Electrochemical cathodic nitrogen and phosphorus crystallization recovery constructed wetland

Abstract

The application provides an electrochemical cathode nitrogen and phosphorus crystallization recovery artificial wetland, a filter material layer of which is provided with magnesium-containing filter material, the artificial wetland is provided with an electrochemical reaction device, and both a cathode and an anode of the electrochemical reaction device are arranged into the filter material layer; the cathode rod is inserted into the isolation water-permeable pipe, the isolation water-permeable pipe allows water in the filter material layer to enter the isolation water-permeable pipe, but separates the cathode rod and the filter material, forms a flocculation space in the pipe, and the water in the isolation water-permeable pipe and the water in the filter material layer are connected into an integral water body; the artificial wetland is further provided with a discharge pipe, and the discharge pipe is communicated with the lower end of the isolation water-permeable pipe. The application not only can strengthen the nitrogen and phosphorus removal effect of the artificial wetland, but also can realize resource recycling of ammonia nitrogen and phosphate ions, and can realize efficient removal and recovery of nitrogen and phosphorus without adjusting the PH of the water body, so that the technical problem of low total phosphorus removal rate of the traditional artificial wetland is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of constructed wetlands in environmental engineering, in particular to a constructed wetland for electrochemical cathode nitrogen and phosphorus crystallization recovery. BACKGROUND

[0002] Constructed wetland is a kind of technology that wastewater and sludge are controlledly dosed on the artificial wetland, and the wastewater and sludge are treated by the triple synergistic effect of soil, artificial medium, plants and microorganisms in the process of flowing in a certain direction. The traditional constructed wetland has good removal effect on COD and ammonia nitrogen, but for phosphorus compounds, the traditional constructed wetland mainly removes them through processes such as substrate adsorption, precipitation and plant absorption, and the removal rate of phosphorus is only 10%-15%. At the same time, the substrate adsorption capacity and plant biomass of the constructed wetland are limited, and the phosphorus removal rate of such constructed wetland gradually decreases after long-term operation. On the other hand, the current utilization mode of phosphate rock resources is unsustainable, and most of the phosphorus elements will be discharged into water or sludge and difficult to recover and utilize. As a non-renewable resource, phosphorus recovery will be increasingly important in future wastewater treatment technology.

[0003] At present, the main method to improve the total phosphorus removal rate of the constructed wetland is to improve the phosphorus removal filter material with high porosity in the traditional constructed wetland to realize phosphorus adsorption. This kind of technology can effectively improve the removal rate of phosphorus in wastewater in the constructed wetland, but there are problems such as secondary release of total phosphorus after saturation and difficulty in recycling of total phosphorus adsorbed in the filter material.

[0004] Therefore, it is of great significance to construct a new type of constructed wetland technology for strengthening nitrogen and phosphorus removal and recycling for wastewater treatment and sustainable development of resources. SUMMARY

[0005] The purpose of the present application is to provide an efficient electrochemical reaction constructed wetland system for nitrogen and phosphorus recovery, which solves the technical problems of low total phosphorus removal rate and difficulty in recycling of nitrogen and phosphorus elements in the existing constructed wetland wastewater treatment technology. The basic electrochemical reaction principle of the present application is as follows:

[0006] Cathode reaction: 2e — + 2H2O → H2 + 2OH —

[0007] Anode reaction: Mg - 2e — → Mg 2+

[0008] Overall reaction: Mg 2+ + NH 4+ + PO4 3-+6H2O→MgNH4PO4·6H2O↓(struvite)

[0009] By using electrochemical electrolysis technology, the natural magnesium-containing mineral filter material in the anode area of electrolysis is used as a slow-release magnesium source, and a large amount of hydroxyl ions are released by electrolyzing water in the cathode part to increase the pH near the cathode and create alkaline conditions, which promotes the crystallization of struvite (magnesium ammonium phosphate) in the cathode area of electrolysis. At room temperature, the solubility of struvite in water is 2.5*10^ -13 The ammonia and phosphorus treatment rate recovered by the technology is high, and the crystalline purity is high after enrichment in the cathode, so that some struvite can be used as agricultural phosphorus fertilizer after slight treatment.

[0010] In order to achieve the above purposes, the present application proposes the following technical solutions:

[0011] An artificial wetland for electrochemical cathode nitrogen and phosphorus crystallization recovery, a water distribution system, a filter material layer and a water collection system, characterized in that the filter material layer uses magnesium-containing filter material, the artificial wetland is provided with an electrochemical reaction device, the cathode and the anode of the electrochemical reaction device are arranged into the filter material layer; the electrochemical reaction device uses a cathode rod for the cathode and is also provided with an isolation water permeable pipe, the cathode rod is inserted into the isolation water permeable pipe, the isolation water permeable pipe allows water in the filter material layer to enter the isolation water permeable pipe but separates the cathode rod and the filter material and forms a flocculation space in the pipe, and the water in the isolation water permeable pipe and the water in the filter material layer are connected into a whole water body; the artificial wetland is also provided with a discharge pipe, the discharge pipe is communicated with the lower end of the isolation water permeable pipe, the recovery of ammonia and phosphorus elements is realized, and the purified water is collected and discharged from the water collection system.

[0012] In the present application, the isolation water permeable pipe inserted by the cathode rod separates the filter material layer into an anode area and a cathode area, the anode area is filled with water treatment filter material rich in magnesium elements, which is used as a slow-release magnesium source to dissolve magnesium ions, the magnesium mineral filler is inserted with an anode connected with the anode of the power supply power device, the cathode area is inserted with a carbon rod electrode for forming struvite crystals from dissolved magnesium ions, ammonium and phosphate in the alkaline environment, the carbon rod electrode is connected with the cathode of the power supply power device.

[0013] On the basis of the above technical solutions, the present application can also use the following further technical solutions, or use these further technical solutions in combination:

[0014] The artificial wetland system uses a module combination structure, uses civil engineering or high polymer material as a container to form a module container, and sets the water distribution system, the filter material layer, the water collection system and the electrochemical reaction device in the module container. In the case of civil engineering as a module container, a geomembrane can be arranged on the inner side of the container wall as an anti-seepage and anti-leakage structure, and the high polymer material can use PE or the like.

[0015] The filter material in the artificial wetland is preferably magnesium-rich water treatment filter material;

[0016] For the anode, it can be directly arranged in the filter material layer, and the anode can adopt an anode rod. Both the anode and the cathode can be made of inert materials, such as carbon rods.

[0017] The electrochemical reaction device adopts an anode rod for the anode, and is further provided with an anode rod isolation water permeable pipe, the anode rod is inserted in the anode rod water permeable pipe, and the anode rod becomes a structure convenient to replace, so that the anode can contain magnesium material, which helps to accelerate the electrochemical reaction.

[0018] Optionally, the power supply power device in the electrochemical reaction device can be a conventional power or other new energy such as photovoltaic.

[0019] Due to the technical solutions of the present application, the artificial wetland has the following advantages:

[0020] 1. The nitrogen and phosphorus are recycled by using the technology, which not only can strengthen the nitrogen and phosphorus removal effect of the artificial wetland, but also can realize the recycling and utilization of ammonia nitrogen and phosphate ions.

[0021] 2. The nitrogen and phosphorus are recycled by using the technology without adjusting the PH of the water body, which can realize the efficient removal and recycling of nitrogen and phosphorus, and solve the technical problem of low total phosphorus removal rate of the traditional artificial wetland.

[0022] 3. The nitrogen and phosphorus removal effect of the artificial wetland is strengthened by using the electrochemical method, which can improve the hydraulic load of the artificial wetland, reduce the land occupation area of the artificial wetland, and realize the high integration and modularization of the artificial wetland.

[0023] 4. The electrochemical method is used to precipitate the struvite compound which is extremely difficult to dissolve in water at the cathode, which is especially suitable for the advanced treatment of low-concentration wastewater containing phosphorus.

[0024] 5. The nitrogen and phosphorus flocculent can be precipitated at the cathode by the technology, which can be periodically emptied, which not only can realize the recycling of ammonia and phosphorus elements, but also can improve the service life of the artificial wetland filler and delay the plugging period of the wetland. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a schematic view of the elevation arrangement of the artificial wetland of the present application;

[0026] Figure 2 It is a schematic view of the planar arrangement of the artificial wetland of the present application. DETAILED DESCRIPTION

[0027] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0028] Reference Figure 1 The constructed wetland for electrochemical cathode nitrogen and phosphorus crystallization recovery in this embodiment includes plants 6, a water distribution system, a magnesium-containing filter layer 2, a water collection system, and an electrochemical reaction device.

[0029] In this invention, the constructed wetland can adopt a modular structure using civil engineering structures or containers made of polymer materials such as PE. Each module includes the aforementioned plants 6, a water distribution system, a magnesium-containing filter layer 2, a water collection system, and an electrochemical reaction device. Preferably, the power supply device 3-1 for each electrochemical reaction device can be independent or equipped with a separate switch. When the civil engineering serves as the modular container, an artificial wetland isolation layer 1 can be installed on the inner side of the container wall as a seepage and leakage prevention structure. If modularity is not used, the artificial wetland isolation layer 1 can be arranged at the boundary of the constructed wetland. The artificial wetland isolation layer 1 can be composed of two layers of fabric and one membrane, GCL bentonite waterproof blanket, or other insulating materials; this invention uses a two-layer fabric and one membrane as an example.

[0030] The modular design improves the overall leakage protection performance of the constructed wetland, facilitates maintenance, and allows for timely identification of faulty modules in case of leakage.

[0031] Plants that can be planted in artificial wetlands include emergent plants, aquatic-tolerant small trees and shrubs.

[0032] The water distribution system of the constructed wetland is a device that distributes wastewater in a laminar flow state, with the wastewater flowing at a low speed in the main and branch pipes. The main pipe of this water distribution device is arranged in a ring or "F" shape, and the branch pipes are perforated pipes laid horizontally in a uniform water distribution layer. The water distribution system consists of an inlet main pipe 4-1, water distribution branch pipes 4-2, and a water distribution layer 4-3. The water distribution layer 4-3 is located above the filter media layer 2, and the inlet main pipe 4-1 and water distribution branch pipes 4-2 are buried within the water distribution layer 4-3.

[0033] The magnesium filter media layer 2 in the constructed wetland is composed of filter media with different particle sizes. The filler material of the present invention is a known technology, such as magnesium slag, magnesium ore, and combinations of various fillers. This embodiment uses magnesium slag filter media as an example for illustration. The main filter layer is made of magnesium slag filter media with a particle size of 8-12 mm and a thickness of 700 mm.

[0034] The water collection system of the constructed wetland consists of water collection pipes 5-2 laid horizontally in the water collection layer 5-1 at the bottom of the wetland. The water collection pipes 5-2 are distributed in a mesh pattern. The water collection pipes are laterally cut with a width of 2 mm, a length of 200 mm, and a spacing of 100 mm.

[0035] The water distribution layer 4-3 and the water collection layer 5-2 can be constructed using traditional artificial wetland filter media, such as volcanic rock, ceramsite, zeolite, etc., with a particle size larger than that of magnesium-containing filter media layer 2, and uniformly spread.

[0036] The cathode and the anode of the electrochemical reaction device are arranged in the filter material layer 2, and preferably match the thickness of the filter material layer 2. The electrochemical reaction device adopts a cathode rod 3-2 for the cathode and is further provided with a separation water-permeable pipe 3-4, which can be a perforated water-permeable pipe. The cathode rod 3-2 is vertically arranged in the separation water-permeable pipe 3-4, and the upper end of the separation water-permeable pipe 3-4 can extend out of the constructed wetland, so as to facilitate the extraction of the cathode rod 3-2 for the regular maintenance of the cathode rod 3-2. The separation water-permeable pipe 3-4 allows the water in the filter material layer 2 to enter the separation water-permeable pipe 3-4, but separates the cathode rod 3-2 and the filter material, forms a flocculation space in the separation water-permeable pipe 3-4, and the water in the separation water-permeable pipe 3-4 and the water in the filter material layer 2 form an integral water body; the constructed wetland is further provided with a discharge pipe 3-6, which is in communication with the lower end of the separation water-permeable pipe 3-4. A discharge valve 3-5 is arranged on the discharge pipe 3-6, which can be regularly opened to discharge the struvite flocculent crystals precipitated in the cathode.

[0037] The anode can adopt an anode rod 3-3, which can be directly inserted into the filter material layer 2. The anode rod 3-3 and the cathode rod 3-2 can both adopt carbon rods and are perpendicular to the horizontal plane, and are connected with the power supply power device 3-1 through a guide 3-7.

[0038] The arrangement of the cathode rod 3-2 and the anode rod 3-3 of the electrochemical reaction device of the constructed wetland is shown in the schematic Figure 2 The cathode rod 3-2 and the anode rod 3-3 can be connected in parallel in multiple groups according to actual needs, so as to improve the nitrogen and phosphorus precipitation efficiency.

[0039] The cathode and the anode electrode of the electrochemical reaction device of the constructed wetland are generally composed of carbon rods and other inert electrodes. The anode can also be composed of a magnesium alloy active electrode, which serves as a magnesium source for enhancing release, so as to improve the purification effect of the constructed wetland. In this case, an anode rod separation water-permeable pipe can be arranged, the anode rod is inserted into the anode rod separation water-permeable pipe, the anode rod separation water-permeable pipe allows the water inside and outside the pipe to communicate, but prevents the filter material from entering the pipe, and the anode rod separation water-permeable pipe can also be a perforated water-permeable pipe.

[0040] The above is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application. Any equivalent changes and modifications made in accordance with the present application are within the scope of the claims of the present application, and will not be repeated here.

Claims

1. An artificial wetland for electrochemical cathode nitrogen and phosphorus crystallization recovery, comprising a water distribution system, a filter media layer, and a water collection system, characterized in that... The filter media layer uses magnesium-containing filter media. The constructed wetland is equipped with an electrochemical reaction device, with both the cathode and anode of the electrochemical reaction device arranged within the filter media layer. The electrochemical reaction device uses a cathode rod for the cathode and is also equipped with an isolation permeable pipe. The cathode rod is inserted into the isolation permeable pipe, which allows water from the filter media layer to enter the isolation permeable pipe but isolates the cathode rod and the filter media, forming a flocculation space within the pipe. The water in the isolation permeable pipe and the water in the filter media layer are connected to form a single water body. The constructed wetland is also equipped with a drain pipe, the lower end of which is connected to the isolation permeable pipe. The anode is directly arranged in the filter media layer, and the anode contains magnesium-containing material.

2. The constructed wetland for electrochemical cathode nitrogen and phosphorus crystallization recovery as described in claim 1, characterized in that... The constructed wetland adopts a modular structure, using civil engineering or polymer materials as containers to form modular containers, and the water distribution system, filter layer, water collection system and electrochemical reaction device are set inside the modular containers.

3. The constructed wetland for electrochemical cathode nitrogen and phosphorus crystallization recovery as described in claim 1, characterized in that... The electrochemical reaction device uses an anode rod as the anode and is also equipped with an anode rod isolation water permeable pipe, in which the anode rod is inserted.

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