RESEARCH ARTICLE Preparation of activated carbon from dried pods of Prosopis cineraria with zinc chloride activation for the removal of phenol Kaushik Nath & Suresh Panchani & M. S. Bhakhar & Sandip Chatrola Received: 9 July 2012 / Accepted: 12 November 2012 / Published online: 5 December 2012 # Springer-Verlag Berlin Heidelberg 2012 Abstract Utilization of agrowaste materials for the produc- tion of activated carbon, as an excellent adsorbent with large surface area, is well established industrially, for dephenola- tion of wastewater. In the present work, dried pods of Prosopis cineraria—a novel and low-cost agrowaste mate- rial—were used to prepare activated carbons by zinc chlo- ride activation. Batch adsorption experiments were carried out to study the effects of various physicochemical param- eters such as initial phenol concentration, adsorbent dose, initial solution pH, and temperature. Pseudo-first-order second-order and diffusion kinetic models were used to identify the possible mechanisms of such adsorption pro- cess. The Langmuir and Freundlich equations were used to analyze the adsorption equilibrium. Maximum removal ef- ficiency of 86 % was obtained with 25 mgL −1 of initial phenol concentration. The favorable pH for maximum phe- nol adsorption was 4.0. Freundlich equation represented the adsorption equilibrium data more ideally than the Langmuir. The maximum adsorption capacity obtained was 78.32 mg g −1 at a temperature of 30 °C and 25 mgL −1 initial phenol concentration. The adsorption was spontaneous and endo- thermic. The pseudo-second-order model, an indication of chemisorption mechanism, fitted the experimental data bet- ter than the pseudo-first-order Lagergren model. Regenera- tion of spent activated carbon was carried out using Pseudomonas putida MTCC 2252 as the phenol-degrading microorganism. Maximum regeneration up to 57.5 % was recorded, when loaded phenol concentration was 25 mg L −1 . The data obtained in this study would be useful in designing and fabricating an efficient treatment plant for phenol-rich effluents. Keywords Phenol . Adsorption . Activated carbon . Bioregeneration . Isotherm Introduction Phenol is one of the Environmental Protection Agency (EPA)’ s priority pollutants and is a known human carcino- gen of considerable health concern, even at low concentra- tion. It is persistent in the environment when released in large quantities, or if it is continuously released from a source (Sathishkumar et al. 2009). Wastewater from coal gasification sites, petrochemical units, pesticide, paper and pulp, resin, tanning, textile, plastic, rubber, pharmaceutical, and dye manufacturing industries are the major sources of phenol. Ingestion of a small amount of phenol (threshold limit value 5 ppmv) by human beings following dermal exposure may cause gastrointestinal irritation, nausea, or effects ranging from erythema and deep necrosis (Busca et al. 2008). It is toxic for aquatic organisms, and an environ- mental concern level of 0.02 μgL −1 is suggested for water by the World Health Organization; however, USEPA (1987) recommends a maximum allowable limit of 0.001 mgL −1 . Among the various available technologies from literature for the treatment of phenol from water and gaseous streams (Busca et al. 2008), adsorption onto the surface of activated carbon and other adsorbents is still by far the most widely used method for treating domestic and industrial effluents. Large Brunauer–Emmett–Teller (BET) surface area, con- trollable pore structure, thermal stability, and low acid–base reactivity of activated carbon have made it an indispensable adsorbent for wastewater treatment process (Foo and Hameed 2010). Activated carbon adsorption has been Responsible editor: Hailong Wang K. Nath (*) : S. Panchani : M. S. Bhakhar : S. Chatrola Department of Chemical Engineering, G H Patel College of Engineering & Technology, Vallabh Vidyanagar 388 120 Gujarat, India e-mail: kaushiknath2003@yahoo.co.in Environ Sci Pollut Res (2013) 20:4030–4045 DOI 10.1007/s11356-012-1325-y