JPH08267087A - Batch activated-sludge treatment of waste water - Google Patents

Abstract

PURPOSE: To shorten the treating time in the method for removing nitrogen and phosphorus from waste water in batches by detecting the end nitration point in the nitration stage and the end denitrification point in the denitrification stage by the change of an oxdidation-reduction potential and successively changing the succeeding stages. CONSTITUTION: In the activated-sludge treatment, methanol is added in the initial anaerobic stage (2) when the org. matter is deficient in the waste water discharged from a biological reaction tank 1 in the denitrification stage, and activated sludge is charged as a second stage. An aerobic stage (1), anaerobic stage (2), aerobic (2), settling, discharge and standby stages are successively conducted. The ammoniacal nitrogen is nitrated in the aerobic stage (1), and the nitrate nitrogen is removed in the anaerobic stage (2). In this case, the time when an increment of the oxidation-reduction potential amounts to <0.5mV /min in the nitration stage is considered to be the nitration end point, and the time when a decrement of the potential becomes >1.2 times the preceding decrement in the denitrification stage is considered to be the denitrification end point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a batch of wastewater for simultaneously removing both nitrogen and phosphorus from wastewater containing ammonia nitrogen and phosphorous phosphate, such as municipal wastewater, underground water, and food processing industry. Type activated sludge treatment method.

[0002]

2. Description of the Related Art A batch-type activated sludge treatment method (hereinafter, abbreviated as batch-type activated sludge method) is a series of wastewater including inflow of wastewater, aerobic treatment, anaerobic treatment, solid-liquid separation of activated sludge, and discharge of treated water. This is a method of treating wastewater in which a unit treatment operation is performed in a single biological reaction tank. Simultaneous removal of organic matter, nitrogen, and phosphorus can be performed relatively easily, and nitrogen and phosphorus can be removed simply by modifying the existing standard activated sludge process facility.
In recent years, it has become particularly noticeable.

For example, "Steelmaking Research", vol 329, p.
66 and 1988, the following anaerobic 1 step-aerobic 1 step-
A batch type activated sludge method comprising a cycle of anaerobic 2 steps-aerobic 2 steps-stationary step-discharging step is described.

In the anaerobic one step, the phosphoric acid phosphorus (PO ₄ -P) is released from the activated sludge by introducing effluent into the biological reaction tank and maintaining the inside of the biological reaction tank anaerobic at the same time.

In the aerobic one step, by maintaining aerobic inside the biological reaction tank, ammonia nitrogen (NH _{4 -} N) is oxidized (nitrification) to nitrate nitrogen (NO _3- N) to remove organic matter. Simultaneously with oxidative decomposition, phosphorus is removed by incorporating phosphoric acid phosphorus into activated sludge excessively.

In the anaerobic 2 step, the nitrogen in the biological reaction tank is maintained anaerobic to reduce (denitrify) nitrate nitrogen to nitrogen gas and remove nitrogen.

In the aerobic 2 step, the oxidative decomposition of the organic matter is carried out by keeping the inside of the biological reaction tank aerobic.

In the stationary step, the activated sludge is settled by stopping all stirring and aeration in the biological reaction tank.

In the discharging step, the supernatant in the biological reaction tank is discharged as treated water.

[0010]

The batch type activated sludge method requires a nitrification step for nitrifying ammonia nitrogen and a denitrification step for denitrifying nitrate nitrogen. The process time depends on the nitrogen concentration in the wastewater,
It must be decided according to the processing temperature. For example, when the nitrogen concentration in the wastewater is high, it is necessary to make the treatment time longer than in the case where the nitrogen concentration in the wastewater is low, and at the time of low temperature such as winter when the activity of activated sludge decreases,
The treatment time needs to be longer than when the temperature is high such as in summer. In the normal batch activated sludge method, these treatment times are set to a time at which the inflowing wastewater having the maximum nitrogen concentration can be treated even at the lowest temperature in winter, and are operated on the same schedule throughout the year.

However, since the treatment time required for nitrification and denitrification in summer is shorter than that in winter, the actual nitrification and denitrification are already completed before the nitrification and denitrification process is completed. Should be. In this way, maintaining the nitrification and denitrification processes more than necessary not only wastes power consumption due to the operation of blowers and agitators, but also causes auto-oxidative decomposition and bulking of activated sludge due to excessive aeration in the nitrification process. Occurs, and in the denitrification process, phosphate phosphorus taken in in the nitrification process is re-released, which may hinder stable and favorable operation.

Therefore, Japanese Patent Laid-Open No. 61-54296 discloses a method of controlling the time of the nitrification process according to the measured value of the dissolved oxygen amount (DO) in the biological reaction tank.
Japanese Patent No. 127098 describes a method of controlling the time of the nitrification step depending on the water temperature of waste water and the measured value of DO in the biological reaction tank. However, DO almost always shows 0 mg / liter in the denitrification process in an anaerobic state, and it is impossible to control the time of the denitrification process using DO as an index.

An object of the present invention is to appropriately detect the end points of nitrification and denitrification in the nitrification process and denitrification process, and to sequentially change to the next process to process the treatment time of the nitrification process and denitrification process. It is to provide a batch activated sludge method that can be controlled to a minimum required time according to conditions.

[0014]

According to the present invention, nitrification of ammonia nitrogen and denitrification of nitrate nitrogen, incorporation of phosphoric acid phosphate into activated sludge, and separation of activated sludge and treated water into one biological reaction tank. In the batch activated sludge method for wastewater carried out in 1., the end point of nitrification in the nitrification step of ammonia nitrogen in the wastewater and the end point of denitrification in the nitrification step of nitrate nitrogen are taken as redox potential (ORP, silver / silver chloride). This is a batch type activated sludge method for wastewater, which is characterized in that it is detected by the amount of change in the electrode standard) and is changed to the next step one after another. In particular, the end point of the nitrification step should be the time when the increase in the redox potential (ORP, silver / silver chloride electrode reference) per minute in the nitrification step becomes 0.5 mV / min or less. The denitrification step ends when the reduction amount of the redox potential (ORP, silver / silver chloride electrode reference) per minute is 1.2 times or more the reduction amount of the redox potential per minute immediately before that. It is preferable to set it as a point.

[0015]

The redox potential (ORP) is generally defined by the following equation (1). Here, ORP ^* is a standard oxidation-reduction potential specific to the reaction system, K ₀ is a coefficient determined by the Faraday constant and gas constant, T is an absolute temperature, O _x is the concentration of the oxidant,
Red represents the concentration of the reducing substance.

[0016]

Embedded image ORP = ORP ^* + K ₀ · Tlog {(O _x ) / (Red)}

On the other hand, in the nitrification step in the batch activated sludge method, ammonia nitrogen is converted into nitrate nitrogen (NO ₃ ) by the reaction of Chemical formula 2. In this reaction, ammonia nitrogen, which is a reducing substance, decreases, and nitrate nitrogen, which is an oxidizing substance, increases, so that ORP increases.

[0018]

## STR2 ## ^{_{NH 4 + + 2O 2 → NO}} 3 - + H 2 O + 2H +

FIG. 1 shows the changes over time in the ammonia nitrogen concentration, nitrate nitrogen concentration and ORP in the nitrification process (treatment temperature 25 ° C.). The ORP gradually increases as the nitrification of ammonia nitrogen into nitrate nitrogen progresses, but the ORP shows a substantially constant value with the end of nitrification. Therefore, the end point of nitrification can be detected by detecting the point where the ORP shows a substantially constant value. 1 of ORP measured continuously in the nitrification process
When the amount of increase per minute became 0.5 mV / min or less, the amount of ammonia nitrogen in the biological reaction tank was 5 m.
Since it has decreased to g / liter or less, this point can be regarded as the point at which the ORP becomes constant and set as the end point of the nitrification step.

In the denitrification step, nitrate nitrogen is converted into nitrogen gas (N ₂ ) by the reaction of Chemical formula 3. In this reaction, nitrate nitrogen, which is an oxidant, decreases,
The hydrogen donor, which is a reducing substance represented by H in the formula, also decreases. A decrease in nitrate nitrogen tends to decrease ORP, and an increase in hydrogen donor increases ORP. However, a decrease in nitrate nitrogen decreases ORP, and an increase in hydrogen donor increases ORP. Since the rate is higher than the rate of increase, the ORP is lowered as a whole during the denitrification reaction.

[0021]

Embedded image 2NO ₃ ⁻ + 10H → N ₂ + 4H ₂ O + 2OH ⁻

FIG. 2 shows nitrate nitrogen and O in the denitrification process.
The time-dependent change of RP is shown (processing temperature 25 degreeC). ORP gradually decreases as the denitrification of nitrate nitrogen progresses,
It can be seen that the rate of ORP decrease becomes sharp with the completion of denitrification. This is because after the denitrification, organic substances and activated sludge are decomposed in the biological reaction tank, and various kinds of organic acids (reducing substances) are accumulated. Therefore, the denitrification end point can be detected by detecting the point at which the ORP suddenly changes. For that purpose, the ORP reduction amount per minute continuously measured in the denitrification step is 1.2 times the ORP reduction amount per minute immediately before that.
The point at which the denitrification step is doubled may be set as the end point of the denitrification step.

[0023]

EXAMPLE FIG. 3 shows a batch type activated sludge treatment apparatus used for carrying out the present invention.

In the biological reaction tank 1, O of silver / silver chloride electrode
The RP sensor 2, the pH sensor 3, the DO sensor 4, and the stirrer 5 were installed, and the ORP measurement value was input to the control device 6. The stirrer 5, the air blower 8, the waste water supply pump 9, the treated water discharge pump 10, and the methanol supply pump 11 were controlled by the control device 6 and operated as necessary. As the drainage water, the primary treated water of human waste drainage was used.

Table 1 shows the time schedule in one cycle.

[0026]

[Table 1]

One cycle consists of anaerobic 1 step → aerobic 1 step →
The order is anaerobic 2 steps → aerobic 2 steps → static step → discharge step → standby step. For this time schedule,
Nitrification of ammonia nitrogen was performed mainly in the aerobic one step, and denitrification of nitrate nitrogen was mainly performed in the two anaerobic steps.

The waste water was introduced into the biological reaction tank 1 by the waste water supply pump 9 in the anaerobic 1 step, and the treated water was discharged in the discharging step by the treated water discharge pump 10 in an amount half the biological reaction tank volume. In addition, since there was insufficient organic matter in the wastewater to serve as a hydrogen donor during denitrification, methanol / N = 2 (weight ratio) relative to the content (average value) of ammonia nitrogen in the wastewater. ) Was added at the beginning of the anaerobic 2 step. Activated sludge collected from the sewage treatment plant as seed sludge is put into the biological reaction tank 1,
After acclimatization for 1 week, MLSS is 4000-6000mg
It was maintained and managed so that it became / liter.

By the control device 6, the ORP is performed in the aerobic one step.
The amount of decrease in ORP per minute in the anaerobic 2 step is the ORP per minute immediately before that, so that the next step in the anaerobic 2 step is performed when the increase per minute in the above is less than 0.5 mV / min. The control was carried out so that the next two aerobic steps were performed when the amount became larger than 1.2 times the decrease amount. One cycle is 24 hours in total, and the processing time of anaerobic 1 step other than aerobic 1 step, anaerobic 2 steps, aerobic 2 steps, stationary step, and discharging step is always set to be constant, and after the discharging step, The time until the anaerobic one step of the cycle was the standby step. For comparison, an experiment was also conducted in which control by ORP was not performed in the aerobic 1 step and the anaerobic 2 step, and the processing time of all the steps was always set to a constant time.

Table 2 shows the treatment temperature and drainage water quality in each example. The treatment temperature was 20 ° C. or higher in summer, but dropped to 8 ° C. in winter. Moreover, the fluctuation of nitrogen concentration in the wastewater was severe.

[0031]

[Table 2]

Table 3 shows the fluctuations in the processing time of the aerobic 1 step (nitrification step) and the anaerobic 2 step (denitrification step) in each example. In Example 2 in which the concentration of ammonia nitrogen in the wastewater was higher than in Example 1 and in Example 3 in which the treatment temperature was lower, the treatment time was correspondingly longer. Further, in Example 1 in which the treatment temperature was high and Example 3 in which the treatment temperature was low, the ratio of the treatment time of the aerobic 1 step and the anaerobic 2 step also changed. Comparative Example 4
Then, the processing time for the aerobic 1 step was fixed to 14 hours and the processing time for the anaerobic 2 steps was fixed to 6 hours. It was possible to reduce the processing time by 9 hours and 1.2 hours by the anaerobic 2 steps.

[0033]

[Table 3] [Comparative Example 4 fixes the processing time of all steps]

Table 4 shows the quality of treated water in each example.
In any of Examples 1, 2, and 3, ammonia nitrogen,
Nitrate nitrogen is 1 mg / liter or less, and phosphate phosphorus is 2
It was processed well up to mg / liter or less. On the other hand, in Comparative Example 4, although nitrogen was treated well,
Phosphate phosphorus was redissolved from the activated sludge in the anaerobic two steps, and thus the phosphate phosphorus showed a high value of 3.3 mg / liter, and the treatment was poor.

[0035]

[Table 4]

[0036]

INDUSTRIAL APPLICABILITY The present invention determines the treatment time of the nitrification step and denitrification step in the batch activated sludge method,
Since it is changed to the minimum time depending on the processing temperature, it prevents the power consumption due to the excessive operation of the blower and the agitator.
In addition, it is possible to treat ammonia nitrogen and phosphoric acid phosphorus in wastewater while preventing auto-oxidative decomposition of activated sludge in the nitrification process and generation of bulking and re-release of phosphorus from the activated sludge in the denitrification process.

[Brief description of drawings]

FIG. 1 is a diagram showing changes with time of ammonia nitrogen, nitrate nitrogen, and ORP in a nitrification process.

FIG. 2 is a diagram showing changes with time of nitrate nitrogen and ORP in a denitrification process.

FIG. 3 shows an apparatus for carrying out the invention.

[Explanation of symbols]

 1 Biological Reaction Tank 2 ORP Sensor 3 pH Sensor 4 DO Sensor 5 Stirrer 6 Controller 7 Recorder 8 Air Blower 9 Waste Water Supply Pump 10 Treated Water Discharge Pump 11 Methanol Supply Pump

Claims (3)

[Claims] 1. A batch-type activated sludge of wastewater in which nitrification of ammonia nitrogen and denitrification of nitrate nitrogen, incorporation of phosphorous phosphate into activated sludge, and separation of activated sludge and treated water are performed in one biological reaction tank. In the treatment method, the end point of nitrification in the nitrification step of ammonia nitrogen in the wastewater and the end point of denitrification in the nitric acid nitrogen denitrification step are regarded as redox potential (ORP,
A batch type activated sludge treatment method for wastewater, characterized by detecting the amount of change in silver / silver chloride electrode) and sequentially changing to the next step. 2. A redox potential (OR) in the nitrification step.
The batch type activity of the wastewater according to claim 1, wherein the end point of the nitrification step is the time when the increase amount of P, silver / silver chloride electrode) per minute becomes 0.5 mV / min or less. Sludge treatment method. 3. The redox potential (OR
P, the amount of silver / silver chloride electrode) per minute is 1.2 of the amount of decrease in the redox potential per minute immediately before that.
The batch type activated sludge treatment method for wastewater according to claim 1 or 2, wherein a time point at which the denitrification step is doubled or more is set as an end point of the denitrification step.