An overview of the application of Fenton ... - Wiley Online Library

Journal of Chemical Technology and Biotechnology

J Chem Technol Biotechnol 83:1323–1338 (2008)

Review An overview of the application of Fenton oxidation to industrial wastewaters treatment P Bautista, A F Mohedano, J A Casas, J A Zazo and J J Rodriguez∗ ´ Ingenier´ıa Qu´ımica, Universidad Autonoma de Madrid, Crta. de Colmenar Km.15, 28049 Madrid, Spain

Abstract: This review provides updated information on the application of the Fenton process as an advanced oxidation method for the treatment of industrial wastewaters. This technology has been used in recent decades as a chemical oxidation process addressed to meet a variety of objectives including final polishing, reduction of high percentages of organic load in terms of chemical oxygen demand or total organic carbon and removal of recalcitrant and toxic pollutants thus allowing for further conventional biological treatment. The efficiency and flexibility of this technology has been proven with a wide diversity of effluents from chemical and other related industries or activities, including pharmaceutical, pulp and paper, textile, food, cork processing, and landfilling among others.  2008 Society of Chemical Industry

Keywords: Fenton process; chemical oxidation; industrial wastewaters treatment; waste minimization; leachate

INTRODUCTION Industrial activities generate wastewaters with a wide variety of contaminants, such as phenol and derivatives, hydrocarbons, halogenated sulphur and nitrogen-containing organic compounds, heavy metals in the form of cyanides and other organic complexes. Frequently these wastewaters contain a mixed pool of pollutants in a wide range of concentrations. The development of cost-effective technical solutions is needed to successfully deal with the increasingly complex problems arising in the field of industrial wastewaters. In recent decades, chemical treatment methods involving the generation of hydroxyl radicals, known as advanced oxidation processes (AOPs), have been applied successfully for the removal or degradation of recalcitrant pollutants based on the high oxidative power of the HO· radical. Among these AOPs, the Fenton process is a widely studied and used catalytic method based on the generation of hydroxyl radicals (HO·) from hydrogen peroxide with iron ions acting as homogeneous catalyst at acidic pH and ambient conditions.1 The HO· radical has a high standard oxidation potential (2.80 V) and exhibits high reaction rates compared with other conventional oxidants like Cl2 , O2 , O3 , hydrogen peroxide or KMnO4 . This radical reacts with most organic and many inorganic solutes with high rate constants. The generally accepted mechanism of the Fenton process proposes that hydroxyl radicals are produced in accordance with Equation (1), while the catalyst is regenerated through Equation (2), or from the

reaction of Fe3+ with intermediate organic radicals (Equations (3)–(5)):2 – 6 Fe2+ + H2 O2 −−−→ Fe3+ + HO· + HO− k = 76 L mol−1 s−1 Fe

3+

+ H2 O2 −−−→ Fe

2+

+ HO2 · + H

(1) +

k = 0.01 L mol−1 s−1

(2)

RH + HO· −−−→ R · +H2 O

(3)

R · +Fe3+ −−−→ R+ + Fe2+

(4)

+

−

R + HO −−−→ R-OH

(5)

Nevertheless, a number of competitive reactions can also occur (Equations (6)–(9)), which negatively affect the oxidation process: Fe2+ + HO· −−−→ Fe3+ + HO− k = 3.2 × 108 L mol−1 s−1 (6) H2 O2 + HO· −−−→ HO2 · +H2 O k = 2.7 × 107 L mol−1 s−1 (7) HO2 · +HO· −−−→ O2 + H2 O

(8)

HO · +HO· −−−→ H2 O2 k = 5.2 × 109 L mol−1 s−1 (9) The rate of the Fenton reaction should be strongly dependent on the presence of radical scavengers such as t-butanol or chlorine ions, but in some cases, a substantial decrease has

∗

´ Correspondence to: J J Rodriguez, Ingenier´ıa Qu´ımica, Universidad Autonoma de Madrid, Crta. de Colmenar Km.15, 28049 Madrid, Spain E-mail: [email protected] (Received 14 March 2008; revised version received 25 April 2008; accepted 28 April 2008) Published online 6 June 2008; DOI: 10.1002/jctb.1988

 2008 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2008/$30.00

P Bautista et al.

not been observed even at high concentrations of these species.7 This fact led some authors to analyze the presence of additional oxidant species. Using electron paramagnetic resonance (EPR)-spin trapping techniques, experimental evidence has been found for the existence of oxidizing intermediates different from the hydroxyl radical,8 – 11 such as highvalent iron-complexes (e.g. ferryl species Fe(IV), denoted as Fe(OH)2 2+ ; Equation (10)). Depending on the operating conditions (substrate, Fe/H2 O2 ratio, scavengers, etc.) one of them will predominate.

The reaction temperature is another crucial parameter in the Fenton process. In principle, increasing the temperature should enhance the kinetics of the process, but it also favours the decomposition of H2 O2 towards O2 and H2 O, whose rate increases around 2.2 times each 10 ◦ C in the range 20–100 ◦ C.14 The dose of H2 O2 and the concentration of Fe2+ are two relevant factors affecting the Fenton process, being both closely related. The H2 O2 dose has to be fixed according to the initial pollutant concentration. It is frequent to use an amount of H2 O2 corresponding to the theoretical stoichiometric H2 O2 to chemical oxygen demand (COD) ratio,15 although it depends on the response of the specific contaminants to oxidation and on the objective pursued in terms of reduction of the contaminant load. A schematic representation of the Fenton oxidation treatment is shown in Fig. 1. Typically a stirred batch reactor is used where the pH is controlled commonly within the 3–3.5 range. Fe2+ is most frequently added as ferrous sulphate and H2 O2 is usually fed as 35% aqueous solution. The process usually works at ambient temperature and pressure. The reactor vessel must be coated with an acid-resistant material, because corrosion can be a serious problem. Addition of reactants is performed in the following sequence: wastewater, followed by dilute sulphuric acid (for maintaining acidic conditions), the catalyst (Fe2+ salt) in acidic solution, base or acid for pH adjustment and finally hydrogen peroxide. The discharge from the Fenton reactor passes to a neutralization tank and after flocculant addition the Fe(OH)3 and other accompanying solids are separated by settling. If necessary, a final sand-filtration stage can be used. One of the advantages of the Fenton process with regard to other oxidation techniques is that no energy input is necessary to activate hydrogen peroxide, because the reaction takes place at atmospheric pressure and at room temperature. Furthermore, this method requires relatively short reaction times and uses easy-to-handle reagents. The main disadvantages

Fe2+ + H2 O2 −−−→ Fe(OH)2 2+ −−−→ Fe3+ + HO · +HO−

(10)

Whereas the hydroxyl radical reacts by hydrogen abstraction, addition to double bonds or electron transfer, depending on the structure and especially on the ionization potential of the organic pollutant, the ferryl species are only able to oxidize organic molecules by electron transfer. The efficiency of the Fenton oxidation process depends, among other factors, like temperature, pH, hydrogen peroxide and catalyst concentrations, on the Fe3+ reduction to Fe2+ . Thus the presence of reaction intermediates able to reduce Fe3+ and regenerate the catalyst is crucial.3 However, there are reaction intermediates that instead of reducing the Fe3+ remove it from the Fe2+ /Fe3+ cycle, due to the generation of iron complexes, delaying and/or inhibiting the oxidation process. Fenton reaction presents its maximum catalytic activity at pH 2.8–3.0, which drastically diminishes with an increase or a reduction of this pH value. At pH higher than 3 Fe3+ starts precipitating as Fe(OH)3 and breaks down the H2 O2 into O2 and H2 O preferently.12 Besides, the formation of Fe(II) complexes at high pH values leads to a drop of the Fe2+ concentration.13 On the other hand, Fe2+ regeneration by the reaction of Fe3+ with H2 O2 is inhibited at more acidic pH values.4 H2O2 Alkaline agent

Fe(SO4)·7H2O

Flocculant

pH adjusting agent pH control

Raw wastewater

pH control

Treated wastewater

Oxidation tank

Neutralization tank

Flocculation tank

Settling tank Figure 1. Typical scheme for Fenton treatment.

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J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb

Fenton oxidation to industrial wastewaters treatment

are the high cost of hydrogen peroxide and the fact that the homogeneous catalyst, added as iron salt, cannot be retained in the process thus requiring further separation to prevent additional water pollution. In order to avoid the continuous loss of catalyst and the need of removing iron after the treatment, which increases the cost, heterogeneous catalysts can be used. Recent studies have shown that hydrogen peroxide can oxidize organic pollutants in the presence of Fe-bearing solid catalysts. Zeolites,16 – 23 pillared clays,24 – 28 alumina,29 silica,30 mesostructured SBA15,31,32 mesoporous molecular sieves,33,34 niobia,35 iron oxides,36,37 ion-exchange resin38 and activated carbon39,40 have been used as supports to prepare the catalysts.

APPLICATION OF FENTON OXIDATION TO INDUSTRIAL WASTEWATERS Fenton oxidation has been tested with a variety of synthetic wastewaters containing a diversity of target compounds, such as phenols,41 – 44 chlorophenols,45 – 48 formaldehyde,49 2,4-dinitrophenol,50,51 2,4,6-trinitrotoluene,52,53 2,4-dinitrotoluene,54 chlorobenzene,55,56 tetrachloroethylene,57 halomethanes,58 amines,59 hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX).60,61 However, there are many chemicals which are refractory to Fenton oxidation, such as acetic acid, acetone, carbon tetrachloride, methylene chloride, oxalic acid, maleic acid, malonic acid, n-paraffins, trichloroethane, etc.62 It has been demonstrated that these compounds are resistant under the usual mild operating conditions of Fenton oxidation.2,28,40,44 In addition to those basic studies, the process has been applied to industrial wastewaters (such as chemical, pharmaceutical, textile, paper pulp, cosmetic, cork processing wastewaters, etc.), sludge and contamined soils63 – 68 with the result of significant reductions of toxicity, improvement of biodegradability, colour and odour removal. Chemical industry The chemical industry is a major contributor to the nowadays problem of industrial wastewaters, not only in terms of discharge volumes, but also looking at the hazardous nature of many of the pollutants found in the effluents. The increasingly stringent regulations have enforced the application of advanced technologies for complying the discharge limits and allowing for water recycling. Among those technologies, Fenton oxidation has been gaining interest in the last two decades. Barbusinski and Filipek69 analyzed the efficiency of the Fenton technology in the treatment of the wastewaters from pesticides production in southern Poland. Most of the pesticides were completely degraded using a H2 O2 dose of 2.5 g L−1 , corresponding to five times the stoichiometric amount on a COD basis. The best results were achieved for the organophosphorous pesticides, which degraded at 97–100%. The J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb

removal efficiency for organochlorinated was also fairly high (>90%), and the toxicity of the raw wastewater towards the bioluminescent bacteria Vibrio fischeri was dramatically reduced. In a further work, Barbusinski70 studied the application of Fenton process for treating four types of industrial wastewaters collected from two chemical factories in southern Poland. The wastewaters came from the production of maleic acid, maleic anhydride, 2-ethylhexyl alcohol, urea-formaldehyde adhesives and pesticides. Although high removal efficiencies were obtained in terms of COD, these were not always accompanied by a reduction of ecotoxicity (Vibrio fischeri) to sufficiently low levels unless frankly high H2 O2 amounts and reaction times were used. A good example on the benefits of applying Fenton oxidation to wastewaters from chemicals manufacturing is reported by Collivignarelli et al.71 The wastewaters from a detergents producing plant were formerly treated by coagulation–flocculation and filtration, a solution which showed to be not capable of reaching the purification requirements. A new system consisting in a discontinuous Fenton oxidation and neutralisation process, followed by flocculation and sedimentation was successfully implemented. Wastewaters from petroleum extraction, refining and chemical processing have been successfully treated with the Fenton system under ambient conditions of pressure and temperature.72 These authors tested the efficiency of this process for the treatment of two different wastewater samples, one from oil production operations and the other one from a petrochemical plants complex. The treated contaminants, in harzadous concentrations, were the following: m-cresol, 2chlorophenol, methyl-tertbutyl-ether (MTBE) and volatile aromatics (benzene, toluene, ethylbenzene and xylene). In all cases a significant mineralization (namely, complete oxidation) of the contaminants was observed in relatively short periods of time. Acidizing, a technique for improving the permeation ability of rock layers of petroleum wells using diluted inorganic acids such as HCl, has long been one of the most common ways of stimulation to increase the production rate of oil and gas reservoirs. This operation gives rise to about 200–500 m3 waste acidic liquid per well, containing high concentrations of HCl and ferrous ions in addition to a high organic load. Gao et al.73 analyzed the potential of the Fenton process for the simultaneous removal of total organic carbon (TOC) and Fe2+ from these acidic waste liquors, by adding H2 O2 . The samples used in that study were collected from an acidic waste liquor pond in China, with main characteristics: pH = 1.4, 94 mg L−1 TOC and 208 mg L−1 Fe2+ . The optimum molar ratio of H2 O2 /Fe2+ for the removal of Fe2+ was 0.72–0.76, which was determined from the oxygen 1325

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reduction potential (ORP), used as a parameter to indicate the transformation of the Fe3+ /Fe2+ . Under this optimal H2 O2 dose, the minimum Fe2+ final concentration (1.2–1.3 mg L−1 ) occurred at 45 min at 3.3–4.5 pH. TOC removal was affected by oxidation as well as adsorption by ferric hydroxides being dominated by adsorption at a molar ratio H2 O2 /Fe2+ of 0.75, and by oxidation at a molar ratio H2 O2 /Fe2+ of 3.0. In this latter case (380 mg L−1 H2 O2 ), more than three-quarters of the TOC removal was due to oxidation, for a total TOC reduction of 65% in 120 min, at room temperature and pH = 3.25. Leather tanning effluents are a source of severe environmental impacts, since this industry generates an alkaline wastewater with high concentrations of organic matter, sulfides, suspended solids and salts, which shows high toxicity values. The treatment of these industrial wastewaters by combined chemical and biological oxidation was evaluated by Vidal et al.74 In that study Fenton oxidation was used as batch pretreatment. The H2 O2 /Fe2+ and H2 O2 /COD ratios were 9 and 4, respectively, reaching a COD reduction close to 90%. Subsequently, the oxidized effluent was fed to an activated sludge unit, reaching 35–60% and 60–70% of COD and BOD removal, respectively. Therefore, this combined treatment increased the overall COD removal up to more than 95% versus the 60% attained without pre-treatment. Bioassays with D. magna and D. pulex showed that this kind of treatment achieves only a partial toxicity removal of the tannery effluent. Dantas et al.75 evaluated the efficiency of Fenton and photo-Fenton processes for the treatment of wastewaters from the leather industry, investigating the reduction of COD, ammonia-N and toxicity. The results obtained showed that the degradation process involves two stages: an initial fast one, where approximately 70% of the COD reduction takes place, followed by a slow step, where after 4 h reaction time the COD removal reached 90%. The efficiency of the Fenton and photo-Fenton reactions increased from 65 to 90%, since the concentration of HO· radicals increases in the second process. The toxicity (using Artemia salina) decreased upon COD reduction but the residual H2 O2 at the end of the reaction had to be controlled because it affects negatively to the final toxicity values. The cosmetic industry generates wastewaters characterized by high levels of COD, suspended solids, fats and oils and detergents. The reduction of the organic load of these effluents by conventional biological processes is not likely due to its low biological oxygen demand (BOD5 )/COD ratio and thus they are frequently treated by means of coagulation/flocculation with pressure-flotation to separate the resulting sludge. This leads to an important reduction of COD. Nevertheless, the introduction of more stringent regulations concerning public waste disposal makes necessary to 1326

develop new techniques for a more efficient cleaning of this type of wastewaters. A possible strategy can be the use of chemical oxidation as a previous treatment in order to reduce the toxicity and improve the biodegradability of the organic matter in these wastewaters. The removal of organic matter (TOC and COD) by Fenton oxidation from two samples of wastewaters generated in a cosmetic industry in Madrid (Spain) has been evaluated by Bautista et al.76 These two effluents contained significantly different values of COD (4730 and 2660 mg L−1 ). The corresponding TOC values were 1215 and 785 mg L−1 and the BOD5 /COD ratio was 0.133 and 0.169, respectively, indicative in both cases of a low biodegradability. The best results, TOC conversion higher than 45% at 25 ◦ C and 60% at 50 ◦ C, were obtained using an initial pH equal to 3, a Fe2+ dose of 200 mg L−1 and an initial H2 O2 /COD weight ratio corresponding to the theoretical stoichiometric value. Application of Fenton oxidation allowed compliance with the COD regional limit for industrial wastewaters discharges to the municipal sewer system. The overall kinetics of the process was adjusted to a second-order kinetic equation with respect to TOC. This simple equation described well the rate of TOC reduction over a wide range covering up to 80–90% of the maximum achievable TOC removal. A comparison of several AOPs was carried out with a cosmetic industrial effluent by Coste et al.77 After a complete biological treatment by membrane bioreactor (BIOSEP) refractory COD still remained. Six oxidation treatments were compared for COD reduction: Fenton reagent, direct photolysis with a low pressure UV lamp, O3 at acidic pH and pH 6.25, UV/O3 , UV/H2 O2 , O3 /H2 O2 and O3 /UV/H2 O2 . The results obtained seem to indicate that the components of the pre-treated effluent were removable by radical mechanism, but a fraction needed UV photolysis to be completely oxidized. Fenton reagent offered a maximum COD reduction of 80%, presenting a fraction that may be more refractory to free radicals oxidation perhaps due to scavengers competition. Wastewaters from phenolic resins manufacture have a high concentration of phenol and derivatives, which are extremely toxic and refractory. Thus, treating phenolic wastewaters up to harmless level is an arduous task for many biological and chemical processes. Kavitha and Palanivelu78 evaluated the efficiency of different Fenton-related processes, such as Fenton, solar-Fenton and UV-Fenton, for the degradation of phenol in simulated and industrial wastewaters. The real effluent was taken from a resin-manufacturing facility in India and contained 2904 mg L−1 COD, 933 mg L−1 dissolved organic carbon (DOC) and 1215 mg L−1 phenol. Increased degradation and mineralization efficiencies were observed in photo-Fenton processes as compared to conventional Fenton oxidation. The optimum conditions were: room temperature, pH = 3, H2 O2 /COD weight ratio of 2.2 J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb


and Fe2+ /H2 O2 molar ratio of 0.026 for Fenton and 0.013 for solar-Fenton. In both oxidation processes phenol was removed effectively within 5 min of reaction time. However, the degradation (COD) and mineralization (DOC) efficiency of the Fenton process were 82 and 41%, respectively, whereas in solar-Fenton almost complete degradation and 97% mineralization were achieved within 120 min of reaction time. Park et al.79 investigated the feasibility of Fenton oxidation for the removal of colour and the non-biodegradable organics from a wastewater from pigment production. Batch tests were performed in order to determine the optimum conditions for plant operation, such as pH, H2 O2 dosage, H2 O2 /Fe2+ molar ratio and contact time. The initial organic pollution of the raw wastewater was 2700 mg L−1 of COD and it was found that the removal efficiencies reached more than 90% and around 50% for colour and COD, respectively. In addition, the biodegradability of the effluent was significantly improved by means of Fenton oxidation since BOD5 /COD ratio was increased from 0.04 to 0.36. Pharmaceutical industry Treatment of pharmaceutical wastewaters has always been troublesome owing to the wide variety of chemicals used in drug manufacturing, which leads to wastewaters of variable composition and fluctuations in pollutant concentrations. The substances synthesized by the pharmaceutical industry are in most cases structurally complex organic chemicals that are resistant to biological degradation. For this reason, conventional methods are usually inappropriate for the treatment of pharmaceutical wastewaters and advanced oxidation processes can be considered good candidates for providing feasible technical solutions. Fenton oxidation has proved to be a suitable pretreatment for an extremely polluted pharmaceutical wastewater with 362 000 mg L−1 COD, mostly due to recalcitrant compounds, as indicated by a BOD5 /COD ratio as low as 0.008.80 The results reported by these authors show that during the first 10 min of Fenton’s reaction more than 90% of the total COD removal (55–60%) can be achieved. This finding is of special interest for the industrial application of Fenton technology, because it proves that it permits a significant COD reduction in a fairly short period of time. This advantage of the Fenton process with respect to other advanced oxidation processes was ¨ et al.81 , who compared also pointed out by Hofl the efficiency of three AOPs (H2 O2 /UV, O3 /UV and Fenton) for the removal of adsorbable organic halogen (AOX) and COD from a pharmaceutical wastewater. The results showed that the three methods are suitable for the degradation of AOX and COD. UV irradiation involved a high selectivity for the degradation of AOX compared to COD. On the other hand, processes J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb

based on hydroxyl radicals were less selective but considerably more effective in COD degradation. This explains why the combined methods H2 O2 /UV and O3 /UV led both to complete destruction of AOX and high removal of COD. Using Fenton oxidation both AOX and COD could be removed almost completely, being the reaction time needed for this treatment fairly low compared with the other two AOPs. Kulik et al.82 applied modified Fenton oxidation (H2 O2 /Fe2+ system without pH adjustment) in combination with lime coagulation for the treatment of three rinsing wastewater samples from a pharmaceutical plant formulating medical ointments. All samples were pre-treated by adsorption/flocculation/filtration processes with bentonite, but the quality of effluents did not comply with the regulations for wastewater discharge to local sewerage, since the organic matter content of the three effluents in terms of COD was 4000, 5400 and 13 130 mg L−1 . The application of Fenton-like oxidation with subsequent iron(III)/lime coagulation substantially improved the quality and the biodegradability of the pharmaceutical effluents with different chemical characteristics allowing to meet the discharge limits. The rapid pH decrease to acidic values ∼3 during the initial stage of the process for all the effluents suggested that pH adjustment was unnecessary. Under the most favourable treatment conditions (H2 O2 /COD weight ratio of 2:1, H2 O2 /Fe2+ molar ratio of 10:1 and 2 h reaction time), COD removal of 87%, 94% and 96% and BOD7 removal of 79%, 92% and 95% were achieved for the three effluents. Another example of industrial application of the Fenton process for the treatment of pharmaceutical effluents is reported by Tekin et al.83 In their study Fenton oxidation is applied as a pre-treatment for the wastewaters generated by a drug manufacturing plant in Turkey, leading to an improvement of the wastewater biodegradability and a reduction of the toxicity of these effluents. Treatability studies were conducted at lab scale with synthetic aqueous solutions of each chemical produced in the factory in order to establish the operating conditions for the fullscale treatment plant. Optimum pH was found to be 3.5 and 7.0 for the first (oxidation) and second (coagulation) stage of the Fenton process, respectively. The effect of temperature on COD removal was tested at room temperature and at 50 ◦ C, and no significant differences were observed. Similar results were found by San Sebastián et al.80 with this type of wastewater. The industrial treatment plant using Fenton oxidation followed by aerobic degradation in sequencing batch reactors (SBR), provided an overall removal efficiency of 98% for both COD and BOD5 , complying with the discharge regional limits. The COD removal efficiency attained in the Fenton oxidation unit ranged between 45% and 50%. 1327

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Pulp and paper industry The pulp and paper industry is known to generate considerable volumes of wastewaters, about 80 m3 t−1 of paper on average. More than 250 chemicals have been identified in the effluents resulting from the different stages of papermaking. Whereas some of these pollutants are naturally occurring wood extractives (tannins, resin acids, lignin, etc.), others are xenobiotic compounds that are formed mostly in pulp manufacture (chlorinated lignins, phenols, dioxins and furans, among others). These effluents are highly coloured and contain high organic loads, which in some cases can reach more than 10 000 mg L−1 of COD.84 Primary clarification is the most frequently used treatment for this type of wastewaters, sometimes followed by secondary or biological treatment. However, some drawbacks are associated with these methods, such as the large area required for aerobic biological treatment, the difficulty of controlling the population of microorganisms and the rigorous control of pH, temperature and nutrients. Also, the presence of toxic or recalcitrant compounds seriously limits the efficiency of biological treatments. The combination of Fenton and photo-Fenton oxidation has proved to be highly effective for the treatment of pulp bleaching effluents.85,86 Solar photoFenton reduced TOC as much as 93% after 15 min according to the results of these last authors. As indicated before, Fe3+ can also be used to decompose H2 O2 giving rise to oxidative radicals in the so-called Fenton-like process. For most applications no significant differences have been observed when Fe2+ or Fe3+ ions were used to catalyze the reaction, although Pera-Titus et al.87 suggested that if low doses of Fenton’s reagent are used, ferrous ions may be preferable. Tambosi et al.88 evaluated a Fentonlike process (involving oxidation and coagulation) for the treatment of a wastewater generated by a Brazilian paper mill with the objective of reducing COD, colour, odour and aromatic compounds. Batch experiments were carried out in order to determine the optimum operating conditions, which led to 75% COD removal. Based on these optimum conditions, pilot-scale experiments were conducted and revealed a high efficiency in terms of mineralization, namely complete oxidation. Some terpenes identified in the starting wastewater were completely removed by the Fenton-like treatment. Pérez et al.85 evaluated the efficiency of several AOPs for colour and organic matter removal from a cellulose bleaching effluent. The costs of the different technologies per unit of TOC reduction were compared. Fenton, Fenton-like and photo-Fenton achieved higher levels of TOC reduction and at lower costs than photocatalytic treatments. Textile industry Textile industry is particularly known for its high water consumption as well as the amount and variety 1328

of chemicals used throughout the different operations. The environmental problems associated with textile effluents are in a great part due to colour. The biorefractory nature of textile wastewaters from the dyeing and finishing stages is mainly attributable to the extensive use of various dyestuffs and chemical additives (such as polyvinyl alcohol, surfactants, etc.). Therefore, the wastewaters are characterized by a high organic matter content (COD, BOD5 ), suspended solids, colour and pH values up to 2 in the acid range and as high as 12 in the basic.12 Different treatments have been used for the wastewaters generated from textile dyeing. These include activated carbon adsorption, coagulation–flocculation, biological degradation (activated sludge), electrochemical treatment, ozonation, etc., which often produce final effluents still exceeding the discharge limits. Several authors have successfully applied the Fenton process for this kind of industrial effluents. In this way, Flaherty and Huang89 evaluated the efficiency of Fenton oxidation for the treatment of four refractory dyeing wastewaters from a US textile facility. Batch and continuous flow oxidation experiments were carried out, resulting in a 60% and 30% COD reduction, respectively. A significant colour reduction was achieved in all the cases. In addition, these authors performed some experiments using Fe3+ (Fenton-like reaction) instead of Fe2+ , concluding again that Fe3+ has a catalytic effect comparable to the traditionally used Fe2+ . They suggested that FeCl3 or Fe2 (SO4 )3 would be the most practical catalysts for industrial applications of Fenton-like oxidation, due to their strong acidic character. Badawy and Ali90 analyzed the effectiveness of Fenton oxidation for the combined treatment of industrial wastewaters generated from textile, chemical, food and metal finishing industries and domestic effluents from an Egyptian city. They compared the efficiency of a conventional treatment based on coagulation–flocculation with the results obtained by the use of Fenton oxidation. The industrial wastewaters contained 1750–3323 mg L−1 of COD, 900–3000 mg L−1 of SS and 13.2–95.5 mg L−1 of oil and grease in addition to heavy metals. The organic pollutants included refractory, non-biodegradable and toxic compounds, such as the dyestuffs used by the textile industry. The authors found that coagulation–flocculation has a poor effect on the removal of soluble organic compounds such as reactive dyes. The best results were obtained with the Fenton process, reaching as much as 100% colour removal and more than 90% reduction of COD. The results proved that Fenton oxidation could be used for the treatment of such industrial wastewaters without further treatment, since the final effluent complies with the Egyptian law for water reuse under a restricted category. J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb


The effectiveness of Fenton and ozone oxidation have been compared with a coagulation–flocculation process to remove toxicity as well as colour and COD from the wastewater generated by a textile finishing industry located in Istanbul (Turkey).91 The operating conditions for each process were established on the basis of complete removal of the toxicity to Daphnia magna. The results obtained indicate that Fenton oxidation removes COD to a major extent (59%) rather than O3 (33%), while colour removal was similar (89% and 91%, respectively). The coagulation–flocculation treatment yielded COD and colour removal close to those of Fenton oxidation, but it produces a higher volume of sludge containing recalcitrant compounds (dyes, additives, etc.). Although the Fenton process was operated at a higher temperature (40 ◦ C), this was not a drawback since the temperature of the effluent to be treated was above 70 ◦ C. Papadopoulos et al.92 examined the effectiveness of Fenton oxidation for the reduction of the organic content of the wastewater generated from a textile industry in Athens (Greece). The initial organic pollution of the raw wastewater was 1200 mg L−1 of BOD, 8100 mg L−1 of COD and 3010 mg L−1 of TOC. The low BOD/COD ratio, 0.148, indicates that this organic matter is nonbiodegradable. The experimental results showed that the COD decreased by about 45% within 4 h and a higher reaction time did not lead to further significant COD reduction (48% overall reduction after 6 h). The maximum colour removal was 71.5%. As indicated before, heterogeneous Fenton oxidation is an interesting alternative to the traditional homogeneous Fenton process. In this way, Dantas et al.39 studied the treatment of a textile wastewater (COD = 1000 mg L−1 ) in Santa Catarina State (Brazil) by adsorption and simultaneous catalytic wet hydrogen peroxide oxidation using composites of iron oxide and activated carbon (Fe2 O3 /carbon). They pointed out that no iron was leached to the aqueous phase, indicating that the homogeneous Fenton reaction was not significant and the catalyst is fairly stable at pH above 3.0. Besides, a lower hydrogen peroxide consumption than in the homogeneous Fenton process was needed, achieving 71% COD removal at room temperature with a H2 O2 dose lower than 1000 mg L−1 (less than half the stoichiometric amount). Collivignarelli et al.71 described the application of Fenton technology to the wastewaters of a textile factory in substitution of the previously used coagulation–flocculation treatment, which did not allow compliance with the discharge limits. Due to the complexity and high organic matter content of textile effluents several authors have suggested the application of combined treatments J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb

including Fenton oxidation. Pérez et al.93 investigated the simultaneous use of Fenton, Fenton-like and photo-Fenton for the treatment of textile wastewaters generated from a hydrogen peroxide bleaching unit in Spain. The combination of these processes was proved to be highly effective for the treatment of this type of wastewaters. Lin and Peng94 studied the treatment of textile wastewaters from a large dyeing and finishing mill by a continuous process of combined coagulation, Fenton oxidation and activated sludge. An economic evaluation of the process was carried out and the optimum operating conditions were selected, the removal of COD reaching almost 90% in those conditions. Fongsatitkul et al.95 investigated the potential of biological degradation in association with Fenton oxidation for treating the wastewaters from a textile factory in Central Thailand. The authors compared the efficiency of different technologies: biological treatment in a sequencing batch reactor (SBR) as a single process, Fenton oxidation prior to that biological treatment and SBR followed by Fenton oxidation. The best results were obtained by the second arrangement, which attained more than 90% and close to 80% reduction of COD and colour, respectively. Food industry The Fenton technology has also proved to be effective for the treatment of wastewaters generated by the food industry. This includes wastewaters from olive oil extraction plants, commonly named ‘olive mill wastewaters’96 – 98 and wastewaters generated by the table olive producing industry.99 In the former case, the oily juice is extracted from the fruit through simple milling or, more recently, by centrifugation. Table olive production requires a previous treatment in order to eliminate the bitterness of the fruit, due to the presence of polyphenolic compounds. For this purpose, the olives are treated with a 2% sodium hydroxide solution, followed by consecutive water rinsings. The high contaminant load of the wastewaters generated in these processes includes polyphenols among the most important pollutants. Moreover, the chelating character of some compounds present in these effluents leads to the presence of some toxic heavy metals in solution. Anaerobic digestion has been the most frequently used method for treating these wastewaters. However, phenolic compounds inhibit biological treatment to a great extent since phenols are toxic to methanogenic bacteria at relatively low concentrations. Beltrán de Heredia and Dom´ınguez99 applied Fenton oxidation to the treatment of the liquor resulting from black olive pickling, characterized by high COD content (6700 mg L−1 ) and the presence of polyphenolic compounds. After 5–15 min reaction time 73% of COD and 90% of polyphenols were removed. The colour of these wastewaters was also almost completely eliminated. Rivas et al.96 analyzed 1329

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the treatment of an olive oil mill wastewater (CODo = 12.8 g L−1 ) from a southwestern Spain factory by means of the Fenton technology. These authors studied the influence of some operating variables and proposed a kinetic model for the process. The reaction between Fe3+ and H2 O2 was suggested to be the controlling step. The simultaneous inefficient decomposition of hydrogen peroxide into water and oxygen was believed to play an important role. An integrated Fenton–coagulation/flocculation process, using Ca(OH)2 , was applied by Beltrán de Heredia et al.100 to wine distillery wastewaters, commonly known as ‘vinasses’. The experimental variables studied were H2 O2 and Fe doses, [H2 O2 ]o to [Fe2+ ]o molar ratio, the effluent dilution and the way the reagents were added (splitting the reagent doses into different fractions). The optimal operating conditions of the integrated process were established at 17 g L−1 of H2 O2 and a [H2 O2 ]o to [Fe2+ ]o initial molar ratio of 15. The H2 O2 dose was below one-half the stoichiometric amount relative to COD. Under these conditions a COD removal of 74% was attained. Horng et al.101 evaluated the treatment of the wastewater from a brewery plant containing high COD and SS concentrations. The treatment included biological (anaerobic and aerobic) processes and Fenton oxidation. The resulting effluent satisfied the existing local discharge standards. Fenton oxidation was applied to simultaneously remove COD and SS from the aerobic effluent so that a stable effluent quality and increasingly stringent local discharge limits in the future could be addressed. The operating conditions were set at COD/H2 O2 = 1, Fe2+ /H2 O2 = 2 (molar ratio), pH = 2–3 and 1 h reaction time. Gomec et al.102 reported on the improvement of an existing treatment for olive mill wastewaters by including a Fenton oxidation step. COD removal increased from 74 to almost 90%. Cork processing industry The main source of pollution in the cork processing industry comes from the cork boiling step. After harvest from the producer tree, Quercus suber L., the cork is stabilized by drying in open air for approximately 3 months. One of the first stages of industrial preparation of cork consists in its immersion for approximately 1 h in boiling water. This process improves cork textural and plastic properties, making this material more homogeneous, flat and elastic. The same water may be repeatedly used up to 20–30 times, reaching temperatures of about 100 ◦ C during boiling, with variable periods of cooling. The high volumes of wastewaters produced (400 L t−1 of cork) are characterized by high COD, BOD and polyphenols content, in the range of 4.5–5.5 g L−1 , 1.1–1.8 g L−1 1330

and 0.6–0.9 g L−1 , respectively, as well as an acidic pH, around 5. Several authors have proposed different technical solutions for cork processing wastewaters, involving mainly physical-chemical methods. Guedes et al.103 used Fenton oxidation as a pre-treatment step in order to improve biodegradability. The starting wastewater had a high organic pollution (COD = 5000 mg L−1 , TOC = 1505 mg L−1 ) with a low biodegradability (BOD5 /COD = 0.27). The authors accomplished a kinetic study of the process and selected the optimal operating conditions, achieving a COD reduction of 87.3%. A rapid decrease of TOC was observed within the initial 2 min, followed by a significantly slower degradation. The oxidation proceeds through an approximate second-order kinetics during the first 2 min of reaction, while the second phase of the reaction can be described by a zero-order kinetic equation. Due to the complexity of these wastewaters, combined techniques have frequently been suggested to treat them. Peres et al.104 compared coagulation/flocculation with Fenton oxidation followed by coagulation/flocculation. The second arrangement reduced COD, total polyphenols and aromatic compounds by 74, 99 and 98%, respectively, representing a considerable improvement compared with coagulation/flocculation alone. Beltrán de Heredia et al.105 also checked these two methods, reaching similar conclusions. From a kinetic study based on the initial rate method they reported that the rate of COD removal upon Fenton oxidation is maximum when the H2 O2 /Fe2+ initial molar ratio is equal to 10. In addition, these authors analyzed the effect of the way of adding the reagents and observed that the amount of organic matter (as COD) removed by Fenton oxidation is increased by distributing the H2 O2 and ferrous salt feeding in several additions. Another combined process for the treatment of cork boiling wastewater has been investigated by Dias-Machado et al.106 These authors applied Fenton oxidation as a pre-treatment, followed by biological treatment. The use of this chemical–biological combined solution increases the bioavailability of the polyphenols present in the wastewater since these compounds are partially oxidized into simpler molecules, improving their biodegradability. TOC reduction by Fenton oxidation was very fast within the early stage of the process (XTOC = 79% after 6 min), confirming the previous conclusion of Guedes et al.103 in the sense that the first 3–5 min are sufficient to achieve a high degree of chemical degradation. The results obtained by Dias-Machado et al.106 showed that Fenton oxidation, using small amounts of oxidant and catalyst combined with a biodegradative inoculum, added almost simultaneously, allows TOC reductions above 90%, a 20% better than the obtained by chemical oxidation alone. The main advantage of this integrated method is that small amounts of J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb


reagents are required for the Fenton oxidation, less than half that previously recommended as optimal for these wastewaters. Landfill leachates Although landfill leachates have been proved to be toxic and recalcitrant, landfilling still remains one of the main systems for municipal and industrial solid waste disposal. The composition of landfill leachates varies greatly depending on the type of wastes and the age of the landfill. Biological treatments including anaerobic and aerobic processes have shown to be very effective in the early stages when dealing with domestic wastes because the BOD/COD ratio of the leachate has a high value. However, this ratio generally decreases as the age of landfill increases, due to the presence of pollutants that inhibit biomass activity and/or are recalcitrant to biological treatments. To treat these aged or refractory landfill leachates different methods have been used, such as flocculation–precipitation, adsorption on activated carbon, evaporation, chemical oxidation and incineration. Among them, growing interest has been focused on advanced oxidation processes, which can achieve a substantial reduction of COD and improve the biodegradability. Kang and Hwang107 studied the effectiveness of Fenton oxidation against the non-biodegradable organic substances present in a leachate from Kimpo metropolitan landfill in Korea (CODo = 1500 mg L−1 ). The overall COD removal efficiency (by oxidation and coagulation) was maximum around a pH of 3.5 in the oxidation step and drastically decreased beyond pH = 5. Both the overall COD removal efficiency and the efficiency by oxidation itself were increased by increasing the H2 O2 dose. Otherwise, a dose of ferrous sulphate beyond 500 mg L−1 did not increase the percentage of COD eliminated. Lopez et al.108 evaluated the application of the Fenton process as pre-treatment for the leachate from a municipal landfill located in southern Italy (CODo = 10 540 mg L−1 ) with the objective of improving its overall biodegradability (BOD5 /COD ratio) up to a level compatible with a biological treatment (BOD5 /COD ≥ 0.5). The maximum amount of COD that could be removed by the Fenton pre-treatment was about 60%, using reagent dosages of 10 000 mg L−1 of H2 O2 and 830 mg L−1 of Fe2+ . The H2 O2 dose represented less than one-half the stoichiometric amount with respect to COD. Primo et al.109 investigated the treatment of a mature municipal landfill leachate from Cantabria (Spain) in an integrated system pilot facility which operated in batch and continuous mode. The sequence of stages was: Fenton oxidation, neutralization of Fenton effluent and ultrafiltration with submerged membranes. The initial COD of the leachate averaged 2100 mg L−1 and the BOD5 /COD ratio was 0.08. J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb

The final effluent was free of solids, colour and Fe, and the COD reduction reached 80%. This combination of Fenton with membrane filtration showed highly efficient for the removal of recalcitrant pollutants. The Fenton-like process (Fe3+ -H2 O2 ) has also shown to be an efficient treatment for the oxidation of landfill leachate.110 It has been demonstrated that the oxidation state of the catalyst does not affect to the efficiency of the process in terms of COD removal. Working temperatures above 30 ◦ C did not lead to additional COD reduction and a less efficient use of H2 O2 was observed. A rough economic analysis of the process indicates that this treatment can be a suitable alternative to deal with this type of liquid wastes.

SUMMARY Fenton oxidation has been demonstrated in fullscale applications as a feasible technology for the treatment of a wide diversity of industrial wastewaters. It represents a useful solution in many cases where the presence of recalcitrant and toxic pollutants discards the use of conventional biological treatments. Plant design and construction is simple and the process does not imply any operating problem other than controlling a safety handling of hydrogen peroxide. In general it has low energy consumption as it commonly works at ambient temperature and pressure. The main economic drawback derives from the consumption of oxidizing reagent (H2 O2 ) when dealing with high organic loads. Nevertheless, this can be adapted to the case needs using this technique as a conditioning treatment previous to a biological process or in combination with some other techniques, like coagulation–flocculation or membrane systems. The cases described throughout the text are collected in Table 1, which summarizes the state of the art on the application of Fenton technology to the treatment of industrial wastewaters. The economy of this technology is very dependent on the H2 O2 consumption and in this respect the information compiled from the literature reveals that a wide range of H2 O2 to COD ratios have been used in practice. As indicated before, Fenton oxidation has been used in connection with other techniques in integrated wastewater treatments. Table 2 collects a representative list of examples.

ACKNOWLEDGEMENTS The authors greatly appreciate financial support ´ y Ciencia of from the Consejer´ıa de Educacion the CM through the project REMTAVARES (S0505/AMB/0395) and the Spanish MEC through the project CONSOLIDER-TRAGUA (CSD20060044). 1331

1332

Pigment production: CODo = 2700 mg L−1 ; BOD5o /CODo = 0.04; Colouro (454 nm) = 1.479 AU

Cosmetic industry: CODo = 2395 and 4255 mg L−1 ; TOCo = 705 and 1090 mg L−1 ; BOD5o /CODo = 0.133 and 0.169 Phenolic resins manufacture: CODo = 2904 mg L−1 ; DOCo = 933 mg L−1 ; phenolo = 1215 mg L−1

Petrochemical industry: TOCo = 94 mg L−1

Pesticides production: CODo = 235 mg L ; organophosphorouso = 140–158 µg L−1 ; organochlorineo = 16–57.5 µg L−1 Four types of industrial wastewater: CODo = 13 400, 2005, 1494 and 234 mg L−1 Detergents production: CODo = 10 g L−1

−1

Wastewater characteristics

CODo = 964 mg L−1 ; BOD5o /CODo = 0.4; Total solidso = 1396 mg L−1 ; Colouro (PtCo) = 4236 mg L−1 ; Odouro = 31 473 UO m−3

CODo = 1250 mg L−1 ; TOCo = 537 mg L−1 ; Colouro (Pt) = 649 mg L−1

Pulp and paper CODo = 1384 mg L−1 ; TOCo = 441 mg L−1

Pharmaceutical CODo = 362 g L−1 ; BOD5o /CODo = 0.008

Chemical

Industry

Table 1. Summary on the application of Fenton oxidation to industrial wastewaters

Fenton or photo-Fenton. T = 25 and 70 ◦ C; pH = 2.8; H2 O2 /COD = 7.22 (w/w); H2 O2 /Fe2+ = 41 (molar); treaction = 2 h; Vreaction = 100 mL; Solar or Xe light. Fenton or photo-Fenton. T = 30 ◦ C; pH = 3; H2 O2 /COD = 5.76 (w/w); H2 O2 /Fe2+ = 26 (molar); treaction = 15 min; Vreaction = 100 mL; Solar light irradiation. Fenton-like. Batch: room temperature; pH = 2.5; H2 O2 /COD = 1.04 (w/w); H2 O2 /Fe3+ = 4 (molar); treaction = 1 h; Vreaction = 300 mL; Coagulation at pH = 5.

XCOD = 71.7–88.6%; Xtoxicity (to Vibrio fischeri) = 12–52% XCOD = 90%

pH = 3.0–3.5; H2 O2 /COD = 0.37, 2.49, 2.68 and 21.37 (w/w); H2 O2 /Fe2+ = 3–5 (molar); treaction = 1.5 h. Industrial scale. H2 O2 /COD = 0.25 (w/w); H2 O2 /Fe2+ = 2 (molar). T = 20 ◦ C; pH = 3.25; [H2 O2 ]o = 380 mg L−1 ; H2 O2 /Fe2+ = 3 (molar) treaction = 2 h. T = 25–50 ◦ C; pH = 3.0; H2 O2 /COD = 2.12 (w/w); H2 O2 /Fe2+ = 42–74 (molar); treaction = 4 h; Vreaction = 50 mL. Fenton or photo-Fenton (solar). Room temperature; pH = 3; H2 O2 /COD = 2.2 (w/w); H2 O2 /Fe2+ = 38.5 (Fenton) and 77 (photo-Fenton) (molar); treaction = 2 h. T = 20.8 ◦ C; pH = 5; H2 O2 /COD = 1.85 (w/w); H2 O2 /Fe2+ = 10 (molar). Batch: treaction = 0.5 h; Vreaction = 500 mL. T = 40 ◦ C; pH = 4; H2 O2 /COD = 0.28 (w/w); H2 O2 /Fe2+ = 10 (molar); treaction = 1.5 h; Vreaction = 100 mL.

XCOD = 75%; Xcolour = 98%; Xaromatics = 95%; BOD5 /COD = 0.7; Treated wastewater toxic to Artemia salina

Fenton: XTOC = 90%; Photo-Fenton: XTOC = 93%


XCOD = 56.4%

78

Effective removal of phenol within 5 min. Fenton: XCOD = 82%; XDOC = 41%. Photo-Fenton: XCOD = 97%; XDOC = 97% XCOD = 54.2%; BOD5 /COD = 0.36; Xcolour = 91.2%

88

86

85

80

79

76

73

71

70

69

Ref

XTOC = 45–60%; XCOD = 69%

XTOC = 65%

XCOD = 58.7–87.1%; Xorganophosphorous = 97–100%; Xorganochlorine > 90%

Main results

pH = 3.0–3.5; H2 O2 /COD = 21.2 (w/w); H2 O2 /Fe2+ = 3–5 (molar); treaction = 2 h.

Operating conditions

P Bautista et al.



Food

Food

Combined industrial and domestic wastewater: CODo = 1596 mg L−1 ; BOD5o /CODo = 0.31; TSSo = 320 mg L−1 ; oil and greaseo = 5.8 mg L−1 ; heavy metalso = 18.32 mg L−1 CODo = 910 mg L−1 ; BOD5o /CODo = 0.16; Colouro (PtCo) = 1570 mg L−1 CODo = 8100 mg L−1 ; BOD5o /CODo = 0.148; TOCo = 3010 mg L−1

Textile

Olive oil mill wastewater: CODo = 167–181 g L−1 ; TSSo = 36–39 g L−1 ; Total polyphenolso = 5.2 g L−1 ; Turbidityo = 14.6–14.8 NTU Table olive producing industry: CODo = 6700 mg L−1 ; BOD5o /CODo = 0.64; TSS = 5.2 g L−1 ; Total polyphenolso = 0.12 g L−1 ; Aromaticityo (254 nm) = 17.0 AU

Olive oil mill wastewater: CODo = 12.8 g L−1

CODo = 800 mg L−1

CODo = 1000 mg L−1

CODo = 1669 mg L−1 ; TOCo = 605 mg L−1 ; Colouro (Pt) = 40 mg L−1

Four wastewaters: CODo = 3600, 1030, 1970 and 3160 mg L−1


Textile

Industry

Table 1. Continued

T = 30 ◦ C; pH = 4; H2 O2 /COD = 4 (w/w); H2 O2 /Fe2+ = 10 (molar); treaction = 1.5 h; Vreaction = 0.5 L.

T = 20–50 ◦ C; pH = 2.8; H2 O2 /COD = 2.66 (w/w); H2 O2 /Fe2+ = 100 (molar); treaction = 8 h. T = 25 ◦ C; pH = 4; H2 O2 /COD = 0.05 (w/w); H2 O2 /Fe2+ = 8.33 (molar); treaction = 4 h.

T = 40 ◦ C; pH = 3.5; H2 O2 /COD = 0.88 (w/w); H2 O2 /Fe2+ = 12 (molar). Room temperature; pH = 3; H2 O2 /COD = 0.0037 (w/w); H2 O2 /Fe2+ = 1.2 (molar). Batch: treaction = 4–6 h; Vreaction = 2 L. Fenton or photo-Fenton. T = 70 ◦ C; pH = 3; H2 O2 /COD = 6 (w/w); H2 O2 /Fe2+ = 41 (molar); treaction = 2 h; Vreaction = 100 mL; Xe light. T = 25 ◦ C; pH = 3; H2 O2 /COD = 0.5 (w/w); [Fe2 O3 /carbon] = 300 mg L−1 . Batch: treaction = 1 h; Vreaction = 400 mL. Industrial scale. H2 O2 /COD = 1.25 (w/w); H2 O2 /Fe2+ = 1.2 (molar).

Pilot scale (continuous flow): tR = 1 h; Vreaction = 50 L (a series of 2 reactors); Q = 100 L h−1 . T = 25 ◦ C; pH = 3.5; H2 O2 /COD = 0.19–4.7, 0.66–16.5, 0.35–8.63 and 0.22–5.38 (w/w); H2 O2 /(Fe2+ /Fe3+ ) = 1–25 (molar). Batch: treaction = 2 h; Vreaction = 300 mL; Continuous flow: tR = 1 h; Vreaction = 1 L. Room temperature; pH = 3; H2 O2 /COD = 0.34 (w/w); H2 O2 /Fe2+ = 2 (molar).


XCOD = 73%; Xpolyphenols = 26–90%; Xaromatics = 35–94%

XCOD = 56%; Xpolyphenols = 99.5%; Xcolour = 35%; Xaromatics = 33%

XCOD = 65–85%

XCOD = 55%

XCOD = 71%


99

98

96

71

39

93

92

91

90

XCOD = 95%; Xcolour = 100%; BOD5 /COD = 0.625

XCOD = 59%; Xcolour = 89%; Complete removal of the toxicity to Daphnia magna XCOD = 45%; XTOC = 40%; Xcolour = 71.5%; BOD5 /COD = 0.097

89

Ref

XCOD = 60% (batch); XCOD = 30% (continuous flow). Significant colour reduction.

Xodour = 96%; XVOCs (terpernes) = 80%

Main results


1333

1334

CODo = 10 540 mg L−1 ; BOD5o /CODo = 0.22; TOCo = 3900 mg L−1

Leather tannery industry: CODo = 3197–16797 mg L−1 ; BOD5o /CODo = 0.25


Textile

CODo = 697 mg L−1 ; Transparencyo = 3.7 cm

Pharmaceutical Three wastewater samples: CODo = 4000, 5400 and 13 130 mg L−1 ; BOD7o /CODo = 0.33, 0.45 and 0.54 mg L−1 CODo = 35–40 g L−1 ; BOD5o /CODo = 0.06

Chemical

Industry

Lab scale. Fenton-like + lime coagulation. Room temperature. H2 O2 /COD = 2 (w/w); H2 O2 /Fe2+ = 10 (molar); treaction = 2 h; Vreaction = 200 mL. Industrial scale. Fenton + SBR (V = 8 m3 ; 24 h/cycle). Room temperature; pH = 3.5; H2 O2 /COD = 0.26–0.29 (w/w); H2 O2 /Fe2+ = 150 (molar); Vreaction = 2 m3 . Continuous process of combined coagulation, Fenton and activated sludge. pH = 4; H2 O2 /COD = 0.14 (w/w); H2 O2 /Fe2+ = 4.5 (molar); [PAC]o = 100 mg L−1 . Fenton: tR = 1 h; Q = 1 mL min−1 .

Combined Fenton and activated sludge system. H2 O2 /COD = 4 (w/w); H2 O2 /Fe2+ = 9 (molar).


T = 25 ◦ C; pH = 3.5; H2 O2 /COD = 1.1 (w/w); H2 O2 /Fe2+ = 14.7 (molar); treaction = 3 h; Vreaction = 1 L. Room temperature; pH = 3; H2 O2 /COD = 0.31 (w/w); H2 O2 /Fe2+ = 19.7 (molar); treaction = 2 h.

CODo = 1500 mg L−1 ; BOD5o /CODo = 0.02

Operating conditions T= pH = 3.2; H2 O2 /COD = 2.12 (w/w); H2 O2 /Fe2+ = 8.2 (molar); Vreaction = 200 mL. T = 30 ◦ C; pH = 3.5; H2 O2 /COD = 1.84 (w/w); H2 O2 /Fe2+ = 10 (molar); treaction = 2.5 h; Vreaction = 0.5 L.

30 ◦ C;

CODo = 5000 mg L ; BOD5o /CODo = 0.27; TOCo = 1505 mg L−1 CODo = 3702 mg L−1 ; BOD5o /CODo = 0.19; TSSo = 1390–1700 mg L−1 ; Total polyphenolso = 500–620 mg L−1 ; Aromaticityo (254 nm) = 0.96–1.17 AU (1/50 diluted samples)

−1


Table 2. Application of Fenton oxidation in integrated wastewaters treatments

Landfill leachates

Cork processing

Industry

Table 1. Continued

94

83

XCOD = 98%; XBOD = 98%. Fenton unit: XCOD = 45–50%; BOD5 /COD = 0.23

XCOD = 88%; Transparency = 28.2 cm.

82

74

Ref

108

107

105

103

Ref

XCOD = 87–96%; XBOD7 = 79–95%

XCOD ≤ 96% (Fenton: XCOD = 90%; Biological treatment: XCOD = 35–60%; XBOD = 60–70%)

Main results

XCOD = 25%; BOD5 /COD = 0.5

XCOD = 70%

XCOD = 87.3%; XTOC = 66.4%; BOD5 /COD = 0.63 XCOD = 65%

Main results

P Bautista et al.


J Chem Technol Biotechnol 83:1323–1338 (2008) DOI: 10.1002/jctb Comparison of SBR, Fenton + SBR and SBR + Fenton. Lab.scale. Batch. Fenton: T = 28–32 ◦ C; pH = 3; H2 O2 /COD = 0.003–0.03 (w/w); H2 O2 /Fe2+ = 1 (molar); treaction = 0.5 h; Vreaction = 5 L. SBR: Three reactors in parallel mode; T = 28–32 ◦ C; V = 10 L; 24 h/cycle; STR = 60 days Integrated Fenton–coagulation–flocculation process (using Ca(OH)2 ). H2 O2 /COD = 0.92 (w/w); H2 O2 /Fe2+ = 15 (molar). Biological treatment (anaerobic and aerobic processes) and Fenton (pH = 2–3; H2 O2 /COD = 1 (w/w); H2 O2 /Fe2+ = 0.5 (molar); treaction = 1 h).


Integrated system (Fenton + membrane filtration). Pilot plant. Room temperature; pH = 3; Batch: H2 O2 /COD = 4 (w/w); H2 O2 /Fe2+ = 13.8 (molar); treaction = 1 h; Vreaction = 100 L. Continuous: H2 O2 /COD = 3.3 (w/w); H2 O2 /Fe2+ = 11.4 (molar); tresidence = 2 h.

Integrated Fenton–coagulation/flocculation process. CODo = 4250 mg L−1 ; BOD5o /CODo = 0.19; TSSo = 1720 mg L−1 ; Total polyphenolso = 994 mg L−1 ; T = 35 ◦ C; H2 O2 /COD = 4 (w/w); H2 O2 /Fe3+ = 81 Aromaticityo (254 nm) = 2.16 AU (1/25 diluted samples) (molar); treaction = 5 h; Vreaction = 150 mL. CODo = 2300–4600 mg L−1 ; BOD5o /CODo = 0.15–0.21; Fenton oxidation + Biological treatment. T = 30 ◦ C; TOCo = 1220–2000 mg L−1 ; Total pH = 3.5; H2 O2 /COD = 1.09–2.17 (w/w); polyphenolso = 660–780 mg L−1 H2 O2 /Fe2+ = 8.2 (molar); treaction = 0.5 h; Vreaction = 1 L.

Brewery industry: CODo = 16.3 g L−1

Wine distillery industry: CODo = 18.5 g L−1 ; TSSo = 13 g L−1

CODo = 1047 mg L−1 ; BOD5o /CODo = 0.42; Colouro = 544 ADMI units


Landfill leachates CODo = 2100 mg L−1 ; BOD5o /CODo = 0.08

Cork processing

Food

Industry

Table 2. Continued

109

106

XTOC = 92%

XCOD = 80% (batch); XCOD = 83% (continuous); BOD5 /COD = 0.36

104

101

100

95

Ref

XCOD = 74%; Xpolyphenols = 99%; Xaromatics = 98%; BOD5 /COD = 0.50

Anaerobic process (UASB): XCOD = 90%; Aerobic process: XCOD = 80%; Fenton: XCOD = 35% and XSS = 40%

XCOD = 74%

Best option: Fenton + SBR : XCOD = 91%; Xcolour = 80%

Main results


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