Oxidation of aromatic substrates in water/goethite slurry by means of hydrogen peroxide

The oxidation of aromatic derivatives in aqueous goethite slurry at varying catalyst load and hydrogen peroxide concentration is investigated. For adopted experimental conditions only the compounds containing two adjacent -OH groups or one -OH and one -NH2 groups are oxidized. A model previously developed for the oxidation of 3,4-dihydroxybenzoic acid has been satisfactorily used to describe the oxidation of 1,2-benzenediol (catechol), 2-aminophenol and 2,3-dihydroxybenzoic acid.     

Photocatalytic promoted oxidation of phenolic mixtures: an insight into the operating and mechanistic aspects

The photocatalytic oxidation of a phenolic mixture (gallic acid, tyrosol and syringic acid) has been carried out in the presence of titanium dioxide and a selected inorganic peroxide, namely persulphate, monopersulphate or hydrogen peroxide. The results obtained in UVA irradiated solutions reveal that hydrogen peroxide is the most effective option. The influence of some relevant operating parameters (i.e. initial concentration of phenols, hydrogen peroxide or titanium dioxide) has been investigated. In all cases a saturation-like behaviour has been observed. Thus, an increase in oxidation efficiency is observed when raising, up to a certain value, the initial amounts of reagents/catalyst added to the reactor. Nevertheless, a further increase of any of the previous parameters does not lead to the expected enhancement of the process. From the concave shape of the parent compounds’ depletion profiles, it is suggested that the system proceeds through an autocatalytic route, likely involving the action of organic radicals. A pseudoempirical model has been used to acceptably model the experimental data obtained.     

Treatment of trichlorophenol by catalytic oxidation process

The oxidation of 2,4,6-trichlorophenol (TCP) by ferrous-catalyzed hydrogen peroxide was quantified and modeled in the study. TCP was effectively degraded by hydroxyl radicals that were generated by Fe(II)/H(2)O(2) in the oxidation process. The oxidation capacity (OC) of the process depends on the concentrations of oxidant (hydrogen peroxide) and oxidative catalyst (ferrous ion). Up to 99.6% of TCP removal can be achieved in the process, provided the doses of Fe(II) and H(2)O(2) are selected correctly. The OC of the process was successfully predicted through a kinetic approach in a two-stage model with some simple and measurable parameters, which makes the model useful for predicting, controlling and optimizing the catalyzed oxidation process in the degradation of TCP.     

Application of ferrous hydrogen peroxide for treatment of DSD-acid manufacturing process wastewater

A pretreatment method for the biological treatment of wastewater from 4,4'-diaminostilbene-2,2'-disulfonic acid (DSD-acid) manufacturing processes, a refractory dye intermediate wastewater, based on combined ferrous hydrogen peroxide oxidation and coagulation-flocculation, was developed. When the wastewater was treated with ferrous hydrogen peroxide oxidation ([Fe2+] = 2.7 mmol/L, [H2O2] = 0.21 mol/L) after a flocculation using an organic flocculant TS-1 at a dosage of 3 g/L, the overall COD and color removals were 64 and 62%, respectively. BOD5/COD value of the effluent was 0.3. Ferrous hydrogen peroxide oxidation treatment can reduce the solubility of organic molecules with sulfonic group and increase the efficiency of coagulation treatment. The COD and color removals were both more than 90% when FeCl3 was used as the coagulation (dosages of two-step coagulation were 0.031 and 0.012 mol/L respectively) after a ferrous hydrogen peroxide oxidation pretreatment at a H2O2 dosage of 0.06 mol/L.     

A NOVEL CATALYTIC SYSTEM FOR THE OXIDATIVE DESTRUCTION OF TOXIC ORGANIC COMPOUNDS IN INDUSTRIAL WASTEWATERS

This work describes a novel heterogeneous oxidation catalyst which is analogous to the homogeneous-phase Fentons reagent for the successful destruction of a range of organic pollutants. The catalyst is a polyacrylonitrile fibre which was modified to incorporate ligatinggroups, resulting in a transition metal cation being firmly fixed onto the fibre. The novelty of the catalyst resides in its open-knit mesh structure. In the presence of hydrogen peroxide, the catalyst containing ferric ions (as the active site) is shown to rapidly decompose phenol in addition to (a) the anthraquinone dyes: acid blue 45, carminic acid and reactive blue 19, and (b) the azo-dye drimarine red K. B. The decomposition reaction was followed by ultraviolet spectroscopy, and the distribution of ferric ions on the external surface of the fibre was examined by a scanning electron microscope. The mechanical properties of the fibre were found to have decreased on modification but were still sufficient for the manufacture and commercial exploitation of the fibre.     

Solar photocatalytic thin film cascade reactor for treatment of benzoic acid containing wastewater

A solar photocatalytic cascade reactor was constructed to study the photocatalytic oxidation of benzoic acid in water under various experimental and weather conditions at HKUST. Nine stainless steel plates coated with TiO(2) catalyst were arranged in a cascade configuration in the reactor. Photolytic degradation and adsorption were confirmed to be insignificant total organic carbon (TOC) removal mechanisms. A turbulent flow pattern and, hence, improved mixing in the liquid film were achieved due to the unique cascade design of the reactor. The photoinduced consumption of oxygen during reactions was demonstrated in a sample experiment. The proposed rate equations provided good fits to 90 data points from 17 experiments. The regression results showed that the TOC removal rates averaged over 30 min intervals did not illustrate significant dependence on TOC(0) and that I(mean) was more important in affecting the photocatalytic process within the ranges of the data examined. The percentage removal of TOC in 7 l of 100 mg/l (or 100 ppm) benzoic acid solutions increased from 30% to 83% by adding 10 ml of hydrogen peroxide solution (30 wt%). Hydrogen peroxide was also shown to enhance the efficiency of the degradation process at elevated temperatures. Ortho-, meta- and para-hydroxybenzoic acids were identified by HPLC analysis as the intermediates of benzoic acid during reactions without the addition of hydrogen peroxide solutions.     

The role of hydroxyl radicals for the decomposition of p-hydroxy phenylacetic acid in aqueous solutions

The chemical decomposition of p-hydroxyphenylacetic acid, a priority phenolic pollutant present in wastewaters from some agro-industrial plants, is studied by means of a single photochemical process produced by a polychromatic UV radiation and by hydroxyl radicals generated by the combination of UV radiation plus hydrogen peroxide and by the Fenton's reagent (hydrogen peroxide plus ferrous salts). Batch experiments were conducted to establish the degradation levels obtained and the quantum yields in the single photodecomposition process. An improvement in the decomposition of the phenolic acid in the combined UV/H2O2 oxidation is observed, due to the generation of OH radicals, and the contribution of the radical reaction to the global process is determined. In the Fenton's reagent oxidation, the effects of the operating variables (H2O2 and Fe2+ initial concentrations, pH, type of buffer used) are established and the rate constant for the reaction of p-hydroxyphenylacetic acid with OH radicals is evaluated from a kinetic model, its value being 7.02 x 10(8) M-1 s-1 at 20 degrees C.     

Assessment of photo-Fenton and biological treatment coupling for Diuron and Linuron removal from water

The coupling of photo-Fenton (chemical) and biological treatments has been used for the removal of Diuron and Linuron herbicides from water. The chemical reaction was employed as a pre-treatment step for the conversion of the toxic and non-biodegradable herbicides into biodegradable intermediates that were subsequently removed by means of a biological sequencing batch reactor (SBR). Multivariate experimental design was used to select four photo-Fenton reagent dose combinations for the coupling experiments. Concentrations of hydrogen peroxide between 10 and 250 mg L(-1), and iron (II) concentrations between 2 and 20 mg L(-1) have been tested. 15.9 mg L(-1) of Fe(II) and 202 mg L(-1) of H(2)O(2) were needed to convert initial toxic and non-biodegradable herbicides into suitable intermediates for a subsequent biological treatment. Detrimental effects due to the excess of reactants were detected. Chemical oxygen demand (COD), average oxidation state (AOS), total organic carbon (TOC) and hydrogen peroxide concentration are the parameters used to trace the experiments course. Also, toxicity (EC(50)(15)) and biodegradability (BOD(5)/COD) tests were carried out at the end of each chemical oxidation. Complete disappearance of the herbicides from water was observed after the chemical treatment, while 3,4-dichloroaniline and 3,4-dichlorophenyl isocyanate were identified as the main by-products of the degradation process. Complete TOC removal was achieved after biological treatment in a SBR using a hydraulic retention time (HRT) of 2 days.     

Measurement of hydrogen peroxide in an advanced oxidation process using an automated biosensor

A hydrogen peroxide biosensor was used to monitor hydrogen peroxide concentrations in a UV/hydrogen peroxide immobilised Fenton advanced oxidation process (AOP). The biosensor is based on gas phase monitoring and thus is more resistant to fouling from the liquid phase constituents of industrial processes. The biosensor is supplied with catalase continually, therefore overcoming any problems with enzyme degradation, which would occur in an immobilised enzyme biosensor. The biosensors response was linear within the experimental range 30-400mg H(2)O(2)l(-1) with a R(2) correlation of 0.99. The hydrogen peroxide monitor was used to monitor residual peroxide in an AOP, operated with a step overload of hydrogen peroxide, with correlation factors of 0.96-0.99 compared to offline hydrogen peroxide determinations by UV spectroscopy. Sparging the sample with nitrogen was found to be effective in reducing the interference from dissolved gases produced with the AOP itself. It is proposed that this biosensor could be used to improve the effectiveness of AOPs via hydrogen peroxide control.     

Catalytic wet peroxide oxidation of phenol over Fe-exchanged pillared beidellite

This study presents an evaluation of the catalytic performances of a Fe-exchanged Al-pillared synthetic beidellite for the wet hydrogen peroxide oxidation of phenolic aqueous wastes. The catalyst was prepared by a cation doping technique, its properties being determined by DRX, BET and chemical analysis techniques. All the tests were performed on a laboratory scale set-up.Important factors affecting catalyst activity and phenol removal efficiencies were studied, i.e. the effect of pH, temperature, catalyst concentration and the stability of the catalyst. The experimental results indicate that the use of this catalyst allows a total elimination of phenol and a significant removal of chemical oxygen demand, without significant leaching of Fe ions. Thus, considering the lowest Fe concentrations in solution after oxidation, at pH=5, 50 degrees C, and 180 min. COD removal efficiency of 87.9% was obtained. It was also observed that by using this catalyst, it is possible to extend the range of pH values for which Fenton-type oxidations can occur.     

Oxydation catalytique des phenols par le peroxyde d'hydrogene: Etude structurale des catalyseurs Fe/Al2O3 et Fe-Cu/Al2O3 par spectroscopie Mossbauer

This study recalls the results obtained on the oxidation by hydrogen peroxide of a number of hydroxyl aromatic compounds with alumina supported catalysts and more particularly the structural study of these catalysts. The catalysts were prepared under different conditions: without thermic treatment, by oxidation in air at 450°C and by thermic reduction at 500 and 700°C, under hydrogen flow. The structural study by Mössbauer spectroscopy of the catalysts Fe/Al₂O₃ and Fe-Cu/Al₂O₃ made it possible to specify in what form was found the iron, as a function of the conditions under which the catalysts were prepared. For the catalyst prepared by impregnation without thermic treatment the iron on the support was in hematite form (α-Fe₂O₃) well crystallized in small particles with 10–20% iron which could be ferric ions (Fe³⁺) chemically adsorbed on alumina or iron within the structure of the alumina (Figs 7 and 8). Thermic oxidation in air brought about the appearance of hematite in the form of large particles (Fig. 9) whereas the thermic reduction under hydrogen flow led to the formation of crystallized metallic iron (α-Fe) (Fig. 12). The reducibility of iron on the support increased with the increase in temperature of reduction and with the presence of copper (Figs 11 and 13). As for the activity of the different catalysts in oxidation reactions of phenols by hydrogen peroxide, we notice that whatever the form of the catalyst, the activity was more important for pyrocatechol than for phenol (Fig. 3). As far as stability of the metals on the support was concerned, during the oxidation reaction we noticed that it was greater with an oxidized catalyst than with a reduced one (Figs 4 and 5). The comparison between the results obtained in a batch and in a continuous reactor made it possible to show that the first phase of the reaction was probably due to the superposition of the phenomena of homogeneous (by the Fe ions passed into solution) and heterogeneous catalysts (Fig. 6). The comparative structural study reduced before and after use was quite in agreement with the solubilization of iron that we observed during oxidation (Figs 15 and 13). However on the oxidized catalyst hematite was not modified after use and the most significant change on the spectrum was a slight decrease of E_Q (0.1 mm s^?1) in the central doublet (Figs 14 and 9).     

Degradation of protocatechuic acid by two advanced oxidation processes: Ozone/UV radiation and H2O2UV radiation

Two advanced oxidation processes: the combinations of ozone and UV radiation, and hydrogen peroxide and UV radiation, have been used in the chemical degradation of protocatechuic acid, a phenolic pollutant present in the wastewaters from olive oil manufacturing. In the first case, the kinetic study is carried out by taking into account the contributions of the single ozonation and the photochemical reaction and applying the film theory model. The apparent kinetic constants and reaction orders for the combined reaction are deduced and correlated as a function of pH and temperature. In the second case, an empirical reaction rate expression which considers the contribution of both oxidants, UV radiation and hydrogen peroxide, is proposed. The kinetic rate constants for this combined reaction are also obtained and correlated as a function of temperature and pH.     

Pharmaceutical wastewater degradation: effective and economical treatment using waste-metallic iron shavings

Industrial wastewater generated by a drug manufacturing plant located in Spain was degraded by Fenton oxidation processes, which employ waste-metallic iron shavings as heterogeneous zero-valent iron (ZVI) catalyst and hydrogen peroxide. The effluent comprises a complex mixture of organic substances which are very refractory to common conventional treatments and it is characterized by a low BOD/COD ratio. The stirring speed or the particle size has been found to be the determining factors, greatly influencing the degradation of the organic pollutants present in the wastewater. The influence of the initial hydrogen peroxide concentration has also been evaluated. The optimal conditions for degradation led to total organic carbon (TOC) reductions of up to 60%. The remarkable results of TOC mineralization could also be attributed to the physico-chemical modification of the ZVI during the oxidizing process. This study shows that the ZVI/H₂O₂ system can be considered as an easy, economic and effective alternative solution as a pre-treatment step before biological treatments.     

Enhancement of mercury(II) sorption from water by coal through chemical pretreatment

Enhancement of mercury(II) sorption from water by bituminous coal through chemical pretreatment was explored in the laboratory using batch sorption tests and downflow column studies. Both intensity of sorption and equilibrium sorptive capacity were enhanced significantly following nitric acid and hydrogen peroxide oxidation. Sulfurization and manganese oxide impregnation also showed promise. The chemically pretreated coal sorbents exhibited mercury sorption to a level higher than that accomplished using active carbon. Nitric acid or hydrogen peroxide oxidized or sulfurized coal may well replace active carbon in polishing mercury-laden waste following sulfide precipitation or removing mercury during municipal water treatment.     

Application of ferrous-hydrogen peroxide for the treatment of H-acid manufacturing process wastewater

1-Amino-8-naphthol-3,6-disulfonic acid (H-acid) is widely used in chemical industries for synthesis of direct, acid, reactive and azoic dye. The wastewater from H-acid manufacturing process is rich in various substituted derivatives of naphthalene and is one of the most hardly-treated wastewaters. A pretreatment method, ferrous ion-peroxide oxidation combined with coagulation, has been studied. The results have shown that the optimum pH value is below 4 and the suitable ferrous ion dosage is 200 mg/l. The COD removal of H-acid wastewater is about 50% and the residue have proved biodegradable when hydrogen peroxide dosage is 30 g/l. Ferrous ion-peroxide oxidation process can also improve efficiency of coagulation treatment. The overall COD removal can reach 90% or more when the concentration of ferrous ion is 200 mg/l, the dosage of hydrogen peroxide is 3 g/l and the ferric chloride dosage of two stage coagulation treatment is 15 g/l and 5 g/l, respectively. The groups on naphthalene ring, such as − + NO₂, SO⁻₃ etc., are substituted by hydroxyl free radical, and then the ring is broken down during oxidation process of H-acid.     

Catalytic decomposition of hydrogen peroxide and 2-chlorophenol with iron oxides

The aim of this study was to examine the catalyzed decomposition of hydrogen peroxide and 2-chlorophenol (2-CP) in the presence of iron oxides. Granular ferrihydrite, goethite, and hematite were selected as catalysts in this study. 2-CP was used as the model compound because it is a typical toxic compound and has not been investigated in the catalytic decomposition by iron oxides. The catalytic activity for hydrogen peroxide decomposition followed the sequence: granular ferrihydrite > goethite > hematite. However, hematite exhibited the highest activity in catalyzing 2-CP oxidation. The oxidation efficiency of 2-CP corresponded with the inverse sequence of specific area and pHpzc of the iron oxides. The catalytic activity of granular ferrihydrite was affected significantly by the mixing speed and particle size for its large value of Thiele modulus (phi) and Damkohler number (Da). The strong diffusion resistance for granular ferrihydrite was attributed either to its microporous structure or to the formation of oxygen in the pores of the iron oxide leading to the unexpected catalytic activity of granular ferrihydrite to hydrogen peroxide and 2-CP.     

Fenton法处理垃圾渗滤液

介绍了Fenton法处理垃圾渗滤液的中型试验,其中Fenton氧化在连续搅拌反应器（CSTR）中进行。试验表明,当双氧水与亚铁盐的总投加比一定（H2O2／Fe^2 =3.0)时,COD的去除率随双氧水投加量的增加而增加,但与双氧水在两个氧化槽的投加比例无关。当双氧水的总投加量为0.1mol/L时,COD的去除率可达67．5％,这一结果同样适用于其他垃圾填埋场的晚期渗滤液处理。     

Photodegradation of endocrine disrupting chemical nonylphenol by simulated solar UV-irradiation

The photolysis of nonylphenol (NP) was investigated using a solar simulator in the absence/presence of dissolved organic matter (DOM), HCO3-, NO3- and Fe(III) ions. The effects of different parameters such as initial pH, initial concentration of substrate, temperature, and the effect of hydrogen peroxide concentration on photodegradation of nonylphenol in aqueous solution have been assessed. The results indicate that the oxidation rate increases in the presence of H2O2, Fe(III) and DOM with dissolved organic carbon concentrations not higher than 3 mg L(-1). Phenol, 1,4-dihydroxylbenzene and 1,4-benzoquinone were identified as intermediate products of photodegradation of nonylphenol, through an HPLC method. In addition, the disappearance of the estrogenic activity of nonylphenol during irradiation using YES test was investigated. Based upon the YES test results, there was a strong decrease of estrogenic activity of nonylphenol after 80 h irradiation in the presence of hydrogen peroxide.     

Heterogeneous catalytic wet peroxide oxidation systems for the treatment of an industrial pharmaceutical wastewater

The aim of this work was to assess the treatment of wastewater coming from a pharmaceutical plant through a continuous heterogeneous catalytic wet peroxide oxidation (CWPO) process using an Fe₂O₃/SBA-15 nanocomposite catalyst. This catalyst was preliminary tested in a batch stirred tank reactor (STR), to elucidate the influence of significant parameters on the oxidation system, such as temperature, initial oxidant concentration and initial pH of the reaction medium. In that case, a temperature of 80 °C using an initial oxidant concentration corresponding to twice the theoretical stoichiometric amount for complete carbon depletion and initial pH of ca. 3 allow TOC degradation of around 50% after 200 min of contact time. Thereafter, the powder catalyst was extruded with bentonite to prepare pellets that could be used in a fixed bed reactor (FBR). Results in the up-flow FBR indicate that the catalyst shows high activity in terms of TOC mineralization (ca. 60% under steady-state conditions), with an excellent use of the oxidant and high stability of the supported iron species. The activity of the catalyst is kept constant, at least, for 55 h of reaction. Furthermore, the BOD₅/COD ratio is increased from 0.20 to 0.30, whereas the average oxidation stage (AOS) changed from 0.70 to 2.35. These two parameters show a high oxidation degree of organic compounds in the outlet effluent, which enhances its biodegradability, and favours the possibility of a subsequent coupling with a conventional biological treatment.     

Treatment of textile dyehouse wastewater by TiO2 photocatalysis

The oxidative degradation of an actual textile dyehouse wastewater was investigated by means of photocatalysis in the presence of TiO2. The UV-A-induced photocatalytic oxidation over TiO2 suspensions was capable of decolorizing the effluent completely, as well as reducing chemical oxygen demand (COD) sufficiently (COD reduction generally varied between about 40% and 90% depending on the operating conditions) after 4 h of treatment. Two crystalline forms of TiO2, viz. anatase and rutile, were tested for their photocatalytic activity and anatase was found to be more active than rutile. The extent of photocatalytic degradation was found to increase with increasing TiO2 concentration up to 0.5 g/L TiO2, above which degradation remained practically constant, reaching a plateau. Furthermore, textile effluent degradation was enhanced at acidic conditions (i.e. pH = 3) and in the presence of hydrogen peroxide. To assess catalyst activity on repeated use, experiments were performed where the catalyst was recovered and reused; after three successive uses, TiO2 had sufficiently retained its photocatalytic activity. Finally, the luminescent marine bacteria Vibrio fischeri was used to assess the acute ecotoxicity of samples prior to and after the photocatalytic treatment and it was found that ecotoxicity was fully eliminated following photocatalytic oxidation.