Development and optimization of dark Fenton oxidation for the treatment of textile wastewaters with high organic load

The examination of the effectiveness of the chemical oxidation using Fenton's reagent (H(2)O(2)/Fe(2+)) for the reduction of the organic content of wastewater generated from a textile industry has been studied. The experimental results indicate that the oxidation process leads to a reduction in the chemical oxygen demand (COD) concentration up to 45%. Moreover, the reduction is reasonably fast at the first stages of the process, since the COD concentration is decreased up to 45% within four hours and further treatment time does not add up to the overall decrease in the COD concentration (48% reduction within six hours). The maximum color removal achieved was 71.5%. In addition, the alterations observed in the organic matter during the development of the process, as indicated by the ratios of COD/TOC and BOD/COD and the oxidation state, show that a great part of the organic substances, which are not completely mineralized, are subjected to structural changes to intermediate organic by-products.     

Use of EAF dust as heterogeneous catalyst in Fenton oxidation of PCP contaminated wastewaters

In this study, chemical oxidation tests using H2O2 were performed on a solution contaminated with 100 mg l(-1) of pentachlorophenol (PCP). The effectiveness of electric arc furnace dust and hematite as heterogeneous catalysts was evaluated. Reactions were conducted at pH 2 for 24 h. Either H2O2 stabilized with KH2PO4 or un-stabilized H2O2 was used. Total organic carbon (T.O.C.) removal and chloride release from PCP molecule were monitored. Results showed that the maximum removal yields for electric arc furnace (EAF) dust (49.2% T.O.C., 56.7% Cl) were achieved when H2O2:PCP ratio was 10:1 and Fe:H2O2 = 1:5 for unstabilized H2O2 and when H2O2:PCP = 10:1 and Fe:H2O2 = 1:1 for stabilized H2O2 (48% T.O.C., 60.6% Cl). The maximum yield using hematite (45.2% T.O.C., 55.2% Cl) was obtained when H2O2:PCP ratio was 10:1 and Fe:H2O2 was 1:2. When EAF dust was used and Fe:H2O2 > 1:5, Cl release was higher than the one expected from T.O.C. removal.     

Wet air oxidation studies of coal gasification wastewaters

The kinetics of wet oxidation of coal gasification wastewater were studied. Experimental studies explored the effect of temperature and residence time on the extent of reaction by conducting constant volume batch tests in a 1-liter high pressure autoclave. The extent of reaction was determined by measuring the chemical oxygen demand (COD) and phenol concentrations of the wastewater at various times.The effect of temperature was studied from 205 to 251°C with residence times from 30 to 90 minutes. The experimental data obtained were used to fit Arrhenius expressions of the reactions. A mathematical model consisted of two first-order reactions in series showing a maximum COD reduction of 60% and a maximum phenol reduction of 95%, both at 251°C and a 90 minute residence time. The activation energies for COD and phenol reduction were both found to be 8.0 kcall.     

Treatment of industrial oily wastewaters by wet oxidation

In the present work, the homogeneous wet oxidation (WO) of an oily wastewater (COD approximately 11,000 mg l(-1)), composed mainly of alcohols and phenolic compounds, was studied in a high-pressure agitated autoclave reactor in the temperature range of 180-260 degrees C and oxygen pressure 1 MPa. Temperature was found to have a significant impact on the oxidation of the contaminants in the wastewater. Among the compounds contained in the wastewater, ethylene glycol showed great resistance to wet oxidation. Temperatures above 240 degrees C were required for its effective degradation. Organic acids, mainly acetic acid, were the intermediate products of the wet oxidation process and their conversion to carbon dioxide was very slow. A generalised model based on a parallel reaction scheme was used to interpret the experimental data obtained. The activation energies obtained were in the range of 90-130 kJ mol(-1).     

Use of Fenton oxidation to improve the biodegradability of a pharmaceutical wastewater

The applicability of Fenton's oxidation to improve the biodegradability of a pharmaceutical wastewater to be treated biologically was investigated. The wastewater was originated from a factory producing a variety of pharmaceutical chemicals. Treatability studies were conducted under laboratory conditions with all chemicals (having COD varying from 900 to 7000 mg/L) produced in the factory in order to determine the operational conditions to utilize in the full-scale treatment plant. Optimum pH was determined as 3.5 and 7.0 for the first (oxidation) and second stage (coagulation) of the Fenton process, respectively. For all chemicals, COD removal efficiency was highest when the molar ratio of H(2)O(2)/Fe(2+) was 150-250. At H(2)O(2)/Fe(2+) ratio of 155, 0.3M H(2)O(2) and 0.002 M Fe(2+), provided 45-65% COD removal. The wastewater treatment plant that employs Fenton oxidation followed by aerobic degradation in sequencing batch reactors (SBR), built after these treatability studies provided an overall COD removal efficiency of 98%, and compliance with the discharge limits. The efficiency of the Fenton's oxidation was around 45-50% and the efficiency in the SBR system which has two reactors each having a volume of 8m(3) and operated with a total cycle time of 1 day, was around 98%, regarding the COD removal.     

Catalytic thermal treatment of desizing wastewaters

In the present study, catalytic thermal treatment (thermolysis) was investigated for the reduction of COD and color of the desizing wastewater under moderate temperature and atmospheric pressure conditions using various catalysts. The experimental runs were performed in a glass reactor equipped with a vertical condenser. The homogeneous copper sulfate catalyst was found to be the most active in comparison to other catalysts under similar operating conditions. A removal of about 71.6% chemical oxygen demand (COD) and 87.2% color of desizing wastewater was obtained with a catalyst concentration of 4 kg/m(3) at pH 4. The initial pH value of the wastewater showed a pronounced effect on the precipitation process. During the thermolysis, copper gets leached to the aqueous phase, the residue obtained after the treatment is rich in copper and it can be blended with organic manure for use in agricultural fields. The thermogravimetric analysis showed that the thermal oxidation of the solid residue obtained after thermolysis gets oxidized at a higher temperature range than that of the residue obtained from the desizing wastewater. The results lead to the conclusion that thermochemical precipitation is a very fast (instantaneous) process and would need a very small reactor vessel in comparison to other processes.     

Kinetics of 2,6-dimethylaniline oxidation by various Fenton processes

The kinetics of 2,6-dimethylaniline degradation by Fenton process, electro-Fenton process and photoelectro-Fenton process was investigated. This study attempted to eliminate the potential interferences from intermediates by making a kinetics comparison of Fenton, electro-Fenton and photoelectro-Fenton methods through use initial rate techniques during the first 10 min of the reaction. Exactly how the initial concentration of 2,6-dimethylaniline, ferrous ions and hydrogen peroxide affects 2,6-dimethylaniline degradation was also examined. Experimental results indicate that the 2,6-dimethylaniline degradation in the photoelectro-Fenton process is superior to the ordinary Fenton and electro-Fenton processes. Additionally, for 100% removal of 1 mM 2,6-dimethylaniline, the supplementation of 1 mM of ferrous ion, 20 mM of hydrogen peroxide, current density at 15.89 A m⁻² and 12 UVA lamps at pH 2 was necessary. The overall rate equations for 2,6-dimethylaniline degradation by Fenton, electro-Fenton and photoelectro-Fenton processes were proposed as well.     

Biofilm photobioreactors for the treatment of industrial wastewaters

A flat plate and a tubular packed-bed photobioreactor with an algal-bacterial biofilm attached onto Poraver beads carriers, a flat plate and a tubular photobioreactor with the biofilm attached onto the reactor walls, and an algal-turf reactor were compared in terms of BOD removal efficiencies, elimination capacities, and stability. A control column photobioreactor with suspended algal-bacterial biomass was also tested to compare the performance of biofilm photobioreactors with conventional algal-based processes. When the algal-bacterial biomass was immobilized onto Poraver the process never reached a steady state due to a poor homogenization in the bioreactor. When the biofilm was formed onto the reactor wall (or reactor base) the process was stable. A maximum degradation rate of 295mg BODl(-1)h(-1) was achieved in the algal-turf reactor although control experiments performed in the dark showed atmospheric O2 diffusion represented 55% of the oxygenation capacity in this system. BOD removal rates of 108, and 92mg BODl(-1)h(-1) were achieved in the tubular and flat plate biofilm reactors, respectively, compared to 77mg BODl(-1)h(-1) in the control suspended bioreactor. In addition, all biofilm photobioreactors produced an easily settleable biomass. Evidence was found that biomass attachment to the reactor's wall improved stability.     

Chemical oxidation of 2,4-dimethylphenol in soil by heterogeneous Fenton process

Hydrogen peroxide has been used to oxidize a sorbed aromatic contaminant in a loamy sand with 195.9 g kg(-1) of organic carbon by using iron as catalyst at 20 degrees C. The 2,4-dimethylphenol (2,4-DMP) was chosen as pollutant. Because of this soil generates a slightly basic pH in contact to an aqueous phase the solubility of the iron cation was determined in absence and presence of a chelating agent (l-ascorbic acid, l-Asc) and with and without soil. From results, it was found that in presence of soil the iron cation was always adsorbed or precipitaed onto the soil. Therefore, the procedure selected for soil remediation was to add firstly the iron solution used as catalyst and following the hydrogen peroxide solution used as oxidant. As iron cation is sorbed onto the soil before the oxidant reagent is provided a heterogeneous catalytic system results. This modified Fenton runs have been carried out using 0.11 mg(2,4-DMP) g(-1)(soil) and 2.1 mg(Fe) g(-1)(soil). The H(2)O(2)/pollutant weight ratios used were 182 and 364. The results show that H(2)O(2) oxidizes 2,4-DMP producing CO(2) and acetic acid. After 20 min of reaction time a pollutant conversion of 75% and 86% was found, depending on the H(2)O(2) dosage. Moreover, it was found that hydrogen peroxide was heterogeneously decomposed by the soil (due to its organic and/or inorganic components) and its decomposition rate decreases when the iron was previously precipitated-impregnated into the soil.     

Multivariate approach to the Fenton process for the treatment of landfill leachate

Fenton process has been widely used to treat landfill leachate. The "design of experiments" methodology was used to study the main variables affecting the Fenton process as well as their most relevant interactions. Results of two-level-factorial-design indicated that pH, COD, and the interaction of pH and COD gave negative effects, but Fe(II) dosage and H(2)O(2)/Fe(II) mole ratio showed positive effect, respectively. The quadratic model was derived based on the results of both two-level-factorial-design experiment and further runs of star points and center points. The response surface plots of quadratic model were obtained accordingly and the optimal conditions were derived from the quadratic model.     

A kinetic study on the degradation of p-nitroaniline by Fenton oxidation process

A detailed kinetic model was developed for the degradation of p-nitroaniline (PNA) by Fenton oxidation. Batch experiments were carried out to investigate the role of pH, hydrogen peroxide and Fe(2+) levels, PNA concentration and the temperature. The kinetic rate constants, k(ap), for PNA degradation at different reaction conditions were determined. The test results show that the decomposition of PNA proceeded rapidly only at pH value of 3.0. Increasing the dosage of H(2)O(2) and Fe(2+) enhanced the k(ap) of PNA degradation. However, higher levels of H(2)O(2) also inhibited the reaction kinetics. The k(ap) of PNA degradation decreased with the increase of initial PNA concentration, but increased with the increase of temperature. Based on the rate constants obtained at different temperatures, the empirical Arrhenius expression of PNA degradation was derived. The derived activation energy for PNA degradation by Fenton oxidation is 53.96 kJ mol(-1).     

Alkydic resin wastewaters treatment by fenton and photo-Fenton processes

Advanced oxidation processes are an emerging option to treatment of the painting industry effluents. The aim of this study was to compare the effectiveness of the Fenton and photo-Fenton processes in chemical oxygen demand (COD), total organic carbon (TOC) and phenolic compounds removal from wastewaters generated during alkydic resins manufacture. The optimized treatment conditions are the following: pH 3.0, 15.15x10(-3)molL(-1) FeSO(4) and 0.30molL(-1) H(2)O(2) for a reaction time of 6h. photo-Fenton experiments were carried out in the presence of sunlight or artificial radiation and complementary additions of H(2)O(2) were made for all experiments. The best results were obtained with photo-Fenton process assisted with solar radiation, with reductions of 99.5 and 99.1% of COD and TOC levels, respectively. Fenton and photo-Fenton (with artificial irradiation) processes presented lower but not insignificant removals, within 60-80% reduction for both COD and TOC. In addition, an excellent removal (95%) of total phenols was obtained using photo-Fenton process assisted with artificial irradiation. This study demonstrated that the use of photo-Fenton process on alkydic resins wastewater treatment is very promising especially when solar light is used.     

Comparison of disperse and reactive dye removals by chemical coagulation and Fenton oxidation

The composition of wastewater from the dyeing and textile processes is highly variable depending on the dyestuff type and typically has high COD and color. This study examined the decolorization of some of the most commonly used disperse and reactive dyestuffs by combination of chemical coagulation and Fenton oxidation. In addition, performances between Fe3+ coagulation and Fenton oxidation of dye solutions were compared by measuring COD and dye removals, distributions of zeta potential, concentration of suspended solid were investigated. Fenton oxidation in combination with Fe3+ coagulation has shown to effectively remove COD and dye. About 90% of COD and 99% of dye removals were obtained at the optimum conditions. Compared to reactive dyes, disperse dyes have lower solubility, higher suspended solids concentrations and lower SCOD/TCOD ratios. The COD and dye removed per unit Fe3+ coagulant added for disperse dye solutions were higher than those for reactive dye solutions. Therefore, the disperse dye solutions are more easily decolorized by chemical coagulation than reactive dye solutions. Conversely, reactive dye solutions have higher applicability of Fenton oxidation than disperse dye solutions due to their higher solubility, lower suspended solids concentrations and higher SCOD/TCOD ratios. The COD and dye removed per Fe2+ Fenton reagent added for reactive dye solutions are respectively higher than those for disperse dye solutions.     

Sustainable treatment of wastewaters resulted in the textile dyeing industry

Adsorption on fly-ash-based substrates is discussed as a possible alternative to the industrial processes used for the treatment of wastewaters resulted in the dyeing industry. Three samples, containing four dyes and one conditioner, were collected from the dyeing and rinsing baths in a textile company. Adsorption on fly ash was comparatively discussed with adsorption and photocatalysis, both on fly ash and a mixed suspension with TiO₂. The fly-ash crystalline substrates are characterized by X-ray diffraction (XRD) and morphology studies were done using atomic force microscopy. The wastewater, before and after treatment is characterized by quality indicators (pH, TDS, BOD₅, COD, TOC, color, and total chromium content). The studies allow to calculate the efficiency of the dyes removal process and the kinetic parameters, for the pseudo-second order mechanism. The results show that, in designing an industrial wastewater treatment process, the results obtained in the investigations on single-dye solutions must be completed with data specifically obtained on industrial wastewaters. The data also support the assumption of competitive adsorption, between the initial components and between these and the possible by-products resulted after photocatalysis.     

Comparative study of oxidation of dye-Reactive Black B by different advanced oxidation processes: Fenton, electro-Fenton and photo-Fenton

This study makes a comparison between photo-Fenton and a novel electro-Fenton called Fered-Fenton to study the mineralization of 10,000 mg/L of dye-Reactive Black B (RBB) aqueous solution, which was chosen as the model dye contaminant. Results indicate that the traditional Fenton process only yields 70% mineralization. This result can be improved by using Fered-Fenton to yield 93% mineralization resulting from the action of ferrous ion regenerated on the cathode. Furthermore, photo-Fenton allows a fast and more complete destruction of dye solutions and as a result of the action of ferrous ion regenerated by UV irradiation yields more than 98% mineralization. In all treatments, the RBB is rapidly decayed to some carboxylic acid intermediates. The major intermediates found are formic acid and oxalic acid. This study finds that formic acid can be completely mineralized by photo-Fenton, but its destruction is problematic using the Fenton method. Oxalic acid is much more difficult to treat than other organic acids. It could get further mineralization with the use of the Fered-Fenton process.     

Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: a review

Catalytic wet air oxidation (CWAO) is one of the most economical and environmental-friendly advanced oxidation process. It makes a promising technology for the treatment of refractory organic pollutants in industrial wastewaters. Various heterogeneous catalysts including noble metals and metal oxides have been extensively studied to enhance the efficiency of CWAO. The present review is concerned about the literatures published in this regard. Phenolics, carboxylic acids, and nitrogen-containing compounds were taken as model pollutants in most cases, and noble metals such as Ru, Rh, Pd, Ir, and Pt as well as oxides of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and Ce were applied as heterogeneous catalysts. Reports on their characterization and catalytic performances for the CWAO of aqueous pollutants are reviewed. Discussions are also made on the reaction mechanisms and kinetics proposed for heterogeneous CWAO and also on the typical catalyst deactivations in heterogeneous CWAO, i.e. carbonaceous deposits and metal leaching.     

Olive mill wastewater degradation by Fenton oxidation with zero-valent iron and hydrogen peroxide

The degradation of olive mill wastewater (OMW) with hydroxyl radicals generated from zero-valent iron and hydrogen peroxide has been investigated by means of chemical oxygen demand (COD) and phenolic compounds analyses. The effects of the H2O2 dose, the pH and the organic matter concentration have been studied. The optimal experimental conditions were found to have continuous presence of iron metal, acid pH (2.0-4.0), and relatively concentrated hydrogen peroxide (9.5M). Coloration of OMW disappeared and phenolic compound decreased to 50% of initial concentration after 3h reaction time. The application of zero-valent Fe/H2O2 procedure permitted high removal efficiencies of pollutants from olive mill wastewater. The results show that zero-valent Fe/H2O2 could be considered as an effective alternative solution for the treatment of OMW or may be combined with a classical biological process to achieve high quality of effluent water.     

Treatment of jean-wash wastewater by combined coagulation, hydrolysis/acidification and Fenton oxidation

Performance of a full-scale combined treatment plant for jean-wash wastewater (JWW) was investigated. The combined process consisted of chemical coagulation, hydrolysis/acidification and Fenton oxidation. Chemical coagulation treatment with polymeric ferric sulfate (PFS)/lime alone proved to be effective in removing the COD (>70%) and part of the color (>50%) from the JWW. Fenton oxidation combined with hydrolysis/acidification as pretreatment offered a noticeable BOD removal efficiency. The average removal efficiencies for COD, BOD, SS, color and aromatic compounds of the combined process were about 95%, 94%, 97%, 95% and 90%, respectively, with the average effluent quality of COD 58 mg/L, BOD 19 mg/L, SS 4 mg/L and color 15(multiple), consistent with the national discharge limits for textile wastewater. The result indicated that the combined procedure could offer an attractive solution for JWW treatment with considerable synergistic advantages.     

Biological treatment of mixed industrial wastewaters in a fluidised bed reactor

A study has been carried out on the operating parameters that influence the biodegradation of petroleum and brewery wastewaters, with a low-density biomass support. The biodegradation rate of a mixture of two wastes was compared with that of the separate wastes. A low aspect ratio reactor was employed, and this made it possible to operate at low superficial gas and liquid velocities. The gas distributor used created a fluid flow pattern similar to that of a draft tube, which enhanced axial mixing. At a particles loading of 12% (v/v), the optimum superficial gas velocity was 2.5 cm/s for the mixture. The interstice structure of the biomass-support particles, improved microbial attachment due to the resulting large surface area. There was a low biomass concentration when petroleum wastewater was treated alone, however, for a mixture of petroleum and brewery wastewaters, an increase in the concentration was observed. There was a higher gas hold up in the mixture than in the petroleum wastewater, but lower than in the brewery wastewater. An improved biodegradation was achieved when a mixture of brewery and petroleum wastewaters was treated, and this gave an indication that nutrient deficient wastes can be treated together with phosphate and nitrate rich food industry wastewaters.