Recent Advances in Disinfection By-Products

Abstract

Haloacetamides (HAcAms), an emerging class of nitrogen-based disinfection by-products (N-DBPs), have been frequently identified in drinking waters. However, there is a limited understanding on the performance of different treatment technologies in the control of HAcAms. The objective of this study was to evaluate the potential of traditional and advanced treatment technologies, including three pre-treatment processes (i.e., powdered activated carbon [PAC] adsorption, KMnO4 oxidation, and biological contact oxidation [BCO]), two combined conventional treatment methods (i.e. coagulation - inclined plate sedimentation [IPS]-filtration, and coagulation-dissolved air flotation [DAF]-filtration), and an advanced processes (i.e. integrated ozone and biological activated carbon [O3-BAC] treatment), for removing the precursors of HAcAms while minimizing the formation of other typical N-DBPs in water. Among the three pre-treatment processes, PAC adsorption could effectively remove the precursors of chloroform (CF) (42.7%), dichloroacetonitrile (DCAN) (28.6%), dichloroacetamide (DCAcAm) (27.2%) and trichloronitromethane (TCNM) (35.7%), advantageous over KMnO4 oxidation and/or BCO process. In contrast, the removal efficiency of dissolved organic carbon (DOC) by the BCO process (76.5%) was superior to that by PAC adsorption (69.9%) and KMnO4 oxidation (61.4%). However, BCO increased the dissolved organic nitrogen (DON) concentration, thereby leading to the formation of more N-DBPs during the subsequent chlorination. Soluble microbial products including numerous DON compounds produced as a result of the BCO treatment were observed to play an essential role in the DCAcAm formation. Between the conventional processes, the removal of algae, DON, DOC and UV254 by the coagulation-DAF-filtration was better than the coagulation-IPS-filtration. On the average, the former achieved the removal of 53% DOC, 53% DON and 31% UV254, while the latter only removed 47% DOC, 31% DON and 27% UV254. Additionally, the coagulation-IPS-filtration removed less low molecular weight organic molecules than the coagulation-DAF-filtration process. Consequently, the concentrations of CF, DCAcAm and DCAN formed from the coagulation-DAF-filtration treated water reached 13, 1.5 and 4.7 ?g/L during chlorination, respectively, which were lower than those from chlorination of the coagulation-IPS-filtration treated water (17 ?g/L CF, 2.9 ?g/L DCAcAm and 6.3 ?g/L DCAN). Among the advanced treatment processes, O3-BAC significantly improved the removal of turbidity, DOC, UV254, NH+ 4-N, and DON by 98?99%, 58?72%, 31?53%, 16?93% and 35?74%, respectively, and enhanced the removal efficiency of the DBP precursors. However, this option was almost ineffective in removing TCNM and DCAcAm precursors. Ozonation alone could not substantially reduce the DCAcAm formation, and increased the TCNM formation potential (FP). However, it chemically altered the molecular structures of the precursors and increased the biodegradability of N-containing organic compounds. Consequently, the subsequent BAC filtration dramatically reduced the formation of the both TCNM and DCAcAm, thus highlighting a synergistic effect of O3 and BAC. Additionally, O3-BAC was effective at controlling the formation of total organic halogen, which is recognized as an indicator of the formation of unidentified DBPs. Of note, more N-DBP precursors entered into the post-BAC water without pre-ozonation, leading to the formation of more N-DBPs during chlorination, compared with a control group with the pre-ozonation was continuously operated. Moreover, higher DBP FP was observed in the effluent of the BAC filter without pre-ozonation than the FP in the influent of the BAC filter. Therefore, while the intermittent operation of pre-ozonation may have cost and other operational benefits (bromate control), these may be outweighed against the increased N-DBP formation and potential N-DBP associated health risks.Haloacetamides (HAcAms), an emerging class of nitrogen-based disinfection by-products (N-DBPs), have been frequently identified in drinking waters. However, there is a limited understanding on the performance of different treatment technologies in the control of HAcAms. The objective of this study was to evaluate the potential of traditional and advanced treatment technologies, including three pre-treatment processes (i.e., powdered activated carbon [PAC] adsorption, KMnO4 oxidation, and biological contact oxidation [BCO]), two combined conventional treatment methods (i.e. coagulation - inclined plate sedimentation [IPS]-filtration, and coagulation-dissolved air flotation [DAF]-filtration), and an advanced processes (i.e. integrated ozone and biological activated carbon [O3-BAC] treatment), for removing the precursors of HAcAms while minimizing the formation of other typical N-DBPs in water. Among the three pre-treatment processes, PAC adsorption could effectively remove the precursors of chloroform (CF) (42.7%), dichloroacetonitrile (DCAN) (28.6%), dichloroacetamide (DCAcAm) (27.2%) and trichloronitromethane (TCNM) (35.7%), advantageous over KMnO4 oxidation and/or BCO process. In contrast, the removal efficiency of dissolved organic carbon (DOC) by the BCO process (76.5%) was superior to that by PAC adsorption (69.9%) and KMnO4 oxidation (61.4%). However, BCO increased the dissolved organic nitrogen (DON) concentration, thereby leading to the formation of more N-DBPs during the subsequent chlorination. Soluble microbial products including numerous DON compounds produced as a result of the BCO treatment were observed to play an essential role in the DCAcAm formation. Between the conventional processes, the removal of algae, DON, DOC and UV254 by the coagulation-DAF-filtration was better than the coagulation-IPS-filtration. On the average, the former achieved the removal of 53% DOC, 53% DON and 31% UV254, while the latter only removed 47% DOC, 31% DON and 27% UV254. Additionally, the coagulation-IPS-filtration removed less low molecular weight organic molecules than the coagulation-DAF-filtration process. Consequently, the concentrations of CF, DCAcAm and DCAN formed from the coagulation-DAF-filtration treated water reached 13, 1.5 and 4.7 ?g/L during chlorination, respectively, which were lower than those from chlorination of the coagulation-IPS-filtration treated water (17 ?g/L CF, 2.9 ?g/L DCAcAm and 6.3 ?g/L DCAN). Among the advanced treatment processes, O3-BAC significantly improved the removal of turbidity, DOC, UV254, NH+ 4-N, and DON by 98?99%, 58?72%, 31?53%, 16?93% and 35?74%, respectively, and enhanced the removal efficiency of the DBP precursors. However, this option was almost ineffective in removing TCNM and DCAcAm precursors. Ozonation alone could not substantially reduce the DCAcAm formation, and increased the TCNM formation potential (FP). However, it chemically altered the molecular structures of the precursors and increased the biodegradability of N-containing organic compounds. Consequently, the subsequent BAC filtration dramatically reduced the formation of the both TCNM and DCAcAm, thus highlighting a synergistic effect of O3 and BAC. Additionally, O3-BAC was effective at controlling the formation of total organic halogen, which is recognized as an indicator of the formation of unidentified DBPs. Of note, more N-DBP precursors entered into the post-BAC water without pre-ozonation, leading to the formation of more N-DBPs during chlorination, compared with a control group with the pre-ozonation was continuously operated. Moreover, higher DBP FP was observed in the effluent of the BAC filter without pre-ozonation than the FP in the influent of the BAC filter. Therefore, while the intermittent operation of pre-ozonation may have cost and other operational benefits (bromate control), these may be outweighed against the increased N-DBP formation and potential N-DBP associated health risks.