Optimization of electro-oxidation and electro-Fenton techniques for the treatment of oilfield produced water

Electrochemical advanced oxidation processes are the most promising methods for destroying and degrading organic and inorganic pollutants present in produced water effluents. This study presents the electro-oxidation process using graphite electrodes and electro-Fenton process using iron electrodes for the treatment of real produced water. The effect of operating parameters such as current density on chemical oxygen demand (COD) removal efficiency was addressed. The result showed that electro-Fenton process was more efficient than electro-oxidation process where it gave 98% as maximum COD removal efficiency with energy consumption of 1.9 kWh/dm³ at H₂O₂ concentration of 12 mM, current density of 10 mA/cm², temperature of 25°C, pH of 3, and treatment time of 80 min compared with 96.9% as maximum COD removal efficiency with energy consumption of 3 kWh/dm³ at pH of 6, current density of 10 mA/cm², temperature of 40°C, and reaction time of 80 min when using electro-oxidation process. These results demonstrated that electrochemical technologies are very promising methods for the treatment of produced water from oil/gas industry, so it can be safely disposed of or effectively reused for injection and irrigation.     

Degradation of 32 emergent contaminants by UV and neutral photo-fenton in domestic wastewater effluent previously treated by activated sludge

This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L⁻¹, and a real global quantity of micropollutants of 29.5 μg L⁻¹. The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV₂₅₄) alone, dark Fenton (Fe^2+,3+/H₂O₂) and photo-Fenton (Fe^2+,3+/H₂O₂/light). Different irradiation sources were used for the photo-Fenton experiences: UV₂₅₄ and simulated sunlight. Iron and H₂O₂ concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV₂₅₄, 50 mg L⁻¹ of H₂O₂, with and without adding iron (5 mg L⁻¹ of Fe²⁺ added or 1.48 mg L⁻¹ of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treatments. As the H₂O₂ concentration increased (10, 25 and 50 mg L⁻¹), best degradations were observed. UV₂₅₄, Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal.The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations.     

An energy-efficient two-stage passively aerated trickling filter for high-strength wastewater treatment and reuse

This work aimed to assess the technical and energetic feasibility of a passively aerated laboratory-scale trickling filter, configured as a two-stage system, to produce urban wastewater (UWW) reusable in agriculture. The trickling filter was fed continuously with high-strength UWW at four hydraulic retention times (HRTs), that is, 10, 5, 2 and 1 day, corresponding to organic loading rates (OLRs) of 0.1, 0.2, 0.5 and 0.9 kg COD/m³/d, respectively. The results revealed a good performance in organic load removal and nitrification at the four HRTs. The trickling filter showed high organic pollutant removal efficiencies of up to 93%, 94% and 98% for chemical oxygen demand (COD), BOD₅ and total suspended solid (TSS), respectively, as well as high ammonia nitrogen removal above 96% at the shortest HRT of 1 day. All physicochemical parameters were significantly lower than the allowable limits set out in ISO 16075 for category C (non-food crop irrigation) irrigation water. The reuse of treated UWW in irrigation led to germination indexes and growth parameters of triticale (Triticosecale Wittm.) almost equal to those obtained using tap water. Energy use was found to be about 0.2754 kWh/m³ of treated wastewater, making it competitive with trickling filter plants reported in the literature. The simplicity and energy efficiency of the developed trickling filter system, combined with its capacity for almost full nitrification, make it appealing for sewage treatment in small communities in developing countries.     

H2S and VOCs abatement robustness in biofilters and air diffusion bioreactors: A comparative study

The robustness of a conventional biofilter and an air diffusion bioreactor (ADB) was comparatively evaluated in laboratory-scale plants treating a mixture of H₂S, butanone, toluene and alpha-pinene at gas residence times of 50 s. Under steady state conditions, H₂S, butanone and toluene were almost completely degraded, while alpha-pinene removal did not exhibit removal efficiencies (REs) higher than 11.0 ± 2.3%. Fluctuations in temperature from 8 °C to 30 °C did not impact significantly process performance in any of the biotechnologies tested. However, while the ADB unit was able to cope with three and six fold step increases in pollutant loadings, volatile organic compounds (VOCs) REs noticeably decreased in the biofilter when subjected to a six fold step change (i.e. 90% reduction for butanone and 30% for toluene). A process shutdown of five days resulted in the temporary loss of butanone and toluene RE in the ADB system. A lack of irrigation during five days caused a slight decrease in the biofilter REs, while a failure in the pH control system drastically affected the ADB performance. Finally, process robustness was quantified. The calculated overall risks showed that both biotechnologies were reliable for H₂S and VOCs treatment in wastewater treatment plants, ADB diffusion exhibiting a higher robustness towards fluctuations commonly found under routine operation. This robustness was further confirmed by the high stability of the DGGE profiles.     

Impact of salinity and pH on the UVC/H2O2 treatment of reverse osmosis concentrate produced from municipal wastewater reclamation

While reverse osmosis (RO) technology is playing an increasingly important role in the reclamation of municipal wastewater, safe disposal of the resulting RO concentrate (ROC), which can have high levels of effluent organic pollutants, remains a challenge to the water industry. The potential of UVC/H₂O₂ treatment for degrading the organic pollutants and increasing their biodegradability has been demonstrated in several studies, and in this work the impact of the water quality variables pH, salinity and initial organic concentration on the UVC/H₂O₂ (3 mM) treatment of a municipal ROC was investigated. The reduction in chemical oxygen demand and dissolved organic carbon was markedly faster and greater under acidic conditions, and the treatment performance was apparently not affected by salinity as increasing the ROC salinity 4-fold had only minimal impact on organics reduction. The biodegradability of the ROC (as indicated by biodegradable dissolved organic carbon (BDOC) level) was at least doubled after 2 h UVC/H₂O₂ treatment under various reaction conditions. However, the production of biodegradable intermediates was limited after 30 min treatment, which was associated with the depletion of the conjugated compounds. Overall, more than 80% of the DOC was removed after 2 h UVC/3 mM H₂O₂ treatment followed by biological treatment (BDOC test) for the ROC at pH 4-8.5 and electrical conductivity up to 11.16 mS/cm. However, shorter UV irradiation time gave markedly higher energy efficiency (e.g., EE/O 50 kWh/m³ at 30 min (63% DOC removal) cf. 112 kWh/m³ at 2 h). No toxicity was detected for the treated ROC using Microtox^® tests. Although the trihalomethane formation potential increased after the UVC/H₂O₂ treatment, it was reduced to below that of the raw ROC after the biological treatment.     

Surface neutralization and H₂S oxidation at early stages of sewer corrosion: influence of temperature, relative humidity and H₂S concentration

While the involvement of a range of environmental factors in sewer corrosion is known, a comprehensive understanding of the processes involved and the exact role of individual environmental factors in sewer corrosion is still lacking. The corrosion of concrete in sewer systems is reported to be initiated through chemical reactions (involving H₂S and CO₂) that lower the surface pH to a level then conducive for biological activity. However, the specific influence of environmental variables, such as H₂S level, temperature, and relative humidity etc. remains unclear; although, they are expected to control these initial surface reactions of the concrete sewer pipe. We examined changes in the surface chemistry of concrete during the early stages of corrosion by exposing concrete coupons to thirty-six independent conditions in well-controlled laboratory chambers that simulated conditions typically found in various sewer environments across Australia. The conditions employed were combinations of six H₂S levels, three gas-phase temperatures and two relative humidity levels. Our results indicate that the role of CO₂ on initial surface pH reduction is insignificant when compared to the influence of H₂S. Within the first 12 months, a decrease in surface pH by 4.8 units was observed for coupons exposed to 30 °C and 50 ppm H₂S, while significantly lower pH reductions of 3.5 and 1.8 units were detected for coupons exposed to 25 °C and 18 °C respectively, and 50 ppm H₂S. Elemental sulphur was found to be the major oxidation product of H₂S and elevated concentrations were detected at the higher levels of H₂S, temperature and relative humidity. More significantly, the data obtained from the controlled chamber experiments correlated with those obtained from the field-exposed coupons. Hence, these findings can be extended to real sewer corrosion processes.     

Greywater treatment by UVC/H2O2

Greywater treatment by UVC/H₂O₂ was investigated with regard to the removal of chemical oxygen demand (COD). A COD reduction from 225 to 30 mg l⁻¹ (overall removal of 87%) was achieved after settling overnight and subsequent irradiation for 3 h with 10 mM H₂O₂. Most of the contaminants were removed by oxidation since only 13% COD was removed by settlement.The removal of COD in the greywater followed a second-order kinetic equation, r = 0.0637[COD][H₂O₂], up to 10 mM H₂O₂. A slightly enhanced COD removal was observed at the initial pH of 10 compared with pH 3 and 7. This was attributed to the dissociation of H₂O₂ to O₂H⁻. The treatment was not affected by total concentration of carbonate (c_T) of at least 3 mM, above which operation between pH 3 and 5 was essential. The initial biodegradability of the settled greywater (as BOD₅:COD) was 0.22. After 2 h UVC/H₂O₂ treatment, a higher proportion of the residual contaminants was biodegradable (BOD₅:COD = 0.41) which indicated its potential as a pre-treatment for a biological process.     

Treatment of high strength hexamine-containing wastewater by electro-Fenton method

A novel Electro-Fenton (EF–Fere) method, applied H₂O₂ and electrogenerated ferrous ion, was investigated for treating the hexamine-containing wastewater. The performance of Fe²⁺ generation in the electrolytic system was first evaluated, including the factors of the cathode material, initial pH, initial ferric concentration (Fe_i), and current density. When initial pH exceeded 2.5, the current efficiency dramatically decreased, which was due to the formation of Fe(OH)₃. Between 3000 and 10,000 mg/l of Fe_i, the initial current efficiency of Fe²⁺ generation was almost constant (85–87%), which dropped sharply to 39% at 1000 mg/l. In EF–Fere experiments, the COD removal efficiency attained above 94% after 5 h of reaction. The relationship between the temperature, dissolved oxygen, and COD was discussed. The changes in hexamine and its oxidation intermediates (methanol, formaldahyde, formate, ammonium and nitrate) during the reaction were also investigated. Three additional experiments using H₂O₂/Fe²⁺, H₂O₂/Fe³⁺, and direct electrolysis were also conducted to treat the hexamine-containing wastewater for comparison. The results showed that the EF–Fere method was the most efficient.     

Effect of some parameters on the rate of the catalysed decomposition of hydrogen peroxide by iron(III)-nitrilotriacetate in water

The decomposition rate of H₂O₂ by iron(III)-nitrilotriacetate complexes (Fe^IIINTA) has been investigated over a large range of experimental conditions: 3 < pH < 11, [Fe(III)]_T,0: 0.05-1 mM; [NTA]_T,0/[Fe(III)]_T,0 molar ratios : 1-250; [H₂O₂]₀: 1 mM-4 M) and concentrations of HO radical scavengers: 0-53 mM. Spectrophotometric analyses revealed that reactions of H₂O₂ with Fe^IIINTA (1 mM) at neutral pH immediately lead to the formation of intermediates (presumably peroxocomplexes of Fe^IIINTA) which absorb light in the region 350-600 nm where Fe^IIINTA and H₂O₂ do not absorb. Kinetic experiments showed that the decomposition rates of H₂O₂ were first-order with respect to H₂O₂ and that the apparent first-order rate constants were found to be proportional to the total concentration of Fe^IIINTA complexes, were at a maximum at pH 7.95 ± 0.10 and depend on the [NTA]_T,0/[Fe(III)]_T,0 and [H₂O₂]₀/[Fe(III)]_T,0 molar ratios. The addition of increasing concentrations of tert-butanol or sodium bicarbonate significantly decreased the decomposition rate of H₂O₂, suggesting the involvement of HO radicals in the decomposition of H₂O₂. The decomposition of H₂O₂ by Fe^IIINTA at neutral pH was accompanied by a production of dioxygen and by the oxidation of NTA. The degradation of the organic ligand during the course of the reaction led to a progressive decomplexation of Fe^IIINTA followed by a subsequent precipitation of iron(III) oxyhydroxides and by a significant decrease in the catalytic activity of Fe(III) species for the decomposition of H₂O₂.     

Photooxidation of the antidepressant drug Fluoxetine (Prozac®) in aqueous media by hybrid catalytic/ozonation processes

This article examines the oxidative disposal of Prozac^® (also known as Fluoxetine, FXT) through several oxidative processes with and without UV irradiation: for example, TiO₂ alone, O₃ alone, and the hybrid methods comprised of O₃ + H₂O₂ (PEROXONE process), TiO₂ + O₃ and TiO₂ + O₃ + H₂O₂ at the laboratory scale. Results show a strong pH dependence of the adsorption of FXT on TiO₂ and the crucial role of adsorption in the whole degradation process. Photolysis of FXT is remarkable only under alkaline pH. The heterogeneous photoassisted process removes 0.11 mM FXT (initial concentration) within ca. 60 min with a concomitant 50% mineralization at pH 11 (TiO₂ loading, 0.050 g L⁻¹). The presence of H₂O₂ enhances the mineralization further to >70%. UV/ozonation leads to the elimination of FXT to a greater extent than does UV/TiO₂: i.e., 100% elimination of FXT is achieved by UV/O₃ in the first 10 min of reaction and almost 97% mineralization is attained under UV irradiation in the presence of H₂O₂. The hybrid configuration UV + TiO₂ + O₃ + H₂O₂ enhances removal of dissolved organic carbon (DOC) in ca. 30 min leaving, however, an important inorganic carbon (IC) content. In all cases, the presence of H₂O₂ improves the elimination of DOC, but not without a detrimental effect on the biodegradability of FXT owing to the low organic carbon content in the final treated effluent, together with significant levels of inorganic byproducts remaining. The photoassisted TiO₂/O₃ hybrid method may prove to be an efficient combination to enhance wastewater treatment of recalcitrant drug pollutants in aquatic environments.     

The impact of biogas and fuelwood use on institutional kitchen air quality in Kampala,Uganda

Experts have suggested that microscale biogas systems offer a source of renewable energy that improves indoor air quality, but such impacts have not been directly measured. This study documented cooking behaviors and measured 2.5‐μm particulate matter (PM_2.5), carbon monoxide (CO), and sulfur dioxide (SO₂) concentrations within 14 institutional kitchens in Kampala, Uganda, that prepare meals using biogas (n=5), a mixture of biogas and fuelwood (n=3), and fuelwood (n=6). Small institutions (10‐30 people) with biogas kitchens had 99% lower concentrations of PM_2.5 (21 μg/m³) than fuelwood kitchens (3100 μg/m³). Larger institutions (>100 people) had biogas systems that produced insufficient gas and relied on fuelwood to meet over 90% of their energy needs. PM_2.5 concentrations in these biogas‐firewood kitchens were equivalent to concentrations in fuelwood kitchens. Although concentrations of hydrogen sulfide (H₂S) in biogas were as high as 2000 ppm, 75% of systems had undetectable H₂S levels (<100 ppm) in the biogas. Kitchens using biogas with high H₂S had correspondingly higher SO₂ concentrations in the kitchen air. However, even the highest SO₂ concentration in biogas kitchens (150 μg/m³) was lower than SO₂ concentration in fuelwood kitchens (390 μg/m³). The results suggest that biogas systems can offer air quality improvements if sized properly for energy demands.     

Hydroxyl radical involvement in the decomposition of hydrogen peroxide by ferrous and ferric-nitrilotriacetate complexes at neutral pH

The relative rates of degradation of three hydroxyl radical probe compounds (atrazine, fenuron and parachlorobenzoic acid (pCBA)) by Fe^III/H₂O₂ (pH = 2.85), Fe^IIINTA/H₂O₂ (neutral pH), Fe^II/O₂, Fe^IINTA/O₂, Fe^II/H₂O₂ and Fe^IINTA/H₂O₂ (neutral pH) have been investigated using the competitive kinetic method. Experiments were carried out in batch and in semi-batch reactors, in the dark, at 25 °C. The data showed that the three probe compounds could be degraded by all the systems studied, and in particular by Fe^IINTA/H₂O₂ and Fe^IIINTA/H₂O₂ at neutral pH. The relative rate constants of degradation of the three probe compounds obtained for all the systems tested were identical and equal to 1.45 ± 0.03 and 0.47 ± 0.02 for k_Atrazine/k_pCBA and k_Fenuron/k_pCBA, respectively. These values as well as the decrease of the rates of degradation of the probe compounds upon the addition of hydroxyl radical scavengers (tert-butanol, bicarbonate ions) suggest that the degradation of atrazine, fenuron and pCBA by Fe^IINTA/O₂, Fe^IINTA/H₂O₂ and Fe^IIINTA/H₂O₂ is initiated by hydroxyl radicals.     

Oxidative removal of bisphenol A using zero valent aluminum-acid system

Bisphenol A (BPA), a controversial endocrine disruptor, is ubiquitous in the aquatic environment. In this study, the oxidative degradation of BPA and its mechanism using zero valent aluminum (ZVAl)-acid system under air-equilibrated conditions was investigated. Under pH <3.5 acidic conditions, ZVAl demonstrated an excellent capacity to remove BPA. More than 75% of BPA was eliminated within 12 h in pH 1.5 reaction solutions initially containing 4.0 g/L aluminum and 2.0 mg/L BPA at 25 ± 1 °C. The removal of BPA was further accelerated with increasing aluminum loadings. Higher temperature and lower initial pH also facilitated BPA removal. The addition of Fe²⁺ into the ZVAl-acid system significantly accelerated the reaction likely due to the enhancing transformation of H₂O₂ to HO via Fenton reaction. Furthermore, the primary products or intermediates including monohydroxylated BPA, hydroquinone, 2-(4-hydroxyphenyl)propane and 4-isopropenylphenol, were identified and a possible reaction scheme was proposed. The remarkable capacity of the ZVAl-acid system in removing BPA displays its potential application in the treatment of organic compound-contaminated water.     

Optimization of phenol removal from wastewater by activation of persulfate and ultrasonic waves in the presence of biochar catalyst modified by lanthanum chloride

In this paper, the effects of phenol concentration, pH, catalyst dose, persulfate concentration, temperature and contact time on the phenol removal from wastewater by activation of persulfate (S₂O₈^?2) in the presence of biochar modified by lanthanum chloride and ultrasonic waves (US) are optimized. Experimental design and optimization were carried out by response surface methodology. The optimum conditions for the maximum phenol removal were obtained pH of 4, phenol concentration of 86 mg/L, catalyst dose of 43 mg/L, persulfate concentration of 86 mg/L, temperature of 41 °C and contact time of 63 min. The optimum phenol removal from synthetic wastewater was attained 97.68%. Phenol removal by the mentioned system was fitted with the first‐order kinetic model. The combination of the ingredients of ‘S₂O₈^?2/US/Biochar‐LaCl₃’ system had a synergistic effect on the phenol removal.     

As(III) removal by hydrous titanium dioxide prepared from one-step hydrolysis of aqueous TiCl4 solution

Hydrous titanium dioxide (TiO₂·xH₂O) nanoparticles were synthesized by a low-cost one-step hydrolysis process with aqueous TiCl₄ solution. These TiO₂·xH₂O nanoparticles ranged from 3 to 8 nm and formed aggregates with a highly porous structure, resulting in a large surface area and easy removal capability from aqueous environment after the treatment. Their effectiveness on the removal of As(III) (arsenite) from water was investigated in both laboratory and natural water samples. The adsorption capacity on As(III) of these TiO₂·xH₂O nanoparticles reached over 83 mg/g at near neutral pH environment, and over 96 mg/g at pH 9.0. Testing with a As(III) contaminated natural lake water sample confirmed the effectiveness of these TiO₂·xH₂O nanoparticles in removing As(III) from natural water. The high adsorption capacity of the TiO₂·xH₂O nanoparticles is related to the high surface area, large pore volume, and the presence of high affinity surface hydroxyl groups.     

Efficient removal of microcystin-LR by UV-C/H₂O₂ in synthetic and natural water samples

The destruction of the commonly found cyanobacterial toxin, microcystin-LR (MC-LR), in surface waters by UV-C/H₂O₂ advanced oxidation process (AOP) was studied. Experiments were carried out in a bench scale photochemical apparatus with low pressure mercury vapor germicidal lamps emitting at 253.7 nm. The degradation of MC-LR was a function of UV fluence. A 93.9% removal with an initial MC-LR concentration of 1 μM was achieved with a UV fluence of 80 mJ/cm² and an initial H₂O₂ concentration of 882 μM. When increasing the concentration of MC-LR only, the UV fluence-based pseudo-first order reaction rate constant generally decreased, which was probably due to the competition between by-products and MC-LR for hydroxyl radicals. An increase in H₂O₂ concentration led to higher removal efficiency; however, the effect of HO scavenging by H₂O₂ became significant for high H₂O₂ concentrations. The impact of water quality parameters, such as pH, alkalinity and the presence of natural organic matter (NOM), was also studied. Field water samples from Lake Erie, Michigan and St. Johns River, Florida were employed to evaluate the potential application of this process for the degradation of MC-LR. Results showed that the presence of both alkalinity (as 89.6-117.8 mg CaCO₃/L) and NOM (as ∼2 to ∼9.5 mg/L TOC) contributed to a significant decrease in the destruction rate of MC-LR. However, a final concentration of MC-LR bellow the guideline value of 1 μg/L was still achievable under current experimental conditions when an initial MC-LR concentration of 2.5 μg/L was spiked into those real water samples.     

Comparison of the ozonation and Fenton process performances for the treatment of antibiotic containing manure

An integrated treatment method based on magnesium salt extraction followed by chemical oxidation was used for the treatment of a veterinary antibiotic, oxytetracycline (OTC) contaminated cow manure since animal manure can be an important source for antibiotic pollution in the environment. Pretreatment with magnesium salt enhanced the efficiencies of subsequent oxidation processes by extracting 63.9% of OTC from the manure thereby making it more favorable for oxidation with the hydroxyl radicals produced by the Fenton and ozone oxidation processes. Both the 24 h Fenton oxidation process with 434 mM H₂O₂ and 43.4 mM Fe²⁺ doses and the 1-h ozonation process with an applied ozone dose of 2.5 mg min^− 1 provided more than 90% OTC removal from the manure slurry. However, the second-order OTC removal rate constant of Fenton process (119 M^− 1s^− 1) was remarkably lower than that obtained with the ozonation process (548 M^− 1s^− 1). The oxidant dose was a significant factor for the efficiency of the Fenton treatment but not for the ozone treatment. The efficiencies of both the Fenton and ozone oxidation processes were not affected by the pH adjustment of the manure slurry.     

Transformation kinetics of biochemically active compounds in low-pressure UV photolysis and UV/H(2)O(2) advanced oxidation processes

Factors controlling photolysis and UV/H₂O₂ photooxidation rates of the biochemically active compounds (BACs) sulfamethoxazole, sulfamethazine, sulfadiazine, trimethoprim, bisphenol A, and diclofenac were determined. Experiments were conducted with a quasi-collimated beam apparatus equipped with low-pressure UV lamps. The effects of pH, H₂O₂ concentration, and background water matrix (ultrapure water, lake water, wastewater treatment plant effluent) on BAC transformation rates were evaluated. For the sulfa drugs, solution pH affected direct photolysis rates but had little effect on the hydroxyl radical oxidation rate. For sulfamethoxazole, the neutral form photolyzed more easily than the anionic form while the reverse was the case for sulfamethazine and sulfadiazine. For trimethoprim, the hydroxyl radical oxidation rate was higher for the cationic form (pH 3.6) than for the neutral form (pH 7.85). Quantum yields and second order rate constants describing the reaction between the hydroxyl radical and BACs were determined and used together with background water quality data to predict fluence-based BAC transformation rate constants (k′). For both the lake water and wastewater treatment plant effluent matrices, predicted k′ values were generally in good agreement with experimentally determined k′ values. At typical UV/H₂O₂ treatment conditions (fluence = 540 mJ cm⁻², H₂O₂ dose = 6 mg L⁻¹), BAC transformation percentages in North Carolina lake water ranged from 43% for trimethoprim to 98% for diclofenac. In wastewater treatment plant effluent, BAC transformation percentages were lower (31-97%) at the same treatment conditions because the hydroxyl radical scavenging rate was higher.     

Effects of UV/H2O2 advanced oxidation on chemical characteristics and chlorine reactivity of surface water natural organic matter

The advanced oxidation process utilizing ultraviolet and hydrogen peroxide (UV/H₂O₂) is currently applied in commercial drinking water applications for the removal of various organic pollutants. Natural organic matter (NOM) present in the source water can also be oxidized and undergo changes at the fluence and H₂O₂ concentrations applied in commercial drinking water UV/H₂O₂ applications (fluences less than 2000 mJ cm⁻², initial H₂O₂ concentrations less than 15 mg L⁻¹). In this study, the impact of UV/H₂O₂ on NOM’s aromaticity, hydrophobicity, and potential to form trihalomethanes (THMs) and haloacetic acids (HAAs) was investigated for raw surface water and the same water with the very hydrophobic acid (VHA) fraction of NOM removed. During UV/H₂O₂ treatments, NOM in the raw surface water was partially oxidized to less aromatic and hydrophobic characteristics, but was not mineralized, confirming findings from past research. Below fluences of 1500 mJ cm⁻² UV/H₂O₂ treatment of the raw water did not lead to reduction in the formation potential of THMs. The formation potential of HAAs was reduced at a fluence of 500 mJ cm⁻² with only small additional reductions as fluence further increased. For the water from which the VHA fraction was removed, UV/H₂O₂ treatment led to mineralization of NOM suggesting that, when coupled with a pre-treatment capable of removing the VHA fraction, UV/H₂O₂ could achieve further reductions in NOM. These subsequent reductions in NOM led to continuous reductions in the formation potentials of THMs and HAAs as fluence increased.     

Photooxidation and subsequent biodegradability of recalcitrant tri-alkyl phosphates TCEP and TBP in water

Biodegradable organic carbon (BDOC) from OH radical oxidation (UV-H₂O₂) of the recalcitrant industrial anti-foaming agents and flame retardants, tri-n-butyl phosphate (TBP) and tris(2-chloroethyl) phosphate (TCEP), was quantified with respect to the fraction of the TBP or TCEP photooxidized. For 50-96% contaminant oxidation via OH, BDOC was similar in solutions of either compound, and ranged from 0.25 to 0.5 mg L⁻¹ (TBP₀ and TCEP₀ = 5 mg L⁻¹). In addition, for this contaminant oxidation range, complete dehalogenation of TCEP was observed, along with a significant change in pH. Oxidation of TCEP results in both H⁺ and Cl⁻ release, while the TBP mineralization pathway results in CO₂, H₂O, H⁺, and PO₄³⁻. For low μg/L levels of TCEP contamination in treated surface waters, UV-H₂O₂ oxidation of TCEP or TBP would not be expected to impact pH or chloride concentrations, however, a portion of the TCEP or TBP oxidation products, likely in non-halogenated aldehyde form, would become an available carbon source for bacterial growth in storage, distribution, or during further physical treatment.