Feasibility study of biogas upgrading coupled with nutrient removal from anaerobic effluents using microalgae-based processes

Abstract

The present research was conducted to simultaneously optimize biogas upgrading and carbon and nutrient removal from centrates in a 180-L high-rate algal pond interconnected to an external CO2 absorption unit. Different biogas and centrate supply strategies were assessed to increase biomass lipid content. Results showed 99 % CO2 removal efficiencies from simulated biogas at liquid recirculation rates in the absorption column of 9.9 m3 m−2 h−1, concomitant with nitrogen and phosphorus removal efficiencies of 100 and 82 %, respectively, using a 1:70 diluted centrate at a hydraulic retention time of 7 days. The lipid content of the harvested algal–bacterial biomass remained low (2.9–11.2 %) regardless of the operational conditions, with no particular trend over time. The good settling characteristics of the algal–bacterial flocs resulted in harvesting efficiencies over 95 %, which represents a cost-effective alternative for algal biomass reutilization compared to conventional physical–chemical techniques. Finally, high microalgae biodiversity was found regardless of the operational conditions.