Fermentation preparation method of high-COD (Chemical Oxygen Demand) composite carbon source

Abstract

The invention discloses a fermentation preparation method of a high-COD (Chemical Oxygen Demand) composite carbon source, which comprises the following steps: by taking fruit wastes such as apple pomace, grape pomace, banana peel and orange peel as raw materials, carrying out crushing and sterilization pretreatment, then carrying out segmented fermentation, composite enzymolysis and sodium alginate-calcium chloride crosslinking, and finally, carrying out vacuum freeze drying to obtain a powdery carbon source. The COD content of the carbon source reaches 1.5-20 thousand mg / L, the specific surface area is 100-150 m < 2 > / g, the total nitrogen removal rate is larger than or equal to 95% when the adding amount is 200 mg / L, and the turbidity reduction rate is 80-88.2%. According to the method, the integration of a high-COD carbon source and a flocculation function is realized through fruit waste recycling, segmented bioconversion and gel network construction, and the method is suitable for municipal and industrial wastewater treatment.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and specifically proposes a fermentation preparation method for a high-COD composite carbon source. Background Art

[0002] In wastewater treatment, carbon sources play a vital role in microbial growth and metabolism. This is especially true during the denitrification process, where a sufficient and efficient carbon source is crucial for achieving compliance with total nitrogen standards in wastewater. With increasingly stringent environmental standards, restrictions on the discharge of pollutants such as nitrogen and phosphorus in wastewater are becoming increasingly stringent, making the development and application of efficient carbon sources a key area of ​​industry research.

[0003] Traditional carbon sources, such as methanol, sodium acetate, and glucose, have exposed numerous problems in practical applications. Methanol, a Class A hazardous chemical, has extremely strict safety requirements for its storage and use. Improper handling can easily lead to serious safety accidents. Furthermore, methanol is toxic to the human body and poses a potential threat to the environment and the health of operators. While glucose can be utilized by microorganisms, it can easily lead to bacterial proliferation, causing sludge bulking and impacting the stable operation of sewage treatment systems. Sodium acetate has a relatively low chemical oxygen demand (COD) equivalent, requiring a large dosage in actual use. This not only increases costs but also produces a large amount of excess sludge, placing a heavy burden on subsequent sludge treatment.

[0004] To address the drawbacks of traditional carbon sources, composite carbon sources have gradually attracted attention in recent years. However, existing composite carbon source preparation technologies still have some shortcomings. On the one hand, most composite carbon sources are based on agricultural and forestry waste (such as rice husks and straw). The main component of these raw materials is cellulose. Although widely available, the content of easily fermentable components such as sugars is low, resulting in limited COD intensity of the prepared carbon source, making it difficult to meet the needs of high-load sewage treatment. For example, the COD content of composite carbon sources prepared using rice husks as the main raw material using conventional processes is generally only about 12,000 mg / L. When treating high-concentration nitrogen-containing sewage, large amounts of them often need to be added, increasing treatment costs and operational difficulty.

[0005] On the other hand, existing preparation processes mostly rely on pretreatment methods with high energy consumption, such as physical crushing (such as steam explosion), and the carbon source generation mechanism is relatively simple, mainly relying on cellulose degradation to provide carbon sources, and cannot fully utilize the multiple components in the raw materials to achieve synergistic efficiency. For example, some composite carbon sources prepared from a single raw material through simple physical treatment and microbial fermentation have poor performance in denitrification efficiency and carbon source release stability, and are difficult to play a continuous and efficient role under complex water quality conditions. In addition, in terms of functional realization, existing composite carbon sources often only focus on single functions such as nitrogen adsorption, and lack comprehensive consideration of other sewage treatment needs (such as flocculation, etc.), and cannot meet the requirements for the synergistic removal of multiple pollutants in actual sewage treatment processes.

[0006] In terms of raw material selection, fruit waste, as a waste rich in various organic components such as sugar and pectin, has not yet been fully utilized in the field of composite carbon source preparation. A large amount of waste generated during fruit processing, such as apple pomace, grape pomace, banana peel, citrus peel, etc., is usually treated as low-value waste, which not only causes waste of resources but also may cause environmental pollution problems. However, if the rich organic components in these fruit wastes can be converted into efficient composite carbon sources through reasonable technical means, they will have great potential value. However, at present, there is no report on the technical solution of combining these fruit wastes for the preparation of high-COD composite carbon sources. Summary of the Invention

[0007] Based on this background, the present invention aims to develop a new fermentation preparation method for preparing a high-COD composite carbon source using fruit waste, so as to overcome the shortcomings of the existing technology and meet the urgent demand of the sewage treatment industry for efficient, environmentally friendly and multifunctional carbon sources.

[0008] The technical solution of the present invention is achieved as follows: The present invention provides a fermentation method for preparing a high COD composite carbon source, which comprises the following steps: S1. Apple pomace, grape pomace, banana peel, and citrus peel are mixed according to a proportion, crushed, adjusted to a moisture content, and sterilized to obtain a pretreated raw material; S2, performing staged fermentation on the pretreated raw material, firstly producing ethanol by anaerobic fermentation, and then converting it into acetic acid and synthesizing bacterial cellulose by aerobic fermentation; S3, adding a complex enzyme to the fermentation product for enzymatic hydrolysis, and then adding a cross-linking agent to form a gel network; S4. Drying and crushing the gel network to obtain a high COD composite carbon source.

[0009] In some embodiments, the weight percentages of the raw materials are: 30-40% apple pomace, 20-30% grape pomace, 20-30% banana peel, and 10-20% citrus peel.

[0010] In some embodiments, in step S1, the particle size after crushing is 0.5-1 mm, the moisture content is adjusted to 60-70%, and the sterilization condition is high-pressure steam sterilization at 121° C. for 20 minutes.

[0011] In some embodiments, in step S2, the anaerobic fermentation uses Saccharomyces cerevisiae and is fermented at 30°C under sealed conditions for 48 hours; the aerobic fermentation uses a mixed strain of Acetobacter xylinum and cellulolytic bacteria and is fermented at 37°C and 150 rpm under shaking conditions for 72 hours, and the inoculation amount of the mixed strain is 8-12% of the mass of the raw material.

[0012] In some embodiments, in step S3, the complex enzyme includes cellulase and pectinase, and the added amounts are 100-200 U / g raw material and 50-100 U / g raw material, respectively. The enzymatic hydrolysis temperature is 50°C, the time is 12 h, and the cellulose degradation rate is controlled at 20-30%.

[0013] In some embodiments, in step S3, the crosslinking agent is a combination of sodium alginate and calcium chloride, the amount of sodium alginate added is 0.5-1% of the raw material mass, the amount of calcium chloride added is 0.2-0.5%, the crosslinking temperature is 60°C, and the time is 30 minutes.

[0014] In some embodiments, in step S4, the drying method is vacuum freeze drying, the conditions are -40°C, 10Pa, the drying time is 24h, and the particle size after crushing is 80-100 mesh.

[0015] In some embodiments, during the staged fermentation process, the ethanol concentration generated in the anaerobic stage is 5-8 g / L, the acetic acid concentration in the aerobic stage is 3-5 g / L, and the bacterial cellulose growth amount is 15-25% of the raw material mass.

[0016] In some embodiments, the high COD composite carbon source has a COD content of 15,000-20,000 mg / L and a specific surface area of ​​100-150 m 2 / g.

[0017] In some embodiments, the pectin content of the apple pomace is 15-20%, the cellulose content of the grape pomace is 25-30%, the sugar content of the banana peel is 10-15%, and the pectin content of the citrus peel is ≥10%.

[0018] The present invention has the following beneficial effects compared to the prior art: Raw material advantages: Using fruit waste as raw material allows for resource utilization and reduces raw material costs. Fruit waste, such as apple pomace, grape pomace, banana peels, and citrus peels, is widely available and inexpensive. Converting them into a composite carbon source not only solves waste disposal issues but also creates value.

[0019] High COD content: Through a unique segmented fermentation and enzymatic hydrolysis process, the sugar, pectin and other components in fruit waste are fully utilized to prepare a composite carbon source with a COD content of up to 15,000-20,000 mg / L, which is significantly higher than the traditional composite carbon source prepared from agricultural and forestry waste as raw materials (about 12,000 mg / L). It can provide sufficient carbon source for sewage treatment and improve denitrification efficiency.

[0020] Multifunctionality: The bacterial cellulose synthesized during the fermentation process forms a gel network with cross-linking, which makes the composite carbon source have a large specific surface area (100-150m 2 / g), it can not only adsorb nitrogen, but also has a certain flocculation effect, which can simultaneously remove suspended matter in sewage, achieve the coordinated removal of multiple pollutants, and simplify the sewage treatment process.

[0021] Process Advantages: Compared to existing technologies that rely on high-energy physical crushing, the preparation process of this invention is more energy-efficient and environmentally friendly. Furthermore, by precisely controlling fermentation conditions and enzymatic hydrolysis parameters, the stable quality and performance of the carbon source are ensured. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the present invention belong. If the definitions set forth in this section are contrary to or otherwise inconsistent with definitions set forth in the patents, patent applications, published patent applications, and other publications incorporated herein by reference, the definitions listed in this section take precedence over the definitions incorporated herein by reference.

[0024] Unless otherwise specified, the methods used in the following examples are conventional methods. The materials, reagents, and instruments used are conventional materials, reagents, and instruments in the art, unless otherwise specified, and can be obtained commercially by those skilled in the art.

[0025] When an amount, concentration or other value or parameter is expressed as a range, a preferred range or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range "1 to 5" is disclosed, the described range should be interpreted as including the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within the range. In the present specification and claims, range definitions may be combined and / or interchanged, and if not otherwise stated, such ranges include all subranges contained therein.

[0026] In the following examples, the apple pomace used was tested to have a pectin content of 17.5%, the grape pomace cellulose content of 27%, the banana peel sugar content of 12.3%, and the citrus peel pectin content of 11.5%.

[0027] Example 1 Raw material preparation Weigh 350 g of apple pomace (35%), 250 g of grape pomace (25%), 250 g of banana peel (25%), and 150 g of citrus peel (15%), mix and crush them to make the raw material particle size reach 0.5-1 mm, add appropriate amount of distilled water to adjust the moisture content to 65%, and then sterilize them with high-pressure steam at 121°C for 20 min to obtain pretreated raw materials.

[0028] Staged fermentation The pretreated raw materials were placed in a 5L fermenter and inoculated with Saccharomyces cerevisiae for anaerobic fermentation (inoculation size: 0.5% of the raw material mass, i.e. 5g). Fermentation was carried out under sealed conditions at 30°C for 48 hours, and the ethanol concentration reached 6g / L. A mixed strain of Acetobacter xylinum and cellulolytic bacteria was then inoculated (inoculation size: 100g, 10% of the raw material mass, i.e. 100g). Aerobic fermentation was carried out at 37°C and a shaker at 150 rpm for 72 hours, at which point the acetic acid concentration reached 4g / L, and the bacterial cellulose growth reached 20% of the raw material mass.

[0029] Enzymatic hydrolysis and cross-linking Cellulase (150 U / g of raw material) and pectinase (75 U / g of raw material) were added to the fermentation product, stirred thoroughly, and then enzymatically digested at 50°C for 12 hours. The cellulose degradation rate was determined to be 25%. After enzymatic hydrolysis, sodium alginate (0.8% of the raw material mass, or 8 g) and calcium chloride (0.3% of the raw material mass, or 3 g) were added, and cross-linking was carried out at 60°C for 30 minutes to form a gel network.

[0030] Post-processing The gel network was freeze-dried in vacuum (-40°C, 10Pa, 24h), and then crushed to 80-100 mesh to obtain a composite carbon source. After testing, the COD content of the composite carbon source was 17,000 mg / L and the specific surface area was 120m 2 When it was applied to sewage treatment experiments, when the dosage was 200 mg / L, the removal rate of total nitrogen in sewage reached 96%, and the turbidity of sewage was significantly reduced.

[0031] Example 2 Raw material preparation Weigh 400 g of apple pomace (40%), 200 g of grape pomace (20%), 200 g of banana peel (20%), and 200 g of citrus peel (20%), mix and crush them to a particle size of 0.5-1 mm, adjust the moisture content to 60%, and sterilize them with high-pressure steam at 121°C for 20 min.

[0032] Staged fermentation The raw materials were placed in a 3L fermentation tank, inoculated with brewer's yeast (inoculation amount was 0.3% of the raw material mass, i.e. 3 g), and sealed and fermented at 30°C for 48 hours, with an ethanol concentration of 5 g / L; for aerobic fermentation, mixed strains were inoculated (inoculation amount was 8%, i.e. 80 g), and fermented at 37°C and 150 rpm using a shaker for 72 hours, with an acetic acid concentration of 3 g / L and a bacterial cellulose growth amount of 15% of the raw material mass.

[0033] Enzymatic hydrolysis and cross-linking Cellulase (100 U / g raw material) and pectinase (50 U / g raw material) were added, and enzymatic hydrolysis was carried out at 50°C for 12 hours, with a cellulose degradation rate of 20%; sodium alginate (0.5%, i.e. 5 g) and calcium chloride (0.2%, i.e. 2 g) were added, and cross-linking was carried out at 60°C for 30 minutes.

[0034] Post-processing After vacuum freeze drying and crushing, a composite carbon source was obtained. After testing, the COD content was 15,000 mg / L and the specific surface area was 100m 2 / g. Sewage treatment experiments show that when 200 mg / L is added, the total nitrogen removal rate is 95%, which has a certain flocculation effect.

[0035] Example 3 Raw material preparation Weigh 300 g of apple pomace (30%), 300 g of grape pomace (30%), 300 g of banana peel (30%), and 100 g of citrus peel (10%), mix and crush them to a particle size of 0.5-1 mm, adjust the moisture content to 70%, and sterilize them with high-pressure steam at 121°C for 20 min.

[0036] Staged fermentation The raw materials were placed in an 8L fermentation tank and inoculated with brewer's yeast (inoculation amount was 0.7% of the raw material mass, i.e. 7 g). The ethanol concentration of anaerobic fermentation was 8 g / L. For aerobic fermentation, mixed strains were inoculated (inoculation amount was 12% (i.e. 120 g). The fermentation was carried out at 37°C and 150 rpm in a shaking incubator for 72 hours. The acetic acid concentration was 5 g / L, and the bacterial cellulose growth amount was 25% of the raw material mass.

[0037] Enzymatic hydrolysis and cross-linking Cellulase (200 U / g raw material) and pectinase (100 U / g raw material) were added, and enzymatic hydrolysis was carried out at 50°C for 12 hours, with a cellulose degradation rate of 30%; sodium alginate (1%, i.e. 10 g) and calcium chloride (0.5%, i.e. 5 g) were added, and cross-linking was carried out at 60°C for 30 minutes.

[0038] Post-processing After vacuum freeze drying and crushing, the COD content of the composite carbon source is 18,000 mg / L and the specific surface area is 130m 2 / g. In sewage treatment, when adding 200mg / L, the total nitrogen removal rate is 97%, and the turbidity of sewage is effectively reduced.

[0039] Example 4 This embodiment is based on the embodiment 1, and the raw materials are: 25% apple pomace, 35% grape pomace, 20% banana peel, and 20% citrus peel. Other conditions are the same as those in embodiment 1.

[0040] Example 5 In this embodiment, based on the embodiment 1, the temperature of anaerobic fermentation was adjusted to 28° C., the temperature of aerobic fermentation was adjusted to 35° C., and other conditions were the same as those in the embodiment 1.

[0041] Comparative Example 1 Single apple pomace was used as raw material and processed according to the raw material preparation method of Example 1. A 3L fermentation tank was used and Saccharomyces cerevisiae was inoculated (the inoculation amount was 0.5% of the raw material mass). Other conditions were the same as in Example 1. The prepared composite carbon source had a COD content of 13,000 mg / L and a specific surface area of ​​80 m 2 / g. In the sewage treatment experiment, when 200 mg / L was added, the total nitrogen removal rate was 90%. This shows that the combination of multiple fruit wastes can play a synergistic role and improve the performance of the composite carbon source.

[0042] Comparative Example 2 Without staged fermentation, the pretreated raw materials were directly subjected to aerobic fermentation, using a mixed strain of Acetobacter xylinum and cellulose decomposing bacteria (inoculation amount was 10% of the raw material mass), using a 3L fermentation tank, and other conditions were the same as in Example 1. The prepared composite carbon source had a COD content of 14,000 mg / L and a specific surface area of ​​90 m 2 / g, and the total nitrogen removal rate was 92%. This shows that the staged fermentation process can make more effective use of raw materials and improve the quality and performance of the carbon source.

[0043] Comparative Example 3 Cross-linking treatment was performed without the addition of a cross-linking agent, using a 3 L fermenter, and all other conditions were the same as in Example 1. The prepared composite carbon source had poor structural stability during use, making it difficult to effectively exert its adsorption and flocculation effects. The total nitrogen removal rate was 93%, and the reduction in wastewater turbidity was not significant. This indicates that the cross-linking step is crucial for achieving the multifunctionality of the composite carbon source.

[0044] Comparative Example 4 Apple pomace with a pectin content of 12% was used, and other conditions were the same as those in Example 1.

[0045] The composite carbon sources prepared in the above different embodiments and comparative examples were tested for performance parameters such as COD content and specific surface area, and were used for the treatment of simulated sewage of the same batch. The total nitrogen removal rate and turbidity reduction rate in the sewage after treatment were tested, and the results were shown in the following table.

[0046] The simulated sewage was prepared as follows: Weigh 500 mg of glucose, 150 mg of potassium nitrate, and 30 mg of potassium dihydrogen phosphate and dissolve them in 1 L of distilled water. The initial COD is 780 mg / L, the total nitrogen is 35 mg / L, and the turbidity is 850 NTU.

[0047] Processing Flow Take 500 mL of simulated sewage in a 1 L conical flask and adjust the pH to 7.0 ± 0.5; Add 100 mg of composite carbon source (dosage 200 mg / L) and replace the air in the bottle with nitrogen for 30 seconds to create an anaerobic environment; Place in a 30°C constant temperature water bath shaker and shake at 150 rpm for 24 h; After the reaction was completed, the mixture was allowed to stand for 30 min and the supernatant was taken to determine the total nitrogen and turbidity.

[0048]

[0049] The turbidity reduction rates of Examples 1-3 reached 80-88.2%, which were significantly higher than that of Comparative Example 1 (62.4%), demonstrating that the synergistic flocculation effect of the sodium alginate cross-linked network and bacterial cellulose was the key to significantly reducing turbidity.

[0050] The turbidity reduction rate of Comparative Example 3 (without cross-linking agent) was only 70.6%, indicating that the cross-linking step is indispensable for forming an efficient flocculation network.

[0051] In Example 3, while the total nitrogen removal rate was 97%, the turbidity reduction rate reached 88.2%, reflecting the synergistic effect of the "denitrification-flocculation" dual functions.

[0052] 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, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fermentation method for preparing a high COD composite carbon source, characterized in that , including the following steps: S1. Apple pomace, grape pomace, banana peel, and citrus peel are mixed according to a proportion, crushed, adjusted to a moisture content, and sterilized to obtain a pretreated raw material; S2, performing staged fermentation on the pretreated raw material, firstly producing ethanol by anaerobic fermentation, and then converting it into acetic acid and synthesizing bacterial cellulose by aerobic fermentation; S3, adding a complex enzyme to the fermentation product for enzymatic hydrolysis, and then adding a cross-linking agent to form a gel network; S4. Drying and crushing the gel network to obtain a high COD composite carbon source.

2. The fermentation preparation method according to claim 1, wherein The weight percentages of the raw materials are: 30-40% apple pomace, 20-30% grape pomace, 20-30% banana peel, and 10-20% citrus peel.

3. The fermentation preparation method according to claim 1, wherein In step S1, the particle size after crushing is 0.5-1 mm, the moisture content is adjusted to 60-70%, and the sterilization condition is high-pressure steam sterilization at 121° C. for 20 minutes.

4. The fermentation preparation method according to claim 1, wherein In step S2, the anaerobic fermentation uses cerevisiae and is fermented at 30°C under sealed conditions for 48 hours; the aerobic fermentation uses a mixed strain of Acetobacter xylinum and cellulolytic bacteria and is fermented at 37°C and 150 rpm in a shaking table for 72 hours, and the inoculation amount of the mixed strain is 8-12% of the raw material mass.

5. The fermentation preparation method according to claim 1, wherein In step S3, the complex enzyme includes cellulase and pectinase, and the addition amounts are 100-200 U / g raw material and 50-100 U / g raw material respectively. The enzymatic hydrolysis temperature is 50° C., the time is 12 h, and the cellulose degradation rate is controlled at 20-30%.

6. The fermentation preparation method according to claim 1, wherein In step S3, the crosslinking agent is a combination of sodium alginate and calcium chloride, the amount of sodium alginate added is 0.5-1% of the raw material mass, the amount of calcium chloride added is 0.2-0.5%, the crosslinking temperature is 60° C., and the time is 30 minutes.

7. The fermentation preparation method according to claim 1, wherein In step S4, the drying method is vacuum freeze drying, the conditions are -40°C, 10Pa, the drying time is 24h, and the particle size after crushing is 80-100 mesh.

8. The fermentation preparation method according to claim 1, wherein During the staged fermentation process, the ethanol concentration generated in the anaerobic stage is 5-8 g / L, the acetic acid concentration in the aerobic stage is 3-5 g / L, and the bacterial cellulose growth amount is 15-25% of the raw material mass.

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