Industrial wastewater effluent standards in the United States are being established in terms of both conventional parameters like BOD and specific organic compounds called priority pollutants. Some of these compounds are difficult to treat biologically and the removal mechanisms may include biodegradation, stripping, sorption, and/or combinations of these removal mechanisms. Biorefractory organic compounds that are resistant or difficult to biodegrade, toxic, and/or are inhibitory to microbial growth may present problems in biological treatment systems. Powdered activated carbon addition and chemical oxidation with ozone-assisted biological treatment systems have been investigated with some of these compounds. This paper includes data from controlled activated sludge systems, systems receiving powdered activated carbon, and systems with preozonation assist. Complete mass balances, including influent, effluent, waste sludge and off-gas analyses of the specific compounds were conducted to determine the actual fate of these compounds.