In a sewage treatment system, microconstituents, including personal care products and pharmaceutical materials, often difficult to degrade biologically, are removed by supersaturating the untreated wastewater feed with ozone. This breaks down refractory microconstituents into more readily biodegradable materials, subsequently treated preferably in an activated sludge membrane bioreactor process. The oxygen byproduct of ozonation is utilized by feeding the oxygen into an aerobic part of the plant to meet a portion of the biological demand, thereby increasing efficiency of ozone use in the process.