Mixotrophic growth regime of novel strain Scenedesmus sp. DDVG I in municipal wastewater for concomitant bioremediation and valorization of biomass

Availability of cost-effective nutrients for the commercial cultivation of microalgae is one of the major challenges. The present study investigated the feasibility of primary municipal wastewater (PMWW) collected from a local wastewater treatment plant in Minnesota, USA as an alternative to fresh-water microalgae growth media towards high-value bioenergy feedstock production. The novel strain Scenedesmus sp. DDVG I was cultivated in the PMWW under heterotrophic and mixotrophic modes in 250 mL Erlenmeyer flasks. The optimized cultivation mode was further scaled up to the 3-L bubbled bioreactor. The study confirmed the wastewater as a potential growth medium while Scenedesmus sp. DDVG I showed superior biomass productivity (0.069 g/L d), lipid yield (22.5%), and FAME content (22.04% in dry cell weight) over 10 days in the mixotrophic mode. The biomass also showed high essential amino acid content (159.8 mg/g DCW). The corresponding values for bioremediation efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) by Scenedesmus sp. were 75.6% and 99.8% respectively. Meanwhile, ammonia nitrogen (NH3–N) and total phosphorus (TP) were removed at up to 100% removal efficiencies. Analyses of fatty acid profile and different parameters that were required for biodiesel characterization revealed the high-quality nature of the Scenedesmus-derived oil. Overall, the study concluded effective bioremediation of municipal wastewater by Scenedesmus sp. DDVG I with the recovery of valuable resources from the biomass.