Effluent energy recovery system

A septic system thermal recovery mechanism includes a septic tank. The tank has a top, a bottom, and at least one upstanding side wall joining the top to the bottom. The top, bottom, and at least one sidewall define an interior of the tank, and the at least one sidewall is devoid of angular corners. A septic inlet is adapted and constructed to conduct septic waste material into the interior of the tank, and a septic outlet is adapted and constructed to conduct septic waste material out of the interior of the tank. A thermal exchange fluid conduit is embedded in the at least one wall of the tank The thermal exchange fluid conduit is connected to a source of thermal exchange fluid. The mechanism is configured such that thermal exchange fluid can be circulated through the thermal exchange fluid conduit without traversing an angular corner and without contacting the interior of the tank The sidewall can be provided as a cast concrete wall, with the thermal exchange fluid conduit being PVC tubing embedded in sidewall in a spiral configuration at the time the sidewall is cast. The sidewall itself can be configured in any suitable form, such as a substantially contiguous cylindrical wall, or four walls in two substantially parallel pairs of sidewalls, the contiguous sidewalls being connected together with rounded connecting portions. The thermal recovery mechanism can also include a second thermal exchange fluid conduit embedded in the top of the tank. In an embodiment, the mechanism can include first and second tanks constructed as described, with septic waste flowing from the first tank to the second tank. A thermal exchange fluid pump can be connected to circulate thermal exchange fluid sequentially through a return conduit, into a thermal exchange fluid conduit in the second tank, then through a first thermal exchange fluid conduit in the first tank, through a supply conduit and a thermal exchanger, through a thermal output zone, then back through the return conduit.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a heating or cooling system 10 including a septic system 12 having a thermal energy recovery system incorporating the principles of the present invention. The system 10 uses a pump 14 to circulate a thermal exchange medium, for example, a thermal exchange fluid such as a glycol solution. The pump 14 sends fluid exchange medium from a supply conduit 16 past a thermal exchanger 18 , where heat energy is either added to the fluid ( in the case of heating) or removed from the fluid (in the case of cooling), as is known in the art. The fluid then travels to a thermal output zone 20 , which may be a radiator, in-floor system, or other suitable thermal output arrangement. The fluid then travels through a ground loop 21 as is known in the art, then through a return conduit 22 to the septic system 12 having a thermal energy recovery system, as will be described in detail below. The septic system 12 include a septic holding tank 24 that receives waste from a septic inlet 26 and outputs treated waste through a septic outlet 28 . For heating purposes, such waste generally contains heat from its source, and fermentation of the waste within the tank 24 generates additional heat energy, providing a significant heat source during cold periods. The septic system can also act as a cooling element during warmer periods, since the tank is typically installed underground, where temperatures are usually significantly cooler than surface temperatures during warm periods. An alternative system 30 including a septic system 32 having a thermal energy recovery system incorporating the principles of the present invention, is illustrated in FIG. 2 . As with the FIG. 1 system, the system 30 uses a pump 34 to circulate a thermal exchange medium, for example, a thermal exchange fluid such as a glycol solution. The pump 34 sends fluid exchange medium from a supply conduit 36 past a thermal exchanger 38 , where heat energy is either added to the fluid (in the case of heating) or removed from the fluid (in the case of cooling), as is known in the art. The fluid then travels to a thermal output zone 40 , which may be a radiator, in-floor system, or other suitable thermal output arrangement. The fluid then travels through a ground loop 41 as is known in the art, then through a return conduit 42 to the septic system 32 having a thermal energy recovery system, as will be described in detail below. The septic system 32 include a first septic holding tank 44 that receives waste from a septic inlet 46 and outputs treated waste through a septic outlet 48 . Waste from the septic outlet 48 travels through a second septic input 50 into a second tank 52 . Waste from the second tank 52 passes through a second septic output 54 . In use, the tank 44 will contain sludge, i.e., waste containing solids, and the tank 54 will contain liquid waste, i.e., gray water. For heating purposes, such waste generally contains heat from its source, and fermentation of the waste within the tanks 44 , 54 generates additional heat energy, providing a significant heat source during cold periods. The tank 44 , being closer to the waste source, is generally warmer than the tank 54 . Consequently, thermal exchange medium is directed first to the tank 54 , then to the tank 44 , and out through the supply conduit 36 . As with the FIG. 1 embodiment, the septic system can also act as a cooling element during warmer periods, since the tank is typically installed underground, where temperatures are usually significantly cooler than surface temperatures during warm periods. Construction of a tank 56 having a thermal energy recovery system incorporating the principles of the present invention is shown in FIG. 3 . The tank 56 has a top 58 , a bottom 60 , and at least one upstanding side wall 62 joining the top 56 to the bottom 58 , defining an interior 64 of the tank 56 . A septic inlet 66 is adapted and constructed to conduct septic waste material into the interior 64 of the tank 56 , and a septic outlet 68 is adapted and constructed to conduct septic waste material out of the interior 64 of the tank 56 . A thermal exchange fluid conduit 70 is embedded in the sidewall 62 of the tank 56 . The thermal exchange fluid conduit 70 is connected to a source of thermal exchange fluid via a return conduit 72 . The mechanism is configured such that thermal exchange fluid can be circulated through the thermal exchange fluid conduit 70 and out of a supply conduit 74 without traversing an angular corner and without contacting the interior of the tank. To this end, in the FIG. 3 embodiment, the sidewall 62 is provided as a cast concrete wall, with a the thermal exchange fluid conduit 70 being polyextruded polyethylene (PEX) tubing embedded in sidewall 62 in a spiral configuration at the time the sidewall 62 is cast. The sidewall 62 can be configured in any suitable form, and here is shown as a substantially contiguous cylindrical wall, and can be fabricated from any suitable material, such as fiberglass, plastic, or composite materials. It is also contemplated that other shapes, such as oval or octagonal shapes, can be used. The thermal recovery mechanism can also include a second thermal exchange fluid conduit 76 embedded in the top 58 of the tank 56 . The conduit 76 performs in the same manner as the conduit 70 . An alternative tank 78 is shown in FIG. 4 . The tank 78 includes four walls 80 , 82 , 84 , and 86 in two substantially parallel pairs of sidewalls ( 80 , 84 and 82 , 86 ). The contiguous sidewalls are connected together with rounded connecting portions 88 . Septic waste is brought in through an inlet 90 and output through an outlet 92 . Thermal exchange fluid comes into a spirallyconfigured thermal exchange fluid conduit 94 via a return conduit 96 and exits via a supply conduit 98 , as described in the FIG. 1 embodiment. A layer of insulation 100 can be provided to reduce heat transfer. It is contemplated that various modifications can be made to the specific embodiments described. For example, the thermal exchange medium can be provided as any suitable substance, such as recirculating air in a forced-air system. Although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the scope and spirit of the invention as defined by the appended claims.