Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1998-08-25
2001-04-24
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S711000, C210S718000, C210S724000, C210S905000
Reexamination Certificate
active
06221254
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to the treatment of wastewater, and other liquid waste streams, and more particularly to the removal of proteinaceous material and suspended solids from wastewater using only carbon dioxide as a combination of treatment chemical, separation method and anti-biological agent in a manner that conserves and reuses excess carbon dioxide efficiently.
II. Description of the Problem
Businesses engaged in the processing of food and other organic substances, such as poultry processing facilities, generate tremendous quantities of wastewater containing a wide range of dissolved organic fluids and suspended solids. In poultry processing operations, chickens are brought to the facility alive where they are hung upside down, have their throats slit to drain away blood, are scalded to remove feathers, then the internal organs removed, followed by plunging the carcass into a chilled water bath before further processing. Thus, contaminants are added to wastewater stream that may be suspended particles, such as feather pieces, emulsified and partially soluble materials like fats and oils, and dissolved materials such as blood proteins. For the purposes of this disclosure, the blood and other aforementioned biological matter containing proteins will be collectively referred to herein as “proteinaceous material.” During further processing, other particulates such as marinades, oils, fats, breading, batter and seasonings, migrate to the wastewater stream. These substances may come from frying, grilling, roasting, steam cooking, impingement cooking, chilling, freezing and various material handling steps. In many instances, it is through the periodic sanitation phase when machinery is cleaned that many suspended solids enter the wastewater stream.
Another example of a facility wherein such wastewater is generated is in a fully-cooked poultry steam application, where 10,000 gallons per day of liquid enters the waste stream in a typical application. This equates to approximately 80,000 pounds per day at a ten percent (10%) solids content. Currently this level of solids enters the waste stream and places high demand on the treatment system.
The industry attempts to recover as much material as possible in each processing step for reuse by rendering it back into animal feed products. However, since water is a crucial component to the overall process, it invariably contains large amounts of material that must be removed prior to discharge to the environment. Indeed, in recent years, the rapid growth of the poultry processing industry has resulted in large volumes of water being generated in such processing facilities. Pressure is being brought to bear on the industry to suitably clean this water prior to discharge. New technologies, such as the one disclosed herein, may offer the potential to salvage edible materials for human or animal consumption at the point of application, thus resulting in overall decreases in water consumption and treatment chemicals.
The problems associated with the removal of such proteinaceous materials and suspended solids in wastewater streams are well known. Various techniques have been proposed and tried to treat the water with different degrees of success and associated costs. The most common technique has been to perform some mechanical treatment to remove coarse suspended solids and subject the water to both anaerobic and aerobic biological treatment. This technique is often chosen because of its relatively low capital cost. However, most processing facilities of this type make use of large amounts of disinfectants and hot water, which has a profound impact on the required biological processes that is difficult to control.
Because the chicken fecal material contains an abundance of sulfur-reducing bacteria, and because blood protein is also high in sulfur content, the anaerobic ponds typically used as a first step produce hydrogen sulfide gas and other odor compounds that are objectionable to the surrounding area. Furthermore, the anaerobic ponds do not efficiently process the waste and subsequently lose their effectiveness. Since these ponds are normally followed by aerobic treatment, their ineffectiveness results in increased contaminant loads on the aerobic process.
The increased loads on the aerobic system ultimately lead to a failure ofthe aerobic treatment to effectively treat the wastewater. Unfortunately, the poultry industry is faced with increasing the capacity of these facilities in the face of ever more stringent discharge limitations. Since these facilities all require significant amounts of land area, many are limited as to expansion options. Those without available land area are faced with using physical or chemical treatment techniques to try and achieve discharge water quality.
For example, the poultry industry currently employs the addition of chemicals to coagulate the suspended solids, as well as some type of clarification equipment to remove this material. As is common in this particular industry, some dissolved materials require a lowering of the pH of the stream to a point where optimum chemical reactions may proceed to cause the dissolved material to precipitate from the stream in the form of a suspended solid. This is particularly true in the case of blood products mixed into the waste stream. In order to accomplish this, the pH of the waste stream must be reduced to below about pH 4.5 at which level the blood proteins coagulate from solution. This is generally accomplished with an inexpensive inorganic acid, such as sulfuric or hydrochloric acid. In many instances, the pH of the stream and separated solids, after separation of the suspended solids from the stream, is below that pH limit suitable for reuse or discharge to another process or to the environment. When unacceptably low pH conditions exist, the pH of the treated stream or the separated solids must be increased to acceptable levels.
To return the pH to acceptable levels, a base material, again usually inorganic, is added which reacts with the acid. There are several problems associated with chemical treatment processes such as that just described, especially if the acidic pH level is below about pH 4.5. First, although the addition of the acid causes the pH to decrease, it may also bring about an interaction with the suspended and dissolved materials, which consumes the acid and which may create undesirable reaction products. Second, the precipitated material resulting from the reduction in pH will also be acidic in nature and, after separation, may be unsuitable for any reuse unless treated to return the pH to higher levels. Third, the addition of a base to either the liquid stream or the separated solids results in the formation of salts which may not be acceptable in reuse of the solids or the treated liquid. Also, the sedimentation clarifiers typically used in connection with chemical treatment techniques are ineffective in removing oils and grease. Therefore, most designers opt for some type of flotation clarifier as explained further below.
As an alternative to chemical treatment using acids, some facilities have turned to flotation clarifier processes whereby air is injected into the waste stream under pressure. At the appropriate time, the pressure within the chamber containing the wastewater is reduced, producing fine bubbles which adhere to the solids and cause them to float to the surface. The floating solids are then removed by conventional skimming equipment for later use or disposal. However, while those processes involving dissolved air do eliminate some of the problems of chemical treatment, other problems still remain. For example, the added air may promote the growth of bacteria in the separated solids, thereby causing odors and degradation of the material. As a result, the recovered solids may be unfit for reuse, especially in the case of such materials from food processing operations.
An example of physical and chemical treatment is U.S. Pat. No. 5,413,720 issued to Miller.
Dickerson J. Rodney
Moshier Mark W.
Lawrence Frank M.
Miller Kean
Simmons David A.
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