Process and apparatus for the electro-chemical treatment of water contaminated with emerging contaminants
An electrolytic reactor and process for decontaminating wastewater containing emerging contaminants, such as medicament residues or per- and polyfluoroalkyl substances (PFAS) are disclosed. The contaminated wastewater is circulated through one or several reactors for electro-oxidizing and degrading the contaminants. Each reactor comprises an enclosure, an electrode assembly comprising first and second current distribution circuits, a first group of N electrodes connected to the first current distribution circuit, and a second group of N electrodes connected to the second current distribution circuit. According to the polarity of the current provided to the electrodes, the electrodes of the first group form anodes whereas the electrodes of the second group forms cathodes, and vice versa. The electrodes are preferably dimensionally stable anodes (DSA). The reactor and process described herein allow removal of multiple emerging contaminants simultaneously, in addition to reducing the carbon footprint through lower power consumption.
1. A process for treating wastewater contaminated with contaminants comprising chemical residue of medicaments and/or perfluoroalkyl and polyfluoroalkyl substances (PFAS), the process comprising:
circulating the contaminated wastewater through at least one electrolytic reactor comprising electrodes while applying a current to the electrodes, for electro-oxidizing and degrading said emerging contaminants; wherein each of the at least one electrolytic reactor for treating contaminated wastewater comprises:
an enclosure comprising:
a closed end having an inlet,
an open end, opposite to the closed end, forming an aperture and having at least one outlet adjacent the aperture, and
a peripheral wall extending from the closed end to the open end; and
an electrode assembly configured to be inserted into the enclosure through the aperture and to seal the aperture to form the at least one electrolytic reactor, the electrode assembly comprising;
a first group of N electrodes of said electrodes operatively connected to a first current distribution circuit; and
a second group of N electrodes of said electrodes operatively connected to a second current distribution circuit;
wherein:
N is an integer equals to 3, 6, 9, 12, 16 or 18;
the 2N electrodes of the first and second groups are configured to extend from the open end towards the closed end of the enclosure inside the enclosure;
the first and second current distribution circuits are each configured to be operatively connected to an electric power supply, the N electrodes of the first group forming anodes and the N electrodes of the second group forming cathodes, and vice versa, according to a polarity of the current provided to the first and second groups of electrodes; and
the inlet being configured to be fluidly connected to a pump for circulating the contaminated wastewater inside the enclosure from the inlet to the at least one outlet of the at least one electrolytic reactor; and
wherein the electrode assembly comprises a crown member configured to hold the 2N electrodes and secure the current distribution circuits, the crown member being configured to seal the aperture of the enclosure once the electrodes are inserted into the enclosure; and wherein the crown member comprises:
a plate for supporting the electrodes extending therefrom, the plate at least matching in size with the open end of the enclosure to seal the enclosure; and
a tubular insert extending from the plate in an opposite direction than the electrodes, the tubular insert and the plate forming an inner space for securing the current distribution circuits;
wherein the first current distribution circuit comprises a first distribution plate made of an electrically conductive material and defining a first shape, and
the second current distribution circuit comprises a second distribution plate made of the electrically conductive material and defining a second shape,
wherein each plate is configured to connect in parallel the N electrodes of its respective group, and
wherein the first and second shapes allow the distributions plates to be inserted into the inner space of the tubular enclosure while keeping a gap therebetween to avoid electrical contact; and
wherein the first plate has a ring shape extending along a peripheral wall of the tubular insert, and the second plate has a star shape configured in size to be located inside the first plate; and wherein the first ring shaped plate forms a number N of tips extending inwardly, each tip forming an electrical connecting point with one electrode of the same group, whereas the second star shaped plate has a number N of tips extending outwardly toward the first plate, wherein the N tips of the second plate intercalate with the N tips of the first plate along a same circumferential position, the intercalated tips being each electrically connected with one electrode of its respective group.
2. The process according to claim 1 , wherein the current provides a current density to the electrodes from about 10 mA/cm 2 to about 50 mA/cm 2 .
3. The process according to claim 2 , wherein the current density is about 30 mA/cm 2 .
4. The process according to claim 1 , further comprising filtrating the contaminated wastewater exiting the at least one electrolytic reactor for removing degraded contaminants formed by the at least one electrolytic reactor.
5. The process of claim 4 , wherein the filtrating of the contaminated wastewater exiting the at least one electrolytic reactor is performed using a filter comprising activated carbon.
6. The process according to claim 1 , further comprising:
pre-oxidizing the contaminated wastewater with ozone before circulating the contaminated wastewater in the at least one electrolytic reactor.
7. The process according to claim 1 , further comprising:
passing the contaminated wastewater through a membrane before circulating the contaminated wastewater in the at least one electrolytic reactor for concentrating the contaminated wastewater.
8. The process according to claim 1 , further comprising:
adding a given amount of a salt to the contaminated wastewater to increase the conductivity of the contaminated wastewater circulating in the at least one electrolytic reactor.
9. The process according to claim 8 , wherein the salt comprises sodium persulfate (Na 2 S 2 O 8 ).
10. The process according to claim 1 , further comprising:
adding a given amount of a base to the contaminated wastewater to increase the pH of the contaminated wastewater circulating in the at least one electrolytic reactor.
11. The process according to claim 10 , wherein the base comprises sodium hydroxide (NaOH).
12. The process according to claim 1 , wherein the process is performed using two or more of said at least one electrolytic reactor fluidly connected in series, the inlet of a first of the at least one electrolytic reactors being fluidly connected to a pump, and the outlet of a last of the at least one electrolytic reactors being fluidly connected to a filtering module.
13. The process according to claim 1 , wherein the 2N electrodes of each of the at least one electrolytic reactors are dimensionally stable electrodes; and wherein the 2N electrodes are 2N longitudinal rods disposed in a cylindrical manner along the peripheral wall, the N electrodes of the first group alternating with the N electrodes of the second group.
14. The process according to claim 13 , wherein each of the 2N longitudinal rods comprise a core made of titanium covered by a conductive layer of iridium dioxide or platinum.