A water treatment system including: a flow regulation control system configured to combine oxo-anion-contaminated water with a reduction-promoting agent, a hole scavenger, or both; a reactor fluidically coupled to the flow regulation control system; a first set of system control probes configured to monitor the concentration of oxygen and oxo-anion in the contaminated water; a second set of system control probes configured to monitor concentration of the oxo-anion and reduction products of the oxo-anion in treated effluent from the reactor; and a controller configured to control the flow regulation control system, thereby controlling the flow rate of the contaminated water and the at least one of the reduction-promoting agent and the hole scavenger to the reactor based at least in part on the concentration of oxo-anion and the reduction products of the oxo-anion in the treated effluent.