Method for realizing bidirectional control of particle size of aerobic granular sludge by coupling hydraulic selection and floc addition

Abstract

The invention relates to a method for realizing two-way control of the particle size of aerobic granular sludge by coupling hydraulic selection and floc addition, which comprises the following steps: in the aerobic granular sludge culture process, forming hydraulic selection pressure by gradually shortening the precipitation time to promote sludge granulation, and monitoring the particle size change condition of a system in the granulation process; when the particle size of the particles is rapidly increased, taking floc sludge as additional sludge, regularly adding the floc sludge into the system according to a certain proportion, slowing down the granulation speed of the sludge, strengthening the diversity and mass transfer capacity of microorganisms in the system, and monitoring the particle size change condition during the floc adding period; analyzing a regulation and control mechanism of hydraulic selection and floc addition on microbial population sensing behaviors in the granulation process; the particle size of the aerobic granular sludge is subjected to two-way regulation and control by hydraulic selection and floc addition, so that the granulation process is maintained in a reasonable interval, the sacrifice of microbial diversity and particle mass transfer capacity in the granulation process is made up, and the system is more stable in microbial cooperation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sewage biological treatment, and particularly relates to a method for realizing two-way controllable particle size of aerobic granular sludge by coupling hydraulic selection and floc addition. BACKGROUND

[0002] The aerobic granular sludge technology is praised as one of the most promising technologies in the 21st century due to its excellent settling performance, high biomass, good pollutant removal effect and strong impact resistance. However, for a long time, the granular sludge has the problem of easy formation and easy disintegration. On the one hand, from the perspective of microorganisms, the violent hydraulic selection mechanism washes out many microbial populations including hydrolysis bacteria during the cultivation process of aerobic granular sludge, so that the system is extremely fragile, especially under the condition of single influent in the laboratory, the diversity of microorganisms is more likely to be challenged, becoming one of the unstable factors. On the other hand, under the hydraulic washing strategy, large particles are prone to be dominant, which directly leads to mass transfer of granular sludge as another unstable factor. The granular sludge inevitably has a process of floc F-particle formation G1-particle (optimal particle size) G2-particle non-normal increase (microbial surface growth, internal degradation) G3-particle hollowing G4-particle crushing G5, and at the G2 and G3 stages, filamentous bacteria will also grow due to mass transfer, increasing the instability of the granular sludge. In order to avoid entering the G3 stage, a slow growth or satiation-starvation strategy is proposed, which is actually to change the supply of substrate to allow more mass transfer to the inside of the particle, to some extent, to reduce the impact of mass transfer and avoid the occurrence of the G3 stage. This method is the mainstream technology for controlling the stability of granular sludge, but it is at the expense of reducing the growth rate of microorganisms and thus reducing the treatment rate or prolonging the reaction time, thereby reducing the efficiency of the system. Its effectiveness is related to the influent conditions such as C / N ratio and easily biodegradable components (converted into internal carbon source), which limits its application scenarios. The control of mass transfer constraints or the need to provide mass transfer capacity requires the development of new reactors to support, or the need for physical control of particle size itself, such as crushing or cyclone separation.

[0003] In summary, the biological diversity and mass transfer of aerobic granular sludge are related to the stage of the granulation process. During the granulation process, the diversity degenerates and the mass transfer resistance increases, so controlling the granulation process in a reasonable range becomes a key technology for the application of granular sludge.

[0004] The application file with publication number CN109095601A discloses a method for maintaining the running stability of an aerobic granular sludge reactor based on particle size control. A certain volume of sludge-water mixture is periodically taken from the granular sludge reactor for screening, and the collected optimal particle size range is backflowed to the reactor. Other particle sizes of aerobic granular sludge are stored for standby use. In this way, the mass proportion of aerobic granular sludge with the optimal particle size range is gradually increased, and the long-term stable operation of the aerobic granular sludge reactor is handled. The application file with publication number CN106746363A discloses a method and system for continuous-flow aerobic granular sludge cultivation and particle size control. The built-in bar cyclone separator is used to separate the heavy sludge from the effluent of the biochemical tank. The separated heavy sludge is backflowed to the anoxic tank, and the light sludge is sent to the sedimentation tank to realize the long-term operation of the aerobic granular sludge in the continuous flow. The manual intervention and mechanical means involved in these measures only break the large particles from the perspective of particle size, and do not change the types of microorganisms in the particles and the interaction between the microorganisms in the system, which is difficult to fundamentally solve the particle size control problem. SUMMARY

[0005] In order to control the granulation process in the optimal range, the purpose of the present application is to provide a method for coupling hydraulic selection and floc addition to realize the bidirectional controllability of aerobic granular sludge particle size. The hydraulic selection pressure and the floc addition are used as the acceleration and deceleration measures for regulating the granulation process of aerobic granular sludge. The sludge granulation process is accelerated under the action of the hydraulic selection pressure. When the particles enter the rapid formation period, a certain proportion of flocs is added to the system to slow down the granulation speed, and the controllability of the particle size and the granulation process is realized. The present application has the advantages of simple operation, low cost, and easy in-situ regulation.

[0006] In order to achieve the above purpose, the technical solution adopted by the present application is as follows: A method for coupling hydraulic selection and floc addition to realize the bidirectional controllability of aerobic granular sludge particle size, comprising the following steps: Step 1. During the cultivation period of aerobic granular sludge, the settling time of the reactor is shortened from 30 minutes to 5 minutes through multiple times, and the running status of the aerobic granular sludge system is monitored, including but not limited to particle size, granulation speed, water quality, and particle morphology. Step 2. When the aerobic granular sludge enters the rapid growth period, i.e. the particle size rapidly increases, floc sludge is added to the aerobic granular sludge system in step 1 at a mass ratio of 2.5%-5% to slow down the granulation speed of the aerobic granular sludge. Step 3, according to the granulation speed of the aerobic granular sludge system, the proportion of the flocculent sludge is adjusted, wherein the proportion of the flocculent sludge is determined according to the proportion of the flocculent sludge in the aerobic granular sludge system, and the proportion of the flocculent sludge is controlled in the range of 0.1%-20%, so that the granulation speed is completely controllable, and by controlling the granulation speed of the aerobic granular sludge, the optimal particle size range of 200-400 μm is maintained in the aerobic granular sludge system.

[0007] The monitoring method in the step 1 comprises: monitoring the particle size change by using an instrument laser particle size analyzer; monitoring the granulation speed and the granulation state by using a microscope and a culture dish photo; determining the ammonia nitrogen in water by using a sodium reagent photometry; determining the total nitrogen in water by using a potassium persulfate oxidation-ultraviolet spectrophotometry; determining the nitrite nitrogen in water by using an N-(1-naphthyl)-ethylenediamine photometry (GB7493-87); determining the total phosphorus by using a molybdenum-antimony anti-spectrophotometry; and determining the COD by using a rapid digestion spectrophotometry.

[0008] Compared with the prior art, the present application has the following beneficial effects: (1) The granulation speed and the particle size are completely controllable. The particle size of the aerobic granular sludge in the granulation process is controlled by coupling the hydraulic selection and the flocculent addition, the hydraulic selection pressure is shortened step by step to accelerate the granulation, and the flocculent is added to slow down the granulation, so that the granulation speed is accelerated or slowed down, and the granulation speed and the particle size of the aerobic granular sludge are controllable.

[0009] (2) The biological diversity of the aerobic granular sludge system is maintained. In fact, due to the hydraulic selection pressure in the granulation process of the aerobic granular sludge, the hydrolysis bacteria and other microbial populations are forced to wash out of the system, the species diversity is reduced, and the granular sludge system is unstable. The flocculent has better microbial diversity than the granular sludge, and the hydrolysis bacteria and other microbial populations can be retained in the system by adding the flocculent, so that the granulation speed is controllable, the microbial diversity of the system is maintained, and the system is stable.

[0010] (3) The mass transfer capacity of the aerobic granular sludge system is maintained. With the granulation process of the aerobic granular sludge, the particle size is continuously increased, and the large particle size also causes the formation of a mass transfer gradient from the outside to the inside of the granule, the mass transfer resistance is increased, the cavitation occurs in the inside of the granule, and the system is unstable. The flocculent has larger specific surface area and better mass transfer capacity than the granular sludge, so that the system has better particle size proportion and mass transfer efficiency, and the treatment effect of the system is improved.

[0011] (4) The stability of the aerobic granular sludge system is promoted. With the granulation process of the aerobic granular sludge and the increase of the particle size, the microbial diversity in the system is reduced, the mass transfer resistance is increased, and the air voids in the large particles are prone to appear, which leads to the disintegration of the particles, and the system is unstable. The measures for regulating the granulation process based on the coupling of hydraulic selection and floc addition adopted in the present application can not only accelerate the granulation process by gradually shortening the settling time to realize the hydraulic selection pressure, but also maintain the rich microbial diversity and the optimal mass transfer capacity in the system by adding flocs, so that the granulation is realized without sacrificing the microbial diversity and the mass transfer capacity, the granulation process and the treatment efficiency of the system are optimized, and the stable operation of the aerobic granular sludge system is maintained.

[0012] In summary, the present application is a granular sludge control technology and process based on the coupling of hydraulic selection and floc addition to realize the bidirectional controllable particle size, which has the advantages of realizing the bidirectional controllable granulation speed and particle size, maintaining the optimal microbial diversity and mass transfer capacity in the system, and promoting the stable operation of the system. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The reactor and flow chart of the present application.

[0014] Figure 2 The settling time and floc addition of Example 1 of the present application.

[0015] Figure 3 (a) is the particle size distribution diagram of the reactor R1 of Example 1 of the present application, and Figure 3 (b) is the particle size distribution diagram of the reactor R2 of Example 1 of the present application.

[0016] Figure 4 (a) is the microscope photograph of the aerobic granular sludge in the operation process of the SBR reactor R1 of Example 1 of the present application, and Figure 4 (b) is the microscope photograph of the aerobic granular sludge in the operation process of the SBR reactor R2 of Example 1 of the present application.

[0017] Figure 5 (a) is the COD removal effect diagram in the operation process of the SBR reactor R1 and the SBR reactor R2 of Example 1 of the present application, Figure 5 (b) is the ammonia nitrogen removal effect diagram in the operation process of the SBR reactor R1 and the SBR reactor R2 of Example 1 of the present application, Figure 5 (c) is the NO2 - -N diagram in the operation process of the SBR reactor R1 and the SBR reactor R2 of Example 1 of the present application, and Figure 5 (d) is the NO3 - -N diagram in the operation process of the SBR reactor R1 and the SBR reactor R2 of Example 1 of the present application.

[0018] Figure 6 (a) is the settling performance diagram of the aerobic granular sludge of the reactor R1 of Example 1 of the present application, and Figure 6 (b) is the settling performance diagram of the aerobic granular sludge of the reactor R2 of Example 1 of the present application.

[0019] Figure 7(a) is a graph of the EPS of the aerobic granular sludge of the reactor R1 of Example 1 of the present application, and Figure 7(b) is a graph of the EPS of the aerobic granular sludge of the reactor R2 of Example 1 of the present application. DETAILED DESCRIPTION

[0020] The present application will be described in detail below with reference to the accompanying drawings and specific examples, which are used to explain the present application but not to limit the present application.

[0021] A method for realizing two-way controllable aerobic granular sludge particle size by coupling hydraulic selection and flocculus addition, comprising the following steps: Step 1, during the cultivation period of the aerobic granular sludge, the settling time of the reactor is shortened from 30 minutes to 5 minutes through multiple times to realize hydraulic selection pressure granulation, accelerate the rapid formation of the aerobic granular sludge, and monitor the operation condition of the aerobic granular sludge system, which includes but is not limited to particle size, granulation speed, water quality, and particle morphology. The monitoring method includes: using an instrument laser particle size analyzer to monitor the particle size change; using a microscope and a petri dish photo to monitor the granulation speed and the granulation state; using the sodium reagent photometry method to determine the ammonia nitrogen in the water quality; using the potassium persulfate oxidation-ultraviolet spectrophotometry method to determine the total nitrogen in the water quality; using the N- (1-naphthyl) -ethylenediamine photometry method (GB7493-87) to determine the nitrite nitrogen in the water quality; using the molybdenum-antimony anti-spectrophotometry method to determine the total phosphorus; and using the rapid digestion spectrophotometry method to determine the COD.

[0022] Step 2, when the aerobic granular sludge enters the rapid growth period, i.e. the particle size rapidly increases, flocculus sludge is added into the aerobic granular sludge system in step 1 according to a mass ratio of 2.5%-5% to slow down the granulation speed of the aerobic granular sludge, so as to realize the regulation of the granulation speed of the aerobic granular sludge. Step 3, according to the granulation speed of the aerobic granular sludge system, the proportion of the added flocculus sludge is adjusted, wherein the flocculus proportion is determined according to the proportion of the existing flocculus sludge in the aerobic granular sludge system, and the mass proportion of the flocculus sludge is controlled within the range of 0.1%-20% to achieve complete controllability of the granulation speed. By controlling the granulation speed of the aerobic granular sludge, the optimal particle size range of 200-400 μm is maintained in the aerobic granular sludge system.

[0023] Example 1 A method for realizing two-way controllable aerobic granular sludge particle size by coupling hydraulic selection and flocculus addition, comprising the following steps: Step 1, during the aerobic granular sludge cultivation period, the settling time is shortened by PLC control in turn, and is adjusted to 30, 20, 15, 10, 8, 6, 5 minutes, the settling time is gradually shortened to realize the hydraulic selection pressure granulation, accelerate the rapid formation of aerobic granular sludge, and monitor the particle size, granulation speed, water quality, and granule morphology to represent the running state of the aerobic granular sludge system; the monitoring method includes: using the instrument laser particle size analyzer to monitor the particle size change; using the microscope and the culture dish photo to monitor the granulation speed and the granulation state; The sodium reagent photometric method is used to determine the ammonia nitrogen in water quality, the minimum detection concentration of the embodiment of the present application is 0.25 mg L-1 (photometric method), the upper limit of determination is 2 mg L-1 (all in terms of N), the minimum detection concentration is 0.02 mg L-1 by using visual colorimetric method. After the most appropriate pretreatment of the water sample, the embodiment of the present application can be suitable for the determination of ammonia nitrogen in surface water, groundwater, industrial wastewater and domestic sewage; The potassium persulfate oxidation-ultraviolet spectrophotometric method is used to determine the total nitrogen in water quality, the embodiment of the present application is mainly suitable for the determination of total nitrogen in lakes, reservoirs, rivers. The lower limit of detection is 0.05 mg L-1; the upper limit of determination is 4 mg L-1; The N-(1-naphthyl)-ethylenediamine photometric method (GB7493-87) is used to determine the nitrite nitrogen in water quality, the embodiment of the present application is suitable for the determination of nitrite in drinking water, surface water, groundwater, domestic sewage and industrial wastewater, the minimum detection concentration is 0.003 mg / L; the upper limit of determination is 0.20 mg / L nitrite nitrogen.

[0024] Nitrate nitrogen is measured by using the absorption of nitrate ions at a wavelength of 220 nm to quantitatively determine nitrate nitrogen. Dissolved organic matter also has absorption at 220 nm, while nitrate ions have no absorption at 275 nm. Therefore, another measurement is made at 275 nm to correct the nitrate nitrogen value.

[0025] The molybdenum antimony anti-spectrophotometric method is used to determine total phosphorus; the rapid digestion spectrophotometric method is used to determine COD, the minimum detection concentration of the method is 0.01 mg L -1 (absorbance A=0.01, the corresponding concentration); the upper limit of determination is 0.6 mg L -1 . It can be suitable for determining orthophosphate in surface water, domestic sewage, and industrial wastewater in the industries of chemical industry, phosphate fertilizer, metal surface phosphating treatment, pesticide, steel, coking, etc.

[0026] Step 2, the original sludge of the sewage plant is pretreated and used as flocculent sludge for standby, which is added into the system as a measure to slow down the granulation speed in the later stage; Step 3, when the aerobic granular sludge enters the rapid growth period, that is, the particle size rapidly increases, the floc sludge of step 2 is added into the aerobic granular sludge system in step 1 at a proportion of 2.5%, so as to slow down the granulation speed of the aerobic granular sludge, so that the granulation speed of the aerobic granular sludge is controlled; Step 4, according to the granulation speed of the aerobic granular sludge system, the proportion of the floc sludge is adjusted, wherein the proportion of the floc is determined according to the proportion of the existing floc in the aerobic granular sludge system, and the proportion of the floc sludge is controlled in the range of 0.1%-20%, so that the granulation speed is completely controllable, and by controlling the granulation speed of the aerobic granular sludge, the optimal particle size range of 200-400 μm is maintained in the aerobic granular sludge system.

[0027] As shown in Figure 1 , the SBR reactor R1 and the SBR reactor R2 are used for synchronous cultivation of aerobic granular sludge, wherein the SBR reactor R1 is used as a blank group, the hydraulic selection pressure is realized by adjusting the settling time, the SBR reactor R2 is used as an experimental group, the particle size of the aerobic granular sludge is controlled by coupling the hydraulic selection and the floc addition, the SBR reactor R1 and the SBR reactor R2 use the same operating conditions, the influent is flowed into the reactor through the influent port 2 by the influent pump 1, the effluent is flowed out of the reactor through the sampling port 4 by the effluent pump 3, the air pump 5 is connected with the aeration head 6 for aeration, the mechanical stirrer 7 is used for stirring, the water bath layer 8 is used for water bath, and the phases of the reactor are controlled by the PLC 9.

[0028] As shown in Figure 2 , the method for realizing the two-way controllable particle size of the aerobic granular sludge by coupling the hydraulic selection and the floc addition is provided, the hydraulic selection pressure is realized by shortening the settling time to accelerate the granulation process, but when the particles rapidly grow, the floc is added to slow down the granulation speed, so that the granulation speed and the particle size are controllable, so as to ensure the optimal microbial diversity and mass transfer capacity in the system, and the system is stable, and has a good application prospect. The settling time of the SBR reactor R1 and the SBR reactor R2 is adjusted to 30, 20, 15, 10, 8, 6 and 5 minutes respectively on the 1st, 10th, 16th, 18th, 21st, 28th and 34th day of operation, so as to realize the hydraulic selection pressure for accelerating the granulation; the floc sludge is added to the SBR reactor R2 at a proportion of 2.5% from the 44th to 98th day, the addition is stopped on the 99th day, and the floc is added again from the 122nd to 129th day.

[0029] As shown in Fig. 3(a) is the SBR reactor R1 during the cultivation process of particle size change graph, Fig. 3(b) shows the SBR reactor R2 during the cultivation process of particle size change graph, indicating that in the granular sludge cultivation process SBR reactor R1 experienced flocculation period (F), granular formation period (G1), granular stable period (G2), granular disintegration period (G5), and SBR reactor R2 experienced flocculation period (F), granular formation period (G1) in turn. In flocculation period (Day1-44), SBR reactor R1 and SBR reactor R2 are all with the shortening of settling time, the increase of hydraulic selection pressure, the continuous increase of granular particle size, and all in about 140 μm; then in granular formation period (G1), with the increase of granulation degree, the particle size of R1 increases rapidly, and the average particle size reaches 378 μm on the 83rd day, at this time, complete granulation has been realized; in the period of 83-118 days, the granules enter the stable period (G2) and the particle size is maintained above 350 μm, then the particle size decreases continuously, and the granules enter the granular disintegration period (G5). Fig. 3(b) shows that SBR reactor R2 is added with flocculation on the 44th day, enters the granular formation period (G1), and the growth rate of particle size and the granulation speed are obviously slower than R1; on the 98th day, the addition of flocculation is stopped, then the growth rate of particle size accelerates, and the particle size reaches 305 μm on the 118th day, but the granules are still in the granular formation period (G1); on the 121st day, 2.5% flocculation is added to the system again, and it is found that the growth rate of particle size slows down. This shows that under the hydraulic selection pressure, the granulation rate increases, the addition of flocculation leads to the slow growth rate of particle size and the slow granulation speed, after stopping the addition, the growth rate of particle size becomes fast, and the continuous addition leads to the slow growth of particle size, and the addition of flocculation can control the granulation speed and the particle size in a certain range.

[0030] As shown in Fig. 4(a) is the microscope photograph of SBR reactor R1 during the operation process, and Fig. 4(b) shows the microscope photograph of SBR reactor R2 during the operation process, which shows that the change trends of SBR reactor R1 and SBR reactor R2 are consistent, and under the condition of hydraulic selection pressure, the sludge continuously aggregates and the particle size increases during D1-44; then during D44-83, the particle size of SBR reactor R1 continuously increases, small flocculation decreases, and the granules are relatively dense, then the particle size enters the disintegration period, and the large particle size disintegrates in the system, and small flocculation increases. Compared with SBR reactor R1, the addition of flocculation to SBR reactor R2 in D44 leads to the existence of small flocculation in the system all the time, and the granules are relatively dense; thus it can be seen that the present application can supplement the flocculation in the system, and realize the bidirectional regulation of particle size.

[0031] As shown in Fig. 5 (a), it is a COD removal effect diagram of the SBR reactor R1 and the SBR reactor R2 in the operation process of the embodiment of the application, as shown in Fig. 5 (b), it is an ammonia nitrogen removal effect diagram of the SBR reactor R1 and the SBR reactor R2 in the operation process of the embodiment of the application, indicating that the SBR reactor R1 and the SBR reactor R2 both have good pollutant removal efficiency, and the COD and ammonia nitrogen degradation effect of the SBR reactor R2 is not affected by adding the flocs, and is maintained at about 95%; in addition, as shown in Fig. 5 (c), it is a NO2 - -N diagram of the SBR reactor R1 and the SBR reactor R2 in the operation process of the embodiment of the application, Fig. 5 (a) indicates that, compared with the SBR reactor R1, the SBR reactor R2 has higher nitrate accumulation, because the mass transfer efficiency of the system is better due to adding the flocs in the granulation process; and after the SBR reactor R1 system is disintegrated, the small flocs in the system increase, the mass transfer effect is better, and the nitrate accumulation increases; thus, it can be seen that the system still has good pollutant removal effect after adding the flocs in the application. Meanwhile, as shown in Fig. 5 (d), it is a NO3 - -N diagram of the SBR reactor R1 and the SBR reactor R2 in the operation process of the embodiment of the application, Fig. 5 (d) indicates that the SBR reactor R1 has nitrite accumulation phenomenon at D70-90, which is caused by mass transfer in the granulation process. As shown in Fig. 6 (a), it is a settling property diagram of the SBR reactor R1 in the operation process, Fig. 6 (b) is a settling property diagram of the SBR reactor R2 in the operation process, the SBR reactor R1 has enhanced settling property with sludge granulation, SVI5 and SVI 30 of the SBR reactor R1 are continuously reduced, and SVI5 / SVI 30 of the SBR reactor R1 gradually decreases and is maintained at about 1, when the SBR reactor R1 begins to disintegrate, the settling property is poor, and SVI5 / SVI 30 of the SBR reactor R1 increases; the SBR reactor R2 has enhanced settling property with granulation during D1-44, SVI5 / SVI 30 of the SBR reactor R2 decreases, and SVI5 / SVI 30 of the SBR reactor R2 is higher than that of the SBR reactor R1, in the late period of adding the flocs, with the decrease of the particle size, the small flocs increase, the settling property is poor, and SVI5 / SVI 30 of the SBR reactor R2 increases, but after the D98 stops adding the flocs, the settling property is improved, SVI5 / SVI 30 of the SBR reactor R2 decreases, and after the D121 resumes adding the flocs, SVI5 / SVI 30 of the SBR reactor R2 increases compared with before; thus, it can be seen that the floc adding in the application can cause the increase of the floc proportion in the system, and regulate the settling property of the granules.

[0032] Figure 7(a) shows the EPS during the operation of SBR reactor R1, and Figure 7(b) shows the EPS during the operation of SBR reactor R2. It can be seen that as granulation proceeds, the EPS content and PN / PS of SBR reactors R1 and R2 increase. When D44 is added to SBR reactor R2, it stimulates the secretion of EPS, and the EPS content and PN / PS increase. After the addition of flocs is stopped, the EPS content decreases, and the PN / PS first decreases and then increases. It can be seen that the floc addition measure of the present invention can change the EPS secretion of the system and thus regulate the degree of granulation of the system, achieving bidirectional control of particle size.

[0033] Example 2 Step 1: In SBR reactor R3, the settling time is sequentially shortened from 1 to 15 days via PLC control, adjusted to 30, 20, 15, 10, 8, 6, and 5 minutes to achieve hydraulic selective pressure granulation. This accelerates the rapid formation of aerobic granular sludge, and the operation status of the aerobic granular sludge system is characterized by monitoring particle size, granulation rate, water quality, and particle morphology. Monitoring methods include: using an instrumental laser particle size analyzer to monitor particle size changes; using a microscope and petri dish photographs to monitor particle size distribution and particle size distribution; using Sodium's reagent spectrophotometry to determine ammonia nitrogen in water; using potassium persulfate oxidation-ultraviolet spectrophotometry to determine total nitrogen in water; using N-(1-naphthyl)-ethylenediamine spectrophotometry (GB7493-87) to determine nitrite nitrogen in water; using molybdenum-antimony anti-magnesium spectrophotometry to determine total phosphorus; and using rapid digestion spectrophotometry to determine COD.

[0034] Step 2: Cultivate normal granular sludge for 15-60 days, and take raw sludge from the sewage treatment plant for pretreatment as flocculent sludge for later addition into the system as a measure to slow down the granulation rate. Step 3: For 60-112 days, implement micro-flocculation to replace granules. Every two days, remove 5% by mass of granular sludge from the end of aeration. In the influent stage of the next operating cycle, add an equal mass of flocculent sludge from the top of the reactor to slow down the granulation rate of aerobic granular sludge, thereby controlling the granulation rate of aerobic granular sludge. Step 4: Adjust the proportion of flocculent sludge added according to the granulation rate of the aerobic granular sludge system. The proportion of flocculent sludge is determined based on the existing proportion of flocculent sludge in the aerobic granular sludge system. Control the proportion of flocculent sludge within the range of 0.1-20% to achieve complete control over the granulation rate. By controlling the granulation rate of the aerobic granular sludge, the optimal particle size range of 200-400μm is maintained in the aerobic granular sludge system.

[0035] SBR reactor R3 uses bottom influent with a volume exchange ratio of 25%. The operating cycle of SBR reactor R3 is 2 hours, consisting of 12 minutes of influent, 30 minutes of stirring, 67 minutes of aeration, 3 minutes of sedimentation, and 8 minutes of effluent discharge. The temperature is maintained at 20±2°C using a water bath, and the aeration rate is controlled at 1.5 L / min using a rotor flow meter. Excess sludge is discharged 10 minutes before the end of the aeration phase each day, controlling the reactor's SRT to 20 days. The mechanism of particle size distribution and system stability is explored through floc replacement, leading to a new strategy for regulating AGS particle size distribution and stability based on floc replacement.

[0036] From day 1 to 60, the proportion of particles larger than 200 μm in SBR reactor R3 was 82.54%, with an average particle size of 292.6 μm. From day 60 to 112, SBR reactor R3 adopted a floc replacement particle strategy, and at day 111, the proportion of particles larger than 200 μm was 72.48%, with an average particle size of 430.1 μm. The proportion of flocs in SBR reactor R3 remained at 5.45% at day 60, and increased to 12.09% after floc replacement at day 78. The proportion of large particles in SBR reactor R3 was 43.21% at day 112 and 45.89% at day 145.

[0037] From day 1 to day 60, the proportion of flocs decreased, while the proportion of large particles increased slowly. On day 60, the proportion of flocs in R3 decreased from the initial 88.85% to 5.45%. From day 60 to day 112, the proportion of flocs in the SBR reactor R3 increased through the floc replacement of particles strategy. The proportion of flocs increased to 13.63% on day 71, and remained above 10% from day 71 to day 111, with the system maintaining a stable state.

[0038] The sludge settling performance of the reactor exhibited different trends over operating time, reflecting the sludge granulation trend and being influenced by control strategies. From 0 to 60 days, SBR reactor R3 showed a high SVI (Sludge Volume Index). 30 With SVI5 value (SVI 30 >130 mL / g, SVI5>150 mL / g), with loose particle structure and poor settling properties. From 60 to 111 days, the SVI value in SBR reactor R3 remained relatively stable after the micro-floc replacement of particles. From 112 to 145 days, the SBR reactor R3 system maintained stable settling properties, indicating that both micro-floc replacement of particles and micro-floc replacement of large particles ensured the long-term stability of AGS settling properties.

[0039] Example 3 Step 1: In SBR reactor R4, the settling time is sequentially shortened from 1 to 15 days via PLC control, adjusted to 30, 20, 15, 10, 8, 6, and 5 minutes to achieve hydraulic selective pressure granulation. This accelerates the rapid formation of aerobic granular sludge, and the operation of the aerobic granular sludge system is characterized by monitoring particle size, granulation rate, water quality, and particle morphology. Monitoring methods include: using an instrumental laser particle size analyzer to monitor particle size changes; using a microscope and petri dish photographs to monitor particle size distribution and particle size distribution; using Sodium's reagent spectrophotometry to determine ammonia nitrogen in water; using potassium persulfate oxidation-ultraviolet spectrophotometry to determine total nitrogen in water; using N-(1-naphthyl)-ethylenediamine spectrophotometry (GB7493-87) to determine nitrite nitrogen in water; using molybdenum-antimony anti-magnesium spectrophotometry to determine total phosphorus; and using rapid digestion spectrophotometry to determine COD.

[0040] Step 2: Cultivate normal granular sludge for 15-60 days, and take raw sludge from the sewage treatment plant for pretreatment as flocculent sludge for later addition into the system as a measure to slow down the granulation rate. Step 3: For 60-112 days, implement micro-floc replacement of granules. Take out 2.5% by mass of granular sludge at the end of aeration every day. Add an equal mass of flocculent sludge from the top of the reactor during the influent stage of the next operating cycle to slow down the granulation rate of aerobic granular sludge, thereby controlling the granulation rate of aerobic granular sludge. Step 4: Adjust the proportion of flocculent sludge added according to the granulation rate of the aerobic granular sludge system. The proportion of flocculent sludge is determined based on the existing proportion of flocculent sludge in the aerobic granular sludge system. Control the proportion of flocculent sludge within the range of 0.1-20% to achieve complete control over the granulation rate. By controlling the granulation rate of the aerobic granular sludge, the optimal particle size range of 200-400μm is maintained in the aerobic granular sludge system.

[0041] SBR reactor R4 uses bottom inlet and has a volume exchange ratio of 25%. The reactor's operating cycle is 2 hours, consisting of 12 minutes of inlet water, 30 minutes of stirring, 67 minutes of aeration, 3 minutes of sedimentation, and 8 minutes of effluent discharge. The temperature is maintained at 20±2°C using a water bath, and the aeration rate is controlled at 1.5 L / min using a rotor flow meter. Excess sludge is discharged 10 minutes before the end of the aeration phase each day, controlling the reactor's SRT (sludge retention time) to be 20 days. From 1 to 60 days, the proportion of particles larger than 200 μm in reactor R4 is 72.84%, with an average particle size of 263.9 μm. From 60 to 112 days, the SBR reactor R4 adopted a floc replacement particle strategy, and the particle size of the SBR reactor R4 steadily increased. At 111 days, the proportion of particles larger than 200 μm was 72.01%, and the average particle size was 418.5 μm. At 60 days, the proportion of floc in the SBR reactor R4 remained at 5.85%. After floc replacement, the proportion of floc increased to 12.99% at 78 days. At 112 days, the proportion of large particles in the SBR reactor R4 was 41.67%.

[0042] In SBR reactor R4, the proportion of flocs decreased from day 1 to day 60, while the proportion of large particles increased slowly. On day 60, the proportion of flocs in SBR reactor R4 decreased from the initial 88.85% to 5.28%, while the proportion of large particles increased from 0% to 3.37%. From day 60 to day 112, SBR reactor R4 increased the proportion of flocs in the reactor through a floc replacement particle strategy, reaching 12.64% on day 71, and maintaining above 10% from day 71 to day 111. Therefore, the proportion of large particles and the average particle size were high; on day 111, the proportion of large particles in SBR reactor R4 was 41.67%, and the average particle size was 418.5 μm, indicating that the system remained stable.

[0043] During the 0–60 day period, conventional granular sludge cultivation was performed in SBR reactor R4, and the PN and PS ratios remained relatively stable. From 60–111 days, particle size distribution in SBR reactor R4 was adjusted through floc replacement, resulting in an increase in PN content and a stabilization of PS content. Particularly, SBR reactor R4 showed a rapid increase in PN at day 108. From 112–150 days, further floc replacement of large particles in R4 significantly increased the PN / PS ratio, reaching a peak at day 108. This indicates a substantial increase in the protein content of the EPS structure, which is beneficial for enhanced particle adhesion. Overall, floc replacement of particles significantly optimized the EPS composition and effectively enhanced system stability.

Claims

1. A method for achieving bidirectional controllable particle size of aerobic granular sludge by coupling hydraulic selection and floc addition, characterized in that, Includes the following steps: Step 1: During the aerobic granular sludge cultivation period, the reactor settling time is shortened from 30 minutes to 5 minutes multiple times. The operating status of the aerobic granular sludge system is monitored. The operating status of the aerobic granular sludge system includes, but is not limited to, particle size, granulation rate, water quality, and particle morphology. Step 2: When the aerobic granular sludge enters the rapid growth period, that is, when the particle size increases rapidly, add flocculent sludge to the aerobic granular sludge system in Step 1 at a mass ratio of 2.5%-5% to slow down the granulation rate of the aerobic granular sludge. Step 3: Adjust the proportion of flocculent sludge added according to the granulation rate of the aerobic granular sludge system. The proportion of flocculent sludge is determined based on the existing proportion of flocculent sludge in the aerobic granular sludge system. The mass proportion of flocculent sludge is controlled within the range of 0.1%-20% to achieve complete control over the granulation rate. By controlling the granulation rate of the aerobic granular sludge, the optimal particle size range of 200-400μm is maintained in the aerobic granular sludge system.

2. The method for bidirectional control of aerobic granular sludge particle size by coupling hydraulic selection and floc addition as described in claim 1, characterized in that, The monitoring methods in step 1 include: monitoring particle size changes using an instrumental laser particle size analyzer; monitoring particle formation rate and particle formation state using a microscope and petri dish photographs; determining ammonia nitrogen in water using the Nathaniel reagent spectrophotometric method; determining total nitrogen in water using the potassium persulfate oxidation-ultraviolet spectrophotometric method; determining nitrite nitrogen in water using the N-(1-naphthyl)-ethylenediamine spectrophotometric method (GB7493-87); determining total phosphorus using the molybdenum-antimony anti-magnesium spectrophotometric method; and determining COD using the rapid digestion spectrophotometric method.

3. The method for bidirectional control of aerobic granular sludge particle size by coupling hydraulic selection and floc addition as described in claim 1, characterized in that, Includes the following steps: Step 1: During the aerobic granular sludge cultivation period, the settling time is shortened sequentially by PLC control, adjusted to 30, 20, 15, 10, 8, 6, and 5 minutes. The settling time is gradually shortened to achieve hydraulic selective pressure granulation, which accelerates the rapid formation of aerobic granular sludge. The operation status of the aerobic granular sludge system is characterized by monitoring particle size, granulation speed, water quality, and particle morphology. Step 2: Take the raw sludge from the sewage treatment plant, pre-treat it, and use it as flocculent sludge for later addition into the system as a measure to slow down the granulation rate. Step 3: When the aerobic granular sludge enters the rapid growth period, that is, when the particle size increases rapidly, the flocculent sludge from Step 2 is added to the aerobic granular sludge system in Step 1 at a ratio of 2.5% to slow down the granulation rate of the aerobic granular sludge, thereby achieving the regulation of the granulation rate of the aerobic granular sludge. Step 4: Adjust the proportion of flocculent sludge added according to the granulation rate of the aerobic granular sludge system. The proportion of flocculent sludge is determined based on the existing proportion of flocculent sludge in the aerobic granular sludge system. Control the mass proportion of flocculent sludge within the range of 0.1%-20% to achieve complete control over the granulation rate. By controlling the granulation rate of the aerobic granular sludge, the optimal particle size range of 200-400μm is maintained in the aerobic granular sludge system.

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