Preparation method and application of wood fiber-based bionic EPS

Abstract

The present invention discloses a preparation method and application of a wood fiber-based bionic EPS, belonging to the technical field of sewage treatment. The present invention synthesizes a wood fiber-based bionic EPS through the electrostatic interaction of BSA and CDAMC, adds the wood fiber-based bionic EPS to the SBR, and operates in the mode of water intake, stillness, aeration, sedimentation and water discharge. The SBR is completely granulated after 4 to 10 days of operation, and the aerobic granular sludge can still maintain a stable structure after long-term operation. The preparation process of the present invention is green and simple, low-cost, and easy to be applied in engineering. The prepared wood fiber-based bionic EPS can control the size of aerobic granular sludge, promote sludge granulation, shorten the sludge granulation time, and improve the stability of the formed aerobic granular sludge.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and more specifically, relates to a preparation method and application of wood fiber-based bionic EPS. Background Art

[0002] Aerobic granular sludge (AGS) is a wastewater treatment technology with broad application prospects. Compared with activated sludge, it has more significant advantages, such as compact structure, high sedimentation, tolerance to high organic loads and toxicity, and the ability to simultaneously remove nitrogen and phosphorus in a single reactor. In addition, the floor space and operating energy consumption of wastewater treatment plants using the AGS process can be reduced by 75% and 25%, respectively. However, this technology still has problems such as long startup time and easy instability of the AGS structure in long-term operation. These problems are the main bottlenecks in the engineering application of AGS technology.

[0003] To address these issues, researchers have conducted extensive research on accelerating granulation and improving the stability of AGS. Granular sludge formation primarily involves five processes: intercellular interactions, bacterial attachment, self-fixation and aggregation, coagulation by extracellular polymeric substances (EPS), and hydraulic shear, ultimately resulting in densely structured granular sludge. Except for the first step, all other processes are essential for EPS. Therefore, microbial extracellular polymeric substances (EPS) play a crucial role in the formation and stability of AGS. As an adhesive macromolecule, EPS promotes granulation through hydrophobic interactions, adsorption, charge neutralization, adsorption bridging, and sol-gel transition. Furthermore, a reduction in EPS can lead to bacterial detachment from microbial aggregates, hindering biomass accumulation. PN, the primary hydrophobic component of EPS, strengthens the structural stability of microbial aggregates by reducing microbial surface charge and increasing the hydrophobicity of microbial aggregates. It can also cross-link with PS (alginate and granulan) to form a stable hydrogel structure, promoting the adhesion of functional microorganisms. Tay et al. established a "polysaccharide mechanism," proposing that PS can improve microbial adhesion and enhance the structural stability of AGS.

[0004] How to increase the EPS content in the system is important for the rapid granulation and stabilization of granular sludge. It is reported that metal cations and polyaluminum chloride can promote aerobic granulation because they can promote bacterial aggregation by neutralizing the negative charge on the surface of microorganisms and promoting the production of EPS. However, the continuous excessive addition of cationic precipitation in AGS leads to a high ash content in the sludge, which reduces the biological activity of AGS and the disposal of sludge with high metal content is also a serious problem. Liang et al. extracted MBF from the sludge. After adding MBF, the EPS content in the reactor was increased, the hydrolysis resistance of aerobic granules was enhanced, and the formation of aerobic granules was promoted. However, the MBF extraction process is too slow. Therefore, sustainable, natural, and bio-based alternatives are needed to accelerate aerobic sludge granulation. Summary of the Invention

[0005] In response to the above-mentioned problems in the prior art, the present invention aims to provide a method for preparing a wood fiber-based bionic EPS, which is environmentally friendly, simple, and low-cost. Another technical problem to be solved by the present invention is to provide a wood fiber-based bionic EPS that is natural and sustainable. Yet another technical problem to be solved by the present invention is to provide a wood fiber-based bionic EPS for use in enhancing aerobic sludge granulation. The bionic EPS can control the size of aerobic granular sludge, promote sludge granulation, shorten the sludge granulation time, and improve the stability of the formed aerobic granular sludge.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] The invention discloses a method for preparing wood fiber-based bionic EPS, which synthesizes the wood fiber-based bionic EPS through the electrostatic interaction of BSA and CDAMC.

[0008] Preferably, the mass ratio of CDAMC to BSA is 200:60-120.

[0009] A method for preparing wood fiber-based bionic EPS, comprising the following steps:

[0010] 1) Preparation of DAMC fibers

[0011] The dried hardwood pulp is thoroughly disintegrated and homogenized, and then soaked in deionized water until the fibers are fully swollen. Excess water is then poured out, and NaIO4 and sodium chloride are dissolved in deionized water. The soaked wood pulp is added to the solution and stirred at room temperature. Ethylene glycol is then added to quench the residual periodate, thereby obtaining DAMC fibers.

[0012] 2) Preparation of CDAMC fibers

[0013] DAMC fibers, GT solids, sodium chloride, and deionized water were mixed to obtain a suspension, and the pH value of the suspension was adjusted to 4.5 with hydrochloric acid. The suspension was stirred at room temperature, filtered, washed with deionized water, and freeze-dried to obtain brown CDAMC.

[0014] 3) Preparation of cellulose-based biomimetic EPS

[0015] CDAMC and BSA were dissolved in deionized water, mixed completely and allowed to stand to obtain cellulose-based biomimetic EPS.

[0016] Preferably, the mass ratio of the dry hardwood pulp to NaIO4 and sodium chloride in step 1) is 1:0.83-0.98:0.78, and the mass ratio of the dry hardwood pulp to ethylene glycol is 1:1.11.

[0017] Preferably, the mass ratio of DAMC fiber to GT solid, sodium chloride and deionized water in step 2) is 0.5:0.3 to 0.5:1.2:40.

[0018] The preparation method of any one of the wood fiber-based bionic EPSs can obtain the wood fiber-based bionic EPS.

[0019] The application of the wood fiber-based bionic EPS in enhancing aerobic sludge granulation.

[0020] The application in enhanced aerobic sludge granulation comprises the following steps: adding wood fiber-based bionic EPS into the SBR, and operating the SBR in the manner of water inlet, stationary state, aeration, sedimentation and water outlet, with the SBR operating for 4 to 10 days.

[0021] Preferably, the dosage of the wood fiber-based bionic EPS is 0.05-0.10 g / L.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The present invention synthesizes cellulose-based biomimetic EPS through the electrostatic interaction of BSA and CDAMC, which has the advantages of green and simple process, low cost, and easy engineering application;

[0024] 2) The present invention significantly shortens the time required for aerobic granular sludge formation by preparing wood fiber-based bionic EPS. Furthermore, good sludge settling performance can be achieved in the early stages of the reactor startup phase, which is beneficial to the stable operation of the aerobic granular sludge system.

[0025] 3) The wood fiber-based bionic EPS prepared by the present invention can serve as a supporting medium for microbial attachment in activated sludge, promote the granulation process, and shorten the granulation time;

[0026] 4) The cellulose-based biomimetic EPS prepared by this invention can control the size of AGS and promote the secretion of PS, thereby enhancing the long-term stability of AGS. The resulting AGS has excellent removal performance for COD, ammonia nitrogen, and TN in wastewater. The addition of cellulose-based biomimetic EPS enriches the AGS with nitrifying and denitrifying bacteria, improving the nitrification and denitrification performance of the AGS. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the reaction diagram of the lignocellulose-based biomimetic EPS of the present invention;

[0028] Figure 2 SEM images of each step in the preparation of lignocellulose-based biomimetic EPS; a is the starting cellulose fiber, b is DAMC fiber, c / d / h is CDAMC fiber, e / i is CDAMC@BSA, and f / j is EPS;

[0029] Figure 3 FT-IR spectra and XRD spectra of cellulose pulp, DAMC, CDMAC, CDAMC@BSA and EPS; (a) is the FT-IR spectrum, (b) is the XRD spectrum;

[0030] Figure 4 High-resolution C1s spectra; (a) is wood pulp fiber, (b) is CDAMC, (c) is CDAMC@BSA, and (d) is EPS;

[0031] Figure 5 Figure 2 is the effect of different CDMAC dosages on sludge settling performance and the change of Zeta potential under the optimal ratio; Figure (a) is the effect of different CDMAC dosages on sludge settling performance, and (b) is the change of Zeta potential under the optimal ratio;

[0032] Figure 6 The morphology of the sludge before and after adding cationic fiber in different sludge culture periods in SBR: (a) and (c) are without adding material, (b) and (d) are with adding material;

[0033] Figure 7 The graph of the change of sludge concentration and sludge volume index during the operation of the reactor; (a) is the sludge concentration, (b) is the sludge index;

[0034] Figure 8 The particle size distribution diagram of the initial and stable period sludge in the reactor; ad in the figure corresponds to the sludge particle size in R1-R4 respectively, and D10 in the legend is the particle size at 10% of the cumulative distribution, D50 is the particle size at 50% of the cumulative distribution, and D90 is the particle size at 90% of the cumulative distribution;

[0035] Figure 9 The figures are the performance diagrams of the reactor for wastewater treatment; (a) is the COD degradation curve, (b) is the NH4+-N degradation curve, and (c) is the NO2-N and NO3-N change curves;

[0036] Figure 10 Optical photographs of sludge in the reactor at 45 days; in the figure, a is no material added, b is added with CDAMC@BSA-60 solution, c is added with CDMAC solution, and d is added with CDAMC@BSA-120 solution;

[0037] Figure 11 The scanning electron micrographs on day 45 show R1 (a and e), R2 (b and f), R3 (c and g), and R4 particles (d and h).

[0038] Figure 12 Diagram of the mechanism of aerobic sludge granulation and its structural stabilization. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described below in conjunction with specific embodiments. Unless otherwise specified in the following embodiments, the technical means used are conventional means well known to those skilled in the art.

[0040] The sludge in the embodiment is selected from the concentrated sludge of Nanjing Chengbei Sewage Treatment Plant as the inoculated sludge of SBR;

[0041] Hardwood pulp was purchased from Dongjian Pulp & Paper Co., Ltd.; sodium chloride and ethylene glycol were purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium periodate and trimethylammonium chloride acetylhydrazine (GT) were purchased from Aladdin Biochemical Technology Co., Ltd.; hydrochloric acid was purchased from Nanjing Chemical Reagent Co., Ltd.

[0042] The synthetic culture medium used in AGS includes 600 mg / L chemical oxygen demand (COD), 60 mg / L NH4 + -N(NH4Cl), 10mg / L PO4 3- -P(K2HPO4 / KH2PO4), 25mg / L Mg 2+ (MgSO4.7H2O), 30mg / L Ca 2+ (CaCl2) and 1.0 mL / L of trace element solution. The pH was maintained within the range of 7.0-7.5. After inoculation, the initial mixed liquor suspended solids (MLSS) in each reactor was approximately 3000 ± 250 mg / L, and the 5-minute sedimentation volume index (SVI5) was approximately 125 ± 10 mL / g.

[0043] The sequencing batch reactor (SBR) had an effective volume of 2 L, a diameter of 6 cm, and a height of 40 cm. Its operating cycle was 4 hours, consisting of 2 minutes of water inlet, 42-52 minutes of quiescence, 180 minutes of aeration, 5-15 minutes of sedimentation, and 1 minute of water outlet. Aeration was continuously introduced via an electromagnetic pump, maintaining a surface gas upflow velocity of 1.5 cm / s. Dissolved oxygen (DO) was greater than 6 mg / L, and wastewater was withdrawn from the mid-height of the SBR, with a volume exchange ratio of 50% per cycle. The sludge retention time (SRT) was approximately 20 days, and the hydraulic retention time (HRT) was approximately 8 hours. All experiments were conducted at room temperature.

[0044] Example 1

[0045] A method for preparing wood fiber-based bionic EPS comprises the following steps:

[0046] 1) Preparation of DAMC fibers

[0047] 1 g of dry broadleaf pulp was thoroughly disintegrated and homogenized using a decomposer (PJ02), soaked in 50 mL of deionized water, and soaked for 2 h until the fiber was fully swollen. The excess water was poured out, and then 0.98 g of NaIO4 and 0.78 g of sodium chloride were dissolved in deionized water. The soaked wood pulp was added to the solution and stirred at room temperature for 24 h. 1 mL of ethylene glycol was then added to quench the residual periodate to obtain DAMC fiber.

[0048] 2) Preparation of CDAMC fibers

[0049] 0.5 g of DAMC fiber, 0.5 g of GT solid, 1.2 g of sodium chloride and 40 g of deionized water were mixed to obtain a suspension. The pH value of the suspension was adjusted to 4.5 with hydrochloric acid, stirred at room temperature for 25 h, filtered with a Buchner funnel, washed three times with deionized water, and freeze-dried to obtain brown CDAMC.

[0050] 3) Preparation of wood fiber-based biomimetic EPS

[0051] 0.2 g of CDAMC was dissolved in deionized water with 60 mg and 120 mg of BSA, respectively. The mixture was completely mixed after magnetic stirring for 30 min and allowed to stand for 15 min to eliminate bubbles, finally obtaining CDAMC@BSA-60 colloidal solution and CDAMC@BSA-120 colloidal solution.

[0052] like Figure 2As shown in Figure 1, after periodate oxidation, DAMC fibers showed no significant difference from original cellulose fibers, with both fibers having a diameter of approximately 30 μm. However, after reacting with GT, the DAMC fiber diameter expanded more than threefold, reaching approximately 100 μm (Figure c). This is due to the repulsive effect of the positive charge carried by the cationic DAMC fibers, which breaks down the cellulose structure into nanostructures. CDMAC and BSA can be bound together through electrostatic and hydrogen bonding. As shown in Figure i, spheres can be seen on the surface of CDMAC, indicating that bovine serum albumin has been adsorbed on the fiber surface. CDMAC@BSA (wood fiber-based biomimetic EPS) differs significantly from EPS in morphology. EPS appears as granular, adherent material, while CDMAC@BSA is primarily fibrous.

[0053] like Figure 3 As shown in a, after oxidation with NaIO4, DAMC -1 The characteristic absorption peak of aldehyde group appeared at 880 cm -1 The hemiacetal peak intensity at 1650 cm-1 is due to the carbonyl stretching and the hemiacetal bond formed by the dialdehyde group, indicating that the cellulose was successfully oxidized to aldehyde cellulose. An important evidence of the successful grafting of GT and DAMC fibers is the peak at 1650 cm-1. -1 to 1690cm -1 In addition, due to the reaction of the aldehyde group with the hydroxyl group on the cellulose, 1732 cm -1 The carbonyl peak intensity at 100 nm disappeared, indicating that GT was successfully grafted onto DAMC fibers. CDMAC and BSA were combined through electrostatic and hydrogen bonding, and the amide bond strength was enhanced, indicating that the biomimetic EPS was successfully synthesized.

[0054] like Figure 3As shown in b, the crystal structures of virgin wood pulp, DAMC and CDAMC were analyzed by XRD. The diffraction peaks of wood pulp cellulose appear at 2θ=15.98°, 22.54° and 34.4°, which represent the (110), (200) and (004) plane structures of cellulose I, respectively. The crystallinity index (CI) of cellulose content is defined by Segal et al.: CI=[(I200-IAM) / I200]*100%. Where I200 is the intensity of the (200) plane reflection, and IAM is 2θ=18°, corresponding to the minimum value between planes (200) and (110) in the diffraction pattern. Calculated by the "formula" CI=[(I200-IAM) / I200]*100%, it can be seen that the CI of the initial wood pulp fiber is 56.9%, which decreases to 21.62% after periodate oxidation. The amorphous and crystalline surfaces of cellulose are more susceptible to periodate oxidation. This decrease in crystallinity is due to the opening of glucose rings and partial disruption of the ordered structure of the cellulose crystalline regions. The CI of CDAMC fibers decreased to 15.49%, a result of further modification of DAMC fibers with GT. Complexation of BSA with CDAMC further reduced crystallinity, but the change was minimal.

[0055] like Figure 4 As shown, deconvolution of the C1s of wood pulp fiber and CDAMC reveals three similar peaks: Peak 1 at a binding energy of 285 eV corresponds to a carbon atom bound to another carbon atom (C) or a hydrogen atom (CH), Peak 286.6 eV represents a carbon atom bound to a non-carbon oxygen atom (C), and Peak 287.8 eV corresponds to a carbon atom bound to a carbonyl oxygen atom (C=O) or two non-carbonyl oxygen atoms (OCO). For CDAMC, a fourth peak at 288.9 eV corresponds to the O=CN and CN peaks of the GT molecule. The C=N peak is located in the same binding energy region as the CO in Peak 2. Compared to wood pulp fiber, the proportion of Peak 3 in CDAMC is significantly increased, while the proportion of Peak 2 is significantly decreased, indicating that sodium periodate successfully oxidized the hydroxyl groups to aldehyde groups. These aldehyde groups are still present after the reaction with GT, resulting in the appearance of C=N bonds in Peak 2. XPS analysis further confirms that cationic incorporation has occurred. After CDAMC is compounded with BSA, three peaks appear, and all three peaks are significantly enhanced. The enhancement of carbonyl groups is related to the amide bonds in the proteins in bovine serum albumin. In addition, the prepared CDAMC@BSA has close similarities with EPS in functional groups and composition.

[0056] like Figure 5As shown in the figure, the effect of CDMAC fiber on sludge settling performance depends on the charge it carries. When 0.05g / L, 0.1g / L, 0.15g / L and 0.2g / L of CDMAC were gradually added to 100mL of sludge with a sludge volume of 3095mg / L, as the addition amount increased, the SVI decreased when the amount reached 0.1g / L. 30 The zeta potential of the nanofibers with a concentration of 0.1% was tested at different pH values. When the pH was less than 10, the zeta potential was positive.

[0057] like Figure 6 As shown in the figure, when the reactor was started, after adding 0.1% CDMAC fiber, the sludge transformed from uniform scattered flocs to clumped sludge. After the reactor was operated for one week, the flocs were observed to be growing larger, and signs of granulation were already appearing. After the addition of materials, the particles also formed clumps, but the particles were connected to each other and would still break apart under strong aeration. Therefore, the effect of promoting sludge granulation only through the action of charge becomes less and less as the particle size increases.

[0058] Example 2

[0059] 100 mL of concentrated sludge from the Nanjing Chengbei Wastewater Treatment Plant was inoculated into a SBR reactor. After inoculation, the initial mixed liquor suspended solids (MLSS) in each reactor was approximately 3000 ± 250 mg / L, and the 5-minute sedimentation volume index (SVI5) was approximately 125 ± 10 mL / g. Four SBR reactors were set up in parallel: R1 with no material added; R2 with a solution containing 0.2 g of CDAMC@BSA-60; R3 with a solution containing only 0.2 g of CDMAC; and R4 with a solution containing 0.2 g of CDAMC@BSA-120 (starting from the 20th day, the CDMAC dosage was changed to 0.1 g). The operating cycle was 4 h: 2 min of water inlet, 42-52 min of rest, 180 min of aeration, 5-15 min of sedimentation, and 1 min of effluent. The SBRs were operated for 1 to 45 days.

[0060] like Figure 7As shown, the material was added once a day from the first to the third day. By the fourth day, in the R2, R3, and R4 reactors, the biomimetic material had a positive charge, while the bacteria in the sludge were negatively charged. This electrostatic adsorption caused a large number of microorganisms to be adsorbed by the biomimetic material, causing the sludge concentration to increase from 3056, 3226, and 2942 mg / L to 3311, 3445, and 3570 mg / L, respectively. The sludge index decreased from 130.89, 123.99, and 129.16 mL / g to 90.6, 104.49, and 109.24 mL / g, respectively. This indicates that the addition of the positively charged material significantly improved the sludge settling performance. Among them, R2 and R4, where bovine serum albumin was added, had the largest sludge growth. The adhesion of bovine serum albumin can retain a portion of the sludge volume or the bovine serum albumin can be consumed by microorganisms as nutrients. The amount of sludge in the R1 reactor without added materials dropped rapidly, from 3172 mg / L to 2662 mg / L. From the third to the fifth day, no materials were added. Due to the short settling time of 15 minutes, a large amount of activated sludge was discharged from the R2-R4 reactors, and the sludge settling performance also deteriorated. The sludge concentration dropped to 2882, 2466 and 3082 mg / L, and the sludge index also increased to 145.73, 162.2 and 136.27 mL / g, respectively. Therefore, cationic fibers and biomimetic composite materials need to be added every day. Otherwise, due to frequent wastewater replacement, the electrostatic attraction will be reduced and the sludge will be washed out. With the continued addition of materials, sludge volume increased and settling performance improved. By day 45, sludge concentrations in reactors R1-R4 had increased to 2945, 3818, 3462, and 4511 mg / L, respectively, while sludge indices decreased to 129.03, 83.8, 98.2, and 66.5 mL / g, respectively. The results showed that the addition of CDMAC and CDMAC@BSA increased sludge retention and improved sludge settling ability. This is because the positively charged surface of the cationic fiber provides abundant attachment sites for negatively charged microorganisms, preventing sludge loss in the reactor. The addition of CDMAC / BSA (CDMAC@BSA) resulted in improved sludge granulation, suggesting that the function of CDMAC / BSA is closer to that of EPS. The improved sludge granulation after the addition of CDMAC / BSA (CDMAC@BSA) is attributed to the hydrophobic nature of proteins, which promote sludge structural integrity.

[0061] like Figure 8As shown, the particle size of granular sludge is a crucial indicator for evaluating the degree of sludge granulation. The average particle sizes of the initial inoculum sludge were 77.7, 76.22, 73.15, and 73.2 μm, respectively. After the addition of cationic fiber and biomimetic composite materials, the sludge particle size gradually increased. On the fourth day, the sludge particle sizes in reactors R1-R4 increased to 122.3 μm, 198.3 μm, 172.9 μm, and 174.1 μm, respectively. (The particle size was measured immediately after the addition of the materials. After continuous operation throughout the day, the sludge particle size gradually decreased. For accuracy, subsequent measurements were conducted 8 hours after the addition of the materials.) Compared with R1, the sludge particle size in reactors R2-R4 increased significantly. From the third to the fifth day, the absence of cationic fiber and biomimetic composite materials resulted in a decrease in the particle size of reactors R2-R4, while there was no change in reactor R1. On day 25, the granular sludge in reactor R4 reached 200 μm. At this time, the average particle sizes of sludge in reactors R1, R2, and R3 were 153.1, 188, and 191.1 μm, respectively. Finally, on day 30, sludge particles in reactor R1 also reached 200 μm, five days after the addition of cationic fiber. By day 45, the final average particle sizes were 251.6, 339.9, 340.4, and 358.7 μm, respectively. These results indicate that cationic DMAC fiber promotes sludge granulation, with even greater efficacy when CDMAC / BSA, a complex of CDMAC and bovine serum albumin, is added. This suggests that the function of CDMAC / BSA is closer to that of EPS. Microorganisms capable of secreting EPS can help promote the aggregation of other microorganisms while also improving cell surface characteristics and microbial niches. Furthermore, EPS enrichment can accelerate sludge granulation and maintain granular sludge stability.

[0062] like Figure 9 As shown, within one cycle of system operation, reactors R2-R4 achieved similar COD removal rates of 96.5%, 95.4%, and 97.1%, respectively, all significantly exceeding R1's 87%. This is attributed to the larger sludge volume retained in reactors R2-R4. When biological activity remained similar, the greater the sludge volume, the greater the COD removal capacity. Ammonia nitrogen was almost completely removed within four hours, but R2 and R4, which had the highest sludge volumes, exhibited the fastest ammonia oxidation rates. Furthermore, reactors R2-R4 had higher nitrate content and lower nitrite content than R1. This indicates that the reactors incorporating cationic fibers and biomimetic composite materials exhibited improved nitrification performance. Total nitrogen removal rates across the four reactors remained similar, at 57.79%, 57.89%, 56%, and 59.2%, respectively. This may be because the addition of the materials made the sludge looser and more porous, resulting in higher dissolved oxygen levels within the sludge, which is unfavorable for the growth and reproduction of anoxic denitrifying bacteria. The results of this study show that the addition of cationic bionic materials is beneficial to the removal of COD and ammonia nitrogen, and the granular sludge produced in this way is suitable for the nitrification reaction of ammonia nitrogen in sewage.

[0063] like Figure 10 As shown in the figure, the sludge morphology in each reactor was observed under an optical microscope on the 45th day. The granular sludge in R2 and R4 clearly showed large particles with clear boundaries, while the granules in R1 were mostly small particles with a large number of flocs, and the granules in R2 were all small particles. This is because the addition of bovine serum albumin changed the spatial structure of the sludge. Although the addition of cationic fiber alone can promote particle formation, the resulting granules have a loose structure and are not compact enough. This is consistent with the large amount of sludge and good sludge settling performance in the R2 and R4 reactors. Compared with R1, the appearance and shape of the granular sludge in each reactor were clearer. Wood fiber is essentially a polymer polysaccharide, and polysaccharides are an important component of the skeleton structure of granular sludge. The results show that the complex prepared by using cationic wood fiber and bovine serum albumin in this study simulates the effect of EPS in sludge and can promote the formation of granular sludge.

[0064] like Figure 11 Figure 2 shows SEM images of granular sludge from reactors R1-R4. After 45 days of operation, the granules in R2 and R4 showed no significant difference in morphology, being loose and porous. However, compared to R3, they were more compact. This is due to the looser structure of the fibers in the CDMAC@BSA in the granular sludge. In contrast, some sludge granules produced in R1 were smaller and flocculent, while a few were larger and more compact. The sludge microorganisms in R1 were dominated by rod-shaped and coccal bacteria, while those in R2-R4, after the addition of CDMAC and CDMAC@BSA, were dominated by coccal bacteria with a small number of rod-shaped bacteria. These results indicate that the addition of CDMAC and CDMAC@BSA resulted in looser and more porous granules. This structure facilitates nutrient metabolism and oxygen transfer, thus facilitating COD and ammonia nitrogen removal. The addition of CDMAC to bovine serum albumin transformed the loose granular sludge into a more compacted state. Specifically, with the overgrowth of filamentous bacteria and the development of sludge bulking, PS increased, PN decreased, and the EPS content significantly increased, with a lower PN / PS ratio. It has been shown that the accumulation of large amounts of PS can lead to bulking of activated sludge, known as non-filamentous bulking. Therefore, when the amount of polysaccharides is high, it is not conducive to the formation of granular sludge. When the ratio of protein to polysaccharides increases, it is conducive to the formation of granular sludge with a stable structure.

[0065] like Figure 12As shown, CDMAC with positive surface charge promotes the aggregation of microorganisms through electrostatic adsorption, promotes the growth of sludge concentration, and promotes the secretion of EPS, mainly PS. This further promotes the adhesion and aggregation of microorganisms. The granular sludge produced at this time is loose and porous. The addition of bionic EPS promotes the adhesion of microorganisms and the generation of PN, which is beneficial to the integrity of the granular sludge structure. The generated AGS has good removal performance for COD, ammonia nitrogen and TN in wastewater. In addition, the addition of cellulose-based bionic EPS enriches bacteria with nitrification and denitrification capabilities in AGS, thereby improving the nitrification and denitrification performance of AGS.

[0066] The descriptions and practices disclosed in this invention are easy to understand and comprehend for those skilled in the art, and modifications and refinements may be made without departing from the principles of the invention. Therefore, modifications and improvements made without departing from the spirit of the invention should also be considered within the scope of protection of this invention.

Claims

1. A method for preparing wood fiber-based bionic EPS, characterized in that: Here are the steps: 1) Preparation of DAMC fibers The dried hardwood pulp is thoroughly disintegrated and homogenized, and then soaked in deionized water until the fibers are fully swollen. Excess water is then poured out, and NaIO4 and sodium chloride are dissolved in deionized water. The soaked wood pulp is added to the solution and stirred at room temperature. Ethylene glycol is then added to quench the residual periodate, thereby obtaining DAMC fibers. 2) Preparation of CDAMC fibers DAMC fibers, trimethylammonium acetohydrazide chloride, sodium chloride, and deionized water were mixed to obtain a suspension, the pH value of the suspension was adjusted to 4.5 with hydrochloric acid, and the suspension was stirred at room temperature, filtered, washed with deionized water, and freeze-dried to obtain brown CDAMC; 3) Preparation of cellulose-based biomimetic EPS The CDAMC prepared in step 2) and bovine serum albumin were dissolved in deionized water, mixed completely and allowed to stand to obtain a cellulose-based biomimetic EPS.

2. The method for preparing wood fiber-based bionic EPS according to claim 1, characterized in that: The mass ratio of the CDAMC to bovine serum albumin is 200:60-120.

3. The method for preparing wood fiber-based bionic EPS according to claim 1, characterized in that: In the step 1), the mass ratio of the dry hardwood pulp to NaIO4 and sodium chloride is 1:0.83-0.98:0.78, and the mass ratio of the dry hardwood pulp to ethylene glycol is 1:1.

11.

4. The method for preparing wood fiber-based bionic EPS according to claim 1, characterized in that: The mass ratio of the DAMC fiber to trimethylammonium acetohydrazide chloride, sodium chloride, and deionized water in step 2) is 0.5:0.3 to 0.5:1.2:

40.

5. The method for preparing the wood fiber-based bionic EPS according to any one of claims 1 to 4, and the obtained wood fiber-based bionic EPS.

6. Use of the wood fiber-based bionic EPS according to claim 5 in enhancing aerobic sludge granulation.

7. The use according to claim 6, characterized in that The process is as follows: adding wood fiber-based bionic EPS into SBR, and operating it in the mode of water inlet, stillness, aeration, sedimentation and water outlet. The SBR operates for 4 to 10 days.

8. The use according to claim 7, characterized in that The addition amount of the wood fiber-based bionic EPS is 0.05-0.10 g / L.

Images