Note: Descriptions are shown in the official language in which they were submitted.
3~
BACKG~OUND OF TflE~ INVl:NTION
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: 1. Field of the Invention
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The invention relates to methods and apparatus for
the processing of waste water or waste liquid carrying solids
or particulate matter in any proportion, waste sludge and
more particularly relates to the dewatering of sewage, raw
sewage and industrial sludge.
2. Brief Descrip-tion of the Prior Art
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Waste sludges are the residue oE p~imary and secondary
waste water treatments and co~prise mixtures of waste solids and
up to 99 5% by weigh-t of water. Included also are digested
sludges of up to 95~ by weight of water. Sludges are potential
environmental pollutants and pose a disposal problem for municipal
governments, industry and even on occasion the small business man
whose business activity may produce a sludge.
The primary goal of sludge processing has been to
remove as much of the water content as possible. This facilitates
handling, shipping and dispersal o residue solids. A commonly
employed prior art method of dewatering sludges comprises
spreading the sludge on open beds of sand and gravel and allowing
it to dry. After 7 to 14 days of drying, the residue is removed
and used as land fill. One skilled in the art will appreci~te
the extensive land areas reguired by this method of dewatexing.
Other prior art methods of dewatering sludges include
apparatus employing vacuum filters, plate and frame arrangements,
centrifuges, belt presses (see U.S. Patent 4,019,431) and the
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like. In cJeneral~ the~e rn~thods and clevices are not comple-tely
satisf~ctory in that t}ley require high initial cost~, high
operating costs, various deyrees of supervision b~ operatiny
personnel or are of limited efficiency.
The apparatus and me-thod of the present invention
utilize mechanical principles to dewater wasté water of all
types. Minim~lm space requirements are a distinct advan-kage.
The method and appara-tus of the invention are inherently more
efficient than prior art me-thods and apparatus. The apparatus
and method of the invention require relatively little power or
energy consumption and minimal maintenance. Both apparatus and
method are adaptable to automatic control (requiring minimal
supervision) and will function to process a wide variety of waste
and sludges. The apparatus requires only moderate capital .
L5 ¦ investment and moderate operating costs.
Representative of other prior art disclosures is that
of U.S. Patent 3,319,897.
SU~RY OF THE INVENTION
The invention comprises apparatus for dewatering waste
water, and, in accordance with the disclosed successful embodi-
ment, comprises; a sludge particlizer; a reaction vessel; means
for transferring particlized sludge from said particlizer to
said vessel; means for injecting a sludge conditioning agent P
into the particlized sludge; a dewatering press; and means for ~-
transferring the conditioned sludge from said vessel to said
press.
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The invention a:Lso compxises a rnethod of dewa-tering
waste water such as was-te sludge, which comprises; particLizing
said sludge; conditioning the particlized sludge for optimal
mechanical dewatering; and dewatering -the condi~ioned sludge.
The term "waste water" as used throughout the
specification and claims means any combination or mixture of
waste liquids and solids or particulate matter such as
industrial, municipal and commercial waste. In addition, the
term "waste sludge" as used throughout the specification and
claims means municipal sewage sludges including digested and
non-digested primary and secondary sludges, industrial sludges
such as paper and asbestos fiber plant waste sludges, like
waste sludges and mixtures thereof.
BRIEF DESCRIPTION OF THE D~WINGS
. . .
Figure 1 is a schematic diagram showing the components
of a successful embodiment apparatus of the invention.
Figure 2 is an isometric view of a successful embodi-
ment apparatus of the invention.
Figure 3 is a schematic diagram of the apparatus of
~20 Figure 2 and shows the flow process of the invention.
Figure 4 is a cross-sectional-in~part side elevation
of a successful extractor component of the apparatus of the
invention. ~j
Figure 5 is a cross-sectional end view of the
successful screw component of the extractor shown in Figure 4.
Figure 6 is a schematic diagram of embodiment
electrical circuits and controls or the apparatus of Figure 2.
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¦i ~icJ~Ir~ 7 is c, clraph deyicting thc~ y~centaye of
solids in sludcJe cakes Eorm~d from p~;mary sludges oE varying
solid con-tents, at vario~ls feed rates.
Fiyure 8 is a graph depicting -the percentage of solids
content in sludge cakes formed rom 1:1 mixtures of pr,,mary and
secondary municipal sludges (having varying solids contents)
at varying flow rates~
Figure 9 is a graph dep:icting the pe~centage of solids
in sludge cakes formed from 2:1 mixtures of primary and secondary
municipal sludges (of varying sol:ids contents) at varying flow
rates.
Figure 10 is a graph depicting optimum feed rates
for sludges of varied solids con-tent.
DETAILED DESCRIPTION
..
Figure 1 is a schematic diagram of an embodiment
; apparatus of the invention and shows an initial feeding of waste
sludge to a receiving or hol~ing tanX 10 from sludge feed line 12.
The feed line 12 is controlled by a valve 14 controlled from
control panel 16 so that a metered flow of waste sludge may be
'~20 delivered to tank 10. Sensing devices 18 and 20 may be located
in association with tank 10 to monitor the high tl8) and low t20)
levels, respectively, of sludge in the tank 10 and to activate
solenoid means of opening and closing the valve 14. Tank 10
generally receives sludges having a water content of from about ~:
93 percent to about 99 percent by weight of water. Tank 10
should be constructed of sufficient dimensions to handle at
least twice the flow of sludge anticipated in a 10 minute period.
A grinder 22 receives sludge from tank 10 and is controlled to
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~¦ operate from contro:l panel 16 when ther~` is suf~icient sludge
¦¦ in tank 10. Grinder Z2 ensures that rags and other items
deleterious to operation of the apparatus of the inven-tion are
particlized and uniforrnly homogenized. It should be underskood,
that in handling and processing cerkain peculiar and special
types of waste waters where mechanical reduction of particle
size is unnecessary a grinder need not be utilized. The grinder
22 when utilized may be of a type capable of reducing solids to
pumpable dimensions for the process of the invention, i.e.; on
the order of abou-t 7/16 inch or less. In this connection, a
grinder may embrace a comminuter, pulper, shredder or any device
capable of particlizing or reducing particle size of khe solids being handled.
; The ground or particlized sludge is transferred b~ a sludge pump 24
through transfer conduits 26, 28 to a reactor vessel 30. Pump
24 is preferably a positive displacement pump, supplying moti-
vation of the sludge throughout the entire system to be described
more fully hereinafter. The pump 24 is preferably driven at
variable speeds, controlled by control panel 16 as will be
¦ described in greater detall hereinafter. During transfer, the
sludge may be injected with one or more chemical conditioning
agents from storage vessel 32. The agent is pumped directly
into conduit 28 by pump 34 from conduit 36 for admixture with
the sludge. The proportion of agent injecked may be controlled
by activation and inactivation of pump 34 through control panel
16, as will be described in greater detail hereinafter. Pump 34 ~':
is preferably a positive displacement pump whose speed may be
varied and controlled. Reactor vessel 30 is rekention vessel
.
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to hold the condition~d sludge for an optimum residence time
to permit reaction or cuxing of the sludge with the conditioning
agent or agents. For example, certain flocculating agents, as
will he described more fully hereinafter, may be added to the
sludge to condition the sludge and facilitate dewatering and
the capture of fine par-ticles. In the reactor vessel 30, the
flocculating (conditioning) agent causes growth of fine sludge
particles into clus-ters called floc. The quasi-static, time
retention conditions of reactor vessel 30 promote the formation
of floc. The floc should not be exposed to sheer forces which
would disrupt it, but a low speed agitator 38 can be added for
gentle mixing if required to assure further admixture of con-
ditioning agent and sludge. The conditioned sludge is then
gently extruded to the dewatering or extraction press 40 through
conduit 42. Extraction press 40 is operated from control panel
16 and separates the conditioned sludae into a dry sludge cake
delivered from its upper end and a liquid pressate delivered
` - to a pressate collection vessel 44 by conduit 46. The pressage
may be delivered by pump 48 to any desired point for reclamation,
and is operated from control panel 16 by solenoids, directed by
a level sensor 50. The sludge cake may be delivexed to conveyor
or like handling means for disposal.
Figure 2 is an isometric view of a successful emhodi-
ment apparatus of the invention. In Figure 2, components like .
those seen in Figure 1 bear the same numeral identification.
The illustrated apparatus comprises a single receiving tank 10
~; and a single conditioning agent holding tank 32. All of the
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~ rem3~irlin~ components are provided in cluality, i.e.; grinders 22
¦ (only one seen in Figure 2), cJrinder operating mo-tors 23, gear
trains 25, reactor vessels 30, extractiorl presses 40 and all ~he
associated conduits, pumps, etc. The e~odiment apparatus of
Figure 2 has the advantage of operational reliability and con-
tinuity. Thus, one of the dual process lines may be operated
while maintenance is performed on the other process line. One
line may be shut down if the load of sludge does not require both
lines or one process line may be a reserve line for use when
there is a surge o~ sludge ~or treatment. Further details of the
depicted embodimen-t apparatus of Figure 2 may be seen in Figure 3
a schematic diagram of the embodiment apparatus of the invention,
showing the process flow.
It will be appreciated that a critical component o~ the
apparatus of the invention is the extraction press 40. In the
illustrated embodiment apparatus of the invention, the press is a
screw press extractor of particular design and construction.
Figure 4 is a cross-sectional side elevation of such an extractor
press 40. As can be seen in Figure 4, press 40 comprises a
cylindrical shell or housing 60 defining a central conduit 62
; holding a tubular filter screen 64 and a screw 66 having helicoid
flights 68. The screen 64 i5 actually a split screen having
different size apertures in different sections or portions. The
lower portion 64A of the screen has a hole size within the range
of from about .010 inches to about .045 inches diamet~r while the ~:
upper screen 64B has a hole diameter of from about .045 inches
to about .093 inches. Obviously, these sizes and limits will vary
depending on the application of the system and solids being handled.
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Press 40 is position~l ve.rtically with sludg~ beiny E~ in~ ~ lower e~t70
cmd ca~ried upward throuc~h ~e central ~rt oE the cen~al conduit 62 by screw
66. The center portion of central conduit 62 acts as a collect~n chamber
where de~atered sludge is transported via screw 66 through to a plug 80
formed by the dewa-tered sludge and then is carried on to the
chute 71. The outer or periphery channel 72 of cen-tral conduit
62, on the outside of the screen 64 collects the water after it
passes through the screen 64. When sludge is first introduced
. into the center of central conduit 62, and as a result of the
flow pressure, a film of sludge solids lS distributed on the
inside surface of the screen 64. This film, along with the
screen 64 acts as the filter media for sludge dewatering. Ex-
cessive sludge collected along the walls of the screen 64 is
: continuously removed by the action of the screw 66. In effect, r
extractor press 40 acts as a continuous wash filter.
As long as the filtering film described above has de-
- . veloped on the inside surface of screen 64, dewatering of sludge
. is achieved. When sludge is first introduced, the percent solids
. is generally low, i.e.; in the area of 1 to 5 percent by wéight
and thus, for the rapid formation of filtering film, the screen
: 164 openings are relatively small, to trap the solids and form the
¦filtering film. In the successful design,a screeen 64A is located
- . at the end 70 of press 40 and preferably has hole diameter of
. 0.031 inch. As water filters throughthe 0.031 inch screen and :
;- ~5 the sludge becomes thicker, the sludge particles become larger ~:
; and form a film on the screen 64 with different properties;
therefore a scree:n 64B is located near the top of the press 40,
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¦having hole ~iam~ters of preferably 0.062 inches. Sludge cle-
wateriny usiny the above descxibecl arrangement with split screens
64A and 62B takes advantage of the combination of two physical
¦phenomena. These phenomena are the flow pressure to effectively
Idewater the sludge and the s-traininy action of the filtering fi~n
¦of sludye which traps solids within its voids and produces a
¦superior filter per~ormance. As ]ong as the integrity of fhe
¦filtering sludge film is maintained, filtering action proceeds
Iwith the only limita-tion being the pressure head loss through the
filtering sludge film and the screens 64 as the rate of sludge
- application increases. As previously men~ioned, water (pressate)
drains by gravity down the outside of screen 64 and into periphera
collection channel 72 while the solids are propelled upward. The ~
pressate is carried to the vessel 44 (see Figure 1). As previously
mentioned, pressure is also a factor for dewatering sludge, aside
from gravit~. Thus, the effluent or discharge end 74 of press 40
is relatively restricted in comparison to influent end 70. The
sludge, propelled toward end 74 by screw 66 is pressured against
screen 64 to squeeze liquid through screen 64. The compacting of
a solids plug 80 in the ~one 76 of the press 40 also forms a back
pressure on the underlying sludge in central conduit 62. Pre-
ferably screw 66 has nylon fiber or like tipped flights 68
which clean the inner surface of screen 64 simultaneously with
movement of the sludge toward dewatering; see Figure 5 a cross- .
sectional end view of the preferred screw 66.
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The method of the invention is carried out by con-
ditioning the sludc~e for optimal ~echanical dewatering, dewater-
ing and recovering the separa-te solids and liquids. Conditioning
of the sludge is carried ou-t by first mechanically reducing par-
ticulate matter and artiEac-ts -to a pumpable size, i.e.; on the
order of about 7/16 inch diameter (maximum). As previously
stated, in special instances mechanical reduc-tion maynot be
necessary. This is conveniently accomplished with a conventional
¦ grinder 22 as previously described. Although the object of
processing the sludge is to dewater it, at the initial stacJes
of processing a low viscosity, low solids content is desired.
Ideally, the sludge will comprise from about 90% to about 99~
by weight water or other solvent/suspension medium and will have
- pumpability. Water may be added if necessary to condition the
sludge and ideally pressate at the end of the process may be
employed when required to reduce the need for better quality
waters, i.e~, potable or plant water. Prior to water extraction
in the extrac-tion press 40 it may be desirable to treat the
sludge further with chemical conditioning agents such as stabi~
lizers, precipitating agents and the like. Advantageously, the
sludge is conditioned with a flocculating agent to bring abou~ an
aggregation of fine particles in the sludge. The flocculated
sludge is retained better to form the film on the screen 64.
Representative of flocculating agents are cationic, anionic and
nonionic polymers, ferric chloride, and the like. Theproportion
~; of flo~ating agent used will depend on the agent selec~ed and the sludge
being processed but in general will be less than about 0.3
percent by weight of the slud~e. The process of the invention
¦ may be carriecl out uncler ~ wide v~riety of -temperature conditions,
¦ i.e.; on the order of Erc~n between about 5C. to about 90C. being a
¦ practical range. I-t is not generally necessary-to heat the sLudge to be
dewatered. The pressure on the sludge as it passes through the apparatus of
the invention is generally not critic~l and will be within the range of frcm
about 1 to abou-t 10 psig. Residence time of sludge within the apparatus of
the invention is of co~se dependent on -the flow rate which may be within
the range of frcm about 10 -to about 30 gallons per minute per process line.
The residence time of the sludge within reaction vessel 30 may be varied
according to the conditioning treatmen-t being efEected. Advantageously,
vessel 30 will afford a residence time of at leas-t about 5 minu-tes for the
sludge when it is being conditioned with a flocculating agent. As will be
¦ appreciated by those skilled in the art, flow rate will vary with the
¦ diameter of the screw of the hydroextractor. With this in nind these limits
I will vary depending on the size of the hydroextractor employed. Other
factors will also vary flcw rate, pressure, residence time etc. The control o
the residence and flow of sludge in the apparatus of the invention may be
effected through control panel 16 which controls the opening and closing of
valves, the activation and inactivation of pumps and the energizing and de-
energizing of electrical circuits. Figure 6 shows a schematic diagram of
embodiment circuits and controls for the apparatus shcwn in Figure 2. In Fig.
; 6, the following symbols and their meaning are used:
FS - float switch
WL~R - water level control relay
PB - push button .
M - motor st~rter
TR - timer
A ~ R - colored lam~s
CRM- rotor control reL~y
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SOL - so:lenoid
CR - control relay
OL - overload
LT - light
Upon startup, sludge valve 14 opens to admit sludge to tank 10,
sensor 20 having signaled the opening of valve 14. When tank
10 is full, sensor 18 signals the! closing of valve 14 and
actuates grinders 22 and sludge pumps 24. Upon s-tartLng the system,
air vent 31 opens to allow vessel 30 to fill. Simultaneously pump 34 is
energized to inject conditioning agents and stirrer 38 starts up for
: agita-tion of the sludge and the agent. At this point the extractor press 40
drive will start and the syste~ can then be adjusted with respect to polymer
addition and sludge feed rates. When the sludge level in tank 10 reaches
a pre-de!termined high level, sensed by sensor 18, valve 14 closes until the
level falls to the level sensed by sensor 20. If the level continues to
fal~, the press 40 is de-energized, vent 31 opens and the s~stem fills again
as described ab~ve. For shutdown, the fe d sludge 14 valve closes and is not
; reopened when the sludge level is dropped to its nu~LDn~m in t~nk 10. Once
the lcw level is reached, an automatic flush system can be actuated to thin
the remaining sludge prior to dumping (draining) the system.
The follcwing examples describe the manner and process of making and
using the invention and set forth the best ~de contemplated by the inventor
of carrying out the invention, but are not to be construed as limiting. .;
Apparatus according to that shcwn in Figure 2 was provided. The
extractor press 40 :in each instance was 48" long and had a screw diameter of
9 inches. A 0.031 inch holed screen was employed at the influ~nt end and a
0.062 inch holed screen at the effluent end.
The effective size of the screen was 44" long and 9" in
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l~ diarneter, (one i~lal.~ of the ~c:re~n len~Jt}~ hear:i.rlc3'the 0.031 inch
¦ holes and one half bearinc3 the 0.062 inch holes) ~:ie:Ldinc~ a
total area o.E approximately 8~7 square feet. Ilo~ever, effect:ive
area for dewatering was estimated to be in the vicinity oE 5.5
square feet with the remaining area 76 for plug formation and
further densification of the ca~e.
Example 1
Employing the above described apparatus, primary munici .
: ¦ pal sludges of various solid contents were dewatered at various
feed rates employiny various proportions of a flocculating agent
to condition the sludge. The sludge cakes obtained were of high
solids content suitable for incineration or other disposal .
. methods... Table 1 below shows the various runs made, with the
.. feed rates, dosage of flocculating agent (Calgon WT-2640; a
1 polymeric cationic polyelectrolyte; Bull. 12-58A, Calgon Corpor-
ation, Pittsburgh, Pa.), solids content of the feed sludge and
the solids content of the resulting sludge cakes together with
the solids content of pressate. As shown in Table 1, the percent ..
solids in the sludge cake prove to be independent of the p rcent .
solids in the feed. This is clearly seen in Figure 7 a graph de-
picting the.percentage of solids in the sludge cake obtained with
employment of primary sludges of varying solids content, under
: varying feed rates. Feed rates up to 30 gallons per minute con-
. sistently produced ca]ces of high percentage. solids.
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~BI,E 1
Prim~ry MunicLpal Slud~e
.
Flocculating
Agent Dose, Percent Solids
Feed Rate, gpm GPH (5~ Solution) Feed Cake Pressate
! lo ~2.5 ~.4 31.0 1.5
42.5 4.2 39.0 1.5
25.5 3.1 31.2 .9
25.5 3.4 28.9 .9
25.5 4.4 30.4 .3
25.5 4.2 30.4 .3
25.5 4.1 2~.3 1.2
25.5 3.6 25.9 1.2
25.5 2.6 31.4 1.1
25.5 2.5 30.8 1.1
25.5 5.5 32.3 1.1
25.5 5.8 29.6 1.1
25.5 7.6 Z4.3 1.4
25.5 7.3 23.~ 1.4
25.5 2.9 23.5 .2
25.5 2.9 21.4 .2
25.5 1.9 43.5 .7
25.5 1.9 42.1 .7
63.8 3.7 28.8 1.
63.8 3.5 30.3 1.4
, 25 17.0 6.3 19.7 *
17.0 6.3 19.7 *
~3.8 5.3 25.8 1.7
63.8 5.3 25.6 1.7
34.0 4.1 27.0 1.0
34.0 4.0 26.2 1.0
34.0 3.2 26.1 .8
34.0 3.6 27.3 .8
3~.0 3.2 29.0 1.4
34.0 3.1 29.9 1.4
* Not Reported
Note: On Fig. 7, the feed rate values are charted as follows:
o 10 GPM
a 15 GPM
20 GPM
~ 25 GPM
X 30 GPM ~,
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¦ Example 2
l Mixtures of 50~ by volume primary and 50~ by volume
¦ secondary municipal sludges were fed to the apparatus described
¦ above at various feed rates and with varying proportion of
the flocculating agent (Calgon 2640; supra.). ~he feed rates
employed, the proportion oE flocculating agent, the solids
content of the feed and the solids content of the resulting
sludge cake are given in Table 2, below along with the quantity
of pressate recovered. The results shown in Figure 2 are given
graphically in Figure $. It is evident from Figure 8 that
the maximum application rate for this particular mixture is
about 15 gallons per minute. Higher application rates give
cakes of lower percent solids.
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Table 2
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Mixture 1 Primary: 1 Seconclary
Polymer Dose Percent Solids
Feed Rate, qpm GPH ~5~ Solution) FeedCake Pressate
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25.5 3.6 15.6.30
25.5 3.5 15.~.30
25.5 3.2 17.2.7
25.5 3.1 17Ø7
25.5 4.2 19.3.3
25.5 ~.3 21.3.3
25.5 2.3 15.
25.5 2.2 16.01.~
25.5 2.9 16.81.3
25.5 2.9 16.81.5
25.5 3.1 9.61.2
25.5 3.2 10.01.2
25.5 3.0 18.2.2
25 5 3.0 17.~.3
63.8 3.2 15.22.2
63.8 3.1 11.82.2
63.8 3.5 13.92.3
63.8 3.~ 14.12.2
25.5 4.9 13.6.8
25.5 5.1 13.2.8
Note: On Fig. 8 the feed rate values are charted as follows:
.
0 10 GPM
15 GPM
n 20 GP~
.
Example ~
~ Iixtures of 67~ primary and 33~ by volume secondary
municipal sludyes were fed at various rates to the above
described apparatus with conditioning by various proportions
of flocculating agent (Calgon 2640, supra.). The feed rates
¦employed, dosage of flocculating agent, solids content of the feed
and solidscontent of the resulting sludge cakes together with
pressate recovered are given in Tabel 3 below. The results
are also sho~n graphically in Figure 9. It will be observed
that the maximum application rate for this mix-ture is about
25 gallons per minute. Higher application rates give cakes
a lower percent solids.
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¦ Table 3
Mixt ~
_p GPH (5~ Solutiog/ Percent Sollds
0 25,:~ 4.2 28.6 1 1
25.~) 4.8 25v7 --- *
25.~ 2.8 25.8 --- *
*
- 20 255 55 2 6 18 8 .7 ~~
2~ ~' 5 5'7 I4.8 _'4
: ~ 20 25 5- 3 4 2ll 44 1.6
* Not Reported
Note: On Fig. 9, the feed rate values are charted as follows:
10 GPM
15 GPM
O 20 GP~I ,
0 25 GPM
: ~ 30 GPM
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¦ It is reasonable to assume that the sludge film
¦ deposited on the screen in the above examples is densest in case
I of processing primary sludges and decreases in density as the
ratio of secondary to primary sludge in the mixture increases;
therefore, the li~uid portion causing the wash out of the filter-
ing film can break through the sludge film easier when processing
` mixtures oE sludges ~here the secondary sludge portion is higher
than when processing mixtures with a lower portion of secondaxy
sludge.
It may also be observed from the above examples that
when using mixtures of primary and secondary sludges in equal
proportions, a maximum application rate OL 1.75 gallons per
, minute/square feet based on the total screen area of 8.7 square
¦ feet represents the upper limit beyond which there was more "
~¦ water in the feed than could pass through the screen. This ex-
cess water was transported by ~he screw along with the sludge
thus resulting in sludge cakes of lower percent solids. When
¦ using mixtures of primary and secondary munlcipal sludges in the
ratio of 2:1, the maximum rate of application of 2.9 gallons per
minutejsquare ~eet based on the total screen area of 8.7 square
feet represented the upper limit beyond which there was more
water in the feed than can pass through the screen. This water
~- was transported by the screw along with the sludge thus resulting
in sludge cakes of lower percent solids.
In dewatering primary sludge, thickened secondary ~:
sludge nd mixtures of p~imary and secondary sludges, our obser-
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vation has been tha-t the theoretical application rate based on
the percent solids in the feed may be determined by reference
to Fiyure 10, a graph depicting t:he ideal application rate, de-
pendent upon the concentration of solids in the feed sludge.
Those skilled in the art will apprecia-te that many
modifications may be made to the above described apparatus and
method without departing from the spirit and scope of the inven-
tion. Ideally, the apparatus will be constructed of simple and
conventionally available materials to maintain a low initial
capital cost.
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