Synergistic removal method for microplastics and microorganisms in rainwater

Abstract

The invention provides a method for synergistically removing micro-plastics and microorganisms in rainwater, which comprises the following steps: mixing the rainwater to be treated with ferrate, quickly stirring immediately, adding cationic polyacrylamide, adjusting the pH value, and coagulating and filtering to obtain a recyclable water body. According to the method, the micro-plastic and microbial pollution in the rainwater can be efficiently and synergistically removed, so that potential health risks and environmental hazards in the rainwater recycling process are greatly reduced, and a technical support is provided for safe recycling of the rainwater. The method provided by the invention is simple to operate and convenient to operate and manage. According to the method provided by the invention, the removal rate of microorganisms in the roof rainwater reaches 100%, and the removal rate of micro-plastics with the size of 10 microns or above reaches 99%.

Description

Technical Field

[0001] The present invention relates to the field of rainwater reuse, and in particular to a method for collaboratively removing microplastics and microorganisms in rainwater. Background Art

[0002] Due to the increasing shortage of water resources and the frequent occurrence of water pollution problems, water resource recycling and reuse technology has become a research focus in the environmental field in recent years. Rainwater reuse technology is a sustainable water resource utilization method that collects, stores and reuses rainwater to meet the different water use requirements in urban industrial and agricultural fields. This technology opens up a new potential water source, thereby effectively reducing the current supply pressure of tap water and groundwater, and is one of the important methods to solve the problem of water shortage. Rainwater collected by the reuse system can be used in a series of scenarios such as landscape irrigation, building flushing, toilet flushing, etc., so as to achieve the purpose of water saving. It is reported that 20%-50% of municipal water supply can be saved through rainwater reuse.

[0003] However, the pollution of microplastics and pathogenic microorganisms in rainwater seriously threatens ecological and environmental safety and human health. Microplastics (such as polyethylene, polypropylene, polyvinyl chloride, etc.) from rainwater pipes, urban plastic waste and agricultural production will accumulate in rainwater, affecting the quality of rainwater. If these microplastics enter the human body, they will cause inflammation of the immune system and endocrine disorders. In addition to microplastics, a variety of conditional pathogens such as Legionella pneumophila and Pseudomonas aeruginosa in rainwater can cause a series of diseases such as pneumonia and sepsis, threatening human health. More importantly, the special structure of the surface of microplastics can cause microorganisms, especially conditional pathogens, to enrich and reproduce on their surface, thus forming a "plastic world" in rainwater, which causes more harm to the human body and the ecosystem. Therefore, the problem of synergistic pollution of microplastics and conditional pathogens has become a major hidden danger restricting the development of rainwater reuse technology in my country, and it is urgently needed to solve the problem of synergistic removal technology of pollutants.

[0004] Chlorination disinfection can effectively kill microorganisms in water, but chlorination will cause chlorine-containing disinfection by-products to remain in rainwater, causing secondary pollution to rainwater. Although the ultraviolet disinfection method does not cause pollution by disinfection by-products, it itself has a strong selectivity for the removal of microorganisms, and it is difficult to completely remove pathogenic microorganisms in water. Although membrane separation technology, as an effective physical separation method, can intercept microorganisms and microplastics at the same time, these processes can only intercept but not kill bacteria, and still pose safety risks to the environment and require further treatment. Moreover, the equipment used in membrane separation technology is expensive, the maintenance process is complicated, and it is difficult to apply in large-scale rainwater reuse and treatment systems. Therefore, it is very important to seek a method to synergistically control microplastics and pathogenic microorganisms, thereby controlling the safety risks brought by microplastics and pathogenic microorganisms in rainwater systems. Summary of the invention

[0005] In view of the above, the present invention aims to provide a method for the synergistic removal of microorganisms and microplastics in rainwater, which can not only efficiently remove all microorganisms from the water, but also remove most of the microplastics in the rainwater, thereby reducing the risks of rainwater reuse to human health and environmental safety.

[0006] The present invention aims to provide a method for the coordinated removal of microorganisms and microplastics in rainwater, comprising the following steps: The rainwater to be reused is mixed with ferrate and polyacrylamide, and purified reuse water is obtained after sterilization, pH adjustment, coagulation and filtration.

[0007] Furthermore, the specific operation is: add ferrate to the rainwater to be treated, immediately perform the first rapid stirring, then add polyacrylamide and immediately add dilute hydrochloric acid to adjust the pH, then perform the second rapid stirring, then stir at a medium speed, and finally stir at a slow speed.

[0008] Further, the stirring speed of the first and second rapid stirring is 300-400 rpm, the stirring speed of the medium stirring is 150-200 rpm, and the stirring speed of the slow stirring is 50-70 rpm.

[0009] Furthermore, the stirring time of the first rapid stirring should be greater than or equal to 30 minutes, preferably 30-40 minutes.

[0010] Furthermore, the stirring time of the second rapid stirring should be 1-2 min, the stirring time of the medium speed stirring should be 5-10 min, and the stirring time of the slow speed stirring should be 20-40 min.

[0011] Furthermore, the concentration of the dilute hydrochloric acid is 1-5 mol / Lmol / L, and the dilute hydrochloric acid is added until the pH of the water body is between 6.5 and 7.5.

[0012] Furthermore, the concentration of the dilute hydrochloric acid is 1 mol / L, and the dilute hydrochloric acid is added until the pH of the water body is between 6.5 and 7.5.

[0013] Furthermore, after the rainwater is mixed with ferrate, it is filtered through a filter column to obtain purified reuse water. The supporting layer material in the filter column is selected from: one or more of pebbles, gravel, and artificial fiber ball filter materials; the filter layer material in the filter column is selected from: one or more of quartz sand, anthracite, activated carbon, expanded clay, garnet, and fiber balls.

[0014] Furthermore, the supporting layer material is pebbles with a particle size range of 1 cm-1.5 cm, and the filter layer material is quartz sand with a particle size range of 700-1000 μm.

[0015] Furthermore, the dosage ratio of the ferrate to the roof rainwater to be treated is in the range of 2 mg:1L-40 mg:1L, preferably in the range of 30 mg:1L-35 mg:1L, where the dosage of ferrate is based on the mass of Fe.

[0016] Furthermore, the mass dosage ratio of the ferrate to polyacrylamide is in the range of 1 mg:1 mg-3 mg:4 mg (wherein the amount of ferrate added is based on the mass of Fe); the ferrate is selected from one or more of potassium ferrate or sodium ferrate, and the polyacrylamide is cationic polyacrylamide.

[0017] Further, ferrate includes ferrate in the form of potassium ferrate, sodium ferrate, etc., and the source may include ferrate solution prepared by wet oxidation method and electrochemical method, separated and purified, or commercially purchased solid.

[0018] Furthermore, the ferrate is added at a concentration of 2-40 mg / L (based on the mass of iron).

[0019] Furthermore, the source of cationic polyacrylamide may include cationic polyacrylamide prepared by "water phase polymerization" of acrylamide and a cationic monomer (such as dimethylaminoacrylamide) at a specific ratio, or commercially available solids.

[0020] Furthermore, the cationic polyacrylamide is added at a concentration of 2-53 mg / L.

[0021] Furthermore, the dilute hydrochloric acid can be obtained by diluting concentrated hydrochloric acid, or can be purchased commercially.

[0022] Preferably, the second rapid mixing and stirring time is 1-2 min.

[0023] Preferably, the medium-speed stirring time is 5-6 min.

[0024] Preferably, the slow stirring time is 20-30 min.

[0025] Furthermore, the effluent is transferred to a filtration device by a water pump for filtration to obtain recycled water.

[0026] Preferably, the average particle size of the pebbles is 0.5 cm-2 cm, and the average particle size of the quartz sand is 800-1000 μm.

[0027] Preferably, the volume height ratio of the supporting layer to the filter layer in the filter device is in the range of 1:5-1:10.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1) The present invention can efficiently remove microorganisms and microplastics in rainwater by adding ferrate to rainwater. It is widely applicable to the control of pathogenic microorganisms and microplastics in rainwater on various underlying surfaces and the reuse of rainwater.

[0029] 2) Ferrate, as a strong oxidant and bactericide, can destroy the cell walls and cell membranes of microorganisms through strong oxidation. In addition, ferrate can also release active oxygen in water, thereby killing microorganisms.

[0030] 3) The iron oxide or iron hydroxide generated after the reduction of ferrate can be used as a coagulant. With the synergistic effect of cationic polyacrylamide coagulant, microplastics in rainwater can be aggregated. Most of the microplastics in rainwater can be removed by subsequent filtration, including lightweight microplastics that are difficult to remove by coagulation and precipitation.

[0031] 4) Dead microorganisms will be intercepted and removed by the filter material together with microplastic flocs. The microplastic removal rate reaches 99%, and the microbial removal rate reaches 100% (the total colony count of the effluent is reduced to 0 CFU / L), which can meet the requirements of the "Sanitary Standard for Drinking Water" (GB 5749-2006). This method can effectively remove microplastics and microorganisms in a coordinated manner, reducing their harm to human health and the ecological environment.

[0032] 5) The rainwater treatment method provided by the present invention is extremely competitive in terms of the removal effect of microorganisms and microplastics compared to other rainwater treatment processes. The entire process flow is simple to operate, easy to manage, and has low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a dot-line graph of the absolute abundance (in copies per milliliter) and removal rate of microorganisms in rainwater at different potassium ferrate addition concentrations in the example.

[0034] Figure 2 The total colony count (in CFU / mL) of the effluent corresponding to the coagulation and filtration under the best implementation conditions in the embodiment is shown in FIG. Figure 2 Where Fe+PAM+PH is the total colony count recorded in Example 6.

[0035] Figure 3 The concentration of microplastics in the control group, filtration group, and Fe+PAM+PH group (Example 6) when the potassium ferrate addition concentration is 30 mg-Fe / L, and the particle size distribution of microplastics in the control group, filtration group, and Fe+PAM+PH group (Example 6) when the potassium ferrate addition concentration is 30 mg-Fe / L. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0037] The technical solution of the present invention is further explained below in conjunction with implementation cases.

[0038] The present invention has no special restrictions on the underlying surface of rainwater that needs to be treated and reused.

[0039] The ferrate is potassium ferrate, which was purchased from Aladdin Reagent Company.

[0040] The polyacrylamide is cationic polyacrylamide, which was purchased from Aladdin Reagent Company.

[0041] Example 1 In this example, the rainwater to be treated is taken from the roof of the archives of the South Campus of Tongji University in Shanghai. The specific method includes the following steps: Take 1000 mL of roof rainwater and place it in a beaker. Place a magnetic stirrer on a magnetic stirrer. Weigh potassium ferrate solid and add it to the beaker to make it 30 mg-Fe / L. Adjust the speed to 300 rpm. Stir for 30 minutes and keep the speed at 300 rpm. Place the reacted water in a centrifuge tube.

[0042] The water in the above centrifuge tube was centrifuged at 12000 rpm for 2 min, and the precipitate and 1 mL of supernatant were retained. The PMA-qPCR method was used to determine the number of live bacterial DNA copies. The specific steps were: add propidium bromide azide (PMA) to a concentration of 250 μM (about 12.66 μL), react in a dark environment for 10 min, and then irradiate under 465 nm blue light for 15 min. Then the DNA was extracted using a kit (TIANamp Soil DNA Kit). The extracted DNA was used to detect the abundance of the 16s gene using fluorescent quantitative PCR (RT-PCR). The primers used for fluorescent quantitative PCR were 338F (5'-ACTCCTACGGGAGGCAGCAG-3') and 806R (5'-GGACTACHVGGGTWTCTAAT-3').

[0043] Example 2 Same as Example 1, except that the concentration of potassium ferrate is 20 mg-Fe / L.

[0044] Example 3 Same as Example 1, except that the concentration of potassium ferrate is 10 mg-Fe / L.

[0045] Example 4 Same as Example 1, except that the concentration of potassium ferrate is 6 mg-Fe / L.

[0046] Example 5 Same as Example 1, except that the concentration of potassium ferrate is 2 mg-Fe / L.

[0047] Comparative Example 1 Same as Example 1, except that the potassium ferrate concentration is 0 mg-Fe / L.

[0048] The results are as follows Figure 1 As shown, Figure 1 This is the relationship between the concentration of ferrate added and the sterilization effect. Figure 1 It can be seen that the bacteria can be effectively killed after treatment with potassium ferrate. When the concentration of potassium ferrate is increased from 0 mg-Fe / L to 2 mg-Fe / L, the number of bacterial gene copies decreases significantly from 112079 copies / μL to 34048 copies / μL, indicating that the number of live bacteria decreases rapidly and the inactivation rate reaches 68.6%. After increasing the concentration of potassium ferrate, although the inactivation rate of bacteria can be further improved, the improvement effect decreases. At the highest dosage concentration in this example, that is, the dosage of 30 mg-Fe / L, the inactivation rate of microorganisms is the highest, reaching 89.0%, which is only 20.4% higher than the inactivation rate at 2 mg-Fe / L. The above phenomenon shows that a small amount of potassium ferrate can inactivate most of the microorganisms in the roof rainwater. However, some types of microorganisms have a strong tolerance to high iron and need to be inactivated at a higher dosage. Since the rainwater reuse system requires that it cannot contain pathogenic microorganisms, 30 mg-Fe / L is selected as the optimal dosage in this experiment.

[0049] Example 6 Take 4000 mL of roof rainwater and place it in a beaker. Place a magnetic stirrer on a magnetic stirrer. Weigh potassium ferrate solid and add it to the beaker to make the concentration 30 mg-Fe / L. Adjust the first rapid rotation speed to 300 rpm and stir for 30 minutes. Then add 40 mg / L of cationic polyacrylamide, add dilute hydrochloric acid to adjust the pH to 7.0, adjust the second rapid rotation speed to 300 rpm, stir for 1 minute, then stir at a medium speed (150 rpm) for 5 minutes, and finally stir at a slow speed (60rpm) for 20 minutes.

[0050] Use a circulating pump to pump the treated rainwater into the filtration device (the ratio of the filter layer to the support layer is 4:1) to obtain effluent. Take 180 mL of effluent and concentrate it into 30 mL of effluent. Use the 3M total colony count test paper to test the total colony count of the effluent. The results are as follows: Figure 2The remaining water samples were filtered through a 0.45 μm filter membrane, and then the number of microplastics on the filter membrane was counted using a laser confocal Raman microscope. The results are shown in Figure 3 shown.

[0051] Comparative Example 2 Take 4000 mL of roof rainwater and place it in a beaker. Place a magnetic stirrer on a magnetic stirrer. Weigh potassium ferrate solid and add it to the beaker to make the concentration 30 mg-Fe / L. Adjust the first rapid rotation speed to 300 rpm and stir for 30 minutes. Then add 40 mg / L of cationic polyacrylamide, add dilute hydrochloric acid to adjust the pH to 4, adjust the second rapid rotation speed to 300 rpm, stir for 1 minute, then stir at a medium speed (150 rpm) for 5 minutes, and finally stir at a slow speed (60rpm) for 20 minutes.

[0052] The treated rainwater was pumped into the filtration device (the ratio of the filter layer to the support layer height was 4:1) using a circulating pump to obtain effluent. 180 mL of effluent was taken and concentrated into 30 mL of effluent. The total colony count of the effluent was detected using the 3M total colony count test paper, which was 209 CFU / mL. The remaining water sample was filtered through a 0.45 μm filter membrane, and then a laser confocal Raman microscope was used to count the number of microplastics on the filter membrane, which dropped to 19.5 / L.

[0053] Comparative Example 3 Take 4000 mL of roof rainwater and place it in a beaker. Place a magnetic stirrer on a magnetic stirrer. Weigh potassium ferrate solid and add it to the beaker to make the concentration 30 mg-Fe / L. Adjust the first rapid rotation speed to 300 rpm and stir for 30 minutes. Then add 40 mg / L of cationic polyacrylamide, add sodium hydroxide to adjust the pH to 9, adjust the second rapid rotation speed to 300 rpm, stir for 1 minute, then stir at a medium speed (150 rpm) for 5 minutes, and finally stir at a slow speed (60rpm) for 20 minutes.

[0054] The treated rainwater was pumped into the filtration device (the ratio of the filter layer to the support layer height was 4:1) using a circulating pump to obtain effluent. 180 mL of effluent was taken and concentrated into 30 mL of effluent. The total colony count of the effluent was detected using the 3M total colony count test paper, which was 247 CFU / mL. The remaining water sample was filtered through a 0.45 μm filter membrane, and then a laser confocal Raman microscope was used to count the number of microplastics on the filter membrane, which dropped to 30.75 microplastics / L.

[0055] from Figure 2It can be seen that without adding coagulants, the total colony count before and after filtration did not change, both of which were 1400 CFU / mL, indicating that filtration cannot remove microorganisms in rainwater. However, after adding potassium ferrate for coagulation and filtration, the total colony count of the effluent dropped to 245 CFU / mL, and the colony removal rate reached 82.5%, which is similar to the results obtained by PMA-qPCR. In addition, the sterilization rate of coagulation and filtration was basically the same before and after the addition of cationic polyacrylamide coagulation, indicating that cationic polyacrylamide has no effect on sterilization. It is worth noting that under neutral conditions, the removal rate of colonies by potassium ferrate and cationic polyacrylamide synergistic coagulation and filtration reached 100%. This may be because under neutral conditions, the flocs produced by the synergistic coagulation of cationic polyacrylamide and potassium ferrate are larger, which can block the filter material, allowing the filter material to intercept all bacteria.

[0056] from Figure 3 It can be seen that when the dosage of ferrate is 30 mg-Fe / L, the number distribution of microplastics before and after coagulation and filtration. Coagulation and filtration can achieve efficient removal of microplastics in rainwater. Figure 3 As shown in the figure, the number of microplastics in the raw water is 443.25 pieces / L, while after filtration by the filtration device, the number of microplastics drops to 28.25 pieces / L. From the diameter distribution of microplastics, it can be seen that the short axis diameter of the microplastics after filtration is mostly less than 30μm. The above phenomenon shows that filtration can remove microplastics larger than 30μm in rainwater. Under neutral conditions, potassium ferrate and cationic polyacrylamide synergistic coagulation filtration can further remove microplastics of 20-30μm in rainwater, and the concentration of microplastics in the effluent is 2.5 pieces / L, and the removal rate is further increased.

[0057] The above phenomenon shows that ferrate can act as a bactericide and coagulant at the same time, thereby removing microplastics and microorganisms at the same time. In addition, under the coagulant effect of cationic polyacrylamide, the flocs of microplastics are larger, so that more microplastics are filtered and removed. In addition, after adjusting the pH to neutral, the coagulation effect of the system is further enhanced, and the particle size of the flocs is further increased, thereby blocking the filter material, so that microorganisms can also be intercepted by the filter material, thereby improving the removal rate of microplastics and microorganisms at the same time.

[0058] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for the synergistic removal of microplastics and microorganisms in rainwater, characterized in that: The following steps are involved: The rainwater to be treated is mixed with ferrate and polyacrylamide, and purified reused water is obtained after sterilization, pH adjustment, coagulation and filtration.

2. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 1, characterized in that: The specific operation steps are as follows: a certain concentration of ferrate is added to the rainwater to be treated, and the first rapid stirring is immediately performed, followed by adding polyacrylamide and immediately adding dilute hydrochloric acid to adjust the pH, followed by a second rapid stirring, then medium-speed stirring, and finally slow stirring; the stirring speeds of the first and second rapid stirrings are 300-400 rpm, the stirring speed of the medium-speed stirring is 150-200 rpm, and the stirring speed of the slow stirring is 50-70 rpm.

3. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 2, characterized in that: The stirring time of the first rapid stirring should be greater than or equal to 30 minutes.

4. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 3, characterized in that: The stirring time of the first rapid stirring is 30-40 minutes.

5. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 2, characterized in that: The stirring time for the second rapid stirring is 1-2 min, the stirring time for the medium speed stirring is 5-10 min, and the stirring time for the slow speed stirring is 20-40 min.

6. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 2, characterized in that: Add dilute hydrochloric acid until the water pH is between 6.5-7.

5.

7. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 1, characterized in that: After the rainwater is mixed with ferrate, it is filtered through a filter column to obtain purified reuse water. The supporting layer material in the filter column is selected from: one or more of pebbles, gravel, and artificial fiber ball filter materials; the filter layer material in the filter column is selected from: one or more of quartz sand, anthracite, activated carbon, ceramsite, garnet, and fiber balls.

8. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 7, characterized in that: The supporting layer material is pebbles with a particle size range of 1 cm-1.5 cm, and the filtering layer material is quartz sand with a particle size range of 700-1000 μm.

9. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 1, characterized in that: The ratio of the mass amount of iron in the ferrate to the amount of roof rainwater to be treated is in the range of 2 mg:1L-40 mg:1L.

10. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 9, characterized in that: The ratio of the mass dosage of the iron in the ferrate to the dosage of the roof rainwater to be treated is in the range of 30 mg:1L-35 mg:1L.

11. The method for collaboratively removing microplastics and microorganisms in rainwater according to claim 1, characterized in that: The mass ratio of the ferrate iron to the polyacrylamide is in the range of 1 mg:1 mg to 3 mg:4 mg; The ferrate is selected from one or more of potassium ferrate and sodium ferrate; The polyacrylamides described are all cationic polyacrylamides.

Images