Targeted Lead and Copper Removal from Aqueous Streams Using Carbon Electrodes in an Electrochemical Filter

Lead contamination in drinking water is a pervasive health problem across the US, brought into the public spotlight by the 2014 water crisis in Flint, Michigan. The Environmental Protection Agency (EPA) established The Lead and Copper Rule in 1991 to limit exposure of these elements and set the action level to 15 ppb; however, there is no safe level of lead consumption.¹ Despite corrosion prevention measures taken by public water authorities, lead concentrations in drinking water are routinely elevated nationwide.² A reliable long-lasting water filter that can specifically target lead and other metals is currently lacking in the marketplace. Metals removal from wastewater is also a major concern for many industries, where water reuse is becoming commonplace, regulations are getting more stringent, and discharge limits must be met. Much of this current work has focused on lead and copper removal from drinking water and industrial wastewater, with a specific focus on commercializing a technology that can provide clean water in a sustainable manner. Applying this technology to other metals of interest has also been demonstrated.

Conventional and electrochemical methods for metals removal from water cannot effectively distinguish between many dissolved species and behaves more as a bulk removal process. In order to obtain a purified or concentrated stream of a desired metal, additional separation steps need to be used, making the overall process more expensive and complicated. PowerTech Water has developed carbon electrodes in an electrochemical filter that can target specific metals in a water stream to either remove or recover them, depending on the application. The device uses activated carbon electrodes and a small applied voltage (<2.0 V) to induce Faradaic reactions at both the carbon-based anode and cathode within the cell. By tuning the device configuration and operating parameters, a targeted metal will precipitate out of solution, generally according to its Pourbaix diagram, and be trapped within the porous electrode matrix.

Electrochemical water treatment was performed at a constant applied voltage with lead spiked tap water, achieving >90% removal of the target metal, while leaving other species (eg. Na⁺ and Ca²⁺) in solution. SEM and EDX analysis of the used anodes and cathodes confirmed the presence of lead species (Figure 1, right panel). To further understand the mechanisms at play, the near electrode pH and voltage distribution were measured. By varying the applied potential, the pH and voltage at the anode and cathode were recorded, along with the concentration of lead at the inlet and outlet. This information, when combined with the Pourbaix diagram, can be used to help identify the lead speciation at each electrode and optimize device performance. Additional experiments were performed with copper spiked tap water, demonstrating the versatility of the electrochemical filter described here.

References:

1. Suh, R. (2016, June 28). Our Drinking-Water Crisis Goes Far Beyond Flint. Natural Resources Defense Council. Retrieved from: https://www.nrdc.org/experts/rhea-suh/our-drinking-water-crisis-goes-far-beyond-flint

2. Environmental Protection Agency. Lead and Copper Rule. Retrieved from: https://www.epa.gov/dwreginfo/lead-and-copper-rule

Figure 1