Abstract: The effect of different types of alkalinity and different concentrations of the alkalinity on alkalinity, pH, and the removal rates of CODcr in hydrolytic degradation was systematically investigated in a Modified SBBR reactor. In some extension, for the same substrate, the higher alkalinity is, the better result of the hydrolytic degradation will be attained. When using NaOH and NaHCO₃ to adjust alkalinity, a fast hydrolytic degradation phase can be found. As far as Penicillin wastewater is concerned, this phase can last about 1h. This phenomenon that CODcr removal rates is very fast can be explained by the unbalance growth theory. Through experiments result, in some extension of alkalinity, the HRT of hydrolytic degradation can be controlled by alkalinity and pH value.