Hybrid electrodialysis and electrolysis systems and processes
Disclosed are systems and processes for the removal and conversion of pollutants in water. A system includes a set of electrodes with at least one electrode having an integrated catalyst material. The system is operatable in a first, electrodialysis mode in which one or more pollutants are separated from a feedwater stream, and a second electrolysis mode in which the separated pollutant(s) are catalytically converted into benign products by way of the catalyst material of the electrode. Electrodialysis and electrolysis are therefore carried out using the same unit.
1 . A method of removing and electro-reducing nitrate anion from a feedwater comprising nitrate solutes, the method comprising:
providing an integrated electrodialysis and electrolysis hybrid system that includes
a first electrode,
a second electrode disposed opposite the first electrode, and
an anion exchange membrane adjacent to the first electrode and a cation exchange membrane adjacent to the second electrode and between the first and second electrodes to define (i) a feedwater compartment between the respective membranes, (ii) an anion concentration compartment adjacent to the anion exchange membrane, said anion exchange membrane and first electrode defining the anion concentration compartment therebetween, and (iii) a cation concentration compartment adjacent to the cation exchange membrane, said cation exchange membrane and second electrode defining the cation concentration compartment therebetween, and
wherein said first electrode is comprised of a planar electrically conductive material capable of operating as an electrodialysis electrode when operated as an anode and as a catalytically electro-reductive electrode capable of selectively electro-reducing nitrate anion transferred from the feedwater when operated as a cathode; and
wherein said first electrode is the only electrode adjacent to or in direct contact with the anion concentration compartment;
passing the feedwater into the feedwater compartment and providing water to the anion and the cation concentration compartments, and
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 ion in the feedwater compartment that is lower than the incoming feedwater, and producing a water in the anion concentration compartment that includes the nitrate anions passing through the anion exchange membrane and
operating the hybrid system, for a second time period, in an electrolysis mode by reversing the polarity across the first and second electrodes, such that the first electrode becomes cathodic with respect to the second electrode, and whereby the nitrate in the anion concentration compartment is electro-reduced such that the Faradaic efficiency for conversion of nitrate to nitrite is higher than the Faradaic efficiency for conversion of nitrate to nitrogen gas.
2 . The method of claim 1 wherein the first electrode comprises a nanoparticulate catalyst coating.
3 . The method of claim 1 or 2 wherein the first electrode comprises a copper catalyst.