Study On The Behavior Characteristics Of Petroleum Containment In The Soil And Rhizoremediation

Arid and semi-arid area of China is rich in crude petroleum. The crude petroleum production andpetroleum processing capacity are on the rise year by year. However, because of the mining technology,management, accident and other reasons of mining crude oil, transportation and processing, it results in alarge number of petroleum and its products leaking to the soil and water environment. It caused seriouspollution to the fragile natural ecological environment. Because the climate of arid and semi-arid area is notsuitable for the microorganism, the bioremediation technology for soil pollution is very difficult toguarantee long-term effects. It needs to joint plants to achieve good effect.In this study, the research methods combine in-situ testing and physical simulation test, the process ofphytoremediation for arid and semi-arid areas soil petroleum pollution are the main study objectives. Thekinetic processes of volatilation, adsorption, desorption, migration and degradation petroleum form the soilwere observed by experiments. The transportation and degradation characteristics of petroleumcontaminants were monitored in the soil-plant system. The degradation rate of total petroleum hydrocarbon,plant rhizosphere secretions, soil enzyme activity in the soil, plant ecological indicators, soil physicalchemical indicators, soil and plant nitrogen isotopes were monitored. The repairing effects of differentplants were studied. It was used gas chromatography-mass chromatography technology to revealphytoremediation rhizosphere secretions distribution characteristics. The microbial degradation ofpetroleum components and the process, rhizosphere repair mechanism were revealed. The methods ofphytoremediation for soil petroleum pollution were built and provided a scientific basis for the soilpetroleum pollution bioremediation.The main conclusions are as following:1. The petroleum pollutants behavioral characteristics in the soil and soil-plant system, the mainbehavior characteristics includes volatilation, adsorption, desorption, migration and microbial degradation.①the volatile behavior of petroleum pollutants in silty loam can use Elovich dynamics equation m=A+Blntor first-order kinetics equation m=m0e-ktto describe. High ambient temperature, high contents of coarsegrains and high petroleum concentration in the spetroleum were beneficial to petroleum componentsvolatilation from the spetroleum.②The adsorption behavior of petroleum pollutants in silty loam can useLagrange second-order dynamic equation dqt/dt=k2(qe-qt)2to describe. The equilibrium adsorption ofpetroleum pollutants in silt loam were mainly affected by the soil clay content. The equilibrium adsorptionis large of fine grain content of soil. The adsorption process of petroleum onto soil is exotherme and theadsorption reaction is a spontaneous process. The amounts of petroleum adsorption gradually slow down with the temperature increasing. The confusion degree was reduced in the adsorption process.③Thedesorption behavior of petroleum pollutants in silty loam can use the4-parameter biphasic first-orderkinetic to describe. The conclusion showed that fast constant rate of desorption was more than two ordersfor slow constant rate. Under the25°C, the silty loam in Weihe terrace，silty loam in loess tableland andsilty loam in northern Loess Plateau desorption rate for petroleum were43.08%,52.54%and34.60%respectively.④The natural degradation behavior of petroleum pollutants in silty loam can use thefirst-order kinetics equation Ct=C0exp（-kt）to describe. Under the different soil and different petroleumconcentration, the natural degradation rate constant and half life is different. In the silty loam in Weiheterrace3000mg/kg petroleum concentration, the maximum degradation rate constant is1.689d-1, theminimum half-life is410days. In the silty loam in loess tableland10000mg/kg petroleum, the minimumdegradation rate constant is0.984×10-3d-1, the maximum half-life is704days.⑤The migration Behavioralcharacteristic of petroleum contaminants in the soil-plant system: the petroleum contaminants all migratedbelow the90cm soil in the silty loam in Weihe terrace under three concentrations. The oil pollutants werenot penetrate80cm soil in the silty loam in northern Loess Plateau and silty loam in loess tableland under3000mg/kg concentration.The oil pollutants content of each layers in silty loam in northern Loess Plateauplanted with Trifolium repens Linn was more than ryegrass.⑥The TPH degradation rate of Trifoliumrepens Linn soil was highest among four test phytoremediation plant. The order degradation rate of theremaining three plants as follows Agropyron cristatum (L.), Gaertn, Lolium perenne L. andCynodondactylon Linn.Pers. The TPH degradation rate of soil in phytoremediation conditions was higherthan control for35-48%.2、Study the plant rhizosphere secretions under the petroleum pollutio: The organic acid, total sugarand amino acid content in the rhizosphere soil of Trifolium repens Linn under3000mg/kg petroleumpollution were higher than the7000mg/kg and10000mg/kg petroleum pollution.. The contents of plantrhizosphere secretions under the above three pollution concentrations was more than the control.It wasindicated that the low petroleum concentration can promote producing the small molecule organic acid,total sugar and amino acid. It explains that the plants can make positive reaction under petroleum stress.3、Rhizosphere petroleum degradation bacteria screening and degradation characteristics study: thestrains were isolated from the petroleum-contaminated soil which collected from Trifolium repens Linnrhizosphere for petroleum containment soil and with crude petroleum as sole carbon source.10highefficient petroleum-degrading strains were obtained by enriching, domestication and purification. The bestmicroflora was composed SL-1, SL-3, SL-7and SL-9by rescreening and orthogonal experiments. The four strains had the function of degradation straight chain alkane. The two strains had the function ofdegradation cycloalkanes. The strains were identified as Planomicrobium chinense (T), Micrococcus luteus,Bacillus cereus and Bacillus pumilus based on its morphology, Physiology and biochemistry characteristicsand sequence analysis by16SrDNA. The petroleum degrading capacity of four strains was analyzed byGC/MS. The results indicated that the petroleum degradation rate could reach90.50%after54d by mixedstrain, which was67.72%higher than the control. The relative contents of the normal alkanes,isomerization alkane and cycloparafin hydrocarbon are decreased with the biodegradation time prolonged.The relative contents of aromatic hydrocarbons, alcohols, aldehydes and acids are increased.4、Screen the plants to repair the petroleum-contaminated soil: Screen the plants to repair thepetroleum-contaminated soil: It was choosed four types of plants in arid and semi-arid area for repairing thepetroleum pollution soil.It was Trifolium repens Linn、Agropyron cristatum (L.) Gaertn、Lolium perenne L、Cynodondactylon Linn.Pers.respectively. The Trifolium repens Linn and Agropyron cristatum (L.) Gaertnwere the first time to repairing the soil with petroleum pollution.Through the monitoring the TPHdegradation rate, plant growth index, soil main properties and soil plant nitrogen isotope, then screen outadvantage plants. Through the Trifolium repens Linn repaiing the3000mg/kg petroleum contamination inhigh organic matter silty loam, the TPH degradation rate was94.52%, it was higher than Agropyroncristatum (L.) Gaertn、Lolium perenne L and Cynodondactylon Linn.Pers respectively for13.82%、18.28%G and20.82%. From the growth traits, it can be concluded that the Agropyron cristatum (L.) Gaertn hasstrong tolerance to petroleum pollution than the other three plants. The initial height and biomass ofAgropyron cristatum (L.) Gaertn was more than others. Based on soil dehydrogenase activity and hydrogenperoxide enzyme activity and oxidation reduction potential analysis, it was showed that the growth rate ofthree kinds of index with Trifolium repens Linnthe was more than others. Trifolium repens Linn andAgropyron cristatum (L.) Gaertn could be used to repairing petroleum-contaminated soil in arid andsemi-arid areas.