Auswahl der wissenschaftlichen Literatur zum Thema „Free chlorine decay“

The concentration of chlorine in water declines as it reacts with various substances, causing decay of the residual free chlorine until its total consumption. In light of the typical characteristics of the water from protected dug wells and tube wells, this study aimed to evaluate the decay kinetics of free chlorine in the water of alternative individual supply (AIS) solutions used in the city of Porto Velho in the Brazilian Amazon region. The free chlorine decay constant in the water was evaluated by “bottle tests,” applying a first-order model. According to the results, the type of well and initial chlorine concentration significantly influences the free chlorine decay speed. The water samples from the tubular wells had lower chlorine demand levels, attributed to their better water quality. The simulation of the residual chlorine decay in the different supply sources is an important tool to support safe disinfection processes.

Free chlorine decay is a main issue in drinking water treatment since free chlorine concentration is a common indicator in drinking water security. The current view of free chlorine decay is that the process is mainly affected by the natural organic matter in water, temperature and initial chlorine concentration, on which temperature has the most evidently effect. As is generally accepted, total hardness has no effect on it. This paper investigated the impact of water hardness on the chlorine decay. The influence of varying metal ions concentrations which contribute to water hardness on effective chlorine decay constants was assessed. The results implied that total hardness had an evidently influences on the chlorine decay in tap water or DI water. For the range of metal ions concentration in this experiment effective chlorine decay constants ranged from an increase by +182% to +349% from the different concentration of metal ions.

Free chlorination is a widely employed disinfection method in humanitarian water provision due to its many advantages. However, its effective application is hindered by the challenge in determining adequate initial doses to achieve free chlorine residuals that satisfy both health and aesthetic requirements. Current guidelines show varying recommended dosing strategies, and many do not adequately consider chlorine decay mechanisms that occur during water storage. Even though turbidity is commonly used as a criterion for deciding chlorine dose, it may not be an adequate proxy for the water quality in many cases. This paper addresses the fundamental relationships between chlorine decay kinetics and selected key water parameters (i.e., natural organic matter, water temperature, chlorine demand) by conducting chlorine decay tests in controlled conditions and in jerrycans (i.e., simulating humanitarian water treatment conditions). Chlorine decay constant from the Feben and Taras’s empirical model and first order model formed linear and exponential relationships with two water parameters (UVA254 and 30-min chlorine demand). With these relationships, the two chlorine decay models can be calibrated quickly and frequently in the field, allowing effective determination of initial chlorine dose. These two models calibrated based on the suggested water parameters from the study could predict chlorine decay in water having a main chlorine demand-inducing constituents as natural organic matter. However, they underpredicted chlorine decay in surface water with additional chlorine reactants. Further research on additional chlorine decay mechanisms is needed to expand the applicability of the models.

Free chlorine consumption in distribution systems is due both to chemical reactions occurring in the bulk phase and at the pipe walls. Knowledge of the relative importance of these various reactions is needed in order to improve chlorine decay modeling. Experimental results carried out in this study make it possible to propose a hierarchical classification of the main parameters involved in the free chlorine decay observed in distribution systems. Corrosion of metallic pipe appears to be a major parameter, while synthetic materials are of little influence. The rate of chlorine decay in bulk phase can be estimated according to the TOC and the temperature. Influence of biofilms depends on the BDOC content of water, and on the pipe diameter. Chlorine decay due to corrosion phenomena must be modeled according to a zero order kinetics, while chlorine decay due to other parameters can be modeled according to a first order kinetics with respect to chlorine.

Abstract This study compared 3 commonly used quenching agents for dechlorinating samples prior to disinfection byproduct (DBP) analysis under typical drinking water sampling conditions for a representative suite of chlorination byproducts. Ascorbic acid and sodium sulfite quenched the residual free chlorine to below detection within 5 seconds. Ammonium chloride did not quench the chlorine to below detection with up to a 70% molar excess, which agrees with published ammonium chloride-chlorine chemistry. With respect to the DBPs, ascorbic acid worked well for the trihalomethanes and haloacetic acids, except for dibromoiodomethane, which exhibited 2.6–28% error when using ascorbic acid compared to non-quenched control samples. Sodium sulfite also worked well for the trihalomethanes (and performed similarly to ascorbic acid for dibromoiodomethane) and was the best performing quenching agent for MX and the inorganic DBPs, but contributed to the decay of several emerging DBPs, including several halonitromethanes and haloacetamides. Ammonium chloride led to considerable errors for many DBPs, including 27–31% errors in chloroform concentrations after 24 hours of storage. This work shows that ascorbic acid is suitable for many of the organic DBPs analyzed by gas chromatography-electron capture detection and that sodium sulfite may be used for simultaneous chlorite, chlorate, and bromate analysis.

Inactivation of Yersinia enterocolitica by chlorine (0.6 to 20 ppm) was investigated in distilled water and in tryptic soy broth (TSB, 0.015%) at different temperatures (4, 20, and 40°C). In distilled water, chlorine inactivation of Y. enterocolitica was enhanced by increasing the temperature from 4 to 20°C, and survival curves were described by a model that assumed first-order kinetics followed by tailing in which the microbial concentration remained constant. The presence of TSB increased chlorine resistance of Y. enterocolitica, and survival curves were concave downward. These survival curves were described by a model based on the Weibull distribution. Chlorine decay in distilled water was independent of temperature and of the initial concentration of available chlorine and was modeled by first-order reaction kinetics. Chlorine decay in TSB was independent of the initial chlorine concentration but depended on the treatment temperature and was modeled by the addition of two first-order decay equations. The increased resistance of Y. enterocolitica to chlorine in TSB was not due only to the chlorine demand by the TSB components. These components protected Y. enterocolitica cells from the antimicrobial effect of chlorine.

Combined sewer overflow (CSO) water introduces pathogens to receiving waters. To control pathogenic releases, chlorine may be added to disinfect CSO water. The added chlorine may react with water constituents to form oxidative species known as chlorine-produced oxidants (CPO). CPO are the sum of free and combined oxidative species that form upon adding free chlorine-bearing compounds (e.g. gaseous chlorine or hypochlorite) to water. CPO discharge is often regulated by governing agencies. Current methods to model CPO behavior do not account for CPO decay and dilution simultaneously in receiving water. This study creates a novel model for CPO demand and dilution in receiving water from chlorinated effluent in order to determine site-specific practices for implementation of a CSO water disinfection regime. To do this, representative receiving water was collected and dosed with 1, 2, and 4 mg/L chlorine. The residual chlorine was measured at intervals up to 30 min after dosing. The immediate and subsequent chlorine demand was calculated, with the subsequent demand modeled by simultaneous application of dilution and decay using pseudo-first-order decay kinetics. A comparison of model calculations indicates that application of dilution before decay underestimates CPO demand, while application of decay before dilution overestimates CPO demand.

Chlorine is one of the many disinfectants used to ensure bacteriological safety of drinking water. Usually residual chlorine is maintained within the distribution network to combat any probable re-contamination of the distributed water. This residual free chlorine, however, decays in water due to its reaction with the bulk water and the pipe material or deposits on the pipe walls. This study aimed at determining and modelling chlorine decay in the Kumasi water distribution network (KWDN) and determined locations where residual chlorine boosting is necessary. A double-jacketed batch reactor and a constructed pilot distribution system (PDS) were used to determine the bulk and wall decay coefficients. The PDS was run using aged PVC pipes (15–20 years), asbestos concrete pipes (40–50 years) and cast iron pipes (84 years) that have been in use in the KWDN. The SynerGEE® hydraulic model was used to identify the ‘zero chlorine’ points and predict top-up quantities. The bulk decay coefficient was found to be 0.053 h−1 within 8 hours at 26 °C and the residual chlorine decayed within the bulk fluid by 32–34% of its initial dose. Under the conditions tested, the cast iron pipes had the highest overall decay coefficients (K). Five locations within the network were identified as probable chlorine boosting points).

Analysis of free chlorine propagation in water supply network has a significant meaning for the process of water distribution. Results of numerical studies allow the proper selection of disinfectant or suitable monitoring of pipelines endangered by stagnation of water. The first-order reaction of chlorine decay in pipe boundary layer and inside the waterbody is commonly successfully assumed in numerical modeling. The aim of this studies was to analyze transport of chlorine inside the rural water supply system. The calculations were performed with application of Epanet 2.0 with assumed the first-order re action of chlorine decay and empirically determined chlorine decay rate in the mass of waterbody. The periodical disinfection of water in the network with the constant chlorine concentration 0.3 mg·dm-3 introduced during the whole time duration of simulation was assumed to calculations. The obtained results of chlorine distribution showed that even after 4 days there were available pipelines in which concentration of free chlorine was lower than 0.2 mg·dm-3. Thus, the microbiological protection of water quality is unavailable in these pipelines.

The purpose of this study was to identify the effect that water quality, pipe material, pipe size, flow conditions and the use of corrosion inhibitors would have on the rate of free chlorine and chloramine decay in distribution systems. Empirical models were developed to predict the disinfectant residual concentration with time based on the parameters that affected it. Different water treatment processes were used to treat groundwater and surface water to obtain 7 types of finished waters with a wide range of water quality characteristics. The groundwater was treated either by conventional treatment by aeration (G1) or softening (G2) or high pressure reverse osmosis (RO) and the surface water was treated either by enhanced coagulation, ozonation and GAC filtration (CSF-O3-GAC or S1) or an integrated membrane system (CSF-NF or S2). The remaining two water types were obtained by treating a blend of G1, S1 and RO by softening (S2) and nanofiltration (G4). A pilot distribution systems (PDS) consisting of eighteen (18) lines was built using old pipes obtained from existing distribution system. The pipe materials used were polyvinyl chloride (PVC), lined cast iron (LCI), unlined cast iron (UCI) and galvanized steel (G). During the first stage of the study, the 7 types of water were blended and fed to the PDS to study the effect of feed water quality changes on PDS effluent water quality, and specifically disinfectant residual. Both free chlorine and chloramines were used as disinfectant and the PDSs were operated at hydraulic retention times (HRT) of 2 and 5 days. The PDSs were periodically tested for free and combined chlorine, organic content, temperature, pH, turbidity and color. The data obtained were used to develop separate models for free chlorine and chloramines. The best fit model was a first-order kinetic model with respect to initial disinfectant concentration that is dependent on the pipe material, pipe diameter and the organic content and temperature of the water. Turbidity, color and pH were found to be not significant for the range of values observed. The models contain two decay constants, the first constant (KB) accounts for the decay due to reaction in the bulk liquid and is affected by the organics and temperature while the second constant, KW, represents the reactions at the pipe wall and is affected by the temperature of the water and the pipe material and diameter. The rate of free chlorine and chloramine decay was found to be highly affected by the pipe material, the decay was faster in unlined metallic pipes (UCI and G) and slower in the synthetic (PVC) and lined pipes (LCI). The models showed that the rate of disinfectant residual loss increases with the increase of temperature or the organics in the water irrespective of pipe material. During the second part of the study, corrosion control inhibitors were added to a blend of S1, G1 and RO that fed all the hybrid PDSs. The inhibitors used were: orthophosphate, blended ortho-polyphosphate, zinc orthophosphate and sodium silicate. Three PDSs were used for each inhibitor type, for a total of 12 PDSs, to study the effect of low, medium and high dose on water quality. Two PDSs were used as control, fed with the blend without any inhibitor addition. The control PDSs were used to observe the effect of pH control on water quality and compare to the inhibitor use. One of the control PDSs (called PDS 13) had the pH adjusted to be equal to the saturation pH in relation to calcium carbonate precipitation (pHs) while the pH of the other control PDS (PDS 14) was adjusted to be 0.3 pH units above the pHs. The disinfectant used for this part of the study was chloramine and the flow rates were set to obtain a HRT of 2 days. The chloramine demand was the same for PDS 14 and all the PDSs receiving inhibitors. PDS 13 had a chloramine demand greater than any other PDS. The lowest chloramine demand was observed in PDS 12, which received silicate inhibitor at a dose of 12 mg/L, and presented the highest pH. The elevation of pH of the water seems to reduce the rate of decay of chloramines while the use of corrosion inhibitors did not have any effect. on the rate of chloramine decay. The PDS were monitored for chloramine residual, temperature, pH, phosphate, reactive silica, and organic content. Empirical models were developed for the dissipation of chloramine in the pilot distribution systems as a function of time, pipe material, pipe diameter and water quality. Terms accounting for the effect of pH and the type and dose of corrosion inhibitor were included in the model. The use of phosphate-based or silica-based corrosion inhibitors was found to have no effect on the rate of chloramine dissipation in any of the pipe materials. Only the increase of pH was found to decrease the rate of chloramine decay. The model to best describe the decay of chloramine in the pilot distribution systems was a first-order kinetic model containing separate rate constants for the bulk reactions, pH effect and the pipe wall reactions. The rate of chloramine decay was dependent on the material and diameter of the pipe, and the temperature, pH and organic content of the water. The rate of chloramine decay was low for PVC and LCI, and more elevated in UCI and G pipes. Small diameter pipes and higher temperatures increase the rate of chlorine decay irrespective of pipe material. Additional experiments were conducted to evaluate the effect of flow velocity on chloramine decay in a pilot distribution system (PDS) for different pipe materials and water qualities. The experiments were done using the single material lines and the flow velocity of the water was varied to obtain Reynolds' numbers from 50 to 8000. A subset of experiments included the addition of blended orthophosphate corrosion inhibitor (BOP) at a dose of 1.0 mg/L as P to evaluate the effect of the inhibitor on chloramine decay. The effect of Reynolds' number on the overall chloramine decay rate (K) and the wall decay rate constant (W) was assessed for PVC, LCI, UCI, and G pipes. PVC and LCI showed no change on the rate of chloramine decay at any flow velocity. UCI and G pipes showed a rapid increase on the wall decay rate under laminar conditions (Re < 500) followed by a more gradual increase under fully turbulent flow conditions (Re > 2000). The use of the BOP inhibitor did not have an effect on the rate of chloramine decay for any of the pipe materials studied. Linear correlations were developed to adjust the rate of chloramine decay at the pipe wall for UCI and G depending on the Reynolds' number.
Ph.D.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engineering PhD

The diploma thesis deals with the rate of free chlorine dacay in the water supply systems. In the general part of the work are mentioned the forms of chlorine that can be encountered in its use for disinfection of drinking water. Another chapter is the modeling of chlorine decomposition in water during pipeline distribution. This chapter deals with the kinetic reactions of chlorine and their orders, and subsequently with factors influencing the rate of chlorine loss. Closer deals with pipe wall chlorine decay and the bulk water flow chlorine decay. The second part of the diploma thesis is focused on determining the constant kb, which is the rate coefficient of loss of chlorine in the pipeline caused by the flow of water. The work contains several researches of various world studies that deal with this issue. The following is a step-by-step guide to performing this test. The last part deals with the case studies at the waterworks in Kateřinice and Brno. On these tapes the chlorine concentration was measured over time and a constant kb was determined based on these results, expressing the rate of free chlorine decay in bulk water flow.

While free (breakpoint) chlorination is widely utilized in humanitarian water treatment, a main challenge limiting its effective application is in determining the initial dose to satisfy both health requirements and aesthetic considerations (i.e. taste and odour). International guidelines and studies showed varying recommendations for the initial chlorine dose and many did not consider chlorine decay during water transportation and storage for up to 24 hours. The main objective of this thesis is to develop a tool for humanitarian staff to accurately determine the initial chlorine dose for achieving free chlorine residual (FCR) objectives with the limited instrumentation and information in the field. The first manuscript included in the thesis gathered and evaluated seven basic chlorine decay models’ applicability in humanitarian treatment contexts. All seven models were found able to accurately describe chlorine decay in water representative of humanitarian treatment contexts with more than half of the regression resulted in R2 over 0.95. However, each model had its own limitations, which were discussed. The second manuscript involved conducting extensive chlorine decay tests in water with different characteristics, explored the relationships between the estimated chlorine decay constant and several water parameters including pH, turbidity, ultraviolet absorption at 254 nm wavelength (UVA254), temperature and 30-minute chlorine demand. It was found that the UVA254 of water followed linear and exponential relationships with the decay constant in Feben and Taras’s empirical model and that in the first order model respectively. Arrhenius-type relations were verified between the decay constant and water’s temperature. A model developed to predict FCR decay in water with known 30-minute chlorine demand accurately predicted FCR level in synthetic water (with humic acid being the main constituent) but underpredicted FCR decay in water with additional chlorine consuming matter. Further research on additional chlorine decay mechanisms are needed to expand the applicability of the model.
Graduate
2021-04-13