Wastewater treatment method and equipment

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

[Technical Field]

[0001] The present invention relates to a method and apparatus for treating wastewater by coagulation and solid-liquid separation, and more particularly to a method and apparatus for treating wastewater in which a portion of the coagulated sludge is returned to a reaction tank and an alkaline agent such as slaked lime is added to the returned sludge. [Background technology]

[0002] High Density Sludge (HDS) methods, such as the alkaline sludge method, are known as methods for obtaining high-concentration sludge with excellent thickening and dewaterability by subjecting wastewater to coagulation and solid-liquid separation. In the alkaline sludge method, an alkali such as slaked lime (Ca(OH)2) is added to a portion of the sludge that is separated in the solid-liquid separation process that follows the coagulation process and returned.

[0003] Figure 2 is a system diagram showing a typical apparatus for a conventional high-density coagulation sludge treatment method. Raw water is adjusted to a pH of approximately 2.5 to 3.0 by the addition of a pH adjuster in raw water tank 1, and then introduced into reaction tank 2, where it is mixed with and reacted with modified sludge introduced from modification tank 8, which will be described later. This reaction liquid is then sent to coagulation tank 3, where a polymer coagulant is added by polymer coagulant addition means 3a for coagulation treatment, and then undergoes solid-liquid separation in settling tank 4. The supernatant water from settling tank 4 is discharged outside the system as treated water. A portion of the separated sludge extracted from settling tank 4 by pump 5 is returned to modification tank 8 via sludge return line 7, and the remainder is discharged outside the system via discharge line 6.

[0004] In the reforming tank 8, a dissolved / dispersed solution of slaked lime (a liquid in which part of the slaked lime is dissolved and the rest is dispersed) supplied by slaked lime supplying means 9 as an alkaline agent supplying means is mixed with the returned sludge. This mixed solution (modified sludge) is supplied to the reaction tank 2. The reaction in this reaction tank 2 is preferably carried out within a predetermined pH range (for example, 6 to 11, particularly 6 to 8), and the amount of slaked lime supplied to the reforming tank 8 is adjusted based on the pH detected by a pH meter 2a provided in the reaction tank 2 so as to achieve this pH range.

[0005] 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 outside 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 using a control means (not shown). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-7879 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-71469 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-208599 Summary of the Invention [Problem to be solved by the invention]

[0007] In the conventional example shown in Figure 2, when valve 11 is opened, valve 12 is closed, and the entire amount of sludge is discharged outside the system through discharge line 6, there is no sludge return to the reforming tank 8, so the supply of modified sludge (slaked lime-added sludge) from the reforming tank 8 to the reaction tank 2 is reduced or stopped, and the pH of the reaction tank 2 falls below a predetermined range. If valve 12 is then opened and valve 11 is closed to resume sludge return to the reforming tank 8, a large amount of high-pH modified sludge flows in from the reforming tank 8, causing a rapid rise in the pH of the reaction tank 2. Such a rapid pH change can lead to poor sludge modification and coagulation, which can result in a deterioration in the quality of the treated water or a high moisture content of the sludge discharged from the discharge line 6.

[0008] An object of the present invention is to provide a method and apparatus for treating wastewater that can stabilize the flow rate of the alkaline agent-added liquid flowing from the reforming tank to the reaction tank, thereby always maintaining good treated water quality and discharged sludge properties. [Means for solving the problem]

[0009] In order to solve the above problems, the wastewater treatment method and apparatus of the present invention are summarized as follows.

[0010] [1] Add alkaline agent-added return sludge to the wastewater to cause a reaction, then perform coagulation treatment, 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 modification tank, and the alkaline agent is added to the wastewater. In a wastewater treatment method in which the remainder of the sludge is extracted and discharged as sludge, A method for treating wastewater, comprising the step of supplying water to the reforming tank from a water supply line when the return of sludge to the reforming tank is stopped or when the amount of sludge returned falls below a predetermined amount.

[0011] [2] The wastewater treatment method according to [1], wherein water is supplied to the reforming tank through the water supply line when the return of sludge from the settling tank to the reforming tank is stopped.

[0012] [3] The method for treating wastewater 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.

[0013] [4] The method for treating wastewater according to any one of [1] to [3], wherein the water is industrial water.

[0014] [5] A reaction tank in which alkaline agent-added return sludge from the reforming tank is added to the wastewater; a coagulation tank for adding a polymer coagulant to the liquid from the reaction tank; a solid-liquid separation means for separating the flocculation treatment liquid to which the flocculant has been added into solid and liquid; a modification tank in which an alkaline agent is added to a portion of the sludge separated by the solid-liquid separation means to produce alkaline agent-added return sludge; In a wastewater treatment device comprising: The wastewater treatment device is characterized in that a water supply line capable of supplying water to the reforming tank is provided.

[0015] [6] A valve is provided on a line for returning the sludge separated by the solid-liquid separation means to the reforming tank, The wastewater treatment device according to [5], further comprising a water supply control means for supplying water from the water supply line to the reforming tank when the valve is closed. [Effects of the Invention]

[0016] 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 decreases, water is supplied to the reforming tank, and the alkaline agent-added solution is introduced from the reforming tank into the reaction tank, thereby maintaining the pH of the reaction tank within a predetermined range. As a result, coagulation is always performed well, improving the quality of the treated water and reducing the water content of the sludge. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a flow diagram for explaining a wastewater treatment method and device according to an embodiment. [Figure 2] FIG. 1 is a flow chart for explaining a wastewater treatment method and device according to a conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment will be described 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. Note that the same parts as those in Fig. 2 are assigned the same reference numerals.

[0019] In this embodiment, as in Figure 2, raw water is adjusted to a pH of approximately 2.5 to 3.0 by the addition of a pH adjuster in raw water tank 1, and then introduced into reaction tank 2, where it is mixed with and reacted with modified sludge introduced from modification tank 8. This reaction liquid is then sent to coagulation tank 3, where a polymer coagulant is added by polymer coagulant addition means 3a for coagulation treatment, and then undergoes solid-liquid separation in settling tank 4. The supernatant water from settling tank 4 is discharged outside the system as treated water. A portion of the separated sludge extracted from settling tank 4 by pump 5 is returned to modification tank 8 via sludge return line 7, and the remainder is discharged outside the system via discharge line 6.

[0020] In the reforming tank 8, a dissolved / dispersed solution of slaked lime supplied by slaked lime supplying means 9, which serves as an alkaline agent supplying means, is mixed with the returned sludge. This mixed solution (modified sludge) is supplied to the reaction tank 2. The reaction in this reaction tank 2 is preferably carried out within a predetermined pH range (for example, 6 to 11, particularly 6 to 8), and the amount of slaked lime supplied to the reforming tank 8 is adjusted based on the pH detected by a pH meter 2a provided in the reaction tank 2 so as to maintain this pH range.

[0021] 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 outside 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 using a control means (not shown).

[0022] In this embodiment, a water supply line 14 is provided for supplying water to the reforming tank 8, and a valve 13 is provided on the water supply line 14. The valve 13 may be an open / close valve or a flow rate control valve that can adjust the flow rate.

[0023] This valve 13 is opened by a control means (not shown) when valve 11 is open and valve 12 is closed, and when valve 12 is open and valve 11 is closed, valve 13 is closed.

[0024] Examples of water supplied from the water supply line 14 include industrial water, well water, city water, river water, and wastewater treatment process flow water, with industrial water being particularly preferred.

[0025] When valve 12 is closed and valve 13 is opened to supply water to reforming tank 8, the amount of water supplied is preferably set to be the same as the amount of returned sludge when valve 12 is open.

[0026] In this embodiment, when the return of sludge from the settling tank 4 to the reforming tank 8 is stopped, water is supplied to the reforming tank 8 through the water supply line 14, and an alkaline slaked lime-containing liquid is introduced from the reforming tank 8 to the reaction tank 2. As a result, the pH in the reaction tank 2 is always kept within a predetermined range (preferably 6 to 11, and particularly preferably 6 to 8), the coagulation reaction proceeds sufficiently, the treated water quality is improved, and the water content of the coagulated sludge discharged from the discharge line 6 is low.

[0027] Examples of raw water to be treated in the present invention include, but are not limited to, fluorine-containing wastewater, phosphorus-containing wastewater, and wastewater containing heavy metals such as iron, zinc, copper, chromium, nickel, lead, and aluminum.

[0028] In the above embodiment, slaked lime is added as an alkaline agent to the reforming tank 8, but the present invention is not limited to this, and in the case of wastewater containing heavy metals, caustic soda or the like may also be used.

[0029] The above embodiment is one example of the present invention, and the present invention may be embodied in other forms. For example, the valves 12 and 13 may be designed to be flow-adjustable, so that the amount of sludge returned to the reforming tank 8 can be adjusted to increase or decrease, and the amount of water supplied from the water supply line 14 to the reforming tank 8 may be increased so that the amount of sludge returned to the reforming tank 8 becomes smaller than the amount of sludge returned when the valve 12 is fully open. [Explanation of symbols]

[0030] 2. Reaction vessel 3 Coagulation reactor 4 Settling tank 8. Reforming tank 9. Means of adding slaked lime 14 Water supply line

Claims

1. The alkaline agent-added return sludge is added to the wastewater to cause a reaction, followed by coagulation treatment, followed by solid-liquid separation treatment in a settling tank to separate the sludge from the treated water, A part of the separated sludge is used as return sludge, and this return sludge is introduced into a modification tank, an alkaline agent is added, and the alkaline agent-added return sludge is added to the wastewater; In a wastewater treatment method in which the remainder of the sludge is extracted and discharged as sludge, A method for treating wastewater, comprising the step of supplying water to the reforming tank from a water supply line when the return of sludge to the reforming tank is stopped or when the amount of sludge returned falls below a predetermined amount.

2. 2. The method for treating wastewater according to claim 1, wherein water is supplied to said reforming tank through said water supply line when sludge return from said settling tank to said reforming tank is stopped.

3. 3. The method for treating wastewater according to claim 2, wherein the amount of water supplied to said reforming tank is the same as the amount of sludge returned when said sludge extraction is stopped.

4. 4. The method for treating wastewater according to claim 1, wherein the water supplied to the reforming tank is industrial water.

5. a reaction tank in which the alkaline agent-added return sludge from the reforming tank is added to the wastewater; a coagulation tank for adding a polymer coagulant to the liquid from the reaction tank; a solid-liquid separation means for separating the flocculation treatment liquid to which the flocculant has been added into solid and liquid; a modification tank in which an alkaline agent is added to a portion of the sludge separated by the solid-liquid separation means to produce alkaline agent-added return sludge; In a wastewater treatment device comprising: A wastewater treatment device provided with 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; a water supply control means for supplying water from the water supply line to the reforming tank when the valve is closed;

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