A method for promoting methane production by anaerobic fermentation of kitchen waste with high solid content by using segmented micro-aerobic aeration

Abstract

The present invention belongs to the technical field of waste resource utilization, and specifically relates to a method for promoting high-solid content anaerobic fermentation of food waste to produce methane by segmented micro-aeration. The method comprises the following steps: mixing food waste and inoculum, adjusting the solid content to 10% to 15%, and then performing sequential batch anaerobic fermentation; performing intermittent micro-aeration on the fermentation system in the early stage of anaerobic fermentation; not performing micro-aeration on the fermentation system in the middle and late stages of anaerobic fermentation; the early stage of anaerobic fermentation is the 1-9th day from the start of fermentation, and the middle and late stages of anaerobic fermentation are the 10th day from the start of fermentation until the end of fermentation. The method achieves high processing capacity and high gas production of food waste under high-solid content anaerobic fermentation, while having low energy consumption and stable operation, and has broad application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of waste resource utilization, and specifically relates to a method for promoting methane production by anaerobic fermentation of kitchen waste with high solid content by using segmented micro-oxygen aeration. Background Art

[0002] With the improvement of living standards, the amount of organic solid waste generated in urban and rural areas has increased dramatically. Among them, the annual output of food waste has reached 180 million tons, becoming a problem for sustainable development in urban and rural areas. Anaerobic fermentation is the main way to treat and recycle food waste, which can convert food waste into clean energy - biogas energy and biogas fertilizer resources.

[0003] Based on different total solid (TS), anaerobic fermentation processes are generally divided into wet fermentation (TS < 10%), high solid fermentation (TS = 10% ~ 15%) and dry fermentation (TS ≥ 15%). Compared with wet fermentation, high solid and dry anaerobic fermentation has a higher organic matter content, which can effectively increase methane production and food waste treatment. In addition, high solid and dry anaerobic fermentation materials can effectively reduce the moisture content of fermentation residues, making it easier to further process and recycle.

[0004] The TS of food waste is generally above 10% and below 20%. When conducting high solid content and dry anaerobic fermentation, water addition can be reduced or avoided. Therefore, anaerobic fermentation under high solid content or dry conditions is suitable. However, given the high content of organic matter such as starch, protein and oil in food waste, high solid content fermentation conditions will aggravate the production of volatile fatty acids (VFAs) and ammonium nitrogen (NH4 + -N) accumulation, when exceeding a certain content, will poison methanogens, thus inhibiting methane production. Therefore, there are very few applications of anaerobic fermentation technology for high-solid content kitchen waste.

[0005] Microaerobic aeration is a potential solution to the limitation of anaerobic fermentation of high solid content of food waste. Microaerobic aeration technology theoretically has the function of promoting the hydrolysis of organic matter and changing the redox potential of the system, which may have a certain optimization effect on the VFAs production pathway; at the same time, it may stimulate some inactive methanogens to promote methanogenesis. Therefore, whether from the perspective of organic matter hydrolysis or from the direct perspective of microbial stimulation, anaerobic fermentation shows potential sensitivity to aeration response. Summary of the invention

[0006] The purpose of the present invention is to provide a method for promoting methane production by anaerobic fermentation of high-solid content food waste by using segmented micro-aerobic aeration. By performing micro-aerobic aeration in the early stage of fermentation, a high processing volume and a high gas production volume of food waste under anaerobic fermentation of high solid content are achieved. At the same time, the energy consumption is low and the operation is stable, and the method has broad application prospects.

[0007] Specifically, the present invention provides the following technical solutions:

[0008] A method for promoting high-solid-content anaerobic fermentation of food waste to produce methane by using segmented micro-aerobic aeration, comprising the following steps: mixing the food waste with an inoculum, adjusting the solid content to 10% to 15%, and then performing sequential batch anaerobic fermentation;

[0009] In the early stage of anaerobic fermentation, the fermentation system is subjected to intermittent micro-aeration;

[0010] In the middle and late stages of anaerobic fermentation, the fermentation system is not aerated with micro-aeration;

[0011] The early stage of anaerobic fermentation is from the 1st to the 9th day since the start of fermentation, and the middle and late stage of anaerobic fermentation is from the 10th day since the start of fermentation until the end of fermentation.

[0012] The present invention finds that intermittent micro-aeration of the anaerobic fermentation system of high-solid content kitchen waste only in the early stage of anaerobic fermentation can greatly increase the methane production.

[0013] Preferably, the aeration frequency of the intermittent micro-aerobic aeration is 3 to 7 minutes per day, and the aeration volume is 0.5 to 2 L / min per 1L reactor working volume (LR). The present invention has found in experiments that the aeration frequency and aeration volume of intermittent micro-aerobic aeration have a significant effect on the gas production effect. If the aeration time is too long and the aeration volume is too large, there will be a large amount of organic matter being oxidized and a large number of anaerobic bacteria dying. If the aeration time is too short and the aeration volume is too small, there will be VFAs and NH4 + The accumulation of -N and the insufficient activity of methanogens will affect the methane yield.

[0014] Preferably, the food waste and inoculant are mixed in a mass ratio of volatile solid (VS) content of 1:2 to 1:10.

[0015] Preferably, the inoculant is anaerobic digestion sludge.

[0016] Preferably, the temperature of the anaerobic fermentation is 30-40°C.

[0017] Preferably, the anaerobic fermentation time is 20 to 35 days.

[0018] By means of the above technical solution, the present invention has at least the following advantages and beneficial effects:

[0019] The present invention provides a method for promoting methane production by anaerobic fermentation of high-solid content kitchen waste using segmented micro-aerobic aeration, which greatly improves the biogas production and solid waste treatment capacity of high-solid content anaerobic fermentation; saves water addition compared to traditional wet fermentation; only requires initial aeration, and aeration energy consumption is low, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The following is a diagram of the apparatus for conducting anaerobic fermentation experiments in the embodiments and comparative examples; wherein, 1-biogas receiving port; 2-feeding port; 3-agitator; 4-exhaust port; 5-discharge port; 6-heating jacket; 7-check valve; 8-air pump;

[0021] Figure 2 The methane production increase rate of Example 1 and Comparative Examples 2-4 at different aeration stages relative to the non-aeration treatment of Comparative Example 1.

[0022] Figure 3 The maximum cumulative amounts of VFAs under different aeration stage conditions during the fermentation process of Example 1 and Comparative Examples 1-4; wherein (A) is the maximum cumulative amount of formic acid, (B) is the maximum cumulative amount of acetic acid, (C) is the maximum cumulative amount of propionic acid, and (D) is the maximum cumulative amount of butyric acid. DETAILED DESCRIPTION

[0023] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0024] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. All reagents or instruments without manufacturer specified are conventional products that can be purchased through regular channels.

[0025] The device diagram of the anaerobic fermentation experiment in the embodiment is as follows Figure 1 As shown, the agitator 3 is a 5L continuous stirred tank reactor (CSTR) with a working volume (L R ) is 4L, with an inner height and diameter of 0.2m, and is equipped with a removable tank cover and a heating jacket 6. The tank cover of the agitator 3 is arranged with a biogas receiving port 1, a feed port 2 and an exhaust port 4. A discharge port 5 is arranged at the lower part of the agitator 3 to facilitate sampling. By connecting the heating jacket 6 with a rod-shaped temperature sensor to the PC end, it is used for automatic temperature measurement and real-time heating to ensure medium temperature (35±1℃) fermentation conditions. The micro-aerobic aeration system consists of an aeration disc placed at the bottom of the reactor and an air pump 8 with adjustable flow. The aeration volume is regulated by a check valve 7. The aeration disc is connected to 4 evenly arranged round cake-shaped aeration stones (diameter 40mm×height 30mm) using silicone tubes to ensure uniform diffusion of the airflow.

[0026] Example 1

[0027] A method for promoting high-solid-content anaerobic fermentation of kitchen waste to produce methane by using segmented micro-aerobic aeration, comprising the following steps:

[0028] 1. Raw material TS adjustment: Determine the TS of the food waste and the inoculum (anaerobic fermentation sludge), mix the food waste and the inoculum in a ratio of 0.3 / 1 with a volatile solid (VS) content, and add water to adjust the mixture to a TS of 10%;

[0029] 2. Start fermentation: put the mixture into a reactor based on a fully mixed anaerobic reactor (CSTR) system, ensure that the reactor is airtight, and use nitrogen to purge the reactor to achieve anaerobic effect;

[0030] 3. Stirring: The stirring function of the reactor is turned on during the whole anaerobic fermentation process, and the stirring speed is set to 30rpm to ensure that the materials are fully mixed;

[0031] 4. Micro-aeration: Set the aeration volume to 1L / min / LR, and strictly control the aeration for 5 minutes per day in the early stage of anaerobic fermentation (1-9 days), and stop aeration immediately from the tenth day;

[0032] 5. Biogas collection: Use biogas collection containers (including air bags, etc.) to collect biogas products daily and detect the methane content in the biogas;

[0033] 6. End of fermentation: After 35 days of fermentation, the substrate is cleaned out of the reactor and a portion of the fermentation residue is reserved as inoculum for the next batch of fermentation.

[0034] Comparative Example 1

[0035] The only difference between Comparative Example 1 and Example 1 is that no aeration treatment is performed during the entire anaerobic fermentation process.

[0036] Comparative Example 2

[0037] The difference between Comparative Example 2 and Example 1 is that aeration treatment is performed throughout the anaerobic fermentation process (1 to 35 days), and the aeration amount and aeration frequency are the same as those in Example 1.

[0038] Comparative Example 3

[0039] The difference between Comparative Example 3 and Example 1 is that aeration treatment is performed in the middle stage of anaerobic fermentation (10 to 20 days), and the aeration amount and aeration frequency are the same as those in Example 1.

[0040] Comparative Example 4

[0041] The difference between Comparative Example 4 and Example 1 is that aeration treatment is performed in the late stage of anaerobic fermentation (21 to 35 days), and the aeration amount and aeration frequency are the same as those in Example 1.

[0042] Comparison of anaerobic fermentation effects

[0043] Figure 2 The methane production increase rate of Example 1 and Comparative Examples 2-4 at different aeration stages relative to the non-aeration treatment of Comparative Example 1.

[0044] Figure 3 It is the maximum cumulative amount of VFAs under different aeration stage conditions during the fermentation process of Example 1 and Comparative Examples 1-4.

[0045] Depend on Figure 2-3 It can be seen that under the conditions of high solid content of food waste fermentation, compared with anaerobic fermentation without aeration, early aeration can increase the methane production by more than 60% (absolute methane production> 800L / kg food waste VS) ( Figure 2 ), far exceeding other aeration methods. However, traditional full-process aeration reduces methane production by 15% to 20%;

[0046] Compared with other aeration stages, the early aeration promotes hydrolysis, thereby increasing the content of formic acid and acetic acid in the system ( Figure 3 A), which is beneficial to methane production, so the early aeration increases the methane production ( Figure 2 ); There is also a certain increase in methane production during the later aeration, but it is not as obvious as that during the earlier aeration. This may be due to the combined effect of two reasons: first, the amount of organic matter retained in the later stage is small, so the time for aeration to increase the acetic acid content is shorter; second, the later aeration increases the accumulation of propionic acid (the toxicity of propionic acid is the strongest among VFAs), which is not conducive to the production of methane.

[0047] Compared with staged aeration, full aeration lost too much VFAs, depriving methanogens of their nutrient sources, resulting in lower methane production than the non-aerated treatment.

[0048] It can be seen that micro-aeration first improves the hydrolysis and acidification performance of organic matter, so the content of VFAs such as formic acid and acetic acid that are easily directly used by methanogens is increased, which is conducive to methane production; but excessive aeration (full-process aeration) and inappropriate aeration (mid-term aeration) reduce the content of VFAs through oxidation and enhanced volatilization, deprive methanogens of their nutrient sources, and lead to a decrease in methane production; in addition, compared with mid-term and full-process aeration, early aeration avoids the direct inhibition of methanogens by introducing too much oxygen during the peak period of methanogenesis (i.e., mid-term). Therefore, the staged micro-aeration provided by the present invention is an effective means to increase the biogas production of high-solid content anaerobic fermentation of food waste, and can avoid the negative effects of full-process aeration, promote stable operation of the system, and increase methane production by more than 60%, with broad application prospects.

[0049] The above embodiments are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary engineers and technicians in the field should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for promoting anaerobic fermentation of kitchen waste with high solid content to produce methane by using segmented micro-aerobic aeration, characterized in that: The following steps are involved: Mixing the food waste and the inoculum, adjusting the solid content to 10% to 15%, and then performing sequencing batch anaerobic fermentation; The inoculum is anaerobic digestion sludge; In the early stage of anaerobic fermentation, the fermentation system is intermittently aerated with micro-oxygen; the micro-oxygen aeration system is placed at the bottom of the reactor; In the middle and late stages of anaerobic fermentation, the fermentation system is not aerated with micro-aeration to avoid the direct inhibition of methanogens by the introduction of excessive oxygen; The early stage of anaerobic fermentation is from the 1st to the 9th day since the start of fermentation, and the middle and late stage of anaerobic fermentation is from the 10th day since the start of fermentation until the end of fermentation; The aeration frequency of the intermittent micro-aerobic aeration is 3 to 7 minutes per day, and the aeration volume is 0.5 to 2 L / min per 1 L of reactor working volume.

2. The method for promoting high-solid content anaerobic fermentation of kitchen waste to produce methane by using segmented micro-aerobic aeration according to claim 1, characterized in that: The kitchen waste and the inoculum are mixed in a mass ratio of volatile solid content of 1:2 to 1:

10.

3. The method for promoting high-solid content anaerobic fermentation of kitchen waste to produce methane by using segmented micro-aerobic aeration according to claim 1 or 2, characterized in that: The temperature of the anaerobic fermentation is 30-40°C.

4. The method for promoting high-solid content anaerobic fermentation of kitchen waste to produce methane by using segmented micro-aerobic aeration according to claim 1 or 2, characterized in that: The anaerobic fermentation time is 20 to 35 days.

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