A trickling filter is a type of wastewater treatment system. It consists of a fixed bed of rocks, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced-air flowing through the bed or natural convection of air if the filter medium is porous. The treatment of sewage or other wastewater with trickling filters is among the oldest and most well characterized treatment technologies.
A trickling filter plant in the United Kingdom: The effluent from the primary settling tanks is sprayed onto a bed of coarse gravel (Benfleet Sewage Treatment Plant)
Broken trickling filter unit at the sewage treatment plant in Norton, Zimbabwe, showing importance of maintenance to prevent structural failure
A biofilm is a syntrophic community of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances (EPSs). The cells within the biofilm produce the EPS components, which are typically a polymeric combination of extracellular polysaccharides, proteins, lipids and DNA. Because they have a three-dimensional structure and represent a community lifestyle for microorganisms, they have been metaphorically described as "cities for microbes".
Staphylococcus aureus biofilm on an indwelling catheter
Probable cyanobacteria in the vertical section of a silicified biofilm from the Lower Cretaceous. Very shallow hypersaline environment of the Urgonian carbonate platform of Provence, south eastern France.
Biofilm of golden hydrophobic bacteria; ceiling of Golden Dome Cave, a lava tube in Lava Beds National Monument
Five stages of biofilm development (1) Initial attachment, (2) Irreversible attachment, (3) Maturation I, (4) Maturation II, and (5) Dispersion. Each stage of development in the diagram is paired with a photomicrograph of a developing P. aeruginosa biofilm. All photomicrographs are shown to the same scale.
