A method for achieving efficient treatment of low-nitrogen-load wastewater by an anaerobic ammonia oxidation system through adding modified biochar

Abstract

The application discloses a method for realizing efficient treatment of low-nitrogen-load wastewater by an anaerobic ammonia oxidation system through modified biochar addition, and the modified biochar is added to the anaerobic ammonia oxidation system under low-nitrogen-load operation, which helps to improve the activity of anaerobic ammonia oxidation bacteria and the denitrification efficiency of the system, and realizes stable and efficient operation of the system. The modified biochar provided by the application is simple in preparation process, low in cost, and can realize resource utilization of biomass waste. The application makes full use of the biochar, which can be used as an anaerobic ammonia oxidation bacteria enrichment carrier and an electron shuttle to promote the microbial electron transfer process, so that the activity of anaerobic ammonia oxidation bacteria and the overall denitrification efficiency of the system are effectively improved, and a new idea is provided for solving the problem of poor denitrification performance of the anaerobic ammonia oxidation system caused by low nitrogen load.

Description

(I) TECHNICAL FIELD

[0001] The present application belongs to the technical field of wastewater biological treatment, and particularly relates to a method for realizing efficient treatment of low-nitrogen-load wastewater by an anaerobic ammonia oxidation system through addition of modified biochar. (II) BACKGROUND

[0002] Anaerobic ammonia oxidation technology is a biological reaction process in which anaerobic ammonia oxidation bacteria utilize ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor to generate nitrate nitrogen and nitrogen gas under anaerobic conditions. This technology has become a research hotspot in the field of biological denitrification of wastewater due to its advantages of low consumption, high efficiency and greenness.

[0003] At present, anaerobic ammonia oxidation biological denitrification technology has been widely applied in the field of denitrification of high-ammonia-nitrogen wastewater, such as sludge digestion liquid, landfill leachate and coking wastewater. However, this technology still faces many challenges when used for treating low-nitrogen municipal wastewater, such as difficulty in enriching anaerobic ammonia oxidation bacteria, poor system stability and low denitrification efficiency.

[0004] Therefore, in view of the bottleneck problem of low efficiency of anaerobic ammonia oxidation technology in treating low-nitrogen-load wastewater, improving the activity of anaerobic ammonia oxidation bacteria and the denitrification performance of the system is the key to treating municipal wastewater or other low-concentration nitrogen-containing wastewater, and aims to provide a theoretical basis and technical support for the feasibility of anaerobic ammonia oxidation process for treating low-nitrogen-load wastewater. (III) SUMMARY

[0005] The purpose of the present application is to provide a method for realizing efficient treatment of low-nitrogen-load wastewater by an anaerobic ammonia oxidation system through addition of modified biochar. The method involves adding exogenous modified biochar to an anaerobic ammonia oxidation system operating under low-nitrogen load, which helps to improve the activity of anaerobic ammonia oxidation bacteria and the denitrification efficiency of the system, and realizes stable and efficient operation of the system.

[0006] The technical solution adopted by the present application is as follows:

[0007] The present application provides a method for realizing efficient treatment of low-nitrogen-load wastewater by an anaerobic ammonia oxidation system through addition of modified biochar. The method comprises the following steps:

[0008] (1) Preparation of modified biochar: crop waste is used as raw material and placed in a muffle furnace. The temperature is raised to 300-700℃ at a rate of 10-15℃·min -1 -1.5-2.5h under anoxic conditions, and then cooled to room temperature to obtain biochar. Then, the biochar is added to an aqueous solution of FeCl3, stirred at room temperature and 100-200rpm for 1-5h to modify the biochar, filtered, and the filter cake is ground and sieved, then washed repeatedly with deionized water until neutral, and then dried to obtain modified biochar;

[0009] (2) Modified biochar is added to an anaerobic ammonia oxidation reactor operating under low nitrogen load conditions to achieve efficient treatment of low nitrogen load wastewater.

[0010] Preferably, the agricultural waste in step (1) is corn stalks.

[0011] Preferably, step (1) is performed at 10°C·min. -1 The temperature was increased to 300℃ at a rate of 300 mL / min. -1 The pyrolysis was carried out at 300℃ for 2 hours under a continuous argon gas flow in an oxygen-deficient environment.

[0012] Preferably, the biochar modification conditions in step (1) are: stirring at room temperature and 100 rpm for 3 hours.

[0013] Preferably, in step (1), the concentration of FeCl3 aqueous solution is 0.1-1 g / L (preferably 0.3 g / L), and the volume of FeCl3 aqueous solution used is 6-10 mL / g (preferably 8 mL / g) based on the mass of biochar.

[0014] Preferably, the modified biochar in step (2) has a particle size of 0.01 to 0.1 mm, more preferably 0.05 mm.

[0015] Preferably, the total amount of modified biochar added in step (2) is 8-12 g·L based on sludge volume. -1 .

[0016] Preferably, the operation method of the anaerobic ammonia oxidation reactor in step (2) is as follows: an upflow anaerobic sludge bed reactor is used, inoculated with anaerobic ammonia oxidation granular sludge, and an inorganic salt solution containing ammonia nitrogen and nitrite nitrogen substrate is used as influent. Ammonia nitrogen and nitrite nitrogen are provided in the form of (NH4)2SO4 and NaNO2, respectively, with an initial ammonia nitrogen concentration of 20-70 mg·L. -1 Initial concentration of nitrite nitrogen: 20–70 mg·L -1 The molar ratio of ammonia nitrogen to nitrite nitrogen is 1:1; on the first day of operation, 4 g·L⁻¹ is added. -1 Modified biochar was used in a continuous flow reactor at a temperature of 35±1℃ and a hydraulic retention time of 15–25 h. The reactor was operated continuously using a "matrix decrease-biochar increase" mode. The nitrite concentration in the effluent was below 1 mg·L⁻¹. -1 After 3 days of stable operation, the experiment will proceed to the next stage, running until the ammonia nitrogen concentration in the effluent is below 10 mg·L⁻¹. -1 It can also run stably in 3D and above.

[0017] Inorganic salt solution composition: KH₂PO₄ 10 mg·L⁻¹ -1 CaCl2·2H2O 5.6 mg·L -1MgSO4·7H2O 300mg·L -1 and KHCO3 1250mg·L -1 The trace element solution is 0.125 mL / L, with water as the solvent; the composition of the trace element solution is: EDTA 15000 mg·L. -1 FeSO4·7H2O 9140mg·L -1 MnCl2·4H2O 990mg·L -1 ZnSO4·7H2O4 30mg·L -1 CuSO4·5H2O 250mg·L -1 CoCl2·6H2O 240mg·L -1 NaMoO4·2H2O 220mg·L -1 NiCl2·6H2O 210mg·L -1 and H3BO4 14mg·L -1 The solvent is water.

[0018] Furthermore, the concentration of volatile suspended solids in the anammox granular sludge was 12.5 ± 3.8 g·L⁻¹. -1 .

[0019] Furthermore, the method for continuously operating the reactor using the "matrix decreasing-biochar increasing" mode is as follows: On the first day of operation, 4 g·L⁻¹ of biochar is added. -1 Modified biochar, when the nitrite nitrogen concentration in the reactor effluent is less than 1 mg·L⁻¹ -1 After the experiment continued to run stably for 3 days, it entered the next stage. A total of three stages were run, with each stage using 20–30 mg·L⁻¹. -1 Simultaneously reduce the concentrations of ammonia nitrogen and nitrite nitrogen, while maintaining a concentration of 2–4 g·L⁻¹. -1 Gradually increase the biochar concentration until the ammonia nitrogen concentration in the effluent is below 10 mg·L⁻¹. -1 It can also run stably in 3D and above.

[0020] Furthermore, the initial ammonia nitrogen concentration was 70 mg·L⁻¹. -1 Initial concentration of nitrite nitrogen: 70 mg·L -1 Each stage is administered at 20 mg / L. -1 Simultaneously reduce the concentrations of ammonia nitrogen and nitrite nitrogen, while using 4 g·L -1 The concentration of biochar was gradually increased.

[0021] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: (1) The modified biochar provided by the present invention is not only simple to prepare and low in cost, but also can realize the resource utilization of biomass waste; (2) The present invention makes full use of biochar as both an enrichment carrier for anaerobic ammonia oxidizing bacteria and an electron shuttle to promote the electron transfer process of microorganisms, thereby effectively improving the activity of anaerobic ammonia oxidizing bacteria and the overall denitrification efficiency of the system, providing a new idea for solving the problem of poor denitrification performance of anaerobic ammonia oxidation system caused by low nitrogen load. (iv) Description of the attached drawings

[0022] Figure 1 The graph shows the change in nitrogen removal performance and total nitrogen removal efficiency of the anaerobic ammonia oxidation system.

[0023] Figure 2 This is a bar chart showing the change in the specific anaerobic ammonium oxidation activity of the anaerobic ammonium oxidation system. (V) Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0025] The room temperature described in this invention is 25-30℃.

[0026] Example 1: A method for efficiently treating low-nitrogen-load wastewater using an anaerobic ammonia oxidation system by adding modified biochar, comprising the following steps:

[0027] (1) Preparation of modified biochar: Corn stalks were naturally air-dried and pulverized, then dried at room temperature and stored for later use. 15g of corn stalk powder was added to a muffle furnace and heated at 10℃·min. -1 The temperature was increased to 300℃ at a rate of [missing information] and maintained at 300℃ for pyrolysis for 2 hours. The pyrolysis process was carried out at a rate of 300 mL / min. -1 A continuous argon gas flow (99.9% purity) was used to maintain an oxygen-deficient environment throughout the pyrolysis process. After cooling to room temperature, 14.2 g of biochar was obtained. Then, 5 g of biochar was added to 40 mL of 0.3 g·L⁻¹ hydrochloric acid solution. -1 The modified biochar was stirred continuously at 100 rpm for 3 hours in an aqueous FeCl3 solution at room temperature. The mixture was then filtered, and the filter cake was repeatedly washed with deionized water until the pH of the washing water reached 7.5 ± 0.05. The cake was dried at 50°C for 48 hours, ground, and sieved to obtain 4.8 g of modified biochar with an average particle size of 0.05 mm. This process was repeated three times. The modified biochar was stored in a desiccator for later use.

[0028] (2) The inoculated sludge was anaerobic ammonia oxidation granular sludge with a volatile suspended solids concentration of 12.5 ± 3.8 g·L.-1 .

[0029] (3) Reactor grouping: Two upflow anaerobic sludge bed reactors with an effective volume of 1L were adopted and named reactor CK and reactor BC300 respectively.

[0030] Reactors CK and BC300 were wrapped with light-shielding cloth to avoid light inhibition. Each reactor was inoculated with 0.6 L of anaerobic ammonia oxidation granular sludge. The influent consisted of an inorganic salt solution containing ammonia nitrogen and nitrite nitrogen, provided in the form of (NH4)2SO4 and NaNO2, respectively. The initial influent concentrations of ammonia nitrogen and nitrite nitrogen were both 70 mg·L⁻¹. -1 .

[0031] Inorganic salt solution composition: KH₂PO₄ 10 mg·L⁻¹ -1 CaCl2·2H2O 5.6 mg·L -1 MgSO4·7H2O 300mg·L -1 and KHCO3 1250mg·L -1 The trace element solution is 0.125 mL / L, with water as the solvent; the composition of the trace element solution is: EDTA 15000 mg·L. -1 FeSO4·7H2O 9140mg·L -1 MnCl2·4H2O 990mg·L -1 ZnSO4·7H2O4 30mg·L -1 CuSO4·5H2O 250mg·L -1 CoCl2·6H2O 240mg·L -1 NaMoO4·2H2O 220mg·L -1 NiCl2·6H2O 210mg·L -1 and H3BO4 14mg·L -1 The solvent is water.

[0032] (4) Operation of reactor BC300: On the first day of the experiment, 4 g·L⁻¹ of activated sludge was added. -1 Modified biochar was added to reactor BC300 in a continuous flow environment. The reactor operated at a temperature of 35±1℃ and a hydraulic retention time of 20h. The reactor was continuously operated using the "matrix decreasing-biochar increasing" mode shown in Table 1. When the nitrite nitrogen concentration in the reactor effluent was below 0.1 mg·L⁻¹... -1 After 3 days of stable operation, the experiment proceeded to the next stage, consisting of three stages. In each stage, the concentration of the influent substrate was gradually reduced to 20 mg·L⁻¹. -1 Simultaneously reduce the concentrations of ammonia nitrogen and nitrite nitrogen, while using 4 g·L -1The biochar concentration was gradually increased until a final concentration of 12 g·L⁻¹ was achieved. -1 Run until the ammonia nitrogen concentration in the effluent is below 10 mg·L⁻¹ -1 Furthermore, it can operate stably for 3 days or more, at which point the reactor can achieve efficient treatment of wastewater with low nitrogen load.

[0033] (5) Operation of reactor CK: Same as reactor BC300, except that modified biochar is not added, and other operations are the same.

[0034] Table 1 Operating parameters of reactor BC300

[0035]

[0036] (6) Results:

[0037] Total nitrogen removal rate: During operation, ammonia nitrogen and nitrite nitrogen concentrations in the effluent were sampled and tested every 1 day. The total nitrogen removal rate was calculated, and the results are shown in [the table below]. Figure 1 As shown, at the end of Stage I, the total nitrogen removal efficiencies of reactors CK and BC300 were 89.3% and 97.6%, respectively. At the end of Stages II and III, the total nitrogen removal efficiencies of reactor BC300 were 79.9% and 40%, respectively, reaching as high as 97.8% and 92.2%, representing increases of 17.9% and 52.2% compared to CK.

[0038] Compared to anaerobic ammonia oxidation activity:

[0039] The anaerobic ammonium oxidation activity was measured after running reactors BC300 and CK for 9, 23, and 48 days, respectively. The specific steps were as follows: The sampled sludge was washed three times with inorganic salt solution to remove residual matrix, and then added to a serum bottle with an effective volume of 150 mL. The sludge inoculum amount was 2 g VSS·L. -1 Add 6 mL of inorganic salt solution, 1.25 mL of trace elements I and II, and 0.1 mol·L⁻¹. -1 Adjust the initial pH to 7.5 ± 0.1 with HCl or NaOH, and finally bring the volume to 120 mL with distilled water. Aerate the serum bottle with high-purity argon gas for 15 min to maintain anaerobic conditions, immediately seal with butyl rubber stoppers, reinforce with aluminum caps, and place in a constant temperature shaking incubator for incubation in the dark (35℃, 100 rpm). -1 Using a syringe, samples were taken periodically to measure the concentrations of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen, and the VSS value of the sludge in the bottle (i.e., the ratio of substrate consumption rate to sludge concentration, where substrate refers to the total concentration of ammonia nitrogen and nitrite nitrogen) was calculated.

[0040] The formula is SAA = (C0 - C t ) / (M*t)

[0041] In the formula, SAA represents the specific anaerobic ammonium oxidation activity, expressed in mg·TN·g. -1 VSS·h -1 C0: Initial matrix concentration, mg·L -1 C t : Matrix concentration at time t, mg·L -1 M: sludge concentration, g VSS·L -1 T: Reaction time, h.

[0042] The results are as follows Figure 2 As shown, at the end of stages I, II, and III, the specific anaerobic ammonia oxidation activities of reactor BC300 were 76.1±7.0, 69.5±7.3, and 64.3±3.5 mg N·g, respectively. -1 VSS·d -1 Compared with CK, the levels were increased by 1.2, 1.3 and 1.6 times respectively.

[0043] Depend on Figure 1 and Figure 2 It can be seen that when the influent substrate concentration is gradually reduced while the final biochar concentration is gradually increased, the denitrification performance and sludge activity of the anammox reactor are superior to the control group without added biochar, and the system can operate stably. This indicates that adding modified biochar helps the anammox reactor treat low-nitrogen-load wastewater. This invention provides a solution to the bottleneck problem of inefficient treatment of low-nitrogen-load wastewater by using biochar as an exogenous additive, aiming to achieve efficient operation and widespread application of the anammox process system.

Claims

1. A method for efficiently treating low-nitrogen-load wastewater using an anaerobic ammonia oxidation system by adding modified biochar, characterized in that, The method includes the following steps: (1) Preparation of modified biochar: Agricultural waste was used as raw material and placed in a muffle furnace at 10~15 ℃·min -1 The temperature was rapidly increased to 300 ℃~700 ℃, and pyrolyzed under anaerobic conditions for 1.5~2.5 h. After cooling to room temperature, biochar was obtained. Then, the biochar was added to FeCl3 aqueous solution and stirred at room temperature and 100~200 rpm for 1~5 h to modify the biochar. After filtration, the filter cake was ground and sieved, washed repeatedly with deionized water until neutral, and then dried to obtain modified biochar. (2) An upflow anaerobic sludge bed reactor was adopted, inoculated with anaerobic ammonia oxidation granular sludge, and an inorganic salt solution containing ammonia nitrogen and nitrite nitrogen substrate was used as influent. Ammonia nitrogen and nitrite nitrogen were provided in the form of (NH4)2SO4 and NaNO2, respectively; the initial concentration of ammonia nitrogen was 20~70 mg·L. -1 Initial concentration of nitrite nitrogen: 20-70 mg·L -1 The molar ratio of ammonia nitrogen to nitrite nitrogen is 1:1; on the first day of operation, 4 g·L⁻¹ is added. -1 Modified biochar, in continuous flow, reactor operating temperature 35±1℃ o C, the hydraulic retention time is 15-25 h; the reactor is operated continuously using a "matrix decreasing-biochar increasing" mode, and the nitrite nitrogen concentration in the reactor effluent is below 1 mg·L⁻¹. -1 After 3 days of stable operation, the experiment will proceed to the next stage, continuing until the ammonia nitrogen concentration in the effluent is below 10 mg·L⁻¹. -1 Furthermore, it can operate stably for 3 days or more, and the reactor can achieve efficient treatment of wastewater with low nitrogen load. The method of continuous operation of the reactor using the "matrix decreasing-biochar increasing" mode is as follows: on the first day of operation, add 4 g·L -1 Modified biochar, when the nitrite nitrogen concentration in the reactor effluent is less than 1 mg·L⁻¹ -1 After the experiment continued to run stably for 3 days, it entered the next stage. A total of three stages were run, with each stage using 20-30 mg·L⁻¹. -1 Simultaneously reduce the concentrations of ammonia nitrogen and nitrite nitrogen, while maintaining a concentration of 2-4 g·L⁻¹. -1 Gradually increase the biochar concentration until the ammonia nitrogen concentration in the effluent is below 10 mg·L⁻¹. -1 It can run stably for 3 days or more.

2. The method as described in claim 1, characterized in that, The agricultural waste mentioned in step (1) is corn stalks.

3. The method as described in claim 1, characterized in that, Step (1) at 10 ℃·min -1 The temperature was increased to 300 °C at a rate of 300 mL / min. -1 The pyrolysis was carried out at 300℃ for 2 hours under a continuous argon gas flow in an oxygen-deficient environment.

4. The method as described in claim 1, characterized in that, Step (1) Biochar modification conditions: stirring at room temperature and 100 rpm for 3 hours.

5. The method as described in claim 1, characterized in that, Step (1) The concentration of FeCl3 aqueous solution is 0.1-1 g / L, and the volume of FeCl3 aqueous solution used is 6-10 mL / g based on the mass of biochar powder.

6. The method as described in claim 1, characterized in that, The total amount of modified biochar added in step (2) is 8~12 g·L based on sludge volume. -1 .

7. The method as described in claim 1, characterized in that, Initial ammonia nitrogen concentration 70 mg·L -1 Initial concentration of nitrite nitrogen: 70 mg·L -1 Each phase was administered at 20 mg·L⁻¹ -1 Simultaneously reduce the concentrations of ammonia nitrogen and nitrite nitrogen, while at 4 g·L -1 The concentration of biochar was gradually increased.

8. The method as described in claim 1, characterized in that, Inorganic salt solution composition: KH₂PO₄ 10 mg·L⁻¹ -1 CaCl2·2H2O 5.6 mg·L -1 MgSO4·7H2O 300 mg·L -1 and KHCO3 1250 mg·L -1 The trace element solution is 0.125 mL / L, with water as the solvent; the composition of the trace element solution is: EDTA 15000 mg·L. -1 FeSO4·7H2O 9140 mg·L -1 MnCl2·4H2O 990 mg·L -1 ZnSO4·7H2O 430 mg·L -1 CuSO4·5H2O 250 mg·L -1 CoCl2·6H2O 240 mg·L -1 NaMoO4·2H2O 220 mg·L -1 NiCl2·6H2O 210 mg·L -1 and H3BO4 14 mg·L -1 The solvent is water.

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