Combined Advanced Oxidation Processes and Aerobic Biological

Article pubs.acs.org/IECR

Combined Advanced Oxidation Processes and Aerobic Biological Treatment for Synthetic Fatliquor Used in Tanneries Chitra Kalyanaraman,*,† Sri Bala Kameswari Kanchinadham,† L. Vidya Devi,† S. Porselvam,† and J. Raghava Rao‡ †

Environmental Technology Division, Council of Scientific and Industrial Research−Central Leather Research Institute, Adyar, Chennai 600 020, India ‡ Chemical Laboratory, Council of Scientific and Industrial Research−Central Leather Research Institute, Adyar, Chennai 600 020, India ABSTRACT: The use of synthetic oils, fats, and fatliquors in the leather industry has become popular due to their superiority in terms of high emulsifying power when compared to natural oil based fatliquor. Compared to natural oil based fatliquor, the quantity required is lesser and the leather is not unduly loaded with fats and oils to achieve specific softness. Generally, synthetic fatliquors are prepared from paraffins and are made emulsifiable by sulphochlorination to produce chlorinated paraffin sulphonates. Due to the inherent nature of synthetic fatliquor and its low BOD5/COD ratio of 0.077, it is adsorbed over the microbes and reduces the efficiency of the aerobic treatment unit in the treatment plants. Hence the aim of the present study was to evaluate the environment friendliness of synthetic fatliquors containing chlorinated paraffin sulphonates, by undertaking aerobic biodegradation studies at the same operating conditions maintained in the tannery effluent treatment plants, viz., f/m ratio of 0.15 and hydraulic retention time (HRT) of one day. Considering the nature of the compounds present in the synthetic fatliquors, the biodegradability of the fatliquor was sought to be improved by adopting advanced oxidation processes (AOPs) like UV/H2O2 and Fenton’s reagent as pretreatment. AOP pretreatment of UV/H2O2 and Fenton’s reagent improves the BOD5/ COD ratio of synthetic fatliquor from 0.077 to 0.3 and 0.37 and the biodegradable organics are effectively degraded in the aerobic reactor. UV/H2O2 pretreated synthetic fatliquor produced biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) of 45 and 330 mg/L in the aerobic reactor and Fenton’s reagent pretreated fatliquor produced BOD5 and COD of 28 and 240 mg/L in the aerobic treated effluent. It was evident from FT-IR analysis that the chlorinated paraffin sulfonates are degraded efficiently in the batch reactor after AOP pretreatment and short chain chlorinated compounds and carboxylic acids presence are observed in the operating conditions maintained in the batch aerobic reactors.

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INTRODUCTION Fatliquoring is one of the key operations in the manufacturing of leather. Fatliquoring is a process of coating the surface of leather fibers with a thin layer of oil. Proper treatment with oils and fats gives the leather full and soft handling flexibility and additional strength. Fatliquoring improves the tensile strength, stitch-tear resistance, abrasive resistance, water-repellent properties, and resistance toward chemical actions. Fatliquors may be anionic, cationic, or nonionic in nature. Depending upon the source of the oils/fats used, the fatliquors can be classified as vegetable, synthetic, or semi-synthetic.1 The waterinsoluble fatliquoring agents used include natural (animal, vegetable, and fish), synthetic fatty acid esters, and petrochemical products.2 The use of synthetic oils, fats, and fatliquors in the leather industry has become popular due to their superiority over natural products in many respects such as high emulsifying power. The quantity required is less, as a result of which the leather is not unduly loaded with fats and oils to achieve specific softness. Silicone oil and paraffinic hydrocarbons find use in fatliquoring process as components of synthetic fatliquor due to their lubricating and protective action.3 Generally, synthetic fatliquors are prepared from paraffins obtained either by Fischer−Tropsch method of paraffin synthesis or from the petroleum industry. Saturated hydro© 2012 American Chemical Society

carbons in paraffins having chain length ranging from C15 to C24 are chlorinated by chlorine gas in the presence of catalysts and ultraviolet rays. In chlorinated paraffin, the chlorine atoms are firmly attached to paraffins and are not split off even at 150 °C. Chlorinated paraffin is sulphochlorinated and then saponified with caustic soda to produce chlorinated paraffin sulphonates, which is one of the main ingredients for synthetic fatliquor.4 Leather treated with only synthetic fatliquor becomes too dry and flat and shows a strawy feel. To overcome these drawbacks, synthetic fatliquors are always used in conjunction with natural oils; such a blending mixture therefore gives better results and produces much a softer type of leather. The main components of fatliquor are water, natural fats (e.g., fish oils), surfactants, and the chlorinated paraffin (CPs). They are used in conjunction with sulphated or sulphonated oils, chlorosulphonated paraffins, natural fats, and oils. Typically, chlorinated paraffins with relatively low chlorine content (e.g., ≤ 40 wt % Cl) are used in leather applications. The CPs account for about 10% by weight of the formulated fatliquor. The amount of fatliquor used in the fatliquoring step Received: Revised: Accepted: Published: 16171

July 18, 2012 November 16, 2012 November 16, 2012 November 16, 2012 dx.doi.org/10.1021/ie301904g | Ind. Eng. Chem. Res. 2012, 51, 16171−16181

Industrial & Engineering Chemistry Research

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is about 70−120 g of fatliquor/kg of the shaved weight of the leather to be treated. It was reported that about 2% of the CPs are released through the spent fatliquor solution at the end of leather processing.5 The CPs have attracted increasing attention in the past decade as they represent a potential “new” category of persistent organic pollutants (POPs) due to bioaccumulation, persistence, long-range transport, and toxicity. The Canadian Environmental Protection Act has declared that “short, medium and certain long-chain CPs are toxic to the environment”.6 The persistence of the CPs in the environment and their resistance to degradation indicate that the microorganisms are not capable of effectively degrading these compounds in the effluent treatment plants. To deal with wastewater that contains soluble organic compounds that are either toxic or non-biodegradable, application of various oxidation technologies were tried to mineralize or reduce the toxicity of the compounds. Research with different oxidation technologies and different substrates have shown that a partial chemical oxidation of toxic wastewater may increase its biodegradability up to high levels together with destruction of inhibitory species.7,8 During chemical pretreatment, partial oxidation takes place thereby producing/enhancing the biodegradable reaction intermediates for subsequent biological treatment process. Chemical pretreatment process should be optimized in such a way that the percentage of mineralization is minimal and it facilitates only partial oxidation whereby a reduction in operating cost can be achieved.9 Biological treatment plays a predominant role in tannery wastewater treatment. It is the most effective and convenient method to degrade pollution loads, such as chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) and to make the effluent meet discharge standards. Therefore, the biodegradability of a chemical under the conditions of biological treatment in treatment plants is very important. The standard BOD5 tests are generally used as a measure of aerobic biodegradability. By measuring the BOD5/COD ratio, the proportion of the organic materials present, which can be aerobically degraded within 5 days, can be estimated.10 BOD5/COD ratio is specially recommended when biodegradability of volatile and limited water-soluble substances needs to be measured. Moreover, BOD5 has the advantage of being a direct biological measurement of aerobic degradation of the organic compounds.11 Some recent studies have demonstrated the efficiency of oxidation processes, such as ozonation and the Fenton treatment for petroleum hydrocarbons, aniline, and trichloroethylene-contaminated soil remediation. These studies have shown that such treatment technique can be applied both in situ and ex situ for reduction of toxicity of the contaminants and mineralization.12−14 However, no study has been carried out on the biodegradation of anionic paraffin wax-based synthetic fatliquor used in leather processing. Considering the nature of the compounds present in the anionic paraffin waxbased synthetic fatliquor, to improve the biodegradability of the fatliquor, advanced oxidation processes (AOPs) such as UV/ H2O2 and Fenton’s reagent was investigated as a pretreatment. Biodegradation studies were carried out for the anionic paraffin wax-based synthetic fatliquor, with and without application of AOP methods.

Article

MATERIALS AND METHODS

Characterization of Synthetic Fatliquor. Anionic paraffin wax-based synthetic fatliquor was procured from Balmer Lawrie and Co. Ltd., India and was used for the study. It is a multipurpose fatliquor designed for grain lubrication, particularly suitable for uppers as well as for soft, fluffy leathers such as Garment Nappa (http://www. balmerlawrie.com). For preparation of synthetic fatliquor, 1 g of fatliquor was diluted in 1 L of deionized water obtained from a Millipore Milli-Q system. The fatliquor was characterized for physicochemical parameters pH (Part 4500-H+ method B), chemical oxygen demand (COD; Part 5220 method C), biochemical oxygen demand (BOD as BOD5 at 20 °C; Part 5210 method B), hexanextractable matter i.e., oil and grease content (Part 5520 method B), Total Kjeldahl Nitrogen (TKN) (Part 4500-Norg method B), phosphorus (Part 4500-P method E), organic and volatile acids (Part 5560 method C) as per Standard Methods 20th ed.15 Samples were analyzed in triplicate and the average values are reported. The principal characteristics of fatliquors are primarily determined in terms of iodine value and saponification value. Apart from routine physicochemical characterization, the synthetic fatliquor was analyzed for iodine and saponification values also. The iodine value specifies the amount of unsaturated compounds present in fatliquor, whereas saponification value specifies the amount of potassium hydroxide in mg required for neutralizing fatty acids in 1 g of fatty matter. Iodine value was determined according to the ISO 3961 standard method.16 The AOCS standard method Cd 13-60 was used to determine the saponification value.17 Samples were analyzed in triplicate and the average values are reported. Application of Advanced Oxidation Processes As Pretreatment. Advanced oxidation processes (AOPs) have been developed to degrade biorefractory organics in drinking water and industrial effluents. Almost all AOPs are based on the generation of the reactive species, hydroxyl radicals, which degrade a broad range of organic pollutants quickly and nonselectively. In this study, AOPs were applied as pretreatment to produce biodegradable reaction intermediates during chemical oxidation of synthetic fatliquor. In the present study, two such AOP methods, UV/H2O2 and Fenton’s reagent using H2O2 and Fe2+, were selected. The pH of the synthetic fatliquor was adjusted to 3.5 using formic acid, which is similar to the practice for fatliquoring process followed in the tanneries. For the combined UV/H2O2 pretreatment, a 500-mL capacity UV reactor having medium pressure mercury vapor lamp with 400 W power was used. A water jacket was installed around the reactor and continuous water recirculation was used to avoid excessive heating of the irradiated solution.18 Hydrogen peroxide (H2O2) dosages of 200, 400, 600, 800, and 1000 mg/L were selected. For the combined UV/H2O2 process, the H2O2 dose and contact time were optimized. The H2O2 dose and contact time were optimized for oxidation of synthetic fatliquor, considering the increase in BOD5/COD ratio after pretreatment, using UV/H2O2. For pretreatment using Fenton’s reagent, Fe2+, dosages were varied from 10 to 50 mg/L for the optimum H2O2 dose obtained during the combined treatment of UV/H2O2. Contact time and optimum Fenton’s reagent dose was ascertained. Analytical grade chemicals needed for the experiments were procured from Merck. All solutions were prepared with deionized water obtained from a Millipore Milli-Q system. 16172

dx.doi.org/10.1021/ie301904g | Ind. Eng. Chem. Res. 2012, 51, 16171−16181


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Experimental Setup for Biodegradation Studies. To assess the biodegradability of anionic paraffin wax-based synthetic fatliquor, experiments were performed in aerobic condition under ambient temperature (30 ± 2 °C) for UV/ H2O2 and Fenton’s reagent pretreated anionic paraffin waxbased synthetic fatliquor after adjusting the pH to 7.0. Biodegradability studies were carried out in batch reactors of 2.0-L capacity, with working volume of 1.5 L. To maintain aerobic conditions, air was supplied at a rate of 1.5−1.6 L/h through two medium-sized diffusers fitted to an aquarium-type pump. Complete mixing was provided to ensure the dissolved oxygen (DO) concentration of 2−2.5 mg/L throughout the duration of the experiment. The dissolved oxygen was measured using a HACH portable DO meter. The activated sludge used as inoculum in the experiment was collected from the aeration tank of a common effluent treatment plant situated in Chennai, India, exclusively operating for treatment of tannery wastewater. The dominant microbes present in the activated sludge were Pseudomonas sp., Protozoa, rotifers, Arthrobacter, Escherichia coli, and Acinetobacter sp. The activated sludge was characterized for mixed liquor suspended solids (MLSS) concentration (Part 2540 method D) and mixed volatile suspended solids (MLVSS) concentration (Part 2540 method E) as per Standard Methods 20th ed.15 From characterization studies, the MLSS and MLVSS concentration were found to be 6500 ± 100 mg/L and 3500 ± 100 mg/L. The activated sludge was washed several times with distilled water and starved under aeration for 24 h to reduce the amount of dissolved substances present in the mixed liquor. The known concentration of washed activated sludge and the pretreated (UV/H2O2 and Fenton’s reagent) fatliquor and fatliquor without any pretreatment were mixed in aerobic bioreactor for biodegradation studies separately. In India, aerobic treatment units in common effluent treatment plants (CETPs) and individual effluent treatment plants (ETPs) for tannery wastewater treatment are operated at the f/m ratio of 0.15 for a hydraulic retention time (HRT) of one day.19,20 The aim of the present study is to evaluate the biodegradability of anionic paraffin wax-based synthetic fatliquor in an aerobic environment. Hence, operating conditions maintained in CETPs/ETPS were adopted for operation of batch reactors in the present study. A control batch reactor was operated only with inoculum and distilled water. The COD:N:P ratio of 100:5:1 was maintained in the reactors with the addition of necessary nutrients.21−23 Supplementary trace minerals were added into the anionic paraffin wax-based synthetic fatliquor before each experiment as described by Chipasa.24 Biodegradation of anionic paraffin waxbased synthetic fatliquor was evaluated in all the batch reactors by regularly collecting the samples for analysis. The process was evaluated without and with UV/H2O2 and Fenton’s reagent pretreated synthetic fatliquor. The influent and effluent samples were filtered through 0.45-μm filters and the filtered samples were analyzed for BOD5 and COD. Interferences due to residual H2O2 and iron in the samples were eliminated before BOD5 and COD estimation.25 The BOD5 and COD refer to contribution from soluble fraction only. The BOD5 tests were carried at 20 °C for a 5-day period. All batch experiments were performed in duplicate and average values are reported. Fourier Transform Infrared Spectrometry (FT-IR) Analysis. FT-IR analysis was carried out in order to assess the functional groups present in the (i) anionic paraffin waxbased synthetic fatliquor before and after aerobic biodegrada-

tion studies; (ii) UV/H2O2 pretreated anionic paraffin waxbased synthetic fatliquor before and after biological treatment; and (iii) Fenton’s reagent pretreated anionic paraffin wax-based synthetic fatliquor before and after biological treatment. The samples were filtered through a 0.45-μm filter and the filtered samples were analyzed using Fourier transform infrared spectrometry (FT-IR). The samples were lyophilized and the lyophilized samples were pelletized with potassium bromide (KBr) in the ratio of 1:50. The pellets were subjected to FT-IR analysis using transmission mode. The measurements were carried out in the mid-infrared range from 4000 to 500 cm−1, with ABB MB 3000 model FT-IR. Gas Chromatography Mass Spectra (GC-MS) Analysis. A JEOL GCmate II benchtop double-focusing GC mass spectrometer, operating in electron impact ionization (EI) mode, was used for analyzing the synthetic fatliquor before and after pretreatment with UV/H2O2 and Fenton’s reagent. The helium carrier gas was set to 25 mL/minute flow rate and injection temperature of 220 °C (temperature range 70−250 °C). The rate of increase in temperature was set to 15 °C/min.

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RESULTS AND DISCUSSION Characteristics of Synthetic Fatliquor. The synthetic fatliquor was characterized for various physicochemical parameters such as pH, BOD, COD, and hexane-extractable matter, i.e., oil and grease content, and the results are presented in Table 1. It was observed from the characteristics of the Table 1. Characteristics of Synthetic Fatliquor Sl. no.

parameter

average value

1 2 3 4 5 6 7 8

pH chemical oxygen demand (COD), (mg/L) biochemical oxygen demand (BOD5), (mg/L) hexane-extractable matter, i.e oil and grease (mg/L) total Kjeldahl nitrogen (TKN) as nitrogen (mg/L) phosphorus as P (mg/L) iodine value saponification value

5.8 1300 100 480 4.2 2 12 41

fatliquor the ratio of BOD5 to COD was 0.077. Generally, a compound is considered hardly biodegradable when its BOD5/ COD value is lower than 0.20. It is evident from the results that synthetic fatliquor is hardly biodegradable. Zhang26 stated that the low solubility and bioavailability of the petroleum hydrocarbons limit the biodegradation of oily wastewater in activated sludge process. The iodine value and saponification value of synthetic fatliquor was 12 and 41. Iodine value signifies the amount of unsaturated compounds (double bonds) in the fatliquor and saponification value signifies the amount of potassium hydroxide in mg required for neutralizing fatty acids in 1 g of fatliquor. Synthetic fatliquor having very low iodine and saponification value signifies that it is very difficult to degrade due to the presence of more saturated hydrocarbons. Zhaoyang27 studied the biodegradability of rape oil-based fatliquors prepared from different methods, which utilizes double bonds or hydroxyl groups. The results indicated that the presence of fewer double bonds or hydroxyl groups will decrease the biodegradability of fatliquors, while the presence of more double bonds or hydroxyl groups will increase the biodegradability. Pretreatment using UV/H2O2 for Enhancing the Biodegradability of Fatliquor. The AOPs are efficient in 16173



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the Fenton’s reagent is that no energy input is necessary to activate hydrogen peroxide. Furthermore, it requires a relatively short reaction time when compared with other AOPs. The Fenton oxidation process has been employed successfully to treat different industrial wastewaters, including textile, paper, pulp, pharmaceutical, dyes, cork processing, olive oil, and petroleum industry wastewater. The oxidation mechanism by Fenton’s reagent is due to the reactive ·OH radicals generated in an acidic solution by the catalytic decomposition of hydrogen peroxide.32 Reactions between hydrogen peroxide and Fe2+ are given below:

removing priority pollutants, such as refractory organics, by complete mineralization or transformation into simple organic compounds that are easily biodegradable. UV photolysis of H2O2 results in generation of highly reactive hydroxyl radicals. Radiation with a wavelength lower than 400 nm is able to photolyze H2O2 molecules. The reaction mechanism of UV/H2O2 process is listed below and apart from this other reactions can also take place depending on the conditions maintained.28 hυ

H 2O2 → 2•OH H 2O2 + •OH → H 2O + HO2•

Fe 2 + + H 2O2 → Fe3 + + OH− + •OH

•

OH + HO2− → HO2• + OH−

Fe3 + + H 2O2 ⇆ H+ + Fe−OOH2 +

H 2O2 + •OH 2 → HO• + H 2O + O2

Fe−OOH2 + → HO2• + Fe 2 +

The BOD and COD of the synthetic fatliquor without AOP pretreatment were 100 and 1300 mg/L, respectively. As a pretreatment to increase the biodegradability of synthetic fatliquor, UV/H2O2 was selected as one of AOP methods. The results of the optimization of H2O2 dose is depicted in Figure 1 for the contact time of 30 min.

Fe 2 + + H 2O2 → Fe3 + + OH− + •OH

The nature of synthetic fatliquor and its composition clearly indicated low biodegradability and Fenton treatment is an effective oxidation method to mineralize the complex compounds and to increase the biodegradability so that the fatliquor can be effectively treated in an aerobic reactor. Fe2+ dose was optimized for the optimum dose of H2O2 (obtained from UV/H2O2 process) for further improving the biodegradability. The increases in BOD5/COD for different doses of Fe2+ are presented in Figure 2. The optimum dose selected was 30

Figure 1. Optimization of H2O2 dose in UV/H2O2 pretreatment.

The results indicated that an optimum dose of 400 mg/L of H2O2 was needed to increase the BOD5/COD to 0.3 from 0.077. Further increasing the dose did not improve the biodegradability. The reason may be that high concentration beyond the optimum dose of H2O2 acts as a scavenger for hydroxyl radicals and results in lesser degradation of complex organic compounds.29 Oxidation during pretreatment resulted in partial mineralization of organic compounds and this was reflected in reduction of COD from 1300 to 810 mg/L which is equal to 37% reduction of COD. Coelho30 studied the treatment of petroleum refinery sour water by various advanced oxidation processes and found that UV/H2O2 oxidation resulted in dissolved organic carbon (DOC) removal of 25% while Fenton oxidation resulted in DOC removal of 55%. Scott31 studied the removal of naphthenic acids in oil sands process water by adopting ozonation and observed that BOD5/ COD ratio increased from 0.01 to 0.15. Hence in the present study, pretreatment with UV/H2O2 resulted in increasing the biodegradability of the anionic paraffin wax-based synthetic fatliquor. Pretreatment using Fenton Oxidation for Enhancing the Biodegradability of Fatliquor. One of the advantages of

Figure 2. Optimization of Fe2+ dose in Fenton’s reagent pretreatment.

mg/L Fe2+ in combination with 400 mg of H2O2. After Fenton’s reagent pretreatment, the COD concentration was reduced from 1300 to 780 mg/L, which is equal to a reduction of 46% of COD due to the mineralization of compounds difficult to biodegrade. Fenton treatment simultaneously improves the biodegradability and this was reflected in the increase of BOD value to 260 from 100 mg/L. The BOD5/ COD ratio was improved from 0.077 to 0.37 indicating that the produced biodegradable organic compounds can be effectively treated in the aerobic treatment. Millioli33 studied the removal and oxidation of petroleum adhered onto beach sand, after a spill in Brazil, using Fenton oxidation. Analyses performed on the supernatant following Fenton reaction revealed a drop in COD of 60% and showed that the effluent generated is liable to biodegradation. Chromatographic analysis also indicated that Fenton reaction modified the saturated and aromatic fractions of the petroleum 16174



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to facilitate biodegradation. Mater34 studied the influence of H2O2 and a Fe2+ concentration on the mineralization and biodegradability of organic compounds in water and soil contaminated with crude petroleum and found that Fenton oxidation increases the mineralization and also simultaneously enhances the biodegradability of petroleum compounds by a factor of up to 3.8 for contaminated samples of both water and soil. GC-MS Analysis of Synthetic Fatliquor with and without Pretreatment. Chemical nature and formulation of the chlorinated paraffin sulphonates in the commercial product of synthetic fatliquor is unknown. The mean chlorine content for common commercially available CPs varies between 40 and 70%. The main problem with the identification and quantitative detection of CPs is the complexity of their mixtures; the variety of homologues and isomers makes it difficult to separate them from each other. A handicap in analyzing various forms is that a suitable standard for each sample has to be found.35,36 Considering this, a qualitative assessment was done for all the samples to determine the nature of the compounds present in them. The peaks obtained for the synthetic fatliquor containing chlorinated paraffin sulfonates without any pretreatment indicated the presence of fragmented molecular ions. The peak obtained at m/z 71 indicated the presence of fragmented hydrocarbon C5H11• and Cl2. Percent relative abundance was observed for peak at m/z 335 and this was due to the presence of fragmented molecular ions from C14H29SO2Cl, C14H25Cl5, and C17H32Cl4. Fragmented ions from various isomers of CPs were observed at m/z peaks of 276, 365, 423, and 478, respectively. The presence of chlorinated acids, carboxylic acids, and alcohols was observed at m/z 144 and 203. Thus the results clearly indicated the presence of various isomers of chlorinated paraffin sulfonates in the synthetic fatliquor. The result of the GC-MS analysis of synthetic fatliquor without any pretreatment is depicted in Figure 3. Pretreatment with UV/H2O2 resulted in the generation of various fragmented ions. Peak at m/z of 71 indicated 100% relative abundance of C5H11• and Cl2. About 38 and 10% of relative abundance of chlorinated acids and carboxylic acids and alcohols were observed at peaks of m/z 144 and 203. Fragmented ions from various isomers of CPs were observed at m/z peaks 231, 276, 321, and 409, respectively. GC-MS spectra of UV/H2O2 pretreated synthetic fatliquor is depicted in Figure 4. Pretreatment with Fenton’s reagent resulted in 100% relative abundance of C5H11· and Cl2 generation. Chlorinated acids, carboxylic acids, and alcohols were observed at m/z of 144 and 220 at 50 and 20% of relative abundance of ions. Various forms of CPs were observed at m/z of 280, 354, and 435, with lesser abundance when compared with UV/H2O2 pretreatment. GCMS spectra of Fenton’s reagent pretreated synthetic fatliquor are depicted in Figure 5. The GC-MS results obtained for the samples with and without pretreatment by UV/H2O2 and Fenton’s reagent clearly indicated the presence of chlorinated paraffin sulfonates in the synthetic fatliquor along with various isomers of CPs. Degradation products of chloroacids, carboxylic acids, and alcohols were observed in more relative abundance for the pretreated samples. The results obtained were in agreement with the mass spectra obtained for various chlorinated paraffins and sulfonates present in the environment due to its persistent nature.6,37−40 The nominal masses of various isomers of CPs

Figure 3. GC-MS spectra of synthetic fatliquor without pretreatment.

Figure 4. GC-MS spectra of synthetic fatliquor with UV/H2O2 pretreatment.

and the degradation products obtained for synthetic fatliquor containing chlorinated paraffin sulfonates are given in Table 2. AOP pretreatment resulted in the formation of easily biodegradable compounds such as chloroacids, carboxylic acids, and alcohols. Quantification of acids by distillation 16175



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Figure 6. COD and BOD degradation of synthetic fatliquor in aerobic reactor without AOP treatment.

only. These removal efficiencies are also linked with iodine and saponification values of 12 and 41 obtained for synthetic fatliquor and it is very difficult to degrade due to the presence of more saturated hydrocarbons. Iodine value and saponification value of castor oil-based fatliquor used in the tanneries was 72 and 165 and the biodegradability of the fatliquor is very high based on BOD5/COD value of 0.98.41 CPs having a chain length of C16 to C30 is used in fatliquoring process. During biological treatment process, CPs is adsorbed over the microbes rather than degradation.2,5 This could be the reason for the lesser BOD5 and COD removal observed in the present study. However, application of synthetic fatliquor in leather processing is unavoidable for the production of soft leathers. It is also evident from the results obtained from the present study and literature that synthetic fatliquor cannot be efficiently degraded in the biological treatment system. Hence, application of UV/ H2O2 and Fenton’s reagent as pretreatment process was investigated in the present study. The pretreated synthetic fatliquor using UV/H2O2 and Fenton’s reagent was further subjected to biological treatment in aerobic condition for biodegradation. The results are presented in subsequent sections. Batch Aerobic Reactor Studies for UV/H2O2 Pretreated Synthetic Fatliquor. Comparing the BOD5 and COD concentrations of anionic paraffin wax-based synthetic fatliquor without and with pretreatment, an increase in BOD5 value from 100 to 240 mg/L, i.e., 2.4 times, and a decrease in COD value from 1300 to 810 mg/L equal to 37% reduction due to mineralization, were observed. After pretreatment, an increase in BOD5/COD ratio from 0.077 to 0.3 was observed at optimum operating conditions of 400 mg/L H2O2 dose and a

Figure 5. GC-MS spectra of synthetic fatliquor with Fenton’s reagent pretreatment.

method for UV/H2O2 and Fenton’s reagent pretreatment resulted in the generation of 70 and 85 mg/L of acids as acetic acid.

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BATCH AEROBIC REACTOR STUDIES Aerobic Reactor Studies for Synthetic Fatliquor without AOP Pretreatment. The anionic paraffin waxbased synthetic fatliquor having BOD5 and COD values of 100 and 1300 mg/L, respectively, was treated in a batch aerobic reactor. The batch reactor was operated for a residence time of 24 h and the samples were collected in regular intervals of time for analysis of BOD5 and COD concentrations. The results are depicted in Figure 6. It was observed from Figure 6 that a gradual decrease in removal of BOD5 and COD was observed over a period of 24 h. At the end of 24 h the BOD5 and COD concentrations observed were 72 and 1110 mg/L, respectively. Though 28% of BOD5 removal was observed at the end of the residence period of 24 h, COD removal was limited to 14.62%

Table 2. Nominal Masses Observed for Synthetic Fatliquor with and without AOP Pretreatment synthetic fatliquor without pretreatment

synthetic fatliquor with pretreatment with UV/H2O2

synthetic fatliquor with pretreatment with Fenton’s reagent

m/z

probable groups of fragmented ions

m/z


m/z


71 144 203 276 335 365 423 478

Cl2, C5H11· C3H4O2Cl2, C7H15O3, C9H20O C6H8Cl2O4, C11H23O3, C10H19O4 C10H17Cl5 C14H25Cl5, C14H28SO2Cl2, C17H32Cl4 C14H24Cl6, C16H26Cl5 C13H22Cl8 C17H28Cl8, C27H56

71 144 203 231 276 321 409

Cl2, C5H11· C3H4O2Cl2, C7H15O3, C9H20O C6H8Cl2O4, C11H23O3, C10H19O4 C14H29Cl, C14H29S+ C10H17Cl5 C13H23Cl5, C16H30Cl4 C17H30Cl6

71 144 220 280 354 435

Cl2, C5H11· C3H4O2Cl2, C7H15O3, C9H20O C8H12Cl2O4, C14H20O2, C8H14Cl2O2 C13H24Cl4 C13H22Cl6, C16H29Cl5 C14H22Cl8

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pretreatment, an increase in BOD5/COD ratio from 0.077 to 0.37 was observed at optimum operating conditions of 400 mg/ L H2O2 dose, Fe2+ concentration of 30 mg/L, and a contact time of 30 min. Pretreated anionic paraffin wax-based synthetic fatliquor using Fenton’s reagent was further subjected to biodegradation studies in batch reactors in an aerobic environment. The batch reactors were operated for a residence period of 24 h and the samples were collected in regular intervals of time for analysis of BOD5 and COD concentrations. The results are depicted in Figure 8.

contact time of 30 min under UV environment. Coupling of an AOP and a biological treatment has been previously studied for highly toxic wastewaters containing pesticides. BOD5/COD ratio pointed out that biodegradability enhancement starts beyond a 30% mineralization and that this value could be the minimum for starting a further biological oxidation.42 The pretreated anionic paraffin wax-based synthetic fatliquor using UV/H2O2 process was further subjected to biodegradation studies in batch aerobic reactors. The batch reactors were operated for a residence time of 24 h and the samples were collected in regular intervals of time for analysis of BOD5 and COD concentrations. The results are depicted in Figure 7. It

Figure 8. COD and BOD degradation of synthetic fatliquor in aerobic reactor with Fenton’s reagent pretreatment.

Figure 7. COD and BOD degradation of synthetic fatliquor in aerobic reactor with UV/H2O2 pretreatment.

From Figure 8, overall it was observed that the percentage removal of BOD5 was more than that of COD. In 12 h of residence time, 51.43% of COD and 73.08% of BOD5 removals were observed. Comparing the results with UV/H2O2 pretreated samples an additional increase in COD removal of 10.69% and 12.66% BOD5 removal was observed with Fenton process. A linear increase in COD removal was observed after 12 h of residence time and was continued up to 18 h of residence time. In 18 h of residence period, around 68.8% removal was observed, which resulted in COD reduction from 340 to 260 mg/L and BOD reduction from 70 to 35 mg/L. The results indicated the presence of refractory organics in anionic paraffin wax-based synthetic fatliquor requiring longer residence time for biodegradation. Further increasing the residence time beyond 20 h, an increase in BOD and COD removal to 65.71 and 89.23% was observed at the end of 24 h. However, degradation studies were not extended beyond 24 h to align with real operating conditions maintained in the effluent treatments plants operating for treatment of tannery wastewater. At the end of 24 h of residence time, BOD5 and COD concentrations of 28 and 240 mg/L were present in the synthetic fatliquor. Comparing the biodegradation studies using two pretreatment methods, i.e., UV/H2O2 process and Fenton process, the Fenton process was found to be more efficient in removal of BOD and COD when compared with the UV/H2O2 process. Evaluation of FT-IR Spectrum before and after Aerobic Treatment. Presence of various functional groups and chemical bonding of the compounds can be analyzed effectively by using FT-IR. The FT-IR spectrum creates a molecular fingerprint by positive identification of each compound present in the sample matrix. In addition, the size of the peaks in the spectrum is a direct indication of the concentration of compounds present in the sample. FT-IR spectra of samples provide viable information regarding the

was observed from Figure 7 that the percentage removal of BOD5 was more than that of COD. In 12 h of residence time, 40.74% of COD removal, i.e., from 810 to 480 mg/L, and nearly 60.42% of BOD5 removal, i.e., from 240 to 95 mg/L, were observed. In case of reactor without AOP treatment, for the same residence time of 12 h, only 22% of BOD5, i.e., reduction from 100 to 78 mg/L and 12.31% of COD removal, i.e., from 1300 to 1140 mg/L, were observed. A further increase in COD removal was observed after 12 h of residence time and was continued up to 24 h of residence time from 40.74 to 59.26%. The COD was not reduced completely in 24 h of residence time indicating the presence of refractory organics in anionic paraffin wax-based synthetic fatliquor requiring longer residence time for biodegradation. However, degradation studies were not extended beyond 24 h to align with real operating conditions maintained in the effluent treatments plants operating for treatment of tannery wastewater. At the end of 24 h of residence time, 82 and 59% removal of BOD5 and COD was observed. The final treated fatliquor had BOD5 and COD concentrations of 45 and 330 mg/L at the end of 24 h residence time in the aerobic reactor. Batch Aerobic Reactor Studies for Fenton’s Reagent Pretreated Synthetic Fatliquor. By comparing the BOD5 and COD concentrations of anionic paraffin wax based synthetic fatliquor without and with pretreatment, there is an increase in BOD5 value from 100 to 260 mg/L, i.e., 2.6 times, and a decrease in COD value from 1300 to 700 mg/L, i.e., around 0.46 times, was observed. However, comparing the pretreatment methods, i.e., UV/H2O2 process and Fenton process, mineralization of the refractory organics present in anionic paraffin wax-based synthetic fatliquor was more in Fenton’s reagent pretreatment process and resulted in lesser COD values when compared with UV/H2O2 process. After 16177



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of UV/H2O2 pretreated anionic paraffin-based synthetic fatliquor, before and after aerobic treatment, are present in Figure 10. UV/H2O2 pretreatment resulted in generation of

nature of compounds present in the synthetic fatliquor and their presence or absence during AOP pretreatment and aerobic biodegradation. The functional groups present in the anionic paraffin waxbased synthetic fatliquor (i) before and after aerobic biodegradation studies; (ii) UV/H2O2 pretreated anionic paraffin wax based synthetic fatliquor before and after biological treatment; and (iii) Fenton’s reagent pretreated anionic paraffin wax based synthetic fatliquor before and after biological treatment are discussed below in detail. Performance of Aerobic Treatment for Synthetic Fatliquor without AOP Pretreatment. The FT-IR spectra of anionic wax-based synthetic fatliquor, before and after aerobic treatment, are presented in Figure 9. From Figure 9, it

Figure 10. FT-IR spectra of synthetic fatliquor before (b) and after (a) aerobic treatment process using UV/H2O2 pretreatment.

biodegradable organics along with carboxylic acids. From Figure 10, the presence of long linear aliphatic chain compound was identified by the presence of absorption bands at 2929, 2857, 1460, 1304, and 722 cm−1. Presence of carboxylic acid was confirmed by the presence of a sharp absorption band due to carbonyl group of carboxylic acid at 1642 cm−1 and a broad absorption band in the region 3409 cm−1 due to OH group. Presence of Si−H and Si−O−Si stretching due to silicone oil was observed at 2340, 2361, and 1153 cm−1. Asymmetric/ symmetric stretching of SO2 sulfonates was observed at 1147 cm−1; stretching due to C−Cl bond was observed at 666 cm−1. The spectra of synthetic fatliquor indicated the presence of chlorinated paraffin sulphonates, and silicone oil with carboxylic acids. Rein44 stated that the hydroxyl radical is a powerful, nonselective chemical oxidant which acts very rapidly with most of the organic compounds. Once generated, the hydroxyl radicals aggressively attack all organic compounds and result in the oxidation of the organic compounds into intermediate compounds such as carboxylic acids. Aerobic treated UV/H2O2 showed several changes in the spectrum. Presence of long chain aliphatic compounds was not observed by studying the absorption band. Maximum chain length of four carbons was observed and this was indicated by the absorption bands at 2929, 2857, and 742 cm−1. Stretching due to C−Cl bond was observed at 652 cm−1. Carboxylic acid absorption band was observed at 1640 cm−1. Absorption band due to Si−H stretching was observed at 2118 cm−1 but the peak height is almost completely reduced. But Si−O−Si stretching was observed at 1147 cm−1. The results clearly indicated that pretreatment resulted in mineralization and the intermediates produced were effectively treated in the aerobic reactor. Instead of long chain compounds, short chain chlorinated compounds such as chloro-carboxylic acids are produced. This result was supported by the findings of chlorinated paraffin degradation. Brooke5 stated that chloroparaffin degradation involves first dechlorination of the terminal methyl groups, with subsequent oxidation to form chlorinated fatty acids, which are then broken down to 2- or 3chlorinated fatty acids via β-oxidation. Performance of Aerobic Treatment for Synthetic Fatliquor with Fenton’s Reagent Pretreatment. Pretreatment with Fenton’s reagent resulted in generation of

Figure 9. FT-IR spectra for synthetic fatliquor before (b) and after (a) aerobic treatment process.

is shown that synthetic fatliquor before aerobic treatment shows well-defined characteristic absorption bands at 2958, 2860, 1470, and 720 cm−1 due to the presence of long linear aliphatic chain compounds of the paraffin wax. Broad absorption band in the region 3409 cm−1 signifies the presence of OH group. Asymmetric/symmetric stretching of SO2 sulfonates was observed at 1385 cm−1, and CO stretching due to carboxylic acid was observed at 1638 cm−1. Stretching due to C−Cl bond was observed at 655 cm−1. Presence of silicone oil is observed by the stretching absorption band due to Si−H at 2359 and 2336 cm−1 and stretching due to Si−O−Si at 1153 cm−1.43 The results indicate the presence of chlorinated paraffin sulphonates, and silicone oil in the synthetic fatliquor along with carboxylic acid. Aerobic treated synthetic fatliquor showed that almost all the compounds present in the fatliquor are not effectively degraded. The presence of long linear aliphatic chain compound was identified by the presence of absorption bands at 2935, 2862, 1405, and 752 cm−1. A broad absorption band in the region 3390 cm−1 signifies the presence of OH group. Stretching due to Si−H and Si−O−Si was observed at 2330 and 1105 cm−1. Asymmetric/symmetric stretching of SO2 sulfonates and CO of carboxylic acid were observed at 1405 and 1638 cm−1. Stretching due to C−Cl bond was observed at 666 cm−1. Both the spectra are similar in nature and indicate that there is no functional change observed before and after aerobic treatment of anionic paraffin-based synthetic fatliquor. The results clearly indicated that the synthetic fatliquor without pretreatment was not degraded efficiently in the aerobic reactor. Performance of Aerobic Treatment for Synthetic Fatliquor with UV/H2O2 Pretreatment. The FT-IR spectra 16178



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wax-based synthetic fatliquor, with and without application of AOP methods. The biodegradation rate constant for the anionic paraffin wax-based synthetic fatliquor was determined based on the pseudo-first-order kinetic equation:

biodegradable organics. The FT-IR spectra of Fenton’s reagent pretreated anionic paraffin-based synthetic fatliquor, before and after aerobic treatment, are presented in Figure 11. FT-IR

Ct = C0e−kt

The biodegradation rate constants are presented in Table 3. From Table 3, it can be observed that the rate constant k for Table 3. Biodegradation Rate Constant for Anionic Paraffin Wax-Based Synthetic Fatliquor biodegradation rate constant (k)

without AOP pretreatment

UV/H2O2 pretreated synthetic fatliquor

Fenton’s reagent pretreated synthetic fatliquor

k (h−1) BOD5 based k (h−1) COD based

0.0137

0.0697

0.0929

0.0066

0.0374

0.0446

Figure 11. FT-IR spectra of synthetic fatliquor before (b) and after (a) aerobic treatment process using Fenton’s reagent pretreatment.

the anionic paraffin wax based synthetic fatliquor without pretreatment was 0.0137 and 0.0066 h−1 BOD5 and COD based, respectively. The rate constant was increased by application of AOP methods viz., UV/H2O2 and Fenton’s reagent. The rate constant was increased from 0.0697 to 0.0929 k (h−1) BOD5 based and 0.0374 to 0.0446 COD based for UV/ H2O2 and Fenton’s reagent pretreated synthetic fatliquor, respectively. Also, it was evident from the biodegradation studies using two pretreatment methods, i.e., UV/H2O2 process and Fenton process, that the Fenton process was more efficient in removal of BOD and COD when compared with the UV/ H2O2 process.

results indicated the presence of long chain saturated aliphatic compound and this was identified from the absorption bands at 2929, 2858, 1458, 1312, and 721 cm−1. Presence of carboxylic acid was identified by stretching absorption band at 1640 cm−1 and C−Cl stretching at 656 cm−1. Stretching absorption due to SO2 of sulfonates was observed at 1160 cm−1. Stretching due to silicone oil was observed at and 1126 cm−1. Presence of saturated chlorinated paraffin sulfonates with silicone oil and carboxylic acid was identified. Aerobic treatment showed several changes in the spectrum. Presence of long chain aliphatic compounds was not observed as evidenced by the absorption band. Maximum chain length of four carbons was observed and this was indicated by the absorption band at 737 cm−1.45 Stretching due to C−Cl bond was observed at 627 cm−1. Absorption band due to Si−H stretching was not observed, indicating the reduction in concentration of silicone oil after aerobic treatment. Carboxylic acid absorption band was observed at 1639 cm−1. Alkane hydroxylases play an important role in the microbial degradation of oil, chlorinated hydrocarbons, fuel additives, and many other compounds to produce a wide range of alcohols, aldehydes, carboxylic acids, and epoxides.46,47 The results clearly indicated that pretreatment resulted in mineralization and the intermediates produced were effectively treated in the aerobic reactor and short chain chlorinated compounds and carboxylic acids were produced. Cooper48 stated that when organo-chlorines do break down, they usually produce other organo-chlorines, with the carbon−chlorine bond remaining intact as part of another compound. The carbon−chlorine bond is very strong and resists being broken down by physical processes. As a result, many organo-chlorines remain in the environment for long periods of time. FTIR results of synthetic fatliquor without AOP pretreatment indicated that efficient degradation of fatliquor was not taking place in the aerobic reactor. The BOD5 and COD removal observed were mainly due to the adsorption over the microbes. Pretreatment with UV/H2O2 and Fenton’s reagent improves the biodegradability, and short chain chlorinated products are obtained after aerobic treatment as confirmed by FTIR. Biodegradation Rate Constant. The rate constant (k) on BOD5 and COD basis was determined for the anionic paraffin

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CONCLUSIONS The results clearly proved that the compounds present in synthetic fatliquor are difficult to degrade by aerobic treatment without any pretreatment, such as application of AOPs. Based on the f/m ratio of 0.15 and HRT of 1 day adopted in the existing aerobic unit of tannery wastewater treatment plants, batch reactors with and without AOPs pretreatment were operated for the same f/m ratio and residence time. Synthetic fatliquor with BOD5 and COD of 100 and 1300 mg/L were removed to levels of 72 and 1110 mg/L in the aerobic batch reactor and the removal was also due to adsorption over the microbes. Application of UV/H2O2 as pretreatment improves the biodegradability of synthetic fatliquor by increasing the BOD5/COD ratio from 0.077 to 0.3 and it was effectively degraded in the aerobic reactor. BOD5 and COD in the treated effluent were 45 and 330 mg/L for the above-mentioned f/m and residence time. Fenton’s reagent pretreatment helps in mineralization and generation of biodegradable intermediate compounds from the synthetic fatliquor and BOD5/COD ratio was increased to 0.37 from 0.077. Aerobic treatment of Fenton’s reagent pretreated synthetic fatliquor produce effluent with BOD5 and COD of 28 and 240 mg/L. The treatability results clearly indicated that application of AOPs as pretreatment improves the biodegradability of synthetic fatliquor, and the intermediate compounds produced are effectively treated in the aerobic reactor. Since chlorinated paraffin sulphonates are present in the synthetic fatliquor, AOP pretreatment and subsequent aerobic treatment resulted in generation of chlorinated hydrocarbons with shorter carbon chain length. 16179



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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone/fax: 044 24916351. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are thankful to the Director, Central Leather Research Institute (CLRI), Adyar, Chennai, India for permitting us to publish this work.

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