Use of activated carbons for detoxification of a lignocellulosic hydrolysate: Statistical optimisation

Preparation and characterization of bacterial cellulose synthesized by kombucha from vinegar residue

Bacterial cellulose (BC) has been widely applied in various fields due to its excellent physicochemical properties, but its high production cost remains a challenge. Herein, the present study aimed to utilize the hydrolysate of vinegar residue (VR) as the only medium to realize the cost-effective production of BC. The BC production was optimized by the single-factor test. The treatment of 6 % VR concentration with 3 % acid concentration at 100 °C for 1.5 h and 96 U/mL of cellulase for 4 h at 50 °C obtained a maximum reducing sugar concentration of about 32 g/L. Additionally, the VR hydrolysate treated with 3 % active carbon (AC) at 40 °C for 0.5 h achieved a total phenol removal ratio of 86 %. The yield of BC reached 2.1 g/L under the optimum conditions, which was twice compared to the standard medium. The produced BC was characterized by SEM, FT-IR, XRD, and TGA analyses, and the results indicated that the BC prepared by AC-treated VR hydrolysate had higher fiber density, higher crystallinity, and good thermal stability. Furthermore, the regenerated BC (RBC) fibers with a tensile stress of 400 MPa were prepared successfully using AmimCl solution as a solvent by dry-wet-spinning method. Overall, the VR waste could be used as an alternative carbon source for the sustainable production of BC, which could be further applied to RBC fibers preparation.

Detoxification Approaches of Bagasse Pith Hydrolysate Affecting Xylitol Production by Rhodotorula mucilaginosa

In this study, the potential of bagasse pith (the waste of sugar and paper industry) was investigated for bio-xylitol production for the first time. Xylose-rich hydrolysate was prepared using 8% dilute sulfuric acid, at 120 °C for 90 min. Then, the acid-hydrolyzed solution was detoxified by individual overliming (OL), active carbon (AC), and their combination (OL+AC). The amounts of reducing sugars and inhibitors (furfural and hydroxyl methyl furfural) were measured after acid pre-treatment and detoxification process. Thereafter, xylitol was produced from detoxified hydrolysate by Rhodotorula mucilaginosa yeast. Results showed that after acid hydrolysis, the sugar yield was 20%. Detoxification by overliming and active carbon methods increased the reducing sugar content up to 65% and 36% and decreased the concentration of inhibitors to >90% and 16%, respectively. Also, combined detoxification caused an increase in the reducing sugar content (>73%) and a complete removal of inhibitors. The highest productivity of xylitol (0.366 g/g) by yeast was attained after the addition of 100 g/l non-detoxified xylose-rich hydrolysate into fermentation broth after 96 h, while the xylitol productivity enhanced to 0.496 g/g after adding the similar amount of xylose-rich hydrolysate detoxified by combined method (OL+AC2.5%).

Multi-response and multi-criteria optimization of acid hydrolyzate detoxification of cocoa pod husks: Effect on the content of phenolic compounds and fermentable sugars

Dilute acid hydrolysis is the most common and effective method for converting lignocellulosic substrates into fermentable sugars. However, this hydrolysis partially degrades the lignin into phenolic compounds (PC), inhibiting the fermentation medium by retaining it in the hydrolyzate. Response surface methodology is a modeling and optimization technique used to examine the effect of multiple factors on a given response. In this study, shows the removal of PC from cocoa pod husks hydrolyzate, while preserving a considerable level of reducing sugar (RS). An Alkalinization from pH 11 with NaOH, then readjustment of pH to 6 with H₂SO₄ were first carried out, while eliminating 89.39% of PC and 13.41% of sugars. Then, an optimization of the activated carbon detoxification of the hydrolyzate was carried out by considering the contact time factors (X₁), carbon to hydrolyzate ratio (X₂) and the agitation speed (X₃) in a Box-Behnken plan. The optimal conditions were 60 min of contact, a carbon to hydrolyzate ratio of 1.984% (w/v), and a stirring speed of 180 revolutions per minute (rpm). 0.153 mg/mL of PC and 6.585 mg/mL of RS remained in the hydrolyzate, corresponding to 95.18% of PC and 28.88% of RS lost.

Mechanism of microbiologically induced calcite precipitation for cadmium mineralization

Microbiologically induced calcite precipitation (MICP) technology shows potential for remediating heavy metal pollution; however, the underlying mechanism of heavy metal mineralization is not well-understood, limiting the application of this technology. In this study, we targeted Cd contamination (using 15:1, 25:1, and 50:1 Ca²⁺/Cd²⁺ molar ratios) and showed that the ureolytic bacteria Sporosarcina ureilytica ML-2 removed >99.7 % Cd²⁺ with a maximum fixation capacity of 75.61 mg-Cd/g-CaCO₃ and maximum precipitation production capacity of 135.99 mg-CaCO₃/mg-cells. Quantitative PCR analysis showed that Cd²⁺ inhibited the expression of urease genes (ureC, ureE, ureF, and ureG) by 70 % in the ML-2 strain. Additionally, the pseudo-first-order kinetics model (R² = 0.9886), intraparticle diffusion model (R² = 0.9972), and Temkin isotherm model (R² = 0.9828) described the immobilization process of Cd²⁺ by bio calcite in MICP-Cd system. The three Cd²⁺ mineralization products generated by MICP were attributed to surface precipitation (Cd²⁺ → Cd(OH)₂), direct binding with the CO₃^2-/substitution calcium site of calcite (Cd²⁺ → CdCO₃, otavite), and calcite lattice vacancy anchors (Cd²⁺ → (Ca_xCd_1-x)CO₃). Our findings improve the understanding of the mechanisms by which MICP can achieve in situ stabilization of heavy metals.

Finding of Novel Galactose Utilizing Halomonas sp. YK44 for Polyhydroxybutyrate (PHB) Production

Polyhydroxybutyrate (PHB) is a biodegradable bioplastic with potential applications as an alternative to petroleum-based plastics. However, efficient PHB production remains difficult. The main cost of PHB production is attributed to carbon sources; hence, finding inexpensive sources is important. Galactose is a possible substrate for polyhydroxyalkanoate production as it is abundant in marine environments. Marine bacteria that produce PHB from galactose could be an effective resource that can be used for efficient PHB production. In this study, to identify a galactose utilizing PHB producer, we examined 16 Halomonas strains. We demonstrated that Halomonas cerina (Halomonas sp. YK44) has the highest growth and PHB production using a culture media containing 2% galactose, final 4% NaCl, and 0.1% yeast extract. These culture conditions yielded 8.98 g/L PHB (78.1% PHB content (w/w)). When galactose-containing red algae (Eucheuma spinosum) hydrolysates were used as a carbon source, 5.2 g/L PHB was produced with 1.425% galactose after treatment with activated carbon. Since high salt conditions can be used to avoid sterilization, we examined whether Halomonas sp. YK44 could produce PHB in non-sterilized conditions. Culture media in these conditions yielded 72.41% PHB content. Thus, Halomonas sp. YK44 is robust against contamination, allowing for long-term culture and economical PHB production.

Cardoon Hydrolysate Detoxification by Activated Carbon or Membranes System for Bioethanol Production

Advanced biofuels incorporation into the transportation sector, particularly cellulosic bioethanol, is crucial for attaining carbon neutrality by 2050, contributing to climate changes mitigation and wastes minimization. The world needs biofuel to be commercially available to tackle the socioeconomic challenges coming from the continued use of fossil fuels. Cynara cardunculus (cardoon) is a cheap lignocellulosic raw biomass that easily grows in Mediterraneous soils and is a potential renewable resource for a biorefinery. This work aimed to study the bioethanol production from cardoon hemicellulosic hydrolysates, which originated from dilute sulfuric acid hydrolysis pretreatment. A detoxification step to remove released microbial fermentative inhibitors was evaluated by using both activated carbon adsorption and a nanofiltration membrane system. The Scheffersomyces stipitis CBS5773 yeast and the modified Escherichia coli MS04 fermentation performances at different experimental conditions were compared. The promising results with E. coli, using detoxified cardoon by membrane nanofiltration, led to a bioethanol volumetric productivity of 0.30 g·L−1·h−1, with a conversion efficiency of 94.5%. Regarding the S. stipitis, in similar fermentation conditions, volumetric productivity of 0.091 g·L−1·h−1 with a conversion efficiency of 64.9% was obtained. Concluding, the production of bioethanol through detoxification of hemicellulosic cardoon hydrolysate presents a suitable alternative for the production of second-generation bioethanol, especially using the modified E. coli.

Evaluation of detoxified sugarcane bagasse hydrolysate by atmospheric cold plasma for bacterial cellulose production

Cellulosic waste as a major type of agricultural waste can be acid deconstructed as a carbon source for fermentation application. However, various fermented inhibitors, such as formic acid, furfural, and 5-hydroxymethylfurfural, are also produced during processing. In this study, sugarcane bagasse (SB) was hydrolyzed with sulfuric acid, and atmospheric cold plasma (ACP) was used to remove the toxic inhibitors. The detoxified SB hydrolysate was used as alternative nutrients for bacterial cellulose (BC) production. Results showed that degradation rates of formic acid, 5-hydroxymethylfurfural, and furfural respectively reached 25.2%, 78.6%, and 100% with optimized ACP conditions (argon ACP at 200 W for 25 min). In BC production, the ACP-treated SB hydrolysate group (PT) exhibited high BC production (1.68 g/L) but was lower than that from the ACP-untreated SB hydrolysate group (PUT) (1.88 g/L), which suggests that ACP detoxification might also cause some crucial nutrients loss of the SB hydrolysate, leading to a decrease in BC production. The material properties of BC produced from detoxified based medium are also evaluated. These findings have important implications for the broader domain of ACP detoxification for cellulosic acid hydrolysates applied to BC production.

Development of wheat bran hydrolysate as Komagataella phaffii medium for heterologous protein production

Developing a Komagataella phaffii (K. phaffii, named as Pichia pastoris formerly) medium using wheat bran hydrolysate (WBH) is a potential approach for wheat bran utilization and heterologous protein by K. phaffii because K. phaffii is used as protein producer by researchers and engineers widely. In this research, the detoxification process of WBH was optimized to obtain the final procedure as pH adjusting to 10 by calcium hydroxide addition, then, 2.0 g/L active carbon absorption followed by 1 h shaking and 3,600 × g centrifugation for 10 min, finally, 3.75 mmol/L sodium thiosulfate addition for 10 min shaking followed by 3,600 × g centrifugation for 10 min. Recombinant K. phaffii-xynB harboring xylanase B gene from Aspergillus niger ATCC 1015 under alcohol oxidase 1 promoter (P_AOX1) was cultivated in detoxified WBH expressing 1059.8 U/mL xylanase B which was 90.9% of that in complex medium from Pichia protocols. These researches built a solid base for detoxified WBH as a low-cost medium of K. phaffii to express heterologous protein, also provided a bright outlet for wheat bran utilization.