CN114291875B - Method for recycling and purifying ammonia nitrogen by using flowing electrode capacitor based on monovalent cation exchange membrane - Google Patents
Method for recycling and purifying ammonia nitrogen by using flowing electrode capacitor based on monovalent cation exchange membrane Download PDFInfo
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- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims abstract description 17
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Abstract
The invention relates to a monovalent cation exchange membrane-based flow electrode capacitance ammonia nitrogen recovery and purification method, which comprises the steps of supplying wastewater to be treated to a desalting chamber, applying voltage to an anode flow electrode chamber and a cathode flow electrode chamber, enabling anions to pass through an anion exchange membrane to enter the anode flow electrode chamber through an electro-adsorption effect, and containing NH 4 + Through the monovalent cation exchange membrane into the cathode flow electrode chamber and within the cathode flow electrode chamber, utilize a cathodic faraday reaction to promote NH on the electrode 4 + To NH 3 And converting and desorbing to obtain high-purity ammonia water. Compared with the prior art, the method has the advantages of simple operation, high deamination efficiency, good recovery effect, high product purity, effective inhibition of scaling, stable operation and the like, can realize recovery of ammonia nitrogen in the coal gasification grey water in the form of ammonia water on the premise of not increasing energy consumption, not increasing cost, not adding chemical agents and facilitating subsequent treatment, and has very important significance for development of the coal gasification industry.
Description
Technical Field
The invention belongs to the technical field of application of a flow electrode capacitance deionization technology and water treatment, relates to a flow electrode capacitance ammonia nitrogen recovery and purification method based on a monovalent cation exchange membrane, and particularly relates to a method for recovering ammonia nitrogen in coal gasification grey water by using a flow electrode capacitance deionization technology of a coupling monovalent cation exchange membrane.
Background
Coal gasification technology is widely used throughout the world. The domestic energy structure of rich coal, lean oil and less gas makes the coal gasification industry develop vigorously. However, the coal gasification process can produce a large amount of coal gasification grey water which contains a large amount of ammonia nitrogen, phenol, polycyclic aromatic hydrocarbon, cyanide and the like, so that the biodegradability of the wastewater is reduced. The treatment of low C/N wastewater in wastewater treatment systems is often limited due to the inhibition of nitrification. It has been reported that 250 ten thousand tons of ammonia nitrogen are discharged into water each year in China, resulting in serious eutrophication and acute or chronic toxicity to aquatic organisms. In addition, nitrogen demand is expected to increase further due to global population growth and increased living standards. Therefore, ammonia nitrogen should be recovered to improve the biodegradability of coal gasification grey water, and realize sustainable development of global environment. In addition, the gray water has the characteristic of high hardness. Thus, the scaling problem is important in treating coal gasification grey water.
At present, gas stripping, forward osmosis, electrodialysis and the like are adopted for recycling ammonia nitrogen from sewage (waste) water. The stripping requires a large amount of reagent input and has high cost. And stripping columns face fouling challenges. Forward osmosis has high-efficiency water recovery and ammonia nitrogen concentration performance; however, the forward osmosis membrane has a high rejection capacity for all ions, and thus the purity of the ammonia nitrogen product reduces its economic value. ED has proven to require large amounts of chemicals to adjust pH. Therefore, there is a need for a simple and economical technique for selectively separating and recovering high purity ammonia nitrogen from wastewater.
In recent years, technologies based on Capacitive Deionization (CDI) have brought about academic research hotspots in the field of recycling resources due to their low cost, environmental protection, easy electrode management, high water recovery rate, and the like. Flow electrode capacitive deionization (FCDI)The flowing electrode suspension bans the fixed electrodes of CDI and MCDI, and the fluidity of the electrodes allows it to be regenerated outside the FCDI, thus FCDI has the potential to be continuously desalinated and scaled. FCDI has been used to recover ammonia nitrogen from sewage (wastewater) but the recovered product is a low purity ammonium salt. Compared with ammonium salt, the application range of ammonia water is wider, and the added value is higher. Also have studied to utilize NH 4 + And NH 3 The pH-dependent equilibrium reaction between them achieves the production of ammonia-rich solutions, but the grade of the product is lower. In contrast, the ammonia nitrogen concentration in the gasified ash water is higher and the gasified ash water contains Ca with high concentration 2+ Therefore, the operation mode which has high denitrification efficiency, good recovery effect and high product purity and can effectively inhibit scaling of the device and the flowing electrode capacitance deionizing device matched with the operation mode are obtained, and the operation mode has very important significance for stably recovering ammonia nitrogen in coal gasification grey water with low cost, low energy consumption and high efficiency.
Disclosure of Invention
The invention aims to provide the method for recovering and purifying the ammonia nitrogen by the flowing electrode capacitance based on the monovalent cation exchange membrane, which has the advantages of simple operation, no need of adding chemical agents, high deamination efficiency, good recovery effect, high product purity, effective scale inhibition, low treatment cost, low treatment energy consumption, stable operation and no secondary pollution.
The aim of the invention can be achieved by the following technical scheme:
a method for recovering and purifying ammonia nitrogen by using a flow electrode capacitor based on a monovalent cation exchange membrane comprises the steps of adopting an FCDI device coupled with the Monovalent Cation Exchange Membrane (MCEM) to treat wastewater to be treated;
the FCDI device comprises a cathode flowing electrode chamber, a monovalent cation exchange membrane, a desalting chamber, an anion exchange membrane and an anode flowing electrode chamber which are sequentially arranged in parallel, wherein the anode flowing electrode chamber is internally provided with an anode flowing electrode, and the cathode flowing electrode chamber is internally provided with a cathode flowing electrode;
the recovery and purification method specifically comprises the following steps:
supplying wastewater to be treated to a desalination chamber, and flowing the wastewater to an anode flow electrode chamber and a cathode flow electrode chamberApplying a voltage to cause anions to pass through the anion exchange membrane into the anode flow electrode chamber by electro-adsorption, comprising NH 4 + Through the monovalent cation exchange membrane into the cathode flow electrode chamber and within the cathode flow electrode chamber, utilize a cathodic faraday reaction to promote NH on the electrode 4 + To NH 3 And converting and desorbing to obtain high-purity ammonia water.
Wherein the monovalent cation exchange membrane can isolate anions on one hand and can effectively prevent Ca in wastewater to be treated on the other hand 2+ 、Mg 2+ 、Fe 3+ The plasma enters the cathode chamber, thereby effectively slowing down scaling.
Further, an anode circulation chamber is arranged outside the anode flowing electrode chamber, and the anode flowing electrode circularly flows between the anode flowing electrode chamber and the anode circulation chamber;
the cathode flowing electrode chamber is provided with a cathode circulating chamber outside, and the cathode flowing electrode circularly flows between the cathode flowing electrode chamber and the cathode circulating chamber.
Further, the anode flow electrode and the cathode flow electrode both comprise a conductive agent and a solvent; the conductive agent comprises at least one of active carbon and carbon black, and the solvent comprises water.
Further, the conductive agent is a mixture of active carbon and carbon black in a mass ratio of 4:1, and the mass fraction (i.e. carbon content) of the conductive agent in the anode flow electrode or the cathode flow electrode is not more than 10%, preferably not more than 5%, and more preferably 2-5%.
Further, the circulation flow rate of the anode flow electrode or the cathode flow electrode is 20-100mL/min.
Further, the hydraulic retention time of the wastewater to be treated flowing through the desalting chamber is 0.5-1.5min.
Further, the recovery and purification method further comprises the following steps: after the positive voltage is applied to the anode flow electrode chamber and the cathode flow electrode chamber for charging, the reverse voltage is applied to the anode flow electrode chamber and the cathode flow electrode chamberDischarge is carried out by pressing, so that Na in the cathode flowing electrode chamber + 、K + The equivalent monovalent cations are forced back to the desalination chamber, thereby improving the purity of the ammonia water in the cathode flow electrode chamber.
Further, the forward voltage is 1.2-4.5V, and the electrifying time is 75-85min;
the reverse voltage is 0.1-0.3V, and the electrifying time is 10-30min.
Further preferably, the recovery and purification method further comprises: the operation steps of introducing coal gasification water, applying forward voltage and applying reverse voltage are repeated to increase the ammonia concentration in the cathode flowing electrode chamber.
The invention provides a method for recycling ammonia nitrogen in wastewater to be treated (especially coal gasification grey water) by using a flow electrode capacitive deionization (FCDI) technology of a coupling Monovalent Cation Exchange Membrane (MCEM), which adopts an FCDI device of the coupling Monovalent Cation Exchange Membrane (MCEM) to treat the wastewater to be treated. Wherein the MCEM effectively slows down scaling, and realizes recycling of ammonia nitrogen in wastewater to be treated in the form of ammonia water by simply adjusting the charge-discharge process.
Compared with the prior art, the invention has the following characteristics:
1) The invention skillfully uses the pH change brought by the independent closed circulation mode: since the anode flow electrode and the cathode flow electrode are respectively recycled in the respective pipes, the faraday reaction causes the cathode compartment pH to rise and the anode compartment pH to fall. When pK (pK) a >9.3 NH 4 + More easily converted into NH 3(aq) . The NH is generated in the charging process by simply adjusting the charging and discharging process 3(aq) The purity of the product is improved in the reverse discharge process. That is, NH is first made by powering up the FCDI 4 + And Na (Na) + Migrate to the cathode chamber while the pH rise caused by Faraday reaction causes NH 4 + Conversion to NH 3(aq) Then reverse discharge will charge Na + The desalination chamber is forced to return, so that the purity of the ammonia water is improved;
2) According to the invention, by optimizing the voltage applied in the charging process to 4.5V, the removal rate and the removal efficiency are respectively improved by 23% and 12% compared with 1.2V and 4.5V, so that the effluent ammonia nitrogen accords with the standard (GB/T31962-2015) that industrial wastewater enters the municipal sewage pipeline, and at the same time, under the charging voltage, carbon particles of the cathode are not oxidized, and the reason is that the resistances of different CDI components are different, so that the electrode potential is lower than the applied battery potential difference. Namely, the invention can realize better treatment effect without sacrificing long-term stability;
3) The invention provides a method for preparing Ca by arranging a Monovalent Cation Exchange Membrane (MCEM) between a cathode chamber and a desalting chamber 2+ 、Mg 2+ The plasma cannot enter the cathode chamber, so that scaling is effectively inhibited, and long-term stability and treatment effect of the device are ensured. The ammonia nitrogen recovery device still has high stability after continuous operation for 6 times, deamination efficiency, recovery efficiency and recoverability are not reduced, and product purity is improved, so that the ammonia nitrogen recovery device is applicable to recycling ammonia nitrogen from multi-cycle water inflow. Therefore, the method for recycling ammonia nitrogen in coal gasification grey water by utilizing the flowing electrode capacitance deionizing device has the advantages of simplicity in operation, no need of adding chemical agents, high deamination efficiency, good recycling effect, high product purity, effective scale inhibition, low treatment cost, low treatment energy consumption, stable operation and the like, can recycle ammonia nitrogen in the coal gasification grey water in the form of ammonia water on the premise of not increasing the cost, not adding the chemical agents, not causing secondary pollution and facilitating subsequent treatment, and has very important significance for the development of the coal gasification industry;
4) For the flowing electrode, the carbon content of the flowing electrode is optimized to not more than 5%, so that the optimal recovery efficiency can be obtained under the condition, and the cost performance is higher: when the carbon content of the flowing electrode is 10%, the activated carbon itself adsorbs a large amount of NH 3 And the high carbon content can inhibit Faraday reaction, so that NH in ammonia nitrogen in the cathode chamber 4 + The ratio is very large, so that ammonia nitrogen obtained in the charging process is discharged and is left in the cathode flowing electrode by less than 30%, and ammonia nitrogen can be left in the cathode flowing electrode by 50% under the condition of 5% carbon content. Thus, for efficiency maximization and cost-effectiveThe carbon content in the flowing electrode of the present invention is preferably 5% or less.
Drawings
FIG. 1 is a schematic diagram of the structure of a Monovalent Cation Exchange Membrane (MCEM) -coupled FCDI device used in example 1;
FIG. 2 is a graph showing the concentration change of each component when ammonia nitrogen in coal gasification grey water is recovered by the mobile electrode capacitive deionization device in example 1;
FIG. 3 is the effect of carbon content in the anode and cathode flow electrodes on ammonia nitrogen recovery and purification treatment in example 2: (a) NH during charging 4 + -N removal rate (charge time 80 min); (b) NH during charging 4 + -N average removal rate and average current density; (c) Different discharge moments, cathode chamber NH 3 Recovery rate (discharge time 30 minutes); (d) Different discharge moments, cathode chamber NH 4 + -an average migration rate of N from the cathode chamber to the desalination chamber and a maximum pH;
FIG. 4 is a chart showing NH at different hydraulic retention times in example 3 3 -N(NH 4 + -N) concentration profile;
FIG. 5 is the effect of discharge voltage on ammonia nitrogen recovery and purification treatment in example 4: cathode chamber NH 4 + /Na + Selectivity (1);
FIG. 6 is the effect of discharge voltage on ammonia nitrogen recovery and purification treatment in example 4: the average migration rate of cations from the cathode chamber back to the desalination chamber;
FIG. 7 is the effect of discharge voltage on ammonia nitrogen recovery and purification treatment in example 4: per kilogram of NH 3 -N recovery power consumption.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples.
A method for recovering and purifying ammonia nitrogen by using a flow electrode capacitor based on a monovalent cation exchange membrane comprises the step of treating coal gasification grey water by adopting an FCDI device coupled with the Monovalent Cation Exchange Membrane (MCEM).
The structure of the FCDI device is shown in figure 1, and the FCDI device comprises a cathode flowing electrode chamber 1, a monovalent cation exchange membrane 2, a desalting chamber 3, an anion exchange membrane 4 and an anode flowing electrode chamber 5 which are sequentially arranged in parallel, wherein an anode circulating chamber 6 is arranged outside the anode flowing electrode chamber 5, an anode flowing electrode circularly flows between the anode flowing electrode chamber and the anode flowing electrode chamber, a cathode circulating chamber 7 is arranged outside the cathode flowing electrode chamber 1, a cathode flowing electrode circularly flows between the cathode flowing electrode chamber and the cathode flowing electrode, and the circulating flow rates are controlled to be 20-100mL/min.
Specifically, the anode flow electrode and the cathode flow electrode both comprise a conductive agent and a solvent, wherein the solvent can be water, and the conductive agent comprises at least one of active carbon and carbon black, and is preferably an active carbon/carbon black mixture with a mass ratio of 4:1. The mass fraction of the conductive agent in the anode flow electrode or the cathode flow electrode is not more than 10%, preferably not more than 5%, and still more preferably 2 to 5%.
The recovery and purification method specifically comprises the following steps:
1) Driving coal gasification gray water to continuously flow through the desalting chamber 3, and controlling the hydraulic retention time to be 0.5-1.5min;
2) Applying a forward voltage of 1.2-4.5V to the anode flow electrode chamber 5 and the cathode flow electrode chamber 1, wherein the electrifying time is 75-85min;
passing anions through the anion exchange membrane 4 by electro-adsorption into the anode flow electrode chamber 5, containing NH 4 + Through the monovalent cation exchange membrane 2 into the cathode flow electrode chamber 1 and within the cathode flow electrode chamber 1, utilize the cathode faraday reaction to promote NH on the electrode 4 + To NH 3 Converting and desorbing; and effectively prevent Ca in coal gasification grey water through monovalent cation exchange membrane 2 2+ 、Mg 2+ 、Fe 3+ Plasma enters the cathode chamber, so that scaling is effectively slowed down;
3) A reverse voltage of 0.1-0.3V is applied to the anode flow electrode chamber 5 and the cathode flow electrode chamber 1 for 10-30min (preferably 10-20min, more preferably 15 min); flowing Na in the electrode chamber 1 + 、K + The equivalent monovalent cations are forced back into the desalination chamber 3, thereby improving the purity of the ammonia water in the cathode flow electrode chamber 1.
As a preferred technical scheme, the recovery and purification method in the invention further comprises the following steps: repeating steps 1) to 3) to further increase the concentration of ammonia water in the cathode flow electrode chamber 1.
The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following examples.
Example 1:
the embodiment adopts the FCDI device to recycle and purify ammonia nitrogen in the gasified ash water, wherein the gasified ash water is obtained from a Ningbo sea-weight refinery, and comprises the following components and concentrations: 241.64 + -16.08 mg/L NH 4 + -N，52.60±1.40mg/L Na + ，10.63±0.38mg/L K + ，353.53±6.92mg/L Ca 2+ ，12.89±0.54mg/L Mg 2+ ，2.53±0.23mg/L Fe 3+ ，0.47±0.81mg/L Mn 2+ ，0.73±1.27mg/L Al 3+ ，476.10±0.09mg/L TOC，pH＝7.60。
The FCDI device is configured as shown in fig. 1, and comprises a cathode flowing electrode chamber 1, a monovalent cation exchange membrane 2, a desalination chamber 3, an anion exchange membrane 4 and an anode flowing electrode chamber 5 which are sequentially arranged in parallel, wherein the anode flowing electrode chamber 5 is also provided with an anode circulating chamber 6, an anode flowing electrode circularly flows between the anode flowing electrode chamber and the anode circulating chamber, the cathode flowing electrode chamber 1 is also provided with a cathode circulating chamber 7, and a cathode flowing electrode circularly flows between the cathode flowing electrode chamber and the anode circulating chamber. Wherein a monovalent cation exchange membrane (CIMS, astom, japan) and an anion exchange membrane (1201, hangzhou green technology, china) are used to function as ion selective permeation and separation of the water inlet and flow electrodes.
The anode flow electrode and the cathode flow electrode are both prepared by taking water as a solvent, taking an active carbon/carbon black mixture with the mass ratio of 4:1 as a conductive agent, and controlling the carbon content of the suspension to be 5%. The conductive agent can be prepared by the following method: 40g of active carbon and 10g of carbon black are weighed and added into 950mL of water, and the flowing electrode is obtained after the mixture is stirred and mixed evenly by magnetic force. Wherein the activated carbon is YEC-8A type activated carbon (Fuzhou Yi-cyclocarbon Co., ltd.); the carbon black used was Cabot Vulcan XC-72 conductive carbon black (Cabot, usa).
The recovery and purification method specifically comprises the following steps:
1) Continuously pumping coal gasification ash water into a desalting chamber 3 in a unidirectional way through a peristaltic pump, and controlling the hydraulic retention time to be 1.2min; simultaneously, the anode flow electrode and the cathode flow electrode are respectively and independently circulated between the anode flow electrode chamber 5 and the anode circulation chamber 6 and between the cathode flow electrode chamber 1 and the cathode circulation chamber 7 at the flow rate of 50 mL/min;
2) After the conductivity is stable, applying 4.5V forward voltage to the current collecting plates in the anode flow electrode chamber 5 and the cathode flow electrode chamber 1, and entering an ammonia water production stage, wherein the electrifying time is 80min;
passing anions through the anion exchange membrane 4 by electro-adsorption into the anode flow electrode chamber 5, containing NH 4 + Through the monovalent cation exchange membrane 2 into the cathode flow electrode chamber 1 and within the cathode flow electrode chamber 1, utilize the cathode faraday reaction to promote NH on the electrode 4 + To NH 3 Converting and desorbing; simultaneously, ca in coal gasification grey water is effectively prevented by the monovalent cation exchange membrane 2 2+ 、Mg 2+ 、Fe 3+ Plasma enters the cathode chamber, so that scaling is effectively slowed down;
3) Reverse power connection, namely applying reverse voltage of 0.2V to the current collecting plates in the anode flow electrode chamber 5 and the cathode flow electrode chamber 1, wherein the power-on time is 15min; flowing Na in the electrode chamber 1 + 、K + The equivalent monovalent cations are forced back into the desalination chamber 3, thereby improving the purity of the ammonia water in the cathode flow electrode chamber 1.
The concentration of various ions and TOC in the cathode flow electrode and desalter effluent is shown as a function of treatment time in fig. 2. As can be seen from the figure, when ammonia nitrogen in the coal gasification grey water is recovered by adopting the method in the embodiment, the water outlet state of the desalination chamber gradually tends to be stable in the charging process. 81.0% NH 4 + -N、82.5％Na + 、71.3％Ca 2+ 、43.5％K + 、48.7％Mg 2+ And 71.3% toc was removed. After 15 minutes of discharge, 3 were harvested in the cathode chamber as ammonia3.8% of ammonia water with the purity of 64.6%, the final concentration reaches more than 170mg/L, and other competitive cations in the actual wastewater only have very low concentration of Na + And K + Residue. The monovalent cation exchange membrane effectively prevents hardness ions from entering the cathode compartment. The average energy consumption for ammonia recovery and water treatment was 16.2kWh/kg N and 4.19kWh/m, respectively 3 And (3) water.
In summary, the method for recycling ammonia nitrogen in coal gasification grey water by utilizing the flow electrode capacitive deionization (FCDI) technology of the coupling Monovalent Cation Exchange Membrane (MCEM) has the advantages of simplicity in operation, no need of adding chemical agents, high deamination efficiency, good recycling effect, high product purity, effective scale inhibition, low treatment cost, low treatment energy consumption, stable operation and the like, can realize recycling of ammonia nitrogen in coal gasification grey water in the form of ammonia water on the premise of not increasing the cost, adding no chemical agents, causing no secondary pollution and facilitating subsequent treatment, and has very important significance for the development of coal gasification industry.
Example 2:
the influence of carbon content (active carbon/carbon black mass ratio 4:1) in an anode flow electrode and a cathode flow electrode on ammonia nitrogen recovery and purification treatment effect is examined in the embodiment, wherein the carbon content is 2.5, 5 and 10 weight percent, and the discharge time is 30 minutes. The water inlet is simulated coal gasification ash water, and is NH with high-grade purity 4 Cl、CaCl 2 The NaCl and deionized water are prepared, and the specific component concentrations are as follows: 240mg/L NH 4 + -N，370mg/L Ca 2+ ，70mg/L Na + Ph=7.60. The remaining process conditions are the same as in example 1, and the results are shown in fig. 3. It can be seen from fig. 3a,3b that the charging process is better in terms of both removal rate and removal rate, the greater the carbon content, due to the higher carbon content resulting in the formation of a highly interconnected network of particles in the flow electrode, reducing the resistance of the system, and the removal efficiency of the capacitive deionization technique for ions is proportional to the current. The effect of the higher carbon content in the reverse discharge phase is rather poor (FIG. 3 c), on the one hand because the activated carbon adsorbs NH 3 On the other hand, the cathode chamber at 10% pH was lower (FIG. 3 d), calculated according to software minteQ, pHSmaller NH 3 The smaller the duty cycle, the more NH 4 + Is forced out of the cathode chamber. Thus, the optimum carbon content in the present system is 5%.
Example 3:
the influence of Hydraulic Retention Time (HRT) of coal gasification gray water in the desalting chamber 3 on ammonia nitrogen recovery and purification treatment effect is examined in the embodiment, wherein the hydraulic retention time is respectively 0.5, 1, 1.2 and 1.5 minutes. Reverse discharge for 15 minutes. The feed water used was the same as the simulated coal gasification grey water of example 2, the rest of the process conditions were the same as in example 1, and the results are shown in fig. 4. It can be seen from table 4 that the increase in ammonia nitrogen removal rate showed a HRT dependent trend. In China, industrial wastewater needs pretreatment to meet the requirement of subsequent biochemical treatment, wherein the ammonia nitrogen concentration is controlled within 45mg/L (GB/T31962-2015). Therefore, a larger HRT is more suitable to be selected, but 1.2 minutes of HRT is optimal in view of processing efficiency.
Example 4:
the embodiment examines the influence of discharge voltage (namely, reverse voltage in step 3) on the ammonia nitrogen recovery and purification treatment effect, wherein the charge voltage is 4.5V, and the reverse discharge voltage is 0.1, 0.2 and 0.3V respectively. The water feed used was the same as the simulated coal gasification grey water of example 2, the remaining process conditions were the same as in example 1, and the results are shown in FIG. 5. It can be seen from FIG. 5 that a charge voltage of 0.2V exhibited a higher NH after 15 minutes of charging 4 + /Na + To obtain ammonia water with higher purity. Wherein NH is 4 + /Na + The selectivity calculation formula of (2) is as follows:
in the method, in the process of the invention,is the ammonia nitrogen concentration in the cathode chamber->For the concentration of ammonia nitrogen in the water intake, ->Is the concentration of sodium ions in the cathode chamber,>is the concentration of sodium ions in the inlet water.
This phenomenon can be explained by the average migration rate of cations forced from the cathode chamber back into the desalination chamber (fig. 6). The repulsive force caused by 0.1V is too small, so that the rate of cation migration back to the desalting chamber is small, na + Remains largely in the cathode chamber. The invention provides NH by powering up FCDI 4 + And Na (Na) + Migrate to the cathode chamber while the pH rise caused by Faraday reaction causes NH 4 + Conversion to NH 3(aq) Then reverse discharge will charge Na + The desalting chamber is forced to return, so that the purity of the ammonia water is improved. However, too high a discharge voltage would cause a significant drop in pH, at a discharge voltage of 0.3V, the cathode chamber pH was reduced from 11.3 to 10.2 within 30 min; at a discharge voltage of 0.2V, the cathode chamber pH was reduced to 10.7 within 30 min; at a discharge voltage of 0.1V, the cathode chamber pH is reduced by only 0.4 within 30min, resulting in partial NH 3(aq) Conversion to NH 4 + In view of NH 4 + Hydration radius ratio Na of (C) + Is small, 0.3V can cause ammonia nitrogen loss. In addition, as can be seen from fig. 7, the longer the discharge time, the higher the electric energy consumption for recovering ammonia nitrogen. Because the longer the discharge time, the more H will be generated by Faraday reaction + There will be more NH 3(aq) Conversion to NH 4 + Also in this system, na + The concentration of ammonia nitrogen is far lower than Na + In this case, NH 4 + And more tend to be forced back into the desalination chamber. After the discharge time is more than 15 minutes, the ammonia nitrogen concentration of the cathode chamber is remarkably reduced, so that 0.2V discharge for 15 minutes is optimal from the viewpoints of electric energy consumption required for recovering unit ammonia nitrogen and ammonia nitrogen recovery rate.
The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications without departing from the scope of the present invention.
Claims (6)
1. The method is characterized in that the FCDI device comprises a cathode flowing electrode chamber (1), a monovalent cation exchange membrane (2), a desalting chamber (3), an anion exchange membrane (4) and an anode flowing electrode chamber (5) which are sequentially arranged in parallel, wherein an anode flowing electrode is arranged in the anode flowing electrode chamber (5), and a cathode flowing electrode is arranged in the cathode flowing electrode chamber (1);
the recovery and purification method comprises the following steps:
s1: introducing wastewater to be treated into a desalting chamber (3), applying forward voltage to an anode flow electrode chamber (5) and a cathode flow electrode chamber (1) to enable anions to pass through an anion exchange membrane (4) to enter the anode flow electrode chamber (5), wherein the wastewater contains NH 4 + Through the monovalent cation exchange membrane (2) into the cathode flow electrode chamber (1) and to let NH 4 + Conversion to NH 3 ；
S2: applying a reverse voltage to the anode flowing electrode chamber (5) and the cathode flowing electrode chamber (1) to remove cations in the cathode flowing electrode chamber (1) and obtain high-purity ammonia water;
the anode flow electrode and the cathode flow electrode both comprise a conductive agent and a solvent; the conductive agent is a mixture of active carbon and carbon black in a mass ratio of 4:1, and the solvent comprises water; the mass fraction of the conductive agent in the anode flow electrode or the cathode flow electrode is not more than 10%.
2. The method for recovering and purifying the ammonia nitrogen of the flow electrode capacitor based on the monovalent cation exchange membrane according to claim 1, wherein an anode circulation chamber (6) is arranged outside the anode flow electrode chamber (5), and the anode flow electrode circularly flows between the anode flow electrode chamber (5) and the anode circulation chamber (6);
the cathode flow electrode chamber (1) is provided with a cathode circulation chamber (7), and the cathode flow electrode circularly flows between the cathode flow electrode chamber (1) and the cathode circulation chamber (7).
3. The method for recovering and purifying the ammonia nitrogen by using the flow electrode capacitor based on the monovalent cation exchange membrane according to claim 2, wherein the circulating flow rate of the anode flow electrode or the cathode flow electrode is 20-100mL/min.
4. The method for recovering and purifying the ammonia nitrogen by using the flow electrode capacitor based on the monovalent cation exchange membrane according to claim 1, wherein the hydraulic retention time of the wastewater to be treated flowing through the desalting chamber (3) is 0.5-1.5min.
5. The method for recovering and purifying ammonia nitrogen by using a flow electrode capacitor based on a monovalent cation exchange membrane according to claim 1, wherein the forward voltage is 1.2-4.5V, and the energizing time is 75-85min;
the reverse voltage is 0.1-0.3V, and the electrifying time is 10-30min.
6. The method for recovering and purifying ammonia nitrogen by using a monovalent cation exchange membrane-based flow electrode capacitor according to claim 1, wherein the method for recovering and purifying ammonia nitrogen further comprises the steps of: the steps of introducing coal gasification water, applying forward voltage, and applying reverse voltage are repeated to increase the ammonia concentration in the cathode flow electrode chamber (1).
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