Disclosed herein is a plasma reactor insert assembly having in one example an outer casing comprising; a fluid inlet; a fluid outlet; an electric power input; and electric power connector; a transformer bracket coupled to the outer casing; at least one step-up transformer attached to the transformer bracket. The insert in electric communication with the electric power connector; a plurality of substantially parallel dielectric tubes in electric communication with the transformer; at least one grounded plate positioned between each dielectric tube with a fluid gap there between, and; wherein there is no fluid path between the fluid inlet and the fluid outlet except by passing between one of the dielectric tubes and one of the grounded plate. In one form, each grounded plate is v-shaped or arcuate v-shaped in cross-section. A method for disinfecting or sanitizing using the plasma reactor is also described.