Activated sludge acclimated to biodegrade phenol was allowed to attach on and in light porous ceramic carriers and to function as a biofilm in a photolytic circulating-bed bioreactor (PCBBR). Phenol degradation in the PCBBR was investigated following three protocols: photolysis with ultraviolet light alone (P), biodegradation alone (B), and the two mechanisms operating simultaneously (P/B). Phenol was degraded at approximately equal rates by B and P/B, each of which was much faster than the rate by P. Furthermore, phenol was mineralized to a significantly greater extent with P/B than with either P or B. SEM showed that the biofilm survived well inside macropores that presumably shaded the microorganisms from UV irradiation, even though the UV light greatly reduced biofilm on outer surface of the carriers in the P/B experiments. Rapid biodegradation of phenol, enhanced mineralization, and survival of bacteria inside macropores demonstrated that being in a biofilm inside the porous carriers protected the bacteria from UV-light toxicity, allowing intimate coupling of photolysis and biodegradation.