Advanced Oxidation/reduction Processes Research Articles

The utility of ultraviolet beam in advanced oxidation-reduction processes: a review on the mechanism of processes and possible production free radicals.

Advanced oxidation processes (AOPs) and advanced reduction processes (ARPs) are a set of chemical treatment procedures designed to eliminate organic (sometimes inorganic) contamination in water and wastewater by producing free reactive radicals (FRR). UV irradiation is one of the factors that are effectively used in oxidation-reduction processes. Not only does the UV beam cause the photolysis of contamination, but it also leads to the product of FRR by affecting oxidants-reductant, and the pollutant decomposition occurs by FRR. UV rays produce active radical species indirectly in an advanced redox process by affecting an oxidant (O3, H2O2), persulfate (PS), or reducer (dithionite, sulfite, sulfide, iodide, ferrous). Produced FRR with high redox potential (including oxidized or reduced radicals) causes detoxification and degradation of target contaminants by attacking them. In this review, it was found that ultraviolet radiation is one of the important and practical parameters in redox processes, which can be used to control a wide range of impurities.

Fe0Ni0 bimetal co-immobilized horseradish peroxidase on ZIF-8@HMON for degradation of trichloroacetic acid

As a common pollutant in the environment, trichloroacetic acid (TCA) is difficult to be completely degraded by common advanced oxidation processes (AOPs) due to its high C-Cl bond content. Advanced oxidation–reduction processes (AORPs) may improve the degradation performance of TCA. In this work, we use Fe0Ni0 bimetal as reducing catalyst, hollow mesoporous silicone nanoparticles (HMONs) modified by ZIF-8 as immobilized carrier, horseradish peroxidase (HRP) and Fe0Ni0 were fixed in the carrier to form a AORP system for degradation of TCA. The effects of temperature, pH, H2O2 concentration, doping ratio on the degradation performance of the catalyst and the degradation mechanism of the composite catalyst were investigated. Degradation experiments showed that H· and OH· were present in the dual system, dechlorination and decarboxylation exist at the same time. Under the condition of 55 °C and pH = 4, 30 mg Fe0Ni0 and 20 mg immobilized enzyme shows the best degradation on TCA, and 81.48 % of 20 mg·L−1 TCA could be degraded by 2 h.

Advanced oxidation/reduction processes (AO/RPs) for wastewater treatment, current challenges, and future perspectives: a review.

Advanced oxidation/reduction processes (AO/RPs) are considered as effective water treatment technologies and thus could be used to solve the problem of water pollution. These technologies of wastewater treatment involve the production of highly reactive species such as •OH, H•, e-aq, SO4•-, and SO3•-. These radicals can attack the targeted contaminants present in aqueous media and result in their destruction. The efficiency of AO/RPs is highly affected by various operational parameters such as initial concentration of contaminant, solution pH, catalyst amount, intensity of light source, nature of oxidant and reductant used, and the presence of various ionic species in aquatic media. Among AO/RPs, the solar light-based AO/RPs are most widely used nowadays for contaminant removal from aqueous media because of their high environmental friendliness and cost effectiveness. By using these techniques, almost all types of pollutants can be easily removed from aquatic media within short intervals of time, and hence, the problem of water pollution can be solved effectively. This review focuses on various AO/RPs used for wastewater treatment. The effects of different operational parameters that affect the efficiency of these processes toward contaminant removal have been discussed. Besides, challenges and future recommendations are also briefly provided for the researchers in order to improve the efficiency of these processes.

Photocatalytic activation of sulfite using Fe(II) and Fe(III) for Enterococcus sp. Inactivation in urban wastewater

The application of sulfite in advanced oxidation-reduction processes has shown good results in the degradation of organic pollutant, but very few researches have addressed its application for wastewater disinfection. In this study, the efficacy of a sulfite system activated by different iron species and/or UV-A radiation in the inactivation of Enterococcus sp. was studied for the first time, achieving complete disinfection (>5-log) after 90 min. Different sulfite (0.1–10 mM), Fe(II) and Fe(III)-cit (0.1–2 mM) concentrations, were assessed in simulated and real wastewater matrices and experiments with radical scavengers were carried out to identify the main radical species involved in the disinfection. In addition, the influence of the nature of the aqueous matrix and the presence of other bacteria species as E.coli was assessed. Fe(III)-cit was the best sulfite activator, reaching complete bacteria inactivation (>5-log), while a maximum disinfection rate of 2.3-log units was achieved when using Fe(II). The performance of the treatment was greatly affected by the composition of the matrix, as the use of real wastewater resulted in a decrease in the disinfection rate to 0.5 and 1.4-log when using Fe(II) and Fe(III)-cit, respectively. The presence of Escherichia coli also proved to negatively influence the Enterococcus inactivation result, leading to a inactivation of 2.1-log in the sulfite/Fe(III)-cit system, opening the door to new studies to find out the selectivity of the radicals towards the different microorganisms in the matrix. Even though deeper studies are needed for a better understanding of the reaction mechanisms, this work opens the door to the use of sulfite-based processes applied to the disinfection of wastewater, proposing an alternative to the use of traditional oxidants.

Critical Perspective on Advanced Treatment Processes for Water and Wastewater: AOPs, ARPs, and AORPs

Emerging contaminants’ presence in water, wastewater, and aquatic environments has been widely reported. Their environmental and health-related effects, and the increasing tendency towards wastewater reuse require technology that could remove to a greater degree, or even mineralize, all these contaminants. Currently, the most commonly used process technologies for their removal are advanced oxidation processes (AOPs); however, recent advances have highlighted other advanced treatment processes (ATPs) as possible alternatives, such as advanced reduction processes (ARPs) and advanced oxidation-reduction processes (AORPs). Although they are not yet widely diffused, they may remove contaminants that are not readily treatable by AOPs, or offer better performance than the former. This paper presents an overview of some of the most common or promising ATPs for the removal of contaminants from water and wastewater, and their application, with discussion of their limitations and merits. Issues about technologies’ costs and future perspectives in the water sector are discussed.

Enhanced degradation of polychlorinated biphenyls with simultaneous usage of reductive and oxidative agents over UV/sulfite/TiO2 process as a new approach of advanced oxidation/reduction processes

This study relies on the UV irradiation of sulfite and TiO2, i.e. UV/sulfite/TiO2 (UST), as a novel method of Advanced Oxidation/Reduction Processes (AORPs) to generate both oxidative and reductive agents, simultaneously for degradation and mineralization of polychlorinated biphenyls (PCBs).The degradation performances of PCBs by UV alone, UV/sulfite (US) and UV/ TiO2 (UT) were estimated 60%, 81.8% and 92%, respectively under selected conditions (PCB concentration,12 mg L−1; pH, 7; ratio of sulfite/TiO2, 1:1; reaction time, 60 min).The 98.5% degradation of PCBs was obtained when both oxidative and reductive agents (UST) were applied simultaneously. Also, as the kinetic information, value of robs for UST was 27.33, 16.4, 9.84, 8.2, 2.23 and 1.44 times than that of the sulfite, TiO2, TiO2-sulfite, UV alone, US and UT, respectively. Also, values of energy consumption for UV alone, US, UT and UST were calculated 426, 115.13, 74.4 and 51.95 kW h m-3, respectively. The maximum mineralization percentage for UST was obtained 70.92% under selected conditions. The results indicated addition of nitrate and t-But (which are strong scavengers of (eaq- and SO3-) and (O2- and OH radicals, respectively) simultaneously, significantly was diminished the degradation performance from 98.5% (in the absence of scavengers) to 70% (in the presence of nitrate and t-But together); it clearly proved reductive (SO3-and eaq- radicals) and oxidative (OH and O2- radicals) agents plays a noticeable role in the PCB degradation.

Photo-catalytic degradation of Trichlorophenol with UV/sulfite/ZnO process, simultaneous usage of homogeneous reductive and heterogeneous oxidative agents generator as a new approach of Advanced Oxidation/Reduction Processes (AO/RPs)

This study develops UV/Sulfite/ZnO (USZ) photoreactor, as a novel method of Advanced Oxidation/Reduction Processes (AORPs), and employs it for degradation, dechlorination and mineralization of 2, 4, 6-trichlorophenol (TCP) content of wastewaters. Degradation efficiency of the UV-only, UV/ZnO, UV/Sulfite and USZ processes were determined as 23.4%, 37.6%, 44.8% and 87.83% respectively, at 10 min reaction time, 50 mg L−1 TCP concentration and pH of 7. Findings indicated that TCP degrades completely within 15 min treatment of 50 mg L−1 initial TCP concentration. According to Molar ratio evaluations, 1:2:50 is the optimal Molar ratio of sulfite/ZnO/TCP in the USZ process. Analyzing effluents of the USZ reactor by liquid chromatography/mass spectroscopy after 5, 10 and 15 min reaction time revealed that TCP decomposes to ring-shaped compounds in less than 10 min and all TCP and its metabolites convert to linear compounds within 15 min reaction time. Also fourteen little fragments were identified in the degradation of TCP by USZ during 2.5 till 15 min of reaction time. Investigating kinetic of the process through a pseudo first-order model using 10 to 200 mg L−1 TCP over 1 to 15 min reaction time demonstrated that the observed rate constant (kobs) decreases from 0.3811 to 0.0824 min−1 and the observed TCP degradation rate (robs) increases from 3.811 to 16.48 mg L−1 min−1 with increase of TCP concentration. Furthermore, electrical energy consumption (EEO) of the USZ process was calculated with kinetic model 2.21 to 10.25 as 2.19 to 3.55 and with merit-figure model 4.94 to 12.39 kW h m-3 from 10 to 200 mg L−1, respectively. In addition, the effect of co-existing water anions on degradation of 50 mg L−1 TCP was explored during 30 min processing. While 100% degradation was achieved in the absence of any anion, adding nitrate, as the most effective anion, decreased TCP degradation to 78.24%. The highest dechlorination was observed at sulfite/ZnO Molar ratio 1:2 and pH 11.0. Mineralization of TCP by USZ process was achieved 33.2% after 15 min of reaction.

As(III) and Cr(VI) oxyanion removal from water by advanced oxidation/reduction processes-a review.

Water pollution by human activities is a global environmental problem that requires innovative solutions. Arsenic and chromium oxyanions are toxic compounds, introduced in the environment by both natural and anthropogenic activities. In this review, the speciation diagrams of arsenic and chromium oxyanions in aqueous solutions and the analytical methods used for their detection and quantification are presented. Current and potential treatment methods for As and Cr removal, such as adsorption, coagulation/flocculation, electrochemical, ion exchange, membrane separation, phyto- and bioremediation, biosorption, biofiltration, and oxidative/reductive processes, are presented with discussion of their advantages, drawbacks, and the main recent achievements. In the last years, advanced oxidation processes (AOPs) have been acquiring high relevance for the treatment of water contaminated with organic compounds. However, these processes are also able to deal with inorganic contaminants, mainly by changing metal/metalloid oxidation state, turning these compounds less toxic or soluble. An overview of advanced oxidation/reduction processes (AO/RPs) used for As and Cr removal was carried out, focusing mainly on H2O2/UVC, iron-based and heterogeneous photocatalytic processes. Some aspects related to AO/RP experimental conditions, comparison criteria, redox mechanisms, catalyst immobilization, and process intensification through implementation of innovative reactors designs are also discussed. Nevertheless, further research is needed to assess the effectiveness of those processes in order to improve some existing limitations. On the other hand, the validation of those treatment methods needs to be deepened, namely with the use of real wastewaters for their future full-scale application. Graphical abstract ᅟ.

A survey of analytical methods employed for monitoring of Advanced Oxidation/Reduction Processes for decomposition of selected perfluorinated environmental pollutants

The monitoring of Advanced Oxidation/Reduction Processes (AO/RPs) for the evaluation of the yield and mechanisms of decomposition of perfluorinated compounds (PFCs) is often a more difficult task than their determination in the environmental, biological or food samples with complex matrices. This is mostly due to the formation of hundreds, or even thousands, of both intermediate and final products. The considered AO/RPs, involving free radical reactions, include photolytic and photocatalytic processes, Fenton reactions, sonolysis, ozonation, application of ionizing radiation and several wet oxidation processes. The main attention is paid to the most commonly occurring PFCs in the environment, namely PFOA and PFOS. The most powerful and widely exploited method for this purpose is without a doubt LC/MS/MS, which allows the identification and trace quantitation of all species with detectability and resolution power depending on the particular instrumental configurations. The GC/MS is often employed for the monitoring of volatile fluorocarbons, confirming the formation of radicals in the processes of C‒C and C‒S bonds cleavage. For the direct monitoring of radicals participating in the reactions of PFCs decomposition, the molecular spectrophotometry is employed, especially electron paramagnetic resonance (EPR). The UV/Vis spectrophotometry as a detection method is of special importance in the evaluation of kinetics of radical reactions with the use of pulse radiolysis methods. The most commonly employed for the determination of the yield of mineralization of PFCs is ion-chromatography, but there is also potentiometry with ion-selective electrode and the measurements of general parameters such as Total Organic Carbon and Total Organic Fluoride. The presented review is based on about 100 original papers published in both analytical and environmental journals.

Exploring the advanced oxidation/reduction processes in the VUV photoreactor for dechlorination and mineralization of trichloroacetic acid: Parametric experiments, degradation pathway and bioassessment

The present study reports degradation, dehalogenation and mineralization of trichloroacetic acid (TCAA) exploring advanced oxidation/reduction processes (AORPs) in a chemical-less VUV reactor. The performance of VUV process was almost independent of solution pH. The complete degradation and dechlorination of TCAA up to initial concentration of 50mg/L achieved in the VUV process at a neutral solution pH within a relatively short reaction time of 30min. The observed first-order degradation rate of TCAA increased from 2.35 to 12.20mg/L.min with the increase of initial concentration from 1 to 100mg/L. The major water anions did not considerably influenced the decomposition of TCAA. The hydroxyl radical and hydrated aqueous electrons simultaneously contributed in degradation and dechlorination of TCAA in the VUV process. Around 87% of TCAA (10mg/L) was mineralized in the VUV process with 30min. The degradation intermediates determined using LC/MS were found to be simple non-chlorinated substances mainly formic and acetic acids. A low energy was consumed in VUV to attain the efficient decomposition of TCAA. The VUV process was efficiently operated in continuous-flow mode for degradation, dechlorination and mineralization of TCAA. Therefore, the VUV photoreactor is an emerging and feasible chemical-less AORP which can be efficiently operated in continuous-flow regime for high-rate decomposition and mineralization of halogenated organic compounds.

Silicate sol–gel matrix stabilized ZnO–Ag nanocomposites materials and their environmental remediation applications

A facile preparation method was employed to decorate the zinc oxide nanoparticles by aminosilicate sol-gel supported silver nanoparticles (TPDT/(ZnO-Ag) NCMs). The nanocomposite photocatalyst materials were characterized by UV–vis absorption spectra, DRS, XRD, SEM and EDX techniques. The absorption spectral studies showed that the Ag nanoparticles (Ag NPs) were deposited on the ZnO nanoparticles (ZnO NPs) (represented as TPDT/(ZnO-Ag) NCMs) and the NCMs are highly stable. The photocatalytic oxidation and reduction reactions at the TPDT/(ZnO-Ag) NCMs photocatalysts were evaluated by using the toxic methylene blue (MB) dye and hexavalent chromium (Cr(VI)), respectively under visible light irradiation. The photocatalytic activity of the NCMs showed that the MB dye was completely decolorized at TPDT/(ZnO-Ag) 0.1 NCMs photocatalyst when compared to the controlled photocatalyst materials. The photocatalytic reduction of highly toxic Cr(VI) to less toxic Cr(III) was studied at the photocatalyst TPDT/(ZnO-Ag) 0.5 NCMs in the presence of hole scavengers such as oxalic acid. The Ag NPs deposited on the ZnO NPs and dispersed in silicate sol-gel matrix (TPDT/(ZnO-Ag) NCMs) improved the photocatalytic activity of the ZnO NPs photocatalyst with effective interfacial electron transfer processes at the ZnO by minimizing the charge recombination process when compared to the bare ZnO NPs. The TPDT/(ZnO-Ag) NCMs showed promising environmental remediation and water purification processes through the synergistic photocatalytic activity by advanced oxidation-reduction processes.

Free radical destruction of haloacetamides in aqueous solution

Haloacetamides are disinfection byproducts (DBPs) formed through chlorine/chloramine disinfection processes in drinking waters and have been recently highlighted in the US national Reconnaissance Survey. These species occur at low concentrations, but have been determined to have high cytotoxicity and mutagenicity and therefore may represent a human health hazard. Advanced oxidation/reduction processes (AO/RPs) which utilize free radical reactions are new alternatives to degrade these species. This study reports the absolute bimolecular reaction rate constants for 12 haloacetamides with •OH radical and hydrated electron. The •OH radical reaction rates varied from 5.18 × 107 to 1.14 × 1010 M−1 s−1, and hydrated electron reaction rates varied from 5.00 × 109 to 3.64 × 1010 M−1 s−1. Results obtained using an ion chromatograph indicated that ARPs are suitable for dehaloliazation of haloacetamides. These data are required for both evaluating AO/RPs for the destruction of these compounds and for studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime.

Degradation of Diclofenac by Advanced Oxidation and Reduction Processes: Kinetic Studies, Degradation Pathways and Toxicity Assessments

Many pharmaceutical compounds and metabolites are found in surface and ground waters suggesting their ineffective removal by conventional wastewater treatment technologies. Advanced oxidation/reduction processes (AO/RPs), which utilize free radical reactions to directly degrade chemical contaminants, are alternatives to traditional water treatment. This study reports the absolute rate constants for reaction of diclofenac sodium and model compound (2, 6-dichloraniline) with the two major AO/RP radicals: the hydroxyl radical (•OH) and hydrated electron (eaq−). The bimolecular reaction rate constants (M−1 s−1) for diclofenac for •OH was (9.29 ± 0.11) × 109, and for e−aq was (1.53 ± 0.03) ×109. To provide a better understanding of the decomposition of the intermediate radicals produced by hydroxyl radical reactions, transient absorption spectra are observed from 1 – 250 μs. In addition, preliminary degradation mechanisms and major products were elucidated using 60Co γ-irradiation and LC-MS. The toxicity of products was evaluated using luminescent bacteria. These data are required for both evaluating the potential use of AO/RPs for the destruction of these compounds and for studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime.

Titanium dioxide–gold nanocomposite materials embedded in silicate sol–gel film catalyst for simultaneous photodegradation of hexavalent chromium and methylene blue

Aminosilicate sol–gel supported titanium dioxide–gold (EDAS/(TiO 2–Au) nps) nanocomposite materials were synthesized by simple deposition–precipitation method and characterized. The photocatalytic oxidation and reduction activity of the EDAS/(TiO 2–Au) nps film was evaluated using hexavalent chromium (Cr(VI)) and methylene blue (MB) dye under irradiation. The photocatalytic reduction of Cr(VI) to Cr(III) was studied in the presence of hole scavengers such as oxalic acid (OA) and methylene blue (MB). The photocatalytic degradation of MB was investigated in the presence and absence of Cr(VI). Presence of Au nps on the (TiO 2) nps surface and its dispersion in the silicate sol-gel film (EDAS/(TiO 2–Au) nps) improved the photocatalytic reduction of Cr(VI) and oxidation of MB due to the effective interfacial electron transfer from the conduction band of the TiO 2 to Au nps by minimizing the charge recombination process when compared to the TiO 2 and (TiO 2–Au) nps in the absence of EDAS. The EDAS/(TiO 2–Au) nps nanocomposite materials provided beneficial role in the environmental remediation and purification process through synergistic photocatalytic activity by an advanced oxidation–reduction processes.

Removing Estrogenic Steroids from Waters: The Role of Reducing Hydrated Electron Reactions

AbstractThe presence of both synthetic and natural steroids in waters is currently one of the most pressing concerns to water treatment utilities. The use of radical-based advanced oxidation/reduction processes (AO/RPs) to augment standard water treatment methods may be of interest. In support of the application of these AO/RP rate constants have been determined for the reaction of the reducing hydrated electron (e

Treatment of statin compounds by advanced oxidation processes: Kinetic considerations and destruction mechanisms

This study examined the use of advanced oxidation/reduction processes (AO/RPs) for the destruction of cholesterol lowering statin pharmaceuticals. AO/RPs which utilize the oxidizing hydroxyl radical ( OH) and reducing aqueous electron (e − aq), to degrade chemical contaminants are alternatives to traditional water treatment methods, and are alternatives as water reuse becomes more generally implemented. Four major statin pharmaceuticals, fluvastatin, lovastatin, pravastatin and simvastatin, were studied, and the absolute bimolecular reaction rate constants with OH determined, (6.96±0.16)×10 9, (2.92±0.06)×10 9, (4.16±0.13)×10 9, and (3.13±0.15)×10 9 M −1 s −1, and for e − aq (2.31±0.06)×10 9, (0.45±0.01)×10 9, (1.26±0.01)×10 9, and (0.69±0.02)×10 9 M −1 s −1, respectively. To provide additional information on the radicals formed upon oxidation, transient spectra were measured and the overall reaction efficiency determined. Radical-based destruction mechanisms for destruction of the statins are proposed based on the LC-MS determination of the stable reaction by-products formed using 137Cs γ-irradiation of statin solutions. Knowing the reaction rates, reaction efficiencies and destruction mechanisms of these compounds is essential for the consideration of the use of advanced oxidation/reduction processes for the destruction of statins in aqueous systems.

Free-Radical-Induced Oxidative and Reductive Degradation of Fluoroquinolone Pharmaceuticals: Kinetic Studies and Degradation Mechanism

Fluoroquinolones, as a class of broad-spectrum antibiotics, have been detected in both surface and ground waters, and advanced oxidation/reduction processes (AO/RPs) are currently in development to remove these and other pharmaceuticals from wastewater because currently utilized treatment methods have proven to be ineffective. This article reports the reaction kinetics of six common fluoroquinolones with hydroxyl radicals and hydrated electrons, which are the major reactive species involved in AO/RPs. The bimolecular reaction rate constants (M(-1) s(-1)) for orbifloxacin, flumequine, marbofloxacin, danofloxacin, enrofloxacin, and the model compound, 6-fluoro-4-oxo-1,4-dihydro-3-quinoline carboxylic acid, with *OH are (6.94 +/- 0.08) x 10(9), (8.26 +/- 0.28) x 10(9), (9.03 +/- 0.39) x 10(9), (6.15 +/- 0.11) x 10(9), (7.95 +/- 0.23) x 10(9), (7.65 +/- 0.20) x 10(9), and with e(aq)(-), (2.25 +/- 0.02) x 10(10), (1.83 +/- 0.01) x 10(10), (2.41 +/- 0.02) x 10(10), (1.68 +/- 0.02) x 10(10), (1.89 +/- 0.02) x 10(10), and (1.49 +/- 0.01) x 10(10). These rate constants are related to the functional groups attached to the quinolone core, particularly the steric hindrance of the piperazine ring, making it possible to obtain a preliminary estimate of the *OH rate constant of an arbitrary fluoroquinolone by observing the ring constituents. In addition, the products of gamma-irradiation degradation of fluoroquinolones were analyzed by LC-MS to elucidate the probable pathways of AO/RPs degradation. Results indicate that preliminary degradation pathways include hydroxyl radical attack on the aromatic ring with subsequent hydroxylation, the substitution of a fluorine atom with a hydroxyl group, and the removal of the piperazine-derived side chain.

Free-Radical-Induced Oxidative and Reductive Degradation of Fibrate Pharmaceuticals: Kinetic Studies and Degradation Mechanisms

The presence of pharmaceutically active compounds (PhACs) in aquatic systems is an emerging environmental issue and poses a potential threat to ecosystems and human health. Unfortunately, current water treatment techniques do not efficiently remove all of the PhACs, which results in the occurrence of such compounds in surface and ground waters. Advanced oxidation/reduction processes (AO/RPs) which utilize free radical reactions to directly degrade chemical contaminants are alternatives to traditional water treatment methods. This study reports the absolute bimolecular reaction rate constants for three pharmaceutical compounds (fibrates), clofibric acid, bezafibrate, and gemfibrozil, with the hydroxyl radical (*OH) and hydrated electron (e(-)(aq)). The bimolecular reaction rate constants for *OH were (6.98 +/- 0.12) x 10(9), (8.00 +/- 0.22) x 10(9), and (10.0 +/- 0.6) x 10(9), and for e(-)(aq) were (6.59 +/- 0.43) x 10(8), (112 +/- 3) x 10(8), and (6.26 +/- 0.58) x 10(8), for clofibric acid, bezafibrate, and gemfibrozil, respectively. Transient spectra were obtained for the intermediate radicals produced by the hydroxyl radical reactions. In addition, preliminary degradation mechanisms and major products were elucidated using (137)Cs gamma-irradiation and LC-MS. These data are required for evaluating the potential use of AO/RPs for the destruction of these compounds in treating water for various purposes.

Free-Radical Destruction of β-Lactam Antibiotics in Aqueous Solution

Many pharmaceutical compounds and metabolites are being found in surface and ground waters, indicating their ineffective removal by conventional wastewater treatment technologies. Advanced oxidation/reduction processes (AO/RPs), which utilize free-radical reactions to directly degrade chemical contaminants, are alternatives to traditional water treatment. This study reports the absolute rate constants for reaction of three beta-lactam antibiotics (penicillin G, penicillin V, amoxicillin) and a model compound (+)-6-aminopenicillanic acid with the two major AO/RP reactive species: hydroxyl radical ((*)OH) and hydrated electron (e(-)aq). The bimolecular reaction rate constants (M(-1) s(-1)) for penicillin G, penicillin V, amoxicillin, and (+)-6-aminopenicillanic acid for (*)OH were (7.97 +/- 0.11) x 10(9), (8.76 +/- 0.28) x 10(9), (6.94 +/- 0.44) x 10(9), and (2.40 +/- 0.05) x 10(9) and for e(-)aq were (3.92 +/- 0.10) x 10(9), (5.76 +/- 0.24) x 10(9), (3.47 +/- 0.07) x 10(9), and (3.35 +/- 0.06) x 10(9), respectively. To provide a better understanding of the decomposition of the intermediate radicals produced by hydroxyl radical reactions, transient absorption spectra were observed from 1 to 100 micros. In addition, preliminary degradation mechanisms and major products were elucidated using (137)Cs gamma irradiation and LC-MS. These data are required for both evaluating the potential use of AO/RPs for the destruction of these compounds and studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime.

Studies in Radiation Chemistry: Application to Ozonation and Other Advanced Oxidation Processes

Advanced oxidation/reduction processes (AORPs) are an alternative water treatment that is becoming more widely utilized. Our radiation-chemistry based studies are being used to develop a fundamental understanding of AOP treatment options, and are divided into three complementary types of contaminants; disinfection by-products (DBPs), emerging pollutants of concern (EPoCs), and natural organic matter (NOM). More than 600 DBPs have been identified, and one class that appears to have severe potential adverse health effects is the halonitromethanes (HNMs). Of the nine HNMs, trichloronitromethane (chloropicrin) is the most common, with levels up to 180 nM in US drinking waters. EPoCs are of interest because of their biological activity at low concentrations in water and while the initial focus was on endocrine disruptor chemicals (EDCs) this class has now been expanded to include many other recalcitrant chemicals such as hormones, antibiotics, industrial contaminants, and health care products. Natural organic matter is one of the most common radical scavengers in natural waters and therefore may adversely affect AOPs. Our approach is to study NOM both directly and using model compounds thought to be representative of structural components of this complex material.