JPS6014602B2 - Chemical injection control method for water purification equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an improvement in a chemical injection control method for water purification equipment that performs purification treatment by injecting an alkali agent into raw water taken and then injecting a flocculant.

[Background of the invention]

As is well known, in water purification equipment, a flocculant is injected to remove suspended matter contained in raw water.

Aluminum sulfate or polyaluminum chloride is usually used as the flocculant. Conventionally, the injection rate of the flocculant is determined according to the turbidity of the raw water, and the injection rate is calculated by the raw water flow rate to control the flocculant injection amount.

However, although the flocculant reacts with the alkaline component in the raw water to produce aluminum hydroxide, hydrolysis will not be promoted unless the alkaline component necessary for the hydrolysis of the flocculant is present. The alkalinity of raw water changes depending on the season, rainfall, snowmelt, and other weather conditions. If the alkalinity of the raw water is low, hydrolysis cannot be promoted and flocculation cannot be performed well. Therefore, an alkaline agent such as caustic soda is injected to bring the alkalinity of the raw water to a predetermined value or higher. However, even if the alkaline agent is injected under feedforward control, it is impossible to confirm whether or not the coagulant has been sufficiently hydrolyzed. Therefore, the applicant first confirmed through experiments that coagulation was performed well when the alkalinity of the raw water, the alkalinity after injecting the coagulant, and the shoes exceeded the predetermined values. No. (Mochikai Sho 53-10714
8).

Note that the alkalinity and pH after injecting the flocculant are herein referred to as coagulated water alkalinity or coagulated water fence. This Japanese Patent Application Publication No. 52-21562 (Special Publication No. 53-107
No. 148) calculates the alkaline agent injection rate from raw water alkalinity, flocculated water alkalinity, and flocculated water pH, respectively.
The alkaline agent was injected even with the total amount of injection agent determined. This is because safety is important from the viewpoint that if the raw water alkalinity, flocculating water alkalinity, and flocculating water bait are each above the specified value, flocculation by the flocculant can be performed satisfactorily. However, this method requires a large amount of alkaline agent and cannot satisfy the demand for reducing operating costs of water purification plants.

In particular, in recent years, as the amount of water treated at water treatment plants has increased, there has been a strong demand to reduce the amount of chemicals used. [Object of the Invention] The present invention has been made in response to the above-mentioned problems, and its purpose is to provide a Z water purification equipment that can reduce the amount of alkaline agent injected in order to achieve good flocculation of the flocculant. An object of the present invention is to provide a drug injection control method.

[Summary of the invention]

The feature of the present invention is that the alkaline agent injection rate is determined so that the raw water alkalinity, coagulated water alkalinity, and coagulated water axis are each higher than the specified value for each Z, and the maximum alkaline agent injection rate is determined. The reason is that the alkaline agent is injected based on the injection rate.

[Embodiments of the invention] 2 or less,
The present invention will be explained in detail with reference to the embodiment shown in FIG.

In FIG. 1, raw water taken from a water intake source (not shown) is led to a landing well 1, and then quickly flows into Takayo Pond 2. In the rapid lighting pond 2, a flocculant is injected by the flocculant injector 7 to perform rapid lighting. Note that the injection of the flocculant is controlled. In the floc-forming pond 3, gentle drainage is carried out to grow fine flocs and form large flocs. The alkalinity A of the raw water flowing into the receiving well 1 is measured with an alkalinity meter 4 and input to the injection rate calculation circuit 11. Injection rate calculation circuit 1
1 determines the injection rate Q, according to the raw water alkalinity A, as described later. A false flow rate of raw water flowing into the rapid loss pond 2 from the landing well 1 is measured with a flow meter 5. Moreover, before flowing into the rapid fly azusa pond 2, an alkaline agent is injected by a three-alkaline agent injection machine 6. The alkalinity A2 of the flocculated water after the flocculant has been injected into the rapid light Azusa pond 2 is measured using an alkalinity meter 8, and the pH of the flocculated water is also measured using a pH meter 9. The injection rate calculation circuit 12 calculates the injection rate Q according to the pH of the coagulated water (=pH,).
3, and the injection rate calculation circuit 13 calculates the injection rate Q2 according to the coagulated water alkalinity A2. The maximum value selection circuit 14 selects the injection rate QI'Q2 obtained by the calculation circuits 11 to 13.
' The maximum injection rate Qma of q3. is selected and added to the injection amount calculation circuit 15. In this configuration, raw water into which an alkaline agent has been injected as described later is fed to the rapid toyo pond 2 while being injected with a flocculant.

Due to this hawk worship, the suspended solids contained in the raw water coagulate to form fine flocs, and these flocs grow into large flocs in the floc formation pond 3. The flocculated water flowing out of the floc formation pond 3 is led to a sedimentation basin (not shown), where grown flocs are removed by sedimentation, and then filtered in a furnace basin. On the other hand, the alkaline agent is injected as follows.

The injection rate calculation circuit 11 inputs the raw water alkalinity A, measured by the alkalinity meter 4, and sets the injection rate Q to zero if the raw water alkalinity exceeds the specified value As, as shown in FIG. A. When <As, the injection rate Q is determined by the following equation.

q. =Misara A Hada '1' K. :Increase in alkalinity when one alkaline agent is injected.Also, as shown in FIG.
is zero, and when AS2 is reached, the injection rate Q2 is determined by the following formula.

Further, as shown in Fig. 4, the injection rate calculation circuit 12 calculates zero if the measured value p of the coagulated water mother is above, and if it is below the specified value p ratio, the injection rate calculation circuit 12 calculates the following equation. The injection rate shown as 3 is calculated and output.

Q3 = f (pH) ... [3'
f: Function Here, the specified value As in formulas '11 to '31
, , As2, p ratio is the maximum 4. value of raw water alkalinity, coagulated water alkalinity, and coagulated water pH when flocs are well formed.

These specified values are determined by setting a simulated raw water using the river water to be taken and the river bed mud (turbidity to be removed) from this river, and based on the results of a jar test using this raw water.
In a chemical injection control device that the present applicant delivered to a certain water purification plant, the specified values As, AS2, and p are set as follows. As = IQ side A side = 5 legs Wind P ratio = 6 legs plate Also, the function f in the '31 formula depends on the boat's buffering function of river water and cannot be determined theoretically, but is based on a jar test based on simulated source water. determined by

An example of the characteristics is shown in FIG. As shown in FIG. 5, when pH is around 7, the amount of change in alkali injection relative to the amount of change in pH becomes large. As the pH becomes larger or smaller than 7, the amount of change in alkali injection relative to the amount of pH change becomes smaller.

In other words, if a certain amount of alkaline agent is injected, as the value becomes larger or smaller than 7, the rate of pH change increases. The function f is determined by the pH value as described above.
It is determined based on the specified value p ratio, taking into account that the amount of change in alkali injection changes with respect to the amount of change in H. Now, the injection rate Q obtained by the injection rate calculation circuits 11 to 13 as described above.
, , Q2, Q3 are compared in the maximum value selection circuit 14, and the maximum injection rate Qm is added to the injection amount calculation circuit 15.

The injection amount calculation circuit 15 calculates the raw water flow rate Qo measured by the flowmeter 5.
and the injection rate Qmax to determine the amount of alkali agent to be injected.
The alkaline agent injector 6 injects an alkaline agent in accordance with the amount of alkalinity agent to be injected obtained from the arithmetic circuit. The alkaline agent is injected as described above, and the alkaline agent injected to increase the alkalinity of the raw water to a specified value or higher also acts on the alkalinity of the coagulated water and the pH of the coagulated water.

Therefore, raw water alkalinity, coagulated water alkalinity, and coagulated water alkalinity can be reduced by injecting the alkaline agent at the maximum value among the alkaline agent injection rates necessary to maintain the raw water alkalinity, coagulated water alkalinity, and coagulated water pH above the specified values, respectively. It is possible to ensure that both the temperature and the pH of the coagulated water are equal to or higher than the specified values. Therefore, the amount of alkali agent used is small and the flocculant can be flocculated well. 〔Effect of the invention〕
As explained above, according to the present invention, alkali is injected at the maximum calculated alkali agent injection rate in order to raise the alkalinity of raw water, the alkalinity of coagulated water, and the pH of coagulated water to the specified values or higher. Therefore, it is possible to reduce the amount of alkaline agent injected to achieve good aggregation of the flocculant.

It should be noted that although the above-described embodiment is a case of analog control, it is easily understood that digital control using a computer is also possible and can be easily realized.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing one embodiment of the present invention, Figures 2 to 5
Each figure is a characteristic diagram of the injection rate calculation circuit in FIG. 1. 1... Water landing well, 2... Rapid Azusa Pond, 3
...Floc formation pond, 4,8 ...Alkalinity meter, 5 ...Flowmeter, 9 ...Main meter, 6 ... Alkaline agent injection machine, 7... Coagulant injection machine, 11-13... Injection rate calculation circuit,
14... Maximum value selection circuit, 15... Injection amount calculation circuit. Many Z drawings, many 3 drawings, Takako drawings, inferior figures, and Zutsumu J drawings.

Claims (1)

[Claims] 1 In water purification equipment that injects an alkaline agent into the raw water taken and then injects a coagulant to coagulate and precipitate the suspended matter in the raw water, the raw water alkalinity, coagulated water alkalinity, and coagulated water pH are
The raw water alkalinity, flocculated water alkalinity, and flocculated water p are adjusted so that each of them exceeds the specified value.
1. A chemical injection control method for water purification equipment, characterized in that the injection rate of the alkali agent is determined from H, and the alkali agent is injected based on the maximum alkali agent injection rate among the determined injection rates.