Note: Descriptions are shown in the official language in which they were submitted.
CA 02221407 1997-11-18
TITLE OF THE INVENTION
AEROBIC BIOREACTOR FOR TREATING AQUEOUS
WASTES AT HIGH ORGANIC AND SOLIDS LOADINGS
5 FIELD OF THE INVENTION
The present invention generally relates to the treatment
of wastewaters rich in organic content, either soluble or particulate, and
is more specifically concerned with aerobic treatment wherein a
pneumatic bioreactor is capable of handling and treating aqueous wastes
10 at high organic loadings, enabling the production of flocs and the
precipitation of inert organic pollutants, thereby yielding a significant
purification performance of the wastewater. The present invention also
relates to a pneumatic bioreactor enabling an efficient, complete and
environmentally friendly treatment of aqueous wastes at high organic
15 loadings and an environmentally friendly disposal of the treated
wastewater. The bioreactor of the present invention is also designed to
accommodate the treatment of wastewaters containing high
concentrations of suspended solids. In one embodiment, the invention
relates to a pneumatic aerobic bioreactor for the treatment of
20 wastewaters of high organic and solids loadings which enables the
development of the biodegrading flora, the formation of flocs and a
reduction of the amount of phosphorus initially present in the wastewater
of more than 90 %.
25 BACKGROUND OF THE INVENTION
In many countries, waste management, either domestic,
industrial or agricultural, has been and is still carried out without much
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concern to the environment. However, septic tank sludge, animal waste
such as pig slurry, leachates from landfill sites or wastewater from food
processing industries have been the target of restrictions and protective
measures. Some solutions have been applied to solve some of the
5 problems associated with these human activities. In some cases,
however, the lack of an ideal solution has hampered or halted the growth
of some industries. The best example is the pig industry, which has
brought many producing countries into investing significant sums of
money into research and development of technologies for treating pig
10 slurry. In conventional fattening piggeries, the raw slurry containing
animal urine and feces is usually collected and stored in ponds or large
concrete structures where it is allowed to decompose freely until it is used
as fertilizer. Odor production and emissions are left uncontrolled, fertilizer
quality is highly variable and/or potentially lost to the atmosphere, and
15 the volumes are diluted by precipitations. Furthermore, management of
the fertilizer through intensive farming techniques brings a lot of
environmental concern with respect to pollution when it is disposed of on
the land (excess landspreading dosages, surface water runoff,
groundwater contamination). Clearly, an important need for an efficient
20 and environmentally friendly apparatus and method of treating
wastewaters rich in organic content, such as pig slurry remains.
Besides measures proposed for pollution source
reduction, such as pig-on-litter systems, better nutrient assimilation
through enzyme complement to the animal diet, volume reduction through
25 better water management in the piggeries, different strategies for odor
control and several types of physico-chemical treatment processes for
liquid piggery waste have been studied. These include olygolysis, or
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electrolytic treatment, in Germany and Italy (Ranalli et al.,1996, J. Env.
Sci. Health A., 31:1705-1721), thermal dewatering technologies (Sirven
process) or phase separation using membranes, chemical precipitation,
centrifuges or other devices. These technologies either propose only a
5 partial treatment or require major capital investment.
Biological processes for treating liquid piggery waste
have also been developped. For example, pig slurry treatment has been
approached using aerobic or anaerobic technologies or a combination
thereof. Potential applications for these technologies have been looked
10 at either as regional facilities in areas where the pig industry is
concentrated or as local facilities installed at the production site.
Regional facilities using anaerobic technologies exists,
for example, in the Netherlands and in Denmark. Such facilities use the
Promest and Memon systems (Rulkens and Ten Have, 1994, Wat. Sci.
Technol., 30:157-165) or the Ecosun and Lindtrup processes. Because
of high energy costs in those countries, regional facilities using anaerobic
digestion were thought to be economically feasible since the energy input
is very low and the potential recovery of combustible biogases exists.
However, energy yields are low and difficult to optimize, raising the
20 question as to whether large scale projects for the sole purpose of
treating animal waste should go on or be abandoned.
Anaerobic processes (Massé and Droste, 1997, Can.
Agric. Eng., 39:35-41; Massé et al., 1997, Can. Agric. Eng., 39:25-33;
Massé et al., 1996, Can. J. Civ. Eng., 23:1285-1294) or combined
25 anaerobic/aerobic treatment strategies (Le Hy et al., 1989, Wat. Sci.
Technol.,21:1861-1864) in local facilities at the production site, are also
being studied. Althought, these anaerobic processes can be simple in
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design, produce little residual solids and have low energy requirements,
they have several disadvantages. They are sensitive to toxic constituents
of the influent, provide poor clarification, do not assimilate or degrade all
nutrients, and produce noxious and explosive gases.
Aerobic treatment of wastewater is well known and has
been used for many years in its most notorious application: municipal and
industrial wastewater treatment. Inventions that perform this process
have been described (for example, U.S. Pat. Nos. 2,907,463, issued to
Light et al. on Oct. 6, 1959; 4,522,722 issued to Nicholas on June 11,
1985; 4,798,673 issued to Huntington on Jan. 17, 1989; and Canadian
Patent No. 1,117,042 issued to Spector on Jan. 26, 1982). Numerous
variations of the same process are used around the world depending on
the quality of the wastewater, the way by which the wastewater is fed to
the system and the required efficiency to produce an effluent that
complies with local regulations. Most of these systems are large in
dimensions, cor,l"land high capital costs and a significant input in energy,
and have not been designed for compactness and high organic loadings.
Some effort has been dedicated to finding solutions
using various designs that use aerobic or sequential aerobic/anaerobic
processes for the treatment of aqueous wastes at high organic loadings.
More specifically for the treatment of pig slurry, nitrification/denitrificationand aerobic sequential batch reactor processes have been studied and
developped (Fernandes and McKyes, 1991, Trans. ASAE, 34:597-602;
Martinez,1997, J. Agric. Eng. Res.,66:51-62; Su et al., 1997, J. Env. Sci.
Health A., 32:391-405). Treatment at the production site proposed by
some promoters has been considered a potential solution to the problem,
using technologies such as nitrification/denitrification processes for
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.
nitrogen reduction in France (Agroclar, Denitral, Val Épur, Technolyse,
Ternois), or different composting methods of liquid manure in France
(Guernevez, Isateri, and Lisia-post) and Belgium (Ménart). However,
most of the technologies proposed are either expensive to build and/or
5 operale, are complex to operate, or treat the waste material only partially
and therefore do not bring a complete and final solution to the problem.
There thus remains a need to provide an aerobic
treatment of aqueous wastes containing high levels of organic matter and
nutrients that can be oxydized and assimilated under more mineralized,
10 stable and/or innocuous forms during the process. There also remains a
need for an improvement in the concer,l,alion of the fertilizing value in the
sludge in a fraction of the influent volume, odor control, proper handling
of the biological floc for best settling properties, and quality of the
aqueous effluent.
The present invention seeks to meet these and other
needs.
The present description refers to a number of
documents, the content of which is herein incorporated by reference.
20 SUMMARY OF THE INVENTION
An object of the present invention is an aerobic
bioreactor wherein efficient biodegradation of aqueous organic wastes at
high organic loadings takes place. It is also an object of the invention to
provide a bioreactor and method of treatment of aqueous organic waste
25 at high organic loadings which yield a treated water which is substantially
free of phosphorus and nitrogen. Further, it increases the fertilizing value
of the sludge.
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. .
A further object of the present invention is to provide a
bioreactor which can treat the waste without any prior treatment thereof
and provides assimilation of nutrients such as nitrogen and phosphorus.
A further object of the present invention is to provide a
5pneumatic t,oreactor enabling an efficient and complete treatment of the
waste material and improves the concentration of the fertilizing value in
the sludge in a fraction of the influent volume while controlling odor
emissions.
Yet, a further object of the invention is to provide a
10pneumatic bioreactor of compact size which is adapted for the treatment
of wastewaters at high organic loadings and methods of use thereof.
Another object of the invention is an aerobic bioreactor,
wherein organic waste at high organic loadings (above 0,04 Ibm3.d) is
biodegraded while high concentrations of volatile suspended solids (up
15to 30 000 mg VSS/L), i.e. the biocatalyst, are present in the bioreactor.
It is also an object of the invention to provide adequate
control over the shear stress imposed on the biological catalyst to insure
swift and proper separation of the biological solids from the liquid effluent
by simple passive settling.
20Yet another object of the invention is to reduce the
volume of the waste by concentrating organic carbon and assimilated
nutrients in the sludge while producing a large liquid fraction (from 60 to
85 % of the influent volume) that can be easily polished or directly
disposed of in a sewer or water course.
25The invention also relates to a process for the aerobic
biodegradation of aqueous organic wastes at high organic loadings.
Further, the invention relates to a process wherein the biological catalyst
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develops as a free suspension from the facultative flora present in the
waste to be treated. If the waste lacks a proper biocatalyst, start-up can
be initiated using specialized bacteria as inoculum.
Oxidation and assimilation is stimulated through the
supply of air, which generates off-gases rich in carbon dioxide. The off-
gases may also contain volatile compounds in various amounts if those
are present in the influent waste and if the conditions for volatilization
prevail in the bioreactor. For example, excess ammonia could be found
in the off-gas depending on its conce, ILI alion in the influent waste and the
conditions in the bioreactor. Volatization conditions can be adapted to the
specific volatile compound by the person of ordinary skill. For favorizing
the volatization of ammonia for example, the conditions of pH,
temperature, and air flow rate can be varied to affect the volatization of
the ammonia. Other non-limiting examples of volatile compounds include
low molecular weight fatty acids, alcohols, and reduced sulfur
compounds. Certain conditions known to the person of ordinary skill to
which this invention relates can choose conditions that will favor
volatilization in the bioreactor. In the latter case, ammonia gas can be
captured and eliminated by an organic filter.
The influent organic waste material is passively
introduced or continuously pumped directly into the bioreactor from the
source or from an upstream homogenizing tank or basin. The organic
waste then comes into contact with the biological catalyst suspended in
the bioreactor and is oxidized with the addition of air which also provides
agitation. Air is injected through Venturi tubes, and, whenever higher
aeration is needed, through the addition of the appropriate number of air
diffusers. The conlact time between the subslra(e and the catalyst as well
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as oxygen transfer are maximized by the pneumatic Venturis which
continuously recirculate the mixed liquor by discharging it into at least
one channel installed above the liquid surface. The at least one channel
empties its conlenls into the bulk of the liquid at a discharge area located
at the end opposite to the reactor overflow. Pneumatic mixing provides
low shear conditions that preserve the integrity of the biological flocs.
Consequently, the flocs are more amenable to a downstream swift and
passive settling step. After settling, the clarified effluent leaves the
settling unit. The biological sludge rich in assimilated carbon and
nutrients along with the inert solid fraction that may have been present in
the influent material can be collected at that time. The settling unit is
looped with the bioreactor through devices that recycle biological solids
as necessary and return any foam or scum that may form at the surface
of the clarifier.
The quality of the sludge and aqueous outflows of the
settling unit depends on the quality of the influent waste. Final treatment
and/or disposal options will depend on local environmental standards
(sewer and water receiving bodies) and on biomass reuse capabilities of
the local community.
As used herein, the designation "organic wastes" is
meant to cover preferably organic wastes having high organic loadings,
generally known as high charge substrates. Non-limiting examples of
such organic wastes include animal slurries such as pig slurry, septic
tank sludge, landfill site leachate and agro-food or other industrial
wastewater. Preferably, the organic loadings of the wastewaters to be
treated will be between about 0.04 Ibm3.d to 0.16 Ibm3.d. It shall be
understood that the amount of organic loadings in the wastewaters which
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can be efficiently treated in accordance with the present invention is
dependent on the concentration of volatile suspended solids (VSS) or
biocatalyst. For example, an increase in the concentration of VSS should
permit the treatment of wastewaters having higher concenlralions of
5 organic loadings.
The term "biodegradation" denotes the fact that the
treatment or degradation of the organic waste in the bioreactor is enabled
by a biological catalyst which is freely suspended and develops from the
facultative aerobic flora present in the waste to be treated. Of course, it
10 will be understood that the biological catalyst can be added to the waste
to be treated. It will be clear to the person of ordinary skill that flora can
be adapted to the type of pollutant to be removed from the wastewaters.
It should also be understood that the filtration material might contain a
flora which is adapted for the purification of a particular pollutant or family
15 thereof. In addition, inoculation of the bioreactor will often take place
naturally, the flora contained in the wastewaters. It shali also be
understood that a particular type of wastewaters generally contains a
flora which is best adapted to the degradation of the substrate in which
it lives. The bioreactor of the present invention and method of
20 degradation using same, favours and selects for the development of such
a flora, thereby enabling an efficient and complete biodegradation of the
wastewaters. The flora refers generally to bacteria and higher life forms
such as protozoa which colonize the wastewaters. The bioreactor also
enables the production of flocs. Thus, the present bioreactor ans method
25 of using same are adaptable to the biodegradation and treatment of
different types of wastewaters at high organic loadings, provided that the
CA 0222l407 l997-ll-l8
flora adapted to its biodegradation is provided with the necessary growth
conditions inside the bioreactor.
As used herein the term "flocs", well known to a person
of ordinary skill to which the present invention pertains, refers to a
5 flocculant mass formed by the aggregation of particles. The present
invention enables the production of flocs without a dependance on
flocculating agents.
As used herein, "sludge or biological sludge" is well
known is the art and denotes that the sludge is of biological origin and
10 that it provides a biomass. Non-limiting examples of sludge stabilization
include, composting, line treatment, and aerobic or anaerobic digestion.
Sludge disposal usually pertains to disposal in a landfill site unless land
farming is possible and/or permitted. Since flocculating agents are not
required in the method of the present invention, a decrease in the
15 valorization of the sludge by these flocculating agents is avoided.
The recitation "organic loading" can be expressed as a
function of the volume of the reactor or as a function of the concenll alion
of bioc~lalyst in the bioreactor. It is usually expressed in kg COD/day or
kg BOD/day. The value for the organic loadings is therefore expressed
20 in a unit of mass of COD or BOD per unit of volume of reactor per day or
as a unit of mass of DCO or BDO per unit of mass of biocatalyst per day.
The bioreactor and method of the present invention
enable a reduction of organic loading of about 90 %. Depending on the
hydraulic retention time, the reduction can be as high as about 99 %
25 (without the use of a decanter). When the bioreactor is coupled to a
decanter, the reduction of the organic loading can amount to
approximately 99.7 % before polishing. Thus, the bioreactor of the
CA 02221407 1997-11-18
11
present invention and method of treating wastewater at high organic
loadings making use thereof provide the most efficient reduction in
organic loadings of such wastewaters (Sundstrom et al., 1979,
Wastewater Treatment, Prentice-Hall).
The terms "COD" and "BOD", as well known in the art,
relate to the chemical oxygen demand and biological oxygen demand,
respectively. The COD is a chemical oxidation method for the measure
of all the matter which is chemically oxidizable. It is always higher than
the BOD because it includes both bio- and non-biodegradable matter.
The BOD is normally evaluated for live days and represents the quantity
of oxygen used by bacteria to oxidize the biodegradable matter present
in a sample of wastewater.
In this context, wastewaters having a BOD between
about 3,000 to about 30,000 mg BOD/L are encompassed as being within
the scope of present invention. As used herein the BOD values are
pertinent to indicate the type of wastewaters which are within the scope
of the present invention. It should not be used to characterize the size of
the treating units, however. In this context, the size of the unit should be
based on the mass of charge per unit of volume of the reactor (i.e. 3 kg
BOD per m3 of minimal volume per day).
The recitation "freely suspended flora" refers to the
biomass being in suspension as opposed to the biomass fixed on a
support.
The recitation "aqueous organic waste" refers to the fact
that the solvent is water as opposed to an oil or the like.
The bioreactor and method of the present invention
provide the significant advantage of enabling a treatment of influents
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12
containing high solids or suspended solids content. Since the biocatalyst
VSS contributes to the concentration of suspended solids (SS; which
include VSS plus inert suspended solids), a certain concentration of
volatile suspended solids (VSS) will most generally be present in the
5 wastewater. The bioreactor and method of the present invention permit
a treatment of wastewaters containing concentrations of VSS of 5,000 -
30,000 mg/L, preferably of 12,000 - 24,000 mg/L.
It shall be understood that regardless of the suspended
solids in the influent material, the reactor can maintain large
concentrations of VSS up to 30,000 mg/L. The VSS range will vary
according to the BOD, the influent hydraulic retention time (BOD load)
and the biological sludge age. The bioreactors and methods of the prior
art in contraclislinction to the present invention, are absolutely dependent
on a sludge recycling step. Moreover, none of them can operate under
15 VSS concentrations superior to 8,000 mg/L. In general, the preferred
range of operation thereof is 3,000 - 4,000 mg VSS/L.
It is to be understood that the sludge age will have to be
adapted by the person of ordinary skill as a function of the specific type
of treatment and wastewater treated. In certain situations, in which no
20 sludge recycling is used, the sludge age will be equal to the hydraulic
retention time (HRT; the time of incubation of the wastewater inside the
bioreactor). However, in order to ensure an efficacious decanting, there
exists an optimal age of the sludge which is dependent on the type of
wastewater and the HRT. For HRTs superior to 10 days, the sludge age
25 will be equal to the HRT.
. CA 02221407 1997-11-18
It shall also be understood, that bioreactor tank of the
invention can be under or above the ground level or alternatively at
intermediate levels. The person of ordinary skill, will be able to adapt *
While the method of treatment of wastewaters at high
organic loadings and pneumatic bioreactor therefor of the instant
invention are demonstrated with an animal slurry such as pig slurries
(which is a typical wastewater having high organic and solids loadings),
as mentioned, other aqueous organic wastes at high loadings can be
treated in accordance with the present invention. Non-limiting examples
thereof include septic tank sludge, landfill site leachate and agrafood or
other industrial wastewaters.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the invention, reference
will now be made to the accompanying drawings, showing by way of
illustration a preferred embodiment thereof, and in which:
Fig. 1 is a flowchart of a typical aerobic process for
aqueous waste treatment made in accordance with the present invention
(the bioreactor) and showing peripheral units that could or have to be
used in conjunction with the invention;
Fig. 2 is a top plan view of the structure and
configuration of the bioreactor;
Fig. 3 is a cross-sectional view of the structure and
configuration along the length of the bioreactor; and
Fig. 4 is a cross-sectional view of the structure and
configuration along the width of the bioreactor.
CA 02221407 1997-11-18
Other objects, advantages and features of the present
invention will become more apparent upon reading of the following
non-restrictive description of preferred embodiments with reference to the
acco",panying drawing which is exemplary and should not be interpreted
5 as limiting the scope of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Broadly, the treatment process of the present invention
and apparatus therefor consist of the bioreactor and of two standard units
10 (figure 1). A homogenizing tank 2 can be placed upstream of the
bioreactor 10, the subject of the instant invention, and a settling tank 11
installed downstream. The homogenizing tank 2 or basin is optional but
prefer"3d for waste containing settleable solids. The wastewaters A flow
passively or can be pumped into the homogenizing unit 2 either
15 batchwise or continuously by a pump 4. A pump 4 is necessary between
the homogenizing tank or basin 11 and the bioreactor 10 if the oufflow
from the homogenizing unit 2 is located below the inflow of the bioreactor
10 or if the homogenizing unit 2 is fed batchwise.
The bioreactor achieves biological oxidation and
20 flocculation to provide a mixed liquor which can be easily separated in
the settling tank 11 to generate an aqueous effluent H and a biological
sludge mixed liquor overflow (shown as D in Fig. 1 ) can be transferred to
the settling tank 11. The biological sludge produced can be managed
according to the needs of the user and disposed of in different ways
25 known to the person of ordinary skill. I refers to sludge treatment or
disposal. The aqueous effluent, depending on its quality and on local
environmental standards can be polished in further purification steps or
CA 02221407 1997-11-18
disposed of in a sewer system for receiving water bodies as commonly
known in the art. Off-gas (shown as E in Fig. 1 ) can be treated as well
known in the art.
The bioreactor maintains homogeneity of the material
5 to be treated and reduces the organic loading by 90 % to over 99 % (as
expressed by BOD or COD) depending on the hydraulic retention time.
An oxygen containing medium such as an air supply has to be provided
for the oxidation to take place. The bioreactor is designed to handle
influents containing suspended solids of up to 5 % and organic loadings
10 above 0,04 Ib/ft3.d. The bioreactor can be operated at high volatile
suspended solids concentrations (up to 30 000 mg VSS/L). Contaminants
in the off-gases can also be treated before being released to the
atmosphere.
The settling tank 11 passively removes most of the
15 suspended matter leaving the biological unit. The amount removed in
tank 11 depends on the operating conditions of the biological unit. If foam
or scum are present at the surface or the settling unit, these can be
retumed to the bioreactor (shown as F in Fig. 1). Recycling of the sludge
(shown as G in Fig. 1) can be achieved if the hydraulic retention time
20 does not allow the appropriate sludge age in the bioreactor. In such a
case, the old sludge provides the biological catalyst for the next round of
biotreatment of wastewaters.
The bioreactor tank or basin 10 (figures 2, 3 and 4) is
either under or above ground level. At least one channel 12 installed
25 above the operating volume extend(s) over 90 % of the length of unit 10.
Fresh influent material can be fed continuously at any point in the
channel 12 or into the channel discharge area 14 of unit 10 where it
CA 0222l407 l997-ll-l8
16
comes into or is injected directly in the bulk of the wastewaters. The
channel 12 has a slope of at least 1 % to insure a flow of the material and
mixed liquor towards the discharge area 14 located at the end opposite
the overflow 16 of unit 10.
Aeration and agitation is entirely pneumatic and
provided by Venturi tubes 18 connected to the walls of the channel 12
where they empty their contents into the channel 12. Additional aeration
and agitation can be provided by installing air diffusers at the bottom of
the tank or basin. Those diffusers have to be selected according to mass
l,an~rer efficiency and oxygen depletion rates at set operating conditions.
The general arrangement of the Venturis 18 is either in staggered or
parallel rows and the number of Venturis 18 and rows will vary according
to the size of the bioreactor and the number of channels. Each Venturi 18
is equipped with a suction device 20 sitting on a cross support 22.
At least one inverted Venturi 24 having a surface
skimmer 26 can be provided to return foam or scum to the channel 12.
Oxygen containing medium such as air is supplied to the Venturis 18 and
inverted Venturis 24 by individual calibrated pipes 28 linked to a manifold
30. If more flexibility in the liquid flow pattern of the reactor is required,
the air flow through each pipe 10 can be controlled by individual valves
32. Appropriate air source has to be supplied by a surpressor sized as a
function of the organic load and of the hydrostatic pressure.
The mixed liquor leaves the bioreactor 10 passively
through an overflow pipe 16 towards the settling unit 11. The overflow
pipe 16 and its air vent 34 are located at the end of the reactor 10
opposite the channel discharge area 14. Peripheral flows such as for
scum recycle I or sludge recycle G from the settling unit 11 can be
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17
provided by a scum recycle pipe 36 and sludge recycle pipe 38,
respectively installed in the channel discharge area 14. Off-gas can exit
the bioreactor 10 at any appropriate point by an off-gas pipe 40 at the top
of bioreactor 10.
The present invention is illustrated in further detail by
the following non-limiting examples.
EXAMPLE 1
The pig slurry produced by 200 pigs was treated at a
fattening piggery with the present invention using a hydraulic retention
time of 12 days. The system had an homogenizing step as well as a
settling step. Characterization of the influent material and of the
supernatant leaving the settling tank before polishing yielded the
following results:
Influent Settling tank Removal
Analytical parameter concentration supernatant efficiency
(mg/L) (mg/L) (%)
Total COD 59 500 1 100 98.2
Soluble COD 17 600 850 95.2
Total suspended solids 41 500 180 99.6
Total nitrogen (Kjedhal)4 300 80 98.1
Ammonia nitrogen 2 750 25 99.1
Total phosphorus 1 100 60 94.5
25 Conditions were as follows: Food to mass ratio of 0,26 kg COD/kg VSS.d
working at 0,31 Ib total CODm3.d or 0,09 Ib soluble CODm3.d; no sludge
recycle.
CA 0222l407 l997-ll-l8
18
Thus the bioreactor and method exemplified enable a
removal efficiency of the different tested parameters which is almost
maximum. Such a performance is a significant improvement over
conventional l,eal",ent methods which show a removal efficiency of about
5 70 % for total phosphorus for example.
EXAMPLE 2
The pig slurry produced by 300 pigs will be treated at a
10 fattening piggery with the present invention using a hydraulic retention
time of 8 days. The system will use a homogenizing step as well as a
settling step. Characterization of the influent material and of the
supematant leaving the settling tank before polishing is expected to yield
the following results based on results obtained in other experiments:
Influent Settlingtank Removal
Analytical parameter concentration supernatant efficiency
(mg/L) (mg/L) (%)
Total COD 66 500 950 98.6
Soluble COD 18 500 650 96.5
Total suspended solids 41 000 350 99.1
Total nitrogen (Kjedhal)4 100 120 97.1
Ammonia nitrogen 3440 95 97.2
Total phosphorus 1 100 42 96.2
Conditions were as follows: Food to mass ratio of 0 24 kg COD/kg VSS.d;
working at 0 52 Ib total CODm3.d or 0 14 Ib soluble CODm3.d; no sludge
recycle.
CA 0222l407 l997-ll-l8
19
Conclusion
There has thus been described a compact bioreactor for
treating aqueous organic wastes at high organic loadings. The system
concentrates the fertilizer in the biological sludge resulting from the
5 process and may allow discharge of aqueous effluent to a water course
depending on local regulations. The aqueous effluent is odor-free and the
output solids may be processed through a stabilization step if a stable
and odor-free product is needed for further utilization. Off-gases can be
treated if necessary through an organic filter.
The system provides very high reductions in total
suspended solids, organic material (BOD or COD), nitrogen and
phosphorus contaminations that are otherwise discharged into the
environment, treated only partially, or treated through more expensive
technologies based upon biological or physicochemical processes.
Although the present invention has been described
hereinabove by way of preferred embodiments thereof, it can be
modified, without departing from the spirit and nature of the subject
invention as defined in the appended claims.
