A system and method for treating a filamentous bacteria-induced bulking of sludge

Abstract

The present application belongs to the technical field of sewage treatment, and particularly relates to a treatment system and method for sludge bulking caused by filamentous bacteria. The method comprises: performing starvation operation on a sewage biological treatment system in which filamentous bacteria bulking occurs, wherein the starvation operation is to stop or reduce the supply of organic carbon, nitrogen and phosphorus to the sewage biological treatment system; and after the starvation operation, performing supplemental nitrate water feeding on the sewage biological treatment system, wherein the supplemental nitrate water feeding comprises: resuming the supply of water containing an organic carbon source to the sewage biological treatment system, while increasing the concentration of nitrate nitrogen in the water. Through two-stage regulation of “starvation operation + nitrate supplement”, the present application precisely utilizes the metabolic disadvantage of filamentous bacteria under low substrate conditions and the sensitivity of filamentous bacteria to a nitrate environment, so as to selectively inhibit the growth of filamentous bacteria and quickly restore the settling performance of the reactor in a short period of time.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a treatment system and method for sludge bulking caused by filamentous bacteria. Background Technology

[0002] Aerobic granular sludge (AGS) technology is a novel environmental biological wastewater treatment process that has been widely adopted globally in recent years as an important pathway to achieve synergistic effects in pollution and carbon reduction. This technology, with its high density, excellent settling properties, and high biomass concentration of granular sludge, significantly reduces the footprint of biological treatment units and shortens hydraulic retention time. Currently, there are over 100 mainstream AGS engineering applications worldwide, most employing a fully mixed reactor configuration.

[0003] Against the backdrop of the current low-carbon transformation of wastewater treatment plants, municipal wastewater generally exhibits low matrix characteristics, and low dissolved oxygen (DO) operation has become the mainstream control strategy. However, this operating condition also exacerbates the risk of sludge bulking. Among the many factors that induce sludge bulking, bulking caused by filamentous bacteria is the most common—at least 30 species of filamentous bacteria are currently known to cause this problem. Low dissolved oxygen (DO) and low food / microorganism ratio (F / M) are two key contributing factors.

[0004] In a typical completely mixed AGS system, anaerobic, anoxic, and aerobic stages are sequentially formed through periodic aeration regulation:

[0005] First, in the anaerobic stage, slow-growing anaerobic microorganisms such as polyphosphate-accumulating bacteria (PAOs) and polysaccharide-accumulating bacteria (GAOs) are enriched, utilizing the organic matter in the influent.

[0006] Second, during the anoxic stage, denitrifying bacteria (DB) are enriched to reduce the nitrates generated in the aerobic stage into nitrogen gas.

[0007] Third, the aerobic stage mainly relies on ammonia-oxidizing bacteria (AOB) to complete the oxidation and conversion of ammonia nitrogen.

[0008] It is noteworthy that most of the filamentous bacteria that induce expansion are facultative microorganisms, exhibiting a significant competitive advantage in low-DO environments. According to the Monod equation, filamentous bacteria often exhibit higher specific growth rates under low substrate concentration (i.e., low F / M) conditions, thus making them more prone to over-proliferation under these conditions. These filamentous bacteria can compete for niches with target functional microbial communities (such as PAOs, GAOs, AOBs, etc.) in different DO zones of a completely mixed reactor, gradually gaining dominance.

[0009] Mild filamentous bulking typically does not cause irreversible damage to the settling performance of an AGS system; however, under prolonged low F / M and low DO operating conditions, filamentous bacteria may proliferate continuously, leading to malignant bulking. In this case, the surface of the aerobic granular sludge (FAGS) is covered with numerous filamentous / finger-like structures, significantly reducing particle density and drastically deteriorating settling performance. Furthermore, the outer barrier formed by filamentous bacteria hinders the transfer of substrate and oxygen into the granules, further inhibiting the metabolic activity of the core functional microbial community. This results in a continuous decline in the system's removal efficiency for pollutants such as nitrogen and phosphorus, ultimately threatening the stable operation of the entire AGS system.

[0010] As an important development of the activated sludge process, AGS technology also faces the challenge of filamentous bacterial bulking. Therefore, it is urgent to develop a sustainable, low-cost, and highly targeted filamentous bacterial inhibition strategy to ensure that the completely mixed AGS reactor can maintain good settling performance and stably perform efficient nitrogen and phosphorus removal functions under low-carbon (low F / M, low DO) operation mode, thereby achieving long-term reliable operation of the system. Summary of the Invention

[0011] (a) Technical problems to be solved

[0012] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a treatment system and method for sludge bulking caused by filamentous bacteria, which solves the technical problem of filamentous bacteria bulking faced by a completely mixed AGS reactor in the operation mode of low F / M, low DO and low carbon.

[0013] This invention provides a treatment system and method for sludge bulking caused by filamentous bacteria, which solves the technical problems of unpredictable and unstable sludge bulking caused by filamentous bacteria.

[0014] This invention provides a treatment system and method for sludge bulking caused by filamentous bacteria, which solves the technical problems of long time consumption and complex regulation in traditional non-specific control methods.

[0015] (II) Technical Solution

[0016] In a first aspect, the present invention provides a method for treating sludge bulking caused by filamentous bacteria. The method includes: performing starvation operation on a wastewater biological treatment system experiencing filamentous bulking, wherein starvation operation involves stopping or reducing the supply of organic carbon, nitrogen, and phosphorus to the wastewater biological treatment system; after starvation operation, supplementing the wastewater biological treatment system with nitrate influent, wherein supplementing the nitrate influent includes: restoring the supply of influent containing organic carbon sources to the wastewater biological treatment system, wherein the concentration of organic carbon sources in the influent is restored to more than 75% of the normal operating concentration, and simultaneously increasing the nitrate nitrogen concentration in the influent, such that the nitrate nitrogen concentration reaches 4.0-8.0 mg / L at the end of the synchronous influent / effluent stage (excluding biological metabolism).

[0017] "Stop" means to completely stop supplying organic carbon sources, while "reduce" means to reduce the supply of carbon sources by more than 90%.

[0018] Optionally, the starvation operation includes: stopping the influent to the wastewater biological treatment system; or, replacing the influent supplied to the wastewater biological treatment system with water that does not contain organic carbon sources. The aeration intensity remains constant, and the DO curve plateau gradually changes from 1.0 to "Type 2". During the normal operation phase of the system, the controlled-cycle aeration DO plateau is maintained at 0.5-2.5 mg / L. After expansion occurs, the aeration intensity remains constant, the DO type changes, and the plateau DO increases to above 6.0 mg / L. After the DO curve changes from "Type 1" to "Type 2", the aeration intensity during the starvation operation phase can be appropriately increased.

[0019] Optionally, the increase in nitrate nitrogen concentration in the influent is achieved by adding nitrate chemicals to the influent; or by refluxing nitrate-rich nitrate solution back into the influent.

[0020] Optionally, increasing the nitrate nitrogen concentration in the influent results in a nitrate nitrogen mixed concentration C in the influent before it enters the wastewater biological treatment system. 进水 =(C 目标 -C 出水 ×(1-VER)) / VER

[0021] in:

[0022] C 目标 - The target concentration of nitrate nitrogen in the reactor is determined according to the expansion level. For mild expansion, 4.0-5.0 mg / L can be selected; for moderate expansion, 5.0-6.0 mg / L can be selected; and for severe expansion, 6.0-8.0 mg / L can be selected.

[0023] C 出水 -At the end of the previous operating cycle, the nitrate nitrogen concentration in the effluent of the biological wastewater treatment system, mg / L;

[0024] The influent volume exchange ratio of the wastewater biological treatment system described above during a single operating cycle ranges from 0.2 to 0.6.

[0025] Before the “nitrate supplementation influent” stage of this invention begins, this value represents the background concentration of nitrate nitrogen in the residual mixture in the reactor, and is used to calculate the amount of nitrate nitrogen to be supplemented by the new influent to ensure that the target concentration is reached after mixing.

[0026] Optionally, prior to the starvation operation, a step of determining the bulking stage is included, the determination being based on at least one of the following parameters: the dissolved oxygen curve morphology of the wastewater biological treatment system, and the sludge volume index (SVI). 30 SVI5 and SVI 30 The ratio of and the abundance of filamentous bacteria observed under a microscope.

[0027] Sludge Volume Index (SVI) 30 When 120mL / g≤SVI 30 When the concentration is ≤150 mL / g, it is considered mild swelling; when it is 150 mL / g... <SVI 30 When the concentration of SVI is ≤200 mL / g, it is judged as moderate; when the concentration of SVI is ≤200 mL / g, it is judged as moderate. 30 When the concentration is >200 mL / g, it is considered severe swelling;

[0028] SVI5 and SVI 30 The ratio: when SVI5 / SVI 30 When the value is greater than 1.8, it is considered an abnormal settling performance, indicating excessive growth of filamentous fungi;

[0029] Dissolved oxygen curve morphology: During the stable aeration phase, if the DO value is consistently higher than the normal plateau value by more than 0.5 mg / L, and / or the DO surge peak disappears or the amplitude decreases by more than 50% at the end of aeration, it is determined that filamentous bulking has occurred or progressed.

[0030] Microscopic examination of filamentous bacteria abundance: If the area covered by filamentous bacteria is ≥30% under 100x magnification, or if the number of filamentous bacteria per field is ≥15, it is considered as significant filamentous bacteria proliferation.

[0031] Optionally, when increasing the nitrate nitrogen concentration by refluxing the nitrification liquor, the refluxing flow rate of the nitrification liquor is determined based on the following formula:

[0032] [η×C 回流 +(1-η)×C 原水 ]×VER+(1-VER)×C 出水 =C 目标

[0033] in:

[0034] C 回流- Nitrate nitrogen concentration in the reflux nitrification liquor, mg / L;

[0035] C 原水 - Nitrate nitrogen concentration in the influent entering the system during the pretreatment stage, mg / L;

[0036] C 出水 -Restore the nitrate nitrogen concentration in the effluent at the end of the system cycle after the influent is restored, in mg / L;

[0037] η - Nitrification liquor recirculation ratio, which is the ratio of the recirculated nitrification liquor flow rate to the influent raw water flow rate, i.e., R=Q 回流 / Q 进水 The value ranges from 0.25 to 1.0;

[0038] The influent volume exchange ratio of the wastewater biological treatment system described above during a single operating cycle ranges from 0.2 to 0.6.

[0039] C 目标 -Target concentration of nitrate nitrogen in the reactor, determined according to the expansion level, in mg / L.

[0040] Optionally, pending SVI 30 Once the blood pressure drops below 60% of the inflation level, the starvation program ceases; the duration of the starvation program is 3-10 days, depending on the severity of the inflation.

[0041] Mild bloating: starvation for 3-5 days;

[0042] Moderate bloat: starvation for 5-7 days;

[0043] Severe bloat: starvation for 7-10 days.

[0044] Optionally, during the nitrate supplementation influent stage, the ammonia nitrogen removal rate of the wastewater biological treatment system is monitored. When the ammonia nitrogen removal rate recovers and stabilizes above 50%, it is used as one of the criteria for stopping the increase of nitrate nitrogen concentration. For mild to moderate filamentous bulking (SVI)... 30 For nitrate supplementation in the influent (<200mL / g), the typical operating cycle is 3-7 days; if the swelling is severe (e.g., SVI), the nitrate supplementation influent is more effective. 30 (≥200mL / g but not reaching malignant bulking state), this stage can last for 5-10 days.

[0045] In a second aspect, the present invention provides a treatment system for sludge bulking caused by filamentous bacteria, the system comprising: a wastewater biological treatment reactor, an influent unit, an aeration unit, a nitrate dosing unit, and a control unit;

[0046] The wastewater biological treatment reactor provides a site for the biodegradation of wastewater pollutants;

[0047] The water inlet unit and the aeration unit are respectively connected to the wastewater biological treatment reactor;

[0048] The nitrate dosing unit is connected to the water inlet unit; the control unit is signal-connected to the water inlet unit, the aeration unit, and the nitrate dosing unit.

[0049] The control unit is configured to perform the method to enable the wastewater biological treatment reactor, influent unit, nitrate dosing unit and aeration unit to cooperate and coordinate so that the treatment system can switch between a starvation operation mode and a nitrate-supplemented influent operation mode.

[0050] Optionally, the water inlet unit includes: a raw water inlet line and a dilution water inlet line;

[0051] The dilution water inlet line is used to supply water containing no or little organic carbon source to the wastewater biological treatment reactor;

[0052] The control unit is configured to control the dilution water inlet line to supply water to the wastewater biological treatment reactor during the starvation operation phase.

[0053] Optionally, the control unit is configured to control the nitrate dosing unit to add nitrate chemicals to the influent unit during the nitrate replenishment water stage;

[0054] A nitrate nitrogen concentration monitoring module is installed in the inlet water unit to determine whether the inlet water meets the requirements for replenishing nitrate inlet water.

[0055] An ammonia nitrogen concentration monitoring module is installed in the wastewater biological treatment reactor to monitor the ammonia nitrogen removal rate of the wastewater biological treatment system and determine whether to stop increasing the nitrate nitrogen concentration in the influent.

[0056] A DO curve monitoring module is installed in the wastewater biological treatment reactor to determine whether filamentous bacterial bulking has occurred or progressed.

[0057] Optionally, the system further includes a reflux unit configured to reflux nitrified liquid from the wastewater biological treatment reactor or subsequent treatment unit back to the influent unit, and the control unit configured to control the reflux unit to adjust the nitrified liquid reflux flow rate during the supplemental nitrate influent stage.

[0058] In this application, starvation operation refers to the operation of a wastewater biological treatment system in a state of low substrate concentration by stopping or reducing the supply of organic carbon sources to the system.

[0059] Sludge Volume Index (SVI) 30The Sludge Volume Index (SVI) after 30 minutes refers to the volume (in mL / g) of dry sludge per gram after the mixture has been left to stand in a graduated cylinder for 30 minutes. It is a core indicator for evaluating sludge settling performance. 30 The lower the SVI, the better the sludge settling properties; typically, the SVI of an AGS system... 30 It should be below 50 mL / g, and when it continues to rise and exceeds 150 mL / g, it indicates that moderate filamentous swelling may have occurred.

[0060] SVI5 / SVI 30 The ratio reflects the volume change of sludge during the initial settling stage (5 minutes) versus 30 minutes. Normal granular sludge settles rapidly, and the ratio of SVI5 to SVI... 30 The ratios are close to 1; however, when the filamentous bacteria proliferate in large quantities, leading to a loose structure, initial settling is slow, and SVI5 is significantly higher than SVI. 30 A 50% increase in the ratio within a short period can serve as an important criterion for early warning of expansion.

[0061] MLSS (Mixed Liquor Suspended Solids) represents the dry weight (unit: mg / L or g / L) of suspended solids per unit volume of mixed liquor in the reactor. Due to the dense particles and high biomass of AGS systems, MLSS is typically maintained at 6,000-10,000 mg / L, far exceeding that of traditional activated sludge systems, which is fundamental to ensuring high treatment efficiency.

[0062] Dissolved oxygen (DO) not only serves as an electron acceptor for aerobic microbial metabolism, but its periodic variation curve also has diagnostic value. A normal, completely mixed AGS system exhibits a stable DO plateau during the aeration phase, with a significant spike at the end due to substrate depletion. However, during filamentous bacterial bulking, the DO curve plateau rises abnormally and the final spike disappears, which can serve as a basis for online intelligent assessment of bulking status.

[0063] AGS reactors refer to sequencing batch bioreactors that use aerobic granular sludge as the core biological carrier. They are usually of a completely mixed configuration and achieve efficient integrated treatment of organic matter removal, nitrogen removal and phosphorus removal by periodically switching between anaerobic-anoxic-aerobic environments.

[0064] A low F / M (Food to Microorganism ratio) refers to the daily organic load (usually expressed as COD) borne by a unit mass of microorganisms. Municipal wastewater has limited carbon sources, and AGS systems often operate under low F / M conditions (e.g., 0.15-0.4 kg COD / kg MLSS·d). While this is beneficial for simultaneous nitrogen and phosphorus removal, it also provides a competitive advantage for filamentous bacteria, easily inducing bulking.

[0065] VER (Influent Volume Exchange Ratio) is the ratio of the volume of influent to the effective volume of the reactor during a single operating cycle of a wastewater biological treatment reactor. It is a key parameter in wastewater treatment processes that characterizes the intensity of influent during a given cycle.

[0066] (III) Beneficial Effects

[0067] This invention employs a two-stage regulation approach of "starvation operation + nitrate supplementation" to precisely utilize the metabolic disadvantage of filamentous bacteria under low substrate conditions and their sensitivity to nitrate environments. This selectively inhibits their growth, rapidly restoring the reactor's settling performance in a short period. Furthermore, by combining this with the nitrification liquid recirculation within the wastewater treatment plant, it promotes the enrichment of functional bacteria (such as ammonia-oxidizing bacteria) while inhibiting filamentous bacteria, thereby simultaneously achieving effective short-term control of sludge bulking and long-term system stability.

[0068] The method of this invention can significantly improve sludge settling performance within 6-20 days (starvation operation + nitrate supplementation), enabling SVI (Sludge Viscosity Index) to be achieved. 30 Reduced to below 100 mL / g, SVI5 / SVI 30 The ratio was restored to below 1.33, and the ammonia nitrogen removal rate was simultaneously restored to over 90%, avoiding the problems of long time consumption and slow results of traditional control methods.

[0069] The required nitrates can be obtained by adding KNO3 / NaNO3. More preferably, they can be directly returned to the secondary effluent rich in nitrified liquid in the sewage treatment plant, without the need for additional reagent purchase and storage, which greatly reduces operating costs. It is particularly suitable for the low-carbon transformation and smart upgrade of existing municipal sewage treatment plants.

[0070] This method combines the dynamic changes of the DO curve with the inhibition effect of filamentous bacteria to comprehensively evaluate the recovery of the settling performance and the reconstruction of nitrogen metabolism function of the FAGS system, providing a quantifiable, feedback-able, and automated intelligent control path for biological treatment systems based on aerobic granular sludge (AGS).

[0071] Compared with traditional non-specific control methods (such as chlorination, ozone, etc.), this invention does not require the addition of exogenous chemical inhibitors, avoiding problems such as short control period, lack of selectivity and easy relapse after drug withdrawal; compared with existing specific process control methods, this invention significantly shortens the recovery period, is easier to operate, and overcomes the shortcomings of traditional methods that are time-consuming and complex to control. Attached Figure Description

[0072] Figure 1 (a) is a typical dissolved oxygen (DO) curve of a completely mixed AGS reactor. Under normal operating conditions, the curve shows obvious plateau and peak characteristics at the end, reflecting the periodic changes in the aerobic, anoxic and anaerobic stages in the system. Figure 1 (b) is a microscopic image of aerobic granular sludge in the bulking state of filamentous bacteria.

[0073] Figure 2 SVI at each stage of filamentous bacterial swelling, swelling inhibition, and nitrate supplementation in Examples 1, 2, and 3. 30 The changes.

[0074] Figure 3 Examples 1, 2, and 3 show the DO curves and corresponding changes in ammonia nitrogen and total nitrogen (TN) removal rates for each cycle after adopting the filamentous bacteria expansion inhibition strategy.

[0075] Figure 4 This shows the changes in particle morphology of filamentous bulking granular sludge after inhibition treatment.

[0076] Figure 5 For comparison, the expanded granular sludge index (e.g., SVI) is used. 30 The changes in ammonia nitrogen and total nitrogen (TN) before and after starvation control, and the trends in their removal rates. Detailed Implementation

[0077] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0078] The function of this invention in supplementing nitrates is described below:

[0079] Supplementing nitrates while restoring influent aims to synergistically inhibit filamentous bacteria and promote system functional recovery through a dual mechanism. On one hand, nitrates, as alternative electron acceptors, effectively promote the growth and metabolism of non-filamentous functional microorganisms such as denitrifying bacteria, enabling them to compete for niches with filamentous bacteria in the granular sludge microenvironment, thus weakening the survival advantage of filamentous bacteria. On the other hand, the introduction of nitrates helps enrich key functional bacteria such as ammonia-oxidizing bacteria (AOB) and denitrifying bacteria. These bacteria play a central role in the formation and stabilization of granular structure, accelerating the reconstruction of dense bacterial flocs, thereby restoring the good settling performance and efficient pollutant metabolism capacity of aerobic granular sludge. This strategy not only achieves targeted inhibition of filamentous bulking but also simultaneously promotes the synergistic repair of the system's denitrification function and granular structure.

[0080] Following starvation control, the nitrate replenishment stage begins. With the aid of the starvation strategy of this invention, the settling performance significantly improves in the short term after filamentous bacteria are suppressed, thus the VER can be maintained within the range of 0.40-0.60. Specifically, the more severe the expansion, the greater the required starvation pressure, and the VER should be increased accordingly. The reflux nitrified liquid is introduced into the reactor along with the raw influent, with a reflux volume of η×VER×V and a raw water volume of (1-η)×VER×V. The initial reflux ratio increases with the expansion level. The reflux ratio at the initial stage of starvation is: η = 0.25-0.50 for mild expansion, η = 0.30-0.80 for moderate expansion, and η = 0.50-1.00 for severe expansion. With online monitoring, if the nitrogen cycle gradually recovers within the cycle, VER and η can gradually decrease, transitioning from severe expansion to mild expansion.

[0081] Example 1 (Aerobic granular sludge that has undergone long-term mild to moderate expansion)

[0082] In this embodiment, during the operation of the aerobic granular sludge system, sludge bulking caused by filamentous bacteria occurred and remained in a state of slight bulking for an extended period. During operation, the aeration rate was kept constant at 300 mL / min, dissolved oxygen (DO) was controlled at 1.0-1.5 mg / L, a single operating cycle was 3 hours, and the volume exchange ratio (VER) was 0.5. The influent was prepared by diluting high-concentration mother liquor with tap water; specific data are shown in Table 1, where COD and NH4+ are listed. + -N and PO4 3- -P is derived from sodium acetate, ammonium chloride (NH4Cl), and potassium dihydrogen phosphate (KH2PO4), respectively, and supplemented with the trace element solutions shown in Table 2 at a dosage of 1 mL / L.

[0083] The occurrence of expansion is determined through a comprehensive assessment of multiple indicators: laboratory monitoring data shows SVI 30 With SVI5 / SVI30 The sludge volume index (SVI) continued to rise, and within 20 days before the implementation of containment measures, it continued to rise. 30 The average value was as high as 141 mL / g, while the SVI5 / SVI ratio was also high. 30 The ratio increased from 1.1 to 1.85, significantly higher than the typical value (SVI) for the well-structured particle stage. 30 (Approximately 40 mL / g); the DO curve during a typical operating cycle gradually changed from "Type 1," which initially showed rapid oxygen consumption followed by a stable state, to "Type 2," characterized by slow oxygen consumption and a gradual decline. Microscopic observation further confirmed that a large number of filamentous bacteria were attached to the surface of the granular sludge, resulting in a loose structure and loss of compactness. Approximately 20% of the space on the outer side of the granular structure was occupied by filamentous bacteria, indicating that the system had experienced mild to moderate filamentous bulking. Based on the above assessment, the system entered the regulation and intervention phase.

[0084] 1) Starvation Operation Phase

[0085] To weaken the competitive advantage of filamentous bacteria, a 7-day starvation operation was implemented: the original 50% cycle volume exchange ratio was maintained, and the influent was changed to pure tap water (i.e., the addition of carbon, nitrogen and phosphorus sources was stopped); other operating conditions (aeration intensity, cycle duration, etc.) remained unchanged.

[0086] 2) Nitrate supplementation stage

[0087] After the starvation operation, exogenous nitrates were introduced to promote the growth of denitrifying bacteria, inhibit filamentous bacteria, and accelerate the recovery of particle structure. Specifically, the influent was restored, but KNO3 was added to the influent as an electron acceptor. The specific concentration is shown in Table 3. The original carbon and phosphorus ratio and trace element addition were maintained. The system continued to operate at an aeration rate of 300 mL / min and a cycle of 3 h.

[0088] 3) Process monitoring and effect evaluation

[0089] Throughout the entire regulation and recovery process, the system's operational status was continuously monitored. Using a WTWMulti3630 IDS multi-parameter water quality analyzer in conjunction with an FDO925 dissolved oxygen probe, daily dynamic changes in dissolved oxygen (DO) were recorded within typical cycles to assess the recovery of microbial community metabolic activity. Simultaneously, supernatant was collected during the sedimentation phase of each cycle, and nitrogen speciation was determined according to national standard methods: ammonia nitrogen was determined using Nessler's reagent spectrophotometry (HJ535-2009), nitrate nitrogen using ultraviolet spectrophotometry (HJ / T346-2007), and nitrite nitrogen using N-(1-naphthyl)-ethylenediamine spectrophotometry (GB7493-87). Total inorganic nitrogen (N) was then calculated based on these results. ) and its removal efficiency. In addition, the SVI after supplementing the influent with nitrate nitrogen was measured periodically. 30 (like Figure 3 (as shown in a) and captured microscopic images of the sludge (as shown in a). Figure 4 As shown in the figure, this is to track the evolution of sedimentation performance and particle morphology.

[0090] After the implementation of control measures, the system showed a good recovery trend. SVI 30 The DO levels continued to decline and stabilize, with the surface of the granular sludge gradually becoming smooth and dense, and filamentous bacteria significantly reduced. The DO curve of a typical cycle gradually recovered to characteristics close to "Type 1," with the DO plateau during the aeration phase remaining stable at 1.0-1.5 mg / L, reflecting the effective reconstruction of microbial metabolic activity. On the first day after the influent was restored, the ammonia nitrogen removal rate rapidly rebounded to approximately 90%; within a week, the total nitrogen (TN) removal rate also recovered to 70-80%, indicating a significant recovery in the system's denitrification function. Notably, in this embodiment, nitrate addition was not stopped after the settling performance recovered, with the aim of further investigating the long-term impact of exogenous nitrates on the nitrogen metabolism pathway of the AGS system.

[0091] Example 2 (Rapid growth of filamentous bacteria during the transformation of anaerobic particles into aerobic particles)

[0092] In this embodiment, the aerobic granular sludge system was started up using anaerobic granular sludge as the inoculum source. At the initial inoculation, the mixed liquor suspended solids concentration (MLSS) was as high as 8331 mg / L, and the sludge settling performance was good, with a SVI (suspended solids concentration). 30 The value was 30.0 mL / g. Initially, the system showed stable removal capacity for chemical oxygen demand (COD), but total inorganic nitrogen (...)... The removal efficiency is low, only maintained between 20% and 30%, reflecting that the aerobic nitrification and simultaneous nitrogen removal functions have not yet been effectively established.

[0093] As the aerobic granulation process progressed, excessive growth of filamentous bacteria gradually appeared inside the reactor. Despite this, due to the initially high MLSS, SVI... 30 The increase was relatively slow, but the filamentous bulking continued, eventually leading to a large amount of sludge loss, with MLSS dropping below 2000 mg / L and SVI... 30 The concentration was increased to 100.6 mL / g. During operation, the aeration rate was kept constant at 300 mL / min, and the dissolved oxygen (DO) was controlled at 6.5-8.0 mg / L during the initial aeration phase. The influent water quality was prepared according to Table 1 (using sodium acetate, ammonium chloride, and potassium dihydrogen phosphate respectively). and ), and add trace elements according to the values ​​shown in Table 2.

[0094] The occurrence of expansion was confirmed through a comprehensive analysis of multiple indicators: laboratory monitoring showed SVI. 30 and SVI5 / SVI 30The ratio continues to rise; the DO curve during a typical operating cycle exhibits "Type 2" characteristics—that is, a gradual decrease in DO and a low oxygen consumption rate, reflecting abnormal microbial metabolic activity; SVI5 / SVI 30 The concentration increased from 1.53 to 2.33 in a short period of time, and at the same time, filamentous bacteria formed a loosely structured enveloping ring on the particle surface, indicating that the system had entered a period of rapid development of filamentous bacteria expansion.

[0095] 1) Starvation Operation Phase

[0096] To weaken the competitive advantage of filamentous bacteria, a 7-day starvation operation was implemented: the original 50% cycle volume exchange ratio was maintained, and the influent was changed to pure tap water (i.e., the addition of carbon, nitrogen and phosphorus sources was stopped); other operating conditions (aeration intensity, cycle duration, etc.) remained unchanged.

[0097] 2) Nitrate supplementation stage

[0098] After the starvation operation, exogenous nitrates were introduced to promote the growth of denitrifying bacteria, inhibit filamentous bacteria, and accelerate the recovery of particle structure. Specifically, the influent was restored, but KNO3 was added to the influent as an electron acceptor. The specific concentration is shown in Table 3. The original carbon and phosphorus ratio and trace element addition were maintained. The system continued to operate at an aeration rate of 300 mL / min and a cycle of 3 h.

[0099] 3) Process monitoring and effect evaluation

[0100] Using a WTW Multi3630 IDS multi-parameter water quality analyzer with an FDO925 dissolved oxygen probe, the dynamic changes in dissolved oxygen (DO) were recorded daily within a typical cycle. Simultaneously, supernatant was collected during the sedimentation stage of each cycle, and the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen were determined using Nessler's reagent spectrophotometry (HJ535-2009), ultraviolet spectrophotometry (HJ / T346-2007), and N-(1-naphthyl)-ethylenediamine spectrophotometry (GB7493-87), respectively, to calculate total nitrogen (TIN) and its removal rate. In addition, solid oxygen viscous (SVI) was measured periodically. 30 And combined with microscopic imaging (see Figure 4 Observe the evolution of sludge morphology.

[0101] The results showed that the sedimentation performance of the system was significantly improved after nitrate supplementation: SVI 30As the oxygen consumption rate steadily decreased, the original filamentous bacteria on the particle surface were gradually covered by newly formed bacterial flocs, resulting in a denser structure. The DO curve also gradually shifted from "Type 2" to "Type 1," characterized by an increased oxygen consumption rate and a steeper curve slope, indicating that microbial metabolic activity was recovering. Although the stable DO plateau did not reach the expected range of 0.5-2.5 mg / L in the initial recovery phase (approximately two weeks), reflecting that biomass had not yet fully recovered, nitrogen removal performance showed a positive trend: ammonia nitrogen removal rate steadily increased from approximately 20% at the initial recovery influent stage to 60% after two weeks, and total nitrogen (TN) removal rate rose simultaneously to around 40%. This change indicates that as filamentous bacterial bulking was effectively suppressed and the particle structure was gradually rebuilt, the nitrification-denitrification cycle function within the system began to recover initially.

[0102] It is worth noting that in this embodiment, exogenous nitrate is continuously added during the recovery phase, which not only inhibits filamentous bacteria but also provides electron acceptors for building a stable simultaneous nitrification-denitrification (SND) environment, thereby accelerating the reconstruction of the nitrogen removal function of the AGS system.

[0103] Example 3 (Dense activated sludge system with short-term malignant bulking and a sharp drop in ammonia nitrogen removal rate)

[0104] In this embodiment, a wastewater treatment system encountered a short-term malignant bulking problem caused by filamentous bacteria during operation. The previously stable sludge system experienced a rapid drop in MLSS to below 1000 mg / L and SVI within a short period. 30 The concentration of ammonia nitrogen rapidly increased to over 500 mL / g, and the removal rate plummeted to below 50%. The reactor underwent flocculent sludge granulation under the influent conditions shown in Table 1 to improve treatment efficiency. Initially, the average sludge particle size steadily increased, and the pollutant metabolism and settling performance were gradually optimized, resulting in a gradual decrease in effluent TIN concentration. However, this change led to the acid salt concentration falling below the threshold required to inhibit filamentous bulking in the next anaerobic cycle, thus triggering a short-term malignant filamentous bulking event.

[0105] When SVI is detected 30 When the concentration rapidly increased from 115.2 mL / g to 208.4 mL / g, microscopic examination revealed a significant increase in filamentous bacteria, loose particle structure, growth of filamentous bacterial branches, and a rapid drop in ammonia nitrogen removal rate from over 90% to below 50%, it was confirmed that the system had entered a malignant expansion phase.

[0106] 1) Starvation Operation Phase

[0107] To weaken the competitive advantage of filamentous bacteria, a 7-day starvation operation was implemented: the original 50% cycle volume exchange ratio was maintained, and the influent was changed to pure tap water (i.e., the addition of carbon, nitrogen and phosphorus sources was stopped); other operating conditions (aeration intensity, cycle duration, etc.) remained unchanged.

[0108] 2) Nitrate supplementation stage

[0109] After the starvation operation, exogenous nitrates were introduced to promote the growth of denitrifying bacteria, inhibit filamentous bacteria, and accelerate the recovery of particle structure. Specifically, the influent was restored, but KNO3 was added to the influent as an electron acceptor. The specific concentration is shown in Table 3. The original carbon and phosphorus ratio and trace element addition were maintained. The system continued to operate at an aeration rate of 300 mL / min and a cycle of 3 h.

[0110] 3) Process monitoring and effect evaluation

[0111] Using a WTW Multi3630 IDS multi-parameter water quality analyzer with an FDO925 dissolved oxygen probe, the dynamic changes in dissolved oxygen (DO) during a typical operating cycle were recorded daily to assess the recovery of metabolic activity in the microbial community. Simultaneously, supernatant was collected during the sedimentation phase of each cycle, and the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen were determined using Nessler's reagent spectrophotometry (HJ535-2009), ultraviolet spectrophotometry (HJ / T346-2007), and N-(1-naphthyl)-ethylenediamine spectrophotometry (GB7493-87), respectively, to calculate TIN and its removal rate. In addition, SVI was measured periodically. 30 And combined with microscopic imaging (see Figure 4 Observe the evolution of sludge morphology.

[0112] Despite nitrate supplementation, SVI 30 While the concentration was successfully controlled below 200 mL / g, the filamentous bacteria still held a dominant ecological niche, preventing a complete recovery to granular sludge levels within a short period. Furthermore, because the niche of ammonia-oxidizing bacteria (AOB) was occupied by filamentous bacteria, they were unable to effectively utilize oxygen and substrate. Therefore, even with improved or stable settling performance, the removal efficiency of key pollutants such as ammonia nitrogen and total nitrogen (TN) did not significantly improve. The DO curve within a typical cycle still exhibited "Type 2" characteristics—slow DO decline and low oxygen consumption rate—reflecting that the overall metabolic activity of the system had not been fundamentally improved. The cyclic N-cycle failed to establish a pattern consistent with the DO curve elasticity trend. The experiment indicates that the severe bulking of malignant filamentous bacteria significantly disrupts the normal metabolic function of activated sludge. Even if settling performance is temporarily improved through regulatory measures, further spatial restructuring and niche reconstruction are necessary to achieve full functional recovery.

[0113] Table 1: Influent conditions during the filamentous bacteria bulking stage in Examples 1-3

[0114]

[0115] Table 2: Trace element conditions in the influent during the bulking stage of filamentous bacteria in Examples 1-3

[0116]

[0117] Table 3: Influent conditions for nitrate supplementation using starvation suppression methods in Examples 1-3

[0118]

[0119] Comparative Example 1

[0120] This comparative study aims to verify whether relying solely on a starvation operation strategy is sufficient to achieve long-term and effective inhibition of filamentous bulking in aerobic granular sludge systems.

[0121] The initial expansion stage of this comparative system is the same as that of the aerobic granular sludge system in Example 1. The influent water quality conditions are consistent with those in Table 1, and the sludge bulking characteristics are SVI. 30 and SVI5 / SVI 30 SVI continues to rise 30 Within a short period of 3 days, the concentration of bacteria increased from 118 mL / g to 158 mL / g. Microscopic examination clearly showed that about 20% of the particles were covered with filamentous bacteria, and the sedimentation performance deteriorated significantly.

[0122] After confirming the occurrence of expansion, a 9-day starvation operation was implemented, during which the 50% cycle volume exchange ratio was maintained, the influent was completely replaced with tap water, and the addition of carbon, nitrogen and phosphorus sources was stopped. After the starvation ended, no exogenous electron acceptors or functional enhancement methods were introduced. Instead, the original normal influent conditions (i.e., nutrient influent prepared according to Table 1) were directly restored, and no additional nitrates or other regulatory factors were added.

[0123] Initial results show that starvation operation can indeed improve settling performance in the short term, SVI 30 The rapid decline during the starvation phase indicates that filamentous bacteria activity was inhibited to some extent. Meanwhile, within the first week after the water was restored, the removal rates of ammonia nitrogen and total nitrogen (TN) showed a steady upward trend, suggesting that the system's pollutant removal function had recovered to some extent.

[0124] However, this improvement did not last. About a week after returning to normal operation, SVI... 30 The sedimentation performance initially rebounded rapidly and showed a significant upward trend again within two weeks, with settling performance deteriorating further. Simultaneously, ammonia nitrogen and total nitrogen (TN) removal rates also declined, indicating a significant decrease in the system's nitrogen removal capacity. Microscopic observation further confirmed that filamentous bacteria rapidly regained their dominant ecological niche after the influent was restored, and the particle structure failed to be effectively reconstructed.

[0125] The above results indicate that while starvation control alone can temporarily alleviate filamentous bulking symptoms, it cannot fundamentally alter the ecological competitive landscape of the microbial community. Once normal influent is restored, the lack of inhibitory mechanisms such as denitrification electron acceptors leads to a rapid resurgence of filamentous bacteria, causing system instability once again. Therefore, short-term starvation strategies relying solely on nutrient restriction are insufficient for long-term suppression of filamentous bulking. It is essential to combine these strategies with functional regulation methods, such as exogenous nitrate addition, to rebuild a microecological environment conducive to granular sludge stability and efficient nitrogen removal.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating sludge bulking caused by filamentous bacteria, characterized in that, The method includes: starving the wastewater biological treatment system that has experienced filamentous bulking, wherein starving operation means stopping or reducing the supply of nutrients to the wastewater biological treatment system, wherein the nutrients are organic carbon, nitrogen and phosphorus, wherein stopping means completely stopping the supply of the nutrients, and reducing means reducing the supply of nutrients by more than 90%. After the starvation operation, the wastewater biological treatment system is supplemented with nitrate influent. The supplementation of nitrate influent includes: supplying the wastewater biological treatment system with influent containing organic carbon source, and the concentration of organic carbon source in the influent is restored to more than 75% of the normal operating concentration, while increasing the nitrate nitrogen concentration in the influent to 4.0-8.0 mg / L.

2. The method according to claim 1, characterized in that, The starvation operation includes: stopping the influent to the wastewater biological treatment system; or, replacing the influent supplied to the wastewater biological treatment system with water that does not contain organic carbon sources.

3. The method according to claim 1 or 2, characterized in that, The concentration of nitrate nitrogen in the influent can be increased by adding nitrate chemicals to the influent or by refluxing nitrate-rich nitrate solution back into the influent.

4. The method according to claim 1, characterized in that, Prior to the starvation operation, a step is included to determine the bulking stage, the determination being based on at least one of the following parameters: the dissolved oxygen curve morphology of the wastewater biological treatment system, and the sludge volume index (SVI). 30 SVI5 and SVI 30 The ratio of filamentous bacteria observed under a microscope; Sludge Volume Index (SVI) 30 When 120mL / g≤SVI 30 When the concentration is ≤150 mL / g, it is considered mild swelling; when it is 150 mL / g... <SVI 30 When the swelling level is ≤200 mL / g, it is considered moderate swelling; when the swelling level is ≤200 mL / g, it is considered moderate swelling. 30 When the concentration is >200 mL / g, it is considered severe swelling; SVI5 and SVI 30 The ratio: when SVI5 / SVI 30 When the value is greater than 1.8, it is considered an abnormal settling performance, indicating the occurrence or progression of excessive growth of filamentous fungi and filamentous swelling. Dissolved oxygen curve morphology: During the stable aeration phase, if the DO value is consistently higher than the normal plateau value by more than 0.5 mg / L, and / or the DO surge peak disappears or the amplitude decreases by more than 50% at the end of aeration, it is determined that filamentous bulking has occurred or progressed. Microscopic examination of filamentous bacteria abundance: If the coverage area of ​​filamentous bacteria is ≥30% under 100x magnification, or if the number of filamentous bacteria per field is ≥15, it is considered as significant filamentous bacteria proliferation and filamentous bacteria swelling or progression.

5. The method according to claim 1, characterized in that, Once SVI30 drops below 60% of the expansion phase, the starvation operation ceases; the duration of the starvation operation is 3-10 days. Slight bloating, fasting for 3-5 days; Moderate bloating, requiring 5-7 days of starvation; Severe bloating, starvation for 7-10 days.

6. The method according to claim 1, characterized in that, During the nitrate supplementation influent stage, the ammonia nitrogen removal rate of the wastewater biological treatment system is monitored. When the ammonia nitrogen removal rate recovers and stabilizes at above 50%, the criteria for stopping the increase of nitrate nitrogen concentration in the influent are established.

7. A treatment system for sludge bulking caused by filamentous bacteria, characterized in that, The system includes: a wastewater biological treatment reactor, an influent unit, an aeration unit, a nitrate dosing unit, and a control unit; The wastewater biological treatment reactor provides a site for the biodegradation of wastewater pollutants; The water inlet unit and the aeration unit are respectively connected to the wastewater biological treatment reactor; The nitrate dosing unit is connected to the water inlet unit; the control unit is signal-connected to the water inlet unit, the aeration unit, and the nitrate dosing unit. The control unit is configured to perform the method of any one of claims 1 to 6, enabling the wastewater biological treatment reactor, the influent unit, the nitrate dosing unit, and the aeration unit to cooperate and coordinate, so that the treatment system switches between a starvation operation mode and a nitrate-supplemented influent operation mode.

8. The system according to claim 7, characterized in that, The water inlet unit includes: a raw water inlet line and a dilution water inlet line; The dilution water inlet line is used to supply water containing no or low organic carbon sources to the wastewater biological treatment reactor. The water containing low organic carbon sources has a carbon source content of no more than 10% under normal inlet conditions. The control unit is configured to control the dilution water inlet line to supply water to the wastewater biological treatment reactor during the starvation operation phase.

9. The system according to claim 7, characterized in that, The control unit is configured to control the nitrate dosing unit to add nitrate chemicals to the inlet water unit during the supplemental nitrate inlet water phase. A nitrate nitrogen concentration monitoring module is installed in the inlet water unit to determine whether the inlet water meets the requirements for replenishing nitrate inlet water. An ammonia nitrogen concentration monitoring module is installed in the wastewater biological treatment reactor to monitor the ammonia nitrogen removal rate of the wastewater biological treatment system, and then determine whether to stop the operation of increasing the nitrate nitrogen concentration in the influent. A DO curve monitoring module is installed in the wastewater biological treatment reactor to determine whether filamentous bacteria expansion occurs or progresses, thereby determining the timing for starting the starvation operation mode.

10. The system according to claim 7, characterized in that, The system also includes a reflux unit configured to reflux nitrified liquid from the wastewater biological treatment reactor or subsequent treatment unit back to the influent unit. The control unit is configured to control the reflux unit to adjust the nitrified liquid reflux flow rate during the supplemental nitrate influent stage.

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