Michael G. Nickelsen

Decomposition of aqueous solutions of phenol using high energy electron beam irradiation—A large scale study

High-energy electron-beam irradiation was used to remove phenol from aqueous solution. The variables that affected phenol decomposition were solute concentration, absorbed dose and total alkalinity. Experiments were conducted at large scale (480 L min−1), at solute concentrations of 10.6, 106 and 531 μmol L−1 (1, 10 and 50 mg L−1) over the pH range 5–9, and in the presence and absence of solids (3% w/w kaolin clay). Absorbed doses ranged from 0–7 kGy (0–700 krad). At low absorbed doses, catechol, hydroquinone and resorcinol were identified as the major reaction byproducts. These compounds are consistent with hydroxyl radical (OH·) addition to phenol. Subsequent ring cleavage of hydroxylated phenolic radicals and continued oxidative processes resulted in the formation of formaldehyde, acetaldehyde, glyoxal and formic acid. At high doses only trace amounts of the carbonyl derivatives were observed. Two recirculation experiments were conducted at higher phenol concentrations (≈950 μmol L−1) and it was shown that phenol was removed while the total organic carbon of the solution decreased only slightly. These results suggest that phenol was not mineralized but, rather, that irradiation resulted in the possible formation of higher molecular weight polymers.

High energy electron beam generation of oxidants for the treatment of benzene and toluene in the presence of radical scavengers

Abstract High energy electron beam irradiation of benzene and toluene in aqueous solution results in their destruction and the formation of highly oxidized reaction byproducts. The product distribution depends upon absorbed dose and pH and results from the reaction of benzene and toluene with the hydroxyl radical (OH.), followed by continued oxidation of intermediate by-products. The dose required to remove 99% (D0.99) of the benzene from solution, at an initial solute concentration of 17.0 μM (1.3 mg l−1), was 95 krad (0.95 kGy, [OH.] ≈ 2.7 × 10−4 M). In the presence of a known radical scavenger, i.e. 3.3 mM methanol, a dose of 1510 krad ( 15.1 kGy, [OH . ] ≈ 4.2 × 10 −3 M ) was required to achieve the same removal. Toluene showed greater removal, in the absence of methanol, than benzene under similar experimental conditions. The D0.99 required to destroy an initial toluene concentration of 47.7 μM (4.4 mg l−1) was 165 krad (1.65 kGy, [OH.] ≈ 4.6 × 10−4 M), whereas the D0.99 for an initial toluene concentration of 16.4 μM (1.5 mg l−1), in the presence of 3.3 mM methanol, was 2074 krad (20.7 kGy, [OH.] ≈ 5.8 × 10−3 M).

Kinetic modeling of carbon tetrachloride, chloroform and methylene chloride removal from aqueous solution using the electron beam process

An innovative treatment process using high energy electrons has been shown to be effective for the destruction of various toxic (regulated) organic chemicals. This paper presents data for the destruction of chlorinated methanes, carbon tetrachloride, chloroform and methylene chloride in treated groundwater. The studies were conducted at pilot scale, using a 75 kW electron beam at a flow rate of 0.38 m3 min−1. This study examined the effect of solute concentration and total alkalinity on removal efficiency. A kinetic model was used to describe the results of single solute experiments of the three chlorinated methanes. These model predictions were then compared to experimental results and showed a varying degree of predictability for the three compounds. These calculations suggest that the initial reactions which eventually lead to the mineralization of the three chlorinated methanes result primarily from aqueous electron initiated reactions. The subsequent reaction between O2 and the carbon centered radicals with the formation of alkyl peroxides also appears important for their ultimate decomposition.

High energy electron beam irradiation: An innovative process for the treatment of aqueous based organic hazardous wastes

Abstract The use of high energy electrons for the treatment of aqueous solutions appears to be a promising approach in solving the numerous problems associated with contaminated water. Irradiation of aqueous solutions results in the formation of reactive transient species, e– aq, H•, and HO•. In aqueous solutions of toxic and hazardous chemicals, the transient species react with the contaminants resulting in their removal from solution. The study reported in this paper utilizes a pilot plant capable of treating 120 gpm. The accelerating voltage of the electron accelerator is 1.5 MeV with variable current of up to 50 mA. Influent streams of potable water, and raw and secondary wastewater have been used for this study. The compounds studied include halogenated methanes, ethanes, ethenes, benzene and substituted benzenes. Removal efficiencies range from 85 to greater than 99%.

The Removal of Tri- (TCE) and Tetrachloroethylene (PCE) from Aqueous Solution using High Energy Electrons

Trichloroethylene (TCE) and tetrachloroethylene (PCE) are common groundwater contaminants that persist inithe environment. An innovative treatment process employing high energy electron beam irradiation has been shown to be an effective process for treating TCE- or PCE-contaminated water, wastewater, and water containing suspended solids. Experiments conducted at the Electron Beam Research Facility, Miami, Florida, have led to a better understanding of the factors that affect the removal efficiency of TCE and PCE in treated ground water (potable water), secondary wastewater effluent, and raw (untreated) wastewater. The effect of the addition of a hydroxyl radical scavenger, methanol, on the removal of TCE and PCE has also been determined. A quantitative description of TCE and PCE removal efficiency at several carbonate/bicarbonate ion concentrations, and in the presence of 3 percent clay, has also been developed. The reaction by-products have been characterized and chloride ion mass balance determined for...

Empirical models for estimating the destruction of toxic organic compounds utilizing electron beam irradiation at full scale

Abstract The Electron Beam Research Facility (EBRF) located in Miami, Florida houses a 1.5 MeV, 50 mA electron accelerator. Extensive large scale (450 1/min) research on the use of electron beams for the treatment of water and wastewater has been conducted at this facility over the last several years. Recent efforts have focused on developing predictive equations for evaluating the effectiveness of electron beam irradiation for treatment of industrial wastes and contaminated groundwaters. This paper develops descriptive empirical models for estimating the removal of selected organic compounds (benzene, toluene, phenol, PCE, TCE and chloroform) by electron beam irradiation as a function of initial contaminant concentration, pH and the presence or absence of suspended materials. Models to estimate the electron dose required to meet specific treatment objectives are also presented. These dose estimates can be used to evaluate the cost of treatment for treatment systems which utilize electron beam accelerators of various voltages, power, and cost.

Kinetic modeling and simulation of PCE and TCE removal in aqueous solutions by electron-beam irradiation

The irradiation of aqueous solutions of TCEand PCEusing a high-energy electron-beam results in the rapid decomposition of both chemicals. It is known that both TCEand PCEreact with the aqueous electron and the hydroxyl radical with bimolecular rate constants greater than 10 9 M � 1 s � 1 for each reaction. The fact that high-energy electrons produce significant concentrations of both eaq and dOH radicals in water makes it an effective process for the removal of TCEand PCEfrom aqueous solution. We have employed steady state and computer-based chemical kinetic models to simulate and better understand the chemistry and kinetics of e-beam irradiation when applied to natural water systems. Model results were benchmarked to experimental data, allowing for the optimization of the reaction of DOC with the dOH radical. Values for the associated second-order reaction rate constant were found to be 2.5 � 10 8 and 4.0 � 10 8 M � 1 s � 1 , consistent with reported values for kOH;DOC: The models were also used to investigate the possibility of incomplete irradiation during treatment and the presence of proposed chemical reactions of by-products. The reactions involve radicals and radical-adduct species formed by the reaction of TCEand PCEwith the hydroxyl radical. r 2002 Elsevier Science Ltd. All rights reserved.

Figures-of-Merit for Advanced Oxidation Technologies: A Comparison of Homogeneous UV/H2O2, Heterogeneous UV/TiO2 and Electron Beam Processes

Abstract Three Advanced Oxidation Technologies (UV/H2O2, UV/TiO2 and Electron Beam) have been evaluated using the Electrical Energy per Order (EE/O) figure-of-merit. These processes have been tested on two aqueous treatment systems: the bleaching of methylene blue and the decay of phenol. In general, as expected, for a given process, the EE/O increased as the concentration of the contaminant increased. However, when the three processes were compared for the same system at the same concentration, the EE/Os for the UV/H2O2 and Electron Beam processes were very similar, but the EE/O for the UV/TiO2 was much higher than that for the other two processes. The UV/H2O2 process has the disadvantage that there is an added cost of chemicals (principally H2O2) and the E-beam process has the disadvantage that there is a constant power required to run the apparatus even when the beam is off. Nevertheless, the UV/TiO2 system has an inferior performance relative to the other two processes; the principal reason is probably the low quantum yield (~0.04-0.08) for the generation of hydroxyl radicals on the surface of TiO2 particles.

Ionic strength and buffer effects in the elimination reaction of 1,1,2,2-tetrachloroethane

The rate constant for the abiotic reaction of 1,1,2,2,-tetrachloroethane in aqueous solution has been studied as a function of ionic strength, buffer composition, temperature, and pH. The rate of reaction is found to be independent of ionic strength and buffer composition, with the parent compound quantitatively converted into trichloroethene by a base mediated elimination reaction for values of pH > 3.5. The Arrhenius parameters for the elimination reaction are log10 A = 16.32 ± 0.40; Ea = 95.0 ± 2.5 kJ/mol. No evidence for a neutral hydrolysis reaction was found, indicating that the rate constant for such a reaction is <2 × 10−7 s−1 at 90°C.

Benzene destruction in aqueous waste-I. Bench-scale gamma irradiation experiments

Abstract Destruction of the benzene component of a simulated low-level mixed aqueous waste stream by high energy irradiation was explored. This work was motivated by the fact that mixed waste, containing both radionuclides and regulated (non-radioactive) chemicals, is more difficult and more expensive to dispose of than only radioactive waste. After the benzene is destroyed, the waste can then be listed only as radiological waste instead of mixed waste, simplifying its disposal. This study quantifies the removal of benzene, and the formation and destruction of reaction products in a relatively complex waste stream matrix consisting of NO 3 − , SO 4 2− , PO 4 3− , Fe 2+ and detergent at a pH of 3. All of the experiments were conducted at a bench scale using a 60 Co gamma source.