Trihalomethane formation potential

Kusakabe, K., Aso, S., Hayashi, J.-I., Kazuaki, I., and Morooka, S., Decomposition of humic acid and reduction of trihalomethane formation potential in water by ozone with UV irradiation, Water Res., 24, 781-785, 1990. 

As was shown previously in some examples [15-18] in a large ozonation plant for water treatment, residual ozone in the gas exiting the ozonation stages could be sent back to the head of the water plant where it is injected in another compartment to aid flocculation, remove iron and manganese, or reduce the trihalomethane formation potential (see Fig. 8). In these cases, it is not surprising that these plants could also have a final disinfection ozonation step. 

Reactions between aquatic HS and halogen-based oxidants, during water chlorination process, can lead to the formation of trihalomethanes, with potential carcinogenic effects. Carvalho et al. (2004) investigated reactions of tropical aquatic fulvic acids (AFA) with chlorine and formation of trihalomethanes through fluorescence spectroscopy. 

The most common method for reducing the numbers of these organisms is by chlorination of the influent water. Periodically, it may be necessary to clean and disinfect the air stripper by shocking the tower with acid or chlorine, or by surging the tower with peroxide. Routine inspections and cleaning of the air stripper must be considered normal maintenance and a part of the operational expense. In addition, corrosional effects and an increase in the formation potential of THMs (trihalomethanes chloroform and bromoform) may result from chlorination. 

One practical use of Fenton and photo-Fenton processes is the removal of natural organic matter (NOM) from organic rich waters before the chlorine disinfection of drinking water. It was observed that, under optimal conditions, both processes achieved more than 90% TOC removal, leading to the potential formation of trihalomethanes at concentrations below 10 ig IT1, well under UK and US standards [78]. 

Disinfectants are usually only monitored to ensure that disinfection has taken place. Certain disinfectants, such as chlorine, are sometimes monitored at the tap or in the distribution system, as a measure of the quality in distribution. A wide range of potential by-products of disinfection may be formed in treatment, particularly if natural organic matter is present at high concentrations. The most commonly monitored by-products are the trihalomethanes (THMs) formed through chlorination THMs are normally considered to be an adequate marker of the total disinfection by-products from chlorination. Some countries also monitor haloacetic acids, but these are difficult and expensive to analyse because of their high polarity. Bromate is sometimes measured when ozone is used, but its formation relates to bromide concentrations in the raw water and the conditions of ozonation. Analysis can be extremely difficult and monitoring is not usually considered except where standards have been set or on an infrequent basis. 

It is now very well estabhshed that DOM is the major source of trihalomethanes and other disinfection by-products in disinfected water. In fact, the measurement of THMFP is now a routine monitoring task in the water treatment industry, and suppliers in the US are required to advise consumers of the concentrations of trihalomethanes and other disinfection by-products in drinking water. Efforts to remove DOM from waters before they are chlorinated have driven much of the research that has led to advances in membrane-based methods of isolation of DOM from water (see the discussion of UF, NF, etc., in Section 5.10.4.2.2). Nikolaou and Lekkas (2001) have recently reviewed many aspects of the reactions of DOM with chlorine and other disinfectants. They review the relationships between reactivity of DOM (i.e., formation of disinfection by-products) and the chemical properties of DOM and several types of fractions of DOM. They also discuss the formation and potentially adverse effects of several classes of disinfection by-products. Urbansky and Magnuson (2002) have reviewed the subject of disinfection by-products, including a brief discussion of DOM. Both of these reviews are recommended for further up-to-date details on the role of DOM in the formation of disinfection by-products. 

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