Method for improving humification of residual sludge and kitchen waste aerobic composting under low temperature condition by using straw conditioner

Abstract

This invention discloses a method for enhancing the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw as a conditioner. The method includes: sorting, crushing, and pulping the kitchen waste into an organic slurry with a particle size ≤10mm; dewatering the residual sludge to a moisture content of 80%±2% to obtain dewatered sludge; crushing straw to 2-3cm as a conditioner; mixing the three materials, with the straw addition amount being 10%-25% of the total wet weight of the organic slurry and dewatered sludge; aerobic composting at 18℃-25℃ for 25-35 days, turning the compost every 2-4 days; monitoring temperature and pH during composting; and determining the composting process complete when the temperature drops to ≤40℃ for 3 consecutive days after experiencing a high-temperature period above 55℃ and does not rise again, and the pH stabilizes at 7.0-8.5. This invention improves the physicochemical environment of the compost pile by optimizing the straw ratio, achieving rapid start-up, extending the high-temperature period, promoting humification, reducing biotoxicity, and improving carbon sequestration capacity. It is suitable for the resource utilization of organic solid waste under low-temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically a method for improving the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioners. Background Technology

[0002] According to the "China Urban Construction Statistical Yearbook" published by the Ministry of Housing and Urban-Rural Development of the People's Republic of China, by the end of 2022, my country had more than 4,500 urban sewage treatment plants in operation, with a daily treatment capacity exceeding 220 million cubic meters. Along with the increase in sewage treatment capacity, the annual production of residual sludge (with a moisture content of approximately 80%) has exceeded 60 million tons. At the same time, with the acceleration of urbanization and the improvement of residents' living standards, my country's annual production of kitchen waste has exceeded 160 million tons (wet weight). Its main characteristics are high moisture content (70%~90%), rich organic matter content (easily degradable organic matter accounts for 60%-80%), high oil and salt content, and extremely easy rotting and foul odor.

[0003] Currently, landfilling and incineration remain the primary methods for treating wastewater sludge in my country, with treatment costs typically accounting for 40% to 60% of the total operating costs of wastewater treatment plants. The level of resource utilization urgently needs improvement. For food waste, traditional treatment methods such as landfilling easily generate leachate and biogas pollution, while incineration, due to its high water content, consumes enormous amounts of energy, and resource utilization is also insufficient. Food waste and wastewater sludge are two types of organic solid waste with large quantities, complex compositions, and high treatment difficulty. Aerobic composting is one of the effective ways to achieve their synergistic stabilization and resource utilization. However, traditional aerobic composting of mixed food waste and wastewater sludge faces the following technical problems in practical applications:

[0004] First, the physical structure is poor. Both food waste and sewage sludge have high water content. When mixed, they tend to result in low porosity, compact structure, and poor aeration, which affects the activity of aerobic microorganisms.

[0005] Second, it is prone to acidification. Food waste is rich in easily degradable organic matter such as starch, sugars, and proteins. In the early stages of composting, it is rapidly decomposed by microorganisms, producing a large amount of organic acids (such as volatile fatty acids). This causes the pH value of the compost pile to drop sharply (acidification), inhibiting the activity of beneficial microorganisms such as actinomycetes and nitrifying bacteria, and hindering the composting process.

[0006] Third, the high-temperature period is short and unstable. The combined effects of acidification and poor ventilation make it difficult for the reactor to reach and maintain an effective high-temperature period (≥55℃), or the high-temperature period is short, resulting in incomplete elimination of pathogens and insufficient degradation of organic matter.

[0007] Fourth, the degree of decomposition is low and the humification process is slow. The combined effect of the above problems results in low efficiency in the synthesis and conversion of humic substances (such as humic acid and fulvic acid), insufficient decomposition of compost products, potential phytotoxicity (such as low molecular weight organic acids and ammonia), and a low degree of humification (a key indicator reflecting the stability of organic matter and fertilizer efficiency).

[0008] Fifth, greenhouse gas emissions. In an anaerobic microenvironment, the pile is prone to producing strong greenhouse gases such as methane (CH4) and nitrous oxide (N2O).

[0009] The above problems are particularly prominent when the ambient temperature is low (such as 18℃~25℃). Low temperature further inhibits microbial activity, making it more difficult to raise the temperature of the pile, increasing the risk of acidification, making it difficult to start up during the high temperature period, and significantly delaying the humification process, which seriously restricts the promotion and application of this technology in low temperature seasons or low temperature regions.

[0010] Straw, as a widely available agricultural waste rich in cellulose, is characterized by high porosity, strong water absorption, and a high carbon-to-nitrogen ratio (C / N). Theoretically, adding it as a conditioner to a mixed composting system of kitchen waste and sludge can effectively improve the physical structure of the compost pile (increasing porosity and regulating moisture), provide a slow-release carbon source, regulate the C / N ratio, and buffer pH fluctuations. However, existing technologies lack systematic research on the specific addition ratio of straw conditioners, their quantitative impact on the composting process (especially their effects on pile temperature rise, acidification inhibition, maturity enhancement, humification promotion, and carbon fixation under low-temperature conditions), and optimal process parameters.

[0011] Therefore, there is an urgent need to develop an optimization method based on straw conditioning that can effectively improve the compost structure, regulate the fermentation microenvironment, and activate the microbial community, thereby achieving efficient humification and stabilization of kitchen waste and residual sludge in aerobic composting under a wider range of conditions (especially low temperature conditions). Summary of the Invention

[0012] To address the shortcomings of existing technologies, this invention provides a method for enhancing the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioners. By precisely controlling the addition ratio of straw conditioners, the physical and chemical environment of the compost pile is effectively optimized, significantly extending the duration of the high-temperature period, promoting the humification process, reducing the biotoxicity of compost products, improving the fertilizer efficiency and carbon sequestration capacity of the final products, and helping to initiate and maintain an efficient composting process under relatively low-temperature conditions.

[0013] To achieve the above objectives, the present invention employs the following technical solution:

[0014] This invention provides a method for enhancing the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioners, comprising the following steps:

[0015] (1) Pretreatment: The kitchen waste is sorted to remove the non-degradable components, and then crushed and pulped to obtain kitchen waste organic slurry with an output particle size of no more than 10 mm; the remaining sludge is filtered and dewatered to a moisture content of 80% ± 2% to obtain dewatered remaining sludge; the straw is crushed to 2 cm ~ 3 cm to obtain straw conditioner.

[0016] (2) Mixing: The pretreated kitchen waste organic slurry, the dewatered residual sludge and the straw conditioner are mixed to form an initial pile; the amount of straw conditioner added is 10% to 25% of the total wet weight of the kitchen waste organic slurry and the dewatered residual sludge;

[0017] (3) Composting: The initial pile obtained by mixing is subjected to aerobic composting fermentation at an ambient temperature of 18℃~25℃ for 25 to 35 days, and the composting is terminated. During the composting process, the pile is turned over every 2 to 4 days to maintain aerobic conditions.

[0018] (4) Determination of maturity: During the composting process, monitor the temperature and pH of the compost pile. When the temperature of the compost pile drops after experiencing a high temperature period of more than 55℃, and the temperature of the compost pile does not exceed 40℃ for 3 consecutive days and does not rise again, and the pH of the compost pile stabilizes between 7.0 and 8.5, the maturity process is completed. The composting cycle lasts for a total of 25 to 35 days and then the composting is terminated.

[0019] Furthermore, the recalcitrant components in step (1) include bones and / or eggshells.

[0020] Furthermore, the recalcitrant components in the kitchen waste mentioned in step (1) are removed by manual sorting or mechanical screening.

[0021] Furthermore, step (1) also includes dehydrating the organic slurry of kitchen waste so that the moisture content of the organic slurry of kitchen waste is 80%±2%.

[0022] Furthermore, in step (2), the amount of straw conditioner added is 15% of the total wet weight of the kitchen waste organic slurry and the dewatered residual sludge.

[0023] Furthermore, the straw conditioner is corn straw.

[0024] Furthermore, in step (3), the peak temperature of the compost pile reaches above 57°C during the composting fermentation process.

[0025] Furthermore, in step (3), the frequency of turning the compost pile is as follows: once every 2 days when the pile temperature is <40℃; once every 4 days when the pile temperature is ≥40℃.

[0026] Furthermore, after terminating composting in step (4), the total organic carbon (TOC) content of the compost product is not less than 24%.

[0027] Compared with the prior art, the advantages of this invention are as follows:

[0028] 1. This invention effectively treats two major types of organic solid waste: kitchen waste and residual sludge, transforming them into compost products with high decomposition and low biotoxicity, thereby realizing the resource utilization of organic fertilizer and conforming to the policy orientation of circular economy and low-carbon development.

[0029] 2. This invention effectively optimizes the physical structure and chemical environment of the compost pile by precisely controlling the addition ratio of straw conditioner. In terms of physical structure, the high porosity and strong water absorption of straw significantly improve the aeration and humidity of the compost pile, reducing the average humidity of the pile from 83% to 74% and maintaining a suitable aerobic fermentation environment. In terms of chemical environment, the addition of straw effectively buffers the pH drop in the early stage of composting, keeping the pH stable at a slightly alkaline range above 7.0 in the middle and later stages of composting, creating favorable conditions for microbial activity.

[0030] 3. This invention effectively alleviates the acidification problem that is prone to occur in traditional composting, significantly prolongs the duration of the high-temperature period (≥55℃), and achieves rapid start-up. Experimental results show that when the straw addition reaches 15%, the peak temperature of the compost pile can reach above 57℃. It successfully enters and maintains the high-temperature period from the second day to the sixth day, which is conducive to killing pathogens and promoting the full degradation of organic matter. At the same time, this invention helps to start and maintain an efficient composting process under relatively low temperature conditions (ambient temperature 18℃~25℃), and solves the technical problems of difficulty in heating the compost pile and insufficient decomposition under low temperature conditions.

[0031] 4. This invention demonstrates through three-dimensional fluorescence spectroscopy that the addition of straw conditioner significantly promotes the humification process. The fluorescence intensity of humification products (such as fulvic acid and humic acid) increases significantly with increasing straw addition, rising from 1941 without addition to 3325 with 15% addition, an increase of 71.3%. However, when the straw addition reaches 25%, the fluorescence intensity drops to 1896. This significant increase in fluorescence intensity indicates higher compost maturity, increased humus content, and significantly improved stability and fertilizer efficiency.

[0032] 5. This invention demonstrates, through the determination of total organic carbon content by the loss on ignition method, that the addition of straw conditioner effectively reduces the mineralization loss of organic carbon and enhances the carbon fixation effect. Compared with no addition, or adding too low or too high proportions of straw conditioner, the total organic carbon (TOC) content of the compost product produced by the method of this invention is significantly increased. When 15% straw is added, the TOC content can reach more than 24%, effectively reducing the emission of greenhouse gases such as carbon dioxide and demonstrating significant carbon emission reduction benefits.

[0033] 6. This invention demonstrates through cabbage seed germination tests that the addition of straw conditioner significantly reduces the biotoxicity of compost products. As the straw addition ratio increases from 0% to 15%, the cabbage seed germination rate increases from 0% to 34%, and the average root length increases from 0 mm to 2.29 mm. With a further increase in the straw addition ratio to 25%, the cabbage seed germination rate decreases to 7%, and the average root length decreases to 0.56 mm. The significant increase in germination rate and root length indicates a reduction in the content of low-molecular-weight organic acids, ammonia, and other phytotoxic substances in the compost products. The products are more plant-friendly and can be used directly or after simple post-ripening for soil improvement or as organic fertilizer.

[0034] 7. When the straw conditioner is added at 15% and aerobic conditions are maintained throughout the process, after a composting cycle of 25 to 35 days, the compost products can be rapidly decomposed, the biological toxicity can be reduced, the humic content can be increased, and the organic carbon can be effectively fixed simultaneously.

[0035] 8. The straw conditioner used in this invention is widely available and inexpensive. The pretreatment method is simple (only requires crushing to 2cm~3cm), and no complicated equipment or additional reagents are needed. The entire composting process only requires regular turning of the pile to maintain aerobic conditions, without the need for a forced ventilation system. It has low energy consumption and is easy to operate. This method is easy to promote and implement on existing composting facilities and has good economic efficiency and practicality. Detailed Implementation

[0036] The present invention will be further described in conjunction with specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0037] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art by those skilled in the art and the description of the present invention, any prior art methods, equipment, and materials similar to or equivalent to those described, used, and materials in the embodiments of the present invention can be used to implement the present invention.

[0038] To verify the effectiveness of this invention in improving the humification degree and carbon sequestration effect of aerobic composting of residual sludge and kitchen waste under low-temperature conditions, the following comparative experiment was conducted. The experiment was carried out in a simulated low-temperature environment (ambient temperature 18℃~25℃).

[0039] Example 1 (straw addition 5%):

[0040] This embodiment 1 provides a method for improving the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioners, including the following steps:

[0041] (1) Pretreatment: The kitchen waste is sorted to remove the non-degradable components. This can be done by manual sorting or mechanical screening. Obvious debris such as bones and eggshells can be removed by visual inspection. Then, the kitchen waste is crushed, pulped and dewatered to obtain kitchen waste organic slurry with an output particle size of no more than 10 mm and a moisture content of 80%±2%. The remaining sludge is filtered and dewatered to a moisture content of 80%±2% to obtain dewatered remaining sludge. The straw is crushed to 2cm~3cm to obtain straw conditioner.

[0042] (2) Mixing: The pretreated kitchen waste organic slurry, the dewatered residual sludge and the straw conditioner are mixed to form an initial pile.

[0043] Specifically, take 800.0g of organic slurry from kitchen waste (wet weight, moisture content 80%±2%), 800.0g of dewatered sludge (wet weight, moisture content 80%±2%), and 80.0g of dried straw conditioner (accounting for 5% of the total wet weight of organic slurry from kitchen waste and dewatered sludge).

[0044] (3) Composting: The initial pile obtained by mixing is subjected to aerobic composting fermentation at an ambient temperature of 18℃~25℃ for 25 to 35 days, and the pile is turned over every 2 to 4 days during the composting process to maintain aerobic conditions.

[0045] Specifically, the mixed compost is placed in a small aerobic composting reactor of the same size and composted indoors at an ambient temperature of 18℃~25℃ (this temperature is the average daily ambient temperature range of the space where the composting reactor is located). Turning frequency: once every 2 days when the compost temperature is <40℃; once every 4 days when the compost temperature is ≥40℃. Composting cycle: 30 days.

[0046] (4) Determination of maturity: During the composting process, monitor the temperature and pH of the compost pile. When the temperature of the compost pile drops after experiencing a high temperature period of more than 55℃, and the temperature of the compost pile does not exceed 40℃ for 3 consecutive days and does not rise again, and the pH of the compost pile stabilizes between 7.0 and 8.5, the maturity process is completed. The composting cycle lasts for a total of 30 days and then ends.

[0047] The monitoring results of the composting process in Example 1 were as follows: the peak temperature was 42℃, and it did not enter the high temperature period (≥55℃). The average humidity of the compost pile was 81%.

[0048] Analysis of compost product results: pH value was 6.9 (weakly acidic), and total organic carbon (TOC) content was 23.73%.

[0049] Degree of humification: Take the leachate of compost products (1:50 dilution, shake at 180 rpm for 1 hour), and use a three-dimensional fluorescence spectrometer to determine the characteristic fluorescence intensity of the humified products, which is 3175.

[0050] Biotoxicity: The compost product leachate (1:10 diluted, shaken at 180 rpm for 1 hour) was used to conduct a germination test on Chinese cabbage seeds. The germination rate was 3%, and the average root length was 0.43 mm.

[0051] Example 2 (straw addition 10%):

[0052] The difference from Example 1 is that: 800.0g of organic slurry from kitchen waste (wet weight, moisture content 80%±2%), 800.0g of dewatered residual sludge (wet weight, moisture content 80%±2%), and 160.0g of dried straw conditioner (accounting for 10% of the total wet weight of organic slurry from kitchen waste and residual sludge from dewatering).

[0053] The monitoring results of the composting process in Example 2 were as follows: the peak temperature was 50°C, and it did not enter the high-temperature period (≥55°C). The average humidity of the compost pile was 77%.

[0054] Analysis of compost product results: pH value was 7.8 (weakly alkaline), and TOC content was 23.93%.

[0055] Degree of humification: Take the leachate of compost products (1:50 dilution, shake at 180 rpm for 1 hour), and use a three-dimensional fluorescence spectrometer to determine the characteristic fluorescence intensity of the humified products, which is 3188.

[0056] Biotoxicity: The compost product leachate (1:10 diluted, shaken at 180 rpm for 1 hour) was used to conduct a germination test on Chinese cabbage seeds. The germination rate was 11%, and the average root length was 0.87 mm.

[0057] Example 3 (Straw addition amount 15%, preferred embodiment of the present invention):

[0058] The difference from Example 1 is that: there are 800.0g of organic slurry from kitchen waste (wet weight, moisture content 80%±2%), 800.0g of dewatered residual sludge (wet weight, moisture content 80%±2%), and 240.0g of dried straw conditioner (accounting for 15% of the total wet weight of organic slurry from kitchen waste and residual sludge).

[0059] The monitoring results of the composting process in Example 3 are as follows: the high temperature period begins on the second day, with a peak temperature of 57°C. The high temperature period ends on the sixth day, with an average humidity of 74% in the compost pile.

[0060] Specifically, during the composting process, the temperature and pH of the compost pile are monitored. On the second day, the temperature of the compost pile enters a high-temperature period above 55°C (peak temperature 57°C), which lasts until the end of the sixth day. On the ninth day, the temperature of the compost pile does not exceed 40°C for three consecutive days and does not rise again. At the same time, the pH value of the compost pile stabilizes between 7.0 and 8.5, completing the maturation process. After a 21-day post-maturation period, the composting cycle is terminated after a total of 30 days.

[0061] Analysis of compost product results: pH value was 8.3 (weakly alkaline), and TOC content was 24.04%.

[0062] Degree of humification: Take the leachate of compost products (1:50 dilution, shake at 180 rpm for 1 hour), and use a three-dimensional fluorescence spectrometer to measure the characteristic fluorescence intensity of the humified products, which is 3325.

[0063] Biotoxicity: The compost product leachate (1:10 diluted, shaken at 180 rpm for 1 hour) was used to conduct a germination test on Chinese cabbage seeds. The germination rate was 34%, and the average root length was 2.29 mm.

[0064] Example 4 (straw addition 20%):

[0065] The difference from Example 1 is that: there are 800.0g of organic slurry from kitchen waste (wet weight, moisture content 80%±2%), 800.0g of dewatered residual sludge (wet weight, moisture content 80%±2%), and 320.0g of dried straw conditioner (accounting for 20% of the total wet weight of organic slurry from kitchen waste and residual sludge).

[0066] The monitoring results of the composting process in Example 4 were as follows: the peak temperature was 51°C, and it did not enter the high-temperature period (≥55°C). The average humidity of the compost pile was 67%.

[0067] Analysis of compost product results: pH value was 7.9 (weakly alkaline), and TOC content was 23.56%.

[0068] Degree of humification: Take the leachate of compost products (1:50 dilution, shake at 180 rpm for 1 hour), and use a three-dimensional fluorescence spectrometer to measure the characteristic fluorescence intensity of the humified products, which is 2395.

[0069] Biotoxicity: The compost product leachate (1:10 diluted, shaken at 180 rpm for 1 hour) was used to conduct a germination test on Chinese cabbage seeds. The germination rate was 18%, and the average root length was 0.95 mm.

[0070] Example 5 (straw addition 25%):

[0071] The difference from Example 1 is that: there are 800.0g of organic slurry from kitchen waste (wet weight, moisture content 80%±2%), 800.0g of dewatered sludge (wet weight, moisture content 80%±2%), and 400.0g of dried straw conditioner (accounting for 25% of the total wet weight of organic slurry from kitchen waste and dewatered sludge).

[0072] The monitoring results of the composting process in Example 5 were as follows: the peak temperature was 48°C, and it did not enter the high-temperature period (≥55°C). The average humidity of the compost pile was 58%.

[0073] Analysis of compost product results: pH value was 7.4 (weakly alkaline), and TOC content was 23.19%.

[0074] Degree of humification: The characteristic fluorescence intensity of the humification product was measured using a three-dimensional fluorescence spectrometer by taking the leachate of the compost product (1:50 dilution, shaken at 180 rpm for 1 hour). The result was 1896.

[0075] Biotoxicity: The compost product leachate (1:10 diluted, shaken at 180 rpm for 1 hour) was used to conduct a germination test on Chinese cabbage seeds. The germination rate was 7%, and the average root length was 0.56 mm.

[0076] Preparation Example 1 (without straw addition):

[0077] The difference from Example 1 is that: there are 800.0g of organic slurry from kitchen waste (wet weight, moisture content 80%±2%), 800.0g of dewatered sludge (wet weight, moisture content 80%±2%), and 0g of dried straw conditioner (accounting for 0% of the total wet weight of organic slurry from kitchen waste and dewatered sludge).

[0078] The monitoring results of the composting process of this preparation example 1 were as follows: the peak temperature was 43℃, and it did not enter the high temperature period (≥55℃). The average humidity of the compost pile was 83%.

[0079] Analysis of compost product results: pH value was 6.7 (weakly acidic), and TOC content was 23.41%.

[0080] Degree of humification: The characteristic fluorescence intensity of the humification product was determined by three-dimensional fluorescence spectrometry using a 1:50 dilution and shaking at 180 rpm for 1 hour. The result was 1941.

[0081] Biotoxicity: The compost product leachate (1:10 diluted, shaken at 180 rpm for 1 hour) was used to conduct a germination test on Chinese cabbage seeds. The germination rate was 0% and the average root length was 0 mm.

[0082] Table 1 Comparison of key parameters and results of the embodiments.

[0083]

[0084] The turning frequency in Table 1 is as follows: once every 2 days when the pile temperature is <40℃; once every 4 days when the pile temperature is ≥40℃.

[0085] Effect Analysis:

[0086] 1. Improved physical structure of the reactor body

[0087] As the proportion of straw conditioner added increased from 0% to 25%, the average moisture content of the pile decreased significantly from 83% to 58%. The results show that the high porosity and strong water absorption of the straw conditioner effectively improved the pore structure and water retention of the pile, reduced the moisture content of the pile to a suitable value, enhanced the aeration performance, and created favorable conditions for the growth and metabolism of aerobic microorganisms.

[0088] 2. Optimization of the composting process

[0089] (1) Performance during high-temperature periods:

[0090] When the amount of straw conditioner added was 5% or less, the peak temperature of the pile was only 42-43℃, failing to enter the high-temperature period (≥55℃). When the amount of straw conditioner added was 10%, the peak temperature of the pile rose to 50℃, showing a significant increase, but still not reaching 55℃. When the amount of straw added reached 15%, the high-temperature period began on the second day, with a peak temperature of 57℃, and ended on the sixth day. When the amount of straw conditioner added was 20% and 25%, the peak temperature of the pile dropped to 51℃ and 48℃ respectively, neither reaching 55℃. The results indicate that the amount of straw added has a significant impact on the pile temperature. The addition of straw conditioner effectively promoted the heating of the pile, and the optimal addition amount resulted in a faster start to the high-temperature period and a higher peak temperature.

[0091] (2) pH control:

[0092] The addition of straw conditioner effectively alleviated the acidification problem of the compost pile. Without straw conditioner, the pH at the end of composting was 6.7 (slightly acidic); with 5% straw conditioner, the pH was 6.9 (slightly acidic); with 10% straw conditioner, the pH stabilized at 7.8 (slightly alkaline) in the later stages of composting; with 15% straw conditioner, the pH stabilized at 8.3 (slightly alkaline); with 20% straw conditioner, the pH stabilized at 7.9 (slightly alkaline); and with 25% straw conditioner, the pH stabilized at 7.4 (slightly alkaline). The results indicate that when the straw addition is ≥10%, the pH in the later stages of composting can be stabilized within the slightly alkaline range (7.8~8.3), which is more conducive to microbial activity and the humification process.

[0093] 3. Improved maturity and humification

[0094] Three-dimensional fluorescence spectroscopy method: The leachate from the compost product was mixed with deionized water at a ratio of 1:50 (v / v) and shaken at 35°C for 1 hour at 180 rpm. The supernatant was filtered through a 0.45 μm filter membrane. The experiment used an Aqualog standard version (HORIBA, Japan) three-dimensional fluorescence synchronous absorption fluorescence spectrometer. The system used a 150W xenon lamp as the excitation source and a subtractive double-grating monochromator as the excitation monochromator, with an excitation wavelength range of 200 nm to 800 nm. The emission detection unit was an aberration-corrected fixed imaging spectrometer with a focal length of 140 mm and an emission grating of 285 gr / mm, with an emission wavelength range of 250 to 800 nm. The scanning wavelength range was λex 240–650 nm and λem 200–800 nm, with a spectral sampling interval of 5 nm, a maximum scanning speed of 500 nm / s, and a minimum signal integration time of 5 ms. A blank solvent (ultrapure water) from the same batch was simultaneously measured to subtract Raman scattering and solvent background. The excitation wavelength (Ex) scan range was 250–600 nm, the emission wavelength (Em) scan range was 250–600 nm, the scan interval was 5 nm, the slit width was 5 nm, and the scan rate was 300 nm / s. The scanned images were corrected for first-order and second-order Rayleigh scattering and Raman scattering. The fluorescence intensity at Ex / Em = 275 / 320 nm was used as the characteristic fluorescence intensity of humification. Each sample was tested in triplicate, and the average value was taken.

[0095] Three-dimensional fluorescence spectroscopy results showed that when the straw conditioner addition amount was <15%, the characteristic fluorescence intensity of humic products in the compost significantly increased with the increase of the straw conditioner addition ratio. When the straw conditioner addition amount was ≥20%, the characteristic fluorescence intensity of humic products in the compost rapidly decreased with the increase of the straw conditioner addition ratio. The fluorescence intensity increased from 1941 when no straw was added to 3175 when 5% was added, 3188 when 10% was added, and 3325 when 15% was added, an increase of 71.3%. Meanwhile, excessive addition of straw conditioner reduced the characteristic fluorescence intensity of humic products in the compost: 2395 when 20% was added and 1986 when 25% was added. The results indicate that the addition of straw conditioner significantly promoted the humification process, significantly increased the generation of humic products (fulvic acid and humic acid), and significantly improved the maturity of the compost. The optimal humification effect was observed at an addition amount of 15%.

[0096] 4. Enhanced carbon fixation effect

[0097] Total organic carbon (TOC) determination by loss on ignition: Place a clean crucible at 105 °C. o C ignite for 30 minutes, cool to room temperature, and weigh. Repeat until constant weight is achieved. Grind the compost product after 30 days through a 100-mesh sieve and then at 105 °C. oDry the sample at 550°C to constant weight; weigh 2.0 g of the sample and place it in the pre-weighed crucible, ignite it in a muffle furnace at 550°C for 4 hours, cool it to room temperature, weigh it, and calculate the loss on ignition (LOI). Total organic carbon content (TOC%) = LOI × 0.58, where 0.58 is the conversion factor between organic matter and organic carbon (based on the Van Bemmelen factor). Each sample was tested in triplicate, and the average value was taken.

[0098] Results from the loss on ignition method for total organic carbon (TOC) content showed that the TOC content of compost products gradually increased and then decreased with increasing proportion of straw conditioner. The TOC content increased from 23.41% without straw conditioner to 23.73% with 5% addition, 23.93% with 10% addition, 24.04% with 15% addition, 23.56% with 20% addition, and 23.19% with 25% addition. These results indicate that the addition of straw conditioner effectively reduced the mineralization loss of organic carbon and enhanced carbon sequestration. The highest TOC content was observed at a 15% addition level, which is beneficial for reducing emissions of greenhouse gases such as carbon dioxide.

[0099] 5. Reduced biotoxicity

[0100] The germination test results of Chinese cabbage seeds showed that, within an appropriate range, the biotoxicity of compost products significantly decreased with increasing proportions of straw conditioner. Without straw conditioner, the seed germination rate was 0%, and the average root length was 0 mm, indicating high phytotoxicity of the compost products. With 5% straw conditioner, the germination rate increased to 3%, and the average root length was 0.43 mm; with 10% straw conditioner, the germination rate increased to 11%, and the average root length was 0.87 mm; with 15% straw conditioner, the germination rate increased to 34%, and the average root length was 2.29 mm; with 20% straw conditioner, the germination rate decreased to 18%, and the average root length was 0.95 mm; with 25% straw conditioner, the germination rate decreased to 7%, and the average root length was 0.56 mm. The results indicate that the addition of straw conditioner effectively reduced the content of low-molecular-weight organic acids, ammonia, and other phytotoxic substances in the compost products, significantly improving plant compatibility, with the best effect observed at a concentration of 15%.

[0101] The above preparation examples and embodiment data fully demonstrate that the method provided by the present invention for improving the aerobic composting and humification of residual sludge and kitchen waste using straw conditioner, especially the technical solution of adding straw conditioner at 15% of the total dry weight of kitchen waste and residual sludge, can achieve the following significant effects in a low-temperature environment (18℃~25℃):

[0102] (1) Effectively improve the physical structure of the pile: reduce the humidity of the pile and improve the ventilation performance, creating favorable conditions for microbial activities;

[0103] (2) Significantly optimizes the composting process: When 15% straw conditioner is added, composting can start up quickly and extend the high-temperature period by 4 days. It effectively alleviates the acidification of the compost pile and keeps the pH value stable in the weakly alkaline range (7.4~8.3) in the middle and late stages of composting.

[0104] (3) Significantly improves the degree of humification: The fluorescence intensity of humification products is significantly enhanced, and the maturity of compost products is significantly improved;

[0105] (4) Significantly enhances carbon sequestration effect: The total organic carbon (TOC) content of compost products increases to over 24%, and the loss of organic carbon mineralization is reduced;

[0106] (5) Significantly reduced biotoxicity: The germination rate and average root length of cabbage seeds increased significantly, and the compost products were more plant-friendly.

[0107] In summary, the method of the present invention is particularly suitable for achieving efficient composting and resource utilization of kitchen waste and residual sludge in aerobic composting under low-temperature conditions, and has good prospects for promotion and application.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for enhancing the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioners, characterized in that... Includes the following steps: (1) Pretreatment: The kitchen waste is sorted to remove the non-degradable components, and then crushed and pulped to obtain kitchen waste organic slurry with an output particle size of no more than 10 mm; the remaining sludge is filtered and dewatered to a moisture content of 80% ± 2% to obtain dewatered remaining sludge; the straw is crushed to 2 cm ~ 3 cm to obtain straw conditioner. (2) Mixing: The pretreated kitchen waste organic slurry, the dewatered residual sludge and the straw conditioner are mixed to form an initial pile; the amount of straw conditioner added is 10% to 25% of the total wet weight of the kitchen waste organic slurry and the dewatered residual sludge; (3) Composting: The initial pile obtained by mixing is subjected to aerobic composting fermentation at an ambient temperature of 18℃~25℃ for 25 to 35 days, and the composting is terminated. During the composting process, the pile is turned over every 2 to 4 days to maintain aerobic conditions. (4) Determination of maturity: During the composting process, monitor the temperature and pH of the compost pile. When the temperature of the compost pile drops after experiencing a high temperature period of more than 55℃, and the temperature of the compost pile does not exceed 40℃ for three consecutive days and does not rise again, and the pH of the compost pile stabilizes between 7.0 and 8.5, the maturity process is completed.

2. The method for improving the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioner according to claim 1, characterized in that, The recalcitrant components mentioned in step (1) include bones and / or eggshells.

3. The method for improving the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioner according to claim 1, characterized in that, The recalcitrant components in the kitchen waste mentioned in step (1) are removed by manual sorting or mechanical screening.

4. The method for improving the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioner according to claim 1, characterized in that, Step (1) also includes dehydrating the organic slurry of kitchen waste so that the moisture content of the organic slurry of kitchen waste is 80%±2%.

5. The method for enhancing the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioner according to claim 1, characterized in that, In step (2), the amount of straw conditioner added is 15% of the total wet weight of the organic slurry of kitchen waste and the dewatered residual sludge.

6. The method for enhancing the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioner according to claim 1, characterized in that, The straw conditioner is made from corn straw.

7. The method for improving the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioner according to claim 1, characterized in that, In step (3), the peak temperature of the compost pile reaches above 57°C during the composting fermentation process.

8. The method for improving the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioner according to claim 1, characterized in that, Step (3) Frequency of turning the compost pile: once every 2 days when the pile temperature is <40℃; once every 4 days when the pile temperature is ≥40℃.

9. The method for improving the aerobic composting and humification of residual sludge and kitchen waste under low-temperature conditions using straw conditioner according to claim 1, characterized in that, After composting is terminated in step (4), the total organic carbon content of the compost product shall not be less than 24%.

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