Investigating unregulated disinfection byproduct reduction efficiencies in drinking waters using zirconium oxychloride, a novel coagulant

Abstract

Natural organic matter (NOM) may be more effectively removed by using a tetra-valent zirconium coagulant rather than using trivalent aluminium and iron. The objective of this research was to evaluate the effectiveness of employing zirconium oxychloride (ZrOCl2) for reducing NOM from natural water before chlorination in order to reduce unregulated disinfection byproducts (U-DBPs) and compare its effectiveness with alum and ferric sulphate. For the experiments, natural raw waters were collected from four sources with varied levels of dissolved organic carbon (DOC), and one type of synthetic water was prepared using river NOM extract. These five raw waters were then studied using bench-scale coagulation-flocculation experiments in a jar-test apparatus with varying doses of coagulant and different levels of pH. The coagulated-flocculated waters were filtered, chlorinated, and then generated U-DBPs: haloacetonitriles, haloketones, and chloropicrin and also regulated DBPs: trihalomethanes and haloacetic acids were measured. The dose-pH domains for high levels of NOM removal were developed for low, medium, and high Specific UV Absorbance (SUVA) raw water, using ZrOCl2. ZrOCl2 outperformed alum and ferric sulphate based on the reduction efficiencies of DBPs, NOM, and turbidity. ZrOCl2 performance was especially high in low SUVA and low DOC water and medium SUVA and medium DOC river water. Compared to alum and ferric sulphate, ZrOCl2 notably improved the reduction efficiencies of unregulated DBPs more than regulated DBPs. The dose-pH domains developed in our study can be used by utilities to identify the optimal dose and pH for coagulation.