Optimizing Algal Productivity and Nitrogen Recovery from Digestates by Adapting Solid Retention Time and Alkalinity

Combining algae and bacteria in High Rate Algal/Bacterial Ponds (HRABP) is an emerging technology for wastewater treatment benefiting from two theoretical advantages: algae produce oxygen for the bacteria therefore reducing the energy need for oxygen supply, while nitrogen and phosphorus can be recovered in the algal biomass. These conjectural advantages have however never been assessed at large scale. Here we take benefit of a long-term validated model of HRABP to simulate and optimize the complex dynamics of this system when treating digestates at large scale. We propose an optimization scheme considering that a separation system can uncouple Hydraulic Retention Time and Solid Retention Time. We show that increasing the influent alkalinity and imposing a lower SRT, while adapting the water depth can boost the process productivity without meeting conditions favourable to N 2 O emission