CA1236857A - Composition and method for stabilization of sludge - Google Patents

Abstract

A method and means for the stabilization of organic sludges that includes combining the sludge with Portland cement, fly ash, calcium sulfate dihydrate, and lime, optimally with stabilizing agents such as clay, recycled rubber, and asphaltene, and an adsorbent for organic substances.

Description

~3~i8~

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.

.... . .
rm/~l 123685~
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

- 2 -rm/r~ml ~3685~

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 I- rm/~J

1~36~517 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.

, rum Jo ~;~3~85'7 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 ..~,~..
.. / . .

1~36857 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.

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 . .
rum / 'I , :

3~857 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.

rm/~.J

~3685'~

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 /, rum of J

1~36~35~7 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 _ g rum/ Al 1~3685'7 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 rum J

~.~36857 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, rml~) Jo ' 1~3685~

(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.

rmlj~r ~36~35~
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.

., j, ._ rml lot ' ~36857 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.

_., rm/l~r~) ~;~36857 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 rum 1;~3Çi857 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 rml~,i us

Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for the stabilization of organic sludge comprising mixing the sludge with about 1 to about 35% by weight Portland cement, about 10 to about 80% fly ash, about 2 to about 40% calcium sulfate dihydrate, and about 0.05 to about 10% lime, based in each case on the organics and solids content of the sludge.

2. The method of claim 1 wherein the sludge is also mixed with up to about 25% clay based on the organics and solids content of the sludge.

3. The method of claim 1 wherein the sludge is also mixed with up to about 25% recycled rubber based on the organics and solids content of the sludge.

4. The method of claim 1 wherein the sludge is also mixed with up to about 25% asphaltene based on the organics and solids content of the sludge.

5. The method of claim 1 wherein the sludge is also mixed with an adsorbent for organic substances.

6. The method of claim 1 wherein the Portland cement is added after mixture of the sludge with the fly ash, calcium sulfate dihydrate, and lime.

7. The method of stabilizing organic sludge comprising mixing the sludge, with about 5 to about 35% Portland cement, about 20 to about 75% fly ash, about 3 to about 40% calcium dihydrate, and about 0.1 to about 5% lime based in each case on the organics and solids content of the sludge.

8. The method of claim 7 wherein the sludge is also mixed with up to about 25% clay based on the organics and solids content of the sludge.

9. The method of claim 7 wherein the sludge is also mixed with up to about 25% recycled rubber based on the organics and solids content of the sludge.

10. The method of claim 7 wherein the sludge is also mixed with up to about 25% asphaltene based on the organics and solids content of the sludge.

11. The method of claim 7 wherein the sludge is also mixed with an adsorbent for organic substances.

12. A method for the stabilization of organic sludge comprising mixing the sludge with about 10 to about 30%
Portland cement, about 30 to about 70% fly ash, about 5 to about 40% calcium sulfate dihydrate, and about 0.1 to about 5%
lilme based in each case upon the organics and solids content of the sludge.

13. The method of claim 12 wherein the sludge is also mixed with up to about 25% clay based on the organics and solids content of the sludge.

14. The method of claim 12 wherein the sludge is also mixed with up to about 25% recycled rubber based on the organics and solids content of the sludge.

15. The method of claim 12 wherein the sludge is also mixed with up to about 25% asphaltene based on the organics and solids content of the sludge.

16. The method of claim 12 wherein the sludge is also mixed with an adsorbent for organic substances.

17. A composition for the stabilization of organic sludges comprising (a) about 10 to about 30% Portland cement based on the weight of the composition, (b) from about 25 to about 60% fly ash based on the weight of the composition, (c) about 10 to 30% calcium sulfate dihydrate based on the weight of the composition, and (d) about 2 to 10% lime based on the weight of the composition.

18. The composition of claim 17 wherein the composition further comprises up to about 25% clay based on the weight of the composition.

19. The composition of claim 18 wherein the composition further comprises up to about 25% recycled rubber based on the weight of the composition.

20. The composition of claim 19 wherein the composition further comprises up to about 25% asphaltene based on the weight of the composition.

21. The composition of claim 17 wherein the composition further comprises up to about 25% adsorbent for organic substances.