Phsicochemical Treatment of Hazardous Wastes - Chapter 12 doc

12 High-Energy Electron Beam 12.1 Introduction Electron beams have been in commercial use since the 1950s. Early applica- tions involved the cross-linking of polyethylene film and wire insulation. Later, the process was extended to include sterilization of medical supplies, rubber vulcanization, disinfection of wastewater, food preservation, and many more applications. In solving environmental problems, the process has been shown to be efficient for the destruction of several classes of hazardous organic compounds as well as the inactivation of total coliform and bacteria in sewage sludge (Kurucz et al., 1991). It can be applied to treat wastewater from numerous industries such as the food, health, pharmaceutical, pulp and paper, and textile sectors. The groups of compounds from these waste- waters may contain benzene; substituted benzenes such as toluene, m -xylene, and o -xylene; phenol; halogenated ethenes such as trichloroethylene (TCE) and tetrachloroethylene (PCE); halogenated methanes such as trihalom- ethanes (THMs); carbon tetrachloride; and methylene chloride. Table 12.1 shows the removal efficiency of these organic compounds in aqueous solu- tion by high-energy electron beam, as a function of solute concentration, absorbed dose, pH, and scavengers in potable water and raw and secondary wastewaters. This innovative treatment process is not only limited to simple toxic organic chemicals but is also applicable to complex mixtures of organic pollutants under varying water quality. 12.2 Chemistry of Aqueous Electrons 12.2.1 Formation of Radical Species The irradiation of pure water with high-energy electrons generated by an accelerator results in the rapid formation of electronically excited states and/ or free radicals in 10 –14 to 10 –9 s. These reactive species will react with organic TX69272_C12.fm Page 461 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC 462 Physicochemical Treatment of Hazardous Wastes and inorganic compounds in aqueous solutions. The reactions result in either oxidation or reduction of compounds and lead to the formation of end products such as CO 2 , H 2 O, and inorganic salts. After 10 –12 s, an ionization species such as , OH • , and molecular fragments resulting from dissociation of excited-state molecules are in thermal equilibrium with the medium. After 10 –7 s of irradiation, the radiolysis products begin to diffuse, resulting in a fraction of them reacting to form radical products. Because the energy required to produce a chemical change is only a few electron-volts (eV) per molecule, a high-energy electron is capable of initiating several thousand reactions. These reactions can be summarized by the following equation: TABLE 12.1 Summary of Overall Removal Efficiencies for Various Organic Compounds Tested at the Miami Electron Beam Research Facility Compound % Removal Required Dose (krad) Chloroform 83–99 586–650 Bromodichloromethane >99 80 Dibromochloromethane >99 80 Bromoform >99 80 Carbon tetrachloride >99 80 Trichloroethylene (TCE) >99 57–500 Tetrachloroethylene (PCE) >99 241–500 trans -1,2-Dichloroethane 93 800 800 1.1 – Dichloroethene >99 800 1.2 – Dichloroethene 60 800 Hexachloroethane >99 800 1,1,1-Trichloroethane 89 650 1,1,2,2-Tetrachloroethane 88 650 Methylene chloride 77 800 Benzene >99 49–650 Toluene 97 45–650 Chlorobenzene 97 650 Ethylbenzene 92 650 1,2-Dichlorobenzene 88 650 1,3-Dichlorobenzene 86 650 1,4-Dichlorobenzene 84 650 l , m -Xylene 91 650 o -Xylene 92 650 Dieldrin >99 800 Total phenol 88 37–800 TNT a 40 800–1700 DEMP a 90 150–780 DMMP a 90 220–950 a Bench-scale studies using 60 Co. Source: Kurucz, C.N. et al., Radiat. Phys. Chem. , 45(2), 299–308, 1995. With permission. e aq – HO 3 aq + TX69272_C12.fm Page 462 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC High-Energy Electron Beam 463 H 2 O [2.7] • OH + [2.6] + [0.6] • H + [2.7]H 3 O + + [0.45]H 2 + [0.7]H 2 O 2 (12.1) Removal efficiency by high-energy electron beam is usually expressed by G values. The G value is defined as the number of excited states, radicals or other products formed or lost in a system when 100 eV of energy is absorbed (Kurucz et al., 1995b). The G values for each species is shown in the brackets in Equation (12.1). Removal efficiency of solutes can be quantitatively expressed in terms of two constants, G D and k ′ . G D describes the percent removal of solute at a given dose. It is defined by the disappearance of the solute in aqueous solution and is determined experimentally using the fol- lowing equation (Kurucz et al., 1991): G D = [ ∆ C•N A / D (6.24 × 10 17 )] (12.2) where ∆ C is the difference in organic solute concentration ( M ) at dose D and zero dose after irradiation; D is the dose in krad; N A is Avogadro’s number (6.02 × 10 23 ); and 6.24 × 10 17 is the conversion factor from moles to 100 eVL –1 . 12.2.2 Hydroxyl Radical Of the chemical species formed in Equation (12.1), the most reactive are the oxidizing species such as hydroxyl radical ( • OH) and the reducing species such as aqueous electron ( ) and hydrogen atom ( • H). The concentration of the reactive radicals formed in the irradiated solutions can be determined according to the fact that 1 krad of irradiation adsorbed will form 1.04 M reactive species when G equals 1 for a solute. Thus, for a G of 2.7, the concentration of • OH from Equation (12.1) is 0.28 m M at an absorbed dose of 100 krad. Based on these calculations, the total reactive radical species concentration formed usually ranges from 0.40 to 2.23 m M for • OH. The presence of both oxidizing and reducing species is unique to this process and distinguishes it from other treatment processes. Hydroxyl radicals, • OH, can undergo several types of reactions with chem- ical species in aqueous solution. The types of reactions that are likely to occur are hydroxylation, hydrogen abstraction, electron transfer, and radical–rad- ical recombination. Hydroxylation reaction occurs readily with aromatic and unsaturated aliphatic compounds, which result in the formation of hydrox- ylated radicals: • OH + CH 2 = CH 2 → HOCH 2 –CH 2 • (12.3) Hydrogen abstraction occurs with saturated molecules such as aldehydes and ketones: e – e aq – e aq – TX69272_C12.fm Page 463 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC 464 Physicochemical Treatment of Hazardous Wastes • OH + CH 3 –CO-CH 3 → • CH 2 COCH 3 + H 2 O (12.4) When hydroxyl radical is reacting with inorganic species, electron transfer will occur after aqueous solutions are irradiated with high energy electrons. For example, halogen ions (X – ) will react with hydroxyl radical as follows: • OH +X – → X • + OH (12.5) X • + X – → X 2 – (12.6) 12.2.3 Hydrogen Peroxide When two hydroxyl radicals recombine, hydrogen peroxide (H 2 O 2 ) is formed: • OH + • OH → H 2 O 2 (12.7) H 2 O 2 can also be generated in oxygenated aqueous solutions by the reactions of and • H with O 2 . The reactions result in the formation of reduced oxygen, the superoxide radical ion, and/or the conjugate acid: + O 2 → O 2 (12.8) H + O 2 → HO 2 • (12.9) These reactions lead to the formation of H 2 O 2 : 2O 2 – + 2H + → H 2 O 2 + O 2 (12.10) HO 2 – → H 2 O 2 + O 2 (12.11) A further possible reaction that may result is: + H 2 O 2 → • OH + OH – (12.12) This reaction occurs with a second rate constant of 1.2 to 1.4 × 10 10 M –1 s –1 and suggests that the addition of H 2 O 2 would increase the OH • concentra- tion, which would increase the removal efficiency of organic pollutants. 12.2.4 Aqueous Electron Aqueous electron, , is a powerful reducing reagent with an E°= 2.7 V. It reacts with many hazardous halogenated and nonhalogenated organic com- e aq – e aq – e aq – e aq – TX69272_C12.fm Page 464 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC High-Energy Electron Beam 465 pounds during their removal from aqueous solutions. The reaction of an aqueous electron, , is a single electron transfer process: + RCl → R • + Cl – (12.13) The rate constants of organic pollutants with are listed in Table 12.2. 12.2.5 Hydrogen Radical Hydrogen radical ( • H) accounts for approximately 10% of the total free radical concentration in irradiated water. • H undergoes two general types of reactions with organic compounds: • Hydrogen addition: • H + C 6 H 6 → C 6 H 7 (12.14) • Hydrogen abstraction: • H + CH 3 OH → H 2 + • CH 2 OH (12.15) The second-order rate constant of • H with common radical scavengers is relatively small. However, it is large enough to account for the removal of organic compounds. The high-energy electron beam process is the only process that produces these radicals. Table 12.3 summarizes the reaction rate constants of major organic pollutants with • OH, , and • H. TABLE 12.2 Second-Order Rate Constants (M –1 s –1 ) of Selected Compounds for Reactivity with Aqueous Electrons Compound k (M –1 s –1 ) Benzene 9.0 × 10 6 Carbon tetrachloride 1.6 × 10 10 Chlorobenzene 5.0 × 10 8 Chloroform 3.0 × 10 10 1,2-Dichlorobenzene 4.7 × 10 9 1,3-Dichlorobenzene 5.2 × 10 9 1,4-Dichlorobenzene 5.0 × 10 9 trans-1,2-Dichloroethylene 7.5 × 10 9 Nitrobenzene 3.7 × 10 10 Phenol 2.0 × 10 7 Tetrachloroethylene (PCE) 1.3 × 10 10 Toluene 1.4 × 10 7 Trichloroethylene (TCE) 1.9 × 10 9 Vinyl chloride 2.5 × 10 8 Source: Buxton, G.V. et al., J. Phys. Chem. Ref. Data, 17, 513–886, 1988. With permission. e aq – e aq – e aq – e aq – e aq – TX69272_C12.fm Page 465 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC 466 Physicochemical Treatment of Hazardous Wastes 12.3 Irradiation of Toxic Organic Chemicals in Aqueous Solutions High-energy electron beam irradiation can be used to effectively remove and/or destroy toxic organic chemicals in aqueous solutions by oxidation or reduction. It has been used to treat many compounds in water treatment (trihalomethanes) (Cooper et al., 1993b), groundwater contamination (chlo- rinated methanes and ethenes) (Kurucz et al., 1993), and hydrocarbons leak- ing from underground storage tanks (benzene and substituted benzenes) (Nickelsen et al., 1992a,b), as well as many other hazardous organic chemi- cals that are regulated. TABLE 12.3 Rate Constants of Organic Pollutants (M –l s –l ) Organic Chemicals • OH • H Alkyl-substituted benzene m-Xylene 7.5 × 10 9 — 2.6 × 10 9 Ethylbenzene 7.5 × 10 9 —— o-Xylene 6.7 × 10 9 — 2.0 × 10 9 Toluene 3.0 × 10 9 1.4 × 10 7 2.6 × 10 9 Aromatic compound Benzene 7.8 × 10 9 9.0 × 10 6 9.1 × 10 8 Phenol 6.6 × 10 9 2.0 × 10 7 1.7 × 10 9 Chlorinated and brominated aliphatic compounds Tetrachloroethylene 2.8 × 10 9 1.3 × 101˚ — trans-1,2-Dichloroethylene 6.2 × 10 9 7.5 × 10 9 — Trichloroethylene 4.0 × 10 9 1.9 × 10 9 — Chlorinated benzene compounds Chlorobenzene 5.5 × 10 9 5.0 × 108 1.4 × 10 9 1,3-Dichlorobenzene — 5.2 × 10 9 — 1,4-Dichlorobenzene — 5.0 × 10 9 — 1,2-Dichlorobenzene — 4.7 × 1 9 — Chlorinated ethene Vinyl chloride 1.2 × 10 10 2.5 × 10 8 — Chlorinated methanes Chloroform ~5.5 × 10 6 3.0 × 10 10 1.1 × 10 7 Carbon tetrachloride — 1.6 × 10 10 3.8 × 10 7 Methylene chloride 9.0 × 10 7 6.3 × 10 9 4.0 × 10 6 Heterocyclic aromatic compounds Pyridine 3.1 × 10 9 1.0 × 10 9 7.8 × 10 8 Methylated phenols p-Cresol 1.2 × 10 10 4.2 × 10 7 — o-Cresol 1.1 × 10 10 —— Nitroaromatic compounds Nitrobenzene 3.9 × 10 9 3.7 × 10 10 1.0 × 10 9 Source: Buxton, G.V. et al., J. Phys. Chem. Ref. Data, 17, 513–886, 1988. With permission. e aq – TX69272_C12.fm Page 466 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC High-Energy Electron Beam 467 To gain a better understanding of the electron beam process it is necessary to study the kinetics at various solute concentrations, the pH effects, absorbed doses, and the effect of scavengers in various water qualities. Water quality plays an important role in the removal efficiency of toxic chemicals and has led to experiments investigating the destruction of selected organic compounds suspended in different water matrices. Many studies have been conducted in pure aqueous solutions and have not taken into account the presence of inorganic and organic matter that naturally exist in water and may affect removal rates of the solute in question by interacting with the transient reactive species formed during irradiation. In the presence and absence of known scavengers, such as methanol, oxygen, bicarbonate/car- bonate ions, and dissolved organic carbon, the degradation rates change significantly. By examining the rate constants for each transient species with a known scavenger and comparing it with the rate constant of the same transient species with the solute to be removed in a specific water quality, it is possible to predict which will be the preferred reaction, thereby deter- mining the removal efficiency of the solute. The following sections discuss the research results from Cooper and his colleagues at the Miami High-Energy Electron Beam Facility. In a typical experiment, chemicals are injected into different water quality streams at various concentrations, the pH is varied, and samples of the solution are collected and analyzed after it has passed through the beam at various absorbed doses. 12.3.1 Saturated Halogenated Methanes Halogenated methylenes, including carbon tetrachloride, methylene chlo- ride, and four trihalomethanes (THMs), namely, chloroform, bromodichlo- romethane, dibromochloromethane, and bromoform, have been studied. The formation of THMs in drinking water results from chlorination during dis- infection. THMs in drinking water are classified as probable human carcin- ogens. Carbon tetrachloride is used in the production of refrigerator fluid, propellants for aerosol cans, and other end uses and is found in groundwater; it can cause serious health effects and is now regulated by the U.S. Environ- mental Protection Agency at a maximum contaminant level (MCL) of 5 µg/ L. Methylene chloride is used widely in industry as a process solvent in the manufacture of photographic films and pharmaceuticals and as an agent in foam and paint-stripping operations. If consumed, methylene chloride can affect the central nervous system and is therefore regulated at an MCL of 5 µg/L in the United States. Chloroform removal was found to be dependent on the water quality. In potable water, at two solute concentrations of 75 and 750 µg/L, 99% removal was observed at 800 krads (Cooper et al., 1993a). With the similar initial concentrations and irradiation doses in secondary and raw waste- waters, the removal efficiency was 85 and 90%, respectively. However, for TX69272_C12.fm Page 467 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC 468 Physicochemical Treatment of Hazardous Wastes 99% bromoform removal, the effect of water quality was insignificant when the initial concentration was between 100 and 1500 µg/L and the irradia- tion dose was above 300 krads. Three experiments were carried out in potable water of three different compositions: (1) the addition of individual THMs, (2) a mixture of THMs, and (3) the addition of chlorine to form THMs in the water. In each case, G D decreased as the relative percentage of bromide and the dosage increased; in other words, at the low concen- tration, removal is relatively independent of solute concentration. How- ever, at the highest concentration, an increased dose was required to meet the same solute removal. A possible explanation for this is that radical–rad- ical recombination of the OH • and the increases with increasing dosage; therefore, the relative concentration of the reactive species available for the THMs is lowered. Thus, the factors that will most affect the removal effi- ciency of THMs are those that affect the concentration of in solution, because THM removal depends more on the concentration of the than the • OH. This was the general trend noted among other low-molecular- weight organic pollutants, such as CCl 4 and methylene chloride. Two studies were conducted for CCl 4 removal (Cooper, 1993a). One was conducted with three different CCl 4 concentrations at one pH, and the other was conducted with three different pHs at one solute concentration. Removal efficiency was similar to that of the THMs. pH was found not to be a contributing factor in the removal of CCl 4 by high-energy electron beam irradiation. When the pH of water was adjusted to make it potable, the bicarbonate/carbonate equilibrium was disturbed. As the pH increased, so did the alkalinity, resulting in increased scavenging of the • OH, thus reduc- ing the removal efficiency of CCl 4 as well as the THMs. Similar experiments for methylene chloride (CH 2 Cl 2 ) removal were per- formed. The results were similar to those for THM removal. Due to the high solubility of CH 2 Cl 2 , the experiments were carried out at higher concentra- tions. Such concentrations would require a higher dose to meet treatment objectives in the low microgram per liter range. High-energy electron beam degradation of halogenated saturated meth- anes led to the formation of by-products (Mak et al., 1997). To determine which by-products may be formed, the mechanism for the destruction of the compound was investigated. For example, the irradiation of chloroform (CHCl 3 ) and the formation of by-products have been studied by Mak et al. (1997). The formation of oxidized organic compounds such as formaldehyde and formic acid has been observed. However, when chloroform is irradiated and no halogenated compounds have been detected. A mechanism for the decomposition of 0.07-M CHCl 3 at low irradiation dosages is proposed in Equation (12.16) to Equation (12.29), with or without dissolved oxygen. The bimolecular rate constant, k, is in M –1 s –l . The reaction equations were found to be in agreement with experimental data (Dickson et al., 1986): e aq – e aq – e aq – TX69272_C12.fm Page 468 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC High-Energy Electron Beam 469 + CHCl 3 → Cl – + • CHCl 2 ; k = 3.0 × 10 10 (12.16) • H + CHCl 3 → H 2 + • CCl 3 ; k = 2.4 × 10 6 (12.17) → HCI + • CHCl 2 ; k = 1.2 × 10 7 (12.18) • OH + CHCl 3 → H 2 O + • CCl 3 ; k = 5.0 × 10 6 (12.19) • COOH + ·COOH → HOOC–COOH (12.20) → HCOOH + CO 2 (12.21) • CHO + HCCl 3 + H 2 O → • CHCl 2 + HCOOH + HCl (12.22) At the higher solute concentration of 0.07 M CHCl 3 , several radical–radical recombination reactions were inferred from the by-product analysis: H • + • CHCl 2 → CH 2 Cl 2 (12.23) • CHCl 2 + • CHCl 2 → CHCl 2 CHCl 2 (12.24) • CCl 3 + • CHCl 2 → CCl 3 CHCl 2 (12.25) • CCl 3 + • CCl 3 → CCl 3 CCl 3 (12.26) • H + • CHO → HCHO (12.27) In solutions with high oxygen concentrations, the following reactions appear to play an important role in the decomposition of CHCl 3 : • CHCl 2 + O 2 → • O 2 CHCI (12.28) • CCl 3 + O 2 → • O 2 CCl 3 (12.29) At high organic concentration and high radiation dosage, the removal of CHCl 3 was inhibited at high dosages when the oxygen concentration was depleted. This observation suggests that radical–radical recombination has occurred, thus allowing halogenated by-products to remain. In the experi- ments conducted by Mak et al. (1997), formaldehyde was the only aldehyde observed. No halogenated reaction by-products such as haloacetic acids or ketones were observed after irradiation. The relative percent removal of CHCl 3 can be calculated from the bimo- lecular reaction rate constants and the G values for the reaction of CHCl 3 with the three transient species • OH, , and • H. These calculations indicate e aq – e aq – TX69272_C12.fm Page 469 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC 470 Physicochemical Treatment of Hazardous Wastes that the initiates greater than 99% of the removal of CHCl 3 , whereas • OH is responsible for less than 0.2% and • H for less than 0.01%. Therefore, the factors that will affect the removal efficiency of CHCl 3 from solution are those that affect the concentration. 12.3.2 Unsaturated Halogenated Ethenes The removal of TCE and PCE from potable water and secondary and raw wastewater was studied by full-scale experiments at both low and high solute concentrations (Cooper et al., 1993a). TCE removal was found to be dependent on both • OH and , with second-order rate constants of 4.0 × 10 9 and 1.9 × 10 9 M –l s –l (Buxton et al., 1988), respectively. In contrast, PCE removal is dependent primarily on the at 1.3 × 10 10 M –l s –l . Greater than 90% removal was obtained for both TCE and PCE at both concentrations in all waters (Cooper et al., 1993a); however, PCE was not as effectively removed as was TCE in solution of equal solute concentration and water quality. The reason for this may be related to the number of chlorine atoms present in both compounds. Overall, the removal rates of TCE and PCE were best in potable water and about the same for secondary and raw wastewater. Although the percent removal at lower concentration was higher in all waters than at higher concentrations, greater than 90% removal was observed for both TCE and PCE in all waters. Irradiation was also successful in the decomposition of THMs to chloride and bromide ions (Cooper et al., 1993b). Toxic organic by-products such as haloacetic acid, aldehyde, ketones, or halogenated organic compounds were formed after irradiation. It has also been proven effective in the destruction of halogenated ethenes such as TCE and PCE. Removal rates decreased 20-fold in the presence of methanol as opposed to its absence. Aldehydes and formic acid were found when low solute concentrations of TCE and PCE were irradiated; however, at high concentrations no more than 5% formic acid was found. Complete conversion of organic chlorine to chloride ion can be achieved. The G D decreased in all three waters as the radiation dose increased (Coo- per et al., 1992a-c). As the solute concentration was increased tenfold, the G D also increased tenfold. When G D was compared at each radiation dose, the results were remarkably similar regardless of water quality. At high concentration, the G D value for TCE was higher in secondary wastewater than in potable water. This may be due to higher influent solute concentra- tion in the secondary wastewater. Although water quality is a factor in removal efficiency, it does not appear to be as important when compared to other treatment processes. In the presence of 3.3-mM methanol, which is a • OH scavenger, the removal efficiency of the solutes was reduced up to 20-fold when compared to solution with no methanol; however, it is not clear why the removal of e aq – e aq – e aq – e aq – TX69272_C12.fm Page 470 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC [...]... Physicochemical Treatment of Hazardous Wastes H CH3 OH F Cl Br I CN COOSO3 NO2 CF3 CH2OH SH CONH2 SO2NH2 /    m-XC6H4OH – TX69272_C12.fm Page 480 Friday, November 14, 2003 2:10 PM 480 TABLE 12. 5 TX69272_C12.fm Page 481 Friday, November 14, 2003 2:10 PM High-Energy Electron Beam 481 0.75 NO2 CN 0.50 CONH2 SO2NH2 CF3 COOH 0.25 Br I Cl SH 0 F H -0 .25 CH3 OH -0 .50 -1 0 1 2 3 4 η FIGURE 12. 2 – – η as a function of. .. groups © 2004 by CRC Press LLC TX69272_C12.fm Page 478 Friday, November 14, 2003 2:10 PM 478 12. 3.7 Physicochemical Treatment of Hazardous Wastes Radical Scavenger Effect 12. 3.7.1 Methanol Methanol is the primary scavenger of •OH and is naturally occurring in water In all the experiments conducted, 3.3-mM methanol was used as a carrier of the organic solute of interest Methanol was found to react with... meta- and para-substituted compounds of comparable reactivity • Group B includes meta-substituted compounds having higher rate constants than para-substituted compounds (Table 12. 8) © 2004 by CRC Press LLC TX69272_C12.fm Page 483 Friday, November 14, 2003 2:10 PM High-Energy Electron Beam 483 CN I ηC6H5COO- 0.50 Br COOH CL 0.25 F H 0 CH3 0 1 2 3 4 ηC6H6 FIGURE 12. 3 ηC 6 H 5 COO – as a function of ηC... 2COCI–CCl2O• (12. 33) COCI–CCl2O• → •COCI + CCl2O (12. 34) CCl2O + H2O → CO2 + 2CI– + 2H+ (12. 35) COCI + H2O → ·COO– + 2H+ + Cl– (12. 36) COO– + O2 → •O2– + CO2 (12. 37) 2COCI–CCl2 → COCl–C2Cl4 – COCl (12. 38) • • COCl–C2Cl4 – COCl + H2O → HOOC–C2Cl4–COOH + 2Cl– (12. 39) COCl–CCl2 + •COO → COCl–CCl2–COO• (12. 40) COCl–CCl2–COO• + H2O → HOOC–CCl2–COOH + Cl– (12. 41) 2•COO– + 2H+ → HOOC–COOH (12. 42) © 2004 by... TX69272_C12.fm Page 479 Friday, November 14, 2003 2:10 PM High-Energy Electron Beam 479 12. 3.7.4 Oxygen – Oxygen is reduced rapidly by both e aq and •H to form O2– with second-order 10 and 2.1 × 1010 M–1 s–l, respectively For example, rate constants of 1.9 × 10 in the presence of 3.7 mg/L of oxygen, 35% of these two reactive species would be removed at a dose of 100 krad as opposed to 5% at a dose of 800... Res., 28(5), 122 7 123 7, 1992a With permission + OH H OH OH OH + OH OH OH + OH + OH O2 H OH I H O-O II H OH H O -H2O O-OH OH III (O) O IV V O VI O O CH + HC O HCH + H3C CH VII FIGURE 12. 1 Proposed mechanism for the destruction of benzene Identified dose-dependent reaction byproducts include phenol (I), catechol (II), and resorcinol (III) (From Nickelsen, M.G et al., Water Res., 28(5), 122 7 123 7, 1992 With... viruses by one or two orders of magnitude at a dose of about 4 kGy The size of an organism may also play a role in its removal or inactivation For example, the larger the organism, the more effective the removal process by irradiation © 2004 by CRC Press LLC TX69272_C12.fm Page 476 Friday, November 14, 2003 2:10 PM 476 Physicochemical Treatment of Hazardous Wastes The effect of high-energy electrons on selected... result of the mutual inductive effect, their ability to withdraw electrons from the π-orbital of the aromatic nucleus decreases (Taft, 1956) © 2004 by CRC Press LLC TX69272_C12.fm Page 484 Friday, November 14, 2003 2:10 PM 484 Physicochemical Treatment of Hazardous Wastes TABLE 12. 7 The Relative Rates of Reaction of Disubstituted Aromatic Compounds Substituents X Y COO– COO– COO– COO– COO– F Cl Br... generation of oxidants for the treatment of benzene and toluene in the presence of radical scavengers, Water Res., 28(5), 122 7 123 7, 1992a Nickelsen, M.G., Cooper, W.J., Kurucz, C.N., and Waite, T.D., Removal of benzene and selected alkyl-substituted benzenes from aqueous solution utilizing continuous high-energy electron irradiation, Environ Sci Technol., 26, 144, 1992b © 2004 by CRC Press LLC TX69272_C12.fm... constants for substituted benzoic acid and substituted benzenes reacting – with e aq : © 2004 by CRC Press LLC TX69272_C12.fm Page 482 Friday, November 14, 2003 2:10 PM 482 Physicochemical Treatment of Hazardous Wastes TABLE 12. 6 Specific Rate Constants and Relative Rates of Reaction of para-Substituted Benzoic Acids k pXC H – 6 4 COO Log k XC H  6 4 COO – / kC H5COO–   Substituent (M–1 s–1) H O– NH2 . . – – k k k k Xe e para aq aq H CH CH 6 5 66 48 e aq – TX69272_C12.fm Page 479 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC 480 Physicochemical Treatment of Hazardous Wastes TABLE 12. 5 Specific Rate Constants and Relative Rates of Reaction of. With permission. e aq – e aq – e aq – e aq – e aq – TX69272_C12.fm Page 465 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC 466 Physicochemical Treatment of Hazardous Wastes 12. 3 Irradiation of Toxic Organic Chemicals. However, for TX69272_C12.fm Page 467 Friday, November 14, 2003 2:10 PM © 2004 by CRC Press LLC 468 Physicochemical Treatment of Hazardous Wastes 99% bromoform removal, the effect of water quality