Organisms used in water purification

Biota are an essential component of most sewage treatment processes and many water purification systems. Most of the organisms involved are derived from the waste or water stream itself or from the atmosphere or soil water. However some processes, especially those involved in removing very low concentrations of contaminants, may use engineered eco-systems created by the introduction of specific plants and sometimes animals. Some full scale sewage treatment plants also use engineered wetlands to provide treatment.