Prior research reported the sustainable parameter oscillations characterized by long periods and high amplitudes in the continuous ethanol fermentation system when very high gravity(VHG) medium was fed.In this study

a bioreactor system composed of a continuous stirred tank reactor(CSTR) and three-stage tubular bioreactors in series was set up

and the dynamics of the oscillatory behavior in such a fermentation process was investigated by the weighting treatment of the specific growth rate of yeast cells

which considered the lag response of yeast cells to the stress exerted by the environment.Model parameters were estimated and validated by experimental data.Furthermore

the tubular bioreactors were packed with wood chip (5 mm×5 mm×5 mm)

stainless steel net ring (10 mm×10 mm) and polyurethane (10 mm×10 mm×10 mm)respectively which were significantly different in their surface properties and corresponding yeast cell immobilization roles through adsorption.It was found that the wood chip was the best in attenuating the parameter oscillations although its yeast cell immobilization role was between the other two

which indicated that

in addition to the yeast cell immobilization

other factors also significantly contributed to the attenuation of the parameter oscillations.Further investigations revealed that the micro-environmental changes of the tubular bioreactors created by these different packings which inevitably changed the specific growth rate of the yeast cells as well as the dilution rate changes correspondingly after the tubular bioreactors were packed and their working volumes decreased

also contributed to the attenuation of the parameter oscillations.The polyurethane packings showed the best immobilization performance

which increased the biomass concentration and consequently the productivity significantly.