A method for enhancing the dissimilatory reduction of nitrate to ammonium by coupling nanoscale zero-valent iron with low-frequency infrared electromagnetic waves

Abstract

The present invention relates to a method for strengthening the process of dissimilatory reduction of nitrate to ammonium by coupling low-frequency infrared electromagnetic waves with nano-scale zero-valent iron. The method of the present invention is based on the principle of biomagnetic effect, and uses nano-scale zero-valent iron coupled electromagnetic waves 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. The reactor of the present invention adopts a biofilm reactor based on a non-woven fabric membrane component, which provides a place for microorganisms to attach and react, can effectively reduce the loss of biomass, and improve the impact resistance of the reactor, thereby accelerating the start-up of the DNRA process.

Description

Technical Field

[0001] The invention relates to a method for strengthening the process of dissimilatory reduction of nitrate into ammonium by utilizing nano-scale zero-valent iron coupled with low-frequency infrared electromagnetic waves, and belongs to the technical field of sewage treatment. Background Art

[0002] Past research has fundamentally changed our understanding of nitrogen cycling in the biosphere. Denitrification or anaerobic ammonium oxidation is the main way that ecosystems lose nitrogen, and the nitrate reduction to ammonium process (DNRA) converts NO3 - Reduction to NH4 + , and retains nitrogen in the ecosystem. Studying nitrogen loss and retention is important for understanding the nutrient balance of the ecosystem, and the nitrogen retention process of DNRA may be of great significance to the productivity of the ecosystem. In the anoxic layer of marine sediments, denitrification and DNRA directly compete for NO3 with organic carbon and sulfide as electron acceptors. - . The result of the competition determines whether marine sediments serve as the starting point or end point for nitrogen fixation, which will affect the nutritional status of the entire ecosystem. At present, the environmental factors that affect the balance between DNRA, denitrification and other nitrate reduction pathways in aquatic ecosystems are not fully understood. However, the retention of bioavailable nitrogen by DNRA is of great significance for understanding how ecosystems respond to nitrogen transformation in ecosystems. At present, research on the role of DNRA is mostly concentrated in ecological environments such as surface water sediments and soils such as rivers, lakes and oceans, and is less studied in activated sludge denitrification systems and other biological denitrification systems. A 2 The anaerobic tank in the O system and the anaerobic selection tank in the front section of the oxidation ditch process have a high organic matter concentration and the return sludge brings a small amount of NO3 - , so the C / N in the system is higher; in the biological treatment of industrial wastewater such as batteries and explosives, higher organic matter and NO3 - The concentration makes the nitrogen source required for bacterial growth scarce. It can be seen that there is an environment suitable for the survival of DNRA bacteria in the activated sludge system, but if a large amount of NO3 - Conversion to NH4 via the DNRA process + , then the denitrification efficiency of the system will be greatly reduced, and it is crucial to ensure the proportion of DNRA process. Therefore, for improving the denitrification efficiency of activated sludge, the role of DNRA cannot be ignored, and in-depth and detailed research is urgently needed.

[0003] At present, the research on DNRA in my country is still in the exploratory stage. 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 current technology, especially the long startup time of DNRA and system instability, the present invention provides a method for enhancing the process of dissimilatory reduction of nitrate to ammonium by coupling nanoscale zero-valent iron with low-frequency infrared electromagnetic waves.

[0005] Nano-scale zero-valent iron (nZVI) has strong redox properties. When added to the anaerobic reactor, redox reactions will occur and Fe will be slowly released. 2+ , creating an environment conducive to the survival of anaerobic microorganisms, while coupling electromagnetic waves of a specific intensity can promote cell proliferation and differentiation, DNA synthesis, RNA transcription, protein expression, ATP synthesis and metabolic functions. 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 dissimilatory reduction of nitrate to ammonium by coupling nanoscale zero-valent iron with low-frequency infrared electromagnetic waves comprises the following steps:

[0008] (1) Wash the anaerobic granular 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 low-frequency infrared electromagnetic wave generator is arranged outside the reactor, so that the electromagnetic wave intensity at the center of the reactor is 0.04 to 0.06 μT, and nano-scale zero-valent iron is added into the reactor through the reactor inlet, so that the concentration of nano-scale zero-valent iron in the reactor is maintained at 1 to 5 g / L;

[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 streams 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 is continuously fed 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 anaerobic granular sludge is granular sludge with a suspended solids concentration of 10.0-15.0 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 volume of the reactor.

[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] Preferably according to the present invention, in step (2), the intensity of the electromagnetic wave is 0.055 μT.

[0017] Preferably, according to the present invention, in step (2), the frequency of the low-frequency infrared electromagnetic wave generator is 50 Hz, and the wavelength range is 2-25 μm.

[0018] Preferably according to the present invention, in step (2), the particle size of the nano-scale zero-valent iron is 55-65 nm, and the purity is ≧99.9%.

[0019] Preferably, according to the present invention, in step (2), the amount of nano-scale zero-valent iron added is such that the concentration of nano-scale zero-valent iron in the reactor is maintained at 2-3 g / L.

[0020] Too much or too little addition of nano-zero-valent iron will inhibit the effect of nitrate reduction to ammonium.

[0021] 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.

[0022] Preferably, in step (3), the composition of the nitrogen source influent 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 per liter of influent; the trace element composition per liter of influent is as follows: 20g EDTA-2Na, 2.2g ZnSO4·7H2O, 1.75g ​​CuSO4·5H2O, 5.54g CoCl2·6H2O, 1.1g (NH4)6Mo7O 24 ·4H2O.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The present invention utilizes nano-scale zero-valent iron coupled with low-frequency infrared electromagnetic waves to strengthen the dissimilatory reduction of nitrate to ammonium, creating an environment conducive to the survival of anaerobic microorganisms. At the same time, coupling electromagnetic waves of a specific intensity can promote cell proliferation and differentiation, DNA synthesis, RNA transcription, protein expression, ATP synthesis and metabolic functions. 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.

[0029] 2. The present invention utilizes nano-scale zero-valent iron coupled with low-frequency infrared electromagnetic waves to enhance the dissimilatory reduction of nitrate to ammonium, which effectively improves the ammonia nitrogen conversion efficiency of the DNRA reactor, promotes the activity of DNRA bacteria, and improves the stability of the system.

[0030] 3. The present invention utilizes nano-scale zero-valent iron coupled with low-frequency infrared electromagnetic waves to enhance the dissimilatory reduction of nitrate to ammonium. The membrane components made of non-woven fabrics can reduce the loss of effective bacterial species, enrich DNRA bacteria more quickly, and provide a biofilm that can be attached to the growth of bacterial colonies. At the same time, the radiation effect of low-frequency infrared electromagnetic waves is enhanced. The electromagnetic wave device has low power consumption and will not significantly increase operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1The nitrogen conversion performance of different reactors in long-term operation. (A) Control group Rck; (B) Reactor R1 with nanoscale zero-valent iron; (C) Reactor R2 with low-frequency infrared electromagnetic wave radiation; (D) Reactor R3 with nanoscale zero-valent iron coupled with low-frequency infrared electromagnetic wave radiation.

[0032] Figure 2 is the potential DNRA rate during the stable operation period (80 days) of the reactor in Example 1.

[0033] Figure 3 is the abundance of the nrfA gene in the reactor in Example 1. DETAILED DESCRIPTION

[0034] 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.

[0035] Nano-scale zero-valent iron was purchased from Aladdin Reagent Network, with a particle size of 60nm and a purity of ≧99.9%

[0036] Embodiment 1:

[0037] A method for enhancing the dissimilatory reduction of nitrate to ammonium by coupling nanoscale zero-valent iron with low-frequency infrared electromagnetic waves comprises the following steps:

[0038] (1) Wash the anaerobic granular sludge several times with tap water until the washing liquid becomes transparent, then pour out the washing liquid, add a certain volume of 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 1 / 3 of the reactor volume.

[0039] (2) Artificial synthetic wastewater was introduced from the top of the reactor. The inlet water was divided into two streams. Stream A was the nitrogen source inlet water, and stream B was the carbon source inlet water. The flow rates of the two inlets were kept consistent. The speed of the peristaltic pump was adjusted to control the inlet flow rate to 66 ml / h. 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. The hydraulic retention time was 38 hours. The composition per liter of the nitrogen source inlet water was as follows: 0.197 g MgSO4·7H2O, 1.254 g NaNO3, 1.999 g KH2PO4, 0.04 g NaOH, 0.021 g MnCl2·4H2O, 0.02 g FeSO4·7H2O, 0.022 g CaCl2, 0.01 g yeast powder, and 4 ml trace elements. The trace elements per liter are 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 ethanol with a concentration of 0.964 ml / 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.

[0040] (3) The peristaltic pump speed was adjusted to control the water flow rate to 26 ml / min, and the peristaltic pump was controlled by a time switch, the water discharge time was set to 10 min, the water discharge frequency was set to 1 time / 4 h, and the reactor liquid level was maintained at a height of 27.5-32.5 cm. In addition, an online pH meter was used to control the pH to 7.1±0.1 and the temperature to 23±1°C. A mechanical stirrer was installed on the top of the reactor, and the reactor was sealed and protected from light for 24 hours to achieve rapid start-up of the DNRA process.

[0041] (4) Four reactors were set up: Rck, R1, R2, and R3. R1 was a blank control group (i.e., no nano zero-valent iron particles and electromagnetic wave radiation were added to the reactor), and R3 was an experimental group (reactor of Example 1, with a nano-level zero-valent iron concentration of 2 g / L). In order to further clarify the mechanism of action of nano zero-valent iron coupling electromagnetic waves, R1 and R2 were set up as controls. Except for not adding electromagnetic waves, the other conditions of R1 were consistent with those of R3; except for not adding nano zero-valent iron, the other conditions of R2 were consistent with those of R3; the other conditions of the four reactors were the same. Infrared electromagnetic waves were produced by an infrared electromagnetic wave manufacturer (Xianhe, CQ-28), with a frequency of 50 Hz and a wavelength range of 2-25 μm;

[0042] (5) 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 the DNRA functional gene nrfA, and the DNRA potential rate is measured using 15 This was achieved using N isotope tracing technology.

[0043] Experimental results:

[0044] from Figure 1 It can be seen that although the water quality of the control group and the experimental group fluctuated, compared with the control group, the experimental group was still able to maintain a higher ammonia nitrogen conversion efficiency. R3 had the best effect, followed by R2 and R1, indicating that nanoscale zero-valent iron and electromagnetic waves can not only promote the DNRA process and promote the stability of the sludge system to a certain extent, but also achieve better improvement effect after coupling.

[0045] like Figure 2 As shown, during the stable operation of the reactor, the DNRA potential rates of Rck, R1, R2 and R3 were 8.49, 13.02, 15.81 and 26.43 μmol / (kg·h), respectively, and the DNRA potential rate was: R3>R2>R1>Rck.

[0046] like Figure 3 As shown in Figure 2, nrfA is the gene encoding nitrite reductase in DNRA. When the sludge was just inoculated, the qPCR abundance of Rck, R1, R2, and R3 was 3.93×10 5 4.00×10 5 ,3.93×10 5 and 3.94×10 5 During the domestication process, the gene abundance of Rck, R1, R2, and R3 continued to increase, and the gene abundance remained at: R3>R2>R1>Rck. At 180 days, the gene abundance in Rck, R1, R2, and R3 reached 4.05×10 6 4.94×10 6 , 5.23×10 6 and 5.89×10 6 That is to say, under the influence of electromagnetic wave radiation and nano-scale zero-valent iron, the rapid enrichment of DNRA bacteria was promoted to a certain extent.

Claims

1. A method for enhancing the dissimilatory reduction of nitrate to ammonium by coupling nanoscale zero-valent iron with low-frequency infrared electromagnetic waves, comprising the following steps: (1) The anaerobic granular sludge is washed with tap water until the washing liquid becomes transparent, then the washing liquid is discarded, and then phosphate buffer is added to seal the sludge and allowed to stand overnight. The next day, it is transferred to a sequencing batch biofilm reactor; the anaerobic granular sludge is a granular sludge with a suspended solid concentration of 10.0-15.0 g / L, the pH of the phosphate buffer is 7.2, and the concentration is 0.1-0.3 mol / L. The inoculum amount of sludge in the sequencing batch biofilm reactor accounts for 1 / 5-1 / 2 of the reactor volume; (2) A low-frequency infrared electromagnetic wave generator is arranged outside the reactor, so that the electromagnetic wave intensity at the center of the reactor is 0.055 μT, the frequency of the low-frequency infrared electromagnetic wave generator is 50 Hz, and the wavelength range is 2-25 μm. Nano-scale zero-valent iron is added into the reactor through the reactor inlet, so that the concentration of nano-scale zero-valent iron in the reactor is maintained at 2-3 g / L; the reactor is a sequencing batch biofilm reactor with a non-woven fabric membrane as the membrane material, a water bath layer is set, and the particle size of the nano-scale zero-valent iron is 55-65 nm, and the purity is ≧99.9%; (3) Artificial synthetic wastewater is introduced 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 streams are kept consistent. The speed of the peristaltic pump is adjusted to control the water inlet flow rate. At the same time, the outlet pipe of the membrane module is connected to the peristaltic pump. Water is continuously introduced 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. The peristaltic pump is controlled by a time switch to maintain the reactor liquid level at a specified height; The composition of nitrogen source influent 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 per liter of influent; the composition of trace elements per liter of influent 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 ethanol with a concentration of 0.964 mL / L and a COD concentration of 1400 mg / L; The nitrogen source water and carbon source water were aerated with 99.9% pure nitrogen for 30 minutes, and then aerated for 30 minutes every 24 hours before entering the reactor; (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.

Images