Optimization of Fenton process for the treatment of landfill leachate

The treatment of landfill leachate by Fenton process was carried out in a batch reactor. The effect of operating conditions such as reaction time, pH, H2O2 to Fe(II) molar ratio, Fenton's reagent dosage, initial COD strength, feeding mode, the type of polymer, and temperature on the efficacy of Fenton process was investigated. It is demonstrated that Fenton's reagent can effectively degrade leachate organics. Fenton process was so fast that it was complete in 30 min. The oxidation of organic materials in the leachate was pH dependent and the optimal pH was 2.5. The favorable H2O2 to Fe(II) molar ratio was 1.5, and organic removal increased as dosage increased at the favorable H2O2 to Fe(II) molar ratio. The efficacy of Fenton process was improved by adding Fenton's reagent in multiple steps than that in a single step. Furthermore, the stepwise addition of both hydrogen peroxide and ferrous iron was more effective than that of hydrogen peroxide only. Sludge settling characteristics were much improved with the addition of the proper polymer. Temperature gave a positive effect on organic removal.     

Removal of COD from landfill leachate by electro-Fenton method

The treatment of landfill leachate by electro-Fenton (E-Fenton) method was carried out in a batch electrolytic reactor. The effect of operating conditions such as reaction time, the distance between the electrodes, electrical current, H(2)O(2) to Fe(II) molar ratio, Fenton's reagent dosage and H(2)O(2) feeding mode on the efficacy of E-Fenton process was investigated. It is demonstrated that E-Fenton method can effectively degrade leachate organics. The process was very fast in the first 30 min and then slowed down till it was complete in 75 min. There exists an optimal distance range between the electrodes so that an over 7% higher chemical oxygen demand (COD) removal was achieved than the electrodes positioned beyond this range. COD removal efficiency increased with the increasing current, but further increase of current would reduce the removal efficiency. Organic removal increased as Fenton's reagent dosage increased at the fixed H(2)O(2) to Fe(II) molar ratio. COD removal was only 65% when hydrogen peroxide alone was applied to the electrolytic reactor, and the presence of ferrous ion greatly improved COD removal. COD removal efficiency increased with the increase of ferrous ion dosage at the fixed hydrogen peroxide dose and reached highest at the 0.038 mol/L of ferrous ion concentration. COD removal would decrease when ferrous ion concentration was higher than 0.038 mol/L. The stepwise or continuous addition of hydrogen peroxide was more effective than the addition of hydrogen peroxide in a single step. E-Fenton method showed the synergetic effect for COD removal as it achieved higher COD removal than the total COD removal by electrochemical method and Fenton's reagent.     

Physical and oxidative removal of organics during Fenton treatment of mature municipal landfill leachate

Municipal landfill leachate, especially mature leachate, may disrupt the performance of moderately-sized municipal activated sludge wastewater treatment plants, and likewise tend to be recalcitrant to biological pretreatment. Recently, Fenton methods have been investigated for chemical treatment or pre-treatment of mature leachate. In this paper, the results of laboratory tests to determine the roles of oxidation and coagulation in reducing the organic content of mature leachate during Fenton treatment are presented. The efficiencies of chemical oxygen demand (COD) oxidation and coagulation were tested, and the ratio of COD removal by oxidation to that by coagulation was assessed, under various operating conditions. Low initial pH, appropriate relative and absolute Fenton reagent dosages, aeration, and stepwise addition of reagents increased COD removal by oxidation and the importance of oxidation relative to coagulation. Simultaneous aeration and stepwise reagent addition allowed comparable treatment without initial acidification pH, due to the generation of acidic organic intermediates and the continuous input of CO2. On the other hand, high COD oxidation efficiency and low ferrous dosage inhibited COD removal by coagulation. At significantly high oxidation efficiency, overall COD reduction decrease slightly due to low coagulation efficiency. Under the most favorable conditions (initial pH 3, molar ratio [H(2)O(2)]/[Fe2+]=3, [H2O2]=240 mM, and six dosing steps), 61% of the initial COD was removed, and the ratio of COD removal oxidation to coagulation was 0.75. Results highlighted the synergistic roles of oxidation and coagulation in Fenton treatment of mature leachate, and the role of oxidation in controlling the efficiency of removal of COD by coagulation.     

Use of Fenton reaction for the treatment of leachate from composting of different wastes

The oxidation of leachate coming from the composting of two organic wastes (wastewater sludge and organic fraction of municipal solid wastes) using the Fenton's reagent was studied using different ratios [Fe(2+)]/[COD](0) and maintaining a ratio [H(2)O(2)]/[COD](0) equal to 1. The optimal conditions for Fenton reaction were found at a ratio [Fe(2+)]/[COD](0) equal to 0.1. Both leachates were significantly oxidized under these conditions in terms of COD removal (77 and 75% for leachate from wastewater sludge composting and leachate from organic fraction of municipal solid wastes, respectively) and BOD(5) removal (90 and 98% for leachate from wastewater sludge composting and leachate from organic fraction of municipal solid wastes, respectively). Fenton's reagent was found to oxidize preferably biodegradable organic matter of leachate. In consequence, a decrease in the biodegradability of leachates was observed after Fenton treatment for both leachates. Nevertheless, Fenton reaction proved to be a feasible technique for the oxidation of the leachate under study, and it can be considered a suitable treatment for this type of wastewaters.     

Degradation of 4-nitrophenol in aqueous medium by electro-Fenton method

The degradation of 4-nitrophenol by electro-Fenton (E-Fenton) method was carried out in batch recirculation mode. The effect of operating conditions such as electrical current, Fenton's reagent dosage, Fe(II) to H(2)O(2) molar ratio, and H(2)O(2) feeding time on the efficiency of E-Fenton process was investigated. It was found that E-Fenton method showed the synergetic effect on COD removal. The increase of Fenton's reagent dosage, Fe(II) to H(2)O(2) molar ratio, and the electrical current would lead to the increase of COD removal efficiency. Continuous addition of hydrogen peroxide was more effective than the addition of hydrogen peroxide in a single step and there existed an optimal H(2)O(2) feeding time for COD removal. The reaction system was modeled as a plug flow reactor (PFR) in series with a continuous stirred tank reactor (CSTR), and the pseudo-first order rate constant of COD removal was determined from the model based on the experimental data.     

Color, TOC and AOX removals from pulp mill effluent by advanced oxidation processes: a comparative study

Pulp mill effluent containing toxic chemicals was treated by different advanced oxidation processes (AOPs) consisting of treatments by hydrogen peroxide, Fenton's reagent (H2O2/Fe2+), UV, UV/H2O2, photo-Fenton (UV/H2O2/Fe2+), ozonation and peroxone (ozone/H2O2) in laboratory-scale reactors for color, total organic carbon (TOC) and adsorbable organic halogens (AOX) removals from the pulp mill effluent. Effects of some operating parameters such as the initial pH, oxidant and catalyst concentrations on TOC, color, AOX removals were investigated. Almost every method used resulted in some degree of color removal from the pulp mill effluent. However, the Fenton's reagent utilizing H2O2/Fe2+ resulted in the highest color, TOC and AOX removals under acidic conditions when compared with the other AOPs tested. Approximately, 88% TOC, 85% color and 89% AOX removals were obtained by the Fenton's reagent at pH 5 within 30 min. Photo-Fenton process yielded comparable TOC (85%), color (82%) and AOX (93%) removals within 5 min due to oxidations by UV light in addition to the Fenton's reagent. Fast oxidation reactions by the photo-Fenton treatment makes this approach more favorable as compared to the others used.     

Importance of H(2)O(2)/Fe(2+) ratio in Fenton's treatment of a carpet dyeing wastewater

The effectiveness of the Fenton's reagent (H(2)O(2)/Fe(2+)) in the treatment of carpet dyeing wastewater was investigated under different operational conditions, namely, H(2)O(2) and FeSO(4) concentrations, initial pH and temperature. Up to 95% COD removal efficiency was attained using 5.5 g/l FeSO(4) and 385 g/l H(2)O(2) at a pH of 3, temperature of 50 degrees C. The H(2)O(2)/Fe(2+) ratio (g/g) was found to be between 95 and 290 for maximum COD removal. It was noteworthy that, keeping H(2)O(2)/Fe(2+) ratio constant within the range of 95-290, it became possible to decrease FeSO(4) concentration to 1.1 g/l and H(2)O(2) concentration to 96.3 g/l, still achieving nearly the same COD removal efficiency. The relative efficiencies of Fenton's oxidation and coagulation stages revealed that Fenton's coagulation removed organic compounds which were not removed by Fenton's oxidation, indicating that the Fenton's coagulation acted as a polishing step.     

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.     

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.     

Effects of reaction conditions on nuclear laundry water treatment in Fenton process

This study presents the efficiency of Fenton process in the degradation of organic compounds of nuclear laundry water. The influence of Fe(2+) and hydrogen peroxide ratio, hydrogen peroxide dose, pH and treatment time were investigated. The degradation of non-ionic surfactant and other organic compounds was analysed as COD, TOC and molecular weight distribution (MWD). The most cost-effective degradation conditions were at H(2)O(2)/Fe(2+) stoichiometric molar ratio of 2 with 5 min mixing and H(2)O(2) dose of 1000 mg l(-1). With the initial pH of 6, the reductions of COD and TOC were 85% and 69%, respectively. However, the removal of the organic compounds was mainly carried out by Fenton-based Fe(3+) coagulation rather than Fenton oxidation. Fenton process proved to be much more efficient than previously performed ozone-based oxidation processes.     

Monitoring of decolorization kinetics of Reactive Brilliant Blue X-BR by online spectrophotometric method in Fenton oxidation process

Online spectrophotometry method is employed to monitor simulated Reactive Brilliant Blue X-BR (RBB X-BR) in aqueous solution in Fenton oxidation process. The effects of initial dosage of FeSO(4) and H(2)O(2), pH value, initial concentration of dye and temperature have been studied. The results show that online spectrophotometric method is a quick, feasible and convenient technique to monitor color removal of RBB X-BR in Fenton process. The optimal dosage of H(2)O(2) and pH is 3.529mM and 3, respectively. The optimal dosage of Fe(2+) for color removal is 0.1618mM. The concentration of initial FeSO(4) against the reaction rate constant (k(ap)) for decolorizing is linear correlation as: k(ap)=0.1354[Fe(2+)](o) (R(2)>0.99). The apparent activation energies of reaction is 25.21kJmol(-1) (R(2)>0.99). The intrinsic reaction rate constant of OH with RBB X-BR in aqueous solution is 7.396x10(10)M(-1)s(-1). The molecule structure of RBB X-BR is decomposed and not mineralized by Fenton's reagent. The main intermediate products are 1,2-diacetylenzene and 2,5-diritrobenzoic acid. The probable mechanism of the decoloration of RBB X-BR is also discussed.     

Removal of COD and color from livestock wastewater by the Fenton method

The Fenton method was applied to the removal of chemical oxygen demand using chromate (CODcr) and color from high-strength livestock wastewater in which the initial CODcr was 5000-5700 mg/L. The optimum ratio of H2O2 (mg/L) to the initial CODcr was 1.05 and the optimum molar ratio of H2O2/Fe2+ was 2. The optimum initial pH and the optimum reaction time were 3.5-4 and 30 min, respectively. Under optimal conditions, the removal ratios of CODcr and color of the supernatant after static precipitation of the produced sludge were 88 and 95.4%, respectively. Addition of Fenton's reagents in several aliquots did not affect the efficiencies of CODcr and color removal.     

Photo-Fenton process as an efficient alternative to the treatment of landfill leachates

Advanced oxidation processes (AOPs), namely photo-Fenton, Fenton-like, Fenton and UV/H(2)O(2), have been investigated in the removal of organic matter and colour from landfill leachates. The leachate was characterised by high COD, low biodegradability and intense dark colour. Evaluation of COD removal as a function of the operation variables (H(2)O(2), Fe(2+), Cu(2+), UV) led to results that ranged between 30% and 77% and it was observed that the removal efficiencies decreased in the order: photo-Fenton>Fenton-like>Fenton>UV/H(2)O(2)>UV. Thus, a detailed experimental analysis was carried out to analyse the effect of the hydrogen peroxide and iron concentrations and the number of reagent additions in the photo-Fenton process, observing that: (i) the COD removal ranged from 49% to 78% depending on the H(2)O(2) dose, (ii) the total amount of organic matter removed was increased by adding the reagent in multiple steps (86%), (iii) iron concentration corresponding to a Fe(2+)/COD mass ratio=0.33 was found to be the most favourable and, (iv) after a neutralization step, the colour and residual concentrations of iron and H(2)O(2) were practically negligible in the final leachate solution.     

Improvement of COD and color removal from UASB treated poultry manure wastewater using Fenton's oxidation

The applicability of Fenton's oxidation as an advanced treatment for chemical oxygen demand (COD) and color removal from anaerobically treated poultry manure wastewater was investigated. The raw poultry manure wastewater, having a pH of 7.30 (+/-0.2) and a total COD of 12,100 (+/-910) mg/L was first treated in a 15.7 L of pilot-scale up-flow anaerobic sludge blanket (UASB) reactor. The UASB reactor was operated for 72 days at mesophilic conditions (32+/-2 degrees C) in a temperature-controlled environment with three different hydraulic retention times (HRT) of 15.7, 12 and 8.0 days, and with organic loading rates (OLR) between 0.650 and 1.783 kg COD/(m3day). Under 8.0 days of HRT, the UASB process showed a remarkable performance on total COD removal with a treatment efficiency of 90.7% at the day of 63. The anaerobically treated poultry manure wastewater was further treated by Fenton's oxidation process using Fe2+ and H2O2 solutions. Batch tests were conducted on the UASB effluent samples to determine the optimum operating conditions including initial pH, effects of H2O2 and Fe2+ dosages, and the ratio of H2O2/Fe2+. Preliminary tests conducted with the dosages of 100 mg Fe2+/L and 200 mg H2O2/L showed that optimal initial pH was 3.0 for both COD and color removal from the UASB effluent. On the basis of preliminary test results, effects of increasing dosages of Fe2+ and H2O2 were investigated. Under the condition of 400 mg Fe2+/L and 200 mg H2O2/L, removal efficiencies of residual COD and color were 88.7% and 80.9%, respectively. Under the subsequent condition of 100 mg Fe2+/L and 1200 mg H2O2/L, 95% of residual COD and 95.7% of residual color were removed from the UASB effluent. Results of this experimental study obviously indicated that nearly 99.3% of COD of raw poultry manure wastewater could be effectively removed by a UASB process followed by Fenton's oxidation technology used as a post-treatment unit.     

Oxidation of dichlorvos with hydrogen peroxide using ferrous ion as catalyst.

This study examines how Fenton's reagent (Fe2+ and H2O2) decomposed dichlorvos insecticide. Results showed that dichlorvos decomposed in a two-stage reaction. The first stage is a Fe2+/H2O2 reaction in which dichlorvos swiftly decomposed. In the second stage, dichlorvos decomposed somewhat less rapidly, and it is a Fe3+/H2O2 reaction. The detection of ferrous ions also supports the theory of the two-stage reaction for the dichlorvos oxidation with Fenton's reagent. The dissolved oxygen of the solution decreased rapidly in the first stage reaction, but it slowly increased in the second stage with a zero-order kinetics. The Fenton system decomposed dichlorvos most rapidly when the initial pH in the solution is 3-4. In addition, increasing the concentration of hydrogen peroxide or ferrous ions can enhance the decomposition of dichlorvos. Consequently, the relationship of rate constant (kobs), [H2O2] and [Fe2+] at initial pH 3 is determined as kobs = 2.67 x 10(4)[H2O2]0.7[Fe2+]1.2.     

Application of the central composite design and response surface methodology to the advanced treatment of olive oil processing wastewater using Fenton's peroxidation

The central composite design (CCD) technique was used to study the effect of the Fenton's peroxidation on the removal of organic pollutants from olive oil mill wastewater (OMW). The ratio of hydrogen peroxide-to-Fe(II) (x1) was between 1.67 and 8.33. Fe(II) concentration was constant at 0.03 M while the H2O2 concentration was set at three levels: 0.05, 0.15 and 0.25 M. Based on the molarity ratio, the selected ratio were in the low range of Fe(II)-to-H2O2 ratio (<1). While based on the wt/wt ratio, the tested Fe(II)-to-H2O2 ratios were in the range of < or =1:5. pH (x2) was between 3 and 5. The concentration of OMW (x3) was varied between 40 and 100%. The influence of these three independent variables on the four dependent variables, i.e. COD, total phenolics (TP), color and aromaticity removal was evaluated using a second-order polynomial multiple regression model. Analysis of variance (ANOVA) showed a high coefficient of determination (R2) value of 0.902-0.998, thus ensuring a satisfactory adjustment of the second-order regression model with the experimental data. H2O2-to-Fe(II) ratio had significant effect on all the four dependent variables. The positive sign for the regression coefficient of this regressor variable indicated that the level of the pollutant removal increased with the increased levels of factor x1 from 1.67 to 8.33 and this effect was the most pronounced for TP removal. pH had also significant effect on the pollutant removal and the effect was the most noticeable for TP reduction. The negative coefficient of this variable (pH) indicated that level of the pollutant removal decreased as the pH increased from 3 to 5. The negative coefficient of the interaction between variable x1 and x2 indicated that a simultaneous increase in H2O2-to-Fe(II) ratio with decrease in the pH of the reaction led to an increase in the COD, TP and color removal. Quadratic models were predicted for the response variable, i.e. pollutant removal, and the maximum model-predicted removals were 56, 100, 33 and 32% for COD, TP, color and aromaticity, respectively. Optimum conditions for this wastewater treatment was obtained based on the performance of the Fenton's peroxidation in the experiment where the H2O2-to-Fe(II) ratio was at its high level (8.33) and the pH and OMW concentration were 4 and 70%, respectively.     

Combined Fenton oxidation and aerobic biological processes for treating a surfactant wastewater containing abundant sulfate

The present study is to investigate the treatment of a surfactant wastewater containing abundant sulfate by Fenton oxidation and aerobic biological processes. The operating conditions have been optimized. Working at an initial pH value of 8, a Fe2+ dosage of 600mgL(-1) and a H2O2 dosage of 120mgL(-1), the chemical oxidation demand (COD) and linear alkylbenzene sulfonate (LAS) were decreased from 1500 and 490mgL(-1) to 230 and 23mgL(-1) after 40min of Fenton oxidation, respectively. Advanced oxidation pretreatment using Fenton reagent was very effective at enhancing the biodegradability of this kind of wastewater. The wastewater was further treated by a bio-chemical treatment process based on an immobilized biomass reactor with a hydraulic detention time (HRT) of 20h after Fenton oxidation pretreatment under the optimal operating conditions. It was found that the COD and LAS of the final effluent were less than 100 and 5mgL(-1), corresponding to a removal efficiencies of over 94% and 99%, respectively.     

Kinetic and mechanistic investigations of mesotrione degradation in aqueous medium by Fenton process

In this work, chemical oxidation of mesotrione herbicide by Fenton process in acidic medium (pH 3.5) was investigated. Total disappearance of mesotrione and up to 95% removal of total organic carbon (TOC) were achieved by Fenton's reagent under optimized initial concentrations of hydrogen peroxide (H(2)O(2)) and ferrous iron (Fe(2+)) at pH 3.5. The time-dependent degradation profiles of mesotrione were satisfactorily fitted by first-order kinetics. Competition kinetic model was used to evaluate a rate constant of 8.8(± 0.2) × 10(9)M(-1) s(-1) for the reaction of mesotrione with hydroxyl radicals. Aromatic and aliphatic intermediates of mesotrione oxidation were identified and quantified by high performance liquid chromatography (HPLC). It seems that the degradation of mesotrione by Fenton process begins with the rupture of mesotrione molecule into two moieties: cyclohexane-1,3-dione derivative and 2-nitro-4-methylsulfonylbenzoic acid. Hydroxylation and release of sulfonyl and/or nitro groups from 2-nitro-4-methylsulfonylbenzoic acid lead to the formation of polyhydroxylated benzoic acid derivatives which undergo an oxidative opening of benzene ring into carboxylic acids that end to be transformed into carbon dioxide.     

A simple methodology to evaluate influence of H2O2 and Fe(2+) concentrations on the mineralization and biodegradability of organic compounds in water and soil contaminated with crude petroleum

Simple measurements of H2O2 concentration or CO2 evolution were used to evaluate the effectiveness of the use of Fenton's reagent to mineralize organic compounds in water and soil contaminated by crude petroleum. This methodology is suitable for application in small treatment and remediation facilities. Reagent concentrations of H2O2 and Fe(2+) were found to influence the reaction time and temperature, as well as the degree of mineralization and biodegradability of the sample contaminants. Some H2O2/Fe(2+) combinations (H2O2 greater than 10% and Fe(2+) greater than 50mM) resulted in a strong exothermic reaction, which causes peroxide degradation and violent gas liberation. Up to 75% TOC removal efficiency was attained in water and 70% in soil when high H2O2 (20%) and low Fe(2+) (1mM) concentrations were used. Besides increasing the degree of mineralization, the Fenton's reaction enhances the biodegradability of petroleum compounds (BOD5/COD ratios) by a factor of up to 3.8 for contaminated samples of both water and soil. Our experiments showed that low reagent concentrations (1% H2O2 and 1mM Fe(2+)) were sufficient to start the degradation process, which could be continued using microorganisms. This leads to a decrease in reagent costs in the treatment of petroleum-contaminated water and soil samples. The simple measurements of H2O2 concentration or CO2 evolution were effective to evaluate the Fenton's reaction efficiency.     

A review of classic Fenton's peroxidation as an advanced oxidation technique

Hydrogen peroxide (H(2)O(2)) is a strong oxidant and its application in the treatment of various inorganic and organic pollutants is well established. Still H(2)O(2) alone is not effective for high concentrations of certain refractory contaminants because of low rates of reaction at reasonable H(2)O(2) concentrations. Improvements can be achieved by using transition metal salts (e.g. iron salts) or ozone and UV-light can activate H(2)O(2) to form hydroxyl radicals, which are strong oxidants. Oxidation processes utilising activation of H(2)O(2) by iron salts, classically referred to as Fenton's reagent is known to be very effective in the destruction of many hazardous organic pollutants in water. The first part of our paper presents a literature review of the various Fenton reagent reactions which constitute the overall kinetic scheme with all possible side reactions. It also summarises previous publications on the relationships between the dominant parameters (e.g. [H(2)O(2)], [Fe(2+)], . . .). The second part of our review discusses the possibility of improving sludge dewaterability using Fenton's reagent.