George Kastl

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.

Suitability of chlorine bulk decay models for planning and management of water distribution systems

Effective disinfection planning and management in large, complex water distribution systems requires an accurate network water quality model. This model should be based on reaction kinetics, which describes disinfectant loss from bulk water over time, within experimental error. Models in the literature were reviewed for their ability to meet this requirement in real networks. Essential features were identified as accuracy, simplicity, computational efficiency, and ability to describe consistently the effects of initial chlorine dose, temperature variation, and successive rechlorinations. A reaction scheme of two organic constituents reacting with free chlorine was found to be necessary and sufficient to provide the required features. Recent release of the multispecies extension (MSX) to EPANET and MWH Softs H2OMap Water MSX network software enables users to implement this and other multiple-reactant bulk decay models in real system simulations.

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.

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.

A comprehensive bulk chlorine decay model for simulating residuals in water distribution systems

Abstract Chlorine decay models provide efficient ways to develop disinfection strategies for water distribution systems, provided they account separately for bulk and wall decay, and accurately describe decay with a single set of coefficients. The augmented two-reactant (2RA) model is shown to be the simplest model to accurately describe effects of rechlorination dose/timing on bulk chlorine decay, in combination with effects of initial concentration and temperature over long periods. The two-reactant (2R) and variable reaction-coefficient (VRC) models provided predictions of comparable accuracy under higher and successive rechlorination doses at constant temperature. However, the 2RA model provides a more general basis for strategy development, as the VRC model cannot describe the effect of temperature variation. The minimal data-set required for 2RA calibration was similar for all cases considered. The 2RA model is readily applied by incorporation into system modelling software such as the multi-species extension (MSX) to EPANET software.

Comment on “A Variable Rate Coefficient Chlorine Decay Model”

We commend Jonkergouw et al. (1) for adopting the goal of developing a chlorine decay model that is practical for “...day-to-day water distribution network modelling purposes and chlorine dosing optimisation studies” in the sense that the model coefficients are independent of loading conditions (initial and rechlorination doses).

A selection framework for NOM removal process for drinking water treatment

AbstractNOM (natural organic matter) is increasing in water resources worldwide and is becoming more difficult to treat. Drinking water guidelines are becoming more stringent so NOM removal is becoming more critical and requires consideration as a major treatment process, rather than just a polishing step on top of turbidity removal. In this study, a review of available methodologies to determine the required degree of NOM removal was undertaken. It is demonstrated that chlorine decay and THM (trihalomethane) formation modelling of laboratory-treated water samples provides a sound guide to determine the level of NOM removal needed for a given situation. The level of NOM removal needed is linked to a specific distribution system at given water temperature and water age profile. A sample of raw water treated by a given NOM removal process is tested for chlorine decay rates and THM formation kinetics, and these results are used to evaluate the performance of a distribution system with a given configuration. ...

General Model of Chlorine Decay in Blends of Surface Waters, Desalinated Water, and Groundwaters

AbstractManagement goals for many distribution systems include maintaining a minimum level of free chlorine and limiting disinfection by-products. As water resources become scarce and quality deteriorates, blends are often required, so achieving these goals becomes increasingly difficult. The augmented two-reactant (2RA) model describes chlorine decay in a single water, for various dosing levels and water temperatures. However, it is not known whether there is any effect on chlorine decay (either synergistic or antagonistic) arising from blending waters of distinctly different quality. Linked 2RA models of source waters were used to determine whether bulk decay in blends of various source waters could be accurately and generally modeled. Results showed that chlorine decay in blends of various waters could be described accurately without synergistic or antagonistic effects, implying that each water’s reactants reduced chlorine independently. This held for pairs of surface waters, groundwaters, and raw or t...