Chlorination is most widely used disinfection method in water and wastewater treatment. This process has demonstrated its effectiveness in protecting the public health. However, chlorine reacts with natural organic matter (NOM) to form disinfection by-products (DBPs). Trihalomethanes (THMs) and haloacetic acids (HAAs) are the most prevalent compounds. Many studies have conducted to investigate the factors such as chlorine dosages, characteristics of NOM, bromide ion concentration in the formation of these DBPs, but there are few investigations on the influence of organic nitrogen compounds. Besides, DBP formation in chlorination of wastewater is unclear but of concern in recent years....[ Read more ]

Chlorination is most widely used disinfection method in water and wastewater treatment. This process has demonstrated its effectiveness in protecting the public health. However, chlorine reacts with natural organic matter (NOM) to form disinfection by-products (DBPs). Trihalomethanes (THMs) and haloacetic acids (HAAs) are the most prevalent compounds. Many studies have conducted to investigate the factors such as chlorine dosages, characteristics of NOM, bromide ion concentration in the formation of these DBPs, but there are few investigations on the influence of organic nitrogen compounds. Besides, DBP formation in chlorination of wastewater is unclear but of concern in recent years.

In this study, breakpoint chlorination of wastewater effluents from different sources was conducted to study the formation of DBPs including THMs and HAAs in wastewater chlorination. Synthetic solutions containing ammonia, humic acid, organic-N compounds, and bromide were chlorinated under different experimental conditions to study the effect of organic-N compounds on the formation of DBPs. Glycine was chosen as the primary model organic-N compound and effects of other model organic-N compounds were also evaluated for comparison. Samples were periodically withdrawn and subjected to analyses for evaluating chlorine residuals and the formation of THMs, HAAs and cyanogen halides (CNXs).

Results of the study showed large variations in the patterns of THMs and HAAs from breakpoint chlorination of different wastewater effluents. However, the formation of THMs and HAAs increased sharply at chlorine dosages above the breakpoint. In chlorination of synthetic solutions, the formation of THMs and HAAs were found to decrease with increasing glycine and ammonia concentrations, but increase with increasing bromide ion concentration. CNXs formation was found to be highly sensitive to free-chlorine-to-glycine ratio and its formation trend was significantly affected by the presence/absence of ammonia. The incorporation of bromine changed the by-product speciation towards the brominated species and enhanced the yields of total THMs, HAAs and CNXs. Different model organic-N compounds exerted different effects on the formation of THMs, HAAs, and CNXs. The variations are likely attributable to the reactivity and the structure of the organic-N compounds.