Preparation of a distillers’ grains derived lignin-chitosan adsorbent for enhanced the distillery wastewater treatment

Preparation of a distillers’ grains derived lignin-chitosan adsorbent for enhanced the distillery wastewater treatment | 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 Article Preparation of a distillers’ grains derived lignin-chitosan adsorbent for enhanced the distillery wastewater treatment Yijie Wang, Haiqing Wang, Jingtao Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8248335/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 22 Mar, 2026 Read the published version in Scientific Reports → Version 1 posted 12 You are reading this latest preprint version Abstract The distillers' grains and wastewater produced by alcohol fermentation process pose a threat to the ecological environment. This study has designed a method of treating waste with waste, which uses the lignin from distillers’ grains as the base and combining with chitosan to prepare an efficient adsorbent for distillery wastewater treatment. The prepared lignin-chitosan adsorbent was characterized by various methods, its surface was rough and had abundant functional groups, which facilitated the adsorption of pollutants. The COD, TP, TN and NH 4 + -N were selected as the typical wastewater indicators to evaluate the treatment effect of the adsorbent on the distillery wastewater. The results showed that lignin-chitosan adsorbent reached adsorption equilibrium for the four pollutants at 120 mins, and the adsorption rates were all above 85%. The adsorption process was in good accordance with the quasi-second-order kinetics dominated by chemical adsorption, and it indicates that the adsorption rate of the adsorbent to the pollutant mainly depends on the interaction between the adsorbate and the surface active site. In addition, the removal rate can still achieve 75% after 5 adsorption cycles. These findings indicate its potential for large-scale applications and promise as a green alternative to activated carbon or synthetic adsorbents. Physical sciences/Chemistry Earth and environmental sciences/Environmental sciences Adsorbent Chitosan Distiller's grains Eutrophic compounds Lignin Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction With the rapid development of the global economy and the acceleration of industrialization, the demand for renewable energy has continued to rise. In the process of alcohol production, a by-product known as distillers' grains is generated-specifically, 3.5 tons of distillers' grains are produced for every 1 ton of alcohol manufactured 1 , 2 . Historically, distillers' grains were directly discharged into the environment as waste; the decomposition of organic matter within them would subsequently cause significant environmental harm 3 . Notably, distillers' grains contain abundant lignin-a rigid biopolymer that accounts for approximately 10% of its composition. Lignin possesses functional groups including aromatic rings, phenolic hydroxyl groups, and methoxy groups 4 , which enables efficient capture of pollutants such as heavy metals, dyes, and nutrients through ion exchange, hydrogen bonding, and π-π interactions 5 , giving it the potential to serve as a low-cost adsorption framework. However, the inherent limitations of natural lignin restrict its direct application, such as low specific surface area and poor solubility. Strategies like modification or compounding are required to unlock its adsorption potential. Additionally, while producing distiller's grains, factories also generate distiller's grains wastewater containing various pollutants-including substances that cause water eutrophication 6 . If lignin extracted from wheat distiller's grains is used as an adsorbent to treat pollutants in distillery wastewater, a green economic cycle can be achieved. Current research on lignin-based adsorbents for organic pollutant removal remains relatively limited. Existing studies have demonstrated that lignin-based adsorbents exhibit excellent adsorption performance for various dye pollutants, such as methylene blue and Congo red 7 , 8 . Through modification or compounding, lignin can be tailored to adsorb different types of pollutants. Lignin modification typically encompasses chemical and physical approaches, with chemical modification being the most widely used method to enhance lignin’s adsorption capacity. Sulfonation modification improves lignin’s water solubility and dispersibility by introducing sulfonic acid groups. This process usually involves reacting lignin with sodium sulfite at elevated temperatures to graft sulfonic acid groups onto its side chains or benzene rings, thereby enhancing its adsorption capacity for ionic pollutants 9 . The Mannich reaction is another key chemical modification technique: it uses amine compounds and formaldehyde to introduce amine groups onto the lignin structure, increasing the material’s nitrogen content and consequently boosting its adsorption performance for heavy metals and dyes 10 . Additionally, graft copolymerization employs initiators to graft monomers (e.g., acrylamide and acrylic acid) onto the lignin backbone, introducing functional groups such as carboxyl and amide groups, this significantly improves the adsorbent’s ability to capture pollutants 11 . Physical modification methods, by contrast, primarily focus on optimizing lignin’s pore structure and specific surface area. Treatments including heat, microwave, or ultrasound can disrupt lignin’s dense inherent structure, increasing its porosity and specific surface area to enhance adsorption capacity 12 . Constructing composite adsorbent materials represents another effective strategy to improve lignin’s adsorption performance. Lignin-based hydrogels, for instance, form a three-dimensional network structure by incorporating polymers like polyacrylic acid; they possess excellent water absorption and retention capabilities, making them suitable for adsorbing dyes and heavy metals 13 . Lignin-based magnetic nanocomposite particles, on the other hand, combine lignin with magnetic particles (e.g., iron tetroxide). This design enables easy separation and recovery of the adsorbent via an external magnetic field, facilitating reuse 14 . However, a critical gap exists in the field of lignin-based adsorbents: most studies prioritize optimizing pollutant adsorption efficiency while often neglecting preparation costs and environmental sustainability. The synthesis routes of most existing lignin-based adsorbents are complex, their production costs are high, and the materials used in synthesis are not environmentally friendly-these issues constitute important challenges that warrant urgent solutions. In this study, a green synthesis method for a lignin-chitosan composite adsorbent is proposed. The synthesis process is straightforward, and the lignin used as a raw material is extracted from distillers' grains (a by-product of alcohol production), which not only reduces synthesis costs but also realizes waste valorization. Additionally, chitosan-a biodegradable amino-polysaccharide-possesses protonated amino groups (-NH 2 ) that enhance the electrostatic adsorption of anionic pollutants (e.g., phosphates, nitrates) 15 . This functional attribute complements lignin’s inherent capability for adsorbing cationic pollutants 16 , 17 . The resulting lignin chitosan composite adsorbent was applied to target eutrophication-causing pollutants (COD, TP, TN, NH 4 + -N) in food industry wastewater, simultaneously addressing waste management and water pollution remediation challenges. Adsorption experiments investigated the effects of temperature, contact time, adsorbent dosage, and pH value on removal efficiency, and analyzed the adsorption mechanisms. Although preliminary progress has been made in distiller's grain-derived lignin-chitosan adsorbents, the existing process still has defects in lignin extraction yield and composite adsorbent stability, which needs further optimization. Thus, the objectives of this study are threefold: (1) Lignin was extracted from distillers' grains using a reusable organic solvent and a simple and green method was used to prepare a lignin-chitosan adsorbent with low cost and reusable characteristics; (2) Through a series of characterization tests of lignin-chitosan adsorbent, the adsorption potential of this adsorbent for organic pollutants in distillery wastewater was proved (SEM, FT-IR, XPS, BET, TG); (3) Lignin-chitosan adsorbent has a good removal effect on organic pollutants (COD, TP, TN, NH 4 + -N) in distillery wastewater. The adsorption mechanism of this adsorbent was explored through static adsorption experiments and adsorption kinetics. 2 Materials and methods 2.1 Materials and reagents Distillers' grains are provided by a food factory in Shandong, China; Chitosan, analytical grade, purchased from Shanghai Maclean Biochemical Technology Co., LTD; The wastewater treated by adsorption is the distiller's grains wastewater from the sedimentation tank of a certain food factory. Chitosan, sodium hydroxide, formaldehyde and sodium sulfite are all of analytical purity and are sourced from Solebo Bio Inc. 2.2 Preparation of lignin-chitosan adsorbent The 40% p-toluenesulfonic acid solution was prepared in a round bottom flask and preheated to 80°C in a constant temperature stirring water bath. Add wheat distillers’ grains dry powder in a certain proportion and boil for 30 mins, and install a condensing tube to prevent the solution from evaporating. After the reaction was completed, the filtrate was obtained by vacuum suction filtration, and the filtrate was diluted in distilled water to the concentration of p-toluenesulfonic acid of 10% before stopping. At this point, a large amount of lignin is precipitated to form lignin sediment. The supernatant is discarded after centrifugation at 5500 rpm with a medical centrifuge. The lignin is then dried in a constant temperature drying oven at 65℃ to obtain the final product. Dissolve 4 g of lignin in 50 mL of 0.4 M NaOH solution. Add 2 mL of formaldehyde and 2 g of sodium sulfite to the lignin suspension, heat to 80℃ and allow the reaction to proceed for more than 3 h. Dissolve 1 g of chitosan in 100 mL of acetic acid aqueous solution (with a 2% volume ratio) and stir thoroughly to form a uniform solution. Add the lignin solution obtained after the reaction to the dissolved chitosan solution, and let it react at a speed of 300 rpm/min for 3 h. After the reaction is completed, the precipitate is collected by centrifugation at 3000 rpm in a medical centrifuge and then dried at room temperature for 36 h. The lignin adsorbent was ground into powder, then washed with double-distilled water, and dried at 65℃ to obtain the lignin-chitosan adsorbent. 2.3 Material testing characterization methods The morphological characteristics and microstructure of the three materials were analyzed through SEM testing, and the test was conducted using the German-ZEISS-Sigma 360 instrument. The main chemical structures and adsorption functional groups of the materials were analyzed through Fourier Transform Infrared Spectroscopy (FTIR) testing. The test was conducted using the Japanese-SHIMADZU-IRTracer-100 instrument. The types and oxidation states of elements in the three materials were determined by X-ray photoelectron spectroscopy (XPS), and the tests were conducted using the American-Thermo Fisher-ESCALAB 250Xi instrument. The specific surface area and pore diameters of the three materials were analyzed through BET testing, which was conducted using the American-Micromeritics-ASAP 2460 instrument. The thermal stability of the three materials was analyzed through the TG test, which was conducted using the DSC7000 instrument provided by Hitachi of Japan. 2.4 Adsorption performance comparison experiment The fixed experimental conditions were sewage pH 7, sewage volume 100 mL, and temperature at 25 ± 2℃. The adsorption performance of synthetic raw materials (lignin, chitosan) and lignin-chitosan adsorbent towards chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen (NH 4 + -N) in wastewater was tested. The experimental wastewater was from the sedimentation tank of Shandong Zhongyu Food Co., LTD. We take the four measurement parameters of chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen (NH 4 + -N) from the wastewater as the detection items for the static adsorption experiment. After testing, the concentrations of COD, TP, TN, and NH 4 + -N in the wastewater were 60 mg/L, 0.7 mg/L, 15 mg/L and 10 mg/L respectively. Before conducting the adsorption experiment again, the wastewater needs to be filtered to remove suspended solids. Then, the lignin-chitosan adsorbent is used for the adsorption experiment. The amount of sewage used in a single experiment was 100 mL. The dosage of the adsorbent is set at 0.5, 1, 1.5, 2, 2.5 g/L in a gradient, the pH value of the wastewater is set at 3, 5, 7, 9, 11 in a gradient. Lignin was used without any treatment, while chitosan was first dissolved in a 1% acetic acid solution. The chitosan solution was then drawn up with a medical syringe and added dropwise into a NaOH/ethanol coagulation bath to form gel beads, which were used for the adsorption experiments. 2.5 Adsorption kinetics experiment The fixed experimental conditions were sewage pH 5, sewage volume 100 mL, and temperature at 25 ± 2℃. First, the adsorption effect under different time gradients (0, 20, 40, 60, 80, 100, 120, 140 160 mins) was determined through static adsorption experiments. Then, in order to study the kinetic characteristics of COD, TP, TN and NH 4 + -N adsorbed by lignin-chitosan adsorbent, it is proposed to fit the adsorption kinetics by using the pseudo-first-order kinetic equation and the pseudo-second-order kinetic equation. The correlation coefficient is used to determine that the two kinetic equations can more accurately reflect the kinetic process. Proposed first-order dynamic Eq. 8, Eq. ( 1 ): $$\:d{q}_{t}/dt={k}_{1}({q}_{e}-{q}_{t})$$ 1 Integrate based on the boundary conditions t = 0, q t =0, and t = t, q t =q t , Eq. ( 2 ): $$\:{q}_{t}={q}_{e}(1-{e}^{-kt})$$ 2 t: Adsorption time (min); q e : The adsorption capacity of the adsorbent for the adsorbate at adsorption equilibrium (mg/g); q t : The adsorption capacity of the adsorbent for the adsorbate at time t (mg/g); k 1 : The adsorption rate constant of the pseudo-first-order kinetic model (min − 1 ). Graph t with ln(q e -q t ) to obtain a straight line. The values of parameters k 1 and q e can be calculated through the slope and intercept of the line. Quasi-second-order kinetic equation, Eq. ( 3 ): $$\:d{q}_{t}/dt={k}^{2}{({q}_{e}-{q}_{t})}^{2}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:$$ 3 According to the same boundary conditions, its integral expression, Eq. ( 4 ): $$\:\frac{t}{{q}_{t}}=\frac{t}{{q}_{e}}+\frac{1}{{k}^{2}{q}_{e}^{2}}$$ 4 k 2 : The adsorption rate constant of the pseudo-second-order kinetic model (g/(mg·min)); The others are the same as Eq. ( 2 ). A straight line is obtained by plotting t/q t against t. The values of the parameters q e and k 2 can be calculated through the slope and intercept of the line. Based on the proposed first-order kinetic model Eq. ( 1 ) and the proposed second-order kinetic model Eq. ( 2 ), the relationship between adsorption capacity and time is fitted. The dynamic model was used to fit the COD, TP, TN and NH 4 + -N adsorbed by activated carbon in water. 2.6 Adsorbent adsorption cycle experiment After the lignin-chitosan adsorbent has completed the adsorption of pollutants, it can be reused through the heat drying method (at 150℃). An experiment of desorption and reuse of the used lignin-chitosan adsorbent was conducted. Multiple adsorption experiments were carried out on COD, TP, TN, and NH 4 + -N in the distillers' grains wastewater. The adsorbent was recycled 5 times, and the adsorption performance of the reused adsorbent was analyzed. 2.7 Statistical analysis All experiments were conducted in triplicate. The results were analyzed using a one-way analysis of variance (ANOVA) with a least significant difference of P < 0.05. Origin 2021 software (OriginLab, Massachusetts, USA) was used for the statistical analysis. 3 Results and discussion 3.1 Adsorbent characterization Figure 1 SEM micrographs of pure lignin (a and d), chitosan (b and e) and lignin-chitosan adsorbent (c and f) Scanning electron microscopy (SEM) analysis revealed that, at a magnification corresponding to a 20 µm scale, the surface of lignin was generally smooth, with only a few minor protrusions observed locally-likely attributed to sample preparation processes or self-aggregation (Fig. 1 a). At a higher magnification (500 nm), lignin exhibited a dense and relatively uniform granular aggregated structure, where particles were tightly bound with no obvious pores (Fig. 1 d). This morphological feature indicates that lignin molecules form a dense aggregated state via strong intermolecular interactions. Although this structure confers a certain degree of stability, its relatively low porosity may restrict the exposure of active adsorption sites for pollutants and hinder mass transfer efficiency. In contrast, chitosan displayed extensive cracks and a rough surface at the 20 µm scale (Fig. 1 b). At the 500 nm scale, distinct cracks and sheet-like structures were visible in chitosan, with gaps present between the layers formed by particle aggregation (Fig. 1 e). These crack structures are proposed to form due to stress generation during drying or film-forming processes, which accompany volume contraction. While the cracks in chitosan can provide limited mass transfer channels, the lamellar structure exhibits insufficient stability, and the distribution of pores is highly random. For the lignin-chitosan composite adsorbent, a rich hierarchical structure with increased surface folds and a rough interface was observed at the 20 µm scale (Fig. 1 c). At the 500 nm scale, a cross-linked mixed structure was evident, with numerous pores distributed between the structural components (Fig. 1 f). Compared to the single-component materials, the compounding process led to interweaving between the granular structure of lignin and the polymer chains of chitosan. This synergy offers two key advantages: on one hand, the rigid structure of lignin inhibits the cracking of chitosan caused by hydrogen bond-driven contraction; on the other hand, the polymer network of chitosan serves as a dispersion carrier for lignin particles. The porous structure of the lignin-chitosan composite adsorbent not only provides an increased number of active adsorption sites but also accelerates the mass transfer of pollutants through the porous channels. Consequently, the composite adsorbent demonstrates superior performance compared to single-component lignin or chitosan in applications such as the adsorption of heavy metal ions and organic pollutants. FT-IR spectroscopy was employed to characterize the functional group structures of lignin, chitosan, and the lignin-chitosan composite adsorbent. As shown in Fig. 2 , the lignin-chitosan adsorbent exhibited distinct characteristic peaks at 3340 cm − 1 , 2916 cm − 1 , 1638 cm − 1 , 1105 cm − 1 , and 619 cm − 1 after complexation of lignin and chitosan. These peaks are attributed to the broadened overlapping vibrations of O-H and N-H bonds, C-H stretching vibrations, S = O stretching vibrations, and C = C skeletal vibrations, respectively 18 , 19 . Compared with the original lignin, which showed a peak at 3440 cm − 1 (corresponding to O-H stretching), the downshift and broadening of the peak to 3340 cm − 1 in the composite confirm the formation of a hydrogen-bonding network between the -OH of lignin and the -NH 2 of chitosan. In this structure, the -OH groups can capture polar molecules via hydrogen bonding, while the -NH 2 groups are protonated (forming -NH 3 + ) in acidic media-greatly enhancing the electrostatic attraction toward anionic pollutants. The aromatic skeleton vibration peak of lignin (originally at a higher wavenumber) shifted to 1638 cm − 1 with reduced intensity in the composite. This shift reflects that chitosan complexation partially disrupts lignin’s conjugated structure, while still retaining its π-electron system 20 . This retained π-system enables the adsorption of cationic dyes containing aromatic rings through π-cation interactions. Additionally, the protonated -NH 3 + groups carry a positive charge, allowing direct adsorption of anions via electrostatic attraction. Furthermore, the composite adsorbent retained the characteristic peak of lignin’s G-type units at 1265 cm − 1 , which corresponds to C-O stretching vibrations on aromatic rings and C-O-C stretching vibrations of aromatic ether bonds. The oxygen atoms in these C-O groups have lone electron pairs, which can form stable complexes with cationic pollutants-further supporting the adsorbent’s capacity for cationic pollutant removal. Notably, distinct peaks at 1105 cm − 1 and 619 cm − 1 were observed in the composite, corresponding to the symmetric stretching vibrations of S = O bonds in -SO 3 − groups. Raw lignin showed low response in this wavenumber range, confirming the successful anchoring of -SO 3 − groups onto the composite adsorbent skeleton 21 . Moreover, the δ(N-H) bending vibration peak (originally at 1520 cm⁻¹ in pure chitosan) shifted to lower wavenumbers in the composite, indicating electrostatic interactions between the -NH 2 groups of chitosan and the -SO 3 − groups 22 . These spectral changes collectively confirm the successful reaction and complexation between lignin and chitosan. The resulting multi-functional synergistic structure endows the lignin-chitosan composite adsorbent with broad-spectrum adsorption capability for both cationic and anionic pollutants, mediated by multiple mechanisms including hydrogen bonding, electrostatic attraction, π-π stacking, and hydrophobic interactions. Table 1 Element content and sources of the three materials analyzed by XPS Material Name Element Percentage/% C 1s O 1s N 1s S 2p Lignin-chitosan adsorbent 60.11 31.01 6.52 2.31 X-ray photoelectron spectroscopy (XPS) was employed to analyze the elemental composition and chemical state of the lignin-chitosan composite adsorbent. The results indicated that the final prepared composite adsorbent exhibited the elemental characteristics of both raw materials (lignin and chitosan). Specifically, the composite adsorbent contained carbon (C), oxygen (O), nitrogen (N), and sulfur (S) (Fig. 3 a)-a clear indication of the successful binding between lignin and chitosan, as these elements correspond to the characteristic components of the two raw materials. Analysis of the high-resolution S 2p spectrum revealed two characteristic peaks for the composite adsorbent (Fig. 3 b). The peak at 169.13 eV was attributed to the C = S bond, while the peak at 167.99 eV corresponded to the C-S bond; the total peak area of these sulfur-containing bonds accounted for 2.31% of the total spectral signal. This result confirms that the sulfur-containing groups in lignin retained their original chemical state after composite formation, which provides potential active sites for the subsequent adsorption process 23 (Fig. 3 b). The C1s spectrum of lignin-chitosan adsorbents has three characteristic peaks. C-O/C-S bond at 287.98 eV, C-N bond at 286.41 eV and C-C bond at 284.80 eV, respectively, accounting for 60.11% of the peak area. The binding energy of the C-N peak of the adsorbent is located between the two, indicating that lignin and chitosan form a chemical bond by interacting with the amino group at the active site of lignin, thus forming a molecular complex. The C = C peak (284.8 eV) was mainly from the carbon element in lignin, while the C = S peak (287.98 eV) was mainly from the introduced sodium sulfite, which enhanced the adsorption of anionic pollutants 24 , 25 (Fig. 3 c). Deconvolution of the high-resolution N 1s spectrum yielded two peaks (Fig. 3 d): 401.68 eV (assigned to N-H bonds) and 399.49 eV (assigned to C-N bonds), with nitrogen accounting for 6.25% of the total elemental composition of the composite. This result indicates that the amino groups of chitosan were neither oxidized nor protonated after complexation with lignin, thus retaining their chemical activity as active adsorption sites 26 (Fig. 3 e). The high-resolution O 1s spectrum of the composite adsorbent showed a characteristic peak at 532.3 eV (assigned to C-O bonds) (Fig. 3 e), which integrated the O 1s spectral features of both pure lignin and pure chitosan. This observation confirms that the chemical environment of hydroxyl groups (-OH) in the composite changed due to interactions between lignin and chitosan-providing a structural basis for hydrogen bonding and coordination interactions during the adsorption process. In conclusion, XPS analysis clearly demonstrates the successful combination of lignin and chitosan from the perspectives of elemental composition and chemical state. The composite adsorbent simultaneously possesses sulfur-containing active sites (from lignin) and amino/hydroxyl active sites (from chitosan), and these two components form a stable structure via chemical bonding. This provides structural support at the chemical level for the composite’s application in fields such as pollutant adsorption and catalysis. It is worth noting that lignin extraction from wheat distillers’ grains using p-toluenesulfonic acid not only retains the non-condensed structure of lignin (e.g., β-O-4 bonds) but also introduces sulfonic acid groups, which can interact with nitrogen-containing components (amino groups of chitosan) to further stabilize the composite structure. Table 2 Specific surface area, average pore size and average pore volume values of adsorbents Name Specific surface area (m 2 /g) Average aperture (Å) Total pore volume (cm 3 /g) Lignin 1.332 38.48 0.003 Chitosan 1.664 38.38 0.004 Lignin-chitosan adsorbent 3.767 135.46 0.012 The specific surface area of the samples was comprehensively studied using the BET analysis method. The lignin-chitosan adsorbent exhibited a Type IV isotherm and an H3 hysteresis loop, indicating that the slit-like mesoporous structure was the dominant morphology (Fig. 4 a). Its specific surface area was 3.767 m 2 /g, significantly higher than that of raw chitosan (1.664 m 2 /g) and alkali lignin (1.332 m 2 /g). This enhancement was attributed to the flake-like morphology formed by the fiber disintegration of chitosan during the composite process (Table 2 ). In the low-pressure region (P/P 0 < 0.4), monolayer adsorption was dominant, with low adsorption capacity and no significant contribution from micropores. The medium-pressure region (0.4 < P/P 0 < 0.8) showed a distinct capillary condensation effect, and the adsorption capacity increased rapidly, corresponding to the mesopore filling process. The adsorption capacity in the high-pressure region (P/P 0 > 0.9) gradually stabilized, indicating limited macropores or interparticle pores. Analysis of the pore size distribution characteristics revealed that the main peak of the lignin-chitosan adsorbent was at 5 nm, suggesting that mesopores contributed to most of the pore volume. The distribution range was 5–20 nm, and combined with the average pore size (13.5 nm), it can be seen that the pore size distribution was relatively wide, including some larger mesopores (> 10 nm) all higher than the corresponding pore sizes of lignin and chitosan (Fig. 4 b and Table 2 ). Thermogravimetric analysis (TG) was performed to evaluate the thermal stability of the lignin-chitosan composite adsorbent. As shown in Fig. 5 , the composite adsorbent exhibited an initial decomposition temperature of 446.1°C, which corresponds to the cleavage of lignin’s aromatic skeleton 27 . The final pyrolysis temperature of the adsorbent was 717.3°C, indicating excellent thermal resilience compared to single-component lignin or chitosan. Correlation analysis between thermal stability and adsorption performance revealed that the adsorbent’s high-temperature tolerance is critical for its regeneration potential. This superior thermal stability enables the lignin-based composite adsorbent to remove adsorbed pollutants via high-temperature calcination while preserving its intrinsic framework structure-directly supporting cyclic reuse. The synergistic effect between this thermal resilience and the previously characterized porous structure underpins the feasibility of the adsorbent for cyclic adsorption applications. Notably, the inherent G-type and H-type units in lignin not only enhance the composite’s thermal stability but also maintain the integrity of active adsorption sites, delaying the onset of the main decomposition stage. TG analysis further demonstrated that the lignin-chitosan adsorbent possesses good thermal stability and a high carbon structure retention capacity, with a char residue rate of 40.95%, this property supports its application in high-temperature adsorption-regeneration processes., To verify practical recyclability, adsorption cycle experiments were conducted. The results confirmed that the composite adsorbent can be effectively regenerated via high-temperature calcination at 150°C, enabling cyclic use without significant degradation of its adsorption performance or structural integrity. This regeneration protocol, combined with the adsorbent’s robust thermal stability, further reinforces its potential for large-scale, sustainable application in wastewater treatment. 3.2 Sewage adsorption experiment 3.2.1 Adsorption performance of adsorbents Figure 6 The performance of the adsorption materials in adsorbing distillery wastewater Adsorption performance tests were conducted on lignin, chitosan gel particles, and lignin-chitosan adsorbents. The results showed that the adsorption performance of the lignin-chitosan adsorbent for four types of pollutants was higher than that of the individual substances, with a removal efficiency of approximately 90% for all pollutants. Comparing lignin and chitosan gel, it was found that lignin exhibited poor removal efficiency for TP, while chitosan showed poor removal efficiency for NH 4 + -N. Both substances also had relatively low removal efficiency for TN among the four pollutants, but displayed high adsorption efficiency for COD. The reasons for this phenomenon were analyzed as follows: Phosphorus in wastewater exists as anionic pollutants, while ammonia nitrogen in wastewater is usually present in the form of cationic ammonium ions (NH 4 + ) 28 . Lignin is rich in acidic groups such as phenolic hydroxyl and carboxyl groups, so it is generally negatively charged in aqueous solutions. It adsorbs cationic substances through electrostatic interaction and has a strong affinity for hydrophobic organic compounds due to its large phenylpropane skeleton and hydrophobic regions 29 . For chitosan, the core of its adsorption capacity lies in the free -NH 2 on its molecular chain. Under acidic conditions, these amino groups are protonated to form -NH 3 + (positively charged), which strongly adsorbs anionic substances through electrostatic interaction 30 . The lignin-chitosan adsorbent optimizes the adsorption performance for both cationic and anionic pollutants. 3.2.2 Adsorption kinetics of lignin-chitosan adsorbent on distiller's grains wastewater Figure 7 Adsorption kinetics. Effect of adsorption time of adsorbent on pollutant removal rate(a), fitting of first-order adsorption kinetics(b) and fitting of second-order adsorption kinetics (c) Table 3 Fitting results of the proposed first-order and second-order adsorption kinetics Water quality indicators C 0 mg·L − 1 q e, exp mg·g − 1 Quasi-first-order dynamic model Pseudo-second-order dynamic model k 1 min − 1 q e, 1 mg·g − 1 R 2 K 2 min − 1 q e, 2 mg·g − 1 R 2 COD 60 27.6 0.0336 29.76 0.7396 0.0278 35.745 0.9951 TP 0.7 0.333 0.0158 63.29 0.9526 2.4074 0.415 0.9679 TN 15 5.52 0.0214 46.725 0.9273 0.1374 7.235 0.9763 NH 4 + -N 10 4.42 0.027 37.04 0.9404 0.164 6.1 0.9946 In the static adsorption experiment, the adsorption time was set to 8 gradients ranging from 20 to 160 mins. The results showed that when the adsorption time was between 0 and 80 mins, the removal rates of COD and NH 4 + -N first approached equilibrium. However, to achieve high removal rates for TP and TN, the adsorption time needed to be extended to 120 mins (Fig. 7 a). Analysis revealed that this difference could be attributed to the following: the removal of COD and NH 4 + -N is mainly controlled by the dual effects of electrostatic adsorption and chemical adsorption. In contrast, the removal of TP involves the synergistic effect of chemical precipitation and physical interception, while the removal of TN is the result of the synergy of multiple mechanisms (electrostatic adsorption and complexation) 31 , 32 . Based on the pseudo-first-order kinetic model equation (Eq. 1 ) and pseudo-second-order kinetic model equation (Eq. 3 ), the relationships between the adsorption capacities of lignin-chitosan adsorbent for COD, TP, TN, and NH 4 + -N in water and time were fitted. For the pseudo-first-order kinetic model, the R 2 for all pollutants were below 0.95, indicating a poor fitting effect (Table 4 ). The theoretical adsorption capacities for COD, TP, TN and NH 4 + -N were 27.6, 0.333, 5.52 and 4.42 mg/g, respectively. Moreover, in the 0–80 mins adsorption stage, the removal efficiency of COD and NH 4 + -N increased rapidly (Fig. 7 a). The removal of TP and TN tended to be flat during the whole process, and the adsorption rate was constant at 120 mins. For the pseudo-second-order kinetics, the R 2 of the adsorbent for the four pollutants were 0.9951, 0.9679, 0.9763, and 0.9946, respectively. The theoretical equilibrium adsorption capacities of COD, TP, TN, and NH 4 + -N calculated by the pseudo-second-order kinetic equation were 35.745, 0.415, 7.235 and 6.1 mg/g, respectively. The deviation between the theoretical equilibrium adsorption capacity (q e ) and the experimental value (q e, exp ) was less than 15%, indicating a good agreement between the experimentally determined equilibrium adsorption capacity and the theoretical value calculated by the pseudo-second-order model (Fig. 7 c). The overall adsorption process is well described by the quasi-second-order kinetic model. 3.2.3 Static adsorption experiment of lignin-chitosan adsorbent on distillery wastewater Figure 8 Factors affecting the adsorption performance of lignin-chitosan adsorbent (a) dosage amount and (b) pH Static adsorption experiments can be used to determine the optimal adsorption conditions of the adsorbent for pollutants. The dosage of the adsorbent is the primary factor controlling costs. As the dosage amount increases, the removal rate of pollutants significantly improves. When the dosage was 2 g/L, the increase rate of removal efficiency slowed down, with COD and TN showing a significant slowdown. Meanwhile, the removal rates of all pollutants reached over 80%. Although the adsorption capacities for TP and NH 4 + -N still increased slightly when the adsorbent dosage was 2.5 g/L, the change was negligible (Fig. 8 a). This phenomenon may be attributed to the fact that the adsorption sites were nearly saturated. Therefore, the optimal dosage of the adsorbent is 2 g/L. In environmental chemistry, pH has a significant impact on various reactions. Therefore, the influence of pH on the adsorption efficiency of adsorbents for pollutants was investigated. During the entire static adsorption process, the removal efficiency of TP by the adsorbent reached its maximum value of 92% at a pH of 7. The influence of pH on the COD removal rate is relatively small. The removal effect does not change much under different pH conditions. The highest removal efficiency of 90% is achieved when the pH is 5. Furthermore, the removal efficiency of TN by the adsorbent reaches its peak at a pH of 7. The removal efficiency of NH 4 + -N by the adsorbent reaches its maximum value at a pH of 9 (Fig. 8 c). The analysis of the reasons suggests that it occurs under acidic conditions. The protonation of the adsorbent surface promotes the adsorption of negatively charged anionic pollutants TP through electrostatic interactions 33 . TN and COD, as pollutants that are both anions and cations, achieve the highest removal efficiency when the pH is 7. As a cationic pollutant with positive charge, NH 4 + -N has a better removal effect under alkaline conditions 31 . As the pH continues to increase, the lignin-chitosan adsorbent material is corroded under strong alkali conditions and cannot play a role in adsorption. In general, Although the removal rate of TN was slightly lower at pH is 7 than at pH is 5, the removal rates of the other three pollutants reached their maximum values at pH is 7. Therefore, a pH of 7 was chosen as the optimal equilibrium point. In conclusion, the best removal of COD, TP, TN, and NH 4 + -N was achieved at the adsorption time of 120 mins, adsorbent dosage of 2 g/L, and pH of 7, which were 91%, 92%, 89%, and 86%, respectively. The high adsorption performance means that the adsorbent material has a wide range of applications. 3.3 Adsorbent adsorption cycle Figure 9 Adsorption cycle experiments of lignin-chitosan adsorbent Table 4 Comparison of advantages with other similar adsorbents Name Type of pollutants Capacity of adsorption References 3-aminopropyltriethoxysilane Phosphate 21.12 mg/g 34 AL-CTS@MNPs Rhodamine 20.00 mg/g 27 Phosphorus-rich carbon derived from lignin Phosphate 1.6 mg/g 35 Zeolite Ammonia nitrogen 0.256 mg/g 36 Lignin-chitosan adsorbent COD 27.6 mg/g this study Whether the adsorbent can be recycled is one of the important factors for reducing costs and practical application. The results showed, after 5 adsorption cycles of the lignin-chitosan adsorbent, that the removal efficiencies of COD, TP, TN and NH 4 + -N by the adsorbent could still reach more than 75% of the initial removal efficiency (Fig. 9 ). To analyze the reasons, in each adsorption cycle, pollutants would occupy the active sites on the surface of the lignin-chitosan adsorbent. Even after desorption treatment, some pollutants would still remain through physical or chemical adsorption, gradually reducing the available active sites. The repeated adsorption-desorption process would damage the porous structure and functional groups of the adsorbent. The phenolic hydroxyl groups of lignin and the amino groups of chitosan might undergo oxidation, hydrolysis, or cross-linking, causing the adsorption capacity to gradually decrease with the increase of cycle times. The adsorption of COD, TP, and TN by the adsorbent involves multiple mechanisms such as electrostatic interaction, complexation, and pore filling. The functional groups and porous structure supporting these mechanisms are relatively stable in the early stage, so more than 75% of the initial removal efficiency can be maintained. The adsorption of NH 4 + -N by the adsorbent mainly relies on the electrostatic attraction of protonated amino groups (-NH 3 + ) on the chitosan molecular chain. In terms of removal efficiency, the adsorbent still has a good removal effect on pollutants after 5 cycles. Compared with other adsorbents, the prepared lignin-chitosan adsorbent exhibits the characteristic of efficient pollutant adsorption (Table 4 ). Besides, this adsorbent has the advantages of simple preparation method, green recyclability, and the ability to adsorb various organic pollutants, which has the potential for preventive application as a green organic pollutant adsorbent. 4 Conclusion Direct discharge of wheat distillers’ grains poses a significant environmental pollution risk, and converting lignin extracted from these by-products into an adsorbent not only mitigates this pollution but also enhances its added value. In this study, a lignin-chitosan composite adsorbent was developed using lignin from wheat distillers’ grains combined with free radical polymerization, and its efficiency in removing pollutants (COD, TP, TN, NH 4 + -N) from distillery wastewater was evaluated alongside systematic investigation of its adsorption mechanism. Characterization results showed that SEM analysis revealed the composite adsorbent has a rougher surface and broader pore size distribution compared to pure lignin and chitosan; FT-IR and XPS analyses confirmed the successful polymerization of lignin and chitosan, with the adsorbent retaining phenolic hydroxyl and carboxyl groups from lignin, integrating -NH 2 from chitosan, and sulfur (-SO 3 − ) doping further enhancing its adsorption capacity for cationic pollutants; BET analysis verified a favorable pore structure and larger specific surface area that improve pollutant adsorption; thermogravimetric analysis demonstrated excellent thermal stability, enabling cyclic use via high-temperature calcination. Adsorption kinetic studies indicated that the removal of the four target pollutants follows the pseudo-second-order kinetic model, reflecting that the adsorption process is dominated by chemical interactions between surface active sites and adsorbates, with the adsorption rate dependent on the chemical reaction rate between adsorbates and these active sites. Compared with other conventional adsorbents, this composite adsorbent offers advantages including a broad adsorption spectrum, green and straightforward preparation, and cost-effectiveness. Beyond lignin, wheat distillers’ grains contain other active substances (e.g., cellulose, hemicellulose, phenolic compounds) with potential for adsorbent development, and future research should explore these alternative matrix materials. Declarations CRediT authorship contribution statement Yijie Wang : Writing-original draft, Investigation, Data curation, Conceptualization. Haiqing Wang: Writing-review & editing, Investigation, Conceptualization. Jingtao Liu Writing-review & editing, Investigation, Conceptualization. Acknowledgements We acknowledge the contributions of all investigators involved in the original study. Funding Declaration This work was funded by Shandong Provincial Natural Science Foundation (ZR2024QD166) and the Doctoral Start-up Foundation of Shandong University of Aeronautics (2023Y48). Funding information Project Type Project Number Funding agency Provincial Natural Science Foundation ZR2024QD166 Shandong Provincial Natural Science Foundation School-level Doctoral Startup Fund 2023Y48 Doctoral Start-up Foundation of Shandong University of Aeronautics Declaration of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 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05:51:12","extension":"png","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":26305,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/6288b51ff1df9dfa47ec638b.png"},{"id":98483468,"identity":"89247c95-5833-4c71-9987-31f1f03493ab","added_by":"auto","created_at":"2025-12-18 05:51:12","extension":"png","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":28584,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/825c570a5cb903d6d96a3f63.png"},{"id":98483471,"identity":"14d404f7-5c9c-4486-9c22-0bc56eec7f43","added_by":"auto","created_at":"2025-12-18 05:51:12","extension":"xml","order_by":21,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":118349,"visible":true,"origin":"","legend":"","description":"","filename":"57d359472f814fcf83b168a1d60f6add1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/02340f7cb89b68bda6f232c9.xml"},{"id":98483472,"identity":"061411b7-6d36-483d-a2c1-a301f08ca69b","added_by":"auto","created_at":"2025-12-18 05:51:12","extension":"html","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":128283,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/550c773d1557f5946b37f83d.html"},{"id":98483447,"identity":"b431339d-bb90-4bb4-b2bf-660630b99826","added_by":"auto","created_at":"2025-12-18 05:51:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":612652,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSEM micrographs of pure lignin (a and d), chitosan (b and e) and lignin-chitosan adsorbent (c and f)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/4b4a80ee1909066403d02085.png"},{"id":98483449,"identity":"7ad624a6-6061-4af9-af70-ddd2de4641df","added_by":"auto","created_at":"2025-12-18 05:51:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":268973,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFT-IR spectra of lignin (a), chitosan (b) and lignin-chitosan adsorbent (c)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/a5606f34dad78a45622d068f.png"},{"id":98624316,"identity":"7d0c223e-8468-47f0-99b8-6147a48a5ff5","added_by":"auto","created_at":"2025-12-19 17:08:18","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":235999,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eXPS spectra lignin-chitosan adsorbent Total spectrum (a); S 2p (b); C 1s (c); N 1s(d); O 1s(e)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/88dcbfba33cb4febc5d5ce0d.png"},{"id":98623991,"identity":"189cca66-d78f-49a6-8147-9d5131b550fc","added_by":"auto","created_at":"2025-12-19 17:07:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":243391,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eBET surface area and pore analysis Specific surface area analysi (a)s; Analysis of porosity (b)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/a034c20126f3d2332f520fb6.png"},{"id":98624177,"identity":"2213199f-9f25-4726-8c4d-5edd51aaa92f","added_by":"auto","created_at":"2025-12-19 17:08:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":291447,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThermogravimetric (TG) analysis of lignin-chitosan adsorbent\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/6ff4a2cb2c2073f5049d03c1.png"},{"id":98623420,"identity":"1278dbe1-e043-4882-9b50-65f087e3db87","added_by":"auto","created_at":"2025-12-19 17:06:16","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":194514,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe performance of the adsorption materials in adsorbing distillery wastewater\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/54510a4931a2b861dfcfe0c2.png"},{"id":98483477,"identity":"05678b10-8bf1-4413-8811-0197eb102799","added_by":"auto","created_at":"2025-12-18 05:51:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":254215,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdsorption kinetics. effect of adsorption time of adsorbent on pollutant removal rate(a); Fitting of first-order adsorption kinetics(b); Fitting of second-order adsorption kinetics (c)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/cc8b16c2aede3f464a0a8419.png"},{"id":98483456,"identity":"9bca433a-b09b-420f-99e1-59f051cb433e","added_by":"auto","created_at":"2025-12-18 05:51:12","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":180713,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStatic adsorption experiment. Dosage amount (a); pH (b)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/06c97bd2f780a8e76977bdc6.png"},{"id":98623387,"identity":"6a3fbea8-b81c-4236-9b7f-707507b9a541","added_by":"auto","created_at":"2025-12-19 17:06:04","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":314328,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdsorption cycle experiments of lignin-chitosan adsorbent\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/84c11707560e7b39163ca373.png"},{"id":105224739,"identity":"5527d41c-1326-4cb0-92b0-ff7ab44e3819","added_by":"auto","created_at":"2026-03-23 16:15:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4231204,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8248335/v1/a911b5c4-e406-4d2c-85fc-38a806474312.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Preparation of a distillers’ grains derived lignin-chitosan adsorbent for enhanced the distillery wastewater treatment","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the rapid development of the global economy and the acceleration of industrialization, the demand for renewable energy has continued to rise. In the process of alcohol production, a by-product known as distillers' grains is generated-specifically, 3.5 tons of distillers' grains are produced for every 1 ton of alcohol manufactured\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Historically, distillers' grains were directly discharged into the environment as waste; the decomposition of organic matter within them would subsequently cause significant environmental harm\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Notably, distillers' grains contain abundant lignin-a rigid biopolymer that accounts for approximately 10% of its composition. Lignin possesses functional groups including aromatic rings, phenolic hydroxyl groups, and methoxy groups\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, which enables efficient capture of pollutants such as heavy metals, dyes, and nutrients through ion exchange, hydrogen bonding, and π-π interactions\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, giving it the potential to serve as a low-cost adsorption framework. However, the inherent limitations of natural lignin restrict its direct application, such as low specific surface area and poor solubility. Strategies like modification or compounding are required to unlock its adsorption potential. Additionally, while producing distiller's grains, factories also generate distiller's grains wastewater containing various pollutants-including substances that cause water eutrophication\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. If lignin extracted from wheat distiller's grains is used as an adsorbent to treat pollutants in distillery wastewater, a green economic cycle can be achieved.\u003c/p\u003e \u003cp\u003eCurrent research on lignin-based adsorbents for organic pollutant removal remains relatively limited. Existing studies have demonstrated that lignin-based adsorbents exhibit excellent adsorption performance for various dye pollutants, such as methylene blue and Congo red\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Through modification or compounding, lignin can be tailored to adsorb different types of pollutants. Lignin modification typically encompasses chemical and physical approaches, with chemical modification being the most widely used method to enhance lignin\u0026rsquo;s adsorption capacity. Sulfonation modification improves lignin\u0026rsquo;s water solubility and dispersibility by introducing sulfonic acid groups. This process usually involves reacting lignin with sodium sulfite at elevated temperatures to graft sulfonic acid groups onto its side chains or benzene rings, thereby enhancing its adsorption capacity for ionic pollutants\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. The Mannich reaction is another key chemical modification technique: it uses amine compounds and formaldehyde to introduce amine groups onto the lignin structure, increasing the material\u0026rsquo;s nitrogen content and consequently boosting its adsorption performance for heavy metals and dyes\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Additionally, graft copolymerization employs initiators to graft monomers (e.g., acrylamide and acrylic acid) onto the lignin backbone, introducing functional groups such as carboxyl and amide groups, this significantly improves the adsorbent\u0026rsquo;s ability to capture pollutants\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Physical modification methods, by contrast, primarily focus on optimizing lignin\u0026rsquo;s pore structure and specific surface area. Treatments including heat, microwave, or ultrasound can disrupt lignin\u0026rsquo;s dense inherent structure, increasing its porosity and specific surface area to enhance adsorption capacity\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Constructing composite adsorbent materials represents another effective strategy to improve lignin\u0026rsquo;s adsorption performance. Lignin-based hydrogels, for instance, form a three-dimensional network structure by incorporating polymers like polyacrylic acid; they possess excellent water absorption and retention capabilities, making them suitable for adsorbing dyes and heavy metals\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Lignin-based magnetic nanocomposite particles, on the other hand, combine lignin with magnetic particles (e.g., iron tetroxide). This design enables easy separation and recovery of the adsorbent via an external magnetic field, facilitating reuse\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. However, a critical gap exists in the field of lignin-based adsorbents: most studies prioritize optimizing pollutant adsorption efficiency while often neglecting preparation costs and environmental sustainability. The synthesis routes of most existing lignin-based adsorbents are complex, their production costs are high, and the materials used in synthesis are not environmentally friendly-these issues constitute important challenges that warrant urgent solutions.\u003c/p\u003e \u003cp\u003eIn this study, a green synthesis method for a lignin-chitosan composite adsorbent is proposed. The synthesis process is straightforward, and the lignin used as a raw material is extracted from distillers' grains (a by-product of alcohol production), which not only reduces synthesis costs but also realizes waste valorization. Additionally, chitosan-a biodegradable amino-polysaccharide-possesses protonated amino groups (-NH\u003csub\u003e2\u003c/sub\u003e) that enhance the electrostatic adsorption of anionic pollutants (e.g., phosphates, nitrates)\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. This functional attribute complements lignin\u0026rsquo;s inherent capability for adsorbing cationic pollutants\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. The resulting lignin chitosan composite adsorbent was applied to target eutrophication-causing pollutants (COD, TP, TN, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N) in food industry wastewater, simultaneously addressing waste management and water pollution remediation challenges. Adsorption experiments investigated the effects of temperature, contact time, adsorbent dosage, and pH value on removal efficiency, and analyzed the adsorption mechanisms. Although preliminary progress has been made in distiller's grain-derived lignin-chitosan adsorbents, the existing process still has defects in lignin extraction yield and composite adsorbent stability, which needs further optimization. Thus, the objectives of this study are threefold: (1) Lignin was extracted from distillers' grains using a reusable organic solvent and a simple and green method was used to prepare a lignin-chitosan adsorbent with low cost and reusable characteristics; (2) Through a series of characterization tests of lignin-chitosan adsorbent, the adsorption potential of this adsorbent for organic pollutants in distillery wastewater was proved (SEM, FT-IR, XPS, BET, TG); (3) Lignin-chitosan adsorbent has a good removal effect on organic pollutants (COD, TP, TN, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N) in distillery wastewater. The adsorption mechanism of this adsorbent was explored through static adsorption experiments and adsorption kinetics.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and reagents\u003c/h2\u003e \u003cp\u003eDistillers' grains are provided by a food factory in Shandong, China; Chitosan, analytical grade, purchased from Shanghai Maclean Biochemical Technology Co., LTD; The wastewater treated by adsorption is the distiller's grains wastewater from the sedimentation tank of a certain food factory. Chitosan, sodium hydroxide, formaldehyde and sodium sulfite are all of analytical purity and are sourced from Solebo Bio Inc.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of lignin-chitosan adsorbent\u003c/h2\u003e \u003cp\u003eThe 40% p-toluenesulfonic acid solution was prepared in a round bottom flask and preheated to 80\u0026deg;C in a constant temperature stirring water bath. Add wheat distillers\u0026rsquo; grains dry powder in a certain proportion and boil for 30 mins, and install a condensing tube to prevent the solution from evaporating. After the reaction was completed, the filtrate was obtained by vacuum suction filtration, and the filtrate was diluted in distilled water to the concentration of p-toluenesulfonic acid of 10% before stopping. At this point, a large amount of lignin is precipitated to form lignin sediment. The supernatant is discarded after centrifugation at 5500 rpm with a medical centrifuge. The lignin is then dried in a constant temperature drying oven at 65℃ to obtain the final product.\u003c/p\u003e \u003cp\u003eDissolve 4 g of lignin in 50 mL of 0.4 M NaOH solution. Add 2 mL of formaldehyde and 2 g of sodium sulfite to the lignin suspension, heat to 80℃ and allow the reaction to proceed for more than 3 h. Dissolve 1 g of chitosan in 100 mL of acetic acid aqueous solution (with a 2% volume ratio) and stir thoroughly to form a uniform solution. Add the lignin solution obtained after the reaction to the dissolved chitosan solution, and let it react at a speed of 300 rpm/min for 3 h. After the reaction is completed, the precipitate is collected by centrifugation at 3000 rpm in a medical centrifuge and then dried at room temperature for 36 h. The lignin adsorbent was ground into powder, then washed with double-distilled water, and dried at 65℃ to obtain the lignin-chitosan adsorbent.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Material testing characterization methods\u003c/h2\u003e \u003cp\u003eThe morphological characteristics and microstructure of the three materials were analyzed through SEM testing, and the test was conducted using the German-ZEISS-Sigma 360 instrument. The main chemical structures and adsorption functional groups of the materials were analyzed through Fourier Transform Infrared Spectroscopy (FTIR) testing. The test was conducted using the Japanese-SHIMADZU-IRTracer-100 instrument. The types and oxidation states of elements in the three materials were determined by X-ray photoelectron spectroscopy (XPS), and the tests were conducted using the American-Thermo Fisher-ESCALAB 250Xi instrument. The specific surface area and pore diameters of the three materials were analyzed through BET testing, which was conducted using the American-Micromeritics-ASAP 2460 instrument. The thermal stability of the three materials was analyzed through the TG test, which was conducted using the DSC7000 instrument provided by Hitachi of Japan.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Adsorption performance comparison experiment\u003c/h2\u003e \u003cp\u003eThe fixed experimental conditions were sewage pH 7, sewage volume 100 mL, and temperature at 25\u0026thinsp;\u0026plusmn;\u0026thinsp;2℃. The adsorption performance of synthetic raw materials (lignin, chitosan) and lignin-chitosan adsorbent towards chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N) in wastewater was tested.\u003c/p\u003e \u003cp\u003eThe experimental wastewater was from the sedimentation tank of Shandong Zhongyu Food Co., LTD. We take the four measurement parameters of chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N) from the wastewater as the detection items for the static adsorption experiment. After testing, the concentrations of COD, TP, TN, and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N in the wastewater were 60 mg/L, 0.7 mg/L, 15 mg/L and 10 mg/L respectively. Before conducting the adsorption experiment again, the wastewater needs to be filtered to remove suspended solids. Then, the lignin-chitosan adsorbent is used for the adsorption experiment. The amount of sewage used in a single experiment was 100 mL. The dosage of the adsorbent is set at 0.5, 1, 1.5, 2, 2.5 g/L in a gradient, the pH value of the wastewater is set at 3, 5, 7, 9, 11 in a gradient. Lignin was used without any treatment, while chitosan was first dissolved in a 1% acetic acid solution. The chitosan solution was then drawn up with a medical syringe and added dropwise into a NaOH/ethanol coagulation bath to form gel beads, which were used for the adsorption experiments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Adsorption kinetics experiment\u003c/h2\u003e \u003cp\u003eThe fixed experimental conditions were sewage pH 5, sewage volume 100 mL, and temperature at 25\u0026thinsp;\u0026plusmn;\u0026thinsp;2℃. First, the adsorption effect under different time gradients (0, 20, 40, 60, 80, 100, 120, 140 160 mins) was determined through static adsorption experiments. Then, in order to study the kinetic characteristics of COD, TP, TN and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N adsorbed by lignin-chitosan adsorbent, it is proposed to fit the adsorption kinetics by using the pseudo-first-order kinetic equation and the pseudo-second-order kinetic equation. The correlation coefficient is used to determine that the two kinetic equations can more accurately reflect the kinetic process.\u003c/p\u003e \u003cp\u003eProposed first-order dynamic Eq.\u0026nbsp;8, Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:d{q}_{t}/dt={k}_{1}({q}_{e}-{q}_{t})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIntegrate based on the boundary conditions t\u0026thinsp;=\u0026thinsp;0, q\u003csub\u003et\u003c/sub\u003e=0, and t\u0026thinsp;=\u0026thinsp;t, q\u003csub\u003et\u003c/sub\u003e=q\u003csub\u003et\u003c/sub\u003e, Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e):\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{q}_{t}={q}_{e}(1-{e}^{-kt})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003et: Adsorption time (min);\u003c/p\u003e \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e: The adsorption capacity of the adsorbent for the adsorbate at adsorption equilibrium (mg/g);\u003c/p\u003e \u003cp\u003eq\u003csub\u003et\u003c/sub\u003e: The adsorption capacity of the adsorbent for the adsorbate at time t (mg/g);\u003c/p\u003e \u003cp\u003ek\u003csub\u003e1\u003c/sub\u003e: The adsorption rate constant of the pseudo-first-order kinetic model (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eGraph t with ln(q\u003csub\u003ee\u003c/sub\u003e-q\u003csub\u003et\u003c/sub\u003e) to obtain a straight line. The values of parameters k\u003csub\u003e1\u003c/sub\u003e and q\u003csub\u003ee\u003c/sub\u003e can be calculated through the slope and intercept of the line.\u003c/p\u003e \u003cp\u003eQuasi-second-order kinetic equation, Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e):\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:d{q}_{t}/dt={k}^{2}{({q}_{e}-{q}_{t})}^{2}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAccording to the same boundary conditions, its integral expression, Eq.\u0026nbsp;(\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e):\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:\\frac{t}{{q}_{t}}=\\frac{t}{{q}_{e}}+\\frac{1}{{k}^{2}{q}_{e}^{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ek\u003csub\u003e2\u003c/sub\u003e: The adsorption rate constant of the pseudo-second-order kinetic model (g/(mg\u0026middot;min));\u003c/p\u003e \u003cp\u003eThe others are the same as Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eA straight line is obtained by plotting t/q\u003csub\u003et\u003c/sub\u003e against t. The values of the parameters q\u003csub\u003ee\u003c/sub\u003e and k\u003csub\u003e2\u003c/sub\u003e can be calculated through the slope and intercept of the line. Based on the proposed first-order kinetic model Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and the proposed second-order kinetic model Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), the relationship between adsorption capacity and time is fitted. The dynamic model was used to fit the COD, TP, TN and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N adsorbed by activated carbon in water.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Adsorbent adsorption cycle experiment\u003c/h2\u003e \u003cp\u003eAfter the lignin-chitosan adsorbent has completed the adsorption of pollutants, it can be reused through the heat drying method (at 150℃). An experiment of desorption and reuse of the used lignin-chitosan adsorbent was conducted. Multiple adsorption experiments were carried out on COD, TP, TN, and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N in the distillers' grains wastewater. The adsorbent was recycled 5 times, and the adsorption performance of the reused adsorbent was analyzed.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Statistical analysis\u003c/h2\u003e \u003cp\u003eAll experiments were conducted in triplicate. The results were analyzed using a one-way analysis of variance (ANOVA) with a least significant difference of P\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Origin 2021 software (OriginLab, Massachusetts, USA) was used for the statistical analysis.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cp\u003e \u003cb\u003e3.1 Adsorbent characterization\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e \u003cb\u003eSEM micrographs of pure lignin (a and d), chitosan (b and e) and lignin-chitosan adsorbent (c and f)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eScanning electron microscopy (SEM) analysis revealed that, at a magnification corresponding to a 20 \u0026micro;m scale, the surface of lignin was generally smooth, with only a few minor protrusions observed locally-likely attributed to sample preparation processes or self-aggregation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). At a higher magnification (500 nm), lignin exhibited a dense and relatively uniform granular aggregated structure, where particles were tightly bound with no obvious pores (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). This morphological feature indicates that lignin molecules form a dense aggregated state via strong intermolecular interactions. Although this structure confers a certain degree of stability, its relatively low porosity may restrict the exposure of active adsorption sites for pollutants and hinder mass transfer efficiency. In contrast, chitosan displayed extensive cracks and a rough surface at the 20 \u0026micro;m scale (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). At the 500 nm scale, distinct cracks and sheet-like structures were visible in chitosan, with gaps present between the layers formed by particle aggregation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). These crack structures are proposed to form due to stress generation during drying or film-forming processes, which accompany volume contraction. While the cracks in chitosan can provide limited mass transfer channels, the lamellar structure exhibits insufficient stability, and the distribution of pores is highly random. For the lignin-chitosan composite adsorbent, a rich hierarchical structure with increased surface folds and a rough interface was observed at the 20 \u0026micro;m scale (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). At the 500 nm scale, a cross-linked mixed structure was evident, with numerous pores distributed between the structural components (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef). Compared to the single-component materials, the compounding process led to interweaving between the granular structure of lignin and the polymer chains of chitosan. This synergy offers two key advantages: on one hand, the rigid structure of lignin inhibits the cracking of chitosan caused by hydrogen bond-driven contraction; on the other hand, the polymer network of chitosan serves as a dispersion carrier for lignin particles. The porous structure of the lignin-chitosan composite adsorbent not only provides an increased number of active adsorption sites but also accelerates the mass transfer of pollutants through the porous channels. Consequently, the composite adsorbent demonstrates superior performance compared to single-component lignin or chitosan in applications such as the adsorption of heavy metal ions and organic pollutants.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFT-IR spectroscopy was employed to characterize the functional group structures of lignin, chitosan, and the lignin-chitosan composite adsorbent. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the lignin-chitosan adsorbent exhibited distinct characteristic peaks at 3340 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 2916 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1638 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1105 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 619 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e after complexation of lignin and chitosan. These peaks are attributed to the broadened overlapping vibrations of O-H and N-H bonds, C-H stretching vibrations, S\u0026thinsp;=\u0026thinsp;O stretching vibrations, and C\u0026thinsp;=\u0026thinsp;C skeletal vibrations, respectively\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Compared with the original lignin, which showed a peak at 3440 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (corresponding to O-H stretching), the downshift and broadening of the peak to 3340 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the composite confirm the formation of a hydrogen-bonding network between the -OH of lignin and the -NH\u003csub\u003e2\u003c/sub\u003e of chitosan. In this structure, the -OH groups can capture polar molecules via hydrogen bonding, while the -NH\u003csub\u003e2\u003c/sub\u003e groups are protonated (forming -NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) in acidic media-greatly enhancing the electrostatic attraction toward anionic pollutants. The aromatic skeleton vibration peak of lignin (originally at a higher wavenumber) shifted to 1638 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with reduced intensity in the composite. This shift reflects that chitosan complexation partially disrupts lignin\u0026rsquo;s conjugated structure, while still retaining its π-electron system\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. This retained π-system enables the adsorption of cationic dyes containing aromatic rings through π-cation interactions. Additionally, the protonated -NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e groups carry a positive charge, allowing direct adsorption of anions via electrostatic attraction. Furthermore, the composite adsorbent retained the characteristic peak of lignin\u0026rsquo;s G-type units at 1265 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which corresponds to C-O stretching vibrations on aromatic rings and C-O-C stretching vibrations of aromatic ether bonds. The oxygen atoms in these C-O groups have lone electron pairs, which can form stable complexes with cationic pollutants-further supporting the adsorbent\u0026rsquo;s capacity for cationic pollutant removal. Notably, distinct peaks at 1105 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 619 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were observed in the composite, corresponding to the symmetric stretching vibrations of S\u0026thinsp;=\u0026thinsp;O bonds in -SO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e groups. Raw lignin showed low response in this wavenumber range, confirming the successful anchoring of -SO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e groups onto the composite adsorbent skeleton\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Moreover, the δ(N-H) bending vibration peak (originally at 1520 cm⁻\u0026sup1; in pure chitosan) shifted to lower wavenumbers in the composite, indicating electrostatic interactions between the -NH\u003csub\u003e2\u003c/sub\u003e groups of chitosan and the -SO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e groups\u003csup\u003e22\u003c/sup\u003e. These spectral changes collectively confirm the successful reaction and complexation between lignin and chitosan. The resulting multi-functional synergistic structure endows the lignin-chitosan composite adsorbent with broad-spectrum adsorption capability for both cationic and anionic pollutants, mediated by multiple mechanisms including hydrogen bonding, electrostatic attraction, π-π stacking, and hydrophobic interactions.\u003c/p\u003e \u003cp\u003e \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\u003eElement content and sources of the three materials analyzed by XPS\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMaterial Name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eElement Percentage/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC 1s\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eO 1s\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN 1s\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eS 2p\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLignin-chitosan adsorbent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e31.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.31\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\u003eX-ray photoelectron spectroscopy (XPS) was employed to analyze the elemental composition and chemical state of the lignin-chitosan composite adsorbent. The results indicated that the final prepared composite adsorbent exhibited the elemental characteristics of both raw materials (lignin and chitosan). Specifically, the composite adsorbent contained carbon (C), oxygen (O), nitrogen (N), and sulfur (S) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003ea)-a clear indication of the successful binding between lignin and chitosan, as these elements correspond to the characteristic components of the two raw materials. Analysis of the high-resolution S 2p spectrum revealed two characteristic peaks for the composite adsorbent (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The peak at 169.13 eV was attributed to the C\u0026thinsp;=\u0026thinsp;S bond, while the peak at 167.99 eV corresponded to the C-S bond; the total peak area of these sulfur-containing bonds accounted for 2.31% of the total spectral signal. This result confirms that the sulfur-containing groups in lignin retained their original chemical state after composite formation, which provides potential active sites for the subsequent adsorption process\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The C1s spectrum of lignin-chitosan adsorbents has three characteristic peaks. C-O/C-S bond at 287.98 eV, C-N bond at 286.41 eV and C-C bond at 284.80 eV, respectively, accounting for 60.11% of the peak area. The binding energy of the C-N peak of the adsorbent is located between the two, indicating that lignin and chitosan form a chemical bond by interacting with the amino group at the active site of lignin, thus forming a molecular complex. The C\u0026thinsp;=\u0026thinsp;C peak (284.8 eV) was mainly from the carbon element in lignin, while the C\u0026thinsp;=\u0026thinsp;S peak (287.98 eV) was mainly from the introduced sodium sulfite, which enhanced the adsorption of anionic pollutants\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Deconvolution of the high-resolution N 1s spectrum yielded two peaks (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003ed): 401.68 eV (assigned to N-H bonds) and 399.49 eV (assigned to C-N bonds), with nitrogen accounting for 6.25% of the total elemental composition of the composite. This result indicates that the amino groups of chitosan were neither oxidized nor protonated after complexation with lignin, thus retaining their chemical activity as active adsorption sites\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). The high-resolution O 1s spectrum of the composite adsorbent showed a characteristic peak at 532.3 eV (assigned to C-O bonds) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003ee), which integrated the O 1s spectral features of both pure lignin and pure chitosan. This observation confirms that the chemical environment of hydroxyl groups (-OH) in the composite changed due to interactions between lignin and chitosan-providing a structural basis for hydrogen bonding and coordination interactions during the adsorption process. In conclusion, XPS analysis clearly demonstrates the successful combination of lignin and chitosan from the perspectives of elemental composition and chemical state. The composite adsorbent simultaneously possesses sulfur-containing active sites (from lignin) and amino/hydroxyl active sites (from chitosan), and these two components form a stable structure via chemical bonding. This provides structural support at the chemical level for the composite\u0026rsquo;s application in fields such as pollutant adsorption and catalysis. It is worth noting that lignin extraction from wheat distillers\u0026rsquo; grains using p-toluenesulfonic acid not only retains the non-condensed structure of lignin (e.g., β-O-4 bonds) but also introduces sulfonic acid groups, which can interact with nitrogen-containing components (amino groups of chitosan) to further stabilize the composite structure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\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\u003eSpecific surface area, average pore size and average pore volume values of adsorbents\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eName\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecific surface area (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage aperture (\u0026Aring;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTotal pore volume (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLignin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.332\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e38.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.003\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChitosan\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.664\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e38.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.004\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLignin-chitosan adsorbent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.767\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e135.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.012\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\u003eThe specific surface area of the samples was comprehensively studied using the BET analysis method. The lignin-chitosan adsorbent exhibited a Type IV isotherm and an H3 hysteresis loop, indicating that the slit-like mesoporous structure was the dominant morphology (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). Its specific surface area was 3.767 m\u003csup\u003e2\u003c/sup\u003e/g, significantly higher than that of raw chitosan (1.664 m\u003csup\u003e2\u003c/sup\u003e/g) and alkali lignin (1.332 m\u003csup\u003e2\u003c/sup\u003e/g). This enhancement was attributed to the flake-like morphology formed by the fiber disintegration of chitosan during the composite process (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In the low-pressure region (P/P\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.4), monolayer adsorption was dominant, with low adsorption capacity and no significant contribution from micropores. The medium-pressure region (0.4\u0026thinsp;\u0026lt;\u0026thinsp;P/P\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.8) showed a distinct capillary condensation effect, and the adsorption capacity increased rapidly, corresponding to the mesopore filling process. The adsorption capacity in the high-pressure region (P/P\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.9) gradually stabilized, indicating limited macropores or interparticle pores. Analysis of the pore size distribution characteristics revealed that the main peak of the lignin-chitosan adsorbent was at 5 nm, suggesting that mesopores contributed to most of the pore volume. The distribution range was 5\u0026ndash;20 nm, and combined with the average pore size (13.5 nm), it can be seen that the pore size distribution was relatively wide, including some larger mesopores (\u0026gt;\u0026thinsp;10 nm) all higher than the corresponding pore sizes of lignin and chitosan (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThermogravimetric analysis (TG) was performed to evaluate the thermal stability of the lignin-chitosan composite adsorbent. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the composite adsorbent exhibited an initial decomposition temperature of 446.1\u0026deg;C, which corresponds to the cleavage of lignin\u0026rsquo;s aromatic skeleton\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. The final pyrolysis temperature of the adsorbent was 717.3\u0026deg;C, indicating excellent thermal resilience compared to single-component lignin or chitosan. Correlation analysis between thermal stability and adsorption performance revealed that the adsorbent\u0026rsquo;s high-temperature tolerance is critical for its regeneration potential. This superior thermal stability enables the lignin-based composite adsorbent to remove adsorbed pollutants via high-temperature calcination while preserving its intrinsic framework structure-directly supporting cyclic reuse. The synergistic effect between this thermal resilience and the previously characterized porous structure underpins the feasibility of the adsorbent for cyclic adsorption applications. Notably, the inherent G-type and H-type units in lignin not only enhance the composite\u0026rsquo;s thermal stability but also maintain the integrity of active adsorption sites, delaying the onset of the main decomposition stage. TG analysis further demonstrated that the lignin-chitosan adsorbent possesses good thermal stability and a high carbon structure retention capacity, with a char residue rate of 40.95%, this property supports its application in high-temperature adsorption-regeneration processes., To verify practical recyclability, adsorption cycle experiments were conducted. The results confirmed that the composite adsorbent can be effectively regenerated via high-temperature calcination at 150\u0026deg;C, enabling cyclic use without significant degradation of its adsorption performance or structural integrity. This regeneration protocol, combined with the adsorbent\u0026rsquo;s robust thermal stability, further reinforces its potential for large-scale, sustainable application in wastewater treatment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Sewage adsorption experiment\u003c/h2\u003e \u003cp\u003e \u003cb\u003e3.2.1 Adsorption performance of adsorbents\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e6\u003c/span\u003e \u003cb\u003eThe performance of the adsorption materials in adsorbing distillery wastewater\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAdsorption performance tests were conducted on lignin, chitosan gel particles, and lignin-chitosan adsorbents. The results showed that the adsorption performance of the lignin-chitosan adsorbent for four types of pollutants was higher than that of the individual substances, with a removal efficiency of approximately 90% for all pollutants. Comparing lignin and chitosan gel, it was found that lignin exhibited poor removal efficiency for TP, while chitosan showed poor removal efficiency for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N. Both substances also had relatively low removal efficiency for TN among the four pollutants, but displayed high adsorption efficiency for COD. The reasons for this phenomenon were analyzed as follows: Phosphorus in wastewater exists as anionic pollutants, while ammonia nitrogen in wastewater is usually present in the form of cationic ammonium ions (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e)\u003csup\u003e28\u003c/sup\u003e. Lignin is rich in acidic groups such as phenolic hydroxyl and carboxyl groups, so it is generally negatively charged in aqueous solutions. It adsorbs cationic substances through electrostatic interaction and has a strong affinity for hydrophobic organic compounds due to its large phenylpropane skeleton and hydrophobic regions\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. For chitosan, the core of its adsorption capacity lies in the free -NH\u003csub\u003e2\u003c/sub\u003e on its molecular chain. Under acidic conditions, these amino groups are protonated to form -NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e (positively charged), which strongly adsorbs anionic substances through electrostatic interaction\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. The lignin-chitosan adsorbent optimizes the adsorption performance for both cationic and anionic pollutants.\u003c/p\u003e \u003cp\u003e \u003cb\u003e3.2.2 Adsorption kinetics of lignin-chitosan adsorbent on distiller's grains wastewater\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e7\u003c/span\u003e \u003cb\u003eAdsorption kinetics. Effect of adsorption time of adsorbent on pollutant removal rate(a), fitting of first-order adsorption kinetics(b) and fitting of second-order adsorption kinetics (c)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFitting results of the proposed first-order and second-order adsorption kinetics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\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=\"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 \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eWater quality indicators\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eC\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e \u003cp\u003emg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eq\u003csub\u003ee, exp\u003c/sub\u003e\u003c/p\u003e \u003cp\u003emg\u0026middot;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c4\"\u003e \u003cp\u003eQuasi-first-order dynamic model\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c9\" namest=\"c7\"\u003e \u003cp\u003ePseudo-second-order dynamic model\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ek\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003cp\u003emin\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eq\u003csub\u003ee, 1\u003c/sub\u003e\u003c/p\u003e \u003cp\u003emg\u0026middot;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003emin\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eq\u003csub\u003ee, 2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003emg\u0026middot;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCOD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e27.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.0336\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e29.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.7396\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0278\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e35.745\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.9951\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.333\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.0158\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e63.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.9526\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.4074\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.415\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.9679\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.0214\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e46.725\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.9273\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.1374\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e7.235\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.9763\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.027\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e37.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.9404\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.164\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e6.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.9946\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\u003eIn the static adsorption experiment, the adsorption time was set to 8 gradients ranging from 20 to 160 mins. The results showed that when the adsorption time was between 0 and 80 mins, the removal rates of COD and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N first approached equilibrium. However, to achieve high removal rates for TP and TN, the adsorption time needed to be extended to 120 mins (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). Analysis revealed that this difference could be attributed to the following: the removal of COD and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N is mainly controlled by the dual effects of electrostatic adsorption and chemical adsorption. In contrast, the removal of TP involves the synergistic effect of chemical precipitation and physical interception, while the removal of TN is the result of the synergy of multiple mechanisms (electrostatic adsorption and complexation)\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eBased on the pseudo-first-order kinetic model equation (Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and pseudo-second-order kinetic model equation (Eq.\u0026nbsp;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), the relationships between the adsorption capacities of lignin-chitosan adsorbent for COD, TP, TN, and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N in water and time were fitted. For the pseudo-first-order kinetic model, the R\u003csup\u003e2\u003c/sup\u003e for all pollutants were below 0.95, indicating a poor fitting effect (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The theoretical adsorption capacities for COD, TP, TN and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N were 27.6, 0.333, 5.52 and 4.42 mg/g, respectively. Moreover, in the 0\u0026ndash;80 mins adsorption stage, the removal efficiency of COD and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N increased rapidly (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). The removal of TP and TN tended to be flat during the whole process, and the adsorption rate was constant at 120 mins. For the pseudo-second-order kinetics, the R\u003csup\u003e2\u003c/sup\u003e of the adsorbent for the four pollutants were 0.9951, 0.9679, 0.9763, and 0.9946, respectively. The theoretical equilibrium adsorption capacities of COD, TP, TN, and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N calculated by the pseudo-second-order kinetic equation were 35.745, 0.415, 7.235 and 6.1 mg/g, respectively. The deviation between the theoretical equilibrium adsorption capacity (q\u003csub\u003ee\u003c/sub\u003e) and the experimental value (q\u003csub\u003ee, exp\u003c/sub\u003e) was less than 15%, indicating a good agreement between the experimentally determined equilibrium adsorption capacity and the theoretical value calculated by the pseudo-second-order model (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e7\u003c/span\u003ec). The overall adsorption process is well described by the quasi-second-order kinetic model.\u003c/p\u003e \u003cp\u003e \u003cb\u003e3.2.3 Static adsorption experiment of lignin-chitosan adsorbent on distillery wastewater\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e8\u003c/span\u003e \u003cb\u003eFactors affecting the adsorption performance of lignin-chitosan adsorbent (a) dosage amount and (b) pH\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eStatic adsorption experiments can be used to determine the optimal adsorption conditions of the adsorbent for pollutants. The dosage of the adsorbent is the primary factor controlling costs. As the dosage amount increases, the removal rate of pollutants significantly improves. When the dosage was 2 g/L, the increase rate of removal efficiency slowed down, with COD and TN showing a significant slowdown. Meanwhile, the removal rates of all pollutants reached over 80%. Although the adsorption capacities for TP and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N still increased slightly when the adsorbent dosage was 2.5 g/L, the change was negligible (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). This phenomenon may be attributed to the fact that the adsorption sites were nearly saturated. Therefore, the optimal dosage of the adsorbent is 2 g/L.\u003c/p\u003e \u003cp\u003eIn environmental chemistry, pH has a significant impact on various reactions. Therefore, the influence of pH on the adsorption efficiency of adsorbents for pollutants was investigated. During the entire static adsorption process, the removal efficiency of TP by the adsorbent reached its maximum value of 92% at a pH of 7. The influence of pH on the COD removal rate is relatively small. The removal effect does not change much under different pH conditions. The highest removal efficiency of 90% is achieved when the pH is 5. Furthermore, the removal efficiency of TN by the adsorbent reaches its peak at a pH of 7. The removal efficiency of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N by the adsorbent reaches its maximum value at a pH of 9 (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e8\u003c/span\u003ec). The analysis of the reasons suggests that it occurs under acidic conditions. The protonation of the adsorbent surface promotes the adsorption of negatively charged anionic pollutants TP through electrostatic interactions\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. TN and COD, as pollutants that are both anions and cations, achieve the highest removal efficiency when the pH is 7. As a cationic pollutant with positive charge, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N has a better removal effect under alkaline conditions\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. As the pH continues to increase, the lignin-chitosan adsorbent material is corroded under strong alkali conditions and cannot play a role in adsorption. In general, Although the removal rate of TN was slightly lower at pH is 7 than at pH is 5, the removal rates of the other three pollutants reached their maximum values at pH is 7. Therefore, a pH of 7 was chosen as the optimal equilibrium point.\u003c/p\u003e \u003cp\u003eIn conclusion, the best removal of COD, TP, TN, and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N was achieved at the adsorption time of 120 mins, adsorbent dosage of 2 g/L, and pH of 7, which were 91%, 92%, 89%, and 86%, respectively. The high adsorption performance means that the adsorbent material has a wide range of applications.\u003c/p\u003e \u003cp\u003e \u003cb\u003e3.3 Adsorbent adsorption cycle\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e9\u003c/span\u003e \u003cb\u003eAdsorption cycle experiments of lignin-chitosan adsorbent\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of advantages with other similar adsorbents\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eName\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType of pollutants\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCapacity of adsorption\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3-aminopropyltriethoxysilane\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePhosphate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21.12 mg/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003csup\u003e34\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAL-CTS@MNPs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRhodamine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20.00 mg/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003csup\u003e27\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhosphorus-rich carbon derived from lignin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePhosphate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.6 mg/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003csup\u003e35\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZeolite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAmmonia nitrogen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.256 mg/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003csup\u003e36\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLignin-chitosan adsorbent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCOD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.6 mg/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ethis study\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\u003eWhether the adsorbent can be recycled is one of the important factors for reducing costs and practical application. The results showed, after 5 adsorption cycles of the lignin-chitosan adsorbent, that the removal efficiencies of COD, TP, TN and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N by the adsorbent could still reach more than 75% of the initial removal efficiency (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e9\u003c/span\u003e). To analyze the reasons, in each adsorption cycle, pollutants would occupy the active sites on the surface of the lignin-chitosan adsorbent. Even after desorption treatment, some pollutants would still remain through physical or chemical adsorption, gradually reducing the available active sites. The repeated adsorption-desorption process would damage the porous structure and functional groups of the adsorbent. The phenolic hydroxyl groups of lignin and the amino groups of chitosan might undergo oxidation, hydrolysis, or cross-linking, causing the adsorption capacity to gradually decrease with the increase of cycle times. The adsorption of COD, TP, and TN by the adsorbent involves multiple mechanisms such as electrostatic interaction, complexation, and pore filling. The functional groups and porous structure supporting these mechanisms are relatively stable in the early stage, so more than 75% of the initial removal efficiency can be maintained. The adsorption of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N by the adsorbent mainly relies on the electrostatic attraction of protonated amino groups (-NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) on the chitosan molecular chain. In terms of removal efficiency, the adsorbent still has a good removal effect on pollutants after 5 cycles. Compared with other adsorbents, the prepared lignin-chitosan adsorbent exhibits the characteristic of efficient pollutant adsorption (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Besides, this adsorbent has the advantages of simple preparation method, green recyclability, and the ability to adsorb various organic pollutants, which has the potential for preventive application as a green organic pollutant adsorbent.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eDirect discharge of wheat distillers\u0026rsquo; grains poses a significant environmental pollution risk, and converting lignin extracted from these by-products into an adsorbent not only mitigates this pollution but also enhances its added value. In this study, a lignin-chitosan composite adsorbent was developed using lignin from wheat distillers\u0026rsquo; grains combined with free radical polymerization, and its efficiency in removing pollutants (COD, TP, TN, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N) from distillery wastewater was evaluated alongside systematic investigation of its adsorption mechanism. Characterization results showed that SEM analysis revealed the composite adsorbent has a rougher surface and broader pore size distribution compared to pure lignin and chitosan; FT-IR and XPS analyses confirmed the successful polymerization of lignin and chitosan, with the adsorbent retaining phenolic hydroxyl and carboxyl groups from lignin, integrating -NH\u003csub\u003e2\u003c/sub\u003e from chitosan, and sulfur (-SO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) doping further enhancing its adsorption capacity for cationic pollutants; BET analysis verified a favorable pore structure and larger specific surface area that improve pollutant adsorption; thermogravimetric analysis demonstrated excellent thermal stability, enabling cyclic use via high-temperature calcination. Adsorption kinetic studies indicated that the removal of the four target pollutants follows the pseudo-second-order kinetic model, reflecting that the adsorption process is dominated by chemical interactions between surface active sites and adsorbates, with the adsorption rate dependent on the chemical reaction rate between adsorbates and these active sites. Compared with other conventional adsorbents, this composite adsorbent offers advantages including a broad adsorption spectrum, green and straightforward preparation, and cost-effectiveness. Beyond lignin, wheat distillers\u0026rsquo; grains contain other active substances (e.g., cellulose, hemicellulose, phenolic compounds) with potential for adsorbent development, and future research should explore these alternative matrix materials.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eYijie Wang\u003c/strong\u003e: Writing-original draft, Investigation, Data curation, Conceptualization. \u003cstrong\u003eHaiqing Wang:\u0026nbsp;\u003c/strong\u003eWriting-review \u0026amp; editing, Investigation, Conceptualization. \u003cstrong\u003eJingtao Liu\u003c/strong\u003e Writing-review \u0026amp; editing, Investigation, Conceptualization.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe acknowledge the contributions of all investigators involved in the original study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was funded by Shandong Provincial Natural Science Foundation\u0026nbsp;(ZR2024QD166) and the Doctoral Start-up Foundation of Shandong University of Aeronautics (2023Y48).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding information\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eProject Type\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eProject Number\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eFunding agency\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eProvincial Natural Science Foundation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eZR2024QD166\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eShandong Provincial Natural Science Foundation\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eSchool-level Doctoral Startup Fund\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2023Y48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eDoctoral Start-up Foundation of Shandong University of Aeronautics\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe dataset used during the present study is available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBuenavista, R. 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(2019).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Adsorbent, Chitosan, Distiller's grains, Eutrophic compounds, Lignin","lastPublishedDoi":"10.21203/rs.3.rs-8248335/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8248335/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe distillers' grains and wastewater produced by alcohol fermentation process pose a threat to the ecological environment. This study has designed a method of treating waste with waste, which uses the lignin from distillers\u0026rsquo; grains as the base and combining with chitosan to prepare an efficient adsorbent for distillery wastewater treatment. The prepared lignin-chitosan adsorbent was characterized by various methods, its surface was rough and had abundant functional groups, which facilitated the adsorption of pollutants. The COD, TP, TN and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N were selected as the typical wastewater indicators to evaluate the treatment effect of the adsorbent on the distillery wastewater. The results showed that lignin-chitosan adsorbent reached adsorption equilibrium for the four pollutants at 120 mins, and the adsorption rates were all above 85%. The adsorption process was in good accordance with the quasi-second-order kinetics dominated by chemical adsorption, and it indicates that the adsorption rate of the adsorbent to the pollutant mainly depends on the interaction between the adsorbate and the surface active site. In addition, the removal rate can still achieve 75% after 5 adsorption cycles. These findings indicate its potential for large-scale applications and promise as a green alternative to activated carbon or synthetic adsorbents.\u003c/p\u003e","manuscriptTitle":"Preparation of a distillers’ grains derived lignin-chitosan adsorbent for enhanced the distillery wastewater treatment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-18 05:51:04","doi":"10.21203/rs.3.rs-8248335/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-02T10:55:39+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-25T04:43:56+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-22T14:36:57+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-18T06:45:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"277270843977383472222189416208427209192","date":"2025-12-16T11:56:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"328059860147097722723339665578622652674","date":"2025-12-14T13:02:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"183388697316289088912416088063004246290","date":"2025-12-12T13:48:27+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-12T12:04:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-12T09:59:38+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-12-09T09:33:46+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-07T04:50:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-12-07T04:44:45+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2c0c7dbd-a113-4e06-9247-a6867217f69e","owner":[],"postedDate":"December 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":59745783,"name":"Physical sciences/Chemistry"},{"id":59745784,"name":"Earth and environmental sciences/Environmental sciences"}],"tags":[],"updatedAt":"2026-03-23T16:12:20+00:00","versionOfRecord":{"articleIdentity":"rs-8248335","link":"https://doi.org/10.1038/s41598-026-44058-7","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-03-22 15:59:48","publishedOnDateReadable":"March 22nd, 2026"},"versionCreatedAt":"2025-12-18 05:51:04","video":"","vorDoi":"10.1038/s41598-026-44058-7","vorDoiUrl":"https://doi.org/10.1038/s41598-026-44058-7","workflowStages":[]},"version":"v1","identity":"rs-8248335","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8248335","identity":"rs-8248335","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}