A method for increasing acid production from excess sludge through synergistic treatment with composite chelating agents and immobilized enzymes.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-30
- Publication Date
- 2026-08-14
AI Technical Summary
本发明协同解决污泥EPS致密、游离酶易失活、传统预处理污染大等问题，提升VFAs产量，固定化酶可回收，工艺温和、无二次污染，适用于城镇剩余污泥资源化工程应用
[0018]本发明在对剩余污泥进行处理时，先预脱水，接着进行高压脉冲电场处理，利用高强度、短时脉冲产生的电穿孔效应，对污泥絮体进行温和处理，破坏污泥胞外聚合物（EPS）外层的多糖网络结构及其与细胞膜的交联，打开污泥絮体致密结构，在细胞膜和EPS基质上形成可控的微孔道，从而显著提升后续酶制剂的扩散与接触效率；该处理过程以非热效应为主，能够温和地破坏污泥絮体结构，在不过度降解蛋白质、多糖等可利用有机质的前提下，有效提升污泥的生物可处理性；
Smart Images
Figure FT_1 
Figure SMS_1 
Figure SMS_2
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sludge treatment, specifically relating to a method for increasing the acid production of excess sludge through synergistic treatment of immobilized enzymes with a composite chelating agent. Background Technology
[0002] Waste sludge is rich in organic matter such as microbial cells, proteins, polysaccharides, and lipids, and has extremely high potential for resource utilization. Anaerobic fermentation to produce acid can directionally convert the recalcitrant organic matter in the sludge into volatile fatty acids (VFAs), which can be used as an external carbon source for wastewater treatment systems, as well as as raw materials for the synthesis of high-value-added products such as bioplastics and biofuels. This is a core technological path to achieve the synergistic reduction, stabilization, and resource utilization of sludge.
[0003] However, conventional anaerobic fermentation for acid production suffers from common bottlenecks such as low yield, slow rate, and long cycle, severely restricting its engineering application. The excess sludge flocs are formed by dense extracellular polymeric substances (EPS), which contain a large amount of calcium. 2+ Mg 2+ Alkaline earth metals form stable cross-linked networks with polysaccharides and proteins, while the cell wall structure is robust, making it difficult for large organic molecules to dissolve in the cell and between cells, resulting in extremely low hydrolysis efficiency. The anaerobic digestion process is unable to overcome the hydrolysis and acidification limitations, leading to slow accumulation and low yield of VFAs.
[0004] To overcome the barrier of sludge degradation, existing technologies mostly employ physical and chemical pretreatment to enhance cell lysis and cell wall disruption. While physical methods such as hot water hydrolysis, ultrasound, and microwaves can break down sludge structures, they suffer from high energy consumption, harsh conditions, and the potential for excessive degradation of organic matter, resulting in poor economic efficiency and controllability. Chemical pretreatments such as acids, alkalis, and oxidants can destroy EPS and cell walls, but they have drawbacks such as large dosages of chemicals, drastic pH fluctuations, and inhibition of subsequent acid-producing microorganisms. Furthermore, they can easily cause secondary pollution such as heavy metal leaching and salt ion residues, disrupting the anaerobic fermentation microecological balance.
[0005] Enzymatic pretreatment has become a research hotspot for improving sludge acid production efficiency due to its advantages such as high catalytic efficiency, mild action, and environmental friendliness. However, the direct application of free enzymes has significant technical drawbacks: in the complex sludge system, free enzymes are easily deactivated by factors such as heavy metal ions, pH fluctuations, and competition from other bacteria, resulting in poor catalytic stability; free enzymes cannot be recycled and reused, resulting in high enzyme consumption and operating costs; and the contact between free enzymes and sludge substrates is insufficient, leading to inadequate simultaneous hydrolysis of multiple organic components such as proteins, polysaccharides, and lipids, making it difficult to achieve efficient conversion of sludge organic matter.
[0006] While existing immobilized enzyme technology can improve enzyme stability and recyclability, it still suffers from problems such as low carrier specific surface area, limited enzyme loading, weak immobilization binding force and easy detachment, and high mass transfer resistance. Furthermore, it lacks a synergistic adaptation design with sludge pretreatment systems and cannot simultaneously solve multiple bottlenecks such as EPS dense barrier, heavy metal inhibition, poor enzyme stability, and acid-producing microenvironment imbalance.
[0007] Therefore, there is an urgent need to develop a method for the pretreatment and acidification of excess sludge that can synergistically enhance sludge cell disruption, organic matter dissolution, and enzyme catalysis efficiency, while taking into account both environmental friendliness and economic feasibility. Summary of the Invention
[0008] Technical Problem to be Solved: To address the aforementioned technical problems, the purpose of this invention is to provide a method for increasing the acid production of excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes. This method involves first mildly dewatering the sludge, followed by gentle cell disruption under a high-voltage pulsed electric field, then adding a tartaric acid-ethylenediaminedisuccinic acid (EDDS) composite chelating agent to break EPS crosslinking and passivate heavy metals. Subsequently, neutral proteases and β-glucosidases are immobilized using phosphonated lignin-based porous carbon@g-C3N4 (graphite-phase carbon nitride) to efficiently hydrolyze macromolecular organic matter. Finally, high-temperature anaerobic acidification is used to prepare volatile fatty acids. This invention synergistically solves problems such as dense EPS sludge, easy inactivation of free enzymes, and significant pollution from traditional pretreatment methods, increasing VFA production. The immobilized enzymes are recyclable, the process is gentle, and there is no secondary pollution, making it suitable for applications in urban excess sludge resource utilization projects.
[0009] Technical solution: A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes, comprising the following steps: S1. Take the excess sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 80-90% to obtain pre-dewatered sludge; S2. After treating the pre-dewatered sludge with a high-voltage pulse electric field, add a composite chelating agent and stir for 1-2 hours to obtain pretreated sludge. S3. Add immobilized enzyme to the pretreated sludge, react at 45-55℃ and 100-150rpm for 12-24h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5min to remove oxygen, and perform high-temperature anaerobic acidification at 50-60℃ for 2-4 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution.
[0010] Furthermore, in step S2, the electric field strength of the high-voltage pulse electric field is 15-25 kV / cm, the pulse width is 10-20 μs, and the processing time is 1-10 min.
[0011] Furthermore, the amount of the composite chelating agent added in step S2, based on the dry basis of the pre-dehydrated sludge, is 0.2-0.5 g / g dry basis; the composite chelating agent is a mixed solution of tartaric acid and ethylenediamine disuccinic acid, with a mass ratio of 1:(0.5-2).
[0012] Furthermore, the amount of immobilized enzyme added in step S3, based on the dry basis of the pretreated sludge, is 0.15-0.45 g / g dry basis.
[0013] Furthermore, the specific preparation steps of the immobilized enzyme are as follows: Step 1. Wash and dry the lignin, mix and grind it with KOH at a mass ratio of 1:(1.5-2.5), calcine it at 550-650℃ for 1.5-2h under a nitrogen atmosphere, acid wash, water wash until neutral, and dry to obtain lignin-based porous carbon; Step 2. Mix lignin-based porous carbon with dicyandiamide and urea, and calcine at 500-600℃ for 2.5-3h under a nitrogen atmosphere to obtain lignin-based porous carbon@g-C3N4 support; Step 3. Add the lignin-based porous carbon@g-C3N4 support to a mixed aqueous solution of phosphonite and sodium hypophosphite, react in a water bath at 70-90℃ for 3-5 hours, filter, wash with water until neutral, and dry to obtain the phosphonate-modified support; Step 4. Immerse the phosphonate-modified carrier in the composite enzyme solution, shake at 4℃ and 120-150 rpm for 10-14 hours, filter, and the immobilized enzyme is obtained.
[0014] Furthermore, in step 2, the mass ratio of lignin-based porous carbon, dicyandiamide, and urea is 1:(3-6):(3-6).
[0015] Furthermore, in step 3, the mass ratio of phosphonic acid to sodium hypophosphite in the phosphonic acid-sodium hypophosphite mixed aqueous solution is 1:(1-3); the mass-volume ratio of the lignin-based porous carbon@g-C3N4 support to the phosphonic acid-sodium hypophosphite mixed aqueous solution is 1g:(8-15)mL.
[0016] Furthermore, in step 4, the complex enzyme solution is a mixed solution of neutral protease and β-glucosidase, with a mass ratio of 1:(0.8-1); the neutral protease has an enzyme activity of 200,000-500,000 U / g, and the β-glucosidase has an enzyme activity of 100,000-300,000 U / g.
[0017] Furthermore, in step 4, the mass-to-volume ratio of the phosphonate-modified carrier to the composite enzyme solution is 1 g: (10-20) mL. Beneficial effects
[0018] In treating excess sludge, this invention first pre-dehydrates it, followed by high-voltage pulsed electric field treatment. Utilizing the electroporation effect generated by the high-intensity, short-duration pulses, the sludge flocs are gently treated, disrupting the polysaccharide network structure of the extracellular polymeric substance (EPS) layer and its cross-linking with the cell membrane. This opens up the dense structure of the sludge flocs, forming controllable micropores on the cell membrane and EPS matrix, thereby significantly improving the diffusion and contact efficiency of subsequent enzyme preparations. This treatment process is primarily non-thermal, gently disrupting the sludge floc structure and effectively improving the biotreatability of the sludge without excessively degrading usable organic matter such as proteins and polysaccharides. This invention involves adding a tartaric acid-ethylenediaminedisuccinic acid (EDDS) composite chelating agent to the system after high-voltage pulsed electric field treatment. Tartaric acid can chelate the large amount of Ca present in the sludge. 2+ Mg 2+ Alkaline earth metal ions disrupt the cross-linking structure of metal-EPS-organic matter, opening up the gaps between sludge flocs; the EDDS molecular structure contains multiple amino and carboxyl coordination sites, which can chelate Cu. 2+ Zn 2+ Fe 3+ Mn 2+ Transition metal ions prevent heavy metal ions from contacting the active site of enzyme proteins and from penetrating the cell membrane of acid-producing bacteria to produce toxicity, thus passivating the inhibitory effect of heavy metals on enzymes and acid-producing bacteria. The combined use of tartaric acid and EDDS effectively chelates metal ions, and the mixed system has a certain buffering capacity for pH changes in the reaction solution, which helps to maintain the pH of the system within a weakly acidic range that is favorable for subsequent enzyme catalysis, thereby reducing the adverse effects of pH fluctuations on enzyme activity. This invention involves treating residual sludge with a high-voltage pulsed electric field and chelation, followed by the addition of a phosphonate-modified lignin-based porous carbon@g-C3N4 immobilized composite enzyme. For the immobilized enzyme, a lignin-based porous carbon@g-C3N4 carrier is first prepared and then immersed in a phosphonite-sodium hypophosphite composite phosphonation reagent for phosphonate modification, introducing a large number of -PO(OH)2 phosphonate groups onto the carrier surface. Finally, the modified carrier is immersed in a composite enzyme solution (neutral protease, β-glucosidase). The phosphonate groups on the carrier surface form phosphonamide bonds with the amino groups of the enzyme molecules, while the rich porous structure of the carrier provides physical adsorption sites, resulting in a highly loaded, highly stable, and recyclable immobilized composite enzyme. Utilizing the high catalytic activity and stability of the immobilized enzyme, recalcitrant macromolecular organic matter in the sludge can be converted into small-molecule acid precursors (amino acids, monosaccharides, fatty acids, etc.), improving the substrate availability and conversion rate for subsequent anaerobic acid production. Finally, the sludge system after enzyme-catalyzed hydrolysis is transferred to a closed anaerobic acidification reactor. The system is controlled to carry out anaerobic fermentation and acid production under high temperature and anaerobic conditions. The hydrolytic acid-producing bacteria (Clostridium, Vibrio butyricum, Propionibacterium, etc.) in the system have vigorous metabolism and can quickly and efficiently convert the substrate into high-value volatile fatty acids (such as acetic acid, propionic acid, butyric acid, etc.), which greatly improves the resource utilization efficiency and acid production rate of the remaining sludge. Attached Figure Description
[0019] Figure 1 Figures show the sludge after treatment in different embodiments and comparative examples. Detailed Implementation
[0020] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: Example 1
[0021] The specific preparation steps for immobilized enzymes are as follows: Step 1. Wash and dry the lignin, mix and grind it with KOH at a mass ratio of 1:2, calcine it at 600℃ for 2 hours under a nitrogen atmosphere, acid wash, water wash until neutral, and dry to obtain lignin-based porous carbon; Step 2. Mix lignin-based porous carbon with dicyandiamide and urea in a mass ratio of 1:3:3, and calcine at 600℃ for 3 hours under a nitrogen atmosphere to obtain lignin-based porous carbon@g-C3N4 support; Step 3. Add the lignin-based porous carbon@g-C3N4 support to a mixed aqueous solution of phosphonite and sodium hypophosphite (the mass ratio of phosphonite to sodium hypophosphite is 1:1) at a mass-volume ratio of 1g:8mL, react in a water bath at 80℃ for 4h, filter, wash with water until neutral, and dry to obtain the phosphonate-modified support. Step 4. Immerse the phosphonate-modified carrier in a composite enzyme solution (a 1:1 mass ratio of neutral protease and β-glucosidase), wherein the activity of the neutral protease is 300,000 U / g and the activity of the β-glucosidase is 200,000 U / g, and the mass-volume ratio of the phosphonate-modified carrier to the composite enzyme solution is 1 g: 10 mL. React at 4°C and 150 rpm for 12 h with shaking, then filter to obtain the immobilized enzyme. Example 2
[0022] The specific preparation steps for immobilized enzymes are as follows: Step 1. Wash and dry the lignin, mix and grind it with KOH at a mass ratio of 1:2, calcine it at 600℃ for 2 hours under a nitrogen atmosphere, acid wash, water wash until neutral, and dry to obtain lignin-based porous carbon; Step 2. Mix lignin-based porous carbon with dicyandiamide and urea in a mass ratio of 1:3:6, and calcine at 600℃ for 3 hours under a nitrogen atmosphere to obtain lignin-based porous carbon@g-C3N4 support; Step 3. Add the lignin-based porous carbon@g-C3N4 support to a mixed aqueous solution of phosphonite and sodium hypophosphite (the mass ratio of phosphonite to sodium hypophosphite is 1:1) at a mass-volume ratio of 1g:10mL, react in a water bath at 80℃ for 4h, filter, wash with water until neutral, and dry to obtain the phosphonate-modified support. Step 4. Immerse the phosphonate-modified carrier in a composite enzyme solution (a 1:1 mass ratio of neutral protease and β-glucosidase), wherein the activity of the neutral protease is 300,000 U / g and the activity of the β-glucosidase is 200,000 U / g, and the mass-volume ratio of the phosphonate-modified carrier to the composite enzyme solution is 1 g: 15 mL. React at 4℃ and 150 rpm for 12 h with shaking, then filter to obtain the immobilized enzyme. Example 3
[0023] The specific preparation steps for immobilized enzymes are as follows: Step 1. Wash and dry the lignin, mix and grind it with KOH at a mass ratio of 1:2, calcine it at 600℃ for 2 hours under a nitrogen atmosphere, acid wash, water wash until neutral, and dry to obtain lignin-based porous carbon; Step 2. Mix lignin-based porous carbon with dicyandiamide and urea at a mass ratio of 1:6:6, and calcine at 600℃ for 3 hours under a nitrogen atmosphere to obtain lignin-based porous carbon@g-C3N4 support; Step 3. Add the lignin-based porous carbon@g-C3N4 support to a mixed aqueous solution of phosphonite and sodium hypophosphite (the mass ratio of phosphonite to sodium hypophosphite is 1:1) at a mass-volume ratio of 1g:15mL, react in a water bath at 80℃ for 4h, filter, wash with water until neutral, and dry to obtain the phosphonate-modified support. Step 4. Immerse the phosphonate-modified carrier in a composite enzyme solution (a 1:1 mass ratio of neutral protease and β-glucosidase), wherein the neutral protease has an activity of 300,000 U / g and the β-glucosidase has an activity of 200,000 U / g, and the mass-volume ratio of the phosphonate-modified carrier to the composite enzyme solution is 1 g: 20 mL. React at 4°C and 150 rpm for 12 h with shaking, then filter to obtain the immobilized enzyme. Example 4
[0024] The specific preparation steps for immobilized enzymes are as follows: Step 1. Wash and dry the lignin, mix and grind it with KOH at a mass ratio of 1:2, calcine it at 600℃ for 2 hours under a nitrogen atmosphere, acid wash, water wash until neutral, and dry to obtain lignin-based porous carbon; Step 2. Mix lignin-based porous carbon with dicyandiamide and urea at a mass ratio of 1:4:4, and calcine at 600℃ for 3 hours under a nitrogen atmosphere to obtain lignin-based porous carbon@g-C3N4 support; Step 3. Add the lignin-based porous carbon@g-C3N4 support to a mixed aqueous solution of phosphonite and sodium hypophosphite (the mass ratio of phosphonite to sodium hypophosphite is 1:1) at a mass-volume ratio of 1g:10mL, react in a water bath at 80℃ for 4h, filter, wash with water until neutral, and dry to obtain the phosphonate-modified support. Step 4. Immerse the phosphonate-modified carrier in a composite enzyme solution (a 1:1 mass ratio of neutral protease and β-glucosidase), wherein the neutral protease has an activity of 300,000 U / g and the β-glucosidase has an activity of 200,000 U / g, and the mass-volume ratio of the phosphonate-modified carrier to the composite enzyme solution is 1 g: 20 mL. React at 4°C and 150 rpm for 12 h with shaking, then filter to obtain the immobilized enzyme. Comparative Example 1
[0025] The difference between this comparative example and Example 4 is that no phosphonate modification was performed, as detailed below: The specific preparation steps for immobilized enzymes are as follows: Step 1. Wash and dry the lignin, mix and grind it with KOH at a mass ratio of 1:2, calcine it at 600℃ for 2 hours under a nitrogen atmosphere, acid wash, water wash until neutral, and dry to obtain lignin-based porous carbon; Step 2. Mix lignin-based porous carbon with dicyandiamide and urea at a mass ratio of 1:4:4, and calcine at 600℃ for 3 hours under a nitrogen atmosphere to obtain lignin-based porous carbon@g-C3N4 support; Step 3. Immerse the lignin-based porous carbon@g-C3N4 carrier in a composite enzyme solution (a 1:1 mass ratio of neutral protease and β-glucosidase), wherein the neutral protease has an activity of 300,000 U / g and the β-glucosidase has an activity of 200,000 U / g, and the mass-volume ratio of carrier to composite enzyme solution is 1 g: 20 mL. React at 4°C and 150 rpm for 12 h with shaking, and filter to obtain the immobilized enzyme. Porosity and enzyme loading determination:
[0026] Porosity was determined using the nitrogen adsorption method; Enzyme loading rate determination: 1) The total protein concentration in the supernatant before and after immobilization was determined using the BCA protein kit; 2) Take the initial composite enzyme solution from step 4 in the immobilized enzyme preparation process and record the volume V0; 3) After the shaking reaction has been completed for 12 hours, collect the remaining enzyme solution after filtration and record the volume V1; Calculate the enzyme loading rate using the following formula:
[0027] In the formula, C0 is the initial enzyme solution protein concentration (mg / mL), V0 is the initial enzyme solution volume (mL), C1 is the remaining enzyme solution protein concentration (mg / mL), and V1 is the remaining enzyme solution volume (mL).
[0028] Table 1 Porosity and Enzyme Loading Rate
[0029] As shown in Table 1, after phosphonate modification in Examples 1-4, a large number of phosphonic acid groups were introduced into the carrier surface, resulting in a richer pore structure and higher porosity, providing sufficient loading sites for enzyme molecules. Therefore, the enzyme loading rate was significantly higher than that of Comparative Example 1. Comparative Example 1 did not undergo phosphonate modification and relied solely on physical adsorption to load enzyme molecules. As a result, the carrier surface had insufficient active sites and weak binding ability to enzymes, leading to a decrease in both porosity and enzyme loading rate. This indicates that phosphonate modification can effectively improve the carrier porosity and enzyme immobilization capacity.
[0030] Therefore, the immobilized enzyme prepared in Example 4 was selected for subsequent anaerobic fermentation of residual sludge to produce acid. Example 5
[0031] A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge was subjected to high-voltage pulsed electric field treatment with an electric field strength of 15kV / cm, a pulse width of 10μs, and a treatment time of 5min. Then, a composite chelating agent (a tartaric acid-ethylenediaminedisuccinic acid mixed solution with a mass ratio of 1:1) was added. The amount of composite chelating agent added was 0.2 g / g dry basis based on the dry basis of the pre-dewatered sludge. The mixture was stirred and reacted for 2h to obtain pre-treated sludge. S3. Add immobilized enzyme to the pretreated sludge (the amount of immobilized enzyme added is 0.15 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 50℃ for 4 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Example 6
[0032] A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge was subjected to high-voltage pulsed electric field treatment with an electric field strength of 25kV / cm, a pulse width of 10μs, and a treatment time of 5min. Then, a composite chelating agent (a tartaric acid-ethylenediaminedisuccinic acid mixed solution with a mass ratio of 1:1) was added. The amount of composite chelating agent added was 0.2 g / g dry basis based on the dry basis of the pre-dewatered sludge. The mixture was stirred and reacted for 2h to obtain pre-treated sludge. S3. Add immobilized enzyme to the pretreated sludge (the amount of immobilized enzyme added is 0.15 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 50℃ for 4 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Example 7
[0033] A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge is subjected to high-voltage pulsed electric field treatment with an electric field strength of 20kV / cm, a pulse width of 10μs, and a treatment time of 5min. Then, a composite chelating agent (a tartaric acid-ethylenediaminedisuccinic acid mixed solution with a mass ratio of 1:1) is added. The amount of composite chelating agent added is 0.5 g / g dry basis based on the dry basis of the pre-dewatered sludge. The mixture is stirred and reacted for 2h to obtain pre-treated sludge. S3. Add immobilized enzyme to the pretreated sludge (the amount of immobilized enzyme added is 0.15 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 50℃ for 4 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Example 8
[0034] A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge was subjected to high-voltage pulsed electric field treatment with an electric field strength of 20kV / cm, a pulse width of 10μs, and a treatment time of 5min. Then, a composite chelating agent (a tartaric acid-ethylenediaminedisuccinic acid mixed solution with a mass ratio of 1:1) was added. The amount of composite chelating agent added was 0.4 g / g dry basis based on the dry basis of the pre-dewatered sludge. The mixture was stirred and reacted for 2h to obtain pre-treated sludge. S3. Add immobilized enzyme to the pretreated sludge (the amount of immobilized enzyme added is 0.3 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 50℃ for 4 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Example 9
[0035] A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge was subjected to high-voltage pulsed electric field treatment with an electric field strength of 20kV / cm, a pulse width of 10μs, and a treatment time of 5min. Then, a composite chelating agent (a tartaric acid-ethylenediaminedisuccinic acid mixed solution with a mass ratio of 1:1) was added. The amount of composite chelating agent added was 0.4g / g dry basis based on the dry basis of the pre-dewatered sludge. The mixture was stirred and reacted for 2h to obtain pre-treated sludge. S3. Add immobilized enzyme to the pretreated sludge (the amount of immobilized enzyme added is 0.45 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 60℃ for 2 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Example 10
[0036] A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge was subjected to high-voltage pulsed electric field treatment with an electric field strength of 20kV / cm, a pulse width of 10μs, and a treatment time of 5min. Then, a composite chelating agent (a tartaric acid-ethylenediaminedisuccinic acid mixed solution with a mass ratio of 1:1) was added. The amount of composite chelating agent added was 0.4g / g dry basis based on the dry basis of the pre-dewatered sludge. The mixture was stirred and reacted for 2h to obtain pre-treated sludge. S3. Add immobilized enzyme to the pretreated sludge (the amount of immobilized enzyme added is 0.4 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 60℃ for 3 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Comparative Example 2
[0037] The difference between this comparative example and Example 10 is that it did not use high-voltage pulsed electric field treatment, as detailed below: A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. Add a composite chelating agent (a tartaric acid-ethylenediamine disuccinic acid mixed solution with a mass ratio of 1:1) to the pre-dewatered sludge. The amount of composite chelating agent added is 0.4 g / g dry basis based on the dry basis of the pre-dewatered sludge. Stir and react for 2 hours to obtain pretreated sludge. S3. Add immobilized enzyme to the pretreated sludge (the amount of immobilized enzyme added is 0.4 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 60℃ for 3 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Comparative Example 3
[0038] The difference between this comparative example and Example 10 is that no composite chelating agent was added, as detailed below: A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge is subjected to high-voltage pulse electric field treatment with an electric field strength of 20kV / cm, a pulse width of 10μs, and a treatment time of 5min to obtain pre-treated sludge; S3. Add immobilized enzyme to the pretreated sludge (the amount of immobilized enzyme added is 0.4 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 60℃ for 3 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Comparative Example 4
[0039] The difference between this comparative example and Example 10 is that no immobilized enzyme was added; instead, a free enzyme was added directly, as detailed below: A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge was subjected to high-voltage pulsed electric field treatment with an electric field strength of 20kV / cm, a pulse width of 10μs, and a treatment time of 5min. Then, a composite chelating agent (a tartaric acid-ethylenediaminedisuccinic acid mixed solution with a mass ratio of 1:1) was added. The amount of composite chelating agent added was 0.4g / g dry basis based on the dry basis of the pre-dewatered sludge. The mixture was stirred and reacted for 2h to obtain pre-treated sludge. S3. Prepare a composite free enzyme solution, which is a mixed aqueous solution of neutral protease and β-glucosidase, wherein the mass ratio of neutral protease to β-glucosidase is 1:1, the enzyme activity of neutral protease is 300,000 U / g, and the enzyme activity of β-glucosidase is 200,000 U / g. Stir and dissolve until clear, and set aside for later use. S4. Add a compound enzyme solution with a dosage of 0.4 g / g of dry pretreated sludge to the pretreated sludge, react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 60℃ for 3 days. S5. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Comparative Example 5
[0040] The difference between this comparative example and Example 10 is the addition of the immobilized enzyme prepared in Comparative Example 1, as detailed below: A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes includes the following steps: S1. Take the residual sludge from the urban wastewater treatment plant, and lightly dewater it to a moisture content of 85% to obtain pre-dewatered sludge; S2. The pre-dewatered sludge was subjected to high-voltage pulsed electric field treatment with an electric field strength of 20kV / cm, a pulse width of 10μs, and a treatment time of 5min. Then, a composite chelating agent (a tartaric acid-ethylenediaminedisuccinic acid mixed solution with a mass ratio of 1:1) was added. The amount of composite chelating agent added was 0.4g / g dry basis based on the dry basis of the pre-dewatered sludge. The mixture was stirred and reacted for 2h to obtain pre-treated sludge. S3. Add the immobilized enzyme prepared in Comparative Example 1 to the pretreated sludge (the amount of immobilized enzyme added is 0.4 g / g dry basis based on the dry basis of the pretreated sludge), react at 50℃ and 150 rpm for 20 h, then transfer to a closed anaerobic reactor, purge with nitrogen for 5 min to remove oxygen, and perform high-temperature anaerobic acidification at 60℃ for 3 days. S4. After the reaction is complete, the sludge is discharged and dewatered and separated into mud and water using a plate and frame filter press. The separated liquid is a volatile fatty acid solution. Performance testing:
[0041] Volatile fatty acid production 1) Sample pretreatment: Take the mud-water mixture after anaerobic fermentation, centrifuge at 8000 rpm for 10 min, take the supernatant, filter it through a 0.22 μm filter membrane to remove suspended impurities, and obtain the VFAs test solution; 2) VSS determination: The mass of volatile suspended solids (VSS) in the sludge before fermentation was determined by gravimetric method according to the "Standard Test Methods for Urban Sludge" (CJ / T 221-2023), and the unit is g; 3) Determination of volatile fatty acid concentration Gas chromatography conditions: A gas chromatograph equipped with a flame ionization detector (FID) and a capillary column (e.g., DB-FFAP, 30m × 0.25mm × 0.25μm) was used; the injection port temperature was 220℃, and the detector temperature was 250℃; the temperature program was as follows: initial temperature 80℃ held for 2 min, then increased to 180℃ at a rate of 10℃ / min and held for 5 min; the carrier gas was high-purity nitrogen, with a flow rate of 1.0 mL / min and a split ratio of 20:1; the injection volume was 1 μL. Plotting the standard curve: a. Prepare a series of standard solutions with five different concentrations (50, 100, 250, 500, 1000 mg / L) using mixed VFA standards. b. Inject and analyze the standard solutions of each concentration according to the chromatographic conditions described above; c. Plot the standard curves of the six VFAs with the concentration of each VFA component as the abscissa (X) and the corresponding chromatographic peak area as the ordinate (Y), and obtain the linear regression equation and correlation coefficient. Sample determination: The test solution is directly injected for GC analysis. The VFA components are qualitatively identified based on their retention time. Based on their peak areas, the concentration of each VFA in the test solution (unit: mg / L) is calculated by substituting them into the respective standard curve equations. Production Calculation Calculate the total mass of VFAs in the supernatant: Total mass of VFAs (mg) = Σ [Cᵢ (mg / L) × V (L)] Where Cᵢ (mg / L) is the concentration of each VFA in the test solution; i represents acetic acid, propionic acid, butyric acid, isobutyric acid, isovaleric acid, and valeric acid; V (L) is the total volume of the sample. VFAs yield (mgCOD / g VSS) = Total VFAs mass (mg) / Mass of VSS in sludge before fermentation (g) Each volatile fatty acid component was converted according to the theoretical chemical oxygen demand (COD) conversion factor: acetic acid 1.07 mg COD / mg, propionic acid 1.51 mg COD / mg, butyric acid 1.82 mg COD / mg, isobutyric acid 1.82 mg COD / mg, isovaleric acid 2.04 mg COD / mg, and valeric acid 2.04 mg COD / mg.
[0042] Table 2. Production of volatile fatty acids
[0043] Experimental data show that the synergistic treatment process of high-voltage pulsed electric field, composite chelating agent and phosphonate-modified immobilized enzyme in Examples 5-10 can effectively improve the acid production efficiency of anaerobic fermentation of waste sludge. Among them, the VFAs yield of Example 10 reached 378.2 mgCOD / gVSS, while the acid production efficiency of Comparative Examples 2-5 decreased significantly due to the lack of a single core process step. This fully demonstrates that the synergistic effect of each process step in this invention is of great significance for improving the acid production of waste sludge.
[0044] Organic matter dissolution rate 1) Sample pretreatment Take the pre-dehydrated sludge before pretreatment (i.e. after step S1), centrifuge at 8000 rpm for 10 min, take the supernatant and filter it through a 0.45 μm aqueous filter membrane, and collect the filtrate as the sample before pretreatment; take the pretreated sludge after pretreatment (i.e. after step S2), centrifuge at 8000 rpm for 10 min, take the supernatant and filter it through a 0.45 μm aqueous filter membrane, and collect the filtrate as the sample after pretreatment.
[0045] 2) Determination of dissolved chemical oxygen demand (SCOD) The potassium dichromate method was used for determination. An appropriate amount of filtrate was added to a digestion tube, along with potassium dichromate standard solution and a sulfuric acid-silver sulfate catalyst. Digestion was carried out at 165℃ for 15 min. After digestion, the remaining potassium dichromate was titrated with ferrous ammonium sulfate standard solution. The SCOD value in the sample was calculated based on the consumption amount, and the SCOD dissolution rate was calculated using the following formula:
[0046] Among them, SCOD 前 The SCOD concentration (mg / L) of the sludge supernatant before pretreatment. 后 The SCOD concentration (mg / L) is the concentration of the supernatant in the pretreated sludge.
[0047] Determination of soluble proteins The Coomassie Brilliant Blue method was used for determination. Coomassie Brilliant Blue G-250 staining solution was prepared, and a standard curve was established using bovine serum albumin (BSA) as a standard. An appropriate amount of filtrate was mixed with the Coomassie Brilliant Blue staining solution, and after reacting at room temperature for 10 min, the absorbance was measured at a wavelength of 595 nm. The protein concentration (mg / L) in the sample was calculated according to the standard curve, and the protein dissolution rate was calculated using the following formula:
[0048] Determination of soluble polysaccharides The polysaccharide concentration was determined using the phenol-sulfuric acid method, with glucose as the standard. A suitable amount of filtrate was taken, and phenol solution and concentrated sulfuric acid were added. After mixing, the mixture was boiled in a water bath for 15 min, and the absorbance was measured at 490 nm after cooling. The polysaccharide concentration (mg / L) in the sample was calculated based on the standard curve, and the polysaccharide dissolution rate was calculated using the following formula:
[0049] Table 3 Organic matter dissolution rate
[0050] As shown in Table 3, the SCOD dissolution rates of Examples 5-10 of the present invention ranged from 28.6% to 38.5%, the protein dissolution rates ranged from 26.8% to 35.7%, and the polysaccharide dissolution rates ranged from 24.2% to 32.9%. Among them, Example 10 achieved the highest values for all three dissolution rates. The higher the organic matter dissolution rate, the more fully the sludge cell walls were broken, the more macromolecular organic matter was dissolved, the better the substrate availability, and the more conducive it is to subsequent anaerobic fermentation for acid production. In Comparative Example 2, omitting the high-voltage pulsed electric field treatment resulted in a significant decrease in the dissolution rate to below 20%, confirming the crucial role of the electroporation effect of the high-voltage pulsed electric field in sludge cell disruption. In Comparative Example 3, omitting the composite chelating agent resulted in a dissolution rate that, while improved compared to Comparative Example 2, was significantly lower than that of Example 10, indicating that the composite chelating agent can further enhance organic matter release by disrupting the cross-linking structure of metal ions in EPS. The dissolution rates of Comparative Examples 4-5 were similar to those of Example 10, further illustrating that organic matter dissolution mainly depends on the synergistic effect of the pretreatment stage (high-voltage pulsed electric field + composite chelating agent), while the core function of the enzymatic hydrolysis stage is to efficiently convert the dissolved large-molecule organic matter into small-molecule acid precursors.
[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the present invention.
Claims
1. A method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes, characterized in that, Includes the following steps: S1. Take the excess sludge from the urban wastewater treatment plant and dewater it slightly to a moisture content of 80-90% to obtain pre-dewatered sludge; S2. After treating the pre-dewatered sludge with a high-voltage pulse electric field, add a composite chelating agent and stir for 1-2 hours to obtain pretreated sludge. S3. Add immobilized enzyme to the pretreated sludge, react at 45-55℃ and 100-150rpm for 12-24h, then transfer to a closed anaerobic reactor, purge with nitrogen, and perform high-temperature anaerobic acidification at 50-60℃ for 2-4 days. S4. After the reaction is complete, the sludge is discharged, dehydrated, and separated into mud and water. The separated liquid is a volatile fatty acid solution.
2. The method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes according to claim 1, characterized in that: In step S2, the electric field strength of the high-voltage pulse electric field is 15-25 kV / cm, the pulse width is 10-20 μs, and the processing time is 1-10 min.
3. The method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes according to claim 1, characterized in that: The amount of the composite chelating agent added in step S2, based on the dry basis of the pre-dehydrated sludge, is 0.2-0.5 g / g dry basis; the composite chelating agent is a mixed solution of tartaric acid and ethylenediamine disuccinic acid, with a mass ratio of 1:(0.5-2).
4. The method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes according to claim 1, characterized in that: The amount of immobilized enzyme added in step S3, based on the dry basis of the pretreated sludge, is 0.15-0.45 g / g dry basis.
5. The method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes according to claim 4, characterized in that, The specific preparation steps of the immobilized enzyme are as follows: Step 1. Wash and dry the lignin, mix and grind it with KOH at a mass ratio of 1:(1.5-2.5), calcine it at 550-650℃ for 1.5-2h under a nitrogen atmosphere, acid wash, water wash until neutral, and dry to obtain lignin-based porous carbon; Step 2. Mix lignin-based porous carbon with dicyandiamide and urea, and calcine at 500-600℃ for 2.5-3h under a nitrogen atmosphere to obtain lignin-based porous carbon@g-C3N4 support; Step 3. Add the lignin-based porous carbon@g-C3N4 support to a mixed aqueous solution of phosphonite and sodium hypophosphite, react in a water bath at 70-90℃ for 3-5 hours, filter, wash with water until neutral, and dry to obtain the phosphonate-modified support; Step 4. Immerse the phosphonate-modified carrier in the composite enzyme solution, shake at 4℃ and 120-150 rpm for 10-14 hours, filter, and the immobilized enzyme is obtained.
6. The method for increasing acid production from excess sludge through synergistic treatment of immobilized enzymes with a composite chelating agent according to claim 5, characterized in that, In step 2, the mass ratio of lignin-based porous carbon, dicyandiamide, and urea is 1:(3-6):(3-6).
7. The method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes according to claim 5, characterized in that, In step 3, the mass ratio of phosphonic acid to sodium hypophosphite in the phosphonic acid-sodium hypophosphite mixed aqueous solution is 1:(1-3); the mass-volume ratio of the lignin-based porous carbon@g-C3N4 support to the phosphonic acid-sodium hypophosphite mixed aqueous solution is 1g:(8-15)mL.
8. The method for increasing acid production from excess sludge through synergistic treatment with a composite chelating agent and immobilized enzymes according to claim 5, characterized in that, In step 4, the complex enzyme solution is a mixed solution of neutral protease and β-glucosidase in a mass ratio of 1:(0.8-1); the neutral protease has an enzyme activity of 200,000-500,000 U / g and the β-glucosidase has an enzyme activity of 100,000-300,000 U / g.
9. The method for increasing acid production from excess sludge through synergistic treatment of immobilized enzymes with a composite chelating agent according to claim 5, characterized in that, In step 4, the mass-to-volume ratio of the phosphonate-modified carrier to the composite enzyme solution is 1 g: (10-20) mL.