Note: Descriptions are shown in the official language in which they were submitted.
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WASTE WATER TREATMENT PROCESS
The invention relates to a process and an apparatus for
removing dissolved and suspended organic contaminants from waste
water streams, particularly industrial waste water streams.
Many industrial waste streams contain small amounts of
dissolved and suspended organic contaminants which must be
removed in order to permit the waste streams to either be
re-utilized or to be ultimately discharged into the environment.
These contaminants can be toxic and/or otherwise deleterious to
animal an/or plant life and cou;d, for example, adversely effect
further waste water treatment such as biological treatment, or the
environment in general if they were to be released thereinto. ~n
the other hand, if these same waste waters were to be re-utilized,
the organic contaminants might corrode process material, deposit
upon heat exchange surfaces, plug filter beds, and the like. Thus
a quic~ and efficient means for removing these organic contaminants
from waste water streams is highly aesirable.
U.S. Patent Specification 3,658,697 discloses a waste water
treatment process which utilizes a column of activated carbon oper-
ating under anaerobic bacteriological conditions with a subsequent
flocculation utilizing an iron-based flocculant optionally in the
presènce of a polyelectrolyte flocculant. U.S. Patent Specification
4,043,904, discloses a method for removing certain surface active
agents from waste water by first adding an inorganic flocculant material,
optionally coupled with a polymeric flocculating agent, to the waste
water and ~hen adding powdered active carbon to the waste water, and
then filtering the activated carbon from the waste water. Further,
Lettinga et al in Prog. Wat. Tech. Vol. 10, Nos. 1/2, pp. 537-554
(19783 di8close the use of a fluidized bed of polyelectrolyte-
flocculated powdered carbon to treat waste water.
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However, in these citations the rapid and effective
method of the present invention has not been disclosed.
It is an object of the invention to provide a rapid
and effective method and apparatus for removal of dissolved and
suspended organic contaminants from waste water streams.
The invention therefore provides a process for removing
dissolved and suspended organic contaminants from waste water from
a refinery effluent stream or from aqueous process streams in
synthetic pyrethroid manufacture comprising the steps of a)
dispersing by means of a stirrer powdered activated carbon into
said waste water with a contact time of agitation of at least 2
hours to provide adsorption of the contaminants on the carbon,
wherein the ratio of waste water to carbon is in the range of
from about 10 to about 1000, b) treating by means of a stirrer
the carbon-containing waste water with an organic polyelectrolyte
flocculant in a concentration of at least 0.05 ppm in order to
coagulate the suspended solids and the powdered activated carbon
in a supernatant, and c) separating said coagulated solids from
the said supernatant.
The invention also provides an apparatus for carrying
out the above-mentioned process, said apparatus comprising means
for a) dispersing by means of a stirrer powdered activated
carbon into said waste water with a contact time of agitation of
at least 2 hours to provide adsorption of the contaminants on
the carbon, wherein the ratio of waste water to carbon is in the
range of from about 10 to about 1000, means for b) treating by
means of a stirrer the carbon-containing waste water with an
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organic polyelectrolyte flocculant in a concentration of at least
0.05 ppm in order to coagulate the suspended solids and the
powdered activated carbon in a supernatent, and means for c)
separating said coagulated solids from the said supernatant.
In this way equilibrium adsorption on the powdered
active carbon is rapidly achieved thus avoiding the long contact
times needed when granular adsorbents are utilized. The powder-
ed activated carbon is readily flocculated with organic poly-
electrolyte flocculants, particularly anionic polyelectrolyte
flocculants. Therefore, separation of the aqueous effluent from
flocculated powdered active carbon and flocculated suspended
organic contaminants is readily achieved. In an advantageous
embodiment of the invention step a) ranges from about 50 to about
750. In another advantageous embodiment of the invention step
a) ranges from about 100 to about 500.
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The invention will now be described by way of example in more
detail with reference to the drawing, in which the figure is a
schematic flow diagram illustrating an apparatus capable of
performing an embodiment of this invention.
With reference to the figure, a semi-continuous treatment
scheme is schematically illustrated for an example of the
embodiments of the present invention. Untreated waste water enters
the processing system via a stream I to a holding tank ~0 (not to
scalè~. From the holding tank ~0 it is pumped via a stream 2 to
a treatment vessel 1]. While the treatment vessel 11 is being
filled with waste water, powdered carbon from a storage vessel 12
is fed into the treatment vessel ll at a rate depending upon the
organic contaminant level in the waste water. The carbon/waste
water suspension is stirred utilizing a stirrer 15; however, vigorous
agitation is not necessary since powdered carbon is readily
dispersed_ After the treatment vessel ]l is filled to some
predetermined level, say approximately 3/4 full, the stream 2
is cut off and the waste water is allowed to fill up the holding
tank lO. After filling of the treatment vessel, the flocculating
agent is added to the carbon slurry and stirred until flocculation
is complete. Concentrated flocculating agent is stored in a
storage container 13 and metered into a dispersion and delivery
container 14 via a strea~ ; along with water from a stream 6.
A dispersed flocculating agent will be sprayed into the treatment
~5 vessel-via a stream 7. The stirring is stopped after the
flocculation is completed and the floc is allowed to settle. The
floc is removed from the bottom of the treatment vessel via a
stream 3 and may be regenerated or burned or otherwise disposed of
in a appropriate manner and the aqueous effluent is removed from
the treatment vessel via a stream 4. The above described process
has been presented to illustrate an example of possible embodiments
of the present invention and is not intended to limit the present
invention. ~ariations in the described process will be readily
apparent to one skilled in the art.
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The powdered activated carbons useful in the present process are
readily available commercially. They are characterized by high
surface areas and small particle sizes. Typically, the particle
sizes would be less than 200 mesh, in an advantageous embodiment
less than 275 mesh. The powdered activated carbons are prepared
from lignite, bituminous coal, petroleum and other bases.
The organic flocculants suitable for use to produce flocculation
and thereby remove suspended organic contaminants and powdered
activated carbon having adsorbed thereon dissolved and/or suspended
organic contaminants comprise natural and synthetic polyelectrolytes
which may be anionic, cationic or non-ionic.
Organic flocculants for example inclu~e proteins and protein
products, gluten, starches and casein and will not be described in
detail. Polyelectroly~e flocculants and other flocculants as
such, suitable for use with the process of this invention are
known to those skilled in the art and will not be described in
- detail. Polyelectrolyte flocculants as such for use in sewage
treatment systems are also known and will not be described in
detail.
Anionic polyelectrolyte flocculants are found to be
advantageous for flocculating the activated carbon utilized in the
present invention. However, other suspended organic contaminants
found in the waste water may require other types of polyelectrolyte
flocculants for optimum flocculation. Thus, more than one type of
polyelectrolyte flocculating agents may be utilized, as for example
an anionic flocculating agent with a non-ionic flocculating agent.
The use of certain flocculating agents may require the p~ of
the waste water to be adjusted. Suitable inorganic acids or
bases may be used to lower or raise the pH as is necessary.
The length of time which the waste water is in contact with
the activated carbon and the concentration of the flocculants
added to waste water to affect flocculation will depend upon the
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conrentration of contaminants and the degree of purification
desired. Normally7 carbon is added to the waste water such that
the ratio of waste water to carbon is in the range of from about
10 to about 1000, in an advantageous embodiment from about 50
to about 750. Normally, the organic polyelectrolyte flocculant is
added to the waste water in the concentration of at least 0.05 ppm.
The process of this invention is further described by the
following illustrative embodiments which are provided for
illustration and are not be construed as limiting the invention.
As used herein, the term "biological oxygen demand" (BOD) is
the quantity of oxygen used in the biochemical oxidation of
organic matter in 5 days at 20C. "Chemical oxygen demand" (COD)
is the quantity of oxygen expressed in ppm consumed, under
specific conditions in the oxidation of oxidizable organics and
inorganics contained in waste water. These parameters are
known to those skilled in the art and will not be discussed in
detail.
EXAMPLE I
To test the suitability of the adsorption/flocculation
process of the present invention for treating waste waters,
waste water from a refinery effluent stream is utilized. This
waste water stream has a TOC (Total Organic Carbon) of about 10
and a pH of 7. This waste water is spiked with about 50 ppm
of sulfolane and about 50 ppm of phenol in order to pro~ide a
stringent test for the process cf the present invention. Adsorption
isotherms are determined by the conven~iona~ static method, which
involves the agitation of the waste water with the powdered carbon
at various liquid to solid (L/S) weight ratios. The samples are
shaken at 25C for either 2 hours or 24 hours to provide adsorption
of the contaminants on the carbon and then floc is added to the
- containers of these waste water solutions with stirring for 30
seconds fast, 30 seconds slow, with 30 seconds of settling
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allowed. The supernatant is then analyzed for TOC and COD. The
flocculating agent utilized is PURIFLOC A-27~ flocculant manufact-
ured by Dow Chemical Company. This flocculant is an anionic,
hydrolyzed, water-soluble, synthetic organic polyelectrolyte. Two
powdered activated carbons manufactured by ICI are utilized,
Hydrodarco H~ and Hydrodarco C (HDH & HDC)~. These materials are
lignite-based powdered activated carbons made especially for
municipal and industrial waste water treatment. The HDH powdered
carbon has a particle size of at least 70% less than 325 mesh and
a surface area of approximately 475 m /gm. The HDC powdered carbon
has a particle size of at least 70% less than 325 mesh and a
surface area of about 550 m2/gm. Results for these tests are
shown in Tables 1 and 2.
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Table 1
REFINERY EFFLUENT ADSORPTION/FLOCCULATION TESTS
Effluent spiked with 50 ppm sulfolane and 50 ppm phenol
Adsorption: 2 hr contact with agitation
Flocculation: 5 ppm A-27
Stirring: 30 sec fast; 30 sec slow; 30 sec settling
TOC = 60 ppm
Spiked Feed COD = 236 ppm
Treated Effluent
TOC _ COD
Equilibrium g Sorbed Equilibrium g Sorbed
Carbon L~S TOC H o (ppm) 100 g Carbon COD H20 (pp )
HDC 300 20 1.2 58 5.3
HDC 600 25 2.1 65 10.3
HDC1000 36 2.4 84 15.2
HDH 300 19 1.2 67 5.1
HDH 600 30 1.8 76 9.6
HDH1000 38 2.2 139 9.7
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Table 2
REFINERY EFFLUENT ADSORPTION~FLOCCULATION TESTS
Effluent spiked with 50 ppm sulfolane and 50 ppm phenol
Adsorption: 24 hr contact with agitation
Flocculation: 5 ppm A-27
Stirring: 3Q sec fast; 30 sec slow; 30 sec settling
Spiked Feed COD - 236 ppm
Treated Effluent
TOC COD
Equilibrium g Sorbed Equilibrium g Sorbed
H20 (ppm) 100 g Carbon CODH O (ppm) 100 g Carbon
-
HDC300 18 1.2 64 5.2
HDC600 23 2.2 67 10.1
HDC1000 30 3.0 131 10.5
HDH300 19 ].2 74 4.9
HD~600 25 2.1 117 7.1
HDH1000 40 2.0 161 7.5
As can be seen from the tables there is essentially no difference
between the adsorption isotherms obtained with the two carbons
tested. Adsorption kinetics are fast, since a 2 hour contact time
was sufficient for equilibrium. About 6~% of the total organic
carbon is removed at the lowest (300:1) liquid to solid (LtS) ratio
used. Higher removals would be possible at lower L/S ratios. If
the TOC adsorption data were to be plotted logarithmically as
the amount of TOC sorbed per unit weight of carbon versus the
amount of TOC remaining in the solution at various concentrations,
and a straight line were drawn through these data points, the
line would have a slope of about 1.3. This fairly small slope
suggests the possibility of removal of contaminants down to
extremely low levels in the aqueous phase. The HDC carbon flocs
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are noted to settle faster than the HDH carbon flocs in this
system. The use of a cationic flocculating agent, Dow PURIFLOC
C-31~, provides less satisfactory flocculation than did the use
of anionic flocculating agent. Other flocculating agents that
can be utilized and will provide satisfactory results are Dow
products PURIFLOC A-25~, SEPARAN PG-6~, and PURIFLOC N-20X.
EXAMPLE 2
In the manufacture of PYDRIN ~ Insecticide~ which is a
synthetic pyrethroid, this pyrethroid must be removed from aqueous
process streams before these streams can be fed into the biotreater.
The process of the present invention has proved remarkably suitable
for removal of the pyrethroid from these process streams.
Several solid adsorbents are screened for PYDRIN ~
Insecticide removal from simulated wash water so]utions at room
temperature (48 hr contact time of agitation and at a liquid to
solid ratio of 250 to 1). The simulated wash water solution is
prepared by adding 0.5 grams of powdered soap (Pennico Plus)* and
1.0 cc liquid soap (Poly Sol) to 1 litre of tap water. PYDRIN is
added from an acetone or hexane solution to give a final PYDRIN
concentration in the aqueous phase of about 20-50 ppm. Two
different solvents are utilized for the addition of the PYDRIN
Insecticide to the wash water solution because it is believed that
the mechanism of solubilization should differ for each of these
two solvents since heptane is not water soluble and acetone is
miscible with water. The acetone solution would favour formation
of micro-crystalline solid PYDRIN Insecticide particles due to
precipitation in the aqueous phase. The surfactant would be
expected to adsorb on the particles and stabilize them in a
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colloidal state. The heptane solution of PYDRIN Insecticide would not dispersein the aqueous phase and would be expected to form very dilute oil-in-water dis-
persions. In this latter case, the PYDRIN Insecticide would remain primarily in
the oily heptane micro-droplets. This dispersion would be stabilized by surfact-
ant adsorption at the oil/water interface. The equilibrium data for the various
adsorbents are shown in Table 3.
Table 3
PYDRIN Insecticide Adsorption from Simulated Wash Water
Feed 30 ppm PYDRIN
L/S = 250 lb-H2O/lb-solid
room temperature
Final PYDRIN Conc(ppm)
Adsorbent Acetone Heptane
Darco S-51 PAC )* 0.01 0.008
Hydrodarco 3000 GAC )* 0.12 0.056
ICI GACC)* 0.83 17.4
Celite ~ 1.1 8.9
XAD 2C)* 7,5
Pittsburgh Active
Carbon-SGL GAC )I 9.1 7.7
XAD-4e)* 19.8
Alumina 29.5
a) PYDRIN is added to the wash water solution from an acetone or heptane solut-
ion.
b) PAC = powdered active carbon.
c) GAC = granular active carbon.
d) Celite is diatomaceous earth.
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e) XAD-2 and XAD-4 are polymeric adsorbents manufactured by Rohm
& Haas.
As can be seen from Table 3 the powdered activated carbon
(Darco S~51) is the most efficaceous of all the adsorbents tested,
lowering the PYDRIN Insecticide concentration to less than 10
ppb. No difference in results could be attributed to the solvent
utilized to introduce high concentrations of PYDRIN Insecticide
into the aqueous phase. Further tests with the powdered active
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carbon (Darco S-51) at a liquid-solid ratio of 250/1 indicated
that equilibrium adsorption is obtained in less than 8 hours for
this material. In fact, PYDRIN Insecticide concentrations below 10
ppb are achieved after about 1 hour. In comparison, when using the
granulated active carbon Hydrodarco 3000, an equilibrium time
of greater than 2 days is required. Thus, the powdered activated
carbon provides for a much quicker method for removing contaminants
than the granular activated carbon.
The advantages of flocculation will be demonstrated for
example, by adding 100 ppm cf Dow N-20 flocculating agent~ which
is a nonionic polymer, to the waste water slurries of Darco-S-51
powdered active carbons as described above with stirring at
a 140 RPM for approximately 30 minutes. After the stirring is
stopped, the flocculated powdered activated carbon will be
noticed to have settled in less than 1 minute. The supernatant
phase contains no visible suspended carbon fines. The flocculated
carbon particles will not redisperse when the solution is
stirred, which indicates that the floc is stable.
