. As per the authors' knowledge, this is the first review comparing biogas upgrading technologies from a technical, environmental, and economic perspective. Primarily, studies relating to IL-based biogas upgrading are considered, and challenges associated with the large-scale adoption of ILs as absorption media are discussed. Process simulations and techno-economic assessments of IL-based biogas upgrading techniques are presented. A conceptual design approach is proposed for the successful scale-up of IL-based biogas upgrading. Based on results, deep eutectic solvents are recommended as next-generation solvents for absorption as technical and economic aspects are found superior to conventional amines and ionic liquids.

This study aims to investigate treatment efficiency and evaluate the energy efficacy of integrated electrocoagulation system combined with ozonation, Fenton, and photo-Fenton processes for successful textile dye-bath effluents' treatment. In this regard, the characterization of physicochemical parameters such as pH, turbidity, salinity, total dissolved solids (TDS), total suspended solids (TSS), electrical conductivity (EC), and chemical oxygen demand (COD) was analyzed to estimate removal efficiency of each treatment process. Moreover, the electrical energy consumption of all aforementioned processes was measured individually to work out costeffectiveness. Fenton process appeared to be ineffective for reducing COD and other parameters. While the overall performance of ECS alone showed far better results, COD and color removal efficiencies were 57.4%, and 40%, respectively. However, the application of ECS/O 3 resulted in complete decolorization and almost 99.7% COD removal under optimized operating conditions including ozone flow 300 mg/h, pH 7.1, Temperature 25 • C. ECS/photo-Fenton process resulted in COD, and color removal of 95.6%, and 97%, respectively. Electrical Energy per Order of ECS was found 1.58 kWh/m 3 for minimum removal of dyes and COD. ECS/Ozonation is responsible for 100% decolorization but at a very high cost. ECS/photo-Fenton process proved to be the second-best option in terms of treatment and energy consumption. Hence, an integrated treatment system of ECS with AOPs appeared to be the most feasible and eco-friendly. That could lead to the treated wastewater for reuse and recycling purposes within the industry.

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.

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 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.

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.

Energy crisis, solid waste management, ever-increasing CO2 and methane levels, unemployment, deforestation, increased energy generation cost, and depleting fossil fuels are some current challenges faced by developing countries. The biogas production is a sustainable, lenient, and affordable approach to address these issues. This chapter focuses on the history of biogas digesters and their evolution, feasible techniques for biogas production, and methods to enhance biogas quality. It highlights the advantages and limitations of fixed dome digester, floating drum digester, and plug flow digester. Organic waste such as animal dung, food waste, agricultural waste, municipal solid waste, industrial waste, and sewage sludge can be used as feedstock to produce biogas in digesters. Acetic acid produced from glucose and water in acetogenesis process is transformed into methane and by-products through methanogenesis. The efficient production of
biogas is carried out by a complex microbial process in which an appropriate environment is necessary for the multiplication of microbes and their proper functioning. Biogas generated at low temperatures using psychrophilic enzymes has a low methane content; however, other factors such as pH, oxygen content, and salt concentration also affect microbial activities and hence the quality of the biogas. The electrical energy produced by biogas from agricultural waste feedstock
is carbon zero. In Asia, biogas production is the need of the time and will
not only contribute towards a low carbon economy but also will address the longstanding issue of deforestation and environmental pollution. If increasing energy demands of a growing population in Asia and Africa are addressed through this renewable approach, then it will enhance the energy security and environment integrity of these two continents.

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.

The landfill disposal of the massive amount of food waste without treatment and resource recovery is resulting in several public and environmental health concerns. Several technologies have emerged for the conversion of food waste to lactic acid, ethanol, biogas, biohydrogen and volatile fatty acids (VFAs) as value-added products. Food waste is a rich source of essential components such as protein, carbohydrate, oil, mineral, and fat that can be converted to many value-added products as mentioned above. The conversion of food waste to fermentation products such as organic acids, gases, and alcohols requires precise control and optimization of operational conditions, including pretreatment, pH, temperature, and microbes. Therefore, the fermentation technologies for food waste are still developing to solve the technical challenges of pretreatment such as the process economics, reactor design and infrastructure cost and lack of homogeneity in the results of laboratory and large-scale plants. A potential way forward is to optimize the fermentation process conditions along with implementing the strategies to integrate different waste treatment technologies to produce high-quality and cost-effective value-added products at commercial scale.

Addressing the contemporary waste management is seeing a shift towards energy production while managing waste sustainably. Consequently, waste treatment through gasification is slowly taking over the waste incineration with multiple benefits, including simultaneous waste management and energy production while reducing landfill volumes and displacing conventional fossil fuels. Only in the UK, there are around 14 commercial plants built to operate on gasification technology. These include fixed bed and fluidized bed gasification reactors. Ultra-clean tar free gasification of waste is now the best available technique and has experienced a significant shift from two-stage gasification and combustion towards a one-stage system for gasification and syngas cleaning. Nowadays in gasification sector, more companies are developing commercial plants with tar cracking and syngas cleaning. Moreover, gasification can be a practical scheme when applying ultra-clean syngas for a gas turbine with heat recovery by steam cycle for district heating and cooling (DHC) systems. This chapter aims to examine the recent trends in gasification-based waste-to-energy technologies. Furthermore, types of gasification technologies, their challenges and future perspectives in various applications are highlighted in detail.

Hydrogen (H2) has emerged as a promising alternative fuel that can be
produced from renewable resources including organic waste through biological processes. In the Kingdom of Saudi Arabia (KSA), the annual generation rate of municipal solid waste (MSW) is around 15 million tons
that average around 1.4 kg per capita per day. Similalry, a significant
amount of industrial and agricultural waste is generated every year in
KSA. Most of these wastes are disposed in landfills or dumpsites after
partial segregation and recycling and without material or energy recovery. This causes environmental pollution and release of greenhouse gas (GHG) emissions along with public health problems. Therefore, the scope of producing renewable H 2 energy from domestic and industrial waste sources is promising in KSA, as no waste-to-energy (WTE) facility exists. This chapter reviews the biological and chemical ways of H2 production from waste sources and availability of waste resources in KSA.

Plastic usage in daily life has increased from 5 to 100 million tons per year since the 1950s due to their light-weight, non-corrosive nature, durability and cheap price. Plastic products consist mainly of polyethylene (PE), polystyrene (PS), polypropylene (PP) and polyvinyl chloride (PVC) type plastics. The disposal of plastic waste causes environmental and operational burden to landfills. Conventional mechanical recycling methods such as sorting, grinding, washing and extrusion can recycle only 15–20 % of all plastic waste. The use of open or uncontrolled incineration or combustion of plastic waste has resulted in air and waterborne pollutants. Recently, pyrolysis technology with catalytic reforming is being used to convert plastic waste into liquid oil and char as energy and value-added products. Pyrolysis is one of the tertiary recycling techniques in which plastic polymers are broken down into smaller organic molecules (monomers) in the absence of oxygen at elevated temperatures (>400 °C). Use of catalysts such as aluminum oxides, natural and synthetic zeolites, fly ash, calcium hydroxide, and red mud can improve the yield and quality of liquid oil. The pyrolysis yield depends on a number of parameters such as temperature, heating rate, moisture contents, retention time, type of plastic and particle size. A yield of up to 80 % of liquid oil by weight can be achieved from plastic waste. The produced liquid oil has similar characteristics to conventional diesel; density (0.8 kg/m3), viscosity (up to 2.96 mm2/s), cloud point (−18 °C), flash point (30.5 °C) and energy content (41.58 MJ/kg). Char produced from pyrolysis can be activated at standard conditions to be used in wastewater treatment, heavy metals removal, and smoke and odor removal. The produced gases from pyrolysis are hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2) and can be used as energy carriers. This chapter reviews the challenges and, perspectives of pyrolysis technology for production of energy and value-added products from waste plastics.

Many factors enforce the intensification of grassland utilization which is
associated with significant environmental impacts subjected to various legislative
constraints. Nevertheless, the need for diversification in agricultural production and
the sustainability in energy within the European Union have advanced the role of
grassland as a renewable source of energy in grass biomethane production with
various environmental and socio-economic benefits. Here it is underlined that the
essential question whether the gaseous biofuel meets the EU sustainability criteria
of 60% greenhouse gas emission savings by 2020 can be met since savings up to
89.4% under various scenarios can be achieved. Grass biomethane production is
very promising compared to other liquid biofuels either when these are produced
by indigenous or imported feedstocks. Grass biomethane, given the mature and well
known technology in agronomy and anaerobic digestion sectors and the need for
rural development and sustainable energy production, is an attractive solution that
fulfils many legislative, agronomic and environmental requirements.

The energy demand and waste generation have increased significantly in the developing world in the last few decades with rapid urbanization and population growth. The adequate treatment of the waste or sustainable waste management is essential not only from a sanitation point of view but also due to its economic and environmental values including its potential contribution to energy generation in the developing countries. Many of the developed nations have adopted the approach and strategies of the integrated waste management system (Figure 1) to maximize the waste-based revenues in the form of energy, fuels, heat, recyclables, value-added products, and chemicals along with more jobs and business opportunities. As a result, waste is no longer seen as refuse or discarded material, but an asset or resource to reduce not only the landfill volumes but also the dependency on fossil fuels by generating clean fuels.

The Makkah city landfills receive about 2.4
thousand tons of municipal solid waste (MSW) every day. While, these quantities
become 3.1 and 4.6 thousand tons per day during the Ramadan and Hajj respectively.
All of the collected MSW is disposed to landfill sites untreated, which results in
greenhouse gas (GHG) emissions as well as water and soil contamination. The
government considers reuse and recycling as optimum techniques for waste
management following source reduction. However, the current waste recycling has
been carried out mostly by informal sectors and only few recyclable materials such as
paper, cardboard, metals and plastics are recycled (10-15% of total waste). The waste
pickers or waste scavengers take the recyclables from the waste bins, containers and
dumpsites. There is an immediate need to develop public-private partnership (PPP) to
improve MSW management system in Makkah city including waste reuse and
recycling. It is theoretically estimated that only by recycling glass, metals, aluminium
and cardboard, climate will be saved from 5.6 thousand tons emission of methane
(CH4); a major source of GHG emissions and 140.1 thousand Mt.CO2 eq. of global
warming potential (GWP) with carbon credit revenue of worth 67.6 million SAR.
Similarly by recycling above-mentioned recyclables, a net revenue of 113 million SAR
will be added to the national economy every year only from Makkah city. Moreover,
technically, the waste recycling does not require high-skill labour, complex technology
and thus can be easily carried out in any urban areas like Makkah city.

Sorghum Bagasse in recent years has emerged as a promising feedstock for production of biofuel and value-added products following various biological conversion pathways. However, adequate conservation is critical for utilizing sorghum bagasse as raw material for fuel and fiber around the year in biofuels plants. The biomass conservation using drying method depends on different parameters such as energy efficiency, heat integration, emission control and dryer performance. The pressure drop phenomenon in drying systems for biomass conservation has been reported in few studies only. Therefore, this study aims to investigate the pressure drop as a function of airflow velocity and construct Shedd’s curves for energy sorghum bagasse with an ambition to develop large-scale drying systems for biomass conservation. The bagasse was obtained by extracting the juice from the harvested sorghum and passing it through a juicing machine. The bagasse 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. A fan equipped with a regulator to control variable speed was attached to the plenum, having the ability to generate airflow up to 2.15 ms-1. The airflow velocities (0.24 to 1.32 ms-1) caused pressure drop (9.96 to 346.23 Pa) across the empty drum. Similarly, the pressure drop in the drum containing sorghum bagasse ranged from 19.92 to 263.25 Pa due to airflow velocities ranging from 0.043 to 0.799 ms-1, respectively. Pressure drop increased with increasing airflow velocity, and was similar to the pressure drop values for ear and shelled corn, reported in ASABE standards. Shedd’s curves for sorghum bagasse samples were developed; these curves could be used for designing large-scale aeration systems for chopped energy sorghum.

The current electricity demand of the Kingdom of Saudi Arabia (KSA) is around 55 GW, which is projected to reach up to 120 GW by 2032. This energy is mainly produced from fossil fuels, posing a serious risk to human health and environment. Moving towards a sustainable model, KSA government has initiated a plan called the King Abdullah City of Atomic and Renewable Energy (KACARE) to utilize the indigenous renewable energy resources to generate a further 54 GW energy from solar, wind, nuclear, geothermal and waste-to-energy (WTE). The arid nature of the KSA increases the importance of water in daily life and makes the country the third-largest per capita water user worldwide. About 12 thousand industries are working in different sectors, which produce large quantities of wastes and waste sludge on a daily basis. It has been estimated that 2.4 and 0.77 billion m3/ year of municipal and industrial wastewater respectively are produced in KSA, totaling to 3.17 billion m3/ year. Therefore, there is a huge potential of producing bioenergy and bioproducts, if this wastewater is treated in algae biorefinery. Algae as a ‘natural chemical factory’ has gained significant attention to produce several energy carriers, including starches for alcohols, lipids for diesel fuel, and bio-hydrogen (H2) for fuel cells and valuable materials and chemicals. Considerable progress has been made in recent years to optimize the production of energy and value-added products by utilizing algae under algae biorefinery concept. The biorefinery is a multi-process and multi-product system, similar to a petroleum refinery. It utilizes various feedstock to produce useful materials, chemicals, and bioenergy in the form of fuel, power, and heat in an integrated system. Algae contain natural oils, carbohydrates, and proteins for the production of biodiesel, ethanol, and H2. The leftover or residues of algae after oil extraction can be digested anaerobically to produce methane (CH4) as an energy carrier. Furthermore, the AD digestate can be a source of animal feed and organic fertilizer. Although, theoretically algae can produce various fuels, an array of valuable materials and capture carbon emissions, but in practice, profitable algal biofuel production has proven to be quite challenging. Most of these challenges lie in algae production methods, including a selection of suitable algae strain, its cultivation, harvesting, and extraction of value-added materials for energy and bioproducts along with their conversion pathways. The aim of this paper is to review the potential of algae biorefinery in KSA for the treatment of wastewater and production of bioenergy and bioproducts.

Millions of Muslims from all over the world visit the Holy Cities of Saudi Arabia: Makkah and Madinah every year to perform Hajj and Umrah. The rapid growth in urbanization and the local population of Makkah city along with an ever increasing number of visitors result in huge municipal solid waste (MSW) generation every year. Most of this waste is currently dumped into landfill sites without any treatment, thus causing environmental and health issues. For example, on average around 2.4 thousand tons of waste is dumped into Makkah city’s landfill sites every day that increases to around 3.1 and 4.6 thousand tons per day during Ramadan and Hajj periods, respectively. Around 23% on average of this waste is a plastic waste in the form of plastic bottles, water cups, food plates and shopping bags (Abdul Aziz et al. 2007). A pilot scale catalytic pyrolysis process has been used to convert plastic waste into liquid fuel at Center of Excellence in Environmental Studies (CEES) of King Abdulaziz University, Jeddah. The produced liquid fuel has been found to have a high energy value of around 40 MJ/Kg, the viscosity of 0.9 mm2/s, the density of 0.92 g/cm3, the flash point of 30°C, pour point of -18°C and freezing point of -64°C, characteristics similar to conventional diesel. Thus the produced liquid fuel has the potential to be used in several energy-related applications such as electricity generation, transportation fuel, and heating purposes. It has been estimated that the plastic waste in Makkah city in 2016 could produce around 87.91 MW of electricity with net revenue of 297.52 million SAR. This is projected to increase up to around 172.80 MW of electricity and a total net revenue of 584.83 million SAR by 2040.

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.

The concept of the waste biorefinery is known as one of the several energy recovery technologies capable of producing multi-products in the form of biofuels and value-added products treating different fractions of municipal solid waste (MSW). The conversion technologies such as anaerobic digestion (AD), pyrolysis, transesterification, incineration treat food, plastic, meat, and lignocellulosic wastes to produce liquid, gaseous and solid biofuels. Makkah city landfills receive about 2750 tons of waste every day. While during the Ramadan and Hajj seasons, these quantities become 3000 tons and 4706 tons per day respectively. More than 2.5 million animals were sold for slaughtering in 2014 Hajj, and their blood and organic solid waste were disposed of untreated. Similarly, around 2.1 million plastic Zam-Zam cups were wasted every day during the 2014 Ramadan time. In the first three days of 2014's Ramadan, 5000 tons of food was wasted only in Makkah municipality. Collectively, about 3853 tons of waste were generated each day during 2014 Hajj and Ramadan. The waste from Al-Haram and Al-Masha’ir (Mina, Muzdalifah and Arafat) and their surroundings was mainly composed of organics (up to 68.5%). There is no waste-to-energy facility existing in Saudi Arabia. The waste biorefinery in Makkah will divert up to 94% of MSW from landfill to biorefinery. The energy potential of 2171.47 TJ and 8852.66 TJ can be produced if all of the food and plastic waste of the Makkah city are processed through AD and pyrolysis respectively. The development of AD and pyrolysis under waste biorefinery will also benefit the economy with gross savings of 405 and 565.7 million SR respectively, totalling to an annual profit of 970.7 million SR. Therefore, the benefits of waste biorefinery in Makkah city and other parts of the Saudi Arabia are numerous including the development of renewable-energy science and research, solving solid waste problems, new businesses and job creation opportunities and minimizing environmental pollution.

Every year, millions of Muslims gather in the Kingdom of Saudi Arabia (KSA) for worship, i.e. Hajj (Pilgrimage) and Umrah. The Makkah city landfills receive about 2.4 thousand tons of municipal solid waste (MSW) every day. While, these quantities become 3.1 and 4.6 thousand tons per day during the Ramadan and Hajj respectively. All of the collected MSW is disposed to landfill sites untreated, which results in
greenhouse gas (GHG) emissions as well as water and soil contamination. The government considers reuse and recycling as optimum techniques for waste management following source reduction. However, the current waste recycling has been carried out mostly by informal sectors and only few recyclable materials such as paper, cardboard, metals and plastics are recycled (10-15% of total waste). The waste pickers or waste scavengers take the recyclables from the waste bins, containers and dumpsites. There is an immediate need to develop public-private partnership (PPP) to improve MSW management system in Makkah city including waste reuse and recycling. It is theoretically estimated that only by recycling glass, metals, aluminium and cardboard, climate will be saved from 5.6 thousand tons emission of methane
(CH4); a major source of GHG emissions and 140.1 thousand Mt.CO2 eq. of global warming potential (GWP) with carbon credit revenue of worth 67.6 million SAR. Similarly by recycling above-mentioned recyclables, a net revenue of 113 million SAR will be added to the national economy every year only from Makkah city. Moreover,
technically, the waste recycling does not require high-skill labour, complex technology and thus can be easily carried out in any urban areas like Makkah city.

Grass is an excellent energy crop due to long persistence of high yields accompanied by low energy inputs. Approximately 91% of Irish agricultural land is under grass. The national herd has decreased and will continue to do so. Cross compliance does not encourage the conversion of permanent pastureland to arable land; thus we have and will continue to have increased quantities of excess grassland. Therefore, grass must be considered a significant source of biomass. Current grass species and cultivation practices are favourable for anaerobic digestion (AD), which is a mature technology. Upgrading biogas to biomethane, injecting into the gas grid, leads to an effective bioenergy system complete with distribution to all major cities and 620,000 houses. The Renewable Energy Directive allows a double credit for biofuels derived from residues and lignocellulosic material (such as grass). It is shown that 100,000 ha of grass (2.3% of agricultural land) will allow compliance with the 10% renewable energy in transport target for 2010. Alternatively, this would substitute for 35% of residential gas consumption. Reactor design must take account of the specific feedstock or combinations of feedstock; the reactor must be suited to the feedstock. This is not technically difficult. Of significant concern in the sustainability of the biofuel produced is the parasitic energy demand of the process and the vehicle efficiency. Emission reductions are optimised by the use of green electricity and the use of biomass for thermal energy input. On a field-to-wheel basis, it is essential that the vehicle operating on biomethane has an equivalent efficiency (expressed as MJ/km) as the displaced fossil fuel. The Renewable Energy Directive requires an emission savings of 60% compared with the displaced fuel for new facilities constructed after 2017. This is readily achieved for grass biomethane through optimisation of the system. Allowing for carbon (C) sequestration in grassland of 0.6 t C ha/year will lead to emissions savings of 89%. This would suggest that grass biomethane is one of the most sustainable indigenous, non-residue-based transport biofuels. The economics of biomethane are shown to be difficult. There is a requirement for innovative policy and marketing of the industry. A compressed natural gas transport fuel market is an essential prerequisite to using biomethane as a transport fuel. Mandating a certain percentage of biomethane in natural gas sales is of benefit to biomethane as both a transport and a thermal biofuel. Government policy is required to support a biomethane industry. Further research is required in the following areas:
Bioresource mapping: This includes the creation of a Geographical Information System to highlight sources of the organic fraction of municipal solid waste (OFMSW), slurry, slaughter waste and areas of high-yielding silage production. The system would include distribution systems (natural gas grid, electricity grid) and demand nodes (e.g. transport fleets, district heating, new towns) to propose areas with significant potential for biomethane production.
Assessment of biomethane facilities: This includes full life-cycle analysis of different biomethane facilities, including co-digestion of slurries and grass silage, mono-digestion of OFMSW, and mono-digestion of slaughter wastes. The research should allow assessment of the cost of the produced biomethane.
Digester design: This basic research should assess optimal digester systems for different feedstocks.
Agricultural impact of AD: This research includes monitoring carbon sequestration in grasslands where silage is cut and digestate is applied. This should be compared with carbon sequestration on grazed pastures. The fertiliser value of different digestates needs to be assessed along with the emissions associated with application of digestate. The research should also assess the effect on biodiversity.