SELF-REMEDIATING FLUIDS FOR ICE CONTROL

Abstract: The present invention relates to an ice control formulation comprising at least one freezing point depressant and an enzyme system that is capable of degrading the freezing point depressant. In certain embodiments the ice control formulation further comprises a surfactant and anti-corrosion agents. Certain anti-icing formulations further comprise a thickener.

Description: SELF-REMEDIATING FLUIDS FOR ICE CONTROL FIELD OF THE INVENTION The present invention relates to methods and compositions for de- icing and anti-icing surfaces, especially aircraft surfaces, in which the compositions are self-remediating. BACKGROUND OF THE INVENTION Safe operation of aircraft during icing conditions requires the removal of ice and frozen deposits from critical surfaces prior to takeoff. For the past five decades, ice removal (deicing) of commercial and military aircraft have been accomplished by applying heated solutions of water and ethylene glycol (EG) or propylene glycol (PG) freezing point depressants (FPD). These processes use very large quantities of deicing fluids to effectively remove ice from critical aircraft surfaces and prevent its reformation. For example, an aircraft the size of a Boeing 727 commercial airliner can use between 200 and 1000 gallons of deicing fluid for a single pre-takeoff deicing procedure. Recently, airlines have begun to use thickened versions of deicing fluids, referred to as anti-icers, to prevent the reformation of ice after deicing is completed. About 50 gallons of anti-icing fluid are used per aircraft. In addition to deicing aircraft surfaces, chemical deicing/anti-icing materials are used to remove or prevent the accumulation of frost, snow or ice on airfield pavements, such as runways, taxiways, gates and ramps. Current pavement deicing/anti-icing agents include EG, urea, UCAR (which contains 50 percent EG, 25 percent urea and 25 percent water), potassium acetate, sodium acetate, calcium magnesium acetate, sodium formate and magnesium chloride. Non-chemical deicing methods include the use of thermal or mechanical processes to remove ice and snow from aircraft, including the use of forced air/hot air systems and infrared heating. However, at the present time, very few airports use these methods. On the other hand, the primary method of removing heavy accumulations of snow and ice from airport pavements is by mechanical means, with secondary deicing performed using chemical means. During deicing operations, thousands of gallons of aircraft deicing fluids flow off the aircraft and into the environment through storm sewers. According to a Federal Aviation Administration (FAA) survey (Federal Aviation Administration, "FAA Survey Final Report Stormwater Questionnaire Project," DCN T00215, Washington, DC, June 1, 1992), the use of ethylene glycol for deicing airplanes at selected airports ranged from 0.6 gallons to 520,000 gallons per year for each airport and from 200 gallons to 187,000 gallons per year as a pavement deicer. Individual airports reported the use of propylene glycol as an aircraft deicer from 75 gallons per year to 250,000 gallons per year. The annual volume of urea as a pavement deicer ranged from 100 pounds to 715 tons per airport. Approximately 90 percent of deicing fluid and 15 percent of anti-icing fluid runs off in the application area. These sporadic releases of deicing fluids have caused a number of reported incidents of environmental damage near commercial airports and military installations throughout the world. For example, in 1991, the USAF decided to ban further purchase of EG- based deicing fluids because of an incident of groundwater contamination at Griffϊss AFB (New York). Ethylene glycol is a listed hazardous air pollutant (HAP) and a listed groundwater pollutant in several states because of its toxicity and faces regulatory burdens in use, handling, and transportation (Oswalt, B.E., et al., "Use of Hazardous Materials for Aircraft Deicing," Report No. LM 930081, Air Force Logistics Management Agency, May 1993). Propylene glycol, on the other hand, is an FDA approved food additive and has been shown to be virtually non-toxic to humans and terrestrial life. Glycol-based freezing point depressants (EG and PG) have relatively low aquatic toxicity. However, additives such as corrosion inhibitors, surfactants (wetting agents) and thickening agents used in anti-icers increase the aquatic toxicity by orders of magnitude over that of pure EG or PG. Further, the five-day biochemical oxygen demand (BOD) for glycol- based freezing point depressants and commercially available deicing and anti-icing fluids range from about 400 to 800 g/L, much greater than those found in typical raw municipal sewage (DTtri, F.M., "Deiciers in Airport Stormwater Runoff," in Chemical Deicers and the Environment, p. 327, Lewis Publishers, 1991). Urea and glycols are the most commonly used chemical agents at commercial airports for pavement deicing. Urea readily degrades to carbon dioxide and ammonia at 20°C, which can be very toxic to aquatic organisms even at very low concentrations. However, in cold weather, the degradation of urea to ammonia is negligible so that the use of urea may not cause toxic effects to the aquatic environment and may not be as large a concern during winter months. However, because of the potential negative environmental impacts, commercial airports are using more environmentally benign chemical agents, such as potassium actetate, sodium formate and calcium magnesium acetate. Unfortunately, corrosion inhibitors, which exhibit high mammalian and aquatic toxicity, are often added to these deicing agents to meet industry performance specifications. As a result of these adverse environmental impacts, the US Environmental Protection Agency (US EPA), and state and local environmental agencies have promulgated increasingly stringent regulations affecting aircraft deicing fluid runoff. The Clean Water Act Amendment of 1987 requires airports to obtain a National Pollutant Discharge Elimination System (NPDES) permit to discharge deicing fluids into the storm sewer. These permits limit the concentration and nature of pollutants being discharged into the storm sewer and require implementation of a pollution prevention plan to reduce the amount of pollutants released to the environment. The high costs associated with regulating deicing/anti-icing fluid runoff have resulted in the investigation of wide range of pollution prevention methods designed to eliminate or minimize the impact of aircraft and airfield pavement deicing chemicals on the environment (Zuskin, S., "Effluent Guidelines Airport Deicing Operations Study," Report EPA-821-D-99-002, U.S. Environmental protection Agency, Office of Water, Washington, DC, October 5, 1999). These include the development of environmentally benign aircraft and airfield pavement chemicals as alternatives to glycol-and urea- based chemicals, reducing the amount of chemicals fluid applied to aircraft and pavement through improved application methods or innovative deicing/anti-icing strategies, development of glycol recycling methods, and the development of collection and disposal strategies that prevent the release of deicing/anti-icing formulations to the environment. For example, because of the high BOD of the glycol-based deicing/anti-icing fluids, many publicly owned treatment works (POTWs) either refuse to accept glycol-contaminated stormwater or charge high fees for treatment. In order to comply with environmental regulations and reduce the treatment fees, a number of commercial airports have elected to install systems designed to capture and control runoff from deicing operations (op cit., Zuskin, S.). Once the runoff is captured, it must be contained for treatment. Biological treatment of runoff is increasingly gaining favor. This method contains the deicing fluid runoff in holding tanks or lagoons until either the glycol is sufficiently biodegraded or the water can be safely metered out to a publicly owned treatment works (POTW) or an on-site bioreactor. Although the BOD of the waste water after treatment is substantially reduced, the cost of building and maintaining these treatment facilities is quite high. The cost of environmental compliance has greatly increased the life cycle cost of deicing fluids over the past decade. In fact, if the cost of purchase, handling and disposal of deicing fluids is considered, the total life cycle cost of a gallon of glycol based deicer is estimated to be about $20 per gallon as compared to the purchased cost of glycol of about $3 per gallon. It would be desirable to have deicing/ or anti-icing compositions that are biodegradable and non-toxic to animals and the environment. It would also be useful to have ice control formulations that are self-remediating. SUMMARY OF THE INVENTION This invention pertains to the development of environmentally- advantaged ice control materials which meet or exceed current performance requirements and are inherently less damaging to the environment. These formulations can be safely released to the environment without required runoff capture or post-treatment to achieve permit compliance. The term "ice control material" refers to deicers and anti-icers for aircraft and airfield pavement surfaces. Anti-icing fluids for aircraft surfaces offer additional source reduction benefits because less material is wasted on runoff and overspray and repeat applications of fluids are avoided. The invention relates in particular to the development of "self remediating fluids" which degrade to less harmful products prior to entering the ecosystem by means of a triggerable event, e.g., the gel might be sheared open. The invention also relates to a gel-encapsulated FPD-degrading enzyme system that may or may not be contained in the deicing/anti-icing formulation and in which the enzyme is released upon demand and biodegrades the deicing/anti-icing solution prior to its entering the ecosystem. (See Figure 1). The invention relates to microbes that are able to degrade freezing point depressants, e.g., ethylene glycol, propylene glycol, glycerol, 1,3- butanediol, triethylene glycol and other deicing agents, at low temperatures by producing an enzyme that degrades the FPD; the enzymes extracted from these microbes; and the techniques to encapsulate and release these enzymes from the gels on demand. In certain preferred emodiments, the enzyme is harvested from Pseudomonas putida or Xanthobacter autotrophicus. The present invention relates to an ice control formulation comprising at least one freezing point depressant and an enzyme system that is capable of degrading the freezing point depressant. In certain embodiments the ice control formulation further comprises a surfactant and anti-corrosion agents. Certain anti-icing formulations further comprise a thickener. One embodiment of the invention relates to ice control formulations wherein the freezing point depressant comprises a glycol and the enzyme system comprises a glycol -degrading enzyme. In another preferred embodiment, the FPD comprises glycerol and the enzyme system degrades glycerol. In preferred embodiments, the enzyme system comprises an encapsulated enzyme. Preferably the enzyme is encapsulated in a gel. Particularly preferred gels comprise a responsive gel, made of a polysaccharide or protein. Examples of polysaccharides include, but are not limited to starch, dextran, alginic acid or a cellulose ether, such as hydroxypropyl cellulose. An example of a gel-forming protein incudes gelatin. Preferably the responsive gel further comprises a crosslinker. Preferred crosslinkers comprise a multifunctional carboxylic acid derivative, e.g., adipoyl chloride or succinyl chloride for hydroxypropyl cellulose, calcium ions for alginic acid, or glutaraldehyde for gelatin. The gel-encapsulated FPD-degrading enzyme can either be incorporated directly into the deicing/anti-icing formulation or can be stored separately from the deicing/anti-icing formulation and mixed with it when applied. The gel-encapsulated FPD-degrading enzyme can be used with presently known anti-icer and de-icer compositions that utilize the FPD's that are degraded by the enzyme. The invention also relates to a bacterium that degrades the freezing point depressant, e.g., propylene glycol and glycerol, by producing an enzyme that degrades them and, as a result, reduces the BOD of the formulation. In a preferred embodiment, the enzyme is harvested from Pseudomonas putida or Xanthobacter autotrophicus. The invention also relates to a method of making an encapsulated enzyme for use in ice control formulations comprising an aqueous solution of the enzyme and the polymer suspended in an immiscible organic solvent with the polymer gelled by physical or chemical means. One method of encapsulating an enzyme for use in ice control formulations comprises providing an aqueous solution of polymer and enzyme, providing an organic solvent which is immiscible with the solution, and providing a crosslinker which reacts with the polymer, wherein enzyme encapsulating gels are formed. Preferably, when the solution is added to the solvent, it is rapidly stirred. In certain methods, the size of the droplets of the gels is controlled by altering the stirring speed, relative viscosity of the aqueous and organic phases. Examples of polymers useful in this invention include starch, dextran, alginic acid or a cellulose ether. The invention relates to a method of making gels by crosslinking dextran with adipolyl chloride, by crosslinking alginate with calcium or other multivalent ions, and by crosslinking gelatin by using temperature. Thus, another method of encapsulating an enzyme for use in ice control formulations comprises providing an aqueous solution of polymer and enzyme, providing an organic solvent which is immiscible with the solution, heating the solution, adding the heated solution to the solvent, and cooling the resulting mixture, wherein beads are formed upon cooling. An example of a polymer useful in this method is gelatin. The invention also relates to a method of making an ice control formulation comprising: a) providing at least one freezing point depressant; b) providing at least one surfactant; and c) providing at least one enzyme system that degrades the freezing point depressant. In a preferred embodiment, the enzyme system comprises an enzyme that is encapsulated. Alternative application methods include: adding freeze-dried enzyme to the deicing/anti-icing solution just before application; metering enzyme solution into the deicing solution at the time of application or adding live cells to the solution at the time of application. Further alternatives include using the encapsulated enzyme, the freeze dried enzyme, enzyme solution, or live cells as a pollution prevention measure, either applied directly to aircraft runoff, airfield pavements, or used in a treatment lagoon or bioreactor. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the application of environmentally advantaged anti- icing fluid to an aircraft. Figure 2 shows the growth of selected sludge microbes at lower temperatures with PG as the sole carbon substrate Figure 3 shows the growth of mixed x (Xanthobacter autotrophicus) and z (activated sludge) microbes on a five percent propylene glycol solution with and without added growth factors Figure 4 is a photograph of an agar plate containing colonies of the microbial culture grown at 2°C. Figure 5 shows the removal of BOD in the presence of enzyme preparations with and without aeration. Figure 6 shows the residual concentrations of BOD and propylene glycol after incubation at 4°C with aeration. Figure 7 shows the residual concentrations of BOD and propylene glycol after incubation at 4°C without aeration. Figure 8 shows the viability of a biofilm in the presence of a PG- degrading enzyme. Figure 9 shows the relationships between the concentration of tri- ethylene glycol in glycerol and the COD:BOD 2 o ration at 1 percent concentration. Figure 10 shows the growth of microbial cultures on glycerol at varying concentrations at 4°C. Figure 11 shows the growth of Pseudomonas fragi on glycerol at varying concentration at 4°C. Figure 12 shows the biooxidation of tri-ethylene glycol (1 percent) against endogenous respiration. Figure 13 shows the biooxidation of tri-ethylene glycol (20 percent) against endogenous respiration. Figure 14 shows the biooxidation of butanediol (1 percent) at 2.5°C against endogenous respiration. Figure 15 shows the biooxidation of butanediol (20 percent) at 2.5°C against endogenous respiration. DETAILED DESCRIPTION OF THE INVENTION The ice control formulations of the present invention address the issue of BOD reduction in a unique and innovative way. The freezing point depressant in the aircraft anti-icer accounts for a large portion of the BOD. Co-pending application No. , entitled "Environmentally Friendly De-icer and Anti-icer compositions", identifies freezing point depressant materials with lower BOD and toxicity. The teachings in that co-pending application are incorporated herein in its entirety. The present invention relates to a triggerable enzymatic treatment system which is incorporated directly into the fluid. This "self-remediating fluid" is activated during application of the fluid and results in a fluid, which is partially degraded prior to entering the receiving waters. This in situ "pre-treatment" lowers the BOD impact on receiving waters. Deicing and anti-icing solutions containing glycol-based freezing point depressants have an inherently high BOD content. Even though the high performance fluids that have been identified in co-pending application No. , entitled "Environmentally Friendly De-icer and Anti-icer Compositions", have a diminished environmental impact in terms of lower BOD and toxicity, further BOD reductions may be required to meet stricter environmental regulations for POTWs. The present invention provides a new gel-encapsulated glycol-degrading enzyme system that can be incorporated into deicing/anti-icing fluids to reduce the BOD in the runoff. The gels are broken to release the enzymes. For example, in one embodiment, as the fluids are sprayed on the aircraft, the shear from the nozzles break the gels, releasing the enzymes. Because of the low temperatures, the enzymes will not substantially degrade the glycol-based fluids during the holdover time. However, over a period of a few days, the BOD in the runoff will be substantially reduced to allow for further treatment in a POTW or in the storm sewers themselves. Within the term "enzyme" as used herein, is included a protein extract from lysed microbial cells. Examples of microbes include, e.g., Xanthobacter autotrophicus, and pseudomones putida, which have FPD degrading activity. The extract need not be purified, and may consist of several proteins or protein complexes that, taken together, along with cofactors such as ATP and NAD, have the required activity. The term "enzyme system" includes extracted proteins, crude proteins, proteins and cell components, e.g., cell membrane, live microbes as well as lyophilized microbes, and others as described herein. As used herein, the term "gel" refers to a material with properties intermediate between a solid and a liquid; or alternatively has the potential to exhibit these properties. A gel consists of a crosslinked polymer network swollen by one or more solvents. Together, the interactions between the solvent (s) and the polymer network determine the physical and chemical properties of the gel. The crosslinks may be permanent (e.g., covalent bonds) or temporary. The gel may also exhibit a volume phase transition in response to an external stimulus such as temperature, pH, ionic strength or solvent concentration. A gel which has been dried (had its solvent removed) is still referred to as a gel, even though it is necessary to add solvent for the gel to exhibit liquid-like properties. Aircraft ice control fluids (deicers and anti-icers) must meet a rigorous set of performance and materials compatibility requirements, set forth by AMS 1424 (deicing fluids) and AMS 1428 (anti-icing fluids). (Aerospace Material Specification 1424, "Deicing/ Anti-icing Fluid, Aircraft SAE Type I," SEA International, 400 Commonwealth Drive, Warrendale, PA 15096-0001; Aerospace Material Specification 1428, "Fluid, Aircraft Deicing/ Anti-icing Non-Newtonian (pseudoplastic), SAE Types II, III & IV," SEA International, 400 Commonwealth Drive, Warrendale, PA 15096-0001). These requirements differ substantially from the requirements for deicers or anti- icers designed for application to pavement, e.g., roadways or airport runways. Ice control formulations for use on aircraft must have the following characteristics: low freezing point; high flash point; low corrosivity; non-damaging to plastics and coatings; shelf stable and thermally stable. In addition, anti-icers must be capable of preventing ice formation on aircraft surfaces for extended periods of time and be capable of shedding from the aircraft wings on take-off. The compositions of the present invention meet these criteria. The ice control fluids of the present invention preferably have a freezing point that is 10°C below the outside air temperature at which it is applied. AMS 1428 requires a maximum freezing point of -32° C for anti- icing fluids. Deicing fluids can be mixed by the user with water in proportions which supply a suitable freezing point for the conditions of usage. In general, it is desirable for a deicing fluid to be capable of producing an aqueous solution with a freezing point of about -40°C, as this will be suitable under nearly all naturally occurring environmental conditions. The de-icers and anti-icers of the present invention preferably have a high flash point. The flash point of deicing and anti-icing fluids must be greater than 100°C to avoid creating fire hazards when the fluid is heated. This requirement effectively eliminates the use of highly volatile freezing point depressants (those with flash points less than 100°C). The anti-icing and deicing fluids of the present invention preferably are not corrosive to metals commonly found on aircraft, including aluminum alloys, magnesium alloys, titanium alloys, and various types of steel. The fluids do not induce stress corrosion cracking in titanium or hydrogen embrittlement in high strength steels. The anti-icing and deicing fluids of the present invention are also preferably non-damaging to plastics and coatings. Aircraft deicing and anti- icing fluids must not damage typical non-metallic components of aircraft, including aircraft canopy materials and aircraft coatings. This requirement effectively eliminates organic materials with strong solvent characteristics towards polyurethane or a tendency to craze polycarbonate or acrylic materials. Preferred anti-icing and deicing fluids of the present invention have a stable shelf life and are thermally stable. Deicing and anti-icing fluids are purchased, stored, and used in bulk over the course of one or more deicing seasons. Thus, their properties must remain stable over periods of time of up to one year. Anti-icers must also be able to retain their rheological properties after exposure to elevated temperatures for long durations (70° C for 30 days). That is, they are thermally stable. Anti-icers must be capable of preventing ice formation on aircraft surfaces for extended periods of time. This period of time, known as holdover time, is at least about 20 minutes, according to the standard WSET test for fluids designated as Type II and more than about 80 minutes according to the standard WSET test for fluids designated as Type IV. The requirement for extended holdover time implies that an anti-icing fluid must effectively wet out and completely coat an aircraft's surface upon spray application. It also implies that the fluid must form a barrier film of sufficient thickness to prevent freezing precipitation from penetrating to the aircraft surface under low shear conditions. The anti-icers must shed from the aircraft wings on take-off. Thus, the anti-icing fluids possess a non- Newtonian (shear-thinning) viscosity profile with sufficiently low high shear viscosity. The anti-icing compositions of the present invention meet these criteria. There are additional characteristics of deicing and anti-icing fluids, which, although not currently required by AMS 1428 or AMS 1424, are deemed necessary in order to produce a safe, effective, commercially viable deicing or anti-icing fluid. One such notable characteristic is low conductivity. Fluids which are ionic in nature have a much higher electrical conductivity than fluids that are non-ionic. For example, potassium acetate runway deicers have very high electrical conductivities compared to runway deicing fluids based on glycols (ethylene or propylene) which do not contain organic salts. Applying fluids with high electrical conductivity presents a risk to aircraft electrical systems. If a conductive fluid contacts an improperly insulated electrical circuit, short circuiting will result. The compounds of the present invention preferably have low conductivity. Freezing point depressant The deicing fluids of the present invention utilize a freezing point depressant (FPD). A freezing point depressant is used in the formulations to melt any incoming precipitation and to prevent the fluid itself from freezing as the fluid cools to ambient temperature. This ingredient has the highest concentration in the fluid. FPDs for use in the present invention are known in the art. Preferred FPDs include, but are not limited to ethylene glycol, propylene glycol, glycerol, 1,3 -butanediol, triethylene glycol and other deicing agents. Other FPDs useful in the present invention are described in co-pending application No. , entitled "Environmentally Friendly De-icer and Anti-icer Compositions." The environmental issues associated with deicers and anti-icers are mostly due to the type of FPD used. Freezing point depressants are typically toxic to mammals. Development of Microbes The invention relates to microbes that are able to degrade freezing point depressants, e.g., propylene glycols and other deicing agents, at low temperatures, the enzymes extracted from these microbes and the techniques to encapsulate and release these enzymes from the gels on demand. Extensive work has been done for at least the last 45 years on the biodegradation of propylene and ethylene glycols in waste waters (Lamb, C.B. and Jenkins, G.F., "BOD of Synthetic Organic Chemicals," Proc. 7th Ind. Waste Conf., 79, pp. 326-339, 1952.) and in runoff and with various microbial cultures (Haines, J.R. and Alexander M., "Microbial Degradation of Polyethylene Glycols," Appl. Microbiol, 29, pp. 621-625, 1975.), generally at temperatures of from 6 to 25°C. Propylene glycol compounds have been shown to be biodegraded by Bacillus sp. ATCC 51912, particularly the more recalcitrant dinitrate esters. (Sun, W.Q., Meng, M., Kumar, G., Geelhaar, L.A., Payne, G.F., Speedie, M.K. and Stacy, J.R., "Biological Demtrification of Propylene Glycol Dinitrate by Bacillus sp. ATCC 5191," Appl. Microbial Biotechnol, 45 (4), 525-529, 1996.) Metabolites of the parent compound were also shown to be well degraded by these cells. Some of the enzymes involved in the biodegradative activity on the propylene glycol compounds have been isolated and evaluated . Enzymes isolated from a range of microbes for the biodegradation of ethylene glycols can also be used for the degradation of propylene glycols. In unpublished work, Dr. David Stafford successfully biodegraded polyethylene glycol with Xanthobacter autotrophicus at temperatures of from 6 to 25°C. This microbe was grown with substantial activity at glycol concentrations as high as 200,000 mg/L (20 percent). In addition, he found that a species of Pseudomonas and a species of Flavobacterium showed similar activity. Some recent work has focused on the biodegradation of various glycols in soils, including propylene glycol, at low temperatures (Klecka, G.M., Carpenter, CL. and Landenberger, B.D., "Biodegradation of Aircraft Deicing Fluids in Soil at Low Temperature," Ecotoxicology and Environmental Safety, 25, pp. 280-295, 1993.) The organic constituents of these glycols were mineralized to carbon dioxide in soil microcosms incubated at temperatures ranging from -2 to 25°C. The microbial activity, however, is lower at lower temperatures. The present invention is directed to the development of microbes for degrading PG in ice- control formulations that have a high activity at temperatures near the freezing point of water through the use of elective culture techniques. Thus, bacteria that are useful for producing enzymes that degrade FPDs include Bacillus sp. ATCC 51912, Xanthobacter autotrophicus, Pseudomonas species and Flavobacterium species. Other bacteria can readily be screened by workers of ordinary skill in the art in accordance with the teachings herein to select for degradation of certain FPDs. Preferred bacteria are selected from xanthobacter autotrophicus, especially NCI 1171, and pseudomonas putida, as described below. Extraction of Enzymes The enzyme used by the bacteria to degrade the FPD can be extracted and used in the ice control formulations of the present invention. Suitable extraction methods are known in the art and described herein. Both crude and purified enzyme extracts are useful in the present invention. The mechanisms by which glycols are degraded depend on the enzyme cofactors and the energy yields from metabolic pathways. During the bacterial oxidation of propylene glycol using whole cells of Pseudomonas putida or cellular components the electrons produced by its degradation are passed eventually to oxygen. Cytochrome oxidases are the terminal oxidases of the electron transport system, which pass electrons directly to molecular oxygen. Some microbes have more than one terminal oxidase system. In some bacteria the terminal oxidase reacts only with oxygen while others react with other oxidants such as nitrate. Structures associated with the use of molecular oxygen as the terminal acceptor are mainly those associated with membranes. In bacteria, this role is mediated by largely undifferentiated cytoplasmic membranes. Relationships between activities and membrane structure depend on each bacterial system. Thus the location and orientation of the cytochrome c oxidase seems to be important since it is involved with the final reaction with oxygen with electrons from cytochrome chain and protons from water. It was found that with enzyme purification, the addition of membrane debris increases the rate of PG removal, as further described below. If the organic intermediates are to be mineralized with terminal oxygen then the addition of these membranes reduce the overall organic load as determined by the BOD test. Thus, in other embodiments a combination of purified enzyme extract and membrane debris, e.g., cell wall or membranes, can be used to increase the rate of degradation of the FPD by the enzyme. Preferred enzymes are able to degrade the FPD effectively at low temperatures, e.g., between 0°C -25°C. Encapsulation A gel system used for encapsulating the enzyme consists of an enzyme contained within the polymer network of the gel. The gel in which the enzyme is contained may be responsive. Responsive gels are a special class of gels that undergo large changes in volume with small changes in environmental conditions, such as temperature. (Shibayama, M. and Tanaka, T., "Volume Phase Transition and Related Phenomena of Polymer Gels," Advances in Polymer Science, 109, Springer- Verlag Berlin, 1993.) Responsive gels have been used for medical applications involving the absorption and/ or the release of active biological materials. (Gels Handbook (Osada, Y. and Kajiwara, K., eds.), Academic Press, 2000). Responsive gels have been developed that consist of components that are GRAS (Generally Regarded As Safe) by the U.S. Food and Drug Administration. (Lupton, E.G., Private Communication, June 1999). The polymeric backbone of the * network typically consists of a polysaccharide, such as starch, dextran, or a cellulose ether, and the cross-linkers consist of a multifunctional carboxylic acid chloride (e.g., the acid chlorides of adipic acid or succinic acid, namely adipoyl chloride or succinyl chloride). The crosslinkers are not GRAS, but their reaction products with water are GRAS. These families of gels can be made to be pH, temperature, or mechanically responsive. Such gels are known in the art. Other polymers such as sodium alginate may be crosslinked with calcium salts (or other divalent ion salts), some of which are GRAS. Some gels, such as those made from gelatine, a protein, are reversible with temperature or pH. Reversible gels can be made permanent by using a crosslinking agent, which are known in the art. A novel method of loading enzymes into the responsive gels from an aqueous phase using a two-phase loading technology has been developed by Gehrke, et. al. (Gehrke, S.H., et al., Enhanced Loading of Solutes into Polymer Gels, U.S. Patent No. 5,603,955, February 18, 1997). Some polymers in solution are incompatible and will separate into two phases when dissolved in a common solvent. Solutes dissolved in a two polymer system generally partition unevenly between the two phases. By adjusting the polymer and electrolyte concentrations, solutes such as enzymes or bioactive materials will selectively partition into one of the two phases. Stabilizing polymer surfactants and salts are added to protect the bioactive materials against denaturation, aggregation and precipitation in the gel. The gel is then dried with the material encapsulated inside it. Because of this unique technology, a very high loading level can be achieved and efficient use is made of the bioactive matertial. (See Gehrke, above). This encapsulation technology provides substantial protection of the enzymes from thermal or other environmental degradation and prevents the enzyme from diffusing out of the gel matrix until the gel is exposed tp the appropriate environmental condition. (See Gehrke, above). Two methods of incorporating the gels containing the encapsulated enzymes into the deicing/anti-icing fluids are as follows: One method involves mixing the gels directly into the fluids prior to the start of the winter season. The gel encapsulation system has a shelf-life of a year or two and is designed to prevent the enzymes from diffusing out of the gels and prematurely degrading the glycol-based fluids during storage. Alternatively, the gels can be stored dry in a separate tank and mixed together with the deicing/anti-icing fluids upon application to the aircraft. In both cases, the gel-encapsulated enzymes will be distributed uniformly in the runoff after application for efficient and complete degradation. Suspension crosslinking is a general technique which can be used to manufacture beads of a variety of gels. An aqueous solution of polymer is added to a rapidly stirred organic solvent with which the solution is immiscible. With sufficient excess organic solvent the aqueous solution is suspended through the organic phase as individual droplets. The size of the droplets is controlled by the stirring speed, relative viscosity of the aqueous and organic phases, and the optional addition of a surfactant. A chemical crosslinker which reacts with the polymer in the aqueous phase is introduced, and sufficient time is allowed for the crosslinking reaction to go to completion, forming gel beads. Alternatively, physical means such as temperature may be used to induce crosslinking, For example, gelatin beads may be formed in suspension by adding a hot gelatin solution to an immiscible organic phase and allowing the system to cool while stirring vigorously. The gel beads may be removed from the organic solvent by decantation, filtration, or similar methods. An optional washing step to remove traces of the organic phase may be performed. Finally, the gel beads may be dried by a conventional method. The compositions of the present invention can be utilized as other than a one-part system. Examples include: freeze-dried enzyme added to deicing solution just before application; enzyme solution metered into deicing solution at time of application; live cells added to deicing solution at time of application; and using the enzyme or live cells as a pollution prevention measure. The enzymes can be released from the gels by methods known in the art, e.g., by shearing caused by the nozzle used during application. Surfactant Surfactants are used in deicing and anti-icing fluids to decrease the surface tension of the fluids, allowing them to spread out on the aircraft surface and evenly wet the surface. Surfactants commonly used in ice control formulations are useful in the present invention. In preferred compositions of the present invention, the surfactant comprises a biodegradable, non-ionic surfactant, with low aquatic toxicity. Examples include, e.g., ethoxylated sorbitan esters, polyoxyethylene esters, alcohol ethoxylates, and alkyl polyglucosides. The amount of surfactant used in can be readily determined. Preferably, the amount of surfactant needed to lower the surface tension of the solution is up to about 0.4 wt% surfactant. Additives Additives are optionally added to ice control substances to enhance performance or meet specific user requirements. Examples of additives include, but are not limited to, corrosion inhibitors, dyes and buffers. Corrosion inhibitors may be required to allow the fluid to meet stringent corrosivity requirements. The fluid must not be corrosive to aircraft metals, including aluminum, titanium, magnesium, and steel alloys. Dyes are added to deicers and anti-icers in order to aid the user in determining the type of fluid being applied and to enhance the visibility of the fluid on the aircraft wing. Some formulations have additives that are sensitive to the pH level of the fluid (i.e. they only work within certain pH ranges) or have additives that change the pH of the fluid to unacceptable levels. These fluids require a pH-buffering additive. Additives are present in aircraft deicing and anti-icing fluids in small concentrations (representing less than 2% by weight of the total fluid). Thus, even if they are biodegradable, they do not contribute significantly to the BOD of the fluid. However, additives are a primary source of aquatic toxicity in current state-of-the-art deicing and anti-icing fluids. The aquatic toxicity of pure ethylene or propylene glycol is approximately one order of magnitude lower than the aquatic toxicity of a fully formulated deicing fluid containing ethylene or propylene glycol. The aquatic toxicity of the corresponding ethylene or propylene glycol based anti-icer is about two orders of magnitude greater than the pure freezing point depressant. [Kent, Andersen, et al, "Canadian Water Quality Guidelines for Glycols - An Ecotoxicological Review of Glycols and Associated Aircraft Anti-Icing and Deicing Fluids", p. 488, Fig. 2]. An Air Force Institute of Technology (AFIT) study [Cornell, Jeffrey, David Pillard and Mark Hernandez, "Comparative Measures of Component Chemicals in Aircraft Deicing Fluid"] showed similar results. In this study, pure propylene glycol had LC50 values for fathead minnows of about 35,000 mg/L. A combination of PG plus tofytriazole (TTZ; the most toxic corrosion inhibitor in commercially available fluids) yielded an LC50 of about 5000 mg/L. The combination of PG plus the additive package for the commercially available fluid (not including TTZ) had an LC50 of about 1000 mg/L for fathead minnows, and the fully formulated anti-icing fluid had an LC50 of around 1000 mg/L. These results indicate that additives control the aquatic toxicity of the fluid, and that additives found only in anti- icing fluids are more toxic than those in deicing fluids. Thickeners and specific surfactants may be added to anti-icers and may be the source of this added toxicity. Some additives may also represent a human or mammalian toxicity threat. For example, tolytriazole (TTZ) is used in commercially available fluids. TTZ is highly toxic to humans and persists in the environment (it is not biodegradable) . It has been discovered in groundwater near an airport in Bellingham, Washington. Some surfactants are also suspected of having toxic effects on humans. Alkyl phenol ethoxylates (APE's) are popular non- ionic surfactants that may be present in some commercially available fluids. APE's break down into alkyl phenols in the environment. Alkyl phenols are endocrine disrupting compounds and they persist in the environment (i.e. they do not readily degrade). They mimic the activity of estrogen in the human body and are suspected reproductive toxins and may be linked to breast cancer, [reference: Warhust, A. Michael, "An Environmental Assessment of Alkylphenol Ethoxylates and Alkylphenols", published by Friends of the Earth, Scotland, Jan 95]. To any of these formulations, one of ordinary skill in the art could add certain additives, e.g., corrosion inhibitor or water soluble dye, to enhance performance or meet specific user requirements. Thickener The anti-icing compositions of the present invention further comprise a non-Newtonian thickener. A non-Newtonian thickener can be added to the fluid to increase its viscosity at rest. This allows the fluid to stick to vertical or inclined surfaces without running off. The fluid must remain on these surfaces until the aircraft takes off in order to provide protection against incoming frozen or freezing precipitation. Useful thickeners are known in the art and preferred thickeners are described in co-pending application no. Examples of thickeners include polysaccharides, e.g., welan gum, xanthan gum, locust bean gum, and combinations of polysaccharides and clay. The present invention is further illustrated by the following Examples. The Examples are provided to aid in the understanding of the invention and are not construed as a limitation thereof. EXAMPLE 1 - Freezing Point Depressant Degrading Enzyme In unpublished work, Dr. David Stafford showed that Xanthobacter autotrophicus successfully degraded polyethylene glycol (PEG) having a molecular weight of 400 at concentrations as high as 200,000 mg/L (20 percent) and at temperatures of from 6 to 25°C. The microbe was grown in standard media (Table 1). It was also shown that the initial growth rate of the microbe and density of culture was much higher with a Luria-Bertani (LB) growth medium than with the standard medium for the microbe. Table 1 shows the formulations for the standard and Luria-Bertani (LB) growth media. The microbes were grown in the presence of 10, 20 and 30 percent PEG concentrations. Table 1. Media used for the growth of Xanthobacter autotrophicus The microbe Xanthobacter autotrophicus also degraded PG. Table 2 shows the growth of the microbe Xanthobacter autotrophicus NC 11171 in PG and in the LB medium. The microbe was isolated by J. Childs at the University of Exeter. These growth curves were produced by growing the microbe in a shaking incubator at ambient temperature (27° C). The variation in the starting optical density (OD) is due to the different starter cultures being used; all were read against Puritewater. Table 2. Growth of Xanthobacter autotrophicus NC 11171 m. propylene glycol and LB medium The isolated cultures showed similar growth in the presence of higher concentrations of propylene glycol (20 to 25 percent) at room temperature with LB medium as a growth substrate. In addition to propylene glycol, the Luria-Bertani medium contains glucose as a carbon source, in contrast to the standard medium. In order to show the growth of Xanthobacter autotrophicus NCI 1171 with PG as the only carbon source, a basal salts medium (Table 3) was used for growing the cultures. HCl was added to the solution to give a pH less than 1.00. Both solutions were autoclaved separately at 121°C for 15 minutes. The iron and manganese solution was added to the basal salts mixture at the time of use, at a rate of 0.4 mL/L. Table 3. Minimal basal salts medium The culture was grown in the basal salts medium in PG at room temperature. Comparative growth data are shown in Table 4 at four PG concentrations. Optical density was measured on a Shimadzu UV-2101PC UV-vis Scanning Spectrophotometer at 600 nm. This microbe showed good growth at a 10 percent PG concentration at ambient temperatures, without prior exposure to PG. Table 4. Growth curves for Xanthobacter autotrophicus NC 11171 in propylene glycol Growth data of Xanthobacter autotrophicus NC 11171 in PG was also demonstrated at lower temperatures (4°C and 10°C) using the basal salts medium and 10 percent PG as the only carbon source. The flasks were inoculated with Xanthobacter autotrophicus NC 11171, as well as with other microbes selected from an activated sludge system which had been exposed to a wide variety of chemical compounds. The test data are shown in Figure 13 for a 10 percent PG concentration. It is evident from these data that some of the selected sludge microbes have been adapted to grow at 10°C and 4°C. The data indicates very strong growth at 10°C and good growth at 4°C. The microbes produced good degradative enzymes at these low temperatures. Growth data was also obtained at lower temperatures of 1 to 3°C in a 5 percent propylene glycol solution with and without added growth factors. Typical growth curves determined at the lower temperatures are shown in Figure 3. With repeated sub-culturing, the microbes were able to reach full growth potential at these temperatures at an earlier stage in the growth cycle than with previous experiments. These cultures were plated onto selected agars to determine the particular colonies and their respective morphology. On agar containing propylene glycol as the only source of organic carbon, most colonies were round and opaque. Other colony types were rare (see Figure 4). The culture was taken from a flask containing up to 10 percent propylene glycol and was grown at less than 2°C. In a short time period of 2 to 3 days, these colonies were able to grow in the presence of propylene glycol as the sole source of carbon. EXAMPLE 2 - Propylene Glycol Degradation using Crude Enzyme Extract The activity of other microbes with similar or better performance than Xanthobacter autotrophicus with respect to PG biodegradation was investigated. In particular, a Pseudomonas species was isolated from activated microbial sludge and identified as Pseudomonas putida. The microbe which grew best on PG at low temperatures was isolated from activated sludge collected from the Countess Wear sludge plant in Exeter, England. It was identified as Pseudomonas putida using the API 20 NE system, (see Figure 3). This microbe is capable of converting PG into carboxylic acid as an intermediate. A second organism (Aeromonas sp.) was capable of oxidizing these organic acids to carbon dioxide and water, i.e., complete mineralization. In composting experiments in which PG was present, it was shown that the PG contained in the substrate matrix was one of the first compounds to be biodegraded. In further work, it was also shown that in selected soil structure formulations PGs were degraded and no significant buildup of intermediates were observed. The ultimate yields from radioactively labeled PG (as 14 CO 2 ) showed that the compounds were essentially mineralized. To effectively utilize the degradative enzyme activity of the enzyme complex extracted from Pseudomonas putida, the initial rate of degradation as well as the effectiveness of the enzyme over time was determined. Enzyme performance depends on temperature, application method and time of exposure. The enzyme complex was extracted from the bacteria Pseudomonas putida after growing the cells in a fermenter to a volume of 10 liters. A crude enzyme extract was produced after centrifugation, harvesting and sonication. The enzyme was split into two batches and stored for up to 8 days at 4°C and 12°C. Five (5) mL samples of the enzyme were exposed to a PG concentration of 10 percent and the rate of PG degradation determined over the following week. The residual PG concentration in the enzyme/ PG mixture was measured colorimetrically (see Table 5). Table 5. Degradation rates (mg PG removed/liter/hour) of the Pseudomonas putida enzyme complex for an initial propylene glycol concentration of 100,000 mg/L (10 percent) at different temperatures Approximately 10 percent of the propylene glycol was degraded after one day at the lower temperature and 20 percent was degraded after four to eight days. The propylene glycol degrading enzyme complex lost some PG degrading ability when exposed to the atmosphere over time at both incubation temperatures. Loss of activity after one day was 39 percent at 4°C and 10 percent at 12°C. However after 4 to 8 days the losses were more significant, with the enzyme losing about 50 to 80 percent over this period. The bacteria was deposited with ATCC in Manassas, VA, and given accession number . EXAMPLE 3 - Propylene Glycol Degradation Rates using Purified Enzyme Extract In the previous example, it was shown that at 4°C the use of crude enzyme extracts isolated from Pseudomonas putida provide about 20 percent removal of PG at an initial PG concentration of 10 percent in 48 hours. The rate of removal was shown to be about 200 mg/L/hour. Tests were carried out to determine if purification of the enzyme complex would significantly improve the biodegradation rate. The enzyme was purified by a salting technique. The Pseudomonas putida cells were grown and harvested, as previously described, by centrifugation in batches at approximately 20,000g's for 2 hours and were then were sonicated on ice using the MSE Soniprep 150 with 20-one minute bursts with one minute rests. The sonicate was then well mixed and spun down (20,000 g) for 90 minutes. The supernatant was then transferred to a small flask, which was kept on ice ready for the precipitation stage; the pellet was stored in a cold room at 4°c. Precipitation of the supernatant with ammonium sulphate was then carried out to a final concentration of 80 percent at the rate of 561g/L of sample. This stage took about 24 hours, with sulphate being added in small stages as it went into solution. The unusually long time was due to the presence of the phosphate buffer. The mixture was then transferred to Oakridge tubes, 35 mL each in 50 mL tubes and was spun down at 28,000g's for 75 minutes. A pellet of approximately 5 mL formed in each tube. The ammonium sulphate solution was then poured off and each pellet re-suspended in 5 mL of buffer. A desalting column (Pharmacia PD-10 Sephadex G-25M) was equilibrated with 25 mL of phosphate buffer (as per culture medium - but with no substrate) in a cold room. Two (2.0) mL of the protein solution was then placed on top of the column. The protein solution was too concentrated to pass through the column, and after about 2 hours most of the 2 mL was collected back from the top of the column and was replaced with buffer mixed with the residue. This diluted solution was passed through the column and collected in 1.0 mL aliquots. The rest of the protein solution was then placed into a dialysis tube and dialysed against 2.5 L of buffer for 4 hours; the buffer was then replaced with a similar volume of fresh buffer and then dialysed overnight. The protein solution was then divided into 5 tubes. Propylene glycol was added to the protein solution to give final concentrations of 0 percent (control), 20 and 50 percent. The tubes were then incubated on a shaker at 4°C for up to 24 hours to allow degradation to occur. The samples were assayed for residual propylene glycol. The test results are given in Tables 6 and 7. No change was noted in the control. Table 6. PG removal rate for an initial concentration of 20 percent propylene glycol at 4°C Table 7. PG removal rate for an initial concentration of 50 percent propylene glycol at 4°C For both initial concentrations, the percent PG removed with a purified enzyme extract ranged from about 25 to 30 percent for an exposure of 1 to 12 hours, while at 24 hours the amount of PG removed was slightly less than 50 percent. By comparison, in the previous example for the crude enzyme extract, which the removal rate was about 10 percent after 24 hours and 20 percent after 48 hours. The purified enzyme extract has the ability to remove about a factor of five more propylene glycol within 24 hours than the crude extract. The kinetics of the removal may be influenced by co- factors. EXAMPLE 4 - Effect of Membrane Debris on the Reduction in BOD When the Pseudomonas putida cells were disrupted and the various fractions produced for exposure to 20 percent PG, (producing an initial BOD concentration of 280,000 mg/1), the residual concentration of soluble BOD was determined on those exposed samples. The fractions were exposed to PG at 4°C for 24 hours and were either aerated or not aerated. Table 8 shows the test results. Table 8. BOD removed from propylene glycol (initial BOD concentration of 280,000) after 24 hours with various cell fractions of Pseudomonas putida at 4°C without aeration These results indicate that the presence of cell walls increased the rate of oxidation over a 24-hour period. The cell wall enzymes exhibited sufficient PG degrading ability as well as providing enzymes for electron transport. The whole homogenate, which would contain a higher concentration of PG degrading enzyme as well as cell wall debris, showed a higher overall BOD removal rate at almost 40 percent within 24 hours. With aeration over the same period both the purified protein alone and the purified protein and added cell wall fraction increased the ability to remove BOD to 20.7 percent. The addition of oxygen increased the biodegradation rates for the purified protein alone and with added cell walls. However, the whole homogenate did not show an increase with aeration and neither did the cell wall fraction over this period. Of specific interest is the low BOD concentration produced by the presence of the enzyme alone, comprising less than 6 percent of the total BOD load. Thus even when the PG at 20 percent (w/v) is removed, the remaining BOD would not be more than 6 percent of the original mixture EXAMPLE 5 - Reduction in BOD when Propylene Glycol is Exposed to Purified Enzymes and Cell Walls Derived from Pseudomonas Putida Example 3 demonstrated that gel column purified enzymes derived from sonicated cells of Pseudomonas putida were capable of a high degree of PG removal from solution. This was evident even at substrate concentrations as high as 50 percent (w/v) . Residual PG was measured by means of specific colorimetric analysis. Intermediates produced by primary catabolism may also be present. These intermediate compounds may contribute significantly to the organic (BOD) residuals. This example addresses the ability of such enzyme preparations to oxidize organic substrates using terminal electron acceptors such as oxygen. BOD decreases should correlate with the decrease in PG concentration. In order to provide sufficient enzyme for this set of experiments, 30 liters of the Pseudomonas putida culture were grown. The growth medium contained mineral salts, an ammonium salt nitrogen source, and phosphate buffers together with PG (0.5 percent (w/v) as the sole source of organic carbon. The culture was aerated in a laboratory fermenter and grown at 15°C to stimulate production of psychrophilic enzymes capable of degrading PG at a high rate. The cultures were centrifuged, resuspended in buffer and sonicated as previously described. The sonicated preparation was centrifuged at 10,000g's for 2 hours to separate the cell walls from the homogenate. The homogenate was then subjected to an ammonium sulfate, 80 percent (w/v), precipitation procedure as previously described. The precipitate was dialysed in buffer to remove excess ammonium ions and resuspended in buffer for PG exposure experiments. The cell walls were kept as a separate fraction. The purified protein with added cell walls provided a mixed enzyme preparation for PG exposures. The following enzyme preparations were used for determining organic load removal as measured by BOD concentration in the presence of PG as a substrate: 1. Purified protein concentrate. 2. Purified protein plus cell wall preparation, [50:50 mixture (v/v)]. 3. Cell wall alone. 4. Whole cell homogenate (sonicated preparation with no physical separation step) . The preparations (20mL), were incubated at 4°C or 25°C in 50 mL tubes with or without aeration as designated. Samples were taken at 1-day and 4-day incubation times. After exposure of the fractions to PG at 20 percent (w/v) concentration the cultures (lOmL) were removed from the tubes and diluted 1:10 and sent to the South West Water analytical laboratories for determination of BOD by standard methods adopted by the US and UK water regulatory authorities. Figure 5 shows the level of BOD remaining after PG was exposed to the various cell fractions. The initial BOD concentration of the PG solution was 280,000 mg/L. Without aeration, over 40 percent of BOD was removed in a four day incubation period in the presence of cell walls, either alone or within the whole homogenate preparation. With aeration, all of the preparations exhibited a BOD removal of over 40 percent at 4 days incubation, with the whole homogenate showing 53 percent removal of BOD. Of the aerated preparations, three quarters exhibited BOD removal of over 35 percent and 75 percent of the non- aerated preparations showed BOD removals of less than 35 percent. The presence of cell membranes appeared to be important with regard to further oxidation of the parent compound and 60 percent of those preparations showed over 35 percent BOD removal. With no added cell walls, 75 percent of the samples showed less than 35 percent BOD removal. Also the majority of the samples exhibited more BOD removal after 4 days incubation compared with samples only incubated one day. Of interest was whether the trend was to be repeated with the samples incubated at 25°C. Increased activity was evident with and without aeration at this temperature, particularly at 4 days incubation. This is shown in Figure 5. Overall the results indicate that the presence of cell wall membrane enzymes increase the oxidation of the organic intermediate compounds produced subsequent to PG hydroxylation. These enzymes are known to be membrane bound and include those enzyme and co-factor chains accepting electron transfer finally to cytochrome c and ultimately oxygen. Nicotine adenine dinucleotide, (NAD[H]), is key to this transfer and requires re- oxidization by the other enzyme fractions within the electron transport mechanism, which is closely associated with the cell membranes. The fact that, after 4 days, complete organic removal was not achieved indicates some slowing down of the NAD[H] oxidization mechanism. However, substantial oxidation of the contained organics, as measured by BOD concentrations, did occur, and this indicates the potential of adding such enzyme preparations for PG remediation in situ. The requirement for oxygen is demonstrated by the fact that 81 percent of all of the samples that were aerated showed above 40 percent BOD removal and 88 percent of the samples without aeration showed less than 20 percent BOD removal. The longer incubation times showed higher BOD removal and those with added cellular membranes showed higher BOD removal. The overall data are shown in Table 9. All the samples were tested in duplicate and the numbers shown are the averages. The BOD of the enzyme preparations alone were very low, being between 1,000-2,000 mg/L of BOD. This is equivalent to less than 1 percent of the original starting BOD concentration and less than 2 percent after degradation of the PG. Table 9. Removal of BOD by Enzymes Exposed to PG at an Initial Concentration of 280,000 mg/1 BOD Temperature (°C) 4 4 4 4 Aeration No No Yes Yes Incubation (days) 1 4 1 4 Purified Protein 267,000 190,500 225,000 145,500 Purified Protein: Cell 240,000 175,500 198,000 156,000 walls. Cell Walls 195,000 159,000 170,000 175,000 Whole Homogenate 171,000 162,000 225,000 137,000 Temperature (°C) 25 25 25 25 Aeration No No Yes Yes Incubation (days) 1 4 1 4 Purified protein 222,000 213,000 260,000 123,000 Purified protein: Cell 222,000 168,000 260,000 129,000 Walls Cell Walls 225,000 166,500 247,000 127,500 Whole Homogenate. 261,000 150,000 259,000 172,500 The use of whole cells as the active agents, in place of the enzyme preparations, showed little removal over one day, but after 4 days demonstrated significant results, with a removal of about 30 to 57 percent of BOD. This indicated that during the longer exposure period, enzymes in integrated cells were capable of significant oxidation of PG and its metabolic intermediates. In terms of direct correlation between the residual BOD and PG concentrations, the amount of intermediate oxidation using the membrane bound enzymes will depend on the amount of such enzymes available, and the extraneous oxygenation and the re-oxidation of electron acceptors. The trend is shown in Figure 6. The aeration at 4°C after 4 days incubation indicated a better correlation than the data without aeration (see Figure 7). EXAMPLE 6 - Further BOD Reduction on Flat Surfaces using Enzyme Preparations It was shown in the previous example that with freshly prepared enzyme material, the BOD due to PG can be reduced in test tubes with forced aeration. In actual use, deicing fluids will be on surfaces where air currents must provide the oxygen for oxidation. In this example, the enzymes were lyophilized or freeze-dried. This allowed known weights of different enzyme preparations to be added to a known surface area with a known volume of propylene glycol solution. Two (2) mL of 20 percent propylene glycol was smeared over an aluminium plate to which either 50mg or lOOmg freeze dried enzyme was added. Wet weight whole cells (lOOmg) were added to one plate to provide a baseline activity. A control of 20 percent propylene glycol without the addition of enzymes was also included. The plates were taken to a cold room at 2 to 4°C with natural airflow and tested for three days. During this period some desiccation occurred. Pure water was added periodically to each plate to provide suitable conditions for the enzyme or whole-cell biological degrading activity. After the three days the material was removed from the surface of the plates with 40 mL of pure irrigation water. Each plate sample was sent to South West Water analytical laboratories for BOD analysis. The results are shown in Table 10. Table 10. The Effect of Airflow on BOD Removal from Propylene Glycol (initial concentration = 280,000 mg/L BOD) The best reduction occurred using whole homogenate preparations (similar to the test tube experiments) with cell walls included. Whole cells produced a reduction of about 25 percent. Airflow and co-factors for electron transport to oxygen provided sufficient oxidation to reduce the BOD load. The enzymes alone contributed to an increase in the BOD (see Table 11). Table 11. Contributions of Enzymes to BOD Loading Thus the enzyme materials contributed no more than 10.5 percent of the BOD load for the whole homogenate and purified enzyme, and for the cell wall fraction no more than 18 percent of the total BOD load. Doubling the whole homogenate enzyme fraction may increase the added BOD load by a further 10 percent while reducing the PG load contribution by up to 40 percent, providing a significant net reduction EXAMPLE 7 - Radioactively Labeled Propylene Glycol for Determining the Rate of Mineralization Fresh cell concentrate, fresh whole homogenate and freeze-dried whole homogenate preparations of Pseudomonas putida were exposed to radioactively labelled PG to determine the extent of PG mineralization. These were all prepared as previously described, except the freeze dried homogenate, which was used as a suspension in the mineral salts medium/buffer as a thick paste; 1.0 g (approx. 10 mL) of powder in 6 L of buffer. The buffer was made up with glycol at either a 2.0 percent or 21 percent concentration. As described previously, the cell concentrate and fresh homogenate had glycol added to 2 or 21 percent of final volume. A typical metabolic result is shown in Table 12. The data were obtained with a scintillation counter and are expressed in terms of counts per second (cps). Table 12. Mineralization of Propylene Glycol by Whole Cell Concentrate at Ambient Temperature The above data demonstrated that the PG was mineralized significantly to CO 2 by the various preparations within 2 hours. The rate of mineralization after the 2 hours incubation was 3 to 3.5 percent per hour and was relatively independent of the initial PG concentration, indicating a higher specific rate of metabolism at the higher initial concentration. A higher initial glycol concentration increases the initial rate of metabolism. Over a longer time period this rate may slow. The cells demonstrate a higher amount of metabolic intermediates, comprising 18 to 21 percent of the total initial glycol after 2 hours incubation. A freshly prepared whole cell homogenate showed similar results (see Table 13). Table 13. Mineralization of Propylene Glycol by a Freshly Prepared Whole Cell Homogenate at Ambient Temperature Table 13 shows a very similar metabolic activity to the whole cells, whereby the carbon in the glycol is metabolized to carbon dioxide. The controls with no enzyme or whole cells added showed that about 1 percent of the original radioactive material was found on the filter papers. Thus the metabolic activity of the whole cells as well as the freshly prepared homogenate was significant in metabolising the glycol and mineralising it to carbon dioxide. EXAMPLE 8 - Environmental Effects of PG-Degrading Enzyme It was shown in previous examples that the enzyme matrix extracted from Pseudomonas putida effectively degrades the freezing point depressant propylene glycol. This enzyme will be used to degrade aircraft and airport pavement deicing/anti-icing chemical formulations and will eventually end up in storm water or in captured runoff and be treated in a POTW. The biofilms in these waste treatment systems may be contaminated by the enzyme matrix. The effect of different concentrations of the enzyme on the contamination of a biofilm generated from a waste treatment process was determined. A biofilm from a municipal wastewater treatment facility was generated on a flat surface and subsequently exposed to enzymes extracted from Pseudomonas putida in the laboratory. Aluminum plates, 16 cm^ in area, were suspended in the final outfall from an activated sludge unit treating municipal sewage sludge. A biofilm was allowed to build up on the aluminum plates over 7 days. The biofilm included bacteria and eukaryotes, such as algae, and provided representative species for the exposure tests. In the laboratory, the plates containing the biofilms were then exposed at room temperature (at time 0) to different concentrations of the PG degrading enzyme complex derived from Pseudomonas putida. The plates were tested for a viable biofilm population by means of bioluminescence at time 0 and at other times over the 7-day period. To each plate was added 50 μL of a lysing agent to release adenosine triphosphate, (ATP) from the microbes. Next 50 μL of luciferase enzyme preparation was added to the plates with its substrate, and the bioluminecence was measured. The ATP concentration is a measure of microbial viability. If there is inhibition of cell viability due to the presence of a toxic substance, this will reduce the amount of ATP present. The unit of measurement of cell viability is relative light units (RLU's) and is related directly to the number of viable cells present. The instrument used to measure RLU is the Bioprobe (Pall- Gellman, Ann Arbor, Michigan) . The plates were placed directly under the Bioprobe after the extractant and luciferase enzymes were added. Because the biofilm on each plate was variable, the viability of the biofilm was monitored with different exposures to the PG-degrading extracted enzyme on triplicate plates at each time, namely 0, 1, 2, 5 and 9 days. The concentrations of the enzyme were: Neat; 1:2 dilution; 1:5 dilution; 1: 10 dilution and no enzyme added. Water was used as the control exposure. The bioluminescence was measured for each of the triplicate plates in the particular exposure regime and the readings averaged. The initial microbial aluminum plate counts were high and reflected a growing culture with an input of nutrients from the outfall of the activated sludge unit. During the laboratory phase of the study the only liquid that was added to the biofilm was the extracted enzymes; no nutrients were made available to the biofilm. It was expected that the biofilm viability in the control as well as in those exposed to the enzyme concentrations would decrease with time. From Figure 8, however, it is evident that there was little difference between the biofilm exposed to the enzyme compared with the control. The viability of the biofilm was reduced the most upon exposure to the neat enzyme, but not significantly compared with the controls or the other exposure regimes. None of the diluted enzymes were inhibitory to the biofilms and it is expected that when the enzyme reaches such active biofilms in treatment systems that the concentration would be significantly lower than the ones used in this experiment. EXAMPLE 9 - Baseline Degradation Rates The rate of PG removal of the baseline microbial consortium was determined for various initial concentrations of propylene glycol. About 2.5 liters of activated sludge was collected from the Exeter (Countess Wear) (England) activated sludge plant and then transported immediately to the laboratory for microbial studies. The microbes were centrifuged in an MSE Coolspin at 4,000 rpm for 1 hour. The firm microbial pellet was separated from the clear supernatant by decanting and then re- suspended in 100 mL of pure water giving a final volume of about 250 mL. The suspension was sonicated in batches for 40 min. each, consisting of 20 one minute bursts, with one minute rests, to allow cooling of the mixture and to minimize denaturation of the extracted enzyme matrix. The total enzyme suspension was combined and well mixed. The subsequent homogenate was placed into ten 50 mL tubes together with propylene glycol to provide two sets of tubes with the following PG concentrations:-0, 5 10 and 20 percent. The tubes were incubated in a shaker at 4°C for 5 days. At the end of the incubation period the mixture was centrifuged at 4,000 rpm to substantially remove the enzyme matrix as a pellet and to test the supernatant for residual concentrations of PG. The normal colorimetric assay was used for the estimation of soluble PG concentrations in each of the tubes. Table 14 shows the concentrations as estimated from the calibration curves. Table 14. Removal rate after 5 days of incubation The rate of biodegradation is somewhat lower than with enzyme matrices derived from unacclimated cells, especially at the higher 20 percent concentration, where inhibition of the active enzyme in this preparation may have occurred. EXAMPLE 10 - Comparison of Pseudomonas Putida and Activated Sludge Enzyme Degradation Rates per Unit Mass Two and one-half (2.5) liters of fresh activated sludge was collected from the Exeter (Countess Wear) (England) treatment works. This was spun down in a MSE Coolspin centrifuge for 1 hour to give a solid pellet and clear supernatant. The pellet was allowed to drain and had a fresh weight of 95. lOg. The pellet was re-suspended in as small a volume of mineral salts medium as possible prior to sonication and gave a final volume of 260 ml (0.36g/ml). Two and one-half (2.5) liters of a dense culture of Pseudomonas putida was collected from the fermenter. The cells were harvested by centrifugation in a Europa 24 centrifuge in 200 mL batches at approximately 18,000g's for 90 minutes. Although cells were collected by this procedure, no firm pellet was obtained. The fresh weight of cells collected was approximately 5g. The cells were re- suspended in as small a volume of mineral salts medium as practical to give a final volume of 155 ml (0.032g/ml). Both batches were sonicated under identical conditions, in batches of approximately 40ml on ice using a MSE Soniprep 150 sonicator. Each batch was sonicated for 15 one minute bursts, with one minute rests. The sonicate was then bulked up and well mixed and aliquoted into 50 ml tubes. Propylene glycol was then added to each tube to give various concentrations, as listed in Table 15. The final volume in each tube was 25 mL. Controls of 0 percent and 0.5 percent PG were also made up for the final assay. The samples were then incubated at 12°C in an inclined position to give good mixing in a shaking incubator for 90 hours. Samples were then collected and assayed for residual glycol using the normal assay procedure. The results are tabulated separately in Tables 15 and 16. Samples of the original sonicates were retained for assaying for wet weight concentration. Table 15. Removal rates of Pseudomonas putida enzyme matrix Table 16. Removal rates of activated sewage sludge-enzyme matrix The wet weight concentration in the activated sludge is approximately ten times that of the Pseudomonas putida enzyme preparation. For the same initial concentration, the rates of PG biodegradation per wet weight of Pseudomonas putida cell enzymes are between 7 and 10 times that of the activated sludge extracts. Thus the isolation and elective culture of Pseudomonas putida from the baseline microbial activity in the activated sludge showed an order of magnitude improvement on the PG degrading biomass in the activated sludge. EXAMPLE 11. COD and BOD Analyses of Existing and Potential Freezing Point Depressants The BOD5 and BOD20 analyses of existing and potential freezing point depressant formulations, together with chemical oxygen demand (COD) analyses, are shown in Table 17. The data indicated that with a one percent concentration for each formulation, the chemical oxidation potential of each is broadly similar, (17,000-19,800 mg/1) and is relatively independent of chemical formulation. However the biological responses are different. The lower the COD:BOD 2 o ratio the more biologically oxidizable the formulation. Thus from the above data, propylene glycol is more biologically treatable and the glycerol:Tri-EG mixtures are the least biologically oxidizable. Indeed those formulations containing tri-ethylene glycol are slower to degrade biologically than the other formulations (see Figure 9) . Table 17. BOD and COD (mgO 2 /L) Analyses of Existing and Potential Freezing Point Depressant Formulations EXAMPLE 12 - Biodegradation of Alternative Freezing Point Depressants The utilization of PG as an anti-icing chemical may be supplanted by other more environmentally acceptable organics such as glycerol and butanediol. The growth of Pseudomonas putida and similar types of bacteria on glycerol was measured. Pseudomonas putida and other microbes extracted from activated sludge units and previously exposed to organic chemicals were grown up under selective pressure in increasing concentrations of glycerol in a minimal mineral salts medium, where the glycerol was used as the sole carbon source. A pure culture emerged which was shown to grow in the presence of glycerol at increasing concentrations in the growth media. This culture had been isolated onto agar and grown successfully at 2-4°C and was characterized biochemically. By colony morphology, the culture appeared to be similar to Pseudomonas putida. The growth of the culture on glycerol is shown in Figure 10. By comparison, Figure 11 shows the growth of a pure culture of Pseudomonas fragi on glycerol. Pseudomonas fragi is a psychrophilic microbe isolated primarily for growth on butyric acid. Example 13 - Rate of Biooxidation of Freezing Point Depressants using Activated Sludge Microorganisms The biooxidation of de-icing materials, such as glycols, is dependent on the type of microbes present, the temperature and other environmental factors such as pH. It is important to set up a standard procedure that enables a rate determination to be made at different operating temperatures. Since the temperature of the ground and surrounding facilities will be low during usage of these mixtures, say 4°C + 2°C, then the rate has to be determined at these temperatures. If the material enters a waste treatment process, then higher temperatures will be encountered. Oxygen uptake experiments can be determined using a Gilson differential respirometer. The main compartment of the reaction vessel contained suitable buffers with the activated sludge microbes added at time zero from a side bulb to begin the experiment. A center well contained 0.1 ml. of 20 percent KOH solution, together with a small piece of fluted filter paper, to take up released carbon dioxide from the reaction. All respirometric studies were carried out at the appropriate temperature in an atmosphere of air. The lengths of the studies were from several hours to days depending on the rate of uptake compared with controls the controls were formulated without deicers. The concentrations chosen were 1 percent and 20 percent of these materials, being within the range likely to be encountered in receiving waters, on the ground or in treatment facilities. The rates were required to go to as near completion as possible, to determine whether these rates change with lower substrate concentrations or with acclimation of the activated sludge microbes. The biooxidation rates were determined by deducting the endogenous respiration rate. The results for individual formulations are shown in Figures 12 through 15. They are indicative of the behavior of environmental microbes likely to encounter de-icing materials released on the ground or into receiving waters. All these results were obtained at 2-4°C. The overall results for the respirometry indicated that at 2-4°C the potential oxidations were always positive with the FPD concentrations of 1 percent (see Table 18). At 20 percent concentration the rates are reduced to below endogenous, except for glycerol. Some of the formulations were repeated at 20 percent concentration as shown. Table 18. Rates of Oxidation (μL O 2 consumed per hour) at 2-4°C. All figures are shown with the endogenous respiration deducted. The rates of oxidation at the higher temperature of 20EC are shown in Table 19 and indicate a much higher oxidation rate for all components at 1 percent concentration and a more reduced respiration rate at a concentration of 20 percent. This is especially so for 1,3-butanediol and all formulations including tri-ethylene glycol (20 percent). Table 19. Rates of Oxidation (μL O 2 consumed per hour) at 20°C. All figures are shown with the endogenous respiration deducted. Whereas glycerol and propylene glycol were readily oxidized (even at 20 percent concentration), higher rates of oxidation at the higher temperature, the other formulations inhibited microbial respiration. Only glycerol at 20 percent concentration showed positive oxidation at the low temperatures. However, since the de-icing formulations are expected to be diluted by ground-water, receiving water or precipitation, then they are likely to be readily oxidized by environmental microbs. Even formulations including tri-ethylene glycol demonstrate this trend, but to a lesser extent. The above data was supported by the BOD evidence showing inhibition of microbial respiration by tri-ethylene glycol. EXAMPLE 14 - Enzyme Encapsulation and Release Crude enzyme extract from Pseudomonas putida (Example 2) was loaded into dextran gels by the technique of two-phase aqueous partitioning (Gehrke, S.H., Lupton, E.G., Schiller, M.F., Uhden, L. and Vain, N., Enhanced Loading of Solutes into Polymer Gels, U.S. Patent No. 5,603,955, February 18, 1997.) under a variety of conditions. The change in protein concentration in the enzyme loading liquor was monitored. A decrease in protein concentration showed that some of the protein had moved into the gel. It was assumed that the amount of protein loaded into the gel was equal to the difference between the initial and final concentration of the protein in the enzyme liquor. Several samples of enzyme were loaded into several gels in the following manner. Five solutions which contained enzyme, buffer, and in some cases loading salts and loading polymer were prepared. Table 20 shows the composition of the loading solutions. In this table, "enzyme" refers to the enzyme supernatant to which 0.068g Na2HPO4 and 0.07 lg KH2PO4 had been added per lOOg of solution; KI is potassium iodide; "BU4NF" is a 50 percent solution of tetrabutylammonium fluoride in water; and "PEG" is polyethylene glycol (Molecular weight, 10,000 g/mol). Table 20. Loading solution composition Five soaking solutions (A through E) were also prepared; these had the same compositions as the loading solutions (K through O) except that they contained no enzyme. Seven sets of vials were prepared, with two vials in each set. Five sets (K, L, M, N, and O) used the soaking and loading solutions described above in Table 20. The other two sets were controls, one of which was identical to K but contained no enzyme (Labeled No Enzyme 1 and 2), the other of which was identical to K but contained no gel (Labeled No Gel 1 and 2). Dried dextran gel (0.2g) was placed in each of the five lettered and No Enzyme sets. The gel was prepared by cross-linking dextran polymer with 2 percent of vinyl sulfone by weight. Five (5) mis of the corresponding soaking solution were added to each vial in each set. The gels were allowed to swell to equilibrium, which took 2 hours. Next the soaking solution was removed by filtration and the re- weighed gels were placed in new vials for loading. Three (3) grams of the appropriate loading solution were added to each vial and the gels and solutions were allowed to come to equilibrium overnight. The next day a sample of each loading solution was removed for analysis of its protein content by Bradford assay. Results of the assay are shown in Table 21. The decrease in protein concentration in the loading solution indicates that the loading attempts were successful. Table 21. Relative concentration of loading supernatants after exposure to the gel EXAMPLE 15- Preservation of Enzyme Activity by Coating the Gel A dextran gel was loaded with dye. The gel containing the dye was then coated with a polyurethane layer by immersing the gel in a mixture of a diisocyanate and a polyol. (Lupton, E.C., Yu, X., Bromberg, L. and Hand, B., EncapsulatedMaterials, U.S. Patent No. 5,726,456, March 10, 1998.) Neutral red dye (2.4 g) was dissolved in 120 mL of an aqueous solution consisting of 12 wt percent PEG (MW 10,000 g/mol) and KBr (0.22M). Then 500 mg of dextran gel beads were allowed to swell in the solution for 48 hours at ambient temperature. The same experiment was conducted with hemoglobin in place of neutral red dye. Dry gel beads loaded with hemoglobin and neutral red dye were immersed in polyisocyanate Desmodur N-3300 (Bayer Corp.) and subsequently in glycerol. A transparent rubbery layer around a colored center of each bead was observed. Breaking the coating on the gels allows the release of the enzyme at the proper time. EXAMPLE 16 - Encapsulation with Alginate Gel Beads. Alginate polymer was obtained from Sigma Chemical and ProNova Biopolymers. Three grades were purchased from Sigma, of low (250 cps), medium (3500 cps), and high viscosity (14,000 cps), respectively, when prepared as 2 percent solutions in water. Protanal LF 5/60 and 10/60, pharmaceutical grades, were purchased from ProNova. Bovine hemoglobin was obtained from Sigma and was used as a coloring agent and as a model of the Pseudomonas putida enzyme. Calcium chloride hexahydrate was obtained from Aldrich. Alginate gel beads were made with two different techniques; with a syringe and by suspension in an organic solution. First, millimeter size gels were made by filling a syringe with a suitable alginate solution (0.5 to 2 percent) mixed with hemoglobin (4mg/mL makes a dark gel) and dripping the alginate solution into a solution of calcium a good chloride. The gel forming ability and resistance to shear of the low, medium, and high viscosity alginates in calcium chloride solutions (0.1 percent to 10 percent CaCl2 , 6H2θ) were tested. Selected alginates were also tested in solutions of 50 percent and 83 percent calcium chloride. Three trends were observed. How well the gels are formed and their strength (resistance to shear) increases with increasing viscosity of the alginate solution (molecular weight), with increasing concentration of calcium chloride, and with increasing time spent in the cross-linking solution. Well-formed gels were defined as those that adopted a spherical or teardrop shape on contact with the calcium chloride solution. Poorly formed gels did not have enough physical integrity to maintain their shape even without being subjected to shear, and either agglomerated, formed extended structures, or completely dissolved in the calcium chloride solution. Gel shape and integrity are important because the gels have to survive handling, which includes operations such as vacuum filtration, and drying. Gels were subjected to shear by stirring at high speed with a maxi-mix vortexer for 15 seconds at a time. In addition to tests of gel integrity, qualitative results concerning the rate of hemoglobin release into aqueous solutions were obtained. Hemoglobin release from alginates occurred over a period of minutes to hours, which is appropriate for the period after application of the deicer/ anti-icer. The syringe-drop gels were used to explore a method of stabilizing the gel beads so that they can be stored appropriately in the deicing/anti-icing solutions. The previously formed gels were placed in a diluted solution of high molecular weight polyethyleneimine, an organic polycation. Typical polyethyleneimine solutions used were one or two percent by weight in water and 20 minutes was a typical immersion time. The particles shrunk and hardened which is a result of the formation of the polyethylenimine-alginate complex. Visual inspection of the gels under a microscope showed that an outer layer of slightly lighter color had formed. These treated gels were also more resistant to shear stresses. Tests to determine the release of hemoglobin from the stabilized and non- stabilized particles were also conducted. Release was conducted both under mild agitation as well under shear utilizing a high-speed stirrer. The particles with and without polyethylenimine as a stabilizer exhibited dramatic differences in the rate of release, namely, hemoglobin was instantly released from the non- stabilized particles, while the release of hemoglobin from the stabilized particles coated with polyethylenimine was delayed. Small alginate beads were formed by suspension in a rapidly stirring organic solution. Specifically, a solution of 500 ml Norpar-12 mineral oil (Exxon) and lg of Gannex V216 surfactant (International Specialty Products), a hydrophobically modified polyvinylpyrrolidone, was stirred at 1000 rpm in a one liter reactor. To this solution was added 100 mL of 1 percent medium viscosity alginate with hemoglobin. After the alginate had been added, 25 mL of 50 percent was poured into the reactor. The reactor contents were stirred for ten more minutes, and then the alginate beads were collected in a buchner funnel and washed three times with 25 mL portions of hexane. The beads, which clumped slightly, were dark brown from the hemoglobin and were dried under a stream of room temperature air from a blow dryer overnight. In this experiment it appeared that little or no hemoglobin loss to the surrounding solution had occurred. This is because hemoglobin is not soluble in mineral oil, unlike the experiments described above, which involved gel formation in calcium chloride solution. EXAMPLE 17 - Lyophilization of the Pseudomonas putida strain. While the process of freeze-drying the biomass of Ps. putida may vary slightly depending on the particular equipment available, the lyophilized preparation of the microorganism can be manufactured as outlined below. The biomass of Ps. putida is harvested by aseptic centrifugation at 10,000 to 14,000g. The supernatant is discarded. The pellet is resuspended in fresh sterile mineral medium containing no carbon source and centrifuged again. This procedure is repeated twice. The biomass is resuspended in 20% skim milk to a concentration of approximately 10° CFU/mL. The suspension of microorganisms in the skim milk solution is dispensed into borosilicate ampules and transferred to fast freeze at - 40 °C. After a 15-30 minute period the ampules are exposed to vacuum and the following freeze-drying cycle is performed: - - 40 °C for 90 to 120 min, the temperature control is reset to - 10 °C and the temperature allowed to rise to - 10 °C, - - 10 °C for 120 min, temperature control is stopped, drying is continued at room temperature. The vacuum should reach 100 μm Hg within first hour of freeze- drying and should gradually drop to 20 to 30 μm Hg when the suspension nears dryness. The ampules are kept in the lyophilizer under vacuum for at least additional 16 hours to assure the complete dryness. After drying, the ampules are sealed under vacuum at 20 to 30 μm Hg. The lyophilized preparation is kept refrigerated at 4-6 °C. The microorganisms are recovered by aseptic rehydration using mineral medium containing a suitable carbon source (e.g, glycerol, propylene glycol). The microorganisms should remain viable for at least two years. EXAMPLE 18 - Bioreactor and In-situ Biodegradation Processes Previous examples have shown that the enzymatic complexes of the isolated strain of Ps. putida are capable of biodegrading FPDs. Furthermore, it is possible to biodegrade the FPDs using live cells of the strain or even non-living whole cells. Any of these may be used to biodegrade FPDs when applied in situ to aircraft or airport pavement runoff, or, alternatively, in a bioreactor in either batch or continuous modes. In bioreactors, the enzymatic complexes can be used in a suspended or solubilized form or immobilized on a matrix. To improve the biodegradation rates co-factors (e.g., NAD[H], NADP[H]) and microelements (e.g., Zn 2+ , Mg + ) are added to the enzymatic complexes. Recovered deicing/anti-icing liquids and the mineral medium are fed into batch or continuous fermenters which are stirred and/ or sparged. The enzymatic complexes in the form of powder or solution are added to the bioreactor and mixed for the time period required to degrade the FPDs. In order to ensure the required degree of biodegradation, samples from the bioreactor are either removed on a regular basis and analyzed for chemical changes or monitored in situ. The enzymatic complexes can be immobilized on a solid matrix using traditional methods of protein immobilization. For example, they can be attached through silane coupling agents to inorganic supports. The deicing/anti-icing solutions are constantly supplied to the bioreactor and recirculated if necessary. The biodegradation process is monitored, and, as the biodegradation rate declines, the immobilized enzymatic complexes can be partially replenished or completely replaced. Non-living cells are produced by harvesting Ps. putida at the stage where expression of the enzymatic complexes occurs. The cells are harvested by conventional methods (e.g. filtration), preserved by drying (e.g. spray-dried), and stored at room temperature or refrigerated, so that the activity of the enzymatic complex will be retained. Living cells at the same stage can be similarly harvested and preserved by lyophilization and stored at room temperature, or harvested and stored in glycerol suspension frozen at less than -80°C. These cells (living or non-living) can be used in a bioreactor, either suspended or immobilized, just like the enzyme complexes. The addition of co-factors and/or microelements may improve the biodegradation rates, but generally are not required. For in situ application, suspensions or solutions of the enzymatic complexes are used. The required amounts of the enzymatic complexes are determined by laboratory biodegradation studies. During the in situ application the dry powder is suspended in a minimal amount of the mineral medium. The frozen material is defrosted and used without additional dilution. The slurry containing the enzymes can be spread on the spill site surface manually or distributed by a spray using appropriate hardware. If whole non-living or living cell preparations are used, they would be lyophilized as described above, rehydrated in mineral solution, and then either applied in conjunction with the deicer or afterwards. The invention has been described in detail with particular references to the preferred embodiments thereof. However, it will be appreciated that modifications and improvements within the spirit and scope of this invention may be made by those skilled in the art upon considering the present disclosure. The references cited herein are incorporated by reference.

Claims: We claim: 1. An ice control formulation comprising at least one freezing point depressant and an enzyme system that is capable of degrading the freezing point depressant. 2. The ice control formulation according to claim 1 further comprising a surfactant. 3. The ice control formulation according to claim 1 further comprising a thickener. 4. The ice control formulation according to claim 1, wherein the freezing point depressant is selected from ethylene glycol, propylene glycol, glycerol, 1,3-butanediol or triethylene glycol. 5. The ice control formulation according to claim 1, wherein the freezing point depressant comprises a glycol and the enzyme system comprises a glycol -degrading enzyme. 6. The ice control formulation according to claim 1, wherein the freezing point depressant comprises glycerol and the enzyme system comprises a glycerol -degrading enzyme. 7. The ice control formulation according to claim 1, wherein the enzyme system comprises an encapsulated enzyme. 8. The ice control formulation according to claim 7, wherein the enzyme is encapsulated in a gel. 9. The ice control formulation according to claim 8, wherein the gel comprises a responsive gel. 10. The ice control formulation according to claim 9, wherein the responsive gel comprises a polysaccharide or protein. 11. The ice control formulation according to claim 10, wherein the polysaccharide comprises starch, dextran, alginic acid or a cellulose ether. 12. The ice control formulation according to claim 10, wherein the protein comprises gelatin. 13. The ice control formulation according to claim 10, wherein the responsive gel further comprises a crosslinker. 14. The ice control formulation according to claim 13, wherein the crosslinker comprises a multifunctional carboxylic acid derivative. 15. The ice control formulation according to claim 13, wherein the multifunctional carboxylic acid derivative comprises adipoyl chloride or succinyl chloride. 16. The ice control formulation according to claim 7, wherein the enzyme is encapsulated in alginate beads. 17. The ice control formulation according to claim 1, wherein the enzyme system comprises a microbrial system. 18. The ice control formulation according to claim 17, wherein the microbrial system comprises lyophilized microbes that degrade the FPD. 19. A bacteria that degrades a freezing point depressants propylene glycol. 20. A method of encapsulating an enzyme for use in ice control formulations comprising: a) providing an aqueous solution of polymer and enzyme; b) providing an organic solvent which is immiscible with the solution; c) providing a crosslinker which reacts with the polymer, wherein an enzyme encapsulating gel is formed. 21. The method according to claim 20, further comprising, controlling the size of the droplets by altering the stirring speed, relative viscosity of the aqueous and organic phases. 22. The method according to claim 20, wherein the polymer is selected from starch, dextran, alginic acid or a cellulose ether. 23. A method of encapsulating an enzyme for use in ice control formulations comprising: a) providing an aqueous solution of polymer and enzyme; b) providing an organic solvent which is immiscible with the solution; c) heating the solution; d) adding the heated solution to the solvent; e) cooling the resulting mixture, wherein beads are formed upon cooling. 24. The method according to claim 23, wherein the polymer is gelatin. 25. A method of making an ice control formulation comprising: a) providing at least one freezing point depressant; b) providing at least one surfactant; and c) providing at least one enzyme system that degrades the freezing point depressant. 26. The method according to claim 25, wherein the enzyme system comprises an enzyme that is encapsulated.

Inventors: BRYANT JOHN A, GOLD HARRIS, MENDUM THOMAS H E, STAFFORD DAVID A, TEMCHENKO MARINA, WESTMARK CAROLYN S, WILLIS MICHAEL, BRYANT, JOHN, A., GOLD, HARRIS, MENDUM, THOMAS, H., E., STAFFORD, DAVID, A., TEMCHENKO, MARINA, WESTMARK, CAROLYN, S., WILLIS, MICHAEL
Applicants: BRYANT JOHN A, FOSTER MILLER INC, GOLD HARRIS, MENDUM THOMAS H E, STAFFORD DAVID A, TEMCHENKO MARINA, WESTMARK CAROLYN S, WILLIS MICHAEL, BRYANT, JOHN, A., FOSTER-MILLER, INC., GOLD, HARRIS, MENDUM, THOMAS, H., E., STAFFORD, DAVID, A., TEMCHENKO, MARINA, WESTMARK, CAROLYN, S., WILLIS, MICHAEL
Application year: 2000
Main classification: C09K3
IPC codes: C09K3, C12N9, C12N11