Moderate alkali-thermophilic ethanologenesis by locally isolated Bacillus licheniformis from Pakistan employing sugarcane bagasse: a comparative aspect of aseptic and non-aseptic fermentations

Abstract

BackgroundBiofuels obtained from first-generation (1G) sugars-starch streams have been proven unsustainable as their constant consumption is not only significantly costly for commercial scale production systems, but it could potentially lead to problems associated with extortionate food items for human usage. In this regard, biofuels’ production in alkali-thermophilic environs from second-generation (2G) bio-waste would not only be markedly feasible, but these extreme conditions might be able to sustain aseptic fermentations without spending much for sterilization.ResultsPresent investigation deals with the valuation of ethanologenic potential of locally isolated moderate alkali-thermophilic fermentative bacterium, Bacillus licheniformis KU886221 employing sugarcane cane bagasse (SCB) as substrate. A standard 2-factor central composite response surface design was used to estimate the optimized cellulolytic and hemicellulolytic enzymatic hydrolysis of SCB into maximum fermentable sugars. After elucidation of optimized levels of fermentation factors affecting ethanol fermentation using Taguchi OA L27 (3^13) experimental design, free cell batch culture was carried out in bench-scale stirred-tank bioreactor for ethanol fermentation. Succeeding fermentation modifications included subsequent substrate addition, immobilized cells fibrous-bed bioreactor (FBB) incorporation to the basic setup, and performance of in situ gas stripping for attaining improved ethanol yield. Highest ethanol yield of 1.1406 mol ethanol/mol of equivalent sugars consumed was obtained when gas stripping was performed during fed-batch fermentation involving FBB under aseptic conditions. Despite the fact that under non-aseptic conditions, 30.5% lesser ethanol was formed, still, reduced yield might be considered influential as it saved the cost of sterilization for ethanol production.ConclusionEffectual utilization of low-priced abundantly available lignocellulosic waste sugarcane bagasse under non-aseptic moderate alkali-thermophilic fermentation conditions as directed in this study has appeared very promising for large-scale cost-effective bioethanol generation processes.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0785-1) contains supplementary material, which is available to authorized users.

Mixotrophic cultivation of Scenedesmus dimorphus in sugarcane bagasse hydrolysate

“…A steady increase of both human population and their energy demand has resulted in dangerous outcomes from deforestation and fossil fuel exploitation . Consequently, interest in different fuels such as biodiesel, bioethanol, biohydrogen, and biomethane from non‐food biomass and industrial effluents which otherwise represent a major portion of solid waste has been increased . Biomass wastes such as lignocellulosic, food‐industrial, and post‐harvesting agriwastes are reservoirs of polymeric carbon sources from photosynthates and organic nutrients that are currently underutilized …”

Bench‐scale fermentation for second generation ethanol and hydrogen production by Clostridium thermocellum DSMZ 1313 from sugarcane bagasse

“…For this purpose, pure cellulose was replaced with 110 g of SCB. The detailed result of SCB chemical pretreatment steps, obtained by our research group are published already 3 . SCB was pretreated separately with varying chemical concentrations (sulfuric acid, phosphoric acid, hydrochloric acid, and sodium hydroxide) with 1:12 solid‐to‐liquid ratio, autoclaved (30 m in), vacuum filtered three times after washed with distilled water (until neutral pH) and dried (at 60°C) till constant weight obtained.…”

“…Consequently, it is the dire need at the moment to explore such energy sources that prove to be eco‐friendly, low‐cost, and sustainable. In this prospect, biofuels, that is, plant‐based fuels, for instance, bioethanol and biohydrogen (BioH 2 ) are regarded as sustainable, renewable, efficient, and less environmentally toxic 1‐3 . These can be generated through microbial fermentations of lignocellulosic biomass (LCB).…”

“…and biological (such as saccharifying bacteria, commercial enzymes, etc.) are in practice with comparable advantages/disadvantages for LCB hydrolysis 3 …”

“…In this prospect, preliminary study has been executed by author regarding hydrolysis of SCB employing different pretreatment chemicals (H 2 SO 4 , H 3 PO 3 , HCL, and NAOH), selected from literature. No detoxification method was conducted but the SCB pellet was washed multiple times till neutral pH was obtained 3 . Further selection of the preferred SCB can be made when differently pretreated biomass (obtained by all experimental chemicals) can be further subjected to fermentative microorganisms which is the part of the current investigation.…”