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Treatment of industrial organic raffinate containing pyridine and its derivatives by coupling of catalytic wet air oxidation and biological processes
Accepted Manuscript Treatment of industrial organic raffinate containing pyridine and its derivatives by coupling of catalytic wet air oxidation and biological processes Sushma, Anil K. Saroha PII:
S0959-6526(17)31236-2
DOI:
10.1016/j.jclepro.2017.06.066
Reference:
JCLP 9816
To appear in:
Journal of Cleaner Production
Received Date: 8 November 2016 Revised Date:
7 June 2017
Accepted Date: 8 June 2017
Please cite this article as: Sushma , Saroha AK, Treatment of industrial organic raffinate containing pyridine and its derivatives by coupling of catalytic wet air oxidation and biological processes, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.06.066. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Treatment of industrial organic raffinate containing pyridine and its derivatives by coupling of catalytic wet air oxidation and biological processes Sushma and Anil K. Saroha* Department of Chemical Engineering, Indian Institute of Technology, Delhi
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Hauz Khas, New Delhi – 110016, India ABSTRACT
The treatment of non-biodegradable industrial organic raffinate containing refractory and toxic
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organic compounds pyridine, β-picoline and 3-cyanopyridine has been studied by coupling of catalytic wet air oxidation (CWAO) over alumina based platinum catalyst and biological processes. The alumina based platinum catalyst was characterized and the stability of the catalyst
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was studied. The CWAO experiments were performed in a glass reactor at atmospheric pressure and the effluent treatment efficiency was evaluated in terms of chemical oxygen demand (COD) removal. The effect of various parameters such as air flow rate, reaction temperature, platinum loading and catalyst dosage on the COD removal was studied. The optimum values of air flow rate, platinum loading and catalyst dosage were found to be 1 L/min, 1 wt. % and 3 g/L respectively and a COD removal of 45 % was obtained at the optimum conditions at reaction
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temperature of 70oC. The CWAO experimental results were found to be in agreement with the lumped kinetic model. The toxicity test using E. coli bacteria and the biodegradability study were performed. The toxicity of the effluent decreased considerably while the BOD/COD ratio was found to increase significantly after the CWAO. The aerobic biological treatment confirmed the
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biodegradability enhancement and a total COD removal of 98.4 % was obtained after 10 days of aerobic treatment of the CWAO effluent.
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Key words: Catalytic wet air oxidation, Industrial organic raffinate, Platinum catalyst, COD removal, Biodegradability, Toxicity. *Corresponding author Email: [email protected] Tel: +911126591032
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1. Introduction The industrial effluent generated from various industries such as pharmaceutical, textile, chemical and petrochemical contains huge amounts of toxic and refractory organic compounds
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and the improper discharge of the effluent poses a severe threat to the aqueous ecosystem. Various effluent treatment techniques such as physical treatment (adsorption, reverse osmosis, filtration), biological oxidation, physicochemical, incineration and advanced oxidation processes are extensively used for the treatment of aqueous organic pollutants. Sometimes combination of
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these techniques is employed to meet the stringent effluent discharge standards (Rodrigues et al., 2016). Although, conventional biological processes are commonly employed due to environment concerns and cost, they are not suitable for the treatment of effluent containing toxic organics
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due to biomass poisoning. The physicochemical processes such as adsorption, electrocoagulation and precipitation concentrate the pollutants to a new environment and require posttreatment to suitably dispose the concentrated pollutants. Incineration is an effective treatment technology for effluent with a high concentration of organic compounds (COD more than 100 g/L) for the process to become self-sustaining or auto thermal oxidation (Seyler et al., 2005).
furans.
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Further, it is performed at extremely high temperatures and emits toxic gases such as dioxins and
Advanced oxidation processes (AOPs) have the potential for the treatment of effluent containing refractory organic compounds (Chatzisymeon et al., 2013; Güyer et al., 2016). Wet air oxidation
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(WAO) is a promising technology for the treatment of effluent containing toxic as well as biologically refractory compounds (Levec and Pintar, 2007; Kim and Ihm 2011; Arena et al.
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2015). Since WAO is carried out at elevated temperature and pressure, the capital and operating costs are quite high. However, the use of catalyst in WAO called catalytic wet air oxidation (CWAO) makes the process more economical by lowering the severe operating conditions and the oxidation efficiency is also improved. In the CWAO process, the organic pollutants in the effluent are either mineralized into carbon dioxide and water or are partially degraded into biodegradable intermediates which remain in the aqueous phase. Catalytic wet air oxidation can be employed for treatment of toxic effluent when biological techniques are ineffective and the main emphasis is to convert organic pollutants in the effluent into products more amenable to biological treatment as complete oxidation may be too expensive. 2
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A large number of studies using CWAO for the treatment of effluent have been reported in the literature and most of the studies have employed CWAO for the treatment of synthetic solution containing single organic pollutant. But very scanty data are available for treatment of real industrial effluent containing multi-component mixture of organic compounds. Moreover, very
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few studies have reported the toxicity as well as biodegradability of the effluent after CWAO treatment. Wang et al. (2014) reported an enhancement in biodegradability (BOD/COD ratio) of the landfill leachate from 0.1 to 0.39 and the total COD removal of 61 % after CWAO at 150oC and 0.5MPa of oxygen pressure using Co catalyzed NaNO2 catalyst. Tripathi et al. (2013)
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observed enhanced biodegradability (0.11 to 0.46) of NF-reject after CWAO treatment using Pd/activated carbon catalyst at 200oC and 0.69 MPa of oxygen pressure. Bistan et al. (2012) performed the toxicity test using yeast to detect toxicity level of estrogen in CWAO treated
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effluent and complete toxicity removal was observed at 230oC using Ru/TiO2 catalyst. Chen et al. (2012) reported an increment in biodegradability from 0.23 to 0.84 of low biodegradable coking wastewater using CWAO treatment process at 140-160oC and 0.2 to 1MPa partial pressure of oxygen. The biodegradable effluent can be easily treated using biological process for complete removal of organic compounds. Suarez-Ojeda et al. (2007) used the integrated CWAO
containing o-cresol.
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and aerobic biological treatment to obtain COD removal of 98% of a high-strength wastewater
Pyridine and its derivatives are produced in huge quantities due to their high utility as intermediates in the process industries. Pyridine is produced by the synthesis reaction of
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acetaldehyde and ammonia in presence of catalyst and is used as an intermediate in the production of drugs, dyes, water repellants, polycarbonate resins and pesticides. Pyridine
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derivative β-picoline (3- methyl pyridine) is used in the manufacture of vitamins, insecticides and herbicides and production of 3-cyanopyridine by the ammoxidation of β-picoline at elevated temperature (Padoley et al., 2011). Pyridine and β-picoline are completely soluble in water, alcohol and ether and are used as industrial solvents. The industries engaged in manufacturing of pyridine and its derivatives use various compounds such as acetaldehyde, ammonia and catalysts. Therefore, the effluent generated from such industries is toxic and is not amenable to biological treatment.
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Most of the studies reported in the literature have performed CWAO of the effluent at elevated conditions of temperature (higher than 100oC) and pressure. Since the effluent treatment technique should be cost attractive, therefore efforts have been made in the present study for the treatment of highly alkaline industrial organic raffinate containing various toxic contaminants
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such as ammonical nitrogen, pyridine, β-picoline and 3-cyanopyridine by integration of CWAO using platinum (Pt) catalyst at very mild operating conditions and biological technique. The alumina based Pt catalyst was prepared and characterized by different analytical methods such as BET surface area, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy
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(EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The feasibility of the CWAO process was investigated by
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optimizing the various parameters such as air flow rate, catalyst loading and dosage and the results were analyzed in terms of COD removal of the effluent. The CWAO reaction kinetics was studied using a lumped kinetic model. The toxicity test using E. coli bacteria and the biodegradability study of the CWAO effluent were carried out. The aerobic and anaerobic biological treatments of the CWAO effluent were performed in batch reactors to achieve
2. Materials and methods
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degradation of the industrial organic raffinate.
The industrial organic raffinate, collected from a chemical industry producing pyridine and its derivatives, was characterized and the results are shown in Table 1. It can be noticed that the organic raffinate has a high COD value and is highly alkaline due to the presence of nitrogenous
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organic compounds such as ammonical nitrogen and contains pyridine, β-picoline and 3cyanopyridine. The biodegradability of organic raffinate (BOD/COD ratio) is 0.078 suggesting
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that it is not suitable for biological treatment due to the presence of toxic compounds. 2.1. Catalyst preparation
The metallic precursor used in the catalyst preparation [H2PtCl6·xH2O (39.8 % Pt)] was of analytical grade and was procured from CDH India. The catalyst was prepared using incipient wetness impregnation method and different Pt loadings (0.1, 0.3, 0.5, 0.7, 1, 1.5 and 2 wt. %) were supported on Al2O3 support. Initially, 20 g of Al2O3 spheres were dried at 300oC and the dried Al2O3 spheres were placed in rotary vacuum evaporator maintained at 70oC for doping. A 4
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known concentration of Pt solution was added to the spheres and stirred continuously for 3 h. The excess water was evaporated with vacuum evaporator and the residue was then dried at 110°C for 24 h in an oven. Further, the catalyst was calcined at 550°C for 4 h for complete decomposition of Pt oxide salts and deposition of the metal on the support structure followed by
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reduction in presence of H2 gas under controlled temperature condition. The temperature was regulated by increasing the temperature of H2 (flow rate 30 mL/min) from ambient temperature to 400°C at a rate of 10oC and was maintained at 400°C for 2 h to reduce the Pt from oxide state to metal form followed by passivation at room temperature for 30 min by supplying 50% H2 and
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50% N2. The reduced catalysts were used in the CWAO process.
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2.2. Catalyst characterization
The specific surface area, total pore volume and pore size for the different wt. % of Pt/Al2O3 catalysts were determined by adsorption and desorption isotherms of nitrogen at –196oC using a surface area analyzer (Micromeritics, ASAP 2010). The specific surface area was determined using the BET (Brunauer, Emmett, and Teller) method and the pore size distribution was obtained from desorption data by BJH (Barret, Joiner and Halenda) method. The morphology of
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the catalyst was determined with the help of a scanning electron microscope (Carl Zeiss, model SMT EVO 50). The elemental analysis of the catalyst was carried out using EDX equipped with SEM. The particle size analysis of alumina supported Pt catalyst was carried out by TEM analysis (Tecnai G2 F20 S-twin transmission electron microscope). The catalyst sample for TEM
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analysis was prepared by dispersing the catalyst powder in ethyl alcohol and the solution was sonicated for 15 min. A drop of suspension was transferred to a porous carbon film supported on
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copper grid and ethyl alcohol was removed by evaporation. The mounted copper grid was used for TEM analysis. The XRD method was used to obtain information about the crystalline structure and composition of the Pt/Al2O3 catalyst. The XRD measurements were performed using a Philips 1840 powder diffractometer with Cu-Kα radiation (γ =0.154 nm) at 40 kV and 30 mA in the range of 2θ =2o to 80o at a scanning speed of 4o per minute and the results were matched with the JCPDS files to confirm the presence of desired compounds in the catalyst. The average crystallite size of Pt was determined from the broadening of an X-ray diffraction peak, measured at one-half of the height and calculated using Debye- Scherrer’s equation. The TGA 5
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analysis of fresh and used Pt/Al2O3 catalyst was carried out in a TGA analyzer (Seiko TG/DTA 32 SSC5100) to check the deposition of carbon on the catalyst. The TGA analysis was performed in the presence of air and the furnace was heated to 900oC at the rate of 10oC/min.
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2.3. CWAO experiments
The schematic diagram of the experimental setup is shown in Fig 1. The CWAO experiments were performed in a four- neck round bottom glass flask of 3 L capacity. One neck of the flask
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was used for the initial charging of the organic raffinate, addition of the catalyst and withdrawal of the effluent samples at regular time intervals. One neck of the flask was fitted with thermocouple to measure the temperature of the flask. The glass flask was heated with a heating
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mantle (Khera Instruments Pvt. Ltd., India) and the temperature of the flask was kept constant at a desired value using the temperature controller. Continuous stirring of the solution in the flask at a fixed agitation speed of 400 rpm was carried out using a magnetic stirrer. One neck of the flask was used for bubbling air as a source of oxygen in the effluent. Air, drawn from a compressor and regulated by an air flow meter, was bubbled into the organic raffinate in the flask through an ‘L’ shaped tube with holes of 0.2 mm diameter to obtain uniform dispersion of air. A condenser
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was placed at the top of the flask to reflux the contents as there was a possibility of the contents escaping out of the glass flask at high temperature during the experiments. In a typical run, 1 L organic raffinate was charged in the glass flask and the temperature of the flask and the air flow rate were fixed at the desired values followed by the addition of fixed catalyst dosage. The
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progress of the oxidation reaction was monitored by withdrawing 2 mL organic raffinate sample at regular time intervals and determining its COD. The experiments were repeated for checking
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the reproducibility of the results and the deviation in the experimental results was found to be less than 3 %.
2.4. Analytical methods
The experimental results were interpreted in terms of COD removal, a measure of organic strength of effluent, which was determined by the dichromate method (Open reflux, titrimetric method) (APHA, 2005). 6
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The percentage degradation of pollutants, represented in terms of COD, was calculated using equation [1]: COD removal (%) =
ି
·100
[1]
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where, Co is the initial COD and Ct is the COD of the effluent at any time t .
The BOD of the effluent, defined as the amount of oxygen consumed by the microbes in the effluent sample after 5 days at 20oC, was determined according to Standard Methods (APHA,
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2005).
2.5. Toxicity test
The toxicity test was performed to measure the toxicity of the raw organic raffinate and CWAO
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effluent. The test was performed by taking 45 mL of the sample in a 250 mL conical flask and 5 mL broth containing freshly prepared E. coli strain was added to the sample. The flask was plugged tightly with cotton and placed in an incubator shaker at 37oC temperature for 48 h. A 1 mL sample was withdrawn at regular time intervals and centrifuged. The supernatant was discarded and the bacteria pellets were dissolved in ultra pure water and used for the absorbance
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measurement. The absorbance of the sample, representing the growth of bacteria, was measured at 600 nm wavelength using UV/VIS spectrophotometer.
2.6 Aerobic and anaerobic biological treatment
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The aerobic biological treatment of the industrial organic raffinate and CWAO effluent was performed in a glass reactor of 2 L capacity (batch mode). The activated sludge, collected from an activated sludge treatment plant, was used as the inoculum. The effluent sample and the
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activated sludge (20:1 vol. %) were charged in the reactor and air was supplied through three spargers using an aquarium pump. The reactor was kept in an incubator room whose temperature was maintained at 37±1oC for acclimatization of the microbes. The effluent sample was withdrawn daily for 10 days to determine the BOD and COD. The anaerobic treatment was performed in a 2 L capacity glass reactor (batch mode) for the industrial organic raffinate and CWAO effluent. The anaerobic sludge used as inoculum was collected from an anaerobic reactor. The sample and sludge were placed in the reactor (20:1 vol. %) incubated at 37oC and the reactor was closed tightly with cork fitted with a tube 7
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connected to a beaker containing water to evacuate the gases generated during anaerobic biodegradation of organic raffinate. Since the anaerobic microbes require more time than aerobic microbes for acclimatization and growth, the effluent sample was withdrawn after 25 days of
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incubation for COD and BOD analysis.
3. Results and discussion 3.1. Catalyst characterization
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The BET surface area, pore volumes and average pore diameter of the fresh catalysts were determined and are shown in Table 2. It can be noticed from Table 2 that the BET surface area,
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pore volume and pore diameter decreased with an increase in the catalyst loading (wt. % of metal impregnation). The reduction in the pore volume was observed due to closing of pore with deposition of metal particles on the pore mouth. The pore diameter was found to decrease with an increase in the metal loading in the catalyst due to the deposition of metal particles on the pore wall resulting in the partial blockage of the micropores.
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The EDX analysis of the Pt/Al2O3 catalyst (1 wt. %) in the form of energy peaks at different applied voltages confirmed the presence of Pt metal and no other undesired peaks were found indicating that all chloride decomposed completely to their respective states during calcinations (supplementary information Figure S1). The metal content of the Pt/Al2O3 catalyst obtained by
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EDX analysis is given in Table 2 and the Pt metal content was found to be in good agreement with the Pt loading. The SEM image of 1 wt. % Pt/Al2O3 catalyst (Fig. 2a) shows the rough
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surface with clusters of alumina.
The diffraction patterns of Pt/Al2O3 catalysts for different metal loading are shown in Fig. 2b. It can be noticed that alumina has amorphous structure and no characteristic crystalline peak was observed. It can be further noticed that no clear distinct characteristic peak was observed for 0.1 wt. % Pt/Al2O3 but with an increase in the Pt loading, small peaks were observed at 2θ=37.5o, 46o, 66.8o confirming the presence of Pt crystallites (Dükkanci and Gündüz, 2009). It indicates that Pt metal was finely dispersed in small crystallites on the support and the crystal size was found to be 2-4 nm. The TEM image of 1 wt. % of Pt/Al2O3 catalyst is shown in Fig. 2c and it 8
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can be observed that the Pt particles (black dots) are well dispersed over the Al2O3 support. The average particle size of the Pt is 2-4 nm and is in close agreement with the particle size obtained by XRD analysis.
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3.2. Biological treatment of industrial organic raffinate The aerobic and anaerobic biological treatment of industrial organic raffinate was performed to study the applicability of biological methods for its degradation. The aerobic treatment of industrial organic raffinate showed COD removal of 4 % on 3rd day of treatment and no further
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increment in COD removal was observed till 10th day of treatment. The anaerobic treatment of industrial organic raffinate for 25 days resulted in COD removal of 3%. The low reduction in
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COD removal was due to the biomass poisoning caused by the high toxicity imparted by pollutants present in organic raffinate to microorganisms. Therefore, it was decided to use CWAO as a pre-treatment technique to remove the toxicity of the industrial organic raffinate and convert non-biodegradable pollutants into biodegradable compounds to facilitate the use of biological methods for post-treatment of CWAO effluent.
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3.3. Possible adsorption of organic compounds on catalyst surface
An experiment was performed to check the COD removal of the industrial organic raffinate by possible adsorption of organic pollutants on catalyst surface. The adsorption experiment was conducted in the glass flask at atmospheric pressure and 30oC by adding 2 g Pt/Al2O3 (0.1 wt. %)
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catalyst as an adsorbent in 1 L of organic raffinate. The agitation speed was kept constant at 400 rpm and without supply of air to the flask. A COD removal of 7 % was obtained after 9 h of
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contact time.
The WAO experiments were conducted without catalyst at atmospheric pressure with an air flow rate of 2 L/min at 30oC and 70oC and the COD removal of 5 % and 12 % was obtained respectively after 9 h. Further the CWAO of organic raffinate was carried out at atmospheric pressure and 70oC using 3 g/L of Pt/Al2O3 catalyst with an air supply of 1 L/min. The gases coming out of the glass flask were collected after 30 min of reaction time to determine the carbon dioxide concentration using GCMS. The carbon dioxide concentration in the effluent
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gases was found to be 1200 mg/L signifying the oxidation of organic pollutants into carbon dioxide by CWAO.
3.4.1. Effect of air flow rate on organic raffinate degradation
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3.4. Optimization of CWAO operational parameters
The CWAO experiments were performed using Pt/Al2O3 (0.1 wt. %) with 2 g/L catalyst dosage at atmospheric pressure and 30oC temperature. The effect of air flow rate on CWAO was studied by varying the air throughput from 0.4 L/min to 4 L/min and the results are shown in Fig. 3. It
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can be noticed from Fig. 3 that an enhancement in COD removal efficiency was obtained with an increase in air throughput from 0.4 L/min to 1 L/min. However, no significant enhancement in
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COD removal efficiency was obtained on further increasing the air throughput. Subsequently, all further experiments were performed at an air flow rate of 1 L/min. Since the catalyst is in powder form with high surface area, no mass transfer limitations can be assumed and the oxidation of organic raffinate can be considered to be kinetically controlled for an air throughput of 1 L/min. 3.4.2. Effect of Pt loading (wt. %) on organic raffinate degradation
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The oxidation reactions mainly depend on the number of active Pt sites on the catalyst surface, which varies with Pt loading. Therefore, CWAO experiments were performed to determine the efficiency of Pt loading (0.1, 0.3, 0.5, 0.7, 1, 1.5 and 2 wt. % Pt on Al2O3) on organic raffinate degradation and the results are shown in Fig. 4. The experiments were performed at atmospheric
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pressure and 30oC temperature with an air flow rate of 1 L/min and catalyst dosage of 2 g/L. It can be observed from Fig. 4 that there is an increase in COD removal efficiency with an increase
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in the Pt loading up to 1 wt. %. However, no increase in COD removal was observed with further increase in Pt loading beyond 1 wt. %. This is due to the fact that the maximum active catalyst sites are available for the oxidation to occur at 1 wt. % Pt loading and further increase in Pt loading beyond 1 wt. % does not lead to an increase in active sites. At high Pt loading (> 1 wt. %), sintering of Pt occurs resulting in the enlargement of particle size. These enlarged particles are less active and have more inactive reaction sites (Priyanka et al., 2014; Yang et al., 2010). 3.4.3. Effect of catalyst dosage on organic raffinate degradation 10
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The catalyst dosage plays an important role in oxidation of organic compounds. The effect of catalyst dosage on CWAO of organic raffinate was studied by varying catalyst dosage from 1 g/L to 5 g/L and the results are shown in Fig. 5. The experiments were performed at atmospheric pressure and 30oC, while keeping other parameters constant (1 wt. % Pt/Al2O3, air
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flow rate 1 L/min). It can be noticed from Fig. 5 that an enhancement in COD removal was obtained with an increase in catalyst dosage from 1 g/L to 3 g/L and further increase in catalyst dosage did not result in significant enhancement of the COD removal. This may be due to the fact that at high catalyst dosages, the aggregation of Pt particle might decrease the availability of
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active surface sites, resulting in decrease in COD removal (Fathima et al., 2008). Therefore, 3 g/L catalyst dosage was found to be optimum and used in further experiments for the CWAO
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of industrial organic raffinate.
3.4.4. Effect of reaction temperature on organic raffinate degradation Reaction temperature is an important parameter in oxidation of organic compounds as an increase in reaction temperature enhances the oxidation rate. The effect of reaction temperature on the degradation of organic raffinate was studied by performing experiments at temperatures
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from 30 to 80oC and the results are shown in Fig. 6. It can be noticed that the COD removal increases with an increase in reaction temperature. This is due to the fact that an increase in reaction temperature leads to an increase in the reaction rate constant k, resulting in an enhancement of the reaction rate. But further increase in reaction temperature beyond 70oC did
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not lead to significant enhancement of the COD removal. This could probably be due to decrease in oxygen solubility in the organic raffinate and relatively lower adsorption of organic raffinate on the surface of catalyst at reaction temperatures higher than 70oC. The pH of the CWAO
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effluent obtained at 70oC was found to be 8.8 compared to 10.8 of the organic raffinate. 3.5. Kinetic studies
Zhang and Chuang (1999) proposed a lumped kinetic model to describe the kinetic behavior of catalytic wet oxidation of organic mixture containing different types of the organic compounds. The oxidation reactions were lumped into two groups: i.) complete oxidation with formation of carbon dioxide and water; ii) the partial oxidation with formation of all intermediates in the aqueous solution of effluent and are represented by the following equation: 11
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k1
CO2 +H2O (complete oxidation)
A + x·O2=
[2] k2
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B +H2O (partial oxidation)
where, the organic compounds in effluent are lumped as single compound A, all intermediates in the wastewater formed by the partial oxidation are lumped as B and k1, k2 are the rate constants for complete and partial oxidation reactions respectively. The first- order kinetics with respect to
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lumped compound A was assumed for both the reactions.
The rates of reaction for the degradation of A and formation of intermediates B can be expressed
−
ௗ[] ௗ௧
ௗ ௗ௧
= ݇ଵ [ܱ[]ܣଶ ] + ݇ଶ [ܱ[]ܣଶ ]
= ݇ଶ [ܱ[]ܣଶ ]
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as follows:
[3]
[4]
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where, [A] and [B] are the concentrations of lumped compound A and lumped intermediates B and [O2] is the concentration of oxygen in the effluent. The superscripts ‘a’ and ‘b’ represent the order of the complete and partial oxidation reactions with respect to oxygen respectively. The initial concentration of lumped organic compound A was the initial COD value of the organic
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raffinate while the concentration of A and B at any time t were represented by the COD value of the organic raffinate at time t (at time t=0, [A]= [A]o = [COD]o, [B] = 0 and at time t, [A] + [B] = [COD]). Since oxygen supply was in excess, the oxygen concentration in the organic raffinate
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was assumed to be constant. The integration of Eq. (3) and (4) with respect to t from limits 0 to t results as follows: ை ை˳
=
మ భ + ( ା (భ ା మ ) భ మ)
݁ [ି(భ ାమ )௧]
[5]
The kinetic parameters of the lumped kinetic model were obtained by fitting the experimental data to Eq. (5) and solving it using regression method. The estimated values of COD removal obtained by Eq. (5) and the experimental COD removal for different catalyst dosages and 12
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reaction temperatures are shown in Fig. 7a and 7b respectively and a close agreement between the estimated (lines) and experimental (symbols) COD values can be noticed. The values of regression coefficients for Fig. 7a and 7b are in supplementary information (Table S1). The kinetic rate constants k1 and k2 were evaluated from the experimental data and were plotted as
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ln k vs 1/T to determine the activation energy (supplementary information Fig. S2). The activation energy for complete mineralization (21.01 kJ/mol) was found to be higher than partial oxidation (17.5 kJ/mol) and activation energies are in agreement with the results obtained by
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Zhang and Chuang (1999). 3.6. Catalyst stability tests
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The deactivation of catalyst during oxidation reaction due to incomplete oxidation and consequent deposition of carbon is a severe problem for continuous operation of the process. Hence the catalyst’s stability test was conducted to explore its potential for use for continuous process in industrial application. The CWAO experiment was performed at the optimized conditions at 30oC for 9 h and the resultant CWAO effluent was filtered using 0.45 µm size Whatmann filter paper. The residue left on filter paper was washed with distilled water and dried
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in oven at 110oC for 24 h. The dried spent solid catalyst was again used in performing CWAO experiments at optimized conditions and the process was repeated further for third run. The result of three runs for the Pt/Al2O3 catalyst are shown in Fig. 8a and it can be noticed that there is no significant decrease in the COD removal with spent catalyst confirming negligible loss in
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catalytic activity.
The thermo-gravimetric analysis (TGA) of fresh and spent catalysts was performed and the
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results are shown in Fig. 8b for Pt/Al2O3 (1 wt. %) catalyst. A significant weight loss during the initial heating period in the temperature range 100oC-500oC was observed due to removal of moisture on the catalyst surface and adsorbed water inside the pores. A fraction of weight loss of the spent catalyst could be due to removal of easily oxidizable carbonaceous species formed during degradation of organic raffinate (Ersöz and Atalay, 2012). 3.7. Toxicity and biodegradability test
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The biodegradability index of the effluent, defined in terms of BOD/COD ratio, is a measure of the biodegradability of the effluent by microorganisms and the effluent is considered to be completely biodegradable at BOD/COD ratio of 0.4 (Wang et al., 2014). The biodegradability test of the organic raffinate and CWAO effluent (performed at reaction temperature of 30oC and
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70oC) was carried out and the results are shown in Table 3 and Fig. 9. It can be noticed that there is a significant enhancement in the BOD/COD ratio of the effluent obtained after the CWAO treatment. The BOD/COD ratio for the effluent obtained after CWAO at 30oC and 70oC were found to be 0.3 and 0.48 respectively. The enhanced biodegradability was due to oxidation of
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refractory compounds of organic raffinate into biodegradable compounds during CWAO treatment.
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The toxicity test of the organic raffinate and effluent obtained after CWAO at 30oC and 70oC was performed using E. coli bacteria and the results are shown in Fig. 10. A steep decrease in absorbance of the organic raffinate confirms its toxicity as the absorbance represents the growth of bacteria. The decrease in absorbance of the CWAO effluent (30oC) suggests that the effluent is still toxic but in less amounts as compared to the industrial organic raffinate due to reduction in toxicity by CWAO. The increase in absorbance for CWAO effluent (70oC) due to survival and
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growth of E. coli bacteria in the effluent indicates the complete removal of toxicity. The toxicity and biodegradability tests confirmed that effluent obtained after CWAO at a reaction temperature of 70oC was non-toxic and biodegradable.
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3.8. Biological treatment of CWAO effluent
The aerobic treatment of effluent after CWAO treatment at 70oC was performed and the results
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are shown in Table 4. It can be noticed that the BOD and COD of the CWAO effluent were reduced to 23 mg/L and 240 mg/L respectively. Similarly, the BOD and COD of 53 mg/L and 260 mg/L were obtained after 25 days of anaerobic treatment of CWAO effluent. It can be summarized that almost complete mineralization of the industrial organic raffinate was obtained with integration of CWAO and biological treatment. 4. Conclusion
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In the present work, the treatment of industrial organic raffinate containing pyridine and its derivatives was studied by integration of CWAO and biological techniques. The organic raffinate was pre-treated by CWAO using alumina based platinum catalyst at atmospheric pressure to reduce the micro-toxicity and enhance biodegradability to facilitate biological treatment. The
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optimum values of air flow rate, Pt loading and catalyst dosage were found to be 1 L/min, 1 wt. % and 3 g/L respectively and COD removal of 44 % was obtained at reaction temperature of 70oC. The reaction kinetics was studied and the activation energy of complete oxidation was found to be higher than that of partial oxidation. The alumina based platinum catalyst was quite
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stable after 3 cycle runs and can be used for continuous operation in industrial applications. A reduction in the toxicity and enhancement in biodegradability of the organic raffinate was
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obtained after CWAO treatment at 70oC. The COD removal of 98.4 % was achieved by coupling of CWAO and biological treatment. It could be concluded that the industrial effluent containing pyridine and its derivatives can be treated by the combination of catalytic wet air oxidation and biological treatment. Abbreviations:
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TSS, total suspended solids; TDS, total dissolved solids; NTU, nephelometric turbidity unit; k, kinetic constant; Ea1, activation energy for complete oxidation; Ea2, activation energy for partial oxidation. References
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APHA, 2005, Standard methods for the examination of water and wastewater, 21st ed., American Public Health Association (APHA), Washington, DC.
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Arena, F., Chio, Di R., Gumina, B., Spadaro, L., Trunfio, G., 2015. Recent advances on wet air oxidation catalysts for treatment of industrial wastewaters. Inorg. Chim. Acta 431, 101–109. Bistan, M., Tišler, T., Pintar, A., 2012. Ru/TiO2 catalyst for efficient removal of estrogens from aqueous samples by means of wet-air oxidation. Catal. Commun. 22, 74–78. Chen, H., Yang, G., Feng, Y., Shi, C., Xu, S., Cao, W., Zhang, X., 2012. Biodegradability enhancement of coking wastewater by catalytic wet air oxidation using aminated activated carbon as catalyst. Chem. Eng. J. 198–199, 45–51.
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Chatzisymeon, E., Foteinis, S., Mantzavinos, D., Tsoutsos, T., 2013. Life cycle assessment of advanced oxidation processes for olive mill wastewater treatment. J. Clean. Prod. 54, 229234.
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Dükkanci, M., Gündüz, G., 2009. Catalytic wet air oxidation of butyric acid and maleic acid solutions over noble metal catalysts prepared on TiO2. Catal. Commun. 10, 913–919. Ersöz, G., Atalay, S., 2012. Treatment of aniline by catalytic wet air oxidation: Comparative study over CuO/CeO2 and NiO/Al2O3. J. Environ. Manage. 113, 244-250.
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Fathima, N.N., Aravindhan, R. Rao, J.R., Nair, B.U., 2008. Dye house wastewater treatment through advanced oxidation process using Cu-exchanged Y zeolite: a heterogeneous catalytic approach. Chemosphere 70, 1146–1151.
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Güyer, G.T., Nadeem, K., Dizge, N., 2016. Recycling of pad-batch washing textile wastewater through advanced oxidation processes and its reusability assessment for Turkish textile industry. J. Clean. Prod. 139, 488-494. Kim, V.K., Ihm, S., 2011. Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: A review. J. Hazard. Mater. 186, 16-34. Levec, J., Pintar, A., 2007. Catalytic wet-air oxidation processes: A review. Catal. Today 124, 172-184.
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Padoley, K.V., Mudliar, S.N., Banerjee, S.K., Deshmukh, S.C., Pandey, R.A., 2011. Fenton oxidation: A pretreatment option for improved biological treatment of pyridine and 3cyanopyridine plant wastewater. Chem. Eng. J. 166, 1–9.
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Priyanka, Subbaramaiah, V., Srivastava, V.C., Mall, I.D., 2014. Catalytic oxidation of nitrobenzene by copper loaded activated carbon. Sep. Purif. Technol. 125, 284–290.
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Rodrigues, C.S.D., Neto, A.R., Duda, R. M., de Oliveira, R. A., Boaventura, R.A.R., Madeira, L.M., 2016. Combination of chemical coagulation, photo-Fenton oxidation and biodegradation for the treatment of vinasse from sugar cane ethanol distillery. J. Clean. Prod. doi.org/10.1016/j.jclepro.2016.10.104. Suarez-Ojeda, M.E., Guisasola, A., Baeza, J.A., Fabregat, A., Stuber, F., Fortuny, A. Font, J., Carrera, J., 2007. Integrated catalytic wet air oxidation and aerobic biological treatment in a municipal WWTP of a high-strength o-cresol wastewater. Chemosphere 66, 2096–2105. Seyler, C., Hofstetter, T. B., Hungerbuhler, K., 2005. Life cycle inventory for thermal treatment of waste solvent from chemical industry: a multi-input allocation model. J. Clean. Prod. 13, 1211-1224. 16
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Tripathi, P.K., Rao, N.N., Chauhan, C., Pophali, G.R., Kashyap, S.M., Lokhande, S.K., Gan, L., 2013. Treatment of refractory nano-filtration reject from a tannery using Pd-catalyzed wet air oxidation. J. Hazard. Mater. 261 63-71.
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Wang, P., Zeng, G., Peng, Y., Liu, F., Zhang, C., Huang, B., Zhong, Y., He, Y., Lai, M., 2014. 2,4,6-Trichlorophenol-promoted catalytic wet oxidation of humic substances and stabilized landfill leachate. Chem. Eng. J. 247, 216–222. Yang, S., Besson, M., Descorme, C., 2010. Catalytic wet air oxidation of formic acid over Pt/ CexZr1−xO2 catalysts at low temperature and atmospheric pressure. Appl. Catal. B: Environ. 100, 282–288.
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Zhang, Q., Chuang, K.T., 1999. Lumped kinetic model for catalytic wet oxidation of organic compounds in industrial wastewater. AIChE 45, 145–150.
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Figure captions: Fig. 1 Experimental setup for catalytic wet air oxidation
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Fig. 2 (a) SEM image; (b) XRD pattern and (c) TEM image of Pt/Al2O3 catalyst Fig. 3 Effect of air flow rate on COD removal Reaction conditions: Atmospheric pressure, Reaction temperature 30oC, Catalyst 0.1 wt. % Pt/Al2O3, Catalyst dosage 2 g/L
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Fig. 4 Effect of Pt loading on COD removal Reaction conditions: Atmospheric pressure, Reaction temperature 30oC, Air flow rate 1 L/min, Catalyst dosage 2 g/L
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Fig. 5 Effect of catalyst dosage on COD removal Reaction conditions: Atmospheric pressure, Reaction temperature 30oC, Air flow rate 1 L/min, Catalyst 1 wt. % Pt/Al2O3
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Fig. 6 Effect of reaction temperature on COD removal Reaction conditions: Atmospheric pressure, Air flow rate 1 L/min, Catalyst 1 wt. % Pt/Al2O3, Catalyst dosage 3 g/L Fig. 7 Comparison of experimental data with lumped kinetic model (a) for different catalyst dosages; (b) at different reaction temperatures
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Fig. 8 (a) Catalyst stability test; (b) TGA analysis of fresh and used catalyst Fig. 9 Biodegradability test of effluent
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Fig. 10 Toxicity test of effluent
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pH
10.8
COD
15000 mg/L
BOD
1170 mg/L
TDS
9800 mg/L
TSS
720 mg/L
Conductivity
12.2 mS/cm
Turbidity
10.6 NTU
Ammonical nitrogen
57,000 mg/L
Pyridine
500 mg/L
β-Picoline
2200 mg/L
3-Cyanopyridine
200 mg/L
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Value
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Parameter
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Table 1 Characteristics of industrial organic raffinate
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Table 2 Characterization of Pt/Al2O3 catalyst
Pt content (wt. %) as obtained by EDX analysis
BET surface area (m2/g)
Pore volume, V (cm3/g)
Pore diameter, Dp (nm)
Alumina
-
190
0.46
9.6
0.1
0.08
183
0.45
0.3
0.27
179
0.5
0.46
176
0.7
0.67
1
0.98
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Pt loading (wt. %) on alumina
8.9
0.42
8.7
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0.44
173
0.40
8.5
170
0.39
8.3
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Table 3 BOD and COD of industrial organic raffinate and CWAO effluent Effluent obtained after
Effluent obtained after
raffinate
CWAO at 30oC
CWAO at 70oC
BOD (mg/L)
1170
2968
4032
COD (mg/L)
15000
9800
8400
BOD/COD
0.078
0.3
0.48
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Industrial organic
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Parameter
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Table 4 Aerobic biological treatment of effluent obtained after CWAO at 70oC
3 4
5280
64.8
2600
5
4080
72.8
2000
6
2840
81.07
1300
7
1680
88.8
8
920
93.87
9
400
97.33
10
240
98.4
3204
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BOD (mg/L)
5680
COD removal w.r.t. initial COD of organic raffinate (%) 62.13
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COD (mg/L)
900 500 90
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HIGHLIGHTS: Treatment of industrial organic raffinate containing pyridine compounds was studied.
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Pre-treatment by catalytic wet air oxidation (CWAO) at atm. pressure was performed.
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Toxicity of the effluent after CWAO treatment was completely removed.
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Biodegradability of the effluent after CWAO treatment was enhanced.
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Complete mineralization was obtained by integration of CWAO & biological process.
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S0959-6526(17)31236-2
DOI:
10.1016/j.jclepro.2017.06.066
Reference:
JCLP 9816
To appear in:
Journal of Cleaner Production
Received Date: 8 November 2016 Revised Date:
7 June 2017
Accepted Date: 8 June 2017
Please cite this article as: Sushma , Saroha AK, Treatment of industrial organic raffinate containing pyridine and its derivatives by coupling of catalytic wet air oxidation and biological processes, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.06.066. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Treatment of industrial organic raffinate containing pyridine and its derivatives by coupling of catalytic wet air oxidation and biological processes Sushma and Anil K. Saroha* Department of Chemical Engineering, Indian Institute of Technology, Delhi
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Hauz Khas, New Delhi – 110016, India ABSTRACT
The treatment of non-biodegradable industrial organic raffinate containing refractory and toxic
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organic compounds pyridine, β-picoline and 3-cyanopyridine has been studied by coupling of catalytic wet air oxidation (CWAO) over alumina based platinum catalyst and biological processes. The alumina based platinum catalyst was characterized and the stability of the catalyst
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was studied. The CWAO experiments were performed in a glass reactor at atmospheric pressure and the effluent treatment efficiency was evaluated in terms of chemical oxygen demand (COD) removal. The effect of various parameters such as air flow rate, reaction temperature, platinum loading and catalyst dosage on the COD removal was studied. The optimum values of air flow rate, platinum loading and catalyst dosage were found to be 1 L/min, 1 wt. % and 3 g/L respectively and a COD removal of 45 % was obtained at the optimum conditions at reaction
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temperature of 70oC. The CWAO experimental results were found to be in agreement with the lumped kinetic model. The toxicity test using E. coli bacteria and the biodegradability study were performed. The toxicity of the effluent decreased considerably while the BOD/COD ratio was found to increase significantly after the CWAO. The aerobic biological treatment confirmed the
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biodegradability enhancement and a total COD removal of 98.4 % was obtained after 10 days of aerobic treatment of the CWAO effluent.
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Key words: Catalytic wet air oxidation, Industrial organic raffinate, Platinum catalyst, COD removal, Biodegradability, Toxicity. *Corresponding author Email: [email protected] Tel: +911126591032
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1. Introduction The industrial effluent generated from various industries such as pharmaceutical, textile, chemical and petrochemical contains huge amounts of toxic and refractory organic compounds
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and the improper discharge of the effluent poses a severe threat to the aqueous ecosystem. Various effluent treatment techniques such as physical treatment (adsorption, reverse osmosis, filtration), biological oxidation, physicochemical, incineration and advanced oxidation processes are extensively used for the treatment of aqueous organic pollutants. Sometimes combination of
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these techniques is employed to meet the stringent effluent discharge standards (Rodrigues et al., 2016). Although, conventional biological processes are commonly employed due to environment concerns and cost, they are not suitable for the treatment of effluent containing toxic organics
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due to biomass poisoning. The physicochemical processes such as adsorption, electrocoagulation and precipitation concentrate the pollutants to a new environment and require posttreatment to suitably dispose the concentrated pollutants. Incineration is an effective treatment technology for effluent with a high concentration of organic compounds (COD more than 100 g/L) for the process to become self-sustaining or auto thermal oxidation (Seyler et al., 2005).
furans.
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Further, it is performed at extremely high temperatures and emits toxic gases such as dioxins and
Advanced oxidation processes (AOPs) have the potential for the treatment of effluent containing refractory organic compounds (Chatzisymeon et al., 2013; Güyer et al., 2016). Wet air oxidation
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(WAO) is a promising technology for the treatment of effluent containing toxic as well as biologically refractory compounds (Levec and Pintar, 2007; Kim and Ihm 2011; Arena et al.
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2015). Since WAO is carried out at elevated temperature and pressure, the capital and operating costs are quite high. However, the use of catalyst in WAO called catalytic wet air oxidation (CWAO) makes the process more economical by lowering the severe operating conditions and the oxidation efficiency is also improved. In the CWAO process, the organic pollutants in the effluent are either mineralized into carbon dioxide and water or are partially degraded into biodegradable intermediates which remain in the aqueous phase. Catalytic wet air oxidation can be employed for treatment of toxic effluent when biological techniques are ineffective and the main emphasis is to convert organic pollutants in the effluent into products more amenable to biological treatment as complete oxidation may be too expensive. 2
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A large number of studies using CWAO for the treatment of effluent have been reported in the literature and most of the studies have employed CWAO for the treatment of synthetic solution containing single organic pollutant. But very scanty data are available for treatment of real industrial effluent containing multi-component mixture of organic compounds. Moreover, very
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few studies have reported the toxicity as well as biodegradability of the effluent after CWAO treatment. Wang et al. (2014) reported an enhancement in biodegradability (BOD/COD ratio) of the landfill leachate from 0.1 to 0.39 and the total COD removal of 61 % after CWAO at 150oC and 0.5MPa of oxygen pressure using Co catalyzed NaNO2 catalyst. Tripathi et al. (2013)
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observed enhanced biodegradability (0.11 to 0.46) of NF-reject after CWAO treatment using Pd/activated carbon catalyst at 200oC and 0.69 MPa of oxygen pressure. Bistan et al. (2012) performed the toxicity test using yeast to detect toxicity level of estrogen in CWAO treated
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effluent and complete toxicity removal was observed at 230oC using Ru/TiO2 catalyst. Chen et al. (2012) reported an increment in biodegradability from 0.23 to 0.84 of low biodegradable coking wastewater using CWAO treatment process at 140-160oC and 0.2 to 1MPa partial pressure of oxygen. The biodegradable effluent can be easily treated using biological process for complete removal of organic compounds. Suarez-Ojeda et al. (2007) used the integrated CWAO
containing o-cresol.
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and aerobic biological treatment to obtain COD removal of 98% of a high-strength wastewater
Pyridine and its derivatives are produced in huge quantities due to their high utility as intermediates in the process industries. Pyridine is produced by the synthesis reaction of
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acetaldehyde and ammonia in presence of catalyst and is used as an intermediate in the production of drugs, dyes, water repellants, polycarbonate resins and pesticides. Pyridine
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derivative β-picoline (3- methyl pyridine) is used in the manufacture of vitamins, insecticides and herbicides and production of 3-cyanopyridine by the ammoxidation of β-picoline at elevated temperature (Padoley et al., 2011). Pyridine and β-picoline are completely soluble in water, alcohol and ether and are used as industrial solvents. The industries engaged in manufacturing of pyridine and its derivatives use various compounds such as acetaldehyde, ammonia and catalysts. Therefore, the effluent generated from such industries is toxic and is not amenable to biological treatment.
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Most of the studies reported in the literature have performed CWAO of the effluent at elevated conditions of temperature (higher than 100oC) and pressure. Since the effluent treatment technique should be cost attractive, therefore efforts have been made in the present study for the treatment of highly alkaline industrial organic raffinate containing various toxic contaminants
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such as ammonical nitrogen, pyridine, β-picoline and 3-cyanopyridine by integration of CWAO using platinum (Pt) catalyst at very mild operating conditions and biological technique. The alumina based Pt catalyst was prepared and characterized by different analytical methods such as BET surface area, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy
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(EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The feasibility of the CWAO process was investigated by
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optimizing the various parameters such as air flow rate, catalyst loading and dosage and the results were analyzed in terms of COD removal of the effluent. The CWAO reaction kinetics was studied using a lumped kinetic model. The toxicity test using E. coli bacteria and the biodegradability study of the CWAO effluent were carried out. The aerobic and anaerobic biological treatments of the CWAO effluent were performed in batch reactors to achieve
2. Materials and methods
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degradation of the industrial organic raffinate.
The industrial organic raffinate, collected from a chemical industry producing pyridine and its derivatives, was characterized and the results are shown in Table 1. It can be noticed that the organic raffinate has a high COD value and is highly alkaline due to the presence of nitrogenous
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organic compounds such as ammonical nitrogen and contains pyridine, β-picoline and 3cyanopyridine. The biodegradability of organic raffinate (BOD/COD ratio) is 0.078 suggesting
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that it is not suitable for biological treatment due to the presence of toxic compounds. 2.1. Catalyst preparation
The metallic precursor used in the catalyst preparation [H2PtCl6·xH2O (39.8 % Pt)] was of analytical grade and was procured from CDH India. The catalyst was prepared using incipient wetness impregnation method and different Pt loadings (0.1, 0.3, 0.5, 0.7, 1, 1.5 and 2 wt. %) were supported on Al2O3 support. Initially, 20 g of Al2O3 spheres were dried at 300oC and the dried Al2O3 spheres were placed in rotary vacuum evaporator maintained at 70oC for doping. A 4
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known concentration of Pt solution was added to the spheres and stirred continuously for 3 h. The excess water was evaporated with vacuum evaporator and the residue was then dried at 110°C for 24 h in an oven. Further, the catalyst was calcined at 550°C for 4 h for complete decomposition of Pt oxide salts and deposition of the metal on the support structure followed by
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reduction in presence of H2 gas under controlled temperature condition. The temperature was regulated by increasing the temperature of H2 (flow rate 30 mL/min) from ambient temperature to 400°C at a rate of 10oC and was maintained at 400°C for 2 h to reduce the Pt from oxide state to metal form followed by passivation at room temperature for 30 min by supplying 50% H2 and
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50% N2. The reduced catalysts were used in the CWAO process.
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2.2. Catalyst characterization
The specific surface area, total pore volume and pore size for the different wt. % of Pt/Al2O3 catalysts were determined by adsorption and desorption isotherms of nitrogen at –196oC using a surface area analyzer (Micromeritics, ASAP 2010). The specific surface area was determined using the BET (Brunauer, Emmett, and Teller) method and the pore size distribution was obtained from desorption data by BJH (Barret, Joiner and Halenda) method. The morphology of
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the catalyst was determined with the help of a scanning electron microscope (Carl Zeiss, model SMT EVO 50). The elemental analysis of the catalyst was carried out using EDX equipped with SEM. The particle size analysis of alumina supported Pt catalyst was carried out by TEM analysis (Tecnai G2 F20 S-twin transmission electron microscope). The catalyst sample for TEM
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analysis was prepared by dispersing the catalyst powder in ethyl alcohol and the solution was sonicated for 15 min. A drop of suspension was transferred to a porous carbon film supported on
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copper grid and ethyl alcohol was removed by evaporation. The mounted copper grid was used for TEM analysis. The XRD method was used to obtain information about the crystalline structure and composition of the Pt/Al2O3 catalyst. The XRD measurements were performed using a Philips 1840 powder diffractometer with Cu-Kα radiation (γ =0.154 nm) at 40 kV and 30 mA in the range of 2θ =2o to 80o at a scanning speed of 4o per minute and the results were matched with the JCPDS files to confirm the presence of desired compounds in the catalyst. The average crystallite size of Pt was determined from the broadening of an X-ray diffraction peak, measured at one-half of the height and calculated using Debye- Scherrer’s equation. The TGA 5
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analysis of fresh and used Pt/Al2O3 catalyst was carried out in a TGA analyzer (Seiko TG/DTA 32 SSC5100) to check the deposition of carbon on the catalyst. The TGA analysis was performed in the presence of air and the furnace was heated to 900oC at the rate of 10oC/min.
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2.3. CWAO experiments
The schematic diagram of the experimental setup is shown in Fig 1. The CWAO experiments were performed in a four- neck round bottom glass flask of 3 L capacity. One neck of the flask
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was used for the initial charging of the organic raffinate, addition of the catalyst and withdrawal of the effluent samples at regular time intervals. One neck of the flask was fitted with thermocouple to measure the temperature of the flask. The glass flask was heated with a heating
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mantle (Khera Instruments Pvt. Ltd., India) and the temperature of the flask was kept constant at a desired value using the temperature controller. Continuous stirring of the solution in the flask at a fixed agitation speed of 400 rpm was carried out using a magnetic stirrer. One neck of the flask was used for bubbling air as a source of oxygen in the effluent. Air, drawn from a compressor and regulated by an air flow meter, was bubbled into the organic raffinate in the flask through an ‘L’ shaped tube with holes of 0.2 mm diameter to obtain uniform dispersion of air. A condenser
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was placed at the top of the flask to reflux the contents as there was a possibility of the contents escaping out of the glass flask at high temperature during the experiments. In a typical run, 1 L organic raffinate was charged in the glass flask and the temperature of the flask and the air flow rate were fixed at the desired values followed by the addition of fixed catalyst dosage. The
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progress of the oxidation reaction was monitored by withdrawing 2 mL organic raffinate sample at regular time intervals and determining its COD. The experiments were repeated for checking
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the reproducibility of the results and the deviation in the experimental results was found to be less than 3 %.
2.4. Analytical methods
The experimental results were interpreted in terms of COD removal, a measure of organic strength of effluent, which was determined by the dichromate method (Open reflux, titrimetric method) (APHA, 2005). 6
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The percentage degradation of pollutants, represented in terms of COD, was calculated using equation [1]: COD removal (%) =
ି
·100
[1]
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where, Co is the initial COD and Ct is the COD of the effluent at any time t .
The BOD of the effluent, defined as the amount of oxygen consumed by the microbes in the effluent sample after 5 days at 20oC, was determined according to Standard Methods (APHA,
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2.5. Toxicity test
The toxicity test was performed to measure the toxicity of the raw organic raffinate and CWAO
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effluent. The test was performed by taking 45 mL of the sample in a 250 mL conical flask and 5 mL broth containing freshly prepared E. coli strain was added to the sample. The flask was plugged tightly with cotton and placed in an incubator shaker at 37oC temperature for 48 h. A 1 mL sample was withdrawn at regular time intervals and centrifuged. The supernatant was discarded and the bacteria pellets were dissolved in ultra pure water and used for the absorbance
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measurement. The absorbance of the sample, representing the growth of bacteria, was measured at 600 nm wavelength using UV/VIS spectrophotometer.
2.6 Aerobic and anaerobic biological treatment
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The aerobic biological treatment of the industrial organic raffinate and CWAO effluent was performed in a glass reactor of 2 L capacity (batch mode). The activated sludge, collected from an activated sludge treatment plant, was used as the inoculum. The effluent sample and the
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activated sludge (20:1 vol. %) were charged in the reactor and air was supplied through three spargers using an aquarium pump. The reactor was kept in an incubator room whose temperature was maintained at 37±1oC for acclimatization of the microbes. The effluent sample was withdrawn daily for 10 days to determine the BOD and COD. The anaerobic treatment was performed in a 2 L capacity glass reactor (batch mode) for the industrial organic raffinate and CWAO effluent. The anaerobic sludge used as inoculum was collected from an anaerobic reactor. The sample and sludge were placed in the reactor (20:1 vol. %) incubated at 37oC and the reactor was closed tightly with cork fitted with a tube 7
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connected to a beaker containing water to evacuate the gases generated during anaerobic biodegradation of organic raffinate. Since the anaerobic microbes require more time than aerobic microbes for acclimatization and growth, the effluent sample was withdrawn after 25 days of
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incubation for COD and BOD analysis.
3. Results and discussion 3.1. Catalyst characterization
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The BET surface area, pore volumes and average pore diameter of the fresh catalysts were determined and are shown in Table 2. It can be noticed from Table 2 that the BET surface area,
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pore volume and pore diameter decreased with an increase in the catalyst loading (wt. % of metal impregnation). The reduction in the pore volume was observed due to closing of pore with deposition of metal particles on the pore mouth. The pore diameter was found to decrease with an increase in the metal loading in the catalyst due to the deposition of metal particles on the pore wall resulting in the partial blockage of the micropores.
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The EDX analysis of the Pt/Al2O3 catalyst (1 wt. %) in the form of energy peaks at different applied voltages confirmed the presence of Pt metal and no other undesired peaks were found indicating that all chloride decomposed completely to their respective states during calcinations (supplementary information Figure S1). The metal content of the Pt/Al2O3 catalyst obtained by
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EDX analysis is given in Table 2 and the Pt metal content was found to be in good agreement with the Pt loading. The SEM image of 1 wt. % Pt/Al2O3 catalyst (Fig. 2a) shows the rough
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surface with clusters of alumina.
The diffraction patterns of Pt/Al2O3 catalysts for different metal loading are shown in Fig. 2b. It can be noticed that alumina has amorphous structure and no characteristic crystalline peak was observed. It can be further noticed that no clear distinct characteristic peak was observed for 0.1 wt. % Pt/Al2O3 but with an increase in the Pt loading, small peaks were observed at 2θ=37.5o, 46o, 66.8o confirming the presence of Pt crystallites (Dükkanci and Gündüz, 2009). It indicates that Pt metal was finely dispersed in small crystallites on the support and the crystal size was found to be 2-4 nm. The TEM image of 1 wt. % of Pt/Al2O3 catalyst is shown in Fig. 2c and it 8
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can be observed that the Pt particles (black dots) are well dispersed over the Al2O3 support. The average particle size of the Pt is 2-4 nm and is in close agreement with the particle size obtained by XRD analysis.
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3.2. Biological treatment of industrial organic raffinate The aerobic and anaerobic biological treatment of industrial organic raffinate was performed to study the applicability of biological methods for its degradation. The aerobic treatment of industrial organic raffinate showed COD removal of 4 % on 3rd day of treatment and no further
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increment in COD removal was observed till 10th day of treatment. The anaerobic treatment of industrial organic raffinate for 25 days resulted in COD removal of 3%. The low reduction in
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COD removal was due to the biomass poisoning caused by the high toxicity imparted by pollutants present in organic raffinate to microorganisms. Therefore, it was decided to use CWAO as a pre-treatment technique to remove the toxicity of the industrial organic raffinate and convert non-biodegradable pollutants into biodegradable compounds to facilitate the use of biological methods for post-treatment of CWAO effluent.
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3.3. Possible adsorption of organic compounds on catalyst surface
An experiment was performed to check the COD removal of the industrial organic raffinate by possible adsorption of organic pollutants on catalyst surface. The adsorption experiment was conducted in the glass flask at atmospheric pressure and 30oC by adding 2 g Pt/Al2O3 (0.1 wt. %)
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catalyst as an adsorbent in 1 L of organic raffinate. The agitation speed was kept constant at 400 rpm and without supply of air to the flask. A COD removal of 7 % was obtained after 9 h of
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contact time.
The WAO experiments were conducted without catalyst at atmospheric pressure with an air flow rate of 2 L/min at 30oC and 70oC and the COD removal of 5 % and 12 % was obtained respectively after 9 h. Further the CWAO of organic raffinate was carried out at atmospheric pressure and 70oC using 3 g/L of Pt/Al2O3 catalyst with an air supply of 1 L/min. The gases coming out of the glass flask were collected after 30 min of reaction time to determine the carbon dioxide concentration using GCMS. The carbon dioxide concentration in the effluent
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gases was found to be 1200 mg/L signifying the oxidation of organic pollutants into carbon dioxide by CWAO.
3.4.1. Effect of air flow rate on organic raffinate degradation
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3.4. Optimization of CWAO operational parameters
The CWAO experiments were performed using Pt/Al2O3 (0.1 wt. %) with 2 g/L catalyst dosage at atmospheric pressure and 30oC temperature. The effect of air flow rate on CWAO was studied by varying the air throughput from 0.4 L/min to 4 L/min and the results are shown in Fig. 3. It
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can be noticed from Fig. 3 that an enhancement in COD removal efficiency was obtained with an increase in air throughput from 0.4 L/min to 1 L/min. However, no significant enhancement in
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COD removal efficiency was obtained on further increasing the air throughput. Subsequently, all further experiments were performed at an air flow rate of 1 L/min. Since the catalyst is in powder form with high surface area, no mass transfer limitations can be assumed and the oxidation of organic raffinate can be considered to be kinetically controlled for an air throughput of 1 L/min. 3.4.2. Effect of Pt loading (wt. %) on organic raffinate degradation
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The oxidation reactions mainly depend on the number of active Pt sites on the catalyst surface, which varies with Pt loading. Therefore, CWAO experiments were performed to determine the efficiency of Pt loading (0.1, 0.3, 0.5, 0.7, 1, 1.5 and 2 wt. % Pt on Al2O3) on organic raffinate degradation and the results are shown in Fig. 4. The experiments were performed at atmospheric
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pressure and 30oC temperature with an air flow rate of 1 L/min and catalyst dosage of 2 g/L. It can be observed from Fig. 4 that there is an increase in COD removal efficiency with an increase
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in the Pt loading up to 1 wt. %. However, no increase in COD removal was observed with further increase in Pt loading beyond 1 wt. %. This is due to the fact that the maximum active catalyst sites are available for the oxidation to occur at 1 wt. % Pt loading and further increase in Pt loading beyond 1 wt. % does not lead to an increase in active sites. At high Pt loading (> 1 wt. %), sintering of Pt occurs resulting in the enlargement of particle size. These enlarged particles are less active and have more inactive reaction sites (Priyanka et al., 2014; Yang et al., 2010). 3.4.3. Effect of catalyst dosage on organic raffinate degradation 10
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The catalyst dosage plays an important role in oxidation of organic compounds. The effect of catalyst dosage on CWAO of organic raffinate was studied by varying catalyst dosage from 1 g/L to 5 g/L and the results are shown in Fig. 5. The experiments were performed at atmospheric pressure and 30oC, while keeping other parameters constant (1 wt. % Pt/Al2O3, air
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flow rate 1 L/min). It can be noticed from Fig. 5 that an enhancement in COD removal was obtained with an increase in catalyst dosage from 1 g/L to 3 g/L and further increase in catalyst dosage did not result in significant enhancement of the COD removal. This may be due to the fact that at high catalyst dosages, the aggregation of Pt particle might decrease the availability of
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active surface sites, resulting in decrease in COD removal (Fathima et al., 2008). Therefore, 3 g/L catalyst dosage was found to be optimum and used in further experiments for the CWAO
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of industrial organic raffinate.
3.4.4. Effect of reaction temperature on organic raffinate degradation Reaction temperature is an important parameter in oxidation of organic compounds as an increase in reaction temperature enhances the oxidation rate. The effect of reaction temperature on the degradation of organic raffinate was studied by performing experiments at temperatures
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from 30 to 80oC and the results are shown in Fig. 6. It can be noticed that the COD removal increases with an increase in reaction temperature. This is due to the fact that an increase in reaction temperature leads to an increase in the reaction rate constant k, resulting in an enhancement of the reaction rate. But further increase in reaction temperature beyond 70oC did
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not lead to significant enhancement of the COD removal. This could probably be due to decrease in oxygen solubility in the organic raffinate and relatively lower adsorption of organic raffinate on the surface of catalyst at reaction temperatures higher than 70oC. The pH of the CWAO
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effluent obtained at 70oC was found to be 8.8 compared to 10.8 of the organic raffinate. 3.5. Kinetic studies
Zhang and Chuang (1999) proposed a lumped kinetic model to describe the kinetic behavior of catalytic wet oxidation of organic mixture containing different types of the organic compounds. The oxidation reactions were lumped into two groups: i.) complete oxidation with formation of carbon dioxide and water; ii) the partial oxidation with formation of all intermediates in the aqueous solution of effluent and are represented by the following equation: 11
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k1
CO2 +H2O (complete oxidation)
A + x·O2=
[2] k2
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B +H2O (partial oxidation)
where, the organic compounds in effluent are lumped as single compound A, all intermediates in the wastewater formed by the partial oxidation are lumped as B and k1, k2 are the rate constants for complete and partial oxidation reactions respectively. The first- order kinetics with respect to
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lumped compound A was assumed for both the reactions.
The rates of reaction for the degradation of A and formation of intermediates B can be expressed
−
ௗ[] ௗ௧
ௗ ௗ௧
= ݇ଵ [ܱ[]ܣଶ ] + ݇ଶ [ܱ[]ܣଶ ]
= ݇ଶ [ܱ[]ܣଶ ]
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as follows:
[3]
[4]
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where, [A] and [B] are the concentrations of lumped compound A and lumped intermediates B and [O2] is the concentration of oxygen in the effluent. The superscripts ‘a’ and ‘b’ represent the order of the complete and partial oxidation reactions with respect to oxygen respectively. The initial concentration of lumped organic compound A was the initial COD value of the organic
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raffinate while the concentration of A and B at any time t were represented by the COD value of the organic raffinate at time t (at time t=0, [A]= [A]o = [COD]o, [B] = 0 and at time t, [A] + [B] = [COD]). Since oxygen supply was in excess, the oxygen concentration in the organic raffinate
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was assumed to be constant. The integration of Eq. (3) and (4) with respect to t from limits 0 to t results as follows: ை ை˳
=
మ భ + ( ା (భ ା మ ) భ మ)
݁ [ି(భ ାమ )௧]
[5]
The kinetic parameters of the lumped kinetic model were obtained by fitting the experimental data to Eq. (5) and solving it using regression method. The estimated values of COD removal obtained by Eq. (5) and the experimental COD removal for different catalyst dosages and 12
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reaction temperatures are shown in Fig. 7a and 7b respectively and a close agreement between the estimated (lines) and experimental (symbols) COD values can be noticed. The values of regression coefficients for Fig. 7a and 7b are in supplementary information (Table S1). The kinetic rate constants k1 and k2 were evaluated from the experimental data and were plotted as
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ln k vs 1/T to determine the activation energy (supplementary information Fig. S2). The activation energy for complete mineralization (21.01 kJ/mol) was found to be higher than partial oxidation (17.5 kJ/mol) and activation energies are in agreement with the results obtained by
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Zhang and Chuang (1999). 3.6. Catalyst stability tests
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The deactivation of catalyst during oxidation reaction due to incomplete oxidation and consequent deposition of carbon is a severe problem for continuous operation of the process. Hence the catalyst’s stability test was conducted to explore its potential for use for continuous process in industrial application. The CWAO experiment was performed at the optimized conditions at 30oC for 9 h and the resultant CWAO effluent was filtered using 0.45 µm size Whatmann filter paper. The residue left on filter paper was washed with distilled water and dried
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in oven at 110oC for 24 h. The dried spent solid catalyst was again used in performing CWAO experiments at optimized conditions and the process was repeated further for third run. The result of three runs for the Pt/Al2O3 catalyst are shown in Fig. 8a and it can be noticed that there is no significant decrease in the COD removal with spent catalyst confirming negligible loss in
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catalytic activity.
The thermo-gravimetric analysis (TGA) of fresh and spent catalysts was performed and the
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results are shown in Fig. 8b for Pt/Al2O3 (1 wt. %) catalyst. A significant weight loss during the initial heating period in the temperature range 100oC-500oC was observed due to removal of moisture on the catalyst surface and adsorbed water inside the pores. A fraction of weight loss of the spent catalyst could be due to removal of easily oxidizable carbonaceous species formed during degradation of organic raffinate (Ersöz and Atalay, 2012). 3.7. Toxicity and biodegradability test
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The biodegradability index of the effluent, defined in terms of BOD/COD ratio, is a measure of the biodegradability of the effluent by microorganisms and the effluent is considered to be completely biodegradable at BOD/COD ratio of 0.4 (Wang et al., 2014). The biodegradability test of the organic raffinate and CWAO effluent (performed at reaction temperature of 30oC and
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70oC) was carried out and the results are shown in Table 3 and Fig. 9. It can be noticed that there is a significant enhancement in the BOD/COD ratio of the effluent obtained after the CWAO treatment. The BOD/COD ratio for the effluent obtained after CWAO at 30oC and 70oC were found to be 0.3 and 0.48 respectively. The enhanced biodegradability was due to oxidation of
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refractory compounds of organic raffinate into biodegradable compounds during CWAO treatment.
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The toxicity test of the organic raffinate and effluent obtained after CWAO at 30oC and 70oC was performed using E. coli bacteria and the results are shown in Fig. 10. A steep decrease in absorbance of the organic raffinate confirms its toxicity as the absorbance represents the growth of bacteria. The decrease in absorbance of the CWAO effluent (30oC) suggests that the effluent is still toxic but in less amounts as compared to the industrial organic raffinate due to reduction in toxicity by CWAO. The increase in absorbance for CWAO effluent (70oC) due to survival and
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growth of E. coli bacteria in the effluent indicates the complete removal of toxicity. The toxicity and biodegradability tests confirmed that effluent obtained after CWAO at a reaction temperature of 70oC was non-toxic and biodegradable.
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3.8. Biological treatment of CWAO effluent
The aerobic treatment of effluent after CWAO treatment at 70oC was performed and the results
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are shown in Table 4. It can be noticed that the BOD and COD of the CWAO effluent were reduced to 23 mg/L and 240 mg/L respectively. Similarly, the BOD and COD of 53 mg/L and 260 mg/L were obtained after 25 days of anaerobic treatment of CWAO effluent. It can be summarized that almost complete mineralization of the industrial organic raffinate was obtained with integration of CWAO and biological treatment. 4. Conclusion
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In the present work, the treatment of industrial organic raffinate containing pyridine and its derivatives was studied by integration of CWAO and biological techniques. The organic raffinate was pre-treated by CWAO using alumina based platinum catalyst at atmospheric pressure to reduce the micro-toxicity and enhance biodegradability to facilitate biological treatment. The
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optimum values of air flow rate, Pt loading and catalyst dosage were found to be 1 L/min, 1 wt. % and 3 g/L respectively and COD removal of 44 % was obtained at reaction temperature of 70oC. The reaction kinetics was studied and the activation energy of complete oxidation was found to be higher than that of partial oxidation. The alumina based platinum catalyst was quite
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stable after 3 cycle runs and can be used for continuous operation in industrial applications. A reduction in the toxicity and enhancement in biodegradability of the organic raffinate was
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obtained after CWAO treatment at 70oC. The COD removal of 98.4 % was achieved by coupling of CWAO and biological treatment. It could be concluded that the industrial effluent containing pyridine and its derivatives can be treated by the combination of catalytic wet air oxidation and biological treatment. Abbreviations:
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TSS, total suspended solids; TDS, total dissolved solids; NTU, nephelometric turbidity unit; k, kinetic constant; Ea1, activation energy for complete oxidation; Ea2, activation energy for partial oxidation. References
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APHA, 2005, Standard methods for the examination of water and wastewater, 21st ed., American Public Health Association (APHA), Washington, DC.
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Arena, F., Chio, Di R., Gumina, B., Spadaro, L., Trunfio, G., 2015. Recent advances on wet air oxidation catalysts for treatment of industrial wastewaters. Inorg. Chim. Acta 431, 101–109. Bistan, M., Tišler, T., Pintar, A., 2012. Ru/TiO2 catalyst for efficient removal of estrogens from aqueous samples by means of wet-air oxidation. Catal. Commun. 22, 74–78. Chen, H., Yang, G., Feng, Y., Shi, C., Xu, S., Cao, W., Zhang, X., 2012. Biodegradability enhancement of coking wastewater by catalytic wet air oxidation using aminated activated carbon as catalyst. Chem. Eng. J. 198–199, 45–51.
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Chatzisymeon, E., Foteinis, S., Mantzavinos, D., Tsoutsos, T., 2013. Life cycle assessment of advanced oxidation processes for olive mill wastewater treatment. J. Clean. Prod. 54, 229234.
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Dükkanci, M., Gündüz, G., 2009. Catalytic wet air oxidation of butyric acid and maleic acid solutions over noble metal catalysts prepared on TiO2. Catal. Commun. 10, 913–919. Ersöz, G., Atalay, S., 2012. Treatment of aniline by catalytic wet air oxidation: Comparative study over CuO/CeO2 and NiO/Al2O3. J. Environ. Manage. 113, 244-250.
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Fathima, N.N., Aravindhan, R. Rao, J.R., Nair, B.U., 2008. Dye house wastewater treatment through advanced oxidation process using Cu-exchanged Y zeolite: a heterogeneous catalytic approach. Chemosphere 70, 1146–1151.
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Güyer, G.T., Nadeem, K., Dizge, N., 2016. Recycling of pad-batch washing textile wastewater through advanced oxidation processes and its reusability assessment for Turkish textile industry. J. Clean. Prod. 139, 488-494. Kim, V.K., Ihm, S., 2011. Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: A review. J. Hazard. Mater. 186, 16-34. Levec, J., Pintar, A., 2007. Catalytic wet-air oxidation processes: A review. Catal. Today 124, 172-184.
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Padoley, K.V., Mudliar, S.N., Banerjee, S.K., Deshmukh, S.C., Pandey, R.A., 2011. Fenton oxidation: A pretreatment option for improved biological treatment of pyridine and 3cyanopyridine plant wastewater. Chem. Eng. J. 166, 1–9.
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Priyanka, Subbaramaiah, V., Srivastava, V.C., Mall, I.D., 2014. Catalytic oxidation of nitrobenzene by copper loaded activated carbon. Sep. Purif. Technol. 125, 284–290.
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Rodrigues, C.S.D., Neto, A.R., Duda, R. M., de Oliveira, R. A., Boaventura, R.A.R., Madeira, L.M., 2016. Combination of chemical coagulation, photo-Fenton oxidation and biodegradation for the treatment of vinasse from sugar cane ethanol distillery. J. Clean. Prod. doi.org/10.1016/j.jclepro.2016.10.104. Suarez-Ojeda, M.E., Guisasola, A., Baeza, J.A., Fabregat, A., Stuber, F., Fortuny, A. Font, J., Carrera, J., 2007. Integrated catalytic wet air oxidation and aerobic biological treatment in a municipal WWTP of a high-strength o-cresol wastewater. Chemosphere 66, 2096–2105. Seyler, C., Hofstetter, T. B., Hungerbuhler, K., 2005. Life cycle inventory for thermal treatment of waste solvent from chemical industry: a multi-input allocation model. J. Clean. Prod. 13, 1211-1224. 16
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Tripathi, P.K., Rao, N.N., Chauhan, C., Pophali, G.R., Kashyap, S.M., Lokhande, S.K., Gan, L., 2013. Treatment of refractory nano-filtration reject from a tannery using Pd-catalyzed wet air oxidation. J. Hazard. Mater. 261 63-71.
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Wang, P., Zeng, G., Peng, Y., Liu, F., Zhang, C., Huang, B., Zhong, Y., He, Y., Lai, M., 2014. 2,4,6-Trichlorophenol-promoted catalytic wet oxidation of humic substances and stabilized landfill leachate. Chem. Eng. J. 247, 216–222. Yang, S., Besson, M., Descorme, C., 2010. Catalytic wet air oxidation of formic acid over Pt/ CexZr1−xO2 catalysts at low temperature and atmospheric pressure. Appl. Catal. B: Environ. 100, 282–288.
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Zhang, Q., Chuang, K.T., 1999. Lumped kinetic model for catalytic wet oxidation of organic compounds in industrial wastewater. AIChE 45, 145–150.
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Figure captions: Fig. 1 Experimental setup for catalytic wet air oxidation
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Fig. 2 (a) SEM image; (b) XRD pattern and (c) TEM image of Pt/Al2O3 catalyst Fig. 3 Effect of air flow rate on COD removal Reaction conditions: Atmospheric pressure, Reaction temperature 30oC, Catalyst 0.1 wt. % Pt/Al2O3, Catalyst dosage 2 g/L
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Fig. 4 Effect of Pt loading on COD removal Reaction conditions: Atmospheric pressure, Reaction temperature 30oC, Air flow rate 1 L/min, Catalyst dosage 2 g/L
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Fig. 5 Effect of catalyst dosage on COD removal Reaction conditions: Atmospheric pressure, Reaction temperature 30oC, Air flow rate 1 L/min, Catalyst 1 wt. % Pt/Al2O3
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Fig. 6 Effect of reaction temperature on COD removal Reaction conditions: Atmospheric pressure, Air flow rate 1 L/min, Catalyst 1 wt. % Pt/Al2O3, Catalyst dosage 3 g/L Fig. 7 Comparison of experimental data with lumped kinetic model (a) for different catalyst dosages; (b) at different reaction temperatures
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Fig. 8 (a) Catalyst stability test; (b) TGA analysis of fresh and used catalyst Fig. 9 Biodegradability test of effluent
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Fig. 10 Toxicity test of effluent
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pH
10.8
COD
15000 mg/L
BOD
1170 mg/L
TDS
9800 mg/L
TSS
720 mg/L
Conductivity
12.2 mS/cm
Turbidity
10.6 NTU
Ammonical nitrogen
57,000 mg/L
Pyridine
500 mg/L
β-Picoline
2200 mg/L
3-Cyanopyridine
200 mg/L
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Value
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Parameter
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Table 1 Characteristics of industrial organic raffinate
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Table 2 Characterization of Pt/Al2O3 catalyst
Pt content (wt. %) as obtained by EDX analysis
BET surface area (m2/g)
Pore volume, V (cm3/g)
Pore diameter, Dp (nm)
Alumina
-
190
0.46
9.6
0.1
0.08
183
0.45
0.3
0.27
179
0.5
0.46
176
0.7
0.67
1
0.98
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Pt loading (wt. %) on alumina
8.9
0.42
8.7
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0.44
173
0.40
8.5
170
0.39
8.3
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9.2
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Table 3 BOD and COD of industrial organic raffinate and CWAO effluent Effluent obtained after
Effluent obtained after
raffinate
CWAO at 30oC
CWAO at 70oC
BOD (mg/L)
1170
2968
4032
COD (mg/L)
15000
9800
8400
BOD/COD
0.078
0.3
0.48
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Industrial organic
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Table 4 Aerobic biological treatment of effluent obtained after CWAO at 70oC
3 4
5280
64.8
2600
5
4080
72.8
2000
6
2840
81.07
1300
7
1680
88.8
8
920
93.87
9
400
97.33
10
240
98.4
3204
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BOD (mg/L)
5680
COD removal w.r.t. initial COD of organic raffinate (%) 62.13
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COD (mg/L)
900 500 90
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HIGHLIGHTS: Treatment of industrial organic raffinate containing pyridine compounds was studied.
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Pre-treatment by catalytic wet air oxidation (CWAO) at atm. pressure was performed.
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Toxicity of the effluent after CWAO treatment was completely removed.
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Biodegradability of the effluent after CWAO treatment was enhanced.
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Complete mineralization was obtained by integration of CWAO & biological process.
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