REMOVAL OF ACID YELLOW-36 & DIRECT BLUE–86 USING PEANUT SHELL ACTIVATED CARBON FROM WASTEWATER

Abstract

Water is an important component for existence of all living beings. Since the beginning of civilization, mankind flourished around the sources of water. With the skyrocketing growth in population, climatic changes and industrialization, availability of fresh water on earth is declining continuously, on the other hand demand is enlarging. After industrialization our water sources such as oceans, rivers started squeezing in quality, due to anthropogenic activities which have led to degradation of environment. Survival of living beings is threatened and earth’s support system is endangered due to Pollution. Worldwide leading cause of diseases and deaths is due to water pollution. Water is contaminated by numerous inorganic and organic substances such as industrial wastes, fertilizers, toxic chemicals, metals, dyes and its byproducts. Dyes are organic compounds used as colouring material in various industries mainly textiles. Dyes transmit colour to water and a small fraction is easily recognizable, which is aesthetically unacceptable. Due to complex structure, dyes are difficult to degrade. Abundant production of dyes have undesirable environmental effects. Despite the adverse effects caused by dyes to the environment, they are continuously being discharged in water bodies thus disturbing the water cycle. The condition can further intensify without strict remedial action. Thus, prioritizing wastewater treatment is essential to avert crippling water problems. Today world is becoming more eco sensitive which has given new impetus to waste water treatment. Researchers are in constant search of technically feasible and economically viable methods for removing dyes and its toxic effects from the environment. There are different methods that are used for the removal of dyes from wastewater amongst them adsorption has been found to be more advantageous and effective method. Adsorption is easy, reliable and versatile method for the removal of dyes. Over the past few years, trend of using ecofriendly, low cost adsorbent has increased. Focus of this study is on the adsorptive removal of two anionic dyes: Acid Yellow-36(AY-36) and Direct Blue-86 (DB-86) from aqueous solution using low cost activated carbon as adsorbent. So for present study, an agricultural waste, peanut shell was used as raw material for manufacturing peanut shell activated carbon (PnsAC) using H3PO4 as chemical activator. The pyrolysis is carried out under nitrogen environment at a ramp of 10 oC min-1 upto a temperature of 650 oC for 2 hr activation time. iii To test the efficacy of PnsAC different characterization studies were performed. Thermal stability was analyzed using TGA technique. Surface morphology was studied by SEM images and elemental analysis was carried out using energy-dispersive X-ray spectroscopy (EDS). Variation in surface functional groups were interpreted by Fourier Transform Infrared spectroscopy (FTIR). Zero point charge for PnsAC was 2.3. Investigations were done for studying the adsorption potential of PnsAC for the removal of anionic dye AY-36. Batch experiments were conducted to study the effects of pH (2 – 11), adsorbent dose (2 – 6 g L-1), and initial AY-36 concentration (100 – 250 mg L-1). The optimized condition obtained by varying the variables were obtained at temperature 35 oC, initial dye concentration 200 mg L-1, pH 2, PnsAC dose 4 g L-1 and equilibrium time 150 minutes. 98 % removal of AY-36 was achieved at optimized conditions. Equilibrium adsorption isotherms, kinetics, and thermodynamics were investigated. The experimental data were analyzed using different isotherm models: Langmuir, Freundlich, Redlich–Peterson, Sip, and Toth. The kinetics of adsorptive removal of dyes was studied with Pseudo first order, Pseudo second order and intraparticle diffusion model. Equilibrium study revealed that Freundlich isotherm model described best the experimental data. The kinetics of dye adsorption was found to confirm Pseudo second order kinetics with a correlation coefficient value of 0.999. Kinetic study results indicated that the chemisorption likely dominated the adsorption of AY-36 on peanut shell activated carbon (PnsAC). Thermodynamic study revealed that the adsorption process was feasible, endothermic and spontaneous. Another dye DB-86 was adsorbed using PnsAC. Adsorbent dose of PnsAC was investigated through batch experiments at various initial pH and DB-86 concentration, to obtain maximum adsorption. This study showed that 78.6 % removal was obtained for 10 g L-1 PnsAC dose in 150 minutes (equilibrium time) at pH 2, while temperature was maintained at 35 oC. Kinetic, equilibrium, and thermodynamic studies were carried out to validate the results from experiments. Kinetic study confirms that the adsorption phenomena follow the Pseudo second order rate equation. Isotherm study reveals that Freundlich, Redlich–Peterson, Sip, Radke– Prausnitz, Koble-Corrigan, and Fritz–Schlunder isotherm models well explained the experimental equilibrium data. Thermodynamic study showed a negative value of ΔG° which advocated that the process of adsorption was spontaneous. Positive values of ΔH° and ΔS° signified the endothermic and increased disorderness in the adsorption of DB-86, respectively. Further, for effective adsorption, PnsAC was modified with alginate and used for the removal of DB-86 dye. The alginate encapsulated activated carbon (PnsAC-alginate), prepared from waste iv peanut shell was used as an adsorbent. Alginate encapsulation was done by pouring homogenous mixture of sodium alginate and PnsAC into the bath of 1 % calcium chloride solution. The effects of temperature, equilibrium time, adsorbent dose, dye concentration and solution pH on the adsorption of DB-86 onto PnsAC-alginate were studied. To the best of our knowledge, no attempt have so far been made for optimization purpose using response surface methodology (RSM) in the adsorptive removal of DB-86. Central composite design coupled with RSM was used to optimize the adsorption feed conditions in order to achieve maximum dye removal efficiency. The statistical analysis revealed that for maximum dye removal efficiency, the optimal conditions were adsorbent dose of 24.65 g L-1, DB-86 dye concentration of 125.5 mg L-1 and pH of 3.1. Under optimized conditions, experimental dye removal efficiency (98.4 ± 0.1%) agreed closely with the predicted results, thus indicating the suitability of RSM in optimizing the feed conditions. SEM, EDS, TEM, XRD, BET and FTIR analyses showed the surface morphology of the adsorbents and confirmed the adsorption of DB-86 onto PnsAC-alginate. Crystalline behavior of PnsAC-alginate were analyzed using X-Ray diffraction (XRD). Zero point charge for PnsACalginate was 7.8. The experimental results also showed that the dye removal efficiency was increased by 7 % compared to that with peanut shell activated carbon (PnsAC) as an adsorbent. The adsorption kinetics of DB-86 was well described by Pseudo second order kinetic model with intra-particle and film diffusion mechanisms. Langmuir isotherm model provided the best fit to the adsorption equilibrium data, obtaining maximum dye adsorption capacity of 21.6 ± 0.9 mg g-1. Estimation of thermodynamic parameters revealed that the adsorption process was feasible and was spontaneous and endothermic in nature. The present study has demonstrated that the use of positively charged PnsAC-alginate as an adsorbent is a cost effective and suitable alternative for the removal of anionic DB-86 dye from aqueous solutions. From above study we can conclude that, low cost adsorbents PnsAC and PnsAC-alginate can be commercially converted into efficient adsorbents for the removal of AY-36 and DB-86 dyes from aqueous solutions by adsorption.