Abstract:
A system for treating a fluid in a container. The system includes an included airlift tube and active air input into the tube. The air is supplied by a pump that is external to the tank and sized in accordance with the size of the tank. The system is arranged to promote the generation of suspended growth bacteria. The bacteria are provided by an air supply that is diffused in the tube wherein the air carries naturally occurring bacterial spores. The airlift tube includes one or more inlet ports located below an air diffuser. The tube may be located on the floor of the tank, suspended from the ceiling of the tank or arranged to float within the tank. A plurality of tubes may be used together to treat fluids in containers larger than standard septic tanks. A pH neutralizing device may form part of the system.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to wastewater treatment. More particularly, the present invention relates to systems for treating wastewater including in septic tanks. Still more particularly, the present invention relates to wastewater treatment systems including airlift tubes. 
     2. Description of the Prior Art 
     Septic tanks and other sorts of wastewater treatment units are used to reduced the solids content of liquids prior to delivery to a fluid absorption field such as a leach bed. Some septic tanks are fairly stagnant in that incoming streams of solid and liquid waste are allowed to dwell in the tank until solids are separated from the liquid. The septic tank is configured so that the remaining effluent is allowed to flow to the absorption field, either directly or through a filter. Septic tanks with filtered outlets should be particularly effective at solids breakdown or removal to avoid filter clogging. Other types of septic tanks include active means for breaking down solids in the fluid prior to transfer to the absorption field. The present invention is directed to active septic tank systems. 
     Some active septic systems include the introduction of anaerobic bacteria to break down waste, a process which causes large particles of waste and sludge to remain within the septic tank or at least facilitates the transfer of solids to the absorption field. Other types of active septic systems force air into the tank to produce turbulence in the tank and to provide oxygen to aerobic bacteria. The aerobic bacteria sustained by air introduced into the tank interact with solids in the fluid and break them down but do so more quickly than in the systems that use anaerobic bacteria. Existing septic systems provide an anchor of sorts in the form of a bacteria retention medium to retain bacteria within the tank. These media have some porosity to enable bacteria growth therein and thereon. Septic systems including such media are referred to as fixed film systems. However, the growth media can become clogged over time whether by bacteria growth or other solids in the fluid, such as hair, for example, thereby reducing treatment efficiency and increasing maintenance requirements. It is desirable to provide the effectiveness of aerobic bacteria treatment without the limitations associated with the use of fixed film arrangements. Suspended growth systems provide oxygen for unanchored bacteria to grow. 
     Existing septic systems that include air introduction systems such as airlift arrangements include an airlift tube of fixed height. As a result, they are limited in their usage to septic tanks having a capacity of no more than 1500 gallons. Attempts to adjust the positioning of the tube in a larger tank include the addition of spacers under the tube. That haphazard fix in the turbulent environment of the tank can cause the tube to fall over and become substantially ineffective. It is desirable to have a system for treating wastewater in a septic tank or other containment tank that is configured to be functional for any container size. 
     Another limitation of existing systems is that they require the use of ballasting to keep them in a fixed position within the tank. It is desirable to have an airlift configuration that does not require ballasting so that it may be placed in a desirable location and moved, if desired, within the container. It would also be useful to be able to locate the airlift tube anywhere in the tank, including above the floor of the tank. Further, the effectiveness of the aerobic bacteria and the general performance of the septic tank are optimal when the pH in the tank is close to neutral. Unfortunately, there is a tendency for the fluid and contents entering the tank to be acidic. If that acidity is too much, the bacteria can be harmed and thereby rendered ineffective. It is desirable to ensure that the fluid in the tank remains close to neutral pH. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a system for treating wastewater, or other waste fluids, in an aerobic process. It is also an object of the present invention to provide a treatment system that limits or eliminates the chance of bacteria clogging without minimizing the efficiency of the bacterial action on the solids content of the waste fluid. Further, it is an object of the present invention to provide an airlift pump function in a septic tank or other waste fluid container that aerates the fluid effectively regardless of the size of the container. Yet further, it is an object of the present invention to provide an airlift pump based treatment system wherein the pump may be selectably positioned within the container. 
     These and other objects are achieved with a waste treatment system comprising a septic tank with an included airlift tube and active air input into the tube. The air is supplied by a pump that is external to the tank and sized in accordance with the size of the tank. The air is forced by the pump into a conduit associated with the tube and terminating in a diffuser or other form of porous structure. The system is arranged to promote the generation of suspended growth bacteria and with ports that are substantially larger than the pores of existing systems. The bacteria are provided by an air supply that is diffused in the tube wherein the air carries naturally occurring bacterial spores. These design features substantially eliminate the limitations associated with fixed film bacteria growth promotion and any other features that may result in clogging that can impact treatment effectiveness and increase maintenance requirements. Specifically, the airlift tube includes one or more inlet ports and one or more outlet ports that are large enough to ensure that any solids will pass through and not block those ports. 
     The inlet port or ports of the tube of the system may be positioned below the diffuser to maximize fluid flow through the tube. The tube is made of a material selected with a density greater than that of the fluid where it is located to make it negatively buoyant so that the tube remains on the floor of the tank while operational and without the need for ballast. A plurality of tubes may be deployed in a tank. The tube may be fabricated of selectable length to remain functional in tanks of a wide range of sizes, including, but not limited to tanks exceeding 1500 gallons. The tube includes a cross member extending through it, which cross member may be used to select positioning of the tube suspended above the floor of the tank in a selectable location. The tube optionally also includes a float element such as a ring of buoyant material circumscribing and attached to the perimeter of the tube so that it can float in the tank. The tube is configured to maintain fixed spacing from the diffuser within the tube to the surface of the fluid in the tank. This arrangement ensures that the fluid is turbulent enough to effect treatment of the fluid contents. The system further includes an optional pH regulating element that may be positioned within the tube or outside of the tube. The diffuser optionally includes a regulator, such as valve, to control the rate of air bubbling from the diffuser. 
     The system of the present invention extends the functional life of a septic system by reducing clogging conditions without compromising aerobic bacteria action. It is also effective at reducing the waste strength of effluent exiting the tank by, among other things, reducing fats, oils and grease in the effluent. That is accomplished by the turbulent action of the fluid caused by the air diffusion and the effective dispersion of the suspended growth bacteria. While the system of the present invention is suitable for residential and commercial septic systems, it is also suitable for use in other fluid containment systems to be treated including, but not limited to a mechanism to convert agricultural waste into fertilizer. 
     These and other features and advantages of the present invention will be understood upon review of the following detailed description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified partial cross-sectional side view of a fluid containment tank including a first embodiment of the fluid treatment system of the present invention. 
         FIG. 2  is a side view of a first embodiment of the airlift tube of the treatment system. 
         FIG. 3  is a perspective view of a first embodiment of the airlift tube of the treatment system. 
         FIG. 4  is a top view of the first embodiment of the treatment system. 
         FIG. 5  is a plan view of an example of a tank including a plurality of airlift tubes as part of the treatment system. 
         FIG. 6  is a side view of a second embodiment of the airlift tube of the treatment system. 
         FIG. 7  is a perspective view of a third embodiment of the airlift tube of the treatment system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of a treatment system  10  of the present invention is shown in  FIGS. 1-4 . The system  10  includes an airlift tube  12 , an aeration conduit  14  extending on or in the tube  12 , a diffuser  16  within the tube  12  and connected to the conduit  14 , and a pump  18  connectable to the conduit  14 . The pump  18  is selected to be suitable to pump about 40 liters of air per minute into the tube  14 . A suitable pump for that purpose is the Model No. ET40 diaphragm pump available from Charles Austen Pumps Ltd. of Surrey, England. As shown in  FIG. 5 , the system  10  may optionally include a regulating valve  19  to regulate air flow into the conduit  14 . 
     The system  10  can be used in any container with a fluid to be treated to modify or remove solids in the fluid so that the fluid may be transferred to a location for storage, dissipation or another function. The system  10  is described herein with respect to the use in treating a fluid in a commercial or residential septic tank but it is to be understood not to be limited thereto. An example simplified representation of the system  10  in situ is the system  10  in a septic tank  20 . The septic tank  20  includes a septic tank floor  22 , a septic tank ceiling  24 , a septic tank inlet  26  and a septic tank outlet  28 . The septic tank  20  includes an air conduit port  30  through which the aeration conduit  14  passes from outside the septic tank  20  to an interior region  32  of the tank  20 . The port  30  is shown as passing through the ceiling  24 ; however, it may also pass through either of tank wall  34  or wall  36  if that is of use. The port  30  of the ceiling  24  may be part of a removable maintenance cover  38 . 
     The airlift tube  12  provides for the treatment of fluid within the tank  20  with aerobic bacteria delivered into the tank with air from the aeration conduit  14 . That is, naturally occurring bacteria that existing the atmosphere are delivered by the pump  18  into the tank  20  through the conduit  14  and the tube  12  to interact with the contents of the fluid entering the tank  20  through the inlet  26 . The bacteria are provided by the system  10  substantially as suspended growth bacteria introduced by the air from the conduit  14  passing through the diffuser  16 . Specifically, the air conduit  14  delivers air to the diffuser  16  where it is diffused to create small bubbles of air within the tube  12 . An example of a suitable diffuser for the diffuser  16  is the Model No. 01798 fine-bubble diffuser available from Environmental Dynamics International of Columbia, Mo. The diffuser  16  includes an upper portion and a lower portion with a space between the two. The lower portion is removably connected to an air exiting end  42  of the conduit. The air enters the space between the upper and lower portions of the diffuser  16 . The upper portion includes a plurality of pinholes through which the air in the space escapes into an interior  13  of the tube  12 . The air exiting the diffuser  16  mixes with liquid in the interior of the tube  12 , thereby exposing the liquid to treatment by contacting it with the suspended growth bacteria in the air. 
     As is known to those of skill in this field, the tube  12  operates as an airlift tube because the air of very low density and finely dispersed in the tube  12  by the diffuser  16  mixes with the liquid in the tube  12  thereby creating a low-density air-liquid fluid mixture. That fluid mixture, because of its low density, quickly rises to the top of the body of fluid within the tank  20  where the air of the mixture is separated from the liquid portion, which liquid portion mixes with other fluid in the tank  20 . The transition from liquid density to air-liquid mixture density and back to liquid density causes the movement of the fluid into the interior  13  of the tube  12  through one or more fluid inlet ports  44 . It also causes turbulence in the tank  20 , which enhances bacteria contact with the fluid to be treated in the tank  20 . In a tank that is a standard 1500-gallon septic tank, a tube such as the tube  12  with a height of about four feet and a diameter of about 14 inches, and a pump operating at about 40 liters of air per minute is sufficient to provide mixing adequate to treat the fluid prior to its exit through the outlet  28 . 
     The tube  12  is fabricated of a material that is capable of operating for a reasonable period of time within the tank  20  in the conditions expected within the interior region  32  of the tank  20 . The tube  12  may be made of a metallic material or a nonmetallic material. In an embodiment of the system  10 , the tube  12  is fabricated of a nonmetallic material, such as a plastic material. The material of the tube  12  may have a density greater than that of the fluid within the tank  20 . For example, if the fluid is primarily water, which has a density of about 1.0 grams per cubic centimeter, the tube  12  may be made of a material such as polyvinyl chloride, but not limited thereto, having a density of about 1.3 grams per cubic centimeter. Those of skill in the art will recognize that other materials are suitable. This greater density of the material of the tube  12  ensures that it will remain on the tank floor  22  without the need to add ballasting. 
     The tube  12  is advantageous in providing a suspended growth bacteria environment that is effective in treating the fluid. That effective functionality is maintained or enhanced by having the inlet ports  44  located below the diffuser  16  rather than at or above them. The diffuser  16  is positioned within the tube  12  with a bracket  47  that can be located where desired. The bracket  47  may be coupled to the conduit  14  and may include an interface stem  48  that may be removably affixed to the diffuser  16  such as with a screw-type arrangement or it may be permanently affixed to it, such as with an adhesive. 
     The tube  12  is preferably positioned within the tank  12  so that the opening  46  is roughly two inches below a surface of the fluid within the tank  20 . That fluid surface is approximately equal to a bottom  29  of the septic tank outlet  28 . This spacing provides sufficient volume to maximize fluid mixing. For a 1500-gallon septic tank of typical dimensions, a 48-inch height of the tube  12  accomplishes that spacing. The tube  12  also optionally includes a cross member  50  extending through an upper region of the tube  12 . The cross member  50  provides a device to facilitate movement of the tube  12  within the tank  20  to place it in a desired location, including to move it during maintenance. 
     As illustrated in  FIG. 5 , a plurality of tubes  12  may be used in the system  10  when the tank  20  volume exceeds about 1500 gallons. In that regard, one tube  12  is included in the tank  20  for each 1500 gallons of tank volume. In that version of the invention, each of the tubes  12  may be spaced from, and removably connected to, respective adjacent one or ones of other tubes  12  by a spacer bar  58 . The arrangement of the tubes  12  when a plurality is used is selectable but should be configured to provide coverage throughout the tank  20  so that the mixing of liquid and air is as complete as possible. 
     Another embodiment of the invention is shown in  FIG. 6 . In it, the cross member  50  may be used to suspend tube  12 ′ from the ceiling  24  of the tank  20 . The tube  12 ′ includes the same numbered components as shown in  FIGS. 1-4  and further includes a suspension system  51  including a suspension cord  52  that may be joined to the cross member  50 . The cord  52  may be fabricated of metallic or nonmetallic material. A hook  54  is joined to the cord  52  and may be hooked to a fixture located on the ceiling  24  of the tank  20  in a selectable location. This option of the tube  10 ′ allows the use of a tube size that is constant, such as a tube that is four feet in height regardless of the height of the interior region  32  of the tank  20  provided the tube  10 ′ is suspending so that the opening  46  is roughly two inches below the bottom  29  of the outlet  28  shown in  FIG. 1 , or, more generally, the tube  12 ′ is positioned within its container so that its opening  46  is roughly two inches below the surface of the fluid treated. 
     Another option of the tube  12 ″ suitable for use in tanks  20  of dimensions greater than 1500 gallons is shown in  FIG. 7 . The tube  12 ″ is similar to the tube  12 ′ of  FIG. 6  in that it may be operational while above the floor  22  of the tank  20 . However, whereas the tube  12 ′ is fixed with respect to the ceiling  24 , the tank  12 ″ may move around within the interior region  32  of the tank  20 . Specifically, the tube  12 ″ includes a float  60 , which is selected to be of sufficient buoyancy to cause the tube  12 ″ to float in the fluid in the tank  20  provided the opening  46  of the tube  12 ″ remains roughly two inches below the surface of the fluid to be treated. The float  60  may be in the shape of a ring, as shown, that circumscribes the exterior of the tube  12 ″. It may be in a shape other than a ring and may be located within the tube  12 ″ or somewhere other than at an upper region of the tube  12 ″. The float  60  may be fabricated of a material sufficient to make the tube  12 ″ buoyant while maintaining the indicated desired spacing between the opening  46  and the top of the fluid in the tank  20 . The float  60  may be made of polyurethane or polyethylene foam bonded to the tube  12 ″ but is not limited to those materials. 
     The system  10  further optionally includes a pH correction element  62  to aid in the regulation of pH within the tank  20 . Regulating the pH within the tank so that the fluid is approximately of neutral pH reduces the risk of harm to the suspended growth bacteria within the tank  20 . The pH correction element shown in  FIG. 65  includes a porous basket  64  that may be removably coupled to the cord  52  or hooked directly to the fixture at the ceiling  24  of the tank  20 . Alternatively, the basket  64  may be placed elsewhere in the tank  20 . The basket  64  is arranged and configured to retain therein a material to neutralize acidic fluid. The neutralizing material may be sodium hydroxide (lime) such as lime chips. 
     The present invention includes a kit containing the tube  12 , the conduit  14 , the cross member  50 , the diffuser  16 , the bracket  47 , instructions for installing the system  10  and, optionally, the pump  18  and the pH correction element  62 . The instructions include: a) opening the tank  20  either through the cover  38  or before the ceiling  24  has been installed; b) placing the tube  12  in a selectable position within the tank  20  on the floor  22 ; c) inserting the bracket  47  into the tube  12  either before or after placing the tube  12  into the tank  20 ; d) placing the diffuser  16  on the bracket  47 ; e) inserting the conduit  14  into the tank  20 ; f) connecting the end  42  of the conduit  14  to the lower section of the diffuser  16 ; and g) connecting the other end of the conduit  14  to the pump  18 . The pH correction element  62  may also be added. Once any other actions required in the tank  20  have been completed, the tank  20  may be closed and filled and the pump  18  activated when the initiation of treatment within the tank  20  is desired. It is to be understood that tube  12 ′ or tube  12 ″ may be used as replacements for tube  12 . In the case of tube  12 ′, the tube  12 ′ is joined to the ceiling  24  rather than placed on the floor  22 . In the case of the tube  12 ″, the tube  12 ″ may be placed on the floor  22  and allowed to float when the tank  20  is filled with fluid, or it may be inserted in the tank  12  with fluid already in there. 
     The system  10  of the present invention reduces the strength of the waste stream, including fats and oils, exiting the outlet  28 , thereby increasing the life of the containment system, such as a septic system or a municipal sewer system. It saves any type of leach field, not simply trenches. It can also be used to convert agricultural waste into liquid fertilizer by concentrating nitrogen-based content within the container. 
     It is to be understood that various modifications may be made to the system  10  and the components described herein without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the claims appended hereto.