Method for intensifying anaerobic digestion to produce methane

Abstract

The invention belongs to the technical field of waste resource utilization, and provides a method for enhancing anaerobic digestion to produce methane. The invention provides a research and development concept of dynamically regulating and controlling nano bubble water injection in stages. The core breakthrough points of the research and development concept comprise: 1) time sequence optimization; based on the pH value of an anaerobic digestion system, H2-NBW or O2-NBW is injected in stages, and the anaerobic digestion hydrolytic acidification stage and the methane production stage are regulated in a targeted manner. O2-NBW is injected in the hydrolytic acidification stage to promote decomposition of protein and cellulose in a substrate, H2-NBW enriched hydrogen nutrition type methanogenesis is switched in the methanogenesis stage, and a hydrogen nutrition type methanogenesis way is enhanced. And (2) when the pH is more than or equal to 6.5 and less than or equal to 7.5 in a neutral safe region, dynamically adjusting the gas type of the nano bubble water by combining the ORP of the anaerobic digestion system, thereby realizing the accurate gradient control of the oxidation reduction potential and improving the methane yield.

Description

Technical Field

[0001] The present invention relates to the technical field of waste resource utilization, and particularly to a method for enhancing methane production by anaerobic digestion. Background Art

[0002] In the process of industrial intensification, biomass wastes such as food waste, kitchen waste, domestic waste, sludge, planting wastes, and breeding wastes present a dual dilemma of "sharp increase in total amount and lagging treatment". Anaerobic digestion (AD) technology, which combines organic matter degradation, energy recovery, and carbon emission reduction synergistic effects, is regarded as the key path to solve the problem of biomass waste treatment. However, AD technology is easily interfered by environmental conditions, resulting in the dilemmas of low gas production efficiency and poor process stability. For example, anaerobic digestion of food waste is extremely prone to acid inhibition due to load fluctuations; planting and breeding wastes are rich in lignocellulose, and its unique three-dimensional heterogeneous structure - especially the coating effect of lignin on cellulose / hemicellulose - leads to low hydrolysis efficiency, and the actual methane production is often less than 60% of the theoretical value. Therefore, developing low-energy-consuming and environment-friendly enhancement technologies has become the core issue for improving the efficiency of biomass waste AD systems.

[0003] In recent years, nano-bubble water (NBW) has attracted much attention in the field of environmental engineering due to its unique physical and chemical properties. Its sub-micron-sized bubbles (<1μm) have a high specific surface area, a long residence period, and enhanced mass transfer characteristics. In particular, the hydroxyl radicals generated by bubble rupture can effectively cleave fatty acids and deconstruct lignin-carbohydrate complexes, significantly improving acid metabolism efficiency and cellulose bioaccessibility. Multiple studies have shown that CO2-NBW can relieve volatile fatty acid (VFA) inhibition through pH regulation, while O2-NBW can reduce cellulose crystallinity to promote hydrolysis and acidification.

[0004] However, the requirements for redox potential in the hydrolysis and acidification stage and the methane production stage are significantly different, and the existing technologies using a single gas type or timed injection often limit the improvement of methane production rate. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for enhancing methane production by anaerobic digestion. The method provided by the present invention can improve the methane production rate.

[0006] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for enhancing methane production by anaerobic digestion, comprising the following steps:

[0008] Inoculating sludge;

[0009] After inoculating the sludge, the substrate is diluted with the initial diluent and continuously fed for anaerobic digestion;

[0010] When the pH of the anaerobic digestion system is greater than or equal to 6.5 and less than or equal to 7.5, and the oxidation-reduction potential (ORP) is greater than or equal to -300 mV, the diluent is a hydrogen nanobubble water (H2-NBW)-water system;

[0011] When the pH of the anaerobic digestion system is greater than or equal to 6.5 and less than or equal to 7.5, and the oxidation-reduction potential (ORP) is less than -300 mV, the diluent is an oxygen nanobubble water (O2-NBW)-water system;

[0012] When the pH of the anaerobic digestion system is less than 6.5, the diluent is an oxygen nanobubble water-water system;

[0013] When the pH of the anaerobic digestion system is greater than 7.5, the diluent is an oxygen nanobubble water-water system;

[0014] The substrate is biomass waste.

[0015] Preferably, the solid content of the feed is ≤15%.

[0016] Preferably, the initial diluent is an oxygen nanobubble water-water system.

[0017] Preferably, in the oxygen nanobubble water-water system, the volume ratio of oxygen nanobubble water is 20-100%.

[0018] Preferably, in the hydrogen nanobubble water-water system, the volume ratio of hydrogen nanobubble water is 20-100%.

[0019] Preferably, the preparation parameters of the oxygen nanobubble water or hydrogen bubble water independently include: the circulating flow rate of water is 1-2.5 L / min, the gas inhalation rate of the nanobubble water generator is 0.01-0.15 L / min, the pressure is 0.1-0.24 MPa, and the aeration time is 5-60 min, and the gas is oxygen or hydrogen.

[0020] Preferably, the oxygen content in the oxygen nanobubble water is 0.01-0.1 mg / L.

[0021] Preferably, the hydrogen content in the hydrogen nanobubble water is 0.2-1.0 mg / L.

[0022] Preferably, the particle size of the biomass waste is 1-30 mm.

[0023] Preferably, the temperature of the anaerobic digestion is 20-60 °C.

[0024] The present invention provides a method for enhancing anaerobic digestion to produce methane.

[0025] The present invention proposes the R & D concept of "phased dynamic regulation of nano - bubble water injection", and its core breakthrough points include:

[0026] 1) Timing optimization. Based on the pH of the anaerobic digestion system, by injecting H2 - NBW or O2 - NBW in stages, targeted regulation of the hydrolysis - acidification stage and methane - production stage of anaerobic digestion is achieved. Injecting O2 - NBW in the hydrolysis - acidification stage promotes the decomposition of proteins, lignocellulose (including cellulose or hemicellulose) in the substrate, and switching to H2 - NBW in the methane - production stage enriches hydrogenotrophic methanogenesis and enhances the hydrogenotrophic methanogenesis pathway.

[0027] 2) When 6.5 ≤ pH ≤ 7.5 is in the "neutral safety zone", the type of nano - bubble water is dynamically adjusted in combination with the ORP of the anaerobic digestion system to achieve precise gradient control of the redox potential and improve the methane production rate.

[0028] 3) When the pH is less than 6.5, O2 - NBW is selected to be injected to oxidize volatile fatty acids into CO2 and H2O.

[0029] 4) When the pH is greater than 7.5, O2 - NBW is selected to be injected to promote the hydrolysis - acidification process, produce more volatile fatty acids, and reserve "raw materials" for the methane - production stage.

[0030] 5) The present invention integrates pH and ORP to establish a real - time dynamic feedback mechanism.

[0031] The method of the present invention solves the two core problems of stage mismatch and lack of dynamic feedback in the existing application of nano - bubble water. Through timing optimization and dynamic feedback mechanism, an engineering breakthrough in the efficient anaerobic digestion of planting and breeding waste is achieved, providing an innovative solution with both high benefits and low energy consumption for the treatment of planting and breeding waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the logic diagram of phased dynamic regulation of nano - bubble water injection provided by the present invention;

[0033] Figure 2 is the influence of the volume ratios of H2 - NBW and O2 - NBW being 20%, 40%, 60%, 80%, and 100% respectively on the methane production rate of the AD system;

[0034] Figure 3 is the electron paramagnetic resonance spectra of CK, 100% H2 - NBW, and 80% O2 - NBW;

[0035] Figure 4 is the decrease in the crystallinity of lignocellulose in the CK, 100% H2 - NBW, and 80% O2 - NBW treatment groups;

[0036] Figure 5 For the hydrolysis enzyme and methanogenic enzyme activities of the treatment groups with the volume ratios of H2-NBW being 20%, 40%, 60%, 80%, and 100%, the treatment groups with the volume ratios of O2-NBW being 20%, 40%, 60%, 80%, or 100%, and the CK group;

[0037] Figure 6 For the changes in the daily methane production rate and daily methane production of CK, adding only H2-NBW (corresponding to H2-NBW), adding only O2-NBW (corresponding to O2-NBW), and adding 100% H2-NBW and 80% O2-NBW in stages (corresponding to H2 / O2-NBW) to the AD reactor. Detailed implementation mode

[0038] The present invention provides a method for enhancing methane production by anaerobic digestion, comprising the following steps:

[0039] Inoculating sludge;

[0040] After inoculating the sludge, the substrate is diluted with the initial diluent and continuously fed for anaerobic digestion;

[0041] When the pH of the anaerobic digestion system is greater than or equal to 6.5 and less than or equal to 7.5, and the ORP is greater than or equal to -300 mV, the diluent is a hydrogen nanobubble water-water system;

[0042] When the pH of the anaerobic digestion system is greater than or equal to 6.5 and less than or equal to 7.5, and the ORP is less than -300 mV, the diluent is an oxygen nanobubble water-water system;

[0043] When the pH of the anaerobic digestion system is less than 6.5, the diluent is an oxygen nanobubble water-water system;

[0044] When the pH of the anaerobic digestion system is greater than 7.5, the diluent is an oxygen nanobubble water-water system;

[0045] The substrate is biomass waste.

[0046] Unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0047] The present invention inoculates sludge.

[0048] The present invention does not specifically limit the inoculation method of the sludge, and the operations well-known to those skilled in the art can be adopted.

[0049] After inoculating the sludge, the substrate is diluted with the diluent and then subjected to anaerobic digestion.

[0050] Figure 1The logic diagram for phased dynamic regulation of nano-bubble water injection provided by the present invention is described in detail below in combination with Figure 1 the injection method.

[0051] In the present invention, the substrate is biomass waste, and the biomass waste includes but is not limited to food waste, kitchen waste, domestic waste, sludge, crop waste, and livestock waste. In the present invention, the crop waste specifically preferably includes one or more of rice straw, wheat straw, corn straw, rice husk, peanut shell, corncob, sunflower seed shell, and soybean pod, and the livestock waste preferably includes one or more of cow dung, chicken dung, pig dung, sheep dung, and duck dung. In the present invention, the particle size of the biomass waste is preferably 1 to 30 mm.

[0052] In the present invention, the solid content (TS) of the feed is preferably ≤15%, more preferably 0.1 to 15%, and specifically preferably 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0053] In the present invention, the initial diluent is preferably an oxygen nano-bubble water-water system (denoted as the first oxygen nano-bubble water-water system). In the first oxygen nano-bubble water-water system, the water is preferably tap water. In the present invention, in the first oxygen nano-bubble water-water system, the volume ratio of the oxygen nano-bubble water is preferably 20 to 100%, specifically preferably 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%. In the present invention, the oxygen content in the oxygen nano-bubble water is preferably 0.01 to 0.1 mg / L, specifically preferably 0.01 mg / L, 0.02 mg / L, 0.03 mg / L, 0.04 mg / L, 0.05 mg / L, 0.06 mg / L, 0.07 mg / L, 0.08 mg / L, 0.09 mg / L, or 0.1 mg / L; when the oxygen content in the oxygen nano-bubble water is preferably 0.01 to 0.1 mg / L, the redox potential of the oxygen nano-bubble water is -300 mV to -100 mV.

[0054] In the present invention, the preparation parameters of the oxygen nano-bubble water preferably include: the circulating flow rate of water is preferably 1 - 2.5 L / min, specifically preferably 1 L / min, 1.5 L / min, 2 L / min or 2.5 L / min; the gas inhalation speed of the nano-bubble water generator is preferably 0.01 - 0.15 L / min, specifically preferably 0.01 L / min, 0.02 L / min, 0.03 L / min, 0.04 L / min, 0.05 L / min, 0.06 L / min, 0.07 L / min, 0.08 L / min, 0.09 L / min, 0.1 L / min, 0.11 L / min, 0.12 L / min, 0.13 L / min, 0.14 L / min or 0.15 L / min; the pressure is preferably 0.1 - 0.24 MPa, specifically preferably 0.1 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.17 MPa, 0.18 MPa, 0.19 MPa, 0.2 MPa, 0.21 MPa, 0.22 MPa, 0.23 MPa or 0.24 MPa; the aeration time is preferably 5 - 60 min, specifically preferably 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min; the gas is preferably oxygen.

[0055] In the present invention, the initial diluent is selected as the oxygen nano-bubble water - water system, which can promote electron shunt, enhance substrate hydrolysis acidification, and produce more volatile fatty acids (VFAs), reserving "raw materials" for the methanogenesis stage.

[0056] In the present invention, the temperature of the anaerobic digestion is preferably 20 - 60 °C, specifically preferably 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C or 60 °C.

[0057] In the present invention, the anaerobic digestion is preferably carried out in an anaerobic digestion reactor, which preferably includes a reaction tank body, a circulating water bath heating system, a pH on-line monitor, an oxidation-reduction potential (ORP) on-line monitor, a water pump, a mechanical stirring device and a gas collection device. In the present invention, the circulating water bath heating system can heat the feed, and the water pump can deliver the constant temperature water to the jacket layer outside the reaction tank body to achieve the constant temperature control of the anaerobic digestion system. In the present invention, the pH on-line monitor preferably includes a pH electrode and a paperless recorder, the accuracy of the pH electrode is preferably ±0.01, and the pH electrode preferably samples continuously. In the present invention, the oxidation-reduction potential (ORP) on-line monitor preferably includes an ORP electrode and a paperless recorder, the accuracy of the ORP electrode is preferably ±0.01, and the ORP electrode preferably samples continuously.

[0058] In the present invention, when the pH of the anaerobic digestion system is greater than or equal to 6.5, less than or equal to 7.5, and the ORP is greater than or equal to -300 mV, the diluent is a hydrogen nanobubble water-water system. In the present invention, in the hydrogen nanobubble water-water system, the volume ratio of hydrogen nanobubble water is preferably 20-100%, specifically preferably 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%. In the present invention, the hydrogen content in the hydrogen nanobubble water is preferably 0.2-1.0 mg / L, specifically preferably 0.2 mg / L, 0.3 mg / L, 0.4 mg / L, 0.5 mg / L, 0.6 mg / L, 0.7 mg / L, 0.8 mg / L, 0.9 mg / L or 1 mg / L. In the present invention, the preparation parameters of the hydrogen nanobubble water preferably include: the circulating flow rate of water is preferably 1-2.5 L / min, specifically preferably 1 L / min, 1.5 L / min, 2 L / min or 2.5 L / min; the gas inhalation rate of the nanobubble water generator is preferably 0.01-0.15 L / min, specifically preferably 0.01 L / min, 0.02 L / min, 0.03 L / min, 0.04 L / min, 0.05 L / min, 0.06 L / min, 0.07 L / min, 0.08 L / min, 0.09 L / min, 0.1 L / min, 0.11 L / min, 0.12 L / min, 0.13 L / min, 0.14 L / min or 0.15 L / min; the pressure is preferably 0.1-0.24 MPa, specifically preferably 0.1 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.17 MPa, 0.18 MPa, 0.19 MPa, 0.2 MPa, 0.21 MPa, 0.22 MPa, 0.23 MPa or 0.24 MPa; the aeration time is preferably 5-60 min, specifically preferably 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min; the gas is preferably hydrogen. In the present invention, the hydrogen nanobubble water-water system can maintain the ORP of the anaerobic digestion system, ensure its stability, and reduce the oxidative damage of oxygen to anaerobic bacteria; in addition, it can also enhance the hydrogenotrophic methanogenesis pathway, consume CO2, and increase the methane content.

[0059] In the present invention, when the pH of the anaerobic digestion system is greater than or equal to 6.5 and less than or equal to 7.5, and the ORP is less than -300 mV, the diluent is an oxygen nanobubble water - water system (denoted as the second oxygen nanobubble water - water system). In the present invention, in the second oxygen nanobubble water - water system, the volume ratio of the oxygen nanobubble water is preferably 20 - 100%, specifically preferably 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%. In the present invention, the preparation method of the oxygen nanobubble water in the second oxygen nanobubble water - water system is the same as the above - mentioned technical solution and will not be elaborated here. In the present invention, the second oxygen nanobubble water - water system can create a micro - oxygen environment, promote substrate hydrolysis and acidification, and produce more VFAs.

[0060] In the present invention, when the pH of the anaerobic digestion system is less than 6.5, the diluent is an oxygen nanobubble water - water system (denoted as the third oxygen nanobubble water - water system). In the present invention, in the third oxygen nanobubble water - water system, the volume ratio of the oxygen nanobubble water is preferably 20 - 100%, specifically preferably 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%. In the present invention, the preparation method of the oxygen nanobubble water in the third oxygen nanobubble water - water system is the same as the above - mentioned technical solution and will not be elaborated here. In the present invention, the oxygen nanobubble water in the third oxygen nanobubble water - water system can activate facultative hydrolysis - acidification bacteria, oxidize VFAs into CO2 and H2O, and reduce acid accumulation.

[0061] In the present invention, when the pH of the anaerobic digestion system is greater than 7.5, the diluent is an oxygen nanobubble water - water system (denoted as the fourth oxygen nanobubble water - water system). In the present invention, in the fourth oxygen nanobubble water - water system, the volume ratio of the oxygen nanobubble water is preferably 20 - 100%, specifically preferably 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%. In the present invention, the preparation method of the oxygen nanobubble water in the fourth oxygen nanobubble water - water system is the same as the above - mentioned technical solution and will not be elaborated here. In the present invention, the oxygen nanobubble water in the fourth oxygen nanobubble water - water system can promote electron shunt and enhance the hydrolysis - acidification process, produce more VFAs, and reserve "raw materials" for the methanogenesis stage.

[0062] The method of the present invention takes pH as the priority regulation parameter. When 6.5 ≤ pH ≤ 7.5 is in the "neutral safety zone", the type of nanobubble water needs to be selected according to the ORP value. The method of the present invention has the following advantages: 1) Significantly improve methane production rate: By dynamically regulating the gas type (O2-NBW or H2-NBW) and injection timing of nanobubble water, optimize the redox balance and the structure of methanogenic functional microbial communities in the anaerobic digestion system, so that the methane production rate of the anaerobic digestion system of farming and breeding waste is increased by more than 30-40%. 2) Strengthen the hydrolysis and acidification efficiency: Inject different gas nanobubble waters in stages (inject O2-NBW in the hydrolysis and acidification stage, inject H2-NBW in the methanogenesis stage), effectively promote the hydrolysis, acidification and direct electron donation processes of substrates (cellulose, protein), and reduce the accumulation of intermediate products. 3) Enhance the system stability: Combine the monitoring indicators pH and ORP, dynamically adjust the gas type of nanobubble water, effectively relieve acid / oxygen stress, and improve the stability and operation efficiency of the system.

[0063] The following examples are used to illustrate in detail the method for enhancing methane production by anaerobic digestion provided by the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0064] The O2-NBW and H2-NBW used in the following examples were prepared by the gas-water circulation method using a nanobubble water generator. O2 (purity ≥ 99.995%) was provided by Tianjin Anxing Industrial Gas Sales Co., Ltd. (China). Hydrogen (purity ≥ 99.995%) was generated by a hydrogen generator.

[0065] Example 1

[0066] The inoculated sludge for this experiment was taken from a sewage treatment plant in China, and cow dung, the farming and breeding waste, was used as the digestion substrate. The physical and chemical properties of the inoculated sludge and the substrate are shown in Table 1.

[0067] Table 1 Physical and chemical properties of the inoculated sludge and the substrate

[0068] Index Inoculated sludge Digestion substrate Total solid content (%) 8.56±0.33 14.39±0.10 Volatile solid content (%) 5.74±0.30 10.85±0.09 C(％) - 34.04±3.09 H(％) - 1.71±0.11 O(％) - 4.71±0.42 N(％) - 0.35±0.01 <![CDATA[Theoretical methane yield (mLCH4 / gVS)]]> - 483.17±2.13 pH 7.80±0.40 -

[0069] Oxygen and hydrogen were respectively introduced into deionized water and continuously aerated for 20 min to obtain O2-NBW and H2-NBW. The key operating parameters are as follows: the circulation flow rate of deionized water is 2.5 L / min; the gas inhalation speed of the nanobubble water generator is 0.07 L / min; the gas inhalation pressure is 0.24 MPa.

[0070] NBW was introduced into the H2-NBW-water system and O2-NBW-water system at volume ratios of 0% (CK, tap water), 20%, 40%, 60%, 80%, and 100%, and used as a diluent to the AD reactor. The digestion substrate was physically broken to a particle size of 15 mm, and the total solid content of the digestion substrate was adjusted to 8%. Three parallel tests were designed. At the same time, a circulating water bath system was used to heat and maintain the reactor water temperature at 37 ± 1 °C, and the constant-temperature water was transported to the jacket layer outside the tank body by a water pump to achieve the constant-temperature control of the reaction system.

[0071] Figure 2 Effects of volume ratios of 20%, 40%, 60%, 80%, and 100% of H2-NBW and O2-NBW on the methane production rate of the AD system. As Figure 2 shown, in the treatment groups with H2-NBW / O2-NBW volume ratios of 20% - 100%, the cumulative methane production rates were all significantly higher than those of the CK group. In addition, it can be seen that 100% and 80% are the optimal volume ratios of H2-NBW and O2-NBW respectively. The methane production rates were the best at these volume ratios, being 286.13 mL / g·VS and 277.45 mL / g·VS respectively, which were increased by 40.26% and 36.01% compared with CK.

[0072] Take 1 mL each of the diluent with 100% H2-NBW volume ratio, the diluent with 80% O2-NBW volume ratio, and CK (i.e., without adding NBW) samples, add 30 μL of DMPO-OH adduct, and conduct electron paramagnetic resonance detection. The results are as Figure 3 shown. As can be seen from Figure 3 : In the 80% O2-NBW diluent, the DMPO-OH adduct showed a typical 1:2:2:1 quartet characteristic signal (α N = 14.67 G, α β H = 14.67 G, g = 2.006, peak intensity 0.08 a.u.), indicating that significant ·OH was generated during the collapse of its nanobubbles. ·OH may attack the β-O-4 bond between lignin phenylpropane units, destroying the three-dimensional network structure of the complex, thereby enhancing the accessibility of cellulose and reducing its crystallinity. In addition, ·OH can decompose VFAs (such as acetic acid, propionic acid, etc.) into small molecules (CO2, H2O) through non-selective oxidation, reducing their concentration in the system, indirectly increasing the system pH, and improving the stability of AD. In contrast, no obvious quartet signal was found in the 100% H2-NBW diluent, probably because the direct reaction of hydrogen with free radicals (H2 + 2·OH → 2H2O) scavenged them.

[0073] Samples of the treatment group with 100% H2-NBW volume ratio, the treatment group with 80% O2-NBW volume ratio, and the CK group after 25 days of anaerobic digestion were taken for testing the decrease in the crystallinity of lignocellulose. The results are as Figure 4 shown. As Figure 4 shown, compared with CK, the addition of 100% H2-NBW and 80% O2-NBW can significantly reduce the crystallinity of lignocellulose in the substrate to varying degrees. However, the decrease in the crystallinity of lignocellulose in the 80% O2-NBW treatment group is the largest (39.81%), which is 43.25% and 14.86% higher than that of CK (27.79%) and the 100% H2-NBW treatment group (34.66%), respectively. It can be seen that 80% O2-NBW is more conducive to reducing the crystallinity of lignocellulose in the planting and breeding waste, increasing its surface area and accessibility, and thus better promoting AD hydrolysis.

[0074] Samples of the treatment groups with 20%, 40%, 60%, 80%, 100% H2-NBW volume ratio, the treatment groups with 20%, 40%, 60%, 80% or 100% O2-NBW volume ratio, and the CK group after 25 days of anaerobic digestion were taken for testing the activities of enzymes (hydrolytic enzymes and methanogenic enzymes). Among them, the hydrolytic enzymes include cellulase, α-glucosidase, protease, and xylanase, and the methanogenic enzymes include dehydrogenase, coenzyme F420, and acetate kinase; the results are as Figure 5 shown. Figure 5 Among them, the activity units of xylanase, acetate kinase, cellulase, and protease are U / L; the activity units of α-glucosidase and dehydrogenase are IU / L; the activity unit of coenzyme F420 is ng / L. Figure 5 Reveals the differential regulation of the rate-limiting steps of AD by H2-NBW / O2-NBW. Generally speaking, compared with CK, the introduction of various ratios of H2-NBW and O2-NBW into the AD system can specifically increase the activities of key enzymes. Specifically, the activities of dehydrogenase, coenzyme F420, and acetate kinase in the 100% H2-NBW treatment group are 17.41%, 186.31%, and 119.75% higher than those in the 80% O2-NBW treatment group, respectively. It can be seen that H2-NBW promotes the conversion of VFAs to CH4 by enhancing the activity of methanogenic enzymes. While 80% O2-NBW specifically enhances the activity of the hydrolytic enzyme system through micro-oxygen pressure, and the activities of its cellulase, α-glucosidase, protease, and xylanase are 34.65%, 12.91%, 12.79%, and 31.79% higher than those in the 100% H2-NBW treatment group, respectively. This specific regulation shows that H2-NBW directly significantly enhances the methanogenic metabolism at the end of AD, while O2-NBW optimizes the hydrolysis efficiency at the front end of AD by improving the substrate availability.

[0075] Example 2

[0076] The physical and chemical properties of the inoculated sludge and the planting and breeding waste are the same as those in Example 1.

[0077] The volume of the AD reactor is 20 L, and its effective volume is 16 L. Then, 16 L of inoculated sludge is added into the AD reactor. Oxygen and hydrogen are respectively introduced into deionized water for continuous aeration for 20 min to obtain O2-NBW and H2-NBW. The key operating parameters are as follows: the circulation flow rate of deionized water is 1.5 L / min; the gas inhalation speed of the nanobubble water generator is 0.10 L / min; the gas inhalation pressure is 0.20 MPa.

[0078] Before the experiment starts, the digestion substrate is physically broken to make its particle size 21 mm. The total solid concentration of the planting and breeding waste is adjusted to 8% using pure water (CK), 100% H2-NBW, and 80% O2-NBW respectively, and the planting and breeding waste with the adjusted total solid concentration is added into four AD reactors respectively. The water temperature of the reactor is heated and maintained at 37 ± 1 °C using a circulating water bath system, and the constant temperature water is transported to the jacket layer outside the tank body through a water pump to achieve the constant temperature control of the reaction system.

[0079] On the first day of the experiment, feeding starts at an organic loading rate (OLR) of 3 g VS / (L·d), and the normal AD process is started. Thereafter, feeding is carried out at an organic loading of 3 g VS / (L·d) every day, and it operates stably for one hydraulic retention time (31 days) at an organic loading of 3 g VS / (L·d). Subsequently, the load is increased to 4 g VS / (L·d), and it operates stably for one hydraulic retention time (31 days) at a load of 4 g VS / (L·d). After the gas production fluctuation is small, the load is further increased to 5 g VS / (L·d).

[0080] In the four reactors, water (CK), 80% oxygen nanobubble water (80% O2-NBW, that is, the volume ratio of NBW is 80%, the same below), 100% hydrogen nanobubble water (100% H2-NBW), and 100% H2-NBW and 80% O2-NBW are added in stages during feeding. During the experiment, the constant temperature water (37 ± 1 °C) in the circulating water bath is transported to the jacket on the outer wall of the reaction tank through a water pump to ensure the constant temperature of the anaerobic digestion process.

[0081] Figure 6 It shows the changes in the daily methane production rate and daily methane production after adding CK, only adding H2-NBW (corresponding to H2-NBW), only adding O2-NBW (corresponding to O2-NBW), and adding 100% H2-NBW and 80% O2-NBW in stages (corresponding to H2 / O2-NBW) to the AD reactor. Figure 6As shown in the figure, within the first ten days of the 3 gVS / (L·d) load, the daily methane production and daily methane production rate of CK and each treatment group showed an upward trend. However, before the 12th day, compared with CK, there were no significant differences in the daily methane production and daily methane production rate in the treatment groups with only 100% H2-NBW and 80% O2-NBW added. During this period, the daily methane production and daily methane production rate of the treatment group with staged addition of 100% H2-NBW and 80% O2-NBW were significantly higher than those of other groups. At the end of the 3 gVS / (L·d) load, the daily methane production and daily methane production rate of CK, the treatment group with only 100% H2-NBW added, and the treatment group with 80% O2-NBW added were 4.98 L, 8.12 L, 8.16 L, and 82.98 mL / gVS d, 135.31 mL / gVS d, 136.04 mL / gVS d, respectively. The daily methane production and daily methane production rate of the treatment group with staged addition of 100% H2-NBW and 80% O2-NBW were 11.85 L and 184.02 mL / gVS d, respectively. It can be seen that although the addition of NBW can significantly increase the daily methane production and daily methane production rate of AD, the effect of promoting gas production is better by using the mode of staged addition of 100% H2-NBW and 80% O2-NBW. In addition, this result also indicates that the anaerobic digestion process of CK's farming and breeding waste gradually becomes unstable, while the addition of NBW can make the system more stable.

[0082] After the 3 gVS / (L·d) load was stably operated for one hydraulic retention time, the load of the system was increased to 4 gVS / (L·d) on the 33rd day. In the first 10 days after the load increase, the gas production rates of each treatment recovered slowly, and there were no significant differences in the daily methane production and cumulative methane production rate compared with the end of the 3 load. On the 47th day, the daily methane production and daily methane production rate of each treatment group began to increase rapidly, which also indicated that the microorganisms had adapted to the operating conditions of the 4 load. At the end of the 4 load (the 66th day), the daily methane production and daily methane production rate of CK, the treatment group with only 100% H2-NBW added, and the treatment group with 80% O2-NBW added were 1.81 L, 10.88 L, 11.51 L, and 30.20 mL / gVS d, 145.06 mL / gVS d, 153.41 mL / gVS d, respectively. The daily methane production and daily methane production rate of the treatment group with staged addition of 100% H2-NBW and 80% O2-NBW were 22.04 L and 204.54 mL / gVS d, respectively. It can be seen that the gas production performance of the experimental group with nano-bubble water added is far better than that of CK, and the potential of promoting gas production by staged addition of 100% H2-NBW and 80% O2-NBW is greater. The CK group could not withstand the higher load, which led to the instability of the AD system and a significant reduction in gas production.

[0083] During the 4 gVS / (L·d) load period, the CK group system became unstable and could not continue to increase the load. Therefore, on the 63rd day, only the load of the experimental group with NBW added was increased to 5 gVS / (L·d). During the 5 g VS / (L·d) load stage, the daily methane production increase of only the treatment groups with 100% H2-NBW and 80% O2-NBW added was small, only about 12.00 L and 12.78 L respectively at the end stage, while the cumulative methane production finally stabilized at 160.02 mL / gVS d and 190.41 mL / gVS d respectively. In contrast, the daily methane production and daily methane production rate of the treatment group with 100% H2-NBW and 80% O2-NBW added in stages increased significantly to 23.40 L and 260.63 mL / gVS d. The results of this study show that under high organic load conditions, through the combined strategy of adding 100% H2-NBW and 80% O2-NBW in stages, the methanogenesis efficiency can be significantly improved by targeting and regulating each stage of anaerobic digestion.

[0084] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for enhancing methane production by anaerobic digestion, characterized in that, Comprising the following steps: Inoculating sludge; After inoculating the sludge, the substrate is diluted with the initial diluent and continuously fed for anaerobic digestion; When the pH of the anaerobic digestion system is greater than or equal to 6.5 and less than or equal to 7.5, and the redox potential is greater than or equal to -300 mV, the diluent is a hydrogen nanobubble water - water system; When the pH of the anaerobic digestion system is greater than or equal to 6.5 and less than or equal to 7.5, and the redox potential is less than -300 mV, the diluent is an oxygen nanobubble water - water system; When the pH of the anaerobic digestion system is less than 6.5, the diluent is an oxygen nanobubble water - water system; When the pH of the anaerobic digestion system is greater than 7.5, the diluent is an oxygen nanobubble water - water system; The substrate is biomass waste.

2. The method according to claim 1, wherein The solid content of the feed is ≤ 15%.

3. The method according to claim 1, characterized in that The initial diluent is an oxygen nanobubble water - water system.

4. The method according to claim 1 or 3, characterized in that, In the oxygen nanobubble water - water system, the volume ratio of oxygen nanobubble water is 20 - 100%.

5. The method according to claim 1, characterized in that In the hydrogen nanobubble water - water system, the volume ratio of hydrogen nanobubble water is 20 - 100%.

6. The method according to claim 1, wherein The preparation parameters of the oxygen nanobubble water or hydrogen bubble water independently include: the circulating flow rate of water is 1 - 2.5 L / min, the gas inhalation rate of the nanobubble water generator is 0.01 - 0.15 L / min, the pressure is 0.1 - 0.24 MPa, and the aeration time is 5 - 60 min, and the gas is oxygen or hydrogen.

7. The method according to claim 1, characterized in that, The oxygen content in the oxygen nanobubble water is 0.01 - 0.1 mg / L.

8. The method according to claim 1, characterized in that, The hydrogen content in the hydrogen nanobubble water is 0.2 - 1.0 mg / L.

9. The method according to claim 1, wherein The particle size of the biomass waste is 1 - 30 mm.

10. The method according to claim 1, wherein The temperature of the anaerobic digestion is 20 - 60 °C.

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