Note: Descriptions are shown in the official language in which they were submitted.
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Method for the sequenced biological treatment of water implementing
biomass granules
1. Field of the invention
The field of the invention is that of the biological treatment of wastewater
containing organic matter.
More specifically, the invention pertains to a technique for the sequenced
biological treatment of water implementing biomass granules.
2. Prior art
The carbon and nitrogen pollution contained in water, especially
wastewater, is commonly reduced by means of biological treatments, for example
of a sequenced type.
The sequenced biological treatment of water consists in treating a volume
of water by putting it into contact, by successive portions, with biomass
housed in
a reactor. This type of reactor is called an SBR or Sequenced Batch Reactor.
The biomass degrades the carbon pollution during an aerobic phase. The
ammonia is converted into nitrites during this aerobic phase by nitrification
while
the nitrates are degraded into nitrogen during an anoxic phase of
denitrification.
It is then possible to collect treated water, with reduced carbon and
nitrogen pollution, after it has been separated from the biomass.
The treated water is generally separated from the biomass involved in its
treatment during a decantation or settling phase.
However, the biomass is situated in the water essentially in the form of
small, particles of low decanting capacity, generally having a diameter of
less than
1 mm. The result of this is that their decantation is slow. This means that
the time
needed for the biological treatment of water is relatively lengthy.
To overcome this drawback, other techniques have been devised for the
sequenced biological treatment of water. These techniques consist in putting
the
water to be treated in contact with the biomass essentially taking the form of
granules, the diameter of which is generally greater than 1 mm. The biomass
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granules which are bulkier and heavier than classic biomass particles have a
high
decanting capacity.
The implementing of such a technique for treating water has the advantage
of reducing the time needed for the separation by decantation of the biomass
and
of the treated water and, as the case may be, the advantage of reducing the
size of
the apparatuses implemented for this purpose.
The European patent number EP-B1-1 542 932 describes a technique of
this kind.
According to the technique described in this document, a bed of biomass
granules is housed in a reactor.
The water to be treated is introduced into the base of the reactor during an
anaerobic feeding operation. The rate at which water is fed to the reactor is
chosen
in such a way that the feeding is slow. This prevents the formation of a
fluidized
bed of biomass granules.
After completion of the operation for feeding the reactor with water for
treatment, a phase of non-stirred latency is observed in the reactor during
which
the water to be treated is left in contact with the biomass granules. In this
phase,
the nutrients present in the water are assimilated by the biomass, the
granules of
which have their volume and density increasing accordingly.
Oxygen is then introduced into the reactor by means of a nozzle unit
provided in its lower part. The nitrogen pollution contained in the water to
be
treated is then least partly degraded by nitrification-denitrification.
The granules are then extracted and then a decantation is carried within the
reactor before extracting the treated water depleted of nitrogen pollution.
The technique described in this document makes it possible to reduce the
concentration in water of nitrogen pollution and especially in phosphorous. It
nevertheless has a few drawbacks.
3. Drawbacks of the prior art
The feeding of water to the reactor is slow in order to prevent the
fluidizing of the bed of granules. The result of this is that the closer the
granules
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are to the surface of the bed, the lesser the extent to which they are put
into
contact with the organic matter of the water to be treated on which they are
nourished. There is therefore a vertical gradient of concentration in organic
matter
in the granules of the bed and therefore a non-uniform development of the
granules.
To limit this phenomenon, the step of feeding is followed by a step of
latency during which the content of the reactor is flot stirred. The water to
be
treated is then kept in contact with the biomass granules for a sufficiently
lengthy
period of time to allow the granules situated in the upper layers of the bed
enough
time to assimilate the nutrients and grow in volume and density.
The inventors have nevertheless observed that these non-stirred phases of
feeding and latency result in a reduced exchange between the nutrients present
in
the water and the biomass granules. This contributes to:
limiting the assimilation of nutrients by the granules and therefore
reducing their development or growth as well as their decanting capacity;
limiting the depth of penetration of the nutrients in the granules and
therefore reducing their stability, their resistance;
- increasing the minimum concentration in organic matter that the water for
treatment must contain in order to enable the generation of granules having
high decanting capacity;
reducing the maximum concentration in organic matter that the water for
treatment must contain;
- increasing the duration of the anaerobic latency phase and the
decantation
phase and therefore the total duration of the treatment.
Besides, the biomass of which the granules are constituted comprise
especially two types of microorganisms:
GAOs or glucose accumulative organisms;
PAOs or polyphosphate accumulative organisms.
It has been observed that the density of the PAOs is higher than that of the
GA0s.
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Thus, during the extraction of the granules, the PA0s, which are situated
in the lower layers of the bed of granules, are extracted from the reactor in
much
greater proportions than the GA0s. The result of this is that the GAOs start
competing with the PAOs and predominate within the reactor. This phenomenon
has a negative impact on the level of elimination of the phosphorous contained
in
the water to be treated that is subsequently introduced into the reactor.
In addition to the granules, the water contained in the reactor comprises
particles that have lower decanting capacity. These particles are discharged
with
the treated water extracted from the reactor. It is then necessary to carry
out a
polishing treatment downstream to the reactor. This tends to increase the size
of
the water treatment plants as well as the cost of the water treatment.
4. Goals of the invention
The invention is aimed especially at overcoming these drawbacks of the
prior art.
More specifically, it is a goal of the invention to provide a technique for
the biological treatment of water that contributes to improving the formation
of
the biomass granules.
In particular, it is a goal of the invention, in at least one embodiment, to
procure a technique of this kind that enables the formation of solid and
stable
biomass granules.
It is another goal of the invention, in at least one embodiment, to provide a
technique of this kind that improves the decantability of the biomass
granules.
It is yet another goal of the invention, in at least one embodiment, to
provide a technique of this kind that reduces the duration of biological
treatment
of water.
The invention further pursues the goal of providing, in at least one
embodiment, a technique of this kind that maximizes the elimination of the
pollution contained in the water to be treated.
The invention is also aimed, in at least one embodiment, at providing a
technique of this kind that is versatile especially in that it ensures the
treatment of
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different volumes of water having variable pollutant loads.
It is another goal of the invention, in at least one embodiment, to provide a
technique of this kind that is simple to implement and/or reliable and/or
economical.
5 5. Summary of the invention
These goals as well as others that shall appear here below are achieved by
means of a method for treating wastewater containing organic matter within a
reactor housing biomass granules and provided with aeration means.
According to the invention, such a method comprises a plurality of
successive cycles each comprising:
an anaerobic step for feeding wastewater to said reactor during which said
water is mixed with said granules to form a fluidized bed;
an anaerobic step for stirring the content of said reactor;
a step for aerating the content of said reactor;
- a step of decantation;
a step for discharging treated water depleted of organic matter.
Thus, the invention relies on a wholly original approach according to
which a water to be treated is introduced speedily into a reactor within which
it is
placed in contact with biomass granules in an anaerobic environment and then
successive anaerobic phases are implemented for stirring the content of the
reactor, and carrying out aeration, fast decantation and then extraction of
treated
water.
During the anaerobic phase of fast feeding of the reactor, the totality of the
granules of the bed formed in the reactor are promptly brought into contact
with
the water to be treated. Then, a fluidization is observed of the bed of
granules.
This fluidization is maintained during the anaerobic stirring step. The
granules are
then distributed in an appreciably uniform manner and without stratification
within the reactor.
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The stirring generated within the reactor increases the exposure of the
totality of the surface of each granule to the nutrients contained in the
water to be
treated.
The stirring of the granules within the reactor, starting from the feeding
phase itself, improves the exchanges between the water and the granules. The
result of this is that the rate of assimilation by the granules of nutrients
initially
present in the water, which is flot limited by the diffusion, is increased.
The
granules formed then have a volume and a density that are greater than those
obtained by the implementing of the technique according to the invention.
Thus,
the diameter of these granules generally ranges from 1 mm to 5 mm, whereas
their
density generally ranges from 1.02 to 1.10 kg/l. The granules formed then have
a
high decanting capacity.
Given the fact that the diffusion of nutrients within the granules is hardly
limited by the diffusion, these nutrients can penetrate the granules in depth.
The
granules formed therefore have high stability.
The technique according to the invention leads to promoting the growth of
the granules in proportions such that its implementation makes it possible to
reduce the value of the minimum concentration in organic matter that the water
to
be treated must contain to enable the formation of solid granules of high
decanting
capacity. Thus, the technique of the invention generates the formation of
solid
granules of high decanting capacity from water, the minimum concentration of
which in organic matter is of the order of 400 mg/l.
Inasmuch as the technique of the invention increases exchanges between
the water to be treated and the granules, its implementation leads to
improving the
reduction of the organic matter contained in the water to be treated. The
technique
according to the invention therefore can be implemented to efficiently treat
water
whose concentration in organic matter is greater than 1500 mg/I.
Ultimately, the implementing of the technique according to the invention
makes it possible especially to:
- promote the development of voluminous and dense biomass granules;
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- reduce the duration of the phase during which the nutrients, especially
glucose and phosphorous, present in the water are assimilated by the
granules and therefore increase the speed of formation of the granules;
- improve the stability of the biomass granules;
- obtain a better distribution of biomass granules inside the reactor;
diminish the duration of the decantation phase;
improve the elimination of the pollution of the water to be treated;
reduce the overall duration of biological treatment of water.
According to one advantageous characteristic of the invention, the speed at
which water is fed into the reactor during said step for feeding ranges from
10 to
m/h or m3/m2/h. This speed is preferably greater than 8 m/h or m3/m2/h.
Feeding water to the reactor at such a speed causes the bed of granules to
be fluidized and thus improves the contact and therefore the exchanges between
the nutrients present in the water and the biomass granules. Thus, this
fosters the
15 formation of stable and dense granules as soon as the reactor is filled.
Naturally,
the sole fact of choosing such a speed is not necessarily enough to obtain a
fluidized bed. Other parameters must also be taken into account such as for
example the size of the granules, their density and their surface condition.
To
improve the formation of a fluidized bed, the water must also feed the
reactor,
20 preferably in an appreciably homogenous way throughout its surface.
The speed at which water is fed can be expressed equally well in m/h or en
m3/M2/h. In the latter case, m3 corresponds to a volume of water, whereas m2
corresponds to the surface area of the reactor.
According to one preferred embodiment, said anaerobic step for stirring
comprises a recirculation of at least a part of the water contained in said
reactor
from one zone of said reactor towards another.
This implementing generates a stirring within the reactor that is great
enough to promote the growth of voluminous, solid and dense biomass granules,
and small enough to maintain the integrity of the granules.
Preferably, the speed of recirculation will then range from 4 to 8 m/h.
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According to another embodiment, said anaerobic step for stirring includes
a swirling of the contents of said reactor by means of stirrers.
Such an implementation generates an adequate swirling of the content of
the reactor in a simple and efficient manner.
Preferably, the level of stirring within said reactor during said anaerobic
step of feeding ranges from 3 to 30 W/m3.
Advantageously, the level of stirring within said reactor during said
anaerobic step for stirring ranges from 5 to 10 W/m3.
Such levels of stirring within the reactor foster the development of
voluminous, solid and dense granules while at the same time preserving their
integrity.
According to an advantageous embodiment, the level of the water
discharge point during said step for discharging treated water depleted of
organic
matter is variable.
It is thus possible to gradually reduce the level starting from which the
treated water is extracted during the step for extracting. The extraction of
treated
water can then begin without waiting for ail the granules to be decanted. This
reduces the time of extraction of the treated water.
This implementation also makes it possible to bring the bed of granules
present at the bottom of the reactor closer to the level of the water
extraction point
and remove the particles with low decanting capacity that collect in the
course of
time on the surface of the upper layers of the granules of the bed.
This implementation can also permit the growth of a bed of granules of
varying thickness at the bottom of the reactors so as to enable the treatment
of
water having varying levels of pollutant loads.
The level of the water extraction point can also be brought considerably
closer to the surface to the bed of granules present at the bottom of the
reactor. In
this way, almost ail the treated water depleted of organic matter can be
extracted
from the reactor. Thus, the concentration in organic matter inside the reactor
is
reduced at each new feeding operation in limiting the dilution of the water to
be
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treated with the treated water stagnant in the reactor after extraction. The
growth
of the granules is thus promoted because they feed on the organic matter to
grow.
According to an advantageous characteristic, a method according to the
invention comprises a step for extracting granules, said step for extracting
being
preferably implemented after the running of several successive cycles.
This controls the development and the height of the bed of granules within
the reactor as well as the age of the biomass that constitutes them. The
choice of
the height of the bed of granules enables the method to be adapted to the
treatment
of water having different levels of pollutant loads.
Said step for extracting is preferably preceded by a step for stirring said
reactor.
The biomass constituting the granules comprises especially
microorganisms called GAO (glucose accumulative organisms) and
microorganisms called PAO (polyphosphate accumulative organisms). The GAOs
which assimilate glucose are less dense than the PAOs which assimilate
phosphorous. As a result, of the end of the decantation, the PAOs are situated
in
the lower levels of the bed of granules while the GAOs are situated in the
upper
layers of the bed of granules. Stirring the content of the reactor thus
eliminates
this stratification within the reactor and distributes the GAOs and the PAOs
in an
essentially uniform way within the reactor. Thus, during the extraction of the
granules, the GAOs and the PAOs are extracted in substantially identical
proportions. A predominance of the GAOs on the PAOs is then avoided at the
following cycles thus maintaining an efficient level of reduction of
phosphorus.
In this case, said step for stirring preferably comprises a step for aerating
said reactor.
The fact of aerating the reactor before extracting the granules from it
makes it possible flot only to create a stirring therein but also to maintain
an
aerobic ambience and to prevent the phosphorous assimilated by the granules
from escaping therefrom and getting distributed in the reactor before the
granules
are extracted from it. This implementation therefore improves the elimination
of
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phosphorous.
According to one advantageous characteristic of the invention, at least one
of said cycles comprises a step for extracting particles of low decanting
capacity,
said particles of low decanting capacity being flot extracted with said
treated
5 water.
The extracted treated water is thus separated from the particles of low
decanting capacity so that the treated water has a rate of solid particles in
suspension that is low enough to avoid having to implement of a downstream
polishing treatment. Only the extracted particles of low decanting capacity
can be
10 conveyed towards a treatment of this type. Thus, the cost of producing
biologically treated water is limited
6. List of figures
Other features and advantages of the invention shall appear more clearly
from the following description of a preferred embodiment, given by way of a
simple illustratory and non-exhaustive example and from the appended drawings,
of which:
Figure 1 illustrates a first example of a plant for treating water to
implement a method according to the invention;
Figure 2 illustrates a second example of a plant for treating water to
implement a method according to the invention.
7. Description of one embodiment of the invention
7.1. Reminder of the general principle of the invention
The general principle of the invention consists in treating water by
biological means and introducing it rapidly during a phase of anaerobic
feeding
into a reactor within which it is put into contact with biomass granules. The
water
therein then undergoes successive anaerobic phases of swirling of the contents
of
the reactor, aeration, and then fast decantation. Treated water is then
extracted
from the reactor.
7.2. Example of a plant for treating water to implement a method
according to the invention
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Referring to figure 1, we present a plant for treating water to implement a
method according to the invention.
As represented, a plant of this kind comprises a water intake pipe 10 for
leading in water to be treated. The outlet of this pipe is connected to the
inlet of a
T-connector 12. A valve 11 is mounted on the pipe 10.
The T-connector 12 comprises an outlet that is connected to the inlet of a
recirculation pump 13. The T-connector 12 comprises a second inlet that is
connected to the outlet of a recirculation pipe 14 on which a valve 27 is
mounted.
The outlet of the recirculation pump 13 is connected to a collector 15
which opens into the bottom of a biological reactor 16.
The biological reactor 16 comprises a bottom 161, a top part 162 and a
side wall 163. The side wall 163 is crossed by an extraction mouth 17.
The reactor 16 houses means for extracting treated water and/or particles.
These means for extracting comprise a tube 18. The inlet 181 of this tube 18
is
provided with a floater 29. The outlet 182 of this tube 18 is connected to the
extraction mouth 17.
The extraction mouth 17 is connected to a T-connector 19. A first outlet
of this T-connector 19 is connected to a pipe 20 for removing treated water on
which a valve 21 is mounted and a second outlet of this T-connector 19 is
connected to a pipe 22 for removing particles of low decanting capacity and
granules on which a valve 23 is mounted.
The plant comprises means for aerating the reactor 16. These means for
aerating comprise an air intake pipe 24, the outlet of which is connected to a
distributor unit 25 housed at the bottom of 161 of the reactor 16.
The reactor 16 houses a bed constituted by a plurality of biomass granules
26.
The recirculation pipe 14 comprises an inlet 141 that is connected to a
funnel 28 placed in the top part 162 of the reactor 16. In one variant, this
recirculation could be done by using the pipe 20 for removing treated water.
Figure 2 illustrates a variant of the plant for treating water illustrated in
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figure 1.
As can be seen in figure 2, the means for recirculating water which
comprise especially the funnel 28 and the pipe 14 for recirculating are
replaced in
this variant by blade stirrers 200 housed within the reactor 16.
7.3. Example of a method for treating water according to the
invention
During the implementing of a method for treating water according to the
invention, the biological reactor 16 works in sequenced mode as shah l be
explained in detail here below. This is therefore a reactor of the SBR
(sequenced
batch reactor) type in which the total volume of water to be treated is
treated by
successive portions or batches.
A method according to the invention comprises a plurality of successive
cycles each comprising:
an anaerobic step for feeding wastewater to the reactor 16 during which
the water is mixed with the granules to form a fluidized bed;
an anaerobic step for stirring the contents of the reactor 16;
a step for aerating the content of the reactor 16;
a decantation step;
a step for removing treated water depleted of organic matter.
During each feeding step, the valve 11 is open while the valves 27, 21 and
23 are closed. The pump 13 is implemented in such a way that the water to be
treated is introduced into the reactor 16 from its bottom 161 via the intake
pipe
10, the collector 15 and the conduits 151, preferably until the top level of
the
reactor 16 is reached.
The speed at which water is fed to the reactor during the feeding step
ranges from 10 to 20 m/h. The feeding of water to be treated to the reactor is
therefore fast.
Owing to the fast feed, the water to be treated rapidly passes through the
bed of granules present at the bottom of the reactor 16 in such a way that the
bed
is fluidized. Thus, the totality of the granules constituting the bed is
swiftly
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exposed to the water to be treated on the totality of their surface. Thus, as
soon as
the water is fed to the reactor, the exchanges between the water to be treated
and
the biomass constituting the granules are maximized. In other words, as soon
as
the feeding of the reactor is done, the granules start assimilating nutrients.
After the feeding of water to the reactor is completed, its content is kept
stirred in anaerobic conditions.
During this anaerobic stirring step, the stirring within the reactor 16 is
generated by the implementation of stirring means.
In the embodiment illustrated in figure 1, the valve 11 is closed, the valve
27 is open and the pump 13 is implemented in such a way that the water
contained
in the reactor 16 is sucked into the funnel 28 situated at the upper part 162
of the
reactor 16 and flows into the recirculation pipe 14 and is then re-injected
into the
bottom 161 of the reactor 16 via the collector 15 and the conduits 151. During
this
aerobic stirring phase, the speed of recirculation of the water ranges from 4
to 8
m/h.
In the embodiment illustrated in figure 2, the stirring is generated in the
reactor 16 by putting the blade stirrers 200 into rotation.
The implementing of the stirring means in the anaerobic stirring step
creates a level of stirring within the reactor ranging from 5 to 10 W/m3.
Such a level of stirring improves the exchanges between the water to be
treated and the biomass granules while at the same time preserving their
integrity.
The stirring within the reactor ensures that the granules conne into contact
continuously with the water on the totality of their surface throughout the
duration
of the stirring phase. The nutrients, whose assimilation by the granules is
not
limited by the diffusion, can penetrate in depth into the granules. The rate
of
assimilation of the nutrients by the granules is therefore greater than when
implementing the technique according to the prior art. This also increases the
speed at which the PO4-P which is necessary for the biological dephosphatation
by PAO bacteria.
Given the improvement of exchanges between water and the granules, the
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implementing of the technique of the invention, which promotes the development
of the granules, leads to the production of stable granules, i.e. solid
granules
having high density and volume and therefore high capacity for being decanted.
The diameter of the granules thus obtained is generally ranges from 1 to 5
mm while their density generally ranges from 1.03 to 1.5 kg/l.
The technique of the invention also improves the reduction of the
nutrients, especially phosphorous and nitrogen.
After the anaerobic stirring step is completed, a step of aeration of the
contents of the reactor is implemented.
The valve 27 is then closed, the pump 13 stopped and air or another gas
containing oxygen is introduced into the bottom of the reactor 16 via the pipe
24
and the distributor unit 25. The concentration in dissolved oxygen in the
reactor
generally ranges from 1 to 4 mg 02/1.
A part of the bacteria forming the biomass, of which the granules are
constituted, converts the ammonia present in the water in nitrates by
consuming
oxygen. A nitrification of the water is then observed.
Given the thickness of the granules, there is a gradient of concentration in
oxygen: the oxygen concentration within the granules decreases with depth.
Thus,
the oxygen concentration at the core of the granules is substantially zero.
Another part of the bacteria forming the biomass constituting the granules
then degrade the previously produced nitrates into nitrogen gas in an anoxic
phase. Then a denitrification of the water is observed. Thus, the phosphorus
jettisoned during the anaerobic step will be accumulated in the granules.
After the aeration step is completed by stopping the injection of oxygen
into the reactor 16, the granules formed in the reactor 16 swiftly decant
because of
their size. During the decanting phase, the granules of high decanting
capacity
collect at the bot-tom of the reactor 16.
The treated water, depleted of organic matter as well as nutrients, can then
be extracted from the reactor 16. To this end, the valve 21 is opened so that
the
water treated flows from the inlet 181 of the tube 18 floating on the surface
of the
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water. Since the inlet 181 of the tube 18 floats on the surface of the water,
it is
possible to activate the extraction of treated water by opening the valve 21
without waiting for all the granules to be decanted at the bottom of the
reactor 16.
The flow rate of extraction of treated water can thus be chosen so that the
5 lowering of the level of water in the reactor follows the lowering of the
level of
granules in the reactor. The production time for treated water can thus be
reduced. The speed of extraction of the water will preferably range from 10 to
20
m/h.
The level of the extraction point for the treated water, in other words the
10 level of the inlet 181 of the tube 18, is variable and, in this case,
faits during the
extraction. It is thus possible to lower the level of the inlet 181 of the
tube 18 until
it reaches a level close to that of the surface of the bed of granules. Thus,
it
becomes possible to extract a very great volume of treated water, and the
volume
of treated water stagnating within the reactor 14 is reduced accordingly after
15 completion of the step for extracting.
As a result, at the next filling of the reactor 16, the water to be treated
that
is introduced is little diluted with already treated stagnant water whose
concentration in nutrients for the biomass is very low. The development of the
granules at the following cycles is also promoted.
In addition to the granules of high decanting capacity, the water contained
in the reactor contains other less decantable particles. During the
decantation
phase, these particles tend to collect to form a layer on the surface of the
bed of
granules situated at the bottom of the reactor 16.
Thus, during the step for extracting the treated water, the inlet 181 of the
tube is in proximity to the upper surface of the bed of granules, and the
valve 21
can be closed and the valve 23 opened so that the particles of low decanting
capacity can be extracted from the reactor 16 separately from the treated
water.
The treated water extracted from the reactor 16 thus lias a low rate of sot Id
particles in suspension. Thus, the implementation of a polishing treatment
downstream is avoided. The particles of low decanting capacity extracted from
the
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16
reactor 16 can be sent to subsequent treatment. It can happen that such a step
for
extracting the particles of low decanting capacity is flot implemented at each
cycle.
After the step for extracting treated water is completed, a new cycle can be
initiated by implementing a new anaerobic step for the fast feeding of the
reactor
16. As many cycles as necessary will be implemented to carry out the treatment
of
a given volume of water to be treated.
A method according to the invention can include one or more steps for
extracting granules. This step or these steps for extracting granules are
preferably
implemented after the running of several successive cycles.
The granules can be extracted at the end of a step for extracting particles of
low decanting capacity by leaving the valve 23 open.
The step for extracting granules is preceded by a step for stirring the
content of the reactor 16. The stirring can be generated mechanically using
stirrers. It is preferably generated by aerating the interior of the reactor
through
the piping 24 and the distribution unit 25.
In this way, the bed of granules is stirred so that the distribution of the
GAOs and the PAOs contained in the granules is substantially homogenous within
the bed. Thus, during the extraction of granules, the proportions of GAOs and
PAOs discharged from the reactor 16 is substantially identical. Thus, the GAOs
are prevented from being preponderant within the reactor at the subsequent
cycles.
Such preponderance would limit the reduction of the phosphorous.
The aeration of the bed before extraction of granules also makes it possible
to maintain an aerobic state within the reactor 16 and prevent a part of the
phosphorous assimilated by the granules from being rejected into the reactor
before the discharge of the granules. This contributes to improving the
reduction
of the phosphorous.
During the implementing of such a method, the duration of the step for:
anaerobic feeding is equal to 15 minutes and preferably ranges from 10 to
30 minutes;
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- anaerobic stirring is equal to 45 minutes and preferably ranges from
30 to
60 minutes;
- aeration is equal to 120 minutes and preferably ranges from 90 to
180
minutes;
- decantation is equal to 15 minutes and preferably ranges from 10 to 30
minutes;
- extracting treated water is equal to 15 minutes and preferably
ranges from
to 30 minutes.
In the prior-art technique implementing an SBR type reactor without
10 granules, the duration of the step for:
- feeding and latency is equal to 1 to 2 hours;
- aeration is equal to 2 hours;
- decantation is equal to 1 hour;
- extracting treated water is equal to 1 hour.
In the prior-art technique implementing granules, the duration of the step
for:
- feeding and latency is equal to 1 to 2 hours;
- aeration is equal to 2 hours;
- decantation is equal to 2-10 minutes;
- extracting treated water is equal to 2-10 minutes.
The implementing of the technique according to the invention thus reduces
the duration of the treatment.
