Biodegradable sewage treatment filler as well as preparation method and application thereof

Abstract

The invention discloses a biodegradable sewage treatment filler as well as a preparation method and application thereof, and belongs to the technical field of biological sewage treatment, the novel sewage treatment filler is prepared from biodegradable plastics PCL and TPS, the rapid degradation and denitrification nitrogen removal performance of a biodegradable material in the sewage treatment denitrification process is enhanced, and the biodegradable sewage treatment filler belongs to the technical field of biological sewage treatment. Due to the small contact surface between the filler and the bottom and sufficient disturbance, various pollutant degrading microorganisms, PCL efficient degrading microorganisms and the like can be more effectively gathered in a biological treatment reaction tank of a sewage treatment plant, so that efficient utilization of biodegradable materials and a low-carbon denitrification process of sewage microbiological treatment are realized; meanwhile, the filler is used as a slow-release carbon source, so that the rapid carbon source adding amount of a sewage treatment plant is effectively reduced, the cell yield is relatively low, and the effects of reducing sludge, reducing the operation and maintenance cost and the like can be achieved. In addition, PCL is decomposed faster in a sewage treatment system than in a natural habitat, and the natural degradation process of biodegradable materials can be further accelerated.

Description

Technical Field

[0001] The present invention belongs to the technical field of biological sewage treatment, and particularly relates to a biodegradable sewage treatment filler, a preparation method thereof, and an application thereof. Background Art

[0002] The biological method is favored due to its advantages such as simplicity, low cost, and high efficiency. Nevertheless, traditional biological treatment methods still have defects such as large floor area, poor stability, high production of excess sludge, and poor treatment effect in winter. With the improvement of water quality control requirements, challenges such as sludge treatment problems, malodor, and low nitrogen removal efficiency have become increasingly prominent. Currently, low-carbon denitrification has become a key technical problem that urgently needs to be broken through in the sewage treatment industry.

[0003] In traditional biological methods, microorganisms exist in a dispersed form, with slow proliferation and easy to be washed away, resulting in unstable treatment effects. In recent years, research has focused on using microbial fillers to enhance the microbial community effect. After the formation of the biofilm, microorganisms multiply abundantly on it, utilize the nutrients in the water for metabolism, and achieve the effect of purifying sewage. The biofilm is an effective means for low-carbon denitrification and can also reduce excess sludge. However, plastic fillers have high costs and need to be replaced regularly; inorganic fillers cannot be decomposed by microorganisms, resulting in poor surface wetting, low mass transfer performance, and slow attachment growth of microorganisms, affecting the sewage treatment effect.

[0004] Compared with traditional plastic materials, biodegradable plastics have significant advantages such as degradability, environmental friendliness, and resource recycling. During the sewage treatment process, biodegradable plastic waste as a new type of filler can not only provide abundant attachment sites for microorganisms on the surface but also release organic carbon sources during the microbial degradation process, further promoting the growth and metabolism of microorganisms. Especially when treating urban sewage with a low carbon-nitrogen ratio and low COD, the carbon source release effect of biodegradable plastics is particularly significant. Because microorganisms can utilize the organic carbon sources released by the degraded plastics to make up for the lack of carbon sources in the sewage, thereby enhancing the nitrogen removal efficiency. Therefore, the sewage treatment technology using biodegradable plastics as fillers overcomes some technical bottlenecks in traditional methods and provides an important solution for improving sewage treatment efficiency. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide a biodegradable sewage treatment filler, a preparation method thereof, and an application thereof.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] In the first aspect, the present invention provides a preparation method for a biodegradable sewage treatment filler, specifically as follows:

[0008] Mix polycaprolactone (PCL) and thermoplastic starch (TPS) by melt blending to obtain a masterbatch, and then inject the masterbatch into a spherical structure with a number of through-holes. Subsequently, let it stand to eliminate residual stress, and obtain a biodegradable sewage treatment filler.

[0009] Preferably, the moisture content of the thermoplastic starch is within 1%, and the mass ratio of polycaprolactone to thermoplastic starch is 8:2.

[0010] Preferably, the density of the polycaprolactone is 1.1 g / cm 3 , and the density of the thermoplastic starch is 1.3 g / cm 3 , and the density of the masterbatch is 1.14 g / cm 3 .

[0011] Preferably, the stirring speed during the melt blending process is 30 r / min and the time is 3 min; the injection molding temperature is 160 °C.

[0012] Preferably, the outer diameter of the spherical structure is 1.5 cm, the inner diameter is 0.9 cm, the diameter of the through-hole is 0.3 cm, the number of through-holes is 16, the porosity is 117.6%, the density is 1.14 g / cm 3 , and the specific surface area is 8.82 cm 2 / g.

[0013] Preferably, place the injection-molded spherical structure at 23 ± 2 °C / 50% humidity for one day to eliminate residual stress.

[0014] In a second aspect, the present invention provides a biodegradable sewage treatment filler obtained by using the preparation method according to any one of the first aspect.

[0015] In a third aspect, the present invention provides a method for denitrifying and removing nitrogen from sewage based on the biodegradable sewage treatment filler described in the second aspect, specifically as follows:

[0016] Hang the biodegradable sewage treatment filler in a continuous flow reactor for 15 - 20 days to allow functional microorganisms to fully attach to it; then place the filler in the sewage to be treated, and add sodium nitrate at a concentration of 50 - 250 mg / L; as the concentration of sodium nitrate increases, the denitrifying and nitrogen removal effect of the filler improves and the degradation rate accelerates.

[0017] Preferably, the continuous flow reactor is a simultaneous nitrification and denitrification reactor; the dissolved oxygen in the reactor is 2 - 3 mg / L, the stirring speed is 150 rpm, and the effective volume is 4 L.

[0018] Preferably, the functional microorganisms include at least one of nitrifying bacteria Ellin6067 and Nitrosomonas, denitrifying bacteria Thermomonas, and highly efficient degrading bacteria Stenotrophobacter.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Utilizing the characteristics of the large porosity and specific surface area of the hollow porous spherical structure of the filler, more attachment sites are provided for the microorganisms suspended in the sewage, promoting the colonization of microorganisms on the surface of the filler. At the same time, for the specific situation where the density of the biodegradable material is relatively large and it is easy to sink to the bottom, the spherical filler can move under limited water flow disturbance.

[0021] (2) Using PCL and TPS as carbon sources available to microorganisms, promoting the growth of denitrifying bacteria, and achieving the effects of reducing carbon source addition and enhancing nitrogen removal efficiency.

[0022] (3) The addition of TPS enhances the hydrophilicity of the filler, which is beneficial for the attachment of microorganisms. The higher content of PCL improves the impact strength, elongation at break, and toughness of the filler.

[0023] (4) The biofilm formed on the surface of the filler contains a large amount of extracellular polymeric substances (EPS), which accelerates the adhesion and aggregation of microorganisms, effectively adsorbing fine particulate matter, colloidal pollutants, heavy metal ions, and nutrient salts in the sewage. At the same time, the biofilm can help microorganisms survive in low-temperature environments and reduce the amount of excess sludge.

[0024] (5) The density of PCL is 1.1 g / cm 3 , the density of TPS is 1.3 g / cm 3 , and the density of the blend (i.e., the masterbatch) is 1.14 g / cm 3 , which can precipitate in the sedimentation tank to achieve the recycling of the carrier until it is completely decomposed. Description of the Drawings

[0025] Figure 1 is the structural design diagram of the filler;

[0026] Figure 2 is the nitrate nitrogen degradation curve of the PCL group in the denitrification batch experiment;

[0027] Figure 3 is the nitrate nitrogen degradation curve of the TPS group in the denitrification batch experiment;

[0028] Figure 4 is the community characteristics of the PCL filler enrichment;

[0029] Figure 5 is the comparison of the biofilm formation of the K3-shaped fillers made of two different materials;

[0030] Figure 6 Nitrate nitrogen degradation curves of hollow porous spherical fillers and K3-shaped fillers. Specific implementation manners

[0031] The present invention will be further described and explained below in conjunction with the accompanying drawings and specific implementation manners. The technical features of each implementation manner in the present invention can be combined correspondingly on the premise of no conflict with each other.

[0032] The present invention provides a preparation method for a biodegradable sewage treatment filler, and the preparation method is specifically as follows:

[0033] Mix polycaprolactone (PCL) and thermoplastic starch (TPS) and carry out melt blending to obtain a masterbatch. Inject the masterbatch into a spherical structure with a plurality of through holes, and then place it for a period of time to eliminate residual stress, thereby obtaining a biodegradable sewage treatment filler. The filler prepared by the present invention has a hollow perforated spherical structure, can effectively play the functions of a carbon source and a biological carrier, promote the hierarchical attachment and aggregation of nitrifying and denitrifying microorganisms, and achieve highly efficient coupled denitrification.

[0034] As a preferred embodiment of the present invention, the thermoplastic starch is prepared by an existing method, and the preparation method is specifically as follows:

[0035] According to the reference (Wang Yazhou, Yi Pei, Ye Zhengtao. Preparation and properties of thermoplastic starch / polycaprolactone composites [J]. Colloids and Polymers, 2016, 34(02): 65-67. DOI: 10.13909.), weigh a portion of cassava starch, add an aqueous glycerol solution with a mass fraction of 20% (phr), an aqueous citric acid (CA) solution with 0.1 phr, and twice the amount of distilled water. Stir and mix evenly at 90 °C for 40 min, stop heating, dry for 72 h, and then pulverize to obtain thermoplastic starch (control its moisture content within 1%).

[0036] As a preferred embodiment of the present invention, polycaprolactone and thermoplastic starch with a mass ratio of 8:2 can be added to a melt blender and melt blended at 30 r / min for 3 minutes to obtain a masterbatch. Subsequently, injection molding is carried out using a micro-injection molding machine, the injection temperature is 160 °C, and it is placed for one day under the conditions of 23 ± 2 °C / 50% humidity to eliminate residual stress.

[0037] As a preferred embodiment of the present invention, the spherical structure of the filler can be designed as follows: the outer diameter is 1.5 cm, the inner diameter is 0.9 cm, the diameter of the through hole is 0.3 cm, the number of through holes is 16, the porosity is 117.6%, and the density is 1.14 g / cm 3 , and the specific surface area is 8.82 cm 2 / g.

[0038] The biodegradable sewage treatment filler prepared by the above method can be used for denitrification of sewage after biofilm formation, specifically as follows:

[0039] The biodegradable sewage treatment filler is biofilm-formed in a continuous flow reactor for 15 - 20 days to fully attach functional microorganisms thereon, improving the denitrification effect. Subsequently, the biofilm-formed filler is put into the sewage to be treated. Without adding a carbon source, only sodium nitrate with a concentration of 50 - 250 mg / L is provided to carry out the denitrification process of the sewage. During this process, with the increase of the sodium nitrate concentration, the denitrification effect of the filler is improved and the degradation rate is accelerated.

[0040] As a preferred embodiment of the present invention, the continuous flow reactor is a simultaneous nitrification and denitrification reactor; the dissolved oxygen in the reactor is 2 - 3 mg / L, the stirring speed is 150 rpm, and the effective volume is 4 L.

[0041] As a preferred embodiment of the present invention, the functional microorganisms include at least one of nitrifying bacteria Ellin6067 and Nitrosomonas, denitrifying bacteria Thermomonas, and highly efficient degrading bacteria Stenotrophobacter.

[0042] Example

[0043] A biodegradable sewage treatment filler was prepared in this example, and the preparation method is as follows:

[0044] Polycaprolactone (PCL) and thermoplastic starch (TPS) are mixed in a mass ratio of 8:2, and then added to a kneader and kneaded at 30 r / min for 3 minutes to obtain a masterbatch. The masterbatch is injection-molded with a micro-injection molding machine, and the injection temperature is 160 °C. It is placed for one day under the conditions of 23 ± 2 °C / 50% humidity to eliminate residual stress. Among them, the outer diameter of the spherical structure is 1.5 cm, the inner diameter is 0.9 cm, the diameter of the through hole is 0.3 cm, the number of through holes is 16, the porosity is 117.6%, and the density is 1.14 g / cm 3 , and the specific surface area is 8.82 cm 2 / g. The structure of the prepared filler is as Figure 1 shown. It can be seen from the figure that the actual through-hole diameter of the spherical filler is 3 mm, the outer diameter of the sphere is 15 mm, the inner diameter is 9 mm, the thickness is 3 mm, the number of through holes is 16, the porosity is 117.6%, and the density is 1.14 g / cm 3 , and the specific surface area is 8.82 cm 2 / g.

[0045] In order to illustrate the performance of the filler of the present invention, the following experiments were respectively carried out on PCL, TPS, and the porous spherical filler prepared in Example 1 for verification, specifically as follows:

[0046] PCL was added to a reaction flask to conduct a denitrification batch experiment with a total volume of 100 mL, as follows:

[0047] In the experiment, 10 g of PCL was added, the initial concentration of nitrate nitrogen was 50 mg / L, the temperature was 27 °C, the pH was 7.5 - 8.0, and no other carbon sources were added except PCL. The nitrate nitrogen degradation curve was measured as Figure 2 , as can be seen from the figure, the average concentration of nitrate nitrogen in the group with PCL added decreased from 48.3 mg / L to 14.1 mg / L in 10 h, while that in the blank group without PCL added decreased from 48.0 mg / L to 18.5 mg / L in 6 d. This indicates that PCL effectively improved the denitrification efficiency and the experiment had good repeatability.

[0048] TPS was added to a reaction flask to conduct a denitrification batch experiment with a total volume of 100 mL, as follows:

[0049] In the experiment, 10 g of TPS was added, the initial concentration of nitrate nitrogen was 50 mg / L, the temperature was 27 °C, the pH was 7.5 - 8.0, and no other carbon sources were added except TPS. The nitrate nitrogen degradation curve was measured as Figure 3 , as can be seen from the figure, the average concentration of nitrate nitrogen in the group with TPS added decreased from 47.8 mg / L to 5.6 mg / L in 3 h, while that in the blank group without TPS added decreased from 48.0 mg / L to 18.5 mg / L in 6 d. This indicates that TPS highly improved the denitrification efficiency and the experiment had good repeatability.

[0050] Two fillers with the same K3 shape (i.e., the shape of traditional fillers), one made of a blend mainly of PCL (i.e., the masterbatch obtained in the example, denoted as the experimental group) and the other made of polyethylene (denoted as the control group), were used for biofilm formation and denitrification batch experiments. Biofilm formation was carried out using a simultaneous nitrification and denitrification reactor, as follows:

[0051] The process conditions for simultaneous nitrification and denitrification operation were surface aeration to ensure a dissolved oxygen of about 2 mg / L, a stirring speed of 150 rpm, a sludge concentration of 4000 - 5000 mg / L, a hydraulic retention time of 12 h, an operating volume of 4 L, a reactor temperature of 24 - 26 °C, and an operating time of at least 15 days. The results are as Figure 4 shown. This figure is a graph of the sludge community composition enriched by the two fillers based on 16S high-throughput analysis. The ordinate OTU is a taxonomic unit below the species level and can represent the change in the number of classified populations. According to the results, among the nitrifying microorganisms enriched in the experimental group fillers, Ellin6067, Nitrosomonas, the denitrifying bacterium Thermomonas, and the polymer highly degrading bacterium Stenotrophobacter were significantly more enriched than those in the control group fillers.

[0052] The operating conditions for simultaneous nitrification and denitrification are surface aeration to ensure a dissolved oxygen of about 2 mg / L, a stirring speed of 150 rpm, a sludge concentration of 4000 - 5000 mg / L, a hydraulic retention time of 12 h, an operating volume of 4 L, a reactor temperature of 24 - 26 °C, and an operating time of 18 days. After fishing out, observe the biofilm formation situation. As Figure 5 shown, a large amount of sludge adheres to the surface of the packing in the experimental group, while there is no obvious adhesion on the surface of the packing in the control group, indicating that the biofilm formation rate of the materials in the experimental group is faster and more conducive to the adhesion of microorganisms. Subsequently, a denitrification batch experiment was carried out. In the experiment, the total reaction volume was 100 mL, the initial concentration of nitrate nitrogen was 50 mg / L, the temperature was 27 °C, and the pH was 7.5 - 8.0. Except for the packing, no other carbon sources were added, and no additional activated sludge was added. After 5 days of reaction, the concentration of nitrate nitrogen in the control group did not change significantly, and the reaction only lasted for 2 days; the average concentration of nitrate nitrogen in the experimental group decreased from 50.4 mg / L to 0.4 mg / L, significantly improving the denitrification rate.

[0053] The following explains the shape advantages of the present invention:

[0054] Hollow porous spherical packing and K3-shaped packing were respectively prepared using PCL, and biofilm formation and denitrification batch experiments were carried out. A simultaneous nitrification and denitrification reactor was used for biofilm formation. Among them, the operating conditions for simultaneous nitrification and denitrification are surface aeration to ensure a dissolved oxygen of about 2 mg / L, a stirring speed of 150 rpm, a sludge concentration of 4000 - 5000 mg / L, a hydraulic retention time of 12 h, an operating volume of 4 L, a reactor temperature of 24 - 26 °C, and an operating time of 18 days. After biofilm formation, the packing was fished out for a denitrification batch experiment. In the experiment, the total reaction volume was 100 mL, the initial concentration of nitrate nitrogen was 50 mg / L, the temperature was 27 °C, and the pH was 7.5 - 8.0. Except for the packing, no other carbon sources were added, and no additional activated sludge was added. The measured nitrate nitrogen degradation curve is as Figure 6 , as can be seen from the figure, the average concentration of nitrate nitrogen in the K3-shaped packing decreased from 51.9 mg / L to 33.2 mg / L in 7 h, while the average concentration of nitrate nitrogen in the hollow porous spherical packing decreased from 55.1 mg / L to 2.4 mg / L in 7 h, significantly improving the denitrification rate. After the denitrification batch experiment, the packing was fished out, ultrasonically cleaned with a 0.4% mass concentration of NaCl solution for 30 min to obtain a solution with sludge, and after filtration through a filter membrane and drying, the sludge concentration of the K3 and hollow porous sphere denitrification experiments was measured. According to the calculation during the rapid denitrification stage, the denitrification activity was obtained, among which the K3-shaped group: 10.41 mg·N / gVSS·h; the hollow porous spherical group: 53.24 mg·N / gVSS·h. The denitrification activity of the hollow porous sphere is more than 5 times that of the K3-shaped group.

[0055] The following explains the technical advantages of the present invention:

[0056] The hollow spherical degradable filler prepared based on the embodiments can be used for biofilm attachment by the simultaneous nitrification and denitrification process, which can effectively enrich the highly efficient degraders of biodegradable materials, denitrifying bacteria and nitrifying bacteria at the same time and has a faster degradation rate. The thickness of the filler is reasonably set according to the degradation effect. The spherical shape is adopted, and the performance of the biodegradable material is improved by enriching functional microorganisms through different processes. Similar application scenarios such as sewage treatment plants should be included in the scope protected by the present invention.

[0057] The following shows that the present invention can significantly accelerate the degradation of PCL itself:

[0058] According to the references (Abou-Zeid DM, Müller RJ, Deckwer WD. Degradation of natural and synthetic polyesters under anaerobic conditions. J Biotechnol, 2001, 86(2): 113-126. DOI: 10.1016; Narancic T, Verstichel S, Reddy Chaganti S, et al. Biodegradable plastic blends create new possibilities for end-of-life management of plastics but they are not a panacea for plastic pollution. Environ Sci Technol, 2018, 52(18): 10441-10452. DOI: 10.1021.), it can be known that the biodegradation ability of the film-shaped (0.5 mm thick) PCL in the activated sludge under anaerobic conditions reached 30.0% after 42 days, while it could only degrade 2.5% in the anaerobic water condition after 56 days.

[0059] After 5 days of denitrification batch experiments, the hollow porous spherical filler after biofilm attachment in the simultaneous nitrification and denitrification reactor was fished out, ultrasonically cleaned with 0.4% NaCl solution for 30 minutes, and dried in an oven at 45°C. The weight loss rate was measured to be 22.0%. The weight loss rate of the unprocessed PCL particles into hollow porous spheres was 6.07%. The degradation of PCL itself can be accelerated by more than 3 times.

[0060] The present invention uses biodegradable plastics as the main raw material and processes them into hollow porous spherical fillers. Due to the small contact area with the bottom, this shape of filler can be fully agitated, and can more effectively aggregate various pollutant-degrading microorganisms in the biological treatment reaction tank of the sewage treatment plant, including slow-growing denitrifying and nitrogen-removing microorganisms, PCL highly-degrading microorganisms, etc., thereby realizing the efficient utilization of biodegradable materials and the low-carbon nitrogen-removing process of sewage microbial treatment. At the same time, the filler serves as a slow-release carbon source, effectively reducing the dosage of fast carbon source in the sewage treatment plant and having a low cell yield, which can achieve sludge reduction and reduce operation and maintenance costs. In addition, PCL decomposes faster in the sewage treatment system than in the natural habitat, which can further accelerate the natural degradation process of biodegradable materials. Therefore, this invention has engineering practical value of cost reduction and efficiency improvement in the fields of low-energy sewage low-carbon nitrogen removal, solid waste resource utilization, etc.

[0061] The above-described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical fields can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A preparation method of a biodegradable sewage treatment filler, characterized in that, The specific steps are as follows: Mix polycaprolactone and thermoplastic starch through intensive mixing to obtain a masterbatch, and then injection-mold the masterbatch into a spherical structure with a number of through holes, and then place it to eliminate residual stress, thereby obtaining a biodegradable sewage treatment filler.

2. The preparation method of a biodegradable sewage treatment filler according to claim 1, characterized in that The moisture content of the thermoplastic starch is within 1%, and the mass ratio of polycaprolactone to thermoplastic starch is 8:

2.

3. The preparation method of a biodegradable sewage treatment filler according to claim 1, characterized in that, The density of the polycaprolactone is 1.1 g / cm 3 , the density of the thermoplastic starch is 1.3 g / cm 3 , and the density of the masterbatch is 1.14 g / cm 3 .

4. The preparation method of a biodegradable sewage treatment filler according to claim 1, wherein, The stirring speed during the intensive mixing process is 30 r / min, and the time is 3 min; the injection molding temperature is 160 °C.

5. The preparation method of a biodegradable sewage treatment filler according to claim 1, characterized in that, The outer diameter of the spherical structure is 1.5 cm, the inner diameter is 0.9 cm, the diameter of the through-hole is 0.3 cm, the number of through-holes is 16, the porosity is 117.6%, and the density is 1.14 g / cm 3 , and the specific surface area is 8.82 cm 2 / g.

6. The preparation method of a biodegradable sewage treatment filler according to claim 1, characterized in that, Place the injection-molded spherical structure under the conditions of 23 ± 2 °C / 50% humidity for one day to eliminate residual stress.

7. A biodegradable sewage treatment filler obtained by using the preparation method according to any one of claims 1 to 6.

8. A method for sewage denitrification and nitrogen removal using the biodegradable sewage treatment filler described in claim 7, characterized in that, The specific steps are as follows: Hang the biodegradable sewage treatment filler in a continuous flow reactor for 15 - 20 days to allow functional microorganisms to fully adhere to it; then place the filler in the sewage to be treated, and add sodium nitrate at a concentration of 50 - 250 mg / L; as the concentration of sodium nitrate increases, the denitrification and nitrogen removal effect of the filler improves and the degradation rate accelerates.

9. The sewage denitrification and nitrogen removal method according to claim 8, wherein, The continuous flow reactor is a simultaneous nitrification and denitrification reactor; the dissolved oxygen in the reactor is 2 - 3 mg / L, the stirring speed is 150 rpm, and the effective volume is 4 L.

10. The sewage denitrification and nitrogen removal method according to claim 8, characterized in that, The functional microorganisms include at least one of nitrifying bacteria Ellin6067 and Nitrosomonas, denitrifying bacteria Thermomonas, and highly efficient degrading bacteria Stenotrophobacter.

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