2.6. Experiment design
An orthogonal design L9(34) was used to investigate the influence of different supplement dose of inorganic salts, including (NH4)2SO4, K2HPO4 and MgSO4 (all of these were A.R), on ethanol fermentation. The L9(34) orthogonal test is shown in Table 2. The blank factor is a dummy here and is used for error estimation.