Effect of pre-chlorination on the efficiency of iron and manganese removal from surface water by coagulation-flocculation using aluminium sulphate: case of the Okpara dam in the Republic of Benin
Okpara dam water contained significant amounts of iron and manganese that could be problematic for consumers. In this study, we perfected a deferrization and demanganization technique by coagulationflocculationpreceded by chlorination. The maximum iron and manganese concentrations varied from 30 to 50 mg/L and 1.5 to 4.5 mg/L respectively before treatment. Purification yields depended on the conditions of operation. Under the least favourable conditions (coagulation at free pH), the removal yields varied from 10 to 73% for iron and from 2 to 24% for manganese. Under the best conditions (pre-chlorination and coagulation at pH 6.5), we obtained between 50 and 95% elimination for iron and 20 and 45% for manganese. The treatment was therefore little adapted for the removal of manganese
