Preparation method of microorganism carbon sequestration reinforced recycled coarse aggregate

Abstract

The invention relates to the technical field of microbial carbon sequestration, in particular to a preparation method of a microbial carbon sequestration reinforced recycled coarse aggregate, which comprises the following steps: firstly, modifying a carrier with macropores on the surface, and loading active carbon sequestration microorganisms in micropores of the modified carrier; then the modified carrier and the recycled coarse aggregate are mixed under the action of pneumatic stirring, during mixing, the carrier with the small particle size does irregular movement under air pressure, the carrier with the small particle size enters large gaps in the surface of the recycled coarse aggregate to be attached, the gaps are pre-filled, and microorganisms are introduced into the gaps through the carrier; the number of microorganisms and the pre-filling amount of gaps are increased, the deposition amount of calcium carbonate is increased in the subsequent microorganism carbon sequestration treatment, large gaps can be fully filled, the strengthening effect is improved, and the water absorption rate of the product is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of microbial carbon fixation, and in particular to a method for preparing microbial carbon fixation-enhanced recycled coarse aggregate. Background Art

[0002] With the acceleration of industrialization and urbanization, the construction area is increasing day by day, and the amount of waste concrete removed each year is huge, and the accompanying construction waste is increasing year by year. At present, most of the construction waste is directly transported to the suburbs and villages for open-air stacking or landfill treatment, which consumes a lot of land acquisition fees, garbage removal fees, treatment fees and other construction costs.

[0003] According to rough statistics on the loss of construction materials for buildings such as brick-concrete structures, cast-in-place structures and frame structures, 500 to 600 tons of construction waste will be generated during the construction of every 10,000 square meters of buildings. And every 10,000 square meters of old buildings demolished will generate 7,000 to 12,000 tons of construction waste. A large amount of construction waste cannot be used scientifically, which has caused great harm to environmental governance. How to scientifically and effectively solve the current construction waste problem and realize the resource utilization of construction waste is an urgent problem that needs to be solved.

[0004] In order to maintain the sustainable development of the construction industry, alleviate the serious shortage of natural resources, reduce the pollution of waste concrete accumulation, and reduce carbon emissions in the construction industry, the recycling of construction waste has emerged. In the process of recycling construction waste, crushing and screening will produce coarse particles with a particle size greater than 4.75 mm. It is crucial to improve the comprehensive utilization rate of construction waste and realize the resource utilization of the above coarse particles. Nowadays, recycled aggregates obtained by strengthening have been applied to practical projects. However, the recycled aggregates produced by simple crushing processes have low strength, high water absorption, large performance discreteness, and poor quality, which have failed to fundamentally solve the problem of shortage of natural aggregate resources for structural concrete. Therefore, it is urgent to seek a method for preparing high-quality recycled aggregates with high strength, low water absorption, and stable performance. On the other hand, there is currently little research on micropowders, and the utilization rate is extremely low. A large amount of micropowders are directly stacked, landfilled, or used for roadbed materials. How to efficiently utilize micropowders has become a bottleneck for the resource utilization of construction waste and the realization of zero emissions.

[0005] Microbially induced calcium carbonate precipitation (MICP) refers to the process in which carbon-fixing microorganisms in nature capture CO2 from the air and induce calcium ions in the environment to precipitate calcium carbonate. Since this process realizes the conversion of CO2 gas into carbonate minerals, it is also called microbial carbon fixation technology. The mineralization product is calcium carbonate, which is an environmentally friendly natural stone and has excellent compatibility with cement-based materials. In recent years, it has been widely used in the repair of cement-based material defects. In the entire process of biological carbon fixation technology, no matter what kind of bacteria, they mainly play two core roles: one is to provide a carbon source, and the other is to provide nucleation sites for the formation of calcium carbonate crystals.

[0006] Microbial mineralized calcium carbonate deposition has good adhesion, compatibility and self-stability with cement-based materials, and is widely used in concrete defect repair, cementation and solidification of sand, soil improvement, ancient building repair, passivation of heavy metals, etc. With the expansion of application areas, it has also achieved initial results in the resource utilization of solid waste, especially the strengthening of recycled aggregates. A large number of research results show that it is feasible to strengthen recycled aggregates with microbial mineralized deposition technology. Microorganisms deposit calcium carbonate on the surface of recycled aggregates and in crack defects to form a crystal protective layer, which prevents water and other harmful media from entering, reduces water absorption, and improves strength. In addition, microbial calcium carbonate has good compatibility with cement materials, which can improve the performance of the interface transition zone of recycled concrete, thereby improving the mechanical properties and durability of recycled concrete.

[0007] The method of microbial carbon fixation in the prior art is to soak the crushed coarse material particles in a carbon fixation microbial culture solution, and then introduce carbon dioxide for carbon fixation oxidation. The principle is that the microorganisms attached to the gaps between the particles capture CO2 in the air, induce the calcium ions in the environment to precipitate calcium carbonate, and fill the gaps in the aggregate to play a strengthening role while reducing the water absorption rate. However, the technical defect is that the gaps formed by the coarse aggregate during pretreatment such as crushing are of different sizes. For smaller gaps, microorganisms can well deposit and fill calcium carbonate. For some larger gaps, since the number of microorganisms attached to the inner wall of the gap is limited and the space to be filled is large, it is difficult to produce a large amount of calcium carbonate, and the gaps cannot be well filled, reducing the aggregate strengthening effect. Summary of the invention

[0008] In view of the technical problem that in the preparation of microbial carbon fixation strengthened recycled coarse aggregate, the gaps between particles are too large to be effectively filled, which affects the strengthening effect. The present invention provides a method for preparing microbial carbon fixation strengthened recycled coarse aggregate, which can achieve effective filling of large gaps between particles in the preparation of coarse aggregate, thereby improving the strengthening effect.

[0009] The present invention provides a method for preparing microbial carbon fixation-enhanced recycled coarse aggregate, comprising the following steps: (1) taking a carrier having macropores on its surface, immersing the carrier in a first microbial culture solution, stirring, filtering, and naturally drying the carrier to obtain a modified carrier; (2) soaking the recycled coarse aggregate in a second microbial culture solution, stirring, filtering, and naturally drying to obtain modified recycled coarse aggregate; (3) mixing the modified carrier obtained in step (1) with the modified recycled coarse aggregate obtained in step (2), stirring them by spraying, spraying the modified carrier into some gaps of the modified recycled coarse aggregate, and sieving out the modified carrier that has not entered the gaps; (4) Taking the sieved material in step (3), spraying the surface of the sieved material with nutrient solution, and then placing it in a microbial carbonization box, introducing carbon dioxide to carry out microbial carbon fixation treatment, thereby obtaining microbial carbon fixation enhanced recycled coarse aggregate.

[0010] Furthermore, in step (1), the carrier is macroporous silica, and the particle size of the macroporous silica is 10-50 μm.

[0011] Furthermore, the first microbial culture solution includes a microorganism and a culture solution, the microorganism is one of alkaliphilic Bacillus, subtilis or Bacillus subtilis, the inoculation amount of the microorganism in the culture solution is 8.0%, and the culture solution is prepared according to the following concentrations of ingredients: 8 g / L tryptone, 9 g / L soy peptone, and 2 g / L sodium chloride.

[0012] Furthermore, the second microbial culture solution includes a microorganism and a culture solution, the microorganism is one of Bacillus subtilis, Bacillus alkaliphilus or Bacillus mucilaginosus, the inoculation amount of the microorganism in the culture solution is 8.0%, and the culture solution is prepared according to the following concentrations of ingredients: 8 g / L of tryptone, 9 g / L of soy peptone, and 2 g / L of sodium chloride.

[0013] Furthermore, the weight ratio of the carrier to the recycled coarse aggregate is 1~3:15~25.

[0014] Furthermore, in step (2), the recycled coarse aggregate is obtained by crushing, screening, washing and drying construction waste, and the particle size of the recycled coarse aggregate is greater than 4.75 mm.

[0015] Furthermore, in step (2), the recycled coarse aggregate is first pretreated, and the pretreatment includes soaking the recycled coarse aggregate in a mixed solution of urea and ammonia water. The purpose is to utilize the enzymatic activity of urease of carbon-fixing microorganisms to decompose urea to generate carbon dioxide and provide a carbon source. On the other hand, ammonia water provides an alkaline environment to improve the enzyme reaction activity.

[0016] Furthermore, in step (4), the nutrient solution is prepared according to the following concentrations: 8 g / L tryptone, 9 g / L soy peptone, and 2 g / L sodium chloride. The function is to provide an initial activation effect on the carbon fixation reaction of microorganisms and improve the growth efficiency of microorganisms.

[0017] Furthermore, in step (4), the process conditions for microbial carbon fixation treatment are: temperature of 36±3°C, humidity of 80%~90%, time of 5~7 days, and carbon dioxide pressure of 0.2~0.25MPa.

[0018] The beneficial effects of the present invention are: (1) The present invention first modifies a carrier with large pores on the surface, and the modified carrier micropores are loaded with active carbon-fixing microorganisms. The modified carrier is then mixed with recycled coarse aggregate under the action of pneumatic stirring. During mixing, the carrier particles are small and move irregularly under air pressure. The carrier particles with smaller sizes will enter the larger gaps on the surface of the recycled coarse aggregate and attach to them, thereby "pre-filling" the gaps. Microorganisms are introduced into the gaps through the carrier, which increases the number of microorganisms and the pre-filling amount of the gaps. In the subsequent microbial carbon fixation treatment, the deposition amount of calcium carbonate is increased, which is conducive to fully filling the large gaps, improving the strengthening effect, and reducing the water absorption rate of the product.

[0019] (2) The present invention immerses the recycled coarse aggregate in a second microbial culture solution for modification, so that all gaps are loaded with active microorganisms, and small-sized gaps still carry microbial activity for calcium carbonate deposition. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 It is a schematic diagram of the filling structure of the modified carrier in the gap of the modified recycled coarse aggregate according to a specific embodiment of the present invention.

[0022] In the figure, 1-modified recycled coarse aggregate, 11-large-sized gaps, 12-small-sized gaps, and 2-modified carrier. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0024] The recycled coarse aggregate used in the following examples is obtained by crushing, screening, washing and drying construction waste, and the particle size of the obtained recycled coarse aggregate is 5-10 mm.

[0025] Example 1 A method for preparing microbial carbon fixation-enhanced recycled coarse aggregate comprises the following steps: (1) Taking 10 g of a granular macroporous silica carrier (with a particle size of 10 to 20 μm), soaking the carrier in a first microbial culture solution, wherein the first microbial culture solution comprises a microorganism and a culture solution, wherein the microorganism is Bacillus subtilis, and the inoculation amount of the microorganism in the culture solution is 8.0%. The culture solution is prepared according to the following concentrations: 8 g / L of tryptone, 9 g / L of soy peptone, and 2 g / L of sodium chloride. After soaking, the carrier is stirred, filtered, and dried naturally to obtain a modified carrier; (2) 150 g of recycled coarse aggregate is soaked in a second microbial culture solution, the second microbial culture solution includes a microorganism and a culture solution, the microorganism is Bacillus subtilis, the inoculation amount of the microorganism in the culture solution is 8.0%, and the culture solution is prepared according to the following concentrations: 8 g / L of tryptone, 9 g / L of soy peptone, and 2 g / L of sodium chloride, stirred, filtered, and naturally dried to obtain modified recycled coarse aggregate; (3) Mixing the modified carrier obtained in step (1) with the modified recycled coarse aggregate obtained in step (2), and stirring them by spraying. Figure 1 During the spraying, the modified carrier 2 enters the large-size gap 11 of the modified recycled coarse aggregate 1 and adheres thereto. The small-size gap 12 is too small to allow the particles of the modified carrier 2 to enter. The excess modified carrier that does not enter the gap is sieved out. (4) Take the sieve material after sieving in step (3), spray the surface of the sieve material with nutrient solution and place it in a microbial carbonization box. The nutrient solution is prepared according to the following concentrations: 8 g / L tryptone, 9 g / L soy peptone, and 2 g / L sodium chloride. Carbon dioxide is introduced for microbial carbon fixation. The process conditions for microbial carbon fixation are as follows: temperature of 36±3°C, humidity of 80%~90%, time of 5~7 days, and carbon dioxide pressure of 0.2~0.25 MPa, to obtain microbial carbon fixation enhanced recycled coarse aggregate.

[0026] Example 2 A method for preparing microbial carbon fixation-enhanced recycled coarse aggregate comprises the following steps: (1) Taking 30 g of a granular macroporous silica carrier (particle size of 20-50 μm), soaking the carrier in a first microbial culture solution, the first microbial culture solution comprising a microorganism and a culture solution, the microorganism being Bacillus subtilis, the inoculation amount of the microorganism in the culture solution being 8.0%, and the culture solution being prepared according to the following concentrations: 8 g / L of tryptone, 9 g / L of soy peptone, and 2 g / L of sodium chloride, stirring after soaking, filtering, and naturally drying to obtain a modified carrier; (2) soaking 250 g of recycled coarse aggregate in a second microbial culture solution, the second microbial culture solution comprising a microorganism and a culture solution, the microorganism being Bacillus subtilis, the inoculation amount of the microorganism in the culture solution being 8.0%, the culture solution being prepared according to the following concentrations of ingredients: 8 g / L of tryptone, 9 g / L of soy peptone, and 2 g / L of sodium chloride, stirring, filtering, and naturally drying to obtain modified recycled coarse aggregate; (3) mixing the modified carrier obtained in step (1) with the modified recycled coarse aggregate obtained in step (2), stirring them by spraying, spraying the modified carrier into some gaps of the modified recycled coarse aggregate, and sieving out the modified carrier that has not entered the gaps; (4) Take the sieve material after sieving in step (3), spray the surface of the sieve material with nutrient solution and place it in a microbial carbonization box. The nutrient solution is prepared according to the following concentrations: 8 g / L tryptone, 9 g / L soy peptone, and 2 g / L sodium chloride. Carbon dioxide is introduced for microbial carbon fixation. The process conditions for microbial carbon fixation are as follows: temperature of 36±3°C, humidity of 80%~90%, time of 5~7 days, and carbon dioxide pressure of 0.2~0.25 MPa, to obtain microbial carbon fixation enhanced recycled coarse aggregate.

[0027] Example 3 The difference between Example 3 and Example 2 is that in step (2), the recycled coarse aggregate is first pretreated, and the pretreatment includes soaking the recycled coarse aggregate in a mixed solution of urea and ammonia water. The purpose is to utilize the enzymatic activity of urease of carbon-fixing microorganisms to decompose urea to generate carbon dioxide and provide a carbon source. On the other hand, ammonia water provides an alkaline environment to improve the enzyme reaction activity.

[0028] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not contain the mixing operation in step (1) and step (3).

[0029] The recycled coarse aggregates prepared in the embodiments and comparative examples were tested (see GB / T 25177-2010 for the test method). Specific test data are shown in Table 1.

[0030] Table 1 Performance test data of recycled coarse aggregate obtained in various embodiments and comparative examples

[0031] It can be seen from Table 1 that the performance of the recycled coarse aggregate prepared in each embodiment of the present invention meets the performance requirements of Class I recycled coarse aggregate in GB / T 25177-2010, has a lower crushing value and water absorption rate, and the technical effect of the embodiments of the present invention is improved compared with the comparative example.

[0032] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for preparing recycled coarse aggregate enhanced by microbial carbon fixation, characterized in that: The steps include: (1) taking a carrier having macropores on its surface, immersing the carrier in a first microbial culture solution, stirring, filtering, and naturally drying the carrier to obtain a modified carrier; (2) soaking the recycled coarse aggregate in a second microbial culture solution, stirring, filtering, and naturally drying to obtain modified recycled coarse aggregate; (3) mixing the modified carrier obtained in step (1) with the modified recycled coarse aggregate obtained in step (2), stirring them by spraying, spraying the modified carrier into some gaps of the modified recycled coarse aggregate, and sieving out the modified carrier that has not entered the gaps; (4) Taking the sieved material in step (3), spraying the surface of the sieved material with nutrient solution, and then placing it in a microbial carbonization box, introducing carbon dioxide to carry out microbial carbon fixation treatment, thereby obtaining microbial carbon fixation enhanced recycled coarse aggregate.

2. The method for preparing a microbial carbon fixation-enhanced recycled coarse aggregate according to claim 1, characterized in that: In step (1), the carrier is macroporous silica, and the particle size of the macroporous silica is 10-50 μm.

3. The method for preparing a microbial carbon fixation-enhanced recycled coarse aggregate according to claim 1, characterized in that: The first microbial culture solution includes a microorganism and a culture solution. The microorganism is one of alkaliphilic Bacillus, subtilis or mucilaginous Bacillus. The inoculation amount of the microorganism in the culture solution is 8.0%. The culture solution is prepared according to the following concentrations: 8 g / L tryptone, 9 g / L soy peptone, and 2 g / L sodium chloride.

4. The method for preparing a microbial carbon fixation-enhanced recycled coarse aggregate according to claim 1, characterized in that: The second microbial culture solution includes a microorganism and a culture solution. The microorganism is one of Bacillus subtilis, Bacillus alkaliphilus or Bacillus mucilaginosus. The inoculation amount of the microorganism in the culture solution is 8.0%. The culture solution is prepared according to the following concentrations of ingredients: 8 g / L tryptone, 9 g / L soy peptone, and 2 g / L sodium chloride.

5. The method for preparing a microbial carbon fixation-enhanced recycled coarse aggregate according to claim 1, characterized in that: The weight ratio of carrier to recycled coarse aggregate is 1~3:15~25.

6. The method for preparing a regenerated coarse aggregate enhanced by microbial carbon fixation according to claim 1, characterized in that: In step (2), the recycled coarse aggregate is obtained by crushing, screening, washing and drying construction waste, and the particle size of the recycled coarse aggregate is greater than 4.75 mm.

7. The method for preparing a microbial carbon fixation-enhanced recycled coarse aggregate according to claim 1, characterized in that: In step (2), the recycled coarse aggregate is first pretreated, and the pretreatment includes soaking the recycled coarse aggregate in a mixed solution of urea and ammonia water.

8. The method for preparing recycled coarse aggregate enhanced by microbial carbon fixation according to claim 1, characterized in that: In step (4), the nutrient solution is prepared according to the following concentrations: 8 g / L tryptone, 9 g / L soy peptone, and 2 g / L sodium chloride.

9. The method for preparing recycled coarse aggregate enhanced by microbial carbon fixation according to claim 1, characterized in that: In step (4), the process conditions for microbial carbon fixation treatment are: temperature of 36±3°C, humidity of 80%~90%, time of 5~7 days, and carbon dioxide pressure of 0.2~0.25MPa.

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