Research On Bioremediation Of Petroleum Contaminated Soil By Spent Mushroom Substrate And Biochars Combined With Microorganisms

In view of the serious situation of petroleum hydrocarbon contaminated soil,the microbial remediation technology is more and more widely used in soil remediation because of its good remediation effect and no secondary pollution.In this study,high-efficient petroleum hydrocarbon-degrading bacteria were screened from petroleum-contaminated soil,and use agricultural waste named spent mushroom substrate as raw material to prepare biochar by oxygen-limited pyrolysis at different temperatures.Then the degrading bacteria were adsorbed and immobilized in spent mushroom substrate and biochars respectively to explore the optimum adsorption time,adsorption-degradation rate of petroleum hydrocarbons in order to select the optimum carrier materials,which were applied to the remediation of petroleum contaminated soil.In the process of simulated in situ soil remediation,the best way of soil remediation and the mechanism of soil remediation under this way were explored by measuring the residual petroleum hydrocarbon content,microbial quantity and activity,soil ecological toxicity and basic physical and chemical properties of soil at specific period.Eight strains of petroleum hydrocarbon degrading bacteria were screened from aged petroleum contaminated soil.The highest degradation rates of petroleum hydrocarbons in 7d by Q1 and Q3 were 45.50%and 42.74%,respectively.According to the determination of surfactant-producing properties,strain Q1 has the largest oil-discharging ring diameter,5.3 cm,the lowest surface tension,31.78 m N/m and the best emulsifying performance,71%.Strains Q1 and Q3 were identified by 16S r RNA molecular biology as Ochrobactrum and Microbacterium respectively.The degradation of petroleum hydrocarbons by strains Q1,Q3and QH(mixed the two strains in a ratio of 1:1)were determined by ultraviolet spectrophotometry,gravimetry and GC-MS methods.The results showed that strains QH had the best degradation effect and the degradation rates of petroleum hydrocarbon by ultraviolet and gravimetric methods were 52.37%and 59.29%,respectively.Furthermore,the result of GC-MS showed that the degradation effect of each carbon chain component of crude oil degraded by QH bacteria was better than that two single strains,showing a wider and better utilization range of carbon chain in crude oil.Biochar samples were prepared at different pyrolysis temperatures(250-650?)using spent mushroom substrate(SMS)as raw materials.With the increase of pyrolysis temperature,the p H value of biochar and the content of basic functional groups increased,while the ratio of H/C decreased.And the stretching and bending vibration of all groups including-OH,C-H,aromatic ring C-H,C-C and C=O were observed.The SEM showed that the pore structure of biochar gradually opened with the temperature increased.The skeleton structure appears at 550°C,and its specific surface area and pore volume reach the maximum.The effect of different biochar structures on adsorption rate of QH strain,oil and degradation rate were analyzed.The results indicated that 550?-biochar(BC550)has the best adsorption effect on microorganism,which were 2.375×10¹⁰?/g.The SEM analyses showed that most microorganisms were immobilized on the surface of the materials.BC550 immobilized microorganisms had the highest degradation rate of total petroleum hydrocarbons,62.04%,while SMS immobilized microorganisms had the highest degradation rates of resin and asphalte,which were 19.67%and 14.71%.In addition,p H,organic carbon and content had obvious effect on microbial adsorption-degradation rate.Spent mushroom substrate and BC550 biochar were finally selected as immobilized microbial carrier materials for subsequent oil-contaminated soil remediation.After 55 days of soil remediation experiment,the effect of immobilized microorganism groups were obviously better than that of free-microorganism groups and single addition groups.The biodegradation rate of petroleum hydrocarbon was the highest in BIM group,and the content of petroleum hydrocarbon was reduced by 29.76 mg/g soil.This is due to the protective effect of immobilized carrier made the exogenous degrading microorganism became the dominant microorganism group.The quantity and activity of microorganism were better than other experimental groups,and the bioremediation cycle was obviously shortened.In addition,the immobilized microbial remediation has the synergistic mechanism of biostimulation and bioaugmentation.