3.3.1. Screening the significant factors
Experiments were initiated for screening the significant
factors according to the Plackett–Burman design. Algal cells
were grown under 20 different conditions, with cell dry weight
and DHA yield being taken as the responses for each run
(Table 2). With the experimental data, the effects of the
variables on the responses, and their associated F-test and
significant level (P) were calculated (Table 9). Based on the
effects of dummy variables, the standard error of the PB design
was determined as 1.23 g/L for cell dry weight, and 0.21 g/L for
DHA yield. Here, the effects with P < 0.10 were accepted as
significant. It was found that among the 15 factors investigated,
trace metal (PI) solution, NH4Cl, ammonium acetate, and
temperature had significant effects on cell weight and DHA
yield (Table 9).