Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2003-05-05
2004-12-14
Prince, Fred G. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S623000, C210S630000, C210S906000
Reexamination Certificate
active
06830689
ABSTRACT:
FIELD OF INVENTION
The present invention relates to processes and systems for treating wastewater and more particularly to a process for removing phosphorus from wastewater utilizing a triple oxidation ditch system.
BACKGROUND OF THE INVENTION
For many years, ditch processes have been used to treat wastewater. One of the most successful ditch processes known is the Triple Ditch Process. The Triple Ditch Process is particularly known for its ability to perform controlled removal of nitrogen. This process and system differs from conventional activated sludge nitrification and denitrification processes in that it includes no recycle stream or external clarifier. The Triple Ditch system includes three hydraulically interconnected oxidation ditches that alternatively function as aerobic (oxic), anoxic, or quiescent reactors. The aerobic or oxic reactor performs the nitrification. The anoxic reactor performs denitrification. The quiescent reactor performs clarification. Because the flow direction through the oxidation ditches is periodically reversed, there is no need to provide for internal recycle streams or the pumping of return activated sludge. The major advantage of the Triple Ditch system is that it consistently produces a high quality effluent at a significant lower cost than conventional systems.
As noted above, the Triple Ditch Process is effective for nitrogen removal as well as the removal of BOD and suspended solids. However, in many situations it is desirable to remove another nutrient—phosphorus. It is, of course, possible to remove phosphorus from wastewater through either chemical means or biologically. There are many disadvantages to using chemicals, not the least of which is cost. Conventional biological phosphorus removal (BPR) usually entails a series of reactors, an external clarifier, and a pumping system for pumping activated sludge from the external clarifier to the front or initial reactor. See, for example, U.S. RE 32,429, the disclosure of which is expressly incorporated herein. Such conventional wastewater treatment systems require large capital expenditures and are expensive to operate and maintain. In many situations, the cost of a conventional phosphorus removal system is cost prohibited.
Therefore, there has been and continues to be a need for a cost effective and efficient biological wastewater treatment system that will remove phosphorus.
SUMMARY OF THE INVENTION
The present invention entails a multi-phased process for removing phosphorus from wastewater in a triple ditch or basin wastewater treatment facility. In one or more phases of the process, wastewater influent is directed into one of the basins and mixed with activated sludge to form mixed liquor. The mixed liquor in the basin is maintained under anaerobic conditions. Mixed liquor effluent from this basin is directed to the other basins in the facility. In succeeding phases, the wastewater influent is initially directed into other basins. Throughout the phased process, the mixed liquor in various basins is maintained under anaerobic and aerobic conditions while one or more of the basins is used for settling. Anaerobic treatment of the mixed liquor gives rise to the growth of phosphorus storage microorganisms and these phosphorus storage microorganisms take up phosphorus when exposed to aerobic conditions.
In one particular embodiment of the process, the three ditches or basins are referred to as two outer basins and one intermediate or middle basin. In order to balance the biomass in the process and to enhance the efficiency of the process, the wastewater system is provided with a piping network that enables the biomass to be transferred from either or both of the two outer basins to the intermediate basin, or permits the biomass to be transferred back and forth between the two outer basins.
Additionally, in one particular embodiment of the present invention, the volume of the three basins is not equal. In such a design, the volume of the intermediate basin exceeds the volume of either of the two outer basins, and in one particular embodiment the volume of the intermediate basin constitutes as much as 50% of the total volume of all three basins.
Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings, which are merely illustrative of such invention.
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DiMassimo Richard W.
Hong Sun-Nam
Zhao Hong W.
Coats & Bennett P.L.L.C.
Prince Fred G.
United States Filter Corporation
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