JPH0333396B2 - - Google Patents

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to a waste water treatment plant that improves the quality of purified water by minimizing fluctuations in the flow rate of waste water returned to the receiving well during over pond cleaning. The present invention relates to a return flow rate control device.

(Prior Art) Figure 4 shows a general process configuration of a water purification plant. In FIG. 4, raw water 1 arrives at a receiving well 2, and is normally supplied to a consumer 6 via a sedimentation pond 3, a filter pond 4, and a water purification pond 5.

When cleaning the filter basin 4, water for cleaning is supplied to the filter basin 4, washing wastewater flows into the drainage basin 8,
The water is returned to the landing well 2 by the return pump 9 and reused.

Conventionally, the water level h of the drainage pond is detected by the water level meter 12, and the target value Q _r of wastewater return at which the water level h becomes constant is determined.
The amount of wastewater returned Q _b detected by the flowmeter 11
The flow control valve 10 was controlled via the flow control device 7 based on the feedback.

(Problem to be Solved by the Invention) By the way, when cleaning the drainage basin 4, the water level in the drainage basin 8 rises, the wastewater return flow rate Q _b increases, and as a result, an excessive amount of wastewater is returned to the receiving well 2. The disadvantage is that it reduces the quality of purified water.

Here, the present invention calculates a desired wastewater return flow rate target value for the wastewater return flow rate, and controls the wastewater return flow rate and over-basin cleaning timing based on this, thereby keeping the water level of the drainage pond within an allowable range. The object of the present invention is to provide a wastewater return flow rate control device for a water purification plant that obtains appropriate water quality while limiting the water quality.

(Means for Solving the Problems) The present invention provides a wastewater return flow rate control device for a water purification plant that returns cleaning wastewater from a drainage basin to a receiving well via a drainage basin. a means for estimating the amount of purified wastewater flowing into the drain; a means for calculating a target value of the wastewater return flow rate that minimizes fluctuations in the wastewater return flow rate based on the estimated value of the washing wastewater amount and the basin cleaning cycle setting value; A flow control device is provided to control the flow rate of wastewater return according to a target value of the wastewater return flow rate, and a means for calculating the variation in the amount of washing wastewater for each basin based on the tendency of water level changes in the drainage basin, A means for calculating a cleaning cycle target value by correcting the cleaning cycle set value according to the variation, and a cleaning control device for controlling cleaning of the excess pond according to the cleaning cycle target value. This is a wastewater return flow rate control device for a water purification plant that controls the wastewater return flow rate so that fluctuations in the wastewater return flow rate are minimized.

(Operation) The present invention detects a change trend in the drainage pond water level by taking the difference between the previous drainage pond water level maximum value (or minimum value) and the current drainage pond water level maximum value (or minimum value). .

Based on the difference between the maximum water level of the drainage pond between the previous time and this time, and the wastewater return flow rate, the amount of over-basin cleaning wastewater that has flowed into the drainage pond is estimated, and the wastewater return flow rate is calculated according to the cleaning drainage amount and the over-basin cleaning cycle setting value. Calculate the target value.

Based on the difference between the maximum water level of the drainage pond between the previous time and this time, if the water level tends to rise, the target value of the overwater cleaning cycle is corrected in the direction of delay (increase). On the other hand, if the water level is on a downward trend, the target value of the over pond cleaning cycle is corrected in the direction of shortening (decreasing).

(Embodiment) FIG. 1 shows a block diagram showing a circuit configuration in an embodiment of the present invention.

FIG. 2 represents the operation of that embodiment.

Further, FIG. 3 is a characteristic diagram showing the passage of time of the cleaning drainage flow rate in a, the drainage pond water level h in b, and the drainage return flow rate Q _b in c.

In all drawings, the same reference numerals represent the same or corresponding parts.

The raw water 1 to be purified enters the landing well 2 at a flow rate Q _i ,
The water reaches the sedimentation tank 3 via a flow rate adjustment valve (not shown), and enters the sedimentation basin 4 via the flow rate adjustment valve 41. The purified water here enters the water purification pond 5 via the flow rate regulating valve 42, and is sent to the outside via a flow rate regulating means (not shown) as water 6 at a flow rate _Q0 .

When cleaning the overflow pond 4, the flow rate adjustment valve 4
1 and 42 are closed, pumps 51 and 52 supply purified water from the water purification plant 5 to the upper and lower layers of the filter pond, and the water is drained to the filter pond 8 through the fully opened flow rate regulating valve 43. Note that there are a plurality of filter ponds 4, and they are cleaned one after another.

The waste water stored in the drainage pond 8 is returned to the landing well 2 via a return pump 9, a flow rate regulating valve 10, and a flow meter 11, with its return flow rate Q _b being adjusted.

Therefore, in the present invention, the cleaning control device 13 controls the water supply of purified water by the pumps 51 and 52 based on the water level h of the cleaning and drainage pond 8 detected by the water level meter 12, and the water level h of the cleaning and drainage basin 8 detected by the flowmeter 11. A flow rate control device 7 is provided that adjusts the rotation speed of the return pump 9 and the opening degree of the flow rate adjustment valve 10 based on the wastewater return flow rate Q _b .

The flow rate control device 7 and the cleaning control device 13 are each controlled by a wastewater return control device 20 using, for example, an electronic computer according to the flowchart shown in FIG. 2.

The operation of the embodiment will be explained below using FIG. 2.

Step 200 is an initialization program that initializes the memory for tracking the drainage pond water level and various setting values.

In step 201, T ₀ of the overwater cleaning cycle setting value is
, the upper limit set value H _high and the lower limit set value H _lpw of the drainage pond water level, h of the drainage pond water level, and Q _b of the wastewater return flow rate are read.

In step 202, the water level of the drainage pond is stored in time series using, for example, a shift register of the storage means, as shown in the following equation (1).

Every time there is a clock signal, from n=1 to N-1, move the data in the nth shift register to the (n+1)th shift register in the next stage, H(n+1)←H(n); Drainage pond water level Detect h and read it into the first shift register.

H(1)←h; …(1) However, H(i) is the array that constitutes the shift register, N is the size of the array H(i), and is 1.5 times the cleaning cycle.
It is large enough to memorize the drainage pond water level for about twice as long.

Step 203 is a part for detecting a change trend in the drainage pond water level.

In this embodiment, the maximum value of the drainage pond water level h is detected, and the change tendency of the drainage pond water level h is detected. In other words, the maximum value of the drainage pond water level can be calculated using equation (2).
Detect H _nax-1 . The second detected water level is the first
If the current value is higher than that of the first time, and is also greater than that of the third time, the current maximum value of the second detected water level (drainage pond water level) is taken as the current maximum value, and the previous maximum value is replaced.

When H(1)≦H(2) and H(3)<H(2) (2), H _nax-2 ←H _nax-1 H _nax-1 ←H(2) In addition, H _nax-2 is the previous maximum water level in the drainage pond.

In step 204, the target value of the wastewater return flow rate Q _r is determined using equation (3).

Q _r = [Q _b・T+(H _nax-1 −H _nax-2・A+α]・1/T …(3) where A is the cross-sectional area of the drainage pond [m ² ] H _nax-1 is the maximum water level of the drainage pond The value [m] H _nax-2 is the maximum value of the water level of the drainage pond [m], T is the target value of the over pond cleaning cycle [time], α is the control parameter, Q _b is the wastewater return flow rate [m ³ /hour].

In step 205, a target value for the overwater cleaning cycle is calculated using equation (4).

T=T ₀ + (H _nax-1 −H _nax-2 )/Q _r・A・β …(4) However, T ₀ is the overwater cleaning cycle setting value [time], and Q _r is calculated using equation (3). Determined wastewater return flow rate target value [m ³ /
time], β is a control parameter.

In step 206, step 204, step 205
The wastewater return flow rate target value and cleaning cycle target value obtained in step 1 are output online to the flow rate control device (FIG. 1, 7) and the cleaning control device (FIG. 1, 13).

Step 207 is a delay timer for waiting until the next control cycle. A predetermined value of approximately ΔT/10 [period] is used as the delay time.

In this embodiment, the flow rate of cleaning wastewater from the over pond generally changes as shown in FIG. 3, and there is variation a for each over pond. In this embodiment, a target value of the wastewater return flow rate commensurate with the washing wastewater flow rate is calculated, and variations in the washing wastewater amount for each filter basin are absorbed by correction of the washing cycle. As a result, the effect is that fluctuations in the wastewater return flow rate are minimized.

The following means can be considered as other embodiments of the present invention. It is also possible to use the minimum value of the drainage pond water level as a method of detecting a change trend in the drainage pond water level. In this case, equations (3) and (4) become equations (3)' and (4)'.

Q _r = [Q _b・T+(H _nio-1 −H _nio-2 ) ・A+α]・1/T …(3)′ However, H _nio-1 is the minimum value of the drainage pond water level [m], H _{nio- 2} is the previous minimum water level of the drainage pond [m], and the others are the same as those in equation (3).

T=T ₀ + (H _nio-1 −H _nio-2・AQ _r・β …(4)′ [Effect of the invention] As explained above, according to the present invention, the most This makes it possible to return wastewater with little fluctuation, which stabilizes the amount of water supplied to the receiving well, which has a significant impact on the water quality treatment process, thereby making it possible to improve the quality of purified water at the water treatment plant.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the circuit configuration in one embodiment of the present invention, Fig. 2 is a flowchart showing the algorithm of the present invention, and Fig. 3 shows the water level of the drainage pond and the flow rate of wastewater return when this embodiment is applied. FIG. 4 is a diagram showing an example of a process at a water purification plant. 1... Raw water, 2... Landing well, 3... Sedimentation pond, 4
... Pass pond, 5... Water purification pond, 6... Water supply, 7...
Flow rate control device, 8... Drainage pond, 9... Return pump, 10, 41, 42, 43... Flow rate adjustment valve, 1
1...Flowmeter, 12...Water level gauge, 13...Washing control device, 20...Drainage return control device.

Claims (1)

[Scope of Claims] 1. In a wastewater return flow rate control device that returns cleaning wastewater from a drainage basin to a receiving well via a drainage basin, the drainage basin water level and the wastewater return flow rate are automatically input at a predetermined cycle to adjust the drainage basin water level. means having a function of storing temporal changes in the drainage pond water level, means having a function of detecting a change trend of the drainage pond water level based on the stored value of the drainage pond water level change, and a target value of the wastewater return flow rate that minimizes fluctuations in the return flow rate. a calculation logic means for correcting the target value of the over-basing cleaning cycle; a flow rate control device for controlling the flow rate of the wastewater return according to the target value of the wastewater return flow rate; A wastewater return flow rate control device for a water purification plant, characterized in that it is equipped with a cleaning control device that controls cleaning of a filter pond.