Okpara dam water contained significant amounts of iron and manganese that could create problems for consumers. This study perfected a deferrization and demanganization technique preceded or followed by oxidation with potassium permanganate. The maximum iron and manganese contents varied from 30 to 50 and 1.5 to 4.5 mg/L respectively. Under the best conditions, simple coagulation-flocculation was allowed to obtain iron removal yields of 18 to 75%. Manganese was eliminated between 8 and 24%. Pre-oxidation with 2.5 mg/L potassium permanganate allowed attaining of about 99% elimination of iron and about 72% of manganese at a pH of 6.5. The treatment plant composed of a clarification stage followed by oxidation with potassium permanganate at pH 8.5 allowed a complete elimination of iron and manganese.
Key words: Surface water, water clarification, chemical coagulant, potassium permanganate, deferrization, demanganization.
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