Abstract
Cassava rhizome, a by-product from cassava plants, consists mainly of cellulose, hemicellulose and lignin. Thermal pretreatment and alkaline thermal pretreatment were studied. Alkaline thermal pretreatment removed more lignin and hemicellulose than thermal pretreatment. Substrate from alkaline thermal pretreatment showed the maximum cellulose content (81.02%) and hence was hydrolyzed by commercial enzyme preparation (Celluclast 2 L and Novozym 188). The effects of the concentration of substrate (0.75% to 9% w/w) and of enzyme dosage (20 to 30 U/g substrate) were investigated. The highest conentraton of reducing sugar from pretreated substrate (9% w/v) and enzymatic hydrolysis (50 °C, pH 4.8, 48 h) using 30 unit of each enzyme preparation per g of substrate was 72.26 ± 2.11 g/L (89.03% yield). The hydrolysate of Cassava rhizome was used as a carbon source for acetone, butanol and ethanol (ABE) fermentation by Clostridium saccharobutylicum (Cl. saccharobutylicum) in batch culture. The effects of reducing sugar concentrations on the solvents production were investigated in the range of 40~70 g/L as well as the effects of different pH (pH 4.5-6.0). The results showed that Cl. saccharobutylicum BA 117 provided solvent production from cassava rhizome hydrolysate. The optimum pH for ABE production was 5.5 when the initial reducing sugar was 60 g/L. The culture produced only 7.29 g/L ABE from the hydrolysate that had not been treated with polymeric adsorbent resin. The fermentation with inhibitor removal resulted in the production of 10.57 g/L ABE as compared with 13.37 g/L ABE when glucose was used.
