Continuous Waste Water Clarification Process

1. Field of the Invention

This invention relates to a system for treating waste water and, more particularly, to a process utilizing oxidation ditch systems.

2. Prior Art

To remove impurities, such as sugars and other carbohydrates and proteins and other forms of nitrogen, as well as other types of pollutants from domestic sewage, industrial waste water or similar waste water streams, the use of an orbital or oxidation ditch system can be employed.

In its general usage, an orbital waste water treatment system includes an elongated tank having two sidewalls and at least one partition wall mounted vertically in the tank substantially parallel to the two sidewalls and spaced apart from the ends of the tank to form an endless, circuitous channel to contain a portion of the waste water stream. In a conventional system, the waste water is constantly circuitously flowed in the ditch while at the same time aerated to provide oxygen for microorganisms to decompose most of the pollutants. An example of such a system can be seen in U.S. Pat. No. 3,846,292, wherein a portion of the waste water put in the ditch is removed after aeration and then transferred to a conventional clarifier where heavier solid particles are separated out. Because of high construction costs, a system employing the clarifier in the ditch was developed; an example of which is seen in U.S. Pat. No. 4,303,516.

However, because of turbulence in the clarifier used as well as the cost of ditch and clarifier construction due to the use of settlement separation processes, even these systems were not as efficient as desired. This led to the development of improved clarifier designs as shown in applicant's U.S. Pat. Nos. 4,362,625 and 4,383,922, identified above. This invention relates to the improved process of treating waste water streams made possible by these improved clarifier designs.

Therefore, it is an object of this invention to provide an efficient process for treating waste water streams.

Another object of this invention is to provide a process for treating waste water streams at faster rates and less expensively.

Other objects and advantages of this invention shall become apparent from the ensuing descriptions of the invention.

Accordingly, a process for clarifying a waste water stream is provided comprising diverting a portion of the stream to an oxidation ditch having a clarifier provided with a rear opening to receive the liquid from the stream and bottom opening to allow flow out of the clarifier, causing the portion to flow in a direction toward the front of the clarifier, allowing the liquid to flow through the rear opening in a direction opposite that of the flow of the stream portion for a distance sufficient to separate the stream portion into a clarified phase and a sludge phase, removing the sludge phase through the bottom ports and removing the clarified phase to the waste water stream.

FIG. 1 is a schematic top view of a preferred oxidation ditch-clarifier assembly used in the process of this invention.

FIG. 2 is a cross-sectional view taken along lines A--A of FIG. 1, illustrating the phase separation of the waste water liquid in the clarifier.

FIG. 3 is a cross-sectional view taken along lines B--B of FIG. 1 illustrating the flow of the sludge phase out the bottom ports of the clarifier.

Referring now to FIG. 1, waste water in stream 1 is removed through conduit 2 by pumping devices 3 and dumped into oxidation ditch 4 formed by concrete walls 5 and 6, as shown. The diverted portion of the waste water stream is circulated about ditch 4 in the direction of arrow A. If the velocity of the waste water entering ditch 4 is not sufficient to create the necessary waste water flow rate in ditch 4, various conventional means can be used to achieve the desired flow rate.

A clarifier 7, such as described in U.S. Pat. No. 4,362,625 and 4,383,922, is positioned in ditch 4 whereby its front section 8 faces into the direction of arrow A. As is shown more clearly in FIGS. 2 and 3, clarifier 7 is provided with an opening 9 located in the rear section 10, which includes the back sides and the stern, but preferably the stern, and more preferably completely below the level B of the waste water in ditch 4. Clarifier 7 is also provided with a series of rows of ports 11 located in its bottom 12. As seen in FIG. 3, a preferred embodiment of clarifier 7 is the utilization of parallel troughs 13 formed by sloping sidewalls 14 wherein ports 11 are positioned at the bottom of troughs 13.

The movement of the waste water through opening 9 will cause the direction of flow C in clarifier 7 to be directed back toward arrow A. It has been found that this change in flow direction results in less turbulence in clarifier 7, and, thus, enabling a quicker separation of the waste water into a sludge phase 15 and a clarified phase 16.

While this process could be carried out in batch fashion by closing opening 9 after the desired amount of waste water has entered clarifier 7, it is preferred to operate the process in a continuous fashion. This is accomplished by waste water between bottom 12 and ditch floor 17 flowing at a faster rate than the flow rate in other portions of ditch 4. This faster rate creates a head differential between the liquids in the clarifier and in the ditch which results in drawing the waste water, particularly the sludge phase, out of clarifier 7 through ports 11. The flow rate through ports 11 is preferably controlled by varying the total cross-sectional area of ports 11 through which fluids can pass or by varying the head differential between the level of the waste water in the clarifier and the level B of the waste water in the ditch. In a preferred embodiment, the head differential is preferably controlled by raising or lowering clarifier 7 in ditch 4 in order to vary the cross-sectional area ratio of the waste water stream at clarifier 7 to a position in front of clarifier 7. The increased displacement of clarifier 7 in the ditch results in a greater flow rate past ports 11 and increases the flow rate of the sludge phase through ports 11.

As the waste water flows through opening 9 into clarifier 7, its velocity begins to decrease allowing heavier particles to drift toward bottom 12. This results in a liquid or sludge phase containing a higher percentage of the undesired particles located near the clarifier bottom, which are then drawn out through ports 11. It has been found that a preferred maximum flow rate inside clarifier 7 is up to 0.1 ft/sec. which, with proper sizing and positioning of ports 11, can achieve the preferred volume amounts ratio of sludge phase to clarified phase removed of 1:1 to 2:1.

As a final step, the clarified phase 16 is removed through conduit 18 by conventional pumping, gravity or syphon means 19 and returned to stream 1.

There are, of course, many obvious embodiments not specifically described, but which are intended to be included within the scope of this invention as defined by the following claims.