JPH025152B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention minimizes fluctuations in the flow rate returned to the receiving well regardless of fluctuations in the flow rate of wastewater when cleaning a filter or draining a sedimentation basin. This invention relates to a wastewater return flow rate control device for a water treatment plant.

[Technical background of the invention and its problems]

Figure 2 shows the general process configuration of a water treatment plant.

In Figure 2, raw water 1 arrives at landing well 2,
Water is normally supplied to a consumer 6 via a sedimentation tank 3, a filtration tank 4, and a water purification tank 5. That is, the flow of water is indicated by arrows 15. Note that 7 is the filter bed of the filtration pond.

When the sedimentation tank 3 is drained, the water containing the drained sludge flows into the sedimentation tank 3.
It is pulled out from the tank and flows into the drainage pond 8. The flow of water at this time is indicated by an arrow 17.

Further, when cleaning the filter basin 4, the cleaning water is stored in the filter basin 4, and the cleaning waste water flows into the drainage basin 8 along the path indicated by the arrow 16.

The water flowing into the drainage pond 8 is returned to the flow rate control device 20
A return pump 9 and a flow rate node valve 10 controlled by
The water is returned to the landing well 2 via the water receiving well 2 and reused. Note that 11 is a flow meter.

The water level h in the drainage basin 8 rises rapidly during cleaning or mud removal, but the flow rate control valve 10 connected to the return pump 9
When the water level h of the drainage pond 8 is controlled using
Qb increases and as a result, excessive wastewater flows into the landing well 2.
water is sent back to the water, reducing the quality of purified water.

For this reason, the return flow rate is systematically controlled using the wastewater return control device 19 using an optimal planning method that takes into account the inflow flow rate pattern to the drainage basin and the capacity of the drainage basin.
This ensures that the return flow rate is kept as constant as possible.

However, when the optimal planning method and feedback control are combined, the optimal return flow rate target value Qr changes in a step-like manner, so the return flow rate also changes greatly in a step-like manner, and the water quality of the receiving well changes significantly. It also has a negative impact on the quality of treated water.

[Purpose of the invention]

The present invention takes into consideration the inflow flow rate pattern into the drainage basin and the capacity of the drainage basin, calculates a schedule of a desirable wastewater return target value for systematically operating wastewater return, and thereby The object of the present invention is to provide a wastewater return flow rate control device for a water purification plant that obtains appropriate quality of treated water while limiting the water level to an allowable range.

[Summary of the invention]

The present invention provides a wastewater return flow rate for a water treatment plant that controls the wastewater return flow rate for returning cleaning wastewater from a filtration basin or sludge treatment wastewater from a settling basin to a receiving well via a drainage basin in accordance with the above-mentioned wastewater volume and the water level of the drainage basin. The control device includes calculation logic that estimates the daily drainage basin inflow flow rate pattern from the drainage basin inflow flow rate, drainage basin water level, and cleaning cycle or sludge cycle, and minimizes fluctuations in the return flow rate based on the above inflow flow rate estimation pattern. A calculation logic for calculating a wastewater return flow rate plan schedule to be calculated, and a calculation logic for calculating a target wastewater return flow rate pattern obtained by smoothing the return flow rate plan schedule while limiting the drainage pond water level within a predetermined range. The wastewater return flow rate is controlled according to the target pattern, and this allows the wastewater return flow rate to be smoothed out while maintaining the water level in the drainage pond within an acceptable range, regardless of fluctuations in the flow rate flowing into the drainage pond due to cleaning and sludge removal. control and improve water quality in water purification treatment.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

FIG. 1 is a flowchart showing the calculation operation of the wastewater return flow rate control device according to the present invention, which shows the time series data of the drainage basin inflow flow rate Qt, the drainage basin water level h, the filter cleaning cycle △T ₁ , and the sedimentation basin sludge drainage cycle. By inputting ΔT ₂ and time T, the wastewater return flow rate target value Qr for each plan creation cycle is calculated.

In other words, in step (1), each process value and set value are inputted, and in step (2), the estimated hourly flow rate pattern of one day's worth of inflow water to the drainage pond Q^t(k) is calculated.
Calculate [k=1 to 24].

Next, in step (3), a wastewater return flow rate planning schedule Qr ^* (k) [k=1 to 24] is calculated.

In other words, the storage volume of the drainage pond is determined from the drainage pond water level at the time when the plan creation starts, and the desired wastewater return flow rate plan is calculated from the estimated value Q^t(k) of the drainage basin inflow flow rate pattern obtained in step (2) above and the drainage basin capacity. schedule
Calculate Qr ^* (k).

The calculation of the wastewater return flow rate planning schedule Q ^* r(k) is formulated as follows as a minimization problem that minimizes fluctuations in the wastewater return flow rate.

Objective function; ₂₄ 〓 ^k=1 (I・x(k) ² → minimum …(1) Constraints; ｜x(k)｜＜Cx …(2) fn＜Qr ^* (k)＜fx (3) Hn ＜H(k)＜Hx …(4) Here Q^ ^* (k)=Fy(k) y(k)=y(k _-1 )x(k) y(o), H(o): Predetermined Value H(k)=Qt(k)−Qr ^* (k)/A+H(k _-1 ) Also, x=(x ₁ , x ₂ ,…, xd) y=(y ₁ , y ₂ ,…, yd) xi, yi = 0 or 1 (i = 1 to d) F = (f ₁ , f ₂ , ..., fd) fi; Drainage return flow rate change value (i = 1 to d) Cx; 0 or a positive integer x upper limit of norm fx, fm; upper and lower limits of wastewater return flow rate Hx, Hm; upper and lower limits of drainage pond water level I; unit matrix A; drainage basin cross-sectional area H(k); drainage basin water level in time period k Qr ^* (k); Planned value of wastewater return flow rate for time period k Q^t(k); Estimated value of drainage pond inflow flow rate for time period k Formulated as a 0-1 integer programming problem as shown in the above equation, and using the branch and bound method. Then, calculate the wastewater return flow rate plan schedule Qr ^* (k) [k=1 to 24] for the next day.

Next, smoothing is performed in step (4). In other words, since the planned schedule Qr ^* obtained in step (3) changes discontinuously as the time period changes, these can be combined into a continuous planned target pattern Qr'(t) [t=t ₁
~ _t24 ].

For this reason, first, assuming that the wastewater is returned according to the planned schedule Qr ^* , the water level h ^* (k) of the drainage pond in each time period k is estimated using the following equation (5).

h ^* (k)=Qt(k)−Qr ^* (k)/A+h ^* (k−1) …(5) In this case, the drainage pond water level at the start of planning is h ^*
(o).

Generally, the wastewater return flow rate planned value is calculated at time k (time period k
Qr ^* (k) changes stepwise to Qr ^* (k+1) at the end of the period), but it changes linearly from Qr ^* (k) to Qr ^* (k+1) in 2T from time k-T to time k+T. ^With _the ^{slope of}
k) …(6) Here t; Shows the elapsed time from time k-T.
Assuming that the water level is changed by Qr'(t), the estimated water level of the drainage pond k'(t) is given by the following equation (7).

h'=Qrk ^* /A (t-t ² /4T) + H ₀ -Qrk ^* /A・T...(7) Here, Qrk ^* = Qr ^* (k+ ₁ ) - Qr ^* (k) When smoothing, the water level The parameter T is selected so that the fluctuation is below a predetermined value, that is, so that the following equation (8) holds true.

h _HWL ＜h′(t)＜h _LWL …(8) Here k _HWL ; Upper limit of drainage pond water level k _LWL ; Lower limit of drainage pond water level This smoothes the drainage flow rate planning target pattern Qr′(t) [ t=t ₁ , t ₂ ,...,
t ₂₄ ] is calculated.

Next, in step (5), the actual process values, that is, the return flow rate Qb and the drainage pond water level h are input, and in step (6), feedback correction is added to the drainage flow rate planning target pattern Qr'(t) to create the return flow rate target pattern. Qr(t) is calculated and the return flow rate Qb is controlled using this as a target value.

This makes it possible to perform appropriate drainage return control while suppressing rapid fluctuations in the return flow rate.

In the above embodiment, the cleaning cycle and the sludge cycle are used to estimate the inflow flow rate pattern to the drainage pond, but if the sludge treated wastewater is not to be returned to the landing well, only the cleaning cycle may be input.

Furthermore, if the wash water is not to be returned to the receiving well, only the sludge removal period needs to be input.

Furthermore, if cleaning or mud removal is not performed at regular intervals, a cleaning or mud removal schedule may be input instead of the cleaning cycle or mud removal cycle.

Further, in the above embodiment, the target pattern Qr'(t) of the wastewater return flowmeter is given as a linear expression of time t as a function form of equation (6), but it is also possible to give it as a polynomial of time t. It is also possible to use functional forms.

〔Effect of the invention〕

As explained above, according to the present invention, even if the drainage volume temporarily increases due to filter cleaning or sedimentation tank drainage, fluctuations in the flow rate returned to the receiving well can be controlled within the range permitted by the water level fluctuations in the drainage basin. A rational wastewater return flow rate control device for a water treatment plant that can stabilize the quality of treated water can be obtained.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing one embodiment of the present invention, and FIG. 2 is a system diagram showing a general process configuration of a water purification plant. 1... Raw water, 2... Landing well, 3... Sedimentation pond, 4
...Filtration pond, 5...Water purification pond, 8...Drainage pond, 9...
...Return pump, 10...Flow rate control valve, 19...Drainage return control device, 20...Return flow rate control device.

Claims (1)

[Claims] 1. In a wastewater return flow rate control device for a water purification plant that controls the flow rate of washing wastewater from a filtration basin or sludge treatment wastewater from a sedimentation basin and returning it to a receiving well via a drainage basin in accordance with the above-mentioned quantity of wastewater and the water level of the drainage basin. , calculation logic that estimates the daily drainage basin inflow flow rate pattern from the drainage basin inflow flow rate, drainage basin water level, and cleaning cycle or sludge cycle, and wastewater return that minimizes fluctuations in the return flow rate based on the above inflow flow rate estimation pattern. A calculation logic that calculates a flow rate planning schedule, and a calculation logic that calculates a wastewater return flow rate target pattern obtained by smoothing the return flow rate plan schedule while limiting the drainage pond water level within a predetermined range, Therefore, a wastewater return flow rate control device for a water purification plant is characterized in that it controls the wastewater return flow rate.