Method for strengthening sludge anaerobic degradation of BPA by using intracellular metabolite backflow

Abstract

This application discloses a method for enhancing the anaerobic degradation of BPA in sludge by utilizing the reflux of intracellular metabolites. The method includes: screening and settling excess sludge to obtain concentrated sludge; adding BPA mother liquor to the concentrated sludge to prepare a fermentation substrate; adding the fermentation substrate to an anaerobic fermentation reactor for semi-continuous anaerobic culture; during long-term operation of the reactor, the sludge retention time (SRT) is set to 8 days, and the sludge-water mixture is collected daily, centrifuged, and then concentrated by ultrasonic cell disruption, centrifugal filtration, solid-phase extraction, and nitrogen blowing to obtain a concentrated solution of intracellular metabolites; finally, the concentrated solution of intracellular metabolites is refluxed back to the anaerobic fermentation reactor to achieve enhanced anaerobic degradation of BPA in sludge through the reflux of intracellular metabolites. This method is simple, cost-controllable, and easily scaled up for engineering applications, enabling synergistic optimization of the reduction and resource utilization of new phenolic pollutants such as BPA in the sludge treatment process.

Description

Technical Field

[0001] This application relates to a method for enhancing the anaerobic degradation of BPA in sludge by reflux of intracellular metabolites, belonging to the field of solid waste resource utilization and environmental protection technology. Background Technology

[0002] Bisphenol A (BPA) is a typical endocrine disruptor widely used in plastic products, epoxy resins, and other fine chemicals. During production, use, and disposal, BPA enters urban wastewater systems through drainage networks and accumulates highly in sludge, posing potential ecological risks to sludge treatment and disposal. Therefore, achieving efficient BPA removal in sludge treatment is of great significance for the control of new pollutants.

[0003] Anaerobic acidification has become an important approach to sludge treatment due to its advantages such as low carbon footprint, low energy consumption, and recyclable energy. However, if anaerobic acidification of sludge cannot effectively remove BPA, it will enter the environment through subsequent disposal processes such as sludge dewatering filtrate, land application, and ecological restoration, posing serious ecological and health risks. Currently, the degradation of BPA during anaerobic acidification of sludge still faces limitations such as low degradation efficiency and easy generation of toxic byproducts. Conventional enhancement methods, such as adjusting operating parameters or adding external carbon sources, functional materials, and biological agents, generally suffer from technical bottlenecks such as high cost and poor operational stability.

[0004] Therefore, there is an urgent need to develop a low-cost, easy-to-operate, and engineering-replicable enhancement method that can achieve in-situ efficient degradation of BPA during anaerobic acid production in sludge, while also taking into account the synergistic optimization of this resource utilization process of sludge acid production. Summary of the Invention

[0005] The purpose of this invention is to address the generally low degradation rate of BPA in existing anaerobic acidification systems for sludge, and the problems of high cost and poor operational stability associated with conventional enhancement methods. This invention provides a method for enhancing the anaerobic degradation of BPA by reflux of intracellular metabolites.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] This application provides a method for enhancing the anaerobic degradation of BPA in sludge by reflux of intracellular metabolites, comprising the following steps: Step 1): The remaining sludge is screened and allowed to settle, the supernatant is discarded, and the remaining sludge after sedimentation and concentration is obtained. Step 2): Add BPA mother liquor to the remaining sludge after sedimentation and concentration, mix well, and obtain fermentation substrate for later use; Step 3): Add the fermentation substrate to the anaerobic fermentation acid-producing reactor, inoculate with the domesticated acid-producing bacteria solution, mix evenly, and adjust the pH to alkaline. Step 4): Inert gas is introduced into the reactor for constant-temperature anaerobic fermentation. During the fermentation process, the sludge retention time (SRT) is set to 4-10 days. According to the set SRT time, a portion of the sludge-water mixture is discharged daily as recirculated material to be treated. It is centrifuged, the supernatant is discarded, and the bottom sludge phase is collected. The bottom sludge phase is subjected to ultrasonic cell disruption, solid-phase extraction, and concentration to obtain a concentrated intracellular metabolite solution. The concentrated intracellular metabolite solution is returned to the reactor, and fresh substrate containing BPA is added at the same time to keep the volume of the fermentation mixture in the reactor constant during operation. Furthermore, in step 1), the remaining sludge is screened using a sieve with a aperture of 2 mm × 2 mm, and the concentration of the remaining sludge after sedimentation and concentration is 20-30 g TS / L.

[0008] Furthermore, the fermentation substrate in step 2) contains an initial concentration of BPA of 10-30 mg / L.

[0009] Furthermore, in step 3), the volume ratio of the fermentation substrate to the acid-producing bacterial solution is 9:1, and the pH is adjusted to 9-11.

[0010] Further, in step 3), the acclimated acid-producing bacteria solution uses wastewater treatment plant sludge as the initial seed sludge and glucose-infused water as the substrate (initial glucose concentration 5 g / L), and is acclimated for a long period under anaerobic conditions with suitable pH (9-11) and temperature (36-38℃). During the acclimation period, glucose substrate is added to the system every 4 days to restore the glucose concentration to the initial concentration (5 g / L) to maintain the continuous enrichment of the acid-producing bacteria community. The 4-day feeding cycle is chosen because acid-producing bacteria can usually consume glucose and maximize VFA production within 4 days. Finally, after 28-32 days of acclimation, the system gradually forms a sludge community of mixed acid-producing bacteria, mainly composed of hydrolytic acid-producing bacteria, capable of stably producing VFAs.

[0011] Furthermore, in step 4), the constant temperature anaerobic fermentation is carried out by placing the reactor in a constant temperature air shaker for fermentation, with the fermentation temperature being 35-40℃ and the shaker speed being 100-200 rpm.

[0012] Furthermore, in step 4), the sludge retention time (SRT) is 8 days during the long-term fermentation process.

[0013] Furthermore, in step 4), the volume of the mud-water mixture discharged daily is 12.5% ​​of the original fermentation substrate volume, i.e., 1 / 8.

[0014] Further, in step 4), the centrifugation conditions are: centrifugation at 3000-4000 g for 5-10 min at 4℃; the frequency of the ultrasonic cell disruption treatment is 20-24 kH, the sample temperature is controlled at 0-10℃ during the treatment, and the treatment time is 5-20 min.

[0015] Furthermore, in step 4), after the ultrasonic cell disruption treatment is completed, the sample is further subjected to centrifugation and microporous membrane filtration to obtain a crude extract of intracellular metabolites.

[0016] Furthermore, during the fermentation process, the residual concentration of BPA and the yield of volatile fatty acids (VFAs) in the anaerobic acid-producing system need to be measured periodically.

[0017] Further, the specific steps of the solid-phase extraction are as follows: using a solid-phase extraction column (6 mL), first activate the column with 10 column volumes (60 mL) of methanol, then rinse with 3 column volumes of acidified ultrapure water (pH=3); add 50 mL of sample (TOC concentration of 6 mg / L) and let it flow slowly through the extraction column; rinse the extraction column with 3 column volumes (18 mL) of acidified ultrapure water to remove impurities; and slowly dry the extraction column with nitrogen gas.

[0018] Furthermore, after the crude extract of intracellular metabolites is adsorbed by a solid-phase extraction column, 6 mL of methanol is added to elute the target analyte, and the extract is concentrated by nitrogen blowing to obtain a 1 mL volume of concentrated intracellular metabolites.

[0019] Furthermore, 1 mL of the concentrate was refluxed into the anaerobic acid-producing reactor, while 49 mL of fresh substrate containing BPA was added to bring the total feed volume to 50 mL, thereby maintaining the reactor SRT at 8 days.

[0020] This application addresses the generally low degradation rate of BPA in existing sludge anaerobic acidification systems, and the problems of high cost and poor operational stability associated with conventional enhancement methods. During the continuous operation of the original sludge anaerobic reactor, the enhancement effect of intracellular metabolite recirculation from the sludge-water mixture at different sludge retention times (SRT) on BPA degradation and VFA accumulation was compared. It was determined that an SRT of 8 days resulted in the optimal enhancement effect of intracellular metabolite recirculation on BPA degradation. The intracellular metabolites released after cell lysis in the bottom sludge at this stage were then recirculated back into the original anaerobic reactor, thereby enhancing the BPA degradation process and regulating VFA accumulation. Compared with traditional methods for improving BPA degradation efficiency in sludge anaerobic acidification, this method is lower in cost, easier to operate, and more easily replicable in engineering.

[0021] Compared with the prior art, the beneficial effects of this application are as follows: (1) In this application, the intracellular metabolites obtained after cell destruction of bottom sediment are returned to the original anaerobic reactor, making full use of the functional metabolic components generated by the system itself. There is no need to add complex chemical reagents, functional materials or exogenous bacterial agents. The process is simple and the cost is controllable. (2) This application can enhance the degradation effect of sludge anaerobic system on BPA and simultaneously promote the accumulation of acetic acid and total volatile fatty acids, which is conducive to the synergistic regulation of new pollutant removal and anaerobic acid production process. (3) This application can be applied to the existing sludge anaerobic reactor operation system. The operation process is clear and easy to operate continuously and scale up in engineering. Attached Figure Description

[0022] Figure 1 This is a flow chart of the intracellular metabolite reflux reaction process.

[0023] Figure 2 The study presents the BPA and degradation, as well as VFA accumulation, in a sludge anaerobic reactor under different operating conditions. Specifically, (a) shows the BPA content and removal rate after the reactor stabilizes under different pH conditions; (b) shows the VFA content under different pH conditions; (c) shows the BPA content and removal rate after the reactor stabilizes under different SRTs; (d) shows the VFA content under different SRTs; (e) shows the BPA content and removal rate after the reactor stabilizes under different reflux ratios for intracellular metabolites; (f) shows the VFA content under different reflux ratios for intracellular metabolites; (g) shows the BPA content and removal rate after the reactor stabilizes under different enhancement methods; and (h) shows the VFA content under different enhancement methods. Detailed Implementation

[0024] To make the technical solution of this application clearer and easier to understand, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0025] In the following examples and comparative examples, the residual sludge was taken from the secondary sedimentation tank sludge of a wastewater treatment plant in Songjiang District, Shanghai, and the BPA was commercially available analytical grade. Unless otherwise specified, all other materials and reagents used can be obtained commercially.

[0026] Example 1 A method for enhancing BPA degradation during anaerobic acidification of sludge by reflux of intracellular metabolites, the process flow is as follows: Figure 1 As shown, this embodiment investigated the effects of BPA degradation and acid production during the anaerobic acid production of sludge enhanced by the recirculation of intracellular metabolites under different pH conditions (pH=3, 7, 10). The specific steps were as follows: 1. Take the excess sludge from the secondary sedimentation tank of the sewage treatment plant and sieve it through a 2 mm × 2 mm sieve to remove large particulate impurities; let the sieved sludge stand for sedimentation for 24 h, discard the supernatant, and obtain concentrated sludge with a concentration of 27.5 g TS / L for later use.

[0027] 2. Add BPA mother liquor to the obtained concentrated sludge and mix thoroughly. Adjust the initial concentration of BPA in the system to 20 mg / L to obtain the fermentation substrate, and store it at 4℃ for later use.

[0028] 3. Add 360 mL of fermentation substrate and 40 mL of long-term acclimatized acid-producing bacteria inoculum (substrate to inoculum volume ratio of 9:1) to the anaerobic fermentation acid-producing reactor, mix thoroughly, and bring the total volume of the fermentation liquid to 400 mL. The acid-producing bacteria inoculum was prepared using residual sludge from a wastewater treatment plant in Shanghai as the initial seed sludge. Under anaerobic conditions, pH=10, and a temperature of 37℃, glucose aqueous solution was used as the fermentation substrate (initial glucose concentration 5 g / L) (substrate to initial seed sludge volume ratio of 9:1, initial total reaction system volume 400 mL). During the acclimatization period, glucose substrate was added to the system every 4 days to restore the glucose concentration to the initial concentration (5 g / L) to maintain the continuous enrichment of the acid-producing bacteria community. After 7 cycles (28 days) of acclimatization, the system gradually formed a mixed bacterial sludge community dominated by hydrolytic acid-producing bacteria, capable of stably producing VFAs (volatile fatty acids).

[0029] 4. Nitrogen gas is introduced into the reactor to remove dissolved oxygen and gaseous oxygen, and an anaerobic environment is established. The reactor is then sealed and placed in a constant temperature air shaker for long-term fermentation at a temperature of 37°C and a rotation speed of 150 rpm. The fermentation pH is set to pH=3, pH=7, and pH=10 respectively.

[0030] V. During the long-term operation of the reactor, the sludge retention time (SRT) is set to 8 days. 50 mL of fermentation sludge-water mixture is discharged daily and collected into centrifuge tubes. After centrifugation at 4℃ and 3500 g for 6 min, the supernatant is discarded to obtain the centrifuged bottom sludge.

[0031] 6. Add ultrapure water to the sediment for resuspension and wash three times to remove extracellular organic matter and impurities. Finally, resuspend in ultrapure water to a total volume of 10 mL to obtain a sediment resuspension. Sonicate the sediment resuspension at 20 kHz for 5 min under ice bath conditions to fully disperse the sediment clumps and form a homogeneous suspension. Then, continue sonicating at 20 kHz for 10 min under ice bath conditions to break down cells and release intracellular metabolites to obtain a crude extract of intracellular metabolites.

[0032] 7. After cell disruption, the sample was centrifuged at 14,000 rpm for 20 min. The supernatant was collected and filtered through a 0.22 μm microporous membrane. Solid-phase extraction was then performed: a 6 mL solid-phase extraction column was activated and rinsed with 10 column volumes (60 mL) of methanol and 3 column volumes of acidified ultrapure water (pH=3). 50 mL of crude extract (TOC concentration of 6 mg / L) was added and allowed to flow slowly through the extraction column. The column was then rinsed with 3 column volumes (18 mL) of acidified ultrapure water to remove impurities and slowly dried with nitrogen. Finally, 6 mL of methanol was added to elute the extracted sample. The eluent was collected and concentrated with nitrogen to obtain 1 mL of intracellular metabolite concentrate.

[0033] 8. Return 1 mL of intracellular metabolite concentrate to the anaerobic BPA degradation reactor, and simultaneously add 49 mL of fresh sludge substrate containing BPA, so that the total volume of the return concentrate and fresh substrate entering the reactor each day is equal to the volume of the sludge-water mixture discharged that day (i.e., 50 mL).

[0034] 9. Continue anaerobic cultivation under the same operating conditions, and measure the BPA concentration and VFA yield in the system to compare the differences in sludge anaerobic degradation efficiency of BPA and VFA yield under different pH conditions.

[0035] In this embodiment, the BPA removal rate and volatile fatty acid (VFA) content in the system obtained under different pH conditions are shown in the table below:

[0036] As shown in the table above, different pH conditions have a significant impact on the degradation of BPA and the accumulation of volatile fatty acids (VFAs) in the system. Compared with pH=3 and pH=7, the system showed the lowest BPA content (8.92 mg / L) and the highest VFA content (6308.74 mg COD / L) at pH=10. This indicates that under alkaline conditions, the BPA degradation effect is better, and the accumulation of volatile fatty acids is more favorable. Example 2 A method for enhancing the anaerobic degradation of BPA in sludge by recirculating intracellular metabolites was proposed. This embodiment investigated the effects of intracellular metabolite recirculation on BPA degradation and acid production during anaerobic acid production of sludge under different SRT conditions at pH=10. The specific steps are as follows: 1. Take the excess sludge from the secondary sedimentation tank of the sewage treatment plant and sieve it through a 2 mm × 2 mm sieve to remove large particulate impurities; let the sieved sludge stand for sedimentation for 24 h, discard the supernatant, and obtain concentrated sludge with a concentration of 27.5 g TS / L for later use.

[0037] 2. Add BPA mother liquor to the obtained concentrated sludge and mix thoroughly. Adjust the initial concentration of BPA in the system to 20 mg / L to obtain the fermentation substrate, and store it at 4℃ for later use.

[0038] 3. Four parallel anaerobic acid-producing reactors with a fermentation pH of 10 were set up. 360 mL of fermentation substrate and 40 mL of long-term acclimatized acid-producing bacteria inoculum (substrate to inoculum volume ratio of 9:1) were added to the anaerobic fermentation reactors and mixed thoroughly to bring the total fermentation volume to 400 mL. The acid-producing bacteria inoculum was initially sludge from a wastewater treatment plant in Shanghai. Under anaerobic conditions, pH 10, and a temperature of 37℃, glucose aqueous solution was used as the fermentation substrate (initial glucose concentration 5 g / L) (substrate to initial inoculum volume ratio of 9:1, initial total reaction system volume 400 mL). During the acclimatization period, glucose substrate was added to the system every 4 days to restore the glucose concentration to the initial concentration (5 g / L) to maintain the continuous enrichment of the acid-producing bacteria community. After 7 cycles (28 days) of acclimatization, the system gradually formed a mixed bacterial community sludge dominated by hydrolytic acid-producing bacteria, capable of stably producing VFAs.

[0039] 4. Nitrogen gas is introduced into the reactor to remove dissolved oxygen and gaseous oxygen, thus establishing an anaerobic environment. The reactor is then sealed and placed in a constant-temperature air shaker for long-term fermentation at a temperature of 37°C and a rotation speed of 150 rpm.

[0040] V. During the long-term operation of the reactors, the sludge retention time (SRT) of each reactor is set to 4 days, 8 days, 10 days and 16 days, respectively, and 100 mL, 50 mL, 40 mL and 25 mL of fermentation sludge-water mixture are discharged and collected daily.

[0041] 6. Transfer the extracted mud-water mixture into centrifuge tubes and centrifuge at 3500 g for 6 min at 4℃. Discard the supernatant to obtain the centrifuged bottom mud.

[0042] 7. Add ultrapure water to the sediment for resuspension and wash three times to remove extracellular organic matter and impurities. Finally, resuspend in ultrapure water to a total volume of 10 mL to obtain a sediment resuspension. Sonicate the sediment resuspension at 20 kHz for 5 min under ice bath conditions to fully disperse the sediment clumps and form a homogeneous suspension. Then, continue sonicating at 20 kHz for 10 min under ice bath conditions to break down cells and release intracellular metabolites to obtain a crude extract of intracellular metabolites.

[0043] 8. After cell disruption, the sample was centrifuged at 14,000 rpm for 20 min. The supernatant was collected and filtered through a 0.22 μm microporous membrane. Solid-phase extraction was then performed: a 6 mL solid-phase extraction column was activated and rinsed with 10 column volumes (60 mL) of methanol and 3 column volumes of acidified ultrapure water (pH=3). 50 mL of crude extract (TOC concentration of 6 mg / L) was added and allowed to flow slowly through the extraction column. The column was then rinsed with 3 column volumes (18 mL) of acidified ultrapure water to remove impurities and slowly dried with nitrogen. Finally, 6 mL of methanol was added to elute the extracted sample. The eluent was collected and concentrated with nitrogen to obtain 1 mL of intracellular metabolite concentrate.

[0044] 9. Reflux 1 mL of intracellular metabolite concentrate into the anaerobic BPA degradation reactor, and simultaneously add 99 mL, 49 mL, 39 mL, and 24 mL of fresh sludge substrate containing BPA, respectively, so that the total volume of the reflux concentrate and fresh substrate entering the reactor on the last day of each cycle is equal to the volume of the sludge-water mixture discharged on that day.

[0045] 10. Continue anaerobic cultivation under the same operating conditions, and measure the BPA concentration and VFAs yield in the system to compare the differences in sludge anaerobic degradation efficiency of BPA and VFAs yield under different SRT conditions.

[0046] In this embodiment, the BPA removal rate and VFA content in the system under different SRT conditions are shown in the table below:

[0047] As shown in the table above, different SRTs significantly affected the degradation of BPA and the accumulation of volatile fatty acids (VFAs) in the system. Specifically, at an SRT of 8 days, the residual BPA concentration was the lowest, at only 8.92 mg / L, while the VFA content was the highest, reaching 6308.7355 mg / L. This indicates that an SRT of 8 days is the optimal sludge retention time, and the corresponding intracellular metabolites showed the best promoting effect on BPA degradation and VFA accumulation. In contrast, the enhancing effects of SRTs of 4 days and 16 days were weaker.

[0048] Example 3 A method for enhancing the anaerobic degradation of BPA in sludge by utilizing the reflux of intracellular metabolites is presented in this embodiment. The BPA degradation effect was investigated under different reflux ratios (0%, 20%, 40%, 60%, 80%, 100%), and was carried out according to the following steps: 1. Take the excess sludge from the secondary sedimentation tank of the sewage treatment plant and sieve it through a 2 mm × 2 mm sieve to remove large particulate impurities; let the sieved sludge stand for sedimentation for 24 h, discard the supernatant, and obtain concentrated sludge with a concentration of 27.5 g TS / L for later use.

[0049] 2. Add BPA mother liquor to the obtained concentrated sludge and mix thoroughly. Adjust the initial concentration of BPA in the system to 20 mg / L to obtain the fermentation substrate, and store it at 4℃ for later use.

[0050] 3. Six parallel anaerobic acid-producing reactors with a fermentation pH of 10 were set up. 360 mL of fermentation substrate and 40 mL of long-term acclimatized acid-producing bacteria inoculum (substrate to inoculum volume ratio of 9:1) were added to the anaerobic fermentation reactors and mixed thoroughly to bring the total fermentation volume to 400 mL. The acid-producing bacteria inoculum was prepared using residual sludge from a wastewater treatment plant in Shanghai as the initial seed sludge. Under anaerobic conditions, pH 10, and a temperature of 37℃, glucose aqueous solution was used as the fermentation substrate (initial glucose concentration 5 g / L) (substrate to initial seed sludge volume ratio of 9:1, initial total reaction system volume 400 mL). During the acclimatization period, glucose substrate was added to the system every 4 days to restore the glucose concentration to the initial concentration (5 g / L) to maintain the continuous enrichment of the acid-producing bacteria community. After 7 cycles (28 days) of acclimatization, the system gradually formed a mixed bacterial community sludge dominated by hydrolytic acid-producing bacteria, capable of stably producing VFAs.

[0051] 4. Nitrogen gas is introduced into the reactor to remove dissolved oxygen and gaseous oxygen, thus establishing an anaerobic environment. The reactor is then sealed and placed in a constant-temperature air shaker for long-term fermentation at a temperature of 37°C and a rotation speed of 150 rpm.

[0052] V. During the long-term operation of the reactor, the sludge retention time (SRT) is set to 8 days. 50 mL of fermentation sludge-water mixture is discharged and collected daily, placed in centrifuge tubes, and centrifuged at 4℃ and 3500 g for 6 min. The supernatant is then discarded to obtain the centrifuged bottom sludge.

[0053] 7. Add ultrapure water to the sediment for resuspension and wash three times to remove extracellular organic matter and impurities. Finally, resuspend in ultrapure water to a total volume of 10 mL to obtain a sediment resuspension. Sonicate the sediment resuspension at 20 kHz for 5 min under ice bath conditions to fully disperse the sediment clumps and form a homogeneous suspension. Then, continue sonicating at 20 kHz for 10 min under ice bath conditions to break down cells and release intracellular metabolites to obtain a crude extract of intracellular metabolites.

[0054] 8. After cell disruption, the sample was centrifuged at 14,000 rpm for 20 min. The supernatant was collected and filtered through a microporous membrane with a pore size of 0.22 μm. Solid-phase extraction was then performed: a 6 mL solid-phase extraction column was activated and rinsed with 10 column volumes (60 mL) of methanol and 3 column volumes of acidified ultrapure water (pH=3). 50 mL of crude extract sample (TOC concentration of 6 mg / L) was added and allowed to flow slowly through the extraction column. The extraction column was then rinsed with 3 column volumes (18 mL) of acidified ultrapure water to remove impurities and then slowly dried with nitrogen.

[0055] 9. After adsorption by solid-phase extraction, 6 mL of methanol was added to elute the extracted sample. The eluent was collected and concentrated by nitrogen blowing to obtain 1 mL of intracellular metabolite concentrate.

[0056] 10. The obtained intracellular metabolite concentrate was refluxed back into the original anaerobic fermentation acid-producing reactor at concentrations of 0% (no reflux), 20% (0.2 mL), 40% (0.4 mL), 60% (0.6 mL), 80% (0.8 mL), and 100% (1 mL), respectively. At the same time, fresh substrate containing BPA was added to ensure that the total volume of the reflux concentrate and fresh substrate entering the reactor on the 8th day of each cycle was equal to the volume of the mud-water mixture discharged on that day.

[0057] 11. Continue anaerobic cultivation under the same operating conditions, and measure the BPA concentration and VFA content in the system to compare the differences in BPA degradation efficiency and VFA production under different pH conditions.

[0058] In this embodiment, the BPA removal rate and VFA content in the system obtained under different reflux ratios are shown in the following table:

[0059] As shown in the table above, different reflux ratios have a significant impact on BPA degradation and volatile fatty acid (VFA) accumulation in the system. With increasing reflux ratio, the BPA content in the system generally decreases, while the VFA content generally increases. Specifically, the system with the lowest BPA content (8.92 mg / L) and the highest VFA content (6308.7355 mg / L) was observed under a 100% reflux ratio, indicating that a higher reflux ratio is more conducive to enhancing BPA degradation and VFA accumulation in the system.

[0060] Comparative Example 1 This comparative study investigated the effects of adding acetophilic bacteria on BPA degradation and acid production in an anaerobic sludge system without refluxing intracellular metabolites, in order to compare it with the intracellular metabolite refluxing enhancement method described in this application.

[0061] 1. Take the excess sludge from the secondary sedimentation tank of the sewage treatment plant and sieve it through a 2 mm × 2 mm sieve to remove large particulate impurities; let the sieved sludge stand for sedimentation for 24 h, discard the supernatant, and obtain concentrated sludge with a concentration of 27.5 g TS / L for later use.

[0062] 2. Add BPA mother liquor to the obtained concentrated sludge and mix thoroughly. Adjust the initial concentration of BPA in the system to 20 mg / L to obtain the fermentation substrate, and store it at 4℃ for later use.

[0063] 3. Add 360 mL of fermentation substrate and 40 mL of long-term acclimatized acid-producing bacteria inoculum (substrate to inoculum volume ratio of 9:1) to the anaerobic fermentation acid-producing reactor, mix thoroughly, and bring the total volume of the fermentation broth to 400 mL. The acid-producing bacteria inoculum was prepared using residual sludge from a wastewater treatment plant in Shanghai as the initial seed sludge. Under anaerobic conditions, pH=10, and a temperature of 37℃, glucose aqueous solution was used as the fermentation substrate (initial glucose concentration 5 g / L) (substrate to initial seed sludge volume ratio of 9:1, initial total reaction system volume 400 mL). During the acclimatization period, glucose substrate was added to the system every 4 days to restore the glucose concentration to the initial concentration (5 g / L) to maintain the continuous enrichment of the acid-producing bacteria community. After 7 cycles (28 days) of acclimatization, the system gradually formed a mixed bacterial community sludge dominated by hydrolytic acid-producing bacteria, capable of stably producing VFAs.

[0064] 4. Nitrogen gas is introduced into the reactor to remove dissolved oxygen and gaseous oxygen, thus establishing an anaerobic environment. The reactor is then sealed and placed in a constant-temperature air shaker for long-term fermentation at a temperature of 37°C and a rotation speed of 150 rpm.

[0065] V. During the long-term operation of the reactor, the sludge retention time (SRT) is set to 8 days. 50 mL of fermentation sludge-water mixture is discharged daily, and 49 mL of fresh substrate containing BPA and 1 mL of acetic acid-producing proteinophilic bacteria at a concentration of 109 CFU / mL are added simultaneously.

[0066] 7. Continue anaerobic cultivation under the same operating conditions, and measure the BPA concentration and VFAs yield in the system to compare the differences in sludge anaerobic degradation efficiency of BPA and VFAs yield under different pH conditions.

[0067] In this comparative example, the BPA removal rate and VFA content in the system obtained under the condition of adding acetic acid-producing proteinophiles and not refluxing intracellular metabolites are shown in the table below:

[0068] The results of the above examples and comparative experiments clearly show that, during reactor operation, using BPA removal efficiency and VFA accumulation levels as evaluation criteria, the intracellular metabolites obtained at different SRTs (4, 8, 10, and 16 days) were compared. It was determined that recirculating the intracellular metabolites obtained every 8 days resulted in the best enhancement effect. Recirculating the intracellular metabolites released after cell disruption in the sediment at this stage back to the original anaerobic reactor significantly enhanced the system's BPA degradation and promoted VFA accumulation. Different pH conditions significantly affected BPA degradation and VFA accumulation in the system, with alkaline conditions being more conducive to BPA removal and VFA formation. Different recirculation ratios also significantly affected the enhancement effect, with higher recirculation ratios being more beneficial for improving BPA degradation and promoting VFA accumulation. Compared with methods such as not recirculating metabolites or adding exogenous proteophilic lactic acid-producing bacteria combined with intermittent pH adjustment, the intracellular metabolite recirculation enhancement method described in this application is more effective in promoting BPA removal and VFA accumulation. This application demonstrates that it can fully utilize the functional endogenous metabolic components generated by the sludge anaerobic system itself, and effectively enhance the BPA degradation process without the need for additional complex functional materials or large amounts of exogenous enhancers. Moreover, the process is simple, easy to operate, and has high potential for engineering applications.

[0069] The above description is merely a preferred embodiment of this application and is not intended to limit this application in any form or substance. It should be noted that those skilled in the art can make several improvements and additions without departing from this application, and these improvements and additions should also be considered within the scope of protection of this application.

Claims

1. A method for enhancing anaerobic degradation of BPA in sludge by intracellular metabolite backflow, characterized in that, Includes the following steps: Step 1): The remaining sludge is screened and allowed to settle, the supernatant is discarded, and the remaining sludge after sedimentation and concentration is obtained. Step 2): Add BPA mother liquor to the remaining sludge after sedimentation and concentration, mix well, and obtain fermentation substrate for later use; Step 3): Add the fermentation substrate to the anaerobic fermentation acid-producing reactor, inoculate with the domesticated acid-producing bacteria solution, mix evenly, and adjust the pH to alkaline. Step 4): Inert gas is introduced into the reactor for constant-temperature anaerobic fermentation. During the fermentation process, the sludge retention time (SRT) is set to 4-10 days. According to the set SRT time, a portion of the sludge-water mixture is discharged daily as recirculated material to be treated. It is centrifuged, the supernatant is discarded, and the bottom sludge phase is collected. The bottom sludge phase is subjected to ultrasonic cell disruption, solid-phase extraction, and concentration to obtain a concentrated intracellular metabolite solution. The concentrated intracellular metabolite solution is returned to the reactor, and fresh fermentation substrate containing BPA is added at the same time to keep the volume of the fermentation mixture in the reactor constant during operation.

2. The method of claim 1, wherein, In step 1), the remaining sludge is screened using a sieve with a aperture of 2 mm × 2 mm, and the concentration of the remaining sludge after sedimentation and concentration is 20-30 g TS / L.

3. The method of claim 1, wherein, The fermentation substrate in step 2) contains an initial concentration of BPA of 10-30 mg / L.

4. The method of claim 1, wherein, In step 3), the volume ratio of the fermentation substrate to the acid-producing bacteria liquid is 9:1, and the pH is adjusted to 9-11.

5. The method of claim 1, wherein, In step 3), the acid-producing bacteria liquid that has been domesticated and cultured is a mixed bacterial sludge obtained by using the residual sludge of the sewage treatment plant as the initial seed sludge and periodically adding glucose substrate under anaerobic and alkaline conditions.

6. The method of claim 1, wherein, In step 4), the constant temperature anaerobic fermentation is carried out by placing the reactor in a constant temperature air shaker. The fermentation temperature is 35-40℃ and the shaker speed is 100-200 rpm.

7. The method of claim 1, wherein, In step 4), the sludge retention time (SRT) is 8 days during the long-term fermentation process.

8. The method according to claim 7, characterized in that, In step 4), the volume of the mud-water mixture discharged daily is 12.5% ​​of the original fermentation substrate volume.

9. The method of claim 1, wherein, In step 4), the centrifugation conditions are: centrifugation at 3000-4000 g for 5-10 min at 4℃; the frequency of ultrasonic cell disruption is 20-24 kH, the sample temperature is controlled at 0-10℃ during the process, and the processing time is 5-20 min.

10. The method of claim 9, wherein, In step 4), after the ultrasonic cell disruption treatment is completed, the sample is further subjected to centrifugation and microporous membrane filtration to obtain a crude extract of intracellular metabolites.

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