Prediction of significant factors in the production of ethanol by ragi tapai co-culture using Taguchi methodology

Ethanol production by co-culture of ragi tapai and Saccharomyces cerevisiae from unhydrolyzed cassava starch without addition of enzymes was conducted in a 2 L batch fermentor. Taguchi's method with orthogonal array of L8 was applied in design of experiment (DOE) and the results were analyzed using MINITAB v14 software. Seven factors: Nitrogen-phosphorus-potassium (NPK), urea, fermentation temperature, ragi tapai concentration, S. cerevisiae concentration, agitation and co-culturing time were varied at two levels for each factor. The significant factors for the production of ethanol were determined by setting S/N ratio to ``larger-is-better'' for high yield ethanol and ``smaller-is-better'' for low yield of ethanol byproducts. The optimum values obtained for each factor were similar to each other. Both have optimum factors of: Urea at 0.8 w/w%, dry ragi tapai and S. cerevisiae concentrations each at 10 w/w%, co-culturing time at 3 h gap, NPK at 0.09 w/w% and agitation speed at 100 rpm. The fermentation temperature for high ethanol yield was 35 degrees C, whereas for the byproducts was 30 degrees C. From the validation experiment conducted at 30 degrees C in 10 L fermentor, the ethanol concentration obtained was 68.00 g/L, while all byproducts concentrations were below 9.00 g/L at the end of the fermentation