Patent Application
20090095041
The novel technology relates generally to the materials science, and, more particularly, to a method for using porous foamed glass bodies for the filtration of fluids.
As more and more land is being used for either residential or agricultural purposes, available water for drinking, washing and irrigation is becoming scarcer. Water reclamation, recycling and purification is, accordingly, of increasing importance. One method of removing unwanted particulate material from water or other liquids is via filtration. The most common type of commercial or large-scale water filter is a rapid sand filter. Water passes vertically through sand, which is often arranged having a layer of activated carbon or anthracite coal thereabove top remove organic compounds. The space between sand particles is typically larger than the smallest suspended particles, so simple filtration is typically insufficient. This is addressed by extending the volume of the filter through which the water must pass, so that particles tend to be trapped in pore spaces or adhere to sand particles. Thus, effective filtration is a function of the depth of the filter, and in fact if the top portions were to block all of the filtrate particles, the filter would quickly clog.
One drawback of sand filters is their great volume. This is addressed by the use of pressure filters. Pressure filters work on the same principle as gravity filters, but for the enclosure of the filter medium is in a (typically steel) vessel through which water is forced under pressure. Pressure filters may filter out much smaller particles than sand filters can, but require bulky and expensive pressure pumps and containment vessels, and are thus unattractive for smaller scale filtration applications.
Another filtration option is the use of membrane filters. Membrane filters are widely used for filtration of both drinking water and sewage. Membrane filters typically employ thin, porous polymer or ceramic members to filters out virtually all particles larger than their specified pore sizes, typically down to about 0.2 microns. The membranes are quite thin and liquids may thus flow through them fairly rapidly. Membranes may be made strong enough to withstand slightly elevated pressure differentials and may also be back flushed for reuse. However, membrane filters offer a low cross-sectional filtration volume, quickly fill up with filtrate and have to be frequently flushed. Thus, there remains a need for a physical filter and method of filtration that utilizes high pore volume and surface area for reacting and/or collecting relatively high volumes of filtrate. The present novel technology addresses this need.
The present novel technology relates generally to the use of porous foamed glass bodies filters to purify liquids. One object of the present novel technology is to provide an improved method and apparatus for liquid filtration. Related objects and advantages of the present novel technology will be apparent from the following description.
For the purposes of promoting an understanding of the principles of the novel technology, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel technology is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the novel technology as illustrated therein being contemplated as would normally occur to one skilled in the art to which the novel technology relates.
The present novel technology relates to a method of using a porous, open cell foamed glass substrate or filter 10 (see
Typically, as illustrated in
The foamed glass filter media 10 may be monolithic foam systems, where single or multiple foamed glass members 10 are used to filter water or other liquids at up to 80 psi pressure, or the foamed glass filter media 10 may be in the configuration of packed bed filters with pressure tolerance of at least about 160 PSI (see
NH4++O2→NO2−+H++H2O (1)
NO2−+O2→NO3− (2)
As described above, ammonium is oxidized through the involvement of nitrosomonas (1) and nitrobacters (2) to nitrate filer media 10 with nitrite (NO2−) as an intermediate product. The open cell pore network 30 of the foamed glass is an improvement over polystyrene beads, as the foamed glass provides a stronger, more rigid biofilm support medium, and is less prone to picking up static charges. Further, the foamed glass pore network 30 does not substantially change size in response to temperature or to externally applied compressive forces.
Many nuclear wastes are in the form of nitric acid solutions. Most actinide and fission products are stable solutes in the nitric system, and the solutions are not corrosive to stainless steel. Vitrification, a common process for disposition of nuclear wastes, is however, complicated when acids must be converted to silicate (usually borosilcate) glass. Silicates are insoluble in nitric acid, and are thus typically suspended by physical agitation or other means and carefully metered to the furnace to prevent melt inhomogeneity.
Soda-lime glass can be foamed in such a manner to readily sorb nitric acid solutions. The foam glass media 10, in the form of individual particles, can each readily absorb over twice its weight in acid solution and can be directly converted to glass with no physical mixing required. The porous foamed glass media 10 can also act as a carrier of acid solution, as the porous foamed glass media 10 will retain the overwhelming majority of sorbed liquid indefinitely. This allows great range of design for pre-treatment and melter/furnace delivery mechanisms. Further, such a waste disposal system would be attractive in applications where precise knowledge of material accountability is required.
Glasses have been prepared using this novel technology, and are consistent with the requirements for geologic disposal in the U.S. These compositions are borosilicate glasses—part of the highly researched and documented composition range used by the Defense Waste Processing Facility and West Valley Demonstration Project. The novel technology is also compatible with specialty waste disposition and also large-scale melter operations.
Open cell foamed glass bodies 10 are typically derived from glass precursors that are first pulverized and then softened and foamed to achieve about 90% or greater void space. The pores 15 in the resulting foam are typically on the order of about 0.5 to 2 millimeters in diameter, although the pore size may readily be adjusted. The foamed glass typically each have material density of about 0.2 kg/l prior to crushing and sizing. Crushed foam particles have a typical bulk density of about 0.15 kg/l or lower, depending on particle size.
The starting material is typically soda-lime-silica (i.e., window glass); for nuclear processing applications window glass is preferred due to its low concentration of transition metal and sulfur oxides. Foamed glass bodies 10 derived from window glass is pure white (color can be added as required) in color and can be closely sized between ⅛th and 1 inch particles. Monolithic pieces are also readily also be produced.
The porosity of the (>50% open pores) is typically controlled to effectively and rapidly sorb liquids of 10 centipoise or lower viscosity. Typically, a foamed glass body 10 will absorb over 200 percent its weight in water. Further, the foamed glass body typically will retain the liquid indefinitely, with the majority of water loss due strictly to evaporation. Soda-lime glass has excellent chemical stability against nitric acid and is not generally attacked by common acids other than hydrofluoric.
Multiple glass products have been generated using the absorptive foam. All glasses were derived from nitric acid solutions (containing uranium surrogates and other species used to modify the glass processing characteristics) sorbed onto foam glass particles 10. Additionally nitric acid solutions have been prepared with gadolinium and neodymium as a surrogate for uranium. Absorption tests indicate the acid solutions are absorbed in the same manner and to the same degree as water.
In general, the goal was to produce a single phase, homogeneous glass suitable for long-term storage and disposal. As borosilicate glass is the first type of glass accepted for geologic storage in the U.S., the process was tailored to produce a glass of this type, although other glass compositions can likewise be produced. As illustrated schematically in
The preliminary process region appears to be relatively broad, being on the order of:
Wherein Re2O3 represent rare earth oxides. Actinides are nominally less soluble on a molar basis, but have a greater atomic mass. Uranium, especially, is quite soluble in glass. Additional species can be added to the glass composition region if increased durability or decreased viscosity is desired. This process may likewise be used to dispose of waste streams containing non-radioactive heavy metal cations.
While the novel technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the novel technology are desired to be protected.
