Examples of physical waste separation and reaction options are listed in the table. Reasons for selecting physical separation options usually include recovery of a waste component, separation of hazardous from non-hazardous waste components and volume reduction of waste requiring further treatment, or preparation of various components of the waste for reactions to address specific waste characteristics. It could be argued that the waste reaction options listed are reactions used to separate waste components. For example, one major objective of biological treatment is to separate soluble, biodegradable carbon compounds from water. In aerobic biological treatment, carbon compounds are separated from water in the form of carbon dioxide gas and microorganisms that can be removed by gravity clarification.
Incineration is an oxidization process that can separate organic from inorganic carbon compounds.
A major additional benefit of reaction options is that the hazardous wastes often are converted into a more environmentally acceptable form that facilitates disposal and reduces disposal cost. In its basic form, caustic treating of gasoline involves washing the gasoline with a solution of caustic, followed by a water wash of the gasoline to remove any residual caustic from the gasoline product. A number of variations of the basic caustic treating process and various treating technologies are available. Depending on the refinery configuration and the processes used, the production of spent caustic can be in the range of 3 gallons to 70 gallons of spent caustic per barrel of crude oil processed, and can be produced on a semibatch or continuous basis. Although refinery spent caustic usually is not considered a RCRA hazardous waste, it is corrosive and can generate explosive vapors.