Integration of algal production in WWTP sludge line

The integration of a photobioreactor for algal culture in the process scheme of WWTPs could have positive effects on mass and energy balances. The algal biomass could grow on N rich liquids, such as centrates from sludge dewatering, improving N removal and reducing the overall energy consumption, andthen undergo anaerobic digestion generating biogas. The preliminary balance shows thatthe energy cost of the activated sludge process could be reduced by 21%. Expected drawbacks are an increase in the land request and in the soluble N in the AD, thatshould be considered for its possible inhibitory effect on the methanogenesis. To validate computation and optimize a scale‐up, a pilot plant research was started, whose first results are in agreement with the previously obtained lab‐scale results. N removal was 73% (monthly average), specific growth rate 0.07 d‐1 and algal biomass concentration in the photobioreactor effluent 2.03 g SS/L (max 4.7 g SS/L at 10 days HRT).