JPH08192179A - Device for setting residence time of sludge in activated sludge process - Google Patents

Abstract

PURPOSE: To precisely set SRT by determining a set value of SRT by taking into account the amount SS flowing into a treating system measured by a first flowmeter and a concentration meter and the amount SS flowing out of the system measured by a second flowmeter and a concentration meter. CONSTITUTION: Measured values of flow rate of excess sludge measured by excess sludge flowmeters 26, 27 and concentration thereof are inputted into an SRT controller 28 to determine a set value of SRT. And measured values of flow rate and concentration measured by a first flowmeter 29 and a first concentation meter 30 which are provided at a raw water intake part of an aeration tank 21 to measure the flow rate and concentration of the raw water are inputted into the controller 28 to determine a set value of SRT. Further, measured values of flow rate and concentration measured by a second flowmeter 31 and a second concentration meter 32 for measuring flow rate and concentration of treated water of a final settling reservoir 23, also, are inputted into the controller 28 to determine a set value of SRT. At the controller 28, a set value of SRT is determined using each of the measured values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sludge retention time setting device in an activated sludge method.

[0002]

2. Description of the Related Art Various methods have conventionally been proposed for efficiently removing organic matter in wastewater such as sewage and removing nitrogen and phosphorus which are considered to be the causative agents of eutrophication in closed water areas. . Particularly in recent years, it has been required to increase the removal rate of nitrogen, and it is expected that regulations on nitrogen will become stricter.Therefore, it is thought that the number of facilities that employ advanced treatment processes that can remove this will increase. To be

As a biological method for simultaneously removing nitrogen and phosphorus, the anaerobic-aerobic activated sludge method has attracted attention as a modified method of the conventional activated sludge method. The anaerobic-aerobic activated sludge method is, for example, as shown in FIG. 2, the biological reaction tanks are anaerobic tanks 1a and 1b in which dissolved oxygen (hereinafter abbreviated as DO) does not exist.
And a plurality of stages of aerobic tanks 2a, 2b, 2c in which DO exists, and raw water 3 flowing in is divided by the anaerobic tanks 1a, 1b.
The mixture is agitated by an agitation mechanism 10 under anoxic conditions to denitrify it with denitrifying bacteria in the activated sludge, and then the aerobic tanks 2a, 2
By supplying air from the blower 5 to the air diffusing tube 4 arranged inside b and 2c, oxidative decomposition of organic matter by activated sludge and nitrification of ammonia by nitrifying bacteria are carried out in the presence of oxygen by aeration, and finally, Tiered aerobic tank 2c
By feeding the nitrification solution of No. 1 into the anaerobic tank 1a by using the nitrification solution circulation pump 6, the denitrification effect of the anaerobic tanks 1a and 1b is promoted.

The above-mentioned denitrifying bacterium refers to a bacterium that reduces N0 ₂ -N and N0 ₃ -N to N ₂ and NO ₂ by respiration of nitric acid under anaerobic conditions. Also, phosphorus in raw water is anaerobic tanks 1a and 1b.
It is released inside and is taken in and removed by the activated sludge in the aerobic tanks 2a, 2b and 2c. Reference numeral 7 denotes a final settling basin, and the supernatant of the final settling basin 7 is discharged as treated water 11 after passing through a disinfection tank or the like (not shown), and a part of the sludge settled in the final settling basin 7 is Anaerobic tank 1 by sludge return pump 8
The remaining sludge is returned to a and is sent from the excess sludge drawing pump 9 to an excess sludge treatment device (not shown) for treatment.

Excessive sludge removal from the final settling basin 7 is performed by MLSS control in the aeration tank (method of extracting excess sludge using the MLSS concentration in the aeration tank as an index) and F / M ratio constant control (inflow base mass and MLSS amount). The method used to remove excess sludge based on the ratio of (1) was used as the mainstream. However, when advanced treatment such as activated sludge circulation method is adopted for sewage treatment,
Instead of them, SRT (sludge retention time) control (a method of extracting excess sludge using the retention time of activated sludge in the treatment system as an index) has been adopted. This SRT control is a method in which the excess sludge withdrawal amount is reduced to promote the nitrification reaction, and the concentration of activated sludge in the nitrification tank is increased to prevent nitrifying bacteria from being discharged out of the system. By using such an anaerobic-aerobic activated sludge treatment method, it is possible to obtain the same level of effect as the organic substance removal effect achieved by the normal standard activated sludge method, and to remove nitrogen and phosphorus at a higher level than the activated sludge method. Rate is achieved.

[0006]

However, in the case of such conventional anaerobic-aerobic activated sludge treatment method, it is difficult to establish an efficient operation control method, and in particular, the nitrification rate in the aerobic tank is estimated. Therefore, there is a problem in that it is difficult to implement a control that secures the target nitrification rate to increase the nitrification efficiency, and accordingly enhances the denitrification effect in the anaerobic tank. Further, the SRT control that is generally adopted to increase the nitrification rate may not be able to be properly controlled when the water temperature changes rapidly, and there is a problem that a stable nitrification reaction cannot be maintained.

That is, the operation mode in the anaerobic-aerobic activated sludge method can be roughly classified into a denitrification reaction in the anaerobic tanks 1a and 1b and a nitrification reaction in the aerobic tanks 2a, 2b and 2c. The latter, that is, the nitrification reaction, is the rate-determining reaction. In particular, in order to remove nitrogen efficiently by the anaerobic-aerobic activated sludge treatment method, it is required to maintain denitrification in the anaerobic tank and nitrification in the aerobic tank under the optimum operating conditions, and the nitrogen removing step. Is highly influenced by the nitrification process, so that the nitrification reaction must be performed well in order to perform good nitrogen removal.

This nitrification reaction is caused by nitrifying bacteria, and it is known that the activity of this nitrifying bacteria is easily affected by subtle changes such as pH and water temperature. or,
In order to take sufficient aeration time, it is necessary to make the volume of the biological reaction tank 2-3 times larger than in the case of the standard activated sludge method, and it is used under conditions where it is difficult to secure land for urban areas. There is a problem that it is difficult.

On the other hand, in the activated sludge process, the nitrogen component in the raw water is decomposed into ammoniacal nitrogen. This ammoniacal nitrogen is oxidized to nitrate nitrogen under the presence of nitrifying bacteria and in the condition of rich dissolved oxygen. At the sewage treatment plant, it is an important issue in operation management whether the nitrogen component remains ammoniacal depending on the characteristics of the treatment plant or the conditions of the discharge destination, or whether the nitrogen component is oxidized to nitrate nitrogen and then discharged. There is. Especially when nitrite nitrogen is present in the treated water, CO
D (Chemical oxygen demand) increases and requires a large amount of oxidant, and the DO of the treated water discharge destination decreases, which damages the biota of the discharge destination. There is a fear of being lost. Therefore, it is necessary to remove nitrite nitrogen in the treated water as much as possible, but for that purpose, denitrification treatment must be performed in the denitrification tank after aeration treatment in multiple aeration tanks, which requires an increase in facilities. In addition, there is a problem that the processing time is long.

Therefore, if importance is attached to the environment of the water body of the discharge destination, it is preferable to discharge it as nitrate nitrogen, but since this nitrification reaction is slower than general BOD oxidizing bacteria, it is affected by water temperature and load fluctuation. Instability tends to occur and complete nitrification is difficult. Since this incomplete nitrification reaction raises the BOD (biochemical oxygen demand) of the treated water and the COD, the operation for promoting nitrification must be passive. Further, in the case of a circulation method in which nitrogen is removed in order to prevent eutrophication in the water area of the discharge destination, it is an absolute condition to promote nitrification. Thus, promotion of nitrification of nitrogen components is an important factor in sewage treatment.

As one means for promoting the nitrification reaction,
As described above, the SRT that increases the concentration of activated sludge and reduces the amount of excess sludge drawn so that nitrifying bacteria are not discharged to the outside of the system.
(Sludge retention time) control is generally adopted. However, increasing the excess sludge concentration may reduce the solid-liquid separation efficiency in the settling basin and increase the concentration of suspended solids in the effluent, which naturally limits the SRT control. Especially in winter when the water temperature decreases, the activity of nitrifying bacteria also decreases,
It is difficult to maintain a proper nitrification reaction even if the concentration of activated sludge is increased to the limit. Currently, the amount of excess sludge drawn out by SRT control is ML in the aeration tank.
It is calculated only from the amount of SS. However, since the SS amount contained in the inflow water and the outflow water is not considered in this method, there is a problem that an accurate SRT setting is not actually made.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a sludge retention time setting device in the activated sludge method, which enables accurate SRT setting.

[0013]

In order to achieve the above object, the present invention introduces an aeration tank into which raw water flows, an MLSS meter disposed in the tank, and water outflowing from the aeration tank. The final settling basin that uses the supernatant as treated water, the return sludge pump that returns sludge from the final settling basin to the aeration tank, the excess sludge drawing pump that draws excess sludge from the final settling basin, and this surplus A flow meter and a densitometer for measuring the flow rate and the concentration of the excess sludge drawn by the sludge drawing pump, the MLSS measured by the MLSS meter, the flow rate measured by the flow meter and the concentration measured by the densitometer were introduced. , SRT setting is performed with each of these values, and an SRT control unit that controls the excess sludge extraction pump according to these setting values is provided. In a sludge retention time setting device in the mud method, a first flow meter for measuring the flow rate of the raw water, a first concentration meter for measuring the concentration of the raw water, and a flow rate of treated water flowing out from the final settling tank are measured. A second flow meter and a second concentration meter for measuring the concentration of the treated water are provided,
The values measured by the first and second flow meters and the densitometer are the SR
It is characterized in that the SRT setting is performed by inputting to the T control unit.

[0014]

[Function] In order to control the excess sludge extraction pump, the SRT set value is obtained by taking into consideration the flow rate and concentration of raw water and the flow rate and concentration of treated water in addition to the flow rate and concentration of excess sludge removal. Is possible.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.
Reference numeral 21 is an aeration tank into which raw water flows, and an MLSS meter 22 is arranged in this tank 21. MLSS
The measured values of the total 22 are input to the SRT control unit described later in order to obtain the SRT set value. Aeration tank 21
The liquid flowing out of the tank flows into the final settling tank 23, and the supernatant liquid is discharged as treated water via a disinfection tank or the like not shown.
On the other hand, a part of the sludge settled in the final settling tank 23 is returned to the aeration tank 21 by the return sludge pump 24, and the remaining sludge is extracted by the excess sludge extraction pump 25 and sent to the excess sludge treatment device (not shown). It is processed. 26 is a surplus sludge flow meter, 27 is a surplus sludge concentration meter, and the surplus sludge flow meter 26 and the concentration meter 27.
The measured values of the surplus sludge flow rate and the concentration measured in (4) are input to the SRT control unit 28 to obtain the SRT set value.

Reference numerals 29 and 30 denote a first flow meter and a first densitometer, which are provided at the raw water intake portion of the aeration tank 21 and measure the flow rate and the concentration of the raw water. The measured values of the measured flow rate and concentration are input to the SRT control unit 28 to obtain the SRT set value. Reference numerals 31 and 32 denote a second flow meter and a second densitometer for measuring the flow rate and the concentration of the treated water in the final settling tank 23, and the measurement of the flow rate and the concentration measured by the second flow meter 31 and the second densitometer 32. The value is also input to the SRT control unit 28 to obtain the SRT set value. The SRT control unit 28 obtains an SRT set value for each of the input measured values by using an equation described below.

When determining the SRT set value, the SS amount flowing into the processing system (measurement by the first flow meter and the densitometer) and the SS amount flowing out from the processing system (measurement by the second flow meter and the densitometer) are calculated. Since this is taken into consideration, an accurate SRT set value can be obtained. Therefore, the excess sludge extraction pump 25 is SRT controlled based on the accurate SRT set value.

Next, the means for obtaining the SRT set value will be described. The amount of sludge in the aeration tank, the amount of inflow SS per day, the amount of outflow SS per day, and the amount of sludge drawn out per day are expressed as follows. It

Amount of sludge in the aeration tank: SS _at · V _at (mg) Inflow SS amount per day: SS _in · Q _in (mg / day) Outflow SS amount per day: SS _out · Q _out (mg / day) Extracted sludge amount per day: SS _w · Q _w (mg / day) SRT: SRT (day) where SS _at : MLSS concentration in aeration tank (mg / L) SS _w : Extracted sludge concentration (mg / L) ) SS _in : inflow SS concentration (mg / L) SS _out : outflow SS concentration (mg / L) V _at : aeration tank volume (L) Q _in : inflow water amount (L / day) Q _out : outflow water amount (L / day) Q _w : Extraction amount (L / day) SRT: SRT (day). From these, the relational expression of the SRT set value is established from the balance of the sludge amount in the treatment system by the first flow meter and the concentration meter and the sludge amount discharged from the treatment system by the second flow meter and the concentration meter as follows.

SRT = SS _at · V _at / (SS _out · Q _out + SS _w · Q _w −SS _in · Q _in ) Once the SRT set value to be controlled is determined, the amount of sludge drawn from the final settling tank Q _w is _calculated by the following equation.

Q _w = {(SS _at · V _at / SRT) + SS _in · Q _in −S
S _out / Q _out } / SS _w

[0022]

As described above, according to the present invention,
The amount of SS that flows into the processing system with the first flow meter and the concentration meter, and the amount of S that flows out from the processing system with the second flow meter and the concentration meter
Since the S amount is taken into consideration, an accurate SRT set value can be obtained.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

FIG. 2 is a system configuration diagram of a conventional example.

[Explanation of symbols]

 21 ... Aeration tank 22 ... MLSS meter 23 ... Final settling tank 24 ... Return sludge pump 25 ... Excess sludge extraction pump 26 ... Excess sludge flow meter 27 ... Excess sludge concentration meter 28 ... SRT control section 29, 31 ... First, second Flowmeters 30, 32 ... First and second densitometers

Claims (1)

[Claims] 1. An aeration tank into which raw water flows, a MLSS meter disposed in the tank, a final settling tank into which water flowing out from the aeration tank is introduced, and a supernatant liquid flows out as treated water. A return sludge pump that returns sludge from the final settling tank to the aeration tank, an excess sludge drawing pump that draws excess sludge from the final settling tank, and a flow rate that measures the flow rate and concentration of excess sludge drawn by this excess sludge drawing pump. Meter and densitometer, the MLSS measured by the MLSS meter, the flow rate measured by the flow meter and the concentration measured by the densitometer are introduced, and SRT setting is performed at each of these values, and excess sludge is set by these set values. In the sludge retention time setting device in the activated sludge method, which comprises an SRT control unit for controlling a drawing pump, A first flow meter for measuring the amount and a first concentration meter for measuring the concentration of the raw water, a second flow meter for measuring the flow rate of the treated water flowing out from the final settling tank, and the concentration of the treated water. A second densitometer is provided, and the first and second
A sludge retention time setting device in the activated sludge method, characterized in that values measured by a flow meter and a densitometer are input to the SRT control unit to perform SRT setting.