JPH09290273A - Method for adjusting amount of flocculant to be added and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust chemical injection quantity (an addition of a flocculant) to be adequate, even in the case that rainfall water is mixed with the water to be treated due to rainfall. SOLUTION: When the water to be treated flows in a water treating device, at first a flow rate is measured with a flow meter 1, then SS concentration is measured by an SS densitometer 2 and next a flocculant is added (injection of a chemical) from a chemical injection pump 4, and then the water flows in a sludge dehydrator or a flocculating settling basin 3 and a solid-liquid separation treatment is performed with a dehydration treatment or a settling treatment. Detection signals of the flow meter 1 and an SS densitometer 2 and signal from a rainfall detection meter 8 are inputted in an arithmetic device 6. At a rainfall time, a factor of correction (magnification) is used to multiply a chemical injection quantity at a non rainfall time by the factor to correct the chemical injection quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulant addition amount adjusting method and apparatus, and particularly in a sewage treatment plant, a factory wastewater treatment facility, a river water treatment facility, etc. where rainwater due to rainfall may mix with the water to be treated. The present invention relates to a coagulant addition amount adjusting method suitable for use and an apparatus therefor.

[0002]

As is well known, in a sewage treatment plant, a coagulant is mainly added to biologically treated water or sludge after its sedimentation and separation treatment by a chemical injection pump, and then solid-liquid separation treatment is performed. . Similar coagulation separation treatment is also adopted in factory wastewater treatment facilities, river water treatment facilities for treating river water as industrial water, and the like.

Conventionally, the amount of the coagulant added is set in proportion to the amount of SS (suspended substance) flowing into the coagulation treatment apparatus. This SS amount is measured by measuring the amount of inflowing treated water with a flow meter and measuring the SS concentration with an SS concentration meter,
It is obtained by multiplying the density. Then, a chemical injection rate of a predetermined ratio to the obtained SS amount, for example, 0.2 to 0.7% of the SS amount when a polymer coagulant is added to sludge
The drug injection amount is calculated by multiplying the drug injection rate by a certain degree, and a control signal is output to the drug injection pump so that the drug injection amount corresponds to the calculation result.

[0006] This chemical injection rate is selected mainly depending on the SS concentration. For example, at a certain sewage treatment plant, the chemical injection rate of the polymer coagulant is set as shown in FIG. There are cases where the chemical injection rate corresponding to the SS concentration of the water to be treated is uniquely determined based on this graph, and there are cases where the operator in charge sets the chemical injection rate by slightly increasing or decreasing it depending on the aggregation status. .

FIG. 3 is a graph showing the amount of chemicals required to achieve an SS removal rate of 90% or more when the suspension water is subjected to a coagulation treatment with a sulfuric acid band and then to a sedimentation separation treatment.

As is clear from FIGS. 2 and 3, it is necessary to increase the chemical injection rate as the SS concentration decreases. vice versa,
The higher the SS concentration, the lower the drug injection rate. That is, the solid content of SS dry base is 1 kg when the water to be treated has a high SS.
The amount of coagulant added per unit can be small.

[0007]

When the properties of the water to be treated do not change so much, the SS component is efficiently coagulated and separated by controlling the chemical injection pump according to the chemical injection rate obtained from the graphs of FIGS. Although it is possible, it was found that when rainwater was mixed into the water to be treated, the aggregation state deteriorated at this chemical injection rate.

For example, when surface runoff water due to rainfall is mixed with biological sludge-containing treated water, the SS concentration in the treated water considerably rises due to the sediment content of the surface runoff water. As the SS concentration rises, the drug injection rate is correspondingly reduced based on the graphs in Figures 2 and 3. However, even if the drug injection rate is reduced, the way of lowering is insufficient, resulting in excessive drug injection and significant foaming. Was found to cause

The present invention solves the above problems of the prior art and provides a method of adjusting the amount of chemical injection (amount of coagulant added) to an appropriate amount even when water is mixed with water to be treated due to rainfall. The purpose is to provide.

[0010]

The method for adjusting the amount of coagulant added according to the present invention is a method for adjusting the amount of coagulant added in a coagulation separation treatment method in which a coagulant is added to water to be treated and then a solid-liquid separation treatment is carried out. When the water to be treated is mixed with water due to rainfall, a rainfall detector is provided, and the addition amount of the coagulant is adjusted based on the rainfall detection signal from the rainfall detector. .

The coagulant addition amount adjusting device of the present invention comprises a coagulating / separating device for adding a coagulant to a water to be treated containing a suspension for solid-liquid separation, and a flow rate of the water to be treated flowing into the coagulating / separating device. A flow meter for detecting, an SS concentration meter for detecting the concentration of suspended matter in the water to be treated, a rainfall detector for detecting rainfall, an addition amount adjusting means for adjusting the coagulant addition amount, and the addition amount adjustment A calculator for calculating an addition amount signal given to the means, wherein the calculator calculates the coagulant addition amount based on the signals from the flow meter and the SS concentration meter, and the signal from the rainfall detector. Based on the above, a calculation for correcting the addition amount of the coagulant is performed, and the calculation result is output to the addition amount adjusting means.

According to the coagulant addition amount adjusting method and apparatus of the present invention, by controlling the chemical injection amount in response to rainfall, the chemical injection amount at the time of rainfall becomes appropriate.

The present inventor has conducted various studies on the causes of foaming troubles during rainfall in the conventional biological sludge flocculation / separation apparatus. As a result, soil and sand are more easily dehydrated than biological sludge, and therefore SS of treated water flows in with rain. It was found that if the amount of soil (soil) increases, the amount of reduction should be larger (the amount of chemical injection should be smaller) than the amount of reduction in the amount of chemical injection that corresponds to the increase in the concentration of biological sludge.

That is, when the sediment enters the raw water pit of the water treatment equipment with rainfall, the sediment is separated in the first settling basin (first sedimentation) of the water treatment equipment, and the sludge generated from the first sedimentation contains the sediment. The SS concentration increases as much. Normally, in sludge treatment, this initial settled sludge is mixed with excess sludge from the biological process or sludge from the coagulation process to be dehydrated, but the earth and sand are SS components that are relatively easy to dehydrate, and the optimum chemical injection amount is biological sludge. Lower than. Therefore, when the SS concentration increases due to the inflowing sediment, the reduction rate of the chemical injection rate is made larger than that when the SS concentration increases only due to the biological sludge.

After adding the inorganic coagulant to the suspension water,
In the case of a facility for introducing coagulation and separation treatment into a sedimentation basin, when rainwater flows into raw water, not only the SS concentration decreases but also the water area load of the sedimentation basin increases due to an increase in the amount of treated water. Therefore, in this case, a larger dosage than the dosage corresponding to the reduced SS concentration (for example, the dosage read from FIG. 3) is used, which results in large and heavy floc flocs. Is generated.

[0016]

1 is a control system diagram of a water treatment device showing a coagulant addition amount adjusting method and device according to an embodiment.

When the water to be treated (raw water or mud supply) flows into the water treatment device, the flow rate is first measured by the flow meter 1,
Next, the SS concentration is measured by the SS concentration meter 2, and after the coagulant from the chemical injection pump 4 is added (chemical injection), it flows into the solid-liquid separation treatment facility 3 such as a sludge dehydrator or a coagulation sedimentation tank, Solid-liquid separation treatment by dehydration treatment or sedimentation treatment is performed.

The detection signals of the flow meter 1 and the SS concentration meter 2 and the signal from the rainfall detector 8 are input to the calculator 6.

Taking the case of dehydration treatment of biological sludge (the solid-liquid separation treatment equipment of the above reference 3 is a sludge dehydrator. The coagulant is a polymer coagulant) as an example, the amount of sludge supply Q (m
³ / h) is read by the signal from the flow meter 1, and the mud concentration C
(Kg / m ³ ) is read by the signal from the SS densitometer 2.
Next, the SS load F (kgDS / h, where DS is the total dry matter amount) is used as the mud supply amount Q (m ³ / h) and the mud concentration C.
It is determined by the product of (kg / m ³ ), that is, F = C × Q.

When there is no rainfall, this F value (kgDS
/ H) is applied to the graph of FIG. 2 (the contents of this graph are input to the calculator 6 in advance) to read the drug injection rate P (% / DS), and the drug injection rate P and SS load are read. The amount F is multiplied to calculate the drug injection amount. Assuming that the concentration of the chemical liquid to be dosed (concentrating agent concentration) is B (kg / m ³ ), the addition amount A (kg / m ³ ) of the chemical liquid is as follows.

A = P × F / (100 × B) (m ³ / h) This amount of A is the standard chemical injection amount, but when there is rainfall, 0.85 to 0.9 is added to this A. Multiply the degree of correction to obtain the corrected dose. Since this ratio varies depending on the soil and sludge properties at each site, the rate should be set according to the site.

The addition amount adjusting means is provided with an instruction signal indicating the calculated chemical injection amount (the above-mentioned reference chemical injection amount A during non-rainfall, and the corrected chemical injection amount during rain and during a predetermined time after rain). To the medicine injection controller 5, and this medicine injection controller controls the medicine injection pump 4 based on the medicine injection amount instruction signal.

In this way, by performing the chemical injection control in consideration of the SS concentration increase due to the inflow of sediment due to rainfall,
Appropriate aggregation treatment can be performed even during rainfall.

In the embodiment shown in FIG. 1, the water to be treated containing biological sludge is coagulated with a polymer coagulant, but the same control is performed when the suspension water is coagulated and separated with an inorganic coagulant. . However, in this case, the correction rate is set to, for example, 1.05 to 1.15 during rainfall. Using this corrected dosing rate, the dosing amount is calculated based on the total inflow SS amount in the same manner as above.

When the suspension water is subjected to the coagulation separation treatment with an inorganic coagulant such as a sulfuric acid band, the solid-liquid separation treatment equipment indicated by reference numeral 3 in the flow of FIG. 1 is used as a coagulation sedimentation tank. Then, when rainwater flows into the raw water due to rainfall, the chemical injection rate is increased more than the chemical injection rate obtained from FIG. 3 so that large-sized and heavy floc flocs are generated (for example, 1.05-
1.15 times). By generating large and heavy flocs in this way, it is possible to cope with an increase in the sedimentation pond water area load due to an increase in the amount of water accompanying rainwater inflow.

In order to perform such correction of the chemical injection amount, an input means 7 such as a keyboard connected to the arithmetic unit 6 is used.
A constant of 0.85 to 0.9, or 1.05 to 1.15 is given to the calculator 6, and the constant is multiplied by the dose.

Even when the optimum chemical injection rate deviates slightly from the graphs shown in FIGS. 2 and 3 due to variations in the type of sludge, a constant or a constant for compensating for this deviation from the input means 7 is also provided. , Or enter the data to update the graph itself to something else.

In the present invention, any instrument may be used as long as necessary information can be obtained, and a commercially available instrument can be used.

As the rainfall detector, a hygrometer, a rain gauge, a flow meter for grasping the amount of water flowing into the water treatment device, or the like can be used.

The hygrometer determines that there is rainfall when, for example, information of 98% or more relative humidity is input. The rain gauge determines that there is rainfall when a predetermined amount of rainfall is reached. In the flow meter (the installation position may be anywhere such as the inflow part to the raw water tank, any position of the water treatment device, and the treated water discharge part), it is determined that there is rainfall when the normal fluctuation range exceeds a predetermined amount.

The threshold value for determining the presence or absence of rainfall varies depending on the site where the aggregating apparatus is installed, such as the amount of rainfall when soil is mixed, the amount of rainfall when diluted and the agglomeration effect is affected, and so on. It is preferable to set each time from the experience value.

The addition amount adjusting means (chemical injection controller) 5 receives the output signal from the computing unit 6 (for example, DC 4 to 20 mA: the chemical injection amount is instructed to be 0 to 100% within this range) and the chemical injection amount is received. Anything that can control As the chemical-feeding controller, one that controls the number of rotations of a chemical-feeding motor with an inverter or the like and controls the number of rotations of a motor speed reducer is preferably used, but it is one that adjusts the valve opening of the chemical-feeding line. Is also good.

[0033]

As described above, according to the coagulant addition amount adjusting method and apparatus of the present invention, even if water is mixed into the water to be treated due to rainfall, an appropriate chemical dosing amount can be automatically obtained. Can be controlled.

[Brief description of drawings]

FIG. 1 is a control system diagram showing an embodiment.

FIG. 2 is a graph showing the amount of polymer aggregation to be dispensed.

FIG. 3 is a graph showing a dosage amount of a sulfuric acid band.

[Explanation of symbols]

 1 Flowmeter 2 SS Concentration Meter 3 Sludge Dewatering Machine or Solid-Liquid Separation Equipment such as Coagulation Sedimentation Tank 4 Chemical Dosing Pump 5 Addition Adjusting Means (Chemical Dosing Controller) 6 Computer 7 Input Means 8 Rainfall Detector

Claims (2)

[Claims] 1. A method for adjusting the addition amount of a coagulant in a coagulation separation treatment method in which a coagulant is added to treated water, and then solid-liquid separation treatment is performed. A coagulant addition amount adjusting method, wherein a detector is provided, and the coagulant addition amount is adjusted based on a rainfall detection signal from the rainfall detector. 2. An aggregating / separating device for adding a coagulant to water to be treated containing suspensions for solid-liquid separation, a flow meter for detecting the flow rate of the to-be-treated water flowing into the aggregating / separating device, An SS concentration meter for detecting the concentration of suspended solids in the treated water, a rainfall detector for detecting rainfall, an addition amount adjusting means for adjusting the addition amount of the coagulant, and an addition amount signal given to the addition amount adjusting means. And a computing unit that computes the coagulant addition amount based on the signals from the flow meter and the SS concentration meter, and corrects the coagulant addition amount based on the signal from the rainfall detector. Calculation
A coagulant addition amount adjusting device characterized in that the calculation result is output to an addition amount adjusting means.