RSM-BASED FERMENTATIVE ETHANOLOGENESIS EMPLOYING ACID HYDROLYSATE WATERMELON PEELS

Background: Owing to an agricultural country, Pakistan produces a bulk of lignocellulosic wastes such as watermelon peels (WMP) annually whose incongruous disposal makes these waste source of filth and disease outbreaks. Also, energy crisis associated with depleting fossil fuels is compelling researchers all over the world to find alternate, cheaper and sustainable ways of generating energy.

Aim: In order to manage the copious magnitudes of agricultural wastes locally as well as globally and to combat the prevailing extortionate energy crisis, this study is aimed to acquire “energy from waste.

Material and Methods: For this purpose, WMP was used as feedstock for bioethanol production. WMP was hydrolyzed by dilute nitric acid under optimized conditions interpreted by response surface methodology (RSM) of central composite design (CCD). Subsequent methodology involved expounds the ability of yeasts to employ hydrolyzed WMP that contains substantial amount of sugars to ferment into ethanol.

Results: The ethanologenic fermentation was performed under optimized level of fermentation influencing independent parameters (elucidated by CCD) for maximal ethanol yield employing Saccharomyces cerevisiae K7 and Metchnikowia cibodasensis Y34 yeasts. These included concentration of dilute nitric acid pretreated WMP hydrolysate (X1), hydrolysis temperature (X2) and incubation period (X3). The results revealed that maximal ethanol yield was obtained from S. cerevisiae K7 accounting 0.35±0.05 g/g of reducing sugars whereas M. cibodasensis Y34, yielded 0.37±0.01 g ethanol/g of reducing sugars.

Conclusion: From this research, it is concluded that the ethanologenic yeast M. cibodasensis Y34 is significantly capable to tolerate ethanol and contains promising potential of WMP-to-bioethanol valorization in comparison with the traditional baker’s yeast S. cerevisiae K7. Development of industrial fermentation processes as focused in the current study, employing watermelon peels for ethanol production can be highly productive for efficient waste consumption as well as low-cost ethanol production.