Spatial and temporal evaluations of disinfection by-products in drinking water distribution systems in Beijing, China

Disinfection by-products were determined in 15 water treatment plants in Beijing City. The effects of different water sources (surface water source, mixture water source and ground water source), seasonal variation and spatial variation were examined. Trihalomethanes and haloacetic acids were the major disinfection by-products found in all treated water samples, which accounted for 42.6% and 38.1% of all disinfection by-products respectively. Other disinfection by-products including haloacetonitriles, chloral hydrate, haloketones and chloropicrin were usually detected in treated water samples but at lower concentrations. The levels of disinfection by-products in drinking water varied with different water sources and followed the order: surface water source > mixture water source > ground water source. High spatial and seasonal variation of disinfection by-products in the drinking water of Beijing was shown as a result.     

Multivariate statistical techniques for the evaluation of spatial and temporal variations in water quality of Gomti River (India)--a case study

This case study reports different multivariate statistical techniques applied for evaluation of temporal/spatial variations and interpretation of a large complex water-quality data set obtained during monitoring of Gomti River in Northern part of India. Water quality of the Gomti River, a major tributary of the Ganga River was monitored at eight different sites selected in relatively low, moderate and high pollution regions, regularly over a period of 5 years (1994-1998) for 24 parameters. The complex data matrix (17,790 observations) was treated with different multivariate techniques such as cluster analysis, factor analysis/principal component analysis (FA/PCA) and discriminant analysis (DA). Cluster analysis (CA) showed good results rendering three different groups of similarity between the sampling sites reflecting the different water-quality parameters of the river system. FA/PCA identified six factors, which are responsible for the data structure explaining 71% of the total variance of the data set and allowed to group the selected parameters according to common features as well as to evaluate the incidence of each group on the overall variation in water quality. However, significant data reduction was not achieved, as it needed 14 parameters to explain 71% of both the temporal and spatial changes in water quality. Discriminant analysis showed the best results for data reduction and pattern recognition during both temporal and spatial analysis. Discriminant analysis showed five parameters (pH, temperature, conductivity, total alkalinity and magnesium) affording more than 88% right assignations in temporal analysis, while nine parameters (pH, temperature, alkalinity, Ca-hardness, DO, BOD, chloride, sulfate and TKN) to afford 91% right assignations in spatial analysis of three different regions in the basin. Thus, DA allowed reduction in dimensionality of the large data set, delineating a few indicator parameters responsible for large variations in water quality. This study presents necessity and usefulness of multivariate statistical techniques for evaluation and interpretation of large complex data sets with a view to get better information about the water quality and design of monitoring network for effective management of water resources.     

An ATP-based method for monitoring the microbiological drinking water quality in a distribution network

The titration of adenosine triphosphate (ATP) by bioluminescence permits rapid evaluation of the quantity of viable micro-organisms present in a water sample. During two sampling campaigns, Société Anonyme de Gestion des Eaux de Paris (SAGEP) tested a new extraction and titration system of bacterial ATP in the Paris drinking water distribution network. As far as the entire set of results of analyses of water in the network is concerned there is a linear relationship between log [ATP] and log(HPC-R2A/ml). Furthermore, as regards the drinking water originating from treatment of surface waters, some of the results obtained indicate a slight change as regards the Paris network in the microbiological quality. This is certainly linked to the distance travelled from the production location as well as to a reservoir effect observed on a site. Conversely, no change is apparent with regard to waters of underground origin. Lastly, despite changes in temperature and chlorine residual, no significant influence has been observed, essentially because of the very low density of culturable bacteria.     

Regional disparities of microbiological drinking water quality: assessment of spatial pattern and potential sociodemographic determinants

Even in industrialized countries like Germany, drinking water quality is a sensitive issue. Despite a generally high level of drinking water safety, contamination events do occur. We address the question whether demographic change may cause a spatial mismatch between installed capacities at the supply side and actual demand by water users, thereby increasing risks of microbiological contamination. Our investigation is based on a quantitative analysis using the largest publically available data-set on drinking water quality in Germany. We found that the number of reported contamination events in areas affected by population decrease was about twice as high as in areas with a stable or growing population. The relative frequency of microbiological contamination was found to be significantly correlated with rapidly depopulating areas. We conclude that in regions with negative population development, a statistically higher risk of microbiological drinking water contamination may coincide with a greater risk of recontamination during a longer passage in the distribution network.     

Development and validation of a drinking water temperature model in domestic drinking water supply systems

Domestic drinking water supply systems (DDWSs) are the final step in the delivery of drinking water to consumers. Temperature is one of the rate-controlling parameters for many chemical and microbiological processes and is, therefore, considered as a surrogate parameter for water quality processes. In this study, a mathematical model is presented that predicts temperature dynamics of the drinking water in DDWSs. A full-scale DDWS resembling a conventional system was built and run according to one year of stochastic demands with a time step of 10 s. The drinking water temperature was measured at each point-of-use in the systems and the data-set was used for model validation. The temperature model adequately reproduced the temperature profiles, both in cold and hot water lines, in the full-scale DDWS. The model showed that inlet water temperature and ambient temperature have a large effect on the water temperature in the DDWSs.     

The quality of drinking water from private water supplies in Aberdeenshire,UK

The quality of private water supplies within Aberdeenshire sampled between 1992 and 1998 was analysed with respect to the presence of total coliforms (TC), faecal coliforms (FC), and nitrate. Of the approximately 1750 samples analysed, which included multiple samples from larger supply categories, the individual failure rate was 41%, 30% and 15% for TC, FC and nitrate, respectively. A combined failure rate for these samples was 48%. Failure rates on microbiological grounds displayed a seasonal trend being greater during the latter half of the year. Although this observation is likely to be due to a combination of local and regional scale factors, part of the variability in failure rate was explained by a significant positive relationship with rainfall amount. Concentrations of nitrate tended to display an opposite trend with a greater number of failures occurring during the spring period and no relationship with rainfall was immediately apparent. A relatively small number of samples (< 50) failed simultaneously for both coliforms and nitrate suggesting that the mechanism responsible for the contamination differed. A similar failure rate for samples collected directly from the source (i.e. well) compared with those taken from the potable tap (usually kitchen cold water tap) suggests that it is the groundwater source itself that contributes much of the microbiological and nitrate contamination rather than a storage or supply line contamination mechanism. A more frequent and random sampling of category one F supplies suggested a greater overall failure rate, which has its own implications for deciding an appropriate sampling frequency.     

Toxic cyanobacterial breakthrough and accumulation in a drinking water plant: a monitoring and treatment challenge

The detection of cyanobacteria and their associated toxins has intensified in recent years in both drinking water sources and the raw water of drinking water treatment plants (DWTPs). The objectives of this study were to: 1) estimate the breakthrough and accumulation of toxic cyanobacteria in water, scums and sludge inside a DWTP, and 2) to determine whether chlorination can be an efficient barrier to the prevention of cyanotoxin breakthrough in drinking water. In a full scale DWTP, the fate of cyanobacteria and their associated toxins was studied after the addition of coagulant and powdered activated carbon, post clarification, within the clarifier sludge bed, after filtration and final chlorination. Elevated cyanobacterial cell numbers (4.7 × 10⁶ cells/mL) and total microcystins concentrations (up to 10 mg/L) accumulated in the clarifiers of the treatment plant. Breakthrough of cells and toxins in filtered water was observed. Also, a total microcystins concentration of 2.47 μg/L was measured in chlorinated drinking water. Cyanobacterial cells and toxins from environmental bloom samples were more resistant to chlorination than results obtained using laboratory cultured cells and dissolved standard toxins.     

Modeling DBPs formation in drinking water in residential plumbing pipes and hot water tanks

Disinfection byproducts (DBPs) in municipal supply water are a concern because of their possible risks to human health. Risk assessment studies often use DBP data in water distribution systems (WDS). However, DBPs in tap water may be different because of stagnation of the water in plumbing pipes (PP) and heating in hot water tanks (HWT). This study investigated occurrences and developed predictive models for DBPs in the PP and the HWT of six houses from three municipal water systems in Quebec (Canada) in a year-round study. Trihalomethanes (THMs) in PP and HWT were observed to be 1.4-1.8 and 1.9-2.7 times the THMs in the WDS, respectively. Haloacetic acid (HAAs) in PP and HWT were observed to be variable (PP/WDS = 0.23-2.24; HWT/WDS = 0.53-2.61). Using DBPs occurrence data from these systems, three types of linear models (main factors; main factors, interactions and higher orders; logarithmic) and two types of nonlinear models (three parameters Logistic and four parameters Weibull) were investigated to predict DBPs in the PP and HWT. Significant factors affecting DBPs formation in the PP and HWT were identified through numerical and graphical techniques. The R² values of the models varied between 0.77 and 0.96, indicating excellent predictive ability for THMs and HAAs in the PP and the HWT. The models were found to be statistically significant. The models were validated using additional data. These models can be used to predict DBPs increase from WDS (water entry point of house) to the PP and HWT, and could thereby help gain a better understanding of human exposure to DBPs and their associated risks.     

Toxicological relevance of emerging contaminants for drinking water quality

The detection of many new compounds in surface water, groundwater and drinking water raises considerable public concern, especially when human health based guideline values are not available it is questioned if detected concentrations affect human health. In an attempt to address this question, we derived provisional drinking water guideline values for a selection of 50 emerging contaminants relevant for drinking water and the water cycle. For only 10 contaminants, statutory guideline values were available. Provisional drinking water guideline values were based upon toxicological literature data. The maximum concentration levels reported in surface waters, groundwater and/or drinking water were compared to the (provisional) guideline values of the contaminants thus obtained, and expressed as Benchmark Quotient (BQ) values. We focused on occurrence data in the downstream parts of the Rhine and Meuse river basins. The results show that for the majority of compounds a substantial margin of safety exists between the maximum concentration in surface water, groundwater and/or drinking water and the (provisional) guideline value. The present assessment therefore supports the conclusion that the majority of the compounds evaluated pose individually no appreciable concern to human health.     

Implications of sequential use of UV and ozone for drinking water quality

The formation of bromate levels exceeding the drinking water standard of 10 microg L-1 may impose the reduction of ozone doses used in the treatment of drinking water. This paper illustrates the procedure of evaluating the use of reduced ozone doses while implementing an additional UV disinfection step for an actual drinking water treatment plant. Ozonation was performed at low ozone doses in bench-scale experiments with a pretreated river water from the Paris area (France). At the low ozone dose of 0.5 mg L-1, bromate formation could be kept below 0.4 microg L-1, while inactivation of vegetative bacteria and UV-resistant viruses was calculated to exceed 5 log units, and a substantial decoloration (31% of the absorption at lambda=254 nm) was achieved. Based on the measured transient ozone and OH radical concentrations, the oxidation of micropollutants was calculated. Fast reacting micropollutants containing phenol, amine or double bond moieties, such as sulfamethoxazole, diclofenac and 17-alpha-ethinylestradiol, were completely oxidized. Slow-reacting synthetic micropollutants, e.g., atrazine, iopromide and methyl tertiary butyl ether (MTBE), were oxidized by only 20%, 20% and 10%, respectively, and the taste and odor compounds 2-methylisoborneol (MIB) and geosmin by 40% and 50%, respectively. The addition of an UV treatment step to the existing treatment train, which should guarantee disinfection of ozone-resistant pathogenic microorganisms, including Cryptosporidium parvum oocysts, has negligible effects on water matrix components but may induce significant transformation of micropollutants. Overall, the combination of ozonation at reduced doses and UV treatment leads to an improved water quality with regard to disinfection, oxidation of micropollutants and minimization of bromate.     

Perceptions of drinking water quality and risk and its effect on behaviour: A cross-national study

There is a growing effort to provide drinking water that has the trust of consumers, but the processes underlying the perception of drinking water quality and risks are still not fully understood. This paper intends to explore the factors involved in public perception of the quality and risks of drinking water. This purpose was addressed with a cross-national mixed-method approach, based on quantitative (survey) and qualitative (focus groups) data collected in the UK and Portugal. The data were analysed using several methods, including structural equation models and generalised linear models. Results suggest that perceptions of water quality and risk result from a complex interaction of diverse factors. The estimation of water quality is mostly influenced by satisfaction with organoleptic properties (especially flavour), risk perception, contextual cues, and perceptions of chemicals (lead, chlorine, and hardness). Risk perception is influenced by organoleptics, perceived water chemicals, external information, past health problems, and trust in water suppliers, among other factors. The use of tap and bottled water to drink was relatively well explained by regression analysis. Several cross-national differences were found and the implications are discussed. Suggestions for future research are provided.     

Chemical drinking water quality in Ghana: Water costs and scope for advanced treatment

To reduce child mortality and improve health in Ghana boreholes and wells are being installed across the country by the private sector, NGO's and the Ghanaian government. Water quality is not generally monitored once a water source has been improved. Water supplies were sampled across Ghana from mostly boreholes, wells and rivers as well as some piped water from the different regions and analysed for the chemical quality. Chemical water quality was found to exceed the WHO guidelines in 38% of samples, while pH varied from 3.7 to 8.9. Excess levels of nitrate (NO₃⁻) were found in 21% of the samples, manganese (Mn) and fluoride (F⁻) in 11% and 6.7%, respectively. Heavy metals such as lead (Pb), arsenic (As) and uranium (U) were localised to mining areas. Elements without health based guideline values such as aluminium (Al, 95%) and chloride (Cl, 5.7%) were found above the provisional guideline value.Economic information was gathered to identify water costs and ability to pay. Capital costs of wells and boreholes are about £1200 and £3800 respectively. The majority of installation costs are generally paid by the government or NGO's, while the maintenance is expected to be covered by the community. At least 58% of the communities had a water payment system in place, either an annual fee/one-off fee or “pay-as-you-fetch”. The annual fee was between £0.3-21, while the boreholes had a water collection fee of £0.07-0.7/m³, many wells were free. Interestingly, the most expensive water (£2.9-3.5/m³) was brought by truck. Many groundwater sources were not used due to poor chemical water quality. Considering the cost of unsuccessful borehole development, the potential for integrating suitable water treatment into the capital and maintenance costs of water sources is discussed. Additionally, many sources were not in use due to lack of water capacity, equipment malfunction or lack of economic resources to repair and maintain equipment. Those issues need to be addressed in combination with water quality, coordinated water supply provision and possible treatment to ensure sustainability of improved water resources.     

Fluoride in drinking water and dental fluorosis

In this study we determined the fluoride content in drinking water and hair of 12-year-old schoolchildren from different Serbian municipalities, i.e. Valjevo, Veliko Gradiste, Kacarevo and Vranjska Banja. The analyses were performed using composite fluoride ion-selective electrode. Average fluoride levels were 0.10, 0.15, 0.79 and 11 ppm in well water, 0.07, 0.10, 0.17 and 0.15 ppm in tap water, 19.3, 21.5, 25.4, and 32.5 ppm in hair samples, in Valjevo, Veliko Gradiste, Kacarevo and Vranjska Banja, respectively. Correlation analysis indicated statistically significant positive relationship between fluoride in wells water and fluoride in hair, for all municipalities: correlation coefficients were 0.54 (p < 0.05), 0.89, 0.97 and 0.99 (p < 0.001), in Vranjska Banja, Valjevo, Veliko Gradiste, and Kacarevo, respectively. Positive correlation was obtained also between fluoride in tap water and hair samples in all regions under the study, with statistical significance only in Valjevo municipality, p < 0.05. Dental examination of schoolchildren confirmed dental fluorosis only in the region of Vranjska Banja. Moreover, in endemic fluorotic region of Vranjska Banja, positive and statistically significant correlations were confirmed between fluoride in well water and dental fluorosis level (r = 0.61; p < 0.01) and additionally between fluoride in hair and dental fluorosis level (0.62; p < 0.01). The primary findings from this study have shown that fluoride content in hair is highly correlated with fluoride content in drinking water and dental fluorosis level, indicating that hair may be regarded as biomaterial of high informative potential in evaluating prolonged exposure to fluorides and to individuate children at risk of fluorosis regardless of the phase of teeth eruption.     

Combined bioelectrochemical and sulfur autotrophic denitrification for drinking water treatment

A combined bioelectrochemical and sulfur autotrophic denitrification process for drinking water treatment was put forward and investigated extensively in this paper. In this new process, the bioelectrochemical denitrification was carried out in the upper part of the reactor while sulfur denitrification in the lower part. The H+ produced in Sulfur Part could be consumed by hydrogen denitrification in Bioelectrochemical Part. Therefore, the limestone for pH adjustment in Sulfur Part was not necessary in this combined process, which avoided the problem of hardness increase. The sulfate accumulation in this combined reactor was less than that of the sulfur limestone autotrophic denitrification system. The effluent from two parts was kept neutral at optimum operation conditions. When the influent nitrate was 30 mg-N/L, the reactor could be operated efficiently at the hydraulic retention time ranged from 1.9 to 5h (corresponding minimum current was 16-3 mA), i.e. the effluent NO3(-)-N removal ranged from 90% to 100% without nitrite accumulation and the effluent sulfate concentration was lower than 170 mg/L. The maximum volume-loading rate of the reactor was 0.381 kg NO3(-)-N/(m3d). The biomass and scanning electron microscope micrographs of Sulfur Part were also analyzed.     

Investigation of assimilable organic carbon (AOC) in flemish drinking water

The aim of the study was to investigate the drinking water supplied to majority of residents of Flanders in Belgium. Over 500 water samples were collected from different locations, after particular and complete treatment procedure to evaluate the efficiency of each treatment step in production of biologically stable drinking water. In this study assimilable organic carbon (AOC) was of our interest and was assumed as a parameter responsible for water biostability. The influence of seasons and temperature changes on AOC content was also taken into account. The AOC in most of the non-chlorinated product water of the studied treatment plants could not meet the biostability criteria of 10 mug/l, resulting in the mean AOC concentration of 50 microg/l. However, majority of the examined chlorinated water samples were consistent with proposed criteria of 50--100 microg/l for systems maintaining disinfectant residual. Here, mean AOC concentration of 72 microg/l was obtained. Granular activated carbon filtration was helpful in diminishing AOC content of drinking water; however, the nutrient removal was enhanced by biological process incorporated into water treatment (biological activated carbon filtration). Disinfection by means of chlorination and ozonation increased the water AOC concentration while the ultraviolet irradiation showed no impact on the AOC content. Examination of seasonal AOC variations showed similar fluctuations in six units with the highest values in summer and lowest in winter.     

Detection of enteroviruses in treated drinking water

This study deals with the routine monitoring of drinking water for the presence of enteroviruses, over a period of 1 year. A rapid and simple method was employed for the simultaneous detection and typing of enteroviruses in large-volume water samples. This included an integrated cell culture/nested PCR approach, followed by restriction enzyme analysis. The two drinking water supplies studied were derived from acceptable quality surface water sources using treatment processes, which conform to international specifications for the production of safe drinking water. Enteroviruses (predominantly coxsackie B viruses) were detected in 11% and 16% of the drinking water samples from two treatment plants, respectively. This study confirms that acceptable water quality indicators do not necessarily reflect the virus content of drinking water.     

A membrane filter technique for the concentration and detection of Salmonella from drinking water

A methodology for the concentration, detection and enumeration of Salmonella from drinking water by membrane filter technique is described. A single step filtration methodology for enteroviruses and Salmonella was not possible, due to the inactivation of Salmonella at conditions necessary for concentration of enteroviruses, i.e. pH 3.5 and 9.5. Enrichment in selenite cystine broth and incubation at 37°C followed by plating on brilliant green agar provided maximum recovery of Salmonella. Out of 21 drinking water samples in Delhi, India examined during March to May 1991, three were positive for Salmonella.     

Removal of soft deposits from the distribution system improves the drinking water quality

Deterioration in drinking water quality in distribution networks represents a problem in drinking water distribution. These can be an increase in microbial numbers, an elevated concentration of iron or increased turbidity, all of which affect taste, odor and color in the drinking water. We studied if pipe cleaning would improve the drinking water quality in pipelines. Cleaning was arranged by flushing the pipes with compressed air and water. The numbers of bacteria and the concentrations of iron and turbidity in drinking water were highest at 9 p.m., when the water consumption was highest. Soft deposits inside the pipeline were occasionally released to bulk water, increasing the concentrations of iron, bacteria, microbially available organic carbon and phosphorus in drinking water. The cleaning of the pipeline decreased the diurnal variation in drinking water quality. With respect to iron, only short-term positive effects were obtained. However, removing of the nutrient-rich soft deposits did decrease the microbial growth in the distribution system during summer when there were favorable warm temperatures for microbial growth. No Norwalk-like viruses or coliform bacteria were detected in the soft deposits, in contrast to the high numbers of heterotrophic bacteria.     

Denitrification from drinking water using a membrane bioreactor: chemical and biochemical feasibility

Interest is growing in developing membrane bioreactors (MBRs) to replace ion exchange for nitrate removal from drinking water. However, few published studies have successfully managed to retain exogenous or biologically derived carbon. This study determined an optimum C:N by substrate breakthrough rather than maximum nitrate removal. By dosing 相似文献