Total Trihalomethane Formation Research Articles

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.

Predicting Chlorine Residuals and Formation of TTHMs in Drinking Water

Chlorination is the most widely practiced form of disinfection in the United States. It is highly effective against most microbiological contaminants. However, there is concern that the disinfection by-products (DBPs) formed by the use of chlorine might be carcinogenic. One class of DBPs that are formed and the only class of DBPs that currently are regulated are total trihalomethanes (TTHMs). Therefore, much effort is being expended in developing models that can be used to predict both TTHMs and chlorine residual levels in treated drinking water. This paper presents a model that predicts both TTHMs and chlorine residuals based on the consumption of chlorine and can be used to assist in evaluating the complex balance between microbial and DBP risks associated with disinfecting drinking water with chlorine. The parameters of the model have been found to be functions of total organic carbon, pH, temperature, and initial chlorine residual level. Bromide and the subsequent formation of brominated by-products were not considered in this paper.

Chlorine Demand and TTHM Formation Kinetics: A Second-Order Model

Much effort has been expended in attempting to develop mathematical models for chlorine demand in water and wastewater. Most of these efforts have centered around the use of first-order functions or modifications of first-order functions. Recently there has also been interest in characterizing the formation of total trihalomethanes. These efforts have taken on new meaning because of the importance of maintaining chlorine residuals for microbial protection and concerns over the formation of trihalomethanes in drinking water distribution systems. This paper applies second-order kinetics to describe both of these relationships, using data collected from a recent collaborative study between the EPA and the American Water Works Association Research Foundation. It demonstrates that TTHM formation can be characterized as a function of chlorine demand.

Overall chemical reaction model of an ozone contactor for a water purification model

For the removal of odorous compounds such as dimethylisoborneol (2-MIB) and trihalomethanes (THMs) in supplied water, advanced water treatment plants using ozonation and activated carbon absorption processes have been built in Japan. This paper describes an over-all chemical reaction model for the ozone contactor of the ozonation process. In this model, the Potassium Permangante Consumed (PPC) is assumed as an index of typical ozone consuming substances. The experimental data and calculated results for the ozone consuming substances are compared with Total Trihalomethanes Formation Potential (TTHMFP). Furthermore, the promotive or inhibitive reaction of 2-MIB is introduced in the model. This allows the mathematical model to be applied to actual raw water containing many kinds of co-exist substances. The model appropriateness is discussed using pilot plant data for a year's operation.

Effect of ultraviolet irradiation on the characteristics and trihalomethanes formation potential of humic acid

Based on our experiments, ultraviolet irradiation has been found to bring about significant changes of the physicochemical characteristics of humic acid, including the change of TOC concentration, chemical structures, total extractable organic compounds characters and trihalomethanes formation potential.

Overall chemical reaction model of an ozone contactor for a water purification model

For the removal of odorous compounds such as dimethylisoborneol (2-MIB) and trihalomethanes (THMs) in supplied water, advanced water treatment plants using ozonation and activated carbon absorption processes have been built in Japan. This paper describes an over-all chemical reaction model for the ozone contactor of the ozonation process. In this model, the Potassium Permangante Consumed (PPC) is assumed as an index of typical ozone consuming substances. The experimental data and calculated results for the ozone consuming substances are compared with Total Trihalomethanes Formation Potential (TTHMFP). Furthermore, the promotive or inhibitive reaction of 2-NUB is introduced in the model. This allows the mathematical model to be applied to actual raw water containing many kinds of co-exist substances.The model appropriateness is discussed using pilotplant data for a year's operation.

Developing a Computer Model to Simulate DBP Formation During Water Treatment

A computer program was developed to simulate disinfection by‐product formation, removal of natural organic matter, inorganic water quality changes, and disinfectant decay in water treatment processes. This article presents equations that simulate the formation of total trihalomethanes (TTHMs), removal of total organic carbon (TOC) and ultraviolet absorbance by alum coagulation, and changes in alkalinity and pH. These equations represent only a small fraction of the entire computer model. Model simulations are compared with limited sets of observed values. The central tendency of the model is to underpredict finished‐water pH by 4 percent, finished‐water TOC by 7 percent, and simulated distribution system TTHMs by 20–30 percent. A discussion of model limitations and research needs concludes the article.

Continuous-flow method for the determination of total trihalomethane formation potential in waters

A double-tube separation system with an inner tube of microporous PTFE and an outer tube of PTFE is proposed for the continous determination of trihalomethanes (THMs) in waters. The THMs in the sample, after reaction with sodium hypochlorite solution at 98°C and reducing the residual hypochlorite with sodium sulphite, are separated with the double-tube system at 50°C. They are then mixed with alkaline nicotinamide solution and heated at 98°C. After cooling in an ice-bath, the reaction product is fed to a spectrofluorimeter and the emission of fluorescence excited at 372 nm, is measured at 467 nm. The response was obtained within 20 min. The detection limit (signal-to-noise ratio = 3) was 2.2 μg 1 −1. The total THM formation potential obtained by the present method for lake and river waters were in good agreement with those obtained by the Japanese standard batch method.

Organic Carbon and THM Formation Potential in Kansas Groundwaters

Fifty wells in Kansas were sampled to determine the concentrations of total organic carbon (TOC) and trihalomethane formation potential (THMFP) associated with major aquifer systems. The mean TOC and THMFP concentrations were 1.03 ± 0.76 mg/L and 46.7 ± 39.5 μg/L, respectively; THMFP was very strongly correlated with TOC (r = 0.953). Only 8 percent of the THMFP concentrations exceeded 100 μg/L, but 56 percent exceeded 25 μg/L and 90 percent exceeded 10 μg/L, suggesting that many Kansas water utilities using groundwater might have difficulty meeting a substantially lower THM standard. Efforts to control THMs in Kansas groundwater supplies should focus on alluvial aquifers, particularly those with high concentrations of TOC, ammonium, iron, and manganese.

Developing Models for Predicting Trihalomethane Formation Potential and Kinetics

This article describes the overall development, including formulation and calibration, of linear and nonlinear multiple regression models for predicting total trihalomethane formation potential and kinetics during the chlorination of natural waters. The rationale behind each model formulation is discussed, and statistics relating to the calibration of each model are presented. The testing and attempted validation of these models are also addressed. Each model is subjected to a sensitivity analysis and a validation analysis using data derived from the literature.

Surrogate Parameters for Monitoring Organic Matter and THM Precursors

UV absorbance at 254 nm is an excellent surrogate parameter for estimating the raw water concentrations of organic carbon (NPTOC—nonpurgeable total organic carbon) and THM precursors (TTHMFP—total trihalomethane formation potential) in the Grasse River (highly colored water) and the Glenmore Reservoir (protected, upland source). The raw water surrogate equations developed from the Grasse River data were tested successfully on other waters. Direct filtration pilot‐plant data demonstrated that UV can be used to monitor pilot‐plant performance for removals of NPTOC and THM precursors. For two plants studied, UV was an excellent predictor of plant performance for removals of NPTOC and THM precursors. Instantaneous TTHMs of the finished waters can be predicted from raw water UV, finished water pH, chlorine consumption, and temperature data. Particular attention should be given to the selection of sampling locations and to the sample‐handling conditions.

Pilot‐Plant Studies of Slow‐Rate Filtration

Alternatives to conventional water filtration plants, which use coagulation, flocculation, sedimentation, and rapid filtration, may be appropriate for some small utilities. One such alternative is slow‐rate filtration. This article describes pilot‐plant studies that were undertaken to evaluate slow‐rate filtration for the removal of particulates, total coliforms, standard plate count bacteria, and organics (total organic carbon and trihalomethane formation potential). Two pilot‐scale filtration systems were used: a slow sand filter, operated for 800 days, and a second slow sand filter operated in parallel with a slow‐rate filter containing granular activated carbon, operated for 200 days. Results are presented for both systems.

Pretreatment Preferred Over Outlandish Chlorine Doses

In response to “Ann Arbor Controls Trihalomethanes” by Richard Sacks (Journal AWWA, July 1984), White disputes the practice of using chlorine beyond the breakpoint and then adding more ammonia. He suggests use of a 15‐minute chlorine demand surrogate parameter for raw water quality as an adjunct to total trihalomethane formation potential. Sacks replies that the article presented combined chlorination (i.e., adding ammonia to form chloramines) as an economical method of compliance for utilities that cannot meet the THM regulation.

Determination of bromide in natural waters by ion chromatography using a concentrator column

The trihalomethanes (THMs) chloroform (CHCI3), dichlorobromomethane (CHCI2 Br), dibromochloromethane (CHCIBr2) and bromoform (CHBr3) are formed during the disinfection step of water treatment when using chlorine (Rook, 1974). These compounds are suspect as human carcinogens (De Rowen and Diem, 1975). Accumulated knowledge regarding the brominecontaining THMs is far less extensive than that for CHCI3 (Minear et al., 1981). The presence of bromide as a precursor is necessary to the formation reaction of the bromine-containing THMs (Bird, 1979). Research has indicated that p g l -~ levels of bromide directly affect the rate of total trihalomethane (TTHM) formation, the ultimate concentration after prolonged reaction and the product distribution among the four forms (Bird and Minear, 1979). Nonvolatile total organic carbon (NVTOC), pH, temperature and chlorine dose are strongly related to THM concentrations in drinking water. The magnitude of each of these effects on THM formation has been shown to be strongly dependent upon bromide concentrations (Minear and Bird, 1980). This bromide effect may possibly explain apparent discrepancies between other research efforts as regards temperature, pH and chlorine dose effects, and the relationship between NVTOC content and THM production. Unfortunately, few data regarding water supply bromide levels in conjunction with THM formation are currently available since most conventional spectrophotometric applications lack desired sensitivity, as does direct ion chromatography (IC). One spectrophotometric method, that of Skougstad et al. (1978) is suitable for the expected range of bromide ion present in the raw waters. This method is applicable to natural waters having a bromide content in the range of 0.01--0.10 mg I -~, and is based on the catalytic effect of bromide on the

A pilot study of chlorine dioxide use to reduce total trihalomethanes

In the development of a 1500‐ML/day treatment plant, consideration was given to alternative means of disinfection to reduce the formation of total trihalomethanes. Chlorine dioxide (CIO2) was examined on a plant scale of 760 ML/day. This article relates the design considerations and problems encountered in the production of CIO2 free of chlorine (Cl2). The chief problem, which remains unresolved, is the development of an analytical technique that can routinely identify CIO2, CI2, chlorates, and chlorites in the same solution.