Carbon and nutrient removal from centrates and domestic wastewater using algal–bacterial biofilm bioreactors

The mechanisms of carbon and nutrient removal in an open algal–bacterial biofilm reactor and an open bacterial biofilm reactor were comparatively evaluated during the treatment of centrates and domestic wastewater. Comparable carbon removals (>80%) were recorded in both bioreactors, despite the algal–bacterial biofilm supported twice higher nutrient removals than the bacterial biofilm. The main carbon and nitrogen removal mechanisms in the algal–bacterial photobioreactor were assimilation into algal biomass and stripping, while stripping accounted for most carbon and nitrogen removal in the bacterial biofilm. Phosphorus was removed by assimilation into algal–bacterial biomass while no effective phosphorous removal was observed in the bacterial biofilm. Carbon, nitrogen and phosphorus removals of 91 ± 3%, 70 ± 8% and 85 ± 9%, respectively, were recorded in the algal–bacterial bioreactor at 10 d of hydraulic retention time when treating domestic wastewater. However, the high water footprint recorded (0.5–6.7 L m−2 d−1) could eventually compromise the environmental sustainability of this microalgae-based technology.