A Cyanobacterial Sidestream Nutrient Removal Process and Its Life Cycle Implications

This study proposes a novel integration of a municipal wastewatertreatment facility (WWTF) with a cyanobacterial nutrient removal process for sidestream wastewatertreatment. A life cycle assessment (LCA) approach was used to determine the effectiveness and environmental performances of the integrated system. The LCA is populated by models of wastewater process engineering, material balance, cyanobacterial growth, and kinetics of anaerobic digestion. The cyanobacteriagrowth model incorporates chlorophyll synthesis, nitrogen uptake, photosynthesis, centrateinhibition, and competition for nitrogen between cyanobacteriaand nitrifiers. Modeling results are validated against experiments with Synechocystissp. PCC6803 grown in sludge centrate. With a maximum specific growth rate of 1.09 day−1, the nitrogen removal rate of the proposed WWTF would be increased by 15% when compared to the baseline wastewatertreatment facility with a biological nutrient removal process. Incorporating the cyanobacterial nutrient removal process as the sidestream wastewatertreatment of a conventional activated sludgeprocess reduces the total nitrogen concentrations discharged from the WWTF from 25.9 to 15.2 mg 1−1. Methane yield was found to be increased by 4% of the baseline value when cyanobacterial biomass was co-digested with the activated sludge. Life cycle energy use and greenhouse gas emissions were found to be reduced by 8% and 17%, respectively, relative to a baseline wastewatertreatment facility. Overall, a cyanobacteria-based sidestream municipal wastewatertreatment process could be an effective and environmentally sustainable biological nutrient removal process in the future addressing the water-energy-food nexus.