Development of optimal poly-alumino-iron sulphate coagulant

An optimal prepolymerized inorganic coagulant, poly-alumino-iron sulphate (PAFS), was developed and examined for drinking water treatment. PAFS is a new type of prehydrolyzed metal-ion coagulant. An investigation of the conditions for preparing PAFS has been conducted using Al₂(SO₄)₃ with Fe₂(SO₄)₃ as primary raw materials. Optimization of the preparation conditions of the PAFS involved variation of the total metal-ion concentration, oxidation temperature, the molar ratio of the oxidant to metal-ion, and the oxidation period. An evaluation of the coagulation performance with two types of test waters showed that selected PAFS coagulants achieved either a greater or similar removal in terms of percentages of color, UV_(254nm) absorbance and dissolved organic carbon in comparison with another polymeric coagulant, polyferric sulphate (PFS). However, both of these (PAFS and PFS) had a superior performance to ferric sulphate (FS) and aluminum sulphate (AS). Of particular significance was that PAFS achieved the lowest residual metal-ion concentrations, Fe and Al, in comparison with PFS, FS, and AS, respectively.