Patent Application
20210355004
The proposed invention consists of a new method to more efficiently separate the solid waste generated during the process in which corn flour is produced by nixtamalization.
Nixtamilization is the process commonly used to produce corn flour. Food grade corn is added to a hot solution of water containing calcium hydroxide (lime) at an elevated temperature (70-90 C). This softens the corn which is then milled. The milled corn is then processed thru a dryer to produce corn flower and in the process, a waste stream is generated from the milling process. The waste stream primarily consists of water heavily contaminated with corn solids. The corn solids are very difficult to treat and remove.
Typically, this waste stream passes thru some type of dewatering device before going to a biological wastewater treatment plant that reduces TSS, BOD and TKN. Current dewatering devices are very inefficient and can only remove 10-20% of the solids. This means the cost of running a biological treatment plant is high due to loading and solids accumulation which eventually leads to expensive dredging of lagoons on a 5 to 10-year timeline.
Another method to treat contaminated water is described in U.S. Pat. No. 7,497,455B2. The patent describes the use of anionic flocculants and other microparticle aids and coagulants that improve the separation of solids in the thin stillage generated in the ethanol dry grind process. The thin stillage generated in the ethanol process is at a pH of 4.0 to 4.7 which is much different than the high pH seen in the nixtamalization process, where pH is in the range of 12 to 12.5. This method requires large decreases in the pH of the contaminated water which is expensive and difficult.
Another proposed method to treat contaminated water is described in U.S. patent Ser. No. 14/765,256 which describes a method to clean up the water to standards that will allow direct discharge to water streams. The proposed process in this patent reduces the pH to a range of 6 to 8 with sulfuric acid and then enzymatically treats the waste to make it more amenable to treatment with cationic/anionic flocculants and other dewatering/settling aids such as clays. After reducing the solid loading, the clarified waste is processed thru ultrafiltration membrane systems to produce fractionated value-added organic coproducts.
The proposed invention consists of a new method to more efficiently separate the solid waste present in water and generated during the process in which corn flour is produced by nixtamalization. The purpose of this invention is to provide a simple method to more effectively remove the solids loading and reduce the associated costs (short and long term) with the downstream operation of running a biological wastewater treatment system. The benefits of this invention versus current practices are as follows:
The proposed invention is better suited for the nixtamalization process than the method described in the ethanol process (U.S. Pat. No. 7,497,455B2). This approach describes treating waste at the low pH typical in the ethanol production process (4.0-4.7). It is not practical to reduce the pH to this low of a level because of the cost associated with the sulfuric acid and then the need to raise the pH again to provide alkalinity for the biological treatment system. The proposed invention is also superior to the method described in U.S. Ser. No. 14/765,256 because the capital cost and operating cost will be much lower. Most importantly, the proposed invention is much easier to operate due to its simplicity of design than the complexity proposed in U.S. Ser. No. 14/765,256.
The invention consists of a new, simpler method to more efficiently separate the solid waste (including corn solids) generated during the process in which corn flour is produced by nixtamalization.
One method of removing the solids from this aqueous waste stream is to install equipment such as a centrifuge, belt press, screw press (but not limited to these types of liquid-solid separation equipment) options to remove solids before or after chemical pretreatment. This chemical pretreatment typically consists of some type of pH adjustment specifically with the salt of a carbonic acid followed by an anionic and then cationic flocculant. The salt of the carbonic acid creates an in situ coagulum, a process which creates larger solids that when flocculated, are more resistant to shear allowing them to be dewatered on the appropriate equipment.
The proposed invention and method adds a salt of carbonic acid (examples include but are not limited to carbon dioxide, calcium carbonate, sodium carbonate, sodium bicarbonate, and soda ash) after allowing the temperature of the waste stream to drop below 120 F, into a rapidly agitated tank. Since the pH of the contaminated water to be treated is often in a range of 12 to 12.5, the salt of the carbonic acid causes a drop in the pH. After the pH becomes stable (in a range between 8.0 to 10.5), with an optimum range of 10 to 10.3, the aqueous mixture develops colloidal particles (coagulum) as a result of the precipitation of calcium and magnesium compounds. This is like what happens during the process of hot lime softening.
Once the coagulum has formed, the treated waste stream is transferred to a 2nd tank or vessel where a high molecular weight anionic flocculant, (with a charge in the range of 10-50% on a mole basis) is added at a rate of 20 to 1000 ppm (active basis) while gently mixing. The small coagulum particles will start to get larger over a period of several minutes. The proper dosage will create a large stable particle.
The final step in the invention is to gently transfer the anionic flocculated stream to a 3rd vessel while adding a high charge (>50% mole basis), high molecular weight flocculant at a rate of 20-1000 ppm while gently mixing. The addition of the cationic flocculant creates a more shear resistant particle.
From the waste stream contaminated with corn particles, the precipitated waste, removed from the contaminated water, can be used as animal feed, if the flocculants used are nonpoisonous.
So the proposed invention, is a cheaper and more efficient means to purify contaminated water, including nejayote, and results in animal feed. The proposed invention takes contaminated water, purifies the contaminated water and produces animal feed.
The invention is not limited to the structures, methods, and instrumentalities described herein and shown in the drawings. The invention is defined by the claims set forth in this application and subsequent patent.
