Refreshing the headspace at a 10-min interval was an effective
way to maintain a stable DO concentration in the reactor. This
operation consisted of the following steps. (1) A reactor was
taken down from the rotator. (2) Two needles were inserted
through the silicone stopper of the reactor and one of them
was connected with high-purity nitrogen gas (N2) lasting for
20 s. (3) A specific amount of O2 was injected into the headspace.
(4) Two needles were palled out after waiting for 3e5 s,
ensuring that the gas pressure in the reactor was the same as