Biostimulation Method For Oily Soil Remediation And Study On Driving Mechanism Of Key Nutrient Transformation

The large input of petroleum hydrocarbons into the soil,which causes the relative shortage of soil nitrogen sources,is the main reason for the low soil microbial activity and poor metabolic capacity for petroleum hydrocarbons.Therefore,adding external nitrogen sources to the soil for biological stimulation can promote the degradation of petroleum hydrocarbons.Aiming at the problems of lack of nitrogen sources and low microbial activity in petroleum-contaminated soils in northern Shaanxi,the thesis used laboratory simulation remediation and applied different forms of nitrogen sources to petroleum-contaminated yellow soil to study the best suitable for remediation of contaminated soils in northern Shaanxi.Nitrogen source and optimal carbon-to-nitrogen ratio,and the soil microbial changes and nitrogen migration characteristics caused by nitrogen source application were studied.The following conclusions are drawn through research:?1?Apply six different types of nitrogen,such as urea,NH₄Cl?NH₄NO₃?KNO₃?NaNO₃,organic fertilizer,to newly contaminated soil?contaminated for 7 days?and old contaminated soil?contaminated for more than 5 years?to set soil C/N The ratios were100/5,100/10,100/15,100/50,and 100/200,and biostimulation studies were conducted under two different humidity conditions?5%natural humidity and 15%humidity?.The results show that for the yellow cotton soil contaminated by oil in northern Shaanxi,KNO₃ is used as the nitrogen source for the best repair effect.When the C/N ratio is lower than 100/50,for newly contaminated soil,the soil moisture is 15%.When the KNO₃ applied to the soil makes the soil C/N ratio 100/15,the removal rate of total petroleum hydrocarbons is 26.81%;for old contaminated soil,when the soil moisture is15%,KNO₃ is applied to the soil to make the soil C/N ratio 100/5,the removal rate of petroleum hydrocarbon is 17.33%.?2?When KNO₃ is applied to the soil so that the C/N ratio is as high as 100/200,the removal rate of petroleum hydrocarbons in newly contaminated soil and old contaminated soil can reach 51.02%and 40.28%,respectively,under the condition of15%humidity,indicating high carbon The nitrogen ratio is more conducive to the efficient removal of petroleum hydrocarbons.However,the high content of KNO₃ in the soil makes the soil compact,and the simultaneous addition of sterilized organic fertilizer to the soil can alleviate the soil compaction and increase the removal rate of petroleum hydrocarbons in the soil to 57.69%and 43.79%.?3?Under natural humidity,the Shannon index,Ace and Chao1 index values of the newly contaminated soil are the largest in the measured soil samples,which are 7.16,10849 and 8954 respectively.Adding KNO₃ to the soil makes the C/N 100/200 and The soils treated with organic fertilizer at the same time had the smallest Shannon index,Ace and Chao1 indexes,which were 4.75,9076 and 6861,respectively.Adding KNO₃to the C/N 100/10 and C/N 100/200 treated soils,the Shannon index,Ace and Chao1index values decreased slightly,being 6.68,10606,8789 and 7.07,10366,8701,respectively.The diversity index of old contaminated soil has a similar trend.Adding KNO₃ to the soil to make C/N 100/200 and adding organic fertilizer at the same time,the values of Shannon index,Ace and Chao1 index were the smallest,respectively 5.21,9824 and7785.?4?The predominant bacterial phyla in newly contaminated soil includes Proteobacteria?25.21%?,Actinobacteria?23.40%?,Acidobacteria?16.94%?and Planctomycetes?9.08%?.Adding KNO₃ for biostimulation remediation significantly increased the relative abundance of Actinobacteria in newly contaminated and old contaminated soil to 36.20%?40.0%.Adding KNO₃ for biostimulation and remediation treatment increased the abundance of Firmicutes in newly polluted and old contaminated soil to 0.8%?5.0%,becoming the dominant bacterial phylum in soil.The relative abundance of thick-walled bacteria in newly contaminated soil does not change significantly.?5?Nocardioides?Rhodococcus?Bacillus?and Pseudomonas are bacteria that have the ability to degrade petroleum hydrocarbons in petroleum contaminated soil in northern Shaanxi.In the repaired soil,the number of sequencing bands of these genus bacteria was 694,16,141,and 191,respectively;adding KNO₃ to the soil for biostimulation repairing treatment made the number of sequencing bands of these genus bacteria become 4390,2535,308,357.?6?A preliminary study on the distribution of carbon and nitrogen in soil using stable isotope techniques.The relative abundance of?¹³C of the soil repaired by exogenous nitrogen biostimulation is lower than that of unrepaired soil,indicating that the residual petroleum hydrocarbon component has a significantly reduced polarity and relative molecular weight.It is a small molecular weight component.When the amount of KNO₃ added increased by 20 times?the C/N ratio increased from 100/10 to 100/200?,the degradation rate of petroleum hydrocarbons increased significantly.In this process,the macromolecules in petroleum hydrocarbons may be degraded into small molecular organics.The relative molecular mass decreases,so the¹³C value also decreases.The more exogenous nitrogen added to the soil,the greater the d¹⁵N value.When the amount of KNO₃ added increased by 20 times,the activity of the microorganisms increased,and the nitrification and denitrification increased,which caused the d¹⁵N value to increase.