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Microalgae have been widely explored because of the diverse number of their worthwhile applications and potential as a source biomass for the production of biofuels and value-added materials. However, downstream techniques have yet to be fully developed to overcome techno-economic barriers. Flocculation is a superior method for harvesting microalgae from growth medium because of its harvesting efficiency, economic feasibility. Various kind of bio-flocculation harvesting methods are consider as attractive low cost and environmentally friendly options and able to harvest >90% biomass. Lipid recovery from microalgal cells is a major barrier for the biofuel industry because of process complexity and algae cell structure. Thus, the pretreatment method is necessary to disrupt the cell walls of microalgae and enhance lipid extraction. Many techniques, including dry methods of extraction, are already being implemented but found out that they are not efficient and cost-effective. Various new wet harvesting strategies have been claimed to extract major lipids in cost-efficient (30% less than conventional) way as wet technologies can eliminate the cost of cell drying and associated instruments. It is necessary to develop new methods which are energy and cost-effective, and environmentally friendlier for the commercialization of biofuels. Therefore, this review presents the advances in the progress of various flocculation harvesting methods with special emphasis on innovative bio-flocculation, the underlying mechanism of microalgae and flocculation. In this study also summarize the recent progress on microalgal oil extraction processes, and comparison was made between the processes in terms of sustainability, technology readiness, and applications in larger scales. Image 1 • Approaches of the different methods of flocculation have been outlined in depth. • Bio-based flocculation methods could significantly reduce cost of microalgae harvesting. • Green extraction approaches reduce time and energy for industrial viability. • Judicious selection of harvesting and lipid extraction methods ensures economical biofuel production. • Appropriate policy framework is required for commercialization of microalgae biofuels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rice bran biodiesel is produced using ultrasound and infrared radiation. • ANN-GWO is a reliable tool to optimize the transesterification process. • The predicted rice bran yield is 98.16%. • The optimum yield obtained from the experiment is 97.74%. • The FAME content of the optimized biodiesel is 95%. A system combining ultrasound and infrared radiation was used to increase the chemical reactions between incompressible reactants by enhancing their mass transfers with the aim to reduce the energy usage and reaction time. In this study, biodiesel from RBO was produced via transesterification, and the process variables were optimized using the combination of ANN and GWO algorithm. Process parameters considered in this study are ratio of methanol to oil, catalyst concentration, and reaction time. Based on the ANN-GWO algoritm used, the optimum conditions for the process parameters were (1) methanol to oil ratio: 60%, (2) concentration of catalyst: 1 wt%, (3) time: 7.76 min, leading to the metyl ester yield of 98.16 wt%. The algoritm was verified by conducting a triplicate independent experiments using the suggested optimum values, resulting in an average methyl ester yield of 97.74 wt%. Subsequently, properties of rice bran biodiesel were compared to ASTM D6751 and EN 14214 standards, and the obtained values met both the standards. [ABSTRACT FROM AUTHOR]

The rapid increase in the global population and its ever-rising standards of living are imposing a huge burden on global resources. Apart from the rising energy needs, the demand for freshwater is correspondingly increasing. A population of around 3.8 billion people will face water scarcity by 2030, as per the reports of the World Water Council. This may be due to global climate change and the deficiency in the treatment of wastewater. Conventional wastewater treatment technologies fail to completely remove several emerging contaminants, especially those containing pharmaceutical compounds. Hence, leading to an increase in the concentration of harmful chemicals in the human food chain and the proliferation of several diseases. MXenes are transition metal carbide/nitride ceramics that primarily structure the leading 2D material group. MXenes act as novel nanomaterials for wastewater treatment due to their high surface area, excellent adsorption properties, and unique physicochemical properties, such as high electrical conductivity and hydrophilicity. MXenes are highly hydrophilic and covered with active functional groups (i.e., hydroxyl, oxygen, fluorine, etc.), which makes them efficient adsorbents for a wide range of species and promising candidates for environmental remediation and water treatment. This work concludes that the scaling up process of MXene-based materials for water treatment is currently of high cost. The up-to-date applications are still limited because MXenes are currently produced mainly in the laboratory with limited yield. It is recommended to direct research efforts towards lower synthesis cost procedures coupled with the use of more environmentally friendly materials to avoid secondary contamination. [Display omitted] [ABSTRACT FROM AUTHOR]

Corn stover (CS) is one of the most abundant agricultural wastes and is ubiquitous around the world that is left over after grain harvest and accounts for 47–50% dry mass of the total grain yield. The global CS yield is 1661.25 million tons/year, which is 27.2% of the total agricultural waste. CS consists of about 34.5% stems, 32.3% leaves, 14.3% husks, 12.3% cobs and 6.6% flowers, with up to 45% cellulose, 30% hemicellulose and 20% lignin. Due to its favorable economic and environmental potential, CS is considered an ideal raw material for producing biofuels and biobased chemicals, which can largely be divided into carbohydrate and lignin platforms. However, the techno-economic perspectives of CS-based biorefineries have remained questionable due to the inadequate supply chain logistics, lack of cost-effective conversion technologies, limited scale-up of the product-specific technologies, and lower competitiveness in the market compared to their counterparts, such as sugar and starch-based biorefineries. While CS is converted by thermochemical and biochemical approaches, the latter is considered to be more sustainable for its selective conversion under mild conditions using microorganisms. This review aimed to critically discuss the latest research and developments on the biochemical conversion of CS into biofuels and chemicals. In particular, this paper covers the market potential of biofuels and chemicals to which CS can make a significant contribution, technological developments in the microbial conversion of CS, major biofuels and chemicals produced from CS-derived carbohydrates and lignin, and the technoeconomic perspectives of CS-based biorefinery. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal degradation behavior, kinetic and thermodynamic analyses of surface fibers of date palm. • Kinetic analysis was performed on the devolatilization region using the Coats–Redfern model–fitting method. • Surface fibers pyrolysis governed by two diffusion models: one–way transport and Valensi equation. • E a and A were estimated to be 91.40 kJ/mol and 1.59 × 103 –29.39 × 103 min−1, respectively. The potential of the least-exploited date pam waste was presented as feedstock for bio-oil production. The surface fibers of the date palm are widely available as waste material in the Gulf region, the Middle East, and Africa. Chemical composition analysis and physiochemical characterization showed that surface fibers are valuable feedstock for energy production. Surface fibers were analyzed thermogravimetrically at different heating rates (10, 20, and 30 °C /min) in an inert atmosphere. Decomposition was carried out in three stages: dehydration, devolatilization, and solid combustion. Kinetic analysis was performed on the devolatilization region using the Coats–Redfern model–fitting method using twenty–one reaction mechanisms from four different solid-state reaction mechanisms. Two diffusion models: one–way transport (g(x) = α2) and Valensi equation (g(x) = α+(1-α) × ln(1-α)) showed the highest regression coefficient (R2) with the experimental data. The activation energy (E a) and the pre-exponential factor (A) was estimated to be 91.40 kJ/mol and 1.59 × 103 –29.39 × 103 min−1, respectively. The kinetic parameters were found to be dependent on the heating rate. The surface fibers' thermodynamic parameters ΔH, ΔG, and ΔS were 80–97, 151–164, and −0.17- −0.18 kJ/mol, respectively. This indicates that the pyrolysis of surface fibers is endothermal and not spontaneous. Since there is not much experimental work on the pyrolysis of surface fibers available in the literature, the reported results are crucial for designing the pyrolysis process. [ABSTRACT FROM AUTHOR]

This study critically reviewed the prospects, feedstocks and challenges of biodiesel production from two non-edible oil sources, namely Beauty leaf oil (BLT) ( Calophyllum inophyllum ) and Castor oil ( Ricinus communis ). The recent developments and the lifecycle assessment (LCA) of these species such as their habitat, growth, oil content, free fatty acid profile and biodiesel characteristics are briefly discussed. Different oil extraction techniques and biodiesel conversion methods are also presented. The properties of the pure biodiesel and their blends are compared with petroleum diesel under different ASTM and European standards. Furthermore, the literatures on engine performance and emission studies using these biodiesels are reviewed and presented in tabular form. The review found that BLT oil can be catalytically transesterified to produce biodiesel as a potential alternative transport fuel in Australia. The review concludes that castor oil is not only an alternate fuel resource, but it also holds good lubricating properties and hence is a potential bio-lubricant source for internal combustion engines. Further research is needed on combustion, corrosion, tribo-corrosion, long term engine durability tests and tribological performance tests before recommending commercial scale biodiesel production from BLT oil and Castor oil. [ABSTRACT FROM AUTHOR]

Increasing human population, deforestation and man-made climate change are likely to exacerbate the negative effects on freshwater ecosystems and species endangerment. Consequently, the biodiversity of freshwater continues to dwindle at an alarming rate. However, this particular topic lacks sufficient attention from conservation ecologists and policymakers, resulting in a dearth of data and comprehensive reviews on freshwater biodiversity, specifically. Despite the widespread awareness of risks to freshwater biodiversity, organized action to reverse this decline has been lacking. This study reviews prospective conservation and management strategies for freshwater biodiversity and their associated challenges, identifying current key threats to freshwater biodiversity. Engineered nanomaterials pose a significant threat to aquatic species, and will make controlling health risks to freshwater biodiversity increasingly challenging in the future. When fish are exposed to nanoparticles, the surface area of their respiratory and ion transport systems can decline to 60% of their total surface area, posing serious health risks. Also, about 50% of freshwater fish species are threatened by climate change, globally. Freshwater biodiversity that is heavily reliant on calcium perishes when the calcium content of their environments degrades, posing another severe threat to world biodiversity. To improve biodiversity, variables such as species diversity, population and water quality, and habitat are essential components that must be monitored continuously. Existing research on freshwater biota and ecosystems is still lacking. Therefore, data collection and the establishment of specialized policies for the conservation of freshwater biodiversity should be prioritized. • Key threats and impacts of climate change on freshwater biodiversity have been reviewed. • Potential conservation and management strategies for freshwater biodiversity are highlighted. • Engineered nanomaterials pose a serious threat to aquatic species. • Climate change threatens around 50% of all freshwater fish species worldwide. • Species variety, population, and water quality must be regularly monitored to improve biodiversity. [ABSTRACT FROM AUTHOR]

Membrane technology has rapidly gained popularity in wastewater treatment due to its cost-effectiveness, environmentally friendly tools, and elevated productivity. Although membrane performance in wastewater treatment has been reviewed in several past studies, the key techniques for improving membrane performance, as well as their challenges, and solutions associated with the membrane process, were not sufficiently highlighted in those studies. Also, very few studies have addressed hybrid techniques to improve membrane performance. The present review aims to fill those gaps and achieve public health benefits through safe water processing. Despite its higher cost, membrane performance can result in a 36% reduction in flux degradation. The issue with fouling has been identified as one of the key challenges of membrane technology. Chemical cleaning is quite effective in removing accumulated foulant. Fouling mitigation techniques have also been shown to have a positive effect on membrane photobioreactors that handle wastewater effluent, resulting in a 50% and 60% reduction in fouling rates for backwash and nitrogen bubble scouring techniques. Membrane hybrid approaches such as hybrid forward-reverse osmosis show promise in removing high concentrations of phosphorus, ammonium, and salt from wastewater. The incorporation of the forward osmosis process can reject 99% of phosphorus and 97% of ammonium, and the reverse osmosis approach can achieve a 99% salt rejection rate. The control strategies for membrane fouling have not been successfully optimized yet and more research is needed to achieve a realistic, long-term direct membrane filtering operation. [Display omitted] • Strategies to improve membrane performance in wastewater treatment are reviewed. • Despite its increased cost, membrane performance can reduce flow degradation by 36%. • The fouling issue is identified as one of the key issues of membrane technology. • Mitigation techniques like nitrogen bubble scouring can reduce fouling rates by 60%. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is a viable technique to address food waste (FW) problems by converting FW into sustainable energy. Despite the advantages of the AD process, large-scale AD plants like in Germany and the USA have not been developed in Australia. Therefore, this paper aims to study the technological, economic, and environmental feasibility of sustainable energy production from household FW in Australia. In addition, this paper discusses the different waste to energy (WtE) technologies along with the operational parameters as well as the challenges in developing a biogas plant. The energy and economic potential analysis of the AD process indicates that the processing of 10% FW from Australian states and territories can generate 1.22 GWh to 35.4 GWh electricity which can subsequently earn AUD 0.54 million to AUD 15.7 million revenue per year. The greenhouse gas (GHG) emissions analysis indicates that conversion of the 10% of Australian FW has the potential to lower GHG emissions by 639,852 tonnes per annum. Hence, it can be said that FW plays a vital role as a promising source of sustainable energy and is capable of benefiting the country's economy significantly and reducing GHG emissions. • FW is a potential source of sustainable energy. • AD is a useful waste to energy process for producing clean energy. • Conversion of FW into energy can significantly lower GHG emissions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Importance of microbial biotechnology for waste utilization is reviewed. • Utilization of microbes for lignocelluloses utilization and value-addition are discussed. • Importance and possibilities for microbial degradation of plastics are elaborated. • Role of microbes in global warming is demonstrated. This review provides an update on the state-of-the art technologies for the valorization of solid waste and its mechanism to generate various bio-products. The organic content of these wastes can be easily utilized by the microbes and produce value-added compounds. Microbial fermentation techniques can be utilized for developing waste biorefinery processes. The utilization of lignocellulosic and plastics wastes for the generation of carbon sources for microbial utilization after pre-processing steps will make the process a multi-product biorefinery. The C1 and C2 gases generated from different industries could also be utilized by various microbes, and this will help to control global warming. The review seeks to expand expertise about the potential application through several perspectives, factors influencing remediation, issues, and prospects. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) have garnered significant attention as low-cost thermal energy storage systems that efficiently capture and store solar energy. Recent review works have largely focused only on thermal conductivity enhancement techniques, and/or applications of PCMs, while others have mainly discussed the performance enhancement of either heating, cooling, or clean energy storage systems integrating with PCMs. However, not enough studies recently reviewed all of these techniques/systems comprehensively to provide insights into them. This paper thus comprehensively reviews the integration of PCMs as an enhancement to most types of heating, cooling, and clean energy storage system performance, and the techniques to enhance thermal conductivity. The integration of PCMs with these systems has shown promising performance. For instance, an improvement of 13.5% is found in the efficiency of photovoltaic (PV) system when it is integrated with PCM/Al 2 O 3 nanoparticles. In addition, the solar air heater's daily energy efficiency reaches 17% on its own, but when combined with PCM, it reaches 33%. However, the major drawback of using PCM–TES (thermal energy storage) for cooling is that PCM does not entirely solidify at night. The literature also shows that the issues related to PCMs' low thermal conductivity, phase separation, and subcooling/supercooling, their poor compatibility with other materials, and the environmental hazards they pose hinder their application on a large scale. It is necessary to implement international standards for assessing the thermophysical properties of PCMs and compile data to better facilitate the utilization of PCMs by end-users. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the diesel engine performance and emission characteristics fueled with moringa biodiesel and compare those with the performance and emission characteristics of palm biodiesel, jatropha biodiesel, and diesel fuel. In this study, only 20% of each biodiesel (described by MB20, PB20, and JB20, respectively) was tested in diesel engine, given that open literature indicates the possible use of biodiesel of up to 20% in a diesel engine without modification. The physical and chemical properties of all fuel samples are also presented and compared with ASTM D6751 standards. A naturally aspirated multi-cylinder, four-stroke direct-injection diesel engine was used to evaluate their performance at different speeds and full load condition. All biodiesel fuel samples reduce brake power (BP) and increase brake-specific fuel consumption (BSFC) than diesel fuel. Engine emission results indicated that blended fuel reduces the average carbon monoxide (CO) and hydrocarbons (HC) emissions except nitric oxides (NO) emissions than diesel fuel. Among the biodiesel-blended fuel, Palm biodiesel showed better performance and minimal emission than jatropha and moringa biodiesel fuel. Although PB20 showed better performance, but performance of MB20 biodiesel blend is comparable with other fuels. Correspondingly, 20% of moringa biodiesel can be used in a diesel engine without any engine modification. [ABSTRACT FROM AUTHOR]

The transportation, agricultural, and power sector of Bangladesh is largely dependent on fossil fuels that decrease day by day. The government has to import large volumes of fuel from foreign sources to meet the fuel demand for power production, causing a negative impact on the country’s economy. Finding an alternative to fossil fuels is becoming the most urgent issue. Biodiesel can thus be a destined source to future energy demands. Increasing the usage of biodiesel will also decrease the global problem of environmental pollution, as fossil fuels are considered to be the major source of harmful emissions. Biodiesel is renewable, bio-degradable, non-toxic, technologically feasible, and can be used as a bio-lubricant. In this study, the current energy scenario of Bangladesh, available potential biodiesel feedstocks, production process and engine fuel property, environmental impact, performance and emission characteristics on diesel engines, comparison of cost analysis, and future direction are discussed. Various research related to these feedstocks are performed in Bangladesh, which include an overview of biodiesel properties, engine performance, and emission parameters used in diesel engines. All types of biodiesel have similar functional properties compared with diesel fuel and can be successfully used in compression ignition engines. Biodiesel can thus serve as a subsequent replacement of non-renewable fossil fuels. Compared with diesel fuel, CO and HC emission were also low, but a slight increase in NO x was observed in some cases. One of the major advantages is that Bangladesh is a country with plenty of biodiesel feedstock sources, such as mustered, Jatropha curcas , rapeseed, sesame, castor, cottonseed, neem, algae, coconut, and groundnut. In conclusion, producing biodiesel from different feedstocks is greatly possible and can thus assist in future energy needs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cationic PAETAC & PAmPTAC were synthesized by UV-induced radical polymerization. • New polymers showed good flocculation performance of freshwater & marine microalgae. • Optimal doses of PAETAC were 50 and 4.8 mg/g for C. vulgaris & P. purpureum. • PAETAC and PAmPTAC produced stable flocs, supporting simple dewatering step. This study addresses the challenge of microalgae harvesting through the development of flocculants. Two positively charged cationic polymers including poly[2 (acryloyloxy)ethyl]trimethylammonium chloride (PAETAC) and poly(3 acrylamidopropyl)trimethylammonium chloride (PAmPTAC) were synthesized using the UV-induced radical polymerization, for harvesting both freshwater and marine microalgae. The results show that the synthesized polymers have excellent flocculation performance for both freshwater green microalgae (Chlorella vulgaris) and marine red microalgae (Porphyridium purpureum). PAETAC outperformed PAmPTAC for both Chlorella vulgaris and Porphyridium purpureum microalgae. The optimal PAETAC doses for Chlorella vulgaris and Porphyridium purpureum microalgae were 50 and 4.8 mg/g of dry biomass while the optimal PAmPTAC doses were 252 and 35 mg/g of dry biomass respectively. Additionally, the floc formation with the PAETAC was more stable than PAmPTAC, which supported the dewatering step via sieving. The superior performance can be attributed to the higher molecular weight of the PAETAC polymer when compared to the PAmPTAC polymer. In comparison to commercially available polydiallyldimethylammonium chloride (PolyDADMAC), the newly synthesised PAETAC and PAmPTAC polymers demonstrated superior flocculation efficiency at a lower dose. The findings of this study established a platform technology for designing and synthesising cationic flocculants for use in microalgae harvesting. [ABSTRACT FROM AUTHOR]

This study explores the role of renewable energy (RE) penetration in Malaysia's energy security (ES) and its implications for the country's target of 20% capacity in the energy mix by 2025. Renewable energy (RE) is a critical driver of long-term energy security. In 2018, the share of renewable energy in Malaysia's energy mix was 9%, falling far short of the national target of 20% penetration by 2025. This study employs a system dynamics approach to investigate the relationship between RE penetration and correlated indicators from energy security (ES) dimensions: energy availability, environmental sustainability, and socio-economics. The causal relationships between the three-dimensional indicators of ES have been established using causal and stock and flow logic. Simulated results show that energy consumption has increased sharply, while energy efficiency and economic growth have only increased by a small margin with an increase in RE from 2015 to 2020. The energy intensity is expected to rise slightly by the end of the fifth year. As a result, the overall impact is positive for Malaysia's environmental sustainability while reducing its reliance on energy imports and meeting national economic growth demands. • 1. Increase in RE share improves pollution remediation. • 2. RE improves the short and long-term ES of a nation. • 3. Energy intensity, energy efficiency and growth in economic health is noticed. • 4. Reduces dependency on fossil fuels and promotes the use of alternatives such as biofuels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conversion of toxic and hazardous Zanthoxylum armatum seed into biodiesel. • Catalytic application of green nanoparticles of silver oxide has been discussed. • Use of Central Composite Design for optimization reactions of transesterification. • Characterization of nanoparticles using analytical techniques. The cleaner and sustainable production of biodiesel from toxic and hazardous non-edible seed oils offer a remarkable opportunity to deal with energy crises and provide a renewable substitute to depleting fossil fuels. In the current study, the potential of the novel, toxic and non-edible seed oil of Zanthoxylum armatum was investigated for eco-friendly production of biodiesel catalysed by green nanoparticles of silver oxide. Silver oxide nanoparticles were synthesised with aqueous leaf extract of Silybum marianum. Heterogeneous green nanocatalysts were preferred due to their recyclable nature and easy recovery. The maximum yield of 95% of methyl ester was obtained at optimum reaction conditions of oil to methanol molar ratio 1:7, catalyst loading 0.5 (wt.%), reaction temperature 90 °C and reaction time 2 h. Characterisation of synthesised nanoparticles of silver oxide was carried out with X-Ray diffraction (XRD), scanning electron microscopy (SEM), and energy diffraction X-ray (EDX). Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) confirmed the formation of methyl esters. 5, 8-octadecenoic acid was found to be the major fatty acid methyl ester in the biodiesel sample. Fuel properties of biodiesel were investigated and found comparable to international standards of ASTM D-6571 and EN-14214. It was concluded from the current investigation that Zanthoxylum armatum is a potential biomass feedstock for the sustainable production of biodiesel using green nanoparticles of silver oxide. [ABSTRACT FROM AUTHOR]

• Food waste is a potential source of sustainable gaseous biofuel. • Anaerobic digestion is an efficient technology to convert food waste into fuel. • Turning food waste into energy can assist the decarbonisation of the economy. • Converting food waste into sustainable fuel can significantly lower the GHG emission. Food waste is a type of organic waste generated by restaurants, food processing plants, households, and commercial and institutions. This study aims to assess the sustainable biofuel, electricity production and greenhouse gas emission reduction potential of food waste using anaerobic digestion technology. Food waste data was collected from the Australian government database to estimate the biomethane and biogas yield and to evaluate the opportunities to convert the biomethane into electricity and heat. This study found that food waste can yield 47% biomethane and hence for Australia, an estimated total of 0.07 million m3 to 1.54 million m3 of biogas can be produced and up to 414,898 tonnes of greenhouse gas emissions reduced annually. The study also estimated that the generated biogas can replace fossil fuel-based electricity generation of up to 52.36 GW and 554.4 TJ heat per year. The environmental assessment indicated that the complete conversion of food waste can lower greenhouse gas emissions (GHG) by up to 5,07,434 tonnes per year and Australia can earn about $52.38 M revenue from electricity production. Therefore, conversion of food waste into biofuel through the anaerobic digestion process can play a significant role in generating electricity from non-fossil-based sources, reducing GHG emissions and earning revenue. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of antioxidant treatment on 20% PME in diesel on fuel properties were studied. [•] Effect on engine performance and emission was enumerated in a turbocharged diesel engine. [•] Stabilized blends produced 0.3–0.6% higher avg. BP and 0.18–0.64% lower avg. BSFC compared to B20. [•] Stabilized blends reduced about 9.8–12.6% avg. NOx compared to non-stabilized B20. [ABSTRACT FROM AUTHOR]

Abstract: Increasing energy demand and environment concerns have prompted an evolution of alternative fuel sources. As an alternative fuel source, biodiesel is attractive because it reduces engine emissions. However, biodiesel produces higher NO x emissions compared to ordinary diesel fuel. Previous researches have established many factors that cause biodiesel to produce elevated NO x emissions. This study reviews the impacts of biodiesel combustion on NO x emissions and their reduction approaches in diesel engines. The first part of this study recaps the NO x formation mechanisms for understanding the kinetics behind the NO x forming reactions. The second part describes the factors affecting on NO x emissions. This paper established that higher NO x emissions are produced for biodiesel combustion which influenced by several factors such as physicochemical properties and molecular structure of biodiesel, adiabatic flame temperature, ignition delay time, injection timing and engine load conditions etc. The final section discusses on the reduction of NO x emissions from biodiesel fuelled engines for both pre and post combustion techniques. The results of reduction approaches of the NO x emissions implies, exhaust gas recirculation (EGR) and retarded injection timing are effective as well as low cost techniques than others. Between these two techniques, EGR reduces the NO x emissions at 5–25% EGR rate adequately in biofuelled engine by controlling oxygen content and combustion peak temperature with slightly decreasing HC and CO emissions. However this technique shows few penalties on smoke and PM emissions as well as brake specific fuel consumption if not perfectly optimized. [Copyright &y& Elsevier]

The utilization of renewable lignocellulosic biomasses for bioenergy synthesis is believed to facilitate competitive commercialization and realize affordable clean energy sources in the future. Among the pathways for biomass pretreatment methods that enhance the efficiency of the whole biofuel production process, the combined microwave irradiation and physicochemical approach is found to provide many economic and environmental benefits. Several studies on microwave-based pretreatment technologies for biomass conversion have been conducted in recent years. Although some reviews are available, most did not comprehensively analyze microwave–physicochemical pretreatment techniques for biomass conversion. The study of these techniques is crucial for sustainable biofuel generation. Therefore, the biomass pretreatment process that combines the physicochemical method with microwave-assisted irradiation is reviewed in this paper. The effects of this pretreatment process on lignocellulosic structure and the ratio of achieved components were also discussed in detail. Pretreatment processes for biomass conversion were substantially affected by temperature, irradiation time, initial feedstock components, catalyst loading, and microwave power. Consequently, neoteric technologies utilizing high efficiency-based green and sustainable solutions should receive further focus. In addition, methodologies for quantifying and evaluating effects and relevant trade-offs should be develop to facilitate the take-off of the biofuel industry with clean and sustainable goals. • Fundamental and characteristic of microwave assisted pretreatment were introduced. • Effects of microwave irradiation on the lignocellulosic biomass reviewed. • Combination of microwave physicochemical methods obtained higher efficiency. • Energy and economic aspects of microwave-physicochemical methods evaluated. [ABSTRACT FROM AUTHOR]

• High dependency on fossil fuel as main energy source brings excessive CO 2 emission. • CO 2 and CH 4 utilization is one of the solutions to mitigate climate change. • Alternative energy technology has potential in meeting the increasing energy demand. • Four main technologies that used to mitigateclimate change is reviewed. • Their mechanism, limitations, and suggestions for up-scaling purpose are highlighted. The excessive global emission of greenhouse gases (mainly carbon dioxide, CO 2 and methane, CH 4), especially due to the burning of fossil fuel for energy and power generation, is the main cause to the air pollution and greenhouse effect. This has eventually brought many issues, such as climate change and global warming, that will affect the standard life of human beings. Many strategies have been proposed to further reduce the excessive emission of greenhouse gases, including CO 2 and CH 4 utilization. This method not only reduce the CO 2 concentration in the atmosphere, but also producing renewable energy (syngas) at the same time. Hence, CO 2 and CH 4 utilization is also a promising approach to assist in overcoming the energy crisis due to the increasing population in time. Basically, the utilization of CO 2 and CH 4 system can be categorized into four: (i) electrochemical reduction, (ii) advanced catalyst system, (iii) photocatalytic reduction, and (iv) plasma technology. In this review paper, the mechanism implemented on the four abovementioned categories and their respective limitations are presented. Besides, future recommendations to optimize the greenhouse gases utilization system for up-scaling purpose is also highlighted. [ABSTRACT FROM AUTHOR]

Abstract: Biodiesels are gaining more importance as a promising alternative energy resource. Engine performance and emission characteristics of unmodified biodiesel fueled diesel engines are highly influenced by its ignition and combustion behavior. This review article presents the literature review on ignition delay (ID), combustion and emission characteristics of biodiesel fueled diesel engine. More than hundred articles report which have been published mostly in the last decade are reviewed in this paper. The investigation results report that the combustion characteristics of bio fueled engine is slightly different from the engine running with petroleum diesel. Most of the investigation results have reported that as compared to diesel, biodiesel has early start of combustion (SOC) and shorter ID of between 1–5° and 0.25–1.0°, respectively. Higher cetane number (CN), lower compressibility and fatty acid composition of biodiesel have been identified as the main elements for early SOC and shorter ID. In addition, it is also found that, the heat release rate (HRR) of biodiesel is slightly lower than diesel owing to the lower calorific value, lower volatility, shorter ID and higher viscosity. [Copyright &y& Elsevier]

This paper presents the experimental results carried out to evaluate the oxidation and storage stabilities of various biodiesel fuels. The biodiesel fuels are palm methyl ester (PME), jatropha methyl ester (JME), coconut oil methyl ester (COME), 20% blends of PME with diesel fuel and 20% blends of JME with diesel fuel. The ordinary diesel fuel was used for comparison purposes. Various ASTM standard methods were used to evaluate all the samples at the interval of 180 h over a 2160 h (three months) duration. Oxidation stability of the samples was measured by induction period (IP) using a Rancimat instrument. Other properties such as density, viscosity, flash point, total acid number (TAN), and total base number (TBN) were measured. The results show that almost all fuel samples met the standard specifications regarding IP. The trends for density, viscosity and TAN increased, while the TBN decreased due to oxidation. For the flash point, the trend also decreased, but the rate was very low. In overall consideration, among the biodiesels, COME was found to be better in respect to oxidation and storage stabilities. The results of this investigation will be used to sustainable development of biodiesel fuel from various stock resources. [ABSTRACT FROM AUTHOR]

In the present study, a micro combined heat and power (micro-CHP) system using compressed natural gas (CNG) and biogas fuels, was developed. The objective of this research study was to investigate the utilization of nanofluids as a working fluid to improve thermal performance of the micro-CHP system. Three different nanofluids based on the CNT, Al 2 O 3 , and SiO 2 have been investigated. The nanofluids was used as the circulating fluid to recover the heating power from the micro-CHP system. Three different concentration of nanoparticles (25, 50 and 100 ppm) have been used. The efficiency of separated heat and power (SHP) system was 27.6% while using combined heat and power, the total efficiency increased up to 65.3%. The results showed that by using CNG gas thermal efficiency of micro-CHP improve compared to the biogas. The result of the present study showed that nanofluids enhances the thermal efficiency of the micro-CHP system. By using the Al 2 O 3 nanofluid the efficiency of micro-CHP efficiency is 73%. While by using the SiO 2 and CNTs nanofluids the efficiency of micro-CHP efficiency is 70% and 66.3% respectively. So, we can coclude that by using the Al 2 O 3 nanofluid thermal performance of micro-CHP systems improves. [ABSTRACT FROM AUTHOR]

Bioresource valorization to obtain valuable phenolic compounds for medicinal, nutraceutical, food, and cosmetic applications are critical for a current and future sustainable and bio-based economy. Renewable, environmentally friendly, and non-toxic choline chloride-based deep eutectic solvents are the newest and utmost environmentally friendly alternatives to conventional organic solvents for the pretreatment and extraction of phenolic compounds. Recently, numerous studies have focused on phenolic compound extraction using choline chloride-based deep eutectic solvents as solvents or catalysts. Process variable optimization has been reported in terms of kinetic modeling and mechanisms involved in phenolic compounds extraction. This paper describes the cutting-edge methods used to extract phenolic compounds from different bio-based sources using choline chloride-based deep eutectic solvents. In addition, the factors affecting, kinetic models, and mechanisms involved in phenolic compound extraction using choline chloride-based deep eutectic solvents are thoroughly summarized. Moreover, future predictions, challenges, and anticipated growth in this field are addressed and can be used for biomass valorization. • Extraction of phenolic compounds using deep eutectic solvents is promising. • Extraction mechanism depends on the nature of the deep eutectic solvent components. • Scaling up should be optimized using experimental and computational approaches. • Recovery of phenolic compound from solvent is difficult due to low vapor pressure. [ABSTRACT FROM AUTHOR]

Biodiesel is a clean, renewable, liquid fuel that can be used in existing diesel engines without modification as pure or blend. Transesterification (the primary process for biodiesel generation) via heterogeneous catalysis using low-cost waste feedstocks for catalyst synthesis improves the economics of biodiesel production. Heterogeneous catalysts are preferred for the industrial generation of biodiesel due to their robustness and low costs due to the easy separation and relatively higher reusability. Calcium oxides found in abundance in nature, e.g., in seashells and eggshells, are promising candidates for the synthesis of heterogeneous catalysts. However, process improvements are required to design productive calcium oxide-based catalysts at an industrial scale. The current work presents an overview of the biodiesel production advancements using calcium oxide-based catalysts (e.g., pure, supported, and mixed with metal oxides). The review discusses different factors involved in the synthesis of calcium oxide-based catalysts, and the effect of reaction parameters on the biodiesel yield of calcium oxide-based catalysis are studied. Further, the common reactor designs used for the heterogeneous catalysis using calcium oxide-based catalysts are explained. Moreover, the catalytic activity mechanism, challenges and prospects of the application of calcium oxide-based catalysts in biodiesel generation are discussed. The study of calcium oxide-based catalyst should continue to be evaluated for the potential of their application in the commercial sector as they remain the pivotal goal of these studies. [ABSTRACT FROM AUTHOR]

This article aims to comprehensively review the anaerobic digestion (AD) process utilising the organic fraction of municipal solid waste (OFMSW) substrate. The AD of OFMSW has received considerable attention due to its significant energy and nutrient recovery as well as its greenhouse gas (GHG) mitigation potential. AD is a biological process involving treating and stabilising organic matter in the absence of oxygen accomplished by a consortium of microorganisms and occurs under hydrolysis, acidogenesis, acetogenesis, and methanogenesis phases. The hydrolysis phase is recognised as the primary rate-limiting step. Thus, exploring the ways to speed up the hydrolysis process will maximise biogas production. The key factors affecting the digestion efficiency include feedstock quality, pre-treatment process, design and selection of digestion process and process conditions including pH, temperature, carbon to nitrogen (C: N) ratio, organic loading rate and hydraulic retention time. The review reveals that solid-state anaerobic digestion (SSAD) is best suited for OFMSW due to its high solid concentration (>15%) and better process performance. The continuous digestion with thermophilic temperatures was found to be the best condition for high solid AD process. The plug flow and continuous stir tank reactors were the best performing options to control the biological conditions for the digestate post-treatment. Proper selection of the parameters for the whole process is crucial in ensuring process feasibility and economic sustainability of AD of OFMSW. The study revealed that the AD of OFMSW could play a significant role to mitigate waste and waste-related problems. • Studies on organic fraction of municipality solid waste are reviewed. • Pretreatment is required to achieve optimum results in anaerobic digestion. • The digestion operating conditions significantly controls the biogas output. • The products of digestate require post-treatment for maximised output. [ABSTRACT FROM AUTHOR]

The extensive use of fossil fuels and the environmental effect of their combustion products have attracted researchers to look into renewable energy sources. In addition, global mass production of waste has motivated communities to recycle and reuse the waste in a sustainable way to lower landfill waste and associated problems. The development of waste to energy (WtE) technology including the production of bioenergy, e.g. biogas produced from various waste through Anaerobic Digestion (AD), is considered one of the potential measures to achieve the sustainable development goals of the United Nations (UN). Therefore, this study reviews the most recent studies from relevant academic literature on WtE technology (particularly AD technology) for biogas production and the application of a solar-assisted biodigester (SAB) system aimed at improving performance. In addition, socio-economic factors, challenges, and perspectives have been reported. From the analysis of different technologies, further work on effective low-cost technologies is recommended, especially using SAB system upgrading and leveraging the opportunities of this system. The study found that the performance of the AD system is affected by a variety of factors and that different approaches can be applied to improve performance. It has also been found that solar energy systems efficiently raise the biogas digester temperature and through this, they maximize the biogas yield under optimum conditions. The study revealed that the solar-assisted AD system produces less pollution and improves performance compared to the conventional AD system. Unlabelled Image • Waste to Energy technologies can reduce landfill waste and associated problems. • AD is an efficient technology to handle waste that contains high moisture. • Solar-assisted biodigester performance is compared with conventional systems. • Solar-assisted biodigesters improve the performance of the anaerobic digestion process. [ABSTRACT FROM AUTHOR]

• The use of ILs in catalytic systems has been reported extensively. • Ionic liquid with brønsted acidity or basicity produces high biodiesel yield. • Mixed acid catalysts also exhibited excellent catalytic activity. • The increase of surface area between the reactants and catalysts enhance the yield. Biodiesel is considered as a potential substitute for petroleum-based diesel fuel owing to its comparable properties to diesel. Biodiesel is generally produced from renewable sources such as agricultural products and microalgae in the presence of a suitable catalyst. Recently ionic liquid (IL) catalyzed synthesis of biodiesel has become a promising pathway to an eco-friendly production route for biodiesel. This review focuses on the use of ILs both as solvents as well as catalysts for sustainable biodiesel production from agricultural feedstocks and microalgae with high free fatty acid content. Reactions catalyzed by ILs are known to render high reactivity under the mild condition and high selectivity of ester product with simple separation steps. The article first discusses the state of the art of biodiesel production using ILs along with the physicochemical properties of the produced biodiesel. Then, current IL technologies were elucidated in terms of the categories such as acidic and basic ILs. The use of more advanced ILs such as supported ionic liquids and ionic liquid-enzyme catalysts on different biodiesel feedstocks were also discussed. Furthermore, the role of IL catalyst in intensified biodiesel production methods such as microwave and ultrasound technologies were also discussed. Finally, the prospects and challenges of IL catalyzed biodiesel production are discussed in this article. The review shows that ILs with brønsted acidity or basicity not only pose a low risk to the environment but also result in high biodiesel yields with mild reaction conditions in a short time. Brønsted acidic ILs can convert free fatty acids as well as triglycerides to biodiesel without the need for pretreatment, which facilitates in reducing the production cost of biodiesel. From the review, it can be concluded that ILs present great potential as catalysts for biodiesel production. [ABSTRACT FROM AUTHOR]

Today renewable energies such as biodiesel have considerable role in the bio-based economy. Long production time and low efficiency are a number of problems in biodiesel production that is essential to be considered when designing and operating the biodiesel production systems. In this study, using safflower oil in a hydrodynamic cavity reactor, biodiesel fuel was produced in the possible shortest time and maximum efficiency. The effect of reaction time (30, 60 and 90 s), concentration of potassium hydroxide catalyst (0.75%, 1% and 1.25%), alcohol to oil ratio (6, 8 and 10) and rotor-stator distance (1 cm, 2 cm and 3 cm) on the reaction yield were analyzed. The results were analyzed by response surface methodology. Among the independent variables, reaction time was the most important factor on the reaction yield, which had a positive impact on the quality of methyl ester. The optimum values obtained were: 63.88 s reaction time, 0.94% catalyst concentration, 1: 8.36 alcohol to oil molar ratio, 1.53 cm rotor-stator distance, and 89.11% yield. Several properties and compounds of biodiesel obtained were measured and compared with ASTM D6751 (American Society for Testing and Materials) and EN 14214 standard (European Standards). The results showed that most of the features conform to the afore-mentioned standard. Therefore, transesterification of safflower oil with a hydrodynamic cavitation reactor can function as a good alternative to the diesel. [ABSTRACT FROM AUTHOR]

The rapid spread of COVID-19 has led to nationwide lockdowns in many countries. The COVID-19 pandemic has played serious havoc on economic activities throughout the world. Researchers are immensely curious about how to give the best protection to people before a vaccine becomes available. The coronavirus spreads principally through saliva droplets. Thus, it would be a great opportunity if the virus spread could be controlled at an early stage. The face mask can limit virus spread from both inside and outside the mask. This is the first study that has endeavoured to explore the design and fabrication of an antiviral face mask using licorice root extract, which has antimicrobial properties due to glycyrrhetinic acid (GA) and glycyrrhizin (GL). An electrospinning process was utilized to fabricate nanofibrous membrane and virus deactivation mechanisms discussed. The nanofiber mask material was characterized by SEM and airflow rate testing. SEM results indicated that the nanofibers from electrospinning are about 15–30 μm in diameter with random porosity and orientation which have the potential to capture and kill the virus. Theoretical estimation signifies that an 85 L/min rate of airflow through the face mask is possible which ensures good breathability over an extensive range of pressure drops and pore sizes. Finally, it can be concluded that licorice root membrane may be used to produce a biobased face mask to control COVID-19 spread. • Facemasks are healthcare essentials which can limit the spread of coronavirus. • The limited supply of masks during the pandemic can put the public in risk. • Single-use masks made of synthetic polymers are hazardous for the environment. • Licorice roots membrane can be used to produce biobased face masks. [ABSTRACT FROM AUTHOR]

• Impact of water – biodiesel – diesel nano-emulsion fuel on diesel engine parameters investigated. • Nano-emulsion fuel generated less power and torque than diesel. • NO emission of nano-emulsion fuel decreased 9.06% than diesel. • Diesel nano-emulsion fuel is a satisfactory alternative to fossil diesel fuel in diesel engines. The use of emulsion fuel in the engine has been reported as an effective solution to reduce the harmful emission. This experimental study examined the effects of nano-emulsion biodiesel fuel on engine efficiency, gas emission parameters and combustion parameters of a single-cylinder air-cooled diesel engine. Nano-emulsion fuel made of 5% waste cooking oil biodiesel and 5% distilled water were used to test the performance of the diesel engine. This fuel was produced using ultrasonic waves by stabilizing 5% by volume tween 80 and spans 80 surfactants in HLB8 (Hydrophilic-Lipophilic Balance). Performance parameters and pollutants emission of a diesel engine using nano-emulsion fuel were compared with emulsion fuel. This test was performed on four different engine loads (25%, 50%, 75%, and 100%) at different speeds of 1700, 2000, 2300, and 2600 rpm. Power, torque, cylinder pressure levels, and emissions including soot opacity, carbon monoxide (CO), unburned hydrocarbon (UHC), carbon dioxide (CO 2), and nitrogen oxides (NO X) were measured. The test results show that diesel engine power and torque using nano-emulsion fuel improved by about 4.84% and 4.65% compared to emulsion fuel, respectively. The use of nano-emulsion fuel significantly decreased CO (~11%), UHCs (~6%), NOx (~9%) and soot opacity (~10%) emission. However, a small rise in CO 2 (~7%) emission was observed. The combustion result shows that nano-emulsion fuel creates more cylinder pressure (CP) than emulsion fuel during combustion. The highest CP was recorded at 10° crank angle after the top dead centre with diesel fuel. Finally, nano-emulsion fuel can be a satisfactory alternative to diesel fuel in a diesel engine without having to change the engine. [ABSTRACT FROM AUTHOR]

This study investigated real world in-use vehicle emissions using two regulatory techniques simultaneously, namely on-road remote sensing (RS) systems and air quality (AQ) monitoring stations, aiming to provide a full pollution profile from tailpipe to roadside and atmosphere. Two large AQ and RS datasets collected during 2012–2018 were analyzed. The effects of various emission control programmes on the trends of tailpipe emissions and air quality were evaluated. Correlations between tailpipe emissions and roadside and ambient air quality were also explored. The results showed a decreasing trend of NO 2 at both roadside and ambient AQ stations from 2013 to 2016, which was attributed to the intensive implementation of a series of vehicle emissions control programmes. Although NO 2 was decreasing, O 3 was generally increasing for all AQ stations. AQ data showed that O 3 had little correlation with either NO 2 or NO x , but was mainly determined by NO 2 /NO x ratio. Roadside NO 2 /NO x ratio increased first and then decreased or stabilized after 2014, while ambient NO 2 /NO x ratio increased steadily. RS data showed that the overall NO decreased quickly during 2012–2015 and then decreased moderately after 2015. The decrease was mainly attributed to the effective NO reduction from LPG vehicles. However, diesel NO remained high and reduced relatively slowly during the study period. Gasoline vehicles were relatively clean compared with LPG and diesel vehicles. Finally, good correlations were demonstrated between NO measured by RS sites and NO x measured by roadside AQ stations, indicating that vehicle emissions were the major contributor to roadside NO x pollution. Ambient NO x emissions could be affected by various sources, leading to different correlation levels between RS and ambient AQ results. Unlabelled Image • Real driving emissions were measured by both RS systems and AQ stations. • O 3 increased in spite of decreased NO 2 at both roadside and ambient AQ stations. • NO x reduction was mainly attributed to emission control programmes on LPG vehicles. • On-road RS emissions data showed a good correlation with roadside AQ data. [ABSTRACT FROM AUTHOR]

• The effect of pretreatments of the seed kernels on the oil yield was investigated. • The kernels prepared for 14.4 % MC produced the highest oil yield for both methods. • The highest oil yield of 86.4 % was obtained using n-hexane method for the GK. • A comparison of fossil energy ratio (FER) was made between two methods. • The FER of 4.9 and 3.4 was found in-hexane and screw press method, respectively. An experimental investigation was conducted to evaluate the effects of the processing of the raw materials, such as preparation and extraction, grating (whole and grated), drying and moisture conditioning of the seed kernels on the yield of oil extraction. Both mechanical and chemical methods were used to extract oil from the beauty leaf (BL) seed kernel using a screw press expeller and n-hexane as an oil solvent, respectively. Both whole kernel (WK) and grated kernel (GK) were used in screw press technique, whereas, only GK was used in n-hexane technique. The study indicated that the kernels prepared for 14.4 % moisture content (MC) produced the highest yield of oil in both methods. The highest oil yield of 86.4 % was obtained on the basis of the weight of the kernel in n-hexane method for the GK. On the other hand, the oil yield of 78.0 and 72.1 % was achieved using a screw press technique for the GK and WK, respectively. The gas chromatography (GC) analysis was conducted to determine the fatty acid compositions of beauty leaf oil. The physico-chemical properties of the beauty leaf oil (BLO) were evaluated. A comparison of fossil energy ratio (FER) was made between n-hexane and screw press methods. The FER in-hexane method was found 4.9, whereas, in screw press method it was found 3.4 and 3.1 for the GK and WK, respectively, which indicates that n-hexane method is more efficient than screw press technique. This study provides an understanding of the basis of selecting an appropriate oil extraction technique for oil extraction users in large scale applications. [ABSTRACT FROM AUTHOR]

Optimizing the process parameters of biodiesel production is the key to maximizing biodiesel yields. In this study, artificial neural network models integrated with ant colony optimization were developed to optimize the parameters of the two-step Cerbera manghas biodiesel production process: (1) esterification and (2) transesterification. The parameters of esterification and transesterification processes were optimized to minimize the acid value and maximize the C. manghas biodiesel yield, respectively. There was excellent agreement between the average experimental values and those predicted by the artificial neural network models, indicating their reliability. These models will be useful to predict the optimum process parameters, reducing the trial and error of conventional experimentation. The kinetic study was conducted to understand the mechanism of the transesterification process and, lastly, the model could measure the physicochemical properties of the C. manghas biodiesel. [ABSTRACT FROM AUTHOR]