Enhanced Electrokinetic Remediation In Decabromodiphenyl Ether Contaminated Soils

Polybrominated diphenyl ethers (PBDEs) are a new class of global, persistent, and toxic contaminants, and they tend to accumulate in the environment. With the development of e-waste dismantling industry, it is necessary for PBDEs to develop effective and feasiable remediation methods. Recently, electrokinetic remediation has emerged as an interesting alternative to conventional soil treatments due to its peculiar advantages, namely the capability of treating fine and low-permeability materials, as well as that of achieving a high yield in the removal of inorganic and organic pollutants. In this paper, decabromodiphenyl ether (BDE209) was the target contaminant, and the solubility-enhanced electrokinetic method and electrokinetic remediation coupled with zero valent iorn (ZVI) permeable reactive barrier (PRB) were used to remove BDE209 from the contaminated soil under laboratory conditions. The main results are as follows:(1) Desorption characteristics of BDE209 in soil were studied at first. Few desorption of BDE209 was found and the calculated data were fitted with the equation describing a desorption curve with three kinetically distinct phases. It was observed that desorption process of BDE209 was dominated by the very slow compartment and its desorbing fraction was 68%. In order to enhance desorption of BDE209 in soil, HPCD, SDS and HA were introduced, and the efficiency were greatly improved; Additionally, HA presented the best performance.(2) The migration of BDE209 achieved the best effect under the valtage gradient of 2.0 V·cm-1, with 5% HPCD and 0.01 M Na2CO3 addition to the anode and 0.05 M CA addition to the cathode. The removal rate of BDE209 in the anode area reached 26%. Then the movement of BDE209 in the electric field was investigated. During the first 4 days, BDE209 in the anode soil was quickly transported to the cathode area, while the migration rate near the cathode was slow. From 4 to 10 d, BDE209 was driven to the cathode at a rapid speed. During the following 20 days, the migration rate declined and the concentrations of BDE209 gradually became stable.(3) The reductive debromination rate of BDE209 by ZVI was higher under high temperature and acidic conditon. At the initial phase (0-7 d), the debromination of BDE209 followed well to the pseudo-first-order kinetics. The rate decreased as the reaction proceeded, and BDE209 was transformed to lower bromo congeners on day 30, while stepwise reductive debromination to (n-1)-BDEs was the dominant reaction. The main debromination products of BDE209 were tri-BDEs, tetra-BDEs and penta-BDEs.(4) Electrokinetic remediation coupled with ZVI PRB showed higher removal efficiency compared with single electrokinetic process. When PRB was placed in the middle of the reactor, the removal efficiency of BDE209 in the anode area was 29.9%, while the removal rate in the middle area was 36.5%. When PRB was placed in the section near the cathode, the BDE209 removal from the anode to the middle of the reactor were 27.5%,25.2% and 21.3%, respectively.