Light-induced lipid enhancement in domestic wastewater-grown Desmodesmus sp. for biodiesel production and bioremediation

Abstract

Domestic wastewater treatment using microalgae has emerged as a promising alternative to conventional wastewater treatment technologies, as it simultaneously generates valuable biomass that could be utilized for the production of value-added bioproducts, including biodiesel. In the present study, the locally isolated microalga Desmodesmus sp. UOM-DS01 was cultivated in wastewater collected from a cafeteria of the University of Moratuwa, Sri Lanka, to identify its bioremediation potential, while assessing the feasibility of lipid accumulation under light stress for biodiesel production. Accordingly, 75% of cafeteria wastewater (CWW) and Bold’s Basal Medium supplemented with three times the standard nitrate concentration (3N-BBM) were employed as culture media. Desmodesmus sp. UOM-DS01 cultivated in CWW achieved biomass concentration of 0.65 ± 0.03 g/L, comparable to that obtained in 3N-BBM (0.54 ± 0.02 g/L), while simultaneously reducing freshwater consumption by 79.19%. In addition, the system achieved chemical oxygen demand, total nitrogen and total phosphorus removal efficiencies of 75.83 ± 2.10%, 47.69 ± 3.89% and 38.00 ± 3.93% respectively, demonstrating the capability of Desmodesmus sp. UOM-DS01 for simultaneous bioremediation and biomass production. Light-stressed cultivation (450 μmol photons/m 2 /s) enhanced lipid accumulation from 0.31 ± 0.02 g/L to 0.53 ± 0.01 g/L, while the estimated biodiesel properties of the extracted lipids complied with ASTM D6751-12 and EN standard. Nonetheless, further optimization of cultivation parameters and pilot-scale studies using CWW are required prior to large-scale implementation of simultaneous bioremediation and biodiesel production, for the advancement of sustainable resource recovery and renewable energy production.