The Study Of The Effect Of Clogging In The Seepage Zone In The Infiltration Process Of Groundwater Recharge With Reused Water

With the acceleration of urbanization and the increase of urban population in China,the conflict between supply and demand of urban water resources is also intensifying.At the same time,a large amount of urban sewage generated each year also brings a burden on the environment.The reclaimed water which has been purified by sewage treatment plants has become a new source of urban water.Among them,the use of reclaimed water for groundwater charge can not only conserve water sources,but also alleviate environmental hydrogeological problems caused by overexploitation.However,the problem of clogging of infiltration media has always restricted the efficiency of reclaimed water charge.In this paper,the research area is in the Chaobaihe,based on the “Water Diversion from Wenyuhe to Chaobaihe” engineering.Through many years of monitoring data of water quality and water level,combined with sampling results of river water and river sediments,a clogging model of seepage zone was established and the clogging effect was evaluated.The following preliminary cognition was obtained:(1)Analytical results of river water samples and riverbed sediments recovered from reclaimed river reach show that the concentrations of nitrogen,organic carbon and dissolved oxygen in the river water gradually decrease with the water depth,and the organic matter and total organic carbon concentrations in the sediment show the same trend.The hydraulic conductivity of the sediment sampling depth range increases with the depth,from the surface of 0.38 m/d gradually increased to the bottom of 0.55 m/d.(2)The result of the calculation of the water balance in the intake area shows that the rate of reclaimed water in the replenishing channel decreases year by year.The calculation results of the suspended solids clogging model showed that the rate of change of the infiltration rate in the replenishing area was reduced from the initial drop of 2 mm/year to the current 1 mm/year,and about 95% of the suspended solids were trapped on the surface of the seepage zone within 0.5 m depth of the surface layer.(3)Combining the Monod equation,the nitrogen transformation and transport equation,and the Clement equation describing the change of the hydraulic conductivity,a mathematical model for the bioclogging of the seepage zone was established,and the software named COMSOL was used to solve the model.The calculation results show that the effect of microbial clogging decreases with depth.Compared with the initial period of replenishment,the surface hydraulic conductivity decreases by 16% and the lower part decreases by 7% during the simulation period.The recharge concentration of ammonia nitrogen has the greatest impact on biological clogging.