Novel Propagation Strategy of Saccharomyces cerevisiae for Enhanced Xylose Metabolism during Fermentation on Softwood Hydrolysate

An economically viable production of second-generation bioethanol by recombinant xylose-fermenting Saccharomyces cerevisiae requires higher xylose fermentation rates and improved glucose–xylose co-consumption. Moreover, xylose-fermenting S. cerevisiae recognises xylose as a non-fermentable rather than a fermentable carbon source, which might partly explain why xylose is not fermented into ethanol as efficiently as glucose. This study proposes propagating S. cerevisiae on non-fermentable carbon sources to enhance xylose metabolism during fermentation. When compared to yeast grown on sucrose, cells propagated on a mix of ethanol and glycerol in shake flasks showed up to 50% higher xylose utilisation rate (in a defined xylose medium) and a double maximum fermentation rate, together with an improved C5/C6 co-consumption (on an industrial softwood hydrolysate). Based on these results, an automated propagation protocol was developed, using a fed-batch approach and the respiratory quotient to guide the ethanol and glycerol-containing feed. This successfully produced 71.29 ± 0.91 g/L yeast with an average productivity of 1.03 ± 0.05 g/L/h. These empirical findings provide the basis for the design of a simple, yet effective yeast production strategy to be used in the second-generation bioethanol industry for increased fermentation efficiency.

Waste-Based Second-Generation Bioethanol: A Solution for Future Energy Crisis

The demand for more environmentally friendly alternative renewable fuels is growing as fossil fuel resources are depleting significantly. Consequently, bioethanol has attracted interest as a potentially viable fuel. The key steps in second-generation bioethanol production include pretreatment, saccharification, and fermentation. The present study employed simultaneous saccharification and fermentation (SSF) of cellulose through bacterial pathways to generate second-generation bioethanol utilizing corncobs and paper waste as lignocellulosic biomass. Mechanical and chemical pretreatments were applied to both biomasses. Then, two bacterial strains, Bacillus sp. and Norcadiopsis sp., hydrolysed the pretreated biomass and fermented it along with Achromobacter sp., which was isolated and characterized from a previous study. Bioethanol production followed by 72 h of biomass hydrolysis employing Bacillus sp. and Norcadiopsis sp., and then 72 h of fermentation using Achromobacter sp. Using solid phase micro extraction combined with GCMS the ethanol content was quantified. SSF of alkaline pretreated paper waste hydrolysed by Bacillus sp. following the fermentation by Achromobacter sp. showed the maximum ethanol percentage of 0.734±0.154. Alkaline pretreated corncobs hydrolyzed by Norcadiopsis sp. yielded the lowest ethanol percentage of 0.155±0.154. The results of the study revealed that paper waste is the preferred feedstock for generating second-generation bioethanol. To study the possible use of ethanol-diesel blends as an alternative biofuel E2, E5, E7, and E10 blend emulsions were prepared mixing commercially available diesel with ethanol. The evaluated physico-chemical characteristics of the ethanol-diesel emulsions fulfilled the Ceypetco requirements except for the flashpoint revealing that the lower ethanol-diesel blends are a promising alternative to transport fuels. As a result, the current study suggests that second generation bioethanol could be used as a renewable energy source to help alleviate the energy crisis..

Isolation and Identification Cellulolytic Bacteria from Termite Gut Obtained from Indralaya Peatland area

The production of second-generation bioethanol as renewable energy has developed very rapidly and has become a promising alternative energy source. Bioethanol production using biomass can be obtained alternatively from cellulose in wood, sawdust, organic waste, and agricultural waste. This research used termites obtained from Indralaya peatland area as organisms that can decompose cellulose into glucose with the cellulase enzymes produced by bacteria in their digestive tract. Cellulases are enzymes capable of hydrolyzing lignocellulose into glucose. The study aimed to isolate and identify of cellulolytic bacteria from termite gut obtained from Indralaya peatland area. The bacterial isolates were classified by using morphological and biochemical standard methods, and identification based on Bergey’s Manual of Determinative Bacteriology. Cellulolytic bacteria of termite gut were isolated and cultured on CMC (Carboxymethyl cellulose) agar medium. The activity of cellulolytic bacterial was conducted based on halo area and cellulolytic index on CMC agar medium. Among 64 isolates of bacteria, 24 isolates were identified as cellulolytic bacteria. Futhermore, our isolates with higher cellulolytic index were identified as the Staphylococcus, Microbacterium, Bacillus, and Brevibacterium genus.

Criteria prioritization for the sustainable development of second-generation bioethanol in Thailand using the Delphi-AHP technique

Background The availability of underexploited agricultural residues in Thailand opens up the opportunity to supply second-generation bioethanol production. The national implementation of residues-to-biofuel can potentially boost the bioeconomy and greenhouse gas mitigation but requires the involvement of multiple stakeholders in the development of effective policy recommendations. This study aims to optimize the implementation of the national strategy through the use of a multi-criteria approach that involves participatory prioritization by current stakeholders in order to evaluate certain aspects and important indicators for second-generation bioethanol development. Methods The Delphi-AHP technique was used to analyze the degree of importance of different criteria. The evaluation process was conducted with various stakeholders and used a pairwise comparison of 4 dimensions (main criteria) and 12 indicators (sub-criteria). Participants were asked to rate factors related to technical feasibility, environmental impacts, economic feasibility and social impacts in terms of importance. Results Bioethanol stakeholders in Thailand from five different sectors (industry/business, NPO/NGOs, the governmental sector, academic/research institutes and financial institutions/banks) participated in the Delphi survey. The 20 experts’ evaluation of the four dimensions ranked economic feasibility (32.7%) highest in terms of level of importance, followed by environmental impacts (25.1%), technical feasibility (24.9%) and social impacts (17.3%). When assessing the sub-criteria, the participants selected ‘final price per liter’, ‘added value of input materials’ and ‘net energy balance’ as the top three most important indicators among the 12 sub-criteria. In terms of a link between the preferred criteria and the participants’ expertise, the results encouraged taking different backgrounds and affiliations into account in the policy planning phase. Conclusions The stakeholder survey indicated the importance of economic aspects, highlighting the need to take governmental driven policy into consideration. However, implementation scenarios have to be embedded in a broader range of aspects because all the dimensions were rated as being highly impactful. For future sustainable bioenergy, the inclusion of stakeholders’ opinions can result in multifaceted scenarios that can be linked to social acceptance and benefits for all relevant players when developing policy recommendations for advanced bioenergy.