Hydraulic and earth engineering – Subterranean waste disposal – containment – or treatment – With treatment of waste
Reissue Patent
2002-04-08
2003-08-26
Hoey, Betsey Morrison (Department: 1724)
Hydraulic and earth engineering
Subterranean waste disposal, containment, or treatment
With treatment of waste
C210S764000, C210S916000, C071S013000
Reissue Patent
active
RE038238
ABSTRACT:
This invention relates to a method of treating wastewater sludge designed to decontaminate the sludge so that it can be safely applied as fertilizer to agricultural lands.
BACKGROUND OF THE INVENTION
Romans used lime to disinfect and deodorize human waste. The use has continued throughout the development of civilization. However, prior to this invention, the use of lime for wastewater, sludge treatment has been severely limited by governmental regulations including the United States Environmental Protection Agency (EPA).
The EPA has promulgated rules governing the type of processes that can be used to treat wastewater sludge.
Under 40 CFR 257, a Process to Further Reduce Pathogens (PFRP) (See p. 5,6) must be used where sewage sludge or septic tank pumpings are to be applied to a land surface or are incorporated into the soil, and crops for direct human consumption are to be grown on such land within eighteen (18) months subsequent to application or incorporation.
A Process to Significantly Reduce Pathogens (PSRP) (See p. 5) must be used where sewage sludge or septic tank pumpings are to be applied to a land surface or incorporated into the soil and the public will have access to such land within twelve (12) months subsequent to application or incorporation, or grazing animals, whose products are consumed by humans, will have access to such land within one (1) month subsequent to application or incorporation.
Appendix II of 40 CFR 257 classifies the following as PSRP and PFRP processes:
A. Processes to Significantly Reduce Pathogens
Aerobic digestion: The process is conducted by agitating sludge with air or oxygen to maintain aerobic conditions at residence times ranging from 60 days at 15° C. to 40 days at 20° C., with a volatile solids reduction of at least 38 percent.
Air Drying: Liquid sludge is allowed to drain and/or dry on under-drained sand beds, or paved or unpaved basins in which the sludge is at a depth of nine inches. A minimum of three months is needed, two months of which temperatures average on a daily basis above 0° C.
Anaerobic digestion: The process is conducted in the absence of air at residence times ranging from 60 days at 20° C. to 15 days at 35° to 55° C., with a volatile solids reduction of at least 38 percent.
Composting: Using the within-vessel, static aerated pile or windrow composting methods, the solid waste is maintained at minimum operating conditions of 40° C. for 55 days. For four hours during this period the temperature exceeds 55° C.
Lime Stabilization: Sufficient lime is added to produce a pH of 12 after 2 hours of contact.
Other methods: Other methods or operating conditions may be acceptable if pathogens and vector attraction of the waste (volatile solids) are reduced to an extent equivalent to the reduction achieved by any of the above methods.
B. Processes to Further Reduce Pathogens
Composting: Using the within-vessel composting method, the solid waste is maintained at operating conditions of 55° C. or greater for three days. Using the static aerated pile composing method, the solid waste is maintained at operating conditions of 55° C. or greater for three days. Using the windrow composting method, the solid waste attains a temperature of 5° C. or greater for at least 15 days during the composting period. Also, during the high temperature period, there will be a minimum of five turnings of the windrow.
Heat drying: Dewatered sludge cake is dried by direct or indirect contact with hot gases, and moisture content is reduced to 10 percent or lower. Sludge particles reach temperatures well in excess of 80° C., or the web bulb temperature of the gas stream in contact with the sludge at the point where it leaves the dryer is in excess of 80° C.
Heat treatment: Liquid sludge is heated to temperatures or 180° C. for 30 minutes.
Thermophilic Aerobic Digestion: Liquid sludge is agitated with air or oxygen to maintain aerobic conditions at residence times of 10 days at 55-60° C., with a volatile solids reduction of at least 38 percent.
Other methods: Other methods of operating conditions may be acceptable if pathogens and vector attraction of the waste (volatile solids) are reduced to an extent equivalent to the reduction achieved by any of the above methods.
Any of the processes listed below, if added to the processes described in Section A above, further reduce pathogens. Because the processes listed below, on their own, do not reduce the attraction of disease vectors, they are only add-on in nature.
Beta ray irradiation: Sludge is irradiated with beta rays from an accelerator at dosages or at least 1.0 megarad at room temperature (ca. 20° C.).
Gamma ray irradiation: Sludge is irradiated with gamma rays from certain isotopes, such as
60
Cobalt and
137
Cesium, at dosages of at least 1.0 megarad at room temperature (ca. 20° C.).
Pasteurization: Sludge is maintained for at least 30 minutes at a minimum temperature of 70° C.
Other methods: Other methods of operating conditions may be acceptable if pathogens are reduced to an extent equivalent to the reduction achieved by any of the above add-on method.
Prior to this invention, many concerns have been raised about the long term disinfection and stabilization capability of lime treatment. Parrel et al, in “Lime Stabilization of Primary Sludges”, Journal of Water Pollution Control Fed 46, 113 Jan. 1974 published by USEPA, states: “Lime stabilization does not make the sludges chemically stable. The pH eventually falls and surviving bacteria may return if conditions are favorable. . .higher organisms such as Ascaris survive short term exposure to pH of 11.5 and possibly long term exposure.”
In January 1979, the EPA published a Wastewater Sludge Manual (EPA 625/1-79-001) titled “Process Design Manual for Sludge Treatment and Disposal” which states:
“Lime stabilizations a very simple process. Its principal advantages over other stabilization processes are low cost and simplicity of operation. . .lime addition does not make sludges chemically stable; if pH drops below 11.0, biological decomposition will resume producing noxious odors. Second, the quantity of sludge for disposal is not reduced as it is by biological stabilization methods. On the contrary, the mass of dry sludge is increased by the lime added and by the chemical precipitates that derive from the addition. Thus because of the increased volume, the costs of transport and ultimate disposal are often greater for lime stabilized sludges than for sludge stabilized by other method. . .quantitative observation under a microscope has shown substantial survival of higher organisms, such as hook worms, amoebic systs and Ascaris ova after contact time of 24 hours at high pH.”
Reimers, Englande et al (EPA 600/2-81-166) reported that:
“Application of like to primary aerobic digested and anaerobic digested sludge was found to be effective with greater than 80% reduction of Ascaris viability in 5 days following aerobic digestion at a lime dosage of about 1000 mg/gram of sludge solids (one part lime to one part sludge solids). . . In the case of the 35° C. aerobically-digested sludge, there was no apparent effect of lime on the viability of Ascaris eggs at dosages up to 3000 mg of lime per gram of dry sludge solids under anaerobic conditions, in the period of 20 days. However, under aerobic conditions, a 98% reduction of viable Ascaris eggs was observed within one hour at dosages greater than 1000 mg of lime per gram of dry sludge solid, but only 77% reduction of the viable eggs was observed at a dosage of 100 mg lime per gram of dry sludge solids after 20 days. The explanation of these differentials is not apparent.”
In July 1984, the Sandia National Laboratories published a report titled “Pathogens in Sludge Occurrence, Inactivation and Potential for Regrowth” which states:
“To summarize the effects of lime on sludge pathogens viruses are destroyed by high pH values, although it has not been shown that viruses within sludge itself are inactivated; parasite ova are resistant to high pH, and most will probably survive lime treatment; bacteria are rapidly in
Burnham Jeffrey C.
Nicholson John P.
Hoey Betsey Morrison
N-Viro International Corp.
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