Activated Tea Waste as a Potential Low-Cost Adsorbent for the Removal of p-Nitrophenol from Wastewater M. Ahmaruzzaman* and S. Laxmi Gayatri Department of Chemistry, National Institute of Technology, Silchar, Assam-788010, India The aim of this work was to determine the potential of activated tea waste (ATW) as a useful adsorbent for the removal of p-nitrophenol (p-NP) from aqueous systems. The study was realized using batch experiments with synthetic wastewater having a p-NP concentration of 1000 mg · L -1 . The effects of pH, contact time, and presence of anions were investigated. An increase in the pH to above neutrality resulted in a decrease in the p-NP adsorption capacity. The adsorption process reached equilibrium within 5 h of contact time. The Freundlich, Langmuir, Temkin, Dubunin-Radushkevich, and Redlich-Peterson adsorption models were used for mathematical description of the adsorption equilibrium, and it was found that the experimental data fitted very well to the Langmuir isotherm. Batch adsorption studies, based on the assumption of a pseudo-first-order, pseudo-second-order, or intraparticle diffusion mechanism, showed that the kinetic data followed closely a pseudo-second-order rather than a pseudo-first-order mechanism. The adsorption capacity of ATW for the removal of p-NP was found to be 142.85 mg · g -1 . These results clearly indicate the efficiency of activated tea waste (ATW) as a low-cost adsorbent for treatment of wastewater containing p-NP. Introduction The presence of phenolic compounds in waste effluent streams is of growing concern due to their relatively high toxicity. Nitrophenols are of interest, as they are listed as priority toxic pollutants by the United States Environmental Protection Agency. 1 The world production of nitrophenol derivatives is continuously growing. It is mainly used to prepare drugs, fungicides, dyes, darkening leathers, etc. 2 p-Nitrophenol (p-NP), however, is associated with some undesirable properties like irritation of the eyes, skin, and respiratory tract and may cause inflammation of those parts. The Ministry of Environment and Forests (MOEF), Government of India, and EPA, USA, have listed phenol and phenolic compounds on their priority pollutants lists. Their removal from surface water and groundwater is hindered due to their high stability and solubility in water as well as their resistance to traditional water purification methods 3 apart from the adsorption method. Various abatement technolo- gies for phenolic derivatives from wastewater have been proposed in the literature. They include separation by steam-distillation, extraction, adsorption, membrane pervaporation, 4 membrane-based solvent extraction, destruction by catalytic wet air oxidation, 5 oxidation with ozone, hydrogen peroxide, chemical oxidants, photocata- lytic oxidation, etc. Despite the availability of the above- mentioned processes for the removal of organic pollutants, the adsorption process still remains the best because of its simple design and easy operation. Although microbial degradation and chemical oxidation methods can be employed for the removal of nitrophenol, drawbacks like slow reaction rates, disposal of sludges, and control of temperature and pH are associated with microbial degradation, while chemical oxidation is only eco- nomically feasible at high pollutant concentrations. 2,6 Adsorption technology is currently being used extensively for the removal of organic and inorganic micropollutants from the aqueous phase, and activated carbon has been the water industry’s standard adsorbent for reclamation of municipal and industrial wastewater. Activated carbons are the most widely used adsorbents for the removal of pollutants from wastewater due to their extended surface area, microporous structure, high adsorption capacity, and high degree of surface reactivity. Extensive research work has been carried out using activated carbons and resins. 7,8 Despite the prolific use of these adsorbents in wastewater treatment, carbon adsorption remains an expensive treatment process. This has prompted a growing research interest in the production of low-cost alternatives to activated carbon. Some adsorbents that were developed from low-cost materials include fertilizer waste, 9 wood, 10 and rice husk, 11 activated jute stick char 12 by several chemical treatments. The use of sawdust for the removal of phenol from aqueous solution has been studied by Sivanandam and Anirudhan. 13 Dutta et al. 14 carried out studies on adsorption of p-nitrophenol on charred saw dust. Ahmaruzzaman and Sharma 15 investigated the possible use of coal, residual coal, rice husk, and petroleum coke as a means of removal of p-NP from wastewater. A study on tea waste as a low-cost adsorbent for p-NP removal is of interest because of its good removal capacity and also considering the fact that India is the second largest producer of tea (Camellia sinensis) in the world, with the state of Assam alone being a vast producer and consumer of tea. A huge amount of tea waste is being produced from a number of tea industries during the processing of tea leaves, and their disposal is another solid waste disposal problem. Considering the large scale availability of tea waste of Camellia assamica and Camellia sinensis in this region, research work on utilization of the tea waste for p-NP removal will help to some extent in solving this problem besides providing a cost-effective adsorbent requiring no regeneration. Adsorbents of agricultural/lignocel- lulosic precursors often show the presence of functional groups * Corresponding author. E-mail: md_a2002@rediffmail.com. Fax: (03842)- 233797. J. Chem. Eng. Data 2010, 55, 4614–4623 4614 10.1021/je100117s  2010 American Chemical Society Published on Web 06/10/2010