Deep purification and resource utilization process of phosphorus-containing wastewater

Abstract

The invention relates to a deep purification and resource utilization process of phosphorus-containing wastewater. The process comprises three steps of deep purification of the phosphorus-containing wastewater, a phosphorus enrichment process and resource utilization of a phosphorus-containing concentrated solution. The method comprises the following steps: firstly, adsorbing phosphorus in the wastewater by using a high-performance adsorbent to realize deep purification of the wastewater; then, a regeneration solution is added into the adsorbent which is saturated through adsorption, and desorption of phosphorus and regeneration of the adsorbent are achieved; finally, resource utilization of phosphorus is achieved in the mode that ammonium salt and magnesium salt are added into phosphorus-containing enriched liquid obtained through desorption, the phosphorus subjected to resource utilization exists in a solid form, and the phosphorus can be directly used and has good fertilizer efficiency. According to the process, deep purification of the phosphorus-containing wastewater can be realized, the phosphorus content in the purified wastewater is lower than 0.1 mg / L, and the recovery rate of phosphorus is higher than 98%. The deep purification of the phosphorus-containing wastewater is realized, and meanwhile, the obtained product has very good practicability and economic value and has good economic benefits.

Description

Technical Field

[0001] The invention belongs to the field of wastewater phosphorus recovery, and specifically relates to a deep purification and resource utilization process of phosphorus-containing wastewater. Background Art

[0002] Phosphorus, as a mineral element, is essential for plant growth and is also a necessity for modern industry and agriculture. Phosphorus-containing wastewater is inevitably generated during use and discharged into rivers, lakes, oceans and other water bodies, causing a large amount of phosphorus resources to be wasted, while accelerating the eutrophication process of water bodies, which has serious harm to agriculture, fisheries and other industries. It is of great ecological, environmental and economic significance to enrich phosphorus-rich wastewater and recover phosphorus. How to achieve deep purification of phosphorus-containing wastewater and recycle phosphorus resources has become a problem that needs to be solved urgently.

[0003] As more and more people pay attention to the importance of phosphorus recovery process, some phosphorus recovery processes have been developed. The current phosphorus recovery methods are mainly divided into physical methods, chemical methods and biological methods. Among them, Chinese patent application CN116813411A proposes a biological recovery method, which can achieve phosphorus recovery and make it into fertilizer for use, but has limitations when treating phosphorus-containing wastewater with higher concentrations. Chinese patent application CN101439897A discloses a preparation of a sewage phosphorus recovery composite flocculant and a phosphorus recovery process, wherein the material used is a flocculant prepared from metal ions and sodium silicate solution, and the recovery process includes flocculation, filtration, and drying, and the obtained product can be used as a fertilizer. However, the flocculant used is liquid, and the recycling of materials cannot be achieved. Chinese patent application CN101381156A discloses a sewage treatment system and treatment method combining a membrane bioreactor with a phosphorus recovery process, and the phosphorus recovery rate reaches 95%, but the reaction time required for the process is long and is not suitable for the treatment of high-concentration phosphorus-containing wastewater. As a simple and efficient treatment method, the adsorption method has the advantages of simple process, wide application range, green economy, recyclable adsorption materials, and resource recycling. It has been widely used in industry and has great potential for the purification of phosphorus-containing wastewater and the recovery of phosphorus. At the same time, there are also corresponding studies on how to recycle the enriched phosphorus. Chinese patent application CN215208869U adopts the struvite method to achieve phosphorus recovery. The recovered struvite is a good slow-release fertilizer that can be used in agricultural production and has good economic benefits. In summary, the phosphorus recovery process has the defects of long processing time, difficult recycling of materials, and unsuitability for the treatment of high-concentration phosphorus-containing wastewater. Therefore, there is an urgent need for an efficient, green and economical deep purification and resource utilization process for phosphorus-containing wastewater. Summary of the invention

[0004] In view of the shortcomings of the prior art, the first purpose of the present invention is to achieve deep purification of phosphorus-containing wastewater. It has good applicability to phosphorus-containing wastewater with different conditions such as concentration, pH, and ion concentration, and can achieve deep purification of phosphorus-containing wastewater; the second purpose of the present invention is to establish and optimize the corresponding phosphorus recovery process to achieve the regeneration of the adsorbent and the resource utilization of the phosphorus-enriched liquid.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] In the first aspect, the present invention protects a process for deep purification and resource utilization of phosphorus-containing wastewater, which comprises three steps of deep purification of phosphorus-containing wastewater, phosphorus enrichment process, and resource utilization of phosphorus-containing concentrated liquid, and specifically comprises the following steps:

[0007] (1) Deep purification of phosphorus-containing wastewater: The phosphorus-containing wastewater is passed into an adsorption column filled with adsorbent, and samples are taken every 5 minutes for analysis. The samples are filtered using a 0.22 μm filter head, and the phosphorus content of the outlet liquid is measured using a UV-visible spectrophotometer;

[0008] (2) Phosphorus enrichment process: using sodium hydroxide solution to regenerate the adsorbent, mixing the sodium hydroxide solution with the adsorbent saturated with adsorption and continuously stirring, and collecting the phosphorus-containing concentrated solution;

[0009] (3) Resource utilization process of phosphorus-containing concentrated solution: add ammonium salt and magnesium salt to the phosphorus-containing concentrated solution obtained in step (2), filter, and collect to obtain a solid precipitate.

[0010] Furthermore, in the step (1), the concentration of the phosphorus-containing wastewater is 30 to 100 mg / L.

[0011] Furthermore, in the step (1), the adsorbent used includes metal-modified coal-made activated carbon, wood-made activated carbon, still-made activated carbon, etc.; preferably, iron-modified still-made activated carbon.

[0012] Furthermore, in step (2), sodium hydroxide solution is used as the regeneration solution, and the solution mass concentration is 1% to 4%, preferably 2%.

[0013] Furthermore, in the step (2), the solid-liquid (g:mL) ratio of the adsorbent to the sodium hydroxide solution is 1:10 to 1:500, preferably 1:20 to 1:300; more preferably 1:200.

[0014] Furthermore, in the step (2), the regeneration time is 4-6 hours.

[0015] Furthermore, in step (3), the ammonium salt is ammonium chloride, and the magnesium salt is magnesium sulfate.

[0016] Furthermore, in step (3), the molar ratio of ammonium to phosphorus can be selected from 1:0.1 to 1:5, preferably 1:0.9 to 1:1.3; preferably 1:1.3.

[0017] Furthermore, in step (3), the molar ratio of magnesium to phosphorus can be selected from 1:0.1 to 1:5, preferably 1:0.9 to 1:1.5; preferably 1:1.5.

[0018] Furthermore, in the step (3), the pH value of the solution during recovery is 8 to 10, preferably 9.5.

[0019] Furthermore, in step (3), the reaction time is 5-25 min, preferably 15 min.

[0020] In a second aspect, the present invention protects the use of the phosphorus-containing solid product obtained above in the preparation of fertilizers.

[0021] Beneficial Effects

[0022] (1) The present invention can efficiently adsorb and purify phosphorus-containing wastewater, and the phosphorus content of the water after purification is less than 0.1 mg / L.

[0023] (2) The process of the present invention has good applicability to phosphorus-containing wastewater of different concentrations, pH values ​​and ion concentrations.

[0024] (3) The present invention realizes resource utilization of phosphorus, with a utilization rate of 98.2%; at the same time, a solid struvite product is obtained, which is a fertilizer that can be directly used and has good fertilizer effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a process flow chart of the present invention;

[0026] Figure 2 are the XRD patterns of the recovered product (a) and struvite (b). DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below through specific implementation methods. The reagents or instruments used without indicating the manufacturer are regarded as conventional products that can be purchased on the market.

[0028] Example 1

[0029] The research on the phosphorus-containing wastewater adsorption process of this embodiment includes the following steps:

[0030] 219.7 mg of potassium dihydrogen phosphate was dissolved in deionized water and the volume was adjusted to 1 L to obtain a solution with a phosphorus content of 50 mg / L. Sodium hydroxide and hydrochloric acid solutions were used to adjust the pH to 2, 4, 6, 8, 10 or 12. A peristaltic pump was used to pass the solution into an adsorption column containing 1 g of iron-modified residual activated carbon. Sampling and analysis were performed every 5 minutes. The samples were filtered and sampled with a 0.22 μm filter head, and the phosphorus content of the outlet liquid was measured using a UV-visible spectrophotometer. The specific information is shown in Table 1.

[0031] As shown in Table 1, as the pH of the solution increases from 2 to 12, the adsorption of phosphate by the adsorbent gradually decreases from 67.05 mg / g to 30.05 mg / g, and the corresponding complete penetration time decreases from 671 min to 301 min. When the pH of the solution is 2, 1341 mL of phosphoric acid wastewater can be treated, which is significantly higher than other conditions. It can be seen that the adsorbent has a good adsorption capacity for phosphate solution in an acidic environment and has great potential for the purification of acidic phosphorus-containing wastewater.

[0032] Table 1 Effect of solution pH on phosphate adsorption capacity

[0033]

[0034] Example 2

[0035] The research on the phosphorus-containing wastewater adsorption process of this embodiment includes the following steps:

[0036] Dissolve 219.7 mg of potassium dihydrogen phosphate in deionized water and dilute to 1 L to obtain a solution with a phosphorus content of 50 mg / L. Add NaCl and NaNO 3 、Na 2 CO 3 、Na 2 SO 4 By adjusting the anion (Cl- / NO 3 - / CO 3 2- / SO 4 2- ) concentration was 0.1 mol / L, and a peristaltic pump was used to pass the solution into an adsorption column containing 1 g of iron-modified kettle residual activated carbon. Sampling and analysis were performed every 5 minutes, and the samples were filtered with a 0.22 μm filter head. The phosphorus content of the outlet liquid was determined using a UV-visible spectrophotometer. The specific information is shown in Table 2.

[0037] As shown in Table 2, under the condition of pH 2 and without the addition of coexisting anions, the adsorption amount of phosphate by the adsorbent was 67.05 mg / g. However, after the addition of coexisting anions, the adsorption amount decreased. The interference ability of the four coexisting anions was as follows: SO 4 2- >CO 3 2- >NO 3 - >Cl-. The most influential one is SO 3 2- , the adsorption capacity decreased by 55.1%, but it still had an adsorption capacity of 30.08 mg / g; Cl- had the smallest effect, with an adsorption capacity of up to 60.65 mg / g, and it could still treat 1213 mL of phosphoric acid wastewater. It can be seen that the adsorbent has good resistance to a variety of ions and is suitable for the purification of actual phosphorus-containing wastewater with complex anion types and high concentrations.

[0038] Table 2 Effect of coexisting ions on phosphate adsorption capacity

[0039]

[0040] Example 3

[0041] The research of the phosphorus enrichment process of this embodiment includes the following steps:

[0042] According to the operating steps of sequence number 1 in Example 1, phosphorus-containing wastewater adsorption was carried out, the adsorbent saturated with adsorption was added to a conical flask, and the NaOH aqueous solutions with mass concentrations of 1%, 2%, 3%, and 4% were mixed with the adsorbent saturated with adsorption and continuously stirred. Sampling and analysis were carried out every 10 minutes, and the samples were filtered and sampled with a 0.22 μm filter head. The phosphorus content of the outlet liquid was measured using a UV-visible spectrophotometer. The results are shown in Table 3.

[0043] As shown in Table 3, when a 2% NaOH aqueous solution is used as the regeneration solution, the desorption rate increases with the increase of the solid-liquid ratio. When the solid-liquid ratio is 1:20, the desorption rate is only 53%. When it is expanded to 1:200, the desorption rate is 96.1%. When the solid-liquid ratio is further increased, the desorption rate rarely increases. When the concentration of 1, 2, and 4% NaOH aqueous solution is used as the regeneration solution, the corresponding desorption rates are 84.4%, 96.3%, and 98.8%, respectively, indicating that a higher NaOH concentration is conducive to the desorption of phosphorus. In order to reduce the amount of NaOH used, a 2% NaOH aqueous solution is the best choice.

[0044] Table 3 Effect of regeneration liquid concentration and solid-liquid ratio on desorption rate

[0045]

[0046] Example 4

[0047] The research on the phosphorus recovery process in the desorption solution in this embodiment includes the following steps:

[0048] Step (1): Adsorption and desorption were cycled for 5 times according to operation No. 1 in Example 1 and operation No. 2 in Example 3 without replacing the regeneration liquid, and the obtained desorption liquid (phosphorus concentrated liquid) was collected.

[0049] Step (2): adding ammonium chloride and magnesium sulfate to the desorption solution in step (1) at a molar ratio of 1:0.9, 1:1.1, 1:1.3, or 1:1.5 to phosphorus, respectively, adjusting the pH to 8, 8.5, 9, 9.5, or 10, reacting at 25° C. for 25 minutes, filtering to obtain a solid precipitate, and sampling and analyzing the solution at the same time, calculating the phosphorus recovery rate. The results are shown in Table 4.

[0050] As shown in Table 4, in n(Mg 2+ ) / n(P) is 1:1.1, and pH is 9. As n(NH 4 + ) / n(P) increased from 1:0.9 to 1:1.3, and the corresponding recoveries were 74.27% and 80.55%, respectively. It was further found that n(Mg 2+ ) / n(P) was 1:1.5, the phosphorus recovery rate was further increased to 84.44%. 4 + ) / n(P) and n(Mg 2+ ) / n(P) were 1:1.3 and 1:1.5 respectively. It was found that when the pH was 8.5, the phosphorus recovery rate dropped to 69.37%. When the pH was 9.5, the recovery rate was significantly increased to 98.2%, which was the optimal phosphorus recovery process condition.

[0051] Table 4 Effect of ammonium phosphorus ratio, magnesium phosphorus ratio and pH on phosphorus recovery

[0052]

[0053] from Figure 2 It can be seen that (a) is the XRD diagram of the precipitated product, and (b) is the standard spectrum of struvite PDF#15-0762. The positions of the characteristic peaks of the solid product of the present invention are basically consistent with the positions of the characteristic peaks of the standard spectrum of struvite, so it can be determined that the obtained product is struvite crystals.

[0054] The protection content of the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention and are protected by the attached claims.

Claims

1. A process for deep purification and resource utilization of phosphorus-containing wastewater, characterized in that: It includes three steps: deep purification of phosphorus-containing wastewater, phosphorus enrichment process, and resource utilization of phosphorus-containing concentrated liquid, as follows: (1) Deep purification of phosphorus-containing wastewater: The phosphorus-containing wastewater is passed into an adsorption tower filled with a dephosphorization adsorbent. The purified water meets the discharge requirements and is discharged from the top of the tower; (2) Phosphorus enrichment process: mixing and stirring the saturated adsorbent with the regeneration solution, regenerating, and collecting the regenerated phosphorus-containing concentrated solution; (3) Resource utilization of the phosphorus-containing concentrated solution: adding ammonium salt and magnesium salt to the phosphorus-containing concentrated solution obtained in step (2), filtering, and collecting to obtain a solid product.

2. A process for deep purification and resource utilization of phosphorus-containing wastewater according to claim 1, characterized in that: In the step (1), the concentration of phosphorus-containing wastewater is 30 to 100 mg / L.

3. According to the process for deep purification and resource utilization of phosphorus-containing wastewater as described in claim 1, it is characterized in that: In the step (1), the adsorbent used includes metal-modified coal-made activated carbon, wood-made activated carbon or still-made activated carbon; preferably, iron-modified still-made activated carbon.

4. A process for deep purification and resource utilization of phosphorus-containing wastewater according to claim 1, characterized in that: In the step (2), the regeneration liquid used is a sodium hydroxide solution with a concentration of 1% to 4%, preferably 2%.

5. A process for deep purification and resource utilization of phosphorus-containing wastewater according to claim 4, characterized in that: In the step (2), the solid-liquid ratio of the adsorbent to the sodium hydroxide solution is 1g:10mL to 1g:500mL, preferably 1g:20mL to 1g:300mL, and the regeneration time is 4-6h.

6. A process for deep purification and resource utilization of phosphorus-containing wastewater according to claim 1, characterized in that: In the step (3), the molar ratio of ammonium to phosphorus can be selected from 1:0.1 to 1:3, preferably 1:0.9 to 1:1.

3.

7. A process for deep purification and resource utilization of phosphorus-containing wastewater according to claim 1, characterized in that: In the step (3), the molar ratio of magnesium to phosphorus can be selected from 1:0.1 to 1:3, preferably 1:0.9 to 1:1.

5.

8. A process for deep purification and resource utilization of phosphorus-containing wastewater according to claim 1, characterized in that: In the step (3), the pH value is 8-10, preferably 9.

5.

9. A process for deep purification and resource utilization of phosphorus-containing wastewater according to claim 1, characterized in that: In the step (3), the temperature used is 25-50°C; the reaction time is 5-25 min, preferably 15 min.

10. Use of the phosphorus-containing solid product obtained according to claim 1 in preparing fertilizers.

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