APPARATUS FOR TRATING LIQUID EFFLUENT CONTAINING SOLID MATERIAL

Abstract: Apparatus and method for separating solid and liquid fractions from animal waste e.g. cow slurry. The preferred apparatus is a two stage arrangement in which slurry is fed to the nip between a first perforated drum (8) supported internally by intermediate plates and mounted in bearings by end plates and a resilient rubber coated drive roller (12), the solids are scraped off the drum by a special scraper blade (63) and allowed to fall onto the surface of a second drum (20) similarly internally supported and mounted and are then carried between the nip of this drum and a second rubber coated drive roller (24) and the solids are finally scraped off and fall out of the apparatus. The machine is preferably arranged so that the second drum rotates at a slower speed than the first drum because this gives better liquid removal.

Description: APPARATUS FOR TREATING LIQUID ' EFFLUENT CONTAINING SOLID MATERIAL TECHNICAL FIELD The invention relates to apparatus for treating liquid effluent containing solid material, such as cow, pig or poultry manure which is commonly referred to as slurry. Such slurry has great potential for use as a fertiliser, but is difficult to store and distribute by virtue of its great volume, most of which is water. In addition, when spread on fields in its natural state as a fertiliser such slurry tends to scorch the vegetation and to produce an objectionable smell which may be unacceptable to local inhabitants. The storage and use of slurry is made more difficult and costly by health and environmental legislation.. BACKGROUND ART A proposal .has been made in British Patent Specification No. 1,340,323 that a form of filtration apparatus should be used to separate liquids from the slurry, thus producing solids of reduced liquid content. This proposal suggests the use of a hollow perforated cylindrical shell mounted for rotation between inner and outer squeeze, rolls which bear respectively on its inner and outer surfaces, a scraper blade also bearing on the outer surface of the cylinder downstream of the squeeze rolls so as to scrape solids from the surface of the cylinder. This arrangement is unsatisfactory in practice, because, surprisingly, the perforations become blocked with solids despite the teaching in the specification. DISCLOSURE OF THE INVENTION According to the present invention apparatus for treating liquid effluent containing solid material includes a perforated drum mounted in bearings for rotation about its central axis, e.g. by means of a central shaft, a roller engaging the surface of the drum, at least the external surface of which roller is preferably resilient, at least one and preferably both of the roller and the drum being connected to drive means to rotate them about their respective axes, a feed means e.g. a hopper, adapted to deliver effluent to the surface of the drum at a point upstream of the roller seen in the intended direction of rotation of the drum, scraper means, e.g. a scraper .blade, engaging the outer surface of the drum at a point downstream of the roller so as to scrape damp solid material from the drum, and a liquid collection trough situated beneath the drum to collect liquid separated by the drum. The drum preferably has end plates secured at or adjacent its ends and one or more intermediate plates located inside the drum and having their circumferences secured, e.g. welded, (e.g. at spaced apart positions around their circumferences so as to minimize blocking of perforations) to the inside face of the drum. The plates may conveniently be mounted on the central shaft. The thickness of the intermediate plates is preferably not more than twice the size of a perforation. This OM VvIP provides excellent support for the drum surface and thus ensures high pressure in the nip with the roller whilst minimizing blocking of the perforations . The separation of the plates is preferably less than the diameter of the drum, e.g. less than 75% of the diameter of the drum, e.g. in the range 25% to 75%. This achieves good support whilst minimizing interference with liquid flow out of the slur y. The plates are preferably provided with apertures disposed in a ring around their centres. This -Facilitates cleaning of the device without loss of support for the drum. ' The scraper preferably is afforded by a blade which has an upper surface inclined to its lower surface and disposed away from the surface of the drum. This facilitates separation of the solids from the surface of the drum. In the preferred embodiment the apparatus includes a second perforated drum having a central shaft mounted in bearings for rotation about its central axis, a second roller engaging the peripheral surface of the second drum, at least the external surface of which roller is preferably resilient, at least one and preferably both of the second roller and the second drum being connected to drive means to rotate the •about their respective axes, a liquid collection trough beneath the second drum to collect liquid separated by the second drum and means to deliver the damp solid material from the first drum to the periphery of the second drum at a point upstream of the nip between the second roller and the secon ' d drum in the intended direction of rotation of the second drum, which means is preferably constituted by an inclined plate, the upper end of which lies beneath the blade engaging the first drum. The perforations in the first drum are preferably made inwardly so that the external surface of the drum is relatively smooth whilst on the second drum they are outwardly so that its external surface is relatively rough. Preferably the second drum is provided with a second blade engaging its periphery at a point down¬ stream of the second roller to remove solid material from it. In a preferred form of the present invention apparatus for treating a liquid effluent containing solid material comprise a rota-table first perforated drum, feed means for feeding the effluent so as to present the effluent to the outside surface of the drum and carry it between the drum and a resilient surfaced roller which is arranged to be urged towards the outer surface of the drum in driving relationship thereto and which is itself provided with drive means so that on rotation of the first drum in use the solids, whose liquids content has been reduced, are carried into contact with scraper means which bear against the drum downstream of the. roller, the solids thus being separated from the surface of the first drum and delivered to the outer surface of a rotatable second perforated drum so that in use the rotation of the second drum carries the solids between the drum and a resilient surfaced roller which is arranged to be urged towards the outer surface of the drum in driving relationship thereto and which is itself provided with drive means so that on rotation of the second drum in use the solids, whose liquids content has been further reduced, are carried into contact with the scraper means which bear against the drum downstream -of the roller, the solids thus being separated from the surface of the second drum and delivered to the outlet of the apparatus the perforated drums being driven by the said resilient rollers and the drums being mounted on bearings and the perforated surface of each drum being suppported on its inside face by one or more members arranged transverse - to the axis of the ' drum at spacings from the ends of the drum and from each other of less than the diameter of the drum, each scraper means comprising a blade having an upper surface inclined to its lower surface and disposed away from the surface of the drum with which it is associated. The first and second troughs may be separate or may be constituted by single trough large enough to collect liquid from both the drums. Preferably the or each roller is provide . ith means to adjust the pressure with which it contacts its respective drum. Thus the second roller may contact its drum with a greater pressure than that with which the . first roller contacts its drum to fur.ther reduce the liquids content of the solid material. The bearings on which " the drums are mounted produce a reactive force to the force exerted on them by the roller, and ensure that the drums rotate correctly about their central axis which remains stationary. The invention also extends to a preferred method of operating the apparatus. Thus according to the present" invention a method o treating a liquid effluent containing solid material comprises feeding the effluent to the feed means of an apparatus comprising a rotating first perforated drum s as to present the effluent to the outer surface of the drum and carry it between the drum and a resilient surfaced roller which is urged towards the outer surfac of the drum in driving relationship thereto and which i itself driven and then carry the solids, whose liquids content has been reduced, into contact with scraper means which bear against the drum downstream of the roller, the solids thus being separated from the surfac of the first drum and delivered to the outer surface of a rotating second perforated drum so as to carry the solids between the drum and a resilient surfaced roller which is urged towards the outer surface of the drum in driving relationship hereto and which is itself driven and then carry the solids, whose liquids content has been further reduced, into contact with scraper means which bear against the drum downstream of the roller, the solids thus being separated from the surface of the second drum and delivered to the outlet of the apparatus, the second drum being rotated more slowly than the first drum. ύ m- h Oi' We have found that this produces a greatly improved removal of liquids overall as compared with when the drums are run at the same speed. The drums may be of the same or different diameter but assuming the same diameter the ratio of the rate of rotation (in R.P.M.) .of the first drum to that of the second drum is preferably in the range 1:0.9 to 1:0.4 e.g. 1:0.8 to 1:0.5 especially 1:0.7 to 1:0.6. Thus according to a preferred form of the present invention apparatus for treating a liquid effluent - containing solid material comprises a rotatable first perforated drum, feed means for feeding the effluent so as to present the effluent to the outside surface of the drum and carry it between the drum and a resilient surfaced roller which is arranged to be urged towards the outer surface of the drum in driving relationship thereto and which is itself provided with drive means so that on rotation of the first drum in use the solids, whose liquids content has been reduced, are carried into contact with scraper means which are arranged to bear against the drum downstream of the roller, the solids thus being separated from the surface of the first drum and delivered to the outer surface of a rotatable second perforated drum so that in use the rotation of the second drum carries the solids between the drum and a resilient surfaced roller which is arranged to be urged towards the outer. surface of the drum in driving relationship thereto and which is itself provided with drive means so that on rotation of the second drum in use the solids, whose liquids content has been further reduced, are carried into contact with scr-aper.means which bear against the drum downstream of the roller, the solids thus being separated from the surface of the second drum and delivered to the outlet of the apparatus, the drive means being arranged to rotate the second drum at a lower surface speed than the first drum. BEST MODE OF CARRYING OUT THE INVENTION Further features and details of the invention will be apparent from the following description of one specific embodiment which is given by way of example with reference to the accompanying drawing which is a diagrammatic side elevation of an apparatus for separating the solid and liquid constituents of cow - slurry. ■ The apparatus comprises a frame 2 on the upper end of which is mounted a slurry hopper 4 having an outlet at its lower end. The outlet 6 is situated immediately above a perforated circular-section drum 8 having a length of about one metre and a radius of about 25 cm. The drum 8 is provided with a central shaft 10 mounted in two end bearings (not shown) and is thus rotatable about its central axis. The shaft 10 extends along the length of the drum and is secured to it by plates described below (not shown). Adjacent the outlet 6 the periphery of the drum 8 is engaged by a roller 12 havin a length substantially the same as that of the drum and formed of or sheathed in a resilient material such as natural or synthetic rubber or an ela≤tomeric material. At each end of the roller 12 is an adjusting device 14 G ? which serves to adjust the ' pressure with which. the roller contacts the drum. Situated about 80° away from the roller 12 on the side remote from the hopper 4 there is a plate 16 which transfers solids from the drum 8 to the drum 20. The plate extends downwardly away from the drum at about 45°, and adjacent its lower edge is a further perforated drum 20, similar to the drum 8. Similarly to the drum 8, the drum 20 is mounted to rotate about its axis on a shaft 22 and is provided with a resilient- roller 24 similar to the roller 12 and whose contact pressure may be varied by adjusting means 26. In a position corresponding to that of the plate 16 is an outlet plate 28 which extends downwardly at about 45° and whose lower portion constitutes a delivery or outlet slide. Positioned below the drums 8 and 20 there is a respective liquid collecting trough 32 and 34 each having an outlet 36, 38 through which liquid may be withdrawn. Keyed to one end of the two central shafts 10 and 22 is an identical respective pulley 40 and 42, which pulleys are rotated by a rubber V belt 44 which passes around them. Each pulley 40 and 42 is connected to a further pulley 46 and 48 respectively below the associated rubber roller 12 or 24 by a further rubber V belt 50 and 52 respectively carried by a shaft on which is keyed a further pulley or a gear wheel which cooperates with the shafts on which the rollers 12 and 24 are carried to rotate them. The pulleys 40, 42, 46 ^_iE-EΛ OMPI ° and 48 are so dimensioned a ' nd the cooperation of the latter pulleys with the shafts so arranged that the peripheral speed of the two rollers 12 and 24 is identical to that of the drums 8 and 20. The intermediate pulleys 46 and 48 are provided to ensure that the contacting surfaces of the rollers 12 and 24 and their respective drums are moving in the same direction. The shaft 22 is connected by a further pulley (not shown) and a V belt 54 to a drive motor 56, so that, in use, the two drums 8 and 20 and two rollers 12 and 24 are driven in synchronism. Each drum 8 and 20 is 1 metre wide and about 25 cm in diameter and about 3 mms thick (14 gauge) and is made of stainless steel. Each drum is perforated with circular perforations arranged in a triangular pattern, the perforation being 3 mms in diameter and 2.4 mms apart, each perforation having six equally spaced nearest neighbours. The drum 8 " is smooth surfaced with the holes punched inwardly whilst the drum 20 has the holes punched outwardly producing a rough grater-like surface. The rollers 12 and 24 are made of printing blanket type rubber material and consist of a steel rod 2.5 cms - in diameter covered by a 2.5 cms thick sleeve of the printing blanket rubber material. The rubber of this was indented by about 3 mms to 4.5 mms when a rounded pencil point was forced into it with a force of 10 - 14 kgs, the pencil point being rounded to about 0.75 mms diameter. The perforated drums 8 ' and 20 are supported on central rod axes 10 and 22 by two end plates and two intermediate support plates. The end plates extend about 2.5 cms above the outer surface of the perforated drums providing end cheeks, and the ends of the perforated drum are welded to the inside faces of the end plates. The intermediate plates have slightly smaller diameters and have their circumferences welded ' to the inside face of the perforated drum. The end and intermediate plates are each about- 3 mms thick and are provided with eight 10 cms diameter equally spaced apertures converting the plates into webs. The resultant drum is ' stiff and does not flex under hand pressure. Squeegies 61 and 62 bear against the drums upstream of the rollers 8 and 20. Each squeegy is a strip of the printing blanket, material about 3. mms thick, supported in metal backing strips. Squeegy 61 is in trailing relationship to the drum 8 while squeegy 62 is in radial relationship to the drum 20. Squeegy 61 has about 3 mms free, whilst squeegy 62 has about 1.3 cms free. Downstream of each roller 8 and 20 there is a knife blade 63 and 64. The orientation and angle of these blades to the perforated drums are the same and are most important for the satisfactory removal of the solids from the drums. Each blade extends substantially, the full width of the drum and has its cutting edge resting on the surface of the drum. Each blade is " spaced by 15 cms downstream along the surface of the drum from the nip of the drum and the rollers 8 or 20. The blade has a flat bottom surface 65 and a parallel flat top surface 66 and is about 14 cms long and is about 1.3 cms thick. The cutting edge is provided by the bottom surface and an inclined cutting surface 67 which faces away from the surface of the drum, the bottom surface 65 being presented to the drum. The angle between the bottom surface 65 and the inclined top surface 66 or bevel is about 20° , e.g. 10 to 30°. The bottom surface is inclined to a tangent to the surface of the drum at the point of contact of about 25°, e.g. 10 to 40°, and is. inclined to the vertical at an angle of about 50°, e.g.- 40 to 60°. An extension plate 68 is mounted below the rear end of each blade 63- and 64 and is about 6.4 cms long. The bottom surface of each blade is about 5 cms away from the surface of the top end of the plate 16 or 28. A backing plate 69 is also arranged below each blade 63 and 64 and is inclined up to below the edge of the bottom surface of the drums 8 and 20 but out of contact therewith. In a modification of the drive arrangement the pulley 48 is arranged so that the roller 24 (and thus the drum 20) rotates at about half the speed of the roller 12, e.g. 38 R.P.M. for the roller 24 (7 R.P.M. for the drum 20, the ratio of roller to drum circumferences being 5.4:1) ' and 58 R.P.M. for the roller 12 (10.7 R.P.M. for the drum 8, the ratio of roller to drum circumferences being_ 5.4:1) . This results in even greater removal of liquid at the drum 20. The operation of the device is as follows: The motor 56 is switched on to rotate the two drums anti¬ clockwise and the two rollers clockwise. Cow slurry is discharged from the opening 6 of the hopper 4, which is optionally provided with an agitator (not shown) to ensure that the slurry flows freely, on to the upper surface of the drum 8 just upstream of the roller 12. The rotation of the drum 8 carries the slurry into the nip between the roller and the drum and compresses it, such that liquid is squeezed through the perforations in the drum and the solid material in the slurry is left as a damp layer on the surface of the drum. The perforations are dimensioned in accordance with the constituents of the slurry to be treated to achieve efficient separation. The solid " material is left adhered to the drum in a thin layer and is carried round the drum anticlockwise until it reaches the blade 63, the edge of which removes the damp solid material from the drum 8. The solid material slides down the plate 16, or is pushed down by material behind it, and is delivered onto the upper surface of the second drum 20, immediately upstream of the nip formed between it and the roller 24. As before the material is squeezed between the drum and the roller, and more liquid is squeezed out of the solid material and passes through the perforations in the drum OMPI (the contact pressure may if desired be greater than on the first drum) . The solid material is scraped off the surface of the drum by the edge of the blade 64 and falls ~ onto the plate 28 which constitutes an outlet chute of the machine. The liquid separated by each drum drips down into the respective trough 32 and 34 beneath them, and is removed through the outlet pipes 36 and 38. Typically cow slurry contains about 87% liquid and about 13% solid material. The final moisture content o the separated solid material will depend on the pressur with which the rollers contact the drums and the size and spacing of the perforations in the drums. .The separated solids can readily be used as fertilizer - • optionally after composting. The liquid contains considerable quantities of nitrates and thus may be use directly as a fertilizer, or alternatively the nitrates may be removed and stored in concentrated solution or solid form for subsequent use. Although the apparatus has been described as havin two drums and associated rollers, it will be appreciate that under certain circumstances one drum and roller ma be adequate. Alternatively one drum may be used, engaged by two rollers of which the downstream roller preferably engages the drum with a higher pressure than the upstream roller. Other modifications to the described apparatus wil be readily apparent, for example the rollers 12 and 24 may be driven directly from the motor 56 and these rolle ' rs may be used to drive the drums by frictional OMP contact, the drums no longe ' r being driven directly by the motor. INDUSTRIAL APPLICABILITY The apparatus and method of the invention finds industrial applicability in the separation of animal manure wastes into liquid and solid fractions, the liquid being usable as liquid fertilizer since it is readily pumpable and the solids readily composting to produce solid fertilizer in which pathogens and weed seeds have been killed by the composting process.

Claims: - CLAIMS 1. Apparatus for treating liquid effluent containing solid material including a perforated drum mounted in bearings for rotation about its central axis, a roller engaging the surface of the drum, at least one and preferably both of the roller and the drum being connected to drive means to rotate them about their respectively axes, feed means adapted to deliver effluent to the surface of the drum at a point upstream of the roller seen in the intended direction of. rotation, of the drum, scraper means engaging the outer surface of the drum at a point downstream of the roller so as to scrape damp solid material from, the drum, and a liquid collection trough situated beneath the drum to collect liquid separated by the drum. 2. Apparatus as claimed in Claim 1 in which the drum has end plates secured at or adjacent its ends and one or more intermediate plates located inside the drum and having their circumferences secured to the inside face of the drum. 3. Apparatus as claimed in Claim 2 in which the thickness of the intermediate plates is not more than twice the size of a perforation. 4. Apparatus as claimed in Claim 2 or Claim 3 in which the separation of the plates is. less than the diameter of the drum. OMPI 5. Apparatus as claimed in Claim 4 in which the separation of the plates is in the range 25% to 75% of the diameter of the drum. 6. Apparatus as claimed in Claim 2, 3, 4 or 5 in which the or each intermediate plate is secured to the inside surface of the drum at spaced apart positions around its circumference. 7. Apparatus as claimed in any one of Claims -2 to 6 in which the intermediate plates are secured to the end plates by being mounted on a central member on which the end plates are also mounted. 8. Apparatus for treating a liquid effluent containing solid material which comprises a rotatable first perforated drum, feed means for feeding the effluent so as to present the effluent to the outside surface of the drum and carry it " between the drum and a resilient surfaced roller which is arranged to be urged towards the outer surface of the drum in driving relationship thereto and which is itself provided with drive means so that on rotation of the first drum in use the solids, whose liquid content has been reduced, are carried into contact with scraper means which bear against the drum downstream of the roller, the solids thus being separated from the surface of the first drum and delivered to the outer surface of a rotatable second perforated drum so that in use the rotation of the second drum carries the solids between the drum and a -^JRE £Γ c:.'_H resilient surfaced roller which is arranged to. be urged towards the outer surface of the drum in driving relationship thereto and which is itself provided with drive means so that on rotation of the second drum in use the solids, whose liquids content has been further reduced, are carried into contact with scraper means which bear against the drum downstream of the roller, the solids thus being separated from the surface of the second drum and delivered to the outlet of the apparatus, the perforated drums being driven by the sai resilient rollers and the drums being mounted on bearings and the perforated surface of each drum being supported on it's inside face by one or more members arranged transverse to the axis of the drum at spacings from the ends of the ' drum and from each other of less than the diameter of the drum, each scraper means comprising a blade having an upper surface inclined to its lower surface and disposed away from the surface of the drum with which it is associated. 9. Apparatus for treating a liquid effluent containing solid material which comprises a rotatable first perforated drum, feed means for feeding the effluent so as to present the effluent to the outside surface of the drum and carry it between the drum and a resilient surfaced roller which is arranged to be urged towards the outer surface of the drum in driving relationship thereto and which is itself provided with drive means so that on rotation of the first drum in us the solids, whose liquids content has been reduced, are C... carried into contact with scraper means which are arranged to bear against the drum downstream of the roller, the solids thus being separated from the surface of the first drum and delivered to the outer surface of a rotatable second perforated drum so that in use the rotation of the second drum carries the solids between the drum and a resilient surfaced roller which is arranged to be urged towards the outer surface of the drum in driving relationship thereto and which is itself provided with drive means so that on rotation of the second drum in use the solids whose liquids content has been further reduced, are carried into contact with scraper means which bear against the drum downstream of the roller, the solids thus being separated from the surface of the second drum and delivered to the outlet of the apparatus, the drive means being arranged to rotate the second drum at a lower surface speed than the first drum. , 10. A method of treating a liquid effluent containing solid material which comprises feeding the effluent to the feed means of an apparatus comprising a rotating first perforated drum so as to present the effluent to the outside surface of the drum and carry it between the drum and a resilient surfaced roller which is urged towards the outer surface of the drum in driving relationship thereto and which is itself driven and then carry the solids, whose liquids content has been reduced, into contact with scraper means which bear against the drum downstream of the roller, the solids thus being separated from the surface of the first drum and delivered to the outer surface of a rotating second perforated drum so as to carry the solids between the drum and a resilient surfaced roller which is urged towards the outer surface of the drum in driving relationship thereto and which is itself driven and the carry the solids, whose liquids content has been further reduced, into contact with scraper means which bear against the drum downstream of the roller, the solids thus being separated from the surface of the second- dru and delivered to the outlet of the apparatus, the second drum being rotated more slowly than the first drum. 11. Apparatus as claimed in Claim 1 substantially as specifically described herein with reference to the accompanying drawing. 12. A method as claimed in Claim 10 substantially as specifically .described herein " with reference to the accompanying drawing. -^UP. ...

Inventors: FITZGERALD J
Applicants: FITZGERALD J, MURPHY P
Application year: 1981
Main classification: B01D33
IPC codes: B01D33, B30B9