Method for promoting release of phosphorus in digested sludge through combination of three-dimensional electrolysis device and organic acid

Abstract

The invention discloses a method for promoting release of phosphorus in digested sludge through combination of a three-dimensional electrolysis device and organic acid. The method comprises the following steps: crushing epoxy resin particles, carbonizing, sieving to obtain carbon particles, uniformly mixing the carbon particles with digested sludge, putting the mixture into an anode chamber of a three-dimensional electrolysis device, electrifying for electrolysis, and adding an organic acid solution for acidolysis after the electrolysis is finished, thereby obtaining the carbon-containing sludge. According to the method, based on the synergistic effect between three-dimensional electrolysis and organic acid, the technological process is effectively simplified, the phosphorus release rate of the digested sludge is greatly increased, activity [H] can be generated in the three-dimensional electrolysis process, degradation of microbial cell walls and macromolecular organic matter in the sludge is promoted, phosphorus-containing substances in the sludge are exposed, and the phosphorus release rate of the digested sludge is increased. The organic acid is complexed with metal ions in a phosphorus-containing substance, the phosphorus-containing ions are released into the solution, tests show that the phosphorus release rate of the digested sludge by adopting the scheme can reach 85.89-88.53%, the concentration of orthophosphate in supernate after phosphorus release is 336.36-345.87 mg / L, and the phosphorus release rate is improved by 136-195% compared with that of acid leaching phosphorus release of a traditional physical method.

Description

Technical Field

[0001] The present invention relates to a method for releasing phosphorus from digested sludge, and in particular to a method for promoting the release of phosphorus from digested sludge by combining a three-dimensional electrolysis device with organic acid, belonging to the field of resource utilization of digested sludge. Background Art

[0002] Phosphorus is a vital element for biological growth and is crucial for industrial and agricultural production, environmental protection, and national economic security. Currently, the main source of phosphorus is the mining of limited underground phosphate rock. After being utilized by organisms, phosphorus decomposes with the death of organisms and ultimately returns to the environment, migrating to the ocean with surface runoff. Due to the non-volatility of phosphate, there is no effective way for phosphorus to return to land, other than through guano and the harvesting of marine fish. Therefore, the flow of terrestrial phosphorus resources is unidirectional and non-renewable. With the continued growth of the global population, the demand for phosphate rock for industrial and agricultural purposes continues to expand. Analyses of the current distribution and utilization of phosphorus sources worldwide have predicted that by 2035, the global supply of phosphate rock will exceed demand, and existing phosphate rock will be depleted within the next 100-150 years. Furthermore, naturally occurring phosphorus deposits contain excessively high levels of heavy metals (such as cadmium) and radioactive elements (such as uranium and radon), hindering the development of phosphate rock. Therefore, global phosphorus resource shortages will become one of the most formidable challenges of the 21st century.

[0003] In daily life, phosphorus is present in industrial raw materials, agricultural fertilizers, phosphorus-containing detergents, and human excreta. Wastewater from these phosphorus sources is transported through sewage pipe networks to sewage treatment plants for centralized treatment. The influent phosphorus concentration in Chinese sewage treatment plants is 4-5 mg / L. To prevent eutrophication, phosphorus removal at sewage treatment plants typically utilizes activated sludge combined with chemical flocculation. This process utilizes microorganisms to concentrate phosphorus from wastewater into the sludge. Chemical agents such as iron or aluminum salts are added to enhance phosphorus removal, ensuring the effluent phosphorus concentration is below 0.5 mg / L. This transfers over 90% of the phosphorus in wastewater to the sludge, making sewage treatment plant sludge a primary source of phosphorus. Recovering phosphorus from excess sludge not only reduces the phosphorus load on sewage treatment plants, facilitating their operation and improving sludge utilization, but also enables resource recycling and reuse, addressing issues such as phosphorus resource shortages. This process offers significant environmental and economic benefits. Although sludge contains a large amount of phosphorus, it cannot be used directly in agricultural production due to its complex composition, including toxic and harmful heavy metals and bacteria. Therefore, a suitable method is sought to release the phosphorus from the sludge into the supernatant, obtain the phosphorus-containing supernatant through solid-liquid separation, and then recover the phosphorus as a resource through crystallization. Typical technologies for releasing phosphorus from sludge include physical, physicochemical, and biological methods. Physical methods are less effective in releasing phosphorus, but they are simple to operate, low-cost, and stable. Physicochemical methods are more effective than physical methods, but they require complex and strict reaction conditions. Biological methods are not very effective in removing phosphorus from iron-containing sludge.

[0004] To address the above issues, multi-molecular weight organic acids are currently used to acid-leach phosphorus-rich sludge to release phosphorus. Digested sludge is the sludge produced after anaerobic digestion of activated sludge. Its phosphorus content is higher than that of municipal sludge, at 2-5%, and it contains a large amount of organic matter and microorganisms. In particular, the cell wall / cell membrane of microorganisms is a natural protective layer, making it difficult to fully release phosphorus through organic acid leaching alone. If strong acid leaching is used directly, although it can effectively destroy the macromolecular structure and expose more phosphorus sites, it consumes a lot of reagents and corrodes the equipment. On the other hand, the chloride ions and sulfate ions in the industrial strong acid are also very likely to remain in the phosphorus-releasing solution, making it difficult to crystallize and recover the subsequent phosphorus element. Summary of the Invention

[0005] In response to the existing technical problems, the purpose of the present invention is to provide a method for promoting the release of phosphorus in digested sludge by combining a three-dimensional electrolysis device with organic acid. This method is based on the synergistic effect between three-dimensional electrolysis and organic acid, which not only effectively simplifies the process flow, but also greatly improves the phosphorus release rate of digested sludge. After testing, the phosphorus release rate of digested sludge using the technical solution provided by the present invention can reach 85.89%~88.53%, and the concentration of orthophosphate in the supernatant after phosphorus release is 336.36~345.87 mg / L. Its phosphorus release rate is increased by 136~195% compared with the traditional physical acid leaching method.

[0006] To achieve the above technical objectives, the present invention provides a method for promoting phosphorus release in digested sludge using a three-dimensional electrolysis device in combination with an organic acid, which comprises: crushing epoxy resin particles, carbonizing them, sieving them to obtain carbon particles, mixing them evenly with digested sludge, and placing them in the anode chamber of the three-dimensional electrolysis device, applying power for electrolysis, and adding an organic acid solution for acid hydrolysis after the electrolysis is completed, thereby obtaining the obtained carbon particles;

[0007] The mass volume ratio of the carbon particles to the digested sludge is 3-8 g / L; the molar volume ratio of the organic acid solution to the digested sludge is 0.05-0.15 mol / L, calculated as organic acid.

[0008] The phosphorus in digested sludge mainly exists in the form of inorganic phosphorus bound to metals (Ca, Mg, Fe), but some phosphorus still exists in the form of organic phosphorus. The present invention first uses three-dimensional electrolysis to in-situ electrolyze water molecules to produce active [H], which promotes the degradation of microbial cell walls and macromolecular organic matter in the sludge, further exposing the phosphorus-containing substances therein. Then, organic acids are complexed with metal ions in the phosphorus-containing substances to release the phosphorus-containing ions into the solution. This process not only completely releases the inorganic phosphorus in the digested sludge, but also fully exposes the biomass phosphorus and organic phosphorus in the digested sludge, thereby significantly improving the overall phosphorus release rate.

[0009] As a preferred solution, the carbonization process is: placing the crushed epoxy resin particles in a tube furnace, carbonizing them at 400-600° C. for 1-3 hours under a protective atmosphere, and then cooling them to room temperature in the furnace.

[0010] As a preferred solution, the protective atmosphere is at least one of nitrogen, argon and helium.

[0011] As a preferred solution, the particle size of the carbon particles is -0.1 mm.

[0012] As a preferred solution, the digested sludge is sludge after mesophilic anaerobic digestion, with a pH of 8.0-8.5, a moisture content of 85-95%, and a total suspended solid content of 8.9-9.0×10 4 mg / L, and the phosphorus content is 45~55mg / g.

[0013] As a preferred solution, the anode chamber and the cathode chamber in the three-dimensional electrolysis device are separated by a cation exchange membrane, the anode electrode is a ruthenium-iridium-titanium alloy, and the cathode electrode is metallic titanium.

[0014] As a preferred solution, the conditions of the electrolysis process are: the current density is 5~30A / m 2 , the electrolysis time is 0.5~3h.

[0015] As a preferred solution, the organic acid solution is at least one of citric acid, lactic acid, oxalic acid and formic acid solutions.

[0016] As a preferred solution, the concentration of the organic acid solution is 0.5-1.2 mol / L.

[0017] As a preferred solution, the acid hydrolysis conditions are: at 20-60° C., adjusting the pH to 2.8-3.2, and reacting for 0.5-2 h.

[0018] As a preferred solution, the acid hydrolysis is further subjected to solid-liquid separation, the process of which is: centrifuging the acid-hydrolyzed material at 3000-5000 r / min for 5-15 minutes to obtain a supernatant and a mud cake.

[0019] As a preferred solution, the supernatant and mud cake are recovered separately after post-treatment, wherein the supernatant is filtered by a 0.45 μm filter membrane during post-treatment, and the mud cake is dried at 80-105° C. to constant weight.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are:

[0021] 1) The method provided by the present invention is based on the synergistic effect between three-dimensional electrolysis and organic acids. It not only effectively simplifies the process flow but also significantly improves the phosphorus release rate of digested sludge. The method first uses three-dimensional electrolysis to in situ electrolyze water molecules to produce active [H], which promotes the degradation of microbial cell walls / cell membranes and macromolecular organic matter in the sludge, further exposing the phosphorus-containing substances therein. Then, the organic acid complexes with the metal ions in the phosphorus-containing substances, thereby releasing the phosphorus-containing ions into the solution.

[0022] 2) In the technical solution provided by the present invention, the three-dimensional electrolysis treatment method adopted not only increases the contact area between the sludge and the electrode and increases the active sites compared to the traditional two-dimensional electrolysis, but also plays a role in rectification, making the current distribution more uniform, effectively avoiding the edge effect of the traditional electrolysis process, thereby significantly improving the hydrogen production capacity of the electrolysis process.

[0023] 3) In the technical solution provided by the present invention, the raw materials such as epoxy resin and organic acid used are widely available and low in cost. While effectively reducing production costs, it also significantly improves the phosphorus release rate of digested sludge. Tests have shown that the phosphorus release rate of digested sludge using the above solution can reach 85.89% to 88.53%, and the concentration of orthophosphate in the supernatant after phosphorus release is 336.36 to 345.87 mg / L. Its phosphorus release rate is 136 to 195% higher than that of traditional physical acid leaching. Furthermore, the organic acid used in this method does not contain sulfur, which effectively solves the technical problems of unstable phosphorus release in traditional acid leaching and the influence of sulfur on the crystallization and recovery of phosphorus in the released phosphorus solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the three-dimensional electrolysis device used in Examples 1 and 2 of the present invention;

[0025] Figure 2 Schematic diagram of phosphorus concentration in the original digested sludge and the supernatant of the digested sludge after phosphorus release treatment in Examples 1 and 2 of the present invention and Comparative Examples 1 and 2;

[0026] Figure 3 This is a schematic diagram of the phosphorus release rate of digested sludge after phosphorus release treatment in Examples 1 and 2 of the present invention and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0027] For ease of understanding of the present invention, the present invention will be described more fully below with reference to specific implementation examples. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0028] Example 1

[0029] In this embodiment, the digested sludge used was from the sludge in the high-temperature anaerobic digestion tank of a solid waste treatment center in Changsha City, Hunan Province. The basic physical and chemical properties of the sludge were as follows: pH 8.315±0.065, moisture content 90.39±0.51%, total suspended solids (TSS) 89487.47±240.04 mg / L, and phosphorus content 50.12±1.55 mg / g.

[0030] This embodiment provides a method for promoting phosphorus release from digested sludge by combining a three-dimensional electrolysis device with an organic acid. The specific process is as follows:

[0031] Step 1: Place the epoxy resin in a tubular furnace, pass nitrogen as a protective gas, maintain calcination at 500°C for 2 hours, cool to room temperature, and grind the carbon particles to a diameter of less than 0.1 mm to obtain the target carbon particles.

[0032] Step 2: Mix the target carbon particles with the sludge at a concentration of 5g / L and place them in an electrochemical reaction device (such as Figure 1 The anode is shown in Figure 2, at 30A / m 2 Electrolysis was carried out for 1 h at the current density;

[0033] Step 3: Place the electrochemically treated mixed solution in a beaker, add citric acid solution, the mass molar ratio of citric acid to digested sludge is 0.1 mol / L, adjust the pH to about 3.0, stir at 20°C (room temperature) for 1.0 h, and let it stand overnight;

[0034] Step 4: Take 20 mL of the mixed solution and place it in a centrifuge tube. Centrifuge it in a high-speed centrifuge at 4000 r / min for 10 min. Filter the supernatant with a 0.45 μm filter membrane and determine the inorganic phosphorus in the supernatant.

[0035] like Figure 2 As shown in Figure 2, after treatment with citric acid, the inorganic phosphorus content in the supernatant increased from 4.68±0.58 mg / L to 336.36±0.53 mg / L. Furthermore, the solid after solid-liquid separation was placed in an oven at 105°C and dried to constant weight, ground in a mortar, and sealed through a 100-mesh sieve for storage. The changes in phosphorus form content before and after treatment with different organic acids were determined using the SMT (Standards Measurements and Testing) phosphorus form fractionation extraction method. The results are shown in Figure 2. Figure 3 As shown in the figure, the phosphorus release rate of sludge treated with citric acid can reach 85.89%.

[0036] Example 2

[0037] This embodiment is identical to embodiment 1, except that the organic acid used is oxalic acid. Figure 2 As shown in Figure 2, the content of inorganic phosphorus in the sludge supernatant increased from 4.68±0.58mg / L to 345.87±1.59mg / L. Figure 3 It can be seen that the sludge phosphorus release rate reached 88.53%.

[0038] Comparative Example 1

[0039] This comparative example is identical to Example 1, except that no carbon particles are added to the three-dimensional electrolysis device. After treatment, the inorganic phosphorus content in the sludge supernatant was 242.74±0.21 mg / L, and the sludge phosphorus release rate was 72.32%.

[0040] Comparative Example 2

[0041] This comparative example is identical to Example 2, except that no carbon particles are added to the three-dimensional electrolysis device. After treatment, the inorganic phosphorus content in the sludge supernatant was 248.13±0.32 mg / L, and the sludge phosphorus release rate was 79.07%.

[0042] Comparative Example 3

[0043] This comparative case was identical to Example 1, except that only the three-dimensional electrolysis experiment was performed, and no subsequent acid leaching experiment was performed. After treatment, the inorganic phosphorus content in the sludge supernatant was 6.54 ± 0.21 mg / L, and the sludge phosphorus release rate was 22.17%.

[0044] It can be seen from the above embodiments and comparative examples that in the technical solution provided by the present invention, the use of a three-dimensional electrolysis device in combination with an organic acid to release phosphorus from digested sludge can greatly increase the sludge phosphorus release rate, facilitating the subsequent resource recovery of phosphorus by crystallization.

Claims

1. A method for promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid, characterized in that: include: The epoxy resin particles are crushed and carbonized, and then sieved to obtain carbon particles, which are then mixed evenly with digested sludge and placed in the anode chamber of a three-dimensional electrolysis device. Electrolysis is performed by applying electricity, and an organic acid solution is added for acid hydrolysis after the electrolysis is completed. The mass volume ratio of the carbon particles to the digested sludge is 3-8 g / L; the molar volume ratio of the organic acid solution to the digested sludge is 0.05-0.15 mol / L, calculated as organic acid.

2. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 1, characterized in that: The carbonization process is as follows: the crushed epoxy resin particles are placed in a tube furnace, carbonized at 400-600° C. for 1-3 hours under a protective atmosphere, and then cooled to room temperature along with the furnace.

3. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 2, characterized in that: The protective atmosphere is at least one of nitrogen, argon and helium; and the particle size of the carbon particles is -0.1 mm.

4. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 1, characterized in that: The digested sludge is sludge after mesophilic anaerobic digestion, with a pH of 8.0-8.5, a moisture content of 85-95%, and a total suspended fixed mass of 8.9-9.0×10 4 mg / L, and the phosphorus content is 45~55mg / g.

5. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 1, characterized in that: The anode chamber and the cathode chamber in the three-dimensional electrolysis device are separated by a cation exchange membrane. The anode electrode is a ruthenium-iridium-titanium alloy, and the cathode electrode is metal titanium.

6. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 1, characterized in that: The conditions of the electrolysis process are: the current density is 5~30A / m 2 , the electrolysis time is 0.5~3h.

7. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 1, characterized in that: The organic acid solution is at least one of citric acid, lactic acid, oxalic acid and formic acid solutions; the concentration of the organic acid solution is 0.5-1.2 mol / L.

8. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 1, characterized in that: The acid hydrolysis conditions are: at 20-60° C., adjusting the pH to 2.8-3.2, and reacting for 0.5-2 h.

9. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 1, characterized in that: After the acid hydrolysis, solid-liquid separation treatment is required, and the process is as follows: the acid-hydrolyzed material is centrifuged at 3000-5000 r / min for 5-15 minutes to obtain a supernatant and a mud cake.

10. The method of promoting phosphorus release from digested sludge using a three-dimensional electrolysis device combined with organic acid according to claim 9, characterized in that: The supernatant and the mud cake are recovered separately after post-treatment, wherein the supernatant is filtered by a 0.45 μm filter membrane during post-treatment, and the mud cake is dried at 80-105° C. to a constant weight during post-treatment.

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