Mechanism And Effect Of Bioremediation Of Petroleum Contaminated Soil By Combining Biochar Immobilized Microorganisms With Plant

Petroleum hydrocarbons consist of complex mixtures containing hundreds to thousands of compounds.Petroleum hydrocarbons can be released to soil by oil spillage,transportation and seeping,leading to serious and persistent soil pollution.The quality of petroleum-contaminated soil declines significantly as the compactness of the soil increases,and the water-holding capacity,oxygen and nutrients decrease.The highly toxic and mutagenic characteristics of petroleum compounds and their epoxides are harmful to microbes and higher organisms.Therefore,it is necessary to adopt effective methods to repair petroleum contaminated soil.Bioremediation is considered cost-effective and environmentally friendly.Biostimulation by adding biochar,bulking agents,nutrients,surfactants and other materials can accelerate petroleum degradation in soil.In this study,maize straw biochar,bulrush straw biochar and pine needles biochar were used to remediate petroleum-contaminated soil combined with microbial and plant.The petroleum-contaminated soil used in this study was collected from Liaohe Oilfield.The content of C in maize straw biochar,bulrush straw biochar and pine needles biochar increased with the pyrolysis temperature increment,and the content of H and O had the opposite trend.BET SA and TPV of biochar increased and the surface functional groups decreased with the temperature increment.The remediation effect of petroleum contaminated soil with biochar of different types,temperature and percent weight were compared.Bulrush straw biochar had the best remediation effect,followed by maize straw biochar.The suitable preparation temperature is 500?,and the use amount is 5%of the soil weight.In order to study the effect of nutrients,the remediation effect was compared amended with nutrients?nitrogen and phosphorus??T2?,with maize straw powder in combination with nutrients?T3?and biochar in combination with nutrients?T4?.The results showed that adding maize straw powder and biochar could significantly decrease bulk density of soil,increase soil porosity and soil field capacity?p<0.05?.The total bacterial numbers was improved by adding nutrients and bulk materials?T2?T4?,especially in combined treatment group of biochar and nutrients?T4?.The removal of total petroleum hydrocarbon?TPH?and the main hydrocarbon fractions was higher in T3 and T4 after remediation,especially in T4,than in the individual nutrients added treatment and the control treatment.The physicochemical properties,the total bacterial numbers and the removal rate of petroleum hydrocarbon showed significant correlation with each other.Soil porosity and total nitrogen had a great impact on microorganisms,and the effect of microbial on the removal of petroleum hydrocarbon was obvious.In order to study the effect of biomass and biochar,the remediation effect was compared amended with bulrush straw powder?T2?,with biochar alone?T3?and in combination with nutrients?nitrogen and phosphorus??T4?.The characteristics of the polluted soil?water-holding capacity and nutrients?were improved significantly by biochar addition?p<0.05?.The total microbial count increased significantly in the treatment containing biochar and added nutrients?t=23.429,p=0.002?.The degradation of total petroleum hydrocarbons?TPH?and the main hydrocarbon fractions was higher in T3 and T4,especially in T4,than in bulrush straw powder treatment.The intensities of the n-alkane fraction,C27-C29 steranes and C33-C35 homohopanes were efficiently decreased in biochar and nutrients treatment compared to the others.The physicochemical properties of the bioremediated soil were improved in combined treatment of immobilized microorganisms and nutrients in biochar?T4?.The content of TOC decreased by 12.02 g·kg^-1,the proportion of nutrient elements in soil tended to be balanced,and the number of bacteria,fungi,actinomycetes and petroleum hydrocarbon degraders increased in T4.The degradation of TPH and different components of petroleum hydrocarbon,especially the high carbon fractions were obviously better in T4 than that of other treatment groups.With the increase of microorganisms,the degradation rate of petroleum hydrocarbons in each component showed an increasing trend in different degrees.The removal efficiency of petroleum hydrocarbons,microbial number and enzyme activity were significantly improved in the treatment of biochar immobilized microorganisms combined with winter rape and nutrients?T5??p<0.05?.Compared with winter rape treatment,the plant height,root length,biomass,root vigor and chlorophyll content of winter rape were increased in other treatments,especially in T5,and the cell membrane permeability,MDA content and peroxidase activity decreased.The degradation effect of high carbon and resistant fractions of n-alkanes,typical isoprenoid alkanes,steroids and terpenes in T5 was better than other treatments.Compared with other treatments,biochar immobilized microorganisms combined with winter rape and nutrients treatment had the best remediation effect,which could improve soil physical properties and provide sufficient nutrients for microorganisms,thereby enhancing the remediation effect of petroleum contaminated soil.