Development of a hybrid electrokinetic system for the simultaneous removal of heavy metals and PAHs from clayey soil

Several industrial and municipal areas in North America are contaminated with heavy metals and petroleum products. This mixed contamination presents a particularly difficult task for remediation when dealing with clayey soil. The objective of this research was to develop a method to clean mixed contaminated clayey soils. A lab scale multifunctional hybrid electrokinetic method was investigated. Clayey soil, contaminated with lead (555 ppm), nickel (555 ppm) and phenanthrene (600 ppm), was subjected to simultaneous removal using an electrokinetic system. The electrokinetic surfactant supply system was applied to mobilize, transport and remove phenanthrene. A chelation agent (EDTA) was electrokinetically supplied to mobilize heavy metals. These supplied liquids were introduced in various sequences and at different periods in order to optimize the removal of both types of contaminants. The studies were performed on 8 lab scale electrokinetic cells connected to a DC power supply to achieve a voltage gradient of 0.3 V/cm. In order to avoid some negative impacts associated with electrokinetic processes, ion exchange textiles (IET) were incorporated into the system. Electrical parameters, pH, volume supplied and volume discharged were monitored continuously during each experiment. At the end of the tests, the soil and catholyte were subjected to physico-chemical analysis. Results showed that the optimal average simultaneous removal was 85% for lead, 84% for nickel, and 74% for phenanthrene. The highest local removals achieved for lead, nickel and phenanthrene were 96%, 95%, and 84% respectively. For the optimal removal conditions the consumption of energy was 28.4 kWh/m 3 . However, the hybrid method can achieve a two-fold decrease in energy consumption. The results of this study can be applied as an in-situ hybrid electrokinetic technology for the remediation of clayey sites contaminated with petroleum products and heavy metals, (e.g. Manufacture Gas Plant Sites)