Three stage sewage treatment plant

Details Three stage sewage treatment plant Three stage sewage treatment plant

2000-07-13

2002-06-18

Drodge, Joseph W. (Department: 1723)

Liquid purification or separation

With gas-liquid surface contact means

With separator

C210S121000, C210S170050, C210S206000, C210S207000, C210S220000, C210S260000, C210S532200, C137S576000

Reexamination Certificate

active

06406619

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to the treatment of sewage or waste water. More particularly, this invention relates to the treatment of sewage or waste water discharged from houses and other buildings which are not connected to a municipal sewer system such that, after the sewage has passed through the Three Stage Sewage Treatment Plant (TSSTP), it has been cleaned to a level acceptable for discharge into the environment so that it will not contaminate the ground water. Thus, the TSSTP provides an alternative to septic systems for buildings constructed outside of a local municipal sewer system.
The TSSTP expands upon existing sewage treatment technology, particularly the conventional sewage treatment technology which uses aerobic microorganisms to break down sewage. One such conventional sewage treatment device is seen in U.S. Pat. No. 5,549,818. This conventional sewage treatment device consists of a cylindrical tank which encompasses a funnel-shaped clarifier. Thus, the cylindrical tank is divided into an outer chamber, between the outer wall of the tank and the clarifier, and an inner chamber, inside the clarifier. Air is introduced into the outer chamber by multiple air droplines, which are connected to an air compressor and which pump air bubbles into the sewage in the outer chamber. Sewage flows into the outer chamber where it comes in contact with the air bubbles. The introduction of air facilitates the breakdown and digestion of the sewage by aerobic microorganisms present in the sewage. The aerated sewage then proceeds into the clarifier through an opening at the bottom of the funnel-shaped clarifier. Inside the clarifier is a quiescent zone. This area of calm in the inner chamber of the device allows for settling to occur, with the solids falling back out of the clarifier and collecting on the bottom of the treatment tank. Accordingly, the waste water becomes cleaner as it progresses upward in the funnel-shaped clarifier, continuing to allow gravity to separate the solids from the water. So, by the time the sewage has progressed up through the clarifier, it has been substantially cleaned. This treated effluent exits near the top of the clarifier and is discharged.
While conventional one-stage sewage treatment devices, such as that described in U.S. Pat. No. 5,549,818, act to substantially clean sewage, such sewage may be cleaned more thoroughly and processed more effectively by combining this aerobic cleaning process with additional stages. Initially, this was done by connecting the aerobic sewage treatment device to a separate trash tank and, sometimes, to a separate pump tank. This configuration, linking separate elements together, was cumbersome and bulky. Three separate installations were required, with each separate tank then being connected together with pipes in the field to enable sewage flow between the separate tanks. This installation process was slow and, because it essentially required a custom fitting in the field, prone to error and/or expense. Furthermore, the use of three separate devices connected by pipes meant that the complete unit was spread out, requiring extensive digging in order to clear a sufficiently large area for installation. In addition to adding cost to the installation of the unit, this extensive digging was also inconvenient to the landowner because it causes widespread damage to the yard.
In an attempt to overcome several of these problems, single units encompassing multiple stages in a single device have been constructed. One example of a multi-stage sewage treatment device is seen in U.S. Pat. No. 3,741,393. This device divides a single, plastic septic tank into three subtanks: a trash tank, an aerobic tank (although it differs substantially from the aerobic tank seen in U.S. Pat. No. 5,549,818 because it does not employ a clarifier with air droplines), and a settling tank. The use of plastic to construct the tank, however, is problematic. Plastic is not a particularly strong material, which is problematic as the device must be buried beneath the ground, enduring substantial weight over its life. And, plastic may tend to degrade over time, raising the possibility of leakage and groundwater contamination.
Other devices have attempted to overcome these problems by building a multi-stage sewage treatment unit out of concrete, a material which is very strong under compression and which does not degrade over time. Such a device may be seen in U.S. Pat. No. 4,608,157, which has a trash tank, an aerobic tank (although it, again, differs substantially from the aerobic tank seen in U.S. Pat. No. 5,549,818 because it does not employ a clarifier with air droplines), and a settling tank. The problem with concrete, however, is that it is heavy, complicating installation, and brittle. Current concrete multi-unit sewage treatment devices, such as that seen in U.S. Pat. No. 4,608,157, make use of rectangular-shaped tanks. This is not ideal, however, when the aerobic tank employs a clarifier and air droplines (which is a superior process for cleaning sewage) since it results in “dead zones” in the corners of the tank, with the sewage in those zones receiving little, if any aeration. This is a substantial problem, since proper aeration is required in order for the aerobic microorganisms to function to break down the sewage.
Earlier attempts to solve this aeration problem have resulted in prototype designs which combine a cylindrical central aerobic tank with rectangular trash and settling tanks. Unfortunately, these designs have two serious, interrelated flaws which have kept them from being successful: these designs produce either a very heavy device that, while structurally sound (due to the accumulation of large amounts of concrete at the joint locations between the tanks), is heavy and difficult to handle; or, if the design attempts to lighten the device by eliminating some of the concrete at the joints, a device that is fragile and prone to brittle breakage along the joints between the tanks (raising serious environmental contamination concerns).
The Three Stage Sewage Treatment Plant (TSSTP) of the present invention solves all of these problems due to an innovative design that uses the shape of the tanks to shore up the joints between the tanks, preventing brittle breakage. The TSSTP typically combines three separate cleaning stages into a single sewage treatment device. The sewage first enters a pretreatment area, which screens large solids while allowing anaerobic microorganisms to begin breaking down the sewage. The sewage then proceeds into a cylindrical aerobic tank where it is thoroughly aerated as it traverses down the height of the tank and then clarified as it proceeds upward through the clarifier. Finally, the sewage enters a post-treatment tank, where it is chlorinated and stored for additional settling before discharge. This multi-step process produces a cleaner effluent. The three cleaning stages have been combined into a single unit for convenience and ease and installation. And, the device is constructed of concrete, such that it is strong and durable, providing a long operating life without any degradation. Finally, the TSSTP maintains a reasonable weight, again ensuring ease of installation (without the need for expensive lifting equipment), while also overcoming the longstanding problem of brittle breakage along the joints between the tanks with it uniquely shaped design.
The central aerobic tank is cylindrical, such that it has a circular cross-section that eliminates “dead zones.” The side tanks have an arch-shaped horizontal cross-section (when viewed from above) which provides sufficient architectural strength to prevent any brittle breakage. Thus, the TSSTP represents an improved design which overcomes existing problems in the multi-stage sewage treatment field to produce a better product. This novel design can be used to construct a concrete device with one or more side tanks of the designated shape connected to a cylindrical aerobic tank, In the TSSTP, two side tanks are used in conjunc

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