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Understanding the basic chemical structure of lignin macromolecules can facilitate the development of lignin-based materials. In this study, the lignin structure was regulated through different alkali cooking conditions. The acid precipitated lignin from the spent cooking liquor was purified and fractionated with different organic solvents. The lignin samples with different structures were obtained by regulating the cooking time. The structural characteristics of the lignin preparations were systematically investigated. The results revealed that the structure of lignin was regulated by the heating time and the residence time during the cooking process. Non-condensed lignin was achieved after a specific cooking condition; it had higher molecular weight (9686 g/mol), more β-O-4 linkages (25.3/100Ar), but lower phenolic hydroxyl content (1.51 mmol/g) than the counterpart pulping with longer time duration. The non-condensed lignin also had excellent thermal stability. Compared with industrial lignin, the lignin with non-condensed structure can be modified to obtain phenolic resin materials with better performance. The non-condensed structure with the specific characteristics can broaden the valorization of lignin for producing biochemical and biomaterials.

The secondary treated effluents of pulp and paper mills contain high chemical oxygen demand (COD) that is associated with organic matter. Therefore, this study explores the adsorption of substances contributing to COD using CoFe2O4 and quartz sand-coated CoFe2O4 in batch and fixed-bed column experiments. X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller analysis, and X-ray photoelectron spectroscopy were used to characterize the adsorbents. The quartz sand-loaded CoFe2O4 exhibited a larger pore volume and average pore size. Batch experiments revealed that adsorption on CoFe2O4 closely fit the pseudo-second-order model. To explore the effects of bed depth, feed flow rate, and initial solution pH on the breakthrough characteristics of CoFe2O4-coated sand, fixed-bed column experiments were conducted, and the breakthrough curves were drawn from the ratio of influent COD concentration to effluent COD concentration. The breakthrough time decreased with an increase in the feed flow rate and initial pH but increased with the bed depth. According to the X-ray photoelectron spectroscopy analysis, CoFe2O4-coated sand showed excellent stability due to negligible leaching of metallic elements. These findings have important implications for the advanced treatment of industrial wastewater.

The physicochemical properties of dissolved and colloidal substances (DCS) in the old corrugated containers’ (OCC) whitewater were studied. Then, the colloidal substances (CS) were separated from dissolved substances (DS) and the effect of inorganic salts on the stability of CS (not DCS) was studied for the first time. The results showed that many DCS aggregated and attached to the fiber surface when pulping. The primary sources were resin, lignin, adhesives, coating fixatives, and fillers. The colloidal stability of DCS and solids of whitewater differed because the DCS contained less filler. Both Ca2+ and Na+ can affect the stability of CS, but Ca2+ led to more CS instability and aggregated into larger flocculent precipitates. The surprising discovery in the experiment was that when Ca2+ and Na+ were added together, the instability degree of the system was between the addition of Ca2+ and Na+ alone. Ca2+ played a dominant role in affecting the stability of CS, and Na+ competed for adsorption sites.

To understand the effects and the mechanism of sodium carbonate (Na2CO3) addition on the bagasse alkaline black liquor (BABL) pyrolysis, the reaction variables such as temperature, heating rate, and amount of Na2CO3 addition into BABL-solids were investigated under N2 atmosphere from 50 °C to 1000 °C by thermogravimetic analysis (TGA). Scanning electron microscopy (SEM) and the Coats–Redfern method (CRM) were employed for surface microscopic morphology observations and kinetic analysis, respectively. The results showed that Na2CO3 plays an inhibiting and promoting role during devolatilization (200 °C to 650 °C) and the reduction stages (650 °C to 1000 °C), respectively. Adding Na2CO3 into BABL-solids tends to increase the thickness of the salt layer covering the BABL-solids surface, which increases the activation energy and reduces the weight loss ratio of BABL-solids pyrolysis within 200 °C to 650 °C. Adding Na2CO3 into the BABL-solids tends to increase the number of alkaline compounds or the active site of the reduction reaction, which reduces the activation energy and increases the weight loss ratio of BABL-solids pyrolysis within 650 °C to 1000 °C. The role of Na2CO3 as an additive could be well understood by studying the influence mechanism of Na2CO3 on BABL-solids pyrolysis.

A long-acting and slow-release material for chlorine dioxide, based on bagasse pulp (BP) was prepared with a superabsorbent resin as the slow-release substrate and agar as the cross-linking agent. The stable ClO2 solution and the acidic activator were locked into the network structure of the superabsorbent resin, which was prepared with a carboxymethyl cellulose made from bagasse pulp. Because of the network structure of the resin, the diffusion resistance was greatly increased, and the effective release time was up to 2 months. The mechanism for the release process of the ClO2 was explored, and a kinetic model was established based on modified Fick’s diffusion law. The results showed that the release process was a diffusion-controlled process. When compared with a zero-order kinetic model and a Higuchi model, the new established model had better fitting results, and it more fully reflected the release patterns and characteristics of the ClO2.

Bagasse spraying wastewater (BSW) is a source of organic pollutants during bagasse processing. In this study, the feasibility of anaerobic treatment of BSW under different calcium concentrations (60 to 2400 mg/L) was studied. The experiment was performed in a lab-scale up-flow multistage anaerobic reactor (UMAR) inoculated with granular sludge, and operated for 160 days at a constant organic loading rate of 6 kg COD/(m3·d). Treatment of BSW with 60 to 800 mg Ca2+/L resulted in 80.7 to 82.7% of COD removal, 161 to 232.7 mg COD/L of volatile fatty acid (VFA) yield, 0.56 to 0.79 m3/(kgCOD·d) of biogas production rate, and 2.4 to 2.66 m3/(m3·d) of volume loading rate (VLR). The pH remained within the optimal range for anaerobic digestion (adjust to pH = 6.8 to 7.0). The VFAs were composed of 77 to 85% acetic acid, 8.4 to 13.2% butyric acid, and 6.6 to 9.6% propionic acid. At higher influent calcium concentrations (> 800 mg/L), the hydrolysis process appeared to be inhibited, affecting the anaerobic digestion performance of the reactor. In particular, the COD removal efficiency decreased to 55.5%, and the VFA content in the effluent significantly increased due to the lower pH. Microbial community analysis showed that at the end of anaerobic digestion, the Syntrophobacter disappeared, and Clostridium and Anerolineaceae were the main genus and family, respectively. Overall, the results indicated that low calcium (< 300 mg/L) had a positive effect on the UMAR performance.

The production of nanofibrillated cellulose (NFC) from bagasse was optimized through a novel green approach by combining an organosolv pretreatment with microgrinding. Bagasse was processed through organosolv pretreatment with trifluoroacetic acid (OPT) as a catalyst to provide precursor fibers with full control of chemical components for NFC production. The mass balance of the pretreated bagasse through OPT (OPTB) was determined by its chemical components and total organic carbon analysis. OPT was found to be an efficient and energy-saving strategy for recovering cellulose, as well as hydrolyzing hemicellulose and lignin. Noncellulosic contents in OPTB fibers were optimized to obtain a high NFC yield through microgrinding. The highest NFC yield relative to the mass of precursor fibers of 72% was achieved through mechanical defibrillation of the OPTB containing noncellulosic content of 29%, which generated nanofibrils with the average diameter of 9 nm. In biorefinery principles, OPT not only converted 57% of bagasse to solid cellulosic fibers for NFC preparation, but also 30% of bagasse to valuable bioproducts including the hemicellulose-derived xylose (19%) and lignin-derived organosolv lignin (11%). The combined OPT and microgrinding produced NFC and simultaneously extracted bioproducts from bagasse while using easily recoverable and low environmental impact reagents.

Sulfonation chemimechanical pulping (SCMP) of mulberry stalk was studied with different treatment concentrations. The resulting mulberry SCMP pulp contained different content of sulfonic acid groups depending on the concentrations. The brightness, tensile index, and folding resistance of mulberry SCMP pulp increased with the increasing concentration of sulfonation treatment, but the thickness decreased with increasing concentration. There was either a linear or a non-linear relationship between the content of sulfonic groups and the pulp physical properties. The mass average length of mulberry SCMP pulp was 0.66 mm, the fiber width was 16.4 μm, and the content of fine fibers was 20.6%.The mulberry extract and lignin dissolved, and part of soluble lignin may have been deposited on fiber surface in the process of SCMP pretreatment. There were almost no changes to the cellulose crystalline structure.

The effects of substrate Ca2+ concentration were studied relative to the anaerobic digestion and microbial community structure of anaerobic granular sludge. In the treatment of papermaking wastewater by anaerobic granular sludge, the cumulative gas production was maximum at a Ca2+ concentration in the substrate of 120 mg/L, whereas it was the lowest at a concentration of Ca2+ in the substrate of 4000 mg/L. A high Ca2+ concentration in the substrate (≥1200 mg/L) will cause the pH of the fermentation broth to decrease during the fermentation process, which is not conducive to the anaerobic fermentation of the methanogenic process, resulting in unsatisfactory anaerobic digestion of the granular sludge. In addition, when the Ca2+ concentration was below 200 mg/L, the abundance of the important bacterial family Ruminococcaceae (rumen bacteria) in the anaerobic fermentation hydrolysis stage was drastically reduced and methane gas production increased. When the Ca2+ concentration was above 200 mg/L, the abundance of Anaerolineaceae (Anaerobic Streptomyces), which supplies organic acids, was substantially reduced. The methane gas production decreased as the Ca2+ concentration increased. Thus, the results showed that when the concentration of Ca2+ was above 200 mg/L, the methanogenic activity of granular sludge decreased.

Relationships between fiber surface chemical components and the efficiency of chlorine dioxide bleaching were studied using chemical analysis in combination with attenuated total reflectance-Fourier transform infrared spectrscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The amount of surface lignin decreased quickly at the beginning of the bleaching, and the brightness increased during the bleaching. Surface oxidation took place immediately, and the amount of lignin on the fiber surface decreased during the bleaching, especially in the first 5 min. The ratio of aromatic carbons to aliphatic carbons also decreased, which indicated that the lignin was degraded and new aliphatic carbons formed that might noticeably deposit on the surface of the fiber. The aliphatic carbons reacted with the in-situ formed hypochlorous acids, and thus affected the bleaching efficiency. Further bleaching led to the deposition of more acidic functional groups on the fiber surface with increased acidity-basicity ratios, which also affected the whole efficiency of bleaching.

Hexenuronic acid (HexA) not only influences delignification, but it is also one of the major factors producing absorbable organic halogens (AOX) during the chlorine dioxide bleaching of pulps. The efficient removal of the HexA from cooked pulp is important to minimize the need for bleaching and the pollution load from the mill effluent. Response surface analysis (RSA) was applied to determine the optimal oxidative degradation conditions for HexA in bagasse pulp. Based on the previous single-variable test results, reaction temperature, pH, and reaction time were chosen as the independent variables, with the amount of degradation of HexA being the response value in the RSA. According to the central composite experimental design principles, the type of response surface methodology with three factors and three levels was adopted and analyzed to determine the significant factors and the strength of interactions between factors. The optimal conditions determined were as follows: a reaction temperature of 94.7 °C, a pH of 3.7, and a reaction time of 124 min, which resulted in the amount of degradation of HexA at 10.5 µmol/g.

The adsorption effects, thermodynamics, and kinetics of formaldehyde-modified eucalyptus bark on Cr(VI) was investigated. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to verify the adsorption capacity difference between unmodified and modified eucalyptus bark. The results demonstrated that the surface area and active group content was increased by modification, which was conducive to the adsorption of Cr(VI). The effects of pH, time, temperature, initial Cr(VI) concentration, and adsorbent dosage and on adsorption were investigated. The optimal adsorption capacity was 16.50 mg.g-1 under the conditions of 50 mg.L-1 initial Cr(VI) concentration, pH 2.0, 3 g.L-1 adsorbent dosage, 50 °C, and 120 min. The fitting of kinetics indicated that the adsorption was governed by multiple factors. The thermodynamic parameters △H0 > 0 showed that the adsorption process was an endothermic reaction. The value △S0 > 0 indicated that liquid-solid interface disorder increased during the adsorption process and showed a good adsorption performance.

Anaerobic biological technology has been widely used in the treatment of high-concentration organic wastewater such as old newspaper (ONP) pulping wastewater and bagasse spray washing wastewater before pulping. However, due to the high calcium content and complex chemical properties of the ONP pulping wastewater, granular sludge calcification occurs during the anaerobic treatment, which has negative effects. In contrast, calcification does not occur in the bagasse spray washing wastewater. Therefore, a comparative analysis of the biological flora and structure of the granular sludge for these two types of wastewater can provide theoretical and data support for revealing the cause of calcification of granular sludge. The results indicate a considerable difference between the anaerobic granular sludge for the treatment of bagasse spraying wastewater (B-GS) and the treatment of ONP pulping wastewater (P-GS). The microorganisms in the B-GS were mainly Bactericides (25.4%), Proteobacteria (20.2%), Hyd24－12 (14.4%), Chloroflexi (10.6%), and Firmicutes (8.9%). The microorganisms in the P-GS were mainly Bacteroidetes (20.4%), Chloroflexi (19.5%), Proteobacteria (19.3%), Firmicutes (6.2%), Spirochaetae (4.8%), Actinobacteria (4.4%), and Lentisphaerae (4.3%). Methanomassiliicoccus were detected only in the P-GS. The methanogens had a higher relative abundance in the P-GS (50%), and only a small fraction (10%) of methanogens was detected in the B-GS.

The emission standard for adsorbable organic halogen (AOX) has been adjusted as a mandatory assessment indicator in the papermaking industrial pollutants emission standards of China. To provide a theoretical basis to reduce AOX formation, a kinetic model of the first chlorine dioxide bleaching stage (D0) is presented for elemental chlorine-free (ECF) bleaching of eucalyptus kraft pulp. The kinetics of the D0 stage can be expressed as dW/dt = 314.6e-20.53/RT[H+]0.21[ClO2]0.41K0.98, where the reaction series for lignin, chlorine dioxide dosage, and H+ concentration are 0.98, 0.41, and 0.21, respectively. The reaction activation energy was 20.53 kJ.mol-1. R2 was greater than 0.9, which means that the model was shown to have high prognostic ability and feasibility. In the D0 stage, mostly lignin was removed and the reaction was fast. Much AOX was formed at the beginning of bleaching, and the reaction rate was primarily determined by the lignin content and chlorine dioxide dosage. H+ existed primarily as a catalyst and had little influence on AOX formation. The AOX formation occurs easily, as the reaction activation energy is less than 30 kJ.mol-1.

This paper presents a kinetic model of the laccase-aided chlorine dioxide bleaching of bagasse pulp. The kinetic model was based on the rate of reduction of adsorbed organic halogen (AOX). The effects of the laccase enzyme dosage, the mediator 1-hydroxybenzotriazole (HBT) dosage, and the reaction temperature on the AOX content of the bleaching effluent are discussed. Good fits were obtained for the experimental data obtained from the different laccase enzyme dosages, HBT dosages, and reaction temperatures, indicating the feasibility of the kinetic model as a means of predicting the optimal operation conditions for the laccase-aided chlorine dioxide bleaching of bagasse pulp in the future.

The process of dehydration of glucose to 5-hydroxymethylfurfural (HMF), using caprolactam-lithium chloride (CPL/LiCl) as a solvent, was investigated. Dual-wavelength ultraviolet spectrophotometry provides a new approach for the determination of glucose conversion rate and yield of HMF. Experiments were performed to demonstrate the accuracy and precision of this method. Various reaction parameters, such as the ratio of ionic liquid, reaction temperature, reaction time, catalyst dosage, and solid absorbent, were investigated in detail for the dehydration of glucose. The optimal conditions were explored. Finally, a possible mechanism for the dehydration of fructose to HMF was proposed.

In order to further reduce absorbable organic halide (AOX) formation in the bleaching effluent, NH2SO3H and DMSO were added during the elemental chlorine-free (ECF) bleaching (D0EpD1) of bagasse kraft pulp. In the D0 stage, AOX formation decreased by 10% with 0.1% NH2SO3H, and a reduction of 11.2% with 1.0% DMSO, respectively. Ultraviolet (UV) spectra, Fourier transform infrared spectroscopy (FTIR), and gas chromatography-mass spectroscopy (GC-MS) were adopted in characterizing changes of lignin degradation and the main functional groups of bleached pulp. The UV spectrum showed that the quantity of polyphenols decreased after adding the additives. The FTIR spectrum showed that both the content of phenolic-type lignin and the degradation degree of lilac-type lignin decreased after adding NH2SO3H. If was found that DMSO was beneficial in retaining C-O-C and C=O structures in cellulose and hemicellulose, while NH2SO3H decreased the content of β-glycosidic bonds and C-O-C structures in cellulose and hemicellulose. The composition of lignin degradation products in the bleaching effluent was analyzed by GC-MS. The contents of chlorobenzene and chlorophenol decreased notably when additives were added. Compared with DMSO, NH2SO3H exhibited poor inhibition on the formation of some phenols.

A laboratory investigation was developed to confirm and to quantify the reductions in absorbable organic halide (AOX) discharge when sodium sulphide was added during elemental chlorine-free (ECF) bleaching of sugarcane bagasse pulp. After the chlorine dioxide bleaching stage, the pulp was sent directly into the extraction stage without washing. FTIR was employed to determine the breakage of chemical bonds in the pulp, and GC-MS was used to measure the composition of the bleaching effluent. The addition of sodium sulphide caused a reduction in AOX of up to 46.7%. The AOX reduction reached this maximum when the sodium sulphide was added 30 min after the start of the extraction stage and when the pH was higher than 12. FTIR spectroscopy showed that the phenolic lignin of the pulp was degraded by the sodium sulphide and that the syringyl lignin and C-O-C, C=O structure of the pulp holocellulose of the pulp was preserved during the extraction stage. The GC-MS showed that the chlorobenzene and chlorophenol contents decreased noticeably after the addition of sodium sulphide.

In this paper, a kinetic model of the first chlorine dioxide bleaching stage (D0) in an elemental chlorine-free (ECF) bleaching sequence is presented for bagasse pulps. The model is based on the rate of adsorbable organic halogen (AOX) formation. The effects of the chlorine dioxide dosage, the sulfuric acid dosage, and the reaction temperature on the AOX content of wastewater are examined. The reaction of AOX formation could be divided into two periods. A large amount of AOX was formed rapidly within the first 10 min. Ten minutes later, the AOX formation rate significantly decreased. The kinetics could be expressed as: dW⁄dt=660.8•e^(-997.98/T) 〖•[ClO〗_2 ]^0.877•[H2SO4 ]^0.355•W^(-1.065), where W is the AOX content, t is the bleaching time (min), T is the temperature (K), [ClO2] is the dosage of chlorine dioxide (kg/odt), and [H2SO4] is the dosage of sulfuric acid (kg/odt). The fit of the experiment results obtained for different temperatures, initial chlorine dioxide dosages, initial sulfuric acid dosages, and AOX content were very good, revealing the ability of the model to predict typical mill operating conditions.

A superabsorbent resin (SAR) synthesized from carboxymethyl cellulose (CMC) by grafting acrylic acid (AA) was studied using single-factor analysis. The optimum preparation conditions were as follows: plasma discharge power of 250 W, processing time of 90 s, pressure of 300 Pa, m(CMC):m(AA) ratio of 1:9, m(K2S2O8):m(CMC) ratio of 1:4, and neutralization degree of 40%. Under these conditions, the resin has a salt water absorbency of 38.5 g/g and a stable chlorine dioxide solution absorbency of 27.2 g/g. The structural characterization of the SAR was also studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning colorimetry (DSC). The results showed that the resin was synthesized by grafting copolymerization of CMC and AA, and the water absorbency and thermal stability of the resin were greatly improved compared to CMC alone. This method may provide a new way for high value-added utilization of bagasse.

This study investigated the adsorption of the heavy-metal ions Cu(II) and Pb(II) onto a lignin derivative. The lignin derivative was obtained by treating bagasse soda lignin with epichlorohydrin, and subsequently grafting an amine functional group by the Mannich reaction. The morphology of aminated epoxy-lignin was a layered structure with pores characterized by SEM. The heavy-metal ion adsorption data could be described well with the pseudo-first order model for Pb(II) ion and the pseudo-second order model for Cu(II) ion; diffusion was found to be the rate-limiting step when approaching equilibrium. FTIR spectroscopy was used to study the mechanism of heavy-metal adsorption by the derivatized lignin. The results show that the sites for adsorption are related to hydroxyl and amido groups.