Optimization of fermentation conditions using response surface methodology (RSM) with kinetic studies for the production of bioethanol from rejects of Kappaphycus alvarezii and solid food waste

Kappaphycus alvarezii reject (KR) and solid food waste (SFW) are unused sources of carbohydrates; the production of bioethanol from these raw materials has not yet been reported by any researchers so far. The present study was conducted to optimize the fermentation parameters using RSM (Design-Expert version 7.0 software). KR and SFW were fermented by using Saccharomyces cerevisiae for bioethanol production. Logistic and modified Gompertz kinetic models were fitted fermentation time against bioethanol yield data. The gas chromatography flame ionization detector (GC-FID) was used for bioethanol confirmation. The optimum conditions for an incubation time of 24 h, inoculum size of 15 vol%, and agitation speed of 90 rpm at pH 5 were predicted by RSM. Under these experimental conditions, the best yield of bioethanol was 68% (w/w), which is in good agreement with the predicted value from RSM of 70% (w/w) with an R-2 of 0.97. Under the optimized conditions, the reducing sugar reduced from 30.83 to 8.55 g/L with a conversion efficiency of 70%. Overall, KR and SFW were effective resources for the production of bioethanol to meet the future energy demand. The diversion of SFW through their study will provide a breakthrough for the reduction of energy potential SFW to landfills, contributing to the climate change initiative.