GB2300576A - Device for and method of separating suspended solids from liquids - Google Patents

Abstract

A device for separating suspended solids from a liquid comprises a treatment chamber 1 having a piston 7 movable substantially vertically therein between a start position in the upper part of the chamber and an end position in the lower part of the chamber, drive means outside the chamber for moving the piston, a liquid inlet 8 below the piston in the start position thereof, a solids oulet 3 below the piston in the end position therof, and a liquid outlet 27-31 above the piston in the end position thereof, the inlets and the outlets being controlled by valve means 4, 9, 32-36, the piston 7 being permeable to the liquid but substantially impermeable to the solids.

Description

DEVICE FOR AND METHOD OF TREATING LIQUIDS Field of the Invention This invention relates to a device for and a method of separating suspended solids from liquids, and to a method of treating liquids.

Background to the Invention While there are many large scale processes and plant available for the treatment of liquids, for example for the treatment of water for drinking and/or industrial purposes, or for the treatment of trade waste water, and in particular the removal therefrom of dissolved or suspended solids, these are not practical or economic for many smaller businesses to install and use. As a result water may not meet required quality standards and waste water discharges can contain an undesirably high concentrations of contaminants. Where controls are exercised, some industrial processes are not viable on a small scale because of the high cost of the water and/or waste water treatment plant.

The present invention provides a simple but highly effective device for and method of treating waste water and other liquids to remove suspended solids, where necessary with initial precipitation, emulsion breaking, coagulation and/or flocculation treatment to convert dissolved or emulsified contaminants into separable suspended solids.

Summary of the Invention According to the invention, there is provided a device for separating suspended solids from a liquid, comprising a treatment chamber having a piston movable substantially vertically therein between a start position in the upper part of the chamber and an end position in the lower part of the chamber, drive means outside the chamber for moving the piston, means for introducing liquid below the piston in the start position thereof, means for removing solids from below the piston in the end position thereof, and a liquid outlet above the piston in the end position thereof, the piston being permeable to the liquid but substantially impermeable to the solids.

The piston suitably comprises a layer of fibrous material, and may comprise two layers consisting of a lower perforate plate, for example of metal or plastics and an upper fibrous filtration material. The upper layer is preferably spaced from the lower layer, and may comprise a woven or non-woven textile material. It will be appreciated that the invention is not limited to the use of filter cloths as the permeable layer in the filter, although such materials will be especially useful. Any material which is permeable to the liquid, but which will hold back the solids (in the desired size range) may be used. Thus, for example, a piston using porous ceramic materials, or particulate filter materials, or combinations of the two, might also be usable in devices and methods according to the invention.

The piston may be driven between its start and end positions (and vice versa) by a hydraulic or pneumatic ram, mounted vertically over the chamber, or by a helical screw driven by a motor, for example an electric motor, via suitable reduction gearing. Alternatively, the piston may be arranged to descend by gravity, its descent being controlled by a simple hoist, which is then used to return the piston to its start position at the end of the treatment cycle. Any drive mechanism affording controlled slow descent of the piston, and enabling the piston to be recovered to its start position at the return of the treatment cycle may be employed.The speed of downward movement of the piston through the liquid will be chosen so as to be as fast as possible without the solid particles becoming so compacted on the underside of the piston during its descent that they block the permeable layer, thus preventing further movement. Ideally, the solids on the underside of the piston will remain of a sufficiently open structure to permit the passage of the liquid through the layer until the piston reaches the lower limit of its movement, when more intense compaction can be allowed to occur.

The means for removing solids may suitably comprise a springloaded valve which discharges automatically when sufficient solids have built up, a sliding plate valve, manually or mechanically operated, or a bag valve, using a tube of a flexible material which is simply twisted to close the valve and untwisted to release the solids.

The device suitably comprises means for introducing into the liquid beneath the piston in the start position thereof one or more treating agents to cause breaking of an emulsion, precipitation of solids from the liquid and/or coagulation of suspended solids in the liquid. The means for introducing the treating agent or agents preferably comprises at least one pump for injecting the agent or agents into the chamber, for example through a nozzle.

The device may comprise mixing means for mixing the agent or agents with the liquid, for example to promote flocculation. The mixing means preferably comprises a circulating pump outside the chamber and a plurality of inlets to the chamber selectively connectable to the pump, whereby liquid may be drawn from the chamber through a one or more of the inlets and reintroduced into the chamber by the pump through one or more of the remaining inlets.

Means may be provided for spraying cleaning liquid on to the piston either during movement thereof from the end position back to the start position or when the piston is in the start position thereof. Where the piston has two layers spaced apart from each other, the device may be arranged to permit cleaning liquid to be introduced between the two layers at an appropriate point in the cycle of movement of the piston between its start and end positions.

Two or more devices in accordance with the invention may suitably be used in tandem, with one or more filling while the other one or more discharges. Control of the two devices could be by means of a single controller, with the timing of operation being controlled so that nearcontinuous flow can be achieved.

The invention also provides a method of separating suspended solids from a liquid, comprising introducing the solids/liquid mixture into a chamber, driving a piston downwardly in the chamber through the liquid, the piston being permeable to the liquid but substantially impermeable to the solids, compacting the separated solids beneath the piston in the lowermost part of the chamber, removing the liquid from above the piston, and removing the solids from beneath the piston.

The invention further provides a method of liquid treatment comprising introducing a volume of the liquid into a treatment chamber, dispersing into the liquid in the chamber at least one treating agent to cause breaking of an emulsion, precipitation of solids therefrom and/or coagulation of suspended solids therein, driving a piston downwardly in the chamber through the liquid, the piston being permeable to the liquid but substantially impermeable to the solids, compacting the separated solids beneath the piston in the lowermost part of the chamber, removing the liquid from above the piston, and removing the solids from beneath the piston.

The liquid may be water being prepared for drinking, or waste water, for example from an industrial cleaning process or the like, and the treating agent can be a precipitating, coagulating and/or flocculating agent, for example for use in the removal of waste detergents, or in the treatment of emulsions, where emulsion breaking agents may first be added. It is especially suited to the treatment of liquids in batch volumes of 0.5 to 12 m3, but the invention is not limited to devices within this range of capacities.

Brief Description of the Drawings In the drawings, which illustrate diagrammatically exemplary embodiments of the invention: Figure 1 is a representation of a waste water treatment plant including a device in accordance with a first embodiment; Figure 2 is a view corresponding to Figure 1, but including a device according to a second embodiment; Figure 3 is an enlarged view of portion A of Figure 2; and Figure 4 is a representation of a device according to a third embodiment of the invention.

Detailed Description of the Illustrated Embodiments Referring first to Figure 1, the device comprises a closed vertical cylindrical chamber 1 having a frusto-conical lower end 2 provided with a solids outlet 3 controlled by an outlet valve device (for example a shutter) 4. The upper end of the chamber 1 is closed by a removable lid 5 (to permit maintenance and cleaning) through which passes a rigid shaft 6 mounting at its lower end a piston 7. The shaft 6 is suitably driven down and up by a hydraulic ram (not shown), mounted above the chamber. The piston 7 consists of a frame provided with circumferential sliding seals engaging the inner cylindrical surface of the chamber 1, and a layer of a filter cloth or the like stretched across the frame.The filter cloth is chosen so as to permit the passage of water therethrough, but to hold back solid particles having a size above a predetermined minimum permissible in the water for discharge.

Water for treatment is introduced via input line 8 controlled by input valve 9 to the chamber 1 just below the piston in its start or uppermost position. Various treating agents are added to the water in the chamber 1 via lines 21, 22 and 23 and valves 24, 25 and 26 from supply tanks 12 to 15, each having a respective dosing pump 16 to 19. For example, the first two tanks 12 and 13 may contain, respectively, acid and base for the adjustment of pH, the third tank 14 may contain a reagent for causing precipitation of substances dissolved in the water, and the fourth tank 15 may contain a coagulant or flocculating agent for aggregating solid particles, for example in colloidal form.The treating agents may be mixed with the water inside the chamber by means of a circulating pump 20 which can be caused to draw water from the chamber 1 via line 10 and open valve 11 and re-introduce the water into the chamber via a selected one or more of vertically spaced inlets 21 to 23, each controlled by a respective valve 24 to 26. The inlets are arranged so that the liquid streams enter the chamber tangentially thereof. Two alternative modes of mixing can be employed by this arrangement: a rapid mixing to distribute treating agents quickly, and a gentle mixing to promote flocculation. The gentle mixing may be accomplished by setting piping control valves 11 and 24 to 26 to circulate the water in one direction only (clockwise or anticlockwise), while the rapid mixing may be accomplished by setting the piping control valves to discharge water in opposing directions.

After mixing, the water may be allowed to settle, following which the piston 7 is driven downwardly through the water at a controlled rate such that the solids within the water are urged downwardly to settle in the frusto-conical lower end 2 of the chamber 1, the piston tending to compact the solids. While the piston is in its lowermost or end position, the water above the piston is drawn off via vertically-spaced outlets 27 to 31, via control valves 32 to 36, to be discharged to the water supply system to the sewer or to a further treatment stage if required. Several verticallyspaced outlets 27-31 are used to permit extraction of water at a selected height, for example if the piston comes to rest at a higher position as a result of compacted solids. The solids may be evacuated by means of valve 4.This can be a non-return valve with adjustable release pressure, allowing automatic discharge of the solids as they build up. It will allow the degree of dewatering to be controlled, and prevent solids compacting to such an extent that they are difficult to remove from the chamber. Where excessive compaction has occurred, it may be necessary to open the lower end of the chamber to remove the solids, and provision may be made in the construction of the chamber to facilitate this.

Washing of the piston 7 is preferably carried out at the end or beginning of each treatment cycle. This is effected by spraying wash water on to the upper face of the piston, the wash water being introduced by a line 37 connected to the upper end of the chamber via a valve 38, and by the upward movement of the piston through the wash water in the chamber. The line 37 preferably communicates with a plurality of nozzles arranged around the interior of the chamber 1. Alternatively, or additionally, wash water may be introduced to the underside of the piston 7 via line 8, which may also communicate with its own set of nozzles arranged around the interior of the chamber 1.

Referring now to Figure 2, in which corresponding components to those in Figure 1 are given the same reference numerals, the piston 7 consists of two layers 40 and 41 spaced apart from each other vertically, as may be seen more clearly from Figure 3. The upper layer 40 comprises a frame 42 in sealing contact with the inner wall of the chamber via a resilient sealing member 43, and with a filter cloth 44, for example of woven polypropylene or nylon, stretched across the frame. The lower layer 41 is in the form of a perforated metal sheet, with each perforation being formed as a tapering conical hole 45 with its mouth opening downwardly of the piston. The obtuse angle which each hole 45 includes, in crosssection, assists in ensuring that no clogging of the holes in the sheet occurs in use, and that the sheet is easy to clean after use.The lower layer 41 is also in sliding sealing contact with the inner wall of the chamber, through a resilient seal 46, for example of a silicone rubber.

The use of the device with the two-layer piston as shown in Figure 2 is essentially the same as with the device shown in Figure 1, but the cleaning operation differs. In this embodiment, the wash water supplied through line can be fed to the head of the piston and water to be treated can be fed to the space between the layers 40 and 41 by means of line 8.

Alternatively, clean water can be introduced by opening a communicating valve 47 with valve 9 closed. By-pass pipes 48 permit water to flow from the space between the piston layers 40 and 41 to the chamber beneath the piston.

In a method of treating water using the device as shown in Figure 1 or Figure 2, a typical sequence of events will be: a the piston 7 is at its start position; b water is introduced into the chamber 1 beneath the piston through line 8 (Figure 1) or line 8 and by-pass pipes 48 (Figure 2); c the circulating pump 20 is started, and appropriate ones of the inlet valves 24 to 26, together with valve 11, are opened to start rapid mixing; d the dosing system 12 to 19 injects chemicals for the breaking of an emulsion, the precipitating coagulation and/or flocculation of solids in the water (i.e. one or both of dosing pumps 18 and 19 is/are started to pump the chemicals into the circulation mixing system 20 to 26); ; e the mixing system rapidly mixes the liquid in the chamber until the chemicals are thoroughly dispersed, and is then switched to a gentle ("tapered") mixing mode to expedite flocculation (pump 20 is slowed down and/or the valves 21 to 23 are set to ensure that the flow in the chamber is all in the same direction); f after sufficient time to permit completion of flocculation, the mixing is stopped and the piston is moved slowly downwards in the chamber towards its end position, as illustrated by the broken line representation of the shaft 6.This allows liquid to be displaced through the piston to the space above the piston, while confining the solids to the space below the piston; g if the valve 4 is a non-return type, compacting of the solids re sults in discharge of the solids through the valve, but if the valve is not of a non-return type, the solids are discharged through the valve 4 periodically, after suitable accumulation of solids.Discharge of the solids may also be achieved by opening up the end of the chamber 1; h the mixing system 10, 11, and 20 to 26 begins rapid mixing of the water remaining within the chamber 1; i the water in the chamber 1 is then tested, for example by means of probes in the chamber or in the mixing system outside the chamber, and if the water is within acceptable limits for dis charge (e.g. pH between 7 and 10), the mixing system stops and valves 32 to 36 open to discharge the liquid from the chamber; j if the water is not within acceptable limits for discharge, the dosing system adds acid or base from tanks 12 or 13 using pumps 16 or 17 to correct the pH (or other chemicals to correct other deficiencies in water quality), and then the mixing is stopped and the water discharged.

Referring now to Figure 4, the device shown comprises a cylindrical body 50 having frusto-conical top and bottom end portions 51 and 52, the bottom end portion 52 having three support legs 53, 54 and 55 attached thereto to support the body 50 in use. Each leg 53, 54 and 55 is formed as a hollow vessel which can hold a supply of treating agent to be pumped therefrom, when required, by dosing pumps P3, P4 and P5.

Control of the various pumps and valves in the device, as well as movement of the piston 56, is by means of a programmable logic controller (PLC) 57, provided with inputs from appropriate sensors.

The operation of the device is as follows. Waste water is first pumped into the body 50 via pump P1 with the piston 56 fully withdrawn to the top of the body (Pos 1). When the body 50 is full, a level gauge (float switch or the like) signals to the PLC 57, which in turn causes the pump P1 to stop. A circulating pump P2 is then started to recirculate the water from the base of the body 50 via line 58 back to a position in the upper part of the body. A primary coagulant (e.g. ferric sulphate or aluminium sulphate) is introduced from a storage tank in a first of the legs 53 via pump P3 to the body. The dose can be controlled (by the PLC 57) by the length of time for which the pump P3 is operated.A pH probe 60 in the line 58 monitors the hydrogen ion concentration in the water as it circulates, and after a predetermined interval of processing with the coagulant, the pH is readjusted by the addition of an alkali, for example sodium hydroxide solution, from the second of the legs 54 via pump P4, the pump being operated until the probe detects the desired value (typically just below pH7) again. At this stage, a predetermined volume of a polymer flocculant solution is introduced from the third of the leg tanks 55 via pump P5, to cause the effluent within the body 50 to flocculate. Again the recirculation or mixing at this stage using pump P2 is the subject of a timed process under the control of the PLC.

After the predetermined time has elapsed, the pump P2 is stopped and a dwell time is initiated, allowing the flocs to form and to start to precipitate in the body 50. The piston 56 will then start to fall. The speed at which the piston falls is extremely critical; it must be less than the natural settlement velocity of the flocculated solids (flocs), to avoid blockage of the permeable membrane in the piston 56 as it separates water from the solids. Once the piston reaches the lowermost or end position (Pos 3), it activates a sensor (not shown) which signals to the PLC to open the valves V1, V2, V3 and V4, allowing the clean water fraction to be drained away, leaving the sludge below the membrane in the piston.After the water has completely drained away, the lowermost valve V5 is opened to allow discharge of the sludge (it will be appreciated that discharge of the sludge may only be necessary once every few strokes of the piston, when sufficient sludge has built up). After completion of this cycle, the valve V5 will stay open while the piston 56 returns back to its starting position Pos 1, to avoid the creation of a vacuum. The valve V5 closes when the piston reaches Pos 1, and an automatic backwash is carried out by opening valve V6 to allow backwash water to be sprayed on to the upper surface of the piston from a ring of nozzles 61 around the inside of the upper frustoconical portion of the body. The cycle can then recommence with the filling of the body with the next batch of waste water.

It will be appreciated that, while the device has been described in connection with the treatment of water, it may equally be used for other liquids or liquid mixtures in which solids are suspended, or in which dissolved solids can be precipitated out for removal. Oils and greases and the like may cause clogging of the permeable piston and liquids containing high levels of such components may be unsuitable for treatment using the device. The device is especially suited to the treatment of liquids containing fibrous or particulate contaminants, and emulsions.

Claims (15)

1. A device for separating suspended solids from a liquid, comprising a treatment chamber having a piston movable substantially vertically therein between a start position in the upper part of the chamber and an end position in the lower part of the chamber, drive means outside the chamber for moving the piston, means for introducing liquid below the piston in the start position thereof, means for removing solids from below the piston in the end position thereof, and a liquid outlet above the piston, the piston being permeable to the liquid but substantially impermeable to the solids.

2. A device according to Claim 1, wherein the piston comprises a perforate metal or plastics plate below a layer of a filtration material.

3. A device according to Claim 1 or 2, wherein the piston comprises a layer of a fibrous filtration material.

4. A device according to Claim 3, wherein the fibrous filtration layer comprises a woven or non-woven textile material.

5. A device according to any preceding claim, comprising means for introducing into the liquid beneath the piston in the start position thereof one or more treating agents to cause breaking of an emulsion, precipitation of solids from the liquid, coagulation and/or flocculation of solids in the liquid.

6. A device according to Claim 5, wherein the means for introducing the treating agent or agents comprises a pump for injecting the agent or agents into the chamber.

7. A device according to Claim 5 or 6, comprising mixing means for mixing the agent or agents with the liquid.

8. A device according to Claim 7, wherein the mixing means comprises a circulating pump outside the chamber and a plurality of inlets to the chamber selectively connectable to the pump, whereby liquid may be drawn from the chamber through a one or more of the inlets and reintroduced into the chamber by the pump through one or more of the remaining inlets.

9. A device according to any preceding claim, comprising means for spraying cleaning liquid on to the piston either during movement thereof from the end position back to the start position or when the piston is in the start position thereof.

10. A method of separating suspended solids from a liquid, comprising introducing the solids/liquid mixture into a chamber, driving a piston downwardly in the chamber through the liquid, the piston being permeable to the liquid but substantially impermeable to the solids, compacting the separated solids beneath the piston in the lowermost part of the chamber, removing the liquid from above the piston, and removing the solids from beneath the piston.

11. A method of liquid treatment comprising introducing a volume of the liquid into a treatment chamber, dispersing into the liquid in the chamber at least one treating agent to cause breaking of an emulsion, precipitation of solids, coagulation and/or flocculation therein, driving a piston downwardly in the chamber through the liquid, the piston being permeable to the liquid but substantially impermeable to the solids, compacting the separated solids beneath the piston in the lowermost part of the chamber, removing the liquid from above the piston, and removing the solids from beneath the piston.

12. A method according to Claim 11, wherein the liquid is waste water.

13. A device for separating suspended solids from a liquid, substantially as described with reference to, or as shown in, the drawings.

14. A method of separating suspended solids from a liquid, substantially as described with reference to the drawings.

15. A method of liquid treatment, substantially as described with reference to the drawings.