Preparation method and application of biological micro-nano CaCO3 based on sludge pyrolysis liquid and concrete slurry waste

Abstract

The invention provides a method for preparing biological micro-nano CaCO3 based on sludge pyrolysis liquid and concrete slurry waste (CSW) and application of the method. The method comprises the following steps: firstly, regulating a domestic wastewater reactor to be in an alkaline environment, and adding the sludge pyrolysis liquid under a constant-temperature condition for hydrolysis; after reacting for a period of time, carrying out biological aeration, standing, taking supernate, and combining the supernate with CSW to generate CaCO3 micro-nano particles. And centrifuging, drying, enriching and weighing the precipitate. And carrying out structure and particle size analysis on the prepared micro-nano particles by using a scanning electron microscope, and analyzing the composition and crystal structure of the micro-nano particles. After biological aeration and standing, supernate is collected, the content of carbonate radicals and bicarbonate radicals in the supernate is analyzed, heavy metal residues in the supernate and CaCO3 precipitates are measured, and the application environmental protection property and safety of the process are ensured. The method not only can meet the requirement of resourceful treatment of the sludge solid waste, but also can realize the resourceful utilization of the CSW. Moreover, the preparation method is simple in process and convenient to operate, and has good biological micro-nano CaCO3 production efficiency.

Description

Technical Field

[0001] The present invention relates to the field of solid waste treatment, and in particular to a preparation method of biological micro-nano CaCO3 based on sludge pyrolysis liquid and CSW and application thereof. Background Art

[0002] During the concrete production process, a large amount of concrete slurry waste (CSW) is generated due to operations such as concrete truck cleaning, dust removal and ball washing. It is characterized by a pH value of more than 11.5 and is rich in calcium silicate. CSW is classified as a corrosive and hazardous substance. Due to its high pH value, it will have an adverse impact on the surrounding environment and ecosystem if it is abandoned in landfills. In addition, the sedimentation and post-processing processes lead to the accumulation of waste slurry particles, causing dust pollution in the concrete production environment, ignoring the potential recycling of important mineral resources.

[0003] The recycling of CSW is regulated by the Chinese national standard (GB / T 14902-2012). Previous studies have shown that Bacillus can synthesize biological CaCO3 micro-nanoparticles using calcium sources in concrete, which is beneficial for repairing concrete cracks and filling pores. Therefore, microbial induced calcium carbonate precipitation (MICP) provides a viable alternative for the recycling of calcium resources in CSW. CSW is considered to be a potential source of calcium carbonate. After the introduction of CO2 in the aqueous phase, up to 30% of calcium can be extracted from CSW to produce CaCO3 with a purity of more than 97%. However, the low water solubility of CO2 limits the production of CaCO3.

[0004] pH regulation enhances CO2 capture and promotes CO3 2-The generation of CaCO3 is conducive to the generation of abundant CaCO3 micro-nano particles. More importantly, bio-micro-nano CaCO3 is synthesized by urease-producing bacteria and enriched from waste sludge by MICP method, which has multiple applications such as repairing concrete voids, cementing soil, improving soil strength, and inhibiting coal dust in coal mines. The production of micro-nano CaCO3 from carbonized sludge and urine using urease-producing bacteria for the production of sustainable biocement has been explored. The production of bio-CaCO3 using Bacillus pasteurianus has been shown to improve the strength of expansive soil. Bacillus urealyticus ML-2 produces bio-CaCO3 for the treatment of waste sludge and immobilization of heavy metals. Nevertheless, it is important to consider that the use of a single strain and the addition of calcium source and urea to produce bio-CaCO3 may significantly increase the costs involved. The decomposition of urea leads to the excessive production and accumulation of ammonia nitrogen, which in turn acidifies the water body and promotes eutrophication. Direct research on the production of micro-nano-scale bio-CaCO3 using microbial communities in activated sludge and wastewater is still lacking. The biological metabolic mechanism of MICP in CSW to produce micro-nanoparticles is still unclear, especially the effect of pH on biochemical reaction pathways and alkalinity regulation. In addition, as the most important solid waste in municipal treatment, sludge contains a large amount of carbon source. The use of sludge hydrothermal products as a carbon source is beneficial to the CSW calcium source and its synthetic biological CaCO3 micro-nanoparticles. The hydrolysis process decomposes lipids into long-chain fatty acids and volatile fatty acids, and decomposes proteins into ammonia and volatile fatty acids. In the sludge hydrolyzed at 90°C, the degradation of long-chain fatty acids was the lowest. At the same time, the BOD5 / COD ratio greater than 0.6 also indicates its bioavailability.

[0005] In alkaline water, CO2 is converted into CO3 2- and HCO3 - As the pH value increases, HCO3 - Gradually converted into CO3 2- In contrast, as pH decreases, CO3 2- Gradually converted to HCO3 - , followed by the formation of carbonic acid molecules. Carbonic acid molecules are unstable and easily decompose into H2O and CO2, which then escape into the air. Therefore, pH plays a key role in determining the efficiency of carbon capture. At a pH of 7.5-8, CO2 is only converted into HCO3 - In this stage, a large amount of carbon dioxide produced by microbial β-oxidation is released from the water into the air. When the pH reaches 8.5-9, CO2 continues to be converted into CO3 2- and HCO3 - CO3 2- and HCO3 -The combined concentration of (carbon capture efficiency) will increase rapidly within 3 days. In the pH range from 9.5 to 10, the carbon capture efficiency can eventually stabilize at a certain value. Experiments have shown that at a pH of 8.5-9, the growth rate of carbon capture efficiency and the yield of biological CaCO3 are significantly higher than those at a pH of 9.5-10. Generally, for aerobic biological treatment, the pH value is recommended to be between 6 and 9. Too high a pH value can cause the death of some microorganisms, prolong the adaptation period, or potentially inhibit microbial activity. In addition, as the pH value increases, the supernatant of the reactor becomes more and more turbid, which has an adverse effect on the purity of the generated CaCO3. Furthermore, higher pH values ​​will increase operating costs, so establishing a pH value of 8.5-9 is considered to be the optimal alkaline condition for producing biological CaCO3.

[0006] To this end, the present invention utilizes the valuable calcium source of CSW through the biological metabolism process of activated sludge, proposes a new micro-nano calcium carbonate process strategy, and provides guidance for the recycling of CSW and the production of valuable micro-nano calcium carbonate. Summary of the invention

[0007] The main purpose of the present invention is to solve the problem of sludge solid waste treatment and the resource utilization of CSW.

[0008] In order to solve the above problems, the present invention provides a method for preparing biological micro-nano CaCO3 based on sludge pyrolysis liquid and CSW, and the preparation method comprises the following steps: step (1), adding sludge microorganisms, sludge pyrolysis products, CSW and NaOH solution into a reactor and reacting at a constant temperature; step (2), biologically aerating and standing to obtain a mixture, enriching it by centrifugation to obtain micro-nano particle precipitate and supernatant, and drying and weighing the precipitate; step (3), comparing the heavy metal substances in the supernatant and the precipitate according to the standard to observe whether they meet the emission standards; step (4), analyzing the obtained precipitate with an instrument to observe whether the main crystal form and particle size of the precipitated CaCO3 particles meet the requirements.

[0009] Furthermore, the optimum pH in the reactor is 8.5-9, and the constant temperature of 25°C is maintained at the same time.

[0010] Furthermore, in order to make full use of sludge solid waste and CSW and reduce operating costs, sludge pyrolysis liquid and CSW should be recycled.

[0011] Furthermore, the sludge pyrolysis product is the carbon source required for simulating microbial β-oxidation. In actual operation, the septic tank carbon source can be added normally, and the BOD5 / COD ratio should be greater than 0.6.

[0012] Furthermore, the amount of sludge microorganisms added should be approximately half of the reactor volume.

[0013] Furthermore, the reaction period should be 24 hours, including 23 hours of aerobic reaction, 30 minutes for precipitation, and 30 minutes for the formation of CaCO3 particles.

[0014] Furthermore, the reactor can be charged with 0.5 V·cm -1 The DC electric field is conducive to product formation.

[0015] Furthermore, samples need to be acidified before heavy metal content testing.

[0016] Furthermore, the main crystal form of the produced CaCO3 particles is calcite; and the particle size range is 0.7 to 10 μm.

[0017] According to another aspect of the present invention, there is also provided a method for preparing bio-micro-nano CaCO3 based on septic tank wastewater and CSW, wherein the bio-micro-nano CaCO3 is prepared by the above-mentioned preparation method.

[0018] According to a third aspect of the present invention, there is also provided an application of the above-mentioned bio-micro-nano CaCO3 based on sludge hydrolyzate and CSW, wherein the bio-micro-nano CaCO3 is used to repair concrete cracks, etc.

[0019] The beneficial effects of the present invention are:

[0020] Provided are a method for preparing bio-micro-nano CaCO3 based on sludge pyrolysis liquid and concrete slurry waste (CSW) and its application. The preparation method is to first place the reactor in an alkaline environment, add sludge pyrolysis products under constant temperature conditions for hydrolysis reaction, and generate CaCO3 micro-nano particles after biological aeration and standing. The precipitate is enriched by centrifugation, dried and weighed to obtain the product. The method uses sludge pyrolysis liquid and CSW as raw materials for bio-micro-nano CaCO3, which can not only meet the needs of sludge solid waste resource treatment, but also realize the resource utilization of CSW. In addition, the preparation method has a simple process, convenient operation, and good bio-micro-nano CaCO3 production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The effects of different pH values ​​on carbon capture effect and biological CaCO3 output in Examples 1, 2 and 3 of the present invention are shown;

[0022] Figure 2 The effect of the reflux and no reflux modes in Example 2 on carbon capture and bio-CaCO3 production is shown;

[0023] Figure 3 The effect of different electric field strengths on carbonate accumulation in Example 4;

[0024] Figure 4The influence of the composition and distribution of microbial polysaccharides (red) and proteins (green) in Examples 1, 2 and 3.

[0025] Figure 5 It is a schematic diagram of the steps of the preparation method of the present invention. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0027] A method for preparing biological micro-nano CaCO3 based on sludge pyrolysis liquid and CSW, the preparation method comprising the following steps:

[0028] Step (1), adding sludge microorganisms, CSW, sludge pyrolysis products and NaOH solution into a reactor for isothermal hydrolysis reaction;

[0029] Step (2), biologically aerating and standing the mixture to obtain a mixture, centrifuging the mixture to obtain a micro-nano particle precipitate and a supernatant, and drying and weighing the precipitate;

[0030] Step (3), comparing the heavy metal substances in the supernatant and the precipitate according to the standard to observe whether they meet the emission standards;

[0031] Step (4), analyzing the obtained precipitate with an instrument to observe whether the main crystal form and particle size of the precipitated CaCO3 particles meet the requirements.

[0032] The method first adds sludge microorganisms to the reactor and ensures that the sludge is evenly distributed in the reactor through mechanical stirring. In addition, an automatic NaOH injection pump is used to maintain an alkaline pH value. The reactor ensures that a constant temperature is maintained. Sludge pyrolysis products are added to maintain a stable COD value. The reaction cycle is 24 hours, of which aerobic reaction is 23 hours. Then it is precipitated for 30 minutes, and the supernatant is combined with CSW to generate micro-nanoparticles, and 30 minutes is used to generate CaCO3 micro-nanoparticles. The micro-nanoparticle precipitate is enriched by centrifugation, and the supernatant is subsequently discarded, and the enriched precipitate is then dried and weighed.

[0033] In the concrete production process, a large amount of concrete slurry waste (CSW) is generated due to operations such as cleaning, dust removal and ball cleaning of concrete trucks. It is characterized by a pH value exceeding 11.5, rich in calcium silicate, and a wide variety of impurities with varying impurity contents. The method for preparing bio-micro-nano CaCO3 based on sludge pyrolysis liquid and CSW described in the present application does not require the types of impurities in CSW and the calcium content therein.

[0034] In particular, the present invention firstly maintains an alkaline environment by using an automatic NaOH injection pump, and the pH adjustment enhances the capture of CO2, promotes the generation of carbonate ions, and is conducive to the generation of abundant CaCO3 micro-nano particles. In addition, the present invention can make the obtained calcium carbonate particles have a higher purity through a series of operations such as oxidation reaction, standing, precipitation, centrifugal enrichment, and further make the obtained calcium carbonate particles have a better repairing effect.

[0035] Furthermore, the present application further allows the calcium element in CSW to react completely by subjecting CSW to a reflux reaction, which can further increase the yield of biological micro-nano CaCO3 and reduce costs.

[0036] Example 1

[0037] About 4L of sludge microorganisms were added to the 8L reactor. Intermittent aeration was performed at a rate of 7L / min to maintain the dissolved oxygen level between 2 and 5mg / L. Mechanical stirring ensured that the sludge was evenly distributed in the reactor. In addition, an automatic NaOH injection pump was used to maintain the pH value between 7.5-8. The reactor was placed in a water bath system to maintain a constant temperature of 25°C. Sludge pyrolysis products were added to maintain COD at 300mg / L. The reaction cycle was 24h, of which aerobic reaction was 23h. Then it was precipitated for 30min, and the supernatant was combined with CSW to generate micro-nanoparticles, and 30min was used to generate CaCO3 micro-nanoparticles. The micro-nanoparticle precipitate was enriched by centrifugation, and the treated supernatant was then discharged into the municipal pipe network. The enriched precipitate was then dried and weighed. After the aerobic reaction, the supernatant after the sludge sedimentation was collected, and the carbonate ion and bicarbonate ion content were analyzed according to the DZ / T (0064.49-2021) standard. Heavy metals such as Cr, Cu, Zn, Cd and Pb in the supernatant and CaCO3 precipitate after sludge settling were measured by atomic absorption spectrometry. Before measurement, the samples were acid-dissolved.

[0038] Example 2

[0039] The difference from Example 1 is that the pH in step (1) is maintained between 8.5 and 9.

[0040] Example 3

[0041] The difference from Example 1 is that the pH in step (1) is maintained between 9.5 and 10.

[0042] The data obtained in the above examples are recorded in Table 1. It should be further explained here that the waste materials used in the test process are from the same batch, and the test process includes: taking the same amount of the above examples for the same amount of waste materials and reacting for 24 hours. Then, the carbonate ion and bicarbonate ion contents and heavy metal contents of the obtained products at different pH values ​​are measured respectively.

[0043] Table 1

[0044]

[0045] like Figure 1 As shown, in alkaline water, CO2 is converted to CO3 2- and HCO3 - As the pH value increases, HCO3 - Gradually converted into CO3 2- In contrast, as pH decreases, CO3 2- Gradually converted to HCO3 - , followed by the formation of carbonic acid molecules. Carbonic acid molecules are unstable and easily decompose into H2O and CO2, which then escape into the air. Therefore, pH plays a key role in determining the efficiency of carbon capture. At a pH of 7.5-8, CO2 is only converted into HCO3 - In this stage, a large amount of carbon dioxide produced by microbial β-oxidation is released from the water into the air. When the pH reaches 8.5-9, CO2 continues to be converted into CO3 2- and HCO3 - CO3 2- and HCO3 - The combined concentration of (carbon capture efficiency) will increase rapidly within 3 days. In the pH range from 9.5 to 10, the carbon capture efficiency can eventually stabilize at a certain value. Experiments have shown that at a pH of 8.5-9, the growth rate of carbon capture efficiency and the yield of biological CaCO3 are significantly higher than those at a pH of 9.5-10. Generally, for aerobic biological treatment, the pH value is recommended to be between 6 and 9. Too high a pH value can cause the death of some microorganisms, prolong the adaptation period, or potentially inhibit microbial activity. In addition, as the pH value increases, the supernatant of the reactor becomes more and more turbid, which has an adverse effect on the purity of the generated CaCO3. Furthermore, higher pH values ​​will increase operating costs, so establishing a pH value of 8.5-9 is considered to be the optimal alkaline condition for producing biological CaCO3.

[0046] Example 4

[0047] The electrode plates were coated with ruthenium-iridium-titanium and were spaced 5 cm apart. A DC voltage regulator provided the required voltage. The reactor was divided into four groups, and the voltage applied to each group was 0, 0.3, 0.5, and 0.7 V cm -1 The activated sludge was introduced into the reactor and its MLSS was adjusted to 3.5 g·L -1 The total volume of each reactor was 2 liters. The agitator speed was 100 rpm. 80 ml of sludge hydrolyzate was added to the reactor every 24 hours. The aeration intensity was adjusted as needed to maintain the dissolved oxygen level between 2 and 5 mg·L -1 NaOH was supplemented using a syringe pump to maintain the pH in the reactor between 8.7 and 9.0. During the experiment, the supernatant was sampled at 0, 6, 12, 24, 36, 48, 60, 72, 84 and 96 hours to evaluate the cumulative concentrations of carbonate and bicarbonate. In addition, the supernatant was sampled every day at 0, 3, 6, 9, 12, 16, 20 and 24 hours to determine the SCOD. The supernatant was centrifuged at 6000 rpm for 5 minutes and then filtered through a 0.45 μm nanofiltration membrane for carbonate and bicarbonate content analysis.

[0048] Figure 3 a shows the CO3 produced by biological metabolism under different DC electric fields. 2- With HCO3 - Cumulative concentration changes. 0, 0.3, 0.5 and 0.7 V·cm during 0-12 hours on the first day -1 CO3 in an electric field 2- +HCO3 - The cumulative concentrations increased by 160, 194, 215 and 212 mg·L -1 However, the increments of each electric field strength decreased from 12 to 24 h, with the increments being 77, 80, 122, and 82 mg·L, respectively. -1 On the second, third, and fourth days, CO3 2- +HCO3 - The cumulative concentration of CO showed a similar trend to the first day, with the growth rate in the first 12 hours of each day being significantly higher than that in the last 12 hours. 2- +HCO3 - The cumulative concentration increased sharply, with a growth rate of 23 to 38 mg·L -1 ·h -1 Between 12 and 84 hours, the growth rate gradually slowed down to 5-12 mg·L -1 ·h -1 After 84 hours, the cumulative concentration tended to be stable. At 96 hours, 0.3, 0.5 and 0.7 V·cm -1 CO3 in an electric field2- +HCO3 - The cumulative concentrations were approximately 1250, 1400 and 1200 mg·L -1 , compared with 1070 mg·L without electric field -1 At the same time, 0, 0.3, 0.5 and 0.7 V·cm -1 CO3 2- +HCO3 - The multiple increases were 8.09, 9.52, 10.24 and 9.35, respectively. Figure 2 b. CO3 with electric field 2- +HCO3 - The multiple increase is significantly higher than that in the no-electric-field condition.

[0049] Therefore, the DC electric field can promote the formation of carbonate and bicarbonate, where 0.5 V·cm -1 The promotion effect is most significant. Applying an appropriate DC electric field can enhance the metabolic activity of microorganisms and accelerate their reproduction. -1 The promotion effect in the electric field is less than 0.5 V·cm -1 , which may have a lethal effect due to the intensity exceeding the tolerance limit of the microorganisms. Microorganisms have different tolerance levels to DC electric fields. Excessively high field strengths may inhibit the activity of microorganisms or even cause them to rupture and die.

[0050] The precipitate produced in the experiment is in the form of white fine powder after drying. Figure 3 As shown in Figure d, the particles in the concrete wastewater are mainly oval and irregular rhombus shapes. The morphology of the particles is highly similar to the CaCO3 produced by microbial induced calcium carbonate precipitation (MICP) in existing studies. The average particle size of the CaCO3 particles is only 0.99 μm. In addition, after 96 hours, the CaCO3 production under the DC electric field is 1.32 times that without the DC electric field. Figure 3 This suggests that the electric field increases the production of CaCO3 mainly by increasing the amount of carbonate and bicarbonate produced by biological metabolism.

[0051] The above results show that the process of producing micro-nano CaCO3 from concrete waste water can be significantly promoted by DC electric field. This discovery provides a new way to use bioelectrochemical methods to treat waste and produce high-value materials.

[0052] like Figure 4As shown in the figure, the absolute value of nucleic acid in the sludge microbial community increases, indicating an increase in the number of microorganisms. All samples have the same number of cells in the field of view; to illustrate the changes in the relative content of proteins and polysaccharides, the fluorescence area of ​​nucleic acid is used as a reference (blue). As the pH value increases, the area of ​​nucleic acid continues to approach 3,600μm at pH 9.5-10. 2 , while the area occupied by proteins and polysaccharides first increased and then decreased, reaching about 2,100 μm at pH 8.5-9. 2 . The relative proportion of protein decreased from 0.74 to 0.70 and finally to 0.52. This phenomenon may be attributed to the β-oxidation of protein, because the degradation of protein into amino acids, followed by deamination and decarboxylation, promotes the formation of fatty acids that undergo β-oxidation. In contrast, with the increase in pH, the relative proportion of polysaccharides increased from 0.42 to 0.72 and then decreased to 0.49. The increase in polysaccharide content from pH 7.5-8 to 8.5-9 is attributed to the secretion of polysaccharides by microorganisms in response to the alkaline environment. Further increase in pH reduced the relative proportion of polysaccharides to 0.49, but it was still higher than 0.42 at pH 7.5-8. This may be due to the increased solubility of polysaccharides at higher alkalinity. In summary, with the increase in pH, the absolute value of nucleic acids in the sludge microbial community increased, indicating an increase in the number of microorganisms. However, the relative proportion of protein per microorganism decreased, indicating that β-oxidation metabolism of protein occurred. The relative proportion of polysaccharides first increased and then decreased, and this increase was a response to the unfavorable environment of pH 8.5-9.

Claims

1. A method for preparing bio-micro-nano CaCO3 based on sludge pyrolysis liquid and CSW, characterized in that: The steps include: (1) adding sludge microorganisms and sludge pyrolysis products into a reactor, reacting at a constant temperature under alkaline conditions, and obtaining a mixed solution after the reaction is completed; (2) subjecting the obtained mixed solution to biological aeration reaction, standing, centrifuging and enriching to obtain micro-nano particle precipitate and supernatant, and drying and weighing the precipitate; (3) Compare the heavy metal substances in the supernatant and sediment according to the standards to observe whether they meet the emission standards; (4) The obtained precipitate is analyzed by an instrument to observe whether the main crystal form and particle size of the precipitated CaCO3 micro-nano particles meet the requirements.

2. The preparation method according to claim 1, characterized in that In the step (1), the optimum pH in the reactor is 8.5-9, and the solution is an aqueous solution of NaOH, while maintaining a constant temperature of 25°C.

3. The preparation method according to claim 1, characterized in that: The sludge pyrolysis product is the carbon source required for simulating microbial β-oxidation, specifically a septic tank carbon source, and the BOD5 / COD ratio should be greater than 0.

6.

4. The preparation method according to claim 1, characterized in that: The reaction period in step (1) should be 24 hours, including 23 hours of aerobic reaction, 30 minutes of precipitation, and 30 minutes of generation of CaCO3 micro-nanoparticles.

5. The preparation method according to claim 1, characterized in that: In the step (1), the reactor may be externally charged with 0.5 V·cm -1 of DC electric field.

6. The preparation method according to claim 1, characterized in that: In step (3), the supernatant and precipitate samples need to be acidified before measurement.

7. The preparation method according to claim 1, characterized in that: The main crystal form of the produced CaCO3 particles is calcite; the particle size range is 0.7 to 10 μm.

8. Application of the biological micro-nano CaCO3 obtained by the preparation method according to any one of claims 1 to 7 in the field of concrete crack repair treatment.

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