Transport And Biodegradation Of1,2-Dichloroethane In Laboratory Aquifer Columns

Chlorinated solvents are among the most widespread contaminants in groundwater,which are the focus of researchers. They are toxic and strongly volatile, and often exist inthe form of heavy non-aqueous phase due to their low solubility in groundwater.1,2-dichloroethane (1,2-DCA) is one typical kind of chlorinated solvents, and in this study,we investigated its transport in the saturated aquifer and biodegradation process in nitrateconditions through soil column.Quartz sand was selected as filler material of the soil column at first, and investigatedthe effect of packing heights (24cm,32cm,48cm), flow rates (2mL/min,5mL/min,10mL/min), concentrations (5mg/L,10mg/L,20mg/L) and particle sizes (20~40mesh,40~60mesh,60~80mesh) on the transport of1,2-DCA in the saturated aquifer throughbreakthrough curves. The results showed that the higher the packing height was, the morepenetration time needed, but its penetration rate is unchanged; The faster the flow rate was,the less penetration time needed, and the higher penetration rate; Particle size had noobvious effect on the transport, and concentration had no effect on the transport of1,2-DCA in the sand column.On the basis of sand column experiment, the sandy soil from an industrial site as fillermaterial was selected and investigated the transport of1,2-DCA under different flow rates(8cm/h、16cm/h、28cm/h) was investigated. A nonlinear least-squares optimizationapproach (CXTFIT2.1) was used to fit the breakthrough curves. The results showed thatthe faster the flow rate was, the less penetration time needed, and the higher peak value ofthe breakthrough curves it got. Combination of model parameters analysis, we found thatflow rate changes mainly affected the retardation factor R, and the higher the flow rate was,the smaller the R value. Using the model simulation, comparing with the equilibriummodel, the non-equilibrium two-site model could be better to simulate the transport of1,2-DCA in saturated sandy soil. And it showed that, non-equilibrium transport of1,2-DCAin saturated sandy soil was mainly affected by the difference among the adsorptionexchange sites. At last, the biodegradation process of1,2-DCA in nitrate and anaerobic saturatedaquifer was explored. The results showed that concentration of1,2-DCA in effluent waterwas lighter than that in penetration water in every soil column, and the parameter indicatedthe internal conditions of the soil column for anaerobic reducing conditions. No organiccarbon products were obviously detected, but it was found that there were biodegradationof1,2-DCA in every soil column under the nitrates and nitrate-free conditions comparingwith sterilized soil column. During the experiment of81days, the maximum amount ofbiodegradation in soil column were5.007mg/L in nitrates conditions, and3.471mg/L innitrate-free conditions, and they respectively accounted for46.82%and34.09%of the totalattenuation of1,2-DCA, and their half-life were62days and119days respectively.