A bioelectrochemical method for enhancing denitrification performance of horizontal subsurface flow constructed wetland

Abstract

The present application relates to the field of sewage treatment, and particularly relates to a biological electrochemical method for enhancing the denitrification performance of horizontal subsurface flow constructed wetland, comprising the following steps: (1) using graphite felt as filler, adopting SBBR, culturing autotrophic nitrifying biofilm on the surface thereof, installing the same into BES as anode reaction after appropriate trimming to obtain graphite felt attached with electroactive ammonia oxidation biofilm; (2) composing three-dimensional anode by using the graphite felt attached with electroactive ammonia oxidation biofilm and anode layer, composing three-dimensional cathode by using graphite plate and cathode layer, and assembling biological electrochemical functional unit together; (3) laying multiple groups of biological electrochemical functional units in HFCW, transforming into BECW and running. The present application firstly preassembles biological electrochemical functional unit, and then lays multiple groups of biological electrochemical functional units in HFCW to form BECW, after stable running, the concentrations of COD, TP, TN, NH4 + -N in effluent are greatly reduced, and the denitrification performance is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, and particularly relates to a biological electrochemical method for enhancing the denitrification performance of horizontal subsurface flow constructed wetland. BACKGROUND

[0002] Horizontal subsurface flow constructed wetland (HFCW) is widely used for treating various types of wastewater. However, most HFCW has poor reoxygenation capacity, and the substrate layer is mainly in an anaerobic environment, which results in poor nitrification performance of the system; on the other hand, due to the relative scarcity of organic carbon source in the influent, the denitrification performance of HFCW is also at a low level. The above two reasons lead to unsatisfactory denitrification effect of HFCW. Strengthening the nitrification / denitrification of microorganisms in the system is once considered as the most effective measure to improve the denitrification effect of HFCW. Generally speaking, the strengthening of nitrification / denitrification in HFCW can be achieved by regulating the concentration and distribution of dissolved oxygen (DO) and organic carbon source in the system, but it should be noted that when this technology is used for the treatment of low C / N wastewater, the lack of reoxygenation capacity and organic carbon source is always the main factor causing the low denitrification performance of HFCW, and the implementation of related strengthening measures will also cause the increase of construction and operation cost of the wetland system and the increase of its occupied area, and the operation process tends to be more complicated.

[0003] In recent years, some documents have pointed out that the operation performance of constructed wetland can be optimized by means of biological electrochemical method. Due to the high consistency between the redox potential gradient formed in the filler layer of constructed wetland and the process characteristics of biological electrochemical system (BES), the biological electrochemical constructed wetland (BECW) technology has been continuously developed and increasingly valued. Related researches consistently believe that compared with traditional constructed wetland process, the purification capacity (including denitrification capacity) and stability of BECW can be improved.

[0004] It is reported that electrically active ammonia-oxidizing biofilm can be formed in BES, and such biofilm can carry out electrode ammonia oxidation reaction, that is, the electrically active microorganisms in the biofilm can carry out anaerobic oxidation of NH4 + to NO x --N or gaseous nitrogen compounds (such as N2 or N2O, etc.). This discovery immediately provides a new idea for improving the denitrification performance of HFCW, such as using specific means to strengthen the electrode ammonia oxidation in the system, which should compensate for the defects of HFCW in treating ammonia-nitrogen-containing wastewater (especially low C / N wastewater) to some extent, and realize the efficient and stable denitrification performance of HFCW. However, further analysis found that the bioelectrochemical method in this study can only upgrade and improve the HFCW on a small scale, but it is not suitable for pilot and larger scale HFCW systems. In addition, the start-up process of the bioelectrochemical enhanced HFCW in the literature is relatively slow, and the strength of the electrode ammonia oxidation in the device is also low, resulting in unsatisfactory denitrification and power generation performance of the system, so it is necessary to explore more suitable bioelectrochemical methods to optimize the denitrification performance of HFCW. SUMMARY

[0005] (I) To overcome the shortcomings of the prior art, the present application provides a bioelectrochemical method for strengthening the denitrification performance of horizontal subsurface flow constructed wetland, which overcomes the shortcomings of the prior art, has reasonable design, and the COD, TP, TN, NH4 + -N concentration is greatly reduced, and the denitrification performance is significantly improved.

[0006] (II) To achieve the above object, the present application is realized by the following technical scheme: a bioelectrochemical method for strengthening the denitrification performance of horizontal subsurface flow constructed wetland, comprising the following steps,

[0007] (1) using graphite felt as filler, adopting SBBR (sequencing batch biofilm reactor), culturing autotrophic nitrifying biofilm on its surface, and installing it in BES after appropriate trimming as anode reaction to obtain graphite felt attached with electroactive ammonia oxidation biofilm;

[0008] (2) the graphite felt attached with electroactive ammonia oxidation biofilm and the anode layer form a three-dimensional anode, the graphite plate and the cathode layer form a three-dimensional cathode, and they are assembled together to form a bioelectrochemical functional unit;

[0009] (3) multiple bioelectrochemical functional units are arranged in HFCW, which is modified to BECW and runs.

[0010] Graphite felt attached with autotrophic nitrifying biofilm: when the ammonia nitrogen concentration in the influent is (50.87±2.54) mg / L, the NH4 + -N oxidation rate (AOE), NO2 - -N accumulation rate (NiAE) and NO3 - -N accumulation rate (NaAE) are (99.33±0.11) %, (88.08±2.07) % and (2.25±0.42) % respectively, indicating the maturity of autotrophic nitrifying biofilm.

[0011] Graphite felt with electroactive ammonia-oxidizing biofilm: The BES includes a stainless steel cell body as a cathode, a graphite felt with autotrophic nitrifying biofilm as an anode, and a saturated calomel electrode as a reference electrode installed in the stainless steel cell body. ANAMMOX sludge [the sludge is a mixed sludge of floc and granules, with MLSS of about 9500 mg / L, and analysis shows that the AnAOB contained in the sludge is mainly Candidatus Brocadia belonging to Planctomycetota] is inoculated into the BES, and the cathode, anode, and reference electrode in the BES are respectively connected to a potentiostat through wires, and the anode potential is set to 0.60 V by using the potentiostat.

[0012] The BES is continuously operated in a sequencing batch mode, and the method for continuous operation in the sequencing batch mode is as follows: 4 cycles are operated per day, each cycle lasts for 6 h, and each cycle is sequentially divided into an influent period of 15 min, a reaction period of 330 min, a drainage period of 10 min, and an idle period of 5 min. The water temperature is controlled at 20°C during the period. High-purity helium is blown into the BES during the influent period and the idle period to ensure an anaerobic environment.

[0013] Influent in the BES: prepared from 50 mmol / L phosphate buffer (pH = 7.5) containing Na2HPO4·12H2O (14.32 g / L), KH2PO4 (1.36 g / L), NaHCO3 (0.5 g / L), and trace element solution (2 mL / L). This substrate solution is first subjected to high-pressure steam sterilization (T = 121°C, t = 20 min) before use, then high-purity helium is blown into it (t = 20 min) to remove DO, and then it is injected into the BES at the beginning of each cycle. In addition, NH4Cl (0.19 g / L) is added to the influent of the device so that the concentration of NH4 + -N in it is maintained at about 50 mg / L.

[0014] The trace element solution includes: MnCl2·4H2O 0.10 g / L; FeSO4·7H2O 0.30 g / L; CoCl2·6H2O 0.17 g / L; ZnCl2 0.1 g / L; CuSO4·5H2O 0.04 g / L; AlK(SO4)2·12H2O 0.005 g / L; H3BO3 0.005 g / L; Na2MoO4 0.09 g / L; NiCl2 0.12 g / L; NaWO4·2H2O 0.02 g / L; Na2SeO4 0.10 g / L.

[0015] At an applied anode potential of 0.60 V, the anode surface of the BES can form an electroactive ammonia-oxidizing biofilm, the dominant genera in the biofilm include Nitrosomonas (17.67%), Candidatus Brocadia (16.28%), Geobacter (7.59%) and Empodebacter (8.84%); at the same time, the denitrification performance of the BES is also at a high level, and the TN and NH4 + - removal rates can reach (88.36±1.50)% and (96.96±0.54)%, respectively. Accordingly, it is confirmed that the anode surface of the BES can successfully cultivate an electroactive ammonia-oxidizing biofilm after the above preparation process.

[0016] Preferably, in step (2), the shell of the bioelectrochemical functional unit is a cylindrical porous frame, which is filled with a substrate layer, and the substrate layer includes, from bottom to top, a supporting layer, a functional filler layer and a coarse sand layer; the upper half of the functional filler layer is provided with a cathode layer, and a graphite plate felt is embedded in the cathode layer as a cathode, thereby forming a three-dimensional cathode, and the lower half of the functional filler layer is provided with an anode layer, and a graphite felt with an electroactive ammonia-oxidizing biofilm is embedded in the anode layer as an anode, thereby forming a three-dimensional anode; the cathode and the anode are connected by a wire and an external resistance to form a closed loop.

[0017] Preferably, the thickness of the substrate layer is 50-130 cm, and the porosity of the substrate layer is 30-45%, wherein the thickness of the supporting layer is 10-20 cm, the thickness of the functional filler layer is 35-115 cm, the thickness of the coarse sand layer is 5-10 cm, the thickness of the cathode layer is 15-30 cm, and the thickness of the anode layer is also 15-30 cm; the supporting layer is a gravel layer or a cobblestone layer, and the particle size thereof is 2-5 cm; the functional filler layer is any one or a mixed layer of zeolite, waste brick, volcanic rock, steel slag, limestone, centimeter stone and shale, and the particle size thereof is 0.5-1 cm; the cathode layer and the anode layer are both carbonaceous granular fillers, and the particle size thereof is 0.5-1 cm.

[0018] Preferably, the length x width x thickness of the graphite felt with the electroactive ammonia-oxidizing biofilm is 10 x 4 x 1 cm, and the length x width x thickness of the graphite plate is 10 x 4 x 1 cm; the cathode and the anode are connected by a 1 mm titanium wire and a 1 KΩ external resistance to form a closed loop.

[0019] Preferably, the bioelectrochemical functional unit is continuously operated in an upward flow mode, during which the hydraulic load of the device is set to 0.16 m 3 / (m 2 ·d), that is, the water inflow and the hydraulic retention time thereof are about 5 L / d and 2 d, respectively, and the water temperature in the substrate layer of the device is maintained at 14-23℃.

[0020] Preferably, in step (3), the HFCW is a concrete structure, and the bed of the HFCW is divided into a distribution zone, a treatment zone and a collection zone by a diversion wall; the channel width of the distribution zone and the collection zone is 30 cm, and the length and width of the treatment zone are 600 cm and 200 cm respectively.

[0021] Preferably, the distribution zone and the collection zone are filled with 100 cm thick cobblestones, and the treatment zone is filled with 10 cm thick cobblestones, 85 cm thick zeolite-waste brick blocks and 5 cm thick coarse sand from bottom to top in sequence, and the porosity of the filling material in the treatment zone is 30-45%; wherein the particle size of the cobblestones is 2-5 cm, and the particle size of the zeolite-waste brick blocks is 0.5-1 cm.

[0022] Preferably, Acorus calamus is planted in the treatment zone of the HFCW, and the planting density is 16 plants / m 2 .

[0023] Preferably, the arrangement density of the bioelectrochemical functional unit in the HFCW is 0.67 / m 2 .

[0024] Preferably, the HFCW is operated in a continuous flow mode, during which the hydraulic load of the HFCW is set to 0.2 m 3 / (m 2 ·d), the influent amount and the hydraulic retention time are about 2.4 m 3 / d and 2 d respectively, and the sewage water temperature is maintained at 14-23℃.

[0025] (Three) The present application provides a bioelectrochemical method for strengthening the denitrification performance of a horizontal subsurface flow artificial wetland, which has the following beneficial effects:

[0026] The present application first prepares a bioelectrochemical functional unit, and then arranges multiple bioelectrochemical functional units in the HFCW to form a BECW, after stable operation, the concentrations of COD, TP, TN, NH4 + -N in the effluent are greatly reduced, and the denitrification performance is significantly improved.

[0027] The BECW modified in the present application does not require additional aeration and external organic carbon source, can effectively reduce the risk of filler layer blockage and will not cause secondary pollution, and can reduce the amount of greenhouse gas emissions, and is a green and environmentally friendly ecological sewage treatment method. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of the SBBR configuration of the present application;

[0029] Figure 2 is a schematic diagram of the BES configuration of the present application;

[0030] Figure 3A configuration schematic diagram of a bioelectrochemical functional unit of the present application;

[0031] Figure 4 A start-up schematic diagram of the bioelectrochemical functional unit of the present application;

[0032] Figure 5 A configuration schematic diagram of the HFCW of the present application;

[0033] Figure 6 A configuration schematic diagram of the BECW of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application.

[0035] Embodiment 1

[0036] A bioelectrochemical method for enhancing the denitrification performance of a horizontal subsurface flow constructed wetland, specifically comprising the following steps:

[0037] (1) Using SBBR, autotrophic nitrifying biofilm is cultured on the surface of graphite felt as filler, and after appropriate trimming, the graphite felt is installed in BES as an anode reaction to obtain graphite felt attached with electroactive ammonia oxidation biofilm;

[0038] (2) The graphite felt attached with electroactive ammonia oxidation biofilm and the anode layer are combined into a three-dimensional anode, and the graphite plate and the cathode layer are combined into a three-dimensional cathode, and the bioelectrochemical functional unit is assembled together;

[0039] (3) Multiple groups of bioelectrochemical functional units are arranged in the HFCW, which is modified into BECW and operated. In step (2), the bioelectrochemical functional unit is in the form of a cylinder, with a height of 110 cm and an inner diameter of 20 cm, and the configuration is as shown in FIG. 2. Figure 2As shown, the bioelectrochemical functional unit has a cylindrical porous frame made of PVC material, filled with a 100cm thick matrix layer (porosity 37%). This matrix layer, from bottom to top, consists of a 10cm thick gravel support layer (particle size 2cm), a 30cm thick bottom zeolite-waste brick mixture layer (particle size 1cm), a 15cm thick anode layer, a 25cm thick upper zeolite-waste brick mixture layer (particle size 1cm), a 15cm thick cathode layer, and a 5cm thick coarse sand layer. The anode layer is externally wrapped with stainless steel mesh and contains graphite particles with a particle size range of 0.5cm. An embedded graphite felt (length × width × thickness = 10 × 4 × 1cm) with an attached electroactive ammonia oxidation biofilm serves as the anode. The cathode layer is also externally wrapped with stainless steel mesh and contains graphite particles with a particle size range of 0.5cm. An embedded graphite plate (length × width × thickness = 10 × 4 × 1cm) serves as the anode. In the bioelectrochemical functional unit, the graphite felt and graphite plate with electroactive ammonia oxidation biofilm are connected to a 1 mm diameter titanium wire and a 1 KΩ external resistor to form a closed circuit.

[0040] As attached Figure 3 As shown, the bioelectrochemical functional unit is placed in a PVC start-up device of suitable size. This start-up device has an inlet pipe at the bottom and an outlet pipe installed 20cm from the top of the inlet pipe. The bioelectrochemical functional unit is then continuously operated in upward flow mode, with the hydraulic load (HLR) of the functional unit set to 0.16m. 3 / (m 2 •d), that is, its influent flow rate and hydraulic retention time (HRT) are approximately 5L / d and 2d, respectively, and the wastewater temperature in the unit is maintained at 20℃.

[0041] Influent to the bioelectrochemical functional unit: Domestic sewage after primary sedimentation, containing oxygen-consuming organic matter (COD, the same below), TP, TN, and NH4. + -N, NO2 - -N and NO3 - The concentrations of -N were (159.34±8.60), (5.66±0.28), (51.04±1.80), (50.59±1.86), (0.07±0.03), and (0.17±0.07) mg / L, respectively.

[0042] After 36 cycles, the performance of the bioelectrochemical functional unit tends to stabilize. During stable operation, the system's COD, TP, TN, and NH4 levels are stable. +The -N removal rates were (87.01±3.72) %, (94.46±1.96) %, (86.67±4.68) % and (97.23±1.44) %, respectively, and the output voltage, output power density peak value and apparent internal resistance were (529.30±2.42) mV, 883.51 mW / m 3 The water quality met the first level A criteria specified in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002). By analyzing the microbial community structure in the anode and cathode layers, it was found that the functional microorganisms participating in the electrode ammonia oxidation reaction in the anode layer mainly included Nitrosomonas, Geobacter, Empodebacter and Candidutus Brocadia, and the functional microorganisms participating in the NO x - The functional microorganisms of the -N reduction reaction mainly included Thauera, Zoogloea, Denitratisoma, Thiobacillus, Pseudomonas, Dechloromonas and Paracoccus.

[0043] Table 1 Bioelectrochemical functional unit

[0044]

[0045] In step (3), the HFCW is a concrete structure, and the configuration is shown in the accompanying drawings. Figure 4 As can be seen from the drawings, the bed body of the HFCW is divided into a water distribution zone, a treatment zone and a water collection zone by the flow guide wall. The channel width of the water distribution zone and the water collection zone is 30 cm, and both are filled with goose pebbles with a particle size of 3 cm and a filling thickness of 100 cm. The length and width of the treatment zone are 600 cm and 200 cm, respectively, and the inside is filled with a 100 cm thick base layer (porosity is about 37%). The base layer is sequentially composed of a 10 cm thick goose pebble supporting layer (particle size is 3 cm), a 853 cm thick zeolite-waste brick mixed layer (particle size is 1 cm) and a 5 cm thick coarse sand layer from bottom to top. A Acorus calamus is planted in the treatment zone of the HFCW, and the planting density is 16 plants / m 2 . The Acorus calamus has the following advantages: the Acorus calamus is a cold-resistant plant, and the planting of cold-resistant plants helps the ecological treatment process of the constructed wetland to have relatively high purification performance at low temperatures; the Acorus calamus has a well-developed root system, high oxygen secretion capacity and can produce a large amount of root exudates, which can be used as an organic carbon source to improve the strength of the denitrification of the surface layer of the wetland; the Acorus calamus can grow in gravel and stone cracks, and compared with other types of plants, the Acorus calamus is more likely to survive in the system; the Acorus calamus has the ability to repel mosquitoes and insects, and itself is a traditional Chinese medicine with certain economic benefits.

[0046] HFCW runs in continuous flow mode. That is, after the sewage is uniformly distributed in the distribution area through the perforated pipe, it enters the treatment area from the bottom to the top along the guide wall. Then, the sewage flowing through the treatment area enters the collection area through the inverted L-shaped pipe, and finally is discharged from the HFCW through the effluent pipe. During operation, the hydraulic load (HLR) of the HFCW is set to 0.2 m 3 / (m 2 ·d), and the influent and hydraulic retention time (HRT) are about 2.4 m 3 / d and 2 d, respectively. The water temperature in the filler layer is maintained at 20℃.

[0047] Influent of HFCW: The influent of the biological electrochemical functional unit is the same as that of the biological electrochemical functional unit, which is the domestic sewage after primary sedimentation.

[0048] Eight groups of biological electrochemical functional units are arranged in the HFCW (arrangement density is 0.67 / m 2 ), and the arrangement position is shown in the attached Figure 4 , which is transformed into BECW.

[0049] During the stable operation of BECW, the concentrations of COD, TP, TN, NH4 + -N, NO3 - -N and NO2 - -N in the effluent are (21.1±3.5), (0.18±0.05), (1.89±0.31), (1.29±0.24), (0.51±0.06) and (0.09±0.01) mg / L, respectively, and the effluent quality meets the first level A standard of "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant" (GB18918-2002). In addition, through the analysis of the microbial community structure in the anode and cathode layers, it is found that the functional microorganisms participating in the electrode ammonia oxidation reaction in the anode layer mainly include Nitrosomonas, Geobacter, Empodebacter and Candidutus Brocadia, etc., and the functional microorganisms participating in the NO x - -N reduction reaction in the cathode layer mainly include Thauera, Zoogloea, Denitratisoma, Thiobacillus, Pseudomonas, Dechloromonas and Paracoccus, etc. Overall, through the reasonable arrangement of the biological electrochemical functional unit, the denitrification performance has been significantly improved.

[0050] Table 2 BECW

[0051] Category BECW influent concentration, mg / L BECW effluent concentration, mg / L COD 159.34±8.60 21.1±3.5 TP 5.66±0.28 0.18±0.05 TN 51.04±1.80 1.89±0.31 NH4 + -N]]> 50.59±1.86 1.29±0.24 NO3 - -N]] 0.17±0.07 0.51±0.06 NO2 - -N]] 0.07±0.03 0.09±0.01

[0052] Comparative Example 1

[0053] The HFCW structure and operation mode are the same as those of Embodiment 1, except that no bioelectrochemical functional unit is arranged in the HFCW. The influent concentration and effluent concentration detection data are as follows.

[0054] Table 3 HFCW

[0055] Category HFCW influent concentration, mg / L HFCW effluent concentration, mg / L COD 159.34±8.60 25.59±1.73 TP 5.66±0.28 0.22±0.08 TN 51.04±1.80 35.07±4.84 NH4 + -N]] 50.59±1.86 31.51±4.95 NO3 - -N]] 0.17±0.07 3.42±1.75 NO2 - -N]] 0.07±0.03 0.30±0.16

[0056] As can be seen from the comparison of the effluent concentration data in Table 2 and Table 3, compared with the HFCW, the nitrogen removal effect of the BECW is greatly improved after stable operation, further enhancing the purification effect on the sewage.

[0057] The embodiments of the present application disclose the preferred embodiments, but are not limited thereto. Those skilled in the art can easily understand the spirit of the present application according to the above embodiments, and make different inferences and changes, as long as they do not deviate from the spirit of the present application, which are within the protection scope of the present application.

Claims

1. A bioelectrochemical method for enhancing the denitrification performance of a horizontal subsurface flow constructed wetland, characterized in that, Comprise the following steps: (1) with graphite felt as filler, using SBBR, cultivating autotrophic nitrifying biofilm on its surface, after appropriate pruning, installing into BES as anode reaction, obtaining graphite felt attached with electroactive ammonia oxidation biofilm; (2) the graphite felt attached with electroactive ammonia oxidation biofilm and anode layer constitute three-dimensional anode, and graphite plate and cathode layer constitute three-dimensional cathode, and they are assembled into bioelectrochemical functional unit together; In step (2), the shell of bioelectrochemical functional unit is cylindrical porous frame, which is filled with substrate layer, and the substrate layer comprises support layer, functional filler layer and coarse sand layer from bottom to top; the upper half of functional filler layer is provided with cathode layer, and graphite felt is embedded in cathode layer as cathode, thereby forming three-dimensional cathode, and the lower half of functional filler layer is provided with anode layer, and graphite felt attached with electroactive ammonia oxidation biofilm is embedded in anode layer as anode, thereby forming three-dimensional anode; the cathode and anode are connected by wire and external resistance to form a closed loop; The thickness of substrate layer is 50-130cm, and the porosity of substrate layer is 30-45%, wherein the thickness of support layer is 10-20cm, the thickness of functional filler layer is 35-115cm, the thickness of coarse sand layer is 5-10cm, the thickness of cathode layer is 15-30cm, and the thickness of anode layer is 15-30cm; the support layer is gravel layer or cobblestone layer, and the particle size is 2-5cm; the functional filler layer is zeolite-waste brick mixed layer, and the particle size is 0.5-1cm; the particle size of carbonaceous granular filler in cathode layer and anode layer is 0.5-1cm; (3) multiple bioelectrochemical functional units are arranged in HFCW, which is transformed into BECW and runs; In step (3), HFCW is a concrete structure, and the bed body of HFCW is divided into distribution area, treatment area and collection area by flow guide wall; the channel width of distribution area and collection area is 30cm, and the length and width of treatment area are 600cm and 200cm respectively; The distribution area and collection area are filled with 100cm thick cobblestone, and the treatment area is filled with 10cm thick cobblestone, 85cm thick zeolite-waste brick and 5cm thick coarse sand from bottom to top, and the porosity of filling material in treatment area is 30-45%; wherein the particle size of cobblestone is 2-5cm, and the particle size of zeolite-waste brick is 0.5-1cm.

2. A bioelectrochemical method for enhancing the denitrification performance of a horizontal subsurface flow constructed wetland according to claim 1, characterized in that, The length, width and thickness of graphite felt attached with electroactive ammonia oxidation biofilm are 10cm, 4cm and 1cm respectively, and the length, width and thickness of graphite plate are 10cm, 4cm and 1cm respectively; The cathode and anode are connected by 1mm titanium wire and 1KΩ external resistance to form a closed loop.

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