Full-scale Water Treatment Plant Research Articles

Safeguarding reverse osmosis membrane integrity in drinking water production: A pilot study using 2 native bacterial communities and viruses in surface water as integrity indicators

Water treatment train including a reverse osmosis barrier is capable of producing high-quality water coupled with microbial safety. However, analytically proving this with log removal value (LRV) > 3 has remained a challenge. Conservative techniques that quantify salt or sulfate ion passage as virus surrogates are currently used to credit the membrane system for its microbial removal capacity. These methods are insensitive, and it is now understood that the transport mechanism correlation between these surrogates with the actual passage of viruses is weak. There is also a huge gap between the current log credit assigned (using spiking of surrogates in feed) and the actual log removal that can be proven in the drinking water plant. In this paper, we introduce two techniques that exploit the high concentration of microbial communities in fresh surface water by quantifying bacteria through flow cytometry (FC) and native viruses through qPCR assays. These two methods are compared to LRV of conductivity, TOC, and fluorescent markers. That high concentration of bacterial community allowed for LRV > 4 by flow cytometry in an intact module. After inflicting damage with a 1.5 mm defect, the FC method detected the damage, and a bacterial cell count >103 cell count/ml was measured in the permeate, while conductivity lacked sensitivity to monitor any integrity loss. Furthermore, after chlorine exposure to the membrane, both bacteria and virus detected no leakage, proving the membrane's intactness and also demonstrating the effect of chlorination on the passage of small solutes. The implementation of the two microbial quantifying methods in full-scale water treatment plants facilitates higher sensitivity in membrane integrity loss than currently used methods.

Data-driven modeling techniques for prediction of settled water turbidity in drinking water treatment

Drinking water treatment is a complex system of chemical, physical, and biological processes that is highly dependent on water quality and the design of the treatment process. To create decision-support tools, the prediction of key performance indicators, such as settled water turbidity, is needed. A variety of data-driven modeling techniques is available to formulate such predictions. Data-driven models provide valuable tools for formulating predictions where there is a lack of mechanistic models or the mechanisms are not fully understood, as in surface water treatment. The objective of this paper is to evaluate and compare the effectiveness of various data-driven techniques for this important, but difficult, problem. Recognizing that the size and quality of the dataset are most critical in this kind of analysis, this work uses one of the largest datasets used in this context consisting of 2,527 vectors of water quality and operational data (2,527 X nine data frame) from a full-scale water treatment plant. The paper constructs and compares the performance of the several data-driven models including k-nearest neighbor (KNN) regression, polynomial regression, and artificial neural networks (ANN). Based on test scaled root mean square error (RMSE), the ANN model was the most predictive (0.124). Similarly, the ANN model had the best predictive performance based on total scaled RMSE (0.086). These results show that ANNs have a high potential for the development of a future decision support system in selecting appropriate coagulant doses based on settled water turbidity.

Demonstrating scale-up of a novel water treatment process using super-bridging agents

Fiber-based materials have emerged as a promising option to increase the efficiency of water treatment plants while reducing their environmental impacts, notably by reducing the use of unsustainable chemicals and the size of the settling tank. Cellulose fiber-based super-bridging agents are sustainable, reusable, and versatile materials that considerably improve floc separation in conventional settling tanks or via alternative screening separation methods. In this study, the effectiveness of fiber-based materials for wastewater treatment was evaluated at lab-scale (0.25 L) and at pilot-scale (20 L) for two separation methods, namely settling and screening. For the fiber-based method, the performance of floc separation during settling was slightly affected by an 80x upscaling factor. A small decrease in turbidity removal from 93 and 86 % was observed for the jar and pilot tests, respectively. By contrast, the turbidity removal of the conventional treatment, i.e., no fibers with a settling separation, was largely affected by the upscaling with turbidity removals of 84 and 49 % for jar and pilot tests, respectively. Therefore, results are suggesting that fiber-based super-bridging agents could be implemented in full-scale water treatment plants. Moreover, the tested fibers increase the robustness of treatment by providing better floc removal than conventional treatment under several challenging conditions such as low settling time and screening with coarse screen mesh size. Furthermore, at both lab-scale and pilot-scale, the use of fiber-based materials reduced the demand for coagulant and flocculant, potentially lowering the operational costs of water treatment plants and reducing the accumulation of metal-based coagulants and synthetic polymers in sludge. Acute toxicity tests using the model organism Daphnia magna show that the cellulose fibers introduce insignificant toxicity at the optimized fiber concentration. Although dedicated mechanistic studies are required at various scales to understand in detail the influence of fibers on water treatment (coagulation/flocculation time, floc formation, floc size distribution velocity gradient, etc.), the efficacy and scalability of the fiber-based approach, along with its minimal environmental impact, position it as a viable and sustainable option for existing and future wastewater treatment plants.

Application of full-scale aerobic granular sludge technology for removing nitrate from groundwater intended for human consumption

The dependence on groundwater for human consumption has increased worldwide in the last decades. Nitrate (NO3−) often reaches groundwater and causes significant degradation in groundwater quality. In an effort to address this issue, a full-scale water treatment plant using aerobic granular sludge (AGS) technology was built to remove NO3− from nitrate-polluted groundwater intended for human consumption in a rural village. The impact of changes in the operational conditions of hydraulic retention time (HRT) and organic matter loading (OML) rate on NO3− removal, overall system performance, and the granule microbiome were studied. Regardless of the HRT, the AGS technology was successful in removing NO3− with removal rates >50 % with an optimal OML rate of 75 mg L−1. No significant variations in the total abundance of any of the denitrification genes were observed. The composition of prokaryotic and eukaryotic communities was affected by changes in the HRT and OML rate. Specific prokaryotic taxa were identified as responsive to changes in operational parameters and their abundances were linked to the removal of NO3−, confirming that the microbes are critical to the NO3− removal process. This study demonstrates that the AGS technology can be successfully implemented to treat nitrate-polluted groundwater in rural villages to produce water of drinking quality. In addition, the reported hydraulic retention times and organic matter loading rate can be used to further improve the system performance to remove nitrate from groundwater.

Molecular insights towards changing behaviors of organic matter in a full-scale water treatment plant using FTICR-MS

The changing behavior of organic matter in a full-scale water treatment process was characterized based on the three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Polyaluminum chloride (PAC) as a coagulant can help to effectively remove soluble microbial by-products-like and aromatic protein-like substances during coagulation and sedimentation, corresponding to tannin and coagulated aromatic regions. The leakage of soluble microbial products during sand filtration resulted in an increase in the intensity of biomass-like regions. Nitrogen-containing compounds have higher weighted average value of double bond equivalents (DBEw) and the modified aromaticity index (AImod-w) than nitrogen-free compounds. Water treatment can preferentially remove unsaturated nitrogen-containing compounds with more O atoms and higher-oxidation-state carbon. The dissolved organic carbon (DOC) and UV254 were not correlated well with changes in nitrogen-containing compounds due to the preferential removal of nitrogen-containing compounds. This study revealed the specificity of organic matter removal during water treatment, and it was helpful in optimizing treatment processes for various raw water to ensure water quality.

Multi-scale Investigation of Ammonia-Oxidizing Microorganisms in Biofilters Used for Drinking Water Treatment.

Ammonia-oxidizing microorganisms (AOMs) include ammonia-oxidizing bacteria (AOB), archaea (AOA), and Nitrospira spp. sublineage II capable of complete ammonia oxidation (comammox). These organisms can affect water quality not only by oxidizing ammonia to nitrite (or nitrate) but also by cometabolically degrading trace organic contaminants. In this study, the abundance and composition of AOM communities were investigated in full-scale biofilters at 14 facilities across North America and in pilot-scale biofilters operated for 18 months at a full-scale water treatment plant. In general, the relative abundance of AOM in most full-scale biofilters and in the pilot-scale biofilters was as follows: AOB > comammox Nitrospira > AOA. The abundance of AOB in the pilot-scale biofilters increased with increasing influent ammonia concentration and decreasing temperature, whereas AOA and comammox Nitrospira exhibited no correlations with these parameters. The biofilters affected AOM abundance in the water passing through the filters via collecting and shedding but exhibited a minor influence on the composition of AOB and Nitrospira sublineage II communities in the filtrate. Overall, this study highlights the relative importance of AOB and comammox Nitrospira compared to AOA in biofilters and the influence of filter influent water quality on AOM in biofilters and their release into the filtrate.

Invited Perspective: Environmental Health Interventions Are Only as Good as Their Adoption.

Vol. 131, No. 1 Invited PerspectiveOpen AccessInvited Perspective: Environmental Health Interventions Are Only as Good as Their Adoptionis companion ofAdoption of Point-of-Use Chlorination for Household Drinking Water Treatment: A Systematic Review Karen Levy Karen Levy Address correspondence to Karen Levy, Department of Environmental and Occupational Health Sciences, University of Washington, Box 351618, 2980 15th Ave. NE, Seattle, WA 98195 USA. Telephone: (206) 543-4341. Email: E-mail Address: [email protected] https://orcid.org/0000-0002-0968-9401 Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington, USA Search for more papers by this author Published:30 January 2023CID: 011303https://doi.org/10.1289/EHP11906AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit “I have not failed. I’ve just found 10,000 ways that will not work.” –Thomas EdisonScientists and engineers often come up with brilliant ideas, but in the end technology is only as good as its adoption and proper use. This is true for regardless of how complicated or simple the technology.Household water treatment, also commonly referred to as point-of-use (POU) water treatment, is a strategy to improve access to safe water that was introduced within the water, sanitation, and hygiene (WASH) field1 because many communities in lower- and middle-income country (LMIC) settings lack access to a full-scale water treatment plant. With POU treatment, residents can conduct at least some elements of treatment (coagulation and sedimentation, filtration, ultraviolet disinfection, or chemical inactivation) in their own homes, offering them the capacity to disinfect their own water. Treating water in the home also has the benefit of minimizing recontamination after collection, a well-documented phenomenon in locations where people fetch their water from locations outside the home.2,3Chlorination has been seen as a particularly promising POU approach because it leaves a residual disinfectant in the water to address microbial intrusion during storage.4 In LMICs, many studies have been carried out on the effectiveness of household drinking water chlorination for preventing diarrhea. A recent systematic review found that, compared with untreated drinking water from an unimproved source, risk of diarrhea was reduced by 44% with POU chlorination of water [lowercase italic n equals 25n=25 studies; 0.66 (0.56–0.77)].5However, although understanding the potential health impact of a technology is important, understanding whether and why people use, or do not use, a proposed technology is equally important. In their review in this issue of Environmental Health Perspectives, Crider et al. do just this, addressing barriers to the adoption of POU chlorination for household drinking water treatment by 46 target populations.6Considering users’ needs and interests is essential to adoption of a technology. For example, the authors found that bad taste, smell, or appearance of treated water was cited by a large percentage of households, as was lack of time to spend on disinfection (a time burden usually placed on women). Most of the intervention groups received chlorination products for free; households in the groups that did not cited price or availability of products as a barrier to repurchase and continued use.In addition to the identification of specific barriers to adoption two other aspects stood out in the review. First, the authors identified a sheer lack of information on barriers to adoption. “Much of the time, the reasons for low adoption are poorly understood simply because the relevant data are not systematically collected,” they stated. The authors excluded 27 of 63 otherwise-eligible studies because quantitative measures of adoption were not reported. Among those that did report a measure of adoption, there was no consensus definition of adoption, and several studies emphasized reasons for use rather than nonuse.Second, lack of attention in the field to user adoption as a signal of intervention success is also belied by the language that researchers use to describe it. Different words used in the literature to describe what Crider et al. appropriately refer to as “adoption” of water chlorination practices range from “adherence” or “compliance” to “use/usage” or “uptake.”6 Public health inherited the language of “compliance” and “adherence” from medicine, where it describes how often patients follow through with a medication regimen.7,8 Although subtle, this language is important because the medical words put the burden of failed adoption on the user, whereas “adoption,” “use/usage,” and “uptake” put this burden on the implementer.Time and again we see environmental health–based interventions fail because we are not focused enough on the actual uptake of a technology. This is also true for other areas of environmental health, such as household air pollution (HAP).9,10 The WASH and HAP fields are increasingly recognizing the importance of applying approaches from systems science and implementation science to increase the chances of success for environmental health interventions.10,11This work is critical. Our practices, and our language, must center on users’ needs and interests if we hope for adoption of new technologies to improve population health related to environmental conditions.

Suppression of performance of activated carbon filter due to residual aluminum accumulation

Extending the lifetime of granular activated carbon (GAC) filters with no significant loss in their effectiveness is a considerable challenge for drinking water supply utilities. However, the effects of residual Al from coagulants on GAC performance are rarely considered. Herein, in-service GAC samples obtained from full-scale water treatment plants were investigated to evaluate the amount of accumulated Al. Although the Al concentration in water was two to three times lower than the Ca concentration, Al exhibited considerable accumulation (second to Ca accumulation) in in-service GAC samples (0.68–8.63 mg g−1). Surface characterization results indicated that Al accumulation could have been caused by the co-precipitation of Al with Ca and Si to form Ca4Al2Si3O10·H2O and Ca4Al6O12SO4, self-precipitation or complexion with −OH/−COOH on the GAC or biofilm surfaces. Correlation analysis of the accumulated Al and GAC properties implied that Al accumulation considerably reduced the surface area of GAC by ∼30%. Lab simulation experiments indicated that the removal of dissolved organic matter was reduced by 6–10% when additional Al was loaded. In addition, results showed that the residual Al (up to 200 μg L−1) considerably affected the extracellular polymeric substance component and microorganism community structure. In summary, strict control of residual Al is beneficial for maintaining the efficacies of GAC and biologically activated carbon.

Chloramine Prevents Manganese Accumulation in Drinking Water Pipes Compared to Free Chlorine by Simultaneously Inhibiting Abiotic and Biotic Mn(II) Oxidation

The oxidation of residual Mn(II) in finished water can lead to MnOx deposit formation in drinking water pipes. Previous work has illustrated that microbes readily cause Mn deposit build-up in nondisinfected pipes. Here, we investigated how disinfectant type and dose affected Mn(II) oxidation and MnOx accumulation through long-term pipe experiments using water produced by a full-scale water treatment plant. The results showed that Mn(II) oxidation initiated quickly in the new pipes chlorinated with 1.0 mg/L free chlorine. After 130 days of MnOx accumulation, 100 μg/L Mn(II) in water could drop to 1.0 μg/L within 1.5 h, resulting from autocatalytic Mn(II) oxidation and Mn(II) adsorption by MnOx deposits accumulated on pipe walls. In contrast to chlorination, chloramination (1.0 mg/L Cl2) caused almost no MnOx accumulation during the entire study period. The underlying mechanism was probably that monochloramine inhibited microbial Mn(II) oxidation without causing significant abiotic Mn(II) oxidation like free chlorine. A low free chlorine dose (0.3 mg/L) also reduced Mn deposit formation by mass but to a lesser extent than chloramination. After disinfection (chlorination or chloramination) was discontinued for days, biotic Mn(II) oxidation occurred, and this process was inhibited again once disinfection was resumed. In addition, Fe(III) of 200 μg/L enhanced the stability of MnOx accumulated on pipe surfaces, while humic acid induced MnOx deposit resuspension. Overall, this study highlighted the regulating role of disinfectants in MnOx formation and provided insights into developing appropriate disinfection strategies for Mn deposit control.

Removal of natural organic matter in full-scale conventional and advanced water treatment plants: Assimilable organic carbon and its precursors

This study aimed to investigate the performance of three full-scale long-time water treatment plants with influent from Taihu Lake for the removal of natural organic matter (NOM) and assimilable organic carbon (AOC), emphasizing on the processes of pre- and post-ozonation and biological activated carbon filtration (BACF). High-performance size exclusion chromatography (HPSEC) separation, hydrophilicity/hydrophobicity resin fractionation and excitation-emission matrix (EEM) fluorescence spectroscopy were applied to determine NOM fraction variation in purification processes and their relationships with AOC. The results indicated that NOM fractions with high hydrophilicity (NHPI) and lower molecular weight (1 kDa - 10 kDa) likely contributed to the majority of AOC. The advanced water treatment processes behaved negative removals of AOC since the BACF with long-time operation introduced large amounts of AOC precursors and could cause drastic rebound of AOC upon chlorination disinfection. Finally, during exposure to ozone, the formation rate of AOC showed a linear relationship with UV254 and total fluorescence intensity (TFI) and each regional fluorescence intensity (RFI) with slight interference by the presence of particulate organic matter (POM). This study provides useful information for variation of NOM and its associated bio-availability during conventional and advanced processes in full-scale water treatment plants.

Differences in removal rates of virgin/decayed microplastics, viruses, activated carbon, and kaolin/montmorillonite clay particles by coagulation, flocculation, sedimentation, and rapid sand filtration during water treatment

One of the main purposes of drinking water treatment is to reduce turbidity originating from clay particles. Relatively little is known about the removal of other types of particles, including conventionally sized powdered activated carbon (PAC) and superfine PAC (SPAC), which are intentionally added during the treatment process; microplastic particles; and viruses. To address this knowledge gap, we conducted a preliminary investigation in full-scale water treatment plants and then studied the removal of these particles during coagulation-flocculation, sedimentation, and rapid sand filtration (CSF) in bench-scale experiments in which these particles were present together. Numbers of all target particles were greatly decreased by coagulation-flocculation and sedimentation (CS). Subsequent rapid sand filtration greatly reduced the concentrations of PAC and SPAC but not the concentrations of viruses, microplastic particles, and clay particles. Overall removal rates by CSF were 4.6 logs for PAC and SPAC, 3.5 logs for viruses, 2.9 logs for microplastics, and 2.8 logs for clay. The differences in removals were not explained by particle sizes or zeta potentials. However, for clays, PAC and SPAC, for which the particle size distributions were wide, smaller particles were less efficiently removed. The ratios of both clay to PAC and clay to SPAC particles increased greatly after rapid sand filtration because removal rates of PAC and SPAC particles were about 2 logs higher than removal rates of clay particles. The trend of greater reduction of PAC concentrations than turbidity was confirmed by measurements made in 14 full-scale water purification plants in which residual concentrations of PAC in treated water were very low, 40–200 particles/mL. Clay particles therefore accounted for most of the turbidity in sand filtrate, even though PAC was employed. The removal rate of microplastic particles was comparable to that of clays. Sufficient turbidity removal would therefore provide comparable removal of microplastics. We investigated the effect of mechanical/photochemical weathering on the removal of microplastics via CSF. Photochemical weathering caused a small increment in the removal rate of microplastics during CS but a small reduction in the removal rate of microplastics during rapid sand filtration; mechanical weathering decreased the removal rate via CS but increased the removal rate via rapid sand filtration. The changes of removal of microplastics might have been caused by changes of their zeta potential.

Computational fluid dynamics–based modeling and optimization of flow rate and radiant exitance for 1,4-dioxane degradation in a vacuum ultraviolet photoreactor

1,4-Dioxane is one of the most persistent organic micropollutants in conventional drinking-water-treatment processes. Vacuum ultraviolet (VUV) treatment is a promising means of removing micropollutants such as 1,4-dioxane from source water, but this approach has not yet been implemented in a full-scale water treatment plant, partly because the operating parameters for pilot and full-scale VUV photoreactors have not been optimized. Here, we developed a computational fluid dynamics–based method for optimizing VUV photoreactor performance through energy-based analyses that take into account the effects of two important operating parameters—flow rate and radiant exitance. First, we constructed a computational fluid dynamics model and determined the sole parameter required for the model, the pseudo-first-order rate constant for the reaction of 1,4-dioxane, by simple batch experiment. Then, we validated the model by using a pilot-scale flow-through annular photoreactor. Finally, we used the validated model to examine the effects of flow rate and radiant exitance on the efficiency of 1,4-dioxane degradation in a virtual annular photoreactor. Radiation efficiency, which was defined as the ratio of the logarithmic residual ratio of 1,4-dioxane to the theoretical minimum logarithmic residual ratio (best possible performance) under the given operating conditions, was calculated as an energy-based index of cost-effectiveness. Radiation efficiency was found to increase with increasing flow rate but decreasing radiant exitance. An electrical energy per order (EEO) analysis suggested that VUV treatment under laminar flow was most economical when low-power lamps and a high flow rate were used. In contrast, VUV treatment under turbulent flow was suggested to be most economical when high-power lamps were used at a high flow rate.

Toxic cyanobacteria in water supply systems: data analysis to map global challenges and demonstrate the benefits of multi-barrier treatment approaches

Abstract The occurrence of toxic cyanobacteria in surface waters and their impact on drinking water treatment plants (WTPs) is a growing, global concern. The main objective of this paper was to assess the presence of cyanobacteria in surface water sources and associated cell removal efficiency in full-scale WTPs across the world. Previously unpublished data was collected from WTPs experiencing cyanobacterial blooms in either their managed surface waters or recreational waters. In total, data were collected from 31 surface water sources and 21 WTPs in North and South America, Europe, Asia, and Australia. The most commonly detected species were identified in both the surface waters, including Microcystis, Anabaena, Nostoc, Oscillatoria, and Planktolyngbya, and water treatment plant intakes, including Microcystis, Cylindrospermopsis, Anabaena, Pseudanabaena, and Aphanizomenon. In the intakes, cyanotoxins and taste and odor (T&O) compounds frequently co-occurred (80%) as did multiple cyanotoxins (39%). Conventional treatment saw a wide range of removal depending on the density of cells, species, and metabolites. Although more than 28% of sampling events displayed negligible or even negative removals of metabolites or cells due to accumulation within the clarifier, filtration, or water recycling, the presence of multiple treatment barriers, particularly advanced treatments like granular activated carbon and nanofiltration, allowed for the cells and their metabolites of concern to be removed to below guideline values. During treatment, total microcystins were often removed without releasing their intracellular fraction, whereas cylindrospermopsin, geosmin, and 2-MIB were commonly detected as entirely extracellular at the plant's intake. The maximum tolerable cell (MTC) counts for cyanotoxin- or T&O-producing cells were calculated using guideline values, average removal efficiency, and the average cell quota derived from data. The 21 WTPs in this work were found to be able to tolerate approximately 74,000 cells/mL for microcystins, 8,000 cells/mL for cylindrospermopsin, and 1,200 cells/mL for geosmin and 2-MIB before exceeding guideline values. These levels provide guidance for water treatment plant operators to assess the potential risk associated with cells capable of producing cyanotoxins or T&O compounds.

River water treatment using electrocoagulation for removal of acetaminophen and natural organic matter

Electrocoagulation (EC) was assessed for removal of acetaminophen and natural organic matter (measured as UV254) from river water. Process was assessed for time, electrode materials, inter electrode distance, and voltage. Best conditions for removal of acetaminophen and UV254 absorbance were 60 min reaction time, aluminum-aluminum electrodes, 2 cm inter electrode distance, and 9 V. Acetaminophen tested at 1, 2, 5, 10, and 20 mg L−1 showed that treatment efficiency decreased as the concentration increased. The main mechanism for removal of acetaminophen was H bonding with Al(OH)3 flocs; this was confirmed by XRD and FT-IR spectrum. Pseudo-second order kinetics model exhibited a good fit on experimental data for acetaminophen removal at different concentrations. Univariate ANOVA indicated statistically significant difference between treatments for acetaminophen removal (F2.76 = 136, P = <0.001). A significant linear correlation was found between UV254 absorbance and acetaminophen removal at different concentrations. Preliminary analysis suggest that EC will cost US$ 0.22/m3 for river water treatment. The lab-scale EC process was compared with a full-scale water treatment plant for removal of natural organic matter. Water treatment plant after multiple levels of purification was not able to fully remove UV254 absorbance whereas EC treatment showed good efficiency.

Complex odor control based on ozonation/GAC advanced treatment: optimization and application in one full-scale water treatment plant

BackgroundTaste and odor problem in drinking water is one major concern for consumers and water supply. Exploring the odor characteristics and the major odor causing compounds in the source water is the base for odor control in drinking water treatment plant (WTP). In this study, focusing on a newly constructed reservoir with Huangpu River as the source water, the occurrence of typical odorants and their variations were first identified. Correspondingly, the removal behavior in an ozone/GAC advanced treatment process was investigated.ResultsThe results indicated that 2-methylisoborneol (2-MIB), geosmin (GSM), and bis (2-chloroisopropyl) ether (BCIE) have major contribution to the musty/earthy and chemical/septic odors in the source water, respectively. Pre-ozonation alone (1 mg L−1) showed limited removal for 2-MIB and BCIE, at less than 30% and 20%, respectively, while combining with coagulation, sedimentation, and sand filtration, the removals were improved to higher than 50%. After post-ozonation, the desired removal was achieved at a 1.5 mg L−1 dosage with all the odorants decreased below the corresponding odor threshold concentrations (OTCs) in the effluents. Furthermore, at a 1 mg L−1 post-ozone addition, by combining with subsequent GAC process, the odor problem was solved as well.ConclusionTo resolve the odor problem in the drinking water, the concentrations of the odorants at less than their OTCs need to be achieved. As 2-MIB and BCIE have low reactivity towards direct ozonation, a subsequent GAC is needed with a moderate dosage of post-ozonation (1 mg L−1). Thus, for the odor problem in the source water, the suggested operation is: 1 mg L−1 of pre-ozonation in combination with coagulation, sedimentation, and sand filtration, followed by a 1 mg L−1 dosage of post-ozonation and finished by a GAC process.

Effect of disinfectant residuals on infection risks from Legionella pneumophila released by biofilms grown under simulated premise plumbing conditions

The ubiquitous presence of biofilms in premise plumbing and stagnation, which commonly occurs in premise plumbing, can exacerbate the decay of chlorine residual in drinking water. Using biofilms grown in a simulated premise plumbing setup fed directly with freshly treated water at two full-scale water treatment plants, we previously determined the mass transfer coefficients for chlorine decay in premise plumbing. These coefficients coupled with inactivation kinetics of L. pneumophila released from biofilms reported previously were integrated into a Monte Carlo framework to estimate the infection risk of biofilm-derived L. pneumophila from 1 to 48 h of stagnation. The annual infection risk was significantly higher when water stayed stagnant for up to 48 h in pipes covered internally with biofilms, compared to clean pipes without biofilms. The decay of residual chlorine due to biofilms during 48-hour stagnation led to up to 6 times increase in the annual infection risk compared to the case where biofilms was absent. Global sensitivity analysis revealed that the rate of L. pneumophila detachment from biofilms and the decay of chlorine residual during stagnation are the two most important factors influencing the infection risks. Stagnation caused by water use patterns and water-saving devices in the premise plumbing can lead to increased infection risk by biofilm-derived L. pneumophila. Overall, this study’s findings suggested that biofilms could induce chlorine decay and consequently increase L. pneumophila infection risk. Thus, reducing stagnation, maintaining residual chlorine, and suppressing biofilm growth could contribute to better management of L. pneumophila infection risk.

Drinking Water Treatments for Arsenic and Manganese Removal and Health Risk Assessment in White Rock, Canada

The City of White Rock, Canada has been facing challenges of elevated concentrations of arsenic and manganese in its drinking water supply. A pilot water treatment study was conducted to explore effective contaminant removal solutions for human health risk mitigation. The arsenic and manganese removal performance of four treatment processes, including ozonation-manganese greensand filtration (OSF), OSF-iron-based granular media adsorption (OSFIA), the Burgess Iron Removal Method (BIRM), and BIRM-iron-based granular media adsorption (BIA) were evaluated. The non-cancer health risks and the incremental lifetime cancer risks (ILCR) posed by arsenic in different water sources were also assessed. The results show that OSFIA treatment achieved the highest arsenic and manganese removal. An average arsenic removal rate of 68.5% (initial concentration = 9.3 μg/L) was observed using OSFIA during two months of treatment, while manganese (initial concentration = 133.9 μg/L) can be completely removed. The arsenic removal was mainly be attributed to the adsorption of iron-based granular media. The mean values of non-cancer health risks of arsenic exposure due to oral intake of treated water were identified to be lower than the critical threshold for different age groups. In addition, the probability of critical ILCR occurrence can be greatly reduced. Based on the results from the pilot study, OSFIA was selected to construct a full-scale water treatment plant. Arsenic and manganese concentrations in the effluent from the plant can be reduced to a low-to-undetectable level, achieving negligible health risks to the residents of the city.

Membrane ageing in full-scale water treatment plants

Membrane filtration is a rapidly expanding choice for drinking water treatment. Unfortunately, there is limited data on long-term changes in the membranes’ performance as they age. The present research investigated changes in performance factors as well as chemical characteristics for hollow-fibre ultrafiltration membranes that ranged in age from 8 full-scale drinking water treatment plants. Membranes were harvested by plant operators regularly and analyzed using standardized laboratory tests. Approximately half of the membranes were a new PVDF-based chemistry. These were observed to have insignificant changes in performance factors and chemical characteristics since their beginning of operation. However, because these membranes were newer, only data for the first 5 years of operation was available. The other half of the membranes, with an older PVDF-based chemistry, were observed to have stable behaviour until approximately 5 years of operation; after this time, performance factors and chemical characteristics of the membranes began to change significantly. For these membranes, the clean water resistance and fouling rate increased after 5 years of operation. The mechanical properties of these membranes also deteriorated after 5 years of operation, suggesting that their susceptibility to breach is higher after prolonged use. These changes in performance factors paralleled, and were possibly caused by, the removal of hydrophilic additives from the membrane material. Clean water resistance was identified as a good benchmark for all the parameters studied, a finding that is useful for water treatment facilities in quickly assessing the status of their membranes. Finally, although cumulative exposure dose (C*t) was not used as a metric of membrane age, we observed that when higher doses of hypochlorite were applied, all metrics changed faster than expected based only on years of operation. Therefore, limiting the magnitude of the cumulative hypochlorite dose is essential in managing membrane deterioration. This research illuminates the knowledge gap between bench-scale ageing studies and operational water treatment plants.

Composition and Dynamics of Bacterial Communities in a Full-Scale Mineral Water Treatment Plant.

The aim of this study was to gain insight into the bacterial composition and dynamics in a mineral water treatment system (MWTS). The bacterial community of a full-scale mineral water treatment plant in the Maofeng Mountain, South China, was studied using high-throughput sequencing combined with cultivation-based techniques in both the dry and wet season. Overall, adenosine tri-phosphate (ATP) concentration (6.47 × 10-11 – 3.32 × 10-8 M) and heterotrophic plate counts (HPC) (3 – 1.29 × 103 CFU/mL) of water samples in the wet season were lower than those (ATP concentration 5.10 × 10-11 – 6.96 × 10-8 M, HPC 2 – 1.97 × 103 CFU/mL) in the dry season throughout the whole MWTS. The microbial activity and biomass of water samples obviously changed along with treatment process. All 300 isolates obtained using cultivation-based techniques were distributed in 5 phyla, 7 classes, and 19 genera. Proteobacteria accounted for 55.7% (167) of the total isolates, among which predominant genus was Pseudomonas (19.3%). Illumina sequencing analysis of 16s rRNA genes revealed 15 bacterial phyla (relative abundance >0.1%) as being identified in all water samples. Among these, Proteobacteria constituted the dominant bacteria microbiota in all water samples. A large shift in the proportion of Bacteroidetes, Actinobacteria, and Firmicutes was obtained during the treatment process, with the proportion of Bacteroidetes, Actinobacteria decreasing sharply, whereas that of Firmicutes increased and predominated in the final water product. The core microbiome, which was still present in whole MWTS comprised several genera including Pseudomonas, Acinetobacter, Clostridium, and Mycobacterium, that contain species that are opportunistic pathogens, suggesting a potential threat for mineral water microbiology safety. This study is the first to investigate the bacterial community of a full-scale mineral water treatment plant in China. The results provided data regarding the bacteria composition and dynamics in an MWTS, which will contribute to the beneficial manipulation of the mineral water microbiome.

Treatment performance comparison between regular O3\u2013BAC and O3\u2013BAC with rear sand filtration: verification in a full-scale study

BackgroundTo improve the microbial safety of drinking water, an arrangement of O3–BAC with rear sand filtration (O3–BAC–sand) has been proposed. In this study, efforts were devoted to evaluate the benefits and drawbacks of O3–BAC–sand in a full-scale water treatment plant. The performance of the two configurations was compared in terms of particles, turbidity, CODMn and typical odorants and pesticides.ResultsThe O3–BAC–sand yielded lower turbidity but higher CODMn (by approximately 7%) in the finished water than regular O3–BAC (sand–O3–BAC). Both systems removed odors in raw water; however, sand–O3–BAC was more effective on septic and musty odorants. The total pesticide removals by sand–O3–BAC and O3–BAC–sand were 78% and 72%, respectively; though the latter had shorter activated carbon durable years.ConclusionThe re-location of the sand filter would sacrifice the BAC efficiency in removals of organic matter and micropollutants. This tradeoff is a result of the loss of the particulate organic matter removal by sand filters, because locating the sand filter behind BAC causes particle load increase on BAC; some measures of enhanced coagulation should be suggested to improve the turbidity and particle removal. The study will be helpful for improvement of the O3–BAC process in drinking water treatment.