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Sweet sorghum juice supplemented with 0.5% ammonium sulphate was used as a substrate for ethanol production by Saccharomyces cerevisiae TISTR 5048. In batch fermentation, kinetic parameters for ethanol production depended on initial cell and sugar concentrations. The optimum initial cell and sugar concentrations in the batch fermentation were 1 · 10 8 cells ml -1 and 24°Bx respectively. At these conditions, ethanol concentration produced (P), yield (Y ps ) and productivity (Q p ) were 100 g l -1 , 0.42 g g -1 and 1.67 g l -1 h -1 respectively. In fed-batch fermentation, the optimum substrate feeding strategy for ethanol production at the initial sugar concentration of 24°Bx was one-time substrate feeding, where P, Y ps and Q p were 120 g l -1 , 0.48 g g -1 and 1.11 g l -1 h -1 respectively. These findings suggest that fed-batch fermentation improves the efficiency of ethanol production in terms of ethanol concentration and product yield.

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Optimization of three parameters: agitation rate (A; 100, 200 and 300 rpm), aeration rate (B; 0.5, 1.5 and 2.5 vvm) and aeration timing (C; 2, 4 and 6 h), for ethanol production from sweet sorghum juice under very high gravity (VHG, 290 g L−1 of total sugar) conditions by Saccharomyces cerevisiae NP 01 was attempted using an L9 (34) orthogonal array design. The fermentation was carried out at 30 °C in a 2-L bioreactor and the initial yeast cell concentration was approximately 2 × 107 cells mL−1. The results showed that the optimum condition for ethanol fermentation should be A2B3C2 corresponding to agitation rate, 200 rpm; aeration rate, 2.5 vvm and aeration timing, 4 h. The verification experiments under the optimum condition clearly indicated that the aeration and agitation strategies improved ethanol production. The ethanol concentration (P), productivity (Qp) and ethanol yield (Yp/s) were 132.82 ± 1.06 g L−1, 2.55 ± 0.00 g L−1h−1 and 0.50 ± 0.00, respectively. Under the same condition without aeration (agitation rate at 200 rpm), P and Qp were only 118.02 ± 1.19 g L−1 and 2.19 ± 0.04 g L−1h−1, respectively while Yp/s was not different from that under the optimum condition.

Aims: To study the effect of a quaternary ammonium biocide, didecyldimethylammonium chloride (DDAC), on the treatment efficiency of laboratory-scale rotating biological contactors (RBCs) as well as their component biofilms. Methods and Results: Biofilms were established on the RBCs and then exposed to 0-160 mg l )1 (p.p.m.) DDAC at a flow rate of 2AE5 l h )1 . The treatment efficiency of the RBC and the microbial activity of the biofilms were markedly decreased when 40 mg l )1 DDAC or greater were applied to the units. However, DDAC had no effect on the number of viable bacteria in the biofilms when DDAC concentrations up to 80 mg l )1 were applied to the RBCs. No viable bacteria could be detected in the biofilm when DDAC was applied at 160 mg l )1 . Extended observation over a further 40 d with 20 and 80 mg l )1 DDAC showed similar results in terms of chemical oxygen demand removal, ATP content and viability of biofilms compared with those values over the first 12 d of exposure. Conclusions: There was at least a fourfold difference in the susceptibility of planktonic and sessile bacteria to DDAC. Cells acclimatized to DDAC did not increase their capability to degrade normal carbon sources or DDAC under the conditions used in this study. Significance and Impact of the Study: The results show that RBCs can be used to treat effluents containing DDAC at concentrations up to 20 mg l )1 and that 160 mg l )1 of DDAC was required to eliminate cells in established biofilms.