No abstract

The increasing usage of organic nitrogen-rich wastewater- or algal-impacted waters, and chloramines for secondary disinfection, raises concerns regarding the formation of haloacetonitriles, haloacetamides and other nitrogenous disinfection byproducts (N-DBPs). Previous research obtained contradictory results regarding the relative importance of chlorination or chloramination for promoting these byproducts, but applied chlorine and chloramines at different doses and exposure periods. Additionally, mechanistic work, mostly using model precursors, suggested that haloacetonitrile and haloacetamide formation should be correlated because hydrolysis of haloacetonitriles forms haloacetamides. In this work, the formation of dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) were compared across a range of chlorine and chloramine exposures for drinking waters, wastewater effluents, algal extracellular polymeric substances (EPS), NOM isolates and model precursors. While chlorination favored formation of DCAN over DCAcAm, chloramination nearly always formed more DCAcAm than DCAN, suggesting the existence of haloacetamide formation pathways that are independent of the hydrolysis of haloacetonitriles. Experiments with asparagine as a model precursor also suggested DCAcAm formation without a DCAN intermediate. Application of (15)N-labeled monochloramine indicated initial rapid formation of both DCAN and DCAcAm by pathways where the nitrogen originated from organic nitrogen precursors. However, slower formation occurred by pathways involving chloramine incorporation into organic precursors. While wastewater effluents and algal EPS tended to be more potent precursors for DCAN during chlorination, humic materials were more potent precursors for DCAcAm during chlorination and for both DCAN and DCAcAm during chloramination. These results suggest that, rather than considering haloacetamides as haloacetonitrile hydrolysis products, they should be treated as a separate N-DBP class associated with chloramination. While use of impaired waters may promote DCAN formation during chlorination, use of chloramines may promote haloacetamide formation for a wider array of waters.

Influent and effluent quality of municipal wastewater treatment plants play significant roles in selecting the appropriate treatment technologies and influencing the ecology of receiving water bodies. The quality of reclaimed water sources for water reuse can also be determined based on the influent wastewater and treated effluent information. Comprehensive analyses based on statistical data collected from 3340 Chinese municipal wastewater treatment plants were performed so as to better understand the effects of influent and effluent wastewater quality on the treatment performance, environmental concerns and resources utilization. Provincial characteristics of wastewater quality both in quantity and quality were identified, providing valuable information for the proposal of targeted management strategies in pollution control, water reuse and resources recovery. The influents of municipal wastewater treatment plants in north China had high wastewater pollutant loadings, but the effluent was of high quality due to the wide implementation of water reuse strategies in northern water scarcity regions. The potentials for organic and nutrient recovery from the influents were brought forward based on the mass balance. The importance of wastewater as a resource, and the adoption of advanced treatment and resources utilization in the long-term should be highlighted for sustainable water management.