Performance of CO2 concentrations on nutrient removal and biogas upgrading by integrating microalgal strains cultivation with activated sludge

A CO2 concentration of 45% (v/v) was considered optimum to support CO2 and H2S removals of 74.11%-80.57% and 99.04%-99.42%, respectively. At the CO2 concentration of 45%-55%, the mixed culture containing S. obliquus and C. vulgaris efficiently removed COD (chemical oxygen demand) and TP (total phosphorus), respectively. The mixed culture containing S. obliquus demonstrated high N removal efficiency at CO2 concentration of 45%. Biomass productivity increased at increasing CO2 concentration in a certain range, with a maximum of 0.177 g L−1 d−1 at CO2 concentration of 45% (v/v) for the mixed culture containing S. obliquus, whereas the C, N, and P biomass contents remained constant at 46.73%-52.31%, 7.59%-9.08%, and 0.91%-1.08%, respectively. This study showed the potential of the combination of alga and bacteria to serve as a treatment for nutrient removal and biogas upgrading in algal-bacterial processes.