Editing Environmental engineering (section)

===Wastewater treatment===
[[File:Wonga wetlands sewage plant.jpg|thumb|220px|left|[[Sewage treatment]] plant, [[Australia]]]]There are numerous [[wastewater treatment]] technologies. A wastewater treatment train can consist of a primary clarifier system to remove solid and floating materials, a secondary treatment system consisting of an [[aeration]] basin followed by [[flocculation]] and [[settling|sedimentation]] or an [[activated sludge]] system and a secondary clarifier, a tertiary biological [[nitrogen]] removal system, and a final [[disinfection]] process. The aeration basin/activated sludge system removes organic material by growing bacteria (activated sludge).  The secondary clarifier removes the activated sludge from the water. The tertiary system, although not always included due to costs, is becoming more prevalent to remove nitrogen and [[phosphorus]] and to disinfect the water before discharge to a surface water stream or ocean outfall.<ref>{{cite book|author= Sims, J.|title= Activated sludge, Environmental Encyclopedia |publisher=Detroit|year=2003}}</ref>