heavy metals, biosorption, removal, contact time, pH, algal dose, desorption
Pollution due to heavy metals has become an environmental problem of worldwide concern due to their increased discharge, toxicity, non-biodegradable and persistence nature. Major anthropogenic sources of heavy metals include metal extraction, metal fabrication, metal finishing, electroplating, painting, dyeing, surface treatment industry and printed circuit board manufacture. Conventional heavy metal removal processes from aqueous streams include chemical precipitation, ion exchange, filtration, electrochemical treatment, membrane technologies and evaporation recovery. These processes are expensive or ineffective, especially when the metal concentrations are very low and of the order of 1 to 100 mg/l in the solution. Biosorption is a promising alternative, which utilizes inactive or dead biomass to bind and concentrate heavy metals from the aqueous solutions. Different types of biomaterials have shown different levels of metal uptake. Among the most promising biomaterials studied is algal biomass. Zinc is one of the important heavy metals widely used in the electroplating industries. It is an essential element for enzyme activators in humans, but is also toxic at levels of 100-500 mg/day and is a known carcinogen. The present study was aimed at to investigate the removal of Zn(II) from aqueous solution by biosorption on dried green algae Oscillatoria sp. and Spirogyra sp. as a function of contact time, pH, algal dose, initial zinc ion concentration and temperature. The uptake of Zn(II) by Oscillatoria sp. is rapid than by Spirogyra sp. It was observed that removal of Zn(II) by the non-living Oscillatoria sp. and Spirogyra sp. is highly dependent on pH. Metal uptake capacity of algal biomass increased with increase in initial metal ion concentrations. Oscillatoria sp. was observed to be a superior biosorbent than Spirogyra sp. in the removal of zinc ions. Desorption of the sorbed Zn(II) by 0.1N HCl indicated that recovery of Zn(II) from spent biomass is possible. Results indicated that non-living Oscillatoria sp. and Spirogyra sp of algae can be considered as inexpensive, effective and easily available in abundance biosorbents for the removal of Zn(II) from aqueous solutions.