Effect of C:N ratio on treatment of mixed industrial-domestic wastewater by microalgae-bacteria consortium

In this study, Chlorella vulgaris and aerobic bacteria were co-cultured for the treatment of mixed wastewater with different C:N ratios (5:1, 10:1, 15:1, 20:1, and 25:1). The results showed that the C:N ratio had a significant effect on the growth and treatment efficiency of microorganisms. The low C:N ratio system facilitated the growth of Chlorella, whereas the high C:N ratio system was more beneficial to the growth of aerobic bacteria. As the C:N ratio increased, the chlorophyll content increased and then decreased, and yet the carotenoid content changed in the opposite direction. In all systems, pH gradually increased with incubation time, while dissolved oxygen content first decreased and then increased. The maximum total biomass was obtained from the 15:1 ratio with a value of 0.63 ± 0.02 g/L, where Chlorella and bacteria accounted for 30.68% and 69.32%, respectively. Meanwhile, when treating wastewater with a C:N ratio of 15:1, the microalgal-bacterial consortia system presented the highest removals of COD, NH₃-N, and TP, accounting for 60.89 ± 1.80%, 43.38 ± 1.00%, and 68.55 ± 0.59%, respectively.