Method for preparing biological filler from waste straws and application of biological filler in agricultural sewage treatment

Abstract

The invention discloses a method for preparing a biological filler from waste straws and application of the biological filler in agricultural sewage treatment. The method comprises the following steps: S1, pretreating the straws; s2, physical modification treatment; s3, oxidation modification; s4, preparing the biological filler. According to the biological filler disclosed by the invention, through pretreatment and physical and chemical modification, modified pore channels are more uniform and loose, so that on one hand, microorganisms are favorably attached to the surface of the filler, the biological compatibility of the filler is improved, and on the other hand, the water permeability of the filler is also improved, and the mass transfer performance of the filler is improved; meanwhile, a-OH functional group is introduced through chemical modification, so that the adsorption and enrichment capacity of the biological filler on pollutants such as phosphorus in wastewater is enhanced, a new rural domestic sewage treatment mechanism based on adsorption enrichment-biodegradation regeneration of the novel biological filler is constructed, and staged enrichment and continuous degradation of the pollutants are realized; a new pollutant storage type treatment mode of rural domestic sewage is created, and the method has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of rural domestic sewage treatment technology, specifically to a method for preparing biological packing material from waste straw and its application in agricultural sewage treatment. Background Technology

[0002] With the improvement of living standards and changes in rural lifestyles in my country, the amount of rural domestic sewage generated has also increased. Rural domestic sewage is a major source of non-point source pollution in rural areas and an important factor contributing to eutrophication of rivers and lakes.

[0003] Anaerobic digestion-aerobic oxidation is the most commonly used process for treating rural domestic sewage. In our previous research, patent publication number CN118545838A provided an energy-free rural domestic sewage treatment device, belonging to the field of sewage treatment technology. It includes a filter grit chamber, an anaerobic tank, an aerobic tank, and an aeration pipeline assembly and sewage collection pipeline arranged sequentially along the water flow direction. This invention achieves energy-free aeration and solves the industry problem that the high operating cost of existing rural domestic sewage treatment projects makes them essentially unusable.

[0004] However, traditional biological fillers have poor enrichment performance for pollutants such as phosphorus. To meet the characteristics of large seasonal variations and indirect centralized discharge of agricultural and domestic sewage, huge biological treatment units are required, significantly increasing the construction cost and land area of ​​sewage treatment facilities. While traditional adsorption materials can also efficiently treat rural domestic sewage through adsorption, their poor biocompatibility prevents microorganisms from growing on their surfaces, necessitating manual regeneration of the adsorption fillers after a period of operation. Therefore, developing novel biological fillers that combine good biological activity and pollutant enrichment holds promise for establishing a new mechanism for rural domestic sewage treatment based on "adsorption enrichment—biodegradation and regeneration." This mechanism can address the characteristics of large fluctuations in water quality and intermittent discharge of rural domestic sewage, achieving phased enrichment and continuous degradation of pollutants, thereby pioneering a new paradigm of "pollutant storage-based treatment" for agricultural and domestic sewage. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing biological fillers from waste straw and its application in agricultural wastewater treatment.

[0006] The technical solution of this invention is:

[0007] A method for preparing biological filler from waste straw includes the following steps:

[0008] S1. Straw pretreatment:

[0009] S1-1: After removing impurities from the waste straw, it is successively dried, washed and dried to obtain straw segments;

[0010] S1-2: Crush the straw segments and separate them into high aspect ratio straw segments and low aspect ratio straw segments;

[0011] Wherein, 10 < the length-to-diameter ratio of the high length-to-diameter ratio straw segment < 15, and 2 < the length-to-diameter ratio of the low length-to-diameter ratio straw segment ≤ 10;

[0012] S2. Physical modification treatment: The high aspect ratio straw segment and the low aspect ratio straw segment are physically modified by steam treatment;

[0013] S3. Oxidative modification: The physically modified high aspect ratio straw segments are oxidized to obtain high aspect ratio straw segments containing hydroxyl groups;

[0014] S4. Preparation of biological filler: The high aspect ratio straw segment containing hydroxyl groups and the physically modified low aspect ratio straw segment are mixed evenly at a mass ratio of 1:0.2 to 6 to obtain the biological filler.

[0015] Furthermore, in step S1-1, the drying process is carried out at 45-55°C for 1-2 hours, the washing process is carried out with deionized water 3 times, and the drying process is carried out at 85-90°C for 0.5-1 hours.

[0016] Furthermore, in S2, the steam treatment is carried out under steam conditions of 120-140°C for 30-60 minutes.

[0017] Explanation: High-temperature steam hydrolyzes the hemicellulose in straw (acetyl groups break to produce acetic acid), softens lignin, and destroys the cellulose crystalline region, thus making it more conducive to subsequent oxidative modification.

[0018] Further, in step S3, the oxidative modification involves mixing the physically modified high aspect ratio straw segments with NaIO4 at a ratio of 1g:1mL / 0.1M, stirring at 45-50°C in the dark for 3-4 hours, then adding NaBH4 at a ratio of 1g:2mmol / g, adjusting the pH to 9±0.2, and stirring at room temperature for 1-2 hours to obtain straw powder containing hydroxyl groups.

[0019] Note: The straw powder containing hydroxyl groups obtained through oxidation treatment can further enhance the adsorption of phosphorus and COD in wastewater.

[0020] The present invention also provides the application of the above-mentioned method for preparing biological filler from waste straw in agricultural wastewater treatment, wherein the biological filler prepared in step S4 is applied to the treatment of rural wastewater.

[0021] The beneficial effects of this invention are:

[0022] (1) The biological packing material of the present invention undergoes pretreatment, physical and chemical modification, resulting in more uniform and porous pores. This facilitates microbial attachment to its surface, improving the biocompatibility of the packing material, and also enhances its permeability and mass transfer performance. Simultaneously, the chemical modification introduces -OH functional groups, strengthening the adsorption and enrichment capacity of the biological packing material for pollutants such as phosphorus in wastewater. This gives the biological packing material of the present invention both biocompatibility and excellent pollutant removal capabilities. Furthermore, the raw material for the biological packing material of the present invention is derived from waste straw, providing a new approach for the high-value utilization of agricultural and forestry waste.

[0023] (2) This invention utilizes the good adsorption and enrichment characteristics of biological packing material for pollutants such as phosphorus. When wastewater flows into the packing material, the pollutants in the wastewater are adsorbed and enriched. At the same time, the adsorbed pollutants such as phosphorus are also necessary nutrients for the growth of microorganisms. When no wastewater flows into the packing material, the adsorbed and enriched pollutants are continuously consumed, thereby realizing the "in-situ regeneration" of biological packing material. This ingeniously solves the problem that traditional adsorbents need to be manually regenerated after adsorption saturation, and significantly reduces process maintenance costs.

[0024] (3) Based on the biological packing material of the present invention, a new pollution treatment mechanism of "adsorption enrichment-biodegradation and regeneration" can be constructed. It can achieve phased enrichment and continuous degradation of pollutants in response to the characteristics of large fluctuations in water quality and intermittent discharge of rural domestic sewage, creating a new paradigm of "pollutant storage treatment" for rural domestic sewage. At the same time, this rural domestic sewage treatment model can significantly reduce the construction cost and land area of ​​the treatment unit, and has good prospects for promotion and application.

[0025] (4) The method for preparing biological filler from waste straw of the present invention also provides an extended modification method, in which straw powder containing amino functional groups is obtained by ethylenediamine modification and grafting. Amino groups have strong coordination ability and can form coordination bonds with phosphate ions or interact with them through electrostatic attraction, thereby increasing the adsorption sites for phosphorus and further improving the adsorption capacity for phosphorus. At the same time, it does not damage the original biocompatibility and has strong microbial adhesion ability. The biological filler achieves self-cleaning and self-desorption through the consumption of phosphorus by microorganisms, and maintains good adsorption effect again after the adsorption sites are vacated. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the adsorption effect of different adsorbent materials on COD in wastewater in Experimental Example 2 of the present invention;

[0027] Figure 2 This is a schematic diagram illustrating the adsorption effect of different adsorbent materials on phosphorus in wastewater in Experimental Example 2 of the present invention;

[0028] Figure 3 This is a schematic diagram of the adsorption time and adsorption effect of different fillers in Experimental Example 3 of the present invention;

[0029] Figure 4 This is a schematic diagram of the adsorption effect of pH on different fillers in Experimental Example 4 of the present invention. Detailed Implementation

[0030] Example 1

[0031] A method for preparing biological filler from waste straw includes the following steps:

[0032] S1. Straw pretreatment:

[0033] S1-1: After removing impurities from the waste straw, it is successively dried, washed, and dried to obtain straw segments. The drying process is carried out at 50℃ for 1.5 hours, the washing process is carried out with deionized water 3 times, and the drying process is carried out at 86℃ for 0.75 hours.

[0034] S1-2: Crush the straw segments and separate the high aspect ratio straw segments and the low aspect ratio straw segments;

[0035] Among them, the aspect ratio of the high aspect ratio straw segment is 12, and the aspect ratio of the low aspect ratio straw segment is 5;

[0036] S2. Physical modification treatment: High length-to-diameter ratio straw segments and low length-to-diameter ratio straw segments are physically modified by steam treatment. The steam treatment is carried out at 130℃ for 45 minutes.

[0037] S2-2: The straw segments with low length-to-diameter ratio are physically modified by corona discharge treatment. During the corona discharge treatment, the straw segments with low length-to-diameter ratio are treated at 20kV for 2min.

[0038] S3. Oxidative modification: The physically modified high aspect ratio straw segments were oxidized to obtain high aspect ratio straw segments containing hydroxyl groups. The oxidative modification involved mixing the physically modified high aspect ratio straw segments with NaIO4 at a ratio of 1g:1mL / 0.1M. The mixture was stirred at 46℃ in the dark for 3.5h, and then NaBH4 was added and mixed at a ratio of 1g:2mmol / g. The pH was adjusted to 9, and the mixture was stirred at room temperature for 1.5h to obtain straw powder containing hydroxyl groups.

[0039] S4. Preparation of biological filler: Mix high aspect ratio straw segments containing hydroxyl groups with physically modified low aspect ratio straw segments at a mass ratio of 1:1 to obtain biological filler.

[0040] Example 2

[0041] The difference between this embodiment and Embodiment 1 is that:

[0042] S4. Preparation of biological filler: The high aspect ratio straw segments containing hydroxyl groups and the physically modified low aspect ratio straw segments are mixed evenly at a mass ratio of 1:0.2 to obtain the biological filler.

[0043] Example 3

[0044] The difference between this embodiment and Embodiment 1 is that:

[0045] S4. Preparation of biological filler: The high aspect ratio straw segments containing hydroxyl groups and the physically modified low aspect ratio straw segments are mixed evenly at a mass ratio of 1:0.5 to obtain the biological filler.

[0046] Example 4

[0047] The difference between this embodiment and Embodiment 1 is that:

[0048] S4. Preparation of biological filler: The high aspect ratio straw segments containing hydroxyl groups and the physically modified low aspect ratio straw segments are mixed evenly at a mass ratio of 1:2 to obtain the biological filler.

[0049] Example 5

[0050] The difference between this embodiment and Embodiment 1 is that:

[0051] S4. Preparation of biological filler: The high aspect ratio straw segments containing hydroxyl groups and the physically modified low aspect ratio straw segments are mixed evenly at a mass ratio of 1:4 to obtain the biological filler.

[0052] Example 6

[0053] The difference between this embodiment and Embodiment 1 is that:

[0054] S4. Preparation of biological filler: The high aspect ratio straw segments containing hydroxyl groups and the physically modified low aspect ratio straw segments are mixed evenly at a mass ratio of 1:6 to obtain the biological filler.

[0055] Note: Examples 1-6 provide several biological packing materials with different parameter ratios. Generally, after straw adsorbs phosphorus, smaller-sized biological packing materials are more prone to desorption. Straw segments with low aspect ratios have a larger specific surface area and higher surface energy, which makes the surface forces on phosphorus ions adsorbed on their surface relatively weaker, making it easier to overcome the adsorption force and desorb when external conditions change. In contrast, straw segments with high aspect ratios have a smaller specific surface area and relatively fewer interaction sites between phosphorus ions and the adsorbent surface, but the binding force at each site may be stronger, making desorption relatively more difficult. The purpose of mixing two types of straw with different aspect ratios is that if a single aspect ratio straw is used, a large number of ineffective gaps are formed between the straws due to the "bridging effect". Appropriately mixing low aspect ratio straw with high aspect ratio straw, or mixing high aspect ratio straw with low aspect ratio straw, can fill the gaps between high aspect ratio straws. Low aspect ratio straw alone, due to its small size, is greatly affected by water supply and is lost in large quantities under the flushing of water. Therefore, in actual use, we can make a reasonable selection in Examples 1 to 6 according to the pollutant content of the wastewater and the need for desorption and recovery.

[0056] Example 7

[0057] The difference between this embodiment and Embodiment 1 is that:

[0058] S1-1: After removing impurities from the waste straw, it is successively dried, washed, and dried to obtain straw segments. The drying process is carried out at 45℃ for 1 hour, the washing process is carried out with deionized water 3 times, and the drying process is carried out at 85℃ for 0.5 hours.

[0059] Example 8

[0060] The difference between this embodiment and Embodiment 1 is that:

[0061] S1-1: After removing impurities from the waste straw, it is successively dried, washed, and dried to obtain straw segments. The drying process is carried out at 55℃ for 2 hours, the washing process is carried out with deionized water 3 times, and the drying process is carried out at 90℃ for 1 hour.

[0062] Example 9

[0063] The difference between this embodiment and Embodiment 1 is that:

[0064] The aspect ratio of the straw segment with a high aspect ratio is 14, while that of the straw segment with a low aspect ratio is 8.

[0065] Example 10

[0066] The difference between this embodiment and Embodiment 1 is that:

[0067] The aspect ratio of the straw segment with a high aspect ratio is 11, while that of the straw segment with a low aspect ratio is 3.

[0068] Example 11

[0069] The difference between this embodiment and Embodiment 1 is that:

[0070] S2-1: Physically modify the high length-to-diameter ratio straw segments by steam treatment. During steam treatment, the high length-to-diameter ratio straw segments are treated under steam conditions at 120℃ for 30 minutes.

[0071] S2-2: The straw segments with low length-to-diameter ratio are physically modified by corona discharge treatment. During the corona discharge treatment, the straw segments with low length-to-diameter ratio are treated at 5kV for 1min.

[0072] Example 12

[0073] The difference between this embodiment and Embodiment 1 is that:

[0074] S2-1: Physically modify the high length-to-diameter ratio straw segments by steam treatment. During steam treatment, the high length-to-diameter ratio straw segments are treated at 140℃ for 60 minutes.

[0075] S2-2: The straw segments with low length-to-diameter ratio are physically modified by corona discharge treatment. During the corona discharge treatment, the straw segments with low length-to-diameter ratio are treated at 30kV for 3min.

[0076] Explanation: By bombarding the surface of straw with high-energy electrons / ions, micron-sized pits and cracks are formed, increasing its specific surface area, making it more suitable for the physical modification of straw segments with low aspect ratio.

[0077] Example 13

[0078] The difference between this embodiment and Embodiment 1 is that:

[0079] S3. Oxidative Modification: The physically modified high aspect ratio straw segments were oxidized to obtain high aspect ratio straw segments containing hydroxyl groups. The oxidative modification involved mixing the physically modified high aspect ratio straw segments with NaIO4 at a ratio of 1g:1mL / 0.1M. The mixture was stirred at 45℃ in the dark for 3 hours, and then NaBH4 was added and mixed at a ratio of 1g:2mmol / g. The pH was adjusted to 8.8, and the mixture was stirred at room temperature for 1 hour to obtain straw powder containing hydroxyl groups.

[0080] Example 14

[0081] The difference between this embodiment and Embodiment 1 is that:

[0082] S3. Oxidative Modification: The physically modified high aspect ratio straw segments were oxidized to obtain high aspect ratio straw segments containing hydroxyl groups. The oxidative modification involved mixing the physically modified high aspect ratio straw segments with NaIO4 at a ratio of 1g:1mL / 0.1M. The mixture was stirred at 50℃ in the dark for 4 hours, and then NaBH4 was added and mixed at a ratio of 1g:2mmol / g. The pH was adjusted to 9.2, and the mixture was stirred at room temperature for 2 hours to obtain straw powder containing hydroxyl groups.

[0083] Example 15

[0084] The difference between this embodiment and Embodiment 1 is that:

[0085] After S3 and oxidative modification, further modification will be carried out:

[0086] Amination treatment: The straw powder containing hydroxyl groups was soaked in N,N-dimethylformamide for 11 hours, then dried. The straw powder containing hydroxyl groups was then mixed with an 8% epichlorohydrin solution and reacted at 72°C for 1.5 hours. After cooling to room temperature, the residue was filtered and washed three times with deionized water until neutral. The residue was then dried at 58°C. Subsequently, the straw powder containing hydroxyl groups was mixed with a 15% ethylenediamine solution at a mass-to-volume ratio of 1 g:0.9 mL. The mixture was reacted at 72°C for 1.5 hours and cooled to room temperature. After filtering, the residue was washed three times with deionized water until neutral. The residue was then dried at 58°C to obtain straw powder grafted with amino groups.

[0087] Example 16

[0088] The difference between this embodiment and embodiment 15 is that:

[0089] Amination treatment: The straw powder containing hydroxyl groups was soaked in N,N-dimethylformamide for 10 hours, then removed and dried. The straw powder containing hydroxyl groups was then mixed with a 5% epichlorohydrin solution and reacted at 70°C for 1 hour. After cooling to room temperature, the residue was filtered and washed three times with deionized water until neutral. It was then dried at 55°C. Subsequently, the straw powder containing hydroxyl groups was mixed with a 15% ethylenediamine solution at a mass-to-volume ratio of 1 g:0.8 mL and reacted at 70°C for 1 hour. After cooling to room temperature, the residue was filtered and washed three times with deionized water until neutral. It was then dried at 55°C to obtain straw powder grafted with amino groups.

[0090] Example 17

[0091] The difference between this embodiment and embodiment 15 is that:

[0092] Amination treatment: The straw powder containing hydroxyl groups was soaked in N,N-dimethylformamide for 12 hours, then removed and dried. The straw powder containing hydroxyl groups was then mixed with a 10% epichlorohydrin solution and reacted at 75°C for 2 hours. After cooling to room temperature, the residue was filtered and washed three times with deionized water until neutral. It was then dried at 60°C. Subsequently, the straw powder containing hydroxyl groups was mixed with a 15% ethylenediamine solution at a mass-to-volume ratio of 1 g:1 mL. The mixture was reacted at 75°C for 2 hours and cooled to room temperature. After filtering, the residue was washed three times with deionized water until neutral. It was then dried at 60°C to obtain straw powder grafted with amino groups.

[0093] Example 18

[0094] This embodiment is an application of the method for preparing biological filler from waste straw in Example 1 in agricultural wastewater treatment. The biological filler prepared in S4 is applied to the treatment of rural wastewater, and the amount of biological filler added is 3g / L.

[0095] Example 19

[0096] The difference between this embodiment and embodiment 18 is that:

[0097] The amount of biological packing material added is 1 g / L.

[0098] Example 20

[0099] The difference between this embodiment and embodiment 18 is that:

[0100] The amount of biological packing material added is 5 g / L.

[0101] Note: In Examples 18, 19, and 20, the amount of biological packing material added was positively correlated with the phosphorus content in the wastewater.

[0102] Example 21

[0103] This embodiment is an application of the method for preparing biological packing material from waste straw in Example 15 to agricultural wastewater treatment, where the biological packing material prepared in S4 is applied to the treatment of rural wastewater.

[0104] Experimental Example 1

[0105] Below, we conduct experimental research on the adsorption performance of several biological packing materials prepared in this invention, and compare them with existing packing materials. The main focus is on exploring the removal rates of phosphorus and COD from wastewater by different packing materials. The existing packing materials selected are:

[0106] Comparative Example 1: Straw segments with high aspect ratios that underwent only the physical modification described in Example 1;

[0107] Comparative Example 2: Straw segments with low aspect ratios that underwent only the physical modification described in Example 1;

[0108] Comparative Example 3: Hydroxyapatite (HAP) phosphorus adsorbent;

[0109] In the indoor test phase, we used the above-mentioned packing materials, as well as the biological packing materials in Examples 1 and 15, to adsorb phosphorus-containing simulated wastewater. The addition amount was 2 g / L, the phosphorus concentration was 10 mg / L, the hydraulic retention time was 24 h, the pH was 7, and the temperature was 25 °C. The treatment results are shown in the table below:

[0110] Table 1. Removal rates of phosphorus and COD from wastewater by different packing materials.

[0111] Case Phosphorus removal rate % COD removal rate % Example 1 81.7 79.2 Example 15 82.0 81.7 Comparative Example 1 41.7 72.1 Comparative Example 2 43.9 74.3 Comparative Example 3 88.5 25.8

[0112] It can be seen that the biological packing material of the present invention can simultaneously achieve good adsorption and removal effects on phosphorus and COD in wastewater, while the traditional hydroxyapatite (HAP) phosphorus adsorbent cannot achieve adsorption and removal effects on COD in wastewater. The overall removal effect of preliminarily physically modified straw on phosphorus and COD is also poor. Therefore, the biological packing material of the present invention has certain commercial value in wastewater treatment. At the same time, in the comparison between Example 1 and Example 15, we found that Example 15 underwent further modification, which slightly improved the performance of the biological packing material. This is for the same reason as analyzed above. However, considering factors such as cost, the biological packing material in Example 1 may have better commercial value.

[0113] Experimental Example 2

[0114] Below, we will discuss the continuous adsorption capacity of the biological packing material prepared in Example 1 of this invention. In the indoor test stage, we used the biological packing material in Example 1 to adsorb simulated wastewater containing phosphorus and COD. The simulated wastewater was rural domestic sewage with a TP content of 4.3 mg / L and a COD content of 386. We conducted continuous adsorption under real rural water conditions, collecting effluent data every other day for a total of 10 working cycles, maintaining a pH of 7 and a temperature of 25°C. The added microorganisms were polyphosphate-accumulating bacteria and Pseudomonas spp.

[0115] In an aerobic environment, polyphosphate-accumulating bacteria (PABs) utilize the energy generated from the decomposition of organic matter to absorb phosphorus exceeding their physiological needs from wastewater, synthesizing and storing polyphosphate particles. In an anaerobic environment, PPAs decompose intracellular polyphosphates, releasing phosphorus while simultaneously absorbing volatile fatty acids and other organic matter from the wastewater. Through this process of alternating aerobic and anaerobic cycles in the biological treatment system, PPAs remove phosphorus from wastewater. Simultaneously, the microorganisms need to adapt to the new environment, including wastewater composition, temperature, and pH. During this stage, the number of microorganisms remains relatively stable, with slow growth. They adjust their metabolic mechanisms, synthesizing enzymes and proteins to adapt to the new environment, preparing for subsequent growth and reproduction. Therefore, we first culture the microorganisms with the packing material for 3 days. Once the microorganisms have adapted to the wastewater environment, they enter a rapid growth phase. At this time, the wastewater is rich in nutrients, and the environmental conditions are suitable. The microorganisms utilize organic matter, nitrogen, phosphorus, and other nutrients in the wastewater for massive growth and reproduction, resulting in exponential growth in numbers. This stage is the period of fastest growth and strongest activity for the microorganisms, during which the entire system stabilizes before being put into operation. The final treatment results are as follows: Figure 1 and Figure 2 As shown;

[0116] It can be seen that after adding the biological packing material in Example 1 of the present invention, both phosphorus and COD in the wastewater are effectively removed, and the removal process is relatively stable. In contrast, the traditional biological packing material in Comparative Example 2 can effectively remove COD (<20mg / L, meeting the standard), but its effect on phosphorus removal is limited (>2mg / L, exceeding the standard). In Comparative Example 3, the phosphorus adsorbent can quickly reduce the phosphorus content in the wastewater in the early stage of treatment (<0.1mg / L, meeting the standard), but the effect is not good after continued use, and a rebound will occur. This is because the adsorption reaches saturation, and the final phosphorus content in the wastewater is >2mg / L, exceeding the standard.

[0117] This is because the phosphorus adsorbed on the packing material is also a necessary nutrient for microbial growth. The phosphorus stored in the biological packing material is consumed by the microorganisms, and the adsorption sites are released, achieving a dynamic balance in the internal microsystem of the biological packing material. This indicates that the biological packing material does not affect the adhesion of microorganisms to the wall while adsorbing phosphorus in wastewater, and the packing material has good biocompatibility. At the same time, in subsequent cycles, the position of phosphorus absorption by microorganisms on the packing material tends to be flat, indicating that the ability of microorganisms to absorb phosphorus is also continuously decreasing. This may be because when nutrients in wastewater are consumed in large quantities, nutrients in the environment become scarce, and metabolic products accumulate excessively, which inhibits or toxicizes microorganisms. As a result, the growth rate of microorganisms decreases significantly, the death rate gradually exceeds the growth rate, and the number of microorganisms begins to decrease gradually, entering the decline phase. However, overall, the packing material and microorganisms can still achieve a high comprehensive phosphorus removal effect.

[0118] Experimental Example 3

[0119] Having established that the biological packing material of Example 15 has a better adsorption effect, we will now continue to explore the adsorption performance of the biological packing material.

[0120] The experimental method was the same as in Example 1, with control groups set up as well. Control group 1 consisted of chitosan granules, control group 2 consisted of straw biochar granules, and control group 3 consisted of unsulfurized straw powder granules. The results are as follows: Figure 3 As shown.

[0121] It can be seen that the modified straw biological packing prepared in Example 15 exhibits a rapid stage (0-12h) and a slow stage (12-30h) for the adsorption of phosphorus in wastewater. Among them, chitosan particles (control group 1) showed desorption problems in the later stage of adsorption, while the modified straw biological packing prepared in this application maintained a relatively stable adsorption amount and had the best overall adsorption effect. The adsorption reached stability over time and reached equilibrium after 24h. This is because there are many adsorption sites on the surface of the modified straw biological packing in the early stage of adsorption, and phosphorus in wastewater can easily diffuse to the surface of the packing and bind to it. When the adsorption sites are saturated, the adsorption rate slows down.

[0122] Furthermore, the adsorption effect was the worst when using straw biochar granules alone (control group 2), while the adsorption effect of using unsulfurized modified straw powder granules (control group 3) was better than that of chitosan granules (control group 1). This indicates that the modification in this invention has a significant impact on the final adsorption effect of the filler. After modification, the pore channels are more uniform and loose, which is conducive to loading microorganisms and has good water permeability. It can have good adsorption, fixation and blocking functions for phosphorus in wastewater, and also has a certain degree of biocompatibility.

[0123] Experiment Example 4

[0124] We then investigated the effect of pH on the adsorption efficiency of the modified straw bio-filler of this invention, and the results are as follows: Figure 4 As shown.

[0125] It can be seen that pH has a significant impact on the adsorption effect of the two materials. Under acidic conditions, the adsorption efficiency of both materials is improved to a certain extent. Acidic conditions cause the surface of the filler to be protonated and positively charged, which enhances electrostatic attraction. As the pH increases, electrostatic repulsion is formed between the material surface and phosphorus, especially the chitosan particles in control group 1, which have stronger electrostatic repulsion. The modified straw biological filler in this invention has better anti-static repulsion, and chitosan is easily decomposed when the pH is less than 5. This is also the reason why the modified straw biological filler loaded with iron-manganese composite oxide in this invention is superior to control group 1.

Claims

1. A method for preparing biological filler from waste straw, characterized in that, Includes the following steps: S1. Straw pretreatment: S1-1: After removing impurities from the waste straw, it is successively dried, washed and dried to obtain straw segments; S1-2: Crush the straw segments and separate them into high aspect ratio straw segments and low aspect ratio straw segments; Wherein, 10 < the length-to-diameter ratio of the high length-to-diameter ratio straw segment < 15, and 2 < the length-to-diameter ratio of the low length-to-diameter ratio straw segment ≤ 10; S2. Physical modification treatment: The high aspect ratio straw segment and the low aspect ratio straw segment are physically modified by steam treatment; S3. Oxidative modification: The physically modified high aspect ratio straw segments are oxidized to obtain high aspect ratio straw segments containing hydroxyl groups; S4. Preparation of biological filler: The high aspect ratio straw segment containing hydroxyl groups and the physically modified low aspect ratio straw segment are mixed evenly at a mass ratio of 1:0.2 to 6 to obtain the biological filler.

2. The method for preparing biological filler from waste straw according to claim 1, characterized in that, In step S1-1, the drying process is carried out at 45-55℃ for 1-2 hours, the washing process is carried out with deionized water 3 times, and the drying process is carried out at 85-90℃ for 0.5-1 hours.

3. The method for preparing biological filler from waste straw according to claim 1, characterized in that, In S2, the steam treatment is carried out at 120-140°C for 30-60 minutes.

4. The method for preparing biological filler from waste straw according to claim 1, characterized in that, In step S3, the oxidative modification involves mixing the physically modified high aspect ratio straw segments with NaIO4 at a ratio of 1g:1mL / 0.1M. The mixture is stirred at 45-50°C in the dark for 3-4 hours, followed by the addition of NaBH4 at a ratio of 1g:2mmol / g. The pH is adjusted to 9±0.2, and the mixture is stirred at room temperature for 1-2 hours to obtain straw powder containing hydroxyl groups.

5. The application of the method for preparing biological filler from waste straw according to any one of claims 1 to 4 in agricultural wastewater treatment, characterized in that, The biological packing material prepared in step S4 is applied to rural domestic sewage treatment.

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