A method for enhancing resource recovery from excess sludge

Abstract

The present application belongs to the field of solid resource treatment, and relates to a method for preparing high-efficiency microbial enhancer by using digested sludge and recycling the high-efficiency microbial enhancer in situ to strengthen the anaerobic treatment of methane production of residual sludge. The specific method comprises the following steps: (1) preparing high-efficiency microbial enhancer by using digested sludge as raw material; (2) constructing a semi-continuous reaction device for sludge anaerobic digestion; (3) adding the high-efficiency microbial enhancer to the residual sludge for pretreatment; and (4) adding anaerobic inoculated sludge, setting different sludge retention times for anaerobic digestion, and obtaining high-value-added methane. The present application prepares high-efficiency microbial enhancer by using digested sludge as raw material, which not only provides a new outlet for the large amount of digested sludge, but also enhances the recycling of resource energy in the residual sludge through recycling, so as to treat waste with waste. Compared with the traditional pretreatment method of sludge anaerobic digestion, a large amount of energy and reagents are saved.

Description

Technical Field

[0001] This invention belongs to the field of solid resource utilization and treatment, specifically relating to a method for preparing a highly efficient microbial enhancer using digested sludge and reusing it in situ to enhance the anaerobic treatment of methane generation from excess sludge. Technical Background

[0002] Over the past few decades, with the development of urbanization, the improvement of people's living standards, and the enhancement of environmental awareness in my country, the total amount of sewage discharge has increased significantly, and more and more new sewage treatment facilities have been built. As the scale of sewage treatment increases, the production of excess sludge will also increase year by year. The treatment and disposal of excess sludge is one of the problems currently facing sewage treatment plants. Statistics show that the cost of excess sludge treatment / disposal can reach as much as 40-60% of the total operating cost of a sewage treatment plant.

[0003] On the one hand, waste sludge contains a large amount of organic matter such as proteins, polysaccharides, and lipids, which can be recycled or utilized using specific methods, and its volume can be reduced using specific means. On the other hand, waste sludge contains some potentially toxic organic or inorganic pollutants such as antibiotics, antibacterial agents, heavy metals, organochlorine pesticides, and polycyclic aromatic hydrocarbons. Improper treatment and disposal will inevitably threaten the ecological environment. Therefore, the rational and appropriate treatment and disposal of waste sludge is a formidable task facing my country's environmental protection efforts.

[0004] Anaerobic digestion, which can reduce sludge volume while simultaneously stabilizing and recovering resources, is a highly promising technology already widely used in industry. Waste sludge contains abundant organic matter and recyclable resources such as nitrogen and phosphorus; its effective recovery can significantly reduce the operating costs of wastewater treatment plants. Anaerobic digestion technology can play a crucial role in the sustainable development of wastewater treatment plants. However, anaerobic digestion of sludge suffers from low resource recovery rates and low methane production, necessitating the search for cost-effective and environmentally friendly technologies to enhance methane production from anaerobic digestion of sludge.

[0005] Anaerobic digestion is a complex and sophisticated biochemical process driven by various functional microorganisms, such as hydrolytic bacteria, acidifying bacteria, and methanogenic archaea. Functional microorganisms play a crucial role in methanogenesis during anaerobic digestion; however, the microorganisms involved in sludge treatment are fragile and highly susceptible to environmental factors. Therefore, enhancing the activity of functional microorganisms is key to improving methane production during anaerobic sludge digestion. After anaerobic digestion, sludge is often directly landfilled or incinerated after dewatering, lacking pathways and methods for resource reuse. To date, no methods have been explored for the targeted construction of highly efficient microbial enhancers using digested sludge as raw material and their in-situ reuse to enhance the anaerobic treatment of excess sludge for methane production. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a highly efficient microbial enhancer using digested sludge and for in-situ reuse of the enhanced residual sludge to anaerobic treat methane production.

[0007] To achieve the above objectives, the solution of the present invention is as follows:

[0008] A method for enhancing the recycling of excess sludge resources includes the following steps:

[0009] (1) Preparation of high-efficiency microbial enhancer: Digested sludge obtained from anaerobic digestion reactor is used as raw material. Large particles of digested sludge are removed by sieve and then mixed with clay powder. The mixture is manually granulated into raw material particles with a diameter of about 20 mm. In order to remove the residual free water in the sample, the pellets are dried at 105℃ for 24 hours and the dried pellets are sintered in a furnace to prepare high-efficiency microbial enhancer.

[0010] (2) Reaction device: A semi-continuous reaction device is constructed for the anaerobic digestion of excess sludge. The device mainly includes a sludge storage container, a pretreatment reactor, an anaerobic digestion reactor and a discharge bottle. All units are connected by pipelines, and the feeding and discharging between units are controlled by a peristaltic pump with a timer. Each reactor is equipped with a stirring device to ensure that the sludge is uniformly mixed during the feeding and discharging process.

[0011] (3) Pretreatment: The residual sludge obtained from the secondary sedimentation tank of the urban sewage treatment plant is used as the anaerobic digestion substrate and stored in the sludge storage container. The residual sludge in the sludge storage container is added to the pretreatment reactor, and 5-10 g / L of high-efficiency microbial enhancer is added. The mixture is stirred evenly and pretreated for 1 day at pH 9 and temperature of 35℃.

[0012] (4) Anaerobic digestion: The pretreated sludge is transferred to the anaerobic digestion reactor, the pH is adjusted to 7.0±0.1, and then anaerobic sludge is inoculated; after nitrogen stripping for 2-4 minutes, the digestion reactor is sealed; after 10 days of continuous operation, a portion of the digestion mixture is discharged to the discharge bottle by a peristaltic pump at regular intervals each day, and then an equal amount of pretreated sludge from the pretreatment reactor is added to the anaerobic digestion reactor, and the cycle is repeated daily; then an equal amount of sludge is pumped from the sludge storage container to the pretreatment reactor for pretreatment, and used as feed to the anaerobic digestion reactor, and the cycle is repeated daily.

[0013] Furthermore, the diameter of the sieve in step (1) above is 5 mm. This diameter is sufficient to remove most inorganic particles.

[0014] Furthermore, in step (1) above, the ratio of digested sludge to clay is 7:3 (wt). This ratio can effectively granulate the digested sludge.

[0015] Furthermore, the sintering procedure of the dried pellets in the furnace in step (1) above is as follows: first, the furnace temperature is raised from room temperature to 400℃ at a heating rate of 10℃ / min, and held for 15 minutes; then, the temperature is raised from 400℃ to 1000℃ at a heating rate of 20℃ / min, and held for 20 minutes; then, the furnace temperature is lowered to 600℃ at a cooling rate of 20℃ / min, and finally, the high-efficiency microbial enhancer is naturally cooled to room temperature. Temperature control and residence time are key to the preparation of high-efficiency microbial enhancers. Excessively high temperatures will damage the surface structure of the enhancer, thereby losing its ability to regulate microbial activity; excessively low temperatures will prevent the formation of the enhancer material itself.

[0016] Furthermore, in step (2) above, the flow rate of the peristaltic pump is 60-100 mL / min. The substrate provided at this flow rate can well meet the needs of functional microorganisms.

[0017] Furthermore, in step (2) above, the stirring intensity of the reactor stirring device is 250 rpm / min. This intensity is sufficient for mass transfer.

[0018] Furthermore, the concentration of the remaining sludge in step (3) above is 35 g / L. Too high a concentration is not conducive to mass transfer, while too low a concentration cannot provide sufficient substrate.

[0019] Furthermore, the temperature in the sludge storage container in step (3) above is controlled at 4°C. This concentration inhibits the activity of microorganisms and avoids premature anaerobic digestion.

[0020] Furthermore, in step (4) above, the temperature in the anaerobic digester is controlled at 35°C. At this temperature, methanogenic microorganisms exhibit good activity.

[0021] Furthermore, in step (4) above, the inoculation ratio of residual sludge to anaerobic sludge is 3:1–6:1 (v / v). Both excessively high and low ratios can cause an imbalance between the substrate and functional microorganisms.

[0022] Furthermore, in step (4) above, the sludge retention time in the anaerobic digester is 20 days. After 20 days of anaerobic digestion, the substrate is basically completely consumed, and the maximum methanogenic yield can be obtained.

[0023] By adopting the above technical solutions, the present invention has the following results:

[0024] This invention relates to a method for preparing a highly efficient microbial enhancer using digested sludge and reusing it in situ to enhance the anaerobic treatment of methane generation from excess sludge. This method not only provides a new outlet for the large amount of digested sludge but also enhances the recovery of resources and energy from excess sludge, treating waste with waste. Compared with traditional anaerobic digestion pretreatment methods for sludge, it saves a significant amount of energy and reagents. Attached Figure Description

[0025] Figure 1 The effect of different dosages of highly efficient microbial enhancers on methane production from anaerobic digestion of sludge. Detailed Implementation

[0026] The present invention will be further described below with reference to specific practical examples, but this does not limit the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description should be included within the scope of protection of the present invention.

[0027] Case Study 1: Effects of Different Sintering Temperatures and Residence Times on the Performance of High-Efficiency Microbial Enhancers and Their Effect on Enhancing Methane Production in Anaerobic Sludge Digestion

[0028] (1) Preparation of high-efficiency microbial enhancers: Digested sludge obtained from the anaerobic digestion reactor was used as raw material. Large particles of the digested sludge were removed by sieve with a diameter of 5 mm, and then mixed with clay powder at a ratio of 7:3 (wt). The mixture was manually granulated into raw material particles with a diameter of about 20 mm. In order to remove the residual free water in the sample, the pellets were dried at 105℃ for 24 hours for subsequent sintering experiments. The dried pellets were sintered in the furnace. The sintering procedure is shown in Table 1 to prepare different series of high-efficiency microbial enhancers.

[0029] (2) Reaction device: A semi-continuous reaction device is constructed for the anaerobic digestion of excess sludge. The device mainly includes a sludge storage container, a pretreatment reactor, an anaerobic digestion reactor, and a discharge bottle. All units are connected by g pipelines, and the feeding and discharging between units are controlled by a peristaltic pump with a timer device. The flow rate of the peristaltic pump is 100 mL / min. Each reactor is equipped with a stirring device to ensure that the sludge is uniformly mixed during the feeding and discharging process. The stirring intensity of the reactor stirring device is 250 rpm / min.

[0030] (3) Pretreatment: The residual sludge with a concentration of 35 g / L obtained from the secondary sedimentation tank of the urban sewage treatment plant is used as the anaerobic digestion substrate and stored in a sludge storage container. The temperature in the sludge storage container is controlled at 4℃. The residual sludge in the sludge storage container is added to the pretreatment reactor, and 10 g / L of different series of high-efficiency microbial enhancers are added respectively. The mixture is stirred evenly and pretreated for 1 day at pH 9 and temperature of 35℃.

[0031] (4) Anaerobic digestion: 10L of pretreated residual sludge was transferred to the anaerobic digestion reactor, the pH was adjusted to 7.0±0.1, the temperature was controlled at 35℃, and then anaerobic sludge was inoculated at an inoculation ratio of 5:1 (v / v); nitrogen was blown off for 2-4 minutes and then the anaerobic digestion reactor was sealed; after 10 days of continuous operation, the sludge retention time was set to 20 days, that is, 500mL of digestion mixture was discharged to the discharge bottle by peristaltic pump at 8:00 am every day, and then 500mL of pretreated sludge from the pretreatment reactor was added to the anaerobic digestion reactor, and the cycle was repeated daily; then 500mL of residual sludge was pumped from the sludge storage container to the pretreatment reactor for pretreatment, and used as the feed to the anaerobic digestion reactor, and the cycle was repeated daily. The methane production in the anaerobic digestion reactor was detected by gas chromatography, and the results are shown in Table 1.

[0032] Table 1. Effects of different sintering temperatures and residence times on the performance of high-efficiency microbial enhancers and their effect on methane production from enhanced anaerobic digestion of sludge.

[0033]

[0034]

[0035] The above experimental results show that sintering dried pellets in a furnace by first raising the furnace temperature from room temperature to 400℃ at a rate of 10℃ / min and holding for 15 minutes; then raising the temperature from 400℃ to 1000℃ at a rate of 20℃ / min and holding for 20 minutes; then lowering the furnace temperature to 600℃ at a rate of 20℃ / min; and finally allowing the high-efficiency microbial enhancer to cool naturally to room temperature can successfully prepare a high-efficiency microbial enhancer with the best methanogenic performance.

[0036] Case Study 2: Effects of Different Dosages of High-Efficiency Microbial Enhancers on Methane Production from Anaerobic Digestion of Sludge

[0037] (1) Preparation of high-efficiency microbial enhancer: Digested sludge obtained from the anaerobic digestion reactor was used as raw material. Large particles of the digested sludge were removed by sieve with a diameter of 5 mm, and then mixed with clay powder at a ratio of 7:3 (wt). The mixture was manually granulated into raw material particles with a diameter of about 20 mm. In order to remove the residual free water in the sample, the pellets were dried at 105℃ for 24 hours for subsequent sintering experiments. The dried pellets were sintered in the furnace. First, the furnace temperature was raised from room temperature to 400℃ at a heating rate of 10℃ / min and held for 15 minutes. Then, the temperature was raised from 400℃ to 1000℃ at a heating rate of 20℃ / min and held for 20 minutes. Then, the furnace temperature was lowered to 600℃ at a cooling rate of 20℃ / min. Finally, the high-efficiency microbial enhancer was naturally cooled to room temperature, and the high-efficiency microbial enhancer was successfully prepared.

[0038] (2) Reaction device: A semi-continuous reaction device is constructed for the anaerobic digestion of excess sludge. The device mainly includes a sludge storage container, a pretreatment reactor, an anaerobic digestion reactor, and a discharge bottle. All units are connected by g pipelines, and the feeding and discharging between units are controlled by a peristaltic pump with a timer device. The flow rate of the peristaltic pump is 100 mL / min. Each reactor is equipped with a stirring device to ensure that the sludge is uniformly mixed during the feeding and discharging process. The stirring intensity of the reactor stirring device is 250 rpm / min.

[0039] (3) Pretreatment: The residual sludge with a concentration of 35 g / L obtained from the secondary sedimentation tank of the urban sewage treatment plant was used as the anaerobic digestion substrate and stored in a sludge storage container. The temperature in the sludge storage container was controlled at 4℃. The residual sludge in the sludge storage container was added to the pretreatment reactor, and 0, 5, 10, and 15 g / L of high-efficiency microbial enhancer were added respectively. The mixture was stirred evenly and pretreated for 1 day at pH 9 and temperature of 35℃.

[0040] (4) Anaerobic Digestion: 10L of pretreated residual sludge was transferred to the anaerobic digester. The pH was adjusted to 7.0±0.1, and the temperature was controlled at 35℃. Anaerobic sludge was then inoculated at an inoculation ratio of 5:1 (v / v). After nitrogen stripping for 2-4 minutes, the anaerobic digester was sealed. After 10 days of continuous operation, the sludge retention time was set to 20 days. Every morning at 8:00 AM, 500mL of the digestion mixture was first discharged to the discharge bottle via a peristaltic pump. Then, 500mL of pretreated sludge from the pretreatment reactor was added to the anaerobic digester, and this cycle was repeated daily. Then, 500mL of residual sludge was pumped from the sludge storage container to the pretreatment reactor for pretreatment, serving as the feed to the anaerobic digester, and this cycle was repeated daily. The methane yield in the anaerobic digester was detected using gas chromatography. The results are as follows: Figure 1 As shown.

[0041] After pretreatment of sludge with 0, 5, 10, and 15 g / L of high-efficiency microbial enhancer, the average daily methane production in the sludge anaerobic digestion reactor was 127.5±3.0, 155.2±2.8, 178.4±3.3, and 180.1±5.1 mL / gVS, respectively. This indicates that the addition of high-efficiency microbial enhancer can significantly promote methane production during sludge anaerobic digestion, with a more significant promoting effect at an addition of 5-10 g / L, while no significant increase was observed when the addition was increased to 15 g / L.

[0042] Case Study 3: The Effect of Different Sludge Retention Times on Methane Production from Anaerobic Digestion of Sludge

[0043] (1) Preparation of high-efficiency microbial enhancer: The steps are the same as in Case 2;

[0044] (2) Reaction apparatus: The procedure is the same as in Case 2;

[0045] (3) Pretreatment: The steps are basically the same as in Case 2, but the amount of highly efficient microbial enhancer added is 10g / L;

[0046] (4) Anaerobic digestion: 10L of pretreated residual sludge was transferred to the anaerobic digestion reactor, the pH was adjusted to 7.0±0.1, the temperature was controlled at 35℃, and then anaerobic sludge was inoculated at an inoculation ratio of 5:1 (v / v); nitrogen was blown off for 2-4 minutes and then the anaerobic digestion reactor was sealed; after 10 days of continuous operation, the sludge retention time was set to 15, 20 and 25 days respectively. That is, at 8:00 am every day, 666.7mL, 500mL or 400mL of digestion mixture was discharged to the discharge bottle by peristaltic pump, and then 666.7mL, 500mL or 400mL of pretreated sludge from the pretreatment reactor was added to the anaerobic digestion reactor, and the cycle was repeated daily; then 666.7mL, 500mL or 400mL of residual sludge was pumped from the sludge storage container to the pretreatment reactor for pretreatment, and used as the feed for the anaerobic digestion reactor, and the cycle was repeated daily. The methane production in the anaerobic digestion reactor was detected by gas chromatography.

[0047] In the above treatment process, the sludge retention time was set to 15, 20, and 25 days, respectively. The average daily methane production in the sludge anaerobic digestion reactor was 158.5±2.8, 178.4±3.3, and 161.1±3.5 mL / gVS, respectively. This indicates that the optimal sludge retention time in the anaerobic digestion reactor is 20 days under pretreatment with 10 g / L of highly efficient microbial enhancer.

Claims

1. A method for enhancing the recovery of excess sludge resources, characterized in that, Includes the following steps: (1) Preparation of high-efficiency microbial enhancer: Digested sludge obtained from the anaerobic digestion reactor was used as raw material. Large particles of the digested sludge were removed by sieving and then mixed with clay powder. The mixture was manually granulated into raw material particles with a diameter of 20 mm. In order to remove the residual free water in the sample, the pellets were dried at 105℃ for 24 hours for subsequent sintering experiments. The dried pellets were sintered in a furnace to prepare the high-efficiency microbial enhancer. The sintering procedure of the dried pellets in the furnace was as follows: First, the furnace temperature was raised from room temperature to 400℃ at a heating rate of 10℃ / min and held for 15 minutes. Then, the temperature was raised from 400℃ to 1000℃ at a heating rate of 20℃ / min and held for 20 minutes. Then, the furnace temperature was lowered to 600℃ at a cooling rate of 20℃ / min. Finally, the high-efficiency microbial enhancer was naturally cooled to room temperature. (2) Reaction device: A semi-continuous reaction device is constructed for the anaerobic digestion of excess sludge. The device mainly includes a sludge storage container, a pretreatment reactor, an anaerobic digestion reactor and a discharge bottle. All units are connected by pipelines, and the feeding and discharging between units are controlled by a peristaltic pump with a timer. Each reactor is equipped with a stirring device to ensure that the sludge is uniformly mixed during the feeding and discharging process. (3) Pretreatment: The residual sludge obtained from the secondary sedimentation tank of the urban sewage treatment plant is used as the anaerobic digestion substrate and stored in the sludge storage container. The residual sludge in the sludge storage container is added to the pretreatment reactor, and 5-10 g / L of high-efficiency microbial enhancer is added. The mixture is stirred evenly and pretreated for 1 day at pH 9 and temperature of 35℃. (4) Anaerobic digestion: Transfer the remaining sludge after pretreatment to the anaerobic digestion reactor, adjust the pH to 7.0±0.1, and then inoculate with anaerobic sludge; after nitrogen stripping for 2-4 minutes, seal the anaerobic digestion reactor; after running continuously for 10 days, discharge part of the digestion mixture into the discharge bottle by peristaltic pump every day, and then add an equal amount of pretreated sludge from the pretreatment reactor to the anaerobic digestion reactor, and cycle daily; Then, an equal amount of excess sludge is pumped from the sludge storage container into the pretreatment reactor for pretreatment, and used as feed for the anaerobic digestion reactor, which is circulated daily.

2. The method for enhancing the recovery of excess sludge resources according to claim 1, characterized in that, The diameter of the sieve mentioned in step (1) is 5 mm.

3. The method for enhancing the recovery of excess sludge resources according to claim 1, characterized in that, The ratio of digested sludge to clay powder added in step (1) is 7:3 (wt).

4. The method for enhancing the recovery of excess sludge resources according to claim 1, characterized in that, The flow rate of the peristaltic pump mentioned in step (2) is 60-100 mL / min.

5. The method for enhancing the recovery of excess sludge resources according to claim 1, characterized in that, The concentration of the residual sludge mentioned in step (3) is 35 g / L.

6. The method for enhancing the recovery of excess sludge resources according to claim 1, characterized in that, The temperature in the mud storage container described in step (3) is controlled at 4°C.

7. The method for enhancing the recovery of excess sludge resources according to claim 1, characterized in that, The temperature in the anaerobic digester described in step (4) is controlled at 35°C.

8. The method for enhancing the recovery of excess sludge resources according to claim 1, characterized in that, The inoculation ratio of the residual sludge to the anaerobic sludge in step (4) is 3:1–6:1 (v / v).

9. The method for enhancing the recovery of excess sludge resources according to claim 1, characterized in that, The sludge retention time in the anaerobic digester described in step (4) is 20 days.

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