Nupac breaks the air stream into fine bubbles, resulting in oxygen transfer so efficiently that the system uses only about half the air of conventional fixed-film reactors. The packing has a specific surface area of 38 ft2/ft3, with uniform spacing of the polypropylene rods for easy dislodging of accumulated biofilm.

The packed section is rotated slowly over an airshearing device to control the thickness and age distribution of the attached biofilm, and prevent the development of anaerobic conditions. Although the microbes remain in a high growth phase, they form a fully developed food chain, in which larger organisms consume smaller ones. The net result is more BOD conversion to water and CO2, and less to bio-mass, so that sludge production is minimized.