Disinfectant Residual Concentration Research Articles

Defining Risk-Based Monitoring Frequencies to Verify the Performance of Water Treatment Barriers.

Preventing failures of water treatment barriers can play an important role in meeting the increasing demand for microbiologically safe water. The development and integration of failure prevention strategies into quantitative microbial risk assessment (QMRA) offer opportunities to support the design and operation of treatment trains. This study presents existing failure models and extends them to guide the development of risk-based operational monitoring strategies. For barriers with rapid performance loss, results show that a failure of 15 s should be reliably detected to verify a log reduction value (LRV) of 6.0; thus, detecting and remediating these failures may be beyond current technology. For chemical disinfection with a residual, failure durations in order of minutes should be reliably detected to verify a LRV of 6.0. Short-term failures are buffered because the disinfectant residual concentration sustains a partial reduction performance. Therefore, increasing the contact time and hydraulic mixing reduces the impact of failures. These findings demonstrate the importance of defining precise frequencies to monitor barrier performances during operation. Overall, this study highlights the utility of process-specific models for developing failure prevention strategies for water safety management.

Identification and Modelling of Chlorine Decay Mechanisms in Reclaimed Water Containing Ammonia

Keeping an effective disinfectant residual concentration in reclaimed water is still a challenge, due to its high levels of ammonia and organic matter when compared with those in drinking water. This research proposes the integration of the reaction schemes of monochloramine auto-decomposition with an empirical kinetic mechanism accounting for reactive chlorine species decay in the presence of organic matter, for which three mechanisms were hypothesized and tested. A parallel second order mechanism, where monochloramine reacts both with fast and slow organic matter reactive fractions, was identified as the most suitable. The model, comprising two rate constants and two fictive concentrations of organic matter as parameters, was further successfully calibrated with real reclaimed waters with two initial free chlorine doses of 8.01×10−5 M (≈5 mg/L) and 2.67×10−4 M (≈20 mg/L). The proposed model is believed to support future studies aiming to predict and manage chlorine decay in reclaimed water distribution systems.

Chloramine Concentrations within Distribution Systems and Their Effect on Heterotrophic Bacteria, Mycobacterial Species, and Disinfection Byproducts

Chloramine is a secondary disinfectant used to maintain microbial control throughout public water distribution systems. This study investigated the relationship between chloramine concentration, heterotrophic bacteria, and specific Mycobacterium species. Sixty-four water samples were collected at four locations within the utility's distribution network on four occasions. Water samples were analyzed for total chlorine and monochloramine. Traditional culture methods were applied for heterotrophic bacteria and nontuberculous mycobacteria (NTM), and specific quantitative polymerase chain reaction (qPCR) assays were used to detect and quantify Mycobacterium avium, M. intracellulare, and M. abscessus. Total chlorine and monochloramine concentrations decreased between the distribution entry point (4.7 mg/L and 3.4 mg/L as Cl2, respectively) to the maximum residence time location (1.7 mg/L and 1.1 mg/L as Cl2, respectively). Results showed that heterotrophic bacteria and NTM counts increased by two logs as the water reached the average residence time (ART) location. Microbiological detection frequencies among all samples were: 86% NTMs, 66% heterotrophic bacteria, 64% M. abscessus, 48% M. intracellulare, and 2% M. avium. This study shows that heterotrophic bacteria and NTM are weakly correlated with disinfectant residual concentration, R2=0.18 and R2=0.04, respectively. Considering that specific NTMs have significant human health effects, these data fill a critical knowledge gap regarding chloramine's impact on heterotrophic bacteria and Mycobacterial species survival within public drinking water distribution systems.

Evaluating the impact of sampling design on drinking water quality monitoring program outcomes

Drinking water suppliers around the world are required by regulations to sample and test water quality in their distribution systems with the intention of generating information that can be used to protect human health. Requirements for where samples must be collected can vary and guidance on how to select locations to meet these requirements is limited. There is a need to better define and evaluate the meaning of representative in the context of selecting locations for collecting grab samples while considering the regulatory context and resources available to suppliers. We develop sampling programs for monitoring disinfectant residual concentrations and compare the results and efficacy of these programs using synthetic water quality data for two example distribution systems. Results showed that achieving accurate estimates of worst quality conditions in a network was more likely than achieving accurate estimates of systemwide conditions, and that using constant locations makes it difficult to accurately represent systemwide conditions. Results also showed that timing of sample collection is likely important depending on factors such as consumer demand patterns, and that it is inappropriate to make conclusions about systemwide conditions when few samples are taken over an evaluation period. This research has implications for developing recommendations that water suppliers and regulators can use to design and evaluate effective sampling programs.

Long-term spatial and temporal microbial community dynamics in a large-scale drinking water distribution system with multiple disinfectant regimes

Long-term spatial-temporal investigations of microbial dynamics in full-scale drinking water distribution systems are scarce. These investigations can reveal the process, infrastructure, and environmental factors that influence the microbial community, offering opportunities to re-think microbial management in drinking water systems. Often, these insights are missed or are unreliable in short-term studies, which are impacted by stochastic variabilities inherent to large full-scale systems. In this two-year study, we investigated the spatial and temporal dynamics of the microbial community in a large, full scale South African drinking water distribution system that uses three successive disinfection strategies (i.e. chlorination, chloramination and hypochlorination). Monthly bulk water samples were collected from the outlet of the treatment plant and from 17 points in the distribution system spanning nearly 150 km and the bacterial community composition was characterised by Illumina MiSeq sequencing of the V4 hypervariable region of the 16S rRNA gene. Like previous studies, Alpha- and Betaproteobacteria dominated the drinking water bacterial communities, with an increase in Betaproteobacteria post-chloramination. In contrast with previous reports, the observed richness, diversity, and evenness of the bacterial communities were higher in the winter months as opposed to the summer months in this study. In addition to temperature effects, the seasonal variations were also likely to be influenced by changes in average water age in the distribution system and corresponding changes in disinfectant residual concentrations. Spatial dynamics of the bacterial communities indicated distance decay, with bacterial communities becoming increasingly dissimilar with increasing distance between sampling locations. These spatial effects dampened the temporal changes in the bulk water community and were the dominant factor when considering the entire distribution system. However, temporal variations were consistently stronger as compared to spatial changes at individual sampling locations and demonstrated seasonality. This study emphasises the need for long-term studies to comprehensively understand the temporal patterns that would otherwise be missed in short-term investigations. Furthermore, systematic long-term investigations are particularly critical towards determining the impact of changes in source water quality, environmental conditions, and process operations on the changes in microbial community composition in the drinking water distribution system.

Optimal scheduling of booster disinfection in water distribution networks

ABSTRACTBooster disinfection stations are the solution alternative to maintain required disinfectant residual concentration in water distribution networks. In the present study, an optimisation problem to determine the optimum injection rates is solved. The minimisation of the total injected mass is considered as the objective function which is subjected to bound constraints on chlorine concentration. Two formulations are used for the linear optimisation problem, with and without considering the initial concentrations as unknowns. Determination of variable network hydraulics and chlorine concentrations is achieved by EPANET. A C++ code was developed to interface with EPANET by means of the EPANET Programmer's Toolkit for optimisation of the disinfectant mass applied to the network. Finally, a cross check is achieved in EPANET software for both disinfectant residual concentrations and linear superposition principle.

The Technology of Corrosion Control with Corrosion Inhibitors in Water Pipes

Introduction The principle oxidants in the drinking system are dissolved oxygen and chlorine, and the corrosion of water pipe is going alone because of oxidants reaction. Since 1930, pH control chemicals such as NaOH, Ca(OH)2, NaHCO3, and phosphate corrosion inhibitors have been used to prevent the corrosion of water pipes. However, to directly add Ca(OH)2at inlet of water well in production process of drinking water may cause a problem to make clouding phenomenon in tap water. The objective of this study removes such problems as the turbidity, strengthen more safety of water. Experimental Materials – The iron(carbon steel) was in the form of sheet 0.04 cm in thick and the following analysis: Fe 99.62%, Mn 0.26%, Cu 0.08%, Ni 0.05%, Mo 0.01%. specimens cut from this sheet measured 15cm×1.2cm. The chemicals used as corrosion inhibitors were NaOH, Ca(OH)2, and H3PO4 and tap water used as blank. NaOCl was used to disinfect the drinking water made by the demo plant. In order to examine the effect of disinfectant residual concentration according to adding lime water and corrosion inhibitor such as ortho phosphate(H3PO4), the residual concentration of disinfectant was measured in carbon steel water pipe 50 m in length at the corrosion pilot plant and the temperature of solution was in room temperature between 5°C in the winter to 35°C in the summer. Chlorine residual concentration in the water pipes 50 m in length was measured for 5, 10, 20, 40, 60 min, respectively. The electrochemical tests was measured using Solartron Potentiostat 1480 and the test was performed in a typical three electrode cell which consist of carbon steel as working electrode, saturated calomel electrode as reference electrode, platinum counter electrode. Result s HOCl and OCl- in drinking water which chlorine was added as disinfectant reach in equilibrium state at nearly pH 7.5. As pH increases, more of OCl- exists than the strong disinfectant, HOCl-, Increasing HOCl below pH 7.5 is more benefit in terms disinfectant efficiency. Figure 2 above shows the concentration of free residual chlorine with time. Running drinking water in the pipe, adding PO4 decreased concentration of chlorine from 0.48 to 0.28 ppm for 40 min, NaOH decreased concentration of chlorine from 0.45 to 0.10ppm, Ca(OH)2 decreased concentration of chlorine from 0.24 to 0.10 ppm, but tap water as blank degreased concentration of chlorine from 0.40 to 0.07 ppm for only 10 minutes. Of three corrosion inhibitors, PO4 showed the highest reduced efficiency for the concentration of residual chlorine. To inhibit the reaction of chlorine with metal water pipe is similar to inhibit the corrosion reaction. Reference US EPA, Disinfection Profiling and Benchmarking, EPA Guidance Manual, August 1999. American Society for Testing and Materials, G 4-95(1996). Figure 1

Modelling temperature effects on ammonia-oxidising bacterial biostability in chloraminated systems

The biostability concept has been successfully used to predict the onset of nitrification in drinking water distribution systems, but in certain cases deficiencies have been observed in the predictions, indicating that modifications to parameters were needed. At the biostable disinfectant residual concentration (BRC), the rate of ammonia-oxidising bacterial (AOB) growth due to the substrate (free ammonia) and the rate of inactivation due to the disinfectant are balanced. Growth and inactivation rates vary greatly with temperature, but temperature is yet to be considered in the biostability equation. In this paper, two separate novel models are proposed which take into account the temperature effects on the biostability equation. First, a novel model of specific growth rate variability with temperature was shown to be valid for different bacterial species. Then, the biostability model was modified and validated for ammonia-oxidising bacterial activity using data collected from laboratory and full-scale distribution systems. The proposed model has two important uses: while the specific growth rate model and biostability model can be widely adopted for many microbes, the biostability model for AOB also has the potential to aid water utilities in disinfectant residual management throughout yearly temperature variations.

Impact of UV and secondary disinfection on microbial control in a model distribution system

This study evaluates the synergistic effects of ultraviolet (UV) and secondary disinfectants on water quality in a model distribution system. Chemical disinfectants evaluated for residual disinfection include chlorine dioxide, monochloramine, and free chlorine. Results suggest that there may be synergistic effects between UV and the chemical disinfectants for controlling microbiological re-growth in drinking water distribution systems. UV disinfection appeared to increase the vulnerability of bacteria located in suspension or within biofilms to chemical disinfection, although only at low disinfectant residual concentrations of 0.25, 0.50, and 1.0 mg/L for chlorine dioxide, free chlorine, and monochloramines, respectively. At high disinfectant residual concentrations of 0.50, 1.0, and 2.0 mg/L for chlorine dioxide, free chlorine, and monochloramines, respectively, results indicated that chemical disinfection alone would be adequate for microbial control. In the reactors receiving UV pre-treatment, both chlorine dioxide and free chlorine disinfection were far more effective in reducing the growth of suspended heterotrophic bacteria than without UV pre-treatment. Similar biofilm and suspended bacterial levels were observed without subsequent chemical disinfection regardless of the presence or absence of UV treatment. Overall, these findings imply that UV treatment prior to chemical disinfection enhances microbial control in distribution systems. These results indicate the use of UV pre-treatment can be effective at reducing the disinfectant concentration necessary for microbial control, therefore reducing the potential for the formation of disinfectant by-product in the system.Key words: drinking water, UV pre-treatment, chlorine dioxide, chlorine, monochloramines, disinfection.

Change of bacterial water quality in drinking water distribution systems working with or without low chlorine residual

Investigations into distribution systems (DS) working without or with low disinfectant residuals showed that the main process for the bacteria change in such systems is the release of bacteria from the biofilm, whereas the growth of bacteria in the water can be neglected. Important for the quality are short-term increases of bacteria release connected to an increase of bacteria growth on the inner pipe surface as a result of changes in the concentration of biodegradable organic matter (BOM) in the water. A model to describe the bacterial water quality change was developed on the basis of investigations. In contrast to other models, a consideration of the formation of BOM as a result of NOM oxidation by disinfectant residuals as well as the decreasing effect of inactivation of released bacteria by the decreasing disinfectant residual concentration, were necessary.

Effect of easily biodegradable organic compounds on bacterial growth in a bench-scale drinking water distribution system

Many engineered (e.g., disinfectant residual concentration) and environmental (e.g., temperature) factors influence bacterial regrowth in drinking water distribution systems. This paper examines the effect of nutrients, specifically biodegradable organic matter (BOM) composition, BOM concentration, and hydraulic retention time on bacterial growth in an annular reactor (AR). Drinking water that had an alkalinity of 300 mg/L as CaCO3and a free chlorine residual of approximately 0.2 mg/L was used as process water in the ARs. Prior to entering the ARs, the water was filtered through granular activated carbon (GAC) to remove background chlorine and background organic matter. A cocktail of easily biodegradable organic compounds consisting of carboxylic acids, aldehydes, and free amino acids were spiked into the ARs as the primary carbon source. It was found that the influent BOM concentration (p value = 0.013) and the presence of free amino acids in the BOM cocktail (p value = 0.009) significantly increased the number of viable culturable cells in the biofilm, as measured by heterotrophic plate counts (HPCs). The interaction between the BOM concentration and the presence of amino acids also significantly increased the number of biofilm HPCs (p value = 0.021). Alternatively, the BOM concentration and the amino acid fraction did not affect the number of bulk (i.e., suspended) bacteria. The number of biofilm HPCs in the reactor was approximately 10 times greater than the number of bulk HPCs at high influent BOM concentrations and low retention times (i.e., high BOM loading rates). At low loading rates, the ratio of number of biofilm to bulk cells was less than 2. Consequently, it was deduced that the BOM was utilized predominately by the biofilm cells. This indicates that removal of easily biodegradable organic compounds is an important factor for controlling biofilm growth in distribution systems.Key words: drinking water, distribution systems, biofilm, annular reactor, regrowth.