Laboratory Research On The Laws Of Fe(Ⅲ)clogging During Urban Stormwater Groundwater Recharge

The increase of population,climate change,water pollution,overexploitation of groundwater and other problems make the shortage of available water resources on Earth.Groundwater artificial recharge(GAR)technology has become one of the important means to deal with water shortage and corresponding environmental geological problems.In the process of GAR using rainwater,the infiltration medium is obviously clogged with increase of recharge time,which leads to decrease of the efficiency of the recharge facilities and even the service lifetime.Therefore,solving the problem of clogging has become a key in use of rainwater for GAR.In this paper,the phenomenon of iron clogging and its mechanism in the process of AR using urban rainwater are studied.Based on the domestic and foreign research status,the general characteristics of urban rainwater are analyzed.Based on the results of urban rainwater and water quality survey,the laws of iron ion clogging in urban rainwater AR is studied.The main research results are as follows:(1)The occurrence time,the depth and the degree of Fe(Ⅲ)clogging are all affected by the particle size of infiltration medium,the infiltration concentration and the infiltration velocity.The bigger the medium particle size and the lower the infiltration Fe(Ⅲ)concentration,the later the occurrence time of clogging and the lighter the degree of clogging,but the greater the depth and influence of clogging.The smaller the infiltration flow rate,the clogging occurs more late and more light,the more concentrated in the surface.(2)Fe(Ⅲ)mostly remained near the surface of porous medium,and its retention rate and retention quantity were affected by the particle size of porous medium,the infiltration Fe(Ⅲ)concentration and the infiltration velocity.The particle size more small,the Fe(Ⅲ)more concentrate on the surface layer,the retention quantity more big,the retention rate more fast,the concentration of Fe(Ⅲ)more small,the stability time of the effluent concentration more late.The infiltration concentration of Fe(Ⅲ)is high,the retention quantity is bigger,the retention rate is faster,outflow Fe(Ⅲ)concentration is higher.Infiltration flow velocity is high,more quickly into the sand column in unit time,the remained Fe(Ⅲ)quantity is larger,the occurrence time of stable concentration is earlier and the surface retention rate is larger.(3)The main mechanism of iron clogging can be concluded as filtration.Iron ions will become iron hydroxide precipitate at a pH value greater than 1.87,the aggregation of hydroxide precipitate in porous medium leads to clogging.