Electrochemical MAP method for recovering nitrogen and phosphorus in livestock and poultry manure biogas slurry

Abstract

The invention relates to the technical field of wastewater treatment, in particular to an electrochemical MAP method for recycling nitrogen and phosphorus in livestock and poultry manure biogas slurry. According to a traditional MAP method, excessive expensive magnesium salt needs to be added for treating nitrogen and phosphorus in livestock and poultry manure biogas slurry, and the treatment cost is increased. In order to solve the technical problems, the invention provides the electrochemical MAP method for recovering nitrogen and phosphorus in the livestock and poultry manure biogas slurry, which comprises the following steps: by taking the livestock and poultry manure biogas slurry added with magnesium modified zeolite as an electrolyte, a magnesium electrode plate as an anode and a graphite electrode plate as a cathode, carrying out electrolytic reaction under the action of an external direct-current power supply; the nitrogen element and the phosphorus element in the livestock and poultry manure biogas slurry are converted into struvite crystals, and an electrochemical method is combined with a conventional physical adsorption mode, so that the recovery rate and the treatment efficiency of the nitrogen and the phosphorus in the livestock and poultry manure biogas slurry are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to an electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry. Background Art

[0002] With the improvement of living standards, the scale of livestock and poultry breeding is expanding. The "reduction, resource utilization and harmlessness" disposal of livestock and poultry manure has become the biggest ecological and environmental protection problem faced by the development of animal husbandry. Livestock and poultry manure generally adopts anaerobic fermentation to produce biogas treatment technology, but the final product still contains high concentrations of nitrogen and phosphorus organic matter. Nitrogen and phosphorus are indispensable nutrients in the growth of crops. However, the article "Study on the Accumulation and Impact of Nitrogen and Phosphorus in Protected Soils" published by Xu Xiaofeng et al. in the Journal of Chinese Ecology, Issue 2, 2008, Pages 292-296 pointed out that excessive nitrogen and phosphorus content will cause soil compaction and salinization, reduce soil permeability and air permeability, lead to poor soil quality and damage crops, and then lead to crop yield reduction or death. Therefore, how to efficiently recycle and utilize nitrogen and phosphorus in biogas slurry has become an urgent problem to be solved.

[0003] At present, commonly used nitrogen and phosphorus recovery technologies include biological methods, chemical precipitation methods and adsorption methods, but these methods are prone to cause secondary pollution and have obvious shortcomings in treatment efficiency and cost, especially when treating high-concentration and complex nitrogen and phosphorus wastewater. The limitations are more prominent, that is, the use of MAP method to recover nitrogen and phosphorus in wastewater has become one of the research hotspots at home and abroad. The article "Study on the Characteristics of Nitrogen and Phosphorus Recovery in Mixed Fermentation Liquid of Manure / Straw by Magnesium Ammonium Phosphate (MAP) Crystallization Method" published by Huang Bin et al., reported in the journal "China Biogas" Vol. 36, Issue 3, 2018, pp. 72-77, the article "Research Progress of Phosphorus Recovery Technology in Residual Sludge Based on MAP and HAP Methods" published by Teng Jun et al., reported in the journal "Sichuan Environment" Vol. 42, Issue 4, 2023, pp. 328-337, and the article "Analysis of Nitrogen and Phosphorus Recovery Technology in Biogas Liquid by Struvite Method" published by Zhang Hongliang et al., reported in the journal "Chemical Engineering Management", Issue 5, 2023, pp. 149-151, concluded that the MAP method for removing nitrogen and phosphorus from water bodies has the advantages of easy operation, fast reaction speed and good treatment effect. However, this method requires the addition of excessive amounts of expensive magnesium salts, and livestock and poultry manure treatment is mainly limited to animal husbandry in the agricultural field. The majority of farmers (including some large-scale breeders) face high treatment costs and treatment process technologies, which they often find difficult to accept, limiting the application and promotion of this method in actual projects.

[0004] Zeolite is an economical and efficient adsorbent that exhibits excellent stability in water treatment applications. It will not decompose or deteriorate, nor will it pollute the water body. In addition, due to its negative surface charge and rich pore structure, zeolite has a good adsorption effect on cations, and can also be modified by modification methods to increase its affinity for anions and improve its overall adsorption capacity. For zeolite that has been saturated with adsorption treatment, its adsorption capacity can also be restored through regeneration technology to achieve recycling.

[0005] Based on the above problems, the present invention proposes an electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure slurry, which can effectively solve the above problems. Summary of the invention

[0006] The problem in the prior art is that the traditional MAP method has low efficiency and high cost in treating nitrogen and phosphorus in livestock and poultry manure biogas. In view of the above technical problems, the present invention provides an electrochemical MAP method for recovering nitrogen and phosphorus in livestock and poultry manure biogas. The method uses livestock and poultry manure biogas added with magnesium-modified zeolite as electrolyte, magnesium electrode plate as anode, and graphite electrode plate as cathode. Under the action of an external DC power supply, an electrolytic reaction is carried out, so that the nitrogen and phosphorus in the livestock and poultry manure biogas are converted into struvite crystals (MAP precipitation).

[0007] Preferably, the method for preparing the magnesium-modified zeolite comprises the following steps:

[0008] (1) immersing the zeolite in an alkali solution, stirring in a constant temperature water bath at 60° C. for at least 6 hours, and after stirring, standing at room temperature for 24 hours, and then performing solid-liquid separation and drying to obtain an alkali-modified passivating agent;

[0009] (2) washing the obtained alkali-modified passivating agent with water and anhydrous ethanol in sequence until it becomes neutral, and then drying it to obtain a pretreated zeolite;

[0010] (3) The obtained pretreated zeolite was immersed in a magnesium salt aqueous solution, stirred in a constant temperature water bath at 60° C. for 6 h, and then dried to obtain a magnesium-modified zeolite.

[0011] Preferably, the alkali solution is an aqueous sodium hydroxide solution.

[0012] Preferably, the magnesium salt aqueous solution is one or more of a magnesium chloride aqueous solution, a magnesium sulfate aqueous solution, and a magnesium oxide aqueous solution.

[0013] Preferably, the method for preparing the electrolyte comprises the following steps:

[0014] Magnesium-modified zeolite is added to the livestock and poultry manure biogas slurry, and ammonium chloride and potassium dihydrogen phosphate are added to adjust the N / P ratio (N / P ratio refers to the molar ratio of nitrogen element to phosphorus element) in the biogas slurry to 2-6, and hydrochloric acid and sodium hydroxide aqueous solution are used to adjust the pH of the biogas slurry to 6-10.

[0015] Preferably, the N / P ratio is 4.

[0016] Preferably, the pH=8.

[0017] Preferably, the mass concentration of magnesium-modified zeolite in the livestock and poultry manure biogas slurry is 5±0.002 g / L.

[0018] Preferably, the current of the electrolysis reaction is 10-15A / m 2 .

[0019] Preferably, the voltage of the electrolysis reaction is 4-36V.

[0020] Preferably, the electrolysis reaction time is at least 180 min.

[0021] The present invention has the following beneficial effects:

[0022] (1) The present invention obtains MgCl2-ZO with better adsorption effect through experiments, and uses electrochemical method combined with conventional physical adsorption to significantly improve the recovery rate and treatment efficiency of nitrogen and phosphorus in livestock and poultry manure biogas slurry;

[0023] (2) The external DC power supply used in the present invention can be directly powered by a solar panel, without any electricity cost;

[0024] (3) The method of the present invention is simple to operate, low-cost, and has significant effects and good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 : The structural representation of the single tank electrolytic cell used in the present invention.

[0026] In the figure: 1. anode, 2. cathode, 3. copper core wire, 4. adjustable DC regulated power supply. DETAILED DESCRIPTION

[0027] The present invention is described in detail below with reference to the examples. However, it should be understood that the following examples are only illustrative of the embodiments of the present invention, and are not intended to limit the scope of the present invention.

[0028] The zeolite in the following embodiments of the present invention was purchased from Runjia Water Purification Material Co., Ltd., with the product number: JY-FS, and the specific surface area of ​​the zeolite: 42.3309 m 2 / g.

[0029] Example 1

[0030] The preparation method of magnesium modified zeolite is as follows:

[0031] (1) immersing the zeolite in a 1 mol / L sodium hydroxide aqueous solution, stirring in a constant temperature water bath at 60° C. for 6 h, and after stirring, standing at room temperature for 24 h, and then filtering and drying at 105° C. in sequence to obtain an alkali-modified passivating agent;

[0032] (2) washing the obtained alkali-modified passivating agent with water and anhydrous ethanol in sequence until it becomes neutral, and then drying it to obtain a pretreated zeolite;

[0033] (3) The obtained pretreated zeolite was immersed in a 1 mol / L magnesium salt aqueous solution, stirred in a constant temperature water bath at 60° C. for 6 h, and then dried to obtain a magnesium-modified zeolite.

[0034] When the magnesium salt aqueous solution is a magnesium chloride aqueous solution, the obtained magnesium-modified zeolite is recorded as MgCl2-ZO.

[0035] When the magnesium salt aqueous solution is a magnesium sulfate aqueous solution, the obtained magnesium-modified zeolite is recorded as MgSO4-ZO.

[0036] When the magnesium salt aqueous solution is magnesium oxide aqueous solution, the obtained magnesium-modified zeolite is recorded as MgO-ZO.

[0037] Under room temperature, 400 mL of chicken manure biogas was divided into four equal parts, and the initial contents of nitrogen and phosphorus in the four chicken manure biogas were determined respectively. Then, 5 g of ZO, MgCl2-ZO, MgSO4-ZO and MgO-ZO were added to each chicken manure biogas, respectively, and the adsorption was stirred at a speed of 200 r / min for 120 min, and then filtered. TN was measured by TOC instrument, TAN by salicylic acid spectrophotometry, and TP and TPS by ammonium molybdate spectrophotometry. The adsorption effect of each magnesium-modified zeolite was evaluated according to the contents of nitrogen and phosphorus in the filtrate and the initial chicken manure biogas. The calculation results are shown in Table 1.

[0038] Table 1

[0039]

[0040] It can be seen from the test results in Table 1 that under the same test conditions, MgCl2-ZO has the best adsorption effect.

[0041] Example 2

[0042] An electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry, the specific method is as follows:

[0043] Chicken manure biogas slurry with magnesium-modified zeolite added is used as the electrolyte, the magnesium electrode plate is used as the anode (connected to the positive electrode of the external DC power supply), and the graphite electrode plate is used as the cathode (connected to the negative electrode of the external DC power supply). Under the action of the external DC power supply, the electrolysis reaction is carried out, so that the nitrogen and phosphorus elements in the livestock and poultry manure biogas slurry are converted into MAP precipitation. The adjustable DC regulated power supply voltage is 4-36V, and the current density is 10A / m 2 The electrolysis time is 180 min. The electrolytic cell is a single tank electrolytic cell, and its structural diagram is as shown in the attached manual. Figure 1 shown.

[0044] The preparation method of the electrolyte is as follows:

[0045] MgCl2-ZO is added to the chicken manure biogas slurry, and appropriate amounts of ammonium chloride and potassium dihydrogen phosphate are added to adjust the N / P ratio in the biogas slurry to 2, and 0.1 mol / L hydrochloric acid and sodium hydroxide aqueous solution are used to adjust the pH of the biogas slurry to 8, that is, the mass concentration of MgCl2-ZO in the chicken manure biogas slurry is 5 g / L. After the electrolysis is completed, the electrolyte is filtered, and the contents of residual nitrogen and phosphorus in the filtrate are tested. According to the difference in the nitrogen and phosphorus contents in the solution before and after the electrolysis of the electrolyte, the recovery rates of nitrogen and phosphorus in the electrolyte are calculated.

[0046] The recovery rate is calculated as follows:

[0047] Recovery rate = (C0-C t ) / C0×100%

[0048] t is the electrolysis time, C0 is the initial concentration, C t is the concentration at minute t.

[0049] The specific test results are shown in Table 2.

[0050] Table 2

[0051]

[0052] Example 3 is the same as Example 2, except that the current density during the electrolysis process of Example 3 is 12.5 A / m 2 , the pH of the electrolyte is 10. The recovery rates of nitrogen and phosphorus in the electrolyte of Example 3 are shown in Table 3.

[0053] Table 3

[0054]

[0055] Example 4 is the same as Example 2, except that the current density during the electrolysis process of Example 4 is 15A / m 2, the pH of the electrolyte is 10, and the N / P ratio in the electrolyte is 4. The recovery rates of nitrogen and phosphorus in the electrolyte of Example 4 are shown in Table 4.

[0056] Table 4

[0057]

[0058] Example 5 is the same as Example 2, except that the current density during the electrolysis process of Example 5 is 12.5 A / m 2 , the N / P ratio in the electrolyte is 4. The recovery rates of nitrogen and phosphorus in the electrolyte of Example 5 are shown in Table 5.

[0059] Table 5

[0060]

[0061] Example 6 is the same as Example 2, except that the N / P ratio in the electrolyte of Example 6 is 6. The recovery rates of nitrogen and phosphorus in the electrolyte of Example 6 are shown in Table 5.

[0062] Table 6

[0063]

[0064] The recovery rates of nitrogen and phosphorus in the electrolytes of Examples 2-6 of the present invention are summarized in Table 7.

[0065] Table 7

[0066]

[0067] Comparative Example 1 is the same as Example 2, except that, in Comparative Example 1, no external DC power supply is connected, but the electrolysis method is replaced by a mechanical stirring method at 200 r / min. After stirring and adsorbing for 180 min, the recovery rates of nitrogen and phosphorus in the electrolyte obtained in Comparative Example 1 are shown in Table 8.

[0068] Table 8

[0069]

[0070] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. An electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry, characterized in that: The biogas slurry from livestock and poultry manure with magnesium-modified zeolite added is used as the electrolyte, the magnesium electrode plate is used as the anode, and the graphite electrode plate is used as the cathode. The electrolysis reaction is carried out under the action of an external DC power supply, so that the nitrogen and phosphorus elements in the biogas slurry from livestock and poultry manure are converted into MAP precipitation.

2. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 1, characterized in that: The preparation method of the magnesium-modified zeolite comprises the following steps: (1) immersing the zeolite in an alkali solution, stirring in a constant temperature water bath at 60° C. for at least 6 hours, and after stirring, standing at room temperature for 24 hours, and then performing solid-liquid separation to obtain an alkali-modified passivating agent; (2) washing the obtained alkali-modified passivating agent with water and anhydrous ethanol in sequence until it becomes neutral, and then drying it to obtain a pretreated zeolite; (3) The obtained pretreated zeolite was immersed in a magnesium salt aqueous solution, stirred in a constant temperature water bath at 60° C. for 6 h, and then dried to obtain a magnesium-modified zeolite.

3. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 2, characterized in that: The alkali solution is a sodium hydroxide aqueous solution.

4. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 2, characterized in that: The magnesium salt aqueous solution is one or more of a magnesium chloride aqueous solution, a magnesium sulfate aqueous solution, and a magnesium oxide aqueous solution.

5. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 1, characterized in that: The preparation method of the electrolyte comprises the following steps: The method comprises adding magnesium modified zeolite to the livestock and poultry manure biogas slurry, adding ammonium chloride and potassium dihydrogen phosphate to adjust the N / P ratio of the biogas slurry to 2-6, and using hydrochloric acid and sodium hydroxide aqueous solution to adjust the pH of the biogas slurry to 6-10.

6. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 5, characterized in that: The N / P ratio is 4.

7. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 5, characterized in that: The pH=8.

8. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 5, characterized in that: The mass concentration of magnesium-modified zeolite in the livestock and poultry manure biogas slurry is 5±0.002 g / L.

9. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 1, characterized in that: The current of the electrolysis reaction is 10-15A / m 2 .

10. The electrochemical MAP method for recovering nitrogen and phosphorus from livestock and poultry manure biogas slurry according to claim 1, characterized in that: The voltage of the electrolysis reaction is 4-36V.

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