Process design of ethanol production system from a semi-solid mixture of raw cassava starch, Rhizopus sp. and Saccharomyces cerevisiae by simultaneous saccharification, fermentation and stripping.

A broad study on the process development of an ethanol production system from raw cassava starch has been tackled starting from the screening of the microorganism towards the development of process designs of the fermentation and ethanol dehydration systems. Results showed that the best fungal strain capable of digesting raw starch was a Rhizopus strain cultured by the solid substrate 'koji' method. Better additives for the rice bran culture media was 0.5% 'ipil-ipil' sawdust and 1% sweet potato starch giving optimum glucoamylose enzyme productions at 6 days of culture time. Saccharification process using minibioreactors registered optimum conditions for koji as: 215 g/l substrate, 215 g/l enzyme, 1.5 l/min/l broth air flowrate and 50 degrees Celsius temperature. During saccharification process, the highest reducing sugar produced was about 100 g/l, the 'koji' registering higher production than the same enzyme level of amyloglucosidase. Simultaneous saccharification and fermentation experiments gave a maximum ethanol production of about 11% (v/v) at 3 days fermentation at the optimum substrate level of not more than 265 g/l. Higher substrate level causes inhibition of reaction which has been eliminated by an ethanol stripping and rectifying system. Upon rectification process, the average ethanol concentration of the condensate was about 202 g/l, the maximum ethanol content of the condensate was 285 g/l which has been obtained using Rhizopus koji and the initial starch substrate concentration increased to 400 g/li. The results using koji were higher than that of the results by amyloglucosidase. It was shown that ethanol recovery at higher concentrations was possible. Attempts of the dehydration of hydrous ethanol by adsorption of the water in the ethanol-water vapor mixture through a cassava starch packing has been found to be feasible at a low temperature (40 deg C.) and by using raw cassava starch particles.