Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2001-01-19
2003-12-16
Lithgow, Thomas M. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S704000, C210S724000, C210S652000, C210S806000
Reexamination Certificate
active
06663782
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to liquid flotation separation components, Systems and methods. More particularly, the present invention relates to liquid conditioning components, systems and methods that treat livestock waste to remove contaminants such as nitrates and microbes from carrier water streams such as barn or yard wash water.
Livestock operations produce waste in the form of manure and urine. For the purpose of this application, the term “feedlot” means confined animal or milk production operations in areas that produce no forage. In 1992, the USDA estimated the number of feedlots at 510,000. In addition, there are over 1,000 dairies in California alone. The same year, it estimated the total number of animals in operations with over 500 animals at 6.4 million cattle, 29 million hogs, and 744 million chickens. The average dairy cow produces over a cubic foot of waste daily. It is clear that the tonnage of feedlot waste is high.
Current federal regulations prohibit discharge of feedlot wastewater to surface waters unless extreme storms cause overflows from containment systems designed to hold wastewater and runoff. An extreme storm is defined as 24 hours worth of a 25-year storm. Although these regulations have been in place since 1974, risks to the environment and fisheries persist.
Feedlot waste has contaminated aquifers, the air, and surface waters such as streams, rivers, lakes, bays, estuaries and the ocean. For example, the storms that flooded the east coast of the United States in recent years resulted in discharge of millions of gallons of hog and other livestock waste into the Chesapeake Bay and other fisheries.
Composting of livestock waste into useful materials has been practiced for millennia. However, composting of fresh livestock waste in the quantities in which it is produced on a modern feedlot is impractical. This is because aerobic composting will not take place if: 1) the moisture content is above 65%, which most fresh manure or its carrier streams are; 2) the carbon to nitrogen ratio is not kept within a narrow range; 3) adequate oxygen cannot reach into the waste to support the microbes; or 4) the temperature drops below a minimum necessary to sustain the microbe population. Absent large-scale solids mixing equipment, which is rarely employed, the carbon to nitrogen ratio is fixed by the type of livestock and its feed. In addition, some farms screen out the carboniferous solids for reuse. Thus, the ratio is not adjusted to bring it into the compostable range. Airborne oxygen cannot penetrate more than a few inches into piled manure (e.g. windrows), leaving the volume of manure inside this surface layer deficient in oxygen. Temperatures in most livestock raising areas in the continental U.S. fall below 40° F. for substantial periods. If pile temperature falls below 55° F., microbial activity essential for composting will slow or stop. Thus, direct composting of the entire waste stream in feedlot operations over 300 animals (cattle equivalents) is rarely employed.
Feedlot waste is primarily manure and urine in a carrier stream of water. There is much variability in feedlot waste management. However, most feedlot operations use gravity settling, which removes primarily inorganic constituents from the carrier stream and leaves the organic constituents, followed by some form of biological processing. Usually, the stream passes from settling pits into lagoons, where the organic constituents are food to microbes. Aerobic microbial digestion of the food requires oxygen and results in biomass, heat, carbon dioxide and water according to the following formula:
Food+O
2
→Biomass+energy (heat)+CO
2
+water
As bacteria age and die, their cells create biological oxygen demand (BOD) of their own and the dead bacteria become food for the others. As the cycle repeats, more of the biomass is converted to CO
2
and water. Consequently, the longer the time period allowed for decomposition, the lower the volume of the resulting sludge.
However, if high enough, as in feedlots, this BOD in the carrier stream of water uses up the dissolved oxygen in the water, eventually killing the aerobic bacteria and changing the environment to one that supports anaerobic bacteria. Anaerobic decomposition produces methane, hydrogen sulfide, ammonia, and CO
2
. Hydrogen sulfide and the ammonia are odorous and toxic air contaminants. Also, high BOD surface runoff damages downstream receiving waters by, for example, suffocating fish. Therefore, BOD must be substantially reduced before the water leaves the livestock operation.
The technologies aimed at reducing BOD have evolved with concentrations of human population. Manipulation of contact time has evolved as a primary way to treat organic wastewaters. Technologies have moved from unaerated shallow lagoons through mixed and aerated ponds. These methods share the disadvantages of large land area requirements, inefficient aeration, little process control, and the additional biological oxygen demand generated by the algae that tends to grow on the surface. Trickling filters, which repeatedly flow the water to be treated over a media containing air spaces, addressed the land area problem. However, these filters retain the problem of little process control and suffer from freezing in the winter and plugging.
To address the plugging, freezing, large land requirements and inefficient aeration problems, activated sludge systems were developed and are the main technology used today for human waste. These systems mix food, bacteria nutrients and oxygen enough to prevent flotation and settling. Oxygen is dissolved into the liquid by mechanical means. However, the high cost and complexity of these technologies has been a barrier to their use in feedlot operations.
Instead of employing activated sludge systems, the typical 300+ animal California dairy operation flushes stalls with water, screens the water for solids later processed into bedding, employs sedimentation to separate the mineral particles and other materials heavier than water, sends the supernatant to one or more lagoons where microbes convert dissolved solids to suspended solids in the form of more microbes, and land applies the biologically altered water by irrigation, knifing it into the soil or injecting it into the ground.
The liquid that is land applied typically contains high concentrations of nitrate. This is because the age of the sludge in the lagoons and the liquid from the lagoons that is reused as wash water is over seven days old. Feedlot wastewater systems contain large quantities of nitrifying bacteria, which use ammonia as food, because the wastewater is over 5 days old.
Nitrification increases the BOD of the water. In addition, nitrates are toxic to cattle and humans. Nitrate poisoning in cattle produces spontaneous abortion and death. State and federal regulations prohibit dosing the land with more nitrates than the vegetation grown thereon can take up. This limits the amount of used water that farm operators may dispose of via land application.
U.S. Pat. No. 5,698,110 (Wyatt, et al) addresses animal excrement by filtering the solids, mixing in a lime and cellulose-based deodorizer, and drying. This technology, however, does not address the liquid. Cattle waste averages only 13% solids, the rest being liquid. Thus, the Wyatt invention does not address over ¾ of the waste stream.
U.S. Pat. No. 5,472,472 (Northrup) addresses animal excrement by precipitating solids in a reactor, passing the slurry to a bioreactor where it is aerobically and anaerobically treated, and then to a constructed wetland. It claims to treat the water to a generally nutrient-free discharge that can be used for irrigation. The system requires aerators, mixing of metallic salts to precipitate phosphorous, a pond with aerobic, anaerobic and facultative bacteria, and a wetland divided into cells as the last step. This requires a large land area, has little process control, and is complex. As such, it retains several of the main disadvantages o
Jovine Raffael
Morse Dwain E.
Morse Michael P.
Morse Wade O.
Kelly Bauersfeld Lowry & Kelley LLP
Lithgow Thomas M.
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