Effective flocculation of Microcystis aeruginosa with simultaneous nutrient precipitation from hydrolyzed human urine

Mechanical harvest of massive harmful algal blooms is an effective measure for bloom mitigation. Yet subsequent processing of the resulting water from algae water separation after the harvesting becomes a new problem since individual algal cells or small algal aggregates are still present in the water. Here, we proposed a novel approach for effectively flocculating the cyanobacteria Microcystis aeruginosa with a removal efficiency of 97% in 6 h using hydrolyzed urine. Nitrogen and phosphorus were simultaneously reclaimed through struvite formation. The addition of Mg2+ promoted the flocculation efficiency and nutrient removal as well as the yield of struvite. Ca2+ could enhance the flocculation efficiency by forming calcium phosphate. During the flocculation process, no significant damage in algal cells was observed. This study provides a novel and sustainable potential for subsequent processing of the resulting water after algae water separation with simultaneous nutrient precipitation and reducing nutrient loads to wastewater treatment plants. •Hydrolyzed urine can effectively flocculate algal cells.•Nutrients in urine were removed by struvite precipitation.•Mg2+ addition enhanced the flocculation efficiency and nutrient removal.•High concentration of ammonium is important for effective algal flocculation.