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%) X 1 , pH (4.5-6.5) X 2 , incubation temperature (28 -36 C) X 3 , and fermentation time (12-60 h) X 4 , 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.

Based on a five level central composite design (CCD) involving the variables substrate concentration (C), pH (P), incubation temperature (T) and fermentation time (H), a response surface methodology (RSM) for the production of ethanol from pretreated sugarcane bagasse by cellulase and yeast Kluyveromyces fragilis was standardized. The design contains a total of 31 experimental trials in which the first 24 organized in a factorial design and from 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. Maximum ethanol concentration (32.6 g/l) was obtained from 180 g/l pretreated sugarcane bagasse at the optimized process conditions (temperature 35°C, pH 5.5) in 72 h aerobic batch fermentation. Various kinetic models such as logistic model, logistic incorporated leudeking piret model and logistic incorporated modified leudeking piret model have been evaluated and the constants were predicted.

In the present study, classical statistical tool Response Surface Methodology (RSM) was adopted for the optimization of process variables in the bioconversion of pretreated sugarcane bagasse into ethanol by cellulase and Candida wickerhamii MTCC 3013 based on Central Composite Design (CCD) experiments. A 23 five level CCD with central and axial points was used to develop a statistical model for the optimization of process variables such as incubation temperature (25 – 45°) X1, pH (5.0 – 7.0) X2,and fermentation time (24 – 120 h) X3. Data obtained from RSM on ethanol production were subjected to analysis of variance (ANOVA) and analyzed using a second-order polynomial equation, and isoresponse contour plots were used to study the interactions among three relevant variables. Maximum response for ethanol production was obtained when applying the optimum values for temperature (33°C), pH (5.7), and fermentation time (104 h). Maximum ethanol concentration (4.28 g/l) was obtained from 50 g/l pretreated sugarcane bagasse at the optimized process conditions in aerobic batch fermentation. Various kinetic models such as Modified Logistic model, Modified Logistic incorporated Leudeking – Piret model, and Modified Logistic incorporated Modified Leudeking – Piret model were evaluated and the constants were predicted.