Riboflavin-loaded slow-release carbon source carrier as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of environmental protection engineering, and discloses a riboflavin-loaded slow-release carbon source carrier which comprises the following components in percentage by volume: 30-32% of corncob, 30-32% of poly (hydroxybutyrate-hydroxyvalerate), 5g / L of riboflavin and the balance of polyvinyl alcohol-sodium alginate serving as a crosslinking system, and the total volume of the components is 100%. The surface of the carrier is rough and compact and has obvious lamellar and cluster structures, and particles of different sizes are attached to the carrier. Irregular holes are formed in the surface of the carrier, so that the slow-release carbon source carrier has a higher specific surface area, and attachment and biofilm formation of microorganisms and release of a carbon source are facilitated. PHBV with a smooth surface is wrapped in the lining. Chemical bonds between cellulose are broken through alkali heat pretreatment, and the surface of the corncob is of a rough porous structure after the corncob is modified. The longitudinal section of the carrier presents a large number of closely connected wrinkle and pore structures, which is beneficial to reproduction and growth of microorganisms.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental engineering, relates to wastewater treatment technology, and in particular to a riboflavin-loaded slow-release carbon source carrier, a preparation method and an application thereof. Background Art

[0002] In the process of biological heterotrophic denitrification, carbon source is indispensable as electron donor. When treating low carbon-nitrogen ratio sewage such as slightly polluted surface water, seawater recycling aquaculture wastewater, and secondary effluent from urban sewage treatment plants, it is necessary to add external carbon source to improve denitrification efficiency. Solid phase slow-release carbon source uses water-insoluble solid matter as the attachment carrier of microorganisms, which is biodegraded under the action of microbial enzymes, providing carbon source for denitrification, increasing the abundance of microorganisms, and thus effectively improving denitrification efficiency.

[0003] Redox mediators (RMs) can accelerate the transfer of electrons between electron donors and electron acceptors by cyclically converting their own oxidized and reduced states. At present, the research on electron mediators in the denitrification process mainly focuses on exogenous RMs, especially humus and quinones, most of which are artificially synthesized compounds, which have potential environmental risks. Redox mediators used to improve the efficiency of denitrification usually have the following problems: ① biological toxicity, difficult to control the dosage; ② high cost; ③ easy to be degraded in the reaction or lost with the effluent. At present, traditional carbon sources based on small molecular organic matter and carbohydrates are still the most widely used denitrification carbon sources in urban sewage treatment plants, but the carbon-nitrogen ratio of such fast-acting carbon sources is difficult to control and can easily cause secondary pollution. So far, the solid slow-release carbon source materials for denitrification disclosed in scientific and patent literature usually have the following problems: ① the carbon release time is not long enough and the effect is unstable; ② complex structure and high cost; ③ poor performance in improving denitrification.

[0004] Therefore, one or several new related methods or technologies are urgently needed. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a riboflavin-loaded slow-release carbon source carrier, a preparation method and an application thereof.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A riboflavin-loaded slow-release carbon source carrier comprises the following components by volume percentage: 30-32% corn cob, 30-32% polyhydroxybutyrate-valeric acid copolyester, 5g / L riboflavin, and the remainder is a cross-linking system of polyvinyl alcohol-sodium alginate, and the total volume of each component is 100%.

[0008] Furthermore, the preparation steps of the cross-linking system polyvinyl alcohol-sodium alginate are:

[0009] a. Polyvinyl alcohol and sodium alginate were mixed in a mass ratio of 8:1 and diluted with deionized water. The final mass concentration of polyvinyl alcohol in the mixture was 80 g / L and the final mass concentration of sodium alginate was 10 g / L.

[0010] b. Heat the mixture in a water bath at 95°C for 2h;

[0011] c. Let cool to room temperature.

[0012] Further, the corncob is a modified corncob;

[0013] Alternatively, the polyhydroxybutyrate-valeric acid copolyester is pretreated polyhydroxybutyrate-valeric acid copolyester.

[0014] Furthermore, the modification method of the modified corncob comprises the following steps:

[0015] a. Crush the corn cobs using a crusher and sieve the particles to a size of 1 to 2 mm;

[0016] b. Alkaline heat pretreatment: soak the sieved corn cobs in a 2% sodium hydroxide solution at a volume ratio of 1:2 and heat and boil for 20 minutes;

[0017] c. Wash the corn cobs after alkali heat pretreatment with deionized water until they are colorless and have a neutral pH;

[0018] d. Place the washed corn cob in an oven and bake at 80°C for 4 h to obtain a modified corn cob.

[0019] Furthermore, the pretreatment method of the polyhydroxybutyrate-valeric acid copolyester comprises the following steps:

[0020] a. PHBV is crushed using a crusher to obtain a particle size of 1 to 2 mm;

[0021] b. The sieved polyhydroxybutyrate-valeric acid copolyester was dried at 50° C. for 4 h to obtain the pretreated polyhydroxybutyrate-valeric acid copolyester.

[0022] A method for preparing the riboflavin-loaded sustained-release carbon source carrier as described above comprises the following steps:

[0023] S1: Mix the modified corn cob, the pretreated polyhydroxybutyrate-valeric acid copolyester, riboflavin, and polyvinyl alcohol-sodium alginate, and stir the mixture for 10-20 minutes to obtain a slow-release carbon source mixture;

[0024] S2: Put the slow-release carbon source mixture into a mold and freeze it at -20°C for 12 hours to set;

[0025] S3: After shaping, place in 4% CaCl2-saturated H3BO3 solution and cross-link at 4°C for 24h;

[0026] The preparation steps of the 4% CaCl2-saturated H3BO3 solution are as follows: at 25°C, dissolve 4g H3BO3 in 100mL deionized water, stir well, or heat and stir well, cool naturally and take the upper layer, add 4g CaCl2, stir and dissolve to obtain a 4% CaCl2-saturated H3BO3 solution, and store at 4°C;

[0027] S4: After the cross-linking is completed, the mixture is allowed to stand at room temperature and washed with deionized water until the pH value is neutral to obtain the riboflavin-loaded sustained-release carbon source carrier.

[0028] The use of the riboflavin-loaded slow-release carbon source carrier as described above in the utilization of carbon sources by microorganisms.

[0029] The application of the riboflavin-loaded slow-release carbon source carrier in water purification.

[0030] The method for purifying water using the above-mentioned riboflavin-loaded slow-release carbon source carrier comprises the following steps:

[0031] When purifying water, the slow-release carbon source carrier and the polyethylene net together form a denitrification solid slow-release carbon source filler layer.

[0032] Furthermore, the slow-release carbon source carrier is placed in a partition made of a polyethylene mesh, and the lid of the partition is closed to form a slow-release carbon source carrier filler layer.

[0033] The advantages and positive effects achieved by the present invention are:

[0034] 1. The present invention is observed by Hitachi SU8010 scanning electron microscope (SEM), and it can be seen that the surface of the carrier of the present invention is relatively rough and dense, with obvious lamellar and clustered structures, and particles of different sizes are attached. The irregular holes on the surface of the carrier make the slow-release carbon source carrier have a higher specific surface area, which is more conducive to the attachment of microorganisms and the release of carbon sources. The inside is wrapped with PHBV with a relatively smooth surface. Alkali heat pretreatment breaks the chemical bonds between cellulose, and the surface of the corn cob presents a rough porous structure after modification. The longitudinal section of the carrier presents a large number of closely connected folds and pore structures, which is conducive to the reproduction and growth of microorganisms.

[0035] 2. The present invention took samples from Example 1 and observed them using a Hitachi SU8010 biological scanning electron microscope (SEM). Denitrifying bacteria were attached and grown on the surface and inside of the carrier prepared by the present invention. This indicates that both the surface and the inside of the carrier are conducive to the attachment and growth of microorganisms.

[0036] 3. The present invention uses a Thermo Scientific Nicolet iS20 infrared spectrometer to compare the functional groups of the polyvinyl alcohol-sodium alginate cross-linking system and the carrier of the present invention. It can be seen that the quinone content and phenolic hydroxyl content of the present invention are significantly increased. The oxidizability of biochar is significantly positively correlated with the quinone content on its surface, while the reducibility is significantly positively correlated with the phenolic hydroxyl content on its surface. The quinone group has a strong redox property and is easy to accept or donate electrons to undergo redox reactions. The quinoline ring is the most prominent structure in the riboflavin molecule.

[0037] 4. The present invention prepares a slow-release carbon source carrier (specification: 1 cm 3 The cubes of 10% by volume were placed in ultrapure water, and a static release test was carried out in a conical flask. The ultrapure water was replaced daily, and the concentrations of COD and riboflavin in the leachate were measured. The COD in the leachate was released in sufficient quantity in the early stage, which can effectively improve the activity of denitrifying bacteria. From 17d to 31d, the COD leachate concentration was 20-30mg / L. From 32d to 53d, the COD leachate concentration was generally stable at 5-30mg / L, achieving a stable release. (The detection method of riboflavin refers to the medical detection method, and the specific method is: solvent photometry. Riboflavin has a good linear relationship with the absorbance in the range of 4-14μg / mL. Glacial acetic acid, 4% sodium hydroxide, and deionized water are mixed in a volume ratio of 5:30:965 to prepare a solvent. The extract is diluted to an appropriate concentration using the prepared solvent, and a UV-visible spectrophotometer is used for quantitative testing at 444nm) Within 65 days, the average daily riboflavin concentration extracted was 3.68mg / L, ranging from 0 to 15.13mg / L.

[0038] 5. The present invention uses endogenous redox mediator riboflavin, which is non-biotoxic and low in cost. Polyvinyl alcohol-sodium alginate is used as the cross-linking system, and the production process is simple, and the release amount of carbon source and riboflavin can be effectively controlled, secondary pollution can be avoided, the loss of riboflavin can be reduced, and the dosage can be easily controlled. Its surface rough and dense porous structure makes the denitrification solid slow-release carbon source have a higher specific surface area, which is conducive to the attachment and growth of microorganisms. It has strong operability in practical applications. The composite slow-release carbon source is prepared with corn cob-polyhydroxybutyric acid valeric acid copolyester, and the corn cob is modified by pretreatment. By crushing, the particle size can be effectively reduced and the specific surface area can be increased. The bonds of cellulose and hemicellulose are separated from polysaccharides and lignin by alkaline heat treatment, thereby improving their biodegradability. At the same time, small molecule organic acids, alcohols, and sugars are produced by the decomposition of cellulose and hemicellulose, which are more easily utilized by microorganisms than single chemicals, thereby improving bioavailability. The surface of the green plastic polyhydroxybutyrate-valerate copolyester contains hydrophilic groups such as CO and C=O, which are conducive to the attachment, growth and degradation of microorganisms. As a reaction system of electron donor and microbial carrier, it has fast denitrification start-up, low residual concentration of organic matter in the effluent, high denitrification rate, and continuous and stable denitrification effect. It can achieve the reuse of agricultural waste while releasing carbon in a long-term and stable manner, neutralizing economic benefits.

[0039] 6. The carrier of the present invention is loaded with the endogenous redox mediator - riboflavin, which ensures biological friendliness, promotes the utilization of carbon sources by microorganisms, and improves the efficiency of denitrification and denitrification; the solid slow-release carbon source carrier of the present invention utilizes a polyvinyl alcohol-sodium alginate cross-linking system, which can improve the strength and stability of the carrier, and the porous morphology is convenient for the fixed growth of microorganisms; the present invention modifies, pre-treats and compounds the natural slow-release carbon source corn cobs and biodegradable polymers (BDPs) polyhydroxybutyrate-valerate copolyesters (PHBV) to ensure efficient carbon release in the early stage of release, quickly improve the activity of microorganisms, and achieve long-term stable carbon release, which is convenient for controlling the dosage; on this basis, the present invention designs a fixing material and method for the slow-release carbon source carrier to fix the carrier to avoid loss, which is convenient for release and wide application. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a sample diagram of a riboflavin-loaded slow-release carbon source carrier in Example 1 of the present invention;

[0041] Figure 2 This is the FTIR image of the slow-release carbon source carrier in Example 1 of the present invention;

[0042] Figure 3 This is a SEM image of the slow-release carbon source carrier material of Example 1 of the present invention;

[0043] Figure 4 This is a biological SEM image of the slow-release carbon source carrier in Example 1 of the present invention;

[0044] Figure 5 This is a graph showing the COD value of the slow-release carbon source carrier in the static release experiment of Example 1 of the present invention;

[0045] Figure 6 This is a graph showing the riboflavin value of the slow-release carbon source carrier in Example 1 of the present invention in a static release experiment;

[0046] Figure 7 Schematic diagram of the UASB reactor in Example 2 of the present invention;

[0047] Figure 8 This is a graph showing the removal rate of nitrate nitrogen in the effluent of the slow-release carbon source carrier in Example 2 of the present invention in a UASB reactor experiment;

[0048] Fig. 9 This is a graph of the amount of COD provided by the slow-release carbon source carrier in Example 2 of the present invention for the denitrification process in the UASB reactor experiment;

[0049] Fig.10 This is a diagram of the slow-release carbon source carrier filler layer of Example 2 of the present invention; wherein the left diagram is a diagram of the slow-release carbon source carrier filler layer, and the right diagram is a diagram of the slow-release carbon source carrier filler layer placed in a UASB reactor. DETAILED DESCRIPTION

[0050] The present invention will be further described below in conjunction with the embodiments. The following embodiments are descriptive rather than restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0051] The various experimental operations involved in the specific embodiments are all routine techniques in the art. For parts not specially annotated in this document, ordinary technicians in the art can implement them by referring to various commonly used reference books, scientific and technological literature or related instructions, manuals, etc. before the filing date of this invention.

[0052] A riboflavin-loaded slow-release carbon source carrier comprises the following components by volume percentage: 30-32% corn cob, 30-32% polyhydroxybutyrate-valeric acid copolyester, 5g / L riboflavin, and the remainder is a cross-linking system of polyvinyl alcohol-sodium alginate, and the total volume of each component is 100%.

[0053] Preferably, the preparation steps of the cross-linking system polyvinyl alcohol-sodium alginate are:

[0054] a. Polyvinyl alcohol and sodium alginate were mixed in a mass ratio of 8:1 and diluted with deionized water. The final mass concentration of polyvinyl alcohol in the mixture was 80 g / L and the final mass concentration of sodium alginate was 10 g / L.

[0055] b. Heat the mixture in a water bath at 95°C for 2h;

[0056] c. Let cool to room temperature.

[0057] Preferably, the corncob is a modified corncob;

[0058] Alternatively, the polyhydroxybutyrate-valeric acid copolyester is pretreated polyhydroxybutyrate-valeric acid copolyester.

[0059] Preferably, the modification method of the modified corncob comprises the following steps:

[0060] a. Crush the corn cobs using a crusher and sieve the particles to a size of 1 to 2 mm;

[0061] b. Alkali heat pretreatment: soak the sieved corn cobs in 2% sodium hydroxide at a volume ratio of 1:2 and heat and boil for 20 minutes;

[0062] c. Wash the corn cobs after alkali heat pretreatment with deionized water until they are colorless and have a neutral pH;

[0063] d. Place the washed corn cob in an oven and bake at 80°C for 4 h to obtain a modified corn cob.

[0064] Preferably, the pretreatment method of polyhydroxybutyrate-valeric acid copolyester comprises the following steps:

[0065] a. PHBV is crushed using a crusher to obtain a particle size of 1 to 2 mm;

[0066] b. The sieved polyhydroxybutyrate-valeric acid copolyester was dried at 50° C. for 4 h to obtain the pretreated polyhydroxybutyrate-valeric acid copolyester.

[0067] A method for preparing the riboflavin-loaded sustained-release carbon source carrier as described above comprises the following steps:

[0068] S1: Mix the modified corn cob, the pretreated polyhydroxybutyrate-valeric acid copolyester, riboflavin, and polyvinyl alcohol-sodium alginate, and stir the mixture for 10-20 minutes to obtain a slow-release carbon source mixture;

[0069] S2: Put the slow-release carbon source mixture into a mold and freeze it at -20°C for 12 hours to set;

[0070] S3: After shaping, place in 4% CaCl2-saturated H3BO3 solution and cross-link at 4°C for 24h;

[0071] The preparation steps of the 4% CaCl2-saturated H3BO3 solution are as follows: at 25°C, dissolve 4g H3BO3 in 100mL deionized water, stir well, or heat and stir well, cool naturally and take the upper layer, add 4g CaCl2, stir and dissolve to obtain a 4% CaCl2-saturated H3BO3 solution, and store at 4°C;

[0072] S4: After the cross-linking is completed, the mixture is allowed to stand at room temperature and washed with deionized water until the pH value is neutral to obtain the riboflavin-loaded sustained-release carbon source carrier.

[0073] The use of the riboflavin-loaded slow-release carbon source carrier as described above in the utilization of carbon sources by microorganisms.

[0074] The application of the riboflavin-loaded slow-release carbon source carrier in water purification.

[0075] The method for purifying water using the above-mentioned riboflavin-loaded slow-release carbon source carrier comprises the following steps:

[0076] When purifying water, the slow-release carbon source carrier and the polyethylene net together form a denitrification solid slow-release carbon source filler layer.

[0077] Preferably, the slow-release carbon source carrier is placed in a partition made of polyethylene mesh, and the lid of the partition is closed to form a slow-release carbon source carrier filler layer.

[0078] Specifically, the relevant preparation and detection are as follows:

[0079] Preparation Example 1

[0080] A riboflavin-loaded slow-release carbon source carrier comprises the following steps:

[0081] The corn cob and PHBV were crushed with a pulverizer and sieved to a particle size of 1 to 2 mm. The sieved corn cob and a 2% sodium hydroxide solution were soaked in a volume ratio of 1:2, heated and boiled for 20 minutes, washed with deionized water until colorless and pH neutral, and dried at 80°C for 4 hours until completely dry to obtain a modified corn cob. The sieved PHBV was dried at 50°C for 4 hours until completely dry. 40g of polyvinyl alcohol and 5g of sodium alginate were mixed, diluted to 500mL with deionized water, heated in a water bath at 95°C for 2 hours, and cooled to room temperature to obtain a cross-linked system of polyvinyl alcohol-sodium alginate. By volume percentage: 30% modified corn cob, 30% pretreated PHBV, 5g / L riboflavin, and the remainder was a cross-linked system of polyvinyl alcohol-sodium alginate. The total volume of each component is 100%, and stirred to mix. Put the slow-release carbon source mixture into 1cm 3The riboflavin-loaded slow-release carbon source carrier was placed in a cubic mold, frozen at -20°C for 12 hours to set, and then placed in a 4% CaCl2-saturated H3BO3 solution and cross-linked at 4°C for 24 hours. After the cross-linking was completed, the riboflavin-loaded slow-release carbon source carrier was placed at room temperature and washed with deionized water until the pH was neutral to obtain the riboflavin-loaded slow-release carbon source carrier.

[0082] The preparation steps of 4% CaCl2-saturated H3BO3 solution are as follows: at 25°C, dissolve 4g H3BO3 in 100mL deionized water, stir thoroughly, or heat and stir thoroughly, take the upper layer after natural cooling, add 4g CaCl2, stir and dissolve to obtain 4% CaCl2-saturated H3BO3 solution, and store at 4°C.

[0083] Preparation Example 2

[0084] A riboflavin-loaded slow-release carbon source carrier comprises the following steps:

[0085] The corn cob and PHBV were crushed with a pulverizer and sieved to a particle size of 1 to 2 mm. The sieved corn cob was soaked in a 2% sodium hydroxide solution at a volume ratio of 1:2, heated and boiled for 20 minutes, washed with deionized water until colorless and pH neutral, and dried at 80°C for 4 hours until completely dry to obtain a modified corn cob. The sieved PHBV was dried at 50°C for 4 hours until completely dry. 40g of polyvinyl alcohol and 5g of sodium alginate were mixed, diluted to 500mL with deionized water, heated in a water bath at 95°C for 2 hours, and cooled to room temperature to obtain a cross-linked system of polyvinyl alcohol-sodium alginate. By volume percentage: 30% modified corn cob, 30% pretreated PHBV, and the remainder is a cross-linked system of polyvinyl alcohol-sodium alginate. The total volume of each component is 100%, and stirred to mix. Put the slow-release carbon source mixture into 1cm 3 The solidified carbon source carrier was placed in a cubic mold, frozen at -20°C for 12 hours to set, and then placed in a 4% CaCl2-saturated H3BO3 solution and cross-linked at 4°C for 24 hours. After the cross-linking was completed, the solidified carbon source carrier was allowed to stand at room temperature and washed with deionized water until the pH was neutral to obtain the slow-release carbon source carrier.

[0086] The preparation steps of 4% CaCl2-saturated H3BO3 solution are as follows: at 25°C, dissolve 4g H3BO3 in 100mL deionized water, stir thoroughly, or heat and stir thoroughly, take the upper layer after natural cooling, add 4g CaCl2, stir and dissolve to obtain 4% CaCl2-saturated H3BO3 solution, and store at 4°C.

[0087] Example 1

[0088] The slow-release carbon source carrier prepared in Example 1 (with a size of 1 cm 3 Cube, such as Figure 1)15 capsules were placed in 150 ml ultrapure water and a static release test was conducted in a conical flask. The ultrapure water was replaced daily for a total of 63 days, and the concentrations of COD and riboflavin in the extract were determined.

[0089] The present invention uses a Thermo Scientific Nicolet iS20 infrared spectrometer to compare the functional groups of the polyvinyl alcohol-sodium alginate crosslinking system and the carrier of the present invention. Figure 2 It can be seen that the quinone content and phenolic hydroxyl content of the present invention are significantly increased, making it easier to accept or donate electrons, increasing the redox capacity of the carrier during the denitrification process, and facilitating the utilization of carbon sources by microorganisms. Figure 2 PVA-SA represents the polyvinyl alcohol-sodium alginate crosslinking system prepared in Preparation Example 1, and PPC-VB2 refers to the riboflavin-loaded sustained-release carbon source carrier prepared in Preparation Example 1 of the present invention. Figure 3 It can be seen that the surface of the carrier of the present invention is rough and dense, with obvious lamellar and clustered structures. There are irregular holes on the surface of the carrier, and the higher specific surface area of ​​the slow-release carbon source carrier is conducive to the attachment and biofilm formation of microorganisms. Figure 4 It can be seen that denitrifying bacteria are attached and grown on the surface and inside of the carrier.

[0090] from Figure 5 It can be seen that the COD in the leachate is released in sufficient quantity in the early stage, which can effectively improve the activity of denitrifying bacteria at the initial start-up of the reactor. From 17d to 31d, the COD leachate concentration is 20-30mg / L, and from 32d to 53d, the COD leachate concentration is generally stable at 5-30mg / L, achieving a stable release of carbon source. Figure 6 It can be seen that within 65 days, the average daily leached riboflavin concentration was 3.68 mg / L, ranging from 0 to 15.13 mg / L.

[0091] Example 2

[0092] The solid slow-release carbon source (specification 1cm 3 The volume percentage of the cube is 2.5%, and it is added to the upflow anaerobic sludge blanket reactor (UASB) (such as Figure 7 The sludge was taken from the secondary sedimentation tank of a sewage treatment plant in Tianjin. 500 mL of cleaned sludge was added to each reactor, and the MLSS of the sludge was measured to be 5830 mg / L and MLVSS to be 3556 mg / L. The effective volume of the reactor was 2 L. The solid slow-release carbon source was fixed in the reactor using a polyethylene mesh with a pore size of 3 mm (as shown in Figure 2). Fig.10As shown). Reactor 1# was the control group, only an equal amount of sludge was added, reactor 2# was added with a solid slow-release carbon source without riboflavin (PPC, prepared in Preparation Example 2 of the present invention), and reactor 3# was added with a solid slow-release carbon source with riboflavin (PPC-VB2, prepared in Preparation Example 1 of the present invention). The influent was artificially distributed water, and the distribution water composition was: potassium nitrate 30 mg / L (in terms of N), sodium propionate 60 mg / L (in terms of COD), potassium dihydrogen phosphate 6 mg / L (in terms of P), and trace elements 1 mL / L were added. (The trace element composition is: Na2MoO4·2H2O: 220mg / L, ZnSO4·7H2O: 430mg / L, CaCl2·2H2O: 70mg / L, MnSO4·H2O: 990mg / L, CoCl2·6H2O: 240mg / L, MgSO4: 167mg / L, KI: 0.03mg / L, CuSO4·5H2O: 250mg / L, Na2EDTA·2H2O: 1500mg / L, FeSO4·7H2O: 5mg / L, H3BO3: 0.15mg / L, the solvent is water.) After the sludge is domesticated, the C / N is 2, the HRT is adjusted to 12h, and the reactor is operated for 15d. After adding solid slow-release carbon source materials, the reactor is operated for 42d.

[0093] After adding solid slow-release carbon source, the ammonia nitrogen, nitrite nitrogen and COD in the effluent of reactors 1# and 2# were kept at a low level, so the nitrate nitrogen removal rate was approximately equal to the TN removal rate. Figure 8 It can be seen that after adding solid slow-release carbon source materials, the TN removal rate showed a trend of first increasing and then decreasing. At 57 days, the TN removal rates of reactors 1# and 2# reached the highest. At this time, the TN removal rates of the three reactors were 73.15%, 32.42%, and 92.30%, respectively. Within 42 days, the average TN removal rates of the three reactors were 56.50%, 32.35%, and 69.60%, respectively. It can be seen that within 42 days, the PPC group increased the TN removal rate by an average of 24.15%, and the PPC-VB2 group increased the TN removal rate by an average of 37.25%. The PPC-VB2 group has the best denitrification effect. Calculated according to the following equation: T COD The amount of COD provided by the slow-release carbon source carrier for the denitrification process, mg / d; Q inf is the water inlet flow rate, L / d; C COD is the effluent COD concentration, mg / L; For influent NO3 - -N concentration, mg / L; For effluent NO3 - -N concentration, mg / L, by Fig. 9It can be seen that in the UASB reactor, the amount of COD provided by the slow-release carbon source carrier for the denitrification process decreased from high concentration to low concentration within 42 days, and then maintained a relatively stable level. During the stable carbon supply period, the PPC group provided an average of 223.82 mg of COD for the denitrification process per day, and the PPC-VB2 group provided an average of 275.65 mg of COD for the denitrification process per day, which was 52.83 mg higher than that of the PPC group.

[0094] At the same time, by comparing Preparation Example 1, Preparation Example 2, Example 1, and Example 2, it can be seen that the riboflavin-loaded sustained-release carbon source carrier of the present invention has a synergistic effect between the riboflavin and the polyvinyl alcohol-sodium alginate cross-linking system during preparation, which can synergistically improve the relevant properties of the prepared sustained-release carbon source carrier.

[0095] When a natural slow-release carbon source is used as a denitrification carbon source, the effluent generally has no nitrite accumulation, and the concentration of dissolved organic carbon is low, but the chromaticity is usually high, so the effluent needs to be sand filtered to meet the corresponding emission standards. In addition, due to the complex composition of natural slow-release carbon sources and the large difference in the release rate of organic matter, there is a certain risk of water pollution when natural slow-release carbon sources are used to treat natural water bodies (including surface water bodies and groundwater bodies). The present invention performs alkaline heat pretreatment on corn cobs and removes chromaticity by washing. In addition, the present invention uses a single natural slow-release carbon source and performs a carbon source release rate experiment on the leaching solution, which can provide a theoretical reference for actual engineering, thereby avoiding secondary pollution of effluent COD.

[0096] At the same time, compared with humus and quinone substances, which are currently being studied more, riboflavin, as an endogenous redox mediator, can be reused many times, is non-biotoxic, environmentally friendly, and has high economic benefits. The price of quinone mediators is more than 15 times that of riboflavin (refer to 1,2-naphthoquinone-4-sulfonate sodium for quinone mediators). Studies have shown that the cost of adding riboflavin (10 mg / L) to improve the denitrification process of SBR reactors is 3 Wastewater adds $0.025.

[0097] The carrier skeleton can provide a place for the formation of biofilm, and the comprehensive cost is much lower than BDPs. The external skeleton is used for slow-release carbon source to enhance the mechanical strength of the carbon source. The support and protection of the skeleton to the carbon source material is reflected in the fact that the internal carbon source decomposes first, and the skeleton material decomposes later, and can also be used as a carbon source after being decomposed by microorganisms in the later stage. At present, the immobilization skeleton materials of carbon sources mainly refer to the commonly used materials for microbial embedding, and improper selection may cause secondary pollution. The polyvinyl alcohol-sodium alginate cross-linking system can improve the strength and stability of the filler and achieve high water absorption performance.

[0098] In artificial wetlands and artificial floating islands, a crushed stone layer is usually used to fix the slow-release carbon source carrier up and down, and soil is covered on it to plant wetland plants. The present invention uses a polyethylene net to fix the filler, which can increase the system's ability to resist impact loads, avoid scouring losses of the filler and the medium, and facilitate the replacement of the filler layer. It is suitable for artificial wetlands or directly fixed in natural basins such as rivers and lakes.

[0099] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A riboflavin-loaded slow-release carbon source carrier, characterized in that: The slow-release carbon source carrier comprises the following components by volume percentage: 30-32% corn cob, 30-32% polyhydroxybutyrate-valeric acid copolyester, 5g / L riboflavin, and the remainder is a cross-linking system of polyvinyl alcohol-sodium alginate, and the total volume of each component is 100%.

2. The riboflavin-loaded sustained-release carbon source carrier according to claim 1, characterized in that: The preparation steps of the cross-linking system polyvinyl alcohol-sodium alginate are: a. Mix polyvinyl alcohol and sodium alginate in a mass ratio of 8:1 and dilute with deionized water. The final concentration of polyvinyl alcohol in the mixture is 80 g / L and the final concentration of sodium alginate is 10 g / L. b. Heat the mixture in a water bath at 95°C for 2h; c. Let cool to room temperature.

3. The riboflavin-loaded sustained-release carbon source carrier according to claim 1 or 2, characterized in that: The corncob is a modified corncob; Alternatively, the polyhydroxybutyrate-valeric acid copolyester is a pretreated polyhydroxybutyrate-valeric acid copolyester.

4. The riboflavin-loaded sustained-release carbon source carrier according to claim 3, characterized in that: The modified corncob modification method comprises the following steps: a. Crush the corn cobs using a crusher and sieve the particles to a size of 1 to 2 mm; b. Alkali heat pretreatment: soak the sieved corn cobs in 2% sodium hydroxide at a volume ratio of 1:2 and heat and boil for 20 minutes; c. Wash the corn cobs after alkali heat pretreatment with deionized water until they are colorless and have a neutral pH; d. Place the washed corn cob in an oven and bake at 80°C for 4 h to obtain a modified corn cob.

5. The riboflavin-loaded sustained-release carbon source carrier according to claim 3, characterized in that: The pretreatment method of polyhydroxybutyrate-valeric acid copolyester comprises the following steps: a. PHBV is crushed using a crusher to obtain a particle size of 1 to 2 mm; b. The sieved polyhydroxybutyrate-valeric acid copolyester was dried at 50°C for 4 hours to obtain the pretreated polyhydroxybutyrate-valeric acid copolyester.

6. A method for preparing a riboflavin-loaded sustained-release carbon source carrier according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Mix the modified corn cob, the pretreated polyhydroxybutyrate-valeric acid copolyester, riboflavin, and polyvinyl alcohol-sodium alginate, and stir the mixture for 10-20 minutes to obtain a slow-release carbon source mixture; S2: Put the slow-release carbon source mixture into a mold and freeze it at -20°C for 12 hours to set; S3: After shaping, place in 4% CaCl2-saturated H3BO3 solution and cross-link at 4°C for 24h; The preparation steps of the 4% CaCl2-saturated H3BO3 solution are as follows: at 25°C, dissolve 4g H3BO3 in 100mL deionized water, stir well, or heat and stir well, cool naturally and take the upper layer, add 4g CaCl2, stir and dissolve to obtain a 4% CaCl2-saturated H3BO3 solution, and store at 4°C; S4: After the cross-linking is completed, the mixture is allowed to stand at room temperature and washed with deionized water until the pH value is neutral to obtain the riboflavin-loaded sustained-release carbon source carrier.

7. Use of the riboflavin-loaded slow-release carbon source carrier according to any one of claims 1 to 5 in the utilization of carbon sources by microorganisms.

8. Use of the riboflavin-loaded slow-release carbon source carrier according to any one of claims 1 to 5 in purifying water.

9. A method for purifying water using the riboflavin-loaded slow-release carbon source carrier according to any one of claims 1 to 5, characterized in that: The steps include: When purifying water, the slow-release carbon source carrier and the polyethylene net together form a denitrification solid slow-release carbon source filler layer.

10. The method according to claim 9, characterized in that: The slow-release carbon source carrier is placed in a partition made of a polyethylene net, and the lid of the partition is closed to form a slow-release carbon source carrier filler layer.

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