Insight into enhancing the performance of sludge dewatering using a novel flocculant CS-TA prepared through free radical-mediated conjugation

Insight into enhancing the performance of sludge dewatering using a novel flocculant CS-TA prepared through free radical-mediated conjugation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Insight into enhancing the performance of sludge dewatering using a novel flocculant CS-TA prepared through free radical-mediated conjugation Yuejin Liu, Xiaojun Niu, Dongqing Zhang, lingling Zhou, chunyang Tao, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4014664/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Flocculation is one of the most significant conditioning methods for sludge dewatering. In the present study, a novel flocculant CS-TA, which was prepared through free radical-mediated conjugation of tannic acid (TA) and chitosan (CS), was proposed to improve the performance of sludge dewatering. The findings indicate that the conditioning of CS-TA yielded the best dewatering performance at 30 mg g TS − 1 with water content of 59.78% and capillary suction time of 11.8s, compared to the Wsc of 98.2% and CST of 56.2s in raw sludge. The flocculation efficiency of different influencing factors were evaluated, indicating that CS-TA possessed the capacity for enhancing sludge dewaterability over a wide range of pH. Furthermore, the analysis of particle size implied that the addition of CS-TA favored the formation of larger particles. Meanwhile, the value of zeta potential of sludge was increased form − 24.29 ± 0.49 mV to -17.69 ± 0.35 mV after CS-TA conditioning, suggesting that CS-TA could improve sludge dewatering through charge neutralization, thus accelerating sludge filtration. In addition, extracellular polymer substances (EPS) analysis indicated that the decrease in the polysaccharide (PS) and protein (PN) contents in EPS after CS-TA addition could increase the relative hydrophobicity of sludge, contributing to a decrease in water content. The results of FTIR reinforced the breakdown of hydrophic functional groups of PN and PS, leading to the sludge hydrophobicity. This study provides a comprehensive insights into the exploration of CS-TA for sludge dewatering and the maintenance of ecological security in an eco-friendly way. Sludge dewatering Tannic acid Chitosan Free radical-mediated conjugation Extracellular polymeric substance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Wastewater treatment processes one of the most significant developments in environmental engineering during the twentieth century. As an inevitable by-product in each wastewater treatment process, activated sludge usually consists of numerous contaminants, such as pathogens, nutrients, organic pollutants, heavy metals and other toxic substances, posing a risk to ecosystem and public health of not properly treated (He et al. 2023 , Neyens et al. 2004 , Wu et al. 2020 ) Particularly, large quantities of sludge typically contain high water content (Wc) of more than 90%, which has been identified as one of the main reasons responsible for the ineffective disposal of sludge. Furthermore, the cost for sludge dewatering, depending directly on the sludge volume to be treated and sludge moisture content, usually accounts for more than 50% of the total operation expenditure in the wastewater treatment processes (Hyrycz et al. 2022 , Wei et al. 2018 ). As such, sludge dewatering is of great significance for wastewater treatment, facilitating the subsequent transportation and disposal (Mowla et al. 2013 ). To improve the dewaterability of activated sludge, different conditioning strategies, such as physical, chemical and biological methods, have been extensively explored(Cao et al. 2021 ). Physical methods include pretreatment with non-chemical additives as skeleton builders, microwave conditioning, ultrasound and thermal/freeze pretreatment(Bao et al. 2024 , Yan et al. 2020 , Zhang et al. 2021 ). However, the development and application of non-chemical additives is limited by high dosage addition, while the microwave, ultrasound, and thermal/freeze pretreatment has the drawbacks of low efficiency and high energy consumption. Biological method has great limitations in practical use, due to slow growth of microorganisms. Chemical pretreatment, such as advanced oxidation process (AOP), flocculation and acid/alkali treatment, has the merits of high efficiency and low cost, Among which, flocculation is an effective approach for sludge dewatering, owing to its convenience and excellent performance(Wei et al. 2018 ). However, the commonly used inorganic coagulants, such as alum, poly-aluminum chloride (PAC), FeCl 3 and FeSO 4, are fit for high-pressure dewatering with a narrow pH range. Meanwhile, the large doses for conditioning and the corrosion associated with the treatment equipment may incur the substantial overall treatment cost (Chen et al. 2015 , Liang &Zhou 2022 ). By contrast, organic flocculants, such as polyacrylamide (PAM) and cationic polyacrylamide (CPAM), possess unique advantages, such as low dosage requirement with wide pH range for application (Feng et al. 2022 , Li et al. 2016 ). However, despite its popularity, the use of organic polymers has certain disadvantage relative to the secondary pollution. More recently, the application of natural polymer flocculant (e.g. cellulose, chitosan, amylum) for enhancing the dewaterability performance has become a research hotspot, owing to their high biodegradability and low cost (Guibal et al. 2006 , Wu et al. 2020 ). Nevertheless, sufficient low water content cannot be achieved in many sludge dewatering applications. As such, it is imperative to explore novel flocculants with high effectiveness, low cost and few environmental impact (Lin et al. 2015 , Wang et al. 2016 ). Tannic acid (TA) are a group of naturally occurring polyphenol compounds, appearing widely in various types of trees and higher plant species, such as green tea, coffee, and fresh fruits (Arapitsas 2012 ). Particularly, it has been well documented that phenolic hydroxyl groups of TA is capable of bonding with the amino group of protein, facilitating the formation of non-digestible solidified substances and thereby enhancing sludge dewater process. (Stojadinovic et al. 2013 ). Extracellular polymer substances (EPS) are produced by microbial metabolism and cell lysis and hence contributed significantly to the effluent COD, which is also fractionable according to the varying binding strengths to microorganism cells, producing fractions known as tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS) and soluble EPS (S-EPS).(Xu et al. 2013 ). It has been discovered that EPS is crucial to the dewatering process of sludge, and that it may control sludge characteristics like surface charge, hydrophobicity, bound water content, and floc strength (Hyrycz et al. 2022 ). Previous study indicated that proteins account for more than 40% of EPS in sludge, which may wrap and hinder water flow in the dewatering process, resulting in the poor dewaterability of sludge(Houghton et al. 2001 , Liu &Fang 2002 ). On account of the characteristics of TA in combination with protein, the utilization of TA for enhancing sludge dewatering has attracted much attention in recent years, owing to their abundant functional groups, non-toxicity, and cost-effectiveness(Jing et al. 2022 )(Chen et al. 2022 ). In addition, in view of the reducibility of TA, TA can be utilized to change the valence state of the metal, leading to the effective removal of contaminants can also be achieved through the activation of oxidants. Yang et al investigated the feasibility of MnFe 2 O 4 -biochar (MFB) for enhancing sludge dewatering, which was activated by peroxymonosulfate (PMS) in combination with TA. The authors reported that the combination of TA with protein could not only improve the compressibility and dewaterability of sludge, but also accelerate the valence state transition of Fe and Mn, enhancing the oxidation capacity of the system through PMA activation enhancement (Yang et al. 2022 ). Similarly, Ge et al explored a novel method using Fe 2+ -activated persulfate combined with TA for improving dewatering process, and found that TA effectively raised the flocculability of the sludge and enlarged the size of the sludge particles, making large and compact aggregations(Ge et al. 2020 , Xiao et al. 2020 ). Nevertheless, the practical application of TA used in sludge dewatering was limited due to the narrow pH range (Ge et al. 2019 ). To date, few studies have been conducted to investigate the role of modified TA with a wide range of pH in enhancing sludge dewatering performance. Chitosan (CS) is the second largest natural organic resource on the earth. Owing to its non-toxic, biodegradable, and eco-friendly characteristics, it is an ideal raw material for the synthesis of flocculant for wastewater treatment and sludge dewatering(Wang et al. 2016 , Wang et al. 2019 , Wu et al. 2020 ). In addition, the dewatering performance of the sludge can also be enhanced using CS as a cationic flocculant through charge neutralization(Zhang et al. 2019 ). However, with its poor dissolution performance, it is usually necessary to dissolve CS in acid, prior to the compatibility with water. Furthermore, TA is characterized hydrophilic with an abundant phenolic hydroxyl group, the combination of TA and CS has therefore high potential for improving the solubility of CS, while conferring positive electric groups to TA(Curcio et al. 2009 )(Jing et al. 2019 ). To the best of our knowledge, no thorough investigation has been conducted to far on the effectiveness and suitability of the novel CS-TA flocculants for sludge dewatering.. Within the context, the main objective of this study is to investigate a novel CS-TA flocculant for safe, rapid and efficient sludge dewatering under a wide pH range. More precisely, the goal of this research is to i) assess the factors affecting CS-TA flocculants' flocculation efficacy during sludge dewatering; iii) elucidate the mechanism of CS-TA in sludge dewatering; and iv) examine the role of CS-TA in the removal of organic contaminant. The finding of this study will provide a comprehensive insight into the better understanding for the feasibility and mechanism of the modified tannic acid used in the field of sludge dewatering. 2. Materials and methods 2.1 Sludge source and chemicals Raw Sewage Sludge was collected from a wastewater treatment plant in Guangzhou, Guangdong province. The sewage treatment plant uses modified A2/O process with a handing capacity of 1,200,000 m 3 per day. The sludge samples were stored at 4 ℃ (for less than 1 week) prior to use for minimizing the change of its physicochemical properties. The main parameters of raw sludge are shown in Table 1 .TA, CS, hydrogen peroxide, and ascorbic acid, was procured from Shanghai Aladdin Biochemical Technology Co., Ltd, China. Table 1 Characteristics of the raw sewage sludge. Water content (%) SRF×10 12 (m.kg − 1 ) CST (s) pH TSS (g L − 1 ) Zeta (mV) 98.20 18.94 56.20 7.1 20.45 -28.4 ± 0.30 ± 4.53 ± 2.33 ± 0.08 ± 1.95 ± 0.49 2.2. Preparation of dewatering agents In this study, TA was first introduced onto CS utilizing a redox pair consisting of ascorbic acid and hydrogen peroxide. Simply put, 4 mL of hydrogen peroxide solution (0.216 mol L-1) was mixed with 1.0 g of ascorbic acid to produce ascorbate and hydroxyl radicals. 2g of CS were entirely dissolved in 1% acetic acid. After that, the two solutions were stirred for 30 minutes (200 r min-1) to generate hydroxyl radicals, which are the result of the reaction between hydrogen peroxide and ascorbic acid. The hydrogen atoms are then extracted from the amino and hydroxyl groups of CS by the hydroxyl radicals, forming macromolecular CS radicals. Afterward, TA was added to the CS solution at a molar ratio of 0.08:1 repeat units(Jing et al. 2019 ). As such, CS-TA was formed when TA molecules in close proximity to the reactive sites acted as acceptors for CS radicals. After that, the mixture was well combined and left to stand at room temperature for 24 hours. Following the introduction of the obtained solution into a dialysis bag (MwCO 8000–14000 D), dialyzing against deionized water for 48 hours, and then freeze-drying for 72 hours resulted. 2.3. Sludge conditioning and dewatering The sludge conditioning and dewatering was divided into two stages. In the first stage, the optimal conditions of CS-TA for sludge dewatering were investigated, including the optimal doses, optimal pH and temperature. In the second stage, the sludge dewatering performance was evaluated, based on the different pretreatment conditioners, which can be categorized into several groups: i) TA only; ii) CS only; iii) CS-TA; iv) TA + CS; and vi) CS + TA, the different sludge conditioning procedures were shown in Table 2 (the optimal dosage of Tannic acid and chitosan was chosen according to Fig S1 ). Table 2 Different sludge conditioning procedures. Symbol Conditioners Dosage Conditioning TA (mmol/g TS) CS (mg/gTS) CS-TA (mg/gTS) RS None 0 0 0 200 rpm/1 min → 80 rpm/5 min TA TA only 0.15 0 0 200 rpm/1 min CS CS only 0 20 0 200 rpm/30s → 80 rpm/5 min CS-TA CS-TA only 0 0 30 200 rpm/30s → 80 rpm/5 min TA + CS First TA then CS 0.15 20 0 TA→ 200 rpm/1 min → CS solutions→ 200 rpm/30s→ 80 rpm/5 min CS + TA First CS then TA 0.15 20 0 CS solutions → 200 rpm/30s→ 80 rpm/5 min TA→ 300 rpm/2 min For each experimental set-up, the glass beakers were filled with 200 ml raw sludge. After treatment, 5 ml of the sludge was used for determination of Capillary Suction Time (CST).50 ml of the sludge were taken out to determine the amount of water content. The filtered sludge cake was dried in the oven at 105℃ for 2 hours to obtain a constant weight, which were employed for analysis of contact angle and bound water content. 1 ml of the sludge was diluted 50 times for the measurement of zeta potential and particle size. 50 ml of the sludge was extracted for analysis of protein and polysaccharide. 2.4 Analytical methods 2.4.1 Characterization of dewatering agents The formation of covalent bonds between TA and CS was verified by (FTIR, Tensor 27, Bruker, Germany) with the wavelength of 500–4000 cm − 1 and Bruker D8 X-ray diffractometer (XRD, Empyrean, Panalytical, Netherland) with Cu and Kα irradiation in the range of 2θ = 10–80°(Cui et al. 2023a ). 2.4.2 Sludge dewaterability Water contents were determined based on standard method of vacuum filtration described by He et al. The negative pressure and duration time of vacuun filtration were 0.06 Mpa and 30min, respectively(He et al. 2022 ). CST was determined with a 304M CST instrument (model 304M, Triton, UK). Using a differential scanning calorimetry analyzer (DSC 214 Polyma, Netzsch, Germany), the bound water content of the sludge was ascertained(Feng et al. 2022 ). Briefly, the temperature of sludge was first decreased to -30℃ and then increased to 20℃ at a rate of 5℃ min − 1 . While the total water content was recorded as Wt, the bound water content was recorded as Wb. The relationship can be expressed by the following equation: $$\text{W}\text{b}=(\text{W}\text{t}-\frac{\text{Q}}{\varDelta \text{H}})/(1-\text{W}\text{t})$$ 1 where Q indicatesDSC enthalpy of the sludge sample; \(\varDelta \text{H}\) denotes the standard melting heat of ice and equals to 334.7 (J g − 1 ). 2.4.2 Physicochemical characteristics of the sludge The particle size of the sludge was determined by a Mastersize (Mastersizer 2000; Malvern, UK) with the instrument shading rate of 15–20%. The zeta potential of sewage sludge was determined with a Zetasizer (Nano ZS90, Malvern, UK), which were carried out in each condition as six measurement replicates in order to provide a trustworthy data foundation for ZP value. The micromorphology of sludge was visualized and photographed with 10kX using a scanning electron microscope (SEM, Ultra 55, Carl Zeiss, Germany). The determination of the functional groupings was made utilizing Fourier transform infrared spectrometer (FTIR) (FTIR, Tensor 27, Bruker, Germany). 2.4.3 EPS extraction and analysis EPS fractions of sludge were produced by applying an extraction method that has been previously documented.(Ge et al. 2019 ). Briefly, After centrifuging a 30 mL sludge sample for 10 minutes at 4000 g, the supernatant, or soluble EPS (S-EPS), was collected. Following this, a 0.05% NaCl solution heated to 70°C was added to the centrifuge tubes to dilute the residual sludge particles to their original volume. The material was then centrifuged at 4000 g for 10 minutes after being subjected to shear pressures for 1 minute. The supernatant was classified as loosely-bound EPS (LB-EPS). After adding the preceding NaCl solution, the tightly-bound EPS (TB-EPS) was collected and maintained in a water bath at 60°C for 30 minutes. The combined liquid was then centrifuged for 15 minutes at 4°C at 4000 g. It was believed that the new supernatant was TB-EPS. Each extracted supernatant (i.e., S-EPS, LB-EPS, and TB-EPS) was filtered using the 0.45-µm cellulose acetate membrane filter (Φ25mm, Jinteng, China). Proteins and polysaccharides in EPS fractions were determined using the Bradford assay and anthrone-sulfuric acid method, (using glucose as the standard), respectively (Chen et al. 2020 ). The contact angle of sludge was measured by an optical contact angle meter (DSA25, Kruss, Germany). Infrared spectra of sludge before and after reaction was detected by FTIR (Tensor 27, Bruker, Germany) with the wavelength of 500–4000 cm − 1 . Meanwhile Three-dimensional fluorescence excitation emission matrix were analyzed according to Text S1(Cui et al. 2023b ). 2.5 Statistical analysis All the tests were performed in triplicate. As a statistical analysis tool, pearson's correlation were performed to determine the significance among the results. In this study, p < 0.05 was considered statistically significant. An analysis of variance was used to evaluate the significance of results with SPSS.20. 3. Results and discussion 3.1 Characterization of CS-TA To identify the conjugation of CS with TA, the FTIR spectra of TA-CS were analyzed. As illustrated in Fig. 1a. The stretching vibration absorption peaks of the hydroxyl group caused the strong absorption peak at around 3000–3500 cm − 1 . Several peaks at 1716cm − 1 , 1620cm − 1 , and 1535cm − 1 , were observed, which were assigned to the aromatic rings of TA(Liu et al. 2020 ). These findings supported the conjugation of CS and TA. Furthermore, the CS-TA spectrum revealed the saccharide chain structure of CS, which constituted the foundation of the system. This structure was identified by the peaks at 1097cm-1 (asymmetric stretching of the C-O-C bridge) and 894cm-1 (stretching of the saccharide ring)(Nawaz et al. 2023 , Rahmani et al. 2016 ). XRD was used to determine the crystalline structures of CS-TA and its substrates, as shown in Fig. 1b. While CS demonstrated conventional peaks at 2θ = 11.6° (crystal form I) and 2θ = 20.2° (crystal form II), respectively, TA showed a peak at 2θ = 25.2° (Fig. 6). Following conjugation, a broad peak was seen in CS-TA at 2θ = 23.5°, suggesting that CS-TA had less crystallinity than TA but more than CS. According to the earlier analysis, the high degree of crystallinity in CS can be attributed to the strong hydrogen bonds that exist both within and between molecules(Hu et al. 2016 ). However, during the grafting process, the aromatic rings of TA may prevent CS from forming hydrogen bonds, which would reduce the crystallinity of CS-TA. 3.2 The performance of CS-TA on sludge dewatering 3.2.1 Factors affecting performance of sludge dewatering Water content and CST of the sludge were used as the judgment basis to investigate the influencing factors affecting performance of sludge dewatering, such as doses of CS-TA, stirring time, pH and reaction temperature. Figure 2a and Fig. 2b shows the impact of CS-TA dosages and stirring time on sludge dewaterability performance. It was found that 30 mg CS-TA g − 1 total solid (TS) showed the highest dewaterability compared to other doses. This finding might have been attributed to the poor flocculation and aggregation ability of the sludge with low concentrations of CS-TA(Lu et al. 2014 ). While the doses greater than 30 mg CS-TA g − 1 total solid (TS) also exhibited the worse dewaterability, presumably due to the complete coverage of the surface chains, preventing further particle aggregation and flocculation growth(Blanco et al. 2005 , Hyrycz et al. 2022 ). As the stirring time increased from 0 to 30 min, the flocculant showed the best dewatering performance at 1 min, as shown in Fig. 2a and Fig. 2b. Similar finding was observed by (Ge et al. 2019 ), who indicated that the CST reduced rapidly when the stirring time was increased from 0 to 1 min. Especially, the lowest Wsc (59.78%) and CST (11.8s ) value was observed at 1 min. Nevertheless, our finding was inconsistent with the results observed by Zhang et al (Ge et al. 2019 ), who reported that CST values were increased significantly with the increase in stirring time after TA conditioning. The reason behind this phenomenon was because TA cross-linked the biopolymers and aggregated into larger complexes within 1min, but the coalescent aggregations were easy to be destroyed caused by its loose structure and small density, resulting in the deterioration of the sludge dewaterability. However, in the present study, no significant increase in CST was observed, presumably due to the enhanced shear resistance of sludge flocs through the electrostatic neutralization of chitosan amino group. Therefore, 1 min was chosen as the optimal conditioning time in this study, which was shorter than those in previous report and suggested that CS-TA could quickly promote sewage sludge dewatering. Figure 2c and Fig. 2d depicted the effect of different pH and different temperature on CS-TA for sludge dewatering. As presented in Fig. 2c, the raw sludge exhibited the better dewaterability under both acidic and alkaline conditions, being consistent with previous study conducted by Wang et al., who indicated that acidification was able to destruct the aggregation of sludge via catalyzing the hydrolysis of polysaccharide and protein (Chen et al. 2020 , Wang et al. 2017 ). However, in the present study, no pronounced changes in sludge dewatering performance were observed under both acidic and alkaline conditions. Meanwhile, the alkaline condition showed the worse dewatering performance than acid conditions, presumably due to the fact that the alkaline conditions were more unfavorable to binding TA and protein. Therefore, in contrast to the TA, CS-TA exhibited a good dewatering efficiency over a wide range of pH. In terms of the effect of temperature on dewatering performance, the best dewaterability of raw and treated sludge was observed at 35℃, as illustrated in Fig. 2d. The increase in temperature would cause the release of sludge EPS, resulting in the deterioration of sludge filtration performance. However, the high temperature would cause the poor stability of the combined flocs after treatment, resulting in the increase in bound water content.(Wang et al. 2017 ) These findings suggested that CS-TA possessed the capacity for enhancing sewage sludge dewatering over a wide range of pH under normal temperature. 3.2.2 Effects of pretreatment under different synergistic condition on sludge dewatering performance To better understand the effects of flocculants on sludge dewatering performance, further study on the physicochemical characteristics and microstructural properties of flocculants were investigated. As presented in Fig. 3a It was found that CS-TA exhibited the best dewaterability, with the Wsc and CST values of 64.21% and 19.2s, respectively. With respect to TA + CS and CS + TA, the values for water content were 66.12% and 65.12% respectively, while CST value were 37.4s and 36.9s respectively, indicating that synergistic conditioning achieved better filterability, compared with that of raw sludge and single conditioning. However, these values of TA + CS and CS + TA were higher than CS-TA, reinforcing that CS-TA was more efficient on sludge dewatering, compared to TA + CS and CS + TA. The reason behand this phenomenon was that if the sludge was first conditioned with the chitosan/tannic acid, a large and dense agglomeration would be initially formed, which prevented some of the inner flocs from working when floccutant was dosed later. As a result, following fast mixing quickly broke apart the agglomeration. The variations in bound water content in sludge were shown in Fig. 3b. The lowest content of bound water in sludge was observed in the treatment with CS-TA conditioning, implying that the new flocculant successfully strengthened flocculation ability, thus enhancing the dewatering performance of the sludge. It was widely accepted that bound water in sludge was more difficult to extract than free water because it tended to cling firmly to EPS and sludge particles via chemical bonds and intermolecular interactions found inside sludge flocs(Zhu et al. 2020 ). Therefore, one of the key factors influencing sludge dewaterability was the amount of bound water present in the sludge. Numerous research revealed that effective methods to improve sludge dewatering include enhancing sludge filterability and changing the affinity of EPS for water molecule capture (bound water).(Guo et al. 2018 ) The capacity of CS-TA to liberate bound water into free water may have played a role according to these results, which supported the fact that CS-TA was more effective at dewatering sludge. 3.3The performance of CS-TA on physical characteristics of sludge Sludge particle size was recognized as a vital parameter influencing sludge dewaterability (Lu et al. 2014 ).Prior research revealed a strong correlation between the rise in floc size and the increase in sludge dewatering capacity(He et al. 2021 ). The finding might attributed to the fact that the extremely small particle size of the sludge could absorb more bound water and was difficult to remove by an external force. Consequently, a key tactic for improving sludge dewatering efficiency is the addition of flocculant to agglomerate sludge flocs in order to increase particle size. In the present study, as illustrated in Fig. 3(c), the sludge particle size were 86.40 um of raw sludge, 108.62 um for TA treated sludge and 117.41um of CS-TA treated sludge. This finding implied that the addition of CS-TA favored the formation of larger particles compared to the raw sludge, and CS-TA facilitated to flocculate fine particles into larger agglomerations. The higher particle size of CS-TA-treated sludge indicates that after the introduction of chitosan, the adsorption bridging effect, which CS-TA displayed, was crucial to the flocculation conditioning procedure of sludge dewatering.. The morphology and dewatering efficiency of sludge flocs were significantly influenced by the zeta potential of the sludge, which was the primary factor governing colloidal stability(He et al. 2024 ). Because of the ionization of the anionic functional groups of EPS, the sludge particles are negatively charged. Figure 3(d) presents the zeta potential of dewatering agents. After TA treatment, zeta potential of sludge decreased to − 25.73 ± 0.61 mV from − 24.29 ± 0.49 mV, which was caused by the negative charge of tannic polymers. This finding was consistent with the study conducted by Ge et al(Ge et al. 2019 , Ge et al. 2019 ), who reported that zeta potential was lifted after CS-TA conditioning. The phenomenon was attributed to the introduction of anionic functional groups in chitosan, facilitating the neutralization of the surface charge of the sludgeand reducing the repulsive force among the particles in the sludge The change in morphology of sludge was investigated using by SEM, as illustrated in Fig. 4. The comparison between the raw and treated sludge showed that the particles in the sludge treated using CS-TA were entangled in the precipitation of the flocs, due to the interaction of flocculant and the particles(Li et al. 2006 ), reinforcing the complexation adsorption abilities of CS-TA. In terms of the treated sludge, as illustrated in Fig. 4(d) the treated sludge exhibited a higher porosity than that of the raw sludge. This finding suggested that this microstructure provided more channels for the release of water, which was beneficial for improving the dewatering performance. As a result, the sludge cake that was left over after dehydration had disconnected surfaces with voids, which allowed the structure to offer unobstructed water outflow channels during mechanical dewatering.(Wang et al. 2017 ) 3.4 Effects of CS-TA on the destruction of EPS EPS were large molecular weight biopolymers that were produced by the lysis and metabolism of microorganisms as well as the adsorption of organic materials from wastewater. Examples of these biopolymers include proteins, polysaccharides, and nucleic acids(Zhen et al. 2013 ). Figure 5 showed the profiles of proteins and polysaccharides in various EPS fractions. Neyens' assessment of the literature revealed that the concentration of EPS has a significant impact on the dewatering ability of sewage sludge(Neyens et al. 2004 ). Regarding the effects of different EPS components on sludge dewatering, previous studies revealed a negative correlation between sludge filtration and PN content in S-EPS(Wei et al. 2018 ). As presented in Fig. 5, the initial concentrations of PN and PS were 1.22g L − 1 and 0.86 mg g − 1 TS, respectively. It could be observed that PN concentration was decreased after treatment with CS, TA and CS-TA. This result could have been explained by the flocculation weakening the force of repulsion between the particles of sludge, resulting in the compression of the layered structure of EPS and PN migration. Furthermore, another possible explanation for this discrepancy may be the combination of TA with protein. Furthermore, because the molecular chain of PN contains basic (such as -NH2) and acidic (such as -COOH) groups, CS-TA can cross-link with PN released into S-EPS by hydrogen bond and electrostatic interaction to create complex and lower the PN content. The decrease in PS further suggested that the improvement in sludge dewaterability was facilitated by the elimination of hydrophilic components. As illustrated in Fig. 5, the concentration of PS was decreased in each layer of EPS. Nevertheless, previous studies indicated that the correlation between PS change and sludge dewatering was much smaller than that between PN and sludge dewatering.(Yang et al. 2022 ). In addition, as can be seen from the Fig S2, the kurtosis of the treated sludge fluorescence decreased in SEPS, LBEPS and TBEPS, which also indicates that CS-TA can reduce the sludge organic matter,the 3D-EEM fluorescence spectra was in agreement with the results obtained from FT-IR result. Moreover, the contact angle usually indicates the hydrophilic and hydrophobicity of the sludge. The smaller the contact angle is, the more hydrophilic the sludge fraction is. On the contrary, the larger the contact angle is, the more oleophilic the powder surface is(Ahmad et al. 2018 ). Hydrophilic functional groups (such as -OH and -NH2) and hydrogen bonds are generally present in polysaccharides and proteins, and they facilitate the interaction of these molecules with water molecules(Tao et al. 2022 ). Furthermore, a prior study found that, rather than the sludge contents, the water-holding capabilities of sludge are more reliant on the spatial distribution of hydrophilic/hydrophobic functional groups(Wu et al. 2020 ). While hydrophilic components are primarily found inside sludge, hydrophobic components may be more prevalent on the outside of the sludge(Yu et al. 2021 ). It was later discovered that the CS-TA treatment raised the contact angle of sludge from 68.04° to 91.44°, as shown in Fig. 6. This result showed that water molecules had trouble adhering to the surface of bioflocs, indicating that the hydrophobicity of the sludge had increased(Li et al. 2020 ). These findings provided more evidence that lowering the PS and PN concentrations in EPS could improve the dewaterability and relative hydrophobicity of sludge. The FTIR analysis of raw sludge and sludge treated with CS-TA is presented in Fig. 6a. The FTIR peak locations and numbers of EPS fractions in the raw and treated sludge were comparable, suggesting that the chemical group types were also identical in both samples.The functional group -OH was ascribed to a peak that appeared at 3440 cm-1, indicating the presence of hydroxyl groups in the sludge cake.(Xu et al. 2018 ) Also discovered were the bands at 2858 and 2927 cm − 1 , which are connected to the C-H stretching vibrations of aliphatic and lipid molecules, respectively. Additionally, at transmission spectra of 1649cm − 1 , C-N stretching vibrations from the protein's amide I group and C = O stretching vibrations from the ester were detected. Furthermore, CO-NH from the amide II group exhibited both C-N and N-H stretching, with an absorption intensity peak detected at around 1546 cm − 1 . The vibration absorption peak of hydroxyl in polysaccharides was linked to the peak at approximately 1045 cm − 1 , which was ascribed to O-H, C-O-C, and C-C vibration. The strength of this peak was significantly higher in raw sludge than in treated sludge. Significantly, following CS-TA treatment, the hydrophilic funditonal groups of PN and PS broke down as seen by the reduction in peak intensities of 2927, 1649, 1546, and 1045 cm − 1 . the disruption of functional group cleavage or started hydroxylation of aromatic rings, which causes EPS disintegration(Menon et al. 2020 ). 4. Conclusion In this study, we applied a novel flocculant CS-TA to enhance the sludge dewaterability. The characterization of sludge using FTIR and XRD analysis indicated that CS chain was the backbone of CS-TA, and aromatic rings of CS-TA confirmed the conjugation of CS with TA. CS-TA exhibited the best dewaterability, with the Wsc and CST values of 64.21% and 19.2s, respectively. 30 mg CS-TA g − 1 TS showed the highest dewaterability compared to other doses. In contrast to TA, CS-TA exhibited a good dewatering efficiency over a wide range of pH. Meanwhile, the dewatering mechanism of CS-TA was analyzed by physicochemical characteristics and microstructural properties of sludge. The analysis of particle size, zeta potential and microscope images implied that CS-TA improved sludge dewatering performance through adsorption bridging effect and charge neutralization. In addition, the analysis results of EPS showed a decrease in the concentration of PN and PS which was closely related the performance of sludge dewatering. These findings are expected to advance our understanding for the development a novel CS-TA flocculent and optimization of synergestic pretreatment condition for sledge dewatering enhancement. Declarations Funding This work was supported by the National Natural Science Foundation of China (NO. 42177369), National Key Research and Development Program of China (NO. 2019YFA0210400), Guangdong Basic and Applied Basic Research Natural Science Funding (NO. 2023A1515012130), Maoming Sci. Technol. Program (NO.2021S0054) and Maoming Green Chemical Industry Research Institute Fund (MMGCIRI-2022YFJH-Y-01). C ompeting Interests The authors have no relevant financial or non-financial interests to disclose. Author Contributions All authors contributed to the study conception and design. Yuejin Liu : Investigation, Data curation, Formal analysis, Writing - original draft. Xiaojun Niu: Conceptualization, Funding acquisition. Dongqing Zhang: Resources, Writing - review & editing. Lingling Zhou: Visualization. Chunyang Tao: Methodology. Yu Lin: Supervision. Siping, Chen: Validation. Yawen Chen : Methodology. Zhang Lin: Funding acquisition.All authors read and approved the final manuscript. Ethical Approval Not applicable Consent to Participate Not applicable Consent to Publish Not applicable References Ahmad D, van den Boogaert I, Miller J, Presswell R, Jouhara H (2018): Hydrophilic and hydrophobic materials and their applications. Energy sources. Part A, Recovery, utilization, and environmental effects 40, 2686-2725 Arapitsas P (2012): Hydrolyzable tannin analysis in food. FOOD CHEM 135, 1708-1717 Bao P, Du C, Li Y, Jiang H, Zhou L, Yu G, Sun S, Zhou L, Li X, Teng J, Wang X, Wang J (2024): Application of skeleton builders to sludge dewatering and disposal: A critical review. SCI TOTAL ENVIRON 906, 167106 Blanco A, Negro C, Fuente E, Tijero J (2005), Effect of shearing forces and flocculant overdose on filler flocculation mechanisms and floc properties. IND ENG CHEM RES 44, 9105-9112 Cao B, Zhang T, Zhang W, Wang D (2021): Enhanced technology based for sewage sludge deep dewatering: A critical review. WATER RES 189, 116650 Chen N, Tao S, Xiao K, Liang S, Yang J, Zhang L (2020): A one-step acidification strategy for sewage sludge dewatering with oxalic acid. CHEMOSPHERE 238, 124598 Chen R, Dai X, Dong B (2022): Decrease the effective temperature of hydrothermal treatment for sewage sludge deep dewatering: Mechanistic of tannic acid aided. WATER RES 217, 118450 Chen Z, Zhang W, Wang D, Ma T, Bai R (2015): Enhancement of activated sludge dewatering performance by combined composite enzymatic lysis and chemical re-flocculation with inorganic coagulants: Kinetics of enzymatic reaction and re-flocculation morphology. WATER RES 83, 367-376 Cui J, Niu X, Zhang D, Ma J, Zhu X, Zheng X, Lin Z, Fu M (2023a): The novel chitosan-amphoteric starch dual flocculants for enhanced removal of Microcystis aeruginosa and algal organic matter. CARBOHYD POLYM 304, 120474 Cui J, Niu X, Zhang D, Ma J, Zhu X, Zheng X, Lin Z, Fu M (2023b): The novel chitosan-amphoteric starch dual flocculants for enhanced removal of Microcystis aeruginosa and algal organic matter. CARBOHYD POLYM 304, 120474 Curcio M, Puoci F, Iemma F, Parisi OI, Cirillo G, Spizzirri UG, Picci N (2009): Covalent Insertion of Antioxidant Molecules on Chitosan by a Free Radical Grafting Procedure. J AGR FOOD CHEM 57, 5933-5938 Feng Q, Guo K, Gao Y, Liu B, Yue Q, Shi W, Feng C, Zhou J, Wang G, Gao B (2022): Effect of coagulation treatment on sludge dewatering performance: Application of polysilicate and their mechanism. SEP PURIF TECHNOL 301, 121954 Feng X, Wan J, Deng J, Yue X, Yang Y, He Z, Fang X, Chen T, Li S, Lu J, Long Y (2022): Study on the regulation of sludge dewatering by hydrophobically associating cationic polyacrylamide coupled with framework materials. Journal of Water Process Engineering 45, 102502 Ge D, Yuan H, Xiao J, Zhu N (2019): Insight into the enhanced sludge dewaterability by tannic acid conditioning and pH regulation. SCI TOTAL ENVIRON 679, 298-306 Ge D, Yuan H, Shen Y, Zhang W, Zhu N (2019): Improved sludge dewaterability by tannic acid conditioning: Temperature, thermodynamics and mechanism studies. CHEMOSPHERE 230, 14-23 Ge D, Zhang W, Yuan H, Zhu N (2019): Enhanced waste activated sludge dewaterability by tannic acid conditioning: Efficacy, process parameters, role and mechanism studies. J CLEAN PROD 241, 118287 Ge D, Dong Y, Zhang W, Yuan H, Zhu N (2020): A novel Fe2+/persulfate/tannic acid process with strengthened efficacy on enhancing waste activated sludge dewaterability and mechanism insight. SCI TOTAL ENVIRON 733, 139146 Guibal E, Van Vooren M, Dempsey BA, Roussy J (2006): A Review of the Use of Chitosan for the Removal of Particulate and Dissolved Contaminants. SEP SCI TECHNOL 41, 2487-2514 Guo J, Chen C, Jiang S, Zhou Y (2018): Feasibility and Mechanism of Combined Conditioning with Coagulant and Flocculant To Enhance Sludge Dewatering. ACS SUSTAIN CHEM ENG 6, 10758-10765 He D, Bao B, Sun M, Chen J, Luo H, Li J (2021): Enhanced dewatering of activated sludge by acid assisted Heat–CaO2 treatment: Simultaneously removing heavy metals and mitigating antibiotic resistance genes. J HAZARD MATER 418, 126248 He D, Sun M, Bao B, Chen J, Luo H, Li J (2022): Rethinking the timing of flocculant addition during activated sludge dewatering. Journal of Water Process Engineering 47, 102744 He D, Zhu T, Sun M, Chen J, Luo H, Li J (2024): Unraveling synergistic mechanisms of polyacrylamide coagulation and Fe2+/CaO2 Fenton-like oxidation to enhance sludge dewatering. CHEM ENG J 479, 147576 He Z, Wang F, Zou Z, Tang C, Zhou A, Liu W, Ren Y, Li Z, Wang A (2023): Recent advances and perspectives in roles of humic acid in anaerobic digestion of waste activated sludge. CHEM ENG J 466, 143081 Houghton JI, Quarmby J, Stephenson T (2001): Municipal wastewater sludge dewaterability and the presence of microbial extracellular polymer. WATER SCI TECHNOL 44, 373-9 Hu Q, Wang T, Zhou M, Xue J, Luo Y (2016): In Vitro Antioxidant-Activity Evaluation of Gallic-Acid-Grafted Chitosan Conjugate Synthesized by Free-Radical-Induced Grafting Method. J AGR FOOD CHEM 64, 5893-5900 Hyrycz M, Ochowiak M, Krupińska A, Włodarczak S, Matuszak M (2022): A review of flocculants as an efficient method for increasing the efficiency of municipal sludge dewatering: Mechanisms, performances, influencing factors and perspectives. SCI TOTAL ENVIRON 820, 153328 Jing W, Xiaolan C, Yu C, Feng Q, Haifeng Y (2022): Pharmacological effects and mechanisms of tannic acid. BIOMED PHARMACOTHER 154, 113561 Jing Y, Diao Y, Yu X (2019): Free radical-mediated conjugation of chitosan with tannic acid: Characterization and antioxidant capacity. Reactive and Functional Polymers 135, 16-22 Li J, Liu L, Liu J, Ma T, Yan A, Ni Y (2016): Effect of adding alum sludge from water treatment plant on sewage sludge dewatering. Journal of Environmental Chemical Engineering 4, 746-752 Li T, Zhu Z, Wang D, Yao C, Tang H (2006): Characterization of floc size, strength and structure under various coagulation mechanisms. POWDER TECHNOL 168, 104-110 Li Y, Zhu Y, Wang D, Yang G, Pan L, Wang Q, Ni B, Li H, Yuan X, Jiang L, Tang W (2020): Fe(II) catalyzing sodium percarbonate facilitates the dewaterability of waste activated sludge: Performance, mechanism, and implication. WATER RES 174, 115626 Liang J, Zhou Y (2022): Iron-based advanced oxidation processes for enhancing sludge dewaterability: State of the art, challenges, and sludge reuse. WATER RES 218, 118499 Lin Q, Peng H, Zhong S, Xiang J (2015): Synthesis, characterization, and secondary sludge dewatering performance of a novel combined silicon–aluminum–iron–starch flocculant. J HAZARD MATER 285, 199-206 Liu H, Fang HHP (2002): Extraction of extracellular polymeric substances (EPS) of sludges. J BIOTECHNOL 95, 249-256 Liu L, Ge C, Zhang Y, Ma W, Su X, Chen L, Li S, Wang L, Mu X, Xu Y (2020): Tannic acid-modified silver nanoparticles for enhancing anti-biofilm activities and modulating biofilm formation. BIOMATER SCI-UK 8, 4852-486 Lu L, Pan Z, Hao N, Peng W (2014): A novel acrylamide-free flocculant and its application for sludge dewatering. WATER RES 57, 304-312 Menon U, Suresh N, George G, Ealias AM, Saravanakumar MP (2020): A study on combined effect of Fenton and Free Nitrous Acid treatment on sludge dewaterability with ultrasonic assistance: Preliminary investigation on improved calorific value. CHEM ENG J 382, 123035 Mowla D, Tran HN, Allen DG (2013): A review of the properties of biosludge and its relevance to enhanced dewatering processes. Biomass and Bioenergy 58, 365-378 Nawaz A, Atif M, Naz I, Khan A, Naz F, Ali N (2023): Comparative robustness and sustainability of in - situ prepared antimony nanoarchitectonics in chitosan / synthesized carboxymethyl chitosan in environmental remediation perspective. INT J BIOL MACROMOL 235 Neyens E, Baeyens J, Dewil R, De Heyder B (2004): Advanced sludge treatment affects extracellular polymeric substances to improve activated sludge dewatering. J HAZARD MATER 106, 83-92 Rahmani S, Mohammadi Z, Amini M, Isaei E, Taheritarigh S, Tehrani NR, Tehrani MR (2016): Methylated 4 - N , N dimethyl aminobenzyl N , O carboxymethyl chitosan as a new chitosan derivative : Synthesis , characterization , cytotoxicity and antibacterial activity. CARBOHYD POLYM 149, 131-139 Stojadinovic M, Radosavljevic J, Ognjenovic J, Vesic J, Prodic I, Stanic-Vucinic D, Velickovic TC (2013): Binding affinity between dietary polyphenols and 尾-lactoglobulin negatively correlates with the protein susceptibility to digestion and total antioxidant activity of complexes formed. FOOD CHEM 136, 1263-1271 Tao N, Hu L, Fang D, Tarabara V, Zhou L (2022): Supplementation of tea polyphenols in sludge Fenton oxidation improves sludge dewaterability and reduces chemicals consumption. WATER RES 218, 118512 Wang D, Zhao T, Yan L, Mi Z, Gu Q, Zhang Y (2016): Synthesis, characterization and evaluation of dewatering properties of chitosan-grafting DMDAAC flocculants. INT J BIOL MACROMOL 92, 761-768 Wang H, Ma Y, Wang H, Hu H, Yang H, Zeng RJ (2017): Applying rheological analysis to better understand the mechanism of acid conditioning on activated sludge dewatering. WATER RES 122, 398-406 Wang J, Chon K, Ren X, Wu H, Kou Y, Hwang MH, Chae KJ (2019): Combined use of polymeric ferric sulfate and chitosan as a conditioning aid for enhanced digested sludge dewatering. ENVIRON TECHNOL 40, 2695-2704 Wang L, Qian C, Jiang J, Ye X, Yu H (2017): Response of extracellular polymeric substances to thermal treatment in sludge dewatering process. ENVIRON POLLUT 231, 1388-1392 Wei H, Gao B, Ren J, Li A, Yang H (2018): Coagulation/flocculation in dewatering of sludge: A review. WATER RES 143, 608-631 Wu B, Dai X, Chai X (2020): Critical review on dewatering of sewage sludge: Influential mechanism, conditioning technologies and implications to sludge re-utilizations. WATER RES 180, 115912 Wu P, Yi J, Feng L, Li X, Chen Y, Liu Z, Tian S, Li S, Khan S, Sun Y (2020): Microwave assisted preparation and characterization of a chitosan based flocculant for the application and evaluation of sludge flocculation and dewatering. INT J BIOL MACROMOL 155, 708-720 Xiao J, Ge D, Yuan H, Zhu N (2020): Waste activated sludge conditioning in a new Fe 2+ / persulfate / tannic acid process : Effectiveness and optimization study to enhance dewaterability. JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING 8 Xu H, Yu G, Jiang H (2013): Investigation on extracellular polymeric substances from mucilaginous cyanobacterial blooms in eutrophic freshwater lakes. CHEMOSPHERE 93, 75-81 Xu Q, Wang Q, Zhang W, Yang P, Du Y, Wang D (2018): Highly effective enhancement of waste activated sludge dewaterability by altering proteins properties using methanol solution coupled with inorganic coagulants. WATER RES 138, 181-191 Yan Y, Qin L, Gao J, Nan R, Gao J (2020): Protein extraction and sludge dewatering performance of ultrasound-assisted enzymatic hydrolysis of excess sludge. ENVIRON SCI POLLUT R 27, 18317-18328 Yang X, Zeng L, Huang J, Mo Z, Guan Z, Sun S, Liang J, Huang S (2022): Enhanced sludge dewaterability by a novel MnFe2O4-Biochar activated peroxymonosulfate process combined with Tannic acid. CHEM ENG J 429, 132280 Yang Y, Yang X, Yang Q, Zhang H, Xu W, Zhu L, Ma P, Li Y (2022): Exploring the feasibility and potential mechanism of synergistic enhancement of sludge dewaterability by ultrasonic cracking , chitosan re-flocculation and sludge - based biochar adsorption of water-holding substances. JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING 10 Yu W, Wen Q, Yang J, Xiao K, Zhu Y, Tao S, Liang S, Hu S, Wu Q, Hou H, Liu B, Hu J (2021): Novel Insights into Extracellular Polymeric Substance Degradation, Hydrophilic/Hydrophobic Characteristics, and Dewaterability of Waste Activated Sludge Pretreated by Hydroxylamine Enhanced Fenton Oxidation. ACS ES&T Engineering 1, 385-392 Zhang C, Ho S, Chen W, Eng CF, Wang C (2021): Simultaneous implementation of sludge dewatering and solid biofuel production by microwave torrefaction. ENVIRON RES 195, 110775 Zhang W, Wang H, Li L, Li D, Wang Q, Xu Q, Wang D (2019): Impact of molecular structure and charge property of chitosan based polymers on flocculation conditioning of advanced anaerobically digested sludge for dewaterability improvement. SCI TOTAL ENVIRON 670, 98-109 Zhen G, Lu X, Niu J, Su L, Chai X, Zhao Y, Li Y, Song Y, Niu D (2013): Inhibitory effects of a shock load of Fe ( II )- mediated persulfate oxidation on waste activated sludge anaerobic digestion. CHEM ENG J 233, 274-281 Zhu Y, Xiao K, Zhou Y, Yu W, Tao S, Le C, Lu D, Yu Z, Liang S, Hu J, Hou H, Liu B, Yang J (2020): Profiling of amino acids and their interactions with proteinaceous compounds for sewage sludge dewatering by Fenton oxidation treatment. WATER RES 175 Supplementary Files SupplementaryMaterial.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 09 Apr, 2024 Editor invited by journal 21 Mar, 2024 Editor assigned by journal 08 Mar, 2024 First submitted to journal 06 Mar, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4014664","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":289222489,"identity":"73b06397-0836-409e-a395-2dd756e42f32","order_by":0,"name":"Yuejin Liu","email":"","orcid":"","institution":"South China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yuejin","middleName":"","lastName":"Liu","suffix":""},{"id":289222490,"identity":"dfc999e9-210f-4945-a0a8-7bfa2ee00581","order_by":1,"name":"Xiaojun Niu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxUlEQVRIiWNgGAWjYBADOSBmPMDAkECUasYGIGHMwMDMQJqWxAaitci3nzF/8HHH4fR+ifwDBz5UpDHwt3fj12dwJsewceaZw7kzZyQzHJxxJodB4szZDfi1SPAYNvO2peVuuJHMcJi3rQIokotfi/wMoJa/bWnpBkRrYbgB1MLYZpMA1ZJDWIvBmbTCmb1tNoYzex4bAP2SxkPQL/Lthzd8+NkmIc/PnvjwwYeKZDn+9l4CDkMHPKQpHwWjYBSMglGAFQAAGx9JK6q43TcAAAAASUVORK5CYII=","orcid":"","institution":"South China University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Xiaojun","middleName":"","lastName":"Niu","suffix":""},{"id":289222491,"identity":"54326113-6d46-4a54-85ac-189c645b1d59","order_by":2,"name":"Dongqing Zhang","email":"","orcid":"","institution":"Guangdong University of Petrochemical Technology","correspondingAuthor":false,"prefix":"","firstName":"Dongqing","middleName":"","lastName":"Zhang","suffix":""},{"id":289222492,"identity":"3977a568-f379-4927-a944-1cbc8e29b0ac","order_by":3,"name":"lingling Zhou","email":"","orcid":"","institution":"South China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"lingling","middleName":"","lastName":"Zhou","suffix":""},{"id":289222493,"identity":"f7a09958-43e5-41bd-a95d-0477524c9505","order_by":4,"name":"chunyang Tao","email":"","orcid":"","institution":"South China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"chunyang","middleName":"","lastName":"Tao","suffix":""},{"id":289222494,"identity":"e7acac31-ed3f-461c-8a73-eeeabdd78b4a","order_by":5,"name":"yu Lin","email":"","orcid":"","institution":"guangzhou urban drainage limited","correspondingAuthor":false,"prefix":"","firstName":"yu","middleName":"","lastName":"Lin","suffix":""},{"id":289222495,"identity":"a150734e-a49c-4837-8593-41d5158fddf6","order_by":6,"name":"siping Chen","email":"","orcid":"","institution":"Guangdong University of Petrochemical Technology","correspondingAuthor":false,"prefix":"","firstName":"siping","middleName":"","lastName":"Chen","suffix":""},{"id":289222496,"identity":"9d3de806-66b7-4c0a-9e6c-c49cfb6bfb17","order_by":7,"name":"yawen Chen","email":"","orcid":"","institution":"Guangdong University of Petrochemical Technology","correspondingAuthor":false,"prefix":"","firstName":"yawen","middleName":"","lastName":"Chen","suffix":""},{"id":289222497,"identity":"c7852201-d587-4981-9680-eb7d0d973c87","order_by":8,"name":"zhang Lin","email":"","orcid":"","institution":"South China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"zhang","middleName":"","lastName":"Lin","suffix":""}],"badges":[],"createdAt":"2024-03-05 00:42:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4014664/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4014664/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54561710,"identity":"5aa6a489-adf0-4ce1-82f4-8b1193ff5022","added_by":"auto","created_at":"2024-04-12 10:05:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":380626,"visible":true,"origin":"","legend":"\u003cp\u003eCharacterization of CS, TA and CS-TA: (a)FTIR, (b)XRD.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4014664/v1/3b11abb57227b6fd7541a4ba.png"},{"id":54561670,"identity":"486374b0-2056-4f03-a658-21e950d5a809","added_by":"auto","created_at":"2024-04-12 10:05:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":120794,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of CS-TA on Wsc and CST: (a)Wsc of different doses, (b)CST of different doses, (c)pH (d)T.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4014664/v1/7230c568ca984b56d252350c.png"},{"id":54561672,"identity":"9720dfe4-35c7-424f-a0f0-9d45ab3f42de","added_by":"auto","created_at":"2024-04-12 10:05:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":57601,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of different treatment on : (a)Wsc and CST, (b)Bound water, (c) Particle size, (d) Zeta potential.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4014664/v1/d71ee8839ca047f9fe4eec85.png"},{"id":54561668,"identity":"60934bdd-8f1a-4859-83e6-d44f71eb8618","added_by":"auto","created_at":"2024-04-12 10:05:18","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":423377,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of conditioned sludge: (a)(c) Raw sludge, (b)(d)Treated sludge.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4014664/v1/8791e444d79c7d698dfd281b.png"},{"id":54562204,"identity":"ad6b358f-b4e3-49ff-b2f5-892991c6a66f","added_by":"auto","created_at":"2024-04-12 10:13:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":43974,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of different conditioning pretreatments on (a) the concentration of protein (PN) in the extracellular polymeric substance (EPS); (b) the concentration of polysaccharide (PS) in the extracellular polymeric substance (EPS).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4014664/v1/85ae934b3248f3177aa10446.png"},{"id":54561673,"identity":"8fb92ee0-24b8-45fe-a3ea-69d7b015c943","added_by":"auto","created_at":"2024-04-12 10:05:20","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":76951,"visible":true,"origin":"","legend":"\u003cp\u003e(a)FTIR of sludge Before and After reaction; Contact angle: (b) Raw sludge, (c) TA treated sludge, (d) CS-TA treated sludge.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4014664/v1/67205c07e67d1ad5f662f806.png"},{"id":54562578,"identity":"fad36da6-1efc-4f8a-aad5-ccf21c464602","added_by":"auto","created_at":"2024-04-12 10:21:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1394613,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4014664/v1/3fc7ae6b-94c8-4c91-9f07-0e1ba9617db2.pdf"},{"id":54561669,"identity":"48143dbf-930a-4fa6-927f-681fa71e924b","added_by":"auto","created_at":"2024-04-12 10:05:19","extension":"docx","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":302606,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-4014664/v1/0ea67a7534fc034602cee2e7.docx"}],"financialInterests":"","formattedTitle":"Insight into enhancing the performance of sludge dewatering using a novel flocculant CS-TA prepared through free radical-mediated conjugation","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWastewater treatment processes one of the most significant developments in environmental engineering during the twentieth century. As an inevitable by-product in each wastewater treatment process, activated sludge usually consists of numerous contaminants, such as pathogens, nutrients, organic pollutants, heavy metals and other toxic substances, posing a risk to ecosystem and public health of not properly treated (He et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, Neyens et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2004\u003c/span\u003e, Wu et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) Particularly, large quantities of sludge typically contain high water content (Wc) of more than 90%, which has been identified as one of the main reasons responsible for the ineffective disposal of sludge. Furthermore, the cost for sludge dewatering, depending directly on the sludge volume to be treated and sludge moisture content, usually accounts for more than 50% of the total operation expenditure in the wastewater treatment processes (Hyrycz et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, Wei et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). As such, sludge dewatering is of great significance for wastewater treatment, facilitating the subsequent transportation and disposal (Mowla et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo improve the dewaterability of activated sludge, different conditioning strategies, such as physical, chemical and biological methods, have been extensively explored(Cao et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Physical methods include pretreatment with non-chemical additives as skeleton builders, microwave conditioning, ultrasound and thermal/freeze pretreatment(Bao et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e, Yan et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Zhang et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, the development and application of non-chemical additives is limited by high dosage addition, while the microwave, ultrasound, and thermal/freeze pretreatment has the drawbacks of low efficiency and high energy consumption. Biological method has great limitations in practical use, due to slow growth of microorganisms. Chemical pretreatment, such as advanced oxidation process (AOP), flocculation and acid/alkali treatment, has the merits of high efficiency and low cost, Among which, flocculation is an effective approach for sludge dewatering, owing to its convenience and excellent performance(Wei et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). However, the commonly used inorganic coagulants, such as alum, poly-aluminum chloride (PAC), FeCl\u003csub\u003e3\u003c/sub\u003e and FeSO\u003csub\u003e4,\u003c/sub\u003e are fit for high-pressure dewatering with a narrow pH range. Meanwhile, the large doses for conditioning and the corrosion associated with the treatment equipment may incur the substantial overall treatment cost (Chen et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, Liang \u0026amp;Zhou \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). By contrast, organic flocculants, such as polyacrylamide (PAM) and cationic polyacrylamide (CPAM), possess unique advantages, such as low dosage requirement with wide pH range for application (Feng et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, Li et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). However, despite its popularity, the use of organic polymers has certain disadvantage relative to the secondary pollution. More recently, the application of natural polymer flocculant (e.g. cellulose, chitosan, amylum) for enhancing the dewaterability performance has become a research hotspot, owing to their high biodegradability and low cost (Guibal et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, Wu et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Nevertheless, sufficient low water content cannot be achieved in many sludge dewatering applications. As such, it is imperative to explore novel flocculants with high effectiveness, low cost and few environmental impact (Lin et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, Wang et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTannic acid (TA) are a group of naturally occurring polyphenol compounds, appearing widely in various types of trees and higher plant species, such as green tea, coffee, and fresh fruits (Arapitsas \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Particularly, it has been well documented that phenolic hydroxyl groups of TA is capable of bonding with the amino group of protein, facilitating the formation of non-digestible solidified substances and thereby enhancing sludge dewater process. (Stojadinovic et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Extracellular polymer substances (EPS) are produced by microbial metabolism and cell lysis and hence contributed significantly to the effluent COD, which is also fractionable according to the varying binding strengths to microorganism cells, producing fractions known as tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS) and soluble EPS (S-EPS).(Xu et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). It has been discovered that EPS is crucial to the dewatering process of sludge, and that it may control sludge characteristics like surface charge, hydrophobicity, bound water content, and floc strength (Hyrycz et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Previous study indicated that proteins account for more than 40% of EPS in sludge, which may wrap and hinder water flow in the dewatering process, resulting in the poor dewaterability of sludge(Houghton et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2001\u003c/span\u003e, Liu \u0026amp;Fang \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). On account of the characteristics of TA in combination with protein, the utilization of TA for enhancing sludge dewatering has attracted much attention in recent years, owing to their abundant functional groups, non-toxicity, and cost-effectiveness(Jing et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)(Chen et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In addition, in view of the reducibility of TA, TA can be utilized to change the valence state of the metal, leading to the effective removal of contaminants can also be achieved through the activation of oxidants. Yang et al investigated the feasibility of MnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-biochar (MFB) for enhancing sludge dewatering, which was activated by peroxymonosulfate (PMS) in combination with TA. The authors reported that the combination of TA with protein could not only improve the compressibility and dewaterability of sludge, but also accelerate the valence state transition of Fe and Mn, enhancing the oxidation capacity of the system through PMA activation enhancement (Yang et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Similarly, Ge et al explored a novel method using Fe\u003csup\u003e2+\u003c/sup\u003e-activated persulfate combined with TA for improving dewatering process, and found that TA effectively raised the flocculability of the sludge and enlarged the size of the sludge particles, making large and compact aggregations(Ge et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Xiao et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Nevertheless, the practical application of TA used in sludge dewatering was limited due to the narrow pH range (Ge et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). To date, few studies have been conducted to investigate the role of modified TA with a wide range of pH in enhancing sludge dewatering performance.\u003c/p\u003e \u003cp\u003eChitosan (CS) is the second largest natural organic resource on the earth. Owing to its non-toxic, biodegradable, and eco-friendly characteristics, it is an ideal raw material for the synthesis of flocculant for wastewater treatment and sludge dewatering(Wang et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, Wang et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, Wu et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In addition, the dewatering performance of the sludge can also be enhanced using CS as a cationic flocculant through charge neutralization(Zhang et al. \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, with its poor dissolution performance, it is usually necessary to dissolve CS in acid, prior to the compatibility with water. Furthermore, TA is characterized hydrophilic with an abundant phenolic hydroxyl group, the combination of TA and CS has therefore high potential for improving the solubility of CS, while conferring positive electric groups to TA(Curcio et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e)(Jing et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). To the best of our knowledge, no thorough investigation has been conducted to far on the effectiveness and suitability of the novel CS-TA flocculants for sludge dewatering..\u003c/p\u003e \u003cp\u003eWithin the context, the main objective of this study is to investigate a novel CS-TA flocculant for safe, rapid and efficient sludge dewatering under a wide pH range. More precisely, the goal of this research is to i) assess the factors affecting CS-TA flocculants' flocculation efficacy during sludge dewatering; iii) elucidate the mechanism of CS-TA in sludge dewatering; and iv) examine the role of CS-TA in the removal of organic contaminant. The finding of this study will provide a comprehensive insight into the better understanding for the feasibility and mechanism of the modified tannic acid used in the field of sludge dewatering.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Sludge source and chemicals\u003c/h2\u003e \u003cp\u003eRaw Sewage Sludge was collected from a wastewater treatment plant in Guangzhou, Guangdong province. The sewage treatment plant uses modified A2/O process with a handing capacity of 1,200,000 m\u003csup\u003e3\u003c/sup\u003e per day. The sludge samples were stored at 4 ℃ (for less than 1 week) prior to use for minimizing the change of its physicochemical properties. The main parameters of raw sludge are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.TA, CS, hydrogen peroxide, and ascorbic acid, was procured from Shanghai Aladdin Biochemical Technology Co., Ltd, China.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of the raw sewage sludge.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWater content\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSRF\u0026times;10\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(m.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCST\u003c/p\u003e \u003cp\u003e(s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTSS\u003c/p\u003e \u003cp\u003e(g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eZeta\u003c/p\u003e \u003cp\u003e(mV)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e98.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e56.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e20.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e-28.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;4.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;2.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;1.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.49\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Preparation of dewatering agents\u003c/h2\u003e \u003cp\u003eIn this study, TA was first introduced onto CS utilizing a redox pair consisting of ascorbic acid and hydrogen peroxide. Simply put, 4 mL of hydrogen peroxide solution (0.216 mol L-1) was mixed with 1.0 g of ascorbic acid to produce ascorbate and hydroxyl radicals. 2g of CS were entirely dissolved in 1% acetic acid. After that, the two solutions were stirred for 30 minutes (200 r min-1) to generate hydroxyl radicals, which are the result of the reaction between hydrogen peroxide and ascorbic acid. The hydrogen atoms are then extracted from the amino and hydroxyl groups of CS by the hydroxyl radicals, forming macromolecular CS radicals. Afterward, TA was added to the CS solution at a molar ratio of 0.08:1 repeat units(Jing et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). As such, CS-TA was formed when TA molecules in close proximity to the reactive sites acted as acceptors for CS radicals. After that, the mixture was well combined and left to stand at room temperature for 24 hours. Following the introduction of the obtained solution into a dialysis bag (MwCO 8000\u0026ndash;14000 D), dialyzing against deionized water for 48 hours, and then freeze-drying for 72 hours resulted.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Sludge conditioning and dewatering\u003c/h2\u003e \u003cp\u003eThe sludge conditioning and dewatering was divided into two stages. In the first stage, the optimal conditions of CS-TA for sludge dewatering were investigated, including the optimal doses, optimal pH and temperature. In the second stage, the sludge dewatering performance was evaluated, based on the different pretreatment conditioners, which can be categorized into several groups: i) TA only; ii) CS only; iii) CS-TA; iv) TA\u0026thinsp;+\u0026thinsp;CS; and vi) CS\u0026thinsp;+\u0026thinsp;TA, the different sludge conditioning procedures were shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (the optimal dosage of Tannic acid and chitosan was chosen according to Fig \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDifferent sludge conditioning procedures.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSymbol\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eConditioners\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eDosage\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eConditioning\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTA\u003c/p\u003e \u003cp\u003e(mmol/g TS)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCS\u003c/p\u003e \u003cp\u003e(mg/gTS)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCS-TA\u003c/p\u003e \u003cp\u003e(mg/gTS)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e200 rpm/1 min \u0026rarr; 80 rpm/5 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTA only\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e200 rpm/1 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCS only\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e200 rpm/30s \u0026rarr; 80 rpm/5 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCS-TA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCS-TA only\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e200 rpm/30s \u0026rarr; 80 rpm/5 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTA\u0026thinsp;+\u0026thinsp;CS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst TA then CS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTA\u0026rarr; 200 rpm/1 min \u0026rarr;\u003c/p\u003e \u003cp\u003eCS solutions\u0026rarr; 200 rpm/30s\u0026rarr; 80 rpm/5 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCS\u0026thinsp;+\u0026thinsp;TA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst CS then TA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCS solutions \u0026rarr; 200 rpm/30s\u0026rarr; 80 rpm/5 min\u003c/p\u003e \u003cp\u003eTA\u0026rarr; 300 rpm/2 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFor each experimental set-up, the glass beakers were filled with 200 ml raw sludge. After treatment, 5 ml of the sludge was used for determination of Capillary Suction Time (CST).50 ml of the sludge were taken out to determine the amount of water content. The filtered sludge cake was dried in the oven at 105℃ for 2 hours to obtain a constant weight, which were employed for analysis of contact angle and bound water content. 1 ml of the sludge was diluted 50 times for the measurement of zeta potential and particle size. 50 ml of the sludge was extracted for analysis of protein and polysaccharide.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Analytical methods\u003c/h2\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1 Characterization of dewatering agents\u003c/h2\u003e \u003cp\u003eThe formation of covalent bonds between TA and CS was verified by (FTIR, Tensor 27, Bruker, Germany) with the wavelength of 500\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eand Bruker D8 X-ray diffractometer (XRD, Empyrean, Panalytical, Netherland) with Cu and Kα irradiation in the range of 2θ\u0026thinsp;=\u0026thinsp;10\u0026ndash;80\u0026deg;(Cui et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2 Sludge dewaterability\u003c/h2\u003e \u003cp\u003eWater contents were determined based on standard method of vacuum filtration described by He et al. The negative pressure and duration time of vacuun filtration were 0.06 Mpa and 30min, respectively(He et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). CST was determined with a 304M CST instrument (model 304M, Triton, UK). Using a differential scanning calorimetry analyzer (DSC 214 Polyma, Netzsch, Germany), the bound water content of the sludge was ascertained(Feng et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Briefly, the temperature of sludge was first decreased to -30℃ and then increased to 20℃ at a rate of 5℃ min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. While the total water content was recorded as Wt, the bound water content was recorded as Wb. The relationship can be expressed by the following equation:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\text{W}\\text{b}=(\\text{W}\\text{t}-\\frac{\\text{Q}}{\\varDelta \\text{H}})/(1-\\text{W}\\text{t})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere Q indicatesDSC enthalpy of the sludge sample; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\varDelta \\text{H}\\)\u003c/span\u003e\u003c/span\u003e denotes the standard melting heat of ice and equals to 334.7 (J g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2 Physicochemical characteristics of the sludge\u003c/h2\u003e \u003cp\u003eThe particle size of the sludge was determined by a Mastersize (Mastersizer 2000; Malvern, UK) with the instrument shading rate of 15\u0026ndash;20%. The zeta potential of sewage sludge was determined with a Zetasizer (Nano ZS90, Malvern, UK), which were carried out in each condition as six measurement replicates in order to provide a trustworthy data foundation for ZP value. The micromorphology of sludge was visualized and photographed with 10kX using a scanning electron microscope (SEM, Ultra 55, Carl Zeiss, Germany). The determination of the functional groupings was made utilizing Fourier transform infrared spectrometer (FTIR) (FTIR, Tensor 27, Bruker, Germany).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.4.3 EPS extraction and analysis\u003c/h2\u003e \u003cp\u003eEPS fractions of sludge were produced by applying an extraction method that has been previously documented.(Ge et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Briefly, After centrifuging a 30 mL sludge sample for 10 minutes at 4000 g, the supernatant, or soluble EPS (S-EPS), was collected. Following this, a 0.05% NaCl solution heated to 70\u0026deg;C was added to the centrifuge tubes to dilute the residual sludge particles to their original volume. The material was then centrifuged at 4000 g for 10 minutes after being subjected to shear pressures for 1 minute. The supernatant was classified as loosely-bound EPS (LB-EPS). After adding the preceding NaCl solution, the tightly-bound EPS (TB-EPS) was collected and maintained in a water bath at 60\u0026deg;C for 30 minutes. The combined liquid was then centrifuged for 15 minutes at 4\u0026deg;C at 4000 g. It was believed that the new supernatant was TB-EPS. Each extracted supernatant (i.e., S-EPS, LB-EPS, and TB-EPS) was filtered using the 0.45-\u0026micro;m cellulose acetate membrane filter (Φ25mm, Jinteng, China). Proteins and polysaccharides in EPS fractions were determined using the Bradford assay and anthrone-sulfuric acid method, (using glucose as the standard), respectively (Chen et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The contact angle of sludge was measured by an optical contact angle meter (DSA25, Kruss, Germany). Infrared spectra of sludge before and after reaction was detected by FTIR (Tensor 27, Bruker, Germany) with the wavelength of 500\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Meanwhile Three-dimensional fluorescence excitation emission matrix were analyzed according to Text S1(Cui et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical analysis\u003c/h2\u003e \u003cp\u003eAll the tests were performed in triplicate. As a statistical analysis tool, pearson's correlation were performed to determine the significance among the results. In this study, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant. An analysis of variance was used to evaluate the significance of results with SPSS.20.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Characterization of CS-TA\u003c/h2\u003e \u003cp\u003eTo identify the conjugation of CS with TA, the FTIR spectra of TA-CS were analyzed. As illustrated in Fig.\u0026nbsp;1a. The stretching vibration absorption peaks of the hydroxyl group caused the strong absorption peak at around 3000\u0026ndash;3500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Several peaks at 1716cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1620cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 1535cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, were observed, which were assigned to the aromatic rings of TA(Liu et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These findings supported the conjugation of CS and TA. Furthermore, the CS-TA spectrum revealed the saccharide chain structure of CS, which constituted the foundation of the system. This structure was identified by the peaks at 1097cm-1 (asymmetric stretching of the C-O-C bridge) and 894cm-1 (stretching of the saccharide ring)(Nawaz et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, Rahmani et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eXRD was used to determine the crystalline structures of CS-TA and its substrates, as shown in Fig.\u0026nbsp;1b. While CS demonstrated conventional peaks at 2θ\u0026thinsp;=\u0026thinsp;11.6\u0026deg; (crystal form I) and 2θ\u0026thinsp;=\u0026thinsp;20.2\u0026deg; (crystal form II), respectively, TA showed a peak at 2θ\u0026thinsp;=\u0026thinsp;25.2\u0026deg; (Fig.\u0026nbsp;6). Following conjugation, a broad peak was seen in CS-TA at 2θ\u0026thinsp;=\u0026thinsp;23.5\u0026deg;, suggesting that CS-TA had less crystallinity than TA but more than CS. According to the earlier analysis, the high degree of crystallinity in CS can be attributed to the strong hydrogen bonds that exist both within and between molecules(Hu et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). However, during the grafting process, the aromatic rings of TA may prevent CS from forming hydrogen bonds, which would reduce the crystallinity of CS-TA.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.2 The performance of CS-TA on sludge dewatering\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Factors affecting performance of sludge dewatering\u003c/h2\u003e \u003cp\u003eWater content and CST of the sludge were used as the judgment basis to investigate the influencing factors affecting performance of sludge dewatering, such as doses of CS-TA, stirring time, pH and reaction temperature. Figure\u0026nbsp;2a and Fig.\u0026nbsp;2b shows the impact of CS-TA dosages and stirring time on sludge dewaterability performance. It was found that 30 mg CS-TA g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total solid (TS) showed the highest dewaterability compared to other doses. This finding might have been attributed to the poor flocculation and aggregation ability of the sludge with low concentrations of CS-TA(Lu et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). While the doses greater than 30 mg CS-TA g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total solid (TS) also exhibited the worse dewaterability, presumably due to the complete coverage of the surface chains, preventing further particle aggregation and flocculation growth(Blanco et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2005\u003c/span\u003e, Hyrycz et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). As the stirring time increased from 0 to 30 min, the flocculant showed the best dewatering performance at 1 min, as shown in Fig.\u0026nbsp;2a and Fig.\u0026nbsp;2b. Similar finding was observed by (Ge et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), who indicated that the CST reduced rapidly when the stirring time was increased from 0 to 1 min. Especially, the lowest Wsc (59.78%) and CST (11.8s ) value was observed at 1 min. Nevertheless, our finding was inconsistent with the results observed by Zhang et al (Ge et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), who reported that CST values were increased significantly with the increase in stirring time after TA conditioning. The reason behind this phenomenon was because TA cross-linked the biopolymers and aggregated into larger complexes within 1min, but the coalescent aggregations were easy to be destroyed caused by its loose structure and small density, resulting in the deterioration of the sludge dewaterability. However, in the present study, no significant increase in CST was observed, presumably due to the enhanced shear resistance of sludge flocs through the electrostatic neutralization of chitosan amino group. Therefore, 1 min was chosen as the optimal conditioning time in this study, which was shorter than those in previous report and suggested that CS-TA could quickly promote sewage sludge dewatering.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;2c and Fig.\u0026nbsp;2d depicted the effect of different pH and different temperature on CS-TA for sludge dewatering. As presented in Fig.\u0026nbsp;2c, the raw sludge exhibited the better dewaterability under both acidic and alkaline conditions, being consistent with previous study conducted by Wang et al., who indicated that acidification was able to destruct the aggregation of sludge via catalyzing the hydrolysis of polysaccharide and protein (Chen et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Wang et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, in the present study, no pronounced changes in sludge dewatering performance were observed under both acidic and alkaline conditions. Meanwhile, the alkaline condition showed the worse dewatering performance than acid conditions, presumably due to the fact that the alkaline conditions were more unfavorable to binding TA and protein. Therefore, in contrast to the TA, CS-TA exhibited a good dewatering efficiency over a wide range of pH. In terms of the effect of temperature on dewatering performance, the best dewaterability of raw and treated sludge was observed at 35℃, as illustrated in Fig.\u0026nbsp;2d. The increase in temperature would cause the release of sludge EPS, resulting in the deterioration of sludge filtration performance. However, the high temperature would cause the poor stability of the combined flocs after treatment, resulting in the increase in bound water content.(Wang et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) These findings suggested that CS-TA possessed the capacity for enhancing sewage sludge dewatering over a wide range of pH under normal temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 Effects of pretreatment under different synergistic condition on sludge dewatering performance\u003c/h2\u003e \u003cp\u003eTo better understand the effects of flocculants on sludge dewatering performance, further study on the physicochemical characteristics and microstructural properties of flocculants were investigated. As presented in Fig.\u0026nbsp;3a It was found that CS-TA exhibited the best dewaterability, with the Wsc and CST values of 64.21% and 19.2s, respectively. With respect to TA\u0026thinsp;+\u0026thinsp;CS and CS\u0026thinsp;+\u0026thinsp;TA, the values for water content were 66.12% and 65.12% respectively, while CST value were 37.4s and 36.9s respectively, indicating that synergistic conditioning achieved better filterability, compared with that of raw sludge and single conditioning. However, these values of TA\u0026thinsp;+\u0026thinsp;CS and CS\u0026thinsp;+\u0026thinsp;TA were higher than CS-TA, reinforcing that CS-TA was more efficient on sludge dewatering, compared to TA\u0026thinsp;+\u0026thinsp;CS and CS\u0026thinsp;+\u0026thinsp;TA. The reason behand this phenomenon was that if the sludge was first conditioned with the chitosan/tannic acid, a large and dense agglomeration would be initially formed, which prevented some of the inner flocs from working when floccutant was dosed later. As a result, following fast mixing quickly broke apart the agglomeration.\u003c/p\u003e \u003cp\u003eThe variations in bound water content in sludge were shown in Fig.\u0026nbsp;3b. The lowest content of bound water in sludge was observed in the treatment with CS-TA conditioning, implying that the new flocculant successfully strengthened flocculation ability, thus enhancing the dewatering performance of the sludge. It was widely accepted that bound water in sludge was more difficult to extract than free water because it tended to cling firmly to EPS and sludge particles via chemical bonds and intermolecular interactions found inside sludge flocs(Zhu et al. \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Therefore, one of the key factors influencing sludge dewaterability was the amount of bound water present in the sludge. Numerous research revealed that effective methods to improve sludge dewatering include enhancing sludge filterability and changing the affinity of EPS for water molecule capture (bound water).(Guo et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) The capacity of CS-TA to liberate bound water into free water may have played a role according to these results, which supported the fact that CS-TA was more effective at dewatering sludge.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.3The performance of CS-TA on physical characteristics of sludge\u003c/h2\u003e \u003cp\u003eSludge particle size was recognized as a vital parameter influencing sludge dewaterability (Lu et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).Prior research revealed a strong correlation between the rise in floc size and the increase in sludge dewatering capacity(He et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The finding might attributed to the fact that the extremely small particle size of the sludge could absorb more bound water and was difficult to remove by an external force. Consequently, a key tactic for improving sludge dewatering efficiency is the addition of flocculant to agglomerate sludge flocs in order to increase particle size. In the present study, as illustrated in Fig.\u0026nbsp;3(c), the sludge particle size were 86.40 um of raw sludge, 108.62 um for TA treated sludge and 117.41um of CS-TA treated sludge. This finding implied that the addition of CS-TA favored the formation of larger particles compared to the raw sludge, and CS-TA facilitated to flocculate fine particles into larger agglomerations. The higher particle size of CS-TA-treated sludge indicates that after the introduction of chitosan, the adsorption bridging effect, which CS-TA displayed, was crucial to the flocculation conditioning procedure of sludge dewatering..\u003c/p\u003e \u003cp\u003eThe morphology and dewatering efficiency of sludge flocs were significantly influenced by the zeta potential of the sludge, which was the primary factor governing colloidal stability(He et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Because of the ionization of the anionic functional groups of EPS, the sludge particles are negatively charged. Figure\u0026nbsp;3(d) presents the zeta potential of dewatering agents. After TA treatment, zeta potential of sludge decreased to \u0026minus;\u0026thinsp;25.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61 mV from \u0026minus;\u0026thinsp;24.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49 mV, which was caused by the negative charge of tannic polymers. This finding was consistent with the study conducted by Ge et al(Ge et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, Ge et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), who reported that zeta potential was lifted after CS-TA conditioning. The phenomenon was attributed to the introduction of anionic functional groups in chitosan, facilitating the neutralization of the surface charge of the sludgeand reducing the repulsive force among the particles in the sludge\u003c/p\u003e \u003cp\u003eThe change in morphology of sludge was investigated using by SEM, as illustrated in Fig.\u0026nbsp;4. The comparison between the raw and treated sludge showed that the particles in the sludge treated using CS-TA were entangled in the precipitation of the flocs, due to the interaction of flocculant and the particles(Li et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), reinforcing the complexation adsorption abilities of CS-TA. In terms of the treated sludge, as illustrated in Fig.\u0026nbsp;4(d) the treated sludge exhibited a higher porosity than that of the raw sludge. This finding suggested that this microstructure provided more channels for the release of water, which was beneficial for improving the dewatering performance. As a result, the sludge cake that was left over after dehydration had disconnected surfaces with voids, which allowed the structure to offer unobstructed water outflow channels during mechanical dewatering.(Wang et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2017\u003c/span\u003e)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Effects of CS-TA on the destruction of EPS\u003c/h2\u003e \u003cp\u003eEPS were large molecular weight biopolymers that were produced by the lysis and metabolism of microorganisms as well as the adsorption of organic materials from wastewater. Examples of these biopolymers include proteins, polysaccharides, and nucleic acids(Zhen et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Figure\u0026nbsp;5 showed the profiles of proteins and polysaccharides in various EPS fractions. Neyens' assessment of the literature revealed that the concentration of EPS has a significant impact on the dewatering ability of sewage sludge(Neyens et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Regarding the effects of different EPS components on sludge dewatering, previous studies revealed a negative correlation between sludge filtration and PN content in S-EPS(Wei et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). As presented in Fig.\u0026nbsp;5, the initial concentrations of PN and PS were 1.22g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 0.86 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e TS, respectively. It could be observed that PN concentration was decreased after treatment with CS, TA and CS-TA. This result could have been explained by the flocculation weakening the force of repulsion between the particles of sludge, resulting in the compression of the layered structure of EPS and PN migration. Furthermore, another possible explanation for this discrepancy may be the combination of TA with protein. Furthermore, because the molecular chain of PN contains basic (such as -NH2) and acidic (such as -COOH) groups, CS-TA can cross-link with PN released into S-EPS by hydrogen bond and electrostatic interaction to create complex and lower the PN content. The decrease in PS further suggested that the improvement in sludge dewaterability was facilitated by the elimination of hydrophilic components. As illustrated in Fig.\u0026nbsp;5, the concentration of PS was decreased in each layer of EPS. Nevertheless, previous studies indicated that the correlation between PS change and sludge dewatering was much smaller than that between PN and sludge dewatering.(Yang et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In addition, as can be seen from the Fig S2, the kurtosis of the treated sludge fluorescence decreased in SEPS, LBEPS and TBEPS, which also indicates that CS-TA can reduce the sludge organic matter,the 3D-EEM fluorescence spectra was in agreement with the results obtained from FT-IR result.\u003c/p\u003e \u003cp\u003eMoreover, the contact angle usually indicates the hydrophilic and hydrophobicity of the sludge. The smaller the contact angle is, the more hydrophilic the sludge fraction is. On the contrary, the larger the contact angle is, the more oleophilic the powder surface is(Ahmad et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Hydrophilic functional groups (such as -OH and -NH2) and hydrogen bonds are generally present in polysaccharides and proteins, and they facilitate the interaction of these molecules with water molecules(Tao et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Furthermore, a prior study found that, rather than the sludge contents, the water-holding capabilities of sludge are more reliant on the spatial distribution of hydrophilic/hydrophobic functional groups(Wu et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). While hydrophilic components are primarily found inside sludge, hydrophobic components may be more prevalent on the outside of the sludge(Yu et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). It was later discovered that the CS-TA treatment raised the contact angle of sludge from 68.04\u0026deg; to 91.44\u0026deg;, as shown in Fig.\u0026nbsp;6. This result showed that water molecules had trouble adhering to the surface of bioflocs, indicating that the hydrophobicity of the sludge had increased(Li et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These findings provided more evidence that lowering the PS and PN concentrations in EPS could improve the dewaterability and relative hydrophobicity of sludge.\u003c/p\u003e \u003cp\u003eThe FTIR analysis of raw sludge and sludge treated with CS-TA is presented in Fig.\u0026nbsp;6a. The FTIR peak locations and numbers of EPS fractions in the raw and treated sludge were comparable, suggesting that the chemical group types were also identical in both samples.The functional group -OH was ascribed to a peak that appeared at 3440 cm-1, indicating the presence of hydroxyl groups in the sludge cake.(Xu et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) Also discovered were the bands at 2858 and 2927 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which are connected to the C-H stretching vibrations of aliphatic and lipid molecules, respectively. Additionally, at transmission spectra of 1649cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, C-N stretching vibrations from the protein's amide I group and C\u0026thinsp;=\u0026thinsp;O stretching vibrations from the ester were detected. Furthermore, CO-NH from the amide II group exhibited both C-N and N-H stretching, with an absorption intensity peak detected at around 1546 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The vibration absorption peak of hydroxyl in polysaccharides was linked to the peak at approximately 1045 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which was ascribed to O-H, C-O-C, and C-C vibration. The strength of this peak was significantly higher in raw sludge than in treated sludge. Significantly, following CS-TA treatment, the hydrophilic funditonal groups of PN and PS broke down as seen by the reduction in peak intensities of 2927, 1649, 1546, and 1045 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. the disruption of functional group cleavage or started hydroxylation of aromatic rings, which causes EPS disintegration(Menon et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this study, we applied a novel flocculant CS-TA to enhance the sludge dewaterability. The characterization of sludge using FTIR and XRD analysis indicated that CS chain was the backbone of CS-TA, and aromatic rings of CS-TA confirmed the conjugation of CS with TA. CS-TA exhibited the best dewaterability, with the Wsc and CST values of 64.21% and 19.2s, respectively. 30 mg CS-TA g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e TS showed the highest dewaterability compared to other doses. In contrast to TA, CS-TA exhibited a good dewatering efficiency over a wide range of pH. Meanwhile, the dewatering mechanism of CS-TA was analyzed by physicochemical characteristics and microstructural properties of sludge. The analysis of particle size, zeta potential and microscope images implied that CS-TA improved sludge dewatering performance through adsorption bridging effect and charge neutralization. In addition, the analysis results of EPS showed a decrease in the concentration of PN and PS which was closely related the performance of sludge dewatering. These findings are expected to advance our understanding for the development a novel CS-TA flocculent and optimization of synergestic pretreatment condition for sledge dewatering enhancement.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (NO. 42177369), National Key Research and Development Program of China (NO. 2019YFA0210400),\u0026nbsp;Guangdong Basic and Applied Basic Research Natural Science Funding\u0026nbsp;(NO. 2023A1515012130), Maoming Sci. Technol. Program (NO.2021S0054) and Maoming Green Chemical Industry Research Institute Fund (MMGCIRI-2022YFJH-Y-01).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003cstrong\u003eompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design.\u0026nbsp;\u003cstrong\u003eYuejin Liu\u003c/strong\u003e: Investigation, Data curation, Formal analysis, Writing - original draft. \u003cstrong\u003eXiaojun Niu:\u0026nbsp;\u003c/strong\u003eConceptualization, Funding acquisition. \u003cstrong\u003eDongqing Zhang:\u0026nbsp;\u003c/strong\u003eResources, Writing - review \u0026amp; editing. \u003cstrong\u003eLingling Zhou:\u003c/strong\u003e Visualization. \u003cstrong\u003eChunyang Tao:\u0026nbsp;\u003c/strong\u003eMethodology. \u003cstrong\u003eYu Lin:\u003c/strong\u003e Supervision. \u003cstrong\u003eSiping, Chen:\u0026nbsp;\u003c/strong\u003eValidation.\u003cstrong\u003e\u0026nbsp;Yawen Chen\u003c/strong\u003e: Methodology. \u003cstrong\u003eZhang Lin:\u0026nbsp;\u003c/strong\u003eFunding acquisition.All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhmad D, van den Boogaert I, Miller J, Presswell R, Jouhara H (2018): Hydrophilic and hydrophobic materials and their applications. Energy sources. Part A, Recovery, utilization, and environmental effects 40, 2686-2725\u003c/li\u003e\n\u003cli\u003eArapitsas P (2012): Hydrolyzable tannin analysis in food. FOOD CHEM 135, 1708-1717\u003c/li\u003e\n\u003cli\u003eBao P, Du C, Li Y, Jiang H, Zhou L, Yu G, Sun S, Zhou L, Li X, Teng J, Wang X, Wang J (2024): Application of skeleton builders to sludge dewatering and disposal: A critical review. SCI TOTAL ENVIRON 906, 167106\u003c/li\u003e\n\u003cli\u003eBlanco A, Negro C, Fuente E, Tijero J (2005), Effect of shearing forces and flocculant overdose on filler flocculation mechanisms and floc properties. IND ENG CHEM RES 44, 9105-9112\u003c/li\u003e\n\u003cli\u003eCao B, Zhang T, Zhang W, Wang D (2021): Enhanced technology based for sewage sludge deep dewatering: A critical review. WATER RES 189, 116650\u003c/li\u003e\n\u003cli\u003eChen N, Tao S, Xiao K, Liang S, Yang J, Zhang L (2020): A one-step acidification strategy for sewage sludge dewatering with oxalic acid. CHEMOSPHERE 238, 124598\u003c/li\u003e\n\u003cli\u003eChen R, Dai X, Dong B (2022): Decrease the effective temperature of hydrothermal treatment for sewage sludge deep dewatering: Mechanistic of tannic acid aided. WATER RES 217, 118450\u003c/li\u003e\n\u003cli\u003eChen Z, Zhang W, Wang D, Ma T, Bai R (2015): Enhancement of activated sludge dewatering performance by combined composite enzymatic lysis and chemical re-flocculation with inorganic coagulants: Kinetics of enzymatic reaction and re-flocculation morphology. WATER RES 83, 367-376\u003c/li\u003e\n\u003cli\u003eCui J, Niu X, Zhang D, Ma J, Zhu X, Zheng X, Lin Z, Fu M (2023a): The novel chitosan-amphoteric starch dual flocculants for enhanced removal of Microcystis aeruginosa and algal organic matter. CARBOHYD POLYM 304, 120474\u003c/li\u003e\n\u003cli\u003eCui J, Niu X, Zhang D, Ma J, Zhu X, Zheng X, Lin Z, Fu M (2023b): The novel chitosan-amphoteric starch dual flocculants for enhanced removal of Microcystis aeruginosa and algal organic matter. CARBOHYD POLYM 304, 120474\u003c/li\u003e\n\u003cli\u003eCurcio M, Puoci F, Iemma F, Parisi OI, Cirillo G, Spizzirri UG, Picci N (2009): Covalent Insertion of Antioxidant Molecules on Chitosan by a Free Radical Grafting Procedure. J AGR FOOD CHEM 57, 5933-5938\u003c/li\u003e\n\u003cli\u003eFeng Q, Guo K, Gao Y, Liu B, Yue Q, Shi W, Feng C, Zhou J, Wang G, Gao B (2022): Effect of coagulation treatment on sludge dewatering performance: Application of polysilicate and their mechanism. SEP PURIF TECHNOL 301, 121954\u003c/li\u003e\n\u003cli\u003eFeng X, Wan J, Deng J, Yue X, Yang Y, He Z, Fang X, Chen T, Li S, Lu J, Long Y (2022): Study on the regulation of sludge dewatering by hydrophobically associating cationic polyacrylamide coupled with framework materials. Journal of Water Process Engineering 45, 102502\u003c/li\u003e\n\u003cli\u003eGe D, Yuan H, Xiao J, Zhu N (2019): Insight into the enhanced sludge dewaterability by tannic acid conditioning and pH regulation. SCI TOTAL ENVIRON 679, 298-306\u003c/li\u003e\n\u003cli\u003eGe D, Yuan H, Shen Y, Zhang W, Zhu N (2019): Improved sludge dewaterability by tannic acid conditioning: Temperature, thermodynamics and mechanism studies. CHEMOSPHERE 230, 14-23\u003c/li\u003e\n\u003cli\u003eGe D, Zhang W, Yuan H, Zhu N (2019): Enhanced waste activated sludge dewaterability by tannic acid conditioning: Efficacy, process parameters, role and mechanism studies. J CLEAN PROD 241, 118287\u003c/li\u003e\n\u003cli\u003eGe D, Dong Y, Zhang W, Yuan H, Zhu N (2020): A novel Fe2+/persulfate/tannic acid process with strengthened efficacy on enhancing waste activated sludge dewaterability and mechanism insight. SCI TOTAL ENVIRON 733, 139146\u003c/li\u003e\n\u003cli\u003eGuibal E, Van Vooren M, Dempsey BA, Roussy J (2006): A Review of the Use of Chitosan for the Removal of Particulate and Dissolved Contaminants. SEP SCI TECHNOL 41, 2487-2514\u003c/li\u003e\n\u003cli\u003eGuo J, Chen C, Jiang S, Zhou Y (2018): Feasibility and Mechanism of Combined Conditioning with Coagulant and Flocculant To Enhance Sludge Dewatering. ACS SUSTAIN CHEM ENG 6, 10758-10765\u003c/li\u003e\n\u003cli\u003eHe D, Bao B, Sun M, Chen J, Luo H, Li J (2021): Enhanced dewatering of activated sludge by acid assisted Heat\u0026ndash;CaO2 treatment: Simultaneously removing heavy metals and mitigating antibiotic resistance genes. J HAZARD MATER 418, 126248\u003c/li\u003e\n\u003cli\u003eHe D, Sun M, Bao B, Chen J, Luo H, Li J (2022): Rethinking the timing of flocculant addition during activated sludge dewatering. Journal of Water Process Engineering 47, 102744\u003c/li\u003e\n\u003cli\u003eHe D, Zhu T, Sun M, Chen J, Luo H, Li J (2024): Unraveling synergistic mechanisms of polyacrylamide coagulation and Fe2+/CaO2 Fenton-like oxidation to enhance sludge dewatering. CHEM ENG J 479, 147576\u003c/li\u003e\n\u003cli\u003eHe Z, Wang F, Zou Z, Tang C, Zhou A, Liu W, Ren Y, Li Z, Wang A (2023): Recent advances and perspectives in roles of humic acid in anaerobic digestion of waste activated sludge. CHEM ENG J 466, 143081\u003c/li\u003e\n\u003cli\u003eHoughton JI, Quarmby J, Stephenson T (2001): Municipal wastewater sludge dewaterability and the presence of microbial extracellular polymer. WATER SCI TECHNOL 44, 373-9\u003c/li\u003e\n\u003cli\u003eHu Q, Wang T, Zhou M, Xue J, Luo Y (2016): In Vitro Antioxidant-Activity Evaluation of Gallic-Acid-Grafted Chitosan Conjugate Synthesized by Free-Radical-Induced Grafting Method. J AGR FOOD CHEM 64, 5893-5900\u003c/li\u003e\n\u003cli\u003eHyrycz M, Ochowiak M, Krupińska A, Włodarczak S, Matuszak M (2022): A review of flocculants as an efficient method for increasing the efficiency of municipal sludge dewatering: Mechanisms, performances, influencing factors and perspectives. SCI TOTAL ENVIRON 820, 153328\u003c/li\u003e\n\u003cli\u003eJing W, Xiaolan C, Yu C, Feng Q, Haifeng Y (2022): Pharmacological effects and mechanisms of tannic acid. BIOMED PHARMACOTHER 154, 113561\u003c/li\u003e\n\u003cli\u003eJing Y, Diao Y, Yu X (2019): Free radical-mediated conjugation of chitosan with tannic acid: Characterization and antioxidant capacity. Reactive and Functional Polymers 135, 16-22\u003c/li\u003e\n\u003cli\u003eLi J, Liu L, Liu J, Ma T, Yan A, Ni Y (2016): Effect of adding alum sludge from water treatment plant on sewage sludge dewatering. Journal of Environmental Chemical Engineering 4, 746-752\u003c/li\u003e\n\u003cli\u003eLi T, Zhu Z, Wang D, Yao C, Tang H (2006): Characterization of floc size, strength and structure under various coagulation mechanisms. POWDER TECHNOL 168, 104-110\u003c/li\u003e\n\u003cli\u003eLi Y, Zhu Y, Wang D, Yang G, Pan L, Wang Q, Ni B, Li H, Yuan X, Jiang L, Tang W (2020): Fe(II) catalyzing sodium percarbonate facilitates the dewaterability of waste activated sludge: Performance, mechanism, and implication. WATER RES 174, 115626\u003c/li\u003e\n\u003cli\u003eLiang J, Zhou Y (2022): Iron-based advanced oxidation processes for enhancing sludge dewaterability: State of the art, challenges, and sludge reuse. WATER RES 218, 118499\u003c/li\u003e\n\u003cli\u003eLin Q, Peng H, Zhong S, Xiang J (2015): Synthesis, characterization, and secondary sludge dewatering performance of a novel combined silicon\u0026ndash;aluminum\u0026ndash;iron\u0026ndash;starch flocculant. J HAZARD MATER 285, 199-206\u003c/li\u003e\n\u003cli\u003eLiu H, Fang HHP (2002): Extraction of extracellular polymeric substances (EPS) of sludges. J BIOTECHNOL 95, 249-256\u003c/li\u003e\n\u003cli\u003eLiu L, Ge C, Zhang Y, Ma W, Su X, Chen L, Li S, Wang L, Mu X, Xu Y (2020): Tannic acid-modified silver nanoparticles for enhancing anti-biofilm activities and modulating biofilm formation. BIOMATER SCI-UK 8, 4852-486\u003c/li\u003e\n\u003cli\u003eLu L, Pan Z, Hao N, Peng W (2014): A novel acrylamide-free flocculant and its application for sludge dewatering. WATER RES 57, 304-312\u003c/li\u003e\n\u003cli\u003eMenon U, Suresh N, George G, Ealias AM, Saravanakumar MP (2020): A study on combined effect of Fenton and Free Nitrous Acid treatment on sludge dewaterability with ultrasonic assistance: Preliminary investigation on improved calorific value. CHEM ENG J 382, 123035\u003c/li\u003e\n\u003cli\u003eMowla D, Tran HN, Allen DG (2013): A review of the properties of biosludge and its relevance to enhanced dewatering processes. Biomass and Bioenergy 58, 365-378\u003c/li\u003e\n\u003cli\u003eNawaz A, Atif M, Naz I, Khan A, Naz F, Ali N (2023): Comparative robustness and sustainability of in - situ prepared antimony nanoarchitectonics in chitosan / synthesized carboxymethyl chitosan in environmental remediation perspective. INT J BIOL MACROMOL 235\u003c/li\u003e\n\u003cli\u003eNeyens E, Baeyens J, Dewil R, De Heyder B (2004): Advanced sludge treatment affects extracellular polymeric substances to improve activated sludge dewatering. J HAZARD MATER 106, 83-92\u003c/li\u003e\n\u003cli\u003eRahmani S, Mohammadi Z, Amini M, Isaei E, Taheritarigh S, Tehrani NR, Tehrani MR (2016): Methylated 4 - N , N dimethyl aminobenzyl N , O carboxymethyl chitosan as a new chitosan derivative : Synthesis , characterization , cytotoxicity and antibacterial activity. CARBOHYD POLYM 149, 131-139\u003c/li\u003e\n\u003cli\u003eStojadinovic M, Radosavljevic J, Ognjenovic J, Vesic J, Prodic I, Stanic-Vucinic D, Velickovic TC (2013): Binding affinity between dietary polyphenols and 尾-lactoglobulin negatively correlates with the protein susceptibility to digestion and total antioxidant activity of complexes formed. FOOD CHEM 136, 1263-1271\u003c/li\u003e\n\u003cli\u003eTao N, Hu L, Fang D, Tarabara V, Zhou L (2022): Supplementation of tea polyphenols in sludge Fenton oxidation improves sludge dewaterability and reduces chemicals consumption. WATER RES 218, 118512\u003c/li\u003e\n\u003cli\u003eWang D, Zhao T, Yan L, Mi Z, Gu Q, Zhang Y (2016): Synthesis, characterization and evaluation of dewatering properties of chitosan-grafting DMDAAC flocculants. INT J BIOL MACROMOL 92, 761-768\u003c/li\u003e\n\u003cli\u003eWang H, Ma Y, Wang H, Hu H, Yang H, Zeng RJ (2017): Applying rheological analysis to better understand the mechanism of acid conditioning on activated sludge dewatering. WATER RES 122, 398-406\u003c/li\u003e\n\u003cli\u003eWang J, Chon K, Ren X, Wu H, Kou Y, Hwang MH, Chae KJ (2019): Combined use of polymeric ferric sulfate and chitosan as a conditioning aid for enhanced digested sludge dewatering. ENVIRON TECHNOL 40, 2695-2704\u003c/li\u003e\n\u003cli\u003eWang L, Qian C, Jiang J, Ye X, Yu H (2017): Response of extracellular polymeric substances to thermal treatment in sludge dewatering process. ENVIRON POLLUT 231, 1388-1392\u003c/li\u003e\n\u003cli\u003eWei H, Gao B, Ren J, Li A, Yang H (2018): Coagulation/flocculation in dewatering of sludge: A review. WATER RES 143, 608-631\u003c/li\u003e\n\u003cli\u003eWu B, Dai X, Chai X (2020): Critical review on dewatering of sewage sludge: Influential mechanism, conditioning technologies and implications to sludge re-utilizations. WATER RES 180, 115912\u003c/li\u003e\n\u003cli\u003eWu P, Yi J, Feng L, Li X, Chen Y, Liu Z, Tian S, Li S, Khan S, Sun Y (2020): Microwave assisted preparation and characterization of a chitosan based flocculant for the application and evaluation of sludge flocculation and dewatering. INT J BIOL MACROMOL 155, 708-720\u003c/li\u003e\n\u003cli\u003eXiao J, Ge D, Yuan H, Zhu N (2020): Waste activated sludge conditioning in a new Fe\u003csup\u003e2+\u003c/sup\u003e/ persulfate / tannic acid process : Effectiveness and optimization study to enhance dewaterability. JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING 8\u003c/li\u003e\n\u003cli\u003eXu H, Yu G, Jiang H (2013): Investigation on extracellular polymeric substances from mucilaginous cyanobacterial blooms in eutrophic freshwater lakes. CHEMOSPHERE 93, 75-81\u003c/li\u003e\n\u003cli\u003eXu Q, Wang Q, Zhang W, Yang P, Du Y, Wang D (2018): Highly effective enhancement of waste activated sludge dewaterability by altering proteins properties using methanol solution coupled with inorganic coagulants. WATER RES 138, 181-191\u003c/li\u003e\n\u003cli\u003eYan Y, Qin L, Gao J, Nan R, Gao J (2020): Protein extraction and sludge dewatering performance of ultrasound-assisted enzymatic hydrolysis of excess sludge. ENVIRON SCI POLLUT R 27, 18317-18328\u003c/li\u003e\n\u003cli\u003eYang X, Zeng L, Huang J, Mo Z, Guan Z, Sun S, Liang J, Huang S (2022): Enhanced sludge dewaterability by a novel MnFe2O4-Biochar activated peroxymonosulfate process combined with Tannic acid. CHEM ENG J 429, 132280\u003c/li\u003e\n\u003cli\u003eYang Y, Yang X, Yang Q, Zhang H, Xu W, Zhu L, Ma P, Li Y (2022): Exploring the feasibility and potential mechanism of synergistic enhancement of sludge dewaterability by ultrasonic cracking , chitosan re-flocculation and sludge - based biochar adsorption of water-holding substances. JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING 10\u003c/li\u003e\n\u003cli\u003eYu W, Wen Q, Yang J, Xiao K, Zhu Y, Tao S, Liang S, Hu S, Wu Q, Hou H, Liu B, Hu J (2021): Novel Insights into Extracellular Polymeric Substance Degradation, Hydrophilic/Hydrophobic Characteristics, and Dewaterability of Waste Activated Sludge Pretreated by Hydroxylamine Enhanced Fenton Oxidation. ACS ES\u0026amp;T Engineering 1, 385-392\u003c/li\u003e\n\u003cli\u003eZhang C, Ho S, Chen W, Eng CF, Wang C (2021): Simultaneous implementation of sludge dewatering and solid biofuel production by microwave torrefaction. ENVIRON RES 195, 110775\u003c/li\u003e\n\u003cli\u003eZhang W, Wang H, Li L, Li D, Wang Q, Xu Q, Wang D (2019): Impact of molecular structure and charge property of chitosan based polymers on flocculation conditioning of advanced anaerobically digested sludge for dewaterability improvement. SCI TOTAL ENVIRON 670, 98-109\u003c/li\u003e\n\u003cli\u003eZhen G, Lu X, Niu J, Su L, Chai X, Zhao Y, Li Y, Song Y, Niu D (2013): Inhibitory effects of a shock load of Fe ( II )- mediated persulfate oxidation on waste activated sludge anaerobic digestion. CHEM ENG J 233, 274-281\u003c/li\u003e\n\u003cli\u003eZhu Y, Xiao K, Zhou Y, Yu W, Tao S, Le C, Lu D, Yu Z, Liang S, Hu J, Hou H, Liu B, Yang J (2020): Profiling of amino acids and their interactions with proteinaceous compounds for sewage sludge dewatering by Fenton oxidation treatment. WATER RES 175\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Sludge dewatering, Tannic acid, Chitosan, Free radical-mediated conjugation, Extracellular polymeric substance","lastPublishedDoi":"10.21203/rs.3.rs-4014664/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4014664/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFlocculation is one of the most significant conditioning methods for sludge dewatering. In the present study, a novel flocculant CS-TA, which was prepared through free radical-mediated conjugation of tannic acid (TA) and chitosan (CS), was proposed to improve the performance of sludge dewatering. The findings indicate that the conditioning of CS-TA yielded the best dewatering performance at 30 mg g TS\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with water content of 59.78% and capillary suction time of 11.8s, compared to the Wsc of 98.2% and CST of 56.2s in raw sludge. The flocculation efficiency of different influencing factors were evaluated, indicating that CS-TA possessed the capacity for enhancing sludge dewaterability over a wide range of pH. Furthermore, the analysis of particle size implied that the addition of CS-TA favored the formation of larger particles. Meanwhile, the value of zeta potential of sludge was increased form \u0026minus;\u0026thinsp;24.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49 mV to -17.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35 mV after CS-TA conditioning, suggesting that CS-TA could improve sludge dewatering through charge neutralization, thus accelerating sludge filtration. In addition, extracellular polymer substances (EPS) analysis indicated that the decrease in the polysaccharide (PS) and protein (PN) contents in EPS after CS-TA addition could increase the relative hydrophobicity of sludge, contributing to a decrease in water content. The results of FTIR reinforced the breakdown of hydrophic functional groups of PN and PS, leading to the sludge hydrophobicity. This study provides a comprehensive insights into the exploration of CS-TA for sludge dewatering and the maintenance of ecological security in an eco-friendly way.\u003c/p\u003e","manuscriptTitle":"Insight into enhancing the performance of sludge dewatering using a novel flocculant CS-TA prepared through free radical-mediated conjugation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-12 10:05:10","doi":"10.21203/rs.3.rs-4014664/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2024-04-09T10:21:29+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2024-03-21T17:21:28+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-08T05:15:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2024-03-06T20:18:28+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"80d27675-13d3-4715-a655-5e53831d24a2","owner":[],"postedDate":"April 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-04-12T10:05:11+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-12 10:05:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4014664","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4014664","identity":"rs-4014664","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}