The present invention relates to a fluid treatment system comprising: an inlet (A) an outlet (B) a fluid treatment zone disposed between the inlet and the outlet. The fluid treatment zone: (i) comprises a first wall surface (320420520620) and a second wall surface opposed to the first wall surface (325425525625), and (ii) having disposed therein at least one array of rows of radiation source assemblies. 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 (322323422423522523622623) and a second fluid deflector element (327328427428527528627628).
