STRATEGIC OPTIMIZATION OF ETHANOL PRODUCTION FROM WATERMELON-RIND WASTE: INTEGRATING ADVANCED MANAGEMENT PRACTICES WITH SEPARATE HYDROLYSIS AND FERMENTATION

Abstract

Prospectively, this study on converting watermelon-rind waste (WW) into bioethanol is extremely relevant as it accounts the critical issues of waste management especially in agricultural countries like Pakistan and their subsequent utilization for renewable energy production, thus mitigating pollution and favoring energy security. The study using the WW, if implemented at large, can support to manage massive waste–to-valued product. In WW, the reducing sugar contents of 15.9±0.05%, total carbohydrates 28.8±0.05%, total lipid 3.3±0.03% and total protein 3.5±0.03% were calculated.  Separate hydrolysis and fermentation (SHF) method was selected here for ethanologenesis. For WW hydrolysis, three saccharification techniques were employed i.e., diluted sulfuric acid, enzymatic using Enterococcus faecium XA2 xylanases, and a combination of acidic and enzymatic hydrolysis. Here enzymatic hydrolysis along with dilute sulfuric acid were selected for their effectiveness in complex polysugars into fermentable monosugars while minimizing toxic metabolites release for subsequent fermentation processes. Based on significance elucidated by Placket Burmen (PB) design, combined was selected for subsequent experiment which released 30.43±0.51 g/L reducing sugar and 46.95±0.10 g/L total sugar were recorded. Central composite design (CCD) based optimization for ethanol yield and titer on saccharified WW hydrolyzates were performed. The maximum ethanol yield 0.38±0.1g/g with Metchnikowia cibodasensis Y34 was obtained at 32.5^oC with 50% combined treated hydrolyzate of WW upto incubation of eight days. It has been found that SHF can be a valuable strategy to increase the possibility of conversion of hemicellulose to fermentable sugars and in turn into bioethanol production at large. The study stands-out by integrating a novel combination of xylanolytic and ethanologenic microbes using WW leveraging cutting-edge microbial efficiencies that are significantly potent in bioconversions compared to conventional methodologies.