A method for deep denitrification and carbon reduction based on biogas substrate biofilm

Abstract

The present application relates to sewage treatment technical field, particularly to a kind of method for deep denitrification and carbon reduction based on biogas substrate biofilm.The present application diffuses biogas mixed substrate to biogas substrate biofilm synchronously in the form of no bubble or microbubble through hollow fiber membrane module, and then provides electron donor, organic carbon source and inorganic carbon source for functional microorganism contained in biogas substrate biofilm.CO2 in the biogas is simultaneously introduced to regulate the pH value in biofilm, so that it is at 7.2-7.6.Deep denitrification and carbon emission reduction of wastewater treatment plant effluent in secondary sedimentation tank at low cost and without secondary pollution are realized through multiple pathways such as anaerobic methane oxidation coupled with denitrification, aerobic methane oxidation coupled with denitrification, hydrogen autotrophic denitrification and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, in particular to a method for deep denitrification and carbon reduction based on biogas substrate biofilm. BACKGROUND

[0002] Nitrate nitrogen (NO3 - -) is a typical oxidizing pollutant in water bodies, which seriously threatens the ecological safety of water bodies and human health. The advancement of urbanization leads to the emission of excess nitrogen, thereby affecting the influent water quality of many sewage treatment plants, resulting in non-compliance of total nitrogen (TN) in effluent or increased cost of denitrification. In addition, with the popularization and application of activated sludge method in municipal sewage treatment plants, a large amount of waste sludge is generated. In order to prevent the easily decomposed organic matter in the sludge from causing serious secondary pollution to the environment, most water plants are equipped with sludge anaerobic digestion devices. Biogas produced by anaerobic digestion contains 50% to 70% CH4, 30% to 55% CO2 and 5% other gases (H2, H2S, etc.).

[0003] At present, the mainstream method for reducing the content of NO3 - -N in wastewater is biological method, but the denitrification process of biological method is affected by the fluctuation of influent water quality and quantity and the lack of carbon source in the denitrification process, resulting in non-compliance of NO3 - -N in effluent. In order to ensure the quality of effluent from sewage treatment plants, additional carbon source needs to be added, which not only increases the operating cost, but also introduces secondary pollution. In addition, at present, most domestic and foreign sewage treatment plants do not have cogeneration technology, and the biogas is burned in the boiler, and a few sewage treatment plants use biogas for heating or power generation. However, these methods only change the form of carbon, and do not slow down the emission of carbon from the root. Therefore, it is of great significance to obtain a method for deep denitrification and carbon reduction based on biogas substrate microorganism, which can improve the water quality of effluent from sewage treatment plants and achieve the strategic goal of carbon emission reduction. SUMMARY

[0004] In order to solve the above problems, the present application provides a method for deep denitrification and carbon reduction based on biogas substrate biofilm. The method provided by the present application realizes low-cost and secondary pollution-free deep denitrification and carbon reduction of the effluent from the secondary sedimentation tank of the sewage treatment plant through anaerobic methane oxidation coupled with denitrification, aerobic methane oxidation coupled with denitrification, hydrogen autotrophic denitrification and other multiple pathways.

[0005] In order to achieve the above purpose, the present application provides the following technical scheme:

[0006] The present application provides a method for denitrification and carbon reduction of wastewater by using biofilm, which comprises the following steps:

[0007] Mixing the sludge in the anaerobic section of the sewage treatment plant and the sludge in the anaerobic section of the brewery wastewater treatment to obtain mixed sludge;

[0008] Inoculating the mixed sludge into a nitrate solution, introducing biogas and / or simulated biogas, first culturing to a nitrate nitrogen concentration of 0 mg / L, to obtain a supernatant as a domesticated bacteria solution; the concentration of nitrogen elements in the nitrate solution is 20 mg / L.

[0009] Inoculating the new mixed sludge and the domesticated bacteria solution into sewage and / or simulated sewage provided with a hollow fiber membrane, introducing biogas and / or simulated biogas, second culturing, to obtain a hollow fiber membrane with a biofilm attached thereto.

[0010] Mixing the sewage to be treated with the hollow fiber membrane with a biofilm attached thereto, introducing biogas and / or simulated biogas, third culturing, to obtain treated sewage.

[0011] Preferably, the volume ratio of the sewage treatment plant anaerobic sludge and the brewery wastewater treatment anaerobic sludge in the mixed sludge is 1:1 to 1:2.

[0012] Preferably, the concentration of nitrate nitrogen in the sewage and / or simulated sewage is 10-30 mg / L in terms of nitrogen element concentration.

[0013] Preferably, the simulated sewage further comprises the following components at the following concentrations: CaCl2 0.5-1 mg / L, CuCl2·2H2O 0.02-0.05 mg / L, ZnSO4·7H2O 0.01-0.05 mg / L, NiCl2·6H2O 0.01-0.05 mg / L, Na2MoO4·2H2O 0.01-0.05 mg / L, Na2WO4·2H2O 0.01-0.05 mg / L, CoCl2·6H2O 0.1-0.2 mg / L, H3BO3 0.1-0.3 mg / L, FeSO4·7H2O 0.01-0.05 mg / L, MnCl2 0.01-0.05 mg / L, Na2SeO3 0.01-0.03 mg / L.

[0014] Preferably, the simulated biogas comprises the following components at the following volume fractions: CH4 54-74 parts, CO2 24-44 parts, H2 1-2 parts, and H2S 0.1-1 part.

[0015] Preferably, the volume ratio of the new mixed sludge to the domesticated bacteria solution is 1:1 to 2.

[0016] Preferably, the temperature of the first culturing is 28-32°C, and the first culturing is carried out in the dark.

[0017] Preferably, the thickness of the biofilm on the hollow fiber membrane with a biofilm attached thereto is 400-800 μm.

[0018] Preferably, the partial pressure of the biogas and / or simulated biogas introduced during the first culture, the second culture or the third culture is 0.06-0.1 MPa.

[0019] Preferably, the hydraulic retention time during the third culture is 6-12 h.

[0020] Beneficial effects:

[0021] The sludge from the anaerobic section of a sewage treatment plant and the sludge from the anaerobic section of a brewery wastewater treatment plant are first domesticated to obtain domesticated bacteria liquid, then the domesticated bacteria liquid and the sludge are mixed and biogas or simulated biogas is introduced to perform biofilm treatment on the hollow fiber membrane to obtain a hollow fiber membrane with biological membrane attached; finally, the biogas or simulated biogas is introduced into the hollow fiber membrane with biological membrane to treat wastewater containing NO3 - -N. The biogas mixed substrate is diffused in the form of bubble-free or micro-bubbles to the biogas substrate biofilm through the hollow fiber membrane assembly, thereby providing the functional microorganisms contained in the biogas substrate biofilm with electron donors, organic carbon sources and inorganic carbon sources. The CO2 in the introduced biogas regulates the pH value in the biological membrane to be 7.2-7.6. The low-cost and secondary pollution-free deep denitrification of the effluent from the secondary sedimentation tank of a sewage treatment plant is realized through multiple pathways such as anaerobic methanotrophic denitrification, aerobic methanotrophic denitrification and hydrogen autotrophic denitrification.

[0022] The efficient use of biogas realizes the self-production and self-sale of greenhouse gases in the wastewater treatment industry, thereby promoting carbon emission reduction and deep denitrification of the effluent from the secondary sedimentation tank. The method provided by the present application has high safety, stability and economy, can be scaled up, has multiple important meanings for the popularization and large-scale application of the biogas substrate biofilm technology, and brings new opportunities for denitrification and carbon reduction in municipal wastewater treatment plants. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows.

[0024] Figure 1 It is a schematic diagram of the biological membrane reactor device and working principle;

[0025] Figure 2 It is a diagram of the NO3 - -N, NO2 - -N and TN concentrations of the effluent from the biological membrane reactor in Example 1;

[0026] Figure 3 It is a diagram of the greenhouse gas (CH4, CO2) leakage of the biological membrane reactor in Example 1;

[0027] Figure 4Figure for greenhouse gas (CH4, CO2) utilization rate of the biofilm reactor in Example 1;

[0028] Figure 5 Figure for NO3 - -N, NO2 - -N concentration and NO3 - Figure for NO3

[0029] Figure 6 Figure for greenhouse gas (CH4, CO2) leakage of the biofilm reactor in Example 2;

[0030] Figure 7 Figure for greenhouse gas (CH4, CO2) utilization rate of the biofilm reactor in Example 2. DETAILED DESCRIPTION

[0031] The present application provides a method for denitrification and carbon reduction of sewage by using a biofilm, comprising the following steps:

[0032] Mixing sludge from an anaerobic section of a sewage treatment plant and sludge from an anaerobic section of a brewery wastewater treatment plant to obtain mixed sludge;

[0033] Inoculating the mixed sludge into a nitrate solution, and introducing biogas and / or simulated biogas, and first culturing to obtain a supernatant as acclimated bacteria liquid, wherein the concentration of nitrogen elements in the nitrate solution is 20 mg / L;

[0034] Inoculating new mixed sludge and the acclimated bacteria liquid into sewage and / or simulated sewage provided with hollow fiber membranes, and introducing biogas and / or simulated biogas, and second culturing to obtain hollow fiber membranes with biofilms attached thereto;

[0035] Mixing sewage to be treated with the hollow fiber membranes with biofilms attached thereto, and introducing biogas and / or simulated biogas, and third culturing to obtain treated sewage.

[0036] In the present application, the volume ratio of the sludge from the anaerobic section of the sewage treatment plant to the sludge from the anaerobic section of the brewery wastewater treatment plant in the mixed sludge is preferably 1:1 to 1:2, and more preferably 1:1.

[0037] After obtaining the mixed sludge, the mixed sludge is inoculated into a nitrate solution, biogas and / or simulated biogas is introduced, the first culture is carried out until the concentration of nitrate nitrogen is 0 mg / L, and a supernatant is obtained as an acclimated bacteria solution; the concentration of nitrogen element in the nitrate solution is 20 mg / L. In the present application, the nitrate preferably includes sodium nitrate; before the mixed sludge is inoculated into the nitrate solution, the nitrate solution is preferably subjected to nitrogen gas exposure deoxygenation treatment; in the first culture process, biogas and / or simulated biogas is introduced into the nitrate solution inoculated with the mixed sludge, which is preferably simulated biogas; the simulated biogas preferably includes the following components by volume: CH4 54-74 parts, CO2 24-44 parts, H2 1-2 parts and H2S 0.1-1 part, and more preferably CH4 69.5 parts, CO2 28 parts, H2 2 parts and H2S 0.5 part; the partial pressure of the introduced biogas and / or simulated biogas is preferably 0.06-0.10 MPa, and more preferably 0.06 MPa; the biogas is preferably biogas produced by anaerobic digestion in a sewage treatment plant. By introducing biogas and / or simulated biogas with a suitable partial pressure, not only can sufficient carbon source and electron donor be provided for the microorganisms in the nitrate solution for denitrification, but also gas leakage and waste can be avoided; by introducing simulated biogas, stable biogas can be provided, and the influence of unstable biogas produced by anaerobic digestion on the stability of the acclimated bacteria solution and the biofilm can be avoided.

[0038] In the present application, the volume ratio of the mixed sludge to the nitrate solution is preferably 1:20-30, and more preferably 1:25; the temperature of the first culture is preferably 28-32℃, and more preferably 30℃; the first culture is preferably light-free culture, and the first culture is preferably shaking culture, and the rotation speed of the shaking culture is preferably 160 r / min.

[0039] As shown in Figure 1 The present application preferably sets a hollow fiber membrane assembly in a device with a water inlet, a water outlet and a gas inlet to obtain a biofilm reactor. The present application does not have special requirements for the source of the biofilm reactor, and commercially available products known to those skilled in the art can be used. In the present application, the hollow fiber membrane assembly is preferably composed of a plurality of hollow fiber membrane filaments, and more preferably composed of 16 hollow fiber membrane filaments; the material of the hollow fiber membrane filament is preferably hydrophilic polyvinyl chloride (PVC); the inner diameter of the hollow fiber membrane filament is preferably 0.8-1 mm, and the outer diameter is preferably 1.5-1.7 mm; the effective length of the hollow fiber membrane is preferably 20-25 cm, the pore diameter of the micropore on the membrane is preferably 0.02 μm, and the total surface area is preferably 160-180 cm 2 .

[0040] After obtaining the acclimated bacteria liquid and the biofilm reactor, the application preferably inoculates the new mixed sludge and the acclimated bacteria liquid into the biofilm reactor, adds sewage and / or simulated sewage, introduces biogas and / or simulated biogas, and carries out secondary culture to obtain the hollow fiber membrane with biofilm attached. In the application, the volume ratio of the new mixed sludge and the acclimated bacteria liquid is preferably 1:1-2, more preferably 1:2; the inoculation amount of the mixture of the new mixed sludge and the acclimated bacteria liquid is preferably 28%-32% of the effective volume of the biofilm reactor, more preferably 30%; the sewage is preferably the sewage to be treated, and the nitrate nitrogen concentration in the sewage and / or simulated sewage is preferably 10-30 mg / L in terms of nitrogen element concentration; the simulated sewage preferably further comprises the following components at the following concentrations: CaCl20.5-1 mg / L, CuCl2·2H2O 0.02-0.05 mg / L, ZnSO4·7H2O 0.01-0.05 mg / L, NiCl2·6H2O 0.01-0.05 mg / L, Na2MoO4·2H2O 0.01-0.05 mg / L, Na2WO4·2H2O 0.01-0.05 mg / L, CoCl2·6H2O 0.1-0.2 mg / L, H3BO3 0.1-0.3 mg / L, FeSO4·7H2O 0.01-0.05 mg / L, MnCl2 0.01-0.05 mg / L, Na2SeO3 0.01-0.03 mg / L, more preferably CaCl2 1 mg / L, CuCl2·2H2O 0.02 mg / L, ZnSO4·7H2O 0.05 mg / L, NiCl2·6H2O 0.03 mg / L, Na2MoO4·2H2O 0.03 mg / L, Na2WO4·2H2O 0.05 mg / L, CoCl2·6H2O 0.2 mg / L, H3BO3 0.3 mg / L, FeSO4·7H2O 0.05 mg / L, MnCl2 0.05 mg / L, Na2SeO3 0.03 mg / L; in the secondary culture process, the biofilm reactor preferably adds simulated sewage, and the simulated sewage is preferably subjected to nitrogen aeration and deoxygenation before being added to form an anaerobic environment, which is conducive to the growth of anaerobic microorganisms and the stable nitrate nitrogen load of the simulated sewage, and is conducive to the biofilm formation. In the application, the temperature of the secondary culture is preferably room temperature; the thickness of the biofilm on the hollow fiber membrane with biofilm attached is preferably 400-800 μm; the biogas and / or simulated biogas introduced in the secondary culture process is preferably the same as that in the first culture, which is not described herein again; the partial pressure of the biogas and / or simulated biogas introduced in the secondary culture process is preferably 0.06-0.1 MPa, further preferably 0.08-0.1 MPa, and more preferably 0.08 MPa.

[0041] After the hollow fiber membrane with biofilm is obtained, the sewage to be treated and the hollow fiber membrane with biofilm are mixed, and biogas and / or simulated biogas are introduced, and a third culture is carried out, so that the treated sewage is obtained. In the present application, the sewage to be treated is preferably the effluent from the secondary sedimentation tank of a sewage treatment plant, and the use of the method of the present application for treating the effluent from the secondary sedimentation tank of a sewage treatment plant can improve the effluent quality of the sewage treatment plant and achieve carbon emission reduction. In the present application, the temperature of the third culture is preferably room temperature; during the third culture, the partial pressure of the introduced biogas and / or simulated biogas is preferably 0.06-0.1 MPa, further preferably 0.08-0.1 MPa, and more preferably 0.1 MPa; during the third culture, the hydraulic retention time is preferably 6-12 h, further preferably 7-10 h, and more preferably 7.6 h; the backflow speed is preferably 80-120 times the influent flow rate; the influent flow rate is preferably 0.2-0.4 mL / min, further preferably 0.2-0.5 mL / min, and more preferably 0.226 mL / min; and the introduced biogas and / or simulated biogas during the third culture is preferably the same as that in the first culture, which will not be described here.

[0042] The present application introduces biogas or simulated biogas into the hollow fiber membrane with biofilm to treat sewage containing NO3 - The present application introduces biogas or simulated biogas into the hollow fiber membrane with biofilm to treat sewage containing NO3

[0043] In order to further illustrate the present application, a method for deep denitrification and carbon reduction based on a biogas substrate biomembrane provided by the present application is described in detail below in combination with the accompanying drawings and examples, but they should not be understood as limiting the scope of protection of the present application.

[0044] Example 1

[0045] 1. Treatment of actual wastewater

[0046] Periodic sampling and testing of the effluent from the secondary sedimentation tank of a small wastewater treatment plant in Guilin City revealed that the total nitrogen (TN) in the effluent exceeded the Class A discharge standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB 18918-2002)" for some periods, with concentrations fluctuating between 9.5 mg / L and 17 mg / L, primarily consisting of NO3. - -N exists in the form of (7 mg / L to 14 mg / L). Therefore, the effluent from the secondary sedimentation tank of the water plant during the period when the total nitrogen concentration exceeded the standard was used as the actual influent of this system (denoted as the wastewater exceeding the standard) to explore the potential of deep denitrification and carbon reduction in the practical application of biogas matrix biofilm method.

[0047] 2. Start-up and biofilm formation in a biofilm reactor

[0048] Sludge from the anaerobic stage of the wastewater treatment plant and anaerobic stage of the brewery wastewater treatment plant were allowed to stand. Sludge from the solid-liquid interface was then mixed at a 1:1 volume ratio and used as the initial mixed anaerobic sludge inoculation (10% of the serum bottle volume). This mixture was added to a 500ml serum bottle, and simulated biogas (partial pressure 0.06 MPa) was introduced. The bottle was then placed in a shaker and cultured in a constant temperature shaker at 30±2℃ and 160r / min in the dark. The simulated biogas consisted of the following components by volume percentage: CH4 69.5%, CO2 28%, H2 2%, and H2S 0.5%. The culture medium in the serum bottle was a 20mg / L sodium nitrate aqueous solution after deoxygenation by N2 aeration.

[0049] NO3 in serum bottle - Once the -N concentration drops to 0 mg / L, the bacterial culture acclimatization is complete, and the supernatant obtained is the acclimatized bacterial culture.

[0050] Mix 20 mL of acclimatized bacterial solution with 10 mL of original mixed anaerobic sludge and inject the mixture into the biofilm reactor using a syringe (e.g., ...). Figure 1 As shown, the effective volume of the biofilm reactor is 130 mL. The biofilm reactor contains a hollow fiber membrane module, which consists of 16 hydrophilic polyvinyl chloride (PVC) hollow fiber membrane filaments. Each filament has a surface with numerous micropores, each with a micropore diameter of 0.02 μm. The inner diameter of the hollow fiber membrane filaments is 0.8 mm, and the outer diameter is 1.5 mm. The effective length of the hollow fiber membrane is 200 mm, and the total surface area is 166.8 cm². 2 Simulated wastewater was added to the biofilm reactor, and simulated biogas was introduced into the hollow fiber membrane under a pressure of 0.06 MPa. Once the biofilm reactor was full of simulated wastewater, the inlet peristaltic pump was turned off, and the reflux peristaltic pump was turned on to circulate the biofilm at a reflux rate of 20 mL / min for three days. This process was used to acclimate the functional microbial community required for the biogas substrate biofilm and to initiate biofilm formation, resulting in a biofilm-attached reactor. The simulated wastewater consisted of 10 mg / L NO3. -- N (as nitrogen element concentration), 1 mg / L of CaCl2, 0.02 mg / L of CuCl2·2H2O, 0.05 mg / L of ZnSO4·7H2O, 0.03 mg / L of NiCl2·6H2O, 0.03 mg / L of Na2MoO4·2H2O, 0.05 mg / L of Na2WO4·2H2O, 0.2 mg / L of CoCl2·6H2O, 0.3 mg / L of H3BO3, 0.05 mg / L of FeSO4·7H2O, 0.05 mg / L of MnCl2, 0.03 mg / L of Na2SeO3.

[0051] 3. The biogas substrate biofilm system for treating actual NO3 - -N wastewater

[0052] In order to verify that the biogas substrate biofilm system in the application can achieve deep denitrification and carbon reduction in actual wastewater (excessive wastewater), a continuous experiment is designed. After 3 days of start-up and domestication, the biogas substrate biofilm method is stably operated, the simulated wastewater is replaced with excessive wastewater, the influent flow rate is 0.262 mL / min, the reflux speed is 20 mL / min, the simulated biogas pressure is 0.08 MPa, and the hydraulic retention time is 7.6 h.

[0053] Sampling and analysis:

[0054] Detection of NO3 - -N, NO2 - -N, TN concentration, and H2, CH4 and H2S concentration in water. The gas in the headspace gas collection bag is taken to detect the leakage of H2, CO2, CH4 and H2S in the headspace of the biofilm reactor. The gas in the effluent of the biofilm reactor is determined by the headspace method, and the gas in the liquid phase is converted to the gas phase by shaking water bath heating, and then the concentration is determined.

[0055] Effluent NO3 - -N, NO2 - -N and TN concentration curves with running time are shown in Figure 2 As can be seen from the figure, the water quality and quantity of the daily influent of the small urban sewage treatment plant in Guilin are quite different. During the 60-day continuous operation of the biofilm reactor, the effluent NO3 - -N concentration fluctuates in the range of 0-9.5 mg / L, the minimum is 0.918 mg / L, and the maximum does not exceed 10 mg / L; the effluent NO2 - -N concentration is stably at 0.1 mg / L, and the maximum concentration does not exceed 0.4 mg / L; the effluent TN concentration fluctuates in 4-13 mg / L, and the concentration can still meet the first level A discharge standard of “Urban Sewage Treatment Plant Pollutant Discharge Standard (GB 18918-2002)”.

[0056] Greenhouse gas (CH4, CO2) leakage in the biofilm reactor as shown in Figure 3 The utilization of greenhouse gases as shown in Figure 4 Figure 3 With Figure 4 It can be seen that the liquid-phase CH4 leakage concentration can be stabilized at about 8-10 mg / L, the headspace CH4 leakage concentration is in the range of 2-4 mg / L, and the headspace CO2 leakage is lower than 9 mg / L. The results show that the biogas substrate biofilm system has good carbon reduction performance in treating actual wastewater, and the CH4 utilization rate can be more than 55%, and the CO2 utilization rate is more than 90%.

[0057] Example 2

[0058] To further explore the denitrification and carbon reduction potential of the biogas substrate biofilm method (i.e. the method of Example 1), the NO3 - -N load in the wastewater exceeding the standard in Example 1 is replaced with simulated wastewater, and the concentration of NO3 - -N (calculated in terms of nitrogen element concentration) in the simulated wastewater is set to 20 mg / L for 150-225 days, and the concentration of NO3 - -N (calculated in terms of nitrogen element concentration) in the simulated wastewater is set to 30 mg / L.

[0059] The simulated wastewater in the sewage container is aerated with nitrogen gas for at least 5 min, and the sewage container is sealed to maintain an anaerobic state (DO < 0.2 mg / L) in the sewage container.

[0060] The simulated wastewater is introduced into the biofilm reactor which has been domesticated for long-term stable operation, the influent flow rate is 0.262 mL / min, the reflux speed is 26.2 mL / min, and the gas pressure is 0.10 MPa.

[0061] The NO3 - -N, NO2 - -N concentration and the NO3 - -N utilization rate as shown in Figure 5 It can be seen from the figure that in the early stage of operation, the high NO3 - -N concentration affects the effluent NO3 - -N concentration is maintained at 10-15 mg / L, and the NO3 - -N removal efficiency is only 20%-40%. After 75 days, the effluent NO3 - -N concentration begins to decrease, and is lower than 10 mg / L after 100 days, and the removal efficiency begins to reach 50%, and after 125 days, the effluent NO3 - -N concentration is basically maintained at about 2-3 mg / L, and there is no NO2 - ​-N accumulation. At 150d, due to the sudden increase of influent load, the removal rate of nitrate nitrogen decreased to about 50%, and fluctuated in the range of 40%~60%, the effluent NO3 - -N concentration was basically maintained at 15mg / L. During this period, NO2 - -N concentration exceeded 1mg / L.

[0062] The greenhouse gas (CH4, CO2) leakage of biofilm reactor is shown in Figure 6 The utilization rate of greenhouse gas (CH4, CO2) of biofilm reactor is shown in Figure 7 The microbial growth was affected by the high influent NO3 - -N load, and the removal efficiency of NO3 - -N decreased, and the leakage concentration of CH4 in liquid phase and the leakage concentration of CH4 in headspace both showed an upward trend. The leakage concentration of CH4 in liquid phase increased to 12~14mg / L, and the highest could reach 16mg / L. The leakage concentration of CH4 in headspace fluctuated between 4~6mg / L, and the utilization rate was about 20%. After 70d, the microorganisms adapted to the high influent NO3 - -N load, the leakage concentration of CH4 in liquid phase and the leakage concentration of CH4 in headspace both began to decrease slowly. The leakage concentration of CH4 in headspace began to stabilize between 1~2mg / L, and the leakage concentration of CH4 in liquid phase began to decrease gradually after 70d, and stabilized below 4mg / L after 100d, and the utilization rate was above 85%. In the biogas substrate biofilm system, CO2 in liquid phase exists as carbonate and bicarbonate ions, and is fixed as an acid-base balancing agent in the biogas substrate biofilm. The leakage of CO2 in headspace was basically stable at 4mg / L, and the utilization rate was stable at 98% throughout the entire continuous experiment. When running to 150d, although the load of simulated wastewater was increased, the utilization rate of greenhouse gas (CH4, CO2) in the reactor did not show a significant increase.

[0063] The results showed that the functional microorganisms contained in the biogas substrate biofilm could utilize CH4 and CO2 in biogas as carbon source or electron donor for denitrification. When the biogas substrate biofilm method removed 20mg / L of simulated wastewater, not only could it remove NO3 - -N without adding carbon source and phosphate buffer in the influent using biogas as substrate, but also the removal rate of NO3 - -N could reach more than 85%(removing 17mg / L of NO3 -CH4 utilization rate can be maintained at 80%~90%, CO2 utilization rate can reach 99%, and carbon utilization rate of biogas substrate biofilm system can reach more than 80%, which shows that the biogas substrate biofilm method has good denitrification and carbon reduction functions. When the concentration of simulated wastewater is increased to 30 mg / L, CH4 utilization rate is still maintained at about 85%, and CO2 utilization rate is more than 95%. However, the method is affected by the influent load, and the highest denitrification efficiency can only reach 60% (18 mg / L of NO3 - Therefore, it can be predicted that the biogas substrate biofilm method has strong carbon reduction stability and high denitrification potential, and has the ability to achieve deep denitrification and carbon reduction of the effluent from the secondary sedimentation tank of the wastewater treatment plant.

[0064] Example 3

[0065] In order to further verify the potential of the biogas substrate biofilm method (i.e. the method of Example 1) in practical application, the actual biogas produced by anaerobic digestion of wastewater in a wastewater treatment plant was used to treat actual wastewater (excessive wastewater). The biogas produced by anaerobic digestion in the wastewater treatment plant was pumped into a sealed gas collection bag using a vacuum pump, and then poured into a 4L gas cylinder for experimental use. In order to avoid accidental experiments, gases of different time periods were extracted, and the specific components are shown in Table 1. Then, 40L of excessive wastewater of the water plant on a certain day was selected, which was deoxygenated by nitrogen gas (5min) and then introduced into the biogas substrate biofilm (i.e. the hanging biofilm reactor obtained in step 2 of Example 1) which was domesticated by simulated biogas and simulated wastewater. The biogas pressure was set to 0.10 MPa, the influent flow rate was 0.262 mL / min, and the reflux speed was 26.2 mL / min. The TN and NO3 - The concentrations of TN and NO3

[0066] Table 1 Actual biogas component supply

[0067] Days Collection phase CH4(%) CO2(%) [H2 (%)] [H2S (%)] Other (%) 1～7 Anaerobic digestion early stage 56.078 35.126 3.446 0.518 4.832 8～14 Anaerobic digestion middle stage 69.424 23.595 2.505 0.426 5.05 15～21 Anaerobic digestion late stage 62.444 29.88 2.735 0.688 4.253

[0068] Table 2 TN and NO3 - concentrations in influent and effluent

[0069] Days Influent TN (mg / L) Influent NO3 - - N (mg / L) Effluent TN (mg / L) Outflow NO3 - - N (mg / L) 2 19.2 16.4 12.9 10.2 4 19.2 16.4 10.8 7.5 6 19.2 16.4 11.1 9.1 10 19.2 16.4 9.8 7.8 12 19.2 16.4 9.2 7.3 14 19.2 16.4 9.3 7.6 17 19.2 16.4 9.8 8.1 19 19.2 16.4 9.2 7.7 21 19.2 16.4 9.7 7.6

[0070] According to the data in Table 1 and Table 2, the real-time changes of each component in the process of biogas production by sludge anaerobic digestion can be known. In the first 7 days of operation of the biogas substrate biofilm method, the TN in the effluent fluctuated in the range of 10.8 mg / L to 12.9 mg / L by inputting the biogas collected in the early stage of anaerobic digestion. The proportion of CH4 in the early stage of anaerobic digestion was low, and the proportion of CO2 was more than 35%. The electron donor provided by the biogas collected in this stage was also limited. And the higher CO2 supply would lead to the decrease of water pH, thereby resulting in the lower denitrification efficiency of the biogas substrate biofilm. In the middle and late stages of anaerobic digestion, the proportion of CH4 increased significantly, and the proportion of CO2 decreased by 5% to 10%. At this time, the electron donor and pH value in the biofilm increased. The TN in the effluent of the biogas substrate biofilm method fluctuated in the range of 9.2 mg / L to 9.8 mg / L, the denitrification efficiency increased significantly, and the effluent water quality was more stable.

[0071] No matter which stage of anaerobic digestion is used to produce biogas to treat the actual wastewater (excessive wastewater), the TN in the effluent can meet the first level A emission standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002). Therefore, the potential of the biogas substrate biofilm method in practical engineering application is further verified.

[0072] In summary, the system and method of the application can effectively enrich and remove the functional bacteria of greenhouse gases and denitrification in the biogas substrate, and can realize the deep denitrification and carbon reduction of the effluent from the secondary sedimentation tank of the wastewater treatment plant in a green, safe, economical and efficient manner. It has strong anti-pollution load capacity, and proves that the method of deep denitrification and carbon reduction based on the biogas substrate biofilm can achieve the goal of deep denitrification and carbon reduction of the wastewater treatment plant.

[0073] Although the above embodiment has made a detailed description of the application, it is only a part of the embodiment of the application, not all the embodiments, and other embodiments can be obtained according to the embodiment without creativity, which all belong to the protection scope of the application.

Claims

1. A method for denitrification and carbon reduction of wastewater using a biofilm, characterized in that, Includes the following steps: Sludge from the anaerobic section of a wastewater treatment plant and anaerobic section of a brewery wastewater treatment plant are mixed to obtain mixed sludge. The mixed sludge was inoculated into a nitrate solution, and biogas and / or simulated biogas were introduced. The mixture was cultured until the nitrate nitrogen concentration reached 0 mg / L, and the supernatant was obtained as the acclimatization bacterial solution. The nitrogen concentration in the nitrate solution was 20 mg / L. The new mixed sludge and the acclimated bacterial solution are inoculated into wastewater and / or simulated wastewater equipped with hollow fiber membranes, biogas and / or simulated biogas are introduced, and a second culture is carried out to obtain hollow fiber membranes with attached biofilm. The wastewater to be treated is mixed with the hollow fiber membrane with attached biofilm, biogas and / or simulated biogas are introduced, and after a third culture, the treated wastewater is obtained. The simulated biogas comprises the following components by volume: CH4 54-74 parts, CO2 24-44 parts, H2 1-2 parts, and H2S 0.1-1 parts.

2. The method according to claim 1, characterized in that, The volume ratio of the anaerobic sludge from the wastewater treatment plant to the anaerobic sludge from the brewery wastewater treatment plant in the mixed sludge is 1:1 to 1:

2.

3. The method according to claim 1, characterized in that, The concentration of nitrate nitrogen in the wastewater and / or simulated wastewater is 10~30 mg / L, based on nitrogen element concentration.

4. The method according to claim 3, characterized in that, The simulated wastewater also includes the following components at the following concentrations: CaCl2 0.5~1 mg / L, CuCl2·2H2O 0.02~0.05 mg / L, ZnSO4·7H2O 0.01~0.05 mg / L, NiCl2·6H2O 0.01~0.05 mg / L, Na2MoO4·2H2O 0.01~0.05 mg / L, Na2WO4·2H2O 0.01~0.05 mg / L, CoCl2·6H2O 0.1~0.2 mg / L, H3BO3 0.1~0.3 mg / L, FeSO4·7H2O 0.01~0.05 mg / L, MnCl2 0.01~0.05 mg / L, and Na2SeO3 0.01~0.03 mg / L.

5. The method according to claim 1, characterized in that, The volume ratio of the new mixed sludge to the acclimatized bacterial solution is 1:1~2.

6. The method according to claim 1, characterized in that, The temperature of the first culture is 28~32℃, and the first culture is carried out in the dark.

7. The method according to claim 1, characterized in that, The thickness of the biofilm on the hollow fiber membrane to which the biofilm is attached is 400 μm to 800 μm.

8. The method according to claim 1, characterized in that, During the first culture, the second culture, or the third culture, the partial pressure of the biogas and / or simulated biogas introduced is 0.06~0.1MPa.

9. The method according to claim 1 or 8, characterized in that, During the third culture process, the hydraulic retention time is 6-12 hours.

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