GB2261432A - Treatment plant - Google Patents

Abstract

The invention relates to a compact sewage treatment apparatus 11 having three treatment zones respectively a contact zone 31 for contacting settled raw sewage with air, a settlement zone 21 of inverted pyramidal shape with an inlet in the form of a stilling chamber fed from the zone 31 and a stabilization zone 41 fed with sludge from the zone 21 via an air lift pump in a pipe 42. The sewage is pumped continuously round the apparatus for treatment of sewage. <IMAGE>

Description

TREATMENT PLANT This invention relates to a treatment plant, particularly to a temporary or auxiliary treatment plant for sewage treatment.

Circumstances can occur where a sewage treatment works experiences a complete breakdown of the treatment process. Alternatively for operational reasons the biological process must be shut down for a period of time. During these periods it is necessary to take steps to prevent pollution of a receiving watercourse.

According to the invention there is provided apparatus for treating a liquid containing solids, comprising a container containing a plurality of discrete treatment zones including a contact zone for contacting liquid with a gas, a settlement zone for settlement of solids, and a stabilization zone, and means for continuously circulating liquid to be treated from the contact to the stabilization zone through the settlement zone.

The apparatus may be for treating liquid sewage, and comprise three zones, and the circulatory means rhay comprise an inlet for sewage and/or a pump in one or more of the zones. This provides for a continuous operation which is virtually self-regulating.

There may be two pumps and each may comprise an air lift pump, and one may be adapted for passing at least settled solids from the settlement zone to the stabilization zone, and the other may be at least for desludging the apparatus.

This provides for a relatively simple construction and operation.

The settlement zone may be intermediate the contact zone and the stabilization zone. This provides for a compact unit.

The stabilization zone may comprise an inverted pyramidal body. This provides for ease of sludge collection, particularly where the pyramidal body may have walls which slope at approximately 600 to the horizontal. This is an optimum angle for sludge collection.

The settlement zone may have an inlet for sewage which may comprise a stilling chamber.

The stilling chamber may comprise an open cylinder at an upper (in use) end of the settlement zone and connected with the contact zone via an open feed pipe.

This provides for efficient separation of sludge.

The upper in use boundary surface of the body may comprise a weir and channel for effluent. This provides a relatively simple way of separating the effluent and sludge.

The apparatus may comprise a substantially rectangular container with respective inlets for sewage and air, effluent outlet, an overflow and an auto-desludging outlet being treated at one end thereof. This again provides a compact and efficient construction.

The stabilization zone may include a plurality, suitably five, of air diffuser means for contacting the sewage with air for treatment. This provides for thorough mixing of the sewage with air.

The air bubble diffuser means may each have a magnetic base. This provides for ease of adjustment in position and location in the apparatus.

The stabilization zone may comprise a sludge return pipe which extends through the settlement zone to rise through the contact zone. This is a compact construction.

The invention has particular utility when a works experiences a complete breakdown of liquid treatment process or when for operational reasons the treatment process must be shut down for a period of time. During these periods it is necessary to take steps to prevent pollution of the place where the liquid leaves the works. It is possible to make the plant compact, being fabricated to the same dimensions as a standard lorry container for ease and speed of transport. No moving parts are necessary leading to very low maintenance costs.

Treatment plant embodying the invention is now described, by way of example, with reference to the accompanying drawings.

Fig. 1 is a diagrammatic longitudinal vertical section through sewage treatment apparatus according to the invention; Fig.2 is a plan of the apparatus of Fig.1; and Fig.3 is an end elevation of the apparatus of Fig. 1.

Referring to the drawings, there is shown a sewage treatment plant comprising apparatus in the form of a standard rectangular container 11, divided into three compartments, corresponding to the distinct zones, namely a contact zone 31, a settlement zone 21 and a stabilizer zone 41.

The contact zone 31 is a zone where incoming sewage meets returned activated sludge. In the contact zone, colloidal finely suspended and dissolved organics are rapidly absorbed onto the activated sludge solids.

The settlement zone 21 is a zone where the sludge is separated from the treated liquid effluent. This is typically in the embodiment a central conical vessel of inverted square pyramidal shape as shown. The sludge is passed from zone 21 to the stabilization zone 41 while the liquid can be discharged as a fully treated effluent.

The stabilization zone 41 is a zone where the absorbed solids on the activated sludge are oxidised.

An inlet 12 for sewage liquid to be treated opens into the contact zone or compartment 31 at one end 27 of the container 11 and the liquid in this compartment is aerated by air bubbling from pipe 13, fed from manifold 51, to assist contact with the activated sludge in the contact compartment 31. Material passes from the lower region of this compartment 31 to the upper region of the central zone or settlement compartment 21 through a pipe 32 which opens through a wall or baffle 23.

The settlement zone 21 is defined by the walls 22 and 23 inclined at 600 to the horizontal, so that it has the inverted square pyramid shape referred to previously. At the top (as shown) of compartment 21 there is a weir 24. This weir 24 runs round the top of the settlement zone 21 and is thus substantially square in plan, and connects with the four walls 22, 23 defining baffles, to form a square channel 25 around the outside of the weir 24. The channel 25 connects at one side with an effluent outlet conduit 26 leading to the outside of the container 11 at one end 27. Treated effluent therefore overflows the weir 21 into the channel 25 and flows out through the outlet conduit or pipe 26. The weir 24 prevents scum passing from the compartment 21 to the outlet conduit or pipe 26.

Sewage entering the compartment 21 through the pipe 32 is delivered to a stilling chamber in the form of a cylinder 33 with no top or bottom. The cylinder has a vertical axis and its walls extend above the top of the weir 24 and below the (upper) outlet of the pipe 32. Sewage entering the settlement zone or compartment 21 must therefore pass downwardly from the outlet of the pipe 32 to reach the weir 24, thus encouraging heavier material to settle out and sink to the bottom 28 of the compartment 21, leaving cleaner liquid to pass over the weir 24 to the outlet conduit 26. Stated in another way the sewage flow is stilled in chamber 33, aiding the settlement of solid particles that drop to the bottom 28 of the settlement zone 21 forming a sludge. Treated effluent spills over the top of the weir 24 and flows out through the channel 25 and pipe 26 as described previously.Sludge in the form of the settled solids particles passes from an outlet and enters the end or stabilization zone 41 through an open conduit 42 terminating at the mid-height region of the compartment 41 adjacent the left hand (as viewed) baffle 22. Passage through the conduit 42 is assisted by an airlift pump 43 supplied from air manifold 51 having an air inlet pipe 52 leading from the end 27 and suitable control valves 53. Material in the zone 41 is stabilised with the assistance of air fed from several aerating pipes 44 also fed from the manifold 51 from which air bubbles to the surface, similarly to the aeration in compartment 31. Surplus sludge build-up which occurs naturally during the treatment process can be extracted from the bottom 45 of the third compartment 41 through a further conduit 46, also assisted by an airlift pump 47 supplied from the manifold 51 and can be dumped or, as illustrated, returned to the top of the first compartment 21 to provide the sludge to treat further liquid from the inlet 12.

There is a continuous circulation of sewage liquid between the zones 31, 21, 41, which circulation is assisted by the aeration, by the air lift pumps, which varies the liquid density. These pumps operate by bubbling air into a rising pipe containing the sewage. This lowers the density of the liquid above the unaerated part thereof giving it a much lower hydrostatic head so that the head of liquid beneath the air inlet pushes the liquid up and out of the top of the pipe. The density variation is then used to cause flow past the point of aeration due to the different pressure heads.

There are two such pumps in the embodiment, driving the circulation of the sewage liquid one at the junction of the pipe 43 with the pipe 42 and one at the point 47 in the upper leg of the pipe 46, which is of 'L'-shape as shown. The airlift pump at the pipe 42 pumps settled sludge up through the pipe 42 and into the stabilization zone 41. This in turn causes the effluent level to drop in the settlement zone 21 and therefore causes more effluent to be drawn into the stilling chamber 33 from the contact zone owing to the hydrostatic head between those zones 31, 21. The air lift pump 47 pumps stabilized sludge from the stabilization zone 41 into the contact zone 31 through pipe 46.The pump 47 can be used to desludge the apparatus by diverting returned sludge to the outside The inverted square pyramid shape of the settlement zone 21 assists the guidance of settled material to the pipe 32 leading to the stabilization zone 41, remote from the end 27. The volumes in the first and third zones 21, 41 below the inclined walls 22, 23 are prevented from becoming stagnant volumes by the aeration of those compartments.

The advantage of contact stabilization is that the relatively high initial organic loading in the contact zone 31 produces a sludge with good settling characteristics and thus a smaller settlement zone 21 can achieve the degree of separation required. If this is combined with the pumped feed being at a constant rate the plant can treat up to 300 Population Equivalent (P.E.) of settled sewage.

It may be possible to treat 500 P.E. although probably not to a fully nitrified nitrified state.

The plant requires only an air supply to operate. This can be supplied by any suitable blower unit. Air is used to pump the liquid from zone to zone and to provide process air to the aeration zones via fine bubble diffuser domes. The air supply from an electrically driven blower unit (not shown) is connected via a single flanged coupling to the distribution manifold 51 through a control valve coupling. Adjustment of the air supply to each outlet is thus a very simple operational procedure. If the site has no power supply for the air blower, it can be run from a diesel powered generator.

Since there are no internal moving parts all maintenance can be carried out with the tank in full operation. Since all services, inlets and outlets are at one end 27 of the plant it can be located in a confined area with access at the one end 27 only. There is almost full utilization of all the internal volume of the unit as either aeration zones or settlement zones. Using the standard lorry container size enables rapid deployment of the unit to a flat base with a nearby liquid discharge point, which can result in only three days from request for treatment to provision of treatment. Once connected approximately three tanker loads (27 cubic metres) of activated sludge mixed liquor solids will make the plant operational.

There is in the stabilization zone 41 a plurality of air diffusers, in the embodiment five thereof, which each have a magnetic base. This means that they can be readily located on the base of the apparatus, and also are adjustable in position as required. There is also a double submersible pump which plugs into a blowing housing for operation of same. It will be understood that when the auto-desludging mode is used, sludge passes from the stabilization zone through the pipe 46 to a sludge holding tank. Also, the air bubble diffusers are so arranged that a quiescent zone is formed in the stabilization zone adjacent the open inlet (left hand as viewed in Fig.1) end of the pipe 46, so that settled, treated sludge is readily removed as desired.

To summarise the process activated settled raw sewage liquor is passed into the contact zone where it meets returned sludge from the settlement zone and is mixed with air passed into it from pipe 53'. The solids are settled into mixed liquor return solids and then settled in the settlement zone, before passing by the first air lift pump to the stabilization zone. The solids effectively therefore circulate round and round the system while the liquor passes out of the apparatus, the process ensuring that the biomass and oxygen from the air circulate fully with the sludge so that by the time the sludge reaches any quiescent parts, the sludge is fully digested.

The process can be started with one tanker load of activated sludge liquor.

Claims (16)

1. Apparatus for treating a liquid containing solids comprising a container containing a plurality of discrete treatment zones including a contact zone for contacting liquid with a gas, a settlement zone for settlement of solids, and a stabilization zone, and mean for continuously circulating liquid to be treated from the contact to the stabilization zone through the settlement zone.

2. Apparatus according to Claim 1, for treating liquid sewage, comprising three zones.

3. Apparatus according to Claim 2, the circulating means comprising an inlet for sewage and/or a pump in one or more of the zones.

4. Apparatus according to Claim 3, there being two pumps each comprising an air lift pump, one being adapted for passing at least settled solids from the settlement zone to the stabilization zone, and the other being at least for desludging the apparatus.

5. Apparatus according to any preceding claim, the settlement zone being intermediate the contact zone and the stabilization zone.

6. Apparatus according to Claim 5, the stabilization zone comprising an inverted pyramidal body.

7. Apparatus according to Claim 6, the pyramidal body having walls which slope at approximately 600 to the horizontal.

8. Apparatus according to Claim 7, the settlement zone having an inlet for sewage comprising a stilling chamber.

9. Apparatus according to Claim 8, the stilling chamber comprising an open cylinder at an upper (in use) end of the settlement zone and connected with the contact zone via an open feed pipe.

10. Apparatus according to any of claims 6 to 9, the upper in use boundary surface of the body comprising a weir and channel for effluent.

11. Apparatus according to any preceding claim, comprising a substantially rectangular container with respective inlets for sewage and air, effluent outlet, an overflow and an auto-desludging outlet being treated at one end thereof.

12. Apparatus according to any of Claims 2 to 11, the stabilization zone including a plurality of air diffuser means for contacting the sewage with air for treatment.

13. Apparatus according to Claim 12, there being five air bubble diffuser means.

14. Apparatus according to Claim 13, the air bubble diffuser means each having a magnetic base.

15. Apparatus according to Claim 14, the stabilization zone comprising a sludge return pipe which extends through the settlement zone to rise through the contact zone.

16. Apparatus for treating a liquid containing solids, substantially as hereinbefore described with reference to the accompanying drawings.