Comparison of wastewater coagulation efficiency of pre-polymerised zirconium and traditional aluminium coagulants

Abstract

This study proposes pre-polymerised zirconium salts with different basicities as alternative coagulants for domestic wastewater treatment. We compared the efficiency of pre-polymerised zirconium coagulants and commercial aluminium coagulants (pre-polymerised polyaluminium chloride and aluminium sulphate) in simultaneously removing turbidity (TU), total suspended solids (TSS), and phosphates (OP) from synthetic wastewater. Increasing the basicity of the coagulants resulted in an increase in the removal rate of TSS and TU and a decrease in the removal rate of OP from wastewater. The zirconium coagulants demonstrated a higher efficiency of TSS, TU, and OP removal compared to the aluminium coagulants with comparable basicities. The maximum rates of TSS, TU, and OP removal by the zirconium and aluminium coagulants were 92.5% and 91.0%, 97.1% and 96.4%, and 97.6% and 93%, respectively. The maximum degree of binding of phosphate ions by metal ions was observed as 0.862 with non-pre-polymerised zirconium coagulant Zrp/ZrT, which was almost two times higher than with non-pre-polymerised aluminium coagulant Alp/AlT, calculated as 0.434. The analysis of thermodynamic data of the main reactions in the coagulation process indicated that the higher OP removal efficiency for zirconium coagulants was due to the greater reactivity of ions and hydroxo-complexes of zirconium with phosphate ions compared to aluminium hydroxo-complexes. Thus, zirconium coagulants are effective for domestic wastewater treatment. These findings highlight the potential of zirconium coagulants in the efficient treatment of domestic wastewater.