JP3467905B2 - How to measure respiration rate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a respiration rate in controlling an activated sludge process. [0002] Conventionally, as an evaluation of the activity in an activated sludge process, a respiration rate meter for activated sludge (hereinafter referred to as "Rr meter") is known. The respiration rate [Rr] represents the amount of oxygen consumed per unit time when organic matter-decomposing bacteria decompose organic matter in the aeration tank, and the activity of aerobic bacteria can be known from this [Rr]. Is an important control factor in sewage treatment. For example, when sewage or other wastewater is treated by the activated sludge method, if the aeration becomes excessive, the sludge is subdivided and the power cost increases. Insufficient aeration may cause decay of activated sludge or accumulation on the bottom of the tank, which may deteriorate the quality of treated water. Therefore, to maintain and maintain the aeration tank optimally, oxygen must be supplied at a rate equal to or slightly above the oxygen utilization rate of the activated sludge. [0004] The oxygen utilization rate [rr] in the aeration tank is indicated by the amount of oxygen (mg / l.h) used by a unit volume of liquid per unit time. The oxygen utilization rate coefficient [Kr] of the activated sludge is determined by the amount of oxygen (mg / g) used by a unit weight (g) of activated sludge in a unit time.
・ Time). In order to automatically measure the respiratory rate [Rr], an apparatus shown in FIG. 4 is generally used. The structure and operation will be briefly described.
b denotes a drain port, 14 denotes a measuring tank, and tubes 15 and 16 forming a water passage are connected to the inlet and outlet sides of the measuring tank 14. V ₁ is an upper pinch valve, V ₂ is a lower pinch valve, 17, 18 and 19 are air inlets, and tubes 15 and 16 are pinched and released by air injection and exhaust from air inlets 17 and 19. And the opening / closing operation is performed. Reference numeral 20 denotes a DO electrode as a dissolved oxygen concentration detection unit, and 21 denotes a stirrer. When measuring the respiration rate of activated sludge,
First, air is introduced from the air inlet 18 to form an air lift, the pinch valves V ₁ and V ₂ are opened, and the activated sludge liquid in the aeration tank (not shown) is measured from the water sampling port 13 a to the measuring tank 1.
4 is introduced. Next, the lower pinch valve V ₂ is closed by injecting air from the air inlet 17, and air is sent from the air inlet 18 into the measuring tank 14 for aeration.
(Dissolved oxygen) concentration to a certain value, for example, 5 (mg / l)
Up to. When the DO concentration rises to the set value, the aeration is stopped, and the upper pinch valve V ₁ is closed by injecting air from the air inlet 19 to start stirring by the stirrer 21. Then, the DO concentration decreases with the consumption of oxygen by activated sludge (aerobic microorganisms).
The respiration rate [R is measured by the least square method from the decreasing rate of DO measured by the electrode 20 and a DO meter (dissolved oxygen meter) not shown.
r] is calculated. [0008] Such a conventional Rr
The meter measures the respiration rate [R after once collecting activated sludge from the aeration tank (not shown) into the measurement tank 14 during measurement.
r], there is a problem that the measurement requires a considerable amount of time and cannot be measured in real time. Further, when aerobic microorganisms in the activated sludge adhere to the inner wall surface of the measuring tank 14, the respiration rate of the microorganism is added as an error, so that the respiration rate [Rr] becomes higher than the actual value. Accuracy may be reduced. In particular, if contaminants such as sludge adhere to and proliferate in the auxiliary equipment such as the DO electrode 20 or the stirrer 21 as the detector in the measuring tank 14 or the measuring tank 14 itself, the apparent sludge concentration in the sampled water will be increased. Is increased, which may cause a measurement error. Therefore, in the standard activated sludge method, it is usually necessary to carry out the sterilization cleaning operation in the measuring tank 14 using a chemical such as sodium hypochlorite once a day. Contains activated sludge, and the means for returning the liquid in the measuring tank 14 to the aeration tank in order to treat the activated sludge increases the amount of chemicals used. Become. Therefore, the present invention solves the above-mentioned problems of the conventional measuring method, and provides a highly accurate respiratory rate measuring method which does not require a special device for the measurement and shortens the measuring time. It is intended to provide. According to the present invention, in order to achieve the above object, the amount of raw water flowing into an aeration tank [Q], the amount of air blown by a blower [G], and the temperature of raw water [T]. And a dissolved oxygen concentration [DO] and constants [alpha] and [beta] are used as measurement factors, and each factor is input to a respiration rate calculation means to calculate the respiration rate of the activated sludge by calculation. The above constants α and β are values satisfying the equation [K _LA ] = αG ^β (K _LA : overall oxygen transfer capacity coefficient). Further , [Rr] =-{(Q.DO) / (V)} + αG ^β (14.16−0.3943T + 0.007714T ² −0.0000646T ³ −DO) (V: aeration tank) The respiration rate [Rr] is determined by the following equation. According to the method for measuring the respiratory rate, [K _LA ] (overall oxygen transfer capacity coefficient) of the aeration tank is determined in advance.
To determine the constants α and β from the equations, and then to calculate the inflow Q of raw water into the aeration tank, the DO measured by a DO meter (dissolved oxygen concentration meter), the blower G of the blower, and the water temperature T. , The respiration rate [R
r] can be quickly and easily obtained by calculation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for measuring a respiration rate according to the present invention will be described below with reference to the drawings. In the schematic diagram shown in FIG. 1, 1 is an aeration tank, 2 is a blower,
Reference numeral 3 denotes an air diffuser, 4 denotes an inflow path of raw water, 5 denotes a respiration rate calculating means, and a flow meter 6 is installed in the inflow path 4. The blower 2 measures the amount of air supplied to the air diffuser 3. Flow meter 7
Is installed. A thermometer 8 and a DO meter 9 (dissolved oxygen meter) are provided in the aeration tank 1. The flow meters 6, 7 and the thermometers 8 and D
Each measurement value of the O meter 9 is input to the respiration rate calculation means 5, and the output 11 of the respiration rate calculation means 5 is the calculated respiration rate [Rr]. Reference numeral 10 denotes αβ calculating means which is a constant used when calculating the respiration rate. Details of the calculation formula by the respiration rate calculating means 5 and the meaning and use of the constant obtained by the αβ calculating means 10 will be described later. FIG. 2 is a flow chart showing a practical example of a method of measuring a respiration rate according to the present embodiment.
The α value and β value obtained by the αβ calculation means 10, the inflow rate [Q] of the raw water, the air flow rate [G] of the blower 2, the water temperature [T] of the raw water, and the DO measured by the DO meter 9 [ DO] value is input, and the respiration rate [Rr] value is extracted as an output 11 from the respiration rate calculation means 5. The principle of measuring the respiration rate according to this embodiment will be described below. In general, the overall oxygen transfer capacity coefficient [K _LA ] represents the oxygen supply capacity in the aeration tank 1 and is important in the design of the aeration tank 1 and is measured by measuring the [K _LA ] during maintenance. There is an advantage that an efficient operation plan can be set and clogging of the air diffuser can be checked. However, in actual processing, water temperature or MLSS
(Activated sludge suspended matter concentration) [K _LA ] fluctuates due to external factors such as a change in concentration. Therefore, the quality of the inflow water into the aeration tank 1 and the sludge settling speed are measured together.
It is necessary to set operating conditions comprehensively. The above-mentioned overall oxygen transfer capacity coefficient [K _LA ] is measured based on the unsteady method and the steady method. The principle of measurement is shown by the following equation (1). (DC / dt) = K _LA (C _S −C) −Rr (1) where (dC / dt): change amount of dissolved oxygen C _S : Saturated oxygen concentration of mixed solution in aeration tank (mg / l) C: dissolved oxygen concentration of mixed solution in aeration tank (m
g / l) Rr: oxygen utilization rate of the mixture in the aeration tank (mg / l · hr) K _LA (C _S -C): supply rate of dissolved oxygen from the air diffuser. The unsteady method is when there is no oxygen consumption,
The dissolution rate of oxygen in water can be expressed by equation (2). (DC / dt) = K _LA (C _S -C) (2) On the other hand, the amount of air blown from the blower 2 to the aeration tank 1 The characteristic is that [K _LA ] increases as G increases. This relationship is shown in equation (3). [K _LA ] = αG ^β (3) where α , Β are constants. FIG. 3 is a graph showing the logarithms of [K _LA ] and [G] of the aeration tank obtained in a laboratory experiment, where R is a correlation coefficient. The slope of the approximate straight line of this graph is β in equation (3), and the intercept is log α
It is. Generally, the above [Rr], [DO], [K _LA ]
And the following equation (4) holds. (DDO / dt) = {( Q · DO O -Q · DO) / V} + K LA (DO S -DO) -Rr ····· (4) where Q: flow rate of raw water V: Aeration Tank Volume DO _O : Inflow DO concentration DO: DO concentration in the aeration tank DO _S : Saturated DO concentration Further, the above DO _S is a function of the water temperature [T] as shown in the following (5).
It can be expressed as an equation. DO _S = 14.16−0.3943T + 0.007714T ² −0.0000646T ³ (5) In the case of the standard activated sludge method, an Rr meter is installed at the forefront of the aeration tank 1, and the circulating nitrification denitrification method is used. Or disgust-
In the case of the aerobic activated sludge method, it is installed at the uppermost stream of the aerobic tank. Since DO in the inflow water or the anaerobic tank is almost 0, the respiration rate [Rr] is calculated from the equations (3), (4), and (5) as follows: [Rr] = − {(Q · DO) / (V)} + αG ^β (14.16−0.3943T + 0.007714T ² −0.0000646T ³ −DO) (6) Therefore, according to this embodiment, the inflow amounts Q and D of the raw water
Rr can be easily obtained by calculation if the DO in the O-total 9 input portion, the air flow rate G of the blower 2 and the water temperature T are known. When calculating Rr, it is necessary to investigate [K _LA ] of the aeration tank in advance and to obtain the constants α and β based on equation (3). As described above in detail, according to the method for measuring a respiration rate according to the present invention, [K _LA ] (overall oxygen transfer capacity coefficient) of an aeration tank is investigated, and a constant is calculated by an equation. After obtaining α and β, the flow rate of raw water into the aeration tank, Q, DO, the air flow rate of the blower, G, and the water temperature, T, are calculated.
Can be quickly and easily obtained by calculation. In particular, in the present invention, no special device is required for the measurement, and the step of sampling the activated sludge from the aeration tank at the time of the measurement is omitted. Can be. Further, it is not necessary to frequently sterilize and clean the inner wall surface of the measuring tank using chemicals as in the prior art, which simplifies maintenance and eliminates adverse effects on the process due to excessive chemicals, and achieves high accuracy. You can measure your breathing speed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing one embodiment of a method for measuring a respiration rate according to the present invention. FIG. 2 is a flowchart of the embodiment. FIG. 3 is a graph showing the logarithm of the relationship between [K _LA ] and [G] of the aeration tank. FIG. 4 is a vertical sectional side view showing an example of a conventional respiration rate meter. [Explanation of Signs] 1 ... Aeration tank 2 ... Blower 3 ... Aerator tube 4 ... Inflow path 5 ... Respiration rate calculation means 6,7 ... Flow meter 8 ... Temperature meter 9 ... DO meter (dissolved oxygen meter) 10 ... αβ calculation means

Claims (1)

(57) [Claims] [Claim 1] Inflow rate of raw water into the aeration tank [Q], air flow rate of blower [G], water temperature of raw water [T], dissolved oxygen concentration [DO] and constant α the beta and measured factors, there is a respective factors enter into the respiratory rate calculating means obtains the respiration rate of the activated sludge by calculation, the constant alpha, beta is [K _LA] = alpha] G ^beta · · · · · ···················· ......... (3): a value satisfying the (K _LA overall volumetric oxygen transfer coefficient) formula , by the respiratory rate calculating means, [Rr] = - {(Q · DO) / (V)} + αG β (14.16-0.3943T + 0.007714T 2 -0.0000646T 3 -DO) (V: volume of the aeration tank) - ... A method for measuring a respiratory rate, wherein the respiratory rate [Rr] is determined by equation ( 6) .