On the degradability of printing and dyeing wastewater by wet air oxidation

A review on the removal of Cl(-I) with high concentration from industrial wastewater: Approaches and mechanisms

Large quantities of wastewaters containing high concentrations of Cl(-I) can be generated in several industries when chloride-containing materials and additive agents are employed. Because Cl(-I) is unavailable to microorganisms, physicochemical methods are generally used for the removal of Cl(-I); however, as the most stable form of chlorine under aqueous conditions, Cl(-I) in wastewaters is difficult to remove to achieve low residual concentrations through common physicochemical methods. This paper provides new insights into traditional precipitation, oxidation, ion exchange and physical separation methods, as well as newly developed approaches, for Cl(-I) removal from various industrial wastewaters through analysis of the mechanisms, applicable conditions, optimum parameters, and method advantages and disadvantages. Moreover, the developmental trends and potential improvements to these approaches are also presented. Currently, precipitation is the most common and efficient Cl(-I) removal method, for which ultraviolet (UV) light is regarded as an effective means of improvement. Additionally, advanced oxidation processes (AOPs), where Cl(-I) can be oxidized to generate Cl radicals, Cl₂^- radicals, Cl₂ gas, etc., show great promise for Cl(-I) removal. This review provides a theoretical foundation for the effective treatment and for the secondary utilization of industrial wastewaters containing Cl(-I).

Recycling Iron-Containing Sludges from the Electroflocculation of Printing and Dyeing Wastewater into Anode Materials for Lithium-Ion Batteries

Iron-containing sludges (DW/Fe) were prepared by the electroflocculation of industrial printing and dyeing wastewater (DW). To investigate the formation process and the properties of the DW/Fe sludges and their application in anode materials in Li-ion batteries, the DW/Fe sludges were compared to three other sludges (MB/Fe, RB/Fe, Ta/Fe) prepared from model solutions that contained either methyl blue (MB), rhodamine B (RB), or tartrazine (Ta). The DW/Fe sludges were calcined at 500 °C under N₂ to form iron oxide/carbon composite C-DW/Fe. The composition and structure of the sludges and the C-DW/Fe composite were analyzed by using FTIR spectroscopy, XRD, thermogravimetric analysis, SEM, TEM, and X-ray photoelectron spectroscopy, and their performances as anodes of Li-ion batteries were studied by adding different proportions of conductive agent (super P® conductive carbon black). Our results show that the sludges are a complex mixture of Fe₃ O₄ and organic matter. The specific capacity and stability can be improved during the charge-discharge test by increasing the amount of carbon black. Importantly, this improvement is more pronounced on DW/Fe that does not require high-temperature carbonization, which means that the sludges cannot only protect the environment and avoid the waste of resources but also can be used directly and widely in decentralized energy storage devices.

Kinetic study of glyphosate degradation in wet air oxidation conditions

Glyphosate is one of the most widely used herbicides in the world against perennial and annual weeds. It has been reported to be a micro pollutant, and its degradation in different wastewater treatment processes must be studied. For that purpose, the kinetics of wet air oxidation of glyphosate was studied in an autoclave reactor at a temperature range of 423-523 K and under a total pressure of 15 MPa. Oxidation reactions obeyed the first-order kinetics with respect to glyphosate concentration. The activation energy for glyphosate oxidation was found to be equal to 68.4 kJ mol-1. Furthermore, the possible reaction intermediates and main end products of glyphosate degradation in the wet air oxidation process were identified and quantified using UV-spectrophotometry and liquid chromatography coupled to high resolution mass spectrometry. A degradation pathway for glyphosate oxidation was proposed.

TiO2 nanodots anchored on nitrogen-doped carbon nanotubes encapsulated cobalt nanoparticles as photocatalysts with photo-enhanced catalytic activity towards the pollutant removal

Constructing hierarchical structure is an effective approach to improve the activities of catalysts. Herein, a novel hierarchical structure of TiO₂ nanodots anchored on N-doped carbon nanotubes encapsulated Co nanoparticles (TiO₂/Co@NCT) was synthesized by a simple pyrolysis method. Their catalytic performances were examined in the oxidative and light-assisted degradation of recalcitrant pollutants in the presence of the peroxymonosulfate (PMS). The Orange II removal efficiency within 15 min reached about 98.48% in TiO₂/Co@NCT/PMS system. In this system, Co⁰ is used to react with PMS to generate free radicals for the degradation of dyes. The carbon shell benefits the adsorption of dyes and prevents the catalysts from dissolving in the solution. Besides, under light irradiation, TiO₂ nanodots can be excited to generate photo-induced electrons, which can reduce inner Co²⁺ to Co⁰ in the degradation process, thus TiO₂/Co@NCT exhabited high activity and outstanding stability in degradation process. The as-prepared TiO₂/Co@NCT catalyst showed efficient degradation and superior stability, which would make it a great promise in practical applications for sewage treatment.

Catalytic wet air oxidation of aqueous solution of phenol in a fixed bed reactor over Ru catalysts supported on ceria promoted MCM-41

Catalytic wet air oxidation (CWAO) of phenol was carried out in a fixed bed reactor over a noble metal (Ru) supported on silica MCM-41 material.

MIL-53(Fe) as a highly efficient bifunctional photocatalyst for the simultaneous reduction of Cr(VI) and oxidation of dyes

A bifunctional photocatalyst-Fe-benzenedicarboxylate (MIL-53(Fe)) has been synthesized successfully via a facile solvothermal method. The resulting MIL-53(Fe) photocatalyst exhibited an excellent visible light (λ≥ 420nm) photocatalytic activity for the reduction of Cr(VI), the reduction rate have reached about 100% after 40min of visible light irradiation, which has been more efficient than that of N-doped TiO2 (85%) under identical experimental conditions. Further experimental results have revealed that the photocatalytic activity of MIL-53(Fe) for the reduction of Cr(VI) can be drastically affected by the pH value of the reaction solution, the hole scavenger and atmosphere. Moreover, MIL-53(Fe) has exhibited considerable photocatalytic activity in the mixed systems (Cr(VI)/dyes). After 6h of visible light illumination, the reduction ratio of Cr(VI) and the degradation ratio of dyes have been exceed 60% and 80%, respectively. More significantly, the synergistic effect can also be found during the process of photocatalytic treatment of Cr(VI) contained wastewater under the same photocatalytic reaction conditions, which makes it a potential candidate for environmental restoration. Finally, a possible reaction mechanism has also been investigated in detail.

Ceria promoted γ-Al2O3 supported platinum catalyst for catalytic wet air oxidation of oxalic acid: kinetics and catalyst deactivation

Alumina-supported platinum catalysts were prepared for catalytic wet air oxidation of oxalic acid.

Ni/Fe-supported over hydrotalcites precursors as catalysts for clean and selective oxidation of Basic Yellow 11: reaction intermediates determination

In this work, Basic Yellow 11 (BY 11) was employed as model compound to study catalytic wet air oxidation as a pre-treatment step to the conventional biological oxidation. Ni and Fe catalysts supported over hydrotalcite (HT) were prepared by incipient wetness and excess impregnation to obtain catalysts with different metal loadings (from 1 to 10 wt.%). HTs were synthesized by co-precipitation and characterized with XRD, X-ray fluorescence (XRF), BET, thermogravimetric analysis and SEM. Results showed that dye conversion increased with Ni and Fe content up to 7 wt.% and that the most effective catalyst were prepared by incipient wetness impregnation. The influence of metal loading in the catalyst, and the preparation method as well as the reaction conditions was investigated. A mechanism and reaction pathways for BY 11 during catalytic liquid phase oxidation have also been proposed.

Treatment of a non-azo dye aqueous solution by CWAO in continuous reactor using a Ni catalyst derived from hydrotalcite-like precursor

Catalytic wet air oxidation (CWAO) of a Basic Yellow 11 (BY11) aqueous solution, chosen as a model of a hardly biodegradable non-azo dye was carried out in a continuous-flow trickle-bed reactor, using nickel supported over hydrotalcite precursor calcined at 550°C. An increase in the reaction temperature (120-180°C), and a decrease in dye concentration (1000-3000 ppm) or liquid flow rate (0.1-0.7 mL min(-1)) enhanced the CWAO performance in a 30 and 19% for the variation of the temperature and concentration respectively. After a small leaching observed within the first hours, the catalyst proved to be very stable during the 65-day reaction. The CWAO process was found to be very efficient, achieving BY11 conversion up to 95% and TOC conversion up to 85% at 0.1 mL min(-1) and 180°C under 5 MPa air.

Improving the simultaneous removal efficiency of COD and color in a combined HABMR-CFASR system based MPDW. Part 1: optimization of operational parameters for HABMR by using response surface methodology

The aim of this study was to implement central-composite design (CCD) and response surface methodology (RSM) to optimize the operational parameters for hybrid anaerobic baffled microbial reactor (HABMR) remedying mixed printing and dyeing wastewater (MPDW). The individual and interactive effects of three variables, hydraulic retention time (HRT), pH, sludge loading rate (SLR) on the COD and color removal rates were evaluated. In the area of HRT: 12.5-13.9 h, pH: 9.0-9.5 and SLR: 0.27-0.33 kg COD/(kg MLVSSd), COD and color removal rates of HABMR exceeded 40% and 60%, simultaneously. The check experiment revealed that the amount of COD and color in the effluent could be decreased by 9.97% and 10.12% compared to the usual operating conditions, respectively. The results verified that the RSM was useful for optimizing the operational parameters of HABMR in treating MPDW.

Treatment of municipal landfill leachate by catalytic wet air oxidation: Assessment of the role of operating parameters by factorial design

The wet air oxidation (WAO) of municipal landfill leachate catalyzed by cupric ions and promoted by hydrogen peroxide was investigated. The effect of operating conditions such as WAO treatment time (15-30min), temperature (160-200°C), Cu(2+) concentration (250-750mgL(-1)) and H(2)O(2) concentration (0-1500mgL(-1)) on chemical oxygen demand (COD) removal was investigated by factorial design considering a two-stage, sequential process comprising the heating-up of the reactor and the actual WAO. The leachate, at an initial COD of 4920mgL(-1), was acidified to pH 3 leading to 31% COD decrease presumably due to the coagulation/precipitation of colloidal and other organic matter. During the 45min long heating-up period of the WAO reactor under an inert atmosphere, COD removal values up to 35% (based on the initial COD value) were recorded as a result of the catalytic decomposition of H(2)O(2) to reactive hydroxyl radicals. WAO at 2.5MPa oxygen partial pressure advanced treatment further; for example, 22min of oxidation at 200°C, 250mgL(-1) Cu(2+) and 0-1500mgL(-1) H(2)O(2) resulted in an overall (i.e. including acidification and heating-up) COD reduction of 78%. Amongst the operating variables in question, temperature had the strongest influence on both the heating-up and WAO stages, while H(2)O(2) concentration strongly affected the former and reaction time the latter. Nonetheless, the effects of temperature and H(2)O(2) concentration were found to depend on the concentration levels of catalyst as suggested by the significance of their 3rd order interaction term.

Assessment of the manganese content of the drinking water source in Yancheng, China

Excessive intake of manganese can damage the nervous system of the human body. In August 2009, the manganese content of the drinking water source in Yancheng exceeded the national standard of drinking water source, which influenced the daily life of the local residents. The aim of this study was to investigate the factors leading to the manganese content of river water in Yancheng exceeding the national standard. To the data, the manganese content of surface water in Yancheng already met the national standard of drinking water source in September 2009, but the manganese content of river sediment was relatively high, especially in Mangshe River and Tongyu River. It was worthwhile to note that the soluble manganese content of the sediment in Mangshe River was even as high as 270 mg kg(-1), which suggested that the release of manganese from the sediment was the major cause of the pollution. The manganese content of the soil near the rivers was also determined, and the results indicated that the wastewater and waste slag discharged by the stainless steel factories nearby were the main pollution sources of manganese. Furthermore, the environmental factors affecting the release of manganese from the sediment were also investigated.

Decolorization of cationic red X-GRL by wet air oxidation: performance optimization and degradation mechanism

The decolorization of a strong colored azo dye solution of cationic red X-GRL was investigated by wet air oxidation under relatively mild conditions (60-180 degrees C, PO2 = 0-1.2 MPa). Mono-factor experiments were carried out to investigate the effect of the operation factors and the relatively important parameters were selected for optimization using response surface methodology to explore the interactions of these relatively important parameters. Model regeneration analysis and the check experiments showed that the data of the general linear model agreed with the experiment results well. With multistage Monte-Carlo optimization, the best region of these variables could be predicted to dye color removal. At typical operational conditions, the intermediates of dye degradation were detected and confirmed by GC/MS system. Considering the intermediates and the structure analysis with the help of Gaussian 03W (version 6.0) and the theory of dye color, a possible degradation mechanism for the wet air oxidation of cationic red X-GRL was discussed and the probable degradation pathway was deduced.

An assessment of the suitable operating conditions for the CeO2/gamma-Al2O3 catalyzed wet air oxidation of phenol

It has been shown that the CeO2/gamma-Al2O3 catalyst is a feasible alternative to CeO2 for the catalytic wet air oxidation (CWAO) of phenol because it remains an effective catalyst and yet is cheaper to prepare. In this study, we found that the optimal cerium content in the CeO2/gamma-Al2O3 catalyst was 20 wt.%, regardless of catalyst loading. Furthermore, at 180 degrees C, with a phenol concentration of 1000 mg l(-1), and an O2 partial pressure of 1.0M Pa or 1.5M Pa, the optimal catalyst loading was 3.0 gl (-1). The efficacy of CWAO of phenol improved with O2 partial pressure, although the effects of O2 pressure were more significant between 0.5 MPa and 1.5 MPa than between 1.5 MPa and 2.0 MPa. After 2 h of reaction, approximately 100% phenol conversion and 80% total organic carbon (TOC) removal was recorded at 180 degrees C, 1000 mg l(-1) of phenol and 3.0 g l(-1) of catalyst. Because these percentages subsequently leveled off, it is suggested that 2 h is a suitable time over which to run the reaction. The efficacy of CWAO of phenol decreased as initial phenol concentration was raised (from 400 to 2500 mg l(-1)), with the exception of phenol conversion after about 2 h, for which 400 mg l(-1) produced the lowest phenol conversion figure. Higher phenol concentrations require both catalyst loading and O2 partial pressure to be increased to maintain high performance. For example, for 2000 mg l(-1) and 2500 mg l(-1) phenol, nearly 100% phenol conversion and 90% TOC removal after 4 h of reaction at 180 degrees C required 4.0 g l(-1) of catalyst and 2.0 MPa.

Wet air oxidation of a reactive dye solution using CoAlPO(4)-5 and CeO(2) catalysts

Wet air oxidation of a prepared reactive dye solution was performed to assess the efficacy of CoAlPO(4)-5 and CeO(2) as catalysts in the reaction. Via adsorption and oxidation of dye, CoAlPO(4)-5 effectively decreased American Dye Manufacturers Institute and chemical oxygen demand (COD) values in the dye solution. At a reaction temperature of 135 degrees C and an applied pressure of 1.0 MPa, color and COD removal were as high as 95% and 90%, respectively, after 2 h. Active sites on the outer surface of CoAlPO(4)-5 are responsible for adsorption and decomposition of dye while active sites in the pores dominate further destruction and oxidation of intermediate products. Since the outer surface only represents a minor part of the total surface, the color removal does not increase appreciably with loading of CoAlPO(4)-5. The CeO(2) catalyst, calcined from cerium chloride under high thermal impact (type A CeO(2)) was very effective in removing color and COD from the solution. This catalyst demonstrated near 100% color removal at temperatures above 135 degrees C and the COD removal could be above 95% at 165 degrees C. With both CoAlPO(4)-5 and CeO(2) catalysts, COD rose and then fell back during the reaction, a feature typical of a consecutive reaction. In contrast to prepared CeO(2), a commercial CeO(2) did not exhibit any catalytic ability for the removal of color and COD. The durability of both CoAlPO(4)-5 and prepared CeO(2) is considered to be fair.

Catalytic wet air oxidation of phenol by CeO2 catalyst--effect of reaction conditions

The effect of catalyst loading, oxygen pressure, reaction temperature and phenol concentration on phenol conversion and total organic carbon (TOC) conversion, using CeO(2) as the catalyst, was investigated. There appeared a maximum rate of phenol conversion and TOC conversion as the catalyst loading increased. With phenol concentrations in the range of 400-2500 mg/L and oxygen pressure of 0.5 or 1.0 MPa, the optimal catalyst loading was 1.0 g/L, while it was 2.0 g/L at an oxygen pressure of 1.5 MPa. With a phenol concentration of 5000 mg/L, the optimal loading was 2.0 g/L for all oxygen pressures tested. Catalyst loading influences the reaction via the free-radical chain reaction involved in the catalytic wet air oxidation of phenol. Regarding oxygen pressures, at a phenol concentration of 400mg/L, the influence of the tested pressures (0.5, 1.0 and 1.5 MPa) on the 3h conversion of phenol was negligible, while the effect was significant for higher concentrations of phenol. The effect of oxygen pressure on TOC conversion was more profound, especially at a higher phenol concentration. At a pressure of 0.5 MPa, except for concentration of 400mg/L, the CO(2) selectivity barely exceed 80% at best, and was less than 25% with a phenol concentration of 5000 mg/L. At a pressure of 1.5 MPa, the selectivity was as high as 90% even for a concentration of 5000 mg/L. As was expected, increase of reaction temperature shortened the time taken to reach 50% phenol conversion. In addition, TOC conversion also increased with reaction temperature. Working from these observed results, optimal operating conditions were proposed.

Catalytic wet air oxidation of phenol using CeO2 as the catalyst. Kinetic study and mechanism development

Using a CeO2 catalyst prepared from CeCl3.7H2O under high thermal impact, the catalytic wet air oxidation (CWAO) of phenol was effectively implemented. With initial phenol concentrations of between (400 and 2500) mg/L, and at a temperature of 160 degrees C, the rate of phenol conversion increased with increased catalyst loading (0.2g/L-1.0g/L) and oxygen pressure (0.5 MPa-1.5 MPa). Even at an initial concentration of 2500 mg/L, conversion of phenol was as high as 95% after 3 h reaction. The effect of phenol concentration, catalyst loading, and oxygen pressure on the initial rate of phenol conversion was evaluated in a kinetic study. The initial rate equation derived from kinetic study is: Ro=k1 x [Ph]1.3-1.4 x W0.5-0.6 x PO2(0.9-1.1), where k1 is a rate constant, and [Ph], W and PO2 refer to phenol concentration, catalyst loading and oxygen pressure, respectively. A free-radical involved reaction mechanism was proposed and an initial rate expression based on this mechanism was derived: Ro = k2 x [Ph]1.5 x W0.5, where k2 is also a rate constant. Fitting of experimental data with the theoretically derived initial rate equation resulted in good correlation: the coefficient is greater than 0.99.

Wet oxidation: a pre-treatment procedure for sludge

Wet oxidation process is specially effective for wastes with a high organic matter which can not be removed by conventional treatment methods. The digested and raw activated sludges of PAKMAYA yeast factory are treated by wet oxidation process. The liquid-phase organic matter concentration [as total organic carbon (TOC)] was increased by 16.5% in 10 min during the wet oxidation in the presence of Cu as catalyst and H2O2. Lenghtening the period of the wet oxidation, the TOC-concentration was increased by 66% in 120 min. The biodegradability of the sludge after wet oxidation process was also examined. A very little development in the biodegradability was observed, when wet oxidation was applied as pre-treatment to the digested sludge (5% decrease as TOC, in the presence of Cu catalyst and H2O2). However, in the case of digestion of the raw sludge after the application of wet oxidation, the biodegradability increased significantly (approximately 75%, as TOC). Moreover, wet oxidation improved the ability of settling of sludge solids, as well as enhancing the treatment efficiency. Finally, the volume of settled solids was decreased by 80% in the presence of Cu and H2O2. NH3+-N, NO2(-)-N and NO3(-)-N concentrations in the supernatant decreased with the wet oxidation. pH value of the sludge increased from 6.6 to 7.8-8.0. Since stable sludge was taken from the digester where the nitrification process was progressing, a decrease in the nitrite concentration, with an increase in nitrate was observed in the digestion continuing after the wet oxidation pre-treatment. However, in the raw activated sludge, there was a nitrite formation only in the non-pretreated sludge.