A method for enhancing the process of dissimilatory reduction of nitrate to ammonium by using electric field coupled magnetic field

Abstract

The present invention relates to a method for strengthening the dissimilatory reduction of nitrate to ammonium by using an electric field coupled with a magnetic field. The present invention utilizes the coupling effect of an electric field and a magnetic field to promote the rapid start-up of a DNRA reactor and improve the stability of the system, while improving the activity of DNRA bacteria and the abundance of the functional gene nrfA. At the same time, the application of an electric field and a magnetic field promotes the activity of DNRA bacteria, shortens the cycle of enrichment culture, and achieves the purpose of rapid start-up of the reactor. The equipment used to generate an electric field and a magnetic field has low energy consumption, and in particular, the magnetic field generated by a permanent magnet does not require energy consumption, has a long duration, is safe and harmless to the environment, and is convenient for engineering applications.

Description

Technical Field

[0001] The invention relates to a method for strengthening the process of dissimilatory reduction of nitrate to ammonium by utilizing electric field coupled magnetic field, and belongs to the technical field of sewage treatment. Background Art

[0002] In the process of biological denitrification of sewage, the nitrate produced in the nitrification stage is reduced to nitrogen gas through denitrification, thereby achieving the purpose of denitrification. However, in addition to being reduced to nitrogen gas, nitrate may also be reduced to ammonium (CH 3 COO - +NO 3 - +2H + →CO 2 +NH 4 + +HCO 3 - ), namely the DNRA process. Since the DNRA process can not only reduce greenhouse gas N 2 O emissions, and can also convert the more difficult to utilize NO 3 - -N is converted into NH3 which is more easily utilized by microorganisms 4 + -N, therefore, its role in the nitrogen cycle has received more and more attention and recognition. However, most of the current research on the DNRA process is concentrated in soil systems, and relatively few studies are conducted in water systems. In natural water bodies, although the DNRA process cannot reduce total nitrogen to a certain level, it can reduce greenhouse gas N by competing with the denitrification process. 2 In artificial water bodies, such as sewage treatment plants, the DNRA process can reduce NO in wastewater to 3 - Reduced to emission standards, while the generated NH 4 + The wastewater can be processed into nutrient fertilizer through secondary treatment, realizing the resource utilization of wastewater.

[0003] The activated sludge process is a commonly used method in sewage treatment. For the denitrification part of the three-stage process and the treatment of high nitrate nitrogen industrial wastewater, ammonia nitrogen, as a common nitrogen source for microbial growth, is very scarce. The three-stage process includes carbon removal, nitrification and denitrification, each with a corresponding sedimentation tank and sludge return system, and the three systems operate relatively independently. The post-denitrification process used for nitrogen removal usually encounters the problem of insufficient carbon or nitrogen sources, and nitrogen and carbon sources need to be added to ensure the growth of microorganisms and the denitrification process. Industrial wastewaters such as explosives and polysilicon batteries contain high concentrations of nitrate nitrogen, and ammonia nitrogen needs to be added to maintain the normal growth of activated sludge. Factors such as temperature, C / N, and pH have an impact on activated sludge denitrification, and these factors are also directly related to the DNRA process. By adjusting key factors, a certain proportion of nitrate nitrogen can be made to undergo DNRA to produce ammonia, providing a nitrogen source for the normal growth of denitrifying functional bacteria. The remaining nitrate nitrogen is removed by denitrification, saving the cost of nitrogen source addition while ensuring a high denitrification efficiency. However, if more NO 3 - Instead of being removed from water bodies by denitrification, it is converted into NH by DNRA. 4 + , it will affect the denitrification efficiency of the process. Therefore, it is very important to control the proportion of nitrate nitrogen that is acted on by DNRA. At present, my country's research on DNRA is still in the exploratory stage, and the influence mechanism of relevant factors in the denitrification system on DNRA is still unclear. It is necessary to establish a reactor enriched with DNRA bacteria to further study the transformation pathway. However, the long startup time of DNRA and the unstable performance of the reactor have always been the bottleneck of DNRA research. Summary of the invention

[0004] In view of the shortcomings of the existing technology, especially the long startup time of DNRA and the instability of the system, the present invention provides a method for strengthening the process of dissimilatory reduction of nitrate to ammonium by coupling electric field with magnetic field.

[0005] The present invention changes the permeability of the cell membrane of the microbial flora through electric and magnetic field coupling, which will also affect the growth and reproduction of the microbial flora, and has a significant impact on intracellular enzymes and extracellular enzymes. By stimulating enzymes, various reactions in the microbial flora can be specifically promoted, greatly improving the performance and stability of the bioreactor. The method of the present invention can effectively accelerate the start-up of DNRA, promote the growth of DNRA functional bacteria and the abundance of functional enzymes, and improve the stability of the DNRA reactor.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for enhancing the process of dissimilatory reduction of nitrate to ammonium by using electric field coupled magnetic field, the specific steps are as follows:

[0008] (1) Wash the flocculent sludge with tap water until the washing liquid becomes transparent, then pour out the washing liquid, add phosphate buffer solution, seal the sludge and let it stand overnight, and transfer it to a sequencing batch biofilm reactor the next day;

[0009] (2) A permanent magnet is set outside the reactor to make the magnetic field strength at the center of the reactor between 20 and 100 mT. A constant voltage electric field is set inside the reactor to adjust the plate voltage strength to -2.2 to 0.6 V. SCE between;

[0010] (3) introducing artificial synthetic wastewater from the top of the reactor, the water inlet is divided into two streams, stream A is nitrogen source water inlet, and stream B is carbon source water inlet, the flow rates of the two water inlets are kept consistent, the speed of the peristaltic pump is adjusted to control the water inlet flow rate, and the outlet pipe of the membrane module is connected to the peristaltic pump at the same time, the water inlet is continuously supplied for 24 hours, the hydraulic retention time is 10-48 hours, the speed of the peristaltic pump is adjusted to control the water outlet flow rate, and the peristaltic pump is controlled by a time switch to maintain the reactor liquid level at a specified height;

[0011] (4) The pH in the reactor was maintained at 7.1±0.1, the temperature was maintained at 23±1°C, a mechanical stirrer was installed on the top of the reactor, the reactor was sealed and protected from light, and it operated continuously for 24 hours to achieve rapid start-up of the DNRA process.

[0012] Preferably, according to the present invention, in step (1), the flocculent sludge is a mixed liquid with a suspended solid concentration of 4.0-8.0 g / L.

[0013] Preferably according to the present invention, in step (1), the pH of the phosphate buffer is 7.2, and the concentration is 0.1-0.3 mol / L.

[0014] Preferably, according to the present invention, in step (1), the inoculation amount of sludge in the sequencing batch biofilm reactor accounts for 1 / 5-1 / 2 of the reactor volume.

[0015] Preferably, according to the present invention, in step (2), the reactor is a sequencing batch biofilm reactor using a non-woven membrane as the membrane material, and a water bath layer is provided.

[0016] According to the preferred embodiment of the present invention, in step (2), the magnet used in the present invention is a common commercially available ferromagnetic material, and an electromagnetic field can also be used. The magnetic field strength is measured at the center of the reactor, and a Waite WT103 permanent magnet surface magnetic field measuring instrument is used. The electric field strength of the present invention is controlled by a constant voltage instrument, and a carbon felt (3cm×3cm) is used as a working electrode, a graphite sheet is used as a counter electrode, and a saturated calomel electrode is used as a reference electrode.

[0017] Preferably, according to the present invention, in step (2), a permanent magnet is arranged outside the reactor so that the magnetic field strength at the center of the reactor is 35-45 mT.

[0018] According to the preferred embodiment of the present invention, in step (2), a constant voltage electric field is set inside the reactor, and the plate voltage intensity is adjusted to be controlled at 0.01 to 0.5 V. SCE .

[0019] Preferably, according to the present invention, in step (3), the material of the membrane assembly in the reactor is polymethyl methacrylate, the pore size of the non-woven fabric is 0.1 mm, and the membrane assembly is tightly fixed on the membrane support with non-woven fabric and placed symmetrically in the reactor.

[0020] According to the preferred embodiment of the present invention, in step (3), the composition of the nitrogen source influent is as follows: 0.197 g MgSO per liter of influent 4 7H 2 O, 1.254 g NaNO 3 , 1.999g KH 2 PO 4 , 0.04 g NaOH, 0.021 g MnCl 2 ·4H 2 O, 0.02gFeSO 4 7H 2 O, 0.022 g CaCl 2 , 0.01g yeast powder, 4mL trace elements; the trace element composition per liter of water is as follows: 20g EDTA-2Na, 2.2g ZnSO 4 7H 2 O, 1.75 g CuSO 4 ·5H 2 O, 5.54 g CoCl 2 6H 2 O, 1.1 g (NH 4 ) 6 Mo 7 O 24 ·4H 2 O.

[0021] Preferably according to the present invention, in step (3), the carbon source influent is ethanol with a concentration of 0.964 mL / L and a COD concentration of 1400 mg / L.

[0022] Preferably, according to the present invention, in step (3), the nitrogen source influent and the carbon source influent are aerated with pure nitrogen (99.9%) for 30 minutes, and then aerated for 30 minutes every 24 hours before being introduced into the reactor.

[0023] Preferably according to the present invention, in step (4), the pH in the reaction is controlled by an online pH meter, and the temperature is controlled by a constant temperature circulator.

[0024] The water quality was monitored by measuring the concentrations of nitrate nitrogen, ammonium nitrogen and nitrite nitrogen in the reactor. The functional gene was monitored by measuring the abundance of the DNRA functional gene nrfA using qPCR technology. The potential rate of DNRA was determined using 15 This was achieved using N isotope tracing technology.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The present invention changes the permeability of the cell membrane of the microbial flora through the coupling of electric and magnetic fields, which will also affect the growth and reproduction of the microbial flora, and has a significant effect on both intracellular and extracellular enzymes. By stimulating enzymes, various reactions within the microbial flora can be specifically promoted, greatly improving the performance and stability of the bioreactor. The method of the present invention can effectively accelerate the start-up of DNRA, promote the growth of DNRA functional bacteria and the abundance of functional enzymes, and improve the stability of the DNRA reactor.

[0027] 2. The present invention effectively improves the ammonia nitrogen conversion efficiency of the DNRA reactor through the coupling of electric and magnetic fields, promotes the enrichment of DNRA bacteria, and improves the stability of the system. The biofilm reactor with non-woven fabric as the membrane component provides a biofilm that can be attached to the growth of the bacterial community, which can reduce the loss of effective bacterial species and improve the biomass retention capacity. The interception effect of the membrane increases the number of microorganisms in the reactor, improves the stability of the system, and ensures a high sludge concentration inside the equipment. The stirring system promotes the mixing of the matrix and the bacterial community, improves the mass transfer efficiency, and forms a mud film symbiotic system with a high microbial concentration. While achieving biomass interception, the microorganisms are fully in contact with the raw water, creating a stable habitat suitable for the survival of DNRA bacteria and ensuring the activity of DNRA functional microorganisms. DNRA bacteria are enriched faster, and a biofilm that can be attached is provided for the growth of the bacterial community, while strengthening the radiation effect of the magnetic field.

[0028] 3. The method of the present invention has low operating costs, the energy consumption of the constant voltage instrument is low, the magnetic field generated by the permanent magnet does not require energy consumption, and has a long duration, is safe and harmless to the environment, and is convenient for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The nitrogen conversion performance of the reactor in the application test example during long-term operation. (A) Control group Rck; (B) Experimental group R1; (C) Experimental group R2; (D) Experimental group R3.

[0030] Figure 2 is the potential DNRA rate during the stable operation period (80 days) of the reactor in the application test example.

[0031] Figure 3 is the abundance of nrfA gene in the reactor in the application test example. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] A method for enhancing the process of dissimilatory reduction of nitrate to ammonium by using electric field coupled magnetic field, the specific steps are as follows:

[0035] (1) Wash the flocculent sludge several times with tap water until the washing solution becomes transparent, then pour out the washing solution, add phosphate buffer (pH = 7.2, 0.2M), seal the sludge and let it stand overnight, and transfer it to a sequencing batch biofilm reactor the next day. The inoculated sludge in the reactor accounts for about one-fifth of the reactor volume;

[0036] (2) A permanent magnet is set outside the reactor to make the magnetic field strength at the center of the reactor 40 mT, a constant voltage electric field is set inside the reactor, and the plate voltage strength is adjusted to be controlled at 0.01 to 0.5 V SCE ;

[0037] (3) Artificial synthetic wastewater was introduced from the top of the reactor. The inlet water was divided into two streams. Stream A was nitrogen source inlet water, and stream B was carbon source inlet water. The flow rates of the two inlet waters were kept consistent. The speed of the peristaltic pump was adjusted to control the inlet flow rate. At the same time, the outlet pipe of the membrane module was connected to the peristaltic pump. The water was continuously fed for 24 hours, and the hydraulic retention time was 24 hours. The composition of the nitrogen source inlet water per liter was as follows: 0.197gMgSO 4 7H 2 O, 1.254 g NaNO 3 , 1.999g KH 2 PO 4 , 0.04 g NaOH, 0.021 g MnCl 2 ·4H 2 O, 0.02gFeSO 4 7H 2 O, 0.022 g CaCl 2 , 0.01g yeast powder, 4ml trace elements. The trace elements per liter are as follows: 20g EDTA-2Na, 2.2g ZnSO 4 7H 2 O, 1.75 g CuSO 4 ·5H 2 O, 5.54 g CoCl2 6H 2 O, 1.1 g (NH 4 ) 6 Mo 7 O 24 ·4H 2 O. The carbon source influent was anhydrous sodium acetate with a concentration of 5.4 g / L and a COD concentration of 1400 mg / L. The nitrogen source influent and carbon source influent were aerated with pure nitrogen (99.9%) for 30 min, and then aerated for 30 min every 24 h before entering the reactor;

[0038] (4) Adjust the speed of the peristaltic pump to control the water flow rate, and use a time switch to control the peristaltic pump, set the water discharge time to 10 minutes, the water discharge frequency to 1 time / 4 hours, and maintain the reactor liquid level at a height of 27.5-32.5 cm. Use an online pH meter to control the pH to 7.1±0.1 and the temperature to 23±1°C. Install a mechanical stirrer on the top of the reactor, seal the reactor to avoid light, and operate continuously for 24 hours to achieve rapid start-up of the DNRA process.

[0039] Application test examples

[0040] Four reactors were set up, namely the control group Rck and the experimental groups R1, R2, and R3. The control group Rck was not set up with electric field and magnetic field effects, the experimental group R1 was only set up with magnetic field, the experimental group R2 was only set up with electric field, and the experimental group R3 was set up with magnetic field and electric field coupling effect effects (Example 1); the experiment was carried out according to the method of Example 1.

[0041] The magnets used (12cm×6cm×1.5cm) are the most common ferromagnetic materials. The magnetic field strength is measured at the center of the reactor using a Waite WT103 permanent magnet surface magnetic field measuring instrument, with a magnetic field strength of about 40mT. The electric field is controlled by a constant voltage instrument, using a carbon felt (3cm×3cm) as the working electrode, a graphite sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The working electrode voltage is controlled by a constant voltage instrument to be 0.01 to 0.5V SCE .

[0042] During the operation of the reactor, water quality, functional gene abundance, DNRA potential rate and other parameters are continuously monitored. The water quality is monitored by measuring the concentrations of nitrate nitrogen, ammonium nitrogen and nitrite nitrogen in the reactor, the functional gene is monitored by measuring the abundance of DNRA functional gene nrfA, and the DNRA potential rate is measured by using 15 This was achieved using N isotope tracing technology.

[0043] Test results:

[0044] from Figure 1The figure shows the changing trends during the startup of the four reactors. The startup time of the experimental groups was greatly shortened. The effect of applying a magnetic field coupled with an electric field was the most obvious, followed by applying a magnetic field and an electric field alone. This may be because the appropriate magnetic field and electric field promoted the DNRA process, allowing DNRA to dominate in a short period of time. During the long-term operation of the reactor under the influence of different electromagnetic effects, the reactor did not show obvious differences in the ammonia nitrogen conversion efficiency during stable operation, but under the influence of the magnetic field and electric field coupling effect, the reactor showed a relatively high ammonia nitrogen conversion efficiency and the overall stability of the system. For nearly three months after the successful startup, the conversion rate of R3 has been maintained at around 64.02%, and the effluent water quality is stable, indicating that the appropriate electric field and magnetic field strength will not only promote the startup of the DNRA process, but the coupling of the two electromagnetic effects will further promote the DNRA process and improve the stability of the DNRA system to a certain extent.

[0045] like Figure 2 As shown in the figure, the DNRA potential rates of Rck, R1, R2 and R3 are 52.07, 88.49, 160.17 and 174.30 μmol / (kg·h), respectively. Basically consistent with the water quality data, the experimental groups affected by magnetic field and electric field showed higher DNRA rates than the control group, among which the effect of the reactor affected by electric field coupled magnetic field was the most obvious. The DNRA process is NO 3 - -N is gradually reduced to NH 4 + -N, so in the R1 reactor with the highest DNRA potential rate, the DNRA bacteria showed the highest activity and the highest ability to convert nitrate nitrogen into ammonia nitrogen. From the results, the application of electric and magnetic fields greatly promoted the activity of DNRA bacteria in the reactor. It may be that the combined effect of electric and magnetic fields promoted the succession of microbial communities, making the DNRA process in the system dominant in a shorter period of time.

[0046] like Figure 3 As shown in Figure 2, nrfA is the gene encoding nitrite reductase in DNRA. At 40 days, the abundance of nrfA gene in the R3 reactor was the highest, reaching 3.54×10 6 copies / ng DNA, Rck abundance was 1.80×10 6 copies / ng DNA, R1 abundance is 2.0×10 6 copies / ng DNA, R2 abundance was 3.24×10 6 At 80 days, the gene abundance of nrfA in the reactor continued to double, and the abundance of nrfA gene in the R3 reactor was still the highest, reaching 4.72×10 6copies / ng DNA, the abundance of Rck was 2.91×10 6 copies / ng DNA, R1 abundance was 3.23×10 6 copies / ng DNA, R2 abundance was 4.33×10 6 The qPCR data show that applying electric and magnetic fields can effectively increase the abundance of DNRA functional populations, and coupling the two magnetic effects can achieve a better promotion effect.

[0047] (9) In summary, all data show that applying electric and magnetic fields can shorten the start-up time of DNRA, and the effect of electric field coupling magnetic field is the most obvious. Long-term experimental results show that the coupling effect of electric and magnetic fields also has a certain promoting effect on the stability of the system. The DNRA potential rate and qPCR results also show that the coupling effect of electric and magnetic fields promotes the activity of DNRA bacteria and increases the abundance of functional genes.

Claims

1. A method for enhancing the process of dissimilatory reduction of nitrate to ammonium by using electric field coupled magnetic field, the specific steps are as follows: (1) Wash the flocculent sludge several times with tap water until the washing liquid becomes transparent, then pour out the washing liquid, add pH=7.2, 0.2M phosphate buffer, seal the sludge and let it stand overnight, and transfer it to a sequencing batch biofilm reactor the next day. The inoculated sludge in the reactor accounts for one-fifth of the reactor volume; (2) A permanent magnet is set outside the reactor to make the magnetic field strength at the center of the reactor 40 mT, a constant voltage electric field is set inside the reactor, and the plate voltage strength is adjusted to be controlled at 0.01-0.5 VSCE; (3) Artificial synthetic wastewater was introduced from the top of the reactor. The water inlet was divided into two streams. Stream A was nitrogen source water inlet and stream B was carbon source water inlet. The flow rates of the two streams were kept consistent. The speed of the peristaltic pump was adjusted to control the flow rate of the water inlet. At the same time, the outlet pipe of the membrane module was connected to the peristaltic pump. The water was continuously introduced for 24 hours, and the hydraulic retention time was 24 hours. The composition of nitrogen source inlet water per liter is as follows: 0.197g MgSO4·7H2O, 1.254g NaNO3, 1.999g KH2PO4, 0.04g NaOH, 0.021g MnCl2·4H2O, 0.02g FeSO4·7H2O, 0.022g CaCl2, 0.01g yeast powder, 4ml trace elements, and the composition of trace elements per liter is as follows: 20g EDTA-2Na, 2.2g ZnSO4·7H2O, 1.75g ​​CuSO4·5H2O, 5.54g CoCl2·6H2O, 1.1g (NH4)6Mo7O 24 4H2O; The carbon source influent was anhydrous sodium acetate with a concentration of 5.4 g / L and a COD concentration of 1400 mg / L; The nitrogen source water and carbon source water were aerated with pure nitrogen (99.9%) for 30 minutes, and then aerated for 30 minutes every 24 hours before entering the reactor; (4) Adjust the speed of the peristaltic pump to control the water flow rate, and use the time switch to control the peristaltic pump, set the water discharge time to 10 minutes, the water discharge frequency to 1 time / 4 hours, and maintain the reactor liquid level at a height of 27.5-32.5 cm. The pH was controlled at 7.1±0.1 and the temperature was maintained at 23±1°C using an online pH meter. A mechanical stirrer was installed on the top of the reactor. The reactor was sealed and protected from light and operated continuously for 24 hours to achieve rapid start-up of the DNRA process.

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