MXPA99002384A - Process for disinfecting organic waste sludge - Google Patents

Abstract

Disclosed is a process for disinfecting the sludge byproduct of an organic waste stream of pathogenic bacteria and helminth ova commonly found in organic sludges, which includes the step of intimately contacting sludge with an effective amount of an aqueous solution having a solute of at least one of a class of chemical compounds which liberate methyl-isothiocyanate gas upon commingling with organic sludge. Following disinfection the sludge may be subjected to supplemental process for extermination of enteric virus and/or conditioned for recycling as a nutritious plant medium.

Description

PROCESS TO DISINFECT MUDS FROM ORGANIC WASTE This application is a PCT application that relates to United States Patent Application Serial Number 08/341, 8'01 previously filed, by Peltier, et al, filed November 18, 1994 (original presentation) and U.S. Patent Application Serial Number 08 / 444,144 of Peltier, et al, presented on May 5, 1995 (which is a continuation request in part of the United States Patent Application Serial Number 08 / 341,801 of Peltier, et al, filed on November 18, 1994), both of which are pending applications. In the United States of America, this application is a continuation application in part of the United States Patent Application Serial No. 08 / 444,144 of Peltier, et al. There is no vindication of the date of international priority under the PCT rules, since this request is filed more than one year after the date of presentation of the identified applications.

REF .: 29780 1. Field of the Invention The invention described herein refers in general to the field of sludge treatment which is formed as a by-product of the waste stream, comprised of organic waste, sometimes referred to as organic waste sludge. Typically deposited as a segment, these sludges are typically comprised of organic solids, precipitated and 50-80 percent, by weight, of moisture content. These sludges are typically in the form of an odoriferous, semi-physical, consistent, moist mass. Because of their biological origin, these sludge are usually inoculated with a variety of pathogenic organisms, including pathogenic bacteria and helminthic ovules. Due to the high organic and moisture content of these sludges, typically pathogenic bacteria and helminth ovules bloom in them; presenting in this way biological hazards to human, animal and plant life that comes in contact with these sludges. These sludges also tend to attract numerous carriers (such as insects, rodents and birds) that tend to directly and indirectly spread the hazards of the sludge beyond the point of collection or disposal. Therefore, organic waste sludge, which is not disinfected, is not only unpleasant to handle, but also difficult to transport safely, dispose of or reuse beneficially. On the other hand, the high organic and nitrogen content makes them ideal for recycling as a nutritious planting medium, with the condition that they could be disinfected without depleting their nitrogen content substantially. Accordingly, the invention disclosed herein provides a process for the extermination of pathogenic bacteria and helminth ovules in organic waste sludge without substantially depleting the nitrogen content of these sludges.

Description of Related Art Organic waste sludge is an inevitable byproduct of waste streams containing organic material, such as municipal and private waste treatment plants, feed lot operations, sawmills, paper mills, livestock slaughter operations and other operations where waste of organic origin is collected as a consequence of the main operations that are carried out. These sludges are typically formed as a sediment from the waste stream comprised of precipitated matter of biological origin and water; that exist in the form of a consistent, moist, carrier-attracting, odoriferous mass. As a consequence of their biological origin, these sludges are frequently contaminated with pathogenic bacteria and helminth ovules. Therefore, non-disinfected organic waste sludge is typically hazardous to human, animal and plant life, are stinking, have physical characteristics that make them difficult to handle and transport, and are attractive to numerous carriers that tend to spread the hazards of the mud beyond the point of its collection or disposal. In an effort to deal with the substantial problem of pathogens in organic waste sludge, a number of methods have been developed. Many of the currently used methods are listed in the North American Code, 40 CFR part 257. These include aerobic digestion, anaerobic digestion, lime stabilization, air drying, fertilization, thermal drying, heat treatment, gamma irradiation, electron irradiation, and other methods shown in Table 6-1 of this regulation. In addition, U.S. Patent Nos. 5,281,341 and 4,793,927 to Rei er describe methods for disinfecting an organic waste sludge with nitrous acid and ammonia. U.S. Patent No. 3,942,970 to O'Donnell discloses a method for disinfecting organic waste sludge with N-methylol-urea solution and then reacting the methylol solution with an acid. All previously known methods for the disinfection of organic waste sludges comprise one or more of the following disadvantages: a) substantial time of treatment, b) high energy treatment, c) use of complex, expensive, permanently placed equipment d) transportation of sludge transporting pathogens to a treatment facility, permanently placed, e) use of expensive, difficult to handle and / or hazardous chemicals that can leave substantial chemical residue and / or) substantial depletion of the nitrogen content of the sludge The invention described herein substantially reduces the above disadvantages by providing a simple, fast and effective method for disinfecting organic waste sludge; with cheap chemical products and cheap equipment that can be portable, without substantial reduction of the nitrogen content of the sludge and without leaving a substantial chemical residue. While it is generally known that several solutions generating methyl isothiocyanate are effective, by reducing the population of certain microorganisms, it is believed that these solutions have not previously been used for the disinfection of organic waste sludge according to the present invention. , nor have these solutions been described as being effective as a helminth ovicide in organic waste sludge. Previously, helminth ovules have been considered highly resistant to extermination by aqueous-based salt solutions. While no claim is made to the exact biological process by which the solutions described here exterminate the helminth ovules, it is believed that the methyl isothiocyanate gas, released upon mixing the solutions described and the sludge, is capable of penetrating the difficult outer covering of the helminthic ovules, of forming thioureas substituted within amino groups of the ovules themselves, thus inhibiting the enzymatic activity essential for the continuous viability of the ovules, resulting in the death of the ovules.

BRIEF DESCRIPTION OF THE INVENTION The main objects of the invention described herein will provide a simple, rapid and effective means for disinfecting organic sludge from pathogenic bacteria and helminth ovules without substantially depleting the nitrogen content of the sludge. Another object of the invention is to provide an improved means for reducing the odoriferous characteristics and attracting carriers of the organic waste sludge. A further object of the invention is to provide a method for treating organic waste sludge that is practiced with cheap chemicals and inexpensive equipment that can be portable. The invention described herein can be used to achieve each of the above objects discussed above. The pathogenic bacteria and the helminthic ovules found in the organic sludge are effectively killed by the step of completely contacting the organic sludge with an effective amount of aqueous solution containing a solute of one or more chemical salts that release gas from the organic sludge. Methyl is-otiocyanate when mixed with organic sludge. This step also reduces the odoriferous characteristics and attraction to mud carriers,. without substantially depleting the nitrogen content of the sludge. In addition to the disinfection of pathogenic bacteria and helminthic ovum, the sludge can be further treated, by known means, for virus disinfection and / or improving its physical properties for recycling as a fertilizer. ' DESCRIPTION OF THE PREFERRED MODALITY In the preferred embodiment of the invention, the preferred method for disinfecting an organic waste sludge from pathogenic bacteria and helminth ovules includes the step of completely mixing the sludge with an effective amount of aqueous solution containing an N-methyldithiocarbamate solute. of sodium. In the concentrated aqueous solution, the sodium N-methyldithiocarbamate is considered a stable solution, but when it is diluted to form a diluted solution it decomposes releasing methyl isothiocyanate gas. While no claim is made to the exact biological process by which methyl isothiocyanate is an effective biocide of pathogenic bacteria found in organic waste sludge, it is believed that. methyl isothiocyanate alters the structure of the primary or secondary amine groups of the biologically important molecules of bacteria, such as peptides and proteins, forming substituted thioureas. These altered molecules seem to have an inhibited enzymatic activity. Once "sufficient enzyme activity is inhibited, bacteria become non-viable." Since methyl isothiocyanate reacts with a wide variety of biomolecules, it is an effective biocide for all known pathogenic bacteria found in sludge. Also, the present invention describes that the complete mixing of organic waste sludge, containing approximately 50-80 'percent (by weight) of moisture content with a sufficient amount of aqueous solution containing a solute. A chemical salt that liberates methyl isothiocyanate gas when it is diluted, such as sodium N-methyldiocarbamate, is an effective biocide for helminthic ovules in this sludge.Previously, helminth ovules were considered in Generally, they are resistant to extermination by water-based saline solutions, while the exact reason why the ovules of lmintio are resistant to previously known saline solutions, it is believed that the outer lining of the ovules is generally impermeable to liquid penetration; in this way, water can not transport biocidal salts to the ovules themselves. However, it is known that the cover of the helminthic ovules is permeable to at least some gases, such as an exchange of oxygen that occurs through the lining (the ovules will die if they are kept for a sufficient time in an environment deprived of oxygen. ). While no claim can be made to the particular biological mechanism by which salts liberate methyl isothiocyanate form an effective biocide for helminthic ovules, it is believed that methyl isothiocyanate gas is able to penetrate the ovum shell , and once admitted to the ovules, it is able to form thioureas in the biologically essential molecules of the ovules, altering the function of the molecules and thus causing the ovules to die. While an aqueous solution containing a solute of sodium N-methyl-methiocarbamate is preferred, it is assumed that due to its general availability and low cost, there is a class of chemical salts that also release methyl isothiocyanate gas when they are diluted in an organic waste sludge that contains a substantial moisture content. These chemical salts include potassium N-me t i-ldi thiocarbamate and tetrahydro-3,5-dimethy1-2H-1,3,5-diaz azine-2-thione which are commonly used as soil "fumigants" to control the germinative weeds, the nematodes' parasites, fungi and insects. Also included are any metal salt of monomethyldi thiocarbamate or monoalkyl idi thiocarbamate of any cation, such as sodium, potassium, lithium, cesium or heavy metals of this class, but they are more expensive to manufacture and are not generally commercially available. Alkaline earth metal salts, such as magnesium, calcium, strontium, etc., of monomethyldi thiocarbamate or monoalkyl idi thiocarbamate are also included in the class, but are also more expensive to manufacture and less commercially available. Any guímica salt is used that liberated gas of isothiocyanate of methyl, or a plurality of salts, in aqueous solution to exterminate the pathogenic bacteria and ovules of helmintio in muds of organic waste, the effective biocide of these organisms is isothiocyanate of methyl. While testing has determined that a concentration as low as 40 parts per million of methyl isothiocyanate release salt is effective as a biocide for pathogenic bacteria and helminthic ovules in an organic waste sludge, to provide a margin of safety in the preferred embodiment, sufficient aqueous solution (which may vary according to the concentration of the solution) is thoroughly mixed with the organic waste sludge to be treated, so that the mixture contains a concentration of at least 150 parts by weight. million salt of methyl isothiocyanate release. Concentrations as high as 1350 parts of methyl isothiocyanate release salt have been tested without any depletion of the sludge nitrogen content. In fact, after application, a byproduct of methyl dithiocarbamate is methylamine which is eventually converted to an ammonium ion, carbon dioxide and water which improves the fertilization quality of the sludge. However, there is some sodium residue, albeit little in the preferred concentration described, of the use of sodium N-methyldi thiocarbamate as the methyl isothiocyanate release salt. Therefore, if the disinfected sludge is to be applied as a fertilizer to the soil that is already loaded with sodium chloride (a condition that exists in some areas), potassium N-methyl iodide thiocarbamate, or one of the Other sodium-free, isothiocyanate-free chemical release salts, described above. In the preferred embodiment of the invention, the complete mixing of sludge with the disinfectant solution described above is easily accomplished by an auger / paddle mixer., double, portable, such as a Roto-Mix 6000. The use of the portable device, such as the Roto-Mix 6000, allows the treatment of organic waste sludge at its collection point instead of having to transport the hazardous sludge and difficult to manage to a facility permanently placed. Mixing must be of sufficient speed and duration to ensure intimate mixing of the sludge and the disinfectant solution. With the Roto-Mix 6000 it has been found that mixing at a higher speed for about 5 minutes provides sufficient mixing to ensure the extermination of all pathogenic bacteria and helminthic ovules. Other apparatuses capable of intimately mixing a consistent, sticky, moist mass with a relative amount of a liguid will be equally satisfactory. While many pathogenic bacteria in an organic sludge are killed almost instantaneously by exposure to methyl isothiocyanate, after mixing as before, in the preferred embodiment of the invention, the treated sludge is preferably stored temporarily in a container, which it can be dewatered atmospherically, for about 24 hours to insure complete penetration of the methyl isothiocyanate into distant and similar slits which may exist in various materials in the form of particles included in the sludge. During this 24-hour period care is taken to avoid the addition of acid substances to the sludge, since these substances are known to neutralize the carbamate solutions and extinguish the additional generation of methyl isothiocyanate. At the end of the 24-hour period, in atmospherically degassed situations, the generation of methyl isothiocyanate has substantially ended, leaving only a small amount of chemical residue, mainly of the cationic metal (eg, sodium, in the case of the use of N-methyldithiocarbamate), in the mud. Simultaneously with the disinfection according to the present invention of the organic waste sludge, this sludge can also be disinfected from enteric viruses by the alkaline treatment. The methyl isothiocyanate release salts described above have an additive effect in these treatments; that is, the mixing of these salts with the mud increases the mud pH, requiring less inclusion of alkaline solution to produce a sufficiently high pH (generally a pH of 12 or more) for the killing of enteric viruses. Simultaneously with the disinfection of the organic waste sludge, according to the present invention, this sludge can also be treated with a water-based, electrolytic soil additive. In the preferred embodiment of the invention, approximately 118.28-354.8 ml (4-12 ounces) of weight per ton of sludge produces at least two beneficial effects. First, the wetting properties of this additive aids in the penetration of water, which has dissolved salts of methyl isothiocyanate release, and between matter in the form of mud particles, thereby increasing the likelihood of contact of methyl isothiocyanate with all the pathogenic bacteria and helminthic ovules that they could have. Second, the inclusion of this electrolytic additive results in disinfected sludge that has improved qualities as a plant medium. Additionally, simultaneously with the disinfection of the organic waste sludge, according to the present invention, it can then also be conditioned, for recycling as a plant medium, by adding a hydrophilic polymer, such as potassium polyacrylate. This polymer absorbs the excess water of mud, "drying" in an affective way to it, making the mud less consistent and easier to handle. The addition of the polymer also improves the water retention characteristics of the mixture, which produces a number of desirable effects. First, the improved water retention characteristics reduce the availability of odoriferous molecules to escape from the mixture, further reducing the odor and attraction of carriers. Second, the increased water absorption provides an increased retention time of methyl isothiocyanate dissolved therein, thereby providing an increased period of contact between methyl isothiocyanate and pathogenic organisms. Finally, increased water retention and reduced evaporation improves the characteristics of disinfected sludge for use as an agricultural medium and / or soil conditioning agent. The mixing of approximately 0.908 kg (2 pounds) of powdered potassium polyacrylate per ton has been found to be effective for sludges having approximately 80% water content. However, the dose can be varied depending on the absorption capacity of the particular hydrophilic polymer chosen. Any amount of hydrophilic polymer can be added to produce a final product having the desired physical properties. A final step, also optional, in the development of an agricultural medium, easily usable, is the inclusion of organic packaging material and / or non-organic, non-pathogenic, bulk. In general, in the preferred embodiment, the inclusion of the uninfected packaging material will occur after the sludge disinfection is completed before, in order to avoid the use of large quantities of disinfection chemicals that will be required to produce concentrations effective amounts of methyl isothiocyanate release salts in a larger mass. An almost endless variety of these materials can be used to join the highly enriched organic sludge to the particulate matter that tends to remain in place in the soil and impart the soil conditioning characteristics appropriate to the product. final. The organic, common conditioning material may include seed shells, barks, shells, sawdust, shells of land and bone animals, boiler ashes, crop stubble, leaves, hay, grass, charcoal, carbon black, soil of diatomaceous, and other non-pathogenic material of biological origin. The conditioning material, not organic, common will include sand, mica, vermiculite, limestone and the like. Any amount of conditioning material can be included in the disinfected sludge to produce a final product having desired properties. Once these materials are mixed with the mud (specifically the sewage sludge), the consistent texture of the sludge is reduced further. In the preferred embodiment, sufficient conditioning material is usually included to produce a final product having the texture of a fine, potted soil mixture. This texture facilitates the application of mud to farmland with conventional agricultural equipment or use as a potted soil. In a field trial, approximately 635 kg (1400 pounds) of treated sludge were disinfected and thoroughly mixed with approximately 1271 kg (2800 pounds) of sawdust. The final product was a powder, not consistent, finely divided, dark, having a slight aroma of freshly carved earth that was free of pathogenic bacteria and helminth ovules. The preferred embodiment described above must be construed as illustrative and not in any way limiting the scope of the invention, which is set forth in the following claims.

It is noted that in relation to this date, the best method known to the applicant to carry out the present invention is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property:

Claims (34)

1. A process for disinfecting organic waste sludge, characterized by comprising the step of completely mixing the organic waste sludge with a water-based solution having a solute of an effective amount, of at least one of a group of chemical salts, salt that spontaneously releases methyl, gaseous isothiocyanate when the solution is mixed with the organic sludge.

2. The method according to claim 1, characterized in that the group of chemical salts comprises at least one of a group of monomethyldithiocarbamate salts of any cation. •

3. The method according to claim 2, characterized in that the monometyldithiocarbamate salt used comprises at least one having a metal cation.

4. The compliance method. with claim 3, characterized in that the monomethyldithiocarbamate salt having a metal cation comprises at least one having a sodium cation.

5. The method according to claim 4, characterized in that the monomethyldithiocarbamate salt having a sodium cation comprises sodium N-methyldithiocarbamate.

6. The method according to claim 3, characterized in that the monomethyldithiocarbamate salt having a metal cation comprises at least one having a potassium cation.

7. The method according to claim 6, characterized in that the monomethyldithiocarbamate salt having a potassium cation comprises potassium N -methyl thiocarbamate.

8. The method according to claim 1, characterized in that the group of chemical salts comprises at least one of a group of salts of monoalkyl-idithiocarbamate of any cation.

9. The method according to claim 1, characterized in that the group of chemical salts comprises trahydro-3,5-dimethyl 1-2H-1,3,5-thiadiazine-2-thione.

10. The method according to claim 1, characterized in that the effective amount of the chemical salts is at least 1000 parts of chemical salt per parts per million of mud.

11. The method according to claim 1, characterized in that the effective amount of the chemical salts is at least 150 parts of chemical salt per parts per million of mud.

12. The method according to claim 1, characterized in that the effective amount of the chemical salts is at least 70 parts of chemical salt per parts per million-of-mud.

13. The method according to claim 1, characterized in that the effective amount of the chemical salts is at least 40 parts of chemical salt per parts per million of mud.

14. The method according to claim 1, characterized in that it further comprises the step of completely mixing the sludge with an effective amount of a water-soluble alkali.

15. The method according to claim 1, characterized by further comprising the step of completely mixing the sludge with an aqueous solution having an effective amount of alkaline solute.

16. The method according to claim 14, characterized in that the effective amount of water-soluble alkali is such that it produces a pH of 12 or more of sludge.

17. The method according to claim 15, characterized in that the effective amount of aqueous solution having an effective amount of alkaline solute is such that the amount produces a pH of 12 or more of sludge.

18. The method according to claim 1, characterized in that it further comprises the step of completely mixing the sludge with an effective amount of ground, electrolytic, water-based additive, with the organic sludge.

19. The method according to claim 14, characterized in that it further comprises the step of completely mixing the sludge with an effective quantity of soil, electrolytic, water-based additive in the organic sludge.

20. The method according to claim 15, characterized in that it further comprises the step of completely mixing the sludge with the effective amount of ground, electrolytic, water-based additive, with the organic sludge.

21. The method according to claim 1, characterized in that it further comprises the step of completely mixing an effective amount of hydrophilic polymer with the organic sludge.

22. The method according to claim 18, characterized in that it further comprises the step of completely mixing an effective amount of hydrophilic polymer with the organic sludge.

23. The method according to claim 14, characterized in that it further comprises the step of completely mixing an effective amount of hydrophilic polymer with the organic sludge.

24. The method according to claim 15, characterized in that it further comprises the step of completely mixing an effective amount of hydrophilic polymer with the organic sludge.

25. The method according to claim 14, characterized in that it further comprises the step of completely mixing an effective amount of hydrophilic polymer with the organic sludge.

26. The method according to claim 20, characterized in that it further comprises the step of completely mixing an effective amount of hydrophilic polymer with the organic sludge.

27. The method according to claim 1, characterized in that it further comprises the step of completely mixing an effective amount of at least one of a group of non-pathogenic conditioning material with the organic sludge.

28. The process according to claim 14, characterized in that it further comprises the step of completely mixing an effective amount of at least one of a group of a non-pathogenic conditioning material with the organic sludge.

29. The compliance process according to claim 15, characterized in that it further comprises the step of completely mixing an effective amount of at least one of a group of packaging material, non-pathogenic with the organic sludge.

30. The process according to claim 18, characterized in that it further comprises the step of completely mixing an effective amount of at least one of a group of packaging material, non-pathogenic with the organic sludge.

31. The process according to claim 19, characterized in that it further comprises the step of completely mixing an effective amount of at least one of a group of packaging material, non-pathogenic with the organic sludge.

32. The process according to claim 20, characterized in that it further comprises the step of completely mixing an effective amount of at least one of a group of non-pathogenic conditioning material with the organic sludge.

33. The process according to claim 25, further characterized by comprising the step of thoroughly mixing an effective amount of at least one of a group of packaging material, non-pathogenic with the organic sludge.

34. The process according to claim 26, characterized in that it further comprises the step of completely mixing an effective amount of at least one of a group of non-pathogenic conditioning material with the organic sludge.