It has been reported previously that the negative impact of certain fermentation inhibitors may be mitigated by using a larger yeast inoculum (Navarro, 1994). In the current study, the ethanol production is further improved by using a precultured yeast. The beneficial effect of additional and/or precultured yeast was further evaluated by measuring the levels of inhibitors remaining after SSF (Fig. 5). The results show that additional, and pre-conditioned (SE) yeast demonstrated significant decreases in the levels of inhibitors. Compared with the costs of wheat straw biorefining to produce ethanol (Littlewood et al., 2013), the lower levels of enzyme and inoculum required for duckweed biorefining indicate that the cost of ethanol production are likely to be lower. In addition, duckweed-derived protein in the co-product may also create an economic advantage as in first generation biorefining.