High-concentration kitchen biogas slurry treatment and recycling method

Abstract

The invention provides a high-concentration kitchen biogas slurry treatment and recycling method which comprises the following steps: carrying out struvite reaction treatment, hydrolytic acidification treatment, anaerobic bacteria conversion, activated sludge aeration treatment, anaerobic ammonia oxidation treatment and AO tank treatment on high-concentration kitchen biogas slurry to obtain treated water; the treated water meets the B-level standard of Water Quality Standard for Sewage Discharge to Municipal Sewers (GB / T 31962-2015), the resource recovery of methane and nitrogen and phosphorus is realized in the process, and the efficient purification and resource utilization of the kitchen biogas slurry are realized.

Description

Technical Field

[0001] The present application relates to the technical field of wastewater treatment and resource utilization, and in particular to a method for treating and utilizing high-concentration food waste liquid. Background Art

[0002] The production base of food waste is substantial and continues to rise. As a highly energy-efficient organic resource, it can be converted into high-value-added products such as biogas, organic fertilizer, and bioethanol through processes such as anaerobic fermentation, offering significant potential for resource utilization. However, the biogas slurry produced during food waste treatment is a complex, high-concentration wastewater characterized by high chemical oxygen demand (COD), high ammonia nitrogen concentrations, high levels of suspended solids, and recalcitrant organic matter, making it a key bottleneck restricting the industry's development.

[0003] Currently, the treatment of food waste liquid faces multiple technical challenges. It is difficult to treat due to problems such as low carbon-nitrogen ratio and high concentration of ammonia nitrogen that inhibits the production of free ammonia (FA). Studies generally believe that when the ammonia nitrogen concentration is greater than 1500 mg / L or the FA concentration is greater than 150 mg / L, it can disrupt microbial metabolism and have a toxic effect on hydrolytic acid-producing and anaerobic methanogenic microorganisms, significantly inhibiting the removal rate of hydrolysis and anaerobic reactors. Traditional food waste liquid treatment processes are difficult to solve the problem of ammonia inhibition and have defects such as low denitrification efficiency, high sludge yield, and the need for external carbon source addition, which significantly increases the treatment cost. On the other hand, food waste liquid contains rich organic matter and nitrogen and phosphorus resources. If it is directly treated and discharged, it will cause serious waste of resources. Therefore, the development of a new combined process that combines efficient pollutant removal and targeted resource recovery has become an urgent need to solve the dilemma of food waste liquid treatment. Summary of the Invention

[0004] The present invention provides a method for treating and recycling high-concentration restaurant biogas slurry to solve the problems existing in related technologies. The technical solution is as follows:

[0005] In a first aspect, the present invention provides a method for treating and recycling high-concentration food waste liquid, including the following steps:

[0006] The high-concentration food biogas slurry is subjected to struvite reaction treatment, hydrolysis and acidification treatment, anaerobic bacteria conversion, activated sludge aeration treatment, anaerobic ammonia oxidation treatment and AO tank treatment to obtain treated wastewater.

[0007] In one embodiment, after the anaerobic bacteria are transformed, the supernatant after the anaerobic bacteria transformation is subjected to an electrocatalytic treatment step under a low-voltage electric field using an anode and cathode composed of carbon fiber fillers; the supernatant after the electrocatalytic treatment is refluxed for hydrolysis and acidification treatment.

[0008] In one embodiment, the low voltage electric field operating voltage is 0.1-2 V, the operating current is 5-50 mA, and the supernatant treatment time is: HRT is 0.3-2 h.

[0009] In one embodiment, the treatment volume of the electrocatalytic treatment is 30%-50% of the supernatant after anaerobic bacteria conversion.

[0010] In one embodiment, the struvite reaction is the biogas slurry according to Mg 2+ :PO4 3- :NH4 + Phosphate and magnesium salt are added in a substance amount ratio of (1.0-1.5):(1.0-1.3):1.0 to carry out the reaction.

[0011] In one embodiment, the reaction conditions are: 20-35° C., pH 7.5-9.0, and stirring at 100-180 rpm for 1-3 hours.

[0012] In one embodiment, the phosphate is Na2HPO4 or a hydrate thereof; the magnesium salt is MgCl2 or a hydrate thereof.

[0013] In one embodiment, the hydrolysis and acidification process is performed by maintaining the pH at 5.5-6.5 for 8-48 hours.

[0014] In one embodiment, during the anaerobic conversion process, the HRT is 24-72 hours; the anaerobic bacteria are methanogens.

[0015] In one embodiment, the activated sludge aeration treatment specifically comprises: inoculating a high aeration tank with municipal activated sludge, including water inlet / outlet, aeration, and sedimentation cycles;

[0016] In a single operation cycle, the water inlet / outlet time is 0.5-1h, the aeration time is 5.25-7.25h, and the sedimentation time is 0.25-0.5h; the drainage ratio is controlled at 20-50%;

[0017] The dissolved oxygen is 1.0-4.0 mg / L, the sludge concentration is 6000-12000 mg / L, the HRT is 24-72h, and the sludge age is controlled at 5-15d.

[0018] In one embodiment, the anaerobic ammonium oxidation treatment body is: using short-cut nitrification sludge and anaerobic ammonium oxidation granular sludge inoculated at a volume ratio of 1: (2.5-3.5); including water inlet / outlet, aeration, and sedimentation cycles;

[0019] In a single operation cycle, water inlet / outlet is 1-2 hours, aeration is 3.5-4.5 hours, and sedimentation is 0.5 hours;

[0020] The sludge concentration after inoculation of the anaerobic ammonium oxidation tank is 4000-8000 mg / L, the HRT is 24-72h; the reaction temperature is 28-35℃, the dissolved oxygen is 0.02-0.5 mg / L, and the pH is 7.0-8.0.

[0021] In one embodiment, the dissolved oxygen in the anoxic section of the AO tank is 0.02-0.5 mg / L, the dissolved oxygen in the aerobic section is 1.0-3.0 mg / L, and the total HRT is 8-12 h;

[0022] After treatment in the aerobic section, the wastewater is returned to the anoxic section for repeated treatment, with a reflux ratio of 150 to 300%.

[0023] In one embodiment, the high-concentration restaurant biogas slurry has a COD of 10,000-30,000 mg / L, a TN of 2,000-4,000 mg / L, ammonia nitrogen of 2,000-3,500 mg / L, a TP of 100-500 mg / L, a pH of 7.5-9.0, and a suspended solids of 3-12 g / L;

[0024] In the treated wastewater: COD≤500mg / L, BOD5≤350mg / L, NH4 + ≤45mg / L, TN≤70mg / L, TP≤8mg / L.

[0025] The advantages or beneficial effects of the above technical solution include at least:

[0026] The present invention discloses a method for treating and recycling high-concentration food waste liquid. The front end uses a struvite crystallization method to precipitate and recover ammonia nitrogen in the food waste liquid in the form of struvite crystals (MgNH4PO4·6H2O), while reducing the risk of ammonia inhibition and providing stable conditions for subsequent biological treatment. The middle stage uses a hydrolysis acidification and electrocatalytic anaerobic coupling process to efficiently degrade large molecular organic matter and difficult-to-degrade components into methane through bioelectrochemical enhanced electron transfer. The end stage introduces an anaerobic ammonium oxidation process to achieve efficient denitrification through an autotrophic method without the need for an exogenous carbon source. Compared with traditional processes, this method reduces the dosage of reagents by 40%, aeration energy consumption by 60%, and sludge yield by approximately 40%. Not only does it recover ammonia nitrogen and carbon (methane) in the wastewater, but the treated wastewater also meets emission standards, achieving wastewater treatment and resource utilization. The present invention's high-concentration food waste liquid treatment and resource utilization method can provide sustainable development for the full-scale resource treatment of food waste.

[0027] The above summary 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 the present application will be readily apparent by reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the multiple drawings represent the same or similar components or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings only depict some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0029] Figure 1 The composition of microbial communities at the gate level in a certain restaurant biogas slurry electrocatalytic device;

[0030] Figure 2 Process flow chart for this application;

[0031] Figure 3 This is a schematic diagram of the structure of the regulating tank, flotation unit and struvite reaction tank in the high-concentration food biogas slurry treatment and resource utilization system;

[0032] Figure 4 This is a schematic diagram of the structure of the hydrolysis tank and anaerobic tank in the high-concentration food biogas slurry treatment and resource utilization system;

[0033] 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 the high-concentration food biogas treatment and resource utilization system. DETAILED DESCRIPTION

[0034] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present application. Therefore, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0035] To address the problems of low efficiency and resource waste in traditional treatment processes for high-concentration food biogas slurry due to high ammonia nitrogen, low carbon-nitrogen ratio and difficult-to-degrade organic matter, the present invention proposes a multi-stage synergistic combination process to achieve efficient denitrification and carbon removal, nitrogen and phosphorus resource recovery, and increased biogas production from food biogas slurry.

[0036] A method for treating and recycling high-concentration restaurant biogas slurry, comprising the following steps: the high-concentration restaurant biogas slurry is subjected to struvite reaction treatment, hydrolysis and acidification treatment, anaerobic bacteria conversion, activated sludge aeration treatment, anaerobic ammonium oxidation treatment and AO tank treatment to obtain treated wastewater. Figure 2 shown.

[0037] For high-concentration food biogas, high ammonia nitrogen concentrations can be toxic to microbial metabolism, impacting subsequent treatment processes. Therefore, this application uses a struvite reaction to precipitate ammonia nitrogen in the biogas as struvite crystals, which can be recycled as nitrogen and phosphorus fertilizer. This reduces ammonia nitrogen concentration while also minimizing the risk of ammonia inhibition, providing stable conditions for subsequent biological treatment.

[0038] As one embodiment, the present invention is suitable for treating food wastewater with COD levels 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, a pH of 7.5-9.0, and suspended solids (SS) of 3-12 g / L. It can be seen that the indicators for various pollutants are high, far exceeding the standards.

[0039] Because larger impurities and suspended matter interfere with the struvite reaction and affect the purity of struvite crystals, which is detrimental to recovery, one implementation method is to remove suspended matter from high-concentration food biogas slurry before the struvite reaction. Preferably, air flotation is used to remove suspended matter. Specifically, the biogas slurry first enters the flotation unit from the regulating tank, mainly to remove larger impurities, while reducing ss from 3 to 12 g / L to 1.0 to 3.0 g / L, effectively avoiding interference of suspended matter with subsequent struvite reaction and recovery.

[0040] As one embodiment, the present invention adds phosphate and magnesium salt to high concentration of food biogas; the phosphate is Na2HPO4 or its hydrate; the magnesium salt is MgCl2 or its hydrate. The struvite reaction is based on the concentration of ammonium ions in the biogas slurry, according to Mg 2+ :PO4 3- :NH4 + Phosphate and magnesium salt are added in a molar ratio of (1.0-1.5): (1.0-1.3): 1.0 for reaction; the reaction conditions are 20-35°C, pH 7.5-9, and stirring at 100-180 rpm for 1-3 hours; the reaction generates struvite crystals and precipitates, which are discharged by sedimentation separation and dehydration to achieve nitrogen and phosphorus recovery.

[0041] In one implementation method, the addition of phosphate and magnesium salts is automatically adjusted. The dosage is dynamically controlled based on the target effluent ammonia nitrogen concentration threshold of less than 1500-2500 mg / L. When the online ammonia nitrogen detector shows that the ammonia nitrogen concentration is greater than the set target effluent ammonia nitrogen concentration threshold, the PLC control system starts the dosing device and stops when the ammonia nitrogen concentration falls below the set target effluent ammonia nitrogen concentration threshold.

[0042] After the biogas slurry is treated with struvite, the ammonia nitrogen removal rate of the effluent can reach 20-60%, the total phosphorus removal rate can reach 30-70%, and the free ammonia concentration can be reduced from the initial 150-4000 to 50-1500 mg / L. At the same time, the carbon-nitrogen ratio of the biogas slurry can be improved, which is beneficial to subsequent biochemical treatment.

[0043] As one of the implementation methods, the biogas slurry treated with struvite reaction is subjected to hydrolysis and acidification treatment. By regulating the free ammonia concentration in the hydrolysis tank, the risk of free ammonia inhibition is reduced, and the dosage of phosphate and magnesium salts in the front-end struvite reaction tank is reduced. In addition, the hydrolysis and acidification effect decomposes large-molecule organic matter and difficult-to-degrade components into small-molecule organic acids, thereby improving biodegradability. Specifically: maintain the pH at 5.5-6.5, the biogas slurry residence time (HRT) is 8-48h, and after 8-48h of hydrolysis and acidification, the large-molecule organic matter and difficult-to-degrade components in the biogas slurry are decomposed into small-molecule organic acids; biodegradability is improved. Free ammonia is further reduced, and the inhibitory and toxic effects on microbial activity are eliminated. The free ammonia concentration can be reduced from the initial 150-1500mg / L to <150mg / L.

[0044] In one embodiment, an online free ammonia monitoring system and an acid dosing device are provided. When the online free ammonia monitoring system detects an FA concentration greater than 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 falls below the set threshold, the dosing is stopped. The pH range is 5.5 to 6.5, and the set FA concentration threshold range is less than 150 mg / L. In this embodiment, the acid is concentrated sulfuric acid and / or concentrated hydrochloric acid.

[0045] In one implementation, after struvite reaction and hydrolysis and acidification, the FA content in the biogas slurry has been reduced to below 150 mg / L, reducing ammonia inhibition and addressing the ammonia inhibition issue in traditional high-concentration food biogas treatment processes. This allows the biogas slurry to undergo anaerobic conversion. The HRT for anaerobic conversion is 24-72 hours. During the anaerobic conversion process, methanogens use small organic acids produced in the hydrolysis tank as substrates to produce methane, which is then recycled in a biogas recovery unit.

[0046] As one of the implementation methods, after the anaerobic bacteria are transformed, the electrocatalytic treatment step is performed on the supernatant after the anaerobic bacteria transformation under a low-voltage electric field using anodes and cathodes composed of carbon fiber fillers. Under the action of the low-voltage electric field, the transmission and transfer of electrons are enhanced, and electroactive microorganisms and hydrolytic acidifying bacteria are enriched in a direction. At the same time, electron acceptors are provided by micro-aerobic aeration and the redox potential (ORP) of the electrocatalytic reaction is regulated. The ORP range is -300 to -200mV, and the difficult-to-degrade macromolecular organic matter in the effluent after the anaerobic bacteria transformation is broken, opened, and decomposed. Furthermore, the working voltage of the low-voltage electric field is 0.1-2V, and the working current is 5-50mA; the HRT of the biogas slurry is 0.3-2h.

[0047] As one embodiment, the electrocatalytic device uses the electrocatalytic system and electrode assembly disclosed in CN117699954A for anaerobic biological treatment technology.

[0048] As one embodiment, the electrocatalytic treatment amount is 30%-50% of the supernatant after anaerobic bacteria conversion; the remaining supernatant after anaerobic bacteria conversion is directly subjected to activated sludge aeration treatment.

[0049] The composition of microbial communities at the phylum level during the electrocatalytic treatment step is shown in Figure 2. Figure 1 As shown in the figure, a large number of electrochemically active microorganisms are enriched in the electrocatalytic device, 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 (Synergistota) accounts for the highest proportion (42.49%). It directly participates in the electron transfer process by establishing a mutualistic metabolic relationship with hydrogenotrophic methanogens, significantly improving the electron transfer efficiency and thus accelerating methane production. Firmicutes (Firmicutes, 23.39%), as a key hydrolytic acidifying bacterial group, can efficiently convert long-chain fatty acids into acetic acid, providing an easily usable substrate for methanogens; at the same time, Chloroflexi (Chloroflexi, 2.07%) degrades volatile fatty acids such as propionic acid and butyric acid into acetate, providing a direct substrate for methane production. In addition, Firmicutes, Acetothermia, Chloroflexi, Thermotogota and Synergistota are all typical hydrolytic acidifying microorganisms. These microorganisms decompose large-molecule refractory organic matter into small-molecule organic acids through hydrolytic acidification, significantly improving the biodegradability of the biogas slurry and promoting the anaerobic reaction process. This shows that the electrocatalytic device promotes the anaerobic reaction process by directional enrichment of electroactive microorganisms and hydrolytic acidifying bacterial groups, accelerates the production of methane, and achieves increased biogas production.

[0050] As one of the implementation methods, the supernatant of the electrocatalytic treatment effluent is refluxed to the hydrolysis and acidification treatment step through a lifting pump to perform secondary hydrolysis and acidification on the refractory organic matter. By externally refluxing to the hydrolysis and acidification treatment step, direct reflux to the anaerobic conversion step is avoided, and dissolved oxygen is brought into the anaerobic conversion step to destroy the anaerobic environment and avoid cross-contamination between the electrogenic bacteria and the methanogens in the anaerobic conversion step, thereby competing for substrates. At the same time, micro-oxygen in the reflux liquid is brought into the hydrolysis and acidification treatment step, and the ORP in the hydrolysis tank is regulated by micro-oxygen, and the ORP range is -350 to -250 mV. The redox environment in the hydrolysis and acidification treatment step is improved by micro-oxygen, and the efficiency of the hydrolysis and acidification reaction is promoted, thereby providing substrates for the methanogens in the anaerobic conversion step to increase methane production.

[0051] After the biogas slurry is finally treated by hydrolysis and acidification and electrocatalytic anaerobic bacteria conversion, the effluent COD is 4000-10000 mg / L and the COD removal rate can reach 30-55%.

[0052] In one embodiment, the biogas slurry after anaerobic conversion is subjected to activated sludge aeration. This step is carried out in a high aeration tank inoculated with municipal activated sludge and operated in a modified sequencing batch sludge (SBR) process.

[0053] In this embodiment, a modified sequencing batch activated sludge process (SBR) includes inlet / outlet, aeration, and sedimentation cycles. In a single operating cycle, inlet / outlet cycles are 0.5-1 hour, aeration is 5.25-7.25 hours, and sedimentation is 0.25-0.5 hours. The discharge ratio is controlled at 20-50%. In this embodiment, the dissolved oxygen (DO) is 1.0-4.0 mg / L, the sludge concentration is 6,000-12,000 mg / L, the HRT is 24-72 hours, and the sludge age is controlled at 5-15 days.

[0054] The operating cycle depends on COD and TN concentrations. When COD is 1500-4000 mg / L, COD removal efficiency is 60-85%, effluent TN concentration is 800-2000 mg / L, and the effluent COD / TN ratio is (1-2):1, activated sludge aeration treatment is completed and effluent is discharged. Activated sludge aeration treatment removes most of the COD, providing an optimal carbon-nitrogen ratio for subsequent anaerobic ammonium oxidation (ANAMMOX) treatment. Under this operating mode, the ammonia nitrogen nitrification rate can reach 40-60%, providing nitrite nitrogen to supplement the downstream ANAMMOX tanks and reducing the aeration demand for ANAMMOX tanks.

[0055] As one implementation method, activated sludge aeration treatment is followed by anaerobic ammonium oxidation treatment, and the process is operated in a modified sequencing batch sludge (SBR) mode.

[0056] The modified sequencing batch activated sludge process (SBR) model includes inlet / outlet, aeration, and sedimentation cycles; in a single operation cycle, the inlet / outlet is 1-2 hours, the aeration is 3.5-4.5 hours, and the sedimentation is 0.5 hours; in the anaerobic ammonium oxidation treatment, short-cut nitrification sludge and anaerobic ammonium oxidation granular sludge are inoculated at a volume ratio of 1:(2.5-3.5); the sludge concentration after inoculation of the anaerobic ammonium oxidation tank is 4000-8000 mg / L, the HRT is 24-72 hours; the reaction temperature is 28-35°C, the dissolved oxygen is 0.02-0.5 mg / L, and the pH is 7.0-8.0.

[0057] The operating cycle depends on COD and TN concentrations. Anaerobic ammonium oxidation treatment ends when COD is 600-1000 mg / L and effluent total nitrogen is 50-200 mg / L. Under this operating mode, total nitrogen removal rates reach 85-95%. The anaerobic ammonium oxidation tank efficiently removes nitrogen through a short-circuit nitrification-anaerobic ammonium oxidation reaction, requiring no external carbon source. Compared to traditional processes, this process reduces chemical dosage by approximately 40%, aeration energy consumption by 60%, and sludge yield by approximately 40%.

[0058] As one embodiment, the effluent after anaerobic ammonium oxidation treatment enters the AO tank. The dissolved oxygen in the anoxic section of the AO tank is 0.02-0.5 mg / L, and the dissolved oxygen in the aerobic section is 1.0-3.0 mg / L, with a total HRT of 8-12 hours. In this embodiment, after treatment in the aerobic section, the effluent is returned to the anoxic section for repeated treatment, with a reflux ratio of 150-300%. After treatment in the OA tank, the remaining pollutants are removed, and nitrate nitrogen is degraded by denitrification. After concentration and dehydration, the sludge is partially returned to the activated sludge aeration treatment, and the remaining sludge is transported for disposal.

[0059] The final system effluent can meet the B-level standard of "Water Quality Standard for Sewage Discharge into Urban Sewers" (GB / T 31962-2015), including COD≤500mg / L, BOD5≤350mg / L, NH4 + ≤45mg / L, TN≤70mg / L, TP≤8mg / L, realizing efficient purification and resource utilization of restaurant biogas slurry.

[0060] The following is a further description with reference to specific embodiments.

[0061] Example 1

[0062] Comparison of the influent and effluent of a restaurant biogas slurry after struvite reaction treatment and hydrolysis acidification treatment. Taking the ammonia nitrogen concentration threshold of the effluent from struvite reaction treatment as 2000 mg / L as the benchmark, the Mg 2+ :PO4 3- :NH4 + Na₂HPO₄·12H₂O and MgCl₂·6H₂O were added in a molar ratio of 1.3:1.2:1.0. Acidification was used to lower the pH and free ammonia concentration in the hydrolysis tank, with the free ammonia concentration in the hydrolysis tank below 150 mg / L. The results of the biogas slurry before and after struvite reaction and hydrolysis-acidification treatment are shown in Table 1.

[0063] Table 1 Influent and effluent indicators of restaurant biogas slurry after struvite reaction treatment and hydrolysis acidification

[0064]

[0065] The ammonia nitrogen content of the effluent from the struvite reaction treatment was 2197.4±146.8 mg / L, the FA concentration was reduced by 61.9%, and the effluent COD / TN was increased to 6.52.

[0066] The pH of the hydrolysis and acidification treatment was 7.55±0.11, and the FA concentration was 75.5±24.1 mg / L, which were lower than the free ammonia inhibition threshold in the study.

[0067] Example 2

[0068] Table 2 shows the treatment effects of another biogas slurry after struvite reaction and hydrolysis and acidification treatment, followed by anaerobic conversion and electrocatalytic treatment, as well as the treatment effects of Comparative Example 1 without struvite reaction and hydrolysis and acidification treatment; after anaerobic conversion but without electrocatalytic treatment; and the treatment effects of Comparative Example 2 after struvite reaction and hydrolysis and acidification treatment; after anaerobic conversion but without electrocatalytic treatment.

[0069] Table 2 Anaerobic bacteria conversion indicators of effluent without and after pretreatment

[0070]

[0071] In Comparative Example 1, the FA concentration of the anaerobic effluent without pretreatment was as high as 538.8±209.8 mg / L, the anaerobic bacteria conversion was severely inhibited, the COD removal rate was only 11.3±3.5%, and the methane yield was 0.12±0.04 L / g COD.

[0072] In Comparative Example 2, after struvite reaction treatment and hydrolysis and acidification treatment to reduce ammonia inhibition pretreatment, the FA concentration of the effluent converted by anaerobic bacteria was 55.7±20.3 mg / L, the FA concentration was reduced by 86%, the COD removal rate was increased to 32.9±5.1%, and the methane yield was 0.38±0.06 L / g COD, which significantly reduced the toxicity of free ammonia and restored the metabolic activity and system stability of anaerobic microorganisms.

[0073] After pretreatment, the electrocatalytic anaerobic process in Comparative Example 2 enhanced the degradation of organic matter, and the FA was further reduced to 22.4±6.8 mg / L, far below the inhibition threshold. The COD removal rate was increased to 50.3±4.7%, and the methane yield reached 0.45±0.05 L / gCOD. The methane yield increased by 275% compared with the anaerobic reactor without pretreatment.

[0074] Example 3

[0075] Table 3 shows the changes in water quality of another biogas slurry before and after treatment using the treatment method of the present application.

[0076] Table 3 shows the inlet and outlet water indicators of a restaurant biogas slurry after treatment by this process

[0077] sample COD (mg / L) TN (mg / L) NH4+(mg / L) TP Water ingress 23680.5±6743.4 3534.5±212.3 3198.5±152.7 373.8±21.4 Water 295.5±139.5 46.8±17.9 25.9±16.8 4.2±1.7

[0078] As can be seen from Table 3, after the restaurant biogas liquid is treated by the method of this application, the final system effluent can meet the B-level standard of the "Water Quality Standard for Sewage Discharge into Urban Sewers" (GB / T 31962-2015), in which COD≤500mg / L, NH4 + ≤45mg / L, TN≤70mg / L, TP≤8mg / L, realizing efficient purification and resource utilization of restaurant biogas slurry.

[0079] This application provides a high-concentration restaurant biogas slurry treatment and resource recovery system, the structure of which is as follows Figure 3 、 Figure 4 and Figure 5 The system comprises a struvite reaction tank 3, a hydrolysis tank 4, an anaerobic tank 5, a high aeration tank 7, an anaerobic ammonium oxidation tank 9, and an AO tank 10 which are connected in series along the flow direction of the biogas slurry.

[0080] The struvite reaction tank 3 can precipitate ammonia nitrogen in the biogas slurry in the form of struvite crystals by adding phosphates and magnesium salts, which can be recycled as nitrogen and phosphorus fertilizers. This reduces the ammonia nitrogen concentration and the risk of ammonia inhibition, providing stable conditions for subsequent biological treatment.

[0081] Therefore, as one embodiment, the struvite reaction tank 3 further includes a phosphate dosing device 31 and a magnesium salt dosing device 32. The phosphate dosing device 31 and the magnesium salt dosing device 32 are connected to the struvite reaction tank 3 via a dosing pipe. 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.

[0082] As one embodiment, the struvite reaction tank 3 further includes a stirrer 34 disposed in the center of the reaction chamber. The stirrer 34 can fully mix the biogas slurry with the phosphate and magnesium salts to ensure a thorough reaction.

[0083] As one embodiment, the struvite reaction tank 3 also 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 through 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.

[0084] Different effluent ammonia-nitrogen concentration thresholds are set based on the quality of the food processing biogas slurry. When the online ammonia-nitrogen concentration detector 36 detects a concentration greater than 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 struvite crystals to reduce the ammonia-nitrogen concentration in the biogas slurry. When the concentration falls below 1500-2500 mg / L, the dosing is stopped. This preventative mechanism controls the ammonia-nitrogen concentration in the biogas slurry effluent and reduces the risk of ammonia inhibition in the biogas slurry.

[0085] As one embodiment, the struvite reaction tank 3 has a conical mud collecting hopper at the bottom of its reaction chamber, and a struvite recovery port 33 is provided at the mud discharge valve outlet at the bottom of the mud collecting hopper.

[0086] The struvite crystals, a product of the struvite reaction, are separated from the biogas slurry via a solid-liquid separation process. The precipitate settles in a conical sludge collection hopper and is recovered via a struvite recovery port 33 located at the outlet of the sludge valve at the bottom of the hopper. In this embodiment, solid-liquid separation is achieved via a solid-liquid separation assembly 35, which is comprised of an inclined plate.

[0087] As one embodiment, the high-concentration food biogas treatment and resource utilization system also includes a regulating tank 1 and a flotation unit 2; the regulating tank 1 is connected to the flotation unit 2, and the flotation unit 2 is connected to the water inlet pipe at the bottom of the struvite reaction tank 3. Because larger impurities and suspended matter interfere with the struvite reaction and affect the purity of struvite crystallization, which is not conducive to recovery, the present embodiment also includes a regulating tank 1 and a flotation unit 2. Before the struvite reaction treatment, the high-concentration food biogas is first treated with the flotation unit 2 to remove suspended matter by flotation. Specifically, the biogas first enters the flotation unit 2 from the regulating tank 1, mainly to remove larger impurities, effectively avoiding the interference of suspended matter on the subsequent struvite reaction and recovery. The biogas from which the suspended matter has been removed from the flotation unit 2 enters the struvite reaction tank 3 for reaction.

[0088] The biogas slurry after 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 arranged in the center of the hydrolysis tank, and the liquid phase outlet of the struvite reaction tank 3 is connected to the first water distribution system 44 of the hydrolysis tank 4, such as Figure 3 A and Figure 4 A connection; the separated biogas slurry evenly enters the bottom of the hydrolysis tank 4 from the first water distribution system 44.

[0089] By regulating the free ammonia concentration in the hydrolysis tank 4, the risk of free ammonia inhibition is reduced, and the dosage of phosphate and magnesium salt in the front-end struvite reaction tank is reduced. In addition, the hydrolysis and acidification effect decomposes large molecular organic matter and difficult-to-degrade components into small molecular organic acids, thereby improving biodegradability.

[0090] As one embodiment, 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 arranged in the hydrolysis tank 4 and is 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.

[0091] 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 is stopped; the pH range is 5.5-6.5, and the set FA concentration threshold range is less than 150 mg / L.

[0092] After treatment in the struvite reactor 3 and hydrolysis and acidification in the hydrolysis tank 4, the FA content in the biogas slurry has been reduced to below 150 mg / L, reducing ammonia inhibition and resolving the ammonia inhibition issue in conventional high-concentration food waste biogas treatment processes. This makes the biogas slurry suitable for anaerobic conversion. This anaerobic conversion occurs in the anaerobic tank 5.

[0093] As one embodiment, the anaerobic tank 5 includes a second water distribution system 54 and an electrocatalytic device 51; the water inlet area of ​​the electrocatalytic device 51 is connected to the water outlet of the anaerobic tank 5 through a return pipe 53; the water outlet area of ​​the electrocatalytic device 51 is connected to the hydrolysis tank 4 through a pipe via a lifting pump.

[0094] The supernatant of the hydrolysis tank 4 flows through the effluent weir and the pipeline to the second water distribution system 54 of the anaerobic tank 5; part of the supernatant of the effluent of the anaerobic tank 5 flows to the electrocatalytic device 51 through the reflux pipeline 53, and the supernatant of the effluent area of ​​the electrocatalytic device 51 is returned to the first water distribution system 44 of the hydrolysis tank 4 through the lifting pump to realize external circulation; the remaining part of the supernatant of the effluent of the anaerobic tank 5 is passed to the high aeration tank 7.

[0095] The effluent from hydrolysis tank 4 flows into the bottom of anaerobic tank 5. A portion of the supernatant (anaerobic effluent) from the treatment in anaerobic tank 5 is returned to electrocatalytic device 51 for further treatment, with a return rate of 30-50%. The supernatant from electrocatalytic device 51 then flows through first water distribution system 44 to the bottom of hydrolysis tank 4 for further treatment. The remaining anaerobic effluent is passed to high-temperature aeration tank 7.

[0096] The anaerobic tank 5 contains anaerobic bacteria, which are methanogens. The methanogens in the anaerobic tank 5 use the small molecular organic acids produced in the hydrolysis tank 4 as substrates to produce methane, which is then recycled by the biogas recovery device 52.

[0097] In one embodiment, the electrocatalytic device 51 includes an anode and cathode 512 composed of electrocatalytic fillers 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. The low-voltage electric field accelerates electron transfer and conducts targeted enrichment of electroactive microorganisms and hydrolytic acidifying bacteria. Combined with bottom microaerobic aeration 513, the redox potential (ORP) is adjusted to cause chain scission, ring opening, and decomposition of recalcitrant macromolecular organic matter in the effluent of the anaerobic tank 5. The supernatant from the effluent of the electrocatalytic device 51 is then returned to the hydrolysis tank 4 via a lift pump to undergo secondary hydrolysis and acidification of the recalcitrant organic matter, promoting further degradation of the recalcitrant organic matter in the anaerobic tank 5. The microaerobic content of the reflux liquid regulates the ORP environment in the hydrolysis tank, promoting hydrolysis and acidification to produce organic acids that provide substrate for methanogens in the anaerobic tank 5, thereby increasing methane production. In addition, the external circulation of the hydrolysis tank 4 avoids cross contamination between the electrogenic bacteria enriched in the electrocatalytic device and the methanogens in the anaerobic tank, thereby preventing competition for substrates.

[0098] As 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, as shown in FIG. Figure 4 B and Figure 5 The first intermediate water tank 6 is connected to the high aeration tank 7 through a lifting pump pipeline.

[0099] High aeration tank 7 is seeded with municipal activated sludge and operates in a modified sequencing batch sludge (SBR) process, including inlet / outlet, aeration, and sedimentation cycles. This removes the majority of COD, providing an optimal carbon-nitrogen ratio for anaerobic ammonium oxidation tank 9. Furthermore, under this operating mode, the ammonia nitrogen nitrification rate can reach 40-60%, providing nitrite nitrogen to the downstream anaerobic ammonium oxidation tank 9 and reducing the aeration requirement.

[0100] As 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 lifting pump pipeline.

[0101] Anaerobic ammonium oxidation tank 9 operates using a modified sequencing batch activated sludge (SBR) process, including inlet / outlet, aeration, and sedimentation cycles. It is inoculated with short-cut nitrification sludge and anaerobic ammonium oxidation granular sludge at a volume ratio of 1:2.5-3.5. Short-cut nitrification converts ammonia nitrogen into nitrite nitrogen, which is then converted into nitrogen gas and nitrate nitrogen by anaerobic ammonium oxidizing bacteria.

[0102] The effluent from the anaerobic ammonium oxidation tank 9 flows to the AO tank 10, which is set to return to the A tank from the O tank. Finally, the AO tank 10 further removes residual organic matter and nitrate nitrogen, and the effluent meets the Class B standard of the "Water Quality Standard for Wastewater Discharge into Urban Sewers" (GB / T31962-2015).

[0103] During the entire process, pretreatment is performed in the struvite reaction tank 3 to remove part of the ammonia nitrogen and reduce ammonia inhibition, and the hydrolysis tank 4 is coordinated to regulate and reduce free ammonia, thereby solving the ammonia inhibition problem in the traditional treatment process of high-concentration food biogas. The anaerobic tank 5 is coupled with electrocatalysis to further decompose the difficult-to-degrade organic matter in the anaerobic tank and return it to the hydrolysis tank 4 for secondary hydrolysis and acidification, thereby improving biodegradability. In addition, the crystallized sludge produced in the struvite reaction tank 3 can be made into fertilizer after dehydration, and the biogas produced by the hydrolysis tank 4 and the electrocatalytic anaerobic tank 5 is utilized for energy, realizing the whole process of biogas purification and resource recovery.

[0104] The high-concentration restaurant biogas slurry treatment system operates according to the following process: Figure 2 shown.

[0105] The food waste liquid first enters the flotation unit 2 from the regulating tank 1. Flotation removes suspended matter and some colloids. The purified and impurity-free biogas flows into the struvite reaction tank 3. Phosphate 31 and magnesium salt 32 are added proportionally to the struvite reaction tank 3. A mixer 34 mixes and reacts the mixture to form struvite crystals. Nitrogen and phosphorus are then 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 water quality of the food waste liquid. When the online ammonia nitrogen concentration detector detects an ammonia nitrogen concentration greater than 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 form struvite crystals and reduce the ammonia nitrogen concentration in the biogas liquid. When the detected ammonia nitrogen concentration is less than 1500-2500 mg / L, the dosing is stopped. By setting up a first prevention mechanism, the ammonia nitrogen concentration of the biogas slurry effluent is controlled to reduce the risk of ammonia inhibition in the biogas slurry; then the precipitate is separated from the biogas slurry through the solid-liquid separation component 35.

[0106] The biogas slurry flows evenly into the bottom of the hydrolysis tank 4 from the first water distribution system 44. A free ammonia monitoring system 41, a second PLC control system 42 and an acid dosing device 43 are provided in the hydrolysis tank 4. 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 lower the pH and free ammonia concentration in the hydrolysis tank 4. When the free ammonia concentration is less than the set threshold, the dosing is stopped. 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, and the dosage of phosphate and magnesium salt in the front-end struvite reaction tank 3 is reduced. The refractory large-molecule organic matter is decomposed into small-molecule organic acids through hydrolysis and acidification in the hydrolysis tank 4, thereby improving biodegradability; the biogas slurry after hydrolysis and acidification is evenly transported from the second water distribution system 54 to the bottom of the anaerobic tank 5, and the methanogens in the anaerobic tank 5 use the small-molecule organic acids produced in the hydrolysis tank 4 as substrates to produce methane, which is recycled and utilized by the biogas recovery device 52. The supernatant of the anaerobic tank 5 enters the electrocatalytic device 51 from the reflux pipe 53, and the power adapter box 511 outputs a low-voltage electric field to the electrocatalytic filler structure composed of carbon fibers. The formed anode and cathode 512 accelerate electron transfer and transmission under the action of the low-voltage electric field, directionally enrich electroactive microorganisms and hydrolytic acidifying bacteria, and combine with the bottom micro-aerobic aeration 513 to adjust the redox potential (ORP), and break the chain, open the ring, and decompose the difficult-to-degrade large molecular organic matter in the effluent of the anaerobic tank 5. The supernatant in the effluent area of ​​the electrocatalytic device 51 is returned to the hydrolysis tank 4 through the lifting pump to perform secondary hydrolysis and acidification on the difficult-to-degrade organic matter, thereby promoting further degradation of the difficult-to-degrade organic matter in the anaerobic tank 5. At the same time, the reflux liquid contains micro-oxygen, which can regulate the ORP environment in the hydrolysis tank 4, promote hydrolysis and acidification to generate organic acid, which provides substrate for methanogens in the anaerobic tank and increases methane production.

[0107] The effluent from the anaerobic tank 5 flows into the first intermediate water tank 6 and then into the high aeration tank 7, where the remaining COD is rapidly degraded by the high sludge concentration, providing a suitable carbon-nitrogen ratio for the back-end anaerobic ammonium oxidation; the biogas slurry then enters the second intermediate water tank 8 and then into the anaerobic ammonium oxidation tank 9, where ammonia nitrogen is converted into nitrite nitrogen through short-range nitrification, and then the anaerobic ammonium oxidizing bacteria convert ammonia nitrogen and nitrite nitrogen into nitrogen gas and nitrate nitrogen; finally, the residual organic matter and nitrate nitrogen are further removed through the AO tank 10.

[0108] In the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. Moreover, the specific features, structures, materials, or characteristics described may be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0109] 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 being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0110] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various modifications or substitutions within the technical scope disclosed in this application, and such modifications or substitutions should be included within the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for treating and recycling high-concentration restaurant biogas slurry, characterized in that: The following steps are involved: The high-concentration food biogas slurry is subjected to struvite reaction treatment, hydrolysis and acidification treatment, anaerobic bacteria conversion, activated sludge aeration treatment, anaerobic ammonia oxidation treatment and AO tank treatment to obtain treated wastewater.

2. The method for treating and recycling high-concentration restaurant biogas slurry according to claim 1, characterized in that: After the anaerobic bacteria are transformed, the supernatant after the anaerobic bacteria transformation is subjected to an electrocatalytic treatment step under a low-voltage electric field using anodes and cathodes composed of carbon fiber fillers; the supernatant after the electrocatalytic treatment is refluxed for hydrolysis and acidification treatment.

3. The method for treating and recycling high-concentration restaurant biogas slurry according to claim 2, characterized in that: The treatment capacity of electrocatalytic treatment is 30%-50% of the supernatant after anaerobic bacteria conversion; The working voltage of the low-voltage electric field is 0.1-2V, the working current is 5-50mA; the supernatant treatment time is: HRT is 0.3-2h.

4. The method for treating and recycling high-concentration restaurant biogas slurry according to any one of claims 1 to 3, characterized in that: The struvite reaction is the slurry in Mg 2+ :PO4 3- :NH4 + Phosphate and magnesium salt are added in a molar ratio of (1.0-1.5):(1.0-1.3):1.0 to react; The reaction conditions are: 20-35°C, pH 7.5-9.0, stirring at 100-180 rpm for 1-3 hours; The phosphate is Na2HPO4 or its hydrate; the magnesium salt is MgCl2 or its hydrate.

5. The method for treating and recycling high-concentration restaurant biogas slurry according to claim 4, characterized in that: The hydrolysis and acidification treatment process is as follows: the pH is maintained at 5.5-6.5 for 8-48 hours.

6. The method for treating and recycling high-concentration restaurant biogas slurry according to claim 4, characterized in that: During the anaerobic transformation process, the HRT is 24-72 hours; the anaerobic bacteria are methanogens.

7. The method for treating and recycling high-concentration restaurant biogas slurry according to claim 4, characterized in that: Activated sludge aeration treatment specifically involves: inoculating municipal activated sludge in high aeration tanks, including inlet / outlet, aeration, and sedimentation cycles; In a single operation cycle, the water inlet / outlet time is 0.5-1h, the aeration time is 5.25-7.25h, and the sedimentation time is 0.25-0.5h; the drainage ratio is controlled at 20-50%; The dissolved oxygen is 1.0-4.0 mg / L, the sludge concentration is 6000-12000 mg / L, the HRT is 24-72h, and the sludge age is controlled at 5-15d.

8. The method for treating and recycling high-concentration restaurant biogas slurry according to claim 4, characterized in that: The anaerobic ammonium oxidation treatment process is: using short-cut nitrification sludge and anaerobic ammonium oxidation granular sludge inoculated at a volume ratio of 1: (2.5-3.5); including water inlet / outlet, aeration, and sedimentation cycles; In a single operation cycle, water inlet / outlet is 1-2 hours, aeration is 3.5-4.5 hours, and sedimentation is 0.5 hours; The sludge concentration after inoculation of the anaerobic ammonium oxidation tank is 4000-8000 mg / L, the HRT is 24-72h; the reaction temperature is 28-35℃, the dissolved oxygen is 0.02-0.5 mg / L, and the pH is 7.0-8.

0.

9. The method for treating and recycling high-concentration food waste liquid according to claim 4, characterized in that: The dissolved oxygen in the anoxic section of the AO tank is 0.02-0.5 mg / L, the dissolved oxygen in the aerobic section is 1.0-3.0 mg / L, and the total HRT is 8-12 hours; After treatment in the aerobic section, the wastewater is returned to the anoxic section for repeated treatment, with a reflux ratio of 150 to 300%.

10. The method for treating and recycling high-concentration restaurant biogas slurry according to any one of claims 1 to 9, characterized in that: The high-concentration restaurant biogas slurry has a COD of 10,000-30,000 mg / L, a TN of 2,000-4,000 mg / L, ammonia nitrogen of 2,000-3,500 mg / L, a TP of 100-500 mg / L, a pH of 7.5-9.0, and a suspended solids of 3-12 g / L. In the treated wastewater: COD≤500mg / L, BOD5≤350mg / L, NH4 + ≤45mg / L, TN≤70mg / L, TP≤8mg / L.

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