WO2005110932A1

WO2005110932A1 - Packaged wastewater treatment unit and flow-through media

Info

Publication number: WO2005110932A1
Application number: PCT/US2005/014242
Authority: WO
Inventors: Richard J. Petrone
Original assignee: Jrj Holdings, Llc
Priority date: 2004-04-29
Filing date: 2005-04-26
Publication date: 2005-11-24

Abstract

A packaged wastewater treatment unit has a compact configuration into which all subcomponents may be integrally molded. A clarifying unit (22) and a basin (20) into which a biological digester (24) is mounted are formed within the top surface of a tank (12), which contains a collecting compartment (13) separated from a secondary compartment (15) by a baffle (46). The digester may use a plurality of flow-through media (62) having a truncated conical shape, a plurality of internal ribs, and a plurality of external ribs.

Description

PACKAGED WASTEWATER TREATMENT UNIT AND FLOW-THROUGH MEDIA

BACKGROUND

1. Technical Field fOOOl] The present invention relates to wastewater treatment systems.

2. Background Information

|0002] To meet local health and water regulations in areas where no municipal waste treatment hook-ups are available, household wastewater treatment systems should be capable of converting a stream of wastewater into a condition suitable for discharge into the surrounding ecosystem. However, there are regions where soil conditions do not permit the use of conventional septic systems. [0003] Alternatives to septic systems are available that can treat wastewater to a quality suitable for above-ground discharge. However, due to their size, cost and complexity, these systems typically require custom-solution engineering and as such are predominantly used for industrial wastewater treatment. These systems may contain a number of optional components, including components to stage the waste stream, meter the flow into a digester, digest the impurities, clarify the effluent, and ultimately disinfect the output stream, depending on the treated water quality to be obtained.

[0004] One type of digester that may be used in such a wastewater treatment system is a rotating biological contactor (RBC). RBCs host aerobic bacteria and provide those bacteria with a continual supply of all life-supporting ingredients by exposing them to effluent, their source of food, and air, their source of oxygen. These bacteria may then be used to digest impurities in a stream of wastewater. An RBC may be a stack of parallel plates on a rotating shaft or may be a rotating enclosure containing a plurality of media onto which aerobic bacteria can attach. Examples of RBCs are disclosed in U.S. Patent Nos. 5,350,507 to McManus; 4,137, 172 to Sako et al.; 4,200,532 to Iwatani et al.; and 4,333,893 to Clyde. Examples of media are disclosed herein and in U.S. Patent No. 5,401,398, to McManus. The above references are hereby incorporated herein by reference. [0005] These prior wastewater treatment systems have several disadvantages. First, they consist of several individual components that must be separately transported, installed and maintained. Second, they consume a large amount of space, causing the systems to be unwieldy to transport and to require a substantial amount of labor to install. Third, such systems typically are not available for household use. Although prior wastewater treatment systems may include a combination of known components for treating wastewater (see e.g., U.S. Patent No. 4,687,574 to Hellman), these systems do not provide a compact, one-piece unit that houses all the components necessary to efficiently convert a household wastewater stream into an effluent that is suitable for above-ground discharge. [0006] Original RBCs consisted of plastic sheets attached to a central shaft. Bacteria would attach themselves onto the plastic sheets, and the bacteria would be exposed to both food and water by rotating the shaft and sheets into a bath of wastewater. One limitation with this design is that the bacteria are allowed to grow and die in a normal life cycle without a cleansing function. The result is a buildup of dead bacteria carcasses (slough) around the shaft, creating a "dead zone" in the system and a weakening of the shaft.

[0007] Subsequent RBC designs attempted to eliminate the buildup of slough by replacing the central shaft and plastic sheets that were used in prior designs with a randomly organized group of plastic media in a rotating cage or basket. One example of such an assembly is described in U.S. Patent No. 5,401,398, to McManus, which is incorporated herein by reference. The various arrangements of the plastic media provide the surface area onto which the bacteria can attach. The rotation of the basket forces the media into and out of the bath of wastewater, exposing them to the requisite food and oxygen.

[0008] One type of media used in these subsequent RBCs, for example the media disclosed in U.S. Patent No. 5,401 ,398, to McManus, has a cup-like or hemispherical shape to assist in bailing the wastewater. These shapes, by their basic design, incorporate a "dead zone" at the bottom of the cups where the slough builds up, substantially reducing the overall performance of the wastewater treatment system. [0009] Another type of media is a Rashig ring type media, which is described in U.S. Patent No. 3,540,589, to Boris, in an apparatus for the purification of polluted water, for example. Rashig rings may be short tubular elements that do not contain any protrusions into the interior of the tube. Although this type of media does not have a closed end in which bacteria slough can accumulate, it has the disadvantage that there is insufficient surface area upon which bacteria can attach. Further, this type of media has no mechanism for assuring that the rings undergo sufficient tumbling action to provide maximum contact with the wastewater.

[0010] Other types of media have been disclosed by others. For example,

U.S. Patent No. 3,914,351, to McKeown et al. describes a polypropylene media element for use in a packed bed tower where the media has "the form of a truncated cone, the longitudinal axis of which preferably defines an angle of not more than 30° at the hypothetical apex thereof." The ratio of the diameter to the width (i.e., longitudinal length) is preferably more than 1.5: 1. The media may have a series of full length internal ribs. Despite the extra surface area of the ribs, the short stature of the media relative to their diameter make them undesirable for use in rotating digesters, which require media more susceptible to random tumbling rather than an ordered packed arrangement of a packed bed. [0011] Thus, there is a need for a type of media that may be used in wastewater treatment systems and that overcomes the disadvantages of the prior art by providing sufficient contact area onto which bacteria can attach, reducing the accumulation of slough on the media, and providing sufficient tumbling action to assure maximum efficiency of the wastewater treatment system. There is also a need for a compact, efficient wastewater treatment system and methods for treating household wastewater.

SUMMARY

[0012] The present invention is intended to meet the above-mentioned needs. One aspect of the invention in its various embodiments and aspects is an apparatus for wastewater treatment. In one embodiment of the first aspect of the present invention, a wastewater treatment system includes a tank having a bottom, side walls, and a top, the top having a first and second basin therein; a generally cylindrical enclosure adapted for containing a plurality of bacteria-hosting media, the enclosure rotatably mounted partially within the first basin; and means for destroying microscopic organisms in a stream of effluent from the second basin. [0013] In a second embodiment of the first aspect of the present invention, a wastewater treatment system includes a closed tank divided into two interior compartments - a collecting compartment and a compartment that receives liquid overflow from the collecting compartment. The top surface or lid of the closed tank includes two basins formed therein. The first basin receives a rotating biological digester enclosing bacteria-hosting media, and the second basin is a clarifying unit. Preferably, a third basin, configured for receiving a disinfecting unit, is also formed in the top surface of the tank. An effluent stream may be transported through the system by a series of pumps, overflow weirs and spillways. After exiting the system, the final effluent may optionally be subjected to a sand filtration unit or a distribution pump.

[0014] A second aspect of the invention involves a method for treating wastewater. In one embodiment of the second aspect, the method includes providing an enclosure having an interior and a top, the interior being adapted to form a collection tank and the top being molded to form a digesting basin and a clarifying chamber; feeding the wastewater to the collection tank to obtain a liquid first effluent; transporting the liquid first effluent to the digesting basin having a biological digester mounted therein to obtain a second effluent; transporting the second effluent to the clarifying chamber to obtain a third effluent; and transporting the third effluent to a disinfector to obtain a fourth effluent, wherein the disinfector comprises means for destroying microscopic organisms. Preferably, the enclosure provided is an integrally molded monolithic enclosure. [0015] A third aspect of the present invention involves a flow-through media element having an outer wall defining a truncated conical shape with two open ends and a plurality of internal ribs. In one embodiment, the length of the media element is greater than the largest diameter of both open ends. The internal ribs may extend through the outer wall to create external ribs, or separate external ribs may be affixed to the outer wall. The flow-through media may also optionally contain a rim along the perimeter of either end of the media element or both ends. The configuration of the media element of the present invention is believed to create a venturi-like effect that promotes tumbling of the media elements, contact of fluid with the media member, and removal of unwanted debris within the media element.

[0016] Another aspect of the present invention involves a method of treating effluent, which includes placing a plurality of the media elements of the present invention in an enclosure partially submersed in the effluent and rotating the enclosure to expose the media to the effluent and to a source of oxygen. This method provides an efficient way to remove impurities from a wastewater stream. [0017] Additional features and advantages of the present invention will be apparent to one of ordinary skill in the art from the drawings and detailed description of the preferred embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1A is a perspective view of one embodiment of the packaged wastewater treatment unit of the present invention.

[0019] Figure IB is a magnified top view of the disinfector unit and surrounding areas enclosed by circle IB shown in Figure 1 A.

[0020] Figure 2 is a top view of the unit shown in Figure 1A.

[0021] Figure 3 is a sectional view of the unit shown in Figure 2, taken along line 3-3.

[0022] Figure 4A is a sectional view of the unit shown in Figure 2, taken along line 4A-4A.

[0023] Figure 4B is a detailed sectional view of the unit in the area enclosed by circle 4B shown in Figure 4A.

[0024] Figure 5A is a perspective view of a rotating biological digester used in the embodiment of the invention shown in Figure 1A. [0025] Figure 5B is a magnified view of the sprocket and end disc enclosed by circle 5B shown in Figure 5A.

[0026] Figure 6 depicts a detailed sectional view of a basket bearing, sprocket, and drive chain system.

[0027] Figure 7 is a perspective view of a chain sprocket used in the system shown in Figure 6.

[0028] Figure 8 is a perspective view of a basket bearing used in the system shown in Figure 6.

[0029] Figure 9 is a schematic diagram of the process flow through one embodiment of the apparatus of the present invention.

[0030] Figure 10 is a perspective view of one embodiment of a media member that may be used in the apparatus of the present invention.

[0031] Figure 1 1 is another perspective view of one embodiment of a media element of the present invention.

[0032] Figure 12 is a sectional view of the media element shown in Figure 11, taken along line 3-3.

[0033] Figure 13 is a perspective view of another embodiment of a media element of the present invention, which includes a rim on each end of the media element.

[0034] Figure 14 is a sectional view taken along line 5-5 of Figure 13.

[0035] Figure 15 is an end view of the media element shown in Figure 13.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

[0036] The present invention overcomes the disadvantages of existing wastewater treatment systems by providing a compact and efficient system. Preferably, the compartments, basins and chambers of the waste treatment system may be integrally molded as a single monolithic compact unit. The compactness of the unit results from the strategic arrangement of the components within the unit. With the use of appropriate media, such as the media disclosed herein and in U.S. Patent No. 6,852,227 (incorporated herein by reference), the resulting effluent may be compliant with the National Sanitation Foundation requirements for households and, therefore, may be installed as a household unit. In addition, the compactness of the unit facilitates transporting and installing the system in a confined household or residential environment, as well as in other settings. [0037] Now with particular reference to the drawings, Figures 1 A and 2 show one embodiment of the packaged wastewater treatment unit of the present invention. This embodiment of the packaged unit 10 contains a wastewater inlet 1 1 to a tank 12 having a bottom 14, four side walls 16, and a top 18. Preferably, the tank 12 is a sealed enclosure. Within the top 18 of the unit 10 is a first basin 20, in which a rotating digester 24 may be mounted, and a second basin 22 which serves as a clarifying unit. The top 18 also contains apertures 94 that serve as access panels to the tank interior. Covers may be placed on these apertures 94. The tank 12 may be installed underground to protect it against freezing, and a cover (not shown) may be positioned over the top 18 of the tank 12 and the digester 24 to protect them from the effects of the environment. [0038] Figures 3, 4A, and 4B depict cut-away perspectives of the unit 10 and the system components shown in Figures 1 A and 2. Upstanding from the bottom 14 of the tank 12 of this embodiment, is a vertical baffle 46, separating the tank 12 into two compartments - a collection tank 13, which is located beneath the digester basin 20, and a secondary tank 15, which is located beneath the clarifier basin 22 and the disinfector basin 56. The baffle 46, which may be integrally molded with the bottom 14 of the tank 12, assists in holding back the solids in the incoming stream from the liquid. The collection tank 13 receives the effluent to be treated and serves as the sludge settlement and holding area. The presence of naturally-occurring anaerobic bacteria in the collection tank 13 allows preliminary digestion of organic waste matter to occur. The secondary tank 15 is sized to accommodate overflows that occur during peak periods. The high liquid level resulting from these peak periods will then be worked down as the liquid is processed out of the secondary tank 15 at a relatively constant rate over a 24-hour period into the digester basin 20. [0039] The first basin 20 is configured to contain a significant volume of wastewater and to receive a rotating biological digester 24 for aerobic bacterial treatment of the wastewater. The digester 24 is mounted partially within the basin 20. Preferably, between 30% to 50% of the diameter of the digester is immersed in the effluent contained in the basin 20. More preferably, 40% of the diameter of the digester is immersed in the effluent contained in basin 20. [0040] The biological digester 24 used in this embodiment of the invention is preferably a generally cylindrical, cage-like enclosure, as described in more detail below, adapted for receiving a plurality of bacteria-hosting media. Alternatively, though less preferred, the digester 24 may contain an enclosure on a central shaft or with stub shafts, for example. See e.g., U.S. Patent Nos. 4,137,172 to Sako and 5,350,507 to McManus. Even less preferred is the use of conventional sheet or plate rotating contactors on a central shaft.

[0041] In this embodiment, as shown in Figures 1 A and 3, the digester 24 is rotated by two drive chains 32, attached to a bearing 42 and axle 30 system, which is driven by a motor 26 and gear box 28. Although the bearing and axle may be made of many suitable materials, ultra high molecular weight polyethylene is preferred. Other arrangements for driving the digester may also be used. [0042] Figure 5A shows a preferred embodiment of a rotating biological digester 24 that may be used in the unit 10 of the present invention. The digester 24 includes two circular end disks 52 connected along their peripheries by a plurality of rods 60, sprockets 68 with teeth 74, and end caps 72. Although other materials may be suitable, preferably these components are made of a reinforced plastic such as fiberglass.

[0043] The end disk 52 of the digester 24 is supported by a bearing 58, as shown in Figure 4A. Although a pair of bearings 58 is the preferred means of supporting the digester 24, alternatively, a center shaft, end stub shafts, or other means of support may be used. The bearing used in the embodiment shown in Figure 4A is further illustrated in Figures 6 and 8.

[0044] Figure 6 shows the cross-sectional detail of the end disk 52 of the digester 24 supported by bearing 58. The bearing 58 may be anchored to the wall 16 of the unit 10 by bolts 64, preferably made of stainless steel. A rod 60 extends through the end disk 52 and through a sprocket section 68, which is illustrated in further detail in Figure 7. The end disk 52 and sprocket section 68 are separated by a spacer 70. The sprocket 68 is held in place by an end cap 72. A drive chain 32, preferably made of stainless steel, is attached to the sprocket 68 which has a plurality of teeth 74, as shown in Figure 7. The drive chain 32 catches every other tooth 74 of the sprocket 68. As shown in Figures 6 and 8, the bearing includes an upper surface for supporting the end wall 52 of the digester basket, and a lower bearing surface acting as a chain guide.

[0045] Preferably, the rotating digester 24 contains a plurality of bacteria hosting media, which have a relatively large surface area per unit of occupied bulk volume. Examples of media that may be used in the digester 24 include the media disclosed herein and in U.S. Patent Nos. 6,852,227 to Petrone (most preferred), 5,401,398 to McManus, 3,540,589 to Boris, and 3,914,351 to McKeown et al, which are hereby incorporated herein by reference.

[0046] Preferably, the bulk volume of the media occupies about 45% to 95% by volume of the space in the digester enclosure, and more preferably, about 80% by volume of the enclosure. Also, the preferable rate of rotation of the enclosure is about 1 revolution per minute (rpm) to 3 rpm, and more preferably 1.5 rpm. [0047] As shown in Figures 2, 3 and 4A, the second basin 22 is configured to operate as a clarifying unit. In this embodiment, the clarifying unit 22 has a partial, truncated conical shape with a flat side 48. Preferably, the angle of the side wall of the clarifying unit 22 is less than 30°. Alternatively, other types of clarifiers may be used, such as truncated conical clarifiers (see e.g., U.S. Patent No. 4,650,577 to Hansel), clarifiers having inclined flow passages (see e.g., U.S. Patent No. 4,089,782 to Huebner), and integral clarifiers (see e.g., U.S. Patent No. 6,572,774 to Ricketts), which patents are hereby incorporated herein by reference. The size and shape of the clarifier basin 22 provides low turbulence and low flow conditions so that any solids remaining in the effluent stream received from the digester basin 20 can settle to the bottom 34 of the clarifier basin. [0048] Figures 4A and 4B show a disinfector basin 56 containing two ultraviolet bulbs 54, separated by a baffle 92. The ultraviolet light destroys any remaining microscopic organisms in the effluent stream. Alternatively, a one-bulb disinfector or a chlorination unit may be used. In the embodiment shown in Figures 4A and 4B, the housing for the disinfector 56 is a rectangular chamber that may be molded into the top 18 of the tank 12. Alternatively, the disinfector bulbs may be housed in a large pipe, for example.

[0049] The top of the unit 10 shown in Figures 1-4AB also includes spillways 40, 44 and 50, and a weir plate 38. A first spillway 44 transports effluent from the digester basin 20 to the clarifier basin 22. A second spillway 40 transports the effluent from the clarifier basin 22 to a disinfecting basin 56 (shown in Figures 4A and 4B). A third spillway 50 transports the effluent from the disinfecting basin 56 to a sump tank 36. The sump tank may contain a float-activated pump that distributes the cleansed effluent for above ground discharge. [0050] In this preferred embodiment, the tank 12, the digester basin 20, clarifier basin 22 and disinfecting basin 56 are integrally molded into a monolithic one-piece unit 10. Optionally, the disinfecting basin 56 may be replaced with alternative disinfecting means external to the monolithic unit 10. Conventional roto-molding techniques may be used to manufacture a monolithic enclosed tank as shown in these figures. Alternatively, one skilled in the art will understand that the tank and other elements of the system may be fashioned from several pieces that are assembled into a single unit. Although other materials may be suitable, preferably, the unit is made of polyethylene.

[0051] In normal operation, wastewater from a household flows into the collection tank 14. The overflow over the baffle 46 spills into the secondary tank 15. The effluent in the secondary tank 15 is pumped into the digester basin 20. The digester 24 rotates into and out of the digester basin 20, which thereby exposes the effluent to the aerobic bacteria residing on the media contained inside the digester 24. These bacteria digest additional impurities in the effluent. Next, the overflow effluent flows through the first spillway 44 to clarifier basin 22, where solids remaining in the effluent settle to the bottom 34. The overflow liquid then flows through the second spillway 40 into the disinfector 56, where any remaining living organisms are destroyed. Finally, the liquid flows through the third spillway 50 to tank 36. The liquid may then be subjected to a sand filtration unit (not shown) or released for above-ground discharge by gravity flow or a pumping unit.

[0052] In addition to the household wastewater fed into the collection tank 13, sediment or slough from the clarifier basin 22 may be periodically pumped to the collection tank. Preferably, a submersible sump pump is located in the clarifier basin 22 for this service. This periodic discharge causes a stirring action in the collection tank 13, and allows the anaerobic bacteria to continue with the primary digestion stage. After the effluent passes over the baffle 46 and into the secondary tank 15, the anaerobic bacteria continue to break down the suspended solids. Preferably, in a low wastewater flow situation, liquid contained within the system may be re-circulated to allow for continuous system operation. [0053] A programmable logic controller (PLC) may be used with the system of the present invention to continuously monitor and control system variables. Pumps, level controllers, diagnostic equipment, and other sensors may be tied into the controller. The controller may also be used to detect a low- flow situation and make an appropriate adjustment in flow, such as internal recirculation of effluent. Likewise, the controller may be programmed to trigger an indicator inside a home when a drive chain used to rotate the digester breaks or when an ultraviolet bulb used in the disinfector burns out. The controller may be provided with a wireless communication system to send a diagnostic message to a remote service center when maintenance is needed.

[0054] One embodiment of the packaged unit 10 of the present invention has an operational capacity of about 300 to 700 gallons of effluent per day, which is suitable for a single household use. Preferably, the unit has an operational capacity of at least 350 gallons per day, and more preferably, of about 400 to 600 gallons per day. The tank 12 has a volume of between about 100 cubic feet and 300 cubic feet. Preferably, the tank 12 has a volume of less than about 250 cubic feet, and more preferably, of about 160 cubic feet. [0055] Although many variations in the dimensions are contemplated for the packaged unit 10, the following dimensions are preferred to meet the above-noted capacity: tank exterior - 4 feet wide by 8 feet long by 5 feet high; digester basket - 3 feet in diameter by 3 feet long; basin which houses biological digester - 3 feet wide by 3 feet long by 1.5 feet deep; disinfector housing - 8 inches by 4 inches by 22 inches (6 - 7 gallon capacity); collecting tank - 550 gallon capacity; and secondary tank - 450 gallon capacity.

[0056] Figure 9 is a process flow schematic that illustrates a preferred embodiment of the method of the present invention. The effluent stream to be treated enters the collection tank 13 through inlet port 11. The inlet port 1 1 may be, for example, a standard four-inch line directly from a house. Sediment 80 remains in the collection tank 13, while the remaining liquid moves over the baffle 46 and into the secondary tank 15. Based on the reading of a level indicator 82, pump 88 transports a precise amount of liquid into basin 20. The digester 24 then rotates into and out of the liquid, allowing the aerobic bacteria attached to the media within the digester 24 to perform their cleansing function. At the end of their life cycle, the aerobic bacteria die and their carcasses drop into the liquid and are carried with the liquid into the clarifier 22 by means of spillway 44. [0057] In the clarifier 22, any remaining solids present in the effluent, including the bacteria carcasses, settle to the bottom 34 of the clarifier 22, where a computer-controlled sump pump 86 periodically transports the settled solids 78 to the collecting tank 13 to be cycled back through the entire system. Preferably, pumps 86 and 88 are submersible. After the effluent enters clarifier 22, it is forced under baffle 76 and then is transported to disinfector 56 by means of spillway 40. The effluent leaves the disinfector 56 by means of spillway 50 and enters tank 36. [0058] From tank 36, the liquid may be transported to an optional sand filtration unit 84 by means of pump 90. The resulting stream may be discharged to the atmosphere. Alternatively, the output of tank 36 may be discharged directly to the atmosphere by gravity flow or a pump.

[0059] Figures 10, 11 and 12 show one embodiment of the flow-through media element 62 of the present invention. This type of media allows for adequate flushing of dead bacteria through the media members 62 so that it can be transported to the clarifier 22, where it settles to the bottom 34. Moreover, the shape and dimensions of this media promote adequate tumbling action and contact with the effluent to ensure efficient system performance. [0060] Figure 11 shows another perspective view of the embodiment of the media element in Figure 10. Figure 12 shows a sectional view taken along line 3- 3 of the embodiment of the media element shown in Figure 1 1. The outer wall 114 of the media element 62 defines a truncated conical shape having a central longitudinal axis 1 18. This embodiment contains eight internal ribs 98. The internal ribs 98 extend radially from the central longitudinal axis 118 and adjoin with the outer wall 1 14 of the media element 62, and extend longitudinally from a first end 120 to a second end 1 16 of the media element 62. In this embodiment, the internal ribs 98 are equidistant from each other and are of similar length and width.

[0061] This embodiment also contains a plurality of external ribs 96 on the outer wall. These external ribs 96 may be continuations of the internal ribs 98 which extend outwardly through the outer wall 114 of the media element 62. Alternatively, the external ribs 96 may be separate ribs affixed to the outer wall, either aligned or offset from the internal ribs 98, and may be of a number greater than or less than the number of internal ribs 98. These external ribs 96 provide texture to the outer wall 114 and provide additional surface area upon which bacteria can attach. The outer wall 114 and plurality of ribs 96 preferably have a continuous non-perforated surface. A rim 100 may circumscribe the diameter of the second end 1 16 and serve as a smooth endpoint at which the external ribs 96 may be attached, such that the ends of the ribs do not protrude beyond the smooth "envelope" of the media element.

[0062] The presence of the internal ribs 98 and the external ribs 96 on the media element 62 of the invention increases the surface area onto which bacteria can attach. As a result, the fluid stream that enters the media element 62 has sufficient contact with the bacteria to remove the impurities from the stream. [0063] The first end 120 of the media element 62 has a diameter Dl that is smaller than the diameter D2 of the second end 116. In addition, the length Ll of the media element 62, which extends from the first end 120 to the second end 1 16, exceeds the diameter D2 of the second end 1 16. Preferably, the ratio of length Ll to diameter D2 is between 1 :1 and 2:1, and more preferably, between 1 :1 and 1.5: 1. Most preferably, the ratio of length Ll to diameter D2 is about 1.1 : 1. [0064] The angle formed by the outer wall 114 of the media element 62 and the central longitudinal axis 18 of the media element 62 is between 0° and 45°, preferably between 10° and 30°, and more preferably between 15° and 25°. Most preferably, the angle is about 18.5°.

[0065] Figures 13, 14, and 15 show another embodiment of a media element of the present invention. Figure 14 is a sectional view taken along line B-B of Figure 13. Figure 15 is a bottom perspective view of the embodiment of Figure 13. These figures illustrate eight internal ribs 98 contained within a truncated conical shape having a central longitudinal axis 118 and eight external ribs 96 on the outer wall 1 14 aligned with the internal ribs 98. The internal ribs 98 extend radially from the central longitudinal axis 118 and adjoin with the outer wall 1 14 of the media element 62, and extend longitudinally from a first end 120 to a second end 116 of the media element 62. In this embodiment, the internal ribs 98 are equidistant from each other and are of equal length and width. The external ribs 96 may be continuations of the internal ribs 98 which extend outwardly through the outer wall 1 14 of the media element 62, or they may be separate ribs affixed to the outer wall 114. The outer wall 1 14 and external ribs 96 preferably have a continuous non-perforated surface.

[0066] This embodiment also contains a rim 100 that circumscribes the periphery of the larger end 116 of the media element 62 and a rim 126 that circumscribes the periphery of the smaller end 120. Alternatively, the rim may circumscribe only one end of the media element 62. The rims have an outer surface that is coaxially aligned with the central longitudinal axis 1 18. [0067] Similar to the embodiment illustrated in Figures 10, 1 1 and 12, the embodiment illustrated in Figures 13, 14 and 15 has a first end 120 of the media element 62 having a diameter Dl that is smaller than the diameter D2 of the second end 1 16. In addition, the length Ll of the media element 62 exceeds the diameter D2. Preferably, the ratio of length Ll to diameter D2 is between 1 : 1 and 2:1 , and more preferably, between 1 : 1 and 1.5: 1. Most preferably, the ratio of length L 1 to diameter D2 is about 1.1 :1. The angle formed by the outer wall 114 of the media element 62 and the central longitudinal axis 1 18 of the media element 62 is between 0° and 45°, preferably between 10° and 30°, and more preferably between 15° and 25°. Most preferably, the angle is about 18.5°. [0068] The media of the present invention may be made of plastic. Preferably, the media are made of polypropylene. Alternatively, the media may be made of other suitable materials, such as metal or ceramic, which provide suitable support and adhesion to the aerobic bacteria in the biological digester. [0069] Other embodiments of the media element may contain different numbers of radial ribs. Desirably, the media element contains between four and twelve ribs. More desirably, the media element contains between six and ten ribs. Most desirably, the media element contains eight ribs. As the number of ribs within the media element increases, the surface area in contact with the wastewater also increases. Too many ribs, however, may restrict the smaller open end of the media element and impede the flow of fluid through the media element, which increases the potential for clogging. Consequently, the number of ribs should not exceed about fourteen, depending on the diameter of the smaller end. [0070] The media element of the preferred embodiment has several advantages over the prior art. First, the open design of the media element allows fluid to pass into one end of the media element and out the other end without allowing slough to accumulate in a "dead zone," such as the bottom of a cup-like or hemispherical media element. The open conical design is believed to provide a venturi-like effect, which not only assures adequate contact of the bacteria with the entering fluid, but also assures that the slough is scoured off and washed through the media element rather than being retained within it.

[0071] Second, and without the invention being bound by any theory of operation, the conical shape and extended length of the flow-through media is believed to create venturi-like movement of fluid therethrough. The fluid movement causes a momentum transfer resulting in random tumbling action in the rotating basket of a biological digester to ensure maximum performance and efficiency of the digester. When fluid passes from the larger first end 16 of the media element 62 to the smaller second end 120, a constriction in flow results. . Conversely, when fluid passes from the smaller second end 120 of the media element 62 to the larger first end 116, a drop in pressure results, thereby creating a backwash turbulence. Without being bound by any theory, it is believed that these random changes in flow produce a hydraulic flow situation which maximizes system performance by creating a tumbling action to: (1) prevent nesting of the media elements, (2) ensure adequate contact of the fluid with the media elements, and (3) flush the media elements to prevent the accumulation of slough within them.

[0072] The media elements of the present invention may be used in a wastewater treatment assembly containing a rotating biological contactor, exemplified by U.S. Patent No. 5,350,507, to McManus. Preferably, the media elements are used in the packaged wastewater treatment unit described above. A plurality of media elements may be placed inside a rotating biological digester basket or other enclosure in the wastewater treatment unit. The media elements and their ribs provide adequate surface area onto which aerobic bacteria may attach. As the rotating digester basket presents the media elements into the wastewater, water will enter some of the media elements through the smaller end and it will enter other media elements through the larger end, resulting in a random tumbling action of the media elements against each other and against the wall of the rotating basket. Preferably, after the fluid stream leaves the basin containing the digester basket, the fluid enters a clarifier where any remaining solids are removed. Then, the clarified fluid enters a disinfector where any residual bacteria is removed by exposing the stream to ultraviolet radiation or a chlorinating injector, resulting in an effluent that satisfies the requirements of the National Sanitation Foundation for surface discharge. [0073] The media elements of the present invention may also be used in other types of systems used to treat polluted liquids or other effluents. For example, the media elements of the present invention may be used in scrubbers or packed towers that use random or dumped packings.

[0074] Another aspect of the present invention is directed to a method of treating effluent in a rotating biological digester. The method includes placing a plurality of media elements in an enclosure partially submersed in the effluent containing organic waste and rotating the enclosure to expose alternately the media to the effluent and to a source of oxygen. Desirably, the bulk volume of the media occupies between about 40% and about 95% by volume of the enclosure. More desirably, the bulk volume of the media occupies about 80% by volume of the enclosure. Rotating the enclosure with the noted loading causes the media elements to tumble randomly. Thus, the media elements are presented alternately into and out of the effluent such that the effluent flows through some of the media randomly in either one end or the other and out the opposite end. [0075] One type of effluent that may be treated using the method of the present invention is wastewater effluent. Preferably, the wastewater is sewage from a typical household. By passing a stream of wastewater through the media element 62 of the present invention and exposing the bacteria on the media element 62 to sources of food and oxygen, the bacteria serves to remove the impurities from the wastewater.

[0076] It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.

Claims

1. A wastewater treatment system comprising: a tank having a bottom, side walls, and a top defining an interior of the tank, the top having a first and second basin integrally molded therein, the first basin being in fluid communication with the second basin; an inlet in fluid communication with the interior of the tank; means for transporting wastewater from the tank to the first basin; a generally cylindrical enclosure adapted for containing a plurality of bacteria-hosting media, the enclosure rotatably mounted partially within the first basin; and means for destroying microscopic organisms in a stream of effluent from the second basin.

2. The system of claim 1 wherein the tank further comprises a baffle upstanding from the bottom of the tank separating the tank into a first compartment and a second compartment.

3. The system of claim 2 wherein the baffle is integrally molded with the bottom of the tank.

4. The system of claim 1 wherein the enclosure is rotated by a motor and drive chain.

5. The system of claim 2 further comprising a recirculating pump for witdrawing liquid from the second basin and pumping into the first compartment of the tank.

6. The system of claim 1 wherein the second basin comprises a truncated conical shape with a flat side.

7. The system of claim 1 wherein the means for destroying microscopic organisms is housed in a third basin integrally molded in the top of the tank.

8. The system of claim 7 further comprising a first open channel in communication between the first basin and the second basin, a second open channel in communication between the second basin and the third basin, and a third channel in communication between the third basin and an effluent port.

9. The system of claim 8 further comprising a second tank in communication with the third channel.

10. The system of claim 1 wherein the cylindrical enclosure comprises a pair of circular end disks and a plurality of rods connecting the perimeters of the end disks.

11. The system of claim 1 further comprising a sump pump that periodically removes sediment from the second basin.

12. The system of claim 1 further comprising a cover disposed over the top of the tank and the generally cylindrical enclosure.

13. A wastewater treatment system comprising: a tank having a bottom, side walls, and a top, the top having a first and second basin therein, the first basin being in fluid communication with the second basin; an inlet in fluid communication with the interior of the tank; means for transporting wastewater from the tank to the first basin; a generally cylindrical enclosure adapted for containing a plurality of bacteria-hosting media, the enclosure rotatably mounted partially within the first basin; means for destroying microscopic organisms in a stream of effluent from the second basin; and a controller operatively coupled with sensors mounted on the tank.

14. The system of claim 13 further comprising means for transporting wastewater from the second basin to the tank.

15. The system of claim 14 wherein the controller is adapted to detect a low flow of wastewater in the tank and cause the transport of effluent from the second basin to the tank.

16. The system of claim 13 wherein the enclosure comprises a plurality of rods connecting the perimeters of two end disks.

17. The system of claim 16 wherein the end disks comprise solid disks having teeth along their perimeters.

18. The system of claim 17 wherein the end disks are driven by a motor and drive chain, the chain intermeshing with the teeth on the perimeter of the end disks.

19. A method for treating wastewater comprising the steps of: providing an enclosure having an interior and a top, the interior being adapted to form a collection tank and the top being integrally molded to form a basin and a clarifying chamber; feeding the wastewater to the collection tank to obtain a liquid first effluent; transporting the liquid first effluent to the first basin having a biological digester mounted therein to obtain a second effluent, the biological digester containing a plurality of bacteria-hosting media; transporting the second effluent to the clarifying chamber to obtain a third effluent, wherein the clarifying chamber comprises means for separating contaminants from a stream of wastewater; and transporting the third effluent to a disinfector to obtain a fourth effluent, wherein the disinfector comprises means for destroying microscopic organisms.

20. A flow-through medium for use in a biological digester comprising: an outer wall defining a truncated conical shape having a central longitudinal axis, a first opening at a first end having a first diameter and a second opening at a second end having a second diameter, wherein the first diameter is less than the second diameter, and having a longitudinal distance between the first end and second end greater than the second diameter; and a plurality of internal ribs extending radially from the central axis and adjoined with the outer wall and extending longitudinally from the first end to the second end.

21. The medium of claim 20 wherein the plurality of internal ribs extend outwardly through the outer wall to provide a plurality of external ribs.

22. The medium of claim 20 wherein the medium comprises polypropylene.

23. The medium of claim 20 wherein the outer wall and plurality of ribs have a continuous non-perforated surface.

24. The medium of claim 20 further comprising a rim circumscribing the periphery of at least one of the first end or second end of the outer wall, the rim having an outer surface coaxially aligned with the central axis.

25. The medium of claim 20 wherein the ratio of the longitudinal distance to the second diameter is such that the fiow-throυgh medium will undergo tumbling.

26. A method of treating sewage effluent in a biological digester comprising: placing a plurality of media, said media having an outer wall defining a truncated conical shape having a central longitudinal axis, a first opening at a first end having a first diameter and a second opening at a second end having a second diameter, wherein the first diameter is less than the second diameter, and having a longitudinal distance between the first end and second end greater than the second diameter; and a plurality of internal ribs extending radially from the central axis and adjoined with the outer wall and extending longitudinally from the first end to the second end, in an enclosure partially submersed in the effluent; and rotating the enclosure to expose the media to the effluent and to a source of oxygen.

27. The method of claim 26 wherein the rotating comprises repeatedly presenting the media into and out of the effluent such that the effluent flows through some of the media randomly in either of the first end or second end and out the opposite end.