Treehugger.com has an interesting article about the use of shipping containers as housing for waste water treatment facilities. The units were developed by Texas Research Institute for Environmental Studies at Sam Houston State University and PCDworks with funding from the US military. From the article:
The system is able to convert wastewater to EPA acceptable standards within 24-48 hours and being housed in a 40-foot-long shipping container makes it completely portable. DAAB is able to treat wastewater for up to 600 people per day; roughly a battalion of soldiers. The biological processing unit uses specially selected bacteria to “clean” wastewater, removing organic and inorganic materials so water can be released into the environment with no harmful consequences.