Method for accelerating straw composting by utilizing magnetite and compound microorganisms to drive biological advanced oxidation

Abstract

The invention discloses a method for accelerating straw composting by utilizing magnetite and compound microorganisms to drive biological advanced oxidation, and belongs to the technical field of efficient composting of agricultural organic solid wastes. The method comprises the following steps: (1) uniformly mixing straws and excrement as a compost body, adjusting the C / N ratio and the water content, adding magnetite, a bacillus subtilis liquid and a crushed white rot fungus liquid, and putting the mixture into a composting device; (2) intermittent aeration is carried out, the temperature is 28-32 DEG C, and the composting period is 40-50 days. According to the composting method, through intermittent aeration, controllable aerobic conditions and anoxic conditions are formed in a compost body, under the anoxic conditions, ferric iron is subjected to dissimilatory iron reduction to generate ferrous iron, and under the aerobic conditions, compound microorganisms reduce oxygen through extracellular electron transfer to form hydrogen peroxide, so that the composting effect is improved. Divalent iron and hydrogen peroxide are subjected to a Fenton-like reaction to generate hydroxyl free radicals with high oxidizing property, so that decomposition of straw lignocellulose is accelerated, and the composting efficiency of compost is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of efficient composting of agricultural organic solid waste, and in particular relates to a method for accelerating straw composting by utilizing magnetite and composite microorganisms to drive biological advanced oxidation. Background Art

[0002] Composting technology is currently one of the most realistic and effective methods to realize the resource utilization of agricultural organic solid waste. The high temperature stage of aerobic composting can decompose complex organic matter and convert it into simple and stable humus in the maturity stage. However, the lignocellulose contained in agricultural organic waste has a stable structure and a slow decomposition rate, resulting in problems such as long composting cycle and low maturity.

[0003] Straw composting can accelerate the degradation of lignocellulose by adding composite microbial agents to the compost. For example, adding white rot fungi to the compost can secrete lignin peroxidase, cellulase, laccase and other efficient lignocellulose decomposing enzymes, thereby improving the composting effect of straw. However, the temperature of the compost is in a constant change process, and the activity of microorganisms will also change accordingly, so the improvement of the maturity of the straw compost is not obvious.

[0004] Some studies have also tried to add biochar to improve the efficiency of straw composting. The added biochar is mainly to accelerate the decomposition rate of microorganisms, but the effect is not obvious. Therefore, how to destroy the lignin fiber structure faster and more effectively is the key to improving the effect of straw composting.

[0005] Most of the patents that have been published so far use additives or composite microbial agents to strengthen straw composting. For example, a patent proposes adding biochar containing magnetite to compost, using its strong adhesion to functional microorganisms and rich functional groups to improve the composting effect. Another patent proposes adding Bacillus and Pseudomonas to compost at the same time to speed up composting by increasing the temperature of the pile. None of these patents involve how to construct microbial advanced oxidation in compost to decompose lignocellulose. Summary of the invention

[0006] The present invention proposes a method for accelerating straw composting by biological advanced oxidation driven by magnetite and composite microbial agents. Through intermittent oxygen supply, alternating aerobic and anoxic conditions are formed in the compost body: under anoxic conditions, the composite agent with extracellular electron transfer ability reduces magnetite to Fe(II); under aerobic conditions, the composite agent with extracellular electron transfer ability reduces oxygen to H 2 O 2 ;H 2 O 2 It undergoes a Fenton-like reaction with Fe(II) to generate ·OH, thereby enhancing the decomposition of straw wood fiber and improving the composting effect.

[0007] The present invention provides a method for accelerating straw composting by using magnetite and composite microorganisms to drive biological advanced oxidation, the method comprising the following steps:

[0008] (1) mixing straw and feces in a wet weight ratio of 0.8-1.2:0.8-1.2 as a compost, adjusting the C / N ratio to 25-30:1 with urea, adjusting the water content to 55%-60%, adding magnetite, Bacillus subtilis liquid and crushed white rot fungus liquid, and placing in a composting device;

[0009] The OD600 of the Bacillus subtilis liquid is 1.2-1.6, and the volume mass ratio of the liquid to the pile is 0.8-1.2% ml / g;

[0010] The volume mass ratio of the crushed white rot fungus liquid to the pile is 0.8-1.2% ml / g;

[0011] The amount of magnetite used is 1.5-2.5% of the mass of the pile;

[0012] (2) The composting device is aerated intermittently, with an interval of 15 minutes per hour and an aeration rate of 40-50 ml / kg per minute. The leachate produced by fermentation in the compost pile is collected every day. The temperature in the composting device is 28-32 °C. The composting cycle is 40-50 days, during which the compost is turned several times, such as on the 9th, 20th and 33rd days to ensure that the compost is fully mature.

[0013] According to some embodiments of the present invention, the OD600 of the Bacillus subtilis bacterial solution in step (1) is 1.4.

[0014] According to some embodiments of the present invention, in step (1), the volume mass ratio of the Bacillus subtilis bacterial solution to the biomass is 1% in ml / g.

[0015] According to some embodiments of the present invention, the volume mass ratio of the crushed white rot fungus liquid to the pile in step (1) is 1% ml / g.

[0016] According to some embodiments of the present invention, in step (1), the wet weight ratio of straw to feces is 1:1.

[0017] According to some embodiments of the present invention, the amount of magnetite used in step (1) is 1% of the mass of the pile.

[0018] According to some embodiments of the present invention, in step (1), the particle size of the magnetite is 0.1-0.2 mm, and the Fe content is 62%-70%.

[0019] According to some embodiments of the present invention, the intermittent aeration in step (2) is performed at an interval of 15 minutes per hour, and the aeration volume per minute is 45 ml / kg.

[0020] According to some embodiments of the present invention, the temperature inside the composting device in step (2) is 30°C.

[0021] According to some embodiments of the present invention, the composting period in step (2) is 45 days.

[0022] The application mechanism of the present invention is:

[0023] (1) The degradation of organic matter by white-rot fungi in the composite microorganisms is more obvious. Some organic matter in TOC is released in the form of carbon dioxide or other gases through the respiration and mineralization of microorganisms. White-rot fungi have a positive effect on the decomposition of organic matter. At the same time, white-rot fungi can also produce H under aerobic conditions. 2 O 2 This is mainly because under aerobic conditions, white rot fungi oxidize lignin-derived quinones into semiquinone free radicals by secreting related enzymes. Semiquinone free radicals can be automatically oxidized into quinones and produce superoxide free radicals. The dismutation of superoxide free radicals leads to the formation of hydrogen peroxide. Bacillus subtilis extract has high cellulase activity in the process of cellulose decomposition and can also effectively promote the degradation of cellulose.

[0024] (2) Composite microorganisms can increase the production of ·OH in an iron-rich environment. Intermittent aeration can cause the pile to form alternating aerobic and anoxic conditions. These composite microorganisms with extracellular electron transfer capabilities can reduce magnetite to Fe(II) under anoxic conditions and reduce extracellular oxygen to H under aerobic conditions. 2 O 2 ;H 2 O 2 It reacts with Fe(II) in a Fenton-like reaction to generate ·OH. At the same time, magnetite has good conductivity, which can promote extracellular electron transfer and increase the yield of ·OH.

[0025] (3) The generated reactive oxygen species (·OH and H 2 O 2 ) can react with the sugar chains in the cellulose molecules, destroying their molecular structure, and oxidize the sugar chains in the hemicellulose, causing them to break or change their structure. At the same time, active oxygen can also destroy the aromatic ring structure in the lignin molecule through oxidation reactions, leading to the destruction of the lignin molecular structure.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) Intermittent aeration allows the compost to alternate between aerobic and anoxic conditions. Under anoxic conditions, magnetite undergoes dissimilatory iron reduction to generate Fe(II). Under aerobic conditions, the complex microorganisms reduce extracellular oxygen to H 2 O 2 The two undergo a Fenton-like reaction to produce ·OH. Magnetite is an environmentally friendly material, and the composite bacterial agent also comes from nature and is harmless to humans and animals.

[0028] (2) The method of the present invention has high biocompatibility. It generates active oxygen through biological advanced oxidation, destroys the fiber structure, and accelerates the composting maturity, thus solving the problem of long composting cycle and low maturity caused by slow decomposition of lignocellulose in straw composting.

[0029] In summary, the method of accelerating straw composting by using magnetite and composite microorganisms to drive biological advanced oxidation accelerates the decomposition rate of straw by generating a large amount of active oxygen, alleviates the problem of low straw composting efficiency caused by the complex structure of lignocellulose, and improves the composting efficiency. The technology has low investment cost, simple operation, obvious improvement effect, and microorganisms only need to be added for the first time, without repeated addition. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram of a composting device of the present invention, wherein: 1. a temperature probe; 2. a barrel cover; 3. a barrel body; 4. a composting layer; 5. a porous baffle; 6. a leachate outflow port; 7. a leachate valve; 8. a leachate collecting barrel; 9. an air inlet; 10. an air inlet valve; 11. an air pump; and 12. an air outlet.

[0031] Figure 2 It is a top view of the composting device of the present invention. DETAILED DESCRIPTION

[0032] The method of accelerating straw composting by using magnetite and composite microorganisms to drive biological advanced oxidation is used as follows: Figure 1 The composting device shown in the figure comprises a barrel body 3 with an outer insulation layer, a temperature probe 1, a barrel cover 2, a composting layer 4, a porous baffle 5, a leachate outflow port 6, a leachate valve 7, a leachate collecting barrel 8, an air inlet 9, an air inlet valve 10, an air pump 11, and an air outlet 12, which are arranged from top to bottom.

[0033] The method of accelerating straw composting by using the above device to drive biological advanced oxidation using magnetite and composite microorganisms includes the following specific operation steps:

[0034] (1) Bacillus subtilis (Bibio, BNCC 109047) was cultured in LB medium for 24 h until OD600 was 1.4. The optimal value was added at a ratio of 1% (v / w). For example, 50 ml of Bacillus subtilis culture solution was added to a 5 kg pile.

[0035] White rot fungi (Beina Biotechnology Henan Industrial Microbial Strain Engineering Technology Research Center, BNCC 336257) were cultured with PDB medium for 48 hours, and the white rot fungi were directly crushed. The best value was to weigh the crushed solution at a ratio of 1% (v / w), for example, 50 ml of white rot fungus spore suspension was added to a 5 kg pile.

[0036] Weigh 2% of the optimum value of magnetite and add it to the above pile. For example, for a 5kg pile, weigh 100g of magnetite with a particle size of about 0.15mm and an Fe content of 62%-70%.

[0037] The straw and manure are mixed in a wet weight ratio of 1:1, and urea is used to adjust the C / N ratio to 25:1-30:1, and then the water content is adjusted to 55%-60% with tap water, and magnetite and the above-mentioned bacteria are added, placed in the compost layer 4 and mixed evenly, and the barrel cover 2 is covered.

[0038] (2) The air pump 11 is used for intermittent aeration, with an interval of 15 minutes per hour and an aeration volume of 45 ml / kg per minute. The air inlet valve 10 is closed every day, and the leachate valve 7 is opened to collect the leachate into the leachate collection bucket 8. After the collection is completed, the air inlet valve 10 is opened. The temperature in the composting device is controlled at 30°C. The entire composting cycle is 45 days. The temperature of the compost layer is detected every day using the temperature probe 1. Samples are taken after manual stirring and mixing on the 1st, 5th, 9th, 14th, 20th, 27th, 33rd, 39th and 45th days to detect the physical and chemical indicators of the compost layer 4, such as organic matter content, moisture content, pH, conductivity and maturity index.

[0039] Example 1

[0040] The composting device has an effective volume of 25L, the substrate is 2.5kg corn stalks, 2.5kg pig manure (water content 78%), the aeration interval is 15 minutes per hour, the aeration volume per minute is 45ml / kg, the initial organic matter content is 89.52%, and the C / N is adjusted to 25:1 by adding urea, and the moisture content is adjusted to 60%. The temperature is controlled at 30℃ by the insulation device. 100g magnetite (powdered, particle size of about 0.15mm) and composite microbial agent (1% Bacillus subtilis and 1% white rot fungi) are added to the substrate and run for 45 days. Finally, the maximum ·OH concentration is 0.080mmol / kg, H 2 O 2 The highest concentration was 4.3 mmol / kg, the humic acid content increased by 24.87%, and the seed germination rate (determination method see NYT525-2021 organic fertilizer standard) reached 95.02% on the 45th day.

[0041] Comparative Example 1

[0042] No magnetite was added, and other treatment conditions were the same as those in Example 1. Finally, the maximum concentration of ·OH was 0.065 mmol / kg, and H 2 O 2 The highest concentration was 2.7mmol / kg, the humic acid content was only 292mg / kg, and the seed germination rate (determination method see NYT525-2021 organic fertilizer standard) only reached 71.81% on the 45th day.

[0043] Comparative Example 2

[0044] Aeration was continued, and other treatment conditions were the same as those in Example 1. Finally, the maximum concentration of ·OH was 0.071 mmol / kg, and H 2 O 2 The highest concentration was 3.4mmol / kg, the humic acid content was only 308.35mg / kg, and the seed germination rate (determination method see NYT525-2021 Organic Fertilizer Standard) only reached 81.82% on the 45th day.

[0045] It can be seen that the effects of Comparative Examples 1 and 2 are not as good as those of Example 1.

[0046] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for accelerating straw composting by using magnetite and composite microorganisms to drive biological advanced oxidation, characterized in that: The method comprises the following steps: (1) mixing straw and feces in a wet weight ratio of 0.8-1.2:0.8-1.2 as a compost, adjusting the C / N ratio to 25-30:1, the water content to 55%-60%, adding magnetite, Bacillus subtilis liquid and crushed white rot fungus liquid, and placing in a composting device; The OD600 of the Bacillus subtilis liquid is 1.2-1.6, and the volume mass ratio of the liquid to the pile is 0.8-1.2% ml / g; The volume mass ratio of the crushed white rot fungus liquid to the pile is 0.8-1.2% ml / g; The amount of magnetite used is 1.5-2.5% of the mass of the pile; (2) The composting device is aerated intermittently, with an interval of 15 minutes per hour and an aeration rate of 40-50 ml / kg per minute. The leachate produced by fermentation in the composting body is collected every day. The temperature in the composting device is 28-32°C. The composting cycle is 40-50 days, during which the compost is turned several times.

2. The method according to claim 1, characterized in that The OD600 of the Bacillus subtilis bacterial solution in step (1) is 1.

4.

3. The method according to claim 2, characterized in that In the step (1), the volume mass ratio of the Bacillus subtilis liquid to the pile body is 1% in ml / g.

4. The method according to claim 3, characterized in that The volume mass ratio of the crushed white rot fungus liquid to the pile in step (1) is 1% in ml / g.

5. The method according to claim 4, characterized in that In the step (1), the wet weight ratio of straw to feces is 1:

1.

6. The method according to claim 5, characterized in that The amount of magnetite used in step (1) is 2% of the mass of the pile.

7. The method according to any one of claims 1 to 6, characterized in that: In the step (1), the particle size of the magnetite is 0.1-0.2 mm, and the Fe content is 62%-70%.

8. The method according to claim 7, characterized in that In the step (2), the aeration interval is 15 minutes per hour, and the aeration volume per minute is 45 ml / kg.

9. The method according to claim 8, characterized in that In the step (2), the temperature inside the composting device is 30°C.

10. The method according to claim 9, characterized in that The composting period in step (2) is 45 days.

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