Method for extracting soluble organic matters in sludge

Abstract

The invention discloses a method for extracting soluble organic matters in sludge, which comprises the following steps: firstly, carrying out micropore activating treatment on the sludge, and then, carrying out focused ultrasonic wave and hydraulic pulse alternating action to obtain pretreated sludge; in a low-temperature environment of 5 DEG C, continuously introducing ozone into the pretreated sludge, then sequentially carrying out separation by virtue of a ceramic microfiltration membrane and an organic nanofiltration membrane, then applying pulse voltage to a separation liquid for treatment, and then treating the concentrated separation liquid by virtue of concentration, evaporation and a nitrogen cyclone drying system, so as to obtain a DOM powdery product of which the water content is less than or equal to 3%. According to the invention, through micropore activation treatment, sound pressure pulse crushing treatment and the like, specific dissociation of the organic matter-colloid complex can be promoted, no chemical additive is involved, and no secondary pollution risk and other problems are caused.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge treatment, and particularly relates to a method for extracting soluble organic matter from sludge. Background Art

[0002] Sludge is a product after sewage treatment and is an extremely complex heterogeneous body composed of organic fragments, bacterial cells, inorganic particles, colloids, etc. The main characteristics of sludge are high water content (up to over 99%), high organic matter content, easy to rot and stink, and fine particles, small specific gravity, and colloidal liquid state. It is a thick substance between liquid and solid, can be transported by pump, but it is very difficult to separate solid and liquid by sedimentation.

[0003] The extraction technology of soluble organic matter in sludge is an important research direction in the field of waste resource utilization. With the acceleration of the urbanization process, the sludge production increases year by year, and a large amount of organic matter (such as proteins, polysaccharides, and humic acids, etc.) contained in it has potential resource value. Traditional sludge treatment aims at reduction and harmlessness, but the direct incineration or landfill of organic matter is likely to cause resource waste and environmental pollution. How to efficiently extract soluble organic matter and achieve resource conversion has become the core issue of current technological development.

[0004] In traditional methods, physicochemical treatment changes the sludge structure by adding alkaline solutions or chemical agents to promote the dissolution of organic matter, and then obtains the target substance through precipitation separation, but there are defects such as large consumption of agents and high risk of secondary pollution. Biochemical treatment relies on microbial metabolism to decompose organic matter. Although the cost is relatively low, the purity and efficiency of the extraction products are limited by microbial activity and reaction cycles. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for extracting soluble organic matter from sludge.

[0006] The technical solution of the present invention is: a method for extracting soluble organic matter from sludge, comprising the following steps:

[0007] S1. Perform microporous activation treatment on the sludge, and then in a constant temperature bath at 18 - 25 °C, use a focused ultrasonic wave with a frequency of 1.0 - 1.5 MHz and an acoustic intensity of 0.5 - 1 W / cm 2 , and cooperate with a hydraulic pulse of 3 - 6 MPa (pulse width 50 μs) to act alternately for 40 - 50 min to obtain pretreated sludge; specifically dissociate the organic matter - colloid complex; destroy the cell wall structure and release intracellular organic matter;

[0008] S2. Continuously introduce ozone into the pretreated sludge in a low-temperature environment of 5°C for a contact time of 15 - 25 minutes to promote the dissolution of organic matter. Subsequently, separate it through a ceramic microfiltration membrane and an organic nanofiltration membrane in sequence to obtain a separation liquid. It is carried out in two stages, and gradient membrane separation realizes the fractional collection of macromolecular humic acid and small-molecule DOM.

[0009] S3. Apply a pulsed voltage to the separation liquid for 35 - 45 minutes to increase the DOM concentration to 1500 mg / L. Subsequently, maintain the temperature of the concentration device at 4°C, and concentrate the separation liquid to 1 / 5 of the original volume through vacuum evaporation (vacuum degree -0.08 MPa) to obtain a concentrated separation liquid.

[0010] S4. Use a -30°C nitrogen cyclone drying system to treat the concentrated separation liquid, instantaneously solidify the active components of the organic matter, and obtain a DOM powdery product with a moisture content ≤ 3%.

[0011] Furthermore, the method of the microporous activation treatment is as follows: Place the sludge with a moisture content of 80 - 90% in a subcritical carbon dioxide environment, maintain the pressure at 8 MPa for 25 - 40 minutes.

[0012] Note: Subcritical CO2 has high solubility and diffusivity, can effectively extract lipophilic organic matter or target substances in the sludge, improve the treatment efficiency, and can expand the diffusion channels of organic matter by treating in a subcritical carbon dioxide environment to activate the sludge micropores and improve the extraction rate of DOM from the subsequent sludge.

[0013] Even further, after 10 - 15 minutes in the subcritical carbon dioxide environment, apply a pulsed direct current electric field to the sludge for 90 - 150 minutes. The field strength of the pulsed direct current electric field is 12 - 15 V / cm, the pulse width is 1 ms, and the interval is 3 - 5 ms, to prompt the negatively charged dissolved organic matter to migrate and aggregate towards the positive electrode.

[0014] Note: By utilizing the characteristics of the directional arrangement of the electric field, use a pulsed direct current electric field to treat the sludge after microporous activation treatment. Under the electrophoresis enrichment effect, prompt the negatively charged dissolved organic matter to migrate and aggregate towards the positive electrode, thereby enhancing the subsequent extraction effect of DOM from the sludge.

[0015] Furthermore, the alternating mode of the focused ultrasonic wave and the hydraulic pulse is as follows: Each alternating cycle includes 10 - 12 s of acoustic pressure crushing of the focused ultrasonic wave and 5 - 7 s of hydraulic impact of the hydraulic pulse.

[0016] Description: By subjecting the pretreated sludge to acoustic pressure pulse crushing, using the alternating method of focused ultrasonic waves and hydraulic pulses, under the action of cavitation dissociation, it can promote the specific dissociation of organic matter-colloid complexes. The acoustic pressure crushing and hydraulic impact in the above alternating cycle have the best effect on sludge crushing treatment, thus promoting the extraction rate of DOM in the sludge in subsequent treatment.

[0017] Furthermore, during the ozone injection, ultrasonic waves with a frequency of 40 kHz and a gradually decreasing power density are supplemented for co-treatment. After the ultrasonic power density decays to 0.1 W / mL, the ozone injection concentration is increased at a rate of 2 - 5 mg / L per minute.

[0018] The initial power density of the ultrasonic waves is 0.5 W / mL, the decay rate is x W / mL, and the co-treatment time of the ultrasonic waves is t, satisfying the following formula:

[0019]

[0020] Among them, the constant i takes 1 or 2.

[0021] Description: Using ultrasonic waves for co-assistance in the early stage of ozone injection can promote the diffusion of ozone in the sludge, and the ultrasonic waves can crush ozone into microbubbles, significantly increasing the dissolution rate and expanding the reaction interface, thereby promoting the dissolution of organic matter. However, as the ozone continues to be injected, the co-effect of the ultrasonic waves gradually decreases, and at this stage, continuous use of ultrasonic waves with a high power density is likely to affect the dissolution of organic matter. Therefore, in the above operation, while using ultrasonic waves to co-treat with ozone in the initial stage, it can significantly enhance the treatment effect of ozone on the sludge and improve the dissolution of organic matter.

[0022] Furthermore, the pulsed voltage is applied using a titanium-based ruthenium-iridium electrode, and the current density is 0.5 - 1 A / m 2 , the pulsed voltage lasts for 8 - 15 s at 5 V in the positive direction and 3 - 8 s at 3 V in the negative direction.

[0023] Description: By using pulsed voltage for post-treatment of the separation liquid, the DOM concentration can be further increased, thereby promoting the treatment effects of subsequent low-temperature concentration and low-temperature drying, and obtaining high-quality DOM powder.

[0024] Furthermore, the operating pressure of the ceramic microfiltration membrane is 2.0 - 3.0 bar, and the operating pressure of the organic nanofiltration membrane is 8.0 - 10.0 bar.

[0025] Description: By adopting two-stage membrane filtration for gradient membrane separation of sludge, the fractional collection of macromolecular and small-molecular DOM can be realized. Under the above operating pressure, the ceramic microfiltration membrane and the organic nanofiltration membrane can perform effective filtration.

[0026] Furthermore, the gas velocity of the nitrogen cyclone drying system is 10 - 12 m / s, and the residence time is 12 - 15 s.

[0027] Explanation: By adopting the above nitrogen cyclone drying system, the organic matter active components can be instantaneously solidified, thereby obtaining a DOM powdery product with a moisture content ≤ 3%.

[0028] The beneficial effects of the present invention are as follows:

[0029] (1) The method for extracting soluble organic matter from sludge of the present invention can promote the specific dissociation of the organic matter - colloid complex by using microporous activation treatment, acoustic pressure pulse fragmentation treatment, etc. Without the intervention of chemical additives and the risk of secondary pollution, etc., and the recovery rate of organic matter can reach 85 - 90%, which is 25 - 30% higher than that of the traditional method.

[0030] (2) The method for extracting soluble organic matter from sludge of the present invention can significantly enhance the treatment effect of ozone on sludge and improve the dissolution of organic matter by using the synergistic treatment of ozone and ultrasonic waves while using the ultrasonic wave to synergistically treat ozone in the initial stage.

[0031] (3) The method for extracting soluble organic matter from sludge of the present invention can achieve the hierarchical collection of macromolecular and small - molecular DOM by adopting two - stage membrane filtration for the gradient membrane separation of sludge, thereby providing more operation options for the extraction of soluble organic matter. Specific Embodiments

[0032] The following further describes the present invention in detail in combination with specific embodiments to better reflect the advantages of the present invention.

[0033] Example 1: A method for extracting soluble organic matter from sludge, comprising the following steps:

[0034] S1. Perform microporous activation treatment on the sludge. The method of microporous activation treatment is as follows: Place the sludge with a moisture content of 85% in a sub - critical carbon dioxide environment, maintain the pressure at 8 MPa for 35 min, and then in a constant - temperature bath at 23°C, use a focused ultrasonic wave with a frequency of 1.2 MHz and an acoustic intensity of 0.8 W / cm 2 to act alternately with a 5 MPa hydraulic pulse (pulse width 50 μs) for 45 min. The alternating manner of the focused ultrasonic wave and the hydraulic pulse is: Each alternating cycle includes 11 s of acoustic pressure fragmentation of the focused ultrasonic wave and 6 s of hydraulic impact of the hydraulic pulse to obtain pretreated sludge; specifically dissociate the organic matter - colloid complex; destroy the cell wall structure and release intracellular organic matter;

[0035] S2. In a low-temperature environment of 5°C, ozone is continuously introduced into the pretreated sludge for 20 minutes of contact time to promote the dissolution of organic matter. Subsequently, separation is carried out successively through a ceramic microfiltration membrane and an organic nanofiltration membrane. The operating pressure of the ceramic microfiltration membrane is 2.5 bar, and the operating pressure of the organic nanofiltration membrane is 9.0 bar to obtain a separation liquid. It is carried out in two stages, and gradient membrane separation realizes the fractional collection of macromolecular humic acid and small-molecule DOM.

[0036] S3. The separation liquid is treated with a pulsed voltage for 42 minutes, applied with a titanium-based ruthenium-iridium electrode, and the current density is 0.8 A / m 2 , the pulsed voltage is 5 V in the positive direction for 12 s and 3 V in the negative direction for 5 s, and the DOM concentration is increased to 1500 mg / L. Subsequently, the temperature of the concentration device is maintained at 4°C, and the separation liquid is concentrated to 1 / 5 of the original volume by vacuum evaporation (vacuum degree -0.08 MPa) to obtain a concentrated separation liquid.

[0037] S4. The concentrated separation liquid is treated with a -30°C nitrogen cyclone drying system. The gas velocity of the nitrogen cyclone drying system is 11 m / s, and the residence time is 14 s to instantaneously solidify the active components of the organic matter and obtain a DOM powdery product with a moisture content ≤ 3%.

[0038] Example 2: The difference between this example and Example 1 is that sludge with a moisture content of 80% is placed in a subcritical carbon dioxide environment, and the pressure is maintained at 8 MPa for 25 minutes.

[0039] Example 3: The difference between this example and Example 1 is that sludge with a moisture content of 90% is placed in a subcritical carbon dioxide environment, and the pressure is maintained at 8 MPa for 40 minutes.

[0040] Example 4: The difference between this example and Example 1 is that in an 18°C constant temperature bath, a focused ultrasonic wave with a frequency of 1.0 MHz and an acoustic intensity of 0.5 W / cm 2 is used, and it is alternately acted with a 3 MPa hydraulic pulse (pulse width 50 μs) for 40 minutes. The alternating mode of the focused ultrasonic wave and the hydraulic pulse is: each alternating cycle includes 10 s of acoustic pressure crushing of the focused ultrasonic wave and 5 s of hydraulic impact of the hydraulic pulse to obtain pretreated sludge.

[0041] Example 5: The difference between this example and Example 1 is that in a 25°C constant temperature bath, a focused ultrasonic wave with a frequency of 1.5 MHz and an acoustic intensity of 1 W / cm 2 is used, and it is alternately acted with a 6 MPa hydraulic pulse (pulse width 50 μs) for 50 minutes. The alternating mode of the focused ultrasonic wave and the hydraulic pulse is: each alternating cycle includes 12 s of acoustic pressure crushing of the focused ultrasonic wave and 7 s of hydraulic impact of the hydraulic pulse to obtain pretreated sludge.

[0042] Example 6: The difference between this example and Example 1 is that in a low-temperature environment of 5°C, ozone is continuously introduced into the pretreated sludge for 15 minutes of contact time to promote the dissolution of organic matter; then, separation is carried out successively through a ceramic microfiltration membrane and an organic nanofiltration membrane. The operating pressure of the ceramic microfiltration membrane is 2.0 bar, and the operating pressure of the organic nanofiltration membrane is 8.0 bar to obtain a separation liquid.

[0043] Example 7: The difference between this example and Example 1 is that in a low-temperature environment of 5°C, ozone is continuously introduced into the pretreated sludge for 25 minutes of contact time to promote the dissolution of organic matter; then, separation is carried out successively through a ceramic microfiltration membrane and an organic nanofiltration membrane. The operating pressure of the ceramic microfiltration membrane is 3.0 bar, and the operating pressure of the organic nanofiltration membrane is 10.0 bar to obtain a separation liquid.

[0044] Example 8: The difference between this example and Example 1 is that the separation liquid is treated with a pulsed voltage for 35 minutes, applied using a titanium-based ruthenium-iridium electrode, and the current density is 0.5 A / m 2 , the pulsed voltage is 5 V in the positive direction for 8 s and 3 V in the negative direction for 3 s.

[0045] Example 9: The difference between this example and Example 1 is that the separation liquid is treated with a pulsed voltage for 45 minutes, applied using a titanium-based ruthenium-iridium electrode, and the current density is 1 A / m 2 , the pulsed voltage is 5 V in the positive direction for 15 s and 3 V in the negative direction for 8 s.

[0046] Example 10: The difference between this example and Example 1 is that a -30°C nitrogen cyclone drying system is used to treat the concentrated separation liquid. The gas velocity of the nitrogen cyclone drying system is 10 m / s, and the residence time is 12 s.

[0047] Example 11: The difference between this example and Example 1 is that a -30°C nitrogen cyclone drying system is used to treat the concentrated separation liquid. The gas velocity of the nitrogen cyclone drying system is 12 m / s, and the residence time is 15 s.

[0048] Example 12: The difference between this example and Example 1 is that after 12 minutes in the subcritical carbon dioxide environment, a pulsed DC electric field is applied to the sludge for 135 minutes. The field strength of the pulsed DC electric field is 14 V / cm, the pulse width is 1 ms, and the interval is 4 ms, prompting the negatively charged dissolved organic matter to migrate and aggregate towards the positive electrode.

[0049] Example 13: The difference between this example and Example 12 is that after maintaining in the subcritical carbon dioxide environment for 10 min, pulsed direct current electric field treatment is applied to the sludge for 90 min. The field strength of the pulsed direct current electric field is 12 V / cm, the pulse width is 1 ms, and the interval is 3 ms, which promotes the negatively charged dissolved organic matter to migrate and aggregate towards the positive electrode.

[0050] Example 14: The difference between this example and Example 12 is that after maintaining in the subcritical carbon dioxide environment for 15 min, pulsed direct current electric field treatment is applied to the sludge for 150 min. The field strength of the pulsed direct current electric field is 15 V / cm, the pulse width is 1 ms, and the interval is 5 ms, which promotes the negatively charged dissolved organic matter to migrate and aggregate towards the positive electrode.

[0051] Example 15: The difference between this example and Example 12 is that during the ozone injection, ultrasonic wave with a frequency of 40 kHz and gradually decaying power density is applied for cooperative treatment. After the ultrasonic power density decays to 0.1 W / mL, the ozone injection concentration is increased at a rate of 4 mg / L per minute.

[0052] The initial power density of the ultrasonic wave is 0.5 W / mL, the decay rate is x W / mL, and the ultrasonic wave cooperative treatment time is t, which satisfies the following formula:

[0053]

[0054] Among them, the constant i takes 1, x takes 0.1 W / mL, and it is calculated that t = 4 min.

[0055] Example 16: The difference between this example and Example 15 is that the constant i takes 1, x takes 0.2 W / mL, and it is calculated that t = 2 min.

[0056] Example 17: The difference between this example and Example 15 is that the constant i takes 2, x takes 0.1 W / mL, and it is calculated that t = 8 min.

[0057] Example 18: The difference between this example and Example 15 is that the constant i takes 2, x takes 0.2 W / mL, and it is calculated that t = 4 min.

[0058] Example 19: The difference between this example and Example 15 is that the ozone injection concentration is increased at a rate of 2 mg / L per minute.

[0059] Example 20: The difference between this example and Example 15 is that the ozone injection concentration is increased at a rate of 5 mg / L per minute.

[0060] Application experimental example:

[0061] The sludge samples in a certain area of the city are now subjected to the extraction operation of soluble organic matter using the extraction methods of each embodiment, and a TOC analyzer is used to measure the DOC concentration in the separation liquid, unit: mg / L. The calculation formula is as follows:

[0062]

[0063] The formula for the total extraction rate is as follows:

[0064]

[0065] Among them, the total organic matter content of the sludge is measured by the ignition method at 550 °C; the measurement results of the DOM extraction rate are shown in Table 1 below:

[0066] Table 1 Extraction rates of sludge soluble organic matter in each embodiment

[0067] Project DOM extraction rate Project DOM extraction rate Example 1 85.69％ Example 11 85.56％ Example 2 84.95％ Example 12 88.43％ Example 3 85.71％ Example 13 88.32％ Example 4 84.87％ Example 14 88.41％ Example 5 85.74％ Example 15 90.72％ Example 6 85.11％ Example 16 90.67％ Example 7 85.69％ Example 17 90.73％ Example 8 85.08％ Example 18 90.71％ Example 9 85.27％ Example 19 90.70％ Example 10 85.49％ Example 20 90.55％

[0068] As can be seen from the results in Table 2 above, after adopting the extraction method of soluble organic matter in the sludge of each embodiment of the present invention, the extraction rate can reach 85-90%. At the same time, in order to compare and verify the extraction effect of the extraction method of the present invention, an oxidation-membrane separation combined extraction method is now adopted, which combines low-temperature oxidation pretreatment (Fenton reagent) with inorganic ceramic membrane concentration. The measurement results of its DOM recovery rate are shown in Table 2 below:

[0069] Table 2 Extraction rates of sludge soluble organic matter in the control

[0070] Project DOM extraction rate Control (oxidation - membrane separation combined method) 60.52％

[0071] As can be seen from the above results, under the existing extraction method, the DOM extraction rate of the sludge samples in a certain area of the city is only 60.52%. Its extraction effect is much lower than the extraction efficiency of the extraction method of the present invention. The extraction efficiency of the extraction method of the present invention is increased by about 25-30% compared with this method as a whole.

[0072] At the same time, it can be found from the comparison of the results in Table 1 that different extraction methods and parameters have a certain impact on the DOM extraction rate. The specific comparative analysis is as follows:

[0073] Analysis 1: Examples 2 - 11 are all extraction methods with different parameters from Example 1. By comparing Example 2, Example 3 with Example 1, it can be seen that different times of microporous activation treatment of sludge have a certain impact on the DOM extraction rate. Among them, the microporous activation treatment effect of Example 3 is the best, but the difference in the DOM extraction rate between it and Example 1 is only 0.02%. And Example 3 uses a longer microporous activation treatment time. Therefore, from the perspective of economy and extraction efficiency, the comprehensive extraction effect of Example 1 is better. By comparing Example 4, Example 5 with Example 1, it can be seen that different acoustic pressure pulse crushing treatments of sludge have a certain impact on the DOM extraction rate. Among them, the acoustic pressure pulse crushing treatment effect of Example 5 is the best, but the difference in the DOM extraction rate between it and Example 1 is only 0.05%. And Example 5 uses a larger parameter of acoustic pressure pulse crushing treatment. From the perspective of economy and extraction efficiency, the comprehensive extraction effect of Example 1 is better. By comparing Example 6, Example 7 with Example 1, it can be seen that different ozone treatments of the pretreated sludge have a certain impact on the DOM extraction rate. Among them, the ozone treatment effects of Example 1 and Example 7 are the best. However, Example 7 uses a longer ozone contact time and membrane pressure. Therefore, the comprehensive extraction effect of Example 1 is better. By comparing Example 8, Example 9 with Example 1, it can be seen that different pulsed voltage treatments of the separation liquid have a certain impact on the DOM extraction rate. Among them, the parameter of the pulsed voltage treatment in Example 1 is the best. By comparing Example 10, Example 11 with Example 1, it can be seen that different nitrogen cyclone drying treatments of the concentrated separation liquid have a certain impact on the DOM extraction rate. Among them, the parameter of the nitrogen cyclone drying treatment in Example 1 is the best.

[0074] Analysis 2: Examples 12 - 14 are all based on Example 1, and the sludge after microporous activation treatment is treated with pulsed direct current electric field. By comparing Example 12 with Example 1, it can be seen that by utilizing the characteristic of directional arrangement of the electric field, the pulsed direct current electric field can be used to treat the sludge after microporous activation treatment. Under the electrophoresis enrichment effect, it can promote the negatively charged dissolved organic matter to migrate and aggregate towards the positive electrode, thereby enhancing the subsequent extraction effect of DOM in the sludge. By comparing Example 13, Example 14 with Example 12, it can be seen that under different treatment parameters of the pulsed direct current electric field, it has a certain impact on the DOM extraction rate. Among them, the treatment parameter of the pulsed direct current electric field in Example 12 is the best.

[0075] Analysis 3: Examples 15 - 20 are all based on Example 1, optimizing the ozone treatment. By adopting a controllable ultrasonic assisted treatment, the extraction rate of DOM is enhanced. From the comparison between Example 15 and Example 1, it can be seen that using ultrasonic waves for collaborative assistance in the early stage of ozone introduction can significantly enhance the treatment effect of ozone on sludge while using ultrasonic waves to collaborate with ozone in the initial stage of treatment, improving the dissolution of organic matter. From the comparison between Example 16, Example 17, Example 18 and Example 15, it can be seen that under the calculation of the above formula, the DOM extraction rates of each example are basically the same. Therefore, corresponding parameters can be selected according to the actual production situation to achieve a similar DOM extraction effect. From the comparison between Example 19, Example 20 and Example 15, it can be seen that different ozone elevation rates have a certain impact on the DOM extraction rate, and the DOM extraction rate of Example 15 is the optimal.

Claims

1. A method for extracting soluble organic matter from sludge, characterized in that It includes the following steps: S1. Perform microporous activation treatment on the sludge, and then in a constant temperature bath at 18 - 25 °C, use focused ultrasonic waves with a frequency of 1.0 - 1.5 MHz and an acoustic intensity of 0.5 - 1 W / cm 2 , and alternately apply a 3 - 6 MPa hydraulic pulse for 40 - 50 min to obtain pretreated sludge; S2. In a low-temperature environment of 5°C, ozone is continuously introduced into the pretreated sludge, and the contact time is 15 - 25 min to promote the dissolution of organic matter. Subsequently, it is separated successively through a ceramic microfiltration membrane and an organic nanofiltration membrane to obtain a separation liquid; S3. The separation liquid is treated with a pulsed voltage for 35 - 45 min. Subsequently, the temperature of the concentration device is maintained at 4°C, and the separation liquid is concentrated to 1 / 5 of the original volume by vacuum evaporation to obtain a concentrated separation liquid; S4. The concentrated separation liquid is treated with a -30°C nitrogen cyclone drying system to obtain a DOM powdery product with a moisture content ≤ 3%; 2. The extraction method of soluble organic matter in sludge according to claim 1, characterized in that, The method of the microporous activation treatment is: placing sludge with a moisture content of 80 - 90% in a subcritical carbon dioxide environment, maintaining the pressure at 8 MPa for 25 - 40 min.

3. The method for extracting soluble organic matter from sludge according to claim 2, characterized in that, After continuously staying in the subcritical carbon dioxide environment for 10 - 15 min, a pulsed direct current electric field is applied to the sludge for 90 - 150 min. The field strength of the pulsed direct current electric field is 12 - 15 V / cm, the pulse width is 1 ms, and the interval is 3 - 5 ms.

4. The extraction method of soluble organic matter in sludge according to claim 1, characterized in that, The alternating manner of the focused ultrasonic wave and the hydraulic pulse is: each alternating cycle includes 10 - 12 s of acoustic pressure crushing of the focused ultrasonic wave and 5 - 7 s of hydraulic impact of the hydraulic pulse.

5. The extraction method of soluble organic matter in sludge according to claim 1, characterized in that, During the ozone introduction, ultrasonic waves with a frequency of 40 kHz and a gradually decreasing power density are added for synergistic treatment. After the ultrasonic power density decays to 0.1 W / mL, the ozone introduction concentration is increased at a rate of 2 - 5 mg / L per minute. The initial power density of the ultrasonic wave is 0.5 W / mL, the decay rate is x W / mL, and the ultrasonic synergistic treatment time is t, satisfying the following formula: Among them, the constant i takes 1 or 2.

6. The extraction method of soluble organic matter in sludge according to claim 1, characterized in that The pulsed voltage is applied using a titanium-based ruthenium-iridium electrode, and the current density is 0.5 to 1 A / m 2 , the pulsed voltage is 5 V in the forward direction for 8 to 15 s and 3 V in the reverse direction for 3 to 8 s.

7. The extraction method of soluble organic matter in sludge according to claim 1, characterized in that, The operating pressure of the ceramic microfiltration membrane is 2.0 - 3.0 bar, and the operating pressure of the organic nanofiltration membrane is 8.0 - 10.0 bar.

8. The extraction method of soluble organic matter in sludge according to claim 1, characterized in that, The concentrated separation liquid is treated with a -30°C nitrogen cyclone drying system. The gas velocity of the nitrogen cyclone drying system is 10 - 12 m / s, and the residence time is 12 - 15 s.

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