Screening Of Petroleum Hydrocarbon Degrading And Demulsifying Bacteria And Their Application In Oilfield Produced Water Treatment

With the development of global industry,a large number of crude oil is exploited,accompanied by a large number of oilfield produced water.Untreated oilfield produced water discharge or direct reinjection will cause surface water and groundwater pollution and seriously damage the ecological environment.At present,oilfield produced water is usually treated by physicochemical biochemical combined process,but the characteristics of oilfield produced water,such as high temperature,high salinity,poor biodegradability and so on,hinder the normal operation of biochemical system,resulting in the water is difficult to meet the standard.Under the extreme conditions of deep sea,marine bacteria with high temperature resistance,salt resistance and unique metabolic mechanism may be more suitable for high temperature and high salt oilfield produced water.In order to remove petroleum hydrocarbons which are difficult to degrade in oilfield produced water,marine bacteria with degradation and demulsification functions can be combined into a synthetic community to improve the quality of oilfield produced water.In this experiment,we screened the degrading bacteria with high efficiency of degrading petroleum hydrocarbons and demulsifying function from the deep seabed mud and the marine bacteria bank preserved in our laboratory,and explored the degrading efficiency of degrading bacteria on petroleum hydrocarbons and the influence of various environmental factors on demulsifying effect of demulsifying bacteria;On this basis,the selected degrading bacteria and demulsifying bacteria were synthesized into a biological community with high oil removal efficiency,and the treatment efficiency of the synthetic community for oilfield produced water at 25? and 50?was explored,and the changes of microbial community structure during the operation of the reactor were analyzed.This paper mainly includes the following parts:(1)Four strains of marine bacteria,Halomonas profundus N-1,Bacillus licheniformis W-1,Halomonas titanicae R-1 and Bacillus paramycoides A4-1,were screened out from the deep seabed mud by using petroleum hydrocarbon as the sole carbon source.The subsequent degradation experiments showed that the four strains were all resistant to n-hexadecane,naphthalene,phenanthrene and crude oil have good degradation effect.The results showed that the degradation rate of n-hexadecane,phenanthrene and crude oil reached 84%,78.8%and 44%,respectively,and the degradation rate of naphthalene reached 54%.(2)Through the demulsification test and surface activity test,two strains of marine bacteria Halomonas titanicae 6-2 and Bacillus paramycoides P4-3 with high demulsification ability were screened from deep seabed mud,and the effects of demulsification time,emulsion pH,temperature,salinity,emulsion type,carbon source of culture medium on the demulsification effect of two marine bacteria were further explored.The demulsification activity of different parts of the whole culture medium was analyzed.The results showed that the maximum demulsification rates of demulsifier 6-2 and P4-3 were 24h and 18h,respectively.The maximum demulsification rate of demulsifier 6-2 was at pH=8,50? and 5%salinity,and the maximum demulsification rate of demulsifier p4-3 was at pH=9,55? and 5%salinity.The results showed that the two strains had high demulsification effect on all kinds of emulsions,and the addition of hydrophobic carbon source could improve the demulsification rate.The demulsifying activity of P4-3 was more dependent on the cell.(3)Oil field produced water was treated by inoculating petroleum hydrocarbon degrading bacteria and demulsifying bacteria in 25? and 50? reactors,and the long-term continuous operation treatment effect at two temperatures and the bacterial community structure in the reactors in different treatment periods were investigated.The results showed that the removal rates of TPH and COD in the two reactors at different temperatures were above 90%.The TN content of the effluent at the end of the 25? reactor were lower than those of the 50? reactor,and the sludge volume was higher.Secondly,the diversity of bacterial community in 25? reactor was higher than that in 50? reactor in different periods.With the operation of the reactor,the bacterial community richness in the 25? and 50? reactors increased gradually,and the community structure tended to be stable.In addition,with the operation of the reactor,the relative abundance of Bacillus and Halomonas gradually decreased,while Xanthomarina,Alcanivorax and Marinobacter gradually became the dominant genera.In summary,four strains of marine bacteria with high efficiency of degrading petroleum hydrocarbons and two strains of marine bacteria with high efficiency of demulsification were selected and combined to be used in oilfield produced water treatment system.The harmless and efficient treatment of oilfield produced water is realized,which provides a theoretical basis for the treatment of wastewater generated in the process of oilfield exploitation,and has engineering guiding significance.