For the purification of industrial waste water from the crude oil processing industry, a multiple stage treatment plant is recommended. Biofiltration takes place as a secondary treatment stage. Under plug-flow conditions residual compounds can be treated efficiently with a reduced power requirement. Specialized microorganisms, utilizing compounds which are not readily biodegradable, are immobilized on burned clay. Usually toxic peaks do not inhibit the microorganisms in the biofilm. This depends on the short retention time of the water in fixed bed systems and on the characteristic of the biofilm. Dissolved, colloidal or particulate non-biodegradable substances will be adsorbed on the biofilm and can be removed by backwashing the reactor. A description of the treatment plants at BP-oiltech Hamburg and Shell Refinery Hamburg is given. The design of the fixed film reactors is discussed.

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