Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: REMOVAL OF PHOSPHOROUS FROM WASTEWATER
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] This invention relates to processes, methods and systems for the
treatment of
wastewater, for example, domestic wastewater, which is contaminated with
phosphorus.
In particular, this invention relates to the chemical removal of undesirable
chemicals,
e.g., phosphorous, from wastewater.
Description of the Prior Art
[0002] The presence of phosphorus in sewage effluents has been
recognized as
promoting the growth of algae and aquatic plants in receiving waters by
providing a
source of nutrition. Phosphorus can be found in sewage in a number of forms,
for
instance, as soluble, insoluble or complex phosphorous including within
organic matter.
[0003] Generally, phosphorous is removed from wastewater by chemical
precipitation using salts of multivalent metal ions. The most common
multivalent metal
ions used are calcium, aluminium and iron. Calcium is usually used in the form
of lime
(calcium hydroxide), aluminium in the form of alum (aluminium sulphate), and
iron in
the form of ferric chloride. In addition to using a source of multivalent
metal ions,
polymers are also sometimes added to aid in the formation of flocs. The
precipitation/flocculation process is generally followed by the removal of the
precipitated/flocculated phosphorous using mechanical means such as by
sedimentation
or filtration. More recently, polymeric aluminium products such as PASS
(polyaluminium silicate-sulphate), PASiC (aluminium-silicate polymer
composite), and
PAC (hydroxylated polyaluminium chloride) have also been patented (PASS) and
tested
(PASiC and PAC) in full-scale applications (PASS) and laboratory experiments
(PASiC
and PAC). The PASS formula, as an example, is defined in US patent 5,149,400
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'
patented Sep 22, 1992 by Haase et alas:
A1A(OH)B(504)c(SiOOD(H20)E
[0004] where A is 1.0, B ranges from 0.75 to 2.0, C ranges from 0.3 to
1.12, D
ranges from 0.005 to 0.1, X is greater than 2.0 but less than or equal to 4.0
such as
3=B+2C+2D(X-2), and E is larger than 4 when the product is in aqueous form.
[0005] The use of these coagulants/flocculents is generally followed by
removal of
the resulting precipitate, e.g., by sedimentation or by filtration.
[0006] Many patents have been issued which are directed to the removal
of
phosphorus from wastewater. The more relevant patents are believed to be the
following:
[0007] US Patent No. 4,981,675, patented Jan 1, 1991 by Handy Chemicals
Inc.,
which provided water treatment methods using a polymeric basic aluminium
silicate
sulfate. The treatments were at:
1) 8-9 C at a pH of 6.65 to 6.93 and a concentration of 3-8 ppm
A1203,
2) 25 C and at a pH of 7.14-7.38 at a concentration of 3-8 ppm A1203; and
[0008] US Patent No. 6,165,369, patented Dec 26, 2000, by General
Chemical
Corporation, which teaches a water treatment method that includes the use of
polyaluminium silicate sulfate in conjunction with finely-divided, acid-
insoluble solid
particles.
[0009] Other patents of interest include the following:
U.S. Patent No. 3,171,802, patented Mar 2, 1965 by A.H. Rice;
U.S. Patent No. 3,453,207, patented Jul 1, 1969 by Allied Chemical Corp;
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,
,
U.S. Patent No. 3,506,570, patented Apr 14, 1970 by R.F.Wukusch;
U.S. Patent No. 3,617,569, patented Nov 2, 1971 by The Dow Chemical
Company;.
U.S. Patent No. 3,607,738, patented Sep 21, 1971 by Nalco Chemical Company;
U.S. Patent No. 3,655,552, patented Apr 11, 1972 by Calgon Corporation;
U.S. Patent No. 3,964,998 patented Jun 22 1976 by The South African Invention
Development Corporation;
U.S. Patent No. 4,029,575 patented Jun 14, 1977 by Ewing Engineering
Company;
U.S. Patent No. 4,043,910, patented Aug 23, 1977, by Allied Colloids Limited;
U.S. Patent No. 4,049,545, patented Sep 20, 1977 by P.J. Horvath:
U.S. Patent No. 4,076,615, patented Feb 28, 1978 by Batelle Pacific N.W.
Laboratories;
U.S. Patent No. 4,167,479, patented Sept 11, 1979 by F. Besik;
U.S. Patent No. 4,209,396 patented Jun 21, 1980 by Filters International;
U.S. Patent No. 5,271,848, patented Dec 21, 1993 by R.W. Smith et al;
U.S. Patent No. 5,364,529, patented Nov 15, 1994 by Level Valley Dairy
Company;
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U.S. Patent No. 5,759,401, patented Jun 2, 1998 by Elf Atochem;
U.S. Patent No. 5,853,588, patented Dec 29, 1998 by Polytechnic University;
and
U.S. Patent No. 5,876,606, patented Mar 2, 1999, by University of Waterloo.
[0010] Other non-patent literature includes:
[0011] The publication by Gao et al. in Water Research 36(2002) 3573-3581,
on
pages 38 to 46 taught that PASiC and PAC could be used as a flocculent agents
for water
treatment. While there is a mention of PASS (poly-aluminium silicate sulfate)
there is no
teaching of its use in treating phosphorus-containing water.
[0012] The publication of Boisvert et al. in Water Research 31(1997) 1939-
1946
focuses on the mechanism of flocculation and does not address the performance
with
respect to low phosphorus levels in the residual wastewater.
[0013] Additionally, Boisvert does not disclose or suggest a stage of
filtering the
water.
[0014] Finally, Boisvert concludes that alum performs better that PASS,
(poly-
aluminium silicate sulfate) which should lead a person skilled in the art away
from trying
PASS (poly-aluminium silicate sulfate).
[0015] In some existing, known, multi-stage physical/chemical and/or
biological
wastewater treatment systems, wastewater is processed by a combination of
treatment
technologies. For example, it is first introduced into a primary settling tank
to allow the
sedimentation of significant solids from the liquid. Thereafter, the
wastewater is
introduced into a series of one or more biological reactor tanks, wherein the
wastewater is
agitated in the presence of aerobic bacteria. One existing technology used for
treating the
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wastewater at this stage, hereafter used as an example, is the employment of
rotating
biological contactors (RBC), i.e., large rotating disks serving as a support
to a fixed-film
of bacteria .
[0016] According to known procedures, a flocculent can be added to the
wastewater
while it is in the biological reactor. In some prior art systems, the addition
of flocculent
occurs when the wastewater has been partially, but not fully treated in the
biological
reactor, e.g., in the third stage of a four stage RBC. Because the biological
reactions
using aerobic bacteria must be carried-out at a pH level around 6.8 or higher,
the
coagulant/flocculent according to this known procedure is introduced into
wastewater
which has been adjusted, using another chemical, in order to have a pH of, for
example,
of 6.8 to 7.6.
[0017] Thus, in existing systems, a portion of the phosphorus present in
wastewater is
used for microbial metabolism and another portion precipitates-out and forms
flocs in the
biological reactor. Some of this precipitate in some systems is removed from
the last
stage of the biological reactor and returned to the primary settling tank
where it is
allowed to accumulate. This is done in order to minimize the amount of
precipitate that
is fed to the next stage in the wastewater treatment process.
[0018] In these existing systems, the wastewater leaving the biological
reactor is
typically fed to a second, quiescent, settling tank which is not subject to
mechanical
agitation. There, further settling of precipitated phosphorus is allowed to
occur. The
sludge from the bottom of such second (or final) settling tank is periodically
pumped
back to the primary settling tank where the phosphorus-enriched sludge
accumulates.
Pumping of the sludge from the secondary to the primary settling tank is
optional.
[0019] The removal of phosphorous to very low levels with any degree of
consistency has been problematic. In one aspect, the invention strives for
consistent
phosphorous removal of to such low levels, for example < 0.03 mg/l.
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,
,
[0020] It is thus recognized that there is a need for treatment
processes, methods and
systems for lowering the concentration of phosphorus present in wastewater
that is
effective, does not significantly put other pollutants into the water and uses
materials that
are readily and economically available. This invention addresses this need.
[0021] The present invention can be advantageously combined with
various types of
wastewater treatment systems including Rotating Biological Contactors.
[0022] The invention in its general form will first be described,
and then its
implementation in terms of specific embodiments will be detailed with
reference to the
drawings following hereafter. These embodiments are intended to demonstrate
the
principle of the invention, and the manner of its implementation. The
invention in its
broadest sense and more specific forms will then be further described, and
defined, in
each of the individual claims which conclude this Specification.
SUMMARY OF THE INVENTION
[0023] By a first broad aspect, the present invention provides a
process for lowering
the concentration of phosphorus in wastewater which includes the step of
adding a
suitable amount of an aluminium-based coagulant/flocculent to the wastewater
while
maintaining a pH of between about 4.5 and 6.65. This step provides an eventual
effluent
stream of precipitated aluminium-based, phosphorus-containing flocs dispersed
in the
wastewater that are suitable for removal by physical means such as filtration.
Carrying
through with these steps may provide a wastewater effluent generally
containing less than
about 0.03 mg total phosphorus per liter of wastewater.
[0024] By a second broad aspect, the present invention provides a
process as
described above wherein the aluminium-based coagulant/flocculent is an
aluminium-
silicate based coagulant/flocculent product.
[0025] By a third broad aspect, the present invention provides a
method of reducing
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the content of phosphorus in wastewater by includingthe step of introducing
wastewater
containing phosphorus into a preliminary treatment zone, in which a settling
zone is
cooperatively associated with the treatment zone. The method then includes the
step of
adding aluminium-based coagulant/flocculent to the wastewater in the
preliminary
treatment zone, preferably a less than a suitable amount of aluminium-based
coagulant/flocculent, while maintaining a pH above about 6.8 to about 7.6,
thereby to
produce precipitated aluminium-based phosphorus-containing flocs in the
wastewater.
The method also includes the optional step of removing at least some of the
precipitated
aluminium-based phosphorus-containing flocs from the settling zone. This
latter step can
be taken while settling is allowed to occur or intermittently.
[0026] The latter method also includes the further steps of:
1) passing liquid effluent including some of the precipitated aluminium-
based,
phosphorus-containing flocs from the final settling zone to a mixing zone,
preferably an
in-line mixer;
2) adding upstream or in the mixing zone an additional quantity of an
aluminium-
based coagulant/flocculent to the liquid effluent to achieve a total suitable
amount of the
aluminium-based coagulant/flocculent in the wastewater to react with all of
the
phosphorous contained therein, while maintaining the pH of the wastewater
after such
addition within the range of about 4.5 to 6.65. This second addition of a
quantity of
aluminium-based coagulant/flocculent will have the effect of lowering the pH
to a level
which is generally below the value maintained in the previous step (typically
between of
6.8-7.6, initially). If the pH of the water at this stage is not sufficiently
lower than the
initial pH, it can be further lowered through the addition of an acid, such as
an inorganic
or an organic acid selected from the group consisting of sulfuric acid,
hydrochloric acid,
nitric acid, acetic acid, citric acidõ or any other acid which is appropriate
for lowering
the pH of water at this stage.
[0027] These steps provide an effluent stream of precipitated aluminium-
based
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phosphorus-containing flocs dispersed in the wastewater. The method then
includes the
step of passing the effluent stream of the precipitated aluminium-based,
phosphorus-
containing flocs dispersed in the wastewater to a physical separation zone.
[0028] The method concludes with the steps of:
1) physically removing the precipitated aluminium-based phosphorus-
containing
flocs dispersed in the wastewater; and,
2) recovering substantially precipitate-free wastewater which has passed
through the
physical removal zone.
[0029] These steps allow to produce a wastewater effluent containing
less than about
0.03 mg total phosphorus per liter of wastewater.
[0030] By a fourth broad aspect, the present invention provides a
process as just
described above wherein the aluminium-based coagulant/flocculent is an
aluminium-
silicate based coagulant/flocculent product.
[0031] By a fifth broad aspect, the present invention provides a system for
lowering
the concentration of phosphorus in wastewater. The system includes a first
treatment
chamber which has:
1) wastewater inlet and outlet lines conveying the wastewater in and
out of the
treatment chamber; the treatment chamber itself may include a single or
several treatment
processes hence it may be a simple vessel or may be more complex and include
various
types of treatment equipment, and
2) a coagulant/flocculent inlet line connected to the first treatment
chamber for
the introduction of a first amount of an aluminium-based coagulant/flocculent
into the
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first treatment chamber for the formation of aluminium-based phosphorus-
containing
flocs, and
3) a pH control inlet line connected to the first treatment chamber
for the
introduction of a chemical for the maintenance of the pH in the first
treatment chamber
above about 6.8 to about 7.6.
[0032] Such first treatment chamber is associated to a settling chamber
for the
sedimentation and removal of a part of the precipitated aluminium-based,
phosphorus-
containing flocs that are thereupon formed.
[0033] The system also includes a mixing chamber in direct communication
with the
outlet line from the final settling chamber. The mixing chamber, preferably an
in-line
mixer, includes:
1) A wastewater inlet line; and
2) an inlet line for the introduction of an aluminium-based
coagulant/flocculent
chemical into or upstream the in-line mixing chamber,
3) a pH control inlet line into or upstream the in-line mixing chamber for
the
introduction of a chemical for the maintenance of the pH at about 4.5 to 6.65,
and
4) a wastewater outlet line connected to a physical separation vessel for
the
physical separation of the further precipitated aluminium-based, phosphorus-
containing
flocs from the wastewater; and,
5) an outlet line from the physical separation vessel for the essentially
precipitate-free effluent wastewater stream having a total phosphorus level of
less than
about 0.03 mg per liter of wastewater.
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,
,
[0034]
By a sixth broad aspect, the present invention provides a process as just
described above wherein the aluminium-based coagulant/flocculent is an
aluminium-
silicate coagulant/flocculent product.
[0035] Thus,
according to an aspect of the present invention, a second addition of
flocculent/coagulant is made after the wastewater has left the second,
quiescent, settling
tank. This is conveniently done through an in-line mixer in which or prior to
which
further flocculent/coagulant addition prior to feeding the wastewater to a
final solid/liquid
separator. This final solid/liquid separator may be in the form of a filter
which has the
capability of removing flocculated or very fine phosphorus-containing
particles from the
wastewater, and allows achieving Total Phosphorous levels lower than 0.03
mg/litre.
[0036]
It is a feature of an aspect of the invention that the pH of the wastewater
fed to
the final liquid/solid separator and filter is set in the pH range of 4.5 to
6.65. Many
cogulants/flocculents, and particularly alumina-based coagulants/flocculents,
e.g. aluminium sulfate and alumina-silica-sulfate, have the ability and
tendency to lower
the pH of the wastewater. Accordingly, the mere addition of such
coagulants/flocculents
can be used to adjust the pH of the wastewater as it is being treated in or
upstream the in-
line mixer.
It may be desirable, in order to minimize the use of coagulant/flocculent
needed, to adjust the pH of the wastewater by the adding an appropriate acid,
such as
sulfuric acid, hydrochloric acid, nitric acid, acetic acid, citric acid, etc.
when the
concentration of the coagulant/flocculent is insufficient to reduce the pH
down to the
desired range.
[0037] While it
is useful and possible to add the entirety of the coagulant/flocculent
to be fed to the wastewater in one stage, it has been found advantageous to
use two (or
possibly more) dosing points as follows: a first amount is added to the
wastewater while
in the preferred bioreactor or preliminary treatment zone, and a second amount
which is
typically added downstream from the final settling tank, more preferably in an
in-line
mixing zone or immediately upstream. Such a two-stage addition may have the
benefit
of conserving expensive coagulant/flocculent. The amount of
coagulant/flocculent
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needed is that which will essentially treat all of the phosphorus present in
the wastewater.
The minimum amount required is hereafter referenced as the "suitable amount"
and is the
amount of aluminium-silicate coagulant/flocculent product appropriate to
substantially
precipitate and form floes of most of the phosphorus present in the
wastewater.
[0038]
Typically, the greater part of the total amount needed of coagulant/flocculent
to be consumed-is added in the first stage of the treatment process, i.e., to
the wastewater
when it is present in the biological reactor. Thus,
about 70 to 80%
of the coagulant/flocculent which is to be injected may be added at this
initial
stage. The remaining amount of coagulant/flocculent, according to this
preferred
aspect of the invention, is added to the water in or immediately upstream of
the in-
line mixer upon leaving the final (or secondary) quiescent settling tank.
[0039] The facultative additional use of an acid to the wastewater downstream
from
the quiescent fmal settling tank is not necessary if the wastewater in the
biological reactor
does not have an excessively high pH. The pH of the wastewater in the
biological reactor
is generally maintained in the region of about 6.8 -7.6 by the addition of a
base or
alkaline product. By carefully limiting the amount of base being added at the
earlier
biological reaction stage, the necessity to add either an excessive amount of
acidifying
coagulant/flocculent or another acid can be minimized or eliminated.
[0039A] In another aspect, there is provided a process for lowering the
concentration of
total phosphorus in wastewater discharged from a settling chamber to a level
below 0.03
milligrams per liter comprising: a) treating the wastewater by adding to said
wastewater a
suitable amount of aluminum-based coagulant/flocculent for precipitation of
phosphorus in
said wastewater, the wastewater having a pH of 4.5 to 6.4 during such
treatment, to
provide an effluent stream of wastewater with precipitated aluminum-based,
phosphorus-
containing flocs dispersed in said wastewater; and b) filtering said
precipitated aluminum-
based, phosphorus-containing flocs from said eventual effluent stream of
wastewater to
lower the concentration of total phosphorus in the effluent stream of treated
wastewater to
a level below 0.03 milligrams per liter.
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[0039B] In another aspect, there is provided a process for lowering the
concentration of
total phosphorus in wastewater to a level below 0.03 milligrams per liter
comprising: a)
treating the wastewater by adding to said wastewater a suitable amount of
aluminum-based
coagulant/flocculent for precipitation of the phosphorus in said wastewater to
provide a
stream of wastewater with precipitated aluminum-based, phosphorus-containing
flocs
dispersed in said wastewater; and b) a step of physically removing a necessary
amount of
said precipitated flocs from said stream of wastewater to lower the
concentration of total
phosphorus in a treated effluent stream wastewater to a level below 0.03
milligrams per
liter, and wherein the suitable amount of aluminum-based coagulant/flocculent
is divided
into: c) a first amount of aluminum-based coagulant/flocculent, and; d) a
second amount of
aluminum-based coagulant/flocculent, and wherein the step of adding the
suitable amount
of aluminum-based coagulant/flocculent includes: e) a preliminary step of
adding, in a
preliminary treatment zone, the first amount of aluminum-based
coagulant/flocculent to
said wastewater while the pH of the wastewater is maintained above 6.65 to
produce
precipitated aluminum-based, phosphorus-containing flocs, 1) transferring the
wastewater
from the preliminary treatment zone to a settling zone wherein at least a
portion of the said
flocs is allowed to settle from the wastewater while the wastewater is in the
settling zone,
g) separating the wastewater from the settled flocs, h) a further step adding
the second
amount of aluminum-based coagulant/flocculent to said separated wastewater
while the pH
of the wastewater is maintained at or below 6.4 to produce further
precipitated flocs, and
wherein the step of physically removing precipitated flocs from the wastewater
includes
the step of filtering precipitated flocs from said wastewater sufficiently to
lower the
concentration of total phosphorus in the effluent stream of treated wastewater
to said level
of below 0.03 milligrams per liter.
Other Features of the Invention
[0040] By a broad feature of the process aspects of the present invention,
the suitable
amount of the aluminium-based coagulant/flocculent chemical, e.g., the
aluminium-
silicate coagulant/flocculent product, is from about 15 to about 50 mg of
A1203 per liter
of wastewater. Preferably, the suitable amount of the aluminium-based
coagulant
/flocculent chemical, e.g., the aluminium-silicate coagulant/flocculent
product, is from
about 35 to about 40 mg of A1203 per liter of said wastewater.
[0041] By another broad feature of the process aspects of the present
invention, the
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pH is maintained through the addition of an inorganic acid or an organic acid.
Preferably,
the acid is acetic acid, or citric acid, or sulfuric acid, or hydrochloric
acid or nitric acid.
[0042] By another broad feature of the process aspects of the present
invention, the
aluminiumsilicate coagulant/flocculent product is selected from the group
consisting of
polyaluminium silicate sulfate, polyaluminium silicate chloride, polyaluminium
hydroxychlorosulfate, and polyaluminium chloride. Preferably, the aluminium-
silicate
coagulant/flocculent product is polyaluminium silicate sulfate or PASS.
[0043] By another broad feature of the process aspects of the present
invention, the
process includes the preliminary step of adding an amount of the aluminium-
based
coagulant/flocculent, e.g., the aluminium-silicate coagulant/flocculent
product, to the
wastewater, preferably less than a "suitable" amount, while maintaining a pH
between
about 6.8 to about 7.6 in order to provide precipitated aluminium-based,
phosphorus-
containing flocs prior to the previously-recited steps. This provides an
eventual effluent
stream with precipitated aluminium-based, phosphorus-containing flocs
dispersed in the
wastewater.
[0044] Preferably, such preliminary step is carried out in a preliminary
reaction zone
that also includes an aerobic biological reactor. More preferably, the pH is
maintained at
about 7.0 in such an aerobic biological reactor.
[0045] By another broad feature of the process aspects of the present
invention, the
step of maintaining the pH within about 6.8 to about 7.6 is carried out by the
addition of a
suitable amount of a weak base. Preferably, the weak base is sodium
bicarbonate.
[0046] By another broad feature of the process aspects of the present
invention, the final
settling tank is a zone which is distinct and separate from both the
preliminary treatment
zone and the in-line mixing zone.
[0047] By a broad feature of the method aspects of the present
invention, the less
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than suitable amount of the aluminium-based coagulant/flocculent chemical,
e.g., the
aluminium-silicate coagulant/flocculent product, which is added in said
preliminary
treatment zone comprises about 70% to about 80%, e.g., about 75%, of the
suitable
amount of the aluminium-based coagulant /flocculent chemical, wherein such a
suitable
amount is the amount of aluminium-silicate coagulant/flocculent product
appropriate to
substantially precipitate and form flocs of all of the phosphorus present in
the wastewater.
[0048] By another broad feature of the method aspects of the present
invention, the
method includes the step of removing settled precipitated aluminium-based,
phosphorus-
containing flocs from the final settling zone. Preferably, precipitated
aluminium-based,
phosphorus-containing flocs which have been removed from the final settling
zone are
transferred to the primary settling tank.
[0049] By another broad feature of the method aspects of the present
invention, the
pH of about 4.5 to about 6.65 in the in-line mixing zone is achieved by the
cooperative
addition of a suitable amount of the aluminium-based coagulant/flocculent,
e.g., the
aluminium-silicate coagulant/flocculent product, and/or an acid. Preferably,
the acid is
selected from the group consisting of sulfuric acid, hydrochloric acid, nitric
acid, acetic
acid and citric acid,. Preferably, also, the aluminium-based
coagulant/flocculent
chemical, is polyaluminium silicate sulfate.
[0050] By another broad feature of the system aspects of the present
invention, the
final settling chamber, which is cooperatively associated with the first
treatment chamber,
is a final settling tank that is separate and distinct both from the first
treatment chamber
and from the in-line mixer treatment chamber.
[0051] By another broad feature of the system aspects of the present
invention, the
final settling chamber includes a sludge removal line for the transfer of
settled
aluminium-based, phosphorus-containing flocs. Preferably, such sludge removal
line is
connected to the primary settling tank as a recycle line.
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,
,
[0052] By another broad feature of the system aspects of the
present invention, the
filter chamber is selected from the group consisting of sand filters,
multimedia filters,
ultrafiltration membranes and microfiltration membranes. In particular, the
filter may be
a continuous, self-cleaning sand filter.
[0053] By another broad feature of the system aspects of the
present invention, the
system includes a sludge removal line from the filter chamber for the removal
of the
filtered aluminium-based, phosphorus-containing flocs. Preferably the sludge
removal
line is connected to the primary settling tank as a recycle line.
[0054] By another broad feature of the system aspects of the present
invention, the
first treatment chamber is a rotating biological contactor.
[0055] The foregoing summarizes the main features of the invention
and some of its
optional aspects. The invention may be further understood by the description
of the
preferred embodiments, in conjunction with the drawings, which now follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] In the accompanying drawings,
[0057] FIG 1 is a schematic flow diagram of a system, according to
one embodiment
of the present invention, for carrying out the method according to another
embodiment of
the present invention.
[0058] FIG 2 is a schematic flow diagram of the system of FIG 1 which shows
one
embodiment of a treatment chamber 10 with its associated parts as well as the
relationship between these parts and the associated exterior parts of the
system of the
invention.
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Description of the Preferred Embodiments
[0059] As seen in FIG 1, a first chamber is a primary treatment chamber
10 which
may be of any construction of apparatus which is presently used in the
purification and
treatment of wastewater. For example, in a preferred embodiment in the present
case, this
treatment chamber may be a Rotating Biological Contactor (RBC). This primary
treatment chamber 10 provides a primary treatment zone for the production of
filterable
precipitated flocs dispersed in the wastewater. A wastewater inlet feed line,
pipe or
conduit 12 is connected to the primary settling tank 8 to allow the
sedimentation of
significant solids. The primary settling tank 8 overflows into the treatment
chamber 10
for the introduction of wastewater which is contaminated with phosphorus. The
phosphorus may be in a number of forms, for instance as soluble, insoluble or
complex
phosphorous including within organic matter. A coagulant/flocculent inlet
line, pipe or
conduit 14 is connected to the treatment chamber 10 in order to supply a major
amount of
coagulant/flocculent to the wastewater. The coagulant/flocculent inlet line,
pipe or
conduit 14 is connected to a coagulant/flocculent reservoir tank 16 which
contains
coagulant/flocculent in the form of an aqueous solution. The
coagulant/flocculent is an
aluminium-based coagulant/flocculent chemical, e.g., polyaluminium silicate
sulfate,
polyaluminium silicate chloride, polyaluminium hydroxychlorosulfate, aluminium
sulphate or polyaluminium chloride. Preferably, the aluminium-silicate
coagulant product
is polyaluminium silicate sulfate (PASS). PASS may be obtained from
L'Enyironnement
Eaglebrook Quebec, Varennes, Quebec.
[0060] The amount of aluminium-based coagulant /flocculent chemical or
PASS
added to the primary treatment chamber 10 is a major amount of the total
amount of
PASS to be added for the appropriate precipitatation and flocculation of most
of the
phosphorus present in the wastewater. Such total amount of PASS is from about
15 to
about 50 mg A1203 per liter of wastewater, but preferably from about 35 to
about 40 mg
of A1203 per liter of the wastewater. The major amount of the total amount of
PASS is
generally from about 70% to about 80%, preferably about 75%, of the total
amount.
CA 02555875 2006-08-11
[0061] A pH control inlet line, pipe or conduit 18 is connected to the
treatment
chamber 10 and to a pH control agent reservoir tank 20 which contains a weak
base,
preferably, sodium bicarbonate, in order to supply an amount of a pH control
agent to the
wastewater. In this primary treatment chamber 10, the pH is actually
controlled to stay
within a range of about 6.8 to about 7.6, but preferably to remain at a pH of
about 7.0 in
order to facilitate the biological reactions occuring in parallel to the
phosphorus removal.
Again, the pH is maintained at such level through the addition of the weak
base.
Specifically for phosphorous removal, the addition of a weak base is
contraindicated
since this was believed heretofore by those skilled in the art to be
detrimental to the
efficient phosphorus removal.
[0062] The primary treatment chamber 10 also includes a discharge line
22, e.g., an
overflow line 22, for the discharge of wastewater having filterable,
precipitated flocs
dispersed therein from the primary treatment chamber 10. In this primary
treatment
chamber 10, some of the filterable precipitated flocs are allowed to settle in
what may be
considered an incidental settling chamber.
[0063] A final settling chamber 24 is connected directly to the effluent
from the
primary treatment chamber 10 by the overflow line 22. By means of such
overflow line
22, some of the filterable precipitated flocs are transferred along with the
wastewater
from the primary treatment chamber 10 to the final settling chamber for
further solids
removal. This typically allows wastewater containing a maximum of 1 mg of
phosphorus
per liter of wastewater to leave the final settling chamber 24. A settled
sludge removal
line 26 is connected from the bottom of the final settling chamber 24 to the
primary
settling tank 8 and acts as a solids recycle line. The final settling chamber
24 includes an
upper discharge or outlet line 28.
[0064] While the final settling chamber 24 and the primary treatment
chamber 10 are
shown as two separated and distinct chambers, the final settling chamber 24
can
effectively be present as part of the incidental settling chamber, i.e., as
part of a
compartmentalized version of the primary treatment chamber 10, e.g., by being
separated
16
CA 02555875 2006-08-11
from the primary treatment chamber 10, by an internal overflow weir (not
shown).
[0065] An in-line mixer 30 is directly connected to the final settling
chamber 24 by
means of the upper discharge or outlet line 28. In or upstream the in-line
mixer 30,
additional PASS is added and pH is monitored and maintained in the range of
about 4.5
to 6.65. A coagulant/flocculent inlet line, pipe or conduit 32 is connected
upstream or to
the in-line mixer 30 in order to supply the additional minor amount of
coagulant/flocculent to the wastewater. This second injection allowes to reach
the
previously designated total amount of coagulant/flocculent necessary. The
coagulant/flocculent inlet line, pipe or conduit 32 is connected to a
coagulant/flocculent
reservoir tank 34 which contains coagulant in the form of an aqueous solution.
[0066] The pH control inlet line, pipe or conduit 18 is connected the
treatment
chamber 10 in order to supply a major amount of a pH control agent to the
wastewater
when it is present in the treatment chamber 10. The in-line mixer 30 includes
a pH
control inlet line, pipe or conduit 38 connected thereto. The pH control agent
is connected
to a reservoir tank 36 which contains an acid, preferably, sulfuric acid,
hydrochloric acid,
nitric acid, acetic acid or citric acid. In or upstream this in-line mixer 30,
the pH is
actually controlled to about 4.5 to about 6.65, preferably, to about 6.4.The
pH may be
adjusted by changing the amount of polyaluminium silicate sulfate which is
added, and/or
by introducing a suitable amount of a suitable acid from the reservoir tank 36
through
line, pipe or conduit 38. With such proper total amount of PASS and proper
control of
both the amount of PASS and the amount of acid added to or upstream the in-
line mixer
30, phosphorus levels less than 0.03 mg per liter of wastewater can be
achieved at the exit
of the filter chamber.
[0067] Line, pipe or conduit 40 is connected from the in-line mixer
reaction chamber
to a filter chamber 42 where the filterable, precipitated flocs dispersed in
the
wastewater are filtered out. Any suitable filter may be used in the filter
chamber 42, e.g.,
30 a sand filter, an ultrafiltration membrane or a microfiltration
membrane. If a sand filter is
used, it may be of a type that is continuous, self-cleaning. A stream of
essentially
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CA 02555875 2006-08-11
precipitant-free, phosphorus-free wastewater is withdrawn through outlet line,
pipe or
conduit 44 from filter chamber 42. Such effluent stream typically contains
less than about
0.03 mg of total phosphorus per liter of wastewater.
[0068] A lower sludge removal line 46 is connected to the bottom of the filter
chamber
42. This sludge removal line 46 may be provided to remove and discharge all of
the
filtered flocs. Sludge removal line 46 may include a recycle line 48 to return
the sludge
back to the first treatment chamber 10.
CONCLUSION
[0069] The specific method of treatment of wastewater contaminated with
phosphorus as disclosed hereinabove is able to provide an effluent stream of
substantially
phosphorus-free water which typically contains less than 0.03 mg of total
phosphorus per
liter of wastewater.
[0070] The description has constituted a description of specific
embodiments
showing how the invention may be applied and put into use. These embodiments
are only
exemplary. The invention, in its broadest and more specific aspects, is
further described
and defined in the claims which follow.
[0071] These claims, and the language used therein are to be understood
in terms of
the variants of the invention which have been described. They are not to be
restricted to
such variants, but are to be read as covering the full scope of the invention
as is implicit
within the invention and the disclosure that has been provided herein.
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