Solid-liquid separation process for fine particle suspensions by an electric and ultrasonic field

A method of separating a solid-liquid suspension (e.g. an aqueous coal suspension, a suspension of clay in oil) by concurrently subjecting the suspension to the action of a sonic or ultrasonic field and an electrical field so as to remove the liquid from the suspension. The suspension is moved into a solid-liquid separation chamber between opposing electrodes one of which is permeable to the liquid. The sonic or ultrasonic field is then applied to the suspension concurrently with the electrical field, at a frequency and amplitude adapted to cause the liquid to separate from the suspension particles. The concurrently applied electrical field between the electrodes causes the particles to migrate away from the permeable electrode and liquid to migrate toward the permeable electrode. The liquid is then removed through the permeable electrode. The method requires less energy to remove a unit of liquid, has a faster rate of liquid removal and achieves a lower liquid content than if only an electrical field or acoustical field were used separately or in sequence.

FIELD OF THE INVENTION 
This invention relates to a method of concentrating the finely divided 
solids in solid-liquid suspensions (e.g. colloidal suspensions, sludges or 
fine particle slurries in liquids) by a combination of an electrical 
field, and an acoustical (sonic or ultrasonic) field and removing the 
liquid therefrom. Such sludges and slurries occur, for example, in coal 
washery slimes, ore processing, fuel processing, vegetable oil processing 
dyeing operations, transportation of coal by pipeline and in production of 
ceramics. The method requires less energy for the combination of 
electrical field and acoustical field to remove a unit of liquid from a 
suspension than the energy required if only an electrical field or an 
acoustical (sonic or ultrasonic) field were used separately or in sequence 
to remove that unit of liquid from the equivalent suspension. 
The method is of utility in removing liquids from the above mentioned 
examples and from those described below. 
BACKGROUND OF THE INVENTION 
Conventional methods of separating liquids (e.g. water, oils, liquid 
hydrocarbons) from suspensions, sludges and slurries to improve their 
solid concentration include mechanical solid-liquid separation methods 
such as centrifugation, vacuum filtration, vibration screening; thermal 
drying; ponding; ultrasonic solid-liquid separation; and use of an 
electrical field (electrophoretic or electroosmotic solid-liquid 
separation. Some materials mixed with liquids, however, are not amenable 
to the usual solid-liquid separation methods due to blockage of the filter 
by fine particles so that the rate of filtration slows down significantly. 
In addition solid-liquid separation of colloidal and small particle 
suspensions is difficult with conventional solid-liquid separation 
techniques such as vacuum filtration or centrifugation. Such suspensions 
and slurries can also be thermally dried or extracted; but, the energy 
consumption is very high and it creates problems with dust, and solvent 
recovery. In addition natural settling by ponding requires large land 
areas for lagoons and the like. 
Because of the high cost of energy there has been a renewed effort to 
reappraise all of the above methods and reduce the cost associated 
therewith. The use of an electrical field or acoustical field to separate 
liquids from suspended particles has been studied as further discussed 
below. 
When colloidal particles such as finely divided clay are suspended in 
liquid they become charged and when subjected to an electrical field they 
will migrate towards one or another of the electrodes. The charge will 
depend on the type of suspension or slurry, e.g. certain types of clay 
become positively charged while many coals become negatively charged, thus 
the proper electrode polarity will need to be chosen to cause migration of 
particles away from the liquid permeable electrode and toward the 
impermeable electrode. 
The application of an electrical field can agglomerate particles by 
neutralizing charges, dehydrate solids by electroosmosis, or cause the 
particles to migrate as noted above. The electrically charged collecting 
plates will sequester all migrating particles such as negatively or 
positively charged particles but do not collect the isoelectric particles. 
For example, in proteins, the charges originate from the ionization of 
(COO.sup.-) and NH.sub.3 +) ions. The net charge on protein will depend on 
the number of these groups; the disassociation constant, pH, temperature, 
etc. However, it is an empirical observation that most colloidal protein 
suspensions are usually negatively charged under normal conditions when in 
water. 
Another phenomenon present is that of electroosmosis. Electroosmosis is the 
transport of the liquid medium alongside a surface that is electrically 
charged but stationary. The movement of the liquid medium is in the 
direction of the electrode with the same sign of charge as the immovable 
surface. Thus, as the slurry particles become more densely packed and 
immovable, the liquid between the particles will be subject to 
electroosmotic forces. If the particles are negatively charged, the flow 
of liquid will be toward the negative electrode. Since this electrode will 
also be permeable to liquid, the solid-liquid separation process will be 
further improved. 
Illustrative of the use of an electrical field in the dewatering of coal 
washery slimes is the article by Neville C. Lockhart, Sedimentation and 
Electro-osmotic Dewatering of Coal Washery Slimes, Fuel, Vol. 60, October, 
pp. 919-923. 
The use of ultrasonic energy separately to dewater coal is known, as 
illustrated in the articles by H.V. Fairbanks et al., Acoustic Drying of 
Coal, IEEE Trans. on Sonics and Ultrasonics. Vol. SU-14, No. 4, (October 
1967), pp. 175-177; Acoustic Drying of Ultrafine Coals, Ultrasonics, Vol. 
8, No. 3 (July 1970), pp. 165-167. 
Sonic or ultrasonic energy is a form of mechanical vibratory energy. Sonic 
or ultrasonic energy propagates as waves through all material media 
including solids, liquids and gases at characteristic velocities. The wave 
velocity is a function of the elastic and the inertial properties of the 
medium. 
During the propagation of these waves in a medium very high inertial and 
elastic forces are generated locally due to the high frequency of these 
waves. The amplitude of particle motion in the medium due to the sonic and 
ultrasonic waves range from a few microinches to 5 milliinches (0.005 
inch) (0.127 mm) depending on the power level. The peak acceleration 
developed in the medium due to an ultrasonic wave at 20,000 Hertz and an 
amplitude of 0.001 inch (0.0254 mm) is as high as 40,000 
G(1.5.times.10.sup.6 inch/sec.sup.2) (3.810.times.10.sup.7 mm/sec.sup.2). 
One G(9.807.times.10.sup.3 mm/sec.sup.2) is the acceleration due to 
gravity. The forces generated due to these levels of acceleration are very 
high. 
For any medium these high inertia forces generated due to the sonic or 
ultrasonic waves can cause material failure, disruption and separation. 
The sonic or ultrasonic impedances of different materials, especially in 
solid and liquid phases are different by factors of 3 to 8. If the medium 
is a mixture of different phases of two or more types of materials such as 
water and coal, oil and clay, and tetralin and carbon, etc., the inertia 
and elastic forces between them are likely to be even higher. These high 
inertial and elastic forces are likely to break the surface tension and 
promote separation of liquid from solids. 
In liquids a high level of sonic and ultrasonic energy is also known to 
cause cavitation, a phenomenon of micro bubble formation due to degassing 
and change of phase to vapors. In the presence of solid particulate 
matter, the level of cavitation is higher. The micro bubbles are formed on 
the surface of the solids and assist in the separation of the solid and 
liquid due to the formation of gas liquid surfaces with much lower surface 
energy compared to solid-liquid surface. Cavitation also generates high 
local shock waves and in some cases charged free radicals. Shock waves and 
free radicals are likely to accelerate liquid solid separation. 
High oscillatory forces are developed in a medium due to the application of 
ultrasonic energy. These high oscillatory forces between the solid media 
and liquid in a mixture and ultrasonic cavitation are believed to be the 
major mechanisms of sonic and ultrasonic solid-liquid separation. 
Degassing, decrease of viscosity and decrease of surface tension due to 
ultrasonic vibration are other possible mechanisms. 
Ultrasonic energy is also partially absorbed by the medium and is converted 
to heat. Internal heat generation and the consequent temperature rise will 
further decrease the viscosity and the surface tension of the fluid and 
facilitate its removal. Local temperature rise is also likely to increase 
the cavitation activity and accelerate the rate of fluid removal. 
Therefore internal heating due to the partial absorption of the ultrasonic 
energy has added benefits to accelerate fluid removal as in aqueous 
systems. 
In the U.S. Pat. Nos. 3,864,249 and 4,028,232 to Wallis, there are found 
teachings of the use of acoustical pressure waves and coupling them to a 
separation screen to facilitate separation of a liquid from material to be 
dried. 
The use of an electrical field or acoustical energy separately requires a 
substantial amount of energy and the rate of separation is much slower. 
It is an object of this invention to remedy the above drawbacks by reducing 
the energy requirements for solid-liquid separation, by increasing the 
rate of separation over present methods and by lowering the final liquid 
content of the product. The inventors have discovered that a concurrent 
use of an acoustical field (sonic or ultrasonic), and an electrical field 
(electrophoresis/electroosmosis) gives unexpectedly improved results over 
an acoustical field acting alone or an electrical field acting alone in 
that: 
1. this combination of concurrent use requires less energy than using 
either of the two alone; 
2. this combination of concurrent use, separates liquids from suspensions 
at a faster rate than using either of the two alone; and 
3. this combination of concurrent use gives a lower final liquid content in 
the filter cake than using either of these two alone or using both in 
sequence. 
BRIEF DESCRIPTION OF THE INVENTION 
In accordance with the present invention there is provided a method for 
separating liquids from solids in liquid suspensions of solids e.g. coal 
slurries and other materials as further described below. The method 
comprises concurrently subjecting the suspension to an electrical field 
and an acoustical field (sonic or ultrasonic) so as to separate liquid 
bound to solid particles and cause a migration of the particles and liquid 
so as to form a region depleted of particles. The liquid is then withdrawn 
from the region depleted of particles, such as by gravity or mechanical 
means. The energy required for an incremental amount of separation is less 
with the combination of an electrical field and an acoustical field than 
for either of the two separately or in sequence.

DESCRIPTION OF THE INVENTION 
The drawing shows a (separation zone) or a chamber 10 bounded by electrodes 
11 and 12 connected to an external supply 200 of direct current connected 
by electrical leads 111 and 112. Electrode 11 is liquid permeable with 
openings 13. A filter 14 may be employed if the electrode 11 does not have 
sufficiently small openings 13 to retain the particles in the suspension. 
An acoustical generating means 15 produces an acoustical field having 
sonic or ultrasonic waves (not illustrated) that are transferred 
throughout the mass of the suspension in the separation zone. 
In operation, the suspension to be treated is moved into the separation 
zone 10 and subjected to the acoustical field (sonic or ultrasonic) of 
such a frequency and amplitude as to cause separation of liquid from the 
particles in the suspension. Concurrently, a D.C. voltage is applied 
between the electrodes 11 and 12 to cause migration of charged particles 
in the suspension away from the liquid permeable electrode 11 and toward 
the liquid impermeable electrode 12 and movement of liquid toward the 
permeable electrode. 
Sonic or ultrasonic waves prevent packing of the suspended particles and 
facilitate flow of liquid toward the liquid permeable cathode. As the 
slurry passes through the separation zone 10 the liquid is removed through 
the liquid permeable electrode 11 and the solid-liquid separated 
suspension emerges at the other end of the zone 10. Removal of liquid 
through the liquid permeable electrode 11 may be increased by augmentation 
means 16 such as by reducing the pressure outside the permeable electrode, 
by increasing the pressure within the zone or by a combination of the 
above. The process of the invention is operable without these augmentation 
means. It is preferred, however, that augmentation means be used. The 
means used for reducing the pressure at the outer surface of the permeable 
electrode or for increasing the pressure within the separation zone are 
those conventionally used for pressure reduction or increase for 
augmenting filtration. 
The separation zone 10 may be bounded by two walls (not shown) that connect 
between the two electrodes 11 and 12 so as to contain the suspension 
within the zone 10. The walls are insulated from the electrodes 11 by 
insulating materials not shown or the walls may be of an electrically 
nonconductive material. 
In this embodiment the electrical field and acoustical waves are applied 
concurrently while the suspension flows through the separation zone 10. 
In other embodiments parameters for the electrical field and acoustical 
energy may be changed to remove additional liquid from the suspension by 
flowing it through additional apparatus of the kind illustrated in FIG. 1. 
In still other embodiments the suspension may be pretreated or posttreated 
by acoustical energy or an electrical field separately before being 
subjected to the concurrent method of the invention. 
The frequency of operation of the sonic/ultrasonic generator may be about 
5,000 to 100,000 Hertz, but preferably about 20,000 to 40,000 Hertz so as 
to minimize the effects of audible noise on the work environment and to 
keep the efficiency at a high level. The amplitude of the sonic and 
ultrasonic waves can be any amplitude sufficient to separate liquid bound 
to particles but is preferably in the range of about 0.002 mm to 0.01 mm. 
The applied voltage may be any voltage that will cause a sufficient 
electrical field and a current to flow so as to cause a migration of the 
charged particles and liquid so as to improve the separation process by 
reducing total energy requirements over the above mentioned methods used 
separately. 
The method may be used with aqueous coal slurries such as those produced 
when coal is shipped by pipeline; coal washery slimes when coal is 
separated from contaminants after mining, suspensions produced in ore 
processing such as illmenite ore processing slurries or sludges or 
haematite ore processing slurries or sludges; clay suspensions produced in 
production of ceramics; fermentation and sewage sludges; and protein 
hydrolysates; fuel materials such as tar sands, oil sands, oil shale, coal 
liquified products, pitch, and their slimes produced during processing; 
organic liquid suspensions including as examples those where carbon is the 
solid suspended, alcohol and organic dye suspensions, oil-clay 
suspensions, oil filter cakes obtained in pressing operations, the organic 
liquids may be alcohols, ketones, alkanes, aromatic, alicyclic, aliphatic, 
and heterocyclic compounds and the like. The organic liquids may be 
nonpolar hydrocarbons or have polar groups. It was noted that lower 
molecular weight organic compounds with low boiling points were not 
readily amenable to the procedure since the vacuum used caused them to 
evaporate during tests. This problem can be remedied by reducing the 
vacuum, lowering the temperature, or using other augmentation means 16 
such as centrifugation. It is believed that the method of the invention is 
generally applicable to the above listed sludges and slurries. 
Separation may be further augmented by addition of small quantities of 
surface modifiers such as detergents or surfactants. Examples of these 
surface modifiers are polyacryl amide gels, polystyrene sulfonates and the 
like. The preferred amount is capable of being readily determined by those 
skilled in the art. These surfactants are to be added prior to the 
concurrent application of the acoustical and electrical fields. The types 
of surfactants could be nonionic, anionic or cationic types. The 
surfactants because of their hydrophobic nature attach to the coal surface 
and release the water. 
Certain types of materials, when mixed with water, e.g. certain clays and 
coals, do not exhibit sufficient conductivity to allow for proper current 
flow during application of the electrical field. In this situation the 
conductivity of the mixture must be enhanced by the addition of a salt or 
conductive enhancer e.g. NaCl, KCl, Na.sub.2 SO.sub.4, NaOH, KOH, NH.sub.4 
Cl or by adjusting the pH of the suspension. The same effect can be 
achieved by changing the pH of the solution appropriately. This will 
insure proper current flow and migration of the particles. 
The method may be used in the solid-liquid separation of any size particles 
mixed with liquids discussed herein. The preferred particle size range is 
from about 10 micrometers to 100 micrometers. 
According to the method of the present invention it is important that the 
sonic and ultrasonic waves and the electrical field be applied to the mass 
of the mixture so as to penetrate throughout the mixture itself. If the 
sonic and ultrasonic waves do not penetrate throughout the mixture to be 
separated, an efficient separation of liquid from the solids will not take 
place. 
While the foregoing discussion and the following examples use a vacuum in 
combination with ultrasonic and electrical field solid-liquid separation 
it is to be understood that use of a vacuum is not mandatory and that 
other means 16 may be used to augment the solid-liquid separation process 
of the invention. Further, the following examples serve to illustrate and 
not limit the present invention. Unless otherwise indicated, all 
percentages are by weight. 
Reference to a vacuum herein is in the colloquial sense only and is used to 
refer to the application of a reduced pressure (below atmospheric) to the 
samples. 
Coal 
A coal slurry with coal particles having a maximum Tyler mesh size of -200 
was prepared and is that used for the tests of Examples 1 through 4. 
The slurry was prepared using a dry coal to water ratio of 1:1 resulting in 
a slurry of fifty percent (50%) water by weight. About 0.1g NaCl was added 
to all samples. 
The particles were mixed with the water with a magnetic stirrer until a 
homogeneous suspension resulted. 
EXAMPLE 1 
This comparative example illustrates how much water is removed by usual 
vacuum filtration. 
TABLE I 
______________________________________ 
Dewatering by Vacuum Only 
Time Vacuum 
Sample (min) (cm. of Hg) % H.sub.2 O 
______________________________________ 
1 1 51 44.46 
2 4 38 (25" at 3 min) 
42.0 
3 7 38 (13" at 6 min) 
39.0 
4 10 38 (13" at 6 min) 
39.06 
______________________________________ 
Sample size 35 g. 
This initial experiment was performed with vacuum only using a typical 
water faucet aspirator. From FIG. 2 it can be observed that the solids 
concentration achieved after the first ten minutes levels off with little 
change thereafter. This is due to the formation of a cake which retards 
the rate of filtration. Also, the solids concentration obtained is rather 
low due to the limiting properties exhibited by the particles. The water 
held by surface tension forces, capillary forces, etc. is still being 
retained. The water removed is mostly bulk water. From past experience the 
results from 50g samples would not deviate much from the results of the 
35g samples. Thus the above results are valid for comparison purposes. 
EXAMPLE 2 
This comparative example illustrates the use of an electrical field, 
(electrophoresis and electroosmosis) (E) and a vacuum. The slurry was the 
same as that prepared earlier. Sample size was 35 g for Samples 1, 2, and 
3 and 50 g for Samples 4, 5, and 6. 
TABLE II 
__________________________________________________________________________ 
E 
E E Energy 
Initial 
Energy 
Corrected 
Water 
Vacuum 
Temp. 
Time 
Power 
(Watt 
(Watt Content 
Sample 
(cm. of Hg) 
(.degree.C.) 
(min) 
(Watts) 
Hours) 
Hours) 
% H.sub.2 O 
__________________________________________________________________________ 
1 38 -- 0.7 12.5 
0.141 
0.0705 
38.5 
2 38 -- 1.4 12.5 
0.283 
0.1415 
35.6 
3 38 -- 2.9 12.5 
0.567 
0.283 36 
4 38 -- 5 78 -- 1.365 34.8 
5* 38 100 4 120 -- 2.127 27 
6* 38 100 4 220 -- 3.201 28 
__________________________________________________________________________ 
*Samples not used in FIGS. 2 and 4 due to water loss from high 
temperature. 
This example performed with an electrical field and a vacuum only gave 
improved performance over a vacuum alone. This is shown in FIG. 2. Using 
only a vacuum as in Example 1 the moisture content after two minutes was 
only about forty-three percent (43%). In the presence of an electrical 
field under similar conditions the moisture concentration was reduced to 
about thirty-five percent (35%). The time and power levels for Samples 1, 
2, and 3 have been corrected to those for 50 g samples by a direct 
algebraic ratio to allow direct comparison with 50 g samples from other 
tests. 
It was noted that the power used dropped rapidly as the dewatering process 
continued. This is shown in FIG. 3 for Samples 4, 5, and 6. Thus for 
Samples 1, 2, and 3 a first approximation that assumed that the power 
level was reduced linearly during the time the test was used. For Samples 
4, 5, and 6 the energy required was obtained by assuming a straight line 
between the data points and calculating the area under each curve. 
At higher current throughput (1-2 amp) for longer periods of time, the 
electrodes became hot. Therefore the potential between electrodes was 
correspondingly decreased to allow smaller amounts of current flow. 
EXAMPLE 3 
Example 3 was a comparative example performed using only ultrasonics (U) 
and a vacuum. The slurry was the same as that prepared earlier. Sample 
size was 50 g. Frequency was 20,000 Hertz. 
TABLE III 
______________________________________ 
U 
U Energy 
Moisture 
Vacuum Temp. Time Power (Watt Content 
Sample 
(cm. of Hg) 
(.degree.C.) 
(min) (Watts) 
Hours) 
% H.sub.2 O 
______________________________________ 
1 64 25 1 160 2.67 29.0 
2 30 36 6 160 16.0 24.0 
3 -- -- 10 160 26.7 22.0 
4 53 56 1 280 4.67 26.7 
5 -- 68 6 280 28.0 19.3 
6* 66 96 10 280 46.7 5.2 
7 61 42 1 480 8.0 24.8 
8 58 74 3 480 24.0 20.5 
9* 56 91 6 480 48.0 17.3 
______________________________________ 
*Samples not used due to high temperatures. 
By using ultrasonics and a vacuum, filtration rates were much higher than 
either vacuum alone or vacuum and an electrical field. As explained 
previously, dewatering in the presence of ultrasonic energy occurs mainly 
due to cavitation phenomena. At two minutes the solids concentration 
achieved is about twenty-three percent (23%) as compared to about 
thirty-five percent (35%) in the presence of the electrical field of 
Example 2. However, it should be mentioned that there was generation of 
heat from the horn at longer experimental duration. In order to reduce 
this effect, an external cooling coil was used. The temperature of the 
slurry was constantly monitored by means of a thermocouple. 
EXAMPLE 4 
This example was performed using a combination of electrical field effects 
(electrophoresis/electroosmosis) (E), ultrasonics (U) and a vacuum. The 
slurry was the same as that prepared earlier. Sample size was 50 g except 
as noted in Table IV. 
TABLE IV 
__________________________________________________________________________ 
E U E U ENERGY 
ENERGY 
VACUUM TEMP. 
TIME TIME POWER POWER TOTAL CORRECTED 
MOISTURE 
SAMPLE 
(CM. OF Hg) 
(.degree.C.) 
(MIN.) 
(MIN.) 
(WATTS) 
(WATTS) 
(WH) (WH) % 
__________________________________________________________________________ 
H.sub.2 O 
1 58.4 -- 2 4 100 62.5 7.50 5.84 16.5 
2 63.5 84 1.5 8.5 100 62.5 11.35 10.1 16.2 
.sup. 45.7up.a 
108 1.5 11.5 100 62.5 14.48 13.23 10.5 
4 61 78 1.5 3.5 50 62.5 4.89 4.26 14.8 
5 45.7 66 1.5 8.5 50 62.5 10.10 9.47 13.0 
6 55.9 -- 1.5 11.5 50 62.5 13.23 12.60 11.0 
7 66.0 33 1.5 3.5 50 62.5 4.90 4.27 19.0 
8 38.1 -- 1.5 3.5 50 62.5 4.90 4.27 21.3 
9 45.7 -- 1.5 5.0 50 62.5 6.46 5.83 18.9 
10 38.1 -- 1.5 8.0 50 62.5 9.58 8.95 13.0 
11 45.7 -- 1.5 11.0 50 62.5 12.70 12.07 13.7 
12 61.0 64 1.5 2.0 150 62.5 5.83 3.95 16.2 
13 61.0 81 1.5 3.5 150 62.5 7.40 5.52 18.7 
.sup. 14.sup.a 
61.0 105 1.5 7.0 150 62.5 11.04 9.16 8.9 
15 61.0 50 1.5 3.5 10 40 2.58 2.45 29.5 
16 63.5 54 1.5 8.5 10 40 5.92 5.79 19.6 
17 55.9 69 1.5 11.5 10 40 7.92 7.79 14.1 
18 -- -- 0.5 0.5 12.5 168 -- -- 30 
.sup. --8**.sup.b 
-- 0.71 
0.71 -- -- 2.143 2.07 30 
19 -- -- 1.0 1.0 12.5 168 -- -- 19.5 
.sup. --9**.sup.b 
-- 1.43 
1.43 -- -- 4.287 4.14 19.5 
20 45.7 -- [20 sec] 
1.0 [42] 25 0.83 0.83 30.4 
[40 sec] [16] 
.sup. 21.sup.c 
45.7 -- [10 sec] 
1.5 [64] 25 1.085 1.20 25.6 
[50 sec] [16] 
[30 sec] [8] 
.sup. 22.sup.d 
45.7 -- [10 sec] 
1.0 [15] 62.5 1.28 1.25 30.6 
[50 sec] [15] 
.sup. 23.sup.e 
50.8 -- [10 sec] 
2 [15] 62.5 2.92 2.89 27 
[110 sec] [7] 
__________________________________________________________________________ 
.sup.a Samples not used because of water loss due to high temperature. 
.sup.b All data corrected to 50 g. Sample size was 35 g for samples 18 an 
19. 
.sup.c 45 g sample corrected to 50 g. 
.sup.d 51 g corrected to 50 g. 
.sup.e 50.5 g corrected to 50 g. 
WH = watt hours 
The results of the combination of both electrical field and ultrasonics are 
shown in Table IV and FIGS. 2 and 4. The moisture concentration achieved 
in two minutes was about eighteen percent (18%) as opposed to about 
twenty-three percent (23%) by ultrasonics or about thirty-five percent 
(35%) by use of an electrical field. At comparable power inputs the same 
relationships were observed. For example the combination of electrical 
field and ultrasonics at 112.5 watts gave a liquid concentration of about 
fifteen percent (15%) while that for electrophoresis alone at 120 watts 
and ultrasonics at 160 watts was much higher. At comparable power levels 
the rate of dewatering is also much higher. 
FIG. 4 shows the variation of percent moisture content of the slurry or 
suspension versus energy consumed. The energy values for an electrical 
field alone and in combination have been corrected to reflect the 
reduction in energy used as the dewatering process proceeds. This 
correction has been made using a straight line approximation. The actual 
and corrected values are shown in the previous tables. 
To achieve similar amounts of dewatering in the samples the combination of 
an electrical field and ultrasonics gave much lower values than either 
method alone. For example at four watt hours, the percent moisture content 
in the presence of an electrical field is about thirty-five percent (35%) 
while in the presence of ultrasonics it is about twenty-six percent (26%). 
The combination of both techniques concurrently; however, gives a much 
lower moisture content of about nineteen percent (19%). 
These tables and figures show that the rate of dewatering, power 
consumption and ultimate solids content are superior for the combination 
of the techniques than the individual techniques. 
The data further indicates that optimum separation is obtained when the 
energy input from the electrical field and acoustical field are 
approximately equal. Thus Samples 15, 16, 17, 18, and 19 which have a much 
larger proportion of their energy input as ultrasonic energy initially 
give data similar to samples using only ultrasonics but gradually decrease 
to separation levels of the combination. Other samples, such as 1 through 
13, 20, and 21, where power levels for the two effects are more nearly 
equal give better results. Once knowing the teaching and advantages of the 
invention a person skilled in the art can readily determine the optimum 
power ratios to be used. 
Vacuum figures in Example 1, Samples 2, 3, and 4, Example 2, Samples 1 
through 6 and Example 4, Sample 8 were lower than those for the remainder 
of the data. This is not believed to affect the results of the 
experiments. A higher vacuum, above that used in the above cited samples 
will not give an increased dewatering rate or a final lower moisture 
content. 
Temperatures were measured for some of the samples with a thermocouple. 
Certain data points in the tables were not used in the graphs. These points 
exhibited higher temperatures in the slurry. It is believed their 
presentation would give unreliable or erroneous results for moisture 
content in that higher temperatures would cause water loss by 
vaporization. While a moderate temperature increase benefits the 
dewatering process as discussed earlier, excessive temperatures are 
generally avoided in that it is difficult to clearly demonstrate the 
significant differences of the process of utilizing a smaller amount of 
energy in dewatering coal with a combination of an electrical and 
ultrasonic field. Generally a temperature above 90.degree. C. is deemed 
excessive. 
Ceramic Slurry 
EXAMPLE 5 
A ceramic slurry was used for Example 5 with the results listed in Table V 
below. The ceramic slurry consisted of very fine clay particles in the 
order of 50-75 .mu.m in size. 
The ceramic slurry is further characterized by having an initial solids 
content of twenty-seven percent (27%). Sample sizes were approximately 100 
g. The voltage during electrophoresis was 50 volts for Samples 3-5 and 25 
volts for Samples 6-8. Frequency of the ultrasonic energy applied was 
20,000 Hertz. 
The procedure differed slightly from that in Examples 1-4 in that 
acoustical energy was not applied initially but only after the slurry had 
begun to form a cake. Water was thus initially removed by vacuum or a 
combination of vacuum and electrophoresis. Acoustical energy was not 
applied until after cake formation because it was noted that application 
of acoustical energy did not improve the dewatering rates until a cake had 
begun to form. This is because the acoustical energy is not needed until 
unbound water has been removed and/or the slurry particles begin to clog 
the filter. 
The figures given in Table V are those where it was determined that the 
dewatering rate had reached an asymptote and no further water could be 
removed. Table V lists the solids content using a vacuum (V) only (Sample 
1), a vacuum (V) and ultrasonics (U) (Sample 2), a vacuum and 
electrophoresis (E) (Samples 3-6) and a combination of a vacuum (V), 
electrophoresis (E) and acoustics (U) (Samples 7-8). 
TABLE V 
______________________________________ 
CERAMIC SLURRY 
Sample 
(cm Hg)Vacuum 
Hours)(WattE 
Hours)(WattU 
Hours)(WattTotalEnergy 
(Solids)PercentMoisture 
##STR1## 
______________________________________ 
1 38 -- -- -- 55 -- 
2 38 -- 4.17 4.17 54 -- 
3 38 5 -- 5 56 0.18 
4 38 4.17 -- 4.17 57 0.41 
5 38 3.75 -- 3.75 58 0.68 
6 38 3.17 -- 3.17 55.5 0.08 
7 38 2.23 3.33 5.57 64 1.24 
8 38 1.67 3.33 5.00 60 0.82 
______________________________________ 
TABLE VI 
______________________________________ 
SEWAGE AND ANTIBIOTIC SLUDGE 
Sample 
(cm Hg)Vacuum 
Hours)(WattE 
Hours)(WattU 
Hours)(WattTotalEnergy 
(Solids)PercentMoisture 
##STR2## 
______________________________________ 
1 38 -- -- -- 25.7 -- 
2 38 3.60 -- 3.60 36 0.59 
3 38 5.67 -- 5.67 34 0.32 
4 38 5.5 5 10.5 45 0.31 
______________________________________ 
WH = watt hour 
It is apparent from Table V that by the use of a combination of 
electrophoresis and acoustics a higher total solids content can be 
achieved. Further, the same energy levels give a higher solids content for 
the combination of electrophoretic and acoustic means over either alone. 
Finally, for incremental water removal W.sub.R, each milliliter of water 
removed for the combination required less energy than the use of either 
electrophoretic or acoustic means alone. In fact, ultrasonics alone was 
detrimental in that it did not improve dewatering characteristics. 
Samples 7 and 8 use a level of ultrasonic energy about double that for 
electrophoresis, it is to be expected that this higher level of ultrasonic 
energy would reduce the dewatering effectiveness over that where the 
energy levels are approximately equal. 
W.sub.R is calculated by dividing the additional water removed, over that 
by vacuum alone, by the total energy used. This method is applicable to 
other materials with characteristics similar to ceramic slurries. 
Sewage and Antibiotic Sludges 
EXAMPLE 6 
The materials used here represented a mixture of sewage sludges and 
antibiotic sludges (fermentation sludges). The antibiotic sludges are 
those typically produced by fermentation processes in the pharmaceutical 
industry. For this example, the antibiotic sludges had been mixed with 
typical sewage sludges. Initial solids concentration in the sludges was 
four percent (4%) and sample size was 50 g. The frequency used for 
acoustical energy was 20,000 Hertz. The voltage for electrophoresis was 50 
V. Except for Sample 2 which was 25 V. As in Example 5 ultrasonic energy 
was not applied until the sludge had begun to form a cake. 
In Examples 5-8 the pH of the materials was monitored and was noted to 
increase slightly during the dewatering process. The material was adjusted 
to low, neutral, and high pH at the start of the dewatering process. From 
this it was determined that best results were obtained when the initial pH 
was about 7.0. 
Table VI lists results for vacuum (V) (Sample 1) vacuum and electrophoresis 
(E) (Samples 2-3) and the combination vacuum, electrophoresis (E) and 
ultrasonics (U) dewatering (Sample 4). The figures given are those where 
it was determined that the dewatering rate had reached an asymptote and no 
further water could be removed. 
In this example ultrasonic data is not listed since no dewatering was 
obtained with a vacuum and ultrasonics alone. The combination of vacuum, 
electrophoretic, and ultrasonic dewatering means gave a higher total 
solids content than either electrophoretic or ultrasonic means, also the 
same energy levels would give a higher solids content for the combination 
of electrophoretic and acoustic means over either alone. Finally, for 
incremental water removal W.sub.R, each milliliter of water removed for 
the combination required less energy than either electrophoretic means or 
ultrasonic means alone. 
This method is applicable to waste activated sludges, anaerobic and 
secondary sludges as well as microbial sludges obtained by fermentation 
processes. 
Protein Hydrolysate 
EXAMPLE 7 
A protein hydrolysate sludge (containing the valuable product in the 
supernatant) was used for Example 7 that is typical of products obtained 
from digestion of for example soybean meal. The product contains a complex 
mixture of proteins and polysaccharides. The hydrolysate suspension is 
characterized by an initial suspended solids content of fifteen percent 
(15%). Sample size is approximately 50 g. The voltage during 
electrophoresis is listed in Table VII. Frequency of the ultrasonic energy 
applied was 20,000 Hertz. As in Example 5 ultrasonic energy was not 
applied until the hydrolysate had begun to form a cake. 
The figures listed in Table VII are those where it had been determined that 
the dewatering rate had reached an asymptote and no further water could be 
removed. Table VII lists the solids content using a vacuum (V) only 
(Samples 1 and 2), a vacuum and ultrasonics (U) (Sample 3), a vacuum and 
electrophoresis (E) (Samples 4 and 5), and a vacuum and the combination of 
electrophoresis (E) and ultrasonics (U) (Samples 6-8). CaCl.sub.2 was 
added to the suspension to improve the dewatering characteristics but had 
no noticeable effect. There is some evidence in the literature that 
calcium ions bind to the proteins and might release the water bound 
between the protein chains. 
It is apparent from the data in Table VII that by the use of a combination 
of electrophoresis and acoustics a higher total solids content can be 
achieved. Further, the same energy levels give a higher solids content for 
the combination than either electrophoresis or ultrasonics alone would. 
Finally, for incremental water removal W.sub.R, each milliliter of water 
removed for the combination required less energy than the use of either 
electrophoretic or acoustic means alone. In fact, the use of ultrasonic 
means alone was detrimental in that it did not improve the dewatering 
characteristics. 
Samples 6 and 7 that use much higher levels of ultrasonic energy show 
reduced dewatering efficiency over that of Sample 8 where the energy 
levels for electrophoresis and ultrasonics are more equal. 
TABLE VII 
__________________________________________________________________________ 
PROTEIN HYDROLYSATE 
Sample 
(cm Hg)Vacuum 
VoltsE 
Hours)(WattE 
Hours)(WattU 
(Watt Hours)Energy Total 
(Solids)PercentMoisture 
##STR3## 
__________________________________________________________________________ 
1 38 -- -- -- -- 50 -- 
2 38 -- -- -- -- 51 -- 
3 38 -- -- 8.33 
8.33 31.9 Negative 
4 38 1 0.125 
-- 0.125 53.2 12.1 
5 38 5 1.04 
-- 1.04 53 1.34 
6* 38 3.5 
0.245 
2.917 
3.16 61 1.62 
7* 38 3.5 
0.546 
3.333 
3.88 62 1.42 
8 38 10 0.375 
0.50 
0.875 61.4 6.03 
__________________________________________________________________________ 
*CaCl.sub.2 added. 
WH = watt hour 
It is noted that the efficiency of water removal as shown by W.sub.R is 
very high for Sample 4 with a value of 12.1 ml removed per watt hour. 
However, a level of only 53.2% solids could be reached; making the use of 
electrophoresis alone not much better than the use of a vacuum only. It is 
expected that the combination of electrophoretic and ultrasonic means 
would give still higher efficiencies when the material is only dewatered 
by 2-3% as in Sample 4. Since each further milliliter of aqueous product 
(protein) removed requires more energy than the previous one, the 
efficiency values will be lower for a solids content of about sixty 
percent (60%) compared to a final solids content of about fifty percent 
(50%). 
Diatomaceous Earth-Oil Suspensions 
EXAMPLE 8 
A suspension of diatomaceous earth particles (similar to clay) in soybean 
oil was used for Example 8. Various samples for this system are listed in 
Table VIII below. The suspension consisted of Celite 503 particles 
obtained from J.T. Baker Chemical Co. The suspension is typical for that 
obtained from diatomaceous earths or clays. The suspension is further 
characterized in having an initial solids content of thirty percent (30%). 
Sample sizes were approximately 50 grams. The voltage during 
electrophoresis was approximately 600 volts. Frequency of the ultrasonic 
energy was approximately 20,000 Hertz. 
The procedure was to apply ultrasonic energy after initial application of 
electrical energy for reasons stated earlier that the combination is not 
needed until unbound liquid is to be removed. The results show that the 
combination of both fields gave a higher average amount of oil removed 
than either field alone or with vacuum only. The results are not so 
dramatically different since it appears that the 30:70 clay:oil ratio gave 
too high of an amount of initial free oil. 
TABLE VIII 
__________________________________________________________________________ 
DIATOMACEOUS EARTH (CLAY):OIL SUSPENSION 
E U E + U 
E U ENERGY ENERGY ENERGY 
ML 
VACUUM TIME 
TIME 
(WATT (WATT TOTAL OF OIL 
SAMPLE 
(CM. OF Hg) 
(MIN.) 
(MIN.) 
MINUTES) 
MINUTES) 
(WM) COLLECTED 
__________________________________________________________________________ 
8-1* 7 -- -- -- -- -- 12.5 
8-2 7 10 4 0.84 40 40.84 13.4 
8-3 7 0 4 0 40 40. 12.9 
8-4 7 15 0 0.66 0 0.66 14.5 
8-5 7 10 0 0.4 0 0.4 11.8 
8-6 7 15 5 0.53 50 50.53 14.5 
8-7 7 12 5 0.4 100 100.4 14.7 
__________________________________________________________________________ 
Sample size: 50 gram total; clay:soya oil ratio 30:70. 
*Vacuum only (20 min.) 
WM = watt minutes 
TABLE IX 
__________________________________________________________________________ 
DIATOMACEOUS EARTH (CLAY):OIL SUSPENSION 
E U 
E U ENERGY ENERGY ENERGY 
ML 
VACUUM TIME 
TIME 
(WATT (WATT TOTAL OF OIL 
SAMPLE 
(CM. OF Hg) 
(MIN.) 
(MIN.) 
MINUTES) 
MINUTES) 
(WM) COLLECTED 
__________________________________________________________________________ 
9-1* 7 -- -- -- -- -- 1.7 
9-2 7 25 0 0.3 0 0.3 4.2 
9-3 7 0 3 0 30 30 1.2 
9-4 7 0 3 0 60 60 1.3 
9-5 7 0 25 0 250 250 3.5 
9-6 7 3 3 0.06 60 60.06 3.9 
9-7 7 3 3 0.07 30 30.07 4.7 
9-8 7 3 3 0.04 60 60.04 3.9 
9-9 7 10 10 0.3 200 200.3 5.8 
9-10 7 25 25 0.45 500 500.45 
8.3 
__________________________________________________________________________ 
Sample size: 30 gram total; clay:soya oil ratio 40:60. 
*Vacuum only (25 min.) 
WM = watt minutes 
EXAMPLE 9 
The experiment was repeated as in Example 8 except that a solid:oil ratio 
of 40:60 was used. The sample size was also reduced to 30 grams. Results 
are shown in Table IX. The higher amount of solids in the samples resulted 
in a greater amount of bound liquid in the sample thus demonstrating the 
effect more clearly than the previous example. 
Sample 9-1 was done with a vacuum only and gave the least recovery. 
Intermediate recovery was obtained by an electric or ultrasonic field 
alone. Best results were obtained for the combined fields. 
The greatest advantage of the invention, in addition to higher efficiency, 
is the much higher separation of liquid from solids resulting in a much 
more valuable product or recovering more product that had previously been 
lost. 
This method is applicable to food products where thermal techniques cannot 
be used due to heat sensitivity and where valuable products are left in 
the filter cake. Efficient recovery of the supernatant is possible by this 
technique. The method is further applicable to materials with 
characteristics similar to those discussed in the text and examples. 
EXAMPLE 10 
An experiment similar to the previous examples was tried except that a 
nonpolar hydrocarbon, tetralin, was used for the liquid and carbon black 
for the suspended solid. These two materials are particularly hard to 
separate. A solid:liquid ratio of 12:88 was used. Sample size was 35 grams 
and all samples were treated for 30 minutes. The results are shown in 
Table X. Sample 10-1 was treated with a vacuum only and separated only 
10.3 ml of tetralin from the carbon black. An electrical field and 
ultrasonic field used on Samples 10-2 and 10-3 removed only 6.0 and 8.5 ml 
respectively. The combined fields; however, removed 16 ml., a 
significantly higher amount of tetralin. 
TABLE X 
__________________________________________________________________________ 
CARBON BLACK:TETRALIN SUSPENSION 
E U 
E U ENERGY ENERGY ENERGY 
ML OF 
VACUUM TIME 
TIME 
(WATT (WATT TOTAL TETRALIN 
SAMPLE 
(CM. OF Hg) 
(MIN.) 
(MIN.) 
MINUTES) 
MINUTES) 
(WM) COLLECTED 
__________________________________________________________________________ 
10-1* 
5 -- -- -- -- -- 10.3 
10-2 5 0 30 0 600 600 6 
10-3 5 30 0 2.04 2.04 8.5 
10-4 5 30 30 0.36 600 600.36 
16 
__________________________________________________________________________ 
Sample size: 35 gram total; tetralin:carbon ratio 88:12. 
*Vacuum only (30 min.) 
WM--- watt minutes 
Examples 8, 9 and 10 employing diatomaceous earth (clay):oil and carbon 
black:tetraline suspensions confirm that the method is applicable to polar 
and nonpolar, aqueous and nonaqueous, organic and inorganic liquids and 
mixtures thereof. 
Examples 1-7 relate to solid-aqueous suspensions while Examples 8-10 relate 
to nonaqueous suspensions. The drawings, FIG. 2-4, illustrate the 
advantages of the aqueous systems. The advantages revealed by these 
figures are obtained by the nonaqueous suspensions also as revealed in 
Tables VIII, IX, X. 
While the forms of the invention herein disclosed constitute presently 
preferred embodiments, many others are possible. It is not intended herein 
to mention all of the possible equivalent forms or ramifications of the 
invention. It is to be understood that the terms used herein are merely 
descriptive rather than limiting, and that various changes may be made 
without departing from the spirit or scope of the invention.