JPS588309B2 - Sludge zone measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the distance from the water surface of a sludge settling tank to the surface of settled sludge in activated sludge treatment equipment.

In activated sludge treatment equipment, treated water containing sludge treated in an aeration tank is introduced into a sludge settling tank to settle the sludge, and supernatant water is discharged.

However, the degree of sludge growth changes due to changes in the properties of wastewater treated in activated sludge treatment equipment or changes in BOD load, etc., so the amount of excess sludge that has accumulated should be changed in accordance with these changes. There is a need.

Therefore, in order to discharge only supernatant water without causing sludge carryover from the settling tank, it is necessary to know the position of the settled sludge surface at all times.

Conventionally, methods for measuring the surface of deposited sludge include methods using electrical conductivity, methods using transmitted light, methods using ultrasonic waves, etc.
“Water and wastewater” vol. 16, No. 2 (1974) 1
79 to 180) have been proposed, but each has advantages and disadvantages and has not been widely used.

Alternatively, a simple method is to insert a transparent glass or resin tube vertically from the water surface to an appropriate depth with both ends open, close the top end, and then gently pull it up from the water surface to the sludge surface. There is a method for measuring the distance, but it has drawbacks such as individual differences in measurement results, and depending on the speed at which the transparent tube is inserted or pulled up, the interface may be disturbed and measurements may be inaccurate.

As a result of intensive study on a method for measuring the sludge zone that does not have the drawbacks of conventional methods, the inventors of the present invention have determined that the sludge surface can be measured from the water surface by utilizing the difference in dissolved oxygen concentration between the supernatant water phase and the sludge zone in the settling tank. The present invention was completed by discovering a method of measuring the depth to

An object of the present invention is to provide an industrially advantageous method for measuring the distance from the water surface of an activated sludge settling tank to the surface of settled sludge. When measuring the distance from the water surface of a settling tank installed to settle sludge by gravity, dissolved oxygen at many points near a single vertical line and at different vertical distances from the water surface is measured. This can be easily achieved by measuring the concentration and measuring the vertical distance from the water surface of a point where the amount of change in dissolved oxygen concentration with respect to a unit displacement in the vertical direction of the test point suddenly changes.

Next, the present invention will be explained in detail.

The method of the present invention is a method of measuring the position of the settled sludge surface by utilizing the difference in dissolved oxygen concentration between the supernatant water phase and the activated sludge phase in the settling tank.

The saturated oxygen concentration in water at normal temperature and pressure is 8 to 9 ppm.
In the supernatant water phase of the sedimentation tank, the dissolved oxygen concentration usually shows a value somewhat lower than the above value (around 5 ppm).In the sludge phase, the dissolved oxygen is consumed by activated sludge. Dissolved oxygen concentration becomes extremely low.

Therefore, by measuring the dissolved oxygen concentration at each depth, it can be seen that a deposited sludge surface exists at a position where the dissolved oxygen concentration suddenly changes.

A diaphragm electrode method is usually used to measure dissolved oxygen concentration.

For example, a diaphragm electrode is used as an indicator electrode, in which the surface of a solid microelectrode made of gold, platinum, rhodium, etc. is covered with a thin film of cellophane, polyethylene, Teflon, etc., and an electrolyte such as potassium chloride is filled between the film and the electrode surface. , a method of measuring the oxygen partial pressure in the sample water using the principle of polarography using silver, silver chloride, etc. as a counter electrode.

To measure dissolved oxygen at each depth of the settling tank, the diaphragm electrode part of the dissolved oxygen concentration analyzer is immersed under the water surface and lowered manually or automatically at a constant speed or in stages. , a method in which a large number of diaphragm electrodes are attached at regular intervals near one vertical line, or a method in which water or water containing sludge at a predetermined depth is extracted using a siphon or pump, and dissolved water is extracted from the extracted water. Various methods can be considered, such as a method for measuring oxygen.

Indicate or record the measured dissolved oxygen concentration on an indicator or recorder, and calculate the vertical distance from the water surface of the test point at the time when the measured value suddenly changes.The obtained distance is the distance from the water surface to the settled sludge surface. corresponds to

The method for determining the distance is to attach a scale to the lead wire connecting the dissolved oxygen analyzer body and the diaphragm electrode part, and read the scale at the water surface when the diaphragm electrode part is suspended below the water surface. Examples include a method of determining the depth of a test point using a device that moves up and down in the vertical direction with a constant amplitude under the water surface, and a method of determining the depth from the water pressure at the test point.

As described above, the simplest method for implementing the present invention is to attach a scale to the lead wire of the diaphragm electrode, and while reading the instructions on the dissolved oxygen concentration indicator, immerse the diaphragm electrode under the water surface and gradually lower it. Then, the distance is determined from the scale of the lead wire when the pointer of the indicator swings significantly.

In addition, if desired, a sudden change in dissolved oxygen concentration for a unit displacement of vertical distance from the water surface can be automatically detected, and the distance from the water surface of the location of the test point at that time can be automatically detected. It is also possible to measure, instruct, display, or record.

As described in detail above, according to the method of the present invention, it is possible to accurately determine the position of the settled sludge surface in the settling tank, and it is very effective for water quality management.

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist of the present invention is exceeded.

EXAMPLE The dissolved oxygen concentration at each depth in the water in the activated sludge settling tank was measured by the following procedure.

(1) Dissolved oxygen concentration analyzer using diaphragm electrode method (“Fie”
ldlab” dissolved oxygen analyzer; Toshiba Beckman Corporation)
Use a scale to mark the lead wire that connects the diaphragm electrode section (hereinafter referred to as the sensor) and the analyzer body.

(2) Immerse the sensor under the water surface of the sedimentation tank and read the indicated value after the indicator has stabilized.

(3) Lower the sensor approximately 0.5m and read the indicated value and the scale of the lead wire after the indicator's indication is stable.

(4) Repeat the operation in (3) until the indicated value on the indicator decreases slightly.

(5) Repeat step (3) with the sensor lowered to a width of 5 to 10 cm.

Figure 1 shows the relationship between depth and dissolved oxygen concentration obtained by the above method.

From this, the distance from the water surface to the deposited sludge surface was measured to be 2.5 m.

[Brief explanation of the drawing]

FIG. 1 illustrates the relationship between the depth and the dissolved oxygen concentration obtained in the example, with the horizontal axis representing the depth and the vertical axis representing the dissolved oxygen concentration.

Claims (1)

[Claims] 1. When measuring the distance from the water surface of a settling tank provided for settling activated sludge suspended in activated sludge-containing water by gravity to the surface of the sedimented sludge, it is necessary to Measure the dissolved oxygen concentration at a number of points with different vertical distances from the water surface, and measure the vertical distance from the water surface of the point where the amount of change in dissolved oxygen concentration with respect to a unit displacement in the vertical direction of the test point suddenly changes. A method of measuring the distance from the water surface to the sludge surface.