The present invention relates to a fluid treatment system comprising: an inlet； an outlet； a fluid treatment zone disposed between the inlet and the outlet. The fluid treatment zone: (i) comprises a first wall surface and a second wall surface opposed to the first wall surface, and (ii) having disposed therein at least one array of rows of radiation source assemblies (30). Each radiation source assembly has a longitudinal axis transverse to a direction of fluid flow through the fluid treatment zone and each of the first wall surface and the second wall surface comprises a first fluid deflector element (222, 227) and a second fluid deflector element (223, 228). The first fluid deflector element (222, 227) projecting into the fluid treatment zone to a greater extent than the second fluid deflector element (223, 228).
