Fixed-film systems (also attached-growth systems) are biological wastewater treatment processes that employ a inert medium such as rock, plastic, wood, or other natural or synthetic solid material, that will support attached growth of biomass on its surface and within its porous structure. Wastewater comes into contact with the film contaiining the active fixed biomass either by pumping the water past the media in packed towers (i.e. trickling filter) or by moving the media past the wasewater to be treated (e.g. rotating biological contactor).
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