Abstract:
A biological treatment system, including a wastewater system drain field and at least one perforated distribution pipe located within the drain field and adapted to receive effluent. At least one perforated outer pipe surrounds the at least one distribution pipe to receive effluent from the at least one distribution pipe and to dispense the effluent to the drain field after it has been biologically treated in the at least one outer pipe. The system also includes a method of biological treatment comprising the steps of supplying effluent to at least one vessel positioned within a wastewater drain field; delivering gas to the at least one vessel to interact with the effluent such that the effluent experiences aerobic biological treatment; and passing biologically treated effluent from the at least one vessel to the wastewater drain field.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/411,773, filed Sep. 17, 2002 and U.S. Provisional Patent Application No. 60/427,507, filed Nov. 18, 2002 which are hereby incorporated herein by reference in their entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Traditionally, conventional onsite wastewater treatment systems (OWTSs) have consisted primarily of a septic tank and a soil absorption field, also known as a subsurface wastewater infiltration system (SWIS). Conventional systems work well if they are: installed in areas with appropriate soils and hydraulic capacities; designed to treat the incoming waste load to meet public health, ground water, and surface water performance standards; installed properly; and maintained to ensure long-term performance. These criteria, however, are often not met.  
           [0003]    Over the past century developing countries have witnessed an explosion in sewage treatment technology and widespread adoption of centralized wastewater collection and treatment services. Scientists, engineers, and manufacturers in the onsite wastewater treatment industry have also developed a wide range of alternative technologies designed to address the shortcomings of traditional conventional systems as well as increased hydraulic loads and water contamination. These “alternative” onsite treatment technologies are more complex than conventional systems and incorporate pumps, recirculation piping, aeration, and other features. As such, alternative technologies are applied to the treatment train beyond the septic tank and often provide environments (e.g., recirculating sand filters, peat-based systems, package aeration units) that promote additional biological treatment.  
           [0004]    Accurate characterization of raw wastewater, including daily volumes, rates of flow, and associated pollutant load, is critical for effective alternative treatment system design. Determining treatment system performance requirements, selecting appropriate treatment processes, designing the alternative treatment system, and operating the system depends on an accurate assessment of the wastewater to be treated and the effluent quality desired.  
           [0005]    There are basically two types of onsite wastewater systems—residential and nonresidential. The required hydraulic capacity for an OWTS can be determined initially from an estimated wastewater flow. For example, the average daily wastewater flow from typical residential dwellings can be estimated from indoor water use in the home. However, maximum and minimum flows, as well as instantaneous peak flow variations, are necessary factors in properly sizing and designing system components. Alternative onsite treatment system designs vary considerably and are based largely on the type of establishment under consideration. Therefore, reliable data on existing and projected flows must be used if onsite systems are to be designed properly and cost-effectively. Accurate wastewater characterization data and appropriate factors of safety to minimize the possibility of system failure are required elements of a successful alternative wastewater system design. All OWTSs should be designed to accept and process hydraulic flows from residential or nonresidential wastewaters while providing necessary pollutant removal efficiency to achieve performance goals.  
           [0006]    The three primary components of a conventional OWTS are: the soil beneath the SWIS; the SWIS (also called a leach field, drain field or infiltration trench); and, the septic tank. The SWIS is the interface between the engineered system components and the receiving ground water environment. SWISs provide both dispersal and treatment of the applied wastewater. Typically, wastewater is transported from the infiltration system through several different soil zones, which can act as fixed-film bisectors, where oxygen in the soil may or may not satisfy the oxygen demand generated by the microorganisms degrading the treated wastewater. If sufficient oxygen is not present, the aerobic metabolic processes of the microorganisms (biomass) can be reduced or halted and both treatment and infiltration of the wastewater can be adversely affected.  
           [0007]    The method and pattern of wastewater distribution in a SWIS are important design considerations. Uniform distribution aids in maintaining unsaturated flow below the infiltration surface which results in wastewater retention times in the soil that are sufficiently long to effect treatment and promote subsoil reaeration. As a result, uniform distribution design can provide more complete utilization of the infiltration surface.  
           [0008]    While many different SWIS designs and configurations are used, all incorporate soil infiltrative surfaces that are located in buried excavations. Typically, a SWIS utilizes perforated pipe to distribute the wastewater over the infiltration surface. A porous medium of aggregate, such as gravel or crushed rock, is often placed in the excavation below and around the perforated distribution pipe to support the pipe and spread the localized flow from the distribution pipe across the excavation cavity. However, the porous aggregate may be substituted by graveness or “aggregate-free” system components.  
           [0009]    Gravelless systems are prominent in the United States today taking on many designs, including open-bottomed chambers, fabric-wrapped pipe, and synthetic materials such as expanded polystyrene foam chips. Many graveness systems use large-diameter corrugated plastic tubing covered with permeable nylon filter fabric not surrounded by gravel or rock. Other graveness systems use leaching chambers that consist of trenches or beds and one or more distribution pipes or open-bottomed plastic chambers.  
           [0010]    Several different biological treatment processes exist for reducing biochemical oxygen demand (BOD) and total suspended solids (TSS) from septic tank effluent to meet higher effluent standards. The activated sludge process is an aerobic suspended-growth process that maintains a relatively high population of biomass by recycling concentrated biomass back to the treatment process. The biomass converts soluble and colloidal biodegradable organic matter and some inorganic compounds into cell mass and metabolic end products. The biomass is separated from the wastewater by settling in a clarifier and recycled or removed to a sludge handling process. Preliminary treatment to remove settleable solids and floatable materials is usually provided by a septic tank or other primary treatment devices.  
           [0011]    Alternatively, fixed-film systems are biological treatment processes that employ a medium of natural or synthetic solid material that will support biomass on its surface and within its porous structure. At least two types of fixed-film systems have been employed—those in which the medium is held in place and stationary relative to fluid flow (trickling filter) and those in which the medium is in motion relative to the wastewater (e.g., rotating biological disk). A third system, which is the focus of the present invention, includes dual-process systems that encompass both fixed and suspended biomass together or in series.  
           [0012]    The state of the art with respect to the present invention is presented in U.S. E.P.A. Office of Water, Office of Research and Development, “Onsite Wastewater Treatment Systems Manual” (Febuary 2002) which is hereby incorporated by reference in its entirety and restated, in part, above. Importantly, improvements can be made to suspended-growth processes, including adding surfaces where biomass can attach and grow, such that the system can be categorized as a dual-process or fixed-film/suspended growth system. The present invention provides an improved fixed-film/suspended, nominally zero-net growth onsite wastewater treatment technology that is incorporated with gravel or graveness SWISs. The coupled contact aeration or controlled biomass system of the present invention is, preferably, preceded by a septic tank and followed by a aggregate or aggregate-free infiltration surface such that a fixed film of biomass can attach and grow on a medium to augment a suspended microbial population thereby providing more biomass to feed on wastewater constituents. Advantages of the well-controlled system of the present invention include increased active microbial mass per unit volume, enhanced potential for nitrification, reduced sludge production, and resilience under variable influent conditions without the need for biomass recycle. Such a controlled biomass system, as the present invention provides, can also be a low-cost means of upgrading existing overloaded OWTSs that do not currently meet BOD or nitrification goals.  
         BRIEF SUMMARY OF THE INVENTION  
         [0013]    Briefly stated, the present invention is directed to a biological treatment system, including a wastewater system drain field and at least one perforated distribution pipe located within the drain field and adapted to receive effluent. At least one perforated outer pipe surrounds the at least one distribution pipe to receive effluent from the at least one distribution pipe and to dispense the effluent to the drain field after it has been biologically treated in the at least one outer pipe.  
           [0014]    In another aspect, the present invention is directed to a method of biological treatment comprising the steps of supplying effluent to at least one perforated distribution pipe; discharging the effluent through the at least one perforated distribution pipe; receiving the effluent in at least one perforated outer pipe surrounding the at least one distribution pipe such that the effluent experiences biological treatment; and passing the biologically treated effluent from the at least one perforated outer pipe to a wastewater drain field within which the at least one outer pipe is located.  
           [0015]    In another aspect, the present invention is directed to a method of flushing a biological treatment system, comprising the steps of positioning at least one perforated flushing pipe adapted to receive liquid within at least one outer pipe; connecting a vacuum system to an end of the at least one outer pipe; starting the vacuum system; and supplying the liquid to the at least one flushing pipe such that the liquid is distributed within the at least flushing pipe and received by the outer pipe before being removed by the vacuum system.  
           [0016]    In yet another aspect, the present invention is directed to a method of biological treatment comprising the steps of supplying effluent to at least one vessel positioned within a wastewater drain field; delivering gas to the at least one vessel to interact with the effluent such that the effluent experiences aerobic biological treatment; and passing biologically treated effluent from the at least one vessel to the wastewater drain field. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0017]    The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:  
         [0018]    [0018]FIG. 1 is a schematic view, partially in cross-section, of an biological treatment system for use with an onsite wastewater system in accordance with a first preferred embodiment of the invention;  
         [0019]    [0019]FIG. 2 is an enlarged cross-sectional view of a section of the biological treatment system of FIG. 1 taken along line  2 - 2  of FIG. 1;  
         [0020]    [0020]FIG. 3 is an enlarged cross-sectional view of the distribution pipe, the flushing pipe, the gas delivery pipe, and the outer pipe shown in FIG. 2, taken along line  3 - 3  of FIG. 2;  
         [0021]    [0021]FIG. 4 is an enlarged cross-sectional view of a portion of an biological treatment system in accordance with a second preferred embodiment of the invention;  
         [0022]    [0022]FIG. 5 is an enlarged cross-sectional view of the distribution pipe, the flushing pipe, the gas delivery pipe, and the outer pipe in accordance with a third preferred embodiment of the invention; and,  
         [0023]    [0023]FIG. 6 is an enlarged cross-sectional view of the distribution pipe, the flushing pipe, the gas delivery pipe and the outer pipe in accordance with a fourth preferred embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    Certain terminology is used in the following description for convenience only and is not limiting. The words “right,” “left,” “lower,” and “upper” designate directions in the drawings to which reference is made. The terminology includes the words above specifically mentioned, derivatives thereof and words of similar import.  
         [0025]    The biological treatment system, generally designated  8 , comprises an OWTS with a conventional gravel or alternative graveness SWIS positioned over a soil infiltration system, as described in more detail below. The biological treatment system  8  is placed on a terrain and/or in a subterranean volume or drain field and is integral to an OWTS such that the system  8  promotes biological treatment to meet high effluent standards. As used herein the term drain field is defined to include at least the SWIS and the soil infiltration system below the SWIS as well as aggregate or aggregate-free components. It will recognized by those skilled in the art from the present disclosure that the present system  8  can also be used to reduce the required size for a drain field. Although not part of the present invention, the biological treatment system  8  preferably includes a septic tank which receives wastewater and sewage from a source such as a house or commercial building and provides for the separation by gravity of gross solids and also the decomposition of bacteria and/or digestion of raw sewage.  
         [0026]    Referring to the drawings, wherein like reference numerals are used to indicate like elements throughout, there is shown in FIG. 1 a holding tank  10  in accordance with a first preferred embodiment of the invention. The holding tank  10  is capable of receiving effluent from a septic tank (not shown) by gravity feed or by pumping through a holding tank inlet pipe  12 . Preferably, the holding tank  10  is made of a high strength generally rigid material, such as concrete or reinforced plastic, although other similar type materials of construction, including other strong plastic materials, are possible. Also, the holding tank  10  should be designed to have sufficient capacity to hold a maximum daily wastewater volume from, for example, a household or a industrial building.  
         [0027]    The holding tank  10 , which is considered integral to the biological treatment system  8 , includes a recycle pipe  14  which allows settled effluent waste to pass through a return pump inlet valve  16 . The return pump inlet valve  16  can be closed thereby isolating the holding tank  10  from a return pump  18 . The return pump  18 , when operated with the return pump inlet valve  16  open, discharges settled waste through a return pump outlet valve  20  to the septic tank. Preferably, the return pump  18  is a centrifugal-type pump, such as the Model  152  pump available from Zoeller Pump Company, located in Louisville, Ky. However, it will be recognized by those of ordinary skill in the art from this disclosure that other types of return pumps could be used, if desired, without departing from the spirit and scope of the invention.  
         [0028]    As shown in FIG. 1, a discharge pipe  22  is connected to the holding tank  10  at a first end and contains a first, second and third discharge pipe branches  24 ,  26 ,  28  at a second end. The first discharge pipe branch  24  is connected to a first isolation valve  30  which is connected to a back pressure valve  32  followed by a second isolation valve  34 . The second discharge pipe branch  26  is connected to a bypass valve  36 . The third discharge pipe branch  28  is connected to a effluent discharge pump inlet valve  38  followed by an effluent discharge pump  40  and a effluent pump discharge outlet valve  42 . The second isolation valve  34 , the bypass valve  36  and the effluent discharge pump outlet valve  42  are connected to a first header pipe branch  44 , a second header pipe branch  46  and a third header pipe branch  48 , respectively. The header branches  44 ,  46 ,  48  connect to a header pipe  50  which connects to one or more distribution pipes  52 . It will be recognized by those skilled in the art from the present disclosure that all the pipes described above are made of a generally rigid material, such as polyvinylchloride (PVC), although other similar materials of construction are possible.  
         [0029]    The holding tank  10  is intended to be designed to operate by gravity flow or, preferably, by dosing utilizing control equipment  53  such that a controlled retention time is provided in the biological treatment system  8  at a design temperature. The design temperature of the system  8  can be estimated based on engineering calculations and/or controlled by a heating means. Preferably, the heating means is hot water supplied, as and if necessary, through a hot water inlet valve  54  to a hot water supply pipe  55  and then to a hot water pump  56 . A hot water discharge pipe  57  is connected to the hot water pump  56  on one end and a hot water outlet valve  58  on the other end such that hot water is supplied, as and if necessary, to the header pipe  50 . The hot water pump  56  is controlled by a temperature sensor  59  in the control equipment  53  such that the temperature of the effluent is determined by placing a thermocouple (not shown) in the header pipe  50  about at the location of the distribution pipes  52 . Preferably, the hot water pump  56  is a centrifugal-type pump, such as a Model 310 pump available from Zoeller Pump Company, located in Louisville, Ky. However, it will be recognized by those of ordinary skill in the art from this disclosure that other types of water pumps could be used, if desired, without departing from the spirit and scope of the invention.  
         [0030]    In an embodiment of the invention, the holding tank  10  discharges effluent by gravity flow by closing the first isolation valve  30 , closing the effluent discharge pump inlet valve  38  and opening the bypass valve  36 ; otherwise, the bypass valve  36  is intended to remain closed. This gravity flow method discharges effluent from the holding tank  10  to the discharge pipe  22 , then the second discharge pipe branch  26 , through the bypass valve  36  to the second header pipe branch  46  to the header pipe  50  to the distribution pipes  52 . However, typically, gravity flow will not distribute the effluent evenly throughout all of the distribution pipes  52  which is one reason gravity flow is not the only method of the present invention.  
         [0031]    Alternatively, the bypass valve  36  is closed, the effluent discharge pump inlet valve  38  is closed and the first isolation valve  30  is open. The back pressure valve  32  and the second isolation valve  34  are open to allow the effluent to siphon from the holding tank  10  to the distribution pipes  52 .  
         [0032]    Dosing is also an aspect of the present invention and timed dosing, as opposed to volume dosing, is preferred. Dosing allows the accumulation of wastewater effluent in the holding tank  10  from which the effluent is periodically discharged in “doses” to the distribution pipes  52  by the effluent discharge pump  40  or by siphoning through the back pressure valve  32 . Both the effluent discharge pump  40  and the back pressure valve  32  can be controlled remotely by the control equipment  54  in a manner well understood by those of ordinary skill in the art. Preferably, the effluent discharge pump  40  is a centrifugal-type pump, such as the Model 152 pump available from Zoeller Pump Company, located in Louisville, Ky. However, it will be recognized by those of ordinary skill in the art from this disclosure that other types of effluent discharge pumps could be used, if desired, without departing from the spirit and scope of the invention.  
         [0033]    The effluent, which can be considered pretreated since it would have already passed through the septic tank, is allowed to accumulate in the holding tank  10  and is discharged when a predetermined effluent level, effluent volume, or elapsed time is reached. The dose volumes and discharge rates are by design such that the distribution pipes  52  are filled or nearly filled, as disclosed in more detail below, resulting in more uniform distribution over the infiltration surface as compared to gravity flow designed systems. Dosing will typically outperform the gravity-flow method of the present invention since dosing provides better distribution of effluent in a more uniform and better controlled manner.  
         [0034]    Two methods of dosing are included as part of this invention—volume or demand dosing and, preferably, time dosing. With demand dosing there are one or more sensors positioned in the holding tank  10  for controlling periodic delivery of dosing of the effluent from the tank  10  to the drain field, as described in more detail hereinafter. When demand dosing is utilized the wastewater effluent rises to a preset level in the holding tank  10 , as determined by a sensor or high level indicator  60  and is lowered to a preset level in the holding tank  10  as determined by a low level indicator  61 . Both the high level indicator  60  and the low level indicator  61  provide an input to a float switch  62  or other mechanism located in the control equipment  53  such that the control equipment  53  activates the effluent discharge pump  40  or the back pressure valve  32  initiating effluent discharge from the holding tank  10 . During peak-flow periods, dosing is frequent with little time between doses for the infiltration system to drain and for the subsoil to reaerate. During low-flow periods, dosing intervals are long which can be an inefficient use of the hydraulic capacity of the system and can reduce treatment system control since desired effluent retention times cannot be maintained.  
         [0035]    The use of time dosing in the present invention overcomes some of the shortcomings of demand dosing. A timer  63  is used to turn the effluent discharge pump  40  on and off at specified time intervals so that only a predetermined volume of wastewater is discharged with each dose. Timed dosing has two distinct advantages over demand dosing. First, the doses can be predetermined at specified times during each day to optimize the use of the soil&#39;s treatment capacity and, second, the distribution pipes  52  receive their designed volume each dose such that desired effluent retention times are achieved.  
         [0036]    Referring again to FIG. 1, a gas delivery inlet valve  64  is connected to a gas delivery pipe  65  which is connected to a gas delivery pump  66 . The gas delivery pump  66  discharges gas, including oxygen, at a pressure greater than atmospheric pressure to a gas delivery header pipe  68 , through a gas delivery outlet valve  69 , and then one or more gas delivery pipes  70 . Alternatively, hot gas, e.g., air from a residential home, can be the heating means previously described and can be supplied to the gas delivery inlet valve  64  and ultimately to the gas delivery pipes  70 , as and if necessary, to control the temperature in the system  8 . An inlet flushing valve  71  provides fluid, which is preferably water, via a flushing inlet pipe  72  to a flushing pump  74  that discharges the fluid to a flushing header pipe  76  then through an outlet flushing valve  77  to one or more flushing pipes  78 . As described below, one or more outer pipes  80 , which are, preferably, covered or blanketed by a barrier  82 , surround and enclose the distribution pipes  52 , the gas delivery pipes  70  and the flushing pipes  78 .  
         [0037]    Preferably, the gas delivery pump  66  and the flushing pump  74  are integral to the biological treatment system  8  but are located remotely from the biological treatment system  8 . However, these pumps can be located in an above-grade or underground housing located in proximity to the biological treatment system  8 . The flushing pump  74  is intended to be used periodically as and if required and, therefore, may be portable.  
         [0038]    The gas supplied by the gas delivery pump is, preferably, air which provides adequate oxygen to the system  8  in order to maintain the system  8  aerobically. In a preferred embodiment, the gas delivery pump  66  operates constantly during the operation of the system  8  and is a 17 Watt oilless linear pump, such as a Model SPP-15GA-101 available from Gast Manufacturing, Inc., located in Benton Harbor, Mich. Also in a preferred embodiment, the flushing pump  74  is not operating and fluid is not provided to the flushing pipes. However, preferably, the flushing pump  74  is a centrifugal-type pump, such as a Model 310 pump available from Zoeller Pump Company, located in Louisville, Ky. However, it will be recognized by those of ordinary skill in the art from this disclosure that other types of gas delivery pumps and flushing pumps or compressors could be used, if desired, without departing from the spirit and scope of the invention.  
         [0039]    The barrier  82  comprises a geofabric or fluid and gas impermeable barrier that is installed over the top and along the sides of the outer pipes  80 . The barrier  82  prevents fill soil, which is preferably located over the barrier  82  from contacting the outer pipes  80  and, preferably, also prevents fluid and gas, which is preferably air, from escaping the biological treatment system  8 . The barrier  82  is, preferably, made of a generally pliable material, such as 30 mil PVC geomembrane sheeting material, although other similar type materials of construction are possible so long as the material is fluid and gas impermeable. For instance, the barrier  82  could be a geofabric, geomembrane and/or a combination of geofabric and geomembrane. Also, it is a preferred design feature of the invention to use a barrier  82  that provides heat transfer and insulating properties to the biological treatment system such that the temperature of the biological treatment system can be determined and/or maintained.  
         [0040]    Referring now to FIG. 2, the outer pipe  80  has a first end  84  and a second end  86 . The first end  84  of each outer pipe  80  is connected to a first end cylindrical cap  88  such that the distribution pipe  52 , the gas delivery pipe  70  and the flushing pipe  78  pass through the cap  88 . It will be recognized by those skilled in the art from the present disclosure that gasket material (not shown) or other sealing means, such as glue or solvent cement, may be necessary, for example, at the locations where the distribution pipe  52 , gas delivery pipe  70 , and the flushing pipe  78  pass through the cap  88  in order to join the pipes in a liquid tight manner. The second end  86  of each outer pipe  80  is connected to a second end cylindrical cap  90  such that no fluid and/or gas can escape from the first end  84  and the second end  86  when the second end cylindrical cap  90  is connected. The second end cylindrical cap  90  is intended to be periodically removed allowing access to each outer pipe  80  as necessary. Preferably, the outer pipes  80  and the cylindrical caps  88 ,  90  are made of a generally rigid material, such as PVC, although other similar materials of construction are possible. The first end  84  and the second end  86  are connected to the first end cylindrical cap  88  and the second end cylindrical cap  90 , respectively, preferably by normal PVC connection techniques or, alternatively, by other techniques well understood by those of ordinary skill in the art.  
         [0041]    As shown in FIG. 2, the distribution pipe  52  is connected to the header pipe  50  at a first end  92  of the distribution pipe  52  such that effluent can flow from the header pipe  50  to the first end  92  and ultimately along a length of the distribution pipe  52 . A second end  94  of the distribution pipe is normally attached to a cylindrical cap  96  which can be periodically removed, as necessary, to gain access inside the distribution pipe  52 . Similarly, the flushing pipe  78 , which is, preferably, located above the distribution pipe  52 , is connected to the flushing header pipe  76  at a first end  98  of the flushing pipe  78  such that fluid can flow from the flushing header pipe  76  to the first end  98  and along a length of the flushing pipe  78 . A second end  100  of the flushing pipe  78  is normally attached to a cylindrical cap  102  which can be periodically removed, as necessary, to gain access inside the flushing pipe  78 . Similarly again, the gas delivery pipe  70 , which is, preferably, located above the flushing pipe  78 , is connected to the gas delivery header pipe  68  at a first end  104  of the gas delivery pipe  70  such that fluid, including gas containing oxygen, can flow from the gas delivery header pipe  68  to the first end  104  and ultimately along the length of the gas delivery pipe  70 . A second end  106  of the gas delivery pipe  70  is normally attached to a cylindrical cap  108  which can be periodically removed, as necessary, to gain access inside the gas delivery pipe  70 . Preferably, the gas delivery header pipe  68 , the gas delivery pipes  70 , the flushing header pipe  76  and the flushing pipes  78 , like the header pipe  50  and distribution pipes  52  described above, are made of a generally rigid material, such as PVC, although other similar materials of construction are possible. The first ends  92 ,  98 ,  104  and the second ends  94 ,  100 ,  106  are connected to the header pipes  50 ,  68 ,  76  and the cylindrical caps  96 ,  102 ,  108  preferably by normal PVC connection techniques or, alternatively, by other techniques well understood by those of ordinary skill in the art.  
         [0042]    Referring to FIGS. 2 and 3, spacers  110  are connected permanently to a bottom outside portion of the distribution pipes  52 , the gas delivery header pipes  68 , the gas delivery pipes  70 , the flushing header pipes  76 , and the flushing pipes  78  such that the spacers  110  are in contact with, but not permanently attached to, a top outside portion of the header pipe  50 , distribution pipes  52 , the flushing header pipes  76 , the flushing pipes  78  as well as a bottom inside portion of the outer pipes  80  to provide support for the pipes  52 ,  68 ,  70 ,  76 ,  78 . Also, the spacers  110  located between the distribution pipes  52  and both the flushing pipes  78  and the outer pipes  80  allow biomass to attach to them. The spacers  110  are, preferably, constructed of the same type of material as the distribution pipes  52 , the gas delivery pipes  70 , the flushing pipes  78  and the outer pipes  80 . It will be recognized by those of ordinary skill in the art from this disclosure that the location and connection of the spacers  110  will depend on the arrangement of the distribution pipes  52 , the gas delivery pipes  70  and the flushing header pipes  76  inside the outer pipes  80 .  
         [0043]    Referring again to FIGS. 2 and 3, the distribution pipes  52  are perforated providing circular distribution pipe holes  112  located, preferably, about every 5-10 feet along a bottom length of the distribution pipe  52 . Similarly, the flushing pipes  78  have circular flushing pipe holes  114  located, preferably, about along a first 5 feet of length from the first end  98  of the flushing pipes  78 . Also, the gas delivery pipes  70  are slotted providing grooves  116  which are located along a portion or the entire length of the gas delivery pipes  70 . It will be recognized by those skilled in the art from the present disclosure that grooves  116  can be placed around only a portion or the entire circumference of the gas delivery pipes  70  in different patterns and designs without departing from the spirit and scope of the invention. Preferably, the gas delivery pipes  70  are slotted PVC Well Screen material available from the Monoflex Division of Campbell Manufacturing, Inc., located in Bechtelsville, Pa. The outer pipes  80  also have circular outer pipe holes  118  located, preferably, about every 5-10 feet along the length of the outer pipes  80  such that the distribution pipe holes  112  are about evenly spaced between the outer pipe holes  118 .  
         [0044]    During maintenance and/or cleaning the system  8  is not operating with the exception of the flushing pump  74  in conjunction with the flushing piping  72 ,  76 ,  78 . During cleaning of the system  8 , for example, fluid, preferably water, is provided from a source (not shown) to the flushing inlet pipe  72  and then to the flushing pump  74  where it is discharged to the flushing header pipe  76 . The fluid then enters the flushing pipes  78  and is discharged through the flushing pipe holes  114 , which are, preferably, located toward the first end  98  of the flushing pipes  78 , to the inside circumference of the outer pipes  80 . Simultaneously, a vacuum system (not shown) is attached to the second end  86  of the outer pipes  80  such that settled effluent, e.g., sludge, and the fluid from the flushing pipes  78  is collected by the vacuum system, removed from the system  8  and placed in a vacuum truck for disposal.  
         [0045]    Referring now to FIG. 3, preferably, the distribution pipes  52 , the gas delivery pipes  70  and the flushing pipes  78  are located inside and completely surrounded by the larger outer pipes  80 . In the first preferred embodiment, the distribution pipe  52  is located below the flushing pipe  78  which is located below the gas delivery pipe  70 . However, it will be recognized by those skilled in the art from the present disclosure that the gas delivery pipes  70  can be located outside and above the outer pipes  80  if gas receiving holes (not shown) are provided on a top portion of the outer pipes  80  and above the outer pipe holes  118 . It will also be recognized by those skilled in the art from the present disclosure that, since the system  8  of the present invention is intended to be a nominally zero-net growth system, it may not be necessary to use the flushing pipes  78  and it may be possible to remove the flushing pipes  78  from inside the outer pipes  80  and still have the system  80  function effectively.  
         [0046]    Preferably, the distribution pipes  52 , the gas delivery pipes  70  and the flushing pipes  78  are ¾-inch inside diameter and the outer pipes  80  are 4-inch or 6-inch inside diameter although other diameters are possible for the distribution pipes  52 , the gas delivery pipes  70 , the flushing pipes  78 , and the outer pipes  80 . For example, if the gas delivery pipes  70  are located outside and above the outer pipes  80  then it is possible to have distribution pipes  52  and flushing pipes  78  that are about 1½-inch in diameter. However, the outer pipes  80  must be larger in diameter than the combined size of the distribution pipes  52  and the flushing pipes  78 . The distribution pipe holes  112  and the flushing pipe holes  114  are intended to be about the same size although this is not critical to the effective operation of the system  8 , and, preferably, are about ¼-inch-½-inch in diameter.  
         [0047]    Referring again to FIG. 3, preferably, the distribution pipe holes  112  are arranged such that they are at the bottom of distribution pipe  52  in relation to a centerline (C L )  120 . Preferably, the flushing holes  114  are about 25 degrees from the left and from the right of the centerline top of the outer pipe  80  or about 40 degrees from each other flushing pipe hole  114  around the circumference of the flushing pipe  78 , although a larger degree or a lesser degree of spacing is possible as long as the flushing pipe holes  114  do not interfere with the operation of the outer pipe or the aerobic treatment system  8 . The slotted grooves  116  are about {fraction (1/100)}-inch wide and are located around a majority of a circumference of a the gas delivery pipe  70  such that the grooves are uniformly located along the length of the gas delivery pipe  70 . Also, preferably, the circular outer pipe holes  118  are about ½-inch-¾-inch in diameter although it will be understood that other diameters can be used effectively. The outer pipe holes  118  are located on either side of the outer pipe  80  at, preferably, about 90-degrees in both directions from the top of the outer pipe  80 . The outer pipe holes  118  are at a height above the bottom of the outer pipe  80  such that a fixed-film of biomass can attach, not only completely around the outside circumference of the distribution pipe  52  and on the inside circumference of the outer pipe  80  to a height of the outer pipe holes  118 , but also on a majority of the outside circumference of the flushing pipe  78 . It will be understood by those skilled in the art that the outer pipe holes  118  can be located at any height above the bottom of the outer pipe  80  as long as the outer pipe holes  118  are below the height of the flushing pipe holes  114 .  
         [0048]    The distribution pipe  52  is, preferably, arranged such that it is not centered inside the outer pipe  80  but is, preferably, below the center of the outer pipe  80  such that the top of the distribution pipe  52  is below the center of the outer pipe  80  and the bottom of the distribution pipe  52  is about ½-inch above the inside bottom section of the outer pipe  80 . Such an arrangement allows a fixed film of biomass, once received from the header pipe  50 , to attach not only on the inside circumference of the outer pipe  80  to a height of the outer pipe holes  118  but also allows a fixed film of biomass to attach completely around the outside circumference of the distribution pipe  52  thereby augmenting the suspended microbial population providing more biomass to feed on wastewater constituents.  
         [0049]    Similarly, the flushing pipe  78  is, preferably, arranged such that it is located above the distribution pipe  52  and about centered inside the outer pipe  80 . However, the flushing pipe  78  must be located high enough inside the outer pipe  80  such that the flushing pipe holes  114  are above the outer pipe holes  118 . Such an arrangement allows a fixed film of biomass to attach around a bottom portion of the circumference of the flushing pipe  78  thereby augmenting the suspended microbial population providing more biomass to feed on wastewater constituents.  
         [0050]    It can be seen in FIG. 3 that a flow line  121 , which runs beneath the outer pipe holes  118 , defines the volume of liquid effluent that can be retained in the outer pipe  80 . This is also the volume available for biological pretreatment in the present invention. This volume can be calculated from the known volume of the outer pipe  80  below the flow line  121  minus the known volume of the distribution pipe  52  and the flushing pipe  78  located below the flow line  121 . Similarly, the wetted surface area available for fixed film biological pretreatment can also be determined. By determining these system parameters the biological treatment system  8  can be controlled in terms of the volume and surface area available for suspended and fixed-film operation. Further, by understanding the volume and surface area available for suspended and fixed-film operation, the effluent retention time in the biological treatment system  8  can be optimized. Also, it can be seen that the flow, distribution, and retention properties of the biological treatment system can be altered in several ways and thus can be tailored to specific sites, applications and volume demands. For example, effluent retention time is a function of the size, number and placement of the distribution pipe holes  112  and the outer pipe holes  118  as well as the lengths and diameters of the distribution pipes  52  and the outer pipes  80 . In addition, the number of distribution pipes  52  and outer pipes  80  can be increased or decreased which also affects retention time of a similar daily flow of wastewater.  
         [0051]    Another aspect of the present invention is to provide a method of treating or pretreating wastewater effluent using the fixed-film/suspended growth biological treatment system already described such that when the system  8  is properly operated effluent is transferred from a septic tank to the holding tank  10  through the distribution pipe(s)  52  to the outer pipe(s)  80  where nominally zero-net growth aerobic activity is maintained by oxygen in the gas provided through the gas delivery pipe(s)  70  before being discharged to the drain field below. The method of this invention, like the system  8  itself, is capable of having and intended to have the following features:  
         [0052]    (a) known and controlled volume and surface area for suspended and fixed film biological treatment processes;  
         [0053]    (b) known and controlled retention times in the biological treatment system;  
         [0054]    (c) known and controlled oxygen supply and oxygen transfer to the biological treatment system; and,  
         [0055]    (d) known and controlled temperature throughout the biological treatment system and process.  
         [0056]    Referring again to FIG. 1, in a first preferred embodiment of the invention effluent is transferred from a septic tank to the holding tank  10  where it is discharged about every 4 hours. Such timed dosing is accomplished by setting the timer  63  such that it turns on the effluent discharge pump  40  every 4 hours for about 2-3 minutes or until the holding tank  10  level reaches a minimum set level as determined by the low level indicator  58 . When the effluent discharge pump  40  turns on, effluent discharges from the holding tank  10 , passes through the effluent discharge pump inlet valve  38  to the effluent discharge pump  40 , past the through the effluent discharge pump outlet valve  42  to the header pipe  50 . The effluent is then delivered to the distribution pipes  52  where it is discharged through the distribution pipe holes  112  to the outer pipes  80  where the effluent experiences biological activity. Aerobic activity can be maintained by oxygen in the gas provided to the gas delivery pipes  70 , via the gas delivery pump  66 , through the grooves  116  in the gas delivery pipes  70 . The treated effluent and the gas is discharged through the outer pipe holes  118  to a conventional leach field  150  which comprises, for example, gravel or crushed stone.  
         [0057]    Referring now to FIG. 4, in a second preferred embodiment, the biological treatment system  8  of the present invention provides effluent to the distribution pipes  52  and the outer pipes  80  in the same manner as described in the first preferred embodiment of the present invention. However, in the second preferred embodiment the effluent discharges from the outer pipes  80 , via the outer pipe holes  118 , to an graveness drain field assembly  160 . Such an alternative graveness drain field assembly  160  can include, for example, distribution pipes  162  having a plurality of holes  164  and void pipes  166  that retain and distribute the treated effluent received from the outer pipes  80  via the distribution pipes  52  of the system  8  of the present invention. The graveness drain field assembly  160  described as part of this embodiment can have various designs and arrangements of pipes such as, for example, that described by Atchley, et al. in U.S. Pat. Nos. 5,516,229 and 5,520,481, which are hereby incorporated by reference in their entirety.  
         [0058]    Referring again to FIG. 4, in an alternative configuration of the second preferred embodiment, the biological treatment system  8  of the present invention provides effluent to the distribution pipes  52  and the outer pipes  80  in the same manner as described in the second preferred embodiment of the present invention. However, in the alternative configuration the outer pipes  80 , with enclosed distribution pipes  52 , gas delivery pipes  70  and flushing pipes  78 , of the biological treatment system  8  are used in lieu of the distribution pipes  162 . As a result, effluent passes from the distribution pipe  52  to the outer pipe  80  where it passes through the outer pipe holes  118  to the void pipes  166  where the effluent is retained and distributed.  
         [0059]    Referring to FIG. 5, in a third preferred embodiment, the aerobic treatment system  8  of the present invention provides effluent to the distribution pipes  52  and the outer pipes  80  in the same manner described in the previous preferred embodiments of the present invention. However, in the third preferred embodiment, the distribution pipe  52  is located inside the outer pipe  80  and above the flushing pipe  78 . Also, the gas delivery pipe  70  is located below the flushing pipe  78 . As such, gas containing oxygen flows from the grooves  116  in the gas delivery pipe  70  directly into the effluent contained in the outer pipe  80  before excess oxygen not absorbed by the effluent surfaces to the flow line  121 . Thus, in addition to supplying oxygen to the space above the flow line  121 , the gas delivery pipe  70  in the third preferred embodiment promotes increased oxygen transfer by supplying gas directly to the effluent where a portion of the oxygen in the gas is absorbed by the effluent and the remainder of the gas disturbs the surface of the flow line  121  thereby ensuring aerobic activity. The third preferred embodiment also allows biomass to attach completely around the outside circumference of the gas delivery pipe  70  and, as previously disclosed, around a majority of the outside circumference of the flushing pipe  78  since a majority of the flushing pipe  78  is located below the flow line  121  and therefore in contact with the effluent. Also, in the third preferred embodiment, the gas delivery pipes  70 , in addition to or in lieu of the slotted PVC Well Screen previously described, can comprise a diffuser-type design such as the Tubeflex® Fine Bubble Air Diffuser Model TFX-26 Type II available from the Red Valve Company, Inc., located in Pittsburgh, Pa. It will be recognized by those skilled in the art that the introduction of gas, e.g., air, by a diffuser submerged in the effluent produces a large quantity of small bubbles as compared to the larger bubbles produced by a slotted Well Screen pipe. As such, it will also be recognized by those skilled in the art that the use of a diffuser provides more bubble surface area for oxygen transfer in the effluent thereby improving oxygen transfer in the effluent in comparison to a similarly submerged slotted pipe.  
         [0060]    Referring now to FIG. 6, in a fourth preferred embodiment, the aerobic treatment system  8  of the present invention provides effluent to the distribution pipes  52  and the outer pipes  80  in the same manner described in the third preferred embodiment of the present invention. However, in the fourth preferred embodiment packing material  170  is placed inside at least a portion of the outer pipe  80  below the flow line  121  in all or a portion of the length of the outer pipe  80  and in available space not otherwise occupied by the gas delivery pipe  70  and the flushing pipe  78 . It will be recognized by those of ordinary skill in the art from the disclosure of this embodiment that sections of the outer pipe  80  can repeatedly be filled with the packing material  170  followed by sections that do not contain the packing material along the length of the outer pipe  80  without departing from the spirit and scope of the invention.  
         [0061]    It will also be recognized by those of ordinary skill in the art from the disclosure of this embodiment that, if desired, the packing material  170  can be placed inside at least a portion of the outer pipe  80  below the flow line  121  in available space not otherwise occupied by the distribution pipe  52  and the flushing pipe  78  as these pipes  52 ,  78  are described in the first and second preferred embodiments and shown, for example, in FIG. 3, without departing from the spirit and scope of the invention. The packing material  170  is inserted to provide additional surface area for fixed-film growth of biomass resulting in increased aerobic activity. Preferably, the packing material only occupies a portion of the available space below the flow line  121  which can be ensured, if necessary by using a screen (not shown) that can be attached by conventional means to the inside circumference of the outer pipe  80 . The use of the screen is not considered critical to the invention, however, if a screen is not used the size of the packing material should be larger than the outer pipe holes  118  so that the packing material is not capable of escaping from inside in the outer pipe  80 .  
         [0062]    The packing material  170  is a generally rigid open-spherical material such as 1-inch polypropylene Jaeger Tri-Packs® available from Jaeger Products®, Inc., located in Houston, Tex. Various types of media, such as a media comparable to the AccuWeb® active fabric media available from Brentwood Industries, Inc., located in Reading, Pa., could be used with or in lieu of packing material in order to provide additional surface area for fixed-film growth of biomass. It will be recognized by those skilled in the art from this disclosure that other types and sizes of packing material and/or media could be used, if desired, without departing from the spirit and scope of the invention. It will also be recognized by those skilled in the art from this disclosure that the size (diameter) of the outer pipe  80 , the distribution pipe  52 , the gas delivery pipe  70  and the flushing pipe  78  can be changed to accommodate a desired amount, type or size of packing material  170  without departing from the spirit and scope of the invention.  
         [0063]    It will be recognized by those skilled in the art from the present disclosure that in order for the system  8  to operate effectively only one or more outer pipe(s)  80  and one or more distribution pipe(s)  52  are necessary such that oxygen is provided to the inside diameter of the outer pipe(s)  80  to allow aerobic activity to take place on a fixed-film/suspended growth of biomass inside the outer pipe(s)  80 . Therefore, it will be recognized by those skilled in the art from the present disclosure that the system  8  can effectively aerobically treat effluent without, for example, the use of the flushing pipes  78  which are intended to be used only periodically as and if necessary to remove waste, e.g., sludge, from inside the outer pipes  80 .  
         [0064]    It will also be recognized by those skilled in the art from the present disclosure that the gas exchange portion of the system  8  need not be provided if treatment of effluent by anoxic or anaerobic organisms is desired. Without fresh air exchange, organisms which require oxygen will die off and anoxic and/or anaerobic organisms will multiply in numbers. Such systems can be used to treat, for example, nitrates in order to prevent them from being discharged into the ground water.  
         [0065]    Further, it will be recognized by those skilled in the art from the present disclosure that the distribution pipes  52 , the gas delivery pipes  70 , the flushing pipes  78  and the outer pipes  80  can be configured such that these pipes contain branches that are arranged in series or parallel to distribute the effluent to the gravel or graveness onsite treatment systems described in the present invention and specifically described in the first and second preferred embodiments of the present invention. Similarly, the particular distribution pipes  52 , the gas delivery pipes  70 , the flushing pipes  78  and the outer pipes  80  are generally in the form of a vessel which provides for enhanced aerobic activity in the drain field. As such it is apparent to one of ordinary skill in the art that the present invention is not limited to the particular distribution pipes  52 , the gas delivery pipes  70 , the flushing pipes  78  and the outer pipes  80  and that other vessels could be used to enhance the aerobic activity within the drain field.  
         [0066]    Finally, it will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad invention concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the present invention.