JP3015426B2 - Wastewater management and treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a treatment facility for nitrifying and denitrifying wastewater containing ammonia nitrogen, which is a polluting factor of water, by repeating aerobic and anaerobic treatments. The present invention relates to a wastewater management treatment method that uses an index for efficient operation.

(Prior art) Biological removal of ammonia nitrogen contained in wastewater is carried out by a nitrification process using nitrifying bacteria (ammonia-oxidizing bacteria and nitrite-oxidizing bacteria) and a denitrification process using denitrifying bacteria. Will be

In more detail, ammonia-oxidizing bacteria oxidize ammonia nitrogen under aerobic conditions to produce nitrite nitrogen. The nitrite-oxidizing bacteria then oxidize the nitrite nitrogen under aerobic conditions to produce nitrate nitrogen.
These reaction formulas are as follows.

Ammonium oxidizing bacteria ^{_{NH 4 + 3 / 2O 2 →}} NO 2 - + H 2 O + 2H + nitrite oxidizing bacteria ^{_{NO 2 - + 1 / 2O 2}} → NO 3 - denitrification of nitrate nitrogen is carried out under anaerobic conditions, In the presence of an organic compound that can be used as an electron donor, it is reduced by denitrifying bacteria to molecular nitrogen and released to the atmosphere.

Denitrifying bacteria ^{_{NO 3 - + 5H → 1 /}} 2N 2 ↑ + 2H 2 O + OH - The ammonia removal method in wastewater, commonly used in biological treatment method shown in the above processes the gray water of domestic wastewater ing.

Wastewater treatment methods for the purpose of removing biological nitrogen can be roughly classified into a microorganism suspension method (modified sludge method, etc.) and a biofilm method (rotating disk method, circulating contact oxidation method, etc.). Among them, the microbial suspension method includes a circulating denitrification method in which aerobic and anaerobic operations are incorporated in the process, and an intermittent aeration method in which aerobic and anaerobic treatment is repeated in a single layer.

In the intermittent aerated activated sludge method, biological nitrification is generally performed by aerating the inside of the tank by aeration in the aeration process, and in the subsequent agitation process, the aeration process is stopped and agitation is performed by a stirrer. The biological denitrification is performed under aerobic conditions in the tank. That is, nitrogen is removed alternately under aerobic and anaerobic conditions by repeating the aeration process and the stirring process.

In order to create appropriate aerobic and anaerobic conditions and to efficiently remove nitrogen, it is important to adjust the amount and duration of aeration. Therefore, in order to set the optimal aeration amount and aeration time, it is indispensable to grasp various control indices such as ammonia nitrogen and temperature and inflow water amount. It is most important to understand the behavior of nitrogen and nitrate nitrogen in drainage and aeration tanks. However, at present, sufficient techniques for quickly and accurately measuring ammonia nitrogen concentration and nitrate nitrogen concentration have not been established, and it is difficult to perform operation management.

Therefore, what is needed as a new index of nitrification and denitrification in operation management is needed.

As a conventional technology, dissolved oxygen concentration (hereinafter referred to as DO)
Value [the 22nd (Showa 60) sewer study presentation lecture collection 454th
~ 456] or redox potential (hereinafter referred to as ORP) [27th (1990) Sewage Works Research Conference Lecture Book 396-3]
Page 98] is used as a control index to know the state of the aerobic / anaerobic atmosphere in the tank, but this method sets the target value of the DO value or ORP value in advance and sets the actual aeration tank. The aeration is continuously measured by a sensor, and the appropriate aeration amount or aeration time is determined so that the target measurement value in each of the aeration and stirring processes is within the set range. .

The problem of this conventional technology is that various factors (BOD load,
Changes in the amount of inflow water, water temperature, etc.). For example, when the BOD load in water is high, the DO value is lower than usual, because more oxidation is required for BOD decomposition. In addition, the ORP value in the tank decreases because the inside of the tank moves more anaerobically. Conversely, when the BOD load decreases, the amount of oxygen consumed decreases and the DO / ORP value increases. Similarly, DO, D, D
The range in which the RP value changes fluctuates. Especially in the day
It is difficult to set a target range of DO / ORP values appropriate for nitrification / denitrification reactions when treating general household wastewater or the like where the BOD load and inflow water amount fluctuate greatly.

(Problems to be Solved by the Invention) As described above, in the prior art, it is difficult to set the target range because the DO / ORP value is greatly affected by various factors such as fluctuations in the BOD load. It had a problem that.

The present invention solves the drawbacks of the prior art, finds a management index capable of detecting the completion of the nitrification / denitrification reaction, and provides a wastewater management treatment method that facilitates operation management. It is intended for.

(Means for Solving the Problems) The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the inflection point of the curve obtained in the continuous measurement of DO / ORP values shows The present invention has been achieved by focusing on the fact that the nitrogen reaction is completed.

That is, the present invention provides a method of treating ammonia nitrogen in wastewater by biological nitrification by an activated sludge method of an intermittent aeration method, wherein the DO (dissolved oxygen concentration) value of the wastewater in the aeration tank is continuously measured. When the DO (dissolved oxygen concentration) curve rises after the start of aeration, the inflection point where the slope of the rise curve sharply increases is detected, and this is used as an indicator of the completion of nitrification, and aeration is stopped. Continuous measurement of the ORP (oxidation-reduction potential) value of the wastewater is performed, and when the ORP (oxidation-reduction potential) curve descends after aeration is stopped, an inflection point where the slope of the falling curve sharply increases is detected and detected. The gist of the present invention is a wastewater management method characterized by restarting aeration as an indicator of the completion of nitrification.

In the wastewater treatment by the intermittent aeration method activated sludge method in the present invention, for example, in the aerobic process, the DO after the start of aeration is used.
When the value curve rises, an inflection point at which the slope of the rising curve sharply increases is detected, and this is used as an indicator of nitrification completion to stop aeration. In the anaerobic process, ORP (oxidation-reduction potential) (2) When the value curve descends, an inflection point at which the slope of the descending curve sharply increases is detected, and this is used as an index of the completion of denitrification, and management operation is performed such that aeration is restarted.

In particular, in the present invention, the above DO (dissolved oxygen concentration)
The aeration time can be set using the value inflection point as an index, and the aeration stop time can be set using the inflection point of the ORP (oxidation-reduction potential) value curve as an index.

Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic view of an example of an apparatus for carrying out the wastewater treatment method of the present invention. The apparatus in Fig. 1 is structurally the same as a general activated sludge method, and has a flow control tank 1, an aeration tank 2,
The aeration tank is divided into a former stage 2 and a latter stage 3, and a part of the treated water from the latter stage 3 of the aeration tank is returned to the former stage 5 of the aeration tank. Aeration was started and stopped simultaneously in the first and second stages of the tank.

Figure 2 shows the location of the measuring instrument in the aeration tank.
The RP sensor measures DO at the middle part of the former stage of the aeration tank 2 and measures DO.
The sensor measured the result of each measurement continuously with the middle part of the latter part of the aeration tank 3 as the measurement point 7. The measurement was performed at the fixed points 6 and 7 on both sides after starting the control operation (when aeration was stopped).
Water was sampled every minute, and each of nitrate nitrogen and ammonia nitrogen was measured.

 Table 1 shows the operating conditions of the examples.

Before the control operation (normal operation), the aeration time is 60 minutes,
The aeration was stopped for 45 minutes, but the end of the aeration in the normal operation was set to 0 minute, the management operation of the present invention was performed, and each measurement was started.

Fig. 3 shows the measurement results of the control operation every 5 minutes. Fig. 3 shows the ORP value and nitrate nitrogen at the measurement point 6 in the former stage 2 of the aeration tank and the DO at the measurement point 7 in the latter stage 3 of the aeration tank. At the measurement point 6 in the first stage 2 of the aeration tank, the slope of the ORP value curve at the time of the drop became sharply large 32 minutes after the start of the measurement (8A). As a result of continuing monitoring until 34 minutes later, it was confirmed that this (8A) was an inflection point in the present invention, and aeration was started (9A). The nitrate nitrogen concentration is 0.1 mg / l after 30 minutes (8B) close in time to the inflection point (8A)
It was clear that the denitrification reaction was completed.

At the measurement point 7 in the latter part of the aeration tank 3, the DO value immediately after the aeration was started (9C) after 34 minutes (10C) showed about 0.2 mg / l, and the DO value curve increased after 46 minutes (11C). Since the inclination of the time suddenly increased, monitoring was continued 51 minutes later (12C). As a result, it was confirmed that this (11C) was an inflection point in the present invention, and the aeration was stopped. At 46 minutes (11D), the ammoniacal nitrogen had decreased to 0.1 mg / min, indicating that nitrification was complete.

In the example, after that, the control operation was continued until 120 minutes later, but the measured values at each measurement point were almost the same as above.

 Table 2 shows the water quality before and after the treatment in the examples.

The result of implementing the management operation of the present invention is as described above.
The ammonia nitrogen in the treated water was 0.1mg / or less, and the nitrogen removal rate was 95%, which was extremely good. It was confirmed that excellent removal rates were obtained for BOD, COD and SS.

(Effects of the Invention) According to the present invention, it is appropriate to use an inflection point that appears when the DO value curve rises during aeration as an index of the completion of the nitrification reaction in the activated sludge wastewater treatment using an intermittent aeration method. Using the inflection point that appears when the ORP value curve descends when aeration is stopped as an indicator of the completion of the denitrification reaction has also been found to be appropriate, and is extremely excellent in controlling wastewater treatment and significantly reduces the treatment efficiency. This makes it possible to perform excellent nitrogen removal.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an embodiment of wastewater treatment according to the method of the present invention, FIG. 2 is a schematic diagram showing two measurement points in a two-piece aeration tank of a treatment apparatus, and FIG. 3 is an aeration tank of the embodiment. It is a figure which shows the behavior of the ORP value and nitrate nitrogen at the measurement point (6) of the former stage, and the DO value and ammonia nitrogen at the measurement point (7) of the latter stage of the aeration tank. 1; flow control tank 2; aeration tank 3; aeration tank 4; sedimentation tank 5; recirculated water 6; measurement point 7 in the front of the tank 7; measurement point 8A in the rear of the tank; 32 minutes after the start of measurement (inflection ORP value at point 8B; nitrate nitrogen value 30 minutes after measurement started 9A; ORP value at 34 minutes after measurement started (aeration started) 9C; DO at 34 minutes after measurement started (aeration started) Value 10C; DO value immediately after the start of aeration 11C; DO value 46 minutes after the start of measurement (inflection point) 11D; ammonia nitrogen value 46C after the start of measurement 12C; 51 minutes after start of the measurement ( DO value of aeration stop)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 3/30 C02F 3/34 101 A C02F 3/12

Claims (1)

(57) [Claims] 1. A method for treating ammonia nitrogen in waste water by biological nitrification by an intermittent aeration type activated sludge method, wherein DO (dissolved oxygen concentration) value of waste water in an aeration tank is continuously measured, and aeration is started. When the DO (dissolved oxygen concentration) curve rises later, an inflection point where the slope of the rising curve sharply increases is detected, and this is used as an indicator of nitrification completion, and aeration is stopped. (Oxidation-reduction potential) value is measured continuously, and when the ORP (oxidation-reduction potential) curve descends after aeration is stopped, the inflection point where the slope of the falling curve sharply increases is detected, A method for managing and treating drainage, comprising restarting aeration as an indicator.