U.S. patent application number 12/760168 was filed with the patent office on 2011-10-20 for anaerobic digester-membrane bioreactor for treating a waste stream.
This patent application is currently assigned to OTV SA. Invention is credited to John Ewing.
Application Number | 20110253624 12/760168 |
Document ID | / |
Family ID | 44787417 |
Filed Date | 2011-10-20 |
United States Patent
Application |
20110253624 |
Kind Code |
A1 |
Ewing; John |
October 20, 2011 |
ANAEROBIC DIGESTER-MEMBRANE BIOREACTOR FOR TREATING A WASTE
STREAM
Abstract
A waste stream having anaerobically biodegradable components is
fed to an anaerobic reactor where the components react with
microorganisms to biodegrade the components and produce biomass and
biogas. Mixing occurs in select portions of the anaerobic reactor,
particularly the bottom and top portions of the reactor. Relatively
heavy solids settle to the bottom and are mixed with the mixed
liquor while relatively light or fine solids float to the top
portion of the anaerobic reactor where they are mixed with the
mixed liquor. This leaves an intermediate or middle portion of the
anaerobic reactor where the concentration of solids is relatively
lower compared to the concentration of solids in the upper or lower
portion of the anaerobic reactor. Mixed liquor is pumped from the
intermediate portion of the anaerobic reactor to a membrane
separation unit where the mixed liquor is separated into a permeate
stream and a retentate stream that is concentrated with solids. The
retentate stream is recycled back to the anaerobic reactor and
mixed with the mixed liquor therein. Further, mixed liquor and the
relatively heavy solids are pumped from the bottom of the anaerobic
reactor to a solids separator such as a hydrocyclone. Here the
mixed liquor and solids are separated into a stream concentrated
with heavier solids including a high percentage of inorganic
precipitants and a lighter solids stream that contains a high
percentage of biomass. This lighter solids liquid stream containing
mixed liquor is recycled back to the anaerobic reactor for further
treatment while the solid stream can be directed to a dewatering
unit.
Inventors: |
Ewing; John; (Camden,
NJ) |
Assignee: |
OTV SA
Saint-Maurice Cedex
FR
|
Family ID: |
44787417 |
Appl. No.: |
12/760168 |
Filed: |
April 14, 2010 |
Current U.S.
Class: |
210/607 ;
210/195.2 |
Current CPC
Class: |
C02F 11/12 20130101;
B01D 2317/022 20130101; C02F 2305/06 20130101; C02F 1/38 20130101;
C02F 1/66 20130101; C02F 2303/10 20130101; Y02W 10/30 20150501;
C02F 2303/16 20130101; Y02E 50/343 20130101; C02F 3/006 20130101;
C02F 3/286 20130101; B01D 61/22 20130101; B01D 2311/04 20130101;
B01D 65/02 20130101; C02F 3/2853 20130101; Y02E 50/30 20130101;
B01D 2321/04 20130101; B01D 2311/04 20130101; B01D 2311/2688
20130101 |
Class at
Publication: |
210/607 ;
210/195.2 |
International
Class: |
C02F 3/28 20060101
C02F003/28 |
Claims
1. A method of treating a waste stream having anaerobically
biodegradable solids in an anaerobic membrane bioreactor, the
method comprising: a. feeding the waste stream having the
anaerobically biodegradable components into an anaerobic reactor;
b. reacting the biodegradable solids with anaerobic biomass in the
anaerobic reactor to reduce the amount of biodegradable solids and
components and in the process produce a biomass and biogas in the
anaerobic reactor; c. providing a mixing action in a lower portion
of the anaerobic reactor and mixing the mixed liquor and relatively
heavy solids in the bottom of the anaerobic reactor; d. providing a
mixing action in an upper portion of the anaerobic reactor and
mixing the mixed liquor and relatively light solids in the upper
portion of the anaerobic reactor; e. wherein mixed liquor in an
intermediate portion of the anaerobic reactor includes a relatively
lower concentration of solids, including biomass; f. pumping mixed
liquor from the intermediate portion of the anaerobic reactor to a
membrane separation unit and separating the mixed liquor into a
permeate stream and a retentate stream concentrated with the
solids; g. recycling at least a portion of the retentate stream to
the anaerobic reactor and mixing the retentate stream with mixed
liquor in the anaerobic reactor; h. pumping mixed liquor and at
least some of the relatively heavy solids from the bottom portion
of the anaerobic reactor to a solids separator and separating the
heavier solids and the lighter solids containing biomass; and i.
recycling at least a portion of the lighter solids containing the
biomass to the anaerobic reactor and mixing the lighter solids in
the anaerobic reactor.
2. The method of claim 1 including directing the heavier solids
from the solids separator to a dewatering unit and dewatering the
heavier solids.
3. The method of claim 1 wherein there is one or more mixers
disposed in the bottom portion of the anaerobic reactor and one or
more mixers disposed in the upper portion of the anaerobic
reactor.
4. The method of claim 3 wherein there are no mixers disposed in
the intermediate portion of the reactor, and wherein the solids
concentration of the mixed liquor in the intermediate portion of
the reactor is less than the solids concentration in the mixed
liquor in the upper portion or bottom portion of the anaerobic
reactor such that fouling of membranes that form a part of the
membrane separation unit is reduced, long term membrane performance
is enhanced and membrane life is extended by minimizing the
frequency of CIP cycles while maintaining a substantial
concentration of mixed liquor volatile suspended solids inside the
reactor.
5. The method of claim 1 including directing a contaminated stream
to a membrane filtering unit and filtering the contaminated stream
to produce a permeate stream and a second retentate stream, and
wherein the permeate stream forms the waste stream that is treated
by the anaerobic membrane bioreactor.
6. An anaerobic membrane bioreactor for anaerobically biodegrading
components in a waste stream, comprising: a. an anaerobic reactor
having an inlet for permitting the waste stream having
anaerobically biodegradable components to be directed into the
anaerobic reactor resulting in the reaction of the biodegradable
components with anaerobic biomass in the reactor to reduce the
amount of biodegradable components and produce biomass and biogas
in the anaerobic reactor; b. one or more first mixers for providing
a mixing action in a lower portion of the anaerobic reactor and
mixing the mixed liquor and relatively heavy solids in the bottom
of the anaerobic reactor; c. one or more second mixers for
providing a mixing action in an upper portion of the anaerobic
reactor and mixing the mixed liquor and relatively light solids in
the upper portion of the anaerobic reactor such that mixed liquor
in an intermediate portion of the anaerobic reactor includes a
relatively lower concentration of solids and biomass; d. a first
pump for pumping mixed liquor from the intermediate portion of the
anaerobic reactor to a membrane separation unit and separating the
mixed liquor into a permeate stream and a retentate stream
concentrated with the biomass; e. a first recycle line for
recycling the retentate stream to the anaerobic reactor and mixing
the retentate stream with mixed liquor in the anaerobic reactor; f.
a second pump for pumping mixed liquor and at least some of the
relatively heavy solids from the bottom portion of the anaerobic
reactor to a solids separator and separating the relatively heavy
solids into two streams, a first stream including relatively heavy
solids and a second stream including relatively lighter solids; and
a second recycle line for recycling at least a portion of the
second stream to the anaerobic reactor and mixing the second stream
with the mixed liquor in the anaerobic reactor.
7. The anaerobic membrane bioreactor of claim 6 wherein the
anaerobic membrane bioreactor is operative to stratify the mixed
liquor into at least three zones in the anaerobic reactor, a lower
zone where the mixed liquor includes relatively heavy solids, an
upper zone where the mixed liquor includes relatively light solids,
and an intermediate zone in the anaerobic reactor between the lower
and upper zones and where the mixed liquor includes a solids
concentration that is measurably less than the solids concentration
in the mixed liquor in the lower zone.
8. The anaerobic membrane bioreactor of claim 7 including a mixed
liquor feed line for directing mixed liquor from the anaerobic
reactor to the membrane separation unit, and wherein the mixed
liquor feed line is plumbed into the anaerobic reactor such that
mixed liquor from the intermediate zone, as opposed to the lower
and upper zones, is pumped into the mixed liquor feed line and
directed to the membrane separation unit.
9. The anaerobic membrane bioreactor of claim 6 further including:
a. a mixed liquor feed line connected between the anaerobic reactor
and the membrane separation unit for directing mixed liquor from
the anaerobic reactor to the membrane separation unit; b. the mixed
liquor feed line connected to the anaerobic reactor such that most
of the mixed liquor directed to the membrane separation unit comes
from the intermediate portion of the anaerobic reactor; c. a mixed
liquor and solids feed line operatively connected between the
anaerobic reactor and the solids separator; and d. the mixed liquor
and solids feed line connected to the lower portion of the
anaerobic reactor such that the mixed liquor and solids fed to the
solids separator comes from the lower portion of the anaerobic
reactor.
10. A method of treating a waste stream having anaerobically
biodegradable components, comprising: a. feeding the waste stream
having the anaerobically biodegradable components into an anaerobic
reactor; b. reacting the biodegradable components with anaerobic
biomass in the anaerobic reactor to reduce the amount of
biodegradable components and in the process produce biomass and
biogas; c. stratifying the mixed liquor in the anaerobic reactor by
forming a first lower mixed liquor zone where the mixed liquor in
the first lower mixed liquor zone includes a relatively high
concentration of solids, and forming a second mixed liquor zone
above the first lower mixed liquor zone where the mixed liquor in
the second zone includes a solids concentration substantially less
than the concentration of solids in the mixed liquor in the first
lower mixed liquor zone; d. directing mixed liquor from the second
mixed liquor zone in the anaerobic reactor to a membrane separation
unit and separating the mixed liquor into a permeate stream and a
retentate stream concentrated with biomass; e. recycling at least a
portion of the retentate stream to the anaerobic reactor and mixing
the retentate stream with mixed liquor in the reactor; f. directing
the mixed liquor and solids from the first lower mixed liquor zone
to a solids separator and separating the mixed liquor and solids
from the first lower mixed liquor zone into a heavier solids stream
and a lighter solids stream containing biomass; and g. recycling at
least a portion of the lighter solids stream containing biomass
from the solids separator to the anaerobic reactor and mixing the
lighter solids stream with the mixed liquor in the anaerobic
reactor.
11. The method of claim 10 including providing a mixing action in
the first lower mixed liquor zone and mixing the mixed liquor and
solids therein; and maintaining the mixed liquor in the second zone
in an unmixed state or in a state where the mixing action in the
second zone is substantially less than the mixing action in the
first lower mixed liquor zone.
12. The method of claim 10 wherein the method includes forming a
third mixed liquor zone over the second mixed liquor zone; and
wherein both the first and third mixed liquor zones are mixed with
relatively heavy solids residing in the first mixed liquor zone and
relatively light solids residing in the third mixed liquor
zone.
13. The method of claim 10 wherein the solids separator includes a
hydrocyclone.
14. The method of claim 10 wherein during certain time intervals
both the membrane separation unit and the solids separator are
operated simultaneously and wherein there is one mixed liquor flow
from the anaerobic reactor to the membrane separation unit and
another mixed liquor flow from the anaerobic reactor to the solids
separator, and wherein the two flows are independent of each
other.
15. The method of claim 12 wherein the second mixed liquor zone is
unmixed and wherein the concentration of solids within the second
mixed liquor zone is less than the concentration of solids in the
first or third mixed liquor zones.
16. A method of treating a waste stream having anaerobically
biodegradable components, comprising: a. feeding a waste stream
having the anaerobically biodegradable components into an anaerobic
reactor; b. reacting the biodegradable components with anaerobic
biomass in the anaerobic reactor to reduce the amount of
biodegradable components and in the process produce biomass and
biogas; c. stratifying the mixed liquor in the anaerobic reactor
into three mixed liquor zones by forming a first lower mixed liquor
zone where the mixed liquor in the first lower mixed liquor zone
includes relatively heavy solids, forming a second mixed liquor
zone above the first lower mixed liquor zone where the mixed liquor
in the second mixed liquor zone includes a solids concentration
substantially less than the concentration of solids in the first
lower mixed liquor zone, and forming a third mixed liquor zone over
the second mixed liquor zone where the third mixed liquor zone
includes relatively light solids; d. directing mixed liquor from
the second mixed liquor zone in the anaerobic reactor to a membrane
separation unit and separating the mixed liquor into a permeate
stream and a retentate stream; and e. recycling at least a portion
of the retentate stream to the anaerobic reactor and mixing the
retentate stream with the mixed liquor in the reactor.
17. The method of claim 16 including directing the mixed liquor
from the first lower mixed liquor zone to a solids separator and
separating the mixed liquor from the first lower mixed liquor zone
into a heavier solids stream and a lighter solids stream containing
biomass.
18. The method of claim 16 including mixing the mixed liquor in the
first lower mixed liquor zone and mixing the mixed liquor in the
third mixed liquor zone.
19. The method of claim 18 wherein the mixed liquor in the second
mixed liquor zone is generally unmixed such that the mixing action
in the first and third mixed liquor zones is greater than the
mixing action in the second mixed liquor zone.
20. The method of claim 19 including providing one or more mixers
in a lower portion of the anaerobic reactor for mixing the mixed
liquor in the first lower mixed liquor zone; and providing one or
more mixers in an upper portion of the anaerobic reactor for mixing
the mixed liquor in the third mixed liquor zone.
21. The method of claim 10 wherein the heavier solids stream
contains a relatively high percentage of inorganic precipitants
compared to the lighter solids stream.
22. A method of treating a stream containing soluble and insoluble
COD in an anaerobic membrane bioreactor, the method comprising: a.
feeding the stream having soluble and insoluble COD into an
anaerobic reactor; b. reacting the soluble and insoluble COD with
anaerobic biomass in the anaerobic reactor to reduce the amount of
soluble and insoluble COD and in the process produce a mixed liquor
and biogas in the anaerobic reactor; c. providing a mixing action
in a lower portion of the anaerobic reactor to mix the relatively
heavy solids in the mixed liquor; d. providing a mixing action in
an upper portion of the anaerobic reactor to mix the relatively
light solids in the mixed liquor: e. wherein in an intermediate
portion of the anaerobic reactor a relatively lower concentration
of solids in mixed liquor is present; f. pumping the mixed liquor
from the intermediate portion of the anaerobic reactor to a
membrane separation unit and separating the mixed liquor into a
permeate stream and a retentate stream which substantially contains
the concentrated biomass; g. recycling at least a portion of the
retentate stream to the anaerobic reactor and; h. pumping mixed
liquor with the relatively heavy solids from the bottom portion of
the anaerobic reactor to a solids separator, and separating the
heavier solids from the lighter solids containing biomass; and i.
recycling at least a portion of the lighter solids containing the
biomass to the anaerobic reactor.
Description
FIELD OF INVENTION
[0001] The present invention relates to an anaerobic membrane
bioreactor for treating waste streams having biodegradable total
solids including soluble and insoluble COD.
SUMMARY
[0002] The present invention relates to a system and method of
treating a waste stream having anaerobically biodegradable solids.
The waste stream is directed into an anaerobic reactor and the
biodegradable solids are converted by anaerobic biomass in the
anaerobic reactor to reduce the amount of biodegradable solids and
in the process produce biogas and biomass. The system and process
stratifies the mixed liquor in the anaerobic reactor into at least
three distinct mixed liquor zones. The first zone located at the
bottom of the tank includes a relatively higher concentration of
solids, specifically heavier biological and precipitated solids;
the second zone above the first zone and located in the middle of
the tank height includes a relatively low concentration of solids;
and the third zone located near the top of the tank contains a
relatively higher concentration of biomass than the middle zone and
these solids consist mainly of lighter solids. Mixed liquor in the
middle stratified zone is pumped to a membrane separation unit, the
membrane separation unit can be submerged or external, such as
tubular, flat sheet, or hollow fiber membranes. In the membrane
unit is where the mixed liquor is separated into a permeate stream
and a retentate stream. Stratification enhances the overall
performance of the system. This results in a higher concentration
of solids being maintained in the reactor while supplying a less
concentrated stream to the membrane separation unit. Over time this
enhances the highest possible membrane flux rates per unit of
membrane system energy input and prevents or reduces fouling and in
turn prolongs the life of the membranes of the membrane separation
unit by minimizing the number of clean in place (CIP) cycles. The
retentate stream is recycled to the anaerobic reactor to maintain
longer solids retention time (SRT).
[0003] In one embodiment, a solids separation system is
incorporated into the overall system and process. In this case,
mixed liquor including solids is pumped from the first lower zone
to a solids separator such as a hydrocyclone. At the hydrocyclone,
the mixed liquor is separated into two streams, the first stream
having a relatively high concentration of heavier solids including
most of the precipitated inorganics, and a second stream having a
relatively low concentration of precipitated inorganic solids and a
higher relative concentration of biological solids. The stream
having the relatively higher concentration of biological solids is
recycled back to the anaerobic reactor to maintain a higher
SRT.
[0004] In another embodiment, the present invention entails an
anaerobic membrane bioreactor that includes an anaerobic reactor
that is operative to stratify mixed liquor in the anaerobic
reactor. In this embodiment, the anaerobic reactor includes one or
more mixers disposed in the lower portion of the reactor and one or
more mixers disposed in the upper portion of the reactor. The
anaerobic reactor is operative to form a first mixed liquor zone in
a lower portion of the reactor, and a second mixed liquor zone in
an upper portion of the reactor. This leaves an intermediate mixed
liquor zone generally disposed between the upper and lower zones.
Solids suspended in the upper and lower mixed liquor zones are
mixed by the one or more mixers disposed in the respective zones.
In one embodiment, mixed liquor contained in the intermediate zone
is relatively unmixed or is unmixed. The mixed liquor in the
intermediate zone in one embodiment is pumped to the membrane
separation unit which separates the mixed liquor into a permeate
stream and a retentate stream. One option is to return the
retentate stream to the anaerobic reactor for further
treatment.
[0005] Other objects and advantages of the present invention will
become apparent and obvious from a study of the following
description and the accompanying drawings which are merely
illustrative of such invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a schematic illustration of the anaerobic membrane
bioreactor and process of the present invention.
[0007] FIG. 2 is a schematic illustration showing an exemplary
membrane separation unit.
DETAILED DESCRIPTION
[0008] With further reference to the drawings, particularly FIG. 1,
an anaerobic membrane bioreactor (sometimes referred to by AnMBR)
is shown therein and indicated generally by the number 10. As is
discussed herein in detail, the anaerobic membrane bioreactor 10 is
a compact purification system combining an anaerobic digestion
process with a membrane separation process. The system and process
is effective to treat waste streams having biodegradable
constituents or components by digesting these constituents and
producing biogas and new biomass. The anaerobic membrane bioreactor
10 basically comprises an anaerobic reactor 12 and a membrane
separation unit 14. Effluent from the anaerobic reactor 12 is
directed to the membrane separation unit 14 that separates the
effluent from the anaerobic reactor into a permeate stream and a
retentate stream where the retentate stream is concentrated with
solids including biomass. The concentrated retentate stream is
recycled back to the anaerobic reactor and mixed with the mixed
liquor therein. The goal of the recycling is to maintain a
relatively higher than usual mixed liquor suspended solids (MLSS)
content inside the reactor 12, and thus prolong the SRT. A typical
range of MLSS concentration inside the anaerobic membrane
bioreactor system would be 0.1-6% solids (1,000-60,000 mg/L as
TSS).
[0009] In the embodiment solids are removed from the anaerobic
reactor 12 by pumping mixed liquor from the bottom zone to a solids
separator such as a hydrocyclone. The solids separator separates
the heavier solids, including the inorganic precipitants formed in
the reactor from the lighter solids including a higher
concentration of biomass. This higher in concentration biomass
stream is recycled back to the anaerobic reactor 12. The retentate
(heavier separated solids) can be subjected to further treatment
such as treatment in a dewatering unit. The purpose of the solids
separator is to maintain or control SRT and to remove from the
reactor 12 the buildup of heavy inorganic solids. It should be
appreciated that there are various ways of removing solids from the
reactor 12. Solids can be directly removed, or as described in more
detail subsequently herein, solids can be removed by directing
mixed liquor from a certain area or zone of the reactor 12 to a
solids separator such as a hydrocyclone. In other embodiments,
solids can be removed by directing a portion of the retentate
stream of the membrane separation unit 14 to a solids separator
such as a hydrocyclone.
[0010] It is beneficial to explain or describe the term "solids" as
used in the present application. Total solids (TS) in environmental
systems are defined as all constituents present in a given sample,
namely as dissolved solids (TDS) and suspended solids (TSS),
besides water. A part of the total solids are biodegradable solids,
both soluble and suspended, that have a certain chemical oxygen
demand (COD) associated with them.
[0011] Forming a part of the anaerobic membrane bioreactor 10 is
the anaerobic reactor 12. Anaerobic reactor 12 is designed to
provide mechanical mixing in a bottom portion of the reactor and
mechanical mixing in an upper or top portion of the reactor. In a
preferred embodiment there is no mechanical mixing or relatively
little mixing in the intermediate or middle portion of the
anaerobic reactor. In the reactor 12, heavy solids, including
larger biological flocks and inorganic precipitated solids that
form, tend to settle to the bottom portion of the reactor and are
mixed with the mixed liquor therein by the mixing that takes place
in the bottom portion of the reactor. Other lighter or finer solids
tend to float to the upper portion of the reactor where the
mechanical mixing that takes place in the upper portion of the
reactor maintains these solids in suspension at the top of the
reactor. This tends to stratify the mixed liquor in the anaerobic
reactor 12 into three distinct zones. That is, the concentration of
solids in the intermediate portion of the reactor is lower compared
to the concentration of solids in the bottom or upper portion of
the reactor.
[0012] Downstream from the anaerobic reactor 12 is a membrane
separation unit 14. Mixed liquor is pumped from the intermediate
portion or zone of the anaerobic reactor 12 to the membrane
separation unit 14. Because of the stratification of the mixed
liquor in the anaerobic reactor 12, the mixed liquor pumped to the
membrane separation unit 14 includes a relatively lower solids
concentration. When it is stated that the mixed liquor in the
intermediate portion or zone of the anaerobic reactor 12 includes a
relatively lower solids concentration, it is meant that the
concentration of solids in this portion of the anaerobic reactor is
lower relative to the concentration of solids in the bottom portion
of the anaerobic reactor and the uppermost portion of the reactor.
There are numerous advantages to directing the mixed liquor from
the intermediate portion or zone of the anaerobic reactor 12 to the
membrane separation unit 14. Overall the stratification that occurs
in the reactor 12 serves to enhance the overall performance of the
system. By stratifying the mixed liquor in the reactor 12, a higher
concentration of solids is maintained in the reactor while
supplying a less concentrated stream to the membrane separation
unit 14. This prevents or reduces membrane fouling and enhances the
highest possible membrane flux rates per unit of membrane system
energy input and in turn prolongs the life of the membranes that
comprise the membrane separation unit 14 by minimizing the number
of clean in place (CIP) cycles. The membrane separation unit 14
separates the mixed liquor into a permeate stream that is
relatively pure and includes low concentrations of COD, BOD and
TSS, and a retentate stream that includes more concentrated solids
including biomass which is recycled to the anaerobic reactor 12 and
mixed with the mixed liquor in the anaerobic reactor.
[0013] The present invention also entails a method of treating a
stream containing soluble and insoluble COD in an anaerobic
membrane bioreactor. In this regard, the method entails feeding the
stream having soluble and insoluble COD into an anaerobic reactor
tank. Thereafter the process entails reacting the soluble and
insoluble COD with anaerobic biomass in the anaerobic reactor to
reduce the amount of soluble and insoluble COD and in the process
produce a mixed liquor and biogas in the anaerobic reactor. One or
more mixers are disposed in a lower portion of the anaerobic
reactor to mix the relatively heavy solids in the mixed liquor.
There is also provided in one embodiment, one or more mixers in the
upper portion of the anaerobic reactor for mixing the relatively
light solids in the mixed liquor. This leaves an intermediate
portion or zone of the anaerobic reactor where there is a
relatively lower concentration of solids in the mixed liquor. The
mixed liquor is pumped from the intermediate portion of the
anaerobic reactor 12 to a membrane separation unit 14 where the
mixed liquor is separated into a permeate stream and a retentate
stream that contains a substantial concentration of biomass. At
least a portion of the retentate stream is recycled to the
anaerobic reactor 12. The method further includes, in one
embodiment, pumping mixed liquor with the relatively heavy solids
from the bottom portion of the anaerobic reactor 12 to a solids
separator and separating the heavier solids from the lighter solids
containing biomass. Finally, at least a portion of the lighter
solids containing the biomass is recycled to the anaerobic
reactor.
[0014] The above discussion presents an overview of the anaerobic
membrane bioreactor 10 and the process for treating a waste stream.
Attention is now directed to the individual components of the
anaerobic membrane bioreactor 10 and to the various processes
performed.
[0015] Located upstream from the anaerobic reactor 12 is an
equalization tank 16. Equalization tank 16 includes one or more
mixers 16A. As viewed in FIG. 1 a waste stream or feedwater stream
is directed into the equalization tank 16 and can be mixed by the
one or more mixers 16A. Various waste streams can be treated
according to the process described herein. In general, the waste
streams will include material or matter that is at least partially
biodegradable by anaerobic bacteria or biomass. Examples of waste
streams that can be treated by the system or process disclosed
herein are: sludge streams from municipal sewage treatment plants;
sludge streams from industrial wastewater treatment facilities;
waste streams from agricultural operations; high strength waste
streams from industrial operations; and any other liquid wastewater
streams that are biologically treatable in an anaerobic
reactor.
[0016] Disposed downstream from the equalization tank 16 is a
mixing tank 18. Mixing tank 18 includes one or more mixers 18A.
Associated with mixing tank 18 is one or more chemical injectors
indicated generally by the numeral 20. Chemical injectors 20
function to inject various chemicals into the mixing tank 18, which
are then mixed with the waste stream. Various chemicals can be
injected into the mixing tank depending on the make up of the waste
stream and what conditions are desired to be maintained throughout
the process, and objectives of the treatment. For example, it may
be desirable to control the pH throughout the process, and in that
case a caustic such as NaOH can be injected and mixed into the
waste stream. Other chemicals such as iron salts, necessary mineral
elements for optimal anaerobic production of biogas, for example,
can also be added if desired. In some embodiments the mixing tank
18 may be unnecessary. Here the chemical or chemicals could be
injected directly into a line or conduit through which the waste
stream passes.
[0017] The influent contained in the mixing tank 18 is directed to
a reactor feed pump 22. Reactor feed pump 22 pumps the waste stream
through a heat exchanger 24. Heat exchanger 24 is operatively
associated with a heat source 26 that provides a heating medium to
the heat exchanger for heating the waste stream passing through the
heat exchanger. In one embodiment, the heat source 26 is a heat
source that is independent of other processes performed by the
anaerobic membrane bioreactor 10. In one embodiment the permeate
produced by the system can be recirculated back through the heat
exchanger 24 to provide heat for heating the incoming waste stream.
Further, as explained subsequently herein, the anaerobic reactor 12
produces a biogas and the biogas can be utilized by the heat source
26 for heating the medium directed to the heat exchanger 24.
[0018] From the heat exchanger 24, the waste stream is directed
into the anaerobic reactor 12. Anaerobic reactor 12 is a closed
system designed to maintain anaerobic conditions within the
reactor. Anaerobic reactor 12 can be of various sizes and
capacities.
[0019] The waste stream introduced into anaerobic reactor 12 is
mixed with the existing material or matter in the reactor to form
mixed liquor. Generally, the biodegradable components in the waste
stream react with anaerobic biomass, including anaerobic (and
facultative) bacteria and methanogenic archea, and reduce the
amount of biodegradable solids contained within the reactor, and in
the process produce biogas and additional biological solids. The
term "mixed liquor" as used herein includes, but is not limited to,
a mixture of organic and inorganic solids, including biomass,
biodegradable and non biodegradable waste, water and biogas. The
mixed liquor may reside within the reactor or be fed into the
reactor as a recycled stream from the membrane system.
[0020] Anaerobic reactor 12 is designed to stratify the mixed
liquor. As seen in FIG. 1 the heavier solids occupy one region in
the anaerobic reactor, and fine or light solids occupy another
region in the anaerobic reactor. And in one region, the mixed
liquor is relatively free of at least the heavier solids or
includes a solids concentration that is measurably less than the
concentration of solids found in other regions or areas within the
reactor. More particularly, the reactor 12 is designed to stratify
the solids as follows. The relatively heavy and larger solids tend
to settle into a bottom portion of the reactor. The relatively
finer or lighter solids tend to float to the top portion of the
reactor. This leaves an intermediate or middle portion 40 of the
reactor that is measurably lower in solids, or at least includes a
solids concentration that is measurably less than the solids
concentration in the bottom portion of the anaerobic reactor.
[0021] Strategically placed in the anaerobic reactor 12 is a series
of mixers. First there is one or more mixers 30 located in the
bottom or lower portion of the reactor. Further there is one or
more mixers 32 located in the top or upper portion of the reactor
12. Thus, it is appreciated that in one embodiment, there are no
mixers located in the intermediate or middle region of the
anaerobic reactor. Mixing the mixed liquor in the lower and upper
portions of the reactor 12 improve and enhance reactions between
the anaerobically digestible components and the anaerobic biomass.
Furthermore, for example, the mixing in the upper portion of the
reactor prevents the solids from forming a blanket in the upper
portion of the reactor 12.
[0022] Mixers 30 and 32 provide a mixing action, resulting in the
bottom and top portion of the anaerobic reactor being completely
mixed. Various types of mixers can be used. In one embodiment the
mixers are what is referred to as sidewall mounted mixers. These
mixers project through the sidewall of the anaerobic reactor 12
with the propeller or mixing portion of the mixers being disposed
internally within the reactor 12. Mixers 30 and 32 are generally
uniformly spaced so as to provide a uniform mixing of the mixed
liquor in the top and bottom portions of the reactor. Although
mechanical mixers are discussed and shown in the drawings, other
types of conventional anaerobic reactor mixers can be used. For
example, mixing can be accomplished by gas injection, mechanical
streams, and mechanical pumps.
[0023] The depth and precise location of the stratified layers in
the anaerobic reactor 12 can vary. In the way of an example, assume
that the anaerobic reactor 12 is approximately 50 feet high. In
such a case the bottom mixers 30 could be centered at approximately
3 feet from the bottom of the anaerobic reactor. Upper mixers 32
could be centered at approximately 38 feet from the bottom of the
anaerobic reactor. In this case, at a height of 20 to 25 feet from
the bottom of the anaerobic reactor, at least a portion of the
intermediate or middle zone 40 would be located. Thus, in this
example, line 50, which feeds mixed liquor from the anaerobic
reactor 12 to the membrane separation unit 14, would be plumbed
into the wall of the anaerobic reactor 12 at an intermediate point
between 20 and 25 feet from the bottom of the anaerobic reactor. At
this point the mixed liquor pumped from the anaerobic reactor would
likely have a solids concentration less than the mixed liquor
disposed in the bottom of the reactor.
[0024] Digesting solids will produce biogas. Biogas produced in the
lower mixing zone will rise through the length of the reactor and
provide gentile low shear mixing of the mixed liquor in the
intermediate zone. Reactor 12 is provided with a biogas outlet that
can pass by the force created by the biological production of
biogas or can be enhanced through utilization of an exhaust blower
34 and a biogas outlet 36. Biogas outlet 36 leads to a flare or can
be directed to a boiler, generator, or other device that can use
the biogas to create usable energy.
[0025] As appreciated by those skilled in the art, the
anaerobically biodegradable material contained in the waste stream
is digested through reactions in the reactor 12 where anaerobic
(and facultative) bacteria and methanogenic archaea convert the
biodegradable material to biogas which is substantially made up of
methane and carbon dioxide and other lesser amounts of other
elements in gaseous form such as hydrogen sulfide. These gaseous
components are generally referred to herein as "biogas". Biogas may
also contain small amounts of water vapor, ammonia, and traces of
other volatile compounds which may be present in the waste stream
or form during biodegradation. Resulting composition of the biogas
by volume percent will vary depending on the particular digestible
organics being processed. Preferred methane levels in biogas formed
in the reactor 12 are in the range of about 50 to about 90 volume
percent. Preferred carbon dioxide levels are in the range of about
5 to about 45 percent (by volume) and hydrogen sulfide levels can
range from about 200 ppm (volume) to about 3 percent by volume.
[0026] Downstream from the anaerobic reactor 12 is the membrane
separation unit 14. Mixed liquor from the anaerobic reactor 12 is
directed to the membrane separation unit 14. In particular, the
mixed liquor is taken from the intermediate or middle zone 40 of
the anaerobic reactor. This means that the mixed liquor directed
from the anaerobic reactor 12 to the membrane separation unit 14
includes a solids concentration less than would typically be found
in the mixed liquor located in the bottom or top portion of the
anaerobic reactor 12. As seen in FIG. 1, line 50 is operatively
interconnected between the anaerobic reactor 12 and the membrane
separation unit 14 and serves to direct or channel mixed liquor
from the reactor to the membrane separation unit. Operatively
connected in line 50 is a membrane feed pump 52. Pump 52 pumps the
mixed liquor from the reactor 12 through line 50 to the membrane
separation unit. The membrane feed pump provides a baseline
pressure to the membrane separation unit. In one embodiment, the
membrane feed pump is replaced with a flow control valve where by
the gravitational force created by the liquid level in the reactor
provides the necessary baseline pressure to the membrane separation
unit. The membrane separation unit 14 is a continuously
recirculated hydraulic loop that includes the membrane modules, the
membrane recirculation pump referred to as pump 54, and required
membrane performance controls. The membrane recirculation pump 54
pumps the mixed liquor in a constant recirculation loop around the
membrane separation unit 14 to provide necessary cross-flow
velocity.
[0027] Basically the membrane separation unit 14 filters or
separates the mixed liquor into two streams, a permeate stream that
is directed from the membrane separation unit 14 through a permeate
line 60, and a retentate stream that is directed from a membrane
separation unit through a retentate line 62. Note that retentate
line 62 is also a recycle line as it recycles the retentate stream
back to line 50 just upstream of membrane feed pump 54. This
permits membrane feed pump 54 to continuously recycle the retentate
stream through the membrane separation unit.
[0028] At least a portion of the retentate stream is returned to
the anaerobic reactor 12 and mixed with the mixed liquor therein.
To return a portion of the retentate stream to the anaerobic
reactor 12 there is provided a return line 64. Thus, as noted
above, a portion of the retentate stream is taken off the recycle
line 62 and returned via reactor recirculation pump 66 to the
anaerobic reactor 12. In one embodiment, pump 66 is replaced with a
flow control valve and the force required to return mixed liquor to
the reactor is provided by the membrane feed pump, pump 52.
[0029] Membrane separation unit 14 retains all or substantially all
suspended solids, thus, all or substantially all suspended solids
are recycled back to the anaerobic reactor. Various types of
membrane separation units 14 can be employed.
[0030] With reference to FIG. 2, a schematic illustration is shown
therein for an exemplary membrane separation unit 14. It is
appreciated by those skilled in the art that various types of
conventional membrane filtration devices can be employed. FIG. 2
illustrates one exemplary membrane filtration unit which can be
used as a part of the anaerobic membrane bioreactor 10. In the case
of the membrane filtration unit 14 shown in FIG. 2, the same is a
sidestream system inasmuch as the membranes are located outside of
the anaerobic reactor 12. In the exemplary membrane filtration unit
14, there is provided a series of cross flow membrane modules 14A.
The number of membrane modules 14A can vary depending on the makeup
of the feedwater and treatment objectives. Membrane modules 14A are
connected in series in this example. Each membrane module 14A
includes an elongated housing with tubular membranes contained
therein. As noted above, the membranes of this example are
tubular-type membranes that extend longitudinally through the
housing of each membrane module 14A. Effluent from the reactor 12
is directed into the individual tubular membranes under pressure.
As the feed or mixed liquor from the anaerobic reactor 12 passes
through the individual membranes, a permeate will be produced and
the permeate will flow outwardly, in a cross flow direction
relative to the feed. The permeate in each membrane module 14A will
be collected and directed out a permeate outlet 14C provided on
each membrane module 14A. Retentate is directed out a retentate
outlet 14B disposed on one end of each module 14A. Respective
retentate outlets and retentate inlets are interconnected by
connecting lines 14E. This allows the retentate from one membrane
module 14A to be directed into another downstream membrane module
14A. Thus, as seen in FIG. 2, the respective membrane modules 14A
are either singular or multiple units connected in series such that
the retentate flows linearly through the singular or series of
connected membrane modules 14A.
[0031] The retentate exiting the last membrane module 14A is
directed into a final outlet line 14F that is connected to the
retentate line 62 shown in FIG. 1. This enables the retentate to be
recycled back to the inlet of the membrane filtration unit 14 or
back to the reactor 12. In one embodiment, there is a substantial
amount of the retentate from the membrane filtration unit 14
recycled back to the inlet of the membrane filtration unit.
[0032] In addition, the final outlet line 14F is communicatively
connected to a cleaning line 90 that leads to a clean-in-place
(CIP) unit 92. The clean-in-place unit 92 is a system or unit that
is operative to periodically, or from time-to-time, clean the
membrane filtration unit 14 by backwashing the respective membranes
that make up the unit. Various membrane cleaning systems can be
employed. Here the clean-in-place unit 92 is designed to utilize
the retentate or retentate from the membrane filtration unit 14 to
backwash and clean the respective membranes of the membrane
filtration unit. Details of the clean-in-place unit 92 are not
dealt with here in detail because such systems or units and how
they operate are well known and appreciated by those skilled in the
art.
[0033] The anaerobic membrane bioreactor 10 also includes a system
and process for removing solids from the anaerobic reactor 12. More
particularly, there is a solids separation process that includes a
solids separator 74 such as a hydrocyclone separator. The solids
separator is designed to preferentially separate heavy solids which
include a relatively high percentage of inorganic precipitants,
from the lighter solids which include a relatively high
concentration of biomass. As noted above, solids are removed from
the anaerobic reactor 12 in order to maintain or control SRT. In
addition, there can be a substantial buildup of heavy inorganic
solids within the anaerobic reactor 12 and these solids can be
removed by directing them from the anaerobic reactor to a solids
separator. In any event, there are various ways of removing solids
from the anaerobic membrane bioreactor 10. For example, in one
embodiment, solids can simply be wasted from the anaerobic reactor
12 in conventional fashion. In another example, solids can be
removed from the retentate stream leaving the membrane separation
unit. In this case a selected or controlled amount of the retentate
stream can be directed to a solids separator. In the embodiment
illustrated herein, solids are pumped from the lower portion of the
anaerobic reactor 12 to a solids separator, which in the case of
the example illustrated, is a hydrocyclone 74. In this regard, line
70 is operatively connected to the anaerobic reactor 12 and
includes a pump 72. Line 70 and pump 72 are operatively connected
to the solids separator 74 for directing mixed liquor including
solids to the solids separator. Note that line 70 is connected to
the reactor 12 such that mixed liquor is pulled from the bottom
portion of the reactor 12. This, as explained above, is where the
heavier solids are contained. In any event, the mixed liquor is
pumped from the bottom portion of the reactor 12 through line 70
into the solids separator 74. Solids separator 74 produces an
underflow which comprises solids that are heavier in nature and an
overflow which comprises solids which are lighter in nature than
the underflow. The overflow is pumped or fed through an overflow
line 78 back to the anaerobic reactor 12 where it is mixed with the
mixed liquor therein. The underflow or heavier solids produced by
the solids separator or hydrocyclone 74 is directed through
underflow line 76 for further treatment. For example, the heavier
solids produced in the underflow can be directed to a dewatering
unit for dewatering and further concentration.
[0034] The solids removal process just described with respect to
the solids separator 74 can be operated in parallel with the
membrane separation unit 14. In some instances, the solids removal
process may be operated continuously while the membrane separation
unit 14 is filtering mixed liquor from the reactor 12. In other
cases the solids removal process may be operated intermittently in
order to maintain a selected SRT. The SRT can vary depending on
circumstances, and conditions. It is contemplated that the SRT for
the embodiments illustrated and discussed herein can range from
approximately 15 to approximately 80 days.
[0035] The solids separator 74 is not an essential component of the
present invention. There are situations when the solids separator
74 is not required. More particularly, the solids separator 74 and
the process of removing solids from the bottom portion of the
anaerobic reactor 12 is useful when the influent stream or the
feedwater stream includes a substantial amount of dissolved solids
that precipitate when undergoing treatment in the process of the
present invention. Some feedwater streams will not include
substantial dissolved solids that will precipitate and in those
cases the solids separation process utilizing the solids separator
74 may not be a requirement in the process of the present
invention.
[0036] For a more detailed understanding of anaerobic reactors and
the process of anaerobic digestion, reference is made to the
disclosures found in U.S. Publication No. 2002/0192809 and U.S.
Publication No. 2008/0302721, the disclosures of which are
expressly incorporated herein by reference.
[0037] The present invention may, of course, be carried out in
other ways than those specifically set forth herein without
departing from essential characteristics of the invention. The
present embodiments are to be considered in all respects as
illustrative and not restrictive, and all changes coming within the
meaning and equivalency range of the appended claims are intended
to be embraced therein.
* * * * *