Research On The Role And Mechanisms Of EPS In The Adsorption Of Copper By Bacteria

Extracellular polymeric substances (EPS, Extracellular Polymeric Substances) is the mixture of some organic macromolecules secreted from bacterial metabolism, play an important role in the adsorption of heavy metals by bacteria. In this paper, Bacillus subtilis (B. subtilis) and Pseudomonas putida (P. putida) were selected as test strains to adsorb the copper. Batch experiments were combined with Fourier Transform Infrared Spectroscopy (FTIR), potentiometric titration, Isothermal Titration Calorimetry (ITC) and other technology to systematically ascertain the influence and role of EPS in the adsorption process of copper by these two bacteria, discuss the thermodynamics and kinetics mechanisms in the interaction between EPS and copper, furthermore the complex of EPS and goethite were formed to investigate its effects and mechanism of adsorption copper in order to provide a theoretical basis for bioremediation of soil and water. The main contents were illustrated as follows:1. The role of EPS in the adsorption of heavy metals by bacteria had been proved. Combine potentiometric titration and FTIR technology to reveal the mechnism of Cu(Ⅱ) adsorbed by two bacteria with and without EPS. The bacteria without EPS have similar functional groups with intact bacteria, such as carboxyl,phosphoryl,hydroxy or amino, but the concentration of these groups decreased observably without EPS. The exist of EPS can increase the adsorption capacity of Cu(Ⅱ) by bacteria notably, and this effect more remarkable to B. subtilis. Phosphoryl and carboxyl play a major role in the process of these two bacteria adsorb of Cu(Ⅱ).2. Expound the thermodynamics and kinetics mechanism of Cu (Ⅱ) adsorbed by EPS. The maximum adsorption capacity of Cu(Ⅱ) adsorbed by EPS was 527.84 mg g-1, observably higher than bacteria. The kinetic process of EPS adsorb Cu(Ⅱ) agree with second order kinetic equation, indicating that the distribution and exchange of the proton involved in EPS and Cu (Ⅱ) is the main force. EPS adsorb of Cu (Ⅱ) was a reaction process with heat absorption and entropy production, probably that the carboxyl functional groups in EPS and the Cu(Ⅱ) coordinated and formed of inner complex compound.3. The compound conditions of EPS and goethite was tested, find out the mechanism of goethite-EPS complex adsorb of copper elementary. The ratio(EPS: goethite)=4:1, pH=3 and reacted for 30 minutes can achieve adsorption equilibrium. The maximum adsorption capacity of copper by the complex of goethite-EPS was higher than the maximum adsorption capacity that goethite adsorption of Cu, but less than the Cu(Ⅱ) adsorption by EPS. Indicated the presence of EPS can increase the content of Cu(Ⅱ) adsorption on goethite. As the pH increased from 2 to 6, the amount of Cu(Ⅱ) adsorbed by these three substances also increased. A new active site, P-O-Fe bond was formed in the complex of goethite and EPS, as a new activity site, together with carboxyl and hydroxyl play an important role in the process of Cu(Ⅱ) adsorbed.