Department of Environmental Engineering,Islamic Azad University
Algae are a group of living organisms that play an important role in heavy metal removal from polluted wastes. Their usage is rather economical, especially if the waste is not heavily polluted. Since the use of live algae creates some problems, products of their dried mass were used in this study. The sargassum species was collected from the Persian Gulf, dried, cut in pieces and then used as the biomass. The adsorption process, with influencing factors such as initial concentrations, retention time, pH and temperature, were considered. In dilute wastewater (less than 25 mg/l), this method can reduce the concentration of remaining heavy metals after 10 min retention time at a suitable level, for discharging into the environment. pH and temperature did not have an effect on the results. Absorption equations for the metals in question have been developed and the economical evaluation was compared using statistical methods. To recover metals and regenerate the biomass, EDTA and HCl were examined. It was found that using EDTA (4 mM) and HCl (pH=2) after 90 min had an efficiency of about %85 and %75 and EDTA is more efficient than HCl. It should also be mentioned that recovery has cost benefit if the metal of interest is noble and valuable. After 5 consequent cycles of adsorption and recovery using HCl and EDTA, the biomass lessened by 30% and 16%, respectively. The remaining heavy metal in the algae is increased gradually until we have 90% reduction in recovery using HCl and 65% using EDTA, because the active cell wall group of algae is damaged by HCl. During the first cycle, most of the metals were recovered. The primary and annual recovery costs were about 90 and 350 times more than the value of recovered heavy metal.