Biofiltration of Cs and Sr Ions from Aqueous Solutions by Native and Chemically Treated Azolla sp.

Abstract

The accumulation of heavy and toxic metals in the environment has become a concern due to growing health risks to the public. These contaminants enter the environment through nuclear activity, industrial waste, mill tailings, smelting and landfill runoff. Azolla sp., an aquatic fern is an ideal candidate for exploitation in constructed wetlands for treating metal-contaminated wastewaters. Biosorption batch experiments were conducted to determine the Cs and Sr binding ability of native biomass and chemically modified biosorbent derived from Azolla sp., namely hydrogen peroxide Azolla sorbent (HAS). Freundlich constants are determined from the Freundlich adsorption isotherms for all of the biosorbents. The applicability of the Freundlich isotherm for representation of the experimental data was investigated. The best Cs and Sr removal results were obtained when Azolla was treated by 2 M MgCl2 and 30 ml H2O2 8 mM at pH 7 for 12 hr and it was then washed by NaOH solution at pH 10.5 for 6 hr. The maximum Cs and Sr sorption capacities of HAS biosorbent were obtained at pH 8 and 9 respectively. Uptake of Cs and Sr by HAS was relatively rapid and the absorption continued slowly there after. Desorption of Cs and Sr from Azolla was completely achieved by applying 1M HNO3 and no significant biomass damage took place after 7 sorption-desorption cycles. The maximum Cs and Sr uptakes were acquired using the large particles of HAS originated from Azolla (2-4 mm).