Production of Ethanol and Biomass from Rice Husk Using Cultures of Aspergillus flavus, Aspergillus eamarii and Saccharomyces cerevisiae

Abstract

Microbial degradation/conversion of agricultural/industrial wastes to useful bio-products such as bioethanol has become increasingly a popular alternative to gasoline worldwide and has been proven to be useful in many industrial and pharmaceutical processes. In this work, microbial hydrolysis of rice husk into fermentable sugars using Aspergillus flavus and Aspergillus eamarii and subsequent fermentation of sugars to ethanol was achieved using Saccharomyces cerevisiae. The rice husks were ground to fine powder and microbially hydrolyzed by incubating with Aspergillus flavus and Aspergillus eamarii in peptone water for 7 days. Determination of reducing sugar using Fehlings’ reagents confirmed the presence of fermentable sugar in both media. Approximately 6.89° Brix in Aspergillus flavus medium was optimized to 24.41° Brix while 7.12° Brix in Aspergillus eamarii was optimized to 24.10° Brix by adding 300g of sucrose and then fermented to ethanol using Saccharomyces cerevisiae isolated from palm wine at room temperature. The results showed a reduction in pH (6.5-4.1 and 6.8-4.1), an increase in temperature (28-30°C and 28-30°C), increase in percentage titratable acidity (0.33-2.96% and 0.27-2.90%), significant increase in alcohol content (0.00-14.89% and 2.42-14.47%), increase in biomass (0.00-2.16g/l and 0.00-2.08g/l) and decrease in specific gravity (1.112-1.005 and 1.114-1.007) in Aspergillus flavus and Aspergillus eamarii media respectively over a period of 7 days of fermentation. Aspergillus flavus and Aspergillus eamarii hydrolysates yielded 14.89% and 14.47% ethanol respectively after distillation. The results of the experiment conducted shows that rice husk and other cellulosic agricultural wastes could be potential substrates which can be exploited by industries for production of bioethanol and other biotechnological products.