Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-06-01
2001-11-06
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S621000, C210S624000, C210S626000, C210S903000, C210S906000
Reexamination Certificate
active
06312599
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to treatment of wastewater produced during food processing operations. It specifically relates to utilizing at least one flow equalization lagoon or basin to perform a controlled hydrolysis stage of biological phosphorus removal, de-nitrification, and partial reduction of 5-day biological oxygen demand (BOD) during flow equalization of 2-to-6-day wastewater inflows to produce substantially uniform 7-day outflows, while maintaining high BOD/TKN and BOD/TP ratios within the influent wastewater of the basin or basins. It further relates to specific recycling steps and a plurality of control methods for maintaining satisfactory anaerobic, anoxic, and aerobic conditions at specific stages of this treatment and at all seasons of the year.
2. Review of the Prior Art
Wastewater treatment, both municipal and industrial, has focussed for years on removal of fats, oil, and grease, suspended solids, and biological oxygen demand (BOD) from wastewater produced by meat processing and other food processing plants, so that lakes and streams into which the treated liquid was discharged would not be de-oxygenated thereby. Then it was realized that the abundance of mineral nutrients from the treated wastewater, combined with sunlight, fostered plant life over animal life, creating eutrophic bodies of water in which the uncontrolled proliferation of various algae and plant species in salt water bays and in fresh water lakes and rivers itself caused de-oxygenation as the dying plants and algae decayed. By E.P.A. estimates, 40 percent of the nation's rivers, 51 percent of the lakes, and 57 percent of the estuaries have been adversely affected by nutrient over-enrichment.
For many years, scientists and engineers attempted to control eutrophication by reducing the amount of ammonia, a poison in itself to aquatic animal life, that was discharged from wastewater treatment plants. Biological aerobic treatment, one of the processes for reducing ammonia, created nitrates and nitrites. Realizing that these are favored plant foods, aerobic treatment of the wastewater was followed by biological anoxic treatment for reducing the nitrates and nitrites to nitrogen gas that harmlessly escaped to the atmosphere.
Next it was realized that denitrification was insufficient because several microbial species can use nitrogen gas from the atmosphere as a source of nitrogen for cellular synthesis. In consequence, phosphorus control was recognized as the key to controlling eutrophication. For years, chemical reactants were added for precipitating phosphorus as sludge. However, this type of phosphorus removal can significantly increase sludge production, typically from 50 percent to 100 percent. In addition to the cost of the chemical reactants, disposal of the additional sludge is expensive.
The poultry industry, for example, has also increased its use of trisodium phosphate (T.S.P.) and other chemical products in order to comply with federal zero-tolerance requirements for eliminating fecal material. The typical poultry plant output of phosphorus is in the range of 15 to 20 mg per liter, but use of T.S.P. in processing operations can increase the phosphorus concentration in the wastewater by 200 percent to 300 percent.
Biological phosphorus removal (BPR) is a simple but effective process that conventionally requires the wastewater to pass through an anaerobic zone and then an aerobic nitrification zone before the mixed liquor is settled in a clarification zone and a portion of the resulting settled sludge is recycled to the aerobic nitrification zone. BPR is improved by inserting an anoxic zone between the anaerobic zone and the aerobic zone so that BPR is combined with biological nitrification and denitrification, as described for municipal wastewater by Dr. Clifford W. Randall, Virginia Polytechnic Institute and State University, in “Theory and Practices of Biological Nutrient Removal.”
In the anaerobic zone, which must be adequately mixed, a population of excess phosphorus-storing (polyP) bacteria, such as acinetobacter and other phosphate-accumulating microorganisms that are able to store high amounts of phosphate, up to 10% by weight as polyPhosphate inside the cells, are present. In addition, a suitable substrate, such as soluble carbonaceous Chemical Oxygen Demand (COD) and BOD, in the form of volatile acids, must be present. The 7.3 kcal/mol of energy per mol of adernosine triphosphate (ATP) that is liberated by the hydrolysis of ATP by the polyP bacteria becomes available to the polyP cells, releasing phosphate and forming adenosine diphosphate, ADP. The polyP bacteria use this released energy to polymerize a substrate of organic compounds, such as acetic acid, propionic acid, and other short-chain volatile fatty acids (VFAs), as well as short-chain alcohols, for intracellular storage as polymerized compounds, such as poly-&bgr;-hydroxybutyrate (PHB) or poly-&bgr;-hydroxyvalerate (PHV).
However, other forms of BOD, such as proteins, cannot be used by the polyP bacteria. Nevertheless, during passage through the basins, a portion of these proteins are gradually broken down by other forms of bacteria into VFAs that gradually become available to the polyP bacteria. This anaerobic breakdown of organic compounds, by enzymes or microorganisms, to simpler products is termed fermentation and occurs naturally in all anaerobic, facultative, and aerobic lagoons. The polyP bacteria actually intercept the breakdown of such organic compounds that would otherwise produce CO
2
and water.
Because the polyP bacteria have no electron acceptors available in the anaerobic zone, they cannot produce new cellular material and multiply in the anaerobic zone, but they can remove certain available organics from solution and sequester them for later utilization in the subsequent aerobic zone where electron acceptors are available. In this aerobic zone, the polyP bacteria have the first opportunity to utilize the BOD so that they have a competitive advantage over the non-polyP bacteria. Thus they can proliferate at a higher rate in the aerobic zone and dominate the activated sludge bacterial population that includes autotrophic nitrifiers using ammonia as their energy source for converting ammonia to nitrite and nitrate.
When the polyP bacteria enter the aerobic zone, they metabolize the stored intracellular compounds for growth and energy. Because excess energy is generated beyond the needs for growth, the polyP bacteria, now much more abundant because of their growth, remove phosphate from solution and store the energy in intracellular phosphate bonds during a “luxury” uptake stage, whereby large quantities of phosphorus are removed from the system in the portion of the sludge that is wasted after clarification. This BPR activity is desirable, but nitrification and de-nitrification are also needed.
The key factor that determines the amount of phosphorus stored in the activated sludge is the amount of readily available organic matter in the anaerobic zone and the absence of electron acceptors such as oxygen and nitrate. The bacteria will preferentially metabolize the organic matter rather than store it if electron acceptors, i.e., dissolved oxygen or oxygen from nitrates and nitrites, are available. Some such electron acceptors are always present in the inflowing wastewater. There must consequently be a large excess of organic matter beyond that needed to deplete the electron acceptors recycled or entrained into the anaerobic zone. In other words, the quantity of stored substrate in the form of organic matter and subsequently the biological removal of phosphorus will be reduced by the quantity of electron acceptors present in the anaerobic zone. U.S. Pat. relating primarily to BPR include U.S. Pat. Nos. 5,288,405; 5,342,522; 5,380,438; 5,480,548; 5,833,856; and 5,853,589.
Biological nitrogen removal (BNR) is another essential wastewater treatment process. It is possible for the BNR process to operate without utilizing an initial anaerobic zone. For example,
Lelong Marion P.
Upton Christopher
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