JPS61212395A - Biological denitrification method for waste water - Google Patents

Abstract

PURPOSE:To make possible the discharge of waste water after controlling efficiently the content of nitrogen therein to a prescribed value or below by measuring the inflow rate of feed water, total nitrogen concn. of the feed water, the concn. of return sludge and the concn. of the activated sludge in circulation water and controlling the flow rates of the circulation liquid and due amt. of the return sludge. CONSTITUTION:The inflow rate of the feed water, the total nitrogen content of the feed water, the concn. of the return sludge and the concn. of the activated sludge in the circulation water are measured in a method for denitrifying biologically the waste water by a nitrifying liquid circulation system. The flow rates of the circulation liquid and the amt. of the return sludge are calculated in accordance with the measured values and the flow rates of the circulation liquid and the amt. of the return sludge are controlled in accordance with the calculated values. As a result, the decrease in the reaction rate caused by the dissolved oxygen carried into an anaerobic tank by the excessive circulation water is prevented and the denitrification efficiency is improved. The cost of the driving power for aeration and liquid circulation is reduced and the cost of the treatment is reduced. The BOD removal efficiency and denitrification efficiency are stabilized as well.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for biological denitrification of wastewater in a nitrification solution circulation system, particularly for urban sewage and industrial wastewater where the amount of wastewater and the nitrogen concentration in the wastewater constantly fluctuate. The present invention relates to a biological denitrification method that can efficiently reduce the nitrogen concentration to a predetermined concentration or lower in wastewater.

Biological treatment methods using activated sludge have traditionally been used for wastewater treatment. Conventional activated sludge treatment is mainly aimed at removing BOD components, and only recently has serious efforts been made to remove nitrogen components. Since the biological denitrification treatment method for wastewater is still in the development stage, its operation and management is currently performed based on default settings and manual management. These initial settings are based on the expected maximum load (wastewater concentration x wastewater volume) and the removal rate at the lowest water temperature. These values vary depending on the day, time, or season, but if operation is performed at the initial set values when the load decreases or the removal rate increases, more circulating water and return sludge will flow than necessary. This results in the following problems.

■ Dissolved oxygen brought in by more circulating water than necessary reduces the anaerobic level in the anaerobic tank and slows denitrification reactions.

■ Dissolved oxygen flows out of the aerobic tank due to more water being circulated than necessary, increasing the power cost required for aeration. Also, when aerating the aerobic tank with a gas containing high concentration oxygen, the amount of oxygen consumed increases. do.

■ Power costs for nitrification liquid circulation and sludge return will increase.

Furthermore, in order to stably perform the denitrification reaction, nitrification reaction, and BOD oxidation reaction in the process, it is necessary to keep the activated sludge concentration in the treatment tank constant at all times. In a general activated sludge process that targets only the removal of BOD components, it is possible to control the activated sludge concentration in the treatment tank by determining the amount of returned sludge from the concentration of raw water and returned sludge, but the nitrification liquid circulation method In the case of the biological denitrification method, it is necessary to set the denitrification rate within an appropriate range, and it is not possible to perform satisfactory management using only this method.

Problems to be Solved by the Invention The present invention aims to improve the operating conditions in the activated sludge treatment process in response to fluctuations in the nitrogen concentration in raw water and the amount of raw water in a biological and chemical denitrification method for wastewater using a nitrification liquid circulation system. An object of the present invention is to provide a biological denitrification method and device for wastewater that can be automatically controlled and efficiently reduced to a nitrogen content below a predetermined value before being discharged. In a method for biologically denitrifying wastewater using a liquid circulation method, the inflow amount of raw water, total nitrogen concentration of raw water, return sludge concentration, and activated sludge concentration of circulating water are measured, and based on the measured values, the circulating fluid is denitrified. The present invention relates to a method for biological denitrification of wastewater, characterized in that the amount of circulating fluid and the amount of returned sludge are controlled based on the calculated values.

An overview of the biological denitrification method using the apparatus of the present invention will be explained using FIG.

Biological denitrification of wastewater using a nitrifying solution circulation method involves a mixture of aerobic bacteria that decompose organic matter, nitrifying bacteria that oxidize Kjeldahl nitrogen to oxidized nitrogen, and denitrifying bacteria that reduce oxidized nitrogen to nitrogen gas. Using single-phase sludge, this is transferred to a denitrification tank (1
) and the nitrification tank (2), and the raw water (4) is introduced into the nitrification tank (2) via the denitrification tank (1), and contains oxidized nitrogen that has been oxidized by air or oxygen aeration in the nitrification tank (2). Nitrification liquid (6
) is circulated to the denitrification tank, and in the denitrification tank, the BOD in the raw water is
A method of denitrification by reducing oxidized nitrogen using a component as an organic carbon source, such as the Rudzak method, improved versions of which are disclosed in JP-A No. 57-10391 and Japanese Patent Application No. 59-26939.
0, Japanese Patent Application No. 59-269391, and the like.

The treated water to be discharged needs to be denitrified and BOD components removed to an extent that it does not cause environmental pollution, that is, to a target value. However, the raw water (4) introduced into the treatment system is, for example, sewage, and the amount of treatment and BOD
Since the amounts of the components and the total nitrogen concentration change from moment to moment, it is necessary to appropriately control other factors in order to keep them within the target values and to operate the treatment system efficiently. In the present invention, the control is performed using a nitrification liquid circulation type (6).
The feature is that this is carried out by controlling the amount of returned sludge (7).

That is, in the present invention, first, the raw water inflow 41 (Q), the total nitrogen concentration (Nin) of the raw water, the returned sludge concentration (CR), and the activated sludge concentration (Cc) of the circulating water are measured by the raw water flow rate measuring means (9).
), raw water total nitrogen concentration measuring means (10), circulating water sludge concentration measuring means (11), and return sludge concentration measuring means (12)
Measure using.

On the other hand, if the target value of the total nitrogen concentration of the treated water is Ng, and the target value of the activated sludge 6 degree in the treatment tank is cg, then the formula: [In the formula, RA and Ra are respectively (1-RA) The denitrification rate in the aerobic tank, (1-R,) indicates the nitrification rate in the aerobic tank, and usually both (1-RA) and (1-R,) are 0.8.
It is set in the range of 0 to 0.98. rl is the ratio of circulating water to inflow water IQ, and r is a value indicating the ratio of returned sludge to inflow water ff1Q].

Therefore, the amount of inflow of raw water (Q), the total nitrogen concentration of raw water (Ni
n), return sludge concentration (CR), activated sludge concentration of circulating water (
Cc) as a control factor, and using the above-mentioned formula to calculate r and r, using the measured value as a control factor, the circulating water amount control means (14) and the return sludge amount control means ( 15) makes it possible to fully automatically and efficiently perform biological denitrification of wastewater.

In addition, in the present invention, the amount of raw water flowing in, the total nitrogen concentration in the raw water, the returned sludge concentration, and the activated sludge concentration in the circulating water are constantly monitored, and based on the measured values, the circulating water amount and returned sludge amount are continuously adjusted. A control method is more preferable, but since analysis requires time in a typical total nitrogen concentration automatic analyzer, the sample sampling period is set to about 15 to 60 minutes. Therefore, the actual control period is preferably set to 15 to 120 minutes, more preferably 30 to 60 minutes. In this case, the average amount of inflow water, average total nitrogen concentration of raw water, average value of returned sludge concentration, and average value of activated sludge concentration of circulating water in each control cycle are predicted using mathematical means, and the average value of activated sludge concentration in circulating water is predicted using mathematical means. It is better to use the data of

An autoregressive model is generally used as a mathematical prediction method.

In the m-th order autoregressive model, the value X(b
) is the value xQ+-t) at time (1+-1).

Value x(t+-2t) at time (t+-2t),・
- Using the value X (b nt) at time (t l - mt), X (L +) - a X (b t) + a X (
t+2t)""+am x(t+-mt). Here, alla, . . . a□ are coefficients of an m-th order autoregressive equation, and can be determined mathematically using existing data regarding the phenomenon. The optimal value of the order m of the autoregressive model is also determined mathematically using existing data, but when the control period is set to 30 to 60 minutes, the value of m is generally 2 to 4.

The present invention will be explained below with reference to Examples.

Food manufacturing wastewater (treated raw water) containing Kannojo gray water was treated using the biological denitrification equipment shown in Figure 1.

The device specifications and processing conditions are as follows.

Note that a comparative example in which the same device was used and the control was performed manually is shown.

Equipment specifications Anaerobic tank: 450Il aerobic tank:
1st nitrification tank 390! Second nitrification tank
3901゜ Raw water inflow measuring means: Electromagnetic flow meter Total nitrogen concentration measuring means of raw water: Total nitrogen automatic analyzer Return sludge concentration measuring means: Scattered light comparison type Circulating water activated sludge concentration measuring means: Scattered light comparison type MLSS meter Pulp Returned sludge amount control means 〃Processing conditions Processing raw water quality: BOD average 250mg/4Total nitrogen amount 23mg/kg Processing raw water inflow: 6.7m'/day Oxygen concentration in aeration gas of No. 1 nitrification tank: 35% Oxygen concentration in the aeration gas of the 2 nitrification tank = 70% The results obtained by the above treatment are shown in Table 1.

Note 1: Although the sludge concentration in the treatment tank in Example (A) can be automatically adjusted by controlling the amount of returned sludge, the target value (Cg) was set to 5000 mg/k.

In Comparative Example (B), the activated sludge was gradually removed manually. Therefore, the sludge concentration is the sum of the decrease due to sampling and the increase due to natural growth.

Note 22 The redox potential represents the level of taste in the tank, and the lower it is, the higher the level of kamaki. It can be seen that in the example, since the amount of circulating water was small, the anaerobic level was kept high.

Note 3: The peak in Comparative Example (D) is due to an increase in the nitrogen concentration in the treated raw water and the amount of raw water, indicating that these effects directly affect the total nitrogen content in the wastewater. .

On the other hand, this example (C) is not affected by fluctuations in the nitrogen concentration or amount in the treated raw water, and can suppress fluctuations in the total nitrogen amount in wastewater by ±1 m
This shows that it is possible to keep the amount within the range of g/11.

Note 4: The amount of circulating water and the amount of returned sludge are the daily total of the amount sent under automatic control in the example, and the fixed amount (
However, the amount of returned sludge is adjusted once a day).

In addition, in the example, treated water with BOD components and total nitrogen removed more than the comparative example was obtained with a smaller amount of circulating water and a smaller amount of returned sludge than the comparative example.

Effects of the invention (1) Excess circulating water prevents a reduction in reaction rate caused by dissolved oxygen brought into the anaerobic tank, and improves denitrification efficiency.

(2) Power costs for aeration and liquid circulation are reduced, reducing processing costs.

(3) BOD removal efficiency and denitrification efficiency are stabilized.

(4) Dissolved oxygen flowing out due to circulating water decreases,
When aeration in an aerobic tank is performed with a high-strength oxygen-containing gas, the amount of oxygen consumed decreases.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the apparatus of the present invention, FIG. 2 is a diagram showing changes over time in sludge concentration in a treatment tank, and FIG. 3 is a diagram showing changes in total nitrogen concentration in wastewater over time. (1) Anaerobic tank (denitrification tank) (2) Aerobic tank (nitrification tank) (2°) First nitrification tank (2”’) Second nitrification tank (3) Sedimentation tank (4) Raw water (5) Treatment Water (6) Circulating water (7) Returned sludge, (8) Excess sludge, (9) Raw water flow rate measuring means, (IO) Raw water total nitrogen concentration measuring means, (2) Circulating water sludge concentration measuring means, (12) return sludge concentration measuring means, (13) calculation unit, (14) circulating water amount control means, (15) return sludge amount control means, (A), (C) results obtained in the examples of the present invention, ( B
), (D) Results obtained in comparative examples. <1/BuJ) *'t-Y'aGuakN5t00QQ
QC! ψ of O d6? ~

Claims (1)

[Claims] 1. In a method of biologically denitrifying wastewater using a nitrifying solution circulation method, the inflow of raw water, total nitrogen concentration of raw water, return sludge concentration, and activated sludge concentration of circulating water are measured, and the circulation is started based on the measured values. A method for biological denitrification of wastewater, which comprises calculating the amount of liquid and the amount of returned sludge, and controlling the amount of circulating liquid and the amount of returned sludge based on the calculated values.