GB1597167A

GB1597167A - Sewage treatment plant

Info

Publication number: GB1597167A
Application number: GB1796577A
Authority: GB
Original assignee: Klargester Environmental Engineering Ltd
Current assignee: Klargester Environmental Engineering Ltd
Priority date: 1977-04-29
Filing date: 1977-04-29
Publication date: 1981-09-03
Also published as: CY1154A; GR73012B

Description

(54) SEWAGE TREATMENT PLANT (71) We, KLARGESTER ENVIRONMENTAL ENGINEERING LIMITED, a British Company, of College Road, Aston Clinton, Aylesbury, Buckinghamshire, 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 plant for the treatment of sewage or waste water of the kind utilising a settlement or septic tank in which precipitation of sludge takes place continually. In this specification, for convenience, the term "sewage" will be employed as a generic term which includes waste water requiring treatment by primary settlement. In such a plant the sludge precipitant is removed from time to time for disposal and the liquid effluent may be disposed of in any suitable known way, for example passed onto the land or into a water course or delivered to a bacteriological filter bed for further processing and/or reuse for any purpose.

A sewage treatment plant of the kind mentioned above is described and claimed in British Patent Specification No. 1,297,959.

The preferred embodiment of the plant described in that Specification comprises a settlement tank divided by two frustoconical partitions into an upper chamber, an intermediate chamber and a lower chamber, the frusto-conical partitions being provided with slots therethrough which allow the passage of effluent liquid from the lower chamber to the intermediate chamber and from the intermediate chamber to the upper chamber. The frusto-conical partitions are arranged so that the lower partition has its larger diameter end attached to the lower edge of the upper tank part and its smaller diameter end uppermost, and the larger diameter end of the upper frusto-conical partition is attached to the top of the tank whence the upper partition projects downwardly through the smaller diameter end of the lower partition. The smaller diameter end of the uppermost partition is provided with a plug to prevent the passage of floating conglomerate and suspended matter directly from the lower or sludge digestion chamber to the upper or final settled effluent chamber. Under normal domestic flow conditions this arrangement of frusto-conical partitions with slots for the passage of effluent liquid produces a final effluent of satisfactory and acceptable quality.

However, under abnormal flow conditions, such as when a plurality of sanitary fittings are discharged into the tank at the same time or in rapid succession, the hydraulic conditions change and this frequently results in an increase in the quantity of suspended matter and floating conglomerate passing through the slots into the intermediate and upper chambers, thus causing a reduction in the quality of the final effluent. The problem arises when the influent velocity is above average, due to the conditions described above, resulting in increased turbulence in the lower chamber which adversely affects the hydraulic conditions in the other two chambers. Occasionally hydraulic conditions can occur in which the aforementioned plug is lifted and suspended matter, paper and other solids pass directly from the lower chamber to the upper chamber.

The present invention aims to provide a sewage treatment plant which considerably reduces or eliminates the occasional disadvantages described above.

According to the invention a sewage treatment plant comprises a settlement tank divided by first and second partitions, each in the form of a hollow frustum, into an upper chamber, an intermediate chamber and a lower chamber, means for delivering raw sewage into the lower chamber, means allowing the passage of effluent liquid through or past said partitions from the lower chamber to the intermediate chamber and from the intermediate chamber to the upper chamber but substantially preventing the passage of solid matter from the lower chamber into the chambers above, and a liquid effluent outlet from said upper chamber, said partitions being arranged so that the first partition has its end of greater cross-sectional area uppermost and located in an upper part of the tank and the second partition has its end of greater cross-sectional area lowermost and below the lowermost end of the first partition, the second partition projecting upwardly through the lowermost end of the first partition and having an openable closure means at its uppermost end.

Advantageously, the uppermost end of the second partition is at least at the level of the uppermost end of the first partition, and preferably above this level.

In a sewage treatment plant in accordance with the invention the arrangement of the first and second partitions leads to the lower chamber having a greater storage capacity than the lower chamber of a plant of the same size constructed as illustrated in the drawing of the aforesaid Specification No. 1,297,959.

This greater storage capacity reduces or even eliminates the possibility of adverse hydraulic rates of flow occurring, and it also leads to more effective settlement and separation of sludge on the floor of the lower chamber and to the collection of suspended matter and other floating conglomerate matter in the uppermost part of the second partition. This establishes an effective "clear zone" between the top of the sludge zone and the bottom of the floating conglomerate zone. This clear zone provides the ideal location for the means allowing the passage of effluent liquid from the lower chamber to the intermediate chamber.

Another advantage of the shape and arrangement of the partitions in a sewage treatment plant in accordance with the invention is that the increase in depth from the bottom of the tank to the uppermost end of the second partition, compared with a plant of the same size constructed as illustrated in the drawing of the aforesaid Specification, facilitates the upward passage and collection of suspended and floating matter at the uppermost end of the second partition where it compacts to a considerable degree. This is an advantage when the tank is being emptied, since the compacted matter readily rises out of the lower chamber when the closure means in the second partition is opened.

Conveniently, the closure means at the uppermost end of the second partition is a buoyant obturating member in the lower chamber which, due to its buoyancy, is urged upwardly by the liquid in the tank into sealing engagement with the aperture at the uppermost end of the second partition. When the latter is of frusto-conical shape, the aperture at its upper end is conveniently of circular shape and said buoyant obturating member is suitably in the form of a ball. When the tank has to be emptied, the buoyant obturating member simply has to be depressed in order to allow a pipe to be introduced into the lower chamber, through the uppermost end of the second partition, for the purpose of sucking sludge out of the lower chamber.

The first and second partitions are preferably frusto-conical. They may, however, be frusto-pyramidal. The means allowing the passage of effluent liquid through or past the partitions may consist of slots, orifices or valves in the partitions. When slots or orifices are used, they are preferably radiussed at their edges to facilitate passage of effluent from one chamber to another. The tank and the partitions may be made of reinforced synthetic resin material.

Sewage treatment plant in accordance with the invention is particularly suitable for the treatment of sewage from dwelling houses, and may be made in sizes suitable for a single house or up to 60 or more houses.

Sewage treatment plant in accordance with the invention may also be made of sizes suitable for a petrol service station, a factory, a hotel or a restaurant or indeed any other installation which has sewage requiring treatment by primary settlement.

The effluent outlet may be arranged to discharge directly to any suitable disposal point, for example a humus tank or sub-surface irrigation system. Alternatively, the effluent outlet may be connected to the inlet side of a pump which is arranged to recycle part of the effluent back to one of the chambers of the tank to achieve a further reduction in suspended solids. Alternatively, the effluent outlet may be arranged to discharge into a filter, for example a biological filter, if necessary a pump being incorporated between the effluent outlet and the filter. In this case the liquid effluent from the filter may all be discharged to a suitable disposal point, or a porportion of it may be re-cycled to one of the chambers of the tank to achieve a still further reduction in suspended solids.

The invention will now be described by way of example, with reference to the drawing accompanying the Provisional specification, the single Figure of which is a schematic sectional view of a sewage treatment plant in accordance with the invention.

Referring to the drawing, the sewage treatment plant shown comprises a closed tank 1 of circular cross-section formed by substantially hemi-spherical upper and lower tank parts la, ib which are connected together by a spigot and socket joint 2. This tank is made of reinforced synthetic resin, for example polyester reinforced with glass fibre or any other suitable material, and the two parts are bonded together at the joint 2 with an adhesive.

Within the tank 1 are two frusto-conical partitions 3, 4 arranged with their axes coincident with the vertical axis of the tank. The partition 3 has its circumferential edge of larger diameter lowermost, this edge being joined to the inner surface of the upper tank part la. The partition 3 may also be made of reinforced polyester resin and preferably it is bonded to the tank part la, for example with polyester resin.

The partition 4 has its circumferential edge of larger diameter uppermost and located in a peripheral rebate 6 moulded in the upper tank part la. If desired the upper edge of the partition 4 may be bonded to the tank with an adhesive. The lower edge of the partition 4 is supported on the partition 3, to which it may be bonded with an adhesive. The partition 4 may be constructed of glass fibre-reinforced polyester resin or any other suitable plastics material or other material.

The partitions 3 and 4 define three chambers within the tank 1, namely a lower chamber 7, an intermediate annular chamber 8 and an upper chamber 9.

The chambers 7 and 8 are in communication with each other via slots 10 and 11 in the partition 3. There are four slots 10 disposed equidistantly from one another around the partition 3 adjacent to the lower circumferential edge of the latter. There are six slots 11 disposed equidistantly around the partition 3 intermediate the lower and upper circumferential edges of the latter.

The chambers 8 and 9 are in communication with each other via eight slots 12 in the partition 4. The slots 12 are disposed equi distantly from one another around the partiton 4 intermediate the lower and upper circumferential edges of the latter.

The numeral 13 designates a vertically dis posed inlet pipe which enters the upper end 14 of the tank 1, passes through the partition 3 and discharges into the chamber 7. The numeral 15 designates a vertically disposed outlet pipe which communicates with the chamber 9 and passes through the upper end 14 of the tank. These pipes 13 and 15 may be made of synthetic resin, for example polyvinyl chloride, or paper impregnated with pitch, and may be bonded to the upper end 14 of the tank.

The numeral 16 designates a vertically disposed access shaft formed integrally with the upper tank part la, the axis of this shaft being aligned with the tank axis. The upper end of the shaft 16 is closed by a removable lid 17.

The partition 3 has its circumferential edge of smaller diameter situated above the par tition 4 close to the top 14 of the tank. The uppermost edge of the partition 3 defines a circular opening 18 aligned with the access shaft 16. A buoyant ball 19, for example of foamed plastic material, of larger diameter than the opening 18 is placed in the chamber 7.

When the plant is in use, the ball 19 rises to the position shown in the Figure to close the opening 18 and prevent the passage of sludge and floating conglomerate matter from the chamber 7 into chamber 9. The ball 19 may be made captive by securing it with a cord (not shown), for example of nylon, to any convenient position in the cone, or it may be left quite free in the chamber 7.

In use of the above described plant raw sewage enters the tank through the inlet pipe 13 and passes straight to the lower chamber 7 which is the sludge storage and digestion chamber. The solids are deposited in this chamber and retained in it.

The settled effluent largely free from solids, flows vertically into the intermediate chamber 8 which is the secondary settlement chamber, admission of the effluent to this chamber being through the slots 10 and 11. These slots assist in reducing velocity within the tank thus encouraging settlement and clarification of the effluent From the chamber 8 the effluent then passes into chamber 9 through the slots 12 which also assist in further reducing velocity and promiting greater clarification of the effluent.

Finally the clarified liquid effluent passes out of the tank through the pipe 15. The numeral 20 indicates the top water level in the tank.

Any fine suspended matter passing into chamber 8 through the slots will settle in chamber 8 and return to chamber 7 through the slots 10.

When it is desired to empty accumulated solid matter from the chamber 7, a pipe (not shown) from a suitable suction device is passed into chamber 7 through the access shaft 16 and the opening 18, the ball 19 being pushed down from the position shown in the Figure in the process.

In one particular sewage treatment plant constructed as shown in the Figure and having a capacity of 600 gallons (2750 litres), the tank had a maximum internal diameter of 1.88 m and a height of 1.6 m.

The slots 10-12 were all rectangular in shape, being 15.2 cm wide and 1.0 cm high.

The outlet pipe 15 may discharge the liquid effluent direct to any suitable dispersal system, for example a subsurface irrigation system. Alternatively the outlet pipe 15 may discharge to a pumpwell (not shown) located beside the settlement tank, and a pump installed in the pumpwell may discharge the effluent to a subsurface irrigation system located at a site remote from the settlement tank or to a biological filter disposed either adjacent to the settlement tank and pumpwell or remotely from it. The biological filtration of the effluent will further reduce uspended solids and biological oxygen demand to produce a higher quality effluent than that which is discharged from the settlement tank.

The liquid discharged from the filter may flow to a ditch, a humus tank, a subsurface irrigation system or any other approved disposal means.

Alternatively a porportion of the liquid discharged from the filter may be returned to chamber 7 or to chamber 9 of the tank to achieve a still further reduction in B.O.D. and suspended solids. This recycled effluent may be fed into chamber 7 to 9 through a return pipe (not shown) similar to pipe 13 or 15.

The remainder of the effluent discharged from the filter would be led to a suitable disposal point.

In a modified form of the settlement tank described above, the slots 10-12 are replaced by circular apertures or valves suitable for the hydraulic conditions of the tank.

It will of course be appreciated that the invention is not limited to the plant described in detail above with reference to the drawing.

Thus, for example, the numbers and sizes of the slots 1012 may differ from those specified above. Generally speaking, the slot area in each partition is chosen so that, when the tank is in use, there will be an adequate velocity of the liquid flowing through the slots, so that the latter are kept free from clogging.

Again, the tank may be of rectangular or other polygonal cross-section, in which case the partitions 3 and 4 may be shaped as frusto-pyramids.

WHAT WE CLAIM IS:- 1. A sewage treatment plant comprising a settlement tank divided by first and second partitions, each in the form of a hollow frustum, into an upper chamber, an intermediate chamber and a lower chamber, means for delivering raw sewage into the lower chamber, means allowing the passage of effluent liquid through or past said partitions from the lower chamber to the intermediate chamber and from the intermediate chamber to the upper chamber but substantially preventing the passage of solid matter from the lower chamber into the chambers above, and a liquid effluent outlet from said upper chamber, said partitions being arranged so that the first partition has its end of greater cross sectional area uppermost and located in an upper part of the tank and the second partition has its end of greater cross-sectional area lowermost and below the lowermost end of the first partition, the second partition projecting upwardly through the lowermost end of the first partition and having an openable closure means at its uppermost end.

2. A sewage treatment plant according to claim 1, in which the uppermost end of the second partition is at least at the level of the uppermost end of the first partition, and preferably above this level.

3. A sewage treatment plant according to claim 1, in which the closure means at the uppermost end of the second partition is a buoyant obturating member in the lower chamber which, due to its buoyancy, is urged upwardly by the liquid in the tank into sealing engagement with the aperture at the uppermost end of the second partition.

4. A sewage treatment plant according to claim 3, in which the uppermost end of the second partition has an aperture of circular shape and said buoyant obturating member is in the form of a ball.

5. A sewage treatment plant according to any of the preceding claims, in which said first partition is of frusto-conical or frustopyramidal shape.

6. A sewage treatment plant according to any of the preceding claims, in which said second partition is of frusto-conical or frustopyramidal shape.

7. A sewage treatment plant according to any of the preceding claims, in which the means allowing the passage of effluent liquid through or past the partitions consists of slots, orifices or valves in the partitions.

8. A sewage treatment plant according to claim 7, in which said slots or orifices are radiussed at their edges to facilitate passage of effluent from one chamber to another.

9. A sewage treatment plant according to any of the preceding claims, in which the lowermost end of the first partition is joined to the second partition intermediate the upper most and lowermost ends of the latter.

10. A sewage treatment plant according to any of the preceding claims, comprising an access shaft on the top of the tank having its axis substantially aligned with the tank axis.

11. A sewage treatment plant according to claim 10, in which the access shaft is provided with a removable cover.

12. A sewage treatment plant according to any of the preceding claims, comprising means for recycling a proportion of the effluent from the upper chamber back to a chamber of the tank.

13. A sewage treatment plant according to claim 12, in which the recycling means comprises a pump having its inlet side connected to the effluent outlet.

14. A sewage treatment plant according to claim 12 or 13, in which a filter is incorporated in the recycling means.

15. A sewage treatment plant according to any of claims 1 to 11, in which the effluent outlet is connected to a filter.

16. A sewage treatment plant according to any of the preceding claims, in which the tank and the partitions are made of reinforced synthetic resin material.

17. A sewage treatment plant constructed and arranged substantially as herein described with reference to the drawing accompanying the Provisional Specification.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. achieve a still further reduction in B.O.D. and suspended solids. This recycled effluent may be fed into chamber 7 to 9 through a return pipe (not shown) similar to pipe 13 or 15. The remainder of the effluent discharged from the filter would be led to a suitable disposal point. In a modified form of the settlement tank described above, the slots 10-12 are replaced by circular apertures or valves suitable for the hydraulic conditions of the tank. It will of course be appreciated that the invention is not limited to the plant described in detail above with reference to the drawing. Thus, for example, the numbers and sizes of the slots 1012 may differ from those specified above. Generally speaking, the slot area in each partition is chosen so that, when the tank is in use, there will be an adequate velocity of the liquid flowing through the slots, so that the latter are kept free from clogging. Again, the tank may be of rectangular or other polygonal cross-section, in which case the partitions 3 and 4 may be shaped as frusto-pyramids. WHAT WE CLAIM IS:-

1. A sewage treatment plant comprising a settlement tank divided by first and second partitions, each in the form of a hollow frustum, into an upper chamber, an intermediate chamber and a lower chamber, means for delivering raw sewage into the lower chamber, means allowing the passage of effluent liquid through or past said partitions from the lower chamber to the intermediate chamber and from the intermediate chamber to the upper chamber but substantially preventing the passage of solid matter from the lower chamber into the chambers above, and a liquid effluent outlet from said upper chamber, said partitions being arranged so that the first partition has its end of greater cross sectional area uppermost and located in an upper part of the tank and the second partition has its end of greater cross-sectional area lowermost and below the lowermost end of the first partition, the second partition projecting upwardly through the lowermost end of the first partition and having an openable closure means at its uppermost end.