Method for separating intermixed solids and liquids

A mixture containing solid and liquid components is saturated with a polyelectrolyte compound, over-flocculating the solids contained therein and causing the solids to coalesce into masses or globules. These coalesced masses may then be separated from the liquid component, yielding substantially separated phases.

BACKGROUND OF THE INVENTION 
This invention relates generally to methods and apparatus for separating 
intermixed solids and liquids, and more specifically relates to methods 
and apparatus for separating industrial wastes into solid and liquid 
phases to facilitate the disposal or recycling of each phase. 
Three principal methods of disposing of waste matter are disposal within 
injection wells, disposal within land fills and incineration. In injection 
well disposal, liquid waste is pumped into relatively porous rock 
formations which are bounded by relatively non-porous formations such that 
the liquid within the porous formation is retained within that formation 
and is restrained from migration into other formations and/or fluid 
reservoirs. It will be readily appreciated that because the liquid waste 
is pumped into a rock formation, such as porous limestone, the liquid must 
be truly liquid, containing little or no particulate matter which would 
act to occlude the pores within the formation. This then may, in some 
cases, require that the liquid contain less than roughly one hundred parts 
per million ("ppm") of solid or particulate matter and may further require 
that such particulate matter be of less than roughly two-to-five microns 
in size, dependent upon the porosity of the formation in which the liquid 
is to be injected. 
In land fill disposal, a pit is formed and a liner of either earthen 
matter, such as clay, or a synthetic material, such as plastic, is placed 
within the pit to retain all of the matter disposed therein. Environmental 
concerns and legislation reflecting those concerns requires that only 
solid matter be disposed of within land fills so as to avoid any leakage 
of contaminated waste should a break or tear occur within the liner. A 
conventional technique of preparing waste containing liquid components for 
disposal is to mix a liquid adsorbing compound such as flyash or portland 
cement with the waste to adsorb the liquid and render the waste into a 
safely disposable solid. Obviously, the greater the liquid component 
within the waste, the more liquid-adsorbing compound which will be 
required to solidify the waste. This presents two significant problems; 
first, the cost of the compound, and second, the greater mass of solid 
waste to be disposed of. Because of the cost and limited volume of the 
land fill site, any increase in waste volume has a significant impact upon 
disposal costs. It is not unrealistic to increase the volume of waste to 
be disposed of by a factor of three by the time a sufficient amount of 
adsorbent compound has been added to adsorb a significant liquid phase 
within the waste matter. 
In some cases, such as where organic solids are retained within the liquid, 
separation of the liquid from the solids may facilitate the disposal of 
the waste solids by incineration. It will be readily appreciated that the 
liquid content of the solids, as well as the composition of the solids, 
will be a major factor in the feasibility of disposal of the waste matter 
by incineration. 
Accordingly, the present invention provides method and apparatus whereby 
solid and liquid waste products may be substantially separated from one 
another with a minimal increase in volume of disposable waste. 
SUMMARY OF THE INVENTION 
The present invention provides a method and apparatus for separating a 
mixture containing both solid and liquid phases. This invention is of 
particular usefulness in separating solid and liquid phase components of 
industrial wastes to facilitate the recycling or disposal of such 
components. In a preferred embodiment, a polyelectrolyte compound is 
introduced into the waste matter in such proportions as to over-flocculate 
the solids therein. The solids are over-flocculated such that they 
coalesce into globules or masses which may then be separated from the 
remaining liquid phase. This separation may be achieved by use of an 
appropriately sized vibrating screen mesh. In such a preferred embodiment, 
the liquid from which the solids have been removed is returned to the 
untreated waste, thereby serving to remove excess polyelectrolyte from the 
liquid and promoting the coalescing of the solids in the waste prior to 
further treatment thereof.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings in more detail, particularly to FIG. 1, 
therein is schematically illustrated a system for separating solids from 
liquids in accordance with the present invention. As will be apparent from 
the discussion to follow, not all components illustrated in FIG. 1 are 
required for the practice of the present invention but are shown as 
forming an optimal system for many applications of the present invention. 
Reservoir 10 represents the pond or tank in which the waste products have 
been retained awaiting treatment and disposal. As stated earlier herein, 
these waste products typically have both solid and liquid components. It 
will be appreciated that these solids may be of such small size as to be 
individually invisible to the naked eye and of such small mass as to be 
consistently held in suspension within the liquid. At the other extreme, 
the solids may be present in such concentrations as to cause the waste 
matter to assume a mushy or semi-fluid character, commonly known as a 
"sludge," for example, in waste matter containing 30-50% solids by dry 
weight. An important and novel feature of the present invention is the 
over-flocculating of the waste matter with a polyelectrolyte, preferably a 
long-chain, high molecular weight polymer compound and most preferably a 
high molecular weight polymer emulsion. The polymer may be of one of three 
types reflecting a state of electrical charge; cationic, anionic, or 
non-ionic. The polymer must be chosen in response to the charge of the 
solids within the sludge. It has been found that optimal efficiency in 
determining the correct polymer in a specific application may be obtained 
by simple empirical experimentation upon samples taken from the reservoir. 
A sample of polymer is mixed with a sample of the waste matter, the 
polymer typically being added to the waste matter in the proportion of 
approximately 200 to 1,000 ppm, though this range may vary significantly 
at each extreme, potentially extending proximate 5,000 ppm. In this 
experimentation, it will be apparent that one charge-type of polymer is 
effective or most effective in drawing the waste solids together. The 
desired effect is that the solids be drawn together into gelatinous masses 
or globules. Once the correct charge polymer is determined, if the first 
polymer of that charge does not yield gelatinous masses of optimal size or 
stability then other polymers of that charge may be experimented with. An 
appropriate gauge for this initial test for the size and stability of the 
coalesced, over-flocculated solids is whether a substantial portion of the 
solids will be retained by screen of thirty five mesh or larger (all 
screen sizes referred to herein are Tyler Standard Screen Scale). Although 
some solids, such as some sands, have been found not to react with the 
polymers to form the desired masses, the vast majority of waste solids 
found in industrial waste should be treatable with this method. Two 
polymers which have been found to be particularly suitable for usage with 
the present invention in many applications are long-chain polyacrylamides 
such as those sold under brand names Tretolite TFL 362 (cationic) and 
Tretolite TFL 381 (non-ionic) manufactured by the Petrolite Corporation, 
Tretolite Division, 369 Marshall Avenue, Saint Louis, Missouri. These 
polymers are emulsions which, as stated previously herein, is the 
preferred form for usage with the present invention, the high molecular 
weight of these emulsions enhancing the formation of relatively large 
gelatinous masses and also being optimally cost effective. 
Once the polymer is chosen and the approximate dose rate determined, the 
treatment of the waste in bulk may begin. In an intended operation in 
accordance with the present invention, waste matter is pumped from 
reservoir 10 by pump 12 into surge tank 14. Because reservoir 10 may be 
very large, having a capacity well in excess of a million gallons, and 
because of the difficulties often encountered in pumping from such a large 
reservoir, including possibly operating such pumping operation from a 
floating platform, surge tank 14 is utilized to provide a constant supply 
of waste matter to the remainder of the processing apparatus. This 
constant supply of waste matter prevents the potential need to shut down 
the processing system if temporary difficulties are encountered in pumping 
from reservoir 10. 
A pressurized air supply, depicted as pump 16 and conduit 18, is preferably 
provided to fluidize or to circulate the waste matter by air sparging, 
thereby promoting fluidity of the waste and the suspension of the waste 
solids within the liquid at least in the vicinity of the pumping intake. 
This air sparging facilitates the pumping operation and promotes a roughly 
consistent, or at least slowly fluctuating, proportional mixture of the 
two components so as to minimize the necessity for adjustment of the 
polymer dose rate as will be discussed later herein. An air pressure in 
the vicinity of 50 pounds per square inch ("psi") has been found 
satisfactory to cause the desired fluidization or circulation in many 
industrial wastes. In some applications, it may be desirable to maintain 
some form of fluidizing or circulating element, such as the 
above-described air sparging, in the surge tank as well, for reasons 
similar to those stated above. 
Where the waste matter contains very large pieces of solids which may be 
easily separated from the liquid, it may be desirable to strain such 
pieces from the waste matter prior to further treatment. A preferred 
method for this would be by straining the matter through a conventional 
screen element having a relatively coarse mesh. The selection of the 
screen mesh size would be a matter of choice readily apparent to one 
skilled in the art. Such coarse screen should freely pass the liquid and 
suspended solids, separating only the larger solids. A pump 22 may be used 
to pump the waste matter from surge tank 14 to coarse screen 20. Separated 
solids will be directed to solids box 24 while the remaining waste matter 
will be directed or pumped to mixing conduit 26. It is in mixing conduit 
26 that the waste will be treated with the polymer previously determined 
in the manner described herein. 
Prior to mixing the polymer and the waste matter, it is highly preferable 
to dilute the polymer with a suitable carrier, typically water. Therefore, 
a mixer 28 is provided to facilitate this mixing. Mixer 28 may be of 
several forms known to the art, such as those known as static mixers. 
Advantageous results have been achieved with a mixer formed of a length of 
pipe, preferably roughly one to one and one-half inches in internal 
diameter, having a flow-disturbing medium disposed longitudinally therein. 
A length of ordinary link chain secured within the length of pipe at the 
upstream end thereof has been found to be highly satisfactory as the 
flow-disturbing medium in mixer 28. 
The polymer will be introduced into the waste matter at a varying rate, 
such rate ranging from extremes as low as a few drops per minute to as 
high in the described embodiment as one-half gallon per minute. In the 
particular embodiment illustrated, an atmospherically sealed polymer 
holding tank 30 containing a quantity of the polymer is pressurized by 
compressed air. Compressed air may be supplied by a second compressor pump 
32 as depicted in FIG. 1, or, alternatively , may be supplied by the first 
compressor pump 16 providing air for inducing circulation in reservoir 10. 
It is to be understood that appropriate valves and pressure regulation may 
be placed on the compressed air supply or supplies as needed or desired in 
accordance with techniques familiar to the art. A valve 34 may then be 
utilized to control the flow rate of the polymer into mixer 28. Similarly, 
a valve 36 may be placed in the water supply line to regulate the flow 
rate of water into mixer 28. It will be noted that the flow rate of water 
is not so critical as is the polymer flow rate and may remain generally 
constant while the polymer flow rate is varied significantly to achieve 
the desired over-flocculation of the waste solids, to be further described 
later herein. 
A conduit 38 is then used to transport the polymer mixture to mixing 
conduit 26. Mixing conduit 26 is of adequate size to adequately carry a 
volume of the waste matter while allowing circulation thereof. A mixing 
conduit 26 of approximately three inches internal diameter has been found 
to be satisfactory in many applications. Pump 40 is used to move the waste 
matter from the tank of coarse screen 20, through mixing conduit 26, to 
separator 42. The flow rate of the waste matter through mixing conduit 26 
may vary drastically but may be on the order of 70 to 150 gallons per 
minute. As the waste matter passes through mixing conduit 26, the polymer 
mixture is induced into the mixing conduit 26. The waste matter is 
over-saturated with the polymer mixture so as to over-flocculate the 
solids therein, causing the solids to coalesce to form gelatinous masses 
as discussed earlier herein. Although a rough dose rate of polymer to 
waste matter may be determined through the pre-treatment testing, the 
over-flocculation should be visually observed to adjust the polymer dose 
rate as necessary. The polymer dose rate should be high enough that the 
gelatinous masses formed are of such size and stability as to be retained 
by separator 42 while the liquids freely pass therethrough. It will be 
appreciated that in applications involving significant solids content 
within the waste, the coalesced solids may assume the general appearance 
of a sludge. At the other extreme, generally, if the liquid assumes a 
milky or cloudy appearance, the dose rate of polymer is too high and 
should be reduced. 
A significant factor in the separation operation is at what point the 
polymer is introduced into the waste material. The polymer mixture must 
have an opportunity to mix with the waste matter and the solids must have 
an opportunity to coalesce before the waste matter reaches separator 42. 
This again is best determined empirically, the optimal point of 
introduction varying with such factors as the material components and 
their relative proportions within the waste matter, the flow rate of the 
waste through mixing conduit 26, the particular polymer being used, and 
the degree to which such polymer is dilluted. 
The over-flocculation described is far in excess of the flocculation which 
would be induced if the solids were to be treated by conventional 
techniques such as conventional clarifier usage. Conventional polymer use, 
such as to clarify liquids, typically recommends a dose rate on the order 
of 10 ppm to 50 ppm. Over-flocculation in accordance with the present 
invention may involve a ratio of polymer to untreated waste a hundred 
times higher than that encountered with such conventional techniques. 
Further, solids flocculated in such conventional manner form very small 
bodies, typically on the order of 0.031 to 0.062 inches in diameter. 
Solids over-flocculated in accordance with the present invention are 
preferably treated to form masses from 0.5 inches in diameter on up. 
Once the solids have been coalesced into the described gelatinous masses, 
they are easily separated from the liquid waste by separator 42. Separator 
42 is preferably a conventional screen and most preferably is a vibrating 
screen having a suitably sized mesh to retain the masses while passing the 
liquid. A screen of 20 meshor larger is typically satisfactory for this 
purpose. A vibrating screen offering sixteen feet of straining surface has 
been found satisfactory in a system having dimemsions as given in this 
exemplary description of one preferred embodiment, although it is obvious 
to one skilled in the art that screens of many different sizes may be used 
and that the screen dimensions may be adapted to suit the particular 
application. It is foreseen that other forms of solid/liquid separators 
which are known to the art could be used in accordance with the present 
invention or could be adapted for such use, however, the described 
vibrating screen has been found highly effective and advantageous. It is 
emphasized that the relatively small bodies produced by conventional 
flocculating techniques as described earlier herein are typically unstable 
and will separate or deform to pass through a vibrating screen mesh, even 
with a screen of 35 mesh, such mesh having orifices proximate 400 microns. 
Conversely, the masses formed through practice of the present invention 
are not only larger but much more stable and facilitate the use of a 
vibrating screen having a screen of 10 to 20 mesh, such screens having 
orifices of from approximately 600 to 800 microns. In some applications, 
even larger screens may be used. These larger screens facilitated by the 
over-flocculating of the solids as described herein serve to maintain a 
free flowing path for the liquid through the screen and therefore promote 
optimal treatment rates in excess of those obtainable with comparable, 
conventional systems. 
The solids separated by separator 42 are passed over chute 44 to solids box 
24 while the fluid is preferably pumped to a holding tank 46. A small 
amount of the fluid typically will not pass through the screen but will 
travel over the screen and pass with the solids into solids box 24. Any 
such liquid may be easily decanted from solids box 24 and transferred to 
tank 46 by a pump 48. The solids within solids box 24 may be transferred 
for disposal, requiring, after the described treatment, relatively 
minimal, if any, addition of adsorbent compound to render them 
satisfactory for land fill disposal. 
The treated fluid within tank 46 will often contain some excess polymer. It 
is therefore advantageous to transfer this treated liquid by means of a 
pump 50 and conduit 52 back into either reservoir 10 or surge tank 14. 
This removes the excess polymer from the liquid and allows the polymer to 
concentrate the solids within the untreated waste prior to any further 
treatment of the waste as described herein. When the liquid is recycled in 
this manner, and the excess polymer removed therefrom, then clean liquid 
may often be decanted from the surface of reservoir 10, as by pump 56 and 
conduit 58. This clean liquid may then be transferred for disposal or 
recycling. It is preferable in such a recycling and decanting operation to 
return the liquid to the reservoir at a location intermediate the pumping 
and decanting locations, which are preferably located proximate opposite 
extremes of reservoir 10. This prior treatment of the waste allows a 
reduction in the amount of polymer which must be introduced into the waste 
matter in mixing conduit 26. This recirculation of the treated liquid 
therefore serves not only to further remove excess polymer from the liquid 
but yields optimum economic efficiency by reducing the volume of fresh 
polymer required for the operation. 
Either before or after such recycling of the treated liquid, the liquid may 
be transferred to disposal or plant recycling. 
It has been found that with proper operation of a system as described 
herein, where the liquid phase is to be recycled or put to another use, 
that the volume of waste to be disposed of may be reduced by approximately 
50 to 75%, such reduction yielding disposable solids which are 
approximately 20 to 30% solids by dry weight. Simultaneously, the 
separated liquid phase, which may be recycled or disposed of as 
appropriate, may be separated to such extent that it contains less than 
approximately 10 to 100 ppm solids. These contents are of the liquid as in 
tank 46 and the solids as in solids box 24, i.e., prior to any filtration. 
Further, a system having dimensions as described herein has been found 
capable of treating roughly 700-1,200 barrels of waste matter per day. 
Further, a specific advantage of the present invention is that an 
apparatus as described herein and depicted in FIG. 1 and capable of the 
above-stated treatment rates may be easily contained upon one or more 
trucks or trailers and thus may be transported from site to site in a 
manner not readily obtainable with conventional systems of such processing 
capabilities. 
Many modifications and variations besides those specifically mentioned may 
be made in the techniques described herein as depicted in the accompanying 
drawings without departing substantially from the concept of the present 
invention. For example, apparatus of significantly different size and/or 
capacities may be employed in accordance with the present invention. 
Further, the individual components as described herein may be arranged or 
modified so as to alleviate the need for some pumps or other apparatus 
disclosed herein. Accordingly, the descriptions given herein are exemplary 
only and are not intended as limitations on the scope of the present 
invention.