Method for reducing and recycling sludge by electrochemically treating excess sludge

Abstract

The invention discloses a method for realizing sludge reduction and reutilization by electrochemical treatment of excess sludge, which comprises the following steps: step 1, extracting excess sludge generated by sewage treatment, conveying the excess sludge into an electrolytic bath of an electrochemical treatment device, starting the electrochemical treatment device, carrying out electrolytic treatment on the sludge in the electrolytic bath; and 2, conveying the electrolyzed sludge to an aerobic zone of the sewage treatment process to be started or intensified short-cut nitrification, so as to realize the reutilization of the sludge. According to the technical scheme, operation is easy, sludge reduction can be achieved in a short time, and short-cut nitrification can be rapidly started to achieve sludge recycling.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage biological treatment, and in particular to a method for sludge reduction and reuse by electrochemical treatment of residual sludge, which is suitable for sludge reduction by electrochemical treatment of sludge, start-up of partial nitrification or as a side-stream bioaugmentation partial nitrification, and sludge reuse. BACKGROUND

[0002] Biological treatment is a commonly used sewage treatment method in current sewage treatment plants, which produces a large amount of residual sludge. Residual sludge is rich in nutrients such as nitrogen and phosphorus, heavy metals, refractory toxic organic pollutants and pathogenic microorganisms, and its composition is complex and its properties are unstable. If not properly treated, it will pose a serious threat to the environment, human health and economic development. In addition, residual sludge is bulky and has high transportation and treatment costs, which can account for 30%-50% of the total operating cost of the entire sewage treatment plant, placing a heavy burden on municipal and local finances. With the continuous improvement of the urban sewage treatment rate in China and the increase in the number of newly built sewage treatment plants, the sludge production continues to grow. Residual sludge must be disposed of in a timely and effective manner to achieve the goals of reduction, harmlessness and resource utilization, thereby ensuring the stable operation and treatment effect of the sewage treatment plant and avoiding secondary pollution to the environment.

[0003] Currently, sludge concentration, digestion, dewatering, drying, incineration, landfill and other post-sludge reduction methods are the most common methods for sludge reduction. However, as the sludge production increases, the disposal cost of post-sludge reduction methods becomes higher and higher, wasting the recyclable resources in the sludge and causing potential harm to the environment. SUMMARY

[0004] In view of the above problems, the present application is proposed in order to provide a method for sludge reduction and reuse by electrochemical treatment of residual sludge, which overcomes the above problems or at least partially solves the above problems.

[0005] According to the present application, a method for sludge reduction and reuse by electrochemical treatment of residual sludge is provided, which comprises the following steps:

[0006] Step one, residual sludge produced by sewage treatment is extracted and transported into an electrolytic cell of an electrochemical treatment device, the electrochemical treatment device is started, and the sludge in the electrolytic cell is subjected to electrolysis treatment;

[0007] Step two, the electrolyzed sludge is transported to the aerobic zone of the partial nitrification process in sewage treatment, and the sludge is reused.

[0008] Optionally, in step one, the electrolysis treatment time is determined in advance by the following steps:

[0009] The optimal electrolysis time was determined through batch trials based on the properties of the sludge and the activity of nitrifying bacteria.

[0010] Optionally, the steps of the batch test include:

[0011] Take sludge treated for different electrolysis times, add ammonia nitrogen to make the ammonia nitrogen concentration reach 18 mg / L to 20 mg / L, and add nitrite nitrogen to make the nitrite nitrogen concentration reach 8 mg / L to 10 mg / L;

[0012] Control the aeration intensity to maintain the dissolved oxygen concentration at 5 mg / L to 6 mg / L, and take a reaction time of several hours. Samples are taken at preset time intervals to determine the concentrations of ammonia nitrogen and nitrate nitrogen.

[0013] The activity of ammonia-oxidizing bacteria is evaluated based on the ammonia nitrogen consumption rate, and the activity of nitrite-oxidizing bacteria is evaluated based on the nitrate nitrogen generation rate. When both the ammonia nitrogen degradation rate and the nitrate nitrogen generation rate drop to zero, it is determined that the activities of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria are completely inhibited. The shortest electrolysis time corresponding to this result is the optimal electrolysis time.

[0014] Optionally, in step one, NaCl is added to the sludge before electrolysis to bring its salinity to about 1%.

[0015] Optionally, in step one, the sludge is circulated within the electrolytic cell via pipelines and pumps.

[0016] Optionally, in step one, the current value is set to 10-20A and the voltage value is set to 20-40V when electrolyzing sludge.

[0017] Optionally, in step one, the electrochemical treatment device further includes an anode plate, a cathode plate, and a power supply. The anode plate is a boron-doped diamond electrode plate, the cathode plate is stainless steel, the distance between the two electrode plates is adjustable, and the power supply is a dual-channel regulated DC power supply.

[0018] Optionally, in step two, the sludge after electrolysis can be used to start up or as a side-flow biological enhancement for short-cut nitrification.

[0019] Optionally, in step two, the concentration of pollutants before and after the reaction in the aerobic zone is sampled and measured periodically, and the nitrite accumulation rate in the aerobic zone is calculated. When the nitrite accumulation rate in the aerobic zone is ≥85% and maintained for more than 10 days, it means that short-cut nitrification has been initiated or the enhancement effect is significant.

[0020] Optionally, in step two, the sludge flow rate and / or reaction time are adjusted to maintain an ammonia nitrogen residue of 10-15 mg / L in the aerobic zone and dissolved oxygen below 1 mg / L.

[0021] The beneficial effects of this invention are:

[0022] According to the technical solution provided by this invention, firstly, sludge volume reduction is achieved through electrochemical electrolysis of excess sludge, while nitrifying bacteria rupture and die during electrolysis. Then, the electrolyzed sludge is transported to the aerobic zone of a wastewater treatment process for treating ammonia-nitrogen-containing wastewater. The surviving ammonia-oxidizing bacteria (AOB) recover faster than nitrite-oxidizing bacteria (NOB), proliferating rapidly. During operation, the difference in quantity and activity between AOB and NOB is amplified, thereby achieving NOB washing and AOB enrichment, and rapidly realizing short-cut nitrification. This method is suitable for the start-up and upgrading of wastewater treatment plants to short-cut nitrification processes, or as a side-flow biological enhancement technology to strengthen short-cut nitrification, allowing for the reuse of excess sludge.

[0023] The technical solution of this invention utilizes electrochemical electrolysis of sludge to generate strong oxidizing substances through electrode reactions. This effectively breaks down the cell walls and colloidal structures of sludge microorganisms, releasing intracellular water and organic matter, thereby achieving significant volume and weight reduction. Electrochemical treatment of waste sludge offers significant advantages: The process is simple, allowing for the integration of electrode systems into existing sludge treatment units in wastewater treatment plants for in-situ treatment; it reduces secondary pollution, primarily relying on electrical energy to drive the reaction, avoiding the chemical residue problems associated with the large-scale addition of flocculants in traditional chemical conditioning methods; it boasts a high degree of automation and ease of control, allowing for precise control of treatment intensity and reaction progress by adjusting electrical parameters such as current density, voltage, and reaction time, facilitating automated operation and precise control; and the reaction is rapid, with a quick start-up process requiring minimal residence time, enabling continuous flow or batch processing for rapid treatment and improved efficiency.

[0024] Short-cut nitrification technology has been proposed as an energy-saving front-end nitrogen removal technology. The short-cut nitrification process is the first half of nitrification, where ammonia-oxidizing bacteria (AOB) convert ammonia nitrogen into nitrite nitrogen, without further oxidation to nitrate nitrogen by nitrite-oxidizing bacteria (NOB). Compared to full nitrification, short-cut nitrification saves 25% of aeration energy consumption. When short-cut nitrification is used as a front-end nitrogen removal process in conjunction with other technologies, its economic and environmental benefits are even more significant. The combined use of short-cut nitrification and denitrification saves 40% of carbon source, and coupling it with anaerobic ammonia oxidation can save 60% of aeration energy, 100% of carbon source demand, and 80% of excess sludge production.

[0025] Furthermore, this invention overcomes the challenge of rapidly starting up NOB through NOB rinsing and short-cut nitrification via an improved process. Typically, AOB exhibits stronger tolerance than NOB in harsh environments, and shows a faster recovery rate when the environment recovers. This invention utilizes this characteristic to strategically reduce the quantity and activity of NOB, thereby achieving NOB rinsing within the system. Excess sludge from wastewater treatment plants, after electrochemical electrolysis, is reintroduced into the aerobic zone, simultaneously achieving sludge reduction and selective NOB rinsing for short-cut nitrification. Attached Figure Description

[0026] Figure 1 This is a schematic flowchart of a method for reducing and reusing sludge through electrochemical treatment of excess sludge in an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of the electrochemical treatment device in one embodiment;

[0028] Figure 3 This is a batch experiment in which the optimal electrolysis time was determined in one embodiment, showing the activity of nitrifying bacteria.

[0029] Figure 4 This example illustrates the changes in sludge concentration and reduction rate before and after sludge electrolysis.

[0030] Figure 5 This is a schematic diagram of a device for restoring sludge microbial community activity to initiate short-cut nitrification in one embodiment.

[0031] Figure 6 This is an example of the change in nitrite accumulation rate during the recovery process after sludge electrolysis. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Example 1

[0034] See Figure 1 and Figure 2 As shown, Example 1 discloses a method for reducing and reusing sludge through electrochemical treatment of excess sludge, comprising the following steps:

[0035] The electrochemical treatment unit includes an electrolytic cell, an anode plate, a cathode plate, and a power supply. The anode plate is made of boron-doped diamond (BDD), and the cathode plate is made of stainless steel. The electrode plates are fixed by grooves at the bottom of the electrolytic cell, and the distance between the two electrode plates is adjustable. The power supply is a dual-channel regulated DC power supply. The electrolytic cell wall has two sludge discharge ports. The inner wall of each port is connected to a flexible hose that contacts the remaining sludge, while the outer wall is connected to a peristaltic pump via a pump pipe to achieve sludge circulation. The current, voltage, and other parameters are adjusted to ensure the normal operation of the equipment.

[0036] Electrolytic treatment of excess sludge reduces sludge volume while inhibiting the growth of nitrifying bacteria. The excess sludge is transported to an electrolytic cell, and NaCl is added to achieve a salinity of 1% to enhance the solution's conductivity. The electrochemical treatment device is started, with the current set to 10–20 A and the voltage to 20–40 V, and the circulating peristaltic pump activated for electrolysis. The electrolysis time is determined based on the sludge properties and nitrifying bacteria activity. Optimal electrolysis time is screened through batch trials. These trials involve taking 500 ml of sludge treated for different times and placing it into separate 500 ml test bottles. Ammonia nitrogen is added to each bottle to achieve a concentration of 18–20 mg / L, and nitrite nitrogen is added to achieve a concentration of 8–10 mg / L. Aeration intensity is controlled to maintain dissolved oxygen concentration at 5–6 mg / L. The reaction lasts for 2 hours, with samples taken every 10 minutes to measure ammonia nitrogen and nitrite nitrogen concentrations. AOB activity was assessed based on the ammonia nitrogen consumption rate, and NOB activity was assessed based on the nitrate nitrogen formation rate. When both the ammonia nitrogen degradation rate and the nitrate nitrogen formation rate dropped to zero, AOB and NOB activities were considered completely inhibited. The shortest electrolysis time corresponding to this result was taken as the optimal electrolysis time. After reaching the optimal electrolysis time, electrolysis was stopped, and the process entered the sludge activity recovery and short-cut nitrification start-up stage.

[0037] The activated recovery treatment initiates short-cut nitrification to reuse excess sludge. The electrolyzed sludge is transported to the aerobic zone of the wastewater treatment process to be started or enhanced, either to initiate or as a side-flow biological enhancement technique to strengthen short-cut nitrification. Flow rate or reaction time is adjusted to maintain a residual ammonia nitrogen level of 10–15 mg / L in the aerobic zone and dissolved oxygen below 1 mg / L. Pollutant concentrations in the aerobic zone are periodically sampled and measured before and after the reaction. The nitrite accumulation rate in the aerobic section is calculated to assess the short-cut nitrification effect of the system. When the nitrite accumulation rate in the aerobic section is ≥85% and maintained for more than 10 days, the short-cut nitrification of the system is considered to have been initiated or significantly enhanced.

[0038] The technical principle of this embodiment 1 is as follows: electrochemical electrolysis of sludge generates strong oxidizing substances through electrode reactions, which can effectively break down the cell walls and colloidal structures of sludge microorganisms, releasing intracellular water and organic matter, thereby achieving volume and weight reduction. Simultaneously, by controlling a reasonable electrolysis time, both AOB and NOB are inhibited or even die under electrolysis conditions. However, surviving AOB, due to its special cell structure, has a strong environmental adaptability and can quickly respond to changes in the external environment. During the recovery process after electrolysis, AOB exhibits a faster recovery rate than NOB. Furthermore, by controlling the residual ammonia nitrogen and dissolved oxygen in the aerobic zone, short-cut nitrification is rapidly achieved, allowing the reuse of excess sludge.

[0039] This embodiment 1 utilizes electrochemical treatment of excess sludge to achieve sludge reduction and reuse, which has the following advantages:

[0040] Electrolysis is a simple process that requires no complex facilities or operations. It occupies little space, starts up quickly, and takes little time. Only a small amount of salinity needs to be added before electrolysis to make the solution conductive and maintain the current path.

[0041] Electrolysis achieves efficient sludge reduction, significantly reducing sludge volume and achieving a high reduction rate, far exceeding many traditional methods.

[0042] Short-cut nitrification has a short start-up time, and the electrolysis and recovery processes can amplify the differences in the quantity and activity of AOB and NOB, allowing the system to achieve a higher nitrite accumulation rate in a shorter time.

[0043] Electrolysis reduces sludge volume while initiating short-cut nitrification for sludge reuse. It requires less economic investment, yields good results, and requires no chemical addition, allowing for direct short-cut nitrification.

[0044] The embodiments of the present invention are highly practical. They can be used in wastewater treatment plants that intend to start or upgrade to a short-cut nitrification process to achieve sludge reduction while quickly starting short-cut nitrification through short-time electrolysis of residual sludge.

[0045] Example 2

[0046] Reference Figure 2 The diagram shows an embodiment of an electrochemical treatment device for reducing and reusing excess sludge through electrochemical treatment. The electrolytic cell 4 has a slot, through which the anode plate 2 and cathode plate 3 are fixed. The excess sludge is transported to the electrolytic cell, the power supply 1 of the electrochemical treatment device is turned on, and the peristaltic pump 6 is simultaneously activated. The sludge is then circulated through the sludge discharge ports 5 and 7.

[0047] according to Figure 1 and Figure 2 The following steps will be taken to reduce and reuse excess sludge:

[0048] The electrochemical treatment device includes an electrolytic cell 4, an anode plate 2, a cathode plate 3, and a power supply 1. The anode plate is made of boron-doped diamond (BDD), and the cathode plate is made of stainless steel. The electrode plates are fixed by grooves at the bottom of the electrolytic cell. The electrolytic cell wall has two sludge discharge ports 5 and 7. The inner wall of each port is connected to a flexible hose that contacts the remaining sludge, while the outer wall is connected to a peristaltic pump 6 via a pump pipe to achieve sludge circulation. The current, voltage, and other parameters are adjusted to ensure the normal operation of the equipment.

[0049] Electrolytic treatment of excess sludge reduces sludge volume while inhibiting the growth of nitrifying bacteria. The excess sludge is transported to electrolytic cell 4, and NaCl is added to achieve a salinity of 1% to enhance solution conductivity. The electrochemical treatment device is started, with a current of 15A and a voltage of 30V, and the circulating peristaltic pump 6 is activated for electrolysis. Electrolysis times are set at 5 min, 7.5 min, and 10 min. 500 ml of sludge treated at different times is collected and placed into 500 ml test bottles. Ammonia nitrogen is added to each bottle to achieve a concentration of 20 mg / L, and nitrite nitrogen is added to achieve a concentration of 8 mg / L. Aeration intensity is controlled to maintain dissolved oxygen concentration between 5 mg / L and 6 mg / L. The reaction lasts for 2 hours, with samples taken every 10 minutes to measure ammonia nitrogen and nitrite nitrogen concentrations. Ambient oxygen (AOB) activity is assessed based on the ammonia nitrogen consumption rate, and nitrogen oxide (NOB) activity is assessed based on the nitrite nitrogen formation rate.

[0050] When both the ammonia nitrogen degradation rate and the nitrate nitrogen generation rate drop to zero, it is determined that the activities of AOB and NOB are completely inhibited. The shortest electrolysis time corresponding to this result is taken as the optimal electrolysis time.

[0051] Specifically, the nitrifying bacteria activity in the batch experiments for which the optimal electrolysis time was determined in this embodiment is as follows: Figure 3 As shown. By Figure 3 As can be seen, after 5 minutes of electrolysis, the activities of AOB and NOB were 3.26 and 2.65 mg N / VSS / h, respectively. After 7.5 minutes and 10 minutes of electrolysis, the activities of both AOB and NOB reached zero. Therefore, 7.5 minutes was determined to be the optimal electrolysis time for this embodiment. Figure 4 The changes in sludge concentration and reduction rate before and after sludge electrolysis show that the mixed suspended solids (MLSS) concentration of the remaining sludge decreased from 13048 mg / L to 6876 mg / L after 7.5 minutes of electrolysis, achieving a sludge reduction rate of 47.3%. After electrolysis, the process enters the sludge activity recovery and short-cut nitrification start-up stage.

[0052] The activation restoration treatment starts short-cut nitrification to achieve the reuse of excess sludge. In order to quickly restore the activity of nitrifying bacteria in the sludge after electrolysis, the electrolyzed sludge is transported to the aerobic zone of the wastewater treatment process to be started or to be enhanced, and either started or used as a side-flow biological enhancement technology to enhance short-cut nitrification.

[0053] refer to Figure 5A schematic diagram of the device structure for restoring sludge microbial activity and initiating short-cut nitrification is shown. The reactor type is a sequencing batch reactor (SBR). The ammonia-nitrogen-containing wastewater inlet tank (1) is connected to the SBR inlet (3) via an inlet peristaltic pump (2) and enters the SBR reactor (14). A stirrer (7) is installed to mix the activated sludge inside the reactor. A rotor flow meter (9) is connected to an air pump (8) and an aeration disc (10) for aeration to control dissolved oxygen in the reactor. Drainage is carried out through an outlet valve (11). Sludge is discharged through a sludge discharge port (13). A pH probe (5) and a DO probe (6) are connected to the WTW host (4) via a data cable to reflect the sludge properties inside the reactor.

[0054] The SBR reactor operates four cycles daily, each lasting 6 hours, including 10 minutes of influent, 50 minutes of anoxic agitation, 180 minutes of aerobic aeration, 30 minutes of sedimentation, 10 minutes of effluent discharge, and 80 minutes of idle time, with a discharge ratio of 50%. During the activity recovery phase, the sludge age is maintained at 15 days. Flow rate or reaction time is adjusted to maintain a residual ammonia nitrogen level of 10-15 mg / L in the aerobic zone and dissolved oxygen below 1 mg / L. Pollutant concentrations in the aerobic zone are periodically sampled and measured before and after the reaction to calculate the nitrite accumulation rate in the aerobic section, thus assessing the short-range nitrification effect of the system. The change in nitrite accumulation rate during the recovery process after sludge electrolysis is shown in the example below. Figure 6 As shown, the nitrite accumulation rate exceeded 85% for 19 consecutive days, indicating that short-range nitrification of the reaction system has been initiated.

[0055] The above provides a detailed description of the method for reducing and reusing sludge through electrochemical treatment of excess sludge according to the present invention. Specific embodiments are used to illustrate the principle and implementation of the present invention. The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for sludge reduction and reuse by electrochemically treating excess sludge, characterized by, The method comprises the following steps: Step one, extracting the residual sludge generated in sewage treatment, and conveying the residual sludge to an electrolytic cell of an electrochemical treatment device, starting the electrochemical treatment device, and electrolyzing the sludge in the electrolytic cell; Step two, conveying the electrolyzed sludge to an aerobic zone of a sewage treatment process to be started or intensified short-cut nitrification, and realizing reuse of the sludge.

2. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to claim 1, characterized in that, In step one, the electrolysis time is determined in advance by the following steps: According to the sludge properties and nitrifying bacteria activity, the optimal electrolysis time is determined through batch tests.

3. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to claim 2, characterized in that, The steps of the batch tests comprise: Taking the sludge treated for different electrolysis times, adding ammonia nitrogen to the sludge to make the ammonia nitrogen concentration reach 18 mg / L to 20 mg / L, and adding nitrite nitrogen to the sludge to make the nitrite nitrogen concentration reach 8 mg / L to 10 mg / L; Controlling the aeration intensity to make the dissolved oxygen concentration maintain at 5 mg / L to 6 mg / L, and reacting for several hours, taking samples every preset time period, and measuring the ammonia nitrogen and nitrate nitrogen concentrations; According to the ammonia nitrogen consumption rate to evaluate the ammonia-oxidizing bacteria activity, and according to the nitrate nitrogen generation rate to evaluate the nitrite-oxidizing bacteria activity, when the ammonia nitrogen degradation rate and the nitrate nitrogen generation rate are both reduced to zero, it is determined that the ammonia-oxidizing bacteria and the nitrite-oxidizing bacteria activity are completely inhibited, and the shortest time corresponding to the result is the optimal electrolysis time.

4. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to any one of claims 1 to 3, characterized in that, In step one, before electrolysis, NaCl is added to the sludge to make the salinity reach about 1%.

5. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to any one of claims 1 to 3, characterized in that, In step one, the sludge is circulated in the electrolytic cell through a pipeline and a pump.

6. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to any one of claims 1 to 3, characterized in that, In step one, when the sludge is electrolyzed, the current value is set to 10 A to 20 A, and the voltage value is set to 20 V to 40 V.

7. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to any one of claims 1 to 3, characterized in that, In step one, the electrochemical treatment device further comprises an anode plate, a cathode plate and a power supply, the anode plate is a boron-doped diamond electrode plate, the cathode plate is stainless steel, the distance between the two electrode plates is adjustable, and the power supply is a double-channel stabilized direct-current power supply.

8. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to any one of claims 1 to 3, characterized in that, In step two, the electrolyzed sludge is used to start or as a side-flow biological intensified short-cut nitrification.

9. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to claim 8, characterized in that, In step two, the pollutant concentrations before and after reaction in the aerobic zone are measured by regular sampling, the nitrite accumulation rate in the aerobic zone is calculated, when the nitrite accumulation rate in the aerobic zone is greater than or equal to 85% and is maintained for more than 10 days, it is determined that the short-cut nitrification has been started or the intensified effect is remarkable.

10. The method of sludge reduction and reuse by electrochemical treatment of excess sludge according to any one of claims 1 to 3, characterized in that, In step two, the sludge flow rate and / or the reaction time are regulated to make the ammonia nitrogen remaining in the aerobic zone be 10 mg / L to 15 mg / L, and the dissolved oxygen maintain below 1 mg / L.

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