Removal of fluoride from drinking water by a membrane coagulation reactor (MCR)

This paper studied the removal of fluoride from drinking water by a membrane coagulation reactor, and aluminium sulfate was used as the major chemical. In a jar test, the optimum pH value for removal of fluoride was found in the range from 6.0 to 6.7. In the laboratory-scale test, when proper dosages of aluminum sulfate and sodium hydroxide were added to the reactor, the concentrations of fluoride were reduced from 4.0 mg/L in raw water to less than 1.0 mg/L in finished water, and the concentrations of residual aluminum in finished water was no more than 0.05 mg/L. The dominant particle sizes of aluminum hydroxide in the mixed liquor were larger than 1 μm. The small particles whose sizes ranged from 0.2 μm to 0.4 μm were less, but they played an important role in the membrane fouling. The volume ratio of treated water to discharged sludge was 350, but it increased to 744 after the sludge was concentrated and dried at normal temperature for 41 days.