JP3385150B2 - Wastewater treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to sewage, domestic wastewater,
The present invention relates to a method for biologically denitrifying and dephosphorizing wastewater such as human waste and industrial wastewater by sequentially flowing them into an anaerobic tank and an aerobic tank.

[0002]

2. Description of the Related Art As a method for treating wastewater such as sewage, domestic wastewater, human waste and industrial wastewater, for example, as shown in FIG. 2, an appropriate amount of raw water from which sand and large contaminants have been removed is added to activated sludge. Absolute anaerobic tank 1, anoxic tank 2 and aerobic tank 3
While sequentially flowing into the aerobic tank 3, a part of the activated sludge mixed solution in the aerobic tank 3 is returned to the anoxic tank 2 as the nitrification circulation liquid 4 to remove nitrogen, organic matter and phosphorus in the raw water by the activated sludge. The way is done.

At that time, in the absolute anaerobic tank 1, while the inside of the tank is maintained in an absolutely anaerobic atmosphere, the polyphosphoric acid-accumulating bacteria and the like in the activated sludge discharge the phosphorus taken into the body into the water. The in-tank mixed liquid 5 containing activated sludge such as phosphorus and polyphosphoric acid-accumulating bacteria that has been ingested and is transferred to the anoxic tank 2.

In the anoxic tank 2, the denitrifying bacteria in the activated sludge decompose the organic matter in the water and reduce the nitrate nitrogen in the oxygen-deficient state in which the nitrification circulation liquid 4 containing nitrate nitrogen is returned. The in-tank mixed solution 6 that has been denitrified and contains activated sludge such as phosphorus and polyphosphate-accumulating bacteria is transferred to the aerobic tank 3.

In the aerobic tank 3, aeration or the like is performed, and in a state where the inside of the tank is maintained in an aerobic atmosphere, polyphosphoric acid-accumulating bacteria decompose the organic substances in the body and use the energy generated thereby. As a result, nitric acid bacteria in the activated sludge oxidize ammonia nitrogen in water to nitrate nitrogen. Part of the in-tank mixed solution containing activated sludge such as polyphosphoric acid-accumulating bacteria that has taken in phosphorus is returned to the anoxic tank 2 as the nitrification circulating solution 4 as described above, and the remaining in-tank mixed solution 7 is precipitated. It is sent to pond 8.

In this way, nitrogen, organic matter and phosphorus in the raw water are removed while the raw water successively and repeatedly passes through the absolute anaerobic tank 1, the oxygen free tank 2 and the aerobic tank 3. Of the mixed solution 7 in the aerobic tank sent to the settling tank 8, the supernatant 9 is discharged as treated water through a sterilization tank (not shown), etc., and a part of the activated sludge that has settled is returned sludge 10. Absolutely anaerobic tank 1
The remaining activated sludge is sent to the sludge thickening tank 12 as excess sludge 11.

The excess sludge 11 sent to the sludge thickening tank 12 is gravity-concentrated, the concentrated sludge 13 that has settled to the bottom is sent to the sludge treatment system, and the supernatant liquid is returned to the absolute anaerobic tank 1 as return water 14. .

[0008]

However, in the conventional method, since the excess sludge 11 containing phosphorus is gravity-concentrated in the sludge thickening tank 12 as described above, the internal excess sludge 11 is in an anaerobic state. Then, the released phosphorus is easily released, and the released phosphorus is contained in the supernatant and returned to the absolute anaerobic tank 1 as the return water 14. Therefore, the balance of phosphorus in the water treatment system is lost, and the wastewater may not be sufficiently treated depending on the activated sludge.

The present invention solves the above problems by effectively removing phosphorus and nitrogen in wastewater by activated sludge,
The purpose is to enable the excess sludge containing phosphorus to be concentrated without releasing phosphorus.

[0010]

In order to solve the above problems, in the wastewater treatment method according to claim 1 of the present invention, wastewater such as sewage is sequentially introduced into an anaerobic tank and an aerobic tank into which activated sludge has been added. In the wastewater treatment method, a part of the activated sludge mixed solution in the aerobic tank is circulated to the anaerobic tank to remove nitrogen and organic matter in the wastewater by the activated sludge and the phosphorus in the wastewater is taken into the activated sludge. The excess sludge containing phosphorus generated in the aerobic tank is sent to a sludge concentrating tank equipped with a submerged membrane separator, and concentrated by performing membrane separation with the submerged membrane separator in an aerobic atmosphere. The concentrated sludge containing phosphorus was taken out of the system.

In the wastewater treatment method according to the second aspect, the anaerobic tank is composed of an absolute anaerobic tank and an anoxic tank, and wastewater such as sewage is sequentially introduced into the absolute anaerobic tank and the anoxic tank, and the aerobic tank. A part of the activated sludge mixed solution is circulated to the anoxic tank.

According to a third aspect of the wastewater treatment method of the present invention, an immersion type membrane separation device is provided in the aerobic tank, and the activated sludge mixed solution in the aerobic tank is subjected to membrane separation by the immersion type membrane separation device. The permeated water is taken out of the tank.

According to the above-mentioned structure of the present invention, since the excess sludge is concentrated in the aerobic atmosphere, phosphorus is not released from the excess sludge, and the concentrated sludge containing phosphorus is taken out. , Discharged to the outside of the water treatment system. At that time, the membrane permeated water separated by the immersion type membrane separation device is
Since it has a good water quality that does not contain SS or phosphorus, it is not necessary to return it to an anaerobic tank like the supernatant water in the conventional sludge thickening tank, and it can be sent to the next treatment step such as sterilization or discharged as it is. . Therefore, phosphorus taken into the excess sludge does not return to the water treatment system again, and stable water treatment can be performed.

According to the second aspect of the present invention, the absolute anaerobic atmosphere necessary for removing phosphorus is secured by the absolute anaerobic tank, and the oxygen-deficient state required for removing nitrogen is secured by the anoxic tank. Both phosphorus and nitrogen are effectively removed.

According to the third aspect of the present invention, the membrane-permeated water that is membrane-separated by the immersion type membrane separator in the aerobic tank is
Since the water quality is good without phosphorus, nitrogen, organic matter, SS, etc., it can be sent to the next treatment step such as sterilization or discharged as it is.

[0016]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to FIG. The basic flow in the wastewater treatment method of this embodiment is almost the same as the conventional treatment flow described with reference to FIG. 2, and an appropriate flow rate of raw water from which sand and large contaminants have been removed is added to activated sludge. Anaerobic tank 1
While sequentially flowing into the anoxic tank 2 and the aerobic tank 3, a part of the activated sludge mixed solution in the aerobic tank 3 is returned to the anoxic tank 2 as the nitrification circulation liquid 4, and nitrogen in the raw water, Organic matter and phosphorus are removed by activated sludge.

However, the submerged membrane separation device 3a is installed inside the aerobic tank 3, and the sludge concentration tank 15 in which the submerged membrane separation device 15a is installed is provided downstream of the aerobic tank 3. . In such an arrangement, in the aerobic tank 3, the mixed liquid 6 sent from the anoxic tank 2 is treated with activated sludge, and a part of the mixed liquid in the tank is returned to the anoxic tank 2 as the nitrification circulation liquid 4. Meanwhile, the mixed solution in the tank is subjected to solid-liquid separation by the membrane separation device 3a, and the membrane permeated water 16 is taken out of the tank. The membrane permeated water 16 is
Since it has a good water quality containing no phosphorus, nitrogen, organic matter, SS, etc., it is discharged as treated water as it is or after passing through a sterilization tank (not shown).

The activated sludge containing phosphorus that has accumulated in the aerobic tank 3 is taken out of the tank as excess sludge 17, a part of it is returned to the absolute anaerobic tank 1 as return sludge 18, and the remaining excess The sludge 17 is sent to the sludge thickening tank 15.

Then, in the sludge thickening tank 15, the surplus sludge 17 is membrane-separated by the immersion type membrane separator 15a in an aerobic atmosphere for aeration, and the membrane permeated water 19 is taken out of the tank.
The concentrated sludge 20 thus concentrated is sent to the sludge treatment system.

Concentrated sludge 20 concentrated under aerobic atmosphere
Contains phosphorus without releasing it, so that the membrane-permeated water 19 has good water quality not containing SS but also phosphorus. Therefore, the membrane permeated water 19 does not need to be returned to the absolute anaerobic tank 1 like the conventional clear water in the sludge concentrating tank, and together with the membrane permeated water 16 in the aerobic tank 3, a sterilization tank (not shown) or the like is used. After that, or as it is, it is discharged as treated water.

Therefore, the phosphorus contained in the excess sludge 17 and taken out from the aerobic tank 3 is not mixed into the water treatment system again, and the water treatment can be stably performed. As the immersion type membrane separation devices 3a and 15a, various types such as a plurality of tubular ceramic separation membranes arranged and joined by a header can be used.

Further, in the above, the absolute anaerobic tank 1 and the anoxic tank 2 are provided to secure the absolutely anaerobic atmosphere necessary for the removal of phosphorus by the absolute anaerobic tank, and the oxygen deficiency state necessary for the removal of nitrogen is provided. The anaerobic tank was used to secure the anaerobic tank, but the raw water was made to flow into one side of the single anaerobic tank, and the nitrifying circulating liquid was made to flow into the opposite side of the single anaerobic tank. An absolute anaerobic part and an anoxic part may be provided.

Depending on the properties of the water to be treated, the absolute anaerobic tank 1, the oxygen-free tank 2 and the aerobic tank 3 may be provided in a plurality of stages for denitrification and dephosphorization in the same manner as described above.

[0024]

As described above, according to the present invention, since the excess sludge containing phosphorus is concentrated by the immersion type membrane separator in an aerobic atmosphere, phosphorus is released from the excess sludge. Instead, it can be sent out of the water treatment system as concentrated sludge containing phosphorus, and it is possible to take out membrane-permeated water of good water quality that does not contain phosphorus, SS, etc. Since water can be returned, stable water treatment can be performed.

Further, since the activated sludge mixed solution in the aerobic tank is subjected to membrane separation by an immersion type membrane separator, it is possible to obtain membrane permeated water of good water quality, which is discharged after treatment such as sterilization or as it is. can do.

[Brief description of drawings]

FIG. 1 is a flowchart explaining a wastewater treatment method of the present invention.

FIG. 2 is a flowchart illustrating a conventional wastewater treatment method.

[Explanation of symbols]

1 absolute anaerobic tank 2 anoxic tank 3 aerobic tank 3a Immersion type membrane separator 4 Nitrification circulating fluid 15 Sludge thickening tank 15a Immersion type membrane separator 16 membrane permeate 17 Excess sludge 19 membrane permeate 20 Concentrated sludge

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiya Ozaki 6-1, Nishijima 2-chome, Nishiyodogawa-ku, Osaka City, Osaka Prefecture Kubota Co., Ltd. Shin-Yodogawa Plant (56) Reference JP-A-7-232192 (JP, A) JP 5-50090 (JP, A) JP 61-178099 (JP, A) JP 56-150487 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C02F 3/30 C02F 11/12

Claims (3)

(57) [Claims] 1. A wastewater such as sewage is introduced into an anaerobic tank by sequentially flowing a wastewater such as sewage into an anaerobic tank containing activated sludge and an aerobic tank, while circulating a part of the activated sludge mixed solution in the aerobic tank. In the wastewater treatment method of removing the nitrogen and organic matter of the wastewater with activated sludge and incorporating the phosphorus in the wastewater into the activated sludge, the surplus sludge containing phosphorus generated in the aerobic tank is provided with an immersion type membrane separation device. The wastewater treatment method is characterized in that the sludge is sent to the sludge concentrating tank, concentrated in the aerobic atmosphere by membrane separation using an immersion type membrane separator, and the concentrated sludge containing phosphorus is taken out of the system. 2. The anaerobic tank is composed of an absolute anaerobic tank and an oxygen-free tank, and wastewater such as sewage is allowed to sequentially flow into the absolute anaerobic tank and the oxygen-free tank so that one of the activated sludge mixed liquids in the aerobic tank is discharged. The wastewater treatment method according to claim 1, wherein the part is circulated to the oxygen-free tank. 3. An immersion type membrane separator is provided in the aerobic tank, the activated sludge mixed solution in the aerobic tank is separated by the immersion type membrane separator, and the permeated water is taken out of the tank. The wastewater treatment method according to claim 1 or 2, characterized in that.