(136d) Practical Applications of Electrokinetic Separations

Separations technologies applied in aqueous phase can be categorized into (i)electrokinetic-driven, (ii)pressure-driven, (iii)thermally driven and (iv)biological-related. In electrokinetic processes, concentrated ions are separated from the water solution in an electric field, and therefore, energy use is correlated with the quantity of ions removed. Electrokinetic processes can provide water desalination at a targeted salinity or preferential ions removal that is “fit-for-purpose”. Electrokinetic processes only remove ionized or ionizable species and is not useful for removing organics or biological species. In pressure-driven processes, purified water is separated from the brine concentrate. Typically, pressure-driven processes cannot tune salinity for fit-for-purpose quality but are effective at organic and biological species removal. Electrokinetic processes encompass electrodialysis (ED), electrodeionization (EDI), capacitive deionization (CDI), cation intercalation desalination (CID), and ion concentration polarization (ICP).

Compared to the pressure-driven membrane separation technologies used most in industrial separations, applications of selective separations have increased in recent years and becomes important to address the challenges of technology adaptation to climate change. For examples, the production of biofuel and bio-products to reduce green-house gas emission from fossil fuel and the non-conventional water supply for water-energy nexus have required high energy efficient and cost effective separation technologies. Innovative electrochemical separations can provide transformational impacts in advancing selective separations for highly energy efficient, small capital footprints and low processing cost. It, thus, enables the paradigm-shift of using alternative fuels and water supplies for industrial applications. We will discuss the key process performance metrics, energy consumption and processing rate, of EDI and CDI applied in the fields of biorefinery, waste to energy and water energy nexus to separate charges species from “dilute” aqueous phase. The ions separation performance demonstrated from various aqueous streams include 1) inorganic and organic salts removal/capture from pretreated hydrolysate, and 2) organic acid capture/production from bioprocessing streams in biofuel production; 3) volatile fatty acid removal/capture from waste anaerobic digester for waste to energy; 4) selective desalination of hardness, alkalinity, silica and ammonia from impaired water for cooling water supply. Critical issues in process design and material property to achieve electrokinetic separation rate and energy efficiency for economic viability will be discussed.