Comparison of Fe-based and Al-based coagulants in the removal of organic and disinfection by-product precursors

Abstract

Surface water is renowned for its natural organic matter, constituting approximately 45% of total dissolved organic carbon (DOC) which can be removed in water treatment plants. However, residual DOC in water can react with chlorine to form several carcinogenic disinfectant by-products (DBPs). This study aimed to examine the molecular weight of organic fractions dissolved in three different water sources that act as precursors to the formation of DBPs species. The coagulants used were Al- and Fe-based, frequently used in water treatment plants to remove organic fractions. Characterization of DOC in source water served as the first step in determining the performance of both coagulants in terms of organic properties. The results showed that the selected surface waters had similar DOC characteristics, including biopolymers, humic substances, building blocks, and a low molecular weight. These fractions contributed to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs). The Fe-based coagulant was more effective than the Al-based coagulant in removing all organic fractions and reducing THMs compared to HAAs. Furthermore, one-way ANOVA analysis showed a significant difference in the average removal of organic fractions and DBP species between the Fe-based and Al-based coagulants. The Fe-based coagulant showed higher efficiency in removing biopolymers, dibromochloromethane, and chlorodibromoacetic acid than the Al-based coagulant. In contrast, the Al-based coagulant had better performance in reducing dibromo HAA and tribromo HAA. Both coagulants had no significant difference in extracting other organic fractions or DBPs species.