A pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction

Abstract

The application discloses a kind of high-efficiency sludge dewatering and antibiotic resistance gene reduction pretreatment methods, it is related to the harmless treatment technical field of pollutant, its steps include adding high ferrate and high periodate to the sludge, after stirring and mixing uniformly, obtain the sludge after pretreatment.The application high ferrate and high periodate pretreatment sludge exhibits significant technical advantages: without adjusting the treatment system to be acidic can generate and stable high-valence strong oxidizing iron ions, ensure that oxidation process is efficient and continuous;By the adjustment two-component regulation system of microorganism, group feeling and IV type secretion system, reduce the abundance of actinobacteria and chlorobi bacteria carrying ARGs, promote the transfer of antibiotic resistance gene from intracellular to extracellular, make it exposed in sludge external environment, promote the removal of sludge ARGs;Optimization and regulation of the surface morphology of sludge, particle dispersion and aggregation ensure its high dewatering performance, realize the efficient dewatering and resistance gene reduction in sludge pretreatment process.

Description

Technical Field

[0001] This invention relates to the field of harmless treatment technology for pollutants, and in particular to a pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction. Background Technology

[0002] With the acceleration of global urbanization, urban wastewater treatment has become a crucial environmental protection issue. Wastewater treatment plants worldwide widely employ activated sludge technology to treat urban wastewater, inevitably generating large quantities of wastewater sludge rich in organic matter and microorganisms. However, wastewater sludge not only contains recyclable resources but also harbors various harmful pollutants, especially antibiotic resistance genes (ARGs) that can be rapidly transferred via mobile genetic elements (MGEs). The presence of these genes poses a serious threat to public health and environmental safety.

[0003] Currently, one of the main challenges in sludge treatment is how to effectively remove harmful pollutants, especially ARGs, from sludge and improve its dewatering performance to facilitate subsequent resource utilization. Mechanical dewatering is a common method in sludge treatment, but the dewatered sludge cake still contains a large number of ARGs in intracellular form, which may rapidly spread in the soil environment after application to the land.

[0004] Extracellular polymeric substances (EPS) in wastewater treatment plant sludge are a major component of activated sludge flocs. EPS directly covers the cell membrane, and its quantity and composition affect the surface properties of activated sludge flocs, thus influencing the adsorption and flocculation performance of the activated sludge. Sludge mainly consists of two parts: cells and EPS. EPS is primarily composed of proteins and polysaccharides. Polysaccharide molecules are rich in hydrophilic functional groups such as hydroxyl and carboxyl groups, which can form a stable and elastic network structure through adsorption and bridging, cross-linking and immobilizing free cells, thus promoting sludge flocculation. Proteins and lipids maintain the stability of the floc structure, correspondingly improving the bioflocculation properties of the sludge. These substances form a tight, high-density network structure through electrostatic forces, hydrogen bonding, ionic attraction, and biochemical interactions, serving as a protective layer for microorganisms against external heavy metals and toxic compounds. Antibiotic resistance genes are abundant in extracellular polymeric substances (EPS). EPS absorbs a large amount of antibiotic resistance genes (ARGs) through bridging, hydrophobic, and entanglement effects, accounting for up to 74.2% of the total ARGs. In addition, some resistance genes in sludge are also distributed within the bacterial genetic material. Therefore, it is evident that a large number of resistance genes in wastewater treatment plant sludge are located within extracellular polymeric substances (EPS). EPS encapsulates ARGs, forming recalcitrant polymer structures. Removing these ARGs is the core and challenging aspect of sludge ARG removal and degradation. Thus, developing efficient technologies for removing ARGs from sludge is a pressing technical challenge in the current sludge treatment field. Summary of the Invention

[0005] To address the common problems in existing sludge treatment technologies, such as unsatisfactory dewatering effects, low removal efficiency of antibiotic resistance genes (ARGs), and cumbersome processes, this invention proposes a ferrate / periodate pretreatment method. Utilizing the synergistic effect of these two methods, ARGs in sludge can be efficiently removed without additional acidification, while significantly enhancing the sludge's dewatering capacity. This technology simplifies the treatment process and achieves both efficient sludge dewatering and effective ARG reduction.

[0006] This invention provides a pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction, wherein ferrate and periodate are added to the sludge, and the mixture is stirred and homogenized to obtain pretreated sludge.

[0007] Furthermore, the ferrate and periodate are added by adding the ferrate to the sludge, stirring for 1-2 minutes, and then adding the periodate.

[0008] Furthermore, the stirring speed is 500–1000 rpm / min.

[0009] Furthermore, the pretreatment time is 30–45 min.

[0010] Furthermore, the weight ratio of the ferrate to the volatile suspended solids in the sludge is 0.01 to 0.04:1, wherein the amount of ferrate used is based on the mass of iron.

[0011] Furthermore, the mass ratio of ferrate to periodate is 5:1 to 2, wherein the amount of ferrate is calculated based on the mass of iron, and the amount of periodate is calculated based on the mass of iodine.

[0012] Furthermore, the periodate is at least one of potassium periodate and sodium periodate.

[0013] Furthermore, the ferrate is at least one of potassium ferrate and sodium ferrate.

[0014] The present invention has the following beneficial effects:

[0015] I. In the pretreatment of sludge using ferrate and periodate, ferrate rapidly generates Fe(V) and Fe(IV) ions with high redox potentials upon entering the sludge. These high-valence iron ions possess strong oxidizing properties but readily decompose into Fe(III) and Fe(II), which have weaker oxidizing properties. The addition of periodate effectively inhibits this process, thereby maintaining the concentration and activity of high-valence iron ions and prolonging the duration of their strong oxidizing properties. Simultaneously, the presence of periodate mitigates the decay of ferrate under alkaline conditions, overcoming its limitations under acidic conditions and maintaining oxidizing capacity over a wider pH range. This allows for efficient pretreatment of the sludge without adjusting its pH, reducing operational steps and saving treatment costs.

[0016] II. Pretreatment of sludge with ferrate and periodate significantly reduced the abundance of Actinobacteria and Chlorophyta carrying ARGs, effectively curbing the spread of ARGs in sludge. Furthermore, pretreatment can promote the transfer of intracellular antibiotic resistance genes (iARGs) to extracellular antibiotic resistance genes (eARGs) by regulating the two-component system, quorum sensing (QS), and type IV secretion system (T4SS) of microorganisms. This process exposes previously difficult-to-treat iARGs to the external environment of the sludge, providing favorable conditions for subsequent ARG removal measures and significantly enhancing the control of antibiotic resistance genes during sludge treatment.

[0017] Third, pretreatment with ferrate and periodate significantly improves the physicochemical properties of sludge. By generating large amounts of highly oxidizing Fe(V) and Fe(IV), these compounds act on the sludge particles, optimizing their surface morphology, disrupting the stable skeletal structure and the bonds between sludge flocs, and effectively lysing sludge cells to release adsorbed and bound water. Furthermore, the particle size distribution of the sludge is effectively regulated, reducing the breakup of large particles and the aggregation of small particles, ensuring the existence of "drainage channels," and improving the dewatering performance of the sludge. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 (a) shows the effect of different dosages of ferrate on the moisture content of sludge filter cake in this invention; (b) shows the effect of different dosages of ferrate on sludge MLVSS; (c) shows the effect of different ferrate / periodate addition ratios on the moisture content of sludge filter cake; (d) shows the effect of different ferrate / periodate addition ratios on sludge MLVSS.

[0020] Figure 2 This invention illustrates the effect of different ferrate / periodate addition ratios on the surface morphology of sludge.

[0021] Figure 3 This invention illustrates the effect of different ferrate / periodate addition ratios on sludge particle size.

[0022] Figure 4 This invention illustrates the effect of different ferrate / periodate addition ratios on sludge transmittance.

[0023] Figure 5 This invention illustrates the effect of different ferrate / periodate addition ratios on the types of extracellular ARGs.

[0024] Figure 6 This invention illustrates the effect of different ferrate / periodate addition ratios on extracellular ARGs.

[0025] Figure 7 This invention illustrates the effect of different ferrate / periodate addition ratios on intracellular ARGs.

[0026] Figure 8(a) shows the effect of different ferrate / periodate addition ratios on microbial phyla in this invention; (b) shows the effect of different ferrate / periodate addition ratios on microbial genera; (c) shows the relationship between microbial genera and ARGs.

[0027] Figure 9 (a) shows the effect of different ferrate / periodate addition ratios on the two-component system in this invention; (b) shows the effect of different ferrate / periodate addition ratios on the quorum sensing system.

[0028] Figure 10 This invention relates to the effects of different ferrate / periodate addition ratios on the type IV secretory system. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise stated, the terms used herein have the following meanings. As used in this invention, “ARGs” refers to antibiotic resistance genes, including “iARGs” (intracellular antibiotic resistance genes) and “eARGs” (extracellular antibiotic resistance genes); “MGEs” refers to mobile genetic elements; “VSS” refers to volatile suspended solids; “MLVSS” refers to volatile suspended solids concentration; “EPS” refers to extracellular polymeric materials, including soluble EPS (S-EPS), loose EPS (LB-EPS), and compact EPS (TB-EPS); and “Wc” refers to the moisture content of the sludge filter cake.

[0031] This invention provides a pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction, wherein ferrate and periodate are added to the sludge, and the mixture is stirred and homogenized to obtain pretreated sludge.

[0032] In this process, ferrate rapidly generates Fe(V) and Fe(IV) with high redox potentials upon entering the sludge. These high-valence iron ions possess strong oxidizing properties but readily decompose into Fe(III) and Fe(II), which have weaker oxidizing properties. The addition of periodate effectively inhibits this process, thereby maintaining the concentration and activity of high-valence iron ions and prolonging the duration of their strong oxidizing properties.

[0033] Fe(V) and Fe(IV) exhibit the highest activity under acidic conditions, but ferrates are prone to decay in alkaline environments, limiting their application range. When used in combination with periodate, the redox balance in the reaction system is adjusted, mitigating the decay of ferrates under alkaline conditions. This allows them to maintain a certain level of oxidation capacity over a wider pH range, achieving efficient pretreatment of sludge without adjusting its pH, reducing operational steps and saving treatment costs.

[0034] PI / Fe(VI) pretreatment generates a large amount of Fe(V) and Fe(IV) with strong oxidizing power, which will destroy the stable skeleton structure of sludge and break the bond between sludge floc particles. The sludge structure is more loose, which can effectively lyse sludge cells, release adsorbed water and internal bound water, and improve the dewatering performance of sludge.

[0035] The PI / Fe(VI) pretreatment process generates a large number of strong oxidizing groups H2O2 and ·O2. - H3Fe IV O4 - IO3·, ·OH, etc., on the one hand, destroy the EPS structure of sludge, causing the bonds between the large polymer structures that are originally densely distributed in EPS to break, generating smaller molecules and looser organic matter groups. At the same time, they partially or completely destroy the resistance genes that are bound to EPS by electrostatic forces, hydrogen bonding, ionic attraction, biochemical and other effects. Furthermore, they can also destroy the cell structure originally wrapped by EPS, enter the cell membrane and oxidize and break down ARGs in intracellular DNA and plasmids.

[0036] In addition, the PI / Fe(VI) pretreatment process modulates the metabolic activities of the two-component system, quorum sensing (QS) and type IV secretion system. On the one hand, it promotes the transport of intracellular ARGs to extracellular ARGs, enabling further oxidative degradation of ARGs. On the other hand, the growth of ARGs host bacteria is inhibited due to the influence of metabolic regulation, resulting in a decrease in the abundance of ARGs carried by the bacteria.

[0037] Furthermore, the ferrate and periodate are added by adding the ferrate to the sludge, stirring for 1-2 minutes, and then adding the periodate.

[0038] This scheme optimizes the addition of ferrate and periodate, controlling the types and concentrations of intermediates in the reaction system. The ferrate added first generates high-valence iron ions Fe(IV) / Fe(V), which, when further added to the periodate system, react with the Fe(IV) / Fe(V) intermediates. This interaction drives these intermediates to participate more in the oxidation of micropollutants, rather than their self-decomposition. This synergistic effect improves the system's removal efficiency for micropollutants, resulting in more stable overall oxidation performance.

[0039] Furthermore, the stirring speed is 500–1000 rpm / min.

[0040] This solution optimizes the stirring speed in sludge treatment, ensuring that ferrates and periodates are fully mixed with the sludge, accelerating pollutant oxidation, promoting the destruction of sludge structure, and avoiding excessive energy consumption.

[0041] Furthermore, the pretreatment time is 30 min to 45 min.

[0042] This solution optimizes the sludge pretreatment time, ensuring that the sludge's dewatering performance is fully improved and released, while maximizing the removal of potential antibiotic resistance factors from the sludge, thereby enhancing subsequent treatment effectiveness. It achieves efficient attainment of treatment objectives while avoiding energy waste caused by excessively long reaction times.

[0043] Furthermore, the weight ratio of the ferrate to the volatile suspended solids in the sludge is 0.01 to 0.04:1, wherein the amount of ferrate used is based on the mass of iron.

[0044] This approach optimizes ferrate dosage by precisely controlling its amount to 0.01–0.04 times the weight of volatile suspended solids (VSS) in the sludge (based on the mass of iron in the ferrate). This optimization method abandons the traditional simple proportional addition based on the total weight of the sludge, instead focusing on the more representative VSS components in the sludge, thereby ensuring that the ferrate can act more effectively on the target pollutants.

[0045] Within this optimal ratio range, ferrates produce Fe(V) and Fe(IV) with strong oxidizing capabilities, which disrupt the sludge floc structure, gradually forming a lamellar structure. This breaks down the bonds between sludge floc particles, making the sludge structure looser. Intracellular organic matter and extracellular EPS are released, decomposing most large organic polymers, including EPS, into smaller organic molecules. A large amount of hydrophilic substances are leached out, a large amount of surface-bound water is released, and even drainage channels are broken. For example, when the Fe(VI) dosage is 40 mg Fe... 6+ / g VSS, the moisture content of the sludge decreased from 89.2% to 70.9%, and the MLVSS reached a minimum of 12.11g / L.

[0046] Furthermore, the mass ratio of ferrate to periodate is 5:1 to 2, wherein the amount of ferrate is calculated based on the mass of iron, and the amount of periodate is calculated based on the mass of iodine.

[0047] This scheme optimized the addition ratio of ferrate and periodate in the pretreatment system. Under the condition of PI / Fe(VI) = 1 / 5, the sludge floc structure was destroyed, resulting in an increase in fine particles and a decrease in transmittance in the filtrate. The minimum moisture content and MLVSS of the sludge cake after pretreatment were 70% and 10.6 g / L, respectively, and the sludge transmittance dropped sharply from 68.9% to 31.9%.

[0048] PI / Fe(VI) pretreatment led to a decrease in total eARGs in sludge. The abundance of ARGs and MGEs in the S-EPS layer decreased significantly by 10.7–31.7 lg(gene copies / g VSS) (p<0.05) and 5.2–5.9 lg(gene copies / g VSS) (p<0.05), respectively. The degree of reduction increased with the decrease of PI / Fe(VI) dosage. The abundance of ARGs and MGEs in LB-EPS decreased significantly by 1.8–18.9 lg(gene copies / g VSS) (p<0.05) and 0.7–5.8 lg(gene copies / g VSS) (p<0.05), respectively.

[0049] PI / Fe(VI) pretreatment significantly promoted the expression of the two-component regulatory system, with significant upregulation of pilR, pilS, pilG, K02484, plnL, and glnG genes. Key genes of the QS system (sdiA, mqsR, bjaR1, cciR, and sinR) were also significantly upregulated, and the total abundance of T4SS genes increased by 22.0%–35.3%. On the other hand, the removal rates of cphA7, ermF, tet(X), aadA14, ErmB, sul3, tetA(60), and tet(M) were significantly reduced due to the decreased abundance of their corresponding host bacteria PHOS-HE28, NitrospiraA, UBA3362, OLB14, Prosthecobacter, and OLB17. This further validates that PI / Fe(VI) pretreatment removes sludge ARGs by reducing the abundance of microorganisms carrying ARGs and promoting the transfer of iARGs to eARGs, thereby exposing the recalcitrant iARGs to the external environment of the sludge.

[0050] Furthermore, the periodate is at least one of potassium periodate and sodium periodate.

[0051] Furthermore, the ferrate is at least one of potassium ferrate and sodium ferrate.

[0052] The above scheme optimizes the selection of ferrate and periodate, specifying that at least one of potassium periodate and sodium periodate is used as the source of periodate, and at least one of potassium ferrate and sodium ferrate is used as the source of ferrate. This is based on their high efficiency of oxidation and also takes into full account the low price and environmental friendliness of the raw materials.

[0053] Example 1

[0054] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 30 mg of Fe. 6+ After adding / g VSS of potassium ferrate, the mixture was stirred at 1000rpm for 1 minute to allow it to react evenly, and then 6mg I was added. 7+ Potassium periodate at a concentration of / g VSS was used for pretreatment with both oxidants, with a total reaction time of 30 min. At 5 min of reaction, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge, including filter cake moisture content, MLVSS, surface scanning electron microscopy, supernatant refractive index, and sludge particle size. At 30 min of reaction, a 300 mL sludge sample was taken from the beaker using a graduated cylinder to evaluate the degradation effect of antibiotic resistance genes in extracellular polymeric substances (EPS) and intracellular antibiotic resistance genes.

[0055] Example 2

[0056] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 30 mg of Fe. 6+ After adding / g VSS of potassium ferrate, the mixture was stirred at 1000rpm for 1 minute to allow it to react evenly, and then 12mg I was added. 7+ Potassium periodate at a concentration of / gVSS was used for pretreatment with both oxidants, with a total reaction time of 35 min. At 5 min of reaction, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge, including filter cake moisture content, MLVSS, surface scanning electron microscopy, supernatant refractive index, and sludge particle size. At 35 min of reaction, a 300 mL sludge sample was taken from the beaker using a graduated cylinder to evaluate the degradation effect of antibiotic resistance genes in extracellular polymeric substances (EPS) and intracellular antibiotic resistance genes.

[0057] Example 3

[0058] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 30 mg of Fe. 6+ After adding / g VSS of potassium ferrate, the mixture was stirred at 1000rpm for 1 minute to ensure uniform reaction, and then 18mg I was added. 7+Potassium periodate at a concentration of / gVSS was used for pretreatment with both oxidants, with a total reaction time of 35 min. At 5 min of reaction, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge, including filter cake moisture content, MLVSS, surface scanning electron microscopy, supernatant refractive index, and sludge particle size. At 35 min of reaction, a 300 mL sludge sample was taken from the beaker using a graduated cylinder to evaluate the degradation effect of antibiotic resistance genes in extracellular polymeric substances (EPS) and intracellular antibiotic resistance genes.

[0059] Example 4

[0060] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 30 mg of Fe. 6+ After adding / g VSS of potassium ferrate, the mixture was stirred at 1000 rpm for 1 min to ensure uniform reaction, and then 24mg I was added. 7+ Potassium periodate at a concentration of / gVSS was used for pretreatment with both oxidants, with a total reaction time of 40 min. At 5 min of reaction, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge, including filter cake moisture content, MLVSS, surface scanning electron microscopy, supernatant refractive index, and sludge particle size. At 40 min of reaction, a 300 mL sludge sample was taken from the beaker using a graduated cylinder to evaluate the degradation effect of antibiotic resistance genes in extracellular polymeric substances (EPS) and intracellular antibiotic resistance genes.

[0061] Example 5

[0062] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 30 mg of Fe. 6+ After adding / g VSS of potassium ferrate, the mixture was stirred at 1000rpm for 1 minute to allow it to react evenly, and then 30mg I was added. 7+ Potassium periodate at a concentration of / gVSS was used for pretreatment with both oxidants, with a total reaction time of 45 min. At 5 min of reaction, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge, including filter cake moisture content, MLVSS, surface scanning electron microscopy, supernatant refractive index, and sludge particle size. At 45 min of reaction, a 300 mL sludge sample was taken from the beaker using a graduated cylinder to evaluate the degradation effect of antibiotic resistance genes in extracellular polymeric substances (EPS) and intracellular antibiotic resistance genes.

[0063] Comparative Example 1

[0064] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer and stir evenly at 1000 rpm for 30 min. After 5 min, take 250 mL of sludge sample from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge, including filter cake moisture content, MLVSS, surface scanning electron microscopy, supernatant refractive index, and sludge particle size. After 30 min of reaction, take 300 mL of sludge sample from the beaker using a graduated cylinder to evaluate the degradation effect of antibiotic resistance genes in extracellular polymeric substances (EPS) and intracellular antibiotic resistance genes.

[0065] Comparative Example 2

[0066] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 10 mg of Fe. 6+ After adding sodium ferrate at a concentration of / g VSS, stir the mixture uniformly at 500 rpm for 30 min. After 5 min, take 250 mL of sludge sample from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge: sludge cake moisture content and MLVSS.

[0067] Comparative Example 3

[0068] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 20 mg of Fe. 6+ After adding sodium ferrate at a concentration of / g VSS, the mixture was stirred uniformly at 600 rpm for 30 min. After 5 min, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge: sludge cake moisture content and MLVSS.

[0069] Comparative Example 4

[0070] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 30 mg of Fe. 6+ After adding potassium ferrate at a concentration of / g VSS, the mixture was stirred evenly at 750 rpm for 30 min. After 5 min, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge: sludge cake moisture content and MLVSS.

[0071] Comparative Example 5

[0072] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 40 mg of Fe. 6+ After adding potassium ferrate at a concentration of / g VSS, the mixture was stirred evenly at 900 rpm for 30 min. After 5 min, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge: sludge cake moisture content and MLVSS.

[0073] Comparative Example 6

[0074] Add 500 mL of fresh raw sludge to a 1000 mL glass beaker placed on a magnetic stirrer, and first add 50 mg of Fe. 6+ After adding potassium ferrate at a concentration of / g VSS, the mixture was stirred uniformly at 1000 rpm for 30 min. After 5 min, a 250 mL sludge sample was taken from the beaker using a graduated cylinder to determine the physicochemical properties of the sludge: sludge cake moisture content and MLVSS.

[0075] The experimental parameters for each embodiment and comparative example are shown in Table 1:

[0076] Table 1. Summary of experimental parameters for each embodiment and comparative example.

[0077]

[0078] Experimental Results and Analysis

[0079] (1) Effects of ferrate and periodate pretreatment on sludge dewatering

[0080] The dewatering performance of sludge pretreated with simple ferrate, ferrate, and periodate was compared through experiments in Comparative Examples 1-6 and Examples 1-5. Figure 1 It can be seen that with the increase of ferrate dosage, the water content of the sludge cake (Wc) decreases sharply. At Fe(VI) concentrations of 10–40 mg / L... 6+ After treatment with / g VSS, the Wc of the sludge cake was significantly lower than that of the original sludge. When the Fe(VI) dosage was 40mg Fe... 6+ / g VSS, Wc reaches its minimum value of 70.9%, at which point the optimal dehydration effect is achieved. When 50mg Fe is reached... 6+ At / g VSS, the Wc of the sludge cake showed a sharp upward trend. From Figure 1 As can be seen from b, the variation of the volatile suspended solids (MLVSS) concentration in the sludge cake is consistent with that of Wc. This is because at high concentrations, the dewatering performance of the sludge changes significantly due to the disruption of the floc structure and integrity, as well as the release of intracellular and extracellular substances.

[0081] like Figure 1 As shown in c and d, during the pretreatment of sludge with ferrate and periodate, the Wc and MLVSS of the sludge cake initially decreased and then increased with the increase of periodate (PI). When the PI dosage was 6 mg I... 7+When PI / Fe(VI) is 1 / 5, the Wc and MLVSS of the sludge cake decrease from 89.2% and 11.75 g / L to 85.1% and 10.6 g / L, respectively. This is because the sludge floc structure is disrupted, promoting the conversion of bound water to free water, thereby improving the dewatering performance of the sludge. From 12 mg I 7+ Starting with a VSS dosage of / g, the Wc and MLVSS of the sludge cake show an upward trend as the PI dosage increases. During the chemical pretreatment process using high-dose oxidants combined with Fe(VI), excessive Fe(V) and Fe(IV) are released, leading to excessive disruption of the sludge structure and the release of large amounts of hydrophilic EPS substances. Fine particles are released into the liquid phase, causing blockage of drainage channels and deteriorating sludge filtration performance.

[0082] The Fe(VI) concentration provided in this invention is 10–40 mg Fe 6+ Under the conditions of / g VSS and PI / Fe(VI) ratio of 1 to 2:5, it has a significant effect on improving sludge dewatering efficiency. At the same time, during the PI / Fe(VI) pretreatment process, the synergistic effect of the two precisely controls the degree of damage to the sludge structure, which not only avoids the decline in dewatering performance caused by excessive damage, but also makes full use of the oxidant to modify the internal structure of the sludge and promotes the effective release of water.

[0083] (2) Effects of PI / Fe(VI) pretreatment on sludge structure

[0084] Figure 2 SEM images of sludge samples from Comparative Example 1 and Examples 1-5, magnified 5000 times, are shown. Figure 2 As shown in Figure a, the RS group in Comparative Example 1 has a smooth surface and an extremely dense flocculent structure, indicating that bound water inside the sludge cannot be released, resulting in poor sludge dewatering capacity. Figure 2 As shown in Figure b, the sludge floc structure was severely damaged after pretreatment with PI / Fe(VI) = 1:5 in Example 1, resulting in a looser sludge structure and numerous drainage channels. This severe damage to the sludge flocs was due to the interaction between PI and Fe(VI), which produced a large amount of highly oxidizing substances (Fe(V) and Fe(IV)). After treatment with Fe(V) and Fe(IV), a large number of tiny, irregular substances adhered to the sludge surface. These substances may be released in the form of intracellular organic matter and extracellular polymeric substances (EPS), and the leaching of a large amount of hydrophilic substances leads to the release of a large amount of surface-bound water into the liquid phase. Figure 2As shown in e to f, with the increase of PI dosage, PI / Fe(VI) breaks down the drainage channels through strong oxidation, and a large amount of material floats in the liquid phase, presenting an aggregated block structure, causing the drainage channels inside the sludge to lose their function during the dewatering process.

[0085] Sludge particle size distribution is a key factor in sludge dewatering performance. A higher proportion of fine particles in the sludge increases its viscosity, leading to poorer dewatering performance. For example... Figure 3 As shown, after pretreatment using the methods described in Examples 1-5, the D50 of the sludge decreased from a minimum of 47.7 μm to 42.517 μm, further demonstrating that the pretreatment severely damaged the sludge flocs, promoted sludge protein denaturation, and caused the tightly bound sludge particles to disintegrate from EPS, resulting in the degradation of large particles into smaller particles and EPS leakage. The D50 value of the sludge further increased after pretreatment with PI / Fe(VI) = 4 / 5 and 5 / 5, indicating that some of the dissociated EPS recombine with the sludge particles to form larger sludge flocs.

[0086] The changes in the physicochemical properties of the sludge were further characterized by the transmittance ratio of the sludge supernatant. For example... Figure 4 As shown, the transmittance of the sludge supernatant decreased after PI / Fe(VI) pretreatment. The PI / Fe(VI) = 1 / 5 group had the lowest transmittance. Compared with control group 1, the transmittance of the sludge after PI / Fe(VI) = 1 / 5 pretreatment dropped sharply from 68.9% to 31.9%. This was mainly because the sludge floc structure was destroyed after PI / Fe(VI) = 1 / 5 pretreatment, resulting in an increase in fine particles in the filtrate and a decrease in the sludge transmittance.

[0087] Therefore, the PI / Fe(VI) pretreatment strategy significantly improves sludge dewatering performance by precisely controlling the destruction and reconstruction of sludge structure. Its advantages lie in its ability to efficiently promote the release of moisture from within the sludge, while simultaneously optimizing the sludge particle size distribution by regulating the release and repolymerization of EPS, thus providing more favorable conditions for subsequent sludge treatment and dewatering.

[0088] (3) Effect of Fe(VI) and PI addition ratio on ARGs removal

[0089] The experiment also investigated the effects of the PI / Fe(VI) pretreatment system on the abundance of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in different forms of extracellular polymeric substances (EPS) in sewage sludge—soluble EPS (S-EPS), loose EPS (LB-EPS), and compact EPS (TB-EPS). The results are as follows.

[0090] In the S-EPS layer, in the untreated sludge of the RS group of Comparative Example 1, the total abundance of ARGs and MGEs in S-EPS was 105.5lg(gene copies / g VSS) and 18.3lg(gene copies / g VSS), respectively. β-lactam and fluoroquinolone ARGs were dominant, while integrase genes (int1) and transposases (tnpA-2) were the main contributors to MGEs. PI / Fe(VI) pretreatment significantly reduced the abundance of these genes, with ARGs decreasing by 10.7–31.7lg(gene copies / g VSS) and MGEs decreasing by 5.2–5.9lg(gene copies / g VSS), and this decreasing trend was inversely proportional to the increase of PI / Fe(VI) dosage. Notably, the abundance of specific subtypes of aminoglycosides, macrolides, sulfonamides, and tetracyclines ARGs also decreased with dosage changes.

[0091] LB-EPS layer: In the untreated sludge LB-EPS of the RS group in Comparative Example 1, the total abundance of ARGs and MGEs was 98.5lg(gene copies / g VSS) and 18.2lg(gene copies / g VSS), respectively. Macrolides and β-lactams accounted for a high proportion of ARGs, while integrase genes (int1) and transposases (tnpA-2) remained the main types of MGEs. PI / Fe(VI) pretreatment significantly reduced the abundance of these genes, but the reduction was smaller than that of S-EPS, and it also showed a decreasing trend with increasing dosage. Notably, in the F5 (Example 5) group, in addition to the reduction of ARGs and MGEs, further reductions in specific ARG subtypes such as β-lactams, macrolides, and multidrug-resistant genes were observed.

[0092] TB-EPS layer: In the RS group of Comparative Example 1, the total abundance of ARGs and MGEs in the untreated sludge was 92.5lg (genecopies / g VSS) and 18.6lg (gene copies / g VSS), respectively. Under PI / Fe(VI) treatment, although the abundance of ARGs and MGEs in the LB-EPS layer in groups F1 (Example 1) and F2 (Example 2) was significantly reduced, the degradation effect of the TB-EPS layer weakened with the increase of PI dosage, and even increased in some cases (such as group F5 corresponding to Example 5). This was attributed to the overexpression of ISCR1 under high-dose PI stimulation, which promoted the spread and proliferation of ARGs.

[0093] Therefore, it can be seen that under optimized addition ratio conditions (such as F1 and F2 groups corresponding to Examples 1 and 2), PI / Fe(VI) pretreatment can effectively reduce the abundance of ARGs and MGEs in EPS of each layer, demonstrating its role and potential in reducing the spread of resistance genes in sludge treatment.

[0094] (4) Effects of Fe(VI) and PI dosage ratio on intracellular and extracellular resistance gene degradation

[0095] like Figure 6 As shown, the total eARGs (extracellular resistance genes) in the sludge reached 351.6 lg (gene copies / g VSS) in the RS group (comparative example 1), with ARGs in the S-EPS, LB-EPS, and TB-EPS layers accounting for 35.2%, 33.2%, and 31.6%, respectively, highlighting the importance of sludge as an ARG reservoir. Typical ARGs such as aadA1 and blaTEM had abundances ranging from 5.4 to 6.6 lg (gene copies / g VSS), with sul1 and aadA1 being the dominant ARGs.

[0096] Ferrate and periodate pretreatment significantly reduced the abundance of total eARGs, and the removal efficiency varied with the PI / Fe(VI) ratio. Specifically, the total eARGs removal rate was as high as 21% under F1 (Example 1) conditions, while the removal rates under other conditions ranged from 1.6% to 12.8%.

[0097] For the individual degradation of ARGs in different EPS layers, it was found that the degradation patterns of genes such as aac(6')-Ib and aadE were similar to those of total eARGs, and were significantly affected by the PI / Fe(VI) ratio. In particular, blaPSE was completely degraded in S-EPS, and the degradation rate in LB-EPS and TB-EPS increased with increasing PI dose, reaching 100% under F3 (Example 3) to F5 (Example 5) conditions. In addition, erm(A) was completely degraded in all pretreatment groups except F5 (Example 5).

[0098] Figure 7 The abundance changes of iARGs (intracellular resistance genes) under different PI / Fe(VI) ratios were shown. Sulfonamide, macrolide, β-lactam, and tetracycline resistance genes were highly abundant in WAS cells, closely related to routine antibiotic use. PI / Fe(VI) pretreatment significantly reduced the abundance of iARGs such as cphA7, ermF, and tet(X) (>50%), while genes such as aadA14 and ErmB showed a decreasing trend, but the degradation rate was not significant. Notably, the abundance of genes such as sul1 and sul2 was dynamic and irregular, even increasing under certain conditions.

[0099] Therefore, PI / Fe(VI) pretreatment has a significant effect on the degradation of eARGs and iARGs in sludge, and the degradation efficiency is affected by the PI / Fe dosage ratio. The optimized pretreatment conditions of this invention can achieve more efficient ARGs removal.

[0100] (5) Effects of Fe(VI) and PI dosage ratio on sludge bacterial community and potential hosts

[0101] To reveal the microbial origin of ARGs, the diversity of the microbial community in the sludge was analyzed. For example... Figure 8 As shown in Figure a, Bacteroidetes, Proteobacteria, Nitrifying Spirogyra, Chlorophyta, and Actinobacteria are the dominant phyla, accounting for approximately 87% of the total community. After PI / Fe(VI) pretreatment, the dominant phyla shifted to Bacteroidetes, Proteobacteria, Chlorophyta, Actinobacteria, and Acidobacteria. Among these, Proteobacteria and Bacteroidetes play key roles in organic matter transformation, while Actinobacteria and Chlorophyta may carry and spread ARGs.

[0102] At the genus level ( Figure 8 (b) The abundance of dominant genera in the original sludge, such as JJ008 and Sulfuritalea, decreased significantly after PI / Fe(VI) treatment, while the abundance of Proteobacteria genera, such as JAABQG01 and Rubrivivax, increased. The degradation effects of dominant genera in the original sludge varied under different treatment ratios, but the overall trend was consistent, namely, the increase of Proteobacteria genera and the decrease of Bacteroidetes genera.

[0103] Further analysis revealed that changes in ARG abundance were closely related to microbial life activities. This was achieved through network analysis (…). Figure 8 c) The experiment revealed a complex network of relationships between microorganisms and ARGs, consisting of 38 nodes and 167 edges. Among these, genera such as *Accumulibacter*, *OLB14*, and *PHOS-HE28* were closely associated with various ARGs. These genera mainly belong to the phyla Proteobacteria, *Chlorophyta*, and *Bacteroidetes*. Furthermore, the ARGs with high removal efficiency (such as *cphA7*, *ermF*, and *tet(X)*) showed a significant positive correlation with the abundance of specific genera. After PI / Fe(VI) pretreatment of the sludge, the levels of Actinobacteria and Chlorophyta were significantly reduced, leading to the effective degradation of these ARGs.

[0104] (6) The response of Fe(VI) and PI dosage ratio to the metabolic pathways of ARGs propagation and gene expression

[0105] The reproduction and spread of ARGs are regulated by multiple functional metabolic pathways, including the two-component regulatory system, quorum sensing (QS), and type IV secretion system (T4SS). These functional metabolic pathways transmit cellular signals through the cytoplasm to the bacterial nucleoid, where gene expression is regulated, thus mediating drug resistance.

[0106] PI / Fe(VI) treatment affected the metabolic activity of the two-component microbial regulatory system in the sludge system, increasing the metabolic activity of the two-component regulatory system from 2154 ppm to 2493 ppm. Figure 9 a) The emergence of a two-component regulatory system increases transduced cellular signaling and gene expression, thereby promoting the transfer of iARGs to eARGs and converting recalcitrant iARGs into eARGs exposed to the external environment. Compared with the control group, the abundance of baeS, K02483, kdpE, and narX, which mediate microbial responses to environmental stimuli, increased by 41.5–66.1%, 31.9–60.8%, 36.4–52.1%, and 0–34.9%, respectively, promoting the spread of ARGs. In fact, most of the key genes involved in two-component signal transduction (i.e., pilR, pilS, pilG, K02484, plnL, and glnG) were significantly upregulated with increasing PI dosage.

[0107] Furthermore, stimulated ARGs hosts trigger the transfer, gene expression, and antibiotic resistance of MGEs through the QS system, thereby controlling the spread of ARGs. The QS system was also observed to be upregulated by PI / Fe(VI), and QS promotes interbacterial communication by regulating the expression of genes related to signal molecule synthesis. Further analysis showed that most key genes involved in the QS system (sdiA, mqsR, bjaR1, cciR, and sinR) were significantly upregulated, with patterns consistent with those observed in iARGs. Figure 9 b). This suggests that PI / Fe(VI) may promote the intraspecific or interspecific spread of ARGs by regulating QS, causing intracellular ARGs to be converted into extracellular ARGs and exposed to the external environment, where they are easily oxidized and decomposed by highly oxidizing high-valence iron ions.

[0108] DNA is actively released into the extracellular environment via the type IV secretion system (T4SS), leading to the transfer of iARGs. A schematic diagram of T4SS is shown in Figure 10. This system consists of 12 proteins (VirB1-11 and VirD4) forming a large macromolecular complex that spans the bacterial envelope. Based on intracellular metagenomic results, PI / Fe(VI) pretreatment increased the abundance of genes encoding nine T4SS proteins, with the total abundance of T4SS genes increasing by 22.0–35.3%. Figure 10The VirD4 gene showed the greatest improvement, increasing by 52% after PI / Fe(VI) pretreatment. The abundance of the VirB1 gene also increased significantly by 33%. VirB1 is a periplasmin that carries a transglycosylation motif and “drills holes” in peptidoglycan to facilitate T4SS assembly.

[0109] Therefore, PI / Fe(VI) pretreatment can also promote the transfer of iARGs to eARGs by regulating the two-component regulation system, quorum sensing (QS) and type IV secretion system (T4SS), expose the recalcitrant iARGs to the external environment of sludge, and promote the removal of sludge ARGs.

[0110] In summary, PI / Fe(VI) pretreatment significantly improves the physicochemical properties of sludge. By generating a large amount of highly oxidizing Fe(V) and Fe(IV) which act on sludge particles, it optimizes the surface morphology of the sludge, disrupts the stable skeletal structure of the sludge and the bonds between sludge floc particles, and effectively lyses sludge cells, releasing adsorbed water and internally bound water. Furthermore, the particle size distribution of the sludge is effectively regulated, reducing the breakup of large particles and the aggregation of small particles, ensuring the existence of "drainage channels," and improving the dewatering performance of the sludge.

[0111] Pretreatment with ferrate and periodate effectively curbed the spread of ARGs in sludge by significantly reducing the abundance of Actinobacteria and Chlorconiobacteria carrying ARGs. Furthermore, pretreatment can promote the transfer of intracellular antibiotic resistance genes (iARGs) to extracellular antibiotic resistance genes (eARGs) by regulating the two-component system, quorum sensing (QS), and type IV secretion system (T4SS) of microorganisms. This process exposes previously difficult-to-treat iARGs to the external environment of the sludge, providing favorable conditions for subsequent ARG removal measures and significantly enhancing the control of antibiotic resistance genes during sludge treatment.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction, characterized in that, Ferrate and periodate are added to the sludge and stirred to obtain pretreated sludge. The mass ratio of ferrate to periodate is 5:1, wherein the amount of ferrate is based on the mass of iron and the amount of periodate is based on the mass of iodine.

2. The pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction according to claim 1, characterized in that, The ferrate and periodate are added by adding the ferrate to the sludge, stirring for 1-2 minutes, and then adding the periodate.

3. The pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction according to claim 2, characterized in that, The stirring speed is 500~1000 rpm / min.

4. The pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction according to claim 3, characterized in that, The pretreatment time is 30-45 minutes.

5. The pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction according to claim 4, characterized in that, The weight ratio of the ferrate to the volatile suspended solids in the sludge is 0.01 to 0.04:1, wherein the amount of ferrate used is based on the mass of iron.

6. The pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction according to claim 1, characterized in that, The periodate is at least one of potassium periodate or sodium periodate.

7. The pretreatment method for efficient sludge dewatering and antibiotic resistance gene reduction according to claim 1, characterized in that, The ferrate is at least one of potassium ferrate or sodium ferrate.

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