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Comparison of four flocculants for removing algae in Dianchi Lake

Ma, Xiaoxue, Wang, Yuanan, Feng, Shuqing, Wang, Shoubing
Environmental earth sciences 2015 v.74 no.5 pp. 3795-3804
flocculants, lakes, turbidity, water temperature, pH, ferric sulfate, Microcystis aeruginosa, surface water, chlorophyll, aluminum chloride, China
Cyanobacterial blooms are a significant concern in Dianchi Lake and other freshwater bodies in China. Effects of dose, duration, pH, and colony size on algae and turbidity removal in artificial water containing Microcystis aeruginosa were investigated for polymeric ferric sulfate (PFS), polymeric aluminum chloride (PAC), Al₂(SO₄)₃·18H₂O, and Fe₂(SO₄)₃. We also investigated the performance of flocculants for removal of chlorophyll a (Chl-a) and turbidity from algae-laden water at different doses and water temperatures. In artificial water experiment (initial cell density: 1.9 × 10⁶ cells/mL; initial Chl-a: 268.00 μg/L) the most effective doses of PFS and PAC were 40 and 50 mg/L, respectively; for Al₂(SO₄)₃·18H₂O and Fe₂(SO₄)₃, it was 50–60 mg/L. During the 24-h experiment, PFS most efficiently removed Microcystis and turbidity at the dose of 50 mg/L. PAC, Al₂(SO₄)₃·18H₂O, and Fe₂(SO₄)₃ were most effective at pH 6–8. For PFS, the optimum pH range was 5–8. Removal rate of PFS, PAC, and Fe₂(SO₄)₃ of large colonies was significantly better than for small colonies. In algae-laden water experiment (initial cell density: 6.47 × 10⁷ cell/mL; initial Chl-a: 11,641.12 μg/L), the most effective doses of PFS, PAC, Al₂(SO₄)₃·18H₂O, and Fe₂(SO₄)₃ were 125, 125, 125, and 250 mg/L, respectively. For water temperatures of 20–30 °C, PFS and PAC were most effective at the dose of 125 mg/L. Considering removal effectiveness, safety, and economy, PFS is recommended for clarifying algae-laden water in Dianchi Lake.