REMOVAL OF TRACE ORGANICS FROM AQUEOUS SOLUTIONS USING LOW-TEMPERATURE ACTIVATED CHARCOAL

Abstract

Phenols are one of the most useful and important organic chemicals used in the industry. As a result of extensive use, it is among the top priority pollutants. Phenolic wastes arise from the distillation of wood, -coke ovens, oil refineries, chemical plants, sheep dips, from human and animal refuse. Adsorption on activated carbon is of environmental significance because in many cases it is the method of choice for the removal of organics. Physical adsorption enables activated carbon to remove taste and odor-causing organic compounds, volatile organic compounds, trihalomethanes and other halocarbons from process water and vapor streams. World-over a considerable amount of work has been done on carbon adsorption, where as in Pakistan, application of carbon adsorption in removal of trace organics has found limited applications. It is so because of the high cost of activation and the fact that the commercially available activated carbon is mostly imported and is very expensive. Research is therefore being done at the Institute of Environmental Science and Engineering (ESE) to effectively use activated charcoal as a low cost alternative to this process. In this context other workers have already done some preliminary work, as part of the MS thesis research. This work is a continuation of the study carried out previously at IESE (Ansari,1998). Keeping in view the results of previous study i.e., adsorption not only takes place on charcoal activated at 800 to 10000C but also at temperatures as low as 200 to 3000 C, using para-nitrophenol as the test compound, this study was conducted to: e 1) Study the potential of low temperature activated charcoal for the removal of trace organics and compare it with high temperature activated charcoal (control at 800 0 C). 2) Do the cost comparison of the low-temperature activated charcoal and high temperature activated charcoal. 3) To devise a method to minimize the weight loss due to the oxidation of the carbon during activation. 4) To develop a low cost method of activation of charcoal. The research was carried out in the f0110'"ing steps: Phase-I: Preliminary studies to find out the removal efficiency in the low temperature range. Establishing a relationship between the weight loss and the activation temperature in this low temperature range for different sizes of charcoal granules. Muffle furnace was used for this study and the charcoal was activated under air environment. In this phase the design and fabrication of the low temperature furnace was started Phase-2: In this phase batch tests were carried out to find out the removal efficiency with the increase in amount of activated charcoal for the same concentration. Continuous tests were also done to find the adsorption capacity of the charcoal. Phase-3: This study was carried out to find out the potential of reactivated charcoal for the removal of frace organics. Recovery, reactivation and reuse were done in this phase. Self designed Lab-scale low- temperature furnace and Muffle furnace were used in this phase. Results of phase-I indicated that the removal efficiency in that temperature range of 250 to 350 0 C is around 30—35% and the weight loss for this range is about 15—40% for all charcoal granule sizes. e ResultS of phase-2 clearly indicate that increasing the amount of charcoal increases the surface area required for maximum removal efficiency. Increasing the quantity of charcoal can considerably increase the efficiency of removal. Results of phase-3 indicate that reactivation at 800 0 C is successful and can be effectively reused for the removal of trace organics. Reactivation at low temperature range is not successful and is not feasible for reuse.