High-concentration kitchen biogas slurry treatment and resource system

Abstract

The application provides a high-concentration kitchen biogas slurry treatment and resource system, which comprises a struvite reaction tank, a hydrolysis tank, an anaerobic tank, a high-exposure tank, an anaerobic ammonia oxidation tank and an AO tank which are connected in sequence. In the front end, ammonia nitrogen in the kitchen biogas slurry is precipitated and recovered in the form of struvite crystallization through the struvite reaction tank, and the ammonia inhibition risk is reduced, thereby providing stable conditions for subsequent biological treatment. In the middle section, a hydrolysis acidification and electrocatalytic anaerobic coupling process is adopted, macromolecular organic matter and refractory components are efficiently degraded and converted into methane through biological electrochemical enhanced electron transfer. In the end, an anaerobic ammonia oxidation process is introduced, efficient denitrification is realized through autotrophic mode, and no external carbon source needs to be added. The combined new process can provide sustainable development for full-scale resource treatment of kitchen waste.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment and resource utilization technology, and in particular to a high-concentration kitchen waste biogas slurry treatment and resource utilization system. Background Technology

[0002] Food waste is presenting a massive and continuously increasing production base. As a high-energy-efficiency organic resource, it can be transformed into high-value-added products such as biogas, organic fertilizer, and bioethanol through processes like anaerobic fermentation, demonstrating significant potential for resource utilization. However, the biogas slurry produced during the treatment of food waste is a complex, high-concentration wastewater characterized by high chemical oxygen demand (COD), high ammonia nitrogen concentration, high suspended solids, and recalcitrant organic matter, making it a key bottleneck restricting the industry's development.

[0003] Current food waste biogas slurry treatment faces multiple technical challenges, including a low carbon-to-nitrogen ratio and inhibition of free ammonia (FA) production from high ammonia nitrogen concentrations, making it difficult to treat. Studies generally agree that ammonia nitrogen concentrations >1500 mg / L or FA concentrations >150 mg / L can disrupt microbial metabolism, toxicizing hydrolytic acid-producing and anaerobic methanogenic microorganisms, significantly inhibiting the removal rates of hydrolysis and anaerobic reactors. Traditional food waste biogas slurry treatment processes struggle to address ammonia inhibition and suffer from low nitrogen removal efficiency, high sludge production, and the need for external carbon source addition, significantly increasing treatment costs. Furthermore, food waste biogas slurry contains abundant organic matter and nitrogen and phosphorus resources; direct treatment and discharge would result in severe resource waste. Therefore, developing novel combined processes that integrate efficient pollutant removal with targeted resource recovery has become an urgent need to overcome the challenges of food waste biogas slurry treatment. Utility Model Content

[0004] This application provides a high-concentration kitchen waste biogas slurry treatment and resource utilization system to solve the problems existing in related technologies. The technical solution is as follows:

[0005] In one aspect, embodiments of this application provide a high-concentration kitchen waste biogas slurry treatment and resource utilization system, comprising a struvite reaction tank, a hydrolysis tank, an anaerobic tank, a high-aeration tank, an anaerobic ammonia oxidation tank, and an AO tank connected in series.

[0006] In one embodiment, it further includes an equalization tank and an air flotation unit; the equalization tank is connected to the air flotation unit (2), and the air flotation unit is connected to the inlet pipe at the bottom of the struvite reaction tank.

[0007] In one embodiment, a first intermediate water tank is provided between the anaerobic tank and the high-aeration tank; the outlet of the anaerobic tank is connected to the first intermediate water tank, and the first intermediate water tank is connected to the high-aeration tank through a booster pump pipeline.

[0008] In one embodiment, a second intermediate water tank is provided between the high aeration tank and the anaerobic ammonia oxidation tank; the effluent from the high aeration tank is connected to the second intermediate water tank, and the second intermediate water tank is connected to the anaerobic ammonia oxidation tank through a lift pump pipeline.

[0009] In one embodiment, the anaerobic tank includes an electrocatalytic device; the inlet area of ​​the electrocatalytic device is connected to the outlet of the anaerobic tank via a return pipe; and the outlet area of ​​the electrocatalytic device is connected to the hydrolysis tank via a booster pump and a pipe.

[0010] In one embodiment, the electrocatalytic device includes an anode and cathode composed of electrocatalytic packing material and a power adapter box; the power adapter box is connected to an external power source and the anode and cathode respectively via cables.

[0011] In one embodiment, the struvite reaction tank further includes a phosphate dosing device and a magnesium salt dosing device, which are connected to the struvite reaction tank via dosing pipes.

[0012] In one embodiment, the struvite reaction tank further includes an online ammonia nitrogen concentration detector and a PLC control system; the electrode probe of the online ammonia nitrogen concentration detector is installed in the reaction chamber of the struvite reaction tank; the online ammonia nitrogen concentration detector and the first PLC control system are connected by a signal line; the PLC control system is electrically connected to the phosphate dosing device and the magnesium salt dosing device respectively.

[0013] In one embodiment, the hydrolysis tank further includes an acid dosing device, a free ammonia monitoring system, and a second PLC control system; the electrode probe of the free ammonia monitoring system is disposed in the hydrolysis tank and connected to the second PLC control system via a signal line; the second PLC control system is electrically connected to the acid dosing device.

[0014] In one embodiment, the hydrolysis tank and the anaerobic tank are respectively equipped with biogas recovery devices; the bottom of the guanoite reaction tank is equipped with a conical sludge collection hopper, and the outlet of the sludge discharge valve at the bottom of the sludge collection hopper is equipped with a guanoite recovery port.

[0015] The advantages or beneficial effects of the above technical solutions include at least the following:

[0016] This invention employs a novel combined process to provide a solution for the treatment of kitchen waste biogas slurry. At the front end, a struvite reactor precipitates and recovers ammonia nitrogen from the biogas slurry as struvite crystals (MgNH4PO4·6H2O), simultaneously reducing the risk of ammonia inhibition and providing stable conditions for subsequent biological treatment. The middle stage utilizes a hydrolysis-acidification and electrocatalytic anaerobic coupling process, enhancing electron transfer through bioelectrochemical processes to efficiently degrade macromolecular organic matter and recalcitrant components into methane. At the end, an anaerobic ammonia oxidation process is introduced, achieving efficient nitrogen removal through autotrophic means without the need for external carbon source addition. This novel combined process provides a sustainable approach for the comprehensive resource treatment of kitchen waste.

[0017] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of this application will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0018] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0019] Figure 1 The microbial community composition at the phylum level of a certain kitchen waste biogas slurry electrocatalytic device;

[0020] Figure 2 This is a process flow diagram for the application.

[0021] Figure 3 This is a schematic diagram of the equalization tank, air flotation unit, and struvite reaction tank in a high-concentration kitchen waste biogas slurry treatment and resource utilization system.

[0022] Figure 4 This is a schematic diagram of the hydrolysis tank and anaerobic tank in a high-concentration food waste biogas slurry treatment and resource utilization system.

[0023] Figure 5 This is a schematic diagram of the structure of the first intermediate water tank, high aeration tank, second intermediate water tank, anaerobic ammonia oxidation tank, and AO tank in a high-concentration kitchen waste biogas slurry treatment and resource utilization system. Detailed Implementation

[0024] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this application. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0025] This application addresses the problems of low efficiency and resource waste in traditional treatment processes for high-concentration kitchen waste biogas slurry due to high ammonia nitrogen, low carbon-to-nitrogen ratio, and recalcitrant organic matter. It proposes a multi-stage synergistic combination process to achieve efficient nitrogen and carbon removal, nitrogen and phosphorus resource recovery, and increased biogas production from kitchen waste biogas slurry.

[0026] This application provides a high-concentration kitchen waste biogas slurry treatment and resource utilization system, the structure of which is as follows: Figure 3 , Figure 4 and Figure 5 As shown, the system includes a struvite reactor 3, a hydrolysis reactor 4, an anaerobic reactor 5, a high-aeration reactor 7, an anaerobic ammonia oxidation reactor 9, and an AO reactor 10, which are connected in series along the direction of the biogas slurry treatment.

[0027] The struvite reaction tank 3 can precipitate ammonia nitrogen in the biogas slurry as struvite crystals by adding phosphate and magnesium salts. This crystals can be recycled as nitrogen and phosphorus fertilizer, reducing the concentration of ammonia nitrogen and mitigating the risk of ammonia inhibition, thus providing stable conditions for subsequent biological treatment.

[0028] Therefore, as one embodiment, the struvite reaction tank 3 further includes a phosphate dosing device 31 and a magnesium salt dosing device 32, which are connected to the struvite reaction tank 3 via dosing pipes. The phosphate dosing device 31 adds phosphate to the struvite reaction tank 3; the magnesium salt dosing device 32 adds magnesium salt to the struvite reaction tank 3. In this embodiment, the phosphate is Na2HPO4 or its hydrate; the magnesium salt is MgCl2 or its hydrate.

[0029] As one embodiment, the struvite reaction tank 3 also includes a stirrer 34 located in the center of the reaction chamber. The stirrer 34 ensures that the biogas slurry is thoroughly mixed with the phosphate and magnesium salts, allowing the reaction to proceed completely.

[0030] In one embodiment, the struvite reaction tank 3 further includes an online ammonia nitrogen concentration detector 36 and a first PLC control system 37; the electrode probe of the online ammonia nitrogen concentration detector 36 is installed in the reaction chamber of the struvite reaction tank 3; the online ammonia nitrogen concentration detector 36 and the first PLC control system 37 are connected by a signal line; the first PLC control system 37 is electrically connected to the phosphate dosing device 31 and the magnesium salt dosing device 32 respectively.

[0031] Different ammonia nitrogen concentration thresholds are set according to the different water quality of the biogas slurry. When the online ammonia nitrogen concentration detector 36 detects an ammonia nitrogen concentration >1500-2500 mg / L, the first PLC control system 37 controls the phosphate dosing device 31 and the magnesium salt dosing device 32 to continuously add chemicals to generate struvite crystals, thereby reducing the ammonia nitrogen concentration in the biogas slurry. When the detected ammonia nitrogen concentration is <1500-2500 mg / L, the addition is stopped. Through this prevention mechanism, the ammonia nitrogen concentration in the biogas slurry effluent is controlled, reducing the risk of ammonia inhibition in the biogas slurry.

[0032] As one embodiment, the guano reaction tank 3 has a conical sludge collection hopper at the bottom of its reaction chamber, and a guano recovery port 33 is provided at the outlet of the sludge discharge valve at the bottom of the sludge collection hopper.

[0033] The struvite reaction product, struvite crystals, is separated from the biogas slurry via solid-liquid separation. The precipitate settles in a conical sludge collection hopper and is recovered through a struvite recovery port 33 located at the bottom of the sludge discharge valve. In this embodiment, solid-liquid separation is achieved through a solid-liquid separation assembly 35, which consists of inclined plates.

[0034] In one embodiment, the high-concentration kitchen waste biogas slurry treatment and resource recovery system further includes an equalization tank 1 and an air flotation unit 2. The equalization tank 1 is connected to the air flotation unit 2, and the air flotation unit 2 is connected to the inlet pipe at the bottom of the struvite reaction tank 3. Because larger impurities and suspended solids interfere with the struvite reaction and affect the purity of struvite crystals, thus hindering recovery, this embodiment also includes an equalization tank 1 and an air flotation unit 2. Before the struvite reaction, the high-concentration kitchen waste biogas slurry is first treated using the air flotation unit 2 to remove suspended solids by air flotation. Specifically, the biogas slurry first enters the air flotation unit 2 from the equalization tank 1, mainly to remove larger impurities, effectively avoiding interference from suspended solids in the subsequent struvite reaction and recovery. The biogas slurry with suspended solids removed from the air flotation unit 2 then enters the struvite reaction tank 3 for reaction.

[0035] The biogas slurry from the solid-liquid separation in the struvite reaction tank 3 enters the hydrolysis tank 4; the hydrolysis tank 4 includes a first water distribution system 44, which is located in the center of the hydrolysis tank. The outlet of the liquid phase zone of the struvite reaction tank 3 is connected to the first water distribution system 44 of the hydrolysis tank 4. Figure 3 A and Figure 4 The A connection is made; the separated biogas slurry is evenly introduced into the bottom of the hydrolysis tank 4 from the first water distribution system 44.

[0036] By adjusting the free ammonia concentration in hydrolysis tank 4, the risk of free ammonia inhibition is reduced. At the same time, the dosage of phosphate and magnesium salt in the upstream struvite reaction tank is reduced. In addition, the hydrolysis acidification process decomposes macromolecular organic matter and recalcitrant components into small molecule organic acids, thereby improving biodegradability.

[0037] In one embodiment, the hydrolysis tank 4 further includes an acid dosing device 43, a free ammonia monitoring system 41, and a second PLC control system 42; the electrode probe of the free ammonia monitoring system 41 is disposed in the hydrolysis tank 4 and is connected to the second PLC control system 42 via a signal line; the second PLC control system 42 is electrically connected to the acid dosing device 43.

[0038] When the free ammonia online monitoring system detects that the FA concentration is greater than the set threshold, the control system controls the acid dosing device to add acid to regulate the pH and FA concentration in the hydrolysis tank. When the FA concentration is less than the set threshold, the dosing stops. The pH range is 5.5-6.5, and the set FA concentration threshold range is <150mg / L.

[0039] After treatment in struvite reactor 3 and hydrolysis acidification in hydrolysis reactor 4, the ammonia (FA) content in the biogas slurry has been reduced to below 150 mg / L, thus reducing ammonia inhibition and solving the ammonia inhibition problem in traditional high-concentration food waste biogas slurry treatment processes. Therefore, this biogas slurry can undergo anaerobic bacterial conversion. Anaerobic bacterial conversion takes place in anaerobic reactor 5.

[0040] In one embodiment, the anaerobic tank 5 includes a second water distribution system 54 and an electrocatalytic device 51; the inlet area of ​​the electrocatalytic device 51 is connected to the outlet of the anaerobic tank 5 via a return pipe 53; the outlet area of ​​the electrocatalytic device 51 is connected to the hydrolysis tank 4 via a pipeline through a booster pump.

[0041] The supernatant from hydrolysis tank 4 flows through an effluent weir and pipes to the second water distribution system 54 of anaerobic tank 5. A portion of the supernatant from the effluent of anaerobic tank 5 flows through a return pipe 53 to the electrocatalytic device 51. The supernatant from the effluent area of ​​the electrocatalytic device 51 is then returned to the first water distribution system 44 of hydrolysis tank 4 via a booster pump to achieve external circulation. The remaining portion of the supernatant from the effluent of anaerobic tank 5 is supplied to the high-aeration tank 7.

[0042] The effluent from hydrolysis tank 4 flows into the bottom of anaerobic tank 5. Part of the supernatant (anaerobic effluent) from anaerobic tank 5 is recycled to electrocatalytic device 51 for further treatment, with a recycling rate of 30-50%. The supernatant from electrocatalytic device 51 then flows into the bottom of hydrolysis tank 4 through the first water distribution system 44 for further treatment. The remaining anaerobic effluent is sent to high-aeration tank 7.

[0043] Anaerobic tank 5 contains anaerobic bacteria, specifically methanogenic bacteria. The methanogenic bacteria in anaerobic tank 5 utilize small-molecule organic acids produced in hydrolysis tank 4 as substrates to produce methane, which is then recovered and utilized by biogas recovery device 52.

[0044] In one embodiment, the electrocatalytic device 51 includes an anode and cathode 512 composed of electrocatalytic packing material and a power adapter box 511. The power adapter box 511 is connected to an external power source and the anode and cathode 512 via cables. The power adapter box 511 outputs a low-voltage electric field to the electrocatalytic anode and cathode 512 composed of carbon fibers. Under the action of the low-voltage electric field, electron transfer and shift are accelerated, electroactive microorganisms and hydrolytic acidifying bacteria are selectively enriched, and combined with bottom micro-aeration 513 to adjust the oxidation-reduction potential (ORP), the recalcitrant macromolecular organic matter in the effluent of the anaerobic tank 5 is broken down, ring-opened, and decomposed. The supernatant from the effluent area of ​​the electrocatalytic device 51 is returned to the hydrolysis tank 4 by a booster pump for secondary hydrolysis and acidification of the recalcitrant organic matter, promoting further degradation of the recalcitrant organic matter in the anaerobic tank 5. At the same time, the return liquid contains micro-aerobic substances that can regulate the ORP environment in the hydrolysis tank, promoting hydrolysis and acidification to generate organic acids, providing substrates for methanogenic bacteria in the anaerobic tank 5 and increasing methane production. In addition, external circulation in hydrolysis tank 4 avoids cross-contamination and competition for substrates between electrogenic bacteria enriched in the electrocatalytic device and methanogenic bacteria in the anaerobic tank.

[0045] In one embodiment, a first intermediate water tank 6 is provided between the anaerobic tank 5 and the high-aeration tank 7; the outlet of the anaerobic tank 5 is connected to the first intermediate water tank 6, such as... Figure 4 B and Figure 5 The B connection connects the first intermediate water tank 6 to the high aeration tank 7 via a booster pump pipeline.

[0046] The high-aeration tank 7 is inoculated with municipal activated sludge and operates using a modified sequencing batch reactor (SBR) process, including influent / effluent, aeration, and sedimentation cycles. The high-aeration tank 7 removes most of the COD, providing a suitable carbon-to-nitrogen ratio for the anammox tank 9. Furthermore, under this operating mode, the ammonia nitrogen nitrification rate can reach 40-60%, supplementing the downstream anammox tank 9 with nitrite nitrogen and reducing the aeration requirements of the anammox tank.

[0047] In one embodiment, a second intermediate water tank 8 is provided between the high aeration tank 7 and the anaerobic ammonia oxidation tank 9; the effluent from the high aeration tank 7 is connected to the second intermediate water tank 8, and the second intermediate water tank 8 is connected to the anaerobic ammonia oxidation tank 9 through a lift pump pipeline.

[0048] Anaerobic ammonia oxidation tank 9 operates using a modified sequencing batch reactor (SBR) process, including influent / effluent, aeration, and sedimentation cycles. Anaerobic ammonia oxidation tank 9 is inoculated with short-cut nitrification sludge and anaerobic ammonia oxidation granular sludge at a volume ratio of 1:(2.5-3.5). Ammonia nitrogen is converted to nitrite nitrogen through short-cut nitrification, and then anaerobic ammonia oxidation bacteria convert the ammonia nitrogen and nitrite nitrogen into nitrogen gas and nitrate nitrogen.

[0049] The effluent from the anaerobic ammonia oxidation tank 9 flows to the AO tank 10; the AO tank 10 has a return flow from the O tank to the A tank. Finally, the AO tank 10 further removes residual organic matter and nitrate nitrogen, and the effluent can meet the Class B standard of the "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T31962-2015).

[0050] Throughout the process, pretreatment in the struvite reactor 3 removes some ammonia nitrogen, reducing ammonia inhibition, and in conjunction with the hydrolysis reactor 4, regulates and reduces free ammonia, thus solving the ammonia inhibition problem in traditional high-concentration kitchen waste biogas treatment processes. The anaerobic reactor 5, coupled with electrocatalysis, further decomposes the recalcitrant organic matter in the anaerobic reactor and returns it to the hydrolysis reactor 4 for secondary hydrolysis and acidification, improving biodegradability. In addition, the crystalline sludge produced in the struvite reactor 3 can be dewatered and made into fertilizer. The biogas produced in the hydrolysis reactor 4 and the electrocatalytic anaerobic reactor 5 is used for energy recovery, realizing the whole process of biogas purification and resource recovery.

[0051] The high-concentration kitchen waste biogas slurry treatment system provided by this utility model operates according to the following process: Figure 2 As shown.

[0052] The kitchen waste biogas slurry first enters the flotation unit 2 from the equalization tank 1. The flotation unit removes suspended solids and some colloidal substances. The purified biogas slurry then flows into the struvite reaction tank 3. In the struvite reaction tank 3, phosphate 31 and magnesium salt 32 are added in proportion and mixed and reacted by a mixer 34 to generate struvite crystals. Nitrogen and phosphorus are recovered from the struvite recovery port 33. The struvite reaction tank 3 is also equipped with an online ammonia nitrogen concentration detector 36 and a first PLC control system 37. Different effluent ammonia nitrogen concentration thresholds are set according to the different water quality of the kitchen waste biogas slurry. When the online ammonia nitrogen concentration detector detects an ammonia nitrogen concentration >1500-2500 mg / L, the first PLC control system 37 controls the phosphate dosing device 31 and the magnesium salt dosing device 32 to continuously add phosphate to generate struvite crystals and reduce the ammonia nitrogen concentration of the biogas slurry. When the detected ammonia nitrogen concentration is <1500-2500 mg / L, the addition is stopped. By setting up the first prevention mechanism, the ammonia nitrogen concentration in the biogas slurry is controlled, reducing the risk of ammonia inhibition in the biogas slurry; then the precipitate is separated from the biogas slurry by the solid-liquid separation component 35.

[0053] The biogas slurry is evenly introduced into the bottom of the hydrolysis tank 4 from the first water distribution system 44. The hydrolysis tank 4 is equipped with a free ammonia monitoring system 41, a second PLC control system 42, and an acid dosing device 43. The free ammonia concentration in the hydrolysis tank 4 is regulated by setting a free ammonia concentration threshold. When the free ammonia concentration is greater than the set threshold, the second PLC control system 42 controls the acid dosing device 43 to reduce the pH and free ammonia concentration in the hydrolysis tank 4. When the free ammonia concentration is less than the set threshold, the dosing stops. The set threshold range is FA concentration < 150 mg / L. By setting up a second prevention mechanism, the risk of free ammonia inhibition in the biogas slurry is reduced, while the dosage of phosphate and magnesium salts in the upstream struvite reactor 3 is decreased. In the hydrolysis tank 4, the recalcitrant large organic molecules are decomposed into small organic acids through hydrolysis and acidification, improving biodegradability. The hydrolyzed and acidified biogas slurry is evenly transported to the bottom of the anaerobic tank 5 through the second water distribution system 54. Methanogenic bacteria in the anaerobic tank 5 use the small organic acids produced in the hydrolysis tank 4 as substrates to produce methane, which is then recovered and reused by the biogas recovery device 52. The supernatant of the anaerobic tank 5 enters the electrocatalytic device 51 through the return pipe 53, and a low-voltage electric field is output from the power adapter box 511 to the electrocatalytic packing composed of carbon fibers. The anode and cathode 512, under the action of a low-voltage electric field, accelerate electron transfer and enrichment of electroactive microorganisms and hydrolytic acidifying bacteria. Combined with bottom micro-aerobic aeration 513 to regulate the oxidation-reduction potential (ORP), the recalcitrant macromolecular organic matter in the effluent of anaerobic tank 5 is broken down, ring-opened, and decomposed. The supernatant from the effluent zone of the electrocatalytic device 51 is returned to the hydrolysis tank 4 by a booster pump for secondary hydrolysis and acidification of the recalcitrant organic matter, promoting further degradation of the recalcitrant organic matter in anaerobic tank 5. At the same time, the return liquid contains micro-aerobic environment that can regulate the ORP environment in the hydrolysis tank 4, promote hydrolysis and acidification, generate organic acids, provide substrates for methanogenic bacteria in the anaerobic tank, and increase methane production.

[0054] The effluent from anaerobic tank 5 flows into the first intermediate tank 6 and then into the high-aeration tank 7. In the high-aeration tank 7, the remaining COD is rapidly degraded through a high sludge concentration, providing a suitable carbon-to-nitrogen ratio for the downstream anaerobic ammonia oxidation. Subsequently, the biogas slurry enters the second intermediate tank 8 and then into the anaerobic ammonia oxidation tank 9. Through short-cut nitrification, ammonia nitrogen is converted into nitrite nitrogen, and then anaerobic ammonia oxidation bacteria convert ammonia nitrogen and nitrite nitrogen into nitrogen gas and nitrate nitrogen. Finally, the residual organic matter and nitrate nitrogen are further removed in the AO tank 10.

[0055] The specific operating parameters for each processing pool are as follows:

[0056] This application applies to the treatment of kitchen waste biogas slurry with COD of 10,000-30,000 mg / L, total nitrogen (TN) of 2,000-4,000 mg / L, ammonia nitrogen (NH3-N) of 2,000-3,500 mg / L, total phosphorus (TP) of 100-500 mg / L, pH of 7.5-9.0, and suspended solids (SS) of 3-12 g / L. It is evident that the levels of all pollutants are high, far exceeding the standards.

[0057] As one implementation method, this application involves adding phosphate and magnesium salt to a high-concentration biogas slurry; the phosphate is Na2HPO4 or its hydrate; the magnesium salt is MgCl2 or its hydrate. The struvite reaction is carried out in a struvite reaction tank, and the amount of magnesium salt is determined according to the concentration of ammonium ions in the biogas slurry, based on the Mg... 2+ :PO4 3- NH4 + The molar ratio is (1.0-1.5):(1.0-1.3):1.0. Phosphate and magnesium salt are added for reaction. The reaction conditions are 20-35℃, pH 7.5-9, and stirring at 100-180 rpm for 1-3 hours. The reaction produces struvite crystals, which are separated by sedimentation and discharged. After dehydration, nitrogen and phosphorus are recovered.

[0058] In one implementation method, the addition of phosphate and magnesium salts is automatically regulated. The dosage is dynamically adjusted based on a target effluent ammonia nitrogen concentration threshold of <1500-2500 mg / L: when the online ammonia nitrogen detector shows an ammonia nitrogen concentration > the set target effluent ammonia nitrogen concentration threshold, the PLC control system starts the dosing device until the ammonia nitrogen concentration falls below the set target effluent ammonia nitrogen concentration threshold.

[0059] After treatment with struvite, the effluent can achieve ammonia nitrogen removal rate of 20-60%, total phosphorus removal rate of 30-70%, and free ammonia concentration can be reduced from the initial 150-4000 mg / L to 50-1500 mg / L. At the same time, it can increase the carbon-nitrogen ratio of the effluent, which is beneficial for subsequent biochemical treatment.

[0060] One implementation method involves hydrolysis and acidification of the biogas slurry treated by struvite reaction. This hydrolysis and acidification process takes place in a hydrolysis tank. By controlling the free ammonia concentration in the hydrolysis tank, the risk of free ammonia inhibition is reduced, while simultaneously decreasing the dosage of phosphates and magnesium salts in the upstream struvite reaction tank. Furthermore, the hydrolysis and acidification process decomposes large molecular organic matter and recalcitrant components into small molecular organic acids, improving biodegradability. Specifically, the pH is maintained at 5.5-6.5, and the biogas slurry retention time (HRT) is 8-48 hours. After 8-48 hours of hydrolysis and acidification, large molecular organic matter and recalcitrant components in the biogas slurry are decomposed into small molecular organic acids, improving biodegradability. This further reduces free ammonia, eliminating its inhibitory and toxic effects on microbial activity; the free ammonia concentration can be reduced from an initial 150-1500 mg / L to <150 mg / L.

[0061] In one implementation, an online free ammonia monitoring system and an acid dosing device are provided. When the online free ammonia monitoring system detects a FA concentration > a set threshold, the control system controls the acid dosing device to add acid to regulate the pH and FA concentration in the hydrolysis tank. When the FA concentration < a set threshold, the dosing stops. The pH range is 5.5–6.5, and the set FA concentration threshold range is <150 mg / L. In this embodiment, the acid is concentrated sulfuric acid and / or concentrated hydrochloric acid.

[0062] In one implementation method, the FA (acetic acid) in the biogas slurry after struvite reaction and hydrolysis acidification treatment has been reduced to below 150 mg / L, thus reducing ammonia inhibition and solving the ammonia inhibition problem in traditional high-concentration kitchen waste biogas slurry treatment processes. Therefore, this biogas slurry can undergo anaerobic bacterial conversion. During the anaerobic bacterial conversion process, the heating time (HRT) is 24-72 h; methanogenic bacteria utilize small-molecule organic acids produced in the hydrolysis tank as substrates to produce methane, which is then recovered and reused via a biogas recovery device.

[0063] In one implementation method, after anaerobic bacterial conversion, the supernatant is subjected to electrocatalytic treatment using a cathode and anode composed of carbon fiber packing material under a low-voltage electric field. Under the influence of the low-voltage electric field, electron transfer and transport are enhanced, electroactive microorganisms and hydrolytic acidifying bacteria are selectively enriched, and electron acceptors are provided through microaerobic aeration, regulating the oxidation-reduction potential (ORP) of the electrocatalytic reaction. The ORP range is -300 to -200 mV, which breaks down, opens rings, and decomposes the recalcitrant macromolecular organic matter in the effluent after anaerobic bacterial conversion. Further, the low-voltage electric field operates at a voltage of 0.1-2 V and a current of 5-50 mA; the HRT of the biogas slurry is 0.3-2 h.

[0064] As one implementation method, the electrocatalytic device uses the electrocatalytic system and electrode assembly disclosed in CN117699954A for anaerobic biological treatment technology.

[0065] In one implementation method, the electrocatalytic treatment volume is 30%-50% of the supernatant after anaerobic bacterial conversion; the remaining supernatant after anaerobic bacterial conversion is directly used for activated sludge aeration treatment. The microbial community composition at the phylum level in the electrocatalytic treatment step is as follows: Figure 1 As shown in the figure, the electrocatalytic device is enriched with a large number of electrochemically active microorganisms, such as Synergistota (42.49%), Firmicutes (23.39%), Desulfobacterota (12.48%), Bacteroidota (6.31%), Actinobacteriota (3.98%), Proteobacteria (3.63%), and Chloroflexi (2.07%). Among them, Synergistota (mutualistic bacteria) has the highest proportion (42.49%). It directly participates in the electron transfer process by establishing a mutualistic metabolic relationship with hydrogen-nutritive methanogens, significantly improving electron transfer efficiency and thus accelerating methane generation. Firmicutes (23.39%), as a key hydrolytic acidifying microbial community, can efficiently convert long-chain fatty acids into acetic acid, providing readily available substrates for methanogens. Simultaneously, Chloroflexi (2.07%) degrades volatile fatty acids such as propionic acid and butyric acid into acetate, providing direct substrates for methane production. Furthermore, Firmicutes, Acetothermia, Chloroflexi, Thermotogota, and Synergistota are all typical hydrolytic acidifying microorganisms. These microorganisms decompose large, recalcitrant organic molecules into smaller organic acids through hydrolysis and acidification, significantly improving the biodegradability of the biogas slurry and promoting the anaerobic reaction process. This indicates that the electrocatalytic device, through the targeted enrichment of electroactive microorganisms and hydrolytic acidifying microbial communities, promotes the anaerobic reaction process, accelerates methane production, and achieves increased biogas production.

[0066] In one implementation method, the supernatant from the electrocatalytic treatment is returned to the hydrolysis and acidification step via a booster pump for secondary hydrolysis and acidification of recalcitrant organic matter. This external return to the hydrolysis and acidification step avoids direct return to the anaerobic conversion step, introducing dissolved oxygen into the anaerobic conversion step to disrupt the anaerobic environment and prevent cross-contamination and substrate competition between electrogenic bacteria and methanogenic bacteria in the anaerobic conversion step. Simultaneously, micro-oxygen from the returned liquid is introduced into the hydrolysis and acidification step. This micro-oxygen regulates the ORP (Optical Return Rate) in the hydrolysis tank, with an ORP range of -350 to -250 mV. Micro-oxygen improves the redox environment in the hydrolysis and acidification step, promoting the efficiency of the hydrolysis and acidification reaction and providing substrate for methanogenic bacteria in the anaerobic conversion step, thus increasing methane production.

[0067] After hydrolysis acidification and electrocatalytic anaerobic bacterial conversion, the COD of the effluent is 4000-10000 mg / L, and the COD removal rate can reach 30-55%.

[0068] In one implementation method, the biogas slurry after anaerobic bacterial conversion is subjected to activated sludge aeration treatment. This step is carried out in a high-aeration tank; the high-aeration tank is inoculated with municipal activated sludge and operated using a modified sequencing batch reactor (SBR) process.

[0069] In this embodiment, the modified sequencing batch reactor (SBR) mode includes influent / effluent, aeration, and sedimentation cycles; in a single operating cycle, the influent / effluent time is 0.5-1 h, the aeration time is 5.25-7.25 h, and the sedimentation time is 0.25-0.5 h; the effluent ratio is controlled at 20-50%. In this embodiment, the dissolved oxygen (DO) is 1.0-4.0 mg / L, the sludge concentration is 6000-12000 mg / L, the humidification time (HRT) is 24-72 h, and the sludge age is controlled at 5-15 days.

[0070] The operating cycle depends on the COD and TN concentrations. When the COD is 1500-4000 mg / L, the COD removal rate is 60-85%, the effluent TN concentration is 800-2000 mg / L, and the effluent COD / TN ratio is (1-2):1, the activated sludge aeration treatment ends, and effluent is discharged. Activated sludge aeration removes most of the COD, providing a suitable carbon-to-nitrogen ratio for subsequent anaerobic ammonia oxidation treatment. Under this operating mode, the ammonia nitrogen nitrification rate can reach 40-60%, which can supplement the downstream anaerobic ammonia oxidation tank with nitrite nitrogen, reducing the aeration requirements of the anaerobic ammonia oxidation tank.

[0071] In one implementation method, the activated sludge is treated with aeration followed by anaerobic ammonia oxidation. The process is operated using a modified sequencing batch reactor (SBR) mode.

[0072] The modified sequencing batch reactor (SBR) process includes influent / effluent, aeration, and sedimentation cycles. In a single operating cycle, the influent / effluent time is 1-2 hours, aeration is 3.5-4.5 hours, and sedimentation is 0.5 hours. In the anammox treatment, short-cut nitrification sludge and anammox granular sludge are inoculated at a volume ratio of 1:(2.5-3.5). After inoculation, the sludge concentration in the anammox tank is 4000-8000 mg / L, and the hysteresis time (HRT) is 24-72 hours. The reaction temperature is 28-35℃, dissolved oxygen is 0.02-0.5 mg / L, and pH is 7.0-8.0.

[0073] The operating cycle depends on the COD and TN concentrations. Anaerobic ammonia oxidation treatment ends when COD is 600–1000 mg / L and effluent total nitrogen is 50–200 mg / L. Under this operating mode, the total nitrogen removal rate reaches 85–95%. The anaerobic ammonia oxidation tank achieves efficient nitrogen removal through a short-cut nitrification-anaerobic ammonia oxidation reaction, requiring no external carbon source. Compared to traditional processes, this process reduces reagent dosage by approximately 40%, aeration energy consumption by 60%, and sludge production by 60%.

[0074] In one implementation method, the effluent from anaerobic ammonia oxidation treatment enters the AO tank. The dissolved oxygen in the anoxic zone of the AO tank is 0.02-0.5 mg / L, and the dissolved oxygen in the aerobic zone is 1.0-3.0 mg / L, with a total HRT of 8-12 h. In this implementation, the effluent from the aerobic zone is recycled back to the anoxic zone for repeated treatment, with a recycling ratio of 150-300%. After treatment in the OA tank, residual pollutants are removed, and nitrate nitrogen is degraded using denitrification. The sludge is concentrated and dewatered, and a portion is recycled back to the activated sludge aeration treatment. The remaining sludge is transported off-site for disposal.

[0075] The final effluent from the system meets the Class B standard of the "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T 31962-2015), with COD ≤ 500 mg / L, BOD5 ≤ 350 mg / L, and NH4 ≤ 50 mg / L. + With concentrations of ≤45mg / L, TN≤70mg / L, and TP≤8mg / L, efficient purification and resource utilization of kitchen waste biogas slurry can be achieved.

[0076] The following is a further explanation using specific embodiments.

[0077] Example 1

[0078] A comparison of the influent and effluent of a certain kitchen waste biogas slurry after treatment by struvite reaction and hydrolysis acidification was conducted. The ammonia nitrogen concentration threshold of the effluent from the struvite reaction treatment was set at 2000 mg / L, and the concentrations were calculated based on Mg... 2+ :PO4 3- :NH4 + Na₂HPO₄·12H₂O and MgCl₂·6H₂O were added in a molar ratio of 1.3:1.2:1.0. With a free ammonia concentration in the hydrolysis tank <150 mg / L as the threshold, acid was added to lower the pH and free ammonia concentration in the hydrolysis tank. The conditions of the biogas slurry before and after struvite reaction treatment and hydrolysis acidification treatment are shown in Table 1.

[0079] Table 1. Influent and effluent indicators of kitchen waste biogas slurry after treatment with struvite reaction and hydrolysis acidification

[0080]

[0081] The ammonia nitrogen in the effluent treated by struvite reaction was 2197.4±146.8 mg / L, the FA concentration decreased by 61.9%, and the effluent COD / TN increased to 6.52.

[0082] The pH of the hydrolysis-acidification treatment was 7.55±0.11, and the FA concentration was 75.5±24.1 mg / L, which was lower than the free ammonia inhibition threshold in the study.

[0083] Example 2

[0084] The treatment effects of another biogas slurry after struvite reaction and hydrolysis acidification followed by anaerobic bacterial conversion and electrocatalytic treatment, as well as the treatment effects of Comparative Example 1 without struvite reaction and hydrolysis acidification treatment, and after anaerobic bacterial conversion but without electrocatalytic treatment; and the treatment effects of Comparative Example 2 after struvite reaction and hydrolysis acidification treatment, and after anaerobic bacterial conversion but without electrocatalytic treatment; are shown in Table 2.

[0085] Table 2. Anaerobic bacterial transformation of effluent indicators in untreated and pretreated water

[0086]

[0087]

[0088] In Comparative Example 1, the FA concentration in the untreated anaerobic effluent was as high as 538.8±209.8 mg / L, anaerobic bacterial transformation was severely inhibited, the COD removal rate was only 11.3±3.5%, and the methane production rate was 0.12±0.04 L / g COD.

[0089] In Comparative Example 2, after pretreatment with struvite reaction and hydrolysis acidification to reduce ammonia inhibition, the FA concentration in the effluent converted by anaerobic bacteria was 55.7±20.3 mg / L, a reduction of 86%. The COD removal rate increased to 32.9±5.1%, and the methane yield was 0.38±0.06 L / g COD. This significantly reduced the toxicity of free ammonia and restored the metabolic activity of anaerobic microorganisms and the stability of the system.

[0090] In contrast, after pretreatment, the electrocatalytic anaerobic process in Comparative Example 2 enhanced the degradation of organic matter, further reducing FA to 22.4±6.8 mg / L, which is far below the inhibition threshold. The COD removal rate increased to 50.3±4.7%, and the methane yield reached 0.45±0.05 L / gCOD, with the methane yield increasing by 275% compared to the untreated anaerobic reactor.

[0091] Example 3

[0092] The changes in water quality before and after treatment with the method of this application for another biogas slurry are shown in Table 3.

[0093] Table 3 shows the influent and effluent indicators of a certain kitchen waste biogas slurry after treatment using this process.

[0094] sample COD (mg / L) TN (mg / L) <![CDATA[NH4 + (mg / L)]]> TP Water ingress 23680.5±6743.4 3534.5±212.3 3198.5±152.7 373.8±21.4 Out of water 295.5±139.5 46.8±17.9 25.9±16.8 4.2±1.7

[0095] As shown in Table 3, after treatment using the method described in this application, the final effluent from the system meets the Class B standard of the "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T 31962-2015), with COD ≤ 500 mg / L and NH4+ ≤ 500 mg / L. + With concentrations of ≤45mg / L, TN≤70mg / L, and TP≤8mg / L, efficient purification and resource utilization of kitchen waste biogas slurry can be achieved.

[0096] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0097] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0098] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this application, and these should all be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A high-concentration kitchen waste biogas slurry treatment and resource utilization system, characterized in that, It includes a struvite reaction tank (3), a hydrolysis tank (4), an anaerobic tank (5), a high-aeration tank (7), an anaerobic ammonia oxidation tank (9), and an AO tank (10) connected in series.

2. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, It also includes an equalization tank (1) and an air flotation unit (2); the equalization tank (1) is connected to the air flotation unit (2), and the air flotation unit (2) is connected to the water inlet pipe at the bottom of the struvite reaction tank (3).

3. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, A first intermediate water tank (6) is provided between the anaerobic tank (5) and the high aeration tank (7); the outlet of the anaerobic tank (5) is connected to the first intermediate water tank (6), and the first intermediate water tank (6) is connected to the high aeration tank (7) through a lift pump pipeline.

4. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, A second intermediate water tank (8) is provided between the high aeration tank (7) and the anaerobic ammonia oxidation tank (9); the effluent from the high aeration tank (7) is connected to the second intermediate water tank (8), and the second intermediate water tank (8) is connected to the anaerobic ammonia oxidation tank (9) through a lift pump pipeline.

5. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, The anaerobic tank (5) includes an electrocatalytic device (51); the inlet area of ​​the electrocatalytic device (51) is connected to the outlet of the anaerobic tank (5) through a return pipe (53); the outlet area of ​​the electrocatalytic device (51) is connected to the hydrolysis tank (4) through a pipe via a booster pump.

6. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, The electrocatalytic device (51) includes an anode and cathode (512) made of electrocatalytic packing material and a power adapter box (511); the power adapter box (511) is connected to an external power source and the anode and cathode (512) respectively via cables.

7. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, The struvite reaction tank (3) also includes a phosphate dosing device (31) and a magnesium salt dosing device (32), which are connected to the struvite reaction tank (3) via dosing pipes.

8. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, The struvite reaction tank (3) also includes an online ammonia nitrogen concentration detector (36) and a PLC control system (37); the electrode probe of the online ammonia nitrogen concentration detector (36) is installed in the reaction chamber of the struvite reaction tank (3); the online ammonia nitrogen concentration detector (36) and the first PLC control system (37) are connected by a signal line; the first PLC control system (37) is electrically connected to the phosphate dosing device (31) and the magnesium salt dosing device (32) respectively.

9. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, The hydrolysis tank (4) also includes an acid dosing device (43), a free ammonia monitoring system (41), and a second PLC control system (42); the electrode probe of the free ammonia monitoring system (41) is set in the hydrolysis tank (4) and connected to the second PLC control system (42) through a signal line; the second PLC control system (42) is electrically connected to the acid dosing device (43).

10. The high-concentration kitchen waste biogas slurry treatment and resource utilization system according to claim 1, characterized in that, The hydrolysis tank (4) and the anaerobic tank (5) are respectively equipped with biogas recovery devices (52); the guano reaction tank (3) has a conical sludge collection hopper at the bottom of its reaction chamber, and the sludge discharge valve outlet at the bottom of the sludge collection hopper is equipped with a guano recovery port (33).

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