Liquid purification or separation – Flow – fluid pressure or material level – responsive – Float
Reexamination Certificate
2000-06-21
2001-08-21
Upton, Christopher (Department: 1724)
Liquid purification or separation
Flow, fluid pressure or material level, responsive
Float
C210S242100, C210S540000
Reexamination Certificate
active
06277273
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the removal of the clear water layer which forms between a floating scum, and descending sludge layer in sequential batch reactors (SBR's), and similar devices. An SBR is a large tank with mixing and aerating means; it is filled with raw sewage during the fill cycle. The sewage is then vigorously aerated and mixed with appropriate chemicals during the aeration cycle (approximately 8 hours). After the aeration cycle, the tank is allowed to go into a quiescent period, a scum layer forms at the surface, and the heavier sludge begins to settle to the lower part of the tank. The clear liquid which is present between the scum and sludge is referred to as “supernatant”, and is suitable for discharge. Without a decanter, it can take as much as 3 hours for the sludge to settle, and another 3 hours to decant the supernatant. This invention provides a means to exclude the raw sewage, sludge, and scum from entering the decanting mechanism, and yet provides a method of decanting the supernatant at a constant rate, thus removing uncontaminated supernatant as the sludge settles saving as much as 3 hours per SBR cycle.
SUMMARY OF THE INVENTION
The objectives of the current invention are to prevent the entry of sewage into the liquid withdrawal drain during the aeration, fill, and initial quiescent periods, while removing sludge- and scum-free supernatant during the decanting period of an SBR or equivalent. The control of the two modes with the present invention is accomplished by the opening and closing of the effluent valve on the SBR.
During the aeration, fill and early quiescent period, the effluent valve on the liquid removal piping is closed, and thus both the decanter and the piping will be filled with water and the fore, aft and central floats must have enough buoyancy to support the system while at rest. A sludge barrier at the flow opening has sufficient weight to sink and thus to block entry of sludge into the decanter, but it is sufficiently light to allow a modest current (0.5 MPH) to be able to push it inward, up and out of the way. A removable sump cover encloses the sump and prevents splash over from the aerated and agitated sewage. The floating weir which is hinged at its outboard end to the outboard end of the sump rises due to sufficient displacement in the weir float so as to form a secondary barrier substantially closing off the inlet to the sump thus preventing substantial amounts of raw sewage from entering the sump and effluent conduit. The displacement of the weir float adds to the general buoyancy of the float structure when the output valve is closed. A fixed plate traverses the area between the floats and extends downward so that it blocks a vertical area from the top of the float tanks, to a position approximately 4 inches below the water line. This plate forms a scum baffle which prevents floating scum from entering the sump.
A hinged plate serves as the sludge barrier, connected to and hanging from the scum baffle, extending to the outer edge of the hinged weir, and thus while the effluent valve is closed, it substantially closes off the opening which would allow liquid to enter the decanter. This plate is made of metal, or other suitable material with a specific gravity greater than that of water so that it will tend to sink in the absence of a supporting stream of water pushing the plate and entering the decanter. This plate becomes a barrier to sludge entering the decanter during the aeration phase. It is thus termed a sludge baffle or barrier. A closure mechanism assures that the sludge barrier will remain tightly closed as long as the effluent valve is closed.
A means of introducing clean water into the system between the decanter and the effluent control valve allows water to raise the elevation of the water in the decanter sump, such that any fluid transfer in the system would be the clean water in the sump being transferred into the SBR rather than the sewage entering the sump. The introduction of water is effective at low volumes because the elevated weir and the closed sludge barrier reduce the open area of the peripheral openings to a few square millimeters.
When the effluent valve on the SBR is opened after a short period of quiescence, water will begin to empty from the sump. As the sump level falls, the floating weir begins to lower as it is floating on the fluid in the sump. This creates a weir over which the supernatant begins to leave the SBR via the fluid conduit between the decanter head and the tank exit. The weir causes a rapid acceleration of water as it approaches the tip. This increase in velocity allows the prescribed amount of supernatant to enter the sump and the exit conduit while maintaining a very low velocity immediately outside the decanter thus minimizing the intake of either scum or sludge during the decant. When the flow begins to enter the sump, the sludge barrier closure mechanism is released and the barrier is deactivated. The vertical plate that traverses the area between the floats acts as an under-surface baffle which deters the entry of any floating scum. A horizontal plate which extends from the lower edge of the sump outward and to either side acts as a spoiler which minimizes any uptake of sludge into the decanter.
The volume of supernatant which leaves the SBR is controlled by amount of closure of the effluent up until the capacity of the weir to deliver supernatant is exceeded. If the capacity of the weir is exceeded, there is a possibility that the entire sump and effluent conduit will empty of water, and thus being so lightened, will elevate the decanter and further constrict the capacity of the weir to deliver supernatant. This out-of-control situation may cause the decanter to rise so high in the water as to skim in scum, or cease delivering supernatant entirely. To prevent this situation from happening, a secondary weir, fixed to the bottom of the sump, retains water in the sump at the precise level of the maximum delivery rate of the weir.
The maximum delivery rate is generally set by the SBR designers, and is generally between 1.8 and 3 cubic meters per minute for each meter of weir length. If the effluent valve is opened enough to exceed the capacity of the floating weir, the fixed weir will limit the floating weir to the specified delivery rate. A void space will form in the effluent conduit which will increase the positive flotation of the decanter, but because of the fixed weir, this increase in flotation will be limited to the conduit only, and the sump of the decanter will still retain the water and the weight of that water. As the conduit begins to empty, the decanter, and accordingly the base of the floating weir, will rise in relation to the water surface. This causes the weir to flatten, and increases the velocity of the water thus maintaining the prescribed delivery rate. This upward movement will be terminated when the loss of displacement from the rising flotation tanks equals the weight of the decanter head and the water retained in the sump by the fixed weir.
This arrangement of weirs and flotation will allow the decanter to deliver supernatant as the demand is increased by the effluent valve, and yet will maintain delivery at the maximum rate even though the effluent valve is opened past the specified decant rate.
REFERENCES:
patent: 3970556 (1976-07-01), Gore
patent: 4693821 (1987-09-01), Goronszy et al.
patent: 4695376 (1987-09-01), Astrom et al.
patent: 5078863 (1992-01-01), Durigon
Colahan Patrick
Gore Douglas J.
Freiburger Thomas M.
U.S. Hydrex, Inc.
Upton Christopher
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