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(254 nm) 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.