In one of its aspects, the present invention relates to a fluid treatment systemcomprising: an inlet an outlet a fluid treatment zone disposed between theinlet and the outlet. The fluid treatment zone: (i) comprises a first wall surfaceand a second wall surface opposed to the first wall surface, and (ii) having disposedtherein at least one array of rows of radiation source assemblies. Each radiationsource assembly has a longitudinal axis transverse to a direction of fluid flowthrough the fluid treatment zone and each of the first wall surface and the secondwall surface comprises a first fluid deflector element and a second fluid deflectorelement. The first fliud deflector element projecting into the fluid treatmentzone to a greater extent than the second fluid deflector element.
