Apparatus and method for sensing the quality of dewatered sludge

A cake sensor which includes a rotatable, hollow cylindrical shell adapted to be positioned within a flow of falling cake material and a piston within the shell. The shell has an opening therein through which the cake material will enter the shell, and to one end of the shell are connected a fluid source and a density sensor. The piston extends through the other end of the cylinder and is driven by a torque motor to compress cake material which falls into the cylinder through the opening. The various measurements developed by the density sensor, the torque developed by the torque motor, and the distance traveled by the piston are utilized to determine the characteristics of the cake material. A method for determining the quality of the cake material is also presented.

BACKGROUND OF THE INVENTION 
The present invention relates to the handling of thick, viscous or 
thixotropic materials, and in particular to the reclamation from storage 
lagoons of dry, semidry or nearly gelatinous sludge produced as a 
by-product of various manufacturing operations and/or various conventional 
waste sludge sewage treatment processes. Most particularly, however, the 
invention relates to a cake sensor which determines the quality of the 
dewatered sludge removed from the lagoons by using as the criteria the 
desirability and suitability of the dewatered sludge for use as land fill 
material. 
Although the actual chemical composition of the materials to be removed 
from catch basins or lagoons will vary from location to location, normally 
such materials have been deposited in a liquid or semiliquid state and 
have been stored in such lagoons or catch basins for a considerable period 
ot time, and this storage results in the thickening of the material due to 
decreasing moisture contents. Moisture content may range from about 99.5% 
to as low as 60%, but commonly is in the range from about 92% to 85% after 
several years of aging in the lagoon. As described in U.S. Pat. No. 
3,796,658, at this common moisture level the sludge does not behave as a 
fluid, but rather, resembles a heavy viscous or soft gelatinous material 
having thixotropic tendencies. 
The problems which are connected in cleaning lagoons or catch basins of 
this type are aggravated by the fact that (depending upon the constituency 
of the waste products disposed therein) chemical reactions, microbic 
growth, local geologic characteristics including soil porosity and water 
table levels, and the particular design and contruction of the lagoon or 
catch basin to be cleaned result in extremely discontinuous deposits of 
materials to be removed. For example, depending on exposure, porosity, 
dwell time in the lagoon, the varying nature of the substances charged 
into the lagoon from year to year, and many other factors, the consistency 
and handleability of waste material to be removed from within any given 
lagoon, much less from one lagoon to the next, will vary markedly by depth 
and region. 
The parent applications referenced above with regard to the present 
invention generally disclose novel catch basin cleaning systems wherein 
various means are provided for transferring material obtained from the 
catch basin to subsequent processing operations only in the event that the 
material is determined by various monitors to be of an optimal nature for 
introducing into the subsequent process phase. For example, a pumping 
means will transfer materials to an equalization means only if that 
material contains a preselected percentage of solids, which percentage is 
selected for its compatability with the subsequent processing means which 
are mounted on an adjacent mobile apparatus. Additional means are provided 
to insure that a maximum flow of material will be produced. For example, 
ejectors are used in combination with novel optimal pumping, monitoring 
and recirculation means in order to insure that the liquid which is 
collected from the catch basin has neither too little or too great a 
solids content for subsequent equalization and dewatering operations. In 
the event that a liquid is being pumped by the pumping means which 
contains the optimum solids content, this liquid is admitted to a 
subsequent equalization process which equalizes, mixes and homogenizes the 
collected material for subsequent treatment. Dewatering, treatment, 
conditioning and discharge follow equalization and interact to produce the 
desired end products which often may be a cake material suitable for use 
as land fill material. Water suitable for return to the process head or 
sanitary sewer may be produced. Alternatively, water may be recirculated 
to be added directly into either the ejector system or to dilute the 
material which is being collected by the pumping system. 
Throughout these processes, material which is collected from the catch 
basin, hereafter referred to as the wash effluent or wash stream, is 
monitored qualitatively and quantitatively at numerous stages of the 
processes. By monitoring the nature and quantity of this flow, the level 
of the equalization means, the density of the dewatering means input, the 
centrate turbidity centrate flow rate and centrate pH, various valves are 
automatically operated which regulate the bypass of the wash effluent back 
into the catch basin, the flow of material to the equalization means, the 
flow of thickened material either to the conditioning means or again to 
the equalization means, the flow of material to the process head or 
ejector, the amount of virgin water added to the pumping means, and the 
rates of the pumping means, dewatering means, treatment (chemical feed) 
means and conditioning means. As a result, these prior applications 
present systems capable of adapting superior dewatering equipment to the 
art of catch basin cleaning which, heretofore, has relied upon settling 
tank type processing in order to collect and then transport materials 
removed from catch basins. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improvement to the 
various prior art dewatering apparatuses which will determine and control 
the handling quality of the cake material obtained by dewatering the 
materials removed from the catch basins. 
It is a further object of the present invention to provide a device which 
will measure the absence of stickiness, squashiness, mud-like character, 
viscosity, etc., which are known in the art to be of great importance in 
determining the desireability of using any particular substance in this 
case particularly the dewatered catch basin material as land-fill 
material. 
These objects are achieved by the cake sensor of the present invention 
which includes a rotatable, hollow cylindrical shell adapted to be 
positioned within a flow of falling cake material and a piston within the 
shell. The shell has an opening therein through which the cake material 
will enter the shell, and to one end of the shell are connected a fluid 
source and a density sensor. The piston extends through the other end of 
the cylinder and is driven by a torque motor to compress cake material 
which falls into the cylinder through the opening. The various 
measurements developed by the density sensor, the torque developed by the 
torque motor, and the distance traveled by the piston are utilized to 
determine the characteristics of the cake material. This information is 
then used to adjust the cake material having the desired characteristics.

DETAILED DESCRIPTION OF THE INVENTION 
Although specific forms of the invention have been selected for 
illustration in the drawings, and the following description is drawn in 
specific terms for the purpose of describing these forms of the invention, 
this description is not intended to limit the scope of the invention which 
is defined in the appended claims. 
In the view of the preferred embodiment of the present invention as shown 
in FIG. 1, the cake sensor 100 is primarily a cylinder or hollow 
cylindrical shell 20 with a plunger or piston 30 movably fitted therein. 
The piston member has a piston head 33 within the cylinder and a piston 
rod 31 connected to the piston head which extends through one end 21 of 
the cylinder and is connected to a torque motor 40. The cylinder is 
preferably rotatable about its longitudinal axis, which coincides with the 
piston rod 31 of the piston 30, and the cylinder is sealed at both ends by 
plates 21 and 22. The cylinder is preferably designed to be rotatable; the 
end plates 21 and 22 are stationary. 
The end plates 21, 22 both have openings therethrough which communicate 
with the interior of the cylinder. The piston rod 31 extends through an 
opening 23 in the first end plate 21, and the opposite end plate 22 has at 
least two openings, 24, 25 therethrough. The first of these two openings, 
24, is adapted to have a fluid source 50 connected thereto, and the second 
opening 25 is designed to receive a density sensing device 60. The fluid 
source 50 provides a pressurized fluid, such as compressed air or a 
liquid, like water, under pressure. The density sensor 60 may be an 
ultrasonic transducer fitted into opening 25. 
In addition to the two open ends which are sealed by the two plates 21, 22, 
the cylinder 20 has an additional opening 26 through the sidewall thereof. 
As will be discussed shortly, this sidewall opening 26 is specifically 
provided to admit cake material into the cylinder so that it can be 
tested. 
When the sensor is being utilized, the cylinder preferably having a 
diameter of 3" to 5" is positioned in a flow stream of the cake material 
to be tested. The sensor is typically situated transverse to the flow 
direction of the cake as shown by arrows B with the sidewall opening 26 
directed against the flow direction, so that the falling cake material 
will enter into the cylinder. During the time when the cake material is 
filling the cylinder, the piston 30 is retracted by the torque motor 40 
toward the end plate 21. After the sample of cake is admitted into the 
cylinder, however, the torque motor is engaged to force the piston toward 
the second end plate 22 and, thus, compress the cake material between the 
piston and the second end plate. The movement of the piston toward the 
second end plate is continued until a predetermined amount of torque is 
attained; the limit of the torque applied to the piston may be determined 
by the stall characteristics of the motor. Or, as is specifically 
preferred, the torque may be controlled by logic circuitry, a computer, or 
a micro-processor which controls the functions of the torque motor 40, as 
well as the functions of the dewatering device with which the cake sensor 
is used. When the piston has moved as far as required in the compressing 
direction, the cylindrical shell 20 is rotated as shown by arrow A so that 
the opening is no longer in alignment with the cake flow; it rotated, for 
example, 90.degree. by a turning motor 70 in contact with the cylinder. 
This rotation of the cylinder will prevent any further cake material from 
entering into the cylinder. Also, after the piston has moved to its fully 
compressed position and before the piston is retracted, the torque applied 
to the piston, the position of the piston with respect to the interior of 
the cylinder as detected by the indexer 32 mounted thereon, and the 
density of the compressed cake as sensed by the ultrasonic transducer are 
each recorded. 
Since the cylinder shell has been rotated so that no more cake material may 
enter through the opening 26, the direction of the piston movement is 
reversed, i.e., toward the first end plate 21, and the torque applied by 
the torque motor is continuously recorded in order to subsequently chart 
or monitor the torque required to move the piston in the reverse direction 
away from the compressed cake as a function of time. Depending on the 
"stickness" or "mud-like" character of the sample which has been collected 
and compressed within the cylinder, the torque applied by the motor in 
order to produce the movement of the piston will vary as the piston is 
retracted, and the stickiness of the sample will be reflected by the 
"hump", i.e., increases in torque required during the initial phases of 
the withdrawal process. Eventually, the torque required to withdraw the 
piston will assume a relatively constant level, whereupon the withdrawal 
away from the compressed cake will be completed and the collection of test 
data may be concluded. 
A typical example of the type of relationship which exists between the 
torque T and the change in direction X of piston is shown in FIG. 2. It 
can be seen that the torque is zero when the cake is compressed and before 
the piston begins to be withdrawn. The torque, however, increases rapidly 
as the piston is withdrawn from the compressed cake as the piston attempts 
to overcome the "stickiness" of the compressed cake and its attraction for 
the piston. As the piston withdraws further, the stickiness is overcome 
and the required torque reduced until it levels off to a constant value. 
After all of the required data is collected, the sample within the cylinder 
is removed so that further samplings can be made in order to maintain a 
continuous watch on the characteristics of the cake material. At this 
point, the piston should have been fully retracted away from the cake, and 
the cake should be able to communicate with the opening 26 in the 
cylinder. The cylinder shell is then, again, rotated, approximately 
90.degree., so that the opening faces, preferably, in a downward position 
180.degree. from the initial position in which the cake material was 
admitted into the cylinder. Or, in other words, the opening process opens 
downwardly in the same direction as the cake flow. Once this position is 
attained, the pressurized fluid, air or liquid, is injected into the 
cylinder through the opening 26 to break up the compressed cake and force 
the cake material from the cylinder. If the fluid is a liquid, it can also 
be used to wash the inside of the cylinder shell, and the wash fluid will 
empty through the opening. 
After the cake material is exhausted from the cylinder, the piston is again 
forced all of the way to the left, against the second end plate, thereby 
closing the opening 26 in the cylinder, and the cylinder is rotated 
180.degree. so that the opening is in a position to receive the falling 
cake material when the piston is next retracted. 
Even though a rotatable cylinder with stationary ends is disclosed in the 
preferred embodiment, it is within the scope of this invention to provide 
a structure wherein the end plates are affixed to the cylinder shell, and 
the fluid attachment and the attachment of the density sensor are flexibly 
connected to the end plate so that the end plate can rotate with the 
cylinder. 
The motor 70 which is provided to rotate the cylinder 20 through the 
various required angles may be any motor which one skilled in the art 
might use to rotate the cylinder. Two examples might be a gear wheel 
connected to the motor which engages a geared portion around the 
circumference of the cylinder, or a resilient member, such as a 
rubber-like member, connected to the motor which rotates the cylinder due 
to engagement with the circumference thereof. 
Furthermore, while it is felt that rotating the cylinder the initial 
90.degree. may adequately prevent further cake material from entering into 
the container, it is recognized that additional mechanical arrangements 
may be provided that will either slide over or in some way block the 
opening 26 to prevent further cake material from entering. These 
additional structures are also considered to be within the scope of this 
invention. 
As indicated previously, this invention is especially useful for 
determining and controlling the quality of cake material obtained by 
dewatering the material removed from catch basins which is intended for 
subsequent use as land fill material. FIG. 3 is a schematic representation 
of the apparatus and system which is presented in the applications 
cross-referenced and incorporated by reference herein. Since a complete 
explanation of the parent application is summarized in the background of 
this application and is fully discussed in detail in these incorporated 
applications, additional description is not presented herein, except as 
necessary to understand the incorporation of the present improvement into 
such an arrangement. 
By the time the material being treated in the apparatus of FIG. 3 reaches 
the centrifuge 42, it is essentially in a form of cake material which, 
hopefully, has the required optimum density. If not, the shunt valve 43 
operates to return the partially dewatered material to the equalization 
tank 26 for further processing. 
When the dewatered cake material is finally processed to a stage where it 
is able to be removed after passing from the centrifuge, the quality of 
the material can easily be tested at that time by incorporating the cake 
sensor 200a of the present invention into the system as shown in FIG. 3. 
By installing the cake sensor 200a as shown, it is possible to take the 
data obtained regarding the cake material quality and feed it into the 
computerized or micro-processor control system regulating the system to 
adjust the various steps in the process and alter the production of the 
cake material as required to arrive at cake material having the desired 
characteristics. 
It is further possible, as shown in FIG. 3, for the cake sensor to be 
incorporated into this system to test the quality of the material leaving 
the dry mixer 48. The dry mixer receives the dewatered cake material from 
the centrifuge along with cake conditioning feed system 44. This 
conditioning material, such as deodorizing and disinfecting materials, is 
added to the cake material in order to make the cake material more 
suitable for use in sanitary land fill situations. Again, the cake sensor 
200b of the present invention may be positioned to test the quality of the 
material discharged from the dry mixer to determine its suitability for 
use as land fill material. 
Finally, a cake sensor 200c of the type disclosed herein may also be 
positioned at the end of conveyor 25 to test the quality of the 
conditioned cake material emanating from the dry mixer and combined with 
the solids removed by the degritter 22 and carried toward the truck 50 by 
the grit conveyor 25. When the cake sensor 200c is so-positioned at the 
end of the process, then the quality of the final product of that 
apparatus for processing catch basin materials can easily be checked. 
By incorporating this cake sensor into a catch basin material recovery 
system, the quality of the cake material produced by the system can be 
periodically tested so that the various steps in the process can be 
suitably adjusted in order to obtain a cake material having the desired 
characteristics in response to the test dates. Preferably, the overall 
sludge treating system will be automatic, that is, controlled by computer 
or micro-processor, so that adjustments to individual process steps will 
be automatically made by the system controls based on the data obtained 
from the cake sensor. It is, however, possible to take the measurements 
produced by the cake sensor manually adjust the various stages of the cake 
producing system in order to vary the quality of the cake material 
produced thereby. 
It will be understood that various changes in the details, materials and 
arrangement of parts which have been herein described and illustrated in 
order to explain the nature of this invention may be made by those skilled 
in the art within the principle and scope of the invention as expressed in 
the following claims. 
It will further be understood that the "Abstract of the Disclosure" set 
forth above is intended to provide a nonlegal technical statement of the 
contents of the disclosure in compliance with the Rules of Practice of the 
United States Patent and Trademark Office, and is not intended to limit 
the scope of the invention described and claimed herein.