The Effect Of Microbial Activities On The Mobility Of Arsenic In The Sediment From An Arsenic Contaminated Lake

Flocculation-precipitation technique has been applied successfully in arsenic contamination treatment in some surface water bodies. But so far there are few data to reveal the mobility and transformation of arsenic after it is precipitated into the sediment by flocculants. Will the arsenic in the sediment leach out and cause secondary pollution? If yes, how and under what conditions will it release? Further researches are needed to answer these questions. Many studies made by other researchers show that microorganisms play a very important role in the absorption/desorption processes of arsenic in the sediment. This study focused on the effect of indigenous microbial activities on the mobility and transformation of arsenic in the sediment after the water with high arsenic concentration wad treated by a ferric flocculant. Based on the simulation experiments in the laboratory, the study examined respectively the effect of microbial activities on the release of arsenic under the following condition combinations: aerobic/anaerobic, and adding carbon/adding no carbon. The study also detected the changes of DO, pH, TOC, Fe and Mn in the processes to explain how the microbial activities effect on the mobility and transfer of arsenic. The following conclusions are drawn by the study:1. Whether under aerobic or anaerobic conditions, microbial activities play a more evident effect than nonbiological activities, which tells us that microorganism is the dominant factor in the release process of arsenic from ferric oxide-hydroxide.2. Under anaerobic and near neutral conditions with adding carbon, a change of rising first and falling later of trivalent arsenic concentration in the solution was observed. While under aerobic condition, because the double bond of arsenic to oxygen formed by arsenic and oxygen accelerates the dissociation of arsenate and increases the pH of the solution, the release of arsenate was enhanced.3. The experiments to add soluble organic carbon into the solution display that organic carbon can enhance both microbial and nonbiological activities to accelerate arsenic release.4. Under the influence of microbial activities, iron and manganese release periodically with arsenic release, which reveals that arsenic release is not only influenced by microbial activities, but also influenced by iron and manganese which have been dissimilated by microbial activities.5. Arsenic release caused by microbial activities is not only more intensive but also more longer than that caused by nonbiological activities, while arsenic release caused by nonbiological activities is faster.