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

Qurat-Ul-Ain Ahmad,Javed Iqbal Qazi,Shang-Tian Yang,Maleeha Manzoor

doi:10.1186/s13068-017-0785-1

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.

Highlights

Biofuels obtained from first-generation (1G) sugars-starch streams have been proven unsustainable as their constant consumption is significantly costly for commercial scale production systems, but it could poten‐ tially lead to problems associated with extortionate food items for human usage
Unlike acid and hydrothermal pretreatments, alkaline pretreatment results in reduced hemicellulose solubilization and lesser fermentation inhibitors production [6]. It results in increased enzymatic convertibility of accessible cellulose and hemicellulose into fermentable sugars, overcoming the biomass recalcitrance that poses itself as a prime impediment for lignocellulosic biomass (LCB) saccharification and subsequent fermentation into ethanol at large [12, 13]
Selection of ethanologenic alkali‐thermophilic bacteria Of the 34 initially selected isolates based on their ethanol production, as assessed by Snell and Snell’s modified method or ethanol quantification, eight were selected for further study

Summary

Introduction

Biofuels obtained from first-generation (1G) sugars-starch streams have been proven unsustainable as their constant consumption is significantly costly for commercial scale production systems, but it could poten‐ tially 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 be markedly feasible, but these extreme conditions might be able to sustain aseptic fermentations without spending much for sterilization. It results in increased enzymatic convertibility of accessible cellulose and hemicellulose into fermentable sugars, overcoming the biomass recalcitrance that poses itself as a prime impediment for LCB saccharification and subsequent fermentation into ethanol at large [12, 13]

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Conclusion