| Heavy metal pollution has extremely harmful effect on environment and how to manage it effectively has attracted extensive attention.Heavy metal polluted water pollution controlled by use of microbial has become a research focus. While the yeast as a class of cheap, easy to get and security industrial microbial are widely used in biosorption of heavy metal ions.In the first part, the adsorption of Cd2+ by baker's yeast was studied before and after treating by formaldehyde, acetone, phenol and sodium hydroxide modification. Using alginate-Gelatin Immobilization of treatment and the orthogonal design were determined on the adsorption conditions for screening. By selecting five factors including pH, chemical modification methods, chemical modification of different bacteria, fungi volume, adsorption time and initial concentration of Cd2+, each factor was designed to take four levels of L16 (45) formed an orthogonal table.The results showed that the most critical factor which affected the adsorption was the initial concentration of Cd2+, followed by pH and adsorbent dosage. From the pespective of adsorption rate, among the 32 experimental groups the absorption rate of 25 were more than 60%,8 were more than 80% and the highest absorption rate was 82.80%, the maximum adsorption capacity was 13.60mg/g, which showed a good adsorption. Strictly controlled the experimental conditions to validate the results,8 sets of parallel experiments were designed and got the maximum average absorption rate was 82.42%, the maximum average adsorption capacity was 13.63mg/g. Under the principles of statistical analysis of orthogonal design this experiment was reasonable and feasible.In the second part, Cd2+ were biosorbed by original baker's yeast and baker's yeast pretreated by nitric acid respectively. The results show that baker's yeast pretreated by nitric acid decreased the amount of adsorption capacity of Cd2+ with the increase in concentration of nitric acid. Moreover, the maximum adsorption capacity of the original baker's yeast (dry weight) and baker's yeast (dry weight) pretreated by 0.5mol/L, 1.0mol/L, 1.5mol/L nitric acid are 8.68,3.45,2.80,2.15mg/g respectively, when pH is 6.0, biosorbent amount is 6g/L, adsorption time is 15min and concentration of Cd2+ is 50mg/L. Two biosorbents were characterized and analyzed by the method of FTIR, SEM and specific surface area measurement and the results indicated the causes of adsorption reduction. The results indicate that Cd2+ are adsorbed by functional groups such as-OH,-NH2,-PO43-,-COOH, etc., on the surface of baker's yeast. Nitric acids pretreatment resulted in oxidation and esterification among the functional groups occurred on the surface of baker's yeast. Furthermore, the adsorption ability of Cd2+ by pretreated baker's yeast is due to the agglutination among the cells of baker's yeast, reduction of specific surface area and the amount of exposed functional groups. The adsorption kinetic isotherms of baker's yeast and baker's yeast pretreated by nitric acid for Cd2+ and methylene blue were investigated, respectively. The results showed that the adsorption process fit well with monolayer adsorption.To analysis the adsorption kinetic isotherms of baker's yeast, baker's yeast treated by nitric acid for Cd2+ and methylene blue, wecould reach the conclusion that the adsorption process fit well with monolayer adsorption.In the third part, the baker's yeast was treated potassium permanganate under conditions of chemical modification. In order to determine the best conditions for modification of baker's yeast by the potassium permanganate, solution pH, adsorption time, Cd2+ concentration and modification of the initial amount of yeast influence on the adsorption of Cd2+. Adsorption results showed that when the concentration of potassium permanganate reached 0.05mol/L the modified yeast bread adsorption rate was the highest. When pH was at 4.0～7.0 there was no obvious effect on the adsorption capacity and adsorption rate. Adsorption rate was fast,30min could reach equilibrium. Under the conditions that the concentration of Cd2+ was higher than 100mg/L and the modified yeast amount was 6g/L, the adsorption was better. The adsorption rate could reach 97% twice of the original yrast under the same conditions. The adsorption kinetics study results showed that among one rate equation, second order rate equation, Elovich equation and two-constant rate equation description, the second rate equation fitted best. When the concentration of Cd2+ was at 20-200mg/L, the behavior of Cd2+ adsorption by modified yeast fit very well with Langmuir equation. Baker's yeast modified with potassium permanganate was characterized through infrared spectroscopy, scanning electron microscopy. We thought that the surface structure of the yeast changed when modified with potassium permanganate, the active sites of Cd2+ adsorption increased and the presence of MnO2 or Mn(Ⅱ;Ⅲ;Ⅳ) may play an important role in the adsorption of Cd2+. v... |
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