JPS6111197A - Control device for air flow rate for sewage treatment plant - Google Patents

Abstract

PURPOSE:To reduce the cost of driving power by dividing air diffusing pipes for feeding air to an aeration tank to plural air diffusing pipe groups of with which the flow rates are adjustable, providing devices for measuring the rate of utilizing oxygen to the respective air diffusing pipe groups and providing an arithmetic part to the device. CONSTITUTION:Sewage flows through a pipeline A into the aeration tank 1 and is mixed with the return sludge returned from a settling basin B through a pipeline C. Air for aeration is fed from the plural air diffusing pipe groups 2 via respective flow rate control valves 3 to the tank 1 and the air flow rate over the entire part is controlled by a blower 4 and a flow rate control valve 5. A water temp. measuring device 6 and sample selector valves 7 which can make sampling with each of the air diffusing pipes and a sampling pump 8 are provided to the tank 1. The rate of utilizing oxygen is measured by each number of the air diffusing pipes.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention is directed to a sewage treatment plant that efficiently controls the amount of air blown to an aeration tank in a sewage treatment plant using activated sludge to the extent that no nitrification reaction occurs. The present invention relates to an air flow rate control device.

[Technical background of the invention and its problems]

The activated sludge method is a type of biological treatment method for organic wastewater (hereinafter referred to as sewage), and uses an aeration tank and a settling tank. After the sewage undergoes primary treatment such as settling, pre-aeration, and sedimentation, it flows into the aeration port and mixes with activated sludge in the aeration tank.

Since air is blown into the aeration tank, activated sludge adsorbs and assimilates organic matter in the sewage and multiplies, thereby treating the sewage.

The treated sewage flows into a settling tank and is separated into solid and liquid. Most of the separated activated sludge is returned to the aeration tank and reused, and the remainder is extracted outside as surplus sludge.

In the activated sludge method, in order to maintain stable wastewater treatment efficiency, it is necessary to properly maintain the state of activated sludge and to appropriately control the amount of air blown to the aeration tank.

The treatment process in the activated sludge method consists of adsorption of organic matter, oxidation of BOD, assimilation, internal respiration, and nitrification, which can be expressed by the following reaction equation.

For example, activated sludge C5H7NO2, organic matter C
x Hy Oz, the adsorption of organic matter is C5H7N
O2+ CXI(YOZ-+C5H7NO2・CxHy
The oxidation of Oz - (1) BOD is YZ Y CXHYO2+ (Xi - child) Q2 → XCO2 + 21 (
20-ΔH+・+ (2) Assimilation is CxHyOz+NH3+Oz→(4ffllfl substance)
+CO2+ Le 0-41 (+++ (3) Internal respiration is (cell matter) +02 → Cot + HtO+ NHs-
ΔH... (4) Nitrification is on the side (, +'02→NO2-+H, 0+2H... (5
)NO! + zOt→NO3...(6).

In sewage treatment, progress to nitrification is small in the normal process, but
Nitrification often progresses when the load is low or when aeration is carried out for a long time.

Conventionally, so-called constant DO control, which maintains the dissolved oxygen concentration in the aeration tank at a constant value, has been used to control the air flow rate in the aeration tank, but as mentioned above, when the load is low or when the water volume is low, When aeration becomes excessive, or when the water temperature in summer is high and the reaction rate is fast, the nitrification reaction occurs, and the above (
As shown in equations 5) and 6, one molecule of NH4 is oxygen 2
Since molecules are taken in, the amount of oxygen required increases rapidly, and therefore, in constant Do control, the amount of air blown increases.

In addition, when a nitrification reaction occurs, activated sludge settles and concentrates in a settling tank; when it is exposed to anaerobic conditions (1) a denitrification reaction occurs, nitrogen gas bubbles are generated, and sludge (-) adheres to the sludge. leading to the emergence of

Therefore, in the conventional constant DO control, when the nitrification reaction occurs, there is a problem that the amount of power increases due to the increase in the amount of air blown, and the quality of the treated water deteriorates due to the floating of sludge.

[Purpose of the invention]

The present invention provides rational air flow control for wastewater treatment plants that controls the air flow within a range in which nitrification reactions do not occur, thereby reducing the power cost of the blower, and preventing sludge from floating to improve the quality of treated water. The purpose is to provide equipment.

[Summary of the invention]

The present invention is an air flow rate control device for a sewage treatment plant that is equipped with an aeration tank and a settling tank, and which blows air into the aeration tank to treat wastewater via activated sludge. The aeration tubes that enter the aeration tank are divided into a plurality of aeration tube groups whose flow rate can be adjusted in the downstream direction of the aeration tank, and the oxygen utilization rate or OD removal at each position of the aeration tank corresponding to each aeration tank is further adjusted. In addition to installing an oxygen utilization rate measuring device that measures the oxygen utilization rate by two methods and the oxygen utilization rate by nitrification reaction, the required air volume for each diffuser pipe group is calculated from the measured value of the rate for WR element by BOD removal. A first calculation unit, a second calculation unit that corrects the required air volume calculation value from the measured value of oxygen utilization by the nitrification reaction, and a second calculation unit that calculates the total required air volume from the output of the second calculation unit, The output of the second calculation section (correspondingly controls the air volume of each diffuser tube group), and the output of the first calculation section (correspondingly controls the air flow rate of the blower, thereby suppressing the occurrence of nitrification reaction) This aims to improve the quality of treated water and reduce the cost of powering the blower.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

In FIG. 1, wastewater that has been pretreated in a pretreatment step (not shown) flows into the aeration tank 11 through pipe A, and flows into the settling tank B.
The sludge is mixed with return sludge returned from the sludge through pipe C.

Aeration air is fed into the aeration tank 1 from a plurality of aeration pipe groups 2 via respective flow rate control valves 3, and the overall air flow rate is divided and controlled by a blower 4 and a flow rate control valve 5.

FIG. 2 is a flowchart showing the operation of the present invention, and the present invention will be described in detail below with reference to FIG.

The aeration tank 1 is equipped with a water temperature measuring device 6, a sample switching valve 7 that can collect samples for each group of aeration tubes, and a sampling pump 8. Speed L RR
Diffusion pipe number I (I = 1 to n
).

The first calculation unit 10 inputs the upper eye's measured value RRBOD (1,) and the water temperature measured value T, and calculates the air blowing amount QA (I) for each diffuser pipe.
is calculated using the following formula (7).

QA(I) −f (RR(I), T )
... (The force storage section 11 stores the above measured value RRs.
os(I) and the output QA(I) of the first arithmetic unit 10 are stored until the next control cycle.

The third determination unit 12 inputs the stored RRNO3(I) and determines the number N of the first diffuser pipe in which the detected value of RRNO8 was detected (that is, the nitrification reaction was detected).

The second storage unit 13 stores the diffuser pipe number N until the next control cycle.

The second determination unit 14 compares the output N of the determination s12 with the output N' of the previous control cycle, which is the output of the second storage unit 13, and determines the diffuser pipe number N'' whose air flow rate should be corrected. .

In other words, when N-A'N', it is N"-N-1, and N<
When N', N'=N-2.

The first calculation unit 10 calculates the QA (
In I), recalculate the air flow rate of the N'th diffuser pipe and below, and compare it with the set upper limit and lower limit,
The value QA'(I)i within that range is modified.

That is, first, when I <: r, for Q (I) = QA (I)
... (8) When I≧N"QA' (I
) = QA(I) X A ...(9).

Here, A is a correction coefficient (A<1), for example 0.
9.

Next, compare the preset maximum air flow rate QA,... with the minimum air flow rate QAm+n, and when x≧QA'(I)≧QAm+n, QA
'(I) = QA'(I)...
・When αQQAm, x< QA (I), QA'(I) = QAffl, -
・-・・-ul) QAml,',> When QR(I), QA (I) −QAmla ・・・
・Make it into sauce.

The third calculation unit 16 calculates the output QA'(I
) The total air flow QAT that should be sent out by the blower 4 from ) is shown below (
13) Calculate using the formula.

QAT = Pu, QA'(I) ・・・・・・(1
:1 where n is the total number of air diffusers 2.

The first controller 17 inputs the QAt and controls the flow control valve 5, thereby controlling the amount of air blown by the blower 4 by QAT+2.

Further, the second controller 18 controls the flow rate control valve 3 of each diffuser pipe, and controls the amount of air blown from each diffuser pipe to QA'(I).

This allows the amount of air blown from the aeration tank to be appropriately controlled within a range that does not cause nitrification reactions.

In the above embodiment, one set of oxygen utilization rate measuring devices is provided and all measurements are performed by switching the sample valves, but if one set is provided for each measurement point (-), the measurement speed can be increased.

Further, although the total amount of air blown is controlled by the flow control valve 5, it is also possible to control the number of air blowers.

〔Effect of the invention〕

As explained above, according to the present invention, effective aeration can be performed without causing a nitrification reaction.

In other words, with constant DO control, which is one of the conventional methods, when the nitrification reaction occurs, the denitrification reaction occurs as described above and nitrogen gas is generated, sludge floats to the surface, worsening the water quality and increasing the amount of air blown. However, with the present invention, the air is blown in proportion to the rate of oxygen utilization, reducing the possibility of nitrification reactions occurring, and reducing the possibility of nitrification reactions occurring. Since the amount of air blown is reduced by the correction calculation ζ2, the progress of the nitrification reaction is inhibited.

Therefore, aeration is performed without causing almost any nitrification reaction, so there is no sludge floating due to denitrification reaction in the settling tank.
The quality of the treated water is improved and it is possible to save energy for blowing air.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention, and FIG. 2 is a flowchart showing arithmetic operations in the present invention. l - Air tank 2 Diffusion pipe group 3 + 5 (/II; Amount adjustment square 4
Water temperature measuring device 7 Sample switching valve 8 Sample pump 9 Oxygen utilization rate measuring device 10, 15.16 Arithmetic section 11.13 Storage section 12, 14 Judgment section 17, 18 Control section 19 Sedimentation tank (8733) Agent Patent attorney Inomata Yoshiaki (and 1 other person) Figure 1 Figure 2

Claims (1)

[Claims] In an air flow control device for a sewage treatment plant that is equipped with an aeration tank and a settling tank, and uses a blower to send air into the aeration tank and treat wastewater through activated sludge, an aeration pipe that sends air to the aeration tank is used. The aeration tank is divided into a plurality of aeration pipe groups whose flow rate can be adjusted in the downstream direction, and the oxygen utilization rate at each position of the aeration tank corresponding to each aeration pipe group is determined by BO.
In addition to providing an oxygen utilization rate measuring device that separately measures the oxygen utilization rate due to D removal and the oxygen utilization rate due to nitrification reaction, a device that calculates the required air volume for each diffuser group from the oxygen utilization rate measurement value due to BOD removal described above is provided. one calculation section, a second calculation section that corrects the calculated value of the required air volume from the measured value of the oxygen utilization rate due to the nitrification reaction, and a third calculation section that calculates the total required air volume from the output of the second calculation section, Sewage treatment characterized by controlling the amount of air diffused in each of the aeration tube groups according to the output of the second calculation section, and controlling the amount of air blown by the blower according to the output of the third calculation section. Plant air flow control device.