Early warning regulation and control method for instability of kitchen waste anaerobic digestion ammonia inhibition system

Abstract

The invention discloses a kitchen waste anaerobic digestion ammonia inhibition system instability early warning regulation and control method, which performs graded early warning on different ammonia inhibition states of kitchen waste anaerobic digestion by monitoring indexes such as pH, total volatile fatty acid (VFA), alkalinity (ALK), total ammonia nitrogen (TAN), methane yield and the like. The different-degree instability early warning system refers to three levels which are progressive step by step under the ammonia inhibition condition: 1) early warning, 2) imbalance early warning and 3) red line early warning, and a regulation and control strategy is given according to the instability of the anaerobic digestion ammonia inhibition system. According to the method, multi-dimensional indexes such as VFA / ALK, CH4 / CO2 ratio and the like are used as risk characteristics of different early warning stages of ammonia suppression, suppression risks of the early stage of ammonia suppression and the unbalance and red early warning stages are accurately identified, the instability state of ammonia suppression is relieved through a regulation and control strategy of adding an exogenous material, accurate identification and regulation and control of problems of an anaerobic digestion system are achieved, and the method is suitable for large-scale popularization and application. And efficient and stable operation is realized.

Description

Technical Field

[0001] This invention relates to a method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste, belonging to the field of anaerobic treatment technology for organic solid waste. Background Technology

[0002] Kitchen waste, as an important component of urban household waste, will not only cause serious waste of resources if it is dumped and landfilled without proper treatment, but will also cause secondary pollution.

[0003] Anaerobic digestion, as an environmentally friendly method for treating food waste, effectively treats organic solid waste and produces biogas as a clean energy source, achieving an organic combination of environmental protection and energy recovery. However, as a long-term operating system, the anaerobic digestion system for food waste is not only affected by operating parameters such as feed load, operating temperature, and pH, but also by the characteristics of food waste, such as high protein, high oil, high salt, and high organic matter content, which leads to ammonia nitrogen release and volatile fatty acid accumulation in the reaction system, resulting in ammonia inhibition. This severely affects the normal reproduction and metabolism of anaerobic digestive microorganisms, making the system highly susceptible to instability during long-term operation.

[0004] Therefore, to ensure the long-term stable operation of anaerobic digestion and improve the efficiency of anaerobic digestion of kitchen waste, it is crucial to accurately monitor the anaerobic digestion process, identify potential risks, and provide early warning and control measures. Currently, domestic early warning methods for anaerobic digestion systems are mostly limited to monitoring and judging the system's instability based on single conventional indicators, lacking analysis of multi-dimensional changes in these indicators and rarely offering graded warnings for different levels of risk (early-stage mild risk, mid-stage imbalance warning, late-stage critical collapse). This results in a deficiency in accurately identifying anaerobic digestion problems. For example, a method for early warning of instability in a single-phase anaerobic digestion system for kitchen waste and an online monitoring and diagnostic system (patent number CN108441583A) calculates the gas production balance index (GBI) using the ratio of daily gas production to the content of volatile organic compounds and total volatile fatty acids in the feed. When the GBI reaches the warning threshold, the system issues an alarm, indicating an imbalance in the anaerobic fermentation process of kitchen waste. However, this method involves few indicators and has a single judgment dimension, failing to analyze the specific instability process and its causes. A method for early warning of anaerobic digestion instability in food waste, which mimics human disease screening (patent number CN118016286A), draws on the human disease prevention system and integrates microbial community analysis to form a three-level risk warning system of potential risk, sub-instability risk, and emergency instability. Although it is more comprehensive than single-indicator warning, the first level of potential risk warning requires 16sRNA sequencing to analyze the abundance of unstable sensitive microorganisms in the system. This not only has high detection complexity and high engineering cost, but also has a detection interval of up to one year or half a year, making it difficult to capture short-term fluctuations to achieve the purpose of early warning. It is also difficult to promote its application in actual engineering practice.

[0005] Furthermore, current domestic patents on anaerobic digestion early warning and control methods primarily focus on constructing an indicator weighting system to improve early warning adaptability, but often neglect the precise control needs behind abnormal indicators. For example, an organic waste anaerobic digestion early warning system and control method (patent number CN117487652A), while calculating the system stability coefficient for the day by integrating multiple sets of monitoring indicators and filtering out alarm situations based on the stability coefficient and prompting corresponding control operations, does not provide a graded early warning judgment for the risk stage of the anaerobic digestion system, and cannot identify the different states of system instability. Moreover, the control measures it provides are mostly qualitative statements such as "appropriately reducing the feed amount" and "adding an alkali source," lacking specific quantitative intervention strategies. In addition, in actual engineering operation, early warning of anaerobic fermentation systems often relies on the operator's experience. Therefore, constructing a graded early warning system for the instability of the ammonia inhibition system in kitchen waste anaerobic digestion and applying specific control strategies to the system's instability state is crucial. Summary of the Invention

[0006] To address the aforementioned technical problems in existing technologies, the present invention aims to provide a method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste. This method utilizes a multi-indicator cross-validation-based hierarchical early warning system to accurately identify and determine the risk level (of varying degrees) of ammonia inhibition during anaerobic digestion, implement efficient control strategies, effectively mitigate the ammonia inhibition effect, improve processing efficiency, reduce operation and maintenance costs, and achieve long-term stable operation of the kitchen waste anaerobic digestion system.

[0007] The technical solution adopted in this invention includes the following steps:

[0008] A method for early warning and control of instability in an ammonia inhibition system during anaerobic digestion of kitchen waste includes the following steps:

[0009] S1: Anaerobic sludge is continuously stirred in an anaerobic digester, and kitchen waste is introduced for anaerobic digestion. The anaerobic digester discharges liquid and gaseous products after anaerobic digestion. During the anaerobic digestion of kitchen waste, gaseous and liquid product parameters of the anaerobic digestion system are collected daily. The gaseous product parameters include multiple indicators of methane and CO2 production, and the liquid product parameters include multiple indicators of pH, total volatile fatty acids (VFA), alkalinity (ALK), and total ammonia nitrogen (TAN). The daily average values ​​are calculated and the data are integrated.

[0010] S2: Provide graded early warning for different ammonia inhibition states in the anaerobic digestion of kitchen waste, including three progressively advancing levels under ammonia inhibition conditions: early warning, imbalance warning, and red line warning. The system status is judged based on the graded early warning indicators, and corresponding alarm prompts are triggered.

[0011] S3: When the system is under ammonia inhibition warning, a control strategy is adopted; when the system is under early warning or imbalance warning, nano-zero-valent iron biochar composite material nZVI / BC is introduced into the anaerobic digester to enhance the activity of methanogenic anaerobic microorganisms; when the system is under red line warning, feeding is stopped, the material in the anaerobic digester is discharged, new anaerobic sludge is inoculated, and feeding is resumed.

[0012] Furthermore, when the following indicators reach the threshold, the system will issue the first-level alarm for ammonia suppression, triggering an early warning system alert (S2A1):

[0013] TAN > 2000 mg / L;

[0014] Or, the volume ratio CH4 / CO2 < 2, the VFA / ALK increase ratio exceeds 20% for 3 consecutive days, and the pH < 7.

[0015] Furthermore, when the following indicators reach the threshold, the ammonia suppression imbalance state S2A2 is reached, and the system issues a second-level alarm for ammonia suppression:

[0016] CH4 / CO2 < 1.5;

[0017] Furthermore, the relative concentration of CH4 decreased by 10% per day.

[0018] And VFA / ALK > 0.5;

[0019] Furthermore, the daily methane production efficiency decreased by more than 20% compared to the average of the previous three days; the daily methane production efficiency is the ratio of daily methane production to the COD value of the feed, expressed in mL / g COD.

[0020] And pH < 6.8.

[0021] Furthermore, when the following indicators reach the threshold, an ammonia suppression red alert S2A3 is triggered, and the system issues a third-level alarm for ammonia suppression:

[0022] The volume ratio of CH4 / CO2 is <1.05;

[0023] And the methane concentration is <45%;

[0024] And VFA / ALK > 1;

[0025] Furthermore, the daily methane production efficiency decreased by more than 40% compared to the average of the previous three days;

[0026] And pH < 6.

[0027] Furthermore, when the system is in an early warning or imbalance warning state, a final concentration of 0.5–2 g / L nZVI / BC is added to the anaerobic digestion system to enhance the activity of the electron transport system in the anaerobic system, strengthen the activity of methanogenic anaerobic microorganisms, and slow down the accumulation of volatile fatty acids (VFA) in the system, thereby alleviating the ammonia inhibition and instability process of the system.

[0028] Furthermore, the TS content of the anaerobic sludge is 8%-15%.

[0029] Furthermore, the preparation method of the nano-zero-valent iron biochar composite material nZVI / BC is as follows: nano-zero-valent iron powder and biochar are mixed at a mass ratio of 40-50:1, and the mixture is ball-milled to obtain the nano-zero-valent iron biochar composite material nZVI / BC.

[0030] Furthermore, the ball milling media are zirconia microspheres with a diameter of 4-8 mm, the ball-to-material ratio is 10-20:1, the ball milling time is 10-15 h, and the ball milling speed is 300-400 rpm.

[0031] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0032] (1) This invention uses a graded early warning system to evaluate the different degrees of ammonia inhibition during the anaerobic digestion of kitchen waste. Through cross-validation of multiple indicators, a three-level dynamic early warning system of “early warning - imbalance state - red warning” is established, which effectively improves the system’s risk prediction capability.

[0033] (2) The regulation strategy of adding nZVI / BC exogenous materials can enhance the activity of the electron transport system in the anaerobic system, strengthen the activity of methanogens to promote methane production, reduce VFA accumulation, and effectively alleviate the negative effects of ammonia inhibition.

[0034] (3) The early warning system of this invention focuses on identifying different risk characteristics and avoids misjudgment caused by a single indicator; the control strategy can effectively reduce ammonia inhibition and achieve long-term stable operation of the system. Attached Figure Description

[0035] Figure 1 The changes in ammonia nitrogen concentration within the anaerobic reactor (ammonia suppression group) for kitchen waste;

[0036] Figure 2 The changes in gas phase parameters of the anaerobic digestion instability system of kitchen waste in the blank control group and the ammonia inhibition group (including (a) daily gas production, (b) daily methane production efficiency, (c) methane concentration, (d) carbon dioxide concentration, and (e) CH4 / CO2 ratio).

[0037] Figure 3The changes in liquid phase parameters of the anaerobic digestion instability system of kitchen waste in the blank control group and the ammonia inhibition group (including (a) VFA concentration in the blank control group, (b) VFA concentration in the ammonia inhibition group, (c) alkalinity, (d) pH, and (e) VFA / ALK ratio).

[0038] Figure 4 The effects of adding nZVI / BC (nano-zero-valent iron biochar composite material) on gas phase indicators during the early warning stage of anaerobic digestion (including (a) daily gas production, (b) daily methane production efficiency, (c) methane concentration, (d) carbon dioxide concentration, and (e) CH4 / CO2 ratio).

[0039] Figure 5 The effects of adding nZVI / BC (nano-zero valent iron biochar composite material) on liquid phase parameters during the early warning stage of anaerobic digestion (including (a) VFA concentration in the ammonia inhibition group, (b) VFA concentration in the nZVI / BC regulation group, (c) alkalinity, (d) pH, and (e) VFA / ALK ratio).

[0040] Figure 6 The effects of adding nZVI / BC (nano-zero-valent iron biochar composite material) on gas phase indicators during the anaerobic digestion imbalance warning stage (including (a) daily gas production, (b) daily methane production efficiency, (c) methane concentration, (d) carbon dioxide concentration, and (e) CH4 / CO2 ratio).

[0041] Figure 7 The effects of adding nZVI / BC (nano-zero valent iron biochar composite material) on liquid phase parameters during the anaerobic digestion imbalance warning stage (including (a) VFA concentration in the ammonia inhibition group, (b) VFA concentration in the nZVI / BC regulation group, (c) alkalinity, (d) pH, and (e) VFA / ALK ratio).

[0042] Figure 8 The effects of adding nZVI / BC (nano-zero-valent iron biochar composite material) on gas phase indicators during the red line warning stage of anaerobic digestion (including (a) daily gas production, (b) daily methane production efficiency, (c) methane concentration, (d) carbon dioxide concentration, and (e) CH4 / CO2 ratio).

[0043] Figure 9 The effects of adding nZVI / BC (nano-zero valent iron biochar composite material) on liquid phase indicators during the red line warning stage of anaerobic digestion (including (a) VFA concentration in the ammonia inhibition group, (b) VFA concentration in the nZVI / BC regulation group, (c) alkalinity, (d) pH, and (e) VFA / ALK ratio). Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0045] This invention provides a construction and control strategy for an instability early warning system of an ammonia inhibition system in anaerobic digestion of kitchen waste, applicable to anaerobic digestion systems for kitchen waste. The specific ammonia inhibition early warning system includes the following:

[0046] Early warning of ammonia suppression: The system issues the first-level alarm for ammonia suppression.

[0047] TAN > 2000 mg / L;

[0048] Alternatively, CH4 / CO2 < 2, and the VFA / ALK ratio increases by more than 20% for 3 consecutive days, and pH < 7.

[0049] The ammonia suppression imbalance has triggered a second-level alarm for ammonia suppression.

[0050] CH4 / CO2 < 1.5;

[0051] Furthermore, the relative concentration of CH4 decreased by 10% per day.

[0052] And VFA / ALK > 0.5;

[0053] Furthermore, the methanogenic yield per unit of anaerobic feed decreased by more than 20%;

[0054] And pH < 6.8.

[0055] Ammonia suppression red alert: The system issues a third-level alarm for ammonia suppression.

[0056] CH4 / CO2 < 1.05;

[0057] And the methane concentration is <45%;

[0058] And VFA / ALK > 1;

[0059] Furthermore, the methanogenesis rate per unit of anaerobic feed decreased by more than 40%;

[0060] And pH < 6.

[0061] Example 1:

[0062] In Embodiment 1 of the present invention, the following operating conditions are adopted:

[0063] Table 1 Characteristics of kitchen waste and inoculated sludge

[0064]

[0065] The experiment used homogenized kitchen waste from an anaerobic fermentation process at a kitchen waste treatment plant as raw material. Its characteristics are shown in Table 1: Total Chemical Oxygen Demand (TCOD) was 110,400 mg / L, with abundant organic matter content. The high VS to TS ratio also demonstrated its good biodegradability. The inoculated sludge was anaerobic sludge from a laboratory facility that had been operating for a long time; its pH was 7.6, indicating a slightly alkaline environment, providing a suitable microbial community for the anaerobic fermentation system.

[0066] The reactor is a 500mL anaerobic glass bottle with an effective working volume of 300mL (i.e., 300mL of anaerobic sludge is inoculated into the anaerobic glass bottle; sludge parameters are shown in Table 1). The anaerobic digestion temperature is maintained at 35±1℃, and continuous stirring is performed during the anaerobic digestion process. Because the organic matter concentration of the kitchen waste raw material is high, it is quantitatively diluted to reduce the reactor's operating load. The reactor feeds 15mL daily, with the 15mL feed liquid consisting of 5mL of kitchen waste raw material + 10mL of diluent, maintaining the reactor's feed organic load at 2kg COD / (m³). 3 •d). Under the above operating conditions, a blank control group and an ammonia inhibition group were set up.

[0067] The blank control group received 15 mL of feed solution, which included 5 mL of kitchen waste raw material and 10 mL of deionized water.

[0068] The feed solution for the ammonia suppression group consists of 15 mL of food waste raw material and 10 mL of ammonium chloride aqueous solution. The ammonia suppression group increases the ammonia nitrogen load of the reactor by gradually increasing the ammonium chloride concentration during the feeding process. The relationship between ammonia nitrogen concentration changes over time in the food waste anaerobic reactor (ammonia suppression group) is shown in [reference needed]. Figure 1 .according to Figure 1 When the reactor has been running for about 51 days, the feed ammonia nitrogen concentration is 3400-3800 mg / L and remains unchanged.

[0069] The comparison of the changes in gas phase parameters over time between the blank control group and the ammonia inhibition group is shown in [link to documentation]. Figure 2 For a comparison of the changes in liquid phase parameters over time, please refer to [link / reference]. Figure 3 .

[0070] After 21 days of operation, the ammonia nitrogen concentration in the anaerobic digester for kitchen waste reached 2000 mg / L. Figure 2 and Figure 3 The methane concentration decreased significantly, the carbon dioxide concentration exceeded that of the blank control group, and the CH4 / CO2 ratio decreased to 1.9. On the other hand, the VFA concentration increased by 33.8% on a single day, the pH decreased to 6.8, and the VFA / ALK ratio increased by 33.8% over three consecutive days. All indicators in the ammonia inhibition group have clearly reached the threshold for early warning of ammonia inhibition, indicating that the anaerobic system has entered the early warning stage.

[0071] Combination Figure 2 and Figure 3 As shown, during the 51-54 days of operation of the ammonia suppression reactor, the daily gas production of the anaerobic system decreased by 31%, the daily methane production efficiency decreased by 32.8%, the methane concentration decreased by more than 13%, and the CH4 / CO2 ratio decreased to 1.3. On the other hand, during this period, VFAs showed a significant accumulation concentration of 4200 mg / L, the pH value decreased to 6.51, and the VFA / ALK ratio reached 0.78. All indicators clearly reached the threshold for ammonia suppression imbalance, indicating that the anaerobic system had entered an imbalance stage.

[0072] Combination Figure 2 and Figure 3 As shown, during the 66–69 days of operation of the ammonia suppression reactor, the daily gas production of the anaerobic system decreased by 40%, the daily methane production efficiency decreased by 44%, the methane concentration decreased to 43%, and the CH4 / CO2 ratio decreased to 1.05. On the other hand, during this stage, the VFA concentration stabilized at its peak (6500–6700 mg / L), and the corresponding reactor pH decreased to 5.80, with the VFA / ALK ratio reaching 1.27. All indicators clearly reached the threshold for the ammonia suppression red warning, indicating that the anaerobic system had entered the red warning stage. Ultimately, the anaerobic system collapsed after 72 days of operation, and gas production ceased.

[0073] In summary, this invention provides the characteristics of early warning indicator changes at different stages of ammonia inhibition in the anaerobic digestion of kitchen waste (early prediction of imbalance, identification of imbalance state, and red line warning), which is expected to further improve the risk prediction capability of anaerobic digestion systems.

[0074] Example 2:

[0075] The anaerobic reactor in Example 2 is the same as that in Example 1, and the operation mode is also repeated in Example 1. The difference from Example 1 is that the focus is on applying a control strategy when the system experiences an early warning of ammonia inhibition. The control group adds a final concentration of 1 g / L of nano-zero-valent iron biochar composite material (nZVI / BC) to the mixed liquor of the reactor when an early warning of ammonia inhibition occurs.

[0076] The specific preparation method of nano-zero-valent iron biochar composite material (nZVI / BC) is as follows: Peanut shells are used as raw materials. After grinding and sieving, they are calcined in a tube furnace. The temperature is uniformly raised to 600℃ at a rate of 5℃ / min and maintained at this temperature for 2 hours. The entire process is carried out in a nitrogen atmosphere to ensure the isolation of oxygen. After natural cooling, the biochar required for the experiment is obtained. Nano-zero-valent iron powder (100nm) and the prepared biochar are mixed at a mass ratio of 47:1 and placed in a ball milling tank containing 6mm zirconia microspheres. The ball-to-material ratio is set to 343:25, the ball milling time is 12 hours, the rotation speed is 350 rpm, and the tank is sealed after being filled with nitrogen for ball milling. After the ball tank cools down, it is transferred to a glove box filled with nitrogen. The ball milling material and microspheres are separated using a 100-mesh nylon sieve. The prepared ZVI / BC is collected and placed in a vacuum desiccator to prevent the material from being oxidized.

[0077] Compared with the blank control group, the ammonia inhibition group, and the ammonia inhibition group (nZVI / BC regulation group added during the early warning stage of anaerobic digestion), the results of the comparison of the changes in gas phase parameters over time among the three groups are shown in [reference]. Figure 4 For a comparison of the changes in the three liquid phase parameters over time, please refer to [link / reference needed]. Figure 5 .Depend on Figure 4 It can be seen that the reactor with the control strategy applied on day 21 showed a methane yield close to that of the control group on day 27 after control, stabilizing at 260–280 mL CH4 / (gCOD·d), which is 20%–30% higher than the ammonia suppression group. Simultaneously, on day 30 (day 9 after control), the methane concentration also showed a significant upward trend, increasing by 5.45% compared to the ammonia suppression group. Furthermore, combined with… Figure 5 As shown, after 33 days of operation, the VFA concentration in the control group reactor decreased from a maximum of 1400 mg / L to 642 mg / L, and further decreased to undetectable levels (<1 mg / L) by day 45. The pH value stabilized at 7.3-7.4 27 days after control, which was 0.7-0.8 higher than that in the ammonia inhibition group.

[0078] In summary, in the early stage of ammonia inhibition imbalance in the anaerobic system of kitchen waste, adding nZVI / BC at a final concentration of 1 g / L can restore and stabilize the methanogenesis efficiency of the anaerobic system, effectively stabilize the internal metabolic balance of the anaerobic system in the long term, and restore the anaerobic system to the normal level in the early stage of ammonia inhibition.

[0079] Example 3:

[0080] The anaerobic reactor in Example 3 is the same as that in Example 1, and the operation mode is also repeated in Example 1. The difference from Example 1 is that the focus is on applying a control strategy when the system experiences an ammonia inhibition imbalance warning. The control group adds a final concentration of 1 g / L of nano-zero-valent iron biochar composite material (nZVI / BC) to the mixed liquor of the reactor when an ammonia inhibition imbalance warning occurs.

[0081] Compared with the blank control group, the ammonia inhibition group, and the nZVI / BC regulation group in the anaerobic digestion imbalance early warning stage of the ammonia inhibition group, the results of the comparison of the changes in gas phase indicators over time among the three groups are shown in [reference]. Figure 6 For a comparison of the changes in the three liquid phase parameters over time, please refer to [link / reference needed]. Figure 7 .

[0082] Depend on Figure 6 It can be seen that in the reactor with regulated treatment at 51 days, the methanogenesis rate stabilized at 160–180 mL CH4 / g COD over the subsequent 33 days, representing a 69% increase in daily gas production and an 84% increase in methanogenesis rate compared to the ammonia inhibition group. This is likely due to the ability of nZVI / BC to enhance the activity of the electron transport system within the anaerobic system, thereby strengthening the activity of methanogenic anaerobic microorganisms. The CH4 / CO2 ratio also stabilized at around 1.3 over 33 days, a 43% increase compared to the ammonia inhibition group, further indicating that the addition of nZVI / BC regulation improved the stability of the anaerobic system. Figure 7 As shown, the maximum VFA concentration in the reactor after regulation was 6000 mg / L, which was 13% lower than that of the ammonia inhibition group, further demonstrating the mitigating effect of nZVI / BC on VFA accumulation. The pH also slowly increased from a minimum of 5.9 to 6.1-6.4, which was 1.1-1.4 higher than that of the ammonia inhibition group.

[0083] In summary, when ammonia inhibition in the anaerobic system of kitchen waste becomes unstable, adding 1 g / L of nZVI / BC can effectively improve and stabilize the methanogenesis efficiency of the anaerobic system, maintain the internal metabolic balance of the anaerobic system, and prevent further deterioration of the anaerobic system under the state of ammonia inhibition imbalance.

[0084] Example 4:

[0085] The anaerobic reactor in Example 4 is the same as that in Example 1, and the operation mode is also repeated in Example 1. The difference from Example 1 is that the focus is on applying a control strategy when the system experiences an ammonia inhibition red line warning. The control group adds a final concentration of 1 g / L of nano-zero-valent iron biochar composite material (nZVI / BC) to the mixed liquor of the reactor when an ammonia inhibition red line warning occurs.

[0086] Compared with the blank control group, the ammonia inhibition group, and the ammonia inhibition group (anaerobic digestion red line warning stage nZVI / BC regulation group), the comparison results of the changes in gas phase indicators over time among the three groups are shown in [reference]. Figure 8 For a comparison of the changes in the three liquid phase parameters over time, please refer to [link / reference needed]. Figure 9 .

[0087] Depend on Figure 8It can be seen that in the reactor with 66 days of regulation, the daily gas production and methanogenesis efficiency rebounded significantly within 3 days, the methane concentration increased slightly, while the carbon dioxide concentration continued to rise in line with the ammonia suppression group. These results indicate that the addition of nZVI / BC has a limited regulatory effect on the red line warning stage of the anaerobic system and cannot be maintained for a long time. After 72 days of operation, the daily gas production and methanogenesis rate of the regulated reactor were already close to those of the ammonia suppression group. Furthermore, as... Figure 9 As shown, after 72 days of operation, the VFA concentration in the control group reactor was 5000 mg / L, which was 20% lower than that in the ammonia inhibition group. However, the changes in indicators such as pH and VFA / ALK were close to those in the ammonia inhibition group, indicating that the addition of nZVI / BC did not change the acid-base imbalance in the anaerobic system.

[0088] Therefore, adding nZVI / BC during the red line warning stage has limited effect on regulating the imbalance state of the anaerobic reactor and cannot alleviate the collapse of the anaerobic system caused by ammonia inhibition.

[0089] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments. Those skilled in the art should understand that equivalent substitutions or modifications can still be made to this invention, as long as they do not depart from the spirit and scope of this technical solution, they are all within the scope of protection of this invention.

Claims

1. A method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste, characterized in that, Includes the following steps: S1: Anaerobic sludge in the anaerobic fermenter is continuously stirred and then fed with kitchen waste for anaerobic digestion. The anaerobic fermenter discharges the liquid and gaseous products after anaerobic digestion. During the anaerobic digestion of food waste, gaseous and liquid phase product parameters of the anaerobic digestion system are collected daily at regular intervals. The gaseous product parameters include multiple indicators of methane production and CO2 production, while the liquid phase product parameters include multiple indicators of pH, total volatile fatty acids (VFA), alkalinity (ALK), and total ammonia nitrogen (TAN). The daily average values ​​are calculated and the data are integrated. S2: Provide graded early warning for different ammonia inhibition states in the anaerobic digestion of kitchen waste, including three progressively advancing levels under ammonia inhibition conditions: early warning, imbalance warning, and red line warning. The system status is judged based on the graded early warning indicators, and corresponding alarm prompts are triggered. S3: When the system is under ammonia suppression warning, a control strategy is adopted; When the system is in an early warning or imbalance warning state, nano-zero-valent iron biochar composite material nZVI / BC is introduced into the anaerobic fermenter to enhance the activity of methanogenic anaerobic microorganisms. When the system is in a red-line warning state, feeding is stopped, the material in the anaerobic fermenter is discharged, new anaerobic sludge is inoculated, and feeding resumes.

2. The method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste as described in claim 1, characterized in that, When the following indicators reach the threshold, the system will issue the first-level alarm for ammonia suppression, triggering the early warning system alert S2A1: TAN > 2000 mg / L; Or, the volume ratio CH4 / CO2 < 2, the VFA / ALK increase ratio exceeds 20% for 3 consecutive days, and the pH < 7.

3. The method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste as described in claim 1, characterized in that, When the following indicators reach their thresholds, the ammonia suppression imbalance state S2A2 is reached, and the system issues a second-level alarm for ammonia suppression: CH4 / CO2 < 1.5; Furthermore, the relative concentration of CH4 decreased by 10% on a single day; And VFA / ALK > 0.5; Furthermore, the daily methane production efficiency decreased by more than 20% compared to the average of the previous three days; the daily methane production efficiency = the ratio of daily methane production to the COD value of the feed, with the unit being mL / g COD; And pH < 6.

8.

4. The method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste as described in claim 1, characterized in that, When the following indicators reach their thresholds, an ammonia suppression red alert S2A3 is triggered, and the system issues a third-level ammonia suppression alarm: The volume ratio of CH4 / CO2 is <1.05; And the methane concentration is < 45%; And VFA / ALK > 1; Furthermore, the daily methane production efficiency decreased by more than 40% compared to the average of the previous three days; And pH < 6.

5. The method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste as described in claim 1, characterized in that, When the system is in an early warning or imbalance warning state, add a final concentration of 0.5~2 g / L nZVI / BC to the anaerobic digestion system.

6. The method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste as described in claim 1, characterized in that, The TS content of the anaerobic sludge is 8%~15%.

7. The method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste as described in claim 1, characterized in that, The preparation method of the nano-zero-valent iron biochar composite material nZVI / BC is as follows: nano-zero-valent iron powder and biochar are mixed at a mass ratio of 40-50:1, and the mixture is ball-milled to obtain the nano-zero-valent iron biochar composite material nZVI / BC.

8. The method for early warning and control of instability in an ammonia inhibition system for anaerobic digestion of kitchen waste as described in claim 7, characterized in that, The ball milling media consisted of zirconia microspheres with a diameter of 4-8 mm, a ball-to-material ratio of 10-20:1, a milling time of 10-15 h, and a milling speed of 300-400 rpm.

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