DECOLOURISATION AND DETOXIFICATION OF WASTEWATER

Abstract

The objective of this study was to evaluate, decolourisation (removal of rhodamine-b, irgalite blue and reactive blue-4 dyes) and detoxification (removal of 2-CP, 4-CP, 2,4-DCP and phenol) of wastewater by simple adsorption, biodegradation and simultaneous adsorption and biodegradation (SAB) using activated carbon prepared from mustard stalk as adsorbent. The microorganism Pseudomonas putida MTCC 1194 was used for biodegradation as well as for simultaneous adsorption and biodegradation (SAB) studies. Low cost activated carbon was prepared from mustard stalk (MSAC) using chemical activation method using H2SO4. Characterization of MSAC showed BET surface area of 129 m2 g-1, BJH adsorption average pore diameter 1.505 A° and BJH cumulative pore volume 13.56 cc/g. Scanning electron microscopy (SEM), EDX and FT-IR were used to characterize the adsorbent. FT-IR spectrum of MSAC showed that the surface functional groups i.e. carboxylic, aliphatic ketones and phenolic groups, were present which contributes interaction between the adsorbates (i.e. dyes and phenolic compounds) and the surface of the prepared MSAC. The XRD pattern of mustard stalk activated carbon, broad peaks indicated the presence of amorphous form of silica. The examination of spectrum indicated the presence of silica and tridymite as major components and other trace minerals such as quartz, alumina, cristobalite, hydroxyapatite, calcium orthosilicate and feldspar. The Scanning Electron Microscopy (SEM) of MSAC showed development of micropores after chemical activation. All the experiments were conducted in batch mode. Various operational parameters such as, effect of adsorbent dosage, initial concentration, contact time, pH, temperature, etc., on the removal of the above adsorbates were studied. The equilibrium isotherms for these studies were analyzed by Freundlich, Langmuir, Temkin and Dubinin–Radushkevich (D-R) models at different temperatures, between 20°C to 35° Decolourisation study results showed that percentage of rhodamine-b dye removal was 82% for adsorption and 99.5% for SAB at pH 6.5, adsorbent dose 10 g/l and temperature 32C. °C. In case of irgalite blue maximum colour removal was 70% for adsorption and 83.3% for SAB at pH 6.9, adsorbent dose 10 g l-1 and temperature 30°C. In case of reactive blue-4, colour removal percentage was 61.2% for adsorption and 70.2% for SAB at pH 7, adsorbent dose 10 g l-1, and temperature 32°C. Effect of initial concentration results showed that adsorptive capacity of dyes increased with increase in concentration from 50 mg l-1 to 200 mg l-1. The adsorption kinetics was found to follow pseudo second order rate kinetic model both for adsorption and SAB, with good R2 value ranging from 0.951 to 0.998. The data indicate that intra-particle diffusion controls the rates of adsorption and SAB processes. Langmuir isotherm showed the best fit among the isotherm models studied (Langmuir, Freundlich, Temkin and Dubinin–Radushkevich). The calculated dimensionless separation factor, RL Biodegradation studies were performed with fixed inoculum concentration of 18.72 mg l , indicated that the adsorptions of the three dyes onto MSAC were favorable. -1 with initial dye concentration ranging from 10 to 250 mg l-1 at pH range from 4 to 9 and temperature range from 28 to 35°C. These results revealed that the percentage removal of dyes were 55%, 69.3% and 85% for reactive blue-4, irgalite and rhodamine–b, respectively, at pH 7 and temperature 30°C. The specific growth rates were 0.55 h−1, 0.58 h−1 and 0.57 h−1 for rhodamine-B, irgalite and reactive blue-4, respectively. Out of six kinetic models (Andrews, Haldane, Webb, Monod, Teissier and Contois) studied, Andrews, Haldane and Webb models were found suitable (R2 Detoxification results of phenolic compounds showed that percentage removal of phenol was 75% for adsorption and 90% for SAB at pH 7, adsorbent dose 10 g l > 0.99) for biodegradation of all dyes by Pseudomonas putida. -1, and temperature 35°C. In case of 2-chlorophenol (2-CP) removal was 82% for adsorption and 92% for SAB and at pH 7, adsorbent dose 10 g l-1 and temperature 32°C. For 4-chlorophenol (4- CP) removal was 86% in case of adsorption and 99% for SAB at pH 7, adsorbent dose 10 g l-1 and temperature 32°C, whereas for 2,4-dichlorophenol (2,4-DCP) removal was 80% for adsorption and 91% for SAB at pH 7, temperature 32°C and adsorbent dose 10 g l-1. The adsorption kinetics was found to follow pseudo second order rate kinetic model both for adsorption and SAB. Weber-Morris plots indicate that intra-particle diffusion controls the adsorption rate. The correlation coefficients (R2 Biodegradation studies of Phenol, 2-CP, 4-CP and 2,4-DCP exhibited inhibitory behavior in the concentration range from 10 to 1000 mg/l. The results showed that percentage removals at pH 7 and temperature 30°C were 89%, 85%, 82% and 75% for Phenol, 4-CP, 2-CP and 2,4- DCP, respectively. Out of six growth kinetic models studied, experimental data could be well ) for the intra particle diffusion model were between 0.995 and 0.990. Langmuir isotherm showed the best fit among the isotherm models studied (Langmuir, Freundlich, Temkin and Dubinin–Radushkevich). correlated by Haldane (R2 value 0.997-0.999), Andrews (R2 value 0.999) and Webb (R2 The studies showed that the process of simultaneous adsorption and biodegradation with activated carbon prepared from mustard stalk and Pseudomonas putida could be effectively used for decolourisation and detoxification of wastewater