Treatment of oily port wastewater effluents using the ultraviolet/hydrogen peroxide photodecomposition system.

This paper presents the nonselective degradation of mechanically pretreated oily wastewater by hydrogen peroxide (H2O2) in the presence and absence of UV irradiation. The effect of chemical oxidation on wastewater biodegradability was also examined. The exclusive use of H2O2 photolyzed by daylight results in quite efficient degradation rates for the low peroxide concentrations used. Higher hydrogen peroxide concentrations inhibit degradation of organic contaminants in the wastewater. The degradation rates of all contaminants are relatively high with an advanced oxidation system (UV/H2O2), but degradation efficiencies are not distinguishably different when 20 or 45 minutes of UV irradiation is used. The excess of H2O2 used in the process can inhibit phenolic degradation and may lead to the formation of a new phenolic fraction. The biodegradability of port wastewater did not increase significantly following the application of the advanced oxidation process.     

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.     

Pre-oxidation and coagulation of textile wastewater by the Fenton process

This paper evaluates the Fenton process, involving oxidation and coagulation, for the removal of color and chemical oxygen demand (COD) from synthetic textile wastewater containing polyvinyl alcohol and a reactive dyestuff, R94H. The experimental variables studied include dosages of iron salts and hydrogen peroxide, oxidation time, mixing speed and organic content. The results show that color was removed mainly by Fenton oxidation. The color removal reached a maximum of 90% at a reaction time of 5 min under low dosages of H2O2 and Fe2+. In contrast, the COD was removed primarily by Fenton coagulation, rather than by Fenton oxidation. The ratio of removal efficiency between Fenton process and ferric coagulation was 5.6 for color removal and 1.2 for COD removal. It is concluded that Fenton process for the treatment of textile wastewater favors the removal of color rather than COD.     

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.     

Atrazine removal by ozonation processes in surface waters

Atrazine (6-chloro-N-ethyl-N'-isopropyl-1,3,5-triazinedyl-2,4-diamine) was treated with ozone alone and in combination with hydrogen peroxide or UV radiation in three surface waters. Experiments were carried out in two bubble reactors operated continuously. Variables investigated were the ozone partial pressure, temperature, pH, mass flow ratio of oxidants fed: hydrogen peroxide and ozone and the type of oxidation including UV radiation alone. Residence time for the aqueous phase was kept at 10 min. Concentrations of some intermediates, including deethylatrazine, deisopropylatrazine and deethyldeisopropylatrazine, were also followed. The nature of water, specifically the alkalinity and pH were found to be important variables that affected atrazine (ATZ) removal. Surface waters with low alkalinity and high pH allowed the highest removal of ATZ to be reached. There was an optimum hydrogen peroxide to ozone mass flow ratio that resulted in the highest ATZ removal in each surface water treated. This optimum was above the theoretical stoichiometry of the process. Therefore, to reach the maximum removal of ATZ in a O3/H2O2 process, more hydrogen peroxide was needed in the surface waters treated than in ultrapure water under similar experimental conditions. In some cases, UV radiation alone resulted in the removal of ATZ higher than ozonation alone. This was likely due to the alkalinity of the surface water. Ozonation and UV radiation processes yield different amounts of hydrogen peroxide. Combined ozonations (O3/H2O2 and O3/UV) lead to ATZ removals higher than single ozonation or UV radiation but the formation of intermediates was higher.     

Novel imazethapyr detoxification applying advanced oxidation processes

Different degradation methods have been applied to assess the suitability of advanced oxidation process (AOPs) to promote mineralization of imazethapyr [(RS)-5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid], a widely used imidazolinone class herbicide, the persistence of which has been demonstrated in surface and ground waters destined to human uses. Independent of the oxidation process assessed, the decomposition of imazethapyr always followed a pseudo-first order kinetic. The direct UV-irradiation (UV) of the herbicide as well as its oxidation with ozone (O?), and hydrogen peroxide tied to UV-irradiation (H?O?/UV) were sufficiently slow to permit the identification of intermediate products, the formation pathway of which has been proposed. Ozonation joined to UV-irradiation (O?/UV), ozonation joined to titanium dioxide photo-catalysis (TiO?/UV+O?), sole photo-catalysis (TiO?/UV), and photo-catalysis reinforced with hydrogen peroxide-oxidation (TiO?/UV+H?O?) were characterized by a faster degradation and rapid formation of a lot of small molecules, which were quickly degraded to complete mineralization. The most effective oxidation methods were those using titanium dioxide photo-catalysis enhanced either by ozonation or hydrogen peroxide. Most of all, these last processes were useful to avoid the development of dangerous by-products.     

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.     

用H2O2/Fe^3＋处理高浓度含甲醛废水的研究

研究采用H2O2/Fe^3＋催化氧化处理高浓度含甲醛废水,探讨了双氧水和催化剂投加量、反应pH及反应温度等操作条件对处理效果的影响,并通过酸溶解回用失活催化剂。结果表明,较优的操作条件为：H2O2/COD（质量比）=2.2～2.6,Fe^3＋/H2O2（摩尔比）=0.048～0.058,反应pH1.80～2.68,反应温度50℃,反应时间40 min;在上述操作条件下,甲醛去除率达到99%以上,COD去除率达到85%以上。失活的催化剂可通过稀酸溶解后循环使用,其效果与三价铁盐作催化剂的基本相同。采用H2O2/Fe^3＋处理含甲醛废水具有比采用H2O2/Fe^2＋较优的效果。     

UV/Fenton技术处理某工厂高浓度乳化油废水

研究了UV/Fenton技术对高浓度金属清洗乳化油废水的处理效果,考察了亚铁与双氧水浓度、pH、反应时间和搅拌对COD去除效果的影响。实验结果表明,UV/Fenton技术对高浓度乳化油废水(COD平均浓度为35 000 mg/L)具有较高的去除效果,最佳工艺条件为:亚铁与双氧水浓度分别为2 400 mg/L和6 000 mg/L,pH为3,经过2 h反应,COD可降低至1 050 mg/L,去除率为97%。搅拌会降低COD的去除率。研究表明,UV/Fenton技术对高浓度乳化油废水具有很好的降解效果,且药品消耗较低,为目前此类高浓度有机废水的处理提供了技术参考。     

Oxidation of diethylene glycol with ozone and modified Fenton processes

This paper describes a study of oxidation of diethylene glycol (DEG) by ozone and modified Fenton process (hydrogen peroxide and ferric salt mixture) in aqueous solution. Both oxidation processes were able to oxidize relatively high concentrations of DEG effectively. DEG reacted primarily through hydroxyl radical produced by decomposition of ozone, and about 3 mol of ozone were consumed per mole of DEG removed during the process. For modified Fenton oxidation, stepwise addition of hydrogen peroxide (H2O2) and ferric salt (Fe(III)) resulted in much higher removal of DEG than one-time pulse addition of the chemicals. The extent of DEG removal increased with increasing concentrations of both H2O2 and Fe(III). Oxidant consumption per mole of DEG oxidized was one order of magnitude higher for hydrogen peroxide than those observed for ozone. Overall, ozonation produced higher concentrations of aldehydes, and modified Fenton treatment produced higher concentrations of carboxylic acids for the same levels of DEG oxidation. The major products of ozonation were glycolaldehyde, glyoxal, formaldehyde, acetaldehyde, and acetic, formic, pyruvic, oxalic and glyoxalic acids. The major products of modified Fenton oxidation were formaldehyde, and formic and acetic acids.     

Modeling the quantum yields of herbicide 2,4-D decay in UV/H2O2 process

The photodecay of herbicide 2,4-D in a hydrogen peroxide-aided photolysis process was studied and modeled. The decay rate of 2,4-D was known to be low in the natural environment, but rate improvement was achieved in an H2O2/UV system. The 2,4-D decay quantum yields under ultraviolet (UV) light at 253.7 nm increased from 4.86 x 10(-6) to 1.30 x 10(-4) as the ratio of [H2O2]/[2,4-D] increased from 0.05 to 12.5. Apparently, in the presence of UV light, the decay rate of 2,4-D could be greatly improved as the concentration of hydrogen peroxide increased. However, the efficiency of 2,4-D photodecay was retarded if the concentration of H2O2 was overdosed, because the excess hydrogen peroxide consumes the hydroxyl radicals (HO*) in the solution, resulting in a much weaker oxidant HO2*. The decay of 2,4-D was also pH dependent. A ranking of acid (highest), base (middle) and neutral (lowest) was observed owing to the property change of reactants and the shifting of dominant mechanisms among photolysis, photohydrolysis and chemical oxidation. Two mathematical models were proposed to predict the quantum yield for various [H2O2]/[2,4-D] ratios and initial pH levels, in which very good correlation was found for the ranges of regular application.     

Photochemical degradation and mineralization of 4-chlorophenol

INTENTION, GOAL, SCOPE, BACKGROUND: Since the intermediate products of some compounds can be more toxic and/or refractory than the original compund itself, the development of innovative oxidation technologies which are capable of transforming such compounds into harmless end products, is gaining more importance every day. Advanced oxidation processes are one of these technologies. However, it is necessary to optimize the reaction conditions for these technologies in order to be cost-effective. OBJECTIVE: The main objectives of this study were to see if complete mineralization of 4-chlorophenol with AOPs was possible using low pressure mercury vapour lamps, to make a comparison of different AOPs, to observe the effect of the existence of other ions on degradation efficiency and to optimize reaction conditions. METHODS: In this study, photochemical advanced oxidation processes (AOPs) utilizing the combinations of UV, UV/H2O2 and UV/H2O2/Fe2+ (photo-Fenton process) were investigated in labscale experiments for the degradation and mineralization of 4-chlorophenol. Evaluations were based on the reduction of 4-chlorophenol and total organic carbon. The major parameters investigated were the initial 4-chlorophenol concentration, pH, hydrogen peroxide and iron doses and the effect of the presence of radical scavengers. RESULTS AND DISCUSSION: It was observed that the 4-chlorophenol degradation efficiency decreased with increasing concentration and was independent of the initial solution pH in the UV process. 4-chlorophenol oxidation efficiency for an initial concentration of 100 mgl(-1) was around 89% after 300 min of irradiation in the UV process and no mineralization was achieved. The efficiency increased to > 99% with the UV/H2O2 process in 60 min of irradiation, although mineralization efficiency was still around 75% after 300 min of reaction time. Although the H2O2/4-CP molar ratio was kept constant, increasing initial 4-chlorophenol concentration decreased the treatment efficiency. It was observed that basic pHs were favourable in the UV/H2O2 process. The results showed that the photo-Fenton process was the most effective treatment process under acidic conditions. Complete disappearance of 100 mgl(-1) of 4-chlorophenol was achieved in 2.5 min and almost complete mineralization (96%) was also possible after only 45 min of irradiation. The efficiency was negatively affected from H2O2 in the UV/H2O2 process and Fe2+ in the photo-Fenton process over a certain concentration. The highest negative effect was observed with solutions containing PO4 triple ions. Required reaction times for complete disappearance of 100 mgl(-1) 4-chlorophenol increased from 2.5 min for an ion-free solution to 30 min for solutions containing 100 mgl(-1) PO4 triple ion and from 45 min to more than 240 min for complete mineralization. The photodegradation of 4-chlorophenol was found to follow the first-order law. CONCLUSION: The results of this study showed that UV irradiation alone can degrade 4-CP, although at very slow rates, but cannot mineralize the compound. The addition of hydrogen peroxide to the system, the so-called UV/H2O2 process, significantly enhances the 4-CP degradation rate, but still requires relatively long reaction periods for complete mineralization. The photo-Fenton process, the combination of homogeneous systems of UV/H2O2/Fe2+ compounds, produces the highest photochemical elimination rate of 4-CP and complete mineralization is possible to achieve in quite shorter reaction periods when compared with the UV/H2O2 process. RECOMMENDATIONS AND OUTLOOK: It is more cost effective to use these processes for only purposes such as toxicity reduction, enhancement of biodegradability, decolorization and micropollutant removal. However the most important point is the optimization of the reaction conditions for the process of concern. In such a case, AOPs can be used in combination with a biological treatment systems as a pre- or post treatment unit providing the cheapest treatment option. The AOP applied, for instance, can be used for toxicity reduction and the biological unit for chemical oxygen demand (COD) removal.     

Photochemical degradation of 1,3-dinitrobenzene in aqueous solution in the presence of hydrogen peroxide

A study on the destruction of 1,3-dinitrobenzene (1,3-DNB) in aqueous solution was carried out under ultraviolet (UV) irradiation alone and UV irradiation in the presence of hydrogen peroxide (H2O2). The combination of UV and H2O2 is significantly effective in degrading 1,3-DNB in terms of initial reaction rate and the mineralization of organic carbons. The photodegradation process can be influenced in certain extent by increasing the content of H2O2 and the acidity of reaction matrices. It was found that a variety of phenolic intermediates and inorganic acid were formed via hydroxyl radicals attacking the parent compound. The UV/H2O2 oxidation of 1,3-DNB was characterized by pseudo-zero order reaction for the degradation of 1,3-DNB with a 20 times enhanced rate constant of 1.36 x 10(-7) Ms(-1) and the initial rate constant was dependent on the initial concentration of 1,3-DNB.     

Partitioning of hydrogen peroxide between the gas and liquid phases in the presence of surfactant

Gas-liquid phase partitioning is a key physical property that can predict the environmental fate of a compound between two phases. Several environmental factors have been known to affect the gas-liquid phase partitioning. We investigated the influence of surfactant on the gas-liquid phase partitioning of hydrogen peroxide (H(2)O(2)). The surfactant used was ammonium perfluorooctanoate (APFO). H(2)O(2) solution containing the surfactant was equilibrated in a closed system and gas phase H(2)O(2) concentration was measured by the peroxyoxalate chemiluminescence (PO-CL) method. Gas phase H(2)O(2) concentrations remained constant below the critical micelle concentration (CMC) and increased linearly with surfactant concentration above the CMC, which indicated that surfactant micelles influenced the gas-liquid phase partitioning of H(2)O(2). This result showed that H(2)O(2)-micelle interactions are less favorable than H(2)O(2)-H(2)O interactions. Surfactant monomers did not affect the gas-liquid phase partitioning of H(2)O(2) due to the absence of micelles. Solvent (methanol) effect was also investigated and showed that gas phase H(2)O(2) concentrations increased with the addition of solvent. This indicated the unfavorable interaction of H(2)O(2) with hydrophobic medium compared to hydrophilic one. It is consistent with the result that H(2)O(2)-micelles has a weaker interaction than H(2)O(2)-water because surfactant micelles are hydrocarbon-like organic phase rather than aqueous phase.     

Hydrogen peroxide mediated photodegradation of phenol as studied by a flash photolysis/HPLC technique

The technique of flash photolysis followed by high-performance liquid chromatography has been applied to the study of the photodegradation of phenol (I) in the presence of hydrogen peroxide. Progress of the reaction of I (0.1 mM) in undegassed aqueous solution ([H2O2]/[I] = 200/l) was observed by using multiple flashes (16 J). Analysis after a single flash indicated that catechol and hydroquinone were the primary products of the reaction. The reaction was found to be independent of pH in the range 7.0-9.0, but the yield of degradation decreased at pH > 9.0 and at pH < 7.0. The effects of the hydrogen peroxide concentration and flash energy on the chemical yield of the pollutant degradation, and product formation, were investigated as well. The mechanism of the reaction is discussed. A possibility of the application of flashlamps as powerful sources of the UV irradiation in industrial reactors for wastewater treatment is suggested.     

Destruction of organic pollutants in reusable wastewater using advanced oxidation technology

This work studied the destruction of various M-EDTA complexes and trace organic pollutants in treated reusable wastewater under advanced oxidation using UV irradiation and ozonation. Effect of dosage of hydrogen peroxide and acidity of reaction matrices on oxidation efficiencies were investigated. The rate constant of mineralization presents a decreasing trend as Fe(III)-EDTA > Fe(II)-EDTA > Al(III)-EDTA > Pb(II)-EDTA > Na(I)-EDTA > Zn(II)-EDTA > Cu(II)-EDTA. The mineralization efficiencies using ozone alone are 15%, 40% and 15% for the water samples after reverse osmosis (RO), microfiltration (MF) and superfiltration (SF) processes, respectively. The presence of hydrogen peroxide in photochemical reaction matrixes can effectively enhance the mineralization of organic carbon species. When 150 mg l(-1) of H2O2 was added in the effluents, the mineralization markedly increased to 80%, 92% and 89%, respectively.     

Photooxidative removal of the herbicide Acid Blue 9 in the presence of hydrogen peroxide: modeling of the reaction for evaluation of electrical energy per order (E EO)

The present work deals with photooxidative removal of the herbicide, Acid Blue 9 (AB9), in water in the presence of hydrogen peroxide (H2O2) under UV light illumination (30 W). The influence of the basic operational parameters such as amount of H2O2, irradiation time and initial concentration of AB9 on the photodegradation efficiency of the herbicide was investigated. The degradation rate of AB9 was not appreciably high when the photolysis was carried out in the absence of H2O2 and it was negligible in the absence of UV light. The photooxidative removal of the herbicide was found to follow pseudo-first-order kinetic, and hence the figure-of-merit electrical energy per order (E Eo) was considered appropriate for estimating the electrical energy efficiency. A mathematical relation between the apparent reaction rate constant and H2O2 used was applied for prediction of the electricity consumption in the photooxidative removal of AB9. The results indicated that this kinetic model, based on the initial rates of degradation, provided good prediction of the E Eo values for a variety of conditions. The results also indicated that the UV/H2O2 process was appropriate as the effective treatment method for removal of AB9 from the contaminated wastewater.     

Decolorization of mono-azo dyes in wastewater by advanced oxidation process: A case study of acid red 1 and acid yellow 23

Advanced Oxidation Processes (AOPs) have been used as emerging wastewater treatment technologies which can effectively handle various hazardous organics in wastewater and groundwater. The photooxidation of two non-biodegradable azo dyes, acid red 1 and acid yellow 23, were studied in an UV/hydrogen peroxide photochemical reactor with a 5 kW low pressure mercury lamp. It was observed that the decomposition of both azo dyes were pseudo-first order reactions with respect to the azo dye concentrations. Simultaneously, the effects of hydrogen peroxide dosage, pH, initial concentration of the azo dyes and intensity of UV light were also studied. Moreover, the time required for the 50% removal of azo dyes and observed pseudo-first order rate constants were used as parameters to show the efficiency of azo dye treatment.     

Degradation of 4-chlorophenol by microwave irradiation enhanced advanced oxidation processes

In this work the synergistic effects of several microwave assisted advanced oxidation processes (MW/AOPs) were studied for the degradation of 4-chlorophenol (4-CP). The efficiencies of the degradation of 4-CP in dilute aqueous solution for a variety of AOPs with or without MW irradiation were compared. The results showed that the synergistic effects between MW and H2O2, UV/H2O2, TiO2 photocatalytic oxidation (PCO) resulted in a high degradation efficiency for 4-CP. The potential of MW/AOPs for treatment of industrial wastewater is discussed.     

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.