Comparison of three flocculants for heavy cyanobacterial bloom mitigation and subsequent environmental impact

Cyanobacteria can accumulate as a heavy biomass on the leeward side of large eutrophic lakes,posing a potential threat to public health.The mitigating capacity of three flocculants and their potential impacts on the major environmental features of water and sediments was evaluated.Results indicate that polyaluminum chloride(PAC)and ferric chloride(FeCl)are efficient flocculants that can rapidly mitigate cyanobacterial blooms with chlorophyll-a concentrations higher tnan 1500 ug/L within 15 min.In comparison,cationic starch with chitosan could only treat cyanobacterial blooms in chlorophyll-a concentrations of less than 200μg/L.The addition of FeClcaused a decline in the pH value,while dissolved oxygen in the water column dropped to 2 mg/L during cationic starch with chitosan treatment for a high cyanobacterial biomass group.Thus,a combination of flocculants and oxygenators should be considered when treating high-concentration cyanobacterial blooms for emergency purposes.Additionally,the cell lysis of cyanobacteria caused by cationic starch with chitosan can result in an increase in total dissolved phosphorus and total dissolved nitrogen.Furthermore,the high accumlation of nutrients in sediments after the settling of cyanobacteria can cause high internal phosphorus pollution.The increase in the total organic carbon of the sediments can threaten lake restoration achieved by planting submerged macrophytes.