Method for improving dewatering performance of sludge by low-temperature hydrothermal coupling deep eutectic solvent

Abstract

The present application relates to sludge dewatering treatment technical field, specifically to a kind of low-temperature hydrothermal coupling deep eutectic solvent improves the method for sludge dewatering performance, comprising the following steps: hydrogen bond donor and hydrogen bond acceptor are put into reactor, heating stirring to obtain deep eutectic solvent;Take the sludge to be handled, add the deep eutectic solvent, and stir mixing reaction;The sludge added with deep eutectic solvent is placed in the hot hydrolysis reaction device with stirring, and hot hydrolysis treatment is carried out, continuous stirring is carried out, and sludge dewatering process is completed. By adding specific DES to sludge, the hot hydrolysis treatment temperature can be reduced, and efficient dewatering can be realized at a lower temperature (<100 DEG C). Not only the processing cost is reduced, but also the safety is improved, which has extremely far-reaching social significance and economic value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge dewatering treatment, in particular to a method for improving sludge dewatering performance by low-temperature hydrothermal coupling deep eutectic solvent. BACKGROUND

[0002] Activated sludge process is the most commonly used wastewater treatment process in sewage treatment plants at present, and excess sludge is an inevitable byproduct in the biological treatment process of wastewater, which is rich in various pollutants and poses a great threat to the environment and human health. The moisture content of raw activated sludge can reach 99%, and it has the characteristics of high moisture content, large volume and poor dewatering performance, and its treatment and disposal cost can account for more than 60% of the operating cost of the sewage plant. The increasing production of excess sludge and the cost of sludge treatment and disposal have become a great challenge for current sewage treatment plants, and improving sludge dewatering performance and reducing the moisture content of excess sludge have become urgent problems to be solved.

[0003] In recent years, the method of using thermal hydrolysis treatment to destroy the water-holding performance of sludge flocs and promote sludge dewatering has attracted more and more attention. This method can destroy the structure of extracellular polymeric substances and cell walls by heating the sludge to a certain temperature in a high-temperature and high-pressure reactor, causing a series of complex free radical reactions in the reactor, resulting in the disintegration of sludge flocs and the release of internal bound water and interstitial water, and improving the dewatering performance of sludge. However, traditional thermal hydrolysis treatment often requires a relatively high temperature when applied to promote sludge dewatering, generally above 140℃, which not only has high energy consumption, but also has safety hazards. Therefore, it is necessary to develop a thermal hydrolysis treatment technology that can effectively improve the dewatering performance of sludge at a relatively low temperature (<100℃). SUMMARY

[0004] To solve the above technical problems, the present application provides a method for improving sludge dewatering performance by low-temperature hydrothermal coupling deep eutectic solvent. The method of the present application is green and environmentally friendly, simple to operate, and can effectively improve the dewatering performance of sludge at a relatively low temperature (<100℃). Deep eutectic solvent (DESs) is a low eutectic mixture composed of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), also known as low eutectic solvent, which has the characteristics of low cost, simple and fast preparation, easy recovery and recycling.

[0005] The purpose of the present application is to provide a method for improving sludge dewatering performance by low-temperature hydrothermal coupling deep eutectic solvent, which comprises the following steps:

[0006] Put the hydrogen bond donor and the hydrogen bond acceptor into the reactor and heat and stir to obtain the deep eutectic solvent;

[0007] Take the sludge to be treated, add the deep eutectic solvent, and stir and mix to obtain the mixed sludge;

[0008] The mixed sludge is placed in a hot hydrolysis reaction device with stirring, and hot hydrolysis treatment is carried out, and the sludge dewatering process is completed.

[0009] In some embodiments of the present application, the hydrogen bond acceptor is choline chloride (ChCl).

[0010] In some embodiments of the present application, the hydrogen bond donor is one or more of formic acid, acetic acid, oxalic acid or citric acid.

[0011] In some embodiments of the present application, the molar ratio of the hydrogen bond acceptor and the hydrogen bond donor is 1:1-1:4.

[0012] In some embodiments of the present application, the amount of the deep eutectic solvent used is 0.2-1.0 g / g of dry sludge.

[0013] In some embodiments of the present application, the heating and stirring conditions are: the reaction temperature is 60-90℃, the stirring time is 2-8 hours, and the stirring speed is 300-500 rpm.

[0014] In some embodiments of the present application, the sludge to be treated is activated sludge, primary sludge or mixed sludge.

[0015] In some embodiments of the present application, the reaction temperature of the hot hydrolysis treatment is 60-100℃, the stirring speed is 100-300 rpm, and the reaction time is 30 minutes-4 hours.

[0016] In some embodiments of the present application, the hot hydrolysis reaction device comprises a hydrothermal synthesis reaction kettle or a high-temperature and high-pressure reaction kettle.

[0017] The above technical solutions of the present application have the following advantages compared with the prior art:

[0018] The method for improving the dewatering performance of sludge by low-temperature hydrothermal coupling deep eutectic solvent according to the present application has the outstanding feature of reducing the temperature of hot hydrolysis treatment by adding a specific deep eutectic solvent to the sludge, and achieving efficient dewatering of the sludge at a lower temperature (<100℃). DESs can not only effectively promote the dissolution and hydrolysis of proteins, carbohydrates and other substances in extracellular polymeric substances as a co-solvent, but also can destroy the stability of the sludge colloidal system by electric neutralization and bridging as a flocculant, making the sludge aggregate, and thus improving the dewatering and settling performance. The method of the present application can greatly reduce the hydrothermal temperature, not only reducing the treatment cost, but also improving the safety, and has extremely far-reaching social significance and economic value. DETAILED DESCRIPTION

[0019] The application will be further described in conjunction with specific examples so that those skilled in the art can better understand the application and implement it. The examples are not intended to limit the application.

[0020] The original activated sludge used in the examples and comparative examples was taken from a sludge settling tank of a sewage treatment plant in Shanghai.

[0021] Comparative Example 1: Source and characteristic parameters of activated sludge

[0022] The original activated sludge sample was stored in a 4°C refrigerator. The characteristic parameters of the activated sludge were as follows: pH value was 7.22, water content was 97.63±0.03%, volatile solids accounted for 61.84±0.34% of the total solids (VS / TS), capillary suction time (CST) was 156 seconds, and the time required for filtration to half the sludge volume (TTF) was 6.5 minutes.

[0023] Comparative Example 2: Effect of low-temperature thermal hydrolysis on sludge dewatering performance (without adding DESs)

[0024] 200 mL of original activated sludge was taken and placed in a 250 mL beaker. The beaker was placed in an electrically stirred water bath, and the stirring reaction was carried out for 20 minutes at a stirring rate of 120 rpm. The stirred activated sludge was then placed in a high-temperature and high-pressure reaction kettle with stirring, and thermal hydrolysis treatment was carried out at 70°C for 1 hour, with continuous stirring at a stirring rate of 150 rpm. Finally, the activated sludge was taken out of the high-temperature and high-pressure reaction kettle, and the dewatering performance parameters of the activated sludge were measured. The CST was 445 seconds, and the TTF was 26.7 minutes.

[0025] Comparative Example 3: Effect of choline chloride on sludge dewatering performance

[0026] 200 mL of original activated sludge was taken and placed in a 250 mL beaker. 0.2 g / g DS choline chloride (0.2 g of choline chloride was added per g of DS dry matter) was added to the beaker. The beaker was placed in an electrically stirred water bath, and the stirring reaction was carried out for 20 minutes at a stirring rate of 120 rpm. The stirred activated sludge was then placed in a high-temperature and high-pressure reaction kettle with stirring, and thermal hydrolysis treatment was carried out at 70°C for 1 hour, with continuous stirring at a stirring rate of 150 rpm. Finally, the sludge was taken out of the high-temperature and high-pressure reaction kettle, and the dewatering performance parameters of the sludge were measured. The CST was 250 seconds, and the TTF was 12.5 minutes.

[0027] Comparative Example 4: Effect of formic acid on sludge dewatering performance

[0028] Take 200 mL of raw activated sludge in a 250 mL beaker, and add 0.2 g / g DS formic acid (0.2 g of formic acid per gram of DS dry matter) to it. Place the beaker in an electrically stirred water bath, and stir for 20 minutes at a stirring rate of 120 rpm. Place the activated sludge with 0.2 g / g DS formic acid in a high-temperature high-pressure reactor with stirring, and perform hot hydrolysis treatment at 70°C for 1 hour, with continuous stirring at a stirring rate of 150 rpm. Finally, take the sludge out of the high-temperature high-pressure reactor, and measure the dewatering performance parameters of the sludge, with a CST of 350 seconds and a TTF of 18.5 minutes.

[0029] Comparative Example 5: Effect of oxalic acid on sludge dewatering performance

[0030] Take 200 mL of raw activated sludge in a 250 mL beaker, and add 0.4 g / g DS oxalic acid (0.4 g of oxalic acid per gram of DS dry matter) to it. Place the beaker in an electrically stirred water bath, and stir for 20 minutes at a stirring rate of 120 rpm. Place the activated sludge with 0.4 g / g DS oxalic acid in a high-temperature high-pressure reactor with stirring, and perform hot hydrolysis treatment at 70°C for 1 hour, with continuous stirring at a stirring rate of 150 rpm. Finally, take the sludge out of the high-temperature high-pressure reactor, and measure the dewatering performance parameters of the sludge, with a CST of 112 seconds and a TTF of 5.1 minutes.

[0031] Example 1: Effect of choline chloride and formic acid on sludge dewatering performance in preparation of deep eutectic solvent

[0032] Add choline chloride and formic acid in a molar ratio of 1:3 to a round-bottom flask, and then place the round-bottom flask in an electrically stirred water bath, and heat and stir at 60°C for 3 hours at a stirring rate of 300 rpm to prepare a deep eutectic solvent. Take 200 mL of raw activated sludge in a 250 mL beaker, and add 0.4 g / g DS deep eutectic solvent to it, with the corresponding addition amount of choline chloride and formic acid being 0.2 g / g DS. Place the beaker in an electrically stirred water bath, and stir for 20 minutes at a stirring rate of 120 rpm. Place the activated sludge with 0.4 g / g DS deep eutectic solvent in a high-temperature high-pressure reactor with stirring, and perform hot hydrolysis treatment at 70°C for 1 hour, with continuous stirring at a stirring rate of 150 rpm. Finally, take the sludge out of the high-temperature high-pressure reactor, and measure the dewatering performance parameters of the sludge, with a CST of 101 seconds and a TTF of 4.0 minutes.

[0033] It can be seen that, compared with Comparative Example 1, the CST of Example 1 is reduced by 35.3%, and the TTF is reduced by 38.5%; compared with Comparative Example 2, the CST is reduced by 77.3%, and the TTF is reduced by 85.0%; compared with Comparative Example 3, the CST is reduced by 59.6%, and the TTF is reduced by 68.0%; compared with Comparative Example 4, the CST is reduced by 71.1%, and the TTF is reduced by 78.4%; the sludge dewatering performance is obviously improved.

[0034] Example 2: Effect of choline chloride and oxalic acid on the dewatering performance of sludge

[0035] Choline chloride and oxalic acid were put into a round-bottom flask at a molar ratio of 1:2, and then the round-bottom flask was placed in an electric stirring water bath, heated and stirred at 80°C for 4 hours, and the stirring rate was 350 rpm. A deep eutectic solvent was prepared. 200 mL of original activated sludge was placed in a 250 mL beaker, 0.6 g / g DS of deep eutectic solvent was added, the corresponding choline chloride dosage was 0.2 g / g DS, and the oxalic acid dosage was 0.4 g / g DS. The beaker was placed in an electric stirring water bath, and the stirring reaction was carried out for 20 minutes at a stirring rate of 120 rpm. The activated sludge with 0.6 g / g DS of deep eutectic solvent was placed in a high-temperature and high-pressure reactor with stirring, and the hot hydrolysis treatment was carried out at 70°C for 1 hour, during which the stirring was continued, and the stirring rate was 150 rpm. Finally, the sludge was taken out from the high-temperature and high-pressure reactor, and the dewatering performance parameters of the sludge were measured. The CST was 62 seconds, and the TTF was 2.3 minutes.

[0036] It can be seen that, compared with Comparative Example 1, the CST of Example 1 is reduced by 60.3%, and the TTF is reduced by 64.6%; compared with Comparative Example 2, the CST is reduced by 86.1%, and the TTF is reduced by 91.4%; compared with Comparative Example 3, the CST is reduced by 75.2%, and the TTF is reduced by 81.6%; compared with Comparative Example 5, the CST is reduced by 44.6%, and the TTF is reduced by 45.1%; the sludge dewatering performance is obviously improved.

[0037] Obviously, the above examples are only examples for the purpose of clarity, and are not limiting to the embodiments. Based on the above description, other different forms of changes or variations can also be made by those skilled in the art. It is not necessary or possible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for improving dewatering performance of sludge by low-temperature hydrothermal coupling deep eutectic solvent, characterized in that, The method comprises the following steps: putting the hydrogen bond donor and the hydrogen bond acceptor into a reactor, heating and stirring to obtain a deep eutectic solvent; adding the deep eutectic solvent to the sludge to be treated, and stirring and mixing the sludge; putting the sludge added with the deep eutectic solvent into a hot hydrolysis reaction device with stirring, and performing hot hydrolysis treatment, continuously stirring, and completing the sludge dewatering process; the hydrogen bond acceptor is choline chloride; the hydrogen bond donor is formic acid; the stirring and mixing condition is 60-90 ℃; the reaction temperature of the hot hydrolysis treatment is 60-100 ℃; the reaction time is 30 minutes-4 hours.

2. The method of claim 1, wherein, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1-1:

4.

3. The method of claim 1, wherein, the dosage of the deep eutectic solvent is 0.2-1.0 g / g of dry weight of the sludge.

4. The method of claim 1, wherein, the heating and stirring condition is that the reaction temperature is 60-90 ℃, the stirring time is 2-8 hours, and the stirring speed is 300-500 rpm.

5. The method of claim 1, wherein, the sludge to be treated is activated sludge, primary sludge or mixed sludge.

6. The method of claim 1, wherein, the stirring time of the stirring and mixing is 2-8 hours, and the stirring speed is 300-500 rpm.

7. The method of claim 1, wherein, the stirring speed of the hot hydrolysis reaction is 100-300 rpm.

8. The method of claim 1, wherein, the hot hydrolysis reaction device comprises a hydrothermal synthesis reaction kettle or a high-temperature and high-pressure reaction kettle.