Using chlorine demand TO PREDICT TTHM and HAA9 formation

Abstract

Because of an increasing need to balance 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. The authors provide a simple mechanistic model to predict total trihalomethane (TTHM) and the sum of nine haloacetic acids (HAA9) formation based on chlorine demand. To evaluate this modeling approach, eight Missouri surface waters (raw and alum-treated) were used in DBP formation and chlorine decay kinetic studies. A parallel first-order reaction model was used to fit the chlorine decay data, and the model coefficients were used to predict THM and HAA formation.Yield coefficients for TTHMs and HAA9 were obtained from fitting the DBP kinetic data. On average, the TTHM and HAA9 yield coefficients for all raw surface waters tested were about 40 µg TTHM/mg Cl 2 and 25 µg HAA9/mg Cl 2 consumed, respectively. In waters subjected to alum coagulation, the average TTHM and HAA9 yield coefficients were 30 µg TTHM/mg Cl 2 and 17 µg HAA9/mg Cl 2 consumed, respectively. The DBP predictive model introduced in this study provided a simple, reliable basis to evaluate treatment options by focusing on chlorine demand. This model can be readily calibrated to local conditions.

Modeling Chlorine Decay in Surface Water

“…Disadvantages of free chlorine use relate to the fact that it can react rapidly with natural organic matter (NOM) in water by oxidation, addition and substitution reactions to form disinfection by-products (DBPs), some of which are of concern from health risk point of view. The goal of maintaining a proper chlorine level for controlling microorganisms while minimizing DBPs formation is forcing utilities to closely examine and optimize their disinfection practices (Gang et al, 2002). Although chlorine is still the most commonly used water disinfectant, its reaction kinetics is not predictable to a large extent.…”

Impacts of Goethite Particles on UV Disinfection of Drinking Water

“…Mechanisms for the reduced chemical disinfection efficiency, analogous to the biofilm system (3,4,8), could be through colonization of particle surfaces by bacteria, where the disinfectant is present at a lower concentration due to (i) the high reactivity of particle surfaces for disinfectant degradation and (ii) limitation of mass transfer to the interface. Particle-attached bacteria are known to be more resistant to chemical disinfection than suspended bacteria (23,30).UV radiation has been increasingly used in the United States as an alternative approach for drinking water disinfection, promoted by the need of reducing potentially carcinogenic disinfection by-products (11,21,22,31). Similar to chemical processes, UV disinfection is also negatively affected by the presence of suspended particles (6,15,19).…”

“…UV radiation has been increasingly used in the United States as an alternative approach for drinking water disinfection, promoted by the need of reducing potentially carcinogenic disinfection by-products (11,21,22,31). Similar to chemical processes, UV disinfection is also negatively affected by the presence of suspended particles (6,15,19).…”

A Study on Removal of Natural Organic Matter (NOM) and Application of Advanced Water Treatment Processes for Controlling Disinfection By-Products

“…특히, 자연유기물질(Natural Organic Matter, NOM)은 인체 에 유해한 소독부산물을 형성하는 전구물질로 작용하기 때 문에 최근 많은 관심의 대상이 되고 있다 (Gang et al, 2002). …”