Electrochemically Mediated Removal of Nitrate on Granular Activated Carbon
Nitrate in drinking water poses a serious public health risk which affects water sources in California and around the world. The environmental risks of nitrate are twofold: as a contaminant in drinking water it threatens the health of infants and pregnant women, and in lakes and coastal regions it contributes to algae blooms, eutrophication, and hypoxic “dead zones.” However, nitrate is an extremely stable and soluble contaminant, which makes cost-effective removal very difficult. Activated carbon adsorption of contaminants is an accessible, economical method of water purification, but activated carbon is highly inefficient at adsorbing nitrate. Electrochemical reduction of nitrate is achievable, but has excessive energy requirements and often necessitates high-pressure or high-temperature water treatment.
Electrochemically-mediated nitrate removal on granular activated carbon (GAC) provides the benefits of both adsorption and electrochemical treatment methods and produces a high-quality permeate stream under room temperature and atmospheric pressure. Application of 5V to a GAC packed-bed filter doubled nitrate removal over 24-hour filtration period with no observed generation of ammonia or nitrate. In addition, a reverse-polarity rinse of the filter system allowed for complete regeneration of the removal efficiency of the GAC.
This removal was determined to be pH-insensitive, linearly dependent on hydraulic retention time, and moderately sensitive to interference by inorganic salt species commonly observed in groundwater. As a new treatment method for nitrate-contaminated water, electrochemically-mediated removal of nitrate on GAC offers a highly efficient, green, and reusable method with significant potential for drinking water applications.