JP2023075533A - Method and apparatus for treating waste water - Google Patents

Abstract

To provide a method and an apparatus for treating waste water which make a flow rate flowing to a reaction tank from a modification tank stable, and can always make treatment water quality and discharged sludge property good.SOLUTION: A method for treating waste water introduces raw water into a reaction tank 2, mixes the raw water with slaked lime addition and return sludge from a modification tank 8, and then adds a polymer flocculant to a flocculation tank 3 and carries out flocculating treatment. The method introduces a flocculated liquid into a precipitation tank 4 and separates the sludge. The method introduces a part of the sludge to the modification tank 8 by a sludge return line 7. When a valve 12 of the sludge return line 7 is closed, the method opens a valve 13 of a water supply line 14, supplies water to the modification tank 8, and supplies slaked lime addition water to the reaction tank 2.SELECTED DRAWING: Figure 1

Description

The present invention relates to a wastewater treatment method and apparatus for flocculating and solid-liquid separation treatment of wastewater, and in particular, part of the flocculated sludge is returned to the reaction tank, and an alkaline agent such as slaked lime is added to the returned sludge. The present invention relates to a method and apparatus for treating wastewater.

A high density sludge method (HDS method) such as an alkaline sludge method is known as a method for obtaining highly concentrated sludge with excellent dehydration properties by subjecting wastewater to coagulation and solid-liquid separation. there is In the alkaline sludge method, an alkali such as slaked lime (Ca(OH) ₂ ) is added to part of the sludge that is separated and returned in the solid-liquid separation treatment in the latter stage of the flocculation treatment.

FIG. 2 is a system diagram showing a typical device for a conventional high-density flocculated sludge treatment method. After that, it is introduced into the reaction tank 2 and mixed with the reformed sludge introduced from the reforming tank 8 to be described later to react. This reaction liquid is then fed to the flocculation tank 3 , where a polymer flocculant is added by the polymer flocculant addition means 3 a to flocculate, and then solid-liquid separation is performed in the sedimentation tank 4 . The supernatant water in the sedimentation tank 4 is discharged out of the system as treated water. A part of the separated sludge withdrawn from the sedimentation tank 4 by the pump 5 is returned to the reforming tank 8 through the sludge return line 7, and the remainder is discharged out of the system through the discharge line 6.

In the reforming tank 8, a slaked lime solution/dispersion liquid (liquid in which slaked lime is partly dissolved and the rest is dispersed) supplied by a slaked lime addition means 9 as an alkali agent addition means is mixed with the returned sludge. be. This mixed liquid (modified sludge) is supplied to the reaction tank 2 . The reaction in this reaction tank 2 is preferably carried out in a predetermined pH range (for example, 6 to 11, particularly 6 to 8). The amount of slaked lime supplied to the reforming tank 8 is adjusted based on the pH.

The sludge discharge line 6 and the sludge return line 7 are provided with open/close valves 11 and 12, respectively. By opening the valve 11 and closing the valve 12, the entire amount of sludge from the pump 5 is discharged out of the system. By opening the valve 12 and closing the valve 11 , the entire amount of sludge from the pump 5 is returned to the reforming tank 8 . The amount of sludge returned to the reforming tank 8 is controlled by switching the opening and closing of the valves 11 and 12 by control means (not shown).

JP-A-5-7879 Japanese Unexamined Patent Application Publication No. 2003-71469 JP 2013-208599 A

In the conventional example shown in FIG. 2, when the valve 11 is opened, the valve 12 is closed, and the entire amount of sludge is discharged from the discharge line 6 to the outside of the system, the sludge is not returned to the reforming tank 8. The supply of modified sludge (slaked lime added sludge) from 8 to reaction tank 2 decreases or stops, and the pH of reaction tank 2 becomes lower than the predetermined range. After that, the valve 12 is opened, the valve 11 is closed, and the sludge return to the reforming tank 8 is restarted. Rise. Due to such a rapid pH change, sludge reforming and coagulation become poor, and the quality of treated water may deteriorate, or the moisture content of the sludge discharged from the discharge line 6 may increase.

An object of the present invention is to provide a wastewater treatment method and apparatus capable of stabilizing the flow rate of an alkaline agent additive liquid flowing from a reforming tank into a reaction tank and constantly improving the quality of treated water and the properties of discharged sludge. and

In order to solve the above problems, the wastewater treatment method and apparatus of the present invention are summarized as follows.

[1] Add alkaline agent-added returned sludge to waste water to react it, then coagulate it, and then separate the sludge from the treated water by solid-liquid separation treatment,
A part of the separated sludge is used as return sludge, and the return sludge is introduced into a reforming tank, and the alkali agent is added to the waste water,
In a wastewater treatment method in which the remaining sludge is extracted and discharged as sludge,
A method for treating wastewater, wherein water is supplied from a water supply line to the reforming tank when the return of sludge to the reforming tank stops or the amount of sludge returned falls below a predetermined amount.

[2] The wastewater treatment method of [1], wherein water is supplied to the reforming tank through the water supply line when the return of sludge from the sedimentation tank to the reforming tank is stopped.

[3] The wastewater treatment method according to [2], wherein the amount of water supplied to the reforming tank is the same as the amount of sludge returned when the sludge extraction is stopped.

[4] The method for treating wastewater according to any one of [1] to [3], wherein the water is industrial water.

[5] a reaction tank for adding alkaline agent-added returned sludge from the reforming tank to waste water;
a flocculation tank for adding a polymer flocculant to the liquid from the reaction tank;
solid-liquid separation means for solid-liquid separation of the aggregating treatment liquid to which the aggregating agent has been added;
A wastewater treatment apparatus comprising a reforming tank, wherein an alkaline agent is added to a portion of the sludge separated by the solid-liquid separation means to produce the alkaline agent-added return sludge,
A wastewater treatment apparatus, comprising a water supply line capable of supplying water to the reforming tank.

[6] A valve is provided in a line for returning the sludge separated by the solid-liquid separation means to the reforming tank,
The waste water treatment apparatus according to [5], comprising water supply control means for supplying water from the water supply line to the reforming tank when the valve is closed.

According to the wastewater treatment method and apparatus of the present invention, even when the amount of sludge returned from the solid-liquid separation means to the reforming tank is reduced, water is supplied to the reforming tank. is introduced into the reaction tank, and the pH of the reaction tank is kept within a predetermined range. As a result, the coagulation is always performed well, the quality of the treated water is improved, and the sludge water content is low.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart for demonstrating the waste-water-processing method and apparatus which concern on embodiment. FIG. 2 is a flowchart for explaining a conventional wastewater treatment method and apparatus.

Embodiments will be described below with reference to the drawings. FIG. 1 is a flow diagram of a wastewater treatment facility to which a wastewater treatment method according to an embodiment of the present invention is applied. The same parts as those in FIG. 2 are denoted by the same reference numerals.

In this embodiment, as in FIG. 2, the raw water is adjusted to about pH 2.5 to 3.0 by adding a pH adjuster in the raw water tank 1, and then introduced into the reaction tank 2 for reforming. It is mixed with the reformed sludge introduced from the tank 8 and reacts. This reaction liquid is then fed to the flocculating tank 3 , where a polymer flocculant is added by the polymer flocculant addition means 3 a to flocculate, and then solid-liquid separated in the sedimentation tank 4 . The supernatant water in the sedimentation tank 4 is discharged out of the system as treated water. A part of the separated sludge withdrawn from the sedimentation tank 4 by the pump 5 is returned to the reforming tank 8 through the sludge return line 7, and the remainder is discharged out of the system through the discharge line 6.

In the reforming tank 8, the slaked lime solution/dispersion supplied by the slaked lime adding means 9 as the alkaline agent adding means is mixed with the returned sludge. This mixed liquid (modified sludge) is supplied to the reaction tank 2 . The reaction in this reaction tank 2 is preferably carried out in a predetermined pH range (Examples 6 to 11, especially 6 to 8). The amount of slaked lime supplied to the reforming tank 8 is adjusted based on the pH.

The sludge discharge line 6 and the sludge return line 7 are provided with open/close valves 11 and 12, respectively. By opening the valve 11 and closing the valve 12, the entire amount of sludge from the pump 5 is discharged out of the system. By opening the valve 12 and closing the valve 11 , the entire amount of sludge from the pump 5 is returned to the reforming tank 8 . By switching the opening and closing of the valves 11 and 12 by control means (not shown), the amount of sludge returned to the reforming tank 8 is controlled.

In this embodiment, a water supply line 14 for supplying water to the reforming tank 8 is provided, and the water supply line 14 is provided with a valve 13 . The valve 13 may be an open/close type valve or a flow control valve capable of adjusting the flow rate.

The valve 13 is opened by control means (not shown) when the valve 11 is open and the valve 12 is closed. Also, when the valve 12 is open and the valve 11 is closed, the valve 13 is closed.

Examples of the water supplied from the water supply line 14 include industrial water, well water, city water, river water, and running water from the wastewater treatment method, among which industrial water is preferred.

The amount of water supplied to the reforming tank 8 by opening the valve 13 when the valve 12 is closed is preferably set to be the same as the amount of returned sludge when the valve 12 is open.

Thus, in this embodiment, when the return of sludge from the sedimentation tank 4 to the reforming tank 8 is stopped, water is supplied to the reforming tank 8 through the water supply line 14. An alkaline slaked lime-containing liquid is introduced into the reaction tank 2 from . For this reason, the pH in the reaction tank 2 is always kept within a predetermined range (preferably 6 to 11, particularly preferably 6 to 8), the aggregation reaction is sufficiently performed, the quality of the treated water is improved, and the discharge line 6 The moisture content of the flocculated sludge discharged from is low.

Examples of raw water to be treated in the present invention include, but are not limited to, fluorine-containing wastewater, phosphorus-containing wastewater, and heavy metal-containing wastewater such as iron, zinc, copper, chromium, nickel, lead, and aluminum.

In the above embodiment, slaked lime is added as an alkali agent to the reforming tank 8, but the present invention is not limited to this, and in the case of heavy metal-containing waste water, caustic soda or the like may be used.

The above-described embodiment is an example of the present invention, and the present invention may be made into aspects other than those described above. For example, the valves 12 and 13 are made flow rate adjustable so that the amount of sludge returned to the reforming tank 8 can be increased or decreased, and the amount of sludge returned to the reforming tank 8 is greater than the amount of sludge returned when the valve 12 is fully open. The amount of water supplied from the water supply line 14 to the reforming tank 8 may be increased as the amount of water decreases.

2 reaction tank 3 coagulation reaction tank 4 sedimentation tank 8 reforming tank 9 slaked lime addition means 14 water supply line

Claims (6)

Alkali agent-added returned sludge is added to the wastewater to react with it, then after flocculation treatment, solid-liquid separation treatment is performed to separate the sludge from the treated water,
A part of the separated sludge is used as return sludge, and the return sludge is introduced into a reforming tank, and the alkali agent is added to the waste water,
In a wastewater treatment method in which the remaining sludge is extracted and discharged as sludge,
A method for treating wastewater, wherein water is supplied from a water supply line to the reforming tank when the return of sludge to the reforming tank stops or the amount of sludge returned falls below a predetermined amount. 2. The method of treating waste water according to claim 1, wherein water is supplied to said reforming tank through said water supply line when the return of sludge from said sedimentation tank to said reforming tank is stopped. 3. The waste water treatment method according to claim 2, wherein the amount of water supplied to said reforming tank is the same amount as the amount of sludge returned when said sludge extraction is stopped. The method for treating wastewater according to any one of claims 1 to 3, wherein the water is industrial water. a reaction tank for adding alkaline agent-added return sludge from the reforming tank to waste water;
a flocculation tank for adding a polymer flocculant to the liquid from the reaction tank;
solid-liquid separation means for solid-liquid separation of the aggregating treatment liquid to which the aggregating agent has been added;
A wastewater treatment apparatus comprising a reforming tank, wherein an alkaline agent is added to a portion of the sludge separated by the solid-liquid separation means to produce the alkaline agent-added return sludge,
A wastewater treatment apparatus, comprising a water supply line capable of supplying water to the reforming tank. A valve is provided in a line for returning the sludge separated by the solid-liquid separation means to the reforming tank,
6. A waste water treatment apparatus according to claim 5, further comprising water supply control means for supplying water from said water supply line to said reforming tank when said valve is closed.

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