GB2317168A

GB2317168A - Sequential batch reactor

Info

Publication number: GB2317168A
Application number: GB9619089A
Authority: GB
Inventors: James Redfern Brown; Robert Kenneth Oram
Original assignee: Balmoral Group Ltd
Current assignee: Balmoral Group Ltd
Priority date: 1996-09-12
Filing date: 1996-09-12
Publication date: 1998-03-18
Anticipated expiration: 2016-09-12
Also published as: GB2317170A; GB2317168B; GB9719518D0; GB9619089D0; GB2317170B

Abstract

A sequential batch reactor comprises a rotationally moulded settlement tank 1, an aerobic digestion tank 13 received within the settlement tank and means to transfer sewage (i) into the settlement tank, (ii) from the settlement tank to the digestion tank and (iii) away from the digestion tank. Preferably the reactor also has a transfer compartment 17 between the settlement tank and digestion tank, the transfer compartment having holes which prevent gross solids from entering. In use, effluent is introduced into the settlement tank 1 via pipe 10, some of the effluent transfers to compartment 17, an airlift pump 20 is periodically activated so as to transfer an aliquot of sewage into the digestion tank 13 and, once treated, the sewage is transferred away via outlet 23 to a drain or sewage system.

Description

SEQUENTIAL BATCH REACTOR This invention relates to a sequential batch reactor for use in treating sewage.

According to the invention there is provided a sequential batch reactor comprising a primary settlement tank having an inlet for introducing effluent into the reactor, an aerobic digestion tank received in the primary settlement tank and having an outlet for transferring digested effluent from the reactor, means for transferring effluent from the primary settlement tank to the aerobic digestion tank and means for transferring treated effluent from the aerobic digestion tank to a drain or sewage system.

Embodiments of the invention will be illustrated by way of non-limiting example to the figures of which: Figure 1 is a cross-sectional view; and Figure 2 is a perspective view of a section of a further embodiment.

The illustrated embodiments comprise a broadly spherical tank 1 having body 2 provided with flat base 3 with a punt 3a and a cylindrical neck 4.

Conveniently tank 1 is rotationally moulded since this allows the tank to be made without an equatorial seam which could leak. The invention is not to be construed as restricted to rotationally moulded tanks. Those skilled in the art will have little difficulty in manufacturing the tank body in other ways for example from glass fibre reinforced plastics material.

In the illustrated embodiment neck 4 is provided with extension piece 6 terminating in access cover 7. An inwardly directed flange 8 of the extension piece 6 abuts inwardly directed flange 9 of the neck 4.

The tank is further provided with an inlet 10 having an upwardly extended member 11 and a downwardly directed member 12.

A digestor tank 13 is received in the body 2 of tank 1. Digestor tank 13 is generally cylindrical and may stand on the base 3 and punt 3a of tank 1. As will become apparent hereinafter it may be desirable to provide a deflector 14 in the digestor tank. This can conveniently be formed in the digestor tank if it too is a rotational molding. In the illustrated embodiment the upper part 16 of the digest or tank is of lesser diameter than the lower.

A compartment 17 is in the illustrated embodiment provided in the tank 1 and defined by walls 18 and 19. This is not essential. Once more the compartment is desirably a rotationally molded product. Holes (not shown) are provided in compartment 17 to allow liquid to flow from the tank into the compartment 17.

A conduit allowing controlled transfer of liquid from the compartment 17 into the digestor tank is provided. In the illustrated embodiment this comprises an airlift pump 20 and pipe 21. A remote compressor (not shown) supplies air to the airlift pump. While an airlift pump is not essential for the performance of the invention it is desirable. In principle other pumps such as immersed mains pumps could be used as could bucket devices and centrifugal pumps. In practice however an air lift pump is advantageous since no moving parts or mains voltage need be present. Reliability and safety can thereby be improved.

Digestor tank 13 is provided with an aerator 22 for passing air bubbles through liquid contained in the digestor tank. Aerator 22 can be supplied by the same compressor as the pump.

A discharge conduit allowing controlled transfer of liquid from the digestor tank to outlet 23 is also provided. The discharge conduit conveniently comprises a pipe 24 and a further airlift pump (not shown).

Typical operation of the device will now be described. Waste enters the tank body through the inlet 10. The outer tank body 2 functions as a primary settlement tank which is to say that solids settle out into the base. After continued operation (typically a year) the accumulated solids may be drawn out by suction hose through either extension piece 11 and 12 or directly, with the reduced diameter portion of the digestor tank facilitating the introduction of a pipe for removal of the solids.

Typically discharge into the tank shows a wide variation in now rate. For example in the early morning and early evening large quantities of effluent are produced by the flushing of lavatories and so forth. In the middle of the night little effluent is discharged. Tank 1 also serves to provide a buffer. In the event of major overload for example due to malfunction liquid will back-up the inlet 10 thereby raising the alarm but will not be discharged through the outlet 23. It may however be covenient to provide an emergency overflow from the outer tank. In some cases anaerobic digestion of the effluent occurs in the tank 1. This is desirable but not essential.

Some of the effluent contained in tank 1 transfers to compartment 17 where fitted. The holes in the compartment wall prevent gross solids from entering the compartment.

At intervals the airlift pump 20 is activated and transfer an aliquot to the digestor tank 13. The level in tank 1 thus falls in preparation for further effluent.

The airlift pump can be controlled by a simple time switch. It is preferred however to employ a programmable logic controller (PLC) so that if there is little or no flow into the device a small transfer only into the digestor occurs so that sufficient nutrients to prevent die back of the micro-organisms contained in the digestor are transferred.

Material in the digestor tank is aerated optionally under timer or PLC control. The combination of nutrients in the effluent and introduced oxygen cause resident microorganisms to degrade the effluent. After a relatively short time typically 6 to 12 hours the suspended solids content and biological oxygen demand (BOD) of the liquor after settlement are dramatically reduced. For example in a trial after stabilisation a reactor of the invention produced product of 10 mg/m3 suspended solids and 10 mg/m3 BOD as compared to a commercially available device which achieved 30 mg/m3 suspended solids and 20 mg/m3 BOD.

At the end of the aerobic digestion and settlement process the clarified and digested effluent is transferred to the outlet 23 leaving an inoculum in the digestor tank 13. Deflector 14 serves to cause mixing of the effluent as it is pumped out thereby ensuring that treated effluent from throughout the tank is withdrawn.

In the event the outlet 23 becomes blocked or some other malfunction occurs the digestor tank fills. When flill it overflows into the tank 1 thereby reducing the likelihood of environmental damage. The resting of the tanks has further advantages. Liquid contained in the outer tank 1 helps maintain the liquid in the digestor at a constant temperature. A more compact installation than those in which the primary settlement/aerobic digestion tank is separate from the aerobic digestion tank. The amount of in soil pipework required in accordance with the invention is reduced and thus the likelihood of damage if the ground is disturbed is reduced. The aerobic digestion tank can be of lighter, and hence cheaper, construction than a separate one which must be designed to tolerate the full local soil loadings.

Claims

1. A sequential batch reactor comprising a primary settlement tank having an inlet for introducing effluent into the reactor, an aerobic digestion tank received in the primary settlement tank and having an outlet for transferring digested effluent from the reactor, means for transferring effluent from the primary settlement tank to the aerobic digestion tank and means for transfering treated effluent from the aerobic digestion tank to a drain or sewage system.

2. A sequential batch reactor as claimed in claim 1 further comprising a transfer compartment intermediate the primary settlement tank and the aerobic digestion tank.

3. A sequential batch reactor as claimed in claim 1 or claim 2 wherein at least one of the primary settlement tank, the aerobic digestion tank and the transfer compartment when present are rotational molded.

4. A sequential batch reactor substantially as hereinbefore described by reference to Figure 1.

5. A sequential batch reactor substantially as hereinbefore described by reference to Figure 2.

6. A method of treating sewage comprising the steps of a introducing the sewage into a primary settlement tank b transferring an aliquot of sewage from the primary settlement tank to an aerobic digestion tank received in the primary settlement tank, c subjecting the aliquot to aerobic digestion so as to obtain a treated sewage and d transferring the treated sewage from the aerobic digestion tank.

7. A method as claimed in claim 6 wherein the sewage is transferred by an airlift pump.

8. A method as claimed in claim 6 or claim 7 wherein intermediate steps a and b the sewage gross solids are filtered from the sewage.

9. A method of treating sewage substantially as hereinbefore described by reference to Figure 1.

10. A method of treating sewage substantially as hereinbefore described by reference to Figure 2.

Amendments to the claims have been fled as follows 1. A sequential batch reactor comprising a rotationally molded primary settlement tank having an inlet for introducing effluent into the reactor; an aerobic digestion tank received in the primary settlement tank and having an outlet for transferring digested effluent from the reactor, means for transferring effluent from the primary settlement tank to the aerobic digestion tank and means for transferring treated effluent from the aerobic digestion tank to a drain or sewage system.

3. A sequential batch reactor as claimed in claim 2 wherein the transfer compartment is rotationally molded.

4. A sequential batch reactor as claimed in any one of claims I to 3 wherein the transfer compartment is rotationally molded.

5. A sequential batch reactor substantially as hereinbefore described by reference to Figure 1.

6. A sequential batch reactor substantially as hereinbefore described by reference to Figure 2.

7. A method of treating sewage comprising the steps of a introducing the sewage into a rotationally molded primary settlement tank b transferring an aliquot of sewage from the primary settlement tank to an aerobic digestion tank received in the primary settlement tank; c subjecting the aliquot to aerobic digestion so as to obtain a treated sewage and d transferring the treated sewage from the aerobic digestion tank.

8. A method as claimed in claim 7 wherein the sewage is transferred by an airlift pump.

9. . A method as claimed in claim 7 or claim 8 wherein intermediate steps a and b the sewage gross solids are filtered from the sewage.

10. A method of treating sewage substantially as hereinbefore described by reference to Figure 1.

11. A method of treating sewage substantially as hereinbefore described by reference to Figure 2.