JPH0141111B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water quality monitoring and control method for monitoring the state of solid-liquid separation in a settling tank in activated sludge treatment and water purification processes, and for predictive control of supernatant water quality.

In the activated sludge treatment process, activated sludge and treated water are separated into solid and liquid in the final settling tank, and as an indicator of the settling characteristics, the 30 minute sludge volume SV ₃₀ has traditionally been used as an indicator of the settling characteristics.
The sludge volume index SVI is used, and an automatic measuring device has also been developed. However, this conventional solid-liquid separation state monitoring has the following drawbacks.

(1) When SVI is small, that is, even when the sedimentation properties of activated sludge are good, the turbidity or suspended solids concentration (SS concentration) of the supernatant water is not necessarily small. There is generally no strong correlation with concentration.

(2) Conventional SV or SVI automatic measuring devices were unable to check whether some or all of the sludge had floated within the measuring tube, and only measured sludge that had settled.

(3) The discharge standard for treated water (effluent) SS after activated sludge treatment is, for example, 70% at a terminal sewage treatment plant.
mg/mg/or less, but it is not possible to take measures to correct the problem by simply monitoring the treated water SS even if it exceeds the standard.

The above problems also occur in the coagulation sedimentation process at water treatment plants.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a water quality monitoring and control method that enables characteristic analysis of activated sludge and predictive control of supernatant water concentration using a sampling method.

The present invention is realized by measuring the turbidity of sample water and calculating the results of the turbidity measurement by this measuring device.

Figure 1 shows the structure of a turbidity measuring device for sampled water. Test water sampled from the treatment facility using an airlift or submersible pump is measured in pipe 1.
will be introduced in An aeration device 2 is installed at the bottom of the measuring tube 1 to generate air bubbles in the sample water, and after the sampling of the sample water is completed, the sample water in the measuring tube 1 is agitated with air for a certain period of time to make it uniform and to eliminate turbidity. Prepare for temperature measurement. A turbidity meter 3, which measures turbidity as a change in the amount of received light using a light transmission type or a light reflection type, is installed above the center of the measuring tube 1, and the stirring is stopped after uniformity adjustment of the sample water by the aeration device 2. Start measuring turbidity changes from this point. After measuring for a period of time necessary for the turbidity change of the sample water to stabilize (e.g. 30 to 60 minutes), the sample water is drained from the drainage device 4, and the inner wall and bottom of the measurement tube are cleaned if necessary. The next water sampling will be carried out. This measurement cycle is continuously repeated and used as calculation data for various water treatment control devices.

The characteristics of the sedimentation measurement results using the above measuring device are as follows:
As shown in FIG. 2, there are four patterns, a to d. In the figure, characteristic a indicates that sludge settles normally, and the turbidity of supernatant water decreases rapidly.
Characteristic b indicates that there is no change from the mixed liquid state (turbidity A) at the initial stage of measurement, and is observed even in actual treatment plants when the 30-minute sludge settling rate SV ₃₀ is 90% or more. Characteristic c indicates a phenomenon observed when sludge floats from the initial stage of measurement. Characteristic d indicates that the sludge once settles at the initial stage of the measurement, but all or part of the sludge rises to the surface during the measurement.

In this way, the sludge sedimentation characteristics in the measurement tube are brought close to free sedimentation using the sampling measuring device, and the turbidity meter 3 measures the change in turbidity over time.
As a result, unlike the complicated movement of sludge in an actual sedimentation tank, the turbidity of the supernatant water of the sedimentation tank or the sedimentation state (solid-liquid separation state) of the suspended solids concentration changes over time and the turbidity shown in Figure 2 changes in a short time. The characteristics of the sludge can be determined by comparison with the change pattern, and before the turbidity of the effluent worsens prior to the actual residence time in the settling tank (about 2 to 4 hours), the effluent can be calculated from a simulation of the condition of the settling tank. (Overflow water) Turbidity can be predicted and applied to effluent water quality treatment.

FIG. 3 shows a case where the above-mentioned sedimentation tank condition prediction data is applied to water quality control in the activated sludge treatment process. After the water to be treated flows into the aeration tank 5 and is aerated, activated sludge is precipitated in the final settling tank 6 and discharged, and the settled activated sludge in the settling tank 6 is returned to the aeration tank 5 in the required amount. be done. In this activated sludge treatment process, when obtaining good treated water quality through advanced treatment in which a flocculant is injected into the aeration tank 5 from the chemical injection device 7 provided at the inlet or outlet side of the aeration tank 5 or at the outlet, it is necessary to In order to determine the injection rate, in addition to the measured value by the inflow load measuring device 8, the calculation unit 10 calculates and determines the effluent water quality using as an indicator the predicted value of effluent water turbidity obtained by the sampling type turbidity measuring device 9 according to the present invention. predictive control to enable good control of effluent water quality. Also. In addition to the above-mentioned advanced treatment, predictive control information can be provided from sludge characteristics and turbidity changes over time for tertiary treatment, which uses activated sludge treated water as inflow water and performs coagulation sedimentation and chlorine injection. In addition, since the coagulation sedimentation tank in a water treatment plant has the same function as the final sedimentation tank in activated sludge treatment, the turbidity of the treated water can be predicted and used as an index for the injection rate into the mixing tank.

As described above, the water quality monitoring and control method for a sedimentation tank according to the present invention enables the early detection of changes over time in the sedimentation characteristics of sludge and the turbidity (or suspended solids concentration) of the supernatant liquid, thereby preventing the conventional SV (SVI) meter from failing. By supplementing sufficient measurements, it is possible to predict and control the turbidity of effluent water before it worsens, enabling better water treatment.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of the turbidity measuring method in the present invention, FIG. 2 is a turbidity characteristic diagram of treated water,
FIG. 3 is a block diagram showing an example of application of the present invention to an activated sludge treatment process. 1... Measuring tube, 2... Aeration device, 3... Turbidity meter, 4... Drainage device, 5... Aeration tank, 6... Final sedimentation tank, 7... Chemical injection device, 8... Inflow load Measuring device, 9...turbidity measuring device, 10... computing unit.

Claims (1)

[Claims] 1. Air is stirred for the time necessary to make the sampled test water uniform in turbidity in the measuring tube, and from the time the air stirring is finished, a turbidity meter is installed above the center of the measuring tube. The change over time of the turbidity of the sample water is measured, the state of solid-liquid separation of the treated water in the sedimentation tank is monitored from this change over time, and the characteristics of the treated water in the sedimentation tank are predicted from the pattern of the change over time. A water quality monitoring and control method characterized by performing water quality treatment predictive control on the treated water.