A comparative study on bacterial conversion of selected agricultural biomass to ethanol

Abstract

The aim of the study was to investigate the bioethanol production potentials by indigenous bacterial isolates screened for amylolytic and cellulolytic activities. Cassava peels were obtained from local 'garri' producers, while corn grains and corn cobs were gotten from retailers within the Erinfun farm settlement along Afe Babalola University Road, Ado-Ekiti, Ekiti State, Nigeria on June 4, 2015. The substrates (corn flour, corn cob and cassava peels) were sundried for 5 days and ground into fine powder using a hammer mill and analyzed for proximate nutrient composition and reconstituted to a 5% concentration in water before fermentation. The fermentation was set up for 20 days using single cultures of bacteria and co-cultures of bacteria and yeast selectively isolated and screened for amylolytic and cellulolytic activities. Parameters such as pH, total titratable acidity, reducing sugar and optical density were taken at intervals of 5 days and ethanol production was analyzed at the end of fermentation. Three bacterial isolates (Bacillus macerans, Bacillus subtilis and Micrococcus varians) yielded ethanol in all the feed stocks. The highest percentage ethanol yield was observed in the fermentation of corn flour and corn cobs with B. macerans which were 3.6 ± 0.009 and 3.5 ± 0.009, respectively. There was reduction in the pH and total titratable acidity and increase in the reducing sugar content and optical density. B. macerans exhibited the highest average ethanol production (3.5±0.07%). A proximate analysis of the feed stocks showed presence of nitrogen, protein, fat, carbohydrate and ash. This study investigated the potentials of wastes (cassava peels and corn cob) used as feed stocks for bio-ethanol production, in substantially replacing major food crops (corn) as a case study.