SIS Process Converts Hazwaste For Reuse

The stabilizatiodsolidijication process, a relatively new treatment option for hazardous waste, has been identified as the best demonstrated available technology for various RCRA wastes,

such as sludges, spent cleaning materials and combustion residues.

onsider a pile of used sand- blasting grit. C Because the

paints removed by the grit contained low Tevels of haz- ardous substances such as lead, copper and unreacted resin residual, the grit pile has been classified as a hazardous waste under the provisions of the Resource Conservation and Recovery Act (RCRA).

Treatment options such as incineration are not via- ble for erit contaminated

By Karl W. Nehring and Susan E. Brauning

other binders; let the mix- ture set. Now the waste is transformed into a solid form that is easier to han- dle and less likely to expose the environment to toxic contaminants. However, the chemistry of S/S is not so simple, and treating hazardous wastes with S/S in a way that complies with regula- tions is much more complicated than simply dumping a few bags of Portland cement into a mixer and combining it ” - with metals. N~~ is i t A solidificatiodstabilization process was used to treat sandblasting grit containing with the waste.

hazardous materials. The treated grit then was mixed with asphalt and laid on a desirable for the @it to be section of road as part of a test to determine the treatment’s effectiveness. Photo disposed of in a landfill in courtesy of the Naval Civil Engineering Laboratory.

To understand how to apply S/S processes suc-

its current form. Just what can be done with this pile of unwanted grit?

For such problematic wastes, an increasingly important treatment option is solidificatiodstabilization, commonly referred to as “S/S.” S/S processes are used t o convert hazardous materials into non-hazardous materials that are accept- able for disposal under applicable fed- eral, state or local standards. S/S tech- nologies also are used frequently to develop materials that have potential reuse value - such as construction material or fill - thereby eliminating the expense of disposal and the unneces- sary use of valuable landfill space. S/S processes can treat effectively a

variety of otherwise intractable waste materials; they are flexible enough to accommodate mixtures of contaminants;

and they are economical enough to be applied to large volumes of waste. In addition, S/S processes can provide the means for a hazardous waste generator to comply with increasingly stringent regulatory requirements.

For example, S/S processes are used widely in Superfund remediation pro- jects and have been identified as the Best Demonstrated Available Technology for a number of RCRA wastes. S/S processes have been applied to a variety of indus- trial wastes such as sludges, spent clean- ing materials, plating wastes and combustion residues. Most often, S/S processes are used to treat sludges or soils contaminated with metals.

The basic concept of S/S is deceptively simple: Mix the waste with Portland cement, asphalt or any of a number of

cessfully, the first thing needed is a clear definition of the terms “solidification” and “stabilization” as well as an explanation of how S/S technologies work and what kinds of S/S processes are available.

Furthermore, process users need knowledge of the regulatory compliance process. They need to know not only which regulations apply to S/S processes and S/S-treated wastes, but also how to screen available S/S processes to decide which, if any, are appropriate for a particular application, taking into account both the advantages and disad- vantages of S/S.

Finally, we would like to see some examples of successful SIS applications - and find out what happened to that pile of contaminated sandblasting grit.

Solidification refers to a process in

14 ENVIRONMENTAL PROTECTION

which materials are added to the waste to produce a solid. The solidification

process may or may not involve a chemi- cal bonding between the toxic contami- nant and the additive. In solidification, the mechanical binding of contaminants can be on the microscale (microencapsu- lation, absorption or adsorption) or the macroscale (macroencapsulation).

Because cement-like materials are employed as binders so commonly, many people might be led to believe that SIS processes result in concrete-like mono- liths. However, in many cases, the solidi- fied waste is in a granular form, which may have materials-handling advan- tages over a solid monolith. The particu- lar physical form of an S/S-treated waste is not as important a consideration as its potential for releasing contaminants into the environment. If a granular form suffices to prevent leaching, for example, then that form might be much more desirable for certain applications than a more monolithic product.

Stabilization refers to processes by which wastes are converted to a more chemically stable form. The process

involves solidification, but also includes use of chemical reactions to transform the toxic component to a new non-toxic compound or form that will be less readily transported into the environ- ment.

Contaminant Leaching The process of slow extraction of

contaminants from the SIS-treated waste -typically by groundwater -is called leaching. SIS processes employ various binders and additives that are mixed with the hazardous waste to reduce the rate of contaminant leach- ing, either by reducing the mobility of the contaminants (stabilization) or reducing access of water to the contam- inant (solidification), or both. In addi- tion, these binders and additives often improve the handling and physical characteristics of the waste.

The basic SIS processes are generic, and many of the basic materials used as binders and additives are readily available. SIS binders generally can be grouped into two major classifications: inorganic (cement-based and pozzo-

lanic - for example, fly ash) and organic (thermoplastic and thermoset- ting polymers).

Cement-based and pozzolanic proc- esses or a combination of cement and pozzolans are the methods of choice in the SIS industry today because of their relatively low cost, their applicability to treating a variety of waste types, and the ease of using them in the field. The most common inorganic binders are: Portland cement, limelfly ash, kiln dust (lime and cement) or combina- tions thereof.

Because of their high cost and some- times difficult application, organic bind- ers usually are limited to special waste types such as radioactive wastes or hazardous organics that cannot be destroyed thermally. Organic binders that have been tested or applied for SIS include asphalt (bitumen), polyethylene, polyesters, polybutadiene, epoxide, urea formaldehyde, acrylamide gel and pol- yolefin encapsulations. In addition to the individual use of inorganic and organic binders, some systems combine organic

continued on page 16

APRIL 1992 Circle 8 on card.

15

How to remove radon

trom your water svstem before it

J /1

Qoes too far,

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We cover the waterfront.

16 Circle 9 on card.

SolidificatiodS tabilization

continued from page I5

with inorganic binders, such as diatoma- ceous earth with cement and polysty- rene.

SIS technology is offered commercially by a large number of SIS vendors, who generally use conventional binders sup- plemented by a variety of additives and know-how from previous experience. The specifics of vendor technology are in most cases considered as proprietary and are not disclosed to the potential user except under agreement of confidentiality.

Some commonly used additives and their applications include soluble sili- cates, such as sodium silicate or potas- sium silicate, which will generally “flash set” Portland cement to produce a low- strength concrete; selected clays, such as bentonite, to absorb water required in low solids mixtures; emulsifiers and surfactants, which can allow the incorpo- ration of immiscible organic liquids; activated carbon, used primarily as a sorbent for organics; lime, soda ash, fly ash, sodium hydroxide and magnesium hydroxide, added for maintaining alka- line conditions; and reducing agents such as ferrous sulfate and blast furnace slag.

Unfortunately, many binders and additives may work well for stabilizing one contaminant but have the opposite effect for a different contaminant. The optimum waste/binder/additive formu- lation will vary with the waste compo- sition, the presence of other binder constituents, and other factors, such as the disposal environment itself. The overall performance of the waste, binder, additives and the disposal environment should be evaluated as a system as part of the screening process for choosing the appropriate S/S process for a particular application. This will ensure that regula- tory compliance is achieved.

SIS regulatory considerations pri- marily are related to RCRA and its amendments. In addition, some wastes that are candidates for S/S may be regulated by the Comprehensive Envi- ronmental Compensation and Liability Act (CERCLA) of 1980. Generally, CER- CLA sites are not regulated by RCRA directly. However, CERCLA response actions are required to comply with other environmental laws that are “applicable or relevant and appropriate require- ments” (ARARs).

If portions of RCRA regulations are ARARs, then the RCRA regulations apply to the CERCLA sites. In addition, state and local regulations may apply,

1.

Workers take samples of used grit for the pilot-scale treatment study designed to evahc- ate the reuse of treated hazardous material.

During the process in which the contaminated grit was treated and combined with asphalt, plant employees performed air monitoring for dust and chemical emissions.

and requirements can vary widely. Therefore, it is always important to consult the regulatory authorities responsible for your particular site or area before treating the waste.

The Land Disposal Restrictions (LDRs) have been a major influence on the use of S/S. Whenever hazardous materials are placed directly in or on the land (for example, in a landfill), there is always a risk that the contaminants will be released to the environment. Recog- nizing this risk, Congress passed specific provisions restricting the direct land disposal of RCRA hazardous wastes and requiring treatment of hazardous wastes prior to their land disposal.

The LDRs required EPA to establish treatment standards for each of seven groups of RCRA hazardous wastes. The specific wastes and their treatment stan- dards are listed in 40 CFR Part 268. These treatment standards, which were established on the basis of Best Demon- strated Available Technology rather than on risk-based or health-based stan- dards, may be expressed as concentra-

ENVIRONMENTAL PROTECTION

d L 2

The final test strips of the gritlasphalt blend will be monitored long term for mobility of contaminants and durability of the material.

tion levels to be achieved prior to dis- posal or as a specified technology to be used prior to disposal.

The majority of LDR treatment stan- dards promulgated to date specify con- centration levels. For these treatment standards, any technology that can achieve the required levels may be used unless that technology is otherwise pro- hibited (in other words, the Best Demon- strated Available Technology used by EPA to set the standards need not be used). S/S technologies are required as the technology treatment standard for some wastes and also may be used as a means to achieve the concentration treatment standards in other wastes. To determine whether a particular SIS

process will meet regulatory require- ments for a given waste, a systematic technology screening process tha t includes treatability studies should be undertaken.

The process of technology selection, evaluation and optimization frequently is referred to as technology screening. An sfs treatment process that has been screened properly and subjected to a rigorous treatability study prior to full- scale implementation has the highest probability of success in the field.

Treatability studies provide valuable site-specific data needed to select and implement the appropriate remedy.

Screening factors tha t can be addressed through treatability studies include overall protection of human health and the environment; compliance with ARARs; implementability; reduc- tion of contaminant toxicity, mobility or volume; short-term effectiveness; cost; and long-term effectiveness. In addition, community and state acceptance should be considered and may influence the decision to conduct treatability studies on a particular technology.

For most SIS projects, resource restric- tions will dictate that the treatability

testing program cannot encompass all of the contaminants present at the site, but must be restricted in scope to a selected few. The contaminants to be evaluated should be selected based on the following criteria:

Toxicity or carcinogenicity - select the most harmful contaminants.

Mobility - select the most soluble contaminants.

Geochemistry - select a represen- tative contaminant from each of the major functional types present.

Concentration - all factors being equal, select the contaminants present at the highest concentrations.

Generally, if the number of contami- nants being evaluated in treatability testing exceeds five at any one time, it becomes increasingly difficult to satisfy the performance objectives for all of the contaminants. The screening process is an important step in ensuring that the advantages of a particular S/S process outweigh the disadvantages for the par- ticular waste or combination of contami- nants to be treated.

Advantages And Disadvantages There is no perfect treatment tech-

nology for hazardous wastes. Like any other technology, S/S has both advan- tages and disadvantages. Chief among the advantages of S/S technology is that in many applications, costs are low because the materials and equipment needed (for example, Portland cement) are inexpensive and readily available. In addition, SIS processes can handle sludges, making them easy to work with, and SIS processes are effective in treat- ing wastes contaminated with metals.

On the other hand, the apparent simplicity of S/S processes can be decep- tive. The chemistry of stabilization is complex, and there are no “sure-fire’’ recipes for success. Some wastes, partic- ularly those with significant organic contaminants, are not amenable to SIS treatment; moreover, small amounts of impurities such as grease or oil in a waste can inhibit the SIS process from working properly.

Another potentially significant dis- advantage of SIS processes is that they can result in an increase in waste volume, meaning more physical product for disposal. If the S/S-treated waste is in a form that can be used in another application, however, rather than dis- posed of, then the issue of waste volume

continued on page 38

- ~ _ ~ _ _ _ ~ _ ~~~ ~

Howa .

pre-engineered air stripper can save

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’ flow rates from one to 3500 gpm, in sizes from 8 in. to 11-1/2 ft. in diameter by 16 to 38 ft. in height, with packing selected to suit site conditions. Towers under 20 inches in diameter are made of stainless steel; larger towers from marine grade aluminum. So, if you would like to know more about pre-engineered strippers, and how fast and economically one could be getting rid of contamination in your water supply -or, if you are interested in any of our other professional and construction services in ground water remediation and water supply-just complete the reader service card or contact us at Hydro-Group, Inc., 101 1 Route 22, Bridgewater, NJ 08807. 1-800-524-2725, (In NJ, 908-563-1400).

We cover the waterfront.

APRIL 1992 Circle 10 on card. 11

Risk Assessment

haracterize con in terms of potent onmental impact nefit derived fro Guidance for

Health Evalua- 0/1-89-002. 1989.

decisions regarding actions. For a health

fensible, it is impor- environmental scientists Research

cognize endpoints of con- m a risk assessment, ’. t h guidelines estab- Supe

dous us w a to be accurate and Reference*

the National Academy of (D

6. USEPA. “Review of Ecological Risk Assessment Methods.” Office of Policy Plan- ning and Evaluation. Washington, D.C. EPA

7. Oak Ridge National Laboratory (ORNL). ‘‘User’s Manual for Ecological Risk Assessment.” Oak Ridge, Tenn. 1986.

8. USEPA. 40 CFR 300-399. “Protection of Environment.” USEPA, The Office of the Federal Register National Archives and Records Administration, Washington, D.C. 1991.

9. Kelly, K.E. and N.C. Cardon. “The Myth of 10“ as a definition of acceptable risk (or, In Hot Pursuit of Superfund’s Holy Grail).” Presentation of the 84th Annual Meeting of the Air and Waste Management Association, Vancouver, B.C. 1991.

10. Cohrssen, J. and V. Covello. ‘‘Risk Analysis: A Guide to Principles and Methods for Analyzing Health and Environmental Risk.’’ Council on Environmental Quality, Executive Ofice of the President, Washing- ton, D.C. 407 pp. 1989.

230-10-88-041.1988.

I

SolidificatiodStabilization

Circle 29 on card. 38

continued from page 17

may cease to be a problem, as we can see when we discover what happened to that pile of contaminated sandblasting grit.

In a demonstration project for the U.S. Naval Civil Engineering Laboratory (NCEL), scientists from Battelle Memo- rial Institute worked with NCEL to evaluate S/S options for treating the grit. Working closely with regulatory agen- cies, the scientists were able to demon- strate through careful technology screen- ing and treatability testing that the contaminated grit could be incorporated into an asphalt mixture that then could be used as a roadbed. A section of road has been laid using this asphalt, and will be monitored for long-term performance.

In another S/S demonstration project for NCEL, engineers and scientists eval- uated a cement-based vendor technology for treating lead-contaminated soil from a rifle range berm at a Navy practice range. The resulting granular product passed regulatory standards and was reburied in the berm, where it now poses much less of a threat to the environment.

These projects are only two examples of innovative successful applications of S/S technology to hazardous wastes, which is in wide application at hazardous waste sites throughout the United States and in many foreign countries. While S/S may not be a perfect technology for

treating hazardous wastes, when used effectively, it can be a relatively inex- pensive way to help achieve regulatory compliance and protect the environ- ment. (D

References 1. Conner, J.R. “Chemical Fixation and

Solidification of Hazardous Wastes.” Van Nos- trand Reinhold, New York, N.Y., 1990.

2. Gilliam, T.M. and C.C. Wiles (eds.). “Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes, Second Vol- ume.” ASTM STP 1123. American Society for Testing and Materials, Philadelphia, Pa. 1992.

3. USEPA. “Handbook for Stabilization/ Solidification of Hazardous Waste.” EPA/540/2- 86/001. Hazardous Waste Engineering Research Laboratory, Cincinnati, Ohio. 1986.

4. USEPA (Environmental Protection Agency). Immobilization Technology Seminar, Speaker Slide Copies and Supporting Informa- tion. CERI-89-222. 1989.

5. Center for Environmental Research Infor- mation, Cincinnati, Ohio. October.

6. USEPA. “Technical Resources Document on SolidificatiotdStabiliiation and its Appli- cation to Waste Materials.” Report in prepa- ration by Battelle for Risk Reduction Engi- neering Laboratory, Cincinnati, Ohio. 1992.

Karl Nehrrrig LS administrative coordinator for the Environmental Technolot) Department ai Barielle in Coliimbu, Ohio He is cirrrently etigaged in writing sections of a iechnical resources clocumeni or1 sohdificatio~srabilizairoli processes far US EPA Sirsan Brarmrrig, who IS a research scientisi in Batielle J Envrronmental Echnology Deparimeni, also is asslstrng in the preparaiiori of the EPAk SIS docirmeniaiion She also has eiperrence 111 environmental field sampling, field evaliiairons of setlands putrriiiiint and coniplianci iiith enwro~imentoi rcgirlnfioni

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ENVIRONMENTAL PROTECTION