A bioelectroactive ammonia extraction membrane for ammonia recovery in wastewater and a preparation method thereof

Abstract

The present invention discloses a bioelectroactive ammonia extraction membrane for ammonia recovery in wastewater, including a cation exchange membrane; a bioanode and an ammonia extraction cathode are respectively provided on opposite sides of the cation exchange membrane; a flow channel network in contact with wastewater is laid on the bioanode side, and a flow channel network in contact with air is laid on the ammonia extraction cathode side. The present invention also discloses a method for preparing the above-mentioned bioelectroactive ammonia extraction membrane. The bioelectroactive ammonia extraction membrane of the present invention is applied to high-organic and high-ammonia nitrogen wastewater for ammonia recovery, which can not only obtain a high-purity ammonia solution, but also achieve an ammonia recovery energy consumption as low as 1.16 kWh / kg NH3-N. Compared with the traditional electrochemical ammonia recovery technology under the same conditions, the ammonia extraction energy consumption of the present invention is reduced by more than 65%.

Description

Technical Field

[0001] The invention relates to a bio-electroactive ammonia extraction membrane for recovering ammonia in wastewater, and also to a preparation method of the bio-electroactive ammonia extraction membrane, belonging to the technical field of wastewater treatment. Background Art

[0002] Conventional biological denitrification (BNR) converts NH3-N into free N2, which not only results in an energy consumption of 12.5 kWh / kg NH3-N, but also contributes 0.9 kg CO2 / m 3 Carbon emissions from wastewater may even cause emissions of high-warming potential N2O. However, ammonia and its derivative chemicals are key efficient fertilizers for sustainable agriculture. Currently, almost all ammonia production relies on the Haber-Bosch process (~14 kWh / kg NH3-N), which accounts for 1.0% of global energy consumption and contributes 1.4% of global carbon emissions. Therefore, recovering ammonia from wastewater is both environmentally sustainable and economically necessary.

[0003] Traditional wastewater ammonia recovery technologies mainly include air stripping, chemical precipitation, and ion exchange. The air stripping method is simple to operate and is suitable for high-concentration ammonia nitrogen wastewater, with an ammonia removal rate of more than 80%. However, due to the complex composition of the wastewater, the purity of the recovered ammonium sulfate and ammonia water is not high, which cannot offset the alkali cost of increasing the pH of the wastewater by ammonia stripping or ammonia evaporation, ultimately making the denitrification cost of the wastewater high. The chemical precipitation method has a fast reaction rate and is suitable for high-concentration wastewater, and the struvite produced can be used for resource recovery, but this method requires the addition of a large amount of chemical agents and has a high operating cost. The ion exchange method has the characteristics of good continuity, but it also has the disadvantages of large amounts of resin, zeolite, and regeneration salt solution, easy clogging of the resin, and small processing capacity. Therefore, energy consumption, operating costs and investment costs are high, and it is difficult to obtain high-purity and high-value ammonia extraction products, which is one of the key technical bottlenecks in the current recovery of ammonia nitrogen wastewater. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a bioelectroactive ammonia extraction membrane for recovering ammonia from wastewater, which can effectively reduce the energy consumption of the ammonia extraction process and obtain a high-purity ammonia product; another purpose of the present invention is to provide a method for preparing the above-mentioned bioelectroactive ammonia extraction membrane.

[0005] Technical solution: The bioelectroactive ammonia extraction membrane described in the present invention includes a cation exchange membrane; a bioanode and an ammonia extraction cathode are respectively provided on two opposite sides of the cation exchange membrane; a flow channel network in contact with wastewater is laid on the bioanode side, and a flow channel network in contact with air is laid on the ammonia extraction cathode side.

[0006] Wherein, the cation exchange membrane is Nafion 117 or Nafion 115.

[0007] Wherein, the bioanode is a carbon-based current collector loaded with activated sludge, and the ammonia extraction cathode is a carbon-based current collector loaded with an oxygen reduction catalyst, and the carbon-based current collector is preferably carbon paper.

[0008] The wastewater side flow channel net and the air side flow channel net are made of polypropylene or nylon, with a thickness of 0.2-2.0 mm and a mesh size of 20-100 meshes; preferably, the mesh size is 40 meshes of polypropylene. Setting the flow channel net can increase the mass transfer rate between the membrane and the liquid, and also improve the contact efficiency between the electrode (ammonia extraction cathode) and the air, thereby improving the reaction efficiency between the membrane and the wastewater and air, and improving the overall ammonia extraction efficiency of the device.

[0009] The method for preparing the above-mentioned bio-electroactive ammonia extraction membrane comprises the following steps:

[0010] (1) Add glass beads to the activated sludge, shake and disperse it to form a uniform activated sludge dispersion; the glass beads are used to disperse the flocculent sludge. The smaller the size of the glass beads, the smaller the particle size of the sludge particles formed after the sludge is dispersed. The smaller the particle size of the sludge particles, the easier it is for them to enter the carbon-based current collector, thereby increasing the loading amount of the activated sludge on the carbon-based current collector. On the other hand, it is easier for them to form biofilms, thereby increasing their biological activity.

[0011] (2) The activated sludge dispersion is evenly loaded onto the carbon-based current collector by suction filtration to form a bioanode;

[0012] (3) adding the multi-walled carbon nanotubes and Nafion solution into anhydrous ethanol and performing ultrasonic treatment to form a uniform multi-walled carbon nanotube dispersion;

[0013] (4) adding the oxygen reduction catalyst into anhydrous ethanol and subjecting it to ultrasonic treatment to form a uniform oxygen reduction catalyst dispersion;

[0014] (5) adding the oxygen reduction catalyst dispersion dropwise into the multi-walled carbon nanotube dispersion, stirring and mixing, to form an ammonia-extracting cathode precursor solution;

[0015] (6) uniformly loading the ammonia extraction cathode precursor liquid onto the carbon-based current collector by spraying to form an ammonia extraction cathode;

[0016] (7) fixing the bioanode on one side of the cation exchange membrane and fixing the ammonia extraction cathode on the other side of the cation exchange membrane;

[0017] (8) A flow channel network is laid on the biological anode side and the ammonia extraction cathode side of the cation exchange membrane to obtain a bioelectroactive ammonia extraction membrane.

[0018] Wherein, in step (1), the average diameter of the glass microbeads is 50-200 μm.

[0019] Wherein, in step (1), the activated sludge comes from a microbial fuel cell reactor, and the sludge concentration of the activated sludge dispersion is 1.0-10 g / L.

[0020] Wherein, in step (2), the loading amount of activated sludge on the carbon-based current collector is 10-1000 mg / cm 2 .

[0021] In step (2) and step (6), the thickness of the carbon-based current collector is 0.1-0.5 mm, and the volume density is 0.3-0.5 g / cm 3 , the porosity is 70~80%, and the resistivity is less than 100 mΩ·cm.

[0022] Wherein, in step (3), the concentration of the multi-walled carbon nanotube dispersion is 0.5-2.0 g / L; the concentration of the Nafion solution is 1.0-20 wt %; and the volume ratio of the Nafion solution to anhydrous ethanol is 1:1000-1:10000.

[0023] Wherein, in step (4), the oxygen reduction catalyst is iron phthalocyanine and / or manganese phthalocyanine; and the concentration of the oxygen reduction catalyst dispersion is 1.0-100 mg / .

[0024] Wherein, in step (5), the dropping speed of the oxygen reduction catalyst dispersion is 0.1-100 mL / min.

[0025] Wherein, in step (6), the loading amount of the oxygen reduction catalyst on the carbon-based current collector is 0.1-1.0 mg / cm 2 .

[0026] An ammonia recovery device containing the above-mentioned bioelectroactive ammonia extraction membrane comprises a reactor and a bioelectroactive ammonia extraction membrane arranged in the reactor, wherein the bioelectroactive ammonia extraction membrane separates the reactor into two independent cavities; wherein the bioanode side corresponds to the cavity through which wastewater flows, and the ammonia extraction cathode side corresponds to the cavity through which air flows; dry air enters the cavity from the air inlet of the cavity through which air flows, and the air outlet of the cavity through which air flows is connected to a condensation absorber for separating air and ammonia; the bioelectroactive ammonia extraction membrane is connected to an external power supply through a wire.

[0027] High-organic and high-ammonia nitrogen wastewater is pumped into the wastewater flow chamber. The organic matter in the wastewater is catalytically degraded under the action of electroactive bacteria in the bioanode and releases electrons. The electrons are transferred to the external circuit through the bioanode interface. After reaching the ammonia cathode, the electrons reduce O2 in the air under the action of the catalyst to produce OH - , forming a local strong alkaline microenvironment; under the action of the electric field, NH4 + Across the cation exchange membrane, the ammonia cathode and OH -The generated NH3(g) enters the low-temperature water absorption liquid through the air flow network to form an ammonia solution, thereby realizing the recovery of high-purity ammonia in the wastewater. The bio-electroactive ammonia extraction membrane of the present invention is used for ammonia extraction in high-organic and high-ammonia nitrogen wastewater, which can realize low-energy wastewater ammonia recovery and directly obtain a high-purity ammonia solution.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the bioelectroactive ammonia extraction membrane of the present invention is applied to high-organic and high-ammonia nitrogen wastewater for ammonia recovery, which can not only obtain a high-purity ammonia solution, but also achieve an ammonia recovery energy consumption as low as 1.16 kWh / kg NH3-N. Compared with traditional electrochemical ammonia recovery technology under the same conditions, the energy consumption of ammonia extraction of the present invention is reduced by more than 65%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of ammonia extraction by an ammonia recovery device containing a bio-electroactive ammonia extraction membrane; wherein A is a schematic diagram of the structure of an ammonia recovery device containing a bio-electroactive ammonia extraction membrane; B is a schematic diagram of the structure of a bio-electroactive ammonia extraction membrane;

[0030] Figure 2 The ammonia extraction Faraday efficiency and energy consumption of the bioelectroactive ammonia extraction membrane at different current densities; a, c, e correspond to the ammonia extraction Faraday efficiency when the air flow rate is 20 mL / min, 30 mL / min, and 80 mL / min, respectively, and b, d, and f correspond to the energy consumption when the air flow rate is 20 mL / min, 30 mL / min, and 80 mL / min, respectively;

[0031] Figure 3 To determine the purity of the recovered ammonia solution. DETAILED DESCRIPTION

[0032] like Figure 1 As shown, the bioelectroactive ammonia extraction membrane of the present invention comprises a cation exchange membrane; a bioanode and an ammonia extraction cathode are respectively arranged on opposite sides of the cation exchange membrane; a flow channel network in contact with wastewater is laid on the bioanode side, and a flow channel network in contact with air is laid on the ammonia extraction cathode side; wherein the cation exchange membrane is Nafion 117.

[0033] The above-mentioned bio-electroactive ammonia extraction membrane is composited by a wastewater side flow channel network, a bioanode, a cation exchange membrane, an ammonia extraction anode, and an air side flow channel network. The preparation method thereof specifically comprises the following steps:

[0034] (1) Adding glass beads with an average diameter of 100 μm into activated sludge, shaking and dispersing the beads to form an activated sludge dispersion with an MLSS of 7.0 g / L; wherein the activated sludge comes from a microbial fuel cell reactor;

[0035] (2) The activated sludge dispersion is evenly loaded onto a carbon-based current collector by suction filtration to form a bioanode; the product model of the carbon-based current collector is TGP-H-060, the thickness is 0.19 mm, and the volume density is 0.44 g / cm 3 , porosity is 78%, resistivity is 80 mΩ·cm; the loading amount of activated sludge on the carbon-based current collector is 63.3 mg / cm 2 ;

[0036] (3) 100 mg of multi-walled carbon nanotubes (MWCNTs, Aladdin, C139872) and 20 μL of 5 wt% Nafion solution (Dupont, D-520) were added to 100 mL of anhydrous ethanol and ultrasonically treated for 4.0 h to form a 1.0 g / L multi-walled carbon nanotube dispersion.

[0037] (4) 1.0 mg of iron phthalocyanine (FePc, Aladdin, I157718) was added to 100 mL of anhydrous ethanol, and after 4.0 h of ultrasonic treatment, an oxygen reduction catalyst dispersion with a concentration of 10 mg / L was formed;

[0038] (5) Add the above 100 mL of oxygen reduction catalyst dispersion dropwise into 100 mL of multi-walled carbon nanotube dispersion at a dropping speed of 5.0 mL / min, and stir to form an ammonia-extracting cathode precursor solution;

[0039] (6) The ammonia cathode precursor liquid is evenly loaded onto a 2.0×2.0 cm 2 An ammonia-extracting cathode is formed on a carbon-based current collector (naturally air-dried after spraying); the loading amount of iron phthalocyanine on the carbon-based current collector is 0.25 mg / cm 2 ;

[0040] (7) fixing the bioanode on one side of the cation exchange membrane and fixing the ammonia extraction cathode on the other side of the cation exchange membrane;

[0041] (8) Polypropylene with a thickness of 1.0 mm and a mesh size of 40 is cut into the size of a cation exchange membrane and laid on the bioanode side and the ammonia extraction cathode side of the cation exchange membrane to obtain a bioelectroactive ammonia extraction membrane; the flow channel network, the carbon-based current collector and the cation exchange membrane are fixedly connected at the outer edge.

[0042] The ammonia recovery device containing the above-mentioned bio-electroactive ammonia extraction membrane comprises a reactor and a bio-electroactive ammonia extraction membrane arranged in the reactor, wherein the bio-electroactive ammonia extraction membrane separates the reactor into two independent chambers; wherein the biological anode side corresponds to the wastewater flow-through chamber, and the ammonia extraction cathode side corresponds to the air flow-through chamber; dry air enters the chamber from the air inlet of the air flow-through chamber, and the air outlet of the air flow-through chamber is connected to a condensation absorber for separating air and ammonia (the condensation absorber contains low-temperature water absorption liquid), and the mixed gas of air and ammonia is separated in the condensation absorber, the separated air is discharged, and the separated ammonia is absorbed by the low-temperature water absorption liquid to form an ammonia solution; the bio-electroactive ammonia extraction membrane is connected to an external power supply through a wire. A water inlet is provided on one side of the wastewater flow-through chamber, and the external wastewater to be treated enters the wastewater flow-through chamber through the water inlet, and a water outlet is provided on the other side of the wastewater flow-through chamber, and the denitrified wastewater flows out of the wastewater flow-through chamber from the water outlet.

[0043] The above ammonia recovery device is applied to livestock and poultry breeding wastewater for ammonia extraction. The specific operation process is as follows:

[0044] The water quality characteristics of poultry wastewater are as follows: COD concentration ~3000 mg / L, ammonia nitrogen concentration ~820 mg / L, pH between 6 and 8;

[0045] (1) Livestock and poultry wastewater is pumped into the wastewater flow chamber with a hydraulic retention time of 2.0 h;

[0046] (2) Dust-free and dry air was pumped into the air flow chamber at flow rates of 20 mL / min, 30 mL / min, and 80 mL / min, respectively;

[0047] (3) The air flows through the air outlet of the cavity and is connected to a device containing 4°C low-temperature water absorption liquid. The mixed gas is sent into the 4°C low-temperature water absorption liquid to separate the ammonia and air. The air is discharged and the ammonia forms an ammonia solution.

[0048] By testing the concentration of ammonia solution at different current densities, the Faraday efficiency and energy consumption of ammonia extraction by the bioelectroactive ammonia extraction membrane at different current densities were calculated.

[0049] The results are as follows Figure 2 As shown, at 1.12 mA cm -2 , the Faradaic efficiency of ammonia extraction was 75.7%, 81.5% and 76.6% under the conditions of air flow rate of 20 mL / min, 30 mL / min and 80 mL / min respectively. Figure 2 Middle a, Figure 2 Middle c, Figure 2 In the figure (e), the voltage on both sides of the bio-electroactive ammonia extraction membrane is 0.49 V ( Figure 2 Middle a, Figure 2 Middle c, Figure 2 e), the corresponding ammonia extraction energy consumption is 1.23 kWh / kg NH3-N, 1.16 kWh / kg NH3-N, 1.22 kWh / kg NH3-N ( Figure 2 Middle b, Figure 2 Middle d, Figure 2 f); at 1.76 mA cm -2 , the Faradaic efficiency of ammonia extraction was 62%, 71.4% and 77.4% under the conditions of air flow rate of 20 mL / min, 40 mL / min and 80 mL / min respectively. Figure 2 Middle a, Figure 2 Middle c, Figure 2 In the figure (e), the voltage on both sides of the bioelectroactive ammonia extraction membrane is 0.64 V ( Figure 2 Middle a, Figure 2 Middle c, Figure 2 e), the corresponding ammonia extraction energy consumption is 1.98 kWh / kg NH3-N, 1.72 kWh / kg NH3-N, 1.58 kWh / kg NH3-N ( Figure 2 Middle b, Figure 2 Middle d, Figure 2 f), which is comparable to the most advanced electrochemical ammonia recovery energy consumption of 1.61 kWh / kg NH3-N reported in the literature. In addition, the purity of the recovered ammonia solution reached 96.8 wt% (e.g. Figure 3 As shown), the purity requirement of industrial-grade ammonia solution is achieved.

Claims

1. A wastewater ammonia recovery device containing a bio-electroactive ammonia extraction membrane, characterized in that: It comprises a reactor and a bio-electroactive ammonia extraction membrane arranged in the reactor, wherein the bio-electroactive ammonia extraction membrane separates the reactor into two independent cavities; wherein the bio-anode side corresponds to the cavity through which wastewater flows, and the ammonia extraction cathode side corresponds to the cavity through which air flows; dry air enters the cavity from the air inlet through which air flows, and the air outlet through which air flows is connected to a condensation absorber for separating air and ammonia; the bio-electroactive ammonia extraction membrane is connected to an external power source through a wire; The bio-electroactive ammonia extraction membrane comprises a cation exchange membrane; a bioanode and an ammonia extraction cathode are respectively arranged on opposite sides of the cation exchange membrane; a flow channel net in contact with wastewater is laid on the bioanode side, and a flow channel net in contact with air is laid on the ammonia extraction cathode side; the wastewater side flow channel net and the air side flow channel net are made of polypropylene or nylon, with a thickness of 0.2-2.0 mm and a mesh size of 20-100 meshes; The preparation method of the above-mentioned bio-electroactive ammonia extraction membrane comprises the following steps: (1) adding glass microbeads to activated sludge, shaking and breaking up to form a uniform activated sludge dispersion; (2) uniformly loading the activated sludge dispersion onto a carbon-based current collector by suction filtration to form a bio-anode; (3) adding multi-walled carbon nanotubes and Nafion solution into anhydrous ethanol, ultrasonically treating to form a uniform multi-walled carbon nanotube dispersion; (4) adding an oxygen reduction catalyst into anhydrous ethanol, ultrasonically treating to form a uniform oxygen reduction catalyst dispersion; (5) adding the oxygen reduction catalyst dispersion dropwise into the multi-walled carbon nanotube dispersion, stirring and mixing to form an ammonia extraction cathode precursor; (6) uniformly loading the ammonia extraction cathode precursor onto a carbon-based current collector by spraying to form an ammonia extraction cathode; (7) fixing the bio-anode on one side of the cation exchange membrane, and fixing the ammonia extraction cathode on the other side of the cation exchange membrane; (8) laying a flow channel network on the bio-anode side and the ammonia extraction cathode side of the cation exchange membrane, respectively, to obtain a bio-electroactive ammonia extraction membrane.

2. The wastewater ammonia recovery device containing a bio-electroactive ammonia extraction membrane according to claim 1, characterized in that: The cation exchange membrane is Nafion 117 or Nafion 115.

3. The wastewater ammonia recovery device containing a bio-electroactive ammonia extraction membrane according to claim 1, characterized in that: The thickness of the carbon-based current collector is 0.1-0.5 mm, and the volume density is 0.3-0.5 g / cm 3 , the porosity is 70~80%, and the resistivity is less than 100 mΩ·cm.

4. The wastewater ammonia recovery device containing a bio-electroactive ammonia extraction membrane according to claim 1, characterized in that: In step (1), the average diameter of the glass microspheres is 50-200 μm; the sludge concentration of the activated sludge dispersion is 1.0-10 g / L; in step (2), the loading amount of activated sludge on the carbon-based current collector is 10-1000 mg / cm 2 .

5. The wastewater ammonia recovery device containing a bio-electroactive ammonia extraction membrane according to claim 1, characterized in that: In step (3), the concentration of the multi-walled carbon nanotube dispersion is 0.5-2.0 g / L; the concentration of the Nafion solution is 1.0-20 wt %; and the volume ratio of the Nafion solution to anhydrous ethanol is 1:1000-1:10000.

6. The wastewater ammonia recovery device containing a bio-electroactive ammonia extraction membrane according to claim 1, characterized in that: In step (4), the oxygen reduction catalyst is iron phthalocyanine and / or manganese phthalocyanine; the concentration of the oxygen reduction catalyst dispersion is 1.0-100 mg / L; in step (5), the drop rate of the oxygen reduction catalyst dispersion is 0.1-100 mL / min; in step (6), the loading amount of the oxygen reduction catalyst on the carbon-based current collector is 0.1-1.0 mg / cm 2 .

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