Humic Aacid Removal From Water By Enhanced Coagulation

In this paper, the optimum coagulation conditions on humic acid removal from water by FeCl3 and Al-based coagulants were studied, and chroma and residual aluminium of coagulated water were considered simultaneously. The influences of the main factors, such as coagulant kind and dosage, pH values, cations addition, kaolin addition, temperatures, on coagulation process were discussed. The coagulation behavior and mechanism of coagulants in enhanced coagulation were further studied. The results will provide for the competitive coagulation technology to source water with different quality and source from theory and application.The humic acid removal from water by FeCl3 enhanced coagulation indicates that the removal rate of UV254 and TOC are of great correlation. With a humic acid concerntration of 10 mg/L and pH value of 7.8, the suitable dosage of FeCl3 is 0.39 mmol/L, considering humic acid removal and residual chroma simutaneously. The initional humic acid concentration has no obvious influence on the optimum coagulation pH value, and no chroma pollution is resulted for the coagulated water. Humic acid removal can be enhanced with the existence of turbidity materials under a low humic acid concentration (2.5 mg/L), while there is no insignificant effect under a high humic acid concentration (5,10mg/L). The moderate addition of Ca2+ is able to weaken the influence of a low water temperature for humic acid removal.Polyaluminum PAC-Al30 with a B value of 2.0, 2.2 and 2.4 were prepared by heating and refluxing PAC-Al13. They keep stable in 90 days as coagulants. The results of controlling residual humic acid and residual aluminum in water by Al coagulation show that PAC-Al30 can better control residual humic acid and residual aluminum in water, especially PAC-Al30 with a B value of 2.4, compared with AlCl3 and PAC-Al13. PAC-Al30 and PAC-Al13 have a broader dosage range for efficient coagulation, compared with AlCl3. The moderate addition of Ca2+ benefit humic acid removal by PAC-Al30 (B=2.4) coagulation, and the residual aluminium is lower than 0.1 mg/L. The existence of kaolin is advantageous to humic acid removal by PAC-Al30 (B=2.4) coagulation, which reduce the residual aluminium and do not have significant influence on tubility of coagulated water. Low temperature was disadvantageous to humic acid removal by PAC-Al30 (B=2.4) coagulation.FeCl3 is cheap, and its coagulation effiency to treat the raw water with a low temperature and a low tubility is higher than that of Al-based salts, but it is corrosive and inconvenient to store. With PAC coagulation flocs are formed rapidly, and Al30 is a new active species for coagulation to remove HA from water. The highly polymerized coagulant PAC-Al30 with the dominating species Al30 will possess broad market for its high coagulation efficiency.