A method for preparing cold-pressed eco-bricks using sludge products

Abstract

This invention relates to the field of solid waste treatment and resource utilization technology, and discloses a method for preparing cold-pressed ecological bricks using sludge products, comprising: S1. Aerobic fermentation and drying of first sludge anaerobic digestion residue and agricultural and forestry waste to obtain fermentation products, which are then sieved to obtain fine-particle product A1 and coarse-particle product A2; drying of second sludge anaerobic digestion residue to obtain sludge product B; S2. Mixing sludge product B with fine-particle product A1, followed by grinding and homogenization to break down the sludge's aggregate structure, to obtain homogenized product C; S3. Mixing homogenized product C with coarse-particle product A2 to obtain mixture D; subjecting mixture D to rotary extrusion and friction heating plasticization to obtain intermediate E; S4. Pressing and curing intermediate E. This method is completely binder-free, simple and convenient, and produces bricks with low moisture content, high compressive strength and flexural strength, and wide application scenarios.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment and resource utilization technology, specifically to a method for preparing cold-pressed eco-bricks using sludge products. Background Technology

[0002] Traditional methods of sludge disposal include landfilling, incineration, and composting, but these methods suffer from secondary pollution, high costs, or low resource utilization. Since sludge is rich in organic matter and nutrients such as nitrogen, phosphorus, and potassium, using it as a raw material to prepare ecological materials has become an emerging resource utilization approach. For example, sludge can be pressed into bricks for use as planting material in greenbelts or as an ecological substrate for slope greening. However, existing technologies for preparing high-strength ecological bricks from sludge and its byproducts still face many challenges.

[0003] Currently, some studies have attempted to mix sludge with other materials (such as cement, lime, fly ash and other binders) and press it into bricks to improve its strength and stability. For example, the mechanical properties of sludge bricks can be enhanced by adding cement or chemical curing agents, or their durability can be improved by high-temperature sintering. However, these methods have the following drawbacks: (1) Dependence on external binders: A large amount of cement, lime or other chemical binders are usually required to achieve sufficient strength, which not only increases the cost, but also limits the amount of sludge added, reduces the resource utilization rate, and the addition of alkaline substances will affect the plant adaptability of sludge; (2) Cracking problem: Sludge itself has a high water content and organic matter content. If other inorganic materials are not added, it is easy to shrink and crack during drying or curing, resulting in poor integrity and low strength of the finished bricks, which is difficult to meet the actual application requirements; (3) Complex process: Some technologies require special high-pressure equipment and long-term curing, which consumes a lot of energy and has a long production cycle, which is not conducive to large-scale promotion. Summary of the Invention

[0004] This invention provides a method for preparing cold-pressed eco-bricks using sludge products, in order to solve the problems of existing sludge bricks relying on external binders, being prone to cracking, and having complex processes.

[0005] In a first aspect, the present invention provides a method for preparing cold-pressed eco-bricks using sludge products, comprising the following steps:

[0006] S1. Raw material preparation: The anaerobic digestion residue of the first sludge and agricultural and forestry waste are subjected to aerobic fermentation and drying to obtain fermentation products, which are then screened to obtain fine product A1 and coarse product A2; the anaerobic digestion residue of the second sludge is dried to obtain sludge product B.

[0007] S2. Homogenization of the mixture: After mixing sludge product B with fine particulate product A1, the mixture is ground and homogenized to break down the sludge aggregate structure and obtain homogenized product C.

[0008] S3. Preparation of intermediate: The homogenized product C is mixed with the coarse-grained product A2 to obtain mixture D; mixture D is subjected to rotary extrusion and friction heating plasticization to obtain intermediate E;

[0009] S4. Pressed and cooled ecological bricks: The intermediate E is pressed and cured.

[0010] In an optional embodiment, in step S1, the moisture content of the first sludge anaerobic digestion residue and the second sludge anaerobic digestion residue is 70%~80%, the dry weight percentage of organic matter is 30%~55%, the dry weight percentage of total nutrients nitrogen, phosphorus and potassium is >1%, and the pH value is 6~8.

[0011] In one optional embodiment, in step S1, the water content of the fermentation product is 35%~50%, and the dry weight percentage of organic matter is 30%~40%.

[0012] In one optional embodiment, the fine-grained product A1 has a particle size of <2 mm, a moisture content of 40%~55%, and an organic matter dry weight percentage of 25%~35%.

[0013] In one optional embodiment, the coarse-grained product A2 has a particle size of 2-10 mm;

[0014] In one optional embodiment, the coarse-grained product A2 further needs to be sun-dried and aged for 20 to 40 days, after which the moisture content is 25% to 35% and the dry weight percentage of organic matter is 35% to 45%.

[0015] In one optional embodiment, the sludge product B has a moisture content of 55% to 65%.

[0016] In one optional embodiment, in step S2, the sludge product B and the fine particulate product A1 are mixed at a mass ratio of 1:(1~2.5).

[0017] In one optional embodiment, in step S2, the homogenized product C has a water content of 50%~60% and a particle size of <0.5mm;

[0018] In one optional embodiment, the proportion of particles with a diameter <0.3 mm in the homogenized product C is not less than 60 wt%.

[0019] In one alternative embodiment, the homogenized product C has a fine texture and no obvious granular structure.

[0020] In one optional implementation, in step S2, the homogenization is performed using a conventional colloid mill at a rotation speed of 3000 r / min.

[0021] In an optional embodiment, in step S3, the homogenized product C and the coarse-grained product A2 are mixed at a mass ratio of (2~4):(1~2.5).

[0022] In an optional embodiment, in step S3, during the rotary extrusion and friction heating plasticization, a screw extrusion molding machine with a screw length of 30~50cm and a screw speed of 60~120rpm is used.

[0023] In one optional embodiment, during the rotary extrusion and friction heating plasticization, the cavity temperature is controlled at 45~65℃;

[0024] In one optional embodiment, the moisture content of the mixture D is 35% to 45%;

[0025] In one optional embodiment, the intermediate body E has a thickness of 0.5~2cm, a width of 2~4cm, a surface temperature of 45~65℃ when discharged, a plasticity index >10, no surface cracks, and can break but not shatter when dropped freely from a height of 10cm onto a hard platform.

[0026] In one optional embodiment, in step S4, the pressing pressure is 10~20MPa, the mold depth is 10~20cm, the thickness of the pressed brick is 5~10cm, and the surface is flat and without cracks.

[0027] In one alternative implementation, the curing conditions are to allow the plant to air dry naturally in a cool, well-ventilated place for 10 to 20 days.

[0028] Secondly, the present invention provides a cold-pressed ecological brick prepared by the above-mentioned method for preparing cold-pressed ecological bricks using sludge products, wherein the cold-pressed ecological brick has a moisture content of <20%, a compressive strength of 4~10MPa, and a flexural strength of 0.5~1.5MPa.

[0029] The technical solution of this invention has the following advantages:

[0030] 1. The present invention provides a method for preparing cold-pressed ecological bricks using sludge products, comprising the following steps: S1. Raw material preparation: Anaerobic digestion residue of first sludge and agricultural and forestry waste are subjected to aerobic fermentation and drying treatment to obtain fermentation products, which are then sieved to obtain fine-particle product A1 and coarse-particle product A2; anaerobic digestion residue of second sludge is dried to obtain sludge product B; S2. Mixture homogenization: Sludge product B and fine-particle product A1 are mixed and then ground and homogenized to break down the sludge aggregate structure, resulting in homogenized product C; S3. Preparation of intermediate: Homogenized product C is mixed with coarse-particle product A2 to obtain mixture D; mixture D is subjected to rotary extrusion and friction heating plasticization to obtain intermediate E; S4. Pressing and cold-pressing ecological bricks: Intermediate E is pressed and cured. The cold-pressed ecological bricks prepared by this invention use anaerobic digestion residue of sludge and agricultural and forestry waste as raw materials, and have the following advantages: (1) Completely free of binders: Self-bonding is achieved by utilizing the components of sludge itself and physical modification, reducing costs, and at the same time, no alkaline substances are introduced, and the plants are well adapted; (2) Solve the cracking problem: Grinding and homogenization are carried out by using a colloid mill, which can greatly reduce the granular structure in sludge and fully homogenize the material, reducing the possibility of cracking. At the same time, the shear stress of the sludge product mixture is increased by spiral extrusion, and the plasticity and adhesion of the sludge product mixture are increased by friction heating; (3) The pressing process is simple and convenient, and the pressure requirement of the brick press is low.

[0031] 2. The cold-pressed ecological bricks prepared by the method of preparing cold-pressed ecological bricks using sludge products provided by the present invention have a brick body moisture content of <20%, a compressive strength of 4~10MPa, and a flexural strength of 0.5~1.5MPa. They can be directly used in planting concrete, slope greening substrate, horticultural greening grid, desert mud grid and other scenarios, and have both environmental protection and functionality. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is an external view of intermediate E in Embodiment 1 of the present invention. Detailed Implementation

[0034] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0035] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0036] Anaerobic digestion residue: comes from municipal sludge anaerobic digestion plants, and is the solid residue after anaerobic digestion of sludge.

[0037] Agricultural and forestry waste mainly consists of agricultural and garden waste, including straw, rice husks, branches, and leaves.

[0038] In the following examples, the intermediate products were determined using conventional methods. Moisture content was determined by drying; organic matter dry weight was determined according to the standard "Soil Testing Part 6: Determination of Soil Organic Matter" (NY / T 1121.6-2006); particle size was directly determined using a laser particle size analyzer. Specifically, organic matter was first removed with hydrogen peroxide, followed by separation of particles using a dispersant and ultrasonic treatment. During measurement, the treated particle suspension was injected into the instrument's sample cell, and the shading rate was controlled between 10% and 20% to ensure appropriate concentration. The instrument automatically analyzed and output the volumetric particle size distribution based on the laser scattering signal of the particles; the plasticity index was determined using the combined plastic limit determination method according to the standard "Specifications for Geotechnical Testing of Highways" (JTG 3430-2020).

[0039] Example 1

[0040] This embodiment provides a method for preparing cold-pressed eco-bricks using sludge products, including the following steps:

[0041] (1) Raw material preparation: Anaerobic digestion residue of some municipal sludge and garden waste were subjected to aerobic fermentation and drying treatment (fermentation conditions: 25 days, turning over once every 10 days) to obtain soft and odorless fermentation products (moisture content of 41.6% and organic matter dry weight ratio of 32.3%). The fermentation products were screened to obtain fine product A1 and coarse product A2. Another part of anaerobic digestion residue was dried to obtain sludge product B with a moisture content of 60.2%.

[0042] The anaerobic digestion residue from municipal sludge had a moisture content of 78.3%, an organic matter dry weight percentage of 41.5%, a total nutrient nitrogen, phosphorus, and potassium content on a dry basis of 1.42%, and a pH of 7.03. Fine-grained product A1 had a particle size <2mm (passes through a 2mm sieve), a moisture content of 46.7%, and an organic matter dry weight percentage of 27.3%. Coarse-grained product A2 had a particle size of 2-10mm (passes through a 10mm sieve but not a 2mm sieve). After 30 days of sun-drying and aging, coarse-grained product A2 had a moisture content of 29.5% and an organic matter dry weight percentage of 38.1%.

[0043] (2) Homogenization of mixture: After fully mixing sludge product B and fine particle product A1 at a mass ratio of 1:1.5, the mixture is placed in a colloid mill for grinding and homogenization. The homogenization speed is 3000 rpm to break the sludge granular structure and obtain homogenized product C.

[0044] Among them, the homogenized product C has a water content of 52.4% and a particle size of <0.5mm, of which more than 72% of the particles have a particle size of <0.3mm, and is fine with no obvious granular structure;

[0045] (3) Preparation of intermediates: Homogenized product C and aged product A2 are thoroughly mixed at a mass ratio of 3:1.5 to obtain mixture D. Mixture D is placed in a screw extrusion molding machine (screw length 40cm, screw speed 80rpm) for rotary extrusion and friction heating plasticization to obtain intermediate E, such as Figure 1 As shown in the figure, the three products are intermediate E from the same batch of material, with the same shape and properties, but slight errors in length and width.

[0046] The mixture D has a water content of 44.9%; the intermediate E has a thickness of 0.82 cm, a width of 2.61 cm, a surface temperature of 52.2℃ at discharge, a plasticity index of 12, no surface cracks, and can break but not shatter when dropped freely from a height of 10 cm onto a hard platform.

[0047] (4) Cold-pressed bricks: The intermediate body E is placed in a cold-pressed brick machine with a mold depth of 15.6cm. After pressing at 15MPa, it is placed in a cool and ventilated place to dry naturally for 15 days, and a cold-pressed ecological brick with a thickness of 7.2cm is obtained.

[0048] Example 2

[0049] This embodiment provides a method for preparing cold-pressed eco-bricks using sludge products, including the following steps:

[0050] (1) Raw material preparation: Part of the municipal sludge anaerobic digestion residue was aerobically fermented and dried with garden waste (fermentation conditions: 25 days, turned over once every 10 days) to obtain a soft, odorless fermentation product (moisture content 44.9%, organic matter dry weight percentage 30.2%). The fermentation product was screened to obtain fine-grained product A1 and coarse-grained product A2; another part of the municipal sludge anaerobic digestion residue was dried to sludge product B with a moisture content of 62.2%;

[0051] The municipal sludge anaerobic digestion residue had a moisture content of 78.3%, an organic matter dry weight percentage of 41.5%, a total nutrient nitrogen, phosphorus, and potassium content on a dry basis of 1.42%, and a pH value of 7.03. Fine-grained product A1 had a particle size <2mm (passes through a 2mm sieve), a moisture content of 48.3%, and an organic matter dry weight percentage of 25.2%. Coarse-grained product A2 had a particle size of 2-10mm (passes through a 10mm sieve but not a 2mm sieve). After 25 days of sun-drying and aging, coarse-grained product A2 had a moisture content of 30.8% and an organic matter dry weight percentage of 34.5%.

[0052] (2) Homogenization of mixture: After fully mixing sludge product B and fine particle product A1 at a mass ratio of 1:2, the mixture is placed in a colloid mill for grinding and homogenization. The homogenization speed is 3000 rpm to break the sludge granular structure and obtain homogenized product C.

[0053] Among them, the homogenized product C has a water content of 53.1% and a particle size of <0.5mm, of which more than 68% of the particles have a particle size of <0.3mm, and is fine with no obvious granular structure;

[0054] (3) Preparation of intermediate: The homogenized product C and the aged product A2 are thoroughly mixed at a mass ratio of 1.2:1 to obtain mixture D. The mixture D is placed in a screw extrusion molding machine (screw length is 40cm, screw speed is 80rpm) for rotary extrusion and friction heating plasticization to obtain intermediate E;

[0055] The mixture D has a moisture content of 44.6%; the intermediate E has a thickness of 0.82 cm, a width of 2.61 cm, a surface temperature of 50.2℃ at discharge, a plasticity index of 13, no surface cracks, and can break but not pulverize when dropped freely from a height of 10 cm onto a hard platform.

[0056] (4) Cold-pressed bricks: The intermediate body E is placed in a cold-pressed brick machine with a mold depth of 15.6cm. After pressing at 12MPa, it is placed in a cool and ventilated place and naturally dried for 20 days to form a finished cold-pressed ecological brick with a thickness of 7.6cm.

[0057] Example 3

[0058] This embodiment provides a method for preparing cold-pressed eco-bricks using sludge products, including the following steps:

[0059] (1) Raw material preparation: Part of the municipal sludge anaerobic digestion residue and garden waste were subjected to aerobic fermentation and drying treatment (fermentation conditions: 22 days, turned over once every 8 days) to obtain a soft, odorless fermentation product (moisture content 41.3%, organic matter dry weight percentage 37.6%). The fermentation product was screened to obtain fine-grained product A1 and coarse-grained product A2; another part of the anaerobic digestion residue was dried to obtain sludge product B with a moisture content of 56.3%;

[0060] The municipal sludge anaerobic digestion residue had a moisture content of 80%, an organic matter dry weight ratio of 30%, a total nutrient nitrogen, phosphorus, and potassium content on a dry basis of 1.12%, and a pH value of 7.67. The fine-grained product A1 had a particle size of <2mm (passing through a 2mm sieve), a moisture content of 46.2%, and an organic matter dry weight ratio of 30.5%. The coarse-grained product A2 had a particle size of 3-7mm (passing through a 3mm sieve, but not a 7mm sieve). After 20 days of sun-drying and aging, the coarse-grained product A2 had a moisture content of 28.1% and an organic matter dry weight ratio of 44.2%.

[0061] (2) Homogenization of mixture: After fully mixing sludge product B and fine particle product A1 at a mass ratio of 1:1, the mixture is placed in a colloid mill for grinding and homogenization. The homogenization speed is 3000 rpm to break the sludge granular structure and obtain homogenized product C.

[0062] Among them, the homogenized product C has a water content of 51.2% and a particle size of <0.5mm, of which more than 62% of the particles have a particle size of <0.3mm, and is fine with no obvious granular structure;

[0063] (3) Preparation of intermediate: The homogenized product C and the aged product A2 are thoroughly mixed at a mass ratio of 2:2.5 to obtain mixture D. Mixture D is placed in a screw extrusion molding machine (screw length is 40cm, screw speed is 80rpm) for rotary extrusion and friction heating plasticization to obtain intermediate E;

[0064] The mixture D has a water content of 38.7%; the intermediate E has a thickness of 1.93 cm, a width of 3.87 cm, a surface temperature of 60.3℃ at discharge, a plasticity index of 11, no surface cracks, and can break but not shatter when dropped freely from a height of 10 cm onto a hard platform.

[0065] (4) Cold-pressed bricks: The intermediate body E is placed in a cold-pressed brick machine with a mold depth of 15.6cm. After pressing at 10MPa, it is placed in a cool and ventilated place and naturally dried for 20 days to obtain a cold-pressed ecological brick product with a thickness of 7.1cm.

[0066] Example 4

[0067] This embodiment also provides a method for preparing cold-pressed ecological bricks using sludge products, including the following steps:

[0068] (1) Raw material preparation: Part of the municipal sludge anaerobic digestion residue and garden waste were subjected to aerobic fermentation and drying treatment (fermentation conditions: 25 days, turned over once every 10 days) to obtain a soft and odorless fermentation product (moisture content of 37.3% and organic matter dry weight ratio of 39.4%). The fermentation product was screened to obtain fine product A1 and coarse product A2. Another part of the anaerobic digestion residue was dried to sludge product B with a moisture content of 55.6%.

[0069] Among them, the anaerobic digestion residue of municipal sludge has a moisture content of 75.8%, an organic matter dry weight ratio of 33.7%, a total nutrient nitrogen, phosphorus and potassium content on a dry basis of 1.53%, and a pH value of 7.33; the fine-grained product A1 has a particle size of <2mm (passes through a 2mm sieve), a moisture content of 44.3%, and an organic matter dry weight ratio of 35.1%; the coarse-grained product A2 has a particle size of 2~10mm (can pass through a 10mm sieve, but not a 2mm sieve), and after 40 days of sun-drying and aging, the moisture content after aging is 25.7%, and the organic matter dry weight ratio is 44.5%;

[0070] (2) Homogenization of mixture: Sludge product B and fine particle product A1 are thoroughly mixed at a mass ratio of 1:1.5 and then put into a colloid mill for grinding and homogenization. The homogenization speed is 4000 rpm to break the sludge granular structure and obtain homogenized product C.

[0071] Among them, the homogenized product C has a water content of 48.8% and a particle size of <0.5mm, of which more than 78% of the particles have a particle size of <0.3mm, and is fine with no obvious granular structure;

[0072] (3) Preparation of intermediate: The homogenized product C and the aged product A2 are thoroughly mixed at a mass ratio of 1:1 to obtain mixture D. Mixture D is placed in a screw extrusion molding machine (screw length is 30cm, screw speed is 60rpm) for rotary extrusion and friction heating plasticization to obtain intermediate E;

[0073] The mixture D has a water content of 37.3%; the intermediate E has a thickness of 0.52 cm, a width of 3.87 cm, a surface temperature of 62.1℃ at discharge, a plasticity index of 13, no surface cracks, and can break but not shatter when dropped freely from a height of 10 cm onto a hard platform.

[0074] (4) Cold-pressed bricks: The intermediate body E is placed in the mold of a cold-pressed brick machine with a mold depth of 10cm and pressed at 20MPa. It is then placed in a cool and ventilated place and allowed to dry naturally for 10 days to form a finished cold-pressed ecological brick with a thickness of 4.36cm.

[0075] Example 5

[0076] This embodiment provides a method for preparing cold-pressed eco-bricks using sludge products, including the following steps:

[0077] (1) Raw material preparation: Part of the municipal sludge anaerobic digestion residue and garden waste were subjected to aerobic fermentation and drying treatment (fermentation conditions: 15 days, turned over once every 10 days) to obtain a soft and odorless fermentation product (moisture content of 48.9% and organic matter dry weight ratio of 30.2%). The fermentation product was screened to obtain fine product A1 and coarse product A2. Another part of the anaerobic digestion residue was dried to sludge product B with a moisture content of 61.3%.

[0078] The municipal sludge anaerobic digestion residue had a moisture content of 71.9%, an organic matter dry weight percentage of 48.3%, a total nutrient nitrogen, phosphorus, and potassium content on a dry basis of 1.21%, and a pH value of 7.51. Fine-grained product A1 had a particle size <2mm (passes through a 2mm sieve), a moisture content of 51.2%, and an organic matter dry weight percentage of 26.4%. Coarse-grained product A2 had a particle size of 2-10mm (passes through a 10mm sieve but not a 2mm sieve). After 20 days of sun-drying and aging, coarse-grained product A2 had a moisture content of 33.6% and an organic matter dry weight percentage of 37.9%.

[0079] (2) Homogenization of mixture: After the sludge product B and the fine particle product A1 are fully mixed at a mass ratio of 1:1.3, they are put into a colloid mill for grinding and homogenization. The homogenization speed is 2000 rpm to break the sludge granular structure and obtain homogenized product C.

[0080] Among them, the homogenized product C has a water content of 56.4% and a particle size of <0.5mm, of which more than 65% of the particles have a particle size of <0.3mm, and is fine with no obvious granular structure;

[0081] (3) Preparation of intermediate: The homogenized product C and the aged product A2 are thoroughly mixed at a mass ratio of 4:2.5 to obtain mixture D. Mixture D is placed in a screw extrusion molding machine (screw length is 50cm, screw speed is 60rpm) for rotary extrusion and friction heating plasticization to obtain intermediate E;

[0082] The mixture D has a moisture content of 44.5%; the intermediate E has a thickness of 0.52 cm, a width of 3.87 cm, a surface temperature of 51.6℃ at discharge, a plasticity index of 12, no surface cracks, and can break but not shatter when dropped freely from a height of 10 cm onto a hard platform.

[0083] (4) Cold-pressed bricks: The intermediate body E is placed in a cold-pressed brick machine with a mold depth of 20cm. After pressing at 10MPa, it is placed in a cool and ventilated place and naturally dried for 15 days to form a finished cold-pressed ecological brick with a thickness of 11.9cm.

[0084] Comparative Example 1

[0085] The difference between this comparative example and Example 1 is that the sludge product B is replaced with fine-particle product A1.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 1 is that in step (2), only sludge product B and fine particulate product A1 are mixed, and the grinding and homogenization steps of the colloid mill are omitted.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 1 is that in step (3), the particle size of the aged product A2 is >10mm (cannot pass through a 10mm aperture sieve).

[0090] Comparative Example 4

[0091] The difference between this comparative example and Example 1 is that the spiral extrusion molding step is omitted in step (3), and only the homogenized product C and the aged product A2 are mixed evenly.

[0092] Experimental Example 1

[0093] 1. Moisture content determination

[0094] The moisture content of cold-pressed ecological bricks was determined by the drying method. Specifically, a certain mass of intermediate product or cold-pressed ecological bricks was taken, broken into small pieces <1cm, and placed in a dried weighing box (mass M0). The initial total mass (M1, accurate to 0.1g) was weighed. The sample and box were placed together in a drying oven at 105±5℃ and dried to constant weight. The total mass (M2) was weighed again. The formula for calculating the moisture content is: Moisture content = (M1-M2) / (M1-M0)×100%.

[0095] The moisture content of the cold-pressed ecological bricks prepared in each embodiment and comparative example is shown in Table 1.

[0096] 2. Determination of compressive and flexural strength of bricks

[0097] Method for determining compressive strength: Using the standard testing machine method, 10 specimens were prepared. The upper and lower pressure surfaces were accurately leveled by the slab-sitting method. After measuring the dimensions, the specimens were placed in the center of a special compressive strength fixture and pressurized at a specified rate until failure. The maximum load was recorded, the compressive strength was calculated, and the average value of the 10 specimens was taken.

[0098] Method for determining flexural strength: The three-point bending method is used to determine flexural strength. Ten intact brick samples are taken, and the width and height of the specimens are measured. The samples are placed stably on two parallel supports of the flexural testing apparatus (span equal to the brick length minus 40 mm). A loading rod is applied above the mid-span at a uniform rate of 50–150 N / s until the specimen fractures. The failure load is recorded, and the flexural strength of a single specimen is calculated using the following formula. Finally, the arithmetic mean of the results from the ten specimens is taken. The formula for calculating flexural strength is:

[0099] R=3PL / (2bh) 2 )

[0100] In the formula, R refers to the flexural strength of the specimen (MPa); P refers to the maximum load applied when the specimen breaks (N); L refers to the span between the two supports (mm); b refers to the width of the specimen cross-section (mm); and h refers to the height of the specimen cross-section (mm).

[0101] The compressive strength and flexural strength of the cold-pressed ecological bricks prepared in each embodiment and comparative example are shown in Table 1.

[0102] Table 1 Properties of Cold-Pressed Ecological Bricks

[0103]

[0104] In Comparative Example 1, the sludge product B was replaced with fine-particle product A1 of equal mass. The reason why its moisture content is less than 20% is that the moisture content of fine-particle product A1 is lower than that of sludge product B. In the actual drying process, sludge product B is more difficult to dehydrate than fine-particle product A1 (stabilized product) due to its high hydrophilicity. Therefore, the moisture content of the ecological brick after replacement is lower. The reason why its compressive strength and flexural strength are lower than those of Example 1 is that fine-particle product A1 is a stabilized product (soft) after sludge and sludge fermentation and is mixed with some auxiliary materials. Its viscosity will be significantly reduced compared with sludge product B, which will affect the overall bonding strength. In addition, the low moisture content of fine-particle product A1 will reduce the moisture content of homogenized product C and affect the later strength.

[0105] In Comparative Example 2, the grinding and homogenization process of the colloid mill was omitted in step (2), and the moisture content was less than 20% because grinding and homogenization do not significantly affect the curing and drying efficiency of the ecological bricks, so the final moisture content is similar. The compressive strength and flexural strength are lower than those of Example 1 because grinding and homogenization can break down the "large particle" agglomerates in the mud, avoiding a large number of sticky particles after mixing with coarse product A2. Without this step, these large particle sticky particles are not easy to mix evenly with other materials, which will lead to uneven water loss during the drying process of the brick, resulting in microcracks or cavities in the brick and reducing the strength of the brick.

[0106] In Comparative Example 3, the particle size of the aged product A2 in step (3) is >10mm (cannot pass through a 10mm sieve), and its moisture content is less than 20% because: the particle size of coarse product A2 will not significantly affect the curing and drying efficiency of the ecological brick; its compressive strength and flexural strength are lower than those of Example 1 because: coarse product A2 contains a large amount of undecomposed auxiliary materials, such as branches and leaves. The larger the particle size, the more residual auxiliary materials there are. These residual auxiliary materials themselves do not have adhesive properties, are not easy to mix evenly with sludge products, and will affect the uniformity of water loss during the drying process of the brick, significantly affecting the compressive and flexural strength.

[0107] In Comparative Example 4, the spiral extrusion molding step in step (3) was omitted, and the homogenized product C was mixed evenly with the aged coarse product A2. The reason for its higher water content is that spiral extrusion helps to break the binding structure of some extracellular polymers in the sludge, reducing its high hydrophilicity and adsorption of water, thereby improving the dewatering performance of the sludge product. Without this step, the final ecological brick will have a relatively high water content. The reason for its compressive strength and flexural strength being lower than those of Example 1 is that repeated extrusion and mixing of the mud by spiral extrusion can make the moisture, particle distribution and density of the mud more uniform, improve plasticity and molding stability, significantly reduce brick cracking, and improve strength. This is a key step. Without this step, the strength of the brick will be significantly reduced.

[0108] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method of preparing cold-pressed eco-bricks using a sludge product, characterized by, Includes the following steps: S1. Raw material preparation: The first sludge anaerobic digestion residue and agricultural and forestry waste are subjected to aerobic fermentation and drying to obtain fermentation products. The fermentation products are screened to obtain fine product A1 and coarse product A2. The second sludge anaerobic digestion residue is dried to obtain sludge product B. The particle size of the fine product A1 is <2mm. The coarse-grained product A2 has a particle size of 2~10mm; S2. Homogenization of the mixture: After mixing sludge product B with fine particulate product A1, the mixture is ground and homogenized to break down the sludge aggregate structure and obtain homogenized product C. S3. Preparation of intermediate: The homogenized product C is mixed with the coarse-grained product A2 to obtain mixture D; mixture D is subjected to rotary extrusion and friction heating plasticization to obtain intermediate E; S4. Pressed and cooled ecological bricks: The intermediate E is pressed and cured.

2. The method for preparing cold-pressed eco-bricks using sludge products according to claim 1, characterized in that, In step S1, the moisture content of the first sludge anaerobic digestion residue and the second sludge anaerobic digestion residue is 70%~80%, the dry weight percentage of organic matter is 30%~55%, the dry weight percentage of total nutrients nitrogen, phosphorus and potassium is >1%, and the pH value is 6~8.

3. The method for preparing cold-pressed eco-bricks using sludge products according to claim 1, characterized in that, In step S1, the water content of the fermentation product is 35%~50%, and the dry weight percentage of organic matter is 30%~40%. And / or, the fine-particle product A1 has a moisture content of 40%~55% and an organic matter dry weight percentage of 25%~35%; And / or, the coarse-grained product A2 needs to be dried and aged for 20 to 40 days, after which the moisture content is 25% to 35% and the dry weight percentage of organic matter is 35% to 45%; And / or, the water content of the sludge product B is 55%~65%.

4. The method for preparing cold-pressed eco-bricks using sludge products according to claim 1, characterized in that, In step S2, the sludge product B and the fine particle product A1 are mixed at a mass ratio of 1:1 to 2.

5.

5. The method for preparing cold-pressed eco-bricks using sludge products according to claim 1, characterized in that, In step S2, the homogenized product C has a water content of 50%~60% and a particle size of <0.5mm; And / or, the proportion of particles with a diameter <0.3 mm in the homogenized product C is not less than 60 wt%; And / or, the homogenized product C has a fine texture and no obvious granular structure.

6. The method for preparing cold-pressed eco-bricks using sludge products according to claim 1, characterized in that, In step S3, the homogenized product C and the coarse-grained product A2 are mixed at a mass ratio of (2~4):(1~2.5).

7. The method for preparing cold-pressed eco-bricks using sludge products according to claim 1, characterized in that, In step S3, during the rotary extrusion and friction heating plasticization, a screw extrusion molding machine with a screw length of 30~50cm and a screw speed of 60~120rpm is used. And / or, during the rotary extrusion and friction heating plasticization, the cavity temperature is controlled at 45~65℃.

8. The method for preparing cold-pressed eco-bricks using sludge products according to claim 1, characterized in that, In step S3, the water content of the mixture D is 35%~45%; And / or, the intermediate E has a thickness of 0.5~2cm, a width of 2~4cm, a surface temperature of 45~65℃ when discharged, a plasticity index >10, no surface cracks, and can break but not shatter when dropped freely from a height of 10cm onto a hard platform.

9. The method for preparing cold-pressed eco-bricks using sludge products according to claim 1, characterized in that, In step S4, the pressing pressure is 10~20MPa, the mold depth is 10~20cm, the thickness of the pressed brick is 5~10cm, and the surface is flat and without cracks. And / or, the maintenance conditions are to allow the product to dry naturally in a cool, well-ventilated place for 10 to 20 days.

10. A cold-pressed eco-brick produced from the method of producing a cold- pressed eco-brick from a sludge product according to any one of claims 1-9, characterized in that, The cold-pressed ecological bricks have a moisture content of <20%, a compressive strength of 4~10MPa, and a flexural strength of 0.5~1.5MPa.

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