Search

This virtual special issue published in Renewable and Sustainable Energy Reviews contains 25 high-quality selected extended papers presented at the HERAKLION 2019 7th International Conference on Sustainable Solid Waste Management held in Heraklion, Crete in Greece from 26th to June 29, 2019. 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. • Twenty five high quality peer-reviewed papers were selected from HERAKLION 2019 Conference. • The mian theme of sustainable waste-to-energy systems catogorised into five topics. • It will support advancement of waste-to-energy technologies and circular economy. [ABSTRACT FROM AUTHOR]

The utilization of renewable fuel alternatives holds promise for reducing the financial burden of regulatory compliance and the social responsibility associated with greenhouse gas emissions. Hydrothermal liquefaction (HTL) is one of the most versatile technologies for converting renewable biomass feedstocks (especially in the wet state) into biofuel (biocrude oil) in a compact plant. Therefore, this review is devoted to thoroughly reviewing and critically discussing biocrude oil production from biomass feedstocks through the HTL process. This review starts by discussing the principles of biomass HTL processing and product upgrading, aiming to provide a grounded and broad understanding of current developments in this domain. The data reported in the published literature are analyzed and visualized in order to scrutinize the effects of the main process parameters on the quantity, quality, cost, and environmental impacts of resultant biofuels. Higher biocrude oil yields are obtained at temperatures, pressures, and residual times between 300 and 350 °C, 24–27 MPa, and 15–25 min, respectively. Concerning yield and calorific value, biocrude oil derived from homogeneous catalysts demonstrates figures of 23.6 % and 32.1 MJ/kg, whereas that from heterogeneous catalysts exhibits percentages of 66.8 % and 40 MJ/kg, respectively. The challenges and prospects for the future development of biocrude oil are also discussed. HTL has a long way to go before being used for biofuel production on a large scale. Future studies appear to be directed towards the use of HTL technology under the biorefinery framework to maximize the exploitation of biomass into value-added products, while minimizing waste generation. [Display omitted] • Biocrude oil production from biomass by hydrothermal liquefaction is reviewed. • The principles of hydrothermal liquefaction and biocrude oil upgrading are discussed. • The effects of the main parameters on various aspects of biocrude oil are investigated. • The higher biocrude oil yields are obtained at 300–350 °C, 24–27 MPa, and 15–25 min. • Environmental and economic aspects of biocrude oil production are thoroughly discussed. [ABSTRACT FROM AUTHOR]

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 (1H, 13C)). Additionally, the determined fuel properties, such as density (0.8612 kg/L), kinematic viscosity (4.11 mm2/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 (R2 = 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. • Potential of novel Prunus cerasoides seed oil as renewable energy. • Maximum biodiesel yield of 85% was obtained at reaction temperature of 120 °C. • The optimum methanol/oil ratio of 12:1 at 4.0% catalyst loading for 5 h was observed. • Pseudo-first-order kinetics was found fit with experimental data (R2 = 0.9172). • Clay-based catalyst exhibited cost effectiveness and high stability during the reaction. [ABSTRACT FROM AUTHOR]

The sustainable and eco-friendly 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 challenges, 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 based on the export value and revealed comparative advantage (RCA). Argentina has the most exports (9.59 billion USD), with seven biowaste products having RCA >1. The product space model (PSM) was employed to evaluate the income potential of biowaste and to appraise the studied countries overall level of sophistication, and then a suitable industrial policy was proposed according to PSM indicators. All the considered biowaste products have low-income potential, so it is better to produce bioenergy from these products. Thailand has the highest country-level sophistication, followed by India, Brazil, Ukraine, and Argentina. However, according to the PSM, the EXPY values exhibit significant growth for India (52.3%) and Thailand (31.9%), while the remaining countries experience moderate EXPY growth. Furthermore, Thailand and Ukraine can generate more revenues by opting to bio-energy production. On the PSM industrial policy map, India, Thailand, Brazil and Ukraine lie in "let it be quadrant", while Argentina is in a "parsimonious industrial policy" region. The implementation of the suggested industrial policies can enhance the productive structure of the studied countries and help them achieve their projected growth targets. • Application of Product Space Model is presented in the study. • Product-space analysis considering PRODY, EXPY and Open Forest is carried out. • Ukraine and Thailand can generate more revenues by opting to bio-energy production • Thailand and India have high values of EXPY that shows high potential for future growth. • Brazil, Ukraine, Thailand and India lie in the most desired quadrant of product space [ABSTRACT FROM AUTHOR]

Liquid transportation biofuel production is a promising strategy to reduce greenhouse gas emissions. Hydrothermal gasification (HTG) has shown great potential as an effective method for valorizing wet biomass. The high-quality syngas produced using the HTG process can be chemically/biochemically converted to liquid biofuels. Therefore, this paper aims to comprehensively review and critically discuss syngas production from biomass using the HTG process and its conversion into liquid biofuels. The basics and mechanisms of biomass HTG processing are first detailed to provide a comprehensive and deep understanding of the process. Second, the effects of the main operating parameters on the performance of the HTG process are numerically analyzed and mechanistically discussed. The syngas cleaning/conditioning and Fischer-Tropsch (FT) synthesis are then detailed, aiming to produce liquid biofuels. The economic performance and environmental impacts of liquid biofuels using the HTG-FT route are evaluated. Finally, the challenges and prospects for future development in this field are presented. Overall, the maximum total gas yield in the HTG process is obtained at temperature, pressure, and residence time in the range of 450–500 °C, 28–30 MPa, and 30–60 min, respectively. The highest C 5+ liquid hydrocarbon selectivity in the FT process is achieved at temperatures between 200 and 240 °C. Generally, effective conversion of biomass to syngas using the HTG process and its successful upgrading using the FT process can offer a viable route for producing liquid biofuels. Future studies should use HTG technology in the biorefinery context to maximize biomass valorization and minimize waste generation. [Display omitted] • Syngas production from biomass using hydrothermal gasification is thoroughly reviewed. • Conversion of syngas into liquid biofuels using Fischer-Tropsch synthesis is discussed. • The mechanisms of hydrothermal gasification and Fischer-Tropsch synthesis are detailed. • The economic and environmental aspects of biofuel production from syngas are evaluated. • The challenges and prospects for future development in this field are highlighted. [ABSTRACT FROM AUTHOR]

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 (1H and 13C) 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. • Biodiesel was produced from novel non-edible caper (Capparis spinose L.) seed oil. • An efficient and recyclable Cu–Ni doped ZrO 2 catalyst was synthesized and used. • Response surface methodology based on Box-Behnken design used for process optimization. • Maximum biodiesel yield of 90.2% was obtained at optimum process conditions. • Biodiesel showed excellent potential as a sustainable and renewable source of bioenergy. [ABSTRACT FROM AUTHOR]

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. Image 1 • Blending practices of municipal solid waste with biomass are critically reviewed. • Hybrid configurations of gasification are assessed to overcome technological limitations. • Gasification of biomass and waste could reduce toxic elements and harmful gases. • Practical approaches of the gasification process are till on an initial point of utilization. • Hybrid systems with gasification would enhance process efficiency and energy. [ABSTRACT FROM AUTHOR]