Simultaneous removal of fuel hydrocarbons and heavy metals from a railroad soil using electrokinetic remediation

초록

The feasibility of the electrokinetic (EK) process for remediation of railroad soil contaminated simultaneously with organic and inorganic contaminants was studied. Also, the effect of pH conditioning during EK process on the system’s performance was evaluated. The target soil collected near a maintenance facility of railroad was contaminated with various heavy metals including As, Cd, Cu, Pb and Zn, as well as fuel hydrocarbons, over 12,000 mg/kg of total petroleum hydrocarbon (TPH). Although it was reported around 30 % of polluted sites were known to be mixed contaminated, there have been few techniques to remove both of organic and inorganic contaminants successfully. In this study, EK remediation process was applied with pH-conditioning in catholyte using nitric acid in order to enhance the removal of heavy metals and TPH. 0 M to 1.0 M of nitric acid and 0.01 M of Na2HPO4 was supplied into catholyte and anolyte tank, respectively for 15 days of operation. System parameter including electrical density variation, electrolyte pH profile and electroosmotic flow (EOF) was evaluated during operation and soil moisture content, soil pH, residual content of each pollutant were analyzed. As results, it was observed that the higher concentration of nitric acid applied into EK system, the higher electrical density and reverse electroosmotic flow. Catholyte pH stayed around pH 2 when over 0.5 M of nitric acid was used as catholyte and acidic environment established in soil enhanced increased degree of reverse EOF as well as mobility of cationic heavy metals such as Cd, Cu, Pb and Zn. Using 1 M of nitric acid as catholyte, the average removal of Cd, Cu, Pb and Zn were 91.1 %, 74.1 %, 88.9 % and 90.0 %, respectively. On the other hand, As and TPH showed lower removal efficiencies in acidic condition, where the highest removal of As and TPH were 12.6 % and 26.5 % for control test without nitric acid in catholyte tank. In conclusion, EK remediation process is available to remove organic and inorganic pollutants and pH conditioning could dramatically enhance the removal of cationic heavy metals.