A fruit peel biochar, its preparation method, and its application in enhancing methanogenesis from waste sludge.

Abstract

The application provides a fruit peel biochar and a preparation method and application thereof in reinforcing residual sludge methanogenesis, and belongs to the technical field of solid waste resource treatment. The preparation method of the fruit peel biochar comprises the following steps: drying, carbonizing, and grinding banana peels after being cut into pieces to obtain the fruit peel biochar; the heating speed in the carbonizing process is 10-15 DEG C / min, the pyrolysis temperature in the carbonizing process is 500-600 DEG C, and the holding time under the pyrolysis temperature is 1-2 h. The fruit peel biochar has the advantages of strong alkalinity, and the residual sludge is pretreated first, the hydrolysis rate of the residual sludge is improved, the barrier of macromolecular substance dissolution is broken, more organic substrates are provided for the subsequent anaerobic digestion process, meanwhile, the biochar added in the pretreatment stage can still reinforce the effect of the anaerobic digestion in the subsequent stage, and a more competitive new idea for the application of the biochar in the anaerobic digestion is provided.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a fruit peel biochar, its preparation method, and its application in enhancing methanogenesis from residual sludge. Background Technology

[0002] The activated sludge process is one of the most commonly used treatment methods in urban wastewater treatment plants. Inevitably, this process generates a large amount of excess sludge. Reports indicate that the cost of treating and disposing of excess sludge accounts for more than 60% of the total operating costs of wastewater treatment plants. As a major byproduct of the activated sludge process, excess sludge contains, on the one hand, a large number of proliferating microorganisms and various toxic pollutants. If not treated and disposed of in a timely manner, it will seriously endanger environmental safety and human health. On the other hand, excess sludge contains a large amount of bioavailable organic matter such as proteins, polysaccharides, and lipids. Recycling or utilizing it through appropriate methods meets the urgent need for carbon emission reduction.

[0003] Anaerobic digestion, a widely used process for treating waste sludge, can effectively reduce its volume and utilize its bioavailable substances. During anaerobic digestion, these bioavailable substances are converted into more valuable organic compounds such as methane, hydrogen, and short-chain fatty acids. However, anaerobic digestion of waste sludge has drawbacks, including low hydrolysis rates, poor methanogenesis efficiency, and susceptibility to environmental factors in methane production, which limit the extent to which waste sludge can be converted into energy and resources.

[0004] Biochar is a stable, carbon-rich, green material typically prepared by the pyrolysis of municipal solid waste, agricultural solid waste, and sewage sludge under oxygen-limited conditions. The effectiveness of biochar largely depends on its adsorption properties, pH value, electrical conductivity, and surface functional groups. Studies have shown that adding biochar during anaerobic digestion can effectively improve system stability, enhance microbial activity, reduce acid inhibition, and simultaneously increase the fermentation rate and methane yield. The main mechanisms by which biochar promotes anaerobic digestion include assisting in microbial immobilization, providing a buffering effect, and promoting interspecies electron transfer.

[0005] It should be noted that as the pyrolysis temperature increases, the degree of carbonization of biomass increases, leading to an increase in ash content. Consequently, the alkali metals and alkaline earth metals present in the ash as carbonates and carbonates also increase, resulting in a significant increase in the pH of the prepared biochar. Pyrolysis temperature has a significant impact on the pH characteristics of biochar. Generally, the higher the pyrolysis temperature, the more organic acids present on the biochar surface decompose, forming carbonates on the material surface and providing abundant alkalinity. Typically, the pyrolysis temperature at which biochar exhibits the strongest alkalinity is 500-600℃. It is worth noting that biochar prepared from different raw materials has different pH values. Previous technologies using biochar in anaerobic digestion have only treated biochar as an exogenous additive, failing to fully utilize the strong alkalinity advantage of biochar prepared through high-temperature pyrolysis. Previous studies have shown that alkaline pretreatment can significantly promote the dissolution of organic matter (including soluble proteins and soluble polysaccharides) from residual sludge, providing more usable substrate for the subsequent anaerobic digestion methanogenesis stage and significantly increasing methane production. Therefore, pretreating the substrate with the alkalinity of biochar before anaerobic digestion provides a new idea and method for further efficient utilization of biochar to promote anaerobic digestion. Summary of the Invention

[0006] The purpose of this invention is to provide a fruit peel biochar, its preparation method, and its application in enhancing methanogenesis from waste sludge. This invention utilizes the strong alkalinity of biochar to pretreat waste sludge, increasing the hydrolysis rate and breaking down barriers to the dissolution of macromolecules, thus providing more organic substrates for subsequent anaerobic digestion. Simultaneously, the biochar added during the pretreatment stage can still enhance the anaerobic digestion effect in subsequent stages, providing a more competitive new approach to the application of biochar in anaerobic digestion.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing fruit peel biochar, which involves drying, carbonizing, and grinding diced banana peels to obtain the fruit peel biochar.

[0009] The heating rate during the carbonization process is 10-15℃ / min, the pyrolysis temperature during carbonization is 500-600℃, and the holding time at the pyrolysis temperature is 1-2h.

[0010] Preferably, the area of ​​the chopped banana peel is 9–16 cm². 2 .

[0011] Preferably, before cutting the bananas into pieces, the process further includes a step of air-drying the banana peels. The air-drying temperature is 20–30°C, and the air-drying time is 48–96 hours. The drying temperature is 100–110°C, and the drying time is 24–48 hours.

[0012] Preferably, the material obtained after grinding is passed through a 100-140 mesh sieve, and the sieve-passing material is the fruit peel biochar; the pH of the fruit peel biochar is 11.69-13.69.

[0013] The present invention also provides a fruit peel biochar prepared by the above preparation method.

[0014] The present invention also provides an application of the above-mentioned fruit peel biochar in enhancing methanogenesis from waste sludge, comprising the following steps:

[0015] (1) The remaining sludge was pretreated with fruit peel biochar to obtain a pretreated mixed system;

[0016] (2) The pretreatment mixing system is mixed with anaerobic digestion sludge for anaerobic digestion.

[0017] Preferably, the mass ratio of the fruit peel biochar to the VS in the residual sludge is (0.5-2.0):1.

[0018] Preferably, the rotation speed during pretreatment is 100-150 rpm, the temperature during pretreatment is 30-40°C, and the pretreatment time is 1-24 hours.

[0019] Preferably, the mass ratio of VS in the residual sludge to VS in the anaerobic digestion sludge is 1:(1-2).

[0020] Preferably, the pH of the mixed system in step (2) is 6.9 to 7.1; the rotation speed during anaerobic digestion is 100 to 150 rpm; the temperature during anaerobic digestion is 33 to 37°C; and the time during anaerobic digestion is 30 to 40 days.

[0021] This invention provides a fruit peel biochar, its preparation method, and its application in enhancing methanogenesis from waste sludge. Addressing the shortcomings of existing anaerobic digestion technologies, such as low substrate concentrations available for microbial use; complex EPS structures preventing direct contact between large organic molecules and hydrolytic enzymes, thus hindering the hydrolysis reaction; and low electron transfer rates between microorganisms leading to low methanogenesis efficiency, this invention provides fruit peel biochar prepared from banana peel through a high-temperature carbonization process (preparation process as follows...). Figure 1As shown, fruit peel biochar is used to pretreat excess sludge, promoting sludge hydrolysis and dissolving more organic matter. This fully utilizes the strong alkalinity of biochar. Simultaneously, the surface of biochar is rich in oxygen-containing active functional groups, enabling it to act as an electron donor or acceptor at various stages of anaerobic digestion, directly mediating direct interspecies electron transfer during anaerobic digestion. This effectively promotes electron transport performance during anaerobic digestion, efficiently utilizing biochar. The method is simple to operate and low in cost, providing a novel approach to enhance methanogenesis performance in anaerobic digestion by leveraging the alkalinity of biochar coupled with electron transport properties.

[0022] This invention uses fruit peel biochar at a dosage of 2.0 g / g VS to pretreat excess sludge, which can increase methane production in the anaerobic digestion process by 57.6%. The method of using fruit peel biochar to pretreat excess sludge to promote the anaerobic digestion process can significantly improve the productivity of the anaerobic digestion process. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process of preparing biochar using fruit peel according to the present invention.

[0024] Figure 2 The Fourier transform infrared spectrum of the surface functional groups of the fruit peel biochar prepared in Example 1 is shown.

[0025] Figure 3 This is a graph showing the cumulative methane production per unit biomass for each group in the anaerobic digestion process of Example 2.

[0026] Figure 4 This is a graph showing the pH changes of the alkali pretreatment group and the fruit peel biochar pretreatment group during the pretreatment process in Example 3.

[0027] Figure 5 The image shows the three-dimensional fluorescence spectra of the supernatant after pretreatment in the alkali pretreatment group and the fruit peel biochar pretreatment group in Example 3. Detailed Implementation

[0028] This invention provides a method for preparing fruit peel biochar, which involves drying, carbonizing, and grinding diced banana peels to obtain the fruit peel biochar.

[0029] In this invention, the banana peel is preferably washed and air-dried in a dark and ventilated place before being cut into pieces.

[0030] In this invention, the air-drying temperature is preferably 20-30°C, and more preferably 25°C.

[0031] In this invention, the air-drying time is preferably 48 to 96 hours, and more preferably 48 hours.

[0032] In this invention, the area of ​​the diced banana peel is preferably 9-16 cm². 2 Further preferred is 12cm 2 .

[0033] In this invention, the banana peels after being cut into pieces are preferably rinsed with deionized water to completely remove dust and other impurities from the surface of the raw material.

[0034] In this invention, the drying temperature is preferably 100-110°C, and more preferably 105°C.

[0035] In this invention, the drying time is preferably 24 to 48 hours, and more preferably 24 hours.

[0036] In this invention, the heating rate during the carbonization process is preferably 10-15°C / min, and more preferably 10°C / min.

[0037] In this invention, the pyrolysis temperature during carbonization is preferably 500-600°C, and more preferably 600°C.

[0038] In this invention, the holding time at the pyrolysis temperature is preferably 1 to 2 hours, and more preferably 1 hour.

[0039] In this invention, the material after grinding is preferably passed through a 100-140 mesh sieve, and the undersize material is the fruit peel biochar, which is more preferably passed through a 120 mesh sieve.

[0040] In this invention, the pH of the fruit peel biochar is preferably 11.69 to 13.69, and more preferably 12.69.

[0041] The present invention also provides a fruit peel biochar prepared by the above preparation method.

[0042] The present invention also provides an application of the above-mentioned fruit peel biochar in enhancing methanogenesis from waste sludge, comprising the following steps:

[0043] (1) The remaining sludge was pretreated with fruit peel biochar to obtain a pretreated mixed system;

[0044] (2) The pretreatment mixing system is mixed with anaerobic digestion sludge for anaerobic digestion.

[0045] This invention uses fruit peel biochar to pretreat residual sludge to obtain a pretreated mixed system.

[0046] In this invention, the mass ratio of the fruit peel biochar to the VS in the residual sludge is preferably (0.5-2.0):1, and more preferably 2:1.

[0047] In this invention, the rotation speed during pretreatment is preferably 100-150 rpm, and more preferably 120 rpm.

[0048] In this invention, the pretreatment temperature is preferably 30-40°C, and more preferably 35°C.

[0049] In this invention, the pretreatment time is preferably 1 to 24 hours, and more preferably 6 hours.

[0050] The present invention mixes the pretreatment mixing system with anaerobic digestion sludge for anaerobic digestion.

[0051] In this invention, the mass ratio of VS in the residual sludge to VS in the anaerobic digestion sludge is preferably 1:(1-2), and more preferably 1:2.

[0052] In this invention, the pH of the mixed system is preferably 6.9 to 7.1, and more preferably 7.0.

[0053] In this invention, the rotation speed during anaerobic digestion is preferably 100-150 rpm, and more preferably 120 rpm.

[0054] In this invention, the temperature of the anaerobic digestion is preferably 33-37°C, and more preferably 35°C.

[0055] In this invention, the anaerobic digestion time is preferably 30 to 40 days, and more preferably 40 days.

[0056] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] This embodiment provides a fruit peel biochar, and the specific preparation process is as follows:

[0059] (1) Collect banana peel raw materials, rinse them with tap water, and place them in a dark and ventilated place at an ambient temperature of 25℃ for 48 hours to air dry; cut the preliminarily dried banana peel raw materials into pieces with an average piece area of ​​12cm². 2 Then rinse with deionized water to completely remove dust and other impurities from the surface of the raw material; dry the block banana peel raw material in an oven at 105℃ for 24 hours to obtain completely dried banana peel raw material.

[0060] (2) The completely dried, blocky banana peel raw material was placed in a vacuum tube furnace, and the heating rate was set to 10℃ / min. When the temperature reached 600℃, it was pyrolyzed at this temperature for 1 hour. During the pyrolysis process, 99.999% high-purity nitrogen gas was continuously introduced to ensure an oxygen-free environment in the tube furnace, and banana peel biochar was obtained. It was ground in a mortar and passed through a 120-mesh sieve, and the material passing through the sieve was the fruit peel biochar.

[0061] (3) The functional groups on the surface of the fruit peel biochar were scanned using Fourier transform infrared spectroscopy, and the results are as follows: Figure 2 As shown, the surface of biochar contains abundant C-OH, C=C, and C=O oxygen-containing functional groups.

[0062] Example 2

[0063] In this embodiment, the fruit peel biochar from Example 1 is used to pretreat the remaining sludge to promote anaerobic digestion and methanogenesis. The specific process is as follows:

[0064] (1) Control group, pretreatment group and non-pretreatment group were set up respectively. Among them, the control group (Control) did not add fruit peel biochar, the concentration of fruit peel biochar added to pretreatment group 1 and non-pretreatment group 1 was 0.2 g / g VS, the concentration of fruit peel biochar added to pretreatment group 2 and non-pretreatment group 2 was 1.0 g / g VS, and the concentration of fruit peel biochar added to pretreatment group 3 and non-pretreatment group 3 was 2.0 g / g VS.

[0065] Each group was treated separately in 120 mL serum bottles. 28.8 mL of excess sludge (VS of excess sludge was 14.834 ± 0.125 g / L) was added to each serum bottle in a single batch. For the pretreatment group, fruit peel biochar was added at the same concentration. The serum bottles were shaken thoroughly, and no pH adjustment was required. The serum bottles were then placed in a constant-temperature shaker at 35°C and 120 rpm for 6 hours of pretreatment. After pretreatment, a pretreated mixture was obtained. Anaerobic digested sludge (VS of anaerobic digested sludge was 19.190 ± 0.043 mg / L) was inoculated into each serum bottle at a VS(excess sludge):VS(anaerobic digested sludge) ratio of 1:2, and the system pH was adjusted to 7.0.

[0066] No pretreatment was performed in any of the non-pretreatment groups. After adding fruit peel biochar, anaerobic digested sludge was immediately inoculated at an inoculation ratio of VS (excess sludge):VS (anaerobic digested sludge) = 1:2, and the pH of the system was adjusted to 7.0.

[0067] After adding excess sludge to the control group, it was placed in a constant temperature shaker at 35℃ and 120rpm for 6 hours for pretreatment. Then, anaerobic digested sludge was inoculated at an inoculation ratio of VS(excess sludge):VS(anaerobic digested sludge) = 1:2, and the pH of the system was adjusted to 7.0.

[0068] (2) Each group of serum bottle reactors was aerated for 2 minutes with 99.999% high-purity nitrogen to remove oxygen from the serum bottles and headspace, maintaining anaerobic conditions throughout the process. The serum bottle reactors were sealed with butyl rubber stoppers and aluminum caps, and the bottle openings were wrapped with sealing film. Finally, the serum bottles were placed in a constant temperature shaker at 35℃ and 120rpm for incubation. The anaerobic digestion reactors were run continuously for 40 days. Throughout the experiment, the biogas production and composition were measured periodically. The biogas production was determined by the water displacement method, and the composition of the biogas was determined by gas chromatography, mainly the proportion of methane.

[0069] The test results of each group are as follows Figure 3 As shown in the figure, the cumulative methanogenesis per unit biomass in the pretreated group was significantly increased compared to the control group and the non-pretreated group. At a dosage of 2.0 g / g VS of fruit peel biochar, the methane production during anaerobic digestion was increased by 57.6% compared to the control group. This is likely because the abundant C-OH, C=C, and C=O oxygen-containing functional groups on the surface of the biochar accelerate the conversion of volatile fatty acids and other substances into methane. In contrast, the non-pretreated group, which added the same concentration of fruit peel biochar but did not undergo pretreatment, also increased the cumulative methanogenesis to some extent, but only by 25.4%. This indicates that using fruit peel biochar to treat excess sludge can significantly improve the energy efficiency of the anaerobic digestion process, and that biochar pretreatment can further increase methane production.

[0070] Example 3

[0071] In this embodiment, the fruit peel biochar from Example 1 and NaOH were used to pretreat the excess sludge, and the effect of the pretreatment process on the methanogenesis of the sludge was detected. The specific process is as follows:

[0072] (1) A control group without added fruit peel biochar, group A (alkali pretreatment group) without added fruit peel biochar, and group B (fruit peel biochar pretreatment group) with added fruit peel biochar were set up. Each group had three replicates (control 1, control 2, control 3, A1, A2, A3, B1, B2, B3). The control group was treated according to the control group in Example 2; group B was treated according to pretreatment group 3 in Example 2; the pH of the remaining sludge in group A was adjusted to be the same as that in group B using 4mM NaOH solution. The serum bottles from both groups were placed in a constant temperature shaker at 35℃ and 120rpm for 24h of pretreatment. During this period, the pH changes in the system in serum bottles A3 and B3 were measured, and the results are as follows: Figure 4As shown, the pH of the system in the fruit peel biochar pretreatment group decreased more slowly than that in the alkali pretreatment group at the same pH. This may be because biochar has abundant surface functional groups, which have a certain buffering capacity and can alleviate the acidification problem in the system to some extent during the pretreatment process.

[0073] (2) After pretreatment, supernatant was taken from each serum bottle, and the supernatant from the parallel groups was mixed. Three-dimensional fluorescence spectrometry was used to detect the dissolved organic matter in the supernatant of the alkali pretreatment group and the fruit peel biochar pretreatment group after pretreatment. The detection results are as follows: Figure 5 As shown, compared with alkaline pretreatment under the same pH conditions, the three-dimensional fluorescence spectrum of the residual sludge after treatment with fruit peel biochar shows that there is significantly more readily biodegradable organic matter in region I than in the alkaline pretreatment group under the same pH conditions. This indicates that the method provided by the present invention can significantly improve the biodegradability of dissolved organic matter.

[0074] (3) The SCOD content (mgCOD / L) in the residual sludge after pretreatment in each serum bottle was detected, and the statistical results are shown in Table 1.

[0075] Table 1. SCOD content (mg COD / L) in the pretreated residual sludge

[0076] Group Parallel Group 1 Parallel group 2 Parallel Group 3 control group 132 132 132 Alkali treatment group 3354 3351 3345 Fruit peel biochar pretreatment group 3790 3820 3980

[0077] As shown in Table 1, the pretreatment group with a fruit peel biochar dosage of 2.0 g / gVS achieved a SCOD content of 3790–3980 mg COD / L in the sludge after pretreatment, which was 28.71, 28.94, and 30.15 times that of the control group, and 1.13, 1.14, and 1.19 times that of the pretreated residual sludge under the same pH conditions. This indicates that the present invention has a very good effect on promoting the dissolution of organic matter.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. Use of fruit peel biochar in enhancing methanogenesis from excess sludge, characterized in that, The method comprises the following steps: (1) pretreating residual sludge with peel biochar to obtain a pretreated mixed system; (2) mixing the pretreated mixed system with anaerobic digestion sludge and performing anaerobic digestion; The peel biochar is prepared by drying, carbonizing and grinding banana peel after being cut into pieces; The mass ratio of the peel biochar to VS in the residual sludge is (0.5-2.0):1; The rotation speed during the pretreatment is 100-150 rpm, the pretreatment temperature is 30-40 DEG C, and the pretreatment time is 1-24 h; The mass ratio of VS in the residual sludge to VS in the anaerobic digestion sludge is 1:

2.

2. Use according to claim 1, characterized in that, The pH of the mixed system after step (2) is 6.9-7.1; the rotation speed during the anaerobic digestion is 100-150 rpm, the anaerobic digestion temperature is 33-37 DEG C, and the anaerobic digestion time is 30-40 days.

3. Use according to claim 1, characterized in that, The peel biochar is prepared by drying, carbonizing and grinding banana peel after being cut into pieces; The heating rate during the carbonization process is 10-15 DEG C / min, the pyrolysis temperature during the carbonization is 500-600 DEG C, and the holding time at the pyrolysis temperature is 1-2 h.

4. Use according to claim 3, characterized in that, The area of the cut banana peel is 9-16 cm 2 .

5. Use according to claim 4, characterized in that, Before being cut into pieces, the banana peel is air-dried at a temperature of 20-30 DEG C for 48-96 h; the drying temperature is 100-110 DEG C; and the drying time is 24-48 h.

6. Use according to claim 5, characterized in that, After being ground, the obtained product is sieved through a 100-140 mesh sieve, and the undersize is the peel biochar; the pH of the peel biochar is 11.69-13.69.

Images