Research On Inorganic Salt Slow-release Remediation Agent Based On Stimulating Indigenous Microorganisms To Degrade Aromatic Hydrocarbons In Groundwater

With the rapid development of petrochemical,coking,oil and gas mining and other industries,organic pollutants enter the underground environment in many ways,resulting in a very serious problem of organic pollution of groundwater.Among them,typical organic pollutants,aromatic hydrocarbons（benzene series,naphthalene,etc.）are more common and harmful,which brings potential risks and harms to the ecological environment and human health,and becomes an obstacle to the promotion of ecological civilization construction by the country and localities.There is an urgent need for risk control and restoration of groundwater contaminated by aromatic hydrocarbons.As controllable slow-release technology has attracted attention in the field of groundwater environmental remediation,slow-release materials are used to study slow-release agents,prolong the service life of active ingredients,reduce costs,reduce procedures,and improve the timeliness of repair.Controllable slow-release technology has become a solution.Controllable slow-release technology has become one of the research trends to solve the bottleneck of the application of in-situ bioremediation technology to actual engineering.Controllable slow-release technology has become one of the research trends to solve the bottleneck of the application of in-situ bioremediation technology to actual engineering.This thesis is based on Regional Joint Funds of the National Natural Science Foundation of China"Research on Traceability Identification,Mass Transfer Process,In-situ Remediation and Online Monitoring Technology of Groundwater Organic Pollution in Cold Areas（U19A20107）"-"In-situ Enhanced Microbial Remediation Technology for Petroleum Hydrocarbons Based on Reactive Matrix Regulation"And National key research and development program"Groundwater In-situ Bioremediation Regulation Type Nutrient Matrix Slow-release Pharmaceutical Research and Development（2020YFC1808804）",with a petroleum-contaminated site in the northeast as the research area,tracking research trends in related fields at home and abroad,targeting typical aromatic hydrocarbons in groundwater Contaminants（benzene series and naphthalene）,based on the sampling and testing of contaminated sites,analyze the characteristics of the indigenous functional microbial flora,optimize the nutrient composition,and develop an inorganic salt slow-release remediation agent that stimulates the indigenous microorganisms to degrade aromatic hydrocarbons in groundwater,And conducted a small test verification by simulating the in-situ remediation process,and the research results obtained provide important scientific basis for the research and development of in-situ bioremediation and slow-release remediation agents for aromatic hydrocarbon-contaminated groundwater.Through the thesis research,the main research results have been obtained:（1）There is a certain inherent relationship between the distribution of aromatic hydrocarbons and indigenous microorganisms in shallow polluted groundwater.Benzene series—the detection rates of benzene,toluene,ethylbenzene,o-xylene,and p-xylene are 100%,75.00%,18.75%,and 81.25%respectively,and the content range is mainly on theμg/L-mg/L level the content of pollutants has obvious spatial heterogeneity.Among them,the points JC14 and JC3,which are relatively close to the pollution source along the flow direction of groundwater,have the highest content of benzene series.the content of the JC11 point in the downstream is the second,and the co-existing polycyclic aromatic hydrocarbon pollutant is naphthalene,which is relatively low in content.0μg/L-1.00mg/L;the microbial diversity is good,and the Shannon is between 3.002 and 4.852,which has a certain response relationship with the spatial distribution of pollutants.The dominant bacteria in the community mainly include Proteobacteria,Firmicutes,Bacteroidetes,Parcubacteria and Actinobacteria.Among them,Proteobacteria occupies the main position.（2）Using aromatic hydrocarbons as the sole carbon source,screening of inorganic salts that are economical,safe,widely available,and easily ingested by indigenous functional microorganisms,and research on the optimization of the nutritional matrix of indigenous functional microorganisms,through indoor simulation of low temperature and anoxic groundwater microenvironment experiments,combined with modern detection and analysis technology has determined the inorganic nutrients of the indigenous functional microorganisms,and analyzed the composition,physiological and biochemical characteristics and degradation products of the indigenous functional microorganisms.The nutritional formula of the inorganic salt slow-release repair agent is NH₄Cl:KNO₃:KH₂PO₄:Mg SO₄·7H₂O:Na₂HPO₄·12H₂O:Na NO₂=1:150:100:10:100:1,and stimulate the indigenous functional microorganisms to degrade aromatic hydrocarbons to reach a degradation balance within 3 days,and the degradation rate from highest to lowest is toluene（91.22%）,ethylbenzene（83.44%）,benzene（80.11%）,o-xylene（78.10%）,and p-xylene（75.21%）,naphthalene（70.32%）.The dominant bacteria in the community are Phenylobacterium and Bradyrhizobium,accounting for 20.64%and 12.91%,respectively,gram staining is positive.The colony diameter is about 1mm.The strain is short rod-shaped,about 1μm in length and 0.2μm in diameter.Analysis of biochemical and degradation products shows that indigenous functional microorganisms can effectively degrade under the stimulation of inorganic salt nutrients.（3）Sodium alginate is selected as Slow release material,and the low-cost,simple and easy-to-operate drip method and exogenous emulsification method are used to prepare inorganic salt Slow release material.The exogenous emulsification method was determined by investigating the dispersion state and microscopic form of the sustained-release drug in water.By further comparing the encapsulation rate and drug loading rate of the sustained-release drug,the optimal ratio of the inorganic salt sustained-release drug was determined:sodium alginate concentration 2%,Ca Cl₂ concentration 6%,drug concentration 3.62%,microsphere shape,particle size between20-60μm,the encapsulation rate and drug loading rate:53.5%,10.6%,the release law conforms to the Fick diffusion mechanism.Comparing the effects of the dosage of different sustained-release agents and the initial concentration of aromatic hydrocarbons on the degradation of aromatic hydrocarbons,the results show the initial concentration is 1mg/L,that the most suitable dosage of sustained-release agents is 200mg,and which stimulates indigenous functional microorganisms.The degradation rate（%）of benzene,toluene,ethylbenzene,o-xylene,p-xylene and naphthalene when degrading aromatic hydrocarbons for 15 days:88.0,94.00,92.12,85.21,86.08,76.14.（4）The simulated in-situ injection of inorganic slow-release agents stimulates indigenous functional microorganisms in groundwater to degrade aromatic hydrocarbon pollutants.The results show that inorganic salt sustained-release agents can effectively stimulate indigenous functional microorganisms to degrade aromatic hydrocarbons.The sustained-release period is about 7 days.The indigenous functional microbial community responded significantly.Without the addition of inorganic salt agents,the degradation effect of indigenous functional microorganisms is not obvious.The migration speed of aromatic hydrocarbons in the aquifer medium is:benzene>toluene>ethylbenzene>o-xylene>p-xylene>naphthalene,along In the direction of groundwater flow,the degradation rate（%）of benzene,toluene,ethylbenzene,o-xylene,p-xylene,and naphthalene near the chemical injection well（A5）:79.01,90.12,81.10,76.00,76.1,71.12,In the early stage of slow-release,there was an increase in the content of inorganic salts in the effluent,indicating that the scope of the slow-release migration of inorganic salts was large.After repairing,the total amount of DNA of the microbial flora is significantly increased and the diversity is reduced under the stimulation of the sustained-release agent.The dominant abundance genera are Arthrobacter,Masssilia,Pseudomonas,and Rhodococcu.The proportions of Arthrobacter and Acinetobacter increased significantly,with the largest increase of23.31%and 18.17%respectively.Arthrobacter,Acinetobacter,Pseudomonas,and Rhodococcu are common petroleum hydrocarbon degrading bacteria,indicating that inorganic salt slow-release agents can effectively stimulate the growth and degradation of indigenous functional microorganisms in groundwater contaminated by aromatic hydrocarbons.