A method and device for reducing N2O emissions during the denitrification process

Abstract

The present invention discloses a method and device for reducing N2O emissions during the denitrification process, belonging to the technical field of water treatment. An SBR reactor is used, with MLSS = 2700 - 3300 mg / L and the temperature maintained at 30 - 32 °C; a peristaltic pump is used to control the inflow and outflow of water, with a 5-minute water inflow, a 35 - 90-minute reaction time, a 30-minute sedimentation time, and a 5-minute water drainage; a stirrer stirs throughout the reaction cycle; during the reaction process, the hydraulic retention time (HRT) is continuously shortened according to the change in the concentration of nitrite in the effluent. The reactor volume is 5 L, the drainage ratio is 50%, and HRT = 70 - 180 min. C6-HSL is added externally to the simulated wastewater, and the concentration of C6-HSL after being added to the reactor is 20 - 35 mg / g-VSS. The present invention reduces the N2O release amount during the treatment of nitrite wastewater, making the shortcut nitrification-denitrification process more environmentally friendly.

Description

Technical Field

[0001] The present invention relates to a method for reducing N 2 O emissions during the nitrite denitrification process, belonging to the field of biological sewage treatment, and is applicable to the denitrification and nitrogen removal of sewage containing nitrite. Specifically, it is a method and device for promoting the reduction of N 2 O emissions during the nitrite denitrification process by exogenous N-hexanoyl-L-homoserine lactone. Background Art

[0002] Enhancing nitrogen removal in water bodies is beneficial to reducing the risks of water eutrophication and water ecological imbalance. The short-cut nitrification-denitrification process has the advantages of low oxygen demand, low carbon source demand, and low sludge production. In addition, when nitrite is used as an electron acceptor, the denitrification rate increases by 1.5 - 2 times compared with nitrate. N 2 O is an intermediate product in the nitrogen removal process. It is one of the main greenhouse gases, which not only causes the greenhouse effect but also damages the ozone layer. The total N 2 O emissions from sewage treatment plants account for about 4 - 6% of the global emissions. The biological nitrogen removal process is an important source of N 2 O. Using nitrite as an electron acceptor (short-cut nitrification-denitrification, anaerobic ammonium oxidation-denitrification) will increase the N 2 O emissions in the nitrogen removal biological system.

[0003] How to achieve N 2 O emissions reduction in the short-cut nitrification-denitrification process is the main link to make this process more environmentally friendly. Temperature, pH, free ammonia (FA), carbon-nitrogen ratio, and carbon source type, etc., will all affect the release of N 2 O during the nitrogen removal process. However, it is difficult to regulate a single environmental condition to achieve N 2 O emissions reduction in the complex environment of sewage treatment.

[0004] Quorum sensing refers to the change in the physiological and biochemical characteristics of a microbial population during its growth due to the increase in population density, showing characteristics that are not possessed by a small number of cells or single cells. Most anaerobic denitrifying bacteria belong to Gram-negative bacteria. Among them, AHLs are signal molecules in the quorum sensing process of Gram-negative bacteria. Microorganisms release signal molecules into the environment, which can freely circulate between cells. Once their concentration reaches a certain threshold, the cells will activate the expression of specific genes and trigger a series of phenomena, such as increasing bacterial activity and changing the sludge sedimentation performance. Therefore, it is very necessary to develop a method for regulating N 2 O emissions reduction in the denitrification reactor by using quorum sensing.

[0005] The present invention promotes the reduction of N 6-HSL) is added to the nitrite denitrification reactor to regulate the population and the abundance of functional genes, thereby achieving N 2 O emission reduction during the nitrite denitrification process, providing a new technical idea for improving the problem of large greenhouse gas emissions in sewage treatment plants. Summary of the Invention

[0006] Therefore, to address the above deficiencies, the present invention provides a method for N 2 O emission reduction during the denitrification and nitrogen removal process, specifically a method and device for promoting N 2 O emission reduction during the nitrite denitrification process by exogenous N-caproyl-L-homoserine lactone.

[0007] The present invention is implemented as follows: A method for N 2 O emission reduction during the denitrification and nitrogen removal process is constructed.

[0008] The object of the present invention is achieved through the following technical solutions: An SBR reactor is used, and the inoculated sludge is activated sludge that has been placed anoxically for one month, with MLSS = 2700 - 3300 mg / L; A peristaltic pump is used to control the inflow and outflow of water. The water inflow is for 5 minutes, the reaction is for 35 - 90 minutes, the sedimentation time is 30 minutes, and the water drainage is for 5 minutes; The stirrer stirs throughout the reaction cycle; During the reaction process, the hydraulic retention time (HRT) is continuously shortened according to the change in the nitrite concentration in the effluent. The reactor volume is 5 L, the drainage ratio is 50%, and HRT = 70 - 180 minutes. It operates 1 - 2 cycles per day; In the first half month, in order to stabilize the water quality, simulated sewage is used instead of actual sewage. The simulated sewage uses sodium acetate as the carbon source, and sodium nitrite and potassium dihydrogen phosphate provide nitrogen and phosphorus respectively. In addition, the macro elements Mg 2+ and Ca 2+ are provided by magnesium sulfate and calcium chloride respectively. The contents of each component in the simulated sewage are respectively (mg / L): CH 3 COONa 256.4, NaNO 2 197.14, KH 2 PO 4 33.67, CaCl 2 15.00 and MgSO 4 15.00. Additionally, trace elements with a concentration of 1 mL / L are added to the simulated sewage (0.35 g / L MnSO 4 •H 2 O, 0.14 g / L FeSO 4 •7H 2 O, 0.06 g / L NiCl 2 •6H 2 O, 0.02 g / L CuSO 4 •5H2 O, 0.17 g / L ZnCl 2 , 0.049 g / L CoCl 2 •6H 2 O and 0.03 g / L H 3 BO 3 ). A constant temperature device was used to maintain the reactor temperature at 30 - 32 °C.

[0009] Signal molecule C 6 -HSL addition method: Considering that AHLs are easily degradable, during the sludge cultivation period (a total of 12 - 15 days), every time when water was fed into the reactor in each cycle, AHLs were separately added into the reactor by a peristaltic pump along with the influent water. C 6 -HSL concentration after being added to the reactor was 20 - 35 mg / g-VSS. C 6 -HSL storage method: Considering that signal molecules are easily degradable, C 6 -HSL was dissolved in methanol, and 0.1% (v / v) formic acid was added to prevent its decomposition. It was stored in a brown bottle at -20 °C. When in use, it was first dissolved to the specified concentration in the water distribution bucket. The reactor, the signal molecule influent bucket, and the signal molecule inlet pipe also needed to be protected from light.

[0010] After the reactor had been operated for 12 - 15 days, the required denitrifying sludge had been cultivated. At this time, the actual nitrite-containing sewage began to be treated. The sewage composition was: NO 2 - -N: 30 - 50 mg / L, COD: 100 - 250 mg / L. The operation mode was the same as that during sludge cultivation: a peristaltic pump was used to control the influent and effluent water. The influent time was 5 min, the reaction time was 35 - 70 min, the sedimentation time was 30 min, and the drainage time was 5 min; the stirrer was stirred throughout the reaction cycle; during the reaction process, the hydraulic retention time (HRT) was continuously shortened according to the change of the effluent nitrite concentration. The reactor volume was 5 L, the drainage ratio was 50%, and HRT = 70 - 140 min. During the 30-day operation, the denitrification performance remained stable. Importantly, the greenhouse gas N 2 O emissions in the reactor after sludge cultivation decreased significantly.

[0011] In order to investigate the differences between the reactor with added AHLs and the blank group. Two SBR reactors were operated simultaneously. One of them added C 6 -HSL signal molecule, and the other did not add it, and other operating conditions were the same. The influent and effluent nitrite concentrations were measured in each cycle; the MLSS, MLVSS, SV 30 , SVI of the reactor sludge were measured every two days. The C 6- The influence of -HSL on the operation of the denitrification reactor and the sludge sedimentation performance; the sludge volume index SVI is used to evaluate the sludge sedimentation performance; the anthrone reagent method and the improved Lowry method are used to determine the concentrations of polysaccharide (PS) and protein (PN) in extracellular polymeric substances (EPS); the 16s technology is used to determine the abundance of functional microorganisms in the reactor; the qPCR technology is used to analyze the abundance of functional genes in the two reactors.

[0012] Add C 6 -N in the -HSL reactor 2 The difference in N 2 O release between the -HSL reactor and the blank group was investigated through bench-scale tests. The specific steps were as follows: After the sludge cultivation was completed, sludge was taken from the two reactors into flasks respectively. Before adding it to the flasks, the sludge was washed three times with distilled water to eliminate the influence of residual substances. During the reaction, the MLSS in each flask was controlled at 3000 ± 100 mg / L. 250 mL of synthetic wastewater (the same as described above) was injected into each flask. The flasks were sealed with stoppers and rubber tubes were inserted. N 2 was continuously introduced into the flasks for 5 min to remove oxygen. Then, the flasks were placed on a constant-temperature magnetic stirrer with a speed of 150 r / min. The temperature was maintained at 30 ± 1 °C. Liquid samples were taken every 10 min to measure the dissolved N 2 O concentration. After each sampling, N

[0013] A device for N 2 O emission reduction during the denitrification process mainly includes the following parts: SBR reactor, stirrer, heating rod, pH probe, temperature probe, solenoid valve, feed bucket, water inlet bucket, WTW, PLC, computer control system, peristaltic pump one, peristaltic pump two, outlet pipe, signal molecule inlet pipe, sewage inlet pipe, light-shielding device; a stirrer is arranged on the upper part of the SBR reactor, a heating rod, a pH probe, and a temperature probe are arranged inside the SBR reactor, the heating rod is connected to the PLC, the pH probe and the temperature probe are connected to the WTW, the PLC is respectively connected to the WTW and the computer control system, a solenoid valve is arranged at the outlet pipe of the SBR reactor, the feed bucket and the water inlet bucket are respectively communicated with the SBR reactor, and a light-shielding device is arranged outside the feed bucket.

[0014] According to the device described in this application, the SBR reactor has a diameter of 16.8 cm, a height of 26.8 cm, and an effective volume of 5 L; the stirrer maintains the mud-water mixing state during the reaction process; the heating rod maintains the temperature of the reactor; the pH probe, the temperature probe, and the WTW are used to measure the pH and temperature during the reaction process; the feed bucket is used to hold C 6-HSL mother liquor, with a light-shielding device around it; the water inlet bucket is used to hold simulated sewage or actual sewage; PLC10 and the computer control system jointly control the full-automatic operation of the reactor; the signal molecule inlet pipe is an opaque plastic pipe.

[0015] Technical principle

[0016] Before the reaction starts, a certain concentration of AHLs is added to the reactor. When the concentration of the signal molecule reaches a certain threshold, it will regulate the population density of denitrifying bacteria and the expression of nitrogen transformation-related genes, thereby achieving N 2 O emission reduction. Specifically, after adding C 6 -HSL, the abundance of denitrifying bacteria decreases, and the abundances of nitrite reductase genes (nirS and nirK) decrease. At the same time, the abundance of the N 2 O reductase gene nosZ increases. This result causes the value of nosZ / (nirK + nirS) to decrease, and thus the N 2 O production decreases.

[0017] The present invention has the following advantages: The present invention provides a method for promoting N 2 O emission reduction during nitrite denitrification by exogenous N-hexanoyl-L-homoserine lactone, belonging to the field of water treatment technology. An SBR reactor is used, with MLSS = 2700 - 3300 mg / L, and the temperature is maintained at 30 - 32 °C; a peristaltic pump is used to control the inflow and outflow of water, with a 5-minute water inlet, a 35 - 90-minute reaction, a 30-minute sedimentation time, and a 5-minute drainage; the stirrer stirs throughout the reaction cycle; during the reaction process, the hydraulic retention time (HRT) is continuously shortened according to the change in the effluent nitrite concentration. The reactor volume is 5 L, the drainage ratio is 50%, and HRT = 70 - 180 min. Exogenous C 6 -HSL is added to the simulated wastewater, and the concentration of C 6 -HSL after being added to the reactor is 20 - 35 mg / g-VSS. The present invention reduces the N 2 O release amount during nitrite sewage treatment, making the shortcut nitrification-denitrification process more environmentally friendly. The present invention provides a method for promoting N -hexanoyl-L-homoserine lactone to reduce N 2 O emissions during nitrite denitrification. Compared with the traditional denitrification process, it has the following advantages: Compared with the traditional N 2 O emission reduction regulation method, it is more convenient and simple, and has strong feasibility. (1) The greenhouse gas N 2 O production is low, and sewage denitrification is more environmentally friendly. (2) The abundances of sludge microbial communities and functional gene abundances have changed, and the reactor has high stability in treating actual sewage. Brief description of the drawings

[0018] Figure 1 is a diagram of the reactor device;

[0019] Figure 2 is the C 6 -HSL group and the blank group N 2 O release difference;

[0020] Figure 3 is the difference in the abundance of functional microorganisms;

[0021] Figure 4 is the difference in the abundance of functional genes.

[0022] Among them: SBR reactor 1, stirrer 2, heating rod 3, pH probe 4, temperature probe 5, solenoid valve 6, feed bucket 7, water inlet bucket 8, WTW9, PLC10, computer control system 11, peristaltic pump One 12, peristaltic pump two 13, water outlet pipe 14, signal molecule inlet pipe 15, sewage inlet pipe 16, light-shielding device 17, reactor light-shielding device 18. Specific implementation manners

[0023] Next, the present invention will be described in detail in conjunction with the attached Figures 1 - 4 The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] As Figure 1 shown, the present invention provides a method for promoting N 2 O emission reduction during the denitrification of nitrite by improving exogenous N-hexanoyl-L-homoserine lactone. Its device mainly includes the following parts: The reactor is an SBR reactor 1, with a diameter of 16.8 cm, a height of 26.8 cm, and an effective volume of 5 L; the stirrer 2 maintains the mud-water mixing state during the reaction; the heating rod 3 maintains the temperature of the reactor; the pH probe 4, the temperature probe 5, and the WTW9 are used to measure the pH and temperature during the reaction; the peristaltic pump one 12, the peristaltic pump two 13, and the water outlet pipe 14 jointly control the inflow and outflow of water; the feed bucket 7 is used to hold the C 6 -HSL mother liquor, and there is a light-shielding device 17 around it; the water inlet bucket 8 is used to hold simulated sewage or actual sewage; the PLC10 and the computer control system 11 jointly control the full-automatic operation of the reactor; the signal molecule inlet pipe 15 is an opaque plastic pipe.

[0025] Example 1

[0026] Reactor operation during the sludge cultivation stage

[0027] The SBR reactor 1 is adopted, and the inoculated sludge is the activated sludge that has been placed anoxically for one month. At this time, the sludge has a certain denitrification ability, and MLSS = 2700 - 3300 mg / L; before the reaction, the peristaltic pump 12 starts to work first, and the feeding time is 2 min, and C 6 -HSL is added into the reactor; meanwhile, the stirrer 2 starts to work to ensure the mixing state of the mud and water; the peristaltic pump 13 is turned on to start water inlet, and the time is 5 min; after the water inlet is completed, it is the reaction stage, and the reaction lasts for 35 - 90 min, HRT = 70 - 180 min, and the nitrite concentration in the effluent is continuously detected to shorten the hydraulic retention time to avoid unnecessary energy consumption; after the reaction is completed, the stirrer 2 stops working, and the reactor is left to settle for 30 min; the solenoid valve 6 starts to work, and the treated sewage is discharged through the outlet pipe 14. The heating rod 3 only works when the reactor is running, so that the reactor temperature is maintained at 30 - 32 °C. The functions of the PLC 10 and the computer automatic control system 11 are to supply power and cut off power to each part of the reaction device regularly to ensure the normal operation of the reactor. In the first half month, in order to stabilize the water quality and maintain the stability of the signal molecules, simulated sewage is used instead of actual sewage. The simulated sewage uses sodium acetate as the carbon source, and sodium nitrite and potassium dihydrogen phosphate respectively provide nitrogen and phosphorus. In addition, the macro elements Mg 2+ and Ca 2+ are provided by magnesium sulfate and calcium chloride respectively. The contents of each component in the simulated sewage are respectively (mg / L): CH 3 COONa 256.4, NaNO 2 197.14, KH 2 PO 4 33.67, CaCl 2 15.00, MgSO 4 15.00. In addition, trace elements with a concentration of 1 mL / L are added to the simulated sewage (0.35 g / L MnSO 4 •H 2 O, 0.14 g / L FeSO 4 •7H 2 O, 0.06 g / L NiCl 2 •6H 2 O, 0.02 g / L CuSO 4 •5H 2 O, 0.17 g / L ZnCl 2 , 0.049 g / L CoCl 2 •6H 2 O and 0.03 g / L H 3 BO 3 ).

[0028] In order to confirm the addition of C 6-HSL does have an effect. A set of control reactors was operated simultaneously, and they were operated in the same manner as the aforementioned reactors. The difference is that the peristaltic pump -12 and the signal molecule feed tank 7 were not set in the blank group. Additionally, after the sludge cultivation was completed, sludge samples were taken and the microbial community and functional gene differences were determined using 16S and qPCR techniques. At the same time. The N 2 O release differences between the two reactors were also measured.

[0029] Example 2

[0030] Reactor operation during the treatment of actual sewage

[0031] When treating actual sewage, the required sludge has been cultivated, and no more C 6 -HSL was added to the reactor. The peristaltic pump -13 was turned on to start the water inlet for 5 minutes; at the same time, the stirrer 2 started to work to ensure the mud-water mixing state; after the water inlet was completed, it was the reaction stage, and the reaction lasted for 35 - 90 minutes, with HRT = 70 - 180 minutes; the effluent nitrite concentration was continuously detected to shorten the hydraulic retention time to avoid unnecessary energy consumption; after the reaction was completed, the stirrer 2 stopped working, and the reactor was left to settle for 30 minutes; the solenoid valve 6 started to work for drainage. The heating rod 3 only worked when the reactor was operating to keep the reactor temperature at 30 - 32°C. The role of the PLC 10 computer automatic control system 11 was to supply power and cut off power to each part of the reaction device at regular intervals to ensure the normal operation of the reactor. The sewage composition was: NO 2 - -N: 30 - 50 mg / L, COD: 100 - 250 mg / L. During the 30-day operation, the denitrification performance remained stable. Importantly, the greenhouse gas N 2 O emissions from the reactor after sludge cultivation decreased significantly.

[0032] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for reducing N 2 O emissions during the denitrification process It is characterized in that It includes the following steps: (1) An SBR reactor was used, and the inoculated sludge was activated sludge that had been placed anoxically for one month, with MLSS = 2700 - 3300 mg / L. A peristaltic pump was used to control the influent and effluent. The influent time was 5 min, the reaction time was 35 - 90 min, the sedimentation time was 30 min, and the drainage time was 5 min. A heating rod was used to maintain the reactor temperature at 30 - 32 °C. The stirrer was stirred throughout the reaction cycle. During the reaction process, the hydraulic retention time was continuously shortened according to the change of the effluent nitrite concentration. The reactor volume was 5 L, the drainage ratio was 50%, and HRT = 70 - 180 min. It was operated 1 - 2 cycles per day. 6 The concentration of -HSL after being added to the reactor was 20 - 35 mg / g-VSS. The sludge cultivation period was 12 - 15 days, and simulated sewage was used instead of actual sewage. The contents of each component in the simulated sewage were as follows: CH 3 COONa 256.4 mg / L, NaNO 2 197.14 mg / L, KH 2 PO 4 33.67 mg / L, CaCl 2 15.00 mg / L and MgSO 4 15.00 mg / L; In addition, trace elements with a concentration of 1 mL / L were added to the simulated sewage: 0.35 g / L MnSO 4 •H 2 O, 0.14 g / L FeSO 4 •7H 2 O, 0.06 g / L NiCl 2 •6H 2 O, 0.02 g / L CuSO 4 •5H 2 O, 0.17 g / L ZnCl 2 0.049 g / L CoCl 2 •6H 2 O and 0.03 g / L H 3 BO 3 ; (2) After the reactor had been operating for 12 to 15 days, the required denitrifying sludge had been cultivated; at this time, the actual nitrite-containing sewage began to be treated, and C 6 -HSL was no longer added; the sewage composition was: NO 2 - -N: 30 to 50 mg / L, COD: 100 to 250 mg / L; the operation mode was the same as that during sludge cultivation: water inlet for 5 min, reaction for 35 to 70 min, sedimentation time for 30 min, and drainage for 5 min; the stirrer was stirred throughout the reaction cycle; during the reaction process, the hydraulic retention time was continuously shortened according to the change of the nitrite concentration in the effluent; The reactor volume is 5 L, the drainage ratio is 50%, HRT = 70 - 140 min; the temperature is maintained at 30 - 32 °C.

2. Method for reducing N 2 O emissions during the denitrification process, It is characterized in that It also includes the following operations; signaling molecule C 6 - Addition method of C-HSL: Considering that AHLs are easily degraded, during the 12 - 15-day sludge cultivation period, when the water is fed into the reactor in each cycle, AHLs are separately added to the reactor by a peristaltic pump along with the influent water; C 6 - The concentration of C-HSL after being added to the reactor is 20 - 35 mg / g-VSS.

3. The method for reducing N 2 O emissions during the denitrification process according to claim 1, It is characterized in that It also includes the following operations; to examine the differences between the reactor with added AHLs and the blank group; two SBR reactors are operated simultaneously, with one adding the C 6 -HSL signaling molecule and the other not adding it, with the same other operating conditions; the influent and effluent nitrite concentrations are measured in each cycle; the MLSS, MLVSS, and SV of the reactor sludge are measured once every two days 30 、SVI; evaluate the effect of C 6 -HSL on the operation of the denitrification reactor and the sludge settling performance; The sludge volume index SVI is used to evaluate the sludge sedimentation performance; the anthrone reagent method and the improved Lowry method are used to measure the concentrations of polysaccharides and proteins in extracellular polymers; the 16s technology is used to measure the abundance of functional microorganisms in the reactor; the qPCR technology is applied to analyze the abundance of functional genes in the two reactors.

4. Method for reducing N 2 O emissions during the denitrification process, It is characterized in that It also includes the following operations; adding C 6 - The release of N in the -HSL reactor 2 - The difference in NO release from the -HSL reactor compared to the blank group was investigated through bench-scale tests. The specific steps were as follows: After the sludge cultivation was completed, sludge was taken from the two reactors into flasks respectively. Before adding it to the flasks, the sludge was washed three times with distilled water to eliminate the influence of residual substances; During the reaction process, the MLSS in each flask was controlled at 3000 ± 100 mg / L; 250 mL of synthetic wastewater was injected into each flask; the flasks were sealed with stoppers and rubber tubes were inserted; N 2 was continuously introduced into the flasks for 5 min to remove oxygen; Then, place the flask on a constant-temperature magnetic stirrer with a speed of 150 r / min; keep the temperature at 30 ± 1 °C; take a liquid sample every 10 min to measure the dissolved N 2 O concentration; introduce N 2 into the flask after each sampling to balance the pressure inside and outside the flask.

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