BACKGROUND: Chloride salts are major impurities in biodiesel-derived crude glycerol that can impact dihydroxyacetone (DHA) production. Ion exchange was performed to remove these salts. DHA production from crude glycerol was investigated, before and after an ion exchange treatment in shake-flask fermentation and batch fermentation. DHA production from treated crude glycerol was further studied in fed-batch fermentation. RESULTS:In shake-flask fermentation, the DHA production from the treated crude glycerol was 56.1 ± 1.87 g L −1 . This is 16.2 g L −1 (41%) higher than the DHA production from crude glycerol without the ion exchange treatment at 72 h. The DHA production from the treated crude glycerol was 61.9 ± 2.57 g L −1 , with a DHA production yield (DHA moles per glycerol moles) of > 99 ± 4.4% at 138 h in the batch fermentation. The DHA concentration from the treated crude glycerol was 8.1 g L −1 higher than in the crude glycerol fermentation. In fed-batch fermentation, the DHA production was not significantly higher than that in the batch fermentation due to product inhibition when the DHA concentration reaches 65.05 ± 4.52 g L −1 or more, after 156 h.CONCLUSION: This study shows that salt impurities in crude glycerol negatively impact the DHA production by Gluconobacter thailandicus TBRC 3351 cultured in crude glycerol minimal media. Removing chloride salts from crude glycerol can improve the DHA yield, both in the shake-flask and the batch fermentation. Fed-batch fermentation can also increase the DHA production, but to a lesser extent because of the product inhibition mechanism.

Z. mobilis has been widely studied as a potential microbe for consolidated bioprocessing to convert lignocellulosic biomass to fermentable sugars while at the same time producing ethanol. To achieve this goal, Z. mobilis must be evaluated for the production of cellulolytic enzyme. This work reports on the potential of intracellular and extracellular crude extracts from Z. mobilis ZM4 and TISTR 551 to hydrolyze various cellulosic materials including carboxymethylcellulose (CMC), delignified rice bran, microcrystalline cellulose, and filter paper. Crude intracellular extracts from ZM4 and TISTR 551 showed high endoglucanase activity with CMC substrates at an optimal pH of 6 to 7 and temperature range of 30 to 40 °C. The endoglucanase activity from the crude extracts was significantly higher than the exoglucanase activity. Of the high crystalline celluloses substrates tested, the best results were obtained for the hydrolysis of delignified rice bran by crude intracellular enzyme extracts of Z. mobilis TISTR 551.