The Migration And Transformation Of Cyanobacterial Cells During The FeCl₃ Coagulation Process

In recent years, eutrophication and cyanobacterial blooms ocuured frequently, threating the safety of drinking water. The major reason why the cyanobacterial blooms have negative effects on drinking water quality is due to the damage of algae cells would release the toxic intracellular metabolites which influence the taste and odor of drinking water even threating the health of human and animal. Microcystis aeruginos(M. aeruginosa), as one of the most common harmful algal bloom species in our country, would release microcystins (MCs) with high acute toxicity have positive correlation with the human cancer, cause the attention of the whole world. In the drinking water treatment process, the coagulation is key process for algae remove. After coagulation, the algae cells accumulate into floes as sludge. There is limited research on the migration and transformation of mass algae cells in the drinking water treatment process during the cyanobacterial blooms outbreak period, especially cells damage and toxins release in the drinking water treatment process. Thus, it is imperative to clarify the mechanism of cells remove and damage to supply theoretical guidance to algae containing drinking water treatment.Simulation an algal bloom in high algae laden period, using the ferric chloride as coagulant to investigate the M. aeruginosa cell integrity and toxins release during the FeCl3 coagulation-sedimentation process, the properties of algae containing iron drinking water sludge and the toxin release during the sludge dewatering process. During the research, the following results were obtained:(1) According to this study, the optimum coagulation conditions for the effective removal of cyanobacterial cells (M aeruginosa FACHB-905) in blooms are coagulant dosage 50 mg/L (FeCl3), rapid mixing for 0.5 min at 250 rpm and slow mixing for 30 min at 20 rpm.(2) In the FeCl3 coagulation process, most of cells were removed intactly, the variety of coagulant dosage and mechanical actions did not cause any damage to cell integrity.(3) In the flocs storage processes, the formation of flocs brought a protection for cyanobacterial cells and the majority of M. aeruginosa cells retained cell integrity up to 10 d. A number of MCs, tyrosine/tryptophan protein-like substances, tyrosine/tryptophan-like substances, as well as humic and fulvic acid like substances released into the surrounding water. But the MCs could totally degraded by the bacteria in the water.(5) In the sludge dewatering process, the optimal conditions are the centrifugal speed of 4000 rpm and centrifugal time of 16 min. The centrifugation process did not damage the algae cells. And the algae containing sludge under different storage times was centrifuged, the concentration of MCs and extracellular polymeric substance in supernatants before and after centrifugation showed no obvious changes.