A deep dehydration method of digestion solution based on iron / sulfur synergistic mixed bioleaching

Abstract

The application discloses a kind of based on iron / sulfur synergistic mixed biological leaching digestion liquid deep dehydration method, comprising the following steps: to livestock and poultry manure anaerobic digestion liquid is added Fe 2+ And elemental sulfur, inoculate acidophilic ferrous Thiobacillus and acidophilic Thiobacillus, obtain biological leaching liquid, carries out biological leaching reaction, after reaction, carries out mechanical dehydration;In the biological leaching liquid, the concentration of Fe 2+ 1.0~2.0 g / L;The concentration of elemental sulfur is 1.0~2.0 g / L.The application utilizes acidophilic ferrous Thiobacillus and acidophilic Thiobacillus synergistic effect, by regulating iron, sulfur input and ratio, make digestion liquid dehydration process deviate ROS mediated pathway, to realize higher efficient dehydration effect with lower reagent consumption.

Description

Technical Field

[0001] This invention relates to the field of digestive fluid dehydration technology, and in particular to a method for deep dehydration of digestive fluids based on iron / sulfur synergistic mixed bioleaching. Background Technology

[0002] Anaerobic digestion is a crucial approach for the resource utilization of livestock and poultry manure, enabling the reduction, harmlessness, and energy conversion of organic waste. However, the digestate produced after anaerobic digestion still contains a large amount of suspended solids, colloidal particles, and extracellular polymeric substances (EPS), resulting in high water content and poor dehydration performance, which poses significant challenges to subsequent transportation, storage, and resource utilization. Therefore, improving the dehydration performance of digestate has become an important research direction in the field of organic waste treatment.

[0003] Currently, the mainstream technologies for dewatering digestate mainly include chemical flocculation, chemical conditioning, and iron / sulfur enhanced dewatering. Chemical flocculation typically uses flocculants such as ferric chloride, ferric sulfate, polyaluminum chloride, and polyacrylamide. Through charge neutralization, adsorption bridging, and netting / sweeping effects, it promotes particle aggregation into larger flocs, thereby improving mechanical dewatering efficiency. This technology has been widely applied in sludge and digestate treatment.

[0004] Building on this, researchers further proposed an iron / sulfur synergistic conditioning technique, which involves adding ferrous ions (Fe2+) to the digestive fluid. 2+ ) and elemental sulfur (S) 0 Iron ions hydrolyze sulfur-containing compounds to form iron-based flocs, while iron-sulfur oxidation promotes pollutant transformation. The Fe / S system can improve the dehydration performance of digestion fluid and promote EPS degradation to some extent. However, it still has the following drawbacks and shortcomings:

[0005] (1) Limited improvement in dehydration efficiency. Existing technologies mainly rely on iron-based flocculation to promote particle aggregation, but they are difficult to effectively release the bound water and internal water bound to a large amount of EPS in the digestion liquid, thus limiting the overall dehydration effect. The fundamental reason is that flocculation can only improve the aggregation state between particles and cannot effectively destroy the three-dimensional water-retaining network structure formed by EPS.

[0006] (2) The dosage of reagents is relatively large and the operating cost is relatively high. In order to obtain a better flocculation effect, it is usually necessary to add a high concentration of iron salts or other chemical reagents. As the dosage of reagents increases, not only does the treatment cost increase, but the burden of subsequent disposal of residual metal ions and chemical sludge also increases.

[0007] (3) It is difficult to effectively degrade proteins, polysaccharides and aromatic structures in EPS. The existing Fe / S system mainly plays a physicochemical flocculation role, and has limited ability to destroy the high molecular organic components in EPS, resulting in the continued existence of a large number of hydrophilic functional groups, and the difficulty in converting bound water into free water.

[0008] (4) It is impossible to simultaneously achieve low chemical consumption and high dehydration efficiency. Traditional technologies often rely on increasing the dosage of chemicals to achieve better flocculation effects, but increasing the dosage of chemicals does not simultaneously improve the efficiency of bound water release. Therefore, there is a problem of increased chemical consumption and limited dehydration benefits. Summary of the Invention

[0009] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the purpose of this invention is to provide a deep dehydration method for digestion fluid based on iron / sulfur synergistic mixed bioleaching. By utilizing the synergistic effect of Acidithiobacillus acidophilus (A. f.) and Thiobacillus acidophilus (At), and by controlling the input amount and ratio of iron and sulfur, the dehydration process of digestion fluid is biased towards the ROS-mediated pathway, so as to achieve a more efficient dehydration effect with a lower reagent dosage.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] This invention provides a method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching, comprising the following steps:

[0012] Add Fe to the anaerobic digestion liquid of livestock and poultry manure 2+ Elemental sulfur was inoculated with *Thiobacillus acidophilus* and *Thiobacillus acidophilus* to obtain a bioleaching solution, which was then subjected to a bioleaching reaction. After the reaction was completed, mechanical dehydration was performed.

[0013] In the bioleaching solution, Fe 2+ The concentration of is 1.0~2.0 g / L; the concentration of elemental sulfur is 1.0~2.0 g / L.

[0014] In some embodiments of the present invention, the bioleachment contains elemental sulfur and Fe. 2+ The mass ratio is 1:(1.0~1.5).

[0015] In some embodiments of the present invention, in the bioleaching solution, Fe 2+ The concentration of is 1.2~1.8 g / L; the concentration of elemental sulfur is 1.0~1.5 g / L.

[0016] In some embodiments of the present invention, the inoculation with *Thiobacillus acidophilus* and *Thiobacillus acidophilus* specifically includes:

[0017] A bacterial suspension containing *Thiobacillus acidophilus* and a bacterial suspension containing *Thiobacillus acidophilus* were added to the anaerobic digestion solution of livestock and poultry manure. The total volume ratio of the two bacterial suspensions to the volume of the anaerobic digestion solution of livestock and poultry manure was (8-12):100. The bacterial suspensions containing *Thiobacillus acidophilus* and *Thiobacillus acidophilus* had a cell count of 10-1. 8 Order of magnitude.

[0018] In some embodiments of the present invention, the volume ratio of the bacterial suspension containing *Thiobacillus acidophilus* to the bacterial suspension containing *Thiobacillus acidophilus* is 1:(0.8~1.2).

[0019] In some embodiments of the present invention, during the bioleaching reaction, *Thiobacillus acidophilus* promotes sulfur oxidation and acidification, while *Thiobacillus ferroacidus* promotes Fe... 2+ / Fe 3+ Cyclic and oxygen activation work together to generate reactive oxygen species; these reactive oxygen species oxidize and degrade proteins, polysaccharides, and aromatic structures in EPS.

[0020] In some embodiments of the present invention, the reactive oxygen species include superoxide anion, hydroxyl radical, singlet oxygen, and Fe(IV).

[0021] In some embodiments of the present invention, the initial pH of the bioleaching solution is 6.8 to 7.5, and the pH decreases to 2.0 to 3.0 during the reaction.

[0022] In some embodiments of the present invention, the bioleaching reaction takes 40 to 55 hours.

[0023] In some embodiments of the present invention, the temperature of the bioleaching reaction is 20~40°C.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] (1) The deep dehydration method of digestion fluid based on iron / sulfur synergistic mixed bioleaching of the present invention involves inoculating the Fe / S system with *Acidithiobacillus acidophilus* and *Thiobacillus acidophilus*, utilizing the synergistic effect of *Acidithiobacillus acidophilus* and *Thiobacillus acidophilus*, and regulating the generation of endogenous reactive oxygen species (ROS) through the iron / sulfur ratio. Under optimized conditions, ROS plays a dominant role in reducing SRF, achieving a more efficient dehydration effect with lower reagent dosage.

[0026] (2) The method for deep dehydration of digestive fluid based on iron / sulfur synergistic mixed bioleaching of the present invention, wherein the acidophilic thiobacillus promotes sulfur oxidation and acidification, and the acidophilic ferrothiobacillus promotes Fe 2+ / Fe 3+ Cyclic circulation and oxygen activation work together to generate superoxide anions (O2). •– ), hydroxyl radical (•OH), singlet oxygen (1 Active oxygen species such as O2 and Fe(IV) are used to oxidize and degrade proteins, polysaccharides, and aromatic structures in EPS, weakening their water-retention capacity. At the same time, combined with appropriate iron-based flocculation, bound water is released and deep dehydration is achieved.

[0027] (3) The deep dehydration method of digestion liquid based on iron / sulfur synergistic mixed bioleaching of the present invention significantly reduces SRF and water content, and improves solid-liquid separation performance.

[0028] (4) The deep dehydration method of digestion liquid based on iron / sulfur synergistic mixed bioleaching of the present invention improves the hydrophobicity of particles, reduces surface free energy, and promotes water removal.

[0029] (5) The deep dehydration method of digestion liquid based on iron / sulfur synergistic mixed bioleaching of the present invention has good environmental friendliness and engineering application potential.

[0030] (6) The deep dehydration method of digestion liquid based on iron / sulfur synergistic mixed bioleaching of the present invention can achieve excellent dehydration effect with a low amount of reagent added, thereby reducing operating costs. Attached Figure Description

[0031] Figure 1 The following are test results of anaerobic digestate from pig manure under low, optimized, conventional, and excessive Fe / S dosage conditions, based on the deep dehydration method of digestate from iron / sulfur synergistic mixed bioleaching, as an embodiment of the present invention: (a) Dehydration performance of anaerobic digestate from pig manure using the A.f. + A.t. treatment scheme under different Fe / S dosages; (b) Contribution of reactive oxygen species (ROS) and iron-based flocculation to the reduction of SRF; (c) Net accumulation of ROS in the A.f. + A.t. system under different Fe / S dosages.

[0032] Figure 2 The middle section shows different bioleaching treatment conditions. 1 O2(a), O2 •– Concentration distributions of (b), •OH (c), and Fe (IV) (d).

[0033] Figure 3 The relative contributions of reactive oxygen species (ROS) and iron-based flocculation to the bioleaching system are: (a) Af; (b) At; (c) Af + At.

[0034] Figure 4 In the table (a~f), the values ​​represent pH, oxygen reduction potential (ORP), dissolved oxygen concentration (DO), hydrogen peroxide concentration, and Fe under different bioleaching treatment conditions. 2+ Concentration, and Fe 3+ Concentration changes.

[0035] Figure 5 The distribution of protein (a) and polysaccharide (b) in three layers of EPS under different bioleaching treatments.

[0036] Figure 6 The variation of bound water content under different bioleaching treatment conditions.

[0037] Figure 7 The secondary structures of proteins in TB-EPS under different bioleaching treatments are shown.

[0038] Figure 8 For different bioleaching treatment conditions value.

[0039] Figure 9 The Fmax values ​​of the secondary phase components in the three EPS layers under different bioleaching treatment conditions are shown in (a) to (c), where (a) and (c) are the changes in Fmax corresponding to tryptophan, tyrosine and humic substances in S-EPS, LB-EPS and TB-EPS, respectively.

[0040] Figure 10 Van Krevelen diagrams showing the composition of organic matter molecules in TB-EPS under different bioleaching treatments; where (a) Af; (b) At; (c) Af + At. Detailed Implementation

[0041] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0042] In the following examples, the anaerobic digestion fluid of pig manure was obtained from an anaerobic digester at a pig farm in Guangdong, China. The received digestion fluid was immediately stored in a 4.0 °C cold storage before analysis and processing. The strains Af and At used were obtained from the Key Laboratory of Biometallurgy, Ministry of Education, Central South University, China. The strain culture steps were as follows: Af and At were cultured in modified 9K medium. The inoculum was prepared in 250 mL Erlenmeyer flasks and cultured with shaking at 30.0 ± 1.0 °C and 160 rpm until the cell density reached approximately 102. 8 cells / mL.

[0043] In the following examples, the dehydration performance of the digestate was characterized by SRF and water content. SRF was measured using a vacuum filtration apparatus (Daming PSWN066) at 0.05 MPa. Water content was measured after mechanical filtration using a high-pressure plate and frame filter press at 6 MPa. The SRF reduction rate was calculated as the ratio of the change in SRF to the initial SRF (original digestate).

[0044] In the following examples, EPS was extracted using a modified thermal extraction method and separated into three components: soluble EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS). Proteins and polysaccharides in each EPS component were quantified spectrophotometrically. Fluorescent components in EPS were identified using excitation-emission matrix fluorescence spectroscopy analysis with parallel factor analysis (PARAFAC) performed on a Hitachi F4000 fluorescence spectrometer. The secondary structure of proteins in EPS was analyzed using Fourier transform infrared spectroscopy combined with peak deconvolution and curve fitting. The molecular composition of EPS was further characterized using Fourier transform ion cyclotron resonance mass spectrometry.

[0045] In the following examples, the redox potential (ORP) and pH of the digestate were measured using an ORP and pH meter (OHAUS AB33PH). H2O2 concentration was determined by colorimetric titration. Surface charge and floc size were determined using a Zeta potential analyzer (Brookhaven ZetaPALS) and a laser diffraction particle size analyzer (Malvern Mastersizer 3000), respectively. Binding water content and digestate-water interaction were assessed using differential scanning calorimetry (PerkinElmer DSC8000) and contact angle analysis (Dataphysics OCA100). Interfacial free energy was calculated according to the method described by Liang et al. (Overlooked role of singlet oxygen in electrochemical processes for efficient sludge dewatering at neutral pH[J]. Water Research, 2026, 288: 124728.). The contents of free amino and carboxyl groups related to water-holding capacity were determined according to the method described by Wu et al. (Influential mechanism of wateroccurrence states of waste-activated sludge: potential linkage between water-holding capacity and molecular compositions of EPS[J]. Water Research, 2022,213: 118169.). Fe 2+ Fe 3+ The total Fe concentration was determined by the 1,10-phenanthroline colorimetric method.

[0046] Example 1

[0047] The deep dehydration method for digestion fluid based on iron / sulfur synergistic mixed bioleaching in this embodiment includes the following steps:

[0048] Adding different concentrations of Fe to the anaerobic digestion liquid of pig manure 2+ The sample was inoculated with elemental sulfur (see Table 1 below) and *Thiobacillus acidophilus* and *Thiobacillus acidophilus* (inoculation amount: 10% v / v, Af:At = 1:1) to obtain a bioleaching solution. The bioleaching reaction was carried out under the following initial conditions: pH 7.2 ± 0.1, 30.0 ± 1.0 °C. Mechanical dehydration was carried out after 48 hours of reaction.

[0049] Table 1 Fe from different groups 2+ and elemental sulfur concentration

[0050]

[0051] Under low, optimized, conventional, and excessive Fe / S dosage conditions, the dewatering performance of anaerobic digestion liquid from pig manure treated with the Af + At treatment scheme is as follows: Figure 1 As shown in (a). By Figure 1 As shown in (a), the mixed bioleaching method can effectively improve the dehydration performance of the digestate. Compared with the low, conventional and excessive Fe / S addition groups, the SRF value of the optimized group was further reduced by 10.4%, 7.5% and 50.8%, respectively, indicating that the dehydration effect was the best at the optimized Fe / S addition concentration.

[0052] This embodiment uses a quenching test to quantify the effect of reactive oxygen species (ROS) on iron-based flocculation. The results are as follows: Figure 1 As shown in Figure (b), at the optimized Fe / S addition level, ROS contributed 58.3% to the reduction in SRF value, significantly higher than the 41.7% contribution of iron-based flocculation. The dehydration effect of the low Fe / S group was comparable to that of the traditional Fe / S group, mainly due to its 52.0% ROS contribution compensating for the weaker iron-based flocculation effect. In contrast, the traditional Fe / S group mainly relied on iron-based flocculation for dehydration (contribution rate of 66.1%). However, when the Fe / S addition level was too high, although the contribution rate of flocculation increased to 70.5%, the dehydration effect decreased, indicating that under the condition of limited ROS oxidation, particle aggregation alone could not effectively release water. This difference indicates that although iron-based flocculation can improve particle aggregation and solid-liquid separation, it cannot completely release the water retained by EPS and adhesive biopolymers in pig manure digestate. Therefore, under the Af + At treatment conditions, the optimized Fe / S addition amount achieved better dehydration effect by maximizing the utilization of ROS-mediated oxidation reaction and maintaining sufficient flocculation effect.

[0053] Net ROS accumulation in the Af + At system under different Fe / S dosages is as follows: Figure 1 As shown in (c), consistent with the contribution analysis results, the optimized conditions produced the highest reactive oxygen species (ROS) accumulation within 48 hours within the tested Fe / S dosage range. The low Fe / S group exhibited the second highest ROS level, which compensated for its weaker iron-based flocculation effect and explained why its dewatering performance was close to that of the conventional Fe / S group. In contrast, although the conventional and excessive Fe / S dosages increased the Fe / S amount, they produced lower ROS levels, indicating that their dewatering process was mainly driven by flocculation rather than oxidation. Excess Fe... 2+ While sulfur can remove reactive oxygen species (ROS), excessive sulfur oxidation can exacerbate oxygen competition and disrupt the iron / sulfur / oxygen metabolic coupling. Therefore, by adjusting the iron / sulfur ratio, the dehydration process of the digestate can be biased towards a pathway driven by ROS or iron flocculation. The ROS-mediated pathway is more advantageous, thus achieving more efficient dehydration with lower reagent dosages.

[0054] Example 2

[0055] This embodiment sets up an experimental group and a control group:

[0056] Experimental group: Inoculated with 10% v / v Af, At, and Af + At respectively, with other conditions the same as the optimized group in Example 1.

[0057] control group (Fe) 2+ + S 0 ): No bacteria were inoculated, and all other conditions were the same as the optimized group of Example 1.

[0058] This embodiment uses a specific chemical probe to determine... 1 O2, O2 •– The concentrations of OH and Fe(IV) were determined, and the results are as follows: Figure 2 As shown, quantitative analysis indicates that all bioleaching systems can produce detectable oxide species, with the total ROS production capacity in the following order: Af+At > Af > At.

[0059] To clarify the relative contributions of reactive oxygen species (ROS) and iron-based flocculation in the bioleaching system, this embodiment employed a selective ROS scavenger for quenching experiments. The contribution analysis results are as follows: Figure 3 As shown, under A. f. + A. t. treatment conditions, ROS plays a dominant role in the dehydration process of the leachate.

[0060] Figure 4Tables (a) and (b) show the changes in pH and ORP under different bioleaching treatments. The original digestate showed only limited acidification and an increase in ORP, while Fe... 2+ + S 0 The group only caused slight changes, indicating that abiotic Fe / S reactions alone cannot adequately achieve oxidative activation. In contrast, all bioleaching treatments rapidly acidified the digestate to pH < 2.5 and increased ORP to > 350 mV, confirming that microbial activity drove the acidification process and redox activation. At primarily drove acidification through sulfur oxidation and proton release, while Af oxidized Fe. 2+ Fe 3+ This increases the redox potential (ORP). The combined Af + At treatment integrates these two metabolic functions, creating a favorable redox environment that enhances iron cycling and the production of reactive oxygen species (ROS).

[0061] Figure 4 Figures (c) and (d) show the dissolved oxygen (DO) and hydrogen peroxide (HPO) concentration curves under different bioleaching treatment conditions. Compared with the non-bioleaching group and the original digestate group, the DO decrease was more significant in the bioleaching group, indicating that bacterial respiration and iron-sulfur oxidation during bioleaching are accompanied by active oxygen consumption. Meanwhile, HPO significantly accumulated in the bioleaching group, while its content was lower in the non-bioleaching group and the control group. The HPO levels in the Af and Af+At systems were higher than those in the At system, indicating that iron cycling and oxygen activation are the main pathways for HPO generation, a process secondary to O2. •– The generation of.

[0062] Figure 4 Tables (e) and (f) show the experimental results of iron redox reactions under different bioleaching treatments. In all bioleaching treatments, Fe... 2+ All are rapidly consumed, especially in the Af and Af + At treatments, accompanied by Fe. 3+ The corresponding increase. This phenomenon indicates the existence of Fe driven by Af. 2+ Active oxidation and iron redox cycle processes, sulfur oxidation and Fe 2 + / Fe 3+ The conversion processes are coupled together, thereby continuously generating reactive oxygen species (ROS).

[0063] The above test results indicate that the generation of reactive oxygen species (ROS) during mixed bioleaching is jointly regulated by sulfur oxidation, iron redox cycle, and oxygen activation. At mainly creates an acidic and high ORP environment, while As maintains Fe 2+The transfer and activation of oxygen. In the Af + At system, these synergistic effects promote the production of O2. •– The generation of hydrogen peroxide, and its conversion to •OH, Fe(IV) and through iron-mediated oxidation reactions. 1 O2. This mechanism explains the high ROS yield and its dominant role in the leachate dehydration process.

[0064] Figure 5 The distribution of proteins (a) and polysaccharides (b) in three layers of EPS under different bioleaching treatments is shown in Figure 1. The results indicate that oxidative ROS attack drives the decomposition of EPS and weakens the affinity of interfacial water. The mixed treatment group reduced the total protein and polysaccharide content by more than 1.2 times compared with the single strain treatment group, reducing hydrophilic sites and accelerating the release of bound water.

[0065] Figure 6 The diagram shows the changes in bound water content under different bioleaching treatment conditions. For example... Figure 6 As shown, bioleaching treatment significantly reduced the bound water content compared to the control group, with the Af+At group achieving the highest rate of bound water reduction.

[0066] Figure 7 The secondary structures of proteins in TB-EPS under different bioleaching treatments are shown. Compared with the original digested products, the α-helix / (β-sheet + random coil) ratio in TB-EPS decreased significantly after bioleaching, with the most significant decrease exceeding 90% in the Af+At treatment group. This lower ratio indicates a looser protein structure and reduced order, which exposes potential hydrophobic groups, weakens the water-holding capacity of EPS, and promotes the release of bound water.

[0067] Figure 8 For different bioleaching treatment conditions The values ​​indicate that the solid water affinity of the digestive fluid weakens, the surface hydrophobicity increases, and the energy barrier decreases after mixed treatment. This suggests that particle aggregation in the digestive fluid intensifies, water retention capacity decreases, and bound water is more easily released.

[0068] Figure 9The Fmax values ​​of the secondary phase components in three EPS layers under different bioleaching treatment conditions are shown, where (a) to (c) represent the changes in Fmax corresponding to tryptophan, tyrosine, and humic substances in S-EPS, LB-EPS, and TB-EPS, respectively. Experimental results confirm that reactive oxygen species (ROS) generated in the bioleaching system directly participate in the decomposition process of extracellular polysaccharides (EPS). The highest removal efficiency (>40%) was observed in the A. f. + A. t. treatment group, indicating a stronger oxidative removal capacity for the main EPS components responsible for water retention. The reduction of tryptophan-like and tyrosine-like proteins weakened hydrogen bond-mediated water adsorption; while the reduction of humic substances decreased colloidal stability and interfacial water film resistance, thereby promoting particle aggregation and the release of bound water.

[0069] Figure 10 The Van Krevelen diagram shows the composition of organic matter molecules in TB-EPS under different bioleaching treatments. It indicates that densely packed aromatic macromolecules underwent significant degradation, especially in the Af + At treatment group. Consequently, the water retention capacity of EPS decreased, making it easier for water to separate from the digestate matrix.

[0070] Those skilled in the art will readily understand that the above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching, characterized in that, Includes the following steps: Add Fe to the anaerobic digestion liquid of livestock and poultry manure 2+ Elemental sulfur was inoculated with *Thiobacillus acidophilus* and *Thiobacillus acidophilus* to obtain a bioleaching solution, which was then subjected to a bioleaching reaction. After the reaction was completed, mechanical dehydration was performed. In the bioleaching solution, Fe 2+ The concentration of is 1.0~2.0 g / L; the concentration of elemental sulfur is 1.0~2.0 g / L.

2. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 1, characterized in that, The bioleaching solution contains elemental sulfur and Fe. 2+ The mass ratio is 1:(1.0~1.5).

3. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 1, characterized in that, In the bioleaching solution, Fe 2+ The concentration of is 1.2~1.8 g / L; the concentration of elemental sulfur is 1.0~1.5 g / L.

4. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 1, characterized in that, The inoculation with *Thiobacillus acidophilus* and *Thiobacillus acidophilus* specifically involves: A bacterial suspension containing *Thiobacillus acidophilus* and a bacterial suspension containing *Thiobacillus acidophilus* were added to the anaerobic digestion solution of livestock and poultry manure. The total volume ratio of the two bacterial suspensions to the volume of the anaerobic digestion solution of livestock and poultry manure was (8-12):

100. The bacterial suspensions containing *Thiobacillus acidophilus* and *Thiobacillus acidophilus* had a cell count of 10-1. 8 Order of magnitude.

5. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 4, characterized in that, The volume ratio of the bacterial suspension containing *Thiobacillus acidophilus* to the bacterial suspension containing *Thiobacillus acidophilus* is 1:(0.8~1.2).

6. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 5, characterized in that, In the bioleaching reaction, *Thiobacillus acidophilus* promotes sulfur oxidation and acidification, while *Thiobacillus ferrophilus* promotes Fe... 2+ / Fe 3+ Cyclic and oxygen activation work together to generate reactive oxygen species; these reactive oxygen species oxidize and degrade proteins, polysaccharides, and aromatic structures in EPS.

7. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 6, characterized in that, The reactive oxygen species include superoxide anion, hydroxyl radical, singlet oxygen, and Fe(IV).

8. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 1, characterized in that, The initial pH of the bioleaching solution is 6.8-7.5, and the pH decreases to 2.0-3.0 during the reaction.

9. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 1, characterized in that, The bioleaching reaction takes 40 to 55 hours.

10. The method for deep dehydration of digestate based on iron / sulfur synergistic mixed bioleaching according to claim 1, characterized in that, The temperature of the bioleaching reaction is 20~40℃.

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