High-solid chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammonification and membrane distillation

Abstract

The invention discloses a high-solid-content chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammonification and membrane distillation, and belongs to the technical field of solid waste recycling. The process mainly comprises the following steps: carrying out at least two-stage anaerobic ammoniation pretreatment on high-solid chicken manure to efficiently convert organic nitrogen into ammonia nitrogen; after solid-liquid separation, recovering ammonia from the hydrolysate rich in ammonia nitrogen by adopting a non-contact membrane distillation device under strong alkali and high temperature conditions to obtain an ammonium-rich absorption liquid; and finally, mixing the deaminated liquid with the solid residues, and carrying out anaerobic digestion to produce methane. According to the non-contact membrane distillation device, feed liquid is not in direct contact with a hydrophobic membrane through an air gap structure, so that the problems of membrane pollution and wetting during treatment of complex chicken manure hydrolysate are fundamentally solved. According to the invention, efficient and stable recovery of ammonia nitrogen is realized, the carbon-nitrogen ratio of anaerobic digestion feed is accurately regulated and controlled through process coupling, the methane yield is synchronously improved, and an efficient and stable integrated solution is provided for full-quantitative resource treatment of high-solid chicken manure.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, specifically to a high-solids chicken manure nitrogen and carbon co-recovery process based on anaerobic ammoniation and membrane distillation. Background Technology

[0002] Resource-based treatment of livestock and poultry manure is a major issue in environmental engineering and sustainable agricultural development. Chicken manure, in particular, possesses significant resource potential due to its high organic matter and nutrient content, but it also presents serious treatment challenges. Chicken manure, especially high-solids (TS>15%), has a significantly higher nitrogen content than other livestock and poultry manures, with a carbon-to-nitrogen ratio typically between 6:1 and 12:1, far below the optimal carbon-to-nitrogen ratio range (20:1-30:1) required for anaerobic digestion. This characteristic leads to rapid hydrolysis of nitrogenous organic matter such as protein and urea in direct anaerobic digestion, resulting in a large accumulation of ammonia nitrogen (in the form of NH4⁺ and free NH3) in the system. When the ammonia nitrogen concentration exceeds the microbial tolerance threshold, a severe "ammonia inhibition" effect occurs, inhibiting the activity of methanogens, in particular, causing digestive system instability, decreased biogas production, or even digestion failure. Therefore, efficiently relieving ammonia inhibition and recovering nitrogen resources is key to improving the efficiency of anaerobic digestion of chicken manure.

[0003] To alleviate ammonia inhibition, existing technologies mainly focus on pretreatment before anaerobic digestion to separate ammonia nitrogen. Initially, air or steam stripping was the mainstream technology, which strips ammonia from the liquid phase by adjusting the pH and aerating large amounts of gas. While simple, this method is energy-intensive, sensitive to operating conditions, and exhibits significant fluctuations in ammonia recovery efficiency. To seek a more efficient and compact solution, membrane technology has been introduced into this field. For example, Chinese patent CN113754218A discloses a "method for improving methanogenesis from anaerobic digestion of livestock manure by recovering ammonia using hollow fiber membranes," which involves first performing short-term dry anaerobic pre-hydrolysis of livestock manure to dissolve ammonia nitrogen, followed by ammonia recovery using a hollow fiber membrane contactor. Compared to air stripping, membrane absorption offers improvements in mass transfer efficiency and equipment compactness.

[0004] However, both traditional air stripping and membrane absorption methods face fundamental challenges when processing extremely complex real-world materials such as high-solids chicken manure hydrolysate. Chicken manure hydrolysate is a multiphase, highly concentrated complex system containing, in addition to high concentrations of ammonia nitrogen, a large amount of suspended solids, colloids, proteins, polysaccharides, oils, and inorganic salts (such as calcium, magnesium, and phosphates). In contact membrane processes such as hollow fiber membranes, the feed solution is in direct contact with the membrane surface. These contaminants readily undergo irreversible adsorption, deposition, and scaling on the membrane surface and within the pores, leading to a rapid decline in membrane flux and a dramatic increase in mass transfer resistance. More seriously, hydrophilic contaminants can cause localized wetting of hydrophobic membranes, resulting in membrane pore leakage and permanent failure of separation performance. This makes existing membrane technology devices extremely short-lived when processing such materials, requiring frequent offline chemical cleaning, resulting in poor economic efficiency and long-term operational stability, significantly limiting their industrial application prospects.

[0005] Therefore, existing technologies face a significant dilemma: on the one hand, traditional ammonia recovery technologies, such as air stripping, suffer from efficiency and energy consumption bottlenecks when processing high-solids chicken manure; on the other hand, membrane distillation technology, despite its potential for high-efficiency separation, is difficult to apply practically due to its inability to resist contamination from complex materials. Developing a novel process that can avoid membrane fouling mechanisms at the source, maintain high ammonia recovery efficiency, and adapt to the long-term stable operation of complex high-solids chicken manure systems has become a core technical challenge that urgently needs to be overcome in this field. This invention addresses this gap by providing an innovative solution.

[0006] Invention Patent Content (a) The problems to be solved by this invention are: (1) When the carbon-nitrogen ratio of high-solids chicken manure is too low, the organic nitrogen is rapidly hydrolyzed during anaerobic digestion, resulting in a large accumulation of ammonia nitrogen, which strongly inhibits methanogenic bacteria, causing system instability and low methane yield; (2) Existing efficient ammonia recovery technology faces insurmountable membrane fouling and membrane wetting problems when treating high-solids chicken manure hydrolysate with extremely complex composition, resulting in the problem that although the technology is "efficient", it cannot "operate stably".

[0007] (II) Technical Solution A high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation, characterized in that the method is as follows: S1. Multi-stage anaerobic ammoniation pretreatment: High-solids chicken manure with a solids content of 15-25% is subjected to at least two stages of sequential batch anaerobic ammoniation reaction to convert organic nitrogen into ammonia nitrogen and dissolve it to obtain a hydrolyzed mixture; S2. Solid-liquid separation: The hydrolysate mixture is subjected to solid-liquid separation to obtain a hydrolysate rich in ammonia nitrogen and a solid residue containing recalcitrant organic matter; S3. Ammonia recovery by membrane distillation: After adjusting the pH of the hydrolysate to 11-13 and raising the temperature to 50-60℃, the hydrolysate is sent to a non-contact membrane distillation device for ammonia recovery, resulting in an ammonium-rich absorbent and ammonia-free liquid. S4. Anaerobic digestion for methane production: The deaminated liquid is mixed with the solid residue and subjected to anaerobic digestion to recover methane.

[0008] Furthermore, in step S1, two-stage anaerobic ammoniation is performed, wherein the temperature of the second-stage reaction is 35°C and the initial pH is 7; the multi-stage anaerobic ammoniation pretreatment enables the cumulative ammonia nitrogen conversion rate in chicken manure to reach more than 70%.

[0009] Further, in step S3, the hydraulic residence time of the hydrolysate in the non-contact membrane distillation device is 55-100 min; after membrane distillation treatment, the chemical oxygen demand concentration of the deammoniated liquid is increased by more than 15% compared with the influent, and the sulfide removal rate exceeds 85%; in the non-contact membrane distillation device, an air gap is provided between the hydrophobic membrane and the feed hydrolysate to prevent direct contact between the two, and the height of the air gap is 5-20 mm.

[0010] Furthermore, in step S4, the carbon-to-nitrogen ratio of the mixture entering the anaerobic digestion is adjusted to be in the range of 16.5-25.8.

[0011] The beneficial effects of this invention patent are as follows: (1) High and stable ammonia recovery efficiency: Through the creative coupling of "multi-stage anaerobic ammoniation" and "non-contact membrane distillation", the ammonia dissolution is maximized first (cumulative conversion rate > 70%), and then non-contact membrane distillation is used to efficiently and stably recover ammonia from complex hydrolysate. The ammonia recovery rate can be stabilized at over 93.7%, and the device can operate for a long time without serious membrane fouling. (2) Effectively solves the membrane fouling problem: In response to the global problem of easy membrane fouling by high-solids chicken manure hydrolysate, this invention specifically adopts non-contact membrane distillation. By physically isolating the feed liquid and the membrane through the air gap, the deposition and scaling of organic matter, salts, etc. on the membrane surface are fundamentally prevented. This is the key to the continuous operation of this process. (3) Synergistic resource utilization effect: Carbon source quality improvement: The thermal effect and pH environment of the membrane distillation process promote the further hydrolysis of some recalcitrant organic matter in the hydrolysate, increasing the chemical oxygen demand (COD) of the effluent by about 18.7%, providing more high-quality carbon sources for subsequent anaerobic digestion. Toxic substance removal: The membrane distillation process simultaneously removes most of the volatile sulfur compounds (removal rate >86%), significantly reducing their potential inhibition on methanogens. Precise C / N ratio control: By controlling the ammonia recovery rate, the C / N ratio of the anaerobic digestion feed can be directly adjusted to the optimal range, solving the core contradiction of the low C / N ratio of chicken manure raw materials. (4) Significant environmental and economic benefits: This integrated process not only recovers high-purity ammonia resources (which can be made into ammonium salt fertilizer), but also significantly improves the methane yield by relieving ammonia inhibition and optimizing the substrate. Life cycle assessment shows that compared with traditional anaerobic fermentation, the total environmental impact of this process is reduced by about 17.5%, achieving a balance between environmental benefits and resource recovery benefits. Attached Figure Description

[0012] To more clearly illustrate the specific embodiments of this invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0013] Figure 1 A schematic diagram of the method flow provided in the embodiments of the present invention. Figure 2 Contact angle of PTFE membranes in (a) non-contact and (b) contact membrane distillation reactors at the end of the membrane distillation reaction; Figure 3 FTIR spectra of membranes in (a) non-contact and (b) contact membrane distillation reactors at the end of the membrane distillation reaction; Figure 4 The effect of anaerobic ammoniation stage on ammonia production from anaerobic ammoniation of high-solids chicken manure. Detailed Implementation

[0014] The technical solution of this invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0015] like Figures 1-3 As shown, one embodiment of this invention patent provides a high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation.

[0016] Example 1: Optimal Process Implementation Step S1, Multi-stage Anaerobic Ammoniation Pretreatment: 40 kg of high-solids chicken manure with a total solids content (TS) of 20% (elemental analysis: C 24.54%, N 4.33%, C / N = 5.7) was placed in a primary anaerobic ammoniation reactor. Deionized water was added to adjust the system, and the reaction was carried out at 35℃ and 120 rpm for 4 days. Subsequently, solid-liquid separation was performed, and all the separated solid residue was transferred to a secondary anaerobic ammoniation reactor. Water was added to maintain the TS at 20%, and the reaction continued for 4 days at 35℃ and an initial pH of 7.0 (adjusted with dilute NaOH solution). Monitoring showed that after two stages of anaerobic ammoniation, the cumulative ammonia nitrogen conversion rate reached 72.03%, and the acetic acid concentration in the liquid phase reached 15137.8 mg / L at the end of the second stage reaction.

[0017] Step S2, solid-liquid separation: After the completion of the secondary anaerobic ammoniation, the entire mixture is centrifuged at 8000 rpm for 20 minutes to separate the hydrolysate and solid residue.

[0018] Step S3, Ammonia Recovery via Membrane Distillation: The resulting hydrolysate was adjusted to pH 12.0 with 6 mol / L NaOH solution and heated to 55°C. It was then pumped into a non-contact membrane distillation unit at a flow rate of 0.74 mL / min. The feed chamber air gap height was 12.8 mm, and the membrane was a hydrophobic PTFE membrane. A 1 mol / L sulfuric acid solution was circulated in the absorption chamber. The hydraulic retention time (HRT) was controlled at 100 minutes. The system was run continuously for 36 hours.

[0019] Results: Ammonia recovery remained stable at 93.7%. Membrane characterization: Scanning electron microscopy (SEM) showed a clean membrane surface with no fouling; contact angle measurements indicated good hydrophobicity (no significant difference from a new membrane). After membrane distillation, the COD concentration of the effluent increased by approximately 18.7% compared to the influent, with volatile fatty acid and protein content increasing by 12.4% and 3.3%, respectively; sulfide concentration decreased from approximately 110 mg / L initially to 15.5 mg / L, achieving a removal rate of 86%. The C / N ratio of the effluent increased to 361.6.

[0020] Step S4: Anaerobic Digestion for Methanogenesis: The deammoniation effluent obtained in Step S3 is mixed with the solid residue obtained in Step S2. The C / N ratio of the mixture is precisely adjusted to 20.0 by adding a small amount of untreated chicken manure hydrolysate. The mixture is then fed into a mesophilic (35°C) anaerobic digester for methanogenesis experiments. Compared to the control group that directly treated raw chicken manure, the pretreated material from this process showed faster methanogenesis startup and an approximately 35% increase in cumulative methane production.

[0021] Comparative Example 1: The hydrolysate was prepared using the exact same raw materials and methods as in steps S1 and S2 of Example 1. In step S3, a membrane distillation apparatus with identical conditions except for "no air gap structure and direct contact between the feed liquid and the membrane" was used for processing, and the operating parameters (pH, temperature, HRT) were kept consistent with those of Example 1.

[0022] During the initial operation (within 2 hours), the ammonia recovery rate was approximately 65.5%, but the efficiency subsequently declined continuously, and the system essentially failed after 18 hours of operation. Shutdown inspection revealed a dense fouling layer on the PTFE membrane surface, with the contact angle decreasing from an initial 139° to approximately 50-63°, indicating severe membrane wetting. Fourier transform infrared spectroscopy (FTIR) detected characteristic absorption peaks of organic matter such as proteins and carbohydrates on the fouled membrane surface. This indicates that contact membrane distillation is impractical for high-solids chicken manure hydrolysate due to its inability to overcome membrane fouling, thus highlighting the necessity and ingenuity of the non-contact structure employed in this invention.

[0023] Comparative Example 2: Using the same total amount of chicken manure as in Example 1, a single-stage anaerobic ammoniation reaction was carried out at 35°C without adjusting the initial pH, for the same total time as the sum of the two-stage reactions in Example 1. After the reaction, the cumulative ammonia nitrogen conversion rate was only 46.3%, and the acetic acid concentration in the hydrolysate was approximately 9800 mg / L, significantly lower than the results of the two-stage process in Example 1. Although this hydrolysate could be subsequently treated with the non-contact membrane distillation method of this invention, the total ammonia recovery was limited due to the low initial dissolution. This comparison shows that the "two-stage anaerobic ammoniation" of this invention is not simply a matter of extending the reaction time; through specific cascade conditions (such as adjusting the initial pH in the second stage), it significantly promotes favorable succession of the microbial community, thereby producing a synergistic effect of "1+1>2" in terms of ammonia conversion efficiency and simultaneous carbon source (acetic acid) production, which cannot be achieved by a single-stage process.

[0024] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation, characterized in that, The method is as follows: S1. Multi-stage anaerobic ammoniation pretreatment: High-solids chicken manure with a solids content of 15-25% is subjected to at least two stages of sequential batch anaerobic ammoniation reaction to convert organic nitrogen into ammonia nitrogen and dissolve it to obtain a hydrolyzed mixture; S2. Solid-liquid separation: The hydrolysate mixture is subjected to solid-liquid separation to obtain a hydrolysate rich in ammonia nitrogen and a solid residue containing recalcitrant organic matter; S3. Ammonia recovery by membrane distillation: After adjusting the pH of the hydrolysate to 11-13 and raising the temperature to 50-60℃, the hydrolysate is sent to a non-contact membrane distillation device for ammonia recovery, resulting in an ammonium-rich absorbent and ammonia-free liquid. S4. Anaerobic digestion for methane production: The deaminated liquid is mixed with the solid residue and subjected to anaerobic digestion to recover methane.

2. The high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation according to claim 1, characterized in that, In step S1, two-stage anaerobic ammoniation is carried out, with the second-stage reaction occurring at a temperature of 35°C and an initial pH of 7.

3. A high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation according to claim 1 or 2, characterized in that, In step S1, the multi-stage anaerobic ammoniation pretreatment enables the cumulative ammonia nitrogen conversion rate in chicken manure to reach over 70%.

4. The high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation according to claim 1, characterized in that, In step S3, the hydraulic residence time of the hydrolysate in the non-contact membrane distillation device is 55-100 min.

5. The high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation according to claim 1, characterized in that, In step S3, after membrane distillation, the chemical oxygen demand concentration of the deammoniated liquid is increased by more than 15% compared with the influent, and the sulfide removal rate exceeds 85%.

6. The high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation according to claim 1, characterized in that, In step S3, in the non-contact membrane distillation device, an air gap is provided between the hydrophobic membrane and the feed hydrolysate to prevent direct contact between the two, and the height of the air gap is 5-20mm.

7. The high-solids chicken manure nitrogen and carbon synergistic recovery process based on anaerobic ammoniation and membrane distillation according to claim 1, characterized in that, In step S4, the carbon-to-nitrogen ratio of the mixture entering the anaerobic digestion is adjusted to be in the range of 16.5-25.8.

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