WO2022222173A1

WO2022222173A1 - Method for producing fertilizer by means of electrodialysis

Info

Publication number: WO2022222173A1
Application number: PCT/CN2021/090559
Authority: WO
Inventors: 叶志隆; 李叶楠; 陈少华
Original assignee: 中国科学院城市环境研究所
Priority date: 2021-04-19
Filing date: 2021-04-28
Publication date: 2022-10-27
Also published as: CN112978763A

Abstract

A method for producing a fertilizer by means of electrodialysis, comprising: pretreating biogas slurry, removing suspended particulate matters and colloids in the biogas slurry to obtain raw water, and introducing the raw water into a selective electrodialysis system, wherein an ion exchange membrane is arranged in the selective electrodialysis system; and separating the raw water to obtain a divalent anion enriched liquid, a divalent cation enriched liquid, a monovalent ion enriched liquid and desalted water, wherein the desalted water meets a discharge standard. A chemical fertilizer is produced by using the enriched liquid, and the production comprises: adjusting the pH value of the monovalent ion enriched liquid, then carrying out evaporation treatment, absorbing the evaporated gas with sulfuric acid to obtain ammonium sulfate, and crystallizing the evaporated liquid to obtain solid potassium salt. The method effectively solves the problem of resource utilization of the high-salinity concentrated solution after anaerobic biogas slurry is treated by means of selective electrodialysis, and provides a feasible scheme for the recovery of biogas slurry resources.

Description

A kind of method for producing fertilizer by electrodialysis

technical field

The invention relates to water treatment technology, in particular to a method for producing fertilizer by electrodialysis.

Background technique

While the livestock and poultry breeding industry guarantees the supply of livestock and poultry products in urban and rural areas, promotes farmers' income increase, and activates the rural economy, a large amount of nutrients such as nitrogen and phosphorus discharged have become the main source of environmental pollution in my country. The emissions are 10,005,300 tons of chemical oxygen demand, 110,900 tons of ammonia nitrogen, 596,300 tons of total nitrogen, and 119,700 tons of total phosphorus, and large-scale farms account for 70% of the total emissions. At present, the most widely used treatment technology in farms is anaerobic fermentation. The aquaculture wastewater and manure enter the biogas tank for anaerobic fermentation, and the generated biogas is recovered as energy. After anaerobic fermentation of aquaculture wastewater, biogas slurry can degrade COD by 80-90%, but it still contains high levels of ammonia nitrogen, total nitrogen, total phosphorus and other pollutants, which cannot meet the standard of direct discharge; most anaerobic processes The ammonia nitrogen content in the produced biogas slurry is too high, and it is not suitable for direct return to the field. At the same time, the direct return to the field is also limited by the absorption capacity of the surrounding farmland. The biogas slurry cannot be effectively treated, which is likely to cause secondary pollution.

CN110550818A discloses a process for high-efficiency desalination treatment of biogas slurry after fermentation of dairy cattle breeding wastewater, including pretreatment; the biogas slurry is passed through a grid to filter impurities and then passed into a sedimentation tank for precipitation treatment. Clear biogas slurry; flocculation and precipitation treatment; adding coagulant and coagulant aid to the primary supernatant biogas slurry, stirring at the same time, and performing solid-liquid separation to obtain supernatant biogas slurry; membrane separation treatment; supernatant biogas slurry pump Filtration is carried out in a nanofiltration device to obtain a membrane dialysate, which is passed into an electrodialyzer for desalination and concentration treatment, and the electrodialysis desalinated fresh water is obtained and discharged up to the standard. In this method, the electrodialyzer can only complete the desalination of water in batches, and it is difficult to further separate and process the concentrated liquid because the concentrated liquid contains a large number of different types of components.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the problems existing in the existing biogas slurry recycling and processing, and provide a method for producing fertilizer by electrodialysis, which utilizes the electrodialysis technology to separate and process the biogas slurry to obtain ions of different valence states and different charge types. The enrichment liquid, cleverly using the characteristics and correlation of these enrichment liquids, can efficiently produce fertilizers and realize the full utilization of biogas slurry resources.

The traditional treatment methods of biogas slurry include direct discharge and field utilization. Because biogas slurry contains a large amount of nutrients such as ammonia nitrogen and phosphate, as well as pathogenic pollutants such as manure residue and pathogenic bacteria, direct discharge can easily cause environmental pollution and eutrophication of water bodies. However, the use of returning fields is limited by the cost of long-distance transportation and the absorption capacity of the surrounding land. The average farmland can only consume 1-3 pigs to produce manure and biogas slurry, which severely limits the development of intensive farming. The treatment of biogas slurry by selective electrodialysis can not only meet the discharge requirements of the biogas slurry, but also obtain a concentrated solution containing high concentration of nutrients, which greatly reduces the transportation cost and facilitates the subsequent preparation of various fertilizers.

The treatment of biogas slurry raw water by electrodialysis will produce concentrated products with high salinity, which are in the state of solution. Because the distribution ratio of nutrients in the concentrated solution is limited by the quality of raw water, the ratio of nitrogen and phosphorus is seriously unbalanced, and it is difficult to directly apply liquid fertilizers with high salinity. .

Therefore, the desalinated water and concentrated water obtained by electrodialysis are usually discharged. The concentrated water contains a lot of impurity elements, and it is worthless to purify. Nor can it be used directly as fertilizer; the existing method is to transfer it to a treatment plant for treatment, but there is a problem of inconvenient liquid transportation.

The present invention adopts an ion exchange membrane set in a selective electrodialysis system, so that the raw water is separated by selective electrodialysis to obtain a divalent anion enrichment solution, a divalent cation enrichment solution, a monovalent ion enrichment solution and desalinated water, Among them, the desalinated water meets the discharge standards, and the enriched liquid is used to produce fertilizers. According to the nutrient substances of different components such as phosphates, potassium salts, ammonium salts, etc. in the biogas slurry, the present invention can be differentiated according to the number of charges and electrical properties thereof, and the selective electrodialysis process is used to separate and concentrate, so as to realize the separation and concentration of different types of chemical fertilizers. separation. The traditional method is difficult to achieve such separation requirements.

For the biogas slurry after anaerobic fermentation, its conductivity is 2-50mS/cm, ammonia nitrogen concentration is 100-5000mg/L, total phosphorus concentration is 5-200mg/L, potassium concentration is 50-1500mg/L, after ion exchange In the membrane-assisted electrodialysis process, a divalent anion enrichment solution is obtained in the product 1 chamber, which is a phosphate enrichment solution, and a divalent cation enrichment solution is obtained in the product 2 chamber, which is rich in calcium, magnesium ions, and some ammonium salts , a part of potassium salt enrichment solution, monovalent ion enrichment solution is obtained in the concentrated water chamber, which is an enrichment solution rich in part of ammonium salt and part of potassium salt. The above separation is the basis for the next step in fertilizer production.

There are two ideas for producing fertilizer from enriched liquid. The first scheme is shown in Figure 1. It includes: Step 1) Mix the feed liquid obtained from the product 1 chamber with the feed liquid obtained from the product 2 chamber in proportion, adjust the pH, and obtain phosphoric acid The ammonium and magnesium are precipitated, and the clear liquid enters the next process; Step 2) mix the clear liquid obtained in step 1) with the feed liquid obtained in the concentrated water chamber, adjust pH, and evaporate, and the evaporated gas is absorbed by sulfuric acid to obtain ammonium sulfate, The evaporated liquid crystallized as potassium salt. Preferably, air blowing is used for denitrification during evaporation, that is, air is bubbling into the solution during the evaporation process, which is helpful for the removal of ammonia gas.

The second scheme is shown in Figure 2: it includes: step 1) adjusting the pH of the feed liquid obtained in the product 2 chamber, and evaporating, the evaporated gas is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated solid enters the next process; step 2 ) adding the solid obtained in step 1) to the feed liquid obtained in the product 1 chamber, adjusting the pH, and the solid obtained by precipitation is calcium phosphate and magnesium phosphate; step 3) adjusting the pH of the feed liquid obtained in the concentrated water chamber, evaporating, evaporating The obtained gas is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated liquid crystallizes into potassium salt. Preferably, air blowing is used for denitrification during evaporation, that is, air is bubbling into the solution during the evaporation process, which is helpful for the removal of ammonia gas.

In the process of fertilizer production from enrichment liquid, the key is to integrate different enrichment materials to form the target product, and at the same time to effectively separate from other elements. The present invention does not require additional additives, and can realize high-efficiency chemical fertilizer production only by adjusting pH. specific:

In the first step 1) of the scheme, the pH should be adjusted to be greater than 8.00, and the reaction speed is faster when the pH is above 10.00.

In scheme 1, step 2) and scheme 2, step 1), pH should be maintained to be greater than 10.00 during the reaction, and ammonia nitrogen removal is more thorough when pH is greater than 12.00, so that the ammonium sulfate yield is high, and it is ensured that potassium salt does not contain ammonia nitrogen.

Scheme 1, step 2), scheme 2, step 1) and step 3), the method of evaporation is preferably reduced pressure evaporation, and the gas obtained by evaporation should first be passed into sulfuric acid to absorb the ammonia gas therein, and the evaporation temperature can be reduced by reduced pressure evaporation. , reduce heat loss, and greatly reduce energy consumption while accelerating the evaporation rate and ensuring the evaporation effect.

In step 2) of scheme 2, the pH should be adjusted to be greater than 9.00, and the precipitation of calcium and magnesium ions is relatively thorough, thereby improving the yield of phosphate fertilizer.

The specific plans are as follows:

A method for producing fertilizer by electrodialysis, comprising pre-processing biogas slurry, removing suspended particulates and colloids in the biogas slurry to obtain raw water, and then passing the raw water into a selective electrodialysis system for operation, the selecting An ion exchange membrane is installed in the electrodialysis system, so that the raw water is separated to obtain a divalent anion enrichment solution, a divalent cation enrichment solution, a monovalent ion enrichment solution and desalinated water, wherein the desalinated water meets the discharge standard, and the enriched Liquid collection to produce fertilizers, including:

The pH of the monovalent ion enrichment solution is adjusted, followed by evaporation treatment, the evaporated gas is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated liquid crystallizes to obtain solid potassium salt.

Further, the biogas slurry is the biogas slurry after anaerobic fermentation, the conductivity is 2-50mS/cm, the ammonia nitrogen concentration is 100-5000mg/L, the total phosphorus concentration is 5-200mg/L, and the potassium concentration is 50-1500mg /L.

Further, the selective electrodialysis system comprises an anode electrode chamber, a cathode electrode chamber arranged oppositely, and a chamber arranged between the anode electrode chamber and the cathode electrode chamber; the chamber includes N Units connected in parallel, N is a positive integer, and each unit has the same structure, including a product 1 room, a concentrated water room, a product 2 room and a desalination room arranged in sequence; the product 1 room and the concentrated water room are separated by a The valence anion selective exchange membrane MVA is separated, the concentrated water compartment and the product 2 compartment are separated by a monovalent cation selective exchange membrane MVK, and the product 2 compartment and the desalination compartment are separated by a cation exchange membrane SK , the desalination chamber is separated from the product 1 chamber of the next unit by an anion exchange membrane SA; each of the units is separated from the anode electrode chamber and the cathode electrode chamber by a polar film PC-SC;

The anode electrode chamber and the cathode electrode chamber are respectively connected to the positive electrode and the negative electrode of the DC power supply, and the anode electrode chamber, the cathode electrode chamber, the chamber and the DC power supply form a series loop, so that the chamber Under the action of the current, a divalent anion enrichment solution is obtained in the product 1 chamber, a divalent cation enrichment solution is obtained in the product 2 chamber, and a monovalent ion enrichment solution is obtained in the concentrated water chamber liquid, and desalinated water is obtained in the desalination chamber.

Further, the two sides of the product 1 chamber are a monovalent selective anion exchange membrane MVA and an anion exchange membrane SA, and a divalent anion enrichment solution is obtained in the product 1 chamber, which is a phosphate enrichment solution; the product 2 Both sides of the chamber are monovalent selective cation exchange membrane MVK and cation exchange membrane SK, and the divalent cation enrichment solution is obtained in the product 2 chamber, which is rich in calcium, magnesium ions, and part of ammonium salts and part of potassium salts. Collecting liquid; both sides of the concentrated water chamber are anion exchange membrane SA and cation exchange membrane SK, and monovalent ion enrichment solution is obtained in the concentrated water chamber, which is enriched solution rich in part of ammonium salt and part of potassium salt.

Further, in the selective electrodialysis system, the product 1 chamber of each unit is connected to the product 1 chamber feed tank, and the product 2 chamber of each unit is connected to the product 2 chamber feed liquid. The concentrated water chamber of each of the units is connected to the concentrated water chamber material tank, and the desalination chamber of each of the units is connected to the desalination chamber material tank, so as to realize the selective electrodialysis system. All the circulation of the feed liquid in the product 1 chamber, all the circulation of the feed liquid in the product 2 chamber, all the circulation of the feed liquid in the concentrated water chamber, and all the circulation of the feed liquid in the desalination chamber; the anode electrode chamber and The cathode electrode chamber is connected to the electrode liquid tank to realize the circulation of the electrode liquid, with a total of 5 circulation loops, wherein the feed liquid in the desalination chamber, the product 1 chamber, the product 2 chamber and the concentrated water chamber The flow is in parallel in the same direction, and the flow of the electrode liquid in the anode electrode chamber and the cathode electrode chamber is in reverse series.

Further, the raw water is added to the feed liquid tank of the desalination chamber for circulation, and an equal volume of a strong electrolyte solution with an electrical conductivity of not less than 5mS/cm is added to the feed liquid tank of the product 1 chamber and the product 2 chamber respectively. Circulation is carried out in the feed liquid tank and the feed liquid tank of the concentrated water chamber feed liquid tank, and the electrode liquid with an electrical conductivity of not less than 5mS/cm is added to the electrode liquid tank, and the anode electrode chamber and the cathode electrode are placed in the anode electrode chamber and the cathode electrode. Circulation is performed in the chamber; DC current is applied to the selective electrodialysis system through the DC power supply to carry out the selective electrodialysis process, and finally the desalinated water is obtained in the feed liquid tank of the desalination chamber, and the product 1 chamber Divalent anion enrichment solution, divalent cation enrichment solution, and monovalent ion enrichment solution are obtained from the feed solution tank, the product 2-chamber feed solution tank and the feed solution tank of the concentrated water chamber feed solution tank, respectively.

Further, the use of the enriched liquid to produce chemical fertilizers includes: step 1) mixing the feed liquid obtained in the product 1 room with the feed liquid obtained in the product 2 room in proportion, adjusting the pH, and obtaining the precipitation of magnesium ammonium phosphate, and the clear liquid enters the next step. Procedure; Step 2) mix the clear liquid obtained in step 1) with the feed liquid obtained in the concentrated water chamber, adjust pH, and evaporate, and the evaporated gas is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated liquid crystallizes into potassium salt.

Further, in step 1), the pH is adjusted to be greater than or equal to 8.00, preferably 10.00-14.00;

Optionally, in step 2), the pH is adjusted to be greater than or equal to 10.00, preferably 12.00-14.00;

Optionally, in step 2), the evaporation is reduced pressure evaporation, the gas obtained by evaporation is passed into sulfuric acid to absorb the ammonia gas therein, and the evaporated liquid crystallizes into potassium salt.

Further, the use of the enriched liquid to produce chemical fertilizer includes: step 1) adjusting the pH of the feed liquid obtained in the product 2 chamber, and evaporating, the evaporated gas is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated solid enters the next process; Step 2) Add the solid obtained in step 1) to the feed liquid obtained in the product 1 chamber, adjust the pH, and precipitate the solid obtained as calcium phosphate and magnesium phosphate; step 3) Adjust the pH of the feed liquid obtained in the concentrated water chamber, and evaporate , the gas obtained by evaporation is absorbed by sulfuric acid to obtain ammonium sulfate, and the liquid crystallized after evaporation is potassium salt.

Further, in step 1) and/or step 3), the pH is adjusted to be greater than or equal to 10.00, preferably 12.00-14.00;

Optionally, in step 2), the pH is adjusted to be greater than or equal to 9.00, preferably 10.00-14.00;

Optionally, in step 1) and/or step 3), the evaporation is reduced pressure evaporation, and the gas obtained by evaporation is passed into sulfuric acid to absorb the ammonia gas therein.

Beneficial effects:

The method for producing fertilizer by electrodialysis of the present invention uses selective electrodialysis to obtain different types of high-salinity concentrates from anaerobic biogas slurry, and realizes the multi-stage recycling of different components, and it is difficult to directly The anaerobic biogas slurry used is prepared into a variety of high-value fertilizers to fully utilize the biogas slurry resources.

Description of drawings

In order to illustrate the technical solutions of the present invention more clearly, the accompanying drawings will be briefly introduced below. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present invention, rather than limit the present invention.

Fig. 1 is a schematic flow chart of scheme one provided by the invention;

Fig. 2 is the schematic flow chart of scheme two provided by the present invention;

3 is a schematic diagram of the principle of a selective electrodialysis system provided by an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a continuous processing device provided in Embodiment 2 of the present invention.

Detailed ways

Preferred embodiments of the present invention will be described in more detail below. While preferred embodiments of the present invention are described below, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. If no specific technology or condition is indicated in the examples, the technology or condition described in the literature in the field or the product specification is used. The reagents or instruments used without the manufacturer's indication are conventional products that can be obtained from the market. In the following examples, "%" refers to weight percentage unless otherwise specified.

Example 1

A continuous method for selective electrodialysis of biogas slurry, comprising the following steps: pretreatment of biogas slurry to remove suspended particulate matter and colloid in the biogas slurry to obtain raw water. The way of pretreatment can include coagulation sedimentation, filtration, ultrafiltration/microfiltration.

After that, the raw water is fed into the selective electrodialysis system for operation. Refer to Figure 3 for the working principle of the selective electrodialysis system. The selective electrodialysis system includes an anode electrode chamber, a cathode electrode chamber, and a chamber disposed between the anode electrode chamber and the cathode electrode chamber. The chamber includes N parallel units, and N is a positive integer. Each unit has the same structure, including product 1 chamber, concentrated water chamber, product 2 chamber and desalination chamber arranged in sequence; product 1 chamber and concentrated water chamber are separated by a monovalent anion selective exchange membrane MVA, and concentrated water chamber and product The 2 compartment is separated by a monovalent cation selective exchange membrane MVK, the product 2 compartment is separated from the desalination compartment by a cation exchange membrane SK, and the desalination compartment is separated from the product 1 compartment of the next unit by an anion exchange membrane SA; each unit is It is separated from the anode electrode chamber and the cathode electrode chamber by the polar film PC-SC;

The anode electrode chamber and the cathode electrode chamber are respectively connected to the positive electrode and the negative electrode of the DC power supply. The anode electrode chamber, the cathode electrode chamber, the chamber and the DC power supply form a series circuit, so that the current passes through the chamber, and under the action of the current, in the product 1 chamber Divalent anion enrichment solution is obtained, divalent cation enrichment solution is obtained in the product 2 chamber, monovalent ion enrichment solution is obtained in the concentrated water chamber, and after the conductivity is ≤0.5mS/cm in the desalination chamber, the ammonia nitrogen concentration is ≤20mg/ L, desalinated water with total phosphorus concentration ≤5mg/L.

The system can process the biogas slurry after anaerobic fermentation, the conductivity is 2-50mS/cm, the ammonia nitrogen concentration is 100-5000mg/L, and the total phosphorus concentration is 5-200mg/L, preferably: the conductivity is 10-50mS/L cm, ammonia nitrogen concentration is 1000-5000mg/L, and total phosphorus concentration is 20-200mg/L.

Example 2

In order to realize the process method in Example 1, refer to Fig. 4 to design a continuous treatment device, including a screw stacker, a filter tank and a desalination chamber feed tank F, and the three are connected in sequence, wherein the inlet of the screw stacker is connected to the biogas slurry, The desalination chamber feed tank F is connected to the selective electrodialyser SED.

The selective electrodialyser SED includes an anode electrode chamber, a cathode electrode chamber, and a chamber disposed between the anode electrode chamber and the cathode electrode chamber. The chamber includes N parallel units, and N is a positive integer. For ease of description, a selective electrodialyser SED comprising 1 unit is described below; in other embodiments, N is a positive integer of 10-1000, preferably a positive integer of 100-800.

The chamber in the selective electrodialyzer SED includes product 1 chamber, concentrated water chamber, product 2 chamber and desalination chamber; the product 1 chamber and the concentrated water chamber are separated by a monovalent anion selective exchange membrane MVA, and the concentrated water chamber and the product The 2 compartment is separated by a monovalent cation selective exchange membrane MVK, and the product 2 compartment and the desalination compartment are separated by a cation exchange membrane SK. The product 1 chamber is connected to the product 1 chamber feed tank AP, the product 2 chamber is connected to the product 2 chamber feed tank CP, the concentrated water chamber is connected to the concentrated water chamber feed tank B, and the desalination chamber is connected to the desalination chamber feed tank F. The anode electrode chamber and the cathode electrode chamber are respectively connected to the electrode liquid tank R, and the electrode liquid tank is used for storing and circulating the electrode liquid.

Preferably, the selective electrodialysis device SED is also connected to the acid cleaning tank AC, which is used for storing the acid solution for cleaning the electrodialysis membrane module.

The use method of the above device is as follows: the biogas slurry enters the screw stacker after coagulation to remove suspended solids and insoluble substances therein, and then secondary filtration in the filter tank obtains raw water suitable for electrodialysis treatment, and the raw water enters the desalination chamber. Slot pending.

The raw water enters the desalination chamber of the selective electrodialyser SED in the feed tank of the desalination chamber for circulation, and an equal volume of strong electrolyte solution with a conductivity of not less than 5mS/cm is added to the feed liquid tank of product 1 chamber and the material of product 2 chamber respectively. Circulate in the liquid tank and the liquid tank of the concentrated water chamber, add the electrode liquid with a conductivity of not less than 5mS/cm into the electrode liquid tank, and circulate in the anode electrode chamber and the cathode electrode chamber; through the DC power supply to the selective electrodialysis The system applies direct current to carry out the selective electrodialysis process, and finally the desalinated water is obtained in the feed tank of the desalination chamber. Divalent anion enrichment solution, divalent cation enrichment solution, and monovalent ion enrichment solution.

It should be noted that only one unit is illustrated in this device, so the above-mentioned circulation means that the feed liquid circulates between the feed liquid tank and the corresponding chamber. In essence, when the number of units N>1, the circulation is between N units, that is, the circulation of the feed liquid in all products 1 in the selective electrodialysis system, the circulation of feed liquid in all products 2, and the feed liquid in all concentrated water. circulation, as well as the circulation of all liquids in the desalination chamber. At the same time, the anode electrode chamber and the cathode electrode chamber are connected to the electrode liquid tank to realize the circulation of the electrode liquid, a total of 5 circulation loops, among which the flow of the feed liquid in the desalination chamber, the product 1 chamber, the product 2 chamber and the concentrated water chamber is parallel in the same direction. , the flow of the electrode liquid in the anode electrode chamber and the cathode electrode chamber is reverse series.

The discharging method of the system is described below. During the electrodialysis process, when the conductivity of the biogas slurry in the feed tank of the desalination chamber drops to 0.5 mS/cm, part of the solution in the feed tank of the desalination chamber (the discharged part is the desalinated water) is discharged. ), and add fresh raw water; when the volume ratio of the raw water entering the selective electrodialysis system to the volume ratio of the solution in the feed liquid tank of the product 1 room reaches more than 10, discharge the solution in the feed liquid tank of the product 1 room, and add Fresh strong electrolyte solution with the same volume as the discharge solution; when the volume ratio of the raw water entering the selective electrodialysis system to the volume ratio of the solution in the feed liquid tank of the product 2 chamber reaches more than 10, the solution in the feed liquid tank of the product 2 chamber is discharged , and add a fresh strong electrolyte solution with the same volume as the discharged solution; when the conductivity of the solution in the feed tank of the concentrated water chamber is greater than 90mS/cm, discharge the solution in the feed tank of the concentrated water chamber, and add the same volume as the discharged solution. Fresh strong electrolyte solution to ensure continuous operation of selective electrodialysis system.

Through the above method, different products can be discharged from the system separately without interfering with each other, ensuring the continuous operation of the entire system.

Further, in order to maintain the liquid circulation in the pipeline, when the selective electrodialysis system discharges the solution, the relative speed of the feed liquid added and the discharged feed liquid is adjusted to retain 10-20 volume% of the feed liquid in the selective electrodialysis system. pipes and/or membrane stacks.

Example 3

The device in Example 2 is used, with 400 units (N=400), to process anaerobic biogas slurry in a pig farm, with a processing capacity of 5m ³ /day, as follows:

After the anaerobic biogas slurry is pretreated by coagulation, sedimentation and filtration, the raw water contains 1900 mg/L ammonia nitrogen, 25 mg/L phosphate, 890 mg/L potassium, 75 mg/L calcium, and 30 mg/L magnesium. In an electrodialysis system, the continuous concentration and separation of ions is carried out at a constant voltage. When the conductivity of the solution in the feed tank of the desalination chamber is less than 0.5mS/cm, since the feed tank of the desalination chamber is connected to each desalination chamber of the electrodialysis system, each desalination chamber has produced desalinated water that meets the discharge requirements and can be discharged Part of the solution in the feed tank of the desalination chamber is added, and the next batch of raw water is added for electrodialysis. At this time, by detecting the phosphate concentration in the feed tank of the product 1 chamber, the phosphate concentration in the product 1 chamber can be obtained, which is 226 mg/L. Similarly, it can be known from the detection that the ammonia concentration in the concentrated water chamber is 9680 mg/L. , the potassium concentration is 4586mg/L, the calcium ion concentration in the product 2 chamber is 358mg/L, and the magnesium ion concentration is 114mg/L, which have basically reached the goal of concentration and enrichment, and can be discharged in time, or at the next batch processing. .

The specific working process of the system is described below: the anaerobic biogas slurry is continuously fed into the screw stacker to remove suspended solids and insoluble substances therein, and then secondary filtration is performed in the filter tank to obtain raw water suitable for electrodialysis treatment. It acts as a temporary storage tank for raw water. A valve is set between the filter tank and the desalination chamber material tank. The supernatant in the filter tank is controlled by the valve to enter the desalination chamber material tank in batches, so as to enter the electrodialysis system for circulating treatment. , the process is as follows:

Open the valve between the filter tank and the feed liquid tank of the desalination chamber, add 1000L of raw water obtained after biogas slurry pretreatment into the feed liquid tank of the desalination chamber for circulation, and circulate to the feed liquid tank of the product 1 room, the feed liquid tank of the product 2 room, and the concentrated liquid tank of the product 2 room. 500L of NaCl solution with a concentration of 15g/L was added to the water chamber feed tank for circulation, and 500L of sodium sulfamate solution with a concentration of 0.5mol/L was added to the electrode chamber (electrode liquid tank in Figure 4) for circulation; The DC power supply applies a constant DC voltage to the selective electrodialysis system to carry out the selective electrodialysis process to separate and concentrate the nutrient ions such as phosphate, ammonia nitrogen and potassium salt in the biogas slurry. The density of the direct current is 10-200 A/m ² , preferably 100 A/m ² .

When the conductivity of the solution in the feed tank of the desalination chamber drops to 0.5mS/cm, discharge 1000L of the solution in the feed tank of the desalination chamber (that is, desalinated water), and add 1000L of fresh biogas slurry (that is, pretreated by coagulation, sedimentation, filtration, etc.) After the raw water), continue the electrodialysis process. The discharge rules for other chambers are as follows: when the volume ratio of the raw water entering the selective electrodialysis system to the volume ratio of the solution in the feed liquid tank of the product 1 chamber reaches more than 10, the solution in the feed liquid tank of the product 1 chamber is discharged, and the same The fresh strong electrolyte solution of the same volume of the solution is discharged; when the volume ratio of the raw water entering the selective electrodialysis system to the volume ratio of the solution in the feed liquid tank of the product 2 chamber reaches more than 10, the solution in the feed liquid tank of the product 2 chamber is discharged, And add fresh strong electrolyte solution with the same volume as the discharged solution; when the conductivity of the solution in the feed tank of the concentrated water chamber is > 90mS/cm, discharge the solution in the feed tank of the concentrated water chamber, and add the same volume of fresh solution as the discharged solution. Strong electrolyte solution to ensure continuous operation of selective electrodialysis system.

When the accumulated volume of biogas slurry reaches 5000L, at this time, due to the influence of resistance such as osmotic pressure, the efficiency of electrodialysis decreases, and the material liquid in the material liquid tank of product 1 room, the material liquid tank of product 2 room, and the material liquid tank of concentrated water room is discharged to Subsequent fertilizer preparation process, thereby improving the efficiency of subsequent electrodialysis.

In order to maintain the liquid circulation in the pipeline, when the selective electrodialysis system discharges the solution, by adjusting the relative speed of the feeding liquid and the discharged material liquid, 10-20 volume% of the feeding liquid is retained in the corresponding pipeline and/or the selective electrodialysis system. Or in the membrane stack, to maintain the continuity of electrodialysis.

Example 4

Utilize the enrichment solution obtained in Example 3, namely discharge the 2L enriched solution produced from the feed liquid tank of product 1 chamber, the feed liquid tank of product 2 chamber, and the feed liquid tank of concentrated water chamber, wherein the material of product 1 chamber is The liquid contains 226 mg/L of phosphate, the feed liquid of the concentrated water chamber contains 9680 mg/L of ammonia, 4586 mg/L of potassium, and the feed liquid of the product 2 chamber contains 358 mg/L of calcium ions and 114 mg/L of magnesium ions.

Mix 200 mL of product 1-chamber feed solution with 300 mL of product 2-chamber feed solution, adjust pH to 9.50, and let stand for precipitation. According to XRD analysis, the obtained solid is NH ₄ MgPO ₄ ·6H ₂ O, and the recovery efficiency of phosphate is greater than 96.70%. Take the supernatant, adjust the pH to 11.09, perform rotary evaporation under a water bath at 80°C, and absorb the evaporated gas in 200 mL of 10% sulfuric acid. The solid obtained by evaporation is NaCl by XRD analysis, and the solid obtained by concentrating and crystallizing the absorption liquid is (NH ₄ ) ₂ SO ₄ by XRD analysis.

Take 500 mL of concentrated water chamber feed liquid, adjust the pH to 10.00, and perform rotary evaporation in a water bath at 80°C. The gas obtained by evaporation is absorbed by 200 mL of 10% sulfuric acid, and the ammonia nitrogen recovery efficiency is greater than 71.26%. The absorption liquid was concentrated and crystallized, and the obtained solids were analyzed by XRD to be (NH ₄ ) ₂ SO ₄ and NH ₄ HSO ₄ .

Example 5

Using the enriched solution obtained in Example 3, the 2L enriched solution produced is discharged from the feed liquid tank of product 1 room, the material liquid tank of product 2 room, and the feed liquid tank of concentrated water chamber, wherein the feed liquid of product 1 room is discharged It contains 226 mg/L of phosphate, 9680 mg/L of ammonia and 4586 mg/L of potassium in the feed liquid of the concentrated water chamber, 358 mg/L of calcium ions and 114 mg/L of magnesium ions in the feed liquid of the product 2 chamber.

The pH of 200 mL of the feed liquid in the product 2 chamber was adjusted to 11.00, and it was rotary evaporated in a water bath at 80°C, and the gas generated by evaporation was absorbed by 200 mL of 10% sulfuric acid. The solid obtained by evaporation was added to 400 mL of product 1-chamber feed solution to dissolve, the pH was adjusted to 9.00, and the mixture was left to stand and centrifuge for precipitation. The precipitate was analyzed by XRD as a mixture of calcium phosphate and magnesium phosphate. Get supernatant and mix with concentrated water chamber feed liquid, adjust pH to 10.00, under 80 ℃ of water baths, rotary evaporation, the gas that evaporates obtains is absorbed through 200mL 10% sulfuric acid, and the absorption liquid is through concentrated crystallization, and the solid obtained is through XRD analysis ( NH ₄ ) ₂ SO ₄ and NH ₄ HSO ₄ .

The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention. These simple modifications All belong to the protection scope of the present invention.

In addition, it should be noted that each specific technical feature described in the above-mentioned specific implementation manner may be combined in any suitable manner under the circumstance that there is no contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

In addition, the various embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the contents disclosed in the present invention.

Claims

A method for producing fertilizer by electrodialysis, which is characterized in that: pretreatment of biogas slurry to remove suspended particles and colloids in the biogas slurry to obtain raw water, and then feeding the raw water into a selective electrodialysis system for operation, An ion exchange membrane is set in the selective electrodialysis system, so as to separate the raw water to obtain a divalent anion enrichment solution, a divalent cation enrichment solution, a monovalent ion enrichment solution and desalinated water, wherein the desalinated water meets the discharge standard , the use of enrichment liquid to produce fertilizers, including:

The pH of the monovalent ion enrichment solution is adjusted, followed by evaporation treatment, the evaporated gas is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated liquid crystallizes to obtain solid potassium salt.
The method for producing fertilizer by electrodialysis according to claim 1, wherein the biogas slurry is biogas slurry after anaerobic fermentation, the conductivity is 2-50mS/cm, the ammonia nitrogen concentration is 100-5000mg/L, the total phosphorus The concentration is 5-200mg/L, and the potassium concentration is 50-1500mg/L.
The method for producing fertilizer by electrodialysis according to claim 1 or 2, characterized in that: the selective electrodialysis system comprises an anode electrode chamber and a cathode electrode chamber arranged oppositely, and the anode electrode chamber and the cathode electrode are arranged in the anode electrode chamber and the cathode electrode chamber. The chamber between the electrode chambers is composed; the chamber includes N parallel units, N is a positive integer, and each unit has the same structure, including a product 1 chamber, a concentrated water chamber, a product 2 chamber and Desalination chamber; the product 1 chamber and the concentrated water chamber are separated by a monovalent anion selective exchange membrane MVA, and the concentrated water chamber and the product 2 chamber are separated by a monovalent cation selective exchange membrane MVK, so The product 2 chamber and the desalination chamber are separated by a cation exchange membrane SK, and the desalination chamber and the product 1 chamber of the next unit are separated by an anion exchange membrane SA; each of the units is separated from the anode electrode chamber, The cathode electrode chamber is separated by a polar film PC-SC;

The anode electrode chamber and the cathode electrode chamber are respectively connected to the positive electrode and the negative electrode of the DC power supply, and the anode electrode chamber, the cathode electrode chamber, the chamber and the DC power supply form a series loop, so that the chamber Under the action of the current, a divalent anion enrichment solution is obtained in the product 1 chamber, a divalent cation enrichment solution is obtained in the product 2 chamber, and a monovalent ion enrichment solution is obtained in the concentrated water chamber liquid, and the desalinated water is obtained in the desalination chamber.
The method for producing fertilizer by electrodialysis according to claim 3, wherein the two sides of the product 1 chamber are a monovalent selective anion exchange membrane MVA and an anion exchange membrane SA, and the product 1 chamber obtains a divalent anion rich The liquid collection is a phosphate enrichment solution; the two sides of the product 2 chamber are monovalent selective cation exchange membrane MVK and cation exchange membrane SK, and a divalent cation enrichment solution is obtained in the product 2 chamber, which is rich in calcium , magnesium ions, and the enrichment solution of part ammonium salt and part potassium salt; both sides of the concentrated water chamber are anion exchange membrane SA and cation exchange membrane SK, and monovalent ion enrichment solution is obtained in the concentrated water chamber, which is An enrichment solution rich in part ammonium salts and part potassium salts.
The method for producing fertilizer by electrodialysis according to claim 4, characterized in that: in the selective electrodialysis system, the product 1 chamber of each of the units is connected to the product 1 chamber feed tank, and each of the product 1 chambers The product 2 chamber of the unit is connected to the product 2 chamber feed tank, the concentrated water chamber of each unit is connected to the concentrated water chamber feed tank, and the desalination chamber of each unit is connected to the desalination chamber Feed tank to realize the circulation of feed liquid in all the product 1 chambers in the selective electrodialysis system, the circulation of feed liquid in all the product 2 chambers, the circulation of feed liquid in all the concentrated water chambers, and the circulation of all feed liquids in the concentrated water chamber. The circulation of the feed liquid in the desalination chamber; the anode electrode chamber and the cathode electrode chamber are connected to the electrode liquid tank to realize the circulation of the electrode liquid, a total of 5 circulation loops, wherein the desalination chamber, the product 1 chamber, the The flow of the feed liquid in the product 2 chamber and the concentrated water chamber is in parallel in the same direction, and the flow of the electrode liquid in the anode electrode chamber and the cathode electrode chamber is in reverse series.
The method for producing fertilizer by electrodialysis according to claim 5, characterized in that: adding the raw water to the feed liquid tank of the desalination chamber for circulation, and adding a strong electrolyte solution with an equal volume of electrical conductivity not less than 5mS/cm into the Circulation is carried out in the feed liquid tank of the product 1 chamber, the product 2 chamber feed tank and the feed liquid tank of the concentrated water chamber, and an electrode solution with a conductivity of not less than 5mS/cm is added to the electrode The liquid tank is circulated in the anode electrode chamber and the cathode electrode chamber; DC current is applied to the selective electrodialysis system through the DC power supply to carry out the selective electrodialysis process, and finally the material in the desalination chamber is The desalinated water is obtained in the liquid tank, and the feed liquid tank of the product 1 room, the product 2 room material tank and the feed tank of the concentrated water room material tank respectively obtain a divalent anion enrichment solution, and the divalent anion enrichment solution is obtained. Cation enrichment solution, and monovalent ion enrichment solution.
The method for producing fertilizer by electrodialysis according to any one of claims 4-6, characterized in that: the use of enriched liquid to produce chemical fertilizer comprises: step 1) the feed liquid obtained in product 1 room and the material obtained in product 2 room The liquid is mixed in proportion, and the pH is adjusted to obtain the precipitation of magnesium ammonium phosphate, and the clear liquid enters the next process; step 2) mix the clear liquid obtained in step 1) with the feed liquid obtained in the concentrated water chamber, adjust the pH, evaporate, and evaporate The latter gas is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated liquid crystallizes into potassium salt.
The method for producing fertilizer by electrodialysis according to claim 7, characterized in that: in step 1), the pH is adjusted to be greater than or equal to 8.00.
The method for producing fertilizer by electrodialysis according to claim 8, characterized in that: in step 1), pH is adjusted to be 10.00-14.00.
The method for producing fertilizer by electrodialysis according to any one of claims 7-9, characterized in that: in step 2), the pH is adjusted to be greater than or equal to 10.00.
The method for producing fertilizer by electrodialysis according to claim 10, characterized in that: in step 2), the pH is adjusted to be 12.00-14.00.
According to the method for producing fertilizer by electrodialysis according to any one of claims 7-11, it is characterized in that: in step 2), the evaporation is reduced pressure evaporation, and the gas obtained by evaporation is passed into sulfuric acid to absorb ammonia gas therein, and evaporated The resulting liquid crystallizes as potassium salt.
The method for producing fertilizer by electrodialysis according to any one of claims 4-12, characterized in that: the use of enriched liquid to produce chemical fertilizer comprises: step 1) adjusting the pH of the feed liquid obtained in the product 2 chamber, and evaporating , the evaporated gas is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated solid enters the next process; step 2) the solid obtained in step 1) is added to the feed liquid obtained in product 1 chamber, the pH is adjusted, and the solid obtained by precipitation is phosphoric acid Calcium and magnesium phosphate; Step 3) Adjust the pH of the feed liquid obtained in the concentrated water chamber and evaporate, and the gas obtained by evaporation is absorbed by sulfuric acid to obtain ammonium sulfate, and the evaporated liquid crystallizes into potassium salt.
The method for producing fertilizer by electrodialysis according to claim 13, characterized in that: in step 1) and/or step 3), the pH is adjusted to be greater than or equal to 10.00.
The method for producing fertilizer by electrodialysis according to claim 14, characterized in that: in step 1) and/or step 3), the pH is adjusted to 12.00-14.00.
The method for producing fertilizer by electrodialysis according to any one of claims 13-15, characterized in that: in step 2), the pH is adjusted to be greater than or equal to 9.00.
The method for producing fertilizer by electrodialysis according to claim 16, characterized in that: in step 2), the pH is adjusted to be 10.00-14.00.
According to the method for producing fertilizer by electrodialysis according to any one of claims 13-17, it is characterized in that: in step 1) and/or step 3), the evaporation is reduced pressure evaporation, and the gas obtained by evaporation is passed into sulfuric acid for absorption Ammonia in it.