As more sorbents come in the market the buyer and user are confronted by a more difficult and confusing buying decision. The variety of sorbents available now ranges from sawdust, recycled newspapers, feathers, straw, peat moss, clay and diatomaceous earth to old rags, your wife's wool sweater and synthetics such as the variety of polypropylenes now on the market. If one is to believe CGSB standards evaluation, the best absorbent is your wife's wool sweater, but the cost of and your wife may not agree to this as a viable alternative.

It is becoming more difficult to determine what is the best for you and what really works and satisfies environmental concerns. In addition, the ever-increasing number of environmental rules and regulations restricts how spilled materials can be retrieved and what can be done with waste materials recovered. The following will help to define some of the issues involved and how they can influence you're decisions making process.

In addition competitiveness in the market place has resulted in a lot of misinformation being generated and distributed throughout the industry. Some statements and claims made in recent publications are so off the wall that one wonders if the author actually has his tongue in cheek.

For starters, the sorbent you use will depend upon the liquid to be controlled and the conditions under which the spill exists. Most sorbents, organic or inorganic, will safely handle all but some strong acids and strong caustics. In the rare occasions that there are the liquids that are concerned with, clays, diatomaceous earth or some synthetics is the best bet. For 99 percent of spilled liquids, including liquids such as battery acid, the majority of organic and virtually all inorganic sorbents will work.

Temperature is also a factor. Although all of the sorbents may work in your shop it may be a different story outside in a sub-freezing temperatures. While many of the organics continue to work well down into the minus temperature ranges, the performance of synthetics (polypropylene) drops off significantly at very low temperatures. 

The choice of water attracting or water resistant is another concern. In most dry or indoor industrial environments, the wisest choice will be a sorbent that controls all liquids including water. Water is the source of more problems and industrial accidents than all other liquids combined. If the sorbent is to be used to pick up oil on water or oil in a wet environment such as a rainstorm, water-repelling materials are the choice.

There is an ever widening range of organics as well as the old standby synthetics that can satisfy these basic criteria. Here again, the application is of concern. If the sorbent is to sit on the water for extended periods, synthetics will float longer. Organics are generally biodegradable and will eventually begin to break down in a wet environment. 

This breakdown will eventually result in the degradation of the sorbent material and sinking or break-up.

If quick control and maximum absorption of a spill are of prime importance, some organics will leave polypropylene in the dust, absorbing two to three times as much oil off of water in a fraction of the time. Some of the earlier water resistant organics used unfriendly chemicals to make them water resistant but more resent developments have resulted in the use of water resistant material that are environmentally sound. Any sorbent that satisfy California State's Department of Fish and Wildlife toxicity tests and have thereby obtained OSCA approval are sure to be OK.

If the sorbent catching on fire is a real concern, the best answer is earthen materials such as clay. A non-combustible sorbent may not prevent a fire because if the liquid picked up is volatile it will still burn. The fact that earthen materials do not burn can be a disadvantage in that they leave ninety-nine percent ash content upon incineration. Earthen materials also suffer from low performance characteristics. A better answer can be some organics that exhibit a “controlled” burn and burn cleanly. These absorb the liquids and minimize the gaseous vapors that are exposed and ignitable and, if they do ignite, they tend to slow the burn down to a more controlled rate. 

The worst alternative is synthetics sorbents. Polypropylene catches on fire relatively easily and produces some very toxic products of combustion. In the internationally recognized reference manual. “Dangerous Properties of Industrial Materials” bye Sax and Lewis, Published by Van Nostrand Reinhold, the combustion products of polypropylene enjoy a Hazard rating in the “worst hazard level” as a producer of highly toxic gases. The mortality rate among lab animals breathing polypropylene fumes is greater than 50 percent within ten minutes. This is not nice stuff! In the words of those that are familiar wit the burning of used synthetics after a spill response, you light the fire and stand up wind.

Sparks from discharge of static electricity build-up can also be a concern, particularly around volatile vapors in a dry environment. Sorbents that are classified as a static discharge medium are least likely to cause such sparks. Earthen sorbents are generally static free and some cellulose material such as paper fiber sorbents are classified as static discharge mediums and therefore will not build up a static change themselves and can help to reduce the likelihood of static discharge from other sources. Polypropylenes naturally tend to build up a static charge and can be a source of electrical discharge sparks. In recent years, a new breed of polypropylene that is specially treated and classified as static resistant has become available. These synthetics are more less likely to create a static discharge hazard.

Among fire issues, spontaneous combustion can also be a factor. Contaminant saturated sobents can heat up and ignite were they sit if the proper conditions for spontaneous combustion exist. There is not a generally a problem with earthen materials or synthetics but can be a problem with most organic sorbents. A notable exception is processed wood fiber (clean paper products). During the manufacture of these paper products, the fatty acids and lignin that support spontaneous combustion are removed resulting in absorbents that do not support spontaneous combustion.

Liquid retention is also a major factor in evaluation sorbents. Liquids that have been retrieved should remain retrieved. Many so-called absorbents are really adsorbents that do not hold onto the liquids picked up. This often leads to a secondary spill when the liquids leach back out of the sorbent into a beach or dock, into the sand or back into the water, or out of the transport vehicle. A number of sorbent manufacturers have advertised the reusability of their sorbents. This is a flat out admission that their materials do not retain the liquids picked up. You will see this reusability factor advertised less because it is becoming letter known that reuse is illegal.

Federal Regulations under Article 2001.4 specifically prohibit the reintroduction of harmful substance into the water. This includes the reintroduction of sorbents that have been wrung out. This Federal Regulation precludes the reuse of sorbents and renders the suggestion of reuse as invalid. The federal EPA and Cost Guard are responsible for policing this and their enforcement is increasing.

Polypropylene sorbent suppliers have been the most common to claim reusability and their products have poor retention characteristics. Synthetics and earthen sorbents are primarily adsorbents that are to say that the liquids only coat the fibers and pieces of sorbent and are therefore easily released. Some organics such as virgin paper fiber are absorbents where the liquid penetrated throughout the fibers and is therefore not so easily released.

Disposal alternatives are in increasingly important factor in selecting sorbents. The cost of disposal continues to rise and available alternatives appear to be diminishing. From the viewpoint of the owner of the contaminant, the best alternative is the least expensive one that eliminates any future liability for the material. This generally means complete destruction of the contaminant because certified destruction is the best way to assure the elimination of any future obligation.

The most cost effective way to get rid of the contaminant is to reuse it as an alternative fuel source. 

If your contaminant/sorbent combination qualifies as a clean fuel source it can be used in industrial burners, cement kilns or as thermal energy for various applications. If you're lucky, or a good negotiator, you can make money on the sale of your “fuel”. To qualify for this use, the “fuel” and the ash from the fuel often must satisfy TCLP (Toxicity Characteristic Leaching Procedure) criteria. All but a few sorbents that contain such things as toxic recycled inks or glues will satisfy TCLP criteria. The bigger challenge is to confirm that the contaminant can satisfy these criteria. Note that some materials that pass TCLP tests prior to burning can fail them as an ash because the burning process can remove the inert materials while concentrating the toxic fraction.

The two most common forms of disposal today are land filling and incineration, both of which are under fire. With landfills being over-stressed the way they are, the increasing restrictions on the use and opening of new landfills, it is unlikely that incineration use is going to diminish. Further constraints on the output from incinerator in order to minimize potential air pollution are very likely but incineration is a cost effective and relatively complete and environmentally sound way to dispose of waste. Until a better alternative is found, incineration is likely to continue and increase to use.

Any sorbent that passes TCLP requirements should be acceptable in high temperature incinerators. Most organics and synthetics burn cleanly and leave very little ash at high temperatures. Earthen sorbents have the disadvantage of yielding almost the same bulk in ash as was put into the incinerator. In all cases, the properties of the waste material are more of a determining factor that the sorbent itself. A non-toxic ash is important because it becomes a disposal problem for which incineration is not an alternative. This ash almost invariably becomes landfill and therefore must satisfy landfill acceptance criteria.

Although low temperature incineration and “back yard” burning are becoming less acceptable (banned in some regions) this type of disposal is still common in many areas. Given that the liquid contained burns in an acceptably clean manner, the sorbent used can make a big difference to the toxic gages and other pollutants produced upon burning. Some organics and earthen materials will burn clean (clean meaning no toxic gases or ash) although their relative volume of ash production is very different. Some organics and all polypropylenes can produce dirty and very toxic gases if the burn temperature is not high enough.

The most common method of disposal is in landfills. Landfills are targeted as a growing problem and greater restrictions are being put on what can be accepted in existing landfills and on the opening of the new landfills. One of the greatest theoretical concerns surrounding sorbents and landfills in the ability of the sorbent to retain the liquid picked up and thereby prevent or limit the amount of liquid that may leach out of the sorbent and contaminate the surrounding area. In theory, sorbents with the best retention characteristics, particularly in the relatively homogeneous, high compression and anaerobic environment of a landfill should be the sorbents of choice for landfill disposal. Or, to be more direct, sorbents that do not exhibit these characteristics should be the first to be restricted.

Earthen sorbents do not generally control large amounts of liquid per volume but neither do they lose the liquids picked to due to compression. As adsorbents rather than absorbents they are more likely to lose contained fluids due to simple migration.

Synthetics and other adsorbent medium that release liquids upon compression are the most likely to yield free liquids in a typical landfill environment. Polypropylenes have advertised themselves as reusable for years. Their “reuse” was attained by squeezing out the liquids, exactly the property not wanted in a landfill.

From the user's viewpoint, landfills should be the least preferred disposal to result in major liquid loss during landfill compression, alternative if any hazardous or potentially hazardous materials are being disposed of. Materials in a landfill that have been appropriately treated and therefore remain their hazardous form can remain a potential liability for the originator of such waste. Waste destruction or complete neutralization is generally a safer and better alternative for the generator.

Landfills and the erroneous red herring RCRA issue.

Biodegradation, bioremediation, land farms, bio piles, liquid waste treatment centers. White rot fungi, genetically engineered bugs, biodegradation enhancing materials.

Liquid waste treatment centers:

• Bioremediation/biodegradation incineration (done?)
• Landfills and logic behind alternatives.

Liquid waste treatment centers are another terminal disposal alternative available to some sorbent users. This basic for liquid waste treatment process, becomes a benign substance and it must be acceptable in a solution form. Materials that do not easily accept liquefaction will accumulate and can fill and/or clog up the liquid based system.

These criteria eliminate many sorbents including synthetic, and most minerals basted materials. These are some mineral based sorbents that go into solution (emulsify) easily but even then their bulk density and volume displacement per unit of liquid picked up results in poor efficiencies and solid build-up when the material settles out of solution. Synthetics are non-biodegradable plastics, which will remain in the system for extended periods and do not meet the criteria of quickly breaking down to natural components and also contribute to the unwanted build up of solid waste.

Organics are a mixed bag. To confirm their non-toxic nature, a minimum of TCLP test or satisfaction of stringent criteria such as the California State Water Resources Board's abalone larvael test may be required. In the wet environment full of biodegradation accelerating enzymes present in a waste treatment plant, some organic sorbents will break down in a matter of hours or days. Of more concern in this case is the material pickled up. IF the organic sorbent satisfies the about criteria and the controlled liquid is acceptable, the liquid/sorbent combination should also be acceptable.

Bioremediation and biodegrading are receiving greater acceptance as final and environmentally preferred disposal alternatives. A good bio-pile will degrade waste material in a matter of weeks to a few months and the resulting residue is a natural organic material that is non-threatening and can often be used as a fertilizer or soil enhancer. 

Biodegradation requires combination of air circulation and moisture to progress quickly, The ideal sorbent for these applications will degrade with the material picked up and will support the biodegradation process. Preliminary elimination of materials that do not support biodegration is relatively easy. Synthetics will not readily biodegrade or support biodegradation. Nor will they, within a reasonable time frame, break down to support the use of the residual waste material as soil base.

Clays and other earthen materials are too compact to allow the circulation of moisture and air but, given that the contaminants can be biodegraded, the resulting degraded material is natural earthen material and can be disposed for accordingly or may be appropriate for use as an agricultural base.

Clays an other earthen materials are too compact to allow the circulation of moisture and air but, given that the contaminants can be biodegraded, the resulting degraded material is a natural earthen material and can be disposed of accordingly or may be appropriate for use as an agricultural base. These are many organics and an equally wide range of abilities to support biodegradation. Some recycled papers can contain recycled inks or other impurities that kill the degrading microorganisms. Vermiculite can pose a similar problem due to impurities it may contain. As before, the ability to pass a TCLP test or the California State Fish and Wildlife aquatic toxicity tests are good criteria for gauging suitability for disposal through biodegrading. Meat moss, corncobs and rice hulls support biodegradation reasonably well and are good base for later deposition or as an agricultural base. There are virgin paper based products that do a much better job of allowing free circulation of air and moisture and therefore support a much quicker, more through degradation.