Note: Descriptions are shown in the official language in which they were submitted.
` 1~93Z~9
Specification:
_
This invention relates to an improved method and
apparatus for floating particulates from wastewater.
The use of small diameter bubbles to float impurities
from a wastewater has been known as a valuable tool in reducing
the level of particulates in municipal and industrial waste-
waters. For example, in the Ramirez, U.S. Patent
No. 4,012,319, issued March 15, 1977, there is
disclosed the use of a decreasing gradient of
bubble densities to float particulates. This patent
also recognizes that most wastewaters, especially
those from meat treating operations or edible oil plants,
have one common characteristic which must be overcome in
clarifying these wastewaters. These wastewaters contain
suspended, charged particulate matter which will not settle
out on their own even if allowed to stand for months on end.
These particulates usually carry an electrostatic charge,
and it is recognized that in order to coalesce these
particulates, their charge must be substantially reduced.
In publications such as Komline et al, U.S. Patent
No. 3,723,712 and Carlson, U.S. Patent No. 3,594,313, negatively
charged wastewater particles are reduced to particles having
approximately zero charge by adding to the wastewater quantities
of coagulants that provide positive charges, such as metal
chlorides, sulfates or salts. It is also known, for example
from these two patents, that optimum particle charge reduction
is accomplished when the zeta potential of the wastewater is
adjusted and maintained near a zero value. Generally, in
these publications the metal coagulants serve to neutralize
the charge on the particles and then to coalesce them. It
is also known that these coalesced particles will form a
buoyant floc when brought into contact with small bubbles.
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1~ ~ 3 Z ~ 9
The buoyant floc may then be removed from the surface of the thus
clari~ied wastewater. These floc that are removed may be re-
ferred to as skimmings. It has been found that systems that
use significant amounts of metal coagulants are hampered in
their effectiveness by the formation of large amounts of metal
hydroxides that are collected in the skimmings. These metal
hydroxides unfortunately bind not only the particulates but
also substantial quantities of water so that the skimmings con-
tain about 95 percent water, meaning that the solids content
of the skimmings is especially low. These binding properties
also tend to increase the effort needed to "render" the
skimmings when it is desired to recover valuable materials such
as minerals, proteins, fats and oils present in the raw waste-
water. Metal coagulants also tend to taint the recovered
materials with residue from the metal coagulants and result
in recovered products that have an undesirable color.
Also, the use of metal coagulants produces a relative-
ly large volume of skimmings, on the order of 2 to 5 volume
percent of the wastewater treated. Likewise, the metal coagu-
lants themselves are particulate matter which add to the totalsuspended solids content of the wastewater. Another disadvan-
tage is that the cost of metal coagulants is high when compared
with the cost of non-coagulant inorganic acids or bases.
It has now been determined that acceptable wastewater
clarification can be accomplished on certain types of waste-
waters by adjusting the streaming potential thereof to near
zero by means of a non-coagulant, thereby lessening the
difficulties encountered when metal coagulants are used.
It has also been determined that, quite unexpectedly,
an embodiment of the method and apparatus of this invention
can cause significant reduction in the content of ions in
wastewaters by transferring significant amounts thereof into
1~93Z;~9
the skimmings. While it is believed that this phenomenon
itself had been at work, unrecognized, in systems of the
type disclosed in said U.S. Patent No. 4,012,319 and
in U.S. Patents No. 3,959,131, No. 3,969,245, and No.
3,975,269, this particular embodiment of the present invention
accomplishes even better ion removal than that of these systems.
Accordingly, an object of this invention is an
improved method and apparatus for removing appreciable
quantities of charged particulates from a wastewater while
using no metal coagulants to form a buoyant floc that is
readily renderable, of increased solid to liquid ratio, and
of reduced relative volume.
It is a further object of the invention to provide
an improved method and apparatus to clarify wastewaters by
means of forming buoyant floc having improved color and odor
properties.
One other object of this invention is an improved
method and apparatus for clarifying wastewater by separating
out buoyant floc containing a large percentage of particulates,
while maintaining the volume of floc formed and collected
below 2 volume percent of the wastewater treated.
An object of one embodiment of this invention is
the provision of an apparatus and process that accomplishes
significant reductions in the content of certain adsorbable
ions in wastewater simultaneously with the removal of parti-
culates.
This invention is an improved method and apparatus
for clarifying wastewaters by flotation. A flow of wastewater
containing charged particulate matter is adjusted to near
its zero streaming potential value by adding a non-coagulant.
The adjusted wastewater flow is then directed to a confined
location containing dense quantities of small bubbles.
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The overflow from the confined location enters a flota-
tion zone having a partially baffled flow and also a
quiescent zone at its downstream end~ Positioned above both
the confined location and the flotation zone is a floc
removal means, the clarified wastewater exiting downstream
of the quiescent zone. In one embodiment, these features
are combined with forming the bubbles by eIectrolytic
decomposition of water to accomplish an improved simultaneous
passage of ions from the wastewater into the floc.
Additional objects, if not set forth specifically
herein, will be readily apparent to those skilled in the art
from the detailed description of the invention which follows
and from the drawings in which:
FIGURE 1 is a plot of streaming detector readings
against turbidity.
FIGURE 2 is a plot of streaming detector readings
against hexanes analyses.
FIGURE 3 is an elevation view of the preferred
apparatus of this invention.
FIGURE 4 is a plan view of the preferred apparatus.
FIGURE 5 is a bar graph representation of the
tests reported in Example IV.
The method of this invention accomplishes the
removal of charged particulates from a flow of wastewater.
The wastewater to be treated is mixed with a quantity of a
non-coagulant to adjust the streaming potential to near zero.
The thus adJusted wastewater flows into a confined location
wherein it is combined with a dense supply of small bubbles
that form buoyant gas-particulate composites. The wastewater
and composites then flow together upwardly and over an
impermeable barrier and into a baffled long flotation zone.
The flotation zone preferably provides a steady gradient
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supply of bubbles, with the greatest quantity of bubbles in
the flotation zone being provided adjacent the barrier. The
bubble supply quantity gradually diminishes toward the
downstream portion of the flotation zone, culminating in
the quiescent zone. A clarified wastewater exit communicates
with the quiescent zone. Meanwhile, a buoyant floc is formed
along the top surface of both the confined zone and the
long flotation zone. The floc is directed along said
surface toward the confined location, after which it is
removed and collected.
The preferred method clarifies waters that have in-
soluble or insolulizable charged particulates. It is particu-
larly suitable for packinghouse and meat processing wastewaters,
especially beef and pork operations, that contain protein, fat
and oil particulate materials which carry a measurable charge.
Generally, wastewaters having a particulate content that is
highly emulsified will not be successfully clarified by this
invention. For example, attempts to use this invention to
clarify both commercial laundry and tannery wastewaters having
a high surfactant content have not been successful. This
process is also particularly suitable for insolubilizing and
removing dissolved heavy metals, especially from waters used
during the beneficiation of metallic ores. Typically, fats
and oils particulates and ore beneficiation waters will have a
negative streaming potentialO Protein particulates will tend
to exhibit a positive streaming potential. Almost all waste-
waters have a net zeta potential that is negative. It has
been found that when a mineral acid is added to a water having
insoluble charged particulates, it is brought to approximately
zero streaming potentialO The preferred mineral acid is sul-
phuric acid. Other suitable mineral acids include hydrochloric
acid. A wastewater that might have a net streaming potential
that is positive would call for the addition of a mineral base.
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It has also been found that streaming potentials of ore benefi-
ciation waters, although they generally are negative, are
brought to near zero streaming potential by the addition of a
mineral base. The preferred mineral base is calcium hydroxide.
Other suitable mineral bases include sodium hydroxide and lime.
With the streaming potential near zero, the particu-
lates -are no longer charged or carry only very low charges.
This means that the charge repulsion present among the parti-
culates prior to treatment has been removed or at least substan-
tially lessenedO Wititout this adjustment, the particulateswill remain dispersed throughout the wastewater and will be
resistant to the bubble treatments of the subsequent steps. The
streaming potential adjustment markedly increases the tendency
of the particulates to unite and grow with the small bubbles to
form the floc without having to use metal coagulants.
In the next step of this method, the streaming
potential adjusted wastewater flows into the confined location
having a continuous supply of bubbles. The density of this
supply is such that the bubbles comprise 1/2 to 6 volume
percent of the wastewater in the confined location to effi-
ciently form the buoyant gas-solid composites. These bubbles
may be provided by electrolytic decomposition of wastewater
or by pressurized gas dissolution and should be in the size of
between 30 to 500 microns, preferably 50 to 200 microns in
diameter. Dissolved gas bubbles are preferred because of
their lower cost and smaller average size.
While dissolved gas is used in the preferred embodi-
ment, an alternate embodiment employes electrolytic bubbles,
which have a particular advantage in that they result in a
marked reduction in the amount of certain adsorbable ions that
might be present in the raw wastewater. Such ions include am-
monia-nitrogen, cyanide, phenols, polybrominated biphenyls,
and various other organic toxic pollutants. The reduction is
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significant, with these ion values being enriched in the floc.
The degrèe of reduction is reported elsewhere herein as a
partition coefficient, defined as the concentration of ions in
the floc phase over the concentration of ions in the mother
liquor, here the wastewater. This feature results in a parti-
tion coefficient in excess of 30/lo
The reason for this highly beneficial phenomenon
is not presently known. The following is offered as an
hypothesis. Hydrogen bubbles appear to act as a catalyst in
that they attach to the particulates to form the two-phase
composites, hydrogen being the gas phase. It is postulated
that ions are then adsorbed, either physically, chemically,
or by ion exchange, onto the solids at the gas-solid interphase.
When these two-phase composites enter the floc later on in
this method, these values are thus removed from the wastewater.
It is further postulated that some ions that are not so
adsorbed are destroyed by electrolytic actionD
In an optional step, a polymer flocculant may be
added into the confined location while the composites are
being formed and before the mixture passes over the impermeable
barrier to initiate the separation procedure. This feature
is not essential, but it usually noticeably improves the
consistency of the overall process by increasing the stability
of the composites formed, making them less susceptible to
being damaged during the subsequent separation procedure.
Any polymer flocculant (anionic, cationic, or nonionic) may be
used in concentrations between about 1/2 and 15 ppm. The
preferred polymers are polyelectrolytes in the form of
polyacrylic acrylamides, which are copolymers of from about
50 to 90 weight percent acrylamides or methacrylamides, and
from about 10 to 50 weight percent acrylic or methacrylic
acid or water soluble salts thereof. These polymers are
i~ ~ 3 Z Z 9
characterized by weight average molecular weights of about 2
million and usually the molecular weights range between
about 7 to 12 million as measured by light scattering tech- !
niques. The preferred concentration range for the polymer
flocculant is between about 1 to 3 ppm.
Irrespective of the makeup of the gas-solid com-
posites formed in the preceding steps, the next step in the
present method begins the process of separating the two-
phase composites from the wastewater. The wastewater and
the composites mixed therein flow together out of the confined
location by passing over the impermeable barrier into the
long flotation zone. Preferably, additional bubbles are
provided from the bottom of the upstream portion of the zone
for assisting in the flotation separation of the composites.
The long flotation zone includes a downstream, or quiescent,
portion into which no bubbles are supplied. The volume of
the upstream porton is generally about 3 to 10 times the
volume of the downstream quiescent portionO
When, as preerred, bubbles are added from near
the bottom of the upstream portion, the additional bubbles
are preferably supplied by electrolytic decomposition of
water. They also may be provided by gases dissolved in
water. These bubbles should be provided in a pattern that
gradually decreases in density in the downstream direction.
Best results have been observed when the decrease is geometric.
In any event, the decrease should be such that the bubble
density at the upstream end of the long flotation zone is 2
to ~ times greater than the bubble density at the mid-line
of the zone.
In an alternative embodiment, no additional bubbles
are added at the bottom of the long flotation zone. Instead,
excess bubbIes are added within the confined location so
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that significant amounts (preferably about 4 volume percent
of the flow) of free bubbles unattached to particulates flow
over the impereable barrier and down into the long flotation
zone. Substantial quantities of these free bubbles flow
toward the bottom of the flotation zone, especially at its
upstream end, thereby approximating but not equalling the
effect that is achieved by the added gradient bubble supply.
As a rough approximation, about 0.4 volume percent of the flow
will still be free bubbles at the approximate mid-line of the
long flotation zone in this embodiment. This alternate
embodiment is assisted greatly by the preferred vertical,
perforated baffles of this invention. It is also improved
as the sizes of the free bubbles decrease, since smaller
bubbles rise slower than large bubbles and are more likely
to flow toward the bottom of the ~one.
Often the desired bubble density can be achieved
by providing the bubbles in a number of stages, preferably
in four quartile stages. For example, when the bubbles are
supplied electrolytically, one can express the bubble density
as the average amount of amperage supplied per square foot
of each quartile, calculated based on the floor area covered
by the quartile stage. In the preferred quartile arrangement,
the first, upstream quartile current ~ensity is between
about 7.5 to 2~ amperes per square foot; in the second
quartile it is between about 3.5 to 10 amperes; in the third
quartile it is between about 1.5 to 5 amperes; and in the
fourth, quiescent quartile, no current is supplied.
Within the long flotation zone as a whole, the
mixture passing over the impermeable barrier is separated,
the composites rising to the surface to form the skimmings,
and the wastewater flowing the length of the zone and out at
the downstream end of the quiescent portion. In the preferred
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process, vertical, perforated baffles are placed transverse
to the flow throughout the long flotation zone. The baffles
have from about 30 to 80 percent, preferably from 50 to 60
percent uniform free passage therethrough as the wastewater
flows downstream through the zone. They significantly
reduce turbulence, channelling and back diffusion within the
zone which would develop if the baffles were not present
and which would cause disruption of the separation process
to decrease the final clarity of the wastewater.
FIGURES 1 and 2 illustrate the relationship between
streaming potential values and wastewater clarification. The
readings are reported in streaming detector units which are
qualitative approximations of zeta potential values which were
measured on a detector manufactured by Water Associates,
Inc. of Framingham, Massachusetts. There is a precise relation-
ship between streaming units and zeta values, disclosed, for
example, in Encyclopedia of Electrochemistry, editor Clifford
A. Hampel, Rehinhold Publishing Corporation, New York, N.Y.,
r~ 1964, at page 384~. incorporatcd herein by referene~
FIGURE 1 illustrates the effects on turbidity
(measured in Jackson turbidity units) when a particular meat
paeking wastewater is treated with sulfuric acid and 12 ampere-
minutes per gallon of treated wastewater are applied at various
streaming potential units. The greatest clarity results when
the streaming potential is zero. FIGUR~ 2 illustrates the
effect on hexane extractables or FOG (fats, oils and greases)
values when a meat processing wastewater is subjected to treat-
ment according to this process, using 8 ampere-minutes per
gallon of wastewater treated, except that streaming potential
values other than zero are used. The lowest hexane values occur
when the streaming potential meter reading is zero. These
figures illustrate that there is a maximization of treatment
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~9~
of these wastewaters at zero streaming potential, with in-
creasingly poorer results occurring when the streaming
potential increases, either negatively or positively.
Table I illustrates that there is a wide variation,
from wastewater to wastewater between the pH and the streaming
potential of the raw wastewater and the pH of that wastewater
at zero potential. One would adjust to the pH listed in the
last column to adjust to approximately zero zeta potential in
accordance with this process.
TABLE
Raw Wastewater pH of Waste-
General Streaming water at Near
Type of Detector Zero Streaming
Wastewater pH Readin~ Current
Brewery 3.8 +2O6 units 4.2
Beef packing and marinating 5.0 +2.2 units 6.2
Meat packing 6.5 -10.0 units 3.5
Metal processing8.5 -10.0 units 2.8
Meat packing 7.0 -16.6 units 4.8
Meat packing 7O0 -19.4 units 4.5
Mineral ore beneficiation5~8 -30 units 9.2
Oil barrel manufacture8~2 -37.0 units 3.7
Shortening manufacture11.5 -51.0 units 3~4
FIGURE 3 is an elevation view of the preferred appar-
atus, generally indicated by reference numeral 11. Impermeable
ba~fle 12 separates chamber 13 from basin 14~ Chamber 13 in-
cludes a means, such as electrodes 15, for providing dense
quantities of gas bubbles for developing turbulent contacts
with particulate matter within chamber 13. The gas bubbles may
be supplied in any manner provided they are small enough and
dense enough to provide adequate contacts. When electrodes
15 are used, they are pre~erably pro~ided in two or more
staggered rows as depicted in FIGURE 3.
Basin 14 has an upstream portion 16 and a downstream
portion 17. Upstream portion 16 may include means, such as
i~93Z29
electrodes 18 to supply bubbles for flotation and separation
of composites formed in chamber 13 from the wastewater. No
bubbles are added in downstream portion 17; this provides a
quiescent environment. The preferred bubble supply means in
basin 14 provides bubbles in quantities that decrease in the
downstream direction. The object of this structure is separ-
ation. The bubbles may be supplied by electrodecomposition
of water at electrodes 18 or by releasing pressurized gas
dissolved in water through one or more gas pressure release
inlets 19 (FIGURE 4). One other conventional bubble supply
means, dispersion, is presently believed to be an unsatis-
factory means for adding bubbles to basin 14.
Perforated transverse baffles 21 are provided
throughout the basin 14. The perforations 22 are generally
evenly distributed throughout each baffle 21 and make up
about 30 to 80 percent, preferably about 50 to 60 percent, of
the surface area of the baffles 21. It is also preferred
that these transverse baffles 21 be spaced from each other a
distance of approximately 1/4 to 1/2 the width of the basin.
Such perforated baffles 21 prevent turbulence, channeling
and back diffusion to thereby improve the overall effectiveness
of the apparatus. The preferred perforations are circles of
diameters between about two inches and three inches. Other
sizes and shapes are often adequate, for example, squares of
two inches to three inches on each side, rectangles, triangles
or other polygons which allow for the specified amount of free
passage through the baffles 21.
Downstream of quiescent portion 17 is outlet 23
for passage of the clarified effluent. The floc passes
out of basin 14 with the assistance of a floc removal means,
such as a skimmer 24, a beach 25 and a trough 2~.
Upstream of chamber 13 is injector 31 for introducing
chemicals needed to adjust the streaming potential of the waste-
water. It is preferred that a holding means, such as hold tank
32, be provided at this approximate location so the streaming
potential of the wastewater may be stabilized and verified if
desired before subsequent treatment steps. Also present may
be one or more injectors 33 which can be used to add a polymer
flocculant to increase the size and stability of the buoyant
gas-solid composites.
FIGURE 4 presents a plan view of the apparatus, with
the skimmer 24 and beach 25 having been omitted for clarity.
In this figure the means for providing bubbles in chamber 13
takes the form of one or more gas pressure release inlets 34
for releasing pressurized dissolved gas bubbles.
The following Examples are set forth as illustrative
embodiments of the invention and are not to be taken in any
manner as limiting the scope thereof as defined by the
appended claims.
E X A M P L E
Wastewater from a meat processing plant was analyzed
to have the following characteristics: 300 ppm total BOD; 212
ppm FOG; and 240 ppm suspended solids. The pH of the waste-
water was measured at 7.5. Streaming potential values (-14
units) taken on this wastewater showed the particles to be
negatively charged. By adding a mineral acid and at a p~ of
approximately 4.5, the zeta potential, measured as a stream-
ing potential value, was found to be approximately zero.
The wastewater then was passed through an electrolytic micro-
bubble cloud to the extent of 5 milliamperes per gallon, and
the treatment continued for 8 minutes. Analysis of this
treated wastewater indicated 120 ppm total BOD; 15 ppm FOG;
and 20 ppm suspended solids.
Another portion of this same wastewater, without
having been adjusted from its original streaming potential
value of -14 units, was also passed through the electrolytic
microbubble cloud under exactly the same conditions. The
analysis for this treatment indicated 200 ppm total BOD; 80
ppm FOG; and 150 ppm suspended solids.
E X A M P L E II
In a pilot operation carried out at a meat packing
plant, raw wastewater flow rates from the plant and through the
apparatus of the preferred structure were maintained between 7
and 10 gallons per minute. Approximately 400 ppm of mineral acid
was used to keep the streaming potential near zero for this
wastewater, the pH ranging between 3.5 and 4Ø Several hours of
testing provided the following data, reported as average values:
Raw Treated %
Pollutant WastewaterWastewater Reduction
Total BOD 1~545 ppm100 ppm 94%
Total suspended solids 1,733 ppm 110 ppm 94%
Hexane extractables 1,572 ppm40 ppm 97%
~fats and oils)
Skimmings obtained while conducting these tests had a
solids content (100-water content) of 31%; a fat and oil
content based on dry solids of 80%; a protein content based on
dry solids of 10%; and the skimmings volume as a percent of the
wastewater process was only 0.34%.
Similar tests were run 7 these not in accordance with
the present invention since zero streaming potential adjustments
were not made. Results comparable to those listed in the first
part of this Example required the addition of 1,000 ppm of alum,
which resulted in the pH of 5o8~ followed by 4 ppm of an anionic
polymer flocculant. A summary of these results shows that the
present process, when operating on a wastewater having high fat
content, can be just as effective as one requiring the use of
substantial quan~ities of metal coagulant:
3 ~9
Raw Treated %
Pollutant WastewaterWastewater Reduction
Total BOD 1~545 ppm 90 ppm 94%
Suspended solids 1,733 ppm 100 ppm 94%
Hexane extractables1,572 ppm 32 ppm 98%
(fats and oils)
The skimmings obtained in this run not in accordance with the
present invention were distinctly different from and definitely
inferior to those according to the invention. More partic-
ularly, the percent solids were substantially lower, only
9.4%; the percent fats and oils were lower, only 60%; the
percent protein was lower, only 8%; and the volume of skimmings
produced and thus requiring further handling was greater,
0087%.
E X A M P L E III
Tests were run at a slaughterhouse having a raw
wastewater with the following average values of pollutant
load: 900 ppm total BOD; 520 ppm suspended solids; and 350
ppm hexane extractables. Using about 200 ppm sulfuric acid,
the pH was adjusted within the range of 4.5 to 5Ø A hold
tank was not provided and this adjustment had to be made to
the wastewater while it was flowing through the system at a
rate between 5 and 8 gallons per minute. Within this pH
range, the streaming potential as meausred in the labcratory
was found to approximately zero. Shortly before entering the
long flotation basin of the preferred apparatus, approximately
2.5 ppm of an anionic polyelectrolyte polymer flocculant
were added to the flow. These conditions were maintained
during 8 hour periods on three different days. An averaged
summary of these runs showed that the total BOD was reduced
about 67% (to 300 ppm), the suspended solids reduced about
83% (to 90 ppm), and the hexane extractables reduced about
86% (to 50 ppm). The floc collected was found to contain
lVS~'3Z~9
26% solids, 63% fat (dry basis), and 18% protein (dry basis),
and to have a tallow color of 12, a tallow percent moisture
of 0.16, a percent unsaponifiables value of 0.07, and a
volume percent floc of wastewater treated of only 0.39%.
The floc was rendered with very favorable results.
E X A M P L E IV
Wastewater flows from a cattle and hog slaugh~ering
plant had the following average pollutant loads: 5,080 ppm
total BOD; 2,750 ppm suspended solids; and 1,950 ppm hexane
extractables. The water was treated on a pilot plant scale
at a flow rate of 10 gallons per minute and using 14 ampere-
minutes per gallon of wastewater treated. One series of
tests were run without baffles in the flotation basin, while
another series was run with baffles in the basin, there
being eleven perforated baffles having 1-1/2 inch diameter
holes providing 50% free passage through the perforated
baffles. The results, plotted in FIGURE 5, show the improve-
ment in final results achieved when the perforated baffles
were employed. Also, with the baffles used, the skimmings
included 33% solids and 42% hexane extractables.
E X A M P L E V
Two and one half weeks of pilot experimentation
were carried out at a pork slaughterhouse plant. The raw
wastewater flow was split so as to permit tests to be run on
a raw wastewater especially high in fat content, this being
a wastewater from the slaughter floor only. After proceeding
with the process of this invention, the following summary of
analyses were accumulated. The total BOD was reduced 76%
(from 1,442 ppm to 346 ppm). The suspended solids were
reduced 86% (from 881 ppm to 120 ppm). The hexane extract-
ables were reduced 89% (from 482 ppm to 53 ppm). The ammonium
ion concentrations were reduced 63% (from 18.9 ppm to 7.0
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Z,'29
ppm). The ammonium ion removal is believed to be of note,
since it represents an improvement over the approximately
50% maximum reductions obtainable under similar processes
that do not adjust to zero streaming potential.
In this particular series of tests, the zero
streaming potential was found to occur at a pH of 4.5. The
energy input was 12 ampere-minutes per gallon of wastewater
treated, and 2 ppm of an anionic polymer flocculant were
added. The tests were run over two 8 hour periods on two
different days~
E X A M P L E VI
In the same pork slaughtering plant operation of
Example V, similar tests were run, except that the bubbles
were provided by dissolved air, with the streaming potential
being adjusted to near zero (at a pH of 5.0). Reductions in
total suspended solids and hexane extractables were achieved
over the same process when run without adjusting to near
zero streaming potential. At the same time, the renderability
of the floc was found to be quite acceptable. The floc itself
contained approximately 20 weight percent solids and 15
weight percent fat.
E ~ A M P L E VII
Beef packinghouse wastewater, before being passed
through a 20 gallon per minute pilot plant in accordance
with this invention, had the following characteristics:
1,010 ppm total BOD: 750 ppm total suspended solids; 400 ppm
hexane extractables; and 30 ppm ammonia-nitrogen. This
wastewater was adjusted to near zero streaming potential,
the pH being at a value of 4.5. Using Duriron electrodes
provided with an energy input of 10 ampere-minutes per
gallon of wastewater treated, a floc floated on the treated
wastewater. The treated wastewater had the following
1093ZZ9
characteristics: 310 ppm total BOD; 90 ppm total suspended
solids; 50 ppm hexane extractable; and 8 ppm ammonia-nitrogen.
Analysis for ammonia-nitrogen in the floc showed a 610 ppm
content. This amounts to a partition coefficient of ammonia-
nitrogen equal to 76/lo More than 70 percent of the ammonia-
nitrogen in the raw wastewater was concentrated into the
floc leaving only approximately 30 percent of the original
ammonia-nigrogen in the treated wastewater.
E X A M`P L E VIII
A pork packinghouse wastewater with the following
characteristics was treated in the 20 gallon per minute
pilot plant of Example VII: 1,442 ppm total BOD; 881 ppm
total suspended solids; 482 ppm hexane extractables; and 19
ppm ammonia-nitrogen. This raw wastewater had a pH of 7.8.
This wastewater was adjusted to near zero streaming potential
with sulfuric acid, the pH reading being about 4.5. It was
then passed through an electrolytic cell where Duriron
electrodes were employed and wherein energy input of 11
ampere-minutes per gallon was applied. This resulted in only
a 0.4 volume percent of the wastewater treated being converted
to floc~ Dwell time of the wastewater in the electrocoagu-
lation apparatus was 30 minutes. The chemical characteristics
of the wastewater leaving the pilot unit were: 350 ppm
total BOD; 120 ppm total suspended solids; 53 ppm hexane
extractables; and 7 ppm ammonia-nitrogenO Reduction in
ammonia-nitrogen values in the effluent wastewater as compared
to the raw wastewater was noted to be 63 percent. The value
of ammonia-nitrogen content in the floc was observed to be
530 ppm. The partition coefficient for ammonia-nitrogen was
75/1.
E X A M P L E IX
Packinghouse wastewater containing 42 ppm of
- 18 -
1093Z~9
ammonia-nitrogen was treated with sulfuric acid to bring it
to its zero streaming potential, which was found to be at a
pH of 4.5~ This wastewater was then treated with 11 ampere-
minutes per gallon of electrolytic current wherein 90 percent
of the suspended material was removed from the wastewater in
the form of skimmings. Analysis of the wastewater treated
showed the ammonia-nitrogen value was reduced to 3.7 ppm.
This corresponds to a 91 percent reduction in ammonia-
nitrogen values of the treated wastewater.
E X A M P L E X
Wastewater used for the beneficiation of molybdide
ores had a streaming potential reading of about -20 units, had
a pH of 5.8, and contained appreciable amounts of dissolved
heavy metals and 0.7 ppm of cyanide values. This water was
treated with 150 ppm of lime to adjust the streaming potential
to near zero (about -10 units), the pH increasing to about 9~1.
It was then processed with a total of 8 ampere-minutes per
gallon of water treated, which processing included the addition
of 2 ppm of a polyacrylic acrylamide copolymer flocculant.
Analysis of the effluent waters showed that more than 90 per-
cent of the heavy metals (copper, zinc, cadmium, iron, manga-
nese) were insolubilized and removéd, and that the cyanide
value of 0.7 ppm was reduced to 0.08 ppm, an 88 percent re-
duction.
Obviously, many modifications and variations of
the invention as hereinbefore set forth may be made without
departing from the spirit and scope thereof, and only such
limitations should be imposed as are indicated in the appended
claims.
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