Sulfite Pretreatment Research Articles

Mild and efficient approach to aromatic backbone cleavage using copper-lignosulfonate/hydrogen peroxide system

This study investigates the dual role of copper ions in catalysis and complexation during the oxidation of lignosulfonates with hydrogen peroxide (H2O2) under alkaline conditions. The presence of copper ions reduces partial oxidation by 86 % compared to H2O2 treatment alone, enhancing overall conversion efficiency to 63 % under increased oxidative conditions. Analyses reveal that copper-lignosulfonate complexes facilitate redox cycling and hydroxyl radical generation through interactions with H2O2, confirming copper’s dual functions. This mechanism mitigates the hindrance of sulfonic groups on hydroperoxide anions, leading to lignosulfonate degradation into dicarboxylic acids. These findings provide novel insights into the copper-lignosulfonate/H2O2 system, expanding the understanding of oxidative degradation mechanisms beyond traditional Fenton-like reactions. Furthermore, this system offers a simplified and efficient alternative for industrial applications, particularly in integration with the sulfite pretreatment process of woody biomass for producing valuable co-products.

Effects of sulfite and freezing co-pretreatment on the volatile fatty acids production of waste activated sludge in anaerobic fermentation

Volatile fatty acids (VFAs) produced during the anaerobic fermentation of waste activated sludge (WAS) are renewable energy sources. However, the biodegradability of untreated WAS is significantly low, thereby imposing a substantial constraint on the generation of VFAs during anaerobic fermentation of WAS. In this study, the experimental results showed that freezing and sulfite co-pretreatment had a synergism on the disintegration of WAS and the production of VFAs. The optimal freezing temperature for VFAs production were −20 °C, 8 h and sulfite dosage of 1400 mg/L resulted in the VFAs reaching a highest concentration of 627.58 mg/L, which was 17.41 times higher than that of the blank group. In addition, the disintegration effect of WAS has been improved, the concentration of soluble chemical oxygen demand (SCOD), proteins and polysaccharides were 7.21, 5.56 and 2.58 times than the blank group, respectively. The microbial community analysis revealed an increase of the OUT of co-pretreatment. Also showed that co-pretreatment could increase the abundance of Levilinea, Unclassified_Anaerolineaceae and Blvii28_wastewater_sludge_group, which might increase VFAs production. Furthermore, compared to sulfite pretreatment or freezing pretreatment, the co-pretreatment significantly enhanced the disintegration efficiency of WAS; shortened the hydrolysis required time for WAS; provided the higher concentration of substrates for VFAs production; and improved the overall efficiency of sludge anaerobic fermentation.

Sulfate-reducing bacteria decreases fractional pressure of H2 to accelerate short-chain fatty acids production from waste activated sludge fermentation assisted with zero-valent iron activated sulfite pretreatment

The production of short-chain fatty acids (SCFAs) is constrained by substrate availability and the increased fractional pressure of H2 emitted by acidogenic/fermentative bacteria during anaerobic fermentation of waste activated sludge (WAS). This study introduced a novel approach employing zero-valent iron (ZVI)-activated sulfite pretreatment combined with H2-consuming sulfate-reducing bacteria (SRB) mediation to improve SCFAs, especially acetate production from WAS fermentation. Experimental results showed that the combined ZVI-activated sulfite and incomplete-oxidative SRB (io-SRB) process achieved a peak SCFAs production of 868.11 mg COD/L, with acetate accounting for 80.55 %, which was 7.90- and 2.18-fold higher than that obtained from raw WAS fermentation, respectively. This could be firstly attributed to the SO4− and OH generated by ZVI-activated sulfite, which significantly promoted WAS decomposition, e.g., soluble proteins and carbohydrates increased 14.3- and 10.8-fold, respectively, over those in raw WAS. The biodegradation of dissolved organic matter was subsequently enhanced by the synergistic interaction and H2 transfer between anaerobic fermentation bacteria (AFB) and io-SRB. The positive and negative correlations among AFB, nitrate-reducing bacteria (NRB) and the io-SRB consortia were revealed by molecular ecological network (MEN) and Mantel test. Moreover, the expression of functional genes was also improved, for instance, in relation to acetate formation, the relative abundances of phosphate acetyltransferase and acetate kinase was 0.002 % and 0.005 % higher than that in the control test, respectively. These findings emphasized the importance of sulfate radicals-based oxidation pretreatment and the collaborative relationships of multifunctional microbes on the value-added chemicals and energy recovery from sludge fermentation.

Tuning Structural Characteristics of Corn Stover Through Ammonium and Sodium Sulfite (ASS) Pretreatment for Enhanced Enzymatic Hydrolysis.

The ammonia fiber expansion (AFEX) pretreatment of lignocellulosic biomass offers a significant advantage in terms of obtaining high glucan conversion, with the added benefit of ammonia being fully recyclable. However, despite the high efficiency of AFEX in pretreating lignocellulose, relatively high enzyme loading is still required for effective cellulose conversions. In this study, we have updated the AFEX pretreatment method; ammonia and sodium sulfite (ASS) can be used to produce a more digestible substrate. The results demonstrate that ASS-pretreated corn stover (CS) yields a higher fermentable sugar yield compared with AFEX pretreatment, even at lower enzyme loadings. Specifically, at an enzyme loading of 12 mg protein/g glucan, ASS-CS achieved 88.8% glucose and 80.6% xylose yield. Characterization analysis reveals that lignin underwent sulfonation during ASS pretreatment. This modification results in a more negative zeta potential for ASS-CS, indicating a reduction in nonproductive adsorption between lignin and cellulase through increased electrostatic repulsion.

Enhancing enzymatic digestibility of bamboo residues using a combined low severity steam explosion and green liquor-sulfite pretreatment.

In this study, the effect of the green liquor (GL)-sulfite pretreatment on bamboo for enzymatic hydrolysis was investigated. The performance characterization of the pretreated bamboo substrates, including the chemical composition, and the structural characteristics was carried out. The results showed that 91.3% of lignin removal was achieved when the sample was treated with a GL loading of 12.0 mL per g-DS at 120 °C for 1 h. After 120 h hydrolysis with 18 FPU per g-cellulose for cellulase and 27 CBU per g-cellulose for glucosidase, the glucose yield increased from 54.6% to 89.6%. The SE-treated bamboo could bind more easily to cellulase than GL-sulfite treated bamboo could. The structural changes on the surface of the samples were characterized by SEM. The results indicated that the surface lignin could be effectively removed during pretreatment, thereby decreasing the enzyme-lignin binding activity.

Heat-enhanced sulfite pretreatment improves the release of soluble substances and the stimulation of methanogenic pathways for anaerobic digestion of waste activated sludge

Waste activated sludge pretreatment is effective in improving sludge hydrolysis rate and methane production. Our previous study revealed that sulfite could be a viable method for sludge pretreatment. To further improve methane production, this study employed an integrated strategy by combining sulfite and heat pretreatment. WAS from a local full-scale plant was pretreated with heat-enhanced sulfite pretreatment (HESP) at 25, 35, 55 °C. Compared with the control (no sulfite, 25 °C), soluble substances (e.g., chemical oxygen demand, protein, polysaccharides, nitrogen and phosphorus) could be significantly enhanced by the absence of sulfite and the increasing temperature. A variation of − 8.32–19.90% in cumulative methane production was observed. Moreover, methane production could be significantly enhanced by 14.15% at sulfite of 300 mg S/L and temperature of 35 °C, while kinetic analysis showed that the highest methane production potential (1.43 times of the control) was obtained at this level. Besides, the microbial structure and pathways reveal that HESP promotes the enrichment of methanogenic bacteria and facilitates methanogenic metabolism. The findings of this study suggest that the HESP could be promising in enhancing methane production, particularly considering the reuse of sulfite-laden industrial wastes and the heat as the by-products of the anaerobic digestion plant with biogas power generation, but certain experimental conditions should be verified case by case.

Zero valent iron catalyzing sulfite improves the quality and quantity of short-chain fatty acids from anaerobic fermentation of sewage sludge

The quality and quantity of short chain fatty acids (SCFAs) production from anaerobic fermentation of sewage sludge is generally constrained by low organics solubilization and poor substrate-availability. This study provided an environmentally friendly strategy with zero valent iron (ZVI) activating sulfite pretreatment to overcome this limitation and advance the sludge anaerobic fermentation. Experimental results showed that the maximal SCFAs production and acetate proportion promoted by 5.7 and 2.75 times respectively at 500 mg S/L and the ZVI/sulfite ratio of 1.25. Mechanism analysis elucidated that the free radicals of SO4-· and ·OH produced from ZVI-sulfite pretreatment accelerated the disintegration of sludge-flocs and decreased the value of α-helix and ratio of α-helix/ (β-sheet + random coil) from 21.64 % and 44.23 % to 17.80 % and 38.67 %, respectively, which provided more easily- and bio- available substance for functional anaerobes. The ZVI-sulfite pretreatment enhanced the ability of functional anaerobes for SCFAs production processes as hydrolysis, acidogenesis and acetogenesis and reduced the SCFAs consumption as methanogenesis, which ultimately promoted SCFAs accumulation. Microbial community illustrated that ZVI-sulfite pretreatment enriched the relative abundance of functional anaerobes related to hydrolysis, acidogenesis and acetogenesis bioprocesses. PICRUSt analysis demonstrated that the pretreatment boosted the functional genes abundance involved in pathway of butyrate and acetate formation. Moreover, the enrichment genes of acetate formation were consistent with the increase of acetate proportion.

Sulfite pretreatment enhances the medium-chain fatty acids production from waste activated sludge anaerobic fermentation

Production of high-value medium chain fatty acids (MCFAs) from anaerobic fermentation of waste activated sludge (WAS) has been considered as a promising alternative for renewable energy resources. However, the low biodegradability of WAS greatly limits the anaerobic fermentation performance. This study proposed and demonstrated a novel approach, sulfite pretreatment, to efficiently produce MCFAs through anaerobic fermentation of WAS. Pretreatment of WAS at a sulfite concentration of 100–500 mg S/L for 24 h effectively improved the MCFAs production and MCFAs selectivity and the promotion effect was positively correlated with the sulfite concentration used in pretreatment (Pearson's R > 0.9). The maximum MCFAs production of 6.84 g COD/L and MCFAs selectivity of 39.1 % were both achieved under 500 mg S/L sulfite pretreatment, which accounts for 2.6 times and 2.4 times of the control, respectively (MCFAs production of 2.62 g COD/L and MCFAs selectivity of 16.4 % in the control). Sulfite pretreatment also enhanced the WAS degradation from 25 ± 2 % in the control to a maximum of 39 ± 2 % under 500 mg S/L sulfite pretreatment. The electron transfer efficiency and COD flows from the substrate to products were enhanced by up to 25 % due to the sulfite pretreatment, which supports the enhanced WAS degradation. Sulfite pretreatment also promoted the solubilization, hydrolysis, and acidification processes during the anaerobic fermentation by up to 200 %, 60 %, and 45 %, respectively, which subsequently makes more substrates available for MCFAs production. The findings from this study provide a potential solution of using industrial sulfite-laden wastes for WAS pretreatment, to enhance the MCFAs production at a minimized cost.

Comparison of Alkaline Sulfite Pretreatment and Acid Sulfite Pretreatment with Low Chemical Loading in Saccharification of Poplar.

Sulfite pretreatment is a productive process for lignin dissolution in lignocelluloses and to reduce the hydrophobicity of lignin by sulfonation, thus promoting the hydrolyzability of the substrate. Previously, sulfite pretreatment needs high dosages of chemicals and thus results in the high cost of the pretreatment and the great pressure of environmental pollution. To overcome these problems, it was crucial to research whether alkaline sulfite pretreatment (ALS) and acid sulfite pretreatment (ACS) with low chemical loading could enhance the saccharification of poplar. In this work, the results indicated that with low loading of chemicals in sulfite pretreatment, ALS pretreatment (1.6% Na2SO3 and 0.5% NaOH) at 180°C removed more lignin, resulted in lower hydrophobicity and higher cellulase adsorption capacity of poplar than ACS pretreatment (1.6% Na2SO3 and 0.5% H2SO4) at 180°C. A satisfying glucose yield of 84.9% and a xylose yield of 76.0% were obtained from poplar after ALS pretreatment with 1.6% Na2SO3 and 0.5% NaOH at 180°C for 1h using 10 FPU cellulase/g dry matter, saving sodium sulfite by 60.0% compared to the loading of sulfite in traditional sulfite pretreatment. The strategy developed in this work reduced chemical loading and cellulase loading in alkali sulfite pretreatment for the saccharification of poplar.

Long-term effects of sulfite pretreatment on the continuous anaerobic sludge digester for improving methane production and volatile solid reduction: Towards sustainable sludge treatment

Using sulfite pretreatment to improve anaerobic sludge digestion has been proved to be effective. However, the effect of sulfite pretreatment on sludge digestion was verified by the batch tests in previous work, and its effects on continuous operation remain unclear, which is crucial to determine the long-term viability of using sulfite pretreatment in the real application. In this study, the impacts of sulfite pretreatment on the continuously operated anaerobic sludge digester were experimentally investigated to reveal its long-term role. The methane production and volatile solid reduction of sulfite-pretreated sludge were significantly improved by 25 % with pretreatment at sulfite of 100 mg S/L, pH of 6 for 24 h, while more ammonium and phosphorus were released during the anaerobic digestion. Moreover, sulfite pretreatment stimulated more organics extracted from sludge for methane conversion. The methanogens and syntrophic bacteria in the bioreactor were spurred by sulfite pretreatment to uptake diverse substrates for methanogenesis. Adopting sulfite pretreatment for sludge management could overall enhance energy recovery by 37.40 %, save operational cost by 31.43 %, and reduce carbon emission by 37.80 %, implying the potential of sulfite-based technology for sludge treatment towards environmental sustainability.

Improve Enzymatic Hydrolysis of Lignocellulosic Biomass by Modifying Lignin Structure via Sulfite Pretreatment and Using Lignin Blockers

Even traditional pretreatments can partially remove or degrade lignin and hemicellulose from lignocellulosic biomass for enhancing its enzymatic digestibility, the remaining lignin in pretreated biomass still restricts its enzymatic hydrolysis by limiting cellulose accessibility and lignin-enzyme nonproductive interaction. Therefore, many pretreatments that can modify lignin structure in a unique way and approaches to block the lignin’s adverse impact have been proposed to directly improve the enzymatic digestibility of pretreated biomass. In this review, recent development in sulfite pretreatment that can transform the native lignin into lignosulfonate and subsequently enhance saccharification of pretreated biomass under certain conditions was summarized. In addition, we also reviewed the approaches of the addition of reactive agents to block the lignin’s reactive sites and limit the cellulase-enzyme adsorption during hydrolysis. It is our hope that this summary can provide a guideline for workers engaged in biorefining for the goal of reaching high enzymatic digestibility of lignocellulose.

Effects of UV/Fe(II)/sulfite pre-treatment on NOM-enhanced Ca2+ scaling during nanofiltration treatment: Fouling mitigation, mechanisms, and correlation analysis of membrane resistance

This study was aimed to evaluate the effects of a pre-treatment involving sulfite (S(IV)) synergistically activated by ultraviolet (UV)/Fe(II) on natural organic matter (NOM)-enhanced Ca2+ scaling during nanofiltration treatment. Based on the variations in the physicochemical properties and correlation analyses of irreversible resistance, the intrinsic fouling mechanisms were revealed from two aspects: bulk crystallization (interaction between NOM and inorganic ions) and surface crystallization (morphology of surface crystallization and a change in the Ca2+ concentration in the scaling layer). Furthermore, the degradation contribution rates of different free radicals during the UV/Fe(II)/S(IV) (UFS) treatment process were evaluated. During the reactions in the UFS, three free radicals (SO·–4, OH·– and e- aq) were generated, and in-situ Fe(III) was formed in-situ. The carboxyl groups of the NOM were attacked by the free radicals, resulting in decreased of carboxyl concentration and density. In addition, the bond between Ca2+ and NOM weakened, and hydrophobic (HPO) substances were mineralized. However, the Fe(III) formed in-situ was active and electropositive, competing with Ca2+ for the complexation active sites on the NOM. The synergy effect of bulk crystallization and surface crystallization led to a significant decrease in the particle size of feed solution. The crystal size and roughness of membrane surface also decreased, which was conducive to reducing the membrane irreversible resistance. Correlation analysis revealed that the HPO ratio, carboxyl density and particle size (> 100 nm) ratio were effective characterization parameters for predicting irreversible resistance. This study not only provides guidance for alleviating membrane fouling caused by NOM-enhanced Ca2+ scaling during the nanofiltration process, but also presents the rationality of irreversible resistance during nanofiltration process and various indicators with strong linear correlation.

The effects of sulfite pretreatment on the biodegradability and solubilization of primary sludge: Biochemical methane potential, kinetics, and potential implications

Sulfite is effective in the waste activated sludge (WAS) pretreatment for enhancing its solubilization, disintegration, and biodegradability. Given the various structures and constituents of the WAS and primary sludge (PS), how sulfite pretreatment affects the characteristics of the PS remains unclear. This study is the first to consider the application of the sulfite pretreatment to a full-scale-plant-derived PS treatment to reveal the changes in sludge properties. The methane production from the PS, pretreated with 500 mg SO32−-S/L of sulfite, was reduced by up to 37%. However, the solubilization of the PS was enhanced by the sulfite pretreatment, leading to substantial substrates being released from the PS, namely soluble polysaccharides, by 96%, and soluble proteins, by 304%. Sulfite directly reduced the concentration of the aromatic amino acid tryptophan in the PS, while the functional groups of key substances in the PS were destroyed by sulfite. Moreover, the dewaterability and degradation extents of the PS were enhanced following the sulfite pretreatment with a low capillary suction time and high solid reduction. The findings of this study suggest that the sulfite-based technology is viable for PS pretreatment prior to the dewatering and final disposal stages towards efficient post sludge treatment.

Sulfite-based pretreatment promotes volatile fatty acids production from microalgae: Performance, mechanism, and implication

Volatile fatty acids (VFAs) production from anaerobic fermentation of microalgae is generally constrained by low organics solubilization and poor substrate-availability. In this study, sulfite-based pretreatment was developed to overcome such situation. Experimental results showed that the maximum concentration of VFAs (467.5 mg COD/g VSS) and corresponding acetate proportion (54.5%) was obtained at 200 mg sulfite-S/L with fermentation time of day 8, which was respectively 2.1- and 1.9-fold of control. It was found that after sulfite pretreatment, more and relatively easy biodegradable organics were released into liquid phase, providing available substrate for acid-producing bacteria. The rigid cell wall of microalgae was destroyed, evidenced by the decreased particle size and increased surface area, which made the microalgae more accessible for subsequent hydrolysis and acidification. Meanwhile, the sulfite-induced sulfate-reducing bacteria facilitated the acetate generation pathway. The accelerated activities of β-glucanase, β-glucosidase, and acetate kinase involved in anaerobic fermentation further validated the above results.

Sulfite pretreatment enhances the biodegradability of primary sludge and waste activated sludge towards cost-effective and carbon-neutral sludge treatment.

Sulfite pretreatment is effective for enhancing the biodegradability of waste activated sludge (WAS). However, the mixture of primary sludge (PS) and WAS is normally collected and treated together, and the effect of sulfite on the sludge mixture remains unclear. Here, we reported that sulfite pretreatment could disintegrate the flocs of the sludge mixture and improve sludge biodegradability. The substrate release from the sludge mixture after sulfite pretreatment (100, 300, and 500mg SO32--S/L) could be enhanced with soluble chemical oxygen demand by up to 1.58 times, soluble nitrogen by up to 1.38 times, soluble polysaccharides by up to 3.04 times and proteins by up to 6.08 times. Further analysis on flocs structure suggests that sulfite may destruct the functional groups of proteins and amino acids and lyse the main structure of sludge cell walls. Moreover, methane production from the sludge mixture could be enhanced by 16% after pretreated by sulfite at 500mgS/L (i.e., 123.59 CH4/kg VSadded), whereas the digested sludge volume could be reduced by 1.51 times. Environmental implications suggest that sulfite pretreatment could save sludge treatment costs by 1.06 $/PE/y and reduce CO2-equivalent emissions by 5.19kg CO2/PE/y, demonstrating its potential as a cost-effective and carbon-neutral technology for sludge management.

Fractionation of broom (Cytisus striatus) biomass components via mild sulfite pretreatment and enzymatic hydrolysis

The potential of broom biomass to produce oligo- and monosaccharides was investigated using mild sulfite pretreatment conditions followed by enzymatic hydrolysis. Both treatments were analyzed via response surface methodology using an experimental central composite rotatable design 24 + star, which explored the following variables: sulfuric acid charge (0% to 3%), sodium sulfite charge (0% to 4%, maximum temperature (150 °C to 190 °C), and time at maximum temperature (0 min to 30 min). Oligo- and monosaccharides in the pretreatment hydrolysates were determined using high performance liquid chromatography. The amount of total extracted xylose, mannose, and galactose ranged from 3.5% to 15.8% of the initial biomass, while the model estimated optimal reaction conditions enabled the extraction of practically all hemicellulose in the raw material. However, the mildest pretreatment reaction conditions, with low temperature and low sulfuric acid charges, provided a hydrolysate where a major part of the extracted polysaccharides remained in oligomer form, enabling their separation by filtration. The cellulose-rich solid residue was submitted to enzymatic hydrolysis using a Novozymes® enzymatic cocktail. The enzymatic hydrolysis was successful, but some polysaccharides remained in the solid residue, mainly composed of lignin. An enzymatic yield of 60% was attained with no added sulfite in the pretreatment at 190 °C, despite the confirmed positive role of sulfur content in the solid residues.

A Comprehensive Approach of Eucalyptus globulus Acid Sulfite Pretreatment for Enzymatic Hydrolysis

The effect of different acid sulfite pretreatment conditions on released components in the hydrolysates and the pretreated solid residues’ response to enzymatic hydrolysis for Eucalyptus globulus chips was investigated. Sodium bisulfite (0–15%), and sulfuric acid (0–5%) were used to pretreat chips at 170 °C and 190 °C, for as long as 30 min. The hydrolysates were analyzed through high-performance liquid chromatography (HPLC) and spectrophotometry. Overall porosity and pores larger than 2.65 nm (size of a typical cellulase) on the solid residues were estimated using glucose and two dextrans with different hydrodynamic radii as probes. The external specific surface area was analyzed by dynamic light scattering. The solid residues underwent enzymatic hydrolysis with an enzymatic cocktail. Very high (84–95%) carbohydrate conversion was achieved for either an extensively delignified biomass or a biomass with very high content of sulfonated residual lignin (23.4%), since internal porosity enables enzymes accessibility. At least 5% sodium bisulfite and 1% sulfuric acid was required to attain a carbohydrate release above 90% in the enzymatic hydrolysis. Results suggest that the presence of sulfonated lignin does not impair the enzymatic hydrolysis rate and extent. The increase of pretreatment temperature had a positive effect mainly on the initial rate of carbohydrates release in the enzymatic hydrolysis. The increase of the wood material dimensions from pins to conventional chips significantly decreased the hemicellulose removal in acid sulfite pretreatment but had a small effect on the enzymatic yield.

Pretreatment of Bamboo by Ammonium Sulfite for Efficient Enzymatic Hydrolysis

In order to find out the potential effect of ammonium sulfite pretreatment on bamboo for efficient enzymatic saccharification, various ammonium sulfite loadings were conducted to pretreat bamboo at 180 °C for 1–8 h with the solid–liquid ratio of 1:6, respectively. The results verified that ammonium sulfite pretreatment could effectively disrupt the recalcitrance of bamboo and create highly enzymatic hydrolysis sugar yield for further utilization. The contents of lignin in the substrates decreased significantly (from 22.94% to 1.21%) after pretreated and the higher lignin removal with higher chemical loading and longer reaction time during pretreatment. The cellulose-to-glucose conversion yield of pretreated bamboo substrates could achieve almost 100% within 48 h by enzymes loading of 15 FPU of cellulase and 30 IU of β-glucosidase per gram glucan. Therefore, ammonium sulfite pretreatment is argued to be a potential alternative technology for pretreatment of bamboo.

Exploring surface properties of substrate to understand the difference in enzymatic hydrolysis of sugarcane bagasse treated with dilute acid and sulfite

The sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) is beneficial to subsequent enzymatic hydrolysis. In this study, to elucidate enzymatic hydrolysis mechanism of SPORL treated sugarcane bagasse (SCB), the surface properties of SPORL and dilute acid (DA) treated SCBs were compared, including cellulase adsorption isotherm and kinetics, specific surface area and average size of pores, water retention value (WRV), element composition and percentages of different chemical bonds on the substrate surface. The results showed the hydrolysis yield of SPORL SCB (76.16 %) was higher than that of DA (57.82 %) and SPORL SCB had better adsorption capacity, lower binding strength, a higher cellulase adsorption rate, larger specific surface area and higher WRV, and these two SCBs might adsorb cellulase by COR bonds (R: organic groups), suggesting SPORL SCB’s surface was more advantageous to enzymatic hydrolysis. This study could help understand the mechanism of lignocellulosic hydrolysis in depth.

Sulfite serving as a pretreatment method for alkaline fermentation to enhance short-chain fatty acid production from waste activated sludge

Alkaline anaerobic fermentation has been reported to be effective for short-chain fatty acids (SCFAs) production from waste activated sludge, but is still limited by the high alkalis consumptions and long fermentation time. This study offers a novel pretreatment strategy for alkaline fermentation, i.e., using sulfite to treat sludge for 1 d. Experimental results showed the optimal SCFAs production of 324.8 ± 9.5 mg COD/g VSS (volatile suspended solids) was obtained at 500 mg Sulfite-S/L pretreatment integration with 4 d of pH 9.5 fermentation, which was 16.2-, 2.0- and 2.9-fold of that in the blank, sole pH 9.5 and sole sulfite pretreatment systems, respectively. Acetic acid comprised 56.2% of SCFAs in this integration system compared with 32.4% in the blank and 45.7% in the sole pH 9.5 systems. And the total time of this integration system was only 5 d, whereas the corresponding time was 9 d in the blank and 7 d in the sole pH 9.5 systems. Mechanism investigations revealed that sulfite pretreatment significantly facilitated the solubilization of both extracellular polymeric substances and cell envelope of sludge flocs, as well as the biodegradability of the released substrates. The reactive derivatives from acidified-sulfite (e.g., H2SO3, HSO3−) contributed the most to the enhanced SCFAs production, while the residual SO32− facilitated the conversion of propionate and butyrate acid to acetate during alkaline fermentation. Illumina MiSeq sequencing analyses showed that the abundance of bacteria related to hydrolysis and acidification, especially the acetogenesis, including Proteiniclasticum sp., Alkaliphilus sp., Romboutsia sp., Tissierella sp., etc, were improved in integration system.