Heterotrophic bacteria isolated from a chloraminated system accelerate chloramine decay.

This work comprehensively demonstrates the ability of heterotrophic bacteria, isolated from a chloraminated system, to decay chloramine. This study non-selectively isolated 62 cultures of heterotrophic bacteria from a water sample (0.002 mg-N/L nitrite and 1.42 mg/L total chlorine) collected from a laboratory-scale reactor system; most of the isolates (93.3%) were Mycobacterium sp. Three species of Mycobacterium and one species of Micrococcus were inoculated to a basal inorganic medium with initial concentrations of acetate (from 0 to 24 mg-C/L) and 1.5 mg/L chloramine. Bacterial growth coincided with declines in the concentrations of chloramine, acetate, and ammonium. Detailed experiments with one of the Mycobacterium sp. isolates suggest that the common mechanism of chloramine loss is auto-decomposition likely mediated by chloramine-decaying proteins. The ability of the isolates to grow and decay chloramine underscores the important role of heterotrophic bacteria in the stability of chloramine in water-distribution systems. Existing strategies based on controlling nitrification should be augmented to include minimizing heterotrophic bacteria.

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.

The role of pH on sewer corrosion processes and control methods: A review.

The production and emission of hydrogen sulfide (H2S) in sewer systems is associated with the corrosion of sewer structures and harmful odour. Numerous studies have been conducted to find the best solution to overcome this issue. The pH plays a critical role not only on microbial and chemical processes that are responsible for all processes of corrosion but also on the efficiency of several control methods. This paper first critically reviews the literature on the interplay between pH and various chemical and microbial in-sewer processes, followed by a review of the control methods that depend on pH or indirectly alter pH. The paper argues that proper evaluation of each method should include the impact the control method has on downstream processes. This paper concludes the raising of pH has several benefits but is operationally difficult to implement. It also emphasises single control method may not be as efficient as combination of one or two methods in controlling the production and emission of H2S. Finally, the research requirements and future directions in relation to emerging and potential methods that are not heavily reliant on pH control are discussed.

Simplified chemical chloramine decay model for water distribution systems.

This paper, presents a simplified model for predicting chemical chloramine loss in ultrapure water as a function of various measurable parameters, which otherwise requires the simulation of a complex mechanistic model involving the implementation of a number of ordinary differential equations (ODE), using specialised software. The complexity of the mechanistic model is evidenced by its lack of use outside chemical reaction modelling academics. We developed a simplified model as a single-line equation with eight fixed coefficients to predict the first-order decay coefficient. The developed model accurately predicts the first-order chloramine decay coefficient as a function of the water pH (7.5-8.5), chlorine-to-ammonia mass ratio (3.0-4.5), initial chloramine dose (1.5-5.0 mg/L), and alkalinity (up to 200 mg/L CaCO3) at 25 °C in ultrapure water samples. The user either has to input all the above mentioned water quality parameters or can evaluate the relative effect of water quality parameters individually or collectively, by using a relative model. The decay coefficient for temperature between 4 and 35 °C can be obtained by applying Arrhenius equation. To predict the chloramine profile, the initial chloramine concentration has to be decreased slightly (4% when pH < 7.8 to no adjustment at pH > 8.2) before the first order model is applied. Such a model will help in adding the effect of other parameters such as NOM, bromide, and microbiological decay in the future to facilitate easy adaptation by the water utilities.

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.

Hydrogen sulphide control in sewers by catalysing the reaction with oxygen.

This work for the first time shows possible advantage of using ferrous as a catalyst to selectively oxidise hydrogen sulphide in sewer water where biological activity is present. Ferrous catalysed the oxidation reaction in all conditions, but the oxygen requirement for the chemical oxidation of sulphide varied depending on the initial conditions (pH, concentrations of sulphide and oxygen). For initial concentrations of O2 and S2- exceeding 2 mg/L, and a pH between 7.3 and 8.3, approximately 1 mg-O2 was required to oxidise 1 mg-S2-. For the typical conditions experienced in a sewer (pH < 8.0 and O2 and S2- < 2.0 mg/L), approximately 2.0 mg-O2 is required to oxidise 1 mg-S2-. The most efficient O2 usage of 0.25-0.5 mg-O2 was observed with initial O2 and S2- concentrations below 2.0 mg/L and a pH >8.1. The developed mathematical model described the experimental results over a wide range using only three coefficients. The catalytic effect of ferrous selectively increased the oxidation rate of S2- in sewer water samples in which biochemical oxygen utilisation competes for oxygen. Further trials are needed to optimise the method for application in sewer systems where biofilm is present and varying conditions (temperature, H2S concentration, oxygen consumption rate) exist.

New model of chlorine-wall reaction for simulating chlorine concentration in drinking water distribution systems.

Accurate modelling of chlorine concentrations throughout a drinking water system needs sound mathematical descriptions of decay mechanisms in bulk water and at pipe walls. Wall-reaction rates along pipelines in three different systems were calculated from differences between field chlorine profiles and accurately modelled bulk decay. Lined pipes with sufficiently large diameters (>500 mm) and higher chlorine concentrations (>0.5 mg/L) had negligible wall-decay rates, compared with bulk-decay rates. Further downstream, wall-reaction rate consistently increased (peaking around 0.15 mg/dm2/h) as chlorine concentration decreased, until mass-transport to the wall was controlling wall reaction. These results contradict wall-reaction models, including those incorporated in the EPANET software, which assume wall decay is of either zero-order (constant decay rate) or first-order (wall-decay rate reduces with chlorine concentration). Instead, results are consistent with facilitation of the wall reaction by biofilm activity, rather than surficial chemical reactions. A new model of wall reaction combines the effect of biofilm activity moderated by chlorine concentration and mass-transport limitation. This wall reaction model, with an accurate bulk chlorine decay model, is essential for sufficiently accurate prediction of chlorine residuals towards the end of distribution systems and therefore control of microbial contamination. Implementing this model in EPANET-MSX (or similar) software enables the accurate chlorine modelling required for improving disinfection strategies in drinking water networks. New insight into the effect of chlorine on biofilm can also assist in controlling biofilm to maintain chlorine residuals.

Effectiveness of breakpoint chlorination to reduce accelerated chemical chloramine decay in severely nitrified bulk waters.

Rectifying the accelerated chloramine decay after the onset of nitrification is a major challenge for water utilities that employ chloramine as a disinfectant. Recently, the evidence of soluble microbial products (SMPs) accelerating chloramine decay beyond traditionally known means was reported. After the onset of nitrification, with an intention to inactivate nitrifying bacteria and thus maintaining disinfectant residuals, breakpoint chlorination followed by re-chloramination is usually practiced by water utilities. However, what actually breakpoint chlorination does beyond known effects is not known, especially in light of the new finding of SMPs. In this study, experiments were conducted using severely nitrified chloraminated water samples (chloramine residuals <0.5 mg Cl2 L−1, nitrite residuals >0.1 mg N L−1 and an order of magnitude higher chloramine decay rate compared to normal decay) obtained from two laboratory scale systems operated by feeding natural organic matter (NOM) containing and NOM free waters. Results showed that the accelerated decay of chloramine as a result of SMPs can be eliminated by spiking higher free chlorine residuals (about 0.92 ± 0.03 to 1.16 ± 0.12 mg Cl2 L−1) than the stoichiometric requirement for breakpoint chlorination and nitrite oxidation. Further, accelerated initial chlorine decay showed chlorine preferentially reacts with nitrite and ammonia before destroying SMPs. This study, clearly demonstrated there is an additional demand from SMPs that needs to be satisfied to effectively recover disinfection residuals in subsequent re-chloramination.

Experimental investigation and modeling of dissolved organic carbon removal by coagulation from seawater.

Coagulation removes colloidal matters and dissolved organic carbon (DOC) which can cause irreversible membrane fouling. However, how DOC is removed by coagulant is not well-known. Jar test was used to study the removal of hydrophobic and hydrophilic DOC fractions at various doses (0.5-8.0 mg-Fe(+3) L(-1)) of ferric chloride (FeCl3) and pH (5.0-9.0). Natural organic matter (NOM) in seawater and treated seawater were fractionated by liquid chromatography-organic carbon detector (LC-OCD). Compared to surface water, the removal of DOC in seawater by coagulation was remarkably different. Majority of DOC could be easily removed with very low coagulant dose (<5.0 mg-Fe(+3) L(-1)) and the removal efficiency did not vary with pH, but the DOC composition in treated water had significantly changed. Hydrophobic fraction (HB) was better removed at high pH while hydrophilic fraction (HF) was better removed at low pH. A modified model of Kastl et al. (2004) which assumed that the removal occurred by adsorption of un-dissociated compounds onto ferric hydroxide was formulated and successfully validated against the jar test data.

A suitable model of combined effects of temperature and initial condition on chlorine bulk decay in water distribution systems.

Maintaining a chlorine residual is a major disinfection goal in many water distribution systems. A suitable general model of chlorine decay in the transported bulk water is an essential component for efficiently modelling chlorine concentration in distribution systems. The two-reactant model meets basic suitability criteria, including accurate prediction of chlorine residual over hundreds of hours, commencing with chlorine concentration 0-4 mg/L. This model was augmented with an equation that increases the decay coefficients with temperature according to Arrhenius theory. The augmented model was calibrated against decay-test data sets to obtain a single invariant set of parameters for each water. Model estimates of chlorine residuals over time closely matched decay-test data, over the usual operating ranges of initial chlorine concentration (1-4 mg/L) and temperature (3.5-28 °C). When the augmented model was fitted to partial data sets, it also predicted the data reserved for validation very well, suggesting that this model can accurately predict the combined effect of initial chlorine concentration and temperature on chlorine bulk decay in distribution systems, using a single set of invariant parameters for a given source water.

Evaluation of suitable chlorine bulk-decay models for water distribution systems.

Maintaining the chlorine residual is a major disinfection goal for many water distribution systems. A suitable general chlorine bulk-decay model is required for simulation of chlorine profiles in networks to assist disinfection planning/management efficiently. The first-order model is unsuitable due to inaccuracy and inability to represent rechlorination. Three potentially suitable, simple, reactant models were compared. The single-reactant model was found to be unsuitable, as it was inaccurate when restricted to using a single set of invariant parameters. The two-reactant model was more suitable than the variable-rate-coefficient model, although both models were accurate under the same restriction. The two-reactant model was then calibrated against datasets consisting of multiple decay tests for five distinctly different waters. It accurately predicted data reserved for validation over the chlorine concentration range of 0-6 mg/L, using a single set of invariant parameters, and is therefore the simplest, generally suitable model for simulating chlorine profiles in distribution system networks.

Effects of stratification on chloramine decay in distribution system service reservoirs.

Water quality in chloraminated distribution systems is affected by microbial activity, particularly due to nitrifiers that accelerate chloramine decay. In summer, continuous thermal stratification increases retention time and lowers chloramine residual in some parts of a system service reservoir (tank), relative to fully mixed conditions. According to temperature and chemical indicators, cooling in winter destratifies these reservoirs naturally. Traditional (chemical) indicators of nitrification also suggest that destratification occurs with respect to microbiological activity. In contrast, the microbial decay factor (F(m)) method, which separates microbiological and chemical decay in bulk water, identifies strong microbial stratification, even in winter. F(m) can also be used to predict the exacerbated loss of chloramine residual in the following summer, which enables early intervention by system managers to minimise such loss, and so maintain an adequate residual through the distribution system.

Simple method for quantifying microbiologically assisted chloramine decay in drinking water.

In a chloraminated drinking water distribution system, monochloramine decays due to chemical and microbiological reactions. For modeling and operational control purposes, it is necessary to know the relative contribution of each type of reaction, but there was no method to quantify these contributions separately. A simple method was developed to do so. It compares monochloramine decay rates of processed (0.2 microm filtered or microbiologically inhibited by adding 100 microg of silver/L as silver nitrate) and unprocessed samples under controlled temperature conditions. The term microbial decay factor (Fm) was defined and derived from this method, to characterize the relative contribution of microbiologically assisted monochloramine decay to the total monochloramine decay observed in bulk water. Fm is the ratio between microbiologically assisted monochloramine decay and chemical decay of a given water sample measured at 20 degrees C. One possible use of the method is illustrated, where a service reservoir's bulk and inlet waters were sampled twice and analyzed for both the traditional indicators and the microbial decay factor. The microbial decay factor values alone indicated that more microbiologically assisted monochloramine decay was occurring in one bulk water than the other. In contrast, traditional nitrification indicators failed to show any difference. Further analysis showed that the microbial decay factor is more sensitive and that it alone can provide an early warning.