Saccharide sodium acetate composite carbon source for enhanced denitrification in sewage and wastewater treatment

Abstract

The invention relates to the technical field of sewage treatment, in particular to a saccharide sodium acetate composite carbon source for enhanced denitrification in sewage and wastewater treatment. The composite carbon source is prepared by compounding starch-embedded saccharides, modified sodium acetate and trace elements consisting of iron, boron, selenium and molybdenum, the starch-embedded saccharides are prepared by gelatinizing and drying processes, and the modified sodium acetate is prepared by esterification reaction of sodium acetate and unsaturated alcohol. According to the composite carbon source, heterotrophic infectious microbe competition is inhibited through modified sodium acetate, slow-release supply of the carbon source is realized through starch embedding saccharides, and the denitrification key enzyme activity is activated by microelements, so that the problems of low denitrification efficiency, carbon source waste and high sludge yield of a traditional carbon source are solved through synergism of the three. The preparation process is simple, the raw materials are easy to obtain, the total nitrogen removal effect can be remarkably improved, the treatment cost is reduced, and the catalyst is suitable for denitrification nitrogen removal treatment of various water bodies such as municipal sewage and industrial wastewater and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment. Background Technology

[0002] In the field of wastewater treatment and water purification, the removal of nitrogen pollution (such as ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen) is one of the core tasks for improving eutrophication and ensuring water environment safety. Denitrification, in particular, utilizes denitrifying bacteria to remove nitrate nitrogen (NO3). - -N) and nitrite nitrogen (NO2) - The key process in denitrification is the reduction of nitrogen (N-N) to nitrogen (N2), which requires a sufficient amount of organic carbon source as an electron donor. The type, availability, and utilization efficiency of the carbon source directly determine the rate and cost of denitrification. Currently, commonly used carbon sources for denitrification in the industry are mainly divided into two categories: sugars (such as monosaccharides and disaccharides like glucose, lactose, sucrose, xylose, and arabinose) and small molecule organic acids (such as sodium acetate and sodium formate). However, both have significant drawbacks in practical applications, making it difficult to balance denitrification efficiency, carbon source utilization, and system stability.

[0003] Easily degradable sugars such as glucose, lactose, and sucrose are widely used due to their simple structure and low price. However, their easy degradation makes them a preferred carbon source for heterotrophic bacteria (Bacillus, Enterobacteriaceae, etc.) in wastewater, directly leading to carbon waste and a significant increase in sludge volume. These monosaccharides or disaccharides have simple chemical structures and can be directly absorbed and utilized by microorganisms without complex enzymatic hydrolysis. However, heterotrophic bacteria commonly found in wastewater (such as non-denitrifying strains of Bacillus, Escherichia coli, and Pseudomonas) have a much higher affinity for glucose than denitrifying bacteria. These heterotrophic bacteria have extremely short growth and reproduction cycles, much faster than denitrifying bacteria. After carbon source addition, they rapidly initiate metabolism, preferentially consuming sugars for self-proliferation, resulting in insufficient available effective carbon sources for denitrifying bacteria. Simultaneously, since the main component of sludge is microbial cells, and the cell yield of heterotrophic bacteria is much higher than that of denitrifying bacteria, this means... This means that, with the same amount of carbon source added, the glucose consumed by the bacteria will be converted into a large amount of excess sludge. The surge in sludge will not only increase the sludge disposal cost of the wastewater treatment system, but will also lead to a chain of problems such as a shortened sludge age in the denitrification tank and intensified competition for dissolved oxygen: Excessive sludge will accelerate the accumulation in the sedimentation tank, forcing the system to increase the sludge discharge frequency, causing denitrifying bacteria to be unable to establish themselves stably due to insufficient sludge age; at the same time, the aerobic respiration of heterotrophic bacteria will consume the limited dissolved oxygen in the water, destroy the anoxic environment required for denitrification, further inhibit the activity of denitrifying bacteria, and form a vicious cycle of carbon source waste, sludge surge, and decreased nitrogen removal efficiency.

[0004] Sodium acetate, due to its rapid decomposition in water, is often used in combination with carbohydrate carbon sources. Its rapid decomposition allows for a quickly achieved high C / N ratio in water, thus rapidly initiating the denitrification process. However, this process faces the same problems as carbohydrate carbon sources: some heterotrophic bacteria compete with denitrifying bacteria for carbon sources, leading to reduced carbon source utilization and increased sludge production. Simultaneously, during denitrification, sodium acetate is decomposed by microorganisms into acetate and sodium ions. Acetate serves as a carbon source in the denitrification reaction. The denitrification process relies on the synergistic action of key enzyme systems such as nitrate reductase, nitrite reductase, and nitric oxide reductase. The activity of these enzymes is extremely sensitive to the ionic environment; sodium ions compete with metal ions at the enzyme's active site for binding sites, causing changes in the enzyme's spatial conformation and loss of catalytic function. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and propose a sodium acetate composite carbon source for enhanced denitrification of sugars in sewage and wastewater treatment.

[0006] To achieve the above objectives, the present invention provides a sodium acetate composite carbon source for enhanced denitrification of wastewater, comprising the following raw materials in parts by weight: starch-encapsulated sugars: 60-70 parts, modified sodium acetate: 30-40 parts, and trace elements: 0.5-1 parts.

[0007] Preferably, the starch-encapsulated sugars are selected from one or more of glucose, sucrose, lactose, fructose, xylose, and arabinose.

[0008] Preferably, the method for preparing the starch-encapsulated sugars is as follows: Add corn starch to deionized water and stir for 30-60 minutes to obtain a corn starch suspension. Then place it in a water bath and heat it to 70-80℃, stirring continuously for 10-20 minutes to obtain gelatinized starch. Cool the gelatinized starch to 50-60℃, add sugars, and stir at 500-700 rpm for 20-40 minutes to obtain a mixed gelatinized material. Pour the mixed gelatinized material into a flat mold, level it, and place it in an oven at 40-50℃ for low-temperature drying for 8-12 hours to obtain a solidified block. Then crush it and pass it through a 20-mesh sieve to obtain starch-encapsulated sugars.

[0009] Preferably, the corn starch, deionized water and sugar are in a weight ratio of 1:5-10:0.7-0.9.

[0010] Preferably, the modified sodium acetate is prepared as follows: Under nitrogen protection, sodium acetate, methylpropenol, and toluene were added to a reaction vessel equipped with a water separator. Concentrated sulfuric acid was added with stirring, and the temperature was raised to 110-120℃. The reaction was stirred for 4-8 hours, cooled to room temperature, and the pH was adjusted to neutral with saturated sodium bicarbonate. The mixture was washed three times with deionized water, dried with anhydrous sodium sulfate, filtered, and the filtrate was concentrated under reduced pressure to recover toluene. The crude product was distilled under normal pressure, and the fraction collected at 85℃ yielded modified sodium acetate. The chemical reaction equation is as follows: The product was characterized by 1H NMR.

[0011] Preferably, the molar ratio of sodium acetate to methacrylate is 1:0.8-1.

[0012] Preferably, the sodium acetate, toluene, and concentrated sulfuric acid are in a weight ratio of 1:8-12:0.01-0.03, and the concentration of the concentrated sulfuric acid is 98%.

[0013] Preferably, the trace elements refer to a mixture of two or more of ferrous sulfate, boric acid, sodium selenite, and sodium molybdate.

[0014] Furthermore, the present invention also provides a method for preparing the above-mentioned sodium acetate composite carbon source for enhanced denitrification of wastewater treatment, comprising the following steps: starch encapsulating sugars and trace elements, mixing them evenly, adding modified sodium acetate while stirring at 400-600 rpm, and maintaining stirring for 10-20 min to obtain the sodium acetate composite carbon source for enhanced denitrification of wastewater treatment.

[0015] Preferably, the mechanism of action of the sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to the present invention is as follows: When a composite carbon source is added to the wastewater to be treated, both heterotrophic bacteria (such as Bacillus and Enterobacteriaceae strains) and denitrifying bacteria (such as Pseudomonas and Paracoccus denitrifying strains) present in the wastewater can secrete esterases (heterotrophic bacteria mainly secrete carboxylesterases, while denitrifying bacteria mainly secrete acetylesterases). Both types of esterases can catalyze the hydrolysis of the ester bonds in the modified sodium acetate molecule, generating two core active components: acetic acid and methylpropenol. This hydrolysis reaction conforms to the general mechanism of esterase catalysis: the active site of the esterase binds to the ester group oxygen atom of the modified sodium acetate through hydrogen bonds, while the serine residue of the active site attacks the carbonyl carbon of the ester bond to form an acyl-enzyme intermediate. Subsequently, water molecules attack the intermediate to complete the hydrolysis, releasing acetic acid and methylpropenol, thus regenerating the enzyme molecule.

[0016] As an antibacterial active ingredient, methyl allyl alcohol mainly disrupts the physiological functions of heterotrophic bacteria through two pathways: (1) Inhibition of protein synthesis: The unsaturated double bond (C=C) of methacryl alcohol can bind to the 16S rRNA of the 30S subunit of the heterotrophic bacteria ribosome, blocking the tRNA from entering the A site (aminoacyl site) of the ribosome, causing the amino acids to be unable to connect in the codon sequence of the mRNA to form a polypeptide chain. The protein synthesis rate of heterotrophic bacteria is extremely fast. The inhibition of ribosome function will cause them to stop proliferating rapidly due to the inability to synthesize structural proteins and enzyme proteins, and even die. (2) Disruption of cell membrane permeability: The hydroxyl group (-OH) of methacryl alcohol can form hydrogen bonds with the phospholipid bilayer of the heterotrophic bacterial cell membrane. At the same time, its hydrophobic carbon chain inserts into the intermolecular space of phospholipid molecules, disrupting the ordered structure of the cell membrane and increasing its permeability. After the cell membrane integrity is disrupted, important substances such as potassium ions and nucleotides leak out in large quantities, while harmful substances from the outside (such as heavy metal ions in sewage) can easily enter, ultimately leading to an imbalance in cell osmotic pressure and cell lysis. The tolerance of denitrifying bacteria to methyl allyl alcohol stems from their unique metabolic and structural characteristics, which significantly differ from heterotrophic bacteria. (1) Metabolic conversion ability of methacryl alcohol: Denitrifying bacteria (such as Pseudomonas) can secrete dehydrogenases extracellularly to oxidize methacryl alcohol to methacrylic acid, and further decompose it into acetyl coenzyme A through the β-oxidation pathway. Finally, it participates in denitrification metabolism as a carbon source. That is, denitrifying bacteria can convert antibacterial components into their own nutrients, while heterotrophic bacteria lack such extracellular metabolic enzyme systems and cannot degrade methacryl alcohol. They can only passively bear its toxicity. (2) Stability of cell membrane structure: The content of unsaturated fatty acids in the cell membrane of denitrifying bacteria is lower than that of heterotrophic bacteria, and it contains more cyclopropane fatty acids, which makes the cell membrane more rigid and makes it difficult for methylpropene alcohol to insert into the phospholipid bilayer and destroy the structure. At the same time, the efflux pump proteins on its cell membrane (such as the MexAB-OprM system) can actively expel methylpropene alcohol that has entered the cell, reducing the intracellular toxic concentration.

[0017] While methacrylic acid inhibits heterotrophic bacteria, denitrifying bacteria achieve efficient nitrogen removal through rapid utilization of the initial carbon source and continuous supply of the slow-release carbon source. Acetic acid, produced by the hydrolysis of modified sodium acetate, is the preferred carbon source for denitrifying bacteria. Acetic acid transport proteins (such as ActP protein) on the cell membrane of denitrifying bacteria can efficiently recognize and transport acetic acid into the cell. Acetic acid is rapidly converted into acetyl-CoA intracellularly, and through the tricarboxylic acid cycle, it generates NADH and FADH2, providing electron donors for the denitrification process. At this time, heterotrophic bacteria, inhibited by methyl allyl alcohol, cannot compete for acetic acid. Denitrifying bacteria can rapidly initiate the denitrification reaction within 1-2 hours after addition, initially reducing nitrate nitrogen to nitrite nitrogen. The starch in the composite carbon source encapsulates sugars, which gradually release sugars (glucose, sucrose, etc.) into the wastewater, providing a continuous carbon source for denitrifying bacteria. (1) The starch-encapsulated structure gradually swells under the hydration of sewage. The α-amylase and saccharifying enzyme secreted by denitrifying bacteria can catalyze the hydrolysis of starch glycosidic bonds and gradually release monosaccharides such as glucose. This process is slow and controllable, avoiding the instantaneous excessive release of sugars.

[0018] (2) At this time, the heterotrophic bacteria have been inhibited by methyl allyl alcohol. Even if a few heterotrophic bacteria are not inhibited, since the heterotrophic bacteria absorb and utilize carbon sources mainly in the form of small-molecule monosaccharides, they are absorbed into the cell and then decomposed and metabolized by intracellular enzymes. Starch, a polysaccharide, has a larger molecular structure and cannot be directly absorbed and utilized by heterotrophic bacteria. Therefore, the starch-encapsulated sugars are protected from competitive utilization, ensuring that nitrate nitrogen and nitrite nitrogen are continuously reduced to nitrogen gas (N2).

[0019] The beneficial effects of this invention are: 1. This invention utilizes the antibacterial properties of modified sodium acetate to effectively inhibit the proliferation of heterotrophic bacteria in wastewater, creating a non-competitive growth environment for denitrifying bacteria. Simultaneously, the acetic acid produced by the hydrolysis of modified sodium acetate can rapidly provide energy for denitrifying bacteria. Combined with the carbon source continuously released from starch-encapsulated sugars, this ensures the continuous and efficient metabolism of denitrifying bacteria. The added trace elements can specifically activate the activity of key enzymes such as nitrate reductase and nitrite reductase, accelerating the conversion of nitrate nitrogen to nitrogen gas, significantly improving denitrification efficiency, and achieving deep removal of total nitrogen from wastewater.

[0020] 2. Traditional carbon sources lack antibacterial properties, easily leading to the proliferation of heterotrophic bacteria and excessive sludge production. The modified sodium acetate in this invention inhibits protein synthesis and cell membrane integrity in heterotrophic bacteria, reducing bacterial cell generation at the source. The slow-release structure of starch-encapsulated sugars prevents instantaneous carbon source overload, reducing secondary bacterial proliferation caused by carbon source waste. Under these dual effects, sludge yield is significantly reduced, not only lowering sludge treatment costs but also reducing the environmental pressure from sludge disposal.

[0021] 3. The dense encapsulation structure of starch-encapsulated sugars used in this invention can avoid the loss caused by rapid release of sugars, allowing the carbon source to be released slowly according to the denitrification requirements, ensuring that denitrifying bacteria can fully absorb and utilize it; the rapid carbon source provided by modified sodium acetate and the slow-release carbon source encapsulated by starch form a tiered supply, which is adapted to the carbon source requirements of different stages of denitrification; at the same time, trace elements optimize the carbon source metabolic pathway of denitrifying bacteria, reduce the conversion of carbon source into ineffective metabolism, significantly improve the carbon source utilization rate, and reduce the amount of carbon source added and the treatment cost.

[0022] 4. The raw materials used in this invention are starch, sugars, sodium acetate, and common trace elements, which are widely available and inexpensive. Starch-encapsulated sugars are prepared through conventional gelatinization and drying processes. The esterification reaction conditions of the modified sodium acetate are mild and easily controlled. The overall preparation process requires no complex equipment, is simple to operate, and has low energy consumption, making it suitable for large-scale industrial production. Furthermore, the composite carbon source exhibits strong stability, is easy to store and transport, and the dosage can be flexibly adjusted according to wastewater quality, further reducing application costs.

[0023] 5. The composite carbon source of this invention exhibits excellent tolerance to fluctuations in wastewater quality. Whether it is municipal wastewater or industrial wastewater (such as food processing or aquaculture wastewater), stable denitrification can be achieved by adjusting the dosage. The antibacterial effect of modified sodium acetate is unaffected by common impurities in wastewater. Starch-encapsulated sugars can stably release carbon sources under different pH and temperature conditions. Trace elements can be adapted to the needs of different denitrifying bacteria communities, making it suitable for denitrification units in various wastewater treatment systems, with flexible and diverse application scenarios. Attached Figure Description

[0024] Figure 1 The 1H NMR spectrum of the modified sodium acetate prepared in Example 5 of this invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0026] Preparation Example 1: The specific preparation method of starch-encapsulated sugars is as follows: Add 100g of corn starch to 500g of deionized water and stir for 30 minutes to obtain a corn starch suspension. Then place it in a water bath and heat it to 70℃, stirring continuously for 10 minutes to obtain gelatinized starch. Cool the gelatinized starch to 50℃ and add 70g of sugar (glucose, sucrose, and lactose mixed in a weight ratio of 1:1:1). Stir at 500rpm for 20 minutes to obtain a mixed gelatinized material. Pour the mixed gelatinized material into a flat mold, smooth it, and place it in a 40℃ oven to dry at a low temperature for 8 hours to obtain a solidified block. Then crush it and pass it through a 20-mesh sieve to obtain starch-encapsulated sugars.

[0027] Preparation Example 2: The specific preparation method of starch-encapsulated sugars is as follows: Add 100g of corn starch to 700g of deionized water and stir for 45min to obtain a corn starch suspension. Then place it in a water bath and heat to 75℃, stirring continuously for 15min to obtain gelatinized starch. Cool the gelatinized starch to 55℃ and add 80g of sugars (glucose, sucrose, lactose, fructose, xylose, and arabinose mixed in a weight ratio of 1:1:1:1:1:1). Stir at 600rpm for 30min to obtain a mixed gelatinized material. Pour the mixed gelatinized material into a flat mold, level it, and place it in a 45℃ oven for low-temperature drying for 10h to obtain a solidified block. Then crush it and pass it through a 20-mesh sieve to obtain starch-encapsulated sugars.

[0028] Preparation Example 3: The specific preparation method of starch-encapsulated sugars is as follows: Add 100g of corn starch to 1kg of deionized water and stir for 60min to obtain a corn starch suspension. Then place it in a water bath, heat to 80℃, and stir continuously for 20min to obtain gelatinized starch. Cool the gelatinized starch to 60℃ and add 90g of sugars (sucrose, fructose, and xylose mixed in a weight ratio of 1:1:1). Stir at 700rpm for 40min to obtain a mixed gelatinized material. Pour the mixed gelatinized material into a flat mold, smooth it, and place it in a 50℃ oven for low-temperature drying for 12h to obtain a solidified block. Then crush it and pass it through a 20-mesh sieve to obtain starch-encapsulated sugars.

[0029] Preparation Example 4: The specific preparation method of modified sodium acetate is as follows: Under nitrogen protection, 100g of sodium acetate, 70.33g of methylpropenol and 800g of toluene were added to a reaction vessel equipped with a water separator. 1g of 98% concentrated sulfuric acid was added with stirring. The temperature was raised to 110℃ and the reaction was stirred for 4 hours. After cooling to room temperature, the pH was adjusted to neutral with saturated sodium bicarbonate. The mixture was washed three times with deionized water, dried with anhydrous sodium sulfate, filtered, and the filtrate was concentrated under reduced pressure to recover toluene. The crude product was distilled under normal pressure, and the fraction collected at 85℃ was used to obtain modified sodium acetate.

[0030] Preparation Example 5: The specific preparation method of modified sodium acetate is as follows: Under nitrogen protection, 100g of sodium acetate, 79.12g of methylpropenol and 1kg of toluene were added to a reaction vessel equipped with a water separator. 2g of 98% concentrated sulfuric acid was added with stirring. The temperature was raised to 115℃ and the reaction was stirred for 6 hours. After cooling to room temperature, the pH was adjusted to neutral with saturated sodium bicarbonate. The mixture was washed three times with deionized water, dried with anhydrous sodium sulfate, filtered, and the filtrate was concentrated under reduced pressure to recover toluene. The crude product was distilled under normal pressure, and the fraction collected at 85℃ was used to obtain modified sodium acetate.

[0031] Preparation Example 6: The specific preparation method of modified sodium acetate is as follows: Under nitrogen protection, 100g of sodium acetate, 87.91g of methylpropenol, and 1.2kg of toluene were added to a reaction vessel equipped with a water separator. 3g of 98% concentrated sulfuric acid was added with stirring. The temperature was raised to 120℃, and the reaction was stirred for 8 hours. After cooling to room temperature, the pH was adjusted to neutral with saturated sodium bicarbonate. The mixture was washed three times with deionized water, dried with anhydrous sodium sulfate, filtered, and the filtrate was concentrated under reduced pressure to recover toluene. The crude product was distilled under normal pressure, and the fraction collected at 85℃ was used to obtain modified sodium acetate.

[0032] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 2 is that the sugars are not coated with starch. The specific preparation method is as follows: The specific preparation method for starch-encapsulated sugars is as follows: 80g of sugars (made by mixing glucose, sucrose, lactose, fructose, xylose and arabinose in a weight ratio of 1:1:1:1:1:1) were stirred at 600rpm for 30min to obtain a sugar mixture.

[0033] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 2 is that corn starch and sugars are physically mixed to prepare a starch-sugar mixture. The specific preparation method is as follows: The specific preparation method for starch-encapsulated sugars is as follows: Mix 100g of corn starch and 80g of sugars (glucose, sucrose, lactose, fructose, xylose, and arabinose in a weight ratio of 1:1:1:1:1:1) at 600rpm for 30min to obtain a starch-sugar mixture.

[0034] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 2 is that only glucose is used as the carbohydrate.

[0035] Example 1: A specific preparation method of a sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment is as follows: 60g of starch-encapsulated sugars prepared according to Preparation Example 1 and 0.5g of trace elements (ferrous sulfate and boric acid mixed in a weight ratio of 1:1) were mixed evenly. 30g of modified sodium acetate prepared according to Preparation Example 4 was added while stirring at 400rpm. Stirring was maintained for 10min to obtain a sodium acetate composite carbon source for enhanced denitrification of wastewater.

[0036] Example 2: A specific preparation method of a sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment is as follows: 65g of starch-encapsulated sugars prepared according to Preparation Example 2 and 0.75g of trace elements (ferrous sulfate, boric acid, sodium selenite, and sodium molybdate mixed in a weight ratio of 1:1:1:1) were mixed evenly. 35g of modified sodium acetate prepared according to Preparation Example 5 was added while stirring at 500rpm. Stirring was maintained for 15min to obtain a sodium acetate composite carbon source for enhanced denitrification of wastewater.

[0037] Example 3: A specific preparation method of a sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment is as follows: 70g of starch-encapsulated sugars prepared according to Preparation Example 3 and 1g of trace elements (sodium selenite and sodium molybdate mixed in a weight ratio of 1:1) were mixed evenly. 40g of modified sodium acetate prepared according to Preparation Example 6 was added while stirring at 600rpm. Stirring was maintained for 20min to obtain a sodium acetate composite carbon source for enhanced denitrification of wastewater.

[0038] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the starch-coated sugars prepared according to Preparation Example 2 are replaced with the sugar mixture prepared according to Comparative Preparation Example 1.

[0039] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the starch-coated sugars prepared according to Preparation Example 2 are replaced with the starch-sugar mixture prepared according to Comparative Preparation Example 2.

[0040] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the starch-coated sugar prepared according to Comparative Example 2 is replaced with the starch-coated sugar prepared according to Comparative Example 3.

[0041] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that the starch-coated sugars prepared according to Preparation Example 2 are replaced with glucose.

[0042] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that the modified sodium acetate prepared according to Preparation Example 5 is replaced with sodium acetate.

[0043] Performance testing: 1. Effects of modified sodium acetate on the activity of heterotrophic bacteria and denitrifying bacteria in wastewater: The modified sodium acetate prepared in Preparation Examples 4-6 was used as the experimental group, and sodium acetate was used as the control group. The heterotrophic bacteria selected were *Escherichia coli* ATCC 25922, *Bacillus subtilis* ATCC 6633, and *Enterobacter cloacae* ATCC 13047. The denitrifying bacteria selected were *Pseudomonas denitrificans* ATCC 13867, *Paracoccus denitrificans* ATCC 19367, and *Thauera aromatica* DSM 6984. These bacteria were cultured for 24 hours in suitable medium (LB medium for heterotrophic bacteria and denitrifying medium for denitrifying bacteria) under suitable conditions (heterotrophic bacteria: 37°C, 180 rpm shaking culture; denitrifying bacteria: 30°C anaerobic culture) using the corresponding medium. The cultures were then diluted to OD using the appropriate medium. 600 =0.5, the effect of addition amounts of 30 μg / ml, 50 μg / ml, 100 μg / ml and 200 μg / ml on the activity of the above heterotrophic bacteria and denitrifying bacteria was tested in the experimental group and the control group, respectively. The addition amount refers to the amount of modified sodium acetate or sodium acetate used in the experimental group and the control group. The inhibition rate of heterotrophic bacteria = [(control group OD 600 -Experimental group OD 600 ) / Control group OD 600 The inhibition rate was 30%-70% for effective inhibition, >70% for strong inhibition, and <30% for no inhibition. The time to reach the maximum inhibition effect was recorded. The inhibition rate of denitrifying bacteria was expressed as the ratio of the nitrate reduction rate of the experimental group to the nitrate reduction rate of the control group. The experimental time was 8 hours after the addition of modified sodium acetate. The inhibition rate of denitrifying bacteria after 8 hours was calculated as [(nitrate reduction rate of control group - nitrate reduction rate of experimental group) / nitrate reduction rate of control group] × 100%. The experimental results are shown in Table 1-6.

[0044] 2. Total Nitrogen Removal Rate Test: The selected wastewater to be treated first entered the sedimentation tank, where the colloids and fine suspended solids were coagulated into flocs under the action of coagulants. After the flocs were separated and removed, the wastewater entered the aerated biological filter for carbonization and nitrification reactions. The effluent from the aerated biological filter then entered the denitrification filter. The total nitrogen content of the water was tested at this time, C1 = 48.53 mg / L. Denitrification was carried out with the assistance of a composite carbon source to remove the total nitrogen in the water. The composite carbon sources prepared in Examples 1-3 and Comparative Examples 1-5 were added to the denitrification filter at a ratio of 500 mg of composite carbon source per liter of wastewater. After 1 day, the treatment was completed, and the total nitrogen content C2 was tested. The removal rate was calculated as C1 - C2 / C1 × 100%. The experimental results are shown in Table 7.

[0045] 3. Sludge Yield Test: The composite carbon sources prepared in Examples 1-3 and Comparative Examples 1-5 were added to the above-mentioned denitrification filter at a ratio of 500 mg of composite carbon source per liter of wastewater. The filter was run continuously for 72 hours, during which the mixed liquor suspended solids concentration (MLSS) in the reactor was recorded every 24 hours. After the reaction, the remaining sludge was dewatered using a plate and frame filter press. The weight of the dewatered sludge was weighed, and the sludge yield (g·VSS) corresponding to the unit COD removal was calculated. -1 / g·COD -1 The experimental results are shown in Table 7.

[0046] 4. Carbon Source Utilization Test: In the above denitrification reaction system, the COD concentration of water samples in Examples 1-3 and Comparative Examples 1-5 was determined using the potassium dichromate method at the beginning and end of the reaction, and the COD removal rate was calculated. Simultaneously, combined with the total nitrogen removal rate, the COD removal rate was calculated based on the stoichiometric relationship of the denitrification reaction (5COD - 2NO3). - The theoretical oxygen demand was calculated using the COD removal rate (actual COD removal / theoretical COD demand) and then the carbon source utilization rate (actual COD removal / theoretical COD demand × 100%) was obtained. The experimental results are shown in Table 7.

[0047] 5. Denitrification Rate Test: The selected wastewater to be treated first enters the sedimentation tank, where the colloids and fine suspended solids are coagulated into flocs under the action of coagulant. After the flocs are separated and removed, the wastewater enters the aerated biological filter for carbonization and nitrification reactions. The effluent from the aerated biological filter then enters the denitrification filter. The nitrate nitrogen concentration C1 in the water is measured at this time, which is 30.47 mg / L. Denitrification is carried out with the assistance of a composite carbon source to remove nitrate nitrogen from the water. The composite carbon sources prepared in Examples 1-3 and Comparative Examples 1-5 are added to the denitrification filter at a ratio of 500 mg of composite carbon source per liter of wastewater. After 1 day, the treatment is completed, and the nitrate nitrogen concentration C2 is measured. The removal rate is calculated as C1 - C2 / C1 × 100%. The experimental results are shown in Table 7.

[0048] Table 1. Effects of modified sodium acetate on the activity of Escherichia coli in wastewater.

[0049] Table 2. Effects of modified sodium acetate on the activity of Bacillus subtilis in wastewater.

[0050] Table 3. Effects of modified sodium acetate on the activity of common Enterobacteriaceae in wastewater.

[0051] Table 4. Effects of modified sodium acetate on the activity of Pseudomonas aeruginosa in wastewater.

[0052] Table 5. Effects of modified sodium acetate on the activity of denitrifying paracocci in wastewater.

[0053] Table 6. Effects of modified sodium acetate on the activity of Tauella bacteria in wastewater.

[0054] Table 7 Tests of total nitrogen removal rate, sludge production rate, carbon source utilization rate, and denitrification rate

[0055] Performance Analysis: As can be seen from the experimental data in the table, Examples 1-3, with their synergistic system of starch-encapsulated sugars, modified sodium acetate, and trace elements, are significantly better than the comparative examples in terms of total nitrogen removal, sludge yield control, carbon source utilization, and denitrification efficiency. Among them, Example 2 exhibits the best comprehensive performance due to its most balanced component combination and optimized process parameters.

[0056] In Example 2, the modified sodium acetate used had a suitable reaction temperature and time, and the amount of methacryl alcohol bound was sufficient and of high purity. After addition, it could be rapidly hydrolyzed to produce acetic acid and methacryl alcohol. Methacryl alcohol can effectively inhibit the protein synthesis of heterotrophic bacteria and destroy their cell membranes, avoiding competition for carbon sources from other bacteria. Acetic acid, as the preferred carbon source for denitrifying bacteria, can be rapidly converted into an electron donor through transport proteins on the cell membrane of denitrifying bacteria, ensuring that the denitrification reaction starts in a short time. At the same time, denitrifying bacteria can convert methacryl alcohol into their own nutrients through metabolism, and their cell membrane structure is stable and their efflux pump function is active, so they are not affected by the toxicity of methacryl alcohol. In Example 2, the starch-encapsulated sugars are a mixture of various sugars, which are then moderately gelatinized and dried to form a dense encapsulated structure. In wastewater, the sugars can slowly swell and gradually release, avoiding the proliferation of miscellaneous bacteria caused by excessive instantaneous release of sugars. At the same time, as a polysaccharide, starch cannot be directly absorbed by heterotrophic bacteria. Even if there are a small number of uninhibited miscellaneous bacteria, they are unlikely to utilize the encapsulated sugars, ensuring a continuous carbon source supply to denitrifying bacteria. The amylase secreted by denitrifying bacteria can further catalyze the hydrolysis of starch, ensuring the continuity of carbon source supply and supporting the continuous denitrification reaction. Example 2 uses a mixture of four trace elements to specifically activate key enzyme systems in the denitrification process: ferrous sulfate and sodium molybdate can enhance the activity of nitrate reductase and nitrite reductase, accelerating the conversion of nitrate nitrogen to nitrogen gas; boric acid can promote the synthesis of denitrifying bacteria cell membranes and enhance cell stability; sodium selenite participates in the formation of enzyme active sites, further optimizing enzyme catalytic efficiency. The synergistic effect of multiple trace elements significantly improves the conversion efficiency of denitrifying bacteria to carbon sources and increases carbon source utilization. In Example 2, the proportions of starch-encapsulated sugars, modified sodium acetate, and trace elements, as well as the preparation process, were all within the optimal range: the proportion of starch-encapsulated sugars was moderate, providing a sufficient and continuous carbon source without causing insufficient initial carbon source due to excessive encapsulation; the dosage of modified sodium acetate balanced the antibacterial effect with the carbon source supply, avoiding excessive or insufficient antibacterial activity; the amount of trace elements added was reasonable, activating enzyme activity without causing ionic toxicity; and the components were thoroughly mixed during the preparation process to ensure synergistic function, achieving simultaneous optimization of denitrification, sludge control, and carbon source utilization.

[0057] In Comparative Example 1, unencapsulated free sugars were used instead of starch-encapsulated sugars. Without the physical barrier protection of starch, the sugars were rapidly released after addition and preferentially consumed by heterotrophic bacteria with a stronger affinity for carbon sources, significantly reducing the carbon source available to denitrifying bacteria. At the same time, the free sugars accelerated the proliferation of heterotrophic bacteria, leading to a significant increase in sludge production. Furthermore, the aerobic respiration of these bacteria consumed dissolved oxygen, disrupting the anoxic environment for denitrification. Ultimately, the total nitrogen removal rate and carbon source utilization rate were much lower than in Example 2, while the sludge production rate was much higher. Comparative Example 2 only physically mixes corn starch and sugars without gelatinization, which makes it impossible to form a dense encapsulation network. The sugars are easily leaked in the sewage and utilized by miscellaneous bacteria. Although it has a certain inhibitory effect compared to free sugars, the encapsulation effect is far worse than the gelatinized encapsulation structure of Example 2. Therefore, its total nitrogen removal rate and carbon source utilization rate are lower than those of Example 2, while its sludge yield is higher than that of Example 2. In Comparative Example 3, only glucose was used as the starch-encapsulated sugar, while in Example 2, a mixture of sugars was used. Glucose alone has poor compatibility with denitrifying bacteria and cannot meet the carbon source preferences of different denitrifying bacteria, resulting in insufficient synergistic denitrification capacity of the bacteria. At the same time, the single carbon source also limits the metabolic diversity of denitrifying bacteria, resulting in a lower denitrification rate and carbon source conversion efficiency than in Example 2. The total nitrogen removal rate and denitrification rate are correspondingly reduced, while the sludge yield is slightly higher than in Example 2 due to insufficient carbon source utilization. Comparative Example 4 directly replaced starch with glucose to encapsulate sugars. It lacked both the slow-release effect of the encapsulation structure and the protective effect of starch against competition from other bacteria. The glucose was almost completely consumed by other bacteria, and the denitrifying bacteria could only utilize a small amount of the remaining carbon source. The proliferation of a large number of other bacteria also led to a significant increase in sludge production and intensified competition for dissolved oxygen, which seriously damaged the denitrification environment. Therefore, its total nitrogen removal rate, carbon source utilization rate and denitrification rate were the lowest among all groups, while its sludge production rate was the highest. The performance difference from Example 2 was the most significant. In Comparative Example 5, unmodified sodium acetate was used instead of modified sodium acetate. Due to the lack of the antibacterial effect of methacryl alcohol, heterotrophic bacteria could freely compete with denitrifying bacteria for carbon sources, and the absorption rate of carbon sources by heterotrophic bacteria was faster, resulting in insufficient carbon sources for denitrifying bacteria. At the same time, the sodium ions produced by the decomposition of unmodified sodium acetate would compete with the metal ions in the active center of denitrifying enzymes for binding sites, inhibiting enzyme activity. Therefore, its total nitrogen removal rate, carbon source utilization rate and denitrification rate were all lower than those of Example 2, while the sludge yield was higher than that of Example 2 due to the proliferation of heterotrophic bacteria.

[0058] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment, characterized in that, The ingredients include the following parts by weight: starch-encapsulated sugars: 60-70 parts, modified sodium acetate: 30-40 parts, and trace elements: 0.5-1 parts.

2. The sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to claim 1, characterized in that, The starch-encapsulated sugars are selected from one or more of glucose, sucrose, lactose, fructose, xylose, and arabinose.

3. The sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to claim 1, characterized in that, The method for preparing the starch-encapsulated sugars is as follows: Add corn starch to deionized water and stir for 30-60 minutes to obtain a corn starch suspension. Then place it in a water bath and heat it to 70-80℃, stirring continuously for 10-20 minutes to obtain gelatinized starch. Cool the gelatinized starch to 50-60℃, add sugars, and stir at 500-700 rpm for 20-40 minutes to obtain a mixed gelatinized material. Pour the mixed gelatinized material into a flat mold, level it, and place it in an oven at 40-50℃ for low-temperature drying for 8-12 hours to obtain a solidified block. Then crush it and pass it through a 20-mesh sieve to obtain starch-encapsulated sugars.

4. The sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to claim 3, characterized in that, The corn starch, deionized water, and sugars are in a weight ratio of 1:5-10:0.7-0.

9.

5. The sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to claim 1, characterized in that, The modified sodium acetate is prepared as follows: Under nitrogen protection, sodium acetate, methacrylate, and toluene were added to a reaction vessel equipped with a water separator. Concentrated sulfuric acid was added with stirring, the temperature was raised to 110-120℃, and the reaction was stirred for 4-8 hours. After cooling to room temperature, the pH was adjusted to neutral with saturated sodium bicarbonate, and the mixture was washed three times with deionized water. The organic phase was dried with anhydrous sodium sulfate, filtered, and the filtrate was concentrated under reduced pressure to recover toluene. The crude product was distilled under normal pressure, and the fraction collected at 85℃ was used to obtain modified sodium acetate.

6. The sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to claim 5, characterized in that, The sodium acetate and methacrylate are in a molar ratio of 1:0.8-1.

7. The sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to claim 5, characterized in that, The sodium acetate, toluene, and concentrated sulfuric acid are in a weight ratio of 1:8-12:0.01-0.03, and the concentration of the concentrated sulfuric acid is 98%.

8. The sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to claim 1, characterized in that, The trace elements refer to two or more of the following: ferrous sulfate, boric acid, sodium selenite, and sodium molybdate.

9. The method for preparing a sodium acetate composite carbon source for enhanced denitrification of sugars in wastewater treatment according to any one of claims 1-8, characterized in that, Includes the following steps: Starch is used to encapsulate sugars and trace elements, which are then mixed evenly. Modified sodium acetate is added while stirring at 400-600 rpm, and stirring is maintained for 10-20 minutes to obtain a sodium acetate composite carbon source for enhanced denitrification of wastewater.

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