Trihalomethane Precursors Research Articles

Ozonation of aqueous solutions of resorcinol and phloroglucinol. 1. Stoichiometry and absorption kinetic regime

In the first part of this work, chlorination of diluted aqueous solutions of resorcinol and phloroglucinol in the presence of bromide ion with and without preozonation has been carried out. The results obtained show that both phenols are strong trihalomethane precursors and that preozonation considerably reduces the formation of these organohalogen compounds. Subsequently, ozonation of resorcinol and phloroglucinol in an agitated tank has been conducted at different experimental conditions

Pyrolysis–GC–MS for Investigating High‐Molecular‐Weight THM Precursors and Other Refractory Organics

Specific problems encountered during water treatment are known to be a function of the type of macromolecules present. The pyrolysis–GC–MS analytical technique described in this article shows the inadequacy of existing models to accurately reflect the complex mixture that comprises the organic matrix of natural waters. In fact, the highly condensed aromatic cores described by most of these models were determined by the research reported here to be minor constituents.

Removal of organohalogens and organohalogen precursors in reclaimed wastewater—I

Fractionation, using synthetic resins, of dissolved organic material in filtered secondary effluent from an advanced wastewater reclamation facility and unpolluted source water, based upon acidity, solubility and adsorbability indicated a strong correlation between organohalogen formation potential (THMFP, TOXFP) and organic carbon (NVTOC). Background organohalogens were quantified as TOX. In addition to humic substances, the classic trihalomethane precursors, hydrophilic substances that comprised the largest fraction of the dissolved material, were implicated for their tendency to form organic halogens upon chlorination. Evaluation of an existing comprehensive advanced treatment process for reclamation of municipal wastewaters indicated that it provides a high level of treatment with respect to removal of organohalogens and precursor organics.

Decomposition of humic acid and reduction of trihalomethane formation potential in water by ozone with u.v. irradiation

Humic acids dissolved in water are decomposed by ozone under u.v. irradiation at pH 6.9. The decomposition rate of the total organic carbon (TOC) is obtained as functions of the u.v. intensity and the residual ozone concentration, assuming the reaction obeys first order kinetics with respect to reactive TOC concentration. Major final products are acetic acid, formic acid and oxalic acid, which are refractory to ozonation and are no longer precursors of trihalomethanes. The amount of chloroform and total organic chlorides generated by chlorination are drastically decreased by u.v. irradiation. No increase in the trihalomethane formation potential is observed in the course of u.v. ozonation.

Removal of Dissolved Organic Matter by Nanofiltration

A nanofiltration module is studied to determine its ability to remove dissolved organic matter (DOM) from two water sources: An effluent-impacted ground water and a low-turbidity surface water. Both feed and product waters from a single nanofiltration module are analyzed for trihalomethane precursors, as measured by bulk water dissolved organic carbon (DOC), UV absorbance, and trihalomethane formation potential (THMFP), as well as molecular weight (MW) distributions of these parameters. Results indicated excellent rejection of DOM accompanied by good rejection of inorganics, as reflected by conductivity data. Nanofiltration is very effective in rejecting higher molecular weight DOM (>1,000 amu) while moderately effective in rejecting lower molecular weight material (<1,000 amu).

Evaluation of THM Precursor Contributions From Agricultural Drains

More than 200 agricultural drains in the Sacramento River Delta contribute significant levels of trihalomethane (THM) precursors to California State Project water. It has been hypothesized that these drains, associated with crop irrigation involving highly organic peat soils, are probably responsible for the higher levels of dissolved organic carbon and THM formation potential in the California Aqueduct emanating from the delta in comparison with the principal freshwater tributaries entering the delta. The purpose of this study was to evaluate this hypothesis. It was found that the dissolved organic matter from drains is characterized by a higher molecular weight and greater THM reactivity than that found in delta tributaries.

Committee Report: Membrane Desalting Technologies

Many decision‐makers in the water supply field are not familiar with advances in membrane technologies for desalting, softening, trihalomethane precursor removal, and wastewater reuse. Membrane technologies should be considered as a water treatment alternative, particularly when adequate low‐cost freshwater supplies are not available. Two such technologies, reverse osmosis and electrodialysis, are described in this report, as well as system design considerations and costs.

Synergistic effects of potassium permanganate and PAC in direct filtration systems for THM precursor removal

Some traditional methods for reducing trihalomethane concentrations in finished water may be less effective or inappropriate for direct filtration water treatment systems. Reduced prefiltration hydraulic detention times and mass solid loading considerations affect the use of potassium permanganate (KMnO 4) and powdered activated carbon (PAC) in direct filtration systems. KMnO 4 and PAC were investigated both individually and in combination to determine the effectiveness in reducing maximum total trihalomethane potential (MTP). The effectiveness of the chemicals was evaluated by using jar tests and/or a 23,850 l d −1 direct filtration pilot plant. The results indicated that permanganate oxidation of THM precursors to reduce MTP was ineffective at low concentrations (< 1 mg l −1) and prefiltration contact times (< 1 h) typical of direct filtration systems. PAC (30 mg l −1) adsorption of THM precursors reduced MTP by 10–26%, however, the time of pilot filter run length was reduced by 40%. Combined use of permanganate (2 mg l −1) and PAC allowed effective control of excess residual permanganate ion and exhibited a synergistic effect by reducing MTP up to 35%, which was a greater reduction than achieved by either compound individually.

Humic substance removal through surface water potabilization processes

Chlorination of natural waters during potabilization process has proven to produce trihalomethanes (THM) as well as other higher molecular weight halogenated organic compounds, presumably through reactions with humic substances present in natural waters (THM precursors). This work shows the removal of humic substances obtained by using a laboratory-scale surface water potabilization process. Monitoring of precursors removal was achieved by adding excess amounts of chlorine to water samples taken through the process, and then measuring THM formation via a purge-and-trap of volatiles concentration and gas-liquid chromatographic analysis. It was demonstrated that both preozonation followed by coagulation-flocculation-sedimentation, and activated carbon filtration, remove important amounts of THM precursor. OOn the other hand, filtration through inert media (sand, anthracite) do not exert a significant influence on THM precursors content of water. These results support the idea of the humic nature of THM precursors.

Low-energy membrane nanofiltration for removal of color, organics and hardness from drinking water supplies

The field of desalination is becoming increasingly more complex and interesting. The original concept of the production of potable water from seawater and brackish water now describes only one area in which desalination technology may be applied to the supply of safe drinking water. Reverse osmosis membrane manufacturers are becoming adept at tailor-making membranes to fill other water treatment applications. Ultra-low pressure nanofiltration is a new tool for removal of hazardous organic contaminants in preference to low molecular weight salts. Demands for water quality are becoming increasingly more stringent. In 1986, the USEPA targeted 83 contaminants for which regulations will be developed. Maximum contamination levels MCL's) have already been set for certain constituents which have been identified as possible carcinogens, such as trihalomethanes (THMs). THMs are reaction products from chlorination of water containing natural substances such as humic and fulvic acids, called THM Precursors (THMPs). MCLs for total trihalomethanes (TTHMs) have been set at 100 ppb and will probably be lowered to 50 ppb in the near future. Because of the number of components which are being considered for regulation and because of the diversity of their physical and chemical properties, their removal presents a formidable challenge to the water treatment/desalination engineer. Because of their ability to reject high percentages of many dissolved components, nanofiltration membranes offer a single treatment alternative for removing many of these contaminants. Recent developments in membrane technology have created a new generation of membranes which are much more cost-competitive for treating lower TDS waters for removal of specific contaminants. These new membranes are classified as nanofiltration or ultra-low pressure membranes, typically providing 90–95% rejection of THMPs, 85 to 95% rejection of hardness and over 70% rejection of monovalent ions when operated at only 70 to 100 psi driving pressure. Field testing is now underway in Florida, where substantial THMPS are found in the shallower aquifers. This new technology should be of particular interest where water resource conservation procedures involve blending of desalted water product with untreated groundwater, surface water and/or catchment storage, followed by chlorine disinfection.

Application of Granular Activated Carbon in the Water Industry

ABSTRACTUntil the mid 1980s granular activated carbon (GAC) was used in only a small number of water‐treatment plants in the UK. Since then the material has been installed in over 30 plants, either as a result of an operational decision to treat the water by GAC or for the purpose of full‐scale experiments. GAC is used for a variety of reasons including taste and odour control, removal of a wide range of synthetic organic compounds (for example volatile chlorinated solvents, pesticides, oils) of molecular weight 100–500, and adsorption of trihalomethane precursors (molecular weight 103‐105). The performance of different GACs for a particular duty may vary by a factor of 10, and the best GAC for one application may be the worst for another. Thus, to minimize the cost of GAC treatment, it is essential to identify the purpose for which GAC is being used and then to select, by pilot trials or by more rapid laboratory procedures and mathematical modelling, the most appropriate GAC for that particular application.

THM precursor removal and softening - Ft. Myers 12 MGD RO membrane plant, Florida USA

The City of Ft. Myers currently line softens up to 10 MGD (1600 m3/hr) of raw water from a well field in a process including aeration, lime softening, clarification, recarbonation, chlorination, and media filtration. The water, as presently treated, exceeds the regulatory limit for THM by a factor of four (400 ug/L versus regulatory limit of 100 ug/L). Due to a need to expand capacity and comply with THM regulations, the City investigated process alternatives, and found that membrane separation of organics (THM precursor) and hardness, more reliably meets existing requirements and proposed future THM limits, at no additional cost compared to more conventional chemical processes. Subsequent to the treatment study, membrane pilot testing was conducted, a membrane supplier was selected, and proof testing was successfully completed during the summer of 1988. This paper describes the project background, and membrane proof test objectives, procedures, equipment, and results.

Potential Links Between Eutrophication and the Formation of Carcinogens in Drinking Water

ABSTRACT Eutrophication in lakes and reservoirs is a recreational problem and a drinking water quality problem. A major concern is trihalomethane (THM) formation from the reaction of chlorine, a disinfectant, with organic matter in natural water during drinking water treatment. Trihalomethanes, such as chloroform, are known or suspected carcinogens. Algae and allochthonous humic substances are known contributors to the THM precursor pool. Other in-reservoir precursor sources, macrophytes, and sediments, have not been investigated. The authors examined precursor generation in an Ohio water supply reservoir. A three-year input-output study demonstrated that 30 percent of the precursors entering the treatment plant were generated within the reservoir. Laboratory experiments revealed that macrophytes and sediments produce THM precursors. Estimated THM precursor contributions to the reservoir from macrophyte growth and sediment release were small, but algal productivity and macrophyte decomposition may contrib...

Evaluation of Chlorine Dioxide in Potable Water

A problem with trihalomethane (THM) levels in its finished water required the Crawford Country Rural Water District Number 6 (CCRWD), Parsons, Kansas, to investigate methods of oxidizing THM precursors. Testing indicated that chlorine dioxide is a viable alternative for control of THMs at CCRWD. Furthermore, chlorine dioxide satisfactorily addressed the plant's problems with iron and manganese and with taste and odor, while allowing a very significant savings on activated carbon and potassium permanganate.

La chloropicrine dans les eaux potables: Conditions de formation et evolution le long des filieres de traitement

Abstract Chloropicrin, a known toxic substance, has been found in several prechlorinated waters. Nowadays little is known about the conditions of its formation from different precursors and its evolution during the different steps of treatment. In this article, it is shown that chloropicrin may be present in surface water in the microgram per liter range when the total dissolved organic concentrations approaches 10 mg/1. Precursors to the formation of chloropicrin include a variety of nitrogen containing organic compounds, however nitrites, free chlorine and THM precursors are most important. Although chloropicrin in effectively removed by CAG filtration, the simplest means of controlling its appearance, is to abandon the practice of prechlorination.

Chlorine Dioxide Effects on THMFP, TOXFP, and the Formation of Inorganic By‐products

An investigation of raw and finished waters was conducted (1) to determine whether chlorine dioxide pretreatment lowers trihalomethane (THM) and total organic halide (TOX) formation, (2) to evaluate the rate of chlorine dioxide consumption and the corresponding rate and extent of chlorite formation, and (3) to investigate the stability of chlorite in treated water and its interaction with chlorine. Results of these experiments showed that chlorine dioxide can reduce THM and TOX precursor concentrations and that when added to raw water, chlorine dioxide will not persist long enough to maintain oxidizing conditions through flocculation–sedimentation basins. Utilities should be able to meet the recommended limit of 1.0 mg/L for the sum of the residual chlorine dioxide species by not exceeding a chlorine dioxide dosage of 1.2—1.4 mg/L.

Applying Membrane Processes to Groundwater Sources for Trihalomethane Precursor Control

The use of membrane processes for controlling trihalomethanes (THMs) was investigated for Florida groundwater sources and one surface water source. All of the sources were used for public supply and had excessive THMs (&gt;300 μg/L) in the finished water. The performance and projected cost of the membrane system using groundwater sources are reported in this article.

Removing Trihalomethane Precursors by Coagulation

The removal of trihalomethane precursors by coagulation was studied with low turbidity, low alkalinity waters containing high levels of aquatic humic matter. Jar tests were conducted with synthetic and natural waters using alum, high‐molecular‐weight polymers, cationic polymers, and various combinations of these coagulants. Cationic polymers alone were found to be less effective than alum in the coagulation of humic substances. High‐molecular‐weight polymers used as coagulant aids with alum improved turbidity removal but not precursor removal, whereas high‐charge‐density cationic polymers with alum as a coagulant aid provided good precursor removals at low alum dosages.

Testing and validation of a multiple nonlinear regression model for predicting trihalomethane formation potential

This paper summarizes a testing and validation analysis of a previously developed model for predicting trihalomethane formation potential (THMFP) in chlorinated waters containing THM precursors. The original model, in the form of a nonlinear multiple regression equation, tended to overpredict THM formation potential at lower chlorine concentrations and underpredict at higher chlorine concentrations. The model proved to be more accurate in simulating THM formation potential in waters with moderate levels of organic carbon/THM precursors. While the model did not provide a high degree of predictive accuracy, the general format of the nonlinear model represents a rational framework for developing source specific models applicable to a given water source.

Organics, Polymers, and Performance in Direct Filtration

The effects of raw water quality, chemical variables, and physical filter variables on direct filtration performance are examined. Cationic polyelectrolytes as sole coagulants are effective in treating low turbidity, colored waters by direct filtration. The polymer dosage is related to the raw water concentration of dissolved organic carbon. Cationic polymers can remove approximately 40% of the TOC and THM precursors. Filtration rate, direct filtration mode (in‐line versus flocculation), and water temperature did not have a significant effect on removals. Greater removals were achieved by alum. Direct filtration with cationic polymers is a feasible method of treatment for waters containing 5 mg/L TOC or less. For waters containing relatively high concentrations of humic matter (color) or submicron size particles, direct filtration with a flocculation period produces less head loss development and longer filter runs. UV absorbance is an excellent surrogate parameter for monitoring the removals of TOC and THM precursors.