A Comparative Study of Pre-hydrolysed Coagulants and Alum in Surface Water Clarification

Abstract

The aim of the present study was to evaluate the performance of two pre-hydrolyzed aluminum coagulants (PAX-XL6 and PAX-XL8) in comparison with aluminum sulfate (alum) for surface water clarification. Jar-test experiments were conducted with coagulant doses ranging from 0 to 15 mg Al/L to determine the optimal dose. Results demonstrated that both the coagulant type and dosage strongly influenced clarification performance. The pre-hydrolyzed coagulants achieved the bests results, with maximum color removal efficiencies of 91.8% and turbidity removals of 89.3% (PAX-XL6) and 84.6% (PAX-XL8) at an optimal coagulant dose of 4 mg Al/L. In contrast, alum showed the lowest clarification performance, achieving maximum color removal of 87.5% and turbidity removal of 80.3%. At 4 mg Al/L, the pre-hydrolyzed coagulants met WHO drinking water guidelines for color and turbidity, whereas alum failed to meet color standard. Beyond 8 mg Al/L, all coagulants exhibited a decrease in clarification efficiency due to colloid restabilization. Regarding water chemistry, PAX-XL6 and PAX-XL8 induced only moderate reductions in pH and alkalinity, whereas alum caused significant acidification and a marked decrease in alkalinity. None of the coagulants affected water hardness. Overall, the pre-hydrolyzed coagulants demonstrated superior clarification performance and reduced chemical impact, confirming their potential as efficient and sustainable alternatives to alum for surface water treatment.