A mobile, modular water treatment system for the production of ultrapure water includes a storage tank, an actinic radiation treatment apparatus disposed on a mobile platform, an electrically driven water treatment apparatus disposed on the mobile platform, downstream of the actinic radiation treatment apparatus, an ion exchange media apparatus disposed on the mobile platform downstream of the electrically driven water treatment apparatus, and a pressure driven filtration sub-system disposed on the mobile platform downstream of the ion exchange media apparatus. The pressure driven filtration sub-system outputs the ultrapure water and is connectable to a water distribution system for a point of use and for recirculation of a portion of the ultrapure water to the storage tank.

Methods, systems, and devices for PFAS destruction including providing water containing PFAS to a reactor vessel, irradiating the water with UV light under conditions to destroy at least a portion of the PFAS, passing the treated water through a selective membrane to form permeate and membrane reject comprising PFAS, providing the membrane reject back to the reactor vessel, providing additional water containing PFAS to the reactor vessel within the reactor vessel or before being provided to the reactor vessel, and irradiating the membrane reject and the additional water containing PFAS within the reactor vessel with UV light. The steps may be repeated a plurality of times such that PFAS that is not destroyed is recycled through the reactor vessel. Sensitizers may be added and may also be recycled in the membrane reject with the PFAS.