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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: Suh, R. (2016, June 28). Our Drinking-Water Crisis Goes Far Beyond Flint. Natural Resources Defense...

Selective separations are needed in a wide variety of industrial and commercial applications where discharge to publicly owned treatment works (POTW) requires certain metals concentrations to be sufficiently low to protect public health and the surrounding environment. Metals such as lead (Pb), copper (Cu), chromium (Cr), nickel (Ni), zinc (Zn), and cadmium (Cd) represent a non-exhaustive list of compounds requiring removal for discharge regulations. Typically, coagulants such as iron and aluminum combined with precipitation chemistry or ion exchange processes are used to meet these regulations.1 However, these methods are not particularly selective and can produce sizable sludge waste that must be disposed of properly. Size-selective membranes are one alternative approach, but the pretreatment requirements for these membranes further complicates the water treatment process. Capacitive deionization (CDI) is an emerging water treatment option as well with notable advances in recent years, but it currently lacks the selectivity needed for many industrial streams.2 Therefore, alternative methods are being sought to realize these separations. The use of electrochemical processes offers a number of benefits such as a defined interface for interaction with the metal of interest, the ability to modulate the interface easily and quickly through changes in localized voltage, use of the electrical current to monitor system conditions, and the in situ generation of chemical species that can aid in the separation. Of particular interest in a wide variety of industrial applications is the removal or Cu from water being discharged to the POTW. Cu is found in waste streams emanating from electroplating, electronics, semiconductor, and battery manufacturing operations. While coagulation approaches mentioned above can often be used to meet effluent regulations, metal recovery through an electrochemical process can be highly effective and efficient, reaching current efficiencies in excess of 95% in many applications. The ability to plate Cu at a cathode under highly localized conditions affords the removal of Cu down to levels <100 ppb. Electrowinning has been used for over a century in the creation of purified metals such as Cu, so the concept is not entirely new, but the design of electrode materials and overall cell construction capable of removing Cu to such low concentrations in streams that have conductivities <1 mS/cm opens up new avenues for water treatment in industrial and commercial waste. In this talk, electrochemical cell design and operation as well as feed water conditions will be reviewed towards the development of selective metal removal technologies. Copper removal will be highlighted as an example, but the concept will also be applied to other metals of interest, demonstrating the more ubiquitous nature of the approach. References: Azimi, A. Azari, M. Rezakazemi and M. Ansarpour, Removal of Heavy Metals from Industrial Wastewaters: A Review, ChemBioEng Reviews, 4, 37-59 (2017). Gao, A. Omosebi, J. Landon, and K. Liu, Energy Environ. Sci., 8 (3), 897-909 (2015). Boehme, C. Lippert, and J. Landon. “Faradaic Porosity Cell.” U.S. Patent 16/520,340 & PCT/US2019/043129, filed July 23, 2019. Figure 1