The experiments involving the utilization of UVA or UVC irradiation were performed in annular cylindrical reactors operated in batch mode (BRa and BRb), in total recirculation (TrBRa and TrBRb), or configured as CSTR. The annular cylindrical photoreactors have irradiated (working) volumes of 0.5 L and 1.5 L for reactor A and reactor B, respectively. Both reactors have sampling ports on the top, magnetic stirrer, and water jacket for temperature control (Fig. 1). The irradiation sources used were low-pressure mercury UV lamps; PenRay 90-001904 (365 nm) and PenRay 90-0004-07 (254 nm) all UVP-Ultra Violet Products, Cambridge, UK. UV lamps were immersed axially in a quartz tube inside the reactor. Schematics and geometric characteristics of cylindrical reactor are given in Fig. 1. Data for each photoreactor key dimensions and lamp specifications are summarized in Table 1. In the case of total recirculation mode (TrBRa and TrBRb), the photoreactor system was accompanied with a stirred tank (Vtotal = 2 L). In CSTR, experimental setup consisted of feed tank (Vfeed = 6 L), reactor B, and collecting tank. All photocatalytic tests were performed in the slurry reactors. Temperature was maintained at 22.0 ± 1.5 ºC by circulating tap water through the jacket of the photoreactor. The working procedure in each photoreactor was as follows; in a typical experiment, a suspension of TiO2 in selected model wastewater was prepared and transferred to the reactor (BRa and BRb) or tank (TrBRa, TrBRb, CSTR), which was fitted with a mixing unit. When working in total recircu