Patent Application
20110168721
Concrete wastewater treatment tanks, such as those disclosed in U.S. Pat. No. 5,484,524, are currently manufactured through local distributors. Pre-cast concrete wastewater treatment tanks weigh approximately 10,000 pounds, cost approximately $400-$700 to manufacture, and can be very expensive to ship to distant installations. Furthermore, in some situations shipping distance or space restrictions prevent the use of a pre-cast concrete tank, but the soil adjacent an installation location is too wet or soft to support the weight of a concrete delivery truck.
The settled liquid is then flowed into the biofilm-aeration chamber 7 from the pre-treatment chamber 4. The biofilm-aeration chamber comprises, in the preferred embodiment, plastic biofilm support structure 12 coated with a biofilm (sometimes referred to as “biomass” or “biological agents” herein) and a submerged mechanical aerator. The liquid is immediately combined with mixed liquor that already is undergoing treatment in the chamber by the swirling action of a hollow aspirator tip 8 which is connected to an electric motor 11 (e.g., 3450 RPM) by a hollow shaft 9.
Because of the rotation of an aspirator, a drag force is created at the apertures of the tips and a pressure differential is also produced here. Air is drawn into the hollow aeration tube 9 through the vent cap 22 down to the aspirator tip 8 where the air is injected into the mixed liquor as tiny bubbles. Rapid mixing of the tiny bubbles occurs once they emerge from the tips of the aspirator 8. High oxygen transfer is accomplished by this high speed mechanical rotation and air injection process.
The submerged aspirator tip 8 rotates at speeds sufficient to reduce the average particle size of the mixed liquor suspended solids (MLSS) into much reduced-size particles. It has been found that aspirator arm tip speeds of 20 ft/sec and higher are effective for performing the particle size reduction function. The swirling motion created by the aspirator tip together with the lifting motion of the air injected into the mixed liquor circulates the smaller organic particles through the plastic biofilm support structure 12 on which the biofilm is growing.
Circulation of the mixed liquor is created in the biofilm aeration chamber by the swirling motion of the aspirator tip 8 and by virtue of air that is injected into the mixed liquor radially from the hollow aspirator tip, which produces the fluid flow.
The amount and physical configuration of biofilm support structure present in the process typically comprises a volume of biofilm of between 10% and 99% of the total volume of the biofilm aeration tank and provides an effective treatment of wastewater with the combination of other elements of the present invention. It has been found that apertures in the biofilm of ½″ and larger are satisfactory diameters for use in such systems.
The mixed liquor passes through the biofilm coated tubes due to fluid flow generated by the rapidly rotating aspirator. The small MLSS particles and dissolved organic matter are readily adsorbed onto the surface of the biofilm which is growing on the tube walls. The microorganisms of the biofilm are in an oxygen-rich, nutrient-rich environment, and the organic matter and pollutants are digested by the biomass. Thus the mixed liquor is purified by this digestive action of the biofilm.
Any large particles of organic material that remain undigested by the biofilm and any old pieces of biofilm which may slough off the interior of the biofilm tube walls fall into the mixed liquor and again are immediately reduced in size by the rapidly moving aspirator tips. The resulting biofilm particles and organic matter are again circulated through the biofilm tubes where biological digestion continues. The resultant suspended solids from this process is extremely low.
While most of the fluid flow circulates in the biofilm aeration chamber 7, as the volume of fluid in the biofilm aeration chamber increases as a result of continuing influent some of the fluid that has been treated flows or is displaced through a gap between wall 14 and baffle 15 into the settling chamber 16. Any settled solids in the settling chamber 16, which might consist of small pieces of biofilm or suspended solids that are not small enough, are returned to the biofilm aeration chamber 7 by a circulation force created by the circulation current in the biofilm aeration chamber.
Walls 14 and 15 of
The supernatant in the settling chamber 16 is collected and flows out through an effluent pipe 20.
The disclosed embodiments provide a fiberglass (i.e., fiberglass-reinforced polymer) wastewater treatment tank that has at least one lower portion and an upper portion that are joined above the tank water line. The lower portion or portions is/are tapered to allow a plurality of tanks to be nested in a shipping configuration. The top portions may optionally be tapered to allow them to also nest during shipping. Interior tank elements such as clarifier walls, risers, BAT media, aerators, divider walls, piping, etc. can be stacked and shipped within the uppermost of the nested lower portions or possibly used as packing material between nested tanks to prevent settling.
IEmbodiments disclosed herein have a lighter weight alternative that can be used to service installations that cannot be reached with a concrete tank due to either space restrictions or shipping costs. Various embodiments are able to be affordably shipped to remote locations, such as outside of the country.
Additionally, a lighter weight tank that mirrors the inside dimensions of the concrete waste treatment plants may not require a re-test and recertification.
In order to provide a fiberglass (i.e., fiberglass-reinforced polymer) wastewater treatment tank/plant that matches currently-certified tanks/plants, there are several design considerations that should be taken into account. Current plants hold approximately 1,250 gallons of water and anything that can be flushed down a toilet will end up in this tank, so the tank must be capable of resisting normal household chemicals and waste at least as well as concrete. The tank must also be capable of being buried 3-5 feet below the ground. As such, the polymer selected should be resistant to household chemicals and have sufficient thickness and reinforcing fiberglass to withstand the expected loading.
Such tanks will be periodically pumped out as part of the normal maintenance. This means that there should be some method of securing the tank so that it does not float when it is pumped out. When the tank is pumped, one side of the tank or the other will be fully pumped out before the other side is. This means that the wall between the two compartments (pre-treatment and aerator or plural aerator compartments) must be capable of holding back the weight of the water from the other tank. The tank must also support the 30 pound aerator, typically via a riser. Embodiments must also provide access ports as found in certified systems (as depicted in
Preferably, the tanks should be able to nest to reduce shipping costs. One way to allow the tanks to nest is to taper at least some of the side walls of the tank sections. Because the tanks will be installed underground, the structure must be strong enough to resist the ground pressures created by the below ground installation. The installed tank must also be water-tight when installed. In order to allow the tanks to be used in both single aerator and dual aerator configurations, preferably both the pretreatment and treatment compartments of the plant should be configured with the necessary supports to hold media and an aerator. The media supports should be sufficiently strong to hold heavy media containing wet biomass when the compartment has been pumped out. Because the present embodiments will be competing with concrete tanks and competitive fiberglass and roto-molded systems, cost and weight are important.
A first embodiment, in which a wall between the pretreatment chamber and the treatment chamber is “cast” into the lower portion of the tank 100, is disclosed in
The lids 112 in the first embodiment can be stackable or nestable (using tapered walls) and the lower portion 110 has tapered walls so as to be nestable for storage and shipping. The lid 112, hanging baffle 14 between the treatment chamber 7 and settling chamber 16, and media supports 12a and 15 have interlocking channels 50, 50′ to facilitate location and installation of the clarifier wall 14 and media after shipping to the final destination. As shown in the top view of
A second embodiment, in which a wall 60 between the pretreatment chamber 4 and the treatment chamber 7 is field-installed into the lower portion 110 of the tank 100, is disclosed in
The lids 112 in the second embodiment can be stackable or nestable (using tapered walls) and the lower portion 110 has tapered walls so as to be nestable for storage and shipping. The lid 112, divider wall 60, hanging baffle 14 between the treatment chamber 7 and settling chamber 16, and media supports 15 and 12a have interlocking channels 50, 50′ to facilitate location and installation of the divider wall 60, the clarifier wall 14 and media after shipping to the final destination. As shown in the top view of
A third embodiment, in which the pretreatment chamber 4 and the treatment chamber 7 are formed by separate lower tank portions, is disclosed in
The lids 112 in the third embodiment can be stackable or nestable (using tapered walls) and the lower portions have tapered walls so as to be nestable for storage and shipping. The lid 112, hanging baffle 14 between the treatment chamber 7 and settling chamber 16, and media supports 15, 12a have interlocking channels 50, 50′ to facilitate location and installation of the clarifier wall 14 and media after shipping to the final destination. As shown in the top view of
In another (non-illustrated) embodiment, the risers can be tapered and formed integral with tapered lids so as to nest within one another.
Baffle walls 14, divider walls (not illustrated), and media supports 17 for the plurality of plants can be stacked and stored inside the uppermost nested tank portion. These components, as well as BAT media, piping, risers, aerators, electrical controls, etc. can also be stored and shipped inside the uppermost tank. The plurality of lids 112 can be nested or stacked on top of the nested lower portions 110 for storage and shipping. If suitably designed, the packing material 18 can be formed of components, such as risers and supports, so as to allow additional space for plant components and the like in the uppermost tank.
While it is preferable that the wastewater treatment plant maintain the dimensions of certified plants, it is also possible to use other dimensions. In order to provide light weight and strength, the fiberglass-reinforced polymer walls of the treatment plant can be formed with corrugations, ribs, webs, and other such structures as generally disclosed in co-pending U.S. application Ser. No. 11/949,900 so as to increase the strength of the walls, which is hereby incorporated by reference. (Note: do we want to claim priority to this application??)
IN view of the above, in a basic embodiment, a tank for a wastewater treatment plant, comprises at least one lower tank portion having a bottom wall and side walls, wherein at least some of the side walls are tapered so as to allow identical lower tank portions to nest therein, wherein the side walls extend above a waterline of the treatment plant, and at least one lid portion for joining to the at least one lower portion, wherein the at least one lower portion and the at least one lid portion are formed from fiberglass-reinforced polymer. A first variation of this embodiment comprises a single lower tank portion with a tapered pair of walls forming a divider wall between a pretreatment chamber and a treatment chamber. Preferably, the first embodiment comprises a single lid portion, wherein the single lid portion preferably comprises a reinforcement spanning the divider wall in the single lower portion.
In another embodiment, the tank for the wastewater treatment plant comprises one lower tank portion and a separate divider wall for on-site installation between a pretreatment chamber and a treatment chamber. This second embodiment may further comprise raised portions in the bottom wall for assisting in sealing the divider wall. Preferably, this second embodiment comprises a single lid portion, wherein the single lid portion preferably comprises a reinforcement spanning the divider wall in the single lower portion.
In yet another embodiment, the tank for the wastewater treatment plant comprises two lower tank portions with a first lower tank portion forming a pretreatment chamber and second lower tank portion forming a treatment chamber and a settling chamber. Preferably, this third embodiment comprises a single lid portion, wherein the single lid portion preferably comprises a reinforcement spanning the first lower tank portion and the second lower tank portion.
Preferably, all of the embodiments further comprise media supports formed in at least the treatment chamber and preferably in both the pretreatment chamber and the treatment chamber.
A system and method for providing a lightweight, transportable wastewater treatment plant has been described. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the scope of the invention disclosed and that the examples and embodiments described herein are in all respects illustrative and not restrictive. Those skilled in the art of the present invention will recognize that other embodiments using the concepts described herein are also possible. Further, any reference to claim elements in the singular, for example, using the articles “a,” “an,” or “the” is not to be construed as limiting the element to the singular.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/256,134, filed Oct. 29, 2010, which is hereby incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61256134 | Oct 2009 | US |
