Volume 20, Issue 2

We develop numerical model to discuss the number density and excitation kinetics of O( 1 D) state in low-pressure discharge oxygen plasma. The governing equations are the Boltzmann equation to describe the electron energy distribution function and the rate equations of the relevant excited states. We have calculated them back and forth until self-consistent solution is obtained. When the rate coefficient of the electron impact dissociation of O 2 to O( 3 P) and O( 1 D) atoms is assumed to be functions of electron temperature T e with Maxwellian electron energy distribution, the obtained results are found to be inappropriate. When the rate coefficients are written as functions of electron energy distribution function, satisfactory results are obtained as number density distribution of excited states. We also experimentally examined and confirmed the validity of the model by actinometry measurement for number density of the O( 3 P) state. It is found that we should consider the electron energy distribution function in describing the excitation kinetics of O( 1 D) state in low-pressure oxygen plasma.

In this research, photocatalytic degradation of diazinon by amino-functionalized Fe 3 O 4 -WO 3 nanoparticles under UV irradiation was investigated with variation of pH, nanocatalyst dose, initial diazinon concentration, different purging gases, H 2 O 2 concentration, and type of organic compounds. Under optimal conditions: pH= 7, [Diazinon] 0 = 20 mg.L –1 , nanocatalyst dosage= 0.25 g.L –1 , H 2 O 2 = 5 mM, 99.23 % of the insecticide was removed after 120 min. A decrease was observed in the removal efficiency of diazinon in the presence of different purging gases and organic compounds. Based on the three kinetic models developed in this study, it was found that the removal of diazinon followed the first order kinetic. Also, application of the UV/amino-functionalized Fe 3 O 4 -WO 3 nanoparticles both increased the performance and decreased electric power consumption. However, 86.17 % of diazinon in real water samples was removed under the optimized conditions. Furthermore, the photocatalytic activity was kept after five successive cycles.

A high salinity wastewater from epoxy resin was treated with the catalytic wet peroxide oxidation (CWPO) process, so that it can be reused as the chlor-alkali process feedstock. Both bench and pilot scale trials were conducted out in this research. The effect of oxidant (hydrogen peroxide) and catalyst (ferrous sulfate) dosages, and their dosing methods, pH value, temperature, and reaction time on TOC removal by the CWPO process were evaluated through bench experiment. The obtained optimal reaction conditions for the CWPO process were as following: H 2 O 2 dosage = 0.735 M, Fe 2+ dosage = 0.027 M, temperature = 90ºC, pH = 3.0–3.5, and reaction time = 200 min. Multiple additions of oxidant and catalyst significantly enhanced TOC removal compared to adding the same total dosage in one step. In a pilot trail, 735 moles of H 2 O 2 and 27 moles of Fe 2+ were continuously added to a 1000 L wastewater over 3 hours while the pH and temperature of the reaction solution were automatically controlled at 3.3 ± 0.5 and 90 ± 2℃, respectively, the wastewater TOC values were reduced to less than 150 mg/L from 2500–2700 mg/L, which satisfies the influent TOC limit (200 mg/L) of the diaphragm electrolytic cell. In addition, both the iron ion and sulfate ion concentrations in the pilot effluent were less than their influent limits of the diaphragm electrolytic cell, thus the treated wastewater had been successfully applied in a chlor-alkali plant for production chlorine and caustic soda.

Per- and polyfluoroalkyl substances (PFASs) have been recently listed as emerging contaminants (ECs) and persistent organic pollutants (POPs) due to their human and environmental health concerns. In the last 10 years, their detection and remediation have progressed significantly. Herein, we critically review recent developments in electrochemical advanced oxidation process (EAOP) towards their remediation. Particular attentions are paid to perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), which present the main concerns of PFASs at this time. Due to the persistence of those PFASs, other remediation approaches may experience difficulty in degrading them, whilst EAOP has demonstrated success. The fundamentals of EAOP are highlighted and the scale-up application is discussed regarding the future research directions.

The effect of CH 4 , C 2 H 4 , CO 2 , CH 3 OH, and (CH 3 S) 2 on activity and selectivity of V-Mo-Nb-Te-O x catalyst for ethane oxidative dehydrogenation is studied. Methane acts as a chemically inert diluent of the gas mixture. Presence of ethylene in feed stream does not have significant effect on the rate of ethane dehydrogenation but causes slight drop in ethylene selectivity. CO 2 added is not involved in chemical transformations but suppress slightly ethane conversion and selectivity. Contamination of the gas stream with small amounts of either methanol or dimethyldisulfide (DMDS) does not reduce either activity or selectivity of the catalyst in ethane oxidative dehydrogenation.

The discharge of effluents from the textile industry into water bodies has a severe impact on water quality. The photocatalytic degradation of two typical azo dyes used in the textile industry (Acid Brown 83 and Direct Blue 1) was studied using the catalysts titanium dioxide (TiO 2 ) and zinc oxide (ZnO) supported on polyethylene terephthalate (PET) and polystyrene (PS) substrates. For these dyes, degradation reactions using different initial pH values and supported catalysts were carried out. Adsorption isotherms were obtained and analyzed. No significant statistical differences were found between the use of PET and PS as substrates on degradation rate constants for both dyes. For Acid Brown 83 the highest rate constant was obtained at pH 2.5 using TiO 2 . For Direct Blue 1, the rate constant showed a significant difference only between the treatment at pH 2.5 using TiO 2 and the treatment al pH 11.0 using ZnO. The adsorption of both dyes was higher on TiO 2 than on ZnO.

The effects of calcination temperature on properties of porous lanthanum titanate using PEG4000 template in a sol-gel route were studied. Photocatalytic degradation of Reactive Brilliant Red X3B on the materials was evaluated. Monoclinic La 2 Ti 2 O 7 was synthesized in all the samples. The growing up of La 2 Ti 2 O 7 crystals leads to apparent increases in crystallite size and cell volume with increasing calcination temperature. The E g values for the samples are 3.38, 3.40, 3.33 3.36 and 3.44 eV when calcination temperature increases from 600 °C to 1,000 °C. High temperature calcination leads to apparent loss of both specific surface area and pore volume, although the average pore size is nearly unchanged. The decoloration efficiency by adsorption is in close relationship to the surface area of the materials. The sample prepared at 900 °C has the maximum photocatalytic activity on degradation of Reactive Brilliant Red X3B in aqueous solution. A continuous loss of degradation efficiency is observed after recycling of the material due to complex reasons.

Separation of oil and water is well known as a key process in the oil industry. For the purpose of improving the efficiency of the oil-water separation, a novel ClO 2 -oxidation-based demulsification method for the treatment of oil-water transition layer in oil settling tanks was proposed and studied in the present paper. A series of lab experiments were performed to investigate the techniques and conditions of the ClO 2 -oxidation-based demulsification, including the reaction temperature, time, concentration, etc. It was observed that a high dehydration rate of 86.11 % was achieved under an optimal reaction condition of 50 o C, 4 hours, 3.5‰ ClO 2 concentration and 0.5 % acid by volume. Tests concerning the corrosion to the steel tank illustrated that the corrosion rate of water layer after treated by ClO 2 was lowered to 0.151 mm/a, which was below the national standard. Based on the theoretical analysis and experimental results, a mechanism was presented for understanding the ClO 2 demulsification. The developed ClO 2 -oxidation-based demulsification technology can be practically applied to the pilot operations in oilfields.

The indiscriminate use of hair dyes has attracted great deal of attention due to its toxicological and mutagenic aspects demonstrated by some of these substances. Thus, the effluent from beauty salons and domestic sewages if not properly treated can reach water treatment plants and water sources, enhancing human health and environmental protection concern. This work explores the application of photoelectrocatalytic process on Basic Brown 16 and Basic Blue 99 degradation as model of basic hair dyes pollutants. W/WO 3 electrode was used as photoanode under optimized conditions of 0.10 mol L –1 Na 2 SO 4 as electrolytic solution, pH 2.0, under 1.25 mA cm –2 of controlled current density application and visible light irradiation. The process leads to complete color removal, and up to 59 % and 44 % mineralization of Basic Brown 16 and Basic Blue 99, respectively. The use of W/WO 3 photoanodes under visible irradiation could assist on development of wastewater treatment technology.

Advanced oxidation processes (AOPs) constitute a promising technology to treat wastewater containing organic pollutants that are not easily biodegradable. They have received increasing attention in the research and development of wastewater treatment technologies in recent decades for their removal or degradation of recalcitrant pollutants or as pretreatments to convert pollutants into smaller compounds, which can be treated using conventional biological methods. Polyvinyl alcohol (PVA) is a typical refractory organic pollutant. It has received special attention due to its low biodegradability and the large amount of PVA-containing wastewater discharged from textile and paper mills. This review focuses on PVA removal and PVA wastewater pretreatment by AOPs, which include ozonation, Fenton oxidation, persulfate oxidation, ultrasound cavitation, ionizing radiation, photocatalytic oxidation, wet air oxidation and electrochemical oxidation. The mechanistic degradation pathways of PVA by AOPs are also discussed. In addition, a new classification of AOPs is applied for PVA treatment.

Imidacloprid is one of the most widely used insecticides in agriculture. The fate of this highly recalcitrant pollutant and its by-product of incomplete degradation in water is of great concern due to the hazardous effects usually associated to pesticides. In the present manuscript, imidacloprid degradation by hydroxyl radical produced in-situ by conventional Fenton process is discussed. Furthermore, it has been studied the influence of propylene glycol, which is a usual excipient found in the commercial pesticides containing imidacloprid, on the conventional Fenton process performance. A two-stage degradation kinetics was observed: (i) a rapid initial decay on the first 5 min of treatment, followed by (ii) a slower kinetics defined by the Fenton-like reaction of Fe 2+ catalyst regeneration. The influence of several variables on the abatement of imidacloprid such Fe 2+ and H 2 O 2 initial concentration or propylene glycol ratios have been evaluated. Experimental results demonstrate that complete imidacloprid abatement is attained under optimal conditions of 8.0 mM of H 2 O 2 and 0.8 mM of Fe 2+ after 120 min of treatment at acidic pH. However, increasing concentrations of propylene glycol diminishes the overall performance due to the competitive consumption of hydroxyl radicals.

Flower-structured BiOBr photocatalyst has been synthesized successfully with Gemini surfactant as bromine source through chemical precipitation procedure. The structure, morphology and optical absorption property of the product have been characterized. The results reveal that the product is pure tetragonal phase BiOBr with band gap energy ( E g ) of 2.7 eV. Gemini surfactant 1,2-bis (dodecyldimethylammonio) ethane dibromide exhibits a significantly impact on the morphology of flower-structured BiOBr. A possible formation mechanism is proposed. In addition, the BiOBr shows excellent photocatalytic activity and high stability towards rhodamine B (RhB) degradation, which can be attributed to its flower-shaped structure, low E g , and high photocurrent density. Considering the facile and eco-friendly procedure for the fabrication of BiOBr with superior visible light-induced photoactivity, it is possible to apply this semiconductor material in the field of waste water treatment practically.

In the present research, titanium nanotubes were synthesized via the soft hydrothermal method. A study on the effect of the synthesizing parameters such as aging temperature and time of the hydrothermal process on the photocatalytic paraquat degradation was explored. Central Composite Design (CCD) was used to determine the influence of the preparation parameter on the optimal condition, main and interaction effects on crystalline size, percent paraquat removal by adsorption and photocatalytic degradation as responses. The XRD pattern of the synthesized nanomaterial reported the anatase phase of titania nanotubes. SEM image of the prepared nanomaterial clearly indicated the agglomerated with tubular structure. Band gap energy of the nanotubes was found lower than that of the pure anatase TiO 2 . Paraquat removal by adsorption is more effective than by photocatalytic degradation. The error of the model remains insignificant for all the three responses.

Profenofos, an organophosphorus pesticide, has been reported its contamination in groundwater. The current study emphasized on the use of integrated bioaugmentation and biostimulation techniques to enhance profenofos bioremediation. A profenofos-degrading consortium including Pseudomonas strains was chosen as a bioaugmented culture. For stimulated condition adjustment, sodium succinate as an additional organic carbon supplement (4-500 mg-carbon/L) was applied in batch experiment. Column experiment was carried out for investigating profenofos remediation with different infiltration rates and cell numbers of 25 to 100 cm/d and 10 5 and 10 15 CFU/mL, respectively. The batch result showed that the experiment with sodium succinate supplement efficiently degraded profenofos of more than 80%. At profenofos concentrations of 20 to 120 mg/L, the profenofos degradation ranged from 85 to 91%. For the column experiment, profenofos removal was between 30 to more than 90%. The infiltration rates and microbial numbers significantly affected the profenofos degradation. Lower infiltration rates or higher cell number resulted in higher profenofos removal performance. Based on the result from this study, it indicated that the profenofos degradation by the bioaugmented consortium under stimulated condition is effective and potential for future remediation practice.

Present work investigated the degradation of phenol based on theoretical knowledge of bubble dynamic and experimental studies. Optimum parameters of theoretical knowledge such as initial concentration of phenol: 1.1 mole/L; concentration of additive: 2 g/L; liquid medium temperature: 35°C and pressure of liquid medium: 101325 Pa were considered for the experimental study. The degradation was further explored in the presence of zinc oxide (effect of particle size), hydrogen peroxide (effect on hydroxyl radical concentration), and sodium chloride (effect of a change in liquid properties) and its effect on degradation of phenol. The degradation of phenol increased in the presence catalyst such as 0.61±0.013 moles L -1 min -1 (hydrogen peroxide), 0.44±0.014 moles L -1 min -1 (zinc oxide), and 0.5±0.013 moles L -1 min -1 (sodium chloride) compare to the absence of catalyst 0.24±0.009 moles L -1 min -1 . The results confirmed that maximum degradation of phenol obtains in the presence of hydrogen peroxide (cavitational yield: 15.9×10 -5 mg/J, the rate constant: 4.8×l0 -5 min -1 , and TOC removal 28.5%). The presence of sodium chloride showed the considerable effect on degradation and TOC removal. Results confirmed that the degradation of phenol is driven by the hydroxyl radicals’ mechanism and increased with increase in the concentration of hydroxyl radicals. The degradation of phenol was highly dependent on the concentration of phenol near vicinity of the liquid-bubble interface.

A bacterial culture, which was mixed by three thermophilic iron-oxidizing bacteria, namely Sulfobacillus thermosulfidooxidans , Leptospirillum ferriphilum and Acidithiobacillus caldus , was used to solubilize low grade rock phosphate (RP) in 9K basal salts medium containing pyrite as an energy substrate. Culture of a single mesophilic iron-oxidizing bacterium Acidithiobacillus ferrooxidans was used as control. Experimental results show that the phosphate solubilizing capacity of the mixed thermophilic iron-oxidizing bacteria was more effective than that of the single bacterium, and such positive effect was mainly attributed to the bioaugmentation of pyrite oxidation with coinoculation of these thermophilic iron-oxidizing bacteria. Results also show that the biosolubilization of low-grade RP by the mixed thermophilic iron-oxidizing bacteria was influenced markedly by environmental conditions. The highest phosphate releasing rate was achieved at 45-50°C. The rate of phosphate released was highest when the pH was at range from 2.0 to 2.5. The increase in pulp density generates a decrease in the phosphate releasing rate, if the pulp density exceeded 3% w/v. The culture led to the highest phosphate releasing rate when the mass ratio of pyrite to RP was at 2:1 or 3:1. However, volume ratio between thermophilic iron-oxidizing bacteria had no significant effect on the rate of phosphate released.

The dielectric barrier discharge (DBD) technique based cylindrical water falling film reactor was used for degrading an azo dye methyl orange (MO). The primary conditions affecting the degradation of methyl orange were systematically investigated. After 30 min plasma treatment, the degradation rate of MO was as high as 93.7% with gas velocity of 300 mL/min and the input energy of 72.5W. The influences of initial pH and conductivity of MO solution were also explored. The results indicated that the optimum pH value was 3.02 and 99.1% removal of MO was achieved within 30 min. Three catalytic systems DBD/Fe 2+ , DBD/PS (persulfate) and DBD/Fe 2+ /PS were examined to improve the degradation rate and the chemical oxygen demand (COD) removal rate of MO. The highest degradation rate (100%) and COD removal rate (72.4%) happened in DBD/Fe 2+ /PS system. The degradation products were analyzed by LC-MS in DBD system and DBD/Fe 2+ /PS system respectively, and then the possible degradation pathways of MO were proposed.

The electrochemical generation of hydrogen peroxide with boron doped diamond electrodes was experimentally investigated to assess the influence of basic operating parameters on H 2 O 2 production rate. Experiments were conducted in an undivided electrolytic cell, at room temperature, and different operating conditions of air bubbling, stirring and current density. Current density was the most influencing parameter affecting H 2 O 2 generation. Therefore, an equation was proposed to describe hydrogen peroxide generation at BDD electrodes as a function of current density and electrolysis time. Experimental data showed that H 2 O 2 concentration significantly increased during the first 45 min of electrolysis, and thereafter it remained constant until the end of the reaction. The equation was able to describe well this H 2 O 2 production pattern. Additional experiments were conducted to validate the proposed equation. Good agreement between theoretical predictions and experimental data, as assessed by the Chi square goodness of fit test, was observed.