Efficient treatment of wastewater using electrochemical cell
An efficient method and system for the electrochemical treatment of waste water comprising organic and/or inorganic pollutants is disclosed. The system comprises an electrolytic cell comprising a solid polymer, proton exchange membrane electrolyte operating without catholyte or other supporting electrolyte. The cell design and operating conditions chosen provide for significantly greater operating efficiency.
1. A method for the energy efficient treatment of polluted wastewater comprising:
providing a solid polymer electrolyte electrolytic cell comprising an anode comprising an anode catalyst layer and the anode catalyst layer comprising an anode catalyst, a cathode comprising a cathode catalyst layer and the cathode catalyst layer comprising a cathode catalyst wherein the cathode is liquid-electrolyte free, and a solid polymer membrane electrolyte separating the anode and the cathode;
supplying a flow of wastewater comprising a pollutant to the anode of the electrochemical cell;
providing a voltage less than about 3 volts across the electrolytic cell wherein the anode is positive with respect to the cathode;
operating the electrolytic cell at an operating temperature and a current density less than about 20 mA/cm2, thereby degrading the pollutant and generating hydrogen gas at the cathode; and
exhausting the generated hydrogen gas from the cathode.
2. The method of claim 1 comprising operating the electrolytic cell at a current density less than about 10 mA/cm2.
3. The method of claim 1 comprising supplying the flow of wastewater to the anode without an added supporting electrolyte.
4. The method of claim 1 comprising operating the electrolytic cell at an operating temperature in the range from about 3 to 95° C.
5. The method of claim 1 wherein the spacing between the anode and the cathode is less than about 30 micrometers.
6. The method of claim 1 wherein the anode catalyst is selected from the group comprising platinum, tin oxide, antimony tin oxide, niobium doped antimony tin oxide, graphite, and manganese oxide.
7. The method of claim 1 wherein the cathode catalyst is selected from the group comprising platinum, manganese oxide, graphite, and carbon.
8. The method of claim 1 wherein the anode comprises a fluid distribution layer and a microporous sublayer between the anode catalyst layer and the fluid distribution layer.
9. The method of claim 1 wherein the anode comprises a fluid distribution layer comprising niobium mesh and tungsten gauze.
10. The method of claim 1 wherein the cathode comprises a gas diffusion layer and a microporous sublayer between the cathode catalyst layer and the gas diffusion layer.
11. The method of claim 1 wherein the anode catalyst layer additionally comprises carbon or graphite particles having a surface area greater than 280 m2/g.
12. The method of claim 1 wherein the anode catalyst layer additionally comprises Ta, Nb, or TiC particles having a particle size less than 45 microns.
13. The method of claim 1 wherein the pollutant is an organic.
14. The method of claim 13 wherein the pollutant is Acid Blue dye, phenol, acetaminophen, formic acid, ibuprofen or Kraft effluent.
15. The method of claim 1 comprising recovering the exhausted generated hydrogen gas produced at the cathode and converting the hydrogen gas back into electricity.
16. The method of claim 1 comprising a post treatment step for removing free chlorine selected from the group consisting of: reducing electrochemically, adsorbing, decomposing by contacting a transition metal, reacting with a salt, reacting with a chemical reducing agent, reacting with organic matter, decomposing by contacting a redox filter, decomposing by light exposure, and decomposing by heating.
17. The method of claim 1 comprising a step for preventing formation of chlorine selected from the group consisting of: controlling the pH of the wastewater to be greater than about 2, increasing the ionomer concentration at the anode fluid delivery layer, increasing the ionomer concentration at the anode catalyst layer, and incorporating materials that catalyze the decomposition of free chlorine into the anode.
18. The method of claim 1 comprising a cleaning step selected from the group consisting of: ion exchanging in-situ, purging the cathode with a cleaning solution, and potentiostatic cleaning.