Article pubs.acs.org/IECR
Treatment of Highly Polluted Hazardous Industrial Wastewaters by Combined Coagulation−Adsorption and High-Temperature Fenton Oxidation Gema Pliego,* Juan A. Zazo, Sonia Blasco, Jose A. Casas, and Juan J. Rodriguez Ingenieria Quimica, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid, Spain S Supporting Information *
ABSTRACT: A coupled coagulation−adsorption and high-temperature Fenton oxidation treatment has been applied for the treatment of three different industrial wastewaters bearing high concentrations of hazardous pollutants. High percentages of chemical oxygen demand (COD) removal (>85% for the pesticide and security inks effluents and 65% for the cosmetics ones) were achieved in a first step using FeCl3 as coagulant and bentonite as adsorbent. This reduced dramatically the amount of H2O2 required in the further high-temperature (120 °C) Fenton oxidation (HTF). Using the stoichiometric amount relative to COD around 70% of the remaining organic load was mineralized. The combined treatment allowed achieving the regional discharge limits of COD and ecotoxicity at a cost substantially lower than the solution used so far where the three wastewaters are managed as hazardous wastes. Working at high temperature would not represent an important drawback since around 90% of heat can be recovered from the treated off-stream.
1. INTRODUCTION Contamination of water bodies by industrial discharges has become a problem of increasing concern within the past decades. Pesticide manufacture generates wastewater containing toxic, chemically stable, and recalcitrant compounds.1,2 Due to their persistence and bioaccumulation and consequent longterm toxicity they have been designated as priority pollutants in European Union (EU) legislation3 (Directive 2000/60/EC). Industrial effluents from ink manufacture contain also a great variety of pollutants such as pigments, binders, carriers, and additives,4 and the wastewater resulting upon cleaning/washing of the industrial equipment are highly colored and in general contaminated with different organic materials.5 Acrylics often used in ink formulations and pigments are very difficult to break down biologically, so this type of wastewater represents a serious environmental problem.6 The cosmetic industry generates wastewater characterized by high levels of chemical oxygen demand (COD), mainly proceeding from the cleaning process of batch reactors and mixers.7 These effluents contain xenobiotics including many toxic chemical compounds such as phenol derivatives, mixtures of surfactants, dyes, fragrances, and cosolvents which make conventional biological treatment unlikely.8 Although these industrial activities are fairly different, all of them generate wastewater containing organic compounds refractory to conventional biological oxidation and therefore a number of studies have been focused on attempts to develop suitable technical solutions for this type of effluents.9 The combination of coagulation and Fenton oxidation has been successfully used for the treatment of highly contaminated wastewater such as cosmetics, olive-mill, textile, and pharmaceutical effluents.7,10−13 Coagulation is a wellestablished technology for the removal of suspended solids (SS) and high molecular weight compounds.13 Ferric salts are largely used as cost-effective coagulants with no problems of toxicity. The use of bentonite as adsorbent has been reported to improve COD and color removal.14,15 © 2012 American Chemical Society
The Fenton process is a well-known advanced oxidation technology based on the catalytic generation of free radicals, such as •OH and •OOH, resulting from the chain reaction between ferrous ion and hydrogen peroxide at acidic pH. Although it has been recognized as one of the most feasible advanced oxidation processes (AOPs),1,16−21 its application to the treatment of real effluents has been so far limited because of the high consumption of both H2O2 and iron and the generation of iron-containing sludge from the neutralization step before discharge.22−24 Therefore, the working conditions, such as pH, H2O2, and Fe doses and temperature, require case-study optimization for a costeffective application of that technology. Despite the extensive literature on the Fenton process, there is so far a lack of information on the effect of temperature most probably associated with the assumption that thermal decomposition of H2O2 into O2 and H2O may represent a serious drawback. In this sense, Zazo et al.25 demonstrated in a recent paper, using phenol as a target compound, the dramatic beneficial effect of increasing the temperature on the oxidation rate and the degree of mineralization, allowing work with lower doses of H2O2 and Fe2+ and therefore reducing operational costs. Working at temperatures well above the ambient (even up to 100−120 °C) does not necessarily imply an economic drawback, since most of the heat can be recovered by simply preheating the inlet stream with the one exiting the reactor so that the thermal needs can be substantially reduced. Besides, some well-established industrial applications based on the Fenton process operate at temperatures higher than 100−130 °C.20 Thus, OHP process26 developed by FMC FORET Company, which works at temperature amid 110 and 120 °C, is included in the latest Received: Revised: Accepted: Published: 2888
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oxidant (ISO 6060). The TOC and COD of the pretreated (C−F or C−A) effluents were measured after gravity filtration through filter paper. Hydrogen peroxide concentration was determined by colorimetric titration using the TiOSO4 method.29 A gas chromatography−mass spectrometry (GC-MS) system in electron impact ionization mode was used for chemical analyses of the initial and treated effluents. The analyses were performed by gas chromatography/ion trap mass spectrometry (CP-3800/Saturn 2200, Varian, equipped with an automatic injector CP-8200/SPME, solid-phase microextraction). A 30 m length and 0.25 mm i.d. capillary column (Factor Four VF-5 ms) was used. The carrier gas (helium) flow rate in the GC was 1 mL/min. The SPME was carried out with a fiber cartridge (poly(dimethylsiloxane) red), using adsorption and desorption times of 30 and 5 min, respectively. The sample injection was conducted at 220 °C. The temperature program used in the GC-MS analyses ramped as follows: 40 °C for 5 min, increased to 250 °C at 15 °C/min, held at 250 °C for 10 min, increased to 300 °C at 20 °C/min, and held at 300 °C for 2 min. Compounds identification was assessed using the National Institute of Standards and Technology (NIST) database. Short-chain organic acids were analyzed by ion chromatography with chemical suppression (Metrohm 790 IC) using a conductivity detector. A Metrosep A supp 5−250 column (25 cm length, 4 mm i.d.) was used as stationary phase and 0.7 mL of an aqueous solution of 3.2 mM of Na2CO3 and 1 mM of NaHCO3 as mobile phase. The ecotoxicity was determined by means of a bioassay following the standard Microtox procedure (ISO 11348-3, 1998) based on the decrease of light emission by Photobacterium phosphoreum. A Microtox M500 analyzer (Azur Environmental) was used. To prevent pH effects, the pH of each sample was adjusted into the range of pH 6−8 using a NaOH solution (1 N). More details relative to ectoxicity measurement are given elsewhere.30
BREF review for the treatment of wastewater as the best available technology (BAT) for large-volume organic chemical industry. Also, in some of these applications a second catalyst is often mentioned besides Fe, probably Cu. This paper reports on the feasibility of a technical solution for the treatment of three different real industrial wastewaters from pesticides, security inks, and cosmetics manufacture. So far these wastewaters have been managed as hazardous wastes at high cost so that the companies involved are looking for some alternative less expensive but capable of fulfilling the COD and ecotoxicity limits regionally (Madrid, Spain) established for industrial wastewater discharge into the municipal sewer system. In that sense, we explore a combined treatment based on a first coagulation (FeCl3) and adsorption (bentonite) step followed by Fenton oxidation at 120 °C. The study includes cost estimation and a kinetic approach for total organic carbon (TOC) removal upon Fentonoxidation.
2. MATERIALS AND METHODS 2.1. Materials. Three real wastewaters from different industrial activitiesnamely, pesticides, security inks, and cosmetics manufacturewith significantly different values of COD, TOC, and ecotoxicity were used in this study. Wastewater samples were stored at low temperature (4 °C) and in the dark immediately after reception from the factories. Samples were analyzed by duplicate. 2.2. Experimental Procedure. Coagulation−flocculation (C−F) and coagulation−adsorption (C−A) experiments were carried out in a 6 × 1 L jar-test system (Selecta) filled with 500 mL each of raw wastewater. FeCl3 (500 mg/L) was used as coagulant, whereas anionic polyelectrolyte PA-18 (12 mL/L) and bentonite were used as flocculant and adsorbent, respectively. Due to the different starting COD, the adsorbent dose was varied between 1 g/L for the cosmetics wastewater and 4 g/L for the pesticides and security inks ones. High-temperature Fenton (HTF) runs were carried out in a 500 mL stoppered glass batch reactor (Büchi, inertclave Type I) equipped with a back-pressure controller. The reactor was filled with 470 mL of the clarified wastewater from the C−A step and heated to 120 °C. The pH value was set at 3 by adding HCl (37% (w/v), Panreac). Once the required temperature was reached, 25 mL of an aqueous solution of H2O2 was fed into the system to supply the desired starting amount of H2O2, amid 20 and 100% of the stoichiometric theoretically needed for complete mineralization of COD (2.125 g of H2O2/g of COD). The Fe2+ dose was adjusted at 10 and 100 mg/L by adding 5 mL of aqueous solution of FeSO4·7H2O of the required concentration. The progress of the reaction was followed by measuring overall parameters such as COD, TOC, and ecotoxicity but also the concentration of intermediates once H2O2 was completely converted in order to avoid interferences in the COD measurements.27,28 Besides, kinetic experiments were carried out using the stoichiometric amount of H2O2 and 100 mg/L Fe2+. In these cases, the evolution of the reaction was followed by measuring the TOC and the residual H2O2 concentration at predetermined times. Blank experiments in the absence of Fe2+ and H2O2 were performed. 2.3. Analytical Procedure. Total organic carbon was determined with a TOC analyzer (Shimadzu, model TOC VSCH). The chemical oxygen demand measurements were performed by the closed reflux colorimetric method using a UV−vis spectrophotometer (Shimadzu, model. UV-1603) in accordance with a standard method using potassium dichromate as
3. RESULTS AND DISCUSSION Table 1 shows the representative analyses of the three wastewaters as received, in terms of TOC, COD, and ecotoxicity. The Regional Table 1. Representative Analyses of the Wastewaters As Received TOC (mg/L) COD (mg/L) ecotoxicity (Equitox/m3)
pesticide
security inks
cosmetics
14648 ± 520 52280 ± 2806 1483 ± 30
11580 ± 375 37234 ± 1104 54 ± 3
4042 ± 224 14955 ± 530 79 ± 7
Community of Madrid, where the three factories are located, establishes maximum allowable limits for industrial wastewater discharge into the municipal sewer system through the 10/1993 Act. Those limits are fixed at 1750 mg/L for COD and 25 Equitox/m3 for ecotoxicity. As can be seen the three wastewaters show values far above those limits for COD. The ecotoxicity is also above the limit, most in particular in the case of the wastewater from pesticide manufacture. More detailed chemical analyses were carried out by GC-MS (Figure 1) for the sake of both identifying representative species and following their evolution upon treatment. Table 2 collects the main species identified out of a larger list which covered a total of 88 compounds for the pesticides wastewater, 48 for the security inks, and 36 for the cosmetics ones. 2889
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Figure 1. Initial chromatogram for pesticides (A), security inks (B), and cosmetics (C) raw wastewaters (see Table 2 to assign the compound names to the peaks).
3.1. Pretreatment Step. The high COD values of the three wastewaters demand some kind of pretreatment before proceeding to Fenton oxidation. Otherwise their high organic
loads would make unfeasible the application of this last technique since prohibitive amounts of H2O2 would be needed to achieve the aforementioned allowable limit for COD. In this 2890
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Table 2. Main Compounds Identified by GC-MS in the Three Wastewaters no.
pesticides
security inks
cosmetics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
o-xylene cychlohexanone 3-(trifluoromethyl)phenylisocynate 2-ethyl-1-hexanol 4-isopropylphenylisocynate octyl methoxyacetate N,N-dimethyldecanamide Dimethoate tert-butylazine methyl hexadecanoate Ethofumesate Linuron Metolachlor methyl octadeca-9,12-dienoate methyl oleate Fenamiphos Oxifluorfen Propiconazole
heptadecylcyclohexane p-ethyltoluene 1,2,3-trimethylbenzene m-ethyltoluene 1,3,5-trimethylbenzene 1-(2-methoxypropoxy)-2-propanol 1,2,4-trimethylbenzene n-heptylcyclohexane 3-propyltoluene 1,4-diethylbenzene sec-butylbenzene 4-ethyl-o-xylene p-cymene 1,2,4,5-tetramethylbenzene 1-terpinenol o-cymene 1,2,3,4-tetrahydronaphthalene terpenol
2-ethyl-1-hexanol eucalyptol dihydromyrcenol tetrahydrolinalool ethylhexanoic acid oleic acid α-terpineol carvestrene 2-phenoxyethanol dihydroterpineol dimethylphenylethyl carbinol dimethylbenzylcarbinyl acetate n-capric acid p-acetanisole 4-tert-butylacetophenone methyl ionone benzophenone isopropyl palmitate
sense C−F and C−A were checked in the conditions described in the Experimental Procedure for the sake of reducing the organic load. As can be seen in Table 3, fairly important Table 3. COD Values and Removal Percentages after C−F and C−A Pretreatment ([FeCl3] = 500 mg/L; [PA-18] = 12 mL/L; [Bentonite] = 4 g/L) for the Pesticide and Security Inks Wastewaters and 1 g/L for the Cosmetics One COD (mg/L)/reduction (%) treatment
pesticides
security Inks
cosmetics
C−F (FeCl3 + PA-18) C−A (FeCl3 + bentonite)
47 052/11.2 6 990/86.6
29 415/21.0 5 149/86.1
5 200/49.9 7 178/65.3
Figure 2. Removal of components from pesticide wastewaters upon C−A pretreatment.
reductions of COD were achieved by using FeCl3 and bentonite. The addition of FeCl3 reduced around 10 times the needs of bentonite alone for achieving similar COD reduction. Thus, coagulation seems to have a major effect on COD reduction. The C−A pretreatment allowed removal of most of the species identified in the three wastewaters given in Table 2. In the case of the security inks wastewater, only three of the main compounds, 1-(2-methoxypropoxy)-2-propanol, 1-terpinenol, and terpenol, remained after the C−A pretreatment. For those compounds, reductions in terms of GC peak areas of 20, 43, and 27% were achieved, respectively. Similar results were obtained for the cosmetics wastewater, where 2-ethyl-1-hexanol, dihydromyrcenol, and α-terpineol were the only three compounds detected after the C−A pretreatment, and their peak area reduction percentages were 88, 89, and 28%, respectively. Figure 2 shows the reduction (in terms of GC peak area) of the main components identified in the pesticides wastewater upon C−A pretreatment. The ecotoxicity values after that pretreatment were 24, 20, and 21 Equitox/m3 for the pesticides, security inks, and cosmetics wastewaters, respectively. Those values are below the aforementioned 25 Equitox/m3 allowable limit, but respirometry tests showed a frankly poor response to biodegradation in the three cases. The most important reduction of ecotoxicity upon the C−A pretreatment took place by far for the pesticide wastewater. 3.2. High-Temperature Fenton Oxidation. After the C−A pretreatment the three wastewaters were submitted to HTF for
the sake of achieving the allowable COD limit of 1750 mg/L and improving the biodegradability of the resulting effluents. The HTF experiments were carried out at 120 °C following the conclusions of a previous work with phenol.25 A lower temperature (50 °C) was also tested, but fairly poor reductions of COD and TOC were observed. Experiments performed at the stoichiometric H2O2 dose confirmed that, as expected, increasing the initial Fe2+ concentration from 10 to 100 mg/L decreased dramatically from about 30 h to around 4 h the reaction time required to achieve the maximum COD reduction in the case of the three wastewaters. Nevertheless, that maximum COD reduction was finally quite similar at the two above-mentioned Fe2+ doses. This simply confirms the effect of the Fe2+ concentration on the rate of formation of HOx• radicals. In the following a 100 mg/L Fe2+ initial concentration will be always used. Figure 3 depicts the results obtained at different H2O2 doses within the range of 0.2−1 times the theoretical stoichiometric amount relative to the initial COD. As expected, the TOC and COD removal increased with the H2O2 dose as the result of a higher overall HOx• generation. Using the stoichiometric H2O2 amount, COD and TOC removals of 70 and 60%, respectively, were achieved in all cases and the discharge limit for COD was fulfilled for the three wastewaters. The HTF process removed the majority of the identified compounds remaining in the pretreated effluents even at a H2O2 dose as low as 0.2 times the stoichiometric dose. In the case of the pesticides wastewater, only four pesticides (tert-butylazine, 2891
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and COD would decrease linearly with TOC. The trend showed in Figure 4 indicates that the evolution of the organic load upon
Figure 4. Evolution of TOC vs COD upon HFT of the three pretreated (by C−A) wastewaters. (Experimental conditions: [Fe2+] = 100 mg/L, T = 120 °C, pH = 3, tR ≤ 4 h.)
HTF treatment occurs mainly through total rather than partial oxidation in all cases. 3.3. Ecotoxicity. Figure 5 gathers the ecotoxicity values upon adsorption−flocculation and high-temperature Fenton
Figure 3. Results from HTF treatment at different H2O2 doses of (A) pesticides, (B) security inks, and (C) cosmetic pretreated (by C−A) effluents. (Experimental conditions: [Fe2+] = 100 mg/L, T = 120 °C, pH = 3, tR ≤ 4 h.)
Fenamiphos, Propiconazole, and Metolachlor) were detected in the final effluent, although reduction percentages around 99% of the corresponding chromatographic peak area were achieved in all cases. Doubling the H2O2 dose up to 0.4 times the stoichiometric allowed the disappearance of the first three above-mentioned pesticides, whereas traces of Metolachlor remained in the effluent even using the stoichiometric amount of H2O2. Regarding the cosmetics wastewater, 4-tert-butylacetophenone was the only compound identified that was not completely converted (peak area reduction around 78%) using 0.2 times the stoichiometric H2O2 amount. Again, no traces of any of the previously identified compounds in this effluent remained after HTF treatment at 0.4 times the stoichiometric H2O2 dose. Finally, in the case of the security inks, none of the identified compounds remained in the effluent after HTF treatment at 0.2 times the stoichiometric H2O2 amount. Organic load oxidation degree is another aspect to be considered in order to determine the efficiency of this treatment. For this purpose, Mantzavinos et al.31 and Fotiadis et al.32 assessed the TOC versus COD evolution. Thus, a horizontal line corresponds to ideal partial oxidation; that is, TOC would remain unchanged throughout the reaction and COD would decrease, whereas a diagonal line corresponds to ideal complete oxidation
Figure 5. Evolution of ecotoxicity upon C−A pretreatment and HTF process at different H2O2 doses. (Experimental conditions: [Fe2+] = 100 mg/L, T = 120 °C, pH = 3, tR ≤ 4 h.)
treatments. A very important reduction of ecotoxicity was achieved upon the C−A pretreatment, leading in all cases to values bellow the allowable limit established by the 10/1993 Act of the Regional Community of Madrid. This suggests that the identified compounds (Table 2), almost completely removed by that pretreatment, must be the main factor responsible for the ecotoxicity of those effluents. In the case of the pesticide effluent, the high initial value of ecotoxicity can be associated with an important synergistic effect between the different pesticides.33,34 It is noticeable the increase of this parameter after the HTF treatment at 0.2 times the stoichiometric amount of H2O2 in the pesticide and cosmetics effluents. This is in agreement with recent studies about the use of substoichiometric H2O2 concentrations on Fenton oxidation35 that 2892
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in the latest steps of the oxidation pathway of many organic compounds with Fenton reagent. As can be observed, formic, acetic, and oxalic were the main organic acids detected in all cases. The last two appear refractory or highly resistant to Fenton oxidation in spite of the high temperature used in this case. Nevertheless, high-temperature Fenton oxidation was found capable of mineralizing those organic acids in a previous work using phenol as starting compound.25 In the current work the persistence of acetic and oxalic acids is only apparent and due to the exhaustion of H2O2 as will be seen later (Figure 7). In the
could lead to the production of oxidation byproduct with higher toxicity than the initial compounds. Nevertheless, beyond that point, ecotoxicity decreased as H2O2 dose increased, reaching significantly lower values than discharging limits in all cases. GC-MS analyses of the samples after HTF treatment with H2O2 at 0.2 times the stoichiometric dose (see chromatograms in the Supporting Information) revealed the presence of several oxidation byproducts, none of which had been detected in the effluent after the C−A step. Among them, some chlorine- and nitrogen-bearing aromatic compounds, such as 2,6-dichloro-4methylphenyl, 2,4-dichlorobenzoate, and 2,6-diethylaniline, could contribute to the observed increase of ecotoxicity in the pesticide wastewater. Increasing the H2O2 dose up to around 80% of the stoichiometric further reduction of the ecotoxicity was achieved and frankly low values were reached with H2O2 at the stoichiometric dose (13, 6, and 4 Equitox/m3 for the pesticides, security inks, and cosmetics wastewater, respectively). Besides, HTF samples were analyzed by ion chromatography in order to quantify the presence of short-chain organic acids. The results are depicted in Figure 6. Those compounds usually appear
Figure 7. Time evolution of TOC and H2O2 upon HTF of (A) pesticides, (B) security inks, and (C) cosmetics pretreated (by C−A) wastewaters. (Experimental conditions: [Fe2+] = 100 mg/L, [H2O2] = 100% of the stoichiometric amount, T = 120 °C, pH = 3.)
pesticides effluent, traces of fumaric and cloroacetic acids were also detected. The amount of carbon in those compounds accounts for around 80% of the measured TOC in the case of the cosmetics and security inks effluents and 60% for the pesticides wastewater. Figure 6. Evolution of short-chain organic acids upon HTF treatment at different H2O2 doses: (A) pesticides, (B) security inks, and (C) cosmetics pretreated (by C−A) wastewater. (Experimental conditions: [Fe2+] = 100 mg/L, T = 120 °C, pH = 3, tR ≤ 4 h.)
4. KINETIC STUDY A kinetic model proposed by the authors in previous works has been tested for describing the time evolution of TOC upon 2893
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Fenton oxidation.25,36 It provides a simple and easy-to-apply approach based on the following scheme:
constants obtained by fitting the model to the experimental results using Scientist 3.0 software. The correlation coefficients are also included. The values of k2 were almost zero in all cases (lower than 10−22 L2·mg−2·min−1), which indicates that in the case of the three wastewaters tested, direct mineralization of the starting compounds (those remaining after the C−A pretreatment) upon Fenton oxidation is unlikely. The values of k3, also negligible, suggest that complete mineralization can be achieved as far as H2O2 is still available. Figure 7 serves to demonstrate the validity of the model. The remaining TOC is consistently explained by H2O2 depletion.
As indicated before, in the C−A pretreatment the dose of FeCl3 has been fixed at 0.5 g/L and bentonite needs have been established at 4 g/L for pesticides and security inks wastewater and at 1 g/L for the cosmetics one. For the HFT process, operational cost were estimated considering 0.1 kg/m3 of Fe2+ and the stoichiometric amount of H2O2 relative to COD. As described throughout the paper, these were the conditions that allow reaching the discharge limits imposed by the regional regulations affecting the industrial plants of this study. The amount of sludge generated after the C−A pretreatment corresponds to the experimentally determined (by gravity filtration) in all cases. Thus, 17.5 and 24.1 kg of sludge/m3 of treated wastewater were collected for pesticides and security inks effluents, respectively. For the cosmetics one, in spite of the lower starting COD, the sludge quantity increased up to 28.5 kg/m3 because of the large amount of suspended solids initially present. For the HTF process, we assumed a Fe(OH)3 sludge production of 0.67 kg/m3 (sludge consistency 15%) according to the data reported by Georgaki et al.40 A ΔT of 10 °C was taken to estimate the heating needs since that would be a reasonable temperature difference in the heat exchanger (preheating of the wastewater entering HTF with the treated exiting stream). As can be seen, the coagulation−adsorption pretreatment is by far more cost-effective than the HFT in terms of COD removal. Nevertheless, that first step is not sufficient to fulfill the discharge limits. The estimates given in Table 5 refer only to the main operating costs and thus to have a complete sight on the economy of the technical solution hereby proposed they should be included the fixed costs derived from the investment as well as the maintenance and other minor operational costs. Regardless, this solution represents a considerable improvement with respect to that currently used, where these wastewaters are being externally managed as hazardous wastes at a much higher cost (around 100−150 €/m3). Moreover the reduced overall waste production, 0,67 kg/m3, would represent a significant improved with respect to established technologies as OHP that uses iron concentrations between 10 and 20 g/L.26
5. COST ESTIMATION Table 5 summarizes the estimated main operating costs (chemicals, energy, and sludge disposal) for the treatment of the three wastewaters upon C−A pretreatment followed by high-temperature Fenton oxidation. The estimates are given in the most common approach of per unit volume of wastewater but values per unit of COD removed are also included for the sake of comparison. Current average prices for Spain have been used for sludge treatment.
6. CONCLUSIONS A combined treatment based on coagulation−adsorption (FeCl3−bentonite) followed by high-temperature (120 °C) Fenton oxidation has proved to be a potential solution for highly polluted hazardous industrial wastewater from three different manufacturing activities (pesticides, security inks, and cosmetics). This solution allows achieving the regionally established discharge limits for COD and ecotoxicity and represents a considerable improvement with respect to that
This pathway segregates the TOC in three lumps depending on the degradability, TOCA, TOCB, and TOCC, which correspond to easily oxidizable, partially oxidizable, and refractory organic matter, respectively. The model assumes second-order kinetics with respect to TOC and first-order with respect to H2O2 concentration, whose evolution is directly related to the generation of HO•x. Table 4 reports the values of the rate Table 4. Values of the Rate Constants (k1−k4, L2·mg−2·min−1; k5, min−1) (Experimental Conditions: [Fe2+] = 100 mg/L, [H2O2] = 100% of the Stoichiometric Amount, T = 120 °C, pH = 3, tr = 4 h) wastewater pesticide security inks cosmetics a
k1 × 108
k2
k3
k4 × 108
k5
r2
1.29 6.12 29.5
≈0 ≈0 ≈0
≈0 ≈0 ≈0
1.88 7.16 32.8
0.09 0.18 0.70
0.99 0.99 0.99
a
a
