Abstract: Photocatalytic water treatment methods that can be particularly beneficial in degradation of PFAS and reactors and reactor systems that can be useful in carrying out the PFAS degradation protocols are described. Methods utilize bismuth phosphate-based semiconductors as catalysts in particulate or other effective high-surface area water-contacting form. The catalysts can be excited by UV light to induce reduction reactions that degrade or transform PFAS contaminants in the water. Reactor systems include multiple reactors in series and/or parallel. Each reactor includes mixers to encourage turbulent flow within the reactor, control of which is isolated from residence time control within the reactor. The reactors include a light source to deliver about 200 W/L or less of activating radiation emission to the internal volume of the reactor, providing a highly efficient photocatalytic reaction system.