Photocatalytic degradation of lignin and lignin models, using titanium dioxide: the role of the hydroxyl radical

The role of hydroxyl radicals on the degradation of lignins during a cellulosic pulp bleaching process including a photocatalytic stage, was assessed using peroxyformic acid lignins EL1 and REL1 and two phenolic niphenyl lignin models 1 and 2. The irradiations were performed in the absence of photocatalyst TiO2 and H2O2 (condition a), in the presence of TiO2 (condition b) and in the presence of H2O2 (condition c). The experiments were conducted in alkaline (pH approximately 11) aqueous ethanol solutions with oxygen bubbling. The relative phenolic content of the irradiated solutions, which is indicative of the involvement of hydroxyl radicals, was determined by ionization absorption spectroscopy. The results obtained show that the catalyzed reaction involves both degradation of the phenolate groups by electron transfer and hydroxylation of the lignin aromatic structure. Benzyl alcohol structural elements in sodium borohydride reduced lignin REL1 and compound 2 were also found as good trapping agents for the hydroxyl radicals. The degradation of EL1 was studied by measuring its fluorescence emission by comparison to the fluorescence of compound 2. The emission spectra indicate that some biphenyl phenolate anions in EL1 are reacting under UV/visible irradiation and some others, probably polyphenolic chromophores emitting less fluorescence, are formed.     

Bioremediation of chlorobenzene-contaminated ground water in an in situ reactor mediated by hydrogen peroxide

New in situ reactive barrier technologies were tested nearby a local aquifer in Bitterfeld, Saxonia-Anhalt, Germany, which is polluted mainly by chlorobenzene (CB), in concentrations up to 450 microM. A reactor filled with original aquifer sediment was designed for the microbiological remediation of the ground water by indigenous bacterial communities. Two remediation variants were examined: (a) the degradation of CB under anoxic conditions in the presence of nitrate; (b) the degradation of CB under mixed electron acceptor conditions (oxygen+nitrate) using hydrogen peroxide as the oxygen-releasing compound. Under anoxic conditions, no definite degradation of CB was observed. Adding hydrogen peroxide (2.94 mM) and nitrate (2 mM) led to the disappearance of CB (ca. 150 microM) in the lower part of the reactor, accompanied by a strong increase of the number of cultivable aerobic CB degrading bacteria in reactor water and sediment samples, indicating that CB was degraded mainly by productive bacterial metabolism. Several aerobic CB degrading bacteria, mostly belonging to the genera Pseudomonas and Rhodococcus, were isolated from reactor water and sediments. In laboratory experiments with reactor water, oxygen was rapidly released by hydrogen peroxide, whereas biotic-induced decomposition reactions of hydrogen peroxide were almost four times faster than abiotic-induced decomposition reactions. A clear chemical degradation of CB mediated by hydrogen peroxide was not observed. CB was also completely degraded in the reactor after reducing the hydrogen peroxide concentration to 880 microM. The CB degradation completely collapsed after reducing the hydrogen peroxide concentration to 440 microM. In the following, the hydrogen peroxide concentrations were increased again (to 880 microM, 2.94 mM, and 880 microM, respectively), but the oxygen demand for CB degradation was higher than observed before, indicating a shift in the bacterial population. During the whole experiment, nitrate was uniformly reduced during the flow path in the reactor.     

Solar light induced and TiO2 assisted degradation of textile dye reactive blue 4

Aqueous solutions of reactive blue 4 textile dye are totally mineralised when irradiated with TiO2 photocatalyst. A solution containing 4 x 10(-4) M dye was completely degraded in 24 h irradiation time. The intensity of the solar light was measured using Lux meter. The results showed that the dye molecules were completely degraded to CO2, SO4(2-), NO3-, NH4+ and H2O under solar irradiation. The addition of hydrogen peroxide and potassium persulphate influenced the photodegradation efficiency. The rapidity of photodegradation of dye intermediates were observed in the presence of hydrogen peroxide than in its absence. The auxiliary chemicals such as sodium carbonate and sodium chloride substantially affected the photodegradation efficiency. High performance liquid chromatography and chemical oxygen demand were used to study the mineralisation and degradation of the dye respectively. It is concluded that solar light induced degradation of textile dye in wastewater is a viable technique for wastewater treatment.     

Wet peroxide degradation of atrazine

The high temperature (150-200 degrees C), high pressure (3.0-6.0 MPa) degradation of atrazine in aqueous solution has been studied. Under these extreme conditions atrazine steadily hydrolyses in the absence of oxidising agents. Additionally, oxygen partial pressure has been shown not to affect atrazine degradation rates. In no case mineralisation of the parent compound was observed. The addition of the free radical generator hydrogen peroxide to the reaction media significantly enhanced the depletion rate of atrazine. Moreover, partial mineralisation of the organics was observed when hydrogen peroxide was used. Again, oxygen presence did not influence the efficiency of the promoted reaction. Consecutive injections of hydrogen peroxide throughout the reaction period brought the total carbon content conversion to a maximum of 65-70% after 40 min of treatment (suggesting the total conversion of atrazine to cyanuric acid). Toxicity of the effluent measured in a luminometer decreased from 93% up to 23% of inhibition percentage. The process has been simulated by means of a semi-empirical model.     

Determination method of singlet oxygen in the atmosphere by use of α -terpinene

A chemical determination method of singlet oxygen in the atmosphere was established. The method employs a specific reaction of α -terpinene with singlet oxygen to produce the single product, ascaridole. Amberlite XAD-2 coated with α -terpinene was packed into a glass tube shielded from light and sample air was passed through the tube. Ascaridole formed was extracted with hexane from Amberlite XAD-2 and was determined by gas chromatography. The amount of singlet oxygen was calculated from that of ascaridole. Ascaridole was not formed by oxidation of α -terpinene with ozone, hydrogen peroxide and hydroxyl radical, and ascaridole formed by singlet oxygen was stable against these oxidants. The method was applied to actual polluted air and diurnal variations in the singlet oxygen were observed.     

Nutrient release from fish silage using microwave-enhanced advanced oxidation process

The microwave-enhanced advanced oxidation process was used to treat fish silage for nutrient release and solids reduction prior to its use as a fertilizer for greenhouse operations. Fifteen sets of experiments with varying hydrogen peroxide dosages and treatment temperatures were conducted to evaluate the effectiveness of the process on the solubilization of fertilizer constituents. It was found that up to 26% of total Kjeldahl nitrogen could be released as ammonia with 6% hydrogen peroxide dosage at 170°C. An increase of nitrate/nitrite concentration was observed with higher hydrogen peroxide dosage and higher microwave temperature; the highest concentration of 10.2 mg L^{? 1} nitrates/nitrites was achieved at at 170°C and 6% H₂O₂ dosage. Up to 20 ± 9.5% of total chemical oxygen demand was reduced at temperatures between 120 and 170°C. Large quantities of volatile fatty acids were generated at lower temperatures, corresponding to an increase in soluble chemical oxygen demand, but not at higher temperatures. The treatment of fish silage using the microwave-enhanced advanced oxidation process appears to be promising.     

碳纳米管电极原位产生过氧化氢及其对亚甲基蓝脱色效果简

将碳纳米管固定化制成多孔疏水性导电薄膜构建电化学阴极还原体系,实现过氧化氢在阴极的原位产生。电极特性研究表明,电极在较宽的电压范围内均具有较好的活性。考察了阴极电位、电极成分、氧气流量和电解质浓度对过氧化氢原位产生的影响,在优化条件下经过120 min后过氧化氢达到66.17 mg/L,并探讨过氧化氢原位产生的机理。在此基础上考察原位过氧化氢氧化工艺下对亚甲基蓝的脱色效果,并分析其脱色机理。     

碳纳米管电极原位产生过氧化氢及其对亚甲基蓝脱色效果

将碳纳米管固定化制成多孔疏水性导电薄膜构建电化学阴极还原体系,实现过氧化氢在阴极的原位产生。电极特性研究表明,电极在较宽的电压范围内均具有较好的活性。考察了阴极电位、电极成分、氧气流量和电解质浓度对过氧化氢原位产生的影响,在优化条件下经过120min后过氧化氢达到66．17mg／L,并探讨过氧化氢原位产生的机理。在此基础上考察原位过氧化氢氧化工艺下对亚甲基蓝的脱色效果,并分析其脱色机理。     

Treatment of two insecticides in an electrochemical Fenton system

Abstract

The ability of an electrochemical Fenton system to degrade the organophosphorous insecticides malathion and methyl parathion was studied. A combination of hydrogen peroxide and electrochemically‐generated iron was found to be successful in degrading the two insecticides, and optimization of the system was pursued. Augmentation with near UV light at an intensity of 1.67xl0¹⁷ quanta/sec and centered at a wavelength of 370 nm improved the degradation of malathion at low iron concentrations but did not affect other treatments. Adding the hydrogen peroxide slowly over the course of treatment rather than all at once at the beginning of each treatment did, however, greatly improve the system. Removal efficiencies of 98.0% or greater were achieved for both pesticides.     

Oxidative and energetic efficiency of different electrochemical oxidation processes for chloroanilines abatement in aqueous medium

The oxidative efficiency and energy consumption, in the degradation of chloroanilines by anodic oxidation, indirect oxidation with electrogenerated hydrogen peroxide and electro-Fenton have been compared, using a laboratory system driven by a LabVIEW virtual controller. Solutions were oxidized in an undivided cell, where H(2)O(2) was generated electrochemically by reduction of atmospheric oxygen bubbled at a carbon cloth cathode. The electro-Fenton process showed the best degradation power, in terms of efficiency of removal and energy consumption. This process was applied to the purification of a solution obtained by washing a polluted soil. Under laboratory conditions, electro-Fenton removed 75% COD of this wastewater with a specific energy consumption of 0.3kWh per gram of COD, corresponding to 41.8kWhm(-3).     

Hydrogen peroxide photolysis, fenton reagent and photo-fenton for the degradation of nitrophenols: a comparative study

The kinetics of the degradation of seven nitrophenols (2-nitrophenol, 4-nitrophenol, 2,5-dinitrophenol, 2,6-dinitrophenol, 2,4-dinitrophenol, 2-methyl-4,6-dinitrophenol, 4-methyl-2,6-dinitrophenol) with the Fenton reagent, photo-Fenton, and hydrogen peroxide photolysis was investigated. The efficiency and operating costs for the studied treatments were evaluated and compared. The Fenton reagent was found to be the most efficient and the cheapest way for the nitrophenols (NPs) degradation. The formation of nitrate as a result of mineralisation of organically bounded nitrogen was observed during the treatment of NPs with studied treatment processes. The degrees of organically bounded nitrogen conversion to nitrate after 90% degradation of NPs with the Fenton, photo-Fenton and hydrogen peroxide photolysis were 51-67%, 85-90%, and 50-60%, respectively. According to Daphnia magna acute toxicity test, the Fenton treatment led to complete detoxification of NPs.     

Photocatalytic degradation of imazethapyr herbicide at TiO2/H2O interface

The photocatalytic degradation of imazethapyr, a herbicide of the imidazolinone family, was investigated in an aqueous suspension of titanium dioxide used as a catalyst. A pseudo-first order kinetic model was employed to discuss the results. The effect of catalyst loading, initial concentration of imazethapyr, hydrogen peroxide, pH value, and temperature were investigated. Imazethapyr disappearance as a function of irradiation time was analyzed by HPLC. The ammonium ion formation was determined spectrophotometrically at 694 nm. The degradation was observed to proceed more favorably at natural pH (ca. 4.4) when the pH was varied in the range from 2 to 11. The addition of hydrogen peroxide to the TiO2 suspension enhanced the degradation rate constant up to 5.0x10(-3) mol l-1, but decreased it at higher concentrations. The degradation rate constants decreased by 19% with a temperature increase from 20 to 40 degrees C in the TiO2 suspension, whereas a 16% increase in imazethapyr direct photolysis was observed for the same temperature range. This behavior indicates the occurrence of physisorption between TiO2 and imazethapyr molecules.     

Photocatalytic degradation of lignin using Pt/TiO2 as the catalyst

Photocatalytic degradation of lignin was studied with the use of catalysts TiO(2) and Pt/TiO(2). The influence of several experimental parameters, i.e. pH, catalyst dosage and illumination on lignin degradation was investigated. The results showed that application of UV irradiation alone has almost no effect on the reduction of dissolved organic carbon (DOC) and American Dye Manufacture Institute value (ADMI). However, the addition of TiO(2) and Pt/TiO(2) reduced the original DOC (251 mg l(-1)) by more than 40% within 30 min of treatment and the reaction can be simulated with pseudo-first order kinetics. Rapid degradation of lignin was observed in acidic solution using either TiO(2) or Pt/TiO(2) as the catalyst compared to high pH cases. The content of Pt in the Pt/TiO(2) catalyst is 1%. In addition, too much catalyst addition has not increased the DOC and ADMI reduction proportionally. The investigation also indicated that the photocatalytic degradation rates could be enhanced 1-6 times faster after doping TiO(2) with Pt in different pH cases. A modified Nernst type model was adopted to simulate the decoloring process using TiO(2) and Pt/TiO(2) based on the profiles of oxidation reduction potential during the photocatalytic reaction. The developed equation can be used to predict the color removal efficiency of lignin wastewater by the photocatalytic process.     

Photolysis of atrazine in aqueous solution: role of process variables and reactive oxygen species

Photochemical advanced oxidation processes have been considered for the treatment of water and wastewater containing the herbicide atrazine (ATZ), a possible human carcinogen and endocrine disruptor. In this study, we investigated the effects of the photon emission rate and initial concentration on ATZ photolysis at 254 nm, an issue not usually detailed in literature. Moreover, the role of reactive oxygen species (ROS) is discussed. Photon emission rates in the range 0.87?×?10¹⁸–3.6?×?10¹⁸ photons L^?1 s^?1 and [ATZ]₀?=?5 and 20 mg L^?1 were used. The results showed more than 65 % of ATZ removal after 30 min. ATZ photolysis followed apparent first-order kinetics with k values and percent removals decreasing with increasing herbicide initial concentration. A fivefold linear increase in specific degradation rate constants with photon emission rate was observed. Also, regardless the presence of persistent degradation products, toxicity was efficiently removed after 60-min exposure to UV radiation. Experiments confirmed a noticeable contribution of singlet oxygen and radical species to atrazine degradation during photolysis. These results may help understand the behavior of atrazine in different UV-driven photochemical degradation treatment processes.     

Decolourization and removal of some organic compounds from olive mill wastewater by advanced oxidation processes and lime treatment

Background Olive mill wastewater (OMW) generated by the olive oil extracting industry is a major pollutant, because of its high organic load and phytotoxic and antibacterial phenolic compounds which resist biological degradation. Mediterranean countries are mostly affected by this serious environmental problem since they are responsible for 95% of the worldwide oliveoil production. There are many methods used for OMW treatment, such as adsorption, electro coagulation, electro-oxidation, biological degradation, advanced oxidation processes (AOPs), chemical coagulation, flocculation, filtration, lagoons of evaporation and burning systems, etc. Currently, there is no such economical and easy solution. The aim of this study was to evaluate the feasibility of decolourization and removal of phenol, lignin, TOC and TIC in OMW by UV/H₂O₂ (AOPs). The operating parameters, such as hydrogen peroxide dosage, times, pH, effect of UV and natural sunlight were determined to find the suitable operating conditions for the best removal. Moreover, there is no study reported in the literature related to the use of UV/H₂O₂ and lime together in OMW treatment. Methods OMW was obtained from an olive-oil producing plant (Muğla area of Turkey) which uses a modern production process. No chemical additives are used during olive oil production. This study was realised by using two different UV sources, while taking the time and energy consumption into consideration. These two sources were mercury lamps and natural sunlight. Before starting AOPs experiments, one litre of OMW was treated by adding lime until a pH of 7.00. Then, 100 ml was taken from each sample, and 1 to 10 ml of a 30% H₂O₂ (Riedel-deHaen) solution was added. These solutions in closed vessels were laid in the natural sunlight for a week and their compositions and colour changes were analysed daily by UV-Vis spectrophotometer. At the end of the one-week period, they were treated with lime. In this study, the effect of changes in the initial pH, times and H₂O₂ concentrations on removal was investigated. At the end of all experiments, changes in colour, phenol, lignin, TOC and TIC concentrations were analysed according to standard methods. Results and Discussion In the samples exposed to natural sunlight and having an H₂O₂/OMW ratio of 3 ml/100 ml, a significant colour removal was achieved approximately 90% of the time at the end of 7 days. When the same samples were treated with lime (pH: up to 7), 99% efficiency was achieved. When phenol and lignin removals were examined in the same concentration, phenol and lignin removal were found 99.5%, 35%, respectively. However, for maximum lignin removal, more use of H₂O₂ (10 ml H₂O₂/100 ml OMW) was found to be necessary. Under these conditions, it was found that lignin can be removed by 70%, but to 90% with lime, at the end of a seven-day period. Rate constants obtained in the experiments performed with direct UV were found to be much higher than those of the samples exposed to natural sunlight (k^a _lignin = 0.3883 ≫ k^b _lignin = 0.0078; k^a _phenol = 0.5187 ≫ k^b _phenol = 0.0146). Moreover, it should be remembered in this process that energy consumption may induce extra financial burden for organisations. Conclusions It was found, in general, that colour, lignin, total organic carbon and phenol were removed more efficiently from OMW by using H₂O₂ UV and lime OMW. Moreover, in the study, lime was found to contribute, both initially and after radical reactions, to the efficiency to a great extent. Recommendations and Perspectives Another result obtained from the study is that pre-purification carried out with hydrogen peroxide and lime may constitute an important step for further purification processes such as adsorption, membrane processes, etc.     

The importance of atmospheric ozone and hydrogen peroxide in oxidising sulphur dioxide in cloud and rainwater

The process by which sulphur dioxide is oxidised in atmospheric droplets has been studied in laboratory experiments designed to collect a large amount of chemical data pertinent to the atmospheric situation. Thus the oxidation of sodium sulphite solutions by oxygen, ozone and hydrogen peroxide has been studied at different pH's and temperatures. In all cases the reaction is first order with respect to sulphite ion but the order with respect to oxidant differs. For oxygen the order is zero whereas the order for ozone and hydrogen peroxide is one. Varying the hydrogen ion concentration has little effect on the oxygen reaction rate between pH 6 and 9; the ozone reaction rate is inversely proportional to the square root of the hydrogen ion concentration and the hydrogen peroxide rate is almost directly proportional to the hydrogen ion concentration. These last two observations are very important since in the case of ozone it indicates that the reaction proceeds via a free radical mechanism involving hydroxyl radicals and in the case of hydrogen peroxide it is the only oxidation process of sodium sulphite so far investigated that shows a positive response to the presence of hydrogen ions.The experimental data was used to calculate the rate of sulphate formation in water droplets under atmospheric conditions for each of the three oxidants. If it is assumed that the ozone and hydrogen peroxide gas phase concentrations are initially 50 parts in 10⁹ and 1 part in 10⁹ by volume respectively, then the rates of sulphate formation are equal in cloud water at pH 5.8. Above this pH the ozone reaction is faster and below it the hydrogen peroxide reaction is faster due to the positive catalysis by hydrogen ions; the oxygen rate is unimportant by comparison at all pH's below 7. The rate of hydrogen peroxide reaction is such that substantial amounts of sulphate can still be formed rapidly in water droplets at pH values from 3 to 5, and thus this process will be very important in creating acidity in rainwater.     

Environmentally acceptable effect of hydrogen peroxide on cave "lamp-flora", calcite speleothems and limestones

Mosses, algae, and cyanobacteria (lamp-flora) colonize illuminated areas in show caves. This biota is commonly removed by a sodium hypochlorite solution. Because chlorine and other deleterious compounds are released into a cave environment during lamp-flora cleansing, hydrogen peroxide was tested as an alternative agent. In a multidisciplinary study conducted in the Kateinská Cave (Moravian Karst, Czech Republic), 12 algae- and cyanobacteria taxons and 19 moss taxons were detected. The threshold hydrogen peroxide concentration for the destruction of this lamp-flora was found to be 15 vol.%. Based on laboratory experiments in stirred batch reactors, the dissolution rates of limestones and calcite speleothems in water were determined as 3.77 x 10-3 and 1.81 x 10-3 mol m-2 h-1, respectively. In the 15% peroxide solution, the limestone and speleothem dissolution rates were one order of magnitude higher, 2.00 x 10-2 and 2.21 x 10-2 mol m-2 h-1, respectively. So, the peroxide solution was recognised to attack carbonates somewhat more aggressively than karst water. In order to prevent the potential corrosion of limestone and speleothems, the reaching of preliminary peroxide saturation with respect to calcite is recommended, for example, by adding of few limestone fragments into the solution at least 10 h prior to its application.     

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.     

Kinetics of low frequency sonodegradation of linear alkylbenzene sulfonate solutions

The decomposition of sodium dodecylbenzene sulfonate (SDBS) in water by means of ultrasound irradiation at 20kHz was investigated. Experiments were conducted at surfactant concentrations of 175, 260 and 350 mg l(-1), liquid volumes of 120, 170 and 220 ml, temperatures of 20, 30 and 45 degrees C and applied power of 40, 80 and 125 W. The extent of degradation was followed monitoring substrate and organic carbon concentrations, while hydrogen peroxide concentration was also measured; the latter is a product of water sonolysis due to hydroxyl radical recombination. 80% SDBS conversion was achieved after 120 min of sonication at 125 W and 30 degrees C; nonetheless, SDBS and its degradation intermediates proved difficult to oxidise as only about 20-25% of the initial carbon content was transformed to carbon dioxide. At the initial stages of the reaction, degradation rate appears to be only weakly dependent on the substrate concentration with the rate increasing from 3.1 to 4 mg l(-1)min(-1) with increasing concentration from 175 to 350 mg l(-1). Degradation appears to occur at the bubble-liquid interface through hydroxyl radical-mediated reactions whose role was established by performing experiments in the presence of radical scavengers, namely potassium bromide and sodium benzoate. Degradation rates increased with increasing power and decreasing temperature and volume.     

Treatment of polychlorinated biphenyls in two surface soils using catalyzed H₂O₂ propagations

Two surface soils contaminated with polychlorinated biphenyls (PCBs) collected from Superfund sites in the New England region of the United States, Fletcher Paints and Merrimack Industrial Metals, were evaluated for field treatment at the bench level using catalyzed H₂O₂ propagations (CHP—modified Fenton’s reagent). The two soils were first evaluated for the potential for in situ treatment based on two criteria: (1) temperature (<40 °C after CHP reagent addition), and (2) hydrogen peroxide longevity (>24 h). In situ CHP remediation was more applicable to the Fletcher soil, while the Merrimack soil was better suited to ex situ treatment based on temperature increases and hydrogen peroxide lifetimes. Using the highest hydrogen peroxide concentrations appropriate for in situ treatment in each soil, PCB destruction was 94% in the Fletcher soil but only 48% in the Merrimack soil. However, 98% PCB destruction was achieved in the Merrimack soil using conditions more applicable to ex situ treatment (higher hydrogen peroxide concentrations with temperatures >40 °C). Analysis of degradation products by gas chromatography/mass spectroscopy showed no detectable chlorinated degradation products, suggesting that the products of PCB oxidation were rapidly dechlorinated and degraded. The results of this research document that the two PCB-contaminated soils studied can be effectively treated using aggressive CHP conditions, and that such a detailed bench study provides important information before implementing field treatment.