CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in- part (CIP) of the co-pending patent application filed March 19, 1992, having U.S. Serial No. 07/853,935, and that patent application is herein incorporated by reference.

DESCRIPTION

BACKGROUND OF THE INVENTION

Field of the Invention

This invention is generally related to the use of enzymes to destroy bacteria and viruses which may be pathogenic and which are commonly found on medical waste and other waste products. More particularly, the invention is directed to a waste disposal system which employs enzymes at controlled pH and temperature conditions to render waste products safe for disposal in sewers and landfills and to reduce the volume of waste ultimately deposited in a landfill.

Description of the Prior Art

Waste disposal has become a huge problem for modern American society and environmentally safe disposal of medical waste poses particularly

demanding challenges. Infectious waste is generated by a wide variety of health care providers such as hospitals, nursing homes, clinics, physician's and dental offices, and blood banks. The form of waste generated by these facilities varies widely and includes intravenous (IV) tubing, syringes, wound care bandages, suction catheters, disposable instruments, mattress covers, and the like, as well as biopsies, blood, body fluids, tissues, gallstones, and other body members. The medical waste can contain a host of pathogens dangerous to human beings including a variety of disease causing bacteria and viruses. In the past, medical waste has been disposed of by unsterilized landfilling. However, disposal by this method is generally unacceptable since pathogens in the waste may present a danger to human beings in the surrounding area. Moreover, the health care provider may be liable for injuries resulting from the waste which would make disposal by this method enormously risky.

Recently, there have been efforts to safely dispose of contaminated medical waste in landfills or at sea by encapsulating the waste in a thermoplastic or thermosetting resin prior to disposal. This is discussed in detail in both U.S. Patent 4,919,569 to Wittenzelliner and U.S. Patent 4,992,217 to Spinello. While this solution may reduce the escape of hazardous pathogens into the surrounding environment, it has the drawbacks of generating more trash which will rapidly fill a landfill and requiring expenditures for the encapsulating material.*

Steam sterilization is a process by which the pathogens are killed from exposure to a high temperature moist heat under pressure in an autoclave. A big drawback of autoclaving is that there is no physical change in the appearance of the waste (e.g., an expert would find it difficult to distinguish an autoclaved syringe from a non- autoclaved syringe) . The lack of a physical change would encourage cheating by some health care providers and would make landfills less likely to accept infectious waste which a health care provider has represented to have been autoclaved. Autoclaving also suffers from being a rate limited process, and it requires standard loads for validation of the process.

U.S. Patent 5,048,766 to Gaylor et al. discloses a method for converting infectious waste to a non-infectious form which utilizes heating, wherein the waste is first ground to small particles to allow better penetration of the heat. In addition to allowing better heat treatment, the prior grinding step would also change the general appearance of the waste which might make it more acceptable to a landfill operator. However, it should be understood that shredded waste which has not been autoclaved would appear very similar to shredded waste which has been autoclaved. Autoclaving has the drawback of being an expensive means for sterilization since the autoclave itself is a high capital investment and autoclaves use enormous amounts of energy.

U.S. Patent 5,035,858 to Held et al. discloses disinfecting medical materials by heating and

simultaneous exposure to gamma radiation. In addition to the radiation hazard presented by this method, the resulting product may also suffer from the lack of an easily identified physical change in the waste.

Another method which has been used for handling medical waste is to grind and shred the waste and then expose it to a sterilizing, germicidal solution containing toxic chemical constituents which will kill bacteria and viruses. Variations on this method are disclosed in U.S. Patent 4,971,261 to Solomons, U.S. Patent 4,979,683 to Busdecker, U.S. Patent 5,025,994 to Maitlen, U.S. Patent 5,035,367 to Nojima, and U.S. Patent 5,064,124 to Chang. The use of a powerful sterilizing fluid presents safety problems for both the operator and the environment since the fluids used would be harmful to human beings. In addition, the use of large quantities of disinfectant and disposal to the sewer might result in disruption of the microbial treatment in the waste water plant.

Currently, the most popular medical waste disposal method is incineration. Basically, all forms of medical waste are collected, shredded, and burned in an incinerator or disintegrator. U.S. Patent 5,054,696 to Mennel et al. discloses that a liquid disinfectant can be added to the shredded waste prior to disintegration. Besides having a very high building cost, there are extensive licensing procedures for incinerating medical waste because of the highly toxic residues that can be produced by the process. Moreover, the nature of

the smoke emanating from an incinerator smoke stack is still not well understood and may vary depending on the type of waste being burned.

The biological treatment of waste water and other aqueous wastes is well known. Specifically, U.S. Patent 3,591,491 to Smith et al. , U.S. Patent 4,721,585 to Melchiorri Santolini et al. , U.S. Patent 4,882,059 to Wong et al. , U.S. Patent 4,940,539 to Weber, and U.S. Patent 4,992,174 to Caplan et al. all disclose the use of activated bacteria and enzymes to degrade waste materials in aqueous media. However, none of the above patents disclose the destruction of pathogens which are present in infectious waste material. Moreover, the biological solutions disclosed in the above patents could not be used to destroy all bacteria present in waste material since the "activated" bacteria in the solution would also be destroyed. U.S. Patent 4,936,994 to Wiatr discloses that a blend of cellulase, an enzyme which reduces cellulose to glucose, amylase, an enzyme which reduces starch to sugars, and proteases, enzymes which hydrolyze peptide bonds, can be used to control industrial slime. In operation, the enzymes breakdown the extracellular slime produced by certain slime forming bacteria and render the bacteria more easily susceptible to biocidal challenge. Wiatr does not use the enzyme solution to metabolize and destroy the slime producing bacteria.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a system and method for infectious waste disposal which overcomes the disadvantages of the prior art. It is another object this invention to use enzymatic action to destroy pathogenic bacteria and viruses present on a wide variety of waste products. It is yet another object of this invention to provide an infectious waste disposal system and method which significantly reduces the volume of treated waste.

It is still another object of this invention to provide an infectious waste disposal system and method which is both environmentally and aesthetically sound, and protective of the public health.

According to the invention, enzymes are employed at low levels under controlled pH and temperature conditions to destroy pathogenic viruses and bacteria found on infectious waste products. In operation, infectious waste products are ground to a fine particle size and deposited in an enzyme bath. The enzyme or enzyme combinations used in the bath are chosen to destroy or disable pathogenic bacteria and viruses, and the pH and temperature conditions are controlled for optimum performance of the enzyme or enzyme combinations. In some instances, different enzymes and different operating conditions may be more suitable for destroying certain bacteria or viruses than other bacteria or viruses. In those instances, either

two or more different enzyme baths may be employed in the infectious waste disposal system, or conditions within the same enzyme bath could be adjusted after a certain time interval to accommodate the requirements for the new enzyme. Agitation can be employed in the enzyme bath to enhance enzymatic activity and speed up the disposal process. The time the infectious waste products remain in the enzyme bath should be sufficient to destroy or disable the pathogens on the infectious waste products. In addition to destroying pathogens, enzymatic activity can be used to substantially reduce the volume of treated waste, thereby extending the life expectancy of sanitary landfills. The system can be installed on-site at a health care facility, thus eliminating the cost of waste packaging and transport, as well as eliminating the potential threat of environmental spillage.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of the preferred embodiments of this invention with reference to the drawings, in which:

Figure 1 is a schematic drawing of an enzyme bath system with controlled pH, temperature, agitation, and timing parameters;

Figure 2 is a flow chart showing a process for rendering bacteria and viruses inactive through enzymatic activity;

Figure 3 is a graph showing the effect of protease on four test organisms at pH 4.3 and 50°C;

Figure 4 is a graph showing the effect of protease on four test organisms in the presence of 10% waste product at pH 4.3 and 50°C;

Figure 5 is a bar graph showing the enhanced killing activity of an alkaline protease on human poliovirus;

Figure 6 is a bar graph showing the enhanced killing activity of an enzyme mixture, under acidic conditions, on human poliovirus;

Figure 7 is a bar graph showing the enhanced killing activity of different alkaline and acid proteases under alkaline and acidic conditions on canine parvovirus;

Figures 8a-c are line graphs showing the enhanced killing activity of proteases, as compared to cellulases and amylases, at low pH conditions;

Figure 9 is a schematic drawing showing a medical waste treatment system; and

Figure 10 is a schematic drawing of a medical waste container opening station which can be used in the medical waste treatment system of Figure 10.

DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS OF THE INVENTION

The Resource Conservation and Recovery Act (RCRA) requires treatment of hazardous waste to eliminate or reduce the hazard associated with that waste. Although medical waste is not considered hazardous under RCRA, it is appropriate to consider similar criteria for its treatment. In their 1986

"EPA Guide to Infectious Waste Management", the Environmental Protection Agency (EPA) recommended only incineration, autoclaving, and chemical disinfection as economically feasible and effective mechanisms for reducing the number of infectious agents in medical waste. Since that time, numerous alternative methods of treatment have been developed, evaluated and approved as effective.

The major public concerns with medical waste have been the potential for the spread of infectious diseases, and esthetics. Infectious agents require very specific micro-environments for survival and growth, and as such are subject to rapid destruction in hostile environments. Unlike infectious agents, toxic, hazardous chemicals pose a significant environmental problem because they are not easily destroyed. Their continued presence in the environment results in significant damage to the ecology. Human pathogenic viruses such as HBV and HIV, require specific living cells for survival and growth. Mammalian cells are exquisitely sensitive to changes in their micro-environment and do not survive when removed from the body, except under very stringent laboratory conditions. Since their host cells die very quickly in the environment, viruses will not increase in number, and are unlikely to survive the degradative activity of soil organisms. Other infectious agents (bacteria, fungi, and parasites) also have a specific range of temperature, moisture, and nutrient requirements for survival and multiplication. These conditions are not generally found in sanitary landfills and,

therefore, the organisms cannot survive for long periods of time before they are overgrown and destroyed by the normal saprophytic flora of the waste. Because most pathogenic microorganisms are unlikely to survive in the environment for extended periods, a medical waste treatment system which significantly reduces the numbers of organisms present in or on the waste should be effective in protecting the public health and the environment. This invention provides an alternative disposal system and method for handling infectious waste. In the treatment system, enzymes are used to destroy microorganisms, such as bacteria and viruses, in and on infectious waste products. Experimental results discussed in detail below demonstrate that pathogenic microorganisms are destroyed by enzymatic action under controlled temperature and pH conditions. The experiments were conducted with different types of enzymes (amylases, cellulases, proteinases) and using various kinds of enzymes within each type. The pH, temperature, and treatment time parameters for the enzyme system have been investigated to determine optimum operating conditions for the infectious waste disposal system.

Figure 1 shows the infectious waste disposal system contemplated by this invention, Figure 2 outlines its method of operation. The heart of the system is an enzyme bath 10 in which ground up infectious waste products are subjected to enzymatic action at controlled temperature and pH conditions. Infectious waste 12, which can include syringes, IV tubes, mattress sheets, bandages, or

the like, as well as biopsies, blood, body fluids, tissues, gallstones, and other body members, as well as a wide variety of other byproducts from health care, laboratory, and other industries, is ground to a small particle size (e.g., less than one half inch in length) and introduced into the enzyme bath 10 at the direction of the system controller 14. In addition, one or more selected enzymes from enzyme stores 16, 18, and 20, which are chosen to destroy microorganisms which may be present in or on the infectious waste 12, are supplied to enzyme bath 10, and suitable buffers 22 are supplied to enzyme bath 10 under the direction of the system controller 14. The temperature of the enzyme bath 10 is carefully controlled using heating/cooling coils 24.

The temperature and pH conditions in the enzyme bath 10, which are governed by the coils 24 and buffers 22, respectively, are adjusted to levels which provide the optimum microorganism killing capacity for the enzymes used in the enzyme bath. As is shown by the experimental results below, certain enzymes have enhanced killing capacity for certain microorganisms at varying temperature and pH conditions. Therefore, the system controller 14 plays an important function in maintaining and adjusting the conditions in the enzyme bath 10 to achieve optimum performance of the system. The system controller 14 may also control the operation of an agitator 26 positioned inside the enzyme bath 10. Agitation of the infectious waste product aids in releasing the microorganisms from

the waste product such that they may be exposed to the temperature, pH, and enzyme conditions in the bath. The most ideal type of agitator 26 is believed to be similar to that used in a washing machine, whereby the bath swirls materials back and forth in a reciprocating action.

The system controller 14 also controls the length of time the waste 12 is treated in the enzyme bath 10. The length of time depends on the amount of waste 12 introduced, the type of enzymes used, as well as on the pH and temperature parameters. As shown in Figure 1, treated waste exits the enzyme bath 10 via a conduit 28, and system controller 14 regulates the access of the waste into conduit 28. After a prescribed period of time for killing certain numbers and types of microorganisms, the treated waste progresses down conduit 28 for disposal. The treated waste is much smaller in volume than the initial waste product, because the enzymes within the enzyme bath breakdown (e.g., hydrolyze) the materials which make up the waste product. Cellulases can be used in the enzyme bath to breakdown paper and other fibrous materials. Lipases can be used in the enzyme bath to breakdown oil, grease, and fatty products. Amylases can be used in the enzyme bath to breakdown starch and sugar based materials. Proteases are primarily responsible for killing the microorganisms, but also function to breakdown protein based waste products. The treated waste effluent is consolidated at station 30 by a screw or drier to separate the solid waste product from the fluid waste. Fluid waste can safely be

directed to the sewer system (or be recycled) and solid waste can safely be directed to the landfill because the treatment provided in the enzyme bath greatly reduces or eliminates the pathogenic microorganisms associated with the infectious waste 12. The treated solid waste 32 directed to the landfill will have a greatly reduced volume and microbial load, thus, the life expectancy of existing landfills will correspondingly be lengthened.

Figure 2 outlines the operations of the infectious waste disposal system contemplated by this invention. First, enzymes, waste products and buffers are added to an enzyme bath. The bath is agitated as needed to keep the waste products and enzymes in constant contact. A feedback control system is used to assure that the temperature and the pH of the enzyme bath is kept an optimum level for enzymatic killing of microorganisms. The optimum levels, of course, depend on the enzymes chosen, and different enzymes perform best under widely varying conditions. After the requisite period of time for achieving a specified drop off in microorganism numbers, the enzyme bath is emptied so that the waste fluid and solids can be directed for disposal. The waste fluid might be recycled into the enzyme bath for treatment of the incoming waste since it will contain mainly enzymes. This will reduce the overall cost of the enzymes on the infectious waste disposal system. Sometimes, as evidenced by the experiments discussed below, one enzyme may be better for killing viruses or certain kinds of bacteria, while

another enzyme may be better for killing other viruses or bacteria. Figure 2 shows this invention allows for using different types of enzymes to meet these needs. After the utility of one enzyme has expired, another enzyme can be added to the bath and the pH and temperature conditions of the bath will be adjusted to meet the optimum performance of the new enzyme. A slight variation on this concept would be to use cellulases first to breakdown paper products in the waste materials, then to subject the enzyme bath to proteases which will both destroy the pathogenic viruses and bacteria which were associated with the waste and will breakdown the cellulases, since they themselves are proteinaceous in character.

In a first set of experiments, the following organisms were used to assess antimicrobial activity of proteases: Staphylococcus aureus (ATCC #6538), Salmonella choleraεuis (ATCC #10708), Escherichia coli (ATCC #26) , and Streptococcus faecalis (ATCC #6569) . The S. aureus and S. cholerasuis were chosen because they are human pathogens that are routinely used in the testing of disinfectants and are universally accepted for the purpose. The JE?. coli and the S. faecalis were chosen because they are routinely used in Public Health testing for waste water contamination of water supplies. Collectively, the organisms selected are organisms that are used in disinfectant testing and/or used as indicators of potential public health hazard. Demonstration of antimicrobial activity against such organisms is strong evidence of the efficacy of the infectious

waste disposal method.

In the experiments, approximately 10 ⁶ CFU/ l titers of bacteria were placed in an agitated water bath maintained at pH 4.3 and at a temperature of approximately 50°C. The bath contained 1% protease 64 (P64) available from Genencor. Periodically at selected time periods after inoculation, samples were plated out and counted to determine the effect exposure to the bath had on the viable numbers of organisms. Figure 3 shows that there was a six log reduction (reduced by 99.9999%) in S. cholerasuis occurred within one hour after inoculation, and that there was at least a three log reduction in viable bacteria of each type within three hours of inoculation.

To study the antimicrobial performance of the enzyme activity in the presence of waste products, the baths were inoculated with the test bacteria where the baths included 10% by weight of waste material; specifically, waste paper, bandages, etc. The baths were maintained at pH 4.3 and at 50°C, and were agitated to enhance antimicrobial activity. Figure 4 shows that in the presence of 10% waste, all of the test bacteria experienced a six log reduction in viability within three hours. In fact, Figure 4 shows the enzymatic action on the test bacteria was enhanced in the presence of waste products.

The same experiments were performed with "clinical strains" (e.g., bacteria actually found at a hospital) of the same indicator organisms (e.g., S. aureus, S. cholerasuis, E. coli and S. faecalis) . It was determined that the clinical

strains were more easily and quickly killed than the indicator organisms obtained from the ATCC. Hence, the results with "clinical strains" indicate that the indicator organisms are appropriate for validating the infectious waste disposal method of this invention, and that the performance of the indicator organisms provide a margin of safety with regard to the efficacy of the system.

In addition to demonstrating a significant reduction in numbers of microorganisms present in waste in a short period of time, the antimicrobial experiments have shown a reduction in waste volume as a result of treatment. For example with respect to Figure 4 where 10% surrogate waste was added to the enzyme bath, the waste paper and other organic materials present in the waste was hydrolyzed by the enzymes within fifteen to thirty minutes. Hydrolysis resulted in a slurry of waste material being formed which was significantly less in volume than the original starting material.

In a second set of experiments the treatment efficacy against viral indicators was investigated. Human Poliovirus and Canine Parvovirus-2 were selected for the experiments. Human Poliovirus is an RNA virus and a member of the highly resistant Picornaviridae virus family. This virus was selected because it is an important human pathogen with considerable public health significance that is found in swimming pools, open waste waters, and conceivably in hospital waste. The second virus, Canine Parvovirus-2 is a single stranded DNA virus which is a member of the extremely resistant Parvoviridae virus family. This agent, although

not a human pathogen, was selected because of its extreme resistance against physico-chemical effects.

Viruses can grow only in living cells. Enzymes contained in the emcellulation system may be toxic to various degrees to cultured cells. If the enzymes kill the cultured cells, they destroy the means by which viability of enzyme treated viruses are tested. By testing enzymes for toxicity against cultured cells, it was determined that amylase was not toxic, cellulase was mildly toxic (with toxicity emerging at concentrations too high to be practically employed in the emcellulation system) , and proteases were highly toxic.

To eliminate the enzyme toxicity problem, the enzyme was adsorbed to a sephadex gel slurry in a column while allowing the viruses, which are not adsorbed because they are much larger than the enzyme molecules, to pass through the column with the void volume. The cultured cells were routinely inoculated with the detoxified viruses. Hence, this methodology allowed for performing accurate viral inactivation assays. The test results indicated that human poliovirus was resistant to pH (between 3.0 and 10.6), but was sensitive to temperatures above 45°C. Relatively short treatment times with temperatures above 45°C and pH values not far from neutral resulted in a decrease in viral titers. Figures 5 and 6 show that when enzymes are employed, titers of the human poliovirus can be reduced considerably within a short period of time.

Specifically, Figure 5 shows that including "esperase, a protease which has optimum efficacy at pH 9 and 80% efficacy between pH 7 and pH 8, in an enzyme bath at 45°C and pH 9 achieved a two log reduction in human poliovirus titers after three hours, and Figure 6 shows that including an enzyme mixture available from Genencor, which includes 1% protease 64, 0.5% cellulase, and 0.5% amylase, in an enzyme bath at 50°C at pH 4.3 reduced the titers of human poliovirus down to the limit of detection (e.g., 10 ¹ - ⁷⁵ median tissue culture infective dose (TCID ₅₀ ) ) within three hours. These results clearly demonstrate that selection of the enzyme must be paired with the pH and temperature conditions in the enzyme bath, so that the enzyme achieves its optimum microorganism killing capacity. As discussed in conjunction with Figure 1, the system controller 14 assures that the pH and temperature conditions in the enzyme bath will be optimized for the enzyme being used.

As expected, the canine parvovirus proved to be much more resistant than human poliovirus. In particular, it was resistant to pH conditions ranging from pH 3.0 to pH 10.6, and was much more resistant to temperature. Nevertheless, when enzymes are used in combination with controlled temperature and pH conditions, canine parvovirus can be effectively destroyed. Figure 7 shows that "esperase", the alkaline protease shown in Figure 5 as being capable of killing human poliovirus, also can kill canine parvovirus at pH 9 and 50°C. In addition, the acid protease, "newlase", a Genencor acid fungal protease, was found to be effective for

killing canine parvovirus at pH 3 and another alkaline protease, "alcalase", was found to be effective for killing canine parvovirus at pH 9. The mixture of proteases, amylases and cellulases which worked well on human polioviruses did not perform as well against the "tougher" canine parvovirus.

The virus studies indicated that pH conditions play a large role in the efficacy of the treatment process. In general, the pH in the enzyme bath should be optimized for the enzymes performance and should not be more than plus or minus one or two pH levels from the optimum (pH 9 protease enzyme bath preferably at pH 9, but certainly within the range pH 7-11) . In addition, an alkaline enzyme may be more efficient than acid enzyme at killing certain viruses, and vice versa. In those situations, either the enzymes can be used sequentially in the bath with a pH and temperature adjustment being performed as required (note Figure 2), or both enzymes can be added simultaneously to the bath and the pH conditions in the bath can be adjusted after preset time intervals. Since one enzyme will be dormant at its non-optimum pH, adjusting the pH of the bath will activate that enzymes killing potential after the utility of the other enzyme has expired.

In a third set of experiments, Bacillus subtilis spores were subjected to proteases, cellulases, and amylases at varying pH and temperature conditions. Figures 8a-c demonstrate that the protease (Genencor P64) is primarily responsible for killing the spores. Figures 8a-c

further emphasizes that the operating conditions in the enzyme bath must correspond to the optimum performance criteria for the enzyme being used, and the different enzymes are better than others for killing certain microorganisms.

Figure 9 shows a system schematically for handling medical waste. Medical waste is collected in leak proof containers 100 from various health care providers. The medical waste in the containers 100 can be any of a wide variety of items including syringes, IV tubes, mattress sheets, bandages, or the like, as well as biopsies, blood, body fluids, tissues, gallstones, and other body members, all of which are byproducts of providing health care. The medical waste is typically contaminated with a wide variety of pathogenic bacteria and viruses found in the health care environment. Most regulations governing the disposal of medical waste, including those governing incineration, require it to be bagged in a plastic, leak proof bag and boxed in a cardboard box. It is contemplated that the containers 100 used in this process will be similar in character. Containers 100 of medical waste are transported by conveyor 112 towards the box opening station 114. Prior to opening the containers 100, they are screened for radioactivity at station 116. The boxes may be screened at station 116 using a Geiger counter or other radioactivity detector positioned over the conveyor 112, or by having personnel pass a detector wand over the outside of each container 100. Many immunoassays conducted by health care providers include the use of

radioactive labels. In addition, some treatments for cancer include the use of radioactive compounds. Because of environmental concerns, items contaminated by radioactive elements must be disposed of according to strict regulations. While health care personnel are instructed to dispose of radioactive materials in identifiable containers, human error can often lead to radioactive waste being combined with ordinary medical waste. In order to prevent the medical waste disposal system of the present invention from being contaminated by radioactive materials, station 116 serves as a means to screen out containers 100 which are radioactively contaminated prior to their being opened and treated. Any radioactive containers 100 identified at station 116 are removed and disposed of according to prescribed procedures.

In addition to radioactive waste, hazardous chemical waste will need to be handled by the generator in a manner consistent with existing regulations for the treatment and disposal of such wastes.

After the containers 100 are screened at station 116, they are transported to the box opening station 114. Figure 10 shows that the box opening station 114 preferably includes a water filled tank 118 and has a plurality of knife edges 120 that project from the inside walls. A water slide 122 moves the containers from the conveyor 112 into the tank 118. Spray nozzles 124 as well as water 126 supplied in water slide 122 are used to fill the tank 118 to level 128 above the containers 100. A compactor ram 130 which fits

within the tank 118 has a semispherical surface 132 that forces the containers 100 against the knife edges 120 to open and cut apart the containers 100 as the ram 130 is translated towards the bottom of the tank 118. After the containers 100 are opened, a valve 134 allows the liquid and medical waste mixture to be transported to a chopping and grinding station.

The purpose of the box opening station 114 is to prevent the escape of easily airborne pathogens present in or on the medical waste to the surrounding atmosphere. By keeping the containers 100 closed until they are under water, the pathogens cannot escape to the atmosphere when the containers 10 are opened. Other methods may be available for preventing the escape of airborne pathogens. For example, the containers 100 could be opened in a compartment under vacuum pressure. If negative pressure is used to eliminate aerosolization problems, the exhaust should be filtered. Moreover, other fluids besides water, and different container 100 opening mechanisms besides the ram 130 and knife edges 120, might also be used at box opening station 114. The important problem taken care of at box opening station 114 is that pathogens in or on medical waste which might become airborne are prevented from escaping to the environment, as would occur if the waste containers 100 were simply dumped into the hopper of a waste grinder.

With reference back to Figure 9, the mixture of medical waste, container boxes and water is then sent to a high powered chopper-grinder 136 which

can reduce the waste and boxes to a fine particle size (e.g., preferably less than one half to one quarter an inch in length) . Suitable chopper- grinders 136 are available from the Hamilton company, the Vaughan company of Washington state, and others. Suitable chopper-grinders 136 would preferably have steel impellers driven by a high powered motor. The purpose of the chopper-grinder 136 is to make pathogens in the medical waste more accessible for enzymatic action (e.g., it will knock some pathogens off medical waste pieces and will reduce the overall size of medical waste pieces) . In certain kinds of medical waste, such as IV tubing, wrapped up bandages, syringe barrels, and the like, pathogens might not become exposed to the low pH conditions and the enzymes in the enzyme bath 138 if they are not ground up to a fine particle size. The smaller surface area of waste fragments achieved after grinding makes the pathogens more accessible to enzymatic activity.

In addition, syringes and other medical implements having sharp metal members are made more safe by reducing their size and exposing their inner surfaces. The duration of operation of the chopper-grinder 136 will depend on its power and the amount of waste to be chopped and ground; however, chopping and grinding should proceed to a point where all large materials are reduced to fine particle size (e.g., approximately half an inch, or as small as practical using currently available technology) .

After being ground to a small particle size, a slurry of medical waste in water is transported to

enzyme bath 138 using a pump 140 or other means. As discussed above in conjunction with Figure 1, a system controller (not shown in Figure 10) will be used to adjust the pH and temperature conditions within the enzyme bath 138 for optimum killing of microorganisms which are in or on the medical waste supplied to the enzyme bath 138. The pH and temperature conditions used within the enzyme bath 138 will depend on the types of enzymes supplied to the bath by enzyme tanks 142.

As discussed above, different proteases, lipases, amylases, and cellulases, all of which are protein based enzymes that are generally regarded as safe (GRAS) . Lipases are enzymes which hydrolyze ester bonds and can convert triglycerides to free fatty acids, partial glycerides and glycerol. Lipases are produced commercially from porcine and bovine pancreas and from microorganisms such as the yeast Candida and Asperigullus Rhizopus . Commercial applications of lipases include hydrolysis of oils for soap manufacture, in detergents, as digestive aids, and in the manufacture of flavorings. Cellulase and amylase are both enzymes which reduce carbohydrates such as cellulose and starch, respectively, to simple sugars. Commercially used cellulases are produced from strains of Asperigillus niger, Trichoderma reeεei , Penicillium funiculosum, and Rhizopus spp. Amylase is commercially produced from Bacillus amloliquefacienε, Bacillus licheniformiε,

Asperigillus oryzae, and Bacillus subtilus . Cellulases and amylases are used in fruit juice and beer making, respectively. As explained above,

proteases are available from a wide variety of commercial sources and appear to play an important role in killing bacteria, viruses, etc. Proteases have a wide range of industrial uses including wheat gluten degradation in the baking industry, chillproofing in the brewing industry, curd formation in the cheese industry, and meat tenderizing. Subtilisin Carlsberg is a well known serine protease produced from Bacillus licheniformiε which is used extensively in detergents.

Different additives, such as stabilizers, buffers, preservatives, which are found in stock enzyme preparations can enhance microorganism killing activity in the enzyme bath. Experiments have shown that enzyme stock solutions that include one such additive, sodium bisulfite, can have enhanced killing activity.

In the enzyme bath 138, cellulases can be used to hydrolyze particles of the cardboard containers 100 and the other waste paper of the medical waste. It is estimated that up to 40% of the waste in medical waste is paper based (e.g., wipes, paper towels, gauze pads, etc.). Hydrolyzing is a process by which the cellulose (paper-based) materials have water added to the bonds of the molecules. Breakdown of the paper based trash by hydrolysis causes the pathogens adhering to the paper based waste to be released. It should be understood that hydrolyzing is different from digesting the paper-based waste. Digesting is a process which breaks down a material into its molecular components and results in volume

* reduction. Hydrolyzing occurs more quickly than digestion, and the infectious waste disposal process of this invention may be speeded up by merely hydrolyzing the waste rather than digesting it, with the hydrolyzed paper subsequently being disposed of in a landfill. However, digestion of the waste may be more desirable because significant waste volume reduction can be achieved, thus extending the useful life of a landfill. The pH in the enzyme bath 138 can be adjusted to low levels by adding an organic buffering agent such as acetic acid or calcium carbonate to the aqueous fluid (tap water) which fills the enzyme bath 138. Alternatively, the enzymatic action of the cellulase and other enzymes can themselves effect the pH in the enzymatic bath 138; therefore, the controller can utilize these expected changes in pH resulting from enzymatic action.

Lipases in enzyme bath 138 can act on the fat (lipid) cover and membranes of the pathogenic bacteria and viruses and either destroy them or render them more susceptible to destruction by the conditions in the bath 138.

Amylases in the enzyme bath 138 can serve as extremely effective cleaners for plastic surfaces such as IV tubing, sample cups, test tubes, and the like. By scrubbing the plastic materials with amylase action, microorganisms are freed into the harsh conditions of the enzyme bath. In addition, amylases can digest or partially digest starch based materials in the medical waste.

Preferably, the ground up medical waste is exposed to the conditions in the enzyme bath 138

for less than one-three hours (e.g., most preferably on the order of minutes) ; however, it should be understood that the duration of exposure will be a function of the tank used, the concentration of the enzymes, the temperature and pH of the enzymatic solution, the speed of the agitator 144, as well as other factors. The medical waste should remain in the enzyme bath until all or a great majority of the pathogens have been destroyed.

The enzymes used in the bath 138 might be grown in the tanks 142 at the site of the waste disposal system using suitable bacteria or yeasts; however, because these enzymes are readily available commercially, it may be more advantageous to purchase and store them in tanks 142.

As discussed above, the killing capacity of the enzyme solution in the enzyme bath 138 should be optimized by controlling the temperature while the medical waste is being metabolized. The temperature can be controlled by connecting a heater to the enzyme bath 138 or by using tap water of a high enough temperature in the box opening station 114. Preferably, the fluid in the enzyme bath 138 is kept relatively constant and suitable temperature controls are well understood in the fermentation business (e.g., fluid cooled jackets used in wine making, etc.) . Care should be taken to not raise the temperature in the enzyme bath 138 to a point where the enzymes become denatured and inactive (e.g., temperatures in excess of 100°C) . The activity of the enzyme bath 138 can also be optimized by using agitator 144 to move the

waste slurry around. The agitator 144 can be a motor driven propeller or the like. It is anticipated a reciprocating motion like that used in a washing machine would be ideal. Agitation will cause quicker exposure of more of the surface area of the waste to the enzymes in bath 138 and will also aid in freeing microorganisms from the waste.

As discussed above, it may be advantageous to treat infectious waste with more than one kind of enzyme, and the enzymes used may have widely varying pH and temperature requirements for optimum killing activity. One technique for handling this type of problem in a waste disposal system would be to provide a second enzyme bath 139 which has pH and temperature parameters optimized to a second enzyme or group of enzymes. Another technique, would be to simply adjust the pH and temperature parameters after the utility of the first enzyme or set of enzymes has expired, as is best discussed in conjunction with Figure 2.

Another use for a second enzyme bath 139 would be to provide the infectious waste disposal system with an increased digestion capacity. For example, enzymes in enzyme bath 138 would be primarily responsible for killing the microorganisms, while enzymes in enzyme bath 139 would be primarily responsible for reducing the volume of the waste material. This may provide advantages in terms of cost and speed of handling. For example, it may be determined that more expensive enzymes are best for destroying infectious microorganisms, and these enzymes could be used in smaller quantities in

enzyme bath 138, while less expensive cellulases, amylases, lipases, and proteases could be used in enzyme bath 139. An advantage of using proteases in enzyme bath 139 would be that the enzymes used in enzyme bath 138, which themselves are proteinaceous in character, would be degraded in enzyme bath 139. This has the advantage of reducing the biological oxygen demand of the treated waste that will be sent to a landfill. In addition, the second enzyme bath 139 could serve as a holding/digestion tank, while the first enzyme bath 138 is freed up for treating additional infectious waste products. Moreover, if some viable pathogens survive the enzyme bath 138, it is expected that the enzymes in enzyme bath 139 would serve as a back up destruction mechanism.

While the preferred mode of operation contemplates cellulases, amylases, lipases and proteases being used to enzymatically act on the medical waste to both free pathogens from waste items and help destroy the pathogens, it should be understood that both fewer and greater types of enzymes, as well as a plurality of enzymes of one type (e.g., using two or more different proteases), may be used within the practice of the invention. For example, the enzyme bath may only contain proteases or cellulases. Likewise, the enzyme bath may contain DNase, an enzyme which breaks down deoxyribonucleic acid, or other suitable enzymes. Preferably, the enzymes are present at a concentration of less than one percent in the enzyme bath (although test data noted above demonstrates higher concentrations are also

effective) . For example, one pound of waste and one gallon of water, which together have a total weight of nine pounds, would be combined with nine tenths of a pound of enzymes. After enzymatic treatment of the infectious waste, the effluent should be both safe and nontaxing on a sewage system 146. Large undigested materials such as metals, hydrolyzed paper products, and tubing pieces can be separated by filtration at solid separator 148 for disposal in a land fill. Metal pieces might be separated using a magnet and sent to a recycling firm. It may also be advantageous to sterilize the ground waste/liquid effluent using chlorine or ozone at sterilizer 149, prior to its being disposed of in a sewage system 146. Sterilizing is required by many States and can be performed under mild conditions and will prevent bacterial growth in the effluent discharged from the medical waste disposal system. Destroying most or all of the pathogens prior to sterilizing should reduce the amount of sterilizing agent required.

While Figure 1 shows the use of a controller to precisely adjust the pH and temperature conditions of an enzyme bath, it should be understood that enzymes can be selected for mediums having known pH and temperature conditions to kill microorganisms (e.g., viruses, bacteria, spores, etc.) in the medium. The enzymes selected would have optimum microorganism killing activity at the pH and temperature conditions which exist in the medium.

EXAMPLE

Experiments were conducted with vegetative bateria (Staphylococcus aureus ATCC 6538 and Pseudomonas aeruginosa ATCC 15442) , fungi { Candida albicans ATCC 18804) , mycobacterium (Mycobacterium phlei ATCC 117588), spores (Bacillus subtilis ATCC 19659), protozoa (Giardia) , and viruses (Human Poliovirus (HPV2) . The experiments involved the use of enzymes at 1% final concentration in simulated waste which included 10% paper based waste and 1% blood. The enzymes employed were cellulases (e.g., Cytolase or Celluclast with an activity of 90 GCU/ml at pH 4.8-5.2; cellobiase (Novozyme 188) ) with 250 cellobiase units per gram (CBU/g) at pH 4-6), glucose oxidase (e.g., Novozyme 188 with 2,000 GOX/ml at pH 3.5-7) or hydrogen peroxide (H ₂ 0 ₂ ) at 1% concentration, and alkaline Protease (Alcalase with 2.77 Anson Units/g at pH 6.5-8.5). As discussed above, different cellulase, glucose oxidase, and protease enzymes could be used. While 1% enzyme solution was employed, it is aniticipated that substantially lower enzyme concentrations (e.g., .1%) could be employed. Sodium bisulfite at 1% concentration was used in combination with the cellulase enzymes. The experiments utilized 10 ⁹ CFU/ml of the vegetative bacteria, fungi, and myobacterium, 10 ¹⁰ CFU/ml of the spores, 500,000 cysts of Giardia as discussed in the excistation assay described in the US

Environmental Protection Agency for the testing of public water systems (1991) , and 10% virus concentration having titer of 10 ⁵ - ⁵ TCID ₅₀ /0.2 ml.

Log 10 ⁶ reductions for the vegetative bacteria, fungi, mycobacterium, and spores, 99.7% excystation reduction for Giardia, and reduction of virus down to limits of detection were obtained using the experimental treatment process. The experimental treatment process is follows:

1) Expose the waste with microorganism cantaminants to cellulases plus sodium bisulfite at 40-60°C, pH 4-6, in an enzyme bath. The cellulases reduce the waste volume by breaking down the paper based waste. The sodium bisulfite acts to destroy some of the microorganism contaminants, particularly bacteria. Exposure is preferably for 30 minutes to two hours. The pH in the enzyme bath can be adjusted by the addition of organic acids (acetic acid) or inorganic acids (HCl) .

2) After treatment with cellulases, expose the waste material to either glucose-oxidase or hydrogen peroxide at 40-60°, pH 4-6. The glucose- oxidase or hydrogen peroxide treatment has been found to enhance spore kill. In operation, glucose-oxidase may create peroxide from the waste material itself.

3) Maintaining the temperature at 40-60°C during the treatment process has been found to be responsible for killing the protozoa.

4) Adjust the pH in the enzyme bath to pH 8.5 using 1 N NaOH. Then, expose the waste material to alcalase. Exposure to alcalase, as well as other proteases, has been found to destroy viral contaminants in the waste material. Alcalase also destroys proteinaceous tissue which results in further reduction in waste volume.

5) Recover a waste product having substantially reduced volume and microbial load.

While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.