Hybrid electrodialysis and electrolysis systems and processes

A method for removing and electro-reducing nitrate anion from feedwater comprising nitrate or nitrite solutes, the method comprising:

• providing an integrated electrodialysis and electrolysis hybrid system comprising a first electrode comprised of an electrically conductive chemically inert scaffold material having a coating of selective electro-reductive catalyst for nitrogen-based anion reduction, a second electrode positioned opposite the first electrode, and a first ion exchange membrane adjacent to the first electrode, and a second ion exchange membrane adjacent to the second electrode and positioned between the first and the second electrodes to define a central compartment between the anion exchange membrane and the cation exchange membrane, a first electrode compartment defined between said first ion exchange membrane and the first electrode, and a second electrode compartment defined between said second ion exchange membrane and the second electrode;
• passing the feedwater water into the central compartment and the first and the second electrode compartments;
• operating the hybrid system for a first time period in an electrodialysis mode by imposing an anodic polarity across the first electrode and a cathodic polarity across the second electrode to produce a concentration of nitrate or nitrite ion in the central compartment that is lower than the concentration of nitrate or nitrite ion in the feedwater, and producing a water in the first electrode compartment that includes nitrate or nitrite anions;
• and
• operating the hybrid system, for a second time period, in an electrolysis mode by reversing the polarity across the first and the second electrodes, such that the first electrode becomes cathodic with respect to the second electrode, and whereby nitrogen-based anions in the first electrode compartment are electro-reduced to form one or a combination of reaction products comprising nitrite, ammonia, ammonium, or nitrogen gas.

A system for removing and electro-reducing nitrogen-based anions from feedwater comprising nitrogen-based solutes, the system comprising:

• an integrated electrodialysis and electrolysis device comprising a first electrode;
• a second electrode positioned opposite the first electrode;
• a first ion exchange membrane adjacent to the first electrode, and a second ion exchange membrane adjacent to the second electrode and positioned between the first and the second electrodes, a plurality of ordered and repeating cation exchange membranes and anion exchange membranes positioned between said ion exchange membranes, and defining a plurality of central compartments forming alternating diluting and concentrating compartments between the ion exchange membranes, a first electrode compartment defined between said first ion exchange membrane and the first electrode, and a second electrode compartment defined between said second ion exchange membrane and the second electrode;
• feedwater inlets and effluent outlets in fluid communication with said central compartments and said first electrode compartment and said second electrode compartment;
• and
• a source of DC electrical power connected to said first electrode and said second electrode.