Effect Of Extracellular Polymeric Substances On The Interface Process Between Microbial And Iron Minerals

Extracellular polymeric substances (EPS) are secreted by fungi and bacteria whichcan be divided into aerobic bacteria and anaerobic bacteria under certain conditions.EPS are key material in determining the surface properties of the microorganism, andmaintaining the integrity of the structure and function of various microbial aggregates.EPS also plays an important role in adsorption and decomposition of minerals. In thispaper, Acidithiobacillus ferrooxidans (A. ferrooxidans) and Sulfate Reducing Bacteria(Desulfovibrio desulfuricans, D. desulfuricans) are studied as a representative ofaerobic and anaerobic bacteria respectively; the optimal EPS extraction methods andeffect of EPS on the interaction process between microbial and iron minerals areinvestigated.The efficiencies of extracting extracellular polymeric substances (EPS) from A.ferrooxidans and SRB using ethylene diamine tetraacetic acid disodium salt (EDTA),cation exchange resin (CER), NaOH, H2SO4, heating method, sonication andcentrifugation were compared. EPS constituents such as carbohydrate, protein, nucleicacid in the extracted EPS samples were analyzed. The UV–visible spectrum was alsoemployed to evaluate the extent of cell lysis for making a judgment on EPS extractionmethods. Results showed that EDTA method was most effective extraction method forboth A. ferrooxidans and SRB.The interaction of Fe3+and EPS which extracted from A. ferrooxidans by usingEDTA method and its effect on microbial decomposition of pyrite under different pHare investigated. The electrochemical characteristic of EPS and iron-containing EPSwere analyzed by the measurement of Zeta potential and cyclic voltammetry curves.Results showed that both EPS solution were positively charged at lower pH and couldbe easily attached to the negatively charged surface of pyrite, and iron-containing EPSsolution is more conducive to the oxidation reaction of pyrite. Experimental results ofthe pyrite decomposition indicated that the promoting effect of EPS on thedecomposition process of pyrite oxidized by Fe3+was not obvious at lower pH, whereasthe promoting effects was significant at higher pH.Characterization methods such as chronoamperometry, potentiometric titration andFTIR are employed to study the property of EPS extracted from the anaerobic sludge-goethite system. The results showed that there are positive correlation between themethane yield and the electron acceptor capacity QEACin the system of moderate surface area of goethite, the greater the electron acceptor capacity, the more methaneproduction; The potentiometric titration results indicated that the primarily functionalgroup of EPS extracted from the system of sludge-mineral were carboxyl,phosphorus-containing group, hydroxyl group and amine groups, EPS extracted fromthe system which produced the more methane had higher adsorption sites concentration.FTIR showed that EPS extracted from the system of more methane production havemore amount of amide group; this indicated that certain protein in EPS solution havinga promoting effect on the production of methane, and the protein of EPS extracted fromanaerobic sludge could be promoted by adding goethite.