Fluid Treatment System

A fluid treatment system (2) for treating a fluid (4), the system (2) comprises: -a translucent sleeve (6) surrounding at least one light source (8) and mounted within a cell (10) of the system (2); -a housing (12) configured to receive the sleeve (6) therein, a hollow cavity (18) is defined between an outer surface (14) of the sleeve (6) and an inner surface (16) of the housing (12) defining a cavity for flowing the fluid (4) therein. The system (2) further comprises: -a fluid flowing device (22) to flow said fluid (4) through the hollow cavity (18) at a velocity of 3 m/s or higher such that the velocity of the fluid in relation to the outer surface (14) prevents fouling and/or scaling from aggregating on the outer surface (14) of the sleeve (6), -a recirculation assembly (24) configured to recirculate said fluid (4) through said hollow cavity (18). In addition a method is provided for treatment of a fluid in the fluid treatment system.