Preparation and Characterization of Novel Activated Carbons for Adsorption and Adsorption Assisted Biodegradation of Organic and Inorganic Water Pollutants

Abstract

The primary sources of water contamination are industrialization, urbanization, and agricultural activities, which are harmful to the environment and the living beings. The wastewater treatment is very necessary for saving the water to emancipate the living organisms. Among various treatment technologies, adsorption and biodegradation are the most efficient methods for removing various pollutants from wastewater. The integration of adsorption and biodegradation processes for the treatment of organic compounds leads to the enhancement of the degradation rate and adsorption capacity. Among various adsorbents used, the activated carbon is one of the most efficient adsorbents due to high surface area and developed pore structures, and a actual support media for microbial growth.
In this study, the Fox nutshell has been used as a novel precursor material for the preparation of activated carbons. These are the residue with no commercial value. The Fox nutshell contains low ash (5%) content and high volatile matter (70.1%) that is favorable for activated carbon preparation. Therefore, the Fox nutshell has been a worthwhile material for the preparation of the activated carbon. The activated carbons were prepared by chemical activation method using zinc chloride, orthophosphoric acid, and potassium carbonate. The effect of various process parameters such as heating rate, activation time, carbonization temperature and impregnation ratio on porous characteristics of the prepared activated carbons has been investigated. The proximate and ultimate analyses of the prepared activated carbons was carried out by using standard methods and CHNS analyzer, respectively. The prepared activated carbons were characterized by using N2 adsorption-desorption isotherm at 77 K. The surface functional groups present on the prepared ACs surface were determined by the Fourier Transform Infrared Spectroscopy (FTIR) analysis. The Field Emission Scanning Electron Microscope (FESEM) analysis revealed the surface texture of the ACs while Transmission Electron Microscopy (TEM) analysis is used to visualize the presence of micropores network.
The prepared activated carbon with a ZnCl2 activator (ACZC-600-2.0) which has the highest BET surface area of 2869 m2/g and pore volume of 1.96 cm3/g is obtained at the following conditions: 600 ºC carbonization temperature, 2 impregnation ratio and one hr activation time. The prepared activated carbon with an H3PO4 activating agent (ACPA-700-1.5) has the BET surface area of 2636 m2/g and pore volume of 1.53 cm3/g is obtained at 700 ºC carbonization temperature, 1.5 impregnation ratio and one hr activation time. The another prepared activated carbon with a K2CO3 activator (ACKC-800-0.5) has the BET surface area of 1236 m2/g and pore volume of 0.98 cm3/g which has the highest surface area and pore volume is obtained at 800 ºC carbonization temperature, 0.5 impregnation ratio and activation time of one hr.
Batch adsorption experiments of phenol, methylene blue (MB) and Cr(VI) onto prepared activated carbons were carried out at various initial concentration. Adsorption kinetics of phenol, MB and Cr(VI) were studied by using different kinetic models, i.e., the pseudo-first-order model, the pseudo-second-order model, and the intraparticle diffusion model. The experimental adsorption isotherms of these adsorbates on the prepared activated carbons were analyzed using the Langmuir, Freundlich, and Temkin isotherm models. adsorption capacity (qe) of 500 mg/L of initial phenol concentration onto ACZC-600-2.0 and ACPA-700-1.5 are 75.37 and 83.21 mg/g, respectively. The equilibrium adsorption capacity (qe) of MB onto ACZC-600-2.0 and ACPA-700-1.5 are 968.74 and 766.53 mg/g, respectively for 500 mg/L of initial concentration. Adsorption capacity (qe) of 10 mg/L of initial Cr(VI) concentration onto ACZC-600-2.0 and ACPA-700-1.5 are 43.45 and 56.31 mg/g, respectively. The potential applications of the prepared activated carbons for removal of adsorbates have been studied in fixed bed column. The effects of the bed height and flow rate of phenol, MB and Cr(VI) adsorption onto prepared activated carbons were also studied.
The bacterial strain of Pseudomonas putida (MTCC 1194) has been taken for the phenol biodegradation in both suspended and immobilized phase. The bacterial strain has been acclimatized up to 1000 mg/L of phenol concentration. Biological granular activated carbon (BGAC) shows more efficiency than the free cells for phenol removal due to both adsorption and biodegradation process. The BGAC has been used in fluidized bed bioreactor for treatment of synthetic phenol wastewater. In fluidized bed bioreactor, effects of inlet flow rate of the wastewater, different phenol concentration solutions, and the ratio of bed (settled) volume to bioreactor volume (Vb/VR) on the removal of phenol were studied.