Anaerobic digestion efficiency improving method for regulating micro-aeration based on oxidation-reduction potential

Abstract

The invention relates to the technical field of anaerobic digestion, and discloses an anaerobic digestion efficiency improving method based on oxidation-reduction potential (ORP) regulation and control micro-aeration, which is suitable for traditional completely mixed anaerobic digestion of organic solid waste and high-inherent-sewage-content wastewater and a novel anaerobic membrane bioreactor process. Monitoring the ORP of the anaerobic digestion sludge mixed liquid in real time, starting the micro-aeration device to supply oxygen when the ORP is lower than a target lower limit, and stopping when the ORP is higher than a target upper limit. The ORP target lower limit is set as a stable value when aeration is not carried out, the upper limit is the lower limit + 10-100 mV, and the optimal value is dynamically adjusted according to the load of the solid organic matter through a test. The micro-aeration device is composed of an air source, an air blower / compressor, an aerator, a flow meter, a pressure gauge and the like. According to the method, ORP periodic fluctuation is realized, a suitable ecological niche is provided for hydrolytic acidification bacteria, hydrogen-producing acetogens and methanogens, the organic matter removal performance, the methane recovery performance and the mud-water separation performance are improved, and the comprehensive efficiency and stability of anaerobic digestion are enhanced.

Description

Technical Field

[0001] This invention relates to the field of anaerobic digestion technology, and more specifically, to a method for improving the efficiency of anaerobic digestion based on oxidation-reduction potential-regulated micro-aeration oxygen supply. This method is applicable to both traditional completely mixed anaerobic digestion and emerging anaerobic membrane bioreactor processes for treating organic solid waste and wastewater with high organic content. Background Technology

[0002] Anaerobic digestion technology, as an important means to reduce organic pollutants, recover energy (such as methane), and recycle resources (such as nitrogen and phosphorus), is a core treatment and disposal link for organic solid waste such as waste sludge, kitchen waste, and agricultural and forestry biomass waste, as well as high-solids wastewater such as livestock and poultry breeding wastewater, landfill leachate, and fermentation wastewater. It plays a key role in promoting the carbon neutrality strategy. However, the slow dissolution / hydrolysis rate of solid organic matter and the poor solid-liquid separation performance of the digestate are technical bottlenecks that restrict its anaerobic digestion efficiency. This results in traditional completely mixed anaerobic digestion processes having long hydraulic retention times, large footprints, low efficiency in organic matter removal and methane conversion, and high solid-liquid separation costs.

[0003] Although the anaerobic membrane bioreactor (AnMBR) process utilizes membrane separation technology to replace traditional gravity settling, achieving separation of hydraulic retention time (HRT) and sludge retention time (SRT), and significantly extending the residence time of suspended and macromolecular organic matter, thus improving organic matter removal, methane recovery, and sludge-water separation, it has not solved the problem of slow dissolution / hydrolysis rates of solid organic matter and has also introduced membrane fouling issues. To address these problems, some researchers have attempted to introduce micro-aeration technology to stimulate the activity of facultative anaerobic bacteria, thereby increasing the dissolution / hydrolysis rates of suspended and macromolecular organic matter and improving the sludge-water separation performance of the sludge mixture. However, the aeration rate is difficult to control precisely; excessive oxygen supply can disrupt the anaerobic environment and inhibit methanogenic bacteria activity, while insufficient oxygen supply renders it ineffective. Furthermore, dissolved oxygen (DO) monitoring instruments have limited sensitivity to trace amounts of oxygen, making it difficult to meet the requirements for precise control. Oxidation-reduction potential (ORP), as a key parameter reflecting the microenvironmental state of the anaerobic system, is more sensitive to changes in trace amounts of oxygen within the system, and its value can more accurately characterize whether the aeration rate is appropriate. However, existing technologies have not yet established a mechanism for micro-aeration based on ORP regulation, making it impossible to dynamically optimize aeration strategies in real time based on ORP. This makes it difficult to synergistically improve the methanogenesis and sludge-water separation / membrane fouling control efficiency of traditional anaerobic digestion and AnMBR processes.

[0004] Therefore, there is an urgent need to develop a method for improving the efficiency of anaerobic digestion based on ORP-regulated micro-aeration, in order to solve problems such as inaccurate aeration control, difficulty in balancing methanogenesis and sludge-water separation / membrane fouling control in existing technologies, and to improve the stability and overall efficiency of anaerobic digestion systems. Summary of the Invention

[0005] In view of this, the present invention proposes a method for improving the efficiency of anaerobic digestion based on micro-aeration with redox potential regulation, aiming to solve the problems of inaccurate aeration control and difficulty in balancing methanogenesis and sludge-water separation / membrane fouling control in the current technology.

[0006] This invention proposes a method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration, comprising the following steps: S1. Connect the micro-aeration gas source to the air inlet pipeline and then to the aerator in the anaerobic digester; S2. Set the target value for ORP increase, the gas flow rate, the interval aeration period and the air intake mode in the micro-aeration control system, and stop aeration when the target value for ORP is reached; S3. Turn on the air source and micro-aeration control system to automatically supply oxygen to the anaerobic digestion sludge mixture through micro-aeration.

[0007] Furthermore, in step S1, the micro-aeration gas source is a gas containing a certain proportion of oxygen, including air and oxygen.

[0008] Furthermore, in step S1, the micro-aeration gas source is a gas containing a certain proportion of oxygen, including air and oxygen.

[0009] Furthermore, in step S1, a pressure gauge is installed on the air intake pipe to detect pressure changes in real time.

[0010] Furthermore, in step S1, the aerator can be configured as a perforated aeration pipe, a microporous aeration disc, a microporous aeration membrane, or a non-porous aeration membrane.

[0011] Furthermore, in step S1, the aerator is placed at the bottom of the anaerobic digester and is designed for uniform aeration.

[0012] Furthermore, in step S2, the gas flow rate is set by controlling a small amount of gas intake through a gas quality controller and recording the intake volume.

[0013] Furthermore, in step S2, the ORP is set within the range of -500 mv to 0 mv.

[0014] Furthermore, in step S2, the air intake mode is either continuous air intake or intermittent air intake.

[0015] Furthermore, in step S2, the interval aeration period is generally 0.5 days to 2 days or is set to automatically aerate when the ORP drops to a certain target level.

[0016] Furthermore, in step S3, the sludge mixture is a mixture of anaerobic digested activated sludge and organic solid waste or wastewater with high organic content.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: By setting upper and lower limits for ORP to control the oxygen supply through micro-aeration, the periodic fluctuations of ORP within the anaerobic digester are achieved. This provides suitable ecological niches for various functional microorganisms participating in anaerobic digestion (hydrolytic acidifying bacteria, hydrogen-producing and acetic-producing bacteria, and methanogens) for a certain period of time. This avoids excessive aeration from disrupting the anaerobic environment and inhibiting methanogen activity, while ensuring precise supply of micro-oxygen to fully stimulate the activity of facultative anaerobic bacteria, significantly improving the dissolution / hydrolysis efficiency of suspended and large molecular organic matter, thereby enhancing methanogenesis. Simultaneously, precise aeration promotes the formation of large-particle sludge flocs, reducing the colloidal content in the mixed liquor, thus improving the sludge-water separation performance of the mixed liquor. This reduces the sludge dewatering cost of traditional anaerobic digestion processes and the membrane fouling potential and total life-cycle cost of membrane modules in AnMBR processes. Furthermore, the sensitive response and dynamic control of ORP make the system microenvironment more stable, achieving synergistic optimization of organic matter degradation efficiency, methane yield, and sludge-water separation performance, significantly improving the overall efficiency and operational stability of the anaerobic digestion reaction system. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of the periodic fluctuations of ORP in the anaerobic digester of the control group and the aeration group in an embodiment of the present invention. Figure 2 This is a schematic diagram of methane production in the anaerobic digestion reactors of the control group and the aeration group in an embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the organic matter removal effect in the anaerobic digestion reactors of the control group and the aeration group in an embodiment of the present invention. Figure 4 This is a schematic diagram of the particle size distribution of the sludge mixture in the anaerobic digestion reactors of the control group and the aeration group in this embodiment of the invention. Figure 5 This is a schematic diagram of the microfiltration performance of the sludge mixture in the anaerobic digestion reactor of the control group and the aeration group in the embodiments of the present invention. Figure 6 This is a schematic diagram of the microfiltration membrane fouling potential of the sludge mixture in the anaerobic digestion reactor of the control group and the aeration group in the embodiments of the present invention. Figure 7 This is a schematic diagram illustrating the steps of the method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration, as provided in an embodiment of the present invention. Detailed Implementation

[0019] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] like Figures 1-7 As shown, in some embodiments of this application, the following are included: Control group: Sequencing batch anaerobic digester for treating pig manure, without micro-aeration, with a stable ORP value of -277mV.

[0021] Aeration Group 1: Based on the control example, oxygen was supplied by micro-aeration using a pure oxygen bubble-free aeration membrane, with ORP upper and lower limits of -260 / -277mV.

[0022] Aeration Group 2: Based on the control example, oxygen was supplied by micro-aeration using a pure oxygen bubble-free aeration membrane, with ORP upper and lower limits of -250 / -277mV.

[0023] In this embodiment, actual pig manure was selected as the treatment object to investigate the treatment effect of ORP-controlled micro-aeration oxygen supply on this type of high-solids-content, recalcitrant organic wastewater. Three groups of sequencing batch anaerobic digestion experiments were set up under different micro-aeration conditions: a control group with no aeration and ORP = -277 mV, an aerated group with ORP upper and lower limits of -260 / -277 mV, and an aerated group with ORP upper and lower limits of -250 / -277 mV. Each group of experiments was inoculated with the same anaerobic activated sludge and pig manure, and a mesophilic anaerobic digestion experiment was carried out until no methane was produced. COD removal and sludge-water separation performance of the mixed liquor were monitored to evaluate the comprehensive anaerobic digestion efficiency of different ORP-controlled micro-aeration oxygen supply.

[0024] Figure 1 It can be seen that the entire anaerobic digestion process lasted 12 days, with a total of 11 micro-aerations. Both aeration groups started aeration on the first day, reached the target ORP, stopped aeration, and then resumed aeration at the same time the following day. Throughout the anaerobic digestion process, the ORP of the aeration groups consistently fluctuated within a cycle. The ORP of the non-aerated control group remained stable at -277 ± 2 mV. The ORP of aeration group 1 fluctuated between -277 mV and -260 mV. The ORP of aeration group 2 fluctuated between -277 mV and -250 mV.

[0025] Figure 2The results showed that aeration group 1, with an ORP fluctuating between -277 and -260 mV, had the highest methane production; aeration group 2, with an ORP fluctuating between -277 and -250 mV, had a moderate methane production; and the control group, with an ORP stable at -277 mV, had the lowest methane production. Aeration group 1, with an ORP fluctuating between -277 and -260 mV, had a 26.8% higher methane production compared to the control group with an ORP stable at -277 mV. Aeration group 2, with an ORP fluctuating between -277 and -250 mV, had a 12.3% higher methane production compared to the control group with an ORP stable at -277 mV. This indicates that micro-aeration can effectively improve the methane production of pig manure, but a higher ORP does not necessarily mean better treatment results. In this example, the optimal ORP range for methane production from pig manure treated was between -277 mV and -260 mV.

[0026] Figure 3 The results showed that the aeration group 1, with an ORP fluctuating between -277 and -260 mV, had the highest organic matter removal rate at 17.7%; the aeration group 2, with an ORP fluctuating between -277 and -250 mV, had a moderate organic matter removal rate at 13.8%; and the control group, with an ORP stable at -277 mV, had the lowest organic matter removal rate at only 11.7%. These results are consistent with... Figure 2 The results corresponded and corroborated each other, confirming that the ORP-controlled micro-aeration method effectively improved the removal of organic matter from pig manure.

[0027] Figure 4 Particle size analysis of the sludge mixed liquor showed that, compared with the control group whose ORP was stable at -277 mV, the particle size distribution of aeration group 1 (ORP fluctuating between -277 and -260 mV) and aeration group 2 (ORP fluctuating between -277 and -250 mV) both exhibited a significant increasing trend. This indicates that ORP regulation of micro-aeration oxygen supply promotes sludge floc aggregation, thereby improving sludge-water separation performance. The average particle size of aeration group 1 (ORP fluctuating between -277 and -260 mV) was 41.94 μm, the average particle size of aeration group 2 (ORP fluctuating between -277 and -250 mV) was 47.19 μm, and the average particle size of the control group (ORP stable at -277 mV) was 27.37 μm, demonstrating that the higher the ORP, the larger the average particle size.

[0028] Figure 5The filtration performance of the sludge mixture (filtration performance refers to the ability to pass through a 0.45μm microfiltration membrane under the same pressure of 10 kPa per unit time) was tested using a constant pressure dead-end filtration system. The sludge mixtures of the control group with a stable ORP of -277 mV, aeration group 1 with an ORP fluctuating between -277 and -260 mV, and aeration group 2 with an ORP fluctuating between -277 and -250 mV were all diluted 10 times and placed in a filter cup. The pressure inside the cup was adjusted to 10 kPa using a nitrogen cylinder and a pressure control element. The filtered filtrate was collected in a beaker and the real-time volume change of the filtrate was recorded using a program established between an electronic balance and a computer. Figure 5 The results showed that the filtrate volume increase curve of aeration group 1, with ORP fluctuations between -277 and -260 mV, increased at the fastest rate, indicating that its microfiltration membrane had the best filtration performance. Aeration group 1, with ORP fluctuations between -277 and -260 mV, had the highest membrane flux of 43.42 L / m. 2 For the aeration group 2, with an ORP fluctuating between -277 and -250 mV (h(LMH),) the membrane flux was moderate at 22.57 LMH, while the control group, with an ORP stable at -277 mV, had the lowest membrane flux at 15.18 LMH. This indicates that ORP-controlled micro-aeration is beneficial for improving the filtration performance of sludge mixed liquor, enhancing sludge-water separation and dewatering in traditional anaerobic digestion processes, and mitigating membrane fouling in anaerobic membrane bioreactor processes.

[0029] Figure 6 The modified membrane fouling index (MFI), characterizing the microfiltration membrane fouling potential of anaerobic sludge mixed liquor, was further determined. Based on a cake-layer filtration model, the relationship between filtration time and cumulative filtrate volume was measured continuously or frequently. The MFI was calculated using a cake clogging model through linear fitting, resulting in more stable and repeatable results. A higher MFI value indicates a thicker cake layer formed on the membrane surface and greater resistance to filtrate passage. The lowest MFI (0.241 s / ml) was observed in aeration group 1, with ORP fluctuations ranging from -277 to -260 mV. 2 The median MFI for aeration group 2, with ORP fluctuating between -277 and -250 mV, was 0.343 s / ml. 2 The control group, with an ORP stable at -277 mV, had the highest MFI of 0.379 s / ml. 2 Therefore, when the ORP-regulated micro-aeration oxygen supply is in aeration group 1 with ORP fluctuations of -277 to -260 mV, the sludge mixed liquor obtains the lowest microfiltration membrane fouling potential and has the best filtration performance. This is beneficial for improving the dewatering effect of traditional anaerobic digestion processes and the membrane fouling control effect of emerging anaerobic membrane bioreactor processes.

[0030] Figure 7This is a schematic diagram illustrating the steps of the method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration provided in an embodiment of the present invention. The specific steps are as follows: Connect the micro-aeration gas source (air or oxygen) to the matching pipeline system, and connect the pipeline to the pre-installed aerator (such as perforated aeration pipe, microporous aeration disc, etc.) in the anaerobic digester. In the micro-aeration control system, a target value for the rise of ORP is preset, and the gas flow rate, interval aeration cycle duration and aeration mode of micro-aeration are configured. It is also set that when the measured value of ORP of anaerobic digested sludge mixture reaches the target value, an aeration stop command is automatically triggered. By turning on the micro-aeration air source and micro-aeration control system, the sludge mixture in the anaerobic digester can be automatically micro-aerated and oxygenated according to the preset parameters mentioned above.

[0031] In the above embodiments, an ORP meter is installed in the anaerobic digester to monitor the ORP of the anaerobic sludge mixture in real time and transmits the signal to the control system. The ORP value is compared with the target value. When the measured ORP value is lower than the lower limit of the target value, the control system sends a signal to activate the micro-aeration device to supply oxygen to the anaerobic digester. When the measured ORP value is higher than the upper limit of the target value, the control system sends a signal to shut down the micro-aeration device, stopping the supply of oxygen to the anaerobic digester. The lower limit of the ORP target value should preferably be set to the stable value when the anaerobic digester is not aerated, and the upper limit of the ORP target value should preferably be set to the lower limit value +10-100 mV. The optimal value is related to the solid organic matter load and can be dynamically adjusted through experiments. The micro-aeration device consists of an air source (air or oxygen), a blower or compressor, aerators (perforated aeration pipes, microporous aeration discs, micro / non-porous aeration membranes), and connecting pipe fittings (flow meters, pressure gauges, valves, etc.). The above method can achieve periodic fluctuations in ORP within the anaerobic digester, thereby providing suitable ecological niches for various functional microorganisms (hydrolytic acidifying bacteria, hydrogen-producing and acetic-producing bacteria, and methanogenic bacteria) participating in anaerobic digestion for a certain period of time, thus improving the overall efficiency and stability of anaerobic digestion, including organic matter removal, methanogenic recovery, and sludge-water separation performance.

[0032] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program goods. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program goods embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0033] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program goods according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0034] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0035] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration, characterized in that, Includes the following steps: S1. Connect the micro-aeration gas source to the air inlet pipeline and then to the aerator in the anaerobic digester; S2. Set the target value for ORP increase, the gas flow rate, the interval aeration period and the air intake mode in the micro-aeration control system, and stop aeration when the target value for ORP is reached; S3. Turn on the air source and micro-aeration control system to automatically supply oxygen to the anaerobic digestion sludge mixture through micro-aeration.

2. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S1, the micro-aeration gas source is a gas containing a certain proportion of oxygen, including air and oxygen.

3. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S1, a pressure gauge is installed on the air intake pipe to detect pressure changes in real time.

4. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S1, the aerator can be configured as a perforated aeration pipe, a microporous aeration disc, a microporous aeration membrane, or a non-porous aeration membrane.

5. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S1, the aerator is placed at the bottom of the anaerobic digester and is designed for uniform aeration.

6. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S2, the gas flow rate is set by controlling a small amount of gas intake through a gas quality controller and recording the intake volume.

7. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S2, the ORP setting range is between -500 mv and 0 mv.

8. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S2, the air intake mode is either continuous air intake or intermittent air intake.

9. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S2, the interval aeration period is generally 0.5 days to 2 days or is set to automatically aerate when the ORP drops to a certain target level.

10. The method for improving anaerobic digestion efficiency based on redox potential-regulated micro-aeration according to claim 1, characterized in that, In step S3, the sludge mixture is a mixture of anaerobic digested activated sludge and organic solid waste or wastewater with high organic content.

Images