| The situation of petroleum hydrocarbon-contaminated soil is becoming more and more serious,which poses a great threat to ecological environment and human health.Due to its characteristics of environmental friendliness,low cost,high efficiency,etc,bioremediation technology has been playing a growingly important role in various remediation technologies.However,the high salinity and alkaline environment in the actual remediation site greatly limits the ability of conventional microorganisms to decontaminate the pollutants.This article first analyzed and explored the extraction and analysis method of petroleum hydrocarbons in the soil.Then the salt tolerant bacteria were extracted from the actual oil contaminated saline alkali sites,cultivate and domesticate them under the high oil and high salt stress conditions.This ariticle studied the physiological characteristics of salt-tolerant bacteria group in the process of domestication,probed into the petroleum hydrocarbon degradation characteristics of advantageous salt resistant strains both in water and soil environment.It also analyzed some key issues concerning to the popularization and application of the constant resistance to salt and oil degradation bacteria,like remediation reagents,slow release agent,carrier materials,bacterium agent preparationetc,and designed a set of intelligent,modular,skid mounted bioremediation equipment used in petroleum contaminated saline field.Soil petroleum hydrocarbon extraction,analysis results show that:in the soil under the condition of initial oil concentration of 10000 mg/kg,with five different extraction methods,soil petroleum hydrocarbon extraction rate of Soil—Determination of petroleum oil—Infrared spectrometry method(SDPO)(106.45%)>Determination method for municipal sludge in waste water treatment plant(CJ/T 221-2005)(DMMS)(90.73%)>Trickling-Filter-Based extraction(TFBE)(76.3%)>Oscillation-Centrifugation-Based extraction(OCBE)(74.7%)>Oscillation-Filtration-Based extraction(OFBE)(68.3%),the reason is to extract time different caused by contact with contaminated soil.T The compliance rates of OFBE,OCBE,TFBE and SDPO with DMMS were75.35%,82.3%,84.1%and 117.33%,respectively.The coincidence rates of OFBE,OCBE,TFBE and DMMS with SDPO are 85.23%,64.16%,70.16%and 71.68%,respectively.Compared with the five extraction methods,The SDPO has the highest extraction accuracy,while the OFBE takes the shortest time.Under the premise of correction ratio of correction coefficient,it can be used in the case that a large number of samples need to be processed quickly.Screening and domestication experiments of halotolerant bacteria showed:There were native microorganisms that could tolerate saline environment and degrade petroleum hydrocarbons in saline field which have been contaminated with oil for years.Besides,the saline tolerance and degradation ability of these microorganisms could be improved continuously through the screening and domestication method.The mean pH value of the domestication culture medium of salt-tolerant bacteria decreased from 7.6(initial stage)to 5.9(late stage),indicating that the culture medium would change from neutral to weak acid in the process of adapting to the environment and degrading petroleum hydrocarbons.It might be due to the production of carbonates during the decomposition of petroleum hydrocarbons by salt-tolerant bacteria.The conductivity of culture medium fluctuated between 55 and 115 ms/cm.The reason was that a large amount of internal electrolyte infiltrated into the culture medium,resulting in the change of the conductivity of culture medium after the death of the strain that could not adapt to the environment.The changes of particle size and morphology of oil droplets in culture medium showed that a large number of surfactant metabolites were produced in the growth and development stage of salt-tolerant bacteria.This resulted in partial emulsification while reducing the particle size of petroleum hydrocarbon.The experiment of salt-tolerant bacteria in repairing water body polluted by petroleum hydrocarbon showed that:A total of 6 strains of salt-tolerant bacteria were extracted from the bacteria screened in the early stage.Among them,No.1 strain(dominant salt-tolerant strain)had the best ability to solve high concentration of petroleum hydrocarbons under the condition of extreme salinity.The optimum living conditions of the strain were pH of 9,oil concentration of 5000 mg/L,temperature of 30?,and the high survival activity of it were pH of 7?9,oil concentration of 0.5%?5%,and temperature of 20?40?.In 15%?36% saline medium,the strain showed the highest degradation efficiency at 20% salt content(82.6%).In the medium of 5000?50000 mg/L oil concentration,the degradation rate of 10000 mg/L group was the highest(79.47%).The degradation rate of pH=8 group was the highest(76.9%)in pH 5?9 medium.The highest degradation rate was found in the 30?experimental group(64.93%).The degradation rate of CaCl2 group was the highest(90.3%)in the medium of different salt components.What's more,it was detected that the strain could produce lipopeptide biosurfactant,amylolytic enzyme and catalase,which could promote the degradation of the strain while promoting the emulsification of petroleum hydrocarbon.The experiment of salt-tolerant bacteria in remediation of petroleum hydrocarbon contaminated soil showed that:At the initial soil oil content of 10000mg/kg,the treatment effect of No.1 strain degraded by 25d was the best(65%)among No.1 strain,No.5 strain,No.6 strain and their mixture.At this time,the remaining oil content in the soil was 3856.5mg/kg.In the experimental group of the soil salt content 0?50%(mass ratio),the degradation rate in the 25% experimental group was the highest(91.1%),and the residual oil concentration was 887 mg/kg.This was close to the screening value for petroleum hydrocarbons(826 mg/kg)of the first type of construction land stipulated by GB3660-2018,but lower than the screening value of the second type of construction land(4500 mg/kg).The pollutant removal rate of the strain in different soils was sandy soil(66.1%)>loam(61.4%)>clay(35.2%).In the experiment of soil oil concentration of 1000?150000 mg/kg,the degradation rate of the experimental group of 50000 mg/kg was the highest(69.9%),and the residual oil concentration was 15040 mg/kg.The reason for the failure was that the oil concentration of the soil itself was too high.In the experiment of 20?100% water content,the removal rate of the 40% experimental group was the highest(64.9%),and the residual oil concentration was 3509mg/kg.In the environmental temperature experiment of 10?50?,the removal rate of the 40?experimental group was the highest(66.58%),and the residual oil concentration was 3342 mg/kg,which all met the screening value of the second type of construction land(4500 mg/kg).GC-MS detection showed that after the degradation of No.1 strain,the abundance of various characteristic pollutants in petroleum hydrocarbon pollution significantly decreased.Among them,tri(2-chloroethyl)phosphite,sym-trimethylbenzene and other pollutants were almost completely eliminated,while 2,4-tert-butyl phenol,n-butyl benzene sulfonamide and other pollutants still had more residues.The content of 2,3-dimethylnaphthalene increased,which might be caused by some biochemical reaction to decompose the macromolecules.In addition,No.1 strain belonged to titanicae of halomonas according to 16sRNA gene identification.At the same time,combined with the effective degradation of petroleum hydrocarbons in 36% salinity environment,it was speculated that it was a severe halophilic oil degradation bacteria.Furthermore,we analyzed the requirements and development directions of repair agent,slow-release agents,carrier materials and other materials needed for salt-tolerant bacteria restoration in the actual site of the high-salinity environment,and preliminarily designed the dose production program of salt-tolerant bacteria.At the same time,a set of pilotscale equipment for salt-resistant bacteria remediation in oil-contaminated sites was designed from the thinking plan,process design,structure design,investment and operation cost.It was indicated that the system could solve the problems of low equipment degree and high cost of bacteria agent in bioremediation of organic contaminated sites,and was suitable for in-situ and ectopic restoration projects. |
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