A method to improve the efficiency of low-temperature anaerobic ammonium oxidation for nitrogen removal

Abstract

A method for improving the denitrification efficiency of low-temperature anaerobic ammonia oxidation includes simultaneously adding iron-sulfur-loaded hydrothermal char and raw hydrothermal char to a low-temperature operating anaerobic ammonia oxidation reactor at a rate of 1-10 g per liter. The operating temperature of the anaerobic ammonia oxidation reactor is 10-35°C, more preferably 10-15°C. The iron-sulfur-loaded hydrothermal char is obtained by roasting alkali-resistant aerobic denitrification granular sludge, loading it with iron and sulfur sequentially, and then drying it. The particle size of the iron-sulfur-loaded hydrothermal char is 10-500 μm, with an iron content of 1-5 wt% and a sulfur content of 0.5-3 wt%. The iron element is attached to the biochar in the form of Fe3O4, Fe2O3, and iron-sulfur compounds. The raw hydrothermal char is obtained by roasting alkali-resistant aerobic denitrification granular sludge at a roasting temperature of 150-250°C for 10-120 min. This method has the advantages of low biochar dosage, short adaptation period, good performance of anaerobic ammonia oxidation for nitrogen removal under low temperature conditions, and stable treatment effect.

Description

Technical Field

[0001] This invention relates to a method for improving the efficiency of low-temperature anaerobic ammonia oxidation denitrification, belonging to the field of wastewater treatment technology. Background Technology

[0002] With the rapid development of industry and agriculture, a large amount of nitrogen is discharged into water bodies, resulting in excessively high nitrogen content in the water, which in turn leads to environmental problems such as eutrophication.

[0003] Anammox is a process that removes ammonia using anammox bacteria in an anaerobic environment. The process uses ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. Compared to traditional nitrification-based biological nitrogen removal technologies, Anammox technology offers advantages such as no need for external carbon sources, low sludge production, and minimal secondary pollution, making it considered an economical, efficient, and low-carbon wastewater nitrogen removal technology. However, anammox bacteria are sensitive to environmental factors such as temperature, substrate concentration, and organic matter content. Especially at low temperatures, their doubling time is long, their activity is low, and nitrogen removal is ineffective, limiting the application of this technology in low-temperature nitrogen removal processes. Researchers have detected abundant and active anammox bacteria in sediments from the southern North Sea during winter (<10℃), offering the possibility of using anammox for treating low-temperature wastewater. Exploring ways to improve the bioactivity of anammox bacteria under low-temperature conditions is crucial for promoting the engineering application of this technology in cold regions.

[0004] Biochar is a porous, stable carbon material derived from biomass, characterized by its high specific surface area, strong adsorption capacity, abundant functional groups, and excellent electron transfer efficiency, which can accelerate the metabolic processes of microorganisms. Studies have shown that biochar can improve the nitrogen removal efficiency of anammox by promoting the secretion of extracellular polymers and increasing the protein-to-polysaccharide ratio, thereby improving sludge stability; it can also alleviate the stress effect of chemical oxygen demand on the anammox reaction. Although some scholars have explored the effect of biochar on improving the nitrogen removal efficiency of anammox processes and elucidated its mechanisms by analyzing extracellular polymers, microbial community structure, and metabolic functions, existing studies have found that certain biochars added to reactors have long adaptation periods, unstable treatment effects, and limited improvement effects.

[0005] CN114477663A discloses a system for preparing large-sized lapis lazuli from kitchen waste via hydrothermal carbonization. The system uses a two-stage fluidized bed as its core equipment, employing ferric iron (Fe3+) as the iron source. Anaerobic sludge reduces the ferric iron to ferrous iron (Fe2+), which then combines with phosphates in the hydrothermal carbonization liquid of the kitchen waste. Under the upward flow velocity of the fluidized bed, large-sized lapis lazuli are formed. This system effectively removes phosphates from the hydrothermal carbonization liquid of kitchen waste, avoiding the problem of impurity caused by ferrous oxidation. It also generates large-sized lapis lazuli crystals that are easy to separate and collect.

[0006] CN106365308A discloses a method for activating thiocyanate-contaminated anaerobic ammonia oxidation granular sludge. The method employs an upflow anaerobic sludge bed reactor, inoculating it with thiocyanate-contaminated anaerobic ammonia oxidation granular sludge, using simulated wastewater containing ferric salts as influent, and operating under anaerobic and light-protected conditions (9.6–17.3℃, pH 7.2–7.4, hydraulic retention time 3–5 h) for 30–60 days. This results in an increase of over 40% in the activity of the granular sludge in the reactor, obtaining activated anaerobic ammonia oxidation granular sludge. This method can efficiently remove thiocyanate adsorbed on the surface of the granular sludge and rapidly activate the denitrification performance of the anaerobic ammonia oxidation granular sludge. Summary of the Invention

[0007] This invention addresses the problems of poor nitrogen removal efficiency in anaerobic ammonia oxidation under low-temperature conditions, secondary pollution from exogenous functional materials, and long adaptation time and limited nitrogen removal effect of anaerobic ammonia oxidizing bacteria. It proposes a method to rapidly improve the nitrogen removal efficiency of low-temperature anaerobic ammonia oxidation.

[0008] A method for improving the denitrification efficiency of low-temperature anaerobic ammonia oxidation includes simultaneously adding iron-sulfur-loaded hydrothermal char and raw hydrothermal char to a low-temperature operating anaerobic ammonia oxidation reactor at a rate of 1-10 g per liter. The operating temperature of the anaerobic ammonia oxidation reactor is 10-35℃, more preferably 10-15℃. The iron-sulfur hydrothermal char is obtained by roasting alkali-resistant aerobic denitrification granular sludge, sequentially loading it with iron and sulfur, and then drying it. The particle size of the iron-sulfur-loaded hydrothermal char is 10-500 μm, with an iron content of 1-5 wt% and a sulfur content of 0.5-3 wt%. The iron element is attached to the biochar in the form of Fe3O4, Fe2O3, and iron-sulfur compounds. The raw hydrothermal char is obtained by roasting alkali-resistant aerobic denitrification granular sludge at a roasting temperature of 150-250℃ for 10-120 min.

[0009] After operating at low temperature for 15 days, the anaerobic ammonia oxidation reactor showed a 15-26% increase in nitrogen removal rate and a 12.5 mg N (g sludge·day) increase in sludge activity.

[0010] The iron-sulfur loaded hydrothermal char and the original hydrothermal char can be added at once or in multiple batches. Preferably, they are added in 2-5 batches. The iron-sulfur biochar and the original hydrothermal char are applied simultaneously in a mass ratio of 1:1-4:1. After 13 days, the anaerobic ammonia oxidation denitrification rate increases by more than 30%.

[0011] The preparation methods of the original hydrothermal carbon and iron-sulfur hydrothermal carbon include the following steps: (1) cultivating alkali-resistant aerobic denitrification granular sludge; (2) drying, calcining and grinding the alkali-resistant aerobic denitrification granular sludge to obtain the original hydrothermal carbon; (3) impregnating the hydrothermal carbon with an iron-containing solution and calcining it to obtain iron-loaded hydrothermal carbon; (4) impregnating the hydrothermal carbon with a sulfur-containing component and washing, drying and pulverizing it to obtain iron-sulfur hydrothermal carbon.

[0012] The alkali-tolerant aerobic denitrifying granular sludge mentioned in step (1) is an alkali-tolerant granular sludge cultivated under the following conditions: influent pH value of 9-11, organic matter concentration of 400-1000 mg / L, nitrate nitrogen concentration of 100-200 mg / L, phosphate concentration of 20-50 mg / L, and sodium carbonate concentration of 1-3 g / L. The sludge particle size is above 250-500 μm, and the carbon-nitrogen ratio is 8:1-12:1. Preferably, the influent pH value is 10-11, organic matter concentration is 800-1000 mg / L, nitrate nitrogen concentration is 100-130 mg / L, phosphate concentration is 30-40 mg / L, sodium carbonate concentration is 1.5-2.5 g / L, and the carbon-nitrogen ratio is 9:1-10:1. The alkali-tolerant aerobic denitrifying granular sludge is cultivated using alkali-tolerant denitrifying bacteria as the inoculum source.

[0013] Preferably, the alkali-resistant aerobic granular sludge in step (1) is cultivated by alternating the carbon-nitrogen ratio. The alkali-resistant aerobic sludge is first run at a carbon-nitrogen ratio of 8-12:1 for 3-4 days, then the carbon-nitrogen ratio is reduced to 5-7:1 and run for 1-2 days, and then the carbon-nitrogen ratio is increased to 8-12:1 and run for 3-4 days.

[0014] The drying in step (2) involves adjusting the solid-liquid ratio in the alkali-resistant aerobic denitrification granular sludge to 40-80g:100ml, preferably 50-60g:100ml; the drying is carried out at 0.001-0.05MPa and 80-95℃; the calcination temperature is 180-200℃ and the calcination time is 30-90min.

[0015] The iron-containing solution mentioned in step (3) is one or more of ferric sulfate, ferric nitrate, and ferric chloride, and the molar concentration of iron ions in the iron-containing solution is 1-5 mol / L; the mass ratio of the iron-containing solution to the hydrothermal carbon is 0.1-0.5:1, and the impregnation time is 6-36 h; after impregnation, it is continuously heated at 150-250℃ for 3-12 h to obtain iron-loaded hydrothermal carbon.

[0016] The sulfur-containing component in step (4) is one of carbon disulfide, sulfur powder, sodium sulfide, and potassium sulfide, preferably carbon disulfide; the mass ratio of the iron-loaded hydrothermal carbon to the sulfur-containing component is 1:2-1:5; the impregnation loading time is 6-36 h; the washing is done with ethanol or propanol; the drying temperature is 90-120 °C; preferably, the iron-loaded hydrothermal carbon and the sulfur-containing component are treated for 60-120 minutes under conditions of pH 8-10 before mixing.

[0017] The beneficial technical effects of this invention are: the method has the advantages of good performance of anaerobic ammonia oxidation for nitrogen removal under low temperature conditions, simple operation, and stable treatment effect. Detailed Implementation

[0018] Example 1

[0019] The preparation of iron-sulfur-loaded hydrothermal carbon includes the following steps: (1) alkali-resistant aerobic granular sludge is cultivated under the conditions of influent pH value of 11, organic matter concentration of 800-1000 mg / L, nitrate nitrogen concentration of 100-130 mg / L, phosphate concentration of 30-40 mg / L, and sodium carbonate concentration of 1.5-2.5 g / L; (2) the cultivated alkali-resistant aerobic granular sludge is dried, calcined, and ground to obtain raw hydrothermal carbon; (3) under the conditions of solid-liquid ratio of 50 g: 100 ml and Fe2(SO4)3 to sludge mass ratio of 0.2:1, the temperature inside the reactor is controlled at 210℃ and heated continuously for 6 hours to obtain iron-loaded hydrothermal carbon; (4) the obtained iron-loaded hydrothermal carbon is further treated under the condition of pH 9 for 120 minutes, and then carbon disulfide is added at a solid-liquid ratio of 1:2 and shaken at low temperature for 120 minutes. The obtained sample is rinsed and dried to obtain iron-sulfur-loaded hydrothermal carbon.

[0020] The original hydrothermal carbon and iron-sulfur loaded hydrothermal carbon were added to the anaerobic ammonia oxidation reactor at a rate of 5g per liter. After the reactor was run at 15℃ for 15 days, the anaerobic ammonia oxidation denitrification rate increased by 20-30% compared with that without the addition of iron-sulfur loaded hydrothermal carbon, and the sludge activity increased by an average of 15mg N (g sludge·day).

[0021] Example 2

[0022] The hydrothermal carbon was added in three stages, with a volume ratio of 1:100 each time. Other processes were the same as in Example 1. After the anaerobic ammonia oxidation reactor operated at 15°C for 8 days, the nitrogen removal efficiency of anaerobic ammonia oxidation increased by more than 30%.

[0023] Example 3

[0024] The other steps are the same as in Example 1, except that the carbon-to-nitrogen ratio is alternately changed during the cultivation of alkali-tolerant aerobic granular sludge. The alkali-tolerant aerobic sludge is first run for 3 days at an influent carbon-to-nitrogen ratio of 10:1, then the influent carbon-to-nitrogen ratio is reduced to 6:1 and run for 2 days, and then the influent carbon-to-nitrogen ratio is increased to 10:1 and run for 3 days. After the anaerobic ammonia oxidation reactor operates at 15°C for 20 days, the nitrogen removal efficiency of anaerobic ammonia oxidation is improved by 25%.

[0025] Comparative Example 1

[0026] Adding 5g of ordinary wastewater treatment plant sludge-based hydrothermal carbon per liter to an anaerobic ammonia oxidation reactor operating at low temperature for 20 days at 15℃ increased the total nitrogen removal rate by 3-8%.

[0027] Comparative Example 2

[0028] Hydrothermal carbon was added at a rate of 5g per liter in the anaerobic ammonia oxidation reactor operating at low temperature. The preparation method of the hydrothermal carbon included the following steps: (1) culturing alkali-tolerant aerobic granular sludge under the conditions of influent pH 11, organic matter concentration of 800-1000mg / L, nitrate nitrogen concentration of 100-130mg / L, phosphate concentration of 30-40mg / L, and sodium carbonate concentration of 1.5-2.5g / L; (2) preparing hydrothermal carbon by drying and grinding the cultured alkali-tolerant aerobic granular sludge and then heating the reactor to 180-200℃. After the anaerobic ammonia oxidation reactor operated at 15℃ for 15 days, the total nitrogen removal rate increased by 10%, and the sludge activity increased by 10mg N (g sludge·day).

[0029] Comparative Example 3

[0030] Iron-loaded hydrothermal carbon was added at a rate of 5g per liter in an anaerobic ammonia oxidation reactor operating at low temperature. The preparation method of the iron-loaded hydrothermal carbon includes the following steps: (1) alkali-tolerant aerobic granular sludge was cultivated under the conditions of influent pH value of 10, organic matter concentration of 8000-1000mg / L, nitrate nitrogen concentration of 100-130mg / L, phosphate concentration of 30-40mg / L, and sodium carbonate concentration of 1.5-2.5g / L; (2) the cultivated alkali-tolerant aerobic granular sludge was dried and ground to obtain hydrothermal carbon; (3) under the conditions of solid-liquid ratio of 50g:100ml and Fe2(SO4)3 to sludge mass ratio of 0.2:1, the temperature was controlled at 200℃ and heated continuously for 6 hours to obtain iron-loaded hydrothermal carbon. After the anaerobic ammonia oxidation reactor was operated at 15℃ for 20 days, the total nitrogen removal rate increased by 10%.

[0031] The above embodiments are merely illustrative of implementation methods of the present invention, but the scope of protection of the present invention is not limited to the embodiments. Those skilled in the art can make various changes and modifications without departing from the spirit and essence of the present invention, and all such changes and modifications will be covered within the scope of protection of the present invention.

Claims

1. A method for improving the denitrification efficiency of low-temperature anaerobic ammonia oxidation, comprising simultaneously adding iron-sulfur-loaded hydrothermal char and raw hydrothermal char at a rate of 1-10 g per liter to a low-temperature operating anaerobic ammonia oxidation reactor, wherein the operating temperature of the anaerobic ammonia oxidation reactor is 10-15℃; the iron-sulfur-loaded hydrothermal char is obtained by roasting alkali-resistant aerobic denitrification granular sludge, sequentially loading iron and sulfur, and then drying; the particle size of the iron-sulfur-loaded hydrothermal char is 10-500 μm, wherein the iron content is 1-5 wt% and the sulfur content is 0.5-3 wt%, and the iron element is attached to the biochar in the form of Fe3O4, Fe2O3, and iron-sulfur compounds; the raw hydrothermal char is obtained by roasting alkali-resistant aerobic denitrification granular sludge at a roasting temperature of 150-250℃ for a roasting time of 10-120 min.

2. The method according to claim 1, characterized in that... After operating at low temperature for 15 days, the anaerobic ammonia oxidation reactor showed a 15-26% increase in nitrogen removal rate and a 12.5 mg N (g sludge·day) increase in average sludge activity.

3. The method according to claim 1, characterized in that... The iron-sulfur loaded hydrothermal carbon and the original hydrothermal carbon can be added at once or in multiple batches.

4. The method according to claim 3, characterized in that... The iron-sulfur loaded hydrothermal carbon and the original hydrothermal carbon are added in 2-5 batches.

5. The method according to claim 3, characterized in that... The iron-sulfur loaded hydrothermal carbon and the original hydrothermal carbon are applied simultaneously at a mass ratio of 1:1 to 4:

1.

6. The method according to claim 1, characterized in that... The preparation methods of the original hydrothermal carbon and iron-sulfur loaded hydrothermal carbon include the following steps: (1) cultivating alkali-resistant aerobic denitrification granular sludge; (2) drying, calcining and grinding the alkali-resistant aerobic denitrification granular sludge to obtain the original hydrothermal carbon; (3) impregnating the original hydrothermal carbon with an iron-containing solution and calcining it to obtain iron-loaded hydrothermal carbon; (4) impregnating the load with sulfur-containing components and washing, drying and pulverizing it to obtain iron-sulfur loaded hydrothermal carbon.

7. The method according to claim 6, characterized in that... The alkali-resistant aerobic denitrification granular sludge mentioned in step (1) is cultivated under the conditions of influent pH value of 9-11, organic matter concentration of 400-1000 mg / L, nitrate nitrogen concentration of 100-200 mg / L, phosphate concentration of 20-50 mg / L, sodium carbonate concentration of 1-3 g / L, and carbon-nitrogen ratio of 8:1-12:1, with sludge particle size of 250-500 µm.

8. The method according to claim 7, characterized in that The alkali-tolerant aerobic denitrifying granular sludge mentioned in step (1) is cultivated under the following conditions: influent pH value of 10-11, organic matter concentration of 800-1000 mg / L, nitrate nitrogen concentration of 100-130 mg / L, phosphate concentration of 30-40 mg / L, sodium carbonate concentration of 1.5-2.5 g / L, and carbon-nitrogen ratio of 9:1-10:1; the alkali-tolerant aerobic denitrifying granular sludge is obtained by sludge cultivation using alkali-tolerant denitrifying bacteria as the inoculum source.

9. The method according to claim 6, characterized in that... The alkali-tolerant aerobic denitrification granular sludge described in step (1) is cultivated by alternating the carbon-nitrogen ratio. The alkali-tolerant aerobic denitrification granular sludge is first operated for 3-4 days at an influent carbon-nitrogen ratio of 8-12:1, then the influent carbon-nitrogen ratio is reduced to 5-7:1 and operated for 1-2 days, and then the influent carbon-nitrogen ratio is increased to 8-12:1 and operated for 3-4 days.

10. The method according to claim 6, characterized in that... The drying in step (2) involves adjusting the solid-liquid ratio in the alkali-resistant aerobic denitrification granular sludge to 40-80g:100ml; the drying is carried out at 0.001-0.05MPa and 80-95℃; the calcination temperature is 180-200℃ and the calcination time is 30-90min.

11. The method according to claim 10, characterized in that... The drying process described in step (2) involves adjusting the solid-liquid ratio in the alkali-resistant aerobic denitrification granular sludge to 50-60g:100ml.

12. The method according to claim 6, characterized in that... The iron-containing solution mentioned in step (3) is one or more of ferric sulfate, ferric nitrate, and ferric chloride, and the molar concentration of iron ions in the iron-containing solution is 1-5 mol / L; the mass ratio of the iron-containing solution to the original hydrothermal carbon is 0.1-0.5:1, and the impregnation time is 6-36 h; after impregnation, it is continuously heated at 150-250℃ for 3-12 h to obtain iron-loaded hydrothermal carbon.

13. The method according to claim 6, characterized in that... The sulfur-containing component in step (4) is one of carbon disulfide, sulfur powder, sodium sulfide, and potassium sulfide; the mass ratio of the iron-loaded hydrothermal carbon to the sulfur-containing component is 1:2-1:5; the immersion loading time is 6-36h; the washing is done with ethanol or propanol; and the drying temperature is 90-120℃.

14. The method according to claim 13, characterized in that... The sulfur-containing component mentioned in step (4) is carbon disulfide; the iron-loaded hydrothermal carbon and the sulfur-containing component are treated for 60-120 minutes at pH 8-10 before mixing.

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