Wastewater-Grown Algal Biomass as Carbon-neutral, Renewable, and Low Water Footprint Feedstock for Clean Energy and Bioplastics

Purpose of Review Growing algae in wastewater offers carbon-neutral biomass production and pollutant removal. However, practical applications of wastewater-grown algal biomass have social acceptability issues in the food and feed industries due to unexpected threats (such as human/animal pathogens and toxins) associated with the wastewater-grown biomass. Therefore, considering the substantial pollutant removal potential of microalgae and the abundance of wastewater as a growth media, alternative bioprocessing routes of the wastewater-grown biomass should be developed. This review highlights some non-food and non-feed applications of wastewater-grown algae biomass. Recent Findings Wastewater-grown algal biomass contains high amounts of carbohydrates, proteins, and lipids depending upon the composition of wastewater and algal species grown. These three significant metabolites are precursors to bioenergy and biomaterial products such as bioethanol, biogas, and bioplastics. Hydrolysis of the wastewater-grown algal biomass can be easily improved to enhance the microbial fermentation yields to produce bioethanol and biobutanol. Fresh algal biomass, residual biomass, or both can be used as feedstocks in anaerobic digestion/co-digestion to produce biogas. Depending upon the selected species, wastewater-grown algal biomass can also produce biopolymers whose productivity depends on growth conditions, wastewater composition, and biopolymer synthesis method. Enzymatic, eco-friendly chemicals and mechanical approaches used to prepare biopolymers from algal biomass should be optimized for higher yields of biopolymers. Summary Although wastewater-grown biomass has acceptability issues, it offers certain environmental benefits, including atmospheric carbon capture, phycoremediation of pollutants, and water recycling. This manuscript highlights the recent progress and emerging trends of wastewater-grown algal biomass as a feedstock with potential applications for fermentation, anaerobic digestion, and bioprocessing to produce clean energy and bioplastics. Graphical Abstract