JP2556409B2 - Treatment of organic wastewater containing nitrogen and phosphorus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating nitrogen- and phosphorus-containing organic wastewater, and more particularly to denitrification in biological treatment of nitrogen- and phosphorus-containing organic wastewater such as sewage, night soil and industrial wastewater. The present invention also relates to a treatment method that enhances and stabilizes the dephosphorization ability, and at the same time improves the clarification degree of treated water and reduces the amount of sludge generated.

[0002]

2. Description of the Related Art In recent years, due to the development of nitrification solution circulation type anaerobic aerobic activated sludge method (so-called A ₂ O method) based on nitrification solution circulation type denitrification activated sludge method and anaerobic aerobic type activated sludge method, It has become possible to remove nitrogen and phosphorus simultaneously in the treatment process. However, since the growth rate of nitrifying bacteria responsible for nitrifying reaction is smaller than that of other bacteria (eg, BOD oxidizing bacteria and denitrifying bacteria), the sludge retention time (SRT) is lengthened to prevent washout of nitrifying bacteria. There was a need. As a result, an aeration tank with a large hydraulic retention time (HRT) was required. For example, denitrifying urban sewage,
An aeration tank having an HRT of 14 to 16 hours was required for the dephosphorization treatment. Considering that the HRT of the standard activated sludge method is 6 to 8 hours, its size can be understood.

Therefore, recently, by immobilizing nitrifying bacteria on an immobilizing carrier, the substantial SRT of the nitrifying bacteria is increased to prevent washout of the nitrifying bacteria, and HRT8-
A method that enables denitrification and dephosphorization under operating conditions for about 12 hours is being developed. Here, this technique is referred to as a circulation type anaerobic aerobic activated sludge method in combination with an immobilized carrier. The main reason why this method can shorten the HRT is the aerobic tank HRT: 2
Because nitrification can be completed in 3 hours. FIG. 3 shows a flow of the circulation type anaerobic aerobic activated sludge method in combination with an immobilized carrier. According to this method, it is possible to remove nitrogen, phosphorus, and organic substances in general, but it is also clear that it has the following problems. (A) It was often found that ammonia remained in the treated water in the low water temperature period. (B) Clarity of treated water was generally poor and colloidal turbidity was observed. (C) The sludge generation amount was significantly higher than that of the standard activated sludge method.

Upon pursuing the causes of these problems, the following causes have become clear. (1) Remaining cause of ammonia When the water balance of the aerobic tank was investigated in detail, it was found between the decrease in nitrification activity and the solubility BOD in the aerobic tank (that is, the solubility BOD in the second anaerobic tank effluent). A correlation was observed, and it was observed that the higher the solubility BOD flowing into the aerobic tank, the lower the nitrification performance. Therefore, the cause of the decrease in nitrification performance is
BOD-oxidizing bacteria adhere and grow on the surface of the aerobic tank-immobilized carrier
It was considered that the BOD-oxidizing bacteria and the immobilized nitrifying bacteria competed for the uptake of dissolved oxygen, and as a result, the activity of the nitrifying bacteria was decreased.

(2) Regarding the cause of decrease in clarification degree of treated water A multiple regression analysis was conducted between the clarification degree of treated water and various operational factors, and the clarification degree of treated water decreased as the aeration time of floating activated sludge decreased. It was confirmed that the value decreased. The aeration time of the floating activated sludge corresponds to the residence time of the aerobic tank. From this, the reason for the decrease in the clarity of treated water is that the suspended activated sludge has a relatively short time to be placed in an aerobic environment, so the suspended matter adsorption capacity that ordinary activated sludge has is fixed. The cause was considered to be that the activated sludge of the circulation type anaerobic / aerobic activated sludge method combined with activated carbon did not have.

(3) About the cause that the amount of sludge generated is larger than that of the standard activated sludge method In this case as well, as a result of multiple regression analysis, a correlation was observed between the increase in the amount of sludge generated and the suspended activated sludge and the aeration time. It was observed that the shorter the time, the greater the amount of sludge generated. From this, the cause of increased sludge generation is that the activated sludge of the circulation type anaerobic aerobic activated sludge method combined with immobilized carrier is relatively shorter in the aerobic environment than ordinary activated sludge. In addition, it was considered that the reduction amount of sludge due to aerobic digestion was small.

[0007]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and in the circulation type anaerobic aerobic activated sludge method of a combination immobilization carrier type, (a) a nitrifying bacterium immobilization carrier By reducing the chance of contact with soluble BOD components,
Suppress the growth of BOD-oxidizing bacteria on the surface of the nitrifying bacteria-immobilized carrier and stabilize the activity of nitrifying bacteria. (B) Appropriately distribute the anaerobic tank retention time and aerobic tank retention time of floating activated sludge. Accordingly, the present invention provides a method for treating nitrogen- and phosphorus-containing organic wastewater, which can keep the treated water clarity high and suppress an increase in the amount of sludge generation.

[0008]

In order to solve the above-mentioned problems, in the present invention, in a treatment method in which nitrogen, an anaerobic process of phosphorus-containing organic wastewater, an aerobic process, and a solid-liquid separation process are sequentially passed, The anaerobic process comprises a first anaerobic process containing floating activated sludge and a second anaerobic process containing floating activated sludge and a microorganism-immobilized carrier, and the aerobic process includes a first aerobic process including floating activated sludge and floating activated sludge. And a second aerobic step containing a microorganism-immobilized carrier, the activated sludge separated in the solid-liquid separation step is returned to the first anaerobic step, and the second aerobic step effluent is circulated to the second anaerobic step. And the two aerobic steps
The hydraulic retention time of the first anaerobic process to the second aerobic process
Up to 40% of the total hydraulic retention time . In the present invention, the first anaerobic process and the second anaerobic process or the first aerobic process and the second aerobic process do not have to be two completely separated reaction tanks. For example, a partition may be provided so that the reaction liquids of both processes are not mixed in one reaction tank.

Granular carriers such as activated carbon, plastics, sponges and hydrophilic gels are suitable as the immobilizing carrier to be added to the second anaerobic process and the second aerobic process, but are not limited thereto. In addition, it is also possible to use a fixed bed such as Hanicom or a string-shaped filter medium, a rotating disk, or the like. When using the granular carrier, it is necessary to provide a carrier separating means such as a screen at the inlet and outlet of the second anaerobic process and the second aerobic process so that the immobilized carrier does not flow out. As a filling rate of the granular carrier, 5 to 25% by volume is suitable. As a method for immobilizing the microorganisms on the immobilization carrier, an adhesion immobilization method of spontaneously adhering to the surface of the carrier (carrier binding method) is often adopted, but a gel entrapping immobilization method is also applicable.

Further, in the present invention, the hydraulic retention time of the aerobic process (first aerobic process + HRT of the second aerobic process) is determined by the total hydraulic retention time (first anaerobic process to second preferred aerobic process). It is preferably 40% or more of the HRT up to the air process. This allows
The floating activated sludge can be kept for a relatively long time in an aerobic environment, (a) the clarification of treated water can be maintained high, and (b) an increase in sludge generation can be reduced. The abscissa of FIG. 2 plots (aerobic tank retention time / total retention time) ratio, and the ordinate plots (permeability of treated water) and (amount of sludge generated per removed BOD). From the figure, it is clear that when the horizontal axis is 40% or more, the transparency of treated water and the amount of sludge generated become almost constant, and there is no difference.

Further, in the present invention, the size of the first aerobic process is preferably 5 to 30% of that of the second aerobic process. As a result, the soluble BOD of the aerobic process inflow water (that is, the second anaerobic process outflow water) is taken into the body of the suspended activated sludge in the first aerobic process, and thus the soluble BO that flows into the second aerobic process.
D is extremely small. As a result, nitrifying bacteria proliferate predominantly on the immobilized carrier in the second aerobic step, and the adherent growth of BOD-oxidizing bacteria is suppressed. The volume ratio of the first aerobic process and the second aerobic process is appropriately adjusted depending on the solubility BOD of the second anaerobic process outflow water, but a range of 5 to 30% is usually suitable, and 5 to 20 among them is preferable. It should be%.

[0012]

In the conventional circulation type anaerobic aerobic activated sludge method combined with immobilization carrier, due to the effect of soluble BOD brought into the aerobic process, BOD oxidizing bacteria grow on the nitrifying bacteria immobilization carrier and nitrifying bacteria Competing for oxygen uptake tended to destabilize nitrification capacity. According to the present invention, most of the BOD components brought into the aerobic process are taken into the activated sludge body by the activated sludge in the first aerobic process before contacting with the immobilization carrier of nitrifying bacteria. Therefore, the growth of BOD-oxidizing bacteria on the surface of the carrier immobilized with the second aerobic step is suppressed. Therefore, since there is no competition for oxygen uptake between the immobilized nitrifying bacteria and BOD-oxidizing bacteria, it is possible to maintain the nitrifying ability at a high level. Further, in the present invention, the suspended activated sludge can be sufficiently exposed to the aerobic environment for a long time as compared with the conventional method, so that the suspended matter adsorption capability of the suspended activated sludge is increased. As a result, the clarity of treated water becomes higher than that of the conventional method. Further, since the aerobic digestion of the suspended activated sludge progresses more than the conventional method, the increase in the sludge generation amount can be suppressed.

[0013]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. Example 1 The denitrification and dephosphorization performances of the treatment method of the present invention and the conventional method (circulation type anaerobic aerobic activated sludge method combined with immobilized carrier), treated water permeability, and excess sludge generation amount under the following conditions: Compare by experiment. (A) Organic wastewater to be treated-Inflow water quality: BOD = 150 mg / l, Kjeldahl nitrogen = 30 mg / l, oxidized nitrogen = tr. , Total phosphorus = 3mg
/ L, SS = 100 mg / l ・ Treatment water temperature: 14 to 17 ° C.

(B) Present Invention FIG. 1 shows a processing flow. In FIG. 1, the wastewater passes from the inflow pipe 1 through the first anaerobic process 2 and the second anaerobic process 3 to the first anaerobic process 2.
The treated water passes through the aerobic process 15 and the second aerobic process 16 and is solid-liquid separated in the solid-liquid separation process 7, the treated water is discharged from 12, and the sludge is returned to the first anaerobic process 2 by a pipe 8, The part is discharged 11 as excess sludge. A part of the treated water that has exited the second aerobic process 16 is circulated to the second anaerobic process 3 through the nitrification liquid circulation pipe 9. 10 is air piping, 6 and 14 are carriers 5,
13 separators.

-Aerobic process: First anaerobic tank ... 200 liters (HRT = 2.5 hours) Second anaerobic tank ... 300 liters (HRT = 2.0 hours) First aerobic tank ... 50 liters (HRT = 0.5 hours) Second aerobic tank ... 250 liters (HRT = 3.0 hours) ─────────────────────── ───── Total 800 liters (HRT = 8.0 hours) ・ Treatment water amount: 2.4 m ³ / day ・ Returned sludge amount: 1.2 m ³ / day ・ Nitrification solution circulation amount: 4.8 m ³ / day ・Aeration rate: 40 Nl / min ・ Immobilization carrier Second anaerobic tank: Sponge (10 mm × 12.5 mm × 1)
2.5 liter) 60 liters. In order to prevent the sponge from flowing out, a 7.5 mm screen is installed at the inlet and outlet of the second anaerobic tank. Second aerobic tank: hydrophilic gel (main chain polyvinyl alcohol,
Introduce 50 liters of particle size 5 mm). In order to prevent the gel from flowing out, a screen with a 4 mm opening is installed at the inlet / outlet of the second aerobic tank.

(C) Conventional method: The processing flow is as shown in FIG. In FIG. 3, FIG.
The same symbols as have the same meaning, but the aerobic process is 1 tank 4
Only.・ Aerobic process: First anaerobic tank: 200 liters (HRT = 2.5 hours) Second anaerobic tank: 300 liters (HRT = 3.0 hours) Aerobic tank: 300 liters (HRT = 2.5 hours) ─────────────────────────── Total 800 liters (HRT = 8.0 hours) ・ Treatment water volume: 2.4 m ³ / day ・ Returned sludge volume: 1.2 m ³ / day ・ Nitrification solution circulation rate: 4.8 m ³ / day ・ Aeration rate: 40 Nl / min ・ Immobilization carrier: Hydrophilic gel (main chain polyvinyl alcohol, particle size 5 mm ) Add 60 liters to the aerobic tank. In order to prevent the gel from flowing out, a screen with an opening of 4 mm is installed at the inlet and outlet of the aerobic tank.

(D) Results of operation FIG. 4 shows the daily changes of total nitrogen and total phosphorus in the treated water. In the treated water of the conventional method, 0.5 to 10 mg / liter of ammonia remained and TN was 10 to 20 mg / liter, whereas the treated water of the present invention always contained 0.1 to 10.
˜1 mg / liter and TN was 10 mg / liter or less. Regarding the phosphorus, the total phosphorus in the treated water in the conventional method was 0.5 to 1.2 mg / liter, whereas the total phosphorus in the present invention was 0.5 to 1.0 mg / liter.
As described above, according to the present invention, the removal of nitrogen was stabilized and the removal of phosphorus was possible.

FIG. 5 shows the daily change in the transparency of treated water.
While the transparency of the conventional method remained at 20 to 30 cm, the transparency of the present invention was 30 to 50 cm, and the treated water of the present invention had high clarity. Table 1 shows the amount of excess sludge generated (per removed BOD).

[Table 1] Thus, the present invention produced less sludge than the conventional method.

[0019]

Industrial Applicability As described above, according to the present invention, stable denitrification and dephosphorization are possible in the treatment of nitrogen- and phosphorus-containing organic wastewater, and the treated water clarity is kept high and sludge It is possible to reduce the amount generated compared to the conventional method. We believe that the present invention will be widely adopted in the future physiological treatment method of nitrogen- and phosphorus-containing organic wastewater.

[Brief description of drawings]

FIG. 1 is a flow configuration diagram showing a processing method of the present invention.

FIG. 2 is a graph showing the relationship between the ratio of residence time of aerobic tank / total residence time, the transparency of treated water, and the amount of sludge generated.

FIG. 3 is a flow configuration diagram showing a processing method of a conventional method.

FIG. 4 is a graph showing a processing result.

FIG. 5 is a graph showing a processing result.

[Explanation of symbols]

1: Organic wastewater inflow pipe to be treated 2: First anaerobic process 3:
Second anaerobic process, 4: Aerobic process, 5: Immobilized carrier, 6: Carrier separation device, 7: Solid-liquid separation process, 8: Return sludge pipe, 9:
Nitrification liquid circulation pipe, 10: air pipe, 11: surplus sludge discharge pipe, 12: treated water pipe, 13: immobilized carrier, 14: carrier separation device, 15: first aerobic process, 16: second aerobic process

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masami Kitagawa 4-2-1 Honfujisawa, Fujisawa City, Kanagawa Prefecture, Ebara Research Institute, Ltd. (56) Reference JP-A-60-251997 (JP, A) JP 61-220792 (JP, A)

Claims (2)

(57) [Claims] 1. An anaerobic process for organic wastewater containing nitrogen and phosphorus,
In a treatment method in which each step of an aerobic step and a solid-liquid separation step is sequentially passed, the anaerobic step comprises a first anaerobic step containing floating activated sludge and a second anaerobic step containing floating activated sludge and a microorganism-immobilized carrier, and The aerobic step comprises a first aerobic step containing floating activated sludge and a second aerobic step containing floating activated sludge and a microorganism-immobilized carrier, and the activated sludge separated in the solid-liquid separation step is a first anaerobic step. The second aerobic process effluent is circulated to the second anaerobic process,
The hydraulic residence time varies from the first anaerobic process to the second aerobic process.
The method for treating nitrogen- and phosphorus-containing organic wastewater is characterized in that it is 40% or more of the total hydraulic retention time in . 2. A method according to claim 1 Symbol placement nitrogen and wherein the magnitude of the first aerobic step is 5-30% of the second aerobic step, the processing method of the phosphorus-containing organic waste water.