Polyvinyl alcohol modified coupling denitrification biological filler, preparation method and application thereof

Abstract

The application discloses a polyvinyl alcohol modified coupling denitrification biological filler, a preparation method and application thereof, and belongs to the technical field of sewage treatment. The polyvinyl alcohol modified coupling denitrification biological filler is formed by adding polyvinyl alcohol (PVA) and a small amount of straight-chain starch to sulfur powder as a main component, and adding an auxiliary agent. The PVA can be used as a slow-release carbon source together with the small amount of straight-chain starch in addition to being used as an adhesive. During the heat treatment process, the rearrangement of the PVA molecular chain not only enhances the strength of the filler, but also makes the filler swell and deform, and the cavity volume increases. After being combined with an adsorbent, the porosity of the filler is increased. On the other hand, the PVA and the auxiliary agent react to dehydrate and etherify, and the number of hydroxyl groups on the molecular chain is consumed, which weakens the hydrophilicity of the PVA, and further prolongs the slow-release time and slow-release stability of the carbon source in the filler, thereby creating better coupling conditions for sulfur autotrophic and heterotrophic denitrification.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a polyvinyl alcohol modified coupled denitrification biological packing material, its preparation method, and its application. Background Technology

[0002] Among various ecological problems, nitrogen pollution in water bodies is a major issue facing my country today. Currently, biological nitrogen removal methods are frequently used in practical engineering projects due to their advantages such as low treatment cost, simple operation, and stable results. Biological methods guide the nitrogen cycle through the action of microorganisms, converting target nitrogen pollutants into environmentally harmless nitrogen forms. Currently, technologies related to biological nitrogen removal mainly focus on three aspects: heterotrophic denitrification, autotrophic denitrification, and heterotrophic-autotrophic coupled nitrogen removal.

[0003] Heterotrophic denitrification is a nitrogen removal technology that uses heterotrophic bacteria to convert nitrate nitrogen into nitrogen gas under suitable organic carbon source conditions. This method is relatively mature and currently the most widely used. When the external carbon source is suitable, the microbial proliferation rate is relatively fast, resulting in good denitrification efficiency. However, this method also has obvious drawbacks: it is difficult to achieve maximal denitrification, and insufficient carbon source leads to reduced denitrification efficiency. Furthermore, adding an external carbon source increases treatment costs and introduces secondary pollution.

[0004] Autotrophic denitrification technology uses reducing elements such as sulfur and iron as a substrate to cultivate autotrophic denitrifying bacteria, which then convert nitrate nitrogen into nitrogen gas for removal. The advantages of this method are that it does not require an external carbon source and can achieve maximal nitrogen removal. The disadvantages are low microbial multiplication rate and poor environmental adaptability, which affects the treatment effect in practical engineering.

[0005] Heterotrophic-autotrophic denitrification synergistic nitrogen removal technology refers to the combination of solid carbon sources such as sawdust or liquid organic carbon sources with electron donors such as sulfur and iron, achieving nitrogen removal through the synergistic effect of heterotrophic and autotrophic bacteria. This technology, through the cultivation of heterotrophic denitrifying bacteria, can compensate for the low proliferation efficiency and poor shock resistance of autotrophic bacteria; however, this nitrogen removal scheme requires the integration of two nitrogen removal methods, increasing the difficulty of controlling the actual nitrogen removal operation.

[0006] Currently, there are many reports on the coupling of the above technologies in the field of wastewater treatment. For example, patent CN111777179A utilizes heterotrophic denitrification coupled with sulfur autotrophic denitrification to enhance nitrogen and phosphorus removal from wastewater with a low carbon-to-nitrogen ratio. Elemental sulfur and an added liquid organic carbon source are used as electron donors for sulfur autotrophic and heterotrophic denitrification, respectively, to achieve nitrate reduction. However, this method increases the difficulty of controlling the actual denitrification operation and easily leads to excessive carbon source, causing secondary pollution. Patent CN114873741B uses alkali-modified corn cob powder and polyhydroxy fatty acid esters as solid slow-release carbon sources, with sulfur as the sulfur source. It utilizes the coupling effect of heterotrophic denitrification and sulfur autotrophic denitrification to achieve deep denitrification of nitrogen-containing wastewater. However, the slow-release carbon source in this method is mainly natural material with a high lignin content, which has low biodegradability for microorganisms, hindering their metabolic activities and affecting nitrogen removal. Furthermore, during carbon release, these natural materials also release other substances such as N and P, which are difficult to control and affect the quality of the effluent.

[0007] Considering that polyvinyl alcohol (PVA) is a biodegradable organic polymer, not only inexpensive and readily available, but also possessing advantages such as high barrier properties, wear and corrosion resistance, and excellent mechanical properties, and that starch can be extracted from agricultural crops in a wide variety of forms, is a natural renewable resource and is completely biodegradable, and that the two, after processing and combination, complement each other and can serve as an excellent slow-release carbon source, a packing material made primarily of elemental sulfur, PVA, and a small amount of starch could be considered to achieve the coupling of sulfur autotrophic and heterotrophic denitrification. Furthermore, no reports have been found on biological packing materials made primarily of these three materials. Summary of the Invention

[0008] This invention provides a polyvinyl alcohol-modified coupled denitrification biological packing material, its preparation method, and its application. The provided biological composite packing material can serve as both a microbial carrier and a carbon and sulfur source donor for biological reactions. By utilizing the coupling effect of heterotrophic denitrification and sulfur autotrophic denitrification, efficient denitrification of nitrogen-containing wastewater can be achieved.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A polyvinyl alcohol modified coupled denitrification biological packing material, the raw materials include the following components by weight: 60-80 parts sulfur powder, 8-15 parts polyvinyl alcohol powder (PVA), 1-2 parts amylose, 5-10 parts calcium carbonate, 2-5 parts adsorbent, and 2-5 parts auxiliary agent.

[0011] Of the components described above, the sulfur powder has a sulfur content exceeding 95% and a particle size of 150-250 mesh.

[0012] The PVA has a degree of polymerization of 1700 and a degree of alcoholysis of 88%.

[0013] The adsorbent is powdered activated carbon with a particle size of 200-400 mesh;

[0014] The auxiliary agent is composed of the following components by weight percentage: 10-20% plasticizer, 10-20% viscosity stabilizer, and 60-80% etherifying agent;

[0015] The plasticizer is calcium thiocyanate or ethylene glycol; the viscosity stabilizer is sodium thiocyanate, phenol or butanol; the etherifying agent is ethylene oxide or epichlorohydrin.

[0016] The preparation method of the above-mentioned polyvinyl alcohol modified coupled denitrification biological packing includes the following steps:

[0017] S1: Add a certain amount of sulfur powder, PVA, and calcium carbonate to the reactor and inject deionized water, then stir and heat the reactor.

[0018] S2: After adding the amylose, adsorbent and auxiliary agent into the reactor in sequence and stirring, the mixture is thoroughly mixed to obtain a thickened substance. After maintaining the mixture at 160-180℃ for a period of time, it is melt-granulated.

[0019] S3: Finally, the moisture in the spherical packing is removed by hot air drying, and after cooling, spherical composite packing is obtained.

[0020] In the steps described above, the temperature inside the reactor in S1 is raised and maintained at 80-95°C, and the rotation speed is 100-200 rpm;

[0021] In S2, the resulting thickened material is heat-treated at 160–180 °C for 10–40 min.

[0022] The spherical particles produced by melt granulation in S2 have a particle size of 1-8 mm.

[0023] The drying temperature described in S3 is 80~100℃, and the time is 6~10h;

[0024] The polyvinyl alcohol modified coupling denitrification biological packing prepared above is used for the treatment of nitrogen-containing wastewater. The packing has a filling rate of 60% to 80% and the nitrate nitrogen content in the water is not less than 100 mg / L. Preferably, the nitrate nitrogen content in the water is 100 mg / L to 500 mg / L, for example, 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L, and 500 mg / L.

[0025] Beneficial effects: This invention provides a polyvinyl alcohol-modified coupled denitrification biological packing material, its preparation method, and its application, which has the following advantages compared with the prior art:

[0026] 1. In addition to acting as a binder, the PVA added to the packing material in this invention can also be used together with amylose as a slow-release carbon source to enhance heterotrophic denitrification, thereby improving the pH stability of the coupled system and reducing SO4 in the effluent. 2- The content is low, which greatly avoids secondary pollution of water bodies. In addition, PVA in the filler is a chemical compound that is widely available and inexpensive.

[0027] 2. The linear starch used in the filler of this invention has excellent water resistance and strength. After combining with PVA in the filler, it prolongs the slow release time of the carbon source in the filler and also increases the mechanical strength of the filler.

[0028] 3. After heat treatment, on the one hand, the PVA molecular chains in the composite packing rearrange, which not only enhances the strength of the packing but also causes it to expand and deform, increasing the cavity volume and increasing the porosity of the packing after combining with the adsorbent; on the other hand, PVA reacts with the auxiliary agent, dehydrates and etherifies, consumes the number of hydroxyl groups on the molecular chain, weakens the hydrophilicity of PVA, and thus prolongs the slow release time and slow release stability of the carbon source in the packing, creating better coupling conditions for sulfur autotrophic and heterotrophic denitrification.

[0029] 4. The packing material prepared by this invention has significantly improved porosity and carbon source slow release performance. It can not only improve the biofilm formation efficiency of the sulfur autotrophic and heterotrophic coupling system, but also effectively enhance the start-up speed and operation effect of the coupling process. It can achieve ultimate denitrification and adapt well to fluctuations in influent water quality.

[0030] 5. The filler prepared by this invention not only does not require an external carbon source, but also has a low cost. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating the preparation process of the polyvinyl alcohol-modified coupled denitrification biological packing material in this embodiment of the invention.

[0032] Figure 2 The NO3 in the effluent from bioreactors R1, R2, and R3 at each stage in this embodiment of the invention. - -N concentration curve;

[0033] Figure 3 This invention illustrates the effect of bioreactors R1, R2, and R3 on NO3 at each stage in embodiments of the invention. - -N removal rate curve;

[0034] Figure 4 This is a graph showing the pH change curves of bioreactors R1, R2, and R3 at each stage in an embodiment of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0036] In the following examples, the filler is composed of: sulfur powder, polyvinyl alcohol powder (PVA), linear starch, calcium carbonate, adsorbent, and auxiliary agent, and the number of each component is by weight.

[0037] The selected sulfur powder has a sulfur content of over 95% and a particle size of 200 mesh. The degree of polymerization of PVA is 1700 and the degree of alcoholysis is 88%. The selected adsorbent is powdered activated carbon with a particle size of 300 mesh. Among the selected auxiliary agents, the plasticizer is calcium glycerothiocyanate, the viscosity stabilizer is sodium thiocyanate, and the etherifying agent is ethylene oxide, with each having a mass fraction of 20%, 20%, and 80%, respectively. Example 1

[0038] A method for preparing a polyvinyl alcohol-modified denitrification biological packing material includes the following steps:

[0039] Step 1: Add 70 parts sulfur powder, 8 parts polyvinyl alcohol powder (PVA), and 5 parts calcium carbonate to the reactor and inject deionized water. Stir the mixture and heat the reactor to 85°C at a speed of 120 rpm.

[0040] Step 2: Add 1 part of amylose, 5 parts of powdered activated carbon and 3 parts of auxiliary agent into the reaction vessel in sequence and stir. After mixing thoroughly, a thickened substance is obtained. After heat treatment at 170℃ for 10 minutes, it is melt-granulated. The particle size of the spherical particles is about 3 mm.

[0041] Step 3: Dry the spherical packing with hot air at 80℃ for 8 hours to remove moisture. After cooling, obtain spherical composite packing. Example 2

[0042] A method for preparing a polyvinyl alcohol-modified denitrification biological packing material includes the following steps:

[0043] Step 1: Add 70 parts sulfur powder, 11 parts polyvinyl alcohol powder (PVA), and 7 parts calcium carbonate to the reactor and inject deionized water. Stir the mixture and heat the reactor to 85°C at a speed of 120 rpm.

[0044] Step 2: Add 1 part of amylose, 5 parts of powdered activated carbon and 5 parts of auxiliary agent into the reaction vessel in sequence and stir. After mixing thoroughly, a thickened substance is obtained. After heat treatment at 170℃ for 20 minutes, it is melt-granulated. The particle size of the spherical particles is about 3 mm.

[0045] Step 3: Finally, the spherical filler is dried with hot air at 80℃ for 8 hours to remove moisture. After cooling, the spherical composite filler is obtained. Example 3

[0046] A method for preparing a polyvinyl alcohol-modified denitrification biological packing material includes the following steps:

[0047] Step 1: Add 80 parts sulfur powder, 11 parts polyvinyl alcohol powder (PVA), and 10 parts calcium carbonate to the reactor and inject deionized water. Stir the mixture and heat the reactor to 85°C at a speed of 120 rpm.

[0048] Step 2: Add 1 part of amylose, 5 parts of powdered activated carbon and 5 parts of auxiliary agent into the reaction vessel in sequence and stir. After mixing thoroughly, a thickened substance is obtained. After heat treatment at 180℃ for 30 minutes, it is melt-granulated. The particle size of the spherical particles is about 3 mm.

[0049] Step 3: Finally, the spherical filler is dried with hot air at 80℃ for 8 hours to remove moisture. After cooling, the spherical composite filler is obtained.

[0050] The above-prepared packing materials were applied in wastewater treatment. The packing materials prepared in Examples 1, 2, and 3 were placed in a 1L small upflow anaerobic reactor with a packing filling rate of 70%. The biofilter reactor formed in Example 1 was designated R1, the biofilter reactor formed in Example 2 was designated R2, and the biofilter reactor formed in Example 3 was designated R3. A continuous flow experiment was conducted under the same conditions to verify their nitrogen removal efficiency.

[0051] The operating parameters, such as the influent nitrate nitrogen concentration, are shown in Table 1. The hydraulic retention time was set to 6 hours, the temperature was room temperature, and the pH was controlled at 8. The specific operating steps of the experiment are as follows:

[0052] (1) Before the denitrification filter is put into operation, the biological filter needs to be treated with biofilm formation. Activated sludge from the anaerobic tank of a sewage treatment plant is inoculated into the three biological filters. Biofilm formation sludge is inoculated once every 5 days. After 3 cycles, water quality indicators (culture medium utilization) are monitored daily. When the water quality indicators are stable for 3 consecutive cycles and the culture medium utilization is good, biofilm formation is considered successful.

[0053] (2) After the biofilm is attached to the biological filter, simulated wastewater is prepared using laboratory tap water. Potassium nitrate (KNO3) is used as the only nitrogen source. The nitrogen load is increased in increments of 100 mg / L. The specific influent water quality at each stage is shown in Table 1. Water samples are taken from the effluent tank once a day and each water quality indicator is tested.

[0054] Table 1. Specific influent water quality at each stage

[0055] stage Days <![CDATA[Influent NO3 - -N (mg / L)]]> <![CDATA[Inlet SO4 2- (mg / L)]]> 1 1-21 100.31±1.69 34.62±3.10 2 22-42 200.06±2.67 34.08±4.17 3 43-63 300.28±3.34 34.69±2.66 4 64-84 400.76±4.41 34.54±3.50 5 85-105 500.76±5.41 34.04±2.60

[0056] Figure 2-4The diagram shows the treatment effect of reactors R1, R2, and R3 on the simulated wastewater. From this, we can see that:

[0057] (1) The packing material with a lower polyvinyl alcohol content (prepared in Example 1) had a slightly worse treatment effect, which was due to the lower concentration of carbon source released in reactor R1;

[0058] (2) Although the nitrogen removal effects of reactors R3 and R2 were similar in the first stage, and even the pH effect of R3 was better, as the influent concentration increased stepwise, the nitrogen removal performance of reactor R3, which had a higher sulfur content, became worse than that of R2, and the pH of the effluent also became lower.

[0059] (3) Overall, reactor R2 performed better, and even under high nitrate load in stage 5, it achieved a nitrate removal rate of nearly 90%, and the system had the best pH stability.

[0060] In summary, the long-term stable treatment capacity of reactor R2 indicates that the presence of elemental sulfur in the packing material ensures the stable operation of the sulfur autotrophic denitrification reaction. The modified PVA and trace amounts of starch can slowly and stably release organic carbon sources, which is beneficial to the long-term denitrification operation of the reactor. Moreover, the treatment effect is very ideal. Therefore, the biological packing material provided by this invention can achieve excellent denitrification effect in the treatment of nitrogen-containing wastewater and has good application value.

[0061] The above are merely preferred embodiments of the present invention, which will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that for those skilled in the art, any modifications and improvements made without departing from the concept of the present invention are protected by the present invention.

Claims

1. A method for preparing polyvinyl alcohol modified coupled denitrification biological filler, characterized in that, The method comprises the following steps: S1: adding 60-80 parts of sulfur powder, 8-15 parts of polyvinyl alcohol powder and 5-10 parts of calcium carbonate into deionized water and stirring, and heating; S2: adding 1-2 parts of straight-chain starch, 2-5 parts of adsorbent and 2-5 parts of auxiliary agent into the mixture obtained in S1 in sequence and stirring, fully mixing and uniformly mixing to obtain thickening material, and then performing heat treatment and melt granulation, wherein the PVA molecular chain is rearranged, swelling and deforming occurs, and the PVA and the auxiliary agent react to dehydrate and etherify; the auxiliary agent is composed of the following components in mass percentage: 10%-20% plasticizer, 10%-20% viscosity stabilizer and 60%-80% etherifying agent; S3: removing water in the spherical filler, and obtaining spherical composite filler after cooling.

2. The preparation method of the polyvinyl alcohol modified coupled denitrification biological packing material according to claim 1, characterized in that, The heating temperature in S1 is 80-95℃.

3. The preparation method of the polyvinyl alcohol modified coupled denitrification biological packing material according to claim 1, characterized in that, The heat treatment temperature in S2 is 160-180℃, and the time is 10-40 min.

4. The method for preparing polyvinyl alcohol-modified coupled denitrification biological filler according to claim 1 or 3, characterized in that, The particle size of the spherical particles prepared after melt granulation in S2 is 1-8 mm.

5. The preparation method of the polyvinyl alcohol modified coupled denitrification biological packing material according to claim 1, characterized in that, The water in the spherical filler is removed by hot air drying in S3, the drying temperature is 80-100℃, and the time is 6-10 h.

6. A polyvinyl alcohol modified coupled denitrification biological packing, characterized in that, The biological filler is prepared by the method in any one of claims 1-5.

7. The polyvinyl alcohol modified coupled denitrification biological packing material according to claim 6, characterized in that, The sulfur powder has a sulfur content of more than 95% and a particle size of 150-250 mesh; the PVA has a polymerization degree of 1700 and an alcoholysis degree of 88%; and the adsorbent is powdered activated carbon with a particle size of 200-400 mesh.

8. Use of the polyvinyl alcohol modified coupled denitrification biological filler according to any one of claims 6-7, characterized in that, The filler is used for denitrification of sewage.

9. Use of polyvinyl alcohol modified coupled denitrification biological packing according to claim 8, characterized in that, The filling rate of the filler is 60%-80%.

Images