JPH11253990A - Treatment of nitrogen-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimally control the proper flow rate of raw water in intermittent aeration treatment aeration quantity during an aerobic time and the loadings of a hydrogen donor during an anaerobic time even if the concn. of nitrogen in raw water changes. SOLUTION: The pH change in a reaction tank where intermittent aeration treatment is performed is measured and, from the flexural point thereof, the completion of nitration reaction is detected and the concn. of nitrogen in raw water is estimated from the obtained nitration time. The flow rate of raw water is controlled from the concn. of nitrogen in raw water in order to keep the nitrogen load to the reaction tank constant. Or, aeration quantity at a time of an aerobic state is controlled corresponding to the concn. of nitrogen in raw water. Or, the loadings of a hydrogen donor in an anaerobic state are controlled with respect to nitrogen load varied corresponding to the concn. of nitrogen in raw water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to secondary sewage water,
The present invention relates to a method for treating nitrogen-containing wastewater of an intermittent aeration type, which can efficiently remove nitrogen from nitrogen-containing wastewater such as leachate from a landfill, rivers, human waste, and industrial wastewater.

[0002]

2. Description of the Related Art In order to remove nitrogen from wastewater, a nitrification process of oxidizing organic nitrogen or ammonia nitrogen in wastewater in the presence of oxygen in an aerobic tank and converting it into nitrate nitrogen is performed. A denitrification process of converting nitrate nitrogen into nitrogen gas in an anaerobic tank is required. Usually, an aerobic tank and an anaerobic tank are arranged in series to remove nitrogen. In this case, two tanks are required,
An intermittent aeration process in which aerobic conditions and anaerobic conditions are alternately created by performing intermittent aeration in a single reaction tank to remove nitrogen is also known.

An important operating factor in the intermittent aeration treatment is how to take an aerobic time (nitrification time) and an anaerobic time (denitrification time).
Processing is performed by setting each time in advance, such as time. However, since the nitrification capacity and the denitrification capacity differ depending on environmental conditions such as the water temperature and the ratio of the organic component to the nitrogen component in the wastewater, it is desired to control these times according to the environmental conditions. Therefore, DO in the processing tank
It has already been proposed to control aerobic time and anaerobic time by measuring (dissolved oxygen concentration), OPR (redox potential) and the like.

However, although the aerobic time and the anaerobic time can be controlled by such a method, an appropriate raw water flow rate, an aeration amount during the aerobic time, and an addition amount of the hydrogen donor during the anaerobic time are controlled. I couldn't do that. That is, these are all values to be determined according to the raw water nitrogen concentration, but it is necessary to use a general analysis method for measuring the raw water nitrogen concentration, or to introduce an expensive automatic nitrogen measurement device, For example, it has not been possible to perform real-time economical control on wastewater whose raw water nitrogen concentration fluctuates greatly, such as leachate from a landfill.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides an appropriate raw water flow rate in intermittent aeration treatment, aeration during aerobic time, hydrogen donor addition during anaerobic time, and the like. The present invention has been made to provide a method for treating nitrogen-containing wastewater in which nitrogen can be efficiently removed by optimally controlling the concentration of nitrogen in raw water in real time.

[0006]

Means for Solving the Problems As a result of research conducted by the present inventors to solve this problem, when a pH change in a reaction tank is measured under aerobic conditions, a bending point appears at the same time as the end of the nitrification reaction. It was also found that the nitrogen concentration in the raw water can be estimated from the time required for this nitrification and the nitrification rate according to the previously measured temperature. The present invention has been made based on these findings, the first invention is to detect the end of the nitrification reaction from the inflection point by measuring the pH change in the reaction tank where intermittent aeration treatment is performed, The nitrogen concentration of raw water is estimated from the obtained nitrification time, and the flow rate of raw water is controlled based on the nitrogen concentration of raw water to keep the nitrogen load of the reaction tank constant.

The second invention measures the pH change in the reaction tank where the intermittent aeration process is performed, detects the end of the nitrification reaction from the inflection point, and estimates the nitrogen concentration of the raw water from the obtained nitrification time. Then, the amount of aeration in an aerobic state is controlled with respect to the nitrogen load fluctuating from the raw water nitrogen concentration, and the third invention is characterized in that the pH change in the reaction tank where the intermittent aeration is performed is controlled. While measuring and detecting the end of the nitrification reaction from the inflection point, the raw water nitrogen concentration is estimated from the obtained nitrification time, and the addition amount of the hydrogen donor in the anaerobic state with respect to the nitrogen load fluctuating from the raw water nitrogen concentration is determined. It is characterized by controlling.

In the intermittent aeration treatment in which the aerobic state and the anaerobic state are repeatedly repeated in a single reaction tank, if the aerobic time and the anaerobic time are predetermined (for example, up to 30 minutes), the nitrification reaction by the microorganism is terminated and the reaction is terminated. When the ammonia nitrogen disappears from the tank, a bending point appears on the pH change curve as shown in FIG. There is a correlation between the time (t) required for this nitrification and the ammonia nitrogen concentration of the raw water.

For example, in an intermittent aeration apparatus in which a reaction vessel is filled with 40% polyvinyl alcohol gel as a carrier, the residence time is 12 hours, and the number of repetitions of the aerobic state and the anaerobic state is 12 times. It was confirmed that the relationship shown in FIG. 2 was established between the nitrification time (time from the start of nitrification to the appearance of the inflection point) and the concentration of ammonia nitrogen in the raw water under the condition of 20 ° C. The reason why such a correlation is established is as follows.

First, the rate of reduction of ammonia nitrogen under an aerobic condition depends on the nitrification rate of nitrifying bacteria in a reaction tank. Therefore, if the nitrification rate is known, the ammonia nitrogen at the start of the aerobic state is shorter than the nitrification time. The concentration can be estimated. At this time, since the nitrification rate is affected by the water temperature as shown in FIG. 3, the nitrification rate in consideration of the relationship with the water temperature is used.

The ammonia nitrogen concentration at the start of the aerobic state and the ammonia nitrogen concentration in the raw water are defined as follows: when the nitrification reaction is completed during the aerobic state and when the denitrification reaction is completed during the anaerobic state, It is represented by Equation 1. Here, the ammonia nitrogen concentration at the start of the aerobic state is C _NH4 , the ammonia nitrogen concentration in the raw water is C ₀ , and the number of repetitions of the aerobic state and the anaerobic state is N.

## EQU1 ## C _NH4 = C ₀ (1−exp (− ／ N))

For this reason, the nitrification time can be determined from the inflection point of the pH change in the reaction tank, and the nitrogen concentration of the raw water can be estimated from the nitrification time. In order to efficiently remove nitrogen from raw water from the raw water nitrogen concentration obtained as described above, the present invention employs the means shown in the following embodiments.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION (First Invention) A change in pH in a reaction tank where an intermittent aeration process is performed is continuously measured by a known pH meter, and the end of the nitrification reaction is detected from the inflection point, and nitrification is performed. The nitrification time, which is the time from the start until the inflection point appears, is calculated. From the nitrification time and the previously determined nitrification rate, the raw water nitrogen concentration is estimated by the above equation. In the first invention, the flow rate of the raw water is controlled based on the nitrogen concentration of the raw water in order to keep the nitrogen load of the reaction tank constant.

Normally, when the nitrogen load in the reaction vessel fluctuates, the intermittent aeration treatment cannot be performed properly unless the amount of aeration in the aerobic state or the amount of the hydrogen donor added in the anaerobic state is adjusted. However, in the first invention, the flow rate of the raw water is controlled using the nitrogen concentration of the raw water as an index, and the amount of ammonia nitrogen flowing into the treatment tank within a unit time is kept constant. As a result, even for wastewater in which the concentration of nitrogen in the raw water is significantly fluctuating, efficient nitrogen removal can be performed by intermittent aeration.

(Second Invention) In the second invention, the aeration amount in the aerobic state is controlled according to the raw water nitrogen concentration obtained as described above, and an appropriate air supply amount is always maintained. . Specifically, when the raw water nitrogen concentration is high, the output of the blower is increased to increase the aeration amount, and when the raw water nitrogen concentration is low, the output of the blower is reduced. As a result, it is possible to efficiently remove nitrogen by intermittent aeration even for wastewater in which the concentration of nitrogen in the raw water is significantly fluctuating.

(Third Invention) In the third invention, the amount of the hydrogen donor added in an anaerobic state is controlled with respect to the nitrogen load that fluctuates according to the raw water nitrogen concentration obtained as described above. When methanol is used as a hydrogen donor, 2.47 g of methanol is required for 1 g of nitrate nitrogen. Therefore, when nitrification is completely performed, methanol is added at least 2.47 times the amount of ammonia nitrogen in the raw water. This allows efficient nitrogen removal for fluctuating nitrogen loads.

[0017]

As described above, according to the present invention, it is possible to accurately estimate in real time the concentration of nitrogen in raw water, which could not be quickly grasped in the past, and to obtain an appropriate raw water flow rate and aerobic flow in intermittent aeration processing. By optimally controlling the amount of aeration during time and the amount of hydrogen donor added during anaerobic time, nitrogen can be removed efficiently. For this reason, efficient treatment is possible even for wastewater in which the concentration of raw water nitrogen, such as leachate from a landfill site, fluctuates greatly.

[Brief description of the drawings]

FIG. 1 is a graph of a pH change curve in an intermittent aeration process.

FIG. 2 is a graph showing the relationship between nitrification time and raw water nitrogen concentration.

FIG. 3 is a graph showing the relationship between water temperature and nitrification rate.

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[Procedure amendment]

[Submission date] February 4, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006]

Means for Solving the Problems As a result of research conducted by the present inventors to solve this problem, when a pH change in a reaction tank is measured under aerobic conditions, a bending point appears at the same time as the end of the nitrification reaction. It was also found that the nitrogen concentration in the raw water can be estimated from the time required for this nitrification and the nitrification rate according to the previously measured temperature. The present invention has been made based on these findings, the first invention is to detect the end of the nitrification reaction from the inflection point by measuring the pH change in the reaction tank where the intermittent aeration treatment is performed, From the obtained nitrification time, the raw water nitrogen concentration is estimated, and based on this raw water nitrogen concentration, the nitrogen flow in the reaction tank is controlled within a unit time to keep the nitrogen load of the reaction tank constant.
It is characterized in that the flow rate of raw water is controlled so as to keep the amount of nitrogen introduced constant .

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

The second invention measures the pH change in the reaction tank where the intermittent aeration process is performed, detects the end of the nitrification reaction from the inflection point, and estimates the nitrogen concentration of the raw water from the obtained nitrification time. From this raw water nitrogen concentration ,
Increase the amount of aeration when it is high, decrease it when it is low
The amount of aeration in an aerobic state is controlled with respect to such a fluctuating nitrogen load.
In an anaerobic condition, the pH change in the reaction tank where the intermittent aeration process in which the hydrogen donor is added is performed, and the end of the nitrification reaction is detected from the inflection point, and the raw water nitrogen concentration is estimated from the obtained nitrification time. From this raw water nitrogen concentration ,
When the concentration of is high, increase the amount of hydrogen donor added, and
In some cases, the amount of the hydrogen donor added in an anaerobic state is controlled with respect to a fluctuating nitrogen load so as to reduce the amount.

Claims (3)

[Claims] Claims: 1. pH in a reaction tank where intermittent aeration is performed
The change is measured and the end of the nitrification reaction is detected from the inflection point.The raw water nitrogen concentration is estimated from the obtained nitrification time, and the raw water flow rate is determined from this raw water nitrogen concentration to keep the nitrogen load of the reaction tank constant. A method for treating nitrogen-containing wastewater, comprising controlling. 2. The pH in a reaction tank where intermittent aeration is performed.
The change is measured, the end of the nitrification reaction is detected from the inflection point, and the raw water nitrogen concentration is estimated from the obtained nitrification time, and the amount of aeration in the aerobic state is controlled for the nitrogen load fluctuating from this raw water nitrogen concentration. A method for treating nitrogen-containing wastewater. 3. The pH in a reaction tank where intermittent aeration is performed.
The change is measured, the end of the nitrification reaction is detected from the inflection point, and the raw water nitrogen concentration is estimated from the obtained nitrification time, and the addition of the hydrogen donor in an anaerobic state to the nitrogen load fluctuating from the raw water nitrogen concentration A method for treating nitrogen-containing wastewater, comprising controlling the amount.