Photocatalytic and photoelectrocatalytic humic acid removal and selectivity of TiO(2) coated photoanode

In this study, photocatalytic (PC) and photoelectrocatalytic (PEC) treatment methods were comparatively investigated as a possible means of removing humic acid (HA) following absorbance at 254nm (UV(254)) and total organic carbon (TOC) analysis. The enhanced HA degradation rates were obtained in the PEC system over the conventional PC process under acidic, neutral and alkaline conditions. Preliminary and binary experiments were performed to determine the selectivity of the photoanode in terms of HA and chloride oxidation. TOC, chlorine and photocurrent parameters proved that HA was selectively removed before chlorine generation. The inhibitory effect of carbonate ions on the performance of photoanode was also studied under different pH values.     

O3、H2O2／O3及UV／O3在焦化废水深度处理中的应用

采用O3、H2O2／O3及UV／O3等高级氧化技术（AOPs）对某焦化公司的生化出水进行深度处理,考察了O3与废水的接触时间、溶液pH、反应温度等因素对废水COD去除率的影响,确定出O3氧化反应的最佳工艺参数为：接触时间40min,溶液pH8．5,反应温度25℃,此条件下废水COD及UV254的去除率最高可达47．14％和73．47％;H2O2／O3及UV／O3两种组合工艺对焦化废水COD及UV254的去除率均有一定程度的提高,但H2O2／O3系统的运行效果取决于H2O2的投加量。研究结论表明,单纯采用COD作为评价指标,并不能准确反映出O3系列AOPs对焦化废水中有机污染物的降解作用。     

An investigation into reservoir NOM reduction by UV photolysis and advanced oxidation processes

A comparison of four treatment technologies for reduction of natural organic matter (NOM) in a reservoir water was made. The work presented here is a laboratory based evaluation of NOM treatment by UV-C photolysis, UV/H(2)O(2), Fenton's reagent (FR) and photo-Fenton's reagent (PFR). The work investigated ways of reducing the organic load on water treatment works (WTWs) with a view to treating 'in-reservoir' or 'in-pipe' before the water reaches the WTW. The efficiency of each process in terms of NOM removal was determined by measuring UV absorbance at 254 nm (UV(254)) and dissolved organic carbon (DOC). In terms of DOC reduction PFR was the most effective (88% removal after 1 min) however there were interferences when measuring UV(254) which was reduced to a lesser extent (31% after 1 min). In the literature, pH 3 is reported to be the optimal pH for oxidation with FR but here the reduction of UV(254) and DOC was found to be insensitive to pH in the range 3-7. The treatment that was identified as the most effective in terms of NOM reduction and cost effectiveness was PFR.     

Photodegradation of humic acids in the presence of hydrogen peroxide

A batch photoreactor was used to evaluate the UV/H2O2 oxidation process for the removal of humic acids in water. A 450-W UV lamp with high-pressure mercury vapor was employed as the light source. The residues of humic acids and hydrogen peroxide were measured for assessment of process performance and understanding of process reaction behavior. The UV photolysis alone can play an important role in the degradation of humic acids. The presence of hydrogen peroxide was found to promote the degradation efficiency. However, excessive dosage of H2O2 does not further improve the degradation of humic acids. On the contrary, the lower the H2O2 dosage the higher the amount of humic acids which can be removed. Aeration with air does not favor the removal efficiency of humic acids as the oxidation lasts for a sufficiently long time. The presence of carbonate species deteriorates the humic acids' removal, whereas it results in a larger amount of H2O2 decomposition.     

Using FeGAC/H2O2 process for landfill leachate treatment

Due to the growing concern of highly contaminated landfill leachate problems in Taiwan, an innovative advanced catalytic oxidation (FeGAC/H(2)O(2)) process was developed and employed in this research to treat the landfill leachate from central Taiwan. Experimental results indicated that the FeGAC/H(2)O(2) process could effectively remove organic compounds from landfill leachate. The presence of iron oxide coated granular activated carbon (FeGAC) greatly improved the oxidative ability of H(2)O(2) for the removal of humic acids, fulvic acids and non-humic substance from leachate. For instance, at pH 6, the removal efficiencies of FeGAC/H(2)O(2) and H(2)O(2) processes were 70% and 8%, respectively. FeGAC/H(2)O(2) combined both advantages of FeGAC and H(2)O(2) where FeGAC had good organics adsorption ability and could effectively catalyse the hydrogen peroxide oxidation reaction for organics removal.     

Decolorizing of lignin wastewater using the photochemical UV/TiO2 process

Studies on applying the photochemical UV/TiO2 oxidation process to treat the lignin-containing wastewater for dissolved organic carbon (DOC), color and reducing A254 (the absorption at the wavelength of 254 nm) have been carried out. The data obtained in this study demonstrate that the UV/TiO2 process is effective in oxidizing the lignin thus reducing the color and DOC of the wastewater treated. The combined UV/TiO2 treatment can achieve better removal of DOC and color than the UV treatment alone. Color removal, based on American Dye Manufacture Index (ADMI) measurement, is greater than 99% if the pH is maintained at 3.0 with the addition of 1 g l(-1) TiO2. When 10 g l(-1) TiO2 is applied, the oxidation reduction potential (ORP) value is reached to result in an 88% removal of both DOC and color. A model was developed based on the variation of ORP during the photochemical reaction to simulate the decoloring process. The proposed model can be used to predict the color removal efficiency of the UV/TiO2 process.     

改性TiO2/浮石光催化去除二级出水中有机物

为了实现城市污水厂二级出水的回用,将La3+、Fe3+共掺杂TiO2/浮石光催化用于二级出水中有机物的去除。在优化工艺条件下,该方法对TOC的去除率为49.0%,对UV254的去除率为76.5%;出水BDOC/DOC值大幅度提高,由最初的0.21提高到0.56,增加了出水的可生化性;二级出水中存在着影响光催化去除有机物的因素,其中阴离子对有机物的去除有一定的抑制作用;光催化反应在通过O3强化后对有机物的去除率得到提高,TOC的去除率达到75.0%,光催化和O3氧化对有机物的去除具有协同效应;随着光催化反应次数的增加,催化剂活性有下降趋势,使用10次后TOC去除率下降到第一次使用时的16.7%,再生能够使催化活性恢复到使用前的95%,催化剂在使用15次以内稳定性较好。     

Degradation of the pharmaceutical metronidazole via UV, Fenton and photo-Fenton processes

Degradation rates and removal efficiencies of Metronidazole using UV, UV/H2O2, H2O2/Fe2+, and UV/H2O2/Fe2+ were studied in de-ionized water. The four different oxidation processes were compared for the removal kinetics of the antimicrobial pharmaceutical Metronidazole. It was found that the degradation of Metronidazole by UV and UV/H2O2 exhibited pseudo-first order reaction kinetics. By applying H2O2/Fe2+, and UV/H2O2/Fe2+ the degradation kinetics followed a second order behavior. The quantum yields for direct photolysis, measured at 254 nm and 200-400 nm, were 0.0033 and 0.0080 mol E(-1), respectively. Increasing the concentrations of hydrogen peroxide promoted the oxidation rate by UV/ H2O2. Adding more ferrous ions enhanced the oxidation rate for the H2O2/Fe2+ and UV/H2O2/Fe2+ processes. The major advantages and disadvantages of each process and the complexity of comparing the various advanced oxidation processes on an equal basis are discussed.     

臭氧光催化降解地下水中天然有机物的研究

在现场开展了中试规模的臭氧光催化降解天然有机物的研究.研究表明,对大分子天然有机物占很大比例且重碳酸盐含量较高的地下水,臭氧投加量10 mg/L和反应时间10 min条件下,TOC的去除率不到20%,但UV254和三卤甲烷生成潜力(THMFP)去除率分别达到近60%和33.5%.臭氧光催化与活性炭吸附相连,能显著提高UV254的THMFP的去除率,但TOC去除率并不明显高于单独活性炭吸附.臭氧光催化使大分子有机物转化为小分子有机物,后者在活性炭上的吸附性提高且生化性改善,可望在生物活性炭上更有效地去除.     

Temperature activated degradation (mineralization) of 4-chloro-3-methyl phenol by Fenton's reagent

With the aim to evaluate the effect of temperature, 4-chloro-3-methyl phenol (CMP) degradation by Fenton's reagent was investigated at 25 and 70 degrees C under the following initial conditions: [CMP]0 = 10 mM, [Fe2+]0 = 0.5 mM; ([H2O2]0/[CMP]0) = 80, pH0 = 3. The results indicated that CMP degradation was strongly influenced by temperature. In fact, the maximum TOC removal, achieved after ca. 24h, was by far greater at 70 degrees C (85%) than at 25 degrees C (36%). The same happened for organic chlorine (TOX) conversion into inorganic chloride, i.e. 100%, after 3 h at 70 degrees C, and 87%, after 27 h at 25 degrees C. As the recorded trends of CMP removal and chloride formation were basically the same, hydroxy substitution (ipso-substitution) was hypothesised as one likely mechanism of CMP degradation. The higher level of mineralization recorded at 70 degrees C was ascribed to: (i) a greater *OH concentration; (ii) a consequently greater extent of CMP oxidation to organic acids; (iii) a higher decarboxylation rate of such acids. An interesting consequence of such extended organic acids decarboxylation was a pH increase up to 8 that, in turn, caused, in the treated mixture, the decomposition of excess H2O2 as well as the precipitation of iron ions. These two latter outcomes are technologically important considering that usually, before discharging Fenton treated wastewater, specific polishing steps are required just to remove iron ions, decompose excess hydrogen peroxide and neutralise the pH.     

Photo-fenton assisted reaction of dimethoate in aqueous solutions

The photo-Fenton reaction of an organophosphorus insecticide, dimethoate (O,O-dimethyl methylcarbamoylmethyl phosphorodithioate), was studied by following the identification and determination of the decomposition products and the total carbon removal rate. The reactions were performed in a batch recycle reactor, at room temperature, using UV radiation, H2O2 as oxidant, and FeCl3 x 6H2O as catalyst. The oxidation results were determined with a total organic carbon (TOC) analyzer and ion chromatography. The presence of reaction products was identified by gas chromatography-mass spectrometry (GC-MS). Apart from the sulfate, phosphate, and ammonium ions, the presence of dimethyl phosphite, N-methyl-acetamide, and formic acid was also detected. Excess of H2O2 concentration did not influence the reaction rate. The expression for the total carbon removal was assessed and the TOC removal rate constants were calculated.     

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).     

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).     

A comparative study of the removal of 3-indolebutyric acid using advanced oxidation processes

In this study, advanced oxidation technologies, namely Fenton Process (FP), Fenton-Like Process (FLP), ozonation (O3) and O3/H2O2 processes, were applied to synthetic wastewater containing 3-indolebutyric acid (IBA). The effectiveness of each process was investigated at different pH values, Fe(+2), Fe(+3), O3 and H2O2 concentrations with respect to the removal efficiencies for chemical oxygen demand (COD) and total organic carbon (TOC). The best removal efficiencies were seen at pH 3 and 2 mM Fe concentration in both FP and FLP, in which the optimum H2O2 concentrations were 6 mM for FP and 10 mM for FLP. Optimum process conditions were pH 12 for the O3 process, pH 9 for the O3/H2O2 process and 1:1 O3/H2O2 molar ratio. The highest COD removal efficiency was 86 percent, obtained in the O3/H2O2 process and the highest TOC removal efficiency was obtained at 77 percent in the FP.     

Critical effect of hydrogen peroxide concentration in photochemical oxidative degradation of C.I. Acid Red 27 (AR27)

The photochemical decolorization of C.I. Acid Red 27 (AR27), an anionic monoazo dye, was studied in the UV/H2O2 process by using a batch reactor with a UV-C lamp emitting at 254 nm (30 W). The decolorization rate follows pseudo-first order kinetic with respect to the AR27 concentration. The results indicate that the apparent reaction rate constant in the UV/H2O2 process is a function of H2O2 concentration. In this work, a mathematical relation between the apparent reaction rate constant of the AR27 removal and used H2O2 was established. The applied amount of H2O2 was performed in two forms: (i) the light fraction absorbed by H2O2 in 254 nm, (ii) the initial concentration ratio of H2O2 to AR27. The results obtained from this mathematical model are in good agreement with experimental results.     

Degradation of aquatic humic material by ultraviolet light

Natural humic water was treated with ultraviolet (UV) light and UV + hydrogen peroxide (UV/H₂O₂. The effects on the dissolved organic carbon content (DOC), the UV-absorbance at 254 nm (UV-abs.), the molecular size distribution, pH, and mutagenic activity were monitored, and the identity and concentrations of the most abundant gas chromatographable organic degradation products were determined.

The DOC content and the UV-abs. of the water decreased substantially during treatment with UV/H₂O₂. The decreases were dependent on the time of irradiation (UV dose) as well as on the H₂O₂ dose applied. The humus macromolecules were degraded to smaller fragments during irradiation. At higher UV doses, however, part of the dissolved organic matter (DOM) was found to precipitate, probably as a result of polymerization. Oxalic acid, acetic acid, malonic acid, and n-butanoic acid were the most abundant degradation products detected. These acids were found to account for up to 20% and 80% of the DOM in UV- and UV/H₂O₂-treated waters, respectively. No mutagenic activity was generated by the UV irradiation or the UV/H₂O₂ treatment. It is further concluded that the substantial mutagenic activity formed during chlorination of humic waters cannot be decreased by using UV irradiation as a pretreatment step.     

土壤渗滤对有机微污染物去除性能研究

采用土壤柱试验研究了土壤渗滤对再生水中有机微污染物的去除性能。结果表明,土壤柱对再生水中的DOC、UV₂₅₄、总氮和总磷有较好的去除效果,并具有较高的抗冲击负荷的能力;土壤表层10 cm厚度对DOC的去除起主要作用;UV₂₅₄和AOX在土壤表层10 cm厚度降解效果不明显,随着深度增加去除率逐渐升高;液相色谱有机碳探测(LC-OCD)检测结果表明,土壤柱对溶解性有机物质的去除主要体现在对多糖物质的降解上,其次是有机酸类,对腐殖质也有一定的去除作用。     

Applicability of Fenton and H2O2/UV reactions in the treatment of tannery wastewaters

In this paper we evaluated the H2O2/UV and the Fenton's oxidation processes for the treatment of tannery wastewater under different experimental conditions. Efficiencies were judged by the amounts of organic substances degraded or eliminated under these treatment techniques. Daphnia magna and Vibrio fischeri were used to monitor toxicity. Organic compounds contained in the untreated and treated tannery wastewater were determined and identified using substance specific techniques. Gas chromatography-mass spectrometry (GC-MS) in positive electron impact (EI(+)) mode was applied to determine volatile organics. Atmospheric pressure ionization (API) mass (MS) and tandem mass spectrometry (MS-MS) coupled with flow injection analysis (FIA) or liquid chromatography (LC) were used to detect or identify polar organic pollutants. The experimental results indicated that both oxidation processes--H2O2/UV at pH 3 and Fenton at pH 3.5--are able to reduce TOC content by mineralisation of the organic compounds.     

Mineralization of dinitrotoluenes and trinitrotoluene of spent acid in toluene nitration process by Fenton oxidation

Fenton's reagent, UV/H2O2 and UV/Fenton's reagent were employed to mineralize dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) of spent acid in toluene nitration process. The bench-scale experiments were conducted to elucidate the influence of various operating variables on the performance of removal of total organic compounds (TOC) from spent acid, including reaction temperature, concentration of ferrous ion and H2O2 dosage. It is remarkable that organic compounds were completely mineralized by Fenton oxidation, of which removal efficiency is superior to that of UV/H2O2. Nevertheless, it makes slight difference between Fenton oxidation and UV/Fenton oxidation. According to the spectra identified by gas chromatograph/mass spectrometer (GC/MS), it is proposed that oxidative degradation of DNT isomers leads to o-, m-, p-mononitrotoluene (MNT) and 1,3-dinitrobenzene respectively. Besides, the oxidation of 2,4,6-TNT gives the 1,3,5-trinitrobenzene intermediate. Apparently, Fenton oxidation is promising for purification of spent acid industrially.     

AOX Formation and Elimination in the Oxidative Treatment of Synthetic Wastewaters in a UV-Free Surface Reactor (6 pp)

Intention, Goal, Scope, Background The effect of chloride concentration and pH on the UV oxidation systems was examined. Phenol and methanol were used as organic substances. The treatment of these chemicals by UV oxidation using a newly developed lab scale pretest UV-Free Surface Reactor (UV-FSR) with and without Cl– addition at different pH values, is evaluated. Results of this study indicated that the Cl– concentration of the water and the chemical structure of the substances is more important than the pH of the water. There was no AOX at the beginning of the experiments, but a de-novo synthesis of AOX was observed during the batch experiments. This is caused by the high chloride content of the wastewaters. It can be supposed that OHradicals oxidize some chloride-ions to form chlorine, which further reacts with organic compounds. During the treatment, these AOX compounds which are produced from the beginning of the reaction are destroyed again. Evaluations of these experiments were done according to TOC and AOX results. Approximately 80% and 99% TOC removal efficiencies were obtained for the treatment of Phenol and Methanol-containing wastewaters, respectively. Objective In the literature, there are no relevant publications concerning the AOX formation of wastewater by wet oxidation- iron catalysed or by application of UV. For that reason, the main objectives of this study were: 1. to see the influence of chloride concentration and pH on the AOXde-novo formation with newly developed UV-Free Surface Reactor (UV-FSR), 2. to make a comparison of different AOPs, 3. to observe the effect of the chloride concentration on the TOC degradation efficiency, 4. to optimise reaction conditions. Methods In synthetic wastewaters, Methanol (CH3OH) and Phenol (C6H5 OH) are used as pollutants. The concentration of each substance was 1000 mg/l and COD values were calculated theoretically. The H2O2 addition was calculated according to the COD with a convenient stoichiometric factor (e.g. 1). During experiments, the pH was always kept constant with the addition of either 25% H2SO4 or 33% NaOH depending on the experimental conditions. Each substance was treated with the addition of 1000 mg/l Cl–, 10000 mg/l Cl– and without Cl– addition at pH 3, pH 7 and pH 10, respectively. NaCl was used as a Cl– source. Adsorbable Organic Halogenides (AOX) were determined using a TOX analyser (European Standard EN 1485 H 14, 1996). TOC measurements were carried out using an Elementar High TOC Analyzer equipped with an auto sampler. The H2O2 concentration was measured according to German Standard Methods (DIN 38409, Part 15, 1987). Results and Discussion The first step was to determine the effect of pH on the AOX formation in the process. Therefore, experiments were carried out at three different pHs: acidic (pH 3), neutral (pH 7) and basic (pH 10) conditions at a constant initial Methanol concentration of 1000 mg/l and a hydrogen peroxide concentration of 3185 mg/l (1 x stoichiometric). All results were evaluated according to applied pH. At these conditions, the amount of H2O2 (53 ml / 10 l) concentration was nearly zero after 1 hour batch treatment of Methanol. There was no AOX at the beginning of the experiments, but the AOX value increased after 6–18 min. At the end of 1 hour batch treatment this produced AOX was treated again. The maximum AOX production was obtained with the addition of 10000 mg/l Cl–, whereas there is no AOX production during the experiment when Cl– was not used. In all studies, however, TOC values decreased to almost zero after 1 hour batch treatment. After the experiments with Methanol, Phenol treatment was carried out at different pHs as a second experiment. pH was kept constant with the addition of either H2SO4 or NaOH depending on the experimental conditions. During experiments with Phenol, the colour of the water changed from colourless to a yellowish- red. After 1 hour treatment, the colour of the water was red. Therefore, these experiments were continued until the water became colourless again, and this took about 5 hours. Although there was no AOX at the beginning of the experiments, it increased after 30 min to 1 hour oxidation with the addition of 1000 mg/l Cl– and 10000 mg/l Cl–. There was no AOX production during the experiments when Cl– was not added. At the end of 5 hours of treatment, formed AOX was degraded and the TOC concentration decreased from 766 mg/l to approximately 200 mg/l. Conclusion. These experiments of this study showed that the effects of Cl– concentration of the water and the chemical structure of the substances is more than that of the pH on the AOX formation. During the batch experiments, a de-novo synthesis of AOX was observed very impressively due to the high chloride content of the wastewaters. It can be implied that OH-radicals oxidize some chloride-ions to form chlorine, which further reacts with organic compounds so that AOXde-novo is formed. At the end of the reaction times these AOX compounds are also destroyed. Recommendation and Outlook It is more cost effective to use these processes for only purposes such as toxicity reduction, enhancement of biodegradability, decolourisation and removal of micropollutants. However, the most important point is the optimization of the reaction conditions for the process of concern. The AOP applied can be used, for instance, for AOX reduction and TOC removal of industrial wastewaters.