Abstract: An ultraviolet fluid treatment system having feedback control using a kinetic model and a reactor model that interact with one another. The kinetic model uses readily measured fluid properties upstream and downstream of a radiation zone to calculate the conversion of a target contaminant as it passes through the fluid treatment system. This obviates the need to measure the contaminant concentration directly, which generally is too slow to permit real-time control. A reactor model relates system operating cost to system operating parameters, such as electrical power consumption and/or rate of oxidant addition, where applicable. The reactor model is linked to the kinetic model and is used to optimize operating cost by adjusting system operating parameters based on a comparison between the conversion obtained from the kinetic model and the overall treatment objectives. A control center, an ultraviolet fluid treatment apparatus, and a method of treating a fluid are also disclosed.