Microbial Remediation Of PAHs Contaminated Soil Based On Slurry System

This study simulates soil slurry,uses phenanthrene and pyrene as representative Polycyclic Aromatic Hydrocarbons(PAHs)to research the removal of these two PAHs and its influencing factors(microbes,soil water ratio,the concentration of glucose,starch and salicylic acid)by mixed microbes(thermophilic bacteria and PAHs degrading bacteria)in soil slurry.The temperature is 40 ? that these two kinds of microbe can both quickly grow and reproduce.The results showed that the removal of PAHs is significant by this mixed microbes(P<0.01).The maximum removal rate of phenanthrene in a single day was 20%,and that of pyrene was 15.3%.With the progress of the reaction,the removal of phenanthrene and pyrene improve significantly,but the removal rate is gradually decreased.The half-life of phenanthrene was 1.8 d,less than 4.9 d of pyrene,so the removal of phenanthrene is faster than that of pyrene.The most appropriate water soil ratio for the mixed microbes to degrade PAHs in soil slurry is 2:1,the carbon source is glucose,the concentration is TOC glucose:TOC PAHs = 2:1.In order to approach the actual PAHs contaminated soil,we make an exploration on the compound polluted soil,to disicuss the effect of different degree of heavy metals Zn,Cu,Cr,Pb,Cd on the degradation of phenanthrene and pyrene by mixed microbes(thermophilic bacteria and PAHs degrading bacteria).We also make an exploration on the effect of aging treatment and biosurfactant on the degradation of phenanthrene and pyrene in the soil slurry system.The results show that the effect of heavy metals on the degradation of PAHs can be inhibited or promote.Low concentration of heavy metals(Zn,Cu,Cr and Cd)can promote the degradating of phenanthrene and pyrene in the soil slurry system,but high concentration of heavy metals inhibite or promote weakening effect.On the contrary,Pb can promote the degradating of phenanthrene and pyrene at low concentration and inhibite at high concentration,or the promotion effect is more significant with the increasing pollution degree.The removal of phenanthrene and pyrene is slower after aging treatment,and the half-life of phenanthrene and pyrene is longer.In this research,the removal rate of phenanthrene and pyrene can increase with a certain amount of rhamnolipid in aging soil slurry system.The concentration parameters is 5.0 CMC of rhamnus which can increase the removal rate of phenanthrene and pyrene to a maximum.Soil bacteria and fungi content,the dynamic changes of the activity of catalase and polyphenol oxidase were researched during the remmediation.At the same time,the intermediate product of the degradation of phenanthrene and pyrene in the single pollution system was tested to analyse the possible degradation pathway.The results show that the change of soil microorganisms(bacteria and fungi)content is basically the same with the change of catalase oxidase activity,the trend is increasing at first and then decreasing.The change of polyphenol oxidase activity is consistent with the change of soil microorganisms(bacteria and fungi)content.The polyphenol oxidase is the key enzyme effecting on the middle biodegradation process of polycyclic aromatic hydrocarbons.The bacterial degradation of phenanthrene is initiated by 9,10-dioxygenation to yield cis-9,10-dihydroxy-9,10-dihydrophenanthrene,which undergoes enzymatic dehydrogenation to genarate 9,10-dihydroxyphenanthrene.The ring is opened and cleavaged to form phthalate and eventually degraded into CO2 and H2O via phthalic acid degradation pathway.The bacterial degradation of pyrene is initiated by 4,5-dioxygenation and the ring is opened and cleavage to form phenanthrene derivative,and then enter the degradation pathway of phenanthrene.The results of this research can provide theoretical basis and technical support for the research and application of bioslurry remediation of PAHs contaminated soil.