Note: Descriptions are shown in the official language in which they were submitted.
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A PROCESS AND APPARATUS FOR TREATING
WASTE WATER
FIELD OF THE INVENTION
The present invention relates to a process and an
apparatus for treating waste water from houses or
dwellings, hotels, restaurants, schools, institutions,
factories, commercial buildings, etc. as well as to
large housing developments. More particularly, the
present invention relates to a system combining a septic
tank in series with a biological reactor, preferably a
sequencing batch reactor (SBR).
The basic principle of the present invention lies
in the fact that it utilizes two already known
technologies operating in series in a special way so
that the resulting effect provides some outstanding
features and benefits as well as very high and reliable
biological treatment performance.
These two known technologies are the septic tank
technology combined with a biological reactor
technology, preferably of the SBR type.
BRIEF DESCRIPTION OF THE PRIOR ART
For the last hundred years, septic tank technology
has been developed and used all over the world. It
consists of a simple pretreatment with no mechanical
maintenance except the fact that the sludge has to be
removed therefrom after a certain number of years of
utilization. Most of the time, this system works by
gravity and allows the settleable solids to be captured
and digested anaerobically during two years typically.
No screening is necessary. All fibrous materials and
inert solids simply settle down in the tank at the same
time that the floatable solids are also retained by
baffled partition wall(s).
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For more stringent water quality, in most of the
advanced countries, the septic tank effluent is directed
into a gravity aerated tile field to provide a secondary
quality water treatment before discharging into the
"water table" as final treatment, e.g. percolating
through the natural ground.
The tile field constitutes a secondary biological
treatment using fixed media process and aerobic
bacteria. The pretreated waste water is allowed to
percolate through a matrix of aerobic biological film
which is fixed and allowed to grow on the surface of a
stone bed. This treatment is very similar to the one of
an aerobic trickling filter even if the stone bed may be
temporarily submerged during the course of its
operation, particularly when fed with a syphon or a pump
to achieve a more uniform water distribution throughout
the entire tile field.
The tile bed activity is also related to a very
active biomass growth mixed with the first two or three
centimeters of soil. This part of the tile bed is often
responsible for most of the waste water treatment and
must also remain aerobic.
The septic tank tile field concept has proven to
work very well with no maintenance in all cases where
adequate conditions exist in terms of flow, solid
content, grease content and particularly where the soil
conditions and natural water table also meet all
requirements for the good operation of such simple
installations.
However, one of the main drawbacks of the septic
tank tile field installation comes particularly from the
solid content load, flow conditions, grease
concentration and, of course, from improper soil
granulometry or high water table conditions. Today,
millions of septic tank tile field installations in each
country are totally inadequate and are not working well
because the tile field is plugged internally with
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grease, soil or organic solids or simply because the
"water table" has raised and physically submerged the
"underground bioreactor" section of the tile bed or
because the soil conditions do not permit the proper
percolation rate so that the aerobic bacteria cannot
absorb the organic before the water is finally
discharged into the "water table".
Another drawback with the use of a septic tank in
combination with a tile field is the fact that the
sludge settling in the septic tank has to be removed
regularly to avoid any transfers of sludge to the tile
field.
In order to solve these drawbacks, the present
invention proposes a combination of a traditional septic
tank in series with a biological reactor such as a SBR.
Biological reactors wherein the waste water is
aerobically treated are also known in prior art but they
are not combined with septic tanks which are also
already known in prior art.
More particularly, SBR are known in prior art. SBR
reactors are described, by way of example, in Canadian
laid-open application no. 2,099,514 and in Canadian
patent no. 2,041,329. These documents do not suggest to
treat the waste water under anaerobic conditions, as in
a septic tank that can accumulate the solids for many
years, before treating it in a SBR. The first activated
sludge system, such as SBR, was developed using "fill-
draw" methodology. SBR technology was reintroduced on
the market in the early '80's as a very advanced
technology including outstanding biological controls
where secondary and tertiary treatment can be achieved
in one single tank. In other words, not only can
biochemical oxygen demand (BOD) and suspended solids be
captured, but nitrogen and phosphorus can 'also be
removed using very specific cyclology in terms of
following the actual bacteria activities in a given
reactor. These activities can be controlled by a simple
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timer where anoxic conditions, meaning that no free
dissolved oxygen is available except under nitrate form,
anaerobic conditions, where no free oxygen is available
in the waste water neither under nitrate forms, aerobic
conditions and free dissolved oxygen are available in
the waste water (with or without the presence of
nitrates).
SBR technology is still a technology "on the go" as
several groups of searchers are still conducting
research work based on all the possibilities offered by
such a controllable process where the food quality, the
feed modes, the reaction time and the ptiority of the
biological reactions can be controlled.
One of the most interesting advantages of SBR is
the fact that it is possible to control the activities
of the bacteria as well as its settleability
characteristics by using the feed mode. In other words,
it is well known today that activated sludge can be
separated easily by simple gravity sedimentation if the
right kinds of bacteria are encouraged to grow in a
given reactor. By rapidly feeding a new batch into a
reactor, a very effective "biological selector effect"
can be observed. This means that the activated sludge
will be separated very efficiently, providing very clear
liquid as a treated effluent. Also, this type of feed
mode provides several other advantages such as "enhanced
kinetics" for the removal rate of organic, which is
related to the quantity of organic that the bacteria
actually "sees" available for food at a given time in
the operating sequence. Such a feed mode and an enhanced
kinetics combination allow to save precious time,
gaining overall hydraulic and organic treatment
capacities.
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OBJECTS OF THE INVENTION
A first object of the present invention is to
provide a process for treating waste water, which
process offers a total treatment of the waste water and
the sludge altogether for an extended period of time (5-
15 years), without having to remove any by-products for
immediate treatment. This sludge handling capacity is
called "total sludge management".
Another object of the present invention is to
propose a waste water treatment system for use to carry
out the process according to the invention.
SUMMARY OF THE INVENTION
In accordance with the invention, the first object
listed above is achieved with a process for treating
waste water, preferably domestic waste water, comprising
the steps of:
a) supplying the waste water to be treated to a
septic tank;
b) accumulating the waste water in the septic tank;
c) retaining in the septic tank any scum forming on
top of the waste water and allowing any sludge therein
to settle;
d) biologically treating the waste water and the
sludge in the septic tank under anaerobic conditions;
e) transferring a given amount of the treated waste
water from the septic tank into a biological reactor
containing a sludge-contained liquor;
f) mixing and aerating the waste water within the
biological reactor, such a mixing and aerating causing
activation of the sludge and clarification of the waste
water;
g) allowing the activated sludge in suspension in
the liquor to settle; and
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h) decanting an upper layer of clarified water
formed above the mixed liquor after the settling period.
Preferably, in this process, use is made of a
sequencing batch reactor (SBR) as the biological
reactor. Moreover, in step e) which, in this case, is
occurring simultaneously with step h), the waste water
is rapidly transferred to the SBR by separate batches.
Preferably also, the process according to the
present invention comprises the additional steps of:
i) removing excess sludge formed in the SBR; and
j) transferring into the septic tank the excess
sludge removed from the SBR so that the excess sludge be
treated in the septic tank by anaerobic digestion.
In accordance with the invention, there is also
provided a system for use to treat waste water according
to the process mentioned hereinbefore. This waste water
treatment system comprises a septic tank for
accumulating waste water and wherein scum is forming on
top of the waste water and sludge is settling down and
accumulates in the tank. The waste water and sludge are
biologically treated under anaerobic conditions in the
septic tank. The septic tank comprises means for
retaining the scum forming therein. The waste water
treatment system also comprises a biological reactor for
further treating the waste water under aerobic
conditions. The reactor contains a sludge-contained
liquor and comprises means for mixing and aerating the
waste water within the reactor such a mixing and
aerating causing activation of the sludge and
clarification of the waste water. The reactor also
comprises means for decanting an= upper layer of
clarified water formed above the mixed liquor after a
settling period following the mixing and aerating of
waste water. Means for removing excess sludge forming
therein is also provided and means for transferring the
treated waste water from the septic tank to the
biological reactor.
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Preferably, the septic tank according to the
invention comprises a baffle wall extending upwardly
from a floor of the septic tank. The baffle wall defines
a first chamber where the sludge may settle and
accumulate and where anaerobic fermentation is
occurring. The baffle wall also defines a second
treatment chamber where the waste water is anaerobically
digested. In use, the waste water is flowing from the
first chamber to the second chamber by passing over the
baffle wall.
Preferably also, the transferring means of the
treatment system is devised for selectively transferring
the treated waste water from the first or the second
chamber of the septic tank to the biological reactor.
As can now be understood, the process and treatment
system according to the present invention is
advantageous in that it solves the problems mentioned
hereinbefore, associated with the existing septic
tank/tile field installations, by replacing the tile
field element with a biological reactor. Advantageously
also, with this process, the sludge settling in the
septic tank does not require to be removed for five to
fifteen years.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and the way it works will be better
understood upon reading of the following, more detailed
but non-restrictive description thereof given with
reference to the accompanying drawings in which:
FIG. 1 is a side elevational view of a waste water
treatment system adapted to carry out the process
according to the invention. -
FIG. 2 is a schematic block diagram of the process
according to the invention.
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DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
OF THE TREATMENT SYSTEM ACCORDING TO THE INVENTION
Referring to FIG. 1, the treatment system according
to the present invention basically comprises a modified
septic tank 10 followed by a biological reactor 40,
preferably a SBR treatment reactor. The treatment system
also comprises transferring means for transferring the
waste water from the septic tank 10 into the biological
reactor 40. These two technologies interact with each
other to form the global process according to the
present invention. For the purpose of simplifying the
following description, this process will be called
"BioCycle".
The BioCycle system is designed to solve the
problems associated with septic tank/tile field existing
installations by replacing the tile field element with
one SBR reactor. Also, the BioCycle system can be
designed for new installations using a specially
engineered septic tank technology followed by a rapid
batch feed SBR technology.
Septic tank
As illustrated in FIG. 1, the septic tank 10
comprises an inlet 12 for receiving the influent of the
waste water and an outlet 14 from which the water
treated in the septic tank 10 is evacuated. The septic
tank 10 further comprises a baffle wall 16 extending
upwardly from the floor 18 of the septic tank 10. The
baffle wall 16 defines a first treatment chamber 20
where the sludge may settle and accumulate and where
anaerobic fermentation is occurring and a second
treatment chamber 22 where the waste water. and the
settleable solids are anaerobically digested.` In use,
the waste water is flowing from the first chamber 20 to
the second chamber 22 by passing over the baffle wall
16.
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A grease baffle wall 24 is provided. It defines a
grease trap chamber 26 to accumulate the non-emulsified
grease content and most of the floating material present
in the waste water influent. This chamber 26 is located
at the front end of the septic tank 10. The grease
baffle wall 24 is provided over a much more extended
vertical distance towards the floor 18 of the tank 10 as
in a normal septic tank to reflect an equalization
function of the tank 10 as it will be further discussed
hereinafter. The extension of the grease baffle wall 24
is sufficient to capture and store the floating
material, scum and grease, even when the water level
falls to its minimum level in the tank 10.
As mentioned hereinbefore, the remaining portion of
the septic tank 10 downstream the grease baffle wall 24,
is separated by an intermediate baffle wall 16 extending
from the floor 18 of the tank 10. This intermediate
baffle wall 16 defines the two treatment chambers 20,22.
As it will be further discussed, this baffle wall 16
separates the acidogenic fermentation from the
methanogenic digestion. This wall 16 is also very
important as it will promote an early accumulation of
the solids into this first chamber 20 acting as an
anaerobic fermenter. As the solids accumulate, their
concentration also increases much more rapidly in this
chamber 20 (4-7% dry solid content). Such high
concentration of microorganisms enhances the
fermentation reaction.
Preferably, the middle baffle wall 16 has an
elevation equivalent to close to 50% of the total water
depth and will correspond to the invert elevation of the
effluent port of the tank 10 toward the SBR 40. Its
elevation can vary slightly. It depends on the
calculation of the accumulation of solids and on the
equalization capacity required. The location and
elevation of the baffle wall 16 of this preferred
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embodiment allows to improve the process and simplify
the structural construction of the septic tank 10.
The second treatment chamber 22 is solely used for
further digestion, preferably methanogenic digestion,
and accumulation of the solids.
As illustrated in FIG. 1, the septic tank 10 is
preferably designed so that the entire surface area of
the tank 10 including each of the chambers 20,22, can be
used for hydraulic equalization capacity.
Preferably also, the septic tank 10 is also
designed to handle very important scum accumulation. As
the system is built in view of the accumulation of
solids over 5-15 years, the septic tank 10 is designed
to accept an important volume of floating solids over
the whole septic tank 10 surface including each of the
chambers 20,22.
Biological reactor
The SBR 40 used to treat the waste water under
aerobic condition contains a sludge-contained liquor
(not illustrated). The SBR 40 comprises an air diffuser
system 42 for aerating and mixing the waste water within
the reactor 40. As illustrated in FIG. 1, the air
diffuser 42 is connected to an air blower 44 located
outside the SBR 40. Such a mixing and aerating causes
activation of the sludge and clarification of the waste
water. Any other means for mixing and aerating the waste
water known in the art such as any means selected from
the group consisting of jet aerators, air diffusers,
submerged turbines and mechanical mixers, may be used.
The SBR 40 also comprises a syphon decanter 46 for
decanting an upper layer of clarified water 41 formed
above the mixed liquor after a settling period following
the mixing and aeration of waste water. Alterriatively,
the decantation means of the SBR 40 may be fixedly
mounted inside the SBR at a given height, hereinafter
called "clear water level", and in and through which the
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upper layer of clarified water on top of the liquor
within the SBR may freely enter and be discharged out.
Other fixed or floating decanters may also be supplied.
Means for removing excess sludge forming in the SBR
40 are also provided. This means comprises an air-lift
pump 48 also connected to the air blower 44. This air-
lift can also be replaced by another pumping device.
As mentioned before and referring to Figs. 1 and 2,
the treatment system is also provided with means for
transferring the waste water from the septic tank 10 to
the SBR. Preferably, this transferring means is designed
for selectively transferring the treated waste water
from the first or the second chamber 20,22 of the septic
tank, as it is schematically illustrated in Fig. 2. The
transferring means may easily comprise a first pipe 21
having an inlet for receiving the waste water from the
first chamber 20 and a second pipe 23 having an inlet
for receiving the waste water from the second chamber
22. Each of the first and second pipe 21,23 has an
outlet connected directly to a separate transfer device
or to a valve which is connected to an inlet of a third
pipe 50. This third pipe 50 has an outlet connected to
an inlet 52 of the biological reactor. This transferring
means also comprises pumping or transfer means for
pumping the waste water from the septic tank 10 into the
biological reactor 40 through the first or second pipe
and the third pipe. Preferably, as illustrated in
FIG. 1, this pumping means is designed for rapidly
introducing waste water into the SBR, such a rapid
introduction causing the level of the liquor within the
SBR reactor to raise from a bottom water level (BWL) to
a top water level (TWL) and to be lowered back to the
BWL once the waste water has been treated using the
syphon canter 46. The waste water is then discharged out
of the SBR.
This pumping means comprises a vertical liquid
transfer tube 54 enclosed in the SBR 40 and in open
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communication with the inlet 52 of the SBR 40 for
monitoring the waste water level of the septic tank 10
without having to access the septic tank 10. Another
airlift transfer pump 56 enclosed in the vertical tube
54 is also provided for transferring the water from the
septic tank 10 to the SBR. This special vertical liquid
transfer tube 54 connects the septic tank liquid 10 to
the interior of the biological reactor 40. Such a tube
54 forms a sealed vertical compartment in direct
communication with the liquid in the septic tank 10.
This transfer tube 54 has dimensions sufficient for
monitoring the liquid level of the septic tank 10
directly without having to access the septic tank. Also,
it can be used to install an airlift transfer pump 56 or
other pump to actually transfer the liquid from the
septic tank 10 to the biological reactor 40. This
transfer tube 54 is then designed with sufficient
vertical length to provide the necessary submergence for
efficient operation of the airlift pump 56.
Alternatively, the air-lift pump 56 can be economically
incorporated into a transfer tube 54 installed between
the septic tank 10 and the SBR 40 to enable the rapid
transfer of each waste water batch from the septic tank
10 to the SBR. The air-lift transfer pump 56 may use the
blower 44 provided for the aeration of the SBR 40.
Preferably, as illustrated in FIG. 2, the treatment
system may advantageously comprise a phosphorus release
tank 58 for removing phosphorus contained in the excess
sludge from the SBR when required. Obviously, with this
alternative, any means known in the art for transferring
the excess sludge from the SBR 40 into the release
phosphorus tank 58 and the treated excess sludge from
the release tank 58 into the septic tank 10 is also
provided.
Preferably also, another air-lift pump (not
illustrated) may be provided for transferring the last
amount of treated water back to the inlet of the
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biological reactor tank during extended "no-flow"
periods towards the influent of the septic tank 10.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PROCESS
ACCORDING TO THE INVENTION
In the BioCycle process according to the present
invention, the septic tank 10 is utilized in a very
special way described in the following sections.
1- Equalization of all flow and organic
Using a pumping station 56 for transferring the
waste water from the septic tank 10 to the SBR reactor
40, the septic tank 10 is used as an equalization tank
in which the water level will vary according to the
frequency of operation of the pumping device and the
incoming raw sewage rates. The BioCycle process
preferably utilizes a "rapid batch feed" operation mode
where every batch of waste water is pumped out quickly
from the septic tank 10 into the SBR 40 reactor
(typically within 5 to 30 minutes maximum).
The septic tank 10 equalizes all the hydraulic
loads so that no hydraulic peak flow can disturb the SBR
final treatment system. Obviously, by doing so, all
organic peak loads are also equalized into the same
septic tank 10. Furthermore, the SBR final treatment is
also protected from organic concentratiori, toxic
concentration, detergent concentration and other
physical and chemical effects such as pH and temperature
variations. Anaerobic biomass is very resistant to these
perturbations and acts as an efficient protection for
the final aerobic treatment.
The septic tank 10 is acting as a.low rate
anaerobic digester combining organic and hydraulic
equalization capacities from which is fed a biological
reactor, preferably a SBR aerobic reactor system using
a rapid-batch waste water introduction mode.
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The septic tank 10, as a low rate anaerobic
digester, is capable of transforming the complex
organics contained in the waste water into simple ones
such as fatty acid compounds readily biodegradable by
the anaerobic methane bacteria present in the septic
tank 10 and by the aerobic bacteria, present in the
following SBR reactor 40. The fermenter concept is quite
special in many ways. In this sense, it does not use any
external means of mixing the content other than the flow
velocities. Also, the sludge detention time or sludge
age of the fermentative biomass is normally controlled
by the height of the division baffle wall between the
fermenter compartment and the digester compartment. For
additional control on the sludge age, different
withdrawal points can be installed along the waste water
path (circuit) in the septic tank so that the waste
water can be transferred sooner to the SBR aerobic
reactor.
2- Compartmented degreaser
The SBR reactor 40 cannot likely get plugged with
grease or solids like a tile bed. But, considering
potential grease content in the waste water, the
BioCycle process makes use of a degreaser baffle wall 24
ahead of the septic tank 10 to form a grease trap
chamber 26 in the septic tank 10. This grease trap
chamber 26 i's also accessible to remove the excess of
floating material from an access manhole when required.
3- Fibrous and inert material removal and elimination
All fibrous solids such as paper, cloth and other
inorganic/inert solids simply settle down and accumulate
into the septic tank 10 without requiring any mechanical
equipment, eliminating all associated maintenance and
operation. These solids are eliminated to a substantial
degree due to a very long digestion time allowed and
some natural resolubilization reactions.
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4- Removal and elimination of organic solids
The settleable part of the organic solids settles
down into the septic tank 10. These solids will also be
digested in a very effective manner and the rest will
accumulate at a certain rate, depending on the waste
water temperature which will affect the anaerobic
digestion of the solids. The digested part of these
solids will disappear from the tank and will, therefore,
be eliminated under water, CO2, CH4 and H2S gas form,
therefore reducing significantly the solid weights and
their effective volume being actually accumulated.
5- Anaerobic treatment
Anaerobic treatment occurs in the septic tank 10.
Such treatment can be decomposed into two main phases.
Fermentation of organics
The first phase is called "fermentation" and
consists of an acidogenic transformation of the organic
solids which are mainly converted into "fatty acid
compounds" such as acetates, butyrates and propionates
organic forms. Such organic forms represent the simplest
organic material which will be available later on for
storage and/or absorption by either the aerobic
microorganisms or by anaerobic (methane) bacteria. As
preferred intention of this process, these fatty acids
are to be first stored and then absorbed by the aerobic
biomass contained in the SBR, particularly when
biological phosphorus removal is required. The
fermentation process is a transformation process only.
It does not reduce the organic load of the waste water.
Methanogenic digestion
This is the second stage of the anaerobic treatment
where the organics are digested.
During the following methanogenic digestion phase,
the BOD load will be reduced as the organic is used by
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the anaerobic methane bacteria for their own growth and
is transformed mainly into CH4 and COZ gas. BOD is,
therefore, reduced typically by 35% to 80% depending
mainly on detention time, anaerobic (methane) bacteria
population and the reactor content temperature.
The process uses the anaerobic treatment in a
controlled way, depending on the effluent quality
required. In other words, when biological phosphorus
removal is required, the effective detention time of the
waste water through the septic tank will be controlled
so that a sufficient quantity of fatty acids still be
contained in the waste water before proceeding to the
sequencing batch reactor. This control is simply
realized by repositioning the effluent withdrawal point
towards the entrance of the septic tank 10 instead of
towards the normal effluent end of the tank 10, when
maximum BOD reduction/without phosphorus removal is
required. In this case, the second half of the tank is
simply used as accumulation and digestion of solids.
When no biological phosphorus reMoval is required,
then, the effluent of the septic tank 10 is positioned
at the further end of the septic tank 10 so that the
waste water fully travels across the tank 10 to achieve
its maximum detention time. In doing so, the process
requirement is only to achieve a maximum reduction of
the BOD loading to ultimately save energy, as it is no
longer concerned with the conservation of a sufficient
quantity of fatty acids to obtain biological phosphorus
removal in the sequencing batch reactor. Clearly, these
fatty acids are then consumed by the anaerobic methane
bacteria resulting in the organic load reduction.
The process preferably uses a septic tank with a
"hydraulic plug flow" configuration so that each
physical and biological reaction can be achieved
following a priority order dictated by the prevailing
conditions along the liquid course as it travels across
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the septic tank 10. This hydraulic plug flow is achieved
by using a septic tank 10 as described hereinbefore.
6- Biological phosphorus removal
As explained hereinbefore, a preferred embodiment
of the present invention addresses to biological
phosphorus removal. Several different biological
phosphorus removal systems exist on the market today.
They are all based on an early creation of "fatty acid
compounds" generated in a prefermentation reaction prior
to another anaerobic/aerobic reacting phase. The
efficiency of biological phosphorus removal will
directly depend on the quantity of fatty acids generated
in the prefermented phase and not destroyed by other
micro-organisms before the aerobic phosphorus removal
bacteria can store them during an anaerobic period and
absorb them later on during an aerobic period.
The principle of operation can be resumed as
follows. First, organic matter has to go through the
first stage of anaerobic treatment called
"fermentation". This phase consists of acidogenic
transformation of the organic into fatty acids. These
fatty acid compounds represent the most easily
biodegradable organic available to the bacteria. Such
compounds can be readily "stored" by the phosphorus
removal bacteria under anaerobic conditions e.g. without
requiring oxygen as the energy source. The energy source
used by the bacteria to proceed with this storage is the
bacteria polyphosphate intracellular reserve. So, the
bacteria will release their polyphosphate content as
they will accept and store a proportional quantity of
fatty acids (select-food). At that stage, the bacteria
do not absorb/use/digest or consume any of this."select-
food". When the fatty acids have been completely stored,
the aeration system can then be started. Under
oxygenated conditions, the phosphorus removal bacteria
will start to consume the previously stored fatty acids.
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As they do so, they will begin to recapture their
polyphosphates previously released in the waste water in
order to basically tend to keep a stable energy level
inside their cells. So, with a very efficient
fermentation, sufficient fatty acid compounds can be
generated to permit very large quantities of phosphorus
to be reabsorbed by the biomass, in excess of their
synthesis needs for reproduction.
In other words, in the septic tank 10, fatty acid
compounds are generated through the acidogenesis
fermentation stage. Such fatty acid is to be later on
stored by the phosphorus removal bacteria present in the
biological reactor biomass during the anaerobic period
of the engineered treatment sequence. During this stage
of treatment, the fatty acid -compounds are first
"stored" in the bacteria permanently. The energy used
for such anaerobic reaction is the release of the
polyphosphates from the bacteria back in the mixed
liquor. When the oxygen is later on available to these
bacteria, the fatty acids are then consumed by the
bacteria. At the same time, the bacteria reabsorb its
polyphosphates previously released plus important
additional quantities if sufficient fatty acids have
been stored in the bacteria previously. This way, very
important quantities of polyphosphates can be
reaccumulated into the phosphorus removal bacteria and
very efficient phosphorus removal can be achieved
biologically without the use of chemicals.
Thanks to the present invention, release of
phosphorus backed in the waste water is avoided when the
excess sludge, rich in phosphorus content, will be
returned eventually to the front end of the septic tank
10 for further anaerobic treatment. During the digestion
of these solids under anaerobic conditions, the
phosphorus would again be resolubilized, eliminating
therefore the effectiveness of the biological phosphorus
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removal process as the phosphorus would be reinjected
into the waste water being treated.
The present invention overcomes this obvious
problem by promoting an early phosphorus release from
the phosphorus-rich wasted sludge 57 into a phosphorus
release tank (PRT) 58 installed beside the septic tank
and the SBR reactor 40. So, the excess wasted sludge
from the SBR reactor 40 is first directed into the PRT
phosphorus release tank 58. The pump transfer energy is
10 simply used as a gentle mixing to provide an efficient
reaction. Then the sludge is allowed to settle down
under anoxic and further anaerobic conditions.
Therefore, phosphorus will be released back into the
water content over a controllable period of time. As the
wasted sludge is admitted in the form of several batches
per day, sufficient mixing is provided in the PRT 58 to
separate the phosphorus from the biological settling
solids. The PRT 58 is designed to encourage the release
of the phosphorus from the bacteria to the water content
over anaerobic/static conditions. This operation is done
as a batch process using a sequence in which the inlet
flow velocity is used to provide the necessary energy to
control the uniformity of the reaction. The phosphorus-
free sludge is then separated by gravity sedimentation.
After this reaction is completed, then the supernatant
water, rich in phosphorus, is decanted and may be
directed into a short tile field or an absorption trench
for phosphorus absorption by the soil, as is the case
for the standard septic tank/tile field technology. As
the wasted sludge only represents 1-5% of the total
influent, the quantity of water to dispose of in the
tile field is quite small. Therefore, the tile field
itself can be built quite compact and without important
expenses. Alternatively, the phosphorus could be
recovered through a filtration process 60 utilizing
"peat moss" as an absorbent. As the natural soil and the
peat moss absorb 10-35% of the total phosphorus content,
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another media can be used called "LECA'"" (special clay
product) which can retain almost 100% of the phosphorus.
Of course, these media must be replaced when saturated.
They can be disposed of for gardening, as fertilizers
62. The phosphorus-free sludge 59 from the PRT and the
phosphorus-free water 61 from the filtration process 60
may be transferred back to the septic tank 10. Alumina
can also be used as a very effective phosphorus
exchanger for this purpose.
This allows the phosphorus to be removed
biologically right until the end of the process while
all the sludge produced by the process can be eventually
digested completely without causing any process
interf erence .
7- Maintaining efficient treatment during extended
periods without flow
In the event of long periods of flow or influent
interruption, the present invention offers a unique
advantage as it can basically utilize all the organic
material stored in the septic tank 10 in order to
eventually feed the SBR reactors 40 on a daily basis.
This way, the SBR reactor 40 can be kept in good
operating condition for weeks and months even if the
interruption of the incoming flow to the septic tank 10
is for extended periods of time such as in work camps,
schools, hotels, etc.
Preferably, the process according to the present
invention can be reduced to practice as follows.
The operation of the treatment plant may be managed
by logic controls 70 or more sophisticated electrical
controls. When the equalization capacity provided in the
septic tank 10 has been exhausted, the controls will
acknowledge this situation and will
automatically/continuously recirculate the last treated
water batch(es) back to the septic tank influent.
Therefore, this quantity of water will automatically
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generate a permanent available source of waste water for
the aerobic final treatment as long as organics are
present in the septic tank 10 for resolubilization in
the water being recirculated. In another preferred
embodiment of the present invention, the plant may also
be managed by manual control but for more efficiency, a
sophisticated control is favoured.
In other words, the septic tank 10 may be used for
storing an enormous quantity of organics that can be
used totally or partially to feed a conventional bio-
reactor, an activated sludge process, preferably an SBR
aerobic reactor, during long and even very extended
periods of time where the flow is completely interrupted
at the influent end of the BioCycle treatment plant, for
example in schools, factories in industrial parks, work
camps, hotels, hospitals, etc. During such periods, the
system may be controlled by the "logic command" and the
last batch of treated water is recycled ahead of the
septic tank 10 influent, in case of a SBR system,
instead of being discharged to the normal receiving
effluent stream. This last quantity of water enables the
biological reactor 40 to be fed daily at the desirable
rate, regardless of the "no flow" conditions. In case of
a continuous flow system, the logic controls sense the
flow signal and initial a minimum flow recirculation
from the final clarifier back to the septic tank 40
influent.
Using the same logic controls, the septic tank is
also reactivated at the end of every cycle when the
excess sludge is eventually transferred from the aerobic
SBR reactor to the septic tank. This amount of sludge
represents a valuable amount of organic matter available
to feed the anaerobic reactor (septic tank) even during
the extended "no flow" periods. Alternatively, during
extended periods without flow, the process in the SBR
may be restricted to the mixing and aerating step. In
this case, the septic tank is reactivated and fed with
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waste water from the SBR which has not gone through
settling and decanting steps.
8- Extended sludge management
The present invention also offers another great
advantage by allowing to manage all the generated sludge
for extended period of time. This advantage of the
invention is as far as its capacity to manage all
generated sludge in the complete BioCycle system
(anaerobic and aerobic) for extended periods of time.
Preferably, this system could be designed so that all
sludge could be accumulated in the septic tank 10 for
periods ranging from 5, 10 and up to 15 years without
having to remove the sludge from the septic tank 10.
The septic tank 10 may receive all sludge from
primary clarification and from the excess sludge
generatiori from the secondary aerobic system, the SBR
40. It then acts as a primary clarifier, scum removal
and a digester tank at the same time.
As the present invention uses a very long sludge
detention time, the sludge accumulation cannot be
calculated using conventional "model" (equations for
calculation) as conventional treatment plants utilize a
sludge detention time of 5-90 days typically, including
digestion.
Under a very long sludge detention time, several
other reactions occur and will furthermore reduce the
quantity of sludge that will actually accumulate in the
septic tank 10. These reactions greatly affect every
form of solids present, as follows:
Anaerobic digestion of biodegradable volatile solids.
Of course, this part of the solids represents the
truly biodegradable organic solids and is, therefore,
almost completely digested within the first months of
operation, depending on the water temperature in the
tank. This portion is, therefore, readily/mostly
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transformed under gas form and, consequently, is not
occupying any significant volume in the septic tank 10
after a few years of operation.
Anaerobic digestion of non biodegradable volatile
solids.
These solids are mostly the fibrous material,
paper, cloth, hair, nails, etc. By standard definition,
these solids cannot be biodegraded, e.g. during a
conventional 5-90 days of solids detention time,
including the digestion time. But, as the present
invention preferably utilizes much longer detention time
e.g. 5, 10 and up to 15 years of sludge detention time,
the non biodegradable solids are transformed into
biodegradable volatile solids and, therefore, are fully
digested and are not occupying a significant volume in
the septic tank also.
Removal/reduction of the inert material.
Inert material content is quite important in
domestic waste water. It can be accounted for 10-30% of
the total solids with a normal average value of 20%.
These solids are referred to as the salts, the soil, the
sand, some polymer products, etc. Also, by standard
definition, these solids directly accumulate without any
reduction in volume as, in standard sewage plants, the
sludge/solid detention time varies between 5 and 90 days
maximum, including the digestion time. Under these
conditions, it is true that these kinds of solids cannot
disappear. But, in the present invention, as the sludge
detention time may vary from 5, 10 and 15 years as
stated earlier, the most part of these solids is
resolubilized in the water under ionic form or soluble
salt such as silicon, calcium, sodium, mAnganese,
magnesium, etc., and is therefore slowly but
continuously leaving the treatment plant diluted in the
treated effluent without causing any real pollution.
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Therefore, this important part of the inert does not all
directly accumulate in the septic tank neither.
These three basic phenomena explain a low
accumulation rate of the solids in the septic tank 10
used according to the present invention.
In brief, a preferred embodiment of the present
invention offers a total sludge management system using
a septic tank 10 designed according to a mass balance of
the solids generated/digested and resolubilized. A self-
contained capacity of 5 to 15 years can be realized due
to the enhanced digesting and resolubilizing effects
over a very long sludge retention time. Such a digestion
period is sufficient to largely digest the volatile
biodegradable solids as well as the volatile non
biodegradable solids, by conventional definition. Also,
this total sludge management capacity is greatly
assisted by the resolubilization of the inert material
leaving the septic tank 10 and the biological reactor
daily in the form of ionic compounds such as salts, etc.
Advantageously, the use of a SBR reactor 40 with a
septic tank 10 enhances the treatment capacity using
rapid feed of the SBR 40 reactor by means of a pumping
device such as electric pump or air lift devices. This
rapid feed mode is used to enhance the SBR 40 treatment
capacity by using a short filling period and also by
promoting maximum biodegradability rates from the
bacteria due to the high food to microorganism ratio
(F/M) at the beginning of each treatment cycle. Equally
important, this "rapid-feed" operation mode also allows
for very efficient control of suspended solids of the
treated effluent by creating a biological "selector
effect" at the beginning of each treatment cycle. Such
a selective effect Cinhances the growth rate of the
"floc-forming" bacteria over the "filamentous"'bacteria
by promoting a very efficient way of feeding/developing
the growth of the "floc-forming" bacteria rather than
encouraging the growth of the "filamentous" bacteria.
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The floc-forming bacteria then grows over the
filamentous bacteria population, in minority, to form
larger floc which will gather the small isolated
pinpoint floc during its global sedimentation movement
occurring during the settle period of the treatment
sequence.
Also, as the SBR reactor is fed rapidly,
appreciable time is gained within the actual time
sequence. This combined with the enhanced kinetic
activities of the bacteria also translates into a gain
in the overall treatment capacity of the BioCycle plant.
Although only one preferred embodiment of the
invention has been described in detail hereinabove and
illustrated in the accompanying drawings, it is to be
understood that the invention is not limited to this
precise embodiment and that various changes and
modifications may be effected therein without departing
from the scope or spirit of the invention.
