Typically, the biodegradation of organic material by microorganisms in the technosphere (sewers, wastewater treatment plants ) and relevant aqueous compartments (receiving freshwater environment, marine environment ) takes place under aerobic conditions (i.e. in the presence of oxygen ). Due to the fact that aerobic biodegradation requires high amounts of oxygen, under certain conditions the supply with oxygen could become rate limiting. Moreover, such low oxygen levels could hamper aerobic life in receiving surface waters. At such low oxygen levels (as e.g. encountered in WWTP sludge digester tanks or (anoxic) sediments), however, anaerobic biodegradation by specialized microorganisms may take place, if the chemical structures of the molecules are susceptible for anaerobic biodegradation.
Although these processes are in principle comparable with aerobic biodegradation, they differ considerably in detail. In the case of surfactants, which are quantitatively discharged after use via the wastewater path, anaerobic degradation in WWTP digester tanks is important to reduce their concentration in the sludge to a level that is limiting terrestrial toxicity.
Anaerobic degradability is also important for natural compartments with a depleted level of oxygen (e.g. anaerobic or anoxic sediments), because it prevents the accumulation of organic substances like surfactants) in these habitats.
Moreover, minimum requirements for anaerobic biodegradation – play a pivotal role in European environmental labelling schemes (e.g. European Ecolabel, Nordic Swan, Blauer Engel).