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

Abstract

The invention relates to the technical field of sludge dewatering treatment, in particular to a method for improving sludge dewatering performance through low-temperature hydrothermal coupling of a deep eutectic solvent, which comprises the following steps: putting a hydrogen bond donor and a hydrogen bond acceptor into a reactor, heating and stirring to obtain the deep eutectic solvent; taking sludge to be treated, adding the deep eutectic solvent, and stirring and mixing for reaction; and putting the sludge added with the deep eutectic solvent into a thermal hydrolysis reaction device with a stirring function, carrying out thermal hydrolysis treatment, and continuously stirring to complete the sludge dewatering process. By adding specific DES into the sludge, the thermal hydrolysis treatment temperature can be reduced, and at the lower temperature (lt; the method realizes high-efficiency dehydration at the temperature of 100 DEG C, not only reduces the treatment cost, but also improves the safety, and has extremely profound social significance and economic value.

Description

Technical Field

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

[0002] The activated sludge method is the most commonly used sewage treatment process in sewage treatment plants. Excess sludge is an inevitable byproduct of the biological treatment of sewage. It is enriched with a variety of pollutants and poses a great threat to the environment and human health. The water content of the original activated sludge can reach 99%. It has the characteristics of high water content, large volume and poor dehydration. Its treatment and disposal costs can account for more than 60% of the operating costs of the sewage plant. The increasing production of excess sludge and the cost of sludge treatment and disposal have become a huge challenge facing current sewage treatment plants. Improving the dehydration performance of sludge and reducing the moisture content of excess sludge have become issues that need to be solved urgently.

[0003] In recent years, the use of thermal hydrolysis to destroy the water-holding capacity of sludge flocs and promote sludge dehydration has attracted more and more attention. This method heats the sludge to a certain temperature in a high-temperature and high-pressure reactor. A series of complex free radical reactions occur in the reactor, which can destroy the extracellular polymers and cell wall structure, causing the disintegration of sludge flocs, releasing the bound water and interstitial water inside the sludge, and improving the sludge dehydration performance. However, traditional thermal hydrolysis treatment often requires higher temperatures when used to promote sludge dehydration, generally above 140°C, which not only consumes a lot of energy, but also poses safety risks. Therefore, it is necessary to develop thermal hydrolysis treatment technology that can effectively improve sludge dehydration performance at lower temperatures (<100°C). Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for improving the dewatering performance of sludge by using a low-temperature hydrothermal coupled deep eutectic solvent. The method of the present invention is green and environmentally friendly, simple to operate, and can effectively improve the dewatering performance of sludge at a relatively low temperature (<100°C). Deep eutectic solvents (DESs) are low eutectic mixtures composed of hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA), also known as low eutectic solvents, which have the characteristics of low cost, simple and fast preparation, easy recovery and recyclability.

[0005] The object of the present invention is to provide a method for improving sludge dewatering performance by using a low-temperature hydrothermal coupled deep eutectic solvent, comprising the following steps:

[0006] Putting a hydrogen bond donor and a hydrogen bond acceptor into a reactor, heating and stirring to obtain a deep eutectic solvent;

[0007] Taking the sludge to be treated, adding the deep eutectic solvent, stirring and mixing to react, and obtaining mixed sludge;

[0008] The mixed sludge is placed in a thermal hydrolysis reaction device with stirring, and thermal hydrolysis treatment is carried out with continuous stirring to complete the sludge dehydration process.

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

[0010] In some embodiments of the present invention, 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 invention, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1-1:4.

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

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

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

[0015] In some embodiments of the present invention, the reaction temperature of the thermal hydrolysis treatment is 60-100° C., the stirring speed is 100-300 rpm, and the reaction time is 30 minutes to 4 hours.

[0016] In some embodiments of the present invention, the thermal hydrolysis reaction device includes a hydrothermal synthesis reactor or a high-temperature and high-pressure reactor.

[0017] The above technical solution of the present invention has the following advantages compared with the prior art:

[0018] The present invention proposes a method for improving the dewatering performance of sludge by coupling a low-temperature hydrothermal deep eutectic solvent. The outstanding feature is that a specific deep eutectic solvent is added to the sludge to reduce the temperature of the thermal hydrolysis treatment, and the sludge can be efficiently dehydrated at a relatively low temperature (<100°C). DESs can be used as a co-solvent to effectively promote the dissolution and hydrolysis of proteins, carbohydrates, etc. in extracellular polymers. On the other hand, it can also be used as a flocculant to destroy the stability of the sludge colloidal system through electrical neutralization and bridging, so that the sludge can be agglomerated, thereby improving the dewatering and sedimentation performance. The method of the present invention can greatly reduce the hydrothermal temperature, which not only reduces the treatment cost, but also improves safety. It has extremely far-reaching social significance and economic value. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0020] The original activated sludge used in the examples and comparative examples of the present invention 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 refrigerator at 4°C. The characteristic parameters of the activated sludge were as follows: pH value was 7.22, moisture content was 97.63±0.03%, volatile solid ratio in total solids (VS / TS) was 61.84±0.34%, capillary water absorption time (CST) was 156 seconds, and the time required to filter to half the sludge volume (TTF) was 6.5 minutes.

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

[0024] Take 200mL of original activated sludge and place it in a 250mL beaker. Place the beaker in an electric stirring water bath and stir for 20 minutes at a stirring rate of 120rpm. Place the stirred activated sludge in a high-temperature and high-pressure reactor with stirring and perform thermal hydrolysis at 70°C for 1 hour. Stir continuously during the period at a stirring rate of 150rpm. Finally, take out the activated sludge from the high-temperature and high-pressure reactor and measure the dewatering performance parameters of the activated sludge. The CST is 445 seconds and the TTF is 26.7 minutes.

[0025] Comparative Example 3: Effect of Choline Chloride on Sludge Dewatering Performance

[0026] Take 200mL of original activated sludge and place it in a 250mL beaker, add 0.2g / gDS choline chloride (0.2g choline chloride is added per gram of DS dry matter, DS refers to the dry matter in the sludge), place the beaker in an electric stirring water bath, stir and react for 20 minutes, and the stirring rate is 120rpm. The stirred activated sludge is placed in a high-temperature and high-pressure reactor with stirring, and thermal hydrolysis is carried out at 70°C for 1 hour, during which continuous stirring is carried out at a stirring rate of 150rpm. Finally, the sludge is taken out from the high-temperature and high-pressure reactor, and the dewatering performance parameters of the sludge are measured. The CST is 250 seconds and the TTF is 12.5 minutes.

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

[0028] Take 200mL of original activated sludge and place it in a 250mL beaker, add 0.2g / g DS formic acid (0.2g formic acid is added per gram of DS dry matter), place the beaker in an electric stirring water bath, stir and react for 20 minutes, and the stirring rate is 120rpm. The activated sludge with 0.2g / g DS formic acid is placed in a high-temperature and high-pressure reactor with stirring, and thermal hydrolysis is carried out at 70°C for 1 hour, during which continuous stirring is carried out at a stirring rate of 150rpm. Finally, the sludge is taken out from the high-temperature and high-pressure reactor, and the dewatering performance parameters of the sludge are measured. The CST is 350 seconds and the TTF is 18.5 minutes.

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

[0030] Take 200mL of original activated sludge and place it in a 250mL beaker, add 0.4g / gDS oxalic acid (0.4g oxalic acid is added per gram of DS dry matter), place the beaker in an electric stirring water bath, stir and react for 20 minutes, and the stirring rate is 120rpm. The activated sludge with 0.4g / gDS oxalic acid is placed in a high-temperature and high-pressure reactor with stirring, and thermal hydrolysis is carried out at 70°C for 1 hour, during which continuous stirring is carried out at a stirring rate of 150rpm. Finally, the sludge is taken out from the high-temperature and high-pressure reactor, and the dewatering performance parameters of the sludge are measured. The CST is 112 seconds and the TTF is 5.1 minutes.

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

[0032] Choline chloride and formic acid were added to a round-bottom flask at a molar ratio of 1:3, and the round-bottom flask was placed in an electric stirring water bath, heated and stirred at 60°C for 3 hours, with a stirring rate of 300rpm to obtain a deep eutectic solvent. 200mL of original activated sludge was placed in a 250mL beaker, and 0.4g / gDS deep eutectic solvent was added thereto. The corresponding choline chloride and formic acid dosages were both 0.2g / gDS. The beaker was placed in an electric stirring water bath, stirred for 20 minutes, and the stirring rate was 120rpm. The activated sludge with 0.4g / gDS deep eutectic solvent was placed in a high-temperature and high-pressure reactor with stirring, and thermal hydrolysis was carried out at 70°C for 1 hour, with continuous stirring during the period, and the stirring rate was 150rpm. Finally, the sludge was taken out from the high-temperature and high-pressure reactor, and the dewatering performance parameters of the sludge were measured, with CST of 101 seconds and TTF of 4.0 minutes.

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

[0034] Example 2: Effect of deep eutectic solvent prepared by choline chloride and oxalic acid on sludge dewatering performance

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

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

[0037] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for improving sludge dewatering performance by low-temperature hydrothermal coupling deep eutectic solvent, characterized in that: The following steps are involved: Putting a hydrogen bond donor and a hydrogen bond acceptor into a reactor, heating and stirring to obtain a deep eutectic solvent; Take the sludge to be treated, add the deep eutectic solvent, and stir to mix and react; The sludge added with the deep eutectic solvent is placed in a thermal hydrolysis reaction device with stirring, and thermal hydrolysis treatment is carried out with continuous stirring to complete the sludge dehydration process.

2. The method according to claim 1, characterized in that The hydrogen bond acceptor is choline chloride.

3. The method according to claim 1, characterized in that The hydrogen bond donor is one or more of formic acid, acetic acid, oxalic acid or citric acid.

4. The method according to claim 1, characterized in that The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1-1:

4.

5. The method according to claim 1, characterized in that The deep eutectic solvent is used in an amount of 0.2-1.0 g / g sludge dry weight.

6. The method according to claim 1, characterized in that The heating and stirring conditions are: reaction temperature is 60-90° C., stirring time is 2-8 hours, and stirring speed is 300-500 rpm.

7. The method according to claim 1, characterized in that The sludge to be treated is activated sludge, primary sludge or mixed sludge.

8. The method according to claim 1, characterized in that The stirring and mixing reaction conditions are 60-90° C., the stirring time is 2-8 hours, and the stirring speed is 300-500 rpm.

9. The method according to claim 1, characterized in that: The reaction temperature of the thermal hydrolysis treatment is 60-100°C, the stirring speed is 100-300 rpm, and the reaction time is 30 minutes to 4 hours.

10. The method according to claim 1, characterized in that The thermal hydrolysis reaction device includes a hydrothermal synthesis reactor or a high-temperature and high-pressure reactor.