GB1573312A - Tratment of sewage by oxygenation - Google Patents

Description

(54) TREATMENT OF SEWAGE BY OXYGENATION (71) We, BOC INTERNATIONAL LI MITED, 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 of sewage by oxygenation while it is being held in or is flowing through a sewer and is an improvement in, or modification of, the invention described in the complete specification of UK patent number 1 452 961, (hereinafter referred to as the 'patent case').

It is proposed in the parent case to treat sewage in a sewer by injecting oxygen-rich gas under pressure into the sewage in the sewer system. More specifically, the gas is injected into the sewage flowing through the sewer conduit, 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 to its being pumped through the sewer.

The applicant has now appreciated that a convenient and expeditious method of introducing oxygen-rich gas into the sewage is to introduce such gas into the inlet of a pump for passing the sewage through the sewer, or into any conduit associated with such inlet through which sewage is drawn into the pump.

Accordingly, the invention provides a method of treating sewage while it is being held in or is flowing through a sewer, which method comprises introducing oxygen-rich gas into an inlet of a pump for passing the sewage through the sewer, or into a conduit associated with an inlet through which sewage is drawn into the pump, the gas being introduced in bubbles of such a small size and at such a controlled rate that operation of the pump for pumping the sewage is not adversely affected.

The bubbles of gas need not dissolve completely in the sewage prior to reaching the pump since they will be shattered within the pump into even finer bubbles which will be of a size that are able to dissolve in, or be consumed within, the pressurised sewage downstream of the pump. The introduction of the gas is controlled such that the gas is released into the sewage as fine bubbles and at a rate which will not result in formation of any gas pockets in the pump which would reduce or prevent effective pumping of the sewage. The gas may be introduced under pressure and preferably through a diffuser or it may be allowed to be drawn into the flow of sewage moving towards the pump.

In the latter case, a venturi device may be provided in the pump inlet or inlet conduit to increase the suction effect of the flowing sewage, a gas line communicating with the venturi. In embodiments of the invention in which the gas is drawn into the flow of sewage by the suction effect thereof, any suitable low pressure source of gas can be used, for example, oxygen-rich gas produced by a pressure swing adsorption unit.

The term 'sewer' as used herein includes within its scope a conduit which is connected between a source of untreated sewage and a treatment plant (eg an activated sludge or biological filtration plant or a place of disposal or collection.

The term 'oxygen-rich' gas is used herein to mean oxygen, or a gaseous mixture having a proportion of oxygen greater than that of air. Preferably, the oxygen-rich gas has a proportion of oxygen greater than 80% by volume, and most preferably greater than 95% by volume.

When a pressurised source of oxygen-rich gas is required, it could be provided by an insulated vessel in which liquid oxygen is stored and passed through an evaporator prior to its introduction into the sewage.

Alternatively the gas could be supplied from one or more cylinders.

Typically, the bubbles of gas introduced into sewage in the sewer each have a diameter in the range 0.05 to 0.15 mm.

It is thought that in some cases the gas could be first introduced into a pressurised stream of sewage or water, which is then introduced into the sewage flowing to the aforesaid pump inlet. The sewage for said stream could be taken from the sewage passing into, or through, the sewer. This may be performed in accordance with the process described in greater detail in UK patent specification number 1 455 567 whereby a pressurised stream of liquid containing dissolved gas and undissolved bubbles of gas is produced and introduced into a main body of liquid to be treated.

Thus, the gas may be introduced into the stream in the form of undissolved bubbles of gas, the velocity of the stream being sufficient to prevent such bubbles from coalescing to form a discrete continous gas phase, and the stream introduced into the sewer under turbulent conditions so that the bubbles of undissolved gas are shattered into smaller bubbles which readily dissolved in or are readily consumed within the sewage in the sewer.

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 an apparatus for pumping sewage through a sewer in accordance with the invention.

Referring to the drawing, there is shown a pumping station for a rising main sewer.

The station 10 comprises a sump 11 which receives sewage from an inlet 12, and a pump 13 having an conduit 14 connecting the pump inlet to the outlet of the sump, and a further conduit 15 connecting the outlet of the pump to the inlet of a sewer conduit (not shown). A gas diffuser 16, is located in the intake conduit 14 and is connected by a gas line 17 to a vacuum insulated vessel 18 containing liquid oxygen.

The line 17 includes a heat exchanger 19 for vaporising the liquid gas. A flow control valve 20 is also provided in line 17 to allow adjustment of the gas flow. This valve is desirably a solenoid operated valve which may be controlled automatically to adjust the rate of flow of oxygen in accordance with variation in the concentration of dissolved oxygen measured at a convenient point in the sewage flow. The oxygen is introduced into the sewage in the form of fine bubbles which rapidly dissolve in, or are consumed by, the sewage.

WHAT WE CLAIM IS: 1. A method of treating sewage while it is being held in or is flowing through a sewer, which method comprises introducing oxygen-rich gas (as hereinbefore defined) into an inlet of a pump for passing the sewage through the sewer, or into a conduit associated with an inlet through which sewage is drawn into the pump, the gas being introduced in bubbles of such a small size and at a such controlled rate that the operation of the pump for pumping the sewage is not adversely affected.

2. A method as claimed in claim 1 wherein the gas is injected into the sewage under pressure.

3. A method as claimed in claim 1 wherein the gas is drawn into the sewage by a suction effect created by the flow of such sewage moving towards the pump.

4. A method as claimed in claim 3 wherein the gas is introduced at the location of a venturi device through which the sewage flows thereby to increase the aforesaid suction effect.

5. A method as claimed in any one of the preceding claims wherein the gas is introduced into the sewage through a diffuser.

6. A method as claimed in claim 1 wherein the gas is introduced into a pressurised stream of water or sewage, which stream is then introduced into the sewage flowing to the aforesaid pump inlet.

7. A method as claimed in claim 6 wherein the said stream is taken from sewage passing into, or through, the sewer.

8. A method as claimed in claim 6 or claim 7 wherein the gas is introduced into the stream in the form of undissolved bubbles of gas, the velocity of the stream being sufficient to prevent such bubbles from coalescing to form a discrete continuous vapour phase, and the stream is introduced into the sewer under turbulent conditions so that the bubbles of undissolved gas are shattered into smaller bubbles which readily dissolve in, or are readily consumed within, the sewage in the sewer.

9. A method as claimed in any one of the preceding claims wherein the bubbles of gas introduced in sewage in the sewer have a diameter in the range 0.05 to 0.15 mm.

10. A method as claimed in any one of the preceding claims wherein the oxygenrich gas contains more than 80% by volume of oxygen.

11. A method as claimed in any one of the preceding claims wherein the oxygenrich gas contains more than 95% by volume of oxygenmethod as claimed in claim 1, 12. A substantially as hereinbefore described with reference to the accompanying drawing.

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

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. one or more cylinders. Typically, the bubbles of gas introduced into sewage in the sewer each have a diameter in the range 0.05 to 0.15 mm. It is thought that in some cases the gas could be first introduced into a pressurised stream of sewage or water, which is then introduced into the sewage flowing to the aforesaid pump inlet. The sewage for said stream could be taken from the sewage passing into, or through, the sewer. This may be performed in accordance with the process described in greater detail in UK patent specification number 1 455 567 whereby a pressurised stream of liquid containing dissolved gas and undissolved bubbles of gas is produced and introduced into a main body of liquid to be treated. Thus, the gas may be introduced into the stream in the form of undissolved bubbles of gas, the velocity of the stream being sufficient to prevent such bubbles from coalescing to form a discrete continous gas phase, and the stream introduced into the sewer under turbulent conditions so that the bubbles of undissolved gas are shattered into smaller bubbles which readily dissolved in or are readily consumed within the sewage in the sewer. 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 an apparatus for pumping sewage through a sewer in accordance with the invention. Referring to the drawing, there is shown a pumping station for a rising main sewer. The station 10 comprises a sump 11 which receives sewage from an inlet 12, and a pump 13 having an conduit 14 connecting the pump inlet to the outlet of the sump, and a further conduit 15 connecting the outlet of the pump to the inlet of a sewer conduit (not shown). A gas diffuser 16, is located in the intake conduit 14 and is connected by a gas line 17 to a vacuum insulated vessel 18 containing liquid oxygen. The line 17 includes a heat exchanger 19 for vaporising the liquid gas. A flow control valve 20 is also provided in line 17 to allow adjustment of the gas flow. This valve is desirably a solenoid operated valve which may be controlled automatically to adjust the rate of flow of oxygen in accordance with variation in the concentration of dissolved oxygen measured at a convenient point in the sewage flow. The oxygen is introduced into the sewage in the form of fine bubbles which rapidly dissolve in, or are consumed by, the sewage. WHAT WE CLAIM IS:

1. A method of treating sewage while it is being held in or is flowing through a sewer, which method comprises introducing oxygen-rich gas (as hereinbefore defined) into an inlet of a pump for passing the sewage through the sewer, or into a conduit associated with an inlet through which sewage is drawn into the pump, the gas being introduced in bubbles of such a small size and at a such controlled rate that the operation of the pump for pumping the sewage is not adversely affected.

2. A method as claimed in claim 1 wherein the gas is injected into the sewage under pressure.

3. A method as claimed in claim 1 wherein the gas is drawn into the sewage by a suction effect created by the flow of such sewage moving towards the pump.

4. A method as claimed in claim 3 wherein the gas is introduced at the location of a venturi device through which the sewage flows thereby to increase the aforesaid suction effect.

5. A method as claimed in any one of the preceding claims wherein the gas is introduced into the sewage through a diffuser.

6. A method as claimed in claim 1 wherein the gas is introduced into a pressurised stream of water or sewage, which stream is then introduced into the sewage flowing to the aforesaid pump inlet.

7. A method as claimed in claim 6 wherein the said stream is taken from sewage passing into, or through, the sewer.

8. A method as claimed in claim 6 or claim 7 wherein the gas is introduced into the stream in the form of undissolved bubbles of gas, the velocity of the stream being sufficient to prevent such bubbles from coalescing to form a discrete continuous vapour phase, and the stream is introduced into the sewer under turbulent conditions so that the bubbles of undissolved gas are shattered into smaller bubbles which readily dissolve in, or are readily consumed within, the sewage in the sewer.

9. A method as claimed in any one of the preceding claims wherein the bubbles of gas introduced in sewage in the sewer have a diameter in the range 0.05 to 0.15 mm.

10. A method as claimed in any one of the preceding claims wherein the oxygenrich gas contains more than 80% by volume of oxygen.

11. A method as claimed in any one of the preceding claims wherein the oxygenrich gas contains more than 95% by volume of oxygenmethod as claimed in claim 1,

12. A substantially as hereinbefore described with reference to the accompanying drawing.