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•Biodiesel is a renewable and ecofriendly biofuel.•It can be produced using transesterification, emulsification and pyrolysis process etc.•Enzyme catalyzed and biomass derived ...catalysts reactions are economic and ecofriendly.•Process intensification technology results in higher yield with lower wastes.
Biodiesel is a non-toxic renewable energy source that is gaining attention globally owing to its direct applicability in preexisting engines without any modification. Various technologies from laboratory scale to industrial scale have been developed, and many plants have been established for biodiesel production using various feedstocks. Using biobased technology in biodiesel production is advantageous as these methods generate less waste and are considered ecofriendly. This article mainly discusses the availability of various oil resources (edible, non-edible, waste cooking oils (WCO)) and the advancements in technology related to oil extraction. Specifically, biobased methods, such as immobilized enzymes (matrix) and heterogeneous catalysts (derived from biomass), reported to catalyze the transesterification reaction for biodiesel production are discussed in detail. Biodiesel production using conventional technologies results in low yield and purity and is time-consuming. Newly introduced process intensification technologies (microreactor, membrane reactor, microwave, reactive distillation, and centrifugal contractor) to overcome these issues are also discussed. The need to develop integrated process technologies for biodiesel production to make the process more economical is emphasized.
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•Valorization of lignin towards chemicals and fuels is reviewed.•Various process routes are evaluated for efficient lignin depolymerization.•Detrimental reactions in depolymerization ...of lignin are discussed.•Biorefinery aspects for value added products generation are outlined.•Perspectives towards the biorefinery scheme is recommended.
In recent years, lignin valorization is commercially an important and advanced sustainable process for lignocellulosic biomass-based industries, primarily through the depolymerization path. The conversion of the lignin moieties into biofuels and other high value-added products are still challenging to the researchers due to the heterogeneity and complex structure of lignin-containing biomass. Besides, the involvement of different microorganisms that carries varying metabolic and enzymatic complex systems towards degradation and conversion of the lignin moieties also discussed. These microorganisms are frequently short of the traits which are obligatory for the industrial application to achieve maximum yields and productivity. This review mainly focuses on the current progress and developments in the pretreatment routes for enhancing lignin degradation and also assesses the liquid and gaseous biofuel production by fermentation, gasification and hybrid technologies along with the biorefinery schemes which involves the synthesis of high value-added chemicals, biochar and other valuable products.
The growing population and increased disposal of end-of-life (EoL) electrical and electronic products have caused serious concerns to the environment and human health. Electronic waste (e-waste) is a ...growing problem because the quantity and the rate at which it is generated has increased exponentially in the last 5 years. The rapid changes or upgradation in technologies, IT requirements for working or learning from home during COVID-19, manufacturers releasing new electronic gadgets and devices that serves the consumers comfort and a declension in services has contributed to an increase in the e-waste or waste of electrical and electronic equipment (WEEE) generation rates. The current status of e-waste generation, handling procedures and regulatory directives in USA, EU, China, India, Vietnam and Gulf Cooperation Council (GCC) countries are presented in this review. The recent developments in e-waste recycling methods/recovery of base and precious metals, the advantages and limitations of hydrometallurgy, pyrometallurgy, biohydrometallurgy and pyrolysis are discussed. Considering the impediments in the present technologies, the extraction of valuable resources, i.e. precious metals, from e-waste using suitable biocatalysts shows promising applications. This review also stresses on the research needs to assess the economic effects of involving different unit operations/process industries for resource recovery, reuse and recycling.
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•E-waste generation in developing and developed countries were analyzed.•E-waste treatment options for resource recovery (i.e. precious metals) were reviewed.•Biohydrometallurgy: eco-friendly, less energy requirement and cost effective.•Preventative, recycling and e-waste reduction routes were recommended.
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•This review focused on the methane generation using micro and macroalgae.•Discussed key issues and pretreatment strategies to improve AD and methane yield.•Summarized co-digestion ...process using algal biomass to enhance methane yield.•Enlightened future perspectives and challenges for algal methane production.
Biogas production using algal resources has been widely studied as a green and alternative renewable technology. This review provides an extended overview of recent advances in biomethane production via direct anaerobic digestion (AD) of microalgae, macroalgae and co-digestion mechanism on biomethane production and future challenges and prospects for its scaled-up applications. The effects of pretreatment in the preparation of algal feedstock for methane generation are discussed briefly. The role of different operational and environmental parameters for instance pH, temperature, nutrients, organic loading rate (OLR) and hydraulic retention time (HRT) on sustainable methane generation are also reviewed. Finally, an outlook on the possible options towards the scale up and enhancement strategies has been provided. This review could encourage further studies in this area, to intend and operate continuous mode by designing stable and reliable bioreactor systems and to analyze the possibilities and potential of co-digestion for the promotion of algal-biomethane technology.
With the growing use of fossil fuels and industrial activity, the amount of carbon dioxide (CO2) emission is continuously increasing and is considered a primary contributor to climate change. CO2 ...emissions from stationary resources (coal fire, cement plants, and other industry) can be reduced by using various carbon capture and sequestration (CCS) technologies. In this article, recent advancements in various biological methods (i.e., carbonic anhydrase (CA), hydrogenation of CO2 to formate, reduction of CO2 to methane, CO2 conversion into methanol by enzyme cascade, and the role of RuBisCo enzyme) that have been reported for CO2 capture are discussed, along with their advantages and limitations. A brief overview of other physicochemical (absorption, adsorption, cryogenic, and membrane) technologies is also provided. Although biological methods are ecofriendly and can be performed under ambient conditions, these approaches are still not cost effective, as the reactions require cofactors, and the enzymes lose activity when exposed to hot flue gas and ionic liquids. Most captured CO2 is stored by mineralization using a geological and ocean storage method without providing any economic benefit. It is a question of interest as to how we can utilize CO2 and generate revenue. Utilization of CO2 as a feedstock to produce bioenergy is a possible approach. Various microbes capable of utilizing CO2 as feedstock and producing biofuels (biodiesel and bioalcohol) have been reported. These two technologies, i.e., CO2 capture and bioconversion of CO2 into bioenergy, can be integrated to develop a process that not only mitigates CO2 effects on the environment but also solves energy problems while generating revenue.
•Carbon dioxide (CO2) is contributing in global warming.•CO2 can be used as a resource for bioenergy production.•Electro-biological and integrated system are efficient methods for CO2 to bioenergy conversion.
Microbial electrolysis cell (MEC) holds the flexible potentials for waste biorefinery, pollutants removal, CO2 capture, and bioelectrosynthesis of clean and renewable electrofuels or valuable ...chemical commodities, dealing with the depletion of fossil fuels and environmental deterioration issues. Although substantial advances in process design and mechanisms exploration have greatly promoted the development of MEC platform from a concept to a technology, how to virtually utilize it in real-world scenario remains a big challenge. There are numerous technical issues ahead for MEC to be tackled towards up-scaling and real implementations. This review article presents a state-of-the-art overview of the fundamental aspects and the latest breakthrough results and accomplishments obtained from the MEC platform, with a special emphasis on mapping the key extracellular electron transfer (EET) mechanisms between electroactive microorganisms and electrode surface (including i: cells→e−anode; and ii: cathode→e−cells). A unified discussion of different process design: inoculation methods for rapid start-up, role of membranes, modification of cathode materials, cathodic catalysts (i.e. noble, un-noble metal catalysts and biocatalysts) as well as designs and configurations of versatile bioelectrochemical cells, is also involved. Finally, the major challenges and technical problems encountered throughout MEC researches are analyzed, and recommendations and future needs for the virtual utilization of MEC technology in real waste treatment are elaborated.
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•Performance of anaerobic co-digestion of microalgae with food waste was examined.•Kinetic modeling and synergistic impact evaluation were performed.•Co-digestion achieved 4.99-fold ...methane increase than that of microalgae alone.•Cone model had the highest reliability to describe the co-digestion kinetics.•The synergy improved methanogenesis rate and subsequent methane output.
Continuous primary energy consumption has motivated the scientists of the world to search for renewable energy sources that could substitute fossil fuels. Microalgae can be an alternative substrate for renewable energy recovery. In this study, biochemical methane potential (BMP) assays were used as a tool to examine the technical potential of methane production from microalgae (MA) through co-digesting with food waste (FW) at different MA: FW ratios on volatile solids (VS). Three mathematical models (i.e. first-order kinetic, modified Gompertz, and Cone models) were also utilized to fit the experimental data, with the purpose of elucidating the biological degradation and principle kinetics of the co-digestion. The results showed that supplementing food waste significantly improved microalgae digestion performance, with the highest methane yield of 639.8±1.3mL/g VSadded obtained at a MA:FW ratio of 0.2:0.8, which was 4.99-fold increase with respect to that (106.9±3.2mL/g VSadded) of the microalgae alone. Cone model had the best fitness and reliability to the experimental results and could describe the co-digestion kinetics more reasonably. Parameter analysis and synergistic impact evaluation together revealed that the improvement in methanogenesis potential (fd) caused by the synergy of co-digestion might be the fundamental cause for the upgraded methane production. These results validated the superiority of co-digestion as a step towards maximizing methane production from microalgae, aiding the development of multi-biomass co-disposal and ultimately bioenergy recovery techniques.
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•Challenges and opportunities of AnMBRs are critically reviewed.•Novel configurations of AnMBRs are presented to overcome technology limitations.•Energy demand and energy production ...potential with different AnMBRs are analyzed.•Innovative strategies to reduce energy demands and fouling are critically discussed.•Future perspectives and key issued required urgent attention are highlighted.
Water shortage, public health and environmental protection are key motives to treat wastewater. The widespread adoption of wastewater as a resource depends upon development of an energy-efficient technology. Anaerobic membrane bioreactor (AnMBR) technology has gained increasing popularity due to their ability to offset the disadvantages of conventional treatment technologies. However there are several hurdles, yet to climb over, for wider spread and scale-up of the technology. This paper reviews fundamental aspects of anaerobic digestion of wastewater, and identifies the challenges and opportunities to the further development of AnMBRs. Membrane fouling and its implications are discussed, and strategies to control membrane fouling are proposed. Novel AnMBR configurations are discussed as an integrated approach to overcome technology limitations. Energy demand and recovery in AnMBRs is analyzed. Finally key issues that require urgent attention to facilitate global penetration of AnMBR technology are highlighted.
The conventional fossil fuel showed a persistent and intense decline steadily over the past two decades have led to global deterioration of limited sustainable energy supplies. Furthermore, price ...fluctuations and its serious ecological consequences had piqued the interest of researchers mostly in domain of alternative renewable energy. Among all existing fuels, biohydrogen is documented because of its carbon-neutral, simple and sustainable output, low carbon emissions, and large energy density. Hydrogen (H2) generation from dark fermentation of biowaste is an enticing sustainable method which promotes in the creation of low carbon economy. This review details the overview of hydrogen yield form renewable feedstock through dark fermentation. It also detailed the recent trends such as pretreatment, addition of various additives, integrated options, etc., employed towards the enhancement of fermentation process to enrich the hydrogen production. Discussion about the inhibitory substances that affects the performance of fermentation process was incorporated. In addition, it elaborates the economic feasibility, challenges and limitation of the process along with future scope for the development of sustainable hydrogen economy.
•Dark fermentative biohydrogen production, conditions, and yield are reviewed.•Recent approaches to enhance dark fermentative process.•Inhibitors are present in inoculum or substrates or produced during fermentation.•Many stability and productivity issues are associated with the process itself.•Hydrogen strategy enabling low carbon green economy.
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•Polyhydroxyalkanoates a potential biopolymer substitute for conventional plastics.•Critically reviewed various waste streams for sustainable and inexpensive PHA production.•Recent ...advances on fermentation strategies & synthetic biology for higher PHA production.•Discussed PHA- nanocomposites and their application in various sectors.•Future perspectives & technical challenges for efficient waste-bioplastic production addressed.
Polyhydroxyalkanoates (PHA) are appealing as an important alternative to replace synthetic plastics owing to its comparable physicochemical properties to that of synthetic plastics, and biodegradable and biocompatible nature. This review gives an inclusive overview of the current research activities dealing with PHA production by utilizing different waste fluxes generated from food, milk and sugar processing industries. Valorization of these waste fluxes makes the process cost effective and practically applicable. Recent advances in the approaches adopted for waste treatment, fermentation strategies, and genetic engineering can give insights to the researchers for future direction of waste to bioplastics production. Lastly, synthesis and application of PHA-nanocomposites, research and development challenges, future perspectives for sustainable and cost-effective PHB production are also discussed. In addition, the review addresses the useful information about the opportunities and confines associated with the sustainable PHA production using different waste streams and their evaluation for commercial implementation within a biorefinery.
