A method of acid resistant two-phase anaerobic digestion

Abstract

The present application relates to the technical field of organic waste treatment, and particularly discloses a method for acid-resistant two-phase circulating anaerobic digestion, which comprises a two-phase circulating anaerobic digestion system mainly comprising sequentially connected acid-producing phase reactors, methane-producing phase reactors, solid-liquid separation units, side-flow ammonia stripping units, gas treatment and recycling units and circulating pipelines; the present application directly combines the side-flow ammonia stripping unit with the acid-producing phase reactor, realizes source control and resource utilization of ammonia nitrogen, rather than treating ammonia nitrogen in the methane-producing phase or effluent thereof, reuses hydrogen and carbon dioxide formed by desulfurization and partial decarburization of acid-producing phase biogas to synthesize hydrogen for the methane-producing phase, creates carbon-hydrogen circulation, cooperatively improves methane production and consumes by-product hydrogen, returns effluent of the methane-producing phase to the acid-producing phase, builds internal circulation of alkalinity and bacterial flora in the system, and enhances the buffering capacity and stability of the system.

Description

Technical Field

[0001] This invention relates to the field of organic waste treatment technology, specifically to a method for acid-resistant two-phase cyclic anaerobic digestion. Background Technology

[0002] Chicken manure, as a high-concentration organic waste, is efficiently recycled through anaerobic digestion. In a closed anaerobic environment, microorganisms decompose organic matter into biogas (mainly methane), enabling energy recovery for power generation or heating. Simultaneously, it significantly reduces organic matter, pathogens, and odor in the manure, lowering the risk of environmental pollution. The digested biogas residue and slurry are nutritionally stable and can be used as high-quality organic fertilizer, thus forming a green cycle of "waste-energy-fertilizer," offering both environmental and economic benefits.

[0003] However, traditional single-phase anaerobic digestion processes face significant challenges when treating chicken manure: ① Prone to acidification and collapse: Chicken manure is rich in easily degradable organic matter. Under high load conditions, the rate of hydrolysis and acid production is much higher than the rate of methanogenesis, which leads to the rapid accumulation of volatile fatty acids (VFA), a decrease in system pH, and acidification. This inhibits the activity of methanogenic bacteria, reduces system treatment efficiency, and may even cause system collapse. ② Ammonia nitrogen inhibition: Chicken manure has a high nitrogen content, and after degradation, it produces high concentrations of ammonia nitrogen (mainly NH4+ and NH3), which has significant toxicity to methanogens, further limiting the system's treatment capacity and stability; ③ Poor biogas quality: Instability of the system and the presence of sulfides result in low CH4 content and high H2S content in the biogas produced, resulting in low utilization value.

[0004] Although existing technologies employ two-phase anaerobic digestion to separate acid-producing and methanogenic processes, problems still exist, such as the direct entry of ammonia nitrogen from the acid-producing phase into the methanogenic phase causing inhibition, insufficient utilization of matter and energy within the system, and limited buffering capacity against high-load shocks. Summary of the Invention

[0005] The purpose of this invention is to provide an acid-resistant two-phase circulating anaerobic digestion method that can effectively prevent system acidification, reduce ammonia nitrogen inhibition, and improve biogas yield and quality, thereby achieving ammonia resource recovery.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for acid-resistant two-phase circulating anaerobic digestion, the method comprising a two-phase circulating anaerobic digestion system, the two-phase circulating anaerobic digestion system mainly comprising, in sequence, an acid-producing phase reactor, a methanogenic phase reactor, a solid-liquid separation unit, a side-flow ammonia stripping unit, a gas treatment and reuse unit, and a circulation pipeline.

[0007] Preferably, the acid-producing phase reactor is a fully mixed stirred tank reactor, and the interior of the acid-producing phase reactor is equipped with a first stirrer and a first heating coil.

[0008] Preferably, the methanogenic phase reactor is a CSTR reactor, and the methanogenic phase reactor is equipped with a second stirrer and a second heating coil inside.

[0009] Preferably, the screw extruder of the solid-liquid separation unit receives the methane-producing phase output.

[0010] Preferably, the side-flow ammonia stripping unit includes a stripping tower and an acid absorption tower, and the feed end of the stripping tower is connected to the bottom of the acid-producing reactor through a side-flow pipeline.

[0011] Preferably, the gas treatment and reuse unit includes an acid-producing gas holder connected to the top of the acid-producing phase reactor, a methanogenic gas holder connected to the top of the methanogenic phase reactor, and an H2S treatment device connected to the outlet of the acid-producing gas holder. The gas treatment and reuse unit also includes a CO2 absorption tower and a syngas reuse pipeline, wherein the syngas reuse pipeline is connected to the outlet of the CO2 absorption tower and the bottom of the methanogenic phase reactor.

[0012] Preferably, the circulation pipeline includes a return pipe that returns the effluent from the methanogenic phase reactor to the feed end of the acidogenic phase reactor.

[0013] The method using the above-mentioned two-phase circulating anaerobic digestion system includes the following steps: Step a: Hydrolyze and acidify the chicken manure slurry in an acid-producing reactor; Step b: A portion of the fermentation broth produced in step a is directed to the side-flow ammonia stripping unit for stripping, ammonia removal, and resource recovery; Step c: The biogas produced in the acid-producing phase is introduced to the gas treatment and reuse unit for desulfurization and partial decarbonization to enrich hydrogen, and the resulting syngas is sent back to the methanogenic phase reactor. Step d: Recirculate a portion of the effluent from the methanogenic reactor back to the feed end of the acidogenic reactor.

[0014] Preferably, in step b, the stripping gas used for stripping and deammoniation is biogas produced by the acid-producing phase.

[0015] Preferably, in step c, the molar ratio of H2 to CO2 in the syngas fed back to the methanogenic reactor is controlled between 3:1 and 5:1.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves source control and resource utilization of ammonia nitrogen by directly combining the side-flow ammonia stripping unit with the acidogenic phase reactor, instead of treating it in the methanogenic phase or its effluent. The hydrogen and carbon dioxide syngas formed from the desulfurization and partial decarbonization of the biogas in the acidogenic phase are recycled to the methanogenic phase, creating a hydrocarbon cycle. This synergistically increases methane production and consumes by-product hydrogen. By recirculating the effluent from the methanogenic phase to the acidogenic phase, an internal cycle of alkalinity and microbial community is constructed within the system, enhancing the system's buffering capacity and stability. Furthermore, the system is systematically integrated, forming a multi-layered synergistic anti-acidification and efficiency-enhancing mechanism for the high-concentration anaerobic digestion of chicken manure. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the two-phase circulating anaerobic digestion system in this invention.

[0018] In the diagram: 1. Acid-producing reactor; 1a. First stirrer; 2. Methan-producing reactor; 2a. Second stirrer; 4a. Stripping tower; 4b. Acid absorption tower; 5a. Acid-producing gas holder; 5b. Methan-producing gas holder; 5c. H2S treatment device; 5d. CO2 absorption tower. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1 As shown, an acid-resistant two-phase circulating anaerobic digestion method is disclosed. The method includes a two-phase circulating anaerobic digestion system, which mainly includes an acid-producing phase reactor 1, a methanogenic phase reactor 2, a solid-liquid separation unit, a side-flow ammonia stripping unit, a gas treatment and reuse unit, and a circulation pipeline connected in sequence. The acid-producing phase reactor 1 is a completely mixed stirred tank reactor (CSTR). The acid-producing phase reactor 1 is equipped with a first stirrer 1a and a first heating coil inside, which are used to realize the hydrolysis and acidification of chicken manure slurry.

[0021] The methanogenic phase reactor 2 is a CSTR reactor, and the methanogenic phase reactor 2 is equipped with a second stirrer 2a and a second heating coil.

[0022] The screw extruder in the solid-liquid separation unit receives the methane-producing phase discharge and performs solid-liquid separation. The side-flow ammonia stripping unit includes a stripping tower 4a and an acid absorption tower 4b. The feed end of the stripping tower 4a is connected to the bottom of the acid-producing phase reactor 1 through a side-flow pipeline, and is used to strip a portion of the acid-producing phase fermentation broth of ammonia. The gas treatment and reuse unit includes an acid-producing phase gas tank 5a connected to the top of the acid-producing phase reactor 1, a methanogenic phase gas tank 5b connected to the top of the methanogenic phase reactor, an H2S treatment device 5c connected to the outlet of the acid-producing phase gas tank 5a, a CO2 absorption tower 5d containing alkaline solution, and a syngas reuse pipeline connecting the outlet of the CO2 absorption tower 5d to the bottom of the methanogenic phase reactor. The circulation pipeline includes a reflux pipe that returns the effluent from the methanogenic phase reactor to the feed end of the acid-producing phase reactor 1.

[0023] The method for acid-resistant two-phase circulating anaerobic digestion uses the above-mentioned two-phase circulating anaerobic digestion system, and the method includes the following steps: Step a: Hydrolyze and acidify the chicken manure slurry in the acid-producing reactor 1; Ammonia stripping in the acid-producing phase (source control): A portion of the fermentation broth is drawn from the bottom of the acid-producing phase reactor 1 through a side-flow pipeline and enters the side-flow ammonia stripping unit. In the stripping tower 4a, the fermentation broth is heated to 40-60℃ and biogas produced by the acid-producing phase is introduced for aeration and stripping, causing free ammonia (NH3) to escape. The escaped ammonia-containing gas enters the acid absorption tower 4b and is absorbed by the sulfuric acid solution to generate ammonium sulfate fertilizer. The fermentation broth after ammonia stripping is returned to the acid-producing phase reactor 1, removing a large amount of ammonia nitrogen before it enters the methanogenic phase, thus reducing inhibition at the source. Step b: A portion of the fermentation broth produced in step a is directed to the side-flow ammonia stripping unit for stripping, ammonia removal, and resource recovery. The stripping gas used for ammonia removal is biogas produced by the acid-producing phase. Syngas Recycling Enhanced Methanogenesis: Biogas (rich in H2 and CO2) produced in the acidic phase enters the gas treatment and recycling unit. First, most of the H2S is removed by the H2S treatment device. Then, it is passed into the CO2 absorption tower for 5 days to selectively remove some of the CO2 with alkaline solution, enriching the hydrogen. The enriched H2 is mixed with the remaining gas in a certain proportion to form syngas. This syngas is then passed from the bottom into the methanogenic phase reactor through the syngas recycling pipeline. This syngas can be used as a substrate for hydrogen-nutritional methanogenic bacteria and directly converted into CH4, significantly improving the total methane production and system energy efficiency. Step c: The biogas produced in the acid-producing phase is introduced to the gas treatment and reuse unit for desulfurization and partial decarbonization to enrich hydrogen, and the resulting syngas is returned to the methanogenic reactor 2. The molar ratio of H2 to CO2 in the syngas returned to the methanogenic reactor 2 is controlled between 3:1 and 5:1. System internal circulation stabilization: The effluent from the methanogenic phase reactor is returned to the feed end of the acidogenic phase reactor 1 through the return pipe. This effluent has high pH and high alkalinity, which can effectively neutralize the acidity of the acidogenic phase and provide a natural pH buffer. At the same time, the methanogenic bacteria contained in the return liquid can replenish the bacterial species. This circulation establishes the material and microbial balance inside the system and enhances the overall stability. Step d: Recirculate a portion of the effluent from the methanogenic reactor 2 back to the feed end of the acidogenic reactor 1; Zoned treatment and optimization: The acid-producing phase is operated at a shorter hydraulic retention time (HRT, such as 3-5 days) and at a medium or high temperature (such as 35-55℃) to promote hydrolysis and acidification, while the methanogenic phase is operated at a longer HRT (such as 15-30 days) and at a medium temperature (such as 35±2℃) to ensure methanogenic efficiency.

[0024] Example: Fresh chicken manure from a large-scale chicken farm, with a total saturation (TS) of approximately 25%; 1. System Start-up and Operation: Mix chicken manure and water in a certain proportion to form a slurry with a TS of about 10%, and pump it into the acid-producing phase reactor 1. The effective volume of the acid-producing phase reactor 1 is 200L, which is a CSTR type. The temperature is controlled at 55℃, and the HRT is 4 days. Continuous stirring is carried out. The acid-producing phase acidified liquid is pumped into the methanogenic phase reactor, which has an effective volume of 800L, is a CSTR type, and the temperature is controlled at 37℃ with an HRT of 20 days. 2. Side-flow ammonia stripping operation: Fermentation broth is drawn from the bottom of acid-producing reactor 1 through a side-flow pipeline at a flow rate of 10% of the total feed and pumped into stripping tower 4a. The biogas produced by the acid-producing phase is introduced from the bottom of stripping tower 4a as stripping gas. The ammonia-containing gas stripped is introduced into acid absorption tower 4b containing 10% dilute sulfuric acid to generate ammonium sulfate solution. The deammoniated fermentation broth is returned to acid-producing reactor 1. 3. Syngas reuse operation: The biogas from the acid-producing phase first passes through a desulfurization tower 5c to remove H2S. Then, the gas enters a CO2 absorption tower 5d, which contains 30% NaOH solution to remove approximately 50% of the CO2, increasing the H2 content in the gas. The hydrogen-rich gas is mixed with the remaining gas (adjusting the H2 / CO2 molar ratio to approximately 4:1) and introduced from the bottom into methanogenic reactor 2 through a syngas reuse pipeline. 3. Internal circulation operation: The effluent from the methanogenic reactor is periodically pumped back to the feed end of the acidogenic reactor 1 through the reflux pipe and mixed with fresh chicken manure slurry.

[0025] Results: Under these conditions, the system operated stably for two months without acidification. The average methane yield was 35% higher than that of systems without this process under the same conditions. The average methane content in the biogas was 70%, and the ammonia nitrogen concentration in the effluent remained stable below 1500 mg / L, indicating smooth system operation.

[0026] 1. Significantly improved system stability: By controlling ammonia nitrogen at the source and supplementing alkalinity through internal circulation, the accumulation of VFA and sudden drop in pH caused by high load are effectively resisted, fundamentally avoiding system acidification and collapse; 2. Significantly improved energy recovery efficiency: Syngas reuse maximizes the utilization of hydrocarbon elements in the raw materials. Small-scale test data show that when the fermentation concentration is 13%, the CH4 content in biogas remains stable at over 70%. 3. High degree of resource utilization: The pollutant ammonia nitrogen was successfully recovered in the form of ammonium sulfate, realizing the resource utilization of waste; at the same time, the value of high-quality biogas and biogas fertilizer was enhanced. 4. Reduced operating costs: The internal circulation of the system reduces the dependence on the addition of external alkali agents, thereby reducing the cost of chemical consumption.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for acid-resistant two-phase circulating anaerobic digestion, the method comprising a two-phase circulating anaerobic digestion system, characterized in that: The two-phase circulating anaerobic digestion system mainly includes an acid-producing phase reactor (1), a methanogenic phase reactor (2), a solid-liquid separation unit, a side-flow ammonia stripping unit, a gas treatment and reuse unit, and a circulation pipeline connected in sequence.

2. The method for acid-resistant two-phase cyclic anaerobic digestion according to claim 1, characterized in that: The acid-producing reactor (1) is a fully mixed stirred tank reactor, and the interior of the acid-producing reactor (1) is equipped with a first stirrer (1a) and a first heating coil.

3. The method for acid-resistant two-phase cyclic anaerobic digestion according to claim 1, characterized in that: The methanogenic phase reactor (2) is a CSTR reactor, and the methanogenic phase reactor (2) is equipped with a second stirrer (2a) and a second heating coil.

4. The method for acid-resistant two-phase cyclic anaerobic digestion according to claim 1, characterized in that: The solid-liquid separation unit's screw extruder receives the methane-producing phase as output.

5. The method for acid-resistant two-phase cyclic anaerobic digestion according to claim 1, characterized in that: The side-flow ammonia stripping unit includes a stripping tower (4a) and an acid absorption tower (4b). The feed end of the stripping tower (4a) is connected to the bottom of the acid-producing reactor (1) through a side-flow pipeline.

6. The method for acid-resistant two-phase cyclic anaerobic digestion according to claim 1, characterized in that: The gas treatment and reuse unit includes an acid-producing gas tank (5a) connected to the top of the acid-producing reactor (1), a methanogenic gas tank (5b) connected to the top of the methanogenic reactor (2), and an H2S treatment device (5c) connected to the outlet of the acid-producing gas tank (5a). The gas treatment and reuse unit also includes a CO2 absorption tower (5d) and a syngas reuse pipeline. The syngas reuse pipeline is connected to the outlet of the CO2 absorption tower (5d) and the bottom of the methanogenic reactor (2).

7. The method for acid-resistant two-phase cyclic anaerobic digestion according to claim 1, characterized in that: The circulation pipeline includes a return pipe that returns the effluent from the methanogenic reactor (2) to the feed end of the acidogenic reactor (1).

8. A method for acid-resistant two-phase circulating anaerobic digestion according to any one of claims 1-7, employing the above-mentioned two-phase circulating anaerobic digestion system, characterized in that: The method includes the following steps: Step a: Hydrolyze and acidify the chicken manure slurry in the acid-producing reactor (1); Step b: A portion of the fermentation broth produced in step a is directed to the side-flow ammonia stripping unit for stripping, ammonia removal, and resource recovery; Step c: The biogas produced in the acid-producing phase is introduced to the gas treatment and reuse unit for desulfurization and partial decarbonization to enrich hydrogen, and the resulting syngas is sent back to the methanogenic phase reactor (2). Step d: Return a portion of the effluent from the methanogenic reactor (2) to the feed end of the acidogenic reactor (1).

9. The method for acid-resistant two-phase cyclic anaerobic digestion according to claim 8, characterized in that: In step b, the stripping gas used for stripping and deammoniation is biogas produced by the acid-producing phase.

10. The method for acid-resistant two-phase cyclic anaerobic digestion according to claim 8, characterized in that: In step c, the molar ratio of H2 to CO2 in the syngas fed back to the methanogenic reactor (2) is controlled between 3:1 and 5:1.

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