Sequential electrochemical treatment of dairy wastewater using aluminum and DSA-type anodes

Dairy wastewater is characterized by a high content of hardly biodegradable dissolved, colloidal, and suspended organic matter. This work firstly investigates the performance of two individual electrochemical treatments, namely electrocoagulation (EC) and electro-oxidation (EO), in order to finally assess the mineralization ability of a sequential EC/EO process. EC with an Al anode was employed as a primary pretreatment for the conditioning of 800 mL of wastewater. A complete reduction of turbidity, as well as 90 and 81 % of chemical oxygen demand (COD) and total organic carbon (TOC) removal, respectively, were achieved after 120 min of EC at 9.09 mA cm^?2. For EO, two kinds of dimensionally stable anodes (DSA) electrodes (Ti/IrO₂-Ta₂O₅ and Ti/IrO₂-SnO₂–Sb₂O₅) were prepared by the Pechini method, obtaining homogeneous coatings with uniform composition and high roughness. The ^·OH formed at the DSA surface from H₂O oxidation were not detected by electron spin resonance. However, their indirect determination by means of H₂O₂ measurements revealed that Ti/IrO₂-SnO₂–Sb₂O₅ is able to produce partially physisorbed radicals. Since the characterization of the wastewater revealed the presence of indole derivatives, preliminary bulk electrolyses were done in ultrapure water containing 1 mM indole in sulfate and/or chloride media. The performance of EO with the Ti/IrO₂-Ta₂O₅ anode was evaluated from the TOC removal and the UV/Vis absorbance decay. The mineralization was very poor in 0.05 M Na₂SO₄, whereas it increased considerably at a greater Cl^? content, meaning that the oxidation mediated by electrogenerated species such as Cl₂, HClO, and/or ClO^? competes and even predominates over the ^·OH-mediated oxidation. The EO treatment of EC-pretreated dairy wastewater allowed obtaining a global 98 % TOC removal, decreasing from 1,062 to <30 mg L^?1.     

Particle formation events measured at a semirural background site in Denmark

The particle formation and growth events observed at a semirural background site in Denmark were analyzed based on particle number size distribution data collected during the period from February 2005 to December 2010. The new particle formation (NPF) events have been classified visually in detail according to 3D daily plots in combination with an automatic routine. A clear seasonal variation was found in the way that events occurred more frequently during the warm season from May to September and especially in June. The mean values of the apparent 6 nm particle formation rates, the growth rate and the condensation sink were about 0.36 cm^?3 s^?1, 2.6 nm h^?1, 4.3?×?10^?3 s^?1, respectively. A positive relationship of oxidation capacity (O_X?=?O₃?+?NO₂) of the atmosphere and the appearance of NPF events was found indicating that the oxidation of the atmosphere was linked to the formation of new particles. An analysis of a 3-day backward trajectories revealed that NW air masses from the North Sea were giving the highest probability of NPF events, namely between 20 and 40 %.     

Rate Constants for the Reaction of OH with Halocarbons in the Presence of O2 + N2

Rates of CO₂ production in the reaction CO + OH and CO + OH + halocarbon have been used to determine rate constants for some OH + halocarbon reactions at 29.5°C relative to that of k(CO + OH) = 2.69 × 10^?13 cm³ molecule^?1 sec^?1. The following rate constants were obtained: k(OH + CH₃Cl) = 3.1 ± 0.8, k(OH + CH₂Cl₂) = 2.7 ± 1.0, k(OH + C₂H₅Cl) = 44.0 ± 25, k(OH + CICH₂CH₂CI) = 6.5, (<29) and k(OH + CH₃CCl₃) = 2.1 (<5.7) cm³ molecule^?1 sec^?1 × 10^?14. The k values, CH₂Cl₂ excepted, are in substantial agreement with determinations made in nonoxygen environments. The present results for CH₂Cl₂ are almost certainly in error due to difficulties with the competitive approach used.     

Influence of the current density on the electrochemical treatment of concentrated 1-butyl-3-methylimidazolium chloride solutions on diamond electrodes

This paper focuses on the influence of the current density treatment of a concentrated 1-butyl-3-methylimidazolium chloride (BMImCl) solution on an electrochemical reactor with a boron-doped diamond (BDD) anode. The decrease in the total organic carbon (TOC) and the BMImCl concentration demonstrate the capability of BDD in oxidizing ionic liquids (ILs) and further mineralizing (to CO₂ and NO₃ ^?) more rapidly at higher current densities in spite of the reduced current efficiency of the process. Moreover, the presence of Cl^? led to the formation of oxychlorinated anions (mostly ClO₃ ^? and ClO₄ ^?) and, in combination with the ammonia generated in the cathode from the nitrate reduction, chloramines, more intensely at higher current density. Finally, the analysis of the intermediates formed revealed no apparent influence of the current density on the BMImCl degradation mechanism. The current density presents therefore a complex influence on the IL treatment process that is discussed throughout this paper.     

Electro-oxidation of the dye azure B: kinetics,mechanism, and by-products

In this work, the electrochemical degradation of the dye azure B in aqueous solutions was studied by electrochemical advanced oxidation processes (EAOPs), electro-Fenton, and anodic oxidation processes, using Pt/carbon-felt and boron-doped diamond (BDD)/carbon-felt cells with H₂O₂ electrogeneration. The higher oxidation power of the electro-Fenton (EF) process using BDD anode was demonstrated. The oxidative degradation of azure B by the electrochemically generated hydroxyl radicals (^?OH) follows a pseudo-first-order kinetics. The apparent rate constants of the oxidation of azure B by ^?OH were measured according to pseudo-first-order kinetic model. The absolute rate constant of azure B hydroxylation reaction was determined by competition kinetics method and found to be 1.19?×?10⁹ M^?1 s^?1. It was found that the electrochemical degradation of the dye leads to the formation of aromatic by-products which are then oxidized to aliphatic carboxylic acids before their almost mineralization to CO₂ and inorganic ions (sulfate, nitrate, and ammonium). The evolution of the TOC removal and time course of short-chain carboxylic acids during treatment were also investigated.     

Principal component analysis to assess the efficiency and mechanism for enhanced coagulation of natural algae-laden water using a novel dual coagulant system

A novel dual coagulant system of polyaluminum chloride sulfate (PACS) and polydiallyldimethylammonium chloride (PDADMAC) was used to treat natural algae-laden water from Meiliang Gulf, Lake Taihu. PACS (Al_n(OH)_mCl_3n-m-2k(SO₄)_k) has a mass ratio of 10 %, a SO₄ ^2?/Al₃ ⁺ mole ratio of 0.0664, and an OH/Al mole ratio of 2. The PDADMAC ([C₈H₁₆NCl]_m) has a MW which ranges from 5?×?10⁵ to 20?×?10⁵ Da. The variations of contaminants in water samples during treatments were estimated in the form of principal component analysis (PCA) factor scores and conventional variables (turbidity, DOC, etc.). Parallel factor analysis determined four chromophoric dissolved organic matters (CDOM) components, and PCA identified four integrated principle factors. PCA factor 1 had significant correlations with chlorophyll-a (r?=?0.718), protein-like CDOM C1 (0.689), and C2 (0.756). Factor 2 correlated with UV₂₅₄ (0.672), humic-like CDOM component C3 (0.716), and C4 (0.758). Factors 3 and 4 had correlations with NH₃-N (0.748) and T-P (0.769), respectively. The variations of PCA factors scores revealed that PACS contributed less aluminum dissolution than PAC to obtain equivalent removal efficiency of contaminants. This might be due to the high cationic charge and pre-hydrolyzation of PACS. Compared with PACS coagulation (20 mg L^?1), the removal of PCA factors 1, 2, and 4 increased 45, 33, and 12 %, respectively, in combined PACS–PDADMAC treatment (0.8 mg L^?1?+?20 mg L^?1). Since PAC contained more Al (0.053 g/1 g) than PACS (0.028 g/1 g), the results indicated that PACS contributed less Al dissolution into the water to obtain equivalent removal efficiency.     

Radical-driven carbonyl-to-acid conversion and acid degradation in tropospheric aqueous systems studied by CAPRAM

Model studies on the aqueous phase radical-driven processing of carbonyl compounds and acids in clouds and deliquescent particles were performed. The model exposed that aqueous radical conversions of carbonyl compounds and its oxidation products can contribute potentially to the formation of functionalised organic acids. The main identified C₂–C₄ organic gas phase precursors are ethylene glycol, glycolaldehyde, glyoxal, methylglyoxal and 1,4-butenedial. The aqueous phase is shown to contribute significantly with about 93%/63%, 47%/8%, 31%/4%, 7%/4%, 36%/8% to the multiphase oxidative fate of these compounds under remote/urban conditions. Interestingly, the studies revealed that aqueous chemical processing is not only limited to in-cloud conditions but also proceeds in deliquescent particle phase with significant fluxes. Oxalic acid is shown to be formed preferably in deliquescent particles subsequent to the in-cloud oxidations. Mean aqueous phase oxalate formation fluxes of about 12, 42 and 0.4 ng m^?3 h^?1 in the remote, urban and maritime scenario, respectively. Additionally, the turnovers of the oxidation of organics such as methylglyoxal by NO₃ radical reactions are identified to be competitive to their OH pendants. At the current state of CAPRAM, mean C₂–C₄ in-cloud oxidation fluxes of about 0.12 and 0.5 μg m^?3 h^?1 are modelled under the idealised remote and urban cloud conditions.Finally, turnovers from radical oxidations were compared with those of thermal reactions. It is demonstrated that, based on the sparse kinetic data available organic accretion reaction might be of interest in just a few cases for cloud droplets and aqueous particles but generally do not reach the oxidative conversion rates of the main radical oxidants OH and NO₃. Interestingly, oxidation reactions of H₂O₂ are shown to be competitive to the OH radical conversions in cases when H₂O₂ is not readily used up by the S(IV) oxidation.     

Effect of ethylenediamine-N,N′-disuccinic acid on Fenton and photo-Fenton processes using goethite as an iron source: optimization of parameters for bisphenol A degradation

The main disadvantage of using iron mineral in Fenton-like reactions is that the decomposition rate of organic contaminants is slower than in classic Fenton reaction using ferrous ions at acidic pH. In order to overcome these drawbacks of the Fenton process, chelating agents have been used in the investigation of Fenton heterogeneous reaction with some Fe-bearing minerals. In this work, the effect of new iron complexing agent, ethylenediamine-N,N'-disuccinic acid (EDDS), on heterogeneous Fenton and photo-Fenton system using goethite as an iron source was tested at circumneutral pH. Batch experiments including adsorption of EDDS and bisphenol A (BPA) on goethite, H₂O₂ decomposition, dissolved iron measurement, and BPA degradation were conducted. The effects of pH, H₂O₂ concentration, EDDS concentration, and goethite dose were studied, and the production of hydroxyl radical (^?OH) was detected. The addition of EDDS inhibited the heterogeneous Fenton degradation of BPA but also the formation of ^?OH. The presence of EDDS decreases the reactivity of goethite toward H₂O₂ because EDDS adsorbs strongly onto the goethite surface and alters catalytic sites. However, the addition of EDDS can improve the heterogeneous photo-Fenton degradation of BPA through the propagation into homogeneous reaction and formation of photochemically efficient Fe-EDDS complex. The overall effect of EDDS is dependent on the H₂O₂ and EDDS concentrations and pH value. The high performance observed at pH 6.2 could be explained by the ability of O ₂ ^?? to generate Fe(II) species from Fe(III) reduction. Low concentrations of H₂O₂ (0.1 mM) and EDDS (0.1 mM) were required as optimal conditions for complete BPA removal. These findings regarding the capability of EDDS/goethite system to promote heterogeneous photo-Fenton oxidation have important practical implications for water treatment technologies.     

Decomposition of phenylarsonic acid by AOP processes: degradation rate constants and by-products

The paper presents results of the studies photodegradation, photooxidation, and oxidation of phenylarsonic acid (PAA) in aquatic solution. The water solutions, which consist of 2.7 g dm^?3 phenylarsonic acid, were subjected to advance oxidation process (AOP) in UV, UV/H₂O₂, UV/O₃, H₂O₂, and O₃ systems under two pH conditions. Kinetic rate constants and half-life of phenylarsonic acid decomposition reaction are presented. The results from the study indicate that at pH 2 and 7, PAA degradation processes takes place in accordance with the pseudo first order kinetic reaction. The highest rate constants (10.45?×?10^?3 and 20.12?×?10^?3) and degradation efficiencies at pH 2 and 7 were obtained at UV/O₃ processes. In solution, after processes, benzene, phenol, acetophenone, o-hydroxybiphenyl, p-hydroxybiphenyl, benzoic acid, benzaldehyde, and biphenyl were identified.     

Kinetics of Sulfur-Oxide Formation in Flames: II. Low Pressure H2S Flames

The microstructure of 1/10 and 1/20 atmosphere, lean H₂S—O₂—N₂ flames is developed using the mass-spectrometric flame-sampling technique. The flame mechanism developed is in agreement with that determined from an earlier study on 1-atm H₂S flames. The formation of SO₂ appears to be primarily related to the production of SH and the ensuing oxidation steps SH + O₂ = SO + OH and SO + O₂ = SO₂ + O. While there is some question whether SO₂ formation occurs via an SO or an S₂O intermediate, the present study does not give direct support to the role of S₂O in the oxidation mechanism. However, the presence of significant quantities of free sulfur in the pre-flame zone may be indicative of S₂O formation via SO + S → S₂O, and, possibly, via the disproportionation of SO, 3SO → S₂O + SO₂. Kinetic analyses of some of the pre-flame reactions indicate an apparent activation energy of 17,300 calories/mole for the decomposition of H₂S. The actual initiation process in the flame mechanism requires further examination. The specific rate for the reaction step H₂S + O = OH + SH is given by k ₆ = 1.45 × 10₁₅ exp ( – 6600/RT) cm³ mole^–1 sec^–1, and the specific rate for the oxidation of SO, SO + O₂ = SO₂ + O, is given by k ₅ = 5.2 × 10₁₄ exp (—19,300/RT) cm³ mole^–1 sec^–1.     

Stability of 6:2 fluorotelomer sulfonate in advanced oxidation processes: degradation kinetics and pathway

Perfluorooctane sulfonate (PFOS), a widely used mist suppressant in hard chrome electroplating industry, has been listed in the Stockholm Convention for global ban. 6:2 Fluorotelomer sulfonate (6:2 FTS) acid and salts have been adopted as alternative products in the market, but no data about their abiotic degradation has been reported. In the present study, the degradability of 6:2 FTS potassium salt (6:2 FTS-K) was evaluated under various advanced oxidation processes, including ultraviolet (UV) irradiation, UV with hydrogen peroxide (H₂O₂), alkaline ozonation (O₃, pH = 11), peroxone (O₃/H₂O₂), and Fenton reagent oxidation (Fe²⁺/H₂O₂). UV/H₂O₂ was found to be the most effective approach, where the degradation of 6:2 FTS-K followed the pseudo-first-order kinetics. The intermediates were mainly shorter chain perfluoroalkyl carboxylic acid (C₇ to C₂), while sulfate (SO₄ ^2?) and fluoride (F^?) were found to be the final products. The high yields of SO₄ ^2? and F^? indicate that 6:2 FTS-K can be nearly completely desulfonated and defluorinated under UV/H₂O₂ condition. The degradation should firstly begin with the substitution of hydrogen atom by hydroxyl radicals, followed by desulfonation, carboxylation, and sequential “flake off” of CF₂ unit. Compared with PFOS which is inert in most advanced oxidation processes, 6:2 FTS-K is more degradable as the alternative.     

On the oxidation of SO2 to sulfate in atmospheric aerosols

This paper presents the results of a study to investigate the atmospheric oxidation of sulfur dioxide (SO₂). A detailed model of gas-phase chemistry, aerosol thermodynamics and aerosol chemistry is employed to simulate atmospheric sulfate formation. The calculations indicate that, in addition to the gasphase oxidation by hydroxyl (OH) radicals, SO₂ oxidation in aqueous aerosols may also contribute significantly to sulfate formation. Reactions of SO₂ with hydrogen peroxide (H₂O₂) and O₂ (catalyzed by Fe³⁺ and Mn²⁺) are identified as principal aqueous-phase oxidation mechanisms. The results of this study confirm the conclusions drawn from the analysis of ambient aerosol data qualitatively. However, some discrepancies also exist between the results of our modeling study and field data. Such discrepancies emphasize the need for the collection of ambient data for a more rigorous and quantitative evaluation of atmospheric aerosol models.     

FTIR gas-phase kinetic study on the reactions of some acrylate esters with OH radicals and Cl atoms

Acrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298?±?2 K) and atmospheric pressure (708?±?8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm³ molecule^?1 s^?1): (3.27?±?0.33)?×?10^?11 and (4.43?±?0.42)?×?10^?11, for CH₃CH═CHC(O)OCH₃ and (CH₃)₂CH═CHC(O)OCH_3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N₂ and air were used as the bath gases. The following rate coefficients were obtained (in cm³ molecule^?1 s^?1): k₃ (CH₂═CHC(O)O(CH₂)₅CH₃?+?Cl)?=?(3.31?±?0.31)?×?10^?10, k₄(CH₂═CHC(O)OCH₂CH(CH₂CH₃)(CH₂)₃CH₃?+?Cl)?=?(3.46?±?0.31)?×?10^?10, k₅(CH₂═CHC(O)O(CH₂)₅CH₃?+?OH)?=?(2.28?±?0.23)?×?10^?11, and k₆(CH₂═CHC(O)OCH₂CH(CH₂CH₃)(CH₂)₃CH₃?+?OH)?=?(2.74?±?0.26)?×?10^?11. The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in –C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do not influence global warming.     

The chemical composition of cloud and rainwater. Results of preliminary measurements from an aircraft

Using an aircraft, preliminary investigations have been carried out into the chemical composition of clouds. The emphasis was on testing the sampling devices under several conditions. The results clearly show a considerable spatial distribution in pollutant concentrations that must have been caused by the contribution of many plume sources and the inhomogeneity of cloudwater density as well. Rather high concentrations of H₃O⁺. Cl⁻, NO⁻₃, SO²⁻₄, NH⁺₄ and H₂O₂ were measured. Except for H₂O₂, these components are scavenged very fast during travel over short distances over source regions. Moreover H₃O⁺, NO⁻₃ and SO²⁻₄ are likely to be formed by chemical reactions of gaseous precursors with oxidants in the liquid phase. This may explain the marked decrease in high background H₂O₂ concentrations (ppm range). Relatively high (molar) NO⁻₃ /SO²⁻₄ ratios mainly varying from 1 to 2 were measured over The Netherlands near source areas. The lower values found during a flight over southern Scandinavia are in agreement with data from literature. Occasionally the chloride concentration was found to be much higher than could be expected from rain network data.     

Sources of hydrogen peroxide in cloudwater

Results of a theoretical investigation of H₂O₂ formation in cloud droplets arising from gaseous HO₂ radical scavenging are presented. It is shown that this process is pH dependent with the maximum rate of H₂O₂ production occurring below pH 3. This dependence arises as a result of the dissociation of HO₂ in water (pK_a = 4.9) and the subsequent disproportionation reaction of HO₂ and O₂⁻ to form hydrogen peroxide. O₂⁻ is also removed by reaction with O₃ to produce OH radicals and this process becomes more competitive as both the pH and $\text{O}{}_2{}^{\mathrm{-}}\text{HO}{}_2$ ratio increase. The presence of soluble organic species, such as aldehydes, in cloudwater counteracts the effect of ozone by converting OH back to HO₂. For low pHs (< 3) the net contribution of organic solutes of H₂O₂ production is predicted to be relatively small, being limited by the availability of OH radicals scavenged from the gas phase. Existing cloud chemistry models may overestimate the rate of aqueous oxidation of formaldehyde by OH radicals.Under conditions where scavenging of gas-phase free radicals by cloud droplets is efficient, uptake of HO₂ radicals may be reversible. The aqueous concentration of OH is unlikely to approach thermodynamic equilibrium with the gas phase (H ∼-30 M atm⁻¹ and can be treated as irreversible. In clouds with a small mean droplet radius, efficient scavenging of precursor OH radicals should result in a decrease in gas-phase HO₂ production with a reduction in the yield of aqueous H₂O₂, although this is offset by the presence of soluble organic species. A similar effect is predicted for clouds with a high liquid water content.The supply of HO₂ and OH radicals to cloud droplets is controlled by gas-phase ozone chemistry which is in turn dependent on the solar u.v. radiation intensity. The u.v. density in clouds may be higher than in clear air when the solar zenith angle is small, thus enhancing H₂O₂ production, but falls off markedly as the solar zenith angle becomes larger. Predicted rates of H₂O₂ formation in clouds based on midday conditions are likely to be considerably higher than the average daytime value, particularly in summer. Diurnal and seasonal effects on H₂O₂ generation are expected to be more marked in clouds than in clear air.     

Kinetics of imidazolium-based ionic liquids degradation in aqueous solution by Fenton oxidation

In the last few years, several works dealing with Fenton oxidation of ionic liquids (ILs) have proved the capability of this technology for their degradation, achieving complete ILs removal and non-toxic effluents. Nevertheless, very little is known about the kinetics of this process, crucial for its potential application. In this work, the effect of several operating conditions, including reaction temperature (50–90 °C), catalyst load (10–50 mg L^?1 Fe³⁺), initial IL concentration (100–2000 mg L^?1), and hydrogen peroxide dose (10–200% of the stoichiometric amount for the complete IL mineralization) on 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) oxidation has been investigated. Under the optimum operating conditions (T = 90 °C; [Fe³⁺]₀ = 50 mg L^?1; [H₂O₂]₀ = 100% of the stoichiometric amount), the complete removal of [C₄mim]Cl (1000 mg L^?1) was achieved at 1.5-min reaction time. From the experimental results, a potential kinetic model capable to describe the removal of imidazolium-based ILs by Fenton oxidation has been developed. By fitting the proposed model to the experimental data, the orders of the reaction with respect to IL initial concentration, Fe³⁺ amount and H₂O₂ dose were found to be close to 1, with an apparent activation energy of 43.3 kJ mol^?1. The model resulted in a reasonable fit within the wide range of operating conditions tested in this work.     

Chemical degradation of chlorophenols with Fenton's reagent (Fe + H2O2)

Aqueous solutions of Fenton's reagent (Fe²⁺ + H₂O₂) have been used to effect the total decomposition of the chlorophenols: 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 3,4-dichlorophenol and 2,4,5-trichlorophenol. The mineralization of these chlorinated aromatic substrates to CO₂ and free Cl⁻ has been studied as a function of [Fe²⁺] and [HClO₄]. Increasing the concentration of Fe²⁺ enhances the decomposition process, while an increase in the concentration of HClO₄, inhibits the reaction. The presence of Fe³⁺ alone (without any Fe²⁺) with H₂O₂ has no effect on the degradation of the chlorophenols. In all cases, the stoichiometric quantity of free Cl⁻ was obtained at the completion of the decomposition reaction; but the rates of disappaearance of the chlorophenol and of the formation of the Cl⁻ are not similar. This suggests that some chlorinated aliphatic species may be formed as possible intemediates.     

辉光放电等离子体氧化降解水中邻苯二甲酸二丁酯

研究了辉光放电等离子体降解水中典型的环境内分泌干扰物邻苯二甲酸二丁酯(DBP)及降解过程中过氧化氢(H2O2)的生成规律。考察了电解质种类、共存污染物(甲醇、叔丁醇)及催化剂等条件对DBP降解及H2O2生成的影响。结果表明,在硫酸钠溶液中DBP降解效率和H2O2生成速率最高;甲醇、叔丁醇等共存污染物对DBP降解和H2O2生成有抑制作用;Fe2+,Fe3+和Cu2+对DBP的降解有催化作用,其催化效果为Fe2+>Fe3+>Cu2+。用高效液相色谱、离子色谱及气质联用仪等仪器分析了降解中间产物,提出了可能的降解机理。     

Electrooxidation of industrial wastewater containing 1,4-dioxane in the presence of different salts

The treatment of 1,4-dioxane solution by electrochemical oxidation on boron-doped diamond was studied using a central composite design and the response surface methodology to investigate the use of SO₄ ^2? and HCO₃ ^? as supporting electrolytes considering the applied electric current, initial chemical oxygen demand (COD) value, and treatment time. Two industrial effluents containing bicarbonate alkalinity, one just carrying 1,4-dioxane (S1), and another one including 1,4-dioxane and 2-methyl-1,3-dioxolane (S2), were treated under optimized conditions and subsequently subjected to biodegradability assays with a Pseudomonas putida culture. Electrooxidation was compared with ozone oxidation (O₃) and its combination with hydrogen peroxide (O₃/H₂O₂). Regarding the experimental design, the optimal compromise for maximum COD removal at minimum energy consumption was shown at the maximum tested concentrations of SO₄ ^2? and HCO₃ ^? (41.6 and 32.8 mEq L^?1, respectively) and the maximum selected initial COD (750 mg L^?1), applying a current density of 11.9 mA cm^?2 for 3.8 h. Up to 98 % of the COD was removed in the electrooxidation treatment of S1 effluent using 114 kWh per kg of removed COD and about 91 % of the COD from S2 wastewater applying 49 kWh per kg of removed COD. The optimal biodegradability enhancement was achieved after 1 h of electrooxidation treatment. In comparison with O₃ and O₃/H₂O₂ alternatives, electrochemical oxidation achieved the fastest degradation rate per oxidant consumption unit, and it also resulted to be the most economical treatment in terms of energy consumption and price per unit of removed COD.     

Removal of imidazolium- and pyridinium-based ionic liquids by Fenton oxidation

The oxidation of imidazolium (1-hexyl-3-methylimidazolium chloride, HmimCl) and pyridinium (1-butyl-4-methylpyridinium chloride, BmpyrCl) ionic liquids (ILs) by Fenton’s reagent has been studied. Complete conversion was achieved for both ILs using the stoichiometric H₂O₂ dose at 70 °C, reaching final TOC conversion values around 45 and 55% for HmimCl and BmpyrCl, respectively. The decrease in hydrogen peroxide dose to substoichiometric concentrations (20–80% stoichiometric dose) caused a decrease in TOC conversion and COD removal and the appearance of hydroxylated oxidation by-products. Working at these substoichiometric H₂O₂ doses allowed the depiction of a possible degradation pathway for the oxidation of both imidazolium and pyridinium ILs. The first step of the oxidation process consisted in the hydroxylation of the ionic liquid by the attack of the ·OH radicals, followed by the ring-opening and the formation of short-chain organic acids, which could be partially oxidized up to CO₂ and H₂O. At H₂O₂ doses near stoichiometric values (80%), the resulting effluents showed non-ecotoxic behaviour and more biodegradable character (BOD₅/COD ratio around 0.38 and 0.58 for HmimCl and BmpyrCl, respectively) due to the formation of short-chain organic acids.

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