Note: Descriptions are shown in the official language in which they were submitted.
2~7~
1 The present invention is directed to apparatus for use
in treating sewage and more particularly to apparatus for use in
removing water from sludge such that the solid material in the
sludge can be ~urther processed.
In the treatment of sewage sludge, belt presses are
commonly employed in the removal of water from the processed
sewage sludge so as to permit separation of solid material and
water. The solid materials having a high water content are fed
to a belt press where this material is compressed between a pair
of fabric or mesh belts and the material is compressed between
the belts as the belts pass between a plurality of pairs of
rollers. As the material is compressed, the water is forced
through the permeable mesh belts. The belt presses thus produce
a solid cake of material which can then be delivered to
additional apparatus for further processing such as drying or
disposal.
One of the problems with the prior art apparatus for
use in removing water from sludge has been that the costs of
manufacture or construction of the belt presses place limits on
the capability of the presses to handle large quantities of
sewage sludge. If the belt presses are re~uired to handle large
quantities of sludge, it is necessary that the belt presses
employ relatively wide belts. Use of wide belts requires the
construction of relatively long rollers to support the beltsO
During the operation of the belt press the rollers are subjected
to substantial ~orces and bending moments when they apply
compressive force on the belt. With the employment of relatively
long rollers in high capacity belt presses, the rollers are
subjected to substantial moments, and accordingly, the rollers
must have substantial strength and must be supported by bearings
capable of withstanding the forces applied by the rollers. Due
to the cost of construction of belt presses having such elongated
rollers, it is preferred that the presses employ relatively
narrow belts and rollers of reduced length.
Prior art apparatus for use in treating sewage sludge
also includes free drain decks or gravity belt thickeners. The
prior art gravity belt thickeners include a mesh belt supported
r~
-2- ~ 2 ~7 5~ 0
1 by a pair of horizontally spaced apart rollers. The mesh belt
includes an elongated horizontal upper belt flight. Sewage
sludge having a relatively low solids content is deposited onto
one end of the belt and is carried by the belt toward the
opposite end of the gravity belt thickener. Water in the sludge
drains through the mesh belt, and accordingly the sludge at the
discharge end of the belt will have a higher solids content.
Prior art methods and apparatus for use in processing
sewage sludge also commonly include the step of mixing a polymer
material, such as that described in Great Britain Patent
1,602,677, with tne sewage sludge to cause flocculation of the
solid materials in the sludge. The formation of flocculant is
desired in order to permit increased drainage of the water away
from the solid materials during the dewatering or removal of the
water from the solid materials. The addition of the polymer
material to form the flocculant or floc has the effect of
producing a product which is relatively fragile. Rough handling
of the floc material causes the floc to break down and inhibit~
drainage of water from the solids. Once the floc has been
~C handled roughly and broken down, it is then necessary to add
additional p~lymer in order to reform or regenerate the floc and
thereby requiring overdosing of polymer. It will be readily
understood that the addition of polymer to the liquid sludge
results in expense, and repetition of this step of introducing
polymer to the sludge should be avoided if possible.
Accordingly, it is preferred that the sludge be processed soon
after the reaction of polymer with the sludge in such a manner
that the water can be removed from the sludge or floc in a single
step and the floc is also to be handled in a relatively gentle
manner to prevent the floc from breaking down before the removal
of the water.
The present invention provides a combination of a
gravity belt thickener and a belt press adapted to be used to
remove water from sewage sludge. The gravity belt thickener and
the belt press are positioned such that sludge is first delivered
to the gravity belt thickener wherein a substantial quantity of
water in the sludge is removed by the gravity belt thickener to
thereby decrease the volume of the sludge. The thickened sludge
-3- 3~2~;7~
1 material from the gravity belt thickener is then delivered to the
belt press wherein the sludge is compressed between a pair of
belts for additional removal of water from the sludge material.
The present invention provides a gravity belt thickener which has
a belt having a width substantially greater than the width of the
belts employed in the belt press, and wherein the width of the
belts of the belt press is dependent on the reduction of the
volume of ~he sludge achieved by removal of water from the sludge
by the gravity belt thickener. The capacity of the belt press is
dependent on the volume of the sludge fed to the belt press, not
on the water content of the sludge, and the width of the belts of
the belt press can be reduced with respect to the width of the
belt of the gravity belt thickener proportionately to the
reduction in volume of the sludge achieved by the gravity belt
thic~ener. For example, in one form of the invention, where the
gravity belt thickener is effective to remove sufficient ~ater
from the sludge that the volume of the sludge is reduced to half,
the gravity belt thickener will have a belt for supporting the
sludge having a width of approximately two meters and the belt
press will employ belts having widths of approximately one meter.
The use of the gravity belt thickener and the belt
press having a belt width ratio as set forth above permits the
use of a relatively narrow belt press in applications where the
prior art arrangements required a larger belt press of
substantially greater capacity, and use of the narrower belt
press substantially reduces the cost of the belt press since the
narrow belt presses are less expensive to manufacture than a belt
press employing elongated rollers. The use of the smaller belt
press also provides for an overall reduction in the volume of
apparatus needed to remove water from the sludge.
Various other features and advantages of the invention
will be apparent by reference to the following description of a
preferred embodiment, from the claims and from the drawings.
A more thorough understanding of the present invention
will be gained by reading the following description of the
preferred embodiments with reference to the accompanying drawings
in which:
-4- ~Z57~
l Fig. 1 is a side elevation view of a gravity belt
thickener and belt press embodying the present invention.
Fig. 2 is a plan view of the gravity belt thickener and
belt press illustrated in Fig. 1.
Fig. 3 is an enlarged cross~section elevation view of
the gravity belt thickener and distribution box illustrated in
Fig. 1.
Fig. 4 is a partial plan view of the gravity belt
thickener and distribution box illustrated in Fig. 3.
Fig. 5 is a partial cross section view taken along line
5-5 in Fig. 3.
Fig. 6 is an enlarged exploded perspective view of the
plow support means illustrated in Figs. 2 and 3-4.
Before describing at least one embodiment of the
invention in detail, it is to be understood that the invention is
not limited in its application to the details of construction and
to the arrangement of the components set forth in the following
description or illustrated in the drawinqs. The invention is
capable of other embodiments and of being practiced and carried
out in various ways. Also, it is to be understood that the
phraseology and terminology employed herein is for the purpose of
description and should not be regarded as limiting.
Illustrated in Fig. 1 is a dewatering table or gravity
belt thickener 10 embodying the present invention and adapted to
receive generally liquid activated sludge material from waste
treatment means in a waste treatment facility. The gravity belt
thickener 10 is intended to provide a means for removing water
from the sludge so as to reduce the liquid content of the sludge
and to facilitate further processing of the solid components of
the sludge.
Generally the gravity belt thickener 10 includes a
fabric or mesh belt 12 supported by a pair of spaced-apart
rollers 14 and 16 positioned at opposite ends of the gravity belt
thickener. The generally liguid sludge is deposited on one end
of the upper flight of the belt 12. The mesh belt 12 is of the
type conventionally used in gravity belt thickeners and belt
-5- ~L2~7~0
] presses and is sufficiently fine that it can support the solid
material of the sludge, but the water in the sludge drains
through the belt. Solid material is carried to the opposite end
of the gravity belt thickener 10 and is deposited onto a belt 18
of a belt press 20.
The belt press 20 includes a frame 26 supporting a
plurality of parallel horizontally extending rollers. The
rollers are positioned so as to support a pair of water permeable
belts 18 and 30 of the type employed on th~ gravity belt
thickener-1G, these belts 18 and 30 being supported such that
they can compress or squeeze the thickened sludge and thereby
force liquid material out of the sludge and further reduce the
water content. More specifically the belt press 20 includes an
upper belt 30 supported by a plurality of rollers 32. The lower
belt 18 is supported by a plurality of rollers 3~. Solid
material is deposited on a flight 35 of the lower belt 18 by the
gravity belt thickener 10. The upper belt 30 includes a portion
or flight 36 which is located above the flight 35 so as to house
the sludge material therebetween. The pair of belts 18 and 30
having sludge material sandwiched therebetween pass around a
plurality of rollers 38, and the belts 18 and 30 are subjected to
substantial tension. Accordingly, as the belts pass around the
rollers 38, they apply a substantial compressive force on the
sludge therebetween. Since the belts 18 and 30 are comprised of
a mesh or fabric material, the water in the sludge is forced
through the belts 18 and 30 and separated from the solid
material.
In a preferred form of the invention the gravity belt
thickener 10 will have a belt 12 having a width which is
substantially greater than the width of the belts 18 and 30 of
the belt press 20. The capacity of the belt press 20 to handle
sludge is dependent on the volume of the sludge rather than the
volume of solid material in the sludge. The size of the belt
press can thus be reduced in direct proportion to the reduction
of the volume of the sludge being fed to the belt press. By
providing a gravity belt thickener to remove water from the
sludge prior to feeding the sludge to the belt press 20, the
-6- ~2~7~
l volume of the sludge can be decreased substantially, and ~he
capacity of the belt press can be reduced. While the capability
of the gravity belt thickener 10 to remove water from the sludge
is dependent in part on the characteristics of the sludge, as an
example of one application of the invention, it has been found
that a belt press 20 having belts 18 and 30 approximately 1 meter
wide and a gravity belt thickener 10 having a belt 2 meters wide
are effective in dewatering sludge while being relatively
economical to manufacture.
While in the illustrated arrangement, the belt press is
shown as being supplied by a single gravity belt thickener in
other applications, two or more gravity belt thickeners 10 could
supply thickened sludge to a single belt press 20.
Fig. 1 also generally illustrates a means for
delivering sludge to the dewatering table or gravity belt
thickener 10 in a generally uniform flow pattern. This means,
which comprises a distribution box 40, includes a means for
mixing a polymer material with the sludge to provide formation of
a floc immediately prior to delivery of the sludge to the gravity
belt thickener 10. The distribution box 40 is mounted on one end
of the gravity belt thickener 10. The distribution box 40
comprises a tank or housing 42 (Fig. 3) for holding the generally
liquid sludge material. Liquid sludge is supplied to the
distribution box 40 through coupling 92 adapted to be connected
to a pipe from a clarifier or the like. A conventional polymer
material is supplied to the distribution box through a polymer
supply coupling 94. The polymer mixes with the liquid sludge in
the distribution box 40 and causes flocculation or formation of
floc.
The distribution box also includes a discharge ramp 44
wherein sludge from the distribution box 40 can flow in a
generally uniform pattern down onto the end of the belt 12 of the
gravity belt thickener. The discharge ramp 44 is smooth and has
a relatively gentle slope so as to control ~he turbulence of the
sludge as it is deposited on the belt 12. The ramp 44 also has a
width which is substantially the same as that of the belt such
that the sludge is deposited evenly over the entire width of the
belt 12 of the gravity belt thickener.
-7- ~.257~
l While the gravity belt thickener 10 could have other
constructions, in the particular arrangement illustrated, it
includes an elongated frame 46 supported by vertical legs 48.
The elongated frame 46 in turn supports an elongated belt
supporting frame 50. The elongated belt supporting frame 50 is
supported at one end by legs 52. The lower ends of the legs 52
are pivotally connected by pins 54 to the elongated frame member
46. The lower ends of the legs 55 supporting the opposite end of
the elongated belt supporting frame 50 are joined by pins 5~ to
the opposite end of the elongated frame 46. In a preferred form
of the invention, either the lower ends of the legs 55 or the
frame member will be provided with a plurality of vertically
spaced holes 58 adapted to receive the pins 56. That end of the
frame 50 is thus supported for vertical adjustment so that the
height of one end of the upper flight of the belt 12 of the
gravity belt thickener 10 can be varied with respect to the
height of the other end of the belt. In one preferred form of
the invention, the gravity belt thickener has been found to
perform particularly well if the belt is elevated at an angle of
approximately 1-1/2 so that the upper belt flight carries the
sludge upwardly toward the discharge end of the gravity belt
thickener. While the gravity belt thickener 10 is described as
providing for adjustment of the angle of inclination of the belt
12, in other arrangements the frame could be rigid and have a
fixed inclination.
Means are also provided for rotatably supporting the
rollers 14 and 16 on opposite ends of the elongated frame 50. In
the illustrated construction the means for supporting the rollers
14 and 16 includes pillow blocks 60 at one end of the frame 50,
the pillow blocks 60 supporting bearings~ in turn, supporting the
roller 1~. The roller 16 is supported by a conventional takeup
bearing provided to permit control of belt tracking.
The gravity belt thickener 10 also includes means for
catching the wa~er draining through the belt 12. While various
means could be provided, in the illustrated arrangement, a drain
pan 22 is supported by the belt supporting frame ~0 and is
positioned beneath the upper flight of the belt 12, the drain pan
..,
-8- ~75~
l 22 extending from one end of the belt 12 along substantially its
entire length. The drain pan 22 includes a sloped bottom
terminating in a discharge coupling 24, the coupling 24 being
adapted to be connected to a drain pipe (not shown) whereby water
draining through the belt 12 of the gravity belt thickener 10 can
be conveyed to a suitable processing tank or other disposal
means.
Means are also provided for rotatably driving at least
one of the rollers 14 and 16 of the gravity belt thickener so as
to drive the belt at a suitable speed. In a preferred form of
the invention the means for driving the belt will include a
variable speed drive so that the belt speed can be adjusted to
accommodate the characteristics of the sludge being deposited on
the belt.
Means are also provided for supporting the upper flight
of the belt 12 in planar relation and for scraping the lower
surface of the upper flight of the belt 12 to thereby facilitate
removal of water from the belt and facilitate consequent removal
of water from the solid material supported on the belt. In the
illustrated construction, this means includes a rigid planar grid
64 having a flat upper surface 66 for supporting the belt 12 and
including a lattice work or grid structure forming a plurality of
openings 68 (Fig. 4) adapted to permit water to readily drain
through the grid 64. The rigid planar grid 6~ is positioned
beneath the upper flight of the belt 12 such that the upper
surface 66 of the grid 64 engages the lower surface of the upper
flight of the belt 12. As the belt 12 moves from right to left
as seen in Fig. 3 and from one end of the gravity belt thickener
10 to the other, it moves across the upper surface 66 of the grid
structure 64. As the grid scrapes along the bottom of the belt
12 it causes water to be removed from the belt and thereby
improves the drainage of the water through the belt. The upper
surface 66 of the grid 64 includes sharp upper edges, and these
sharp upper edges scrape the water off of the underside of the
35 belt 12 and prevent water from adhering by surface tension to the
belt.
9 ~2~7~
l In operation of the gravity belt thickener 10, sludge
having, for example, less than 1~ solid material is deposited by
the distribution box 40 on an end of the upper belt flight of the
gravity belt thickener to form a pool of generally liquid
material. The belt 12 is supported such that the upper flight is
inclined slightly upwardly and away from the distribution box 40
and away from the pool of liquid material. As the belt moves
away and upwardly from the pool of liquid material, solid
materials are carried by the belt 12 out of the pool and move
with the belt toward the opposite end of the gravity belt
thickener. As the solid material or floc moves along the belt,
the water with this material will tend to drain through the belt
and at the end of the belt the thickened sludge will comprise,
for example, about 4% or more solids.
Means are also provided for causing controlled movement
of the solid material or floc on the surface of the belt as the
floc moves with the belt toward the discharge end of the belt.
This means for causing controlled movement of the floc is
intended to improve discharge of water from the floc, i.e.,
drainage of the water through the belt. This means includes a
plurality of plows 70 supported above the upper surface of the
belt and supported in such a manner as to cause the floc on the
upper surface of the belt to form rows or furrows 72 as
illustrated in Fig. 4, and to cause the floc to move back and
forth on the belt as the belt moves toward the discharge end.
The plows 70 also cause the formation of troughs 74 between the
furrows 72 of floc material. As the plows roll the sludge
material over to form the rows or furroughs, water trapped in the
sludge is released, and the provision of the furrows 72 and
troughs 74 thereby providing open areas of the belt surface
permits water to drain from the furrows into the troughs, and the
water can then drain through the belt 12. As the belt 12
continues to move, the next row of plows 70 will then cause the
floc to be moved or rolled laterally again on the belt 12 such
that the furrows 72 tend to be rolled over as the belt moves
toward the discharge end. This rolling of the furrows 72 and
floc material further improves the drainage of the water from the
floc and increases the efficiency of operation of the gravity
. , o 3L257550
l belt thickener 10. In a preferred form of ~he ~nvention the
plows engage the surface of the mesh belt so as to scrape the
surface of the belt, removing the sludge from portions of the
surface of the belt, to form the troughs. If the sludge is
distributed uniformly across the surface of the belt, the sludge
layer tends to seal the mesh and restricts drainage through the
belt. By removing the sludge layer from portions of the mesh
belt, free drainage is provided.
In the ill~lstrated construction a plurality of rows 76
of the plows 70 are provided, the rows 76 being spaced apart and
extending along the entire length of the gravity belt thickener
beyond the pool 41. Each plow 70 comprises a relatively thin
generally planar blade, ~he plow blades lying in generally
parallel planes spaced apart across the width of the belt 12.
Each plow 70 is positioned at an acute angle with respect to the
longitudinal axis of the gravity belt thickener such that as the
floc moves along the length of the gravity belt thickener it will
impinge against first one plow and then another and will be
rolled back and forth across the upper surface of the belt 12.
While the plows 70 could have other constructions, in
the illustrated arrangement, each plow 70 comprises a thin, flat
rectangular planar blade having a generally planar bottom edge 78
adapted to be positioned so as to engage the upper surface of the
belt 12. In the illustrated arrangement, the leading end of the
plow, i.e., that end facing away from the direction of movement
of the upper belt flight, includes a bevelled or rounded edge
80. This bevelled or rounded lower edge 80 prevents the plow 70
from catching or snagging the fabric belt 12 as the belt moves
beneath the forward edge of the plow. While the length of the
plow blades could vary, in one preferred embodiment the plow
blades can have a length of approximately 1~ inches.
Means are also provided for supporting the plows 70
adjacent the surface of the upper flight of the belt 1~. While
the plow supporting means could have other constructions, in the
illustrated arrangement, this means includes a plurality of
horizontally extending plow support frames 82 supported by the
frame 50 above the upper belt flight in spaced relation from the
,5~5SO
l upper flight and extending across the belt 12 perpendicularly to
the direction of movement of the upper belt flight. In the
particular construction illustrated in the drawings each plow
support frame includes an elongated support plate 84 with the
opposite ends of the plate 84 supported by stub shafts 86. The
stub shafts 86 are in turn supported by the frame 50. Each plow
support frames 82 also includes support arms 88 welded to the
opposite ends of the elongated support plate 84 and having free
ends including stub shafts 110 also supported by the machine
frame 50. The plow support frame 82 each support a plurality of
hangers 112 suspended from the lower surface of the plow support
frames 82. Each hanger 112 comprises an angle having a planar
horizontal portion adapted to be positioned adjacent the lower
surface of the elongated support plates 84 and secured thereto by
a bolt 114 extending through the horizontal portion and through a
hole in the elongated support plate 84. The hanger 112 also
includes a vertical planar portion 116 having a smooth vertical
surface adapted to support one of the plows 70 for vertical
slideable movement. To facilitate such vertical movement of the
plows 70, the vertical portion 116 of the hangar 112 includes a
pair of vertically extending slots 118 and the plow 70 is
supported between a backing plate 120 and the vertical portion
116 of the hanger. A pair of bolts 122 extend through the
backing plate 120, plow 70 and the slots 116 of the hanger 112 so
as to loosely secure these members together, and ~he vertically
extending slots 118 permit relatively free vertical movement of
the bolts 122 in the slots 118 so as to provide for floating
movement of the plows 70 with respect to the hanger 112.
In operation of the plows 70, the lower edge of the
plows 70 will rest on the upper surface of the belt 12, and since
the plows 70 are relatively free floating, the weight of the
plows 70 will maintain them against the surface of the belt 12.
The angle of the position of the plows 70 with respect to the
direction of movement of the belt 12 can also be readily adjusted
by pivoting the plows 70 about the vertical axis of the bolt 11
securing the hangers 112 to the elongated support plate 84.
-12- ~2~
l The preerred angular position of the plow blades 70
depends upon the length of the plow blades and upon the solid
content of the sludge deposited on the mesh belt. Since ~ater
drains through the belt as the sludge moves along the length of
the gravity belt thickener, the solid content of the sludge is
greater at the discharge end of the belt. The water content of
the sludge may also vary with different applications of the
gravity belt thickener and with the source of supply of sludge to
the gravity belt thickener. The means provided by the present
invention -for permitting adjustment of the plows independently
and facilitating relatively easy adjustment of the plo~s permits
the plows to be properly positioned so as to best handle the
sludge supplied to the gravity belt thickener.
With the illustrated arrangement, the plow support
frame 82 can also be pivoted about the stub shafts 86 supporting
the opposite ends of the elongated support plates 84 so that the
plows can be lifted away from the belt 12 for cleaning or
maintenance.
Referring now more particularly to the distribution box
40, it comprises a means fsr mixing a polymer material with the
sewage sludge to provide for formation of the floc. The
distribution box 40 also provides a means for containing the
sludge and polymer in a relatively quiescent state to permit
maximum formation of the floc. The distribution box 40 comprises
a generally vertically oriented rectangular chamber 90 with a
lower end including a coupling 9~ adapted to be connected to a
pipe for supplying liquid sludge material to the distribution
box. In a preferred form of the invention the liquid sludge
supplied to the distribution box will also include a small amount
of primary sludge, for example 20%, mixed with the activated
sludge to be processed. A means is also provided for introducing
a liquid polymer into the sludge housed in the chamber 90. While
various means could be provided for introducing the polymer into
the distribution box 40, in the illustrated construction a
polymer supply line 94 enters a lower end of the distribution box
to cause polymer ~o be mixed with the sludge as the sludge enters
the distribution box 40. Suitable polymers are conventional and
will not be described in detail.
_, 3_ ~2~i7~
l The distribution box 40 also includes means for
depositing the sludge material containing floc onto the belt 12
of the gravity belt thickener and for evenly dis~ributing that
material across the surface of the belt. The distribution box is
constructed so as to relatively gently deposit the sludge
material onto the belt in such a manner that the floc formed in
the distribution box 40 is not broken up. The floc material
formed in the distribution box is relatively fragile and rough
handling or turbulence of the liquid material will cause the floc
structure in the sludge to break down. Destruction of the floc
decreases the facility of the floc or sludge material to drain.
Referring more particularly to the means of the
distribution box for depositing the sludge material on the belt
12, the distribution box 40 includes a generally horizontally
extending chamber 96 projecting horizontally from the upper end
of the vertical chamber 90 of the distribution box. The
horizontal chamber 96 extends over one end of the gravity belt
thickener and includes a free end housing a broad crested dam or
weir 98 for restraining the sludge material in the distribution
box. In a preferred form of the invention, the weir 98 includes
a relatively wide, flat upper surface and this broad crest on the
weir 98 minimizes break up of the floc as compared to a sharp
crested weir. The ramp 44 extends downwardly from the upper
portion of the weir 98 and includes a lower or discharge end 100
positioned closely adjacent to the surface of the belt 12.
In operation, the sludge material in the distribution
box 40 flows over the top of the weir 98 and down the ramp 44
onto the end of the belt 12. In a preferred form of the
invention the ramp 44 will have a relatively gradual incline such
that the sludge will be deposited relatively gently on the upper
surface of the belt 12 and in such a manner that the floc will
remain intact. ~n a preferred form of the invention, the upper
edge of the weir 98 is horizontal such that the sludge will flow
over the weir 98 across its entire length in the direction
transverse to the direction of movement of the belt and so as to
distribute the sludge or floc material evenly across the entire
width of the belt 12 of the gravity belt thickener 10.
f~
-14-
l In a preferred form of the invention means are further
provided or washing or cleaning the belt 12 so as to facili~ate
drainage of water through the belt. During operation of the
gravity belt thickener 10, as the belt carries floc away from the
pool 41, and as the floc is distributed on the belt by the plows,
solid material can become lodged in the mesh of the belt and can
restrict drainage of water through the belt and thereby prevent
efficient operation of the gravity belt thickener. The means for
washing the-belt provides a means for continuously cleaning the
belt to remove solid particles from the belt mesh.
In the illustrated construction the gravity belt
thickener 10 includes a belt washing assembly mounted beneath the
horizontally extending portion of the distribution box 40 and
adapted to clean the belt and remove any solid material from the
belt mesh immediately before the floc is deposited on the belt by
the distribution box.
In the particular arrangement illustrated the means for
washing the belt includes a spray assembly 124 having an upper
housing 126 housed in the cavity 125 provided by the lower
surface of the weir 98 and positioned above the upper flight of
the belt 12. The spray assembly 124 also includes a lower
housing 128 positioned immediately below the upper housing and
the belt flight. The housings 126 and 128 span the width of the
belt 12. The upper housing 126 contains a spray header including
a water pipe 132 having a plurality of spray nozzles 134
extending along the length of the water pipe 132.
In opera~ion of the spray assembly 124, water from the
nozzles 134 will impinge against the belt 12 and force any solid
material embedded in the belt mesh through the belt, and it will
drain into the lower housing 128.
One of the features of the illustrated construction is
that the distribution box 40 and spray assembly 124 are
constructed so that they fit together in a compact nested
relation, with the upper housing conveniently positioned in the
cavity 125 provided by weir 98.
~2~7~
-15-
l It should also be understood that while in the present
invention the spray assembly 124 includes only a single spray
header positioned above the belt 12, in other alternatiYe
embodiments of the invention, spray means could also be
positioned beneath the belt 12 so that both sides of the beltwould be sprayed.
By use of a gravity belt thickener or free drain deck
10 of the type as described above in combination with the belt
press 20 in the illustrated relation, and wherein the belt of the
gravity belt thickener has a width approximately twice that of
the belt press, it has been found that substantially greater
~uantities of sewage sludge can be processed by the belt press 20
than could be processed using a similar belt press alone or in
prior art combinations. The gravity belt thickener 10 has a
capacity based on its capability to drain water out of the
sludge. A belt press, on the other hand, has a capacity based on
the total volume of the sludge. By using the combination of the
gravity belt thickener 10 and belt press 20 as described above,
water will be removed from the sludge prior to delivery of the
sludge to the belt press, and the capacity of the belt press can
be based on the anticipated solids content of the sludge, not on
the total volume of the sludge to be processed.
Another advantage of the illustrated combination and
the employment of a gravity belt thickener and belt press in
~5 series and in immediately adjacent relation as described herein
is that polymer is added to the sludge only once, just prior to
the sludge being deposited on the gravity belt thickener. Since
the floc is handled by the belt press immediately after it is
handled by the gravity belt thickener, the floc remains intact
and it is not necessary to add polymer a second time when the
sludge is supplied to the belt press.
Various features of the invention are set forth in the
following claims.
