Effects of Ferric Salt of Different Forms on Phosphorus Removal

This paper has studied phosphorus removal effects of ferric chloride (ionic state), polyferric chloride (polymer state) and ferric hydroxide (gel state) on the effluent of a municipal sewage treatment plant. The total phosphorus (TP) in the effluent was 1.74 mg·L-1. Results showed that ferric chloride was the best phosphorus remover among the three forms of ferric salt coagulants. With a dosage of 40 mg·L-1, its phosphorus removal rate could reach 90% and TP in the treated wastewater was reduced to less than 0.17 mg·L-1. After the treatment, the effluent quality met the first level A criteria in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002). At the same doage of 40 mg·L-1, the phosphorus removal rates of polyferric chloride and ferric hydroxide were 62% and 59%, respectively, lower than the rate of ferric chloride.