Patent Application
20060222574
This invention relates to the field of waste disposal and, more particularly, to a system and method for the digestion and sanitary disposal of waste material, such as infectious waste material and other hazardous, biohazardous, or radioactive waste.
Many facilities, such as hospitals, various health-care facilities, research and teaching institutions, food preparation facilities, and the like, produce considerable amounts of infectious, biohazardous, or radioactive waste. Such waste may include surgical and pathological tissues, animal tissues, cadavers, blood and other bodily fluids, disposable matter exposed to blood, and other potentially infectious or dangerous body fluids of patients or animals. Such waste is classified in the United States as “regulated medical waste” (RMW) under state regulations, and must be disposed of in strict compliance with the applicable governmental regulations.
Health-related organizations and governmental regulatory agencies have become increasingly concerned with the adequacy of existing cleaning and disposal methods. It has been discovered that some potentially biohazardous agents, such as prokaryotes, or infective proteins (prions) do in fact survive standard autoclaving procedures. Thus, more effective sterilization techniques have been sought for treating solid infectious biomedical waste and aqueous solutions containing such waste.
In addition, universities and other research facilities likewise produce significant amounts of such waste. For example, in conducting experiments in cell lines, tissues, or animals, it is common to introduce dyes, toxic chemicals, or infectious agents into the test subject. Moreover, radioactive materials are also commonly used as a tool to enhance chemical, biochemical, pharmaceutical, biomedical, and biological research. It is common to label drugs or chemical compounds with radioisotopes in order to study efficiently and accurately where these compounds are metabolized and incorporated within the body. After completion of the test and analysis, due to the introduction of infectious agents or hazardous or radioactive material into the tissue, the remaining tissue or animal carcass may fall under the classification of “regulated medical waste,” hazardous waste, or low-level radioactive waste (“LLRW”). In addition, animal waste, animal bedding, handling materials, and other matter exposed to any animal body fluids or excretions may also need to be treated as infectious or hazardous waste material, thus requiring disposal in accordance with the applicable governmental regulations.
Moreover, it is common today for health care organizations to clean material, instruments or surface areas exposed to infectious agents, including zoonotic agents, with disinfectants such as formaldehyde or glutaraldehyde. Spent cleaning solution is considered hazardous liquid waste and must also be disposed of in compliance with governmental regulations. The cost of disposing of such waste, on an institutional basis, can be quite high. Further, formaldehyde, glutaradehyde, phenols and like materials, are commonly used for embalming tissues and in fixation of infectious biological materials. Thus, these tissues and the fixative agents may also have to be disposed of as “regulated medical waste,” hazardous waste, or mixed waste in compliance with the applicable governmental regulations.
Further, animal carcasses containing compounds labeled with 14C or 3H or other radioisotopes are classified as LLRW. Because state and federal guidelines regulate the disposal of LLRW, special precautions must be followed in their disposal. Currently, the two methods commonly used in disposing of this type of waste are incineration and land burial. Presently, federal law allows for incineration only when the animal carcass contains a radioisotope concentration below a certain level. However, even when radioisotope concentrations are below this level, incineration may be further limited by state and local agencies. When the levels of radioactivity in the animal carcasses are below acceptable de minimis levels as defined by federal, state, and local authorities, the disposal thereof is not subject to any additional regulation as a radioactive waste. However, to further complicate matters, the incineration of radioactive animal carcasses at any level is prohibited in certain major metropolitan areas. Nonetheless, the general process of incineration itself, even when no radioactive materials are involved, is subject to additional regulations, such as those requiring licensing from a state or local environmental agency. Additionally, future increases in the requirements for incinerator designs and function under clean air regulations put in doubt the continued availability of incineration as a practical method for disposing of animal carcasses classified as LLRW or for any non-radioactive carcasses or human pathological waste.
Presently, the only real alternative to incineration for radioactive animal carcasses is burying the carcasses in a licensed LLRW disposal facility. This method entails the packing of the entire carcasses in lime and adsorbents, repacking them in special drums and shipping the drums to a LLRW site. Currently there are only two such sites in the United States, located at Hanford, Wash., and Barnwell, S.C. Due to the limited number of land burial sites currently operating in the United States, it is extremely costly to dispose of any radioactive waste by this method; it is disproportionately costly for animal carcasses containing low level radioactive waste due to the size and weight of the carcass. Due to the extremely high cost associated with land burial and the limitations on access to current sites, the feasibility of land burial as a method of disposing of animal carcasses classified as LLRW remains in doubt.
It is known in the art that low levels of certain radioactive waste may be disposed of to a sanitary sewer under federal regulations with appropriate record keeping and/or monitoring. This includes isotopes in aqueous solution at levels below the maximum permissible concentration (MPC) as defined by 10 C.F.R. 20 and radioisotopes in human waste. Such a procedure has been utilized, for example, in the disposal of radioactive waste generated by many patients undergoing treatments for cancer. Today, a common method of treating cancer is by radiation therapy, which often involves the absorption of radioactive compounds. Many of these radioactive compounds eventually leave the body through fecal and urinary excretions. These excretions will contain small amounts of radioactive material. However, this radioactive material is disposed of through the general sewage system because the level of the radioactive materials discharged by the body into the sewer system is sufficiently diluted such that it no longer poses any hazard to public health and safety. This process is well within the state and federal disposal regulations for LLRW disposal. However, LLRW contained in animal remains are not readily capable of disposal through such means because the animals are naturally solid waste.
It is also known in the art that substances containing keratin, such as hair and nails, may be dissolved by means of acid or alkaline hydrolysis, as disclosed in U.S. Pat. No. 1,974,554 issued to Ziegler. It is further known that hydrolysis of proteins containing keratin may be carried out with alkaline solvents. It is even further disclosed in U.S. Pat. No. 5,332,532 to Drs. Kaye and Weber, which patent is commonly owned by the assignee of the present application, that such hydrolysis may be utilized on proteins contaminated with radioactive materials.
Of the known methods of disposing of infectious, biohazardous, or low-level radioactive waste, each faces an indeterminable future under the ever-changing breadth of the environmental laws. Furthermore, each is extremely costly, putting an unneeded drain on already strained research and waste management budgets of hospitals, universities and other institutions. Thus, a need persists for means of safely and inexpensively treating and disposing of organic waste matter.
The present invention addresses this need.
The present invention relates to a system for degrading, digesting or neutralizing undesirable materials by subjecting them to a controlled alkaline hydrolysis cycle. In one form, the system includes an apparatus having means for receiving the undesirable materials, such as a closeable reaction vessel. The apparatus further includes means for controlling the operation of the system. The apparatus also includes means for introducing water within the interior of the vessel in a predetermined amount based on the maximum volume of the vessel and means for introducing an alkali compound within the interior of said vessel in predetermined amount based on the maximum volume of the vessel. Additionally, the apparatus includes means for heating the interior of the vessel to a first predetermined temperature level after the introduction of water and alkali compound into the interior of the vessel for a duration sufficient to produce a safely disposable resultant.
The method provided by the invention generally comprises the steps of providing a sealable vessel, filling the vessel with a highly alkaline solvent, immersing the waste matter containing the undesirable elements within the highly alkaline solvent, and heating the highly alkaline solvent. The waste matter is allowed to remain within the highly alkaline solvent until the hydrolyzable matter is degraded or digested (i.e., substantially hydrolyzed), thereby forming a sterile solution and sterile solid waste. The aqueous solution and any resultant solid waste may then be disposed of through conventional means, such as a sanitary sewer, anaerobic fermentor, local landfill facility, or, if appropriate, by land application as fertilizer (either in liquid or solid form) or by mixing with peat, compost, or other cellulosic material.
One object of the present invention is to provide an improved system, method and apparatus for disposing of hydrolyzable waste matter. Related objects and advantages of the present invention will be apparent from the following description.
This invention involves a system and method for treating and safely disposing of waste matter containing undesirable agents or elements, such as but not limited to animal carcasses, animal tissue, organic material, organophosphate pesticides and nerve gasses, nitric esters and aromatic nitro-compounds, chemotherapeutic agents and related alkylating agents (such as sulfur mustards, nitrogen mustards, and phosgene), antibiotics, plant, animal, and bacteriological toxins, non-protein toxins (such as aflatoxin and tetrodotoxin), animal venoms (such as snake, spider, scorpion, fish and amphibian venoms), plant catechols, polyphenols, infectious, biohazardous, hazardous, and radioactive materials. The system and method of this invention is designed and intended to comply with all federal, state, and local laws or regulations presently in existence applicable to the disposal of such waste.
The method of the invention comprises the steps of providing a sealable vessel, providing a highly alkaline solvent, immersing the waste matter containing the undesirable elements within the solvent within the interior of the vessel, heating the solvent and the waste matter, and allowing the waste matter to remain within the solvent until digested or degraded, thereby forming a sterile aqueous solution and sterile solid waste. The extent of digestion or degradation of the waste matter may be increased by treating the waste under pressures above one atmosphere, by adding catalytic agents to the solvent bath, or both. After cooling, the post-digestion end product may then be directly disposed of through conventional disposal means, such as a sanitary sewer or landfill, or even used as a fertilizing agent in land use applications. If preferred, the post-digestion stage may also include rinsing or flushing of the resultant waste product and the interior of the vessel. The system and method of this invention also substantially reduce the amount of post-digestion solid waste to be disposed of.
The inventors herein have determined that completeness of degradation/digestion (time vs. temperature curves) may be determined by measuring the rate of production of amino acids as the digestion process proceeds. When that process reaches an asymptote, digestion is considered complete.
In operation, when the operator is ready to dispose of the waste matter, such as animal carcasses or remains, for example, the waste matter is placed within a holding container that is then placed within the interior of the vessel. The lid of the vessel is then secured by way of conventional lid clamps. The load of waste matter placed in the vessel for digestion should be at least 10% of the capacity of the vessel (by weight) but not more than 60% of the total weight of the capacity of the vessel. The digestion cycle is then initiated, ultimately resulting in the waste matter being completely immersed in the highly basic solvent.
For the purposes of this application, a “highly alkaline solvent” or “highly basic solvent” may include a 1-2 molar (M) aqueous solution of an alkali metal hydroxide, an alkaline earth metal hydroxide or an alkaline earth metal oxide. Preferably, this solvent should have a pH of at least above 13, preferably in the range of 13 to 14. An aqueous solution of sodium hydroxide (NaOH—also commonly known as caustic soda or sodium hydrate) or potassium hydroxide (KOH—also commonly known as caustic potash or potassium hydrate) is preferred. While an aqueous solution of NaOH or KOH is preferred, solutions containing calcium oxide (CaO—also commonly known as burnt lime, calx or caustic lime), ammonium hydroxide (NH4OH—also commonly known as aqua ammonia) or magnesium hydroxide are also suitable for some applications. An example of a suitable highly basic solvent may consist of a 0.1 M to 2.5 M solution of NaOH in water, or approximately 0.4%-10% sodium hydroxide (by weight) in water.
During digestion, the hydrolyzable material should be immersed in a sufficient amount of solvent such that the material may be degraded or digested. One ratio assuring excess base to carry out the digestion of the waste matter to completion, particularly animal tissue, is a 1:10 ratio of alkali metal hydroxide to wet tissue weight. A further expression of this ratio is 40 kilograms of NaOH dissolved in 900 liters of water added to 100 kilograms dry weight protein or 40 kilograms of NaOH in 500 L H2O added to 500 kilograms fresh or frozen waste matter by weight. These ratios are given only as instruction as to how to conduct the method and operate the system stated herein and not to limit the nature or scope of the invention; one using the system and method described herein may find ratios more economical and exact as the invention is practiced. In order to assure degradation of all infectious wastes, including prokaryotes, the highly basic solvent should be heated to a temperature of at least about 90° C., and preferably 110° C. to 150° C.
It is preferable to allow the reaction to proceed in a closed reaction vessel after the waste matter has been immersed within the solvent. Reducing the amount of CO2 available to the reaction is beneficial in order to maintain the ideal rate and stoichiometry of the reaction. This may be done by simply removing or limiting any contact that the highly basic solvent has with the environment.
In the event the reaction between the waste matter such as an animal carcass and the highly basic solvent were allowed to proceed at its natural rate, it may take an impractical amount of time. Therefore, it is advantageous to increase the reaction rate beyond its natural progression. One way to increase the speed of the reaction process is to heat the solvent, preferably to temperatures of 110° C. to 150° C. Conducting the reaction in a sealed vessel under increased atmospheric pressure also reduces the reaction time needed to digest the animal tissue. A preferred mode includes heating the solvent to a temperature of about 150° C. for a duration of about three (3) hours at a pressure of about 55 PSIG (or about 3.8 atmospheres). It has been found that the basic rule of thermodynamics or the “Q10 Rule” applies to this invention as well in that for every 10 degrees Celsius rise in temperature, the reaction rate for the chemical reaction taking place within the closed vessel increases two-fold, thereby resulting in the digestion time being reduced by approximately 50%. Such phenomenon is based on the Arrhenius equation.
Furthermore, detergents to a concentration of up to 1% to the solvent, examples being sodium lauryl sulfate or deoxycholate, may also be added to increase the rate of digestion, if desired. It should also be noted that addition of detergents to the solvent also has the added advantage of dispersing nonsaponifiable lipids, and aiding in the sterilization of biological materials.
Ultimately, the reaction rate will depend on specific variables such as: the temperature of the solvent, pressure in the reaction vessel, the nature and volume of the waste matter, i.e., the physical size of the carcasses or waste tissue, and the ratio of waste matter to the volume of the highly basic solvent. As the reaction rate will vary, the time that the waste matter must remain immersed in the solvent will also vary. However, regardless of the reaction rate, the waste matter should remain completely immersed within the solvent until solubilized and hydrolyzed. Allowing the waste matter to remain within the solvent until digestion is achieved will also help produce a more sterile solution.
Once the waste matter such as animal tissue has been digested, two types of solid debris often remain. The first type of debris consists of rubber, plastic, or cellulosic materials that a lab animal may have ingested, as well as debris remaining from experimental or surgical procedures, such as surgical clips, sutures, glass, and bits of plastic or paper. Solid items such as these never incorporate the radioactive isotopes. Once sterilized, such solid items are also not considered biomedical waste in most jurisdictions. This type of debris may often be simply disposed of as ordinary sterile solid waste upon being isolated from the solution and washed.
The second type of solid debris remaining undissolved includes inorganic portions of an animal's skeletal structure and teeth. Unless a radioisotope capable of incorporation into the inorganic portion of bones and teeth is used, the inorganic component of the skeletal remains will not contain the radioactive isotope and may be disposed of as solid sterile waste. The skeletal remains, when removed from the solvent and washed, are extremely friable.
After the biological waste matter has been digested within the solvent and the solid debris removed, the solution may comprise a diluted concentration of radioactive isotopes that meet the MPC requirements under the federal regulations, as well as an alkaline mixture of alkai metal salts of amino acids and peptides, sugar acids, nucleotides, small peptides, fatty acids from lipids, phosphates from lipid and nucleic acid breakdown, soluble calcium salts, pigments, sugars, sugar alcohols, hydrocarbons, and inorganic acids derived from the electrolytes normally within solution in body fluids. These by-products are identical to those released in vast amounts from cooking leftovers and waste from all commercial and household kitchens. Thus, the solution contains compounds that are non-toxic and are biodegradable by bacteria or fungi found in soil and sewage treatment systems, and possibly a very dilute amount of radioactive solute.
Because the solution at the end of the digestion cycle contains only non-toxic biodegradable materials and the water released from the animal tissue, further dilution of the solution may not be required for safe disposal. Further dilution to reduce the alkalinity of the solution will be accomplished, however, by the rinsing of the vessel and the inorganic remains with excess water, by the temperature regulating co-flush for the effluent, and the general daily effluent volume of the site, institution, or company. (Deliberate dilution of soluble radioactive waste is usually not permitted by the applicable local, state, federal and national regulations.) Further, carbon dioxide may be injected into the solution at this stage to adjust its pH down to between about 7.5 and 10. At this stage, however, the concentration of radioisotope in the solution should be well within the level that may be safely released to a sanitary sewer.
This sterile, neutral, aqueous solution that contains the breakdown products of cells and tissues, and may contain remnants of radioisotopically labeled solutes may be safely disposed of utilizing methods commonly used to dispose of everyday nontoxic and biodegradable substances. It is entirely safe to dispose of this solution using disposal means such as sanitary sewage systems and other disposal means appropriate for the disposal of these simple biodegradable compounds.
Now turning to
The system and method carried out by this invention are controlled by a conventional programmable logic controller (PLC) means (not shown) defined by a programmable multi-loop machine controller, computerized for automated operation. Such control means preferably includes an information screen, a disk drive for the automation program software, a disk drive or like recording means for recording process parameters and data during operation, and a keyboard for alternative manual input or operation.
System 10 further includes a weight transducer 18 (shown schematically) coupled to one or more of the legs of the vessel 12 for determining the weight of the waste matter received within the vessel and for generating an output signal indicating such weight data. The transducer is preset such that the weight of the vessel without contents equals zero weight. The contents weight data is then inputted to the PLC control means for, based on the weight output data, determining the appropriate amounts of water and solvent to introduce into the interior of the vessel, utilizing a water supply 20, via conduit 20a, and a spray ball or nozzle 20e located within the vessel interior, and solvent supply 22, via solvent loop conduit 24 and pump 26. Solvent is injected into the interior of vessel 12 via injector means 28, which are shown schematically in
It should be appreciated that this invention is not limited to the agitating injector means described and shown herein but contemplates any means that introduces the solvent into the interior of the vessel. The mere introduction of solvent into the vessel will “mix” the alkali-water solution with the waste matter. Introducing heat also induces mixing. Moreover, agitation of the contents may be achieved by various means, including external mechanisms coupled to the vessel, such as a rocking or shaking assembly that physically moves the vessel. All such alternative means of mixing or agitating the vessel contents are contemplated by this invention.
As noted above, the preferred process requires that the solvent solution be heated in order to accelerate the digestion process to completely dissolve the animal tissue, carcasses, or medical waste. To that end, further included in system 10 is a heating means preferably defined by a stainless steel steam jacket 30 arranged circumferentially about the vertical sides and base of vessel 12 for heating the interior of the vessel to a first predetermined temperature level after the introduction of water and solvent into the vessel interior 14. Heated water or steam is circulated between the walls of the double walled vessel 12. While the steam jacket defines a preferred embodiment, any heating means commonly known and used for heating solutions could be utilized in this invention. Steam is supplied to jacket 30 by a steam supply 32 and conduit 32a provided with a cut-off valve 32b and a regulating valve 32c. The system further includes a vent 34, which is disposed in the open state upon initiation of the cycle and thereafter closed by PLC control means when the temperature within the vessel reaches a predetermined first temperature. The temperature within the vessel 12 is gauged by a vessel thermocouple 36a, while the pressure within the vessel is gauged by a PSI transducer 38. The temperature within the solvent loop is gauged by a loop thermocouple 36b.
In the preferred embodiment, an eductor apparatus 40 is utilized for creating a vacuum within the vessel interior 14. When vent 34 is open and flushing water is admitted to the eductor by the water supply 20 via conduit 20b, the action of the eductor draws the air and any odorous gas from within the interior of the vessel through conduit 34a, whereupon the air and odorous gas is eventually entrapped with the flushing water at eductor 40 to, in turn, be removed from the system via drain conduit 42a to sanitary drain 42. The temperature of the fluid at the drain may be gauged by a thermocouple 44 to monitor the effluent temperature prior to disposal in a sanitary sewer system. The vacuum-creating eductor substantially reduces the odorous gases that may escape from rotting carcasses while the vessel is filling, before the vent valve 34 is closed.
In cycle, once the contents of the vessel are drained after the digestion cycle (heating and cooling), the interior of the vessel is rinsed with cold water via sprayball 20e with the drain valve 41 open. After a few minutes, the drain valve 41 is closed to allow the vessel to begin to fill with water. Once the vessel is filled to the point where the waste matter is covered, the contents are then agitated by injecting the water solution through injector means 28 for a few minutes to increase the rinsing effect. Drain valve 41 is then re-opened and the liquid contents of the vessel are allowed to drain. Thereafter, if desired or necessary, the drain valve 41 is closed for a second time and the vessel is allowed to again fill with water. Heat may then be applied again to the vessel to heat the liquid within the vessel to approximately 95° C. (203° F.), whereupon an enhanced rinse is initiated. The time and temperature used in this post-digestion heating stage may vary.
To balance or control the vacuum being created within the vessel during the post-digestion cooling cycle and to prevent the vacuum from impeding the draining of the vessel, a vacuum balancing device 46 shown and discussed below in relation to
Referring now to
The preferred system further includes a permeable container capable of holding the waste tissue or remains or medical waste within the vessel interior 14 during the digestion cycle to completely immerse the waste material within the solvent solution. As shown in
As noted above, the preferred embodiment includes agitating injector means 28 shown in
As shown in
Next, the system goes into the cooling cycle after digestion whereupon cooling water is admitted to the steam jacket interior 30 from water supply 20 (
This invention also presents a method for digesting or neutralizing waste matter comprising organic tissue or infectious, biohazardous, hazardous, or radioactive agents, by subjecting the waste matter to a controlled alkaline hydrolysis cycle and generating a sterile resultant suitable for conventional sanitary disposal. The preferred method compromises the steps of:
It should be noted that the fill levels discussed above may be modified as a function of waste material load size, with larger loads requiring higher fill levels. In other words, enough liquid should be added such that the waste material is completely submerged for reduction by the alkaline solution.
As mentioned above, an additional feature of the closed vessel is to allow the solid waste remains to be removed from a secondary opening (not shown) arranged on the vertical side of the vessel. This feature allows the vessel to be positioned in such a configuration that the primary opening may be located within a contaminated portion of the facility, while the remaining portions of the system are located within a clean portion of the facility. This would allow contaminated materials to be processed and sterilized, then for the sterile solid waste remains to be removed from the secondary opening as sterile remains into a clean area for final disposal. Thereafter, the secondary opening would be sealed prior to the opening of the primary opening for the loading of waste for another processing cycle. Such a configuration is referred to as “dirty side feed/clean side removal.” Such an embodiment would alter step (u) above to read as follows:
Finally, set forth below is an example of the system of this invention and its method of operation in use.
Prior to filling the vessel with, for example, animal carcasses containing infectious or hazardous agents, the lid of the vessel is closed in order to “zero” the load scale. The lid is then opened and the vessel filled with waste matter to the desired volume. Preferably, the load should be at least 20% of the vessel's capacity (by weight) but not more than the weight capacity of the vessel, in which case the system will not operate and the excess weight must be removed. The vessel lid is then closed and secured. The PLC controller is then activated to initiate the digestion process by first determining the weight of the waste matter within the vessel. The digestion cycle is then initiated whereby water is preferably added at the rate of 60% water to 40% tissue by weight, alkali is added at the predetermined concentration based on the tissue weight. Such concentration is normally equivalent to a solution of 50% NaOH added by weight at a ratio of 15 to 20% of the total tissue weight.
The heating step is then initiated to raise the temperature of the interior of the vessel to the predetermined first digestive cycle temperature for a predetermined duration to completely digest the carcasses. In a preferred mode, the cycle holds the digestion temperature to at least 110° C., preferably about 130° C., and most preferred about 150° C. At 150° C., the digestion cycle is normally about 3 hours in duration.
Once the digestive cycle is complete, the PLC control means initiates the cooling cycle, utilizing cold water flushed through the sleeve jacket 30 of the vessel. Once the vessel has cooled sufficiently, the vessel is drained to the sewer, then partially refilled with cold water and the interior rinsed. The vessel is then drained again, partially refilled again and this second rinse solution heated if desired. After this hot rinse, the vessel is then drained and it contents sprayed with a final spray rinse. The cooling cycle is then complete and the system shuts down while the drain is opened to empty completely the interior of the vessel.
If the operator is present at the completion of the cooling cycle, the vessel may at that point be opened and the waste-carrying basket removed and emptied. The basket is then replaced, making the system ready for a new cycle. In the event, however, the operator is not present when the cooling cycle is complete, when the cycle runs at night for example, the operator should initiate the spray rinse cycle for a short duration, preferably about 30 seconds. After the final spray is complete, the vessel may be opened and the waste safely disposed of.
Preferably, a portion of the vessel 112 is defined by a double-walled structure. Also preferably, the vessel interior 114 should be coated with an alkaline resistant material, such as stainless steel or a ceramic material. More preferably, the vessel 112 is constructed from a material capable of withstanding the combination of pH levels, temperatures, and pressures it may be subjected to during a hydrolysis operation. Suitable materials include certain formulations of stainless steel. The vessel 112 is preferably capable of being closed in an air tight fashion to provide the necessary environment within the vessel interior 114 for the controlled alkaline hydrolysis cycle to be carried out to completion, as well as to prevent the highly alkaline solvent and waste materials from escaping into the environment. Thus, the lid or cover 116 of the vessel 112 is preferably capable of being closed tightly and sealed shut to withstand the temperatures and pressures of the digestion cycle and prevent the inadvertent introduction of atmosphere (particularly carbon dioxide) into the vessel 112 interior and, more importantly, prevent the escape or inadvertent exhausting of the contents of the vessel 112 interior to atmosphere. Such closure of the vessel 112 may be achieved by conventional lid clamps well known in the industry (not shown), or by any convenient closure means available to one of ordinary skill in the art.
The system 110 further includes an electronic controller 1117, such as the conventional programmable logic controller (PLC) means described above. Preferably, the system 110 further includes a weight sensor or transducer 118 (shown schematically) operationally coupled to the vessel 112 and electrically coupled to the electronic controller 117 for determining the weight of the waste matter received within the vessel 112 and for generating an output signal to the controller 117 including such weight data. The transducer 118 is normally preset such that the weight of the vessel 112 without contents equals zero weight. The contents weight data may then be inputted to the electronic controller 117 for, based on the weight output data, determining the appropriate amounts of water and solvent to introduce into the interior of the vessel 112. In the case of smaller vessels 112 (having capacities, for example, to digest from about 2 to about 20 pounds of waste material) a predetermined amount of alkaline solvent (formulated to digest the maximum waste material load of the vessel 112) may be preferred for use with any amount of waste material up to the maximum load of the vessel 112. In this case, the weight data may instead be used to disable the system 110 if the maximum capacity of the vessel 112 is exceeded.
The system 110 further includes connecting a water supply 120 operationally connected to the vessel 112, such as via conduit 120a. The highly alkaline solvent is produced in the vessel 112 by mixing water and dry alkaline earth, alkali hydroxides, or alkali metal oxides therewith to form a highly alkaline solution. Alternately, a highly alkaline solution may first be prepared and then added into the vessel 112.
As with the previous embodiment, it is preferred that the so-formed solvent solution be heated in order to more efficiently and quickly accomplish the chemical reduction of the hydrolyzable waste material. Therefore, the system 110 preferably includes a heater 130 operationally connected to and positioned in thermal communication with the vessel 112. More preferably, the heater 130 is an electric hot plate in thermal contact with the base of the vessel 112 capable of heating the interior of the vessel 112 to a first predetermined temperature level after the introduction of water and solvent into the vessel interior 114. Alternately, any convenient type of heater 130 may be used to heat the vessel 112, such as the steam jacket described in the previous embodiment or any other heating means known to one of ordinary skill in the art. Electricity is supplied to the heater 130 by a power supply 132 via conduit 132a. Preferably, a temperature sensor 119 (such as a thermocouple or the like) is positioned in thermal communication with the interior of the vessel 114 such that the temperature of the interior of the vessel 114 may be continuously monitored or queried upon demand. More preferably, the heater 130 and the temperature sensor 119 are both connected in electric communication with electronic controller 117, such that electronic controller 117 may regulate the output of the heater 130 to maintain the temperature of the interior of the vessel 114 according to a predetermined or desired time/temperature profile.
The system 110 also preferably includes a vent 140 (discussed in greater detail below), which is preferably disposed in the open state upon initiation of the cycle and thereafter is preferably closed by the electronic controller 117 when the temperature within the vessel 112 reaches a predetermined first temperature. The temperature within the vessel 112 is gauged by the vessel thermocouple 119, while the pressure within the vessel 112 may be measured by a pressure sensor (not shown) such as a PSI transducer.
The system 110 also preferably includes agitation means 133 for circulating and mixing solvent and partially dissolved waste matter. Agitation means 133 is preferably magnetic, such as a magnetic stirrer 135 positioned such that a magnetic field may be generated within the vessel 112 and used to rotate one or more magnetic stir rods 137 positioned within the vessel 112. The magnetic stirrer 135 may be functionally combined with the heater 130, such as in a hot plate/stirrer combination readily known to one of ordinary skill in the art. While a magnetic stirrer 135 is preferred, agitation means 133 may include any convenient stirring means familiar to one of ordinary skill in the art to mix and agitate the contents of the vessel interior 114. Such agitation enhances the interaction between the highly alkaline solvent and the dissolving waste matter to keep the vessel contents moving and to prevent waste matter from accumulating at the bottom of container 112. A further benefit of agitation is the reduction of digestion cycle time. Agitation of the contents may be achieved by various means, including external mechanisms coupled to the vessel 112, such as rocking or shaking assembly that physically moves the vessel 112. All such alternative means of mixing or agitating the vessel contents are contemplated by this invention.
Preferably, the system 110 also includes a ventilation system for relieving excess pressure from the vessel interior 114 when the vessel 112 is closed. A fluid conduit 142 connects the vent 140 to a drain line 144. Preferably, a check valve 146 is connected between the 140 and the drain line 144 to prevent contamination of the vessel 112. The drain line 144 is also connected to a water outlet 148 formed in the vessel 112 for drainage of the solvent solution and any dissolved waste matter.
The system may also include an eductor 150 connected between the water outlet 148 and the drain line 144. Flushing water is admitted to the eductor 150 by the water supply 120 via conduit 120b. The action of the eductor 150 draws the air and any odorous gas from within the interior of the vessel 112 through fluid conduit 142, whereupon the air and odorous gas is eventually entrapped with the flushing water at eductor 150 to, in turn, be removed from the system via drain conduit 144. The temperature of the fluid at the drain may be gauged by a thermocouple (not shown) to monitor the effluent temperature prior to disposal in a sanitary sewer system. The vacuum-creating eductor 150 substantially reduces the odorous gases that may escape from rotting carcasses while the vessel 112 is filling, and may also be actuated to draw gasses from the vessel 112 while or after the waste is being hydrolyzed, if desired.
In operation, once the contents of the vessel are drained after the digestion cycle (heating and cooling), the interior of the vessel may be rinsed with cold water via water inlet 128 with the water outlet 148 open. After a few minutes, the water outlet 148 is closed to allow the vessel 112 to begin to fill with water. The vessel 112 is now considered ready for another hydrolysis cycle, and may be filled with waste for reduction. Once the vessel 112 is filled with a predetermined amount of water (at least enough such that the waste matter is covered) a predetermined amount the highly alkaline powder is added and combined with the water to form a highly alkaline solvent solution. The contents are then agitated by the magnetic stirrer 135 and stir rod 137, and the contents are heated to about 98 degrees Celsius for a predetermined period of time to chemically reduce the waste material. The vessel 112 is then allowed to cool, and the water outlet 148 is opened and rinse water is introduced into the vessel 112. The water outlet may be closed to allow rinse water to accumulate and rinse any remaining solids. The water outlet 148 is then re-opened and the liquid contents of the vessel 112 are allowed to drain. Thereafter, if desired or necessary, the water outlet 148 is closed for a second time and the vessel 112 is allowed to again fill with water. Heat may then be applied again to the vessel 112 to heat the liquid within the vessel to approximately 95° C. (203° F.), whereupon an enhanced rinse/diffusion is initiated. The time and temperature used in this post-digestion heating stage may vary.
The preferred system further includes a liquid permeable container 160, such as a basket, capable of holding the waste material within the vessel interior 114 during the waste reduction operation to completely immerse the waste material within the solvent solution. Referring again to
The method of using the system 110 is similar to that of the first embodiment discussed above, and includes the elements of providing a substantially alkaline-resistant vessel, providing a highly alkaline solvent, providing an amount of waste matter having a mass less than or equal to a predetermined maximum mass, immersing the waste matter in the solvent within the interior of the vessel, heating the solvent and the waste matter, and allowing the waste matter to remain within the solvent until digested to form an aqueous solution with residual solid waste matter. Preferably, the waste matter remains in the solvent for a predetermined length of time calculated to substantially completely dissolve a predetermined maximum mass of waste matter at a predetermined operating temperature. Preferably, the predetermined operating temperature is between about 95 and about 98 degrees Celsius. However, for a given solvent pH or concentration, hydrolysis may be achieved at lower temperatures (i.e., 90 degrees Celsius or even lower) by increasing the cycle time according to the Q10 Rule, as discussed above. The extent of digestion or degradation of the waste matter may be increased by lengthening the amount of time the waste matter is immersed in the solvent at the predetermined temperature, increasing the temperature of the solvent and waste matter, adding a catalyst material, or some combination of the above.
After cooling, the post-digestion end product may then be directly disposed of through conventional disposal means, such as a sanitary sewer or landfill, used as a fertilizing agent in land use applications, or the like. If preferred, the post-digestion stage may also include rinsing or flushing of the resultant waste product and the interior of the vessel. The system and method of this invention also substantially reduce the amount of post-digestion solid waste to be disposed of.
The system 210 further includes an electronic controller 217, such as the conventional programmable logic controller (PLC) means described above. Preferably, the system 210 further includes a weight sensor or transducer 218 (shown schematically) operationally coupled to the vessel 212 and electrically coupled to the electronic controller 217 for determining the weight of the waste matter received within the vessel 212 and for generating an output signal to the controller 217 including such weight data. The transducer 218 is normally preset such that the weight of the vessel 212 without contents equals zero weight. The contents weight data may then be inputted to the electronic controller 217 for, based on the weight output data, determining the appropriate amounts of water and solvent to introduce into the interior of the vessel 212. In the case of smaller vessels 212 (having capacities, for example, to digest from about 200 to about 500 pounds of waste material), or, optionally, in the case of larger vessels, a predetermined amount of alkaline solvent (formulated to digest fixed increments of waste material load) may be preferred for use with any amount of waste material up to the maximum load of the vessel 212. In this case, the weight data may instead be used to disable the system 210 if the maximum capacity of the vessel 212 is exceeded.
The system 210 further includes connecting a water supply 220 to the vessel 212, such as via conduit 220a. The highly alkaline solvent is produced in the vessel 212 by mixing water and dry alkaline earth, alkali hydroxides, or alkali metal oxides therewith to form a highly alkaline solvent solution. Conduit 220a connects through valves 224 to water inlet 226 and/or injector means 228 for introducing water into the vessel 212.
As with the previous embodiments, it is preferred that the so-formed solvent solution be heated in order to more efficiently and quickly accomplish the chemical reduction of the hydrolyzable waste material. Therefore, the system 210 preferably includes a heater 230 operationally connected to and positioned in thermal communication with the vessel 212 or immersed in the liquid contents of the vessel 212. More preferably, the heater 230 is a burner (such as a natural gas burner, and oil burner, or the like) extending below the vessel 212 and in thermal communication therewith or inserted into the vessel 212 and in direct thermal communication with the vessel contents. The burner is preferably adapted to generate sufficient thermal energy to heat the interior of the vessel 214 to a first predetermined temperature level after the introduction of water and alkaline solvent thereinto. Alternately, any convenient type of furnace or heater 230 may be used to heat the vessel 212, such as the steam jacket described in the previous embodiment or any other heating means known to one of ordinary skill in the art.
Preferably, a temperature sensor 219 (such as a thermocouple) is positioned in thermal communication with the interior of the vessel 214 such that the temperature of the interior of the vessel 214 may be continuously monitored or queried upon demand. More preferably, the heater 230 and the temperature sensor 219 are both connected in electric communication with electronic controller 217, such that electronic controller 217 may regulate the output of the heater 230 to maintain the temperature of the interior of the vessel 214 according to a predetermined or desired temperature profile.
The system 210 may also optionally include agitation means for circulating and mixing solvent and partially dissolved waste matter. The system 210 may also preferably include a vent 240, which is preferably disposed in the open state upon initiation of the cycle and thereafter is preferably closed by the electronic controller 217 when the temperature within the vessel 212 reaches a predetermined first temperature. A fluid conduit 242 connects the vent 240 to a fluid drain line or flue 244. The temperature within the vessel 212 is gauged by the vessel thermocouple 219, while the pressure within the vessel 212 may be measured by a pressure sensor (not shown) such as a PSI transducer.
In cycle, once the contents of the vessel are drained after a previous digestion cycle (heating and cooling), the interior of the vessel may be rinsed with cold water via water inlet 228 with the water outlet 248 open. After a few minutes, the water outlet 248 is closed to allow the vessel 212 to begin to fill with water. The vessel 212 is now considered ready for another hydrolysis cycle, and may be filled with waste for reduction. Once the vessel 212 is filled with a predetermined amount of water (at least enough such that the waste matter is covered) a predetermined amount the highly alkaline powder is added and combined with the water to form a highly alkaline solvent solution. Alternately, a concentrated alkaline solution may be added to the water to yield a highly alkaline solvent solution. The contents are then agitated by a stirring means, such as by pumping the highly alkaline solvent solution through the vessel 212, and the contents are heated to about 98 degrees Celsius for a predetermined period of time to chemically reduce the waste material. The vessel 212 is then allowed to cool, and the water outlet 248 is opened and rinse water is introduced into the vessel 212. The water outlet may be closed to allow rinse water to accumulate and rinse any remaining solids. The water outlet 248 is then re-opened and the liquid contents of the vessel 212 are allowed to drain. Thereafter, if desired or necessary, the water outlet 248 is closed for a second time and the vessel 212 is allowed to again fill with water. Heat may then be applied again to the vessel 212 to heat the liquid within the vessel to approximately 95° C. (203° F.), whereupon an enhanced rinse is initiated. The time and temperature used in this post-digestion heating stage may vary.
The preferred system further includes a liquid permeable container 260, such as a basket, capable of holding the waste material within the vessel interior 214 during the waste reduction operation to completely immerse the waste material within the solvent solution. The container 260 is preferably a basket shaped to fit into the vessel 212 and is preferably formed of alkaline-resistant perforated stainless steel. The perforation is preferably defined as a pattern of 6 mm (⅜ inch) holes formed through the steel basket 260. After the waste reduction operation has completed, the container 260 may be hoisted out of the vessel 212, thereby removing the undigested solid debris remaining within the container 260.
The method of using the system 210 is similar to that of the embodiments discussed above, and includes the elements of providing a substantially alkaline-resistant vessel, providing a highly alkaline solvent, providing an amount of waste matter having a mass less than or equal to a predetermined maximum mass, immersing the waste matter in the solvent within the interior of the vessel, heating the solvent and the waste matter, and allowing the waste matter to remain within the solvent until digested to form an aqueous solution with residual solid waste matter. Preferably, the waste matter remains in the solvent for a predetermined length of time calculated to substantially dissolve a predetermined maximum mass of waste matter at a predetermined operating temperature. Preferably, the predetermined operating temperature is between about 95 and about 98 degrees Celsius. The extent of digestion or degradation of the waste matter may be increased by lengthening the amount of time the waste matter is immersed in the solvent at the predetermined temperature, increasing the temperature of the solvent and waste matter, adding a catalyst material, or some combination of the above. After cooling, the post-digestion end product may then be directly disposed of through conventional disposal means, such as a sanitary sewer or landfill, used as a fertilizing agent in land use applications, or the like. If preferred, the post-digestion stage may also include rinsing or flushing of the resultant waste product and the interior of the vessel. The system and method of this invention also substantially reduce the amount of post-digestion solid waste to be disposed of.
Although the invention has been described with preferred embodiments, those skilled in the art will understand that modifications and variations may be made without departing from the scope of the inventions as set forth in the following claims. Such modifications and variations are considered to be within the purview and scope of the appended claims.
This application claims priority on PCT patent application no. PCT/US2003/031184, filed Oct. 1, 2003 and having a priority date of Oct. 2, 2002. This application is also related to U.S. patent application Ser. No. 09/171,447, filed Oct. 20, 1998, titled “Methods for Treatment and Disposal of Regulated Medical Waste,” and U.S. Pat. No. 6,437,211, issued Aug. 20, 2002, both of which are incorporated herein by reference.
