Efficient denitrification process of sewage based on graphene modified filler

Abstract

The application discloses a wastewater efficient denitrification process based on graphene modified filler, and belongs to the field of water treatment. The application aims to solve the problems that existing water treatment fillers are prone to hardening, cannot be uniformly contacted with wastewater, and thus have low utilization rate and low denitrification and dephosphorization efficiency. The method comprises the following steps: 1, filtering wastewater into a grid pool; 2, introducing the wastewater into a flocculation tank for treatment; 3, introducing the wastewater into a sedimentation tank for treatment; 4, introducing the wastewater into a nitrosation process unit for treatment; 5, introducing the wastewater into a reactor of a sulfur autotrophic denitrification process for treatment; 6, introducing the wastewater into a sulfuric acid salt adsorption tank for treatment; and 7, introducing the wastewater into a filter column filled with fine sand for treatment. The application uses graphene to prepare the filler, and combines the sulfur autotrophic denitrification process to realize deep denitrification and dephosphorization of the wastewater, so that the TN of the effluent can stably reach the first level A standard.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, specifically relating to a high-efficiency denitrification process for wastewater based on graphene-modified filler. Background Technology

[0002] Biological treatment technology is one of the most widely used methods in modern wastewater treatment. Nitrogen pollution is a major cause of water pollution, and domestic sewage contains a certain amount of nitrogen. Therefore, denitrification is almost an essential step in the wastewater treatment process.

[0003] Rural environmental governance has received increasing attention in recent years, with water environment management being the most prominent and sensitive aspect. Due to difficulties in securing funding for construction, operation, and maintenance, a lack of professional and technical personnel, and inappropriate selection of treatment processes, rural domestic sewage treatment has become a significant weakness in the current rural living environment improvement efforts. In particular, sewage treatment technologies for water quality-sensitive areas with high total nitrogen removal requirements are still relatively lacking.

[0004] Common biological nitrogen removal processes consist of nitrification and denitrification. In nitrification, biological nitrogen in wastewater undergoes ammonification to form ammonia nitrogen, which is then converted from nitrite to nitrate nitrogen by chemoautotrophic bacteria. In denitrification, under anaerobic conditions, nitrate nitrogen acts as an electron acceptor, and organic matter as an electron donor. Heterotrophic bacteria reduce nitrate nitrogen to nitrogen gas, which is then released into the atmosphere, thus removing total nitrogen from wastewater. Traditional biological nitrogen removal processes, such as A... 2 Biological denitrification processes, such as those involving recirculation, primarily rely on internal backflow for nitrogen removal, which limits their efficiency and increases energy costs. Furthermore, the resulting effluent often fails to achieve a total nitrogen concentration below 10 mg / L. To improve effluent quality, some wastewater treatment plants now connect secondary denitrification equipment, such as denitrifying biological filters, after traditional biological denitrification processes to achieve denitrification and ensure a total nitrogen concentration below 10 mg / L.

[0005] Sulfur autotrophic denitrification technology uses sulfur as an electron donor to convert nitrate nitrogen into nitrogen gas under the action of sulfur autotrophic microorganisms, thus completing the denitrification process. This process does not require an external organic carbon source, which can save operating costs and reduce sludge production. However, the reaction process consumes alkalinity, which can easily lower the system pH, generally requiring alkalinity replenishment. Furthermore, elemental sulfur is easily lost, and using it alone may lead to problems such as excessive sulfate content.

[0006] Therefore, developing a sulfur-containing filler material with enhanced denitrification that is suitable for use in biological ponds and avoids secondary pollution is the key to the friendly utilization of sulfur autotrophic denitrification technology.

[0007] Currently, commonly used water treatment packing materials are prone to caking during use, making it difficult to make uniform contact with wastewater, resulting in low packing material utilization and low nitrogen and phosphorus removal efficiency. Summary of the Invention

[0008] The purpose of this invention is to solve the problems of existing water treatment packing materials being prone to caking during use, failing to make uniform contact with wastewater, resulting in low packing material utilization and low nitrogen and phosphorus removal efficiency, and to provide a high-efficiency wastewater denitrification process based on graphene-modified packing materials.

[0009] A highly efficient nitrogen removal process for wastewater based on graphene-modified packing material is specifically completed according to the following steps:

[0010] 1. The wastewater is passed into a grit chamber for filtration to remove large solids, resulting in filtered wastewater;

[0011] 2. The filtered wastewater is introduced into a flocculation tank to remove organic matter, SS and TP from the wastewater, resulting in wastewater treated by the flocculation tank;

[0012] Third, the wastewater treated in the flocculation tank is introduced into the sedimentation tank for further treatment to separate the wastewater and sludge, resulting in wastewater treated in the sedimentation tank.

[0013] IV. The wastewater treated in the sedimentation tank is introduced into the nitrification process unit for further treatment, where some of the ammonia nitrogen in the wastewater is converted into nitrite nitrogen, resulting in wastewater treated by the nitrification process unit.

[0014] 5. The wastewater treated by the nitrification process unit is introduced into the reactor of the sulfur autotrophic denitrification process for deep denitrification and phosphorus removal, resulting in wastewater treated by the sulfur autotrophic denitrification process.

[0015] The packing material used in the sulfur autotrophic denitrification process described in step five consists of packing material A and packing material B;

[0016] The method for preparing filler A described in step five is specifically completed according to the following steps:

[0017] Eggshell powder, tourmaline powder, and carbon fiber powder are mixed evenly to obtain mixture I; mixture I is immersed in surface modification solution I and left to stand for a period of time, then removed and dried to obtain filler A;

[0018] The preparation method of the filler B is specifically carried out according to the following steps:

[0019] Volcanic rock, pyrite, and diatomaceous earth were mixed evenly to obtain mixture II; mixture II was added to surface modification solution II to obtain mixture; the mixture was transferred to a hydrothermal reactor and reacted at 150-200℃ for 3-6 hours; the reaction product was washed with deionized water and dried to obtain filler B;

[0020] 6. The wastewater treated by the sulfur autotrophic denitrification process is introduced into a sulfate adsorption tank filled with hydrotalcite to adsorb sulfate ions in the wastewater, thus obtaining the wastewater after sulfate adsorption tank treatment.

[0021] 7. The wastewater treated in the sulfate adsorption tank is introduced into a filter column filled with fine sand to filter the effluent from the sulfate adsorption process, thus obtaining water with high efficiency denitrification.

[0022] The beneficial effects of this invention are:

[0023] I. The present invention first filters the wastewater through a bar screen to remove large solids, and then introduces it into a flocculation tank to remove organic matter, suspended solids (SS), and total phosphorus (TP). After these two steps, 70% to 80% of COD, 85% to 90% of SS, 80% to 90% of TP, and 15% to 20% of TN can be removed from the wastewater.

[0024] II. This invention combines chemical flocculation, nitrification, and sulfur autotrophic denitrification to improve nitrogen removal efficiency.

[0025] Third, this invention prepares packing material A and packing material B, which, combined with sulfur autotrophic denitrification denitrification process, achieve deep denitrification and phosphorus removal of wastewater, so that the effluent TN can stably reach the Class A standard (GB18918-2002).

[0026] IV. The filler A prepared by this invention is made from eggshell powder, which can dissolve carbonate ions. As an alkaline substance, it can neutralize the hydrogen ions generated by elemental sulfur as an electron acceptor in the denitrification reaction, so that the pH value of the environment in the sulfur autotrophic deep denitrification process is always maintained within the pH value range suitable for the growth of denitrifying sulfur bacteria.

[0027] V. The packing material B prepared in this invention uses graphene, which can bond with nitrogen to further remove nitrogen from wastewater.

[0028] This invention provides a highly efficient wastewater denitrification process based on graphene-modified packing material. Detailed Implementation

[0029] Specific Implementation Method 1: This implementation method describes a high-efficiency nitrogen removal process for wastewater based on graphene-modified packing material, which is specifically completed according to the following steps:

[0030] 1. The wastewater is passed into a grit chamber for filtration to remove large solids, resulting in filtered wastewater;

[0031] 2. The filtered wastewater is introduced into a flocculation tank to remove organic matter, SS and TP from the wastewater, resulting in wastewater treated by the flocculation tank;

[0032] Third, the wastewater treated in the flocculation tank is introduced into the sedimentation tank for further treatment to separate the wastewater and sludge, resulting in wastewater treated in the sedimentation tank.

[0033] IV. The wastewater treated in the sedimentation tank is introduced into the nitrification process unit for further treatment, where some of the ammonia nitrogen in the wastewater is converted into nitrite nitrogen, resulting in wastewater treated by the nitrification process unit.

[0034] 5. The wastewater treated by the nitrification process unit is introduced into the reactor of the sulfur autotrophic denitrification process for deep denitrification and phosphorus removal, resulting in wastewater treated by the sulfur autotrophic denitrification process.

[0035] The packing material used in the sulfur autotrophic denitrification process described in step five consists of packing material A and packing material B;

[0036] The method for preparing filler A described in step five is specifically completed according to the following steps:

[0037] Eggshell powder, tourmaline powder, and carbon fiber powder are mixed evenly to obtain mixture I; mixture I is immersed in surface modification solution I and left to stand for a period of time, then removed and dried to obtain filler A;

[0038] The preparation method of the filler B is specifically carried out according to the following steps:

[0039] Volcanic rock, pyrite, and diatomaceous earth were mixed evenly to obtain mixture II; mixture II was added to surface modification solution II to obtain mixture; the mixture was transferred to a hydrothermal reactor and reacted at 150-200℃ for 3-6 hours; the reaction product was washed with deionized water and dried to obtain filler B;

[0040] 6. The wastewater treated by the sulfur autotrophic denitrification process is introduced into a sulfate adsorption tank filled with hydrotalcite to adsorb sulfate ions in the wastewater, thus obtaining the wastewater after sulfate adsorption tank treatment.

[0041] 7. The wastewater treated in the sulfate adsorption tank is introduced into a filter column filled with fine sand to filter the effluent from the sulfate adsorption process, thus obtaining water with high efficiency denitrification.

[0042] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the flocculation tank described in step two employs a micro-aeration process. The design and operating parameters of the flocculation tank are as follows: sludge load of 5–6 kg BOD5 / (kg MLSS·d), HRT of 0.5–2 h, SRT of 0.5–1 d, and DO concentration of 0.5–0.8 mg / L; PAM is added to the flocculation tank in step two at a concentration of 0.2–0.6 mg / L. All other steps are the same as in Specific Implementation Method One.

[0043] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the HRT of the sedimentation tank in step three is 2-3 hours, and the sludge return ratio is 30-50%. Other steps are the same as in Specific Implementation Method One or Two.

[0044] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the nitrification process unit described in step four uses pure cultured AOB bacteria for inoculation, and AOB bacteria are enriched using suspended packing. The process parameters of the nitrification process unit are: HRT of 3-6 h, DO of 0.5-1.0 mg / L, continuous or intermittent aeration, pH of 7.5-8.5, and when using suspended packing to enrich AOB, the filling ratio is 20-40%. Other steps are the same as in Specific Implementation Methods One to Three.

[0045] Specific Implementation Method Five: The difference between this implementation method and Specific Implementation Methods One to Four is that the packing material used in the sulfur autotrophic denitrification process described in step five consists of packing material A and packing material B, with a mass ratio of (1-2):(3-4). The other steps are the same as in Specific Implementation Methods One to Four.

[0046] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the mass ratio of the eggshell powder, tourmaline powder, and carbon fiber powder is (1-2):(0.5-1):(3-4). The other steps are the same as in Specific Implementation Methods One to Five.

[0047] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the surface modification solution I is an aqueous solution of glucose and tannic acid, wherein the concentration of glucose is 2 g / L to 6 g / L and the concentration of tannic acid is 5 g / L to 8 g / L. The other steps are the same as in Specific Implementation Methods One to Six.

[0048] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the soaking time is 24 to 36 hours. The other steps are the same as in Specific Implementation Methods One to Seven.

[0049] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the mass ratio of volcanic rock, pyrite, and diatomaceous earth is (0.5–1):(1–2):(2–3); the surface modification solution II is an aqueous solution of graphene, ferric chloride, and cobalt chloride, wherein the concentration of graphene is 8 g / L–10 g / L, the concentration of ferric chloride is 3 g / L–4 g / L, and the concentration of cobalt chloride is 2 g / L–5 g / L. The other steps are the same as in Specific Implementation Methods One to Eight.

[0050] Specific Implementation Method Ten: The difference between this implementation method and Specific Implementation Methods One to Nine is that the graphene accounts for 0.1% to 0.3% of the mass of mixture II. The other steps are the same as those in Specific Implementation Methods One to Nine.

[0051] The beneficial effects of the present invention are verified using the following embodiments:

[0052] Example 1: A high-efficiency nitrogen removal process for wastewater based on graphene-modified packing material, specifically completed according to the following steps:

[0053] 1. The wastewater is passed into a grit chamber for filtration to remove large solids, resulting in filtered wastewater;

[0054] The total nitrogen concentration in the wastewater described in step one is 280 mg / L, and the total phosphorus concentration is 12 mg / L.

[0055] 2. The filtered wastewater is introduced into a flocculation tank to remove organic matter, SS and TP from the wastewater, resulting in wastewater treated by the flocculation tank;

[0056] The flocculation tank described in step two uses a micro-aeration process. The design and operating parameters of the flocculation tank are as follows: sludge load of 5.5 kg BOD5 / (kg MLSS·d), HRT of 1 h, SRT of 1 d, and DO concentration of 0.6 mg / L; PAM is added to the flocculation tank in step two at a concentration of 0.4 mg / L.

[0057] Third, the wastewater treated in the flocculation tank is introduced into the sedimentation tank for further treatment to separate the wastewater and sludge, resulting in wastewater treated in the sedimentation tank.

[0058] The sedimentation tank HRT mentioned in step three is 3 hours, and the sludge return ratio is 40%.

[0059] IV. The wastewater treated in the sedimentation tank is introduced into the nitrification process unit for further treatment, where some of the ammonia nitrogen in the wastewater is converted into nitrite nitrogen, resulting in wastewater treated by the nitrification process unit.

[0060] In step four, the nitrification process unit is inoculated with pure cultured AOB bacteria and enriched with suspended packing. The process parameters of the nitrification process unit are: HRT is 4h, DO is 1.0mg / L, continuous aeration or intermittent aeration is used, pH is 7.5-8.5, and when enriching AOB with suspended packing, the filling ratio is 30%.

[0061] 5. The wastewater treated by the nitrification process unit is introduced into the reactor of the sulfur autotrophic denitrification process for deep denitrification and phosphorus removal, resulting in wastewater treated by the sulfur autotrophic denitrification process.

[0062] The packing material used in the sulfur autotrophic denitrification process described in step five is filled in a cylindrical reactor equipped with an inlet, an outlet, a backwash water outlet, and a water quality testing port. Water enters from the bottom of the reactor and exits from the top, allowing the nitrogen gas generated in the reaction to escape upwards with the water flow. The top of the reactor is equipped with a perforated cover to facilitate the escape of nitrogen gas generated by denitrification, while also preventing oxygen in the air from dissolving in the water and affecting the quality of the effluent.

[0063] The packing material used in the sulfur autotrophic denitrification process described in step five consists of packing material A and packing material B, with a mass ratio of 2:3 between packing material A and packing material B.

[0064] In step five, packing material A and packing material B account for 30% of the reactor volume of the autotrophic denitrification process.

[0065] The method for preparing filler A described in step five is specifically completed according to the following steps:

[0066] Eggshell powder, tourmaline powder, and carbon fiber powder are mixed evenly to obtain mixture I; mixture I is immersed in surface modification solution I and left to stand for 30 hours, then removed and dried to obtain filler A; the surface modification solution I is an aqueous solution of glucose and tannic acid, wherein the concentration of glucose is 4 g / L and the concentration of tannic acid is 6 g / L; the mass ratio of eggshell powder, tourmaline powder, and carbon fiber powder is 2:0.5:3.

[0067] The preparation method of the filler B is specifically carried out according to the following steps:

[0068] Volcanic rock, pyrite, and diatomaceous earth were mixed evenly in a mass ratio of 0.5:1:2 to obtain mixture II. Mixture II was added to surface modification solution II to obtain another mixture. The mixture was transferred to a hydrothermal reactor and reacted at 180°C for 4 hours. The reaction product was washed with deionized water and dried to obtain filler B. Surface modification solution II was an aqueous solution of graphene, ferric chloride, and cobalt chloride, wherein the concentration of graphene was 8 g / L, the concentration of ferric chloride was 3 g / L, and the concentration of cobalt chloride was 3 g / L. The mass percentage of graphene in mixture II was 0.3%.

[0069] 6. The wastewater treated by the sulfur autotrophic denitrification process is introduced into a sulfate adsorption tank filled with hydrotalcite to adsorb sulfate ions in the wastewater, thus obtaining the wastewater after sulfate adsorption tank treatment.

[0070] In step six, the volume of hydrotalcite in the sulfate adsorption tank is 70% of the volume of the sulfate adsorption tank.

[0071] 7. The wastewater treated in the sulfate adsorption tank is introduced into a filter column filled with fine sand to filter the effluent from the sulfate adsorption process, thus obtaining water with high efficiency denitrification.

[0072] In step seven, the filter column filled with fine sand consists of two layers of fine sand, each layer supported by gravel. The particle size of the fine sand does not exceed 1.0 mm, and the particle size of the gravel does not exceed 10 mm.

[0073] Compared with Example 1: The difference between this embodiment and Example 1 is that the use of packing material A and packing material B is omitted in step five. All other steps and parameters are the same as in Example 1.

[0074] Comparative Example 2: The difference between this example and Example 1 is that packing material B is omitted in step five, and the reactor of the sulfur autotrophic denitrification process is filled entirely with packing material A, which occupies 30% of the reactor volume. All other steps and parameters are the same as in Example 1.

[0075] The water after efficient denitrification in step seven of Example 1, Comparative Example 1 and Comparative Example 2 was tested to determine the total nitrogen concentration and total phosphorus concentration in the water. The test data are listed in Table 1.

[0076] Table 1

[0077] Example 1 Compare with Example 1 Compare with Example 2 Total nitrogen concentration 2mg / L 60mg / L 10mg / L Total nitrogen removal rate 99.3％ 78.6％ 96.4％ Total phosphorus concentration (mg / L) 0.05 mg / L 2mg / L 0.31 mg / L Total phosphorus removal rate (%) 99.6％ 83.3％ 97.4％

[0078] As shown in Table 1, this invention prepared packing material A and packing material B, which, combined with a sulfur autotrophic denitrification process, achieve deep nitrogen and phosphorus removal from wastewater, resulting in a total nitrogen concentration as low as 2 mg / L and a total phosphorus concentration as low as 0.05 mg / L in the effluent. Furthermore, the nitrogen and phosphorus removal effect of using packing material A alone is not as good as that of using packing material A and packing material B together. Packing material A and packing material B can play a synergistic role in removing total nitrogen and total phosphorus from wastewater.

Claims

1. A high-efficiency nitrogen removal process for wastewater based on graphene-modified packing material, characterized in that... The efficient wastewater denitrification process based on graphene-modified packing material is specifically completed according to the following steps:

1. The wastewater is passed into a grit chamber for filtration to remove large solids, resulting in filtered wastewater; 2. The filtered wastewater is introduced into a flocculation tank to remove organic matter, SS and TP from the wastewater, resulting in wastewater treated by the flocculation tank; Third, the wastewater treated in the flocculation tank is introduced into the sedimentation tank for further treatment to separate the wastewater and sludge, resulting in wastewater treated in the sedimentation tank. IV. The wastewater treated in the sedimentation tank is introduced into the nitrification process unit for further treatment, where some of the ammonia nitrogen in the wastewater is converted into nitrite nitrogen, resulting in wastewater treated by the nitrification process unit.

5. The wastewater treated by the nitrification process unit is introduced into the reactor of the sulfur autotrophic denitrification process for deep denitrification and phosphorus removal, resulting in wastewater treated by the sulfur autotrophic denitrification process. The packing material used in the sulfur autotrophic denitrification process described in step five consists of packing material A and packing material B, with a mass ratio of (1~2):(3~4). The method for preparing filler A described in step five is specifically completed according to the following steps: Eggshell powder, tourmaline powder, and carbon fiber powder are mixed evenly to obtain mixture I; mixture I is immersed in surface modification solution I and left to stand for a period of time, then removed and dried to obtain filler A; the surface modification solution I is an aqueous solution of glucose and tannic acid; The preparation method of the filler B is specifically carried out according to the following steps: Volcanic rock, pyrite, and diatomaceous earth are mixed evenly to obtain mixture II; mixture II is added to surface modification solution II to obtain a mixture; the mixture is transferred to a hydrothermal reactor and reacted at 150~200℃ for 3~6 hours; the reaction product is washed with deionized water and dried to obtain filler B; the surface modification solution II is an aqueous solution of graphene, ferric chloride, and cobalt chloride.

6. The wastewater treated by the sulfur autotrophic denitrification process is introduced into a sulfate adsorption tank filled with hydrotalcite to adsorb sulfate ions in the wastewater, thus obtaining the wastewater after sulfate adsorption tank treatment.

7. The wastewater treated in the sulfate adsorption tank is introduced into a filter column filled with fine sand to filter the effluent from the sulfate adsorption process, thus obtaining water with high efficiency denitrification.

2. The efficient wastewater denitrification process based on graphene-modified packing material according to claim 1, characterized in that... The flocculation tank described in step two uses a micro-aeration process. The design and operating parameters of the flocculation tank are as follows: sludge load of 5~6 kg BOD5 / (kg MLSS∙d), HRT of 0.5~2 h, SRT of 0.5~1 d, and DO concentration of 0.5~0.8 mg / L; PAM is added to the flocculation tank described in step two at a concentration of 0.2~0.6 mg / L.

3. The efficient wastewater denitrification process based on graphene-modified packing material according to claim 1, characterized in that... The sedimentation tank HRT mentioned in step three is 2~3h, and the sludge return ratio is 30~50%.

4. The efficient wastewater denitrification process based on graphene-modified packing material according to claim 1, characterized in that... In step four, the nitrification process unit is inoculated with pure cultured AOB bacteria and enriched with suspended packing. The process parameters of the nitrification process unit are: HRT of 3-6h, DO of 0.5-1.0mg / L, continuous or intermittent aeration, pH of 7.5-8.5, and when enriching AOB with suspended packing, the filling ratio is 20-40%.

5. The efficient wastewater denitrification process based on graphene-modified packing material according to claim 1, characterized in that... The mass ratio of the eggshell powder, tourmaline powder and carbon fiber powder is (1~2):(0.5~1):(3~4).

6. The efficient wastewater denitrification process based on graphene-modified packing material according to claim 1, characterized in that... The surface modification solution I is an aqueous solution of glucose and tannic acid, wherein the concentration of glucose is 2 g / L to 6 g / L and the concentration of tannic acid is 5 g / L to 8 g / L.

7. The efficient wastewater denitrification process based on graphene-modified packing material according to claim 1, characterized in that... The soaking time is 24h~36h.

8. The efficient wastewater denitrification process based on graphene-modified packing material according to claim 1, characterized in that... The mass ratio of the volcanic rock, pyrite, and diatomite is (0.5~1):(1~2):(2~3); the surface modification solution II is an aqueous solution of graphene, ferric chloride, and cobalt chloride, wherein the concentration of graphene is 8g / L~10g / L, the concentration of ferric chloride is 3g / L~4g / L, and the concentration of cobalt chloride is 2g / L~5g / L.

9. The efficient wastewater denitrification process based on graphene-modified packing material according to claim 1, characterized in that... The graphene accounts for 0.1-0.3% of the mass of mixture II.