Photocatalytic reactors for water treatment can generally be classified into two main configurations, depending on the deployed state of the photocatalysts: (1) reactors with suspended photocatalyst particles and (2) reactors with photocatalyst immobilized onto continuous inert carrier. Various types of reactors have been used in the photocatalytic water treatment, including the annular slurry photoreactor, cascade photoreactor, downflow contactor reactor, etc.