Chlorine Decay Kinetics Research Articles

Model for halo-acetic acids formation in bulk water of water supply systems.

With increased understanding of the differences in toxicity between species of haloacetic acids (HAAs) and the possibility of more stringent regulations, the ability to predict individual HAA species formation is important. Nine different haloacetic acids are regulated and their total concentration is referred to as HAA9. A mathematical model to predict concentrations of HAA species was proposed and tested using independent data sets. The amount of HAA9 formed per unit amount of chlorine consumed (μg-HAA9/mg-consumed chlorine) remained constant throughout the reaction times in each sample. Similarly, the fraction of a given HAA species largely remained constant during most of the reaction time. Thus, each HAA species was assumed to have its own yield with respect to consumed chlorine in a given water sample. The parallel second-order (2R) model describing chlorine decay kinetics was then extended to predict HAA species formation kinetics. The combined chlorine and HAA species model closely predicts all tested HAA species and its sum with standard error ≤ 5 μg/L. Within the tested waters having Cl2/N mass ratio ≥ 10.7 (g-Cl2/g-N), ammonia did not impact the mass yield. The mass yield of each HAA species can be calculated from three measurements (e.g. at 0, 4 and 24 h) of HAA species and chlorine. Once the yield is known, HAA species concentrations could be predicted for up to 120 h with only chlorine measurements. The model extends the previous work of predicting the trihalomethane species formation kinetics to HAA species formation kinetics. Further research is needed to understand how the yield varies with source water quality, treatment and in distribution systems.

Chlorine decay and disinfection by-products formation during chlorination of biofilms formed with simulated drinking water containing corrosion inhibitors

Corrosion inhibitors used to reduce pipe corrosion can alter the physical structure and biochemical components of the biofilm in premise plumbing systems. We studied the effects of corrosion inhibitors on chlorine decay and associated disinfection by-products (DBPs) formation by biofilms grown with simulated drinking water amended with silicate, phosphate, and the phosphate blends. Experiments were conducted with either intact biofilms or biofilm materials dispersed in solution during sonication (referred to as biomass). While there was no significant difference in chlorine decay among biomass from different biofilms, biomass from the phosphate blend biofilm showed the lowest trihalomethane (THMs) and haloacetic acids (HAAs) formation. The chlorine decay rate constants from the biofilm experiment were ranked as: phosphate blends > phosphate ≈ groundwater (GW) > silicate. The kinetics of chlorine decay and formation of DBPs were successfully described by pseudo-first-order kinetics. These fitting parameters were used to predict the DBPs formation in a realistic premise plumbing system. The results showed that biofilm-derived THMs and HAAs increased with increasing chlorine concentration, while THMs and HAAs first increased and then stabilized to a maximum with increasing biofilm total organic carbon (TOC) concentration. In general, the biofilms grown with phosphate-based corrosion inhibitors resulted in lower DBPs formation yield but higher bacterial release, which could potentially increase the risk of user exposure to opportunistic pathogens in drinking water. The silicate biofilms showed the largest yield coefficient of DBPs formation but had the least biomass and lower bacterial release.

Study on Shock Disinfection in a Fire Extinguishing Water Supply System

The biofilms generated in a fire extinguishing water supply system can cause corrosion and a reduction in the water supply capacity; thus, degrading the system performance. To mitigate microbial corrosion, appropriate disinfection measures are necessary. In this study, the secondary addition of chlorine is employed to investigate the kinetics of chlorine decay, and shock disinfection is applied to investigate the removal efficiency of corrosion bacteria, and the microbial composition of a biofilm on the pipe wall was also clarified. The results show that the residual chlorine content in the secondary chlorination process was directly correlated with the decay rate of residual chlorine and the corrosion rate of the pipe wall. Additionally, the chlorine impact disinfection method could reduce the electrochemical corrosion phenomenon of the pipe wall. When the concentration of chlorine was 3 mg/L, the removal rate of corrosion bacteria was higher in 60 min than in 30 min. Specifically, most of the bacteria were inactivated in 60 min and the biofilm was severely damaged. Shock disinfection could significantly inactivate all microflora in the biofilm; the relative abundances of microflora varied significantly, while the change of microflora at the phylum level was insignificant. This study can provide theoretical support for the secondary addition of chlorine and shock disinfection in a fire extinguishing water supply system.

Trihalomethane species model for drinking water supply systems

Despite the existence of significant knowedge on complex mechanisms of THM formation, a simple kinetic model to predict THM species concentration is not available, hindering application of knowlwdge for regulatory, monitoring and operational control. The parallel second order reaction (2R) model containing fast and slow reactants has been well established to describe the chlorine decay kinetics under distribution conditions. The proposed THM species model expands the 2R model by systematically incorporating the initial unproductive (not forming THM) chlorine consumption and assuming each THM species is formed at a fixed yield (µg-THM species/mg- productive chlorine consumption). The model concept is tested on 15 water samples that contain a wide range of dissolved organic carbon, specific UV absorbence, and bromide concentrations collected from Australia and US. In all samples, the model describes the THM species concentrations well (error < 3 µg/L in 84% of model estimates) as long as the chlorine profile is described accurately (R2 > 0.984). The model formulated from the minimum data (initial and two other data points of Cl2 and THM species) predicts the rest of concentrations of THM species from only chlorine measurements. To fully optimise the system or adopt in regulatory monitoring, the effect of changes due to bulk water quality, operational conditions and wall (and biofilm) effects on THM formation kinetics should be established. A similar concept could be extended to other DBP, but rigorous testing is needed.

Towards a Predictive Model for Initial Chlorine Dose in Humanitarian Emergencies

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.

WATER QUALITY ASSESSMENT, STATISTICAL ANALYSIS AND KINETICS OF TRIHALOMETHANES FORMATION IN DRINKING WATER SUPPLIES - A COMPLETE BATCH STUDY

The study attempted to identify the best suited models to determine the kinetics of chlorine decay and trihalomethanes (THMs) formation in drinking water supplies. Batch experiments were conducted on synthetic water samples to simulate the characteristics of raw water collected from Maithon water treatment plant (MWTP), Dhanbad, Jharkhand, India. Influence of various parameters like total organic carbon (TOC), reaction time, pH and chlorine dose on the rate of THMs formation were analysed. The studies revealed that above 50% of THMs were formed within the first 83.65 min. Later on the reaction rate decreases and it takes 7.329.26 hours for 99% formation of total THMs. Pearson correlation matrix dictated strong correlation of reaction time followed by pH, dose and TOC with THMs formation. Principal component analysis (PCA) demonstrated that dissolved organic carbon (DOC) is the most influencing parameter for THMs formation. Chlorine decay kinetics followed second order reaction and the rate constant was found to be 0.0131 L/mg.min-1. THMs formation kinetics was analysed by Clark and Kavanaugh model. Validation results indicated lower error of prediction (< 6%) for Clark s model than Kavanaugh model (< 20%). Thus, it was observed that Clark's model more suitably predicts the formation of THMs in Indian drinking water supplies.

Influences of model structure and calibration data size on predicting chlorine residuals in water storage tanks

This study evaluated the influences of model structure and calibration data size on the modelling performance for the prediction of chlorine residuals in household drinking water storage tanks. The tank models, which consisted of two modules, i.e., hydraulic mixing and water quality modelling processes, were evaluated under identical calibration conditions. The hydraulic mixing modelling processes investigated included the continuously stirred tank reactor (CSTR) and multi-compartment (MC) methods, and the water quality modelling processes included first order (FO), single-reactant second order (SRSO), and variable reaction rate coefficients (VRRC) second order chlorine decay kinetics. Different combinations of these hydraulic mixing and water quality methods formed six tank models. Results show that by applying the same calibration datasets, the tank models that included the MC method for modelling the hydraulic mixing provided better predictions compared to the CSTR method. In terms of water quality modelling, VRRC kinetics showed better predictive abilities compared to FO and SRSO kinetics. It was also found that the overall tank model performance could be substantially improved when a proper method was chosen for the simulation of hydraulic mixing, i.e., the accuracy of the hydraulic mixing modelling plays a critical role in the accuracy of the tank model. Advances in water quality modelling improve the calibration process, i.e., the size of the datasets used for calibration could be reduced when a suitable kinetics method was applied. Although the accuracies of all six models increased with increasing calibration dataset size, the tank model that consisted of the MC and VRRC methods was the most suitable of the tank models as it could satisfactorily predict chlorine residuals in household tanks by using invariant parameters calibrated against the minimum dataset size.

Desalinated seawater into pilot-scale drinking water distribution system: chlorine decay and trihalomethanes formation

Residual chlorine decay and trihalomethanes (THM) formation of desalinated seawater by ultrafiltration (UF) and nanofiltration (NF) membranes in a pilot-scale water distribution system (DWDS) were investigated. Three-dimensional fluorescent features of two source waters including NF permeate and municipal water were studied. Sixteen groups of data-sets were obtained to explore the effects of initial chlorine concentration (ICC), dissolved organic carbon (DOC), and temperature on chlorine decay and THM formation in laboratory conditions and pilot-scale DWDS, respectively. A first-order model was applied to evaluate the chlorine decay of desalinated seawater and a new model combining ICC, DOC concentration, and temperature was obtained to determine the first-order decay coefficient. Other seven models describing the kinetics of chlorine decay were also applied and compared in this study. Total trihalomethanes (TTHM) formation kinetics was studied and first-order model was suggested to describe this formation. The relationship between TTHM formation and chlorine demand was demonstrated and the results showed that second-order polynomial model better described the relationship.

Assessment and speciation of chlorine demand in fresh-cut produce wash water

For the fresh-cut produce industry, a critical area of concern is potential pathogen cross-contamination during wash operations when wash water is reused and re-circulated in wash systems continuously imputed with fresh-cut produce. However, little research has focused on the chemical properties of wash water. Organic input from residual soil and vegetable material deteriorates water quality and creates increasing chlorine demand within this wash water.This study evaluated the origins of chlorine demand input and chlorine decay kinetics of fresh-cut produce wash water. Using a model system, vegetable juice released per kg of processed produce for shredded romaine lettuce, shredded iceberg lettuce, shredded carrot and baby spinach was 82.1 mL/kg, 94.5 mL/kg, 158 mL/kg, and 2.26 mL/kg, respectively. Batch water analysis revealed a rapid reaction between constituents in the wash water and chlorine where over a 90 min observation period, 50% of chlorine demand occurred within first 5 min, underscoring the challenge for any water treatment process to reduce chlorine demand once vegetables are deposited into washing systems. Moreover, the results also showed sustained chlorine demand over 90-min periods, indicating an accumulative effect on chlorine consumption with continuous organic input. Additionally, HPLC-SEC analysis showed that the constituents contributing to chlorine demand are predominantly dissolved small molecules (<3400 Da), which will challenge water reuse treatment approaches. This study provides quantitative information of chlorine demand origins and chlorine decay kinetics in wash water and provides baseline data critical for integrating water reuse in the fresh produce processing industry.

Changes in physicochemical properties and bactericidal efficiency of acidic electrolyzed water ice and available chlorine decay kinetics during storage

Acidic electrolyzed water ice (AEW ice) is a new kind of bactericide used in preservation or cold sterilization of food products. The aim of this study was to investigate changes in the physicochemical properties (oxidation reduction potential (ORP), pH value and available chlorine concentration (ACC)), bactericidal efficiency, and decay kinetics of available chlorine in AEW ice during 10 h of storage time. Results indicated that pH changes of AEW ice did not have a significant difference (p > 0.05) during the first 6-h storage, after 6 h, the pH of AEW ice prepared with ≤1 g/l NaCl solution changed more slowly than that of AEW ice prepared with >1 g/l NaCl solution. Both ORP and ACC decreased with storage time. The ACC of AEW ices prepared from >1.5 g/l NaCl solutions decreased faster and in a greater extent than those prepared from ≤1.5 g/l NaCl solutions. According to the correlation analysis, the correlation coefficients between pH, ORP, and ACC and Vibrio parahaemolyticus inactivation were −0.831, 0.787 and 0.944, respectively, and those between the above parameters and Listeria monocytogenes inactivation were −0.814, 0.701 and 0.97, respectively. Based on the kinetic study, the decay of ACC fitted the first order kinetics.

Determination of trihalomethanes levels in a selected area of Amman’s drinking water distribution system: case study

Water quality model is a helpful management tool for water distribution system. Estimation of growth coefficients is an important and challenging component of water quality modeling. Reactions occurring in the bulk flow for both trihalomethanes (THMs) formation and chlorine decay kinetics in Zai drinking water have been studied. It was found that both THMs and chlorine kinetics follow first-order reactions for growth and decay, respectively. A numerical model for predicting THMs formation in drinking water distribution system networks has been developed and applied. THMs measurements were taken at three locations over 106 h from a northern portion of Sport City area (Kharabshe Reservoir), while the water quality time step is set to 3 min, to insure predicting accurate total trihalomethanes (TTHMs) concentrations. The bulk flow for TTHMs formation rate constant value is determined and set to 5.82 × 10−2/h. The modeled results for THMs formation in the field network were compared favorably with the observed data for three sampling points in the network. The THMs formed inside the selected network of this case study was sixfolds higher than that formed in Zai treatment plant; and 113% higher than that formed in Kharabshe Reservoir. The model proved to be an effective tool for prediction of THMs formation in drinking water distribution systems.

Analytical and experimental investigation of chlorine decay in water supply systems under unsteady hydraulic conditions

This paper investigates the impact of the dynamic hydraulic conditions on the kinetics of chlorine decay in water supply systems. A simulation framework has been developed for the scale-adaptive hydraulic and chlorine decay modelling under steady- and unsteady-state flows. An unsteady decay coefficient is defined which depends upon the absolute value of shear stress and the rate of change of shear stress for quasi-unsteady and unsteady-state flows. By coupling novel instrumentation technologies for continuous hydraulic monitoring and water quality sensors for in-pipe water quality sensing a pioneering experimental and analytical investigation was carried out in a water transmission main. The results were used to model monochloramine decay and these demonstrate that the dynamic hydraulic conditions have a significant impact on water quality deterioration. The spatial and temporal resolution of experimental data provides new insights for the near real-time modelling and management of water quality as well as highlighting the uncertainty and challenges of accurately modelling the loss of disinfectant in water supply networks.

The Effect of Membrane Treatment on Chlorine Decay and Trihalomethanes Formation in Water Distribution Systems

The experiment was carried out to measure the effect of membrane treatment on the kinetics of chlorine decay in PE pipes in the water distribution systems. The results revealed that water had the potential to form halomethane compounds with chloroform being the most dominant. The formation of THMs is no longer relatively exponential relationship with the reaction time, but also decided by complex elements, including DOC, pH, conductivity, flow rate, and several other indexes. Since Chloroform (CHCl3) has the maximum concentration of the four THMs, clear understanding of its causes, pathway and mechanism will help to regulate and solve the THMs problem.

Small Water Distribution System Operations and Disinfection By Product Fate

The Stage-2 Disinfectant and Disinfection By-Product (D/DBP) regulations force water utilities to be more concerned with their finished and distributed water quality. Compliance requires changes to their current operational strategy, which affect the formation of DBPs over time. This study quantifies changes in DBP formation and chlorine decay kinetics under different operational conditions and pipe materials found at many small-scale water utilities. A physical model (Pipe Loop) of a distribution system was used to evaluate the change in water quality from conditions such as having a high chlorine dosage entering the distribution system, using a chlorine booster system in the distribution system, and operation of clearwells/storage tanks. The High Chlorine Run (HC) is least favorable option with approximately 64% and 30% higher TTHMs than Normal Run (NR) and Chlorine Booster Run (CB), respectively. High Chlorine conditions also minimize the wall effects. The location of Boosters should always be after the storage systems to avoid extra contact time that can produce approximately 23% - 78% higher TTHMs. The following trends are discovered from the data analysis: Chlorine residual HC > CB > NR and TTHM NR > CB > HC.

Rapid water quality characterization for chlorine demand and THM formation in drinking waters

The quality of drinking water generally deteriorates when it is delivered through a distribution system due to the decay of disinfectant, which subsequently allows the re-growth of microorganisms in the distribution system in addition to the formation of trihalomethane (THM). Therefore, a model which describes the changes that occur in the water quality in the distribution system is needed to determine whether to enhance the treatment processes or to improve the distribution system so that microbiological criteria are met. In this paper the chlorine decay kinetics and THM formation in treated water is modeled considering the reaction of chlorine with fast and slow reacting organic and nitrogenous compounds which are present in that water. The treated water was also passed through three types of resins to fractionate very hydrophobic acids (VHA), slightly hydrophobic acids (SHA), hydrophilic charged (CHA) and hydrophilic neutral (NEU) compounds which are present in the water. Chlorine decay tests were conducted on the effluents emerging from the resins to evaluate the chlorine demand and THM formation potential of those organic fractions. The model shows that the CHA presented in the waters has a very high THM formation potential (around 62% of the THM produced). VHA, NEU and CHA contributed to chlorine demand in the water.

Removal of disinfection by-products precursors by polyaluminum chloride coagulation coupled with chlorination

The effect of coagulation coupled with chlorination (i.e., pre-, inter-, and post-chlorination) on the formation of disinfection by-products (DBPs) and the removal efficiency of DBPs precursors were investigated. Compared with coagulation coupling with pre-chlorination, coagulation coupled with inter-chlorination could lead a higher removal efficiency of dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA) and chloroacetic acids formation potential (CAAsFP). The CAAsFP/DOC value of residual DOC showed that coagulation with inter-chlorination has a beneficial effect on CAAs precursors removal. More DBPs were produced during inter-chlorination than that of pre-chlorination at pH 7.5, while less DBPs were produced during inter-chlorination than that of pre-chlorination at pH 5.5. In addition, the precipitate of humic acid (HA) after coagulation was chlorinated to study the kinetics of chlorine decay. The results showed that coagulated-HA had a higher reactivity with chlorine than aqueous-HA at pH 7.5. Furthermore, the trends of zeta potential during coagulation process suggested that the distribution of chlorine species had significant influence on the removing of DBPs precursors by coagulation coupled with chlorination.

Modeling of chlorine effect on floc forming and filamentous micro-organisms of activated sludges

Chlorination is the most economical, non-specific method to control the excessive growth of filamentous micro-organisms causing bulking in activated sludge systems in the treatment of food industrial wastewaters; it was one of the first methods used to control filamentous bulking and is still widely employed. Considering that chlorination affects both floc-forming and filamentous micro-organisms and leaves undesirable disinfection by-products, it is necessary to define the adequate doses to control bulking, minimizing the effect on floc-forming bacteria. In the present work the effect of biomass concentration and type of micro-organism on chlorine decay kinetics was evaluated; the inactivation of either a filamentous ( Sphaerotilus natans) or a floc-forming ( Acinetobacter anitratus) micro-organism due to chlorination was also analyzed. For chlorine decay assays, the samples were treated in a batch system with sodium hypochlorite ranging between 9.8 and 56.6 mg Cl 2 (gVSS) −1. Respirometric assays were used to evaluate the effect of chlorine on micro-organisms respiratory activity; in these cases, sodium hypochlorite doses ranged between 2.5 and 18 mgCl 2 (gVSS) −1. A model that allowed to predict simultaneously chlorine consumption and respiratory activity decay for both micro-organisms as a function of time was proposed. The model includes three coupled differential equations corresponding to respiratory inhibition, readily organic matter oxidation by chlorine and chlorine decay. The rate of chlorine decay depended on both, type and concentration of the micro-organisms in the system. Chlorine consumption rate due to S. natans was 2–4 times faster than A. anitratus. Using the proposed model initial critical chlorine doses (the lowest initial dose that leads to a total inhibition of the respiratory activity) were calculated for both micro-organisms and values of 11.9 mgCl 2 (gVSS) −1 for S. natans and 4.5 mgCl 2 (gVSS) −1 for A. anitratus were obtained. These critical doses indicated that in non flocculated pure cultures, floc-former bacteria A. anitratus was more susceptible to chlorine action than S. natans.

Relationship of chlorine decay and THMs formation to NOM size

Because of increasing concern about balancing health risks for pathogen control and disinfection by-product (DBP) formation in water supplies, utilities are forced to closely examine and optimize their disinfection practices. A better understanding of the relationship between the molecular weights of the natural organic matter (NOM), chlorine decay kinetics and THMs formation can help the utilities to minimize the DBP concentrations, providing healthier and microbially safer water. The authors present data on chlorine decay kinetics and total trihalomethanes (TTHM) formation kinetics and modeling with different molecular weights NOM fractions of Mississippi River water. TTHM modeling results indicated that the TTHM formation in fractionated NOM was a function of chlorine consumption. TTHM yield coefficients ranged from 31 to 42 μg-TTHM/mg-Cl 2. As the molecular weight of the fractions decreased, TTHM yield coefficients increased.

Chlorine Decay KINETICS of a Reservoir Water

Massachusetts Water Resources Authority started adding sodium hypochlorite to its raw water (Wachusett Reservoir) in September 1997 to achieve compliance with the requirements of the Surface Water Treatment Rule for unfiltered surface water supplies, mainly the 3‐log C × T (concentration times time) value for Giardia inactivation. There were concerns about the chlorine dosage necessary to achieve pathogen inactivation and the effect of that dosage on the amount of disinfection by‐products (DBPs) formed. Weekly chlorine decay tests were initiated in April 1998 to gather information on chlorine decay so that the necessary parameters to produce an integrated C × T value could be developed (area under the chlorine decay curve). Wachusett Reservoir water quality is also affected by transfer of water from the Quabbin Reservoir, which has lower total organic carbon and UV254 absorbance levels. A model was developed to describe the rate constant as a function of hydroxide concentration (taking both pH and temperature effects into account through the ion product of water), UV254 absorbance, and chlorine dose only. The availability of kinetic parameters allows development of a method for calculating C × T achievement for primary disinfection. Models for DBP formation will be presented in another article. These models together allow for better determination of the necessary chlorine dosage to achieve the required C × T value and minimize DBP formation.

Modeling DBP formation

Disinfection by‐product concentrations in a transmission system can change in response to downstream treatment processes.Semimechanistic models that describe the formation of disinfection by‐products (DBPs) (including trihalomethanes and haloacetic acids) were developed for the Massachusetts Water Resources Authority, an unfiltered surface water system using chlorine. The model's parameters were hydroxide concentration, chlorine decay kinetics or chlorine reacted, ultraviolet light absorbance at 254 nm, and algae concentration. One of the challenges in estimating or predicting DBP concentrations is that treatment processes at various points in the transmission system have substantial effects on the factors that affect DBP formation and rates of DBP formation. This article describes the formation of total trihalomethanes and haloacetic acids in the Massachusetts Water Resources Authority system and takes into account three treatment processes within the system. Coefficients used in the model were based on monitoring data collected from October 1997 to July 1999 and were validated with monitoring data from August 1999 to January 2000.