Simultaneous formation and biodegradation of HAAs in slow sand filters: Effects of residual chlorine in filter influent

Haloacetic acids (HAAs) are one of the major groups of chlorinated disinfection by-products in drinking water. This study explored the formation, speciation, and aerobic biodegradation of HAAs under different influent chlorine doses in batch reactor and simulated slow sand filtration (SSF) columns. The results showed that 90% of HAAs were biodegraded when no residual chlorine was present in SSF influents, and the bromine-HAAs were more biodegradable than chlorine-HAAs. In the batch systems, presence of 0.1 mg/L of free chlorine decreased both the heterotrophic plate counts and HAAs removal rates. The HAAs concentration increased predominantly when the chlorine concentration was higher than 0.5 mg/L. In the simulated labscale SSF columns, the 60 cm depth of SSF column provided the highest HAA percentage removal. When the influent chlorine concentration was higher than 0.5 mg/L, HAA formation was observed and particularly for the tri-haloacetic acids. The results of HAAs analysis in different bed depth showed that the middle and bottom sections of SSF also play an important role for HAA degradation.