Method for degrading anaerobic digestion sludge siloxane by reinforced alkali ultrasonic pretreatment

Abstract

The application provides a method for degrading anaerobic digestion sludge siloxane by reinforced alkali ultrasonic pretreatment, and belongs to the technical field of water pollution control and environmental chemical degradation mechanism, and the optimal process parameters (including pH, ultrasonic frequency, ultrasonic time, etc.) and the half-life variation of siloxanes with different side chain groups under the conditions of alkali and ultrasonic sludge pretreatment are compared, and the optimal conditions of the composite process are screened by combining the type, structure analysis and key chemical bond cleavage behavior of the degradation products, and the reaction path and degradation efficiency of the target pollutants are systematically inferred. The method firstly applies degradation kinetics and degradation mechanism verification to the pollution control research of siloxane in municipal sewage / sludge, and comprehensively determines the degradation law, reaction activity and deep degradation potential of siloxanes with different structures.

Description

Technical Field

[0001] This invention belongs to the field of water pollution control technology and environmental chemical degradation mechanism technology, specifically involving a method for enhanced alkali addition and ultrasonic pretreatment to degrade siloxanes in anaerobic digested sludge. Background Technology

[0002] Siloxanes, as a typical new type of pollutant, refer to silicone compounds whose main chain is composed of saturated Si-O-Si bonds and whose branches are composed of methyl, phenyl, vinyl, etc. Due to their excellent properties such as low surface tension, high lubricity, electrical insulation, resistance to high and low temperatures, and physiological inertness, siloxanes are widely used in many fields of production and daily life as advanced lubricants, insulating agents, defoamers, cosolvents, and hydraulic oils. Among them, siloxane compounds whose branches are entirely composed of methyl groups are called methylsiloxanes, such as D5. Siloxanes whose branches are partially substituted with phenyl groups are called phenylsiloxanes, such as... Figure 1 P3 is shown.

[0003] Wastewater treatment plants, acting as both a sink and a source of siloxanes, play a significant role in contributing to environmental pollution from methylsiloxanes. Due to their high organic carbon-water partition coefficients (D5-D6: Log Koc = 4.2-5.86, P3-P4: 8.06-10.11) and poor biodegradability, cyclic methylsiloxanes and phenylmethylsiloxanes are primarily adsorbed into sludge in wastewater treatment systems and subsequently disposed of along with the remaining sludge. If effective measures are not taken to remove these remaining siloxanes, their high volatility will lead to their volatilization into biogas during subsequent sludge disposal processes, such as typical biological anaerobic digestion. During biogas utilization, these siloxanes are oxidized into microcrystalline SiO2, which can severely damage engine life. For phenylmethylsiloxanes, there is also the potential for benzene release. Furthermore, microcrystalline SiO2 released into the atmosphere is a typical carcinogen. Therefore, this study aims to address the bottleneck problem of reducing the volatilization of these two types of siloxanes during anaerobic sludge digestion and improving their degradation rate. Previous studies have reported that the degradation of siloxanes is a multi-step process. The low hydrophobicity of siloxanes limits their bioavailability. They can first undergo hydrolysis through the breaking of Si-O bonds, and then form the intermediate product—dimethylsiloxane-α,ω-diol [HO(Me2SiO)]—through ring-opening hydrolysis. n[H, n = 1-5], which is then further hydrolyzed into dimethylsilanediol, which can then be directly biodegraded into the final products SiO2, CO2, and H2O. Therefore, the ring-opening hydrolysis of siloxanes is a key step affecting their degradation. Literature reports that alkaline conditions in water can significantly promote the hydrolysis of siloxanes. On the other hand, ultrasound can generate cavitation bubbles, and the shock waves generated by their breakage produce strong mechanical shear forces, which may break the Si-C bonds on the macromolecular chains, thereby degrading siloxanes. At the same time, ultrasonic cavitation can generate abnormally high temperatures (1900-5000 K) and high pressures (50 MPa), and the extreme physical environment can also promote the breakdown of macromolecules into smaller molecules. According to the mechanism of ultrasound-induced free radicals, cavitation bubbles under the high-frequency action of ultrasound can also generate some free radicals such as ·OH and HO2·, and strong oxidizing free radicals can further degrade siloxanes. Because siloxanes are highly hydrophobic, this study proposes to use ultrasonic alkaline pretreatment technology to promote the release of these pollutants from the organic phase of sludge and achieve better hydrolysis. This involves adding alkali and using ultrasound to disrupt the EPS and even the cell structure of the sludge, releasing more DOM and maximizing the dissolution of adsorbed siloxanes. Then, alkaline catalysis is used to hydrolyze the siloxanes, and ultrasonic energy and strong oxidative free radicals are used to break down Si-C, achieving maximum degradation of siloxanes in the sludge. This allows the siloxanes to be utilized by microorganisms during the subsequent anaerobic digestion of the sludge, promoting ring-opening, hydrolysis, and oxidative transformation of siloxanes and improving their further degradation.

[0004] Surface response methodology (SRM), as an efficient experimental design and optimization tool, can establish mathematical models among multiple process variables and determine optimal operating conditions through optimization algorithms. Therefore, this study used SRM to screen for the optimal process conditions for siloxanes in the alkali-ultrasonic combined pretreatment process, maximizing the degradation rate of these pollutants in sludge and making their degradation products more readily available for utilization by microorganisms in the subsequent anaerobic digestion of sludge. Finally, under optimal conditions, a non-target screening technique was used to comprehensively screen the degradation products of both types of organosilicones, inferring their degradation pathways and revealing their degradation mechanisms in this pretreatment combined process. This provides theoretical and technical support for reducing the economic cost of siloxane removal from biogas and also provides a scientific basis for sludge reuse. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a method for enhancing the degradation of siloxanes in anaerobic digested sludge through enhanced alkali addition and ultrasonic pretreatment. The optimal conditions for the degradation of organosilicon by alkali addition and ultrasonic pretreatment alone are obtained through simulation experiments. Combined with surface response method, the composite process conditions are optimized, providing a new approach and technical solution for the degradation of siloxanes in municipal sewage / sludge.

[0006] To solve the above problems, the present invention adopts the following technical solution: A method for enhancing the degradation of siloxanes in anaerobic digestion sludge through ultrasonic pretreatment with alkali addition, the method comprising the following steps: S1: Collect municipal waste sludge samples, and accurately quantify the background concentrations of D5 and P3 in the sludge after sludge pretreatment and gas chromatography-mass spectrometry analysis. S2: Prepare several small glass vials, and add 1 / 3 of the volume of the remaining sludge sample to each vial; add 50 µL of a mixed standard solution of D5 and P3 in acetone as the solvent to half of the vials as the experimental group, and add only an equal volume of acetone to the other half of the vials as the blank control group. The experimental group and the blank control group are set up in closed and open systems, respectively. Under each experimental condition, two parallel samples are set up at each sampling time point. S3: Divide the vials of the experimental group described in S2 into 3 groups, and then divide each group into 3 groups. Treat each group with different pH values, different ultrasonic frequencies, and different ultrasonic times. Each group is divided into a closed system and an open system. Divide the vials of the blank control group described in S2 into 3 groups, and calculate the degradation half-life and evaporation half-life of D5 and P3 respectively. S4: Using Design-Expert software and the Box-Behnken response surface methodology, a quadratic regression model was established with pH, ​​ultrasonic frequency, and ultrasonic time as independent variables and the D5 degradation half-life and P3 degradation half-life as response values, respectively. The effects of pH, ultrasonic frequency, ultrasonic time, and their interaction on the degradation effect were then analyzed. S5: Based on the optimized process conditions predicted by the quadratic regression model established in S4, conduct the verification experiment again, calculate the actual degradation half-life of D5 and P3 according to the verification experiment results, and compare them with the predicted values ​​of the quadratic regression model. S6: Non-target screening of degradation products of D5 and P3 under alkali addition and sonication processes was performed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR / MS), revealing the degradation pathways of two types of siloxanes under alkali addition and sonication conditions. S7: Using the optimal composite process conditions obtained in this experiment, alkaline coupled ultrasonic pretreatment of actual municipal sludge was carried out to investigate the changes in the concentrations of D5 and P3 in the sludge before and after the application of this composite process, and to obtain the removal effect.

[0007] Furthermore, in S3, the specific steps for each group of operations are as follows: S301: Take 1 / 3 of the vials from S2, which belong to the experimental group, and divide them into 3 groups. Adjust the pH value of the sludge to 9, 11 and 13 respectively. Divide the vials with the same pH value into closed system and open system. Take 1 / 3 of the vials from S2, which belong to the blank control group, and take samples at different time intervals. After pretreatment, detect the types of remaining parent D5 and P3, monosilanol and degradation products in the vials and perform semi-quantitative analysis by internal standard method. Two samples are considered as a parallel group. Calculate the degradation half-life and volatilization half-life of D5 and P3. S302: The other 1 / 3 of the vials in S2 were subjected to different ultrasonic frequencies. The vials under the same power conditions were divided into closed systems and open systems. The remaining D5 and P3 in the blank control group of 1 / 3 of S2 were measured at different time intervals. Two samples were used as a parallel group. The degradation half-life and volatilization half-life of D5 and P3 were calculated according to the formula. S303: Perform ultrasonic treatment on the last 1 / 3 of the vials in S2 for different durations, and divide the vials under the same ultrasonic treatment time into closed and open systems; take the last 1 / 3 of the blank sample vials in S2, and detect the remaining D5 and P3 in the vials at different time intervals. Two samples are considered as a parallel group, and calculate the degradation half-life and evaporation half-life of D5 and P3 according to the formula.

[0008] Furthermore, in S301, the pH value was adjusted using 6 mol / L sodium hydroxide, and the remaining parent compounds D5 and P3 were detected using gas chromatography-mass spectrometry (GC / MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FRI).

[0009] Furthermore, in S3, the calculation formula is: The first-order kinetic equation for the hydrolytic degradation of siloxanes in a closed system is as follows: ; The formula for calculating the evaporation rate constant of siloxanes is as follows: ; in, t The end time of the experiment. C 0 and C t These represent the initial concentration and the concentration at time t, respectively, of the siloxane in the simulation experiment. K The degradation coefficient is , This is the hydrolysis degradation rate constant. Let be the evaporation rate constant. The slope of the semi-logarithmic curve of the open system; The formula for calculating the hydrolysis half-life is as follows: ; The formula for calculating the volatile half-life is as follows: .

[0010] Furthermore, in S5, the specific steps of the verification experiment are as follows: take sludge samples with D5 and P3 simultaneously spiked, perform alkaline ultrasonic combined treatment under optimized pH, optimized ultrasonic frequency, and optimized ultrasonic time conditions, and set up a closed system, an open system, and a blank control group; take samples at different time intervals to detect the content of remaining D5 and P3 in the sludge, calculate the actual degradation half-life of D5 and P3 according to the experimental results, and compare them with the predicted values ​​of the quadratic regression model to verify the accuracy of the model and the reliability of the optimized process conditions.

[0011] Furthermore, in S5, the model calculation formula is as follows: ; in, β 0 , β i , β ii and β ij These are the regression coefficients for the offset term, linear term, quadratic term, and interaction term, respectively. X i and X j surface Show Independent factors in generalized equations ε This represents random error.

[0012] Advantages of this invention: 1. Compared with traditional anaerobic digestion of sludge, this technology can achieve a higher bioavailability of siloxanes, thereby improving the biodegradability of siloxanes in sludge and reducing the environmental emissions of siloxanes from sludge.

[0013] 2. By using the surface response method model to optimize composite process conditions, process parameters can be precisely adjusted to achieve efficient process design. Attached Figure Description

[0014] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0015] Figure 1A flowchart illustrating a research method for enhancing the degradation process and mechanism of siloxanes in anaerobic digested sludge through ultrasonic pretreatment with alkali addition; Figure 2 The surface response plot shows the effect of the interaction between pH, ultrasonic frequency, and ultrasonic time on the half-life of D5. Figure 3 The surface response diagram shows the effect of the interaction between pH, ultrasonic frequency, and ultrasonic time on the half-life of P3. Figure 4 The results of screening for degradation products of D5 and P3 in pretreated sludge and their degradation pathways are presented. Detailed Implementation

[0016] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, the main variations are obvious within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0017] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0018] like Figure 1 As shown, this scheme provides a method for enhanced alkali addition and ultrasonic pretreatment to degrade siloxanes in anaerobic digestion sludge, specifically including the following steps: S1: Collect municipal waste sludge samples, and accurately quantify the background concentrations of D5 (decamethylcyclopentasiloxane) and P3 (trimethyltriphenylcyclotrisiloxane) in the sludge after sludge pretreatment and gas chromatography-mass spectrometry analysis.

[0019] S2: Prepare several small glass vials, and add 1 / 3 of the volume of the remaining sludge sample to each vial; add 50 µL of a mixed standard solution of D5 and P3 in acetone as the solvent to half of the vials as the experimental group, and add only an equal volume of acetone to the other half of the vials as the blank control group. The experimental group and the blank control group are set up in closed and open systems, respectively. Under each experimental condition, two parallel samples are set up at each sampling time point.

[0020] In this embodiment, 360 15 mL glass vials were prepared, with 5 mL of residual sludge sample added to each vial. 50 µL of a mixed standard solution of D5 and P3 (8 mg / L, based on total Si mass) in acetone was added to 180 vials; the other 180 vials contained only an equal volume of acetone as a blank control group. Both the experimental group and the blank control group were set up in closed and open systems, respectively. Under each experimental condition, two parallel samples were taken at each sampling time point.

[0021] S3: Divide the vials of the experimental group described in S2 into 3 groups, and then divide each group into 3 groups. Treat each group with different pH values, different ultrasonic frequencies, and different ultrasonic times. Each group is divided into a closed system and an open system. Divide the vials of the blank control group described in S2 into 3 groups, and calculate the degradation half-life and evaporation half-life of D5 and P3 respectively.

[0022] In this embodiment, the specific operation steps are as follows: S301: Take 60 vials from S2 above that have been treated with D5 and P3, divide them into 3 groups of 20 vials each, and add 6 mol / L sodium hydroxide to each of the 3 groups of vials to adjust the pH value of the sludge to 9, 11 and 13 respectively. In each group of 20 vials with the same pH value, seal 10 vials to form a closed system, and leave the other 10 vials unsealed to form an open system. Sixty blank sample vials from S2 without added D5 and P3 were simultaneously sampled at different time intervals (0, 12, 24, 48, and 72 h). After pretreatment, the remaining parent D5 and P3, monosilanols, and degradation products in the vials were detected by gas chromatography-mass spectrometry (GC / MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESIFT-ICR / MS). Semi-quantitative analysis was performed using the internal standard method. Two samples were considered as a parallel pair, and the degradation half-life and volatile half-life of D5 and P3 were calculated. S302: Another 60 vials containing D5 and P3 were treated with ultrasonic frequencies of 20 kHz, 40 kHz, and 60 kHz. Referring to S3, under the same power conditions, 10 of the 20 vials in each group were capped as a closed system, and the other 10 were left uncapped as an open system. The 60 blank sample vials from S2 without added D5 and P3 were taken, and the remaining D5 and P3 levels in the vials were measured at different time intervals (0, 12, 24, 48, and 72 h). Two samples were considered as a parallel group. The degradation half-life and evaporation half-life of D5 and P3 were calculated using the formulas. S303: The last 60 vials containing D5 and P3 were subjected to ultrasonic treatment for different durations: 30 min, 60 min, and 90 min. Referring to S3, within each group of 20 vials under the same ultrasonic treatment time, 10 vials were capped as a closed system, and the other 10 were left uncapped as an open system. The 60 blank sample vials mentioned in S2 without added D5 and P3 were taken, and the remaining D5 and P3 levels in the vials were measured at different time intervals (0, 12, 24, 48, and 72 h). Each pair of samples was considered a parallel group. The degradation half-life and evaporation half-life of D5 and P3 were calculated using the formulas.

[0023] The calculation formula is: The first-order kinetic equation for the hydrolytic degradation of siloxanes in a closed system is as follows:

[0024] The formula for calculating the evaporation rate constant of siloxanes is as follows:

[0025] in, t The end time of the experiment. C 0 and C t These represent the initial concentration and the concentration at time t, respectively, of the siloxane in the simulation experiment. K The degradation coefficient is , This is the hydrolysis degradation rate constant. Let be the evaporation rate constant. The slope of the semi-logarithmic curve of the open system; The formula for calculating the hydrolysis half-life is as follows:

[0026] The formula for calculating the volatile half-life is as follows:

[0027] S4: Using Design-Expert software and the Box-Behnken response surface methodology, a quadratic regression model was established with pH, ​​ultrasonic frequency, and ultrasonic time as independent variables and the D5 degradation half-life and P3 degradation half-life as response values, respectively. The effects of pH, ultrasonic frequency, ultrasonic time, and their interactions on the degradation effect were then analyzed.

[0028] S5: Based on the optimized process conditions predicted by the quadratic regression model established in S4, conduct a new verification experiment. Calculate the actual degradation half-life of D5 and P3 based on the verification experiment results, and compare them with the predicted values ​​of the quadratic regression model.

[0029] In this embodiment, samples were taken at 0, 12, 24, 48, and 72 h to detect the remaining D5 and P3 content in the sludge. The actual degradation half-lives of D5 and P3 were calculated based on the experimental results and compared with the predicted values ​​from the response surface methodology to verify the accuracy of the model and the reliability of the optimized process conditions.

[0030] The model calculation formula is as follows:

[0031] in, β 0 , β i , β ii and β ij These are the regression coefficients for the offset term, linear term, quadratic term, and interaction term, respectively. X i and X j surface Show Independent factors in generalized equations ε Indicates random error S6: Non-target screening of degradation products of D5 and P3 during alkali addition and sonication processes was performed by ESI FT-ICR / MS to identify the degradation pathways of the two types of siloxanes under alkali addition + sonication conditions. S7: Using the optimal composite process conditions obtained in this experiment, alkaline coupled ultrasonic pretreatment of actual municipal sludge was carried out to investigate the changes in the concentrations of D5 and P3 in the sludge before and after the application of this composite process, and to obtain the removal effect.

[0032] The method will be further explained below with reference to specific embodiments.

[0033] As a preferred embodiment of the present invention, taking a sludge treatment plant in Tianjin as the research object, the specific steps for optimizing the process conditions are as follows: (1) Collect municipal residual sludge samples, and accurately quantify the background concentrations of D5 and P3 in the sludge after sludge pretreatment and gas chromatography-mass spectrometry analysis; (2) Prepare 360 ​​15 mL glass vials, and add 5 mL of residual sludge sample to each vial. Add 50 µL of D5 and P3 standard solutions (8 mg / L, based on total Si mass) in acetone to 180 vials respectively; add an equal volume of acetone to the other 180 vials as a blank control group. Both the experimental group and the blank control group were set up in closed and open systems respectively. Under each experimental condition, two parallel samples were set up at each sampling time point; (3) Take 60 vials from S2 that have been treated with D5 and P3, divide them into 3 groups of 20 vials each, and add 6 mol / L sodium hydroxide to each of the 3 groups of vials to adjust the pH of the sludge to 9, 11 and 13 respectively. In each group of 20 vials with the same pH value, seal 10 vials to form a closed system and leave the other 10 vials unsealed to form an open system. Take 60 blank sample vials from S2 that have not been treated with D5 and P3, and take samples at different time intervals (0, 12, 24, 48 and 72 h). After pretreatment, the remaining parent D5 and P3, monosilanol and degradation products in the vials are detected by gas chromatography-mass spectrometry (GC / MS) and ESI FT-ICR / MS respectively. Semi-quantitative analysis is performed by internal standard method. Two samples are considered as a parallel group. Calculate the degradation half-life and volatilization half-life of D5 and P3. (4) Another 60 vials containing D5 and P3 were treated with different ultrasonic frequencies, namely 20 kHz, 40 kHz and 60 kHz. Referring to S3, in each group of 20 vials under the same power conditions, 10 vials were capped as a closed system and the other 10 vials were left uncapped as an open system. Take the 60 blank sample vials from S2 that did not contain D5 and P3 and detect the remaining D5 and P3 in the vials at different time intervals (0, 12, 24, 48 and 72 h). Two samples were used as a parallel group. The degradation half-life and evaporation half-life of D5 and P3 were calculated according to the formula. (5) The last 60 vials containing D5 and P3 were subjected to ultrasonic treatment for different times: 30 min, 60 min, and 90 min. Referring to S3, in each group of 20 vials under the same ultrasonic time condition, 10 vials were capped as a closed system, and the other 10 vials were left uncapped as an open system. The 60 blank sample vials mentioned in S2 without added D5 and P3 were taken, and the remaining D5 and P3 in the vials were measured at different time intervals (0, 12, 24, 48, and 72 h). Each pair of samples was considered as a parallel group, and the degradation half-life and evaporation half-life of D5 and P3 were calculated according to the formula. (6) Using Design-Expert software, based on the Box-Behnken response surface design method, with pH, ​​ultrasonic frequency and ultrasonic time as independent variables, and the D5 degradation half-life and P3 degradation half-life as response values, a quadratic regression model was established, and the effects of pH, ultrasonic frequency, ultrasonic time and their interaction on the degradation effect were analyzed. (7) The validation experiment was carried out again according to the optimized process conditions predicted by the quadratic regression model in S6. Sludge samples with D5 and P3 simultaneously spiked were taken and subjected to alkaline ultrasonic combined treatment under optimized pH, optimized ultrasonic frequency, and optimized ultrasonic time conditions. A closed system, an open system, and a blank control group were set up. The remaining D5 and P3 content in the sludge was measured at 0, 12, 24, 48, and 72 h. The actual degradation half-lives of D5 and P3 were calculated based on the experimental results and compared with the predicted values ​​of the quadratic regression model to verify the accuracy of the model and the reliability of the optimized process conditions.

[0034] (8) Non-target screening of the degradation products of D5 and P3 during alkali addition and sonication was performed by ESI FT-ICR / MS to determine the degradation pathways of the two types of siloxanes under alkali addition and sonication conditions.

[0035] (9) The optimal composite process conditions obtained in this experiment were used to pretreat the actual municipal sludge from a sludge plant in Tianjin. The changes in the concentrations of D5 and P3 in the sludge before and after the application of the composite process were investigated, and the removal effect of the process was evaluated to guide engineering applications.

[0036] like Figure 2 As shown, Figure 2 (a) is a surface response diagram showing the effect of pH-ultrasonic frequency on the D5 half-life; Figure 2 (b) Surface response plot of the effect of pH-ultrasonic time on D5 half-life; Figure 2 (c) Surface response diagram of the effect of ultrasonic frequency-ultrasonic time on the half-life of D5. The optimal conditions for D5 in alkaline ultrasonic treatment are: pH=11.3, ultrasonic frequency=42.7 kHz, and ultrasonic time=62.2 min. Under these conditions, the degradation half-life of D5 in the alkaline ultrasonic combined pretreatment sludge system is the shortest, which is 27.7 h.

[0037] like Figure 3 As shown, Figure 3 (a) is a surface response diagram showing the effect of pH-ultrasonic frequency on the half-life of P3; Figure 3 (b) Surface response plot of the effect of pH-ultrasonic time on the half-life of P3; Figure 3 (c) Surface response diagram of the effect of ultrasonic frequency-ultrasonic time on the half-life of P3. The optimal conditions for P3 in alkaline ultrasonic treatment are: pH=11.1, ultrasonic frequency=42.4 kHz, and ultrasonic time=66.4 min. Under these conditions, the half-life is the shortest, which is 2.53 h.

[0038] like Figure 4 As shown, under the simulated alkaline conditions (pH=9-13), the intermediate products screened by the non-target included C. 10 H 32 O6Si5, C6H20 O4Si3,C 21 H 26 O4Si3,C 14 H 18 O3Si2 was also detected by GC / MS, along with two types of monosilanols (C2H8O2Si and C7H...). 10 O2Si), in conjunction with references, C 10 H 32 O6Si5 is the main product formed after the ring-opening hydrolysis of D5, and its structure can be represented as HO-[Si(CH3)2-O]5-H. This product still retains 5 Si atoms, but the original ring structure has been broken. Its concentration ranges from 2.18 to 9.52 μg / L, making it the most abundant component among the D5 degradation products, indicating that alkaline conditions can effectively promote the ring-opening hydrolysis of D5. As the reaction continues, the hydrolysis product after ring opening can further undergo Si-O bond cleavage to generate C6H. 20 O4Si3 and C2H8O2Si, with concentrations ranging from 0.625 to 2.56 μg / L and 0.311 to 1.12 μg / L, respectively. C2H8O2Si is the monosilanol formed at the end of hydrolysis, and its concentration continuously increases with alkaline catalysis time. This indicates that continuous hydrolysis occurs after D5 ring opening, leading to the gradual accumulation of monosilanol products. Furthermore, the further mineralization of C2H8O2Si is the rate-limiting step, meaning that under purely alkaline conditions, organosilicon is difficult to achieve advanced oxidation, such as the breaking of the Si-C bond or the hydroxylation of -CH3 in Si-CH3. 21 H 26 O4Si3 is the main hydrolysis product formed by the cleavage of the Si-O-Si bond and the addition of H2O to form the ring-opening product of P3. This product retains the original methyl and phenyl side chains of P3, and its concentration (0.926-4.11 μg / L) is lower than that of the ring-opening hydrolysis product C of D5. 10 H 32 O6Si5 is obtained because the conjugation electron donation of the phenyl group reduces the positive charge of Si in P3, thereby weakening the OH group. - Nucleophilic attraction; however, D5 contains only weakly electron-donating -CH3, resulting in a higher degree of electron deficiency in Si, thus making it more susceptible to OH. - Attack. As the reaction continues, the hydrolysis products after ring opening can further undergo Si-O bond breaking, hydrolyzing to generate C. 14 H 18 O3Si2 and monosilyl alcohol C7H 10The concentrations of O2Si ranged from 0.263 to 1.57 μg / L and from 0.0824 to 0.935 μg / L, respectively. This indicates that the degradation of P3 is also mainly characterized by ring-opening hydrolysis of the Si-O-Si backbone, accompanied by further chain scission to generate small oligomeric silanol products. However, advanced oxidation reactions also occur, such as the breaking of Si-C bonds in Si-CH3 or Si-ph, or -CH3 hydroxylation, and the formation of phenol.

[0039] Under ultrasonic conditions, in addition to the hydrolysis products of D5 or P3 (see Tables 1-1 and 1-2), the products screened by non-target processes also showed that ultrasound promoted the continuous advanced oxidation reaction of siloxanes and hydrolysis products under alkaline conditions, i.e., the oxidation reaction of side-chain Si-C occurred. The concentration of hydroxyl radicals in the bulk liquid phase of sludge generated during the ultrasonic process after alkaline hydrolysis, measured by electron spin resonance spectroscopy (ESR), ranged from 22.3 to 80.5 μmol / L, and was positively correlated with ultrasonic time or power. This indicates that the formation, expansion, and instantaneous rupture of cavitation bubbles during ultrasound can generate reactive species such as hydroxyl radicals. EPS and humic acid have a significant quenching effect on free radicals diffused into the bulk, and the supply of oxidant is limited under homogeneous conditions. However, the hydroxyl radicals generated by ultrasonic cavitation are highly enriched at the gas-liquid interface, with extremely high instantaneous concentrations; strongly hydrophobic siloxanes tend to accumulate at the interface, effectively avoiding the ineffective quenching of most organic matter. Simultaneously, ultrasonic continuous lysis of water generates free radicals, which are replenished through hydrogen peroxide and endogenous iron. Even with a steady-state average concentration of hydroxyl radicals only in the μmol / L range, the sludge ultrasonic system does not suffer from severe oxidant deficiency. Organic matter quenching only causes a certain efficiency loss. Hydroxyl radicals can destroy the Si-CH3 or Si-ph side chain groups in D5 or P3, oxidizing them to form Si-CH2OH or causing hydroxylation of the benzene ring in P3, generating oxidation products containing phenolic hydroxyl structures. Non-target screening detected C... 10 H 30 O6Si5 and C 10 H 32 O7Si5 is an oxidation product containing a -CH2OH functional group, formed by the oxidation of the side chains of D5 and its ring-opening hydrolysis products. Its concentration ranges are 0.322-1.76 μg / L and 0.0613-1.11 μg / L, respectively, significantly lower than the concentration of the ring-opening hydrolysis products of D5. Simultaneously, the continuous hydrolysis product C6H of D5 was also detected. 20 One of the -CH3 groups in O4Si3 is replaced by ·OH to form C5H. 18O6Si3 (concentration range: 0.0107-0.616 μg / L). For P3, its advanced oxidation has two preferential reaction pathways: ① Electrophilic addition of ·OH to the benzene ring, rapidly generating a hydroxycyclohexadiene radical, the product being a Si-linked phenolic group; ② The benzylic hydrogen (Si-C6H5 ortho-position) is readily abstracted, generating a stable benzylic radical. Non-target screening results detected C 21 H 24 O4Si3 is either the product containing the -CH2OH functional group formed by the oxidation of the P3 side chain or the hydroxylation of the benzene ring attached to the Si atom into a phenolic group. Its concentration is 0.422-1.13 μg / L and 0.536-1.71 μg / L, respectively, which is lower than the concentration of the ring-opening hydrolysis and chain-severing products of P3. It is the C4Si3 generated by the oxidation of the D5 side chain. 10 H 32 The concentration of O7Si5 was 0.38–27.89 times higher than that of D5 because P3 contains an electron-donating phenyl group, exposing the π electron cloud outside the benzene ring, making it highly susceptible to attack by ·OH. The activation energy of benzene ring addition and benzylic hydrogen abstraction reactions is much lower than that of methyl hydrogen abstraction in D5, resulting in a higher overall molecule affinity for ·OH compared to D5. Therefore, the reaction rate of P3 is significantly higher than that of D5 for both the formation of phenolic groups and hydroxymethyl groups. Meanwhile, non-target results also screened for C… 21 H 26 O5Si3 and C 20 H 24 O5Si3, with concentrations ranging from 0.0931 to 0.896 μg / L and 0.0284 to 0.622 μg / L, is a further hydroxylation product of the ring-opening hydrolysis product of P3.

[0040] Table 1-1 Concentration of D5 and its polar degradation products in pretreated sludge

[0041] Table 1-2. Concentrations of P3 and its polar degradation products in pretreated sludge

[0042] The above examples have provided a detailed description of this embodiment, but the content is only a preferred embodiment and should not be considered as limiting the scope of implementation of this embodiment; all equivalent changes and improvements made in accordance with the scope of this embodiment should still fall within the patent coverage of this embodiment.

Claims

1. A method for enhancing the degradation of siloxanes in anaerobic digestion sludge through ultrasonic pretreatment with alkali addition, characterized in that: The method includes the following steps: S1: Collect municipal waste sludge samples, and accurately quantify the background concentrations of D5 and P3 in the sludge after sludge pretreatment and gas chromatography-mass spectrometry analysis. S2: Prepare several small glass vials, and add 1 / 3 of the volume of the remaining sludge sample to each vial; add 50 µL of a mixed standard solution of D5 and P3 in acetone as the solvent to half of the vials as the experimental group, and add only an equal volume of acetone to the other half of the vials as the blank control group. The experimental group and the blank control group are set up in closed and open systems, respectively. Under each experimental condition, two parallel samples are set up at each sampling time point. S3: Divide the vials of the experimental group described in S2 into 3 groups, and then divide each group into 3 groups. Treat each group with different pH values, different ultrasonic frequencies, and different ultrasonic times. Each group is divided into a closed system and an open system. Divide the vials of the blank control group described in S2 into 3 groups, and calculate the degradation half-life and evaporation half-life of D5 and P3 respectively. S4: Using Design-Expert software and the Box-Behnken response surface methodology, a quadratic regression model was established with pH, ​​ultrasonic frequency, and ultrasonic time as independent variables and the D5 degradation half-life and P3 degradation half-life as response values, respectively. The effects of pH, ultrasonic frequency, ultrasonic time, and their interaction on the degradation effect were then analyzed. S5: Based on the optimized process conditions predicted by the quadratic regression model established in S4, conduct the verification experiment again, calculate the actual degradation half-life of D5 and P3 according to the verification experiment results, and compare them with the predicted values ​​of the quadratic regression model. S6: Non-target screening of degradation products of D5 and P3 under alkali addition and sonication processes was performed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR / MS), revealing the degradation pathways of two types of siloxanes under alkali addition and sonication conditions. S7: Using the optimal composite process conditions obtained in this experiment, alkaline coupled ultrasonic pretreatment of actual municipal sludge was carried out to investigate the changes in the concentrations of D5 and P3 in the sludge before and after the application of this composite process, and to obtain the removal effect.

2. The method for enhanced alkali addition and ultrasonic pretreatment to degrade siloxanes in anaerobic digestion sludge according to claim 1, characterized in that: In S3, the specific steps for each group of operations are as follows: S301: Take 1 / 3 of the vials from S2, which belong to the experimental group, and divide them into 3 groups. Adjust the pH value of the sludge to 9, 11 and 13 respectively. Divide the vials with the same pH value into closed system and open system. Take 1 / 3 of the vials from S2, which belong to the blank control group, and take samples at different time intervals. After pretreatment, detect the types of remaining parent D5 and P3, monosilanol and degradation products in the vials and perform semi-quantitative analysis by internal standard method. Two samples are considered as a parallel group. Calculate the degradation half-life and volatilization half-life of D5 and P3. S302: The other 1 / 3 of the vials in S2 were subjected to different ultrasonic frequencies. The vials under the same power conditions were divided into closed systems and open systems. The remaining D5 and P3 in the blank control group of 1 / 3 of S2 were measured at different time intervals. Two samples were used as a parallel group. The degradation half-life and volatilization half-life of D5 and P3 were calculated according to the formula. S303: Perform ultrasonic treatment on the last 1 / 3 of the vials in S2 for different durations, and divide the vials under the same ultrasonic treatment time into closed and open systems; take the last 1 / 3 of the blank sample vials in S2, and detect the remaining D5 and P3 in the vials at different time intervals. Two samples are considered as a parallel group, and calculate the degradation half-life and evaporation half-life of D5 and P3 according to the formula.

3. The method for enhanced alkali addition and ultrasonic pretreatment to degrade siloxanes in anaerobic digestion sludge according to claim 2, characterized in that: In S301, the pH was adjusted using 6 mol / L sodium hydroxide, and the remaining parent compounds D5 and P3 were detected using gas chromatography-mass spectrometry (GC / MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FROM).

4. The method for enhanced alkali addition and ultrasonic pretreatment to degrade siloxanes in anaerobic digestion sludge according to claim 1, characterized in that: In S3, the calculation formula is: The first-order kinetic equation for the hydrolytic degradation of siloxanes in a closed system is as follows: ； The formula for calculating the evaporation rate constant of siloxanes is as follows: ； in, t The end time of the experiment. C 0 and C t These represent the initial concentration and the concentration at time t, respectively, of the siloxane in the simulation experiment. K The degradation coefficient is , This is the hydrolysis degradation rate constant. Let be the evaporation rate constant. The slope of the semi-logarithmic curve of the open system; The formula for calculating the hydrolysis half-life is as follows: ； The formula for calculating the volatile half-life is as follows: 。 5. The method for enhanced alkali addition and ultrasonic pretreatment to degrade siloxanes in anaerobic digestion sludge according to claim 1, characterized in that: In S5, the specific steps of the verification experiment are as follows: take sludge samples with D5 and P3 simultaneously spiked, perform alkaline ultrasonic combined treatment under optimized pH, optimized ultrasonic frequency and optimized ultrasonic time conditions, and set up a closed system, an open system and a blank control group; take samples at different time intervals to detect the content of remaining D5 and P3 in the sludge, calculate the actual degradation half-life of D5 and P3 according to the experimental results, and compare them with the predicted values ​​of the quadratic regression model to verify the accuracy of the model and the reliability of the optimized process conditions.

6. The method for enhanced alkali addition and ultrasonic pretreatment to degrade siloxanes in anaerobic digestion sludge according to claim 1, characterized in that: In S5, the model calculation formula is as follows: ； in, β 0 , β i , β ii and β ij These are the regression coefficients for the offset term, linear term, quadratic term, and interaction term, respectively. X i and X j surface Show Independent factors in generalized equations ε This represents random error.

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