A combined plasma photolysis (CPP) method for removal of CS2 from gas streams at atmospheric pressure

A combined plasma photolysis (CPP) reactor that utilizes a dielectric barrier discharge (DBD) plasma and 207 nm UV radiation from discharge-driven KrBr^* excimers was designed and constructed. Gas streams containing CS₂ were treated with stand-alone DBD and CPP at atmospheric pressure. In comparison to DBD, CPP greatly enhanced the removal efficiency at the same applied voltage, waste gas concentration and gas residence time. Thus the applied voltage could be reduced to a certain extent in the plasma processing of industrial wastes. Influences of the KrBr^* radiation, inlet CS₂ concentration and gas residence time on CS₂ removal by CPP were also studied. In addition, the likely reaction mechanisms for the removal of CS₂ by CPP are suggested based on the byproducts analysis. The enhanced removal efficiency and reaction mechanisms implied that the CPP process would probably be suitable for the removal of a large number of gaseous pollutants.     

Determination of dithiocarbamate fungicide propineb and its main metabolite propylenethiourea in airborne samples

A simple, rapid and sensitive GC–MS method for the determination of dithiocarbamate fungicide propineb [polymeric zinc propylenebis (dithiocarbamate)] and an improved HPLC procedure for the simultaneous determination of its main metabolite, propylenethiourea, and ethylenethiourea, the main metabolite of all ethylenedithiocarbamates, in airborne samples are described. The method for the analysis of propineb involves the evolution of carbon disulfide (CS₂), under acidic conditions in the presence of stannous chloride, extraction of the generated CS₂ into a layer of isooctane which is then analyzed for CS₂ content by GC–MS in SIM mode. Under the optimum conditions, the retention time of CS₂ was 1.89 min and the total time of chromatographic analysis was 5 min. Recoveries from spiking glass microfibre filters (GF/A) and silica gel filters were 86 ± 7 (n = 9) and 89 ± 4 (n = 9), respectively. The limit of detection is 0.7 ng per filter, which is equivalent to about 0.8–1.0 ng m⁻³ in air. In parallel, an HPLC method with ultraviolet detection is presented for the simultaneous analysis of the metabolites. Separation of the two metabolites was attained in less than 5 min. Recoveries from spiking GF/A and silica gel filters for ethylenethiourea were 100 ± 1 (n = 3) and 98 ± 2 (n = 3), respectively, while for propylenethiourea were 102 ± 1 (n = 3) and 98 ± 1 (n = 3), respectively. The detection limits are about 36–43 and 40–49 ng m⁻³ in air for ethylenethiourea and propylenethiourea, respectively. All the analytes spiked in the filters are proven to be stable for more than one month, at −4 °C.     

Photochemical oxidation of reduced sulfur compounds in an urban location based on short time monitoring data

This study examines the oxidation of reduced sulfur compounds (RSCs) in urban ambient air. The photochemical conversions of RSC (such as DMS, CS₂, H₂S, DMDS, and CH₃SH) to a further oxidized form (e.g., SO₂, MSA, and H₂SO₄) were assessed using a photochemical box model. For our model simulation of RSC oxidation, measurements were taken at an urban monitoring station in Seoul, Korea (37.6° N, 127° E) during three separate time periods (e.g., Sept. 17–18, Oct. 23, and Oct. 27–28, 2003). The results indicate that DMS and H₂S were the dominant RSCs with concentrations of 370 ± 140 and 110 ± 60 pptv, respectively. The photochemical conversion of DMDS to SO₂ was found to occur more efficiently than other RSCs. The overall results of our study suggest that photochemical conversion of RSCs accounted for less than 15% of the observed SO₂ during the measurement period. The SO₂ production from DMS oxidation (mainly by the reaction with OH) was found to be affected primarily by the abstraction channel due to high NO_x levels during the experimental conditions.     

Effects of Fe2O3, organic matter and carbonate on photocatalytic degradation of lindane in the sediment from the Liao River,China

Fourteen sediment samples with different content of Fe₂O₃ were collected from the lower reaches of the Liao River in China. The photodegradation of lindane on the surfaces of these sediments was investigated to observe the effects of Fe₂O₃ and other photoinducable substances, such as TiO₂ and organic substances, on photodegradation of lindane. A partial least-squares (PLS) analysis model was developed to find out the statistical relationship between the photodegradation and the contents of these photoinducable substances. It was concluded from the PLS analysis that inorganic carbon and organic carbon have negative effects, whereas Fe₂O₃ and TiO₂ accelerate the photodegradation of lindane in the sediment samples when 365 nm UV light was used as light source. In all cases of the experiments, the photodegradation of lindane in the sediment samples were fitted for pseudo-first-order kinetics.     

湖北省能源消费CO2与大气污染物协同减排研究

以2015年为基准年,基于拓展的STIRPAT模型预测2025年湖北省能源消费CO2和主要大气污染物排放量.通过设置基准(记为BAU)情景、低碳(记为LC)情景和强化低碳(记为ELC)情景3种控制情景,测算CO2和主要大气污染物的减排量,并运用污染物减排量交叉弹性法评价了CO2减排对主要大气污染物的协同效应.结果表明,...     

Linear free energy relationships for dechlorination of aromatic chlorides by Pd/Fe

Reductive dechlorination rate constants for five chlorobenzenes in the presence of Pd/Fe as catalyst were determined experimentally. Linear free energy relationships (LFER) for the dechlorination rate constants of five chlorobenzenes and three chlorophenols were developed by partial least squares (PLS) regression based on quantum chemical parameters computed by PM3 Hamiltonian. The optimal LFER model obtained is

logk=−1.63+1.46×10⁻³ΔH_f−7.69×10⁻¹E_LUMO

where k stands for the dechlorination rate constants, ΔH_f is the standard heat of formation, and E_LUMO is the energy of the lowest unoccupied molecular orbital. The Q²_cum value of the model is 0.879, indicating good robustness and predictive power of the model.     

Modelling the environmental degradation of water contaminants. Kinetics and mechanism of the riboflavin-sensitised-photooxidation of phenolic compounds

The aerobic visible-light-photosensitised irradiation of methanolic solutions of either of the phenolic-type contaminants model compounds (ArOH) p-phenylphenol (PP), p-nitrophenol (NP) and phenol (Ph), and for two additional phenolic derivatives, namely p-chlorophenol (ClP) and p-methoxyphenol (MeOP), used in some experiments, was carried out. Employing the natural pigment riboflavin (Rf) as a sensitiser, the degradation of both the ArOH and the very sensitiser was observed. A complex mechanism, common for all the ArOH studied, operates. It involves superoxide radical anion (O₂^√−) and singlet molecular oxygen (O₂(¹Δ_g)) reactions. Maintaining Rf in sensitising concentrations levels (≈0.02 mM), the mechanism is highly dependent on the concentration of the ArOH. Kinetic experiments of oxygen and substrate consumption, static fluorescence, laser flash photolysis and time-resolved phosophorescence detection of O₂(¹Δ_g) demonstrate that at ArOH concentrations in the order of 10 mM, no chemical transformation occurs due to the complete quenching of Rf singlet excited state. When ArOH is present in concentrations in the order of mM or lower, O₂^√− is generated from the corresponding Rf radical anion, which is produced by electron transfer reaction from the ArOH to triplet excited Rf. The determined reaction rate constants for this step show a fairly good correlation with the electron-donor capabilities for Ph, PP, NP, ClP and MeOP. In this context, the main oxidative species is O₂^√−, since O₂(¹Δ_g) is quenched in an exclusive physical fashion by the ArOH. The production of O₂^√− regenerates Rf impeding the total degradation of the sensitiser. This kinetic scheme could partially model the fate of ArOH in aquatic media containing natural photosensitisers, under environmental conditions.     

Direct measurement of denitrification activity in a Gulf coast freshwater marsh receiving diverted Mississippi River water

Wetland loss along the Louisiana Gulf coast and excessive nitrate loading into the Gulf of Mexico are interrelated environmental problems. Nitrate removal by soil denitrification activity was studied in a ponded freshwater marsh receiving diverted Mississippi River water for the purpose of reversing or slowing wetland loss. Labeled ¹⁵N-nitrate was applied at 3.8 g N m⁻² into four replicate study plots after removing above ground vegetation. Nitrogen gas (N₂) and nitrous oxide (N₂O) emissions from the plots were determined by isotope ratio mass spectrometry (IRMS). Nitrous oxide emissions were also compared with the results determined by gas chromatograph (GC). Results showed that it took 2 weeks to remove the added nitrate with N₂O emission occurring over a period of 4 d. The apparent denitrification dynamics were assumed to follow the Michaelis–Menten equation. The maximum denitrification rate and K_m value were determined as 12.6 mg N m ⁻² h⁻¹, and 6.5 mg N l⁻¹, respectively. Therefore the maximum capacity for nitrate removal by the marsh soil would be equivalent to 110 g N m⁻² yr⁻¹, with more than 30% of nitrogen gas evolved as N₂O. For typical nitrate concentrations in Mississippi River water of about 1 mg N l⁻¹, nitrate would be removed at a rate of 14.7 g N m⁻² yr⁻¹ with N₂O emission about 1.5%. A denitrification dynamic model showed that the efficiency of nitrate removal would largely depend on the water discharge rate into the ponded wetland. Higher discharge rate will result in less retention time for the water in the marsh where nitrate is denitrified.     

Impacts of some meteorological parameters on SO2 and TSP concentrations in Erzurum, Turkey

The air pollution is the one of the most important environmental problems in Erzurum, situated in the eastern of Turkey, during winter periods. The unfavorable climate as well as the city’s topography, and inappropriate urbanization cause serious air pollution problems. The air pollutant concentrations in a city have a close relationship with its meteorological parameters. In the present study, the relationship between daily average total suspended particulate (TSP) and sulphur dioxide (SO₂) concentrations with meteorological factors, such as wind speed, temperature, relative humidity, pressure and precipitation, in 1995–2002 winter seasons was statistically analyzed using the stepwise multiple linear regression analysis. According to the results obtained through analysis, higher TSP and SO₂ concentrations are strongly related to colder temperatures, lower wind speed, higher pressure system and weakly lower precipitation and higher relative humidity. The statistical models of SO₂ and TSP including meteorological parameters gave R² of 0.74 and 0.88, respectively. Furthermore, the correlation between the previous day’s SO₂, TSP concentrations and actual concentrations of these pollutants on that day was investigated and found as 0.84 and 0.53, respectively. In order to develop this model, previous day’s SO₂ and TSP concentrations were added to the equations. The new model for SO₂ enhanced considerably (R² = 0.92), but for TSP new model was not enhanced (R² = 0.89).     

Photocatalytic degradation of phenol by visible light-responsive iron-doped TiO2 and spontaneous sedimentation of the TiO2 particles

Fe-doped TiO₂ was prepared by the calcination of Fe_xTiS₂ (x = 0, 0.002, 0.005, 0.008, 0.01) and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible diffuse reflectance spectra. All the Fe-doped TiO₂ were composed of an anatase crystal form and showed red shifts to a longer wavelength. The activity of the Fe-doped TiO₂ for the degradation of phenol was investigated by varying the iron content during UV (365 nm) and visible light (405 nm and 436 nm) irradiation. The degradation rate depended on the Fe content and the Fe-doped TiO₂ was responsive to the visible light as well as the elevated activity toward UV light. The molar ratio of 0.005 was the optimum for both the UV and visible light irradiations. The result was discussed on the basis of the balance of the excited electron–hole trap by the doped Fe³⁺ and their charge recombination on the doped Fe³⁺ level. The Fe-doped TiO₂ (x = 0.005) was more active than P25 TiO₂ under solar light irradiation. The suspended Fe-doped TiO₂ spontaneously precipitated once the stirring of the reaction mixture was terminated.     

Oxidative treatment of simulated dyehouse effluent by uv and near-UV light assisted Fenton's reagent

UV/Fenton, near-UV-visible/Fenton, dark Fenton, and H₂O₂/UV reactions have been used to treat simulated dyehouse effluents representing wastewater from the textile dyeing and rinsing process. Experiments were carried out in a lab - scale photochemical reactor using concentrations of 0.5–25 mM H₂O₂, 0.04-0.5 mM Fe²⁺-ion and different dilutions of textile wastewater. To assess the extent of mineralization, decolourization kinetics and the effect of different fight sources on treatment efficiency, DOC, optical density at 254 nm and 600 nm wavelength and residual H₂O₂ concentrations were measured during the course of the advanced oxidation reactions. Comparative evaluation of the obtained results revealed that the decolourization rate increased with applied H₂O₂ and Fe²⁺-ion dose as well as the strength of the synthetic textile wastewater. The best results were obtained by the near - UV/visible/Fenton process with a decolourization rate constant of 1.57 min⁻¹, a UV_254nm reduction of 97% and a DOC removal of 41% at relatively low doses of the H₂O₂ oxidant and Fe²⁺-ion catalyst within 60 min treatment time.     

Fenton''s type reaction and chemical pretreatment of PCBs

This study evaluates the effects of Fenton's reagent (FR) on the rate and extent of the oxidative degradation of individual mono, di-, tri- and tetrachlorobiphenyls in the commercial mixture DELOR 103, equivalent to AROCLOR 1248. The oxidation effect of FR strongly increased with increasing the molar ratio of Fe²⁺/H₂O₂. The most effective oxidation of DELOR 103 (10 μg.ml⁻¹) was achieved in a solution containing 1M H₂O₂ and 1 mM Fe²⁺. The FR elimination rate constants of PCB congeners decrease with increasing number of chlorine substituents in the biphenyl molecule and show a good correlation with the values of molecular weights of the PCB congeners and their 1-octanol/water partition coefficients.     

Postmetamorphic Xenopus laevis shows decreased plasma triiodothyronine concentrations and phosphorylase activity due to subacute phytosterol exposure

Postmetamorphic South African clawed frogs (Xenopus laevis) were exposed to a phytosterol mixture (ca. 80% β-sitosterol and less sitostanol, campesterol, and campestanol) for 14 days at 30 μg l⁻¹ in a flow-through system. The effects of phytosterols (PS) on the plasma thyroid hormone (T₃ and T₄), testosterone, leptin-immunoreactive peptide and tissue glycogen concentrations were determined. The following enzyme activities were also analyzed from the liver and muscle: glycogen phosphorylase and lipase, and from the liver only: glucose-6-phosphatase. The plasma T₃ concentration was lower in the PS-exposed female frogs. Both muscle lipase and glycogen phosphorylase activities were also lower in the PS-exposed animals. These results could indicate that the basal metabolic rate and locomotion activity of the frogs were decreased. The effects could not be attributed to the possible estrogenicity of the PS mixture. Further studies will be needed to evaluate the possible significance of these effects.     

Sequential photochemical-biological degradation of chlorophenols

UV/TiO₂/H₂O₂, UV/TiO₂ and UV/H₂O₂ were compared as pre-treatment processes for the detoxification of mixtures of 4-chlorophenol (4CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) prior to their biological treatment. When each chlorophenol was initially supplied at 50 mg l⁻¹, UV/TiO₂/H₂O₂ treatment supported the highest pollutant removal, COD removal, and dechlorination efficiencies followed by UV/TiO₂ and UV/H₂O₂. The remaining toxicity to Lipedium sativum was similar after all pre-treatments. Chlorophenol photodegradation was always well described by a first order model kinetic (r² > 0.94) and the shortest 4CP, DCP, TCP and PCP half-lives of 8.7, 7.1, 4.5 and 3.3 h, respectively, were achieved during UV/TiO₂/H₂O₂ treatment. No pollutant removal was observed in the controls conducted with H₂O₂ or TiO₂ only. Inoculation of all the photochemically pre-treated mixtures with activated sludge microflora was followed by complete removal of the remaining pollutants. Combined UV/TiO₂/H₂O₂-biological supported the highest detoxification, dechlorination (99%) and COD removal (88%) efficiencies. Similar results were achieved when each chlorophenol was supplied at 100 mg l⁻¹. COD and Cl mass balances indicated UV, UV/H₂O₂, and UV/TiO₂ treatments lead to the formation of recalcitrant photoproducts, some of which were chlorinated.     

TiO2-assisted degradation of a perfluorinated surfactant in aqueous solutions treated by gliding arc discharge

The plasma–chemical degradation of Forafac 1110, a perfluorinated non-ionic surfactant, in aqueous solutions was investigated using TiO₂ catalysts. The considered plasma was the gliding arc in humid air, which results from an electric discharge at atmospheric pressure and quasi-ambient temperature. Two titanium dioxide powders were used and their synergistic effects on the Forafac degradation were compared. The results were discussed through the evolution of the pH, the conductivity, the fluoride ions concentration released in solutions, the surfactant concentration remaining after treatment and the chemical oxygen demand (COD) measurement.

The combination of the plasma–chemical treatment with heterogeneous catalysis through the use of TiO₂ accelerated the Forafac degradation, since only 60 min was sufficient to remove 96% instead of 360 min needed in the absence of TiO₂. The use of anatase and rutile under the trade-name of Rhodia TiO₂ and Merck TiO₂, respectively, led to different results, because Rhodia TiO₂ has proven to be more efficient. It would seem that the crystalline phase as well as the crystallite size, explain the efficiency of anatase. The advantage of the plasma-catalysis is due to the fact that there is a significant production of the OH^• radicals not only generated by the gliding arc discharge but also by TiO₂.     

As(V) adsorption on amorphous iron oxide: Triple layer modelling

The adsorption of As(V) by amorphous iron oxide was investigated at 25°C, 0.01 M NaNO₃ background electrolyte as a function of solution pH(4–10) at three initial As(V) concentrations and two Fe(III) concentrations. As(V) adsorption increased with decreasing pH. A modified Langmuir isotherm has been used for describing an equilibrium partition existing between solid and liquid phases. The triple-layer model was used for simulating As(V) adsorption on iron oxide surface. This model was able to describe As(V) adsorption over the pH range 4–10, all at the concentrations of As(V) and Fe(III) studied. =Fe(H₂AsO₄)⁰, = Fe(HAsO₄)⁻ and = Fe(AsO₄)²⁻ have been shown through simulation with inner-sphere complexation products to be more consistent with experimental adsorption observations than complexation with other surface species.     

Effect of void structure of photocatalyst paper on VOC decomposition

TiO₂ powder-containing paper composites, called TiO₂ paper, were prepared by a papermaking technique, and their photocatalytic efficiency was investigated. The TiO₂ paper has a porous structure originating from the layered pulp fiber network, with TiO₂ powders scattered on the fiber matrix. Under UV irradiation, the TiO₂ paper decomposed gaseous acetaldehyde more effectively than powdery TiO₂ and a pulp/TiO₂ mixture not in paper form. Scanning electron microscopy and mercury intrusion analysis revealed that the TiO₂ paper had characteristic unique voids ca. 10 μm in diameter, which might have contributed to the improved photocatalytic performance. TiO₂ paper composites having different void structures were prepared by using beaten pulp fibers with different degrees of freeness and/or ceramic fibers. The photodecomposition efficiency was affected by the void structure of the photocatalyst paper, and the initial degradation rate of acetaldehyde increased with an increase in the total pore volume of TiO₂ paper. The paper voids presumably provided suitable conditions for TiO₂ catalysis, resulting in higher photocatalytic performance by TiO₂ paper than by TiO₂ powder and a pulp/TiO₂ mixture not in paper form.     

Investigation on the adsorption capability of egg shell membrane towards model textile dyes

Adsorption isotherms of Direct Red 80 (DR80) and Acid Blue 25 (AB25) on the egg shell membrane (ESM) were performed at 20 ± 1 °C. Physical characteristics of ESM such as surface area and presence of functional groups were verified. The Fourier transform infra-red (FTIR) spectra proved the presence of fuctional groups such as hydroxyl, amine and carbonyl groups in ESM. The surface area of ESM was found to be 2.2098 m²/g. The effects of operational parameters such as initial dye concentration, pH₀, contact time, particle size and ESM doses were studied. The Langmuir, Freundlich, BET, Redlich-Peterson and Temkin adsorption models were applied to describe the equilibrium isotherms. The pseudo-first-order and pseudo-second-order kinetics models were examined to evaluate the kinetics data at different pH₀ values (2–12) and the rate constants were calculated. Maximum desorption of 81.8% was achieved for both dyes in aqueous solution at pH₀ 12. Also scanning electron micrographs (SEM) of the treated and untreated adsorbent were performed. Results indicate that ESM could be employed as a natural and Eco-Friendly adsorbent material for the removal of trace organics in solutions.     

Comparative study of the oxidation of atrazine and acetone by H2O2/UV, Fe(III)/UV, Fe(iii)/H2O2/UV and Fe(II) or Fe(III)/H2O2

In this study, the rates of degradation of organic compounds by several AOPs (H₂O₂/UV, Fe(III)/UV, Fe(III)/H₂O₂/UV, Fe(II)/H₂O₂ and Fe(III)/H₂O₂) have been compared. Experiments were carried out at pH ≈ 3 (perchloric acid / sodium perchlorate solutions) and with UV reactors equipped with a low-pressure mercury vapour lamp (emission at 253.7 run). The data obtained with atrazine ([Atrazine]_o = 100 μg/L) showed that the rate of degradation of atrazine in very dilute aqueous solution is much more rapid with Fe(III)/UV than with H₂O₂/UV. Photo-Fenton process (Fe(III)/H₂O₂/UV) was found to be more efficient than H₂O₂/UV and Fe(II)/H₂O₂ for the mineralization of acetone ([Acetone]_o = 1 mM).     

Biodegradation of nonylphenol in sewage sludge

We investigated the effects of various factors on the aerobic degradation of nonylphenol (NP) in sewage sludge. NP (5 mg/kg) degradation rate constants (k₁) calculated were 0.148 and 0.224 day⁻¹ for the batch experiment and the bioreactor experiment, respectively, and half-lives (t_1/2) were 4.7 and 3.1 days, respectively. The optimal pH value for NP degradation in sludge was 7.0 and the degradation rate was enhanced when the temperature was increased and when yeast extract (5 mg/l) and surfactants such as brij 30 or brij 35 (55 or 91 μM) were added. The addition of aluminum sulfate (200 mg/l) and hydrogen peroxide (1 mg/l) inhibited NP degradation within 28 days of incubation. Of the microorganism strains isolated from the sludge samples, we found that strain CT7 (identified as Bacillus sphaericus) manifested the best degrading ability.