Liquid purification or separation – Gravitational separator – Heavier constituent trap – chamber – or recess
Reexamination Certificate
1998-10-20
2001-02-27
Popovics, Robert J. (Department: 1723)
Liquid purification or separation
Gravitational separator
Heavier constituent trap, chamber, or recess
Reexamination Certificate
active
06193888
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This is application is based on, and claims priority of Canadian Patent Application No. 2,238,792, filed on May 27, 1998.
MICROFICHE APPENDIX
Not Applicable
SUMMARY OF THE INVENTION
The term “clarifier” as used herein shall be understood to refer to both primary and secondary clarifiers used in waste water treatment plants (WWTPs).
This invention relates sewage treatment processes, and in particular to a method and apparatus for converting a conventional sewage clarifier for use where anaerobic treatment processes downstream of the clarifier is contemplated.
Conventional waste water treatment plants (WWTPs) typically employ multi-stage treatment of sewage. Typically, raw sewage is fed into one or more clarifiers in which heavy solids settle out of suspension by gravity. Because of the volume of raw sewage which must be handled in modem installations, and the necessity of reducing turbulence in the flow, the clarifiers tend to be very large structures, ranging between 10 and 300 feet in diameter, and are typically open to the atmosphere. Conventionally, the clarifier is circular (although rectangular clarifiers are known) and raw sewage is supplied to the clarifier through a centrally located pipe. As the sewage flows away from the inlet pipe, it slows down and becomes sufficiently quiescent that heavy solids will settle out of suspension. Frequently, lighter materials will also accumulate on the surface as a scum layer, which can be removed by suitable dams or the like. Water (minus the heavy solids) flows over a V-notch weir and cascades into a trough (called an “Effluent launder”) which surrounds the clarifier. This clarifier effluent may be directed into a secondary clarifier for further solid separation, or into other equipment for secondary and tertiary water treatment, which typically utilize microbiological processes.
Traditionally, secondary and tertiary water treatment processes have been aerobic, so that it has been desirable to introduce as much oxygen (O
2
) into the clarifier effluent stream as possible. Accordingly, the V-notch weir and effluent launder of conventional clarifiers are typically constructed so that the water experiences a significant drop (generally 2-4 feet in height) into the effluent launder so as to maximize oxygen uptake by the water prior to secondary treatment of the waste water stream.
While effective at introducing oxygen into the effluent, this arrangement has several disadvantages. In particular, numerous odorous and noxious gases, such as hydrogen sulfide, ammonia, mercaptans, thioethers, indoles, skatoles, chlorine, carbon dioxide, carbon monoxide, and sulfur dioxide, are continuously released into to the atmosphere. These gases create major safety and health concerns, as well as environmental pollution. Additionally, the continuous cascade of water into the effluent launder generates a substantial amount of noise. Consequently, a WWTP tends to be a noisy, hazardous, and odorous facility, especially in the vicinity of the clarifiers, resulting in numerous citizens' complaints, and often necessitate the installation and operation of costly odor containment and removal systems.
Furthermore, the conventional V-notch weir/effluent launder arrangement is unsuitable where modem biological phosphorus removal (BPR), or biological phosphorus and nitrogen removal (BPNR) processes are to be used for subsequent processing of the waste water, downstream of the clarifiers. In BPR or BPNR processes, wastewater flows from the clarifiers to open-air reactors where biological removal of nitrogen and phosphorus takes place. Each reactor has three different process zones: anaerobic, anoxic, and aerobic. The first portion of each reactor is the anaerobic zone, which must have no dissolved oxygen (DO
2
) and have as high concentrations of volatile fatty acids (VFAs), such as acetic acid, propionic acid, butyric acid, as possible. The anaerobic zone acts as a “biological selector” that allows the exclusive growth and reproduction of naturally-occurring phosphorus removal bacteria (such as Acinetobacter and Pseudomonas ), which are also called BioP bacteria. These bacteria thrive under anaerobic conditions, and VFAs are the only types of food that BioP bacteria can utilize for their growth and reproduction. The higher the concentrations of VFAs are in the anaerobic zone, the more growth and reproduction BioP bacteria will have, and the more stable and efficient the BPR and BPNR treatment processes will be.
In the anaerobic zone, DO2 must be kept as close as possible to 0 mg/L. Any DO
2
, present will allow other wastewater microorganisms to consume the VFAs that must be reserved solely as substrate for the exclusive growth and reproduction of BioP bacteria. However, the conventional V-Notch weir/effluent launder arrangement of clarifiers is designed to maximize DO
2
in the waste water downstream of the clarifiers. Furthermore, significant amounts of VFAs are released into the atmosphere along with the malodorous gasses described above, thereby reducing the materials which are essential to the growth and reproduction of BioP bacteria.
Because of this deficiency of conventional clarifiers, and the high capital cost of their replacement with updated clarifier designs, the utilization of BPR or BPNR processes has been severely limited, in-spite of their improved efficiency.
An object of the present invention is to provide a method an apparatus for overcoming the above-noted deficiencies in the prior art by achieving significant reductions in the production of noise, and the release of noxious gasses and VFA's as compared to conventional clarifiers.
Another object of the invention is to provide a retrofitable apparatus which can be used to convert a conventional clarifier for use with BPR and/or BPNR processes.
Accordingly, an aspect of the present invention provides a method of converting a conventional waste water treatment plant for use with BPR and/or BPNR processes downstream of a clarifier, the method comprising flooding the effluent launder of the clarifier, and minimizing the turbidity of water flowing into the outlet of the effluent launder.
A further aspect of the present invention provides a dam assembly designed to be installed into the effluent launder of an existing clarifier to flood the effluent launder. The dam assembly generally comprises a dam wall and a sluice ramp secured in the effluent launder by supporting members. The dam wall includes a narrow opening at its base, and the sluice ramp includes a complementary opening, so that some water in the flooded effluent launder passes under the dam assembly, thereby preventing suspended solids from settling near the dam assembly. The majority of the waste-water stream flows over the top of the dam wall and down the sluice ramp. The sluice ramp is angled so that turbidity of the waste-water down-stream of the dam assembly is minimized, thereby minimizing oxygen uptake by the waste-water. A control dam prevents waste-water from passing over the V-notch weir in the immediate vicinity (and down-stream) of the dam assembly.
A pair of dam assemblies are used, one on each side of the effluent launder outlet. This ensures that most of the effluent launder is flooded, and the required length of the control dam is minimized.
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Definition of “Sluice”—p. 1265—Websters New World Dictionary—3rd College Edition, 1988.
Popovics Robert J.
Sughrue Mion Zinn Macpeak & Seas, PLLC
The City of Calgary
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