Evaluation of waste activated sludge as a potential nutrient source for cultivation of Chlorella sorokiniana

Economical and sustainable microalgal biomass production is crucial for its commercial scale application for energy and other commodities. This work elucidates a novel cultivation strategy where nutrient-rich waste activated sludge (WAS) and final effluent (FE) from a municipal wastewater treatment process is used for microalgal biomass generation. This strategy reduces the use of synthetic nutrients, fertilizers and fresh water. Strategy development included investigation of pre-treatment/extraction methods for effective nutrient release and bacterial load reduction. Evaluation of growth kinetics, photosynthetic performance, nutrient removal efficiencies and biochemical composition of microalgae under mixotrophic (Mixo) and heterotrophic (Hetero) modes of cultivation was performed. Urea supplementation is studied to enhance the biomass productivity. Microalgae cultivation in acid pre-treated WAS + FE with urea supplementation of 1500 mg L-1 showed biomass productivity of 298.75 mg L-1 d(-1). Microalgal biomass grown with WAS + FE using developed strategy showed higher lipid and protein productivities and comparable carbohydrate yields to the synthetic media.