| In recent years,with the progress of microbial technology and the pursuit of green and environmental arsenic removal technology,people began to pay more and more attention to the application of microorganisms in the remediation and treatment of arsenic pollution in water.Among them,microbial oxidation is a promising method,which can be used in combination with adsorption and removal technology without adding chemicals or producing toxic by-products.Most of the existing researches used engineering model bacteria or purified bacteria and enrichment culture extracted from polluted water to oxidize As(III).These bacteria are easily affected by environmental changes and can not be well applied to in-situ remediation of groundwater.However,in the natural groundwater environment,there are relatively few studies on the removal effect of arsenic when a variety of microorganisms coexist.At the same time,most of the groundwater belongs to the poor nutrition environment with lack of organic components,and the activity of bacteria is not strong.It is widely used in groundwater remediation by adding organic substances to promote microbial activity.Based on this,this study explored the method of reducing arsenic toxicity by enhancing the activity of indigenous microorganisms in groundwater by fermenting pine bark and peanut shell.The results of static batch experiments show that the coupling of chemical oxidation and biological oxidation process in groundwater can promote As(Ⅲ)to As(Ⅴ),thus reducing the toxicity of arsenic.In the early stage of the reaction,chemical oxidation is the main way,and the oxidation speed is fast,which results in the rapid decrease of As(Ⅲ)concentration;in the later stage,biological oxidation is the main way,and the decrease of As(Ⅲ)concentration is slow,but the reaction is more lasting.The concentration of arsenic in different forms of three experimental systems(Adding fermented pine bark,adding fermented peanut shell and control group without organic substrate)was determined.It was found that the concentration of As(Ⅲ)in the system with peanut shell added at 1 day of reaction had decreased to 3.50% of the initial value;On the 10 th day,As(Ⅲ)concentration in pine bark group and peanut shell group decreased to 0.40% and 0.47% of the initial value respectively;However,the control group did not decrease to less than 1% of the initial value until the 20 th day.Indicate the removal efficiency of As(Ⅲ)can be improved by adding organic matrix,and the effect of peanut shell is better than that of pine bark.Through the chemical environment and microbiological environment characterization of the experimental system,we found that the main mechanism of organic matrix promoting As(Ⅲ)detoxification is as follows: a)releasing organic matter,resulting in the increase of Eh value(i.e.the increase of oxidation),thus promoting the chemical oxidation reaction of As(Ⅲ);b)providing organic carbon source for the growth of microorganisms,promoting the growth of arsenic metabolizing bacteria,arsenic oxidizing bacteria and denitrifying bacteria,so as to strengthen the microbial oxidation of As(Ⅲ).In addition,the adsorption of arsenic by organic matrix also reduced the concentration of arsenic to a certain extent.The results reveal a new idea of using agricultural waste to treat arsenic pollution in groundwater,which is to use agricultural waste organic matrix as the reaction filler of permeable reaction barrier(PRB)to continuously provide nutrition for indigenous microbial communities in groundwater through organic matrix,so as to strengthen the process of microbial remediation of shallow arsenic polluted groundwater,which has a certain scientific value for in-situ green remediation of arsenic contaminated groundwater. |
