Fe (II) composite alkalized corncob carbon source slow-release material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of water treatment and water body remediation, and discloses a Fe (II) composite alkalized corncob carbon source slow-release material as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing framework material hydrogel from polyvinyl alcohol and alginate, mixing alkalized corncobs, poly (butylene succinate) and ferrite into the framework material hydrogel, performing reverse mold forming, and performing crosslinking by using a saturated boric acid solution as a chemical crosslinking agent to prepare the Fe (II) composite alkalized corncob carbon source slow-release material. The Fe (II) composite alkalized corncob carbon source slow-release material provided by the invention has excellent carbon source slow-release performance, and can strengthen the denitrification nitrogen removal effect and improve the nitrogen removal rate; moreover, pores in the surface of the carbon source slow-release material can provide stable survival conditions for microorganisms, so that the microorganisms are easy to attach, biofilm-form and grow, and the carbon source slow-release material can serve as a biofilm carrier.

Description

Technical Field

[0001] The invention belongs to the field of water treatment and water body restoration technology, and specifically relates to an Fe(II) composite alkalized corncob carbon source slow-release material and a preparation method and application thereof. Background Art

[0002] Most sewage treatment plants use biological denitrification, which requires sufficient carbon sources as nutrients and electron donors for denitrifying bacteria. Currently, the most commonly used drainage system is the combined system, and its water quality C / N ratio is generally low, making it difficult to denitrify sewage.

[0003] To address this problem, sewage treatment plants often use external liquid carbon sources, such as methanol, acetic acid, etc. However, traditional liquid carbon source addition not only requires strict and complex process control to avoid the risk of over- or under-dosing, but also has unstable output. Therefore, solid carbon sources become a better choice due to their slow-release properties.

[0004] Solid slow-release carbon sources for treating low C / N wastewater can be roughly divided into two categories: natural or modified cellulose solid carbon sources and biodegradable polymers. Cellulose solid carbon sources are cheap and widely available, but they release carbon quickly, easily cause effluent pollution, and are not sustainable, requiring frequent and regular replacement to meet the carbon consumption requirements of denitrification; although biodegradable polymers release carbon slowly and the carbon release effect can last for about half a year, they can avoid risks such as high effluent color and organic pollution, but their high price and complex preparation limit their large-scale application in practice.

[0005] In recent years, although some researchers have combined two or more carbon sources with complementary properties to develop multi-carbon source composite materials to optimize the performance of a single solid carbon source and meet the requirements of denitrification, the research is still in the initial laboratory exploration stage, and the research results pay less attention to the physical properties of the materials, resulting in the fact that most of the materials prepared do not have the premise for actual engineering application, such as: in actual engineering applications, there may be problems such as material disintegration, large amounts of deposition at the bottom of the reaction tank or floating on the water surface. Therefore, the development of carbon source slow-release composite materials with low cost, good slow-release performance and enhanced denitrification performance, excellent physical properties, and practical engineering application prospects is of great significance for the upgrading and transformation of sewage treatment plants and river restoration. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a Fe(II) composite alkalized corn cob carbon source slow-release material and its preparation method and application. The Fe(II) composite alkalized corn cob carbon source slow-release material provided by the present invention not only has excellent carbon source slow-release performance, but also can act as a biofilm carrier, which is conducive to the growth of microorganisms on the wall in practical applications. The material will not disintegrate, nor will it be deposited in large quantities at the bottom of the reaction tank or float on the water surface.

[0007] The invention provides a method for preparing a Fe(II) composite alkalized corncob carbon source slow-release material.

[0008] Specifically, a method for preparing a Fe(II) composite alkalized corncob carbon source slow-release material comprises the following steps:

[0009] Polyvinyl alcohol and alginate are used to make a skeleton material hydrogel, and then alkalized corn cob, polybutylene succinate and ferrous salt are mixed into the skeleton material hydrogel. After reverse molding, boric acid solution is used as a chemical cross-linking agent for cross-linking to obtain a Fe(II) composite alkalized corn cob carbon source sustained-release material.

[0010] Preferably, the preparation method of the Fe(II) composite alkalized corncob carbon source slow-release material comprises the following steps:

[0011] Dissolving and mixing polyvinyl alcohol and alginate to prepare a skeleton material hydrogel;

[0012] adding an alkaline solution to the corn cob for alkalization treatment to obtain an alkalized corn cob;

[0013] The alkalized corn cob, polybutylene succinate and ferrous salt are added to the skeleton material hydrogel, mixed and molded; then a saturated boric acid solution is used for cross-linking and curing, and a sulfate solution is used for secondary cross-linking and curing; finally, the Fe(II) composite alkalized corn cob carbon source sustained-release material is obtained after drying.

[0014] Preferably, the mass ratio of the polyvinyl alcohol to the sodium alginate is (6-10):1.

[0015] Preferably, the alkaline solution includes NaOH solution and / or KOH solution; the mass fraction of the alkaline solution is 0.5% to 3%, such as 1%, 1.5%, 2%, 2.5%, 3%, etc. The OH- in the alkaline solution destroys the lignin structure on the surface of the material, reduces its content, and breaks the chemical bonds between cellulose, thereby enhancing the carbon release performance of the material.

[0016] Preferably, the solid-liquid ratio of the corn cob to the alkaline solution is 1 g: (5-15) mL; further preferably, the solid-liquid ratio of the corn cob to the alkaline solution is 1 g: (8-12) mL.

[0017] Preferably, the temperature of the alkalization treatment is 15-30°C, and the time of the alkalization treatment is 5-20 hours; further preferably, the temperature of the alkalization treatment is 18-25°C, and the time of the alkalization treatment is 8-15 hours.

[0018] Preferably, the mass ratio of the alkalized corn cob to the polybutylene succinate (PHB) is (0.8-1.2):1.

[0019] Preferably, the ferrous salt is one of ferrous sulfate, ferrous chloride, and ferrous nitrate; further, preferably, the ferrous salt is ferrous sulfate, such as ferrous sulfate heptahydrate. Among the above ferrous salts, ferrous chloride has a lower cost, so it is considered to be selected as an additive, but studies have found that the Fe(II) composite alkalinized corncob carbon source slow-release material prepared using it will affect the physiological activities of microorganisms along with the increase of chloride ion concentration, which is not conducive to the wall growth of microorganisms.

[0020] Preferably, the amount of ferrous salt added is: 15-40g of ferrous salt is added to every 1L of the skeleton material hydrogel; further preferably, the amount of ferrous salt added is: 20-35g of ferrous salt is added to every 1L of the skeleton material hydrogel.

[0021] Preferably, the process of reverse molding is: placing the mixed material in a mold, freezing it at -25 to -15°C for 10 to 20 hours, then thawing it at 15 to 25°C, repeating the cycle 3 to 6 times, and demolding it after molding.

[0022] Preferably, the saturated boric acid solution contains 1% to 3% CaCl2.

[0023] Preferably, the sulfate solution is a sodium sulfate solution, and the concentration of the sodium sulfate solution is 0.5-1.0 mol / L.

[0024] Preferably, the cross-linking and curing time is 18 to 36 hours, and the secondary cross-linking and curing time is 1 to 3 hours.

[0025] The invention also provides a Fe(II) composite alkalized corncob carbon source slow-release material.

[0026] Specifically, a Fe(II) composite alkalized corncob carbon source slow-release material is prepared by the above preparation method; the dry density of the Fe(II) composite alkalized corncob carbon source slow-release material is 0.720-0.760 g / cm 3 , saturated water density is 1.240~1.280g / cm 3The porosity is 33.0% to 35.0%, the compressive strength is 215 to 220N, and the maximum water absorption swelling degree is 130% to 135%.

[0027] Preferably, the dry density of the Fe(II) composite alkalized corncob carbon source slow-release material is 0.730-0.750 g / cm 3 , saturated water density is 1.240~1.270g / cm 3 The porosity is 33.0% to 34.0%, the compressive strength is 215 to 218N, and the maximum water absorption swelling degree is 130% to 133%.

[0028] The present invention also provides application of the Fe(II) composite alkalized corncob carbon source slow-release material.

[0029] Specifically, the above-mentioned Fe(II) composite alkalized corn cob carbon source slow-release material is used in sewage treatment.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The Fe(II) composite alkaline corn cob carbon source slow-release material provided by the present invention not only has excellent carbon source slow-release performance, but also can stably and continuously release the carbon source required for the denitrification process during the sewage treatment process, thereby strengthening the denitrification and denitrification effect and improving the nitrogen removal rate; moreover, the pores on the surface of the carbon source slow-release material can provide stable living conditions for microorganisms, making it easy for microorganisms to attach and form biofilms, and can act as a biofilm carrier. The material will not disintegrate, nor will it be deposited in large quantities at the bottom of the reaction tank or float on the water surface.

[0032] (2) In the preparation method provided by the present invention, the raw materials used include agricultural waste materials such as corn cobs, which are used as a carbon source for sewage treatment, practicing the environmental protection concept of "treating waste with waste", and are easy to obtain and low in cost; the alkalization treatment of corn cobs is performed to improve the biomass utilization rate of the material matrix; the alkalized corn cobs and polybutylene succinate with complementary properties are combined and wrapped in polyvinyl alcohol, sodium alginate and ferrous sulfate heptahydrate to prepare a gel skeleton of the composite material, which greatly improves the sustained release performance, denitrification performance and physical properties of the material, making it have the premise for practical engineering application.

[0033] (3) The composite material synthesized by the present invention is not only low in cost, but also has good physical properties and biofilm formation performance, and also has good carbon source slow-release performance, so that it can not only release enough carbon source for denitrifying bacteria to utilize over a long period of time, but also avoid the risk of secondary pollution caused by rapid release of carbon source. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1It is a graph of cumulative carbon release concentration in the leachate of the corn cob material before alkalization (M0) and the alkalized corn cob material (M3) in Example 1 of the present invention;

[0035] Figure 2 It is a three-dimensional fluorescence spectrum diagram of the leachate of the corn cob material before alkalization (M0) and the alkalized corn cob material (M3) in Example 1 of the present invention;

[0036] Figure 3 The scanning electron microscope images of the corn cob material (M0) before alkalization and the alkalized corn cob material (M3) before and after carbon release in Example 1 of the present invention are shown;

[0037] Figure 4 This is a graph of the cumulative carbon release concentration in the leachate of the Fe(II) composite alkalized corncob carbon source slow-release material prepared in an embodiment of the present invention;

[0038] Figure 5 This is the nitrogen element transformation relationship diagram of the control group (no carbon source added) in the enhanced denitrification experiment;

[0039] Figure 6 This is a nitrogen element conversion relationship diagram in the enhanced denitrification experiment of the alkalized corncob material in Example 1 of the present invention;

[0040] Figure 7 A diagram showing the relationship between nitrogen element conversion in an enhanced denitrification experiment of the Fe(II) composite alkalized corncob carbon source slow-release material prepared in Example 1 of the present invention;

[0041] Figure 8 This is a diagram showing the total nitrogen removal effect of the alkalized corncob material and the Fe(II) composite alkalized corncob carbon source slow-release material in Example 1;

[0042] Fig. 9 The three-dimensional fluorescence spectrum of the leachate of the Fe(II) composite alkalized corncob carbon source slow-release material prepared in Example 1 of the present invention;

[0043] Fig.10 The scanning electron microscope image of the surface of the Fe(II) composite alkalized corncob carbon source slow-release material prepared in Example 1 of the present invention before and after carbon release;

[0044] Fig.11 This is a scanning electron microscope image of the surface of the Fe(II) composite alkalized corncob carbon source slow-release material prepared in Example 1 of the present invention after the enhanced denitrification experiment;

[0045] Fig.12 This is an analysis chart of iron leaching of the Fe(II) composite alkalized corncob carbon source sustained-release material prepared in Example 1 of the present invention;

[0046] Fig.13This is a graph showing the nitrogen release of the leachate of the Fe(II) composite alkaline corncob carbon source slow-release material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0048] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0049] Example 1

[0050] A method for preparing a Fe(II) composite alkalized corncob carbon source slow-release material comprises the following steps:

[0051] (1) Preparation of skeleton material hydrogel: 40±1g polyvinyl alcohol and 5±0.1g sodium alginate were added to 250mL ultrapure water respectively, and allowed to stand for 30min to allow it to fully absorb water and swell, then slowly stirred and uniformly heated to 95°C. After 4h, a uniform polyvinyl alcohol and sodium alginate solution was obtained. The polyvinyl alcohol solution and the sodium alginate solution were fully mixed in a ratio of 1:1 to obtain a uniform hydrogel, which was allowed to stand to room temperature;

[0052] (2) Preparation of alkalized corn cobs: Take a certain amount of dried corn cobs and add them to a 2% NaOH solution, keeping the solid-liquid ratio at 1:10. Then, place the mixture reactor in a constant temperature water bath and heat it at 20°C. After 12 hours, take out the corn cobs, wash them with neutral water, and dry them in an oven at 60°C to a constant weight, thus obtaining the alkalized corn cobs.

[0053] (3) Low temperature freezing solidification: (10.0±0.5) g of cellulose agricultural carbon source: alkalized corn cob, (10.0±0.5) g of biodegradable polymer carbon source: PHB, and 13.5±0.5 g of ferrous sulfate heptahydrate were added to the prepared hydrogel, stirred thoroughly until mixed, and poured into a volume of 3.375 cm 3 The mold was placed in a square mold, frozen at -20°C for 16 hours, thawed at 20°C for 4 hours, and repeated 4 times. The mold was then demoulded.

[0054] (4) Chemical crosslinking: The demoulded material was immediately placed in a saturated boric acid solution containing 2% CaCl2 for crosslinking and curing. After 24 hours, it was rinsed with ultrapure water for 4 times and then placed in a 0.8 mol / L sodium sulfate solution for secondary crosslinking for 2 hours. All crosslinking was carried out at 4°C. After crosslinking, the material was rinsed with ultrapure water for 4 times to remove the crosslinking agent remaining on the surface.

[0055] (5) Drying and storage: The prepared composite material was dried at 60°C for 8 h until the material had a constant weight, and then sealed and stored in a refrigerator at 4°C for future use.

[0056] Product effect testing

[0057] 1. Test the physical properties of the Fe(II) composite alkalized corncob carbon source sustained-release material prepared in Example 1, as follows:

[0058] ① Dry density: obtained by mass / volume, wherein the volume was determined by the quartz sand volume difference method; ② Saturated density: obtained by mass / volume, wherein the volume was determined by the pure water volume difference method; ③ Porosity: determined by the solution standing method; ④ Mass transfer and adsorption performance: 200 mL of 6 mg / L methylene blue solution and 3.5 g of the composite material were added to a 250 mL conical flask, and the group without material was used as a blank control. The mixture was shaken in a constant temperature shaker at 30°C and 180 r / min, and samples were taken at 0.5 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 36 h, 48 h, 72 h, 96 h, 120 h, 144 h, and 168 h, respectively, and the absorbance of the methylene blue solution of each group was measured at 665 nm. ④ Mechanical stability: 30 structurally intact composite materials were placed in a 250mL conical flask and 250mL ultrapure water was added. The material was placed on a magnetic stirrer and completely fluidized and stirred at 25°C and 550r / min to simulate the application of the material in actual engineering. After 48 hours, the number of intact particles was counted, and the ratio of the number of intact particles to the total number of original particles was the mechanical stability of each skeleton. ⑤ The compressive strength was measured using a pointer-type push-pull dynamometer. ⑥ Water absorption and swelling capacity: Take 5 multi-carbon source composite materials with complete structure, weigh their mass as m0 (g), put them into a 250mL ground-mouth conical flask filled with 100mL ultrapure water, soak them at 20℃, take out the materials at 5min, 10min, 15min, 20min, 25min, 30min, 40min, 50min, 60min, 80min, 100min, 120min, 150min, 180min, 240min, 360min, 480min, 720min, 1440min, 2880min, 4320min, 5760min, wipe the surface moisture with absorbent paper and weigh them immediately, and calculate the water absorption and swelling degree (SW,%) of the composite material at equilibrium. The test results are shown in Table 1.

[0059] Table 1 Physical properties characterization of Fe(II) composite alkalized corncob carbon source slow-release materials

[0060] index Index value Dry density <![CDATA[0.739±0.005(g / cm 3 )]]> Saturated density <![CDATA[1.249±0.009(g / cm 3 )]]> Porosity 33.353％ Equilibrium adsorption of methylene blue 0.213mg / g Mechanical stability 90％ Compressive strength 216.84N Maximum water swelling 131.347％

[0061] 2. Analysis of the components of the leachate of the alkalized corncob material prepared in step (2) of Example 1 in clear water

[0062] 5 g of corn cob material (M0) before alkali treatment in Example 1 and alkalized corn cob material (M3) prepared in step (2) of Example 1 were taken respectively, put into a 250 mL ground conical flask, 250 mL of clean water was injected, the solid and liquid were shaken and sealed, and the mixture was allowed to stand at room temperature. Samples were taken after the carbon source was released for 0 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 36 h, 48 h, 72 h, 96 h, 120 h, 144 h, and 168 h. After the water sample was filtered through a 0.45 μm filter membrane, the COD in the leaching solution was determined. Before each determination of the index, the conical flask was shaken and allowed to stand for 30 min before taking the supernatant. The test water was replaced every 24 h.

[0063] Figure 1 Graph showing the cumulative carbon release concentration in the leachate of the corncob material M0 before alkalization and the alkalized corncob material M3 in Example 1 of the present invention. Figure 1 As shown in the figure, the cumulative carbon release of M0 and M3 has the same trend over time, that is, rapid release in the early stage and then reaching equilibrium, and the corresponding release rate continues to decrease. Among them, the carbon release of alkalized corn cob M3 is only slightly less than that of M0 in the first hour, and it is much higher than that of M0 in the rest of the time. At the same time, the release rate of M0 in the first 24 hours is 55.018 mg / (g·d), while the carbon release rate of M3 in the first 24 hours is 82.118 mg / (g·d), an increase of 49.26%. On the 7th day, the cumulative carbon release of M0 was 1413.85 mg / L, while the cumulative carbon release of M3 was 2036.614 mg / L, an increase of 44.04%, and the carbon release efficiency was greatly enhanced, indicating that the alkali modification prepared in the experiment enhanced the carbon release performance of corn cob.

[0064] Figure 2 The corncob material M0 before alkalization in Example 1 of the present invention (such as Figure 2 A) and alkalized corncob material M3 (such as Figure 2 B) is a three-dimensional fluorescence spectrum (3D-EEM) of the leaching solution. Figure 2As shown, the alkaline corncob M3 extract showed more obvious fluorescence intensity in the three regions II, IV, and V, and showed a peak value much higher than that of M0 at Ex / Em=270 / 345nm representing tryptophan-like proteins. In addition, a new peak at Ex / Em=375 / 380nm appeared in the M3 extract in region V, indicating that the decomposition of lignin and hemicellulose after alkali treatment produced more fulvic acid. The alkaline corncob M3 extract contained a higher content of tryptophan, tryptophan-like and tyrosine proteins. These small molecular organic substances are highly biodegradable, and a certain relative concentration of fulvic acid appeared. Fulvic acid is a low molecular weight macromolecular organic substance with strong biological inertia and high physiological activity. It is easier to be used by microorganisms than other macromolecular organic substances.

[0065] Figure 3 The scanning electron microscope images of the corn cob material (M0) before and after carbon release and the alkalized corn cob material (M3) in Example 1 of the present invention are shown in FIG. Figure 3 As shown in (a), the surface structure of the alkalized corncob is relatively smoother, with only some shallow grooves, and no obvious pore structure is observed. In addition, the electron microscope shows that there is no connectivity between these grooves, making it difficult for microorganisms to form biofilms. Figure 3 As shown in (b), after the clean water carbon release experiment, deeper grooves and holes appeared on the surface of the alkalinized corn cob, and traces of small molecular organic matter dissolution can be observed, which is more conducive to the biofilm formation of microorganisms. When alkalinized corn cobs are added as carbon sources to treat low C / N sewage in actual projects, the anoxic environment is the key to achieving SND. The presence of pores can serve as a channel for matrix transfer, so a higher porosity indicates that it is more available.

[0066] 3. Analysis of the components of the leachate of the Fe(II) composite alkalinized corncob carbon source slow-release material prepared in Example 1 in clear water

[0067] 5g±0.1g of the Fe(II) composite alkalized corncob carbon source slow-release material prepared by the present invention was added to a conical flask, 250mL of ultrapure water was replaced every day and sealed, and stirred on a magnetic stirrer at a speed of 150r / min. COD in the leaching solution was sampled and measured at regular intervals (0h, 1h, 2h, 4h, 8h, 12h, 24h, 36h, 48h, 72h, 96h, 120h, 144h, 168h) at room temperature to investigate the clean water carbon release characteristics of the composite material.

[0068] Figure 4 This is a graph showing the cumulative carbon release concentration in the leachate of the Fe(II) composite alkaline corncob carbon source slow-release material prepared in Example 1 of the present invention. Figure 4 It can be seen that the first 24 hours is a rapid carbon release stage. The carbon release rate of alkalized corncob M3 in the first 24 hours is 82.118 mg / (g·d) (see Figure 1), while the carbon release rate of Fe(II) composite alkalized corn cob carbon source slow-release material in the first 24 hours was 3.87 mg / (g·d), which was only 4.7% of that of alkalized corn cob M3. From the 24th to the 72nd hour, it was in a slow carbon release period. After 72 hours, it was in a stable carbon release stage, and the carbon release rate basically reached equilibrium. At the end of the experiment (400 hours), the cumulative carbon release concentration was 293.238 mg / L. The results show that in the early rapid carbon release stage, the carbon release rate of the carbon source slow-release material was less than 5% of that of the alkalized corn cob, and the carbon release capacity of the carbon source slow-release material was greatly improved compared with PHB, which effectively solved the problem of large carbon release from corn cob, which easily caused organic pollution, and small carbon release from PHB.

[0069] 4. Test the effect of Fe(II) composite alkalized corncob carbon source slow-release material prepared in Example 1 on enhancing denitrification

[0070] Weigh 10.0±0.5g of pre-alkalized corncob material (M0) and Fe(II) composite alkalized corncob carbon source slow-release material into a conical flask, then add 400mL of simulated water (the formula is shown in Table 2, and the formula of trace elements in Table 2 is shown in Table 3) to maintain NO3 - -N concentration was 150mg / L, and 100mL of pretreated activated sludge was inoculated, and its MLSS concentration was determined to be 7.92g / L. The reactor was then placed on a magnetic stirrer for stirring. After that, samples were taken every day to determine the TN, COD, and NO3 in the supernatant. - -N, NO2 - -N and NH4 + -N concentration changes and calculate its denitrification rate.

[0071] Table 2 Simulated water distribution for denitrification experiment

[0072] Element <![CDATA[KNO3]]> <![CDATA[KH2PO4]]> <![CDATA[NaHCO3]]> Trace Elements Concentration (g / L) 1.083 0.1317 0.42 1mL

[0073] Table 3 Trace element formula

[0074]

[0075]

[0076] Figure 5 , Figure 6 , Figure 7 These are the nitrogen element conversion relationship diagrams in the enhanced denitrification experiment of the control group (no carbon source added, i.e. no carbon source material was added to the activated sludge), the alkalized corncob material and the Fe(II) composite alkalized corncob material in Example 1 of the present invention. Figure 5 , Figure 6 , Figure 7It can be seen that during the experiment, the highest average denitrification rate of Fe(II) composite alkaline corn cob carbon source slow-release material reached 4.483 mg / (gMLSS·d), and the nitrate nitrogen concentration was reduced to 9.301 mg / L by the 7th day, while the nitrate nitrogen concentration of alkali-treated corn cob composite material was 27.253 mg / L during the same period, and the total nitrate reduction reached 57.874 mg; during the experiment, the highest denitrification rate of alkaline corn cob material was 4.059 mg / (gMLSS·d), and by the end of the experiment, NO3 - -N concentration was reduced to 17.590 mg / L. Total nitrate was reduced by 50.372 mg. The nitrate concentration of the control group (without carbon source) was still greater than 80 mg / L until the 10th day. This shows that after adding Fe(II) composite alkalized corn cob material, the nitrate removal rate in the reactor was significantly improved.

[0077] Figure 8 This is a diagram showing the total nitrogen removal effect of the alkalized corncob material and the Fe(II) composite alkalized corncob carbon source slow-release material in Example 1. Figure 8 It can be seen that Fe(II) composite alkalized corncob carbon source slow-release material ( Figure 8 The COD concentration of (a)) was in the rising period in the first 2 days, and the effluent concentration reached 57.300 mg / L and 144.546 mg / L, respectively, which was higher than that of the alkaline corncob material ( Figure 8 (b)); After a slight decrease in TN concentration on the first day, the TN concentration reached a maximum of 36.9 mg / L on the second day, which was also higher than that of the alkaline corn cob. In the first 6 days of the experiment, the daily reduction of the Fe(II) composite alkaline corn cob carbon source slow-release material was greater than that of the alkaline corn cob. Until the 7th day, the TN concentration of the Fe(II) composite alkaline corn cob carbon source slow-release material dropped to 10.093 mg / L, and the reduction was 11.991 mg / L (<20 mg / L), a decrease of 7.99% (greater than 5%). It can be considered that denitrification is complete and the Fe(II) composite alkaline corn cob carbon source slow-release material still has denitrification potential. At this time, the cumulative TN reduction concentration of the Fe(II) composite alkaline corn cob carbon source slow-release material reached 139.909 mg / L, and the cumulative reduction reached 55.963 mg, which is 1.33 times that of the alkaline corn cob (42.148 mg). According to the results of carbon release in clear water, the carbon release concentration of Fe(II) composite alkaline corn cob carbon source slow-release material is lower than that of alkaline corn cob. In the enhanced denitrification experiment, due to the simultaneous release of inorganic Fe(Ⅱ) and organic electron donors in the carbon source, the two synergistically denitrify under the co-substrate mode, and the Fe(Ⅲ) generated by the oxidation of Fe(Ⅱ) can also increase the activity of denitrification-related microorganisms. Under multiple influences, the denitrification process is accelerated, making the COD and TN reduction concentrations of Fe(II) composite alkaline corn cob carbon source slow-release material higher than those of alkaline corn cob.

[0078] Fig. 9 This is a three-dimensional fluorescence spectrum of the Fe(II) composite alkalized corncob carbon source slow-release material leachate prepared in Example 1 of the present invention. Fig. 9 It can be seen that the leachate of Fe(II) composite alkaline corncob carbon source sustained-release material showed obvious fluorescence intensity in three regions Ⅰ, Ⅱ, Ⅲ and Ⅳ, and peaks representing tryptophan-like proteins appeared in region Ⅳ, indicating that the leachate was rich in small molecular substances and the composite material was completely feasible as a solid carbon source and biomaterial.

[0079] Fig.10 This is a scanning electron microscope image of the surface of the Fe(II) composite alkalized corncob carbon source slow-release material prepared in Example 1 of the present invention before and after carbon release. Fig.10 As shown in Figure A, the surface structure of the Fe(II) composite alkalinized corncob carbon source slow-release material is relatively smoother, with only some shallow grooves, and no obvious pore structure was observed. In addition, the electron microscope showed that there was no connectivity between these grooves, making it difficult for microorganisms to form biofilms. Fig.10 As shown in Figure B, after carbon release, more pores are formed on the surface of the Fe(II) composite alkaline corn cob carbon source slow-release material due to the dissolution of Fe(II), and electron microscopy shows that it has a certain degree of pore size and depth, which is more suitable for microbial attachment.

[0080] Fig.11 This is a scanning electron microscope image of the surface of the Fe(II) composite alkalized corncob carbon source slow-release material prepared in Example 1 of the present invention after the enhanced denitrification experiment. Fig.11 As shown in Figures A and B, the biofilm of Fe(II) composite alkalinized corncob carbon source slow-release material has been improved to a certain extent after the denitrification test, and more microorganisms were observed in the gullies, depressions and holes. Fig.11 Figure B shows that microorganisms formed a tightly bound biofilm on the surface of the Fe(II) composite alkaline corn cob carbon source slow-release material, and a wide variety of bacterial communities appeared.

[0081] 5. Analysis of iron leaching from the Fe(II) composite alkaline corn cob carbon source slow-release material prepared in Example 1 During the first 7 days of the clean water carbon release process of the Fe(II) composite alkaline corn cob carbon source slow-release material, its Fe(Ⅱ) and total Fe conditions were monitored, and the Fe(Ⅲ) content was estimated based on the Fe(Ⅱ) and total Fe contents. Fig.12 This is the iron leaching analysis diagram of Fe(II) composite alkalized corncob carbon source slow-release material. Fig.12It can be seen that the iron release law of Fe(II) composite alkaline corn cob carbon source slow-release material is similar to its carbon release law, in which Fe(II) iron release belongs to the rapid stage in the first 24 hours, with a release rate of 0.478 mg / (g·d), and then slows down until equilibrium. At the end of the experiment (168h), the cumulative iron release concentration of Fe(II) released by Fe(II) composite alkaline corn cob carbon source slow-release material reached 10.708 mg / L; Fe(III) belongs to the rapid stage in the first 48 hours, with a release rate of 0.520 mg / (g·d), and at the end of the experiment, the cumulative concentration is 26.423 mg / L; total Fe also has a relatively fast release rate in the first 48 hours, with a release rate of 0.768 mg / (g·d), and the final concentration reaches 37.131 mg / L. In addition, except for the early stage of iron release (less than 4h), the concentration of Fe(III) is greater than that of Fe(II). In general, the Fe(II) composite alkaline corn cob carbon source slow-release material has a low iron release rate, which can ensure that the microorganisms will not be poisoned by the intervention of a large amount of Fe in a short period of time, and has application significance in practical engineering.

[0082] 6. Analysis of the pollution of the leachate of Fe(II) composite alkalinized corncob carbon source slow-release material

[0083] In order to evaluate whether the introduction of Fe(Ⅱ) and Fe(Ⅲ) would change the characteristics of the nitrogen leaching solution of the material, the nitrogen content of the effluent was monitored every day. Fig.13 This is a graph showing the nitrogen release of the leachate from the Fe(II) composite alkalinized corncob carbon source slow-release material. Fig.13 It can be seen that only a certain concentration of NH4 was detected in the leachate. + -N. Alkalinized corncob material and Fe(II) composite alkalinized corncob carbon source slow-release material produced NH4 in the first day of effluent + -N concentrations were 1.682mg / L and 2.362mg / L, respectively, and then dropped significantly. NH4 + -N concentration does not exceed 0.200 mg / L. Due to the increase in porosity, the ammonia nitrogen concentration of Fe(II) composite alkalized corncob carbon source slow-release material is also higher than that of alkali-treated corncob material. This result shows that adding Fe(II) to the carbon source material will cause less pollution to the leaching solution.

[0084] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a Fe(II) composite alkalized corncob carbon source sustained-release material, characterized in that: The following steps are involved: Polyvinyl alcohol and alginate are used to make a skeleton material hydrogel, and then alkalized corn cob, polybutylene succinate and ferrous salt are mixed into the skeleton material hydrogel. After reverse molding, saturated boric acid solution is used as a chemical cross-linking agent for cross-linking to obtain a Fe(II) composite alkalized corn cob carbon source sustained-release material.

2. The preparation method according to claim 1, characterized in that: The preparation method of the Fe(II) composite alkalized corncob carbon source slow-release material comprises the following steps: Dissolving and mixing polyvinyl alcohol and alginate to prepare a skeleton material hydrogel; adding an alkaline solution to the corncob for alkalization treatment to obtain an alkalized corncob; The alkalized corn cob, polybutylene succinate and ferrous salt are added to the skeleton material hydrogel, mixed and molded; then cross-linked and cured with a boric acid solution, and then secondary cross-linked and cured with a sulfate solution; finally, dried to obtain the Fe(II) composite alkalized corn cob carbon source sustained-release material.

3. The preparation method according to claim 2, characterized in that: The alkaline solution includes NaOH solution and / or KOH solution; the mass fraction of the alkaline solution is 0.5% to 3%.

4. The preparation method according to claim 3, characterized in that: The temperature of the alkalization treatment is 15 to 30° C., and the time of the alkalization treatment is 5 to 20 hours.

5. The preparation method according to claim 3 or 4, characterized in that: The mass ratio of the alkalized corn cob to the polybutylene succinate is (0.8-1.2):

1.

6. The preparation method according to claim 2, characterized in that: The ferrous salt is one of ferrous sulfate, ferrous chloride and ferrous nitrate; the added amount of the ferrous salt is: 15 to 40 g of ferrous salt is added to every 1 L of the skeleton material hydrogel.

7. The preparation method according to claim 2 or 3, characterized in that: The process of the reverse molding is as follows: the mixed material is placed in a mold, frozen at -25 to -15°C for 10 to 20 hours, then thawed at 15 to 25°C, the cycle is repeated 3 to 6 times, and demolded after molding.

8. The preparation method according to claim 2 or 3, characterized in that: The saturated boric acid solution contains 1% to 3% CaCl2.

9. A Fe(II) composite alkalized corncob carbon source slow-release material, characterized in that: Prepared by the preparation method described in any one of claims 1 to 8; the dry density of the Fe(II) composite alkalized corncob carbon source sustained-release material is 0.720 to 0.760 g / cm 3 , saturated water density is 1.240~1.280g / cm 3 The porosity is 33.0% to 35.0%, the compressive strength is 215 to 220N, and the maximum water absorption swelling degree is 130% to 135%.

10. Use of the Fe(II) composite alkalized corncob carbon source slow-release material according to claim 9 in sewage treatment.

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