| Seasonal frozen soil exists in most parts of northern China,and the oil industry in these areas is developed,which inevitably produces oil pollution.BTEX is one of the components of petroleum pollution,which is harmful to human body due to its difficult degradation and toxicity.Freezing and thawing,as a typical physical process in seasonal frozen soil areas,affects the occurrence of BTEX in soil and the process of adsorption analysis and microbial community change in soil,which determines its pollution hazard and natural degradation process to some extent.Therefore,it is important to study the distribution and transformation of BTEX in soil under freezing and thawing conditions.In this paper,black calcium soil distributed in Daqing area was used as the tested soil.The artificial soil temperature method was used to alternately freeze-thaw the mixture of test soil and BTEX solution under different temperature conditions,and the temperature was controlled at 5 °C(Unfrozen group),5 °C ~-5 °C(freeze-thawing group),5 °C ~-10 °C(freeze-thawing group),5 °C ~-10 °C(freeze-thawing group),time period is60 days,the freezing period of the freeze-thaw group is 21 to 40 days.,and the freezing and thawing time was 12 h.BTEX content in the solution and the soil were determined,and BTEX solution control group without adding the soil sample under the same conditions was set.The distribution characteristics of benzene series solution and soil were correlated with soil physicochemical properties for statistical analysis.At the same time,DGGE method was used to analyze the changes of microbial community,and the mechanism and microbial community characteristics of soil benzene-based soils were discussed.For the experimental group of BTEX and soil mixed solution,the content of BTEX in the solution and soil under continuous freezing and thawing conditions showed a continuous downward trend;the content of BTEX in the solution under different freezing and thawing conditions continued to decrease.The content of BTEX in soil decreased first and then increased.The total content of BTEX in solution and soil showed a continuous downward trend.The lower the freezing and thawing temperature,the higher the content of BTEX in solution and soil.The BTEX content in the BTEX solution control group under the same temperature condition is lower than the sum of the BTEX content in the solution and soil in the experimental group.Analysis of the causes of changes in benzene content,the SEM results show that the freeze-thaw changes promote the uniformity of soil aggregate size.The lower the freeze-thaw temperature,the better the uniformity,and the freezing period will reduce the degree of soil cementation.X-ray diffraction analysis of mineral changes reveals that the freeze-thaw change will cause clay content.The specific surface area indicates that the decrease in temperature leads to an increase in soil adsorption capacity.The better the uniformity of soil aggregates,the higher the degree of cementation,the higher the clay content and the stronger the analytical ability of adsorption,the greater the distribution concentration of benzene series in the soil,thus reducing the volatilization degree,increased BTEX content in freeze-thaw soil and mixed systems.The behavior of benzene in soil also affects microbes.The microbial community structure changes in freeze-thaw systems are studied by DGGE technology.Under the condition of no-freezing and thawing,the microbial community structure changed due to the decrease of the concentration of BTEX,and the microbial abundance increased gradually.Under freezing and thawing conditions,the microbial community changed with the decrease of BTEX content and freeze-thaw temperature,and the microbial uniformity increased gradually under the influence of different freezing and thawing temperature and BTEX concentration.With the decrease of freezing and thawing temperature,the microbial community no longer changes,and the decrease of freezing and thawing temperature and the increase of BTEX content have simple effects on microbial community structure changes. |
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