Abstract
Background: The high rate of propagation and easy availability of water hyacinth has made it a renewable carbon source for biofuel production. The present study was undertaken to screen the feasibility of using water hyacinth's hemicelluloses as a substrate for alcohol production by microbial fermentation using mono and co-cultures of Trichoderma reesei and Fusarium oxysporum with Pichia stipitis. Results: In separate hydrolysis and fermentation (SHF), the alkali pretreated water hyacinth biomass was saccharified by crude fungal enzymes of T. reesei, F. oxysporum and then fermented by P. stipitis. In simultaneous saccharification and fermentation (SSF), the saccharification and fermentation was carried out simultaneously at optimized conditions using mono and co-cultures of selected fungal strains. Finally, the ethanol production kinetics were analyzed by appropriate methods. The higher crystalline index (66.7%) and the Fourier transform infrared (FTIR) spectra showed that the lime pretreatment possibly increased the availability of cellulose and hemicelluloses for enzymatic conversion. In SSF, the co-culture fermentation using T. reesei and P. stipitis was found to be promising with a higher yield of ethanol (0.411 g g �1 ) at 60 h. The additional yield comparable with the monocultures was due to the xylanolytic activity of P. stipitis which ferments pentose sugars into ethanol. In SHF, the pretreatment followed by crude enzymatic hydrolysis and fermentation resulted in a significantly lesser yield of ethanol (0.344 g g �1 )a t 96 h. Conclusions: It is evident from the study that the higher ethanol production was attained in a shorter period in the co-culture system containing T. reesei and the xylose fermenting yeast P. stipitis. SSF of pretreated water hyacinth biomass (WHB) with P. stipitis instead of traditional yeast is found to be an effective biofuel production process.
Highlights
The high rate of propagation and easy availability of water hyacinth has made it a renewable carbon source for biofuel production
The fungal strains of T. reesei and F. oxysporum were isolated by primary selection from a naturally contaminated water hyacinth, and the isolates were confirmed by their morphology and colony characteristics [18]
The current results clearly demonstrated the saccharification potential of T. reesei and F. oxysporum, where the performance of both strains in co-cultures with P. stipitis was significantly higher than their respective single culture
Summary
The high rate of propagation and easy availability of water hyacinth has made it a renewable carbon source for biofuel production. The present study was undertaken to screen the feasibility of using water hyacinth's hemicelluloses as a substrate for alcohol production by microbial fermentation using mono and co-cultures of Trichoderma reesei and Fusarium oxysporum with Pichia stipitis. Hemicellulose is a viable source of fermentable sugars such as xylose for biorefining applications. It was suggested that the production of fuel-grade ethanol from xylose requires a microorganism capable of producing 50 to 60 g/L ethanol within 36 h with a yield of at least 0.4 g ethanol per gram of sugar [6]. Only few xylose-fermenting microorganisms have been reported earlier [7], and it is generally known that Pichia stipitis is superior to all other yeast species for ethanol production from xylose
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