CN103922461B - A kind of method monitoring Sewage Biological Treatment oxygen uptake rate and control aeration rate - Google Patents

Abstract

The invention relates to a method for monitoring the oxygen absorption rate of sewage biological treatment and controlling the aeration amount. The present invention measures the oxygen transfer coefficient K _L a (d ^‑1 ) and saturated dissolved oxygen concentration mg/L of aeration and oxygenation under different air flow q, temperature and set sludge concentration conditions, and obtains the oxygen transfer coefficient K _L a, gas supply q, temperature T, under the condition of knowing the set oxygen transfer coefficient K _L a(d ^‑1 ) and dissolved oxygen concentration, by fitting the dissolved oxygen change curve within a certain period of time, using the previous Oxygen absorption rate in a period, as the possible oxygen absorption rate in the next stage, the minimum aeration q required for the next period, in the next period, the air volume q, the dissolved oxygen change curve, to find the oxygen in this period absorption rate. The invention overcomes the defects of large equipment investment, complicated structure or low testing frequency in the prior art. The present invention can continuously monitor OUR only by using the dissolved oxygen probe without adding additional secondary reactors, dissolved oxygen probes and sewage transmission equipment.

Description

A method for monitoring the oxygen absorption rate and controlling the aeration rate of sewage biological treatment

technical field

The invention belongs to a process monitoring and control technology of sewage biological treatment, in particular to a method for monitoring oxygen absorption rate and controlling aeration amount of sewage biological treatment.

Background technique

The method of sewage biological treatment is also called activated sludge method. Since the invention of activated sludge method in the early 20th century, it has been the main method of domestic sewage treatment in all countries in the world. It uses active microorganisms to oxidize organic matter and ammonia nitrogen in sewage under the condition of providing dissolved oxygen to achieve the purpose of removal. The supply of dissolved oxygen is usually accomplished by blower aeration. Aeration is the main energy consumption in the sewage treatment process, usually accounting for more than 50% of the energy consumption in the sewage biological treatment process. Therefore, on the premise of ensuring the treatment effect, finding ways to reduce the aeration rate of sewage treatment is an important means to reduce the energy consumption of sewage treatment. One of the important monitoring indicators is to determine the biological oxygen uptake rate (OUR).

Before the present invention was made, the biological OUR was an important index reflecting the degradation rate of pollutants in the sewage biological treatment process and the activity of activated sludge. The traditional method for measuring OUR includes two methods of intermittent and continuous determination. The intermittent method is to record the value of dissolved oxygen (DO) in the sewage treatment reactor within a certain period of time after the aeration is stopped, and divide the two to obtain OUR. This method has a low measurement frequency and cannot be used as a continuous method. The online monitoring method, and the measured value is generally small; the continuous method is to install a small secondary reactor (or other glass container) next to the main reactor, and the activated sludge mixture is continuously input from the main reactor into the secondary reactor. , and then back to the main reactor, and simultaneously measure the dissolved oxygen concentration in the main and auxiliary reactors. The ratio of the concentration difference and the residence time (HRT) of the auxiliary reactor is OUR. Dissolved oxygen probes are installed in the reactors, and sewage reflux equipment is required, the structure is complex, and equipment investment is increased. Moreover, this method measures the OUR in the secondary reactor and cannot fully reflect the OUR in the main reactor.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects and develop a method for monitoring the oxygen absorption rate and controlling the aeration rate of sewage biological treatment.

Technical scheme of the present invention is:

A method for monitoring the oxygen absorption rate and controlling the aeration rate of sewage biological treatment, the main technical feature of which is to follow the steps below:

(1) Measure the oxygen transfer coefficient K _L a(d ^-1 ) and saturated dissolved oxygen concentration mg/L of aeration and oxygenation under different air flow q, temperature and set sludge concentration conditions, and obtain the oxygen transfer coefficient Quantitative relationship between K _L a and gas supply q and temperature T:

KLa=aqb ^T-20 (1)

(2) Through the following formula:

$\frac{\mathrm{<span\; class="notranslate">\; dDO</span>}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; KLa</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; Sat</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; do</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; OUR</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

$\frac{\mathrm{<span\; class="notranslate">\; dDO</span>}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; KLa</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; Sat</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; do</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; OUR</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; do</span>}}{\mathrm{<span\; class="notranslate">\; HRT</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Under the condition of knowing the set oxygen transfer coefficient K _L a(d ^-1 ) and the dissolved oxygen concentration in the saturated state, by fitting the dissolved oxygen change curve in a certain period of time, the oxygen absorption rate in this period is calculated, For sequencing batch reactors, use the previous formula (2-1), and for continuous reactors, use the latter formula (2-2);

(3) Use the oxygen absorption rate in the previous period as the possible oxygen absorption rate in the next stage, and also use the formula in step (2) to find the minimum required for the next period to reach the set dissolved oxygen concentration Aeration rate q;

(4) In the next period of time, apply the air quantity q obtained in step (3) to the reactor, measure the dissolved oxygen change curve in this period, and use the method of step (2) to obtain the air volume q in this period Actual oxygen absorption rate, repeat the above steps (1), (2), (3), (4) until the end of the reaction.

The measurement of dissolved oxygen concentration and the measurement of oxygen absorption rate in the invention are all completed in the same main reactor.

The measured OUR in the invention is the oxygen absorption rate value in the actual sewage treatment reactor.

The invention utilizes the continuity of the oxygen absorption rate to control the aeration amount in the sewage treatment process.

The determination of the oxygen absorption rate of the invention and the control of the aeration rate are all completed by the formula described in step 2.

The present invention has the following beneficial effects:

1) The present invention can continuously measure OUR without adding additional secondary reactors, dissolved oxygen probes and sewage transmission equipment;

2) OUR measured by the present invention is the OUR value in the actual sewage treatment reactor, which is closer to the actual situation;

3) The present invention can also be used to control the aeration rate in the sewage treatment process, the control effect is better than the traditional PID control, and it can achieve aeration according to the oxygen absorption rate and avoid excessive aeration.

4) The present invention does not need to set up a secondary reactor, and only utilizes the dissolved oxygen probe installed in the sewage biological treatment reactor to continuously monitor OUR. Traditional sewage biological treatment aeration rate control generally uses a programmable logic controller (PLC), using the PID control principle to set appropriate PID parameters to keep the dissolved oxygen in the aeration tank at the set concentration. Due to the composition and flow of sewage in the morning and evening, as well as seasonal changes, it is usually difficult to achieve a better control effect in another period of time with appropriate PID parameters in a certain period of time. The invention utilizes the monitored OUR to accurately control the aeration rate and ensure that the dissolved oxygen concentration in the reactor is at a set value.

5) The present invention can be applied to continuous or sequential batch reactors.

Description of drawings

Fig. 1 - the schematic flow chart of the system of the present invention.

Fig. 2 - The present invention calibrates the graph of oxygen transfer coefficient of different air flows, wherein (A) is a graph of estimated endogenous respiratory oxygen transfer rate, and (B) is a graph of measured oxygen transfer coefficient.

Fig. 3 - the implementation effect diagram of the sequencing batch reactor of the present invention, wherein (C) is an air flow diagram, (D) is a dissolved oxygen diagram, and (E) is a monitored oxygen absorption rate diagram.

Fig. 4 - the implementation effect diagram of the continuous reactor of the present invention, wherein (F) is an air flow diagram, (G) is a dissolved oxygen diagram, and (H) is a monitored oxygen absorption rate diagram.

Each label in the figure indicates the corresponding component name as follows:

Liquid inlet tank 1, reactor 2, dissolved oxygen probe 3, gas supply system 4, data acquisition and control system 5, computer 6, agitator 7, water inlet pump 8, temperature probe 9.

detailed description

The specific implementation of the present invention in typical sequence batch (SBR) and continuous activated sludge processes will be described below in conjunction with specific examples.

The sewage in the liquid inlet tank 1 is transferred to the reactor 2 through the inlet pump 8, the agitator 7 is installed in the reactor 2 for mixing and stirring under low aeration, and the dissolved oxygen probe 5 is installed in the reactor 2 And submerged in the liquid, the temperature probe 9 is also installed in the reactor 2 and submerged in the liquid, and the gas supply system 4 stretches into the liquid in the reactor 2; the data measured by the dissolution probe 3 and the temperature probe 9 are collected through data collection and The control system 5 sends to the computer 6, and the data acquisition and control system 5 outputs instructions to control the water inlet pump 8 and the air supply system 4.

The specific implementation of Sequencing Batch (SBR) and continuous activated sludge process will be described below.

Embodiment 1: sequence batch (SBR) activated sludge method

The specific steps are as follows:

Step 1: Measure the oxygen transfer coefficient K _L a(d ^-1 ) and saturated dissolved oxygen of aeration and oxygenation under different air flow q (0, 30, 40, 60, 80, 120L/h) and temperature changes Concentration Osat (mg/L), obtain the quantitative relational expression of oxygen transfer coefficient K _L a and gas supply q, temperature T.

The method for determining the quantitative relationship between the oxygen transfer coefficient K _L a and the gas supply q is as follows:

1) The activated sludge in the reactor is continuously aerated for more than 12 hours, so that the sludge is in an endogenous respiration state, and the sludge concentration is kept stable during the measurement process, thereby avoiding the influence of the sludge concentration on K _L a and Osat;

2) Stop the aeration for 15 minutes, use the computer data acquisition system to record the dissolved oxygen concentration at a frequency of once every 10 seconds, and calculate the endogenous oxygen respiration rate (OUR _end mg/(L×d)) by curve fitting, As shown in Figure 2(A);

3) Set a certain air flow rate to be measured, start aeration for 45 minutes, record the dissolved oxygen concentration and temperature at a frequency of once every 10 seconds, and use the following formula to perform curve fitting on the dissolved oxygen concentration after the aeration is over:

$\frac{\mathrm{<span\; class="notranslate">\; dDO</span>}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; KLa</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; Sat</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; do</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; OUR</span>}}_{\mathrm{<span\; class="notranslate">\; end</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, DO is the recorded dissolved oxygen concentration, and OUR _end is determined in step 2. By curve fitting (as shown in Figure 2(B)), the oxygen transfer coefficient K _L a(d ^-1 ) and the saturated dissolved oxygen concentration Osat(mg/L) can be obtained;

4) Repeat steps 2 and 3 in this step, measure K _L a and Osat three times in total, and take the average value as the measured value;

5) Repeat 2, 3, 4 in this step to measure K _L a and Osat under other gas supply q conditions;

6) Obtain the quantitative relational expression of oxygen transfer coefficient K _L a and gas supply q, as follows:

KLa＝4.3042q1.017 ^T-20 (4)

Where a, b are coefficients, q is air flow (L/h), T is temperature (Celsius)

Step 2: Estimate OUR online within a 5-minute period (T ₁ ). Provide air flow rate q ₁ =23L/h to the reactor. During the next 5 minutes, use the computer data acquisition system to record the dissolved oxygen concentration according to the frequency of once every 10 seconds. After the recording is completed, use the formula (3— 1), fitting the obtained dissolved oxygen concentration, and estimating the oxygen uptake rate (hereinafter referred to as OUR) within this 5-minute period.

Among them, the KLa value can be converted according to the formula (4), and Osat is selected according to the temperature T. In the formula (2-1), only OUR is unknown. By fitting the obtained dissolved oxygen concentration curve, the OUR in this period can be obtained = 19.2 mg O ₂ /(L*h);

Step 3: Calculate the gas supply volume in the next 5-minute period (T ₂ ). Use the OUR (19.2mg O ₂ /(L*h)) obtained in step 2 as the OUR for the next 5-minute period, and use formula (2-1) to calculate the required minimum KLa value, so that in this 5-minute period The final dissolved oxygen concentration is close to the set value (DO _set = 1.0mg/L). Then calculate the required air supply volume q ₂ =9.7L/h by formula (4), and the computer control system will instruct the air supply system to implement the air supply volume q ₂ ;

Step 4: Repeat steps 2 and 3 to calculate the actual OUR value in the time period (T ₂ ) and the gas supply volume in the next 5 minutes (T ₃ ), and repeat steps 2, 3 and 4 until the reaction ends. As can be seen from Fig. 3(C), the present invention can continuously control the aeration rate, so that the dissolved oxygen is maintained at the set value of 1.0mg/L (Fig. 3(D)), and continuously monitors OUR (Fig. 3(E) )).

Embodiment 2: continuous activated sludge process

The specific steps are as follows:

Step 1: Transform the reactor in the SBR implementation case to make it continuously feed water, change the feed water flow rate, make the residence time (HRT) of the continuous reactor be 8 hours, and set up a sedimentation tank with a residence time of 4 hours, the sedimentation tank The sludge reflux ratio is 2. The influent flow is continuously changed based on the 8-hour average residence time to simulate the fluctuation of sewage volume within a day. The relationship between the oxygen transfer coefficient K _L a and the gas supply q in the continuous reactor is the same as that in the SBR reactor, see formula (4).

Step 2: Estimate OUR online within a 5-minute period (T ₁ ). Provide air flow rate q ₁ =10L/h to the reactor. During the next 5 minutes, use the computer data acquisition system to record the dissolved oxygen concentration at a frequency of once every 10 seconds. After the recording is completed, use the formula (2— 2), fitting the obtained dissolved oxygen concentration, and estimating the OUR in this 5-minute period.

Among them, the KLa value can be converted according to the formula (4), and Osat is selected according to the temperature T. In the formula (2-2), only OUR is unknown. By fitting the obtained dissolved oxygen concentration curve, the OUR in this period can be obtained = 10.2 mg O ₂ /(L*h);

Step 3: Calculate the gas supply volume in the next 5-minute period (T ₂ ). Use the OUR obtained in step 2 as the OUR for the next 5-minute period, and use the formula (2-2) to calculate the required minimum KLa value, so that the dissolved oxygen concentration at the end of this 5-minute period is close to the set value (DO _set = 1.0mg/L). Then calculate the required air supply volume q ₂ =4.1L/h from the formula (4), and the computer control system will refer to the air supply volume q ₂ to implement the current air supply system;

Step 4: Repeat steps 2 and 3 to calculate the actual OUR value in the time period (T ₂ ) and the gas supply volume in the next 5 minutes (T ₃ ), and repeat steps 2, 3 and 4 until the reaction ends. As shown in Figure 4, the present invention can continuously regulate the gas supply q (Figure 4(F)), so that dissolved oxygen remains at 1.0 mg/L (Figure 4(G)), and continuously monitor OUR (Figure 4(H) )).

Claims (5)

1. monitor Sewage Biological Treatment oxygen uptake rate and the method controlling aeration rate for one kind, it is characterised in that according to such as Lower step is carried out:

(1) measure under the conditions of different aeration rate q (L/h), temperature T (DEG C) and setting sludge concentration, obtain K_La Quantitative relation formula with q, T:

K_LA=aqb^T-20

Wherein, K_LA is oxygen transfer ratio K_La-d^-1；A and b is coefficient, dimensionless unit；

(2) equation below is passed through:

$\frac{dDO}{dt}=K_{L}a(O_{Sat}-DO)+OUR$

$\frac{dDO}{dt}=K_{L}a(O_{Sat}-DO)+OUR-\frac{DO}{HRT}$

Wherein DO is dissolved oxygen concentration (mg/L)；T is the time (d)；O_SatFor saturated dissolved oxygen concentration (mg/L)；OUR For oxygen uptake rate (mgO₂/(L*d))；HRT is hydraulic detention time (d)；

At the K set_LA and O_SatUnder under the conditions of, by the dissolved oxygen change curve in the matching period, obtain this time OUR in Duan, for sequence batch reactor with, uses previous formula, for flow reactor, uses later Formula；

(3) OUR of a upper period was utilized, as the OUR that next stage is possible, also with the public affairs that step (2) is inner Formula, obtains the dissolved oxygen concentration reaching to set, the aeration rate q of required subsequent period；

(4) within the ensuing period, applying the aeration rate q tried to achieve by step (3) in reactor, measuring should Dissolved oxygen change curve in period, the method utilizing step (2), obtain the actual OUR of this period, Repeat the above steps (1), (2), (3), (4), until reaction terminates.

A kind of side monitoring Sewage Biological Treatment oxygen uptake rate and controlling aeration rate the most according to claim 1 Method, it is characterised in that the mensuration of dissolved oxygen concentration and the mensuration of oxygen uptake rate are all in same main reactor Complete.

A kind of side monitoring Sewage Biological Treatment oxygen uptake rate and controlling aeration rate the most according to claim 1 Method, it is characterised in that the OUR of mensuration is the oxygen uptake rate value in actual sewage-treating reactor.

A kind of side monitoring Sewage Biological Treatment oxygen uptake rate and controlling aeration rate the most according to claim 1 Method, it is characterised in that utilize the seriality of oxygen uptake rate, the control to sewage disposal process aeration rate.

A kind of side monitoring Sewage Biological Treatment oxygen uptake rate and controlling aeration rate the most according to claim 1 Method, it is characterised in that utilize the mensuration of oxygen uptake rate, and the control of aeration rate is all public affairs described in 2 in steps Formula completes.