WO1994017001A1

WO1994017001A1 - Process and apparatus for treating sludge from waste water, especially from sewage

Info

Publication number: WO1994017001A1
Application number: PCT/NO1994/000016
Authority: WO
Inventors: Bernhard Bongom
Original assignee: Bergen Kommune, Ktu
Priority date: 1993-01-22
Filing date: 1994-01-20
Publication date: 1994-08-04
Also published as: NO177900B; AU6011594A; NO930237L; NO177900C; NO930237D0

Abstract

A process for draining sludge from waste water, comprising a crude purification step, a fine purification step and a draining step. From the fine purification step sludge is conducted to an intake gap (12a) between two elongate, horizontal pinch rollers (17, 18) in a press (12). The sludge is pressed to a thin walled layer of material having a low moisture content on the discharge side (12b) of the press, while waste water is diverted via an overflow threshold (at 17a) on the intake side of the press. An apparatus for draining of sludge comprising a press (12) having intake gap (12a) tapered obliquely downwards between two elongate, horizontal pinch rollers (17, 18).

Description

Process and Apparatus for treating sludge from waste water, especially from sewage.

The present invention relates to a process for treating sludge from waste water, especially from sewage, comprising a crude purification step, in which objects or coarse particles, such as plastic, textiles, bottle caps and the like are screened from unpurified waste water, and a fine purification step, in which sludge is screened from crudely purified waste water, and also a subsequent draining step for draining of the sludge.

In purification plants for sewage unpurified waste water will normally first pass a crude purification arrangement, for example a so-called machine-cleaned grating, in order to retain coarse particles, such as plastic, textiles, bottle caps, and the like. Thereafter the crudely purified waste water will pass a fine purification arrangement in order to retain sludge, which is to be further transported to a remotely disposed depositing location.

The problem with such a solution has been that the sludge has a relatively large volume and large weight and demands relatively large transportation capacity, as a consequence of relatively large water content.

From NO 154 666 a crude purification arrangement is known, where unpurified waste water is conducted from a water discharge conduit inwardly into a stocking of wire netting, which can retain objects, coarse particles and sludge, while the crudely purified waste water is filtered off from the wire netting stocking. The wire netting stocking can be drawn off from a folded together supply of stocking material, which is arranged outside said conduit. The drawing off can occur by means of a combined drawing and pressing arrangement, the netting stocking with contents being able to be pressed together simultaneously for the expelling of waste water from the wire netting stocking and its contents. The result of the expelling of water from the wire netting stocking and its contents is in all cases rather limited, as a consequence of the content of coarse particles (objects such as textiles, plastic, bottle caps, syringe needles and the like) . A product is necessarily obtained which includes a large quantity of water. The purification operation must in this instance be described as crude purification, since a large portion of the sludge becomes necessarily drained off/ filtered off/pressed out together with the crudely purified waste water. There is need for fine purification in addition. This can present problems by the very fact that large portions of fibre-formed material have already been removed in the withdrawn sludge.

With the present invention the aim initially is to effect a separate crude purification step, in which there are substantially removed certain waste materials which have a relatively solid consistency, that is to say waste materials whose consistency substantially deviates from the consistency of waste materials of the "sludge materials" type. Consequently the initial objective is to remove the content of relatively large and coarse particles or objects, as it is difficult to handle together with the remaining waste materials, such as sludge. Thereafter the aim is to effect a separate fine purification step, in which water is removed and is collected as far as possible separately of the residual sludge, that is to say both residual coarse particles and also fine particles.

The present invention relates to concretely draining off sludge which is produced by the afore-mentioned fine purification step.

In GB patent 2 017 519 two elongate rollers are shown which are disposed parallel to each other in a common plane. This plane preferably slopes downwardly from the intake end of the press towards a fluid discharge at the opposite end of the press. The material supplied is discharged into a deep gap between the rollers and can be allowed to flow ("trickle") from the one end towards the other end, all according to the viscosity of the material which is to be pressed. The fluid of the press is led away from the elongate rollers at their lower end, while the material of the press is discharged vertically below the gap between the two rollers mutually parallel in the oblique plane. The press fluid is consequently forced to travel the whole length of the roller in order to be dischargeable at the opposite end of the press. By this one will have a supply of fluid over large portions of the length of the press and the relative moisture increases in the longitudinal direction of the press. This can involve the press material flowing more or less unhindered the longer this comes in the longitudinal direction of the press and there is a danger of significant portions of the press material being discharged together with the press fluid. It is proposed in DE 10 32 178 to remove sludge substances in connection with a fine purification operation by means of a two roller drier, the sludge being discharged into a gap between two horizontal rollers which have axes of rotation arranged in a common horizontal plane. The total quantity of sludge (both dry stuff and water) is guided between the rollers. Waste water is evaporated directly from the roller surfaces, while the sludge after drying is mechanically removed from the roller surfaces. A significant supply of heat is required in order to effect the intended evaporation of the waste water. It is furthermore proposed in DE 18 13 953 to use a two roller drier, comprising an upper drier roller and a lower transfer roller for transferring sludge material from the transfer roller to the drier roller. In this case also a significant heating effect is required in order to effect the intended evaporation of the waste water from the drier roller. Sludge is sprayed directly against the outer surface of the lower transfer roller on an upper portion of this. Thereafter the sludge is led in a largely S-shaped path along the outer surface of the transfer roller and further along the drier roller to a scraping location on the discharge side of the drier, the sludge first being conducted into an annular gap between the transfer roller and a surrounding cap and thereafter being pressed by means of (the lower) transfer roller against (the upper) drier roller, while the rollers are rotated in a relatively slow, rolling movement against each other.

Generally various types of press are known for draining off fluid from a water-containing starting material. Such presses are usually relatively complicated and expensive. In addition the end product is most often a tightly packed together press cake which is not immediately suitable for further treatment and which for example is not suited for degradation processes which require the supply of air internally in the product. With the present invention the aim is to provide a process where, with the aid of simple mechanical means and with minimal need of power, the sludge can be drained to a significant degree for the production of a product having a low water content, primarily with a view to low total weight of the end product with a view to transportation, storage, and the like. In addition the aim is to produce a product which is well suited for a subsequent, separate degradation process.

The process according to the invention is characterised in that the sludge is conducted from the fine purification step to an inlet gap between two elongate, horizontal pinch rollers rollable against each other in a press, where the pinch rollers comprise a lower pinch roller and an upper pinch roller and where the pinch rollers form a mutual abutment at a level substantially above the axis of rotation of the pinch roller, the sludge on the inlet side of the press being conducted to the bottom of the inlet gap between the pinch rollers and pressed between the pinch rollers in the direction of rotation of the pinch rollers, to form a relatively thin layer of material having a low moisture content on the discharge side of the press on one side of the rollers, while the pressed out waste water is led away from the other side of the rollers via a relatively low overflow threshold on the inlet side of the press in a direction in counterflow to the direction of rotation of the pinch rollers.

By effecting according to the invention the driving of water by means of two pinch rollers which are arranged in the afore-mentioned manner a dry stuff product can be obtained in the form of a sheet-like or flock-like material, which has a relatively large surface area and which in addition is sufficiently light in weight for the material to be dischargeable into an environment having large air access without substantial arrangements.

By providing according to the invention for sludge having a sufficiently large portion of fibre-formed coarse particle material to be conducted almost instantaneously directly to the bottom of the gap between the pinch rollers, one has the possibility of effectively catching the sludge itself by means of the two pinch rollers rotatable against each other, so that the sludge is effectively carried along with the pinch rollers in their mutual rolling movement. At the same time one achieves by this an intended removal of the dry stuff and water separately, the draining of the sludge occurring in that the sludge is compressed to a high dry stuff content and is delivered to one side of the press, that is to say the discharge side, and the water is simultaneously pressed out in a direction opposite to the direction of rotation of the pinch rollers and the water is delivered on the other side of the press, that is to say the intake side. In other words the squeezed waste water can be drawn off by a simple overflow above the top of the lower pinch roller by allowing movement of the waste water in counterflow to the rotary movement of the pinch roller. In addition the waste water can be conducted laterally away from the pinch rollers at their one or opposite ends.

It is preferred that the sludge is supplied batch- wise to the press, since one can thereby ensure by simple means a batch-wise handling of the sludge with effective and relatively instantaneous backward pressing of the water content of the sludge, opposite to the supply direction of the sludge, particularly in the first phase of the squeezing operation in the press. In addition there can be obtained a desired additional draining off of water along the pinch rollers between each batch-wise supply of sludge.

Even if the sludge is supplied batch-wise it is desirable to let the pinch rollers rotate with a moderate peripheral speed, for example with a peripheral speed of 2-10 revolutions per minute and preferably about 5-6 revolutions per minute for a lower pinch roller having a diameter of about 20 cm. By this one can ensure inter-alia that the running off of water can occur with a greater relative speed than the speed of rotation of the peripheral surface of the pinch rollers. Consequently the pressed out waste water can be relatively easily removed in counterflow to the rotational movement of the pinch rollers and be led away longitudinally along the pinch rollers along towards their one end (at a certain oblique position of the pinch rollers) or at opposite ends (by using horizontal pinch rollers) .

Furthermore the invention relates to an apparatus for draining sludge from waste water, especially from sewage, comprising a crude purification arrangement, such as a so- called machine-cleaned grating, in which unpurified waste water is adapted to be screened off objects and coarse particles, such as plastic, textiles, bottle caps and the like, and a fine purification arrangement, in which crudely purified waste water is adapted to be screened off sludge, together with a subsequent draining arrangement for draining of the sludge where the draining arrangement comprises a press having a pair of pinch rollers which are rollable against each other reckoned in the supply direction of the sludge.

According to the invention the aim is to produce an especially simple and relatively inexpensive apparatus, which can be operated in an easy manner with minimal power requirements, but with a favourable mode of operation.

The apparatus is characterised in that the press has a horizontal elongate intake in the form of an intake gap tapered obliquely downwards relative to a horizontal plane, which is defined between the two elongate horizontal pinch rollers, arranged one above the other, and that the pinch rollers comprise a lower pinch roller and an upper pinch roller, which form a mutual abutment at a level above the axis of rotation of the lower pinch roller. By the apparatus according to the invention provision is made for the sludge, which is conducted to the press, to almost instantaneously come into squeezing engagement between the two pinch rollers of the press rotatable against each other in the intake gap tapered obliquely downwards. By this one is ensured that the sludge can be guided in the intended manner directly into place in the press in a direction which coincides with the direction of rotation of the pinch rollers and thereby the sludge can come into engagement with the pinch rollers in a controlled manner.

In order to prevent the water which is pressed out of the sludge from being squeezed between pinch rollers of the press together with the dry material in the sludge, it is preferred that a first vertical plane through the axis of rotation of a lower pinch roller, reckoned in the supply direction of the sludge, is arranged somewhat in front of a second vertical plane through the axis of rotation of an upper pinch roller, a sludge collection pocket being formed between the first vertical plane and the bottom of the intake gap, while a water overflow threshold is formed at the top of the lower pinch roller. By arranging the axes of rotation of the two pinch rollers horizontally displaced relative to each other, that is to say arranged in their respective vertical plane, the contact point between the pinch rollers can be arranged between the vertical planes of the axes of rotation of the two pinch rollers, that is to say somewhat downstream in relation to the top of the lower pinch roller. The bottom itself of the gap between the pinch rollers, that is to say the said sludge collection pocket between the pinch rollers, will thereby lie just below the top of the lower pinch roller. This will involve the dry stuff in the sludge being effectively forced between the pinch rollers, while a substantial portion of the fluid, which is pressed from the sludge, can be readily pressed past the top of the lower pinch roller and can thereby be diverted with simple means in a direction away from the gap between the pinch rollers.

Further features of the invention will be evident from the description having regard to the accompanying drawings, in which : Fig. 1 shows a schematic diagram of components which are included in the process according to the invention. Fig. 2 shows a front view of the sludge draining arrangement.

Fig. 3 shows a side view of the sludge draining arrangement according to Fig.2.

Fig. 4 shows schematically a side view of a press which forms a part of the sludge draining arrangement of Fig. 2 and 3.

In Fig. 1 there is shown a waste water or sewage conduit 1 for a crude purification arrangement 2. By an arrow 3 there is shown a discharge for screened objects, such as plastic, paper, textiles, bottle caps, injection needles, and the like. For example there can be employed a grating having a grating breadth opening of 3mm. The crudely purified water is conducted via a conduit 4 to a fine purification arrangement 5. By an arrow 6 there is shown a discharge for finely purified waste water. For example there can be employed a sieve having mesh openings of 0.2-1.5 mm. By an arrow 7 there is shown a discharge for sludge. The sludge is discharged into an intake 8a for a draining arrangement 8. By broken lines there is shown a conduit 9 and associated pump 10 for feeding back waste water from the draining arrangement 8 to the fine purification arrangement 5. The draining arrangement 8 delivers drained material on its outlet side 8b directly into a dry material container 13. The crude purification arrangement 2 may consist for example of a so-called machine-cleaned grating and/or other suitable crude purification equipment, in which objects can be screened having a consistency substantially more solid than the consistency of the sludge, the waste water with associated sludge being diverted to the fine purification arrangement 5.

The fine purification arrangement 5 consists in the illustrated embodiment of a container 5a having a number of vertically disposed disc filters having a first type of intermediate space for the collection of sludge and a second type of intermediate space for the removal of drained, finely purified water. By means of scrapers or similar pushing means, sludge, which is collected in the intermediate spaces of the first type, is pushed batch- wise via hatches 5b outwardly from the container 5a on a discharge board 11. By way of experiment disc filters have been employed having a "mesh size" of 0.2 mm, but as a result of problems with the deposition of fat materials on the disc filters one has chosen in practice to employ a mesh size of 0.5 mm. Under certain conditions the use of disc filters having a mesh size of 1-1.5 mm has also been employed.

The draining arrangement for the sludge, which is emptied on the discharge board, comprises a press 12. The press 12 is connected to the container 5a via the discharge board 11 equipped with funnel-shaped downwardly extending side guide surfaces, the discharge board 11 being deflected downwardly about 60° relative to a horizontal plane. In practice the sludge slides batch-wise in a controlled manner downwardly along the discharge board and is correspondingly discharged batch-wise and is delivered directly into an intake gap 12a in the press 12. During use it has been observed that batch-wise feeding of the sludge from the fine purification arrangement to the press provides a simpler and better controlled treatment of the fed sludge in the press. The press 12 is arranged between the fine purification arrangement 10 and the dry stuff container 13, that is to say in an intermediate space 14 laterally between the containers 5a and 13 and as to height just above the dry stuff container 13. Drained waste water is diverted via the intermediate space 14 from the press directly to a discharge gutter 15, which is arranged beneath the press 12 and arranged laterally between the containers 5a,13 and forms a part of the conduit 9 (Fig. 1) . The drained waste water becomes automatically recirculated from the discharge gutter 15 to the fine purification arrangement 5.

Hitherto it has been usual to empty the sludge from the fine purification arrangement 5 directly into the dry stuff container 13. In such a case drainage water has the opportunity to percolate downwardly through the sludge in the container towards the bottom of the container 13 during filling as well as during a respite, and to be emptied from the bottom of the container before the sludge is transported to the depositing location. At the same time the sludge has a tendency to be packed together in the container to form a relatively non-porous mass. On transportation of the non-porous mass to the depositing location the water content of the sludge, despite the gradual percolating off, nevertheless constitutes a large portion of the weight of the sludge in the container.

By using the draining arrangement or the press 12 according to the invention one has been able to save significant transportation costs by removing significant amounts of water from the sludge and thereby increase the transport capacity of each container to a significant degree.

The press 12, as shown in Fig. 2 and 3, comprises a lower, horizontal pinch roller 17 and an upper, horizontal pinch roller 18, which are carried in a common framework 19. In practice an oblique positioning of the pinch rollers of some few degrees relative to the horizontal plane can be undertaken, in order to achieve an easier drainage of water from the intermediate space between the pinch rollers of the press. The pinch rollers 17,18 rotate in direct abutment with each other. With a pinch roller diameter of about 20 cm the pinch rollers can be driven at a speed of rotation of 2-10 revolutions per minute and preferably at a speed of rotation of about 6 revolutions per minute. There is exerted a certain pressure loading from the upper pinch roller against the lower pinch roller, produced by the force from a pair of compression springs or compression cylinders 19a, which are arranged at a respective end of the upper pinch roller 18. The squeezing force can be regulated as required all according to the desired force between the pinch rollers. The lower pinch roller 17 is rotated, as shown by arrow A in Fig. 4, in the clockwise direction, while the upper pinch roller 18 is rotated, as shown by arrow B in Fig. 4, in the counterclockwise direction. The pinch roller 17 is driven via a speed alternator 20 from an electric motor 21, which is controlled via a panel 22 having start/stop button 23 and emergency stop button 24.

The upper, pressure loaded pinch roller 18 is pressed in the illustrated embodiment with a regulatable pressure force against the pinch roller 17 in order to be driven by this by frictional engagement on direct rolling of the pinch rollers against each other.

According to the invention provision is made for the sludge to be conducted as is shown in Fig. 4 from the discharge board 11 directly to the top 17a of the lower pinch roller 17 of the press 12. In this connection provision is made for a contact line 25 between the lower pinch roller 17 and an upper pinch roller 18 in a horizontal direction to be somewhat displaced relative to the top 17a of the lower pinch roller 17. More specifically the contact line 25 is arranged between a first vertical plane 17' through the axis of rotation of the lower pinch roller 17 and a second vertical plane 18' through the axis of rotation of the upper pinch roller 18, the first vertical plane 17' being arranged somewhat in front of the second vertical plane 18' . A plane 19' through the axes of rotation is obliquely disposed about 60° relative to the vertical plane 17' . By this one is able to ensure that all the sludge is drained in an easy and controlled manner inwardly into the press without substantial spill and that the pressed out dry stuff and the pressed out water can be separated in an effective manner in the press and delivered from the press on mutually opposite sides of this. According to the invention a relatively large top surface area of the lower pinch roller is exposed for the reception of the sludge from the discharge board 11, so that the sludge can be brought, almost instantaneously, into direct contact with the lower pinch roller 17 and immediately thereafter can be brought into contact with the upper pinch roller 18. Provision is made for the sludge to be fed batch-wise along the discharge board 11 from the openings 5b to the supply gap 12a between the pinch rollers 17,18. By this there can be ensured an effective feeding of the sludge between the pinch rollers 17,18 and hence it follows an effective pressing out of water from the sludge along the top of the pinch roller 17 in a direction opposite to the direction of rotation of the pinch roller 17. Provision is made for the occurrence of a suitably narrow drainage gap for drained water between the discharge board and the lower pinch roller 17. The breadth of the gap can if necessary be regulated as required. The result is that one can get drained water separately on the intake side of the press at 12a, while the press material P is ejected in a strongly drained condition on the discharge side 12b of the press 12. By increasing or reducing the diameter of the lower pinch roller the surface area for the alighting of the sludge on the lower pinch roller can be correspondingly increased or reduced. Alternatively, the discharge board can be guided to regulatable positions relative to the lower pinch roller.

In order to prevent the drained press material, which possibly attaches itself to the pinch rollers on the discharge side of the press, being carried along to the intake side of the press, there is arranged a scraper 26 to the rear/below on the lower pinch roller 17 and an equivalent scraper 27 to the rear/above on the upper pinch roller 18.

In order to obtain an as far as possible effective drainage of water from the sludge in the gap between the pinch rollers, the pinch rollers are provided with an outer rubber coating 17b, 18b of relatively elastic rubber. In the illustrated embodiment (see Fig.3) framework 19 of the press 12 is fastened below to a base 28 by means of angularly regulatable support means 29 and fastened above to the container 10a by means of equivalent axially regulatable support means 29, in order thereby to regulate the angular position of the framework 19 and position relative to the discharge board 11.

In practice one achieves delivery from the press of the dry stuff in the sludge in the form of a light weight sheet-formed or flock-formed fibre cloth-like material, which provides the basis for the formation of significant air pockets in the material which is put down in the dry material container. By discharging this relatively dry and light material in bulk form into the dry material container 13, one can, as a result of the air pockets, produce a significant supply of air even to the interior of the container, so that the material can be additionally dried out and furthermore can thereby yield a lower weight. At the same time the conditions are arranged so that a fermentation process can be started up in the material with an associated heat action in the material and thereby additional evaporation of moisture already during the filling of the dry material container. By extending the time of the fermenting material in the container at the filling location, after effecting filling of the container, the fermenting process can if desired be continued in the container or in a silo suitable for this purpose and thereby a corresponding further weight reduction of the contents of the container can be ensured before this is transported to the final deposit location. It will also be possible to feed extra air to the material in the container as well as in the silo via suitable air supply systems stationarily arranged in the same.

In addition this involves that the dry material in the container, either at the treatment location or after final transportation to the depositing location, has started a desired degradation process which can readily be continued by simple means.

Claims

P A T E N T C L A I M S

1. Process for treating sludge from waste water, especially from sewage, comprising a crude purification step (2), in which objects or coarse particles, such as plastic, textiles, bottle caps, and the like are screened from unpurified waste water, and a fine purification step (5) , in which sludge is screened from crudely purified waste water, together with a subsequent drainage step (8) for draining the sludge, characterised in that the sludge is conducted from the fine purification step (5) to an intake gap (12a) between two elongate, horizontal pinch rollers (17,18) rollable against each other in a press (12), where the pinch rollers (17,18) comprise a lower pinch roller (17) and an upper pinch roller (18) and where the pinch rollers form a mutual abutment at a level substantially above the axis of rotation of the lower pinch roller (17) , the sludge on the intake side of the press (12) being conducted to the bottom of the intake gap (12a) between the pinch rollers (17,18) and pressed between the pinch rollers in the direction of rotation of the pinch rollers, to form a relatively thin layer of material of low moisture content on the discharge side (12b) of the press on one side of the rollers (17,18), while pressed out discharge water is diverted from the other side of the rollers (17,18) via a relatively low overflow threshold (17a) on the intake side (12a) of the press in a direction in counterflow to the direction of rotation of the pinch rollers (17,18).

2. Process in accordance with claim 1, characterised in that the sludge is discharged batch-wise to the intake gap (12a) for the pressing out of equivalent flock-shaped dry stuff material (P) on the discharge side (12b) of the press (12) for reception of the same in arbitrary bulk form in an adjacent dry stuff container (13) .

3. Apparatus for draining sludge from waste water, especially from sewage, comprising a crude purification arrangement (2) , such as a so-called machine-cleaned grating, in which unpurified waste water is adapted to be screened of objects or coarse particles (3) , such as plastic, textiles, bottle caps and the like, and a fine purification arrangement (5) , in which crudely purified waste water is adapted to be screened of sludge, together with a subsequent draining arrangement (8) for draining of the sludge, where the draining arrangement (8) comprises a press (12) having a pair of pinch rollers (17,18) which are rollable against each other reckoned in the supply direction of the sludge, characterised in that the press (12) has a horizontal elongate intake in the form of an intake gap (12a) tapered obliquely downwards relative to a horizontal plane, which is defined between the two elongate, horizontal pinch rollers (17,18) , and that the pinch rollers (17,18) comprise a lower pinch roller (17) and an upper pinch roller (18) , which form a mutual abutment at a level above the axis of rotation of the lower pinch roller (17) .

4. Apparatus in accordance with claim 3, characterised in that a first vertical plane (17') through the axis of rotation of a lower pinch roller (17) , reckoned in the supply direction of the sludge, is arranged somewhat in front of a second vertical plane (18') through the axis of rotation of an upper pinch roller (18) , a sludge collection pocket being formed between the first vertical plane (17') and the bottom of the intake gap (12a), while a water overflow threshold is formed at the top (17a) of the lower pinch roller (17) .

5. Apparatus in accordance with claim 3 or 4, characterised in that the pinch rollers (17,18) are provided with an elastically yielding rubber coating (at 17b, 18b) .