| Algal blooms of potable water sources pose a great challenge for water treatment process. Algae can cause changes in turbidity, dissolved oxygen, pH and taste and odour, as well as production of toxins, formation of disinfection by-products. These variations can negatively impact water quality and threaten the drinking water security. Therefore, advanced technology for more efficient and safer treatment of algae-containing water is timely needed.Due to the small proportion, high Zeta potential and high stability of algal cells in water, which make algal cells difficult to remove with traditional drinking water treatment processes. Algal cells carried negative charge, therefore cationic polyelectrolyte coagulants such as polyaluminium chloride (PAC) can be used to remove the algal cells by surface charge neutralization, adsorption bridging and enmeshment. The algae are expected to be removed efficiently by combined with clay mineral.Microcystis aeruginosa (M.A.) was selected to explore the removal performance of enhanced coagulation by combining PAC with diatomite. The effects of PAC dosage, diatomite dosage, initial solution pH, concentration of humic acid, surfactant, anion and heavy metal on the removal of algae and turbidity were investigated. The algae removal property was analyzed through the floc characteristic. The zeta potential of the reaction system in coagulation processes was determined. The followings are the main research contents and conclusions. The followings are the main conclusions:(1) The M.A. in the water could be removed effectively by PAC. And the best removal effect was achieved at pH7.00-8.00or so. The algal removal efficiency was increased with the addition of KMnO4for pre-oxidation. However, when the dosage of KMnO4was higher than1.0mg/L or the interaction time with algal cells longer than15minutes, the water quality became deterioration. More than0.5mg/L of HA could significantly affect the Zeta potential and inhibit the flocculation process seriously. Cation surfactant CTMAB could help raised algal removal rate in a certain concentration. The co-existing anions H2PO4-, Cl-and high concentration of SO42-inhibited PAC coagulation to remove M.A. and affected the flocs formed quickly. However, anion surfactant SDS, co-existing anions NO3-, heavy metals C and Pb2+had little side effects on removal of algae. (2) Clay minerals could promote the removal efficiency of M.A. as coagulant aids. The addition of diatomite is advantageous due to great improvement of algal removal and reduction of the PAC dose required for satisfactory treatment of algae. It could mostly save about50%of PAC dose. It found that30mg/L diatomite combined6.0mg/L PAC was a quite cost-efficient composite ratio. The Chl-a removal rate was increased to96.06%and the residual turbidity was decreased to0.89NTU by enhanced coagulation of diatomite combining PAC.(3) The influencing factors, such as pH value, HA, CTMAB and co-existing anions SO42-、H2PO4-、Cl-, of M.A. removal by enhanced coagulation combining diatomite and PAC were investigated. It showed that the enhanced coagulation is less sensitive to these influencing factors; the addition of diatomite could mitigate the negative effect to some extent. It reflects its excellent performance. |
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