Study On The Process Of Scale Crystal Depositing On The Surface Of Microorganism In Oilfield Extraction Wastewater

Ordos Basin is one of the largest oil-producing areas in China,including Changqing oilfield and Yanchang oilfield,which entered the waterflood development stage of the crude oil extraction,and the rejection after non-costratum mining and mixed treatment of produced water become the main method of oilfield production.The water treatment technology of produced water mainly includes coagulation,air flotation and microorganism method,microorganism method is increasingly applied on a small scale due to the advantage of enter disposal,non-secondary-pollution,andlesssludgeproduction.However,when microorganism method is used for the treatment of highly scale mixing produced water of non-costratum mining and incompatible,scale crystal deposition on the surface of crude oil degradation bacteria,which cut off energy and nutrient pathways between the bacteria and its environment,can lead to decline in crude oil biodegradation degree,even paralysis of treatment process.In order to explore the effect law of cale crystal surface deposition on crude oil biodegradation degree and establish the pretreatment technology of microorganism method of highly scale produced water,In the present work,the following subjects were studied:?1?The highly efficient crude oil-degrading bacteria is obtained through screening,enrichment,separation from contaminated soils.Preliminary identification of the bacterial strains was performed through a comparison of morphological characteristics,physiological and biochemical tests,and comparison with data from previous studies.Deoxyribonucleic acid?DNA?sequencing via 16 SrDNA sequence analysis was also performed.Optimal growth conditions for P.aeruginosa were determined.?2?The effects of calcium carbonate scaling crystals and calcium sulphate scaling crystals on Pseudomonas aeruginosa crude oil degradation rate were studied,and the effect mechanism and the deposition processes were discussed by optical microscope and transmission electron microscopy.?3?Clay particle and chitosan-loaded clay particle were taken as the research object,owing to whose size and surface properties is similar to that of microbial particles,and Optical microscope,Laser particle analyzer and Zeta potential analyzer were utilized to study the micro-morphology,particle size and Zeta potential of surface sediment scale,to explore the deposition law and to analyze the processes and influencing factors of scale crystal depositing on the surface of clay particles,to establish the model for the deposition-aggregation of scale crystals on the surface of clay particles.?4?The mixing water extracted from different reservoir layers,was treated by using the microbial methods,could generate large quantities of scale crystals,which gathering and depositing on the surface of crude oil degradation bacteria would decrease its the degradation ability.In this paper,combination of adsorption induced descaling and coagulating sedimentation,as the pre-processing technique of the microbial treatments of the highly scaled produced water was explored.The results were found as followings:?1?In this study,6 highly efficient crude oil-degrading bacteria?Microbacterium sp.,Ochrobactrumintermedium,Alcaligenesfaecalis,Brevibacilluslaterosporus,Stenotrophomonas,and P.aeruginosa?were isolated,cultivated,and purified from soils exposed to long-term crude oil contamination.For P.aeruginosa,the most efficient conditions for oil degradation were found to be pH of 7–8,inoculums size of 6%,oil content of 4%,salt content of 0.8%,shake speed of 180 r/min,a constant temperature of 37°C,and a degradation time of 7 days.?2?The results showed that the crude oil degradation rate all bluff type drop can happen,decreased from 57.72%to 23.73%when the amount of calcium carbonate scaling increased from 983 mg/L to 1057 mg/L,from 51.68%to 24.92%when calcium sulfate scaling of 575mg/L to 1017 mg/L.Optical microscopy showed scaling surface deposition could make bacteria get bigger,aggregation,poor activity ability,and smaller moving range.when scaling deposition amount reach to a certain extent,bacteria become unable to move and lose activity ability.Combined with transmission electron microscopy,we concluded that scaling crystals wrapping in the bacteria and hindering crude oil intake were the main reason for out of degradation ability.?3?The deposition-aggregation model comprised three stages.The first stage was the induction period of the deposition of calcium sulfate scale crystals on the surface of clay particles.In the second stage,the formation stage of the scale nuclei,scale nuclei began to precipitate,covering the surface of the clay particles and forming the first layer of calcium sulfate scale crystal,this process was called monolayer adsorption.In the third stage,called the growth stage of the scale crystal,the scale crystal nucleuses adopted a colloidal form on the surface of clay particles.The surface of the CaSO₄ scale crystal particles could absorb excess Ca²⁺counter ions;thus,the structure of the colloid with a electronegative outer layer,sulfate ions in the saturated solution would combine with calcium ions to replace chlorine ions,promote the scale crystal growth along the crystalline face in the monolayer.?4?With the increasing of deposition yield of scale crystal,temperature,and stirring rate,the induction period of scale deposition on the surface of Chitosan-loaded clay was falling,and the constant of scale nucleation rate increased.In addition,the increasing of Ca²⁺,SO₄^2-concentration was conducive to the deposition of scale crystals on the surface of clay particle.The determination method of scale creation of effluent was established by the way of adsorption-gathered function of clay according to the above conclusions..?5?The adsorption-induced descaling time and scale creation of the supernatant of simulated water after coagulation sedimentation could be minished by the he addition of chitosan-loaded clay.Chitosan-loaded clay could be served as adsorption-induced descaling agent to reduce scale creation of treated water and scale deposition time.?6?The results showed that the mixing water from the chang 2 layer and the chang 6layer could produce 25 mg/L-2990 mg/L of scaling,crude oil degradation degree of Pseudomonas aeruginosa decreased from 50.53%-56.25%in 25 mg/L-745 mg/L of scaling of mixing water to 19.75%-26.51%in 1020 mg/L-2990 mg/L of high scaling.?7?Descaling technique of adsorption-induced and coagulation precipitation was established,mainly included two contents:First,scale crystal was adsorption-induced and deposition on the surface of chitosan-loaded clay.Second,the mixture of scale crystal and chitosan-loaded clay was sedimented in coagulation,pH value,flocculant and coagulant aid needed to be optimized.The descaling technique could be used as the technology of for the water quality stabilization and the pretreatment of microbiological method of highly scale produced water.Transmittances,scaling amounts,degradation degrees of supernatants of mixing waters reached 99.18%,27 mg/L,58.15%,respectively,with 60 mg/L of chitosan modified bentonite,30 min of adsorption-induced time,7.5 of pH,60 mg/L of PFS,0.6 mg/L of PAM?The molecular weight is 12 million.?.These findings provide some valuable information for further researches in the treatment technique of microbiological method of highly scale produced water.The systematic study on the effect of scale crystal deposition on the surface of crude oil degradation bacteria are of momentous current significance in application of microbiological method of oily sewage treatment,waterflood development of Changqing oilfield and Yanchang oilfield in Ordos Basin,and regional environmental protection...