GB2421696A

GB2421696A - Sewage treatment unit

Info

Publication number: GB2421696A
Application number: GB0427152A
Authority: GB
Inventors: Andrew John Skilling
Original assignee: APCO HOLDINGS Ltd
Current assignee: APCO HOLDINGS Ltd
Priority date: 2004-12-13
Filing date: 2004-12-13
Publication date: 2006-07-05
Anticipated expiration: 2024-12-13
Also published as: GB0427152D0; GB2421696B

Abstract

A sewage treatment unit comprises at least a treatment zone 12, a settlement zone 16 and means for removing treated effluent from the settlement zone wherein the means is an air-lift arrangement 50 with an inlet 64 associated with a protective member (80, Fig 2) arranged to shroud the inlet and has an upper end provided with a removable closure means 78. In use foul water, preferably treated effluent containing small particles in suspension enters the treatment unit through a pipe 19 and is encouraged to aerate and mix in the treatment zone 12 with air supplied from aerator 38, the water then passes to the settlement zone 16 via holes in a tube 15 and finally the air-lift arrangement 50 acts to air-lift treated water from the settlement zone to an outlet 58 via tubes 62, 54. Preferably, the sewage treatment unit is installed below ground and can treat dwellings not connected to a main sewer.

Description

SEWAGE TREATMENT UNIT

This invention relates to sewage treatment units.

In particular, it concerns such units which are configured to be suitable for installation below ground. Moreover, the invention is especially applicable to relatively small-scale sewage treatment units which are utilised to service the output of just a few dwellings or even a single dwelling.

In recent years, there has been an increasing emphasis placed on pollution control of all kinds. One area which has received particular attention is the treatment of the foul water output from dwellings, where such dwellings are not connected to a main sewer. Conventionally, the foul water has been collected in a cess-pit which has to be emptied periodically by means of a road tanker, or alternatively the sewage has been passed through a multi-stage septic tank installation. However, cesspits may not be emptied frequently enough, with the result that foul (perhaps toxic) waste water can overflow into a natural water course. On the other hand, the biological oxygen demand (BOD) of the liquor from a septic tank very often is too high for discharge directly into a natural watercourse, especially during the winter months when the * S.....

bacteriological activity in the septic tank may be at a low level.

In an attempt to improve this situation, there have been proposals to use percolating filter beds in small-scale treatment plants, but such plants have S proved to be unsatisfactory. A percolating filter bed is commonly used for the treatment of sewage in relatively large-scale sewage treatment plants. With the kind of filter media which has to be used in such plants, it is most important that the media at no time is allowed to dry out, to maintain the bacteriological action. In the case of a largescale sewage treatment installation, this presents little problem for the waste from the relatively large number of dwellings serviced will provide sufficient effluent to ensure that liquid may continuously be passed over the percolating filter media. However, if such a bed is used on a smallscale plant, in view of the irregular outflow which can be expected from only a few dwellings, acute problems can be experienced in maintaining a flow over the filter media. One proposal previously suggested, employed a reservoir tank collecting all the outflow and liquid being pumped from the reservoir tank at a constant rate over the percolating filter media - but experience has shown that it is impractical to provide a sufficiently large reservoir tank able adequately to cope with the peaks and troughs of the outflow.

It is an object of the present invention to provide a sewage treatment unit which overcomes the problems of the various prior art proposals, which is both suitable for installation below ground, and is able to service a relatively small number of dwellings. More particularly, the invention seeks to provide a sewage treatment unit which can operate for long periods without requiring attention and will, moreover, be able to cope with power failures so that it can * * * * S. S S be restarted and be immediately operational when power is restored.

According to one aspect of the invention, there is provided a sewage treatment unit comprising a plurality of zones between an inlet for sewage to be treated and an outlet for treated effluent, the zones including a treatment zone S...

and a settlement zone, the unit further comprising means for removing treated effluent from the settlement zone, said means comprising an airlift arrangement having an inlet, said air-lift inlet having associated therewith a protective member being arranged to shroud the inlet and wherein the upper end of said protective member is provided with a removable closure means.

Preferably, said protective member is of generally tubular form.

Said closure means may be in the form of a cap adapted to fit to the protective member and said cap may have a peripheral rim which is received within the protective member.

Further, said closure means may be of plastics material.

Preferably, the wall of said protective member has a plurality of perforations therethrough.

Preferably, said air-lift inlet is formed by a first conduit extending generally vertically into the protective member and the lower end of the protective member is provided with a further closure means provided with an aperture through which the first conduit projects into the interior of the protective member.

The unit may comprise a support member on which the protective member is supported, with the first conduit projecting through an aperture in a support member **S*Se A second conduit may extend generally vertically adjacent to the first conduit, said second conduit acting to supply treated effluent to the exterior of the unit via the outlet The settlement zone is preferably defined within a tubular member, ; extending generally vertically within the vessel.

An aerator conduit may be connected to an aerator, which supplies air to the treatment zone and an air supply conduit may supply air to said airlift arrangement. Preferably, said air supply conduit is connected to an adjustable valve adapted to supply air to said aerator conduit and an adjustable valve is also connected to the air supply conduit and controls the supply of air to the air- lift arrangement.

In another aspect, the invention provides a method of constructing a sewage treatment unit utilising an existing sewage-receiving vessel in situ, said method comprising the provision of means for defining a treatment zone and a settlement zone within the vessel and further comprising the installation within the vessel of an arrangement for removing treated effluent from the settlement zone, said arrangement comprising an air-lift having an inlet, said air-lift inlet having associated therewith a protective member being arranged to shroud the inlet, wherein the upper end of said protective member is provided with a removable closure means.

The sewage treatment unit thus constructed may incorporate any of the optional features of the unit as delineated above.

By way of example only, an embodiment of the invention will now be described with reference to the accompanying drawings in which:- Figure 1 is a view of a sewage treatment unit constructed in accordance

S

*SS...

with the invention with certain components shown in section; Figure 2 is a detailed view of the air-lift arrangement of the sewage treatment unit of Figure 1, although with certain dimensions altered in the ". S...

interests of clarity; and *:.

Figure 3 is a section of the detailed view of Figure 2.

The sewage unit 1 shown in Figure 1 is constructed of corrosion free materials. It is to be positioned underground and contains no electrical or mechanical moving parts so as to be both safe in use and easy to maintain The unit 1 comprises a main sewage-receiving vessel 10. The vessel 10 may be of any suitable shape and size, but as an example of a vessel 10 suitable for use by up to 15 persons, the vessel would be cylindrical, arranged in use with its longitudinal axis horizontal, and having a length of 3.2m and a diameter of 1.9m.

It is to be understood further that, in practice, a vessel already present in situ may be utilised in constructing the sewage treatment unit (see below).

In the embodiment of the invention shown, a tubular projection 20 integral therewith extends vertically upwards from the vessel 10. The upper end of the projection 20 is arranged at ground level and is closed off e.g. by a man- hole cover which is removable to allow access to the vessel 10.

Foul water is supplied to the vessel 10 by means of at least one inlet arrangement comprising a generally horizontally extending pipe 18 and a generally vertically extending pipe 19 which extends downwards into vessel 10 e.

The upper end of pipe 19 is arranged at ground level and is closed off by a cover removable to give access to the inlet arrangement.

The vessel 10 has defined therein at least two zones through which the foul water sequentially passes. More particularly there is defined a first zone * being an aeration/mixing treatment zone 12, in which the aeration and mixing encourage the growth of aerobic bacteria which carry out the main part of the treatment process The minimum liquid level of the foul water in treatment zone 12 during normal use is marked by dot- dash line 14 (see below).

Extending upwardly from the interior bottom surface of vessel 10 and partway into the projection 20 is a fixed tube 15 whose interior defines a second zone, being a final settlement zone 16 of the unit 1, which zone 16 contains the liquid constituting the final treated effluent. Effluent passes from zone 12 to zone 16 via transfer holes in the tube 15.

Around the lower part of the tube 15 is positioned a tubular member or shroud 17, which is arranged so as to allow the contents of the first zone 12 to pass into the second zone 16 whilst retaining any settled sludge within first zone 12. As shown, the member 17 is positioned eccentrically around the tube 15, being spaced from tube 15 in the region of a draught tube 36 (see below) and abutting or at least being closely adjacent to the external surface of the tube 15 diametrically opposite that region.

Air for both aeration and for removing treated effluent from the unit 1 is supplied to the unit 1 via an air inlet conduit 30. The conduit 30 receives air under pressure from a fan or blower mounted externally of the unit 1 e.g. under.

cover in a building, outhouse or in a custom-built enclosure. The conduit 30 is connected to the inlet port of an adjustable valve 32 which supplies air to an aerator conduit 34 which extends downwardly through vessel 10, the conduit 34 eTs.

being mounted externally of but alongside tube 15.

S *SS*

Upstream of valve 32, a tapping 33a into an elbow 35 in conduit 30 provides a supply of air to an adjustable needle valve 33 through which air is supplied to a small diameter conduit 40 which constitutes the air supply to the final effluent air -lift arrangement 50 (see below).

The aerator conduit 34 extends into the shroud 17 and extends through the draught tube 36. Towards the lower end of draught tube 36, the conduit 34 leads into an aerator 38 which supplies the air to the aeration/mixing zone 12.

The draught tube 36 in co-operation with member 17 causes air supplied via aerator 38 to rise in tube 36 thereby generating circulation of the contents of the first zone 12. Simultaneously it causes withdrawal of any settled sludge from the second zone 16.

The small diameter conduit 40 is tapped into a T-junction 60 at point 52 (see Fig. 3) and is thereby connected to the final effluent air-lift arrangement 50. The arrangement 50 comprises a main tube 54 extending generally vertically from the bottom of the vessel 10, through the tube 15 and into tubular projection 20. Adjacent the upper end of tube 54 the tube 54 is connected by a 1-connection 56 to an outlet tube 58.

The outlet tube 58 extends generally horizontally out of the vessel 10 and acts to remove treated effluent from the unit. The tube 58 may be connected inter a/ia to a water course or soak-away (not shown). *

The T-junction 60 is connected to a conduit in the form of a tube 62 which extends upwardly through the vessel 10. es S

The upper end 64 of the tube 62 constitutes the inlet to the final effluent *S..

S S...

air-lift arrangement 50, the upper end being at the level 14. The height of the inlet 64 is adjustable to suit individual site requirements. The arrangement is such that as sewage enters the unit 10 through inlet 18, liquid in the form of treated effluent containing small particles in suspension enters the zone 16 from zone 12. Quiescent conditions allow the solid particles to settle in zone 16, the clear treated effluent being drawn into the air-lift arrangement 50 via inlet 64.

The conduits 34 and 62 extend through respective apertures in a support member 70 mounted within the tube 15. The support member 70 may take any appropriate form but may for example, be formed as a plastics spacer bar affixed to the internal surface of tube 15.

Affixed to the support member 70 and extending upwardly therefrom is a protective member 80 which surrounds the upper part of tube 62. The protective member 80 acts as a shroud to prevent floating material e.g. grease or fat entering, and hence blocking, the air-lift arrangement 50. The protective member 80 as shown is of tubular form but other forms are possible.

The tubular protective member 80 is formed with a plurality of perforations 72 through which treated effluent passes to inlet 64 but the perforations are sized to prevent large masses of floating material such as grease or fat passing therethrough. *e.

* S....

In the lower end of the protective member 80 as seen in Figure 3 there is provided a fixed closure member 74 constructed, as shown, as a blankingoff plate and having an aperture 76 through which final effluent tube 62 extends er,.

into member 80. The upper end of tubular member 80 is provided with a *.S.

closure means 78 to prevent ingress of material into member 80 from above, for example in the event of a power failure, so allowing the liquid level in the vessel 10 to rise above the upper level of the tubular member 80. The closure means 78 is removable whereby access to the interior of the member 80 and to the air-lift inlet 64 may be obtained for cleaning and servicing of the air-lift arrangement. Although any suitable removable closure means may be provided it is particularly envisaged that the means will comprise a flexible plastics cap 78 whereof the external rim surface 79 will seal against the internal diameter of member 80. The cap has a radially outwardly extending portion 81 which rests on the upper surface of the member 80.

In use, the air-lift arrangement 50 acts to air-lift (i.e. bubble-lift) final treated effluent material up through the tube 54 to outlet 58.This material reaches the tube 54 via inlet 64 and tube 62.

As indicated above, the shroud and closure arrangement prevents material liable to block inlet 64 from coming into contact therewith. This includes material which may fall into the tank via the access shaft (tubular projection 20) i.e. leaves and stones as well as such material as grease and fat, as mentioned above.

Moreover, in the event of an electrical power failure the fan or blower which supplies air to conduit 30 will cease to function. Air supply to the sewage * *S*** treatment unit will cease and effluent will no longer be discharged. The unit will * S *S.*s.

overfill with continuing flow of sewage into the vessel through the inlet arrangement. Floating material e.g. paper and rag will concentrate in the access shaft i.e. projection 20. The floating material can thereby gain access to

S *SSS

the second zone from which it is normally excluded but the shroud and closure arrangement prevents this material gaining access to the air-lift entry and - 10- thereby blocking it. On resumption of the power supply, discharge will resume and the water level in the unit will be lowered It is to be understood that the invention encompasses a method of constructing a sewage treatment unit in circumstances where the vessel 10 already exists in situ and equipment including an air-lift arrangement as described above is installed in that vessel on site.

S * S * S. * S

* S... * S

5, . S S ( * S. * * p p * * * p. * *SS. 5..

Claims

1. A sewage treatment unit comprising a plurality of zones between an inlet for sewage to be treated and an outlet for treated effluent, the zones including a treatment zone and a settlement zone, the unit further comprising means for removing treated effluent from the settlement zone, said means comprising an air-lift arrangement having an inlet, said airlift inlet having associated therewith a protective member being arranged to shroud the inlet and wherein the upper end of said protective member is provided with a removable closure means.

2. A unit as claimed in Claim 1, wherein said protective member is of generally tubular form.

3. A unit as claimed in Claim 1 or Claim 2 wherein said closure means is in the form of a cap adapted to fit to the protective member.

4. A unit as claimed in Claim 3 wherein said cap has a peripheral rim which is received within the protective member.

5. A unit as claimed in any preceding claim wherein said closure means is of plastics material.

6. As unit as claimed in any preceding claim wherein the wall of said ".

* i.a.

protective member has a plurality of perforations therethrough. *

*.J4e.

7. A unit as claimed in any preceding claim wherein said air-lift inlet is formed by a first conduit extending generally vertically into the protective member.

8. A unit as claimed in Claim 7 wherein the lower end of the protective member is provided with a further closure means provided with an aperture through which the first conduit projects into the interior of the protective member.

9. A unit as claimed in any preceding claim comprising a support member on which the protective member is supported.

10. A unit as claimed in Claim 7 or Claim 8 wherein the first conduit projects through an aperture in a support member

11. A unit as claimed in any one of Claims 7, 8 and 10 comprising a second conduit extending generally vertically adjacent to the first conduit, said second conduit acting to supply treated effluent to the exterior of the unit via the outlet jo

12. A unit as claimed in any preceding claim wherein the settlement zone is defined within a tubular member extending generally vertically within the vessel.

13. A unit as claimed in any preceding claim comprising an aerator conduit connected to an aerator, which supplies air to the treatment zone.

14. A unit as claimed in any preceding claim comprising an air supply conduit for supplying air to said air-lift arrangement.

15. A unit as claimed in Claim 13 and Claim 14 wherein said air supply conduit is connected to an adjustable valve adapted to supply air to said.

aerator conduit.

16. A unit as claimed in Claim 15 wherein an adjustable valve connected to the air supply conduit controls the supply of air to the air-lift arrangement

17. A sewage treatment unit substantially as hereinbefore described and as " la.$ illustrated in the accompanying drawings.

18. A method of constructing a sewage treatment unit utilising an existing sewage-receiving vessel in situ, said method comprising the provision of means for defining a treatment zone and a settlement zone within the vessel and further comprising the installation within the vessel of an arrangement for removing treated effluent from the settlement zone, said arrangement comprising an air-lift having an Inlet, said air-lift inlet having assocIated therewith a protective member being arranged to shroud the inlet, wherein the upper end of said protective member is provided with a removable closure means.

19.

constructed to Incorporate the features of any one of Claims 2 to 17.

S S. * * S. * S

S.....

S * S

S.....

S S. * *5 S * I. S... * S IS.. 5..

S S...