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Highlights • Coupling aerobic composting exhaust and algae cultivation were proposed. • This process can minimize the CO 2 supplied cost as well as algae can fix CO 2. • Produced biomass is suitable for biofuel production. • This method worked as two-edged solution to mitigating waste & produce biofuel. Abstract Aerobic composting is an effective way to dispose of organic waste. However, considerable carbon is converted into CO 2 and emitted into the atmosphere, which is a waste of the carbon resource and has the potential for the greenhouse gas effect. In this study, an innovative approach coupling aerobic composting exhaust and Spirulina platensis cultivation has been proposed and investigated, resulting in a double-edged solution to mitigating waste and co-generating biomass with a minimal cost of CO 2 supplied in the culture. Experimental results showed that the maximum biomass productivity ranged from 56.61 to 58.38 mg·L−1·day−1 was achieved using aerobic composting exhaust as a carbon source. Moreover, the CO 2 fixation rates of 46.36 mg·L−1·day−1 and 76.81 mg·L−1·day−1 were obtained by S. platensis cultivation. Finally, the chemical composition analysis of S. platensis biomass obtained in an optimum condition showed an abundance of proteins and lipids, thereby indicating its great potential for biofuel industry. [ABSTRACT FROM AUTHOR]

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]

• 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]