Optimization of ethanol production from food waste hydrolysate by co-culture of Zymomonas mobilis and Candida shehatae under non-sterile condition

Abstract

A complete conversion of the hexose and pentose sugars in the food wastes hydrolysates (FWH) to ethanol is a prerequisite for maximizing the profitability of an industrial process for bioethanol production. Response surface methodology (RSM) was employed to optimize the effects of nitrogen source [(NH 4) 2 SO 4 ], phosphorus source (KH 2 PO 4), yeast extract and inoculum size on ethanol production from FWH by co-culture of Zymomonas mobilis and Candida shehatae under non-sterile condition. The optimal conditions for ethanol production were 1.15 g/L of (NH 4) 2 SO 4 , 0.95 g/L of KH 2 PO 4 , 1.38 g/L of yeast extract and 14.75%v/v of inoculum. The results indicate that the most significant parameters affecting ethanol production from FWH by co-culture under non-sterile condition was yeast extract. Ethanol production of 77.6 g/L obtained under optimized condition was 56% increased as compared with the use of raw FWH (34 g/L) and was in good agreement with the value predicted by quadratic model (79.98 g/L), thereby confirming its validity. Ethanol yield of FWH in batch fermentation by co-culture was 0.15 g-ethanol/g-food waste (77.6 g/L), which was 94.6% of the theoretical yield while Z. mobilis alone yielded 0.11 g-ethanol/g-food waste (54.2 g/L) and C. shehatae alone yielded 0.09 gethanol/g-food waste (48 g/L). Ethanol production from FWH in 1-L fermentor by co-culture also gave ethanol yield of 0.16 g-ethanol/g-food waste (78.8 g/L) which was 96% of the theoretical yield. Despite of being a waste, an ethanol yield of 0.16 g-ethanol/g-food waste demonstrated the potential of food waste as a promising biomass resource for ethanol production.

Application of Response Surface Methodology for Optimizing the Production of Bioethanol from Calabash (Crescentia cujete) Substrate Using Saccharomyces cerevisiae

“…Standard solid medium of composition: Yeast extract10g/l, peptone 20 g/l, glucose 20 g/l, agar 15 g/l, pH 6.8 was used. Glucose was filter sterilized and added after autoclaving the other ingredients [22,17].…”

Bioethanol Production from an Underutilized Plant, Calabash (Crescentia Cujete) Using Co-Culture of Saccharomyces Cerevisiae and Cronobacter Malonaticus

“…The pulp has a carbohydrate content of 18.61% and mean values of 59.86%, 25.09% and 18.24% for sucrose, fructose and galactose respectively [12]. These fermentable sugars no doubt when utilized by appropriate microorganisms will yield several commodity products as their metabolic materials such as ethanol, methanol and acetic acid, etc [13]. The choice for the substrate in this study was formed on these assumptions.…”

“…The choice of these microorganisms was based on reports by Akponah et al [15] and Piyapong et al [13] Saccharomyces cerevisiae was isolated from palm wine, while Cronobacter malonaticus was isolated from spoilt orange. Saccharomyces cerevisiae have been previously isolated from palm wine [16,17].…”