Modified activated carbon and methods of using same
Modified activated carbon is disclosed for use in water treatment. In at least some embodiments, activated carbon may be treated with a positively-charged surfactant, i.e. a quaternary ammonium-based surfactant, to promote the removal of poly- and perfluorolkyl substances from water.
1. A method of treating water containing perfluoroalkyl and/or polyfluoroalkyl substances (PFASs), comprising:
providing a first activated carbon bed comprising granular activated carbon (GAC) directly coated with an effective amount of a positively-charged surfactant;
monitoring PFAS concentration of the water containing PFASs;
introducing the water containing PFASs to the first activated carbon bed to promote adsorption of the PFASs and produce a product stream comprising treated water;
monitoring a PFAS breakthrough level in the product stream; and
bringing a second activated carbon bed comprising the GAC directly coated with the positively-charged surfactant online in anticipation of a predicted PFAS breakthrough time when the PFAS breakthrough level will exceed a predetermined threshold value.
2. The method of claim 1 , wherein the PFASs comprise perfluorooctane sulfonic acid (PFOS) or perfluorooctanoic acid (PFOA).
3. The method of claim 1 , wherein the positively-charged surfactant is a quaternary ammonium-based surfactant.
4. The method of claim 3 , wherein the quaternary ammonium-based surfactant is cetyltrimethylammonium chloride (CTAC).
5. The method of claim 4 , wherein the GAC of the first activated carbon bed is directly coated with at least 0.25 grams of cetyltrimethylammonium per gram of activated carbon.
6. The method of claim 1 , further comprising introducing the product stream of the first activated carbon bed to a downstream unit operation for further treatment.
7. The method of claim 6 , wherein the downstream unit operation comprises at least one of an activated carbon treatment and an ion exchange treatment.
8. The method of claim 1 , further comprising regenerating the GAC of the first activated carbon bed to produce a regenerated GAC.
9. The method of claim 8 , further comprising directly coating the regenerated GAC with the positively-charged surfactant.
10. The method of claim 1 , wherein the PFAS level of the water containing PFASs is at least 230 ng/L and the predetermined threshold value is 1 ng/L.
11. The method of claim 1 , wherein the predetermined threshold value is a factor of one or more of the PFAS concentration of the water containing PFASs, flow rate of the water containing PFASs, bed size of the first activated carbon bed, and empty bed contact time of the first activated carbon bed.
12. The method of claim 1 , wherein the predetermined threshold value is selected considering historical data.
13. The method of claim 1 , further comprising monitoring flow rate of the water containing PFASs.
14. The method of claim 1 , further comprising generating a service request based on a number of bed volumes remaining within the predicted PFAS breakthrough time.
15. The method of claim 14 , wherein the service request is generated based on anticipated service lag time.
16. The method of claim 1 , wherein performance of the first activated carbon bed measured as bed volumes to breakthrough is at least doubled in comparison to water treatment with an uncoated GAC.
17. The method of claim 1 , wherein the coated GAC exhibits a positive surface charge greater than about 0.09 milliequivalents/g, as measured in accordance with a Surface Charge Titration Protocol at a pH of 7.5.
18. The method of claim 1 , wherein the second activated carbon bed is in parallel with the first activated carbon bed.
19. The method of claim 1 , wherein the second activated carbon bed is in series with the first activated carbon bed.