POTENTIAL OF TEA FACTORY WASTE IN REMOVAL OF SELECTED HEAVY METAL IONS FROM SIMULATED CONTAMINATED WASTE WATER

Abstract

Pollution of water resources has increased with human activities world over and heavy metals are major contaminants. In this study, removal of Cd2+, Cr3+, Cu2+, Pb2+ and Zn2+ ions from simulated contaminated water using tea waste has been investigated. The objective was to find out the efficiency of tea waste in removing these ions. Tea waste was collected from Nandi Hills Factory which processes tea leaves from Nandi Tea Estates farm, Eastern Produce Company farm and individual farms around Nandi Hills Town. The tea waste was then washed with hot water, air dried, ground and sieved through a mesh of size 10 (0.5 mm diameter). The ability of tea waste in removing the selected metal ions was investigated by studying from biosorption parameters namely pH, contact time, initial concentration and presence of other ions. A 0.3 g of the dry tea waste was used for 100 ml of model aqueous solution containing heavy metal ions. Solutions of 5 ppm which corresponds to the upper limit for the permissible concentration by World Health Organization (WHO) recorded in appendix 1 and 50 ppm which is far higher than the WHO permissible concentration limits of metal ions were used to represent low and high concentrations, respectively at optimum pH of 5 and room temperature, for single and mixed metal ions at both levels. Flame atomic absorption spectrometer (FAAS) was used to determine metal ion concentrations. The results show that biosorption is a two stage process, the first being rapid followed by a gradual one. Initial concentration affected the rate of biosorption for both single and mixed metal ions. Biosorption also differed significantly when the ions were mixed and especially in presence of Cr3+ ions. The data from the study fitted the Langmuir isotherm more than the Freundlich isotherm implying that the biosorption process took place at specific homogenous sites and the mechanism followed pseudo second order kinetics. Tea waste was effective in removing the selected ions with the highest percentages being; 66.8 % for Cd2+ single ions at low concentration, 75.5 % for Cr3+ mixed ions at high concentration, 87.6 % for Cu2+ single ions at low concentration, 93.7 % for Pb2+ single ions at low concentration and 86.7 % for Zn2+ single ions at low concentration. Tea waste was therefore found to be an efficient biosorbent for the selected heavy metal ions with the preference order being: Pb2+ > Cu2+ > Zn2+ > Cr3+ > Cd3+.