AU6334096A - Apparatus for solid particle reduction - Google Patents

Description

APPARATUS FOR SOLID PARTICLE REDUCTION

CROSS REFERENCE TO RELATED CASES

This application claims the benefit of U.S. Provisional Application No. 60/014,743, filed March 28, 1996, incorporated herein by reference.

TECHNICAL FIELD This invention relates to the processing of a wastewater stream to reduce solids to a size acceptable for treatment in a downstream wastewater plant.

BACKGROUND OF THE INVENTION

In a conventional screening device, large solid material is removed from a wastewater stream for disposal, decreasing the loading on a wastewater plant. However, the undigested solids removed from the wastewater stream must be handled and disposed of and create an odor problem. U.S. Patent No. 4,812,231, for example, describes an apparatus that filters particles larger than 0.5 mm from a water stream by means of a series of pivot members supporting an assembly of spaced apart straight links forming endless loop sections. These sections move in an elliptical path along the interior of the water filter apparatus receiving chamber.

Instead of removing large solids, some facilities employ a screen to separate large solids from a wastewater stream, deliver the large solids to a grinder, then return the ground solids to the wastewater stream. See, U.S. Patent Nos. 5,061,380 (Stevenson) and 5,333,801 (Chambers, Sr. et al.). However, grinder systems described for this purpose are very large and expensive, since the entire wastewater flow must pass through small openings in the grinder system. U.S. Patent No. 5,102,536 (Wiesemann) provides a smaller, less expensive apparatus.

SUMMARY OF THE INVENTION A wastewater treatment apparatus includes a continuously rotating elongated drum- type filter screen and a grinder suitable for reducing solid debris to a size suitable for processing by a downstream wastewater treatment facility. The drum screen includes a continuous loop of closely spaced link members. The front end of the drum is open to allow the waste effluent to flow into an inner drum chamber defined by the drum screen. Part of the water moves out through the sides and bottom of the drum chamber after passing between the links. Particles that are too large to pass through the links are trapped on or between the links and are carried upwards by the drum screen as the links rotate in an elliptical pattern. These large-sized particles are dislodged from the top of the drum screen by a water flushing system.

In one embodiment, the dislodged solids fall back into the inner chamber. The rest of the water, together with solid waste, passes through an outlet in the rear of the drum into a grinder unit that macerates the solid waste and discharges the macerated solids to rejoin the wastewater which passed through the drum screen. The drum screen is oriented so that the flow path to the grinder is straight and unobstructed.

In another embodiment of the present invention, solids dislodged from the top of the drum screen by the water flushing system are directed into a macerator/grinder. Macerated solids which leave the macerator/grinder are directed into a dewatering screw compactor and are conveyed away from the filter screen apparatus, by the dewatering screw compactor, for disposal.

The invention may be best understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus for reducing the size of solids in a stream of water.

FIG. 2 is a top plan view of the apparatus of FIG. 1 with a portion cut away to show interior detail. FIG. 3 is a front elevational view of the top portion of the apparatus of FIG. 1 with the cover plate of the filter screen portion removed.

FIG. 4 is a right side elevation view of the apparatus of FIG. 1.

FIG. 5 is a sectional view of the apparatus of FIG. 1, taken along line 5-5 of FIG. 4, showing a loop section and a driving chain. FIG. 6 is a front elevational view of another apparatus for reducing the size of solids in a stream of water.

FIG. 7 is a sectional view of the apparatus of FIG. 6, taken along line 7-7 of FIG. 6.

FIG. 8 is a front elevational view of another apparatus for reducing the size of solids in a stream of water, which apparatus employs two grinders side-by-side.

FIG. 9 is a top schematic view showing apparatus for securing a filter screen apparatus to a grinder, fhe top of the filter screen apparatus being cut away to show interior detail.

FIG. 10 is a top schematic view showing another apparatus for reducing the size of solids in a stream of water.

FIG. 11 is a top plan view showing another apparatus for reducing fhe size of solids in a stream of water, with a portion broken away to show internal detail. FIG. 12 is a sectional view of the apparatus of FIG. 11, taken along line 12-12 of FIG. 11.

FIG. 13 is a sectional view of the apparatus of FIG. 11, taken along line 13-13 of FIG. 12. FIG. 14 is an enlarged front elevational view of fhe top portion of the apparatus of

FIG. 11, taken along line 13-13 of FIG. 12.

FIG. 15 is an enlarged side elevational view of the conveyer of the apparatus of FIG. 11, taken along line 12-12 of FIG. 11.

DETAILED DESCRIPTION

Throughout the following detailed description of fhe embodiments of FIGS. 1-10, the same reference numerals refer to corresponding elements in all figures. A different numbering system is used for the embodiment of FIGS. 11-15.

FIGS. 1-5 show a self-cleaning filter screen/grinder apparatus 5 according to one embodiment of fhe invention. The filter screen/grinder 5 comprises a filter screen apparatus 10 mounted within an interior portion of a supporting housing which includes a frame 11. The filter screen/grinder is located in a wastewater effluent channel 12 with a weir 14 on each side of an opening 16 into the water filter screen apparatus 10. The opening 16 serves as an inlet for receiving a liquid stream, containing water and solids, from the channel 12. The screen apparatus includes a continuously rotating screen assembly 26 which includes two cylindrical, endless-loop filter sections 28 of generally elliptical cross-section. The filter sections 28 are formed from multiple spaced-apart links 32 as shown in FIG. 3. The screen assembly 26 defines a drum chamber or longitudinal bore 18 positioned to receive a stream of wastewater. A rear baffle wall 20 defines an end outlet 98, the path from the inlet 16 to the outlet 98 being substantially straight and unobstructed. The screen assembly has an axis of rotation 33 that is substantially parallel to the direction of flow of the liquid stream into the inlet 16.

A first portion 29 of the water and small-sized solid material can exit radially through the bottom 22 or sides 24 of the filter screen apparatus 10, such bottom 22 or sides 24 thus serving as a first outlet from the chamber 18 and the housing. Debris that is too large to pass through the screen either is entrained on the inner surface of the screen or between links of the screen assembly or travels with a second portion 31 of the water directly through the chamber 18 and outlet 98. The outlet 98 thus serves as a second outlet from the chamber 18 and the housing. The multiple links 32 are supported by rods 34 connecting to a pivot member 36 on each side. The pivot members move within a guide track 30. Each pivot member 36 as shown in FIGS. 3 and 5 has a top surface containing notch 42. The links 32 and the support rods 34 together with the chains and other metal fittings are made from stainless steel to retard rusting and all exterior surfaces of the housings are painted to protect the surfaces from rusting. The pivot member 36 is preferably made from a high strength polymer, such as a polyamide or polycarbonate.

In each screen assembly section 28 the bottom surface of the pivot member 36 is proximal to the interior of chamber 18 with a foot 58 on each link 32 protruding below the pivot member 36 so as to face inwardly in chamber 18. The notch 42 of pivot member 36 is engaged by a lug 60 mounted on a bottom surface of an endless loop gear chain 62 as seen in FIG. 3.

The endless loop transfer chain 65 is engaged at one end to gear 66 and another end to a drive gear 64. The drive gear 64 drives shaft 52 as seen in FIG. 3. Shaft 53 is directly connected to a gear reducer 68 that is driven by a drive motor 70 mounted on the top of the water filter screen apparatus 10. Rotation of chain 62 by gear 74 driven by shaft 52 causes the lugs 60 to engage within the notch 42 of the pivot member 36 and causes the entire screen assembly 26 to move in a clockwise direction. At least two lugs are always in engagement with adjacent pivot members 36 while the screen assembly is moving. As seen in FIG. 5, an adjustment gear 72 moves in response to drive gear 74 and together with idler gear 76 supports chain 62. Shaft 75 connects all three idler gears 76. This arrangement adjusts tension on the screen assembly 26. Tension is manually adjusted on gear 72 to desired levels by movement of a bolt on tension adjusting bracket 73.

The filter screen/grinder apparatus includes a water flushing system for screen unloading. The water flushing system includes an inlet pipe 92 leading to spray headers 94, 96 which flush the top of fhe screen assembly 26 as seen in FIGS. 1-5, thereby preventing solid material from building up on the screen assembly 26. Alternatively, solid material can be removed from fhe screen assembly 26 by alternative solids dislodger mechanisms, e.g., a cam mechanism that drives solid pieces of plastic into the gaps between links 32, scrapers, squeegees, brushes, an air stream, vibration, and the like.

In one embodiment according to the invention, the drum chamber 18 has a depth of about thirty-two inches and a width of thirty-six inches and can handle about twenty million gallons of water per day.

Further details of the filter screen portion of the apparatus, particularly arrangements of screen links, are as shown in U.S. Patent No. 5,102,536 (Wiesemann), incorporated herein by reference. Such apparatus are commercially available in 24", 36", 48", 60" and 72" widths to treat wastewater flows from below 20 million gallons per day (mgd) to over 100 mgd (WIESE-FLO^® screening systems, Wheelabrator Water Technologies Inc., Sturbridge, MA). Solid material that is too large to pass through the sides or bottom of fhe filter screen apparatus is urged by the wastewater flow to exit the drum chamber 18 via outlet 98, together with a portion of the wastewater, into a grinder 100. The grinder 100 includes two parallel shafts 102, 103, mounted with cutter teeth 104, which rotate in opposite senses. The shafts are rotatably driven by drive motor (not shown), which is mounted above the grinder 100. A number of existing grinders, such as Wiesemann Macerator/Grinder model W24CH (Wiesemann Products, Sturbridge, MA), which is complete with hydraulic drive motor, speed reducer, and cutters, are suitable for use in the present invention. The macerated solids, which are also referred to as "fines, and the second portion 31 of the water are discharged through a grinder outlet 108.

The fines typically include both fecal matter and non-biodegradable material such as plastic and rubber. These fines and the accompanying second portion 31 of water are returned directly to the stream 29 of wastewater that has passed through a side or the bottom of fhe screen assembly 26. In the embodiments of FIGS. 1-10, the fines and both portions of water are combined in a common vessel 109, which is a downstream portion of fhe channel 12 in the illustrated embodiments. Alternatively, non-biodegradable material can be removed from the macerated solids by conventional means. Or, as described below, certain large solids can be diverted and transported to a location for processing separate from the wastewater stream. It is helpful to provide a fastener system which joins the filter screen apparatus 10 and the grinder 100 detachably. The downstream side of the baffle wall 20 can be provided with brackets or tracks 112 which define channels as shown in the embodiment of FIG. 9. The grinder 100 can have opposed flanges 113 which mate with the brackets 112 so that the grinder 100 can be slid vertically into place and easily removed, by raising the grinder vertically, for servicing without removing the filter screen 10 as well. The grinder 100 can also be attached to the rear baffle wall 20 by a hinged mechanism 114, as shown in FIG. 7, to allow the grinder 100 to be swung away and allow wastewater to bypass the grinder 100 in emergency conditions. The illustrated hinge mechanism has a vertical hinge axis 115 so that the grinder 100 rotates horizontally. It is desirable recycle the solids captured by the screen. This can be accomplished by dislodging the solids from fhe screen and carrying fhe dislodged solids into the grinder by the dropping the solids into water at a location upstream of the grinder, most efficiently into the second portion 31 of water which is traveling through fhe center of the chamber 18. Some embodiments of the invention include a baffle system which extends upstream from the wall 20 and which can be used to assist the channeling of recycled solids to the grinder 100. As shown in FIGS. 6-7 and 9, the system can include multiple vertically-oriented baffles 110 which defme a region 111 upstream of fhe opening 98 to fhe grinder 100. The baffles channel a center portion 116 of the liquid stream into fhe grinder 100 and divert side portion 118 of fhe wastewater flow away from the grinder 100 and toward the filter screen 10. In the arrangements shown in FIGS. 6-7 and 9, the side portion 118 corresponds to the first portion 29 of water, and the center portion 116 corresponds to the second portion 31 of water. Other baffle arrangements could be used; for example a U-shaped baffle (not shown), generally concentric and conforming to the sides 24 and bottom 22 of fhe screen, could extend from the wall 20. For efficiency, it is best for the baffle system to be open at fhe top and for one or both of the spray headers 94, 96 to be positioned at an elevation above the baffle system at a location such that at least a portion of fhe solids flushed from the top of the screen fall into the region 111, for example between the baffles 110, or into the center portion of the liquid stream upstream of the baffle system. This feature is particularly suitable for larger filter screen/grinder apparatuses with correspondingly large flow rates.

The flow rate of a larger filter screen/grinder apparatus can be improved by including two (or more) grinders 100 side-by-side on the baffle wall 20, as shown in FIG. 8. An example filter screen/grinder apparatus with two grinders has a capacity of about 90 mgd. This filter screen/grinder design offers important advantages over previous designs.

The axis of rotation of fhe screen assembly 10 is substantially parallel to the wastewater flow path through the screen assembly 10, the outlet 98, and the grinder 100. (By "substantially parallel" is meant an angle of no greater than approximately 15° from the parallel.) There are no obstructions in the flow path to the grinder, and the entire volume of the liquid stream is channeled directly toward the grinder. The force of the wastewater stream thus carries entrained solid debris directly into the grinder 100, together with a portion of the water flow. Another portion of the water flow exits the apparatus radially through the screen assembly 26, but large solids do not escape by this route. The apparatus is significantly more compact than other combination filter/grinders. The filter screen 10 and grinder 100 are rotatably driven by a hydraulic drive and chain-linkage mechanism. A variety of conventional drive and linkage mechanisms, including, direct drives, can also be used.

In order to service the filter screen/grinder apparatus, the channel 12 leading to the unit being serviced or the outlet 98 can be closed off. Alternatively, the entire filter screen/grinder apparatus can be removed from fhe channel 12, or one can remove either the screen apparatus 10 or grinder 100 independently. If the apparatus is equipped as shown in FIG. 9, a solid plate or sheet of bar screen (not shown) can be slid into fhe channels provided by tracks 112, after the grinder 100 is removed, to cover the opening 98 so that flow can continue through the filter screen 10 and through the bar screen, if any. The filter screen/grinder apparatus 5 includes a water flushing system for screen unloading. The illustrated water flushing system includes an inlet pipe 92 leading to spray headers 94, 96 which flush the screen unloading area 124 located at the top of screen assembly 26, as seen in FIGS. 5, to prevent the buildup of solid material on the screen assembly 26. Preferably, the spray headers 94, 96 have spray outlets that are spaced longitudinally to provide overlapping coverage of fhe screen unloading area 124. Alternatively, solid material can be removed from the screen assembly 26 by other mechanisms, e.g., a cam mechanism that drives solid pieces of plastic into the gaps between links 32, scrapers, squeegees, brushes, an air stream, vibration, and the like. Solids dislodged from the screen assembly 26 are directed back into the liquid flow stream that travels toward the grinder 100.

Since wastewater flows often vary, reaching a peak flow of as much as two or more times the average flow, the use of multiple units in parallel allows a facility to bring additional standby apparatus units "on line" to handle peak flows. Moreover, the use of multiple units in parallel allows for continued operation while one unit is being serviced. Not all of the units in parallel need be equipped with grinders. As shown in FIG. 10, large solids captured by a filter screen 120 lacking a grinder (of the type shown in U.S. Patent No. 5,102,536) can be conveyed via a screw conveyer 122 or other conventional means (or allowed to passively migrate) to filter screen/grinder apparatus 5 according to the present invention. Solids from the screen 120 are deposited in front of a device 5 so that they will flow to the grinder 100. Alternatively, a single filter screen apparatus can deliver large solids to two or more grinders in series (not shown), i.e., deliver large solids a first grinder, which in turn delivers the resulting smaller solids to a second grinder. Other configurations will be apparent to those of ordinary skill in fhe art. FIGS. 11-15 show a self-cleaning filter screen/grinder apparatus 200 according to another embodiment of the invention. The filter screen/grinder 200 comprises a filter screen apparatus 210 which includes a supporting frame 212 located within a wastewater effluent channel 214 with a weir 216 on each side of an opening 218 into the water filter screen apparatus 210. A drum chamber 220 receives wastewater from the channel 214. The filter screen apparatus 210 is similar in design and operation to filter screen apparatus 10 described above, except that a rear baffle wall 222 has no opening and thus deflects water so that it must exit through the bottom 224 or sides 226 of the filter screen apparatus 210. The drum chamber 220 is enclosed by a rotating screen assembly 230 formed by two endless loop filter sections as described above. Debris that is too large to pass through the screen either is entrained on the inner surface 232 of the screen assembly 230 or between links (not shown). The filter screen/grinder apparatus 200 includes a water flushing system or other means for screen unloading essentially as described above. The water flushing system includes spray headers 234 that provide overlapping coverage to effectively flush the top of the screen assembly 230. Solid material dislodged from the screen assembly are carried by the water spray and gravity into a chute 238, which directs the solid material into a macerator or grinder 240. The grinder 240 includes two parallel shafts 242, 244, mounted with cutter teeth 246, which rotate in opposite senses. The shafts are rotatably driven by drive motor 248.

Macerated solids which leave the grinder 240 fall by gravity through a chute 250 into a dewatering screw compactor 252 to dewater and compact the macerated solids. The compactor 252 acts as a screw conveyer to carry the fines to a location away from the screen assembly for further processing or disposal. The screw compactor 252 has a closed tubular body 254 extending from an inlet end 256 located under chute 250 to an outlet end 258. A helical augur screw 260 is centrally disposed within the body 254 and driven by a motor 266. The inlet end 256 is attached to the supporting frame (not shown) for support; additional support may be provided at the outlet end 258 and/or at other points between the inlet end 256 and outlet end 258 by conventional hangers or other supports. As needed, standard length sections may be coupled together to form the body of the screw compactor 252. Movement of the solid material in the screw compactor 252 is from the inlet end 256 to the outlet end 258, thereby carrying the solid material away for disposal.

The inlet end 256 has a wall or inner sleeve 262 and outer sleeve (not shown), one of which may be less than a complete cylinder, that are rotatable or slidable with respect to each other. The inner sleeve 262 and the outer sleeve each defme a plurality of openings 270. The openings of each sleeve are arranged in patterns such that openings in one sleeve register with openings in the other sleeve when the sleeves are in proper alignment. Thus, rotation or sliding of fhe inner and outer sleeves, relative to each other, adjusts fhe rate of dewatering by regulating water flow and the size of particles which can pass through the openings. For most efficient operation, the conveyer is positioned so that water which escapes through the openings 270 is returned to the liquid stream in the channel 12, upstream or downstream of the filter screen apparatus 210. This can be accomplished by positioning the openings 270 over fhe channel 12 so that the escaping water can simply fall by gravity into the channel.

The screw compactor 252 can be can be operated at a substantial angle of inclination or declination. Best results are achieved with the screw compactor 252 inclined during operation at an inclination of about 5 to 30 degrees from the horizontal. The screw compactor 252 can be oriented to extend either upstream or downstream from the chamber 220 of the filter screen/grinder 200.

Multiple filter screen/grinder apparatuses or various configurations of screen assemblies and grinders in series or in parallel may be employed, if desired. A single filter screen apparatus can employ more than one grinder, side-by-side or in series, if necessary to accommodate large flow rates.

Having illustrated and described the principles of the invention in preferred embodiments, it should be apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles.

Claims (18)

WHAT IS CLAIMED IS:

1. An apparatus for treating a liquid stream, the apparatus comprising: a housing having (a) an inlet for receiving a liquid stream that contains water and solids, (b) a first outlet, and (c) a second outlet; a continuously rotating screen assembly mounted in the housing, the assembly being substantially cylindrical, defining a substantially unobstructed longitudinal bore, and having an axis of rotation that is substantially parallel to the direction of flow of the liquid stream, the screen assembly being positioned so that (a) a first portion of the water passes radially through the screen to the first outlet and at least a portion of the solids in the first portion of the water is captured by the screen assembly, and (b) a second portion of the water passes directly through the bore defined by the screen and is discharged from fhe housing via the second outlet; and a grinder disposed relative to fhe screen assembly so that the solids and the second portion of fhe water travel directly to the second outlet and into the grinder wherein fhe size of the solids is reduced to produce fines, the grinder having a grinder outlet for discharging the fines and fhe second portion of the water that passes through the grinder.

2. The apparatus of claim 1 wherein the first and second outlets open into a common vessel so that the fines and the second portion of the water, both of which are discharged via the grinder outlet, join the first portion of fhe water which is discharged from the first outlet.

3. The apparatus of claim 1 further comprising a solids dislodger which causes captured solids to fall from the screen assembly back into the liquid stream at a location upstream of the grinder.

4. The apparatus of claim 1 further comprising a baffle system for dividing the liquid stream inside the bore so that the first portion of the water is urged toward the screen and the second portion of the water is channeled toward the grinder.

5. The apparatus of claim 4 further comprising a solids dislodger which causes at least a portion of the solids captured by the screen assembly to fall from the screen assembly into the second portion of the water so that the second portion of the water carries dislodged solids into fhe grinder.

6. The apparatus of claim 1 further comprising a fastener system for connecting the screen assembly to the grinder such that the grinder can be separated from fhe screen assembly by raising the grinder vertically.

7. The apparatus of claim 1 further comprising a hinge mechanism for connecting the screen assembly to the grinder, the hinge mechanism having a vertical hinge axis such that the grinder can be moved away from the second outlet by swinging the grinder about the hinge axis.

8. An apparatus for treating a liquid stream, fhe apparatus comprising: a housing having (a) an inlet for receiving a liquid stream that contains water and solids, (b) a first outlet, and (c) a second outlet; a continuously rotating screen assembly mounted in the housing, the assembly being substantially cylindrical, defining a substantially unobstructed longitudinal bore, and having an axis of rotation that is substantially parallel to the direction of flow of fhe liquid stream, the screen assembly being positioned so that (a) a first portion of the water passes radially through the bottom and the sides of the screen to the first outlet and at least a portion of the solids in the first portion of the water is captured by the screen assembly, and (b) a second portion of the water passes directly through the bore defmed by the screen and is discharged from the housing via the second outlet; a grinder disposed relative to the screen assembly so that the solids and fhe second portion of the water travel directly to fhe second outlet and into the grinder wherein the size of the solids is reduced to produce fines, the grinder having a grinder outlet for discharging the fines and the second portion of the water that passes through the grinder; a solids dislodger which causes captured solids to fall from the screen assembly back into the liquid stream at a location upstream of the grinder; and a vessel which is positioned to receive the first portion of the water after that first portion has passed through the screen and which is positioned to receive fhe fines and the second portion of the water after the fines and the second portion have been discharged via the grinder outlet.

9. An apparatus for treating a liquid stream, the apparatus comprising: a housing having an inlet for receiving a liquid stream that contains water and solids and an outlet; a continuously rotating screen assembly mounted in the housing and having an upper portion, the assembly being substantially cylindrical, defining a substantially unobstructed longitudinal bore, and having an axis of rotation that is substantially parallel to the direction of flow of the liquid stream, the screen assembly being positioned so that the liquid stream passes radially through the screen to the outlet and at least a portion of the solids in the water is captured by the screen assembly; a solids dislodger adjacent the upper portion of the screen to dislodge the solids captured by the screen assembly; a grinder disposed to receive solids dislodged from the screen so that the dislodged solids are reduced in size to produce fines, the grinder having a grinder outlet for discharging the fines; and a conveyer for receiving fines discharged from the grinder and for carrying the fines away from the screen assembly, the conveyer being positioned such that fhe fines fall by gravity to the conveyer after the fines are discharged from the grinder outlet.

10. The apparatus of claim 9 wherein the conveyer is a screw conveyer.

11. The apparatus of claim 10 wherein the screw conveyer has a wall which defines openings so that water can escape to dewater the fines, the conveyer being positioned such that water which escapes through the openings is returned to the liquid stream.

12. A method for reducing the size of solids in a liquid stream, the method comprising: directing a liquid stream containing water and solids into a continuously rotating screen assembly which defmes an inlet to receive the liquid stream, and an end outlet to discharge a portion of the liquid stream, and a longitudinal bore that extends between the inlet and the outlet, fhe screen assembly being substantially cylindrical and having an axis of rotation that is substantially parallel to the direction of flow of the incoming liquid stream, so that a portion of the liquid stream is directed into the end outlet, a portion of the liquid stream is directed against an interior surface of the screen assembly, a portion of the liquid stream passes through openings which extend radially through the screen assembly, and a portion of the solids are captured by the screen assembly; dislodging captured solids from the screen assembly in such a manner that at least a portion of the dislodged solids are delivered into the portion of fhe liquid stream that is directed into the end outlet and are transported by that portion of the liquid stream through the end outlet to a grinder; and grinding the solids transported to the grinder to produce fines.

13. The method of claim 12 further comprising combining fhe fines with water which has passed through the screen assembly.

14. The method of claim 12 further comprising: channeling at least a portion of the liquid stream through the bore along a substantially straight path from the inlet to the end outlet; providing the grinder in alignment with the end outlet so that at least a portion of the liquid stream passes through the end outlet and into the grinder to accomplish fhe grinding; and directing the dislodged solids into the liquid stream at a location upstream of the grinder.

15. A method for reducing the size of solids in a liquid stream, the method comprising: directing a liquid stream containing water and solids through an inlet and into a longitudinal bore which are defmed by a continuously rotating screen assembly, the assembly being substantially cylindrical and having an axis of rotation that is substantially parallel to the direction of flow of the incoming liquid stream, so that the liquid stream is directed against an interior surface of the screen assembly, at least a portion of the liquid stream passes through the screen assembly, and at least a portion of fhe solids are captured by the interior surface of the screen assembly; dislodging captured solids from the screen assembly at such a location that the dislodged solids fall by gravity into a grinder; and grinding the dislodged solids to produce fines.

16. The method of claim 15 further comprising dewatering the fines.

17. The method of claim 15 further comprising conveying the fines away from the screen assembly.

18. The method of claim 17 further comprising dewatering the fines.