Trihalomethanes removal

RO membrane separation has been traditionally used for seawater and brackish water desalination, and production of high-purity water for food, pharmaceutical processing and industrial waste treatment, as discussed in Chapter 1. The development of nanofiltration (NF) membranes has opened up many areas of apphcation including water softening, removal of disinfection by-product precurson (trihalomethanes), removal of total organic carbon (TOC), food processing and industrial water treatment [5]. 

Waniek, A., Bodzek, M., and Konieczny, K. (2002). Trihalomethanes removal from water using membrane processes. Polish J. Environ. Stud. 11(2), 171-178. 

AC filtration does remove some organic chemicals that can be harmful if present in quantities above the EPA Health Advisory Level (HAL). Included in this category are trihalomethanes (THM), pesticides, industrial solvents (halogenated... 

Brewing Potable water treatment Removal of trihalomethanes (THM) and phenolics... 

Activated carbon filters are employed primarily as RW contaminant removal systems for chlorine (by chemisorption) and various organics such as trihalomethanes (THMs), petroleum products, and pesticides (by adsorption). In addition, they act as physical filters and therefore incorporate sufficient freeboard in their designs to permit periodic backwashing. 

Although reactions carried out by ozone have attracted enormous attention in the atmospheric environment, ozone has also been used extensively in the treatment of drinking water without the production of undesirable trihalomethanes from the use of molecular chlorine (Richardson et al. 1999). It has been examined for the removal of a number of contaminants, and ozone is considered to be a selective oxidant, even though quite complex reactions may occur. 

There are a few reports on the combined application of ultrasound and ultraviolet light (UV) for the destruction of chemical pollutants. A study of the oxidation of humic acid and trihalomethane precursors with ozone revealed that the most effective destruction of the organic carbon compounds was achieved when both uv and ultrasound were used in combination with ozonation [35]. In other cases e. g. the removal of 1,1,1-tri-chloroethane from aqueous solutions, the combined application of ultrasound and UV proved to be more efficient than the use of either technique individually [36]. 

Neely, J. W. A Model for the Removal of Trihalomethanes from water by Ambersorb XE-340 ACS Meeting, Miami Beach, Florida, September 1978. 

Trihalomethanes, such as trichloromethane (chloroform), are quite reactive toward strong base. The base, such as hydroxide, removes the hydrogen of HCC13 as a proton much more rapidly than it attacks the carbon in the SK2 manner. The carbanion so formed, Cl3C e, is unstable and loses chloride ion to form a highly reactive neutral intermediate, CC12, called dichlorocarbene ... 

Dickson, L.W., Lopata, V.J., Toft-Hall, A., Kremers, W., and Singh, A., Radiolytic removal of trihalomethanes from water, in Proc. from the 6th Symp. on Radiation Chemistry, 1986, pp. 173-182. 

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. 

Finally, Sotelo et al. [179], while studying the ozonation of resorcinol and phloroglucinol, two precursors of trihalomethanes (THM) during water chlorination, found some polar intermediates that confirmed the proposed phenol mechanism reported elsewhere [42]. From the identified intermediates it was deduced that ozonation of phenols yields more oxygenated compounds that eventually could be removed in biological steps. 

Glaze WH, Wallace JL, Wilcox D, Johansson KR, Scalf B, Noack R, Busch AW. Pilot scale evaluation of ozone-granular activated carbon combinations for trihalomethane precursor removal. McGuire MJ, Suffet IH eds. Advances in Chemistry Series, No. 202, Treatment of water by granular activated carbon. American Chemical Society, New York 1983 3 221-229. 

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]. 

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. 

Use of granular activated carbon (GAC) is considered to be the best currently available technology for removing low-solubility contaminants such as disinfection by-products (usually from chlorination) that include trihalomethanes (THM), detergents, pesticides, herbicides, polyaromatic hydrocarbons, and some trace metals. The amendments to the Safe Drinking Water Act. state that other treatment technologies must be at least as effective as GAC [66]. 

Studies of adsorption of nonaromatic organic compounds are not as abundant but they are very diverse (and are cited here only to illu.strate and emphasize this diversity). They go back to the interwar period (see, for example, Refs. 571-573, when activated charcoal was being developed for chemical and biological defen.se and its properties were intensely studied [2,3]). More recently, the removal of trihalomethanes [574-579], amines [580,581], acetic acid [582, the pesticide thiram [583], chlorinated organic compounds [584,552,585,586,403, 587-591], alcohols [572,592,593-597], carboxylic and fatty acids [592,483, 598,594,599], N-acetylcysteine [600], amino acids [601], benzo-15-crown-5 ether [602], quaternary ammonium compounds [603], organophosphates and or-ganophosphonates [604] has been studied. Adsorption of surfactants has also been of continued interest [605-614,143,6l5-617. ... 

---