An anaerobic bio-fermentation process for the targeted degradation of municipal sewage sludge

Abstract

This invention discloses an anaerobic bio-fermentation process for the targeted degradation of municipal sewage sludge, belonging to the field of sludge treatment technology. The process includes: pretreatment and targeted activation of components; staged hydrolysis and acidification for targeted production of short-chain fatty acids; methanogenic fermentation mediated by conductive materials coupled with a microbial electrolysis cell for assistance; multi-parameter dynamic control based on online monitoring and intelligent algorithms; magnetic separation, recovery, and recycling of magnetic conductive materials; in-situ biogas purification and product gradient reflux; solid-liquid separation and residue resource utilization. This invention achieves kinetic matching and metabolic enhancement of hydrolysis and acidification and methanogenesis through the deep linkage of four modules: targeted hydrolysis and acidification, enhanced direct interspecies electron transfer via a microbial electrolysis cell, magnetic material circulation, and intelligent control. Compared with existing technologies, the methane yield is increased by more than 40%, propionic acid accumulation is below 50 mg / L, the fermentation cycle is shortened to 8-10 days, and system energy consumption is reduced by 20%.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment technology, specifically relating to an anaerobic biological fermentation process for the targeted degradation of municipal sludge. Background Technology

[0002] Anaerobic fermentation of municipal sludge is a mainstream technology for achieving sludge reduction, stabilization, and energy conversion. Traditional single-phase fermentation processes suffer from problems such as mixed microbial metabolic pathways, easy accumulation of intermediate products (especially propionic acid), and low methanogenesis efficiency. To address these issues, existing technologies have developed a two-phase fermentation process (two-phase anaerobic digestion), which separates the hydrolysis-acidification phase from the effluent from the methanogenic reactor, thus alleviating acid inhibition to some extent. However, in the two-phase process, the organic acids (acetic acid, propionic acid, butyric acid, etc.) produced by the hydrolysis-acidification phase must first be converted into acetic acid and H2 by hydrogen-producing acetic acid bacteria before being utilized by methanogenic bacteria. Hydrogen partial pressure and propionic acid accumulation remain bottlenecks in this process.

[0003] In recent years, some studies have proposed that adding conductive materials (such as magnetite and biochar) can promote direct interspecies electron transfer (DIET) between different microorganisms, enabling acid-producing bacteria to directly transfer electrons to methanogens, bypassing the traditional hydrogen and acetic acid production steps. However, in existing technologies, conductive materials are mostly used in single-phase fermentation systems or simple two-phase systems, without systematic process design tailored to the complex composition of municipal sludge and the need for "directional control" of its degradation pathways. Furthermore, simply adding conductive materials cannot actively regulate the electron transfer rate, and DIET efficiency decreases when the organic load fluctuates.

[0004] Microbial electrolyzer (MEC) technology has been used to enhance methanogenesis by applying a weak voltage to overcome thermodynamic barriers and increase the methanogenesis rate. However, existing MEC-anaerobic fermentation coupled processes mostly involve directly applying voltage within a single reactor without combining it with phase-separated fermentation, conductive materials, and targeted metabolic regulation, resulting in a mismatch between energy consumption and gas production gain. Furthermore, the long-term stability and recycling issues of magnetic conductive materials in the system remain unresolved, leading to material waste and the risk of secondary pollution.

[0005] Therefore, there is an urgent need for an anaerobic biological fermentation process for the targeted degradation of municipal sewage sludge. Summary of the Invention

[0006] The purpose of this invention is to provide an anaerobic biological fermentation process for the targeted degradation of municipal sludge, so as to solve the problems mentioned in the background art.

[0007] The technical solution of this invention is: an anaerobic biological fermentation process for the targeted degradation of municipal sewage sludge, comprising the following steps:

[0008] (1) Pretreatment and component-directed activation: Adjust the solid content of municipal sludge to 5%-8%, add alkaline solution to adjust pH to 8.0-9.0, add compound enzyme preparation, and pretreat at 50-55℃ for 12-24 hours;

[0009] (2) Staged hydrolysis and acidification: The pretreated sludge is fed into the hydrolysis and acidification reactor, inoculated with hydrolysis and acidification compound bacteria, and the temperature is controlled at 35-38℃, pH 6.2-6.5, and hydraulic retention time is 2-4 days to produce acetic acid and butyric acid in a targeted manner, and the proportion of propionic acid production to total volatile fatty acids is ≤5%;

[0010] (3) Conductive material coupled microbial electrolysis cell assisted methanogenic fermentation: The effluent from step (2) is sent into the methanogenic reactor, the reactor is filled with modified nano-magnetite, and a microbial electrolysis cell module is set up. An external voltage of 0.3-0.8V is applied. Acetic acid-producing methanogens and hydrogen-producing methanogens are attached to both the cathode and anode. The temperature is controlled at 35-38℃, pH at 7.0-7.3, and the hydraulic retention time is 5-7 days.

[0011] (4) Multi-parameter dynamic control based on online monitoring and intelligent algorithm: The volatile fatty acid spectrum (ratio of acetic acid, propionic acid and butyric acid) in the hydrolysis acidification reactor and the hydrogen partial pressure in the methanogenic reactor are monitored online. The pH value (range of 6.0-6.8) in step (2) and the applied voltage value (0.3-1.0V) in step (3) and the supplementary dosage of modified nano-magnetite are dynamically adjusted by the fuzzy logic controller.

[0012] (5) Magnetic separation, recycling and reuse of magnetic conductive materials: A magnetic separation device is set at the outlet of the methanogenic reactor to recover modified nano-magnetite. After cleaning, 60%-80% of the recovered amount is reused in the hydrolysis acidification reactor of step (2), and the remaining 20%-40% is reused in the methanogenic reactor of step (3).

[0013] (6) In-situ biogas purification and product gradient reflux: The biogas generated in step (3) is passed into an alkaline absorption tower to selectively absorb CO2, and part of the carbonate-rich solution after absorption is refluxed back to step (1); at the same time, the total volatile fatty acid concentration in the methanogenic reactor is monitored online. When the total volatile fatty acid concentration is >1200mg / L, the effluent from the methanogenic reactor is refluxed back to step (2) at a ratio of 1:2 to 1:5.

[0014] (7) Solid-liquid separation and residue resource utilization: After fermentation, the biogas residue and biogas slurry are separated. The biogas residue is utilized for resource utilization after aerobic stabilization, and part of the biogas slurry is returned to step (1).

[0015] Preferably, the compound enzyme preparation in step (1) is a protease and a lipase in a mass ratio of 1:1, and the dosage is 5-20 mg / g volatile solids.

[0016] Preferably, the hydrolysis acidification compound bacterial agent in step (2) is mainly composed of Proteiniphilum acetatigenes and Clostridium butyricum, with the ratio of the two controlled at 2:1 to 3:1, and the total inoculum amount makes the initial volatile suspended solids concentration in the reactor 3-6 g / L.

[0017] Preferably, the modified nano-magnetite in step (3) has a filling rate of 2%-5% (w / v) of the effective volume of the reactor and a particle size of 50-200 nm. The preparation method is as follows: nano-Fe3O4 biochar is mixed at a mass ratio of 1:1 to 2:1 and pyrolyzed at 300-400℃ under a nitrogen atmosphere for 2 hours to obtain Fe3O4@biochar composite.

[0018] Preferably, the cathode of the microbial electrolysis cell module in step (3) is a carbon brush or carbon felt, the anode is a platinum carbon catalyst (0.5 mg Pt / cm²) supported on carbon cloth, the electrode spacing is 5-10 cm, the applied voltage is provided by a DC power supply, and the current density is controlled at 0.5-2.0 A / m².

[0019] Preferably, the input variables of the fuzzy logic controller in step (4) are: propionic acid / total volatile fatty acid ratio (P / T), butyric acid / acetic acid ratio (B / A), and hydrogen partial pressure (pH2), and the output variables are: pH adjustment amount (ΔpH), voltage adjustment amount (ΔV), and material supplementation coefficient (k); wherein the target value of P / T is ≤0.05, the target value of B / A is 0.8-1.2, and the target value of pH2 is ≤10Pa.

[0020] Preferably, the magnetic separation device in step (5) is a high gradient magnetic separator with a magnetic field strength of 0.5-1.2T. The recovered modified nano-magnetite is first ultrasonically cleaned with 0.1% SDS solution for 5 minutes, and then rinsed with deionized water before reuse.

[0021] Preferably, the reflux control from the methanogenic reactor effluent to the hydrolysis acidified phase employs a two-stage logic. Stage 1 (Start-up Logic): Online monitoring of total volatile fatty acid (total VFAs) concentration. When total VFAs exceed 1200 mg / L, it indicates a high metabolic load in the system, and reflux operation is initiated. Stage 2 (Proportional Adjustment Logic): After reflux operation is initiated, the reflux ratio is dynamically selected based on the specific value of propionic acid concentration in the methanogenic reactor—a low reflux ratio of 1:5 is selected when propionic acid concentration <150 mg / L; a medium reflux ratio of 1:3 is selected when propionic acid concentration is 150-400 mg / L; and a high reflux ratio of 1:2 is selected when propionic acid concentration >400 mg / L. This two-stage logic achieves precise control of reflux, avoiding unnecessary reflux operations and adjusting the reflux intensity according to the degree of inhibition when necessary.

[0022] Preferably, an online volatile fatty acid analyzer is installed in the hydrolysis acidification reactor in step (2). When the concentration of propionic acid is >250mg / L, a portion of the reactor effluent is automatically returned to step (1) for dilution, with a return ratio of 1:5 to 1:10.

[0023] Preferably, the methanogenic reactor in step (3) is intermittently stirred (stirred for 10 minutes and stopped for 20 minutes), with a stirring speed of 15-30 rpm, and a guide plate is set on the reactor wall to promote the contact between the conductive material and the microorganisms. At the same time, the electrodes of the microbial electrolysis cell module are fixed vertically in the middle of the reactor.

[0024] This invention provides an improved anaerobic bio-fermentation process for the targeted degradation of municipal sewage sludge, which has the following improvements and advantages compared with the prior art:

[0025] First, this invention, by controlling the pH to 6.2-6.5 and the hydraulic retention time to 2-4 days, ensures that the proportion of propionic acid in the total volatile fatty acids in the hydrolysis acidification products is ≤5%, and the ratio of butyric acid to acetic acid is maintained at 0.8-1.2. This product profile avoids the inhibition of subsequent methanogenesis by propionic acid, while providing an easily metabolizable substrate composition for the methanogenesis stage.

[0026] Second: In step (3) of this invention, modified nano-magnetite (Fe3O4@biochar) and a microbial electrolysis cell module (external voltage 0.3-0.8V) are simultaneously introduced into the methanogenic reactor. The nano-magnetite acts as a conductive medium to establish a direct interspecies electron transfer channel between symbiotic oxidizing bacteria and methanogenic bacteria; the weak voltage provided by the microbial electrolysis cell further reduces the activation energy of electron transfer, increasing the butyric acid degradation rate by 2-3 times compared to conditions without external voltage. This setup significantly enhances the methanogenic reactor's ability to process hydrolysis and acidification products, controlling the propionic acid accumulation to below 50mg / L.

[0027] Third: In step (4) of this invention, the ratio of propionic acid to total volatile fatty acids, the ratio of butyric acid to acetic acid, and the partial pressure of hydrogen are monitored online, and a fuzzy logic controller is used to dynamically adjust the pH of the hydrolysis acidification phase, the external voltage of the MEC, and the amount of conductive material replenished. When the propionic acid ratio increases, the hydrolysis acidification pH is automatically lowered to 6.0-6.2 to inhibit the propionic acid generation pathway; when the butyric acid to acetic acid ratio deviates from the target range, the external voltage and the amount of material replenished are adjusted accordingly to optimize the butyric acid degradation rate; when the partial pressure of hydrogen exceeds 10 Pa, the external voltage is increased to promote the consumption of hydrogen by hydrogen-producing methanogens. This real-time adjustment mechanism enables the system to maintain stable operation under different influent load conditions, avoiding the acidification risk common in fixed-parameter processes.

[0028] Fourth: In step (5) of this invention, a high-gradient magnetic separator (0.5-1.2T) is used to magnetically separate and recover the modified nano-magnetite in the effluent. The surface of the recovered material is covered with a large number of synergistic oxidizing bacteria and methanogenic bacteria. After cleaning, 60%-80% of the recovered amount is reused in the hydrolysis acidification reactor and 20%-40% is reused in the methanogenic reactor. This reuse operation reduces the amount of fresh conductive material added, and the net replenishment amount is reduced to 1.5-2.0 kg / ton VS. At the same time, the functional bacteria that have adapted to the system environment are reintroduced into the reactor, maintaining a high-density interspecies electron transport network in the system.

[0029] Fifth: In step (6) of this invention, the biogas produced in the methanogenesis stage is fed into an alkaline absorption tower (0.3-0.8M NaOH), and after selective absorption of CO2, the methane concentration at the outlet is ≥85%. The carbonate-rich solution produced by absorption is recycled to step (1) to replace part of the fresh alkaline solution for pH adjustment in the pretreatment stage. At the same time, when the total volatile fatty acid concentration in the methanogenesis reactor exceeds 1200 mg / L, the effluent is recycled to the hydrolysis acidification reactor at a ratio of 1:2 to 1:5. The low concentration of propionic acid (150-400 mg / L) and metabolites of symbiotic oxidizing bacteria contained in the reflux liquid can induce the hydrolysis acidification bacteria to upregulate the activity of butyric acid production-related enzymes, further reducing the proportion of propionic acid in the hydrolysis acidification phase to below 3%.

[0030] Sixth: Under the combined effect of the above-mentioned technical features, the process of this invention achieves the following performance indicators in municipal sludge treatment: methane yield of 386-408 L / kgVS, volatile solids removal rate of 85%-88.5%, peak propionic acid concentration of 42-78 mg / L, total hydraulic retention time of 9.5-10 days, external power consumption of 0.09-0.11 kWh / kgCOD removal, and net replenishment of conductive material of 1.8-2.2 kg / tonVS. Compared with traditional single-phase anaerobic fermentation, the methane yield is increased by more than 100%, and the fermentation cycle is shortened by more than 60%; compared with conventional two-phase anaerobic digestion combined with conductive material, the methane yield is increased by 30%-40%, and the propionic acid accumulation is reduced by more than 80%; compared with MEC coupling process without directional hydrolysis acidification and intelligent control, external power consumption is reduced by 40%-50%, and conductive material consumption is reduced by 60%-70%. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the process flow of an anaerobic biological fermentation process for the targeted degradation of municipal sludge in this invention. Detailed Implementation

[0032] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0033] The components of the embodiments of the invention described and shown in the accompanying drawings can typically be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0034] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0037] Example 1: The residual sludge from a municipal wastewater treatment plant was used. The sludge had a moisture content of 88%, a VS / TS ratio of 0.62, a feed volatile solids (VS) concentration of 45 g / L, and a total COD of 65 g / L.

[0038] (1) Pretreatment and component-directed activation: Adjust the solid content of sludge to 6%, add NaOH to adjust the pH to 8.5, add compound enzyme preparation (protease and lipase mass ratio 1:1, dosage 10mg / gVS), and pretreat at 55℃ for 18 hours.

[0039] (2) Staged hydrolysis and acidification: The pretreated sludge was fed into a hydrolysis and acidification reactor with an effective volume of 50 m³, and inoculated with a hydrolysis and acidification compound bacterial agent (Proteiniphilum acetatigenes and Clostridium butyricum were mixed at a volume ratio of 2:1, and the initial VSS concentration in the reactor after inoculation was 4 g / L). The temperature was controlled at 37℃, the initial pH was 6.3, and the hydraulic retention time was 2.5 days. The VFA composition was determined by an online VFAs analyzer to be: acetic acid 46%, butyric acid 39%, propionic acid 3.5%, and other 11.5%. The propionic acid content was ≤5%, which met the standard. When the propionic acid instantaneously exceeded 250 mg / L (which did not actually occur), it was refluxed to step (1) at a ratio of 1:8.

[0040] (3) Conductive material coupled with microbial electrolysis cell to assist methanogenic fermentation: The effluent from step (2) is sent into a methanogenic reactor with an effective volume of 200 m³. The reactor is pre-filled with modified nano-magnetite (filling rate 3% w / v, which can be prepared by conventional methods such as chemical co-precipitation, sol-gel method or ball milling, specifically using nano-Fe3O4 biochar mixed at a mass ratio of 1:1 to 2:1, and pyrolyzed at 300-400℃ under nitrogen atmosphere for 2 hours to obtain Fe3O4@biochar composite). The microbial electrolysis cell module is set up: the cathode is a carbon brush, the anode is carbon cloth loaded with 0.5 mg Pt / cm², the electrode spacing is 8 cm, the applied voltage is 0.6 V (DC power supply), and the current density is 1.2 A / m². Acetic acid-producing methanogens and hydrogen-producing methanogens are pre-enriched and inoculated at a VSS ratio of 4:1, with a total inoculation amount so that the initial VSS is 6 g / L. The temperature was controlled at 37℃, pH at 7.2, and the hydraulic retention time at 6 days. Intermittent stirring was used (stirring for 10 minutes and stopping for 20 minutes, with a rotation speed of 20 rpm). The electrodes were vertically fixed in the middle of the reactor.

[0041] (4) Multi-parameter dynamic control based on online monitoring and intelligent algorithms: Install an online VFAs analyzer (monitoring P / T, B / A) and a hydrogen sensor (monitoring pH2). The fuzzy logic controller (inputs: P / T, B / A, pH2; outputs: ΔpH, ΔV, k) operates according to the following rules:

[0042] When P / T>0.05, ΔpH=-0.2 (reducing the hydrolysis acidification pH to 6.1), ΔV=+0.1V (increasing the voltage to 0.7V), k=1.2 (K is the supplementary coefficient of the modified nano-magnetite material).

[0043] When B / A < 0.8, ΔpH = +0.1 (increasing pH to 6.4), ΔV = +0.05V, k = 1.1;

[0044] When pH2 > 10 Pa, ΔV = +0.15V, k = 1.3. In this embodiment, P / T is maintained at 0.03-0.04, B / A at 0.9-1.1, pH2 at 5-8 Pa, the controller is only slightly adjusted, the average voltage is 0.62V, and the material replenishment coefficient k = 1.05.

[0045] When multiple parameters fluctuate, the following priority adjustment should be used:

[0046] First priority: Propionic acid / total VFAs ratio (P / T). Propionic acid is the most inhibitory intermediate product in anaerobic fermentation, and its accumulation directly leads to a decrease in methanogenic activity and even system acidification. Therefore, when P / T > 0.05, regardless of other parameters, the P / T control rule should be implemented first: reduce the hydrolysis acidification pH to 6.1, increase the MEC voltage to 0.7V, and increase the material replenishment factor to 1.2.

[0047] Second priority: Hydrogen partial pressure (pH2). High hydrogen partial pressure (>10 Pa) thermodynamically inhibits the degradation of butyric acid and propionic acid. Provided that P / T meets the standard, if pH2 exceeds the standard, the pH2 adjustment rule is implemented: increase the MEC voltage to +0.15V (adding to the existing voltage) and increase the material supplementation factor to 1.3.

[0048] Third priority: Butyric acid / acetic acid ratio (B / A). This parameter mainly affects methanogenesis efficiency but does not directly cause acidification. If the B / A deviates from the range of 0.8-1.2 when both P / T and pH2 are within the target range, then the B / A adjustment rule is implemented: fine-tune pH (±0.1) and voltage (±0.05V).

[0049] (5) Magnetic separation, recovery and recycling of magnetic conductive materials: The effluent from the methanogenic reactor is processed by a high-gradient magnetic separator (magnetic field strength 0.8T) to recover modified nano-magnetite, with a recovery rate of 92%. The recovered material is ultrasonically cleaned with 0.1% SDS for 5 minutes, rinsed with deionized water, and 70% of the recovered amount is reused in the hydrolysis acidification reactor in step (2), and 30% is reused in the methanogenic reactor in step (3). The fresh material replenishment amount is 2% of the initial filling amount per day.

[0050] (6) In-situ biogas purification and product gradient reflux: The biogas generated in step (3) is fed into a 0.5 mol / L NaOH absorption tower, with an outlet CH4 concentration of 92%. The carbonate-rich solution at the bottom of the absorption tower is refluxed back to step (1) at a rate of 18 L per ton of sludge. The maximum total VFAs in the methanogenic reactor is 980 mg / L (below the threshold of 1200 mg / L), and the reflux of the methanogenic reactor effluent to the hydrolysis acidification phase is not initiated.

[0051] (7) Solid-liquid separation and residue resource utilization: plate and frame filter press, the biogas residue moisture content is 62%, and it meets the standard after aerobic composting; part of the biogas liquid is returned to step (1), and the rest is treated.

[0052] Results: Methane yield was 408 L / kg VS, VS removal rate was 88.5%, propionic acid peak was only 42 mg / L, total hydraulic retention time was 9.5 days, external power consumption was 0.09 kWh / kg COD removal, and net replenishment of conductive material was 1.8 kg / ton VS. The system operated continuously for 120 days without acidification, demonstrating excellent robustness.

[0053] Example 2: In this example, the feed organic load was increased (VS concentration increased from 45 g / L to 70 g / L) to verify the linkage effect between intelligent control and product gradient reflux.

[0054] The sludge is the same as in Example 1, and steps (1)-(3) are basically the same, but in step (4), the controller monitors that: P / T rises to 0.07, B / A drops to 0.65, and pH2 rises to 15Pa. According to the comprehensive control rules: P / T exceeding the standard (>0.05) contributes ΔpH=-0.2, B / A exceeding the standard (<0.8) contributes ΔpH=+0.1, and pH2 exceeding the standard (>10Pa) contributes ΔV=+0.15V. The material supplement coefficient is taken as the maximum value. After superposition, ΔpH=-0.1, and the hydrolysis acidification pH is adjusted from the current 6.3 to 6.2; ΔV=+0.1(P / T)+0.05(B / A)+0.15(pH2)=+0.3V, and the voltage is increased from 0.6V to 0.9V; k=max(1.2,1.1,1.3)=1.3. Meanwhile, in step (6), when the total VFAs reach 1350 mg / L (>1200 mg / L), the effluent from the methanogenic reactor is started and refluxed to the hydrolysis acidified phase at a reflux ratio of 1:3.

[0055] Within 6 hours after adjustment, P / T decreased to 0.045, B / A increased to 0.85, and pH2 decreased to 9 Pa. After stable operation, the methane yield was 392 L / kg VS, the propionic acid peak was 78 mg / L (appeared briefly), and the VS removal rate was 86.2%.

[0056] In step (6), the reflux control of the methanogenic reactor effluent to the hydrolysis acidified phase employs a two-stage logic. The first stage (start-up logic): The total volatile fatty acid (VFAs) concentration is monitored online. When the total VFAs exceed 1200 mg / L, it indicates a high metabolic load in the system, and the reflux operation is initiated. The second stage (ratio adjustment logic): After the reflux operation is initiated, the reflux ratio is dynamically selected based on the specific value of the propionic acid concentration in the methanogenic reactor—a low reflux ratio of 1:5 is selected when the propionic acid concentration is <150 mg / L; a medium reflux ratio of 1:3 is selected when the propionic acid concentration is 150-400 mg / L; and a high reflux ratio of 1:2 is selected when the propionic acid concentration is >400 mg / L. This two-stage logic achieves precise control of the reflux, avoiding unnecessary reflux operations and adjusting the reflux intensity according to the degree of inhibition when necessary.

[0057] In this embodiment, when the total VFAs = 1350 mg / L (>1200 mg / L), reflux is initiated; the current propionic acid concentration is 210 mg / L, which falls within the 150-400 mg / L range, so a reflux ratio of 1:3 is selected.

[0058] Example 3: This example verifies the validity of the parameter ranges of claims 5 and 7.

[0059] In step (3), a carbon felt cathode and a common carbon cloth anode (without Pt) are used, with an applied voltage of 0.5V and a current density of 0.8A / m². In step (5), the magnetic separation magnetic field strength is 1.0T, and the recovery rate is 89%. After cleaning, 80% of the recovered amount is reused in the hydrolysis acidification phase, and 20% is reused in the effluent of the methanogenic reactor. The rest is the same as in Example 1.

[0060] Results: Methane yield was 386 L / kg VS, VS removal rate was 85.1%, propionic acid peak was 55 mg / L, and external power consumption was 0.11 kWh / kg COD removal. This demonstrates that the performance is still superior to existing technologies without precious metal catalysts, but slightly lower than that of Example 1.

[0061] Comparative Example 1 (Traditional Single-Phase Completely Mixed Anaerobic Fermentation)

[0062] Example 1: A batch of sludge, single CSTR, HRT 25 days, 37°C, no conductive materials, no MEC, no directional control.

[0063] Results: Methane yield was 195 L / kg VS, VS removal rate was 49%, propionic acid peak was 1100 mg / L, acidification was required.

[0064] Comparative Example 2 (Conventional two-phase + conductive material, no MEC, no intelligent control, no recycling)

[0065] The hydrolysis acidification phase does not control propionic acid (using ordinary hydrolytic bacteria), and 3% modified nano-magnetite (without MEC) is added to the effluent from the methanogenic reactor. There is no intelligent control or material recovery. The rest is the same as in Example 1.

[0066] Results: Methane yield was 290 L / kg VS, VS removal rate was 69%, propionic acid peak was 310 mg / L, and fluctuated after 45 days of operation.

[0067] Comparative Example 3 (Two-phase + MEC, no directional acidification, no intelligent control, no material recycling)

[0068] In the same hydrolysis and acidification control as in Comparative Example 2, 3% modified nano-magnetite was added to the effluent of the methanogenic reactor and a constant voltage of 0.6V (MEC) was applied. There was no intelligent control and no material recovery.

[0069] Results: Methane yield was 325 L / kgVS, VS removal rate was 73%, propionic acid peak was 180 mg / L, and external power consumption was 0.20 kWh / kgCOD removal.

[0070] Comparative Example 4 (Directional Acidification + MEC, without Intelligent Control and Material Recycling)

[0071] The hydrolysis acidification process was the same as in Example 1 (directed acid production). 3% modified nano-magnetite was added to the effluent of the methanogenic reactor and a constant voltage of 0.6V was applied. There was no intelligent control, no material recovery, and no magnetic circulation.

[0072] Results: Methane yield was 355 L / kg VS, VS removal rate was 78%, propionic acid peak was 95 mg / L, external power consumption was 0.18 kWh / kg COD removal, and conductive material consumption was 6.5 kg / ton VS.

[0073] Performance summary and synergistic effect analysis:

[0074] process Methane yield (L / kg vs) VS removal rate (%) Propionic acid peak value (mg / L) Cycle (days) External power consumption (kWh / kg COD) Net material consumption (kg / ton vs) Example 1 408 88.5 42 9.5 0.09 1.8 Example 2 392 86.2 78 10 0.11 2.2 Example 3 386 85.1 55 10 0.11 2.0 Comparative Example 4 355 78 95 12 0.18 6.5 Comparative Example 3 325 73 180 14 0.20 6.2 Comparative Example 2 290 69 310 15 - 6.0 Comparative Example 1 195 49 1100 25 - -

[0075] Synergy effect calculation:

[0076] Contribution of targeted acidification: Compared with Comparative Example 3 (non-targeted) → Comparative Example 4 (targeted), the yield increased by 30 L / kg VS (325 → 355), and the energy consumption decreased by 0.02 kWh / kg COD.

[0077] MEC contribution: Compared with Comparative Example 2 (without MEC) → Comparative Example 3 (with MEC), the yield increased by 35 L / kg VS (290 → 325), and the energy consumption increased by 0.20 (new addition).

[0078] Intelligent control + material recycling contribution: Compared with Comparative Example 4 (no intelligence, no recycling) → Example 1 (all included), the yield increased by 53L / kg VS (355→408), energy consumption decreased by 0.09, and material consumption decreased by 72%.

[0079] If the contributions of each component are simply added linearly, the expected yield = 195 (benchmark) + 30 + 35 + 53 = 313 L / kgVS. However, the actual benchmark should be Comparative Example 2 (290) or Comparative Example 3 (325). A more reasonable benchmark is the traditional two-phase + conductive material (Comparative Example 2: 290 L / kgVS). The improvements when each technology is applied individually to this benchmark are as follows:

[0080] Directional acidification only (Comparative Example 4 vs. Comparative Example 3): 355 - 325 = 30

[0081] MEC only (Comparative Example 3 vs. Comparative Example 2): 325 - 290 = 35

[0082] Intelligent control and recycling only (no experiment, but can be estimated at around 70%)

[0083] The total sum is 290 + 30 + 35 + 70 = 425, while the actual sum in Example 1 is 408, slightly lower than the theoretical sum (due to parameter overlap), but much higher than any single technology or any combination of two. More importantly, this invention achieves a significant reduction in both energy consumption and material consumption simultaneously.

[0084] Conclusion: This invention, through directional hydrolysis acidification, MEC-enhanced DIET, intelligent multi-parameter control, and magnetic material recycling, significantly outperforms existing technologies in terms of gas production performance, stability, energy consumption, and material cost, demonstrating outstanding substantial progress and industrial applicability.

[0085] The foregoing description enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An anaerobic biological fermentation process for the targeted degradation of municipal sewage sludge, characterized in that, Includes the following steps: (1) Pretreatment and component-directed activation: Adjust the solid content of municipal sludge to 5%-8%, add alkaline solution to adjust pH to 8.0-9.0, add compound enzyme preparation, and pretreat at 50-55℃ for 12-24 hours; (2) Staged hydrolysis and acidification: The pretreated sludge is fed into the hydrolysis and acidification reactor, inoculated with hydrolysis and acidification compound bacteria, and the temperature is controlled at 35-38℃, pH 6.2-6.5, and hydraulic retention time is 2-4 days to produce acetic acid and butyric acid in a targeted manner, and the proportion of propionic acid production to total volatile fatty acids is ≤5%; (3) Conductive material coupled microbial electrolysis cell assisted methanogenic fermentation: The effluent from step (2) is sent into the methanogenic reactor, the reactor is filled with modified nano-magnetite, and a microbial electrolysis cell module is set up. An external voltage of 0.3-0.8V is applied. Acetic acid-producing methanogens and hydrogen-producing methanogens are attached to both the cathode and anode. The temperature is controlled at 35-38℃, pH at 7.0-7.3, and the hydraulic retention time is 5-7 days. (4) Multi-parameter dynamic control based on online monitoring and intelligent algorithm: The volatile fatty acid spectrum (ratio of acetic acid, propionic acid and butyric acid) in the hydrolysis acidification reactor and the hydrogen partial pressure in the methanogenic reactor are monitored online. The pH value (range of 6.0-6.8) in step (2) and the applied voltage value (0.3-1.0V) in step (3) and the supplementary dosage of modified nano-magnetite are dynamically adjusted by the fuzzy logic controller. (5) Magnetic separation, recycling and reuse of magnetic conductive materials: A magnetic separation device is set at the outlet of the methanogenic reactor to recover modified nano-magnetite. After cleaning, 60%-80% of the recovered amount is reused in the hydrolysis acidification reactor of step (2), and the remaining 20%-40% is reused in the methanogenic reactor of step (3). (6) In-situ biogas purification and product gradient reflux: The biogas generated in step (3) is passed into an alkaline absorption tower to selectively absorb CO2, and part of the carbonate-rich solution after absorption is refluxed back to step (1); at the same time, the total volatile fatty acid concentration in the methanogenic reactor is monitored online. When the total volatile fatty acid concentration is >1200mg / L, the effluent from the methanogenic reactor is refluxed back to step (2) at a ratio of 1:2 to 1:

5. (7) Solid-liquid separation and residue resource utilization: After fermentation, the biogas residue and biogas slurry are separated. The biogas residue is utilized for resource utilization after aerobic stabilization, and part of the biogas slurry is returned to step (1).

2. The process according to claim 1, characterized in that, The compound enzyme preparation mentioned in step (1) is a combination of protease and lipase in a mass ratio of 1:1, with an addition amount of 5-20 mg / g volatile solids.

3. The process according to claim 1, characterized in that, The hydrolysis acidification compound bacterial agent mentioned in step (2) is mainly composed of Proteiniphilum acetatigenes and Clostridium butyricum, with the ratio of the two controlled at 2:1 to 3:

1. The total inoculum amount makes the initial volatile suspended solids concentration in the reactor 3-6 g / L.

4. The process according to claim 1, characterized in that, The modified nano-magnetite in step (3) has a filling rate of 2%-5% (w / v) of the effective volume of the reactor and a particle size of 50-200 nm. The preparation method is as follows: nano-Fe3O4 biochar is mixed at a mass ratio of 1:1 to 2:1 and pyrolyzed at 300-400℃ under a nitrogen atmosphere for 2 hours to obtain Fe3O4@biochar composite.

5. The process according to claim 1, characterized in that, The cathode of the microbial electrolysis cell module in step (3) is a carbon brush or carbon felt, the anode is a platinum carbon catalyst supported on carbon cloth (0.5 mg Pt / cm²), the electrode spacing is 5-10 cm, the applied voltage is provided by a DC power supply, and the current density is controlled at 0.5-2.0 A / m².

6. The process according to claim 1, characterized in that, The input variables of the fuzzy logic controller in step (4) are: propionic acid / total volatile fatty acid ratio (P / T), butyric acid / acetic acid ratio (B / A), and hydrogen partial pressure (pH2). The output variables are: pH adjustment amount (ΔpH), voltage adjustment amount (ΔV), and material supplement coefficient (k). Among them, the target value of P / T is ≤0.05, the target value of B / A is 0.8-1.2, and the target value of pH2 is ≤10Pa.

7. The process according to claim 1, characterized in that, The magnetic separation device mentioned in step (5) is a high gradient magnetic separator with a magnetic field strength of 0.5-1.2T. The recovered modified nano-magnetite is first ultrasonically cleaned with 0.1% SDS solution for 5 minutes, and then rinsed with deionized water before reuse.

8. The process according to claim 1, characterized in that, In step (6), the reflux control from the methanogenic reactor effluent to the hydrolysis acidified phase employs a two-stage logic. Stage 1 (Start-up Logic): Online monitoring of total volatile fatty acid (total VFAs) concentration. When total VFAs exceed 1200 mg / L, it indicates a high metabolic load in the system, and reflux operation is initiated. Stage 2 (Proportional Adjustment Logic): After reflux operation is initiated, the reflux ratio is dynamically selected based on the specific value of propionic acid concentration in the methanogenic reactor—a low reflux ratio of 1:5 is selected when propionic acid concentration <150 mg / L; a medium reflux ratio of 1:3 is selected when propionic acid concentration is 150-400 mg / L; and a high reflux ratio of 1:2 is selected when propionic acid concentration >400 mg / L.

9. The process according to claim 1, characterized in that, In step (2), an online volatile fatty acid analyzer is installed in the hydrolysis acidification reactor. When the propionic acid concentration is >250mg / L, a portion of the reactor effluent is automatically returned to step (1) for dilution. The reflux ratio is 1:5~1:

10.

10. The process according to any one of claims 1-9, characterized in that, The methanogenic reactor in step (3) is intermittently stirred (stirred for 10 minutes and stopped for 20 minutes), with a stirring speed of 15-30 rpm. A guide plate is set on the reactor wall to promote the contact between the conductive material and the microorganisms. Meanwhile, the electrodes of the microbial electrolysis cell module are fixed vertically in the middle of the reactor.

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