Comparison of advanced oxidation processes and identification of monuron photodegradation products in aqueous solution

The photodegradation of monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in aqueous solutions under simulated solar irradiation has been conducted by different advanced oxidation processes (UV/H(2)O(2), UV/H(2)O(2)/Fe(2+), UV/H(2)O(2)/TiO(2), UV/TiO(2), dark H(2)O(2)/Fe(3+)). The degradation rates were always higher for the homogeneous catalysis in photo-Fenton reactions (UV/H(2)O(2)/Fe(2+)) compared to the heterogeneous photocatalytic systems (TiO(2)/UV and UV/H(2)O(2)/TiO(2)). Optimal concentrations of Fe(2+) and H(2)O(2) for the abatement of the herbicide in the photo-Fenton system were found to be 1 mM Fe(II) and 10 mM H(2)O(2). Several intermediary products were identified using large volume injection micro-liquid chromatography with UV detection (mu-LC-UV), mu-LC-MS and GC-MS techniques and a degradation mechanism has been proposed.     

Homogeneous degradation of 1,2,9,10-tetrachlorodecane in aqueous solutions using hydrogen peroxide, iron and UV light

The homogeneous degradation of the polychlorinated n-alkane, 1,2,9,10-tetrachlorodecane (T4C10), was studied in aqueous solutions of hydrogen peroxide, including Fenton and photo-Fenton reaction conditions. All solutions were adjusted to a pH of 2.8 and an ionic strength of 0.1 M NaClO4 prior to photolysis. T4C10 (2 x 10(-6) M) was substantially degraded by the H2O2/UV system (1.0 x 10(-2) M H2O2), with 60% disappearance in 20 min of irradiation in a photoreactor equipped with 300 nm lamps of light intensity 3.6 x 10(-5) Ein L(-1) min(-1) (established by ferrioxalate actinometry). The reaction produced stoichiometric amounts of chloride ion indicating complete dechlorination of the chlorinated n-alkane. T4C10 degraded very slowly under Fenton (Fe2+/H2O2/dark) and Fenton-like (Fe3+/H2O2/dark) conditions. However, when the same solutions were irradiated, T4C10 degraded more rapidly than in the H2O2/UV system, with 61% disappearance in 10 min of exposure. The rapid degradation is related to the enhanced degradation of hydrogen peroxide to oxidizing *OH radicals under photo-Fenton conditions. Degradation was inhibited in both the H2O2/UV and photo-Fenton systems by the addition of KI and tert-butyl alcohol due to *OH scavenging.     

Synergy of ozonation and photocatalysis to mineralize low concentration 2,4-dichlorophenoxyacetic acid in aqueous solution

Concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) may affect its degradation kinetics in advanced oxidation systems, and combinations of two or more systems can be more effective for its mineralization at low concentration levels. Degradations and mineralizations of 0.045mM 2,4-D using O(3), O(3)/UV, UV/TiO(2) and O(3)/UV/TiO(2) systems were compared, and influence of reaction temperature on the mineralization in O(3)/UV/TiO(2) system was investigated. 2,4-D degradations by O(3), O(3)/UV and UV/TiO(2) systems were similar to the results of earlier investigations with higher 2,4-D concentrations. The degradations and total organic carbon (TOC) removals in the four systems were well described by the first-order reaction kinetics. The degradation and removal were greatly enhanced in O(3)/UV/TiO(2) system, and further enhancements were observed with larger O(3) supplies. The enhancements were attributed to hydroxyl radical (()OH) generation from more than one reaction pathway. The degradation and removal in O(3)/UV/TiO(2) system were very efficient with reaction temperature fixed at 20 degrees C. It was suspected that reaction temperature might have influenced ()OH generation in the system, which needs further attention.     

Comparisons of polychromatic and monochromatic UV-based treatments of bisphenol-A in water via toxicity assessments

Polychromatic ultraviolet irradiation, such as from medium pressure (MP) Hg lamps may enhance the UV degradation of environmental pollutants as compared to low pressure (LP) Hg UV sources emitting monochromatic irradiation. Typically, studies involving destruction of environmental pollutants such as endocrine disrupting compounds (EDCs) are based on measurement of the parent compound decay using analytical chemistry, but such information is insufficient to determine an effective treatment endpoint because the identity and biological activity of many transformation products remain unknown. Bioanalytical methods to assess residual biological activity of a treated water offers one means to compare removal efficiency of EDC activity between MP- and LP-UV lamps under photolysis and UV/H2O2 oxidation. In this study, changes in estrogenic activity of bisphenol-A (BPA) as a function of UV treatment were evaluated using both an in vitro yeast estrogen screen and in vivo vitellogenin assay with Japanese medaka (Oryzias latipes) fish. Decay of BPA parent compound and formation of degradation products were followed using HPLC analysis. Results demonstrated that MP-UV direct photolysis more effectively removed BPA and associated estrogenic activity compared to LP-UV lamps. UV in combination with H2O2 significantly removed estrogenic activity in vitro and in vivo compared to direct photolysis; however, no significant difference in removal rates was found between the two lamps under UV/H2O2 oxidation. Furthermore, the UV/H2O2 process was effective for reducing embryo toxicity of BPA, but resulted in the production of acidic intermediates, causing acute toxicity and delayed hatching in some medaka embryos.     

Decomposition of gas-phase trichloroethene by the UV/TiO2 process in the presence of ozone.

The decomposition of gas-phase trichloroethene (TCE) in air streams by direct photolysis, the UV/TiO2 and UV/O3 processes was studied. The experiments were carried out under various UV light intensities and wavelengths, ozone dosages, and initial concentrations of TCE to investigate and compare the removal efficiency of the pollutant. For UV/TiO2 process, the individual contribution to the decomposition of TCE by direct photolysis and hydroxyl radicals destruction was differentiated to discuss the quantum efficiency with 254 and 365 nm UV lamps. The removal of gaseous TCE was found to reduce by UV/TiO2 process in the presence of ozone possibly because of the ozone molecules could scavenge hydroxyl radicals produced from the excitation of TiO2 by UV radiation to inhibit the decomposition of TCE. A photoreactor design equation for the decomposition of gaseous TCE by the UV/TiO2 process in air streams was developed by combining the continuity equation of the pollutant and the surface catalysis reaction rate expression. By the proposed design scheme, the temporal distribution of TCE at various operation conditions by the UV/TiO2 process can be well modeled.     

Radiolysis of aqueous phenol solutions with nanoparticles. 1. Phenol degradation and TOC removal in solutions containing TiO2 induced by UV,gamma-ray and electron beams

Aqueous phenol solutions containing TiO(2) nanoparticles were irradiated with ultraviolet (UV), gamma-ray and electron beams. Organic compounds were fully removed by each type of radiation in the presence of the particles. The absorbed energy of the ionizing radiation (gamma-ray and electron beams) needed for removal was much lower than that of UV photocatalysis. Phenol was decomposed by the ionizing radiation in the absence of the nanoparticles and the addition of TiO(2) had no significant effect on phenol decomposition rate. Instead, total organic carbon (TOC) removal using the ionizing radiation was accelerated drastically by TiO(2). It is suggested that TiO(2) particles affect the intermediate compounds produced through the decomposition of phenol. The amount of removed TOC per absorbed energy were compared in the absence and the presence of TiO(2) nanoparticles. Radiolysis with the nanoparticles showed consistently high rate and high efficiency of TOC removal.     

臭氧与TiO2/UV协同降解对氯苯酚

利用O3／UV、TiO2／UV和O3／TiO2／UV降解对氯苯酚表明，臭氧与TiO2／UV具有明显的协同作用，如在本实验条件下降解5min后，上述3者对对氯苯酚的去除率分别为55％、10％和77%。O3／TiO2／UV协同作用的本质是由于臭氧能带走二氧化钛光致电子空穴对中的电子，从而产生了更多的羟基自由基，加速了有机物的降解。     

光催化氧化深度处理电镀有机废水的工程化实验

采用光催化氧化联用技术对电镀有机废水进行深度处理工程化实验。探讨了uV、uV＋H2O3、uV＋H2O2＋TiO2、uV＋H2O2＋FeSO4、uV＋H2O2＋FeSO4＋TiO2、uV＋O3＋TiO2和uV＋03＋TiO2＋H2O2等体系对废水有机污染物去除率的影响。结果表明，相较于其他反应体系，uV＋O3＋TiO2＋H2O2体系具有更好的氧化效果，经碳滤处理后去除率达到90％以上，最终出水水质满足GB18918-20O2-级标准（A标准）的要求。实际运行项目偿还期5．33年，NPV〉0，内部收益率大于基准值10％。研究表明，uV＋O3＋TiO2＋H2O，体系能降低加药量，工作量及运行成本。可为电镀企业实际废水处理提供现实依据，为优化电镀废水的处理工艺提供参考。     

不同高级氧化法对水中低浓度药物甲硝唑降解过程的比较

采用UV、H₂O₂、UV/H₂O₂、Fenton、UV/Fenton和UV/TiO₂方法，对水中低浓度的药物甲硝唑进行降解。通过HPLC和UV-Vis光谱得到的甲硝唑去除率。详细讨论了Fe²⁺、TiO₂和H₂O₂的初始浓度以及溶液的初始pH值对降解效率的影响。结果表明，UV/Fenton和UV/TiO₂ 2种系统对水中低浓度甲硝唑均有很好的去除效果，但前者的光催化效率更高。在甲硝唑浓度=6 μmol/L，H₂O₂和Fe²⁺的初始浓度分别为0.5 mg/L和2.94 μmol/L，pH=4的条件下，UV/Fenton方法对甲硝唑水溶液光催化的最佳效率为95.8%。     

A tubular ceramic membrane coated with TiO2-P25 for radial addition of H2O2 towards AMX removal from synthetic solutions and secondary urban wastewater

Environmental Science and Pollution Research - This work aims to integrate several hydrogen peroxide (H2O2) activation mechanisms, photolysis (UVC irradiation), chemical electron transfer (TiO2-P25...     

Fe<Superscript>0</Superscript>-based system as innovative technology for degrading trichloromethane: Redox removal characteristics

BACKGROUND: The spent waste of aliphatic chlorinated solvents has caused severe deterioration of groundwater quality. Trichloromethane (TCM), which shows health and toxicological effects on human beings, was selected as a model compound to be dechlorinated through a redox system. METHODS: The Fe0-based system including Fe0/H2O, Fe0/UV, Fe0/H2O2, and Fe0/UV/H2O2 was explored to evaluate its performance in dechlorinating TCM. H2O2 was dosed at later reaction time points to initiate Fenton or photo-Fenton reactions. The first two systems demonstrate the reductive dechlorination of TCM by Fe0-released electrons, while the latter two show dechlorination of TCM by both electron reduction and hydroxyl radical oxidation. The system parameters of TCM remaining, Cl- buildup, Fe2+ accumulation, H2O2 residue, and ORP were measured to describe different redox characteristics of TCM dechlorination. The Cl- buildup was used as a way to describe the degree of TCM dechlorination in an open reaction system. RESULTS: Reductive dechlorination efficiencies of TCM were 5% and 6% for the systems of Fe0/H2O and Fe0/UV, respectively. In contrast, the Fe/H2O2 and Fe0/UV/H2O2 systems were capable of dechlorinating TCM reductively and oxidatively by 14% and 15%, respectively. The presence of UV light was found to retard the dissolution of Fe2+, but it enhanced the rate of chloride buildup, based on the comparison of Fe0/H2O and Fe0/UV systems. In addition, WV irradiation plays only a minor role in the Fe0/UV/H2O2 system, in view of TCM dechlorination. Application of small amount of H2O2 results in the increase of Fe2+ accumulation rate in the Fe0/H2O2 system. CONCLUSIONS: TCM was dechlorinated mostly through post Fenton oxidation; reductive reaction represents a less efficient way to dechlorinate TCM. The efficiencies of overall TCM dechlorination for the two systems of Fe0/H2O2 and Fe0/UV/ H2O2 are comparable to each other, and this implies that the presence of UV irradiation imposes no significant enhancement. RECOMMENDATIONS AND OUTLOOKS: It is highly recommended to initiate effective redox dechlorination of TCM with the system of Fe0/H2O2, where the H2O2 in excess is applied at a later reaction time point.     

The role of organic ligands in ferrous-induced photochemical degradation of 2,4-dichlorophenoxyacetic acid

Recent studies have shown that hydrogen peroxide is generated in a ferrioxalate-induced photoreductive reaction, but information about the effect of organic ligands on the photochemical behaviour of ferrous species is limited. The degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by a ferrous-catalyzed oxidation in the presence of various ligands such as formate, citrate, malelate, oxalate, and ethylenediaminetetra-acetic acid (EDTA) was studied. The experiments were conducted under either dark or irradiated (350n m) conditions. Forty-two percent and 34% of 2,4-D were removed by the Fe(2+)/oxalate/UV and Fe(2+)/citrate/UV processes, respectively, after 30 min of reaction and oxidative intermediates were obtained in both cases. The presence of hydroxylated intermediates suggests that 2,4-D may be attacked by hydroxyl radicals, which are the products of the photo-Fenton-like reaction. As such, hydrogen peroxide was produced by the photolysis of ferrous oxalate or ferrous citrate, referred to hereafter as photogenerated H(2)O(2). As expected, the total removal percentage of 2,4-D jumped to 97% when 1mM of hydrogen peroxide (so-called spiked H(2)O(2)) was externally added to the reaction vessel to initiate the Fe(2+)/oxalate/UV process. Therefore, the treatment of 2,4-D by the Fe(2+)/oxalate/H(2)O(2)/UV system can be operated in two steps: the photolysis of ferrous oxalate first, followed by adding the spiked H(2)O(2) sometime after the commencement of the reaction. A two-phase model has been developed to describe this tandem ferrous-catalyzed photooxidation, which would help to achieve the mineralization of 2,4-D.     

Photolysis of low concentration H2S under UV/VUV irradiation emitted from microwave discharge electrodeless lamps

The photolysis of simulating low concentration of hydrogen sulfide malodorous gas was studied under UV irradiation emitted by self-made microwave discharge electrodeless lamps (i.e. microwave UV electrodeless mercury lamp (185/253.7 nm) and iodine lamp (178.3/180.1/183/184.4/187.6/206.2 nm)). Experiments results showed that the removal efficiency (eta H2S) of hydrogen sulfide was decreased with increasing initial H2S concentration and increased slightly with gas residence time; H2S removal efficiency was decreased dramatically with enlarged pipe diameter. Under the experimental conditions with pipe diameter of 36 mm, gas flow rate of 0.42 standard l s(-1), eta H2S was 52% with initial H2S concentration of 19.5 mg m(-3) by microwave mercury lamp, the absolute removal amount (ARA) was 4.30 microg s(-1), and energy yield (EY) was 77.3 mg kW h(-1); eta H2S was 56% with initial H2S concentration of 18.9 mg m(-3) by microwave iodine lamp, the ARA was 4.48 microg s(-1), and the EY was 80.5mg kW h(-1). The main photolysis product was confirmed to be SO4(2-) with IC.     

Photodegradation of alachlor with the TiO(2) film immobilised on the glass tube in aqueous solution

Alachlor photodegradation was performed using TiO(2), which was synthesized by a modified sol-gel method. The thickness of a TiO(2) film immobilised by a 5-time dip-coating was 174 nm and the average diameter of TiO(2) particles was about 10-15 nm in SEM images. The crystal structure of a TiO(2) film calcinated at 300 degrees C for 1 h was observed as a typical anatase type. The stability of a TiO(2) film by a modified sol-gel method was 4% better than TiO(2) by a typical sol-gel method.The removal rate of alachlor with both Fe(3+) and UV radiation in the absence of TiO(2) was 0.28 mg/l/h in 10 h and the removal rate of alachlor with Fe(3+)/UV in the presence of TiO(2) was 0.32 g/l/h, which was higher by 14% than that with Fe(3+)/UV system. TOC concentration during the alachlor degradation with both TiO(2) and UV radiation in the absence of added Fe(3+) decreased from 100%, through 81% and 51%, to 44% with time elapses of 4, 8, and 10 h, respectively, while TOC concentration with both added Fe(3+) and UV radiation in the absence of TiO(2) decreased from 100% to 70% in 10 h.     

Biological assessment of bisphenol A degradation in water following direct photolysis and UV advanced oxidation

Endocrine disrupting compounds (EDCs) are exogenous environmental chemicals that can interfere with normal hormone function and present a potential threat to both environmental and human health. The fate, distribution and degradation of EDCs is a subject of considerable investigation. To date, several studies have demonstrated that conventional water treatment processes are ineffective for removal of most EDCs and in some instances produce multiple unknown transformation products. In this study we have investigated the use of direct photolysis with low-pressure (LP) Hg UV lamps and UV+hydrogen peroxide (H(2)O(2)) advanced oxidation process (AOP) for the degradation of a prototypic endocrine disrupter, bisphenol A (BPA), in laboratory water. Removal rates of BPA and formation of degradation products were determined by high performance liquid chromatography (HPLC) analysis. Changes in estrogenic activity were evaluated using both in vitro yeast estrogen screen (YES) and in vivo vitellogenin (VTG) assays with Japanese medaka fish (Oryzias latipes). Our results demonstrate that UV alone did not effectively degrade BPA. However, UV in combination with H(2)O(2) significantly removed BPA parent compound and aqueous estrogenic activity in vitro and in vivo. Removal rates of in vivo estrogenic activity were significantly lower than those observed in vitro, demonstrating differential sensitivities of these bioassays and that certain UV/AOP metabolites may retain estrogenic activity. Furthermore, the UV/H(2)O(2) AOP was effective for reducing larval lethality in treated BPA solutions, suggesting BPA degradation occurred and that the degradation process did not result in the production of acutely toxic intermediates.     

Fresnel lens to concentrate solar energy for the photocatalytic decoloration and mineralization of orange II in aqueous solution

The decoloration and mineralization of the azo dye orange II under conditions of artificial ultraviolet light and solar energy concentrated by a Fresnel lens in the presence of hydrogen peroxide and TiO(2)-P25 was studied. A comparative study to demonstrate the viability of this solar installation was done to establish if the concentration reached in the focus of the Fresnel lens was enough to improve the photocatalytic degradation reaction. The degradation efficiency was higher when the photolysis was carried out under concentrated solar energy irradiation as compared to UV light source in the presence of an electron acceptor such us H(2)O(2) and the catalyst TiO(2). The effect of hydrogen peroxide, pH and catalyst concentration was also determined. The increase of H(2)O(2) concentration until a critical value (14.7 mM) increased both the solar and artificial UV oxidation reaction rate by generating hydroxyl radicals and inhibiting the (e(-)/h(+)) pair recombination, but the excess of hydrogen peroxide decreases the oxidation rate acting as a radical or hole scavenger and reacting with TiO(2) to form peroxo-compounds, contributing to the inhibition of the reaction. The use of the response surface methodology allowed to fit the optimal values of the parameters pH and catalyst concentration leading to the total solar degradation of orange II. The optimal pH range was 4.5-5.5 close to the zero point charge of TiO(2) depending on surface charge of catalyst and dye ionization state. Dosage of catalyst higher than 1.1 gl(-1) decreases the degradation efficiency due to a decrease of light penetration.     

Comparison of the degradation of p-hydroxybenzoic acid in aqueous solution by several oxidation processes

A comparative study is made of 12 methods of chemical oxidation applied to degrading p-hydroxybenzoic acid in aqueous solution. The oxidation processes tested were: UV, O3, UV/TiO2, O3/Fe2+, O3/H2O2, O3/UV, UV/H2O2, H2O2/Fe2+, H2O2/Fe2+/O3, UV/H2O2/O3, H2O2/Fe2+/UV and O3/UV/H2O2/Fe2+. The 12 processes were ranked by reactivity. In a kinetic study, the overall kinetic rate constant was split up into three components: direct oxidation by UV irradiation (photolysis), direct oxidation by ozone (ozonation), and oxidation by free radicals (mainly OH*).     

Photo-oxidation of cork manufacturing wastewater

Several photo-activated processes have been investigated for oxidation of a cork manufacturing wastewater. A comparative activity study is made between different homogeneous (H2O2/UV-Vis and H2O2/Fe2+/UV-Vis) and heterogeneous (TiO2/UV-Vis and TiO2/H2O2/UV-Vis) systems, with degradation performances being evaluated in terms of total organic carbon (TOC) removal. Results obtained in a batch photo-reactor show that photo-catalysis with TiO2 is not suitable for this kind of wastewater while the H2O2/UV-Vis oxidation process, for which the effect of some operating conditions was investigated, allows to remove 39% of TOC after 4 h of operation (for C(H2O2)=0.59 M, pH=10 and T=35 degrees C). The combined photo-activated process, i.e., using both TiO2 and H2O2, yields an overall TOC decrease of 46% (for C(TiO2)=1.0 gl(-1)). The photo-Fenton process proved to be the most efficient, proceeds at a much higher oxidation rate and allows to achieve 66% mineralization in just 10 min of reaction time (for C(H2O2)=0.31 M, T=30 degrees C, Fe2+:H2O2=0.12 (mol) and pH=3.2).     

Photooxidation of naphthalenesulfonic acids: comparison between processes based on O(3), O(3)/activated carbon and UV/H(2)O(2)

The aim of the present study was to analyze and compare the efficacy of UV photodegradation with that of different advanced oxidation processes (O(3), UV/H(2)O(2), O(3)/activated carbon) in the degradation of naphthalenesulfonic acids from aqueous solution and to investigate the kinetics and the mechanism involved in these processes. Results obtained showed that photodegradation with UV radiation (254 nm) of 1-naphthalenesulfonic, 1,5-naphthalendisulfonic and 1,3,6-naphthalentrisulfonic acids is not effective. Presence of duroquinone and 4-carboxybenzophenone during UV irradiation (308-410 nm) of the naphthalenesulfonic acids increased the photodegradation rate. Addition of H(2)O(2) during irradiation of naphthalenesulfonic acids accelerated their elimination, due to the generation of ()OH radicals in the medium. Comparison between UV photodegradation 254 m and the advanced oxidation processes (O(3), O(3)/activated carbon and UV/H(2)O(2)) showed the low-efficacy of the former in the degradation of these compounds from aqueous medium. Thus, among the systems studied, those based on the use of UV/H(2)O(2) and O(3)/activated carbon were the most effective in the oxidation of these contaminants from the medium. This is because of the high-reactivity of naphthalenesulfonic acids with the *OH radicals generated by these two systems. This was confirmed by the values of the reaction rate constant of *OH radicals with these compounds k(OH), obtained by competitive kinetics (5.7 x 10(9) M(-1) s(-1), 5.2 x 10(9) M(-1) s(-1) and 3.7 x 10(9) M(-1) s(-1) for NS, NDS and NTS, respectively).     

Removal of Cr(VI) and humic acid by using TiO2 photocatalysis

The removal efficiencies of Cr(VI) and HA, using a TiO(2)-mediated photocatalytic process, were investigated with variations in the pH, TiO(2) dosage and Cr(VI)/HA ratio. During the photocatalytic reaction, the total removal of Cr(VI) occurred through adsorption onto TiO(2), as well as its reduction to Cr(III). However, oxidation and adsorption were identified as important removal processes for the treatment of HA. Due to the anionic type adsorption onto TiO(2) and its acid-catalyzed photocatalytic reduction, the removal of Cr(VI) decreased with increasing pH, while that of HA increased with increasing pH. The TiO(2) dosage was also an important parameter for the removal of Cr(VI). As the TiO(2) dosage was increased to 2.5 g l(-1), the removal of Cr(VI) was continuously enhanced, but decreased at dosages above 3 g l(-1) due to the increased blockage of the incident UV light used for the photocatalytic reaction. The removal of Cr(VI) was greatly enhanced when the system contained both HA and Cr(VI) compared to Cr(VI) alone. Also, the removal of HA was greatly enhanced when the system contained both HA and Cr(VI) compared to HA alone. The removal of Cr(VI) was continuously enhanced as the HA concentration gradually increased; however, no further increase was observed above 20 mg l(-1) HA due to the increased absorption of the UV light. This result supports that the photocatalytic reaction, with illuminated TiO(2), could be applied to more effectively treat wastewater containing both Cr(VI) and HA than that containing a single species only.