Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-10-16
2002-08-06
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S639000, C210S651000, C210S652000, C210S728000, C210S734000, C210S735000
Reexamination Certificate
active
06428705
ABSTRACT:
FIELD OF THE INVENTION
The present invention involves the treatment and purification of wastewater at high flow rates (gallons per minute, gpm), low pressures (psig), and high flux values (gallons/ft
2
/day, GFD). Specifically, the present invention relates to the process and apparatus for removing metals and other inorganic and organic contaminants from large volumes of wastewater in a single pass. The process and apparatus are particularly useful to effect the separation of contaminants to a level that the effluent meets specified regulatory standards for discharged water compliance. Additionally, the effluent from the system may meet or exceed those requirements for use as gray-water or for feed to a reverse osmosis system. In particular, the process and apparatus in this invention are useful for the treatment of municipal and industrial wastewaters.
BACKGROUND OF THE INVENTION
Many manufacturing operations generate large quantities of water containing heavy metals and other inorganic and organic contaminants. These industries include, but are not limited to, agriculture, petroleum, chemical, pharmaceutical, mining, metal plating, metal finishing, textile, pulp/paper, brewing, beverage, distilling, food processing, and semiconductor industries. These industries are strictly regulated with regards to the level of contaminants in their discharged wastewater. This is a result of the toxicity problems caused by the contamination of waterways by heavy metals, suspended solids, and organic materials. Strict discharge limits have been adopted for heavy metal contaminants deemed harmful to humans and aquatic organisms, and include cadmium, chromium, copper, lead, mercury, nickel, zinc, and semi-metals such as arsenic and selenium. Discharge limits also exist in many other industries. Discharge of wastewater containing large amounts of suspended solids is also harmful to ecosystems due to silting and the decrease in available light for photosynthesis.
One example is the large volumes of arsenic bearing waters generated by the mining industry. Mining draw-down wells which are used to de-water deep mining operations can generate up to 75,000 gpm (gallons per minute) of water and may contain up to 400 ppb (parts per billion) of arsenic. Additionally, it has been recognized that many potable water sources are contaminated with unacceptable levels of arsenic and may represent a serious health risk. The current maximum contaminant level (MCL) imposed by the EPA is 50 ppb, but is expected to decrease to somewhere in the range of 2 to 20 ppb in the year 2000. Because of the large volumes of water generated by both mining operations and contaminated wells, there is a need for arsenic treatment systems that can handle high flows of contaminated water.
Another example is the wastewater streams generated by the semiconductor industry. In the fabrication of integrated circuits (IC), chemical-mechanical polishing (CMP) is an essential process used to reduce topological defects. Because defect reduction is especially critical in the production of new generation ICs, the use of CMP slurries is expected to grow at a greater rate than any other integrated circuit manufacturing category. Until recently, CMP wastewater was not a major issue. However, as the volume of CMP wastewater increases, typical acid waste neutralization systems at IC manufacturing operations are not capable, nor are they equipped, to treat the high levels of suspended solids, fluoride, and heavy metals found in CMP wastewater. Flow rates from CMP operations typically range from 10 to 500 gpm. To effectively meet the new regulatory challenges and the safe treatment of CMP wastewater, it is imperative to develop a simple and robust wastewater treatment system.
Semiconductor, hydrocarbon refining, and other manufacturing processes may also generate large quantities of fluoride ions that must be removed from wastewater. Various processes have been proposed, with only marginal success, for removing fluoride from wastewater. Such processes include treatment with calcium, magnesium, phosphate, and/or aluminate.
Yet another example is the large quantities of water containing dyes from many industrial dyeing operations, such as pulp, paper, fiber, and textile dyeing processes. For example, textile mills can generate millions of gallons of dye wastewater every day. The dyes and other organic compounds found in such effluent wastewater steams rarely conform to governmental standards restricting color value, biological oxygen demand (BOD), and chemical oxygen demand (COD) of industrial discharge.
A further example is the large quantities of wastewater from food processing operations, including meat and poultry feedlots and processing operations. Wastewater from these operations may contain organic and inorganic contaminants to be removed prior to environmental discharge. Such wastewater may also contain biological contaminants.
In general, a variety of processes have been proposed to reduce contaminants in industrial wastewater to meet the increasingly stringent discharge limits. These include large settling ponds, clarifiers, and sand filter systems utilizing inorganic coagulants, lime, and large quantities of high molecular weight polymer additives. Although such systems are typically able to achieve 90% compliance with regards to discharge regulations, many metal and non-metal contaminants cannot be safely discharged into the environment unless their concentration is much less than 0.5 ppm (parts per million). For example, if influent arsenic levels are greater than 300 ppb, clarifier/gravity settling and sand filter systems are not able to consistently provide discharge levels less than 50 ppb. Likewise, effective removal of suspended solids via gravity settling schemes rely on high doses of lime and high molecular weight anionic polymer flocculants. These systems are susceptible to upsets due to varying effluent composition, which results in failures to meet regulatory compliance. In addition, system maintenance is extensive, and large land areas (footprint) are required for the system installation.
Microfiltration has been considered to remove heavy metals and suspended solids from wastewater. One example, cross-flow microfiltration, typically operates at 25 to 75 psig or greater, and may yield a flux ranging from 10-150 GFD. Because of the low flux and the constant recycle and reconcentration mode of the apparatus, cross-flow filtration is typically unable to process very large amounts of wastewater. For example, at a flux of 150 GFD, it would be necessary to have at least 24,000 square feet of membrane to process 2,500 gpm of wastewater. If the wastewater flow rate were 7,500 gpm, then the membrane size would need to be at least 72,000 square feet. Because it would take a very large number of costly cross-flow membranes to process these high flow rates, the system in turn would be prohibitively large and expensive. An additional drawback of cross-flow filtration is the need to use high pressure to force the water through the membranes. High pressure operation results in increased maintenance costs, the need for larger capacity pumps, increased power consumption, and increases the potential to “blind” or foul the membranes with particles. Finally, cross-flow systems are inherently inefficient because the reject water stream must go through multiple passes or recirculation cycles before the water is completely treated.
Because of the shortcomings of both gravity settling/clarifier and cross-flow filtration schemes, it would be a significant advancement in the art to provide a process and system for removing metals and other contaminants from large quantities of wastewater, at low pressure (<25 psig) and a high flux (>200 GFD).
It would also be a major advancement in the art to provide a process and microfiltration system for removing metals and other inorganic and organic contaminants from large quantities of wastewater in which relatively simple and inexpensive membranes are used.
It would also be a major improvement in the art
Allen Stephen D.
Golden Josh H.
Madson & Metcalf
Microbar Incorporated
Therkorn Ernest G.
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