Note: Descriptions are shown in the official language in which they were submitted.
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MULTI-PHASE DUAL CYCLE INFLUENT PROCESS
FIELD OF THE INVENTION
This invention relates to the field of biological
waste water treatment, and more particularly, to the
use of a combination of sequencing batch reactions and
continuous flow processes to effect removal of
nutrients, organic matter, and solids.
BACKGROUND OF THE INVENTION
The strategy of utilizing microorganisms, chiefly
bacteria contained in an activated sludge, to effect
breakdown of organic wastes in influent streams, while
simultaneously removing nutrients, is now almost
universal in the field of sewage treatment. This raw
sewage has a relatively high biological oxygen demand
i5 (BOD), and the breakdown products are typically lower
molecular weight volatile fatty acids (VFA) such as
acetic, propionic, or butyric acids. The composition is
also high in suspended solids. Nitrogen is present as
ammonia and organic, and phosphorous is present as
inorganic phosphates.
It is known that the naturally occurring
populations of microorganisms found in activated sludge
are highly diverse, and represent a spectrum of genera
ranging fr'bm strict aerobes to facultative anaerobes to
obligate anaerobes. Each of these classes of organisms
under appropriate manipulation can achieve some
objective of the waste treatment process.
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Increasingly, it has become an objective of waste water
treatment processes to remove nutrients such as total
nitrogen including organic nitrogen, ammonia nitrogen, ,
and oxidized nitrogen, and phosphates in addition to
achieving removal of organic matter, which can affect
delicate ecological balances. An understanding of the
metabolism and catabolism of different classes of
microbes has led to the design of various treatment
protocols taking advantage of these natural processes.
Organic compounds provide food for bacterial
growth. The organics, both simple and complex,
contained in waste water fuel this growth. Under
aerobic conditions, three types of metabolism can
occur: (1) substrate oxidation in which organic
compounds are converted to carbon dioxide and water;
(2) synthesis in which organic compounds and nutrients
are converted to cell protoplasm; and (3) endogenous
respiration in which protoplasm is converted to carbon
dioxide, nutrients, and water, as described in Metcalf
& Eddy, Waste Water Engineering, 3rd ed., McGraw-Hill:
1991. In addition, energy and a metabolizable carbon
source are also needed for nutrient utilization. Under
anaerobic conditions, organic compounds can be further
fermented to VFAs, primarily by the facultative
species. The two principal nutrients requiring removal
from waste water are inorganic phosphate and
nitrogenous compounds. Influent waste water typically
contains organic nitrogen and ammonia in the form of
ammonium (NH4+). Hydrolysis of organic nitrogen and
conversion of ammonia to free nitrogen gas (NZ) which
can readily be stripped from solution to the atmosphere
requires two distinct processes. During nitrification, -
ammonia is converted first to nitrite (NOz-) by
autotrophic oxidation involving Nitrosomonas spp. and
related organisms, followed by further oxidation to
nitrate (N03-) involving Nitrobacter spp. A relatively
broad range of heterotrophic facultative organisms then
convert nitrate to free nitrogen (Nz) in a series of
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steps. The basic multi-step process for nitrification
and denitrification is set forth in the following
reactions:
Nitrification:
NH4+ + 1. 5 O2 - - - - > NOZ- + 2H+ + H20 { 1 )
(Ni trosomonas)
NOZ- + 0.5 OZ ----> N03- (Nitrobacter) {2)
Denitrification:
N03 - + organic carbon- - - - - > Nz + COZ + OH- { f acult . ) ( 3 )
Studies have shown that step (1) is rate limiting for
nitrification and that Nitrobacter converts NOZ- as an
electron acceptor very quickly to N03-. Meanwhile,
denitrification is dependent on the availability of
organic carbon sources.
It will be apparent that the nitrogen removal
process requires first an aerobic step in which
oxidation of ammonia to nitrate occurs (nitrification),
followed by an anoxic step in which facultative
organisms convert nitrate and nitrite to free nitrogen
which can be released (denitrification). The earliest
and most basic biological water treatment utilized
constant aeration. These are of two treatment methods:
fill, reactions and draw, and conventional flow through
reaction followed by settling.
In more recent fill, reactions and draw, waste
water is introduced to a single tank containing
activated sludge. Alternating anaerobic/anoxic and
aerobic phases are carried out to attain carbonaceous
organic oxidation, nitrification, and denitrification.
.. After settling, the clarified water is drawn off. In
the multi-cell system, primary clarified water is mixed
with activated sludge to form a mixed liquor, which is
then passed through multiple aerobic/anoxic cells in a
continuous flow process, and finally it enters a
secondary clarifier. A portion of the sludge which
settles out is returned to be mixed with waste water to
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form the mixed liquor. The aeration step helps to
create biomass under the two aerobic processes outlined
above, and also to nitrify ammonia. Denitrification
then occurs to some extent upon establishment of anoxic
conditions in the anoxic cells and secondary clarifier.
In the latter, denitrification depends only on
endogenous respiration.
Modern systems also seek to remove phosphorus
species while simultaneously exchanging VFAs for
phosphates. Removal of phosphates occurs in two steps
and is mediated by a group of phosphorous rich
microorganisms (Bio-P), principally Acinetobacter spp.
and some Aeromonas. These organisms, when present in
sludge passing through an anaerobic zone, use stored
energy in the form of poly-phosphate to absorb food
materials, principally VFA, and store it as poly-~i-
hydroxybutyrate (PHB). In the process, the organisms
release phosphates as the polyphosphates are broken
down to release energy. This treatment zone must be
anaerobic rather than anoxic, so that it is depleted of
nitrates which would otherwise inhibit phosphate
release and VFA absorption by the microorganism.
Occasionally, raw waste water contains oxidized
nitrogen species which may inhibit the process.
In the second step of phosphate removal, the
aerobic bacteria contained in the sludge now moving
through an aerobic zone metabolize the PHB and take up
phosphates as biomass increases. Since more phosphate
is taken up by the Bio-P organisms than was previously
released, the difference is known as luxury uptake. In
many conventional processes, VFAs from primary sludge
fermentation is added to provide a carbon source for
growth, and a low molecular weight carbonaceous
compound such as acetic acid or methanol is added to
provide an organic carbon source during
denitrification. As cell growth depletes the absorbed
organic carbon source with concomitant phosphorus
uptake, the organisms switch to endogenous respiration
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with formation of flocks of senescent cells which
settle out typically in a secondary clarifier.
The metabolic characteristics of these classes of
organisms have been exploited in configuring a number
of industrial processes designed to improve the
efficiency of waste water treatment. In the basic A/O
system (a single-sludge suspended growth system that
combines anaerobic and aerobic sections in sequence),
two successive tanks or basins are provided. Influent
water first undergoes an anaerobic digestion step in
which organics are fermented to VFAs along with
phosphorous release and VFA absorption, followed by an
aerobic step in a separate tank. The effluent is then
further purified by settling in a clarifier From a
nutrient standpoint, denitrification can occur in the
first tank, with further nitrification of ammonia and
stripping of nitrogen gas in the second tank. In this
process, the recycling of sludge is important for two
reasons: the biomass acts as a source of mixed liquor
in the first tank, and the recycled nitrates are
denitrified. Phosphates are released under the
anaerobic conditions of the first tank, and taken up
under the aerobic conditions in the second tank.
Examples of a basic A/0 type process are disclosed in
U.S. Patent Nos. 4,162,153 (Spector) and 4,522,722
(Nicholas).
Even though there is a coupling of anaerobic and
aerobic processes, this system is relatively
inefficient, with large volumes of fluid and long
retention types. Inorganics, nutrients, and organic
matter escape into the clarifier because not all of the
dissolved material is distributed properly. Another
source of inefficiency is the constant dilution of raw
. material in the anaerobic tank with recycled sludge
containing oxidized nitrogen and new influent.
There are many modifications of the basic A/O type
process, which can generally be divided into linear
versus sequencing (nonlinear) categories. Variations
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of the A/O linear configuration include the A20 process
which includes separate anaerobic, anoxic, and aerobic
zones with two recycle loops, one from the final
clarifier to the anaerobic zone, and one from the
aerobic outlet to the anoxic zone. The A20 system
splits the anaerobic and aerobic zones to several
cells, and is very similar to the Bardenpho process.
The advantage of this system is that it does not
compromise the anaerobic zone by recycling material
containing high levels of nitrates. Rather the high
nitrate material is returned to anoxic conditions for
denitrification. The five stage Bardenpho process adds
a second anoxic and aerobic zone in series to the
anaerobic, anoxic and aerobic AZO system, but retains
the A20 recycle loops. While theoretically increasing
the capacity of the system, it also has the advantage
of combining the nutrient/BOD reducing recycle steps
with a separate anoxic, aerobic cycle which treats the
entire effluent volume.
Other linearly configured treatment systems are
disclosed in U.S. Patent No. 4,271,185 (Chen) in which
a second oxic cell is provided after settling and prior
to mixing to form mixed liquor, U.S. Patent No.
4,488,967 which contains a number of linear treatment
cells connected by bottom disposed apertures, and U.S.
Patent No. 4,650,585 (Hong) which has a series of
anaerobic cells, and aerobic cells interconnected
within a treatment series by bottom disposed apertures,
but where the anaerobic cell series is connected to the
aerobic series by a top disposed aperture, which in
turn communicates through a top aperture with a
clarifier. An interesting variation is disclosed in
U.S. Patent No. 5,160,043 (Kos) in which recycled
sludge from the oxic tank is returned to the anaerobic
tank after being retained in an exhaust tank to deplete
nitrate levels. Another more complex linear-type
system is disclosed in U.S. Patent No. 5,213,681 (Kos)
in which a series of anaerobic/aerobic treatment loops
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containing an exhaust tank are connected together in
series with a terminal recycle after clarification to
the influent line.
In the alternating or sequencing reactor systems,
mixed liquor or treatment sludge can be directed to
more than one tank destination at various times. Thus,
a given tank can carry out one treatment process in one
step and another treatment process in a different step.
There is generally a more efficient use of equipment
because each tank or treatment cell is not dedicated to
a single treatment step. This provides for
considerable flexibility in designing treatment
protocols, especially in varying treatment times for
different steps in response to the content of the
influent.
An early sequencing system is disclosed in U.S.
Patent No. 3,977,965 (Tholander) in which influent is
directed to one of two raceways interconnected by a
valued conduit. Water entering one raceway can be
treated under aerobic or anaerobic condition as
desired, passed to the second raceway also capable of
varied treatment, and is then discharged to a large
clarifier. In a second cycle, influent is directed to
the second raceway, passed to the first, and is
discharged to the same clarifier. These systems are
also known as DE-Ditch processes when influent and
mixed liquor is first conditioned in an anaerobic tank.
In a variation, a clarifier can be eliminated by using,
alternatively, one or the other ditch as a settling
container, with clarified water being discharged over
an adjustable weir. An advantage of the process is
creation of an anoxic zone in a non-aerated ditch,
while providing a carbon source for denitrification, in
. this case by adding influent waste water containing
degradable carbon.
Finally, U.S. Patent No. 5,228,996 (Lansdell)
discloses an alternating system having three series of
cells linearly interconnected for continuous flow
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operation in which two of the three cell series are
operated aerobically at any given time, and one series
operates anoxically. At each treatment cycle, a
different set of two series is aerobic, and the other
set is quiescent for settling. The system operates
without a separate clarifier, and is not equipped with
a sludge return. This is possible because the
activated sludge is alternately subjected to anoxic or
aerobic conditions by changing the conditions in the
respective cell series. The alternating conditions
thus are the biological equivalent of a return cycle to
the counterconditions of an earlier treatment phase.
In a variation of Tholander, U.S. Patent No.
5,137,636 (Bundgaard) combines the alternating two tank
anoxic/aerobic treatment strategy with a second aerobic
treatment cell followed by a clarifier. Clarified
sludge is returned to the inlet manifold. Phosphate
removal is surprisingly efficient in this system which
does not contain an ostensible anaerobic zone.
SUMMARY OF THE INVENTION
The goal of modern waste water treatment systems
is efficiency and the capability of simultaneously
removing nutrients and BOD. Efficiency factors include
the size and configuration of tanks or other
receptacles, the number and timing of process steps,
flexibility in process adjustments, and control of
solids formation and distribution in the system. The
present invention comprises a process strategy and
apparatus which favorably impact these efficiency
f actors .
More specifically, it is an object of the
invention to provide the process control and uniformity
of a batch system without interrupting the flow of
waste water into the system and treated effluent out of
it. A further object is to prevent dilution of mixed
liquor with partially nitrified water which occurs in
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previous sludge recycle loops. It is a still further
object to effect the distribution of organic carbon
throughout the system. Finally, it is an object of the
invention to quickly create a clear supernatant in
final stage settling step prior to effluent discharge,
without a separate clarifies. Satisfaction of all
these objects increases efficiency of the overall
process significantly, as will be apparent hereafter.
The present invention embodies a process in which
waste water is first mixed anaerobically with a
concentrated recycle sludge phase obtained by a phase
separation, secondly mixing mixed liquor with a
nitrified suspension having both a liquid phase and a
solid activated sludge phase under essentially anoxic
conditions to denitrify the solution and convert the
nitrates to free nitrogen gas and metabolize organic
compounds, and thirdly separating the activated sludge
phase from the denitrified suspension in a phase
separation, for recycling.
Overflow of the mixed denitrified sludge
suspension into a separator permits partial separation
of the liquid and solid phases with settling of a
portion of the solid fraction into a concentrated
sludge phase for recycling. Since the concentrated
solid phase sludge is mixed directly into mixed liquor,
there is minimal dilution of VFAs contained in the
waste water, which would result in their earlier
depletion as organic carbon and energy sources, as
occurs in other processes. The dilution factor of
the sludge recycle is typically less than 1Q,
preferably less than 0.5Q, and may even be a negative
value by appropriate adjustment of the hydrostatic
head. The mixing of this mixed liquor with a
. substantially nitrified suspension is performed in a
separate cell, and is continued for a time sufficient
to substantially denitrify the oxidized nitrogen.
Alternatively, the mixed liquor may be subjected to
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more than one denitrification or nitrifying step,
depending on the nitrogen content of the waste water.
Denitrification results from endogenous
respiration. In the separator chamber, the rate of
denitrification increases as the concentration of
solids increase, thereby accounting for the very low
level of oxidized nitrogen in the sludge returning to
the anaerobic cell.
The phase separator allows the concentrated
activated sludge (greater than 1200 mg/L solids) to be
returned to the anaerobic cell resulting in the
following:
1. Elimination of any remaining oxidized nitrogen
species (nitrate and nitrite) and perhaps also some
dissolved oxygen in the recycle sludge from a
denitrification cell by reducing the total quantity of
return sludge in volume.
2. Since the return concentrated activated sludge
goes through a relatively highly concentrated sludge
blanket at the bottom of the phased separator, the high
endogenous respiration of the concentrated activated
sludge (with higher population of living organisms) in
the sludge blanket will consume the remaining dissolved
oxygen and oxidized nitrogen. Therefore few oxygen-
containing species will remain in the limited volume of
the return sludge to the anaerobic cell.
3. The reduction of the total return sludge
eliminates the dilution and wash out of available raw
waste water organic carbon, especially the VFAs,
increasing the concentration of VFA and other organic
carbon. This results in enhancement of phosphorus
release, VFA absorption, and PHB storing of the Bio-P
organisms.
4. The reduction of the total return sludge volume
also increases the actual waste water and mixed liquor
retention time in the anaerobic cell. The longer
retention time results in more non-VFA, slowly
biodegradable organic carbon species or compounds being
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converted to VFA, increasing the VFA availability in
the anaerobic cell, greater opportunity for Bio-P
organism to release phosphorus, absorb VFA, and convert
VFA to PHB.
5. Reduction of the dilution factor also promotes the
activated sludge population of organisms in the
anaerobic cell, thereby enhancing phosphorus release,
VFA absorption, and PHB conversion.
In water treatment systems, the volume of influent
water entering the system is commonly referred to as
"Q" for quantity. In a continuous flow system with 1Q
entering the system, the outflow from the system must
also be 1Q. In the treatment system, there will be a
number of situations where the flow is partially
diverted or where flows converge. Thus, the flow at
that point may be a fractional or multiple Q. In
typical conventional recycle loops, the flow Q of the
loop is either 1 or a multiple. If it is 1, then the
total Q throughput is 2, and the retention time of
liquid in that process step is one half.
In the separator and separation step of the
present invention, the flow of the recycle sludge is
diverted, so that the important solids component is
less than 1Q, and the supernatant which passes to
another (aerobic) step is greater than Q. Thus, in the
present invention, the recycle sludge mixed with waste
water to form mixed liquor under aerobic conditions
contains the same amount of solids as 1Q, but is
contained in less than 1Q of volume, thereby extending
hydraulic retention time and lessening dilution of VFAs
thus making it process efficient to recycle to the
anaerobic step. In general, any recycle sludge
equivalent to 1Q of flow contained in a volume of less
than Q will have efficacy, but a recycle volume of less
than 0.5Q or 0.25Q is preferred in the practice of the
invention. Note that Q can actually attain negative
values by an appropriate adjustment of the operating
hydrostatic head in the anaerobic cell. Thus a
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negative flow may occur even if there is still net
return solids.
In another aspect of the invention, phosphorous in
the form of inorganic phosphates is released into
solution by Bio-P organisms, principally the
Acinetobacters under anaerobic conditions. Further
processing of the mixed liquor under anoxic conditions
then permits denitrification. The process for
biological removal of both nitrogen and phosphorous
thus involves mixing a return sludge containing a solid
phase activated sludge component and a liquid phase
component with mixed liquor to form a blend under
anaerobic conditions.
In a second step, mixed liquor is denitrified
under anoxic conditions. The denitrified, inorganic
phosphate rich liquid is then aerated in the presence
of fresh mixed liquor to remove the phosphates by
luxury phosphate uptake. In many Bio-P BNR systems, an
easily biodegradable organic compound is added to
provide an organic carbon and energy source to fuel
phosphate uptake incident to the increase in biomass,
and to enhance the denitrification in the anoxic zone.
Applicant has discovered that transferring mixed liquor
containing organic carbon to any point in the process
where extra organic carbon and energy are needed for
denitrification, avoids the need for expensive
exogenous carbon/energy sources, and extra recycle
loops.
After aeration, the biomass is passed through a
sludge blanket or filter in a quiescent vessel where
the sludge has been allowed to settle. Filtering the
sludge blend through a sludge blanket permits further
denitrification without appreciable phosphate release.
The liquid component of the blend can then be decanted
from the system to a discharge outlet.
Applicant has discovered that a highly efficient
treatment system embodying the foregoing inventive
steps involves a multiphase process in which cycling of
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the process between two or more sequencing cells
results in repeated exposure of residual biomass to
successive alternating aerobic and anoxic treatments.
The use of a modified batch treatment in several of
these phases ensures uniformity in the treatment step
and a uniform distribution of microbial populations and
suspended solids. A modified sequencing batch reactor
for removing organic matter and nutrients while
maintaining continuous influent flow into a separator
blending vessel with continuous clarified effluent flow
from an alternating sequencing vessel in a dual cycle
comprises a first cycle in which continuous influent
waste water is mixed in a first phase with concentrated
sludge under anoxic conditions to form mixed liquor.
Part of this mixed liquor is passed to a first
sequencing vessel where it is mixed with a nitrified
suspension containing a solid sludge component and a
liquid component to form a blend. This is important
because this step combines the organic carbon source
contained in the mixed liquor with the population of
microorganisms undergoing a high rate of endogenous
respiration, thereby supplying a large energy reservoir
for denitrification.
Another portion of the mixed liquor is
simultaneously transferred to an aeration vessel under
conditions of continuous mixing and aeration. The
foregoing sets forth the essential process steps in
carrying out the waste water treatment in a five
chamber system.
The sequencing batch reactor system has the
advantages of utilizing the same cell for different
process steps and for temporarily isolating the process
steps for the benefit of batch uniformity. However,
the entire process can be replicated in a flow through
system, where each step is assigned to a dedicated
cell. Such a system embodies all the inventive aspects
set forth herein, and represents yet another embodiment
of the invention.
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Thus, the present process may vary according to
the cycles required to carrying out the particular
treatment objective. In the basic denitrification
process a mixed liquor is formed under anaerobic
conditions from influent waste water and denitrified
sludge obtained from the separator. The mixed liquor
is combined with nitrified sludge to form a blend,
which is mixed under anoxic conditions to obtain
substantial but incomplete denitrification. In the
separator, the blend which has a suspended solids
content capable of being separated by settling into a
supernatant and a concentrated sludge portion,
separates, and the sediment is recycled by combining
with raw waste water to initiate a new round of anoxic
denitrification. Further denitrification occurs in the
separator as the sludge becomes somewhat compacted by
settling, thus accounting for very low levels of
oxidized nitrogen in the anaerobic cell.
When mixed liquor is formed under anaerobic
conditions, the bio-P microorganisms release phosphates
and take up volatile fatty acids. Under the anoxic
conditions of denitrification, such phosphate release
ceases, and then in a subsequent aerobic step, luxury
uptake of phosphorus and further metabolism of VFAs
occurs. After filtering through a sludge blanket at
the bottom of the open sequencing cell or final
clarifier in which treated water enters at the bottom
of the cell, the clarified water is discharged.
Further variations in the process include mixing the
blended mixed liquor and nitrified waste water under
anoxic conditions a second time, or aerating a second
time depending on the content of the waste water. In
each instance, however, there is recycle of activated
denitrified sludge sediment back to mixed liquor under
anaerobic conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
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Figure 1 is a cross sectional view of the
separator.
Figure 2 is plan view of the configuration of
cells in a typical four tank sequencing batch reactor.
Figure 3 is a cross sectional view showing the
position of the aeration cell in the system disclosed
in Figure 2.
Figure 4a-c are plan views of the configuration of
a system having an anoxic cell interposed between the
mixed liquor cell and the aerobic cell.
Figure 5a-c is another embodiment of the
sequencing batch reactor system in which a second
aeration step is included. In Figures 4 and 5, the "a"
frame shows the spacial configuration of the system,
frame "b" depicts the process steps, and also
represents a flow through diagram if each step has a
dedicated cell, and frame "c" shows the cellular
configuration with respect to the separator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In one aspect of the present invention, release of
inorganic phosphate and uptake/utilization of VFA by
Acinetobacter spp. and related organisms is facilitated
by maintaining strictly anaerobic conditions, high VFA
concentrations, and providing concentrated activated
sludge having a high population of organisms and mixed
liquor suspended solids. The concentrated sludge
suspended solids level is typically greater than 2000
mg/L, preferably in a range of at least 1200 mg/L to
2500 mg/L. In most conventional sludge recycle
- systems, the concentrated sludge is simply redirected
to different process cells by pumping through pipes.
Organic matter dilutes the suspension contained in the
destination cell. In the present invention, a phase
separator allows denitrified sludge to sediment by
gravity to high concentration, and then be combined
directly with influent waste water under anaerobic
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conditions without transfer by pumping so as to dilute
the mixed liquor.
Referring to Figure 1, a longitudinal cross-
section view, the separator comprises an anaerobic
reaction reservoir 1 and a separator 4 separated by a
generally vertical dividing wall 13. The separation
chamber 4 is bounded by two side walls (not shown) and
an inclined retaining wall 11 intersecting the bottom
wall 12 of the anaerobic reaction reservoir 1. The
vertical dividing wall 13 extends only part way to the
bottom of the separator thereby providing a
communicating aperture 15 through which the sludge
sediment passes to the anaerobic reservoir 1 (shown as
arrows). Figure 1 also depicts an influent inlet 6
through which waste water enters the anaerobic reaction
cell, mixing means 9a, and an optional conduit 23 for
removing mixed liquor.
Water being processed under anoxic conditions
either before or after denitrification enters at the
top of the separation chamber 4. The supernatant exits
at a discharge port or weir 10, and the sediment sludge
settles to the bottom of the separation chamber 4.
Further concentration of sludge is effected by the
inclined wall, which through gravity forces the
sediment into a progressively smaller volume. The
settled sludge is resuspended by the mixing action
within the anaerobic reaction reservoir 1. A high
recycle rate causing dilution of the return sludge is
thereby avoided. The two chamber separator has several
advantages over conventional recycling.
In the present separator, the recycled sludge only
minimally dilutes the mixed liquor. This is important
because the sludge contains the Bio-P microorganisms
which take up VFAs and release inorganic phosphates in
the anaerobic reaction cell. The VFAs are a source of
organic carbon and energy for the microorganisms, and
the process is much more efficient at high VFA
concentration. By reducing dilution of the mixed
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liquor, the mixed liquor can also act as an organic
carbon and energy source during subsequent
denitrification, thereby avoiding the need for
exogenous sources. This obviates the need, as in
conventional systems, for return to the primary sludge
fermenter, an extra procedure which includes not only
primary sludge fermentation, but also a sludge
thickening step. A second advantage is that the
concentration of oxidized nitrogen in the sediment due
to denitrification through endogenous respiration of
high concentration of microorganisms at the bottom of
the separator, is quite low, resulting in a low total
quantity of oxidized nitrogen entering the anaerobic
cell, so that the sludge recycle does not disturb the
anaerobic condition of the anaerobic reactor reservoir.
A third advantage is that, because of the lower
dilution of the mixed liquor, the total volume of
suspension moving through the anaerobic reactor cell is
less for any given flow rate, so that the hydraulic
retention time (HRT) increases. This means there is
better conversion of organic matter in the influent
water to VFAs than in conventional processes, and there
is more PHB storage in the Bio-P bacteria. Greater
conversion of VFAs and greater phosphorous release is
achieved from increased HRT.
From the foregoing, it is apparent that the
separator as disclosed performs the intended function
of avoiding the substantial dilution of influent water
and mixed liquor in prior art processes efficiently,
and without expenditure of energy, the separation
itself taking place by gravity with blending of the
- concentrated sludge via a mixing action in the
reservoir. The separator apparatus as disclosed herein
is very efficient in its construction, with no pumping
or other conveying means being required to transfer the
solids contained in a given volume of liquid back to
the anaerobic cell. In fact, however, in different
embodiments of the present method, a gravity clarifies
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unit might be positioned between the sludge return and
the anaerobic cell, to accomplish much the same
function, but without the same efficiency. It is
therefore intended that the separation can be carried
out by any means known in the art for transferring a
sludge sediment to a vessel of mixed liquor with a
dilution factor less than 1Q of flow in the recycle
loop, and preferably a dilution factor of less than
0.5Q.
The communicating two cell construction of the
separator/anaerobic reaction cell may be configured in
several ways. The geometry and volume of the
respective cells or chambers are dictated largely by
the anticipated content and flow rate of the waste
water. The basic requirements are that (1) the
anaerobic reactor reservoir is a mixing chamber with
continuous agitation sufficient to resuspend densely
settled sludge which settles to a lower chamber portion
of the separation chamber, (2) the walls of the
separation chamber or separator chamber be generally
downwardly inclined, so that sedimenting sludge will be
compacted, and (3) there be a communicating aperture at
the base of the separator chamber, and a lower portion
of the mixing chamber in proximity thereto, to receive
the sludge into the base of the anaerobic reservoir.
The downwardly inclining walls may be three sided, or
even circular. The size of the aperture may be
adjusted to accommodate the amount of sludge to be
recycled.
In all of the process variations of the present
invention, mixed liquor is combined with highly
nitrified waste water, and is treated under anoxic
conditions to achieve denitrification. In a first
embodiment as illustrated in Fig. 2, mixed liquor is
combined with a nitrified suspension prior to
separation with sludge recycle. In a second embodiment
as illustrated in Fig. 4a, denitrification occurs after
phase separation and sludge recycle. The first
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embodiment has the advantage of maintaining
substantially all of the suspension contained in the
separator cell 4 under anoxic conditions thus reducing
the probability that any oxidized nitrogen will remain
to inhibit phosphate release in the anaerobic reactor
reservoir. The advantage of the second embodiment is
that the process cycle is simplified by allowing
simultaneous phosphorous removal and denitrification,
as will be apparent hereafter.
The denitrification step is followed by an aerobic
treatment step in which oxygen is provided by an
aeration means while the suspension is vigorously
mixed. The aerator is any conventional design; however,
sizing of the apparatus according to recognized
engineering principles is strongly advised, so that
excess energy is not expended. The nitrification
results in the conversion of organic and ammonia
nitrogen to nitrate. Luxury uptake of inorganic
phosphate occurs during aeration with concomitant
aerobic metabolism of PHB stored within the Bio-P
organisms. Efficient use of oxygen is important to
cost containment. For example, there should not be a
recycling of aerated waste water to an anoxic zone,
because reestablishment of anaerobic conditions is
energetically expensive, and contrary to nutrient
removal strategy. After a period of quiescent
settling, the clarified water can be discharged from
the system. Applicant has discovered that the mixed
liquor containing the organic carbon of influent waste
water is an excellent organic carbon and energy source
for denitrification as shown in Figures 5a-c.
- Diversion of a portion of the mixed liquor to the
anoxic cells) eliminates the need for external organic
carbon sources. The utility of mixed liquor for this
purpose is enhanced by the minimal dilution thereof by
recycling mixed liquor.
Figure 2 is a diagrammatic representation of one
embodiment of a waste water treatment system embodying
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the principles of the present invention. The system
comprises a basin segregated into a plurality of
distinct treatment cells, or compartments. These
treatment cells are an influent anaerobic reaction
reservoir 1, a first sequencing treatment cell 2, a
second sequencing treatment cell 3, a separation
chamber 4, and an aeration cell 5. The biological
treatment process comprises two (2) consecutive cycles,
each consisting essentially of five (5) successive
phases to provide a total of ten (10) phases. The
treatment system and process accommodate a continuous
influent of untreated, or raw waste water simultaneous
with continuous discharge of effluent water.
In Phase No. 1 of Cycle No. 1 in the treatment
process, raw waste water influent is continuously
passed through influent means 6 into the influent
anaerobic reaction cell 1. Therein, the influent is
mixed on a continuous basis by the mixing means 9a with
activated sludge from the adjacent separation chamber 4
to produce mixed liquor under substantially anaerobic
conditions. The mixing means 9a employed to mix the
contents of the influent anaerobic reaction cell 1, and
those 9b-a of the two sequencing treatment cells 2, 3
and aeration cell 5, are illustrated symbolically
within the context of the drawings, however the mixing
means 9a-a may consist of any one of, or a combination
of any conventional means known in the art.
The settled sludge in the separation chamber 4
passes in a downward direction along the downwardly
inclined wall 11, into the lower portion of the
influent anaerobic reaction cell 1. While the sludge
passes downwardly along the inclined wall 11 into the
lower portion of the influent anaerobic reaction
reservoir 1 to be mixed to form mixed liquor,
substantially clear supernatant is passed from the
upper portion of the separation chamber 4 to the
aeration cell 5 through a controllable transfer means
16. By passing settled activated sludge into the
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influent anaerobic reaction cell 1 and by passing
supernatant into the aeration cell 5, the separation
chamber 4 serves as an internal dedicated phase
separator. The contents of the aeration cell 5 are
continuously mixed and aerated throughout the entirety
of the ten-phase, dual-cycle treatment process.
Similar to the mixing means 9a-e, the aeration
means 18a-d employed to aerate the contents of the
aeration cell 5 and those of the two sequencing
treatment cells 2, 3 are illustrated symbolically
within the context of the drawings; however the
aeration means 18a-d may consist of any one of, or a
combination of, any conventional means known in the
art. Simultaneously, mixed liquor is recycled from the
influent anaerobic reaction cell 1 to the first
sequencing treatment cell 2 via a controllable recycle
means 19. The contents of the first sequencing
treatment cell 2, consisting of highly nitrified
activated sludge suspension from a previous cycle and
mixed liquor entering from the anaerobic cell 1, are
mixed without aeration. Under these conditions
denitrification occurs with the evolution of nitrogen
gas.
A portion of the cell 2 contents pass into the
separation chamber 4 through a controllable transfer
means 21 located between the first sequencing treatment
cell 2 and the separation chamber cell 4. Mixed liquor
also passes directly from the influent anaerobic
reaction cell 1 to the aeration cell 5 via a
controllable transfer means 23. This may occur during
all of the ten treatment phases. Absorption of the
high VFA content of the mixed liquor can be metabolized
during aeration. If the mixed liquor transfer occurs
during all phases of both treatment cycles, it must
occur at a flowrate that is less than, or equal to, the
flowrate of mixed liquor recycled from the influent
anaerobic reaction cell 1 to one of the sequencing
treatment cells 2, 3. Aerated mixed liquor from the
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aeration cell 5 is passed into the second sequencing
treatment cell 3 via a controllable transfer means 24
located between the aeration cell 5 and the second
sequencing treatment cell 3. The second sequencing
treatment cell 3 serves as a settling zone in all five
(5) phases of treatment Cycle No. 1, and substantially
clear liquor is passed out of the treatment system
through the effluent means 26 located at the end of the
second sequencing treatment cell 3.
Phase No. 2 of Cycle No. 1 is essentially the same
as Phase No. 1, with the following two exceptions: (1)
the recycle flow of mixed liquor from the influent
anaerobic reaction cell 1 to the first sequencing
treatment cell 2 via the recycle means 19 ceases, and
(2) aerated mixed liquor is passed from the aeration
cell 5 to the first sequencing treatment cell 2 via a
controllable recycle means 19 for anoxic mixing. As in
Phase No. 1 of Cycle No. 1, untreated waste water
continues to be passed into the influent anaerobic
reaction cell 1 where it is mixed by mixing means 9a
with activated sludge from the separation chamber 4
under substantially anaerobic conditions to form mixed
liquor. Flow of supernatant from the separation
chamber 4 to the aeration cell 5 via the transfer means
16 located between the separation chamber 4 and the
aeration cell 5 continues. Mixed liquor may also be
passed directly from the influent anaerobic reaction
cell 1 to the aeration cell 5 via the controllable
transfer means 23 connecting the two cells 1, 5.
Aerated mixed liquor from the aeration cell 5 continues
to pass into the second sequencing treatment cell 3 via
the controllable transfer means 24 located between the
aeration cell 5 and second sequencing treatment cell 3.
The second sequencing treatment cell 3 continues to
serve as a settling zone, and substantially clear
liquor continues to pass out of the treatment system
through the effluent means 26 located at the end of the
second sequencing treatment cell 3.
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Phase No. 3 of Cycle No. 1 differs from the
previous phase in the following three ways: (1) the
flow of mixed liquor from the first sequencing
treatment cell 2 to the separation chamber 4 via the
controllable transfer means 21 located between the
separation chamber 4 and the first sequencing treatment
cell 2 ceases; (2) the aeration means 18a employed to
aerate the contents of the first sequencing treatment
cell 2 continues aeration throughout the entire phase
l0 to aerate the mixed liquor, and; (3) aerated mixed
liquor from the first sequencing treatment cell 2 is
recycled to the aeration cell 5 via the controllable
recycle means 19. Flow of aerated mixed liquor passes
into the first sequencing treatment cell 2 through the
controllable transfer means 28 where it is further
aerated and mixed. Aerated mixed liquor continues to
pass from the aeration cell 5 to the second sequencing
treatment cell 3 via the controllable transfer means 24
located between the aeration cell 5 and the second
sequencing treatment cell 3. The second sequencing
treatment cell 3 continues to function as a settling
zone and substantially clear liquor continues to pass
out of the treatment system through the effluent means
26 located at the end of the second sequencing
treatment cell 3.
Phase No. 4 of the treatment Cycle 1 differs from
the immediately previous Phase No. 3 in two respects:
(1) the recycle flow of aerated mixed liquor from the
first sequencing treatment cell 2 to the aeration cell
5 via recycle means 19 ceases, and (2) the flow of
aerated mixed liquor from the aeration cell 5 to the
first sequencing treatment cell 2 via the controllable
transfer means 28 located between the aeration cell 5
and the first sequencing treatment cell 2 ceases.
Phase No. 5 of treatment Cycle No. 1 differs from
previous Phase No. 4 in only one respect: the aerating
18a and mixing 9b means used to aerate and mix the
contents of the first sequencing treatment cell 2
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cease. This initiates the settling of solid materials
within the first sequencing treatment cell 2 in
preparation for the passing of substantially clear
liquor from cell 2 during the entirety of treatment
Cycle No. 2, Phases 1 through S. The concentration of
solids in the settling process enhances filtration of
incoming liquid, and allows completion of
denitrification by endogenous respiration.
Treatment Cycle No. 2 is a "mirror image" of
treatment Cycle No. 1 in terms of the functions of the
first and second sequencing treatment cells 2, 3.
Their functions "rotate", or "sequence" as each
treatment cycle is initiated. Throughout the entirety
of treatment Cycle No. 1, Phases 1 through 5, the
second sequencing treatment cell 3 serves as a settling
zone in which aerated mixed liquor is received from the
aeration cell 5 through the controllable transfer means
24 located between the two cells 3, 5 and substantially
clear liquor is passed out of the system through the
effluent means 26. In treatment Cycle No. 1, Phases 1
through 4, the first sequencing treatment cell 2 serves
as a true "treatment" cell where mixing or mixing plus
aeration occur. At the initiation of treatment Cycle
2, the two (2) sequencing treatment cells 2, 3 switch
roles: the second sequencing treatment cell 3 becomes
a "treatment" cell and the first sequencing treatment
cell 2 becomes a settling zone.
The following summarizes the significant
biological process parameters occurring in each of the
five phase cycles described hereinabove:
Phase 1: redistribution of suspended solids; anoxic
mixing for denitrification together with raw waste
containing organic carbon added to enhance
denitrification.
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Phase 2: redistribution of suspended solids; continued
denitrification with consumption of organic carbon and
endogenous respiration of microorganism.
Phase 3: redistribution of suspended solids; aeration
for removing remaining organic carbon; stabilization of
suspended solids, and stripping the formed nitrogen
gas.
Phase 4: continued aeration without distribution of
suspended solids between cells 2 or 3 and aeration cell
5.
Phase 5: flocculation and settling to create a sludge
blanket for final polishing in the next cycle.
Figure 3 is a longitudinal cross-sectional view of
the separator depicted in Figure 1, showing, in
addition, the relation of the aeration cell 5 to the
settling chamber 4 of the separator, according to the
configuration set forth in Figure 2. In this
embodiment, supernatant from the settling chamber 4
passes directly to the aeration cell 5 via means 10.
The source of the supernatant is partially clarified,
denitrified water from the anoxic cell. Also depicted
are the mixing means 9b and the aeration means 18c.
Figure 3 also shows the transfer of mixed liquor from
cell 1 to aeration cell 5 via transfer means 23.
In an alternate embodiment, the process is
shortened by eliminating recycling to the side cell 2
or 3. Referring to Figure 4a, in a first phase, mixed
liquor is passed to an anoxic cell 6 interposed between
the separator and the aerobic cell 5 depicted in Figure
2. The arrows indicate the directionality of flow
among the cells. Thus, in Phase 1, mixed liquor formed
anaerobically in the reservoir 1 proceeds to
denitrification in the dedicated anoxic cell 6 before
flowing into the aerobic cell 5. A portion of the
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aerated suspension is passed through a first sequencing
cell 2, while a second portion of equal volume is
passed through a sludge blanket in sequencing cell 3,
acting as a clarification tank. Thus, the separator
functions in this embodiment to collect concentrated
sludge from a nitrified and partially denitrified
suspension. Since the oxidized nitrogen is soluble, it
passes to the anoxic cell in the supernatant, whereas
the sediment is sufficiently low in nitrate quantity
not to interfere with the anaerobic processes in
reservoir 1. The recycle line from cell 5 to cell 6,
as indicated by the dotted arrow, brings more oxidized
nitrogen into the anoxic cell to enhance the
denitrification.
The latter embodiment employs six rather than five
cells. It has the advantage of eliminating the pumped
recycle to the side cell with Q recycle increasing from
1 to 2 in three steps. Figure 4b is the flow through
system version of the embodiment of Figure 4a. Figure
4b is the process configuration of Figure 4a. Figures
4a and 4c diagram the physical configuration of cells
for carrying out the process. An, Ax, and Ae are
standard abbreviations for anaerobic, anoxic, and
aerobic conditions respectively. The numbered cells or
steps correlate the process steps to the apparatus
cells of corresponding number in Figures 2 and 4.
A comparison of the two embodiments reveals many
common elements, but also some that differ. In both
systems, concentrated sludge is mixed with influent
water and mixed liquor to form more mixed liquor in
which the dilution factor in combining the sludge is
minimal, and the concentration of suspended solids is
greater than 1500 mg/L in the sludge. There is also a
feed step which delivers mixed liquor as an organic
carbon source to any point in the process where
external energy would otherwise be required, as in
phosphorus release or denitrification.
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The processes differ in that the denitrification
takes place mainly in a separate anoxic cell in the six
cell system, and it occurs only in the sequencing
treatment cell in the five cell system. The separator
in the five cell system operates as effectively as the
six cell system in the anaerobic phase, possibly
because the nitrates generated during aeration are in
the supernatant phase which is drawn off to the anoxic
cell 6.
In a further embodiment shown in Figure 5a, an
anoxic cell 6 and a further secondary aeration cell 7
are interposed between the main aeration cell 5 and the
sequencing treatment cells 2 and 3. This variation is
especially efficacious in situations in which the
influent organic and ammonia nitrogen is unusually
high, as the system provides two sequential
denitrification steps. An important feature of the
system is the split flow of mixed liquor. Mixed liquor
is combined with the supernatant discharge from the
separator before entering the main anoxic cell 6, which
is the equivalent of adding mixed liquor to the
sequencing treatment cell 2 in Figure 2. Since organic
carbon is required for effective denitrification, a
portion of the split flow of mixed liquor from the
anaerobic cell containing high concentrations of
organic carbonaceous materials is added to the anoxic
cell 6.
The precise number and timing of process steps is
largely dictated by the composition of the influent
waste water. In a typical cycle for the five cell
system, a 10-15 minute feeding of mixed liquor to an
anoxic cell and the aeration cell is followed by anoxic
mixing leading to denitrification. This is generally
the longest process step, running 50-70 minutes.
Aeration in the cell will occupy only about 15-20
minutes total time including the mixing phase combining
the water under continuous aeration in the aeration
cell with the side cell water. This permits very
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efficient utilization of oxygen, low oxygen demand due
to low endogenous respiration rate with less organism
population, and the preparing of the cell for settling
and clarification. The presettling stage lasts 30 to
40 minutes, and results in formation of an efficient
sludge filter clarifying the entering suspended solids.
In the treatment system, the average solids level
is about 2000-2800 mg/L. In the cell after settling,
solids often reach 4000-5000 mg/L. In a conventional
anaerobic cell (such as UCT process), the concentration
of solids is usually only 50a of other cells due to the
dilution factor. In the present invention, the solids
content in the anaerobic cell is maintained higher than
the remaining cells. In this unique mixed liquor, the
concentration of VFAs in the anaerobic cell ranges from
80-150 mg/L, nearly double the concentration in other
phosphorous removal in common waste waters. This is
accomplished through solids separation with less than
10 percent volume dilution. Thus, the nutritive mixed
liquor capable of providing a food source at critical
process points such as anoxic denitrification and
aerobic luxury phosphorus uptake by Bio-P has a solids
content of 800-1500 mg/L and a VFA content of 80-150
mg/L. By varying the process cycles and regulating the
flow among the various cells, the suspended solids
content can vary, but maintaining the organic carbon
content in the mixed liquor of the anoxic cell at this
high level permits utilization of the raw waste as an
organic carbon source without additional external
chemicals such as methanol.
While the sequencing batch reactor system has the
advantages of economies of space, and the uniformity of
the batch step, it is possible to carry out all the
important steps of the inventive process in a flow
through mode. This means that instead of utilizing the
sequencing treatment cells for multiple successive
process steps, there are provided a number of dedicated
treatment cells equal to the number of process steps,
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so that there is no batch treatment at any step. The
operation of the flow through mode is illustrated in
the Figures 4b and 5b, corresponding to the process
steps since each process step has a dedicated cell, so
that none of the steps occur in batch mode.
Further advantages of the present invention will
be apparent from the Example which follows.
EXAMPLE
A pilot study of the four cell system was carried
out using apparatus containing cells configured as
shown in Figure 2 for a modified sequencing batch
reactor (MSBR°). The system was designed to be overall
6.5 feet wide, 14 feet long, and 7 feet tall, having an
average working capacity of 1200 gallons. Flow was
adjusted so that 1200 gallons could be processed daily.
The system treated raw sewerage obtained from the
municipal waste water treatment facility at Rockton,
Illinois.
The following abbreviations apply to the table of
data showing the results:
COD = chemical oxygen demand
BODS = biological oxygen demand (5 days)
TSS = total suspended solids
TKN = total kjeldahl nitrogen
NH4-N = ammonia nitrogen
N03-N = nitrate nitrogen
NOZ-N - nitrite nitrogen
TN = total nitrogen
TP = total phosphorus
VSS = volatile suspended solids
Ortho P = orthophosphorus ( P04'3 )
MLSS = mixed liquor suspended solids
The system required an operational hydraulic
retention time of 24 hours because of the high nitrogen
content of the waste water.
The MSBR~ pilot unit consisted of the following
general components: aeration system, controls, mixers,
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pumps, tankage and valves. All controls, mixers,
motors, and valves were designed for on/off duty and
extended operation life.
Almost all of the existing biological phosphorus
removal processes (such as Bardenpho, A/O, and UCT)
have an anaerobic recycle flow of 1Q (an average daily
raw waste water flowrate) or higher. Recycle flows
that contain no readily biodegradable organic carbon
(RBCOD) source will dilute the carbonaceous organic
concentration and VFA concentration in the anaerobic
cell. A 1Q recycle means the available VFA and RBCOD
in the anaerobic cell are reduced by one half. With
the phase separator, the recycle flow to the anaerobic
cell is decreased to 0.2Q to 0.3Q. This means the VFA
dilution reduced the recycle to only about 15 to 200.
Without considering other positive factors, the VFA
concentration in the anaerobic cell will increase to
more than 60o as compared with a 1Q anaerobic recycle
system. The reduced recycle flow enhances the PHB
storage for the Bio-P organisms, which in turn brings
about a higher driving force for phosphorus uptake in
the later stages.
The low recycle flow can provide a higher actual
HRT. When the recycle flow entering the anaerobic cell
drops from 1Q to 0.25Q, the total flow through the
anaerobic cell is decreased from 2Q to 1.25Q. This
will increase the actual HRT by 60% for the anaerobic
cell. The longer anaerobic HRT allows ordinary
heterotrophs to convert more non-VFA RBCOD to VFA
through acid fermentation. This increases the VFA
concentration. The longer HRT also allows Bio-P
organisms to have more time for storage of available
VFA's and for converting it to PHB. Therefore, more
phosphorus can be taken up in the following
denitrification and oxidation steps when the PHB is
metabolized inside of the Bio-P organism, improving the
phosphorus removal efficiency.
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During the first step of the half cycle, mixed
liquor is transferred from the anaerobic cell to the
sequencing treatment cell instead of directly feeding
raw waste water to the sequencing treatment cell. This
allows an increase in organic carbon concentration in
the sequencing treatment cell which can enhance the
denitrification rate in the cell. The stored PHB
inside the Bio-P organisms from the transferred mixed
liquor will be metabolized along with phosphorus uptake
and denitrification using nitrate and nitrite as
electron acceptors, more efficiently utilizing the
available organic carbon source. Other PHB stored in
the Bio-P organism will be oxidized in the main
aeration cell and the sequencing treatment cell during
the aeration time along with phosphorus uptake.
The fully automated, skid-mounted MSBR pilot unit
used in this study was configured as shown in Figure 2.
The pilot unit was fabricated from painted carbon
steel, with the internal reactor dimensions of 75" x
94" with a 48" sidewell depth to a accommodate a 42"
depth of water. The total volume of the reactor was
about 1280 gallons at above water depth. Steel slots
were incorporated into the bottom and sides of the
reactor to facilitate the insertion of flexible
fiberglass sheets. These sheets served as movable
walls and baffles which could be adjusted to simulate
various system treatment configurations.
After start up of the system, the geographical
area experienced an unexpectedly early winter. The low
temperatures (<5°C) made the start up very difficult
with a very slow growth of microorganisms.
Once mechanical problems were corrected and the
operation temperature was raised above 10°C, the
effluent total phosphorus dropped to less than 1 mg/L
while effluent Ortho-phosphorus decreased to less than
0.5 mg/L. The system removed an average of 11.4 mg/L
of total phosphorus, a 93 percent of removal, during
the period. The results showed that the existing
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nitrite in the raw waste water and recycle flow would
reduce phosphorus removal efficiency in a biological
phosphorus system. The unique design of the phase
separator for the recycle activated sludge prevented
the oxidized nitrogen from the recycle flow from
entering the anaerobic cell and simultaneously diluting
the organic carbon in the anaerobic cell. Although
the system received an average of 28 mg/L of oxidized
nitrogen from the raw waste water, the system still
maintained a very low phosphorus discharge, especially
the soluble Ortho-phosphate. The elimination of the
nitrate/nitrite recycle prevented any additional
oxidized nitrite loading to the anaerobic cell.
Without dilution, the highly available organic carbon
could denitrify the oxidized nitrogen from the raw
waste water quickly. These results show that the
developed system can efficiently remove phosphorus from
waste water even when the raw waste water contains
significant amounts of oxidized nitrogen.
One week after the start of this data collection,
microscopic examination showed that only a few stalked
ciliated protozoa and crawling protozoa with some
flagellated protozoa were in the activated sludge,
indicating a young sludge age. The young sludge age
with an insufficient microorganism population created
some level of dispersed bacteria in the system, causing
some cloudiness in the effluent. During the first half
of this period, the final effluent TSS remained above
mg/L. The effluent TSS discharge was improved when
30 more stalked ciliated protozoa and crawling protozoa
were built up. By the end of the period, the effluent
total suspended dropped to less than 5 mg/L. The final
effluent suspended solids averaged 16.5 mg/L for the
two week period. The young sludge age also limited the
population of nitrifiers, which brought the final
effluent NH4-N to an average of 2.8 mg/L. The growth
of the microorganism population subsequently improved
the nitrification of the system. The effluent NH4-N
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decreased to about 1 mg/L near the end of the data
collection.
A jet-heater kept the reactor temperature at an
average of 17°C. To enhance the nitrification under
the limited nitrifier population, the system was
operated at a total HRT of 24 hours with an aeration
HRT of 9.8 hours. The average MLSS was 2,495 mg/L. To
build up the microorganism population in the system,
only scums were wasted from the system with no sludge
wasting during the period.
The system achieved good treatment results
especially for the phosphorus removal near the end of
the study.
Overall, the data collected demonstrate that the
MSBR process is capable of achieving high waste water
treatment efficiently in a simple, small volume, single
tank unit. With this simply-operated and fully-
automated system, high influent of BODS, TSS, nitrogen,
and even phosphorus can be removed at low capital and
operating costs.
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Summary of MSBR~ Pilot Study
Influent, mg/1 Effluent, mg/1 Removal,
BODS 310 13.5 96
TSS 332 16.5 95
VSS 288 12.5 96
TKN 48.5 5.75 88
NH4-N 28 2.8 N/A
N03-N 4.7 3.4 N/A
NOZ-N 23.2 3.25 ,N/A
TN 76.5 12.4 84
TP 12.3 0.90 93
Ortho P 6.8 0.57 N/A
HRT=24 hrs
(4 hrs anaerobic, 1.3 hrs liquid solids phased
separator, 8 hrs main aeration)
(5.35 hrs for each sequencing treatment cell)
Temperature=17°C
