BACKGROUND 
     1. Field of the Invention 
     The subject invention relates generally to the treatment of wastewater and sewage with micro-organisms in the presence of oxygen typically supplied as air or some other source of oxygen, and relates more particularly to aerobically treating relatively small quantities of wastewater and sewage, such as that associated with single family homes, small apartment buildings, small office buildings and the like. 
     2. Description of Related Art 
     Ordinary domestic wastewater is comprised of solid materials such as human waste, food scraps, oils, soaps and chemicals. These solid materials must be adequately treated to eliminate health risks, disease control problems, and environmental damage. 
     The solid materials contained in domestic wastewater typically contain organic substances that are biodegradable under certain conditions, which explains why some wastewater treatment systems employ the process of biodegradation to improve the quality of domestic waste. Optimum biodegradation of domestic waste can be achieved through a process which typically includes the steps of finely dividing the solid materials suspended in the wastewater with some form of agitation, homogeneously mixing the finely divided materials with the liquid wastewater, and then aerating the mixture so as to promote the growth of aerobic bacteria which consumes the wastes. This series of biodegradation steps has been accomplished in small above ground systems and smaller below ground systems where the steps are typically combined into a single stage to minimize the size of the system. 
     One disadvantage with the small single stage system is that combining the steps of dividing, mixing, and aerating the domestic waste in a single stage prevents the aerobic bacteria from efficiently and effectively consuming the waste. The oxygen which is vital to aerobic activity only gets a single pass at the bacteria contained inside the system, which inevitably leads to inefficient and ineffective operation. The low efficiency and effectiveness usually results in an outflow that contains dissolved and suspended materials which are only partially decomposed. Decomposition then continues in the effluent line with the inherent acrid odors and clogging of downstream facilities. 
     Another disadvantage of the small single stage system is the absence of a “quiet zone,” wherein suspended organic materials can settle from the effluent liquid and remain in the treatment system for a longer period of time in order to undergo further biodegradation. Agitation within the single stage system suspends the organic substances throughout the system, including the area near and around the discharge line, thereby inevitably causing some of the suspended solids to exit the system through the discharge line with the effluent liquid. 
     To overcome the problems associated with small single stage waste treatment systems, small stirrers have been added to improve the mixing within the system. However, the addition of stirrers require an increased amount of air to maintain biodegradation effectiveness and efficiency, and the pumps and stirring motors that are necessary to operate a stirrer generate noise and consume power. Furthermore, as with the single stage treatment systems, the effluent is often not fully treated by the time it reaches the discharge line, which can lead to offensive odors and clogging of downstream facilities. Still further, the absence of a “quiet zone” allows some of the suspended organic substances to exit the system before it is completely biodegraded. 
     Dual stage treatment systems have been introduced as an alternative solution to the problems inherent with single stage treatment systems. U.S. Pat. No. 5,061,369 to Romero, et al. discloses such a system. In Romero, the containerized domestic waste treatment system includes a liquid containing vessel divided into two chambers. Wastewater is fed into the first chamber where air is introduced to produce mixing and aerobic conditions. Once the wastewater is treated in the first chamber, it migrates into the second chamber where suspended solids are allowed to settle from the liquid before the treated wastewater exits the vessel. The dual stage treatment system is a marked improvement over single stage treatment systems. However, as in the single stage system, the oxygen used to maintain the activity level of the aerobic bacteria is limited to one pass through the system. 
     The apparatus of the present invention provides an energy efficient, low maintenance waste treatment system that thoroughly treats wastewater in multiple steps before the wastewater effluent is released to either the environment or to another downstream treatment facility. The present invention improves efficiency by producing turbulence and introducing oxygen in multiple stages in the waste treatment process, thereby reducing the amount of waste sludge and pollutants in the effluent stream, which in turn eliminates the offensive odors and clogging of downstream facilities. 
     SUMMARY OF THE INVENTION 
     The apparatus of the present invention is a domestic waste treatment vessel that is suitable for sub-soil installation. Internal deflection walls divide the internal compartment of the vessel into multiple adjacent chambers. The deflection walls have liquid flow passageways which connect the adjacent chambers. Each flow passageway has a substantial flow cross-sectional area so as to prevent clogging of the passageway by the occasional presence of solids which are resistant to biodegradation within the waste treatment system. 
     Domestic wastewater containing organic substances enters the vessel into the first of several chambers where it is agitated and aerated with air flowing through a first low-pressure diffuser bar which is disposed near the bottom of the first aeration chamber. The air flowing from the first low-pressure diffuser bar initiates the biodegradation process by producing turbulent mixing of the wastewater and creating a highly aerobic environment in the first aeration chamber. 
     As more domestic wastewater is received into the first aeration chamber, a portion of the biodegraded waste migrates from the first aeration chamber through the flow passageway disposed in the first deflection wall and enters into the second aeration chamber. The biodegradation process continues in the second aeration chamber, enhanced by air flowing through a second low-pressure diffuser bar disposed near the bottom of the second aeration chamber. The air flowing from the second low-pressure diffuser bar rejuvenates the aerobic bacteria thereby creating a second stage of highly aerobic activity to facilitate the continuation of the biodegradation of the organic substances in the second aeration chamber. 
     Additional aeration chambers may be employed after the second aeration chamber to further improve the efficiency and effectiveness of the waste treatment system in order to satisfy any particular environmental regulations or civic requirements. However, field tests have demonstrated that two aeration chambers are sufficient to comply with all current standards. 
     The biodegraded waste from the second (which may be the final) aeration chamber migrates through the flow passageways disposed in the final deflection wall and enters into the clarifier chamber where the homogeneous liquid, which contains finely divided solids, gradually migrates upward toward an effluent line located near the top of the clarifier chamber. During this migration, tranquil conditions within the clarifier chamber allow the solid particles to settle and return to the final aeration chamber for further biodegradation. The solids are directed back into the final aeration chamber by way of three inclined surfaces located at the bottom of the clarifier chamber. The circulating flow pattern of the agitated liquid in the final aeration chamber also helps to draw the settling solids from the clarifier chamber back into the final aeration chamber for further biodegradation. 
     The inlet to the effluent line may comprise discharge fittings through which the effluent must flow, which are designed to deflect solid particles back into the clarifier chamber before the wastewater is discharged from the waste treatment vessel. The deflected solid particles re-enter the tranquil conditions within the clarifier chamber before settling and returning to the final aeration chamber for further biodegradation. 
     The wastewater exiting the waste treatment system is virtually free of waste sludge, pollutants, and offensive odors, all of which can increase the risk of health problems, disease control problems, environmental damage, and clogging of downstream facilities. 
     Other advantages and aspects of the waste treatment system will become apparent to those skilled in the art upon reviewing the following detailed description, the drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric, pictorial, cutaway view of the preferred embodiment of the invention. 
     FIG. 2 is a side elevational cutaway view. 
     FIG. 3 is a top elevational cutaway view. 
     FIG. 4 is an end elevational cutaway view. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While the present invention will be described with reference to exemplary preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments (and legal equivalents thereof falling within the scope of the appended claims. 
     Referring to FIG. 1, the apparatus of the present invention includes a vessel  1  having first side wall  2  and second side wall  3 , first end wall  4  and second end wall  5 , a top  6 , and a bottom  7 . Preferably, side walls  2  and  3  are longer than end walls  4  and  5 , thereby forming a vessel  1  which is rectangular when viewed from above, as shown in FIG.  3 . 
     Referring now to FIGS. 2,  3 , and  4 , vessel  1  is preferably divided into three chambers—a first aeration chamber  8 , a second aeration chamber  9 , and a clarifier chamber  10 —although an alternative embodiment can include additional aeration chambers and/or clarifier chambers when necessary to satisfy more stringent environmental requirements. When the preferred combination of two aeration chambers and one clarifier chamber is utilized, field tests have indicated that the optimum volumes of the respective chambers are approximately 300 gallons for first aeration chamber  8 , 450 gallons for second aeration chamber  9 , and 200 gallons for clarifier chamber  10 . 
     In the preferred embodiment, a first deflection wall  11  is positioned between first aeration chamber  8  and second aeration chamber  9  so as to give first aeration chamber  8  a liquid holding capacity of approximately 300 gallons, thereby providing a wastewater retention time of approximately 18 hours when the wastewater is flowing at a rate of approximately 400 gallons per day. First deflection wall  11  is sealed across bottom  7  and along side walls  2  and  3  from bottom  7  up to a point substantially near top  6 , creating an air space  28  between top edge  11 A of first deflection wall  11  and top  6  of vessel  1 . In the preferred embodiment, air space  28  has a height  28 A of approximately 6 inches. 
     Vessel  1  and deflection walls  11  and  13  may be formed from a variety of materials. By way of example, reinforced concrete may be used, but other materials such as fiberglass, plastics, metal, and the like are all suitable. 
     Flow passageway  12  traverses first deflection wall  11  to allow flow of wastewater from first aeration chamber  8  to second aeration chamber  9 . Flow passageway  12  preferably traverses first deflection wall  11  near top edge  11 A of first deflection wall  11  to enhance agitation and circulation of the wastewater in first aeration chamber  8  and to prevent unbiodegradable solids from entering second aeration chamber  9 , but flow passageway  12  can traverse first deflection wall  11  at any point along the first deflection wall  11 , including at the bottom of first deflection wall  11 . By way of example, flow passageway  12  may be centered approximately six inches below top edge  11 A. Flow passageway  12  should have a flow area sufficiently large to avoid clogging by the occasional (but almost inevitable) introduction of biodegradation resistant solid material into vessel  1 . Field tests have indicated that a circular opening having a diameter of approximately four inches provides the optimum flow area for flow passageway  12 . 
     A second deflection wall  13  is positioned between second aeration chamber  9  and clarifier chamber  10  so as to give second aeration chamber  9  a liquid holding capacity of approximately 450 gallons and clarifier chamber  10  a liquid holding capacity of approximately 200 gallons, thereby providing a wastewater retention time of approximately 27 hours in second aeration chamber  9  and approximately 1 2  hours in clarifier chamber  10  when the wastewater is flowing at a rate of approximately 400 gallons per day. Second deflection wall  13  is sealed along side walls  2  and  3  down from a point at or substantially near top  6  to a point substantially near bottom  7 , creating a bottom edge  13 A on second deflection wall  13  and creating flow passageways  14  between bottom edge  13 A and bottom  7  of vessel  1 . In the preferred embodiment, wall  13  is sealed along top  6  except for a central opening, substantially shaped in the form of a half-circle of about three inches in diameter. Flow passageways  14  allow flow of wastewater from second aeration chamber  9  to clarifier chamber  10 , and also allow solids settling in clarifier chamber  10  to return to second aeration chamber  9 . Flow passageways  14  preferably have a flow area sufficiently large to avoid clogging by solid waste which is highly resistant to biodegradation, but sufficiently small to eliminate undesirable turbulence in clarifier chamber  10 . In the preferred embodiment, flow passageways  14  comprise two lateral rectangular passages, each having a height of about 2½ inches. 
     An influent line  15  supplies domestic wastewater into first aeration chamber  8  near top  6  of vessel  1 . Influent line  15  is preferably located near top  6  of vessel  1  to provide easier access to influent line  15  for maintenance and the like in case vessel  1  is installed underground. 
     In the preferred embodiment, a continuous flow of pressurized air from any convenient remote source is supplied to first aeration chamber  8  and second aeration chamber  9  through line  16  to produce air bubbles to agitate, circulate, and aerate the wastewater flowing through both aeration chambers  8  and  9 . Line  16  enters vessel  1  through top  6  near top edge  11 A of first deflection wall  11 . After entering vessel  1 , and in close proximity to top edge  11 A, line  16  separates into first low-pressure diffuser line  17  and second low-pressure diffuser line  18 . 
     First low-pressure diffuser line  17  extends downwardly into first aeration chamber  8  to a point preferably near bottom  7  of vessel  1 , where a horizontal end section  17 A of first low-pressure diffuser line  17  is horizontally disposed. Preferably, horizontal end section  17 A comprises an air diffuser, such as an air stone, through which low pressure air is supplied thereby generating a large number of relatively small air bubbles. This increases the surface area of air in contact with the wastewater, and enhances aerobic activity. 
     The air flowing through horizontal end section  17 A creates a circulating flow pattern inside first aeration chamber  8  so that suspended solids are swept up along first deflection wall  11  and past flow passageway  12  so as to minimize the amount of suspended solids that enter second aeration chamber  9  through flow passageway  12 , and maximize the time that the suspended solids remain in first aeration chamber  8 . It is desirable to keep the suspended solids in first aeration chamber  8  as long as possible to allow the aerobic bacteria to thoroughly biodegrade the suspended solids before they enter second aeration chamber  9 . 
     Second low-pressure diffuser line  18  extends downwardly into second aeration chamber  9  to a point preferably near bottom  7  of vessel  1 , where a horizontal end section  18 A is horizontally disposed. As with horizontal end section  17 A, horizontal end section  18 A preferably comprises an air diffuser (such as an air stone) through which low pressure air is supplied, thereby generating a large number of relatively small air bubbles which serve to create a second stage of optimum agitation, circulation, and aeration within second aeration chamber  9 . 
     The second stage of agitation and circulation inside second aeration chamber  9  further breaks down the organic substances contained in the wastewater and continues the biodegradation of those organic substances that have been previously subjected to the biodegradation process in first aeration chamber  8 . The air flowing through horizontal end section  18 A creates a circulating flow pattern inside second aeration chamber  9  so that suspended solids are swept up along first deflection wall  11 , down second deflection wall  13 , and past flow passageways  14  so as to draw suspended solids that have settled in clarifier chamber  10  back into second aeration chamber  9  to subject those suspended solids to further agitation, circulation, and aeration within second aeration chamber  9 . Again, it is desirable to maintain the suspended solids in second aeration chamber  9  as long as possible to allow the aerobic bacteria to thoroughly biodegrade the suspended solids before they enter or reenter clarifier chamber  10 . Although various volumetric flow rates are possible, tests have shown that 1.5 to 2.0 cubic feet of air per minute are satisfactory. 
     Positioned near bottom  7  of vessel  1  in clarifier chamber  10  are first inclined wall  19 , second inclined wall  20 , and third inclined wall  21 . These walls direct solids that are settling in clarifier chamber  10  back into second aeration chamber  9  through flow passageways  14  to undergo further biodegradation in second aeration chamber  9 . First inclined wall  19  extends transversely between side walls  2  and  3  and has a lower edge  22  which intersects bottom  7  of vessel  1  in close proximity to second deflection wall  13 . Lower edge  22  preferably intersects with bottom  7  of vessel  1  at such a position that a portion of first inclined wall  19  extends into aeration chamber  9 . From lower edge  22 , first inclined wall  19  is sloped upwardly at an angle  24  until it intersects with end wall  5 . Angle  24  should be sufficiently sloped to prevent settling solids from accumulating in clarifier chamber  10  and also to ensure that the settling solids are directed back into aeration chamber  9  where they will be swept up by the circulating flow within aeration chamber  9  and subjected to further biodegradation. Angle  24  is approximately 60 degrees from horizontal, although angles between 45 and 65 degrees are satisfactory. 
     Second inclined wall  20  and third inclined wall  21  extend longitudinally between second deflection wall  13  and first inclined wall  19 , where they form a wedge shaped structure which slopes from a centrally high point  23  down toward first inclined wall  19  and out toward side walls  2  and  3 . Second inclined wall  20  and third inclined wall  21  are connected edge-to-edge at high point  23  and slope away from each other at an angle  25 . Similar to angle  24 , angle  25  should be sufficiently sloped to prevent settling solids from accumulating in clarifier chamber  10  and to ensure that the settling solids are directed back into aeration chamber  9  for further biodegradation. Angle  25  may be 60 degrees, resulting in second and third inclined walls  20  and  21  being at 60 degrees from horizontal. However, angle  25  may be between 90 degrees and 50 degrees, resulting in second and third inclined walls  20  and  21  being between 45 and 65 degrees from horizontal. 
     Effluent line  26  provides a means for the biodegraded wastewater to exit clarifier chamber  10 . Effluent line  26  is preferably disposed near top  6  of vessel  1  to maximize the amount of solids settling from the wastewater in clarifier chamber  10  and, therefore, minimize the amount of solids entering effluent line  26 . In one embodiment, effluent line  26  is placed at an elevation below an elevation of influent line  15 . A suitable arrangement is effluent line  26  positioned 8 to 12 inches below the top  6  of vessel  1 , and 1 to 3 inches below an elevation of influent line  15 . 
     As shown in FIG. 2, discharge fittings  27  are connected to effluent line  26  and preferably include a pipe tee  28  and a weir-tee flow divider  29 . Pipe tee  28  is connected directly to effluent line  26  and is designed to provide easy access to discharge fittings  27  or effluent line  26  in case either becomes clogged with non-biodegradable material. 
     Weir-tee flow divider  29  extends downwardly from pipe tee  28  and includes a plurality of diverters  30 . Each diverter  30  is preferably a thin, rectangular plate which is sealably disposed through a portion of outer surface  33  of weir-tee flow divider  29  so that cross-sectional area  31  of weir-tee flow divider  29  is partially blocked. Each diverter  30  is preferably positioned at an angle  32  (which may be on the order of 45 degrees from horizontal) which slopes upwardly from within weir-tee flow divider  29  to outer surface  33  of weir-tee flow divider  29 . An opening  34  is placed immediately below the highest point of intersection between weir-tee flow divider  29  and outer surface  33 . As suspended solids enter discharge fittings  27  through bottom  35  of weir-tee flow divider  29 , diverters  30  impede the solids from continuing up through weir-tee flow divider  29  and direct the solids through openings  34  back into clarifier chamber  10 , thereby minimizing the amount of suspended solids entering effluent line  26 . 
     During typical operation of the apparatus of the present invention, domestic wastewater is introduced into first aeration chamber  8  of vessel  1  through influent line  15 . Inside first aeration chamber  8 , the wastewater is circulated, agitated and aerated by means of tiny air bubbles flowing from horizontal end section  17 A of first low pressure diffuser line  17 . The tiny air bubbles provide oxygen to the aerobic bacteria contained inside first aeration chamber  8  to enable the aerobic bacteria to actively biodegrade the organic matter in the wastewater. 
     As more domestic wastewater is fed into first aeration chamber  8 , a portion of the wastewater contained in first aeration chamber  8  flows through flow passageway  12  into second aeration chamber  9 . However, the circular flow pattern within first aeration chamber  8  created by the air bubbles flowing from horizontal end section  17 A of first low pressure diffuser line  17  helps to minimize the amount of suspended solids entering into second aeration chamber  9  by sweeping the suspended solids past flow passageway  12 . This sweeping action maximizes the time period during which the suspended solids remain within first aeration chamber  8  for optimum biodegradation. 
     The wastewater and suspended solids that do manage to enter second aeration chamber  9  through flow passageway  12  are circulated, agitated and aerated by means of tiny air bubbles flowing from horizontal end section  18 A of second low pressure diffuser line  18 . As in first aeration chamber  8 , the tiny air bubbles provide oxygen to the aerobic bacteria contained inside second aeration chamber  9  to enable the aerobic bacteria to continue the biodegradation process initiated in first aeration chamber  8 . 
     Any excess and unused air flowing from first aeration chamber  8  and second aeration chamber  9  exits vessel  1  either through influent line  15 , which is rarely liquid full, or through first manway  36 , which is located on top  6  of vessel  1 . 
     After being circulated, agitated and aerated in second aeration chamber  9 , a portion of the treated wastewater, which is a homogenous mixture of liquid and finely divided solids, flows from second aeration chamber  9  through flow passageways  14  into clarifier chamber  10 . As the homogenous mixture gradually migrates up through clarifier chamber  10 , tranquil conditions within clarifier chamber  10  promote settlement of the finely divided solids onto inclined walls  19 ,  20 , and  21 . Inclined walls  19 ,  20 , and  21  direct the settled solids back into second aeration chamber  9  through flow passageways  14  for further circulation, agitation and aeration. The circular flow pattern within second aeration chamber  9  also helps to sweep the settled solids from inclined surfaces  19 ,  20  and  21  and into second aeration chamber  9 . 
     The biodegraded wastewater exits clarifier chamber  10  near top  6  of vessel  1  through discharge fittings  27  and effluent line  26 . Any suspended solids entering discharge fittings  27  through bottom  35  of weir-tee flow divider  29  are discouraged from entering effluent line  26  by diverters  30 , which direct the suspended solids through openings  34  back into clarifier chamber  10 . The remaining wastewater continues through discharge fittings  27  and ultimately exits vessel  1  through effluent line  26 . 
     The foregoing description is illustrative and exemplary of the invention and various changes may be made without departing from the scope and spirit of the invention.
A sub-soil wastewater treatment vessel, especially for wastewater produced by single family residences and small businesses and the like. The vessel is divided into at least three contiguous chambers by at least two transverse walls, forming at least two contiguous aeration chambers and a clarifier chamber. Wastewater flows into the first aeration chamber via an influent line, thence through an opening in the first transverse wall into the second aeration chamber. From there, wastewater flows through passages at the bottom of the second transverse wall into the clarifier chamber. Air is supplied to the first and second aeration chambers via low pressure diffuser lines. Three inclined surfaces within the clarifier chamber direct solids through passages in the second transverse wall back into the second aeration chamber for further processing. An effluent line connected to the clarifier chamber permits wastewater outflow.