Chlorine degradation rate

TABLE 1.13 Chlorine Degradation Rate Obtained from Each Membrane"... 

Dioxins are not decomposed by heat or oxidation in a 700°C incinerator, but pure compounds are largely decomposed at 800°C. Chlorinated dioxins lose chlorine atoms on exposure to sunlight and to some types of gamma radiation, but the basic dioxin structure is largely unaffected. The biological degradation rate of chlorinated dioxins is slow, although measured rates differ widely. 

Nowell L H, Hoignd J (1992) Photolysis of Aqueous Chlorine at Sunlight and Ultraviolet Wavelength - I Degradation Rates, Water Research 26 593-598. 

To evaluate the effect of the number of chlorines on the degradation rate constants of different chlorophenols, Table 6.2 shows the rate constants of elementary, oxidation, and dechlorination for the ratios of k2 CP/k2/l DcP and 2,4,6-tcp/ 2,4-dcp The relative rate constants are plotted against the number of sites unoccupied by chlorine atoms on the chlorinated phenols in Figure 6.3.A linear correlation between the rate constants and the number of sites available is found with a standard deviation of 0.132. Clearly, the more chlorine atoms the aromatic rings contain, the fewer sites are available for hydroxyl radical attack however, the correlation should not be used for... 

The plot shown in Figure 9.18 for the kinetics of COz formation from hydroxyl radical attack on chlorinated phenols appears to be random. This can be justified by the various intermediates formed along the reaction pathway. Each of these intermediates will have different degradation rates, so COz formation will be different according the reaction. 

Gillham and O Hannesin (1994) reported that the degradation rates increased as the surface area of the iron increased with respect to the volume of the solution. Also, degradation declined with decreasing degree of chlorination. Dichloroethene is the only compound in Table 13.4 not degraded by the zero-valent iron process. 

Our understanding of the iron reactive barrier is, however, still limited. Degradation rates of many chlorinated compounds have been reported, but the exact reaction kinetics and mechanism are much less understood. The long-term stability of the reactive barrier and the effects of other system... 

Oxidation rate constant k, for gas-phase second order rate constants, koH for reaction with OH radical, kNQ3 with N03 radical and kQ3 with 03 or as indicated, data at other temperatures see reference k (oxidative degradation rate constant of water dissolved PCDD by ozone) is 5.46 x io4 L g 1 min 1 under alkaline condition at pH 10 and 20°C (Palauschek Scholz 1987) kOH(calc) = 3.5 x 10 12 cm3 molecule-1 s-1 and a calculated tropospheric lifetime x = 4.4 d based on gas phase OH reactions and a 12-h average daytime OH radical concn of 1.5 x io6 molecule/cm3 for a hepta-chlorinated dioxin at room temp. (Atkinson 1991)... 

In order to further profit from the dual complexing ability of CDs, we have studied Fenton-type processes in the presence of CDs. Several classes of compounds showed enhanced degradation rates in the presence of CDs in aqueous solution PCBs, PAHs, TNT, and chlorinated phenoxyacetic acids [38,102]. Dissolved natural organic matter typically inhibits Fenton degradation by sequestering the iron away from the pollutant [31,32]. However, addition of cyclodextrins overcame the inhibitory effect of the NOM and resulted in enhanced degradation rates [38]. 

Polyamide, composite membranes are very sensitive to free chlorine (recall from Chapter 4.2.1 that cellulose acetate membranes can tolerate up to 1 ppm free chlorine continuously). Degradation of the polyamide composite membrane occurs almost immediately upon exposure and can result in significant reduction in rejection after 200 and 1,000-ppm hours of exposure to free chlorine (in other words after 200-1,000 hours exposure to 1 ppm free chlorine). The rate of degradation depends on two important factors 1) degradation is more rapid at high pH than at neutral or low pH, and 2) the presence of transition metals such as iron, will catalyze the oxidation of the membrane. 

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