Integrated electrokinetic processes for the remediation of phthalate esters in river sediments: A mini-review

Abstract

Concerning the contamination of phthalate esters (PAEs) in river sediments, this mini-review introduces four recently reported novel "integrated electrokinetic (EK) processes" for the remediation purpose, namely two combined technologies of the EK process and advanced oxidation process (EK-AOP Processes) and two combined technologies of the EK process and biological process (EK-BIO Processes). The following is a comprehensive summary for these remediation processes: (1) the EK process coupled with nano-Fe₃O₄/S₂O₈^2- oxidation process - Test results have shown that nanoscale Fe₃O₄ played a significant role in activating persulfate oxidation. Even a recalcitrant compound like di(2‑ethylhexyl)phthalate (DEHP), its concentration in test sediment was reduced to 1.97 mg kg^-1, far below the regulatory levels set by Taiwan EPA; (2) the EK process integrated with a novel Fenton-like process catalyzed by nanoscale schwertmannite (nano-SHM) - Test results have revealed that simultaneous injection of nano-SHM slurry and H₂O₂ into the anode reservoir and sediment compartment is a good practice. 70-99% in removal efficiency was obtained for various target PAEs; (3) enhanced in situ bioremediation coupled with the EK process for promoting the growth of intrinsic microorganisms by adding H₂O₂ as an oxygen release compound (ORC) - Test results have demonstrated that an intermittent mode of injecting lab-prepared ORC directly into the contaminant zone would be beneficial to the growth of intrinsic microorganisms in test sediment for in situ bioremediation of target PAEs; and (4) coupling of a second-generation ORC (designated 2G-ORC) with the EK-biological process - Test results have proved that 2G-ORC is long-lasting and can be directly utilized as the carbon source and oxygen source for microbial growth resulting in an enhanced biodegradation of PAEs. Except DEHP having a residual concentration of 4 μg kg^-1, all other target PAEs in test sediment were totally removed by this novel combined remediation process.

Keywords: Enhanced in situ bioremediation; Fe(3)O(4)/S(2)O(8)(2−) oxidation process; Fenton-like process; Integrated electrokinetic process; Schwertmannite; Second-generation oxygen release compound.