Note: Descriptions are shown in the official language in which they were submitted.
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TITLE.
111ETHOD FOR TREATMENT OF AQUEOUS
STREAMS COMPR.ISING BIOSOLIDS
~
BACKGROUTTD OF THE INWNTION
FIELI) OF THE IhTN'ENTION
This invention relates to a process for clarification of substantially aqueous
process streams, and more panicularly to separation of biosolids, especially
proteins_ from iood processing operations, such as animal processing.
especialk;
poultrv processinp.
1 ~.
DESCRIPTION OF THE RELATEI) ART
Large aniounts of biosolids, such as proteins, carbohydrates, iats and oiis.
are collected in aqueous streams during food processing operations, such as
waste
and wash ,~vaters froni the slaughter of aninlals for food products and other
food
2 0 processing operations such as extraction of proteins during soybean
processinr,
and the like. The aqueous stream niust be clarified, i_e., have suspended
solids
separated and removed to recover valuable product or before being discharged
from the processing plant to a municipal or public water svsten;. 'When
separated
and dried, the biosolids have value, for exaniple, as animal 1eed, crop
fertiiizers, in
pharmaceuticals and in personal care products. In one panicular example,
recovered protein from soybeans niay be used in infant formula.
These biosolids are eomprised of particles having surface charges.
Typically the particles have anionic surface charges at alkaline and neutral
pH.
30 The surface charge generates a repulsive force between particles to keep
them
apart. For individual particles of colloidal size, such as proteins,
gravitational
forces are insufficient to cause them to settle out of the aqueous suspension.
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Simple separation methods, such as filtration, are ineffective to separate
these
protein solids due to blinding of filters or ability of the solids to pass
through
them. Thus separation and hence, recovery of the protein may be low and/or a
waste stream may not be environmentally acceptable for discharge from the
processing plant.
Techniques for removal of proteins, carbohydrates, fats and oils, and other
biological contaminants from aqueous food processing streams are known. A
common practice is to separate the protein, fats and oils from the aqueous
stream
by flocculation with metal salts, especially iron and/or aluminum salts, and
anionic polymers. As it is common to use the recovered proteins,
carbohydrates,
fats and oils in animal feed, there are health issues when metal salts are
used to
separate biosolids. There is concern that the recovered biosolids have high
levels
of metal salts, which may build up in the tissues of the animals to whom the
feed
is given, these tissues being subsequently consumed by humans. Animal
nutritionists are also concerned that metal salts may bind to phosphates in
the feed
so that they are less available as a nutrient. The food processing industry
has
sought alternatives to the use of metal salts for separation of proteins,
carbohydrates, fats, and oils from aqueous streams.
While methods have been disclosed for clarification of aqueous streams
from food processing plants and separation of biosolids therefrom which do not
require metal salts, each of these suffer from disadvantages such as high
costs of
materials and long reaction times to sufficiently clarify the stream. The
present
~invention provides an economic and efficient process to clarify aqueous
streams
from food processing and to separate and recover protein in a form capable of
subsequent conunercial use.
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SUMMARY OF THE INVENTION
The present invention provides a process, for example for use in
clarification of aqueous streams comprising biosolids, the process comprising
contacting an aqueous stream comprising biosolids with an effective amount of:
(1) an anionic inorganic colloid; and
(2) an organic polymer, wt: erein the organic polymer is selected from the
group consisting of cationic polymers and amphoteric polymers and
mixtures thereof, and has a number average molecular weight of
greater than 1,000,000;
whereby flocculated biosolids are produced.
The aqueous stream can be contacted with an acid, if desired, to reduce pH
of the stream to less than pH 7. In one particular embodiment of this
invention,
the aqueous stream is contacted simultaneously with the anionic inorganic
colloid
and an acid to reduce the pH. Subsequent contact of the organic polymer with
the
stream causes flocculation of the biosolids, such that the flocculated
biosolids can
be separated from the stream.
Biosolids are typically suspended in aqueous streams due to surface charge
effects. Surface charge will depend on pH. The present invention further
provides a process which comprises contacting an aqueous stream comprising
biosolids, wherein the biosolids possess surface negative charge sites, with
an
effective amount of:
(a) a first organic polymer, wherein the first organic polymer is a
cationic polymer, to reduce the number of surface negative charge
sites on the biosolids, so that the biosolids have at least some cationic
sites;
(b) an anionic inorganic colloid; and
(c) a second organic polymer, wherein the second organic polymer is
selected from the group consisting of cationic and amphoteric
polymers, and mixtures thereof;
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to produce flocculated biosolids. Alternatively when the anionic inorganic
colloid
is a silica-based colloid, the second organic polymer can be selected from the
group consisting of cationic, anionic, and amphoteric polymers, and mixtures
thereof.
DETAILED DESCRIPTION
Many processing plants generate aqueous streams comprising biosolids
such as proteins, carbohydrates, fats, and oils which must be treated to
remove the
potentially valuable biosolids products and/or before the stream can be
discharged
from the plant. These aqueous streams are often derived from food processing
plants and have solids contents of from about 0.01 % to 5% on a weight basis.
This invention provides a process for clarification of such streams, whereby
the
solids are flocculated, and optional separation therefrom of the biosolids,
which
can be subsequently used for example, in animal feeds.
As defined herein, to flocculate means to separate suspended biosolids,
from a stream comprising biosolids wherein the biosolids become aggregated and
separate to the top or bottom of the stream in which the biosolids had
previously
been suspended. Flocculation produces a flocculated material, which, if
desired,
can be physically separated from the stream. In the present invention, it is
desirable to maximize the size of the flocculated material in order to
facilitate
removal of this material from the stream.
MATERIALS
Aqueous Stream
In the process of this invention, the aqueous stream to be treated can be
from any processing plant that produces an aqueous stream comprising
biosolids,
such as food processing plants. For example, animal slaughterhouses and animal
processing plants and other food processing plants may produce aqueous streams
comprising protein, fats and oil. Animal slaughterhouses and processing plants
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include those for cattle, hogs, poultry and seafood. Other food processing
plants
include plants for vegetable, grain and dairy food processing, for example,
plants
for processing soybeans, rice, barley, cheese, and whey; plants for wet-
milling of
starches and grains; as well as breweries, distilleries and wineries.
Biosolids
present in aqueous streams from these processes may include sugars, starches
and
other carbohydrates in addition to protein, fats, and oils. For example in
processing of soybeans, proteins are extracted into an aqueous stream from
which
they are subsequently recovered. The present invention is especially useful
for
treating streams from animal processing, and more particularly, from poultry
processing.
While this invention is useful in conventional food processing operations,
which produce aqueous suspensions of biosolids, it should be recognized that
this
invention is also useful in treatment of aqueous suspensions of biosolids
derived
from processing of food (animal or vegetable) materials, which may have non-
food end uses. For example, when separated and recovered, proteins are useful
in
certain cosmetics and other skin care formulations; starch has numerous non-
food
uses, including uses in paper manufacture. Further still, this invention is
useful to
treat in general, any aqueous stream comprising biosolids, which may result
from
non-food processing operations. Moreover, though the biosolids, as disclosed
above, are generally suspended in a substantially aqueous stream, a
substantially
concentration of quantity of biosolids can also be dissolved in the stream
depending on the property of the stream or the biosolids such as, for example,
pH,
salinity, or other parameters.
Anionic Inorganic Colloid
Anionic inorganic colloids useful in the process of this invention can
include silica-based and non-silica-based anionic inorganic colloids and
mixtures
thereof. Silica-based anionic inorganic colloids include, but are not limited
to,
colloidal silica, aluminum-modified colloidal silica, polysilicate microgels,
polyaluminosilicate microgels, polysilicic acid, and polysilicic acid
microgels, and
mixtures thereof. Non-silica-based anionic inorganic colloids include clays,
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especially colloidal hentonite clay. Other non-silica-based anionic inorganic
colloids include colloidal tin and titanyl sulfate.
The anionic inorganic colloids used in this invention can be in the fom of
` a colloidal silica sol containing about 2 to 60% by weight of Si02,
preferably
about 4 to 30% bv weight of Si0?. The colloid can have particles writh at
least a
surface laver of aluminum silicate or it can be an aluminum modified silica
soi.
The colloidal silica particles in the sols commonlv have a specific surface
area of
50-1000 m2ig, more preferablv about 200-1000 m2/g, and most preferably a
specific surface area of about 300-700 m2/g. The silica so] can be stabilized -
,vith
alkali in a molar ratio of Si02:M20 of from 10: 1 to 300:1, preferably 15:1 to
100:1 (M is Na, K. 1_i, and N1-14). The colloidal particles have a particle
size of
less tltan 60 nm. xvith an average particle size less than 20 tin7, and most
preferably with an average particle size of fiom about 1 nm to 10 nm.
Micropels are distinct from colloidal silica in that the mierogel particles
usuallv have surface areas of 1000 m2/g or higher and the rnicrogels ar(:
comprised of small ] -2 nni diameter silica particles linked together into
chains
and three-diniensional networks. Polvsilicate microgeis, also lJlo~vn as
actik'c
~ U silicas, have Si02:Na-)0 ratios of 4_ 1 to about 25:1. and are discussed
on pages
174-176 and 225-234 of "The Chemistrti- of Silica" by Kalph K. ller, published
b~
John Wiley and Sons, N. Y., 1979- Yolysilicic acid generally refers to those
silicic
acids that have been formed and par-tially polvmerized i.n the pH range 1-4
and
comprise silica particles generally smaller than 4 nm diameter, which
thereafter
polvmerize into chains and tluee-dimensional networks. Polysilicic acid can be
prepared in accordance with the methods disclosed in U. S. Patents 5,127,994
and
5,626,721 . Polvaluminosilicates are polysilicate
or polvsilicic acid microgels in which aluminum has been incorporated within
the
particles, on the surface of the particles, or both. Polysilicate microgels,
polyaluminosilicate microgels and polysilicic acid can be prepared and
stabilized
at acidic pH. Better results have been generally found to occur with larger
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microgel sizes; uenerally greater than 10 nm size microgels give the best
performance. Microgel size can be increased by any of the known methods such
as of aging of the microgel, changing pH, changing concentrations, or other
methods, kno m to those skilled in the art.
7 he polysilicate microgels and polyalurninosilicate microgels useful in this
invention are conlmonlv formed bv the activation of an alkali metal silicate
under
conditions described in U. S. Patents 4,954,220 and 4,927,498.
However, other methods can also be employed. For
example, polyaluminosilicates can be formed by the acidification of silicate
tirith
mineral acids containing dissolved aluminum salts as described in U. S. Patent
5.482.693 = Alumina/silica microgels can be
formed hv the acidification of silicate -Mth an excess of alum. as described
in
U. S. Patent 2,234.285.
in addition to conventiona] silica sols and silica microgels, silica sols such
as those described in European patents EP 491879 and EP 502089,
can also be used for the anionic inorganic colloid iri this
invention.
The anionic inorganic colloids are used in an effective amount, together
with a organic polymer to produce flocculated biosolids. An effective amount
can
range from about I to 7500 parts per million (ppm) by weight as solids, e_ g.,
as
Si02, based on the solution weight of the aqueous streanl. The preferred range
is
2 5 from about I to 5000 ppm, depending on the anionic inorganic colloid.
Preferred
ranges for selected anionic inorganic colloids are 2 to 500 ppm for
polysilicic acid
or polysilicate microgels; 4 to 1000 ppm for colloidal silica, and 2 to 2000
ppm
for inorganic colloidal clays, such as bentonitee
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Organic Polymers
Organic polymers useful in the process of this invention include cationic
and amphoteric polymers and mixtures thereof. The organic polymers will
typically have a number average molecular weight greater than 1,000,000. These
are generally referred to as "high molecular weight polymers".
High molecular weight cationic organic polymers include cationic starch,
cationic guar gum, chitosan and high molecular weight synthetic cationic
polymers such as cationic polyacrylanmide. Cationic starches include those
formed
by reacting starch with a tertiary or quaternary amine to provide cationic
products
with a degree of substitution of from 0.01 to 1.0, containing from about 0.01
to
1.0 wt% nitrogen. Suitable starches include potato, corn, waxy maize, wheat,
rice
and oat. Preferably the high molecular weight cationic organic polymer is
polyacrylamide.
The high molecular weight cationic organic polymers are used in an
effective amount, together with an anionic inorganic colloid to produce
flocculated biosolids. An effective amount of a cationic polymer can range
from
about 0.2 to 5000 ppm based on the solution weight of the aqueous stream. The
preferred range is from about I to 2500 ppm.
Amphoteric polymers include amphoteric starch, guar gum and synthetic
amphoteric high molecular weight organic polymers. Amphoteric polymers are
typically used in the same amounts as the high molecular weight cationic
polymers.
The present invention further includes a process which comprises
contacting an aqueous stream which comprises biosolids possessing surface
negative charge sites, with an effective amount of a first organic polymer to
reduce the number of the surface negative charge sites. The first organic
polymer
is a cationic polymer, which is used to reduce the number of surface negative
charge sites and to impart some cationic sites. An effective amount is
typically an
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amount sufficient to neutralize at least 1%, and preferably at least 10% of
the
surface negative charge sites on the biosolids. Low or high molecular weight
cationic organic polymers, or mixtures thereof can be used. Low molecular
weight cationic organic polymers are preferred due to their higher cationicity
and
lower cost of use.
Useful high molecular weight cationic polymers include those described
above.
Useful low molecular weight cationic polymers have a number average
molecular weight in the range between about 2,000 to about 1,000,000,
preferably
between 10,000 and 500,000. The low molecular weight polymer can be for
example, polyethylene imine, polyamines, polycyandiamide formaldehyde
polymers, amphoteric polymers, diallyl dimethyl ammonium chloride polymers,
diallylaminoalkyl (meth)acrylate polymers and dialkylaminoalkyl
(meth)acrylamide polymers, a copolymer of acrylamide and diallyl dimethyl
ammonium chloride, a copolymer of acrylamide and diallylaminoalkyl
(meth)acrylates, a copolymer of acrylamide and dialkyldiaminoalkyl
(meth)acrylamides, and a polymer of dimethylamine and epichlorohydrin. These
have been described in U. S. Patents 4,795,531 and 5,126,014.
The first organic polymer, a high or low molecular weight cationic organic
polymer, or mixtures thereof, is added in an effective amount to reduce the
number of surface negative charge sites on the biosolids. An effective amount
is
dependent on several factors, including the number of surface negative charge
sites present on the biosolids in the aqueous stream, the type of biosolid,
and the
pH of the aqueous stream. An effective amount can be determined by means
available and known to those skilled in the art, using techniques such as
colloidal
titration. Generally this amount will be in the range of from about 0.01 to
about
10,000 ppm of polymer, based on total weight of the stream. The term "ppm" is
defmed above.
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After treatment with the first organic polymer, the aqueous stream is
treated with a second organic polymer. The second organic polymer will depend
on the anionic inorganic colloid. The second organic polymer can be selected
from the group consisting of cationic and amphoteric polymers and mixtures
thereof for any anionic inorganic colloid. When the anionic inorganic colloid
is a
silica-based anionic inorganic colloid, the second organic polymer can be
selected
from the group consisting of anionic, cationic, amphoteric polymers and
mixtures
thereof. Cationic and amphoteric polymers are described above and can be high
or low molecular weight polymers.
Anionic polymers that can be used in the process of this invention have a
number average molecular weight of at least 500,000 and a degree of anionic
substitution of at least I mol%. Anionic polymers with number average
molecular
weights of greater than 1,000,000 are preferred. Preferably the degree of
anionic
substitution is 10-70 mol%.
Examples of useful anionic polymers include water soluble vinylic
polymers containing acrylamide, acrylic acid, acrylamido-2-
methylpropylsulfonate and/or mixtures thereof, and can also be either
hydrolyzed
acrylamide polymers or copolymers of acrylamide or a homolog, such as
methacrylamide, with acrylic acid or a homolog, such as methacrylic acid, or
even
with monomers such as maleic acid, itaconic acid, vinyl sulfonic acid,
acrylamido-
2-methylpropylsulfonate, and other sulfonate containing monomers. Anionic
polymers are further described, for example, in U. S. Patents 4,643,801;
4,795,531; and 5,126,014.
Other anionic polymers that can be used include anionic starch, anionic
guar gum and anionic polyvinyl acetate.
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Optional Components
If desired, the pH of the aqueous may be first reduced to less than pH 7
using an acid. Typically, mineral acids such as sulfuric acid, hydrochloric
acid
and nitric acid are preferred. Other useful acids include, but are not limited
to,
carbon dioxide, sulfonic acids, and organic acids such as carboxylic acids,
acrylic
acids and acidic anionic inorganic colloids, partially neutralized acids in
which
one or more protons are replaced with a metal or ammonium ion, and mixtures
thereof. Acidic anionic inorganic colloids include, but are not limited to,
low
molecular weight polysilicic acid, high molecular weight polysilicic acid
microgels, acidic polyaluminosilicates and acid stabilized polysilicate
microgels.
Examples of acid stabilized polysilicate microgels are described in U. S.
Patents
5,127,994 and 5,626,721.
Optionally metal salts can be used in the process of this invention. Iron
and aluminum are particularly useful. Acid metal salts can be used to reduce
pH
and act as a charge donor.
PROCESS
The process of this invention involves treatment of an aqueous stream
containing biosolids, for example, proteins, to reduce suspended solids (as
measured by turbidity) and optionally to separate the biosolids. The biosolids
can
be recovered for subsequent use. It should be recognized that this process can
capture both suspended biosolids as well as soluble materials, such as those
present in blood and sugars.
The process of this invention involves treating an aqueous stream
comprising biosolids by contacting the stream with an anionic inorganic
colloid
and an organic polymer. The aqueous stream can be derived from any number of
processes, which generate such streams, such as from animal and vegetable
processing, including processing for non-food uses. The organic polymer is
selected from the group consisting of cationic and amphoteric polymers having
a
number average molecular weight greater than 1,000,000, and mixtures thereof.
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Optionally the aqueous stream is contacted with an acid to reduce the pH of
the
stream to less than pH 7. Further, a metal salt, especially an iron or
aluminum salt
can be optionally added. These reagents, anionic inorganic colloid, organic
polymer and optional acid and/or metal salt, can be contacted with the stream
in
any sequential order, or one or more can be contacted simultaneously with the
aqueous stream. In one particular embodiment, the stream is simultaneously
contacted with an acid and the anionic inorganic colloid.
The optional reduction of the pH of the aqueous stream to less than pH 7
can be accomplished with any acid, examples of acids being described above.
When an acidic anionic inorganic colloid is used to reduce pH of the stream to
less than pH 7, no additional source of acid or anionic inorganic colloid may
be
needed to flocculate the biosolids in the aqueous stream.
The aqueous stream is contacted with an anionic inorganic colloid and an
organic polymer. This may occur prior to, subsequent to, or simultaneously
with,
reducing pH of the aqueous stream to less than pH 7, should a pH reduction
step
be desired. The inorganic colloid and the organic polymer can be contacted
with
the aqueous stream separately, in either order, or simultaneously. The
combination of contacting an anionic inorganic colloid and an organic polymer
with the aqueous stream produces flocculated biosolids.
The flocculated biosolids can optionally be separated from the treated
stream by conventional separation processes such as sedimentation, flotation,
filtering, centrifugation, decantation, or combinations of such processes. The
separated biosolids can subsequently be recovered and used in numerous
applications. It has also been surprisingly found that the recovered biosolids
from
this process have reduced odor when dry relative to those recovered from a
process using ferric chloride as part of a flocculating system.
It is generally believed that suspended biosolids such as proteins in
aqueous streams carry surface negative charges. The present invention further
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provides a process which comprises contacting an aqueous stream comprising
biosolids with an effective amount of a first organic polymer to reduce the
number
of surface negative charge sites on the suspended biosolids in the stream. The
first organic polymer is a cationic polymer and is used in an amount
sufficient to
impart some cationic sites to the biosolids. Typically sufficient cationic
polymer
is added to neutralize at least 1%, and preferably at least 10% of the surface
negative charge sites on the biosolids. The first organic polymer can be a
high or
low molecular weight cationic organic polymer. Preferably the cationic polymer
is a low molecular weight cationic polymer.
An anionic inorganic colloid and a second organic polymer are contacted
with the aqueous stream prior to, subsequent to, or simultaneously with the
first
organic polymer, to produce flocculated biosolids in the stream. The second
organic polymer is selected from the group consisting of cationic, amphoteric,
and
anionic polymers, and mixtures thereof, depending on the anionic inorganic
colloid. For any anionic inorganic colloid, the second organic polymer can be
selected from the group consisting of cationic and amphoteric polymers and
mixtures thereof. For silica-based anionic inorganic colloids , the second
organic
polymer can be selected from the group consisting of anionic, cationic,
amphoteric polymers and mixtures thereof.
The flocculated biosolids can be separated and recovered by known
techniques, such as those mentioned above.
EXAMPLES
Example I
A sample of a wash water containing about 1000 ppm of un-flocculated
protein containing biosolids was obtained from an Eastern Shore poultry
processing plant. The initial turbidity was > 200. The initial pH was about 7.
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The following reagents were added in all of the runs to a beaker: high
molecular weight cationic polyacrylamide, Percol 182 , available from Ciba
Specialty Chemicals, Basel, Switzerland, 8 ppm; silica microgel solution,
Particol MX, 120 ppm (Si02 basis), available from E. I. duPont de Nemours
and Company. Inc., Wilmington, DE. The amounts given were based on the
solution weight of the wash water.
The reagents were added as follows.
(1) 250 ml of the wash water was stirred at medium speed on a Fisher
Scientific Model #120 MR magnetic stirrer, available from Fisher Scientific,
Pittsburgh, PA. Dilute sodium hydroxide or sulfuric acid was added to adjust
to
pH shown in Table 1.
(2) Cationic polyacrylamide was added at time = 0.
(3) Silica microgel was added at time = 1 minute.
(4) At time = 2 minutes, stirrer speed was reduced to slow.
(5) At time = 4 minutes, the stirrer was stopped and the flocculated solids
were allowed to settle to the bottom of the beaker.
(6) At time = 10 minutes, turbidity of the wash water was measured using
a Hach Ratio Turbidity Meter, available from Hach Company, Loveland, CO, in
NTU, as an indication of water clarification and ability to recover protein.
(7) At time = 20 minutes, a second dose of polyacrylamide, 8 ppm, was
added and the stirrer turned to medium speed.
(8) At time = 21 minutes, the stirrer speed was reduced to slow, and at 23
minutes, the stirrer was stopped.
(9) Turbidity was measured at time = 30 minutes.
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TABLE 1
Turbidity
Run Wash Water pH 10 min. 30 min.
1 8.0 88 63
2 6.9 79 55
3 6.5 77 42
4 5.5 25 2
4.5 30 1
6 3.5 10 2
As seen above in Table 1, the turbidity decreased upon addition of the
cationic polymer and silica microgel. Best results were observed at lower pH.
5 Turbidity improved with the second addition of polyacrylamide with the best
results again occurring at pH less than 7.
Example 2
The poultry processing wash water of Example 1 was used with several
different anionic inorganic colloids. The following anionic inorganic colloids
were used:
LudoxO SM colloidal silica, 30 wt% silica sol, surface area = 300 m2/g.
LudoxO HS-30 colloidal silica, 30 wt% silica sol, surface area = 230 m2/g.
LudoxO 130 colloidal silica, 30 wt% silica sol, surface area = 130 m2/g.
Ludox colloidal silicas are available from E. I. du Pont de Nemours and
Company, Wilmington, DE.
BMA-670, low "S" value colloidal silica sol, surface area = 850 m2/g,
available
from Eka Chemicals AB, Bohus, Sweden.
Colloidal silica sol, 4 nm, surface area = 750 m2/g, available from Nalco
Chemical Company, Naperville, Ill.
Particol0 MX, polysilicate microgel, surface area = 1200 m2/g, available from
E.
1. du Pont de Nemours and Company.
The high molecular weight cationic organic polymer was Percol 1820.
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The following procedure was followed for all of the runs:
(1) In a beaker, while stirring at medium speed, 250 ml of the poultry
processing wash water of Example 1 was adjusted to pH 4.5 by addition of
dilute
sulfuric acid.
(2) An anionic inorganic colloid, 40 ppm on an Si02 basis, based on the
solution weight of the wash water, was added to the acidified wash water at
time = 0.
(3) At time = 1 minute, 4 ppm of the high molecular weight cationic
organic polymer was added.
(4) At time = 2 minutes, the stirrer speed was reduced to its lowest setting.
(5) At time = 4 minutes, the magnetic stirrer was turned off.
(6) At time = 10 minutes, the turbidity of the wash water above the
flocculated solids was measured.
TABLE 2
Colloid Turbidity at 10 min.
Ludox SM 15
Ludox HS-30 24
Ludox 130 28
BMA-670 11
Nalco Si02 sol 11
Particol MX 2.5
As can be seen from Table 2, different anionic inorganic colloids can be
used, all of which are effective to reduce turbidity of the protein containing
wash
water. The flocculated biosolids settled from the water to the bottom of the
beaker.
Exameles 3-8
A second poultry processing wash water containing about 1390 ppm of
biosolids was used in these examples. The initial turbidity was > 200. The
following reagents were added to the wash water per the quantities provided
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below in Tables 3-8: a low molecular weight cationic organic polymer,
diallyldimethylammonium chloride polymer (polydadmac); anionic inorganic
colloids: Nalco colloidal silica sol, Particol polysilicate microgel, and
bentonite
clay; and; a high molecular weight cationic organic polymer, Percol 182 ,
polvacrylamide (PAM). Amounts of reagents added are provided in Tables 3-8,
all amounts are in ppm, based on the solution weight of the wash water.
Example 3 (Comparative)
250 ml of the wash water was stirred at medium speed. Polydadmac was
added at time = 0. At time = 10 seconds, an anionic inorganic colloid was
added.
After 15 seconds, mixing was stopped and the wash water was transferred to an
air
flotation set up comprising a 300 ml tall form beaker equipped with a fritted
glass
sparger (30 mm diameter medium porosity) centered in the beaker.
Approximately 50 ml per minute of air at I psi was sparged into the wash water
until time = 4 minutes, when the air sparging was stopped. Turbidity was
recorded at 5 and 10 minutes.
TABLE 3
Polydadmac Colloid Turbidity
Nalco sol Particol MX
Run ppm Si02, ppm Si02, ppm 5 min. 10 min.
1 10 20 >200 >200
2 10 40 >200 >200
3 10 20 >200 >200
4 10 40 >200 129
5 16 20 >200 >200
6 16 40 >200 >200
7 16 20 >200 >200
8 16 40 >200 112
As can be seen from Table 3, the combination of a low molecular weight
cationic organic polymer and an anionic inorganic colloid is insufficient to
reduce
turbidity to provide a clarified wash water. In Runs 1, 2, 5 and 6 no floc was
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formed. In Runs 3, 4, 7 and 8 a small dispersed floc was formed, which
contained
protein solids, but the floc could not be separated from the wash water.
Example 4
The same process as in Example 3 was followed except with the added
step of adding a high molecular weight cationic organic polymer,
polyacrylamide,
seconds after the addition of the anionic inorganic colloid. Mixing was
stopped 15 seconds after the addition of the polyacrylamide. Table 4 provides
the
quantities of reagents added and results.
TABLE 4
Polydadmac Colloid PAM Turbidity
Nalco sol Particol MX
Run ppm ppm, Si02 ppm, Si02 ppm 5 min. 10 min.
9 10 20 6 >200 66
10 10 40 6 >200 57
11 10 20 6 65 32
12 10 40 6 38 19
13 16 20 6 >200 >200
14 16 40 6 185 82
16 20 6 120 44
16 16 40 6 15 12
As can be seen from Table 4, addition of a high molecular weight cationic
polymer to the combination of a low molecular weight cationic polymer and an
15 anionic inorganic colloid enhances wash water clarification by reducing
turbidity.
In Runs 9, 10, 11, 12, 15 and 16 voluminous flocks were formed which separated
to the top and/or boftom of the wash water. These flocs could be recovered. In
Run 13 , at the higher loading of the cationic polydadmac, the amount of added
anionic inorganic colloid is not effective to neutralize a sufficient amount
of the
negative charge sites present on the solids and significant solids remained in
suspension, hence the high turbidity value.
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Example 5 (Comparative)
The process of Example 3 was repeated with use of bentonite clay as the
anionic inorganic colloid. Table 5 provides the quantities of reagents added
and
results.
TABLE 5
Polydadmac Bentonite Turbidity
Run ppm ppm, Si02 5 min. 10 min.
17 10 100 >200 >200
18 10 200 >200 >200
19 16 100 >200 >200
20 16 200 >200 >200
As can be seen from Table 5, the combination of a low molecular weight
cationic organic polymer and bentonite as the anionic inorganic colloid is
insufficient to reduce turbidity to provide a clarified wash water. Very fine
dispersed flocs were formed which could not be separated from the wash water.
Example 6
The process of Example 5 was repeated using bentonite clay as the anionic
inorganic colloid. Table 6 provides the quantities of reagents added and
results.
TABLE 6
Polydadmac Bentonite PAM Turbidity
Run ppm ppm, Si02 ppm 5 min. 10 min.
21 10 100 6 >200 147
22 10 200 6 84 46
23 16 100 6 >200 >200
24 16 200 6 158 77
As can be seen from Table 6, addition of a high molecular weight cationic
polymer to the combination of a low molecular weight cationic polymer and
bentonite as the anionic inorganic colloid enhances wash water clarification
by
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reducing turbidity. In Runs 21 and 23 fine dispersed flocs were formed, in
which
there was not an effective amount of bentonite added to neutralize a
sufficient
number of the cationic charge sites present. In these runs, the solids did not
separate very well. In Runs 22 and 24 voluminous flocs were formed which
separated to the top and bottom from the wash water.
Example 7
250 ml of the wash water was stirred at medium speed. Dilute sulfuric
acid was added to reduce to pH 3.5. At time = 0, an anionic inorganic colloid
vvas
added. At time = 10 seconds, a high molecular weight cationic polyacrylamide
was added. After 15 seconds, mixing was stopped and the wash water was
transferred to the air flotation set up described in Comparative Example 3.
Air
was sparged into the wash water at a rate of 50 ml per minute of air at I psi
until
time = 4 minutes, when the air sparging was stopped. Turbidity was recorded at
5
and 10 minutes.
TABLE 7
Colloid, ppm, SiO 2 PAM Turbidity
Run Nalco sol Particol MX Bentonite ppm 5 min. 10 min.
20 6 163 151
26 40 6 136 125
27 20 6 29 17
28 40 6 12 10
29 100 6 >200 131
200 6 90 38
As can be seen from Table 7, by lowering the pH of the wash water
20 followed by addition of both an anionic inorganic colloid and a high
molecular
weight cationic organic polymer, turbidity is reduced. In all of the runs,
fine to
large to compact flocs containing solid proteins were formed which separated
to
the top and/or bottom of the wash water. The protein-containing flocs could be
recovered.
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Example 8
250 ml of a poultry processing wash water was stirred at medium speed.
Dilute sulfuric acid was added to reduce to pH 3.5. At time = 0, Particol MX
polysilicate microgel was added. At time = 20 seconds, a high molecular weight
cationic polyacrylamide (PAM) was added. At time = 30 seconds, mixing was
stopped and the wash water was transferred to the air flotation set up
described in
Comparative Example 3. Air was sparged into the wash water at a rate of 100 ml
per minute of air at I psi until time = 4 minutes, when the air sparging was
stopped. Turbidity was recorded at 5 and 10 minutes. The liquid was then
drained from the air flotation set up through a screen at time = 12 minutes
and
turbidity of the drained liquid was measured. The protein containing solids
were
collected on the screen.
TABLE 8
Particol MX PAM Turbidity
Run ppm, Si02 ppm 5 min. 10 min. Drained liquid
31 20 6 51 30 28
32 40 6 14 10 13
As can be seen from Table 8, the turbidity of the wash water was reduced
over time. Further, this example demonstrates separation of the solids from
the
wash liquid as the solids were collected on the screen. The turbidity of the
drained liquid showed little change from the value at 10 minutes, indicating
that
the solids were retained on the screen and did not become redispersed in the
process and pass through.
Example 9
Another sample of a wash water containing about 1000 ppm of un-
flocculated biosolids was obtained from an Eastern Shore poultry processing
plant, having a turbidity of over 200.
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Polysilicate microgel solution, Particol MX, was stabilized with sulfuric
acid. The microgel solution was aged for various periods of time before use,
the
aging times provided in Table 9.
250 ml of the wash water was stirred at medium speed. At time = 0, high
molecular weight polyacrylamide, Percol 182 , 8 ppm, based on the solution
weight of the wash water, was added. At time = 1 minute, the acid stabilized
aged
polysilicate microgel solution was added, 120 ppm, based on the solution
weight
of the wash water. Runs were made for each aging time. At time = 2 minutes,
the
stirring speed was reduced to slow. At time = 5 minutes, the stirring was
stopped.
At time = 15 minutes, turbidity of the wash water was measured.
TABLE 9
Aging Time Turbidity
seconds 122
5 minutes 39
15 minutes 21
45 minutes 5
15 As can be seen from the results in Table 9, the combination of an acid
stabilized polysilicate microgel and cationic polyacrylamide was sufficient to
reduce turbidity of the wash water without the need to first reduce pH to less
than
7. In addition, the results show that longer aging times of the polysilicate
microgel provided further improvements in reducing turbidity. In another
experiment with similarly aged microgel solution, the average size of the
microgel
increased from 5 nm at 15 seconds aging time to 230 nm at 45 minutes aging
time.
Example 10
250 ml of soybean whey solution from Protein Technologies, Inc.
containing 0.51% protein was stirred at medium speed. Dilute sulfuric acid was
added to adjust to pH 2.5. 160 ppm, based on the solution weight of the
soybean
solution, of BMA-9 colloidal silica, available from Eka Chemicals AB, Bohus,
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Sweden, was added at time = 0 and mixed for 10 minutes at medium speed. 8
ppm, based on the solution weight of the soybean solution, of high molecular
weight polyacrylamide, Percol 182 , was then added and mixed for 10 minutes.
The mixture was filtered using glass filter paper 934AH, available from
Whatman,
Clifton, NJ. 0.11 grams of solid protein were recovered. The filtered solution
contained 0.416% protein, representing a 20% reduction in protein content.
Example 11
An aqueous waste stream from an Eastern Shore poultry processing plant
was treated on-stream in accordance with this invention in a continuous
process.
To the waste stream was added simultaneously, sufficient sulfuric acid to
reduce
the pH of the stream to 3.7 and Particol MX, polysilicate microgel, 95 ppm
Si02, based on the solution weight of the stream. Downstream (about 30
seconds) from the point of addition of the acid and the microgel was added
cationic polyacrylamide, Percol 182 , 4 ppm, based on the solution weight of
the
stream. The stream was directed to a dissolved air flotation (DAF) unit, where
the
solids were floated to the surface and skimmed off for recovery. The remaining
aqueous stream was tested for chemical (COD) and biological oxygen demand
(BOD) and total suspended solids (TSS).
COD was determined using a Hach COD Test Kit, available from the
Hach Company, Loveland, CO. TSS was determined by Method 2450 D from
"Standard Methods for Examination of Water and Wastewater", published jointly
by the American Public Health Association, American Water Works Association
and Water Environment Federation. BOD was determined by Method 5210 from
"Standard Methods for Examination of Water and Wastewater".
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TABLE 10
Treatment COD, mg/I BOD, mg/1 TSS, mg/1
None 2970 1393 N/T*
Example 11 180 180 67
*N/T = not tested. But typically this number is about 1000 mg/1 prior to
treatment.
As can be seen from Table 10, the process of this invention reduces
chemical and biological oxygen demand of the waste stream in a continuous flow
process of an actual poultry processing plant.
Example 12
A slurry of 20 grams of Staley Pearl Starch, unmodified corn starch in 980
grams of water was stirred at medium speed. 10 ppm Si02, as Particol MX,
acid stabilized polysilicate microgel solution, based on the weight of the
starch
slurry, was added at time = 0 and mixed for 15 seconds. High molecular weight
polyacrylamide, Percol 182 , 2 ppm, based on the solution weight of the starch
slurry, was then added at time = 15 seconds and mixed for 30 seconds. Mixing
was then stopped. Turbidity measured after 30 seconds of standing, at time =
45
seconds, was 46. The test was repeated, the only difference being 20 ppm of
Si02, as Particol MX, was used. Turbidity at 45 seconds was 29. In a third
comparative test, the Particol MX was not added. Turbidity was 186.
Example 13
A sample of wastewater was obtained from an Eastern Shore poultry
processing plant. The wastewater had a COD of > 2100 ppm, an initial turbidity
of > 200, and a pH of 6.1. Into a 400 ml beaker was placed 250 ml of the
wastewater. The wastewater was stirred using a mechanical propeller type
stirrer
at 275 rpm. The pH of the wastewater was adjusted using dilute H2SO4 to pH
5.5. At time = 0, Particol MX, silica microgel, was added. At time = 15
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seconds, cationic polymer, polyacrylamide (PAM), Percol 182 was added. At
time = 25 seconds, or 10 seconds after the polymer was added, the mixer speed
was reduced to 150 rpm. Mixing was stopped 40 seconds after the addition of
the
polymer. The wastewater was sampled for turbidity measurements at 35 and 95
seconds after mixing was stopped. The pH was measured after the 95 second
turbidity measurement. The flocculated wastewater was then resuspended by
mixing for 30 seconds at 150 rpm. After 1 minute, the agitation was
discontinued
the wastewater was sampled for COD measurements.
COD was determined using 0-1500 ppm COD colorimetric analysis
ampules from CHEMetrics, Calverton, VA and a Milton Roy Spectronic model 20
spectrophotometer set at 620 nm wavelength. Table 11 provides the quantities
of
reagents added and results for these runs, which are 33 and 34.
Example 14
The process of Example 13 was repeated using the same wastewater
sample. However, instead of adding acid, 32 ppm of FeC13 was added 15 seconds
prior to addition of the Particol MX. All times from Example 13 are shifted
by
adding 15 seconds. Quantities of reagents added and results are provided as
Run
35 in Table 11.
Table 11
Run Particol MX, Cationic Turbidity Final pH COD,
ppm, Si02 PAM, ppm 35 sec 95 sec ppm
33 120 12 33 32 5.68 475
34 80 12 10 9 5.63 386
35 120 12 16 14 5.61 415
As can be seen from Table 11, the combined use of acid or ferric chloride,
silica microgel, and cationic polyacrylamide are effective to reduce
turbidity, and
chemical oxygen demand in a wastewater stream containing biosolids.
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Example 15
The process of Example 13 was repeated using the same wastewater
sample. However, there was no step to reduce pH and the organic polymer was
varied. At time = 0, Particol MX was added. At time = 15 seconds, low
molecular weight cationic polymer, polyamine, Agelfloc A50HV, available
from Ciba Specialty Chemicals, was added. At time = 30 seconds, a second
organic polymer was added, either cationic polyacrylamide (PAM), Percol 182
or anionic polyacrylamide (PAM), Percolt 155 PG, also available from Ciba
Specialty Chemicals, was added. At time = 40 seconds, or 10 seconds after the
polymer was added, the mixer speed was reduced to 150 rpm. Mixing was
stopped 40 seconds after the addition of the polymer. The wastewater was
sampled for turbidity measurements at 35 and 95 seconds after mixing was
stopped. The pH was measured after the 95 second turbidity measurement. The
flocculated wastewater was then re-suspended by mixing for 30 seconds at 150
rpm. After 1 minute, the agitation was discontinued the wastewater was sampled
for COD measurements. Table 12 provides the quantities of reagents added and
results.
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TABLE 12
Run Particol MX, Polyamine, Cationic Anionic Turbidity Final COD,
ppm, Si02 ppm PAM, PAM, 35 sec 95 sec pH ppm
ppm ppm
36 50 40 12 185 84 6.03 444
37 50 40 12 33 28 5.98 429
38 100 40 12 5 4 5.99 415
39 100 40 12 6 3 5.99 540
As can be seen from Table 12, different organic polymers and in different
combinations can be used with an anionic colloid to clarify wastewater and
reduce
chemical oxygen demand. In Runs 36 and 38, a low molecular weight cationic
polyamine is used in combination with a high molecular weight polyacrylamide.
In Runs 37 and 39, the polyamine is used in combination with an anionic
polyacrylamide.
Example 16
The process of Example 13 was repeated with the difference of adding
base, sodium hydroxide to increase pH to 6.5 prior to the addition of the
Particol
MX. The remaining steps were performed without change. Table 13 provides the
quantities of reagents added and results.
Table 13
Run Particol MX, Cationic Turbidity Final pH COD,
ppm, Si02 PAM, ppm 35 sec 95 sec ppm
40 80 12 55 55 6.42 766
41 40 12 34 34 6.51 628
As can be seen from Table 13, clarification of the wastewater stream and
reduction of its chemical oxygen demand can be achieved at pH close to 7, with
use of an anionic colloid and cationic polymer.
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