GB2267230A

GB2267230A - Apparatus add method for the treatment of effluent

Info

Publication number: GB2267230A
Application number: GB9211484A
Authority: GB
Inventors: John Geoffrey Dickinson; Andrew Kim Robertshaw
Original assignee: NORTHERN DISPOSAL SERVICES LIM
Current assignee: NORTHERN DISPOSAL SERVICES LIM
Priority date: 1992-05-30
Filing date: 1992-05-30
Publication date: 1993-12-01
Also published as: GB9211484D0

Abstract

A mobile apparatus for treating industrial effluent stored in a tank (16) on site comprises a wheeled chassis carrying a suction source, a series of storage tanks and a separator (23), which may be a belt press or centrifugal decanter, and separates liquid and solid fractions. Initially any oil floating on the surface in tank (16) is drawn into auxilliary tank (15), then the main contents of tank (16) is drawn into tank (14). Upper and lower level detectors (14a, 14b) in tank (14) control the flow into and out of tank (14) to hold the liquid surface between the two levels, liquid flowing only into or out of tank (14) at one time. The liquid is drawn from tank (14) by pump (19) through a muncher (18), which breaks up large solids, and fed to a further tank (20), also provided with level detectors which control pump (19) to maintain a level between (20a) and (20b) to supply separator (23). Solids are removed from separator (23), either as a thick pumpable slurry by pump (32) or by a screw conveyor feeding a belt conveyor. Liquid is removed from separator (23) by a pump (25) to tank (27) with more level detectors which control discharge from tank (27) via pump (28) or valve (U) to a sewer. <IMAGE>

Description

APPARATUS AND METHOD FOR THE TREATMENT OF EFFLUENT The present invention relates to apparatus and method for the treatment of effluent comprising a mixture of liquid and solids, in particular for separating out the liquid and solid components.

Conventionally, effluent which cannot be fed directly to the sewer has to be collected in a storage tank or interceptor, and these have to be emptied regularly and the contents transported by tanker to an effluent treatment works. This results in high transportation costs due to the large volume of effluent being transported, and the effluent treatment works also renders a charge for receiving and treating the effluent.

It is therefore the aim of the present invention to provide apparatus and method for treating effluent which overcomes the abovementioned disadvantages.

According to a first aspect of the present invention there is provided apparatus for treating effluent comprising a mixture of liquid and solids, the apparatus comprising: a tank for connection to a source of effluent to be treated, a separator unit in fluid communication with the tank for separating from the effluent a substantially liquid component and a substantially solid component, the separator unit having a first outlet for removing the substantially liquid component and a second outlet for removing the substantially solid component, first detection means for detecting and signalling a low level of effluent in the tank, second detection means for detecting and signalling a high level of effluent in the vacuum tank, first pump means in fluid communication with the tank for pumping effluent from the tank to the separator unit, second pump means in fluid communication with the separator unit for pumping the substantially liquid component from the separator unit via the first outlet, means for removing solids from the separator unit via the second outlet, and control means for controlling the levels in the tank and the flow of effluent through the apparatus in response, at least partially, to signals from said first and second detection means.

Preferably, the tank is a pressure/vacuum tank.

Preferably, the apparatus also includes a first holding tank having an inlet and outlet, located between and in fluid communication with the pressure/vacuum tank and the separator unit. This first holding tank conveniently includes three detection means in the form of level sensors for detecting and signalling to the control system low, medium and high levels of effluent in the first holding tank, such that when a low level is signalled, the first holding tank outlet opens and effluent is admitted to the separator unit whilst the first holding tank is still receiving effluent from the pressure\vacuum tank.

Subsequently, when the high level is signalled, the control system halts the flow of effluent into the first holding tank, until the medium level is signalled which causes the control system to allow effluent to flow again into the first holding tank until maximum level is again indicated.

Preferably, the apparatus includes means for adding floculant to the effluent on entry to the separator unit, to enhance the solidification occuring in the separator unit.

The separator unit is preferably a de-canter, although other separating means may be employed with equal effect, for example filter presses or belt presses.

Conveniently, the substantially liquid component is pumped from the separator unit to a second holding tank, the primary purpose of which is to enable samples to be taken to ensure that the liquid component is sufficiently solid-free to enable direct dumping to the sewer. This second holding tank has an inlet, an outlet, and two detection means for detecting and signalling low and high levels of liquid. When the high level is signalled, the outlet valve is opened and liquid is either pumped or allowed to drain from the second holding tank until the low level is signalled, when the outlet valve is closed.

The separator means is preferably adjustable so that the degree of. solid\liquid separation effected may be altered. When the separator is set to achieve a high degree of separation, the solids are removed from the separator by means of a screw conveyor, but when it is set to achieve a lesser degree of separation, the "solids" are actually in the form of a slurry and are removed from the separator by means of a pump, for example an impellor pump.

In order to protect the separator unit , a muncher is -preferably included upstream of the separator, between and in fluid communication with the pressure/vacuum tank and the first pump means, for breaking up any large pieces of solid material which might otherwise block the system.

In certain situations, the effluent being treated may contain oil, and therefore the apparatus preferably includes an auxiliary vacuum tank having an inlet for fluid communication with the source of oily effluent, and an outlet which is normally kept closed but may be opened-when required to dump the oil. This auxiliary vacuum tank is operated first, before the main pressure\vacuum tank is brought into operation, so that the oil may be drawn off the surface of the effluent.

According to a second aspect of the present invention there is provided a method of treating effluent comprising a mixture of solids and liquid, the method comprising the steps of: transferring the effluent to be treated into a - tank having first detection means for detecting and signalling a low level of effluent in the tank and second detection means for detecting a high level of effluent in the tank, transferring the effluent-from the tank to separator unit whilst maintaining the level of effluent in the tank at a level between the aforesaid low and high levels, separating in said separator unit a substantially liquid component and a substantially solid component from the effluent, removing the substantially liquid component from- the separator unit, and removing the substantially solid component from the separator unit.

An embodiment of the present invention will-now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a plan view of the general layout of the apparatus, Figure 2 is a side view of the general layout of.the apparatus, Figure 3 is an end view in the direction of arrow X of Figure 2, Figure 4 is a block diagram illustrating the apparatus and its method of operation, and Figure 5 is a flow chart illustrating the sequence of steps followed during operation of the apparatus.

Referring to the drawings, apparatus according to the invention is designated generally by 10 and is mounted on a vehicle or vehicle trailer 12.

The apparatus comprises a pressure/vacuum tank 14 of approximately 5,400 litre capacity having the facility to be connected up to a source of effluent in, for example, an interceptor tank 16 via inlet valve A. Outlet valve B on the pressure/vacuum tank leads to a muncher 18 which is in turn connected to a first holding tank 20 of approximately 2,600 litre capacity, via a slurry pump 19 of 4" capacity. Inlet valve A can be substituted with inlet valve D, likewise outlet valve B can be substituted with outlet valve C. The outlet valve J from the holding tank 20 is connected to a slurry pump 21, also of 4" capacity, which is in turn connected to a separator unit 23 in the form of a de-canter which separates the solid and liquid components from the effluent by centrifugal action. Floculant is stored in mixing and storage vessels 22 and is fed to the effluent in the de-canter 23.

A liquid pump 25 of 2" capacity removes the substantially liquid component from the de-canter 23 and transfers it to 'a second holding tank 27 of approximately 2,600 litres capacity from whence it may be discharged from outlet valve U via a liquid pump 28 of 2" capacity to the sewer, or alternatively it may be allowed to drain directly into the sewer, by-passing pump 28. The solids are removed from the de-canter 23 either by means of a screw conveyor 30 or, in the case where the "soilds" exiting the de-canter are actually in the form of a pumpable sludge, a slurry pump 32 of 4" capacity.

The solids are transferred, by means of the screw conveyor 30 to a hopper 34 of 3 to 4 cubic metre capacity , underneath which there is located a substantially horizontal belt conveyor 36 which transfers solids from the base of the hopper 34 to a second belt conveyor 38, the latter being stowable into the position shown in the drawings, i.e within the general confines of the vehicle trailer.

An auxiliary vacuum tank is also included adjacent the hopper 34, and this may be connected to the effluent source prior to running the apparatus to draw off any oil which may be present on the surface of the effluent. A water tank 37 of approximately 2,400 litre capacity is also included to provide a source of fresh water for mixing floculant, flushing or other purposes.

A control system incorporating a series of detection means in the form of level sensors 20a, 20b, 20c in tank 20, 14a and 14b in tank 14, and 27a, 27b in tank 27, operates the valves A,B,C,D,J and U as well as the other components of the apparatus such as the pumps, conveyors etc in the sequence described hereinafter. Most of the components are driven hydraulically, by means of a diesel engine 39 (125 KW &commat; 1500 r.p.m) and a supply of hydraulic fluid from hydraulic oil tank 40, with the exception of the valves which are driven pneumatically.

To empty the contents of interceptor tank 16, the apparatus is operated as follows: a) any oil on top of the effluent is drawn off into tank 15 by applying a vacuum to tank 15 via compressor 42, the oil then being stored in tank 15; b) the effluent ia drawn into tank 14 by applying a vaccuum to tank 14 via compressor 42; c)with valve B closed, tank 14 fills via open valve A until the level sensor 14a signals a high level, at which time the control system stops the compressor and opens valve B, allowing effluent to flow through the muncher 18 and pump 19 to tank 20 (if the effluent level in tank 14 drops below the level sensor 14b, the control system closes valve B and re-starts the compressor to allow the level to rise again); d)the low level sensor 20c in tank 20 signals a low level and the control system opens valve J and allows effluent to flow through pump 21 to the de-canter 23, pump 25 and tank 27; e)effluent is still flowing into tank 20, so that the level will rise. If it rises sufficiently to trigger the high level sensor 20a, the control system will then stop pump 19 and muncher 18, whereupon the level in tank 20 begins to fall. If the level falls below mid-level sensor 20b, the control system will respond by re-starting the pump 19 and muncher 18, as a result of which the level in tank 20 will rise again towards the level of level sensor 20a; f)tank 27 is filling until the liquid in tank 27 triggers high level sensor 27a, whereupon the control system opens valve U and allows the liquid to flow either directly to the sewer or via pump 28. Once the level in tank 27 falls sufficiently to trigger low level sensor 27b, the control system closes valve U, permitting the tank 27 to fill up again.

The above steps b) to f) are carried out by the control system, but when the operator sees that the interceptor tank 16 is empty, the control system is manually over-ridden by means of control panel 45, and a "shut down" procedure is followed, during which outlet valve U remains open. This procedure involves setting the compressor 42 to pressure mode, and applying pressure to the system to purge the remaining fluids out of the tanks, pumps and interconnecting pipework.

When the de-canter 23 stops, there is a certain amount of solids and liquid in the decanter which then mix together again, creating a sludge. This can be dealt with by pumping the mixture back into the main tank 14, to be put through the system again on the next run. The solids collected in hopper 34 are then discharged via belt conveyors 36 and 38, the latter being deployed for this purpose to the position shown in broken lines in Figure 2.

The floculant feed system is fully automated and under the control of the control system.

The apparatus described above is ideally suited for use as a mobile unit when mounted on a vehicle or vehicle trailer, but it should be appreciated that the invention is not limited to such an application. The invention offers advantages in that the volume of the effluent to be transported to a disposal site is considerably reduced, with resultant cost savings.

Claims

1. Apparatus for treating effluent comprising a mixture of liquid and solids, the apparatus comprising: a tank for connection to a source of effluent to be treated, a separator unit in fluid communication with the tank for separating from the effluent a substantially liquid component and a substantially solid component, the separator unit having a first outlet for removing the substantially liquid component and a second outlet for removing the substantially solid component, first detection means for detecting and signalling a low level of effluent in the tank, second detection means for detecting and signalling a high level of effluent in the vacuum tank, first pump means in fluid communication with the tank for pumping effluent from the tank to the separator unit, second pump means in fluid communication with the separator unit for pumping the substantially liquid component from the separator unit via the first outlet, means for removing solids from the separator unit via the second outlet, and control means for controlling the levels in the tank and the flow of effluent through the apparatus in response, at least partially, to signals from said first and second detection means.

2. Apparatus according to Claim 1 wherein the tank is a pressure/vacuum tank.

3. Apparatus according to Claim 2 wherein there is also included a first holding tank having an inlet and outlet, located between and in fluid communication with the pressure/vacuum tank and the separator unit.

4. Apparatus according to Claim 3 wherein the first holding tank includes three detection means in the form of level sensors for detecting and signalling to the control system low, medium and high levels of effluent in the first holding tank, such that when a low level is signalled, the first holding tank outlet opens and effluent is admitted to the separator unit whilst the first holding tank is still receiving effluent from the pressure\vacuum tank.

5. Apparatus according to Claim 4 wherein when the high level is signalled, the control system halts the flow of effluent into the first holding tank, until the medium level is signalled which causes the control system to allow effluent to flow again into the first holding tank until maximum level is again indicated.

6. Apparatus according to any of the preceding Claims, wherein there is included means for adding floculant to the effluent on entry to the separator unit, to enhance the solidification occuring in the separator unit.

7. Apparatus according to any of the preceding Claims wherein the separator unit is a de-canter.

8. Apparatus according to any of the preceding Claims wherein there is also included a second holding tank for receiving the substantially liquid component which is pumped from the separator unit.

9. Apapratus according to Claim 9 wherein the second holding tank has an inlet, an outlet, and two detection means for detecting and signalling low and high levels of liquid, such that when the high level is signalled, the outlet valve is opened and liquid is either pumped or allowed to drain from the second holding tank until the low level is signalled, when the outlet valve is closed.

10. Apparatus according to any of the preceding Claims wherein the separator means is adjustable so that the degree of solid\liquid separation effected may be altered.

11. Apparatus according to any of the preceding Claims wherein a muncher is included upstream of the separator, between and in fluid communication with the pressure/vacuum tank and the first pump means, for breaking up any large pieces of solid material which might otherwise block the system.

12. Apparatus according to any of the preceding Claims adapted for use with oily effluent wherein there is included an auxiliary vacuum tank having an inlet for fluid communication with the source of oily effluent, and an outlet which is normally kept closed but may be opened when required to dump the oil.

13. A method of treating effluent comprising a mixture of solids and liquid, the method comprising the steps of: transferring the effluent to be treated into a tank having first detection means for detecting and signalling a low level of effluent in the tank and second detection means for detecting a high level of effluent in the tank, transferring the effluent from the tank to a separator unit whilst maintaining the level of effluent in the tank at a level between the aforesaid low and high levels, separating in said separator unit a substantially liquid component and a substantially solid component from the effluent, removing the substantially liquid component from the separator unit, and removing the substantially solid component from the separator unit.

14. A method according to Claim 13 wherein the effluent also contains oil and the method includes the additional step of transferring the effluent to be treated to an auxiliary vacuum tank and drawing off the oil from the surface of the effluent held therein.

15. Apparatus for treating effluent substantially as herein described with reference to and as illustrated in the accompanying drawings.

16. A method of treating effluent substantially as herein described with reference to and as illustrated in the accompanying drawings.