Method for efficiently degrading sludge containing large amount of microplastics through sodium hydroxide hydrothermal pretreatment

Abstract

The invention discloses a method for efficiently degrading sludge containing a large amount of microplastics through sodium hydroxide hydrothermal pretreatment. The method comprises the following steps: injecting sodium hydroxide and activated sludge containing micro-plastics into a reaction kettle together, continuing for 30 minutes under the condition of 170 DEG C, taking out the reaction kettle after the reaction is finished, and naturally cooling. The obtained sludge is fed into a sludge anaerobic reactor in a daily feeding form, all the reactors operate in a water bath at 37 DEG C under the stirring condition of 120 rpm, and various pollutant indexes, methane production amount changes and the like in an anaerobic system are monitored every day. The method can effectively improve the degradation efficiency of the sludge containing a large amount of micro-plastics, improve the stability and resource utilization efficiency of the sludge, obviously reduce the content of the micro-plastics in a sludge system and reduce environmental pollution.

Description

Technical Field

[0001] The present invention belongs to the field of sludge treatment, and specifically relates to a method for efficiently degrading sludge containing a large amount of microplastics through sodium hydroxide hydrothermal pretreatment. The method efficiently degrades sludge containing a large amount of microplastics through sodium hydroxide hydrothermal pretreatment, effectively improves the biodegradability and degradation efficiency of the sludge containing a large amount of microplastics, improves the sludge stability, significantly reduces the microplastic content in the sludge system, and reduces environmental pollution. Background Art

[0002] Plastic pollution is one of the most pressing issues facing humanity in the 21st century. Plastic debris particles smaller than 5 mm are usually defined as microplastics. Microplastics can pose a serious threat to organisms and release toxins during migration, thereby exacerbating the toxic effects on the ecological environment.

[0003] Wastewater treatment plants are widely considered to be the main pathway for the release of microplastics into aquatic environments. Although wastewater treatment processes can remove 90% of microplastics in influent water, studies have found that the main removal mechanism is to transfer them from the liquid phase to the solid phase, so more microplastics are transferred to the sludge.

[0004] Anaerobic fermentation technology is a commonly used treatment technology for excess sludge, which has good sludge reduction effect and high stabilization degree. During the anaerobic digestion of sludge, EPS and cell wall derivatives in the sludge are resistant to the hydrolysis process, resulting in problems such as slow anaerobic digestion of sludge and low organic matter conversion rate. In order to solve the problems of low treatment efficiency of traditional anaerobic digestion technology, thermal hydrolysis pretreatment technology has been developed to effectively destroy extracellular polymers and promote cell lysis. Sodium hydroxide, as a strong alkali, can accelerate cell lysis and organic matter dissolution, assist in breaking down macromolecules in sludge, increase the content concentration of small molecules, and increase the concentration of degradable organic matter in sludge. Therefore, the combination of the two - alkaline heat pretreatment as an efficient sludge pretreatment technology can accelerate the disintegration of sludge floc structure, cell breakage and the release of organic matter, thereby improving the biodegradability of sludge and improving degradation efficiency. Summary of the invention

[0005] The purpose of the present invention is to provide a method for efficiently degrading sludge containing a large amount of microplastics through sodium hydroxide hydrothermal pretreatment, so as to solve the technical problems of large volume of sludge containing microplastics and low treatment efficiency, and reduce the content of microplastics in the treated waste residue.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A method for efficiently degrading sludge containing a large amount of microplastics by sodium hydroxide hydrothermal pretreatment, the method comprising the following steps:

[0008] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant is sedimented and sieved to obtain the desired activated sludge;

[0009] (2) Sodium hydroxide and activated sludge containing microplastics were injected into the reactor at 170°C for 30 minutes. After the reaction was completed, the reactor was taken out and cooled naturally;

[0010] (3) The treated sludge was fed into the sludge anaerobic reactor as daily feed, and all reactors were operated under the conditions of 37°C in a water bath and 120 rpm stirring;

[0011] (4) Daily monitoring of various pollutant indicators in the anaerobic system, changes in methane production, etc., and determination of changes in microplastic content in the sludge from the anaerobic reaction system.

[0012] In step (1), the sludge obtained from the water plant was allowed to stand at 4°C for 24 h, the supernatant was removed, and the precipitate was sieved through an 80-mesh sieve as the activated sludge for subsequent experiments.

[0013] In step (2), microplastics are added to the activated sludge at a content of 200 particles / g TS sludge to simulate sludge containing a large amount of microplastics; at the same time, sodium hydroxide at a content of 0.1-0.2 g / g TS sludge is added to the reactor together with the activated sludge containing microplastics for hydrothermal pretreatment.

[0014] (3) The anaerobic reactor in step (3) was acclimated for two months. After the reactor was running stably, the pretreated sludge was added thereto to keep the inlet and outlet sludge equal. The sludge retention time was adjusted to 30 days to maintain the efficient and stable operation of the Sun reaction system. The reaction conditions of all reactors were 37°C water bath and 120rpm stirring.

[0015] In step (4), the operation of the reaction system and the sludge degradation efficiency are detected by measuring various indicators of the daily sludge output of the reaction system; and the methane production by anaerobic digestion is measured daily by collecting in an air collection bag; at the same time, a certain amount of microplastics in the sludge in the reaction system is regularly extracted to measure the change in its content.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention uses sodium hydroxide to assist in the hydrothermal pretreatment of sludge. The addition of sodium hydroxide can effectively improve the effect of the hydrothermal pretreatment of sludge. The combination of the two accelerates the disintegration of the sludge floc structure, cell disruption and the release of organic matter, so that a large amount of organic matter is released into the liquid phase. Therefore, the SCOD concentration in the sludge system is significantly increased before and after treatment. The added sodium hydroxide can decompose and dissolve the sludge by directly eliminating the Gram-positive microorganisms in the sludge, thereby achieving the effect of reducing the sludge particle size and increasing the release of organic matter. Thereby improving the biodegradability of the sludge and improving the degradation efficiency.

[0018] (2) The present invention can significantly and efficiently reduce the content of microplastics in the sludge by hydrothermal pretreatment of sludge containing a large amount of microplastics with sodium hydroxide, thereby reducing the discharge into the natural environment, avoiding being preyed on and absorbed by aquatic organisms, causing damage to important organs or inflammation, and posing a serious threat to biological formation. At the same time, the toxins released during the migration and transformation of microplastics in the environment are reduced to avoid aggravating the toxicological effects on the ecological environment.

[0019] (3) The present invention has a simple process, a simple device structure, is easy to operate, and is environmentally friendly. In addition, there is no need to modify the equipment. It only needs to pre-treat the feed sludge in the existing process, which can not only increase the content of degradable organic matter in the sludge and improve its biodegradability, but also effectively remove the content of microplastics in the sludge and reduce the discharge into the environment. It has the characteristics of strong operability and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of the efficient degradation of sludge containing a large amount of microplastics by sodium hydroxide hydrothermal pretreatment, 1-sodium hydroxide; 2-microplastics; 3-activated sludge; 4-mixed sludge; 5-reactor; 6-high temperature oven. DETAILED DESCRIPTION

[0021] The present invention is further explained below in conjunction with the embodiments and drawings, but this is not intended to limit the scope of protection of the present application.

[0022] like Figure 1 As shown, microplastics were added to the activated sludge at a content of 200 particles / g TS sludge to simulate sludge containing a large amount of microplastics; at the same time, sodium hydroxide at a content of 0.1-0.2g / g TS sludge was mixed with the activated sludge containing microplastics and put into the reactor for hydrothermal pretreatment at 170°C for 30 minutes. After the reaction was completed, the reactor was taken out and cooled naturally to obtain the sludge required for the reaction. At this point, the sludge pretreatment stage was completed.

[0023] The laboratory anaerobic inoculated sludge was added to the anaerobic digestion reactor, and the pH in each bottle was adjusted to 7±0.1 with NaOH and HCl. Nitrogen was introduced into the bottle for 5 minutes to remove the air and then sealed. It was domesticated in a 37°C water bath and stirred at 120rpm. The domestication was completed when the gas production and various indicators were stable. After completion, the pretreated sludge was added to the reactor for anaerobic digestion. The sludge retention time was adjusted to 30 days. The operation of the reaction system and the sludge degradation efficiency were detected by measuring the various indicators of the daily sludge discharge of the reaction system; and the methane production of anaerobic digestion was measured daily by collecting gas collection bags; at the same time, microplastics in a certain amount of sludge in the reaction system were regularly extracted to determine the changes in its content.

[0024] Example 1

[0025] Step 1: Take the sludge from the secondary sedimentation tank of the urban sewage treatment plant and let it stand at 4°C for 24 hours to settle, remove the supernatant, and sieve the precipitate through an 80-mesh sieve to remove impurities in the sludge, which will be used as the activated sludge for subsequent experiments.

[0026] Step 2: Take a certain amount of activated sludge, add microplastics to the activated sludge at a content of 200 particles / g TS sludge to simulate sludge containing a large amount of microplastics, but do not add any enhancer, and add the prepared sludge to Figure 1 In the reactor shown, the reaction is carried out at 170° C. for 30 minutes. After the reaction is completed, the reactor is taken out and cooled naturally to obtain the sludge required for the reaction. At this point, the sludge pretreatment stage is completed.

[0027] Step 3: Add the experimental sludge obtained in the second step to the domesticated reactor in the form of daily input and output, and detect the operation of the reaction system and the sludge degradation efficiency by measuring the various indicators of the daily sludge output of the reaction system; measure the methane production of anaerobic digestion daily through air collection bags; and regularly extract a certain amount of microplastics from the sludge in the reaction system to measure the changes in its content.

[0028] The experimental results show that the average daily gas production of the reaction system reaches 174 mL / g VS, and the microplastic removal rate reaches 38%.

[0029] Example 2

[0030] The steps of this embodiment are the same as those of embodiment 1, except that sodium hydroxide with a TS sludge content of 0.1 g / g is added in the pretreatment stage for strengthening.

[0031] Step 1: Take the sludge from the secondary sedimentation tank of the urban sewage treatment plant and let it stand at 4°C for 24 hours to settle, remove the supernatant, and sieve the precipitate through an 80-mesh sieve to remove impurities in the sludge, which will be used as the activated sludge for subsequent experiments.

[0032] Step 2: Take a certain amount of activated sludge, add microplastics to the activated sludge at a content of 200 particles / g TS sludge to simulate sludge containing a large amount of microplastics, and at the same time, mix sodium hydroxide with the activated sludge containing microplastics at a content of 0.1g / g TS sludge, and add the prepared sludge to Figure 1 In the reactor shown, the reaction is carried out at 170° C. for 30 minutes. After the reaction is completed, the reactor is taken out and cooled naturally to obtain the sludge required for the reaction. At this point, the sludge pretreatment stage is completed.

[0033] Step 3: Add the experimental sludge obtained in the second step to the domesticated reactor in the form of daily input and output, and detect the operation of the reaction system and the sludge degradation efficiency by measuring the various indicators of the daily sludge output of the reaction system; measure the methane production of anaerobic digestion daily through air collection bags; and regularly extract a certain amount of microplastics from the sludge in the reaction system to measure the changes in its content.

[0034] The experimental results show that the average daily gas production of the reaction system reaches 274 mL / g VS, and the microplastic removal rate reaches 65%.

[0035] Example 3

[0036] The steps of this embodiment are the same as those of embodiment 1, except that sodium hydroxide with a TS sludge content of 0.2 g / g is added in the pretreatment stage for strengthening.

[0037] Step 1: Take the sludge from the secondary sedimentation tank of the urban sewage treatment plant and let it stand at 4°C for 24 hours to settle, remove the supernatant, and sieve the precipitate through an 80-mesh sieve to remove impurities in the sludge, which will be used as the activated sludge for subsequent experiments.

[0038] Step 2: Take a certain amount of activated sludge, add microplastics to the activated sludge at a content of 200 particles / g TS sludge to simulate sludge containing a large amount of microplastics, and at the same time, mix sodium hydroxide with the activated sludge containing microplastics at a content of 0.2g / g TS sludge, and add the prepared sludge to Figure 1 In the reactor shown, the reaction is carried out at 170° C. for 30 minutes. After the reaction is completed, the reactor is taken out and cooled naturally to obtain the sludge required for the reaction. At this point, the sludge pretreatment stage is completed.

[0039] Step 3: Add the experimental sludge obtained in the second step to the domesticated reactor in the form of daily input and output, and detect the operation of the reaction system and the sludge degradation efficiency by measuring the various indicators of the daily sludge output of the reaction system; measure the methane production of anaerobic digestion daily through air collection bags; and regularly extract a certain amount of microplastics from the sludge in the reaction system to measure the changes in its content.

[0040] The experimental results show that the average daily gas production of the reaction system reaches 368mL / g VS, and the microplastic removal rate reaches 71%. In summary, the present invention improves the biodegradability and biogas yield of sludge containing a large amount of microplastics by adding sodium hydroxide, improves the operating efficiency of the anaerobic digestion system, and improves the removal efficiency of microplastics, which can effectively reduce the microplastics in sludge waste and reduce the environmental pollution of microplastics.

[0041] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for efficiently degrading sludge containing a large amount of microplastics by hydrothermal pretreatment with sodium hydroxide, characterized in that The following steps are involved: (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant is sedimented and sieved to obtain the desired activated sludge; (2) Sodium hydroxide and activated sludge containing microplastics were mixed and injected into a reactor at 170°C for 30 minutes. After the reaction was completed, the reactor was taken out and cooled naturally; (3) The treated sludge was fed into the sludge anaerobic reactor as daily feed, and all reactors were operated under the conditions of 37°C water bath and 120 rpm stirring; (4) Daily monitoring of various pollutant indicators in the anaerobic system, changes in methane production, etc., and determination of changes in microplastic content in the sludge from the anaerobic reaction system.

2. The method for efficiently degrading sludge containing a large amount of microplastics by sodium hydroxide hydrothermal pretreatment according to claim 1, characterized in that: In step (1), the sludge obtained from the water plant was allowed to stand at 4°C for 24 h, the supernatant was removed, and the precipitate was sieved through an 80-mesh sieve as the activated sludge for subsequent experiments.

3. The method for efficiently degrading sludge containing a large amount of microplastics by sodium hydroxide hydrothermal pretreatment according to claim 1, characterized in that: (2) In step 1, microplastics were added to the activated sludge at a content of 200 particles / gTS sludge to simulate sludge containing a large amount of microplastics; At the same time, sodium hydroxide at a content of 0.1-0.2 g / g TS sludge was mixed with the microplastic-containing activated sludge and put into the reactor for hydrothermal pretreatment.

4. The method for efficiently degrading sludge containing a large amount of microplastics by sodium hydroxide hydrothermal pretreatment according to claim 1, characterized in that: (3) The anaerobic reactor in step (3) was acclimated for two months. After the reactor was running stably, the pretreated sludge was added thereto to keep the inlet and outlet sludge equal. The sludge retention time was adjusted to 30 days to maintain the efficient and stable operation of the Sun reaction system. The reaction conditions of all reactors were 37°C water bath and 120rpm stirring.

5. The method for efficiently degrading sludge containing a large amount of microplastics by sodium hydroxide hydrothermal pretreatment according to claim 1, characterized in that: In step (4), the operation of the reaction system and the sludge degradation efficiency are detected by measuring various indicators of the daily sludge output of the reaction system; and the methane production by anaerobic digestion is measured daily by collecting in an air collection bag; at the same time, a certain amount of microplastics in the sludge in the reaction system is regularly extracted to measure the change in its content.

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