Phenol-4-sulfonic acid (4-PSA) was photocatalytically degraded in the presence of Degussa P-25 TiO2 catalyst suspensions in a slurry annular bubble column reactor. Artificial UV radiation was employed as the source of photons. The effect of catalyst loading, pH, presence of anions, initial concentration, and photon flux on the rate of photocatalytic degradation was investigated. At the self-pH of 4-PSA (pH congruent to 4.5) the degradation was higher. It was observed that carbonate, chloride, and sulfate have detrimental effects on total organic carbon removal. The effect of the radiation distribution of the UV lamps on quantum yield was also studied. The usage of multiple radiation sources results in higher quantum yield probably as a result of relatively better and uniform illumination inside the reactor. The kinetics of the photocatalytic degradation of 4-PSA has been reported.