Method for removing PET (Polyethylene Terephthalate) microplastics / microfibers in urban sewage

Abstract

The invention belongs to the technical field of urban sewage treatment, and particularly relates to a method for removing PET (Polyethylene Terephthalate) microplastics / microfibers in urban sewage. According to the method, PET micro-plastics with different particle sizes / forms are taken as treatment objects, an activated sludge adsorption-chemical coagulation combined process is adopted for removal, activated sludge is utilized for adsorbing the micro-plastics in sewage, organic matters, ammonia nitrogen and other pollutants are removed at the same time, and a coagulation technology is further adopted for removing residual micro-plastics, turbidity, residual organic matters and the like. The method is simple in process flow, can realize synergistic removal of PET micro-plastics / micro-fibers and other pollutants in sewage, and is suitable for treatment of sewage containing micro-plastics.

Description

Technical Field

[0001] The present invention belongs to the technical field of urban sewage treatment, and in particular relates to a method for removing PET microplastics / microfibers in urban sewage. Background Art

[0002] Although existing sewage treatment plants have a certain removal rate for microplastics, since they are not designed specifically for microplastic removal, a large amount of microplastics are still discharged into the environment through urban sewage treatment plants. The removal efficiency of microplastics in urban sewage treatment plants needs to be improved urgently.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] In view of the problem that the existing process has obviously insufficient efficiency in removing microplastics, and the current situation that PET microplastics / microfibers are present in large amounts in urban sewage and are difficult to remove, the purpose of the present invention is to provide a method for removing PET microplastics / microfibers in urban sewage. Activated sludge is the core technology for urban sewage treatment. In addition to biodegradation, its strong adsorption capacity can adsorb microplastics in sewage into sludge, and chemical coagulation is a commonly used sewage deep treatment process. It is feasible to use chemical coagulation to further remove microplastics in secondary effluent. The present invention utilizes activated sludge adsorption-chemical coagulation to synergistically remove PET microplastics / microfibers. It is simple to operate and easy to promote, and is expected to become an effective method for low-cost transformation of urban sewage treatment plants.

[0005] To achieve the above object, the technical solution of the present invention is as follows: A method for removing PET microplastics / microfibers in municipal sewage, comprising the following steps: Step 1: The wastewater containing PET microplastics / microfibers is subjected to aerobic activated sludge treatment; Step 2: After the aerobic activated sludge treatment is completed, precipitation is performed, the pH of the supernatant obtained by precipitation is adjusted, and a coagulant is added thereto for chemical coagulation treatment; Step 3: The mixed liquid after coagulation treatment is precipitated, and the resulting supernatant is the wastewater from which PET microplastics / microfibers have been removed.

[0006] Furthermore, the conditions for aerobic activated sludge treatment in step 1 are: the concentration of activated sludge mixed solution is 3000-5000 mg / L, the aeration intensity is 20m 3 / (m 2 h), dissolved oxygen concentration is 2-3 mg / L, and aeration time is 6 hours.

[0007] Furthermore, the activated sludge in step 1 is activated sludge from aerobic tanks in municipal sewage treatment plants.

[0008] Furthermore, the precipitation time in step 2 is 1 hour.

[0009] Furthermore, in step 2, the pH of the supernatant obtained by precipitation is adjusted to 7.0±0.1.

[0010] Furthermore, in step 2, the coagulant is ferric sulfate.

[0011] Furthermore, in step 2, the concentration of the coagulant added is 30-50 mg / L.

[0012] Furthermore, the precipitation time in step 3 is 30 minutes.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This study uses actual wastewater spiked with PET microplastics and microfibers as the research subject, employing a combined activated sludge adsorption and chemical coagulation process for advanced treatment. Activated sludge adsorption removes PET microplastics and microfibers, while microbial degradation removes organic matter, ammonia nitrogen, and other contaminants. Chemical coagulation further removes residual PET microplastics and microfibers, turbidity, and other contaminants. This technology effectively removes PET microplastics and microfibers at concentrations of 100-1000 mg / L, achieving a PET microplastic and microfiber removal rate of >96.5%, with effluent COD <60 mg / L, ammonia nitrogen <1.0 mg / L, and turbidity <5 NTU. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a process flow chart for treating sewage according to the present invention.

[0015] Figure 2 This is a diagram showing the effect of the present invention in removing PET microplastics (300 mesh) of different concentrations.

[0016] Figure 3 This is a diagram showing the effect of removing PET microplastics of different particle sizes using the present invention.

[0017] Figure 4 This is a diagram showing the effect of removing PET microplastics / microfibers of different forms by the present invention.

[0018] Figure 5 This is the distribution state of the PET microplastics / microfibers in the activated sludge flocs of the present invention.

[0019] Figure 6 This is the distribution state of the PET microplastics / microfibers in the chemical coagulation flocs of the present invention. DETAILED DESCRIPTION

[0020] To facilitate understanding of the present invention, the present invention will be described more fully below. 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.

[0021] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Example

[0022] In this example, the wastewater containing PET microplastics / microfibers was derived from the effluent from an anoxic tank at a municipal sewage treatment plant, to which PET microplastics / microfibers were added. The activated sludge was derived from an aerobic tank at a municipal sewage treatment plant. After settling for two hours, the sludge concentrate was added to the wastewater containing PET microplastics / microfibers.

[0023] like Figure 1 As shown, a method for removing PET microplastics / microfibers from municipal sewage comprises the following steps: 1) The wastewater containing PET microplastics / microfibers was treated with aerobic activated sludge. The treatment conditions were: the concentration of activated sludge mixture was 3000 mg / L, the aeration intensity was 20 m 3 / (m 2 h), the dissolved oxygen concentration was 3 mg / L, and the aeration time was 6 hours.

[0024] 2) After aerobic activated sludge treatment is completed, the sludge and water are separated by sedimentation in the secondary sedimentation tank for one hour. The pH of the resulting supernatant is adjusted to 7.0 ± 0.1, and a coagulant, ferric sulfate (PFS) solution, is added for chemical coagulation at a concentration of 50 mg / L. The mixture is rapidly mixed for one minute, reacted slowly for 15 minutes, and allowed to settle for 30 minutes. The supernatant is the treated wastewater.

[0025] In this example, the COD in the actual sewage is 70-100 mg / L, the ammonia nitrogen concentration is 10-15 mg / L, and the PET microplastic / microfiber concentration is 100-1000 mg / L. After treatment by this method, the PET microplastic / microfiber removal rate is >96.5%, the effluent COD is <60 mg / L, the ammonia nitrogen is <1.0 mg / L, and the turbidity is <5NTU.

[0026] Figure 2The results show that the removal rate of PET microplastics (300 mesh) with a concentration of 100-1000 mg / L by the combined activated carbon adsorption-chemical coagulation process is between 96.76% and 99.68%. Activated sludge can remove most of the MPs in sewage, and the combined coagulation process can further reduce the concentration of MPs.

[0027] Figure 3 The results show that the removal rate of activated carbon adsorption-chemical coagulation combined process for PET microplastics of different particle sizes (50 mesh, 100 mesh, 300 mesh, and influent microplastic concentration of 200 mg / L) is above 98%.

[0028] Figure 4 The results show that the combined activated carbon adsorption-chemical coagulation process has a removal rate of over 98% for PET microplastics / microfibers in different forms (granular, fibrous, granular / fiber mixed, and influent microplastic / microfiber concentration of 200 mg / L).

[0029] Figure 5 It shows that after adsorption by activated sludge, 300-mesh PET microplastics are evenly distributed in the sludge flocs, with clear particle boundaries and tight integration with the flocs; PET microfibers are evenly dispersed and interspersed in the gaps between the flocs in a slender form.

[0030] Figure 6 It shows that after chemical coagulation treatment, 50-mesh and 100-mesh PET microplastics are loosely embedded on the surface and inside of the flocs; 300-mesh PET microfibers aggregate into a "clustered" structure, promoting the growth of flocs through bridging; PET microfibers and flocs are interwoven into a network, penetrating the structure and enhancing stability; the mixed form shows that PET fibers act as a skeleton and are entangled with the flocs to form a large-area network structure, which is easier to adsorb PET microplastics of different particle sizes.

[0031] The above description is only for better explanation of the embodiments of the present invention and is not intended to limit the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are intended to be within the scope of the present invention.

Claims

1. A method for removing PET microplastics / microfibers from municipal sewage, characterized in that: The steps include: Step 1: The wastewater containing PET microplastics / microfibers is subjected to aerobic activated sludge treatment; Step 2: After the aerobic activated sludge treatment is completed, precipitation is performed, the pH of the supernatant obtained by precipitation is adjusted, and a coagulant is added thereto for chemical coagulation treatment; Step 3: The mixed liquid after coagulation treatment is precipitated, and the resulting supernatant is the wastewater from which PET microplastics / microfibers have been removed.

2. The method for removing PET microplastics / microfibers from municipal sewage according to claim 1, characterized in that: The conditions for aerobic activated sludge treatment in step 1 are: the concentration of activated sludge mixed solution is 3000-5000 mg / L, the aeration intensity is 20m 3 / (m 2 h), dissolved oxygen concentration is 2-3 mg / L, and aeration time is 6 hours.

3. The method for removing PET microplastics / microfibers in municipal sewage according to claim 2, characterized in that: The activated sludge in step 1 is the activated sludge from the aerobic tank of the municipal sewage treatment plant.

4. The method for removing PET microplastics / microfibers from municipal sewage according to claim 1, wherein: The precipitation time in step 2 is 1 hour.

5. The method for removing PET microplastics / microfibers from municipal sewage according to claim 1, characterized in that: In step 2, the pH of the supernatant obtained by precipitation is adjusted to 7.0±0.

1.

6. The method for removing PET microplastics / microfibers from municipal sewage according to claim 1, characterized in that: In the step 2, the coagulant is ferric sulfate.

7. The method for removing PET microplastics / microfibers from municipal sewage according to claim 1, characterized in that: The concentration of the coagulant added in step 2 is 30-50 mg / L.

8. The method for removing PET microplastics / microfibers from municipal sewage according to claim 1, characterized in that: The precipitation time in step 3 is 30 minutes.

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