Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1999-03-23
2001-07-17
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S727000, C210S729000, C210S714000, C210S730000, C210S908000, C210S917000
Reexamination Certificate
active
06261460
ABSTRACT:
BACKGROUND OF THE INVENTION
There is an increased need to reduce levels of organic contaminants in treated industrial wastewater and drinking water. Increased need for treatment of industrial wastewater discharge is the result of the National Pollution Discharge Elimination System (NPDES) which was established as a result of the Clean Water Act of 1972. NPDES controls discharges from point sources of water pollution, and focuses its efforts on monitoring, enforcing and permitting industries that produce waste water. Two organic contaminant classes regulated by NPDES are contaminants leading to biochemical oxygen demand (BOD), and fats, oils and greases (FOG). Both classes of contaminants can be toxic to humans and the environment, and interfere with biologic water treatment systems. Examples of sources of FOG and BOD are petroleum and chemical manufacturing, metal-finishing, food processing, paper-making and textiles.
Additionally, new rules proposed by the Environmental Protection Agency, under the Safe Drinking Water Act, can lead to increased monitoring and regulation of trace organic contaminants in drinking water. Drinking-water purification plants throughout the United States and Europe utilize chlorine as a primary means of disinfection. However, the chlorine reacts with organic contaminants to produce small but significant amounts of compounds such as methylene chloride, methyl chloride, methyl bromide, bromoform, and dichlorobromomethane, collectively called trihalomethanes (THMs). Most THMs are carcenogenic and their concentrations in municipal drinking waters must be closely monitored.
Other organic contaminants in drinking water may be toxic to living organisms, or impart unwanted characteristics to water like taste, odor, color or turbidity. In addition, contaminants may be biologically active pathogenic microorganisms, such as Giardia cysts and Cryptosporidium. Sources of contaminants can be, for example, petroleum from rainwater run-off or leaf-debris or other natural decaying organic matter.
Organic contaminants of this type are generally in the size ranges of about 10
−7
to 10
−2
cm in diameter and are too small to be removed by physical filtration. They also resist settling out by gravity. They can include a wide range of organic debris with different molecular weights, and abilities to form dispersion, polar, hydrogen bonding or other inter-molecular interactions. Some can dissolve in water completely, others can show partial solubilities due to these polar or hydrogen interactions. In addition, there can also be significant amounts of surface-active molecular debris that contain hydrophobic and hydrophilic components. This debris tends to absorb onto other contaminants and impart to them slight but significant polar characteristics, promoting formation of meta-stable colloidal suspensions.
The most economical treatment method for removing these contaminants from drinking and waste water is typically chemical destabilization followed by gravity settling, filtration or dissolved air flotation. Because destabilization chemistry depends on the interactions between polar functional groups contained on the contaminants to achieve coagulation and flocculation, those that do not carry polar groups are not appreciably removed by this chemistry. Additionally, destabilization chemistry can only remove contaminants that are not dissolved in water. These two factors leave the majority of BOD, FOG, and organic contaminants currently outside of the reach of this treatment method.
SUMMARY OF THE INVENTION
This invention is a method for treating drinking water and industrial waste water using small hydrophobic oil droplets that provides an alternative and improved means for removing dissolved and particulate contaminants in water treatment systems where chemical destabilization is part of the treatment protocol. Additionally this invention enhances the removal of contaminants from water when using dissolved air flotation (DAF).
The method includes adding droplets of a substantially non-water soluble oil to contaminated water to form a mixture and to combine with the contaminant. A chemical destabilizer is added to the water to further form a mixture to aggregate the oil droplets. The oil droplets are then separated from the water, thereby removing the contaminant.
In another embodiment of the method, a substantially non-water soluble oil is added to water having a contaminant. A destabilizer is added to the water. The oil, water, contaminant and destabilizer are mixed to form small oil droplets in the water, wherein the oil droplets combine with the contaminant. The oil droplets are separated from the water, thereby removing the contaminant.
A substantially non-water soluble oil is selected, such as an aliphatic oil, that has a low solubility in water and a high affinity for the contaminants, so that it combines with them, making them effectively insoluble in water. The oil is also selected so that it can attain a higher affinity for the contaminants when broken into small droplets or formed into colloidal structures within the water phase. The oil is also selected so that the oil-contaminant mixture can be substantially coagulated and aggregated by use of chemical destabilization. The oil is further selected so that it coats particulate or droplet contaminants, giving these contaminants the ability to be substantially coagulated and aggregated by use of coagulation chemistry. The oil is also selected so that after chemical destabilization, the oil-contaminant mixture can be removed by gravity settling, filtration or DAF. The oil is further selected so that it coats particulate or droplet contaminants, making their surface more hydrophobic thus making them more susceptible to air bubbles attaching to them thus enhancing their removal by DAF. The oil can be derived from petroleum sources or from natural sources such as, for example, soy beans, coconuts or rapeseeds.
In a preferred embodiment, the oil used is a C
16-18
Ester derived from a natural source. The quantity of oil added to the water is about the same as or less than the quantity of contaminant in the water. The oil and water mixture is agitated or stirred sufficiently to cause the oil to break into droplets that are less than about 0.1 millimeter in diameter. The water is then treated with, for example, aluminum sulfate to coagulate the oil-contaminant mixture, and, for example, a flocculant, such as Magnifloc to aggregate the mixture. This mixture is then removed from the water by use of DAF, effectively removing the contaminants from the water.
DETAILED DESCRIPTION OF THE INVENTION
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. All percentages and parts are by weight unless otherwise indicated.
An objective of water treatment is to remove contaminants from water so that it is biologically and chemically safe for its intended use. Water intended for drinking must, of course, be purified to a much greater extent than wastewater that is to be discharged to the environment. However, even this water must be purified to the extent that the remaining contaminants are not toxic to the environment.
When chemical destabilization is used to purify water, contaminants that are either dissolved in the water or that do not carry polar functional groups or that have hydrophilic surfaces are not appreciably removed. It is the purpose of this invention to extend the capability of chemical destabilization to remove these contaminants. These capabilities are realized by adding oil to the water that is easily removed by destabilization. The oil is selected to combine with or capture the contaminants and therefore impart to the contaminants those physical quantities that allows them to be removed by use of chemical destabilization. Therefore, dissolv
Benn James A.
Thode Kenneth C.
Hruskoci Peter A.
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
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