Potential of spent tea leaves as adsorbent for the treatment of tannery effluent

Abstract

Tanning industry is considered as one of the highly polluting industries in Bangladesh and this has an adverse impact on the environment. This sector produces 180 million square feet of hide every year which generates about 20,000 m3of tannery effluent and 232 tons of solid waste per day. Direct discharge of these pollutants to the environment causes serious environmental problems. Tannery wastewater contains very high concentration of organic matter, solids (e.g. fleshing), heavy metals (e.g., chromium), sulfates, sulfides, chloride, etc. Releasing these pollutants to the environment is a driving force for finding efficient, affordable and reliable technologies for wastewater treatment. In this study spent tea leaves collected from local markets was used as an adsorbent for the removal of BOD, COD, Cr and Pb from the tannery wastewater. Batch test was performed to investigate the use of this alternative low cost adsorbent for treatment of tannery wastewater. The characteristics of spent tea leaves were studied using different techniques such as Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Scanning Electron Microscope (SEM). The tannery wastewaters for this study were collected from three different places of Hazaribagh tannery area. The samples were characterized by the parameters of pH, BOD,COD, Cr and Pb. After treatment the tannery wastewater with tea waste BOD, COD and heavy metals (Cr and Pb) were measured. The experiments were performed in a batch process in a series of beakers equipped with stirrers by stirring the tannery effluent. The parameters analyzed in this study are adsorbent dose from 03 to 20 gm/l, different contact time from 30 to 180 minutes and at different pH values from 3 to 10.

After the experiments and analysis of results, it is found that the optimum conditions to remove BOD are at 5 gm/l of adsorbent dose and pH value of 5-6. For COD removal the optimum conditions are at 5 gm/l of adsorbent dose and pH value of 9-10. The optimal condition for Cr removal is 14 gm/l at pH 8-10 whereas for Pb removal is 11 gm/l at pH 8-10. The contact time required to attain equilibrium is dependent of the initial concentrations of the pollutants. For the same concentration, the percentage removal of pollutants increases with increase of contact time till equilibrium is attained. Freundlich and Langmuir equations are used to fit the experimental data. Both Langmuir and Freundlich isotherms are followed by the adsorption except for the lead (Pb) which had lower value of regression coefficient, R2.