JPH0790231B2 - Control method for batch type waste water treatment equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a control method for a wastewater treatment apparatus using batch type activated sludge, and more particularly to a control method for maintaining a stable and high treatment function.

[Prior art]

In recent years, a batch-type activated sludge method (for example, see JP-A-55-152594) is used, which is easier to maintain and is suitable for small-scale wastewater treatment compared to the continuous activated sludge method. .

This method is a treatment method in which each process of inflow, aeration, and settling discharge is repeated in a single treatment tank as one cycle, but in order to maintain stable high treatment performance, appropriate sludge extraction control is required. Need to do.

[Problems to be solved by the invention]

However, in the conventional batch type waste water treatment equipment, the sludge is drawn out once a day or every cycle for a certain period of time, so it is not possible to cope with changes in the sludge production rate due to changes in the inflow load. Therefore, the sludge mixture suspension (MLSS) concentration, which is an important indicator of sludge treatment function, fluctuates as the sludge is drawn out, and the treatment function deteriorates.

It is an object of the present invention to provide a control method for a batch type waste water treatment device that maintains a stable and high treatment function by keeping the sludge mixed liquid suspension (MLSS) concentration at an appropriate value.

[Means for solving problems]

In order to achieve the above object, the present invention is a method for controlling a batch type waste water treatment apparatus in which waste water flows into a treatment tank for aeration treatment, sludge is precipitated, and then supernatant water is discharged. The sensor for detecting the suspended solids concentration of the mixed liquid in the treatment tank installed at the position below the sludge interface of the sludge at a high water level after the inflow of wastewater causes the suspended solids concentration (Cm
₁ ) and the suspended solids concentration (Cm ₂ ) of the settled sludge at the end of the precipitation process are measured, and the suspended solids concentration (Cm ₁ ) of the mixed solution in the stirring state is larger than the preset upper limit suspended solids concentration (Cmax) In addition, the gist of the present invention is to withdraw the sludge in an amount such that the suspended solids concentration of the mixed liquid in the agitated state at a high water level after sludge withdrawal becomes a preset lower limit suspended solids concentration (Cmin) after the completion of the precipitation step.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a batch type waste water treatment apparatus used in the present invention. Reference numeral 1 denotes a raw water tank for storing waste water, which is made to flow into a processing tank 2 by a raw water pump 3. An aeration device 5 is provided on the float 4 on the drainage surface of the treatment tank 2, air is blown into the drainage by the aeration device 5, and necessary agitation is performed by a stirring blade.

The float 4 is provided with a supernatant water withdrawing pipe 7 for extracting the supernatant water, and with an arm 6 so as to follow the water level and swing. It is also possible to perform these aerations with a general blower and an air diffuser.

Next, the sensor 8 of the MLSS concentration meter 9 is provided so as to be located below the sludge interface when the precipitation is completed at a position near the bottom of the treatment tank 2.

The control device 10 has a calculation function, and is a sludge drawing pump.
In addition to turning sludge on and off to control sludge withdrawal, control the entire cycle from the inflow of raw water to the discharge of treated water.

FIG. 2 shows an example of the operation schedule in the present invention. After inflowing raw water, continuous aeration or intermittent aeration is performed to perform biological treatment.

Aeration may be carried out during the inflow of raw water, but it is preferable not to carry out aeration considering the effects of bulking suppression and vaginal and dephosphorization effects. Further, when aeration is stopped, it may be allowed to stand, but anaerobic stirring is preferably performed. In the batch-type waste water treatment device shown in FIG. 1, anaerobic stirring can be performed by closing the vent of the aeration device, but an anaerobic stirring may be performed by separately providing an underwater stirrer. After reaching the high water level (HWL) due to the inflow of raw water, the first MLSS concentration Cm ₁ is measured while the tank is sufficiently agitated by aeration.
When the inside of the tank is uniform due to anaerobic stirring, Cm ₁ may be measured during anaerobic stirring instead of during the aeration period.

After the physical treatment, sludge is precipitated, and the MLSS concentration Cm ₂ at the end of precipitation is measured. Since Cm ₂ is measured as a representative value of the concentration of the settled sludge, that is, the excess sludge concentration at the time of sludge removal, the sensor 8 of the MLSS concentration meter 9 must be installed near the sludge extraction port below the sludge interface. There is.

After measuring the concentration measurement values Cm ₁ and Cm ₂ with the MLSS densitometer 9, (1) Cm ₁ is a preset upper limit suspended matter concentration (Cma 1
x)) (Cm ₁ <Cmax) Sludge is not extracted. At this time, it is appropriate to set the upper limit suspended matter concentration (Cmax) in the tank to about 4,000 mg /. Even if the MLSS concentration in the tank exceeds 4,000 mg /, there is no problem with the treatment function, but the sludge's sedimentation property deteriorates, the sludge is caught in the supernatant water in the discharge process, and the respiratory action of the microorganisms that make up the sludge. This is because there is a problem that the proportion of oxygen consumed is increased and the efficiency of oxygen supply is reduced.

(2) Cm ₁ is the preset upper limit suspended solids concentration (Cma
x)) (Cm ₁ ≧ Cmax) Sludge is removed. Although the sludge is drawn out prior to the discharging step in FIG. 2, it does not matter if it is during the discharging time or after the discharging step. Further, the sludge withdrawal amount (V) at this time is set so that the MLSS concentration at the high water level after the withdrawal becomes the preset lower limit suspended solids concentration (Cmin).

That is, (Ve × Cm ₁ −V × Cm ₂ ) / Ve = Cmin, where Ve: effective volume at high water level The lower limit suspended solids concentration (Cmin) in the tank at this time is 1,500 to
It is appropriate to set it to about 2,000 mg /.

In the batch type waste water treatment equipment shown in Fig. 1, when sludge is drawn out, the measured concentration values from the MLSS concentration meter 9 Cm ₁ and Cm ₂
Is input to the control device 10 having a calculation function, and V is calculated by the above calculation formula based on the values of Ve and Cmin input in advance. Sludge pump 11 according to a command from the controller
Is activated and sludge extraction is started. The withdrawal amount is measured by the integrated flow meter 12 provided in the sludge withdrawal pipe, and is input to the control device. When the withdrawal amount reaches the calculated value V, the sludge pump is stopped by a command from the control device.
However, the cumulative outflow meter 12 is not provided, and based on the drawing flow rate of the sludge drawing pump, the calculator in the control unit calculates the time required for drawing, and when the calculated time has elapsed, the sludge drawing pump is stopped. May be controlled as follows.

After the sludge is drawn out, the treated water is discharged from the supernatant water outlet fixed to the float to the outside of the tank through the supernatant water drawing pipe, and one cycle of operation is completed.

〔The invention's effect〕

According to the present invention, the sensor for detecting the suspended matter concentration of the mixed liquid in the treatment tank provided below the sludge interface at the end of the precipitation step detects the mixed liquid in the agitated state at a high water level after the inflow of wastewater. The suspended solid concentration and the suspended sludge floating concentration at the end of the sedimentation process are measured, and the sludge withdrawal timing and withdrawal amount are controlled based on these both measured values, thus the suspended sludge mixture in the treatment tank (MLSS) The concentration can be accurately maintained at an appropriate value, and a stable and high processing function can be maintained.

[Brief description of drawings]

FIG. 1 is a diagram showing a batch type waste water treatment device used in the present invention, and FIG. 2 is a diagram showing an operation schedule of the present invention. 1 is a raw water tank, 2 is a treatment tank, 3 is a raw water pump, 4 is a float, 5 is an aerator, 6 is an arm, 7 is a supernatant water drawing pipe, 8
Is a sensor, 9 is an MLSS concentration meter, 10 is a control device, 11 is a sludge drawing pump, and 12 is an integrated flow meter.

Claims (1)

[Claims] 1. A method for controlling a batch-type wastewater treatment apparatus in which wastewater flows into a treatment tank for aeration treatment to precipitate dirt mud, and then supernatant water is discharged, which is more preferable than the sludge interface at the end of the precipitation step. The sensor for detecting the suspended solids concentration of the mixed liquid in the treatment tank installed in the lower position, the suspended solids concentration (Cm ₁ ) of the mixed liquid in the stirring state at the high water level after the inflow of wastewater and the settled sludge at the end of the precipitation The suspended solids concentration (Cm ₂ ) of the mixture is measured, and when the suspended solids concentration (Cm ₁ ) of the mixed solution during stirring is higher than the preset upper limit suspended solids concentration (Cmax), stirring at high water level after sludge withdrawal A method for controlling a batch-type wastewater treatment device, which comprises withdrawing an amount of sludge having a floating substance concentration of a mixed liquid in a state of a predetermined lower limit floating substance concentration (Cmin) after completion of a precipitation step.