Method for accurately measuring and calculating external reflux ratio of fully mixed flow A < 2 > O process

Abstract

The invention provides a method for accurately measuring and calculating the external reflux ratio of a fully mixed flow A2O process, and relates to the technical field of sewage treatment. The method is based on an anaerobic tank ammonia nitrogen conservation principle and comprises the following steps: roughly estimating an external reflux proportion and calculating hydraulic retention time of an anaerobic tank; continuously sampling inlet water and external return sludge within the complete hydraulic retention time, and collecting samples in the anaerobic tank at the starting and ending moments; testing related ammonia nitrogen concentration; calculating an external reflux ratio by using a derived formula; and the measurement and calculation precision is improved through iterative optimization. The method solves the problems of experience-dependent estimation, low precision and poor adaptability in the prior art, has the beneficial effects of high measurement and calculation precision, sufficient theoretical basis, simplicity and convenience in operation and high adaptability, can meet different precision requirements through iteration according to actual working conditions, is suitable for external reflux ratio regulation and control of various fully mixed flow A2O processes, and has wide application prospects. The process operation stability and the treatment effect are favorably improved.

Description

Technical Field

[0001] This invention relates to the field of municipal wastewater treatment technology, and in particular to a method for accurately calculating the A value of mixed-flow systems. 2 The method of external reflux ratio in O process. Background Technology

[0002] In the field of wastewater treatment, fully co-current flow (CFC) 2 The O process, due to its simultaneous nitrogen and phosphorus removal capabilities, is widely used in urban sewage and industrial wastewater treatment projects. The external reflux ratio, as a core operating parameter of this process, directly affects the sludge concentration distribution, substrate degradation efficiency, and nitrogen and phosphorus removal effects in the anaerobic, anoxic, and aerobic tanks, and is crucial for the stable operation of the process.

[0003] Currently, the commonly used methods for calculating the external recirculation ratio in the industry mainly rely on operators' experience-based estimations, lacking scientific theoretical basis and precise calculation support. Because the influent water quality (such as ammonia nitrogen and COD concentrations) and flow rate fluctuate over time, and because the process design parameters (such as anaerobic tank volume and influent flow rate) differ among different wastewater treatment plants, the external recirculation ratio estimated based on experience often has significant deviations. This makes it difficult to adapt to complex and changing operating conditions, leading to unstable process treatment effects and even problems such as effluent quality exceeding standards and energy waste. Summary of the Invention

[0004] This invention aims to solve the problems of existing fully mixed-flow A 2 The method for calculating the external reflux ratio in the O process relies on empirical estimation, lacks scientific basis, has large calculation deviations, and is difficult to adapt to changes in different water quality and operating conditions.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A precise measurement method for fully mixed flow A 2 The method for achieving the external reflux ratio in the O process is as follows: Core principle: The calculation method of this invention is based on the principle of ammonia nitrogen conservation in anaerobic ponds: the total ammonia nitrogen in the anaerobic pond remains essentially unchanged due to activated sludge metabolism, and the total ammonia nitrogen at the outlet equals the sum of the total ammonia nitrogen in the influent and the total ammonia nitrogen brought in by the external return sludge. Simultaneously, combining the assumptions of complete mixing (outflow concentration = influent concentration) and no biological transformation (only physical mixing), a material balance differential equation is established. The formula for calculating the external return ratio is derived mathematically, and the calculation accuracy is further improved through iterative optimization.

[0006] Parameter definition: 1. Influent ammonia nitrogen concentration: a (unit: mg / L), which is the mass concentration of ammonia nitrogen in the anaerobic tank influent; 2. External return ammonia nitrogen concentration: b (unit: mg / L), which is the mass concentration of ammonia nitrogen in the external return sludge; 3. Influent flow rate: Q (unit: m³ / h), which is the flow rate of wastewater entering the anaerobic tank; 4. External recirculation flow rate: RQ (unit: m³ / h), where R is the external recirculation ratio (dimensionless). 5. Total inflow rate: Q + RQ = Q(1 + R) (unit: m³ / h); 6. Hydraulic retention time in anaerobic tank: HRT (unit: h), calculated based on the total influent flow rate of the anaerobic tank, satisfying V=HRT·Q(1+R), where V is the volume of the anaerobic tank (unit: m³). 7. Ammonia nitrogen concentration in the anaerobic tank at time t: C(t) (unit: mg / L). Initial conditions: when t=0, C(0)=C0; when t=HRT, C(t)=C t .

[0007] Calculation steps: 1. Roughly estimate the external recirculation ratio and calculate HRT: Based on the fully mixed-flow A 2 The design drawings of the O process are used to obtain the volume V of the anaerobic tank. The influent flow rate Q is obtained through the pipeline flow meter. The external recirculation ratio R0 is roughly estimated (the value range is 0.5-2.0). The hydraulic retention time HRT0 of the anaerobic tank is calculated according to the formula V=HRT·Q(1+R).

[0008] 2. Continuous Sampling: Within a complete HRT0 cycle of the anaerobic tank, continuous sampling is performed on the influent and externally returned sludge. The influent sampling point is set 1-3m from the tank body via the influent pipe, and the externally returned sludge sampling point is set 0.5-2m from the anaerobic tank inlet via the externally returned sludge pipe. The sampling frequency is once every 10-30 minutes, with a single sample volume of 50-100mL. After sampling, the samples are refrigerated at 0-4℃ to prevent ammonia nitrogen volatilization or conversion.

[0009] 3. Sampling in the anaerobic tank: At T=0 (the start time of HRT0) and T=HRT0 (the end time of HRT0), a mixed sample was collected in the middle of the anaerobic tank (sampling depth of 1 / 2-2 / 3 of the tank depth). The sample volume was 50-100 mL, and the sample was also refrigerated.

[0010] 4. Ammonia nitrogen concentration test: Nessler's reagent spectrophotometry or salicylic acid-hypochlorite spectrophotometry was used to test the influent ammonia nitrogen concentration a, the external reflux ammonia nitrogen concentration b, the anaerobic tank ammonia nitrogen concentration C0 at T=0, and the anaerobic tank ammonia nitrogen concentration C at T=HRT0, respectively. t The test accuracy is ≤0.01mg / L.

[0011] 5. First calculation of external reflux ratio: Based on the principle of ammonia nitrogen conservation, the external reflux ratio R1 is calculated using the following formula: ; This formula is derived from the material balance differential equation, which is: ; 6. First iteration: Based on R1 calculated in step 5, combined with the anaerobic tank volume V and influent flow rate Q, recalculate the hydraulic retention time HRT1 of the anaerobic tank according to the formula V=HRT·Q(1+R), repeat steps 2-5, and obtain the external recirculation ratio R2.

[0012] 7. Iterative Optimization: Based on the required accuracy, step 6 can be repeated using R2 to perform iterative calculations, resulting in R3. The number of iterations is generally 1-3. When the iteration reaches R2, it is sufficient to meet the control requirements of most wastewater treatment processes. The more iterations, the higher the accuracy.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. High accuracy of calculation: Based on the principle of ammonia nitrogen conservation and material balance differential equation, the formula for calculating the external reflux ratio is derived through rigorous mathematical derivation. At the same time, the iterative optimization method is introduced, which can effectively reduce the calculation deviation. Iteration to R2 can meet the requirements of conventional process control. After multiple iterations, the accuracy can be further improved, which solves the problem of large deviation in empirical estimation.

[0014] 2. Sufficient theoretical basis: Based on the conservation of total ammonia nitrogen in the anaerobic tank as the core theoretical foundation, the quantitative relationship between the influent ammonia nitrogen concentration, the external return ammonia nitrogen concentration and the ammonia nitrogen concentration in the anaerobic tank is clarified, which makes the calculation process have a solid scientific basis and avoids the blindness of traditional experience estimation.

[0015] 3. Simple and feasible operation: The only parameters that need to be tested are the influent ammonia nitrogen concentration a, the external return ammonia nitrogen concentration b, the anaerobic tank ammonia nitrogen concentration C0 at T=0, and the anaerobic tank ammonia nitrogen concentration C at T=HRT. t The parameters are easy to obtain, and can be obtained using conventional ammonia nitrogen detection methods. No complicated instruments or operating procedures are required, making it easy to promote and apply in practical engineering.

[0016] 4. High adaptability: Suitable for fully mixed-flow A systems with influent COD concentrations of 100-800 mg / L and influent ammonia nitrogen concentrations of 5-50 mg / L. 2 The O process is unaffected by drastic fluctuations in influent water quality and quantity. It can continuously optimize the results through iterative calculations, ensuring an accurate external reflux ratio under different operating conditions. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1This is a schematic diagram of the sampling and process flow of the anaerobic tank in the fully mixed-flow A²O process corresponding to an embodiment of the present invention.

[0018] The components include: 1. Anaerobic tank; 2. Inlet pipe; 3. External sludge return pipe; 4. Inlet sampling point; 5. External sludge return sampling point; 6. Sampling point inside the anaerobic tank; 8. Pipeline flow meter; and 9. External sludge return pump. Detailed Implementation

[0019] The fully mixed flow A²O process (also known as the completely mixed A²O process) is a wastewater treatment technology developed based on the traditional A²O (anaerobic-anoxic-aerobic) biological nitrogen and phosphorus removal process. Its core feature is that through a special structural design, the three functional zones of anaerobic, anoxic and aerobic are completely mixed in the same reaction tank, while retaining the core capability of simultaneous nitrogen and phosphorus removal.

[0020] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Example 1 like Figure 1 As shown, wastewater enters anaerobic tank 1 through inlet pipe 2, and externally returned sludge is returned to anaerobic tank 1 through externally returned sludge pipe 3 (equipped with externally returned pump 9). The influent flow rate is monitored in real time by pipe flow meter 8 on inlet pipe 2. Inlet sampling point 4 is set at 1-3m from anaerobic tank 1 on inlet pipe 2, externally returned sludge sampling point 5 is set at 0.5-2m from the inlet of anaerobic tank 1 on externally returned sludge pipe 3, and sampling point 6 in anaerobic tank 1 is set in the middle of anaerobic tank 1, with a sampling depth of 1 / 2-2 / 3 of the tank depth. The treated mixed liquor enters the subsequent anoxic tank (not shown in the figure) through outlet pipe.

[0022] A municipal wastewater treatment plant uses a fully mixed-flow A²O process. The design dimensions of anaerobic tank 1 are 20m long × 10m wide × 5m deep, therefore the volume of anaerobic tank 1 is V = 20 × 10 × 5 = 1000m³. The flow meter 8 on the influent pipe 2 shows an influent flow rate Q = 500m³ / h. The influent COD concentration is 350mg / L, and the influent ammonia nitrogen concentration is initially monitored to be 20-30mg / L, which is within the applicable scope of this invention (influent COD concentration 100-800mg / L, influent ammonia nitrogen concentration 5-50mg / L).

[0023] 1) Sampling equipment: The SS-3000 automatic sampler is selected, with a sampling accuracy of ±1%, supporting timed continuous sampling, and the single sampling volume can be adjusted from 50 to 500 mL; Storage equipment: A 4℃ portable refrigerator was selected for low-temperature preservation of the samples after sampling. Ammonia nitrogen detection equipment: A DR6000 UV-Vis spectrophotometer was selected, equipped with a Nessler's reagent detection module, with a testing accuracy of 0.01 mg / L, which meets the testing accuracy requirements of this invention.

[0024] 2) Calculation process: 1. Roughly estimate the external recirculation ratio and calculate HRT0: Based on the design drawings and the operating experience of similar wastewater treatment plants, the external recirculation ratio R0 is roughly estimated to be 1.0. According to the formula V=HRT·Q(1+R), the hydraulic retention time of the anaerobic tank HRT0 is calculated as V / [Q(1+R0)]=1000 / [500×(1+1.0)]=1.0h.

[0025] 2. Continuous sampling: During one complete HRT0 (1.0h) in the anaerobic tank, continuous sampling was carried out at the influent sampling point and the external return sludge sampling point using an automatic sampler. The sampling frequency was once every 20 minutes, and the single sampling volume was 80mL. A total of 3 influent samples and 3 external return sludge samples were collected. After sampling, the samples were immediately placed in a 4℃ refrigerator for storage.

[0026] 3. Sampling in the anaerobic tank: At T=0 (sampling start time) and T=1.0h (HRT0 end time), a mixed sample was collected at the sampling point in the anaerobic tank (middle of the anaerobic tank, sampling depth 2.5m, i.e. 1 / 2 of the tank depth) using a sampler. The sample volume was 80mL per sample and stored under cold storage.

[0027] 4. Ammonia Nitrogen Concentration Test: After thoroughly mixing the collected influent samples, the influent ammonia nitrogen concentration (a = 25.32 mg / L) was measured using Nessler's reagent spectrophotometry. After thoroughly mixing the external return sludge samples, the external return ammonia nitrogen concentration (b = 29.87 mg / L) was measured. The ammonia nitrogen concentration (C0) of the anaerobic tank samples at T=0 was measured to be 27.65 mg / L, and the ammonia nitrogen concentration (C) of the anaerobic tank samples at T=1.0 h was measured to be... t =26.98mg / L.

[0028] 5. First calculation of the external reflux ratio R1: Substitute the above test data into the formula: ; Where e - ¹≈0.3679, the calculation process is as follows: numerator = (26.98 - 27.65 × 0.3679) - 25.32 × (1 - 0.3679) = (26.98 - 10.17) - 25.32 × 0.6321 = 16.81 - 16.00 = 0.81; Denominator = 29.87 × (1 - 0.3679) - (26.98 - 27.65 × 0.3679) = 29.87 × 0.6321 - 16.81 = 18.88 - 16.81 = 2.07; Therefore, R1 = 0.81 / 2.07 ≈ 0.391, or 39.1%.

[0029] 6. First iteration calculation of R2: Based on R1=0.391, the hydraulic retention time of the anaerobic tank is recalculated as HRT1=V / [Q(1+R1)]=1000 / [500×(1+0.391)]≈1000 / 695.5≈1.438h.

[0030] Repeat steps 2-5: Within HRT1=1.438h, samples were collected every 20 minutes, for a total of 5 influent samples and 5 external sludge return samples. After mixing, the concentrations were measured as follows: a'=25.18mg / L, b'=29.93mg / L; at T=0, the ammonia nitrogen concentration in the anaerobic tank C0'=27.32mg / L, and at T=1.438h, the ammonia nitrogen concentration C... t =26.75mg / L.

[0031] Substitute into the formula to calculate R2: The numerator is calculated as follows: (26.75 - 27.32 × 0.3679) - 25.18 × (1 - 0.3679) = (26.75 - 10.05) - 25.18 × 0.6321 = 16.70 - 15.92 = 0.78. Denominator = 29.93 × (1 - 0.3679) - (26.75 - 27.32 × 0.3679) = 29.93 × 0.6321 - 16.70 = 18.92 - 16.70 = 2.22; Therefore, R² = 0.78 / 2.22 ≈ 0.351, or 35.1%.

[0032] 7. Accuracy Verification: The process control requirements for this wastewater treatment plant necessitate an external recirculation ratio calculation error of ≤5%. The relative error between R2 and R1 is (0.391-0.351) / 0.391≈10.2%. To further improve accuracy, a second iteration can be performed to calculate R3. However, based on conventional process control requirements, R2 already meets operational needs; therefore, the final external recirculation ratio is determined to be 35.1%.

[0033] 3) Implementation results: After operating for one month using the external recirculation ratio (35.1%) calculated by this invention, the effluent ammonia nitrogen concentration of the wastewater treatment plant stabilized at 1.5-2.5 mg / L, and the COD concentration stabilized at 30-40 mg / L, both meeting the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002). Compared with the previous empirical estimation (external recirculation ratio 50%), the fluctuation range of effluent ammonia nitrogen concentration (2.0-4.5 mg / L) was significantly reduced, and the energy consumption per ton of water was reduced by about 8%. This proves that the calculation method of this invention is accurate and effective, and can significantly improve the stability and economy of process operation.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for accurately measuring the A of fully mixed-flow systems 2 The method for external reflux ratio in process O is characterized by... Includes the following steps: (1) According to the fully mixed flow A 2 The design drawings of the O process are used to roughly estimate the external recirculation ratio R0, and the hydraulic retention time HRT0 of the anaerobic tank is calculated based on R0. The hydraulic retention time HRT0 satisfies the formula V=HRT·Q(1+R), where V is the volume of the anaerobic tank, Q is the influent flow rate, and R is the external recirculation ratio. (2) Within a complete HRT0 of the anaerobic tank, continuous sampling of the influent and external return sludge of the anaerobic tank was carried out; (3) Collect mixed samples in the anaerobic tank at T=0 and T=HRT0 respectively; (4) Test the influent ammonia nitrogen concentration a, the external return ammonia nitrogen concentration b, the anaerobic tank ammonia nitrogen concentration C0 at T=0, and the anaerobic tank ammonia nitrogen concentration C at T=HRT0 of the samples collected in steps (2) and (3) respectively. t ; (5) Based on the principle of ammonia nitrogen conservation in anaerobic tanks, the external recirculation ratio R1 is calculated using the following formula: ； (6) Based on R1 calculated in step (5), recalculate the hydraulic retention time HRT1 of the anaerobic tank, repeat steps (2)-(5), and obtain the external recirculation ratio R2; (7) Based on the required measurement accuracy, R can be used n (n≥2) Repeat step (6) for iterative calculation to obtain a more accurate external reflux ratio R. n+1 .

2. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... In step (2), the frequency of continuous sampling is once every 10-30 minutes, and the single sampling volume is 50-100mL. After sampling, the sample is stored in a refrigerated environment at 0-4℃.

3. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... In step (7), the number of iterations is 1-3 times. When the iteration reaches R2, the accuracy requirements of conventional wastewater process control are met.

4. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... The calculation process is based on the following assumptions: Assumption 1: The anaerobic tank is in a completely mixed state, that is, the ammonia nitrogen concentration of the effluent from the anaerobic tank is equal to the ammonia nitrogen concentration of the mixed liquid inside the tank; Hypothesis 2: Ammonia nitrogen in the anaerobic tank undergoes only physical mixing and does not undergo biotransformation due to activated sludge metabolism.

5. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... In step (4), the ammonia nitrogen concentration is tested by Nessler's reagent spectrophotometry or salicylic acid-hypochlorite spectrophotometry, with a test accuracy of ≤0.01mg / L.

6. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... In step (1), the estimated external reflux ratio R0 ranges from 0.5 to 2.

0.

7. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... In step (2), the influent sampling point is set 1-3m away from the anaerobic tank influent pipe, and the external return sludge sampling point is set 0.5-2m away from the anaerobic tank inlet via the external return sludge pipe; in step (3), the sampling point inside the anaerobic tank is set in the middle of the anaerobic tank, and the sampling depth is 1 / 2-2 / 3 of the tank depth.

8. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... The formula in step (5) is derived based on the material balance differential equation, which is: ； in, for The ammonia nitrogen concentration in the anaerobic tank at all times, This refers to the external return flow.

9. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... In step (1), the volume V of the anaerobic tank is calculated by the dimensions marked on the design drawings, and the influent flow rate Q is obtained by real-time monitoring through the pipeline flow meter.

10. A method for accurately measuring the fully mixed-flow A as described in claim 1 2 The method for external reflux ratio in process O is characterized by... The method is applicable to fully mixed-flow A-type reactors with influent COD concentrations of 100-800 mg / L and influent ammonia nitrogen concentrations of 5-50 mg / L. 2 O process.

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