Efficient composite carbon source as well as preparation method and application thereof

Abstract

The invention provides an efficient composite carbon source as well as a preparation method and application thereof, and relates to the technical field of sewage treatment. The efficient composite carbon source comprises the following components in percentage by weight: 35-45% of fatty acid salts, 35-45% of alcohols and the balance of water. The preparation method comprises the following steps: dissolving the fatty acid salt in water, stirring at normal temperature to completely dissolve the fatty acid salt, adding the alcohol, and uniformly stirring to obtain the product. The efficient composite carbon source has the advantages of high denitrification rate, no nitrite nitrogen accumulation phenomenon, good denitrification and dephosphorization effects in actual sewage treatment, stable effluent, low operation cost and small transportation and storage risks.

Description

Technical Field

[0001] The present application relates to the technical field of sewage treatment, and in particular to a high-efficiency composite carbon source and a preparation method and application thereof. Background Art

[0002] Wastewater treatment plants not only need to follow strict emission standards, but also achieve low-carbon operation. The "Pollutant Emission Standards for Urban Wastewater Treatment Plants (Draft for Comments)" stipulates that from July 1, 2016, the total nitrogen (TN) emissions of newly built sewage treatment plants should reach the Class A standard of 15 mg / L, while in areas where eutrophication of water bodies is prominent, this standard is 10 mg / L. This has brought new challenges to the denitrification work of sewage treatment plants. At the same time, the "Technical Specifications for Low-Carbon Operation Evaluation of Sewage Treatment Plants" launched by the China Environmental Protection Industry Association in June 2022 included carbon source consumption and total nitrogen removal rate (TN) in the evaluation indicators, and evaluated the emissions of CH4 and N2O, which further promoted the development of new, efficient and low-cost carbon sources. TN is the main pollution factor affecting effluent water quality.

[0003] Urban domestic sewage in my country usually has a low carbon-nitrogen ratio, which leads to insufficient carbon source in the biological denitrification process, thus limiting the removal efficiency of TN. Therefore, sewage treatment plants often need to add a large amount of carbon source to meet the denitrification needs. At present, AAO and its variant processes are mainly used, in which nitrogen removal mainly occurs in the denitrification stage of the anoxic tank. The "Outdoor Drainage Design Code" (GB50014-2021) requires that the hydraulic retention time (HRT) of the anoxic tank be 2-10 hours, but the actual situation is often less than 4 hours. With the improvement of TN emission standards, under limited HRT conditions, finding a faster and more efficient denitrification carbon source has become the key to upgrading sewage treatment plants.

[0004] Common carbon sources include methanol, sodium acetate and glucose. When methanol is used as a carbon source, the denitrification rate is fast, the operating cost is low and the sludge production is small, but there are long response times, certain toxicity and transportation and storage risks; sodium acetate has the fastest denitrification rate and short response time, but its operating cost is high and the sludge production is also large; while glucose is relatively cheap, but the denitrification rate is slow and it is easy to cause sludge swelling and nitrite nitrogen accumulation. In addition, the use of a single carbon source will lead to a single activated sludge community structure and excessive dependence on external carbon sources. Once the carbon source is stopped or replaced, the denitrification efficiency will drop rapidly. Therefore, it is particularly important to develop efficient, economical and stable composite carbon sources. Summary of the invention

[0005] In order to improve the current problems of low denitrification efficiency and high operating cost of added carbon sources, the present application provides a high-efficiency composite carbon source and a preparation method and application thereof.

[0006] In the first aspect, the present application provides a high-efficiency composite carbon source, which adopts the following technical solution: A high-efficiency composite carbon source comprises the following components by weight percentage: 35%-45% fatty acid salts, 35%-45% alcohols, and the balance water.

[0007] Optionally, the following components are included by weight: 40% fatty acid salts, 40% alcohols, and 20% water.

[0008] Optionally, the fatty acid salts include any one of sodium acetate, sodium propionate, and sodium butyrate.

[0009] Optionally, the alcohol includes any one of methanol, ethanol and glycerol.

[0010] Optionally, the fatty acid salt is sodium propionate, and the alcohol is ethanol.

[0011] Optionally, the specific denitrification rate of the high-efficiency composite carbon source is 29.85-31.05 mg-N / (gMLVSS·h).

[0012] In the second aspect, the present application provides a method for preparing an efficient composite carbon source, using the following technical solution: Prepare the above raw materials, dissolve the fatty acid salts in water, stir at room temperature to make them completely dissolved, then add the alcohol, stir evenly, and obtain the product.

[0013] On the third aspect, the present application provides the application of a high-efficiency composite carbon source for nitrogen and phosphorus removal in sewage treatment.

[0014] In summary, the present application includes at least one of the following beneficial effects: 1. The high-efficiency composite carbon source provided in this application has a faster denitrification rate and a shorter response time, ensuring that the added carbon source is exhausted in the anaerobic and anoxic functional areas as much as possible, avoiding increasing the burden and operating cost of the subsequent aeration system.

[0015] 2. Compared with the traditional single carbon source, the high-efficiency composite carbon source of the present application has a higher denitrification rate, there is no accumulation of nitrite nitrogen, the denitrification and phosphorus removal effects are very good in actual sewage treatment, the effluent is relatively stable, the operating cost is low, and the transportation and storage risks are small.

[0016] 3. The high-efficiency composite carbon source provided in this application is easily degraded by microorganisms and easily utilized by denitrifying bacteria; it is green and environmentally friendly, and has no harm to humans and the environment; the community structure of activated sludge is complex and stable, and it has no strong dependence on external carbon sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1This is a comparison chart of the denitrification effects of sludge after composite carbon source acclimation on single ethanol, single sodium propionate and composite carbon source C; Figure 2 It is a trend chart of the changes in various indicators in the inlet and outlet water of the AOA system with composite carbon source addition; (a) is the change in COD concentration in the inlet and outlet water and the COD removal rate, (b) is the change in the inlet ammonia nitrogen concentration and the outlet nitrate nitrogen concentration, and (c) is the change in the inlet and outlet TP concentration and the TP removal rate. DETAILED DESCRIPTION

[0018] From the following preferred embodiments in conjunction with the accompanying drawings, the above and other purposes, features and advantages of the present invention will be more clearly understood. However, the present invention is not limited to the embodiments disclosed herein and can be modified into different forms. These embodiments are provided to thoroughly explain the present invention and fully convey the spirit of the present invention to those skilled in the art.

[0019] The core of sewage denitrification is to reduce nitrate nitrogen to nitrogen gas. This process involves complex carbon metabolism and nitrogen metabolism reactions. The electrons generated by carbon metabolism enter the electron transport chain through NADH, become electron donors for nitrogen metabolism, and promote the denitrification process. The main pathway of carbon metabolism is the tricarboxylic acid (TCA) cycle. Different types of carbon sources generate acetyl coenzyme A (CoA) through their own activation pathways, then enter the TCA cycle, and are finally oxidized to CO2 and release electrons and energy. The four-step reduction reaction of nitrogen metabolism is: NO3 - →NO2 - →NO→N2O→N2, which requires a large number of electron donors, and these electrons mainly come from carbon metabolism. Different carbon sources have different metabolic pathways and different electron-providing abilities. Electron competition during nitrogen metabolism may lead to intermediate products such as NO2 - and N2O accumulation. Carbon metabolism and nitrogen metabolism are closely linked through the electron transfer system. The type of carbon source directly affects the carbon metabolism of denitrification, and then affects the bacterial community structure and its nitrogen metabolic function. Different carbon sources are often associated with specific community structures and denitrification metabolic pathways. Studying the relationship between various carbon sources in the denitrification process is helpful for the development of composite carbon sources.

[0020] The applicant found in the study that the denitrification rate of composite carbon sources is usually higher than that of single carbon sources, and carbon sources with similar metabolism can increase the denitrification rate, affecting the overall community structure and function of activated sludge. Substances with similar carbon source metabolism have community similarity, and the use of composite carbon sources with similar metabolism can increase the denitrification rate. Common metabolic pathways allow various carbon sources to be interconnected in metabolism, thereby affecting the overall community structure and function of activated sludge.

[0021] On this basis, the applicant found that ethanol belongs to two-carbon organic matter and sodium propionate belongs to three-carbon organic matter, and the metabolic pathways of the two types of carbon sources are significantly different. By taming the sludge with the composite carbon source formed by ethanol and sodium propionate, the denitrification metabolic diversity of the microbial community can be increased, and the denitrification metabolic pathway can be expanded, thereby achieving the effect of increasing the denitrification rate.

[0022] Next, the technical solution of the present invention will be further described through specific embodiments.

[0023] Examples 1-5 Examples 1-5 provide a high-efficiency composite carbon source respectively, and the specific amount thereof is shown in Table 1. The preparation method of the high-efficiency composite carbon source is as follows: Prepare the raw materials according to Table 1, dissolve sodium propionate in water, stir at room temperature to make it completely dissolved, then add ethanol, stir evenly, and obtain the prepared composite carbon source. The numbers of the prepared composite carbon sources are shown in Table 1.

[0024] Table 1 Raw material dosage of Examples 1-5 Example Sodium propionate(g) Ethanol(g) Water(g) Composite carbon source number Example 1 35 45 20 Composite Carbon Source A Example 2 37 43 20 Composite Carbon Source B Example 3 40 40 20 Composite Carbon Source C Example 4 43 37 20 Composite Carbon Source D Example 5 45 35 20 Composite Carbon Source E Example 6 Example 6 is basically the same as Example 3, except that in Example 6, an equal amount of sodium acetate is used to replace sodium propionate, and the obtained composite carbon source is composite carbon source F.

[0025] Example 7 Example 7 is basically the same as Example 3, except that Example 7 uses an equal amount of sodium butyrate instead of sodium propionate, and the resulting composite carbon source is composite carbon source G.

[0026] Example 8 Example 8 is basically the same as Example 3, except that Example 8 uses an equal amount of methanol instead of ethanol, and the resulting composite carbon source is composite carbon source H.

[0027] Experiment 1: Denitrification carbon source acclimation experiment.

[0028] The denitrification carbon source acclimation test was carried out in an SBR reactor with an effective volume of 8L. The drainage ratio was 1:2, 3 cycles were run per day, the sludge age was 30d, and each cycle of the SBR was run for 8h, including water inlet, stirring, sedimentation and water outlet. The program was automatically controlled by a timer: ① Water inlet: During the water inlet period, the carbon source and nitrogen source are added to the reactor through a peristaltic pump. This stage lasts for 10 minutes, and the water inlet rate is 0.4L / min.

[0029] ② Stirring: Denitrification occurs in the reactor during this stage. The denitrification reaction should be fully carried out to ensure the sedimentation of the sludge. The stirring time is 420 minutes.

[0030] ③ Sedimentation: In this stage, the mud and water are separated under static conditions, and the sedimentation time is 40 minutes.

[0031] ④ Water discharge: The supernatant after precipitation is discharged. This stage lasts for 10 minutes, and the drainage volume is 0.4L / min.

[0032] The activated sludge used for denitrification carbon source domestication was inoculated into the SBR reactor. The seed sludge of the activated sludge system was taken from the anoxic tank of the Qinghe Second Reclaimed Water Plant in Beijing. The sludge mixture was concentrated to about 7000 mg / L, and most of the slag and sand in the sludge were filtered out through a 0.5 mm filter before inoculation into the SBR reactor. The initial sludge concentration of the SBR reactor was about 2000 mg / L.

[0033] The composite carbon sources A to E of Examples 1-5 and sodium propionate, ethanol, methanol, glycerol, glucose, sucrose, and starch were used as single carbon sources to perform denitrification acclimation on activated sludge, respectively. The influent COD concentration was 300 mg / L, the influent NO3 - -N concentration is 50mg / L. In addition, phosphorus sources and various trace elements are added to the influent to ensure the growth of microorganisms. After the start of domestication, the effluent COD and nitrate nitrogen concentrations are monitored every day, and the changes in COD and nitrate nitrogen concentrations during the denitrification stage are measured after a certain period. The domestication of the sludge is judged by measuring the denitrification rate, and the domestication cycle and response time of various carbon sources to the activated sludge are determined. The test results are shown in Table 2.

[0034] Table 2 Denitrification carbon source acclimation results It can be seen from the data in Table 2 that, compared with a single carbon source, the composite carbon sources A to E provided in Examples 1-5 have a higher denitrification rate when used in the denitrification carbon source acclimation test.

[0035] Experiment 2: Denitrification batch experiment.

[0036] The main devices used in the denitrification batch test are a 500 mL conical flask and a constant temperature water bath oscillator. In the denitrification batch test, the 500 mL conical flask is sealed with a rubber stopper, and the initial sludge or the acclimated sludge (the ethanol + sodium propionate composite carbon source used is the composite carbon source C provided in Example 3) is put into the flask, and NO3 is prepared. -The test water was 30 mg / L, and different carbon source substrates were added for denitrification reaction. Two glass tubes with hoses were inserted into the rubber stopper to connect to the outside world. At the beginning of the test and after each sampling, nitrogen was blown into the bottle through the tube below the liquid surface for 30 seconds until the air in the bottle was exhausted, and then a water stop clamp was installed on the hose of the conical bottle to maintain the anoxic environment in the bottle. The speed of the constant temperature water bath oscillator used in the test was set to 105r / min and the temperature was set to 25℃.

[0037] After sealing and stirring evenly, take a sample (recorded as the sample at time 0) and start timing. Take samples every 10 minutes for the first 30 minutes, and every 30 minutes thereafter. After the sample passes through a 0.45μm filter membrane, measure the concentrations of NO3-N and NO2-N in the filtrate, plot the NO3-N and NO2-N concentrations as the ordinate and the time as the abscissa to obtain the denitrification rate. The results are shown in Figure 1 .

[0038] from Figure 1 It can be seen that compared with a single carbon source, the composite carbon source has a good denitrification effect on sewage treatment under the same dosage and the same reaction time. Compared with the sludge domesticated with ethanol as a single carbon source, the denitrification rate of ethanol and sodium propionate in the sludge domesticated with the composite carbon source has increased, and the denitrification rate has increased to 16.61 and 11.28 mg-N / gMLVSS·h. This shows that the composite carbon source effectively enhances the sludge's ability to utilize these two carbon sources. In addition, when the composite carbon source is used, the denitrification rate is increased to 31.05 mg-N / gMLVSS·h, which is close to the sum of the denitrification rates of ethanol and sodium propionate. This shows that the sludge domesticated with the composite carbon source can effectively integrate the denitrification metabolism of ethanol and sodium propionate, and the microorganisms can simultaneously carry out two-carbon and three-carbon metabolism, and promote each other. From the accumulation of NO2-N, the composite carbon source reaches the peak of NO2-N accumulation of 7.23 mg / L within 0.5 hours, which corresponds to the complete conversion of NO3-N, and complete reduction is achieved after 1 hour. This shows that the composite carbon source simultaneously improves the electron transfer efficiency of NO3-N to NO2-N conversion and the electron transfer efficiency of NO2-N reduction. Because microorganisms simultaneously carry out different carbon metabolic pathways, competition in common metabolic pathways is avoided, thereby generating more electron donors and promoting the overall rate increase of each denitrification stage.

[0039] Experiment 3: AOA pilot test.

[0040] Take domestic sewage with insufficient carbon-nitrogen ratio, design an anaerobic-aerobic-anoxic (AOA) process system, and add the composite carbon source as an external carbon source to the anoxic stage for denitrification. The laboratory simulates the denitrification process, using the composite carbon source C prepared in Example 3. During the operation, the inlet and outlet water are sampled and tested regularly, and the water quality indicators are tested after filtration. Comparison data are shown in Figure 2 shown.

[0041] Depend on Figure 2 It can be seen that during the operation, the average COD concentration of the inlet water was 243.12 mg / L, the average COD concentration of the outlet water was 40.54 mg / L, the average COD removal rate was 83.08%, and the outlet NO3 - -N average concentration is 1.28mg / L, effluent NO2 - The average concentration of -N was 1.05 mg / L. The average concentration of TP in the effluent during stable operation was 0.26 mg / L. This indicates that the denitrification and phosphorus removal effects were better under the action of the added carbon source.

[0042] In summary, compared with the traditional single carbon source, the high-efficiency composite carbon source of the present application has a higher denitrification rate, there is no nitrite nitrogen accumulation phenomenon, the denitrification and phosphorus removal effects are very good in actual sewage treatment, the effluent is relatively stable, the operating cost is low, and the transportation and storage risks are small.

[0043] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A high-efficiency composite carbon source, characterized in that: Calculated by weight percentage, it includes the following components: 35%-45% fatty acid salts, 35%-45% alcohols, and the balance water.

2. The high-efficiency composite carbon source according to claim 1, characterized in that: Calculated by weight percentage, it includes the following components: 40% fatty acid salts, 40% alcohols, and 20% water.

3. The high-efficiency composite carbon source according to claim 1, characterized in that: The fatty acid salts include any one of sodium acetate, sodium propionate and sodium butyrate.

4. The high-efficiency composite carbon source according to claim 1, characterized in that: The alcohol includes any one of methanol, ethanol and glycerol.

5. The high-efficiency composite carbon source according to claim 1, characterized in that: The fatty acid salt is sodium propionate, and the alcohol is ethanol.

6. The high-efficiency composite carbon source according to claim 1, characterized in that: The specific denitrification rate of the high-efficiency composite carbon source is 29.85-31.05 mg-N / (gMLVSS·h).

7. The method for preparing a high-efficiency composite carbon source according to any one of claims 1 to 6, characterized in that: Prepare the above raw materials, dissolve the fatty acid salts in water, stir at room temperature to make them completely dissolved, then add the alcohol, stir evenly, and obtain the product.

8. Use of the high-efficiency composite carbon source according to any one of claims 1 to 6 in wastewater treatment for nitrogen and phosphorus removal.

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