Study On The Effect And Prevention Of Groundwater Recharge With Stormwater In Aquifer Media

Artificial recharge of stormwater is to artificially inject reclaimed water into the aquifer through engineering measures,to realize comprehensive utilization of reclaimed water and groundwater and repair the damaged hydrogeological environment.It is one of the effective ways to solve the problems of water shortage and urban waterlogging in China.However,in the process of artificial reinjection,the plugging phenomenon of reinjection well is the main problem that hinders the popularization of reinjection engineering.The primary task to prevent and control the plugging is to study the plugging mechanism and the occurrence of plugging rules.In the process of reinjection by stormwater,except for the suspended particles and chemical precipitation,biogeochemical reactions involving microorganisms have an important influence on the recharge blockage.The metabolites produced by microbial growth and reproduction are important factors for the occurrence of biological blockage.It is of great theoretical and practical significance to study the microbial plugging of reinjection in the water-bearing medium by stormwater.In this paper,the indoor one-dimensional seepage device is used to simulate the microbial plugging process of artificial recharge water-bearing medium by stormwater,and the groundwater in the lower reaches of Dagu River in Qingdao city is taken as the research object to study the microbial plugging mechanism of artificial recharge of stormwater.The temporal and spatial variation and the degree of clogging in the aquifer medium are quantitatively evaluated by the permeability coefficient.By measuring the index of nutrients and the content of extracellular polymeric substance(EPS),then analyzed the law of change with the permeability coefficient.Using 16S rRNA high-throughput sequencing technology,in-depth analysis of microbial community richness,diversity,and species composition characteristics.The correlation analysis between samples and sample bacteria and environmental factors is carried out to reveal the main bacteria species that affect the clogging of stormwater recharge at the genus level,to provide prevention and control basis for the construction and operation of the field recharge projects.The main results are as follows:(1)The variation trend of the permeability coefficient of water-bearing media in each test group was basically the same,and all showed a nonlinear decreasing trend.Among them,the water-bearing media blockage occurred the earliest in the stormwater recharge test group.In space,the change rule of medium permeability coefficient in different seepage layers is closely related to the depth of the medium.The plugging mainly occurs in the surface layer of the medium.The permeability coefficient of the layer decreases by more than 99%and then extends to the interior of the medium.In terms of time,permeability went through a change stage of "stable fluctuation-rapid decline-tending to stability".(2)The variation rule of water quality index with permeability coefficient was basically the same in each experimental group,and the nutrient index of the buffer zone is higher than that of the outlet water.The index of NH4-N?NO3-N?NO2-N?PO43-changes slightly.The concentration of NO2-N and NO3-N increased,and denitrification increased.When Ks'=0.85,the decrease of COD in the buffer zone is the largest.Ks'=0.85 or Ks'=0.65,in buffer zone ORP high peak.When Ks'=0.15,the DO of effluent decreases greatly,and COD and ORP pick up.(3)The variation trend of extracellular polymeric substance content in surface sand samples of water-bearing media in each test group was basically the same as that of permeability coefficient,and the polysaccharide content of each sample is higher than the protein content.When the relative permeability coefficient(Ks')of the water-bearing medium decreases from 1 to 0.35,the EPS content in the surface layer of the sand sample increases continuously,and PS/PN increases.When Ks'decreased to 0.15,the content of EPS showed a low peak,in which more polysaccharide reduction than protein reduction.When the cut-off of reinjection the content of EPS rises again.(4)According to the results of high-throughput sequencing,Bacteria attached to aqueous medium in each test group were mainly distributed in 37 phyla,83 classes,233 orders,385 families,677 genus and 1157 species.The richness,diversity,and evenness decreased.At the end of reinjection,the number of bacteria decreased in each level of classification,and the structure of bacteria changed.Among them,Proteobacteria constitute the main dominant phylum,Proteobacteria?Actinobacteria and Bacteroidetes are the significant influencing bacteria.Gamma Proteobacteria?Alpha Proteobacteria and Actinobacteria are the main dominant classes.Also,Acidovorax,etc.which is the dominant position in biofilm;Pseudomonas?Enterobacter,etc.living in an anaerobic environment and Acinetobacter,bacillus,Pseudomonas,which can secrete extracellular polymeric substances,account for a higher abundance ratio in the cut-off samples.