Adsorption trihalomethanes

Trihalomethanes. Wherever chlorine is used as a disinfectant in drinking-water treatment, trihalomethanes (THMs) generaUy are present in the finished water. The THMs usuaUy formed are trichloromethane (chloroform), bromodichloromethane, dibromochloromethane, and tribromomethane (bromoform). There are four main techniques for the analysis of THMs headspace, Hquid— Hquid extraction (Ue), adsorption—elution (purge—trap), and direct aqueous injection. The final step in each technique involves separation by gas—Hquid chromatography with a 2 mm ID coUed glass column containing 10 wt % squalene on chromosorb-W-AW (149—177 p.m (80—100 mesh)) with detection generaUy by electron capture. 

Suzuki, Y., Koizumi, A. and Takeuchi, Y., Adsorption of trihalomethane from... 

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. 

Alben, K.T., Shpirt, E., and Kaczmarczyk, J.H., Temperature dependence of trihalomethane adsorption on activated carbon implications for systems with seasonal variations in temperature and concentration, Environ. Sci. Technol., 22, 406-412, 1988. 

The flux of DOC from terrestrial landscapes to surface runoff has wide-ranging consequences for aquatic chemistry and biology. DOC affects the complexation, solubility, and mobility of metals (Perdue et al., 1976 Driscoll et al., 1988 Martell et al., 1988 see Chapter 8) as well as the adsorption of pesticides to soils (Senesi, 1992 Worrall et al., 1997). Formation of trihalomethanes when drinking water is disinfected with chlorine, a worldwide threat to water supplies, is also linked to DOC concentrations (Siddiqui et al., 1997). DOC attenuates ultraviolet-B (UV-B) radiation and thus provides some protection to aquatic biota from exposure to harmful UV radiation (e.g., Williamson and Zagarese, 1994). Finally, DOC affects the heat balance and thus stratification in lakes, which is an important constraint for aquatic organisms with limited habitats (Schindler et al., 1996, 1997). 

Trihalomethanes, chloroethanes, dichioroethanes Adsorption on XAD-4 resin and elution with ethanol Study of adsorption of chlorocompounds on XAD4 resin [284, 285]... 

Sakoda, A., Suzuki M., Hirai R., and Kawazoe K. (1991), Trihalomethane adsorption on the activated carbon fibers. Water Research, 25(2), 219-225. 

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. ... 

The US EPA has identified many types of organic compounds in our water supplies. Some of the organic compounds are volatile, and, as a result, aeration would be a good process selection for removing them from water. For compounds that are non-volatile, adsorption would be a better process selection than aeration for their removal from the water. Some common volatiles include trihalomethanes, which have already been discussed chlorobenzene, 1,1,1-trichloroethane, tetrachloroethylene, and trichloroethylene. Aeration can achieve up to 95% removal of these compounds. 

Adsorption has been used in wastewater treatment primarily for taste and odor control, but it is growing more popular for removal of contaminants such as synthetic organic chemicals, color-forming organics, disinfection chemicals and their by-products (the most notorious being the trihalomethanes), and heavy metals. 

Unfouled MF does not retain natural organics unless they are associated with particulates and measured as turbidit). This means that a pretreatment step, such as coaguladon, is required. MF can remove Giardia and Cryptosporidium but the extent of removal of Cryptosporidium depends on size, adsorption and cake layer built-up. Jacangelo et at (1995a) observed that fouling of MF membranes increased rejection of various species. Consequently, Kumar et al. (1998) found a significant removal of trihalomethanes (THMs) by MF in an extended pilot study. 

Surface chemistiy Affects the adsorption process through the presence of surface fionctional groups (aromatics, trihalomethanes) and pH of point of zero charge (acidic or basic compounds)... 

The influence of the pore characteristics of activated carbon on their dynamic properties has been extensively studied. Breakthrough curves obtained with p-nitrophenol and various activated carbons exhibit different shapes due to differences in pore size distribution microporoiis activated carbons induce a slow intraparticular diffusion resulting in flattened curves whereas more meso- and macroporous adsorbents possess a sharper curve because of an enhancement of mass transfer [58]. The adsorption of trihalomethanes on granular and fibrous activated carbon also shows adsorption capacities proportional to the micropore volume [59]. 

Lu, C. Chimg, Y. Chang, K (2005). Adsorption of trihalomethanes from water with carbon nanotubes. Water Research, 39,1183-1189. 

As noted from above, chloroform is effectively removed from the water regardless of the carbonization condition. On the other hand, the membranes are still not able to achieve complete rejection of the monochloroacetic acid. The rejection of monochloroacetic acid for the membranes prepared using condition (CC-I) and condition (CC-11) are between 86-66% and 69-43%. The reasons for the better adsorption of chloroform compared to the monochloroacetic add are due to its smaller molecitlar size and lower solubility in water (higher hydrophobicity). Furthermore, the adsorption of monochloroacetic acid is likely to be affected by the pH of the water, which affects the molecules dissociation degree. This was not addressed as all experiments were carried out at a constant pH of 6. Similar observations have been noted for the lower haloacetic add adsorption on granidar activated carbon as compared with trihalomethanes [18]. 

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