Method for electrochemically activating chlorite to condition dewatering performance of anaerobically digested sludge

Abstract

The application discloses a method for electrochemically activating chlorite to regulate dewatering performance of anaerobic digestion sludge, and belongs to the technical field of sludge treatment. The treatment method comprises the following steps: adding anaerobic digestion sludge into sulfuric acid to adjust pH to obtain acidified sludge; adding sodium chlorite into the acidified sludge, stirring and mixing at room temperature to obtain a mixture; placing the mixture in an electrolytic cell of an electrochemical reaction device; opening a direct current power supply to perform electrochemical reaction, and opening a magnetic stirrer to complete the regulation of the anaerobic digestion sludge. The electrochemical device comprises the electrolytic cell, the magnetic stirrer, the direct current power supply, a cathode and an anode. The cathode is a Ti electrode, and the anode is a Ti4O7 electrode. The method is simple in operation, energy-saving and environment-friendly, and can effectively improve the dewatering performance of the anaerobic digestion sludge. The application provides a promising regulation and dewatering method for the anaerobic digestion sludge in the existing technical field of sludge treatment, and helps to realize efficient dewatering and reduction of the anaerobic digestion sludge.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment technology, and in particular to a method for conditioning the dewatering performance of anaerobic digested sludge using electrochemically activated chlorite. Background Technology

[0002] Wastewater sludge, a byproduct of wastewater treatment, contains a large number of pathogens, parasites, heavy metals, and persistent organic pollutants. According to the Yearbook of the Ministry of Ecology and Environment of the People's Republic of China, sludge production increased from 28.015 million tons in 2014 to 57.307 million tons in 2024. Without proper treatment and disposal, this massive amount of wastewater sludge poses a serious threat to environmental safety and human health. Anaerobic digestion, as one of the mainstream and highly promising technologies for wastewater sludge treatment and disposal, is widely used due to its comprehensive advantages in volume reduction, resource recovery, and energy conservation. However, this results in a large amount of anaerobic digested sludge with high water content (95%~97%) and extremely poor dewatering performance. Without efficient dewatering, the costs of subsequent transportation and disposal will rise sharply. Therefore, developing efficient, economical, and green anaerobic digestion sludge conditioning and dewatering technologies has become a critical issue that urgently needs to be addressed in the entire sludge treatment chain.

[0003] Anaerobic digestion sludge typically exhibits extremely poor dewaterability, fundamentally due to the dynamic network gel structure formed by extracellular polymeric substances (EPS). Studies have shown that EPS accounts for 60%-80% of sludge organic matter, primarily composed of proteins and polysaccharides. These components mechanically capture interstitial bound water through their cross-linked network structure and adsorb interfacial bound water through abundant hydrophilic sites. Furthermore, proteins constitute over 70% of the EPS mass and are rich in highly polar groups such as amino and carboxyl groups. Moreover, research indicates a close correlation between conformational changes in EPS proteins and a decrease in bound water content. Therefore, regulating EPS characteristics during conditioning processes is currently a crucial strategy for overcoming the water-binding barrier in sludge.

[0004] To regulate the EPS (expanded polystyrene) characteristics of anaerobic digestion sludge and promote dewatering, electrochemical advanced oxidation processes have gained attention in recent years due to their reliable technology, easy operation and control, and small footprint. This type of technology mainly generates (·OH) hydroxyl radicals and / or (SO4) radicals during the electrochemical reaction process. ·- Active species such as sulfate free radicals break down anaerobic digestion EPS, thereby disrupting the colloidal structure and releasing bound water. For example, Bai Yaohui et al. demonstrated that electro-activated persulfate conditioning technology based on sacrificial anodes can effectively promote the dewatering performance of anaerobic digestion sludge at a current density of 20 mA / cm³. 2Under conditions of 1% persulfate dosage (dry basis) and a treatment time of 30 min, the capillary water absorption time of anaerobic digestion sludge can be reduced from 576.5 s to 176.0 s. However, this technology has limitations: the conditioner persulfate is expensive and potentially toxic, while the iron anode material has a limited lifespan and its corrosion produces iron sludge. Therefore, it is crucial to seek a green, safe, stable, efficient, and economically feasible electrochemical advanced oxidation conditioning system to achieve efficient dewatering of anaerobic digestion sludge. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings of existing technologies. This invention provides a method for electrochemically activating chlorite to condition the dewatering performance of anaerobic digestion sludge. This method is mainly based on the electrocatalytic output of oxidizing active species (i.e., ClO2 and ·OH) of chlorite by Ti4O7 anode, achieving simultaneous extracellular and intracellular degradation of anaerobic digestion sludge to promote dewatering. Specifically, current electrochemical advanced oxidation dewatering of anaerobic digestion sludge has the following shortcomings: the conditioner persulfate is costly and potentially toxic, while iron anode materials have limited lifespan and their corrosion produces iron sludge. To solve the above technical problems, this invention provides a method for electrochemically activating chlorite to condition the dewatering performance of anaerobic digestion sludge, comprising the following steps:

[0006] (1) Add a certain amount of sulfuric acid solution to the anaerobic digestion sludge to adjust the pH value of the anaerobic digestion sludge and obtain acidified anaerobic digestion sludge;

[0007] (2) Add sodium chlorite to the acidified anaerobic digestion sludge described in step (1), and stir and mix at room temperature to obtain a mixture;

[0008] (3) Place the mixture described in step (2) into the electrolytic cell of the electrochemical device, which is equipped with a cathode and an anode, and stir thoroughly;

[0009] (4) Start the DC power supply of the electrochemical device described in step (3) to carry out the electrochemical reaction and stir at the same time to complete the treatment of anaerobic digestion sludge.

[0010] The preferred embodiment of the above-mentioned treatment method is characterized in that, in step (1), the sulfuric acid concentration is 2 mol / L and the pH value is 2.5~3.5.

[0011] The preferred method described above is characterized in that, in step (2), the amount of sodium chlorite added accounts for 3 to 5% of the dry weight of the acidified anaerobic digested sludge.

[0012] The preferred embodiment of the above-mentioned processing method is characterized in that, in step (3), the electrochemical device includes an electrolytic cell, a magnetic stirrer, a DC power supply, a cathode, and an anode, the length × width × height of the electrolytic cell is 70 mm × 60 mm × 130 mm, and the material of the electrolytic cell is plexiglass.

[0013] The preferred embodiment of the above-mentioned processing method is characterized in that, in step (3), the distance between the anode and the cathode in the electrolytic cell is 40~60 mm.

[0014] The preferred embodiment of the above processing method is characterized in that, in step (3), the anode material is a Ti4O7 electrode and the cathode material is a Ti electrode.

[0015] The preferred embodiment of the above processing method is characterized in that, in step (3), the anode and cathode are both 65 mm × 115 mm in length × width, 2 mm in thickness, and have a mesh shape.

[0016] The preferred method described above is characterized in that, in step (4), the voltage of the electrochemical reaction is 25~30 V.

[0017] The preferred method described above is characterized in that, in step (4), the electrochemical reaction takes 30 to 40 minutes.

[0018] The preferred method described above is characterized in that, in step (4), the stirring rate is 350~400 r / min.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] (1) This invention provides a method for electrochemically activating chlorite to condition the dewatering performance of anaerobic digestion sludge. This method is mainly based on the electro-activation of chlorite by Ti4O7 anode to output oxidizing active species (i.e., ClO2 and ·OH), thereby achieving simultaneous extracellular and intracellular disintegration of anaerobic digestion sludge and promoting dewatering. Specifically, 1) Extracellular oxidation pathway: During the electrochemical process, ·OH (Eq. 1 and 2) generated and released by water oxidation on the surface of Ti4O7 anode can non-selectively oxidize and disintegrate the sludge-bound EPS gel matrix, releasing extracellular bound water. 2) Intracellular oxidation pathway: ClO2 (Eq. 4) generated in situ during the electrochemical process and converted from ·OH can diffuse through the cell membrane of microorganisms in the sludge, selectively oxidizing intracellular proteins, lipids, and other components, destroying cell integrity, and releasing intracellular bound water. The synergistic effect of the above two oxidation pathways is superior to the conditioning effect of a single oxide species.

[0021] <![CDATA[H2O - e - → ·OH ads + H + ]]> Eq. 1 <![CDATA[·OH ads → ·OH free ]]> Eq. 2 <![CDATA[ClO2 - - e - → ClO2]]> Eq. 3 <![CDATA[·OH ads + ClO2 - → ClO2 + OH - ]]> Eq. 4

[0022] (2) Compared to the sacrificial anode electro-activated persulfate conditioning technology, the effective components (such as SO4) ·- (Compared with iron species), the active ingredients in this invention (such as ·OH and ClO2) are environmentally friendly and do not produce harmful chemical residues or toxic byproducts (such as trihalomethanes, other halogenated organic compounds, etc.) during the evolution process.

[0023] (3) Compared with the iron anode used in the electro-activated persulfate conditioning technology of sacrificial anode, the Ti4O7 anode used in the electrochemical device of the present invention has better chemical stability, passivation resistance, oxidative degradation resistance and environmental friendliness.

[0024] (4) The electrochemical device provided in this invention has a simple structure, compact layout, easy operation and control, and high processing efficiency. Attached Figure Description

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0026] Figure 1 This is a schematic diagram of the electrochemical device in an embodiment of the present invention.

[0027] Figure 2 This is a comparison chart of the dehydration effect in the embodiments of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0029] Example

[0030] The materials and instruments used in the following examples are all commercially available.

[0031] Example 1:

[0032] A method for electrochemically activating chlorite to condition the dewatering performance of anaerobic digestion sludge includes the following steps:

[0033] (1) The residual sludge from a sewage treatment plant in Changsha City was anaerobically digested to obtain anaerobic digested sludge. The anaerobic digested sludge had a water content of 97.3% and a pH of 6.95. The pH of the anaerobic digested sludge was adjusted to 3.0 with 2 mol / L sulfuric acid to obtain acidified anaerobic digested sludge.

[0034] (2) Add sodium chlorite at a weight of 3.0% of the dry weight of the sludge to the acidified anaerobic digestion sludge from step (1), and stir and mix at room temperature for 2 min to obtain a mixture.

[0035] (3) Place the mixture described in step (2) into the electrolytic cell of the electrochemical device, and stir it at a rate of 400 r / min for 30 min without powering on to complete the treatment of anaerobic digestion sludge.

[0036] (4) The dewatering performance of the anaerobic digested sludge after step (3) is tested.

[0037] The dewatering performance of the control group and the treated sludge was tested. The test results are shown in [reference needed]. Figure 2 The results are as follows: The anaerobic digestion sludge in the control group had a capillary water absorption time of 244.1 s and a dewatering filter cake moisture content of 95.4%; the anaerobic digestion sludge treated by steps (1) to (4) (i.e., sodium chlorite treatment) had a capillary water absorption time of 345.9 s and a dewatering filter cake moisture content of 95.1%.

[0038] Example 2:

[0039] A method for electrochemically activating chlorite to condition the dewatering performance of anaerobic digestion sludge includes the following steps:

[0040] (1) The residual sludge from a sewage treatment plant in Changsha City was anaerobically digested to obtain anaerobic digested sludge. The anaerobic digested sludge had a water content of 97.3% and a pH of 6.95. The pH of the anaerobic digested sludge was adjusted to 3.0 with 2 mol / L sulfuric acid to obtain acidified anaerobic digested sludge.

[0041] (2) Place the acidified anaerobic digestion sludge from step (1) into the electrolytic cell of the electrochemical device. The electrolytic cell is equipped with a cathode (Ti electrode) and an anode (Ti4O7 electrode). Stir thoroughly.

[0042] (3) Start the DC power supply of the electrochemical device in step (2), carry out the electrochemical reaction for 30 min at 30 V voltage, and stir at 400 r / min to complete the treatment of anaerobic digestion sludge;

[0043] (4) The dewatering performance of the anaerobic digested sludge after step (3) is tested.

[0044] The dewatering performance of the control group and the treated sludge was tested. The test results are shown in [reference needed]. Figure 2 The results are as follows: The anaerobic digestion sludge in the control group had a capillary water absorption time of 244.1 s and a dewatering filter cake moisture content of 95.4%; the anaerobic digestion sludge after treatment in steps (1) to (4) (i.e., electrolytic treatment) had a capillary water absorption time of 93.3 s and a dewatering filter cake moisture content of 94.5%.

[0045] Example 3:

[0046] A method for electrochemically activating chlorite to condition the dewatering performance of anaerobic digestion sludge includes the following steps:

[0047] (1) The residual sludge from a sewage treatment plant in Changsha City was anaerobically digested to obtain anaerobic digested sludge. The anaerobic digested sludge had a water content of 97.3% and a pH of 6.95. The pH of the anaerobic digested sludge was adjusted to 3.0 with 2 mol / L sulfuric acid to obtain acidified anaerobic digested sludge.

[0048] (2) Add sodium chlorite at a dry weight of 3.0% to the acidified anaerobic digestion sludge from step (1), and stir and mix at room temperature for 2 min to obtain a mixture;

[0049] (3) Place the mixture from step (2) into the electrolytic cell of the electrochemical device, which is equipped with a cathode (Ti electrode) and an anode (Ti4O7 electrode), and stir thoroughly;

[0050] (4) Start the DC power supply of the electrochemical device in step (3), carry out the electrochemical reaction for 30 min at 30 V voltage, and stir at 400 r / min to complete the treatment of anaerobic digestion sludge.

[0051] (5) The dewatering performance of the anaerobic digested sludge after step (4) is tested.

[0052] The dewatering performance of the control group and the treated sludge was tested. The test results are shown in [reference needed]. Figure 2 The results are as follows: The anaerobic digestion sludge in the control group had a capillary water absorption time of 244.1 s and a dewatering filter cake moisture content of 95.4%; the anaerobic digestion sludge after treatment in steps (1) to (5) (i.e., electrolysis + sodium chlorite treatment) had a capillary water absorption time of 43 s and a dewatering filter cake moisture content of 86.7%.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, 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 protection scope of the technical solutions of the present invention.

Claims

1. A method for electrochemically activating chlorite to condition the dewatering performance of anaerobic digestion sludge, characterized in that, Includes the following steps: (1) Add a certain amount of sulfuric acid solution to the anaerobic digestion sludge to adjust the pH value of the anaerobic digestion sludge and obtain acidified anaerobic digestion sludge; (2) Add sodium chlorite to the acidified anaerobic digestion sludge described in step (1), and stir and mix at room temperature to obtain a mixture; (3) Place the mixture described in step (2) into the electrolytic cell of the electrochemical device, which is equipped with a cathode and an anode, and stir thoroughly; (4) Start the DC power supply of the electrochemical device described in step (3) to carry out the electrochemical reaction and stir at the same time to complete the treatment of anaerobic digestion sludge.

2. The processing method according to claim 1, characterized in that, In step (1), the sulfuric acid concentration is 2 mol / L and the pH value is 2.5~3.

5.

3. The processing method according to claim 1, characterized in that, In step (2), the amount of sodium chlorite added accounts for 3-5% of the dry weight of the acidified anaerobic digestion sludge.

4. The processing method according to claim 1, characterized in that, In step (3), the electrochemical device includes an electrolytic cell, a magnetic stirrer, a DC power supply, a cathode, and an anode. The length × width × height of the electrolytic cell is 70 mm × 60 mm × 130 mm, and the material of the electrolytic cell is plexiglass.

5. The processing method according to claim 1, characterized in that, In step (3), the distance between the anode and cathode in the electrolytic cell is 40~60 mm.

6. The processing method according to claim 1, characterized in that, In step (3), the anode material is a Ti4O7 electrode and the cathode material is a Ti electrode.

7. The processing method according to claim 1, characterized in that, In step (3), the anode and cathode are both 65 mm × 115 mm in length × width, 1 mm in thickness, and have a mesh shape.

8. The processing method according to claim 1, characterized in that, In step (4), the voltage of the electrochemical reaction is 25~30 V.

9. The processing method according to claim 1, characterized in that, In step (4), the electrochemical reaction takes 30 to 40 minutes.

10. The processing method according to claim 1, characterized in that, In step (4), the stirring rate is 350~400 r / min.

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