Abstract:
An apparatus for producing purified drinking water. The apparatus comprises a container top including an ultrafiltration insert. The container top attaches to the opening of a liquid holding container, such that liquid from the container passes through a filter. The device includes a mechanism for back flushing or cleaning the filter. The resulting water is substantially pure, being free of bacteria, to make it safe for drinking.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. provisional application No. 60/897,355, filed Jan. 25, 2007. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a device for purifying water and more specifically to a device to provide purified drinking water for personal use. 
     BACKGROUND 
     Potable (i.e., drinking) water is a necessity to which millions of people throughout the world have limited access. Water is often seen as the most basic and accessible element of life, and seemingly the most plentiful. There is no standard for how much water a person needs each day, but experts usually put the minimum at 100 liters for adults. Most people drink two or three liters—less than it takes to flush a toilet. The rest is typically used for cooking, bathing, and sanitation. Adult Americans consume between four hundred and six hundred liters of water each day. 
     By 2050, there will be at least nine billion people on the planet, the great majority of them in developing countries. If water were spread evenly across the globe, there might be enough for everyone. But rain often falls in the least desirable places at the most disadvantageous times. More than a billion people lack access to drinking water. Simply providing access to clean water could save two million lives each year. 
     Water purification processes are well known and used throughout the world. Water purification is the removal of contaminants from raw water to produce drinking water that is pure enough for human consumption. Substances that are removed during the process include parasites (such as Giardia or Cryptosporidium), bacteria, algae, viruses, fungi, minerals (including toxic metals such as lead, copper and arsenic), and man-made chemical pollutants. Many contaminants can be dangerous. Other contaminants are removed to improve the water&#39;s smell, taste, and appearance. 
     It is not possible to tell whether water is safe to drink just by looking at it. Simple procedures such as boiling or the use of a household charcoal filter are not sufficient for treating water from an unknown source. Even natural spring water considered safe for all practical purposes in the 1800s must now be tested before determining what kind of treatment is needed. Water emerging from shallow groundwater is usually taken from wells or boreholes. The bacteriological quality can be variable depending on the source. 
     Typically located in the headwaters of river systems, upland reservoirs are usually sited above any human habitation and may be surrounded by a protective zone to restrict the opportunities for contamination. Bacteria and pathogen levels are usually low, but some bacteria, protozoa or algae will be present. Low land surface waters, such as rivers, canals and low land reservoirs, will have a significant bacterial load and may also contain algae, suspended solids and a variety of dissolved constituents. Surface water may be contaminated with biological and chemical pollutants and may potentially transmit diseases such as diarrhea, dysentery, typhoid, cholera and hepatitis. Because of risk of contamination, surface water should never be used for drinking without treatment and/or disinfection. 
     Many processes are available for purification of water, with their use depending on the particular contaminants present in the water. Ultrafiltration membranes are a relatively new development; they use polymer film having microscopic pores that can be used in place of granular media to filter water effectively without coagulants. The type of membrane media determines how much pressure is needed to drive the water through and what sizes of micro-organisms can be filtered out. In ultrafiltration, hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in the filter up to about 0.01 microns in size. This removes bacteria and many viruses (which commonly adhere to the bacteria), but not salts (ions), while water and low molecular weight solutes pass through the membrane. 
     It is desirable to have a reusable water filtration device that attaches to a water bottle or other portable water container and contains an ultrafiltration membrane. The device may provide a design that allows water to pass through the ultrafiltration membrane with minimal pressure. Preferably, the device includes a flushing mechanism that cleans the ultrafiltration membrane without having to disassemble the bottle cap. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to fulfill the need for a reusable bottle cap water filter that can provide purified drinking water free from bacterial contamination. Therefore, the present invention provides a portable and reusable apparatus for purification of water using an ultrafiltration membrane and requires only low pressure, such as may be generated by squeezing the bottle, sucking water through the opening of the bottle cap, or merely through the action of gravity. Preferably, the apparatus comprises a flushing mechanism that is useful for cleaning the ultrafiltration membrane without requiring disassembly of the apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of an embodiment of a water filter unit device which may be attached to a water container. 
         FIG. 2  is a cross section of a water container having an alternative embodiment attached to the top of the water container. 
         FIG. 3  is a cross section of an alternative embodiment having an alternate means of back flushing 
         FIG. 4  is a cross section of a water container and a filter unit which attaches to the top of a water container, with the filter extending into the water container. 
     
    
    
     DETAILED DESCRIPTION 
     At least one advantage of at least some embodiments is that these embodiments provide a reusable bottle cap water filter for use when attached to a water bottle, including an ultrafiltration membrane, and at least one one-way valve to prevent flow of water back into the water bottle. The ultrafiltration membrane is configured such that surface area is maximized, such as by elongated ultrafiltration membrane fibers, and does not require more than minimal pressure to pass water through the filter. The water filter of the present invention would be operable by squeezing the water bottle if the water bottle is made of a resilient polymer compressible skin, or other similar resilient material, thus forcing water through the water filter, by sucking on the outer opening of the bottle cap, thus forcing water through the filter (for use in a rigid polymer or metal container that do not compress), or merely by the action of gravity, inverting the water bottle and allowing water to pass through the filter. 
     In one embodiment, the bottle cap water filter apparatus includes a flushing mechanism for cleaning the ultrafiltration membrane by forcing purified water back through the filter and into the water bottle, thereby flushing any particles off the surface of the ultrafiltration membrane. 
       FIG. 1  is a drawing of one embodiment. The bottle cap may have an elongated, cylindrical shape. In this embodiment, the reusable bottle cap water filter apparatus is attachable to a water bottle, preferably via complementary threading such as on a screw cap. Immediately adjacent to the screw cap is a one-way valve with a mechanical shutoff to prevent water from flowing back through the membrane. 
     With reference to  FIG. 1 , screw cap  50  allows attachment of the water purification device onto a liquid holding container, such as a water bottle. In some applications an air intake tube  44  having an air intake inlet  46  to allow inlet of ambient air and an air intake outlet  48  extending into the bottle may be used to equalize pressure. During backflow, allowing air to leave the container may be desirable. During drinking, inlet  46  may be covered with a finger to prevent water from flowing through the tube. 
     Water may be drawn through the system by a user sucking on opening  12 , by squeezing the bottle onto which the filtration device  10  is placed, or by inverting the bottle. When this is done, water will move past valve  40  into chamber  30  and through ultrafiltration membranes  32 . In the illustrated embodiment, the ultrafiltration membranes are tubular structures, having their open ends potted in membrane holder  34 , such that for water to pass from one side of membrane holder  34  to the other side of membrane holder  34  requires that the water first pass through membrane  32 . The water is drawn through a charcoal filter  18  retained within housing  14 . A user can then drink the water from opening  12 . 
     To backflush the membrane, one way valve  16  is closed using mechanical shutoff  15 . This prevents water from flowing to opening  12 . Flushing mechanism  20  in this example is a simple bulb made of a resilient polymer material. Squeezing flushing mechanism will drive water back through the filtration membrane  32 , effectively back flushing the filter using filtered water. The pores of the ultrafiltration membrane will be cleared; allowing the filtration device to one again is used. 
     Flow into the bottle can be stopped using one-way valve  40  controlled by mechanical shutoff  41 . 
     With respect to  FIG. 2 , the device of  FIG. 1  is shown attached to bottle  60 . The threads on neck  62  of bottle  60  allow screw cap  50  to be screwed onto the bottle. 
     With respect to  FIG. 3 , an alternative embodiment is shown. As before, a screw cap  50  allows attachment to the bottle, an air intake tube  44  includes an inlet  46  and an outlet  48  to allow air to be displaced from a bottle or other container to which the device is attached. As water is drawn into chamber  30 , it filters through filter membrane  32 , flows through membrane holder  34  and is drawn by the user through opening  12 . Here arms  13  attached to mechanical actuator  55  allow the purging of water from chamber  9  by mechanically intruding arms  13  into chamber  9 , which mate to displace some of the contents of chamber  9 . 
     It will be readily understood that a number of different mechanisms may be used for back flushing membrane  32 . Any mechanism that reduces the size of chamber over the membrane will cause liquid to be back flushed through the membrane. 
     With reference to  FIG. 4 , bottle  60  is shown having a neck  62 , which may taper. Held at this neck is membrane  32  held in membrane holder  34 . Membrane holder  34  may be held in neck  62  that tapers. The housing  14  of the water filtration device has a lip  11  which may snap over an annular lip on neck  62 , attaching the filtration device onto the bottle  60 . As in  FIG. 1 , the purified water flows through opening  12  and water may be purged by shutting one-way valve  16  and squeezing flushing mechanism  20 . 
     The apparatus of the above embodiments preferably uses an ultrafiltration membrane capable of filtering bacteria from water, to provide potable water free of contamination. The ultrafiltration membrane of the preferred embodiment has a maximized surface area, produced by stretching the ultrafiltration membrane into tubular filaments. The ultrafiltration membrane used in the preferred embodiment is made from Ultra-Flo DUC 108 ultrafiltration membrane from Ultra-Flo PTE Ltd., 452 Tasgore Industrial Avenue, Singapore 787823. This is described in co-pending application Ser. No. 11/941,713 hereby expressly incorporated by reference for all purposes herein. 
     One embodiment also optionally contains a charcoal filter to further purify and enhance the taste of the water exiting the filter. At the outlet opening of the apparatus is a second, optional one-way valve with mechanical shutoff to prevent water from flowing back into the water bottle during flushing. 
     One problem with ultrafiltration membranes is clogging by particles and bacteria. In the illustrated embodiments, some water is retained within the housing of the filtration device  10  of  FIG. 1  to keep the ultrafiltration membrane wet. Further, additional water is retained in the apparatus at a point subsequent to passing through the ultrafiltration membrane. These embodiments contain a flushing mechanism to force the retained water back in the direction of the water bottle, passing through the ultrafiltration membrane in the opposite direction. By flushing water back through the membrane, the filter is thereby cleaned of any particles sticking to it. 
     As depicted in  FIG. 1 , the flushing mechanism is a portion of the bottle cap that is capable of being compressed or squeezed, creating pressure that forces the water back in the opposite direction. Alternatively, the flushing mechanism is comprised of complementary threaded portions of the bottle cap such that they can be screwed together to compress the area inside the cap and force water back through the ultrafiltration membrane. 
     One advantage of the flushing device of the present invention is that the bottle cap water filter does not need to be taken apart in order to clean the ultrafiltration membrane. By providing the flushing mechanism and a bottle cap water filter that is a single unit that cannot be disassembled, the present invention protects the ultrafiltration membrane from any damage or drying out that could be caused by disassembly.