Method for preparing slow-release organic fertilizer using tofu residue and biogas residue

Abstract

The present invention belongs to the technical field of slow-release organic fertilizers, and specifically relates to a method for preparing slow-release organic fertilizers using tofu dregs and biogas residues, comprising: step (1), pre-treating the biogas residues to obtain a liquid phase portion rich in nitrogen and phosphorus; step (2), pre-treating the tofu dregs to obtain a fiber-based high-water-absorbent material; and step (3), mixing and preparing a slow-release organic fertilizer loaded with nitrogen and phosphorus. The method of the present invention can not only solve the problem of quick disposal of tofu dregs due to their short shelf life and susceptibility to mildew, but also solve the problem of large amounts of biogas residues generated in biogas projects, and can also obtain slow-release organic fertilizers that are beneficial to agricultural development. The method is very suitable for the treatment of tofu dregs and biogas residue waste, resource recovery, and the promotion of green agricultural development, and has a very high prospect for industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of slow-release organic fertilizers, and in particular relates to a method for preparing slow-release organic fertilizers by utilizing bean curd residues and biogas residues. Background Art

[0002] Fertilizers play a vital role in intensive agricultural production. Over the past few decades, large quantities of commercial fertilizers (such as nitrogen and phosphorus fertilizers) have been used to increase crop yields. However, excessive fertilizer use not only results in a significant waste of resources and money due to the inability of crops to absorb nutrients, but also causes serious ecological and environmental problems, such as a significant reduction in biodiversity, eutrophication, and water pollution.

[0003] A promising solution to the problems caused by chemical fertilizers is the development of slow-release organic fertilizers, which gradually release nutrients after use, helping to improve fertilizer utilization efficiency.

[0004] Currently available slow-release organic fertilizers often use chitosan, carboxymethyl cellulose, starch polymers, biochar copolymers, and wheat straw adsorbents as slow-release materials. Current slow-release fertilizers are relatively expensive, primarily due to the high cost of the slow-release materials used and, secondly, the frequent use of chemical fertilizers as a nutrient source. Furthermore, these slow-release fertilizers do not significantly contribute to waste disposal, hindering resource recovery and the development of a circular economy.

[0005] Biogas residue, the residue left after anaerobic fermentation of various perishable wastes, is a common component of large and medium-sized biogas projects in my country, necessitating the development of effective methods for its resource utilization. Furthermore, tofu dregs, a daily processing waste generated by various soy product companies and factories, contain a high amount of crude fiber but are difficult to store at room temperature, presenting a pressing problem for related companies. Summary of the Invention

[0006] In order to solve the above problems, the present invention proposes a method for synergistically processing two types of waste, tofu dregs and biogas residues, into high-value-added slow-release organic fertilizer. This method can not only solve the problem of rapid disposal of tofu dregs with short shelf life and easy mildew, but also solve the problem of large amounts of biogas residues generated in biogas projects, and can also obtain slow-release organic fertilizer that is beneficial to agricultural development.

[0007] Therefore, the present invention provides a method for preparing a slow-release organic fertilizer using bean curd residue and biogas residue, comprising:

[0008] Step (1), pre-treating the biogas residue to obtain a liquid phase rich in nitrogen and phosphorus elements;

[0009] Step (2), pre-treating the tofu dregs to obtain a fiber-based highly absorbent material;

[0010] Step (3), preparing a slow-release organic fertilizer loaded with nitrogen and phosphorus.

[0011] In a preferred embodiment, the step (1) comprises: placing the biogas residue in a microwave oven, sterilizing the biogas residue with the assistance of microwaves, and filtering the treated biogas residue to obtain a liquid phase portion rich in nitrogen and phosphorus elements.

[0012] The biogas residue is the fermentation residue obtained from an anaerobic fermentation tank for treating organic waste.

[0013] Preferably, the microwave treatment power is 600-1000W, preferably the microwave power is 800W; the microwave treatment time is 10-30min, preferably the microwave treatment time is 20min; the turntable speed in the microwave oven is 30-50rpm, preferably the turntable speed is 45rpm.

[0014] The purpose of microwave treatment is to kill pathogenic bacteria in the biogas residue. After microwave treatment, the pre-treated biogas residue is filtered using a suction filtration device to obtain the liquid phase rich in nitrogen and phosphorus elements.

[0015] In a preferred embodiment, the step (2) comprises:

[0016] The first step is to weigh the tofu residue and put it into deionized water to prepare a mixed liquid;

[0017] In the second step, the mixed liquid is placed in an oven for extraction to obtain an extract;

[0018] step three, mixing the extract with ethanol to obtain a mixture;

[0019] The fourth step is to filter the mixture using a suction filtration device to obtain a fiber residue, which is then mixed with a 3% (w / v) sodium dodecyl sulfate (SDS) solution;

[0020] Step 5: placing the mixture obtained in step 4 in an autoclave for high-temperature sterilization;

[0021] Step 6: Filter the autoclaved mixture, and then wash the solid residue with deionized water and ethanol;

[0022] In the seventh step, the mixture obtained in the sixth step is placed in an oven for heating treatment to obtain crude fiber.

[0023] In a preferred embodiment, the extraction temperature in the second step is 80-100°C, preferably 90°C, and the heating time is 4-8h, preferably 6h. This step uses deionized water as a solvent to extract the water-soluble components in the tofu dregs raw material, and the purpose of heating is to accelerate the extraction process. If the extraction process under the above-mentioned heating conditions is not adopted, effective extraction cannot be achieved, resulting in a large amount of water-soluble components remaining in the solid phase components, which in turn leads to poor slow-release effect of the subsequent slow-release fertilizer.

[0024] In a preferred embodiment, in the third step, the volume ratio of the extract to ethanol is 1:1-1:2. Ethanol is used to assist the extraction process of the tofu dregs, thereby promoting the dissolution of components that are easily soluble in ethanol in the liquid phase.

[0025] In a preferred embodiment, in the fourth step, the liquid phase and the solid phase (fibrous residue) are first separated, so that all water-soluble components are separated from the fibrous residue, thereby effectively obtaining the fibrous residue.

[0026] The fiber residue is mixed with an SDS solution to prepare for washing the fiber residue with a neutral detergent (SDS solution) in the next step. More preferably, the amount of SDS solution used should be sufficient to completely soak all of the fiber residue. If the amount of SDS solution used is insufficient, 100% of the soluble components in the fiber residue cannot be washed out, resulting in excessive impurities in the subsequent crude fiber component, which will further lead to poor slow-release effect of the subsequent slow-release fertilizer.

[0027] In a preferred embodiment, in the fifth step, the sterilization temperature is set to 121°C, the treatment time range is 20-40 minutes, and the preferred treatment time is 30 minutes; high temperature is used to promote the washing process of the fiber residue with a neutral detergent (SDS solution); if this high-temperature treatment process is not adopted, the soluble components in the fiber residue cannot be washed out 100%, resulting in excessive impurities in the subsequent crude fiber component, which will further lead to poor slow-release effect of the subsequent slow-release fertilizer.

[0028] The purpose of the sixth step is to use deionized water and ethanol to wash away the soluble components attached to the surface of the solid residue; if deionized water and ethanol are not used for washing, some soluble components will remain on the surface of the solid residue, resulting in excessive impurities in the crude fiber component obtained subsequently, which will further lead to poor slow-release effect of the subsequent slow-release fertilizer.

[0029] In a preferred embodiment, in the seventh step, the heating temperature range is 50-70°C, preferably the heating temperature is 60°C, the heating time range is 12-36h, and preferably the heating time is 24h. The purpose of this step is to use a higher temperature to promote the cleaning process of the solid phase residue with deionized water and ethanol during the cleaning process; if this higher temperature treatment process is not adopted, it is also impossible to wash out 100% of the soluble components in the fiber residue, resulting in excessive impurities in the subsequent crude fiber component, which will further lead to poor slow-release effect of the subsequent slow-release fertilizer.

[0030] In a preferred embodiment, step (3) comprises: mixing the crude fiber obtained in step (2) as a fiber-based highly absorbent material with the liquid phase portion rich in nitrogen and phosphorus obtained in step (1) to prepare a slow-release organic fertilizer loaded with nitrogen and phosphorus.

[0031] In a preferred embodiment, the volume ratio of the crude fiber to the liquid phase is 1:3-1:5.

[0032] Technical Effects

[0033] The method of the present invention creatively integrates the respective characteristics of the two organic wastes, fully utilizes the nutritional components of the biogas residue and the fiber components of the tofu residue, and prepares low-cost slow-release organic fertilizer, greatly reducing the cost of the slow-release organic fertilizer; this method effectively solves the problem of the urgent need for high-value treatment of a large amount of biogas residue, avoids serious environmental pollution, recovers useful resources, and promotes the development of the circular economy.

[0034] The method of the present invention effectively solves the problem that a large amount of tofu dregs are difficult to store, have deteriorated, and need to be processed urgently, which helps to turn waste into treasure and is beneficial to protecting the ecological environment.

[0035] Compared with traditional chemical fertilizers, the slow-release organic fertilizer prepared by the method of the present invention has the characteristics of low nitrogen and phosphorus loss rate in the soil (the nitrogen and phosphorus loss rate of this method is 3-6%, while the nitrogen and phosphorus loss rate of conventional organic fertilizers is as high as 25-33%), high crop one-time fertilizer utilization rate (the fertilizer utilization rate of this method reaches 94-97%; while the fertilizer utilization rate of conventional organic fertilizers is 67-75%), can reduce the environmental pollution problem caused by excessive fertilization, and has significant significance for the sustainable development of ecological agriculture.

[0036] The method of the present invention can not only solve the problem of rapid disposal of tofu dregs due to their short shelf life and easy mildew, but also solve the problem of large amounts of biogas dregs generated in biogas projects, and also produce slow-release organic fertilizer that is beneficial to agricultural development. In short, this method "kills three birds with one stone" by simultaneously achieving the resource recycling of two wastes and the preparation of a high-value-added slow-release fertilizer.

[0037] The method of the present invention is eco-friendly, highly technical and economical, and easy to industrialize and scale up. The obtained slow-release fertilizer is rich in nutrients and easy to store and transport. It is a method that is very suitable for treating tofu residue and biogas residue waste, recycling resources, and promoting green development of agriculture, and has extremely high prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention is a schematic diagram of a method for preparing slow-release organic fertilizer using tofu residue and biogas residue according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following describes several preferred embodiments of the present invention with reference to the accompanying drawings to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0040] Example 1

[0041] A method for preparing slow-release organic fertilizer using tofu residue and biogas residue, the process is as follows Figure 1 As shown, specifically including:

[0042] Step (1), pre-treating the biogas residue to obtain a liquid phase rich in nitrogen and phosphorus elements;

[0043] Step (2), pre-treating the tofu dregs to obtain a fiber-based highly absorbent material;

[0044] Step (3), preparing a slow-release organic fertilizer loaded with nitrogen and phosphorus.

[0045] Specifically, step (1) pre-treating the biogas residue to obtain a liquid phase rich in nitrogen and phosphorus: placing the biogas residue (i.e., the fermentation residue obtained from an anaerobic fermentation tank for treating organic waste) in a 28L microwave oven at a microwave power of 800W for 20 minutes at a microwave speed of 45rpm to kill pathogenic bacteria in the biogas residue. After the microwave treatment, the pre-treated biogas residue is filtered using a suction filtration device to obtain a liquid phase rich in nitrogen and phosphorus.

[0046] Step (2), pre-treating the tofu dregs to obtain fiber-based highly absorbent material, i.e., crude fiber.

[0047] The first step is to weigh the tofu dregs so that the ratio of tofu dregs to deionized water is 1g of tofu dregs corresponding to 10-20mL of deionized water, and then put them into the deionized water;

[0048] In the second step, the extract was placed in an oven with an extraction temperature range of 90°C and a heating time of 6 hours;

[0049] The third step is to mix the extracted mixture with ethanol, with the volume ratio of the extract to ethanol being 1:1-1:2, to assist the filtration process;

[0050] The fourth step is to filter the mixture using a suction filtration device to obtain fiber residues, which are then mixed with a 3% (w / v) sodium dodecyl sulfate (SDS) solution to completely soak all the fiber residues with the SDS solution;

[0051] In the fifth step, the obtained mixture was placed in an autoclave with the temperature set to 121°C and the processing time range of 30 min;

[0052] Step 6: The autoclaved mixture was filtered and then washed with deionized water and ethanol;

[0053] Step 7: Place the mixture obtained in the above steps in an oven for heating at a temperature of 60° C. for 24 hours to obtain crude fiber.

[0054] Step (3) is to prepare a slow-release organic fertilizer loaded with nitrogen and phosphorus: the crude fiber obtained in step (2) is used as a fiber-based highly absorbent material and the liquid phase portion rich in nitrogen and phosphorus obtained in step (1) is mixed, and the volume ratio of the crude fiber to the liquid phase portion is 1:3-1:5, to prepare a slow-release organic fertilizer loaded with nitrogen and phosphorus.

[0055] Example 2

[0056] Preparation of slow-release organic fertilizer. During the pretreatment of tofu residue to obtain fiber-based superabsorbent material, the obtained fiber residue was not mixed with a 3% (w / v) sodium dodecyl sulfate (SDS) solution. Other processes and parameters were the same as in Example 1.

[0057] Example 3

[0058] Preparation of slow-release organic fertilizer. During the pretreatment of biogas residue to obtain the liquid phase rich in nitrogen and phosphorus, the microwave treatment power was set to 400 W. The other processes and parameters were the same as in Example 1.

[0059] Experimental Examples

[0060] The content and characteristics of the slow-release organic fertilizers prepared in Examples 1-3 were measured. The water absorption strength of the slow-release organic fertilizer in Example 1 was 12.6 g water / g slow-release organic fertilizer, and the nitrogen content of the slow-release fertilizer was approximately 4 wt%. In comparison, the water absorption strength of the slow-release organic fertilizer in Example 2 was 5.7 g water / g slow-release fertilizer, and the nitrogen content of the slow-release fertilizer was approximately 2.9 wt%. The water absorption strength of the slow-release organic fertilizer in Example 3 was 8.3 g water / g slow-release fertilizer, and the nitrogen content of the slow-release fertilizer was approximately 3.1 wt%.

[0061] To verify the fertilizer efficiency of the slow-release organic fertilizers prepared in Examples 1-3, a tomato pot test was conducted. Specifically, equal amounts of the slow-release organic fertilizer samples prepared in Examples 1 and 2-3 were added to tomato pots, and the plant growth (height and weight) and soil microbial community were dynamically monitored during the growth of the tomatoes.

[0062] The results show that:

[0063] Nitrogen release:

[0064] The slow-release organic fertilizer of Example 1 released 85% of the nitrogen element within a period of 30 days and 63% of the P element within a period of 60 days; the slow-release organic fertilizer of Example 2 released 51% of the nitrogen element within a period of 30 days and 49% of the P element within a period of 60 days; the slow-release organic fertilizer of Example 3 released 76% of the nitrogen element within a period of 30 days and 45% of the P element within a period of 60 days.

[0065] Plant Growth:

[0066] The slow-release organic fertilizer of Example 1 promotes plant growth by increasing height by 12-19% and weight by 8-17%. The slow-release organic fertilizer of Example 2 promotes plant growth by increasing height by 5-7% and weight by 3-8%. The slow-release organic fertilizer of Example 3 promotes plant growth by increasing height by 9-13% and weight by 6-11%.

[0067] Enrichment of beneficial microorganisms:

[0068] The slow-release organic fertilizer of Example 1 can increase the enrichment of beneficial microorganisms Sandaracinaceae and Sphingomoas in the soil by 2-4 times after use; the slow-release organic fertilizer of Example 2 can increase the enrichment of beneficial microorganisms Sandaracinaceae and Sphingomoas in the soil by 1.1 times after use; and the slow-release organic fertilizer of Example 3 can increase the enrichment of beneficial microorganisms Sandaracinaceae and Sphingomoas in the soil by 1.4 times after use.

[0069] The above results show that the slow-release organic fertilizers prepared by the method of the present invention can achieve the slow-release release of nutrients such as nitrogen and phosphorus, effectively promote plant growth and weight gain, and are beneficial to microbial enrichment. In the specific treatment process, during the sludge treatment process, the sterilization step is conducive to the improvement of the slow-release effect, and has a certain effect on the water absorption strength, NP release, and height and weight gain of the prepared slow-release fertilizer. In the crude fiber treatment process, if SDS solution is not used, all water-soluble components cannot be washed out, resulting in excessive impurities in the subsequent crude fiber components, further resulting in poor slow-release effect of the subsequent slow-release fertilizer, and having a certain effect on the water absorption strength, NP release, and height and weight gain of the prepared slow-release fertilizer.

[0070] The preferred embodiments of the present invention have been described in detail above. It should be understood that numerous modifications and variations based on the concepts of the present invention are possible without inventive effort by those skilled in the art. Therefore, any technical solution that can be derived by one skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for preparing slow-release organic fertilizer using tofu residue and biogas residue, comprising: Step (1), pre-treating the biogas residue to obtain a liquid phase rich in nitrogen and phosphorus elements; Step (2), pre-treating the tofu dregs to obtain a fiber-based highly absorbent material; Step (3), preparing a slow-release organic fertilizer loaded with nitrogen and phosphorus; The step (1) comprises: placing the biogas residue in a microwave oven, sterilizing the biogas residue under microwave assistance, filtering the treated biogas residue to obtain a liquid phase rich in nitrogen and phosphorus elements; the microwave treatment power is 600-1000W; the microwave treatment time is 10-30 minutes; and the turntable speed in the microwave oven is 30-50 rpm; The step (2) comprises: The first step is to weigh the tofu residue and put it into deionized water to prepare a mixed liquid; The second step is to put the mixed liquid into an oven for extraction to obtain an extract. The extraction temperature is 80-100°C and the heating time is 4-8 hours. The third step is to mix the extract with ethanol, wherein the volume ratio of the extract to the ethanol is 1:1-1:2 to obtain a mixture; The fourth step is to filter the mixture using a suction filtration device to obtain fiber residues, which are then mixed with a 3% (w / v) sodium dodecyl sulfate (SDS) solution. The amount of SDS solution used should be sufficient to completely soak all the fiber residues. Step 5: Place the mixture obtained in step 4 in an autoclave for high-temperature sterilization at a temperature of 121°C for a processing time of 20-40 minutes. Step 6: Filter the autoclaved mixture, and then wash the solid residue with deionized water and ethanol; Step 7: placing the mixture obtained in step 6 in an oven for heating treatment to obtain crude fiber, the heating temperature range is 50-70° C., and the heating time range is 12-36 hours; Step (3) comprises: mixing the crude fiber obtained in step (2) as a fiber-based highly absorbent material with the liquid phase portion rich in nitrogen and phosphorus elements obtained in step (1) to prepare a slow-release organic fertilizer loaded with nitrogen and phosphorus.

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