A method for processing kitchen waste

Abstract

The present application relates to solid resource processing and disposal field, especially to a kind of kitchen waste processing method.The kitchen waste processing method includes the following steps: (1) kitchen waste is broken, and ferrous salt is added, stirred uniformly, and mixed material is obtained;(2) in the mixed material, batch addition of urea peroxide is carried out, and then the remaining sludge and anaerobic sludge are added to carry out anaerobic fermentation;Methane and treated kitchen waste are obtained.In the present application, ferrous salt is used to catalyze urea peroxide to pretreat kitchen waste.Compared with directly using kitchen waste and sludge to co-digestion, the present application can use urea peroxide to degrade allicin in kitchen waste into low-toxicity products, reduce the toxicity of allicin on anaerobic functional microorganisms, and improve the production of methane in the anaerobic process.By batch addition, the dosage and mode of reagent are optimized, which reduces the dosage of urea peroxide while increasing the degradation of allicin and enhancing the production of methane.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and disposal, and more particularly to a method for treating kitchen waste. Background Technology

[0002] Food waste, commonly known as swill, consists of leftover food scraps, liquids, and waste oil from restaurants, hotels, hotels, schools, military units, enterprises, and other collective entities during the provision of meals. Discharging food waste scraps and waste oil into sewer systems not only causes blockages but can also lead to anaerobic reactions in enclosed environments, generating biogas and increasing the risk of sewer pipe rupture. The waste liquid is characterized by high levels of organic matter and ammonia nitrogen, rich in animal and vegetable oils and crude fiber, and a low C / N ratio. Direct discharge of this high-ammonia-nitrogen wastewater can cause eutrophication, red tides, and poisoning of aquatic organisms, seriously impacting water resources and the environment, and even endangering human health.

[0003] More importantly, plants from the Allium genus of the Liliaceae family, such as garlic (including cloves and leaves), leeks, and onions, are used in dishes around the world. Due to their distinctive flavors, the bulbs and leaves of these plants are widely used as seasonings and even as main ingredients. Allicin is a crucial active ingredient in Allium plants. Because garlic, onions, and other allicin-containing vegetables are extensively used as seasonings, the concentration of allicin in food waste is high. The literature (Metabolomics reveals the effect of garlic on antioxidant-and protease-activities during Cheonggukjang (fermented soybean paste) fermentation[J]. Food Research International, 2016, 82: 86~94.) states that allicin can interact with thiol free groups during glutathione and protein thiol-disulfide bond exchange, interfering with biochemical metabolic processes and affecting intracellular metabolic activities of microorganisms. Further research has shown that allicin significantly inhibits the rate and yield of methane production during the anaerobic co-digestion of food waste and sewage sludge (Science of the Total Environment, 2021, 776: 145598). Furthermore, allicin has a complex structure and is difficult to biodegrade under anaerobic conditions.

[0004] Existing technology CN 115140890 A discloses a pretreatment method for kitchen waste, including the following steps: sorting the collected kitchen waste to remove non-degradable impurities, crushing and pulping to obtain a mixture; mixing the mixture with deionized water at a mass ratio of 1:(1-3), cooking and cooling to room temperature, removing the floating grease from the upper layer, and centrifuging the remaining slurry to obtain upper wastewater and lower material; subjecting the upper wastewater to short-cut nitrification-denitrification and Fenton oxidation treatments to obtain biodegradable effluent; using the biodegradable effluent to adjust the moisture content of the lower material during fermentation. This pretreatment method for kitchen waste can maximize the separation of non-degradable waste from kitchen waste and recycle grease and residual liquid, creating conditions for subsequent treatment processes. However, it cannot effectively degrade allicin, thus affecting methane production.

[0005] To date, no method has been reported for achieving the degradation of allicin in food waste while simultaneously promoting the co-digestion of food waste and residual sludge to produce methanogens. Summary of the Invention

[0006] The purpose of this invention is to provide a method for treating kitchen waste that effectively and rapidly degrades allicin into low-toxicity products and significantly increases methane production during anaerobic co-digestion.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] A method for treating kitchen waste includes the following steps:

[0009] (1) Crush the kitchen waste, add 50-70 mg / g TSS ferrous salt, stir evenly to obtain a mixture;

[0010] (2) Add 20-40 mg / g TSS urea peroxide to the mixture, then add the remaining sludge and anaerobic sludge for anaerobic fermentation; to obtain methane and treated kitchen waste.

[0011] In one preferred embodiment, the particle size of the food waste is 2 to 10 mm after crushing.

[0012] In one preferred embodiment, the solid mass of the crushed kitchen waste is controlled to be 80-100 g / L.

[0013] Excessive amounts of food waste and total solids can affect the mass transfer of microorganisms during anaerobic treatment, while excessively small particle sizes can increase treatment costs.

[0014] In one preferred embodiment, the food waste has a moisture content of 40% to 50% to facilitate mass transfer by microorganisms.

[0015] In one preferred embodiment, the ferrous salt is ferrous chloride or ferrous sulfate, preferably FeSO4 or FeSO4·7H2O. In the system of the present invention, both ferrous and sulfate ions can play a role in the catalytic process of urea peroxide, thus resulting in better performance.

[0016] In one preferred embodiment, after adding the ferrous salt, the mixture is stirred at 300-350 rpm for 3-7 minutes.

[0017] This stirring speed can accelerate the mixing of reagents and substrates without significantly increasing the cost of treatment.

[0018] In one preferred embodiment, both the ferrous salt and urea peroxide are added in multiple batches.

[0019] In one preferred embodiment, the ferrous salt and urea peroxide are added in 3-4 batches.

[0020] Adding too many or too few batches is detrimental to the degradation rate of allicin and the yield of methane.

[0021] In one preferred embodiment, the addition process of ferrous salt and urea peroxide is as follows: 15-20 mg / g TSS (total amount of solids suspended in water) of ferrous salt is added at a time, stirred at 300-350 rpm for 3-7 minutes, and 8-10 mg / g TSS of urea peroxide is added, and stirred rapidly at a stirring rate of 250-300 rpm, with a total residence time of 6-12 hours.

[0022] In one preferred embodiment, the pH of the system is adjusted to 7.0 ± 0.1 after the addition of urea peroxide.

[0023] By adjusting the dosage of ferrous salt and urea peroxide in different batches, adjusting the pH, and controlling the stirring rate, a certain redox potential is maintained in the reaction system. This is beneficial for maximizing the degradation of allicin by adding the minimum amount of urea peroxide and increasing the yield of methane.

[0024] The purpose of this invention patent is to enhance the degradation of allicin in food waste by catalyzing urea peroxide with ferrous salts, reduce the toxic effects of allicin on microorganisms, and improve the biodegradability of sludge. By adding it in batches, the invention ensures that urea peroxide fully exerts its role in degrading pollutants and enhancing microbial activity, thereby increasing the degradation rate of allicin and the production of methane while reducing the dosage of urea peroxide.

[0025] In one preferred embodiment, the total solids content of the residual sludge is 20–40 g / L.

[0026] In one preferred embodiment, the ratio of the added residual sludge mass to the volatile organic compound content is 1:1 to 2:1. Adding residual sludge helps maintain the C / N ratio in the system, ensuring the stable progress of the anaerobic reaction. Adding too much or too little sludge is detrimental to the anaerobic reaction and affects methane production.

[0027] The excess sludge is taken from the secondary sedimentation tank of the sewage treatment plant and subjected to static sedimentation treatment before use (refer to CN201210236560.8). When used, its main characteristics are: total solids content of 20-40 g / L, volatile organic compound content of 25-30 g / L, and pH of 6.3-6.8.

[0028] In one preferred embodiment, the inoculation ratio of anaerobic sludge to the substrate is 4:1 to 7:1 (v / v), where the substrate is waste sludge and kitchen waste. Anaerobic sludge is sludge particles formed by facultative and obligate anaerobic bacteria and organic impurities in wastewater. It can remove and stabilize 30% to 50% of the organic matter in waste and is rich in methanogens, hydrogen-producing bacteria, and acid-producing bacteria. The addition of anaerobic sludge enhances the presence of key microbial species such as methanogens in the reaction system, facilitating the normal progress of the anaerobic digestion reaction. This inoculation ratio achieves the optimal concentration of key microbial species such as methanogens. Too low an inoculation ratio results in a low concentration of microorganisms, leading to low and slow methane production; too high an inoculation ratio results in an excessive microbial content, resulting in less substrate and more substrate being used for the metabolism of the microorganisms themselves.

[0029] The anaerobic sludge is obtained from the anaerobic digester of a wastewater treatment plant and acclimated. Its main characteristics are: total solids content of 20–25 g / L, volatile organic compound content of 12–16 g / L, pH of 6.2–6.8, and specific methanogenesis rate ≥ 400 ml CH4 / (gVSS). . d). The particle size of anaerobic granular sludge should be 0.5–2 mm, and the settling velocity should be maintained between 50 and 150 m / h.

[0030] In one preferred embodiment, the anaerobic fermentation process is as follows: pH is controlled at 7.0±0.1, stirring intensity is controlled at 100-150 rpm, temperature is controlled at 30-35℃, and digestion time is 15-20 days.

[0031] This stirring speed is beneficial for maintaining the mass transfer capacity of microorganisms without damaging their activity.

[0032] By controlling the inoculation ratio, stirring rate, and digestion temperature, the rate and yield of methane production can be enhanced, thereby accelerating the recovery of resources and energy during the anaerobic process.

[0033] In one preferred embodiment, complete anaerobic conditions are achieved by nitrogen stripping, wherein the nitrogen has a purity of 90.00% to 99.99%.

[0034] The advantages and effects of this invention are:

[0035] (1) In this invention, urea peroxide is used to pretreat kitchen waste. Compared with the direct co-digestion of kitchen waste and sludge, this invention can use urea peroxide to degrade allicin in kitchen waste into low-toxicity products, reduce the toxic effect of allicin on anaerobic microorganisms, and increase the production of methane in the anaerobic process.

[0036] (2) By adding the agent in batches, the dosage and method of the agent are optimized. While reducing the dosage of urea peroxide, the degradation of allicin is increased and the production of methane is enhanced. This improves the economic efficiency of the invention and facilitates its subsequent promotion and use. It also provides a new approach for the treatment of kitchen waste and residual sludge. Attached Figure Description

[0037] Figure 1 The methane yield after different addition methods. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but this should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description should be included within the scope of protection of the present invention.

[0039] Example 1: Effects of a single simple addition of ferrous sulfate and urea peroxide on allicin degradation and methane production

[0040] The collected kitchen waste is sorted by gravity using a kitchen waste treatment device to remove bones, plastics, paper towels, and disposable products. Then, an electric mixer is used to crush the kitchen waste into a slurry with a particle size of about 2-10 mm. Tap water is added to make the moisture content of the kitchen waste between 40-50%. After that, it is transferred to a pretreatment device, and different dosages of FeSO4·7H2O are added to the device and then stirred with a mechanical mixer at a speed of 300 r / min for 5 minutes. Then, different doses of urea peroxide (as shown in Table 1) were added. After addition, the pH was adjusted to 7.0±0.1, and the mixture was rapidly stirred at 300 rpm using a polyethylene folding turbine agitator. The total residence time was 36 h. The pretreated food waste was then transferred to the anaerobic digester. Residual sludge with a volatile solids content of 27.16±1.5 g / L was added to the reactor at a ratio of 1:1 (food waste VS / residual sludge VS) and nitrogen was blown off for 5 min. Then, the mixture was rapidly stirred at 200 rpm for 24 h, while the pH was adjusted to stabilize at 7.0±0.1. Then, anaerobic sludge with a volatile solids content of 14.02±1.1 g / L was inoculated with the mixed substrate at a ratio of 7:1 (v / v). The digester was then sealed, and the temperature was controlled at 35±1℃ using a surrounding hot water heating device. The stirring intensity was 120 rpm, and the total digestion time was 20 days. The methane yield in the reactor was detected by gas chromatography, and the concentration changes of allicin in the food waste were detected by high-performance liquid chromatography. The degradation rate of allicin and the methane yield are shown in Table 1.

[0041] Table 1. Allicin degradation rate and methane production under different doses of Fe(II) and urea peroxide treatment.

[0042]

[0043] The highest allicin degradation rate (60.9%) and methane production (241.58 ml / g VS) were obtained by a single simple addition of 60 mg / g TSS FeSO4·7H2O and 30 mg / g TSS peroxyurea.

[0044] Example 2: Effects of batch addition of ferrous sulfate and urea peroxide on allicin degradation and methane production

[0045] After passing through a food waste treatment device, the kitchen waste was transferred to an anaerobic digester. FeSO4·7H2O was added in two, three, and four separate additions, with each addition of 30, 20, and 15 mg / g TSS of FeSO4·7H2O (to reach a total TSS of 60 mg / g). After addition, the mixture was stirred at 300 rpm for 5 minutes, followed by the addition of 15, 10, and 7.5 mg / g TSS of urea peroxide (to reach a total urea peroxide of 30 mg / g TSS). The pH was adjusted to 7.0 ± 0.1, and rapid stirring was immediately initiated at a rate of 250–300 rpm. Each residence time was 6–12 hours. All other steps were consistent with Example 1. The results were as follows: Figure 1 As shown, the total methane yield and allicin degradation rate were 268.63 and 80.5%, 280.01 and 85.8%, and 270.34 ml / g VS and 85.3%, respectively.

[0046] In the above treatment process, after pretreating the kitchen waste with urea peroxide in three batches, the concentration of allicin in the kitchen waste was detected by high performance liquid chromatography. The concentration decreased from an initial 68.8 mg / L to a final 10.4 mg / L, indicating a higher allicin degradation rate than in Implementation Case 1. In Implementation Case 2, the cumulative methane production and allicin degradation rate from the three-batch urea peroxide pretreatment were both superior to the single-dose simple addition method (Implementation Case 1) and the two- or four-batch method (Implementation Case 2).

Claims

1. A method for treating kitchen waste, characterized in that, Includes the following steps: (1) Crush the kitchen waste, add ferrous salt, and stir evenly to obtain a mixture; (2) Add urea peroxide to the mixture in batches, then add the remaining sludge and anaerobic sludge for anaerobic fermentation; to obtain methane and treated kitchen waste; The ferrous salt is FeSO4•7H2O; The dosage of ferrous salts and urea peroxide is 3-4 times. The addition process of ferrous salt and urea peroxide is as follows: add 15~20 mg / g TSS of FeSO4•7H2O in a single addition, stir at 300-350 rpm for 3-7 minutes, and add 8~10 mg / g TSS of urea peroxide, and stir rapidly at a stirring rate of 250~300 rpm. The total residence time for a single addition is 6~12 h. After adding urea peroxide, the pH of the system was adjusted to 7.0 ± 0.

1.

2. The processing method according to claim 1, characterized in that, The particle size of the crushed food waste is 2-10 mm; the solid mass of the crushed food waste is controlled to be 80-100 g / L.

3. The processing method according to claim 1, characterized in that, The total solids content of the residual sludge is 20-40 g / L; the ratio of the added mass of residual sludge to the volatile organic compound content is 1:1-2:

1.

4. The processing method according to claim 1, characterized in that, The inoculation ratio of anaerobic sludge to the treatment substrate is 4:1 to 7:1 (v / v).

5. The processing method according to any one of claims 1-4, characterized in that, The anaerobic fermentation process is as follows: pH is controlled at 7.0 ± 0.1, stirring intensity is controlled at 100 ~ 150 rpm, temperature is controlled at 30 ~ 35 ℃, and digestion time is 15 ~ 20 days.

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