JP2001252668A - Sewage treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately transfer a sparingly-soluble metal salt formed near an electrode. SOLUTION: The treated water introduced into a tank 1 from its inlet 6 is passed successively through a first anaerobic leakage-bed tank 5, a second anaerobic leakage-bed tank 10 and a contact aeration tank 14 and conducted to a settling tank 19. An electrolytic unit including coupled electrodes 51 and 52 is provided in the aeration tank 14. A metal ion is electrolytically formed by the electrodes 51 and 52, and the metal ion reacts with the phosphorus compound in the treated water to form a sparingly water-soluble metal salt. The electrodes 51 and 52 are set in a case 54. A third diffuser pipe 53 is furnished in the case 54. Bubbles are jetted from the pipe 53 to cause a convection in the case 54, and the phosphorus compound is efficiently supplied near the electrodes 51 and 52. Meanwhile, the case 54 does not have a bottom. Consequently, the sparingly-soluble metal salt formed near the electrodes 51 and 52 is rapidly conducted to the lower part by gravity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sewage treatment apparatus, and more particularly to a sewage treatment apparatus for electrolyzing an electrode to precipitate a phosphorus component in treated water into a hardly soluble metal salt in water.

[0002]

2. Description of the Related Art A conventional sewage treatment apparatus is provided with an electrode,
In some cases, a phosphorus component in the treated water is converted into a metal salt that is hardly soluble in water and precipitated by metal ions generated by electrolysis of the electrode.

[0003] In a conventional sewage treatment apparatus, the electrodes are installed in an electrolytic cell. FIG. 7 schematically shows an electrolytic cell in a conventional sewage treatment apparatus.

Referring to FIG. 7, an electrolytic cell 100 has electrodes 101 and 102 installed therein and an inlet 103 into which treated water is introduced.

The electrodes 101 and 102 are each connected to a power source, and when energized, one of them is electrolyzed. The metal ion generated by this electrolysis reacts with the phosphorus component in the treated water introduced from the inlet 103 to form a metal salt that is hardly soluble in water.

The electrolytic cell 100 is provided with a valve 105 at the bottom. By appropriately operating the valve 105,
The metal salt is discharged out of the electrolytic cell 100.

[0007]

However, in the conventional sewage treatment apparatus, there is a problem that the metal salt is not sufficiently discharged from the electrolytic cell 100, and the electrolysis is inhibited by the metal salt. .

In the conventional sewage treatment apparatus, the electrolytic cell 1
00 was sometimes provided in another tank into which household wastewater was introduced. And the metal salt discharged out of the electrolytic cell 100 was settled together with the sludge settled in the other tank. If the metal salt precipitates with the sludge, it becomes difficult to recycle phosphorus from the metal salt. This has been viewed as an issue as the need for phosphorus recycling has increased.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sewage treatment apparatus for appropriately transferring a generated hardly soluble metal salt.

[0010]

SUMMARY OF THE INVENTION A sewage treatment apparatus according to one aspect of the present invention includes an electrolytic unit having an electrode,
By electrolyzing the electrode in the electrolysis unit, a phosphorus component in the treated water is precipitated as a metal salt that is hardly soluble in water, a sewage treatment apparatus, wherein the electrolysis unit only has a side surface of the electrode. It is characterized by further comprising a covering case.

According to the present invention, since the electrodes are covered with the case, metal ions generated by electrolysis of the electrodes are
It can react with treated water efficiently. Since the case does not have a bottom surface, the metal salt generated by the reaction between the metal ion and the phosphorus component in the treated water can be promptly moved to a place away from the electrode.

Therefore, in the sewage treatment apparatus, the metal salt can move so as not to reduce the efficiency of the electrolysis reaction of the electrode and the reaction between the metal ion and the phosphorus component in the treated water.

In the sewage treatment apparatus according to the present invention, it is preferable that the electrolysis unit further includes a stirring means for stirring a space surrounded by the case.

Thus, metal ions generated by electrolysis of the electrode can be more efficiently reacted with the treated water.

Further, the sewage treatment apparatus according to the present invention further includes an anaerobic tank in which anaerobic microorganisms are present, an aerobic tank in which aerobic microorganisms are present, and a sedimentation tank for sedimenting sludge. The electrolysis unit is preferably installed inside the anaerobic tank, the aerobic tank or the sedimentation tank.

[0016] Thus, the wastewater treatment apparatus can be made more compact. A sewage treatment apparatus according to another aspect of the present invention includes an electrolysis unit having an electrode, and electrolyzes the electrode in the electrolysis unit to convert a phosphorus component in the treated water into a metal salt that is hardly soluble in water. A sewage treatment apparatus, which is further provided with a recovery unit disposed adjacent to the electrolysis unit on the downstream side of the electrolysis unit in order to selectively recover the metal salt. And

According to the present invention, the water-insoluble metal salt precipitated in the sewage treatment apparatus can be recovered by the recovery unit, and the mixing of the metal salt with the sludge in the sewage treatment apparatus can be suppressed.

Therefore, the efficiency with which the above metal salt is recovered in a reproducible state can be increased. For this reason, the recycling efficiency of phosphorus can be improved.

In the sewage treatment apparatus according to the present invention, it is preferable that the recovery unit includes an adsorbent for capturing the metal salt.

Thus, the metal salt can be more reliably recovered in a reproducible state. Further, the sewage treatment apparatus according to the present invention further includes an inflow tank into which household wastewater flows,
Preferably, the electrolysis unit and the recovery unit are installed in the inflow tank.

Thus, the electrolysis unit and the recovery unit are installed in a tank in which the hardly water-soluble metal salt that precipitates in the sewage treatment apparatus easily mixes with the sludge.

Therefore, the phosphorus component can be efficiently supplied to the electrolysis unit, and the effect of the recovery unit can be sufficiently exhibited.

The sewage treatment apparatus according to the present invention further includes an anaerobic tank in which anaerobic microorganisms are present, an aerobic tank in which aerobic microorganisms are present, and a sedimentation tank in which sludge is settled.
The electrolytic unit and the recovery unit, the anaerobic tank, the aerobic tank and the sedimentation tank, and the anaerobic tank, the aerobic tank and the sewage after the treatment in the sedimentation tank is flowed. It is preferable to install it.

This makes it possible to minimize the mixing of the hardly water-soluble metal salt precipitated in the sewage treatment apparatus with the sludge.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. In addition, the sewage treatment apparatus of each embodiment described below is mainly applied to a large-scale wastewater treatment facility for treating domestic wastewater and industrial wastewater. Can be applied to wastewater treatment facilities. In addition, according to the sewage treatment apparatus of each embodiment, the phosphorus compound contained in domestic wastewater, wastewater of a plating factory, and the like can be subjected to coagulation sedimentation treatment.

[First Embodiment] FIG. 1 is a longitudinal sectional view of a sewage treatment system including a sewage treatment apparatus according to a first embodiment of the present invention, and FIG. 2 is a tank shown in FIG. FIG. Note that, for ease of description, FIG. 2 omits some of the members shown in FIG.

Referring to FIG. 1 and FIG. 2, the sewage treatment system according to the present embodiment mainly includes a tank 1. The tank 1 is buried underground. The inside of the tank 1 is divided into a first anaerobic leakage tank 5, a second anaerobic leakage tank 10, and a contact back tank by a first partition 2, a second partition 3, a third partition 4, and a fourth partition 20. 14, a sedimentation tank 19 and a disinfection tank 21. The upper part of the tank 1 is covered with a plurality of manholes 28. Further, members inside the tank 1 are connected to members (the third blower 30 and the like) outside the tank 1. In FIG. 1, members outside the tank 1 such as the third blower 30 are described above the tank 1 for convenience, but these members are not necessarily installed above the tank 1. is not.

The first anaerobic leakage tank 5 has an inflow port 6 into which miscellaneous wastewater flows, and a first anaerobic leakage bed 7 is provided therein. In other words, the first anaerobic leak-bed tank 5 is also a contaminant removal tank in the present embodiment because household wastewater flows in. In the present embodiment, the inflow tank is constituted by the first anaerobic leakage tank 5. In the first anaerobic leakage tank 5,
The hardly decomposable miscellaneous substances in the household wastewater are separated and settled, and the organic substances in the household wastewater are anaerobically decomposed by the anaerobic microorganisms attached to the first anaerobic leaky bed 7. Also, organic nitrogen is anaerobically decomposed into ammonia nitrogen.

Further, the first anaerobic leakage tank 5 is provided with a first advection pipe 8. Also, on the upper part of the first partition 2,
A first water supply port 9 is formed. One end of the first advection pipe 8 is arranged in the first anaerobic leaky tank 5, and the other end is arranged in the second anaerobic leaky tank 10. The treated water anaerobically decomposed in the first anaerobic bed 5 is supplied to the retreating second anaerobic bed 10 via the first advection pipe 8.

In the second anaerobic leakage tank 10, the second anaerobic leakage bed 1
1 is provided. The suspended matter is captured by the second anaerobic leaky bed 11, organic substances are anaerobically decomposed by anaerobic microorganisms, and organic nitrogen is anaerobically decomposed into ammonia nitrogen.

The second anaerobic leakage tank 10 has a second advection pipe 12
Is provided. In addition, on the upper part of the second advection pipe 12,
The ejection device 32 is attached. The ejection device 32 is connected to the third blower 30. In addition, the ejection device 32
Connects the second anaerobic leakage tank 10 and the contact back tank 14 via a second water supply port 13 penetrating the upper part of the second partition wall 3.

When the air is sent from the third blower 30, the jetting device 32 sends the air from the jet port 31 to the second advection pipe 12.
Blow air into. Thereby, the supply of the treated water from the second anaerobic leaky tank 10 to the contact back tank 14 in the second advection pipe 12 is promoted.

The contact back tank 14 has a contact member 15. The contact material 15 is provided to promote the culture of aerobic microorganisms. A first air diffuser 16 is provided near the bottom of the contact back tank 14.

The upper end of the first air diffuser 16 is connected to the first blower 17. In addition, the lower end of the first air diffuser 16 is provided so as to make a round around the inside of the outer periphery of the bottom surface of the contact back tank 14 as described later (see FIG. 2). A plurality of holes (holes 16) are provided on the lower surface side of the first diffuser tube 16.
a: see FIG. 2). Then, when air is sent from the first blower 17, the air is released from the holes as air bubbles. In addition, since the hole is formed on the lower surface side of the first air diffuser 16, the sludge is less likely to enter the inside than when the hole is formed on the upper surface or side surface.

The bubbles are released from the first air diffuser 16 so that the contact back tank 14 is maintained in an aerobic state.
As a result, in the contact back tank 14, the treated water is aerobically decomposed by the aerobic microorganisms, and is also nitrified, whereby the ammonia nitrogen is decomposed into nitrate nitrogen. The aerobic microorganisms in the contact back tank 14 include nitrifying bacteria.
In general, nitrifying bacteria refer to ammonia oxidizing bacteria and nitrifying bacteria.

The contact material 15 has a biofilm which has grown and gradually increased. Then, when air bubbles are released from the first air diffuser 16, the biofilm adhering to the contact material 15 peels off.

A pump 33 is provided below the contact back tank 14.
Is provided. Further, a sludge return path 34 is connected above the pump 33, and a sludge return path 35 is connected to an upper end of the sludge return path 34 so as to extend to the left in the figure. Thereby, the sludge generated in the contact back tank 14 is sent to the first anaerobic leaky tank 5.

Since the third partition wall 4 does not reach the bottom of the tank 1, the contact back tank 14 and the settling tank 19 are connected at the lower part. Thereby, the treated water in the contact back tank 14 also flows into the settling tank 19.

Above the sedimentation tank 19, a disinfection tank 21 is provided. The disinfection tank 21 is configured so that the supernatant of the settling tank 19 flows into the tank. In the disinfection tank 21,
A sterilizer 22 is provided. The sterilizer 22 is provided with a chlorine-based chemical or the like. The treated water that has flowed into the disinfecting tank 19 is disinfected by the chemical and discharged out of the tank 1 through the drain port 23.

The contact back tank 14 and the first anaerobic leakage tank 5
They are connected by a first return pipe 24. First return pipe 2
4 has a second air diffuser 25 therein. The second air diffuser 25 is connected to the second blower 26. The second air diffuser 25 has an ejection hole for ejecting air as appropriate. Then, the second air diffuser 25 blows out the air supplied from the second blower 26 from the outlet, and discharges the treated water in the sedimentation tank 19 through the first return pipe 24 through the first anaerobic leakage bed. Feed into tank 5.

An electrolysis unit including a case 54 is provided above the contact back tank 14. Specifically, the case 54 is a hollow body to which four vertical plate bodies are connected. Inside the case 54, electrode pairs 51 and 52 are provided.
Is provided. The electrode pairs 51 and 52 are each connected to a power supply 57. A third air diffuser 53 is provided inside the case 54. Third diffuser 53
Are connected to a fourth blower 56.

In the case 54, metal ions such as iron ions and aluminum ions are eluted by an electrolysis reaction (abbreviated as electrolysis) at the electrode pairs 51 and 52. As a result, in the contact back tank 14, the eluted metal ions react with the phosphorus compound in the treated water, and a metal salt that is hardly soluble in water is generated and aggregated. Here, as an example, when iron ions are eluted by the electrolytic reaction, main ion reaction formulas assumed at the time of aggregation are shown below.

[0043] _{^{PO 43- + Fe 3+ → FePO 4}} ↓ ... (1) Next, the configuration of the electrolytic unit of the present embodiment will be described with reference to FIGS. FIG. 3 is a perspective view of the electrolysis unit. FIG. 4 is an exploded perspective view of the electrolysis unit.

The case 54 is provided with mounting members 541, 542, 543, and 544 at four positions at the upper end thereof. In addition, the inside of the case 54 is separated by a partition plate 540.
It is divided into two spaces arranged on the left and right. Further, the case 54 has a third diffuser 5 extending from above to below.
3 have been introduced. The third air diffuser 53 has a portion extending from right to left at the lower part of the case 54.

Each of the electrode pairs 51 and 52 has two opposing electrodes 511, 512, 521 and 522, respectively. In the electrode pairs 51 and 52, the two opposing electrodes have their upper ends attached to the electrode supports 510 and 520. In each of the electrode pairs 51 and 52, the electrode is connected to a power supply 57 (see FIG. 1) via connectors 513 and 523.

By mounting both ends of the electrode supports 510, 520 to the mounting members 541, 542, 543, 544, respectively, the electrodes 511, 512 are connected to the partition plate 54.
The electrodes 521 and 522 are installed on the left side of the partition plate 540, respectively, on the right side of 0. On the right side of the partition plate 540,
An electrolytic reaction occurs between the electrodes 511 and 512, and an electrolytic reaction occurs between the electrodes 521 and 522 on the left side of the partition plate 540.

The third air diffuser 53 emits air bubbles, and the air bubbles collide with the inner wall of the case 54, so that
Convection occurs in the case 54. Thereby, the treated water is efficiently supplied to the vicinity of the electrodes 511, 512, 521, and 522. In the present embodiment, the third air diffuser 53 constitutes a stirring means for stirring the space surrounded by the case. In addition, the stirring means is the third diffuser 53
The device is not limited to the device that emits bubbles as described above, and may be a device that stirs water in the case 54.

The metal ions eluted by the above-mentioned electrolytic reaction react with the phosphorus compound in the treated water to form a metal salt which is hardly soluble in water. On the other hand, the case 54 is a hollow body as described above. That is, the case 54 has a shape without a bottom. Therefore, the metal salt generated here is quickly guided to the contact back tank 14 by its own weight.

In the present embodiment described above, the electrolysis unit is provided in the contact back tank 14. The electrolysis unit includes a first anaerobic leaky tank 5 and a second anaerobic leaky tank 1.
0, or may be provided in another tank in the tank 1 such as the sedimentation tank 19. In the present embodiment, the sedimentation tank 19 constitutes a sedimentation tank for sedimenting sludge. Further, the electrolysis unit may be provided outside the tank 1 so as to be adjacent to the inlet 6 and the drain 23.

The circulation flow rate of the tank 1 is 3Q. Here, Q is the amount of water flowing into the tank 1. That is, in the tank 1, the amount of water three times the amount of water flowing in is
Circulated.

The electrolytic reaction in the electrode pairs 51 and 52 is performed so that the concentration of the eluted iron ions or aluminum ions is 1 to 3 times the molar concentration of phosphorus in the treated water. The above-mentioned electrolytic reaction is controlled so that the concentration of iron ions or aluminum ions is preferably about 1 to 2 times, more preferably about 1.5 times, the molar concentration of phosphorus in the treated water. You. For this reason, in the electrolytic reaction, the current density at the electrode is 0.
It is controlled to be 1 mA / cm ² or more, and in many cases, it is controlled to be about 0.3 mA / cm ² .

By controlling the current density in the electrode as described above, it is considered that the formation of an oxide film and organic deposits on the electrode surface can be prevented and these can be removed. This is because it is considered that iron hydroxide and organic deposits which are considered to be generated at the anode side electrode can be removed by hydrogen gas generated at the cathode side or backing by the third diffuser 53. Therefore, when the current density in the above electrolytic reaction is too low, the amount of hydrogen gas generated on the cathode side is low, and it is considered that the deposits on the anode side cannot be sufficiently removed. In addition, the backing amount of the third air diffuser 53 in the electrolysis unit is about 15 L / min.

For example, when the amount of domestic wastewater flowing into the tank 1 per day is 1200 L and the circulation flow rate in each tank in the tank 1 is 6000 L, the electrodes 511 and 51
2 and the current flowing through the electrodes 521 and 522 is 650 m
It is controlled to about A. The current density at each electrode can be controlled by changing the immersion area of each electrode. The distance between the electrodes 511 and 512 and between the electrodes 521 and 522 is set to about 25 mm, and the voltage between the electrodes is constantly monitored. Further, it is preferable that the polarity of each electrode is reversed every predetermined time (for example, every 24 hours).

[Second Embodiment] FIG. 5 is a longitudinal sectional view of a sewage treatment system including a sewage treatment apparatus according to a second embodiment of the present invention. The sewage treatment system shown in FIG. 5 is different from the sewage treatment system shown in FIG. 1 in that the arrangement of the electrolytic units is changed and some components are added. Therefore, in FIG. 5, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description of the components will be omitted.

Referring to FIG. 5, an electrolysis unit including electrode pairs 51 and 52 is installed above first anaerobic leakage tank 5.

Further, the settling tank 19 is provided with a third advection pipe 38 and a pump 39. The treated water in the contact back tank 14 flows into the settling tank 19 via the third advection pipe 38. This flow is promoted by the pump 39.

The electrode pairs 51 and 52 are arranged in the electrolytic cell 59. The electrolytic cell 59 is connected to the first return pipe 24. Thereby, the treated water in the settling tank 19 is led to the electrolytic tank 59 via the first return pipe 24.

The electrolytic cell 59 has a discharge pipe 59 at its upper left.
2 is provided. The supernatant of the treated water guided to the electrolytic cell 59 flows into the first anaerobic leak-leaved tank 5 via the discharge pipe 592.

The electrolytic cell 59 has an outlet 591 at the bottom. Further, a phosphorus recovery unit 60 is provided in the first anaerobic leakage tank 5 and below the electrolytic tank 59 so as to be adjacent to the electrolytic tank 59.

In the electrolytic cell 59, as described in the first embodiment, metal ions are generated by the electrolytic reaction in the electrode pairs 51 and 52, and the metal ions react with the treated water to form a poorly soluble metal ion. It becomes a metal salt. Due to its own weight, the hardly soluble metal salt is supplied to the phosphorus recovery unit 6 through the outlet 591.
It is led to 0. That is, by using the phosphorus recovery unit 60, the hardly soluble metal salt can be selectively recovered.

FIG. 6 is a sectional view of the phosphorus recovery unit 60. The phosphorus recovery unit 60 includes a main body 64, a net 62,
63, an advection tube 61, and an adsorbent 65. Adsorbent 6
Reference numeral 5 is arranged between the nets 62 and 63 to adsorb fine ones among the hardly soluble metal salts, and is made of activated carbon or ceramic. The treated water and metal salt in the electrolytic cell 59 are guided to the main body 64 via the nets 62 and 63. The supernatant of the main body 64 is discharged through the advection pipe 61 to the outside of the main body 64 and into the first anaerobic leakage bed tank 5.

In the present embodiment described above, the phosphorus recovery unit 60 is provided downstream of and adjacent to the electrolysis unit. This allows
The poorly soluble metal salt generated in the electrolytic cell 59 is collected at the bottom of the main body 64 of the phosphorus recovery unit 60 or the adsorbent 65
Is adsorbed. That is, in the sewage treatment system of the present embodiment, the hardly soluble metal salt can be collected so as not to mix with the sludge. In addition, by providing the adsorbent 65, even a fine metal salt can be recovered, so that the recovery efficiency of the metal salt can be improved.

In this embodiment, the electrolysis unit and the phosphorus recovery unit 60 are provided in the first anaerobic leakage tank 5. The electrolysis unit may be provided in another tank in the tank 1, such as the second anaerobic leakage tank 10, the contact back tank 14, or the precipitation tank 19. Further, the electrolysis unit may be provided outside the tank 1 so as to be adjacent to the inlet 6 and the drain 23. However, in the present embodiment, when the electrolysis unit and the phosphorus recovery unit 60 are provided in the first anaerobic leakage bed tank 5 which is also a contaminant removal tank, the effect of the phosphorus recovery unit 60 is more remarkably exhibited. be able to. When the electrolysis unit is provided in the first anaerobic leakage tank 5 without the phosphorus recovery unit 60, the hardly soluble metal salt is recovered as a single item compared to when the electrolysis unit is provided in another tank under the same conditions. This is because it is considered difficult.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a sewage treatment system including a sewage treatment apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the tank shown in FIG.

FIG. 3 is a perspective view of an electrolytic unit of the sewage treatment system of FIG.

FIG. 4 is an exploded perspective view of an electrolytic unit of the sewage treatment system of FIG.

FIG. 5 is a longitudinal sectional view of a sewage treatment system including a sewage treatment apparatus according to a second embodiment of the present invention.

6 is a sectional view of a phosphorus recovery unit of the sewage treatment system of FIG.

FIG. 7 is a diagram schematically showing an electrolytic cell of a conventional sewage treatment apparatus.

[Explanation of symbols]

1 tank, 5 first anaerobic leaky tank, 10 second anaerobic leaky tank, 51, 52 electrode pair, 53 third diffuser, 54 case, 60 phosphorus recovery unit, 65 adsorbent.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/46 101A F-term (Reference) 4D024 AA04 AB12 BA02 BA05 BC01 CA07 DB09 DB12 DB15 DB16 DB21 4D038 AA08 AB46 AB47 BA04 BB06 BB10 BB19 4D040 BB52 BB72 BB82 BB91 4D061 DA08 DB11 EA02 EB02 EB04 EB17 EB19 EB27 EB28 EB39 ED06 FA06 FA14 FA15 GC12 GC16

Claims (7)

[Claims] 1. A sewage treatment apparatus, comprising: an electrolysis unit provided with an electrode, wherein the electrolysis of the electrode in the electrolysis unit causes a phosphorus component in the treated water to precipitate as a metal salt that is hardly soluble in water. The sewage treatment apparatus, wherein the electrolytic unit further includes a case that covers only a side surface of the electrode. 2. The sewage treatment apparatus according to claim 1, wherein the electrolysis unit further includes a stirring means for stirring a space surrounded by the case. 3. An anaerobic tank in which an anaerobic microorganism is present, an aerobic tank in which an aerobic microorganism is present, and a sedimentation tank for sedimenting sludge, wherein the electrolysis unit includes the anaerobic tank and the aerobic tank. Alternatively, it is installed inside the settling tank.
A sewage treatment apparatus according to claim 1. 4. A sewage treatment apparatus, comprising: an electrolysis unit provided with an electrode, wherein the electrolysis of the electrode in the electrolysis unit causes a phosphorus component in the treated water to precipitate as a poorly soluble metal salt in water. A wastewater treatment apparatus further comprising a recovery unit disposed adjacent to the electrolysis unit downstream of the electrolysis unit to selectively recover the metal salt. 5. The sewage treatment apparatus according to claim 4, wherein the recovery unit includes an adsorbent for capturing the metal salt. 6. The sewage treatment apparatus according to claim 4, further comprising an inflow tank into which domestic wastewater flows, wherein the electrolysis unit and the recovery unit are installed in the inflow tank. 7. An anaerobic tank in which an anaerobic microorganism is present, an aerobic tank in which an aerobic microorganism is present, and a sedimentation tank for sedimenting sludge, wherein the electrolysis unit and the recovery unit are anaerobic. The sewage after being treated in the anaerobic tank, the aerobic tank, and the sedimentation tank is installed outside the tank, the aerobic tank, and the sedimentation tank, and the sewage is disposed therein. 6. The sewage treatment apparatus according to 5.