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Hydrogen (H 2) is pivotal to phasing out fossil fuel-based energy systems. It can be produced from different sources and using different technologies. Very few studies comprehensively discuss all available state-of-the-art technologies for H 2 production, the challenges facing each process, and their economic feasibility and sustainability. The current study thus addresses these gaps to effectively direct future research towards improving H 2 production techniques. Many conventional methods contribute to large greenhouse gas footprints, with high production costs and low efficiency. Steam methane reforming and coal gasification dominate the supply side of H 2 , due to their low production costs (<$3.50/kg). Water-splitting offers one of the most environmentally benign production methods when integrated with renewable energy sources. However, it is considerably expensive and ridden with the flaw of production of harmful by-products that affect efficiency. Fossil fuel processing technologies remain one of the most efficient forms of H 2 production sources, with yields exceeding 80% and reaching up to 100%, with the lowest cost despite their high reliance on expensive catalysts. Whereas solar-driven power systems cost slightly less than $10 kg−1, coal gasification and steam reforming cost below $3.05 kg−1. Future research thus needs to be directed towards cost reduction of renewable energy-based H 2 production systems, as well as in their decarbonization and designing more robust H 2 storage systems that are compatible with long-distance distribution networks with adequate fuelling stations. • H 2 production technologies, their economic feasibility and sustainability are reviewed. • Low-cost steam methane reforming and coal gasification dominate the supply side of H 2. • Water-splitting coupled with renewable sources offers one of the most eco-friendly methods. • Future research should focus on decarbonizing and lowering renewable H 2 production cost. [ABSTRACT FROM AUTHOR]

Microalgae originating from wastewater has been exhibiting particularly promising results in terms of biohydrogen production and wastewater treatment. This paper aims to review the factors affecting production, pretreatment techniques to improve synthesis, advanced technologies utilized for enhancing biohydrogen production, and techno-economic feasibility evaluation of the processes at a commercial scale. Microalgae possess metabolic components to synthesize biohydrogen using photobiological and fermentative processes but must undergo pretreatment for efficient biohydrogen production. The efficiency of these processes is influenced by factors such as the microalgae species, light intensity, cell density, pH, temperature, substrates, and the type of bioreactors. Moreover, many limitations, such as oxygen sensitivity, altered thylakoid constitution, low photon conversion efficiency, light capture disruption, and the evolution of harmful by-products hinder the sustainability of biohydrogen production processes. High operational and maintenance costs serve as the major bottleneck in the scaling up of the process as an industrial technology. Therefore, future research needs to be directed towards increasing optimization of the processes by reducing energy and resource demand, recycling metabolic wastes and process components, genetically engineered microalgae to adopt more efficient routes, and conducting pilot studies for commercialization. • Wastewater-based microalgae is a potential source of biohydrogen. • Factors affecting the biohydrogen production from microalgal biomass are discussed. • Technologies related to biohydrogen production from microalgae are reviewed. • Key challenges of biohydrogen production process from microalgae are highlighted. [ABSTRACT FROM AUTHOR]

Microplastic pollution has emerged as a new environmental concern due to our reliance on plastic. Recent years have seen an upward trend in scholarly interest in the topic of microplastics carrying contaminants; however, the available review studies have largely focused on specific aspects of this issue, such as sorption, transport, and toxicological effects. Consequently, this review synthesizes the state-of-the-art knowledge on these topics by presenting key findings to guide better policy action toward microplastic management. Microplastics have been reported to absorb pollutants such as persistent organic pollutants, heavy metals, and antibiotics, leading to their bioaccumulation in marine and terrestrial ecosystems. Hydrophobic interactions are found to be the predominant sorption mechanism, especially for organic pollutants, although electrostatic forces, van der Waals forces, hydrogen bonding, and pi-pi interactions are also noteworthy. This review reveals that physicochemical properties of microplastics, such as size, structure, and functional groups, and environmental compartment properties, such as pH, temperature, and salinity, influence the sorption of pollutants by microplastic. It has been found that microplastics influence the growth and metabolism of organisms. Inadequate methods for collection and analysis of environmental samples, lack of replication of real-world settings in laboratories, and a lack of understanding of the sorption mechanism and toxicity of microplastics impede current microplastic research. Therefore, future research should focus on filling in these knowledge gaps. [Display omitted] • This review investigates MPs to guide better policy action toward MP management. • MPs absorb pollutants like persistent organic pollutants, heavy metals, and antibiotics. • Hydrophobic interactions are the primary sorption mechanism for organic pollutants. • MPs influence the growth and metabolism of organisms. • Innovative sampling and analytical methods are needed to identify MP sources. [ABSTRACT FROM AUTHOR]

Emerging contaminants (ECs) are increasingly recognized as threats to human health and ecosystems. This review evaluates advanced analytical methods, particularly mass spectrometry, for detecting ECs and understanding their toxicity, transformation pathways, and environmental distribution. Our findings underscore the reliability of current techniques and the potential of upcoming methods. The adverse effects of ECs on aquatic life necessitate both in vitro and in vivo toxicity assessments. Evaluating the distribution and degradation of ECs reveals that they undergo physical, chemical, and biological transformations. Remediation strategies such as advanced oxidation, adsorption, and membrane bioreactors effectively treat EC-contaminated waters, with combinations of these techniques showing the highest efficacy. To minimize the impact of ECs, a proactive approach involving monitoring, regulations, and public education is vital. Future research should prioritize the refining of detection methods and formulation of robust policies for EC management. [Display omitted] • Emerging contaminants (ECs) pose significant risks to aquatic ecosystems and human health. • Advanced analytical techniques are effective in detecting ECs in diverse environments. • A comprehensive strategy is most effective for remediating EC-contaminated water. • Future research must focus on detection, source control, monitoring, and public engagement. [ABSTRACT FROM AUTHOR]

This paper offers a comprehensive analysis of algal-based membrane bioreactors (AMBRs) and their potential for removing hazardous and toxic contaminants from wastewater. Through an identification of contaminant types and sources, as well as an explanation of AMBR operating principles, this study sheds light on the promising capabilities of AMBRs in eliminating pollutants like nitrogen, phosphorus, and organic matter, while generating valuable biomass and energy. However, challenges and limitations, such as the need for process optimization and the risk of algal-bacterial imbalance, have been identified. To overcome these obstacles, strategies like mixed cultures and bioaugmentation techniques have been proposed. Furthermore, this study explores the wider applications of AMBRs beyond wastewater treatment, including the production of value-added products and the removal of emerging contaminants. The findings underscore the significance of factors such as appropriate algal-bacterial consortia selection, hydraulic and organic loading rate optimization, and environmental factor control for the success of AMBRs. A comprehensive understanding of these challenges and opportunities can pave the way for more efficient and effective wastewater treatment processes, which are crucial for safeguarding public health and the environment. [Display omitted] • Algal-based MBRs effectively remove hazardous contaminants. • Challenges remain in biomass accumulation, nutrient limitation, and toxicity. • Mitigation strategies include system optimization and use of renewable energy. • Potential applications beyond wastewater treatment include biofuel and bioproduct production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Marine emission possesses both environmental and human health risks. • Alternative fuels including hydrogen can reduce harmful emissions from marine transport. • Alternative fuels have the potential to promote UN Sustainable Development Goals. • The potential challenges of alternative fuel in marine transport are highlighted. The International Maritime Organization (IMO) has placed stricter controls on several aspects of global maritime transport operations to protect the environment. In light of this, the goal of this study is to examine and assess the different prospective paths and technologies that will assist the shipping industry in decarbonizing its operations. We consider how the utilisation of various alternative energy sources reduces greenhouse gas (GHG) emissions from marine transportation and contributes to the promotion of the United Nations Sustainable Development Goals (SGDs). The complexities associated with maritime industry operations using alternative energy sources are also explored. Biofuel as an alternative energy source, including biomethanol and biodiesel, can reduce greenhouse gas emissions in the shipping industry by 25% to 100%. However, the current supply of biofuels can only meet about 15% of the total demand which is not sufficient to sustainably power the entire marine fleet. There are several issues associated with these biofuels, including oxidation, ecological consequences, feedstock availability, technical and operational constraints, and economic factors that must be addressed before their full potential may be achieved. [ABSTRACT FROM AUTHOR]

• Novel conceptual methods for tuning microalgae to aviation biofuel were presented. • Conversion methods that directly act on wet algae biomass are highly desired. • Chemical methods are able to obtain a maximum lipid yield of 98% • Microalgae bio-jet fuel parameters are compiled with ASTM standards. • Zeolite catalytic pyrolysis increased the bio-oil yield from Microalgae to 80 %. Concerns have been raised about the effects of fossil fuel combustion on global warming and climate change. Fuel consumer behavior is also heavily influenced by factors such as fluctuating fuel prices and the need for a consistent and reliable fuel supply. Microalgae fuel is gaining popularity in the aviation industry as a potential source of energy diversification. Microalgae can grow in saltwater or wastewater, capture CO 2 from the atmosphere and produce lipids without requiring a large amount of land. As a result, the production of oil from microalgae poses no threat to food availability. The low carbon footprint of microalgae-derived fuels has the potential to mitigate the impact of traditional aviation fuels derived from petroleum on climate change and global warming. Therefore, aviation fuels derived from microalgae have the potential to be a more environmentally friendly and sustainable alternative to conventional fuels. Gathering microalgal species with a high lipid content, drying them, and turning them into aviation fuel is an expensive process. The use of biofuels derived from microalgae in the aviation industry is still in its infancy, but there is room for growth. This study analyses the potential routes already researched, their drawbacks in implementation, and the many different conceptual approaches that can be used to produce sustainable aviation fuel from microalgal lipids. Microalgae species with fast-growing rates require less space and generate lipids that can be converted into biofuel without imperiling food security. The key challenges in algal-based aviation biofuel include decreased lipid content, harvesting expenses, and drying procedure that should be enhanced and optimized to increase process viability. [ABSTRACT FROM AUTHOR]

• Second-generation feedstocks have potential to be used as aviation fuel. • A multicriteria decision analysis tool is used to assess the suitability of the feedstocks. • The fatty acid-based properties of more than 50% feedstocks meet international biofuel standards. • The modification of some fuel properties is needed to meet the strict aviation fuel standards. This paper examines the potential of suitable second-generation feedstocks for sustainable aviation fuel production, theoretically based on fatty acid-based fuel properties. The fatty acid composition of 38 s-generation feedstocks was collected from the literature. The fuel properties of these feedstocks were then calculated using empirical formula and assessed according to international fuel standards including American and European standards. The selected feedstocks were assessed and ranked using a multi-criteria decision analysis (MCDA) tool, i.e., PROMETHEE GAIA, to identify the suitability of the sources based on kinematic viscosity (KV), density (D), higher heating value (HHV), cetane number (CN), iodine value (IV), oxidation stability (OS), and cold filter plugging point (CFPP). It was found that 20 of the 38 feedstocks meet international fuel standards. The utilisation of the MCDA tool indicates that Ricinus communis is the highest-ranked feedstock for sustainable aviation fuel production, followed by the Azadirachta indica feedstock, with Sterculia feotida L. the lowest-ranked feedstock. The assessment of the properties of ranked feedstock against aviation fuel standards, including Jet A and Jet A1, reveals that the kinematic viscosity of all the feedstocks meets both these standards. However, fatty acid-based fuel properties could not satisfy the international aviation fuel standards for D, HHV, and freezing points. Further experimental work is recommended, including improvements in the processing and modification of biofuel produced from second-generation feedstocks. It is recommended that a comprehensive action plan is required to facilitate the introduction of sustainable biofuel from non-edible sources for the aviation industry, such as the adjustment of the current jet fuel standards. [ABSTRACT FROM AUTHOR]

Bio-electrochemical systems, such as microbial fuel cells (MFCs), serve as greener alternatives to conventional fuel energy. Despite the burgeoning review works on MFCs, comprehensive discussions are lacking on MFC designs and applications. This review paper provides insights into MFC applications, substrates used in MFC and the various design, technological, and chemical factors affecting MFC performance. MFCs have demonstrated efficacy in wastewater treatment of at least 50% and up to 98%. MFCs have been reported to produce ∼30 W/m2 electricity and ∼1 m3/d of biohydrogen, depending on the design and feedstock. Electricity generation rates of up to 5.04 mW/m−2–3.6 mW/m−2, 75–513 mW/m−2, and 135.4 mW/m−2 have been found for SCMFCs, double chamber MFCs, and stacked MFCs with the highest being produced by the single/hybrid single-chamber type using microalgae. Hybrid MFCs may emerge as financially promising technologies worth investigating due to their low operational costs, integrating low-cost proton exchange membranes such as PVA-Nafion-borosilicate, and electrodes made of natural materials, carbon, metal, and ceramic. MFCs are mostly used in laboratories due to their low power output and the difficulties in assessing the economic feasibility of the technology. The MFCs can generate incomes of as much as $2,498.77 × 10−2/(W/m2) annually through wastewater treatment and energy generation alone. The field application of MFC technology is also narrow due to its microbiological, electrochemical, and technological limitations, exacerbated by the gap in knowledge between laboratory and commercial-scale applications. Further research into novel and economically feasible electrode and membrane materials, the improvement of electrogenicity of the microbes used, and the potential of hybrid MFCs will provide opportunities to launch MFCs from the laboratory to the commercial-scale as a bid to improve the global energy security in an eco-friendly way. [Display omitted] • MFCs, serve as greener alternatives to conventional fuel energy. • 30 days of MFC operation can yield up to 10.38 mA current and remove 94.3% of COD by bacterial strains. • MFCs are capable of generating ∼30 W/m2 of electricity and ∼1 m3/d of biohydrogen. • MFCs have a wastewater treatment efficacy of at least 50% and up to 98%. • MFC technology is narrow due to its microbiological, electrochemical, and technological limitations. [ABSTRACT FROM AUTHOR]

• Physical and chemical pretreatment show great effectiveness but need huge energy. • Biological pretreatment can address most challenges but with long incubation times. • Hybrid technologies gain popularity and improve the chemical yield. • Pretreatment of lignocellulosic biomass account for 40% of total production costs. • Optimization of process parameters need for techno-economically feasible. As the world attempts to transition from fossil fuels, lignocellulosic biomass (LCB) serves as a promising alternative due to its high abundance. Hydrolysing LCB can generate various bioproducts, such as biofuels and value-added chemicals. However, the presence of lignin inhibits the solubilization of LCBs, presenting a major techno-economic challenge in the biorefinery concept. Therefore, this paper addresses the gaps left by most of the recent review works that fail to comprehensively review different pretreatment methods and the full scope of applications of LCBs, and do not incorporate techno-economic considerations of the technologies, the latter being the greatest bottleneck in the commercialization of the processes. The literature review revealed that while many of the physical and chemical pretreatment methods exhibit great effectiveness, they have a huge dependence on energy, chemicals, water, and/or specialized equipment, and produce harmful waste and inhibitory compounds. The pretreatment of lignocellulosic biomass can account for 40% of total production costs. Biological pretreatment can address these challenges but is limited by long incubation times. For instance, the bacterial pretreatment can noticeably reduce sawdust cellulose, hemicelluloses, and lignin contents by 35.8%, 37.1%, and 46.2%, respectively. Recently, integrated/coupling (hybrid) methods, such as chemical-assisted liquid hot water/steam and microwave or ultrasound-assisted alkaline pretreatment, have been gaining popularity due to their potential to improve chemical yield, but at the expense of the high cost of operation. To make pretreatment processes more techno-economically feasible, there is a need for process integration and the standardization and optimization of process parameters. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new method is demonstrated for selecting microalgae strain for jetfuel production. • 17 microalgae strains were evaluated against all relevant jet fuel standards. • Chlorella sp. NT8a was the most suitable but could not meet some jet fuel standards. • Further biofuel modification is needed to satisfy all jet fuel standards. This study develops and applies the PROMETHEE-GAIA method as a new tool to select microalgae strains for aviation fuel production. Assessment involves 19 criteria with equal weighting in three aspects, namely biomass production, lipid quality, and fatty acid methylester properties. Here, the method is demonstrated for evaluating 17 candidate microalgae strains. Chlorella sp. NT8a is assessed as the most suitable strain for aviation fuel production. The results also show that unmodified biofuel from the most suitable strain could not meet all jet fuel standards. In particular, microalgae-based fuel could not satisfy the required density, heating value and freezing points of the international jet fuel standards. These results highlight the need for a broad action plan including improvement in the processing or modification of biofuel produced from microalgae and revision of the current jet fuel standards to facilitate the introduction of microalgae-based biofuel for the aviation industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biorefinery concept for sustainable processing of microalgae biomass has been discussed. • Reactor technologies for cultivating microalgae has been reviewed. • Factors affecting the microalgae culture system has been reviewed. • Different technologies to convert microalgae into biofuel and value-added products have been presented. • The utilisation of a biorefinery concept can make the valorisation of microalgae economically viable. Microalgal biomass has been proved to be a sustainable source for biofuels including bio-oil, biodiesel, bioethanol, biomethane, etc. One of the collateral benefits of integrating the use of microalgal technologies in the industry is microalgae's ability to capture carbon dioxide during the application and biomass production process and consequently reducing carbon dioxide emissions. Although microalgae are a feasible source of biofuel, industrial microalgae applications face energy and cost challenges. To overcome these challenges, researchers have been interested in applying the bio-refinery approach to extract the important components encapsulated in microalgae. This review discusses the key steps of microalgae-based biorefinery including cultivation and harvesting, cell disruption, biofuel and value-added compound extraction along with the detailed technologies associated with each step of biorefinery. This review found that suitable microalgae species are selected based on their carbohydrate, lipid and protein contents and selecting the suitable species are crucial for high-quality biofuel and value-added products production. Microalgae species contain carbohydrates, proteins and lipids in the range of 8% to 69.7%, 5% to 74% and 7% to 65% respectively which proved their ability to be used as a source of value-added commodities in multiple industries including agriculture, animal husbandry, medicine, culinary, and cosmetics. This review suggests that lipid and value-added products from microalgae can be made more economically viable by integrating upstream and downstream processes. Therefore, a systematically integrated genome sequencing and process-scale engineering approach for improving the extraction of lipids and co-products is critical in the development of future microalgal biorefineries. [ABSTRACT FROM AUTHOR]

The utilization of microalgae in treating wastewater has been an emerging topic focussed on finding an economically sustainable and environmentally friendly approach to treating wastewater. Over the last several years, different types of con microalgae and bacteria consortia have been experimented with to explore their potential in effectively treating wastewater from different sources. The basic features considered while determining efficiency is their capacity to remove nutrients including nitrogen (N) and phosphorus (P) and heavy metals like arsenic (As), lead (Pb), and copper (Cu). This paper reviews the efficiency of microalgae as an approach to treating wastewater from different sources and compares conventional and microalgae-based treatment systems. The paper also discusses the characteristics of wastewater, conventional methods of wastewater treatment that have been used so far, and the technological mechanisms for removing nutrients and heavy metals from contaminated water. Microalgae can successfully eliminate the suspended nutrients and have been reported to successfully remove N, P, and heavy metals by up to 99.6 %, 100 %, and 13%–100 % from different types of wastewater. However, although a microalgae-based wastewater treatment system offers some benefits, it also presents some challenges as outlined in the last section of this paper. Performance in eliminating nutrients from wastewater is affected by different parameters such as temperature, biomass productivity, osmotic ability, pH, O 2 concentration. Therefore, the conducting of pilot-scale studies and exploration of the complexities of contaminants under complex environmental conditions is recommended. • Utilization of Microalgae is an environment-friendly method to treat the wastewater. • Microalgae removes the suspended nutrients and polluting compounds from wastewater. • The efficiency of microalgae-based wastewater treatment technology is presented. • Challenges of using microalgae in wastewater treatment is discussed. [ABSTRACT FROM AUTHOR]

The majority of research in the carbon-based nanomaterials (CNMs) field has concentrated on the classification and synthesis of CNMs, with relatively few studies focusing on CNMs' roles in photocatalytic hydrogen production. CNMs have proven their potential as an effective addition to the appeal of photocatalytic hydrogen evolution because of their superior chemical and physical properties. This paper explores the recent advancements in photocatalytic hydrogen (H 2) production utilizing CNMs. As evidenced in the literature, carbon quantum dot (CQD)-sensitized titanium dioxide (TiO 2) can demonstrate to have a photocatalytic hydrogen generation activity of 472 mol g−1 h−1 and 1458 mol g−1 h−1 without and with loading metal co-catalyst (Pt). The optimum catalyst, 0.4 CQD/CdS, contributes to the highest H 2 production rate of 309 mmol g−1 h−1 (apparent quantum yield of 32.6%), which is 1.5 times greater than that of bare CdS. This would significantly accelerate the hydrogen production process. There are still challenges to reaching maximum photocatalytic hydrogen production, including low hydrogen storage. The overall price of hydrogen produced via photocatalysis is also higher because of the energy needed to store the hydrogen. Even though the problem is not directly related to the usage of CNMs, this restriction generates uncertainty and limits commercial investment. Given the rising demand for energy and the trend toward green power, it is recommended that extensive industrial uses of photocatalytic hydrogen produced by employing CNMs be investigated for better and more sustainable energy frameworks. • Recent advances in photocatalytic H 2 production are investigated utilizing CNMs. • The optimum catalyst, 0.4 CQD/CdS can produce the highest H 2 at 309 mmol g−1 h−1. • CQD-sensitized TiO 2 can generate 1458 mol g−1 h−1 photocatalytic hydrogen with Pt. • Photocatalytic H 2 production using CNMs should be investigated for industrial use. [ABSTRACT FROM AUTHOR]

[Display omitted] • Continuous algae growth could be achieved by MPR using sludge centrate. • Nutrient loading had indiscernible impact on biomass growth. • Nutrient removal efficiency increased as nutrient loading rate decreased. • Nutrient removal efficiency increased as HRT increased. • Backwashing completely restored water flux decline caused by microalgae deposition. This study aims to evaluate the performance of C. vulgaris microalgae to simultaneously recover nutrients from sludge centrate and produce biomass in a membrane photobioreactor (MPR). Microalgae growth and nutrient removal were evaluated at two different nutrient loading rates (sludge centrate). The results show that C. vulgaris microalgae could thrive in sludge centrate. Nutrient loading has an indiscernible impact on biomass growth and a notable impact on nutrient removal efficiency. Nutrient removal increased as the nutrient loading rate decreased and hydraulic retention time increased. There was no membrane fouling observed in the MPR and the membrane water flux was fully restored by backwashing using only water. However, the membrane permeability varies with the hydraulic retention time (HRT) and biomass concentration in the reactor. Longer HRT offers higher permeability. Therefore, it is recommended to operate the MPR system in lower HRT to improve the membrane resistance and energy consumption. [ABSTRACT FROM AUTHOR]

• Seaweed, a marine biomass, identified as an underutilized renewable resource with potential for biofuel. • Seaweed conversion demonstrated to aid carbon sequestration, nutrient recycling, and waste management. • Marine biomass utilization seen as promising yet intricate pathway to global sustainability. • Future research proposed to involve rigorous feasibility analysis and interdisciplinary collaboration. Amid the global energy crisis and environmental concerns, marine biomass, specifically seaweed, serves as a type of marine biomass with potential for conversion into sustainable energy in alignment with the United Nations Sustainable Development Goals (UN SDGs). There is a pressing need to shift towards sustainable energy resources, and seaweed emerges as an underexplored renewable energy source. A thorough analysis of past, current, and emerging trends in seaweed biomass conversion takes place. Thermochemical processes and other conversion methods are detailed, evaluating their efficiencies, limitations, and advancements. Due to its rapid growth and rich carbohydrate content, seaweed proves to be a prime candidate for bioenergy production. Converting seaweed aids in carbon capture, nutrient recycling, and waste management, which positively impacts several UN SDGs. Challenges, including technological barriers, economic feasibility, and environmental concerns related to large-scale seaweed farming and energy conversion, are present. The potential of marine biomass, especially seaweed, in sustainable energy production becomes evident, highlighting its intricate nature. Advancements in conversion technologies, thorough life-cycle assessments, and stringent sustainability protocols are recommended. Future efforts should concentrate on in-depth feasibility studies and foster inter-disciplinary collaborations to address the multifaceted challenges of this energy transition, aligning it with the UN's sustainability aspirations. [ABSTRACT FROM AUTHOR]

• Implications for efficient pyrolysis processes using municipal green waste. • Potential for increased process economics and sustainability. • Optimal parameters boost bio-oil yield (52.8%) and energy efficiency (72.9%). • Holding time enhances bio-oil and syngas yields, while decreases biochar yields. • Smaller feedstock particle size leads to higher energy and exergy efficiency. This study aims to determine how different operating conditions for a fast pyrolysis process employing municipal green waste (MGW) in an auger reactor affect product yields, overall energy efficiency, and total exergy efficiency. In this study, a range of pyrolysis conditions, including temperatures from 400 to 600 °C (in 50 °C increments), holding times from 1 to 5 min (in 1-minute increments), and feedstock particle sizes from 2 to 10 mm (in 2-mm increments) were used. MGW and pyrolysis products were characterised using separate pieces of equipment and in accordance with applicable ASTM standards. The results demonstrate that a yield of 52.8% for bio-oil and a yield of 23.7% for syngas can be achieved at temperatures of 500 and 600 °C, respectively. At 400 °C, the biochar production was highest as 21.5%. Bio-oil and syngas yields improved with holding times, whereas biochar yields declined. At a feedstock particle size of 2 mm, the overall energy efficiency was at its maximum (72.9%), while the total exergy efficiency was also at its highest (68.4%). As feedstock particle size increased, overall energy efficiency and total exergy efficiency dropped. In conclusion, this study provides valuable insights into the effects of different operating parameters on the pyrolysis process using MGW, which can be used to optimize the process and increase its efficiency. [ABSTRACT FROM AUTHOR]

Discharging microplastics into the environment with treated wastewater is becoming a major concern around the world. Wastewater treatment plants (WWTPs) release microplastics into terrestrial and aquatic habitats, mostly from textile, laundry, and cosmetic industries. Despite extensive research on microplastics in the environment, their removal, and WWTP management strategies, highlighting their environmental effects, little is known about microplastics' fate and behaviour during various treatment processes. Microplastics interact with treatment technologies differently due to their diverse physical and chemical characteristics, resulting in varying removal efficiency. Microplastics removed from WWTPs may accumulate in soil and harm terrestrial ecosystems. Few studies have examined the cost, energy use, and trade-offs of large-scale implementation of modern treatment methods for the removal of microplastics. To safeguard aquatic and terrestrial habitats from microplastics' contamination, focused and efficient management techniques must bridge these knowledge gaps. This review summarizes microplastic detection, collection, removal and management strategies. A compilation of treatment process studies on microplastics' removal efficiency and their destiny and transit paths shows recent improvement. Bioremediation, membrane bioreactor (MBR), electrocoagulation, sol-gel technique, flotation, enhanced filtering, and AOPs are evaluated for microplastic removal. The fate and behaviour of microplastics in WWTPs suggest they may be secondary suppliers of microplastics to receiving ecosystems. Innovative microplastic removal strategies and technologies such as nanoparticles, microorganism-based remediation, and tertiary treatment raise issues. These new WWTP technologies are examined for feasibility, limitations, and implementation issues. Pretreatment modifies microplastic size, adsorption potential, and surface morphology to remove microplastics from WWTPs. Membrane bioreactors (MBR) can remove 99.9% of microplastics more efficiently than other approaches. MBR systems require membrane cleaning and fouling control, which raises operational and capital costs. To reduce MPs, plastic alternatives and strict controls, including microplastic waste transformation, should be prioritized. Microplastics must be controlled through monitoring policy execution and awareness. [Display omitted] • Discharging microplastics (MPs) via industrial wastewater is a pressing global issue. • MPs harm soil and ecosystems requiring a search for effective removal technologies. • Membrane bioreactor (MBR) showed effectiveness in removing more than 99.9 % of MPs. • Despite being expensive, bioremediation is demonstrated as an effective approach. • Plastic alternatives and stringent control approaches should be prioritized. [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]

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]

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]

[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]

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]

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]