Fate of THMs and HAAs in low TOC surface water

Emerging algal organic matter from simulated on-line chemical cleaning of ultrafiltration membranes treating algae-containing water

Massive reproduction of algae due to the eutrophication of water body poses a new challenge to the water ecosystem. Despite ultrafiltration (UF) acting as an effective method to treat algae-containing waters, on-line chemical cleaning is frequently utilized to sustain the permeability of UF membranes. However, little attention is currently paid on the side-effects of practical on-line chemical cleaning on aqueous environments. Therefore, this work evaluated the generation of algae organic matter triggered by diverse membrane cleaning reagents (i.e., HCl, NaOH, NaClO, SDS and CA), and their subsequent fate in terms of biodegradation and membrane retention. The results indicated that NaOH, HCl and NaClO caused serious damage and lysis of algal cells, leading to the significant release of dissolved organic matter (DOM), while CA and SDS induced negligible DOM release. The occurrence of DOM release was able to cause extra biofouling, thus deteriorating the UF permeability. Furthermore, DOM was characterized in terms of three molecular weight ranges, i.e., high molecular weight (HMW, > 3400 Da), medium molecular weight (MMW, 150-3400 Da), and low molecular weight (LMW, <150 Da). Protein-related substances in the range of HMW and MMW were primarily produced under HCl and NaOH exposures. In contrast, NaClO led to an obvious release of humic-like materials with MMW. During the next round of UF operation, roughly 17 % to 31 % of these released DOM could be removed by via the joint actions of suspended algae biodegradation and fouling layer retention. Nevertheless, roughly 69 % to 83 % of these produced DOM eventually entered into the UF permeate, resulting in the deterioration of permeate quality. Consequently, the detailed mechanisms of DOM generation and subsequent removal by UF were proposed, which re-examined the origins of emerging contaminants in aqueous environment and shed new light on the strategies to ameliorate current practice of on-line membrane chemical cleaning.

New methods based on a genetic algorithm back propagation (GABP) neural network and general regression neural network (GRNN) for predicting the occurrence of trihalomethanes in tap water

Monitoring trihalomethanes (THMs) levels in water supply systems is of great significance in ensuring drinking water safety. However, THMs detection is a time-consuming task. Developing predictive THMs models using parameters that are easier to obtain is an alternative. To date, there is still no application of optimization algorithms and general regression neural networks in predicting disinfection by-products levels. This study was to explore the feasibility of back propagation neural network (BPNN), genetic algorithm back propagation (GABP) neural network and general regression neural network (GRNN) for predicting THMs occurrence in real water supply systems. The results showed that the BPNN models' prediction ability was limited (test r_p = 0.571-0.857, N₂₅ = 61.5 %-91.5 %). Optimized by the genetic algorithm (GA), GABP models were generated and exhibited better prediction performance (test r_p = 0.573 and 0.696-0.863, N₂₅ = 68.2 %-93.6 %). However, GABP models took a lot of time and their prediction performance was unstable. A GRNN was then used to generate simpler neural network models, and the resulting prediction performance was excellent (total trihalomethanes and bromodichloromethane: test r_p = 0.657-0.824, N₂₅ = 81.8 %-100 %). In general, GRNN was the best at predicting THMs concentrations among the three models. However, it is worth noting that the prediction accuracy of bromodichloromethane (BDCM) was not high, which may be due to the absence of key parameters affecting BDCM formation. Accurate predictions of THMs by GRNN with these nine water parameters made THMs monitoring in real water supply systems possible and practical.

Spatio-temporal variability of halogenated disinfection by-products in a large-scale two-source water distribution system with enhanced chlorination

Distributions of halogenated disinfection byproducts (DBPs) in a two-source water distribution system (WDS) with enhanced chlorination were investigated. The WDS was divided into different sub-service areas based on different electrical conductivity of two water sources. Results clearly show that the principal halogenated DBPs were trihalomethanes (THMs) (5.06-82.69 μg/L), varying within the concentration range as 2-5 times as the levels of haloacetic acids (HAAs) (1.41-61.48 μg/L) and haloacetonitriles (HANs) (0.21-15.13 μg/L). Different water sources, treatment trains, and enhanced chlorination within the WDS had significant effects on seasonal and spatial variations of the DBP distributions over water conveyance. THM and HAA formation followed the sequence of summer > autumn > winter > spring. On the other hand, the DBP spatial distributions were visualized using the ArcGIS enabled Inverse distance weighting technique. The superposition of different DBP spatial distributions allowed for the identification of the high-risk THMs and HAAs areas based on the average values of THMs (27.49 μg/L) and HAAs (14.06 μg/L). Beyond the comprehensive analyses of DBP distribution in a municipal WDS, the project proposed and validated an innovative methodology to locate the DBP high-risk areas and to reveal the effects of different factors on DBPs distribution in a two-source WDS.

Ozone/peroxide advanced oxidation in combination with biofiltration for taste and odour control and organics removal

The objective of this pilot-scale study was to investigate the effectiveness of incorporating ozone (O₃) and advanced oxidation (hydrogen peroxide/ozone: H₂O₂/O₃) in combination with biofiltration for taste and odour control, organic carbon removal, and disinfection byproduct (DBP) precursor reduction. Implementation of O₃ and H₂O₂/O₃ with and without biofiltration was investigated at pilot-scale in terms of geosmin, 2-methylisoborneol (MIB), and DBP precursor removal efficiency. Two media types (granular activated carbon and anthracite) were compared in conjunction with investigating the impact of pre-oxidation with O₃ (2 mg/L) and varying H₂O₂/O₃ mass ratios (0.1, 0.2, 0.35, and 0.5 mg/mg). When O₃ preceded biologically active carbon (BAC) or biologically active anthracite, geosmin removals of 80% and 81%, respectively, were observed at 10 °C; this increased to 89% and 90%, respectively, at 16 °C. Optimal MIB removal (67%) was achieved with 0.1 H₂O₂/O₃ (mg/mg) in combination with BAC at 16 °C. In general, geosmin proved to be more amenable to biodegradation than MIB. BAC without pre-oxidation removed 87% geosmin and 85% MIB, at 22 °C. MIB removals decreased to 60% and 46%, respectively at 16 °C and 10 °C. The application of 0.2 H₂O₂/O₃ (mg/mg) prior to BAC provided treatment which effectively removed geosmin and MIB. However, in terms of DBP precursor reduction, there was no beneficial impact of H₂O₂ addition on trihalomethane or haloacetic acid formation potentials.

Estimating and comparing the cancer risks from THMs and low-level arsenic in drinking water based on disability-adjusted life years

To determine the priority hazard in drinking water, disability-adjusted life years (DALYs) method was used to evaluate the disease burden induced by trihalomethanes (THMs) and low-level arsenic through multiple exposure routes based on the two-year sampling from drinking water in Xi'an city, Northwest China. The average concentrations of chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), bromoform (TBM) and arsenic were 12.67 μg/L, 1.42 μg/L, 0.60 μg/L, 0.13 μg/L and 1.00 μg/L, respectively, and the total lifetime cancer risks for all THMs and arsenic were 8.54 × 10^-6 and 4.02 × 10^-5, which were 8.54 and 40.2 times of the negligible risk level (1.00 × 10^-6), respectively. The DALYs estimation showed that the total DALYs lost for all age groups was 32.62 person-year, and the average individual DALYs lost was 4.77 × 10^-6 per person-year (ppy), which was 4.77 times of the reference level (1.00 × 10^-6 ppy). About 72.07% of the total disease burden was due to arsenic, which was considered to be the priority hazard in Xi'an drinking water. The age group of 75-80 years was found to be most vulnerable to the induced cancer risk, and skin cancer had the highest disease burden (2.24 × 10^-6 ppy). Due to the relatively high incidence rates of lung cancer and skin cancer, most DALYs lost for males were 2-4 times to that for females in the same age group. Oral ingestion made the most contribution (88.58%) to the total disease burden, followed by inhalation of THMs (11.30%), whereas dermal absorption showed negligible risk (0.12%). As the first to compare the cancer risks of arsenic and THMs to the public in DALYs in China, this study might be useful for potential strategies of risk control and management of hazardous agents in drinking water.

Disinfection byproduct formation in drinking water sources: A case study of Yuqiao reservoir

This study investigated the potential formation of disinfection byproducts (DBPs) during chlorination and chloramination of 20 water samples collected from different points of Yuqiao reservoir in Tianjin, China. The concentrations of dissolved organic matter and ammonia decreased downstream the reservoir, while the specific UV absorbance (SUVA: the ratio of UV₂₅₄ to dissolved organic carbon) increased [from 0.67 L/(mg*m) upstream to 3.58 L/(mg*m) downstream]. The raw water quality played an important role in the formation of DBPs. During chlorination, haloacetic acids (HAAs) were the major DBPs formed in most of the water samples, followed by trihalomethanes (THMs). CHCl₃ and CHCl₂Br were the major THM species, while trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA) were the major HAA species. Chloramination, on the other hand, generally resulted in lower concentrations of THMs (CHCl₃), HAAs (TCAA and DCAA), and haloacetonitriles (HANs). All the species of DBPs formed had positive correlations with the SUVA values, and HANs had the highest one (R² = 0.8). The correlation coefficients between the analogous DBP yields and the SUVA values in chlorinated samples were close to those in chloraminated samples.

Seasonal evaluation of disinfection by-products throughout two full-scale drinking water treatment plants

Carbonyl compounds can occur alpha-hydrogens or beta-diketones substitution reactions with disinfectants contributed to halogenated by-products formation. The objective of this research was to study the occurrence and fate of carbonyl compounds as ozonation by-products at two full-scale drinking water treatment plants (DWTPs) using different disinfectants for one year. The quality of the raw water used in both plants was varied according to the season. The higher carbonyl compounds concentrations were found in raw water in spring. Up to 15 (as the sum of both DWTPs) of the 24 carbonyl compounds selected for this work were found after disinfection. The dominant carbonyl compounds were formaldehyde, glyoxal, methyl-glyoxal, fumaric, benzoic, protocatechuic and 3-hydroxybenzoic acid at both DWTPs. In the following steps in each treatment plant, the concentration patterns of these carbonyl compounds differed depending on the type of disinfectant applied. Benzaldehyde was the only aromatic aldehyde detected after oxidation with ozone in spring. As compared with DWTP 1, five new carbonyl compounds were formed (crotonaldehyde, benzaldehyde, formic, oxalic and malonic acid) disinfection by ozone, and the levels of the carbonyl compounds increased. In addition, pre-ozonation (PO) and main ozonation (OZ) increased the levels of carbonyl compounds, however coagulation/flocculation (CF), sand filtration (SF) and granular activated carbon filtration (GAC) decreased the levels of carbonyl compounds.

Effect of chlorine dosage in prechlorination on trihalomethanes and haloacetic acids during water treatment process

To identify the effect of chlorine dosage in prechlorination on the formation of disinfection by-products during drinking water treatment process, the relationship between chlorine dosage and concentrations of THMs and HAAs was analyzed. Furthermore, the variation about the ratio of THMs/HAAs was also analyzed. The results indicated that concentrations of THMs and HAAs would rise with the increase of chlorine dosage, and TCM was the main product of four THMs, while DCAA and TCAA were the primary products of five HAAs. Moreover, the ratio of THMs to HAAs rose with the chlorine dosage increase. Thus, chlorine dosage in prechlorination had a significant impact on THMs and HAAs and should be controlled effectively.

The removal of organic precursors of DBPs during three advanced water treatment processes including ultrafiltration, biofiltration, and ozonation

The removal efficiency of organic matter, the formation potential of trihalomethanes (THMFP), and the formation potential of haloacetic acids (HAAFP) in each unit of three advanced treatment processes were investigated in this paper. The molecular weight distribution and the components of organic matter in water samples were also determined to study the transformation of organic matter during these advanced treatments. Low-molecular-weight matter was the predominant fraction in raw water, and it could not be removed effectively by ultrafiltration and biofiltration. The dominant species of disinfection by-product formation potential (DBPFP) in raw water were chloroform and monochloroacetic acid (MCAA), with average concentrations of 107.3 and 125.9 μg/L, respectively. However, the formation potential of chloroform and MCAA decreased to 36.2 and 11.5 μg/L after ultrafiltration. Similarly, biological pretreatment obtained high removal efficiency for DBPFP. The total THMFP decreased from 173.8 to 81.8 μg/L, and the total HAAFP decreased from 211.9 to 84.2 μg/L. Separate ozonation had an adverse effect on DBPFP, especially for chlorinated HAAFP. Numerous low-molecular-weight compounds such as aldehydes, ketones, and alcohols were generated during the ozonation, which have been proven to be important precursors of HAAs. However, the ozonation/biological activated carbon (BAC) combined process had a better removal efficiency for DBPFP. The total DBPFP decreased remarkably from 338.7 to 113.3 μg/L after the O3/BAC process, far below the separated BAC of process B (189.1 μg/L).

Assessment, modeling and optimization of parameters affecting the formation of disinfection by-products in water

This study focused on (a) the development of a screening methodology, in order to determine the main experimental variables affecting chlorinated and brominated disinfection by-product (DBP) formation in water during chlorination experiments and (b) the application of a central composite design (CCD) using response surface methodology (RSM) for the mathematical description and optimization of DBP formation. Chlorine dose and total organic carbon (TOC) were proven to be the main factors affecting the formation of total chlorinated DBPs, while chlorine dose and bromide concentration were the main parameters affecting the total brominated THMs. Longer contact time promoted a rise in chlorinated DBPs' concentration even in the presence of a minimal amount of organic matter. A maximum production of chlorinated DBPs was observed under a medium TOC value and it reduced at high TOC concentrations, possibly due to the competitive production of brominated THMs. The highest concentrations of chlorinated THMs were observed at chlorine dose 10 mg L(-1) and TOC 5.5 mg L(-1). The formation of brominated DBPs is possible even with a minimum amount of NaOCl in the presence of high concentration of bromide ions. Brominated DBPs were observed in maximum concentrations using 8 mg L(-1) of chlorine in the presence of 300 μg L(-1) bromides.

Modeling of trihalomethanes (THMs) in drinking water supplies: a case study of eastern part of India

This study aimed at developing a model for predicting the formation of trihalomethanes (THMs) in drinking water supplies. Monitoring of THMs in five major water treatment plants situated in the Eastern part of India revealed high concentration of THMs (231-484 μg l(-1)). Chloroform was predominant, contributing 87-98.9% to total THMs. Seasonal variation in THMs levels dictated that the concentration were higher in autumn than other seasons. Linear regression analysis of data indicated that TOC is the major organic precursors for THMs formation followed by DOC and UV254. Linear and non-linear predictive models were developed using SPSS software version 16.0. Validation results indicated that there is no significant difference in the predictive and observed values of THMs. Linear model performed better than non-linear one in terms of percentage prediction errors. The model developed were site specific and the predictive capabilities in the distribution systems vary with different environmental conditions.

Occurrence of disinfection by-products in tap water distribution systems and their associated health risk

The concentrations of trihalomethanes (THMs), including chloroform, bromodichloromethane, dibromochloromethane, and bromoform, and haloacetic acids (HAAs; monochloroacetic acid, monobromoacetic acid, dibromoacetic acid, dichloroacetic acid, and trichloroacetic acid) were measured in tap waters passing through water distribution systems of six water treatment plants in Seoul, Korea, and their associated health risks from exposure to THMs through ingestion, dermal contact, and inhalation were estimated using a probabilistic approach. The concentration ranges for total THMs and HAA5 were 3.9-53.5 and <LOD-49.5 μg/L, respectively. Among DBPs, chloroform, bromodichloromethane, dichloroacetic acid, and trichloroacetic acid were the most frequently detected. Spatial and seasonal variations in concentrations of THMs and HAAs in the six water distribution systems were significant (P < 0.001).The mean lifetime cancer risks through ingestion, dermal contact, and inhalation during showering ranged as 7.23-10.06 × 10(-6), 2.19-3.63 × 10(-6), and 5.22-7.35 × 10(-5), respectively. The major exposure route to THMs was inhalation during showering. Sensitivity analysis showed that shower time and shower frequency had a great impact on the lifetime cancer risk by the exposure to THMs in tap water.

Optimized chromatographic conditions for separation of halogenated acetic acids by ultra-performance liquid chromatography-electrospray ionization-mass spectrometry

Emerging halogenated acetic acids (HAAs), especially mixed halogenated acids such as chlorobromo-, chloroiodo- and bromoiodo-acetic acids, are unregulated disinfection by-products in drinking water. Because these compounds are hydrophilic and strongly acidic, they are difficult to detect at trace levels using approved analytical methods. In the present study, 13 HAAs were effectively separated on three ultra-performance liquid chromatography columns. The effects of changing in the aqueous mobile phase, acidic solutions and cationic volatile ion pair reagents were investigated. The samples were pretreated by filtration, and extraction, while derivatization and concentration procedures were not required. The limits of quantitation for regulated HAAs were between 0.5 μg/L and 1.7 μg/L and for unregulated HAAs were 1.2 and 5.8 μg/L, especially for the iodinated acetic acids were 1.5 and 2.1 μg/L. The method was applied to two finished water samples collected in China (Shanghai and Xuzhou) from water treatment plants that use chlorine for disinfection. Multiple unregulated HAAs were found in the two samples, but iodoacids were only detected in the water sample from Shanghai, which could be attributed to the characteristics of the source water. The presence of unregulated HAAs, especially mixed bromo- and iodoacetic acids, in the finished water samples could affect human health, and this warrants further investigation.

Control of disinfection by-product formation using ozone-based advanced oxidation processes

The effects of ozone dosage, water temperature and catalyst addition in an ozonation-fluidized bed reactor (O3/FBR) on treated water quality and on the control of chlorinated and ozonated disinfection by-products (DBPs) were investigated. A biofiltration column was used to evaluate its removal efficiency on biodegradable organic matter and to reduce DBP formation. The Dong-Gang River, polluted by agricultural and domestic wastewater in Pingtung, Taiwan, was used as the water source. The treated water quality in terms of dissolved organic carbon (DOC), biodegradable DOC, ultraviolet absorbance at 254 nm (UV254) and specific UV absorbance (SUVA) improved with increasing ozone and catalyst dosages. Catalytic ozonation was more effective than ozonation alone at reducing the formation of DBPs at a given dosage. Experimental results show that water temperature had little effect on the treated water quality with the O3/FBR system used in this study (p > 0.05). The combination of O3/FBR and the biofiltration process effectively decreased the amount ofDBP precursors. The concentration of total trihalomethanes (TTHMs) was less than the maximum contaminant level (MCL) requirement, which is 80 microg/L, for all treated waters and the concentration of five haloacetic acids (HAA5) fell below 60 microg/L with an ozone dosage higher than 2.5 mg/L.

Chlorine residuals and haloacetic acid reduction in rapid sand filtration

It is quite rare to find biodegradation in rapid sand filtration for drinking water treatment. This might be due to frequent backwashes and low substrate levels. High chlorine concentrations may inhibit biofilm development, especially for plants with pre-chlorination. However, in tropical or subtropical regions, bioactivity on the sand surface may be quite significant due to high biofilm development--a result of year-round high temperature. The objective of this study is to explore the correlation between biodegradation and chlorine concentration in rapid sand filters, especially for the water treatment plants that practise pre-chlorination. In this study, haloacetic acid (HAA) biodegradation was found in conventional rapid sand filters practising pre-chlorination. Laboratory column studies and field investigations were conducted to explore the association between the biodegradation of HAAs and chlorine concentrations. The results showed that chlorine residual was an important factor that alters bioactivity development. A model based on filter influent and effluent chlorine was developed for determining threshold chlorine for biodegradation. From the model, a temperature independent chlorine concentration threshold (Cl(threshold)) for biodegradation was estimated at 0.46-0.5mgL(-1). The results imply that conventional filters with adequate control could be conducive to bioactivity, resulting in lower HAA concentrations. Optimizing biodegradable disinfection by-product removal in conventional rapid sand filter could be achieved with minor variation and a lower-than-Cl(threshold) influent chlorine concentration. Bacteria isolation was also carried out, successfully identifying several HAA degraders. These degraders are very commonly seen in drinking water systems and can be speculated as the main contributor of HAA loss.

Temporal variability in trihalomethane and haloacetic acid concentrations in Massachusetts public drinking water systems

Previous epidemiological studies in Massachusetts have reported a risk of adverse health outcomes in relation to disinfection by-product (DBP) exposures. Measurement error due to the use of indirect exposure surrogates can lead to misclassification bias in epidemiological studies; therefore, it is important to characterize exposure variability in these populations to assess the potential for exposure misclassification. We used 19,944 trihalomethane (THM) samples and 9291 haloacetic acid (HAA) samples collected in 201 public water systems (PWSs) in Massachusetts to examine temporal variability under different drinking water sources and disinfection types. Annual and seasonal variability was also examined in 46 PWSs with complete quarterly THM4 (i.e., the sum of 4 individual THMs) data from 1995 to 2004 and 19 PWSs with complete HAA5 (i.e., the sum of 5 individual HAAs) data from 2001 to 2004. The quarterly ratio of THM4 and HAA5 and correlations between THM4, HAA5 and individual DBP species were examined to determine the adequacy of using different exposure surrogates in epidemiological studies. Individual PWSs were used to examine monthly variability in relation to quarterly averages. Based on all available matched samples (n=9003) from 1995 to 2004 data, we found a correlation of 0.52 for THM4 and HAA5. The correlation was stronger among the 62 ground water systems (r(s)=0.62) compared to the 81 surface water (r(s)=0.45) and 40 mixed water (r(s)=0.39) systems. Mean THM4 levels were fairly stable over the 10-year study period for 46 PWSs including 39 PWSs that did not change disinfection. Large reductions (∼40 μg/L) in mean THM4 data were found among seven systems that switched from chlorination to alternative disinfectants. As expected, the highest mean THM4 values were detected for Quarter 3, while the lowest values were found in Quarter 1. The highest HAA5 values were detected in Quarters 2 and 3 and the lowest was found in Quarter 4. Data from four systems showed mean differences up to 66 μg/L (67% change) in successive months and by 46 μg/L compared to quarterly mean concentrations. Although longer-term disinfection by-product temporality may be minimal in this study population, the use of monthly average concentrations for exposure assessment may be needed for some PWSs to minimize misclassification of narrow critical periods of exposure in epidemiological studies.

Characterization of disinfection byproduct formation potential in 13 source waters in China

The formation potential of four trihalomethanes (THMFP) and seven haloacetic acids (HAA7FP) in 13 source waters taken from four major water basin areas in China was evaluated using the simulated distribution system (SDS) chlorination method. The specific ultraviolet absorbance (SUVA254: the ratio of UV254 to dissolved organic carbon (DOC)), which ranged between 0.9 and 5.0 L/(mg x m), showed that the organic compounds in different source waters exhibited different reactivities with chlorine. The HAA7FP of source waters ranged from 20 to 448 microg/L and the THMFP ranged from 29 to 259 microg/L. The HAA7FP concentrations were higher than the THMFP concentrations in all but one of the samples. Therefore, the risks of haloacetic acids (HAAs) should be of concern in some source waters. TCM (chloroform) and BDCM (bromodichloromethane) were the major THM constituents, while TCAA (trichloroacetic acid) and DCAA (dichloroacetic acid) were the major HAA species. Br-THM (brominated THM species) were much higher than Br-HAA (brominated HAA species), and the formation of Br-DBP (Br-THM and Br-HAA) should be of concern when the bromide concentration is over 100 microg/L.