Electrolysis reinforced biochar activated persulfate coupling flocculation sludge advanced dewatering conditioning method and preparation method of modified biochar

Abstract

This invention relates to a method for deep dewatering and conditioning of sludge through electrolytically enhanced biochar activation of persulfate coupled with flocculation, and a method for preparing modified biochar. By coupling persulfate oxidation, electrochemical oxidation, and flocculation, and using modified biochar prepared from wastewater treatment plant sludge to activate the persulfate, strong oxidizing free radicals such as sulfate radicals are generated. These free radicals oxidize and degrade EPS in the sludge flocs, improving sludge dewatering performance. Simultaneously, within the electrochemical system, the modified biochar acts as a microelectrode between the cathode and anode, forming a micro-electrolysis system. This system effectively activates the persulfate to generate strong oxidizing free radicals such as sulfate radicals, thereby enhancing the system's oxidation capacity and achieving deep degradation of sludge EPS. Finally, flocculation conditioning promotes the aggregation of fine sludge particles, increases the aggregation strength of sludge flocs, and constructs a sludge cake structure with good filtration performance, achieving deep sludge dewatering.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment, disposal and resource utilization, specifically involving a method for deep dewatering and conditioning of sludge by electrolytically enhanced biochar activation and persulfate coupled flocculation, and a method for preparing modified biochar. Background Technology

[0002] my country's current urban wastewater treatment capacity exceeds 200 million tons per day, generating over 60 million tons of sludge (with an 80% moisture content) annually. By 2025, this annual sludge production is projected to surpass 90 million tons. Sludge dewatering is a crucial step in the sludge treatment process, effectively reducing sludge volume and lowering subsequent treatment and disposal costs. However, EPS (extracellular polymeric substances) in sludge are highly hydrophilic, and their hydration and adhesion effects on sludge flocs make dewatering difficult, increasing the volume of dewatered sludge and subsequent treatment and disposal costs. Therefore, developing environmentally friendly deep sludge dewatering and conditioning technologies is of paramount importance.

[0003] CN111977939B discloses a method for treating residual sludge dewatering using electrocatalytic coupling of sulfate free radicals. This method uses electrical energy to activate persulfate to condition the sludge and improve its dewatering performance. However, this method has a single activation method for persulfate, generates fewer strong oxidizing free radicals, and has a limited degree of degradation on the sludge. Furthermore, oxidizing the sludge can lead to a smaller sludge particle size, which is not conducive to sludge dewatering. Summary of the Invention

[0004] The purpose of this invention is to provide a method for deep dewatering and conditioning of sludge using electrolytically enhanced biochar-activated persulfate coupled with flocculation, and a method for preparing modified biochar. By coupling persulfate oxidation, electrochemical oxidation, and flocculation based on modified biochar in a sludge dewatering and conditioning reactor, the degradation degree of sludge EPS by the persulfate oxidation and electrochemical oxidation system is enhanced. By coupling with flocculation, the problem of reduced particle size of oxidized sludge, which is not conducive to sludge dewatering, is solved, and a sludge cake structure with good filtration performance is constructed to achieve deep sludge dewatering.

[0005] To achieve the above objectives, the present invention provides a method for electrolytically enhanced biochar-activated persulfate coupled flocculation conditioning of sludge, comprising the following steps: adding the sludge to be conditioned into a conditioning device, adding modified biochar and persulfate, and placing the two electrodes in the conditioning device with inert electrodes as the cathode and anode, and performing electrolytic treatment by applying electricity, with continuous stirring during the conditioning process; after the conditioning is completed, adding flocculant again and stirring and allowing it to stand.

[0006] Preferably, the sludge to be conditioned can be either sludge from urban wastewater treatment plants or sludge from industrial wastewater treatment plants, with a moisture content of 96-99 wt.%.

[0007] Preferably, the dosage of modified biochar is 50~250 mg / g dry weight of sludge.

[0008] Preferably, the dosage of persulfate is 50-300 mg / g dry weight of sludge, and the persulfate is at least one of potassium persulfate, sodium persulfate, ammonium persulfate, and potassium persulfate.

[0009] Preferably, the constant voltage of the electrolytic treatment is 0.5~10V, the energizing time is 30~60min, and the distance between the cathode and anode is 5~20cm.

[0010] Preferably, the dosage of flocculant is 0.5~5 mg / g dry weight of sludge, and the flocculant includes at least one of cationic polyacrylamide, nonionic polyacrylamide, and anionic polyacrylamide.

[0011] Preferably, the stirring and settling process is as follows: first, stir rapidly for 1 to 10 minutes (300 rpm / min), then stir slowly for 5 to 30 minutes (60 rpm / min), and finally let it stand for 30 to 60 minutes.

[0012] As part of the same technical concept of the present invention, the present invention also provides a method for preparing modified biochar, which is used in the above-mentioned method for electrolytically enhanced biochar activation of persulfate coupled flocculation conditioning of sludge. The method for preparing modified biochar includes the following steps: sludge from a wastewater treatment plant is dried, ground, and sieved, and then pyrolyzed to obtain biochar; the biochar is doped with a nitrogen-containing compound; the doped mixture is dried and then pyrolyzed again to obtain modified biochar.

[0013] Preferably, the sludge from the wastewater treatment plant has a moisture content of 96-99 wt.% and an organic matter content of 0.4% or higher; the sludge includes sludge that has been conditioned and dewatered using the above-mentioned method of electrolytically enhanced biochar activation of persulfate coupled with flocculation conditioning, and can be recycled to prepare modified biochar.

[0014] Preferably, the nitrogen-containing compound includes nitrogen-containing inorganic substances or nitrogen-containing organic substances, wherein the nitrogen-containing inorganic substances include NH3, ammonium salts or nitric acid, and the nitrogen-containing organic substances include urea, melamine or aniline.

[0015] Preferably, when the nitrogen-containing compound is urea, the mixing ratio of the biochar to the urea is 5:1 to 1:5, and the mixing ratio is calculated according to the mass ratio of the two; when the nitrogen-containing compound is melamine, the mixing ratio of the biochar to the melamine is 3:1 to 1:3, and the mixing ratio is calculated according to the mass ratio of the two.

[0016] Preferably, during the two pyrolysis processes, the heating rate is 5~30℃ / min, the pyrolysis temperature is 600~800℃, and the holding time is 2~4h.

[0017] Preferably, the products from both pyrolysis processes require acid washing, water washing, and drying; during acid washing, the acidic solution used is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, and dilute phosphoric acid; during drying, the drying temperature is 90~110℃, and the drying time is 12h.

[0018] Compared with the prior art, the advantages of this invention are as follows: 1. This invention uses modified biochar to activate persulfate, while simultaneously coupling electrochemical oxidation and flocculation, which significantly improves the dewatering performance of sludge and achieves deep dewatering of sludge; and avoids the secondary pollution problem of sludge that exists in existing persulfate conditioning technologies.

[0019] To address the structural asymmetry of persulfate, the added modified biochar can activate the unstable S2O8. 2- The modified biochar generates strong oxidizing free radicals such as sulfate radicals, which oxidize and degrade EPS in sludge flocs, altering the EPS composition and improving sludge dewatering performance. Simultaneously, within the electrochemical system, the modified biochar acts as a microelectrode between the cathode and anode, forming numerous micro-electrolysis systems within the coupled electrochemical system. These micro-electrolysis systems effectively activate persulfate to generate strong oxidizing free radicals such as sulfate radicals, thereby enhancing the oxidative degradation of extracellular polymeric EPS by the persulfate system, disrupting the sludge floc structure, releasing bound water, and improving sludge dewatering performance. Furthermore, as a physical conditioner, the modified biochar can construct skeletal channels within the sludge, increasing the structural strength of the sludge cake, improving sludge compressibility, and facilitating rapid water removal from the channels, thus promoting deep sludge dewatering.

[0020] Furthermore, the oxidative degradation of sludge by a single process leads to smaller sludge particle size, which is detrimental to sludge dewatering. Therefore, the sludge conditioning method of this invention, through coupling with a flocculant, enables the oxidatively degraded sludge to re-flocculate, promoting the aggregation of fine sludge particles into clusters, increasing the sludge floc particle size, enhancing the floc structure, and improving sludge dewatering performance.

[0021] This invention utilizes modified biochar prepared from sewage sludge as a catalyst for persulfate treatment, avoiding the introduction of metal ions into the dewatered sludge, reducing secondary pollution, and facilitating subsequent sludge treatment and disposal.

[0022] 2. This invention employs a post-treatment method to dope nitrogen into biochar prepared from sewage sludge from wastewater treatment plants, thereby improving the catalytic efficiency of the biochar.

[0023] This invention discloses a method for preparing modified biochar, employing a post-processing method. The post-processing method involves first preparing biochar, then doping it with nitrogen-containing compounds (including nitrogen-containing inorganic substances such as NH3, ammonium salts, and nitric acid, and nitrogen-containing organic substances such as urea, melamine, and aniline) to obtain modified biochar. Doping biochar with nitrogen atoms introduces surface defect structures, altering its intrinsic properties (such as increasing specific surface area and pore size distribution), increasing the number of Lewis acid sites, thereby expanding catalytically active sites and improving the catalytic efficiency of biochar in the persulfate activation process.

[0024] Furthermore, when using nitrogen-containing compounds to dope biochar, the mixing mass ratio varies, mainly due to the nitrogen content of the compounds. Under lower mixing mass ratios, nitrogen-containing compounds with higher nitrogen content can produce modified biochar with higher nitrogen doping levels. This invention prepared modified biochar through multiple experiments, focusing on the effect of the mixing mass ratio of urea, melamine, and biochar on the prepared modified biochar, thereby determining its optimal ratio.

[0025] 3. This invention enhances the oxidation capacity of the system and reduces the dosage of modified biochar by coupling electrochemical oxidation and persulfate oxidation with modified biochar; furthermore, by utilizing wastewater treatment plant sludge to prepare modified biochar, it solves the problem of sludge volume expansion, and also... This has opened up new avenues for the resource utilization of sewage sludge.

[0026] This invention utilizes modified biochar coupled with electrochemical oxidation and persulfate oxidation. Its purpose is to leverage the synergistic activation of persulfate by modified biochar and electrochemistry to generate a large number of strong oxidizing free radicals, thereby enhancing the system's oxidation capacity. Compared to other methods, the amount of modified biochar added in this invention is significantly reduced. This is because this invention can enhance the system's oxidation capacity through multiple pathways, rather than solely relying on modified biochar to activate persulfate and generate strong oxidizing free radicals such as sulfate radicals. Specifically, this invention mainly enhances the system's oxidation capacity through the following pathways: (1) Electrochemistry can directly activate persulfate, forming strong oxidizing free radicals such as sulfate radicals at a rapid reaction rate. (2) Modified biochar, acting as a microelectrode, can be polarized by the electric fields applied to the cathode and anode, forming a micro-electrolysis system, which effectively increases the contact area between the reactants and the electrodes. The persulfate and organic matter accumulated on the surface of the microelectrode greatly promote the collision and reaction of the reactants during the electrolysis stage, improving the system's sludge degradation efficiency. (3) The electrolysis process can oxidize the modified biochar and generate more oxygen-containing functional groups (such as carbonyl groups), thereby enhancing the activation effect of modified biochar on persulfate.

[0027] Furthermore, this invention utilizes the concept of "treating waste with waste," preparing modified biochar from wastewater treatment plant sludge, and then applying the modified biochar to sludge dewatering, achieving resource recycling and perfecting the closed-loop development of sludge treatment and disposal. Simultaneously, the pyrolysis and carbonization of wastewater treatment plant sludge can consume organic pollutants, kill pathogens, and solidify heavy metals, achieving sludge reduction and harmlessness. The modified biochar also has adsorption capabilities, further adsorbing residual pollutants during dewatering, reducing the pollution of the dewatered filtrate, and enhancing the engineering application value of sludge.

[0028] 4. This invention does not require pH adjustment and can be carried out in a wide pH environment. The reagents used are non-toxic and harmless, the reaction conditions are mild, the operation is simple, and there is no secondary pollution. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the change in moisture content of the sludge cake in Example 3 of this application; Figure 2 This is a schematic diagram illustrating the change in moisture content of the sludge cake in Example 4 of this application; Figure 3 This is a schematic diagram showing the change in moisture content of the sludge cake in Comparative Example 1 of this application. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0031] Because extracellular polymeric substances (EPS) in sludge are highly hydrophilic, and the water content of EPS accounts for 60% to 80% of the total sludge volume, its hydration and adhesion effects on sludge flocs lead to difficulties in sludge dewatering. To address the significant impact of EPS on sludge dewatering performance, this invention couples modified biochar-enhanced persulfate oxidation, electrochemical oxidation, and flocculation into a sludge dewatering conditioning reactor. This enhances the degradation of EPS by the persulfate oxidation and electrochemical oxidation systems. Coupled with flocculation, it solves the problem of reduced sludge particle size, which hinders dewatering, and constructs a sludge cake structure with good filtration performance, achieving deep sludge dewatering.

[0032] Example 1 Example 1 of this invention provides a method for preparing modified biochar, the specific implementation process of which is as follows: Wastewater treatment plant sludge was filtered and dewatered, then dried at 80 °C. The dried sludge was then crushed into powder using a pulverizer and passed through a 100-mesh sieve (particle size less than 0.15 mm). It was then washed with deionized water and dried in a forced-air drying oven at 80 °C. An appropriate amount of the sludge powder was placed in a quartz boat and then carbonized in the center of a muffle furnace. The temperature was raised from room temperature to 700 °C and pyrolyzed for 2 hours, then cooled to room temperature to obtain biochar. The biochar was mixed with a urea solution (the mass ratio of biochar to urea was 2:1, 1:3, or 1:5), magnetically stirred for 12 hours, and then dried in a vacuum drying oven at 80 °C. The resulting solid was then carbonized in the center of a muffle furnace, heated from room temperature to 700 °C and held for 2 hours, then cooled to room temperature to obtain modified biochar.

[0033] Example 2 Example 2 of this invention provides a method for preparing modified biochar, the specific implementation process of which is as follows: Wastewater treatment plant sludge was filtered and dewatered, then dried at 80 °C. The dried sludge was then crushed into powder using a pulverizer and passed through a 100-mesh sieve (particle size less than 0.15 mm). It was then washed with deionized water and dried in a forced-air drying oven at 80 °C. An appropriate amount of the sludge powder was placed in a quartz boat and then carbonized in the center of a muffle furnace. The temperature was raised from room temperature to 700 °C and pyrolyzed for 2 hours, then cooled to room temperature to obtain biochar. The biochar was mixed with a melamine solution (the mass ratio of biochar to melamine was 2:1, 1:1, or 1:3), magnetically stirred for 12 hours, and then dried in a vacuum drying oven at 80 °C. The resulting solid was then carbonized in the center of a muffle furnace, heated from room temperature to 700 °C and held for 2 hours, then cooled to room temperature to obtain modified biochar.

[0034] Example 3 Example 3 of this invention provides a conditioning method for deep dewatering of flocculated sludge by electrolytically enhanced biochar activation of persulfate coupled with flocculation. The specific implementation process is as follows: Wastewater treatment plant sludge with a moisture content of 98 wt.% was selected as the sludge to be conditioned. 100 ml of the sludge was poured into a sludge conditioning device, and modified biochar (50, 150, and 250 mg / g dry weight of sludge) and persulfate (50-300 mg / g dry weight of sludge) prepared in Example 1 were added. Electrolysis was carried out by applying electricity (5 V) for 30 min, with continuous stirring using a magnetic stirrer during the reaction. After the reaction, flocculant PAM (3 mg / g dry weight of sludge) was added again, and the mixture was first stirred rapidly for 1 min (300 rpm / min), then slowly stirred for 5 min (60 rpm / min), and finally allowed to stand for 30 min. After conditioning, the moisture content of the sludge cake was measured (e.g., ...). Figure 1 ).Depend on Figure 1It can be seen that the moisture content of the sludge cake decreases with the increase of persulfate dosage. When the modified biochar dosage is 50 mg / g TS, the moisture content of the sludge cake decreases from 71.71% to 61.83% as the persulfate dosage increases from 50 mg / g TS to 300 mg / g TS. When the modified biochar dosage is 150 mg / g TS, the moisture content of the sludge cake decreases from 67.84% to 60.27% as the persulfate dosage increases from 50 mg / g TS to 300 mg / g TS. When the modified biochar dosage is 250 mg / g TS, the moisture content of the sludge cake decreases from 65.79% to 58.78% as the persulfate dosage increases from 50 mg / g TS to 300 mg / g TS, indicating the best sludge dewatering effect.

[0035] Example 4 Example 4 of this invention provides a conditioning method for deep dewatering of flocculated sludge by electrolytically enhanced biochar activation of persulfate coupled with flocculation. The specific implementation process is as follows: Wastewater treatment plant sludge with a moisture content of 98 wt.% was selected as the sludge to be conditioned. 100 ml of the sludge was poured into a sludge conditioning device, and modified biochar (50, 150, and 250 mg / g dry weight of sludge) and persulfate (50-300 mg / g dry weight of sludge) from Example 2 were added. Electrolysis was carried out by applying electricity (5 V) for 30 min, with continuous stirring using a magnetic stirrer during the reaction. After the reaction, flocculant PAM (3 mg / g dry weight of sludge) was added again, and the mixture was first stirred rapidly for 1 min (300 rpm / min), then slowly stirred for 5 min (60 rpm / min), and finally allowed to stand for 30 min. After conditioning, the moisture content of the sludge cake was measured (e.g., ...). Figure 2 ).Depend on Figure 2 It can be seen that the moisture content of the sludge cake decreases with the increase of persulfate dosage. When the modified biochar dosage is 50 mg / g TS, the moisture content of the sludge cake decreases from 70.99% to 60.07% as the persulfate dosage increases from 50 mg / g TS to 300 mg / g TS. When the modified biochar dosage is 150 mg / g TS, the moisture content of the sludge cake decreases from 65.35% to 59.25% as the persulfate dosage increases from 50 mg / g TS to 300 mg / g TS. When the modified biochar dosage is 250 mg / g TS, the moisture content of the sludge cake decreases from 61.97% to 57.32% as the persulfate dosage increases from 50 mg / g TS to 300 mg / g TS, indicating the best sludge dewatering effect.

[0036] Comparative Example 1 This Comparative Example 1 is a comparative example of Example 4. It provides a method for conditioned sludge using biochar-activated persulfate. Compared to Example 4, Comparative Example 1 does not involve an electrolysis process or a re-addition of flocculant. The specific implementation process of this comparative example is as follows: Wastewater treatment plant sludge with a moisture content of 98 wt.% was selected as the sludge to be conditioned. 100 ml of the sludge was poured into a sludge conditioning device, and modified biochar (250 mg / g dry weight of sludge) and persulfate (50-300 mg / g dry weight of sludge) prepared in Example 2 were added for conditioning. After conditioning, the moisture content of the sludge cake was measured (e.g., ...). Figure 3 ).Depend on Figure 3 It can be seen that as the amount of persulfate added increases, the moisture content of the sludge cake gradually decreases. When the amount of persulfate added increases from 50 mg / g TS to 300 mg / g TS, the moisture content of the sludge cake decreases from 74.05% to 65.17%. This result shows that adding electrolysis and flocculant re-addition steps in Example 4 can significantly reduce the moisture content of the sludge cake.

Claims

1. A method for deep dewatering and conditioning sludge using electrolytically enhanced biochar activation and persulfate-coupled flocculation, characterized in that, The steps of deep dewatering and conditioning of sludge include: adding the sludge to be conditioned into the conditioning device, adding modified biochar and persulfate, and placing the two electrodes in the conditioning device with inert electrodes as the cathode and anode, and performing electrolysis treatment by passing electricity, with continuous stirring during the conditioning process; after the conditioning is completed, adding flocculant again and stirring and letting it stand.

2. The method for deep dewatering and conditioning sludge using electrolytically enhanced biochar activation and persulfate coupled flocculation as described in claim 1, characterized in that, The modified biochar is added at a rate of 50-250 mg / g dry weight of sludge.

3. The method for deep dewatering and conditioning sludge using electrolytically enhanced biochar activation and persulfate coupled flocculation according to claim 1 or 2, characterized in that, The dosage of persulfate is 50-300 mg / g dry weight of sludge, and the persulfate is at least one of potassium persulfate, sodium persulfate, ammonium persulfate, and potassium hydrogen persulfate.

4. The method for deep dewatering and conditioning sludge using electrolytically enhanced biochar activation and persulfate coupled flocculation according to claim 3, characterized in that, The constant voltage of the electrolytic treatment is 0.5~10V, the energizing time is 30~60min, and the distance between the cathode and anode is 5~20cm.

5. The method for deep dewatering and conditioning sludge using electrolytically enhanced biochar activation and persulfate coupled flocculation according to claim 3, characterized in that, The dosage of the flocculant is 0.5~5 mg / g dry weight of sludge, and the flocculant is at least one of cationic polyacrylamide, nonionic polyacrylamide, and anionic polyacrylamide.

6. A method for preparing modified biochar, characterized in that, The modified biochar is the modified biochar used in the deep dewatering and conditioning method for sludge by electrolytically enhanced biochar activation and persulfate coupled flocculation as described in any one of claims 1-5. The steps of the method for preparing the modified biochar include: Biochar is obtained by drying, grinding and screening sludge from sewage treatment plants and then pyrolyzing it. The biochar was doped with a nitrogen-containing compound to obtain a doped mixture. After drying the doped mixture, it is pyrolyzed again to obtain modified biochar.

7. The method for preparing modified biochar according to claim 6, characterized in that, The sludge from the wastewater treatment plant has a moisture content of 96-99 wt.% and an organic matter content of 0.4% or higher. The sludge from the wastewater treatment plant includes sludge that has been conditioned and dewatered using the deep dewatering and conditioning method of electrolytic enhanced biochar activation persulfate coupled flocculation as described in any one of claims 1-5, and can be recycled to prepare modified biochar.

8. The method for preparing modified biochar according to claim 6, characterized in that, The nitrogen-containing compounds include nitrogen-containing inorganic substances or nitrogen-containing organic substances, wherein the nitrogen-containing inorganic substances include NH3, ammonium salts or nitric acid, and the nitrogen-containing organic substances include urea, melamine or aniline.

9. The method for preparing modified biochar according to claim 8, characterized in that, When the nitrogen-containing compound is urea, the mixing mass ratio of the biochar to the urea is 2:1 to 1:5; when the nitrogen-containing compound is melamine, the mixing mass ratio of the biochar to the melamine is 2:1 to 1:

3.

10. The method for preparing modified biochar according to claim 6, characterized in that, During the two pyrolysis processes, the heating rate was 5~30 ℃ / min, the pyrolysis temperature was 600~800 ℃, and the holding time was 2~4h.

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