Microbial electrochemical filters and their methods for removing iron, manganese, ammonia, and nitrogen from groundwater

Abstract

This invention discloses a microbial electrochemical filter and its method for removing iron, manganese, ammonia, and nitrogen from groundwater, belonging to the field of wastewater treatment technology. This invention addresses the problem of poor operational performance and stability of existing biological filters under oligotrophic conditions. The microbial electrochemical filter of this invention comprises a cylinder, an electrochemical system, and a filter column; the electrochemical system and filter column are disposed within the cylinder, with the electrochemical system positioned above the filter column, which is a carrier with a biofilm covering its surface; an outlet is located at the lower part of the cylinder's side wall, and an overflow outlet is located at the upper part. This invention removes some pollutants before they enter the filter column through an electro-oxidation process, reducing the biological removal pressure within the filter column; the electrochemical system enhances the abundance and carbon fixation capacity of autotrophic microorganisms in the biological filter, providing additional carbon sources and electron acceptors for the autotrophic biological filter, promoting the growth and metabolism of the biological community; the microbial electrochemical filter provides conditions for the growth of heterotrophic iron and manganese oxidizing bacteria and achieves the generation and coverage of more active iron and manganese oxide films on the filter media surface.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology; it discloses a biological filtration device and method for treating iron, manganese, ammonia, and nitrogen pollution in groundwater using a coupled electrochemical system. Background Technology

[0002] With the rapid development of industry and economy and the increase in the global population, the comprehensive and effective management and use of groundwater has become a focus of widespread attention in the current water resource development process. 50% of the world's domestic water and 25% of agricultural irrigation come from groundwater. Many arid regions rely on groundwater as their sole water source. In my country, some remote rural communities still rely on wells to obtain groundwater as their drinking water source. Due to natural geological activities and human interference, iron, manganese, and ammonia nitrogen coexist widely in groundwater in their reduced state. Exposure to iron, manganese, ammonia nitrogen can increase the risk of neurological diseases and various cancers in humans. Therefore, in order to protect human health, it is necessary to strictly control the concentration of iron, manganese, and ammonia nitrogen in groundwater to protect the environment and drinking water resources.

[0003] In recent years, biological purification technology has been widely developed in the removal of iron, manganese, and ammonia from groundwater. Biofilters, due to their low cost and environmental friendliness, have rapidly become a core technology in groundwater treatment and are widely used. However, the oligotrophic conditions of groundwater force the slow growth of microorganisms in the filter system, inhibiting the growth of heterotrophic iron and manganese oxidizing bacteria and denitrifying bacteria, resulting in a simple biofilter community structure that is susceptible to external shocks. Due to rapid industrial development, water pollution components are becoming increasingly complex, and pollutant concentrations fluctuate significantly. Maintaining high purification efficiency of biofilters in the long term and enhancing their resilience to shocks are crucial issues that urgently need to be addressed.

[0004] Electrochemical systems can directly degrade pollutants through anodic oxidation, reducing organic load and recalcitrant components, thereby improving the efficiency of subsequent biological treatment. Alternatively, they can indirectly oxidize pollutants by generating active substances such as free radicals. Electrochemical decomposition of recalcitrant organic matter in wastewater produces biodegradable small-molecule carbon, or provides a carbon source by electrochemically biosynthesizing organic matter from atmospheric CO2. This indirectly promotes the biodegradation of pollutants and improves the stability of biological growth in the reactor by promoting the growth of heterotrophic microorganisms.

[0005] There is limited research on integrated processes that couple electrochemical systems with biological filters for groundwater treatment in the current technology. Most of the existing technologies use external, independent electrochemical processes, which increases the footprint and causes significant energy consumption due to the high external voltage, thereby increasing the cost of the entire treatment process. Summary of the Invention

[0006] To achieve long-term and stable treatment of groundwater contaminated with iron, manganese, and ammonia nitrogen, and to address the problem of poor operational performance and stability of existing biological filters under oligotrophic conditions, this invention provides a microbial electrochemical filter and a method for removing iron, manganese, and ammonia nitrogen from groundwater.

[0007] To achieve the above objectives, the microbial electrochemical filter of the present invention comprises a cylindrical body, an electrochemical system, and a filter column; the electrochemical system and the filter column are disposed within the cylindrical body, with the electrochemical system positioned above the filter column, which is a carrier with a biofilm covering its surface; an outlet is provided at the lower part of the side wall of the cylindrical body, and an overflow outlet is provided at the upper part. The technical solution adopted by the present invention includes the following steps:

[0008] Step 1: Construction of a microbial electrochemical filter for removing iron, manganese and ammonia nitrogen from groundwater, comprising a cylinder, an influent system, an electrochemical system, a filter column, an effluent system and a backwashing system.

[0009] Step 2: A method for removing iron, manganese and ammonia nitrogen from groundwater using a microbial electrochemical filter, achieving rapid and stable removal of iron, manganese and ammonia nitrogen from groundwater under autotrophic conditions.

[0010] Further specifying, in step 1, the filter used for coupling the electrochemical system can be a filter commonly used in various water treatment processes, and the carrier can be one or a mixture of several of the following in any proportion: quartz sand, manganese sand, and activated carbon.

[0011] In step 1, preferably, the cylinder is a cuboid or cylinder made of plexiglass, with water sampling ports and sand sampling ports evenly arranged along both sides, an overflow port at a certain distance from the top to maintain a constant pressure head, and a water outlet at the bottom. The surface of the cylinder is wrapped with light-proof material to prevent algae growth and clogging of the filter column.

[0012] In step 1, preferably, the input end of the water inlet system is connected to the outlet of the water storage tank, and is connected through a peristaltic pump and a peristaltic pump pipe. The output end is directly connected to the water distributor and flows into the cylinder from the top of the cylinder under gravity, and flows through the entire filter bed in a downflow manner.

[0013] In step 1, preferably, the electrochemical system consists of a graphite reference plate that exactly covers the cross-section of the filter column and multiple graphite rods placed vertically and uniformly. The graphite reference plate is provided with through holes, and the through holes and graphite rods are arranged alternately. The graphite rods of the two electrodes are placed in parallel and interlaced. The graphite reference plate is separated by a 1mm to 3mm gap with non-conductive material through the diagonal graphite rods to prevent short circuits. The electrode set on the upper part is connected to the positive electrode of the battery, and the electrode set on the lower part is connected to the negative electrode of the battery.

[0014] Preferably, the filter column is a homogeneous manganese sand filter column, and the microbial carrier is mainly manganese sand with a particle size of 2-4 mm.

[0015] Furthermore, a support layer can be set under the carrier. The support layer can be filled with gravel with a particle size of 2cm to 4cm to prevent the biofilm or sludge on the surface of the manganese sand from coming into direct contact with the support plate during the experiment, thus preventing the filter media from being lost or clogging the outlet holes and reducing the resistance to the effluent.

[0016] Furthermore, the height ratio of the filter column to the support layer is (7-10):1.

[0017] In step 1, preferably, the effluent and backwashing system consists of an effluent outlet located 2 cm below the gravel layer and at the bottom of the cylinder. This outlet can be connected to a switchable tee via a flexible hose. One side of the tee is used for effluent discharge, connected to a flow meter, and the effluent is directly introduced into a natural water body or connected to other subsequent water treatment processes. The other side is connected to the pump and backwash water tank in the backwashing device, and backwash sludge flows out from the overflow port. The tee valve is opened and closed according to the operating and backwashing conditions.

[0018] In step 2, based on the raw water quality, large debris, sand, and garbage should be removed by setting up a filtration system such as a bar screen or by natural sedimentation in a water tank before entering the filter system to prevent clogging of the filter column. An aeration system should be set up as needed to oxygenate the raw water, and a dosing and mixing system should be designed to regulate the pH of the raw water. The system should operate at room temperature to avoid extreme growth conditions and meet the requirements for maintaining the survival of microorganisms and the removal of iron, manganese, ammonia, and nitrogen oxidation in the filter system.

[0019] In step 2, during startup, shocks from high concentrations of iron, manganese, ammonia, nitrogen, and significant changes in pollutant concentrations should be avoided. The hydraulic retention time should be maintained at a high level to ensure operation under low pollutant load during the startup phase. After successful startup, gradually increase the influent pollutant concentration and filtration rate. Backwashing should be performed when the effluent flow rate significantly decreases or the effluent quality exceeds standards. Throughout the entire operation, a low voltage should be used to avoid energy loss caused by the electrolysis of water under high voltage.

[0020] In step 2, preferably, a downflow inlet is used. The inlet water should be free of obvious impurities and particles, with dissolved oxygen not less than 5 mg / L, pH value greater than or equal to 7, and temperature maintained at room temperature (20℃-30℃).

[0021] In step 2, preferably, during the start-up phase, the influent iron and manganese concentration should not exceed 1 mg / L, the ammonia nitrogen concentration should not exceed 3 mg / L, and the hydraulic retention time should not be less than 10 hours. During the stable operation phase, the influent iron and manganese concentration should not exceed 2 mg / L, the ammonia nitrogen concentration should not exceed 5 mg / L, and the hydraulic retention time should not be less than 8 hours. The backwash intensity should not exceed 10 L / (m³). 2 The rinsing time is 3-5 minutes. The voltage is maintained between 0.8V and 1.2V throughout the entire operation.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The introduction of an electrochemical system into a microbial electrochemical filter can enhance the initial film-forming efficiency, removal performance, and stability of the biofilter through three pathways: First, the electro-oxidation process removes some pollutants before they enter the filter column, reducing the biological removal pressure within the filter column; second, the electrochemical system enhances the abundance and carbon fixation capacity of autotrophic microorganisms in the biofilter, providing additional carbon sources and electron acceptors to the autotrophic biofilter and promoting the growth and metabolism of the biological community; and third, the microbial electrochemical filter provides conditions for the growth of heterotrophic iron-manganese oxidizing bacteria and achieves the generation and coverage of more iron-manganese active oxide films on the filter media surface.

[0024] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, the accompanying drawings are for reference and illustration only and are not intended to limit the invention. Attached Figure Description

[0025] The accompanying drawings are provided to further clarify the invention.

[0026] Figure 1 This is a schematic diagram of the apparatus according to a specific embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the electrodes according to a specific embodiment of the present invention;

[0028] Figure 3 This is a comparison chart of the pollutant removal effects in specific embodiment 1 of the present invention;

[0029] Figure 4 This is a comparison chart of the pollutant removal effects in specific embodiment 2 of the present invention;

[0030] In the figure, 1—cylinder, 2—electrode, 3—sand sampling port, 4—filter column, 5—support layer, 6—overflow pipe, 7—water sampling port, 8—water outlet, 9—non-conductive material, 2-1—graphite rod, 2-2—through hole, 2-3—graphite reference plate. Detailed Implementation

[0031] To more clearly describe the content of this invention, the objectives, apparatus, method, and advantages of this invention will be further elaborated in detail below with reference to the accompanying drawings and description of specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0032] Example 1

[0033] Step 1, according to Figure 1 and 2The microbial electrochemical filter was constructed. The cylinder 1 was constructed using a 65cm high, 11cm inner side length acrylic cuboid as the homogeneous manganese sand filter media downflow filter. The support layer 5 was filled with gravel to a height of about 5cm, and the filter column 3 was filled with manganese sand to a height of 40cm. The empty bed contact time was 20min.

[0034] Place something like this on top of the filter media in the filter bed. Figure 2 The two electrodes 2 shown are composed of multiple graphite rods placed perpendicularly and evenly to a graphite reference plate. Through holes are provided on the graphite reference plate, and the through holes and graphite rods are arranged alternately. The graphite rods of the two electrodes are placed parallel to each other, and a 1mm gap is created between the graphite reference plates using a non-conductive material through diagonal graphite rods to prevent short circuits. Figure 2 The electrode on top is connected to the positive electrode of the battery, and the electrode on the bottom is connected to the negative electrode of the battery, serving as the anode and cathode of the electrochemical system, respectively.

[0035] In addition, a control group biofilter operating under open-circuit conditions was also set up, with the same reactor configuration and operating parameters as the embodiment.

[0036] Step 2: Soak and inoculate with manganese sand culture medium. Prepare 1L of culture medium containing iron, manganese, ammonia, inorganic carbon and buffer according to the components and ratios in Table 1. Dilute with water from the pipeline network to 20L. Soak for 24 hours and then circulate water at a low filtration rate for 72 hours.

[0037] Table 1. Culture medium composition

[0038]

[0039] Step 3: Artificial water distribution was performed using tap water from the piped network to simulate groundwater commonly contaminated with iron, manganese, and ammonia nitrogen. Anhydrous sodium sulfite was added to remove residual chlorine from the tap water. The operating voltage of the microbial electrochemical filter was 1.2V, and the control group was open-circuited. Operation was carried out at room temperature, with no control over pH, temperature, or dissolved oxygen. The hydraulic retention time was 10 hours, and the initial influent concentrations were 1 mg / L Mn(II), 0.5 mg / L Fe(II), and 3 mg / L NH4+. + -N. Take water samples from the inlet and outlet of the water tank and filter every 3 days to measure relevant indicators.

[0040] Microbial electrochemical filters showed good removal effects on iron, manganese, and ammonia nitrogen in groundwater. The microbial electrochemical filter started up faster, with an effluent manganese concentration of 0.058 mg / L on the 6th day, which met the national secondary standard for integrated wastewater discharge (GB8978-2002) of 0.1 mg / L, while the control group biological filter only reached this standard on the 12th day.

[0041] Microbial electrochemical filters exhibit superior purine metabolism, oxidative phosphorylation, homologous recombination, bacterial secretion systems, pyruvate metabolism, mismatch repair, and DNA replication compared to conventional biofilters. During the startup phase, microbial electrochemical filters demonstrate higher cell activity, faster growth, and quicker biofilm formation. The abundance of manganese and ammonia oxidation genes in microbial electrochemical filters significantly exceeds that in conventional biofilters. The electrochemical system promotes carbon fixation processes, providing a carbon source for the microorganisms and enabling their rapid growth.

[0042] Example 2

[0043] Step 1, according to Figure 1 A microbial electrochemical filter was constructed. A homogeneous manganese sand filter media downflow filter was built using a 65cm high, 11cm inner side length acrylic cuboid. The filling height was 40cm, with a particle size controlled between 2mm and 4mm. Gravel was filled under the carrier to a height of 5cm, with a particle size controlled between 2cm and 4cm. The empty bed contact time was 20min. A filter media such as... was placed on top of the filter media in the filter. Figure 2 The two graphite electrodes shown are arranged as follows: the upper electrode is connected to the positive electrode of the battery, and the lower electrode is connected to the negative electrode, serving as the anode and cathode of the electrochemical system, respectively. In addition, a control group biofilter operating under open-circuit conditions was also included in the experiment, with the same reactor configuration and operating parameters as the example.

[0044] Step 2: Soak and inoculate with manganese sand culture medium. Prepare 1L of culture medium containing iron, manganese, ammonia, inorganic carbon and buffer (see Table 1), dilute with water from the pipeline network to 20L, soak for 24h, and then circulate water at a low filtration rate for 72h to form a biofilm.

[0045] Step 3: Artificial water distribution was performed using tap water from the piped network to simulate groundwater commonly contaminated with iron, manganese, and ammonia nitrogen. Anhydrous sodium sulfite was added to remove residual chlorine from the tap water, and toxic, recalcitrant organic matter was applied to the influent to induce a toxic shock. The operating voltage of the microbial electrochemical filter was set to 1.2V, with the control group operating in an open circuit. Operation was carried out at room temperature, with no control over pH, temperature, or dissolved oxygen. The hydraulic retention time was 10 hours, and the influent concentrations were 2 mg / L Mn(II), 0.5 mg / L Fe(II), and 5 mg / L NH4+. + -N. Take water samples from the inlet and outlet of the water tank and filter every 3 days to measure relevant indicators.

[0046] The resulting favorable outcome is:

[0047] Microbial electrochemical filters exhibit significantly greater stability under shock conditions than conventional biological filters, demonstrating good removal efficiency for iron, manganese, and ammonia nitrogen in groundwater. When the influent contains 10 mg / L 1,4-dioxane, the manganese and nitrogen removal capacity of conventional biological filters is inhibited along the flow path. Under dioxane stress of 20 mg / L, the manganese removal performance of the microbial electrochemical filter is not significantly inhibited, while the manganese removal rate of the conventional biological filter decreases from 96.74% to 88.76%. During dioxane shock events, the ammonia nitrogen removal performance of the microbial electrochemical filter drops from 90% to approximately 27%, while the nitrogen removal performance of the conventional biological filter is completely inhibited.

[0048] Microbial electrochemical filters can remove some pollutants before they enter the filter column through electro-oxidation, which reduces the biological removal pressure inside the filter column and provides additional carbon sources and electron acceptors for autotrophic biofilters. This also alleviates the inhibition of dioxane by maintaining the normal metabolism of the biological community.

[0049] The preferred embodiments disclosed above do not describe all operational details exhaustively, and are only used to further illustrate the invention so that those skilled in the art can better understand and utilize it, and are not intended to limit the specific implementation of the invention. According to the claims, any modifications, equivalent substitutions, variations, improvements, etc., made within the principles of the invention should be included within the protection scope of the invention.

Claims

1. A microbial electrochemical filter, characterized in that, The filter includes a cylindrical body, an electrochemical system, and a filter column; the electrochemical system and the filter column are located inside the cylindrical body, with the electrochemical system positioned above the filter column, which is a carrier with a biofilm covering its surface; an outlet is located at the lower part of the side wall of the cylindrical body, and an overflow outlet is located at the upper part; The electrochemical system includes electrodes. Two electrodes are placed on top of the filter media in the filter bed. The electrodes are composed of multiple graphite rods that are evenly placed perpendicular to a graphite reference plate. The graphite reference plate has through holes, which are spaced apart from the graphite rods. The graphite rods of the two electrodes are placed in parallel and interlaced. The graphite reference plate is separated by a 1mm to 3mm gap using a non-conductive material through diagonal graphite rods to prevent short circuits. The upper electrode is connected to the positive electrode of the battery, and the lower electrode is connected to the negative electrode of the battery. The electrochemical system is configured to provide an additional carbon source and electron acceptor for the autotrophic biofilter, promoting the growth and metabolism of the biological community. The cylinder also includes a support layer, which is located below the filter column and is composed of gravel with a particle size of 2cm to 4cm. The carrier is one or a mixture of several of the following: quartz sand, manganese sand, and activated carbon, with a particle size of 2 mm to 4 mm.

2. The microbial electrochemical filter according to claim 1, characterized in that, The outlet is connected to a switchable tee. One side of the tee is used for water discharge and is connected to a flow meter. The discharged water can be directly fed into a natural water body or connected to other subsequent water treatment processes. The other side is connected to the backwash water tank through a pump, and the backwash sludge will flow out from the overflow port.

3. A method for removing iron, manganese, ammonia, and nitrogen from groundwater, wherein the method uses a microbial electrochemical filter as described in claim 1 or 2, characterized in that, The method is achieved through the following steps: the carrier is soaked and inoculated with a culture medium containing iron manganese ammonia, inorganic carbon and buffer solution. After removing residual chlorine from the groundwater, it is introduced into the filter and operated at room temperature. Backwashing is performed when the effluent flow rate decreases significantly or the effluent quality exceeds the standard.

4. The method for removing iron, manganese, ammonia, and nitrogen from groundwater according to claim 3, characterized in that, During the startup phase, the influent iron and manganese concentrations should not exceed 1 mg / L, the ammonia nitrogen concentration should not exceed 3 mg / L, and the hydraulic retention time should not be less than 10 hours.

5. The method for removing iron, manganese, ammonia, and nitrogen from groundwater according to claim 3, characterized in that, During the stable operation phase, the influent iron and manganese concentration should not exceed 2 mg / L, the ammonia nitrogen concentration should not exceed 5 mg / L, and the hydraulic retention time should not be less than 8 hours.

6. The method for removing iron, manganese, ammonia, and nitrogen from groundwater according to claim 3, characterized in that, Backwash intensity not exceeding 10 L / (m 2 ·s), rinsing time 3min 5 minutes; the voltage remained at 0.8V throughout the entire operation. 1.2V.

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