A long-acting slow-release carbon source for wastewater biological treatment, and its preparation method and application

Abstract

The present invention relates to the technical field of wastewater biological treatment, and in particular to a long-acting slow-release carbon source for wastewater biological treatment, and its preparation method and application. The long-acting slow-release carbon source comprises a composite carbon source core and a slow-release coating coated on the outside of the composite carbon source core; the composite carbon source core comprises a corn cob and starch loaded in the corn cob; the slow-release coating is a composite film composed of polysulfone and polylactic acid, and the polysulfone and polylactic acid form a covalent cross-linked structure through a polyene cross-linking agent under the action of ultraviolet light and a hydrogen abstraction type photoinitiator. The long-acting slow-release carbon source of the present invention can continuously and stably release the carbon source, has a relatively stable carbon release rate, and has a long effective period. When used for wastewater biological treatment, it can maintain a good treatment effect for a long time and reduce the frequency of re-dosing and replacement of the slow-release carbon source.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater biological treatment, and in particular to a long-acting slow-release carbon source for wastewater biological treatment, and a preparation method and application thereof. Background Art

[0002] When using microorganisms to remove wastewater pollutants, additional organic carbon sources are often required to meet the growth, reproduction, and metabolic needs of the microorganisms. However, the dosage of liquid and water-soluble carbon sources is difficult to control. Too much or too little will result in poor wastewater treatment results. Insufficient dosage will result in low efficiency of microbial metabolism to remove pollutants, while excessive dosage will cause some carbon sources to remain unused by the microorganisms, resulting in high COD in the wastewater. Slow-release carbon sources can address these issues to a certain extent, but they still face the problems of unstable carbon release rate and short shelf life.

[0003] The document "Study on the Effect of Slow-Release Carbon Source from Abandoned Crops on Enhanced Denitrification of Wastewater" (Sun Guozheng. Study on the Effect of Slow-Release Carbon Source from Abandoned Crops on Enhanced Denitrification of Wastewater [J]. Water Conservancy Technical Supervision, 2022(10):40-43+52.) uses corn cobs pretreated with alkali heat as a slow-release carbon source. It is easy to obtain, has little secondary pollution, can realize the recycling of waste, and has a stronger carbon release capacity than loofah, and has a better water treatment effect. However, it has the characteristics of faster initial decomposition, slower mid-term decomposition, and slower decomposition in the later stage. There are two cases where the carbon release rate drops sharply on the 5th and 25th days. When the pollutant content in the wastewater to be treated is high, this characteristic of corn cobs can easily cause part of the carbon source released in the early stage to not be used by microorganisms, resulting in a higher COD of the wastewater, and insufficient carbon source released in the later stage, resulting in a decrease in the wastewater treatment effect.

[0004] Patent CN114315293B coats corncobs with a layer of high-molecular-weight polymer (polyether, polysulfone, or polyvinylidene chloride), which can improve the unstable carbon release rate of corncobs. However, as the decomposition rate of the corncobs slows and the carbon source decreases in the later stages, the carbon source release rate still slows significantly, resulting in poor treatment effect on wastewater with high pollutant content. Therefore, to ensure the wastewater treatment effect, the slow-release carbon source in this patent has a short shelf life and requires frequent re-dosing and debugging, which is time-consuming and labor-intensive, resulting in poor long-term efficiency of the wastewater treatment system. In addition, the re-dosing amount is difficult to control, and the wastewater treatment effect is prone to fluctuations after re-dosing. Summary of the Invention

[0005] To address the technical issue of the short shelf life of existing slow-release carbon sources, the present invention provides a long-acting slow-release carbon source for wastewater biological treatment, as well as its preparation method and application. This long-acting slow-release carbon source can continuously and stably release carbon source at a relatively stable carbon release rate and with a long shelf life. When used in wastewater biological treatment, it can maintain good treatment effects over a long period of time and reduce the frequency of re-dosing and replacement of the slow-release carbon source.

[0006] The specific technical solutions of the present invention are:

[0007] In the first aspect, the present invention provides a long-acting slow-release carbon source for biological treatment of wastewater, comprising a composite carbon source core and a slow-release coating coated on the outside of the composite carbon source core; the composite carbon source core comprises a corn cob and starch loaded in the corn cob; the slow-release coating is a composite film composed of polysulfone and polylactic acid, and the polysulfone and polylactic acid form a covalent cross-linked structure through a polyene cross-linker under the action of ultraviolet light and a hydrogen-abstracting photoinitiator.

[0008] In the initial stage of addition of the slow-release carbon source of the present invention, the decomposition and carbon release speeds of the composite carbon source core are relatively fast, but the polylactic acid in the slow-release coating is not degraded, and the polylactic acid has a covalent cross-linked structure with the polysulfone, so the slow-release coating is relatively dense, which is conducive to slowing down the carbon release speed of the slow-release carbon source, thereby avoiding excessive carbon release leading to high COD of wastewater; in the later stage of addition, the decomposition and carbon release speeds of the composite carbon source core slow down, but the polylactic acid in the slow-release coating is gradually degraded under the action of extracellular enzymes secreted by microorganisms, and the pores in the slow-release coating increase, which is conducive to the release of the carbon source, thereby making up for the deficiency of carbon source release in the later stage and extending the effective period of the slow-release carbon source.

[0009] The applicant found in the early stage of the trial that the carbon release rate of the slow-release carbon source can be made more stable by using polysulfone / polylactic acid composite membrane to coat corn cob, and the shelf life of the slow-release carbon source can be extended to a certain extent, but its shelf life is still shorter and can only be maintained for about 2 months. For this reason, the application has loaded starch in corn cob, to increase the carbon source amount in the core body, and at the same time, by adopting a special cross-linked structure (i.e., forming a covalent cross-linked structure by a polyene-based cross-linking agent under the action of ultraviolet light and hydrogen abstraction type photoinitiator) in polysulfone / polylactic acid composite membrane, the following effects can be produced: on the one hand, it is possible to slow down the initial carbon release rate by improving the density of the slow-release coating, and hinder the enzymatic degradation site contact of the microbial extracellular enzyme with the polylactic acid, and then slow down the degradation of polylactic acid; on the other hand, the stability of the covalent connection formed by the polyene-based cross-linking agent under the action of microorganisms is higher, and hydrophilicity is lower, which is more conducive to slowing down the degradation of polylactic acid. By the above-mentioned effects, the shelf life of the slow-release carbon source can be extended.

[0010] In summary, the present invention coats the corn cob / starch composite carbon source with a polysulfone / polylactic acid composite membrane with a special cross-linking structure, which can make the slow-release carbon source more stable in carbon release rate and have a longer effective period when used for wastewater biological treatment (especially biological treatment of wastewater with a high pollutant content), and can reduce the frequency of re-dosing and replacement of the slow-release carbon source.

[0011] Preferably, the polyalkenyl crosslinking agent is a polyalkenyl hydrocarbon compound.

[0012] Furthermore, the polyene-based crosslinking agent is one or more of 1,5-hexadiene, isoprene, 2-methyl-1,4-pentadiene and 2,5-dimethyl-1,5-hexanediamine.

[0013] Preferably, the hydrogen abstraction type photoinitiator includes one or more of benzophenone, 2-hydroxy-2-methylphenylacetone (photoinitiator 1173) and dibenzoyl peroxide (BPO).

[0014] In a second aspect, the present invention provides a method for preparing the long-acting slow-release carbon source, comprising the following steps:

[0015] (1) After fully soaking the corn cob in a starch solution, the product is separated and dried to obtain a composite carbon source;

[0016] (2) mixing polylactic acid, polysulfone, a polyene crosslinking agent, a hydrogen abstraction photoinitiator and a coating solvent to prepare a coating solution;

[0017] (3) After the coating liquid is sprayed onto the surface of the composite carbon source, it is cross-linked under ultraviolet light and dried to obtain a long-lasting slow-release carbon source.

[0018] Preferably, in step (2), the amount of the polyene-based cross-linking agent is 9-15% of the total mass of the polysulfone and the polylactic acid.

[0019] In the sustained-release coating, if the amount of polyene-based cross-linking agent used is too large, the slow-release coating will be denser in the early stage of slow-release carbon source addition, which will cause the carbon source release rate to be slower, and thus the microbial biofilm formation rate to be slower, and the early debugging time to be longer; if the amount of polyene-based cross-linking agent used is too small, the slow-release coating will be less dense, and the degradation rate of polylactic acid will be faster, which will cause the carbon source release rate to be faster and the effective period of the slow-release carbon source to be shorter.

[0020] Preferably, in step (2), the mass ratio of the polysulfone to the polylactic acid is 1:0.1-0.2.

[0021] Preferably, in step (2), the amount of the hydrogen abstraction photoinitiator used is 3 to 8% of the mass of the polyene cross-linking agent.

[0022] Preferably, in step (1), the mass ratio of the corn cob to starch is 1:0.2-0.4.

[0023] Preferably, in step (1), the corn cob is a corn cob that has been pretreated with alkali heat.

[0024] Furthermore, the specific process of the alkaline heat pretreatment includes the following steps: adding corn cob particles into a sodium hydroxide solution, boiling for 20 to 30 minutes, and separating the product.

[0025] In a third aspect, the present invention provides an application of the long-acting slow-release carbon source in a microbial carrier, wherein the microbial carrier comprises a porous substrate and a long-acting slow-release carbon source dispersed in the porous substrate.

[0026] Prior art has reported technologies for loading slow-release carbon sources within porous substrates (e.g., patent CN114315293B). This type of microbial carrier not only provides a place for microorganisms to grow and attach, but also provides a continuous carbon source for the loaded microorganisms, thus having good effects when used for water treatment. By applying the long-acting slow-release carbon source designed in the present invention to the microbial carrier, the long-term shelf life of the long-acting slow-release carbon source can be utilized to extend the replacement cycle of the microbial carrier, reduce the number of times the microbial carrier needs to be re-grown and debugged after replacement, and thus improve the long-term efficiency of the wastewater biological treatment system.

[0027] In a fourth aspect, the present invention provides the use of the long-acting slow-release carbon source or the microbial carrier in biological treatment of wastewater.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) In the long-acting slow-release carbon source of the present invention, by coating the corn cob / starch composite carbon source with a polysulfone / polylactic acid cross-linked composite membrane, the characteristic of polylactic acid being gradually degraded under the action of microbial extracellular enzymes can be utilized to compensate for the insufficient carbon release rate in the later stage and have a longer shelf life;

[0030] (2) In the long-acting slow-release carbon source of the present invention, by loading starch in the corn cob and adopting a special cross-linking structure between the polysulfone and the polylactic acid in the slow-release coating (i.e., a covalent cross-linking structure is formed by a polyene cross-linking agent under the action of ultraviolet light and a hydrogen abstraction photoinitiator), the shelf life of the slow-release carbon source can be further extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The COD removal rate changes over time when the slow-release carbon sources of Examples 1 to 5 are used for wastewater biological treatment;

[0032] Figure 2The COD removal rate changes over time when the slow-release carbon sources of Example 1 and Comparative Examples 1 to 4 are used for wastewater biological treatment;

[0033] Figure 3 The changes in ammonia nitrogen removal rate over time when the slow-release carbon sources of Examples 1 to 5 are used for wastewater biological treatment;

[0034] Figure 4 The figure shows the change of ammonia nitrogen removal rate over time when the slow-release carbon sources of Example 1 and Comparative Examples 1 to 4 are used for wastewater biological treatment. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to the embodiments.

[0036] Overall embodiment

[0037] A long-acting slow-release carbon source for wastewater biological treatment comprises a composite carbon source core and a slow-release coating coated on the composite carbon source core; the composite carbon source core comprises a corn cob and starch loaded in the corn cob; the slow-release coating is a composite film composed of polysulfone and polylactic acid, wherein the polysulfone and polylactic acid form a covalent cross-linked structure through a polyene cross-linking agent under the action of ultraviolet light and a hydrogen abstraction photoinitiator.

[0038] As a specific embodiment, the polyalkenyl crosslinking agent is a polyalkenyl hydrocarbon compound, such as one or more of 1,5-hexadiene, isoprene, 2-methyl-1,4-pentadiene and 2,5-dimethyl-1,5-hexanediamine.

[0039] As a specific embodiment, the hydrogen abstraction type photoinitiator includes one or more of benzophenone, 2-hydroxy-2-methylphenylacetone (photoinitiator 1173) and dibenzoyl peroxide (BPO).

[0040] A method for preparing the long-acting slow-release carbon source comprises the following steps:

[0041] (1) After fully soaking the corn cob in a starch solution, the product is separated and dried to obtain a composite carbon source;

[0042] (2) mixing polylactic acid, polysulfone, a polyene crosslinking agent, a hydrogen abstraction photoinitiator and a coating solvent to prepare a coating solution;

[0043] (3) After the coating liquid is sprayed onto the surface of the composite carbon source, it is cross-linked under ultraviolet light and dried to obtain a long-lasting slow-release carbon source.

[0044] As a specific embodiment, in step (1), the corn cob is a corn cob that has been pretreated with alkali heat, and the specific process of the alkali heat pretreatment includes the following steps: adding corn cob particles to sodium hydroxide solution, boiling for 20 to 30 minutes, and separating the product.

[0045] As a specific embodiment, in step (1), the mass ratio of the corn cob to starch is 1:0.2-0.4.

[0046] As a specific embodiment, in step (2), the amount of the polyene-based crosslinker is 9-15% of the total mass of polysulfone and polylactic acid, the mass ratio of polysulfone to polylactic acid is 1:0.1-0.2, and the amount of the hydrogen abstraction type photoinitiator is 3-8% of the mass of the polyene-based crosslinker.

[0047] The application of the long-acting slow-release carbon source in a microbial carrier comprises a porous substrate and a long-acting slow-release carbon source dispersed in the porous substrate.

[0048] Application of the long-acting slow-release carbon source or the microbial carrier in biological treatment of wastewater.

[0049] Example 1

[0050] A slow-release carbon source is prepared by the following steps:

[0051] (1) Corncob pretreatment:

[0052] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0053] (2) Preparation of composite carbon source:

[0054] Starch was added to water and heated to dissolve to prepare a starch solution with a concentration of 5 wt%, to which 20% of the mass of the starch solution was added alkali-heat pretreated corn cobs, stirred for 12 hours, filtered, and dried to obtain a composite carbon source.

[0055] (3) Preparation of coating solution:

[0056] Polysulfone and polylactic acid are added to tetrahydrofuran and fully dissolved, and then 1,5-hexadiene and benzophenone are added thereto and stirred to prepare a coating solution, wherein the contents of polysulfone, polylactic acid, 1,5-hexadiene and benzophenone are 10.0wt%, 1.5wt%, 1.4wt% and 0.07wt% respectively.

[0057] (4) Encapsulation:

[0058] The composite carbon source was placed in a coating machine. The coating solution was preheated to 55°C and evenly sprayed onto the surface of the composite carbon source. The solution was then irradiated with 365nm ultraviolet light for 15 minutes and dried to obtain a slow-release carbon source. Measurements showed that the slow-release carbon source gained 7.9% more weight after coating than before.

[0059] Example 2

[0060] A slow-release carbon source is prepared by the following steps:

[0061] (1) Corncob pretreatment:

[0062] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0063] (2) Preparation of composite carbon source:

[0064] Starch was added to water and heated to dissolve to prepare a starch solution with a concentration of 5 wt%, to which 25% of the mass of the starch solution was added alkali-heat pretreated corn cobs, stirred for 10 hours, filtered, and dried to obtain a composite carbon source.

[0065] (3) Preparation of coating solution:

[0066] Polysulfone and polylactic acid are added to tetrahydrofuran and fully dissolved, and then 1,5-hexadiene and benzophenone are added thereto and stirred to prepare a coating solution, wherein the contents of polysulfone, polylactic acid, 1,5-hexadiene and benzophenone are 10.0wt%, 1.0wt%, 1.6wt% and 0.05wt% respectively.

[0067] (4) Encapsulation:

[0068] The composite carbon source was placed in a coating machine. The coating solution was preheated to 55°C and evenly sprayed onto the surface of the composite carbon source. The solution was then irradiated with 365nm ultraviolet light for 10 minutes and dried to obtain a slow-release carbon source. Measurements showed that the slow-release carbon source gained 7.0% more weight after coating compared to the pre-coated composite carbon source.

[0069] Example 3

[0070] A slow-release carbon source is prepared by the following steps:

[0071] (1) Corncob pretreatment:

[0072] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0073] (2) Preparation of composite carbon source:

[0074] Starch was added to water and heated to dissolve to prepare a starch solution with a concentration of 5 wt%, to which 12.5% ​​of the mass of the starch solution was added alkali-heat pretreated corn cobs, stirred for 6 hours, filtered, and dried to obtain a composite carbon source.

[0075] (3) Preparation of coating solution:

[0076] Polysulfone and polylactic acid are added to tetrahydrofuran and fully dissolved, and then 1,5-hexadiene and benzophenone are added thereto and stirred to prepare a coating solution, wherein the contents of polysulfone, polylactic acid, 1,5-hexadiene and benzophenone are 10.0 wt%, 2.0 wt%, 1.1 wt% and 0.08 wt% respectively.

[0077] (4) Encapsulation:

[0078] The composite carbon source was placed in a coating machine. The coating solution was preheated to 55°C and evenly sprayed onto the surface of the composite carbon source. The solution was then irradiated with 365nm ultraviolet light for 15 minutes and dried to obtain a slow-release carbon source. Measurements showed that the slow-release carbon source gained 8.3% more weight after coating than before.

[0079] Example 4

[0080] A slow-release carbon source is prepared by the following steps:

[0081] (1) Corncob pretreatment:

[0082] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0083] (2) Preparation of composite carbon source:

[0084] Starch was added to water and heated to dissolve to prepare a starch solution with a concentration of 5 wt%, to which 12.5% ​​of the mass of the starch solution was added alkali-heat pretreated corn cobs, stirred for 6 hours, filtered, and dried to obtain a composite carbon source.

[0085] (3) Preparation of coating solution:

[0086] Polysulfone and polylactic acid are added to tetrahydrofuran and fully dissolved, and then 1,5-hexadiene and benzophenone are added thereto and stirred to prepare a coating solution, wherein the contents of polysulfone, polylactic acid, 1,5-hexadiene and benzophenone are 10.0 wt%, 2.0 wt%, 0.5 wt% and 0.036 wt% respectively.

[0087] (4) Encapsulation:

[0088] The composite carbon source was placed in a coating machine. The coating solution was preheated to 55°C and evenly sprayed onto the surface of the composite carbon source. The solution was then irradiated with 365nm ultraviolet light for 15 minutes and dried to obtain a slow-release carbon source. Measurements showed that the slow-release carbon source gained 8.0% more weight after coating compared to the pre-coated composite carbon source.

[0089] Example 5

[0090] A slow-release carbon source is prepared by the following steps:

[0091] (1) Corncob pretreatment:

[0092] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0093] (2) Preparation of composite carbon source:

[0094] Starch was added to water and heated to dissolve to prepare a starch solution with a concentration of 5 wt%, to which 25% of the mass of the starch solution was added alkali-heat pretreated corn cobs, stirred for 10 hours, filtered, and dried to obtain a composite carbon source.

[0095] (3) Preparation of coating solution:

[0096] Polysulfone and polylactic acid are added to tetrahydrofuran and fully dissolved, and then 1,5-hexadiene and benzophenone are added thereto and stirred to prepare a coating solution, wherein the contents of polysulfone, polylactic acid, 1,5-hexadiene and benzophenone are 10.0 wt%, 1.0 wt%, 3.2 wt% and 0.1 wt% respectively.

[0097] (4) Encapsulation:

[0098] The composite carbon source was placed in a coating machine. The coating solution was preheated to 55°C and evenly sprayed onto the surface of the composite carbon source. The solution was then irradiated with 365nm ultraviolet light for 10 minutes and dried to obtain a slow-release carbon source. Measurements showed that the slow-release carbon source gained 7.4% weight after coating compared to the pre-coated composite carbon source.

[0099] Comparative Example 1

[0100] A slow-release carbon source is prepared by the following steps:

[0101] (1) Corncob pretreatment:

[0102] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0103] (2) Preparation of coating solution:

[0104] Polysulfone and polylactic acid are added to tetrahydrofuran and fully dissolved, and then 1,5-hexadiene and benzophenone are added thereto and stirred to prepare a coating solution, wherein the contents of polysulfone, polylactic acid, 1,5-hexadiene and benzophenone are 10.0wt%, 1.5wt%, 1.4wt% and 0.07wt% respectively.

[0105] (4) Encapsulation:

[0106] The composite carbon source was placed in a coating machine. After preheating the coating solution to 55°C, it was evenly sprayed onto the surface of alkali-heat-pretreated corncobs. The corncobs were then irradiated with 365nm ultraviolet light for 15 minutes and dried to produce a slow-release carbon source. Measurements showed that the slow-release carbon source increased in weight by 7.3% compared to the alkali-heat-pretreated corncobs before coating.

[0107] Comparative Example 2

[0108] A slow-release carbon source is prepared by the following steps:

[0109] (1) Corncob pretreatment:

[0110] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0111] (2) Preparation of composite carbon source:

[0112] Starch was added to water and heated to dissolve to prepare a starch solution with a concentration of 5 wt%, to which 20% of the mass of the starch solution was added alkali-heat pretreated corn cobs, stirred for 12 hours, filtered, and dried to obtain a composite carbon source.

[0113] (3) Preparation of coating solution:

[0114] Polysulfone was added to tetrahydrofuran and fully dissolved, and then 1,5-hexadiene and benzophenone were added thereto and stirred to prepare a coating solution, wherein the contents of polysulfone, 1,5-hexadiene and benzophenone were 10.0 wt%, 1.4 wt% and 0.07 wt% respectively.

[0115] (4) Encapsulation:

[0116] The composite carbon source was placed in a coating machine. The coating solution was preheated to 55°C and evenly sprayed onto the surface of the composite carbon source. The solution was then irradiated with 365nm ultraviolet light for 15 minutes and dried to obtain a slow-release carbon source. Measurements showed that the slow-release carbon source gained 7.5% more weight after coating than before.

[0117] Comparative Example 3

[0118] A slow-release carbon source is prepared by the following steps:

[0119] (1) Corncob pretreatment:

[0120] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0121] (2) Preparation of composite carbon source:

[0122] Starch was added to water and heated to dissolve to prepare a starch solution with a concentration of 5 wt%, to which 20% of the mass of the starch solution was added alkali-heat pretreated corn cobs, stirred for 12 hours, filtered, and dried to obtain a composite carbon source.

[0123] (3) Preparation of coating solution:

[0124] Polysulfone and polylactic acid are added into tetrahydrofuran and fully dissolved to prepare a coating solution, wherein the contents of polysulfone and polylactic acid are 10.0 wt % and 1.5 wt % respectively.

[0125] (4) Encapsulation:

[0126] The composite carbon source was placed in a coating machine, and the coating liquid was preheated to 55°C before being evenly sprayed onto the surface of the composite carbon source and dried to obtain a slow-release carbon source. Measurements showed that the slow-release carbon source after coating increased in weight by 8.0% compared to the composite carbon source before coating.

[0127] Comparative Example 4

[0128] A slow-release carbon source is prepared by the following steps:

[0129] (1) Corncob pretreatment:

[0130] The corn cob was washed and cut into particles with a diameter of 3 to 5 mm. After drying, the particles were added into a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boiled for 30 minutes, filtered after cooling, rinsed with water until neutral, and dried to obtain an alkali-heat pretreated corn cob.

[0131] (2) Preparation of composite carbon source:

[0132] Starch was added to water and heated to dissolve to prepare a starch solution with a concentration of 5 wt%, to which 20% of the mass of the starch solution was added alkali-heat pretreated corn cobs, stirred for 12 hours, filtered, and dried to obtain a composite carbon source.

[0133] (3) Preparation of carboxyl-modified polylactic acid:

[0134] Polylactic acid was dissolved in tetrahydrofuran to prepare a 1.7 wt% polylactic acid solution. After replacing the air in the reaction vessel with nitrogen, aconitic acid and BPO were added to the polylactic acid solution at 7% and 3.5% by weight, respectively, based on the weight of the polylactic acid. The mixture was stirred thoroughly and heated to 75°C and stirred at this temperature for 1 hour. Ethanol was added to the reaction mixture for precipitation, which was then filtered, washed with ethanol, and dried to obtain polycarboxyl-modified polylactic acid.

[0135] (4) Preparation of coating solution:

[0136] Polysulfone and carboxyl-modified polylactic acid are added into tetrahydrofuran and fully dissolved to prepare a coating solution, wherein the contents of polysulfone and carboxyl-modified polylactic acid are 10.0 wt % and 1.5 wt % respectively.

[0137] (5) Encapsulation:

[0138] The composite carbon source was placed in a coating machine. The coating solution was preheated to 55°C and evenly sprayed onto the surface of the composite carbon source. The solution was then irradiated with 365nm ultraviolet light for 15 minutes and dried to obtain a slow-release carbon source. Measurements showed that the slow-release carbon source gained 7.9% more weight after coating than before.

[0139] Application Examples

[0140] The slow-release carbon sources prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were used to carry out biological treatment of wastewater. The specific method is as follows: about 0.5 kg of activated sludge was added to a pool with a volume of 3 L, and then about 0.03 kg of slow-release carbon source was added, and then the wastewater to be treated (pharmaceutical wastewater pretreated from a sewage treatment plant, with an ammonia nitrogen concentration of 285 to 300 mg / L and a COD of 3350 to 3380 mg / L) was introduced therein. Three cycles were run every day, and each cycle included the process of water inlet → aeration → sedimentation → effluent, with a hydraulic retention time of 5 hours. The ammonia nitrogen concentration and COD in the effluent were monitored, and the ammonia nitrogen and COD removal rates were calculated. The results are shown in Tables 1 to 2 and Figures 1 to 4.

[0141] Table 1 Changes in COD removal rate over time (unit: %)

[0142]

[0143]

[0144] Table 2 Changes in ammonia nitrogen removal rate over time (unit: %)

[0145] 5d 10d 30d 50d 80d 100d 110d 115d 120d Example 1 94.2 95.6 92.2 96.4 95.3 94.3 93.7 95.5 94.2 Example 2 90.7 94.3 95.2 93.1 94.0 91.0 90.8 90.1 89.8 Example 3 93.6 94.9 91.8 93.2 90.3 92.4 90.8 92.6 91.7 Example 4 93.8 95.4 94.8 90.7 90.6 93.7 85.2 81.9 76.0 Example 5 78.0 86.2 90.5 89.4 93.3 91.8 88.3 89.6 89.0 Comparative Example 1 92.9 91.5 89.8 89.5 84.4 74.5 67.0 62.8 58.4 Comparative Example 2 93.0 93.6 93.9 90.7 90.9 90.9 84.7 81.3 80.0 Comparative Example 3 95.6 95.2 93.6 96.6 94.9 83.4 76.2 71.6 69.4 Comparative Example 4 93.1 94.2 93.5 92.7 93.6 92.2 89.5 86.2 84.3

[0146] Data analysis and conclusions:

[0147] (1) From Tables 1 to 2, Figure 1 and Figure 3 From the above, it can be seen that the slow-release carbon sources of Examples 1 to 3 can maintain relatively stable COD and ammonia nitrogen removal rates within 4 months, indicating that the slow-release carbon source of the present invention has a relatively stable carbon release rate and a long effective period.

[0148] (2) In Example 1, corn cob / starch composite carbon source was used as the core, while the corn cob of Comparative Example 1 was not loaded with starch. Figure 2 and Figure 4 From the results, we can see that the COD and ammonia nitrogen removal rates of Comparative Example 1 are lower, and from around the 70th day, the COD and ammonia nitrogen removal rates decrease, while those of Example 1 can still maintain a relatively stable level. The reason is that the amount of carbon source in the core of Comparative Example 1 is lower, and the carbon release rate is slower, resulting in poor wastewater treatment effect. Especially in the later stage, the carbon release rate drops significantly, resulting in poor wastewater treatment effect.

[0149] (3) In Example 1, polysulfone / polylactic acid composite membrane was used as sustained-release coating, while in Comparative Example 2, polysulfone was used. Figure 2 and Figure 4 From the above, we can see that the COD and ammonia nitrogen removal rates of Comparative Example 2 decreased from around day 105, while those of Example 1 were still able to maintain a relatively stable level. This is because after the addition of the slow-release carbon source, the polylactic acid is gradually degraded by microorganisms over time, and the pores in the slow-release coating increase, which is conducive to the release of the carbon source. This can compensate for the insufficient release of the carbon source in the later stage, allowing the wastewater treatment effect to be maintained in the later stage and extending the effective period of the slow-release carbon source.

[0150] (4) In Example 1, there is a covalent cross-linked structure in the sustained-release coating, but in Comparative Example 3, there is no covalent cross-linked structure. Figure 2 and Figure 4From the results of the experiments, we can see that the COD removal rate of Comparative Example 3 within 10 days was significantly lower. Starting from around the 95th day, the COD and ammonia nitrogen removal rates decreased, while Example 1 was able to maintain relatively stable COD and ammonia nitrogen removal rates within 4 months. This is because the covalent cross-linking between polysulfone and polylactic acid can improve the density of the slow-release coating, reduce the carbon release rate in the initial stage of slow-release carbon source addition, and prevent excessive carbon release from causing high COD in the wastewater. In addition, it can also slow down the degradation of polylactic acid, thereby extending the shelf life of the slow-release carbon source.

[0151] (5) In Example 1, the polysulfone and polylactic acid in the sustained-release coating are covalently cross-linked by a polyolefin hydrocarbon compound (1,5-hexadiene), while in Comparative Example 4, the cross-linking is by hydrogen bonding. Figure 2 and Figure 4 From the results of the experiment, the COD and ammonia nitrogen removal rates of Comparative Example 4 decreased from around day 105, while those of Example 1 were able to maintain a relatively stable level. This is because, compared with crosslinking via hydrogen bonds, covalent crosslinking via polyalkenyl hydrocarbon compounds is more stable under the action of microorganisms and has lower hydrophilicity, which is more conducive to slowing the degradation of polylactic acid, thereby extending the shelf life of the slow-release carbon source.

[0152] (6) Compared with Example 3, the amount of cross-linking agent (1,5-hexadiene) used in Example 4 was reduced; compared with Example 2, the amount of cross-linking agent (1,5-hexadiene) used in Example 5 was increased. Figure 1 and Figure 3 From the above, it can be seen that the COD and ammonia nitrogen removal rates of Example 4 decreased from around 110 days, while those of Example 3 were still able to maintain a relatively stable level. Compared with Example 2, the COD and ammonia nitrogen removal rates of Example 5 within 10 days were lower. The reason is that if the amount of cross-linking agent used in the slow-release coating is too large, the slow-release coating will be denser in the early stage of slow-release carbon source addition, resulting in a slower release rate of the carbon source, and thus a slower microbial biofilm formation rate, and a longer early debugging time. If the amount of cross-linking agent used is too small, the slow-release coating will be less dense, and the degradation rate of polylactic acid will be faster, which will result in a faster release rate of the carbon source and a shorter shelf life of the slow-release carbon source.

[0153] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0154] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A long-acting slow-release carbon source for wastewater biological treatment, characterized in that: The invention comprises a composite carbon source core and a sustained-release coating wrapped around the composite carbon source core; the composite carbon source core comprises a corn cob and starch loaded in the corn cob; the sustained-release coating is a composite film composed of polysulfone and polylactic acid, wherein the polysulfone and polylactic acid form a covalent cross-linked structure through a polyene cross-linking agent under the action of ultraviolet light and a hydrogen abstraction photoinitiator.

2. The long-acting slow-release carbon source according to claim 1, characterized in that The polyalkenyl crosslinking agent is a polyalkenyl hydrocarbon compound.

3. A method for preparing a long-acting slow-release carbon source as claimed in claim 1 or 2, characterized in that: The following steps are involved: (1) After fully soaking the corn cob in a starch solution, the product is separated and dried to obtain a composite carbon source; (2) mixing polylactic acid, polysulfone, polyene crosslinking agent, hydrogen abstraction photoinitiator and coating solvent to prepare coating solution; (3) After the coating liquid is sprayed onto the surface of the composite carbon source, it is cross-linked under ultraviolet light and dried to obtain a long-lasting slow-release carbon source.

4. The preparation method according to claim 3, wherein In step (2), the amount of the polyene-based cross-linking agent used is 9-15% of the total mass of the polysulfone and the polylactic acid.

5. The preparation method according to claim 3, wherein In step (2), the mass ratio of the polysulfone to the polylactic acid is 1:0.1-0.

2.

6. The preparation method according to claim 3 or 4, characterized in that In step (2), the amount of the hydrogen abstraction photoinitiator used is 3-8% of the mass of the polyene cross-linking agent.

7. The preparation method according to claim 3, wherein In step (1), the mass ratio of the corn cob to the starch is 1:0.2-0.

4.

8. The preparation method according to claim 3 or 7, wherein In step (1), the corn cob is a corn cob that has been pretreated with alkali heat.

9. The use of the long-acting slow-release carbon source in a microbial carrier according to claim 1 or 2, characterized in that: The microbial carrier comprises a porous substrate and a long-acting slow-release carbon source dispersed in the porous substrate.

10. Use of the long-acting slow-release carbon source according to claim 1 or 2 or the microbial carrier according to claim 9 in biological treatment of wastewater.

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