Effect Of Iron-Reducing Bacteria On The Interaction Between Soil Colloid And Arsenic

Arsenic is a toxic element that can be effectively adsorbed by soil colloids.However,the reduction of iron-containing minerals in soil colloids by iron-reducing bacteria causes the release of arsenic.As a typical anaerobic environment,the effect of iron reduction on arsenic removing and transforming in paddy soil has attracted more and more attention.At present,relevant research is focused on the isolation of iron-reduction bacteria,transformation of arsenic and iron species involved in iron-reducing bacteria,and the adsorption of arsenic by iron oxides.However,the changes of microbial community in paddy soil under the influence of AMD with high arsenic concentration,the effects of iron-reducing bacteria on changes in colloidal properties and interactions between soil colloids and arsenic,the effects of iron-reducing bacteria on the release of arsenic and iron under different conditions,are still poorly understood.Based on this,high-throughput sequencing technology was used to study the distribution of iron-reducing bacteria in paddy soil and the change of microbial community structure and diversity of paddy soil irrigated by high arsenic AMD.Samples of soil colloid were prepared into suspension and then incubated anaerobically at a constant temperature for exploration of effects of iron-reducing bacteria on soil colloidal properties and arsenic adsorption.The arsenic-bearing colloid was used to investigate the release of iron and arsenic under the action of indigenous microorganisms and GS-15 in acidic and neutral conditions.The results were as follows.?1?The soil in the sewage irrigation area was affected by the AMD wastewater,which caused the microbial diversity index decreased significantly.There was a significant positive correlation between OUT number and soil pH,significant negative correlation between OUT,Chao1 and ACE index and As content of soil.The microbial community structure changed significantly under the influence of AMD,and high values could be observed for the abundance of acidophilic bacteria and Fe and S metabolic bacteria in sewage irrigation area.A total of 19 species of iron-reducing bacteria were found in paddy soils,including Geobacter,Anaeromyxobacter and Desulfosporosinus,etc.?2?Anaerobic culture experiments show that iron-reducing bacteria GS-15 and indigenous microorganisms can make the colloid particle size became smaller,the specific surface area of colloid increased,and the content of iron decreased.The zeta potential of the colloidal suspension decreased under the action of GS-15 bacteria,while the zeta potential increased under the action of indigenous microorganisms,and the surface morphology of soil colloid did not change obviously.?3?The pH of colloidal suspension first decreased and then increased when GS-15 involved,while the pH increased significantly under the influence of indigenous microorganisms.Both GS-15 and indigenous microorganisms can significantly reduce Eh in soil colloidal suspensions,and the reduction rate of Fe was significantly increased.In the early stage of anaerobic culture,the maximum adsorption capacity of soil colloid on As under the action of GS-15 and indigenous microorganisms was lower than of the control experiment.The adsorption capacity of soil colloid for arsenic decreased with the extending of incubation time in control experiments,whie the adsorption capacity for arsenic increased under the action of bacteria,and there was no significant difference between the treatments after 21 days of incubation.?4?When the initial pH was 3,the pH and Eh of the arsenic-loaded colloidal suspensions did not change significantly,and there wsa no significant difference in Fe?II?concentration.When the initial pH was 7,pH increased and Eh decreased with the extending of incubation time.Compared with the control,the concentration of Fe?II?increased by 0.62³2.26 mg.L^-1 under the action of indigenous microorganisms.The concentration of Fe?II?under the action of GS-15 increased by 2.57²3.21 mg.L^-1after 21 days of incubation.?5?The arsenic-bearing soil colloid with initial pH=3 was mainly released by As?V?,while the initial pH=7 system was mainly released by As?III?.Under the neutral conditions,the release of As increased by 0.01².04 mg.L^-1 under the action of indigenous microorganisms,andt the release of As also increased in the presence of GS-15 with the extending of incubation time.Neutral conditions showed a significant positive correlation between Fe?II?and total arsenic in soil colloidal suspension.