Residual sludge resource utilization method and method for preparing amino acid liquid fertilizer

Abstract

The invention discloses a residual sludge resource utilization method and a method for preparing amino acid liquid fertilizer, and the method comprises the following steps: 1) taking residual sludge as a compost raw material and plant straw as an auxiliary material, mixing to obtain an initial compost substrate, and carrying out aerobic composting; 2) taking compost products in the middle and later periods of the high-temperature period of compost, drying, sieving, grinding, adding a Ca (OH) 2 solution into the ground compost products, mixing, then shaking for 30-120 minutes, carrying out solid-liquid separation, and taking liquid to obtain the amino acid liquid fertilizer; and continuously composting the remaining solid substances, and using the solid substances for land utilization after composting is finished. The amino acid liquid fertilizer is prepared from municipal sludge and straw compost, resource recycling is economically and effectively conducted on amino acid in the amino acid liquid fertilizer, the prepared amino acid liquid fertilizer is rich in amino acid variety and higher in amino acid content, the needed time is short, energy consumption is reduced, and the production cost is reduced. And a green way is provided for safe treatment and high-value recycling of the residual sludge of a sewage treatment plant.

Description

Technical Field

[0001] The invention relates to the technical field of sludge treatment, and in particular to a method for resource utilization of surplus sludge and a method for preparing amino acid liquid fertilizer. Background Art

[0002] In recent years, due to the continuous input of chemical fertilizers and the research and development of new fertilizers, crop yields have increased significantly and food problems have been improved. However, the increase in fertilizer application will also cause a series of environmental problems such as soil degradation and greenhouse gas emissions. Therefore, finding reasonable organic materials to replace chemical fertilizers is an important way to improve the utilization rate of chemical fertilizers, achieve the goal of zero increase in fertilizer application and achieve sustainable agricultural development.

[0003] As a terminal byproduct of urban sewage, residual sludge contains rich plant nutrients (mainly nitrogen and phosphorus) and organic matter, and has high microbial activity. Its resource treatment meets the needs of social development. At the same time, studies have shown that aerobic composting of sludge can not only significantly degrade toxic pollutants and pathogens, but also microorganisms and their metabolites can produce a large number of amino acids, peptides, sugars, etc. under biological action. The compost products can be used as fertilizers and soil conditioners for forests, farmlands, etc.

[0004] Amino acids play multiple roles as biostimulants for plant growth. Their direct impacts on plants include improving crop stress resistance, increasing chlorophyll synthesis (alanine, glutamic acid, lysine), stimulating and regulating rapid plant growth, promoting seed germination (glutamic acid, serine, valine) and plant root development. The preparation of amino acid liquid fertilizer from aerobic composting products can not only realize the resource utilization of sludge, effectively replace chemical fertilizers to increase the sustainable yield of planting systems, but also reduce the harm of excessive application of chemical fertilizers to farmland soil, which is of great significance to environmental protection.

[0005] At present, there are few studies on the extraction of amino acids from aerobic sludge, and there are problems of long composting cycle and high energy consumption. For example, the Chinese invention application with application number CN202210698288.9 provides a method for preparing amino acid liquid fertilizer using sludge and straw as raw materials, and the Chinese invention application with application number CN201710064244.X provides a method for extracting microbial amino acids by acid hydrolysis of sludge, which respectively use high temperature and strong acid hydrolysis extraction treatments, which may damage the structure and properties of amino acids; the Chinese invention patent with application number CN202210544289.8 provides a method for improving alkaline soil and enhancing carbon capture using sludge stabilization products, which involves a long composting cycle; the Chinese invention patent with application number CN202111667090.6 provides a method for increasing the content of sludge-derived aromatic amino acid-derived plant growth promoters, which requires the use of hot steam to thermally hydrolyze the sludge, and the required energy consumption is relatively high.

[0006] In summary, in the prior art, the preparation of amino acid fertilizer using sludge usually has problems such as long composting cycle, high energy consumption and destruction of amino acid structure (activity). The applicant is considering providing a method for rapid and low-cost extraction of free amino acids in sludge. Summary of the invention

[0007] In order to overcome the shortcomings of the above-mentioned technology, the purpose of the present invention is to provide a method for resource utilization of excess sludge and a method for preparing amino acid liquid fertilizer, which can realize the resource utilization of excess sludge and quickly extract rich amino acids in the sludge.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing amino acid liquid fertilizer from excess sludge comprises the following steps:

[0010] 1) taking the residual sludge as the compost raw material and the plant straw as the auxiliary material, mixing them to obtain the initial compost matrix and performing aerobic composting;

[0011] 2) Take the compost products in the middle and late stages of the high temperature period of composting, dry, sieve and grind them, add Ca(OH)2 solution to the ground compost products to mix them, then shake them for 30 to 120 minutes to separate the solid and liquid, and take the liquid to obtain amino acid liquid fertilizer.

[0012] Preferably, the residual sludge is dehydrated sludge after municipal sludge is mechanically dehydrated in a domestic sewage treatment plant, the moisture content of the dehydrated sludge is 85-95%, and the C / N ratio is 10-18%; the plant straw includes one or more of corn straw, wheat straw, and rice straw.

[0013] Preferably, in the initial composting matrix, the weight ratio of the residual sludge to the plant straw is 1.5-2.5:1; the C / N ratio is 20-30:1, and the moisture content is 55-65%. When a high carbon-nitrogen ratio raw material (such as straw) is used for composting, the C / N ratio is adjusted to 20-30:1, and the decomposition rate of organic matter is the highest. The moisture content of the compost is controlled at 55-65%. Too low a moisture content is not conducive to microbial activity. When the moisture content exceeds 65%, water will fill the gaps between the material particles, reducing the air content. The compost will be transformed from aerobic to anaerobic, and the temperature will drop sharply. As a result, stinky intermediates (hydrogen sulfide, mercaptan, ammonia, etc.) are formed and the pile becomes corrupt and black due to sulfide.

[0014] Preferably, in step 1), the first aeration is performed 25 to 35 minutes after the start of aerobic composting, and then aeration is performed every 45 to 55 minutes, and the aeration rate is controlled to be 0.15 to 0.25 L·min -1 kg -1The dry matter of composting substrate can be treated by aeration to achieve the purpose of oxygen supply, dehumidification and cooling, which is more suitable for the growth and metabolism of microorganisms.

[0015] More preferably, the aeration time is 8 to 12 minutes.

[0016] Preferably, in step 2), the middle and late stages of the high temperature period of composting are stages after the composting temperature exceeds the peak temperature during the high temperature period of composting; the high temperature period of composting is the stage during the composting process when the temperature exceeds 50°C.

[0017] Preferably, in step 2), the concentration of the Ca(OH)2 solution is 0.1-0.5 mol / L; the Ca(OH)2 solution is mixed with the ground compost product at a solid-liquid ratio of 1:4-6 (mg:mL). The protein is hydrolyzed by alkali treatment. If the concentration is too low, the protein hydrolysis is incomplete and the amino acid content of the liquid fertilizer is low. If the concentration is too high, the amino acid structure will be damaged.

[0018] Preferably, the method for preparing amino acid liquid fertilizer from excess sludge comprises the following steps:

[0019] 1) Aerobic composting: The activated sludge and crushed corn stalks were mixed evenly with a C / N ratio of 20:1 and a moisture content of 60.95%±0.67%, and then put into the composting reactor. During the composting process, the fan was aerated for 10 minutes at an interval of 30 minutes for the first time, and then aerated every 50 minutes until the end of composting, and the aeration rate was controlled at 0.2L·min -1 kg -1 Composting substrate dry matter; in addition, deodorization is carried out simultaneously during the process;

[0020] 2) Using the compost in the middle and late stages of the thermophilic period to carry out the following steps: weighing an appropriate amount of aerobic compost sludge sample, air-drying the sample until dry, passing the compost sample through a 100-mesh sieve to separate large impurities such as straw, and then fully grinding to obtain thermophilic period compost sludge;

[0021] Alkaline treatment extraction: Take an appropriate amount of ground compost sludge and add 0.2 mol / L Ca(OH)2 solution, mix at a solid-liquid ratio of 1:5 (w / v), shake at 200 rpm for 1 hour, then ultrasonicate for 10 minutes, and centrifuge at 5000g for 10 minutes to separate the solid and liquid;

[0022] The above alkaline treatment extraction operation was repeated three times to ensure complete extraction, and the three supernatants were mixed and filtered through a 0.45 μm filter membrane to remove microorganisms. The filtrate was taken to obtain amino acid liquid fertilizer.

[0023] The present invention also provides an amino acid liquid fertilizer prepared by the above method.

[0024] The present invention also provides the use of the amino acid liquid fertilizer prepared by the method in promoting plant growth.

[0025] The present invention also provides the use of the amino acid liquid fertilizer prepared by the method in promoting the growth of plant stems.

[0026] The present invention also provides a method for resource utilization of excess sludge, comprising the following steps:

[0027] The amino acid liquid fertilizer is prepared by the above method for preparing amino acid liquid fertilizer from excess sludge;

[0028] The solid matter remaining in the process of preparing amino acid liquid fertilizer is further composted and used for land use after the composting is completed.

[0029] Preferably, the land use includes land improvement and restoration, landscaping and agricultural use.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention prepares amino acid liquid fertilizer by composting municipal sludge and straw, and economically and effectively recycles the amino acids therein. Compared with the traditional composting preparation method, the amino acid liquid fertilizer prepared in this way not only has richer amino acid types and higher content, but also requires less time and saves energy. In addition, it is also beneficial to reduce the application amount of chemical fertilizers and improve soil nutrients. The present invention recycles the excess sludge, providing a green way to solve the problem of excess sludge in urban sewage treatment plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the series reactors in Example 1 of the present invention;

[0033] Figure 2 The temperature trend diagram during the composting process in Example 1;

[0034] Figure 3 This is a comparison chart of the amino acid humic acid content in the amino acid liquid fertilizer prepared by composting at different times in Example 1;

[0035] Figure 4 The nitrogen content in the compost at different times in Example 1 is a trend chart;

[0036] Figure 5 This is a diagram showing an example of rice seedling growth in Example 2;

[0037] Figure 6 This is a graph showing the changes in root and stem length and fresh weight of rice seedlings in Example 2;

[0038] Figure 7This is a graph showing the proportion of up-regulated genes at different stages in Example 2;

[0039] Figure 8 Schematic diagram of differentially expressed genes in the transcriptome;

[0040] Fig. 9 This is a flow chart for implementing a method for resource utilization of excess sludge in Example 3 of the present invention. DETAILED DESCRIPTION

[0041] In order to better explain the present invention, the main contents of the present invention are further explained below in conjunction with specific embodiments, but the contents of the present invention are not limited to the following embodiments.

[0042] Example 1: Preparation of amino acid liquid fertilizer by short-term aerobic composting of excess sludge

[0043] A method for preparing amino acid liquid fertilizer from waste sludge, using waste sludge from a sewage treatment plant as composting raw material and corn stalks as auxiliary material for aerobic composting, the basic properties of the raw materials are shown in Table 1. Aerobic composting is carried out as follows Figure 1 The series reactor shown in FIG. The volume of the series reactor is 10 L (height 0.4 m, inner diameter 0.18 m), and the outer wall adopts a heat-insulating interlayer.

[0044] The method for preparing amino acid liquid fertilizer is as follows:

[0045] 1) Aerobic composting: 5.0 kg of activated sludge and 2.5 kg of crushed corn stalks were mixed evenly at a ratio of 2:1, with a C / N ratio of 22.5:1 and a moisture content of 64.23%±0.21%. The basic properties of the activated sludge and corn stalks are shown in Table 1.

[0046] Table 1: Basic properties of activated sludge and corn stover

[0047]

[0048] The mixture of activated sludge and corn stalks was put into the composting reactor. During the composting process, the fan was operated for 10 minutes at an interval of 30 minutes for the first time. From then on, aeration was performed every 50 minutes until the end of composting, and each aeration lasted for 10 minutes. At the same time, the aeration rate was controlled at 0.2L·min -1 kg -1 The composting substrate is dry matter. In addition, deodorization is carried out during the process.

[0049] 2) If Figure 2As shown, in the whole process of composting, the 3rd to 11th day is the high temperature period of composting, and the middle and late stages of the high temperature period of composting are the 5th to 11th day, wherein the temperature peak of the high temperature period of composting appears on the 4th day, and the temperature of the composting on the 5th day after the temperature peak of the high temperature period of composting is 58°C. This embodiment adopts aerobic composting for 5 days of composting to carry out the subsequent steps: weigh an appropriate amount of aerobic composting sludge sample for 5 days of composting, air-dry the sample to dryness, pass the compost sample through a 100 mesh sieve to separate large impurities such as straw, and then fully grind to obtain composting sludge. Take an appropriate amount of ground composting sludge and add 0.2mol / L Ca(OH)2 solution, and mix at a solid-liquid ratio of 1:5 (w / v). Oscillate at 200rmp for 1h, then ultrasonicate for 10min, and separate the solid and liquid after centrifugation at 5000g for 10min. Repeat the above operation three times to ensure complete extraction, and mix the three supernatants, pass through a 0.45μm filter membrane, and take the filtrate to obtain amino acid liquid fertilizer.

[0050] In the actual production process, the compost product after the temperature starts to drop during the high temperature period of composting can be used to prepare amino acid liquid fertilizer.

[0051] The amino acid liquid fertilizer prepared from this embodiment is compared with that prepared from other compost products, and the comparison results are shown in Table 2. The difference between the preparation process of other compost products and this embodiment lies in the different composting time, wherein the traditional compost product is composted to the end of the decomposition process when it reaches 35 days.

[0052] It can be seen from Table 2 that the amino acid content in the product is the highest on the 5th day of composting. The main types and content determination results of the amino acids in the prepared amino acid liquid fertilizer are shown in Table 2. Figure 3 As shown in Table 2, the amino acids in the prepared amino acid liquid fertilizer mainly include 8 essential amino acids and 11 non-essential amino acids, and the contents of glutamic acid, alanine and isoleucine are relatively high. Figure 3 As shown, compared with traditional compost products, the amino acid content in the amino acid liquid fertilizer prepared from the compost products on the 5th day was significantly higher than that of traditional compost products, about 1.84 times that of the 35th day.

[0053] Table 2: Amino acid content at different periods (mg / L)

[0054]

[0055] In the table: D0 is 0 days of composting, D5 is 5 days of composting, D21 is 21 days of composting, and D35 is 35 days of composting.

[0056] The results of determination of organic nitrogen and total nitrogen in compost during the entire composting process up to day 35 are as follows Figure 4 As shown. Figure 4It can be seen that during the whole composting process, the organic nitrogen and total nitrogen contents of the compost first increased and then decreased, reaching the highest during the high temperature period of composting, which were 10777.62 and 12550.10 mg / g-TS, respectively. At this stage, the degradation rate of organic matter was faster than the nitrogen loss rate, which increased the nitrogen content per unit mass and the amino acid content. The nitrate nitrogen content increased overall, reaching a maximum of 1727.54 mg / g-TS on the 9th day, and showed an overall downward trend. The ammonia nitrogen content increased, and the nitrite nitrogen content remained basically unchanged.

[0057] Example 2: Amino acid liquid fertilizer for rice seedling cultivation

[0058] In order to evaluate the advantages of preparing amino acid liquid fertilizer by ultra-short-range aerobic composting, the amino acid liquid fertilizer prepared by the composting product on the 5th day in Example 1 and other composting products was used in a hydroponic experiment on rice seedlings. The experimental results are as follows: Figures 5-6 shown.

[0059] Compared with the blank group, compost products at different periods had a positive effect on stem growth. Among them, the amino acid liquid fertilizer prepared in the middle and late high-temperature period of composting, especially the amino acid liquid fertilizer prepared from the compost products on the 5th day, had the most obvious effect on promoting stem length. After treatment, the stem length could reach 141.54 mm, which was significantly higher than that of traditional compost products on the 35th day (119.15 mm).

[0060] like Figure 6 As shown, the effects of amino acid liquid fertilizer prepared from compost products at different periods on the fresh weight of rice were similar to those on stem length, and the compost product on the 5th day of treatment was significantly higher than that of the traditional compost product.

[0061] At the same time, transcriptomics was used to study the molecular mechanism of compost products stimulating plant growth at the overall level, and the expression level of each gene was calculated to determine the differentially expressed genes between different samples. The amino acid liquid fertilizer prepared from the compost products on the 5th day had up-regulated genes accounting for about 68.79% of the differentially expressed genes, which was higher than the 50.7% of traditional compost products. Figures 7-8 As shown. It mainly promotes "amino acid transport" by upregulating "carboxylic acid transport" and "nitrogen compound transport", further regulating plant growth.

[0062] In summary, amino acid liquid fertilizer made from compost products in the middle and late high-temperature periods of composting is more beneficial to the growth of plant stems.

[0063] Example 3: Method for resource utilization of excess sludge

[0064] A method for recycling waste sludge resources is described, using waste sludge from a sewage treatment plant as composting raw material and corn stalks as auxiliary material for aerobic composting. The basic properties of the raw materials are shown in Table 3. Aerobic composting is performed as follows: Figure 1 The series reactor shown in FIG. The volume of the series reactor is 10 L (height 0.4 m, inner diameter 0.18 m), and the outer wall adopts a heat-insulating interlayer.

[0065] like Fig. 9 As shown, a method for resource utilization of excess sludge comprises the following steps:

[0066] 1) Aerobic composting: 5.0kg of dehydrated sludge and 2.5kg of crushed corn stalks were mixed in a ratio of 2:1. At this time, the C / N ratio was 22:1 and the moisture content was 63.17±0.21%. Then it was put into the composting reactor. During the composting process, the fan was operated for 10 minutes at an interval of 30 minutes for the first time. From then on, aeration was performed every 50 minutes until the end of composting, and the aeration rate was controlled at 0.2L·min -1 kg -1 The composting substrate is dry matter. In addition, deodorization is carried out during the process.

[0067] Table 3: Basic properties of activated sludge and corn stover

[0068]

[0069] 2) Weigh an appropriate amount of aerobic composting sludge sample that has been composted for 5 days, air-dry the sample until dry, pass the compost sample through a 100-mesh sieve to separate large impurities such as straw, and then fully grind it to obtain composting sludge.

[0070] Take an appropriate amount of ground compost sludge and add 0.3mol / LCa(OH)2 solution, and mix at a solid-liquid ratio of 1:5 (w / v). Oscillate at 200rmp for 2h, then ultrasonicate for 10min, and centrifuge at 5000g for 10min to separate the solid and liquid. Repeat the above operation three times to ensure complete extraction, and mix the three supernatants, filter through a 0.45μm filter membrane, and take the filtrate to obtain amino acid liquid fertilizer. Figure 3 As shown, the compost temperature was 58°C on the 5th day.

[0071] 3) The solid after solid-liquid separation in step 2) and the filter cake after the filtration membrane are added back into the series reactor to continue composting until the composting is completed.

[0072] 4) The compost products after decomposition are used for land improvement or restoration, or for landscaping.

Claims

1. A method for preparing amino acid liquid fertilizer from excess sludge, characterized in that: The following steps are involved: 1) taking the residual sludge as the compost raw material and the plant straw as the auxiliary material, mixing them to obtain the initial compost matrix and performing aerobic composting; 2) Taking the compost products in the middle and late stages of the high temperature period of composting, drying, sieving and grinding, adding Ca(OH)2 solution to the ground compost products to mix, then shaking for 30 to 120 minutes, separating the solid and the liquid, and taking the liquid to obtain amino acid liquid fertilizer.

2. The method according to claim 1, characterized in that: The residual sludge is dehydrated sludge after municipal sludge is mechanically dehydrated in a domestic sewage treatment plant; the plant straw includes one or more of corn straw, wheat straw, and rice straw.

3. The method according to claim 1, characterized in that: In the initial composting matrix, the C / N ratio is 20-30:1 and the moisture content is 55-65%.

4. The method according to claim 1, characterized in that: In step 1), the first aeration is performed 25 to 35 minutes after the start of aerobic composting, and then aeration is performed every 45 to 55 minutes, with an aeration rate of 0.15 to 0.25 L·min -1 kg -1 Compost substrate dry matter.

5. The method according to claim 1, characterized in that: In step 2), the middle and late stages of the high temperature period of composting are the stages after the composting temperature exceeds the peak temperature during the high temperature period of composting; the high temperature period of composting is the stage when the temperature exceeds 50° C. during the composting process.

6. The method according to any one of claims 1 to 5, characterized in that: In step 2), the concentration of the Ca(OH)2 solution is 0.1-0.5 mol / L; the Ca(OH)2 solution is mixed with the ground compost product at a solid-liquid ratio of 1:4-6.

7. An amino acid liquid fertilizer, characterized in that: The invention is prepared by the method according to any one of claims 1 to 6.

8. Use of the amino acid liquid fertilizer prepared by the method according to any one of claims 1 to 6 or the amino acid liquid fertilizer according to claim 7 in promoting plant growth.

9. A method for resource utilization of excess sludge, characterized in that: The following steps are involved: Prepare amino acid liquid fertilizer by the method for preparing amino acid liquid fertilizer from surplus sludge according to any one of claims 1 to 6; The solid residues remaining in the process of preparing amino acid liquid fertilizer are further composted and used for land use after the composting is completed.

10. The method for resource utilization of excess sludge according to claim 9, characterized in that: The land use includes land improvement and restoration, landscaping and agricultural use.

Images