Enhanced Membrane Performance Using Ozone

Abstract

In a wastewater treatment process or other water treatment process, wherein ceramic membranes are employed to filter liquid not being treated in a biological process, ozone gas is injected and dissolved into the membrane influent for the purpose of preventing fouling of the membranes, while also enhancing pathogen removal. Ozone concentration as injected is at a concentration greater than 2 mg/l, preferably at least about 5 mg/l.

Claims

1. In a wastewater treatment system with ceramic membrane separation decoupled from any biological process, an ozone gas injection apparatus positioned to inject and dissolve ozone gas into wastewater, with concentration of ozone dissolved in wastewater, as applied at the injection apparatus, being greater than 2 milligrams per liter, whereby fouling or clogging of ceramic membranes is greatly reduced, while pathogen removal is enhanced.

2. The wastewater treatment system of claim 1, wherein said concentration of ozone is greater than 5 milligrams per liter.

3. The wastewater treatment system of claim 1, wherein said concentration of ozone is greater than 10 milligrams per liter.

4. The wastewater treatment system of claim 1, wherein said concentration of ozone is greater than 15 milligrams per liter.

5. The wastewater treatment system of claim 1, wherein the ozone gas injection apparatus comprises an atmospheric pressure gas transfer system wherein infeed wastewater liquid is rotated in a pipe at a point at which the ozone gas is injected.

6. The wastewater treatment system of claim 5, wherein the ozone gas injection apparatus further includes application of high frequency acoustic vibration to the infeed liquid.

7. The wastewater treatment system of claim 1, wherein the system includes primary and secondary treatment, the ceramic membrane separation being downstream of the secondary treatment.

8. A method for reducing or preventing fouling or clogging of ceramic membranes in a water or wastewater treatment system with ceramic membranes, comprising: injecting ozone gas to the water or wastewater, to an ozone concentration greater than 2 milligrams per liter, whereby membrane flux is increased and fouling of the membranes is reduced.

9. The method of claim 8, wherein the concentration of dissolved ozone is greater than 5 milligrams per liter.

10. The method of claim 8, wherein the concentration of dissolved ozone is greater than 10 milligrams per liter.

11. The method of claim 8, wherein the concentration of dissolved ozone is greater than 15 milligrams per liter.

12. The method of claim 8, wherein the ozone gas injection apparatus comprises an atmospheric pressure gas transfer system wherein infeed wastewater liquid is rotated.

13. The method of claim 8, wherein the system includes primary and secondary treatment, the ceramic membrane separation being downstream of the secondary treatment.

14. A method for reducing or preventing fouling or clogging of filtration membranes in a water or wastewater treatment system in which infeed liquid is treated by membrane filtration with ceramic membranes without or after biological treatment of the liquid, comprising: injecting ozone gas to the infeed liquid before entering membrane filtration, to an ozone concentration greater than 2 milligrams per liter, whereby membrane flux is increased and fouling of the membranes is reduced, while pathogen content is also reduced.

15. The wastewater treatment system of claim 14, wherein said concentration of ozone is greater than 5 milligrams per liter.

16. The wastewater treatment system of claim 14, wherein said concentration of ozone is greater than 15 milligrams per liter.

17. The method of claim 14, wherein the ozone gas is injected with an atmospheric pressure gas transfer system, wherein the ozone gas injection apparatus comprises an atmospheric pressure gas transfer system wherein infeed wastewater liquid is rotated in a pipe at a point at which the ozone gas is injected.

18. The method of claim 14, wherein the ozone gas injection apparatus further includes application of high frequency acoustic vibration to the infeed liquid.

Description

DESCRIPTION OF THE DRAWINGS

[0015] FIGS. 1, 2 and 3 are diagrams indicating processes of a wastewater treatment plant, with membrane filtration following addition of ozone.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] In the drawings, FIG. 1 indicates a wastewater treatment system 10, illustrating clarified secondary effluent 12 from a liquid side of a wastewater treatment plant which may be of typical design. Wastewater in a municipal treatment plant typically is treated in a series of biological treatment zones, after which the outflow from the zones is subjected to settling in a clarifier, typically called a secondary clarifier. See, for example, U.S. Pat. No. 6,712,970.

[0017] A clarifier effluent exits the clarifier as the clarified effluent 12. At this point biological treatment of the clarified liquid has been completed, and tertiary treatment, in the illustrated example, occurs in a membrane zone 14 which can be a series of tanks. The micropore membranes produce a highly clarified permeate as indicated at 16, removing considerable amount of particulate matter, some very fine, from the liquid. The membranes can also remove much of the bacteria present in the clarified liquid.

[0018] Pursuant to the invention the feedwater 12 to the membrane separators is injected with ozone, indicated at 18. As explained above, this ozone gas transfer produces a relatively high applied concentration of ozone to the liquid, greater than 2 mg/l, and preferably at least 5 mg/l. The concentration can be greater than 10 mg/l, or even above 15 mg/l, resulting in greater and greater effectiveness in reducing or eliminating fouling of the membranes. These are doses as applied to the liquid. Residual concentrations after application become lower with time, depending on organic concentration in the influent, biological constituents and site specific conditions. The ozone may be essentially fully reacted when the liquid reaches the membranes, or in some cases may still be at 90% or more of the applied dose. A benefit of the ozone injection, in addition to clogging reduction, is removal of pathogens including viruses.

[0019] The gas transfer device employed in the system of the invention preferably is a high efficiency, atmospheric pressure system in which the feedwater flowing through a pipe is rotated as the ozone is injected, producing increased efficiency due to the liquid rotation, which increases available surface efficacy area for mass transfer to take place. For example, a preferred gas transfer system is that referenced above, ROTURI system UP2E! (Eliquo Technologies).

[0020] As explained above, with the ozone injection at a relatively high concentration, and with ozone treatment decoupled from any biological process, membrane fouling is very substantially reduced, and in some cases can even be eliminated, so that the membranes operate more efficiently and over a longer period of time without servicing.

[0021] FIGS. 2 and 3 are similar to FIG. 1 but show different sources of influent for ozone and membrane treatment. In FIG. 2 the source is combined sewage overflow or sanitary sewage overflow 20 which will not be subject to biological treatment. In FIG. 3 the source is surface water 22.

[0022] The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.