Method for improving anaerobic digestion efficiency of excess sludge under low-carbon mode

Abstract

The present application relates to the field of sludge resource utilization, in particular to the technical field of sludge resource treatment method under low-carbon mode, more specifically to a method for improving the anaerobic digestion efficiency of residual sludge under low-carbon mode. The residual sludge is pretreated by calcium hypochlorite combined with low-temperature hydrolysis, which can significantly improve the anaerobic digestion efficiency. According to the calculation, the anaerobic digestion soluble COD of the treated residual sludge is 11.20 times higher than that of the blank group, the cumulative methane yield is increased by 163.9%, and the maximum methane production rate is increased by 158.8%. The daily methane production is increased by 57.9% compared with the blank group. The unit methane carbon emission is reduced by 45.6% compared with the blank group.

Description

Technical Field

[0001] This invention relates to the field of sludge resource utilization, particularly to the technical field of sludge resource utilization methods under low-carbon modes, and more specifically to a method for improving the efficiency of anaerobic digestion of excess sludge under low-carbon modes. Background Technology

[0002] Wastewater sludge originates from the treatment process of municipal wastewater. It is rich in biodegradable organic matter, which can serve as a high-quality carbon source for biotransformation processes. Anaerobic digestion technology has received widespread attention due to its ability to convert organic waste into renewable energy. This technology enables wastewater treatment plants to achieve energy self-sufficiency through methane production, simultaneously achieving the goal of low-carbon wastewater treatment (WAS).

[0003] Extracellular polymeric substances (EPS) in waste sludge are a significant factor affecting methane yield and digestion cycle in anaerobic digestion systems. To address this, various waste sludge pretreatment technologies have been developed to reduce the complex mass transfer barriers caused by EPS and minimize its obstruction of organic components and hydrolytic enzymes. Current pretreatment methods for EPS mainly fall into three categories: biological, physical, and chemical. Biological methods disrupt EPS structure by adding exogenous hydrolytic enzymes to directionally decompose large organic molecules, but these methods are costly. Physical methods disrupt EPS structure and cell integrity by inputting energy, including ultrasound, microwave, and heat treatment. Heat treatment is categorized into high-temperature (160-210℃) and low-temperature (100-140℃) modes. At 160-210℃, EPS breakdown and cell disruption are more effective, but the Maillard reaction is more likely to occur, generating recalcitrant high-molecular-weight melanin-like substances. These melanin-like substances inhibit subsequent anaerobic digestion. While temperatures of 100-140℃ can effectively prevent the Maillard reaction, they significantly reduce the effectiveness of heat treatment in breaking down EPS, thus affecting hydrolysis efficiency. Chemical treatment methods increase the breakdown effect by adding chemical reagents to disrupt the chemical bonds of EPS and cells; however, these reagents also affect microorganisms. Due to the complexity of microorganisms in the waste sludge, the impact of chemical reagents on microorganisms will affect the subsequent anaerobic digestion process. For example, in CN114180799A, although the addition of calcium hypochlorite increased methane production, reaching a maximum of 220.5 mL / g, the increase rate was only 33.8% compared to the blank example.

[0004] Therefore, exploring safe and efficient disposal pathways for residual sludge is of great practical significance. Summary of the Invention

[0005] The present invention aims to provide a method for improving the efficiency of anaerobic digestion of waste sludge, especially a method for improving the efficiency of anaerobic digestion of waste sludge under low-carbon mode.

[0006] Specifically, the method for improving the anaerobic digestion efficiency of excess sludge in a low-carbon mode disclosed in this invention includes the following steps: (1-1) Add 0.05 g / g VSS calcium hypochlorite to the remaining sludge and mix well; (1-2) Adjust the pH of the system to neutral, then heat to 140℃ and heat at 140℃ for 30 min; (1-3) The bottom sediment is obtained after natural cooling to room temperature and used for subsequent anaerobic digestion.

[0007] In the above steps (1-2), adjusting the pH of the system to neutral means adjusting the pH to 6.8-7.5.

[0008] In the above steps (1-3), room temperature refers to 37±1℃.

[0009] In one specific implementation, the residual sludge used in step (1-1) is pre-screened to remove large particles of sand and gravel.

[0010] In one specific technical solution, the sieve is a sieve with a mesh size of 10 or higher.

[0011] Furthermore, anaerobic digestion includes the following steps: (2-1) Mix the bottom mud and seed mud at a volume ratio of 1:1; (2-2) Place the mixed mixture in a reactor, introduce nitrogen gas, seal it, and anaerobic digest it in a nitrogen atmosphere for 30 days.

[0012] Furthermore, in step (2-2), the mixture is stirred twice a day, with a stirring intensity of 150-250 rpm each time.

[0013] Furthermore, in step (2-2), the mixture is stirred twice a day, with a stirring intensity of 200 rpm each time.

[0014] As a preferred technical solution, the pH of the mixture in step (2-2) is maintained at 6.8-7.5.

[0015] In a preferred embodiment, the reactor in step (2-2) is a constant temperature water bath shaker.

[0016] In a specific technical solution, the anaerobic digestion temperature in step (2-2) is 37±1℃.

[0017] This invention provides a novel pretreatment method for anaerobic digestion of waste sludge. After pretreatment using the method disclosed in this invention, the dissolved COD of the waste sludge undergoing further anaerobic digestion is increased by 11.20 times compared to the control group, the cumulative methane production is increased by 163.9%, and the maximum methanogenesis rate is increased by 158.8%. Furthermore, the pretreatment method disclosed in this invention has minimal inhibitory effect on methanogenic bacteria in the waste sludge, ensuring the activity and function of bacteria during subsequent anaerobic digestion. In pilot-scale experiments, the daily methane production after pretreatment of waste sludge using this method increased by 57.9% compared to the control group. It is also noteworthy that this method significantly reduces unit methane carbon emissions compared to existing anaerobic digestion methods, decreasing methane carbon emissions by 45.6% compared to the control group. Detailed Implementation

[0018] To better understand this invention, we will further illustrate it below with reference to specific embodiments. The following detailed description of the invention with reference to embodiments should not be construed as limiting the scope of protection of this invention. Unless otherwise specified, the experimental materials used in the following embodiments can be obtained through conventional commercial channels.

[0019] The calcium hypochlorite used in the embodiments of the present invention is calcium hypochlorite with a purity of ≥98%. Example 1

[0020] Excess sludge from the secondary sedimentation tank of a typical municipal wastewater treatment plant was sieved through a 10-mesh sieve to remove large particles of sand and gravel. Then, the parameters were measured according to the methods published in "Methods for Monitoring and Analysis of Water and Wastewater" (Fourth Edition). The measured parameters of the excess sludge were: TSS = 19.96 ± 0.03 g / L, VSS = 9.32 ± 0.07 g / L, TCOD = 17.84 ± 0.11 g / L. Example 2

[0021] Add 0.05 g / g VSS calcium hypochlorite to the residual sludge obtained in Example 1 and stir for 2 minutes until uniformly mixed; allow the calcium hypochlorite to fully react with the residual sludge. Adjust the pH of the system to 6.8-7.5 and then put it into the reactor. Heat to 140°C and maintain the temperature at 140°C for 30 minutes. After the reaction is completed, cool to 37±1°C and remove the sludge. The pretreatment process is complete, and the resulting bottom sludge is used for subsequent anaerobic digestion. Example 3

[0022] Take an equal amount of residual sludge as in Example 2 and add it to the reactor. Heat the reactor to 140°C and maintain the temperature at 140°C for 30 minutes. After the reaction is complete, cool the reactor to 37±1°C and remove the sludge. The pretreatment process is then finished, and the resulting bottom sludge is used for subsequent anaerobic digestion. Example 4

[0023] Take an equal amount of the remaining sludge from Example 2 and add it to the reactor. Heat the reactor to 180°C and maintain the temperature at 180°C for 30 minutes. After the reaction, cool the reactor to 37±1°C and remove the sludge. The pretreatment process is now complete, and the resulting bottom sludge is used for subsequent anaerobic digestion. Example 5

[0024] The sediments obtained from Example 1 (blank), Example 2, Example 3 and Example 4 were anaerobic digested according to the following method.

[0025] The pretreated substrate and seed substrate (TSS=95.21±0.03 g / L, VSS=29.29±0.10 g / L, TCOD=7.84±0.11 g / L) were inoculated at a 1:1 ratio and placed in a constant temperature water bath shaker at 37±1℃. After sealing, nitrogen gas was introduced for 5 minutes to remove oxygen. Anaerobic digestion was carried out for 30 days under pH=6.8-7.5 conditions. During the anaerobic digestion process, the substrate was stirred twice a day at a stirring intensity of 200 rpm to ensure sufficient contact between the substrate and the microorganisms. The temperature was maintained at 37±1℃ throughout the experiment.

[0026] The anaerobic digestion effect of excess sludge obtained by different pretreatment methods was determined, and the results are shown in Table 1.

[0027] Table 1: Residual sludge treatment methods Dissolved COD concentration after treatment (mg / L) Peak cumulative concentration of volatile acid (mg / L) Cumulative methane production (mL / g VSS) Maximum methanogenesis rate (mL / (g VSS·d)) <![CDATA[Unit methane carbon emissions (kgCO2-eq / m³ CH4)]]> Example 1 349.2±20.4 209.4±2.7 28.48±0.67 5.13±0.38 0.68 Example 2 3472.8±249.4 2083.1±106.9 75.10±1.29 13.28±1.10 0.37 Example 3 3065.7±102.7 1839.0±157.8 45.67±3.32 8.22±0.16 0.44 Example 4 3484.6±196,7 2138.4±102.8 78.39±5.85 13.81±0.90 0.53 Experiments show that, using the method disclosed in this invention, the soluble COD is increased by 11.20 times compared to the control group, the peak cumulative concentration of volatile acids is increased by 8.95 times (of which the acetic acid concentration is increased by 8.99 times), the cumulative methane production is increased by 163.9%, the maximum methane production rate is increased by 158.8%, and the unit methane carbon emission (daily carbon emission at stable conditions / methane production) is reduced by 45.6%.

[0028] It is evident that the method disclosed in this invention can significantly reduce carbon emissions per unit of methane production, meeting the needs of modern green and low-carbon disposal.

[0029] The above describes specific embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for improving the efficiency of anaerobic digestion of excess sludge in a low-carbon mode, characterized by, Includes the following steps: (1-1) Add 0.05 g / g VSS calcium hypochlorite to the remaining sludge and mix well; (1-2) Adjust the pH of the system to neutral, then heat to 140℃ and heat at 140℃ for 30 min; (1-3) The bottom sediment is obtained after natural cooling to room temperature and used for subsequent anaerobic digestion.

2. The method for improving the anaerobic digestion efficiency of excess sludge under low-carbon mode according to claim 1, characterized in that, In steps (1-2), adjust the pH of the system to 6.8-7.

5.

3. The method for improving the efficiency of anaerobic digestion of excess sludge under low-carbon mode according to claim 1, characterized in that, The room temperature in steps (1-3) is 37±1℃.

4. The method for improving the anaerobic digestion efficiency of excess sludge under low-carbon mode according to claim 1, characterized in that, The remaining sludge used in step (1-1) is screened beforehand to remove large particles of sand and gravel.

5. The method for improving the anaerobic digestion efficiency of excess sludge under low-carbon mode according to claim 1, characterized in that, Anaerobic digestion includes the following steps: (2-1) Mix the bottom mud and seed mud at a volume ratio of 1:1; (2-2) Place the mixed mixture in a reactor, introduce nitrogen gas, seal it, and anaerobic digest it in a nitrogen atmosphere for 30 days.

6. The method for improving the anaerobic digestion efficiency of excess sludge in a low-carbon mode according to claim 5, characterized in that, In step (2-2), the mixture is stirred twice a day, with a stirring intensity of 150-250 rpm each time.

7. The method for improving the efficiency of anaerobic digestion of excess sludge under low-carbon mode according to claim 5, characterized in that, In step (2-2), the mixture is stirred twice a day, with a stirring intensity of 200 rpm each time.

8. The method for improving the efficiency of anaerobic digestion of excess sludge under low-carbon mode according to claim 1, characterized in that, The pH of the mixture in step (2-2) is maintained at 6.8-7.

5.

9. The method for improving the anaerobic digestion efficiency of excess sludge under low-carbon mode according to claim 1, characterized in that, In step (2-2), the reactor is a constant temperature water bath shaker.

10. The method for improving the anaerobic digestion efficiency of excess sludge under low-carbon mode according to claim 1, characterized in that, The anaerobic digestion temperature in step (2-2) is 37±1℃.