The performance of a continuous bioreactor under periodic inlet substr
ate concentration is theoretically analyzed for productivity improveme
nt which under conventional steady-state operation shows input multipl
icities in the feed substrate concentration. Two values of feed substr
ate concentration give identical productivity under conventional stead
y-state operation. A periodic rectangular pulse is assumed for the fee
d substrate concentration. It is shown by simulation that under concen
tration forcing the average productivity is significantly different fo
r these two substrate concentrations. The larger value of feed substra
te concentration gives improved average productivity and shows a reson
ance with the period of oscillation. The effect of periodic operation
on the average productivity under the input multiplicities in dilution
rate is also analysed.