Method for composting yellow pulp water and organic solid waste

Abstract

The invention discloses a method for composting yellow pulp water and organic solid waste, belonging to the technical field of composting. The method firstly utilizes yellow pulp water and organic solid waste to seal and stand for short-time biological acidification fermentation to obtain acidified materials with a pH value of 4.0-5.0, and then mixes the acidified materials with organic solid waste and yellow pulp water to perform aerobic composting fermentation as composting materials; nitrogen source substances are provided by the yellow pulp water to adjust the carbon-nitrogen ratio of the materials, and no additional nitrogen source substances need to be added, thereby reducing the production cost of the composting products; and the rich nutrients and trace elements in the yellow pulp water provide favorable conditions for the growth of microorganisms in the organic solid waste, which is beneficial to regulating the metabolism of the microorganisms and accelerating the composting process; the acidified materials are used to effectively adjust the pH value of the composting materials, and no other exogenous pH regulators need to be added; and the acidified materials enable the composting process to have the advantages of fast temperature rise, high temperature peak value in the high temperature period, rapid decomposition, high material decomposition degree, etc., and the composting products are of good quality.

Description

Technical Field

[0001] The invention belongs to the technical field of composting, and in particular relates to a method for composting yellow pulp water and organic solid waste. Background Art

[0002] Yellow pulp water, the wastewater generated during the tofu-making process, is rich in nutrients such as soluble polysaccharides, soybean oligosaccharides, proteins, saponins, amino acids, minerals, B vitamins, soybean isoflavones and carotenoids. At present, yellow pulp water is often used as a microbial culture medium, feed, and raw material for vinegar production, but has not been used in the field of composting.

[0003] Organic solid waste such as straw, branches, livestock and poultry manure, etc. are commonly used aerobic composting materials. Aerobic composting is a process in which aerobic microorganisms degrade macromolecular substances in organic solid waste under sufficient oxygen conditions to complete the process of humification, mineralization, and harmlessness. The mature compost products can be used for subsequent product production. In order to enable the microorganisms in the compost to proliferate and metabolize rapidly, it is necessary to adjust the carbon-nitrogen ratio of the material. If straw, branches, livestock and poultry manure and other materials with high carbon content are directly used for composting, it is easy to cause problems such as difficulty in composting, long composting time, and poor maturity. At the same time, there is usually a problem of high pH value of the material in this process, resulting in a high pH value of the compost product. According to the national standard NY / T 525-2021 "Organic Fertilizer", the pH value of organic fertilizer should be in the range of 5.5 to 8.5. The pH value of the compost product is too high, which is not conducive to the production of high-quality organic fertilizer, especially for alkaline soil.

[0004] The current solutions are as follows:

[0005] In order to obtain a suitable carbon-nitrogen ratio in the raw materials, nitrogen-rich substances are added to the raw materials. One method is to add chemical nitrogen fertilizers, such as urea, ammonia water, ammonium sulfate, etc. The other method is to add organic matter with high nitrogen content to the raw materials, such as amino acids, soybean meal, etc. The above two methods are both costly.

[0006] In order to reduce the pH value of compost, one method is to add inorganic strong acids, such as hydrochloric acid, sulfuric acid, nitric acid, etc., to the raw materials to forcibly control the pH value of the materials. However, the above strong acids are not only costly, but also highly corrosive, and will have a strong killing effect on microorganisms in the materials, such as natural microorganisms and functional microorganisms in the composting agents. The second is to add organic acids, such as humic acid, amino acid liquid, etc., to the raw materials or products, which are relatively expensive. The third is to add other acidic raw materials to the raw materials. For example, the Chinese invention patent with patent number CN202010043386.X discloses a compost additive containing superacidified biogas slurry and its preparation method and application. The invention uses superacidified biogas slurry produced by failed anaerobic biogas fermentation as the main raw material, and after centrifugation, pasteurization and other treatment steps, enzymes such as catalase, Lactobacillus johnsonii, Lactobacillus rhamnosus, vermiculite and diatomaceous earth, active microorganisms, and porous materials are added to prepare a compost additive. The compost additive is used for composting treatment, and it is disclosed that the superacidified biogas slurry contains volatile fatty acids that can adjust the pH value of the system. However, the superacidified biogas slurry in this scheme is a waste product in biogas production, and its source is not fixed. In addition, the superacidified biogas slurry needs to be pasteurized to remove pathogens, and volatile fatty acids also suffer certain losses due to heating. In addition, the composting time is relatively long, requiring 60 days. All of the above schemes require the introduction of exogenous substances into the raw materials to adjust the pH of the materials, which increases the cost investment and is not conducive to large-scale promotion. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a method for composting yellow pulp water and organic solid waste, which reduces the cost input and has a better quality of compost product.

[0008] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0009] A method for composting yellow pulp water and organic solid waste comprises the following steps:

[0010] (1) preparing an acidified material: mixing yellow pulp water and crushed organic solid waste uniformly, wherein the carbon-nitrogen ratio of the material is 29 to 32:1 and the water content is 90% to 94%, and the mixture is sealed and allowed to stand for 4 to 5 days to obtain an acidified material having a pH value of 4.0 to 5.0;

[0011] (2) Aerobic composting fermentation: The acidified material of step (1) is mixed with the crushed organic solid waste and yellow pulp water as compost material for aerobic composting fermentation, wherein the carbon-nitrogen ratio of the compost material is 25-30:1, the water content is 60%-70%, the initial temperature is 30° C.-55° C., the composting time is 16-18 days, and the composting product is obtained by composting.

[0012] Preferably, the carbon-nitrogen ratio of the material is 31:1, the water content is 92%, and it is sealed and left to stand for 4 days; the carbon-nitrogen ratio of the compost material is 25:1, the water content is 60%, the initial temperature is 35° C., and the composting time is 16 days.

[0013] Preferably, during aerobic fermentation, the compost material further includes a composting agent, which is a mixture of bacterial agents, enzyme preparations, and modified biochar.

[0014] Preferably, the bacterial agent accounts for 0.5% to 1% of the total mass of the compost material, the enzyme preparation accounts for 0.5% to 1% of the total mass of the compost material, and the modified biochar accounts for 1% to 3% of the total mass of the compost material.

[0015] It can be seen from the above technical scheme that the present invention provides a method for composting yellow slurry water and organic solid waste. Compared with the prior art, the method has the following beneficial effects: in the method, when preparing acidified materials and compost products, nitrogen source substances are provided by yellow slurry water to adjust the carbon-nitrogen ratio of the materials, and no additional nitrogen source substances need to be added, thereby reducing the production cost of the compost products. In addition, the rich nutrients and trace elements in the yellow slurry water provide favorable conditions for the growth of microorganisms in organic solid waste, which is beneficial for regulating the metabolic process of microorganisms, thereby accelerating the composting process; by adding the prepared acidified material to the original organic waste, the pH value of the compost material can be effectively adjusted, and no other exogenous pH regulators need to be added, thereby reducing the production cost of the compost product. In addition, the addition of the acidified material makes the compost have the advantages of fast heating, high temperature peak value in the high temperature period, rapid decomposition, high material maturity, etc. The high temperature generated when the compost material is piled up is directly used to kill pathogens, insect eggs, etc. in the raw materials, and the compost product has good quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a graph of volatile fatty acid content.

[0017] Figure 2 It is the effect of different additives on compost temperature. DETAILED DESCRIPTION

[0018] The technical solutions and technical effects of the embodiments of the present invention are further elaborated in detail.

[0019] The present invention provides a method for composting yellow pulp water and organic solid waste, comprising the following steps:

[0020] (1) preparing an acidified material: mixing yellow pulp water and crushed organic solid waste uniformly, wherein the carbon-nitrogen ratio of the material is 29 to 32:1 and the water content is 90% to 94%, and the mixture is sealed and allowed to stand for 4 to 5 days to obtain an acidified material having a pH value of 4.0 to 5.0;

[0021] Yellow pulp water is wastewater generated during the production of tofu and soy milk. It is rich in organic nutrients, especially high in nitrogen. The organic waste is any one of livestock and poultry manure, straw, garden waste, agricultural and food industry processing waste, and kitchen waste, or a mixture of two or more. After yellow pulp water is mixed with organic solid waste, nitrogen source substances are provided through the yellow pulp water to adjust the carbon-nitrogen ratio of the material, without the need to add additional nitrogen source substances. During the sealed static process, the natural microorganisms in the organic solid waste use hydrolysis reactions to hydrolyze large molecular organic substances into small molecular soluble substances, such as organic acids, ammonia, H 2 , CO 2 The hydrogen-producing and acetogenic bacteria in organic solid waste degrade the small molecule alcohols and organic acids produced into acetic acid, butyric acid, propionic acid, H 2 , CO 2 Etc., which significantly reduces the pH value of the material and makes it acidic overall.

[0022] (2) Aerobic composting fermentation: The acidified material of step (1) is mixed with the crushed organic solid waste and yellow pulp water as compost material for aerobic composting fermentation, wherein the carbon-nitrogen ratio of the compost material is 25-30:1, the water content is 60%-70%, the initial temperature is 30° C.-55° C., the composting time is 16-18 days, and the composting product is obtained by composting.

[0023] In step (1), after the organic solid waste and yellow slurry water are acidified, the obtained acidified material is acidic as a whole. The purpose of mixing the acidified material with the organic solid waste and yellow slurry water as a compost material is: on the one hand, the yellow slurry water provides a nitrogen source to adjust the carbon-nitrogen ratio of the compost material, and there is no need to add additional nitrogen sources. The rich nutrients and trace elements in the yellow slurry water provide favorable conditions for the growth of microorganisms in the organic solid waste, which is beneficial for regulating the metabolic process of the composting microorganisms, thereby accelerating the composting process; on the other hand, the acidified material is used to adjust the pH of the compost material, and there is no need to add exogenous substances for pH adjustment. This is because the microorganisms in the organic waste can quickly utilize the acidified material. Small molecular organic matter in aerobic composting can be removed, which is beneficial to reducing the pH value of composting materials. Since most functional microorganisms in aerobic composting prefer weak acid environments, acidified materials can provide a suitable environment for functional microorganisms in aerobic composting, accelerate the metabolism and material conversion of aerobic microorganisms, and the metabolism and material conversion process of aerobic microorganisms will generate a lot of heat, thereby promoting the aerobic composting process, making the composting have the advantages of fast heating, high temperature peak value in the high temperature period, rapid decomposition, high material maturity, etc. The high temperature generated when the composting materials are piled up is directly used to kill the pathogens, insect eggs, etc. in the raw materials, and the compost product quality is good.

[0024] Specifically, the carbon-nitrogen ratio of the material is 31:1, the water content is 92%, and it is sealed and left to stand for 4 days; the carbon-nitrogen ratio of the compost material is 25:1, the water content is 60%, the initial temperature is 35° C., and the composting time is 16 days.

[0025] Furthermore, during aerobic fermentation, the compost material further includes a composting agent, which is a mixture of a bacterial agent, an enzyme preparation, and modified biochar. The bacterial agent accounts for 0.5% to 1% of the total mass of the compost material, the enzyme preparation accounts for 0.5% to 1% of the total mass of the compost material, and the modified biochar accounts for 1% to 3% of the total mass of the compost material.

[0026] The present invention is described in detail below with reference to the embodiments.

[0027] The organic solid waste used in the following examples is a mixture of straw and branch powder, and its physical and chemical properties are shown in Table 1.

[0028] Table 1 Basic properties of fermentation materials

[0029]

[0030] The bacterial agents used include cellulose-degrading bacteria, lignin-degrading bacteria and other microorganisms that promote the degradation of fiber-like substances.

[0031] The enzyme preparation used contains enzymes such as cellulose degrading enzyme, laccase, pectinase, etc. that promote the degradation of waste.

[0032] The modified biochar used is nano-iron-chitosan modified biochar or nano-iron-carboxymethyl cellulose modified biochar. Adding nano-iron-chitosan modified biochar or nano-iron-carboxymethyl cellulose modified biochar to compost can significantly promote the metabolic activity of microorganisms during the composting process, and has an adsorption effect on volatile gases such as ammonia and volatile organic acids generated during the composting process, which is conducive to the rapid decomposition of materials, reduces the carbon and nitrogen losses of composting, thereby accelerating the composting process and improving the quality of the compost product.

[0033] The preparation process of the nano-iron-chitosan modified biochar or nano-iron-carboxymethyl cellulose modified biochar is as follows:

[0034] (1) crushing the branches to a particle size of 0.5 mm, pyrolyzing at 400-450° C. in a nitrogen atmosphere at a heating rate of 5-10° C. / min for 20-24 h to obtain biochar;

[0035] (2) dissolving chitosan or sodium carboxymethyl cellulose in deionized water at a mass / volume ratio (m / v) of 1:25 to fully dissolve the chitosan or sodium carboxymethyl cellulose solution to prepare a 40 g / L chitosan solution or sodium carboxymethyl cellulose solution;

[0036] (3) adding zero-valent iron powder to a NaOH solution and stirring until the zero-valent iron is completely dissolved to prepare a 20 g / L zero-valent iron solution;

[0037] (4) Mix the zero-valent iron solution and the chitosan solution or the sodium carboxymethyl cellulose solution in a volume ratio of 1:2.5 to obtain a mixed solution, and add biochar to the mixed solution slowly while stirring. The mass ratio of the mixed solution to the biochar is 4.5:1;

[0038] (5) The mixture was subjected to ultrasonic treatment for 30 min, constant temperature oscillation for 2 h, vacuum filtration and drying. The dried material was placed in a vacuum furnace, nitrogen was passed through, and heated at 700 °C for 2 h. The temperature was cooled to room temperature under nitrogen and maintained for 2 h to obtain modified biochar. The modified biochar was washed with clean water and deionized water until the pH was neutral, and then placed in an oven for drying for later use.

[0039] 1. Preparation of acidified materials

[0040] The yellow pulp water, branch powder and clean water were mixed in a mass ratio of 1:2:20, and the carbon-nitrogen ratio of the material was about 31:1, the water content was 92%, and the acidified material was obtained by sealing and standing for 4 days. The pH value of the acidified material was 4.86, indicating that the acidified material was successfully prepared.

[0041] 2. Organic acids in acidified materials

[0042] Gas chromatography was used to determine the types and contents of organic acids in the acidified material. The results were as follows: Figure 1 As shown in the figure, 7 volatile fatty acids were detected, and the content was in descending order: acetic acid, butyric acid, propionic acid, isobutyric acid, caproic acid, isovaleric acid, and valeric acid. Among them, acetic acid and butyric acid are the main volatile organic acids.

[0043] 3. Effects of acidified materials and ripening agents on composting

[0044] Yellow pulp water, branch powder and acidified materials were mixed in a mass ratio of 1:2:1.7 and used as compost materials for aerobic composting fermentation. The carbon-nitrogen ratio of the compost materials was about 25:1, and a compost material with a water content of 60% was obtained. The effect of acidified materials on composting was studied. Furthermore, while adding acidified materials, decomposition promoters (bacterial agents, enzyme preparations, modified biochar) were also added, wherein the bacterial agents accounted for 0.5% of the total mass of the compost materials, the enzyme preparations accounted for 0.5% of the total mass of the compost materials, and the modified biochar accounted for 3% of the total mass of the compost materials. The effect of the combination of acidified materials and decomposition promoters on composting was studied. The control group was used without adding acidified materials and only adding decomposition promoters. The experimental settings are shown in Table 2 below:

[0045] Table 2 Experimental design

[0046]

[0047] See also Figure 2 The results of the effects of different additives on compost temperature showed that the overall trend of compost temperature change was first rising and then falling. In the early stage of fermentation, the temperature of the pile body rose rapidly. Compared with the case without acidifying materials (T1), the addition of acidifying materials (T3) made the compost material enter the high temperature period 2 days earlier, and the peak temperature of the pile increased by 2.6℃. Compared with the addition of only accelerators (T2) or only acidifying materials (T3), when acidifying materials and accelerators were added together (T4), on the first day of composting, the compost entered the high temperature period, and the pile temperature exceeded 60.0℃, which was 1.8℃ and 3.5℃ higher than that of T2 and T3, respectively. During the composting process, the peak temperature of the T4 treatment was 70.8℃, which was 1.5~3.8℃ higher than that of the composts of other treatments (T1~T3). It shows that the acidifying materials and accelerators have a synergistic effect, jointly promoting the increase of the pile temperature, thereby helping to accelerate the composting process.

[0048] Referring to Table 3, the pH value, conductivity, total nitrogen and total carbon in the composting process were tested. The results show that at the end of composting, the pH value of the compost in the T4 treatment was the lowest, which was 7.31, which was 29.21% to 41.94% lower than that of other treatments. When no acidifying material was added (T1), the conductivity of the compost product was only reduced by 6.25%, while after the addition of acidifying material (T3), the conductivity of the compost product was reduced by 14.11%, and after the acidifying material and the composting agent were added together (T4), the conductivity of the compost product was reduced by 17.18%. The salt content can be reflected by measuring the conductivity. The above results show that the salt content of the compost product obtained by the method of the present invention is significantly reduced, which is beneficial to reduce the risk of salt damage caused by the application of organic fertilizers. Without adding acidifying material (T1), the carbon and nitrogen losses of the compost are 34.21% and 37.36% respectively. After adding acidifying materials (T3), the carbon and nitrogen losses of the compost decreased to 25.92% and 22.65%, indicating that the addition of acidifying materials promoted the material transformation of the compost and reduced the carbon and nitrogen losses. When acidifying materials and accelerators were added together (T4), the carbon and nitrogen losses of the compost were the lowest, at 20.13% and 18.64%, respectively.

[0049] Table 3 Composting parameters

[0050]

[0051] See Table 4. After composting, the available nutrients of the compost products were tested. Compared with T1, after adding acidified materials (T3), the contents of alkaline nitrogen, available phosphorus, and available potassium in the compost products were increased by 14.13%, 4.04%, and 1.45%, respectively. After the acidified materials and the composting agent were added together (T4), the alkaline nitrogen content was 10.22% to 25.77% higher than that of other treatments (T1 to T3), the available phosphorus content was 3.22% to 7.39% higher than that of other treatments (T1 to T3), and the available potassium content was 3.82% to 5.33% higher than that of other treatments (T1 to T3). This shows that the acidified materials and the composting agent have a synergistic effect, which increases the activity of urease, sucrase, and catalase in the compost materials, thereby promoting nutrient conversion.

[0052] Table 4 Available nutrients of compost products treated with different methods

[0053]

[0054] The maturity level of compost can be determined by the biological effect on plants after application. The seed germination index comprehensively reflects the phytotoxicity of compost and is the most sensitive and reliable indicator for evaluating the maturity of compost. Referring to Table 5, the germination inhibition effect of materials on seeds varies with the degree of maturity. According to the national standard NY / T525-2021 "Organic Fertilizer", the technical indicator of organic fertilizer maturity is a seed germination index ≥ 70%. When the compost is fermented to the maturity stage, all treated materials have reached the maturity standard (≥ 80%), and the seed germination index of each treatment is 81.75% to 86.37%. After adding acidified materials (T3 and T4), the maturity time was 18 days and 16 days, respectively, which was shortened by 2 to 4 days compared with the group without acidified materials (T1), indicating that acidified materials can accelerate the maturity of compost. Compared with adding only the composting agent (T2) or only the acidifying material (T3), adding both the acidifying material and the composting agent (T4) resulted in the highest seed germination index of the compost product, reaching 86.37%, and the shortest composting time. The reason is that the acidifying material and the composting agent play a synergistic role, which accelerates the composting.

[0055] Table 5 Compost maturity time and seed germination index of different treatments

[0056]

[0057] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for composting yellow pulp water and organic solid waste, characterized in that: The following steps are involved: (1) Preparing an acidified material: mixing yellow pulp water and crushed organic solid waste uniformly, wherein the carbon-nitrogen ratio of the material is 29-32:1 and the water content is 90%-94%, and the mixture is sealed and allowed to stand for 4-5 days to obtain an acidified material having a pH value of 4.0-5.0; (2) Aerobic composting fermentation: The acidified material of step (1) is mixed with the crushed organic solid waste and yellow pulp water as compost material for aerobic composting fermentation. The carbon-nitrogen ratio of the compost material is 25-30:1, the water content is 60%-70%, the initial temperature is 30°C-55°C, the composting time is 16-18 days, and the compost product is obtained by composting.

2. The method for composting yellow pulp water and organic solid waste according to claim 1, characterized in that: The carbon-nitrogen ratio of the material is 31:1, the water content is 92%, and it is sealed and left to stand for 4 days; the carbon-nitrogen ratio of the compost material is 25:1, the water content is 60%, the initial temperature is 35° C., and the composting time is 16 days.

3. The method for composting yellow pulp water and organic solid waste according to claim 1, characterized in that: During aerobic fermentation, the compost material further includes a composting agent, which is a mixture of a bacterial agent, an enzyme preparation, and modified biochar, wherein the bacterial agent includes cellulose-degrading bacteria and lignin-degrading bacteria, the enzyme preparation includes cellulose-degrading enzyme, laccase, and pectinase, and the modified biochar is nano-iron-chitosan modified biochar or nano-iron-carboxymethyl cellulose modified biochar; The preparation process of the nano-iron-chitosan modified biochar or nano-iron-carboxymethyl cellulose modified biochar is as follows: (1) crushing the branches to a particle size of 0.5 mm, pyrolyzing at 400-450° C. in a nitrogen atmosphere at a heating rate of 5-10° C. / min for 20-24 h to obtain biochar; (2) dissolving chitosan or sodium carboxymethyl cellulose in deionized water at a mass / volume ratio (m / v) of 1:25 to fully dissolve the chitosan or sodium carboxymethyl cellulose solution to prepare a 40 g / L chitosan solution or sodium carboxymethyl cellulose solution; (3) adding zero-valent iron powder to a NaOH solution and stirring until the zero-valent iron is completely dissolved to prepare a 20 g / L zero-valent iron solution; (4) Mix the zero-valent iron solution and the chitosan solution or the sodium carboxymethyl cellulose solution in a volume ratio of 1:2.5 to obtain a mixed solution, and add biochar to the mixed solution slowly while stirring. The mass ratio of the mixed solution to the biochar is 4.5:1; (5) The mixture was subjected to ultrasonic treatment for 30 min, constant temperature oscillation for 2 h, vacuum filtration and drying. The dried material was placed in a vacuum furnace, nitrogen was passed through, and heated at 700 °C for 2 h. The temperature was cooled to room temperature under nitrogen and maintained for 2 h to obtain modified biochar. The modified biochar was washed with clean water and deionized water until the pH was neutral, and then placed in an oven for drying for later use.

4. The method for composting yellow pulp water and organic solid waste according to claim 3, characterized in that: The bacterial agent accounts for 0.5%~1% of the total mass of the compost material, the enzyme preparation accounts for 0.5%~1% of the total mass of the compost material, and the modified biochar accounts for 1%~3% of the total mass of the compost material.

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