ADSORPTIVE TREATMENT OF PYRIDINE AND ITS DERIVATIVES FROM WASTEWATERS

Abstract

Pyridine (Py) and its derivatives, like 2-picoline (2Pi), 4-picoline (4Pi), 3-aminopyridine (AmPy), vinylpyridine, etc. are volatile, toxic and flammable with a pungent and unpleasant odour. Py is the parent of a series of chemicals, and is used as a solvent in paint and rubber preparation, as an intermediate in making insecticides and herbicides for agricultural applications and in research laboratories as extraction solvents. Py and its derivatives are also used to make different products such as medicines, vitamins, food flavorings, dyes, adhesives, and in water proofing for fabrics [Kirk, 1996; Lataye et al., 2006; 2007a-fJ. When heated to decomposition, these compounds emit highly toxic vapours of NOx in an oxidative atmosphere. Adsorption as a wastewater treatment process has aroused considerable interest during recent years. Commercial grade granular activated carbon (GAC) is mostly used as an effective adsorbent for controlling the various organic and inorganic pollutants [Deshpande et al., 1996]. However, due to high cost of GAC and about 10-15 % loss during its regeneration, alternate adsorbents are being explored. Unconventional adsorbents like bagasse fly ash (BFA), rice husk ash (RHA), carbon slurry, kaolin, soil and clay, silica, peat, lignite, bagasse pith, wood, saw dust, molecular sieves, resins, montmorillonite, etc. have attracted the attention of several investigators. Mall et al. [1996] and Bailey et al. [1999] have presented a critical review of such low cost adsorbents for the treatment of various wastewaters. BFA andRHA have been found to be a very effective adsorbent for a number of toxics and pollutants from wastewater. Various physico-chemical and biological treatment techniques are suggested for the treatment of wastewaters containing Py and its derivatives. These techniques include concentration followed by incineration, adsorption [Kumar et al., 1995; Bludau et al., 1998; Mall et al., 2003; Lataye et al., 2006, 2007a-f], biodegradation [Shukla, 1973; Sims et al., 1986; Sandhya et al., 2002], Ozonation [Stern et al., 1997], etc. The adsorption of these toxic materials by using lowcost adsorbents like BFAand RHA has not been reported in the literature. Also, very scarce literature is available on the Taguchi's optimized design of experiments on the single and multicomponent adsorption from aqueous solutions [Srivastava et al., 2007]. In the present study, Taguchi method [Roy, 1990] has been used in the design of adsorption experiments using BFA, RHA and GAC as adsorbents for the removal of Pyand its derivatives. in Abstract Objectives of the Work The present study has been undertaken with the following objectives: 1. Tocharacterize the agri-based waste materials like BFA, RHA and GAC for their physico-chemical and adsorption properties. These characteristics include the analysis of particle size and pore size (and area) distribution, proximate and ultimate analysis, and the surface and functional characteristics by FTIR, XRD, TGA and SEM analyses. 2. To utilize BFA, RHA and GAC as adsorbents for the treatment of Py, 2Pi, 4Pi and AmPy bearing synthetic wastewater and to compare their performance with that of available GAC. 3. To study the effect ofvarious parameters like initial pH (pH0), adsorbent dose (m), contact time (/), initial concentration (C0), and temperature (7) on the removal ofPy, 2Pi, 4Pi and AmPy from the aqueous solution in batch study. 4. To carry out kinetic and equilibrium adsorption studies of Py, 2Pi, 4Pi and AmPy onto various adsorbents and to analyze the experimental data using various kinetic and isotherm models. 5. To understand the thermodynamics of adsorption and to estimate the isosteric heat of adsorption for Py, 2Pi, 4Pi and AmPy using BFA, RHA and GAC as adsorbents. 6. To utilize Taguchi's optimization method for the design of experiments for estimating the effects of various adsorption parameters in single, binary, and multi-component (solute) adsorption systems in the batch adsorption mode. 7. To perform desorption study for the possible regeneration ofadsorbents and to develop amethod for disposing off the spent adsorbents by fixing the pyridine and picoline chemically or physically. 8. To perform the multistage treatment to reduce the residual concentration of Py, 2Pi, 4Pi and AmPy upto the maximum permissible discharge limit in the wastewaters. To fulfill the above objectives, the adsorbents were procured, washed and sieved to the required particle size. The physico-chemical characterization of the adsorbents has been done using standard methods e.g. sieving, scanning electron microscopy (SEM), IV Abstract X-ray diffraction (XRD), FTIR spectroscopy, etc. Pore size distribution and pore area/volume have also been determined. The X-ray spectra of the adsorbents reflected the presence of various types of oxides in all the adsorbents along with some characteristic components. The BFA and RHA showed a mesoporous nature. FTIR spectra of the adsorbents indicated the presence of various types of functional groups e.g. free and hydrogen bonded OH group, the silanol grous (Si-OH), CO group stretching from aldehydes and ketones on the surface of adsorbents. The FTIR of loaded adsorbents show the characteristic bands of Lewis and Bronsted sites. Thermogravimetric analysis exhibited the thermal stability of the adsorbents upto 400 °C. All the batch experiments were carried out at 30 ± 1 °C. For each experimental run, 0.05 dm3 ofsolution ofknown C0,pH0 (2 - 12) andmtaken in a0.25 dm3 stoppered conical flasks, was agitated ina temperature-controlled orbital shaker ata constant speed of 150 ± 5 rpm. Samples were withdrawn at appropriate time intervals and centrifuged using a research centrifuge (Remi Instruments, Mumbai, India). The residual concentration (Cr) of the centrifuged supernatant was then determined using Perkin Elmer double beam spectrophotometer. The optimum dosages of BFA, RHA and GAC were found to be 8, 30 and 20 g dm'3, for C0 =100 mg dm"3 for Py and AmPy respectively. The optimum dosages were found to be 5, 20 and 10 g dm"3 for 2Pi and 4Pi, respectively, for BFA, RHA and GAC for C0=100 mg dm"3. Various kinetic models, viz. pseudo-first-order, pseudo-second-order, intraparticle diffusion, Elovich, Bangham and modified Freundlich models have been used to study the kinetics of adsorption of Py, 2Pi, 4Pi and AmPy onto adsorbents. The pseudo-second-order kinetic model represented the equilibrium data well for all the adsorbate-adsorbent systems. Equilibrium isotherms were analyzed by using Langmuir, Freundlich, Temkin, Redlich-Peterson, Toth and Radke-Prausnitz isotherm models. The removal efficiencies of the pyridine and its derivatives from the synthetic wastewaters were found to be in the range of 95-99%, 84-97%, and 90-98% for BFA, RHA and GAC, respectively. Redlich-Peterson, Toth and Radke-Prausnitz isotherms generally well represent the equilibrium adsorption of Py, 2Pi, 4Pi and AmPy onto BFA, RHA and GAC. The heat of adsorption (A//0) and change in entropy (AS0) for adsorption on BFA, RHA and GAC were found to be in the range of 23-108 kJ mol"1 and 0.12-0.15 kJ mol"1 K"1; 8-21 kJ mol"1 and 0.1-0.13 kJ mol'1 K"1; and 13-26 kJ mol"1 Abstract and 0.1-0.15 kJ mol"1 K'1; respectively. The values of change in Gibbs free energy (&G°aJs) were found in the range of 18-36 kJ mol"1, 14-20 kJ mol"1 and 15-22 kJ mol"1 for BFA, RHA and GAC, respectively. The negative value of change in Gibbs free energy indicated the feasibility and spontaneity ofadsorption on the adsorbents. Batch conditions for individual and simultaneous Py, 2Pi, 4Pi and AmPy removal by BFA, RHA and GAC were optimized by using Taguchi's design of experimental (DOE) methodology. Significant parameters viz. Co, pH0, m, Tand t at three levels with orthogonal array (OA) layout ofL9 (34) for single and binary systems and L27 (313) for ternary system were selected for the proposed experimental design. For single and binary systems, 9 sets ofexperiments were conducted. Whereas, 27 sets of experiments were conducted for the adsorption in ternary system. Taguchi's approach is found to be a potential design methodology for the optimization of adsorption processes. The real wastewater discharged from a unit manufacturing Py and its derivatives was given adsorptive treatment using BFA, RHA and GAC as adsorbents. Taguchi's DOE methodology was used for the purpose. The parameter qt0, was considered to be optimized. The optimum qtol by BFA, RHA and GAC was 9.96, 3.51 and 5.17 mg g"1, respectively. The adsorbent dose was found to have the highest influence on the treatment process. The removal efficiency in the I stage was found to be in the range of 90-95%, 86-92% and 90-95% for BFA, RHA and GAC, respectively. Whereas, at the II stage the efficiency was found to be 71-87%, 58-81% and 76-93% for BFA, RHA and GAC, respectively. For the desorption experiments, water at various pH (2-12), acids, alcohol and soil-water solution have been used. The use of water at lower pH and diluted acids resulted in higher amount of desorption (-80%). The desorption capacity of soil-water solution is found to be very small. The spent BFA and RHA need not be regenerated and can be used as afuel and fired ina furnace to recover their energy value and to dispose them off. The results from the present studies indicate that the use of BFA and RHA which are available at almost no cost could be viable alternatives to the activated carbons for the removal of toxic compounds from aqueous solutions.