Activated sludge acclimatized to 400 ppm phenol was used for the biodegradation of phenol in a batch reactor system and a Rotating Biological Contactor (RBC). Phenol degradation in the batch reactor was studied in relation to supply of oxygen, in addition to the effect of biomass concentration. An aeration pump and oxygen concentrator were used to supply oxygen. It was confirmed that the performance of system improved with increased availability of oxygen, as determined from the phenol degradation rate. Alternatively increasing stirring speed proportionally, increased the mass transfer coefficient of oxygen and also resulted in improved phenol degradation. However, in all the above cases the dissolved oxygen (DO) was zero in the presence of phenol. Studies using the RBC led to amelioration/improvement in DO levels, thus overcoming the limitations of oxygen supply to the process during phenol degradation in the batch mode.