CN102183910B - Method for detecting specific oxygen utilization rate of activated sludge microorganism online based on frequency control - Google Patents

Abstract

The method for on-line detection of the specific oxygen consumption rate of activated sludge microorganisms through frequency conversion speed regulation relates to a fast on-line detection method of process control parameters in the sewage biological treatment process. Most of the existing online detection methods for oxygen consumption rate have disadvantages such as high cost, hysteresis, low accuracy, and difficult maintenance. The method of the present invention mainly utilizes the online frequency parameter obtained in the process of controlling the dissolved oxygen by frequency conversion of the blower to monitor the change of the specific oxygen consumption rate in the aeration stage of the SBR process, thereby obtaining the inflection point of the microbial specific oxygen consumption rate curve in the aeration process, and the automatic control system is online After the inflection point is identified, a control command is issued to control the stop of the aeration device, so as to avoid excessive aeration and save energy consumption in the aeration stage. The method of the invention has the advantages of fast response, on-line detection, convenient operation, low cost, stable operation and the like.

Description

Method for online detection of specific oxygen consumption rate of activated sludge microorganisms by frequency conversion speed regulation

technical field

The invention relates to a rapid on-line detection method of the specific oxygen consumption rate (SOUR) in the sewage biological treatment process, in particular to an SBR process capable of frequency conversion control and automatic control. The technical field is: the theory and technology of activated sludge deep biological denitrification treatment.

Background technique

Generally speaking, the aeration cost of a sewage treatment plant using Roots blower for oxygen supply accounts for 50-60% of the daily operating cost, and there is great potential and space for energy saving and consumption reduction in the aeration stage. Therefore, more and more sewage treatment plants, especially in the SBR process, have begun to widely adopt frequency conversion oxygen supply technology. As the most promising technology in the current sewage treatment process, frequency conversion technology can greatly reduce the energy consumption of aeration in the sewage treatment process, save daily operating costs, and enhance the daily sewage treatment capacity. The SBR process is the abbreviation of the intermittent activated sludge sewage treatment process. Its treatment device has only one SBR reaction tank, and the steps of water intake, reaction, precipitation, and drainage are all carried out in this reaction tank. It is a conventional activated sewage process. Sludge wastewater treatment process. The SBR process has the advantages of time axis characteristics and large driving force, and the oxygen consumption rate change curve is very regular during the aeration process, which is very suitable as a process control parameter for the SBR process.

As one of the important parameters to characterize the microbial activity of activated sludge, the specific oxygen consumption rate (SOUR) of activated sludge reflects the physiological state of activated sludge and substrate metabolism from the perspective of microbial respiration rate. In the early stage of the activated sludge process, the respiration rate of aerobic microorganisms was used as a parameter to detect the biological activity of sludge, and it was widely used in the analysis, evaluation and prediction of system operation status and treatment capacity. The research and application of OUR detection technology in sewage treatment system is of great significance to promote the development of sewage biological treatment technology, strengthen and improve the operation control of sewage biological treatment system.

In the past, most respirators used dissolved oxygen (DO) sensors to detect the DO concentration, and determined the respiration rate according to the change of DO. Respirators using DO sensors can be classified into intermittent and continuous respirators.

The operation steps of the intermittent respiration instrument are to install the mixed liquid to be tested in a completely closed chamber equipped with a sensor connected to the analyzer, first aerate until the dissolved oxygen concentration is close to saturation, then stop the aeration, and the DO meter records the change of the dissolved oxygen concentration in the chamber. The slope of this change curve is the respiration rate. During the detection process, a magnetic stirrer was used for mixing and stirring. Off-line measurement has hysteresis and cannot be detected in real time, but online feedback. Moreover, these off-line measurement methods are only used for laboratory testing, and many measurement methods need to add inhibitors, which will affect the stable operation of the activated sludge system and cannot be used as process control parameters for the long-term operation of the system.

The continuous respirator continuously and alternately detects the dissolved oxygen concentration at the inlet and outlet of the breathing chamber. Sludge is continuously pumped into this breathing chamber. The respiration rate was calculated from the difference between the inlet and outlet dissolved oxygen concentrations and the residence time. At the same time it must be assumed that the dissolved oxygen concentration remains constant. However, due to the high cost of online OUR sensors, cumbersome operation and maintenance, and unstable performance, most actual sewage treatment plants seldom use online OUR sensors to monitor the aeration process in real time, but use other types of sensors to indirectly indicate the aeration process Information.

With the development and wide application of automatic control equipment, online detection instruments (DO sensor, pH sensor, ORP sensor) and frequency conversion technology, favorable conditions have been created for the realization of online detection of SOUR of activated sludge system based on the blower frequency.

Contents of the invention

The purpose of the present invention is to establish a method for rapid and indirect detection of microbial specific oxygen consumption rate (SOUR), and to indirectly indicate the specific oxygen consumption rate of the aeration process through the frequency parameter curve obtained by the frequency conversion control blower to realize the constant dissolved oxygen (DO) technology Rate, by testing its stability under various environmental control parameter conditions, the purpose of rapid detection of specific oxygen consumption rate is achieved, and real-time process control of SBR process is realized.

On the basis of theoretical derivation and repeated tests, the present invention takes the SBR process as the research object, and establishes an online monitoring system for activated sludge SOUR by investigating the correlation between the blower frequency parameter and the microbial specific oxygen consumption rate (SOUR). A linear relational formula is used to formulate a control strategy with SOUR as the control parameter. The SOUR curve characteristics of activated sludge can effectively indicate the biochemical reaction process. Once the inflection point appears, the control system makes a judgment based on the received analog feedback signal, transmits the control signal to the actuator, and directly turns off the blower.

Reactor equipment (Fig. 1) of the present invention comprises reactor system and automatic control system;

The reactor system includes an SBR reactor 1 and a blower 2; the blower 2 is connected to the aeration pipe 3 at the bottom of the SBR reactor 1, and an inlet valve 4 is set between the aeration pipe 3 and the blower 2;

The automatic control system includes a DO sensor, a temperature sensor, a sludge concentration sensor, a DO measuring instrument, a sludge concentration measuring instrument, a process controller and a computer; the DO sensor 5 is connected to the DO measuring instrument 6 through a data line and the data of the process controller The signal input interface 11 is connected, the DO measuring instrument 6 is connected with the frequency converter 7, and the frequency converter 7 is connected with the blower 2 and the data signal input interface 11 of the process controller 13 at the same time, and the data signal output interface 12 of the process controller 13 is connected with the computer 14 The control command sent by computer 14 controls blower blower 2 through output bus; Frequency converter 7 collects change of frequency signal of blower blower 2, and the logic program integrated in the process controller 13 is according to the online frequency signal of frequency converter 7 feedbacks, the temperature of temperature sensor 8 feedbacks The signal and the sludge concentration signal fed back by the sludge concentration sensor 9 calculate the real-time specific oxygen consumption rate of microorganisms in the SBR reactor 1, and the obtained real-time specific oxygen consumption rate data is fed back to the computer 14 through the data line, so that it can be displayed on the software interface of the computer 14 As shown above, the online detection of the specific oxygen consumption rate of microorganisms in the aeration stage is finally realized.

Method of the present invention is as follows:

1) After the water intake of the SBR reactor is completed, the blower starts to aerate, and the frequency converter performs closed-loop control according to the DO signal fed back by the DO measuring instrument and the frequency signal fed back by the blower, and the DO in the control aeration stage remains constant;

II) The logic program in the process controller integrates the linear relationship between the specific oxygen consumption rate and the frequency: SOUR _t = η × f _t + λ; where SOUR _t is the specific oxygen consumption rate at time t, and the unit is mgO ₂ /gMLVSS.h, _{f t} is the frequency value at time t, T is the water temperature in °C, and T is in the range of 15-30 °C, η=MLVSS/2000; λ=α×β×k, where α=S _osat -S _o , S _osat is the saturated dissolved oxygen value in water at T℃, S _o is the dissolved oxygen value displayed by the dissolved oxygen meter, β=exp(T-20/T), k value is in the range of 1.0-2.5, When the temperature is 15°C, the k value is 1.0, and every time the temperature rises by 1°C, the k value increases by 0.1 on the original basis. The selection of the k value has little effect on the linear relationship. The process controller calculates the signal fed back by the sludge concentration sensor to obtain the volatile sludge concentration value to determine η; the mass transfer driving force factors α and β are determined according to the water temperature signal in the SBR reactor and the frequency conversion control constant dissolved oxygen concentration signal value, and then calculate the λ value. After the linear relationship between the specific oxygen consumption rate and the frequency is established, the frequency converter collects the frequency signal at the same time interval, the process controller calculates the online specific oxygen consumption rate according to the frequency signal, and the specific oxygen consumption rate signal is fed back to the computer. The computer draws the curve of the specific oxygen consumption rate, and the inflection point indicating the end point of aeration will appear on the specific oxygen consumption rate curve (see Figure 2);

III) The computer begins to identify the inflection point at least 60 minutes after the start of the aeration, and once the inflection point of the specific oxygen consumption rate occurs, the computer transmits the control variable to the process controller;

IV) The process controller converts the control variable into a control signal through a digital-to-analog converter D/A;

V) The control signal is transmitted to the blower through the output bus, and the aeration of the blower stops.

The advantages of the present invention are: on-line detection, fast response, can be used as a control parameter to control the biochemical reaction process, accurately control the biochemical reaction process, save energy and reduce consumption.

I) The detection method of SOUR has the advantages of simple operation, rapidity and short response time. Through frequency online detection of this index, the operation information of the aeration stage can be fed back in time.

II) High degree of automation, controlled by programmable controller PLC, can quickly calculate the online SOUR value according to the feedback frequency signal.

III) The operation is stable, the result of online detection is reliable, and the reproducibility is good. The frequency signal has strong anti-interference ability, and the measurement results have good reproducibility under different conditions.

Description of drawings

Fig. 1 schematic diagram of the device of the present invention.

Figure 2 SOUR online detection results.

In Fig. 1, 1-SBR reactor; 2-blower; 3-aeration pipe; 4-intake valve; 5-DO sensor; 6-DO measuring instrument; 7-frequency converter; 8-temperature sensor; Sludge concentration sensor; 10-sludge concentration detector; 11-signal input interface; 12-signal output interface; 13-process controller; 14-computer.

Detailed ways

Embodiments, in conjunction with Fig. 1, Fig. 2 illustrates the operation procedure of the method of the present invention.

The domestic sewage discharged from a family area of a university was used as the experimental object (pH=6.8~7.8, COD=160.5~319.8mg/L, NH ₄ ⁺ -N=40~80mg/L. The effective volume of the selected SBR reactor was 7m ^3. The water intake per cycle is 2.7m ³ , the COD concentration of the mixed solution in the reactor is maintained at 190-240mg/L, the NH ₄ ⁺ -N concentration is 30-40mg/L, and the temperature is 15°C. The volume of the external carbon source is The fraction is 95% ethanol. The specific process is as follows:

1) Determination of the linear relationship between the specific oxygen consumption rate and the frequency: when the system conditions (reactor size, aeration device type, temperature, air pressure) were stable, the change of K _LA was mainly related to the change of the aeration rate, The change of aeration volume in the process of frequency conversion control DO is mainly measured and indicated by the frequency parameter f of the blower, and SOUR can be expressed by the following mathematical equation:

SOUR _t = η×f _t +λ

Where SOUR _t is the specific oxygen consumption rate at time t, the unit is mgO ₂ /gMLVSS.h), _{f t} is the frequency value at time t, η is the sludge concentration correction factor, η=MLVSS/2000; λ=α×β × k, where α is a mass transfer constant, α=S _osat -S _o , β is a temperature correction factor, β=exp(T-20/T), and k is a constant, and its value is in the range of 1.0-2.5. After the process controller 13 processes the signal fed back by the sludge concentration sensor 9 to obtain the volatile sludge concentration value MLVSS signal, the sludge concentration correction factor η=MLVSS/2000=2000/2000=1; the process controller collects the temperature sensor Feedback temperature signal, the temperature is 15°C, the saturated dissolved oxygen concentration in water at 15°C is obtained from the database in the computer 14, the saturated dissolved oxygen concentration is S _osat , its value is 10.15mg/L, and the DO signal fed back by the DO sensor is S _o , whose value is 3 mg/L, calculates α=S _osat −S _o =7.15; the process controller 13 calculates β=exp(T-20/T)=0.72 according to the temperature signal fed back by the temperature sensor 8, according to The size of the temperature selected k is 1.0. When the temperature is 15°C, the linear relationship between the determined frequency and the specific oxygen consumption rate is as follows: SOUR _t =1× _ft +7.15×0.72×1.0= _ft +5.18.

II) Real-time control of SBR process:

1) Water inflow: domestic sewage enters the SBR reactor 1, the water inflow stage lasts for 15 minutes, and the inflow volume is 2.7m ³ .

2) After the aeration and water intake, the frequency converter 7 starts to control the SBR reactor by controlling the speed of the blower 2 to keep the dissolved oxygen concentration constant at about 3.0 mg/L during the aeration phase, and the system starts timing at this time. The process controller starts to collect the signals fed back by the DO sensor 5, the temperature sensor 8 and the sludge concentration sensor 9, and determines the linear relationship between the specific oxygen consumption rate and the frequency according to the signals of these sensors. If the DO signal, temperature signal and sludge concentration signal deviate from the signal of the previous cycle, the process controller will make corresponding corrections to the linear relationship. In the aeration stage, the heterotrophic bacteria firstly carry out the reaction of removing organic matter in water, and then the ammonia oxidizing bacteria carry out the ammonia oxidation reaction. After the aeration starts for at least 60 minutes, the frequency converter collects the frequency signal of the blower every 10 seconds, and the process controller can obtain the real-time signal of the frequency. After the controller filters _and compares the frequency signal, it calculates the SOUR signal value according to the linear relationship between the specific oxygen _consumption rate and the frequency parameter _. The frequency value of the blower. The process controller feeds back the SOUR signal to the computer, and the computer issues a control instruction whether to stop the blower through analysis and calculation, and at the same time converts the control instruction into a control signal through the digital-to-analog converter D/A and then transmits it to the blower. When the microorganism no longer consumes oxygen at the end of the ammonia oxidation reaction, an 'inflection point' will appear in the SOUR curve, which is manifested by a sharp drop in the SOUR value, and the first order derivative of the SOUR curve changes from positive to negative. This state is maintained for 5 minutes, and the computer 14 controls the The device 13 sends a control command to close the blower, and the aeration stops, and the result is as shown in Figure 2.

3) Start the denitrification dosing pump with carbon source, add 400ml of ethanol with a volume fraction of 95% as the denitrification carbon source of the SBR system, and stir for 60 minutes at the same time. After the set time is up, the computer-controlled process controller sends a control command to turn off the stirring device, denitrification stops.

4) Set the time of the precipitation SBR system at this stage to 120 minutes, and at this time, the water inlet valve, inlet valve and drain valve are all closed.

5) After the set time for drainage and sedimentation is up, the decanter will be turned on, and the system will automatically drain water. The time is set to 30 minutes. After the drainage is completed, the decanter will be closed.

6) Idle stage In this stage, set the idle time to 4 hours and the sludge discharge time to 10 minutes according to the needs. The sludge discharge pump is turned on under the adjustment of the process controller. When the preset sludge discharge time is reached, the sludge discharge pump is turned off. ; When the preset idle time reaches 4 hours, the system stops running or enters the next cycle.

From the detection result obtained by applying the method of the present invention, the response speed of the system is fast and sensitive, and the specific oxygen consumption rate of microorganisms in the aeration stage can be quickly determined according to the frequency signal fed back by the frequency converter at the same time interval, and the computer can simultaneously The change curve of SOUR can be drawn in real time according to the signal fed back by the process controller; and the off-line respiration instrument (referring to the background technology for the detection process) needs to spend 10-20 minutes to obtain the SOUR value, so the present invention solves the problem of the slow response of the off-line measurement method , has the problem of hysteresis; at the same time, it also overcomes the shortcomings of cumbersome maintenance and poor stability of the online SOUR determination method to a certain extent. In addition, through the online detection of the SOUR curve, the microbial biochemical reaction status at different moments of the system can be obtained. At the same time, the SOUR curve drawn on the computer will have an inflection point at the end of the ammonia oxidation (as shown in Figure 2). Based on the above information, the feedback through the process controller The control command is given to the blower to realize real-time control. The invention lays a solid theoretical foundation and technical support for real-time control with SOUR as a parameter under the condition of frequency conversion control of dissolved oxygen.

Claims (1)

1. The method of detecting the specific oxygen consumption rate of activated sludge microorganisms online through frequency conversion and speed regulation, and the applied detection equipment includes a reactor system and an automatic control system; The reactor system includes an SBR reactor and a blower; the blower is connected to the aeration pipe at the bottom of the SBR reactor, and an inlet valve is set between the aeration pipe and the blower; The automatic control system includes dissolved oxygen sensor, temperature sensor, sludge concentration sensor, sludge concentration detector, dissolved oxygen analyzer, frequency converter, process controller and computer; the sludge concentration sensor is connected to the process control through the sludge concentration detector The temperature sensor is connected to the process controller through the dissolved oxygen measuring instrument; the dissolved oxygen sensor is connected to the dissolved oxygen measuring instrument through the data line and then connected to the data signal input interface of the process controller, the dissolved oxygen measuring instrument is connected to the frequency converter, and the frequency converter At the same time, it is connected to the blower and the data signal input interface of the process controller, and the data signal output interface of the process controller is connected to the computer; the control command sent by the computer controls the blower through the output bus; the frequency converter collects the change of the blower frequency signal, and the process controller The integrated logic program calculates the real-time specific oxygen consumption rate of microorganisms in the SBR reactor according to the online frequency signal fed back by the frequency converter, the temperature signal fed back by the temperature sensor and the sludge concentration signal fed back by the sludge concentration sensor, and the obtained real-time specific oxygen consumption rate The data is fed back to the computer through the data line and displayed on the software interface of the computer; It is characterized in that, comprising the following steps: 1) After the water intake of the SBR reactor is completed, the blower starts aeration, and the frequency converter performs closed-loop control according to the dissolved oxygen signal fed back by the dissolved oxygen meter and the frequency signal fed back by the blower, and controls the dissolved oxygen in the aeration stage to a certain value; II) The logic program in the process controller integrates the linear relationship between the specific oxygen consumption rate and the frequency: SOUR _t = η × f _t + λ; where SOUR _t is the specific oxygen consumption rate at time t, and the unit is mgO ₂ /gMLVSS.h, _{f t} is the frequency value at time t, η=MLVSS/2000; λ=α×β×k, where α=S _osat -S _o , S _osat is the saturated dissolved oxygen value in water at T℃, S _o is the dissolved oxygen value displayed by the dissolved oxygen meter, β=exp(T-20/T), T is the water temperature, the unit is °C, T is in the range of 15-30 °C, and the k value is in the range of 1.0-2.5. When the temperature is 15°C, the k value is 1.0, and every time the temperature rises by 1°C, the k value increases by 0.1 on the original basis. The process controller calculates the signal fed back by the sludge concentration sensor to obtain the volatile sludge concentration value, thereby determining η; Determine the mass transfer driving force factors α and β according to the water temperature signal in the SBR reactor and the frequency conversion control constant dissolved oxygen concentration signal, and then calculate the λ value; after establishing the linear relationship between the specific oxygen consumption rate and frequency, The frequency converter collects frequency signals at the same time interval, the process controller calculates the online specific oxygen consumption rate according to the frequency signal, and the specific oxygen consumption rate signal is fed back to the computer, and the computer draws the curve of the specific oxygen consumption rate, and the specific oxygen consumption rate curve will be The occurrence of an inflection point indicating the end of aeration; III) The computer begins to identify the inflection point at least 60 minutes after the start of the aeration, and once the inflection point of the specific oxygen consumption rate occurs, the computer transmits the control variable to the process controller; IV) The process controller converts the control variable into a control signal through a digital-to-analog converter D/A; The control signal is transmitted to the blower through the output bus, and the blower aeration stops.

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