Surfactant and MGDA enhanced - Electrokinetic treatment for the simultaneous removal of mercury and PAHs from marine sediments

Mercury (Hg) and Hg-PAH removal effectiveness of several electrokinetic (EK) decontamination treatments, including the combined use of eco-friendly enhancing agents, was investigated in this work as a potential remedial treatment of heavily contaminated marine sediments. After a 400-h EK treatment, main results revealed a very poor Hg mobilization without the use of an appropriate conditioning agent, mainly due to the strong Hg-bounds with carbonates, organic matter and sulphides, which were present at high concentrations. The use of EDTA as processing fluid resulted in a slight improvement of Hg removal (∼15%). A further increase in Hg removal rate of ∼39% can be achieved with methylglycinediacetic acid (MGDA) as anodic solution. The best Hg-removal of ∼71% was obtained by means of the simultaneous use of MGDA and Tween® 80 due to their synergistic action in remedial processes. The same type of treatment led to a slightly lower total Hg-removal of ∼67% when a shorter time of 240 h was considered. In the case Hg and PAHs as sediment co-contaminants, results revealed a total PAH-removal of 59.45%. The co-presence of PAHs significantly affected the electric current circulating in the system and the electrosmotic values, leading to a reduction of about 5% in Hg removal respect to the case where PAHs were not present in the sediments. Nevertheless, the combined application of Tween® 80 and MGDA in enhanced-EK treatment allows the possibility to successfully remove both highly persistent Hg and PAHs from marine sediments with high removal percentages. Obtained data can be useful for further enhanced EK treatments of sediments contaminated with Hg and PAHs, as well as providing basic information for future cost analysis.