GB1594225A

GB1594225A - Method and apparatus for treating sewage with oxygen

Info

Publication number: GB1594225A
Application number: GB6491/77A
Authority: GB
Original assignee: BOC International Ltd
Current assignee: BOC Group Ltd
Priority date: 1978-02-06
Filing date: 1978-02-06
Publication date: 1981-07-30

Description

(54) METHOD AND APPARATUS FOR TREATING SEWAGE WITH OXYGEN (71) We, BOC INTERNATIONAL LIM ITED, of Hammersmith House, London W6 9DX, England, an English company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method and apparatus for the treatment of sewage with oxygen and is an improvement in, or modification of, the invention disclosed in United Kingdom Patent Specification No. 1 452961.

It is proposed in the above-numbered specification to treat sewage in a sewer by injecting oxygen-rich gas under pressure into the sewage system. More specifically, the gas is injected through a pipe (having orifices therein) into the sewage flowing through the sewer, into the volute of a pump for driving sewage through a rising main sewer or into a sump in which the sewage is contained prior its being pumped through the sewer.

The present invention resides in a method of treating sewage wherein oxygen-rich gas is injected into sewage within or flowing into a sewer through a gas permeable portion of the wall of a passage which constitutes part of, or communicates with an inlet of, the sewer.

The term 'passage' is used herein to include fluid paths through pumps and associated equipment provided to pump sewage through the sewer, as well as any conduit associated with such pumps.

The invention also resides in apparatus for treating sewage comprising means for injecting oxygen-rich gas into sewage within or flowing into a sewer and wherein such means comprises a gas permeable portion of the wall of a passage which constitutes, or communicates with an inlet of, the sewer.

The invention furthermore resides in a sewer provided with such apparatus.

The term 'oxygen-rich gas' is used herein to mean oxygen or a gaseous mixture having a proportion of oxygen higher than that of air, preferably greater than 95% (by volume) oxygen.

Said gas-permeable wall portion may be in the form of a perforate or porous plate.

Preferably the holes or pores of the plate have greatest transverse dimensions of 0.010 inch or less, and most preferably not greater than 0.005 inch. It is also preferred that each such hole or pore is spaced from its neighbours by a distance substantially greater than the aforesaid transverse dimension, and most preferably spaced apart by a distance of at least 0.030 inch, e.g. a distance of 0.060 inch or greater, to minimise the likelihood of coalescence of bubbles of gas emerging from the holes or pores.

The aforesaid portion may be located directly in the wall of a sewer conduit or, for example, at the throat of a venturi provided in such a conduit to assist in the induction of gas into the sewage flowing through the conduit. Another preferred location is in the wall of the volute of a pump which passes sewage through the sewer, at which location the sewage flow may be highly turbulent which assists the dissolution of the gas.

When the gas is substantially pure oxygen it is conveniently supplied to the sewage from a reservoir of liquefied oxygen contained in a vacuum insulated evaporator, the liquid being evaporated by heat exchange with the ambient atmosphere.

In some methods according to the invention the concentration of dissolved oxygen in the sewage or the biochemical oxygen demand of the sewage may be monitored downstream of the point of gas injection, and the rate of gas injection controlled in accordance with changes in the monitored value.

Such adjustment may take place automatically using a control system, e.g. an analogue or digital computer, which receives signals from a dissolved oxygen meter and emits signals to actuate means for controlling the rate of flow of gas.

One embodiment of the invention will now be described by way of example and with reference to the accompanying drawing which is a diagrammatic representation of apparatus for introducing an oxygen-rich gas into sewage flowing through a rising main sewer.

Referring to the drawing there is shown a rising main sewer 10 leading from a pumping station 11. A sewage inlet 12 is provided to pass sewage to a sump 13. A pump 14 draws the sewage from the sump, pressurises the sewage and delivers it into the sewer conduit 10. A non-return valve 15 is provided in conduit 10 near pump 4 to prevent backflow of sewage into the pump.

Oxygen-rich gas is supplied under pressure through a line 17 and injected into sewage in conduit 10 through a diffuser plate 16 set into the wall of the conduit 10. The plate is made of a porous material, e.g. sintered bronze or unglazed porcelain or plastics material blown in the molten state. In other embodiments the plate may be made of plastics material which is perforated, for example by a high energy beam such as a laser beam or an electron beam, to have a multiplicity of minute apertures.

The gas, when substantially pure oxygen, may be contained in liquid form in a conventional vacuum insulated evaporator whereby the liquid is evaporated by heat exchange with the ambient atmosphere to provide a pressurised supply of gas to conduit 17.

The flow of oxygen-rich gas is controlled by a solenoid operated valve 18 which is operated automatically to adjust the rate of flow of oxygen through line 17 in accordance with variations in the value of the concentration of dissolved oxygen measured at the outfall 19 of the rising main by the concentration of dissolved oxygen measured at the outfall 19 of the rising main by dissolved oxygen meter 20.

In typical example of a process according to the invention using apparatus of the type illustrated in the drawing, sewage is pumped along the conduit 10 at a flow rate of 1 cu.m/min. and at a pressure of 20 metres head while substantially pure oxygen is supplied to the plate 16 at a pressure of 21 metres head and at a rate of flow of 0.1kg/min. The dissolved oxygen content of sewage downstream of the oxygen injection point is of the order of 100 ppm.

In other embodiments of the invention the plate may be located at other positions in the sewer system and preferably at areas of great turbulence which promotes the dissolution of the gas in the sewage. For example, the plate may be set into the wall of the volute of pump 14, or located in the vicinity of valve 15, both areas of increased turbulence in the system, or at the throat of a venturi provided in conduit 10 when a low pressure gas supply is used.

WHAT WE CLAIM IS:- 1. A method treating sewage wherein oxygen-rich gas is injected into sewage within or flowing into a sewer through a gas permeable portion of the wall of a passage which constitutes part of, or communicates with an inlet of, the sewer.

2. A method according to claim 1 wherein said portion is in the form of a perforate or porous plate.

3. A method according to claim 2 wherein the holes or pores of said plate have greatest transverse dimensions of 0.010 inch or less.

4. A method according to claim 2 or claim 3 wherein the holes or pores of said plate are spaced apart by distances substantially greater than the greatest transverse dimensions thereof.

5. A method according to any preceding claim wherein the gas is supplied to the sewage from reservoir of liquefied oxygen.

6. A method according to any preceding claim wherein the dissolved oxygen concentration or biochemical oxygen demand of the sewage is monitored downstream of the point of gas injection and the rate of gas injection is controlled in accordance with changes in the monitored value.

7. A method according to any preceding claim wherein said portion is located at the throat of a venturi provided in a sewer conduit.

8. A method according to any one of claims 1 to 6 wherein said portion is located in the wall of the volute of a pump which passes sewage through the sewer.

9. A method according to any one of claims 1 to 6 wherein said portion is located downstream of a pump which passes sewage through a rising main sewer.

10. Apparatus for treating sewage comprising means to inject air or oxygen-rich gas into sewage within or flowing into a sewer and wherein such means comprises a gas permeable portion of the wall of a passage which constitutes, or communicates with an inlet of, the sewer.

11. Apparatus according to claim 10 wherein said portion is in the form of a perforate or porous plate.

12. Apparatus according to claim 11 wherein the holes or pores of said plate have greatest transverse dimensions of 0.010 inch or less.

13. Apparatus according to claim 11 or claim 12 wherein the holes or pores of said plate are spaced apart by distances substantially greater than the greatest transverse dimensions thereof.

14. Apparatus according to any one of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. rate of flow of gas. One embodiment of the invention will now be described by way of example and with reference to the accompanying drawing which is a diagrammatic representation of apparatus for introducing an oxygen-rich gas into sewage flowing through a rising main sewer. Referring to the drawing there is shown a rising main sewer 10 leading from a pumping station 11. A sewage inlet 12 is provided to pass sewage to a sump 13. A pump 14 draws the sewage from the sump, pressurises the sewage and delivers it into the sewer conduit 10. A non-return valve 15 is provided in conduit 10 near pump 4 to prevent backflow of sewage into the pump. Oxygen-rich gas is supplied under pressure through a line 17 and injected into sewage in conduit 10 through a diffuser plate 16 set into the wall of the conduit 10. The plate is made of a porous material, e.g. sintered bronze or unglazed porcelain or plastics material blown in the molten state. In other embodiments the plate may be made of plastics material which is perforated, for example by a high energy beam such as a laser beam or an electron beam, to have a multiplicity of minute apertures. The gas, when substantially pure oxygen, may be contained in liquid form in a conventional vacuum insulated evaporator whereby the liquid is evaporated by heat exchange with the ambient atmosphere to provide a pressurised supply of gas to conduit 17. The flow of oxygen-rich gas is controlled by a solenoid operated valve 18 which is operated automatically to adjust the rate of flow of oxygen through line 17 in accordance with variations in the value of the concentration of dissolved oxygen measured at the outfall 19 of the rising main by the concentration of dissolved oxygen measured at the outfall 19 of the rising main by dissolved oxygen meter 20. In typical example of a process according to the invention using apparatus of the type illustrated in the drawing, sewage is pumped along the conduit 10 at a flow rate of 1 cu.m/min. and at a pressure of 20 metres head while substantially pure oxygen is supplied to the plate 16 at a pressure of 21 metres head and at a rate of flow of 0.1kg/min. The dissolved oxygen content of sewage downstream of the oxygen injection point is of the order of 100 ppm. In other embodiments of the invention the plate may be located at other positions in the sewer system and preferably at areas of great turbulence which promotes the dissolution of the gas in the sewage. For example, the plate may be set into the wall of the volute of pump 14, or located in the vicinity of valve 15, both areas of increased turbulence in the system, or at the throat of a venturi provided in conduit 10 when a low pressure gas supply is used. WHAT WE CLAIM IS:-

1. A method treating sewage wherein oxygen-rich gas is injected into sewage within or flowing into a sewer through a gas permeable portion of the wall of a passage which constitutes part of, or communicates with an inlet of, the sewer.

14. Apparatus according to any one of

claims 10 to 13 comprising a gas supply in the form of a reservoir of liquid oxygen.

15. Apparatus according to any one of claims 10 to 14 comprising means for monitoring the dissolved oxygen concentration or biochemical oxygen demand of sewage at a selected point in the sewer and means for controlling the rate of gas injection in accordance with changes in the monitored value.

16. A sewer provided with apparatus according to any one of claims 10 to 15.

17. A sewer according to claim 16 wherein said portion is located at the throat of a venturi provided in a conduit of the sewer.

18. A sewer according to claim 16 wherein said portion is located in the wall of the volute of a pump which passes sewage through the sewer.

19. A sewer according to claim 16 being a rising main sewer and wherein said portion is located downstream of a pump which passes sewage through the sewer.

20. A method of treating sewage substantially as hereinbefore described with reference to the accompanying drawing.

21. Apparatus for treating sewage substantially as hereinbefore described with reference to the accompanying drawing.