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Time (min) 0 20 40 60 80 100 120 140 160 180 200 C/Co 0.0 0.2 0.4 0.6 0.8 1.0 1.2 30 mA 60 mA 90 mA 120 mA Time (min) 0 20 40 60 80 100 120 140 160 180 200 C/Co 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Bipolar 50%/50% 33%/67% Problem . Once released to the environment, chlorinated organic compounds (COCs) like trichloroethylene (TCE) have a tendency to cause or contribute to widespread groundwater contamination due to a unique combination of physical and chemical properties. TCE is among substances most commonly found at US EPA Superfund sites. northeastern.edu/protect } Puerto Rico T estsite for Exploring Contamination Threats SRP Center This program is supported by Award Number P42ES017198 from the National Institute of Environmental Health Sciences. Puerto Rico CLOSE to 20% of Preterm Births MORE than 150 Contaminated Sites Prof. Akram Alshawabkeh: email: [email protected] Ljiljana Rajic, PhD; email: [email protected] A THREE ELECTRODE SYSTEM FOR ELECTROCHEMICAL TRANSFORMATION OF TRICHLOROETHYLENE IN GROUNDWATER Ljiljana Rajic, Roya Nazari, Noushin Fallahpour, Akram N. Alshawabkeh Civil and Environmental Engineering Department, Northeastern University, Boston, MA, 02115, USA Proposed Solution . Due to the fast and effective processes, electrocatalytic reduction of COCs in groundwater has gained interest. The main removal mechanism is hydrodechlorination (HDC). To improve the reduction mechanism in mixed electrolyte electrochemical cells, an iron anode can be used. Limitations . The use of an iron anode in the undivided electrochemical cell eliminates the competition between the oxygen (that is produced at the inert anodes) and contaminants for the reduction at the cathode but may cause precipitation and an increase in pH. Improvement . Using an additional anode of inert material with an iron anode (a three electrode system) will create conditions to control precipitation and maintain natural pH value of the groundwater. Compared to the 2 electrode system, the 30 mA /30 mA ratio doubled TCE removal efficiency without any significant change in pH and with a decrease in precipitation by 20% (Figure 1). By reducing precipitation, less cathode surface is covered by the particles thus leaving it available for TCE reduction. Further, we found that increased current intensity to 90 mA and 120 mA, improved TCE removal compared to 60 mA by 12% and 13% (Figure 2), and reduced precipitation formation by 30% and 42%, respectively. However, the higher currents caused an increase of pH to 11. The results of this study show that optimization of anode→anode→cathode arrangement overcome the drawbacks of the use of a single iron anode and increases the removal rate of TCE. This process will allow implementation of an efficient, solar-powered and practical electrochemical system for in situ treatment of contaminated groundwater. RESULTS Experimental setup: Anode (E1): Mesh Ti/MMO Anode (E2): Perforated cast iron Cathode (E3): Iron foam Current intensity: 60 mA Flow velocity: 3 mL min -1 Inter-electrode distance: 2.5 cm Solution: 0.172 g L -1 CaSO 4 ; 0.413 g L -1 NaHCO 3 ; 5.3 mg L -1 TCE Treatment duration: 180 min Current Split (Ti/MMO/Cast Iron anode) Current Intensity (mA) Bipolar 60 50%/50% 30, 60, 90, 120 33%/67% 60 Tested Variables Figure 1. TCE decay during experiments with different current split ratios under 60 mA Figure 2. TCE decay during experiments with different current intensities under 50%/50% split ratio
