Study of Microalgae-bacteria Co-cultures for Wastewater Treatment under Batch and Fed-batch Conditions

The sustainable treatment of wastewater under increasingly stringent discharge limits and energy constraints remains a major challenge in environmental engineering. In this context, microalgae–bacteria co-culture systems have emerged as a promising alternative to conventional activated sludge processes, as they exploit synergistic interactions to simultaneously remove organic carbon and nutrients while reducing aeration demand. In this study, mixed microalgae–bacteria co-cultures were investigated under batch and fed-batch conditions to assess process stability, biomass productivity, and treatment performance. A Chlorella vulgaris strain was co-cultivated with aerobic activated sludge in laboratory-scale flasks using a mixture of simulated wastewater and bold basal medium, under controlled illumination and aeration. The effect of different initial microalgae-to-sludge ratios on system performance was evaluated. Fed-batch operation significantly enhanced biomass accumulation, reaching concentrations up to 1.7 g/L, whereas batch cultures showed a decline in biomass, particularly at lower microalgae-to-sludge ratios. In terms of treatment performance, mixed co-cultures achieved higher removal efficiencies compared to microalgae monocultures, with TOC and TN removal reaching 80–85% and 45–60%, respectively, under fed-batch conditions. Overall, the results demonstrate that fed-batch microalgae–bacteria systems improve both biomass production and wastewater treatment efficiency, highlighting their potential as sustainable, low-energy treatment solutions.