CN112552664B - Polylactic acid and lactide blended slow-release material - Google Patents
Polylactic acid and lactide blended slow-release material Download PDFInfo
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Abstract
The invention discloses a polylactic acid and lactide blending slow-release material which is prepared by blending and granulating polylactic acid and lactide in a mass ratio of (4-19): 1. The sustained-release material can ensure good mechanical property of the blend compared with polylactic acid with high molecular weight, and on the other hand, lactide as a raw material for synthesizing the polylactic acid can be used as an easily-used carbon source in the early stage for supplying denitrifying bacteria for utilization, so that the denitrifying bacteria of the system can be developed for a long time and exist stably after the denitrifying bacteria of the polylactic acid can be domesticated. The sustained-release material is obtained by uniformly mixing polylactic acid and lactide, extruding by an extruder, granulating and cooling at room temperature.
Description
Technical Field
The invention belongs to the technical field of wastewater treatment, and particularly relates to a polylactic acid and lactide blending sustained-release material, and a preparation method and application thereof.
Background
Because of serious pollution of surface water and underground water nitrate caused by agricultural non-point source pollution, livestock wastewater discharge, industrial pollution and the like, the eutrophication of water bodies is easily caused by the large amount of nitrate existing in the water bodies, and the large amount of nitrate in drinking water also easily causes great damage to infants (such as 'blue infant syndrome'). Among the many methods for treating nitrate in water, ion exchange, reverse osmosis, electrodialysis, biological denitrification and the like, biological denitrification is a denitrification method suitable for large-scale application due to the characteristics of economy, practicability, permanent denitrification and the like. However, the problem of insufficient carbon source often occurs in the sewage, and the requirement of the denitrification denitrifier on the carbon source cannot be met, so that an additional carbon source is needed to ensure the smooth proceeding of the denitrification process.
At present, the most studied and mature added carbon sources are water-soluble small molecules such as glucose, ethanol, methanol and the like, but due to high cost, high toxicity (such as methanol), difficult determination of adding amount, complex adding process and the like, researchers make many new attempts and researches on the added carbon sources. Early non-traditional carbon sources generally include landfill leachate, sewage plant sludge, crop straw, waste newspapers, and the like. However, these carbon sources can cause new pollution problems, such as heavy metal poisoning, excessive DOC in the early stage, insufficient carbon source in the later stage, and the like.
The slow release material is another feasible scheme as an external carbon source, and researches in recent years mainly focus on artificially synthesized biodegradable high polymer materials such as polylactic acid, polycaprolactone, polyhydroxyfatty acid and the like. The materials slowly release carbon, and release a proper amount of carbon source according to the carbon source requirement of the denitrification environment, so that the COD (chemical oxygen demand) of the effluent is not too high, and the bio-based biodegradable high polymer materials are non-toxic and do not cause secondary pollution. The biodegradable high polymer materials such as polycaprolactone, polyhydroxy fatty acid and the like are expensive and have high cost. Among these artificially synthesized biodegradable polymer materials, polylactic acid is relatively low in price, but it is reported in literature that when the weight average molecular weight thereof is higher than 9000, the carbon release rate becomes very slow, and it is difficult to satisfy the demand for a denitrification carbon source, and when the molecular weight thereof is low, it is difficult to process and mold, and it is difficult to satisfy the actual engineering demand.
To solve this problem, some modification studies for polylactic acid have begun to appear. Chinese invention patent (application publication No. CN107915969, application publication No. H2018.04.17) and Chinese invention patent (application publication No. CN107935202A, application publication No. H2018.04.20) both disclose a method for synthesizing a mixture of starch and biodegradable polymer, and the synthesized mixture can be used as a denitrification carbon source and also achieve better denitrification effect. The cost of the mixed carbon source is reduced compared with the method of simply using polylactic acid as a carbon source, but in the research of the related paper, when the molecular weight of polylactic acid is higher (>80000), the denitrification effect of the mixed carbon source is obviously reduced after the starch in the mixed carbon source is used up by the microorganisms.
Disclosure of Invention
The invention aims to: the invention aims to solve the technical problem of the prior art, and provides a method for preparing a slow-release carbon source by blending high-molecular-weight polylactic acid and lactide, which improves the biodegradability of the slow-release carbon source, ensures the good mechanical property of the slow-release carbon source and has good engineering utilization potential.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a polylactic acid and lactide blended slow-release material is obtained by blending and granulating polylactic acid and lactide in a mass ratio of (4-19): 1, preferably (9-19): 1. The sustained-release material can ensure good mechanical property of the blend compared with polylactic acid with high molecular weight, and on the other hand, lactide as a raw material for synthesizing the polylactic acid can be used as an easily-used carbon source in the early stage for supplying denitrifying bacteria for utilization, so that the denitrifying bacteria of the system can be developed for a long time and exist stably after the denitrifying bacteria of the polylactic acid can be domesticated.
Preferably, the weight average molecular weight of the polylactic acid is 3-11 ten thousand, the molecular weight distribution coefficient range is 1.56-1.92, the weight average molecular weight is 3-8 ten thousand preferably, and the weight average molecular weight is 3-6 ten thousand more preferably; the purity of the lactide is more than 95%.
Further, the invention provides a preparation method of the polylactic acid and lactide blending sustained-release material, which comprises the following steps:
(1) uniformly mixing polylactic acid and lactide to obtain a mixture;
(2) and (3) extruding the mixture obtained in the step (1) by an extruder, granulating, and cooling at room temperature to obtain the product.
In particular to
In the step (1), the polylactic acid and the lactide are stirred and mixed uniformly by a high-speed pulverizer, and the stirring speed is 20000-25000 r/min.
In the step (2), the temperature range of the extrusion of the extruder is controlled to be 150-175 ℃.
In the step (2), the granules obtained by granulation are hemispherical, the diameter is 5-6 mm, and the surface is smooth.
Furthermore, the invention also provides the application of the polylactic acid and lactide blended slow-release material as a denitrification carbon source and a biomembrane carrier in sewage treatment.
In the process of treating low-C/N wastewater by utilizing biological denitrification, a small molecular carbon source is usually required to be added, but the process has many problems such as difficulty in controlling the adding amount of the small molecular carbon source and complex adding process; the cost of artificially synthesizing the polymer slow-release carbon source is high, the later denitrification effect of the mixed carbon source is reduced, and the like. The invention uses the method of mixing the high molecular weight polylactic acid and the lactide to prepare the slow-release carbon source, improves the biodegradability of the slow-release carbon source, ensures the good mechanical property of the slow-release carbon source and has good engineering utilization potential.
Has the advantages that:
the slow release material integrates the good mechanical property of the high molecular weight polylactic acid and the good biodegradability of the lactide, and is a stable carbon source which can be utilized for a long time; lactide is used as an initial main carbon source, and the lactide is used as a raw material for synthesizing polylactic acid, so the domesticated microorganism can be more suitable for a denitrification system using the polylactic acid as a carbon source, the problem that the denitrification system using a mixture of the polylactic acid and common easily degradable materials such as starch or cellulose as the carbon source is insufficient in the release of the carbon source at the later stage is solved, and the long-term stable operation of the system is facilitated; the slow release material solves the problems that the adding amount of the traditional micromolecular carbon source is difficult to control in the denitrification adding process and the adding process is complex.
Drawings
The foregoing and/or other advantages of the invention will become further apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.
FIG. 1 is an appearance diagram of the blended slow-release material prepared in example 1.
FIG. 2 is a photograph of the test apparatus used in example 1.
Detailed Description
The invention will be better understood from the following examples.
In the following examples, polylactic acid and lactide were both available from the prasuk company, where: the molecular weight distribution coefficient of polylactic acid with the weight-average molecular weight of 3 ten thousand is 1.92; the molecular weight distribution coefficient of polylactic acid with the weight-average molecular weight of 6 ten thousand is 1.69; the molecular weight distribution coefficient of polylactic acid with the weight-average molecular weight of 8 ten thousand is 1.73; the molecular weight distribution coefficient of the polylactic acid with the weight-average molecular weight of 11 ten thousand is 1.56; the purity of the lactide is more than 95 percent.
Example 1
(1) Preparing materials:
weighing 20 g of each part, selecting polylactic acid with the weight-average molecular weight of 3 ten thousand and lactide, and mixing the polylactic acid with the lactide according to the mass ratio of 19: 1 proportion, crushing and uniformly stirring in a high-speed crusher, uniformly adding into an extruder heated to 150-175 ℃, extruding hemispherical particles with the diameter of about 5-6 mm, and cooling at room temperature, wherein the extruder is shown in figure 1.
(2) And (3) testing conditions are as follows:
specification of the reactor: 8cm × 50cm (diameter × height);
the blend is used as a carbon source and a biofilm carrier:
the reactor inlet water is prepared by municipal tap water, potassium nitrate and potassium dihydrogen phosphate.
The reaction apparatus is shown in FIG. 2.
The main body of the reaction device is an up-flow packed bed made of resin glass, the interior of the main body is cylindrical (the inner diameter is 80mm, the height is 500mm), the interior of the main body is uniform in water outlet, and the upper part of the main body is provided with an inverted round table shape and a water outlet weir (the bottom of the inverted round table is 60mm, the upper part of the inverted round table is 100mm, and the height is 100 mm). The polylactic acid lactide blend is filled in the device main body, the flow rate is controlled by a peristaltic pump, waste water enters from a water inlet at the lowest part of the device main body and is treated by an internal system of the reaction device, and then the waste water is discharged from a water outlet at the highest part.
(3) The testing process comprises the following steps:
regulating feed water NO3 --NThe concentration was 20mg/L, the reactor Hydraulic Retention Time (HRT) was 4h, and the experimental ambient temperature was 30 ℃.
(4) And (3) testing results:
the water quality ratio before and after the treatment, for example, in Table 1, shows NO3 -The removal rate of-N is as high as 99.9%, and the denitrification effect is good.
TABLE 1 reactor Water quality comparison
Example 2
(1) Preparing materials:
weighing 20 g of each part, selecting polylactic acid with the weight-average molecular weight of 3 ten thousand and lactide, and mixing the polylactic acid with the lactide according to the mass ratio of 19: 1, crushing and uniformly stirring in a high-speed crusher, uniformly adding into an extruder heated to 150-175 ℃ at a constant speed, extruding hemispherical particles with the diameter of about 5-6 mm, and cooling at room temperature.
(2) And (3) testing conditions are as follows:
specification of the reactor: 8cm × 50cm (diameter × height);
the blend is used as a carbon source and a biomembrane carrier:
the reactor inlet water is prepared by municipal tap water, potassium nitrate and potassium dihydrogen phosphate.
(3) The testing process comprises the following steps:
regulating feed water NO3 -the-N concentration is 50mg/L, the reactor hydraulic retention time is 2h, and the experimental environment temperature is 30 ℃.
(4) And (3) testing results:
the water quality ratio before and after the treatment, for example, in Table 2, shows NO3 -The removal rate of-N reaches more than 97.5 percent, and the nitrogen removal effect is good.
TABLE 2 reactor Water quality comparison
Example 3
(1) Preparing materials:
weighing 20 g of each part, selecting polylactic acid with the weight-average molecular weight of 3 ten thousand and lactide, and mixing the polylactic acid with the lactide according to the mass ratio of 19: 1, crushing and uniformly stirring in a high-speed crusher, uniformly adding into an extruder heated to 15-175 ℃ at a constant speed, extruding hemispherical particles with the diameter of about 5-6 mm, and cooling at room temperature.
(2) And (3) testing conditions are as follows:
specification of the reactor: 8cm × 50cm (diameter × height);
the blend is used as a carbon source and a biofilm carrier:
the reactor inlet water is prepared by municipal tap water, potassium nitrate and potassium dihydrogen phosphate.
(3) The testing process comprises the following steps:
regulating feed water NO3 -the-N concentration is 50mg/L, the reactor hydraulic retention time is 1h, and the experimental environment temperature is 30 ℃.
(4) And (3) testing results:
the water quality before and after the treatment, for example, in Table 3, shows NO3 -The removal rate of-N is as high as more than 96%, and the nitrogen removal effect is good.
TABLE 3 reactor Water quality comparison
Example 4
(1) Preparing materials:
weighing 20 g of each part, selecting polylactic acid with the weight-average molecular weight of 3 ten thousand and lactide, and mixing the polylactic acid with the lactide according to the mass ratio of 9: 1, crushing and uniformly stirring in a high-speed crusher, uniformly adding into an extruder heated to 150-175 ℃ at a constant speed, extruding hemispherical particles with the diameter of about 5-6 mm, and cooling at room temperature.
(2) And (3) testing conditions are as follows:
specification of the reactor: 8cm × 50cm (diameter × height);
the blend is used as a carbon source and a biofilm carrier:
the reactor inlet water is prepared by municipal tap water, potassium nitrate and potassium dihydrogen phosphate.
(3) The testing process comprises the following steps:
regulating feed water NO3 -the-N concentration is 50mg/L, the reactor hydraulic retention time is 1h, and the experimental environment temperature is 30 ℃.
(4) And (3) testing results:
water quality ratio before and after treatment Table 4, it is understood that NO3 -The removal rate of-N reaches 92%, and the nitrogen removal effect is better.
TABLE 4 reactor Water quality comparison
Example 5
(1) Preparing materials:
weighing 20 g of each part, selecting polylactic acid with the weight-average molecular weight of 3 ten thousand and lactide, and mixing the polylactic acid with the lactide according to the mass ratio of 9: 1, crushing and uniformly stirring in a high-speed crusher, uniformly adding into an extruder heated to 150-175 ℃ at a constant speed, extruding hemispherical particles with the diameter of about 5-6 mm, and cooling at room temperature.
(2) And (3) testing conditions are as follows:
specification of the reactor: 8cm × 50cm (diameter × height);
the blend is used as a carbon source and a biofilm carrier:
the reactor inlet water is prepared by municipal tap water, potassium nitrate and potassium dihydrogen phosphate.
(3) The testing process comprises the following steps:
regulating feed water NO3 -The N concentration is 50mg/L, the reactor hydraulic retention time is 0.5h, and the experimental environment temperature is 30 ℃.
(4) And (3) testing results:
the water quality before and after the treatment, for example, in Table 5, it can be understood that NO3 -The removal rate of-N is as high as 94%, and the denitrification effect is better.
TABLE 5 reactor Water quality comparison
Examples 6 to 15 were prepared in a similar manner to example 1, and the specific conditions and test results are summarized in Table 6.
TABLE 6 summary of the conditions of the examples
In order to prove the advantages of the polylactic acid and lactide blending material, a comparative experiment is carried out by taking the polylactic acid and lactide as a single denitrification carbon source.
Comparative example 1
(1) Preparing materials:
weighing 20 g of each part, selecting polylactic acid with the weight-average molecular weight of 3 ten thousand, crushing in a high-speed crusher, adding into an extruder heated to 150-175 ℃ at a constant speed, extruding hemispherical particles with the diameter of about 5-6 mm, and cooling at room temperature.
(2) And (3) testing conditions are as follows:
specification of the reactor: 8cm × 50cm (diameter × height);
the blend is used as a carbon source and a biofilm carrier:
the reactor inlet water is prepared by municipal tap water, potassium nitrate and potassium dihydrogen phosphate.
(3) The testing process comprises the following steps:
regulating feed water NO3 -The concentration of N is 20mg/L, the hydraulic retention time of the reactor is 4h, and the experimental environment temperature is 30 ℃.
(4) And (3) testing results:
the water quality before and after the treatment, for example, in Table 7, it was found that NO was contained3 -The removal rate of-N is less than 30 percent, and the denitrification effect is very goodAnd (4) poor.
TABLE 7 reactor Water quality comparison
Note: since the higher the molecular weight of the polylactic acid, the more difficult it is to degrade, the effect has been poor by using the polylactic acid having a weight average molecular weight of 3w as a single denitrification carbon source, and thus no experiment has been conducted to supplement polylactic acids having weight average molecular weights of 8w and 11w as single denitrification carbon sources.
Comparative example 2
(1) Preparing materials:
the lactide was dried to be white needle-like without pulverization, and the weight was kept in accordance with the other examples, and was weighed in 20 g portions.
(2) And (3) testing conditions are as follows:
specification of the reactor: 8cm × 50cm (diameter × height);
the lactide is used as a carbon source:
the reactor inlet water is prepared by municipal tap water, potassium nitrate and potassium dihydrogen phosphate.
(3) And (3) testing process:
regulating feed water NO3 -The concentration of N is 20mg/L, the hydraulic retention time of the reactor is 4h, and the experimental environment temperature is 30 ℃.
(4) And (3) testing results:
the water quality ratio before and after the treatment, for example, in Table 8, shows NO3 -Removal rate of-N<20%, the denitrification effect is very poor. .
TABLE 8 reactor Water quality comparison
Note: when the experiments were carried out using lactide of the same weight as in the other examples, the carbon source supply was sufficient, but the lactide was easily hydrolyzed into lactic acid, the lactic acid rapidly lowered the pH of the system in water to below 5 and even gradually below 4, and the pH condition suitable for denitrification was 6.5-8.5, the low pH environment rapidly deteriorated the whole system environment, and the denitrification process was naturally very limited.
Compared with the comparative example, the polylactic acid and lactide blended slow-release material disclosed by the invention overcomes the problem that a denitrification system using a mixture of polylactic acid and common easily-degradable materials such as starch or cellulose as a carbon source is insufficient in releasing the carbon source in the later stage. The polylactic acid, starch, cellulose and other substances belong to different types, and in the early use process, the microorganisms preferentially use easily degradable materials such as starch, cellulose and the like as a denitrification carbon source, so that the rapidly-propagating dominant flora in the system is starch-philic or cellulose-philic, and the polylactic acid becomes a main provider of the carbon source when the starch or cellulose in the mixed material is consumed in the later period, and the original dominant flora cannot effectively utilize the polylactic acid which is the main body of the mixed material, so that the carbon source which can be effectively utilized by the microorganisms in the later period is not as sufficient as in the early period; in the invention, lactide (composed of two molecules of lactic acid) is a raw material for synthesizing polylactic acid, the lactide and the polylactic acid are mixed, and in the early stage, the lactide is preferentially released and hydrolyzed into lactic acid to be utilized by microorganisms, so that the dominant flora domesticated in the system can effectively utilize the lactic acid, meanwhile, the polylactic acid can be gradually degraded to release some small molecules and finally hydrolyzed into the lactic acid, so that from top to bottom, an effective carbon source in the system is always lactic acid, even if the lactide is consumed completely in the later stage, the polylactic acid can always provide an effective carbon source for the original dominant flora, and the problem of insufficient effective carbon source in the later stage does not exist.
The invention provides a concept and a method for blending polylactic acid and lactide into a sustained-release material, and a method and a way for realizing the technical scheme are many, the above description is only a preferred embodiment of the invention, and it should be noted that, for those skilled in the art, a plurality of improvements and decorations can be made without departing from the principle of the invention, and these improvements and decorations should also be regarded as the protection scope of the invention. All the components not specified in the present embodiment can be realized by the prior art.
Claims (5)
1. The polylactic acid and lactide blending slow-release material is used as a denitrification carbon source and a biomembrane carrier in sewage treatment, and is characterized in that the polylactic acid and lactide blending slow-release material is obtained by blending and granulating polylactic acid and lactide in a mass ratio of (9-19): 1;
the weight average molecular weight of the polylactic acid is 3-11 ten thousand, and the molecular weight distribution coefficient range is 1.56-1.92; the purity of the lactide is more than 95%.
2. The use according to claim 1, wherein the polylactic acid and lactide blended slow-release material is prepared by the following steps:
(1) uniformly mixing polylactic acid and lactide to obtain a mixture;
(2) and (2) extruding the mixture obtained in the step (1) through an extruder, granulating, and cooling at room temperature to obtain the product.
3. The use according to claim 2, wherein in the step (1), the polylactic acid and the lactide are crushed and mixed uniformly by a high-speed crusher, and the stirring speed is 20000 to 25000 r/min.
4. The use according to claim 2, wherein in step (2), the temperature of the extruder extrusion is controlled to be in the range of 150 to 175 ℃.
5. The use according to claim 2, wherein in step (2), the granules obtained by granulation are hemispherical, have a diameter of 5-6 mm and have a smooth surface.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101220175A (en) * | 2008-01-30 | 2008-07-16 | 清华大学 | Modified starch/lactic acid oligomer reactivity blended full biological decomposition plastics and preparation thereof |
| CN101973642A (en) * | 2010-11-16 | 2011-02-16 | 宜兴汇洋环保科技有限公司 | Method for preparing sustained-release carbon material by using low molecular weight polylactic acid |
| CN102249408A (en) * | 2011-06-09 | 2011-11-23 | 清华大学 | Starch-polylactic acid blend and preparation method and application thereof |
| JP2016132732A (en) * | 2015-01-20 | 2016-07-25 | 株式会社リコー | Polylactic acid composition and manufacturing method therefor |
| EP3162833A1 (en) * | 2015-11-01 | 2017-05-03 | Bio Bond IVS | Bio-based and biodegradable resin suitable for production of composite materials |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101220175A (en) * | 2008-01-30 | 2008-07-16 | 清华大学 | Modified starch/lactic acid oligomer reactivity blended full biological decomposition plastics and preparation thereof |
| CN101973642A (en) * | 2010-11-16 | 2011-02-16 | 宜兴汇洋环保科技有限公司 | Method for preparing sustained-release carbon material by using low molecular weight polylactic acid |
| CN102249408A (en) * | 2011-06-09 | 2011-11-23 | 清华大学 | Starch-polylactic acid blend and preparation method and application thereof |
| JP2016132732A (en) * | 2015-01-20 | 2016-07-25 | 株式会社リコー | Polylactic acid composition and manufacturing method therefor |
| EP3162833A1 (en) * | 2015-11-01 | 2017-05-03 | Bio Bond IVS | Bio-based and biodegradable resin suitable for production of composite materials |
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