Removal of inorganic nickel and organic compounds from source water by enhanced coagulation

Based on the present technology in the water plant, the removal of humic acid and nickel have been enhanced by adding coagulant aid polyaluminium chloride (PAC) or potassium ferrate (K2FeO4). The results show that its pH and the dosage of coagulant aid are the two main factors that have effect on the removal of nickel and humic acid (expressed as total organic carbon, TOC). Charge neutralization was the dominant mechanism by PAC, thus incorporating the humic acid and nickel into flocs more efficiently, producing settleable flocs of greater density, size and strength. When the dose of PAC was 40 mg/L at optimum pH 10, the removal efficiency of nickel and TOC reached 95% and 58.7%, respectively. The removal mechanism of complexes by K2FeO4 can be explained by both oxidation and coagulation. Percentage removals of 90 and 61 for nickel and TOC, respectively, were achieved by the addition of 20 mg/L K2FeO4 at optimum pH 8. It is concluded that the enhanced coagulation through the addition of PAC and K2FeO4, as coagulant and oxygenant, is more effective and efficient than traditional coagulation for economic treatment of micro-polluted humic acid and nickel containing surface water.