Abstract:
A method of disposing of waste material in a waste stream, including positioning a porous foamed glass member characterized by an open-cell interconnected pore network in contact with a volume of liquid to be purified and removing an amount of an undesired material from the volume of liquid.

Description:
TECHNICAL FIELD 
       [0001]    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. 
       BACKGROUND 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
       SUMMARY 
       [0005]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective drawing of a block of open pore foamed glass, a component of one embodiment of the present novel technology. 
           [0007]      FIG. 2  is a partial cutaway view of a liquid filtration apparatus with open cell foamed glass media filters positioned in a liquid tank according to the embodiment of  FIG. 1 . 
           [0008]      FIG. 3  is a partial cutaway view of the block of  FIG. 1  and having a reactive film coating the interior interconnected pore network. 
           [0009]      FIG. 4  is a schematic view of a method of disposing waste material captured in an open cell foamed glass member via fusion. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]    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. 
         [0011]    The present novel technology relates to a method of using a porous, open cell foamed glass substrate or filter  10  (see  FIG. 1 ) for filtering impurities from water as well as for converting certain impurities into more useful materials. Foamed glass media or members have been adapted for agricultural use—predominately in areas where moisture retention and aeration are important factors in plant growth and health. These foamed glass media are generated with substantial open porosity to enhance water uptake and water availability for root systems, and are likewise applicable for liquid filtration. The filtration applications are for both particulate and monolithic foams  10  and in coated/non-coated systems. 
         [0012]    Typically, as illustrated in  FIG. 2  in detail, foamed glass filtration media  10  are prepared with networks of interconnected pores  15  ranging from approximately 0.05 to about 0.25 inches diameter. More typically, the pores  15  are highly interconnected to define a pore network  30 . These foamed glass media  10  have sufficient porosity to uptake over 150% their own mass in water weight. The water may be retained, be released by gravity or under applied pressure as a function of foam design. The foamed glass filtration media  10  are suitable for use in neutral pH solutions and with most acids. 
         [0013]    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  FIG. 3 ). Such foamed glass filtration media  10  may include a reaction layer  20 , such as a biofilm, formed on the inner pore surfaces  25  for converting filtrate into useful material (such as a biofilm  20  for the conversion of ammonia into nitrates for use as fertilizer). Alternately, the open cell pore network  30  of the foamed glass body  10  may be used for the uptake of nitric acid solutions, such as those comprising common nuclear waste streams, wherein particulate nuclear waste is trapped in the pore network, allowing for the glass and waste component to be vitrified or fused into a single phase melt, facilitating ultimate disposal (see  FIG. 4 ). Further, the soda lime silica glass system is compatible with ion-exchange resins and can thereby also act as a combination filter/substrate  10  for water purification. Additionally, non-porous, low density glass beads may also be used in conjunction with ion-exchange media, albeit with a significantly lower absorption coefficient. 
       Biofilter Operation 
       [0014]      FIG. 3  illustrates a filtration system  50  including foamed glass filtration media  10  positioned in liquid communication with a liquid to be purified  55  in a containment vessel  60 . In operation, a biofilm  20  is provided on the interior surface  25  of the pore network  30  of blocks or other bodies  10  of the foamed glass material. The biofilm  20  is typically a bacterial colony or the like and is grown to substantially coat at least a portion of the surface area  25  defined by the pore network  30 . The biofilm  20  is typically selected for its bioreactive properties, such as the conversion of an undesirable component of the liquid to be filtered into a more desirable material. For instance, some liquid waste streams are high in ammonia. Although ammonia may be desirable in some fertilizer uses, some plants, such as greenhouse tomatoes, prefer nitrates (NO3−)to ammonium (NH4+). Thus, it is desirable to convert ammonium to nitrates and, accordingly, a nitrobacter biofilm  20  is desirable. Such a reaction may be described as follows: 
         [0000]      NH 4   + +O 2 →NO 2   − +H + +H 2 O   (1) 
         [0000]      NO 2   − +O 2 →NO 3   −   (2) 
         [0015]    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. 
       Nuclear Waste Disposal 
       [0016]    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. 
         [0017]    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. 
         [0018]    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. 
         [0019]    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. 
         [0020]    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. 
         [0021]    The porosity of the (&gt;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. 
       Experimental Data: 
       [0022]    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. 
         [0023]    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  FIG. 4 , foamed glass bodies  10  were saturated  100  with an acid solution of nuclear waste material  105  and then fused  110  into generally homogeneous, nonporous vitreous masses  120  for disposal. The nitric acid surrogate waste solutions  115  were doped with boron and lithium (a common glass flux) to generate an end product glass  120  with at least 5 percent by weight boron oxide that would melt at or below 1150° C. (mimicking the process/process region used for U.S. high-level nuclear waste glass). All glasses were prepared in an electric furnace. The materials were added solely in the form of pre-saturated foam  125 . No mixing was allowed during the thermal processing. The foam was heated at 5° C. per minute to 800° C. 110 and then additional foam was added as the heated foam re-melted and densified. The final mass was then heated to 1150° C., allowed to soak for 3 hours and then cast onto a cool steel plate to yield a fused, generally nonporous vitreous body  120 . 
         [0024]    The preliminary process region appears to be relatively broad, being on the order of: 
         [0000]    
       
         
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Weight Percent 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Soda-Lime Glass 
                 50 to 80  
               
               
                   
                 Boron Oxide 
                 5 to 15 
               
               
                   
                 Re 2 O 3   
                 0 to 10 
               
               
                   
                 R 2 O 
                 5 to 15 
               
               
                   
                   
               
             
          
         
       
     
         [0025]    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. 
         [0026]    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.