Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to novel compositions and
methods for use in stabilizing liquid or semiliquld waste material,
particularly materials that are classified as organic sludges.
The problems involved in organic sludge disposal
and in organic sludge containing hazardous waste disposal are
numerous, including site selection, handling, shipment, and
ultimate storage. Prior to the present invention, the methods
and manner of treating organic sludges have been costly, dangerous,
and often times ineffective.
The present invention provides method and means for
solidifying organic sludges to a soil-like consistency. Such
alteration of the sludge has a number of beneficial effects.
The sludge can be handled with conventions earth-movlng equipment
resulting in enormous savings to an organic sludge disposal
operation; it allows the sludge (after being cured) to be compacted
to densities that show very low water permeability and high
stability, thus minimizing the danger of leaching that could
lead to contamination of ground water and also minimizing the
danger of run-off after the waste ha been permanently sited;
it permits the treated waste to be shaped to an overall uniform
thickness with a built-in desired gradient without the danger
of settling or distortion after shaping, thus facilitating
the use of normal remedial programs including the use of con-
ventional liner and capping technologies, uncle again resulting
in enormous savings to an organic sludge disposal operation;
and it allows the treated sludge, if need be, to be easily
transported to more suitable landfill sites.
It is therefore an object of the present invention
to stabilize organic sludges in an ecologically and economically
feasible manner.
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It it a further object of the invention to stabilize
organic sludges in a manner permitting them to be handled with
conventional waste-handling equipment.
Another object of the invention it to stabilize organic
sludges to a soil-like consistency.
Another object of the invention it to convert organic
sludges to a stabilized solid form having low water permeability.
A further object of the invention it to stabilize
organic sludge in a form which can be moved and Reaped to an
overall uniform thickness with a built-in desired gradient,
without danger of settling or distortion after shaping, thus
facilitating the use of normal remedial programs including
conventional liner and capping technology.
An additional object of the invention is to stabilize
organic sludge while minimizing the volume thereof.
It it Bill another object of the invention to eta-
Bills organic sludge in a form that can be readily transported
to suitable landfill sites.
In accordance with the present invention, an organic
sludge is stabilized by mixing therewith appropriate amounts
of Port land cement, fly ash, calcium sulfate dehydrate, and
lime. The proportion of Portlsnd cement can suitably range
from about 1 to about 35% by weight based on the organic and
solids content of the sludge, preferably between about 5 and
about 35%, and optimally between about 10 and about 30%; the
fly ash between about 10 and about 80%, preferably between
about 20 and about 75%, and optimally between about 30 and
about 70%; the calcium sulfate dehydrate between about 1 and
about 40%, and optimally between about 5 and about 40X; and
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the lime between about 0.05 and about 10~, and preferably between
about 0.1 and 5%. It should be noted that the fly ash commonly
contains at least a small quantity of lime, which should be
included in the calculation of time added.
If desired, the mixture can also include up to about
25% of additional stabilizing agents such as clay, soil, recycled
rubber, and asphaltenes to modify the properties of the completed
composition, as well as adsorbent substances -- e.g., activated
clay, activated silica, activated carbon, and the like -- to
bind organic substances.
The total combination of sludge and additives should
contain, or have added to it, a sufficient quantity of water
to effect hydration of the cementitious components and to allow
the mixture to be readily commingled. For this purpose, the
amount of water can be determined in a known way, but in all
cases a water content of 25 to 50% by weigh in the total mixture
is sufficient.
Other features and advantages of the present invention
will be apparent from the following description of a preferred
embodiment representing the best mode of carrying out the in-
mention as presently perceived, which description should be
considered in conjunction with the accompanying drawings in
which:
Fig. 1 is a schematic view of the California Bearing
Ratio test equipment used to determine CUR values of the
stabilized organic sludge;
Fig. 2 it a graphic representation of the density
of organic sludge samples stabilized with the compound and
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methods of the present invention in relationship to their
moisture content; and
Fig. 3 is a graphic representation of the grain size
in millimeters of organic sludge samples stabilized with the
compounds and methods of the present invention in relationship
to the % by weight of the stabilized waste samples that hove
grain sizes varying from coarse to fine.
An organic sludge is a collection of organic and
inorganic multi phase solids, semisolids, and liquid waste
resulting from industrial operations. These materials commonly
have no economic productive value or usage. Organic sludges
are found in numerous settings including waste lagoons, settling
ponds, sludge ponds from chemical processing plants and other
waste sites that occur throughout industry. These organic
sludges may also contain hazardous waste (Resource Conservation
and Resource Act, 42 U.S. 6903(5) (1976).
In the present invention, organic sludge is stabilized
by mixing it with Port land cement, fly ash, calcium sulfate
dehydrate, and lime, and, if desired, a stabilizing gent such
as clay, recycled rubber, or asphaltene, sod sun adsorbent sub-
snows Water can be added a needed. These materiels con
be sodded to the organic sludge individually or as a premix.
Any conventional mixing means may be employed -- e.g., a drag
bucket or bsckhoe. The resulting composition his a soil-like
consistency which con be handled with sty conventions earth-
moving equipment. Because of the resultant composition's
physical characteristics, it can be compacted after curing
to densities that show low water permeability sod high stability.
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Also because of the physical characteristic of the resulting
composition, the stabilized organic sludge can be moved and
shaped without fear of settling and distortion, thus focal-
toting the use of normal remedial programs including the use
of various conventional finer and capping technologies.
Additionally, because the stabilized organic sludge does take
on a soil-like consistency, it can be readily transported to
more suitable landfill site, if necessary, with a minimum
of handling cost. The resulting stabilized composition can
be used for land reclamation purposes or for road building.
The chemical reactions that occur when the compositions
of the present invention are mixed with the organic sludges
are not completely understood. Fly Ash is a waste material,
normally recovered from coal-burning furnaces, comprised largely
of silica-alumina and iron compounds, together with unburned
carbon from the coal. In the method of the present invention,
fly Ash is believed to act a a pozzolanic material -- i.e.,
a material that reacts with lime in the presence of water at
ordinary temperatures to produce a cementitious compound.
The calcium sulfate dehydrate is believed to act initially
a an absorbent, and more important as an accelerator for the
rate of hydration of the calcium silicates, while at the same
time retarding the rate of hydration for the calcium acuminates,
thus assuring an even set throughout the admixture. There
it some evidence that it also acts as a plaster-like stabilizer.
This is somewhat surprising as the calcium sulfate dehydrate
would normally have to be calcined to its hemi-hydrate form
before plaster formation could occur. The Port land cement
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acts like other hydraulics, wherein the tricalcium silicate
reacts with water to set up as a hard, infusible mass. It
ha been found from experimentation that it it best to add
the Port land cement last in the mixing process to maximize
its benefit as a binder. In a commercial setting, the mixing
and subsequent stabilization of the organic sludge with the
compositions of the present invention can be carried out with
most conventional mixing techniques. In the laboratory, various
mixing techniques can be utilized as long as a thorough mix
between the waste and the composition of the present invention
is achieved.
The following operating examples will more fully
illustrate the invention and the best mode for the practice
thereof.
EXAMPLE 1
A number of tests were performed on samples of an
organic sludge obtained from a waste lagoon at a chemical plant
engaged in processing petroleum-derived resins and chemicals.
The samples upon analysis typically contained 43% by weight
organic, 3Z solids, and 54% water. Each of the samples was
mixed with Port land cement, fly ash, and calcium sulfate in
the proportions (Z by weight, based on organic and solids
content of the sample) set forth below in Table 1, and, after
thorough mixture, was allowed to cure to a stable penetration
value. The Port land cement and fly ash contained sufficient
lime to assure that the pozzolanic reaction would occur.
Penetrometer readings were then taken to provide measurements
of the degree of solidification that occurred upon reaction
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of the compositions with the waste but prior to compaction
of the resultant mass. The higher the penetrometer reading,
the greater the solidification, 4.5 being the maximum. A soil
test Model CLUE penetrometer was used to take the readings.
The results of those tests are tabulated in Table 1.
Table 1
Test No. Cement Fly Ash Casey Pen
1 32% 54% 54% 2.7
2 32% 54X 43% 2.9
3 32% 54% 32% 2.7
4 32% 54% 22% 2.6
32% 54Z 11% 2.2
6 32% 43% 54% 3.7
7 32% 43X 43% 2.8
8 32% 43% 32% 3.5
9 32X 43X 22% 2.3
32% 43% 11% 2.4
11 32% I 54% 3.0
12 32% 32X 43% 2.3
13 32% 32% 32% 2.8
14 32% 32% 22% 2.2
32% 32% 11% 1.7
16 32% 22% 54% 3.2
17 32% 22% 43% 2.5
I 32% 22% 32% 2.4
These test results demonstrate the fact that the
organic sludge reacted with the compositions of the present
invention to form a firmer, more stable final composition.
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Example 2
In a field test, a conventional road tiller way used
as a high-volume mixing means to commingle an organic sludge,
obtained from another portion of the lagoon of Example 1, con-
twining approximately 50X organic materials, 5% solids, and
approximately 45% water, with about 24% Port land cement, 72%
of a mixture containing equal parts fly ash and filter cake
from a sulfur dioxide scrubbing unit, the filter cake containing
calcium sulfate, calcium sulfite, and time, and 9% clay (all
based on organic and solids of the sludge. The resultant
mix solidified into a soil-like composition after a short
period of time, and could be readily bulldozed and stockpiled
within a few days. The material exhibited superb soil-like
properties with such structural integrity that a caterpillar
bulldozer was readily supported on its surface, thus demon-
striating that a capping operation could be carried out.
Example 3
In a second field test, a drag bucket was used to
mix a composition made in accordance with the present invention
with an organic sludge obtained from another portion of the
waste lagoon of Example 1, having an organic content of approx-
irately 50%, a solids content of approximately 10%, and a water
content of approximately 40%. This waste was mixed with 25.5X
Port land cement, 85% of a mixture containing equal parts fly
ash and filter cake from a sulfur dioxide scrubbing unit (the
filter cake containing calcium sulfate, calcium sulfite, and
lime), and 15X clay (based on the organic and solids content
of the waste). The resultant mix solidified into a stable
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soil-like composition after a short period of time, exhibiting
a number of highly desirable characteristics, including high
density, low permeability, and a low expansion ratio. The
structural integrity and resultant density of the stabilized
sludge was analogous to that experienced in Example 2. The
sludge stabilized to a depth of 6 feet could support heavy
equipment with no notable settling or distortion. The stabilized
sludge was subjected to extensive soil and environmental testing,
the results of which are contained in Table 2.
Table 2
Dry density 92.5 lb/ft3
Moisture content 18.1%
California bearing ratio 4.0
Soil classlflcatlon MCCAULEY - silty clay
Maximum dry density 101.01 lb/ft3
Optimum moisture content 17.0X
Atterberg limits:
Liquid limit 27.7
Plastic limit 22.6
Plastic index 5.1 5
Permeability 2.59 x 10 cm/sec.
Leach ate Quality:
Be 1.2 Mel (limit = 100)
Other metals None detected
Total organic 27.7 Mel
Dicyclopentadiene 1.0 Mel
Naphthslene 3.5 Mel
Trimethylbenzenes 0.3 Mel
Methylnaphthalenes 0.8 Mel
3-ring aromatics 0.2 Mel
Hexachlorocyclopentadiene None detected
Chlordane None detected
Volume increase upon treatment Negligible
The data generated by these extensive soil and
environmental tests, together with visual observation made
after stabilization of the sludge, contained some surprising
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and unexpected results, the -most notable being the low permeability
of the resultant composition, its high density, and its low
expansion ratio after stabilization.
The permeabilities obtained in this and other subsequent
field testing were within 1 to 2 orders of magnitude of the
permeability constants required for liners in the RCRA regulations.
This indicates that the stabilized sludge permits water to
permeate at only a slightly higher rate than that permitted
for liners designed to hold and contain the original sludge
material. The result is an environmentally more secure site.
The California Bearing Ratio value that was obtained in this
and other subsequent field samplings indicates that the stabilized
sludge is of a quality that would support a cap following a
lining and capping operation. In other words, the density
and structural integrity of the resulting composition it such
that it minimizes the amount of settling due to compression.
Once a cap has been formed on the stabilized waste, there is
no danger of settling that would cause distortion of the surface
of the cap, thus destroying its effectiveness.
Finally, the resultant composition showed an extremely
low expansion ratio. The stabilized sludge had little to no
volume increase upon mixing with the composition of the present
invention, unlike many other stabilization techniques in which
a 100% increase in volume is not unexpected. This can be important
to a sludge disposal site operator who wishes to stabilize
his sludge pond, yet has a limited space in which to do 80.
All of the parameters tested, including the California
Bearing Ratio, the Atterberg limits, and the leach ate quality
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levels indicate that the sludge, upon mixing with the composition
of the present invention, had been stabilized to a soil-like
composition that substantially fixed all of the organic in
the sludge material.
~XAHPLE 4
Extensive tests were conducted on samples obtained
from a sludge lagoon containing 14% organic, 47% solids, and
39% water. A preliminary series of small scale tests was run
to determine what percentages of Port land cement, calcium sulfate
dehydrate, fly ash, and lime would yield the most stable end
product upon treatment of the waste from the pond. It was
found that for this particular pond the most effective composition
in terms of result and cost contained 85Z of a mixture containing
equal parts fly ash and filter cake from a sulfur dioxide scrubbing
unit (the filter cake containing calcium sulfate, calcium sulfite,
and lime), and 15% clay (based on the organic and solids content
of the waste). The resultant composition set within a 24-hour
period.
The permeability of the stabilized sludge was determined
at various depths utilizing various parameters. The parameters,
equations, and results of these tests are tabulated in Table
3.
Table 3
Constant Head Permeability
Moisture Sample
Dry Density Content Location
Sample #1 90.9 pal 39.3% B-3 @ 6.5'
Sample #2 89.2 pal 41.2% 8-4 @ 6.0'
Constant head permeability = QL/tHA, = 6.8 x 10 5 cm/sec,
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(continued)
where: Q = total quantity of water which flows through the
sample in an elapsed lime
L = length of sample in permeameter
t = time of test
h = total head lost
A = cross sectional area of the permeameter
Falling Head Permeability
Moisture Sample
Dry Density Content Location
Sample #3 97.0 pal 22.0Z B-3 @ 10.3'
Sample #4 96.2 pal 23.5% B-3 @ 11.0'
Sample #5 95.8 pal 24.2Z B-4 @ 10.3'
Falling head permeability Allah (loglOHO/Hl) where:
a = cross sectional area of the stand pipe
L = length of the sample
A = cross sectional area of the sample
t = time of the test
Ho = original hydraulic head
Hi = final hydraulic head
k = 6.6 x 10 6 cm/sec
The results of the stabilization is a low overall
permeability constant for the treated sludge, within an order
of magnitude of those required under RCRA for liner permeabilities.
Once again, this indicates that the stabilized sludge permits
water permeation at only a slightly greater rate than that
permitted for liners under RCRA regulations. The result is
once again an environmentally more secure pond.
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The density of the material was determined using
tune California Bearing Ratio Test and ASTM D-690 method A.
Referring to Fig. 1, A schematic of the field California Bearing
Ratio equipment set up it illustrated. A mechanical Jack 10
is supported from an A-frame 12 above the test pit 14. The
Jack 10 can deliver various loads to drive a penetration piston
16 into the test material at various depths. The result of
these tests are tabulated in Table 4.
Table 4
Bearing Ratio Valuer
Penetration Load (psi) Field CUR Value
.100 40 4.0
.200 55 3.7
.300 65 3.4
.400 75 3.3
.500 80 3.1
It can be seen from the test results that the stabilized
sludge exhibits excellent soil-like properties. The stabilized
sludge is of such a density and structural integrity that it
provides a stable base upon which capping operations can be
performed without fear of settling due to compression that
can lead to distortion of the cap. A bulldozer operator can
maneuver his equipment upon the treated sludge without fear
that the sludge will not support the bulldozer and the weight
of the cap.
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Referring to Fig. 2, the maximum dry density and
the optimum moisture content of the treated sludge were determined
using ASTM D-690 Method A. It can be seen that the maximum
dry density for the trusted waste WEB 101 pound per cubic
feet, with an optimum moisture content of 17%. The Atterberg
Limits were as follow: liquid limit 27.6; plastic limit 22.6;
and PI 5.1. All these result are indicative of the fact that
the stabilized sludge had taken on soil-like characterlsticfi
that resulted in low permeability and high stability.
The percent of treated sludge having a grain size
identical to that of salt or clay was approximately 92X as
shown in Fig. 3. This characteristic would Abe expected owing
to the low permeability shown by the stabilized sludge.
Once again, it can be seen from the data that organic
sludges stabilized in accordance with the present invention
take on a soil-like character exhibiting numerous properties
that assist an organic sludge disposal site operator in handling
the waste at his facility in a more ecologically and economically
sound manner.
A leach ate quality study was also performed on leach ate
of the treated sludge. Samples 1, 2, 3, 4, 5, and 6 were taken
from various parts of the stabilized sludge lagoon.
The results of these tests are tabulated in Tables
5, 6, 7, and 8.
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Table 5
Organic
SampleMethoxy- Toga-
Sample Description 2,4,-D 2,4,5-TP London Endrin color
(1) Piled Sample 1 ND ND ND ND ND ND
(2) Field Sample 2 ND ND ND ND ND ND
I Field Sample 3 ND ND ND ND ND ND
(4) Field Sample 4 ND ND ND ND ND ND
(5) Field Sample 5 ND ND ND ND ND ND
lo (6) Field Sample 6 ND ND ND ND ND ND
LIMIT OF DETECTION 0.1 0.2 0.06 0.01 5.7 0.5
EP-TOX MAX ALLOWABLE 10.0 1.0 0.4 0.02 10.0 0.5
ND = Not detected at the stated limit of detection
Table 6
Metals
Sample Description Be Or Pub Cud A As So Hug
(1) Field Sample 1 0.9 ND ND ND ND ND ND ND
(2) Field Sample 2 1.5 ND ND ND ND ND ND ND
(3) Field Sample 3 1.2 ND ND ND ND ND ND ND
(4) Field Sample 4 0.6 ND ND ND ND ND ND ND
(5) Field Sample 5 1.6 ND ND ND ND ND ND ND
(6) Field Sample 6 1.8 0.6 ND ND ND ND ND ND
LIMIT OF DETECTION 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.001
EP-TOX MAX ALLOWABLE 100.0 5.0 5.0 1.0 5.0 5.0 1.0 0.2
ND = Not detected at the stated limit of detection
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Table 7
Concentration Breakdown of Organic in Sludge Lagoon
Total Duskily- Nope- Trim ethyl- Methyl- 3-Ring
Organic Pentadiene tone benzenes naphthalene6 Aromatlc8
Sample Mel Mel Mel Mel Mel Mel
(1)3.2 0.4 1.5 0.1 0.4 0.1
(2)24.0 0.3 5.2 1.8 0.4 0.1
(3)27.7 1.0 3.5 0.3 0.8 0.2
(4)17.2 0.2 4.6 0.7 0.5 0.1
(5)12.5 0.1 4.8 0.7 0.5 0.1
(6)5.6 0.1 3.6 0.4 0.4 0.03
Table 8
Percent Breakdown of Organic in Sludge Lagoon
Duskily- Trim ethyl- Methyl- 3-Ring Remaining
Sample pentadiene Naphthalene Benzenes naphthalenes Aromatics Organic
(1) 13 50 1 13 3 I
(2) 1 22 8 2 0.4 66.6
(3) 4 13 1 3 1 78
(4) 1 27 4 4 3 61
(5) 1 38 6 4 1 50
(6) 2 64 7 7 0.5 19.5
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