Showing papers in "Journal of Water Supply Research and Technology-aqua in 2011"
TL;DR: It is indicated that long and needle-shaped algae were less likely to settle and more likely to be present in overflow water and that species that overflowed the basin also clogged the sand filters, leading to a need for repeated backwashing, thus limiting the production of clean water.
Abstract: Problematic algae, species that do not settle or are not easily removed by water treatment processes, are common in many water treatment plants (WTPs). We recorded algae in the water that overflowed from sedimentation basins (SBs) to filtration basins of WTPs in South Korea. Diatoms were common and other algae were not discernible in the flocs. Our field observation indicated that long and needle-shaped algae were less likely to settle and more likely to be present in overflow water. Many diatom cells or colonies that were extremely deformed from spherical had high overflow rates. Another long alga, Phormidium sp. (Cyanobacteria), originated from periphytic biofilms attached to SB walls. Algae that form long cells or colonies are less compact and less likely to settle as poor flocs. Species that overflowed the basin also clogged the sand filters, leading to a need for repeated backwashing, thus limiting the production of clean water. Species that clogged the sand filters included the needle-shaped diatom Synedra acus and the discoid diatom Stephanodiscus hantzschii f. tenuis . We also observed two cases where S. acus clogged WTP filters, requiring frequent backwashing that resulted in reduced production of drinking water and economic loss.
46 citations
TL;DR: In this paper, NOM in water samples from two drinking water treatment trains was characterized using liquid chromatography with organic carbon detection (LC-OCD), and fluorescence excitation-emission matrices (F-EEMs) with parallel factor analysis (PARAFAC).
Abstract: Natural organic matter (NOM) is of concern in drinking water because it causes adverse aesthetic qualities such as taste, odour, and colour; impedes the performance of treatment processes; and decreases the effectiveness of oxidants and disinfectants while contributing to undesirable disinfection by-products. The effective removal of NOM during drinking water treatment requires a good understanding of its character. Because of its heterogeneity, NOM characterization necessitates the use of multiple analytical techniques. In this study, NOM in water samples from two drinking water treatment trains was characterized using liquid chromatography with organic carbon detection (LC-OCD), and fluorescence excitation-emission matrices (F-EEMs) with parallel factor analysis (PARAFAC). These characterization methods indicate that the raw and treated waters are dominated by humic substances. The results show that whereas the coagulation process for both plants may be optimized for the removal of bulk DOC, it is not likewise optimized for the removal of specific NOM fractions. A five component PARAFAC model was developed for the F-EEMs, three of which are humic-like, while two are protein-like. These PARAFAC components and the LC-OCD fractions represented effective tools for the performance evaluation of the two water treatment plants in terms of the removal of NOM fractions.
42 citations
TL;DR: In this article, the authors reviewed evidence on the overall toxicity of disinfected water instead of focusing on the effects of individual disinfection byproducts (DBPs) and recommended a progressive shift towards preventive and holistic DBP management.
Abstract: Chemical disinfection of drinking water results in the formation of disinfection by-products (DBPs) This paper reviews evidence on the overall toxicity of disinfected water instead of focusing on the effects of individual DBPs The possible health effects of ingesting DBPs include development of cancer and adverse reproductive/developmental outcomes Only a few of the 600–700 chlorinated by-products are regulated, accounting for only a small portion of the overall toxicity of DBPs This review showed that current water quality management, based on complying with standard values set for individual DBPs, is insufficient in responding to overall toxicity from DBP species Because water suppliers typically focus their water quality management efforts on meeting the defined maximum concentration standards for individual regulated parameters, current water management practices may not adequately focus on effectively reducing overall DBP toxicity Therefore, we recommend a progressive shift towards preventive and holistic DBP management based on a comprehensive health-based risk assessment that takes into account the overall toxicity and is supported by a validation of the control processes We also present a prioritized research agenda that will help determine risk assessment and management and facilitate the development of regulations This includes the development of an index for overall DBP toxicity
37 citations
TL;DR: The basic methodological framework for an integrated action plan to be developed that will guarantee the reliable calculation of the Full Water Cost (FWC), as defined by the WFD 2000/60/EC is set.
Abstract: This paper attempts to set the basic methodological framework for an integrated action plan (in terms of successive steps) to be developed that will guarantee the reliable calculation of the Full Water Cost (FWC), as defined by the WFD 2000/60/EC. Towards this goal, the crucial role of the water losses occurring in a water distribution system is demonstrated. This will help an effective and socially just water pricing policy to be developed. The cost components (direct – DC; environmental – EC; and resource – RC) comprising the FWC are analysed, introducing approaches for their reliable calculation. Regarding the DC, the marginal capacity cost and the necessary preconditions for its integration to the final water price along with its contribution towards effective water demand reduction are analysed. Regarding the EC, its dynamic character and the ways it interacts with the DC are presented. The role of the stakeholders in setting those price levels is also checked. Crucial parameters are analysed for a socially just water cost allocation to domestic users. The role of the water utility is examined, considering its responsibility in water losses. The basic policies (market-based vs. conventional) used to achieve conservative water use are evaluated. In addition, the role of the State is criticized.
36 citations
TL;DR: In this paper, field investigations were conducted to identify the relationship between leakage rate and pressure in selected areas of the water distribution system of the Holy City of Makkah, Saudi Arabia.
Abstract: Field investigations were conducted to identify the relationship between leakage rate and pressure in selected areas of the water distribution system of the Holy City of Makkah, Saudi Arabia. Noise correlators were used to detect leaks in areas where the water leakage exceeded 20% of the total water supplied. The leakage rate was found to be related to pressure raised to the n th power. The value of n was found to be 0.50 for the network of asbestos-cement pipes and 1.16 for the network of mixed pipes. Considering the age of the network, the leakage rate was found to be linearly related to the age of the network and related to pressure raised to the 1.10 power. About 63.15% of the leaks were found to be at the property connections. The rest were either in the service lines or at the junction of the service lines with the property connections. The galvanized iron property connections were found to be highly corroded, with circular holes and/or longitudinal corrosion cracks.
34 citations
TL;DR: In this article, a case study was carried out to identify potential chemical contaminants migrating to drinking water from polyvinyl chloride (PVC) or polyethylene (PE) pipes, available on the Polish market.
Abstract: Case studies were carried out to identify potential chemical contaminants migrating to drinking water from polyvinyl chloride (PVC) or polyethylene (PE) pipes, available on the Polish market. Analyses were carried out by gas chromatography (GC) coupled with mass spectrometry (MS). Analysis of organotin compounds in water in contact with PVC pipes from different manufacturers found variability: monobutyltin (169 and 425 ng/L) and dibutyltin (51–72 and 249–263 ng/L) were detected in two of three samples, A1 and A2 respectively. Tributyltin was detected only in the second of these (92 ng/L). No organotin compounds were detected in sample A3, but a considerable quantity of lead (0.13–0.82 mg/L) was observed. Nineteen organic compounds, also volatile organic compounds such as xylene, styrene, phenols, and ethylmethylbenzene, were identified during GC-MS analysis of water samples in contact with high density PE pipe. Phenolic compounds related to antioxidants such as ditertbutyl-hydroxytoluene (0.29–3.6 and 0.84–9.8 ppb) and their degradation products such as t-butyl-methylphenol (0.9–11.8 ppb) were also detected.
27 citations
TL;DR: In this article, the relationship between residence times and residual chlorine and trihalomethane (THM) concentrations in a sector supplied with water coming directly from the water treatment plant (WTP) and from a large reservoir within the network was investigated.
Abstract: The most critical water quality conditions are generally found at a water distribution network's extremities, given their high residence times. As chlorine injected at the water treatment plant (WTP) or at rechlorination sites has more time to react, residual chlorine concentrations at the extremities may not be enough to prevent microbial regrowth. This study focuses on the relationships between residence times, and residual chlorine and trihalomethane (THM) concentrations in a sector supplied with water coming directly from the WTP and from a large reservoir within the network. A hydraulic model was calibrated based on residence times obtained from a tracer study and a water quality characterization campaign at 47 sampling sites. Results showed that chlorine decay in water from the reservoir is faster than for water directly from the WTP. THM concentrations differ, with those in water from the reservoir being far higher than those from the WTP. A slight increase in THM concentrations is seen with residence time in both cases. By using a hydraulic model, we can evaluate – at any time and in any place – the impact of a hydraulic change on the network in terms of hydraulics, as well as in terms of the vulnerability associated with low residual chlorine and high THM concentrations.
21 citations
TL;DR: In this article, the impact of plumbing age on copper levels in tap water samples and the internal surface corrosion of copper plumbing were systematically evaluated in 16 buildings with plumbing ages ranging from less than one to 44 years.
Abstract: Theory and practical experiences suggest that higher copper levels in drinking water tap samples are typically associated with newer plumbing systems, and levels decrease with increasing plumbing age. Past researchers have developed a conceptual model to explain the ‘aging effect’ founded in the proposed evolution of copper(II) corrosion by-products on the pipe surface, based on theoretical considerations, anecdotal evidence and some data. In this study, the impact of plumbing age on copper levels in tap water samples and the internal surface corrosion of copper plumbing were systematically evaluated in 16 buildings with plumbing ages ranging from less than one to 44 years, using solids analysis approaches including XPS and XRD. Copper levels decreased with plumbing age and supported theory. A mix of stable and relatively unstable scales appeared on pipes, including cupric hydroxide, cuprite and malachite, although no obvious trend in scale composition with age was noted.
19 citations
TL;DR: In this paper, the problem of optimal operation of river-reservoir systems under flooding conditions is formulated as a combination of particle swarm optimization (PSO) algorithm and a simulation model of river flood routing.
Abstract: The problem of optimal operation of river–reservoir systems under flooding conditions is formulated in this study as a combination of particle swarm optimization (PSO) algorithm and a simulation model of river flood routing. Both hydrologic (Muskingum and Muskingum-Cunge) and hydraulic (solving Saint-Venant equations) flow routing methods are linked to the PSO algorithm with the objective function of minimizing flood damage in downstream areas. The Preissmann method is used to numerically solve the continuity and momentum equations. The developed optimization–simulation models were first tested in the case study of flood control operation of Bishop Dam, a benchmark problem in HEC-5 software. The models' performance was verified through their ability to reduce peak discharge at downstream control points compared to that resulting from applying gate regulation curve (GRC) operation policies available in HEC-5. Then the PSO-Venant model was used in the river–reservoir system of Upper Gotvand dam, a real case study in south-west Iran. Results show the significance of the model in determining optimal reservoir releases and minimizing flood damages.
19 citations
TL;DR: In this article, the authors make use of the AHP technique to improve the decision-making process in order to satisfy new water demands in a local context, which allows the combination of quantitative and qualitative criteria.
Abstract: Despite advances in water conservation, abstraction and transport, water demand has been increasing worldwide in the past few decades. This has resulted in an increased pressure on stakeholders to provide sustainable solutions to meet future water demands. The decision-making process to find those solutions is becoming increasingly complicated. First, owing to the arrival of new technologies or the evolution of existing ones, the number of available alternatives has increased. Additionally, economic criteria have been abandoned as the sole reference for the comparison of alternatives. The increase of both options and restrictions has complicated significantly the choice of the best alternative. Until now, the search for solutions has usually focused on the reduction of all parameters and restrictions to a common denominator or the use of complex and scarcely transparent models. This paper shows how to make use of the AHP technique to improve the decision-making process in order to satisfy new water demands in a local context. This methodology has been widely used in other fields and allows the combination of quantitative and qualitative criteria. Among the virtues of AHP are transparency, simplicity and the fact that it relies on actual opinions from experts.
18 citations
TL;DR: In this article, the authors compared NaOCl and ECA in terms of disinfection efficacy, trihalomethanes (THM) formation, stability and composition, and showed that ECA could be a suitable alternative to NaOCL where decentralized production and use are required.
Abstract: Electrochemically activated (ECA) water is being extensively studied and considered as an alternative to chlorine for disinfection. Some researchers claim that ECA is by and large a chlorine solution, while others claim the presence of reactive oxygen species such as ozone and hydroxyl radicals in addition to chlorine. This study compares sodium hypochlorite (NaOCl) and ECA in terms of disinfection efficacy, trihalomethanes (THMs) formation, stability and composition. The studies were carried out under different process conditions (pH 5, 7 and 9, disinfectant concentrations of 2―5 mg/L and dissolved organic carbon (DOC) concentration of 2-4 mg/L). The results indicated that in the presence of low DOC (<2 mg/L) ECA showed better disinfection efficacy for E scherichia coli inactivation, formed lower THM and had better stability compared with NaOCl at both pH 5 and 7. Stability studies of stock solutions showed that over a period of 30 days, ECA decayed by only 5% while NaOCl decayed by 37.5% at temperatures of 4 °C. In a fresh ECA of 200 mg/L chlorine, about 5.3 mg/L ozone and 36.9 mg/L ClO 2 were detected. The study demonstrates that ECA could be a suitable alternative to NaOCl where decentralized production and use are required.
TL;DR: Artificial neural network (ANN) methodology has found some recent applications as efficient control tools for satisfying free residual chlorine (FR C) levels at critical locations of water distribution systems as mentioned in this paper, and this particular research was started to critically investigate the potential and applicability of the ANN approach as a tool for controlling FRC levels for complex water distribution system supplied by high quality waters with low chlorine demands.
Abstract: Artificial neural network (ANN) methodology has found some recent applications as efficient control tools for satisfying free residual chlorine ( FR C) levels at critical locations of water distribution systems. This particular research was started to critically investigate the potential and applicability of the ANN approach as a tool for controlling FRC levels for complex water distribution systems supplied by high quality waters with low chlorine demands. Konyaalti Water Distribution System, operated by Antalya Water and Wastewater Administration, Turkey, has been selected as a pilot. The selected system is complex in structure and supplied with raw water which has high quality and low decay rate of chlorine. The study has shown that ANN models with high predictive power and precision can be developed for such water distribution systems, and that these models can be utilized for forecasting purposes. The data for model building should be collected properly if the developed A NN models are to be utilized as control instruments for FRC levels within water distribution systems.
TL;DR: In this article, two processes for the treatment of raw water of lake of Garda, drawn from the drinking water treatment plant of Desenzano d/G (Brescia, Italy), spiked with pure microcystin-LR were investigated.
Abstract: Microcystin-LR (MC-L) is among the most toxic and frequent cyanotoxins found in surface water and a provisional value of 0.001 mg/L is indicated by World Health Organization guidelines for water for human consumption. Among the conventional processes used for surface water treatment, the most effective in microcystin removal are chemical oxidation and adsorption. This study investigated two processes for the treatment of raw water of lake of Garda, drawn from the drinking water treatment plant of Desenzano d/G (Brescia, Italy), spiked with pure MC-LR. The experimental tests on adsorption with activated carbon were performed using carbon from both a mineral (M21) and a plant source (C25). Determination of the adsorption isotherm show that the activated carbon M21 is more effective than C25 in MC-LR removal. During the continuous flow column test with the carbon M21, the limit concentration for MC-LR was reached after about 4,000 bed volumes. Finally, chemical oxidation with sodium hypoclorite, which is more effective than chlorine dioxide for MC-LR removal, shows a yield of 80% with a concentration of 3 mgCl2/L with a consequent reduction of MC-LR concentration from 10 to 1.5–2 μg/L.
TL;DR: Findings show that the MC-degrading bacteria are distributed over both communities, and can degrade MCs within the indigenous bacterial community co-existing with M. guttula.
Abstract: Grazing on Microcystis by the flagellate Monas guttula causes simultaneous degradation of microcystins (MCs) produced by Microcystis in culture. Although the MC-degrading bacterial strains that co-exist with M. guttula have been isolated, it is still unknown if the MC-degrading bacteria can degrade MCs within the indigenous bacterial community co-existing with M. guttula . To investigate this, we separated two indigenous bacterial communities (free-living and cell-bound) from M. guttula culture to test the ability of each community to degrade MCs. Results showed that MCs were rapidly degraded to undetectable level, and earlier MC exhaustion due to biodegradation was evident after re-spiking with MCs in both communities. These findings show that the MC-degrading bacteria are distributed over both communities, and can degrade MCs within the indigenous bacterial community co-existing with M. guttula . Denaturing gradient gel electrophoresis (DGGE) revealed differences in species diversity and structure between the two communities. Cluster analysis for DGGE patterns indicated that cell-bound community structures responded more sensitively than free-living community during degradation, and the two community structures evolved closer genetically with each other along the degradation period.
TL;DR: In this paper, the effect of dechlorination chemicals on water quality with respect to pH, turbidity and total organic carbon (TOC) was investigated along with the acute toxicity of the chemicals on the aquatic indicator species Daphnia magna.
Abstract: The impact of water quality parameters such as organic and inorganic matter as well as chlorine species (free chlorine and monochloramine) on the rate of dechlorination by sodium bisulfite (SBS), sodium thiosulfate (STS) and ascorbic acid (AA) were studied. Reaction rate constants determined for the various dechlorination reactions showed that SBS and AA achieved dechlorination at a faster rate than STS. Organic matter present in the test solution increased the rate of dechlorination by STS but not SBS and AA. AA was found to be ineffective for the removal of monochloramine. The effect of dechlorination chemicals on water quality with respect to pH, turbidity and total organic carbon (TOC) was investigated along with the acute toxicity of the chemicals on the aquatic indicator species Daphnia magna . SBS was determined to have an LC 50 of 68 mg/L with no toxicity impacts observed when the concentration was ≤ 20 mg/L for D. magna. AA increased the TOC levels in the treated water and resulted in some D. magna mortality at higher levels. STS had the least impact on daphnia mortality rates, but the use of STS for dechlorination resulted in the largest pH change of test waters compared to the other dechlorination chemicals.
TL;DR: In this article, an assessment of the importance of vortex shedding which occurs from UV lamps on the efficacy of disinfection in UV channels was made, where simulations were performed of the flow around four circular lamps with axes perpendicular to the flow and which are arranged in a diamond configuration.
Abstract: An assessment is made of the importance of vortex shedding which occurs from UV lamps on the efficacy of disinfection in UV channels. The focus is on the high Reynolds-number regime where turbulent flow conditions prevail and where there exists a strong interaction between the periodic mean-flow unsteadiness and the random turbulent motions. Simulations are performed of the flow around four circular lamps with axes perpendicular to the flow and which are arranged in a diamond configuration. Turbulence closure is achieved using a modified version of the k − ɛ model which takes into account the modification of the turbulence energy spectrum due to vortex shedding. The disinfection efficiency is estimated using a Lagrangian approach in which the trajectories of massless particles are tracked to estimate their residence time and the dose received. The modified turbulence model shows that the occurrence of vortex shedding produces wide variation in the particles trajectories and, consequently, in the UV dose received. These and other results strongly suggest that the effects of vortex shedding on disinfection are very important and thus must be accounted for if the uncertainties inherent in the use of computational fluid dynamics (CFD) for the design of UV treatment channels are to be reduced.
TL;DR: In this article, a study of the benthic community structure in Ghanam Creek surrounding an industrial sewage discharge, water and sediment samples were collected at eight sites in the warm season and cold season, and a multivariate analysis was carried out to determine the effect of environmental factors on the biodiversity distribution.
Abstract: A survey was performed to assess organic pollution, water properties and the marine benthic community. The need to assess the environmental status of marine and coastal waters encouraged the design of specific biotic indices to evaluate the response of benthic communities to human-induced changes in water quality. In this study of the benthic community structure in Ghanam Creek surrounding an industrial sewage discharge, water and sediment samples were collected at eight sites in the warm season and cold season. Environmental data on physical and chemical variables were also collected from each site and a multivariate analysis was carried out to determine the effect of environmental factors on the biodiversity distribution. The results indicated that the station furthest from the petrochemical industries (station located in Ghanam Creek) had higher species diversity and consequently a higher value for the Shannon-Weaver diversity index. The present study also showed that polychaetes were more abundant. Although polychaetes were also recorded at all the other stations, these stations had greater biodiversity with different numerically dominant species such as: Isopoda, Decapoda, Gastropoda, Copepoda, Bivalvia, Pennatulacea and Crustacea. Consequently, it was established that macrobenthic biodiversity was related to dissolved oxygen and the percentage of organic matter in the sediment.
TL;DR: In this paper, the authors investigated the removal of iron and manganese from groundwater by aeration, chlorine oxidation and microfiltration (MF) at the Chang-Hua Water Treatment Plant in Taiwan.
Abstract: The aim of this research was to investigate the removal of iron and manganese from groundwater by aeration, chlorine oxidation and microfiltration (MF). Pilot-scale experiments were performed at the Chang-Hua Water Treatment Plant in Taiwan. The raw waters contained soluble iron (0.4 mg/L) and manganese (0.5 mg/L) which were oxidized by chlorine and then filtered by hollow-fiber PTFE-MF. The oxidized particles on membranes under appropriate backwash were also investigated. The particle size and quality of treated water were examined. The experimental results indicated that the concentration of the residual manganese remained greater than 0.1 mg/L in treated water during the initial operation period. However, it decreased to below 0.01 mg/L after 2 weeks processing time. The scanning electron microscopy (SEM) energy dispersive spectroscopy analysis of oxidized metal particles under each process illustrated that the particles accumulated on membrane enhanced removal of iron and manganese, through autocatalytic activity in the accumulated layer on membrane. Moreover, the membrane operation pressure over 120 kPa was suggested for the active backwash process, where no structural damage on membrane was confirmed by SEM analysis.
TL;DR: In this paper, two different modelling approaches have been applied and evaluated to a selected UK drinking water system, one using multiple linear regression with appropriate water quality and operational parameters obtained from sampling, and the second approach employed the simulated distribution system (SDS) test.
Abstract: Haloacetic acids (HAAs) are formed during the chlorination of water containing organic matter but predictive models for their formation are not well established at present and have not been applied to UK water systems. In this paper two different modelling approaches have been applied and evaluated to a selected UK drinking water system. The first approach involved the development of statistical predictive models for the HAA formation by using multiple linear regression with appropriate water quality and operational parameters obtained from sampling, and the second approach employed the simulated distribution system (SDS) test. Statistically significant predictors were trihalomethane (THM) levels, pH, temperature, total chlorine total organic carbon, UV254, bromide concentration and residence time, but the importance of each varied with HAA species. The models that generally explained most of the variance of individual and total HAAs included THMs as a predictor variable. The use of the SDS-HAA test included quantification of individual HAA species. The concentration of total HAA and individual compounds in the SDS test and field samples were comparable immediately after chlorination, but with increasing residence time the concentration of HAAs in the selected water distribution system were greater than those found in the SDS test.
TL;DR: In this paper, the potential of micronized CaCO 3 slurry (MCCS) as an alternative to limestone filtration was investigated, and it was concluded that MCCS is generally not a feasible alternative for limestone filter as a stand-alone option for the conditioning and re-mineralization of drinking water.
Abstract: Worldwide limestone filtration is used in many treatment plants for the conditioning and (re)mineralization of drinking water to increase concentrations of Ca 2+ and HCO 3 − , pH and saturation index, thereby improving the quality of the water regarding corrosion control, buffering and taste. Typical applications include (very) soft groundwater with (very) low alkalinity and desalinated water. In Norway, some plants use a product made of ground natural limestone, called micronized CaCO 3 slurry (MCCS), which is dosed as slurry of fine particles (1–2 μm) into the raw water. In this study the potential of MCCS as an alternative to limestone filtration was investigated. Experiments were performed to determine the dissolution kinetics of MCCS and other CaCO 3 -products, including natural limestone grains and two precipitated CaCO 3 powders. As expected from theory, the dissolution kinetics are strongly influenced by the particle size of the CaCO 3 and the driving force towards the chemical equilibrium. However, all CaCO 3 -products needed substantial detention times (30 min and more) to dissolve completely. It is concluded that MCCS is generally not a feasible alternative for limestone filtration as a stand-alone option for the conditioning and (re)mineralization of drinking water. Applications of MCCS are limited and should either be found in combinations with coagulation/filtration or with other conditioning and (re)mineralization methods.
TL;DR: The ozone/BAF system in particular showed a high degree of effectiveness despite relatively low ozone doses corresponding to a low disinfection target (0.5-log Giardia reduction), demonstrating an important synergy between the ozone and BAF.
Abstract: The removal of selected pharmaceuticals and personal care products, atrazine, and disinfection by-product precursors, was evaluated during a pilot-scale study conducted at the Bollman Water Treatment Plant in Concord, California, USA. Treatment alternatives included ozonation followed by biologically active filtration (BAF), and nanofiltration. Both technologies exhibited excellent broad-spectrum removal of the spiked target contaminants. The ozone/BAF system in particular showed a high degree of effectiveness despite relatively low ozone doses corresponding to a low disinfection target (0.5-log Giardia reduction). The BAF system was observed to remove several contaminants that were relatively unreactive with ozone, demonstrating an important synergy between the ozone and BAF.
TL;DR: In this paper, a new method for detection of urea in surface and tap waters using LC-OCD-OND was developed, which could be shown that urea, ammonia and nitrate could be separated chromatographically from each other and from NOM (natural organic matter).
Abstract: A new method for urea detection in surface and tap waters using LC-OCD-OND was developed. It could be shown that urea, ammonia and nitrate could be separated chromatographically from each other and from NOM (natural organic matter). A direct quantification at its specific retention time is possible using custom-made detectors for nitrogen and for organic carbon. Further, urea can be detected indirectly as urea is transformed to ammonia after enzymatic hydrolysis with urease. After sufficient contact time for complete hydrolysis to ammonia (about 320 minutes) urea concentration can be calculated on the basis of the additional ammonia measured by LC-OCD-OND. The limit of detection of urea as mass was determined as 4 ppb for natural waters and 1 ppb for deionised waters.
TL;DR: Results show that the factors that primarily affect customers' requirements include free residual chlorine, turbidity and trihalomethanes, and utility managers must take action, especially concerning these product characteristics, to satisfy customers' demands.
Abstract: This paper explores the application of the quality function deployment (QFD) approach to identify and prioritize factors to reconcile ‘actual’ risk with ‘perceived’ risk for drinking water in a distribution network. Consumers' complaints (regarding water odour, taste, colour and other problems) and consumers' perception about water safety are used to define customers' requirements (aka ‘whats’). Twelve water quality parameters and distribution network properties (e.g. turbidity, pipe breaks) are used as indicators for drinking water quality – the product characteristics (aka ‘hows’). Correlations between ‘whats’ and ‘hows’ are established using data obtained from a case study. Opinions of experts in drinking water and consumers are used to define correlations between the ‘what’ ‘microbial safety’ and the ‘hows’. The analytic hierarchy process allows prioritizing customer requirements. Three QFD-based methods are applied to prioritize factors affecting water quality in a distribution network. The proposed approach is demonstrated through a case study of a water distribution network in Quebec City (Canada). Results show that the factors that primarily affect customers' requirements include free residual chlorine, turbidity and trihalomethanes. Sensitivity analyses using three scenarios confirm the robustness of the proposed approach. Utility managers must take action, especially concerning these product characteristics, to satisfy customers' requirements.
TL;DR: In this paper, the effectiveness of advanced oxidation processes in wastewater treatment has been evaluated in terms of the number of contaminant molecules transformed per 100 hydroxyl radicals reacting and removal efficiencies of four contaminants: bisphenol A, caffeine, DEET, and sulfamethazine.
Abstract: Advanced oxidation processes, based on hydroxyl radical chemistry, can be used to successfully destroy chemical contaminants in waters intended for reuse. In determining the effectiveness of these radical oxidative degradations and transformations in water, both reaction rate constants and compound removal efficiencies must be considered. Removal efficiencies are defined as the number of contaminant molecules transformed per 100 hydroxyl radicals reacting. Hydroxyl radical reaction efficiencies have been determined for bisphenol A, caffeine, DEET, and sulfamethazine in different qualities of treated and model laboratory wastewaters. While these four contaminants show similar hydroxyl radical reaction rate constants, their removal efficiencies in deionized water varied significantly at 76±7, 92 ±8, 95±9, and 56±7%, respectively. Model wastewater studies showed that dissolved oxygen did not appreciably influence these values, and low levels of dissolved organic matter ( D O M ) reduced the removal efficiencies by an average of approximately 20%. However, the combination of solution alkalinity and DO M had a significant impact in reducing hydroxyl radical reaction efficiencies, although not always in a linear, additive, fashion. These results imply that the effective implementation of advanced oxidation technologies in wastewater treatments might be enhanced by prior removal of organics or alkalinity.
TL;DR: In this article, the effects of pre-chlorination process on each fraction were also studied, and the effect of prechlorination on the formation of trihalomethanes (THMs) and haloacetic acids (HAA S ) was also investigated.
Abstract: Natural organic matter (NOM) in surface water with low specific UV absorbance in Tianjin, China, was fractionated using XAD resins and ultra-filtration membranes into different groups based on hydrophobicity and molecular weight (MW), respectively. The effects of the pre-chlorination process on each fraction were also studied. The hydrophilic acid (HPIA) fraction was the main organic component of NOM and the most significant precursor of trihalomethanes (THMs) and haloacetic acids (HAA S ) formation among the other two fractions (hydrophobic acid, HPOA and transphilic acid, TPHA). HPIA was the most reactive precursor to the formation of THMs, while the HPOA was the most reactive precursor to the formation of HAAs. Pre-chlorination tests were carried out at different contact times. Some of the HPOA and TPHA fractions transformed into HPIA fraction after oxidation of 180 min as deduced from the increase of HPIA and the decreases of HPOA and TPHA fractions. On the other hand, the MW <2 kDa fraction was predominant in source water (approximately 60%) and played the most important role in the formation of THMs and HAAs. Pre-chlorination caused the cleavage of large molecules and altered the MW distribution towards smaller molecules.
TL;DR: Two pond sand filters with modified design were constructed in Pathorghata Upazila of Barguna District located in southern Bangladesh Performance assessment of the PSFs was done after commissioning in terms of quality of filtered water, ease of operation and maintenance, monthly check-up of production capacity/efficiency of the filters, users' participation and acceptability of the modified PSFs as mentioned in this paper.
Abstract: Two pond sand filters (PSFs) with modified design were constructed in Pathorghata Upazila of Barguna District located in southern Bangladesh Performance assessment of the PSFs was done after commissioning in terms of quality of filtered water, ease of operation and maintenance, monthly check-up of production capacity/efficiency of the filters, users' participation and acceptability of the modified PSFs Some important parameters such as total coliform, fecal coliform, turbidity, colour, total suspended solids (TSS), chemical oxygen demand (COD) and pH were measured for the raw water and at the various stages of treatment in order to determine the effectiveness of different units of the PSFs Close observations were made to assess the removal of turbidity in the roughing/pre-filtration chamber to ensure trouble-free operation of the main filter bed In combination with roughing filters, the average turbidity and fecal coliform removal efficiency of the sand filters were found to be 76 and 98%, respectively Filter run of the modified PSFs was also found higher (about 3 months) than the existing PSFs
TL;DR: In this paper, the potential impacts to UF permeate water quality and coagulation pretreatment efficacy in a bench-scale submerged UF membrane system operating with and without waste backwash water recycle were investigated.
Abstract: In drinking water treatment, ultrafiltration (UF) membrane systems are generally operated at 90 to 95% recovery with production losses resulting from waste residual streams such as backwash water and clean-in-place (CIP) liquid residuals. In drought-prone regions, it may be desirable to apply alternative UF plant design configurations to increase recovery rates and minimize water loss. This approach could consist of adding a secondary stage UF membrane for treatment of first stage UF residuals, or recycling the first stage UF waste residuals by blending a percentage of the backwash water with the raw water at the front of the treatment train. For small systems, the second option may present a more cost-effective solution. The overall objective of this research project was to investigate the potential impacts to UF permeate water quality and coagulation pretreatment efficacy in a bench-scale submerged UF membrane system operating with and without waste backwash water recycle. The results of the study showed that blending 10% waste backwash water with raw water did not negatively impact UF permeate water quality. The results also demonstrated that recycling waste backwash water prior to coagulation–UF treatment may improve organic removal and reductions in neat coagulant dosage may be possible to achieve specific DBP precursor removal targets.
TL;DR: In this paper, the authors presented an optimization of various oxide coating processes on quartz sand surface, which showed that IIS and MIOCS media have better As(III) removal potential compared with other media.
Abstract: This paper presents optimization of various oxide coating processes on quartz sand surface. The chemical characteristics of quartz sand collected from the Yamuna river, Allahabad, India, shows 82.022% SiO 2 besides other oxides. The optimal coating temperature was 60°C; optimal pH coating ≈0.5; optimal heating time was 60 hours and percentage iron salt [Fe(NO 3 ) 3· 9H 2 O] was 8―10% w/w for iron oxide coated sand (IOCS) with maximum As(lll) removal efficiency. The 60 h heating time in iron oxide coating process yields maximum Fe (mg/g) on the sand surface. The PH coatin g has shown considerable effect on arsenic removal efficiency during optimization of sulfate modified iron oxide coated sand (SMIOCS) media. The SMIOCS prepared at pH coating <10 was quite efficient compared to media prepared at pH coating ≅neutral and pH coating ≅12.05. The mixed oxide coated sand (MOCS) prepared at ph coating < 1.0 has shown better arsenic removal efficiency in comparison to other mixed oxide coated sand media. The BET surface area varied between 2.55 and 7.895 m 2 /g for particle size ranging from 0.324 mm to 0.716 mm for different coated sand media. The pH z p c values indicate that the IOCS and SMIOCS media are positively charged at neutral pH, whereas uncoated sand is negatively charged. Equilibrium and column studies results show that IIS and MIOCS media have better As(III) removal potential compared with other media.
TL;DR: In this paper, the structure and occurrence of natural organic matter (NOM) in raw water sources is investigated to minimise the formation of chlorination by-products (CBPs).
Abstract: To minimise the formation of chlorination by-products (CBPs) it is imperative that attention is directed towards the structure and occurrence of natural organic matter (NOM) in raw water sources, a ...
TL;DR: In this paper, the authors explored the planning process for adaptation strategies, emphasizing current research and modelling constraints and comparing resilience strategies, where low-regret options designed to protect a site from flooding were chosen and, where the population at risk is high, those were complemented with long term strategies for increased robustness of supply network to a multiplicity of risks.
Abstract: Flooding can have severe impacts on the water supply services and adaptation responses for the provision of high-quality water supplies are necessary to cope with the risks exacerbated by climate change. This paper explores the planning process for adaptation strategies, emphasizing current research and modelling constraints and comparing resilience strategies. The flood hazard, vulnerability and impact were assessed based on information provided by the Environment Agency, local knowledge and network modelling of outages. Improvements in flood estimation were suggested to extend the range of scenarios analysed and the geographic cover and scope of models, whilst reducing and quantifying associated uncertainty. For evaluating consequences of widespread flooding, information on joint flood probabilities would be relevant, particularly where sites are interconnected. Considering the uncertainties in the approach, two strategies were explored to manage the flood risk, i.e. enhanced asset and system resilience. Low-regret options designed to protect a site from flooding were chosen and, where the population at risk is high, those were complemented with long term strategies for increased robustness of supply network to a multiplicity of risks.