Study On Strengthening Fe(0) By Dissimilated Iron Reducing Bacteria To Remediate Cr(?) In Grondwater

Cr(?)has high toxicity and strong fluidity.It is easy to cause groundwater pollution in various areas,causing potential crisis with huge impact and seriously threatening human health.PRB,as a remediation technology for groundwater,has wide prospect for application.Fe(0)is the most widely used filler of PRB at home and abroad.However,PRB Will be blocked andlose efficacy latterly owing to the passivation of Fe(0),affecting the normal operation of the project.For the problems above,In this paper,we screened the dominant bacteriaof Fe(0)passivation called M.morganii subsp from 8 microbial strains.Taking M.morganii subsp+Fe(0)as research subject,We perform the study on the optimization of culture conditions,Cr(?)removal effect and mechanism.We optimize the sintering temperature and the proportion of iron filings,kaolin and straw to make ceramsite After the biofilm formation,the ceramsite verifies the effect of remediation of Cr(?)in groundwater through the column experiment and PRB simulation experiment under the optimized culture condition.Finally,the microstructure of the new ceramsite need to be observed and analyzedThe experimental results are as follows:(1)M.morganii subsp is selected as the target strain of this study.At the same time,M.morganii subsp +Fe(0)system is studied.The optimal carbon source is glucose(4 g / L),the optimal nitrogen source is yeast powder(6 g / L),and the p H value is 7.(2)The synergistic mechanism of M.morganii subsp + Fe(0)is studied.The results show that The removal rate of Cr(?)reached 82% after 72 hours of M.morganii subsp + Fe(0)synergistic reaction.M.Morganii subsp can fix Cr by itself,and the efficiency of collaborative processing is higher than that of single system.The specific process of dissimilated iron reducing bacteria to strengthen the removal of Cr(?)from water by Fe(0)includes the following reactions: zero valent iron chemical adsorption,zero valent iron direct chemical reduction,microbial adsorption,microbial direct reduction,microbial reduction of Fe(?)to Fe(II),coprecipitation of Fe(II)with Cr(?)and Cr(?)and biomineralization under the action of dissimilated iron reducing bacteria.(3)It is determined that the best proportion of ceramsite is 7:3:1 of iron filings,kaolin and straw,and the best sintering temperature is 1000? according to the hardness of ceramsite and solidification rate of Cr(?).Then we form biofilm for the ceramsite and find the best ratio of agar pellet and ceramsite is 2:10.what's more,the total nitrogen(TD)and total phosphorus(TP)emissions are all within the control range of the effective standard.(4)In the experiment of adsorption column,the adsorption capacity and penetration time of M.morganii subsp strengthening zero valent iron ceramsite system are much higher than that of zero valent iron ceramsite system without M.morganii subsp.The adsorption capacity is 108.9 mg / g at 0 d and 112.5 mg / g at 15 d.The penetration time is 10.7h at 0d and increases to 17 h at 15 d.In the simulation experiment of PRB,the Cr(?)concentration in the effluent of ceramsite with membrane is gradually decreased,and it is stable at 5mg / L in 7d,extending the service life and containing the Stable effluent.(5)Scanning electron microscopy(SEM)indicates that the ceramsite is composed of iron filings and kaolin,and has very developed pores,which provides space for the growth of M.morganii subsp.After the film,it can be seen that the microorganism covers the surface of ceramsite,and M.morganii subsp is long granular in appearance.High throughput sequencing of 16 Sr DNA shows that M.morganii subsp is successfully fixed on the coated ceramsite,and the community structure of the microorganism has little change with the passage of time.