BIOLOGICAL REMOVAL OF ZINC FROM INDUSTRIAL WASTE WATER

Abstract

Various types of zinc related diseases have been reported in recent years around the world due to the continuous consumption of zinc contaminated water for drinking purpose. Zinc remediation of aqueous streams is of special concern due to its highly toxic and persistent nature. Various conventional treatment techniques are available for zinc removal from wastewater. Amongst the available techniques activated carbon adsorption process seems to be most popular for the removal of zinc from wastewater due to its low initial cost and sludge free environment. But the application of this technique in zinc removal is also prohibitive due to its high operational cost. Under the .above backdrop, the present study has been undertaken to develop suitable agro based biosorbents for removal of zinc from industrial wastewater. In the continuing search to achieve the desired objective, lemon peel and banana peel were evaluated as new biosorbents for the removal of zinc from aqueous solutions. Batch experiments were performed to study the adsorption of zinc ions on banana peel and lemon peel adsorbents. Characterization of both adsorbents was carried out using various techniques such as Proximate and ultimate analysis, FTIR, TGA, FE-SEM and EDAX. Effects of process parameters like biosorbent concentration, contact time, pH, biosorbent particle size and temperature on the removal of zinc from wastewater have been investigated using the above biosorbents to determine the optimum process conditions for maximum removal of zinc. Effects of initial zinc concentration on the removal of zinc have also been investigated. Optimum adsorbent concentrations for both lemon peel and banana peel for the removal of zinc at agitation period of 6 h are found to be 10 g/l. To facilitate mathematical modelling adsorption kinetic models as well as adsorption isotherms have been developed. Adsorption of Zn(II) on both lemon peel and banana peel has been found to follow pseudo second. order kinetic model. Amongst the conventional isotherms such as Langmuir and Freundlich isotherms, the Langmuir isotherm gave better prediction of specific uptakes for Zn(II) at equilibrium for both the above stated adsorbents. Further, microorganism isolated from petrol pump soil was used in immobilized phase, in batch reactors, for the bio-removal of zinc supplemented with adsorption on adsorbents as well as biomass. It was found that percentage removal by simultaneous adsorption and bioaccumulation exceeded that of adsorption.