Abstract: Refinery waste feedstock is screened to remove large particles and is diluted to less than 5% solids weight percent to form a slurry. The slurry is agitated and heated to 180.degree. F. or higher for a time sufficient to melt waxy petroleum solids, reduce the viscosity of the slurry, reduce the density of petroleum fractions within the slurry, and begin to break surface adhesion of petroleum to residual fines. The conditioned slurry is passed through a first disc/bowl centrifuge which separates more than 80% of the waste volume as a first liquid effluent containing most of the petroleum fractions from the original waste and which may be returned to the refinery for processing. The residual cake is diluted with hot water to form a second slurry and is treated with an amount of hydrogen peroxide for a time sufficient to lyse and/or liberate residual petroleum bound to inert fine particles and to oxidize toxic polycyclic aromatic hydrocarbons to non-toxic derivatives.