A closed-loop bioreactor and its application in groundwater denitrification

Abstract

The present invention discloses a closed-loop bioreactor and its application in groundwater denitrification. The closed-loop bioreactor comprises a peristaltic pump and a reactor body. The reactor body is a hollow cylinder with a triangular bracket disposed at the bottom for securing the reactor body. The reactor body is provided with a sampling port and a liquid outlet at the top and a liquid inlet at the bottom. The reactor body is provided with a first sand and gravel layer, an inorganic matrix layer, a mud and sand layer, a second sand and gravel layer, and a packing layer arranged in sequence from the bottom to the top. The packing layer is provided with multiple fixed disks for securing the packing so that it is evenly distributed throughout the packing layer. The closed-loop bioreactor for groundwater denitrification of the present invention has a simple structure and a high pollutant removal efficiency (over 99%). In practical application, the initial economic cost investment is lower, making industrialization easier.

Description

(1) Technical field

[0001] The invention relates to a method for denitrifying groundwater, in particular to a method for denitrifying groundwater by utilizing bottom mud and brown sugar, and a denitrification device constructed thereby. (2) Background technology

[0002] Groundwater is the primary source of drinking water in many regions of the world. In some arid or rural areas, groundwater is even the sole source of water or is used directly as drinking water. However, the application of fertilizers in agricultural production, the leakage of domestic sewage and nitrogen-containing industrial wastewater, and other factors all lead to the entry of large amounts of nitrogen-containing substances into groundwater, causing nitrate levels to exceed permitted levels. When high-nitrate groundwater is consumed, the nitrate enters the body and forms nitrites in the stomach, causing methemoglobinemia and even chemically stable carcinogens (nitrosamines and nitrosophthalamides), which can induce a range of tumors. Therefore, the prevention and control of nitrate contamination in groundwater is crucial, especially in rural areas.

[0003] The existing methods for denitrification of groundwater are mainly based on biological methods, including in-situ biological denitrification and reactor biological denitrification. In-situ biological denitrification is to denitrify nitrate-contaminated groundwater in situ. Although the operating cost is low, since it is carried out underground, the reaction conditions are difficult to control, the reaction efficiency cannot be guaranteed, and the operation is difficult. Reactor biological denitrification fixes the denitrifying bacteria on a carrier of a certain thickness and uses methanol, ethanol, acetic acid or straw as a carbon source to achieve the effect of biological denitrification. The reactor biological denitrification method has the advantages of simple operation, environmental protection, and low cost, but excessive addition of organic carbon sources (methanol, ethanol, acetic acid) will cause secondary pollution, and if the addition amount is small, denitrification will be incomplete; solid carbon sources (straw) and other microorganisms are difficult to utilize, and the denitrification effect is poor.

[0004] Cheng Yanan and others used methanol as a carbon source in the laboratory to build a homemade electrode biofilm reactor (cathode: cotton microorganisms embedded in stainless steel wire, reduction reaction to remove nitrate components in sewage; anode: carbon rod, the carbon dioxide produced by the oxidation reaction is used as a carbon source to remove nitrogen pollutants and produce reductase to inhibit nitrite production). If the optimal C / N mass ratio is maintained at 1 mg / mg during the entire reaction process, the nitrogen pollutant removal rate can reach 95%. This method requires less carbon source and has a high treatment effect, but it is obvious that in actual production, when treating large amounts of groundwater in this way, not only the scale of the electrolysis reaction must be strictly controlled, but the C / N mass ratio must also be kept at the optimal stage, so the economic investment is huge.

[0005] Chen Lei and his colleagues used biodegradable plastics as a new filler to achieve a slow-release carbon source, overcoming the high risk of secondary pollution caused by improper carbon source control during the original biological denitrification process. Zeolite was used as a carrier (providing a favorable growth environment for microorganisms), resulting in high economic benefits and excellent remediation results (nitrogen removal efficiency reaching 99%). However, achieving this effect requires a 15-25 day process.

[0006] Riverbed mud is rich in organic matter, nutrients such as nitrogen and phosphorus, as well as a wide variety of microorganisms associated with these substances, including denitrifying bacteria. Denitrification, which converts nitrates into nitrogen gas, is the most effective and safest method for removing nitrates from water bodies. Brown sugar is a staple in rural China. If common rural mud and brown sugar were used for denitrification, it would have significant implications for groundwater nitrate control.

[0007] Therefore, it is necessary to design a denitrification method that is efficient in degradation, simple in operation, low in cost, and environmentally friendly, and utilizes the denitrifying bacteria rich in the bottom mud of the water body and uses brown sugar as a carbon source to enhance the denitrification effect. (3) Summary of the invention

[0008] The present invention aims to provide a closed-loop bioreactor and its application in groundwater denitrification. The reactor has a simpler structure but a higher pollutant removal efficiency (over 99%). In actual application, the initial economic cost investment is lower, making industrialization easier. By adding brown sugar as a carbon source, the reaction solution can denitrify groundwater under various environmental conditions within 10 days, with the same degradation effect. The carbon source of the present invention is readily available, clean, has a high denitrification rate, is environmentally friendly, and is simple to operate. When put into actual production, it can balance treatment efficiency and treatment costs.

[0009] The technical solution adopted in the present invention is:

[0010] The present invention provides a closed-loop bioreactor, which consists of a peristaltic pump and a reactor body. The reactor body is a hollow cylinder, and a triangular bracket is provided at the bottom of the reactor body for fixing the reactor body; a sampling port and a liquid outlet are provided at the top of the reactor body, and a liquid inlet is provided at the bottom; a first sand and gravel layer (2), an inorganic matrix layer (3), a mud and sand layer (4), a second sand and gravel layer (5), and a packing layer (7) are sequentially provided inside the reactor body from the bottom to the top; a plurality of fixing plates (6) are provided on the packing layer for fixing the packing so that the packing is evenly distributed in the packing layer.

[0011] Preferably, the reactor body is an organic glass column, more preferably 60 cm in height and 15 cm in diameter. The triangular support is 10 cm in height.

[0012] Preferably, the filling material is bagasse, which is obtained by squeezing sugarcane juice and then drying it in a well-ventilated outdoor area. The filling height of the filling layer is 60-70% of the column height, preferably 66.67%.

[0013] Preferably, the fixing plate is a grid-shaped plastic plate, preferably arranged at a height of 20 cm and 40 cm above the reactor body.

[0014] Preferably, the mud and sand layer is a mixture of riverbed mud and medium sand in a mass ratio of 1:1; the riverbed mud refers to fresh mud with a surface depth of 0-15 cm, and the medium sand has a particle size of 0.5-0.25 mm. This ensures smooth passage of water while providing sufficient pore volume for microbial growth.

[0015] Preferably, the sand and gravel in the first and second sand and gravel layers are natural coarse river sand particles with a particle size of 1-1.5 mm, which are spread on the bottom of the reactor to prevent the water inlet below from being blocked, and on the mud and sand layer to simulate the actual sediment structure.

[0016] Preferably, the inorganic matrix layer is prepared by inactivating and burning the mud and sand in a muffle furnace at 500°C for 2 hours to kill all organic matter, thereby ensuring that water can pass smoothly; the mud and sand is a mixture of riverbed mud and medium sand in a mass ratio of 1:1.

[0017] The present invention also provides an application of the closed-loop bioreactor in groundwater denitrification. The application method comprises the following steps: adding a carbon source to groundwater, adjusting the pH of the water to 5-9.5, adding the water as overlying water from a liquid outlet to a packing layer of a reactor body, controlling the water temperature to maintain at 10-20°C, starting a peristaltic pump, allowing the overlying water to pass through a liquid inlet, a first gravel layer, an inorganic matrix layer, a mud and sand layer, a second gravel layer, and a packing layer, and then be discharged from the liquid outlet and refluxed to the liquid inlet of the reactor body through the peristaltic pump. The water body is controlled to circulate from bottom to top, and the water body of the entire reactor is kept in an internal circulation state. During operation, the COD value of the water body is maintained at 20-150 mg / L by adding a carbon source; the DO value is maintained at 1-6 mg / L by injecting air or argon; overlying water is collected from a sampling port using a pipette every 4 to 8 hours to monitor the concentrations of nitrate, nitrite, and ammonium ions, and the COD value is detected simultaneously. The overlying water is discharged after the groundwater is completely denitrified, thereby achieving the purpose of rapid groundwater denitrification. The carbon source is brown sugar.

[0018] Preferably, the groundwater is taken from well water commonly found in rural areas and towns, and the water body is relatively stable, NO3 - The COD value is maintained at 40-45 mg / L all year round, and the initial COD value is 5-65 mg / L. The overlying water flow rate is maintained at 1.5×10 -6 L / s.

[0019] Preferably, the pH of the water is adjusted to 7.5 and the water temperature is 20°C.

[0020] Preferably, the brown sugar is commercially available 100% pure brown sugar. The amount of carbon source added is such that the C / N mass ratio of the water body is maintained at 4-4.5:1.

[0021] Preferably, during the operation, dissolved oxygen (DO) is maintained at 1.8-2.2 mg / L.

[0022] The effect of the closed-loop bioreactor of the present invention on groundwater denitrification is compared with that of the prior art. The results are shown in Table 1. It can be seen that the economic benefit of the device is superior, and the denitrification rate is higher while ensuring no secondary pollution.

[0023] The references for sodium acetate in Table 1 are (Li Jinshi. Study on the influence of different carbon sources and C / N ratios on denitrification system [D]. Wuhan University of Technology, 2011.), methanol reference (Cheng Yanan, Wang Tiantian, Zhang Peng. Analysis of the influence of carbon-nitrogen ratio on biofilm treatment of nitrogen-contaminated groundwater [J]. Green Technology, 2017(18):109-111.DOI:10.16663 / j.cnki.lskj.2017.18.034.); sawdust and paper scraps reference (Jiang Tingliang. Research on partitioned PRB technology for remediation of nitrogen contaminated groundwater [D]. China University of Geosciences (Beijing), 2014.); combined carbon source reference (Zhang Wen, Yin Lin, Zhou Nian Qing. Research and development of slow-release carbon source materials for in-situ remediation of groundwater nitrogen pollution and their physicochemical-habitat synergistic characteristics [J]. Environmental Science, 2018, 39(09): 4150-4160. DOI: 10.13227 / j.hjkx.201711091.); References for biodegradable plastics (Chen Lei, Jiang Yu, Gong Bin, et al. Study on bioremediation of nitrate nitrogen contaminated groundwater by biodegradable plastics and zeolite carrier system [J]. Environmental Pollution and Control, 2017, 39(04): 345-351+355. DOI: 10.15985 / j.cnki.1001-3865.2017.04.001.).

[0024] Table 1 Comparison of carbon source denitrification rate

[0025]

[0026] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0027] 1) The closed-loop bioreactor for groundwater denitrification of the present invention has a simple structure, an easily available and clean carbon source, a high pollutant removal efficiency (over 99%), and in actual application, lower initial economic cost investment, making industrialization easier to achieve.

[0028] 2) The present invention uses riverbed mud as the inoculum for denitrifying bacteria, which is taken from the natural environment, is easy to obtain, and is pollution-free.

[0029] 3) The carbon source of the present invention is common edible brown sugar, which is easily available and a clean raw material.

[0030] 4) The closed-loop bioreactor of the present invention has a nitrate and nitrite removal rate of over 99% in most environments, and the operation process is completed in 2-10 days. It has a strong denitrification capacity and is relatively stable, with low economic investment and no harmful by-products. (IV) Description of the accompanying drawings

[0031] Figure 1 Schematic diagram of the closed-loop reactor structure: 1-peristaltic pump, 2-first sand and gravel layer, 3-inorganic matrix layer, 4-mud and sand layer, 5-second sand and gravel layer, 6-fixed plate, 7-filler, 8-sampling port. (V) Specific implementation methods

[0032] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0033] Example 1: Closed-loop bioreactor structure and method of use

[0034] 1. Closed-loop bioreactor structure

[0035] Reference Figure 1 The closed-loop bioreactor of the present invention consists of a peristaltic pump 1 and a reactor body, wherein the reactor body is a hollow organic glass column (height 60 cm, diameter 15 cm, volume 10.6 L), and a triangular bracket (height 10 cm) is provided at the lower part of the reactor body for fixing the reactor body; a sampling port 8 and a liquid outlet are provided at the top of the reactor body, and a liquid inlet is provided at the bottom; a first sand and gravel layer 2, an inorganic matrix layer 3, a mud and sand layer 4, a second sand and gravel layer 5, and a packing layer 7 are sequentially provided inside the reactor body from the bottom to the top; a fixed disk 6 is provided in the packing layer, which is respectively arranged at 20 cm and 40 cm of the height of the reactor body; the peristaltic pump 1 model is Lange BT100-3J.

[0036] The mud and sand layer is a mixture of riverbed mud (fresh mud, sampling depth 0-15 cm from the surface of the mud) and medium sand (particle size within the range of 0.5 mm to 0.25 mm) in a mass ratio of 1:1. This ensures that water can pass smoothly and has sufficient pore volume for microbial growth.

[0037] The sand and gravel used in the first and second sand and gravel layers are all natural coarse river sand particles with a particle size of 1-1.5 mm. They are spread on the bottom of the reactor to prevent the water inlet below from being blocked, and are spread on the mud and sand layer 4 to simulate the actual sediment structure.

[0038] The inorganic matrix layer is prepared by inactivating and burning the mud and sand (the mass ratio of riverbed mud to medium sand is 1:1) in a muffle furnace at 500° C. for 2 hours to kill all organic matter, thereby ensuring that water can pass through smoothly.

[0039] The filler is made by squeezing juice from common sugarcane on the market and then airing it in a ventilated place outdoors, and the filling height is 66.67% of the column height.

[0040] The fixing plate is a grid-shaped plastic plate used to fix the filler so that it is evenly distributed in the water body for adsorption by microorganisms in the water body.

[0041] 2. How to use the closed-loop bioreactor

[0042] Groundwater, taken from well water commonly found in rural areas, NO3 - Maintained at 40-45 mg / L, the initial COD value is 5-65 mg / L.

[0043] Add brown sugar to the above-mentioned groundwater so that the C / N mass ratio is 4-4.5:1, adjust the pH of the water to 7.5 as overlying water, add it to the packing layer of the reactor body from the liquid outlet, control the water temperature to maintain at 20±2°C, start the peristaltic pump 1, and the overlying water enters from the liquid inlet through the first sand and gravel layer, inorganic matrix layer, mud and sand layer, second sand and gravel layer, and packing layer. After being discharged from the liquid outlet, it returns to the liquid inlet of the reactor body through the peristaltic pump, and controls the reactor water to circulate from bottom to top to keep the entire reactor water in an internal circulation state. During operation, the COD of the water body is maintained at 20-150 mg / L by adding carbon source; the sampling port cover is opened every 2 hours to measure the DO in the water, and air or argon is filled to keep it at 2 mg / L; every 4 to 8 hours, a pipette is used to collect overlying water from the sampling port, 10 ml of which is used for nitrate, nitrite and ammonium determination (ion chromatograph: Dion ICS-900, water sample is filtered through a 0.22μm filter membrane), and 3 ml is used for COD detection (national standard method: HJ / T 399-2007, a certain concentration of silver sulfate, mercuric sulfate and potassium dichromate solution is added and digested at 165℃ for 15 minutes) to achieve real-time monitoring of nitrate degradation in the water.

[0044] The carbon source is brown sugar sold in supermarkets (ingredients: 100% pure brown sugar).

[0045] Example 2: Application of closed-loop bioreactor in degradation of water bodies with different dissolved oxygen levels:

[0046] The closed-loop bioreactor and method of use of Example 1 were used to set up four parallel reactors.

[0047] Reactor 1 is the closed-loop bioreactor of Example 1. Inside the reactor body, from bottom to top, a first gravel layer 2 with a depth of 1 cm, an inorganic matrix layer 3 with a depth of 6 cm, a muddy sand layer 4 with a depth of 2 cm, a second gravel layer 5 with a depth of 1 cm, and a filler layer 7 with a thickness of 40 cm are sequentially arranged. 0.702 g of brown sugar was added to 7.065 L of groundwater (nitrate concentration 44 mg / L, nitrite concentration 1 mg / L) taken from a well to obtain a C / N mass ratio of 4.25:1. The pH of the water was adjusted to 7.5, and the overlying water was added to the filler layer of the reactor body. The water temperature was maintained at 20°C by the indoor temperature control system, and the flow rate was maintained at 1.5×10 - 6 L / s. During operation, DO=2mg / L was set by filling in air or argon (purchased from Hangzhou Jingong Special Gas Co., Ltd.), and COD of the water body was maintained at 20-150mg / L by adding brown sugar.

[0048] Reactor 2, reactor 3 and reactor 4 have the same structure as reactor 1, except that the DO values ​​are maintained at 1 mg / L, 3.5 mg / L and 6 mg / L respectively by filling with air or argon.

[0049] The dissolved oxygen and temperature of the water were measured using a portable dissolved oxygen meter (T, Lei Ji JPB 607A). The pH of the water was measured using a pH meter (Mettler FG2-FK), and the pH was adjusted using hydrochloric acid and sodium hydroxide.

[0050] When DO=1, 2, 3.5, 6 mg / L, the degradation time of nitrate in the reactor (defined as complete degradation or inability to continue degradation for a long time) was 52, 102, 169, 239 h, respectively, while the degradation time of nitrite was 66, 97, 133, 239 h, respectively. When DO = 1 mg / L, nitrate is completely degraded before nitrite, and nitrite accumulation is obvious. During the operation of the reactor, the total COD consumption is 160-180 mg / L, the nitrate removal efficiency is as high as 100%, and the degradation rate is about 0.15 mgN / h; when DO = 2 and 3.5 mg / L, the generated nitrite is completely degraded before nitrate. During the operation of the reactor, the total COD consumption is 220-240 and 280-300 mg / L, respectively. At this time, the nitrate removal efficiency of the reactor is 100%, and the degradation rates are about 0.0974 and 0.0588 mg N / h; when DO = 6 mg / L, neither nitrate nor nitrite can be completely degraded. During the operation of the reactor, the total COD consumption is 410-430 mg / L. At this time, the nitrate removal efficiency of the reactor is still 99%, and the degradation rate is about 0.0416 mg N / h.

[0051] Table 2: Effect of DO on nitrogen removal

[0052]

[0053] Example 3: Application of the reactor to the degradation of water bodies with different pH values:

[0054] The treatment was the same as that in reactor 1 of Example 2, except that the pH of the water was adjusted to 6, 7.5, and 8.5 respectively after the addition of brown sugar.

[0055] At pH values ​​of 6, 7.5, and 8.5, the degradation time for nitrate in the reactor was 128, 102, and 140 hours, respectively, while the degradation time for nitrite was 128, 97, and 140 hours, respectively. Both nitrate and nitrite were completely degraded, with total COD consumption during operation reaching 270-290, 220-240, and 320-330 mg / L, respectively. At these times, the reactor achieved 100% nitrate removal efficiency, with degradation rates of approximately 0.0776, 0.0974, and 0.071 mg N / h, respectively.

[0056] Table 3: Effect of pH on denitrification

[0057]

[0058] Example 4: Application of the reactor to the degradation of water at different temperatures:

[0059] The treatment was the same as that of reactor 1 in Example 2, except that the temperatures were set at 10°C and 20°C, respectively.

[0060] When the water temperature is 20°C, the degradation time of nitrate and nitrite in the reactor is 102 and 97 hours, and the degradation is complete. During the operation of the reactor, the total COD consumption is 220-240 mg / L. At this time, the nitrate removal efficiency of the reactor is as high as 100%, and the degradation rate is about 0.0974 mg N / h; when the water temperature is 10°C, the degradation time of nitrate and nitrite in the reactor is 148 hours (some residues cannot be degraded). During the operation of the reactor, the total COD consumption is 150-170 mg / L. At this time, the nitrate removal efficiency of the reactor is nearly 90%, and the degradation rate is about 0.0575 mg N / h.

[0061] Table 4: Effect of temperature on denitrification

[0062]

[0063] Example 5: Application of the reactor to the degradation of nitrate water with different concentrations:

[0064] The treatment was the same as that in reactor 1 of Example 2, except that the initial nitrate concentrations in the overlying water were set to 44, 22, and 11 mg / L, respectively.

[0065] When the initial nitrate concentrations were 44, 22, and 11 mg / L, the degradation time of nitrate in the reactor was 102, 73, and 45 h, while the degradation time of nitrite was 97, 73, and 45 h. Both nitrate and nitrite were completely degraded. During the operation of the reactor, the total COD consumption was 220-240, 90-110, and 60-80 mg / L. At this time, the nitrate removal efficiency of the reactor was as high as 100%, and the degradation rates were approximately 0.0974, 0.0681, and 0.0552 mg N / h.

[0066] Table 5: About NO3 - Effect of initial concentration on denitrification

[0067]

[0068] The contents described in the embodiments of this specification are merely an enumeration of the implementation forms of the denitrification method. The scope of protection should not be regarded as limited to the specific forms described in the embodiments, but also includes equivalent technical means that can be conceived by those skilled in the art based on the concepts of this specification.

Claims

1. A method for denitrifying groundwater using a closed-loop bioreactor, characterized in that: The closed-loop bioreactor consists of a peristaltic pump and a reactor body. The reactor body is a hollow cylinder. A triangular bracket is provided at the bottom of the reactor body for fixing the reactor body. A sampling port and a liquid outlet are provided at the top of the reactor body, and a liquid inlet is provided at the bottom. A first sand and gravel layer, an inorganic matrix layer, a mud and sand layer, a second sand and gravel layer, and a filler layer are sequentially provided inside the reactor body from the bottom to the top. The filler layer is provided with multiple fixing plates for fixing the filler so that it is evenly distributed in the filler layer. The filler is sugarcane bagasse. The method comprises the following steps: adding a carbon source to groundwater, adjusting the pH value of the water to 6-8.5, adding the water as overlying water to the packing layer of a reactor body through a liquid outlet, controlling the water temperature to maintain at 10-20°C, starting a peristaltic pump, allowing the overlying water to pass through a first sand and gravel layer, an inorganic matrix layer, a mud and sand layer, a second sand and gravel layer, and a packing layer through a liquid inlet, and then being discharged from the liquid outlet and then refluxed to the liquid inlet of the reactor body through the peristaltic pump, controlling the water body to circulate from bottom to top, and keeping the water body of the entire reactor in an internal circulation state; during operation, maintaining the COD value of the water body at 20-150 mg / L by adding the carbon source; maintaining the DO value at 1-6 mg / L by injecting air or argon; collecting the overlying water through a sampling port using a pipette every 4 to 8 hours to monitor the concentrations of nitrate, nitrite, and ammonium ions, and simultaneously detecting the COD value; and discharging the water body after the groundwater is completely denitrified, thereby achieving the purpose of rapid denitrification of the groundwater; and the carbon source is brown sugar.

2. The method according to claim 1, wherein The reactor body is an organic glass column.

3. The method according to claim 1, wherein The bagasse is obtained by naturally drying the sugarcane in a ventilated place outdoors after squeezing the juice, and the fixed plate is a grid-shaped plastic plate.

4. The method according to claim 1, wherein The mud and sand used in the mud and sand layer is a mixture of riverbed mud and medium sand in a mass ratio of 1:1; the riverbed mud refers to fresh mud with a surface depth of 0-15 cm, and the medium sand has a particle size of 0.5-0.25 mm; the inorganic matrix layer is prepared by inactivating and calcining the mud and sand in a muffle furnace at 500°C for 2 hours.

5. The method according to claim 1, wherein The sand and gravel used in the first sand and gravel layer and the second sand and gravel layer are all natural coarse river sand particles with a particle size of 1-1.5 mm.

6. The method according to claim 1, wherein The groundwater NO3 - Maintained at 40-45 mg / L, the initial COD value is 110-130 mg / L.

7. The method according to claim 1, wherein The amount of carbon source added is to maintain the C / N mass ratio of the water body at 4-4.5:

1.

8. The method according to claim 1, wherein Overlying water velocity 1.5×10 -6 L / s.

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