One-pot simultaneous saccharification and fermentation: a preliminary study of a novel configuration for cellulosic ethanol production

Enzymatically triggered delignification through a novel stable laccase: A mixed in-silico /in-vitro exploration of a complex environmental microbiota

Laccases have been broadly applied as a multitasking biocatalyst in various industries, but their applications tend to be limited by easy deactivation, lack of adequate stability, and susceptibility under complex conditions. Identifying stable laccase as a green-biocatalyst is crucial for developing cost-effective biorefining processes. In this direction, we attempted in-silico screening a stable metagenome-derived laccase (PersiLac1) from tannery wastewater in a complex environment. The laccase exhibited high thermostability, retaining 53.19% activity after 180 min at 70 °C, and it was stable in a wide range of pH (4.0-9.0). After 33 days of storage at 50°C, pH 6.0, the enzyme retained 71.65% of its activity. Various metal ions, inhibitors, and organic solvents showed that PersiLac1 has a stable structure. The stable PersiLac1 could successfully remove lignin and phenolic from quinoa husk and rice straw. In the separate hydrolysis and fermentation process (SHF) after 72 h, hydrolysis was obtained 100% and 73.4% for quinoa husk and rice straw, and fermentation by the S. cerevisiae was be produced 41.46 g/L and 27.75g/L ethanol, respectively. Results signified that the novel lignin-degrading enzyme was confirmed to have great potential for industrial application as a green-biocatalyst based on enzymatically triggered to delignification and detoxify lignocellulosic biomass.

Vacuum-assisted black liquor-recycling enhances the sugar yield of sugarcane bagasse and decreases water and alkali consumption

Black liquor (BL) remains a critical problem during alkaline pretreatment. To solve this issue, a novel pretreatment strategy termed vacuum-assisted black liquor-recycling pretreatment, was established to pretreat sugarcane bagasse (SCB). Firstly, SCB was pretreated with 2% NaOH at 121 °C for 1 h under vacuum conditions. The produced BL was used for subsequent pretreatments after pH recovery with NaOH. The pretreated SCBs were subject to enzymatic hydrolysis and separate hydrolyzation and fermentation (SHF) without washing to neutral pH. BL was recycled on seven occasions. The results indicated that glucose yields did not significantly differ between pretreatment with NaOH and recovered BL. The enzymatic hydrolysis and the fermentation resulted in maximum 0.35 g/g of glucose yield and 116.5 g/kg of ethanol yield respectively. Compared with conventional pretreatment with NaOH, the VABLR method showed high conversion rates of cellulose into monosaccharaides, whilst preserving ~20% and ~46% of alkali and water usage, respectively.

Pretreatment of corn stover by solid acid for d-lactic acid fermentation

Solid acid is a new acid that is safe and green, which has been widely used in the fields of acid pickling. In this study, we adopted solid acid to pretreat corn stover and used the pretreated corn stover in the fermentation of d-lactic acid. Finally, we obtained optimal conditions for the pretreatment of corn stover by solid acid: digestion temperature of 120°C, digestion time of 80min, and solid acid concentration of 1.5%. Then adding cellulase of 30FPU/g, the conversion rate of glucose reached 71.06% after enzymatic hydrolysis for 72h. In addition, the changes of corn stover structure after pretreatment were further represented by using scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). At the same time, we used the pretreated corn stover as fermentation substrate and Lactobacillus. delbrueckii sp. bulgaricus as the starting strain to produce d-lactic acid. The yield reached 18g/L, with the optical purity being 99%e.e. This research has provided a new way to comprehensively utilizae corn stover.

Fungal-mediated consolidated bioprocessing: the potential of Fusarium oxysporum for the lignocellulosic ethanol industry

Microbial bioprocessing of lignocellulose to bioethanol still poses challenges in terms of substrate catabolism. The most important challenge is to overcome substrate recalcitrance and to thus reduce the number of steps needed to biorefine lignocellulose. Conventionally, conversion involves chemical pretreatment of lignocellulose, followed by hydrolysis of biomass to monomer sugars that are subsequently fermented into bioethanol. Consolidated bioprocessing (CBP) has been suggested as an efficient and economical method of manufacturing bioethanol from lignocellulose. CBP integrates the hydrolysis and fermentation steps into a single process, thereby significantly reducing the amount of steps in the biorefining process. Filamentous fungi are remarkable organisms that are naturally specialised in deconstructing plant biomass and thus they have tremendous potential as components of CBP. The fungus Fusarium oxysporum has potential for CBP of lignocellulose to bioethanol. Here we discuss the complexity and potential of CBP, the bottlenecks in the process, and the potential influence of fungal genetic diversity, substrate complexity and new technologies on the efficacy of CPB of lignocellulose, with a focus on F. oxysporum.

Feasibility of a facile butanol bioproduction using planetary mill pretreatment

A facile butanol bioproduction process was developed using planetary milling, and Pinus rigida wood waste as a model substrate for fermentable sugars. The use of planetary milling as the pretreatment eliminates the need for washing and transfer of the biomass prior to enzymatic hydrolysis. Moreover, using this pretreatment process resulted in the production of only 0.072 ± 0.003 g/L soluble phenolic compounds, a concentration that was not inhibitory towards Clostridium beijerinckii NCIMB 8052. As the milling was performed in a compatible buffer (50mM acetate, pH 4.8), the enzymatic hydrolysis step was initiated by simply adding the cellulase cocktail powder directly to pretreated biomass without washing the biomass or exchanging the buffer, resulting in a glucose yield of 31 g/L (84.02%). Fermentation of the hydrolysate samples by C. beijerinckii NCIMB 8052 gave slightly better butanol yields than cultures grown in a typical lab media (P2), with final concentrations of 6.91 and 6.66 g/L, respectively.

2G ethanol from the whole sugarcane lignocellulosic biomass

BACKGROUND

In the sugarcane industry, large amounts of lignocellulosic residues are generated, which includes bagasse, straw, and tops. The use of the whole sugarcane lignocellulosic biomass for the production of second-generation (2G) ethanol can be a potential alternative to contribute to the economic viability of this process. Here, we conducted a systematic comparative study of the use of the lignocellulosic residues from the whole sugarcane lignocellulosic biomass (bagasse, straw, and tops) from commercial sugarcane varieties for the production of 2G ethanol. In addition, the feasibility of using a mixture of these residues from a selected variety was also investigated.

RESULTS

The materials were pretreated with dilute acid and hydrolyzed with a commercial enzymatic preparation, after which the hydrolysates were fermented using an industrial strain of Saccharomyces cerevisiae. The susceptibility to enzymatic saccharification was higher for the tops, followed by straw and bagasse. Interestingly, the fermentability of the hydrolysates showed a different profile, with straw achieving the highest ethanol yields, followed by tops and bagasse. Using a mixture of the different sugarcane parts (bagasse-straw-tops, 1:1:1, in a dry-weight basis), it was possible to achieve a 55% higher enzymatic conversion and a 25% higher ethanol yield, compared to use of the bagasse alone. For the four commercial sugarcane varieties evaluated using the same experimental set of conditions, it was found that the variety of sugarcane was not a significant factor in the 2G ethanol production process.

CONCLUSIONS

Assessment of use of the whole lignocellulosic sugarcane biomass clearly showed that 2G ethanol production could be significantly improved by the combined use of bagasse, straw, and tops, when compared to the use of bagasse alone. The lower susceptibility to saccharification of sugarcane bagasse, as well as the lower fermentability of its hydrolysates, can be compensated by using it in combination with straw and tops (sugarcane trash). Furthermore, given that the variety was not a significant factor for the 2G ethanol production process within the four commercial sugarcane varieties evaluated here, agronomic features such as higher productivity and tolerance of soil and climate variations can be used as the criteria for variety selection.

Ethanol production from xylan-removed sugarcane bagasse using low loading of commercial cellulase

Xylan was always extracted as the feedstock for xylooligosaccharides production. The xylan-removed residue may contain high content of cellulose and thus had a possibility to be converted into ethanol. After soaked in 12% of NaOH at room temperature overnight, solubilization of cellulose, xylan, and lignin was 4.64%, 72.06%, and 81.87% respectively. The xylan-removed sugarcane bagasse (XRSB) was enzymatically hydrolyzed by using decreased cellulase loadings. The results showed that 7.5 FPU/g cellulose could obtain a cellulose conversion yield of 82%. Increasing the cellulase loading did not result in higher yield. Based on this, bioethanol production was performed using 7.5 FPU/g cellulose by employing fed-batch fermentation mode. The final ethanol concentration reached 40.59 g/L corresponding to 74.2% of the theoretical maximum. The high titer ethanol and low cellulase loading may reduce the overall cost.