A slow-release carbon source for treating tail water by microorganisms, a microbial carrier and a preparation method thereof

Abstract

The present invention relates to the technical field of tail water treatment, and in particular to a slow-release carbon source for microbial treatment of tail water, a microbial carrier and a preparation method thereof. The slow-release carbon source includes corncobs and a polysulfone / polycarboxylic acid-modified polylactic acid composite membrane wrapped around the corncobs. The microbial carrier includes the slow-release carbon source and a porous substrate, and the slow-release carbon source is dispersed in the porous substrate. In the slow-release carbon source of the present invention, the corncobs are wrapped with a polysulfone / polycarboxylic acid-modified polylactic acid composite membrane, which can accelerate the release of the carbon source in the later stage, better control the stability of the carbon source release rate, and thus avoid excessive release of the carbon source resulting in a high COD of the tail water, and too little release of the carbon source resulting in poor treatment effect of the tail water. When the slow-release carbon source is used in the microbial carrier, the replacement cycle of the microbial carrier can be extended.

Description

Technical Field

[0001] The present invention relates to the technical field of tail water treatment, and particularly relates to a slow-release carbon source for treating tail water by microorganisms, a microbial carrier and a preparation method thereof. Background Art

[0002] In industrial enterprise production, fishery and livestock farming, and residents' daily life, a large amount of tail water is generated, which has a high chemical oxygen demand (COD), as well as a large amount of pollutants such as nitrogen and phosphorus, and is likely to cause serious environmental pollution. It needs to be harmlessly treated before discharge. Compared with physical and chemical methods, using microorganisms to remove pollutants in tail water has the advantages of low treatment cost and little secondary pollution, and thus is favored by researchers at home and abroad.

[0003] In the process of using microbial metabolism to remove pollutants in tail water, a large amount of organic carbon source is required, but the problem of insufficient carbon source generally exists in tail water. Therefore, an external carbon source needs to be used to promote the growth and metabolism of beneficial microorganisms. The dosage of liquid carbon sources such as methanol and ethanol, and water-soluble carbon sources such as acetic acid and glucose is difficult to control, and it is easy to cause the problem that the COD of tail water increases due to excessive dosing, and the problem that the treatment effect of tail water is poor due to insufficient dosing. The use of slow-release carbon sources can solve the above problems. Corncobs contain a large amount of cellulose and can decompose and release sugar substances. It is a commonly used natural slow-release carbon source, which has the advantages of low price and no biological toxicity. However, the decomposition of corncobs has the characteristics of being fast in the initial stage, moderate in the middle stage, and slow in the later stage, which is likely to cause too high a carbon source release amount in the early stage and insufficient release amount in the later stage.

[0004] Patent CN114315293B discloses a denitrifying and phosphorus-removing non-fired ceramsite and its preparation method and application. The non-fired ceramsite includes rare earth-modified fly ash, modified corncobs, pore-forming agents and cement-based binders. Among them, the modified corncobs include corncob particles and a polymer layer coated on the outer part of the corncob particles. The material of the polymer layer is at least one of polyether, polysulfone or polyvinylidene chloride. By wrapping polyether, polysulfone or polyvinylidene chloride outside the corncobs, this patent can make the release rate of the carbon source more stable to a certain extent. However, in the later stage of wastewater treatment, as the decomposition rate of corncobs slows down and the carbon source decreases, there will still be a phenomenon that the carbon source release rate slows down significantly, which will cause the tail water treatment effect to decline and is not conducive to the treatment of tail water containing high-concentration ammonia nitrogen. If the microbial carrier is replaced, re-film hanging and debugging are required. Therefore, frequent replacement of the microbial carrier will result in low efficiency of the tail water treatment system. Summary of the Invention

[0005] In order to solve the technical problem that the carbon release rate of the existing slow-release carbon source is significantly slowed down in the later stage, the present invention provides a slow-release carbon source for microbial treatment of tail water, a microbial carrier and a preparation method thereof. This slow-release carbon source can accelerate the carbon release rate in the later stage, better control the stability of the carbon release rate, and can extend the replacement cycle of the microbial carrier when used in the microbial carrier.

[0006] The specific technical solution of the present invention is as follows:

[0007] In the first aspect, the present invention provides a slow-release carbon source for microbial treatment of tail water, including corncobs and a polysulfone / polycarboxylic acid-modified polylactic acid composite film wrapped outside the corncobs.

[0008] By adding polycarboxylic acid-modified polylactic acid (i.e., polylactic acid grafted with multiple carboxyl groups on the molecular chain) to the polysulfone film outside the corncob in the present invention, the characteristics of the gradual degradation of polylactic acid under the action of microorganisms and the hydroxyl groups carried on the modified polylactic acid can be utilized to cooperate with polysulfone to make the carbon release rate of the slow-release carbon source more stable. Specifically:

[0009] In the initial stage, the polylactic acid is not degraded, and the carboxyl groups carried after its modification can form hydrogen bonds with polysulfone, so that the composite film structure is relatively dense, which is conducive to slowing down the release of the carbon source; as time goes by, under the action of extracellular enzymes released by microorganisms, the polylactic acid gradually degrades and breaks the chain, and the formed oligomers, dimers and monomers are finally decomposed by microorganisms into CO2 and H2O. During this process, the crosslinking degree of the composite film gradually decreases and the pores increase, which is conducive to the release of the carbon source. Therefore, it can make up for the deficiency of carbon source release in the later stage, maintain a relatively high carbon release rate in the later stage, and thus maintain a good tail water treatment effect.

[0010] Through the above method, when the slow-release carbon source of the present invention is used for tail water treatment (especially for tail water treatment containing high-concentration ammonia nitrogen), it can better control the carbon release rate at a stable level, avoid excessive carbon source release and high COD in the tail water caused by the carbon source not being utilized by microorganisms, and can provide a continuous and controllable carbon source for beneficial microorganisms to improve the tail water treatment effect; moreover, since a relatively high carbon release rate can still be maintained in the later stage, when the slow-release carbon source of the present invention is loaded into a microbial carrier that can provide a place for the growth and attachment of microorganisms, the carbon source can be fully utilized, the replacement cycle of the microbial carrier can be extended, and the working efficiency of the tail water treatment system can be improved.

[0011] Preferably, the mass ratio of the corncob to the polysulfone / polycarboxylic acid-modified polylactic acid composite film is 1:0.09 - 0.13.

[0012] Preferably, the preparation method of the polycarboxylic acid-modified polylactic acid includes the following steps: under the action of a radical initiator, graft aconitic acid onto polylactic acid to prepare polycarboxylic acid-modified polylactic acid.

[0013] Aconitic acid contains three carboxyl groups and one alkenyl group. Under the action of a free radical initiator, the hydrogen on the poly(lactic acid) molecular chain is abstracted to form a free radical, and then aconitic acid is grafted onto the poly(lactic acid) molecular chain through its alkenyl group. By using the carboxyl groups on aconitic acid, hydrogen bonds can be formed between the multi-carboxyl modified poly(lactic acid) and polysulfone, making the composite film coated on the initial corn cob have a relatively dense structure, thus being able to slow down the initial carbon release rate and enabling more carbon sources to accumulate in the later stage to accelerate the later carbon release rate.

[0014] Preferably, the preparation method of the multi-carboxyl modified poly(lactic acid) specifically includes the following steps: dissolving poly(lactic acid) in a reaction solvent, adding aconitic acid and a free radical initiator thereto under the protection of an inert gas, fully mixing, carrying out a grafting reaction, and then separating the product to obtain the multi-carboxyl modified poly(lactic acid).

[0015] Further, the free radical initiator is benzoyl peroxide; the mass ratio of poly(lactic acid) to the initiator is 1:0.02 - 0.04; the temperature of the grafting reaction is 65 - 75 °C, and the time is 1 - 1.5 h.

[0016] Further, the mass ratio of poly(lactic acid) to aconitic acid is 1:0.06 - 0.08.

[0017] Further, the mass-volume ratio of poly(lactic acid) to the reaction solvent is 1 g:50 - 60 mL.

[0018] In a second aspect, the present invention provides a method for preparing the slow-release carbon source, including the following steps: mixing polysulfone, multi-carboxyl modified poly(lactic acid) and a coating solvent to form a coating solution, spraying it onto the surface of corn cob particles, and drying to obtain the slow-release carbon source.

[0019] Preferably, the mass ratio of polysulfone to multi-carboxyl modified poly(lactic acid) is 1:0.10 - 0.15.

[0020] In the composite film outside the corn cob, when the content of the multi-carboxyl modified poly(lactic acid) is too low, there will be fewer pores in the later composite film, which can maintain a high tail water treatment effect; while when the content of the multi-carboxyl modified poly(lactic acid) is too high, the carbon release rate in the middle stage will be too fast, and the released carbon source cannot be decomposed and utilized by the microorganisms attached to the microbial carrier, resulting in a high COD in the tail water. Based on this, the present invention controls the mass ratio of polysulfone to multi-carboxyl modified poly(lactic acid) in the coating solution to 1:0.10 - 0.15, which can better control the carbon release rate, avoid a high COD in the middle-stage tail water, and maintain a good tail water treatment effect in the later stage.

[0021] Preferably, the particle size of the corn cob particles is 0.5 - 0.8 mm.

[0022] Preferably, before spraying the coating liquid onto the surface of the corncob particles, the corncob particles are pretreated. The specific process includes the following steps: adding the corncob particles to a sodium hydroxide solution, boiling for 20 - 30 minutes, and separating the product.

[0023] In a third aspect, the present invention provides a microbial carrier for the slow-release carbon source, comprising a slow-release carbon source and a porous substrate; the slow-release carbon source is dispersed in the porous substrate.

[0024] In the above microbial carrier, the porous substrate can provide a place for the growth and attachment of microorganisms, and the slow-release carbon source can release the carbon source, promoting the growth and metabolism of microorganisms in the porous substrate, thereby promoting biofilm formation and tail water treatment.

[0025] Preferably, the microbial carrier comprises the following components by weight: 3 - 8 parts of cement, 3.5 - 6 parts of slow-release carbon source, 10 - 15 parts of fly ash, 0.3 - 0.5 parts of gypsum, 0.3 - 0.5 parts of lime, and 0.8 - 1.6 parts of hydrogen peroxide.

[0026] In a fourth aspect, the present invention provides a method for preparing the microbial carrier, comprising the following steps: mixing all raw materials with water, granulating, and then foaming and curing to obtain the microbial carrier.

[0027] Preferably, the method specifically includes the following steps: stirring cement, slow-release carbon source, fly ash, gypsum, lime and water evenly, adding an aqueous hydrogen peroxide solution thereto, stirring evenly, making particles with a diameter of 5 - 10 mm, standing and foaming at 40 - 60 °C for 6 - 10 h, and then curing in an environment with a temperature of 20 - 25 °C and a relative humidity of not less than 95% for 1 - 5 days to obtain the microbial carrier.

[0028] In a fifth aspect, the present invention provides the application of the slow-release carbon source or the microbial carrier in microbial treatment of tail water.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) In the slow-release carbon source of the present invention, using a polysulfone / polycarboxyl-modified polylactic acid composite film to wrap the corncob can accelerate the release of the carbon source in the later stage, better control the stable carbon source release rate, thereby avoiding excessive carbon source release resulting in a high COD in the tail water, and too little carbon source release resulting in poor tail water treatment effect;

[0031] (2) In the slow-release carbon source of the present invention, by controlling the ratio of polysulfone to polycarboxyl-modified polylactic acid, the stable carbon source release rate can be better controlled, avoiding too fast a carbon source release rate in the middle stage and too slow a carbon source release rate in the later stage. Description of the Drawings

[0032] Figure 1 Variation of ammonia nitrogen removal rate with time when treating tail water with the microbial carriers of Examples 1, 3 to 5;

[0033] Figure 2 Variation of ammonia nitrogen removal rate with time when treating tail water with the microbial carriers of Example 2 and Comparative Examples 1 to 3;

[0034] Figure 3 Variation of COD removal rate with time when treating tail water with the microbial carriers of Examples 1, 3 to 5;

[0035] Figure 4 Variation of COD removal rate with time when treating tail water with the microbial carriers of Example 2 and Comparative Examples 1 to 3. Detailed implementation manners

[0036] The present invention will be further described below in conjunction with examples.

[0037] General example

[0038] A slow-release carbon source for treating tail water with microorganisms, comprising corncobs and a polysulfone / polycarboxyl-modified polylactic acid composite membrane wrapped outside the corncobs.

[0039] As a specific implementation manner, the mass ratio of the corncobs to the polysulfone / polycarboxyl-modified polylactic acid composite membrane is 1:0.09 to 0.13.

[0040] As a specific implementation manner, the preparation method of the polycarboxyl-modified polylactic acid specifically includes the following steps: dissolving polylactic acid into a reaction solvent, adding aconitic acid and a radical initiator thereto under the protection of an inert gas, fully mixing, performing a grafting reaction, and then separating the product to obtain polycarboxyl-modified polylactic acid.

[0041] Optionally, the radical initiator is benzoyl peroxide (BPO); the mass ratio of the polylactic acid, aconitic acid and the initiator is 1:0.06 to 0.08:0.02 to 0.04; the mass-volume ratio of the polylactic acid to the reaction solvent is 1 g:50 to 60 mL; the temperature of the grafting reaction is 65 to 75 °C, and the time is 1 to 1.5 h.

[0042] A method for preparing the above slow-release carbon source, comprising the following steps: mixing polysulfone, polycarboxyl-modified polylactic acid and a coating solvent to form a coating solution, wherein the mass ratio of the polysulfone to the polycarboxyl-modified polylactic acid is 1:0.10 to 0.15, spraying it onto the surface of corncob particles with a particle size of 0.5 to 0.8 mm, and drying to obtain the slow-release carbon source.

[0043] As a specific embodiment, before spraying the coating liquid onto the surface of the corncob particles, the corncob particles are pretreated. The specific process includes the following steps: adding the corncob particles into a sodium hydroxide solution, boiling for 20 - 30 min, and separating the product.

[0044] A microbial carrier includes the above-mentioned slow-release carbon source and a porous substrate; the slow-release carbon source is dispersed in the porous substrate.

[0045] As a specific embodiment, the microbial carrier, by weight, includes the following components: 3 - 8 parts of cement, 3.5 - 6 parts of slow-release carbon source, 10 - 15 parts of fly ash, 0.3 - 0.5 parts of gypsum, 0.3 - 0.5 parts of lime, and 0.8 - 1.6 parts of hydrogen peroxide.

[0046] A method for preparing the above-mentioned microbial carrier includes the following steps: mixing all raw materials with water, granulating, and then foaming and curing to obtain the microbial carrier.

[0047] As a specific embodiment, the method specifically includes the following steps: uniformly stirring cement, slow-release carbon source, fly ash, gypsum, lime, and water, adding an aqueous hydrogen peroxide solution thereto, stirring evenly, making particles with a diameter of 5 - 10 mm, standing and foaming at 40 - 60 °C for 6 - 10 h, and then curing for 1 - 5 days in an environment with a temperature of 20 - 25 °C and a relative humidity of not less than 95% to obtain the microbial carrier.

[0048] The application of the above-mentioned slow-release carbon source or the above-mentioned microbial carrier in the microbial treatment of tail water.

[0049] Example 1

[0050] Prepare a slow-release carbon source and make it into a microbial carrier. The steps are as follows:

[0051] (1) Pretreatment of corncob:

[0052] After washing the corncob, drying and crushing it, sieving to obtain particles with a particle size of 0.5 - 0.8 mm, adding it to a 2.0 wt% NaOH solution according to a solid-liquid mass ratio of 1:30, boiling for 30 min, filtering after cooling, rinsing with water until neutral, and drying to obtain pretreated corncob particles.

[0053] (2) Modification with polylactic acid:

[0054] Dissolve polylactic acid in tetrahydrofuran to prepare a 1.9 wt% polylactic acid solution. After replacing the air in the reaction vessel with nitrogen, add aconitic acid and BPO with masses of 6% and 3% of polylactic acid respectively to the polylactic acid solution, stir well, heat to 70 °C, and stir at this temperature for 1.5 h. Add ethanol to the reaction mixture for precipitation, filter, wash with ethanol, and dry to obtain multi-carboxyl modified polylactic acid.

[0055] (3) Coating the surface of corn cob:

[0056] Mix polysulfone, multi-carboxyl modified polylactic acid and N,N-dimethylformamide (DMF) to prepare a coating solution, where the contents of polysulfone and multi-carboxyl modified polylactic acid are 7.0 wt% and 0.7 wt% respectively. Place the pretreated corn cob particles in a coating machine, preheat the coating solution to 55 °C, and then evenly spray it onto the surface of the corn cob particles, dry to obtain a slow-release carbon source. After measurement, the weight of the coated corn cob increased by 10.9%.

[0057] (4) Preparation of microbial carrier:

[0058] Weigh the following raw materials by weight: 3 parts of cement, 3.5 parts of slow-release carbon source, 12 parts of fly ash, 0.3 part of gypsum, 0.3 part of lime, 2.9 parts of 27.5 wt% H2O2 solution, and 0.5 part of water. After stirring the cement, slow-release carbon source, fly ash, gypsum, lime and water evenly, add the H2O2 solution under stirring, stir well, and use a disc granulator to make spherical particles with a diameter of 6 ± 1 mm. Let the spherical particles stand and foam at 40 °C for 10 h, then place them in a curing box at a temperature of 25 °C and a relative humidity of 96% for 1 day, and dry naturally to obtain the microbial carrier.

[0059] Example 2

[0060] Prepare a slow-release carbon source and make it into a microbial carrier, and the steps are as follows:

[0061] (1) Pretreatment of corn cob:

[0062] Wash the corn cob, dry and crush it, sieve it to obtain particles with a particle size of 0.5 - 0.8 mm, add it to a 2.0 wt% NaOH solution according to a solid-liquid mass ratio of 1:30, boil for 30 min, cool and filter, wash with water until neutral, and dry to obtain pretreated corn cob particles.

[0063] (2) Modification of polylactic acid:

[0064] Dissolve polylactic acid in tetrahydrofuran to prepare a 1.7 wt% polylactic acid solution. After displacing the air in the reaction vessel with nitrogen, add aconitic acid and BPO with masses of 7% and 3.5% of the polylactic acid respectively to the polylactic acid solution. After stirring evenly, heat to 75 °C and stir at this temperature for 1 h. Add ethanol to the reaction mixture for precipitation, filter, wash with ethanol, and then dry to obtain polycarboxyl-modified polylactic acid.

[0065] (3) Coating the surface of corncobs:

[0066] Mix polysulfone, polycarboxyl-modified polylactic acid and DMF to prepare a coating solution, where the contents of polysulfone and polycarboxyl-modified polylactic acid are 6.2 wt% and 0.7 wt% respectively. Place the pretreated corncob particles in a coating machine. After preheating the coating solution to 55 °C, evenly spray it onto the surface of the corncob particles, and then dry to obtain a slow-release carbon source. After measurement, the weight of the coated corncobs increased by 12.5%.

[0067] (4) Preparation of microbial carriers:

[0068] Weigh the following raw materials by weight: 5 parts of cement, 4 parts of slow-release carbon source, 10 parts of fly ash, 0.4 part of gypsum, 0.4 part of lime, 3.5 parts of 27.5 wt% H2O2 solution, and 0.5 part of water. After stirring the cement, slow-release carbon source, fly ash, gypsum, lime and water evenly, add the H2O2 solution under stirring, and then stir evenly. Use a disc granulator to make spherical particles with a diameter of 6 ± 1 mm. Let the spherical particles stand and foam at 50 °C for 8 h, then place them in a curing box at a temperature of 25 °C and a relative humidity of 96% for 1 day, and then dry naturally to obtain microbial carriers.

[0069] Example 3

[0070] Prepare a slow-release carbon source and make it into a microbial carrier. The steps are as follows:

[0071] (1) Pretreatment of corncobs:

[0072] Wash the corncobs, dry and crush them, and then screen them to obtain particles with a particle size of 0.5 - 0.8 mm. Add them to a 2.5 wt% NaOH solution according to a solid-liquid mass ratio of 1:30, boil for 20 min, cool and then filter, wash with water until neutral, and dry to obtain pretreated corncob particles.

[0073] (2) Modification of polylactic acid:

[0074] Dissolve polylactic acid in tetrahydrofuran to prepare a 1.9 wt% polylactic acid solution. After displacing the air in the reaction vessel with nitrogen, add aconitic acid and BPO with masses of 8% and 4% of the polylactic acid respectively to the polylactic acid solution. After stirring evenly, heat to 65 °C and stir at this temperature for 1 h. Add ethanol to the reaction mixture for precipitation, filter, wash with ethanol, and then dry to obtain polycarboxyl-modified polylactic acid.

[0075] (3) Coating on the surface of corncob:

[0076] Mix polysulfone, polycarboxyl-modified polylactic acid and DMF to prepare a coating solution, where the contents of polysulfone and polycarboxyl-modified polylactic acid are 6.2 wt% and 0.9 wt% respectively. Place the pretreated corncob particles in a coating machine. After preheating the coating solution to 55 °C, evenly spray it on the surface of the corncob particles, and then dry to obtain a slow-release carbon source. After measurement, the weight of the coated corncob increases by 9.3%.

[0077] (4) Preparation of microbial carrier:

[0078] Weigh the following raw materials by weight: 8 parts of cement, 6 parts of slow-release carbon source, 15 parts of fly ash, 0.5 part of gypsum, 0.5 part of lime, 5.5 parts of 27.5 wt% H2O2 solution, and 0.8 part of water. After stirring the cement, slow-release carbon source, fly ash, gypsum, lime and water evenly, add the H2O2 solution under stirring, and then stir evenly. Use a disc granulator to make spherical particles with a diameter of 6 ± 1 mm. Let the spherical particles stand and foam at 60 °C for 6 h, then place them in a curing box at a temperature of 25 °C and a relative humidity of 96% for curing for 1 day, and then dry naturally to obtain the microbial carrier.

[0079] Example 4

[0080] Prepare a slow-release carbon source and make it into a microbial carrier, and the steps are as follows:

[0081] (1) Pretreatment of corncob:

[0082] Wash the corncob, dry and crush it, and then screen it to obtain particles with a particle size of 0.5 - 0.8 mm. Add it to a 2.0 wt% NaOH solution according to a solid-liquid mass ratio of 1:30, boil for 30 min, cool and then filter, wash with water until neutral, and dry to obtain pretreated corncob particles.

[0083] (2) Modification of polylactic acid:

[0084] Dissolve polylactic acid in tetrahydrofuran to prepare a 1.9 wt% polylactic acid solution. After displacing the air in the reaction vessel with nitrogen, add aconitic acid and BPO with masses of 6% and 3% of the polylactic acid respectively to the polylactic acid solution, stir well, heat to 70 °C, and stir at this temperature for 1.5 h. Add ethanol to the reaction mixture for precipitation, filter, wash with ethanol, and dry to obtain multi-carboxyl modified polylactic acid.

[0085] (3) Coating on the surface of corn cob:

[0086] Mix polysulfone, multi-carboxyl modified polylactic acid and DMF to prepare a coating solution, where the contents of polysulfone and multi-carboxyl modified polylactic acid are 7.0 wt% and 0.3 wt% respectively. Place the pretreated corn cob particles in a coating machine, preheat the coating solution to 55 °C, and then evenly spray it on the surface of the corn cob particles, and dry to obtain a slow-release carbon source. After measurement, the weight of the coated corn cob increased by 10.8%.

[0087] (4) Preparation of microbial carrier:

[0088] Weigh the following raw materials by weight: 3 parts of cement, 2 parts of slow-release carbon source, 12 parts of fly ash, 0.3 part of gypsum, 0.3 part of lime, 2.9 parts of 27.5 wt% H2O2 solution, and 0.5 part of water. After stirring the cement, slow-release carbon source, fly ash, gypsum, lime and water evenly, add the H2O2 solution under stirring, stir well, and use a disc granulator to make spherical particles with a diameter of 6 ± 1 mm. Let the spherical particles stand and foam at 40 °C for 10 h, then place them in a curing box at a temperature of 25 °C and a relative humidity of 96% for 1 day, and dry naturally to obtain a microbial carrier.

[0089] Example 5

[0090] Prepare a slow-release carbon source and make it into a microbial carrier, and the steps are as follows:

[0091] (1) Pretreatment of corn cob:

[0092] Wash the corn cob, dry and crush it, and sieve it to obtain particles with a particle size of 0.5 - 0.8 mm. Add it to a 2.5 wt% NaOH solution according to a solid-liquid mass ratio of 1:30, boil for 20 min, cool and filter, wash with water until neutral, and dry to obtain pretreated corn cob particles.

[0093] (2) Modification of polylactic acid:

[0094] Dissolve polylactic acid in tetrahydrofuran to prepare a 1.9 wt% polylactic acid solution. After replacing the air in the reaction vessel with nitrogen, add aconitic acid and BPO with masses of 8% and 4% of the polylactic acid respectively to the polylactic acid solution, stir well, heat to 65 °C, and stir at this temperature for 1 h. Add ethanol to the reaction mixture for precipitation, filter, wash with ethanol, and dry to obtain multi-carboxyl modified polylactic acid.

[0095] (3) Coating the surface of corn cob:

[0096] Mix polysulfone, multi-carboxyl modified polylactic acid and DMF to prepare a coating solution, where the contents of polysulfone and multi-carboxyl modified polylactic acid are 6.2 wt% and 1.5 wt% respectively. Place the pretreated corn cob particles in a coating machine, preheat the coating solution to 55 °C, and then evenly spray it on the surface of the corn cob particles, dry to obtain a slow-release carbon source. After measurement, the weight of the coated corn cob increased by 9.6%.

[0097] (4) Preparation of microbial carrier:

[0098] Weigh the following raw materials by weight: 8 parts of cement, 6 parts of slow-release carbon source, 15 parts of fly ash, 0.5 part of gypsum, 0.5 part of lime, 5.5 parts of 27.5 wt% H2O2 solution, and 0.8 part of water. After stirring the cement, slow-release carbon source, fly ash, gypsum, lime and water evenly, add the H2O2 solution under stirring, stir well, and use a disc granulator to make spherical particles with a diameter of 6 ± 1 mm. Let the spherical particles stand and foam at 60 °C for 6 h, then place them in a curing box at a temperature of 25 °C and a relative humidity of 96% for 1 day, and dry naturally to obtain a microbial carrier.

[0099] Comparative Example 1

[0100] Prepare a slow-release carbon source and make it into a microbial carrier, and the steps are as follows:

[0101] (1) Pretreatment of corn cob:

[0102] Wash the corn cob, dry and crush it, sieve it to obtain particles with a particle size of 0.5 - 0.8 mm, add it to a 2.0 wt% NaOH solution according to a solid-liquid mass ratio of 1:30, boil for 30 min, cool and filter, wash with water until neutral, and dry to obtain pretreated corn cob particles.

[0103] (2) Coating the surface of corn cob:

[0104] Mix polysulfone and DMF to prepare a coating solution, where the content of polysulfone is 6.2 wt%. Place the pretreated corn cob particles in a coating machine, preheat the coating solution to 55 °C, and then evenly spray it on the surface of the corn cob particles, dry to obtain a slow-release carbon source. After measurement, the weight of the coated corn cob increased by 12.5%.

[0105] (3) Preparation of microbial carriers:

[0106] Weigh the following raw materials by weight parts: 5 parts of cement, 4 parts of slow-release carbon source, 10 parts of fly ash, 0.4 part of gypsum, 0.4 part of lime, 3.5 parts of 27.5wt% H2O2 solution, and 0.5 part of water. After mixing cement, slow-release carbon source, fly ash, gypsum, lime and water evenly, add the H2O2 solution under stirring. After mixing evenly, use a disc granulator to make spherical particles with a diameter of 6±1mm. Let the spherical particles stand and foam at 50°C for 8h, then place them in a curing box at a temperature of 25°C and a relative humidity of 96% for 1 day, and dry naturally to obtain microbial carriers.

[0107] Comparative Example 2

[0108] Prepare a slow-release carbon source and make it into a microbial carrier. The steps are as follows:

[0109] (1) Pretreatment of corncobs:

[0110] After washing the corncobs, dry and crush them, and sieve them to obtain particles with a particle size of 0.5-0.8mm. Add them to 2.0wt% NaOH solution according to the solid-liquid mass ratio of 1:30, boil for 30min, cool and filter, wash with water until neutral, and dry to obtain pretreated corncob particles.

[0111] (2) Coating on the surface of corncobs:

[0112] Mix polysulfone, polylactic acid and DMF to make a coating solution, where the contents of polysulfone and polylactic acid are 6.2wt% and 0.7wt% respectively. Place the pretreated corncob particles in a coating machine. After preheating the coating solution to 55°C, spray it evenly on the surface of the corncob particles and dry to obtain a slow-release carbon source. After measurement, the weight of the corncobs after coating increased by 12.5%.

[0113] (3) Preparation of microbial carriers:

[0114] Weigh the following raw materials by weight parts: 5 parts of cement, 4 parts of slow-release carbon source, 10 parts of fly ash, 0.4 part of gypsum, 0.4 part of lime, 3.5 parts of 27.5wt% H2O2 solution, and 0.5 part of water. After mixing cement, slow-release carbon source, fly ash, gypsum, lime and water evenly, add the H2O2 solution under stirring. After mixing evenly, use a disc granulator to make spherical particles with a diameter of 6±1mm. Let the spherical particles stand and foam at 50°C for 8h, then place them in a curing box at a temperature of 25°C and a relative humidity of 96% for 1 day, and dry naturally to obtain microbial carriers.

[0115] Comparative Example 3

[0116] Prepare a slow-release carbon source and make it into a microbial carrier. The steps are as follows:

[0117] (1) Pretreatment of corncob:

[0118] Wash the corncob, dry it, crush it, and sieve it to obtain particles with a particle size of 0.5 - 0.8 mm. Add the particles to a 2.0 wt% NaOH solution at a solid-liquid mass ratio of 1:30, boil for 30 min, cool, filter, wash with water until neutral, and dry to obtain pretreated corncob particles.

[0119] (2) Coating on the surface of corncob:

[0120] Mix polysulfone, starch, and N,N-dimethylacetamide, heat and dissolve to make a coating solution, where the contents of polysulfone and starch are 6.2 wt% and 0.7 wt% respectively. Place the pretreated corncob particles in a coating machine, preheat the coating solution to 55 °C, and evenly spray it onto the surface of the corncob particles, then dry to obtain a slow-release carbon source. After measurement, the weight of the corncob after coating increases by 12.8%.

[0121] (3) Preparation of microbial carrier:

[0122] Weigh the following raw materials by weight: 5 parts of cement, 4 parts of slow-release carbon source, 10 parts of fly ash, 0.4 part of gypsum, 0.4 part of lime, 3.5 parts of 27.5 wt% H2O2 solution, and 0.5 part of water. Stir the cement, slow-release carbon source, fly ash, gypsum, lime, and water evenly, then add the H2O2 solution under stirring, stir evenly, and use a disc granulator to make spherical particles with a diameter of 6 ± 1 mm. Let the spherical particles stand and foam at 50 °C for 8 h, then place them in a curing box at a temperature of 25 °C and a relative humidity of 96% for 1 day, and dry naturally to obtain the microbial carrier.

[0123] Application example

[0124] Use the microbial carriers prepared in Examples 1 - 5 and Comparative Examples 1 - 3 respectively for treating tail water. The specific method is as follows: Lay about 1 kg of microbial carrier at the bottom of a 3 L pool, add about 0.5 kg of activated sludge, and then introduce the tail water to be treated (taken from the pretreated landfill leachate of a sewage treatment plant, with an ammonia nitrogen concentration of 184 mg / L and a COD of 1030 mg / L). Operate for 3 cycles per day, and each cycle includes the processes of influent → aeration → sedimentation → effluent, with a hydraulic retention time of 4 h. Detect the ammonia nitrogen concentration and COD in the effluent every day, and calculate the removal rates of ammonia nitrogen and COD. The results are shown in Figures 1 to 4 .

[0125] Data analysis and conclusion:

[0126] (1) From Figures 1 to 4It can be seen that by using the microbial carriers of Examples 1 to 3, a relatively high COD and ammonia nitrogen removal rate can be achieved, and the COD and ammonia nitrogen removal rates are relatively stable within 10 to 60 days. This shows that by using the microbial carrier of the present invention, the carbon source release rate can be controlled at a relatively stable level, and the effluent COD will not be high due to excessive carbon source release that cannot be utilized by the microorganisms attached to the carrier, nor will the ammonia nitrogen removal effect be poor due to too little carbon source release.

[0127] (2) In Comparative Example 1, the corn cob was wrapped with a polysulfone membrane, while in Example 2, it was a polysulfone / polycarboxyl-modified polylactic acid composite membrane; on the basis of Example 1, Example 4 reduced the content of polycarboxyl-modified polylactic acid in the composite membrane. From Figure 1 and Figure 2 it can be seen that at 50 - 60 days, the ammonia nitrogen removal rate of Example 2 was significantly higher than that of Comparative Example 1, and the ammonia nitrogen removal rate of Example 1 was higher than that of Example 4. This shows that by adding polycarboxyl-modified polylactic acid to the polysulfone membrane outside the corn cob, the ammonia nitrogen removal rate in the later stage of using the microbial carrier can be improved, and when the addition amount of polycarboxyl-modified polylactic acid is small, the improvement effect on the ammonia nitrogen removal rate in the later stage is relatively poor. The reason is that as time goes by, polylactic acid is gradually degraded by microorganisms, the compactness of the composite membrane gradually decreases, and the pores increase, which is beneficial to the release of carbon source. Therefore, it can make up for the lack of carbon source release in the later stage, maintain a relatively high carbon source release rate in the later stage, and thus maintain a good tail water treatment effect.

[0128] (3) On the basis of Example 3, Example 5 increased the content of polycarboxyl-modified polylactic acid in the composite membrane. From Figure 3 it can be seen that at 35 - 50 days, the COD removal rate of Example 5 was significantly lower than that of Example 3. The reason is that when the content of polycarboxyl-modified polylactic acid in the composite membrane is too high, with the degradation of polylactic acid, there are too many pores in the composite membrane in the middle stage, resulting in too fast carbon source release rate, which cannot be fully utilized by the microorganisms in the carrier and causes a higher effluent COD.

[0129] (4) In Comparative Example 2, the used polylactic acid was not grafted with carboxyl, and the other steps were the same as those in Example 2. From Figure 2 and Figure 4 it can be seen that compared with Example 2, the COD removal rate of Comparative Example 2 was lower at 5 - 10 d, and the ammonia nitrogen removal rate decreased at 55 - 60 days. The reason is that by using the carboxyl groups on the molecular chain of the modified polylactic acid, hydrogen bonds can be formed with polysulfone, so that the composite membrane wrapped outside the corn cob in the initial stage has a relatively compact structure, thus slowing down the initial carbon source release rate and enabling more carbon sources to accumulate in the later stage to accelerate the carbon source release rate in the later stage.

[0130] (5) In Comparative Example 3, the polycarboxyl-modified polylactic acid in Example 2 was replaced with starch. From Figure 2 andFigure 4 It can be seen that, compared with Example 2, the COD removal rate of Comparative Example 3 is lower at 5 to 15 days, and the ammonia nitrogen removal rate is lower at 55 to 60 days. The reason is that: compared with polylactic acid, the degradation rate of starch under the action of microorganisms is too fast, and it is easy to release more carbon sources due to the degradation of starch in the early stage. And due to the relatively high porosity in the composite membrane, the carbon source in the corncob is released faster. These excessively released carbon sources will cause a higher COD in the effluent. In the later stage, the decomposition of the corncob is slower and the remaining unreleased carbon source is less, which will cause insufficient carbon source release in the later stage and affect the treatment effect of the tail water.

[0131] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0132] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes and equivalent transformations made to the above embodiments according to the technical essence of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a slow-release carbon source for treating tail water by microorganisms, characterized in that the steps include: S1: Under the action of a free radical initiator, aconitic acid is grafted onto polylactic acid to prepare polycarboxyl-modified polylactic acid; S2: preparing polycarboxyl-modified polylactic acid into a slow-release carbon source for microbial treatment of tail water, wherein the slow-release carbon source comprises corn cobs and a polysulfone / polycarboxyl-modified polylactic acid composite membrane wrapped around the corn cobs.

2. The method according to claim 1, wherein The specific process of step S1 includes: dissolving polylactic acid into a reaction solvent, adding aconitic acid and a free radical initiator thereto under the protection of an inert gas, mixing them thoroughly, performing a grafting reaction, and then separating the product to obtain polycarboxyl-modified polylactic acid.

3. The method according to claim 1, characterized in that The specific process of step S2 includes: mixing polysulfone, polycarboxyl-modified polylactic acid and a coating solvent to prepare a coating liquid, spraying the coating liquid onto the surface of corn cob particles, and drying the mixture to obtain a slow-release carbon source.

4. The method according to claim 3, wherein The mass ratio of the polysulfone to the polycarboxyl-modified polylactic acid is 1:0.10-0.

15.

5. The method according to claim 3, characterized in that, Before spraying the coating liquid onto the surface of the corn cob particles, the corn cob particles are pretreated. The specific process includes the following steps: adding the corn cob particles into a sodium hydroxide solution, boiling for 20 to 30 minutes, and separating the product.

6. A slow-release carbon source for microbial treatment of tail water obtained by the method as claimed in any one of claims 1 to 5.

7. A microbial carrier containing the sustained-release carbon source as described in claim 6, characterized in that, The invention comprises a slow-release carbon source and a porous substrate; the slow-release carbon source is dispersed in the porous substrate.

8. The microbial carrier according to claim 7, wherein, The composition comprises the following components by weight: 3-8 parts of cement, 3.5-6 parts of slow-release carbon source, 10-15 parts of fly ash, 0.3-0.5 parts of gypsum, 0.3-0.5 parts of lime and 0.8-1.6 parts of hydrogen peroxide.

9. A method for preparing the microbial carrier as claimed in claim 8, characterized in that, The method comprises the following steps: mixing all raw materials with water, granulating, and then foaming and curing to obtain a microbial carrier.

10. Use of the slow-release carbon source as claimed in claim 6 or the microbial carrier as claimed in claim 7 or 8 in microbial treatment of tail water.

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