JPS587326B2 - How to manage sludge volume at sewage treatment plants - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously and accurately measuring the amount of sludge deposited in a settling tank in a sewage treatment plant by measuring the sludge concentration distribution.

In sewage treatment, it is important to accurately grasp the amount of sludge deposited in the initial settling tank, final settling tank, or sludge thickening tank in order to operate the entire sewage treatment process efficiently.

When treating organic wastewater that does not contain suspended matter in the raw water using the activated sludge method, the so-called food-microbe ratio (F-M ratio)
It is known that if the value is not maintained within a certain range, for example, 0.2 to 0.5 in sewage treatment, the treatment will be insufficient and the state of sludge sedimentation will deteriorate.

In order to keep the FM ratio constant, there is a method of keeping (amount of generated sludge)/(amount of sludge) constant, and this requires measurement of the amount of sludge.

By the way, the amount of sludge is the sum of the amount of activated sludge in the aeration tank and the amount of sludge in the final settling tank, and the amount of activated sludge in the aeration tank can be determined by finding the concentration using a densitometer and multiplying it by the tank volume. Conventional methods for measuring the amount of sludge include detecting the interface of the sludge accumulated in the sedimentation tank using optical or other methods to determine the sludge volume, and then multiplying this by the concentration of returned sludge to determine the amount of sludge. .

However, even if the sludge interface height is the same, there may be a considerable difference in the amount of solids in the sludge, and with this method, there is a large error between the actual amount of sludge and the amount of excess sludge discharged and the amount inside the system. It was difficult to manage the amount of sludge that should be kept at a minimum.

In addition, it is necessary to control the amount of sludge in the initial sedimentation tank and sludge thickening tank, and the residence time in each sedimentation tank is proportional to the amount of sludge in the sedimentation tank. Measurement is required.

In view of the above-mentioned points, the present invention aims to accurately measure the amount of sludge in a sedimentation tank, and uses a combination of a concentration detector that is immersed in sludge in the sedimentation tank and an amplifier that amplifies its detection output. The sludge concentration meter consists of a concentration detector immersed in the sludge in the settling tank, which is moved up and down by a vertical movement drive device to measure the sludge concentration distribution in the settling tank and calculate the amount of sludge. .

In other words, since the dimensions of each part in the depth direction are clear from the structure of the sedimentation tank, the area below the sludge interface is divided into minute parts in the depth direction, the volume of each part is multiplied by the concentration at that depth, and the total sum is calculated. The amount of accumulated sludge can be calculated by finding .

With this method, the amount of sludge in the sedimentation tank, the state of its accumulation, the concentration distribution, and the fluctuations in the interface can be accurately grasped, so it is not only useful for the operation management of the sedimentation tank, but also the sludge retention time (Solid
DeRetention Time) control and sludge rotation speed (Number of Sludge Revolution)
It can be an effective means for actually applying control methods such as on) control.

Figure 1 is a side view schematically showing the final settling tank in the sewage treatment of the present invention, where 1 is an inflow pipe, 2 is a rectifier plate, 3 is a sludge pipe, 4 is a sludge hopper, 5 is a liquid level, and 6 is a sludge tank. 7 is a scraper chain, 8 is a scraper drive device, 9 is an idler, 10 is an ultrasonic concentration detector, 11 is a suspension cable, and 12 is a detector vertical movement device.

The concentration detector 10 is moved up and down with a suspension cable 11 by a detector vertical movement device installed at the upper part of the sedimentation tank, and the amount of attenuation of the ultrasonic waves is continuously recorded on an XY recorder in accordance with the depth.

When the concentration detector 10 reaches the upper or lower limit, the chart of the XY recorder is automatically advanced to a new surface and the direction of movement of the concentration detector is reversed after a pause for a certain period of time by a timer.

The measurement period can be set arbitrarily by adjusting the pause time as long as it is longer than the time required for the vertical movement of the concentration detector. The amount of sludge is calculated by multiplying by the total amount.

Figure 2 shows an example of the concentration distribution measurement record in the depth direction of the final sedimentation basin measured according to the present invention, where the sludge hopper 4 was measured at a depth of 3 m.
, 3 at a depth of 6.5 m from the bottom of the sludge hopper to the liquid level 5.
The concentration detector is raised and lowered every hour.

As a result, the sludge concentration generally increases deeper than the sludge interface 6, but in some cases there may be a layer of low or high concentration in the middle, as shown in Figure 2A. Furthermore, the concentration of returned sludge in the sewerage system was found to be approximately the same as the concentration at the bottom of the hopper, and higher than the average concentration of accumulated sludge.

Therefore, it has become clear that the conventional method of calculating sludge volume from the product of sludge volume and returned sludge concentration causes a considerable error in terms of the distribution of sludge concentration and the average concentration. .

Figure 3 shows in detail a part of an example of sludge concentration measurement according to the present invention, where the vertical axis d [m] indicates the height from the bottom of the hopper, and curves 3A and 3B show the same point at different measurement dates and times. This is a concentration distribution curve.

From the concentration distribution curves 3A and 3B, the heights of the sludge interface are 2.25 m and 2.1 m, respectively, which are almost the same.

Furthermore, when we extrapolate the curves 3A and 3B to a height of 0 to find the concentration at the bottom of the accumulated sludge, the concentration is 7 kg/m3, respectively.
, 4kg/m3.

From experience, the concentration of returned sludge is considered to be approximately equal to the concentration at the bottom, so in the conventional method, the sludge volume is calculated by multiplying the returned sludge concentration by the sludge volume calculated from the interface height. However, as is clear from curves 3A and 3B, the measurement of the present invention shows that the sludge concentration is not uniform throughout and changes depending on the depth, and the returned sludge concentration indicates the actual concentration in the sludge hopper. However, it was also found that the concentration distribution state differed significantly depending on the date and time, and it was found that the amount of sludge calculated using the conventional method differed greatly from the actual amount of sludge.

The present invention measures the sludge concentration distribution in the sludge hopper by immersing the sludge concentration detector into the accumulated sludge and moving it up and down, and divides the area below the sludge interface into minute volumes in the depth direction. Since the concentration and volume are multiplied for each volume and the sum is determined, the actual sludge volume can be measured accurately, and the concentration distribution of sludge becomes clear, which has the effect of effectively managing the sludge volume. .

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing an outline of the sedimentation tank structure in which the present invention is implemented, FIG. 2 is a graph showing an example of concentration distribution measurement results according to the present invention, and FIG. 3 is a detailed view of a part of the measurement example. It is. 1 is an inflow pipe, 2 is a current plate, 3 is a sludge drain pipe, 4 is a sludge hopper, 5 is a liquid level, 6 is a sludge interface, 7 is a chain of the scraper, 8 is a scraper drive device, 9 is an idler , 10 is a concentration detector, 11 is a suspension cable, and 12 is a detector vertical movement device.

Claims (1)

[Claims] 1. A sludge concentration extractor was immersed in sludge and moved up and down to measure the continuous sludge concentration distribution in the depth direction within the sludge hopper, and measurements were taken for each minute portion divided in the depth direction below the sludge interface. A method for controlling the amount of sludge in a sewage treatment plant, which is characterized by multiplying concentration and volume and detecting the amount of sludge by the sum of the two.