Arsenic Redox Coupled To Fe(â…¢) Reduction By Shewanella Oneidensis MR-1

As is atoxic element,which is known as one of the most important pollutant,widely exists in the water, soil and organism.The redox of iron have important influence on arsenic removing and transforming in nature.The transformation of iron by microorganism is the key factors affecting of the behavior of As.At present,most research focused on microorganism separation in environment, the adsorption, coprecipitation and oxidation of As by iron oxide.But the research in interrelation between the reduction of iron and As oxidation-reduction in the environment participated by the microorganisms are very few.The experiment was conducted under laboratory conditions, we domesticate and pure culture S. oneidensis MR-1,and add As and Fe(Ⅲ) mixed microorganisms at the reaction system,studying the relationship between the Fe(Ⅲ) reduction by S. oneidensis MR-1 and coupling arsenic oxidation-reduction, to provide scientific basis for water pollution control of As.The main research contents and results are as follows:1. The results of microorganism cultivated showed that S. oneidensis MR-1 can grow well in low concentration of As,except its growth being restrained in a certain extent, this restrain was mainly embodied in the lag phase of the extension of bacterial strain growth curve,but had no significant effect on the exponential phase of growth.when the initial concentration of As(Ⅲ)(or As(Ⅴ)) is 1 mg·L-1,the initial growth of S. oneidensis MR-1 has a certain degree of inhibition,and As(Ⅲ) inhibitory effect on the growth was more evident than As(Ⅴ),but both their max growth was chose to the growth when didn’t add As.2. Adding different As concentrations:0,1,2,3,4 mg·L-1 in microorganisms culture system, we found the concentration of As could inhibit the dissimilatory reduction Fe (Ⅲ) by S. oneidensis MR-1. With the increase of As concentration,the more obvious inhibition,the less Fe(Ⅱ) generation.The concentration of As could inhibit S. oneidensis MR-1 grown, with the increase of As concentration. iron reduction rate reduced by adding As, As can inhibit dissimilatory iron reduction by restricting bacteria growth and activity.3. By adding the As and Fe(Ⅲ) mixed microorganisms culture at the same reaction system at the same time,we found that S. oneidensis MR-1 dissimilatory reduction Fe (Ⅲ) caused As(Ⅲ) oxidation,but couldn’t cause As(Ⅴ) reduction. Results showed that accompanied with Fe(Ⅲ) reduction, the oxidization of As(Ⅲ) to As(Ⅴ) occurred,and the processes had a high degree of consistency in time.In the control group,which did not add Fe(OH)3, no As (Ⅲ) oxidation or As(V) reduction happened, it indicated that without Fe(III) S. oneidensis MR-1 had no directly redox effect on As. So we concluded that the dissimilatory iron reduction result to As (Ⅲ) oxidation indirectly.However, As (Ⅲ) couldn’t be oxidized to As (Ⅴ) completely, during the culture time, As (Ⅲ) and As (V) always existed together in a dynamic balance. The oxidation of As (Ⅲ) on iron oxide surface of was accompanied with adsorption.4.A variety of different environmental factors on the influence of As(Ⅲ) oxidation was studied. As the concentration of As(Ⅲ) increased,the oxidation conversion was reduced,when the concentration of As(Ⅲ) was 1 mg·L-1,As (Ⅲ) have the highest oxidation rate. A suitable Fe(Ⅲ) content could promote As(Ⅲ) oxidization strongly, but high Fe(Ⅲ) concentration might lead to Fe(Ⅱ) concentration increasing, which may inhibited As(Ⅲ) oxidization. dissimilatory reduction Fe (Ⅲ) by S. oneidensis MR-1 was a microbial mediated enzymatic reduction process, microorganism had its optimal growth pH and temperature, and iron reduction also required the best reaction pH and temperature, the pH and temperature of environment could directly affect the dissimilatory Fe (Ⅲ) reduction process. Relative to the strong acidic or alkaline, weak alkaline environment was more conducive to As(Ⅲ) oxidization.As (Ⅲ) oxidation rate was highest when the pH was 8.0. Under anaerobic conditions, the best tempreture of As (Ⅲ) oxidization was 30 ℃, temperature not only influenced the enzymatic reaction of S. oneidensis MR-1 dissimilatory iron reduction,but also affected the growth and activity of S. oneidensis MR-land so on, which affect As(Ⅲ) oxidization.