OPTIMIZATION OF PROCESS CONDITIONS USING RESPONSE SURFACE METHODOLOGY (RSM) FOR ETHANOL PRODUCTION FROM WASTE CASHEW APPLE JUICE BY ZYMOMONAS MOBILIS

Ethanol has been known for a long time, being perhaps the oldest product obtained through traditional biotechnology. It is an attractive, sustainable energy source for fuel additives. Based on a four-level central composite design (CCD) involving the variables substrate composition (20–100%) X₁, pH (4.5–6.5) X₂, incubation temperature (28°–36°C) X₃, and fermentation time (12–60 h) X₄, a response surface methodology (RSM) for the production of ethanol using waste cashew apple juice as substrate by Zymomonas mobilis MTCC 090 was standardized. The design contains a total of 31 experimental trials with the first 16 organized in a fractional factorial design and 25 to 31 involving the replications of the central points. Data obtained from RSM on ethanol production were subjected to the analysis of variance (ANOVA) and analyzed using a second-order polynomial equation, which resulted in the optimized process conditions of 62% (v/v) as substrate concentration, pH of 5.5, temperature of 32°C, and fermentation time of 37 h. Maximum ethanol concentration (12.64 g/L) was obtained at the optimized conditions in an anaerobic batch fermentation.