Electrocapacitive Desalination of Brackish Water Using Biochars

R. Vander Wal, A. Sengupta, R. Rajagopalan
Penn State University,
United States

Keywords: desalination, CDI, biochar, brackish


The principle of capacitive deionization (CDI) has been known for some time, as a spin-off of electrochemical capacitance. Instead of storing energy, the purpose of CDI is to store (temporarily) salt, extracted from the water. With ions of opposite charge attracted to and held by electrodes – to which an applied voltage is applied, the dissolved salt is effectively removed from the water – accomplishing desalination. CDI does not require added harsh chemicals, as by conventional precipitation, expensive membranes, as does reverse osmosis, or high-energy inputs, as needed for evaporative techniques. Relative to distillation, evaporative or reverse osmosis, it offers high-energy efficiency. Advancing this technology with new, biomass-derived carbons as electrode materials is the key innovation proposed here. Our approach is to use carbonaceous material produced through pyrolysis of a biomass mixture of cellulosic and lignin components, along with activated carbon. Using a mixture of components decouples the constraints of porosity and high surface area. Separate materials, mixed and bonded together fulfill both criteria. Moreover all such materials are economical, available in bulk and hence well suited for small- and large-scale implementation. The carbon-based materials, in different forms separately provide porosity and high surface area while enabling independent tailoring of each characteristic by their relative amounts and pre-processing, prior to mixing. A capacitive deionization unit, using electrodes fabricated from these carbons is tested for its effectiveness. Key metrics include the salt removal capacity (per unit mass of carbon), removal rate, and cycle life. The project will progress along two stages of development: material development and testing.