JPH08323109A - Flocculating and settling device - Google Patents

Abstract

PURPOSE: To efficiently perform sedimentation to obtain supernatant-treated water by completely preventing a return pipe for returning sludge from a precipitator to a reaction tank from being clogged with sludge, and thereby returning sludge in the precipitator to the reaction tank to add sludge-containing water thereto and heighten sedimentation of sludge in the precipitator. CONSTITUTION: This flocculating and settling device is provided with a reaction tank 10 for receiving raw water, returned sludge and a precipitant to react them with each other, a precipitator 14 for introducing outflow water from the reaction tank to perform solid-liquid separation to settle the reaction product and also discharging the supernatant water, a return pipe 16 for returning the settled sludge in the precipitator 14 to the reaction tank 10, and a sludge discharge pipe 26 having a sludge discharge valve and for discharging the settled sludge outside the system. The precipitator 14 is provided with a sludge concentration detecting part 23 consisting of a sludge gathering and circulating pipe 24 having an opened inlet end near the sludge interface on normal operation to gather sludge in the tank and returning the gathered sludge to the precipitator 14 and a sludge concentration meter 25 connected in midway of the circulating pipe 24, and by a signal of the sludge concentration meter 25, opening/ closing of the sludge discharge valve of the sludge discharge pipe is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to add raw water containing various pollutants to a precipitating agent suitable for the components of the pollutants in a reaction tank and mix them. The present invention relates to a flocculation / sedimentation apparatus that separates and sediments contaminants to obtain supernatant water.

[0002]

2. Description of the Related Art In such coagulation / precipitation treatment, if a part of the sludge settled in the settling tank is returned to the reaction tank, the returned sludge becomes a nucleus during the coagulation reaction and the precipitation reaction in the reaction tank to cause crystallization. Due to the effect and the like, a precipitate is further deposited on the surface of the core, which promotes the densification and size increase of the sludge, resulting in a sludge having an excellent settling property. For this reason, when the raw water containing this sludge is subjected to solid-liquid separation in the settling tank, the sludge is concentrated and the concentration becomes high, and the sludge is discharged to reduce the sludge capacity and the waste sludge volume. However, if such sludge stagnates more than necessary in the settling tank, the sludge is concentrated too much, and the sludge discharge pipe and the return pipe to the reaction tank are clogged with sludge, and the sludge at the bottom of the settling tank is removed. Excessive load is applied to the rake that is pulled into the pit, which may cause malfunction. If sludge is frequently discharged from the settling tank in order to avoid this trouble, only unconcentrated slurry or water will be discharged, and a facility for reconcentrating the slurry is required.

[0003]

Therefore, how much sludge is accumulated in the settling tank is determined by the interface (upper surface) of the sludge.
The sludge is opened to a certain extent and the sludge valve is opened to discharge the sludge from the settling tank, and when the accumulated amount is small, the sludge valve is closed and the sludge is waited for to accumulate. It has been proposed to control such problems and deal with troubles such as clogging of the drainage pipe and return pipe. However, in order to detect the interface of sludge, it is necessary to suspend a sludge interfacial meter using ultrasonic waves in the liquid of the sedimentation tank, or to permanently install the sludge interfacial meter in the liquid of the sedimentation tank. However, since the liquid in the settling tank is dirty, the sensor unit and transmitter of the sludge interface meter are contaminated, and the sludge interface cannot be accurately detected.
Also, when the sludge interfacial meter is suspended in the liquid, the sludge interfacial meter should be frequently raised above the surface of the water to clean the sensor part and the transmission part. The equipment for submersion and withdrawal also becomes large-scale, and maintenance work becomes a difficult task.

[0004]

Means for Solving the Problems The present invention is intended to solve the above-mentioned problems, and is a reaction tank for receiving raw water, return sludge, and a precipitant to react with each other, and water flowing out from the reaction tank. Introduce the solid-liquid separation, settling the reaction product and discharging the supernatant water, and a return pipe for returning the settling sludge of the settling tank to the reaction tank, and a sludge valve, and settling sludge In a coagulation sedimentation device equipped with a sludge pipe that discharges to the outside of the system, in the sedimentation tank, open the inlet end near the sludge interface during normal operation and collect the sludge in the tank and settle the collected sludge. A sludge concentration detection unit consisting of a sludge collection pipe for collecting sludge to be returned to the tank and a sludge concentration meter connected in the middle of this collection and circulation pipe is provided.
It is characterized in that the opening and closing of the sludge discharge valve of the sludge pipe is controlled by a signal from a sludge concentration meter.

[0005]

Embodiment In the illustrated embodiment, 10 is a stirrer 11,
In a reaction tank having a chemical injection device 12, raw water containing contaminants is supplied by a supply pipe 13 and a pump P1. In the illustrated embodiment, raw water containing fluorine is treated, so that the first, second and third reactors are connected in series, and the first reactor 10 is used.
In -1, NaOH is dosed to make the pH of the raw water neutral, and in the second reaction vessel 10-2, a calcium source such as calcium chloride is dosed to make fluorine an insoluble compound of CaF ₂ , and the third reaction vessel 10-2 is used. In -3, a polymer flocculant (polymer) is dosed to cause a flocculation reaction.

In the first reaction tank 10-1, the sludge settled in the settling tank 14 is sludge discharge pit 15 in the tank, a return pipe 16,
It is supplied through the return pump P2 and uniformly mixed by the rotation of the stirrer 11.

The dwell time in each reaction tank is several minutes to several tens of minutes, during which mixing and reaction are carried out, and the reacted raw water is discharged from the third reaction tank 10-3 through the discharge pipe 17. It is supplied to the inside of the feed well 18 at the center of the settling tank 14. The rake 19 rotates along the bottom surface of the sludge basin of the settling tank, and the sludge settling on the bottom surface is scraped into the central discharge pit 15. The rotary shaft 20 of the rake 19 is supported by penetrating the center of the feed well 18, and is rotationally driven by a motor. The sludge sedimentation interface (upper surface) 21 is below the lower end of the feed well 18.

The supernatant water obtained by settling and separating sludge in the settling tank is
It is discharged as treated water above the interface of the settled sludge, for example, from the drain pipe 22 connected to the tank wall at the same level as the discharge pipe 17.

[0009] 24 is the collection of sludge connected to the pump P3,
In the circulation pipe, its inlet end 24 'opens at the sedimentation interface of the sludge during normal operation of the sedimentation tank or at a position slightly higher than that, for example, at a position 5 to 30 cm above the rotary arm of the rake 19, and the pump P3 The sludge is sucked from the inlet end 24 ′ by the operation and supplied into the feedwell 18 from above.
A sludge concentration meter 25 is connected to the sampling and circulation pipe at a position outside the settling tank downstream of the pump P3. Collection of the above sludge,
The circulation pipe 24 and the sludge concentration meter 25 constitute a sludge concentration detection unit 23. The sludge densitometer 25 may be any known one, for example, an ultrasonic turbidimeter, a photoelectric tube turbidimeter, a pressure-sensing densitometer, etc. In short, sludge of sludge liquid flowing in the pipe 24. Anything can be used as long as it is possible to know whether the concentration of is high or low.

Then, a sludge discharge pit 15 or a sludge discharge pipe 2 having a discharge valve V in the return pipe 16 as shown in the drawing.
6 is provided to transmit a signal from the sludge concentration meter 25 to the sludge discharge valve V via the control unit 27 to control the opening / closing of the sludge discharge valve.

The mode of control is as follows. During normal operation of the settling tank, when the sludge is collected and the inlet end 24 'of the circulation pipe is located above the interface 21 of the sludge, the sludge is collected and the concentration of the sludge liquid sucked into the circulation pipe is low. Sludge concentration meter 25
Indicates, for example, several hundred mg / stand. At this time, the sludge valve V
Keep closed. When the sludge interface rises and reaches the inlet end 24 ', a high concentration of sludge liquid is sucked in, and the sludge densitometer measures, for example, several thousand to several hundred thousand mg / liter, depending on the concentration. And the mud discharge valve V is opened at this time. As a result, the sludge in the settling tank is discharged from the sludge pipe 26,
The sludge interface 21 goes down. Then, when the sludge interface is lowered and the concentration of the sludge liquid collected and sucked into the circulation pipe becomes the original state (for example, several 100 mg / stand), the sludge discharge valve is closed.

In this case, when the mud discharge valve is continuously opened, the interface of the sludge is rapidly lowered, and the supernatant water on the interface is discharged from the mud pipe. For this reason, a timer is incorporated in the control unit 27, and when there is a command from the sludge concentration meter 25 to open the sludge valve, the control unit opens the sludge valve intermittently by the timer, and the sludge interface is rapidly opened. It is desirable to prevent the deterioration and clearing of clear water.

FIG. 2 shows the transmitting portion 2 on the inner wall surfaces of a small closed detection chamber 28 connected to a sludge collection and circulation pipe, which face each other.
9 and a receiver 30 are provided, and a sludge densitometer for detecting the concentration of a suspended sludge liquid flowing in the room by changing the amount of light or ultrasonic waves transmitted or reflected, Has an inlet and outlet 31a, 31b for washing water that can be opened and closed with a valve,
It is advisable to flush the cleaning water regularly so that the dirt attached to the transmitter and the receiver can be removed. Also, this detection chamber 2
8 may be detachably provided in the sludge collection and circulation pipes and periodically removed to check the degree of contamination. Furthermore, by forming the detection chamber, sludge collection, and part of the circulation pipe with a transparent member, changes in the sludge concentration can be visually checked and the detection result of the sludge concentration meter can be confirmed.

Further, as shown in FIG. 3, a small open container 32 is connected to the sludge collection and circulation pipe, and a transmitting part 29 and a receiving part 30 are provided on the opposite wall surfaces in this container, as shown in FIG. Similarly, the sludge concentration may be known. In this case, since it is an open type, it is possible to visually check the state of contamination of the transmitting unit and the receiving unit and to easily perform cleaning.

Fluorine concentration of 10 with the coagulation-sedimentation apparatus of FIG.
100 to 2000 mg / liter of raw water was treated. The sludge concentration increased to 400 to 500 g / stand in about one week. Sludge valve V
When the operation was continued while keeping the valve closed, the return pipe and the mud pipe were clogged about one month later. This is because in the circulation method in which the settling sludge in the settling tank is returned to the reaction tank and circulated, the settling property of the sludge generated in the settling tank is extremely good, so if the sludge accumulates too much in the settling tank, it will be concentrated more than necessary. It is presumed that the cause is the occurrence.

On the other hand, every time the sludge interface rises and the sludge concentration meter 25 reaches 10000 mg / stand, the sludge valve V is opened and the sludge is discharged from the sludge pipe 26.
When the mud discharge valve was closed at 00 mg / stand, no blockage occurred in the return pipe or the mud pipe even after continuous operation for 3 months.

[0017]

As is apparent from the above, according to the present invention, it is possible to completely prevent clogging of sludge in the return pipe for returning sludge from the settling tank to the reaction tank and the sludge discharge pipe for discharging sludge. ,
Thereby, the sludge in the settling tank is returned to the reaction tank and mixed with the water containing pollutants, the sedimentation property of the sludge in the settling tank is enhanced, and the sludge is efficiently separated to obtain the supernatant treated water.

[Brief description of drawings]

FIG. 1 is a flow sheet of an embodiment of a coagulating sedimentation device of the present invention.

FIG. 2 is a sectional view of a first example of a sludge concentration meter.

FIG. 3 is a sectional view of a second example of a sludge concentration meter.

[Explanation of symbols]

 10 Reaction Tank 11 Stirrer 12 Chemical Injection Device 13 Supply Pipe 14 Sedimentation Tank 15 Sludge Discharge Pit 16 Sludge Return Pipe 17 Discharge Pipe 18 Feedwell 19 Rake 20 Rake Rotation Shaft 21 Sludge Sedimentation Interface 22 Drainage Pipe 23 Sludge Concentration Detector 24 Sludge collection and circulation pipe 25 Sludge concentration meter 26 Exhaust pipe 27 Control section 28 Sludge concentration meter detection room 29 Transmitting section 30 Receiver section 32 Sludge concentration meter open container

Claims (1)

[Claims] 1. A reaction tank for receiving raw water, returned sludge, and a precipitating agent to react with each other, and introducing outflow water from the reaction tank for solid-liquid separation to precipitate a reaction product and discharge supernatant water. In the coagulating sedimentation device having a settling tank that performs the above, a return pipe that returns settling sludge from the settling tank to the reaction tank, and a sludge discharge valve, and a sludge pipe that discharges the settling sludge to the outside of the system, , Open the inlet end near the sludge interface during normal operation, collect the sludge in the tank, and return the collected sludge to the settling tank. A sludge concentration detector comprising the above sludge concentration meter, and the opening and closing of the sludge discharge valve of the sludge pipe is controlled by the signal of the sludge concentration meter.