Potential of Ulva prolifera in phytoremediation of seawater polluted by cesium and cobalt: an experimental study on the biosorption and kinetics

Radionuclides accidentally released from nuclear power plants,such as ^(137)Cs and ^(60)Co,can lead to severe contamination of marine ecosystems.Living macroalgae are effi cient in absorbing metal elements from seawater.A 10-day simulation was conducted to assess the potential of scavenging cesium(Cs)and cobalt(Co)with live U lva prolifera that was cultured in seawater medium containing Cs and Co in diff erent concentrations(0(the control),10,20,50,and 100 mg/L).In the experiment,5 kg(fresh weight)of U.prolifera was cultured in natural seawater in 90-L tanks.Results showed that after the experiment,the average bioconcentration factors(BCFs)of the control group were 247.2 and 1126.4 for Cs and Co,respectively.The absolute absorption quantity of U.prolifera increased and the BCFs decreased with the increase in Cs and Co concentrations.The biosorption of the two metals on the fi rst day well fi t the pseudo-second-order equation(R^(2)>0.95),indicating that adsorption is the rate-limiting step in the total biosorption process.Concentrations of both metal ions declined signifi cantly in the fi rst hour and decreased by 25.2%and 15.5%in 48 h,respectively.Therefore,live U.prolifera is effi cient at scavenging Cs and Co in seawater,providing potential applications for the phytoremediation of radionuclides contaminated seawaters.

Biosorption mechanism of Cr (Ⅵ) onto cells of Synechococcus sp.

The biosorption mechanism of Cr （Ⅳ） ions on Synechococcus sp. biosorbent was studied by analyzing the biosorption kinetics as well as speciation change and bond formation during the biosorption process. The kinetics study shows that the adsorption process of Cr （Ⅳ） consists of a very fast stage in the first several minutes, in which more than half of the saturation adsorption is attained, and a slower stage that approximately follows the first order kinetic model, basically Freundlich isotherm models were observed. Comparative studies of FT-LR spectra of K2Cr2O7, free cells of Synechococcus sp., and Cr-bound cells of Synechococcus sp show that the speciation of chromium that binds to the cells ofSynechococcus sp. is Cr （Ⅲ）, instead of Cr （Ⅳ）, and the carboxylic, alcoholic, amido and amino groups may be involved in the binding of Cr （Ⅲ）. Integrative analyses of the surface electric potential, the effect of pH value on adsorption behavior of Cr （Ⅵ）, and the results of FT-IR show that the biosorption of Cr （Ⅵ） follows two subsequent steps, biosorption of Cr2O7 ^2- by electrostatical force at the protonated active sites and reduction of Cr2O7^2- to Cr^3＋ by the reductive groups on the surface of the biosorbents.