U.S. patent application number 11/252391 was filed with the patent office on 2006-08-10 for method for biosolid disposal and methane generation.
Invention is credited to Roman Bilak, Michael S. Bruno, Maurice B. Dusseault.
Application Number | 20060178547 11/252391 |
Document ID | / |
Family ID | 27383014 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060178547 |
Kind Code |
A9 |
Bruno; Michael S. ; et
al. |
August 10, 2006 |
Method for biosolid disposal and methane generation
Abstract
A method for the disposal of biosolids, the method comprising a
step for providing a supply of biosolids and a step for disposing
of the supply of biosolids.
Inventors: |
Bruno; Michael S.;
(Monrovia, CA) ; Bilak; Roman; (Calgary, CA)
; Dusseault; Maurice B.; (Osoyoos, CA) |
Correspondence
Address: |
SHELDON & MAK, INC
225 SOUTH LAKE AVENUE
9TH FLOOR
PASADENA
CA
91101
US
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20060084833 A1 |
April 20, 2006 |
|
|
Family ID: |
27383014 |
Appl. No.: |
11/252391 |
Filed: |
October 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10294218 |
Nov 13, 2002 |
6962561 |
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11252391 |
Oct 17, 2005 |
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10123828 |
Apr 15, 2002 |
6491616 |
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10294218 |
Nov 13, 2002 |
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09917417 |
Jul 27, 2001 |
6409650 |
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10123828 |
Apr 15, 2002 |
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09620085 |
Jul 20, 2000 |
6287248 |
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09917417 |
Jul 27, 2001 |
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60150677 |
Aug 25, 1999 |
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Current U.S.
Class: |
588/250 ;
405/129.25; 405/129.35; 405/129.45; 588/254; 588/260 |
Current CPC
Class: |
Y02E 50/30 20130101;
E21B 41/0064 20130101; C02F 11/04 20130101; C12M 21/04 20130101;
C12M 23/36 20130101; C12M 29/00 20130101; C12M 23/18 20130101; E21B
41/0057 20130101; B09B 1/008 20130101; Y02C 10/14 20130101; Y02C
20/40 20200801; C12P 5/023 20130101; Y02E 50/343 20130101 |
Class at
Publication: |
588/250 ;
588/254; 588/260; 405/129.25; 405/129.35; 405/129.45 |
International
Class: |
B09B 3/00 20060101
B09B003/00; A62D 3/00 20060101 A62D003/00 |
Claims
1. A method for the disposal of biosolids, the method comprising:
a) a step for providing a supply of biosolids; and b) a step for
disposing of the supply of biosolids.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/294,218 titled "Method for Biosolid
Disposal and Methane Generation," filed Nov. 13, 2002; which is a
continuation-in-part of U.S. patent application Ser. No. 10/123,828
titled "Method for Biosolid Disposal and Methane Generation" filed
Apr. 15, 2002; which is a continuation of U.S. patent application
Ser. No. 09/917,417 titled "Method for Biosolid Disposal and
Methane Generation" filed Jul. 27, 2001, now United States patent
U.S. Pat. No. 6,409,650 B1, issued Jun. 25, 2002; which is a
continuation-in-part of U.S. patent application Ser. No. 09/620,085
titled "Method for Biosolid Disposal and Methane Generation," filed
Jul. 20, 2000, now U.S. Pat. No. 6,287,248, issued Sep. 11, 2001;
which claims the benefit of U.S. Provisional Patent Application No.
60/150,677 titled "Method for Municipal Waste Disposal and Recovery
of Byproducts," filed Aug. 25, 1999; the contents of each of which
are hereby incorporated herein by reference in their entirety.
BACKGROUND
[0002] Over 10 million tons of biosolids from municipal sewage
sludge are generated each year in the United States alone. The
prevailing methods for the disposal of biosolids include the
application of the biosolids to surface land application, such as
to crop land, range land or forests, composting and landfill
disposal. Each of these methods is associated with
disadvantages.
[0003] For example, one disadvantage of the application of
biosolids to surface lands is the resistance of persons living in
the area of the application because of concerns about nuisances
such as odor and wind-blown dust from the site of application.
Biosolids application to surface land and landfills also creates
risks for contamination of potable surface water and
groundwater.
[0004] Further, disadvantageous weather conditions can delay the
application of biosolids to surface land, and trucking biosolids to
the application site creates pollution and nuisances. Additionally,
the capacity for the disposal of biosolids by application to
surface lands and landfills is limited and the associated costs are
generally high. Also, greenhouse gasses, such as methane and carbon
dioxide, are generated by the decomposition of the biosolids and
these gases are released into the atmosphere at the sites of
surface land application and most landfills.
[0005] Therefore, there is a need for an additional method for the
disposal of biosolids that provides less risk for environmental
contamination. Additionally, there is a need for an additional
method for the disposal of biosolids that is less expensive.
Further, there is a need for an additional method for the disposal
of biosolids that does not permit the release of carbon dioxide and
other green house gases into the atmosphere. Also, there is a need
for an additional method for the disposal of biosolids that can
produce usable byproducts from biosolids.
SUMMARY
[0006] According to one embodiment of the present invention, there
is provided a method for the disposal of biosolids. The method
comprises a) a step for providing a supply of biosolids and b) a
step for disposing of the supply of biosolids, providing a supply
of biosolids.
FIGURES
[0007] The features, aspects and advantages of the present
invention will become better understood with regard to the
following description, appended claims and accompanying figures
where:
[0008] FIG. 1 is a schematic diagram of one embodiment of the
method for the disposal of biosolids according to the present
invention.
DESCRIPTION
[0009] In one embodiment, the present invention is a method for the
disposal of solids, such as biosolids, comprising injecting the
biosolids into deep underground formations. The introduced
biosolids are then allowed to undergo biodegradation, using the
natural geothermal heat in the deep subsurface. Biodegradation
produces carbon dioxide, sulfur dioxide, hydrogen sulfide, methane
and other gases. The generated carbon dioxide is absorbed by
formation waters because it is highly soluble in water, and more
soluble than methane. The residue from the biodegradation is a
carbon-rich solid material that becomes permanently sequestered in
the underground formation.
[0010] In a preferred embodiment, methane generated by the
degrading biosolids is removed for conversion into usable energy,
or storage for subsequent use. In another preferred embodiment, the
rate of biodegradation is increased or the rate of methane
production is increased or the rate of carbon dioxide or other
undesirable degradation products is decreased by altering
environmental conditions in the formation or by adding substances
or bacteria, or by adjusting the biochemical properties of the
biosolids that are introduced into the formation. The present
method provides significant cost savings and environmental benefits
over current technologies for the disposal of biosolids.
[0011] As used in this disclosure, the term "biosolids" is defined
as solid particles of matter that are dominantly comprised of
organic material by weight.
[0012] The method of the present invention will now be discussed in
greater detail. First, a suitable supply of biosolids is provided.
In a preferred embodiment, the biosolids have sufficient
concentration of biodegradable organic matter to generate
exploitable quantities of methane. It is not necessary that all the
wastes be biodegradable or even organic as other solid components
of the introduced biosolids will become permanently entombed in the
introduction formation.
[0013] In a preferred embodiment, the biosolids disposed of by the
present method will be derived from municipal sewage or waste water
treatment wastes, such as produced by a major metropolitan area.
Municipal sewage wastes comprise human biowastes, household scraps,
sanitary paper products and other biological components, as well as
mineral matter and small amounts of chemical products, such as
solvents, acids, alkalies and heavy metals, introduced into the
waste stream through the municipal sewer system such as solvents,
acids, alkalies and heavy metals.
[0014] Another suitable source of the biosolids is animal wastes
from sites where the animals are raised or housed. The animal
wastes can be mixed with other organic materials such as sawdust or
straw, or it may be mixed with mineral wastes. Still other suitable
sources of biosolids are pulp and paper mill sludges, waste oil
products including greases and waxes, and wastes which are rich in
organic debris dredged from harbors or estuaries.
[0015] After providing a suitable supply of biosolids, a suitable
underground formation, designated the "introduction formation" in
this disclosure, is selected below a suitable ground surface
introduction site. Preferably, the formation is a high porosity,
high permeability sand formation, significantly below usable
groundwater, if present. In a particularly preferred embodiment,
the porosity is greater than about 15%. In a particularly preferred
embodiment, the introduction formation is below any groundwater
which could be removed for human use and below multiple, thick and
clearly defined layers of alternating low permeability, fluid flow
barriers and high permeability fluid absorption zones. The high
permeability layers will preferably be sand of high porosity. The
low permeability layers will preferably comprise shales and other
rocks containing clay minerals that have absorptive capacity. In a
preferred embodiment, there should be at least two alternating
layers of high permeability and low permeability separating any
usable groundwater, if present, and the deeper introduction
formation. In a particularly preferred embodiment, there should be
at least five alternating layers of high permeability and low
permeability separating any usable groundwater, if present, and the
deeper introduction formation.
[0016] The total available storage volume of an introduction
formation can be calculated based on the approximate average
thickness and area of the introduction formation, the average
porosity of the introduction formation and the mechanical
compressibility of the introduction formation, as will be
understood by those with skill in the art with reference to this
disclosure.
[0017] In another preferred embodiment, the introduction formation
will be at least about 100 m below the ground surface. This depth
is generally deep enough to insure that the introduced biosolids
will be sequestered, even without thick and clearly defined layers
of alternating low permeability, fluid flow barriers and high
permeability fluid absorption zones specific, and deep enough to
ensure that the introduced biosolids will not pose a potential
threat to the environment or to water supplies, and near enough to
the surface to allow biosolids introduction in a cost-effective
manner. In a particularly preferred embodiment, the introduction
formation is between about 500 m and about 3000 m below the ground
surface.
[0018] The introduction site typically requires less than 10,000
m.sup.2 of surface land, unlike the larger areas required for
surface landfills. Further, use of the surface land itself
according the present method is only temporary, and after the
disposal activity is complete, the surface land can be returned to
other uses.
[0019] The introduction site and introduction formation for use in
the present method should be selected to additionally protect
ground and ocean waters by properly selecting an appropriate
geological interval which does not outcrop or interact with near
surface formations. Geochemical analysis of formation fluids can be
used to verify that particular introduction formations contain only
ancient fluids and are not in communication with shallower water
sources.
[0020] It is also preferred that the selected introduction
formation has pre-existing natural gas because this implies that
the introduction formation is overlain by a suitable methane
accumulation zone and is capped by an unfractured layer of
relatively low permeability so as to inhibit further upward methane
movement. This configuration allows for accumulation of gases
generated by degradation of the biosolids and removal of the gases
for use as a fuel.
[0021] It is further preferred that introduction sites selected for
use with the present method have existing gas collection and
measurement infrastructure, and long histories of contained
introduction operations. For example, preferred introduction
formations include oil and gas trapping anticlines which over
geologic time have proven to be completely isolated.
[0022] The overlying low permeability layers, when present, above
the preferred introduction formation provide a permeability barrier
to upward migration, as can be evidenced by historical oil/water
accumulations, where the oil migrates upward until it is impeded by
a permeability barrier. The at least one additional overlying high
permeability layer acts as a fluid flow sink in the unlikely event
of a well casing cement failure or a breach of a low permeability
layer.
[0023] For example, if the well casing cement fails or a low
permeability layer is breached and fluid migrates above the low
permeability layer, the high permeability layer immediately above
absorbs the excess pressure and migrating fluid. Pressure will then
decline slightly in the introduction formation and increase in the
overlying layer. These pressure changes and fluid migration can be
identified by monitors located in both zones, and periodic wellbore
tracer surveys. Further groundward migration of the waste material
will not occur unless the second higher high permeability layer
also becomes highly pressurized. For material to migrate upwards
from the introduction formation, the process of breach and
absorption in the layers above the introduction formation would
have to be repeated for each set of high permeability and low
permeability layers above the introduction formation.
[0024] As an example, a suitable underground formation for
introduction of biosolids according to the present invention would
be a 100 m thick, unconsolidated sandstone formation lying between
1000 m and 3000 m below the ground surface, where the sands are
poorly sorted and range in texture from very fine to coarse
grained. An approximately 300 m thickness low permeability
formation material would be present in the 1,000 m interval
immediately above the introduction formation, which are interbedded
with high permeability formations providing additional geologic
barriers and safety zones and which could be easily monitored.
[0025] The introduction formation would have been used as a gas
storage field for at least ten years, the geology of the area would
be well characterized and injectivity into the introduction
formation would have been established. A nearby well would
preferably be present which could be used as an observation well
for monitoring purposes. Further preferably, there would be no
groundwater extraction wells in the area and groundwater would be
regularly and extensively monitored.
[0026] In another preferred embodiment, the present invention
includes creating and maintaining fractures within the selected
introduction formation by the introduction of the waste under high
pressure, such as parting pressure, as will be understood by those
with skill in the art with reference to this disclosure.
[0027] After selection of a suitable introduction formation and
introduction site, the introduction equipment and associated
facilities are located in an area adjacent to the introduction
site. Introduction equipment preferably occupies a surface area of
10,000 m.sup.2 or less, with no additional surface construction or
road work required.
[0028] The preferred biosolids introduction apparatuses should be
environmentally secure in the handling of waste material. Further
preferably, they should be able to screen waste streams on a
continuous basis to avoid introduction of any oversize material
into the wellbore that could lead to blockage, as well as to
monitor and register introduction parameters such as rate, total
volumes, pressure, density and temperature in real-time.
[0029] Suitable cased and perforated wells are prepared or existing
wells modified and extended into the introduction formation, and
into the methane accumulation zone if desired. All wells used in
the present method are designed to seal against fluid and gas
migration and are periodically tested to ensure that migration is
not taking place. The capacity for each well is preferably in the
range of 500 to 2000 m.sup.3 per day of biosolids. By selecting
multiple deep introduction targets, and alternating between
multiple wells and intervals, a single site can provide large-scale
biosolids management capacity for many years.
[0030] In a preferred embodiment, each well used in the present
invention has several layers of protection. An outer steel casing
(called the surface casing) extends from the surface to the
lowermost depth of any usable groundwater. This steel casing is
surrounded by cement. One or more additional steel casing strings
(called the production casing) extends from the surface to the
depth of the selected introduction formation. This casing is also
surrounded by cement.
[0031] The biosolids to be disposed are pumped down a steel tubing
past a packer located at an appropriate depth, for example, a depth
of about 1,500 m to 2,000 m. Outside the tubing is an annular
region filled with fluid. The pressure of this fluid will be
constantly monitored to immediately detect any leak in the tubing.
If material introduced down the tubing does leak into the annular
region, the material is still contained within an outer steel
casing, which is in turn surrounded by a cement sheath.
[0032] After selection of a suitable introduction formation and
preparation of the introduction site, the biosolids are transported
to the introduction site. The transport can be by road-based
transport. In a preferred embodiment, however, the biosolids are
transported by pipe from the source directly to the introduction
site, which is located as close to the source of material as
practical.
[0033] In a preferred embodiment, a biosolids mixture is designed
to generate methane efficiently under the conditions present in the
selected introduction formation. This is accomplished by measuring
the chemical and biological properties of the available biosolids
stream, the physical conditions in the target stratum, and
adjusting the physical and chemical properties of the biosolids to
achieve efficient methane generation.
[0034] After the biosolids are introduced into the introduction
formation and locked in by the natural stresses present in the
introduction formation and the low permeability zones immediately
above the introduction formation, the introduced material is
allowed to undergo degradation under anaerobic conditions. Given a
solids mixture undergoing anaerobic digestion, an estimate of
degradation can be obtained from first order kinetics:
W=W.sub.0e.sup.-kt (1) where W=mass of volatile introduced solids
that have not degraded after time t, W.sub.0=mass of solids
deposited, k=decay coefficient, and t=time. In general the value of
k will depend on a variety of factors including pH, temperature,
salinity, mixing amount, and to some extent the concentration of
solids. Typical values for the exponent k are on the order of
10.sup.-3, yielding a value for W of between 40-60% degradation per
year. For continuous introduction, the amount of material remaining
after some time t is determined by integration of equation 1. The
mass of gas produced will in general be equal to the amount of
volatile introduced solids 5 degraded and is typically composed
mainly of methane (50-60%), carbon dioxide (30-40%), nitrogen, and
hydrogen.
[0035] In addition to the mechanical protection provided by the
introduction well design, and the natural protection provided by
the selection of an appropriate introduction formation with
multiple overlying barrier and buffer zones, the present method
preferably includes a continuous real-time recording and display of
pressure response in the introduction zone, in the first overlying
high permeability zone, as well as in the wellbore annulus, to
ensure containment of biosolids in the introduction formation. Any
breach or deviation from anticipated introduction behavior will be
noted while material is still far below the groundwater, allowing
immediate remedial action. Additional process monitoring can
include several types such as pressure recording and analysis,
temperature recordings, surface deformation measurements and
analysis, and microseismic monitoring, such as monitoring pressure
in one or more than one of the alternating layers of high
permeability and low permeability above the introduction formation
during a time selected from the group consisting of before
biosolids introduction, during biosolids introduction, after
biosolids introduction and a combination of before biosolids
introduction, during biosolids introduction and after biosolids
introduction, as will be understood by those with skill in the art
with reference to this disclosure. The monitoring is preferably
performed at several depths below the groundwater base.
[0036] Preferably, fluid introduction into the introduction
formation is episodic in order to facilitate the monitoring of
formation behavior. Bottom-hole pressure in the introduction
formation is preferably monitored continuously during daily
introduction and nightly shut-in. This pressure information is
analyzed to evaluate changing formation flow and mechanical
properties and injectivity, and to determine formation parting
pressure and material containment, as will be understood by those
with skill in the art with reference to this disclosure. Additional
biosolids will not be introduced if pressure in the introduction
formation remains abnormally high. As will be understood by those
with skill in the art, in order for fluid to migrate out of the
introduction formation, a breach must occur and the pressure in the
introduction formation must be higher than the pressure in an
adjacent formation. In addition to the continuous pressure
monitoring and analysis, the present method preferably includes
shutting down the introduction well periodically to perform
extensive well tests, tracer surveys and introduction formation
tests to evaluate well integrity and hydraulic isolation in the
near wellbore area.
[0037] In another preferred embodiment, the present method includes
recovering the methane generated from the degradation of the
introduced biosolids. The methane can then be used as a clean fuel.
Alternatively, the methane produced can be left underground as a
stored supply of future energy. Recovery of the methane is
preferably done by injecting the biosolids into an appropriate
geologic formation with a trapping mechanism. Preferably, the
biosolids are introduced downdip below the water-oil or water-gas
contact in a geologic formation. The generated methane and carbon
dioxide will then migrate upwards due to gravity segregation.
[0038] Methane and carbon dioxide produced by the degradation of
biosolids according to the present invention will percolate through
formation water where much of the carbon dioxide will be
sequestered underground by dissolution in the saline formation
water, and where the high quality methane will accumulate in the
gas trap. The difference in sequestration is due to the much higher
solubility of carbon dioxide in water relative to methane (a ratio
of at least 10:1) at temperature and pressure conditions typical
for deep geologic formations. Methane, in particular, is a potent
greenhouse gas. By injecting biosolids into the deep subsurface,
gas release to the atmosphere is eliminated and carbon is
permanently sequestered in deep saline formations.
[0039] Recovered methane from deep introduction formations used
according to the present invention is of higher quality than that
generated in surface digesters or from surface landfills for two
reasons. First, by percolating through formation waters in the
introduction formation, the carbon dioxide component of the
generated gases will be significantly absorbed due to the much
higher solubility of carbon dioxide relative to methane. Second,
the methane generated according to the present invention is at
higher pressure than methane generated by surface landfills and
requires less compression for storage or use.
[0040] As can be appreciated, once the introduction formation is
filled and the methane extracted, if desired, the equipment used
for introduction of biosolids and recovery of methane can be
removed and the site abandoned. This returns the surface land to
the condition it was in previously and leaves the site
unimpaired.
[0041] In a preferred embodiment, the present method includes
increasing the rate of biodegradation of the introduced biosolids.
This is done by altering environmental conditions in the
introduction formation or by adding substances or bacteria, or by
adjusting the biochemical properties of the biosolids that are
introduced into the formation, or by a combination of these
actions, to optimize the biodegradation process. In another
preferred embodiment, the present method includes decreasing the
rate of production of undesirable products such as carbon dioxide,
sulfur dioxide and hydrogen sulfide.
[0042] For example, the rate of biodegradation can be increased by
adjusting the temperature and salinity of the biosolids so that the
resulting physical properties of the biosolids in the subsurface
provides an optimum environment for biodegradation, given the
species of bacteria present in the biosolids and native to the
introduction formation. In another preferred embodiment,
biodegradation rates can be increased by adding appropriate natural
or genetically engineered bacteria to the biosolids prior to
introduction, or after introduction. The inoculation can be used to
increase the decomposition rate of the biosolids into methane under
the specific temperature and pressure conditions at the
introduction formation depth, or to inhibit the production of
undesirable decomposition products, such as carbon dioxide, sulfur
dioxide and hydrogen sulfide. Further, nutrients and other chemical
or organic agents, such as those that alter acidity, pH, or
oxidation potential, Eh, can be added to the biosolids for the same
purposes.
[0043] For example, bacteria that are relied upon to promote
biodegradation of the introduced biosolids can have high potassium
requirements. Extrinsic potassium, such as soluble salt potassium
chloride (KCl), can be added to an introduced biosolids to promote
bacterial growth.
[0044] In general, it is preferred that chemicals added to the
introduced biosolids be only weakly soluble in water or insoluble
so that any added chemical is not removed during the water
expulsion that accompanies compaction of the introduced material in
the formation. A suitable source of potassium for addition to the
biosolids, therefore, would be finely ground potash feldspar which
contains potassium that is slowly liberated in situ under the
influence of aqueous exposure, high temperatures and bacterial
action.
[0045] For example, biodegradation in an introduction formation can
be limited by the supply of phosphorous present in one introduced
biosolids. In order to improve biodegradation, a second waste
stream rich in phosphorous can be blended with the first waste
stream or introduced separately, either simultaneously or
alternating with the first biosolids. For example, a waste source
rich in phosphorous can come from a chemical plant or from
phosphorus-rich gypsum wastes ("phospho-gyp").
[0046] In another example, some waste streams contain sterile
biosolids due to their alkalinity, such as waste streams from paper
production facilities. In order to promote bacterial degradation of
the wastes, a second waste stream which is acidic can be blended
with the first stream to adjust the pH of the streams to promote
bacterial degradation of the introduced biosolids.
[0047] In yet another example, natural or genetically engineered
bacteria can be added to the introduced biosolids to improve
degradation. In a preferred embodiment, the bacteria added are
anaerobic species because of the low concentration of oxygen in the
introduction formations used in the present invention. In a
particularly preferred embodiment, the bacteria are
methanogenic.
[0048] Additionally, a plurality of biosolids having different
compositions can be blended together to maximize biosolid
degradation in the introduction formation, or to maximize the rate
and quantity of methane generation, or to decrease the rate and
quantity of generation of less desirable decomposition products
such as carbon dioxide, sulfur dioxide or hydrogen sulfide. For
example, a source of animal waste that is rich in organic material
can be blended with a source of waste materia such as a pulp
residue, sawdust from a plywood mill, thermally treated wastes, or
other waste that is less rich in organic material, and that is also
sterile. The two waste streams are blended in the optimum
proportions, as will be understood by those with skill in the art,
with reference to knowledge of the in situ conditions at the
introduction formation and with reference to this disclosure.
[0049] The temperature in the introduction formations used in the
present invention can vary from 25.degree. C. (e.g., 1 km deep
introduction formation in Montana, US) to 100.degree. C. (3 km deep
introduction formation in West-Central California, US). However,
suitable thermophilic bacteria can be used with introduction
formations having considerably higher temperatures. Pressure also
varies at the introduction formation depths anticipated by the
present invention, such as from about 10 MPA at a depth of 1 km
depth to about 40 MPa at depths of between about 3 to 4 km.
Therefore, bacteria added to the biosolids must be chosen to be
suitable to the temperature and pressures that will be encountered
in a specific introduction formation.
[0050] The method for the disposal of biosolids, according to the
present invention, therefore, has several advantages over the
currently used techniques. First, the present method reduces the
potential and real impact on surface waters and groundwater that
can be associated with surface application of biosolids, because
the biosolids are introduced significantly below any usable source
of groundwater. Second, the present method requires significantly
less surface land area than land application for disposal of an
equivalent volume of biosolids. Third, the present method does not
permanently alter the surface land after the disposal at the site
is completed. Fourth, because the biosolids can be pumped to local
sites for disposal, the present method significantly reduces or
eliminates truck traffic to distant disposal sites and, therefore,
reduces the noise and environmental contamination associated with
heavy truck traffic.
[0051] Fifth, the present method reduces the amount of methane and
carbon dioxide released into the atmosphere as compared to surface
application of biosolids. Sixth, methane produced by the
degradation of biosolids according to the present method can be
collected for use as an energy source. Seventh, biosolids disposal
according to the present method can reduce the cost of biosolids
management significantly compared with conventional surface
application methods due to the reduced or eliminated need for
trucking the biosolids to a distance site for disposal.
[0052] Referring now to FIG. 1, there is shown a schematic diagram
of one embodiment of the method for the disposal of biosolids
according to the present invention. A1 represents the surface
facilities (storage, sizing, screening, mixing, blending, process
monitoring and pumping equipment) for the formulation of suitable
biosolids mixtures for introduction into an introduction
formation.
[0053] A2 represents the introduction well (or one introduction
well in an array of introduction wells) that is cased and cemented
in such a manner so as to withstand the introduction pressures
implemented over the life of the facility.
[0054] A3 represents the introduced biosolids that has been placed
and has rapidly, through excess water expulsion, become solidified
by the great weight of the overburden rocks. After all the methane
possible has been generated by the biodegradation process, A3
becomes a dense and relatively low permeability stratum that is
rich in carbon and other organic molecules that were not
biodegradable at the conditions in the introduction formation. The
sequestered carbon and other organic molecules will not enter the
atmosphere creating greenhouse effects.
[0055] A4 represents the introduction formation into which the
biosolids, A3, was introduced. A4 is of sufficient porosity and
permeability as to accommodate the excess biosolids fluids without
long-term pressure build-up or interaction with shallow, usable
groundwaters. In general, the stratum A4 will be chosen as a
laterally continuous stratum of sufficient pore volume and flow
path connectivity with adjacent strata to take all the water
expelled from the biosolids during the compaction process.
[0056] A5 represents the evolution and upward movement path of the
methane generated by the biodegradation process. Such movement
occurs naturally because the methane is of a specific gravity that
is far less than that of any interstitial water, and therefore
tends to rise through the porous medium, displacing liquid from the
pores.
[0057] A6 represents the porous and permeable strata where the
methane collects through the upward migration and pore liquid
displacement process, and from which strata the generated methane
can be extracted for use. This zone, A6, is a "trap" for the
evolved methane because of a suitable geological structure, which
can be in the form of structural closure with folded beds that form
an inverted bowl, as shown, or can be in the form of a change of
rock type, not shown, in a combination of the two, or in some other
suitable disposition of permeable and low-permeability strata.
[0058] A7 represents the rocks overlying the introduction formation
that are of sufficiently low permeability that gas cannot flow
upward through the pore space. Also, the overlying rocks A7 are
non-fractured, or are minimally fractured so that the methane
cannot escape to strata of higher elevation.
[0059] A8 represents one or more conventional gas wells that
extract the methane from the accumulation site A6. The gas wells,
A8, either exist at the site before the disposal operation begins
or are specifically installed as cased, cemented wells, perforated
so that the gas can flow into the wellbore. Depending on the
configuration of the strata, the methane extraction wells A8 may be
vertical, horizontal or inclined.
[0060] A9 represents a surface facility for power generation that
can use the extracted methane as a clean energy source.
Alternately, the extracted methane can be shipped directly to
consumers for home use or industrial users for other purposes.
[0061] Although the present invention has been discussed in
considerable detail with reference to certain preferred
embodiments, other embodiments are possible. For example, the
method of the present invention can be applied to the disposal of
solids other than biosolids. Therefore, the scope of the appended
claims should not be limited to the description of preferred
embodiments contained in this disclosure.
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