Influence of type and dose of coagulants on effectiveness of PAH removal in coagulation water treatment

Abstract

This study evaluated the influence of the type and dose of coagulants on the removal of 16 polycyclic aromatic hydrocarbons (PAHs) in the coagulation process. The effects of coagulant type and dose in reducing water turbidity, colour, and the total content of organic compounds were also assessed. The surface water samples had the turbidity of 9.3–11.2 NTU and colour of 25–35 mg/L. The content of organic compounds determined with total organic carbon (TOC) was 9.2–12.5 mg/L. For the coagulation process, pre-hydrolyzed polyaluminium chloride (PACl) coagulants with basicity values of 41%, 65%, and 85% were used. This shows that water purification performance increased as the basicity of the coagulant increased. When the coagulant with the highest basicity and a dose of 3 mg Al per litre was used, a removal efficiency of 83% in the concentration of benzo(a)pyrene was achieved, and efficiencies for the remaining 15 PAHs ranged from 80% to 91%. These values were 4%–9% higher than those achieved using other coagulants. The removal efficiencies of turbidity, colour, and TOC were 80%, 60%, and 35%, respectively. The water purification performance, including PAH removal, was improved with the increased coagulant dose. Increasing the coagulant dose had more pronounced effects on PAH removal than on the reduction of turbidity and TOC.