Dual role of Chlorella sorokiniana and Scenedesmus obliquus for comprehensive wastewater treatment and biomass production for bio-fuels

Abstract

Microalgal treatment of raw sewage presents many complexities, mainly resulting from the inability of the algal species to sustain increased physiological stresses due to variable nutrient levels and high concentrations of organics. Chlorella sorokiniana and Scenedesmus obliquus have been identified to tolerate higher amounts of organic loading and physiological stresses. Nutrient removal, pathogen removal, and lipid accumulation with secondary or tertiary effluents have been demonstrated independently for these organisms. However, their potentials for accomplishing these objectives simultaneously with raw sewage have not been investigated. This study presents comprehensive investigations of applicability of C. sorokiniana and S. obliquus to wastewater treatment without the requirement for any additional treatment. S. obliquus showed greater potential for removing organic carbon (76.13 ± 1.59% COD removal), nutrients (98.54 ± 3.30% N-removal, 97.99 ± 3.59% P-removal) and comparable pathogens removal (99.93 ± 0.12% total coliforms removal, 100% faecal coliform removal) in comparison to C. sorokiniana (69.38 ± 1.81% COD removal, 86.93 ± 3.49% N-removal, 68.24 ± 11.69% P-removal, 99.78 ± 0.12% total coliforms removal, 100% faecal coliform removal) with 15 days of cultivation with filtered raw sewage, but also encountered increased levels of stress (Fv/Fm of 0.48 ± 0.03) which accounted for increased lipid accumulation in the cells (23.26 ± 3.95% w/w) but might also affect their biomass productivity and treatment potential in longer applications. In comparison, C. sorokiniana demonstrated better adaptability to physiological stresses (Fv/Fm of 0.53 ± 0.01) and may be suitable for achieving comprehensive treatment and sufficient lipid accumulation (22.74 ± 3.11% w/w) without compromising these potentials during prolonged applications. These results highlight the importance of selecting algal species with better stress resistance to extend their applicability for comprehensive wastewater treatment and lipid production.