Screening of the heterotrophic microalgae strain for the reclamation of acid producing wastewater

For the sustainable development of the environment, to reduce the high cost and low productivity of microalgae biofuel, nine microalgae strains were screened to study the growh and nutrient removal properties under heterotrophic culture by using the waste carbon source of volatile fatty acids (VFAs). Chlorella sorokiniana (C.sorokiniana) was selected as the best strain with the highest biomass concentration of 0.77 g L^-1, specific growth rate of 0.25 d^-1, biomass productivity of 91.43 mg L^-1 d^-1, total nitrogen removal efficiency of 95.96% and total phosphorus removal efficiency of 93.42%. To study the utilization potential of acid-producing wastewater by heterotrophic microalgae, actual acid-producing wastewater was recycled three times for the utilization of C.sorokiniana. After the three utilization cultivation, the removal rates of COD, total nitrogen, ammonia nitrogen, and total phosphorus were 74.44%, 88.05%, 79.08%, and 82.69%, respectively. The total utilization rates of acetic acid, propionic acid, and butyric acid were 58.99%, 70.54%, and 81.52%, respectively. In addition, the highest lipid content of 39.15% and protein content of 42.43% achieved at the third cultivation. After the first cultivation, the composition and diversity of the microbial community structure changed dramatically, with Protebacteria, Bacteroidota, Hydrogenophaga, and Algoriphagus becoming enriched. These results showed a promising way of coupling wastewater treatment with biomass production for long-term sustainability of microalgae lipid production.