JP2000015288A - Waste water treatment method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treatment method and apparatus capable of efficiently and inexpensively removing org. matter and nitrogen in waste water within a short time and capable of obtaining treated water of high quality and also reducing the generation amt. of excessive sludge. SOLUTION: In order to remove org. matter and nitrogen in waste water, raw water is successively passed through an anaerobic tank 2, a microaerobic tank 3, an aerobic tank 4 and a sedimentation tank 5 and a part of the outflow liquid from the aerobic tank 4 is circulated to the anaerobic tank 2 and the sludge withdrawn from the sedimentation tank 5 is decomposed by a sludge decomposition tank 9 and a sludge decomposed soln. is introduced into the microaerobic tank 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method and an apparatus for treating wastewater containing organic matter and nitrogen.

[0002]

2. Description of the Related Art Nitrogen in wastewater such as sewage, night soil, and industrial wastewater is considered to cause eutrophication in closed water bodies such as lakes and inner bays. Conventionally, as a nitrogen removal technology for removing nitrogen components from these wastewaters, nitrification and denitrification treatment using microorganisms has been performed, and a representative example thereof is a modified activated sludge circulation method. This method utilizes the ammonia oxidizing ability of nitrifying bacteria, which is an autotrophic bacterium, to oxidize ammonia nitrogen in wastewater to nitrite and nitric acid in an aerobic state, and then to remove heterotrophic bacteria, denitrifying bacteria. The function removes nitrogen from wastewater by reducing nitrous acid and nitric acid to nitrogen in an anaerobic state by using organic substances and the like in the wastewater as electron donors. The activated sludge circulation modification method has two devices: an anaerobic tank that decomposes and denitrifies organic substances in wastewater by denitrifying bacteria, and an aerobic tank that nitrifies ammonia nitrogen in wastewater by nitrifying bacteria. It consists of a tank. The nitrification liquid that has been nitrified in the aerobic tank is circulated to the anaerobic tank, whereby nitrogen components in the wastewater are released to the atmosphere as nitrogen gas and removed.

[0003] Among nitrifying bacteria and denitrifying bacteria, nitrifying bacteria are:
Since the growth rate is slow, in order to maintain a considerable number of bacteria in the activated sludge, it is necessary to secure a sufficient growth time by increasing the residence time of the sludge, which requires an extremely long processing time There is a disadvantage that. Further, the denitrification reaction requires an energy source for reducing power of the denitrifying bacteria, and for example, requires a hydrogen donor such as methanol or hydrogen, and thus has a drawback that the processing cost is increased. Further, in the case of the conventional activated sludge circulation modified method, there is a disadvantage that energy for circulating a large amount of wastewater between the aerobic tank and the anaerobic tank is required. Furthermore, the amount of excess sludge generated was also large. As described above, the conventional biological nitrification and denitrification treatment represented by the modified activated sludge circulation method is not satisfactory in terms of treatment time and treatment cost.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and can remove organic matter and nitrogen in wastewater efficiently, in a short time and at low cost, and can treat high-quality treated water. It is an object of the present invention to provide a method and an apparatus for treating wastewater, in which the amount of excess sludge obtained and generated is small.

[0005]

According to the method for treating wastewater according to the present invention, in order to remove organic matter and nitrogen in wastewater, raw water is sequentially passed through an anaerobic tank, a microaerobic tank, an aerobic tank, and a sedimentation tank. A part of the effluent from the aerobic tank is circulated to the anaerobic tank, and the sludge extracted from the settling tank is decomposed in a sludge decomposition tank. Further, the wastewater treatment apparatus of the present invention comprises an anaerobic tank, a microaerobic tank, an aerobic tank, a sedimentation tank, and a sludge decomposition tank, and a pipe for circulating a part of the effluent from the aerobic tank to the anaerobic tank. A sludge withdrawal pipe from the sedimentation tank is connected to the sludge decomposition tank.

[0006] In the present invention, the sludge decomposition treatment is preferably performed using ozone and ultrasonic waves, and it is preferable to introduce the sludge decomposition liquid generated in the sludge decomposition tank into a microaerobic tank. In the anaerobic tank, nitrous acid or nitric acid is converted into nitrogen gas by microorganisms using organic matter in wastewater as a hydrogen donor, denitrified, and then introduced into a microaerobic tank. In this micro aerobic tank,
In the sludge decomposition tank, a sludge decomposition liquid treated with ozone and ultrasonic waves is supplied, and an organic matter source and oxygen are supplied. Ammonium ions remaining in the microaerobic tank are directly denitrified in the microaerobic tank by the following chemical reaction formula. _{NH 3 + O 2 + 2H +} e → NH 2 OH + H 2 O ··· (1) NH 2 OH + O 2 + 3H + 3e → 1 / 2N 2 + 3H 2 O ··· (2)

In addition to the reactions of the above formulas (1) and (2),
Nitric acid and nitrous acid are denitrified as nitrogen gas using a sludge decomposition solution generated in a sludge decomposition tank. Further, the anaerobic liquid is introduced into the microaerobic tank in the preceding process, but the sludge decomposition liquid containing the exhausted ozone gas is supplied, so that the microaerobic state is maintained. In the present invention, the dissolved oxygen concentration in the microaerobic tank is preferably set to 0.1 to 2 mg / L. If the dissolved oxygen concentration in the microaerobic tank is less than 0.1 mg / L, no effect is obtained, and if it exceeds 2 mg / L, ammonium ions are oxidized to nitric acid or nitrous acid.
The reaction of the formulas (1) and (2) becomes difficult to occur. Normally, the discharged ozone gas must be treated by separately adsorbing it on activated carbon or the like, but is effectively used in the present invention.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a waste water treatment apparatus according to the present invention will be described in detail with reference to the drawings. FIG.
1 is a schematic system diagram of a wastewater treatment device of the present invention. The wastewater treatment apparatus of the present invention mainly includes an anaerobic tank 2, a microaerobic tank 3, an aerobic tank 4, a sedimentation tank 5, and a sludge decomposing tank 9, and a part of the effluent from the aerobic tank 4 is anaerobic. It has a pipe 7 for circulation to the tank 2, and further connects a sludge withdrawal pipe 8 from the settling tank 5 to a sludge decomposition tank 9. In addition, sludge decomposition tank 9
Is provided with an ozone generator 10 and an ozone transmitter 11, where sludge is decomposed and liquefied.
The decomposed sludge decomposed liquid is introduced into the microaerobic tank 3 through a pipe 12.

In order to carry out the treatment method of the present invention using the apparatus shown in FIG. 1, wastewater to be treated is introduced from a raw water supply pipe 1 into an anaerobic tank 2, and then sequentially into a microaerobic tank 3 and an aerobic tank 4. Process,
A part of the effluent from the aerobic tank 4 is circulated to the anaerobic tank 2 by a pipe 7. After the solid-liquid separation in the sedimentation tank 5, the treated water is discharged from a treated water discharge pipe 6, and the sludge is separated from the sludge withdrawal pipe 8.
Is introduced into the sludge decomposition tank 9 where the ozone generator 1
Under the action of ozone and ultrasonic waves by the ozone generator 11 and the ozone transmitter 11, they are decomposed and liquefied. Ultrasound is
It is preferable to operate at 100 to 1000 W / A / min for 0 to 10 minutes. In addition, ozone is 1 to 5 per gram of sludge.
It is preferable to blow at a rate of 0 mg. Sludge is vibrated by using ultrasonic waves, and the contact efficiency of ozone is improved. The liquefied sludge decomposed liquid is sent to the microaerobic tank 3 by the pipe 12, and is useful for replenishment of low molecular weight organic substances and oxygen gas.

[0010]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited by these examples.

Example 1 Sewage (BOD 110 mg / L, COD 75 mg / L, T
-N31 mg / L) was allowed to flow into the anaerobic tank 2 and reacted in the anaerobic tank 2 for a residence time of 5 hours. Thereafter, the reaction was performed in the microaerobic tank 3 for 4 hours and in the aerobic tank 4 for 4.5 hours. Part of the treatment liquid from the aerobic tank 4 (twice the amount of the inflowing raw water) is circulated from the pipe 7 to the anaerobic tank 2, and the rest flows into the sedimentation tank 5. On the other hand, the settled sludge in the settling tank 5 is introduced into the sludge decomposing tank 9, where the sludge is sent to the ultrasonic transmission device 11 (300 W, 400 μA).
And ozone was blown in at a rate of 10 mg / g of sludge. The obtained sludge decomposition liquid was caused to flow into the microaerobic tank 3 through the pipe 12. As a result of this experiment,
The OD was 10 mg / L or less, and the TN was 5 mg / L or less. On the other hand, in the conventional activated sludge circulation modified method, even if the circulating water amount is three times or more the inflow raw water amount, the T-N
Exceeds 5 mg / L, the C / N ratio is large, the energy for oxidizing ammonia is large, the aeration power is large,
A large amount of sludge was generated.

Example 2 Sewage was treated in the same manner as in Example 1, and the relationship between the denitrification rate in a microaerobic tank and the amount of organic matter was examined. The results shown in FIG. 2 were obtained. The denitrification rate was calculated by the following equation (3). Denitrification rate = (inlet nitrogen concentration-outlet nitrogen concentration) / inlet nitrogen concentration (3) From FIG. 2, it can be seen that the denitrification rate increases as the amount of organic matter increases.

[0013]

According to the wastewater treatment method and apparatus of the present invention, organic matter and nitrogen can be efficiently removed in a shorter time and more efficiently than in the conventional activated sludge circulation method. It can be manufactured at low cost, and at that time, the amount of circulating water is small, the amount of energy required for treatment is also small, and the sludge can be decomposed and effectively used for wastewater treatment, so the amount of surplus sludge generated is extremely small .

[Brief description of the drawings]

FIG. 1 is a schematic system diagram of a wastewater treatment apparatus showing one embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the rate of denitrification in a microaerobic tank measured in Example 2 and the amount of organic substances.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water supply pipe 2 Anaerobic tank 3 Microaerobic tank 4 Aerobic tank 5 Sedimentation tank 6 Treated water discharge pipe 7 Pipe 8 Sludge extraction pipe 9 Sludge decomposition tank 10 Ozone generator 11 Ultrasonic transmitter 12 Pipe

Claims (7)

[Claims] 1. To remove organic matter and nitrogen in wastewater, raw water is passed sequentially to an anaerobic tank, a microaerobic tank, an aerobic tank and a sedimentation tank, and a part of the effluent from the aerobic tank is used as an anaerobic tank. A method for treating wastewater, wherein sludge circulated to a sedimentation tank is decomposed in a sludge decomposition tank. 2. The method according to claim 1, wherein the sludge is decomposed by using ozone and ultrasonic waves. 3. The method for treating wastewater according to claim 1, wherein the sludge decomposition liquid generated in the sludge decomposition tank is introduced into a microaerobic tank. 4. The dissolved oxygen concentration in the microaerobic tank is 0.1 to 2
The method for treating wastewater according to claim 1, wherein the amount is mg / L. 5. A anaerobic tank, a microaerobic tank, an aerobic tank, a sedimentation tank, and a sludge decomposition tank, and a pipe for circulating a part of the effluent from the aerobic tank to the anaerobic tank is provided. An apparatus for treating wastewater, wherein a sludge extraction pipe is connected to a sludge decomposition tank. 6. The wastewater treatment apparatus according to claim 5, wherein an ozone generator and an ultrasonic transmitter are provided in the sludge decomposition tank. 7. The wastewater treatment apparatus according to claim 5, further comprising a pipe for introducing the sludge decomposition liquid in the sludge decomposition tank into the microaerobic tank.