Note: Descriptions are shown in the official language in which they were submitted.
1065789
Specification:
The control of the quality of waste water effluent
from industrial plants has received an increasing amount of
attention in recent years due to public concern for the envi-
ronment. In removing suspended charged particles from waste
water, generally two processes are utilized. These may be
classified generally as electrolytic and dissolved air puri-
fication processes.
In the electrolytic process as practiced today,
waste waters are generally treated chemically and then sub-
jected to electrolytic action wherein both a charge transfer
; and formation of microbubbles gradually float foreign parti-
cles and suspended solids together with fats and oils to the
surface of the water being treated. This process has a dis-
advantage in that the floc is totally formed before electro-
r ~ ~ cO~ ~c,~
lytic action initiatoQ. Under the~e conditions an electro-
static charge transfer between microbubbles and the floc takes
plsce slowly and rather inefficiently. As the result of this, -
electrolytic purification processes often have considerable
r-sidual floc carry-over in the effluent waters. Another dis-
advantage of conventional electrolytic treatment of waste wa-
ters is that a large area ~the entire tank) must be electro-
lytically wired and prepared for the process. This involves
high cost and considerable equipment.
In the dissolved air process for purifying waste
waters, the process is based on the formation of microbubbles
once the air pressure is released from the pressurized waters.
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Under these conditions, like~the electrolytic process, micro-
bubbles are formed after the floc has been formed. Here again,
the slow interaction between the formed floc and the micro-
bubbles lowers the over-all efficiency of the flotation pro-
cess .
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Another disadvantage of the dissolved air process
is that it initiates large amounts of turbulence in the water
being purified. This allows much of the residual floc to pass
through the process without being floated. Further, the dis~
solved air microbubbles are not fully charged as are electro-
lytic microbubbles and, therefore, their attraction for oppo-
sitely charged foreign particles in water is less.
Accordingly, it is one purpose of this invention to
provide a waste water treatment process wherein the conditions
are such that an electrostatic charge transfer between micro-
bubbles and the floc takes place efficiently.
Another purpose of this invention is to provide a
process which will generate sufficient microbubbles of the
desired size and number per unit volume so that essentially
all of the suspended solids are floated to the surface in the
system.
Other purposes and advantages are readily set forth
herein will become readily apparent to one skilled in the art
on reading the following description of the invention. ~`
This invention relates to an improved process for
clarifying and removing suspended and dissolved foreign
particles from waste water wherein the waste water is subJec-
ted to flocculating conditions, the improvement which com-
prises first coagulating the foreign particles by mixing
into the waste water from about 10 to about 1000 ppm of a
multivalent metal salt selected from the group consisting of
ferric sulfate, ferric chloride, aluminum sulfate, alum and
lime, next incorporating into the waste water microbubbles
having a diameter of about 10 to 500 mlcrons and in a number
in excess of about 105 per liter of waste water treated 90 as
to interact with the coagulated foreign particles to form
embryo flocs of said microbubbles and coagulated foreign
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1065789
particles to form embryo flocs of said microbubbles and coagu-
lated foreign particles, which embryo flocs and substantially
all of the waste water remain unseparated from each other,
subsequently mixing said unseparated embryo flocs and water
with a polyelectrolyte polymer flocculant so as to combine
a plurality of embryo flocs into a final floc which floats
to the surface of the waste water, said polyelectrolyte
being added in an amount of about 0.1 to 100 ppm based on the
amount of waste water being treated and only after said step
of incorporating microbubbles to form embryo flocs has ceased
and only within a period of from approximately 2 seconds to
about 30 minutes after initiating said step of incorporating ;
microbubbles, and removing from the waste water the final
floc that is floating at the surface of the waste water.
In general, the instant invention takes full advan-
tage of the formation of microbubbles in waste water which in-
teract with suspended material to form an "embryo floc."
For purposes of this invention, an "embryo floc" is that floc
formet by the interaction among coagulant (if used), solid and
liquit colloidal particles and the microbubbles. An "embryo
floc" while usually comprising a coagulant need not of neces-
sity possess a coagulant. The time interval needed to form ~-~
"embryo floc" can vary from about 10 sec. to several minutes.
Under certain circumstances, an embryo forming time can be as
long as 30 minutes or longer. In essence, microbubbles of ~,
either hydrogen, oxygen or air are formed in the waste water
to which multivalent metal ion coagulants have often been
added.
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~065789
The microbubbles are formed in such a number that the number
f~ ~ "ce eG/S A
of microbubbles per liter generally ~*eo4~ about 10 .
Generally speaking, most suspended liquids or solids
~often colloidal emulsions) in waste water are negative in
charge and multivalent metal ~alts are often added to react
with the negative particles, and by coagulation, to break the
emulsion. These coagulants, such as aluminum sulfate, alum,
ferric sulfate, ferric chloride, lime, etc., break down emul-
sions and ionize to their hydroxide structure and form part of
an "embryo floc". In the present invention there is a close
and beneficial interaction between the fine microbubbles and
the water impurities which become attached thereto. This con-
dition allow~ the microbubbles to efficiently attach themselves
to the many colloidal particles with or without the use of
flocculants prior to floc formation.
A second phase of the process is based on the addi-
tion of a polyelectrolyte added to the "embryo floc" after
microbubble formation whereby a complete floc is formed en-
compassing the metal hydroxide, foreign water impurities, the
polyelectrolyte and a sizable volume of microbubbles. This
final floc is a compact structure with a low apparent density
(usually about .7 - .9) which is less than the water itself.
As a result, the formed floc rises rapidly to the surface leav-
ing behind clarified water.
Microbubbles are generated in the waste water system
either by mechanical means (pressurized air or severe agitat-
ion) or by electrolysis. If oxygen or air is dissolved in the
waste water the microbubbles consist of oxygen. If electro-
lysiæ takes place the microbubbles usually consist of hydrogen
and oxygen. The formation of the microbubbles is especially
beneficial since there is a very large interfacial surface for
interaction between the charged microbubbles and the charged
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~065789
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colloidal material in the waste water.
A feature of this invention is that the flocculants
~polyelectrolytes) are added only after (which may be sub-
stantially instantaneously after) the microbubbles have been
formed and thi~ condition leads to the formation of a final
floc consisting of at least three phases; namely, a water
phase, a gas phase (microbubbles) and, finally, a floc phase
; consisting of metal hydroxides and fore~gn water impuritie~.
In the present invention it has1rfound that the gas
bubbles for $1Otation of foreign impurities in water are most
effective between the sizes of about 10 and 500 microns pre-
ferable between about 20 and 300 microns. The invention ur-
ther teaches that the size of the microbubles can readily be `
formed by various mechanical means such as the use of blenders,
Venturi aspirators, mechanical pumps with forced air injection,
and high speed mixers, to name a few. The degree of control of
microbubbles can be achieved by changing parameters in the ~ -
mechanical emulsification of air into water. The p~rticular
invention prefers air bubble size in the 20 to 200 micron size
~diameter); however, it has been found the process will func-
tion properly even when the bubbles are as small as 10 microns ~;
or as large as S00.
It is important, however, that the bubbles be gen-
erated in sufficient quantity to exceed about 10 bubbles per
liter of water treated. Generally, the number of bubbles per
liter will exceed 10 , preferable 106-109, as it has been found
that the greater the number of bubbles the greater the effect.
The upper limit i3 dictated by economics. The microbubbles
rise in the water at a rate which is a function of their dia-
meter, namely, small microbubbles rise slower. This is espe-
cially important because the rate of rise of the gas micro-
bubble determines the time which the bubble resides in the
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106S789
water phase. Larger residence time provides greater proba-
bility for contact and subsequent union with the pollutant
particle.
The instant invention is a waste water treatment
process which may be used in reducing the total suspended
solids of municipal and industrial waste streams. In a par-
ticular embodiment the waste ~tream passes through an electro-
coagulation zone and a flocculation zone. A point can be se-
lected in the waste stream at about a few seconds to several
minute~ flow time removed from the electrocoagulation zone for
the introduction of the polyvalent metal ions. A sufficient
amount of multivalent metal ions (10 to several thousand ppm)
is introduced in the waste water usually prior to contact with
the microbubbles formed in the electrocoagulation cell. In
some systems metal compounds are used to provide about 10 to
about 1000 (preferable 10-400 ppm) parts per million by weight
of aluminum, calcium or iron ions. After allowing the metal
ions to disperse and interact with the microbubbles and pol-
lutants in the aqueous waste stream for a period of time, usu-
ally a fraction of a minute to several minutes, a small amountin the order of from about .1 to about 100 ppm (usually 1-10
ppm) of a polyelectrolyte is introduced into the stream while
the waste water i8 conveyed to a settling treatment basin where
the floc particles are removed from the surface of the waste
water.
~hile the invention is not restricted to a particular
polyelectrolyte, it has been found that high molecular weight ; -
anionic polymers such as copolymers of from 90 to 50 weight
per cent acrylamide or methacrylamide and from 10 to S0 weight
percent acrylic or methacrylic acid or water soluble salts
thereof produce outstanding results. These copolymers are
characterized by a weight average molecular weight of at least
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~()6S"~89
from about 2 million and usually up in the range of about 7 to
12 million as mea~ured by the light scattering technique. Such
polymers are known in the art and are available from several
commercial sources.
It has been found that for effective flotation of
waste water floc, the electrolytic energy needed to form the
"embryo floc" lies between about 1 ampere-minute per gallon
and about 8 ampere-minutes per gallon. While the energy input
may vary between .5 ampere-minute~/gallon (for very lightly
contaminated waters) to up to 50 ampere-minutes per gallon,
usually about 20 ampere-minutes is the upper limit due to
economics. A good operating range is about 1-8 ampere-minutes
per gallon, usually 1.5-4 ampere-minutes per gallon. Under
these conditions the floc formed after the addition of the
polyelectrolyte will surface rapidly and completely.
It has also been found that the volume of the micro-
bubbles needed to carry out efficient and rapid flotation of `
the formed floc lies between about .1 volume percent and 20
volume percent, usually .3 volume percent to 10 volume percent
~standard temperature and pressure) of water volume. Excel-
lent results have been found when the volume percent of gases
in the water was in excess of .3 volume percent, and using ~ -
1.5-50 ampere-minutes per gallon of water treated, 10 - 109 `;
microbubbles per liter and a micron bubble range of 30-200.
While the design of an electrolytic cell can vary
widely it has been found advantageous to ~eep it as small and
compact as possible. In order to keep power cost down, elec-
trode spacing ~surface to surface) in the electrolytic cells ~ ~ -
should be kept less than two inches apart. Usually, anodes
and cathodes are alternately spaced. Circularanode~ and cath-
odes are very effective and the invention is not restricted to
the physical configuration of the electrodes. Accordingly,
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1065789
squares, rectangular sheets and other types of anodes and
cathodes can be used satisPactorily. It has been found, how-
ever, that Duriron (a trade mark for high silicon iron alloy)
anodes produce very good results. However, platinized
titanium, aluminum, platini~ed niobium, graphite, carbon, lead-
antimony-silver and ruthenium oxide deposited on titanium anodes
provide satisfactory results. Electrode current densities should
be as high as practical, between about S and 200 amperes, usual-
ly about 10-100 amperes per square feet of electrode.
The following examples are set forth as illustrated
embodiments of the invention and are not to be taken in any
manner as limiting the scope of the invention which is defined
by the appended claims.
EXAMPLE I
200 cc. of tannery waste water was placed in a beak- --
er. To this were added 500 ppm of ferric sulfate and 100 ppm ~
of calcium hydroxide. This mixture was placed in a household `
blender and blended for 2 seconds. The water contained an ` -~
excess of 105 bubbles per liter. The solution was then removed
from the blender and poured into a beaker. At a point of ~
approximately 30 seconds, 1/2 ppm of a polyelectrolyte (a co- ~ -
polymer of 80 parts of acrylamide and 20 parts of sodium
acrylate) was added to the whipped waste water. The mixture ;`
was then gently hand-stirred and allowed to stand. The floc
formed in the operation was entirely floated to the surface.
Analysis of fats and oils, before and after the operation, are
as follows: hefore operation 650 ppm; after operation 20 ppm.
EXAMPLE II
200 cc. of tannery waste water was placed in a
beaker. To this was added 500 ppm of ferric sulfate and 100
ppm of calcium hydroxide. Ordinary tap water was then placed
into a blender and microbubbles developed therein. This solu-
tion containing microbubbles in excess of 105 per liter was
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10657~9
poured into the waste water. The combination was then manual-
ly mixed to disperse the air bubbles and subsequently within
30 seconds, 1/2 ppm of electrolyte polymer was added. Here
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again the floc was brought to the surface by the L~y4uffK~ of
; the microbubbles. Analysis of the waste water before and
after treatment was as follows: before treatment 650 ppm;
after treatment 20 ppm.
EXA~PLE III
200 cc. of tannery waste was placed in a graduate
(200 cc. graduate), to this, 800 ppm of ferric sulfate and 300
ppm of slaked lime were added with mixing between each addi-
tion. This mixture was placed in an electro coagulation cell
U8 ing platinized tetanium cathodes and anodes. Electrode area
j was .5 in2 for cathode and .5 in2 of anode. Spacing between
electrodes was .3". One-half ampere of current at 15 voltR
was passed through the electro coagulation cell for 20 seconds.
Immediately thereafter, 2 ppm of an anionic polyelectrolyte
(copolymer of acrylamide and Na acrylate) was added to the
waste water. The waste water was then gently agitated for 30
~; 20 seconds.
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'~l`J Immediately thereafter, a buoyant floc formed that
floated to the surface and this was subsequently skimmed off.
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Waste water quality before and after the treatment follow.
Suspended Fats &
BOD Solids Oils
. Before Treatment 985 465 380
After electro
coagulation treatment 220 105 15
Obviou-~ly, many modifications and variations of the
invention as hereinbefore set forth may be made without de-
parting from the spirit and scope thereof, and, therefore,
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; only such limitations should be imposed as are indicated in
the appended claims.
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