Method for reducing filamentous microorganisms in low-temperature expanded sludge

Abstract

The invention provides a method for reducing filamentous microorganisms in low-temperature expanded sludge, and belongs to the technical field of sewage treatment systems. The method comprises the steps that N-butyryl-L-homoserine lactone is added into an activated sludge system in a sequencing batch reactor under the low-temperature operation condition of 6-15 DEG C, treatment is conducted through a sequencing batch activated sludge method, and the activated sludge system contains low-temperature expanded sludge which is expanded due to excessive growth of filamentous bacteria under the low-temperature condition. According to the method, sludge with filamentous bacterium bulking in a reactor running under a low-temperature condition is taken as an improvement object, and N-butyryl-L-homoserine lactone is exogenously added, so that the relative abundance of filamentous microorganisms in the sludge can be reduced, the bulking of the sludge can be inhibited, and the degradation capability of the sludge on pollutants can be improved.

Description

Technical Field

[0001] This application relates to the technical field of sewage treatment systems, and more specifically, to a method for reducing filamentous microorganisms in low-temperature bulking sludge. Background Art

[0002] The activated sludge process is an important technology for treating municipal sewage. It is favored for its economic, efficient, and environmentally friendly characteristics. However, the problem of sludge bulking remains a major challenge in the activated sludge treatment process, affecting the stable operation of the municipal sewage treatment system. Research on the problem of sludge bulking shows that approximately 70% of sewage treatment plants globally experience activated sludge bulking. Notably, nearly 90% of such incidents can be attributed to filamentous bulking caused by excessive growth of filamentous bacteria.

[0003] For many sewage treatment plants with the activated sludge process as the biological treatment unit, lower temperatures can cause problems of sludge bulking. Low temperatures inhibit the overall activity of microorganisms in the sewage biological treatment reactor, thereby reducing the degradation ability of organic pollutants. This causes an excess of undegraded organic matter, especially viscous substances such as polysaccharides, to accumulate on the surface of microorganisms, leading to sludge bulking. Research has found that when operating an SBR reactor under low-temperature conditions, the degree of sludge bulking is much greater than that of a reactor operating at room temperature, and in the later stage of operation, the reactor under low temperature continuously experiences high sludge bulking, indicating that a low-temperature environment is more likely to trigger and maintain the phenomenon of sludge bulking. Some research has found that using the traditional nitrification and denitrification process and reducing the operating temperature to 14°C induces filamentous bacteria sludge bulking. The occurrence of sludge bulking under low-temperature conditions causes an increase in the abundance of filamentous bacterial groups, a reduction in the types of microorganisms in the reactor, and a decrease in the abundance of nitrogen-removing functional microorganisms, affecting the effect of sewage treatment. Under low-temperature conditions, filamentous bacteria have stronger growth competitiveness, so they will multiply in large numbers, leading to sludge bulking and reducing the treatment effect of the reactor.

[0004] However, current research mainly focuses on suppressing sludge bulking in reactors operating under room-temperature conditions; there is a lack of relevant research on how to improve the sludge with filamentous bacteria bulking that has occurred in reactors operating under low-temperature conditions. Summary of the Invention

[0005] Based on the above research findings, the purpose of this application is to provide a method for reducing filamentous microorganisms in low-temperature bulking sludge, taking the sludge with filamentous bacteria bulking that has occurred in a reactor operating under low-temperature conditions as the object of improvement, which can reduce the relative abundance of filamentous microorganisms in the sludge, inhibit sludge bulking, and improve the degradation ability of the sludge to pollutants.

[0006] The embodiments of this application are implemented as follows:

[0007] An embodiment of the present application provides a method for reducing filamentous microorganisms in low-temperature expanded sludge, including:

[0008] Under the low-temperature operating conditions of 6 - 15 °C, add N-butyryl-L-homoserine lactone to the activated sludge system in the sequencing batch reactor, and use the sequencing batch activated sludge method for treatment. The activated sludge system contains low-temperature expanded sludge that expands due to excessive growth of filamentous bacteria under low-temperature conditions.

[0009] In some embodiments, the low-temperature operating conditions are 8 °C.

[0010] In some embodiments, add N-butyryl-L-homoserine lactone once per operating cycle; optionally, after adding N-butyryl-L-homoserine lactone, the initial concentration of N-butyryl-L-homoserine lactone in the sequencing batch reactor is 40 - 120 μg / L.

[0011] In some embodiments, the sludge volume index of the low-temperature expanded sludge > 150 mL / g.

[0012] In some embodiments, the sludge volume index of the low-temperature expanded sludge > 250 mL / g.

[0013] In some embodiments, in the activated sludge system, the initial content of the low-temperature expanded sludge is 2000 - 7000 mg / L.

[0014] In some embodiments, the number of operating cycles is 40 - 80; optionally, the number of operating cycles is 50 - 80.

[0015] In some embodiments, the sequencing batch reactor operates in an intermittent manner, and each operating cycle includes an influent stage, an aeration stage, a sedimentation stage, a drainage stage, and an idle stage in sequence.

[0016] In some embodiments, at least one of the following conditions (a1) - (a6) is satisfied:

[0017] (a1) The duration of each operating cycle is 12 ± 2 h;

[0018] (a2) The duration of the influent stage is 5 - 10 min;

[0019] (a3) The duration of the aeration stage is 10 ± 2 h;

[0020] (a4) The duration of the sedimentation stage is 1.5 ± 0.5 h;

[0021] (a5) The duration of the drainage stage is 5 - 10 min;

[0022] (a6) The duration of the idle stage is 20 ± 10 min.

[0023] In some embodiments, during the influent stage, the influent water quality meets at least one of the following conditions (b1) to (b5):

[0024] (b1) The chemical oxygen demand is 200 - 500 mg / L;

[0025] (b2) The ammonia nitrogen content is 20 - 60 mg / L;

[0026] (b3) The total phosphorus content is 3 - 10 mg / L;

[0027] (b4) The pH value is 7 - 8;

[0028] (b5) The temperature is 6 - 15 °C.

[0029] The method for reducing filamentous microorganisms in low-temperature bulking sludge provided by the embodiments of the present application has at least the following beneficial effects:

[0030] Taking the sludge with filamentous bulking that has occurred in a reactor operating under low-temperature conditions as the improvement object, by externally adding N-butyryl-L-homoserine lactone and combining with the sequencing batch activated sludge process, the relative abundance of filamentous microorganisms in the sludge can be reduced, and some related functional bacteria and the physicochemical properties of the activated sludge can be better regulated, which can inhibit sludge bulking and improve the pollutant degradation ability of the sludge. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is the detection result of the microorganisms in the activated sludge system at the phylum level in each experimental group of the present application;

[0033] Figure 2 It is the detection result of the microorganisms in the activated sludge system at the genus level in each experimental group of the present application;

[0034] Figure 3 It is the detection result of the EPS composition of the activated sludge system in each experimental group of the present application;

[0035] Figure 4 It is the detection result of the microbial activity of the activated sludge system in each experimental group of the present application. Detailed Embodiments

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. For those not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are applied. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0037] It should be noted that "and / or" in this application, such as "Feature 1 and / or Feature 2", refers to three cases: "Feature 1" alone, "Feature 2" alone, and "Feature 1" plus "Feature 2".

[0038] In addition, in the description of this application, unless otherwise specified, "multiple" in "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two end values "a" and "b", and the "measurement unit" in "numerical value a to numerical value b + measurement unit" represents the "measurement unit" of both "numerical value a" and "numerical value b".

[0039] Quorum sensing (QS) is a communication method by which microorganisms adjust their group behavior patterns according to cell density and changes in the surrounding environment. Microorganisms generate signal molecules and release them into the environment. As the concentration of these signal molecules gradually increases and reaches a threshold, they will interact with specific receptor proteins, thereby triggering the transcriptional activation of a series of related genes. N-acyl homoserine lactones (AHLs) are considered the most common autoinducers in Gram-negative bacteria and are also known as signal molecules.

[0040] Quorum sensing (QS) mediated by AHLs widely exists in bacteria and plays a key role in their physiological states. Research shows that AHLs are not only deeply involved in various physiological activities of microorganisms, but also some scholars have proposed that the QS system mediated by AHLs can effectively inhibit sludge bulking, improve microbial activity, and promote the attachment growth of autotrophic nitrifying sludge. AHLs have a hydrophobic homoserine lactone ring as the core, and the side chains increase in increments of 2 carbon units such as C4, C6, C8, etc. Currently, there are more and more studies on the relationship between AHLs signal molecules and sewage treatment systems, and the signal molecules used include C4-HSL, C6-HSL, and C8-HSL.

[0041] However, current research mainly focuses on suppressing sludge bulking in reactors operating under room temperature conditions. On the one hand, it usually aims at preventing sludge bulking in systems where sludge bulking has not occurred yet. On the other hand, in the sludge treatment system, the operating temperature has a great impact on various performances, such as but not limited to the sedimentation performance of activated sludge, the composition of activated sludge microorganisms, the activity of activated sludge microorganisms, the removal effect of organic matter, etc. Therefore, it is difficult to obtain inspiration from existing research on how to improve the sludge with filamentous bulking that has occurred in reactors operating under low temperature conditions.

[0042] Moreover, considering the situation that C4-HSL is easily degraded (in fact, in the technical solution of this application, C4-HSL is added, and C4-HSL cannot be detected in the effluent), current research more commonly uses signal molecules such as C6-HSL and C8-HSL.

[0043] Through research, it is found that taking the sludge with filamentous bulking that has occurred in a reactor operating under low temperature conditions as the object of improvement, C4-HSL unexpectedly shows excellent performance. Specifically, for example, compared with the untreated original filamentous bulking sludge, the exogenous addition of C4-HSL can effectively reduce the relative abundance of filamentous microorganisms in the sludge, can inhibit sludge bulking, and improve the degradation ability of the sludge to pollutants; while the exogenous addition of C6-HSL and C8-HSL instead increases the relative abundance of some filamentous microorganisms. Moreover, compared with the exogenous addition of C6-HSL and C8-HSL, the exogenous addition of C4-HSL can better regulate some related functional bacteria and the physical and chemical characteristics of activated sludge, so as to better inhibit sludge bulking and improve the degradation ability of the sludge to pollutants.

[0044] Based on this, the embodiments of this application provide a method for reducing filamentous microorganisms in low-temperature bulking sludge. The technical solutions of the embodiments of this application will be described exemplarily below.

[0045] The embodiments of this application provide a method for reducing filamentous microorganisms in low-temperature bulking sludge, including: under the low-temperature operating condition of 6-15°C, adding N-butyryl-L-homoserine lactone (abbreviated as C4-HSL) to the activated sludge system in a sequencing batch reactor (abbreviated as SBR reactor), and treating it by the sequencing batch activated sludge method. The activated sludge system contains low-temperature bulking sludge caused by excessive growth of filamentous bacteria under low temperature conditions.

[0046] In the embodiments of this application, filamentous microorganisms refer to a class of microorganisms with slender, filamentous or branched morphologies, such as but not limited to one or more filamentous bacteria, filamentous fungi, and filamentous algae whose cells are connected to form filamentous cell bodies.

[0047] Low-temperature operation conditions, for example but not limited to, are any one of the point values of 6°C, 7°C, 8°C, 9°C, 10°C, 11°C, 12°C, 13°C, 14°C, 15°C or the range values between any two of them.

[0048] As an example, the low-temperature operation condition is 8°C.

[0049] The sequencing batch reactor is abbreviated as and is used to operate the activated sludge system for treating activated sludge by the sequencing batch activated sludge process. In some embodiments, when the sequencing batch activated sludge process is used for treatment, the number of operation cycles is 40 - 80, for example but not limited to any one of the point values of 40, 45, 50, 55, 60, 65, 70, 75, 80 or the range values between any two of them; optionally, the number of operation cycles is 50 - 80. Among them, the number of operation cycles can be determined according to the initial expansion situation of the low-temperature expanded sludge. If the expansion is more serious, a relatively larger number of cycles can be selected.

[0050] It should be noted that, without specific instructions, the steps and process parameters of the sequencing batch activated sludge process can be controlled according to conventional requirements. The steps of each operation cycle, for example but not limited to, include an influent stage, an aeration stage, a sedimentation stage, and a drainage stage in sequence.

[0051] In some embodiments, the sequencing batch reactor operates in an intermittent manner, and each operation cycle includes an influent stage, an aeration stage, a sedimentation stage, a drainage stage, and an idle stage in sequence.

[0052] In this embodiment, after the drainage is completed in each operation cycle, it is idle for a period of time, and then the influent of the next operation cycle starts, so that the sequencing batch reactor operates in an intermittent manner.

[0053] Optionally, the duration of each operation cycle is 12 ± 2 h, for example but not limited to any one of the point values of 10 h, 11 h, 12 h, 13 h, 14 h or the range values between any two of them.

[0054] Optionally, the duration of the influent stage is 5 - 10 min, for example but not limited to any one of the point values of 5 min, 6 min, 7 min, 8 min, 9 min, 10 min or the range values between any two of them.

[0055] Optionally, the duration of the aeration stage is 10 ± 2 h, for example but not limited to any one of the point values of 8 h, 9 h, 10 h, 11 h, 12 h or the range values between any two of them.

[0056] Optionally, the duration of the sedimentation stage is 1.5 ± 0.5 h, for example but not limited to any one of the point values of 1 h, 1.5 h, 2 h or the range values between any two of them.

[0057] Optionally, the duration of the drainage stage is 5 to 10 minutes, for example but not limited to any one of the point values of 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes or the range values between any two of them.

[0058] Optionally, the duration of the idle stage is 20 ± 10 minutes, for example but not limited to any one of the point values of 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes or the range values between any two of them.

[0059] Exemplarily, the duration of each operation cycle is 12 hours; the duration of the water inlet stage is 5 minutes; the duration of the aeration stage is 10 hours; the duration of the sedimentation stage is 1.5 hours; the duration of the drainage stage is 5 minutes; the duration of the idle stage is 20 minutes.

[0060] It should be noted that in the case of no specific instructions, during the water inlet stage, the water inlet quality can be controlled according to the conventional requirements.

[0061] Optionally, the chemical oxygen demand is 200 to 500 mg / L, for example but not limited to any one of the point values of 200 mg / L, 300 mg / L, 400 mg / L, 500 mg / L or the range values between any two of them.

[0062] Optionally, the ammonia nitrogen content is 20 to 60 mg / L, for example but not limited to any one of the point values of 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L or the range values between any two of them.

[0063] Optionally, the total phosphorus content is 3 to 10 mg / L, for example but not limited to any one of the point values of 3 mg / L, 4 mg / L, 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L or the range values between any two of them.

[0064] Optionally, the pH value is 7 to 8, for example but not limited to any one of the point values of 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8 or the range values between any two of them.

[0065] Optionally, the temperature is 6 to 15 °C, for example but not limited to any one of the point values of 6 °C, 7 °C, 8 °C, 9 °C, 10 °C, 11 °C, 12 °C, 13 °C, 14 °C, 15 °C or the range values between any two of them, and for example it is the same as the temperature corresponding to the low-temperature operation conditions of the SBR reactor.

[0066] In the embodiments of the present application, low-temperature bulking sludge refers to activated sludge that has undergone filamentous bulking in a reactor operating under low-temperature conditions, and it is exemplarily sourced from a sewage treatment plant. Among them, the low-temperature conditions are, for example, ≤15 °C, or ≤12 °C. In some exemplary embodiments, the low-temperature conditions can be the same as the specific low-temperature operating conditions (6 - 15 °C) for operating the SBR reactor in the present application.

[0067] In some embodiments, the sludge volume index of the low-temperature bulking sludge > 150 mL / g. Correspondingly, the low-temperature bulking sludge can be activated sludge in the micro-bulking stage or in the malignant bulking stage.

[0068] In some embodiments, the sludge volume index of the low-temperature bulking sludge > 250 mL / g. Correspondingly, the low-temperature bulking sludge is activated sludge in the malignant bulking stage.

[0069] Exemplarily, in the activated sludge system, the initial content of the low-temperature bulking sludge is 2000 - 7000 mg / L, which is, for example but not limited to, any one of the point values 2000 mg / L, 3000 mg / L, 4000 mg / L, 5000 mg / L, 6000 mg / L, 7000 mg / L or the range values between any two of them.

[0070] Among them, the initial content of the low-temperature bulking sludge refers to the initial concentration of the low-temperature bulking sludge in the activated sludge system. The activated sludge system refers to a system composed of the low-temperature bulking sludge and the influent water during the influent stage in the SBR reactor. It can be understood that some other auxiliary components or functional components can also be added as needed.

[0071] In the embodiments of the present application, the operation of adding the C4-HSL signaling molecule can be carried out following the influent water during the influent stage. Exemplarily, N-butyryl-L-homoserine lactone is added once per operating cycle.

[0072] In some embodiments, after adding N-butyryl-L-homoserine lactone, the initial concentration of N-butyryl-L-homoserine lactone in the sequencing batch reactor is 40 - 120 μg / L, which is, for example but not limited to, any one of the point values 40 μg / L, 50 μg / L, 60 μg / L, 70 μg / L, 80 μg / L, 90 μg / L, 100 μg / L, 110 μg / L, 120 μg / L or the range values between any two of them.

[0073] Among them, the initial concentration of the C4-HSL signaling molecule in the sequencing batch reactor refers to the concentration at which the C4-HSL is dispersed in the activated sludge system after the feeding and influent stages are completed and before entering the aeration stage.

[0074] The features and performance of the present application will be further described in detail below in conjunction with the embodiments.

[0075] I. The experimental conditions of each embodiment and comparative example are as follows:

[0076] 1.1. Obtain low-temperature bulking sludge caused by excessive growth of filamentous bacteria under low-temperature conditions. This low-temperature bulking sludge is from a sewage treatment plant and is filamentous bacteria bulking sludge generated at low temperature after sewage treatment by the activated sludge method at low temperature. The SVI of the original low-temperature bulking sludge is 288.

[0077] 1.2. Take the original low-temperature bulking sludge as a control, and the experimental number is recorded as R0.

[0078] 1.3. Use an SBR reactor to inoculate the original low-temperature bulking sludge as the activated sludge in the activated sludge system. Treat it by the sequential batch activated sludge process and operate for 42 cycles under the low-temperature operating conditions of 8°C. Among them, the SBR reactor operates intermittently, and the duration of each operating cycle is 12 h, including the following stages in sequence: a 5-min influent stage, a 10-h aeration stage, a 1.5-h sedimentation stage, a 5-min drainage stage, and a 20-min idle stage.

[0079] The content of low-temperature bulking sludge in the activated sludge system is 3400 mg / L.

[0080] The influent water quality in the influent stage meets the following conditions: chemical oxygen demand is 300 mg / L; ammonia nitrogen (NH4 + [[ID=2@]]-N) content is 40 mg / L; C / N = 7.5; total phosphorus content is 4.5 mg / L; (b4) pH value is 7 - 8; (b5) temperature is 8°C.

[0081] In each embodiment and comparative example, the difference is that different AHLs are added during the influent stage. Specifically, as shown in Table 1.

[0082] Table 1

[0083]

[0084] II. The results of some detection indexes of the experiments in each embodiment and comparative example are as follows:

[0085] 1. The influence results of each group of experiments on the microbial community structure of the activated sludge system

[0086] 1.1. Analysis results of microorganisms at the phylum level

[0087] Perform high-throughput sequencing on the cultured activated sludge and analyze it under the conditions of the phylum level. The results are as Figure 1As shown, the relative abundances of microorganisms in each phylum are arranged from left to right in the order of R0, R1, R2, and R3. The specific results are listed in Table 2 below.

[0088] Table 2. Types and relative abundances of microorganisms at the phylum level

[0089] Number R0 R1 R2 R3 Proteobacteria 0.4291 0.4441 0.3277 0.3260 Chloroflexi 0.1542 0.1300 0.2133 0.2378 Bacteroidota 0.1384 0.1413 0.1601 0.1356 Actinobacteriota 0.1302 0.1271 0.1433 0.1552 Patescibacteria 0.0552 0.0635 0.0438 0.0521 Firmicutes 0.0524 0.0426 0.0428 0.0413 Myxococcota 0.0215 0.0224 0.0235 0.0246 Acidobacteriota 0.0052 0.0051 0.0115 0.0092 others 0.0138 0.0239 0.0340 0.0182

[0090] According to Table 2, the microorganisms in the activated sludge system at the phylum level are mainly Proteobacteria, Chloroflexi, Bacteroidota, Actinobacteriota, Patescibacteria, Firmicutes, Acidobacteriota, and Myxococcota.

[0091] Proteobacteria occupies the largest abundance proportion in each reactor. Among them, the relative abundances of Proteobacteria in R0, R1, R2, and R3 are 42.91%, 44.41%, 32.77%, and 32.60% respectively. The relative abundance of Proteobacteria in R1 increased by 3.50% compared to R0. In the sewage treatment system, the vast majority of microorganisms related to biological nitrogen removal, biological phosphorus removal, and organic matter degradation belong to Proteobacteria, such as ammonia-oxidizing bacteria, denitrifying bacteria, nitrite-oxidizing bacteria, etc. It can be seen that exogenous addition of C4-HSL is beneficial to promoting the removal of pollutants in the reactor.

[0092] The relative abundances of Chloroflexi in R0, R1, R2, and R3 are 15.42%, 13.00%, 21.33%, and 23.78% in turn. The relative abundance of Chloroflexi in R1 decreased by 15.69% compared to R0. Usually, most filamentous bacteria belong to Chloroflexi, indicating that exogenous addition of C4-HSL significantly reduces the relative abundance of filamentous bacteria in the reactor, thereby improving the sedimentation performance of the activated sludge.

[0093] The relative abundances of Bacteroidota in R0, R1, R2, and R3 are 13.84%, 14.13%, 16.01%, and 13.56% respectively. The relative abundances of Bacteroidota in R1 and R2 both increased to a certain extent. The increase in Bacteroidota is beneficial to improving the metabolic level of bacteria, thereby strengthening the degradation ability of microorganisms to pollutants. It can be seen that exogenous addition of C4-HSL and C6-HSL improves the pollutant degradation ability of the activated sludge system.

[0094] The relative abundances of Actinobacteriota in R0 and R1 were 13.02% and 12.71% respectively, and the abundance of Actinobacteriota in the system decreased significantly in R1 compared to R0. During the occurrence of sludge bulking, some filamentous bacterial species in Actinobacteriota may play a key role. Since filamentous bacteria have a large specific surface area and a low oxygen saturation constant, they may be more likely to gain a growth advantage under certain environmental conditions (such as low dissolved oxygen, low load, etc.), resulting in the occurrence of sludge bulking. It can be seen that the addition of exogenous C4-HSL inhibited the occurrence of sludge bulking.

[0095] The relative abundances of Patescibacteria in R0 and R1 were 5.52% and 6.35% respectively, and the abundance of Patescibacteria in the system increased significantly in R1 compared to R0. Some studies have shown that there is a positive correlation between the abundance of Patescibacteria and the nitrification gene amoA; many microorganisms in Patescibacteria are involved in the denitrification process, improving the ability of the activated sludge system to remove pollutants. It can be seen that the addition of exogenous C4-HSL improved the ability of the activated sludge system to remove pollutants.

[0096] In summary, under low-temperature conditions, the addition of the exogenous signaling molecule C4-HSL reduced the relative abundance of filamentous bacteria in the reactor, enhanced the degradation ability of pollutants, and the abundances of related functional genera also increased significantly.

[0097] 1.2 Analysis results of microorganisms at the genus level

[0098] To reveal the change characteristics of the community structure during the process of filamentous bulking, further analysis was carried out at the genus level. The results are as Figure 2 shown, where the relative abundances of microorganisms in each genus are arranged from left to right in the order of R0, R1, R2, and R3. From the sequencing results, the microorganisms in the activated sludge system at the genus level are mainly CandidatusMicrothrix, Trichococcus, norank_f__Saprospiraceae, Tetrasphaera, norank_f__norank_o__Saccharimonadales, etc.

[0099] The relative abundances of Candidatus Microthrix in R0, R1, R2, and R3 were 23.37%, 6.78%, 7.64%, and 8.02% respectively. The relative abundances of Candidatus Microthrix in the activated sludge systems with exogenous signal molecule addition decreased. The relative abundance of Candidatus Microthrix in the activated sludge system of R1 was the lowest, decreasing by 45.20% compared to R0. Candidatus Microthrix belongs to Actinobacteriota. Candidatus Microthrix has a strong reproductive advantage at low temperatures (e.g., ≤12 - 15°C) and is the main genus of bacteria causing activated sludge bulking in cold regions. It can be seen that the addition of exogenous signal molecules (especially C4-HSL) improved the sedimentation performance of the activated sludge and inhibited the occurrence of sludge bulking.

[0100] The relative abundances of Trichococcus in R0, R1, R2, and R3 were 10.67%, 3.28%, 3.33%, and 3.05% respectively. The relative abundances of Trichococcus in R1, R2, and R3 decreased by 69.25%, 68.74%, and 71.36% respectively compared to R0. Trichococcus belongs to Bacillota and is a key genus of bacteria affecting sludge sedimentation performance. The growth of Trichococcus has little correlation with process conditions and is mainly related to the composition of organic matter in the influent. It can cause sludge bulking under low temperature or low dissolved oxygen conditions. It can be seen that the addition of exogenous signal molecules significantly reduced the abundance of Trichococcus in the reactor and inhibited the occurrence of sludge bulking.

[0101] The relative abundances of Tetrasphaera in R0, R1, R2, and R3 were 5.13%, 2.58%, 2.23%, and 2.33% respectively. The addition of exogenous signal molecules significantly reduced the relative abundance of Tetrasphaera in the activated sludge system. Tetrasphaera belongs to Actinobacteriota and is also often present in the activated sludge system, but in small numbers. The filamentous bacteria of this genus can absorb hydrophobic substances such as long-chain fatty acids under aerobic, anoxic, and anaerobic conditions, which gives it an advantageous ecological niche during sludge bulking. It can be seen that the addition of exogenous signal molecules can inhibit sludge bulking and thus improve system performance.

[0102] In summary, it can be seen that under low-temperature conditions, after the exogenous addition of signal molecules, the community structure in the reactor has changed significantly. The relative abundances of the bacterial phyla that cause sludge bulking in the reactor have all changed significantly, and the relative abundances of the vast majority of bacterial phyla show a downward trend, especially in the reactor with exogenous addition of C4-HSL. Therefore, the QS system mediated by C4-HSL has a significant inhibitory effect on sludge bulking.

[0103] 2. Influence results of each group of experiments on the physicochemical properties of the activated sludge system

[0104] 2.1 Influence results of sedimentation performance

[0105] The sludge volume index (SVI) is an index to measure the sedimentation performance of activated sludge. When SVI > 250 mL / g, it is in the stage of malignant bulking (SFB); when 150 mL / g < SVI < 250 mL / g, it is in the stage of slight bulking (LFB); and when SVI < 150 mL / g, it is in the non-bulking stage (NFB).

[0106] After 42 cycles of cultivation in R1, R2, and R3, the percentage reduction of the SVI value in the reactor was 38.19%, 30.90%, and 33.68% respectively. It can be seen that the percentage reduction of the SVI value in R1 is better than that in R2 and R3. The QS system mediated by C4-HSL has a more significant inhibitory effect on sludge bulking.

[0107] After 50 cycles of cultivation, the final SVI values of the three reactors were 148 mL / g, 187 mL / g, and 181 mL / g in sequence.

[0108] 2.2 Influence results of EPS composition

[0109] Extracellular polymeric substances (EPS) are complex macromolecular polymers secreted by microorganisms, and they also originate from microbial excretion, cell lysis, and adsorption of components in wastewater. Polysaccharides (PS) and proteins (PN) are the main components of EPS. PS is the sludge floc and plays an important role in the formation of sludge flocs. PN promotes the aggregation of flocs and the formation of granular sludge to maintain the stability of flocs. Some studies have found that filamentous bulking leads to changes in the content and composition of EPS in sludge.

[0110] The composition and structural changes of EPS in reactors R1, R2, and R3 were measured at 42 cycles, and the results are as Figure 3 shown. Each group of data is arranged in sequence from left to right in the order of R1, R2, and R3.

[0111] Analyzing from the composition of EPS, in terms of the contents of PN and PS, the contents of S-EPS (soluble EPS), LB-EPS (loosely bound EPS), TB-EPS (tightly bound EPS) and T-EPS (total EPS) in R1 are all higher than those in R2 and R3. The contents of total PN and total PS in R1 are 30.05 mg / g·MLVSS and 10.82 mg / g·MLVSS respectively. The content of total PN is increased by 32.53% and 34.55% compared with R2 and R3 in turn, and the content of total PS is increased by 22.19% and 38.52% compared with R2 and R3 in turn. Research shows that EPS is a substance that can help microorganisms cope with external environmental changes, such as assisting microorganisms to resist low temperature; the increase of PN and PS is beneficial to the aggregation and adhesion of microorganisms and is conducive to improving the stability of sludge flocs. It can be seen that the exogenous addition of C4-HSL increases the protein content in the sludge-phase EPS, which is beneficial to promoting microorganisms to secrete more EPS to resist the low-temperature environment and helps the generation of sludge flocs, improving the activity of activated sludge.

[0112] Analyzing from the structure of EPS, when microorganisms secrete polymers, TB-EPS is formed first and tightly adheres to the cells. Then TB-EPS gradually evolves into LB-EPS with a relatively loose structure, and finally LB-EPS will transform into S-EPS. Therefore, the content of TB-EPS is the highest, accounting for about 90%; the content of S-EPS is the lowest; the content of LB-EPS is between the two. Although the contents of LB-EPS and S-EPS are relatively small compared with TB-EPS, they also play an important role in the performance of the system. TB-EPS adheres to the cell surface through strong interactions, affecting the aggregation state of cells; LB-EPS connects microbial flocs with the external area, affecting the flocculation and sedimentation of activated sludge; S-EPS is a soluble by-product pool produced by microbial activities (i.e., substrate metabolism and cell lysis) and can be used as a carbon source by microorganisms.

[0113] The content of LB-EPS in R1 is increased by 57.78% and 97.36% compared with R2 and R3 in turn; the content of TB-EPS in R1 is increased by 13.82% and 18.49% compared with R2 and R3 in turn; the content of T-EPS in R1 is increased by 29.63% and 35.58% compared with R2 and R3 in turn. It can be seen that C4-HSL can promote the aggregation of microorganisms, improve the sludge sedimentation performance and biofilm stability, thereby improving the performance of the activated sludge system.

[0114] 2.3. Influence results on microbial activity

[0115] Adenosine triphosphate (ATP) provides energy for cells and participates in various physiological activities within cells. The ATP content of microorganisms is often used to characterize microbial activity, and the effect of signal molecules on microbial activity is evaluated by detecting the ATP level.

[0116] The final ATP levels of the reactors for measuring R0, R1, R2, and R3 are as follows Figure 4 shown.

[0117] The ATP level in R0 is 1037.24 U / g SS. The ATP levels in R1, R2, and R3 are 1533.56 U / g SS, 1081.02 U / g SS, and 1123.96 U / g SS in sequence. The ATPase activities in R1, R2, and R3 are increased by 47.85%, 4.22%, and 8.36% compared with R0. It can be seen that the ATP concentrations in the reactors cultured with exogenous signal molecules have all increased. The exogenous signal molecules have significantly improved the microbial activity in the reactors. In particular, the exogenous C4-HSL has the best effect on improving the ATP level.

[0118] Under low-temperature conditions, the energy synthesis of microorganisms is inhibited, slowing down their metabolic rate of pollutants and accelerating the death of some microorganisms. And the consumption of intracellular ATP is necessary for their metabolism. It can be seen that C4-HSL based on QS can promote the energy synthesis of bacteria, effectively improve the microbial activity, strengthen their growth and reproduction ability and the ability to metabolize pollutants, so as to ensure good nitrification performance of the activated sludge system under low-temperature conditions.

[0119] The embodiments described above are some, but not all, of the embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application claimed, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

Claims

1. A method for reducing filamentous microorganisms in low-temperature expanded sludge, characterized in that Including: Under the low-temperature operation condition of 6-15 °C, add N-butyryl-L-homoserine lactone to the activated sludge system in the sequencing batch reactor, and adopt the sequencing batch activated sludge method for treatment. The activated sludge system contains low-temperature bulking sludge that bulks due to excessive growth of filamentous bacteria under low-temperature conditions.

2. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to claim 1, wherein The low-temperature operation condition is 8 °C.

3. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to claim 1, characterized in that Add the N-butyryl-L-homoserine lactone once per operation cycle; optionally, after adding the N-butyryl-L-homoserine lactone, the initial concentration of the N-butyryl-L-homoserine lactone in the sequencing batch reactor is 40-120 μg / L.

4. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to claim 1, wherein, The sludge volume index of the low-temperature bulking sludge > 150 mL / g.

5. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to claim 4, characterized in that, The sludge volume index of the low-temperature bulking sludge > 250 mL / g.

6. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to any one of claims 1 to 5, characterized in that, In the activated sludge system, the initial content of the low-temperature bulking sludge is 2000-7000 mg / L.

7. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to any one of claims 1 to 5, characterized in that, The number of operation cycles is 40-80; optionally, the number of operation cycles is 50-80.

8. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to claim 7, characterized in that, The sequencing batch reactor operates in an intermittent manner, and each operation cycle includes an influent stage, an aeration stage, a sedimentation stage, a drainage stage, and an idle stage in sequence.

9. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to claim 8, characterized in that, Meet at least one of the following conditions (a1)-(a6): (a1) The duration of each operation cycle is 12 ± 2 h; (a2) The duration of the influent stage is 5-10 min; (a3) The duration of the aeration stage is 10 ± 2 h; (a4) The duration of the sedimentation stage is 1.5 ± 0.5 h; (a5) The duration of the drainage stage is 5-10 min; (a6) The duration of the idle stage is 20 ± 10 min.

10. The method for reducing filamentous microorganisms in low-temperature expanded sludge according to claim 8, characterized in that, In the influent stage, the influent water quality meets at least one of the following conditions (b1)-(b5): (b1) The chemical oxygen demand is 200-500 mg / L; (b2) The ammonia nitrogen content is 20-60 mg / L; (b3) The total phosphorus content is 3-10 mg / L; (b4) The pH value is 7-8; (b5) The temperature is 6-15 °C.

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