[Study on the removal of arsenic from drinking water by coagulants]

The coagulation method for removing arsenic in drinking water from dispersed water supply was tested. The results showed that the remained arsenic [As(V)] in decanted water could be lower than 0.05 mg/L by directly putting 50 mg/L ferric sulfate into water samples without adjusting pH value (pH 7.82) and settling for 12 hours in room temperature while the original As(V) concentration was 1.0 mg/L. The same removal efficacy could be achieved by putting 30 mg/L ferric sulfate or 40 mg/L aluminum sulfate and filtering after 30-40 min settlement. The removal rates were raised with the increased concentration of coagulants in water. The remained As(V) in filtered water could meet the valid health standard of drinking water (< 0.05 mg/L) when the original concentrations of As(V) were 1.0 mg/L and 0.5 mg/L by using 30 mg/L ferric sulfate and aluminum sulfate respectively. Furthermore, ferric sulfate was more efficient than aluminum sulfate at varied of pH value, water temperature, turbidity and hardness of water, etc. Generally, arsenic in coagulated sludge would not release into water again.