Effects of operating conditions and water quality on THMs and HAAs formation during wastewater chlorination disinfection

Disinfection is the last barrier of the wastewater reclamation process to protect safe ecosystem and human health. Due to the relatively complex and high content of precursors, disinfection by-products(DBPs) problem occurs all through the practice of wastewater disinfection, but its related research is limited. A study was conducted on the effects of the operating conditions and water quality on the formation of trihalomethanes(THMs) and haloacetic acids(HAAs), the two major categories of DBPs produced during the municipal wastewater chlorination disinfection process. The experimental results indicate that chlorine dosage is the most significant factor. The concentration of THMs and HAAs at chlorine dosage of 40 mg/L is 30 and 70 times that at 5 mg/L, respectively. THMs formation is not sensitive to reaction time and temperature changes, while the HAAs reach a peak after 2 hours, then they decrease with extended time and elevated temperature. The most of THMs and the least of HAAs are detected at a near neutral condition, in other words, these two groups of compounds respond to pH variations almost oppositely. Ammonia greatly promotes the formation of HAAs and inhibits the formation of THMs. Bromide enhances the formation of THMs and HAAs, specifically, the chlorine-substituted compounds decrease and the bromide-substituted counterparts increase significantly. The effects of reaction time, temperature, pH and ammonia on THMs and HAAs formation during wastewater chlorination are completely different from those of drinking and surface water disinfection. Therefore, these corresponding measures should be taken to control the formation of DBPs effectively