Biochar-based Immobilized Microorganisms And Restoration Of Oil-contaminated Soils

Soil contamination caused by oil-gas field development has brought enormous threat to ecological environment and human health.For the advantages of efficient,clean and economic,bioremediation technology has become a hot spot in the study of petroleum-contaminated soil remediation.Application of the traditional free bioremediation technology was limited for its shortcomings such as low microbial activity and poor adaptability to the contaminated environment.Immobilized microbe technology based on biochar could intensify remediation of the contaminated soil by increasing microbial density and activity.Choosing biochar of corncob,straw and sawdust as carrier,immobilization study of two petroleum-degrading strains F-3 and R-7 was conducted.The physicochemical properties of biochar were analyzed by FT-IR,BET,elemental analysis and other methods.Performance of immobilized microbes on biochar from different materials was evaluated,and the optimal biochar was decided.In addition,immobilization conditions of microbes on biochar were investigated.Mechanism of the intensifying effect of immobilization on the petroleum-contanminant degradation by microbes was discussed.Variations of degradation rate of petroleum-contaminant,physicochemical and biological properties in soil were investigated,and then mechanism of the intensifying remediation of petroleum-contaminated soil by immobilized microbes was stated.Among 3 biochars,corncob biochar?CC300-CC600?presents the maximum specific surface area which was within the range of 157.11?312.30 m²/g and the most developed pore structure.Zeta potential of corncob biochar was the highest,which was in the range of-30.95?-6.43,showing that the amount of negative charge on corncob biochar's surface was the fewest.FT-IR shows carboxyl,acylamina and other functional groups which contributed to microbial adsorption on the surface of corncob biochar.XRD shows Fe₂O₃ and NaCl which are conductive to microbial growth in corncob biochar.Immobilization rate of microbes on corncob biochar was between 61.8%?71.2%,and the petroleum-degrading rate of immobilized microbes on corncob biochar was between 59.3%-70.7%,both of which were obviously higher than that of straw biochar and sawdust biochar.SEM shows highly developed pore structure of CC500?which was prepared in 600??and the most amount of immobilized microbes on the surface of CC500.At the optimal immobilization time,the petroleum-degrading rate of immobilized microbes on CC500 achieved the highest,which was 71.3%.CC500 was decided as the optimal biochar carrier.When the particle size of CC500 was less than 0.08 mm,inoculum size of mixed bacteria was 10%,immobilization time and temperature were 18 h and 35 ?,respectively,the petroleum-degrading rate of immobilized microbes showed the highest,which was between 70.2%?71.4%.Immobilization markedly improved microbial adaptability to the contaminated environment.The petroleum-degrading rate of immobilized and free strains were respectively 89%and 62.1%at the low contamination concentration,and the values were respectively reduced by 16.6%and 30.3%at the high contamination concentration.Immobilization could weaken the stress effect of heavy metal and organic contaminants on microbes.In the environment with the existence of Cd,Pb,phenanthrene and naphthalene,the petroleum-degrading rate of immobilized and free strains were between 45.8%?67.2%and 22.3%?37.2%,respectively.GC-MS analysis indicates that the saturation and aromatic hydrocarbon of petroleum-contaminant was severally degraded by free bacteria and adsorbed by biochar,both of which were degraded by immobilized microbes.The degradation of petroleum-contaminant was based on the mechanism of both biodegradation and adsorption by immobilized microbes.After adding immobilized microbes,the content of alkali-hydrolyzale nitrogen,available phosphorus and organic carbon in soil shows the most drastic decline,which decreased by 86.0%,58.7%and 52.9%,respectively.The loss rate of moisture content of soil was the lowest,which was 5.2%.pH value was kept within the range of 7.45?7.97.Immobilized microbes improved fertility and water retention of the contaminated soil,kept soil acidity or alkalinity favor of microbial growth,and promoted the adsorption and utilization of soil nutritions by microbes.Within 60 days,the degradation rate of petroleum by immobilized microbes achieved 70.1%in soil,which was higher than that of free bacteria and biochar by 28.8%and 37.2%,respectively.The activity of dehydrogenase,catalase,urease,polyphenol oxidase and microbes in soil added with immobilized microbes were 105.4 ?g TPF/?g·h?,0.79 mL?0.1 KMnO4?/?g·h?,0.44 mg NH3-N/?g·h?,4.85 mg/pyrogallic acid?g·2h?and 6.47 mg/g,respectively.Mechanism of the intensifying remediation of petroleum-contaminated soil by immobilized microbes was the improvement of survival efficiancy and competitiveness of microbes in soil by biochar,which further increased the metabolic activity of petroleum-contaminant by microbes.