Models for predicting carbonaceous disinfection by-products formation in drinking water treatment plants: a case study of South Korea.

Chlorination in a drinking water treatment plant is the critical process for controlling harmful pathogens. However, the reaction of chlorine with organic matter forms undesirable, harmful, and halogenated disinfection by-products. Carbonaceous disinfection by-products, such as trihalomethanes (THMs) and haloacetic acids (HAAs), are genotoxic or carcinogenic and are reported at high concentration in drinking water. This study is aimed at developing a mathematical model for predicting concentration levels of THMs and HAAs in drinking water treatment plants in South Korea because no previous attempts to do so have been reported for the country. The THMs concentration levels ranged from 29 to 39 µg/L, and those for the HAAs from 6 to 7 µg/L. Multiple regression models, i.e., both linear and nonlinear, for THMs and HAAs were developed to predict their concentration levels in water treatment plants using datasets (January 2015 to December 2016) from three treatment plants located in Seoul, South Korea. The constructed models incorporated principal factors and interactive and higher-order variables. The principal factor variables used were dissolved organic carbon, ultraviolet absorbance, residual chlorine, bromide, contact time, chlorine dose and temperature for treated water, and pH for both raw and treated water at the plant. The linear models for both THMs and HAAs were found to give acceptable fits with measured values from the water treatment plants and predictability values were found to be 0.915 and 0.772, respectively. The models developed were validated with a later dataset (January 2017 to July 2017) from the same water treatment plants. In addition, the models were applied to two different water treatment plants. Application and validation results of the constructed model showed no significant differences between predicted and observed values.

Adsorption of soluble microbial products by sediments.

As major precursors of disinfection by-products (DBPs), soluble microbial products (SMPs) generated by sewage discharge can adversely affect drinking water quality. It is essential to understand the adsorption behaviours of SMPs onto sediments and the effect of DBPs formation. In this study, the adsorption ability of sediments was evaluated by adsorption isotherms with respect to temperature and salinity. Adsorption behaviours were investigated using X-ray photoelectron spectroscopy, electron microscopy analysis, and excitation emission matrix fluorescence analysis. Chlorination was also employed to explore the influence of sediment adsorption on drinking water quality. The results indicated that the maximum adsorption potential of sediments to SMPs was 1.60 mg/g, which involved exothermic processes. SMPs adsorption declined with increasing temperature and salinity, and fulvic acid and protein in SMPs were more readily adsorbed on sediments than was humic acid. Correlation analysis results indicated that adsorption behaviours of sediments to SMPs could significantly reduce the generation potential of DBPs (r = 0.882-0.938, p < 0.01). In addition, the decrease of C-DBPs was considerably greater than that of N-DBPs. These research findings are of importance to assessments of the fate and transport of SMPs in water-sediment systems, as well as the effect of following DBPs formation in the drinking water supply.

Formation characteristics of carbonaceous and nitrogenous disinfection by-products depending on residual organic compounds by CGS and DAF.

Allogenic organic matter (AOM) composed of extracellular and intracellular organic matter (EOM and IOM) is a major precursor of halogenated carbonaceous and nitrogenous disinfection by-products (C-DBPs and N-DBPs) upon chlorination. The EOM and IOM extracted from Microcystis aeruginosa were analyzed based on bulk parameters and organic fractions with different molecular weight by liquid chromatography with organic carbon detection (LC-OCD). It investigated the efficiency of a conventional gravity system (CGS) and dissolved air flotation (DAF) in the removal of organic precursors, together with measurement of the formation of four major trihalomethanes (THMs) and haloacetonitriles (HANs) in treated water upon chlorination. The results showed that EOM accounted for 59% of building blocks and humic substances, whereas for IOM, 54% were low molecular weight (LMW) neutrals. Both CGS and DAF showed 57-59% removal of dissolved organic carbon (DOC) from EOM and IOM. Regarding DON removal, DAF was found to be more effective, i.e., 8% higher than CGS for EOM. Moreover, the removal of LMW acids and neutrals (not easy to remove and are major precursors of DBPs) from EOM and IOM by DAF was higher than from CGS. The amounts of DBPs measured in all the samples treated for interchlorination were much lower than in the samples for prechlorination. Although the precursors of EOM had a higher concentration than in IOM, THMs and HANs were detected for IOM at a higher concentration, which might be attributed to higher amounts of aromatic, aliphatic moisture and protein compounds in the IOM. Comparatively, DAF showed lower THM and HAN values than CGS water, particularly for IOM. Also, DAF showed a sharp decrease in THMs and an insignificant increase in HANs according to time.

[Exposure to disinfection by-products during gestation and newborns' small for gestational age].

Objective: To explore the associations between exposure to chlorination disinfection by-products (CDBPs) during gestation and newborns' small for gestational age (SGA). Methods: During April 2010 to July 2012, a total of 3 903 pregnant women who lived in a district with the same water treatment plant in Wuhan, China were recruited to this perspective study. Information about demographic characteristics of pregnant women and their newborns was collected. The tap water samples were monthly collected for 28 months in 3 different sites, with 84 samples, and 4 kinds of trihalomethanes (THMs)(chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM)) and 2 kinds of chlorohaloacetic acids (HAAs) (trichloroacetic acid (TCAA), dichloroacetic acid (DCAA)) were determined. The pregnant women were divided into 4 groups(Q1 to Q4) by quartile method according to their exposure level of CDBPs. Binary Logistic regression models were used to assess the associations between exposure to CDBPs during gestation and newborns' small for gestational age. Results: The average weight of all the newborns was (3 310.19±389.91) g, of which 169 (4.33%) were SGA. The median concentrations of TCM, BDCM, bromo-THMs, total THMs, TCAA, and DCAA during the whole pregnancy were 18.07, 4.93, 8.51, 26.74, 10.65, and 13.77 µg/L, respectively. Binary Logistic regression analysis showed dose-response relationships between elevated TCM and total THMs during the whole gestation and compared with Q1 group, while there was a increased risk of SGA in Q4 group, and OR(95%CI) was 1.87 (1.01-3.49) , 2.30 (1.22-4.35) , respectively (P for trend equaled to 0.044, 0.015). Compare with Q1 group, there also be positive associations between exposure to TCAA (Q4 group) during first-trimester and the whole gestation and SGA, while OR(95%CI) was 2.16 (1.19-3.91) (P for trend equaled to 0.015). Conclusion: Exposure to CDBPs during gestation might increase the risk of newborns' SGA.

Exposure to disinfection by-products during gestation and newborns' small for gestational age / 中华预防医学杂志

Objective@#To explore the associations between exposure to chlorination disinfection by-products (CDBPs) during gestation and newborns' small for gestational age (SGA).@*Methods@#During April 2010 to July 2012, a total of 3 903 pregnant women who lived in a district with the same water treatment plant in Wuhan, China were recruited to this perspective study. Information about demographic characteristics of pregnant women and their newborns was collected. The tap water samples were monthly collected for 28 months in 3 different sites, with 84 samples, and 4 kinds of trihalomethanes (THMs)(chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM)) and 2 kinds of chlorohaloacetic acids (HAAs) (trichloroacetic acid (TCAA), dichloroacetic acid (DCAA)) were determined. The pregnant women were divided into 4 groups(Q1 to Q4) by quartile method according to their exposure level of CDBPs. Binary Logistic regression models were used to assess the associations between exposure to CDBPs during gestation and newborns' small for gestational age.@*Results@#The average weight of all the newborns was (3 310.19±389.91) g, of which 169 (4.33%) were SGA. The median concentrations of TCM, BDCM, bromo-THMs, total THMs, TCAA, and DCAA during the whole pregnancy were 18.07, 4.93, 8.51, 26.74, 10.65, and 13.77 μg/L, respectively. Binary Logistic regression analysis showed dose-response relationships between elevated TCM and total THMs during the whole gestation and compared with Q1 group, while there was a increased risk of SGA in Q4 group, and OR(95%CI) was 1.87 (1.01-3.49) , 2.30 (1.22-4.35) , respectively (P for trend equaled to 0.044, 0.015). Compare with Q1 group, there also be positive associations between exposure to TCAA (Q4 group) during first-trimester and the whole gestation and SGA, while OR(95%CI) was 2.16 (1.19-3.91) (P for trend equaled to 0.015).@*Conclusion@#Exposure to CDBPs during gestation might increase the risk of newborns' SGA.

Control of aliphatic halogenated DBP precursors with multiple drinking water treatment processes: Formation potential and integrated toxicity.

The comprehensive control efficiency for the formation potentials (FPs) of a range of regulated and unregulated halogenated disinfection by-products (DBPs) (including carbonaceous DBPs (C-DBPs), nitrogenous DBPs (N-DBPs), and iodinated DBPs (I-DBPs)) with the multiple drinking water treatment processes, including pre-ozonation, conventional treatment (coagulation-sedimentation, pre-sand filtration), ozone-biological activated carbon (O3-BAC) advanced treatment, and post-sand filtration, was investigated. The potential toxic risks of DBPs by combing their FPs and toxicity values were also evaluated. The results showed that the multiple drinking water treatment processes had superior performance in removing organic/inorganic precursors and reducing the formation of a range of halogenated DBPs. Therein, ozonation significantly removed bromide and iodide, and thus reduced the formation of brominated and iodinated DBPs. The removal of organic carbon and nitrogen precursors by the conventional treatment processes was substantially improved by O3-BAC advanced treatment, and thus prevented the formation of chlorinated C-DBPs and N-DBPs. However, BAC filtration leads to the increased formation of brominated C-DBPs and N-DBPs due to the increase of bromide/DOC and bromide/DON. After the whole multiple treatment processes, the rank order for integrated toxic risk values caused by these halogenated DBPs was haloacetonitriles (HANs)≫haloacetamides (HAMs)>haloacetic acids (HAAs)>trihalomethanes (THMs)>halonitromethanes (HNMs)≫I-DBPs (I-HAMs and I-THMs). I-DBPs failed to cause high integrated toxic risk because of their very low FPs. The significant higher integrated toxic risk value caused by HANs than other halogenated DBPs cannot be ignored.

Disinfection by-product formation during chlor(am)ination of algal organic matters (AOM) extracted from Microcystis aeruginosa: effect of growth phases, AOM and bromide concentration.

Algae organic matter (AOM), including extracellular organic matter (EOM) and intracellular organic matter (IOM), has caused a series of problems to the water quality, among which formation of disinfection by-products (DBPs) during subsequent chlor(am)ination process was especially serious and concerned. This study characterized physicochemical properties of the EOM and IOM solution extracted from different growth phases of Microcystis aeruginosa and investigated the corresponding formation potential of DBPs during chlor(am)ination process. Besides, the effects of initial concentration of xEOM, IOM, and Br- on the yields of disinfection by-product formation potential were studied. The results indicated that the specific UV absorbance (SUVA254) values of IOM and EOM (1.09 and 2.66 L/mg m) were considerably lower than that of natural organic matter (NOM) (4.79 L/mg m). Fluorescence dates showed the soluble microbial by-product was dominant in both EOM and IOM, and the tryptophan was the main component of AOM. From the excitation-emission matrix figure of EOM and IOM, we found that the content of the high molecular weight protein substance in IOM was higher than EOM. During chlorination of EOM and IOM, the yields of four kinds of DBPs followed the order trichloroethene (TCM) > 1,1-DCP > dichloride acetonitrile (DCAN) > trichloronitromethane (TCNM), while the order was TCM > DCAN > TCNM > 1,1-DCP during chloramination process. The bromine substitution factor (BSF) value increased with the increasing of the concentration of Br-. When the concentration of Br- was 500 µg/L, the BSF values of chlorination EOM and IOM were 51.1 and 68.4%, respectively. As the concentration of Br- increased, the formation of Cl-DBPs was inhibited and the formation of Br-DBPs was promoted. Graphical abstract ᅟ.

The enhanced removal of carbonaceous and nitrogenous disinfection by-product precursors using integrated permanganate oxidation and powdered activated carbon adsorption pretreatment.

Pilot-scale tests were performed to reduce the formation of a range of carbonaceous and nitrogenous disinfection by-products (C-, N-DBPs), by removing or transforming their precursors, with an integrated permanganate oxidation and powdered activated carbon adsorption (PM-PAC) treatment process before conventional water treatment processes (coagulation-sedimentation-filtration, abbreviated as CPs). Compared with the CPs, PM-PAC significantly enhanced the removal of DOC, DON, NH3(+)-N, and algae from 52.9%, 31.6%, 71.3%, and 83.6% to 69.5%, 61.3%, 92.5%, and 97.5%, respectively. PM pre-oxidation alone and PAC pre-adsorption alone did not substantially reduce the formation of dichloroacetonitrile, trichloroacetonitrile, N-nitrosodimethylamine and dichloroacetamide. However, the PM-PAC integrated process significantly reduced the formation of both C-DBPs and N-DBPs by 60-90% for six C-DBPs and 64-93% for six N-DBPs, because PM oxidation chemically altered the molecular structures of nitrogenous organic compounds and increased the adsorption capacity of the DBP precursors, thus highlighting a synergistic effect of PM and PAC. PM-PAC integrated process is a promising drinking water technology for the reduction of a broad spectrum of C-DBPs and N-DBPs.

Terminating pre-ozonation prior to biological activated carbon filtration results in increased formation of nitrogenous disinfection by-products upon subsequent chlorination.

Previous research demonstrated that ozone dosed before biological activated carbon (BAC) filtration reduces the formation of disinfection by-products (DBPs) upon subsequent chlorination. The current work aimed to evaluate the impact of terminating this pre-ozonation on the ability of the BAC to remove the precursors of N-DBPs. More N-DBP precursors passed into the post-BAC water when the pre-ozonation was terminated, resulting in greater formation of N-DBPs when the water was subsequently chlorinated, compared to a parallel BAC filter when the pre-ozonation was run continuously. Moreover, the N-DBP formation potential was significantly increased in the effluent of the BAC filter after terminating pre-ozonation, compared with the influent of the BAC filter (i.e. the effluent from the sand filter). Therefore, while selectively switching pre-ozonation on/off may have cost and other operational benefits for water suppliers, these should be weighed against the increased formation of N-DBPs and potential associated health risks.