Low-carbon-nitrogen-ratio wastewater treatment method and reactor

Abstract

The invention relates to a low-carbon-nitrogen-ratio wastewater treatment method and a reactor, denitrification nitrogen removal treatment is performed by using a biological method, and the method specifically comprises the following steps: 1, an organic carbon source can be effectively and slowly released after agricultural waste corncob is pretreated, and two fillers are added into the reactor, so that the organic carbon source can be effectively and slowly released; wherein the filler 1 is a mixture of pretreated corncobs and zeolite, and the filler 2 is a mixture of pretreated corncobs, zeolite and cellulose decomposition bacteria. Two fillers are added into the reactor, so that the biological denitrification efficiency can be effectively improved, and the COD concentration in the discharged water body reaches the standard. Through cooperation of two factors including hydraulic retention time control and arrangement of two fillers in the reactor, ideal denitrification efficiency is achieved, meanwhile, the COD concentration in discharged water is well controlled not to exceed the standard, the COD concentration of effluent is relatively stable, and the COD concentration of the effluent can be further well controlled by controlling the use amount of the reacted fillers in the later period.

Description

Technical Field

[0001] This invention relates to the field of carbon sources for denitrification in wastewater treatment, and in particular to a method and reactor for treating wastewater with a low carbon-to-nitrogen ratio. Background Technology

[0002] Currently, many wastewater treatment effluents, such as those from aquaculture, are characterized by a low C / N ratio. This low C / N ratio effluent cannot be directly discharged and requires treatment. However, during denitrification, the carbon source is insufficient to meet the needs of denitrifying bacteria.

[0003] Currently, commonly used methods for denitrification in aquaculture wastewater are mainly divided into three categories: physical denitrification, chemical denitrification, and biological denitrification. Chemical denitrification involves adding liquid carbon sources (such as methanol and ethanol) to ensure the smooth progress of the denitrification process. However, because the dosage of liquid carbon sources is difficult to control, there is a risk of overdosing, which can easily lead to excessive dissolved organic matter content in the effluent. Furthermore, some liquid carbon sources, such as methanol and ethanol, pose safety hazards during storage, transportation, and handling due to their toxicity and flammability.

[0004] Biological nitrogen removal technology is based on the metabolic processes of microorganisms. Through a coupled nitrification-denitrification process, nitrogenous components such as ammonia nitrogen and nitrate in wastewater are converted into N2 for harmless removal. Biological methods are considered the most widely used method currently, offering advantages such as high treatment efficiency, low cost, and environmental friendliness. The denitrification process relies on heterotrophic denitrifying bacteria to gradually reduce NO3− or NO2− to gaseous nitrogen (N2) through catabolism under anaerobic conditions, thereby facilitating the migration of nitrogen from water bodies to the atmosphere. Supplementing with exogenous organic carbon sources is a key regulatory measure to improve nitrogen removal efficiency. Suitable carbon sources can provide denitrifying bacteria with sufficient energy and electrons, promoting denitrification.

[0005] Agricultural waste, due to its high cellulose content, porous structure, and low cost, is considered an ideal carrier for slow-release carbon. Pretreatment optimization can further control its carbon release rate and microbial availability. However, more carbon released from agricultural waste is not necessarily better; excessive carbon can affect the COD concentration of the effluent, leading to non-compliance with discharge standards. Therefore, continuous optimization of the biological denitrification process is necessary. Summary of the Invention

[0006] The purpose of this invention is to provide a wastewater treatment method and reactor with a low carbon-to-nitrogen ratio, which achieves good denitrification performance while ensuring that the COD concentration of the effluent meets the discharge standards.

[0007] To achieve the objectives of this invention, the technical solution is as follows:

[0008] A method for treating low C / N ratio wastewater, wherein the wastewater has a COD / TN ratio of <7-8, is treated using a biological method for denitrification. The method includes the following steps: 1. Adding biological packing material to a denitrification biological denitrification bioreactor. Two types of packing material are added to the reactor: packing material 1 is a mixture of pretreated corn cob and zeolite, and packing material 2 is a mixture of pretreated corn cob, zeolite, and cellulose-decomposing bacteria; 2. Biofilm formation and microbial acclimation in the reactor; 3. Connecting the inlet tank to the pump inlet, the pump outlet to the wastewater inlet of the denitrification biological denitrification bioreactor, and the outlet of the denitrification biological denitrification bioreactor to the effluent tank; 4. Introducing the wastewater treated by nitrifying bacteria oxidation into the inlet tank; 5. Adjusting the pump flow rate within the range of 0-100 mL / min, and controlling the hydraulic retention time to 6 h.

[0009] The aforementioned low carbon-to-nitrogen ratio wastewater treatment method uses a reactor structure where both the inlet and outlet are located at the bottom.

[0010] Furthermore, a baffle plate is installed in the middle of the bottom of the reactor, extending to approximately one-third of the distance from the top of the reactor. This baffle plate divides the reactor interior into left and right reaction chambers. The inlet of the denitrification biofilm denitrification bioreactor is located at the bottom of the left reaction chamber, and the outlet is located at the bottom of the right reaction chamber. Even further, the low C / N ratio wastewater treatment method also includes an influent tank, a water pump, a denitrification biofilm denitrification bioreactor, and an effluent tank. One end of the water pump is connected to the influent tank, and the other end is connected to the bottom inlet of the denitrification biofilm denitrification bioreactor. The outlet of the denitrification biofilm denitrification bioreactor is located at its bottom and connected to the effluent tank.

[0011] Furthermore, both the left and right reaction chambers of the reactor are equipped with packing material, with packing material 1 in the left reaction chamber and packing material 2 in the right reaction chamber.

[0012] Furthermore, the ratio of pretreated corn cob to zeolite in filler 1 is 1:1 to 1:1.3. The ratio of pretreated corn cob to zeolite in filler 2 is 1:1.5 to 1:1.8, and the mass of cellulose-decomposing bacteria is 0.1-1% of the mass of corn cob. The cellulose-decomposing bacteria can be selected from Bacillus subtilis, Bacillus cereus, Bacillus licheniformis, etc.

[0013] Furthermore, in step 2, the reactor biofilm formation and microbial acclimation method includes mixing the low C / N ratio wastewater to be treated with activated sludge in a specific ratio, inoculating the sludge with denitrifying bacteria, and adding the mixed strains with a MLSS concentration of approximately 2000-2500 mg / L to the reactor. Dissolved oxygen is removed by nitrogen stripping. The mixture is then allowed to stand for biofilm formation, and NO3 in the water is measured periodically. - -N and NO2 - Once the concentration of -N stabilizes, the microbial acclimatization process in the reactor is complete.

[0014] Furthermore, the pretreatment method for corn cobs includes the following steps:

[0015] S1. Place the corn cob in a 1.5% sodium hydroxide solution and let it stand at 22-28℃ for 24-48 h. Then rinse the corn cob and dry it in an oven at 50-60℃ for 10-12 h. S2. Cut the corn cob to a particle size of 8-12 mm.

[0016] The significant advantages of this invention compared to existing technologies are:

[0017] 1. By using agricultural waste corn cobs, pretreatment can effectively release organic carbon sources, realize waste reuse, and solve the problem of insufficient carbon sources and difficulty in biological denitrification; 2. By adding two types of packing materials to the reactor, the efficiency of biological denitrification can be effectively improved, and the COD concentration in the discharged water meets the standards.

[0018] 3. By controlling the hydraulic retention time and the synergistic effect of the two types of packing materials inside the reactor, ideal denitrification efficiency can be achieved while effectively controlling the COD concentration in the discharged water to keep it within the standard. The COD concentration of the effluent is relatively stable, and the COD concentration of the effluent can be further controlled by adjusting the amount of packing materials used in the reaction later. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the low carbon-to-nitrogen ratio wastewater treatment method of the present invention.

[0020] In the diagram, 1 is the inlet water tank, 2 is the pump, 3 is the denitrification biological denitrification bioreactor, 31 is the inlet, 32 is the outlet, 33 is the gas outlet, 34 is the baffle, 35 is the left reaction chamber, and 36 is the right reaction chamber. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the invention.

[0022] The present invention will be further described in detail below with reference to embodiments and specific implementation methods.

[0023] Example 1: Corn cob pretreatment

[0024] The pretreatment of corn cobs is carried out according to the following steps:

[0025] S1. Place the corn cob in a 1.5% sodium hydroxide solution and let it stand at 25°C for 24 hours. Then, rinse the corn cob and dry it in an oven at 60°C for 12 hours.

[0026] S2. Cut the corn cob, with a particle size of 8-12mm.

[0027] Example 2

[0028] A denitrification biological nitrogen removal bioreactor 3 is constructed, and its structural diagram is shown below. Figure 1 As shown, the reactor body is a cylindrical container made of plexiglass, with a height of 70cm and a diameter of 25cm. A partition 34 is located in the middle of the bottom of the reactor, extending to a height of 17cm about one-third of the way up from the top of the reactor. The partition 34 divides the reactor interior into left and right reaction chambers 36. The reactor adopts a bottom-inlet, bottom-outlet design. An air outlet 33 is located at the top of the reactor to facilitate the release of gases from the microorganisms. The wastewater inlet 31 is located at the bottom of the left reaction chamber 35, and the wastewater outlet 32 ​​is located at the bottom of the right reaction chamber 36. Volcanic rock is mixed with the corn cobs pretreated in Example 1. Packing material 1 (pretreated corn cobs to volcanic rock ratio of 1:1) is placed in the left reaction chamber 35. Packing material 2 (pretreated corn cobs to zeolite ratio of 1:1.5, with cellulose-decomposing bacteria added at 1% of the corn cob mass) is also placed in the left reaction chamber 35. The packing material height in both reaction chambers 36 is 15cm.

[0029] Connect the inlet water tank 1 to the inlet of the peristaltic pump 2, connect the outlet 32 ​​of the peristaltic pump 2 to the wastewater inlet 31 of the denitrification biological denitrification bioreactor 3, and connect the outlet 32 ​​of the denitrification biological denitrification bioreactor 3 to the outlet water tank.

[0030] Biofilm formation and microbial acclimatization in the reactor: Wastewater with a low C / N ratio from a wastewater treatment plant was mixed with activated sludge at a 1:1 volume ratio. Highly efficient denitrifying bacteria were then inoculated into the sludge (MLSS concentration of the mixed bacterial solution was approximately 2000 mg / L). The mixture was then introduced into the reactor, and dissolved oxygen was removed by nitrogen stripping. After static biofilm formation, samples were taken every two days to detect NO3 in the water. - -N and NO2 - The concentration of -N was determined, and the microbial domestication in the reactor was considered complete once both concentrations stabilized.

[0031] Water is supplied via peristaltic pump 2, with its flow rate adjustable within the range of 0–100 mL / min. NaNO3 is added to the inlet water tank 1 to adjust the NO3 content. - With a -N concentration of 10 mg / L and a retention time of 2 h, the water quality before and after wastewater treatment is shown in Table 1:

[0032] Table 1

[0033]

[0034] Example 3

[0035] A denitrification biological denitrification bioreactor 3 was constructed, with the same structural diagram as in Example 2. The difference is that both the left and right reactions use packing material 1.

[0036] The reactor biofilm formation and microbial acclimatization methods are the same as in Example 2.

[0037] Water is supplied via peristaltic pump 2, the flow rate of which can be adjusted within the range of 50–100 mL / min. NaNO3 is added to the inlet water tank 1 to adjust the NO3 content. - With a -N concentration of 10 mg / L and a retention time of 2 h, the water quality before and after wastewater treatment is shown in Table 2:

[0038] Table 2

[0039]

[0040] Example 4

[0041] A denitrification biological nitrogen removal bioreactor 3 was constructed, with the same structural diagram as in Example 2. The difference lies in the packing materials used in the left and right reactions: packing material 2 is used in the left reaction chamber 35, and packing material 1 is used in the right reaction chamber 36.

[0042] The reactor biofilm formation and microbial acclimatization methods are the same as in Example 2.

[0043] Water is supplied via peristaltic pump 2, whose flow rate can be adjusted within the range of 50-100 mL / min. NaNO3 is added to the inlet water tank 1 to adjust the NO3 content. - With a -N concentration of 10 mg / L and a retention time of 1 h, the water quality before and after wastewater treatment is shown in Table 3.

[0044] Table 3

[0045]

[0046] Example 5

[0047] Wastewater with a low C / N ratio was treated by nitrifying bacteria oxidation and then filtered before being fed into the influent tank 1 at the end of the experiment in Example 2. The water quality is shown in Table 4.

[0048] Table 4

[0049]

[0050] A peristaltic pump 2 was used for continuous water intake. The flow rate of the peristaltic pump 2 was adjustable within the range of 0-100 mL / min, enabling precise control of the influent flow rate. The operating temperature was maintained at 25±1℃ under different hydraulic retention times (HRT) conditions. The reactor was operated continuously for 15 days, with water samples taken from the outlet for testing. During reactor operation, influent and effluent samples were taken once daily at the same time to measure COD and NO3. - -N and TN were analyzed to determine the changes in water quality indicators, as shown in Table 5.

[0051] Table 5

[0052]

[0053] NO3 in reactor effluent under different HRT conditions - Changes in NO3- concentration in effluent under an HRT of 8 h. - -N concentration was 0.74–1.01 mg / L; when HRT was 6 h, NO3 in the effluent was... - -N concentration was 0.79–1.31 mg / L; HRT was 4 h, NO3 in the effluent was... - -N concentration ranged from 5.35 to 7.29 mg / L. With decreasing HRT, NO3 in the denitrification system effluent... - -N concentration begins to rise, and denitrification efficiency decreases. When the HRT (Heat Retention Time) is shortened, the nitrate nitrogen load entering the reaction system per unit time increases accordingly, which may cause the nitrate nitrogen load to exceed the reactor's maximum treatment capacity. Under an HRT of 8 hours, the reactor exhibits the best denitrification efficiency, allowing microorganisms more time to react with the wastewater. The continuously released carbon source from the treated corn cobs provides ample electron donors for denitrification, resulting in a more thorough denitrification reaction. After reducing the HRT, the NO3 in the reactor effluent decreases. - -N concentration increased. When HRT was shortened to 4 h, NO3 in the reactor effluent... - The concentration of nitrogen (N-N) increased significantly, and the denitrification efficiency decreased markedly. This may be because: the shortened hydraulic retention time (HRT) increased the influent hydraulic load, accelerating the erosion of the biofilm carrier, resulting in the loss of some attached denitrifying microorganisms, ultimately leading to a decline in overall denitrification performance. Furthermore, due to the excessively short retention time, the microorganisms did not have sufficient contact with nitrogenous pollutants in the effluent, and the carbon source released from the corn cob was not effectively utilized by the microorganisms.

[0054] The changes in TN concentration in the effluent under different HRT conditions were investigated. When the HRT was 8 h, the TN concentration in the effluent from the untreated and pretreated slow-release carbon source denitrification reactors ranged from 1.98 to 2.45 mg / L; when the HRT was 6 h, the TN concentration ranged from 2.69 to 4.16 mg / L; and when the HRT decreased to 4 h, the TN concentration ranged from 6.89 to 10.02 mg / L. Overall, as the HRT decreased, the TN concentration in the reactor effluent increased, and the TN removal efficiency decreased.

[0055] The variation of COD concentration in the reactor effluent under different HRT conditions was as follows: When the HRT was 8 h, the COD concentration in the reactor effluent was 34.23–40.31 mg / L; when the HRT was 6 h, the COD concentration was 19.62–25.25 mg / L; and when the HRT was reduced to 4 h, the COD concentration was 13.58–18.79 mg / L. Using an HRT of 8 h could result in an instantaneous COD exceeding 30 mg / L, which would not meet the instantaneous discharge requirements in some areas of Jiangsu province and would exceed the influent COD concentration. When the HRT was reduced to 4 h, the COD concentration in the reactor effluent remained at a low level, but the low carbon release from the corn cob would lead to insufficient carbon source for denitrification, thus affecting nitrogen removal efficiency. In the denitrification system, shortening the hydraulic retention time can effectively reduce the formation of dissolved organic matter. When the hydraulic retention time (HRT) is 6 hours, the COD in the reactor effluent is sufficient to meet the carbon requirements for denitrification, and the organic carbon source released by the corn cob can be effectively utilized. When the hydraulic retention time is extended to 8 hours, the carbon source release exceeds the requirements of the denitrification reaction due to the high carbon release performance of the pretreated corn cob, resulting in a significant increase in the COD concentration in the effluent.

[0056] Example 6

[0057] Wastewater with a low C / N ratio was taken, and after being treated by nitrifying bacteria oxidation and filtered, it was introduced into the influent tank 1 at the end of the experiment in Example 4. The quality of the influent was the same as that in Example 5.

[0058] A peristaltic pump 2 was used for continuous water intake. The flow rate of the peristaltic pump 2 was adjustable within the range of 0–100 mL / min, enabling precise control of the influent flow rate. The temperature was controlled at 25 ± 1℃ under different hydraulic retention times (HRT) conditions. The reactor was operated continuously for 15 days, with water samples taken from the outlet for testing. During reactor operation, influent and effluent samples were taken daily to measure COD and NO3. - -N and TN were analyzed to determine the changes in water quality indicators, as shown in Table 6.

[0059] Table 6

[0060]

[0061] NO3 in reactor effluent under different HRT conditions - Changes in NO3- concentration in effluent under an HRT of 8 h. - -N concentration was 1.85–3.62 mg / L; when HRT was 6 h, NO3 in the effluent was... - -N concentration was 3.85–4.85 mg / L; HRT was 4 h, NO3 in the effluent was... - The -N concentration ranged from 9.5 to 14.23 mg / L. Compared to Example 5, the denitrification performance of this example decreased due to the different placement of the packing material. When the HRT was 4 hours, the denitrification rate was only around 50%.

[0062] The changes in TN concentration in the reactor effluent under different HRT conditions were observed. When the HRT was 8 h, the TN concentration in the reactor effluent was 2.86–3.87 mg / L; when the HRT was 6 h, the TN concentration was 4.23–6.72 mg / L; and when the HRT decreased to 4 h, the TN concentration was 10.23–15.12 mg / L. Compared with Example 5, the denitrification performance of this example decreased due to the different placement of the packing material.

[0063] The variation of COD concentration in the reactor effluent under different HRT conditions was as follows: when the HRT was 8 h, the COD concentration in the reactor effluent was 34.52–50.52 mg / L; when the HRT was 6 h, the COD concentration in the reactor effluent was 31.41–38.13 mg / L; and when the HRT was reduced to 4 h, the COD concentration in the reactor effluent was 21.84–27.31 mg / L. At an HRT of 8 h, the instantaneous COD concentration could exceed 50 mg / L, and at an HRT of 6 h, the instantaneous COD concentration could exceed 30 mg / L, failing to meet the instantaneous discharge requirements. Furthermore, due to experimental limitations, the COD concentration in this example showed a slow upward trend; therefore, if the detection time is extended in later stages, the COD concentration may continue to rise. This is due to the different positions of packing materials 1 and 2 in the reactor. It is possible that because packing material 2 contains decomposing bacteria, the organic matter content in the reactor is initially high and then decreases. Therefore, the COD concentration continues to rise over time, making it difficult to control the amount of packing material used in the reaction. In contrast, the packing material position in Example 5 is the opposite of this example, and the COD concentration of the effluent is relatively stable. In the later stages, the COD concentration of the effluent can be further controlled by controlling the amount of packing material used in the reaction.

Claims

1. A method for treating wastewater with a low carbon-to-nitrogen ratio, wherein the wastewater has a COD / TN ratio of <8, and is treated by denitrification using a biological method, characterized in that: Specifically, the steps are as follows:

1. Add biological packing material to the denitrification biological denitrification bioreactor (3). Two types of packing material are added to the reactor, wherein packing material 1 is a mixture of pretreated corn cob and zeolite, and packing material 2 is a mixture of pretreated corn cob, zeolite and cellulose-decomposing bacteria; 2. Biofilm formation and microbial acclimatization in the reactor; 3. Connect the inlet water tank (1) to the inlet of the pump (2), connect the outlet of the pump (2) to the wastewater inlet (31) of the denitrification biological denitrification bioreactor (3), and connect the outlet (32) of the denitrification biological denitrification bioreactor (3) to the outlet water tank; 4. Put the wastewater treated by nitrifying bacteria oxidation into the inlet water tank (1); 5. Adjust the flow rate of the pump (2) to 0-100 mL / min and control the hydraulic retention time to 6 h.

2. The method for treating low carbon-to-nitrogen ratio wastewater according to claim 1, characterized in that: The denitrification biological denitrification bioreactor (3) has both its inlet and outlet (32) located at the bottom.

3. The method for treating low carbon-to-nitrogen ratio wastewater according to claim 2, characterized in that: The ratio of pretreated corn cob to zeolite in filler 1 is 1:1 to 1:1.3; the ratio of pretreated corn cob to zeolite in filler 2 is 1:1.5 to 1:1.8, and the mass of cellulose-decomposing bacteria is 0.1-1% of the mass of corn cob.

4. A reactor for treating wastewater with a low carbon-to-nitrogen ratio, characterized in that: The reactor is provided with a partition (34) in the middle of the bottom. The partition (34) extends to 1 / 3 of the distance from the top of the reactor. The partition (34) divides the inside of the reactor into left and right reaction chambers 36. The inlet (31) of the denitrification biofilm denitrification bioreactor is located at the bottom of the left reaction chamber (35), and the outlet (32) is located at the bottom of the right reaction chamber 36. The left and right reaction chambers 36 of the reactor are both filled with packing material. The left reaction chamber (35) is filled with packing material 1, and the right reaction chamber (36) is filled with packing material 2.

5. The method for treating low carbon-to-nitrogen ratio wastewater according to claim 1, characterized in that: The reactor biofilm formation and microbial acclimation method in step 2 includes mixing the low C / N ratio wastewater to be treated with activated sludge in a certain proportion, inoculating the sludge with denitrifying bacteria, and adding the mixed strain with a MLSS concentration of approximately 2000-2500 mg / L to the reactor. Dissolved oxygen is removed by nitrogen stripping, the mixture is allowed to stand for biofilm formation, and NO3 in the water is detected. - -N and NO2 - Once the concentration of -N stabilizes, the microbial acclimatization process in the reactor is complete.

6. The method for treating low carbon-to-nitrogen ratio wastewater according to claim 1, characterized in that: The pretreatment method for corn cobs includes the following steps: S1, placing the corn cobs in a 1.5% sodium hydroxide solution and allowing them to stand at 22-28℃ for 24-48 h, then rinsing the corn cobs and drying them in an oven at 50-60℃ for 10-12 h; S2, cutting the corn cobs to a particle size of 8-12 mm.

7. A reactor for treating wastewater with a low carbon-to-nitrogen ratio, characterized in that: The reactor is used in any one of the low carbon-to-nitrogen ratio wastewater treatment methods as described in claims 1 to 6. The equipment used in the low carbon-to-nitrogen ratio wastewater treatment method includes an inlet tank (1), a water pump (2), a denitrification biofilm denitrification bioreactor (3), and an outlet tank. One end of the water pump (2) is connected to the inlet tank (1), and the other end is connected to the bottom inlet (31) of the denitrification biofilm denitrification bioreactor. The outlet (32) of the denitrification biofilm denitrification bioreactor is located at its bottom and connected to the outlet tank. The left and right reaction chambers of the reactor are both equipped with packing material. The left reaction chamber (35) is equipped with packing material 1, and the right reaction chamber (36) is equipped with packing material 2.

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