||The purpose of this work was to investigate the use of nanoscale Fe3O4 as a catalytst for destruction of trichloroethylene (TCE) and 1,2-dichloroethane (1,2-DCA) by persulfate in spiked water and soil. First, nanoscale Fe3O4 was prepared by chemical coprecipitation. X-ray powder diffraction (XRD) was used to confirm the crystal structure; And size identification was performed using the scanning electron microscopy (SEM).|
The effectiveness of using 3 wt% soluble starch (SS) to stabilize nanoscale Fe3O4 was also studied. It was found that SS could effectively disperse the nanoparticles for more than one month. Therefore, SS was chosen to prepare the nanoscale Fe3O4 slurry.
The efficiency of nanoscale Fe3O4 as an activator for persulfate remediation of TCE and 1,2-DCA in aqueous solutions (DI water, simulated groundwater, and actual groundwater) was then investigated. The results showed that all test removal efficiency of TCE and 1,2-DCA was more than 95%. Use of the persulfate for destruction of TCE and 1,2-DCA produced some by-products. The primary reaction products were cis-1,2-Dichloroethylene (cis-1,2-DCE) and trans-1,2-Dichloroethylene (trans-1,2-DCE)； The secondary daughter prodnct was vinyl chloride (VC). The VC produced is gradually degraded to safer substances (ethene, ethane, and methane).
The nanoscale Fe3O4 slurry and the persulfate injection coupled with the electrokinetic (EK) process was tested for remediation of TCE and 1,2-DCA in saturated soil. The results showed that injection of persulfate into the EK reservoir could decrease the electrode polarization, and increase the electroosmotic flow and current density. When persulfate was injected into the cathode reservoir, the derived sulfate radicals would transfer into the soil compartment by ion migration.
The injection of persulfate into the cathode reservoir was more efficient than injection of persulfate into the anode reservoir. The removal efficiency for TCE and 1,2-DCA was more than 96% in all tests.
The remediation system was assessed for potential application in-situ. Soil was spiked with high TCE and 1,2-DCA and aged for a week. The injection of persulfate and nanoscale Fe3O4 slurry coupled with the EK process was tested for remediation of the aged contaminated soil. The results showed that the target contaminants (TCE and 1,2-DCA) met the Taiwan’s EPA’s control standard. After 30 d of remediation, the by-products (cis-1,2-DCE, trans-1,2-DCE, and VC) had also been removed to below the action limit.
A cost analysis was performed in order to demonstrate the economic feasibility of the remediation method in this study. Operating costs (chemicals + electricity bill) of all tests were assessed. The results showed that the costs were 8000-17000 NT$/m3, which is economically reasonable.