Straw-based modified biofilm, preparation method and application thereof

Abstract

The present application provides a straw-based modified biofilm and a preparation method and application thereof, relates to the technical field of biofilm, and the present application liquefies crop straw into mixed organic solvent-bio-polyol, then crosslinks and couples the original straw by using the bio-polyol as a crosslinking agent, adds a curing agent in the process of crosslinking and coupling to enhance the crosslinking effect, obtains a straw-based modified biofilm material with compact structure and excellent adsorption performance, and further applies the straw-based modified biofilm material to the odor control process of aerobic composting, and a remarkable odor emission reduction effect is obtained.

Description

Technical Field

[0001] This invention relates to the field of biofilm technology, and in particular to a straw-based modified biofilm, its preparation method, and its application. Background Technology

[0002] With the advancement of technology and the development of agricultural modernization, the yield of crop straw has been increasing year by year. Agricultural straw generally refers to the residue left after harvesting wheat, rice, corn, potatoes, oilseeds, cotton, sugarcane, and other crops. As a typical high-carbon source of lignocellulosic waste, its resource utilization has always been a matter of great concern. Composting is an effective means of resource-based treatment of livestock and poultry manure. However, the composting process often produces a large amount of odorous gases (NH3, H2S, etc.), which not only reduces the nutrient content of compost products but also harms the health of surrounding people and causes secondary pollution.

[0003] Because crop straw has a high carbon content, large particle size, and strong water absorption, it can regulate the moisture content of the compost pile, increase porosity, and reduce odor emissions, and is often used as an additive in the compost pile. It can also be directly applied to the top of the pile, a simple operation. However, virgin straw is loose in texture, has poor cohesion, high air permeability, and is easily mixed into the pile during turning, resulting in limited and unstable emission reduction effects.

[0004] Currently, there is a smart molecular membrane barrier technology in industry, which uses a specially designed functional membrane as a covering material for the aerobic fermentation treatment of organic waste. This functional membrane has selective permeability, allowing small molecules such as water vapor and carbon dioxide to pass through, while blocking larger molecules such as odorous gases, effectively trapping odors generated during composting. However, molecular membranes are expensive, significantly increasing composting costs and making them difficult to implement in some composting projects. Summary of the Invention

[0005] In view of this, the present invention provides a straw-based modified biofilm, its preparation method, and its application. The present invention liquefies crop straw into a mixed organic solvent—biopolyol—and then uses the biopolyol as a crosslinking agent to crosslink and couple the virgin straw. A curing agent is added during the crosslinking and coupling process to enhance the crosslinking effect, resulting in a straw-based modified biofilm material with a compact structure, high mechanical strength, and excellent adsorption properties. Furthermore, the straw-based modified biofilm material is applied to the odor control process of aerobic composting, achieving a significant odor reduction effect.

[0006] The first objective of this invention is to provide a method for preparing a straw-based modified biofilm, comprising the following steps:

[0007] (1) Mix straw, polyol and curing agent evenly to obtain a mixture for later use;

[0008] (2) The mixture described in step (1) is stretched into a film and placed at 70-80°C for 15-20 minutes to react and then solidified to obtain a straw-based modified biofilm.

[0009] Furthermore, the straw can be any crop straw known in the art, including but not limited to one or more of the following: corn straw, wheat straw, rice straw, potato straw, rapeseed straw, cotton straw, and sugarcane straw. Corn straw is further preferred.

[0010] Furthermore, the mass ratio of straw, polyol and curing agent in step (1) is 1 to 2:5:5.

[0011] Furthermore, the polyol mentioned in step (1) is a biopolyol.

[0012] Furthermore, the preparation method of the biopolyol includes the following steps: mixing straw, liquefying agent and catalyst and reacting them to obtain biopolyol.

[0013] Furthermore, the liquefying agent is a mixture of polyethylene glycol-400 and ethylene glycol, wherein the mass ratio of polyethylene glycol-400 (PEG400) to ethylene glycol (EG) in the mixture is 3:1 to 7:2; the catalyst is concentrated sulfuric acid with a mass concentration of 98%, wherein the amount of concentrated sulfuric acid added is 2.8 to 3.2% of the mass of the liquefying agent; the size of the straw is 2 to 8 mesh, the moisture content of the straw is 5 to 10%, and the mass ratio of the straw to the liquefying agent is 1:7 to 8.

[0014] Furthermore, the reaction temperature is 145–155°C, and the reaction time is 30–40 min.

[0015] Furthermore, the curing agent in step (1) includes any one of polymethylene polyphenyl polyisocyanate (PAPI), toluene diisocyanate (TDI), and diphenylmethane diisocyanate (MDI).

[0016] The curing agent is further preferably polymethylene polyphenyl polyisocyanate (PAPI).

[0017] Furthermore, the total consumption of raw materials for membrane material production—polyols, PAPI, and straw—is 2000±50 g / m³. 3 .

[0018] A second objective of this invention is to provide a straw-based modified biofilm prepared by the method described above.

[0019] Furthermore, the straw-based modified biofilm has a thickness of 0.8–1.2 cm, a tensile strength of 65–75 N, and a bulk density of 19.2–20.2 kg·m³.-3 The saturated water absorption rate is 0.98–1.08 g·g. -1 The color is black.

[0020] This invention uses biopolyol as a crosslinking agent to crosslink and couple straw. In order to enhance the crosslinking effect and ensure that the mixed material can be solidified and molded, this invention also introduces polymethylene polyethyl polyisocyanate (PAPI) of the same mass as the polyol as a curing agent. After the three raw materials are mixed, they are stretched into a film and then subjected to a polymerization reaction to solidify and mold, thus obtaining a straw-based modified biofilm.

[0021] In this invention, a polyol undergoes a polymerization reaction with a curing agent to generate a biodegradable polyurethane foam, which is the main component of the straw-based modified biofilm, giving the membrane material a black appearance. Simultaneously, the straw-based modified biofilm polyurethane foam is endowed with the following properties: its surface is rich in oxygen-containing functional groups, its pore structure is complex, its tensile strength is high and it is flexible, making the material lightweight and easy to transport. Furthermore, the addition of virgin straw provides support within the polyurethane foam, improving the mechanical strength of the biofilm material, while also providing more adsorption sites on the material surface.

[0022] The third objective of this invention is to provide an application of straw-based modified biofilm in in-situ control of odor emissions during aerobic composting.

[0023] Furthermore, the specific steps of the application are as follows: The composting process is carried out in a closed space, and a straw-based modified biofilm is used as an adsorption and retention material to cover the surface of the compost material. During the adsorption process, the moisture content of the compost material is adjusted to 60-70%, the carbon-to-nitrogen ratio is 15-25, and oxygen needs to be supplemented during the in-situ odor emission control process, with a ventilation rate of 0.18-0.24 L·kg⁻¹. -1 DM·min -1 The pile should be turned over every 7 days.

[0024] Furthermore, the indicators for odor reduction effectiveness are the emissions of ammonia (NH3) and hydrogen sulfide (H2S).

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The production of straw-based modified biofilm realizes the resource utilization of crop straw. Its application in aerobic composting can achieve good odor reduction effect and reduce the secondary pollution of compost gas to the environment.

[0027] 2. Compared with molecular membranes, straw-based modified biofilms significantly reduce composting costs while ensuring good odor reduction during composting. Moreover, the straw-based modified biofilms prepared by this invention are easy to move, saving energy consumption of mechanical equipment such as film rolling machines. In the later stages of composting, they can be turned into the compost pile as part of the pile, and their degradable properties can be used to promote the decomposition of the pile. Attached Figure Description

[0028] Figure 1 This is a photograph of the straw-based modified biofilm from Example 1 of the present invention;

[0029] Figure 2 This is an example diagram of the gas emission reduction experiment of aerobic composting of straw-based modified biofilm in Embodiment 1 of the present invention;

[0030] Figure 3 This is an electron microscope scanning image of the surface of the straw-based modified biofilm of Example 1 of the present invention;

[0031] Figure 4 These are Fourier transform infrared spectra of the straw-based modified biofilm and the surface of native corn straw in Example 1 of this invention.

[0032] Figure 5 This describes the emission of ammonia (NH3) and hydrogen sulfide (H2S) during the aerobic composting gas emission reduction experiment of straw-based modified biofilm in Example 1 of this invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] Unless otherwise specified, the test methods or experimental methods described in the following examples are all conventional methods; unless otherwise specified, the raw materials and additives are obtained from conventional commercial sources or prepared by conventional methods.

[0035] The test methods used in the following embodiments and comparative examples are as follows:

[0036] 1) The surface characteristics of the membrane material were observed using a desktop electronic scanner (TM-4000, Japan).

[0037] 2) The types of functional groups on the membrane material and the original straw surface were compared using Fourier transform infrared spectroscopy.

[0038] 3) The temperature of the compost pile was measured twice daily, once at 8:00 AM and once at 8:00 PM, by inserting a portable thermometer into the side of the composting reactor. The H2S content was measured daily using a portable biogas analyzer (Biogas-5000, Geotech), and the daily H2S emissions were calculated using formula (1):

[0039]

[0040] In formula (1), E(g / d·kg DM) -1 Q(m) represents the daily emissions of gas. 3 / h) is the ventilation rate, b (ppm) is the volume fraction of the gas, M (g / mol) is the molar mass of the gas, T0 (°C) is the ambient temperature, and m is the mass of dry matter.

[0041] NH3 was absorbed using 2% boric acid, then quantified by titration with 0.1 mol / L sulfuric acid, and the daily NH3 emission was calculated using formula (2):

[0042]

[0043] Among them, E(g / d·kg DM) -1 ) represents the daily emission of NH3, V (ml) represents the amount of sulfuric acid used, C (mol / L) represents the concentration of sulfuric acid, X (s) represents the time for NH3 absorption, and m represents the mass of dry matter.

[0044] The cumulative emissions of the gas are calculated according to formula (3):

[0045]

[0046] Among them, CE n (g / kg DM) represents the cumulative gas emissions on day n, E i Let be the daily gas emissions on day i.

[0047] Example 1

[0048] A method for preparing a straw-based modified biofilm, the specific steps of which are as follows:

[0049] (1) Liquefaction of crop straw: Polyethylene glycol-400 (PEG400) and ethylene glycol (EG) were selected as liquefying agents and 98% concentrated sulfuric acid was used as catalyst. The catalyst was added to the liquefying agent to obtain a mixed solvent. The amount of catalyst added was 3% of the mass of the liquefying agent. The mass ratio of polyethylene glycol-400 (PEG400) and ethylene glycol (EG) in the liquefying agent was 3:1. The mixed solvent was placed in a double-layered glass reactor with a volume of 5L, stirred and heated. When the temperature reached 150℃, corn straw with a mass of 1 / 7 of the liquefying agent, a size of 2-8 mesh and a moisture content of 8% was added. The heating was continued for 30 minutes. After the straw was fully liquefied, the heating was stopped. After the liquefied product cooled, it was removed from the reactor. The liquefied product was mainly biopolyol.

[0050] (2) The biopolyol, native corn stalks with a size of 2-8 mesh, and polymethylene polyethyl polyisocyanate (PAPI) resin described in step (1) are mixed evenly in a mass ratio of 4:1:4. The mixture is stretched into a film and placed at 75°C. After a polymerization reaction of 15 min, it is solidified to obtain a straw-based modified biofilm.

[0051] The total consumption of raw materials (biopolyols, PAPI, and straw) for membrane material production is 1950 g / m³. 3 .

[0052] The prepared straw-based modified biofilm had a thickness of 1.1 cm, a tensile strength of 69.4 N, and a bulk density of 19.7 kg·m³. -3 The saturated water absorption rate is 1.03 g·g. -1 The color is black.

[0053] The specific steps for applying the straw-based modified biofilm described in step (2) to the in-situ control of odor emissions during aerobic composting are as follows:

[0054] The composting process was carried out in a 60L sealed fermentation tank. The compost material consisted of 85% fresh pig manure and 15% corn stalks (based on wet weight). After mixing the pig manure and corn stalks, the mixture was placed in the sealed fermentation tank, and the moisture content of the compost material was adjusted to 65%, the carbon-to-nitrogen ratio (C / N) was set to 15–25, and the aeration rate was 0.24 L / kg. -1 DM·min -1 Straw-based modified biofilm was applied to the surface of the compost material, and the compost was turned over every 7 days for a total of 42 days. During the composting process, the emission of odor (NH3, H2S) was collected and measured daily.

[0055] The performance of the straw-based modified biofilm prepared in Example 1 was tested, and the results are as follows:

[0056] Figure 3This indicates that the biofilm material prepared in this embodiment has a complex porous structure on its surface, with the original straw portion encapsulated by polyurethane foam generated during the curing process and partially exposed on the material surface. This demonstrates that the membrane material possesses the characteristics of polyurethane foam while retaining, to a certain extent, the properties of the original straw.

[0057] Figure 4 This indicates that the functional groups on the surface of the biofilm material prepared in this embodiment are significantly different from those of native straw. Compared to native straw, the -OH stretching vibration peak on the surface of the biofilm material is smaller, while the peak intensities of CH, C=C, C=O, COC, and CO are larger, and an additional stretching vibration peak of aromatic CH is present. This indicates that the surface of the biofilm material contains more oxygen and active groups.

[0058] Comparative Example 1

[0059] The difference from Example 1 is that the compost material surface is not covered, but the rest of the steps are the same as in Example 1.

[0060] Performance tests were conducted on the emissions of NH3 and H2S during the composting process of Example 1 and Comparative Example 1: Figure 5 The results indicate that the emissions of NH3 and H2S during the composting process may be due to the complex porous structure of the biofilm material and the physicochemical adsorption of odors by the oxygen-containing functional groups on its surface. Compared with the uncovered case in Comparative Example 1, the biofilm material in Example 1 reduced NH3 and H2S emissions by 45.27% and 35.85%, respectively, in the 42-day composting experiment.

[0061] Comparative Example 2

[0062] The difference from Example 1 is that the straw-based modified biofilm was replaced with a molecular membrane (Oxford cloth + expanded polytetrafluoroethylene + Oxford cloth), while the remaining steps remained the same as in Example 1. The results showed that the molecular membrane's effect on reducing compost odor was similar to that of Example 1, but its odor reduction cost was significantly higher than that of Example 1.

[0063] Comparative Example 3

[0064] The difference from Example 1 is that the straw-based modified biofilm was replaced with corn straw, while the remaining steps remained the same as in Example 1. The results showed that corn straw was insufficient to provide stable control over odor emissions from aerobic composting, while the biofilm material prepared in Example 1 not only achieved in-situ control of odor emissions throughout the composting process but also provided a more stable emission reduction effect.

[0065] Comparative Example 4

[0066] The difference from Example 1 is that the straw-based modified biofilm was replaced with biochar. Results showed that biochar had a poor effect on reducing compost odor emissions.

[0067] Comparative Example 5

[0068] The difference from Example 1 is that the straw-based modified biofilm was replaced with microbial inoculants (mainly Lactobacillus, Flavobacterium, Candida, Bacillus, Actinomycetes, Lysozyme, and Psychrobacterium). Results showed that microbial inoculants could effectively control compost odor emissions; however, the use of expensive microbial inoculants significantly increased composting costs.

[0069] This invention also investigated the effects of different sizes and amounts (relative to the mass of biopolyols) of virgin corn stalks on the mechanical strength of membrane materials. Three sizes and four amounts of corn stalks were selected to prepare 12 membrane materials with different structures. The tensile strength of these membrane materials was measured, and the results are shown in the table below:

[0070]

[0071] The results showed that the tensile strength of the membrane material decreased with increasing corn stalk addition. Furthermore, excessive stalk addition led to a decrease in the mechanical strength of the membrane material, making it prone to breakage and inconvenient for transportation or use. When the stalk addition was 25%, the cross-linking between the polyurethane foam and the stalk reached saturation. At this point, the reduction in stalk size weakened the membrane material's support, thus reducing its tensile strength.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The application of a straw-based modified biofilm in in-situ odor emission control during aerobic composting, characterized in that, The method for preparing the straw-based modified biofilm includes the following steps: (1) Mix straw, polyol and curing agent evenly to obtain a mixture for later use; (2) The mixture described in step (1) is stretched into a film, placed at 70~80℃, reacted for 15~20 min, and then solidified to obtain a straw-based modified biofilm; The polyol mentioned in step (1) is a biopolyol.

2. The application of the straw-based modified biofilm according to claim 1 in in-situ control of odor emissions during aerobic composting, characterized in that, The mass ratio of straw, polyol and curing agent in step (1) is 1~2:5:

5.

3. The application of the straw-based modified biofilm according to claim 1 in in-situ control of odor emissions during aerobic composting, characterized in that, The preparation method of the biopolyol includes the following steps: mixing straw, liquefying agent and catalyst and reacting them to obtain biopolyol.

4. The application of the straw-based modified biofilm according to claim 3 in in-situ control of odor emissions during aerobic composting, characterized in that, The liquefying agent is a mixture of polyethylene glycol-400 and ethylene glycol, wherein the mass ratio of polyethylene glycol-400 to ethylene glycol in the mixture is 3:1 to 7:2; the catalyst is concentrated sulfuric acid with a mass concentration of 98%, wherein the amount of concentrated sulfuric acid added is 2.8 to 3.2% of the mass of the liquefying agent; the size of the straw is 2 to 8 mesh, the moisture content of the straw is 5 to 10%, and the mass ratio of the straw to the liquefying agent is 1:7 to 8.

5. The application of the straw-based modified biofilm according to claim 3 in in-situ control of odor emissions during aerobic composting, characterized in that, The reaction temperature is 145~155℃, and the reaction time is 30~40 min.

6. The application of the straw-based modified biofilm according to claim 1 in in-situ control of odor emissions during aerobic composting, characterized in that, The curing agent in step (1) includes any one of polymethylene polyphenyl polyisocyanate (PAPI), toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI).

7. The application of the straw-based modified biofilm according to claim 1 in in-situ control of odor emissions during aerobic composting, characterized in that, Straw-based modified biofilms are applied to the surface of compost materials.

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