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Algal biorefinery is rising as a prominent solution to economically fulfill the escalating global requirement for nutrition, feed, fuel, and medicines. In recent years, scientific productiveness associated with microalgae-based studies has elaborated in multiplied aspects, while translation to the commercial level continues to be missing. The present microalgal biorefinery has a challenge in long-term viability due to escalated market price of algal-mediated biofuels and bioproducts. Advancements are required in a few aspects like improvement in algae processing, energy investment, and cost analysis of microalgae biorefinery. Therefore, it is essential to recognize the modern work by understanding the knowledge gaps and hotspots driving business scale up. The microalgae biorefinery integrated with energy-based products, bioactive and green compounds, focusing on a circular bioeconomy, is urgently needed. A detailed investigation of techno-economic analysis (TEA) and life cycle assessment (LCA) is important to increase the market value of algal products. This review discusses the valorization of algal biomass for the value-added application that holds a sustainable approach and cost-competitive algal biorefinery. The current industries, policies, technology transfer trends, challenges, and future economic outlook are discussed. This study is an overview through scientometric investigation attempt to describe the research development contributing to this rising field.

Sugarcane spent wash generates waste at a large scale that impacts the environment, hence the classic waste reuse technology needs to be implemented. An integrated approach of spent wash and microalgae cultivation to produce biodiesel has gained momentum in recent times. However, the microalgae technology lacks the functional utilization of de-oiled microalgae biomass (DOB). This study proposed the development of a microalgae-based advanced process for distillery spent wash treatment, biomass recovery for biodiesel and utilizing algal residue as a step towards waste management. A novel microalga Coelastrella sp KJ-04 grown in distillery spent wash represented with high biomass (4.61 g/L) and lipid production (3.6 g/L). The significant reduction in Chemical Oxygen Demand (COD, 49.3%), Total Nitrogen (TN, 49.7%), Total Phosphorous (TP, 21.8%), Total Organic Carbon (TOC, 40.2%), Total Sulphur (S, 37.2%) and Potassium (K, 42.5%) were achieved in spent wash. The extracted lipids of Coelastrella sp KJ-04 were converted to Fatty acid methyl ester (FAME) and examined by Gas chromatography -mass spectrometry (GC-MS) to observe the suitability for biodiesel prospect. The de-oiled biomass (DOB) was utilized for the synthesis of Cellulose nanofibers (CNF), purified and estimated with a diameter ranging between 20 and 27 nm. The crystalline structure and functional group of CNF were analyzed by X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FTIR). The unprecedented work demonstrated the microalgae biorefinery approach for spent wash remediation, biodiesel synthesis and simultaneous production of biodegradable CNF from algal residue to support waste-free technology. In future, CNF can be reinforced into material for concrete as it could be the smart alternative to replace synthetic cement plastics.

High cultivation cost and low lipid yield are framed as a major bottleneck for the production of microalgae biodiesel. Hence, we first and foremost highlight a trophic mode transition, coupled with a combinatorial effect of organic carbon, nitrogen and light (C/N/L) on an isolated microalga Chlorococcum sp. SVF in a one pot tri-phasic intermittent feeding system by developing a lab scale Raceway tank (40L). Hitherto, waste molasses syrup without hydrolysis is unexplored in algal bioenergy arena. The direct utilisation capability of sucrose, served by waste unhydrolysed molasses syrup (WUMS), effectively modulates the intrinsic biochemical and physiological characteristics towards microalgae biomass and lipid assimilation. Response surface methodology—central composite design (RSM-CCD) tool has been employed to observe the cumulative impact of light irradiation and nutrient sources (carbon and nitrogen) on cellular stoichiometric analysis. Experimental results exhibit a potentially achievable biomass (18.88 g L(−1)) and lipid accumulation (80.34%) under the light intensity of 75.5 µmol m(−2) s(−1) with stepwise light attenuation strategy. Characterisation of fatty acid methyl esters (FAME) reveals the dominance of oleic acid (32.72%) and palmitic acid methyl esters (32.49%) in mixotrophic condition, which are considered as the upmost indicators of quality biodiesel. The biofuel properties were obtained in acquiescence with American and European standard. These findings are therefore a way forward towards the effective growth of Chlorococcum sp. SVF in sucrose rich inexpensive industrial waste stream that positively influences the lipid yield for large scale sustainable biodiesel production. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02823-7.

Increasing energy demand and limited fossil fuel sources have developed the interest of researchers toward biofuel, as it is regarded as the promising approach for continuous source of energy. Microalgae are considered as a desirable feedstock for biodiesel production due to its inherent capacity to synthesize large amount of oil. The key steps in microalgae biofuel synthesis are cell culture, cell recovery, lipid removal, and fatty acid methyl ester (FAME) production. The high cost of biodiesel production is the major bottleneck in the microalga biofuel technology. Among the four steps, harvesting and lipid extraction count more than 50% of the total cost of biodiesel production. Recently, nanoparticle engineering-based methods have been applied as a powerful tool in algae system to overcome the technical problems. Another problem is the mass cultivation of microalgae, which carries major importance because massive biomass is required for viable production of biodiesel. Closed cultivation system (photobioreactor) and open cultivation system (open raceway ponds) are emerged as a solution for mass cultivation of microalgae, but there is a need to understand the design and principle of cultivation system. In this chapter, a pragmatic and critical discussion is tried to put forward with the ongoing research on microalgae with future trends.

Microalgae have been considered as a potential feedstock for biodiesel production, since its cultivation uses less land than other traditional oil crops and has a higher growth rate. A great challenge is a choice of an effective approach for microalgae biomass recovery and lipid extraction, since the scheduling of these practices are critical and require an economical and environment friendly route. Flocculation has evolved as an efficient and economic approach for harvesting microalgae biomass. This review discussed the recent progress of chemical flocculants including organic and inorganic, bio-flocculants and nanomaterials-based processes for biomass recovery. In addition, the present review describes modifications made in conventional methods for lipid extraction. Several pre-treatment methods such as mechanical, chemical integrated with various solvents and nanoparticles are vastly investigated for lipid extraction. Use of green solvents namely, ionic liquids, supercritical fluids and switchable solvents are also reviewed, with the focus on cleaner biofuel synthesis. Furthermore, the article discusses policies implemented for the advancement in biofuel production, major challenges and considers future directions in microalgae harvesting and lipid recovery processes. This is the first study that extensively compares the recent approaches for biomass and lipid recovery. The present work intended to serve a long-term adaptation of the innovative techniques for copious economic benefit. Thus, this review emphasizes on advanced techniques that influence the microalgae biomass separation and cellular disruption for proficient lipid removal from microalgae, which deliberates towards the development of sustainable microalgae biofuel and heighten the bio-economy strategy.

Present investigation highlighted the capability of microalgae cultivation in sewage wastewater integrated with nanomaterial, addressing wastewater treatment and consequent improvement in lipid for biodiesel application. Herein, the isolated microalga Chlorosarcinopsis sp. MAS04, was cultured in primary treated wastewater (PTWW) and secondary treated wastewater (STWW) incorporated with Zinc Oxide nanoparticles (ZnO- NPs). The characterizations of ZnO-NPs were performed by analytical technique and cytotoxicity assay of microalga against nanoparticles (NPs) was carried out prior to the experiment. The nutrient reduction rate of Chemical Oxygen Demand (COD), Total Nitrogen (TN), Total Phosphorous (TP), and Total Organic Carbon (TOC) by microalga was found higher in PTWW as compared to the STWW when incorporated with the ZnO-NPs. Maximum biomass of 3.43 g/L and 2.14 g/L along with 1.9 and 1.5 folds increase in cellular lipid was recorded in the presence of PTWW and STWW respectively as compared to control (BG-11). The cellular lipids were converted to fatty acid methyl esters (FAMEs) by the process of transesterification and analyzed by Gas Chromatography-Mass Spectrometry (GC–MS). The cells developed in PTWW and STWW incorporated with ZnO-NPs were recorded with a higher amount of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) with controlled polyunsaturated fatty acids (PUFA). Biofuel properties were found in accordance with American and European guidelines. The present report suggested that the Chlorosarcinopsis sp. MAS04 -ZnO NPs association is capable of better nutrient removal from sewage wastewater. Therefore, the nano-bio hybrid opens a new paradigm for efficient wastewater treatment and consequent quality biodiesel production.