Application of an electric field coupled flow field enhanced electrochemical mediated precipitation system

Abstract

The present invention provides an application of an electric field coupled flow field enhanced electrochemical mediated precipitation system, which includes a cathode-anode-cathode reactor, a bypass internal reflux, and an electrolyte system. The electric field coupled flow field enhanced electrochemical mediated precipitation system of the present invention is used to recover orthophosphorus, and the recovery method includes the steps of preparing an electrolyte; adding hydroxyapatite to the electrolyte, building a precipitation system, and operating a reaction. The electric field coupled flow field enhanced electrochemical mediated precipitation system of the present invention can achieve an efficient recovery efficiency of 95.88% of orthophosphorus within half an hour, and the operating energy consumption is only 1.75 kW·h / kg P, which is 0.9%-4.2% of other electrochemical phosphorus recovery processes.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment and resource recovery, in particular to an application of an electric field coupled flow field enhanced electrochemical mediated precipitation system. Background Art

[0002] Phosphorus (P) is an essential element for all living things. With the increasing world population, phosphorus is increasingly used in industrial production, especially the development and application of new materials such as new semiconductor black phosphorus and phosphorus-containing energy batteries, which further stimulates the sharp increase in phosphorus demand. However, non-renewable phosphorus resources (such as phosphate rock) are being depleted, and phosphate rock has been listed as a strategic mineral. At the same time, the discharge of phosphorus-containing wastewater is an important cause of the aggravation of eutrophication of water bodies. The contradiction between phosphorus shortage and phosphorus surplus directly points to the necessity of realizing phosphorus recovery in phosphorus-containing wastewater to solve the current complex phosphorus recovery and pollution problems.

[0003] Even though there are traditional methods for recovering phosphorus, such as flocculation, activated sludge, and adsorption, these methods are costly, require large areas of land, and produce a large amount of sludge, making it difficult to achieve efficient recovery of phosphorus. Although chemical precipitation is currently the most mature method for recovering phosphorus, related challenges such as the addition of chemical agents such as alkali, centralized brine treatment, and material regeneration are still ongoing. As a result, electrochemically mediated precipitation (EMP) has emerged as a sustainable alternative, which avoids the addition of reagents and the discharge of concentrated brine, reducing waste solids by 67-84%. In addition, benefiting from the common calcium ions in wastewater, the recovery of phosphorus in the form of calcium phosphate shows great potential.

[0004] However, high energy consumption and low precipitation efficiency are also major challenges facing EMP. The ion diffusion near the cathode driven by the concentration gradient is very slow, and the Ca 2+ In contrast, due to the electrostatic repulsion of the cathode, the anion PO4 3- The transport rate is reduced and the local Ca 2+ / PO4 3- The ratio is too low, and the OH produced by electrolysis of water cannot be fully utilized. – , which greatly limits the precipitation and energy efficiency of calcium phosphate recovery. In addition, in the traditional electrochemical reaction process, a large amount of hydrogen ions are produced at the anode, causing the anode to be in an acidic environment, thereby increasing the overpotential of the anode and increasing energy loss.

[0005] EMP is highly dependent on the local high pH environment, but the hydroxide ions produced at the cathode in the water electrolysis reaction are easily combined with the hydrogen ions generated at the anode, making it difficult to form a sufficiently alkaline environment to meet the precipitation requirements of calcium phosphate, resulting in a recovery efficiency that is lower than expected, and the pH is prone to instability during operation, resulting in precipitation dissolution. For this reason, most electrochemical systems will set up ion exchange membranes between the two pole chambers. Although the pH of the cathode chamber is increased, the addition of membrane components will increase the operating energy consumption. There are also related inventions that attempt to fill a large amount of calcium carbonate particles into the system to consume the hydrogen ions produced by the anode. A large amount of particles is not only prone to blockage, but also requires the addition of a separation process in the subsequent process, which complicates the process flow and increases the operating cost.

[0006] Therefore, it is of great practical significance and practical value to develop a lower-cost technology that breaks through the limitation of ion transport, improves energy utilization efficiency, and constructs a local high-pH alkaline environment to meet the precipitation requirements of calcium phosphate, thereby achieving high-efficiency and low-consumption technology for phosphorus recovery. Summary of the invention

[0007] The present invention aims to solve the problems of high operating energy consumption, low energy utilization rate and low precipitation recovery rate in the electrochemical method for recovering phosphorus in wastewater treatment. In particular, the present invention provides a reliable technical solution for the technical bottlenecks of low ion transmission efficiency and unstable pH in the cathode chamber in the existing EMP process, which leads to reduced phosphorus recovery efficiency and increased operating energy consumption.

[0008] In order to overcome the limitations of the prior art, the present invention provides an application of an electric field coupled flow field enhanced electrochemical mediated precipitation system, wherein the electric field coupled flow field enhanced electrochemical mediated precipitation system is used to recover orthophosphorus, and the recovery method comprises the following steps:

[0009] Step SS1, preparation of electrolyte: measure ultrapure water and put it into a beaker, add 0.8~1.2M sodium sulfate solution, 50~70mM disodium hydrogen phosphate solution, 110~130mM calcium sulfate solution, stir evenly to obtain electrolyte, the volume ratio of sodium sulfate, disodium hydrogen phosphate, calcium sulfate and ultrapure water is 2.08~3.12:2.14~3.00:2.31~2.73:241~244;

[0010] Step SS2, weighing 0.02-0.03 g of hydroxyapatite and adding it to the electrolyte prepared in step SS1, stirring at a stirring speed of 260 r / min for 10 minutes;

[0011] Step SS3, construction of precipitation system: use acrylic material to make a 50mm*60mm*100mm reactor, select a 50mm*100mm Ru / Ir mesh electrode as the anode, select a 50mm*100mm stainless steel mesh electrode as the cathode, and control the distance between the anode and cathode to be 10~14mm;

[0012] Step SS4, run the reaction: the temperature is 17~23℃, the power supply is adjusted to the constant current mode, and the current density is 0.8~1.2mA / cm 2 , the internal reflux rate is controlled at 65~75mL / min, and the power is turned on and operated for 25~35min;

[0013] When the current density increases, the orthophosphorus recovery efficiency will increase accordingly, but it is still limited to 0.8~1.2mA / cm 2 When the current density continues to increase, the recovery efficiency of orthophosphorus gradually becomes flat, but the operating energy consumption rises sharply. Therefore, 0.8~1.2mA / cm 2 The current density has the highest cost performance.

[0014] The electric field coupled flow field enhanced electrochemical mediated precipitation system is a system comprising a cathode-anode-cathode reactor, a bypass internal reflux and an electrolyte; the cathode-anode-cathode reactor comprises an anode chamber and two cathode chambers, the anode plate is a Ru / Ir mesh electrode, the cathode plate is a stainless steel mesh cathode, and the distance between the cathode and the cathode is 10-14 mm;

[0015] Further, the electrolyte includes sodium sulfate solution, disodium hydrogen phosphate solution and calcium sulfate solution;

[0016] Further, the concentration of the sodium sulfate solution is 0.8-1.2 M; the concentration of the disodium hydrogen phosphate solution is 50-70 mM, and the concentration of the calcium sulfate solution is 110-130 mM;

[0017] Furthermore, 0.02~0.03g of hydroxyapatite is added to the electrolyte. In the experiment to explore the dosage of hydroxyapatite, it was found that when the dosage was less than 0.02g, the system had a poor recovery effect on orthophosphorus. When it reached 0.02~0.03g, the system could be stabilized in a high pH environment, thereby achieving high recovery efficiency. A higher dosage did not bring more obvious results, so 0.02~0.03g was the optimal dosage.

[0018] During operation, the hydroxide ions generated by the cathode can accumulate continuously in the cathode chamber to form a high pH environment. The hydroxyapatite distributed in the cathode chamber stabilizes the high pH environment, providing an excellent supersaturated environment for calcium phosphate and promoting the precipitation of calcium phosphate. At the same time, under the synergistic effect of the dual physical fields, the transmission rate of ions to the electrode is increased, helping anions overcome electrostatic repulsion and increasing the local Ca 2+ / PO4 3- The ratio further promotes the supersaturated environment of the cathode chamber, thereby improving the energy utilization efficiency. The dual cathode setting alleviates the acidic pH environment of the anode and reduces the overpotential of the anode, thereby further reducing the energy loss during the operation and enhancing the energy utilization efficiency of the system.

[0019] In the flow rate exploration experiment, at a reflux rate of 0~75mL / min, it was shown that increasing the flow rate helps to improve the recovery efficiency of orthophosphorus, especially at a reflux rate of 65~75mL / min, which shows the best recovery effect.

[0020] Furthermore, the volume ratio of sodium sulfate, disodium hydrogen phosphate, calcium sulfate and ultrapure water is 2.08~3.12:2.14~3.00:2.31~2.73:241~244, and the mixed solution simulates phosphorus-containing wastewater.

[0021] Furthermore, in the preparation of the electrolyte in step SS1, the stirring speed is 200-300 r / min, and the stirring time is 5-10 minutes.

[0022] Compared with the existing technology, the application of the electric field coupled flow field enhanced electrochemical mediated precipitation system of the present invention has the following significant beneficial effects:

[0023] (1) High efficiency and low consumption of phosphorus recovery: The electric field coupled flow field enhanced electrochemical mediated precipitation system of the present invention can achieve a high efficiency of orthophosphorus recovery (95.88%) within half an hour, and the operating energy consumption is only 1.75kW·h / kgP, which is 0.9%-4.2% of other electrochemical phosphorus recovery processes.

[0024] (2) High-purity products: The present invention recovers phosphorus from wastewater in the form of hydroxyapatite (HAP). During the entire reaction process, no additional chemical agents are added, and only one precipitated product, HAP, is formed. The high-purity HAP also improves the application value of the present invention.

[0025] (3) Innovative concept: The electric field coupled flow field enhanced electrochemical mediated precipitation system proposed in the present invention adopts a dual cathode reactor to couple the electric field and flow field to enhance mass transfer and reduce energy consumption. It also uses hydroxyapatite to further stabilize the high pH environment formed at the cathode, providing excellent supersaturation conditions for calcium phosphate precipitation. This recovery method significantly reduces operating energy consumption while ensuring high recovery efficiency of orthophosphate.

[0026] (4) Effective pH stabilization method: The present invention achieves the stability of the high pH environment in the cathode chamber by adding a small amount of hydroxyapatite to the electrode chamber, providing an excellent supersaturated environment for calcium phosphate precipitation. Different from using expensive ion exchange membranes, this method achieves the ideal experimental effect at a cheaper price.

[0027] (5) Efficient reactor design: The cathode-anode-cathode dual cathode reactor screened by the present invention has the highest phosphorus recovery efficiency under the coupling effect of the electric field and the flow field, and the lowest operating energy consumption, which is 23.15% of the anode-cathode (AC) reaction system and 62.27% of the cathode-anode (CA) reaction system, which greatly reduces the operating cost and reflects great economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a diagram of the experimental setup of the electric field coupled flow field enhanced electrochemical mediated precipitation system of Example 1;

[0029] Figure 2 is the XRD pattern of hydroxyapatite, the precipitated product of Example 1;

[0030] Figure 3 It is a comparison chart of the orthophosphorus recovery efficiency and operating energy consumption of Example 1 and Comparative Example 1, Comparative Example 2 and Comparative Example 3;

[0031] Figure 4 This is a comparison chart of pH and orthophosphorus recovery efficiency of the system of Example 1 and Comparative Example 1;

[0032] Figure 5 It is a comparison diagram of orthophosphorus recovery efficiency and energy consumption at different flow rates in Example 1 and Comparative Example 4;

[0033] Figure 6 This is a comparison chart of orthophosphorus recovery efficiency and operating energy consumption at different current densities in Example 2;

[0034] Figure 7 This is a comparison chart of orthophosphorus recovery efficiency and operating energy consumption at different hydroxyapatite dosages in Example 3;

[0035] Figure 8 This is a diagram showing the effect of long-term circulation operation of Example 4. DETAILED DESCRIPTION

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0037] The technical solution of the present invention is further explained below in conjunction with implementation cases.

[0038] Example 1

[0039] This embodiment provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus, and the recovery method includes the following steps:

[0040] Step SS1, preparation of electrolyte: 250 mL of ultrapure water was measured and placed in a beaker, and 2.5 mL of 1 M sodium sulfate solution, 2.5 mL of 60 mM disodium hydrogen phosphate solution, and 2.5 mL of 120 mM calcium sulfate solution were added. The stirring speed was 260 r / min, and the electrolyte was obtained after stirring for 10 minutes;

[0041] Step SS2, weigh 0.025 g of hydroxyapatite and add it to the electrolyte prepared in step SS1, stirring at the same speed of 260 r / min for 10 minutes;

[0042] Step SS3, construction of precipitation system: use acrylic material to make a 50mm*60mm*100mm reactor, select a 50mm*100mm Ru / Ir mesh electrode as the anode, and a 50mm*100mm stainless steel mesh electrode as the cathode. The distance between the cathode and the anode is controlled at 12mm. The precipitation system includes an anode plate and two cathode plates, such as Figure 1 As shown, the precipitation system is a dual cathode reactor;

[0043] Step SS4, run the reaction: temperature is 20°C, the power supply is adjusted to constant current mode, and the current density is 1 mA / cm 2 The internal reflux rate was controlled at 72 mL / min by a pump and the system was powered on and operated for 30 min.

[0044] Comparative Example 1

[0045] This comparative example also provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus. The recovery method refers to Example 1. The difference between this comparative example and Example 1 is that the precipitation system includes an anode plate and a cathode plate, wherein the cathode is downstream and the anode is upstream, that is, the precipitation system is a cathode-anode single cathode reactor.

[0046] Comparative Example 2

[0047] This comparative example also provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus. The recovery method refers to Example 1. The difference between this comparative example 1 and Example 1 is that there is no step SS2, that is, hydroxyapatite is not added in this comparative example.

[0048] Comparative Example 3

[0049] This comparative example also provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus. The recovery method refers to comparative example 1. The difference between this comparative example and example 1 is that the precipitation system includes an anode plate and a cathode plate, wherein the cathode is upstream and the anode is downstream, that is, the precipitation system is an anode-cathode single cathode reactor.

[0050] Comparative Example 4

[0051] This comparative example also provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus. The recovery method refers to Example 1. The difference between this comparative example 4 and Example 1 is that the flow rate in step SS4 is controlled under the conditions of 0 mL / min, 18 mL / min, and 36 mL / min.

[0052] The recovery efficiency and operating energy consumption of orthophosphorus in the above-mentioned embodiments and comparative examples are calculated by the following formula.

[0053] The recovery efficiency of orthophosphorus is calculated by formula (1):

[0054]

[0055] The reaction operation energy consumption is calculated by formula (2):

[0056]

[0057] Where: C t is the concentration of orthophosphorus after the reaction (mg / L); C0 is the initial concentration of orthophosphorus (mg / L); I is the applied current (A); U is the voltage (U); V is the volume of the solution (mL); T is the reaction time (h); EC is the operating energy consumption, For recycling efficiency.

[0058] The orthophosphorus concentration was determined by molybdate spectrophotometry. Use a 2 mL syringe to draw 2 mL of the solution before and after the reaction, pass through a 0.22µm filter membrane, and determine the orthophosphorus concentration: use a pipette to draw 0.2 mL of the filtered solution into a 10 mL centrifuge tube, add 4.5 mL of ultrapure water, 0.1 mL of 10% ascorbic acid solution, and 0.2 mL of molybdate solution, mix well, and let stand for 15 minutes. Then use a quartz cuvette to measure the absorbance at a wavelength of 700 nm using a UV spectrophotometer model TU 1810. The concentration of phosphorus at a wavelength of 700 nm on a UV spectrophotometer model TU 1810 is determined by ammonium molybdate spectrophotometry.

[0059] like Figure 2 As shown, after XRD detection, the recovered product is hydroxyapatite.

[0060] like Figure 3 As shown, Figure 3 In Figures (a) and (b), the bars from left to right represent the addition of hydroxyapatite in the dual cathode precipitation system, the addition of hydroxyapatite in the cathode-anode single cathode precipitation system, the addition of hydroxyapatite in the dual cathode precipitation system, and the addition of hydroxyapatite in the anode-cathode single cathode precipitation system.

[0061] The recovery efficiency of orthophosphorus in Example 1 is 95.88%, and the operating energy consumption is 1.75 kW·h / kg P, the recovery efficiency of orthophosphorus in Comparative Example 1 is 63.93%, and the operating energy consumption is 2.81 kW·h / kg P, the recovery efficiency of orthophosphorus in Comparative Example 2 is 86.75%, and the operating energy consumption is 3.09 kW·h / kg P, and the recovery efficiency of orthophosphorus in Comparative Example 3 is 37.82%, and the operating energy consumption is 7.56 kW·h / kg P. The operating energy consumption of Example 1 is the lowest, which is 62.27% of the cathode-anode (CA) reaction system of Comparative Example 1 and 23.15% of the anode-cathode (AC) reaction system of Comparative Example 3.

[0062] like Figure 4 As shown, compared with Example 1 and Comparative Example 2, no hydroxyapatite was added in Comparative Example 2, and the experimental results are as follows Figure 4 As shown in (a) in Example 1. When hydroxyapatite was not added, the pH of the system gradually decreased with time. At 30 minutes, the pH was only 8.79, and the recovery efficiency was 69.62%. Figure 4 As shown in (b), the reaction pH tends to stabilize at 10.83 after 10 minutes, and the recovery efficiency of orthophosphorus reaches a peak of 95.50% at 30 minutes. It can be seen that in the dual cathode reaction system defined in the present application, hydroxyapatite plays a role in stabilizing the pH value.

[0063] like Figure 5As shown, compared with Example 1 and Comparative Example 4, the internal reflux flow rate is 72 mL / min, and the difference of Comparative Example 4 is that the internal reflux flow rate is changed to 0, 18, and 36 mL / min. The positive phosphorus recovery effect is as follows Figure 5 As shown in (a) in the figure. Figure 5 As shown in (a), as the flow rate increases, the recovery effect of orthophosphorus increases. When there is no flow field, that is, when the flow rate is 0, the recovery effect of orthophosphorus is only 82.15%, while when the flow rate of Example 1 is 72mL / min, the recovery effect of orthophosphorus is as high as 95.41%. It can be seen that the effect is better after the electric field is coupled with the flow field. Figure 5 As shown in (b) in the figure, as the flow rate increases, the energy consumption gradually decreases.

[0064] Example 2

[0065] This embodiment provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus. The recovery method is referred to Example 1. The difference between this embodiment and Example 1 is that the current density is 0.25 mA / cm 2 , 0.5 mA / cm 2 , 1 mA / cm 2 , 2 mA / cm 2 , 3 mA / cm 2 , after calculation, it can be seen that the recovery efficiency of orthophosphorus is 68.16%, 85.96%, 92.01%, 95.10%, 96.40%, and the operating energy consumption is 0.48 kW·h / kg P, 0.80 kW·h / kg P, 1.64 kW·h / kg P, 3.97 kW·h / kg P, 6.14 kW·h / kg P, respectively. Figure 6 As shown in Figure 1, continuously increasing the current density can gradually improve the phosphorus recovery efficiency, but it will also increase the operating energy consumption. It is worth noting that the recovery efficiency brought about by the increase in current density is not a linear increase. When it reaches a certain limit, the efficiency improvement enters a stable period, but the energy consumption still increases significantly. Therefore, according to Figure 6 The results show that when the current density is 1 mA / cm 2 When the recovery efficiency can reach more than 90%, the operating energy consumption is still only 1.64 kW·h / kg P, so the optimal current density suitable for the present invention is 1 mA / cm 2 .

[0066] Example 3

[0067] This embodiment provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus. The recovery method refers to Example 1. The difference between this embodiment and Example 1 is that the dosage of hydroxyapatite in this embodiment is 0g / L, 0.01g / L, 0.1g / L, 2g / L, and 5g / L, respectively.

[0068] After calculation, it can be seen that the recovery efficiency of orthophosphate is 82.97%, 85.51%, 92.99%, 95.10% and 94.43%. The main role of hydroxyapatite in the system is to stabilize the high pH environment of the system, which is the key to calcium phosphate precipitation. Figure 7 As shown in the figure, when too little hydroxyapatite is added, the phosphorus recovery effect is not ideal, but when the dosage reaches 0.1g / L, the recovery effect can reach more than 90%, and further increasing the dosage does not significantly improve the effect. It can be seen that in this system, 0.1g / L of hydroxyapatite can meet the system requirements, and this dosage is only 1%-10% of the seed dosage in other literatures, which truly embodies the "small volume, big effect".

[0069] Example 4

[0070] This embodiment provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus. The recovery method is similar to that of Example 1. The difference between this embodiment and Example 1 is that this embodiment performs 10 cycle tests under the conditions of Example 1. After each cycle, all the solution in the reactor is discharged, simulated water is added again, and electrolysis is continued for 30 minutes. After the electrolysis is completed, water samples are collected, and the phosphorus recovery efficiency of a single cycle is calculated. At the same time, the operating voltage is monitored in real time to calculate the operating energy consumption.

[0071] Cyclic test results Figure 8 As shown in the figure, during the ten consecutive operations, the system performed stably, the phosphorus recovery efficiency remained above 90%, and the operating energy consumption was maintained at around 1.7 kW·h / kg P. It can be seen that the system has stable performance and considerable practical value.

[0072] Comparative Example 5

[0073] This comparative example provides an electric field coupled flow field enhanced electrochemical mediated precipitation system for recovering orthophosphorus. The recovery method is the same as that of Example 1. The difference between this comparative example and Example 1 is that calcium carbonate particles of equal mass are used instead of hydroxyapatite.

[0074] After calculation, the recovery efficiency of orthophosphorus in this comparative example is 61%, which is much lower than the recovery efficiency of orthophosphorus in Example 1, which is 95.88%. The operating energy consumption of this comparative example is 29 kW·h / kg P, which is much higher than the operating energy consumption of 1.75 kW·h / kgP in Example 1. Compared with this comparative example, Example 1 only adds a very small amount of hydroxyapatite, which can well stabilize the reaction pH and improve the recovery efficiency of phosphorus.

[0075] In summary, the electric field coupled flow field CAC reactor of the present invention can achieve a recovery efficiency of up to 95.88% of orthophosphorus in just half an hour, with an energy consumption of only 1.75 kW·h / kg P, truly achieving high efficiency and low consumption.

[0076] Compared with the traditional phosphorus recovery process, the CAC reactor of the present invention couples the electric field and the flow field, and by regulating the dual physical fields, effectively accelerates the ion transfer rate and improves the energy utilization efficiency. At the same time, the setting of the dual cathode reduces the overpotential of the anode, thereby further reducing the energy loss of the system. In half an hour of operation, the reaction energy consumption is only 1.75 kW·h / kg P, which is 0.9%-4.2% of other electrochemical phosphorus recovery processes. The addition of a small amount of inexpensive hydroxyapatite stabilizes the high pH environment of the system, realizes high-purity and efficient positive phosphorus recovery, and the recovered product is hydroxyapatite with a recovery efficiency of up to 95.88%. In addition, in ten cycle tests, the system showed good stability, and the recovery efficiency was above 90%. Therefore, the invention has the advantages of high efficiency and low consumption, simple operation, low cost, and environmental friendliness in the field of phosphorus recovery, and has considerable practical value and application prospects.

[0077] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. An application of an electric field coupled flow field enhanced electrochemical mediated precipitation system, characterized in that: The electric field coupled flow field enhanced electrochemical mediated precipitation system is used to recover orthophosphorus, and the recovery method comprises the following steps: Step SS1, preparation of electrolyte: measure ultrapure water and put it into a beaker, add 0.8~1.2M sodium sulfate solution, 50~70mM disodium hydrogen phosphate solution, 110~130mM calcium sulfate solution, stir evenly to obtain electrolyte, the volume ratio of sodium sulfate, disodium hydrogen phosphate, calcium sulfate and ultrapure water is 2.08~3.12:2.14~3.00:2.31~2.73:241~244; Step SS2, weighing 0.02-0.03 g of hydroxyapatite and adding it to the electrolyte prepared in step SS1, stirring at a stirring speed of 260 r / min for 10 minutes; Step SS3, construction of precipitation system: use acrylic material to make a 50mm*60mm*100mm reactor, select a 50mm*100mm Ru / Ir mesh electrode as the anode, select a 50mm*100mm stainless steel mesh electrode as the cathode, and control the distance between the anode and cathode to be 10~14mm; Step SS4, run the reaction: the temperature is 17~23℃, the power supply is adjusted to the constant current mode, and the current density is 0.8~1.2mA / cm 2 , the internal reflux rate is controlled at 65~75mL / min, and the power is turned on and operated for 25~35min; The electric field coupled flow field enhanced electrochemical mediated precipitation system is a system comprising a cathode-anode-cathode reactor, a bypass internal reflux and an electrolyte; The cathode-anode-cathode reactor includes an anode chamber and two cathode chambers. The anode plate is a Ru / Ir mesh electrode, the cathode plate is a stainless steel mesh cathode, and the distance between the cathode and cathode is 10~14mm. The electrolyte includes sodium sulfate solution, disodium hydrogen phosphate solution and calcium sulfate solution; The concentration of the sodium sulfate solution is 0.8-1.2 M; the concentration of the disodium hydrogen phosphate solution is 50-70 mM; the concentration of the calcium sulfate solution is 110-130 mM; 0.02-0.03 g of hydroxyapatite is also added to the electrolyte.

2. The application of the electric field coupled flow field enhanced electrochemical mediated precipitation system according to claim 1, characterized in that: The volume ratio of sodium sulfate, disodium hydrogen phosphate, calcium sulfate and ultrapure water is 2.08~3.12:2.14~3.00:2.31~2.73:241~244.

3. The use of the electric field coupled flow field enhanced electrochemical mediated precipitation system according to claim 1, characterized in that: In the preparation of the electrolyte in step SS1, the stirring speed is 200-300 r / min, and the stirring is performed for 5-10 minutes.

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