Microbial electrochemical filter and method for using same to remove iron, manganese and ammonia nitrogen from underground water

Abstract

A microbial electrochemical filter and a method for using same to remove iron, manganese and ammonia nitrogen from underground water, which belong to the technical field of wastewater treatment. The filter and the method solve the problem of existing biological filters having poorer operation performance and stability under oligotrophic conditions. The microbial electrochemical filter comprises a cylinder (1), an electrochemical system, and a filter column (4), wherein the electrochemical system and the filter column (4) are arranged in the cylinder (1); the electrochemical system is arranged above the filter column (4); the filter column (4) consists of a carrier, a surface of which is covered with a biological film; and a water outlet (8) is provided in a lower portion of a side wall of the cylinder (1), and an overflow port is provided in an upper portion of the side wall of the cylinder (1). In the method, by means of an electro-oxidation process, some pollutants are removed before entering a filter column (4), thus reducing the bioremoval pressure in the filter column (4); the abundance and carbon sequestration capability of autotrophic microbes in a biological filter are enhanced by means of an electrochemical system, thereby providing an additional carbon source and an additional electron acceptor for the autotrophic biological filter, and prompting the growth and metabolism of biological communities; and the microbial electrochemical filter provides conditions for the growth of heterotrophic iron-manganese oxidizing flora, and achieves the generation and coverage of more iron-manganese active oxide films on the surfaces of filter materials.

Description

Microbial electrochemical filter and method for removing iron, manganese, ammonia and nitrogen from groundwater Technical Field

[0001] The invention belongs to the technical field of sewage treatment and discloses a biological filtration device and method of a coupled electrochemical system for treating iron, manganese, ammonia and nitrogen pollution in groundwater. Background Art

[0002] With the rapid development of industry and economy and the increase in global population, the comprehensive and effective management and use of groundwater has become a focus of widespread concern in the current water resources development process. 50% of the world's domestic water and 25% of agricultural irrigation come from groundwater. Many arid areas use groundwater as their only water source. In my country, some remote rural communities still rely on drilling wells to obtain groundwater as a source of drinking water. Due to natural geological activities and human interference, iron, manganese and ammonia nitrogen widely coexist in reduced states in groundwater. Exposure to iron, manganese, ammonia and nitrogen will increase the risk of neurological diseases and various cancers in the human body. Therefore, to ensure human health, the concentrations of iron, manganese and ammonia nitrogen in groundwater need to be strictly controlled to protect the environment and drinking water resources.

[0003] In recent years, biological purification technologies have been widely developed for the removal of iron, manganese, and ammonia from groundwater. Due to its low cost and environmental friendliness, the biofilter process has rapidly become a core technology in groundwater treatment and is widely used. However, the oligotrophic conditions of groundwater slow the growth of microorganisms in the filter system, inhibiting the growth of heterotrophic iron and manganese oxidizing and denitrifying bacteria. This results in a monotonous 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 the high purification efficiency of biofilters over the long term and strengthening their ability to withstand shocks are critical issues that need to be addressed.

[0004] Electrochemical systems can degrade pollutants through direct anodic oxidation, reducing organic loads and refractory components, thereby improving the efficiency of subsequent biological treatment, or indirectly oxidize pollutants by producing active substances such as free radicals. Electrochemical decomposition of refractory organic matter in wastewater produces biodegradable small molecular carbon or provides a carbon source by electrochemically biosynthesizing organic matter from CO2 in the air, indirectly promoting the biodegradation of pollutants by promoting the growth of heterotrophic microorganisms and improving the stability of biological growth in the reactor.

[0005] In the existing technology, there is little research on the integrated process of coupling electrochemical systems with biological filters to treat groundwater. Most of them use external independent electrochemical processes, which increases the floor space and causes a large amount of energy loss due to external high voltage, thereby increasing the cost of the entire treatment process. Summary of the Invention

[0006] The present invention aims to achieve long-term stable treatment of groundwater contaminated by iron, manganese, ammonia and nitrogen, and solve the problem of poor operating performance and stability of existing biological filters under oligotrophic conditions. It provides a microbial electrochemical filter and a method for removing iron, manganese, ammonia and nitrogen from groundwater.

[0007] To achieve the above objectives, the present invention comprises a microbial electrochemical filter comprising a cylinder, an electrochemical system, and a filter column; the electrochemical system and the filter column are disposed within the cylinder, with the electrochemical system disposed above the filter column, which is a carrier having a biofilm covering its surface; a water outlet is disposed at the lower portion of the cylinder sidewall, and an overflow port is disposed at the upper portion. The technical solution employed by the present invention comprises the following steps:

[0008] Step 1: Construction of a microbial electrochemical filter for removing iron, manganese and ammonia nitrogen from groundwater, including a cylinder, an inlet system, an electrochemical system, a filter column, an outlet and a backwash system.

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

[0010] It is further defined that 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 of quartz sand, manganese sand, activated carbon, or a mixture of several of them in any ratio.

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

[0012] In step 1, preferably, the input end of the water inlet system is connected to the water outlet of the water tank, and is connected through a peristaltic pump and a peristaltic pump tube. The output end is directly or connected to a water distributor from the top of the cylinder, and is driven by gravity to enter the cylinder, and flows through the entire filter tank in a descending manner.

[0013] In step 1, preferably, the electrochemical system is composed of a graphite reference plate that just covers the cross section of the filter column and a plurality of graphite rods placed evenly vertically. Through holes are set on the graphite reference plate, and the through holes and the graphite rods are arranged at intervals. The graphite rods of the two electrodes are placed in parallel and interspersed, and the diagonal graphite rods are used to separate the graphite reference plates with a gap of 1 mm to 3 mm with non-conductive material to prevent short circuits. The electrode arranged on the top is connected to the positive electrode of the battery, and the electrode arranged on the bottom 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 to 4 mm.

[0015] It is further defined that a supporting layer can be provided under the carrier, and the supporting layer can be filled with gravel with a particle size of 2 cm to 4 cm to prevent the biofilm or sludge on the surface of the manganese sand from directly contacting the supporting plate during the test and causing the filter material to be lost or the water outlet to be blocked, thereby reducing the resistance to the water outlet.

[0016] It is further defined that the height ratio of the filter column to the supporting layer is (7~10):1.

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

[0018] In step 2, depending on the quality of the raw water, large debris, sand, and garbage should be removed before entering the filter system by setting up a filtration system such as a screen or by natural sedimentation in the water tank 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 of maintaining microbial survival and iron, manganese, ammonia and nitrogen oxidation removal in the filter system.

[0019] During step 2, the startup process should avoid the impact of high iron, manganese, ammonia, and nitrogen concentrations, as well as large fluctuations in pollutant concentrations. The hydraulic retention time should be maintained at a high level to ensure operation at a low pollutant load during the startup phase. After successful startup, the influent pollutant concentration and filtration rate should be gradually increased. Backwash should be performed when the effluent flow rate decreases significantly or the effluent quality exceeds the standard. A low voltage should be used throughout the operation to avoid energy loss caused by the electrolysis of water at a high voltage.

[0020] In step 2, preferably, downflow water is used, and the influent should be free of obvious impurity particles, have a dissolved oxygen content of not less than 5 mg / L, a pH value greater than or equal to 7, and be maintained at room temperature (20°C-30°C).

[0021] In step 2, preferably, the inlet iron and manganese concentration in the startup phase does not exceed 1 mg / L, the ammonia nitrogen concentration does not exceed 3 mg / L, and the hydraulic retention time is not less than 10 hours. During the stable operation phase, the inlet iron and manganese concentration does not exceed 2 mg / L, the ammonia nitrogen concentration does not exceed 5 mg / L, and the hydraulic retention time is not less than 8 hours. The backwash intensity does not exceed 10 L / (m2·s), and the flushing time is 3 min-5 min. The voltage is maintained at 0.8 V-1.2 V throughout the operation.

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

[0023] The introduction of the electrochemical system in the microbial electrochemical filter can enhance the initial film-forming efficiency, removal performance and stability of the biological filter in three ways: first, the electrooxidation process can remove some pollutants before entering the filter column, thereby reducing the biological removal pressure in the filter column; second, 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, and promoting the growth and metabolism of the biological community; third, the microbial electrochemical filter provides conditions for the growth of heterotrophic iron and manganese oxidizing bacteria, and realizes the production and coverage of more iron and manganese active oxide films on the filter surface.

[0024] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the accompanying drawings are provided for reference and illustration only and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to further explain the present invention.

[0026] FIG1 is a schematic diagram of a device according to a specific embodiment of the present invention;

[0027] FIG2 is a schematic diagram of an electrode according to a specific embodiment of the present invention;

[0028] FIG3 is a comparison diagram of pollutant removal effects according to a first embodiment of the present invention;

[0029] FIG4 is a comparison diagram of pollutant removal effects according to a second embodiment of the present invention;

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

[0031] To more clearly describe the contents of the present invention, the following will further elaborate on the purpose, apparatus, method, and advantages of the present invention in conjunction with the drawings and descriptions of specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of this new invention. Example

[0032] Step 1: Construct a microbial electrochemical filter according to Figures 1 and 2. A downflow filter using homogeneous manganese sand media was constructed using a 65 cm high, 11 cm inner side rectangular plexiglass cylinder (1). The support layer (5) was filled with gravel to a height of approximately 5 cm, and the filter column (3) was filled with manganese sand to a height of 40 cm. The empty bed contact time was 20 minutes.

[0033] Two electrodes 2 as shown in Figure 2 are placed on top of the filter material in the filter tank. The electrodes are composed of a plurality of graphite rods placed evenly and perpendicularly to a graphite reference plate. Through holes are set on the graphite reference plate, and the through holes are arranged at intervals with the graphite rods. The graphite rods of the two electrodes are placed in parallel and interspersed, and the graphite reference plates are separated by a 1mm gap with non-conductive material through diagonal graphite rods to prevent short circuit (Figure 2). 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, serving as the anode and cathode of the electrochemical system respectively.

[0034] In addition, a control group biofilter operating under open circuit conditions was also set up, and the reactor configuration and operating parameters were the same as those in the embodiment.

[0035] Step 2: Use manganese sand to soak and inoculate with culture medium. Prepare 1L of culture medium containing iron, manganese, ammonia, inorganic carbon and buffer according to the ingredients and ratios in Table 1. Dilute to 20L with pipe network water. After soaking for 24 hours, circulate water at a low filtration rate for 72 hours.

[0036] Table 1 Culture medium components

[0037] Material contentMnSO4·H2O0.0036 g / LFeSO4·7H2O0.0054 g / LNH4 + -N0.0038 g / LNaHCO30.50 g / LHEPES buffer 1M10 mM deionized water 1.0 L

[0038] In step 3, tap water from the network was artificially distributed 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 microbial electrochemical filter was operated at a voltage of 1.2 V, while the control group was open circuit. The filter was operated at room temperature, with no controls for 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. Influent and effluent samples were collected from the water tank and the lower intake of the filter every three days for measurement of relevant indicators.

[0039] The microbial electrochemical filter demonstrated excellent removal of iron, manganese, and ammonia nitrogen from groundwater. The microbial electrochemical filter activated more quickly, achieving an effluent manganese concentration of 0.058 mg / L on the sixth day, meeting the National Integrated Wastewater Discharge Level II Standard (GB8978-2002) of 0.1 mg / L. The control biological filter reached this standard only on the 12th day.

[0040] Purine metabolism, oxidative phosphorylation, homologous recombination, bacterial secretion system, pyruvate metabolism, mismatch repair, and DNA replication are more robust in microbial electrochemical filters than in conventional biofilters. During the startup phase, microbial electrochemical filters exhibit higher cell activity, rapid growth, and faster biofilm formation. The abundance of genes responsible for manganese and ammonia oxidation in microbial electrochemical filters far exceeds that of conventional biofilters. The electrochemical system promotes carbon fixation, providing a carbon source for microbial growth. Example

[0041] Step 1: Construct a microbial electrochemical filter according to Figure 1. A 65 cm high, 11 cm inner side organic glass cuboid was used to construct a homogeneous manganese sand filter media downflow filter. The filling height was 40 cm, the particle size was controlled at 2 mm to 4 mm, the gravel filling height under the carrier was 5 cm, the particle size was controlled at 2 cm to 4 cm, and the empty bed contact time was 20 min. Two graphite electrodes as shown in Figure 2 were placed on top of the filter media in the filter. The upper electrode was connected to the positive electrode of the battery, and the lower electrode was connected to the negative electrode of the battery, serving as the anode and cathode of the electrochemical system, respectively. In addition, a control group biofilter operating under open circuit conditions was also set up for the experiment. The reactor configuration and operating parameters were the same as those in the embodiment.

[0042] Step 2: Use manganese sand to soak and inoculate with culture medium. Prepare 1L of culture medium containing iron, manganese, ammonia, inorganic carbon and buffer (see Table 1), dilute it to 20L with pipe network water, soak it for 24 hours, and then circulate water at a low filtration rate for 72 hours to form a biofilm.

[0043] In step 3, tap water from the network was artificially distributed 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 for a toxic shock. The microbial electrochemical filter was operated at a voltage of 1.2 V, while the control group was left open. The filter was operated at room temperature, with no controls for 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. Influent and effluent samples were collected from the water tank and the lower intake of the filter every three days for measurement of relevant indicators.

[0044] The beneficial results are:

[0045] The microbial electrochemical filter was significantly more stable than a conventional biofilter under shock conditions, demonstrating excellent removal of iron, manganese, and ammonia nitrogen from groundwater. When the influent contained 10 mg / L 1,4-dioxane, the manganese and nitrogen removal capacity of the conventional biofilter was inhibited along the way. Under 20 mg / L dioxane stress, the manganese removal performance of the microbial electrochemical filter was not significantly inhibited, while the manganese removal rate of the conventional biofilter decreased from 96.74% to 88.76%. During the dioxane shock period, the ammonia and nitrogen removal performance of the microbial electrochemical filter dropped from 90% to approximately 27%, and the denitrification performance of the conventional biofilter was completely inhibited.

[0046] Microbial electrochemical filters can remove some pollutants before entering the filter column through electro-oxidation, thereby reducing the biological removal pressure in the filter column and providing additional carbon sources and electron acceptors for the autotrophic biological filter, thereby alleviating the inhibition of dioxane by maintaining the normal metabolism of the biological community.

[0047] The preferred embodiments disclosed above do not describe all operational details in detail. They are intended only to further illustrate the present invention so that those skilled in the art can better understand and utilize it, and are not intended to limit the specific embodiments of the present invention. According to the claims, any modifications, equivalent substitutions, variations, and improvements made within the principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A microbial electrochemical filter, characterized in that: The filter tank comprises a cylinder, an electrochemical system, and a filter column; the electrochemical system and the filter column are arranged in the cylinder, the electrochemical system is arranged above the filter column, and the filter column is composed of a carrier with a biofilm covered on the surface; a water outlet is arranged at the lower part of the side wall of the cylinder, and an overflow port is arranged at the upper part.

2. The microbial electrochemical filter according to claim 1, characterized in that: The cylinder body also comprises a supporting layer, and the supporting layer is arranged below the filter column.

3. The microbial electrochemical filter according to claim 2, characterized in that: The supporting layer is composed of gravel with a particle size of 2 cm to 4 cm.

4. The microbial electrochemical filter according to claim 1, characterized in that: The carrier is one of quartz sand, manganese sand, activated carbon with a particle size of 2 mm to 4 mm, or a mixture of several of them.

5. The microbial electrochemical filter according to claim 1, characterized in that: The electrochemical system includes electrodes, which are composed of multiple graphite rods placed evenly and perpendicularly to a graphite reference plate. Through holes are set on the graphite reference plate, and the through holes are arranged at intervals with the graphite rods. The graphite rods of the two electrodes are placed in parallel and interspersed, and the graphite reference plates are separated by a gap of 1mm to 3mm with non-conductive materials through diagonal graphite rods to prevent short circuits. The electrode set on the top is connected to the positive electrode of the battery, and the electrode set on the bottom is connected to the negative electrode of the battery.

6. The microbial electrochemical filter according to claim 1, characterized in that: The water outlet is connected to a switchable tee. One side of the tee is used for water outlet and is connected to a flow meter. The outlet water is directly connected to the natural water body or 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.

7. The method for removing iron, manganese, ammonia and nitrogen from groundwater by a microbial electrochemical filter according to any one of claims 1 to 6, characterized in that: The method is achieved by the following steps: The carrier is inoculated by soaking in a culture medium of iron, manganese, ammonia, inorganic carbon and buffer solution, and is passed into the filter tank after removing residual chlorine in the groundwater. It is operated at room temperature and backwashed when the effluent flow rate is significantly reduced or the effluent water quality exceeds the standard.

8. The method according to claim 7, characterized in that During the startup phase, the influent iron and manganese concentrations shall not exceed 1 mg / L, the ammonia nitrogen concentration shall not exceed 3 mg / L, and the hydraulic retention time shall not be less than 10 hours.

9. The method according to claim 7, characterized in that: During the stable operation stage, the influent iron and manganese concentrations shall not exceed 2 mg / L, the ammonia nitrogen concentration shall not exceed 5 mg / L, and the hydraulic retention time shall not be less than 8 h.

10. The method according to claim 7, characterized in that Backwash intensity should not exceed 10 L / (m 2 ·s), flushing time 3min-5 min; the voltage was maintained at 0.8V-1.2V during the whole operation.

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