Effect Of Scale On Pseudomonas Microbial Degradation Of Crude Oil

Recent years,most of Chinese oil fields have been in the middle and late stages of development,and the water content of produced fluids from the oil fields is getting higher and higher.Some water content of the produced fluids have even reached more than 90%.The produced water produced by the separation of oil and water in the produced fluid has high oil content,high water temperature,and high salinity,etc.As these properties and the high corrosion and foul of the produced water,the produced water must be processed before being injected back into the stratum.The commonly used treatments for oily wastewater include physical methods,chemical methods,and microbiological methods,among which the microbial treatment method has the advantages of economy and high efficiency,and acts as the development direction of the produced water treatment in the future.When microorganisms are used to treat high salinity and scale-forming oily sewage,scales will accumulate and deposit under the influence of polysaccharides on the surface of microorganisms,restraining the exchanging process of microorganisms with external substances and energy,and affecting the treatment efficiency and effect.It is of great significance for the stable operation of the microbiological treatment process to explore the effects of scale accumulation and deposition processes on the surface of microorganisms and the treatment effect on microorganisms.In this paper,the simulated oily wastewater with strong fouling tendency is taken as the research object,and the crude oil in high scale oil production sewage is degraded by pseudomonas microorganisms.The degradation rate is used as an assessment index to study the effect of scaling on the degradation of crude oil degrading bacteria.The results show that the maximum scale formation of the Chang 2 and Chang 6 layer（as the main oil layer）production water in Shaanbei oilfield is 270 mg/L.The pretreatment of the produced water shows as follows:the mixed water is adjusted to p H 7.5,the dosage of PAC is 80¹00 mg/L and the dosage of PAM（1200 million）is 0.8¹.0 mg/L.The dosing interval between the coagulant and flocculation agent is controlled at 30⁴0 s.After the pretreatment,the water scale was reduced from 342 mg/L to 269 mg/L and was used as a biological degradation research water.The microbial degradation experiment of crude oil by pseudomonas demonstrated that when the amount of CaSO4 in the water is more than 6.8 mg/L,the degradation rate of crude oil will decrease from 39.98%to 20.20%.The main reason is that CaSO₄ scale adhered to the surface of bacteria lead to the reduction of the degradation efficiency of crude oil.As the conductivity change curve illustrates,the crystal formation of calcium sulfate in both of aseptic and bacteriostatic liquids experienced the induction period,the nucleation period and the growth period.As the stirring intensity（rotation speed）increased,the scale formation ions increased,and the temperature increased,the growth rate of crystal nuclei was accelerated,and the induction period of calcium sulfate scale deposition on pseudomonas microbial surface gradually shortened from 18 minutes to 7 minutes.While,the increase of bacterial concentration inhibited the formation of nuclei and the induction period changed from 2 minutes to 20 minutes.