Coupling bioremediation and biorefinery prospects of microalgae for circular economy

The compounding concentration of pollutants in the environment and the drastic decline in fossil fuels reserves perturbed the environmental sustainability. Consequently, the past few decades saw the emergence of researches focussing on the derivation of renewable substitutes for non-renewable energy resources. Microalgae show promise as a feedstock that could efficiently replace or reduce the need of fossil fuels owing to their resilience to adapt in diverse environment and high lipid content. Present comprehensive review offers an in-depth analysis on the various parameters involving the usage of microalgae for wastewater treatment and production of biodiesel along with other value-added products. The critical analysis showed differential responses of microalgae species towards biotic factors which can influence the accumulation of biomolecules. This necessitates a systematic study on the algal biodiversity to determine the optimal growth conditions which determine their economic feasibility in biorefinery, bioremediation, and circular economy. Biomolecules, especially lipid accumulated in microalgae can be extracted, transesterified to produce fatty acid methyl esters, and eventually transformed into biodiesel. In wastewater treatment, algal biomass can reduce Biological and Chemical Oxygen Demand up to the extent of 90%. Succinctly, microalgae also have the ability to sequester major water pollutants such as nitrogen and phosphorus, absorb heavy metals, xenobiotic compounds, and emerging contaminants to ameliorate water quality. Consequently, propagating microalgae in wastewater could couple green approaches like biosorption for wastewater treatment and biodiesel production. This review also showed that the prospects of biorefinery and multiple value-added products from microalgae enhance the economic viability of microalgae to help achieve environmental sustainability, sustainable development goals (SDGs), and energy resilience. [Display omitted] •Microalgae offers sustainable solution to energy scarcity and water pollution.•Coupling microalgae based bioremediation with biorefinery is a sustainable approach.•Coupling addresses economic concerns of biodiesel generation.•Microalgae based biorefinery contributes to UN-SDGs and circular economy.