| Due to the use of oil-based drilling fluids,a large amount of oil-bearing cuttings will be formed during shale gas extraction.After the oily substances are recycled through pyrolysis,a large amount of residues will still be produced.Many industry and local standards suggest that this type of pyrolysis residue can be used to pave roads on well sites or fill potholes in mining areas.In this paper,the following researches have been carried out in response to the above situation,including the basic properties and pollution characteristics of oil-bearing cuttings pyrolysis residues(OCPRs);Adsorption/desorption characteristics of petroleum hydrocarbons in soil based on batch equilibrium test;Vertical migration characteristics of petroleum hydrocarbons in soil based on soil column leaching experiment;Dynamic response of soil microbial ecological effects to petroleum hydrocarbons based on high-throughput sequencing technology.The main research conclusions are as follows:(1)The characteristic pollutant of the OCPRs is petroleum hydrocarbon,and the petroleum hydrocarbon content of the OCPRs is 7643.16±169.67 mg/kg.Among them,C10～C16 accounted for 6.525%,C17～C21 accounted for 41.935%,and C22～C34accounted for 51.54%.The maximum leaching ratio of heavy metals in the OCPRs is only 0.89%.The maximum ecological risk index of single heavy metal was only 16.05,and the comprehensive ecological risk index of multi pollution factors was 46.26,which was in a low risk level.(2)The soil has a strong adsorption capacity for petroleum hydrocarbons and a low desorption rate.The soil-water partition coefficient(K_d)under the adsorption equilibrium state is 51.86 m L/g.The adsorption/desorption kinetics process conforms to the pseudo-second-order kinetic model.The saturated adsorption capacity derived from this model is 125.82 mg/kg,and the equilibrium desorption capacity is 102.04 mg/kg.The adsorption/desorption rate is mainly controlled by the chemical adsorption mechanism.The Freundlich model has the best fitting effect on the adsorption isotherms of petroleum hydrocarbons in soil.It is nonlinear adsorption,which was affected by the combined effects of partition and surface adsorption.The linear model has the best fitting effect of desorption isotherms,and the desorption process is mainly controlled by distribution.(3)The soil column leaching experiment is used to simulate the vertical migration characteristics of petroleum hydrocarbons in the soil when the OCPRs was used as a covering soil material.Four leaching gradients were set:457 ml,1371 ml,2742 ml and5484 m L,the cumulative time of the experiment was 5,15,30 and 60 days,respectively to simulate the leaching situation of 1,3,6 and 12 months.In the soil column leaching experiment,with the increase of the leaching amount,the petroleum hydrocarbon content of the covering layer mainly composed of OCPRs decreased from 18662.51mg/kg to 18400.13±149.07 mg/kg.There was no significant difference in the content and proportion of C10～C16 and C17～C21 components in each leaching period(P>0.05).The content and proportion of C22～C34 components were significantly different(P<0.05),that is,the content and proportion of C22～C34 components decreased with the increase of leaching amount,and C22～C34 components were more likely to migrate downward.Only a small amount of petroleum hydrocarbons entered the soil layer,mainly C22～C34,and the content of C22～C34 in the soil layer of each leaching cycle was extremely different(P<0.01).(4)After leaching,the relative abundances of Proteobacteria,Patescibacteria,and Chloroflexi in the covering soil group increased significantly,with an increase rate greater than 5%,and the relative abundance of Firmicutes decreased the most,with a decrease rate of 52.39%.There are 55 petroleum hydrocarbon-tolerant genera such as Acetobacter in the overburden soil;and 31 genera such as Caenimonas that may be susceptible to the toxic stress of petroleum hydrocarbons in the background soil.The microbial community characteristics of the overburden group showed a very significant linear positive correlation with the leaching amount and the content of C10～C34(P<0.01),and there was no significant linear correlation with other environmental factors(soil depth,water content,p H value,water content,soil organic carbon content,total nitrogen and total phosphorus)(P>0.05).In terms of microbial function,biodegradation and metabolism of exogenous substances are closely related to microbial degradation of petroleum hydrocarbons.The three-stage pathways with high abundance in the overburden group are benzoate degradation(0.73%),aminobenzoate degradation(0.63%),and chloroalkane and chloroalkene degradation(0.38%).In addition to ethylbenzene degradation and drug metabolism(other enzymes),the abundance of the pathway level 3 of xenobiotics biodegradation and metabolism increases with the increase of leaching volume,and they are likely to participate in the biological metabolism of petroleum hydrocarbons. |
PDF Full Text Request