A method for enhancing biological phosphorus removal in a continuous-flow aerobic granular sludge-membrane bioreactor based on F / M regulation

Abstract

This invention belongs to the field of environmental protection technology and discloses a method for biological phosphorus removal in a continuous flow aerobic granular sludge-membrane bioreactor based on enhanced F / M ratio regulation. The method includes the following steps: S1. Calculating the actual F / M value based on the ratio of organic matter content to total sludge volume entering the system; S2. Calculating the deviation (ΔF / M) of the actual F / M value based on the difference between the actual F / M value and the optimal F / M value; S3. Adjusting the actual daily sludge discharge rate of the system to the designed daily sludge discharge rate based on ΔF / M, thereby adjusting the actual F / M value to the optimal F / M value. Specifically, ΔF / M > 0 generally indicates a reduction in the actual daily sludge discharge rate, while ΔF / M < 0 generally indicates an increase in the actual daily sludge discharge rate. This invention achieves in-situ enhanced biological phosphorus removal performance, with advantages such as simple operation, minimal system impact, and low input cost. It is also suitable for treating real urban domestic wastewater with large fluctuations in water quality.

Description

Technical Field

[0001] This invention relates to the field of water treatment, and more specifically, to a method for enhanced biological phosphorus removal. Background Technology

[0002] Aerobic granular sludge (AGS) technology is an aggregate formed by the self-immobilization of microorganisms under aerobic conditions. Compared with the traditional activated sludge process, it has advantages such as good settling performance, small footprint, and strong resistance to shock loads, and has therefore been widely used in various wastewater treatment processes. Sequencing batch reactors (SBRs) have become the most successful method for cultivating AGS due to the ease of controlling granulation conditions such as feast / famine alternation and hydraulic selective pressure, but they are generally suitable for applications with smaller wastewater treatment volumes. Compared with SBRs, continuous flow membrane bioreactors (MBRs) have advantages such as high treatment capacity, easy control of fluid dynamics, thorough mixing, and good mass transfer. Furthermore, converting flocculent sludge into AGS in MBRs helps to further mitigate membrane fouling. However, because the activity of microorganisms related to phosphorus removal is easily affected by various operating conditions, most continuous flow AGS-MBRs face the problem of low and unstable phosphorus removal efficiency, hindering their application in low-concentration municipal wastewater treatment. With increasingly stringent phosphorus emission standards, improving the phosphorus removal performance of the system is imperative.

[0003] Conventional phosphorus removal methods include chemical and biological phosphorus removal. Among these, enhanced biological phosphorus removal (EBPR) is an economical, effective, and environmentally friendly method, primarily achieved by polyphosphate-accumulating organisms (PAOs). These organisms can over-accumulate phosphorus in wastewater under aerobic conditions and release it under anaerobic conditions. In this mode, most phosphorus is transferred and fixed in the sludge; therefore, maintaining the feed-to-microbe ratio (F / M) through sludge removal is feasible and conducive to creating periodic anaerobic-aerobic conditions.

[0004] In biological wastewater treatment systems, the flow rate (F / M) is one of the key operating parameters affecting biomass growth, sludge settling, and granulation degree. Chinese patent application CN 107032482 A discloses a stable operation process for aerobic granular sludge based on F / M regulation. This invention maintains the F / M value by adjusting the influent load, ultimately forming AGS (aggregate sludge) with uniform size, excellent settling performance, stable structure, and rich microbial community. Therefore, for EBPR (Enhanced Biomass Reduction), this invention regulates the F / M value of a continuous flow system through sludge discharge, which has advantages such as simple operation and minimal system impact, making it suitable for large-scale promotion. Summary of the Invention

[0005] The primary objective of this invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for biological phosphorus removal based on the regulation of F / M enhanced continuous flow aerobic granular sludge-membrane bioreactor.

[0006] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0007] A method for phosphorus removal based on enhanced F / M ratio in a continuous flow aerobic granular sludge-membrane bioreactor, using a membrane bioreactor operating in continuous flow mode as the operating system, includes the following steps:

[0008] S1. Calculate the actual F / M value based on the ratio of organic matter content to total sludge volume entering the system;

[0009] S2. Calculate the offset ΔF / M of the actual F / M value based on the difference between the actual F / M value and the optimal F / M value of the system;

[0010] S3. Adjust the actual daily sludge discharge rate of the system to the designed daily sludge discharge rate based on ΔF / M, thereby adjusting the actual F / M value to the optimal F / M value.

[0011] The control method provided by this invention is based on adjusting the actual daily sludge discharge rate (ΔF / M) to bring it closer to the designed daily sludge discharge rate, thereby adjusting the F / M of the system to the optimal value and enhancing the biological phosphorus removal process in the continuous flow aerobic granular sludge-membrane bioreactor. This method is applicable to the treatment of real urban domestic wastewater with significant water quality fluctuations and can provide technical support for the upgrading and renovation of wastewater treatment plants and achieving compliant discharge.

[0012] Furthermore, the specific method in S3 for adjusting the actual daily sludge discharge rate of the system to the designed daily sludge discharge rate based on ΔF / M is as follows:

[0013] When ΔF / M > 0, the organic matter content is relatively excessive, the system is operating under high load, and the actual daily sludge discharge rate should be reduced.

[0014] When ΔF / M < 0, the system is in a low-load operation state, and the actual daily sludge discharge rate should be increased.

[0015] Furthermore, the formula for calculating the actual F / M value is as follows:

[0016]

[0017] Where F / M (kgCOD / kgMLVSS·d) is the food-to-microbe ratio, also known as sludge loading; Q (L) is the daily influent volume; ΔCOD Cr (mg / L) represents the COD difference between the influent and effluent; MLVSS (mg / L) represents the concentration of volatile suspended solids in the mixed liquor of activated sludge in the reactor; V a (L) represents the total amount of sludge from the integrated equipment.

[0018] Furthermore, in the formula for calculating the actual F / M value, BOD5 can be used instead of COD. Cr .

[0019] Further, the suitable range for the F / M value is 0.05-0.15 kg COD / kg MLVSS·d, and the optimal F / M is selected from this range. Preferably, the suitable range for the F / M value is 0.07-0.13 kg COD / kg MLVSS·d, and the optimal F / M is selected from this range.

[0020] Furthermore, the actual daily sludge discharge rate is calculated by multiplying the sludge discharge time, sludge discharge frequency, and instantaneous sludge discharge rate.

[0021] The instantaneous sludge discharge rate is 5-10 t / h, preferably 8-9 t / h; the daily sludge discharge time is 2-15 min, preferably 8-10 min; the sludge discharge frequency (interval time, i.e., shut-off time) is 60-1440 min, preferably 420-540 min; thereby resulting in a sludge yield of 0.10-4.00 gSS / gCOD, preferably 0.40-3.10 gSS / gCOD.

[0022] Furthermore, the calculation formula for the designed daily sludge discharge rate is as follows:

[0023]

[0024] Where v′(t / d) is the design daily sludge discharge rate; θ c (d) represents the SRT value of the reactor.

[0025] Furthermore, the formula for calculating the SRT value is as follows:

[0026]

[0027] Wherein, MLSS (mg / L) is the mixed liquor suspended solids concentration of activated sludge in the reactor; Y (gSS / gCOD) is the sludge yield.

[0028] Furthermore, the concentration of the inoculated sludge in the system is 2000-6000 mg / L, preferably 2500-3500 mg / L; the concentration of TP in the influent is 0.5-15.0 mg / L, preferably 1.0-8.0 mg / L.

[0029] Furthermore, if the factors affecting TP removal rate deviate from the appropriate range, the actual daily sludge discharge rate needs to be adjusted accordingly.

[0030] Specifically, the factors affecting the TP removal rate include at least one of carbon source, biomass, or DO.

[0031] The carbon source is expressed as COD, with a suitable range of 50-600 mg / L, preferably 56.74-359.97 mg / L; the biomass is expressed as MLSS, with a suitable range of 5000-18000 mg / L, preferably 7509-15412 mg / L; the suitable range of DO in the aerobic zone is 2.0-4.0 mg / L, preferably 2.0-3.0 mg / L; and the suitable range of DO in the anaerobic zone is 0-0.2 mg / L.

[0032] Furthermore, by using principal coordinate analysis (PCoA) or Pearson correlation coefficient method, key factors affecting TP removal rate are obtained, and the actual daily sludge discharge rate is adjusted accordingly.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. The enhanced biological phosphorus removal method provided by this invention is applicable to aerobic granular sludge-membrane bioreactors operating in continuous flow mode, which facilitates the upgrading and transformation of existing sewage treatment plants and achieves energy saving, consumption reduction and high treatment performance.

[0035] 2. This invention enhances biological phosphorus removal by removing sludge (rather than regulating the influent load), which is beneficial for dealing with real urban domestic sewage treatment with large fluctuations in water quality.

[0036] 3. This invention enhances the biological phosphorus removal performance of the F / M in-situ enhancement system by regulating its operation. It has advantages such as simple operation, minimal system impact, and low investment cost. It has a wide range of applications and provides a useful reference for further solving problems such as substandard effluent phosphorus and poor stability in biological phosphorus removal. Compared with chemical phosphorus removal, this invention is beneficial for the recovery of irreplaceable and non-renewable phosphorus resources and alleviates the long-term problem of large-scale phosphorus consumption. Attached Figure Description

[0037] Figure 1 This is a flowchart of the method for biological phosphorus removal in a continuous flow aerobic granular sludge-membrane bioreactor based on the regulation of F / M ratio.

[0038] Figure 2 The following are microscopic images of AGS cultured in the examples: (a) stereofluorescence microscopy; (b) micro-CT image; (c) field emission scanning electron microscopy image.

[0039] Figure 3 The graph shows the dynamic changes in phosphorus removal effect and other parameters based on the daily sludge discharge rate controlled by F / M in Examples 1-4.

[0040] Figure 4 The PCoA diagram shows the relationship between the system TP removal rate and other operating parameters for each embodiment. Detailed Implementation

[0041] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0042] The system used in the embodiments of this invention is a pilot-scale continuous flow aerobic granular sludge-membrane bioreactor for treating real urban domestic sewage. Internally, it consists of an aeration zone (also known as the "aerobic zone") and a mixing zone (also known as the "anaerobic zone") with a volume ratio of 1:3, and achieves self-circulation; its effective working volume is 18 m³. 3 The AGS cultured in this invention mostly exhibit an ellipsoidal shape, smooth surface, and brownish color. Figure 2 -a), the inorganic precipitate is uniformly distributed throughout the particles ( Figure 2 -b). By Figure 2 As can be seen from -c, the particles are composed of cocci, short rod-shaped and long filamentous bacteria, which enables the system to remove pollutants.

[0043] Example 1

[0044] Biological phosphorus removal based on the F / M enhanced continuous flow aerobic granular sludge-membrane bioreactor system under conditions where no external factors affect TP removal rate.

[0045] Depend on Figure 3 It is evident that during the stable period of the system, from days 122 to 135, the changes in factors affecting the TP removal rate are negligible, and the actual F / M value of the system stabilizes near the optimal F / M value (0.1 kg COD / kg MLVSS·d). At this time, the phosphorus release rate and phosphorus enrichment rate of the system reach equilibrium, and the TP removal rate stabilizes between 64.10% and 83.87%. However, when the system operates for 136 days, the actual F / M value decreases to 0.06 kg COD / kg MLVSS·d, i.e., ΔF / M is -0.04 kg COD / kg MLVSS·d < 0, indicating that the system is operating under low load. Based on this, according to... Figure 1 The method involved increasing the actual daily sludge discharge rate from 0 t / d to 1.13 t / d (close to the designed daily sludge discharge rate (0.71-1.07 t / d)), thereby maintaining the TP removal rate at approximately 73.32%-81.44%. Finally, after 140 days of system operation, the actual F / M value of the system increased to the optimal F / M value, i.e., 0.10 kg COD / kg MLVSS·d. Given that the above adjustments achieved a satisfactory TP removal rate, the actual daily sludge discharge rate was not precisely controlled within the designed daily sludge discharge rate range during actual operation.

[0046] Example 2

[0047] Biological phosphorus removal based on the F / M ratio enhancement of a continuous flow aerobic granular sludge-membrane bioreactor system under the influence of carbon source.

[0048] The main difference between this embodiment and embodiment 1 is that the COD (i.e., carbon source) of the system influent is the dominant factor affecting the TP removal rate.

[0049] Following the adjustments made in Example 1, the system reached its optimal F / M ratio on day 140. However, thereafter, the influent COD concentration decreased significantly, even reaching as low as 101.14 mg / L on day 147 of system operation. Figure 3 ); and by Figure 4 PCoA analysis shows that TP removal rate is positively correlated with COD influent concentration, and the similarity between the two is the greatest, indicating that COD influent concentration is a key influencing factor on TP removal rate. That is, when the system is operating in a stable period (days 141-152), the TP removal rate drops significantly due to the influence of influent COD concentration. The actual F / M value also decreases to 0.07 kgCOD / kgMLVSS·d on day 150 (the optimal F / M value is 0.1 kgCOD / kgMLVSS·d), meaning ΔF / M is -0.03 kgCOD / kgMLVSS·d < 0. At this point, the actual daily sludge discharge rate is 1.00 t / d, and the system is operating at a low load. The actual daily sludge discharge rate of the reactor should be increased. Based on this, the actual daily sludge discharge rate is increased to 1.07-1.28 t / d, close to the design daily sludge discharge rate (1.07 t / d), to maintain biomass within a certain range (MLSS = 8981-10639 mg / L). After this operation, on the 152nd day of system operation, the actual F / M value of the system recovered to 0.09 kgCOD / kgMLVSS·d, and the TP removal rate of the system was improved and maintained within the range of 61.40%-70.80%. Given that the above adjustments achieved a satisfactory TP removal rate, the actual daily sludge discharge rate was not precisely controlled to the designed daily sludge discharge rate in actual operation.

[0050] Example 3

[0051] Biological phosphorus removal in a continuous flow aerobic granular sludge-membrane bioreactor under the influence of dissolved oxygen (DO) and controlled flow rate (F / M) is achieved.

[0052] The main difference between this embodiment and embodiment 2 is that DO is the dominant factor affecting TP removal rate.

[0053] Following adjustments in Example 2, the actual F / M value of the system recovered to near the optimal F / M value by day 152. However, thereafter, the biomass in the system was low, making it susceptible to dissolved oxygen (DO). Figure 3 It is known that when the system operates for 157 days during the stable period, the actual F / M value drops to the lowest value of the entire operating period (0.05 kg COD / kg MLVSS·d), that is, ΔF / M is -0.05 kg COD / kg MLVSS·d < 0 (the optimal F / M value is 0.1 kg COD / kg MLVSS·d). At this time, the actual daily sludge discharge rate is 0 t / d, and the system is operating under low load. According to the method of this invention, the actual daily sludge discharge rate should be appropriately increased. Based on this, the actual daily sludge discharge rate is increased to 1.07 t / d, close to the design sludge discharge rate (0.88 t / d), in order to maintain MLSS within a certain range (MLSS = 7509 - 10338 mg / L). After this operation, on the 189th day of system operation, the actual F / M value of the system recovered to 0.10 kg COD / kg MLVSS·d, the system DO decreased significantly, the synthesis capacity of the phosphorus removal intermediate product PHB was improved, and the TP removal rate fluctuated and stabilized within the range of 83.93%-93.58%. Given that the above adjustments achieved a relatively satisfactory TP removal rate, the actual daily sludge discharge rate was not precisely controlled to the designed daily sludge discharge rate in actual operation.

[0054] Example 4

[0055] Biological phosphorus removal in a continuous flow aerobic granular sludge-membrane bioreactor based on the regulation of F / M ratio under the influence of biomass.

[0056] The main difference between this embodiment and embodiment 2 is that biomass (i.e., MLSS) is the dominant factor affecting TP removal rate.

[0057] Following adjustments in Example 3, the actual F / M value of the system recovered to its optimal value on day 189. However, thereafter, the biomass in the system was too low, resulting in low PAO abundance, making it difficult to fulfill its functions of excessive phosphorus under aerobic conditions and phosphorus release under anaerobic conditions, and making it more susceptible to other factors. Figure 3As can be seen, when the system reached the 199th day of stable operation, the MLSS value had dropped to the limit (5598 mg / L), and the actual F / M value was 0.13 kg COD / kgMLVSS·d, meaning ΔF / M was 0.03 kg COD / kgMLVSS·d > 0. At this point, the actual daily sludge discharge rate was 1.07 t / d, indicating the system was operating at high load. Based on this, the actual daily sludge discharge rate was reduced to 0.57 t / d, close to the design daily sludge discharge rate (0.66 t / d), to maintain the MLSS within a certain range (MLSS = 8023-9062 mg / L). Ultimately, the TP removal rate surged and stabilized within the range of 77.94%-78.62%. Correspondingly, on the 202nd day of system operation, the actual F / M value of the system also recovered to 0.10 kg COD / kgMLVSS·d. Given that the above-mentioned control measures have achieved a relatively satisfactory TP removal rate, the actual daily sludge discharge rate was not precisely controlled to the designed daily sludge discharge rate in actual operation.

[0058] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for enhancing biological phosphorus removal in a continuous-flow aerobic granular sludge-membrane bioreactor based on F / M regulation, using an aerobic granular sludge-membrane bioreactor operated in a continuous-flow mode as a running system, comprising the following steps: S1.Calculating an actual F / M value according to the ratio of organic matter content to total sludge amount entering the system; S2.Calculating an offset amount ΔF / M of the actual F / M value according to the difference between the actual F / M value and an optimal F / M value of the system; S3.Regulating the actual daily sludge discharge rate of the system to a designed daily sludge discharge rate according to ΔF / M, so as to regulate the actual F / M value to the optimal F / M value; The suitable range of F / M value is 0.05-0.15 kgCOD / kgMLVSS·d, and the optimal F / M value is selected therefrom.

2. The method of claim 1, wherein, The specific method for regulating the actual daily sludge discharge rate of the system to the designed daily sludge discharge rate according to ΔF / M in S3 is as follows: When ΔF / M > 0, the actual daily sludge discharge rate is reduced; When ΔF / M < 0, the actual daily sludge discharge rate is increased.

3. The method of claim 1, wherein, The calculation formula of the actual F / M value is as follows: Wherein, F / M is the food micro ratio; Q is the water inflow per day; ΔCOD Cr is the COD difference between the water inflow and the water outflow; MLVSS is the mixed liquid volatile suspended solid concentration of the active sludge in the reactor; V a is the total sludge amount of the integrated equipment.

4. The method of claim 1, wherein, The actual daily sludge discharge rate is calculated by the product of sludge discharge time, sludge discharge frequency and instantaneous sludge discharge rate.

5. The method of claim 1, wherein, The calculation formula of the designed daily sludge discharge rate is as follows: where v' is the design daily sludge rate; θ c is the SRT value for the reactor.

6. The method of claim 5, wherein, The calculation formula of the SRT value is as follows: Wherein, MLSS is the mixed liquor suspended solids concentration of activated sludge in the reactor; Y is the sludge yield.

7. The method of claim 1, wherein, If the TP removal rate influencing factor deviates from the suitable range, the actual daily sludge discharge rate also needs to be adjusted according to it.

8. The method of claim 7, wherein, The TP removal rate influencing factor includes at least one of carbon source, biomass or DO.

9. The method of claim 8, wherein, The key TP removal rate influencing factor is obtained by principal coordinate analysis PCoA or Pearson correlation coefficient method, and the actual daily sludge discharge rate is adjusted according to it.

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