GB1595191A - Treatment with oxygen of sewage in sewers - Google Patents

Description

(54) TREATMENT WITH OXYGEN OF SEWAGE IN SEWERS (71) We. BOC INTERNATIONAL LIMITED, 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 the treatment with oxygen of sewage while it is being held in or is flowing through a sewer and is an improvement in or modification of the invention disclosed in United Kingdom Patent Specification No. 1 452 961.

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 while it is being held in or is flowing through a sewer, wherein air or oxygen-rich gas is injected into sewage in the sewer through a constricting nozzle to increase the velocity of the gas as it enters the sewage.

The invention also resides in apparatus for treating sewage while it is being held in or is flowing through a sewer comprising means to inject oxygen-nch gas Into the sewage and wherein such means comprises a constricting nozzle to increase the velocity of the gas as it enters the sewage.

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.

An advantage of a method and apparatus according to the invention is that a high velocity stream of oxygen-rich gas can be injected into the sewage so that the gas is more readily broken into a finer bubble form than if the stream issues from an unconstricted open end of a supply conduit.

The creation of finer bubbles facilitates dissolution of the gas in the sewage and can be expected to enable larger quantities of gas to be so dissolved without passing into, or forming, a discrete gas space in the sewer above sewage therein.

lhe nozzle is preferably adapted to form a jet of gas having a velocity at least equal to that of sound in the oxygen-rich gas being of the convergent/divergent type.

When the gas is substantially pure oxygen it is conveniently supplied to the nozzle at the required rate 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 conirolled 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 14 to prevent backflow of sewage into the pump.

Oxygen-rich gas is supplied under pressure through a line 17 and injected into sewage conduit 10 through a convergent/divergent nozzle 16 connected into an aperture in the wall of the conduit 10, the outlet of the nozzle being substantially flush with the internal surface of the conduit. The nozzle accelerates the flow of oxygen-rich gas to provide a high velocity stream which penetrates into the flow of sewage in the sewer and is readily broken into minute bubbles which dissolve in the sewage.

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 1 8 which is operated automatically to adjust the rate of flow of oxygen through line 17 in accor dancc with variations in the value of the concentration of dissolved oxygen measured at the outfall 19 of the rising main by a dissolved oxygen meter 20.

In a typical example of a process according to the invention using apparatus of the type illustrated in the drawing, sewage is pumped along the conduit 1 0 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 nozzle 16 at a pressure of at least 6 atmospheres. from which nozzle a stream of oxygen issucs at a rate 0.1 kg/min.

The dissolved oxygen content of sewage downstream of the oxygen injection point is of the order of 1 OOppm.

WHAT WE CLAIM IS: 1. A method of treating sewage while it is being held in or is flowing through a sewer wherein oxygen-rich gas is injected into sewage in the sewer through a constricting nozzle to increase the velocity of the gas as it enters the sewage.

2. A method according to claim 1 wherein the gas is injected through a nozzle adapted to form a jet of gas having a velocity at least equal to that of sound in the oxygen-rich gas, the nozzle being of the convergent/divergent type.

3. A method according to claim 1 or claim 2 wherein the gas is supplied to said nozzle from a reservoir of liquefied oxygen.

4. 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.

5. A method according to any preceding claim wherein the gas is injected through a nozzle located in the wall of the sewer.

6. A method according to any preceding claim wherein the gas is injected downstream of a pump which passes sewage through a rising main sewer.

7. Apparatus for treating sewage while it is being held in or is flowing through a sewer comprising means to inject oxygenrich gas into the sewage and wherein such mean comprises a constricting nozzle to increase the velocity of the gas as it enters the sewage.

8. Apparatus according to claim 7 wherein said nozzle is a sonic or supersonic nozzle ot the convergent/dlvergent type.

9. Apparatus according to claim 7 or claim 8 comprising a gas supply in the form of a reservoir of liquefied oxygen.

10. Apparatus according to any one of claims 7 to 9 comprising means for monitoring the dissolved oxygen concentration or biochemical oxygen demand of sewage at a sclected point in the sewer and means for controlling the rate of gas injection in accordance with changes in the monitored value.

11. A sewer provided with apparatus according to any one of claims 7 to 10.

12. A sewer according to claim 11 wherein said nozzle is located in the wall of the sewer.

13. A sewer according to claim 11 or claim 1 2 being a rising main sewer wherein the point of gas injection is downstream of a pump which passes sewage through the sewer.

14. A method as claimed in claim 1, substantially as hereinbefore described with reference to the accompanying drawing.

15. Apparatus as claimed in claim 7, substantially as hereinbefore described with reference to the accompanying drawing.

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

Claims (15)

**WARNING** start of CLMS field may overlap end of DESC **. Oxygen-rich gas is supplied under pressure through a line 17 and injected into sewage conduit 10 through a convergent/divergent nozzle 16 connected into an aperture in the wall of the conduit 10, the outlet of the nozzle being substantially flush with the internal surface of the conduit. The nozzle accelerates the flow of oxygen-rich gas to provide a high velocity stream which penetrates into the flow of sewage in the sewer and is readily broken into minute bubbles which dissolve in the sewage. 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 1 8 which is operated automatically to adjust the rate of flow of oxygen through line 17 in accor dancc with variations in the value of the concentration of dissolved oxygen measured at the outfall 19 of the rising main by a dissolved oxygen meter 20. In a typical example of a process according to the invention using apparatus of the type illustrated in the drawing, sewage is pumped along the conduit 1 0 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 nozzle 16 at a pressure of at least 6 atmospheres. from which nozzle a stream of oxygen issucs at a rate 0.1 kg/min. The dissolved oxygen content of sewage downstream of the oxygen injection point is of the order of 1 OOppm. WHAT WE CLAIM IS:

1. A method of treating sewage while it is being held in or is flowing through a sewer wherein oxygen-rich gas is injected into sewage in the sewer through a constricting nozzle to increase the velocity of the gas as it enters the sewage.

2. A method according to claim 1 wherein the gas is injected through a nozzle adapted to form a jet of gas having a velocity at least equal to that of sound in the oxygen-rich gas, the nozzle being of the convergent/divergent type.

3. A method according to claim 1 or claim 2 wherein the gas is supplied to said nozzle from a reservoir of liquefied oxygen.

4. 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.

5. A method according to any preceding claim wherein the gas is injected through a nozzle located in the wall of the sewer.

6. A method according to any preceding claim wherein the gas is injected downstream of a pump which passes sewage through a rising main sewer.

7. Apparatus for treating sewage while it is being held in or is flowing through a sewer comprising means to inject oxygenrich gas into the sewage and wherein such mean comprises a constricting nozzle to increase the velocity of the gas as it enters the sewage.

8. Apparatus according to claim 7 wherein said nozzle is a sonic or supersonic nozzle ot the convergent/dlvergent type.

9. Apparatus according to claim 7 or claim 8 comprising a gas supply in the form of a reservoir of liquefied oxygen.

10. Apparatus according to any one of claims 7 to 9 comprising means for monitoring the dissolved oxygen concentration or biochemical oxygen demand of sewage at a sclected point in the sewer and means for controlling the rate of gas injection in accordance with changes in the monitored value.

11. A sewer provided with apparatus according to any one of claims 7 to 10.

12. A sewer according to claim 11 wherein said nozzle is located in the wall of the sewer.

13. A sewer according to claim 11 or claim 1 2 being a rising main sewer wherein the point of gas injection is downstream of a pump which passes sewage through the sewer.

14. A method as claimed in claim 1, substantially as hereinbefore described with reference to the accompanying drawing.

15. Apparatus as claimed in claim 7, substantially as hereinbefore described with reference to the accompanying drawing.