Formation Of Oxidation By-products Research Articles

Formation of oxidation byproducts during electrochemical treatment of simulated produced water

Electrochemical oxidation (EO) can effectively remove recalcitrant organic contaminants from produced water (PW) but the formation of toxic oxidation byproducts (OBPs) is an unintended consequence. This study has rigorously investigated the OBPs formation during the EO treatment of a simulated PW containing phenol - a common organic contaminant existing in PW, as a model contaminant. In the absence of ammonia, free chlorine was generated from Cl- oxidation to serve as the main oxidant for phenol oxidation. During the EO process, 2,4,6-trichlorophenol and 2,6-dichlorobenzoquinone were identified as the critical intermediates that led to the formation of carbonaceous OBPs (C-OBPs). Some C-OBPs like chloroform (TCM), chloral hydrate (CH), and trichloroacetic acid (TCAA) reached their peak concentrations of 15 – 180 μM that were then reduced to 1 – 115 μM via volatilization and/or electrochemical reduction. When ammonia was present, nitrogenous OBPs (N-OBPs) were formed with the peak levels of 1 – 10 μM at the chlorination breakpoint (when ammonia was completely removed) that were subsequently reduced below 1 uM via volatilization and/or hydrolysis. It was observed that ammonia significantly decreased the formation of both C-OBPs and chlorate due to the consumption of free chlorine. A higher current density accelerated OBPs formation rates with different effects on volatile and non-volatile OBPs. The results of this study will enhance our understanding of OBPs formation precursors and mechanisms during electrochemical process and help develop strategies for proper control of OBPs to achieve safer electrochemical wastewater treatment.

EDTA Degradation by UV/Chlorine Treatment: Efficiency, Formation of Oxidation Byproducts and Toxicity Evaluation

UV and chlorination are worldwide employed tertiary treatment for disinfection/oxidation of secondary effluents in sewage treatment plants. However, However, the combined UV and chlorination process (UV/chlorine) for removing non-biodegradable EDTA in secondary effluents is still unknown. In this study, we evaluated UV/chlorine for EDTA degradation and compared its formation of typical oxidation byproducts and toxicity change with chlorination. UV/chlorine showed synergistic effect on EDTA degradation, with removal efficiency of higher than 90% within 60 s at chlorine dosage of 0.30 mM, compared to UV irradiation of less than 2% and chlorination of about 65%. Increasing chlorine dosage from 0.050 to 0.30 mM and solution pH from 5.0 to 7.0 accelerated EDTA degradation. The coexisting bicarbonate and nitrate showed slight effects on EDTA degradation, but natural organic matter exhibited remarkable inhibition. As well, about 50%-80% of EDTA in realistic secondary effluent was removed by UV/chlorine. Three chlorinated byproducts including trichloromethane (TCM), dichloroacetic acid and trichloroacetic acid were formed in both chlorination and UV/chlorine, and UV/ chlorine treatment slightly enhanced the production of TCM. The acute toxicities of treated wastewater by UV/chlorine to luminescent bacterium and rice seeds were greater than that by chlorination, which deserves extensive concerns in advanced treatment processes for secondary effluents.

Changes of dissolved organic matter fractions and formation of oxidation byproducts during electrochemical treatment of landfill leachates: Development of spectroscopic indicators for process optimization

Electrochemical oxidation (EO) is an attractive option for treatment of dissolved organic matter (DOM) in landfill leachate but concerns remain over the energy efficiency and formation of oxidation byproducts ClO3− and ClO4−. In this study, EO treatment of landfill leachates was carried out using representative active and nonactive anode materials, cell configurations and current densities. Size exclusion chromatograms coupled with 2D synchronous and asynchronous correlation analysis showed that the sensitivity of DOM fractions to EO degradation was dependent on the anode material. The nonactive boron-doped diamond (BDD) anode demonstrated the best performance for DOM oxidation. The humic acid-like fraction (HA, 2.5–20 kDa) predominated the visible absorbance of landfill leachates at λ ≥400 nm, and it generally had the highest reaction rates except the occurrence of the pH-induced denaturation and precipitation of the proteinaceous biopolymer fraction (BP, >20 kDa). During the EO treatment of landfill leachate with BDD anode, the UV absorbance spectra of landfill leachates at wavelengths <400 nm were affected by the formation of free chlorine. Instead, the decrease of Abs420 was found to be a good indicator of the shift of the oxidation from predominantly HA fraction to the proteinaceous BP fraction. The behavior of the Abs420 parameter was also indicative of the transition from the energy-efficient oxidation of DOM to the dominance of side reactions of chlorine evolution and the subsequent formation of ClO3− and ClO4−. These findings suggest that the EO treatment of landfill leachate can be optimized by adjusting the current density with feedback signals from the online monitoring of Abs420, to achieve a trade-off between degradation of DOM and control of ClO3− and ClO4−.

Application of O3/PMS Advanced Oxidation Technology in the Treatment of Organic Pollutants in Highly Concentrated Organic Wastewater: A Review

The ozone/peroxymonosulfate (O3/PMS) system has attracted widespread attention from researchers owing to its ability to produce hydroxyl radicals (•OH) and sulfate radicals (SO4•−) simultaneously. The existing research has shown that the O3/PMS system significantly degrades refinery trace organic compounds (TrOCs) in highly concentrated organic wastewater. However, there is still a lack of systematic understanding of the O3/PMS system, which has created a significant loophole in its application in the treatment of highly concentrated organic wastewater. Hence, this paper reviewed the specific degradation effect, toxicity change, reaction mechanism, various influencing factors and the cause of oxidation byproducts (OBPs) of various TrOCs when the O3/PMS system is applied to the degradation of highly concentrated organic wastewater. In addition, the effects of different reaction conditions on the O3/PMS system were comprehensively evaluated. Furthermore, given the limited understanding of the O3/PMS system in the degradation of TrOCs and the formation of OBPs, an outlook on potential future research was presented. Finally, this paper comprehensively evaluated the degradation of TrOCs in highly concentrated organic wastewater by the O3/PMS system, filling the gaps in scale research, operation cost, sustainability and overall feasibility.

Degradation of Micropollutants and Formation of Oxidation By-Products during the Ozone/Peroxymonosulfate System: A Critical Review

The O3/PMS system has appeared as an effective wastewater treatment method because of the simultaneous generation of hydroxyl radicals (•OH) and sulfate radicals (SO4•−). Many research achievements have been made on the degradation of micropollutants and the reaction mechanism of the O3/PMS system. However, an integral understanding of the O3/PMS system is lacking, which limits the development of safe and effective AOP-based water treatment schemes. Therefore, in this review, the degradation effects, toxicity changes, and reaction mechanisms of various micropollutants in the O3/PMS system are reviewed. The formation of oxidation by-products (OBPs) is an important issue that affects the practical application of O3/PMS systems. The formation mechanism and control methods of OBPs in the O3/PMS system are overviewed. In addition, the influence of different reaction conditions on the O3/PMS system are comprehensively evaluated. Finally, future research needs are proposed based on the limited understanding of O3/PMS systems in the degradation of micropollutants and formation of OBPs. Specifically, the formation rules of several kinds of OBPs during the O3/PMS system are not completely clear yet. Furthermore, pilot-scale research, the operational costs, sustainability, and general feasibility of the O3/PMS system also need to be studied. This review can offer a comprehensive assessment on the O3/PMS system to fill the knowledge gap and provide guidance for the future research and engineering applications of the O3/PMS system. Through this effort, the O3/PMS system can be better developed and turned towards practical applications.

Real-Time Laboratory Measurements of VOC Emissions, Removal Rates, and Byproduct Formation from Consumer-Grade Oxidation-Based Air Cleaners

Levels of volatile organic compounds (VOCs) in the indoor environment can be decreased by the use of “air cleaners”, devices that remove VOCs by sorption and/or oxidative degradation. However, efficacies of these technologies for removing VOCs tend to be poorly constrained, as does the formation of oxidation byproducts. Here, we examine the influence of several oxidation-based air cleaners, specifically ones marketed as consumer-grade products, on the amounts and composition of VOCs. Experiments were conducted in an environmental chamber, with a suite of real-time analytical instruments to measure direct emissions, VOC removal efficacies (by the addition of either limonene and toluene), and byproduct formation. We find that the air cleaners themselves can be a source of organic gases, that removal efficacy can be exceedingly variable, and that VOC loss is primarily driven by physical removal in some cleaners. When oxidative degradation of VOCs was observed, it was accompanied by the formation of a range of oxidation byproducts, including formaldehyde and other oxygenates. These results indicate that some consumer-grade portable air cleaners can be ineffective in removing VOCs and that the air delivered may contain a range of organic compounds, due to direct emission and/or byproduct formation.

Selective oxidation of pharmaceuticals and suppression of perchlorate formation during electrolysis of fresh human urine

Urine comprises only a small (~1%) volumetric fraction of municipal wastewater, but represents a dominant source of pharmaceuticals, many of which may pass through conventional wastewater treatment and pose risks to aquatic ecosystems. Point-source treatment of source-separated urine presents a unique opportunity to degrade pharmaceuticals before dilution with wastewater, and electrochemical advanced oxidation processes are one increasingly investigated option. However, they often lead to the formation of oxidation byproducts including chlorate, perchlorate at very high concentrations. Here, we show that the high urea content of fresh human urine suppresses the formation of oxychlorides by inhibiting formation of HOCl/OCl‒ during electrolysis, while still enabling pharmaceutical degradation due to the slow rate of urea oxidation by •OH. This results in improved performance compared to equivalent treatment of hydrolyzed aged urine. This electrochemical oxidation scheme is shown to degrade the model contaminants cyclophosphamide and sulfamethoxazole with surface-area-to-volume-normalized pseudo-first-order rate constants greater than 0.08 cm/min in authentic fresh human urine. It results in ~100 × decrease in pharmaceutical concentrations in 2 h while generating ~1000 × lower oxychloride byproduct concentrations in synthetic fresh urine than synthetic hydrolyzed aged urine matrixes. Importantly, this proof-of-principle shows that simple and safe electrochemical methods can be used for point-source-remediation of pharmaceuticals in fresh human urine (before storage and hydrolysis), without formation of significant oxychloride byproducts.

Analysis of ultrasonic pre-treatment for the ozonation of humic acids

This paper presents an intensification study of an ozonation process through an ultrasonic pre-treatment for the elimination of humic substances in water and thus, improve the quality of water treatment systems for human consumption. Humic acids were used as representative of natural organic matter in real waters which present low biodegradability and a high potential for trihalomethane formation. Ultrasonic frequency (98 kHz, 300 kHz and 1 MHz), power (10–40 W) and sonicated volume (150–400 mL) was varied to assess the efficiency of the ultrasonic pre-treatment in the subsequent ozonation process. A direct link between hydroxyl radical (HO) formation and fluorescence reduction was observed during sonication pre-treatment, peaking at 300 kHz and maximum power density. Ultrasound, however, did not reduce total organic carbon (TOC). Injected ozone (O3) dose and reaction time were also evaluated during the ozonation treatment. With 300 kHz and 40 W ultrasonic pre-treatment and the subsequent ozonation step (7.4 mg O3/Lgas), TOC was reduced from 21 mg/L to 13.5 mg/L (36% reduction). HO attack seems to be the main degradation mechanism during ozonation. A strong reduction in colour (85%) and SUVA254 (70%) was also measured. Moreover, changes in the chemical structure of the macromolecule were observed that led to the formation of oxidation by-products of lower molecular weight.

Comparison of UV/H2O2, UV/PMS, and UV/PDS in Destruction of Different Reactivity Compounds and Formation of Bromate and Chlorate.

In this study, we compared the decontamination kinetics of various target compounds and the oxidation by-products (bromate and chlorate) of PMS, PDS, and H2O2 under UV irradiation (UV/PMS, UV/PDS, UV/H2O2). Probes of different reactivity with hydroxyl and sulfate radicals, such as benzoic acid (BA), nitrobenzene (NB), and trichloromethane (TCM), were selected to compare the decontamination efficiency of the three oxidation systems. Experiments were performed under acidic, neutral, and alkaline pH conditions to obtain a full-scale comparison of UV/peroxides. Furthermore, the decontamination efficiency was also compared in the presence of common radical scavengers in water bodies [bicarbonate, carbonate, and natural organic matter (NOM)]. Finally, the formation of oxidation by-products, bromate, and chlorate, was also monitored in comparison in pure water and tap water. Results showed that UV/H2O2 showed higher decontamination efficiency than UV/PDS and UV/PMS for BA degradation while UV/H2O2 and UV/PMS showed better decontamination performance than UV/PDS for NB degradation under acidic and neutral conditions. UV/PMS was the most efficient among the three processes for BA and NB degradation under alkaline conditions, while UV/PDS was the most efficient for TCM degradation under all pH conditions. In pure water, both bromate and chlorate were formed in UV/PDS, small amounts of bromate and rare chlorate were observed in UV/PMS, and no detectable bromate and chlorate were formed in UV/H2O2. In tap water, no bromate and chlorate were detectable for all three systems.

Degradation of natural organic matter by UV/chlorine oxidation: Molecular decomposition, formation of oxidation byproducts and cytotoxicity

The degradation of natural organic matters (NOMs) by the combination of UV and chlorine (UV/chlorine) was investigated in this study. UV/chlorine oxidation can effectively degrade NOMs, with the degradation of chromophores (∼80%) and fluorophores (76.4–80.8%) being more efficient than that of DOC (15.1–18.6%). This effect was attributed to the chromophores and fluorophores (double bonds, aromatic groups and phenolic groups) being preferentially degraded by UV/chlorine oxidation, particularly reactive groups with high electron donating capacity. Radical species •OH and •Cl were generated during UV/chlorine oxidation, with the contribution of •OH 1.4 times as high as that of •Cl. The degradation kinetics of different molecular weight (MW) fractions suggests that UV/chlorine oxidation degrades high MW fractions into low MW fractions, with the degradation rates of high MW fractions (>3000 Da) 4.5 times of those of medium MW fractions (1000–3000 Da). In comparison with chlorination alone, UV/chlorine oxidation did not increase the formation (30 min) and formation potential (24 h) of trihalomethanes, but instead promoted the formation and formation potential of haloacetic acids and chloral hydrate. Adsorbable organic halogen (AOX) formed from UV/chlorine oxidation of NOM were 0.8 times higher than those formed from chlorination. Cytotoxicity studies indicated that the cytotoxicity of NOM increased after both chlorination and UV/chlorine oxidation, which may be due to the formation of AOX.

ChemInform Abstract: The Syntheses of α‐Ketoamides via nBu4NI‐Catalyzed Multiple sp3C—H Bond Oxidation of Ethylarenes and Sequential Coupling with Dialkylformamides.

AbstractEthyl arenes with more than one ethyl group such as (Ig) suffer from the formation of oxidation byproducts.

Toxicity of the micropollutants Bisphenol A, Ciprofloxacin, Metoprolol and Sulfamethoxazole in water samples before and after the oxidative treatment

The amount of organic micropollutants detected in surface waters increases steadily. Common waste water treatment plants are not built to remove these substances. Thus there is a need for new technologies. A promising technology is the use of advanced oxidation processes through which organic micropollutants can be removed from waste water. However, the formation of oxidation by-products is likely and needs to be investigated since the by-products not only differ from their parent compounds in regard to their chemical and physical properties but they can also differ in toxicity. Therefore this study was designed to combine chemical and toxicological analyses of the advanced oxidation (O3 [5mg/L] or UV/H2O2 [Hg-LP lamp; 15W; 1g/L H2O2]) of waste water treatment plant effluents and pure water. Effluent samples from conventional activated sludge waste water treatment (mechanical treatment, activated sludge basin, and primary as well as secondary treatment steps) and high-purity deionized water (pure water) were spiked with Bisphenol A, Ciprofloxacin, Metoprolol or Sulfamethoxazole and treated with O3 or UV/H2O2. For the toxicological analyses mammalian cells (CHO-9, T47D) were exposed to the water samples for 24h and were tested for cytotoxicity (MTT Test), genotoxicity (Alkaline Comet Assay) and estrogenicity (ER Calux(®)). The results indicate that the oxidative treatment (O3 or UV/H2O2) of Bisphenol A, Metoprolol, Sulfamethoxazole or Ciprofloxacin in waste water did not result in toxic oxidation by-products, whereas the UV/H2O2 treatment of Bisphenol A and Ciprofloxacin in pure water resulted in by-products with cytotoxic but no estrogenic effects after 60min.

Assessment of Degradation Byproducts and NDMA Formation Potential during UV and UV/H2O2 Treatment of Doxylamine in the Presence of Monochloramine

UV-C radiation is the U.S. EPA recommended technology to remove N-nitrosodimethylamine (NDMA) during drinking and recycled water production. Frequently, H(2)O(2) is added to the treatment to remove other recalcitrant compounds and to prevent NDMA reformation. However, the transformation of NDMA precursors during the UV and UV/H(2)O(2) process and the consequences for NDMA formation potential are currently not well understood, in particular in the presence of monochloramine. In this study, doxylamine has been chosen as a model compound to elucidate its degradation byproducts in the UV and UV/H(2)O(2) process and correlate those with changes to the NDMA formation potential. This study shows that during UV treatment in the presence and absence of monochloramine, NDMA formation potential can be halved. However, an increase of more than 30% was observed when hydrogen peroxide was added. Ultrafast liquid chromatography coupled to quadrupole-linear ion trap mass spectrometer was used for screening and structural elucidation of degradation byproducts identifying 21 chemical structures from the original parent compound. This work shows that further oxidation of NDMA precursors does not necessarily lead to a decrease in NDMA formation potential. Degradation byproducts with increased electron density in the vicinity of the dimethylamino moiety, for example induced by hydroxylation, may have a higher yield of nucleophilic substitution and subsequent NDMA formation compared to the parent compound during chloramination. This work demonstrates the need to consider the formation of oxidation byproducts and associated implications for the control and management of NDMA formation in downstream processes and distribution when integrating oxidative treatments into a treatment train generating either drinking water or recycled water for potable reuse.

Evolution of Toxicity and Mineralization during the Treatment of Diethylphthalate in Water by Ozone and Activated Carbon Coupling

Ozone/activated carbon coupling could be an efficient method to remove micropollutants, such as phthalates, that are refractory to classical treatments. However, this wastewater-treatment process can lead to the formation of oxidation by-products that may be toxic and which also need to be removed. The aim of this work was to study the evolution of the mineralization and the toxicity of the effluent during the treatment process so as to determine the efficiency of this method and the required time of treatment. Analyses (Fourier transformed infrared spectroscopy (FTIR), thermogravimetric analyses, N2 adsorption isotherms) of the adsorbent material were performed to understand the role of activated carbon during the treatment. It is shown that depending on the activated carbon properties and the experimental conditions, a fast and complete removal of diethylphthalate, and total mineralization and detoxification of the treated solution can be obtained. Moreover, it is demonstrated that the activated carbon acts more as a reaction site than as an adsorbent, leading to an in situ renewal of the material during the process. DOI: 10.1061/(ASCE)EE.1943-7870.0000671. © 2013 American Society of Civil Engineers. CE Database subject headings: Coupling; Toxicity; Pollutants; Activated carbon; Ozone; Oxidation; Waste management. Author keywords: Ozone ðO3Þ=activated carbon (AC) coupling; Phthalates; Mineralization; Toxicity; Activated carbon renewal.

Assessment of the formation of inorganic oxidation by-products during the electrocatalytic treatment of ammonium from landfill leachates

This work investigates the formation of oxidation by-products during the electrochemical removal of ammonium using BDD electrodes from wastewaters containing chlorides. The influence of the initial chloride concentration has been experimentally analyzed first, working with model solutions with variable ammonium concentration and second, with municipal landfill leachates. Two different levels of chloride concentration were studied, i) low chloride concentrations ranging between 0 and 2000 mg/L and, ii) high chloride concentrations ranging between 5000 and 20,000 mg/L. Ammonium removal took place mainly via indirect oxidation leading to the formation of nitrogen gas and nitrate as the main oxidation products; at high chloride concentration the formation of nitrogen gas and the rate of ammonium removal were both favored. However, chloride was also oxidized during the electrochemical treatment leading to the formation of free chlorine responsible of the ammonium oxidation, together with undesirable products such as chloramines, chlorate and perchlorate. Chloramines appeared during the treatment but they reached a maximum and then started decreasing, being totally removed when high chloride concentrations were used. With regard to the formation of chlorate and perchlorate once again the concentration of chloride exerted a strong influence on the formation kinetics of the oxidation by-products and whereas at low chloride concentrations, chlorate appeared like an intermediate compound leading to the formation of perchlorate, at high chloride concentrations chlorate formation was delayed significantly and perchlorate was not detected during the experimental time. Thus this work contributes first to the knowledge of the potential hazards of applying the electro-oxidation technology as an environmental technology to deal with ammonium oxidation under the presence of chloride and second it reports efficient conditions that minimize or even avoid the formation of undesirable by-products.

Boron-doped diamond anodic treatment of landfill leachate: Evaluation of operating variables and formation of oxidation by-products

Landfill leachate with a low BOD/COD ratio was electrochemically oxidized by means of a boron-doped diamond anode. In addition to organic matter removal, this study addressed the issue of formation of both chlorinated organic compounds and nitrate ions as a result of organic matter and ammonia and/or organic nitrogen electro-oxidation in the presence of chloride ions. A factorial design methodology was implemented to evaluate the statistically important operating variables: treatment time (1–4 h), pH (5–8), current intensity (6.3–8.4 A) and addition of chloride (2500–4500 mg L−1). The process was evaluated on COD, total nitrogen (TN) and colour removal, as well as on the formation of nitrate, nitrite and chlorinated organics. Of the four variables studied, treatment time and pH had a considerable influence on COD and colour removal. On the contrary, none of the variables had a significant effect on the elimination of TN for which an average removal of 61 mg L−1 was obtained. The studied variables exhibited different effects on the four groups of organo-chlorinated compounds considered in this study, namely trihalomethanes (THMs), haloacetonitriles (HANs), haloketons (HKs) and 1,2-dichloroethane (DCA). Further analysis at more intense conditions, i.e. current intensity up to 18 A and reaction time up to 8 h revealed that high levels of decolourization (84%) could be achieved followed by low COD (51%) and ammonia (32%) removals. Apart from DCA, the concentration of chlorinated organics increased continuously with treatment time reaching values as high as 1.9 mg L−1, 753 μg L−1 and 431 μg L−1 of THMs, HANs and HKs, respectively.

High Yield Synthesis of Pure Alkanethiolate-Capped Silver Nanoparticles

One-phase, one-pot synthesis of Ag(0) nanoparticles capped with alkanethiolate molecules has been optimized to easily achieve a pure product in quantitative yield. We report the synthesis of dodecanethiolate-capped silver particles and the chemophysical, structural, and morphologic characterization performed by way of UV-vis, (1)H NMR, and X-ray photoelectron (XPS) spectroscopies, X-ray powder diffraction (XRD) and X-ray absorption fine structure analysis (XFAS), electron diffraction and high-resolution transmission electron microscopy (HR-TEM), and scanning and transmission electron microscopy (SEM and TEM). Depending on the molar ratio of the reagents (dodecylthiosulphate/Ag(+)), the mean Ag(0) particle size D(XRD) is tuned from 4 to 3 nm with a narrow size distribution. The particles are highly soluble, very stable in organic solvents (hexane, toluene, dichloromethane, etc.), and resistant to oxidation; the hexane solution after one year at room temperature does not show any precipitation or formation of oxidation byproducts.

Formation of oxidation by-products of the iodinated X-ray contrast medium iomeprol during ozonation

The present work describes the investigation of the formation of oxidation by-products of the iodinated X-ray contrast medium (ICM) iomeprol during ozonation in water treatment. Bench-scale investigations revealed that ICM can be partly oxidized during ozonation processes, whereas the ionic diatrizoic acid showed the lowest reactivity. Iomeprol, as a representative of ICM, was not fully mineralized during ozonation. Thus, unknown oxidation by-products were formed. Aqueous solutions of iomeprol were treated by ozonation in order to assess the formation of oxidation by-products. The by-products were characterized by different liquid chromatography methods including detection of single-stage mass spectra, product ion mass spectra, and induced in-source fragmentation for analysis of iodine containing oxidation by-products. Aldehyde and carbonyl containing compounds were proposed to be among the stable by-products. A derivatization step confirms that the aldehyde and carbonyl moieties are major functional groups in oxidation by-products of iomeprol. Furthermore, oxidation by-products of iomeprol were detected at the outlet of an ozone reactor at a full-scale waterworks. However, the toxicological relevance of the by-products is a major future research tasks.

Direct ethylene glycol fuel-cell stack—Study of oxidation intermediate products

In the present paper, a ten 10 cm 2 direct ethylene glycol fuel-cell (DEGFC) stack based on a nanoporous proton-conducting membrane (NP-PCM) is used to study the electro-oxidation of ethylene glycol (EG) in acid medium under initial and steady-state conditions, and under the operating conditions of electrochemical titration. Ethylene glycol (EG) has a theoretical capacity 17% higher than that of methanol in terms of Ah ml −1 (4.8 and 4, respectively); this is especially important for portable electronic applications. EG (bp 198 °C) is also a safer fuel for direct-oxidation fuel-cell (DOFC) applications than is methanol. A maximal power of 12 W (at 0.3 V cell −1) at 80 °C has been achieved for a DEGFC fresh stack fed with 0.5 M EG/1.7 M triflic acid solution at ambient dry air pressure. The formation of oxidation by-products – glycolic and oxalic acids (most likely in parallel reactions) – has been proven by ion-chromatography analysis. On continuous feed of EG in order to maintain a concentration of about 0.5 M, the concentration of intermediates reached a maximum after about two fuel (EG) turnovers. After discharging without feeding the stack with EG, there was no further accumulation of these acids and their concentration decreased to almost zero. This is clear evidence that EG is a real fuel that can be converted completely to CO 2.

Formation of oxidation byproducts from ozonation of wastewater

Disinfection byproduct (DBP) formation in tertiary wastewater was examined after ozonation (O 3) and advanced oxidation with O 3 and hydrogen peroxide (O 3/H 2O 2). O 3 and O 3/H 2O 2 were applied at multiple dosages to investigate DBP formation during coliform disinfection and trace contaminant oxidation. Results showed O 3 provided superior disinfection of fecal and total coliforms compared to O 3/H 2O 2. Color, UV absorbance, and SUVA were reduced by O 3 and O 3/H 2O 2, offering wastewater utilities a few potential surrogates to monitor disinfection or trace contaminant oxidation. At equivalent O 3 dosages, O 3/H 2O 2 produced greater concentrations of assimilable organic carbon (5–52%), aldehydes (31–47%), and carboxylic acids (12–43%) compared to O 3 alone, indicating that organic DBP formation is largely dependent upon hydroxyl radical exposure. Bromate formation occurred when O 3 dosages exceeded the O 3 demand of the wastewater. Bench-scale tests with free chlorine showed O 3 is capable of reducing total organic halide (TOX) formation potential by at least 20%. In summary, O 3 provided superior disinfection compared to O 3/H 2O 2 while minimizing DBP concentrations. These are important considerations for water reuse, aquifer storage and recovery, and advanced wastewater treatment applications.