Method for increasing B / C ratio of kitchen solid residue drying condensate

Abstract

The invention discloses a method for increasing the B / C ratio of kitchen solid residue drying condensate, and belongs to the technical field of kitchen waste resource utilization. The method comprises the following steps: performing three-phase separation on the kitchen waste to obtain solid residues; uniformly adding alkalescent salt into the solid residues, and carrying out anaerobic fermentation to obtain a fermentation product; the fermentation product is dried, dried solid residues are obtained, steam generated in the drying process is collected through a condensation system, and condensate is obtained. According to the method, on the premise that exogenous flora and extra water are not introduced, in-situ and rapid pH regulation and local microorganism activity excitation are directly carried out on the kitchen waste solid residues, short-time rapid fermentation treatment is carried out on the kitchen waste solid residues, the nutritional quality of the dried solid residues as a feed product is ensured, and meanwhile, the quality of the dried solid residues is improved. The biodegradability of the condensate is remarkably improved, and finally the dual recycling target of preparing the feed from the solid residues and using the condensate as the carbon source is achieved.

Description

Technical Field

[0001] This invention relates to a method for improving the B / C ratio of condensate from the drying of kitchen waste, and particularly to a method for converting kitchen waste and its byproduct—condensate—into useful resources through a drying process, belonging to the field of resource utilization of kitchen waste. Background Technology

[0002] The tailings from three-phase separation of food waste are still rich in organic components such as high protein and crude fat, possessing the potential for resource utilization as feed raw materials. However, these tailings typically have a high moisture content, and if used directly as feed in wet form, their application is limited by short shelf life and high transportation costs. Therefore, in actual production, a thermal drying process is often used to reduce the moisture content of the tailings. During the drying process, the tailings release steam rich in organic matter and moisture upon heating, which condenses to form condensate. This condensate is a typical high-concentration organic wastewater, with a chemical oxygen demand (COD) that can reach tens of thousands of milligrams per liter. It contains a certain amount of volatile fatty acids (VFAs) and ammonia nitrogen, but its biodegradability is generally poor, with a BOD5 / COD ratio (B / C ratio) typically below 0.4, limiting its subsequent resource utilization efficiency. If the B / C ratio of the condensate can be significantly increased through targeted regulation, it will have important application significance: since a high B / C ratio is a key indicator of the biodegradability of wastewater, increasing this ratio means that the organic matter in the condensate is more easily degraded and utilized by microorganisms, and can be used as a high-quality alternative carbon source in the denitrification process of wastewater treatment plants, thereby forming an efficient resource recycling model of "treating wastewater with waste liquid", which has both significant environmental benefits and economic value.

[0003] Existing technologies, such as Chinese patent application (publication number: CN118460632A), disclose a method for increasing acid production from organic waste fermentation by stimulating homoacetogenesis. This method stimulates homoacetogenesis in the fermentation system by initially adding bicarbonate, thereby increasing the yield of volatile fatty acids and reducing CO2 emissions. However, this method relies on inoculating exogenous biogas slurry, sludge, etc., and enriching and acclimating them. This process is cumbersome, time-consuming, and costly. In addition, the fermentation system is designed for liquid or low-solids materials, and the long-cycle fermentation mode of 1 to 21 days is difficult to apply to kitchen waste that requires rapid processing. Most importantly, this method aims to increase the amount of acid produced in the liquid phase, without considering the negative impact of long-term fermentation and the possible introduction of liquid substances on the quality of solid residue (such as protein degradation and increased water content). This results in the inability to utilize the solid portion at a high value, and the subsequent drying cost is high. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for improving the B / C ratio of the condensate from the drying of kitchen waste. This method, without introducing exogenous bacteria or additional moisture, directly and rapidly adjusts the pH of kitchen waste solids in situ and activates local microbial activity, enabling short-term rapid fermentation of the kitchen waste solids. While ensuring the nutritional quality of the dried solids as feed products, it significantly improves the biodegradability of the condensate, ultimately achieving the dual resource utilization goals of "solids as feed" and "condensate as a carbon source".

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for increasing the B / C ratio of the condensate from the drying of kitchen waste, comprising the following steps:

[0006] 1) The kitchen waste is separated into three phases to obtain solid residue;

[0007] 2) After uniformly adding weak alkaline salt at a rate of 0.1~1.0 g / kg to the solid residue, place the solid residue at a temperature of 30~35℃ for anaerobic fermentation for 0~4 hours to obtain the fermentation product;

[0008] 3) The fermentation products are dried to obtain dried solid residue, and the steam generated during the drying process is collected by a condensation system to obtain condensate.

[0009] The key to this invention's method for improving the B / C ratio of the condensate from the drying of kitchen waste solids lies in using a weakly alkaline salt to regulate the pH environment of the kitchen waste solids. This allows an effective pH buffer system to be formed in the microenvironment of the liquid film on the surface of the kitchen waste solids, stabilizing the local pH within the range of 4.0 to 5.5, which is the optimal pH range for acid-producing bacteria. This alleviates the inhibition of acid-producing bacteria by excessive acidification and effectively activates the activity of local microorganisms. At the same time, by controlling the amount of weakly alkaline salt added to the kitchen waste solids and controlling the anaerobic fermentation conditions, short-term fermentation is achieved, ensuring the nutritional quality of the dried solids as a feed product while significantly improving the biodegradability of the condensate.

[0010] As a preferred embodiment, the water content of the solid slag is controlled at 70-85 wt%. More preferably, the water content of the solid slag is controlled at 75-80 wt%. If the water content of the solid slag is too high, it may dilute the concentration of alkaline salts and weaken its ability to act as a pH buffer, while insufficient water may limit the metabolic activities of microorganisms, reduce the mass transfer of their life activities, and thus reduce their decomposition capacity.

[0011] As a preferred embodiment, the weakly alkaline salt includes sodium carbonate and / or sodium bicarbonate. Sodium carbonate and / or sodium bicarbonate can dynamically regulate the pH of the anaerobic fermentation system, alleviate the inhibition of acid-producing bacteria activity by acidification, and enhance the microbial capacity to decompose organic matter, thereby significantly improving the biodegradability (B / C ratio) of the condensate within a short period (within 4 hours). A further preferred weakly alkaline salt is sodium bicarbonate, as its use provides a better pH buffering effect while avoiding excessive alkalinity that could inhibit acid-producing bacteria.

[0012] As a preferred embodiment, the weakly alkaline salt is uniformly added to the solid slag at a concentration of 0.1~0.5 g / kg. Insufficient addition of the weakly alkaline salt will fail to regulate the pH, while excessive addition will inhibit the activity of acid-producing microorganisms, leading to a deterioration in process efficiency.

[0013] As a preferred embodiment, the drying temperature is 120~180℃, and the drying endpoint is to control the moisture content of the dried solid slag to be reduced to below 12%.

[0014] As a preferred embodiment, the COD concentration in the condensate is 10,000~20,000 mg / L, and the B / C ratio is ≥0.4. As a more preferred embodiment, the COD concentration in the condensate is 15,000~20,000 mg / L, and the B / C ratio is 0.4~0.5.

[0015] As a preferred embodiment, the dried solid residue is used to prepare feed ingredients or organic fertilizer substrate.

[0016] As a preferred embodiment, the condensate is used in the denitrification process of wastewater treatment.

[0017] As a preferred embodiment, the anaerobic fermentation time is 2-4 hours. Within the preferred anaerobic fermentation time, with the extension of the anaerobic fermentation time, the properties of the condensate are significantly improved, and its B / C ratio increases significantly, reaching a level that is highly biodegradable (B / C>0.5).

[0018] The method for improving the B / C ratio of the condensate from the drying of kitchen waste provided by this invention includes the following specific steps:

[0019] (1) Solid residue pretreatment: Mix the solid residue obtained after the three-phase separation of kitchen waste evenly, and measure its initial moisture content (usually 70~85%). If necessary, drain water appropriately to adjust the moisture content to 75~80%.

[0020] (2) Alkali salt powder addition: Alkali carbonate is uniformly added to the solid residue in powder form. The final concentration of the added amount in the fermentation system is 0.1~1 g / kg. Its mechanism of action is that after the alkali carbonate dissolves in the solid residue system, it can form an effective pH buffer system in the liquid film microenvironment on the surface of the solid residue particles, and stabilize the local pH in the optimal range of 4.0~5.5 for acid-producing bacteria, thereby alleviating the inhibition of acid-producing bacteria activity by excessive acidification and activating the activity of local microorganisms. By adjusting the added salt concentration, the biochemical properties of the condensate product can be improved. The preferred concentration is 0.1~0.5 g / kg, and the carbonate is sodium bicarbonate and sodium carbonate, with sodium bicarbonate having a better effect.

[0021] (3) Short-term fermentation control: The solid residue with added carbonate salts is placed in an environment of 30~35℃ for short-term fermentation, and the fermentation time is controlled within 2~4 hours. The process needs to be sealed, and a small amount of oxygen is allowed to simulate the actual storage conditions before drying. The purpose of this short-term fermentation is not deep conversion, but to make full use of the optimal microenvironment after pretreatment to quickly stimulate and complete the hydrolysis and acidification process of the bacteria attached to the solid surface.

[0022] (4) Thermal drying and condensation collection: The fermented tailings are sent to a thermal drying device and dried at a temperature of 120~180℃ until the moisture content is <12%. The steam generated during the drying process is collected by a condensation system to obtain condensate.

[0023] (5) Physicochemical property testing and carbon source application of condensate: pH, COD, and BOD5 concentrations of the condensate were tested. This method can increase the B / C ratio of the condensate from 0.35 to 0.45, which greatly improves the biodegradability of the condensate and enhances its ability as a carbon source for wastewater treatment and denitrification.

[0024] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0025] 1) This invention improves the biodegradability of condensate by adjusting the solid residue of kitchen waste with weakly alkaline salts, thereby promoting the activity of microorganisms and shortening the fermentation cycle without affecting the properties of high-solid-phase materials.

[0026] 2) The process of treating kitchen waste residue in this invention is simple to operate, does not affect the subsequent drying process, and does not change the physical properties of the waste residue. The dried waste residue can be used to prepare feed raw materials or organic fertilizer substrate.

[0027] 3) The COD concentration in the condensate of this invention is 15,000~20,000 mg / L, and the B / C ratio is 0.4~0.5. It can be used as a carbon source to replace traditional external carbon sources for wastewater treatment, realizing waste-to-waste treatment.

[0028] 4) This invention can improve the biodegradability of condensate by adding weak alkaline salts to achieve fermentation in a short time (2-4 h). However, when the biodegradability of condensate is usually increased by extending the fermentation time, it will affect the nutritional quality of the feed product of dried solid residue.

[0029] 5) This invention does not require the introduction of exogenous strains or complex control systems. It can significantly increase the organic matter content in the condensate by simply adding alkali salts and short-term fermentation, thereby greatly shortening the fermentation time and reducing operating costs.

[0030] 6) This invention uses weakly alkaline salts such as carbonates for mild regulation, which fundamentally eliminates the risks of chloride ion (hydrochloric acid) introduction and protein denaturation, ensuring that the fermentation residue is non-toxic, harmless and nutritionally intact, providing a core guarantee for the subsequent preparation of high-protein, high-quality feed. Attached Figure Description

[0031] Figure 1 shows the COD and B / C ratio of the extracted condensate with and without sodium bicarbonate.

[0032] Figure 2 shows the COD and B / C ratio of the extracted condensate when different concentrations of sodium carbonate and sodium bicarbonate were added.

[0033] Figure 3 shows the COD and B / C ratio of the extracted condensate when different concentrations of sodium bicarbonate were added.

[0034] Figure 4 shows the COD and B / C ratio of the condensate extracted during coupled fermentation time when different concentrations of sodium bicarbonate were added. Detailed Implementation

[0035] The following specific embodiments are intended to further illustrate the content of the present invention, rather than to limit the scope of the claims of the present invention.

[0036] Example 1

[0037] (1) Mix the solid residue obtained after the three-phase separation of kitchen waste evenly and measure its initial moisture content to 80%.

[0038] (2) Sodium bicarbonate is added evenly to the solid residue in powder form, and the final concentration of the added amount in the fermentation system is 0.5 g / kg.

[0039] (3) Place the solid residue with added sodium bicarbonate in a 35°C environment and carry out short-term fermentation in a sealed environment. The fermentation time is controlled at 0, 1, 2, 3, 4, 5 or 6 hours respectively.

[0040] (4) The fermented solid residue is sent to a thermal drying device and dried at 135°C until the moisture content is <12%. The steam generated during the drying process is collected by a condensation system to obtain condensate.

[0041] (5) Detect the pH, COD and BOD5 concentration of the condensate.

[0042] Comparative Example 1

[0043] The only difference compared to Example 1 is that sodium bicarbonate is not added.

[0044] Example 1 and Comparative Example 1: COD and B / C ratio of extract condensate with and without sodium bicarbonate addition. Figure 1 As shown, a comparison of the COD and BOD5 / COD (B / C) of the condensate obtained by the method of this invention (with the addition of sodium bicarbonate) and the traditional method (without any treatment) at different fermentation times reveals that the biodegradability (B / C ratio) is improved, with the experimental group's condensate showing a B / C ratio as high as 0.36~0.47. In contrast, the untreated control group generally had a B / C ratio between 0.32 and 0.36. Therefore, the method of this invention can transform the condensate from organic wastewater with generally low biodegradability into a high-quality, easily biodegradable carbon source, which is crucial for its efficient application in wastewater treatment.

[0045] Example 2

[0046] (1) Mix the solid residue obtained after the three-phase separation of kitchen waste evenly and measure its initial moisture content to 77%.

[0047] (2) Sodium bicarbonate or sodium carbonate in powder form is uniformly added to the solid residue, and the final concentrations of the added amount in the fermentation system are 0.1, 0.5, 1 and 2 g / kg, respectively.

[0048] (3) The solid residue after adding alkaline salt (without fermentation) is sent to a thermal drying equipment and dried at 135°C until the moisture content is <12%. The steam generated during the drying process is collected by a condensation system to obtain condensate.

[0049] (4) Detect the pH, COD and BOD5 concentration of the condensate.

[0050] Adding different concentrations of sodium carbonate or sodium bicarbonate to extract the COD and B / C ratio of the condensate, such as... Figure 2 As shown.

[0051] The figure shows that sodium bicarbonate and sodium carbonate have a significant impact on the properties of kitchen solid residue drying condensate at different dosages. Through systematic analysis of COD ratio and B / C concentration, it can be seen that: (1) When the dosage of sodium bicarbonate is 0.5 g / kg, the COD of the condensate decreases significantly. This may be because the addition of alkali salt has changed some substances in the condensate, and large molecules may be converted into small molecules. The COD value may also decrease due to the removal of stubborn substances, or remain stable due to the contribution of newly formed small molecules. (2) When the dosage of sodium carbonate is 0.1 g / kg, the extremely low dose of sodium carbonate can significantly increase its COD and further improve its biodegradability (B / C ratio), thereby transforming it from a "good carbon source" into a "higher concentration and more easily biodegradable high-efficiency carbon source", indicating that sodium carbonate is also an alkali salt that can improve the biodegradability of condensate.

[0052] Example 3

[0053] (1) Mix the solid residue obtained after the three-phase separation of kitchen waste evenly and measure its initial moisture content to 77%.

[0054] (2) Sodium bicarbonate or sodium carbonate in powder form is uniformly added to the solid residue, and the final concentrations of the added amount in the fermentation system are 0.1, 0.5, 1, 2, 5, 10, and 15 g / kg, respectively.

[0055] (3) The solid residue after adding alkaline salt (without fermentation) is sent to a thermal drying equipment and dried at 135°C until the moisture content is <12%. The steam generated during the drying process is collected by a condensation system to obtain condensate.

[0056] (4) Detect the pH, COD and BOD5 concentration of the condensate.

[0057] The effect of different sodium bicarbonate dosages on the properties of condensate from the drying of kitchen waste is shown in the figure below. As shown, through systematic analysis of COD ratio and B / C concentration, it can be seen that: (1) There is an optimal range of sodium bicarbonate addition of 0.1~0.5 g / kg to improve carbon source quality. When the sodium bicarbonate addition is in the range of 0.1 to 0.5 g / kg, the B / C ratio of the condensate is significantly improved, especially at 0.5 g / kg, which reaches a peak (B / C ratio = 0.49). At this addition, while maintaining a high BOD5 (5700 mg / L), the total COD (11555 mg / L) is reduced to the minimum, indicating that the organic matter is converted into easily degradable components to the maximum extent, and the carbon source quality is optimized. (2) Excessive addition leads to a decrease in product quality. When the addition exceeds 1 g / kg (such as 2 g / kg and 15 g / kg), the B / C ratio of the condensate falls back. This proves that excessive alkali salt will lead to a deterioration in process efficiency, which in turn confirms the necessity of precise control of the addition amount.

[0058] Example 4

[0059] (1) Mix the solid residue obtained after the three-phase separation of kitchen waste evenly and measure its initial moisture content to 77%.

[0060] (2) Sodium bicarbonate was added to the solid residue in powder form, and the final concentrations of the added amount in the fermentation system were 0, 0.1, 0.2 and 1 g / kg, respectively.

[0061] (3) Place the solid residue with added sodium bicarbonate or sodium carbonate in a 35°C environment and carry out short-term fermentation in a sealed environment. The fermentation time is controlled at 2 hours (sodium bicarbonate concentration is controlled at 0, 0.1, 1 g / kg) or 4 hours (sodium bicarbonate concentration is controlled at 0, 0.1, 0.2 g / kg).

[0062] (4) The fermented solid residue is sent to a thermal drying device and dried at 135°C until the moisture content is <12%. The steam generated during the drying process is collected by a condensation system to obtain condensate.

[0063] (5) Detect the pH, COD and BOD5 concentration of the condensate.

[0064] The effect of different sodium bicarbonate dosages and fermentation times on the properties of the condensate from the drying of kitchen waste is shown in the figure below. Figure 4As shown in the figure, (1) when fermentation time is 2 hours, the addition of sodium bicarbonate (whether 0.1 or 1.0) steadily increases the B / C ratio from 0.36 to 0.41, proving its universal quality improvement effect. (2) When the fermentation time is extended to about 4 hours and the addition of sodium bicarbonate is controlled at about 0.2 g / kg, a breakthrough improvement in the properties of the condensate can be achieved, with the B / C ratio increasing by more than 30%, reaching a level that is very easy to biodegrade (B / C>0.5).

Claims

1. A method for improving the B / C ratio of kitchen solid residue drying condensate, characterized in that: The method comprises the following steps: 1) performing three-phase separation on the kitchen waste to obtain solid residues; 2) adding weak alkaline salt to the solid residues at a rate of 0.1-1.0 g / kg, and then performing anaerobic fermentation on the solid residues at a temperature of 30-35°C for 0-4 hours to obtain fermentation products; 3) drying the fermentation products to obtain dried solid residues, and collecting steam generated during the drying process by a condensing system to obtain a condensate.

2. The method of claim 1, wherein the B / C ratio of the kitchen solid residue drying condensate is improved. The water content of the solid residues is controlled to be 70-85 wt%.

3. The method of claim 1, wherein the B / C ratio of the kitchen solid residue drying condensate is improved. The weak alkaline salt comprises sodium carbonate and / or sodium bicarbonate.

4. The method for improving the B / C ratio of the condensate of the kitchen solid residue drying according to any one of claims 1-3, characterized in that: The weak alkaline salt is added to the solid residues at a rate of 0.1-0.5 g / kg.

5. The method for improving the B / C ratio of the condensate of the kitchen solid residue drying according to any one of claims 1-3, characterized in that: The drying temperature is 120-180°C, and the drying endpoint is determined according to the water content of the dried solid residues, which is controlled to be less than 12%.

6. The method of claim 1-3, wherein the B / C ratio of the condensate is improved by the method. The concentration of COD in the condensate is 10000-20000 mg / L, and the B / C ratio is greater than or equal to 0.

4.

7. The method of claim 6, wherein the B / C ratio of the kitchen solid residue drying condensate is improved. The concentration of COD in the condensate is 15000-20000 mg / L, and the B / C ratio is 0.4-0.

5.

8. The method of claim 1, wherein: the dried solid residues are used to prepare feed raw materials or organic fertilizer substrates; the condensate is used in a denitrification process of sewage treatment.

9. The method of claim 1, wherein the B / C ratio of the kitchen solid residue drying condensate is improved. The anaerobic fermentation time is 2-4 hours.

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