| In view of the serious pollution of the surrounding soil caused by the leakage of oil products and the volatilization of oil and gas during the operation of gas stations,this paper puts forward a new idea and method for the in-situ restoration by microbial piles with highly efficient degradation bacteria of petroleum hydrocarbon,Meanwhile,the design,installation and restoration effects of microbial piles are discussed in detail.First of all,Four strains of dominant indigenous bacteria in oil-polluted soil were screened out,including Enterobacter cloacae strain JM11 2-1?11#?,Bacillus toyonensis strain yc-3 3-2?21#?,Enterobacter ludwigii strain ALK512 7-1?12#?and Bacillus toyonensis Strain fs-8 8-1?22#?.Secondly,the author conducted batch and optimization experiments on the optimizing working conditions and influencing factors?temperature,pH,salinity,inoculum?of microbial piles and determined the most suitable working conditions of the biological piles.Then,the petroleum hydrocarbon degradation bacterium immobilization methods and technology are compared.The selective adsorption method was used to fix the strengthen petroleum hydrocarbon degradation microorganisms onto the carrier ceramist made of piles and implanted for in situ repairing contaminated soil on the indoor experiment.Compared with conventional bio-remediation,the repair effect of microbial pile possesses the advantages and good repair effects.Finally,a small-scale pilot study was carried out on the restoration effect of microbial piles to determine the best vertical and horizontal restoration range?oil circle range?,restoration effect and biological pile placement method,which provide the theoretical and technical reference for further field applications.The results show that the microbe pile technology has the advantages of monitoring and controlling the growth state of the strain any time,flexible,convenient,little disturbance to the repair site,no secondary pollution and simple treatment conditions,compared with the ordinary in situ bio-remediation technology.The main research contents are as follows:?1?the soil source of oil-degrading bacteria was obtained from the oil-polluted soil near the gas station of gongjiaping east road,qilihe district,lanzhou city,China?sampling point 1?and the oil-polluted soil near the gas station of feijiaying oil and gas station,anning district,lanzhou city,China?sampling point 2?.From the sequencing results,it was found that 11#and 12#were come from the same source soil,that is,sampling point 1.21#and 22#are soil samples from the same bacterial source,namely sampling point 2.The results of the oil ring diameters and H2O2 enzyme determination were as follows:?1?within 20 days,the rate of oil hydrocarbon degradation for 12#strain was above 40%,the oil ring diameters of 12#strain were larger than that of the strain screened from the same bacterial source soil?1.3±0.08?and the H2O2 enzyme determination results were positive.The degradation rate of 21#strain within 20 days was range from 30%to 40%.there was no connection between the degradation rate of petroleum hydrocarbon of 21#strain and the height of emulsifying layer,the diameter of oil ring,the results of H2O2 enzyme tests.The degradation rate of petroleum hydrocarbon of strain 11#was less than 15%within 20days,indicating that although the strain 11#could survive or grow in the environment with only petroleum hydrocarbon as carbon source,its degradation effect on petroleum hydrocarbon was poor,and this strain was resistant to petroleum hydrocarbon.?2?Optimized experimental study on the factors affecting the degradation of petroleum hydrocarbons:Focus on the 12#strain and 22#strains with degradation rate higher than 40%,the optimized experimental results of pH,salinity,temperature and inoculum were as follows.pH value:When the background value is 0.02,the pH value has a great influence on the 12#strain,that is the 12#strain can only grow well at pH=67 and the growth of the 12#strain has a certain inhibitory effect in other pH value.the pH value has a small effect on 22#,that is 22 strain has a good growth in the range of pH=59 and it can be survive in a larger pH range.Salinity:At the case of a background value of 0.02,the growth status of the two strains of 12#and 22#have not much different and the OD values increase or decrease significantly.The results indicate both strains have certain salt tolerance in the range of 0.5%to 4%salinity.Temperature:When the background value is 0.02,the suitable growth temperature range of the 12#strain is larger than that of the 22#strain,that is 12#strain can grow well in the interval of 20°C to 45°C and The best growth condition was 30oC.The22#strain can only grow better in the interval of 30oCto 45oC and the growth condition is best at 30°C.Inoculation amount:When the background value is 0.027,the inoculum amount has little effect on the two strains,and the trend is relatively stable.?3?The inorganic carrier ceramsite and activated carbon were selected as the adsorption carrier for research.The materials were pulverized to a certain particle size?over 80 mesh sieve?before use.Determine the best fixed condition:download the volume at 10mL at 30oC,the inoculation amount is 20%,and the curing time is 15h,160rpm.The indoor degradation experiments were carried out on the selected high-efficiency petroleum-degrading bacteria,and the repairing effects of microbial piles and common in-situ repair techniques were compared.?1?The trend of soil petroleum hydrocarbon degradation rate is:microbial pile>general in situ repair>natural restoration.?2?Ordinary in situ restoration of the selection of dominant indigenous bacteria has a certain repair effect,but the degradation rate of microbial piles is obviously better than natural repair,which is better than ordinary in situ repair.At the same time,the supplement of N and P nutrition greatly promoted the degradation of soil petroleum pollutants by microorganisms.?3?The results of the second week of in situ repair showed that the degradation rate suddenly decreased.The reason may be that the nutrients in the soil are insufficient for the growth of the selected bacteria and the soil autogenous microorganisms,or the competition of the soil primary bacteria and the selected dominant bacteria.?4?After 16 weeks of repair,the natural and normal in situ repair degradation rates are slowly different.?5?The degradation rate of petroleum hydrocarbons was higher at one week after the sixth week of repair,and the degradation rate was basically stable after 14weeks.After 14weeks,the content of petroleum hydrocarbons in the soil did not change much.When the bioremediation entered the 15th week,the repair entered the lag phase.?6?During the whole repair cycle,although the microbial pile repair effect was slowly stabilized after 15 weeks and the degradation rate was not as good as the previous stage,the overall effect was better than the ordinary in situ repair.After 16 weeks,the degradation rate was still 15%to 30%.?4?Determination of soil permeability and oil degradation rate at different depths;installation of microbial piles:?1?With the increase of time,the penetration effect of oil exposed to the environment in the soil is gradually strengthened,and the oil in the soil is not cleaned.In the case,the longer the time,the higher the oil content in the soil;the possibility of degradation is very small after the oil remained in the environment.After a few weeks,there is still a large amount of oil pollutants;sandy soils have a large permeability and are easily retained by viscous soil.Under the influence of soil profile during the downward infiltration of crude oil,small particles of soil have a greater adsorption and interception effect on petroleum.From the analysis data,more than 80%of the crude oil is trapped above 90 cm in the surface layer.?2?The highest degradation rate of oil was observed in the depth of 30-60cm.It may be caused by the microbial aggregation at 30cm to 60cm,indicating that various conditions are suitable for microbial growth.?3?The microbial pile installation position was determined by the study of the sampling point and the depth about 30-60cm was defined.Through the punching method,the diameter of the hole is decided as follows:the pile is freely inserted and rotated;the pile is not so loose.The diameter of the oil drain ring should be comprehensively considered during determining the installation density of the micro-pile pile-pile spacing. |
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