Experimental Study On Remediation Of Petroleum Polluted Shallow Groundwater By Biological Permeable Reactive Barrier

With the development of industrialization,the oil industry occupies an important economic position in various countries,but once the oil pollutes groundwater,it will cause serious environmental problems.In order to explore the potential remediation technology of petroleum hydrocarbon contaminated groundwater,the crude oil degrading bacteria immobilized on activated carbon were used as the active reaction filling medium of biological Permeable Reactive Barrier（PRB）.The adsorption and degradation characteristics of free bacteria,activated carbon and activated carbon immobilized bacteria were studied through indoor batch simulation experiments,and the adsorption and degradation characteristics of petroleum contaminated groundwater were studied through column experiment and tank experiment.The treatment effect of PRB on petroleum contaminated groundwater by solid slow-release oxygen materials and micro nano bubbles was studied.The results showed that:（1）when the ratio of peanut cake powder and dipotassium hydrogen phosphate was 5:1,the dosage of compound bacteria solution（HL:L4=1:1）was 8m L,the p H value was 7,and the crude oil concentration was1000mg·L^-1,the oil reduction rate of compound bacteria group on crude oil was44.81%;when the dosage of bacteria solution was 12m L,the p H value was 7,and the diesel oil concentration was 500mg·L^-1,the oil reduction rate of compound bacteria group on diesel oil was 59.10%.The results show that coconut shell activated carbon is better than fruit shell and coal based activated carbon in adsorbing oil.The adsorption equilibrium of crude oil and diesel oil is 679.01mg·g^-1and 560.58mg·g^-1in180min and 240min,respectively.The adsorption kinetics and isotherm aer fitted to pseudo second order adsorption kinetics model and Langmuir model,respectively.When the dosage of coconut shell activated carbon is 0.1g,the p H of groundwater is 7,and the reaction temperature is 10℃,the adsorption capacity of coconut shell activated carbon for crude oil and diesel oil is the largest,which are728.84mg·g^-1and 640.90mg·g^-1,respectively.（2）The results showed that the proportion of immobilized Pseudomonas was53.42%～66.93%,and the proportion of Enterobacteriaceae was 33.07%～46.58%by high-throughput sequencing;and the removal rate of crude oil and diesel oil by immobilized activated carbon bacteria was higher than that of single activated carbon and free bacteria.The removal rates of crude oil and diesel oil in seven days were83.63%and 75.20%,respectively,C9-C17 had obvious degradation effect,which could effectively degrade benzene,dibenzothiophene and other components.Activated carbon,free bacteria and activated carbon immobilized bacteria could remove 31.08%,44.98%,63.84%n-alkanes and 68.37%,48.81%,84.65%aromatics in crude oil,and 12.72%,45.63%,25.76%n-alkanes and 64.38%,58.74%,64.33%aromatics in diesel oil,respectively.（3）Solid sustained-release oxygen microspheres were prepared with 4%sodium alginate,4%Ca Cl₂and 1:4 ratio of calcium peroxide and potassium dihydrogen phosphate.The maximum oxygen release was 14.62 mg·L^-1.The results show that the suspension time of micro and nano bubbles is 168s,the particle size range of micro and nano bubbles is 200～600 nm in stable state,and the dissolved oxygen can be maintained at about 10 mg·L^-1in continuous operation.（4）The results showed that the overall removal rate of petroleum hydrocarbons by biological PRB experimental device was as follows:micro nano bubble column Z3>solid slow-release oxygen column Z4>oxygen free column Z5>sterile activated carbon column Z2.Z2～Z5 columns had obvious removal effect on C₉-C₁₈,and Z2～Z5 columns removed 74.17%,77.48%,76.27%and 74%n-alkanes respectively.The p H value fluctuated in the neutral range within 45 days of operation;Pseudomonas accounted for a small proportion after 45 days of operation,and Enterobacteriaceae had a competitive advantage in the case of sufficient oxygen.A large number of long rod-shaped bacteria were observed on the surface of Z3 and Z4columns by electron microscopy,which played a good role in degradation of crude oil.The results showed that the microbial column had a good removal effect on C₁₂-C₂₇.The crude oil removal rates of C2～C4 tanks are 43.99%,81.70%,79.39%and66.99%respectively,40.87%,71.44%,66.48%and 43.65%of n-alkanes were removed from C2～C4 tanks respectively.