Research On The Slow-release Medicament Of Nutrient Based On Biostimulation Remediation Of VCHs Contaminated Groundwater

With the development of key industries such as chemicals,pharmaceuticals and textiles,volatile chlorinated hydrocarbons（VCHs）have been widely used as common organic solvents and important chemical raw materials.The groundwater contaminant caused by them has been general concerned by governments,enterprises and academic field in various countries.The research on the remediation technology of VCHs contaminated groundwater is one of the research hotspots in the field.In recent years,the remediation of groundwater contaminated by VCHs has mainly focused on pump-and-treat,in-situ chemical oxidation,in-situ chemical reduction,multi-phase extraction,etc.When applied to actual remediation projects,there are often problems such as incomplete repair and easy rebound of pollutant content.Many researchers have used slow-release materials to extend the service life of active components to improve the in-situ remediation effect and solve the actual contaminant remediation project requirements.At present,the slow-release agents for VCHs contaminated groundwater are mainly concentrated on reducing agents and reducing synergistic biological agents.There are few studies on slow-release agents that are low-cost and effective to stimulate functional microorganisms in groundwater to repair shallow organic contaminated groundwater in situ.This paper is based on the 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）and the National Key Research and Development Program"Groundwater In-situ Bioremediation Regulation Type Nutrient Matrix Slow-release Pharmaceutical Research and Development（2020YFC1808804）,based on the microbial communities and nutrient matrix optimization of the groundwater contaminated by VCHs,and based on the principle of bio-stimulation repairing VCHs-contaminated groundwater technology and slow-release control technology,research on a nutrient matrix slow-release medicament with bio-stimulation repairing VCHs-contaminated groundwater and small-scale verification.The research results provide an important scientific basis for the in-situ bioremediation of VCHs-contaminated groundwater bioremediation slow-release agents and technology research and development.Through the study of this paper,the main results obtained:（1）The content of VCHs in the groundwater of the contaminated site and the distribution of indigenous microbial communities have certain regularities.The concentration of Dichloroethylene（DCE）,Dichloromethane（DCM）,Trichloromethane（TCM）and Dichloroethane（EDC）at the contaminant source reaches 32.70mg/L,14.50mg/L,1.60mg/L,68.00μg/L,the downstream concentrations are 14.20μg/L,13.30μg/L,12.00μg/L,10.00μg/L.The Shannon index of the indigenous microbial communities are in the range of 4.02-5.23,the dominant bacteria genera mainly include Proteobacteria,Firmicutes,Bacteroidetes,etc.,with abundance values??between 68.06%and 95.25%.（2）Through batches of effective nutrient matrix experiments that stimulate indigenous functional bacteria to degrade VCHs in groundwater,the compound nutrient matrix formula and the characteristics of the indigenous functional microbial community were determined.The compound nutrient matrix component ratio:NH₄Cl:KNO₃:Na₂HPO₄:KH₂PO₄:Ca Cl₂:Mg SO₄:Zn Cl₂:Mn SO₄:CH₃COOH=1:50:50:100:10:500:1:0.1:1,the indigenous functional microorganisms have a strong influence on DCE,DCM,TCM,EDC,and Monochloro-benzene（MCB）degradation rate was 31.32%～78.65%.The main bacteria are Proteobacteria,Firmicutes,Bacteroidetes,Actinobacteria,Chlamydiae,etc.,with abundance values??ranging from 68.91%to 96.80%.（3）Stearic acid and starch are selected as slow-release materials to synthesized the nutrient matrix slow-release medicaments.The comparative analysis determines the optimal preparation conditions,microstructure of the starch slow-release medicament and the functional law of stimulate action of indigenous microorganisms.The structure of the slow-release medicament is relatively smooth,hemispherical,with a diameter of about 1μm～15μm,one-time injection slow-release medicaments with nutrient matrix can be sustained for about 15d.When the dosage of slow-release agent is 50mg,the enhancement effect is basically stable,degradation rate of VCHs was 82.38%～92.38%.（4）Simulated in-situ injection of slow-release medicaments to stimulate indigenous functional microorganisms in groundwater to repair VCHs contaminated groundwater.The research results show that slow-release medicaments can effectively prolong and improve the degradation efficiency of indigenous functional microorganisms.After the indigenous functional microorganisms community was added with slow-release medicament,the degradation effect of indigenous microorganisms reached a balance in about 2d,and the degradation rate of VCHs was76.78%～93.52%.The DNA content increased significantly,and the abundance of Firmicutes in water samples and lithological media（medium sand,coarse sand,pebbles）increased by about 20.00%.