Bioflocculation of microalgae and bacteria combined with flue gas to improve sewage treatment

Although microalgae are promising for a cradle-to-cradle design approach of sewage treatment, their application is hampered by high harvesting costs and low C:N ratios of sewage. Therefore, the potential of microalgal bacterial flocs (MaB-flocs) was investigated for the secondary treatment of sewage supplemented with different flue gas flow rates (FGFRs) from a coal power plant. Effluent (N, P, turbidity and pH) and off gas discharge levels (NOx, SOx) met the European discharge limits with a hydraulic retention time of only 0.67 days and an FGFR of 0.6 L h−1 (0.0025 vvm). This FGFR provided sufficient carbon and resulted in removal efficiencies of 48 ± 7% CO2, 87 ± 5% NOx and 99 ± 1% SO2. MaB-flocs settled fast reaching up to a density of 19 g VSS L−1. High biomass productivities (0.18 g L−1 day−1) were obtained under a low light intensity. This successful reactor performance indicates the large potential for the industrial application of MaB-flocs for flue gas sparged sewage treatment.