page_title: Waste stabilization pond
section_title: Oxygen levels
hierarchical_section_title: Waste stabilization pond / Fundamentals / Oxygen levels
caption_attribution_description: English: The Nyamhunga wastewater treatment plant in Kariba. Photo taken at 4 November 2011 by P. Feiereisen in Kariba, Zimbabwe.
context_page_description: Waste stabilization ponds are ponds designed and built for wastewater treatment to reduce the organic content and remove pathogens from wastewater. They are man-made depressions confined by earthen structures. Wastewater or "influent" enters on one side of the waste stabilization pond and exits on the other side as "effluent", after spending several days in the pond, during which treatment processes take place.
  Waste stabilization ponds are used worldwide for wastewater treatment and are especially suitable for developing countries that have warm climates. They are frequently used to treat sewage and industrial effluents, but may also be used for treatment of municipal run-off or stormwater. The system may consist of a single pond or several ponds in a series, each pond playing a different role in the removal of pollutants. After treatment, the effluent may be returned to surface water or reused as irrigation water if the effluent meets the required effluent standards.
  Waste stabilization ponds involve natural treatment processes which take time because removal rates are slow. Therefore, larger areas are required than for other treatment processes with external energy inputs.
context_section_description: The oxygen concentration varies in the liquid column: Close to the surface, concentrations are high and support the growth of aerobic organisms. Close to the pond bottom, sunlight penetration is low, and thus photosynthetic activity is reduced. This causes oxygen concentrations to be low there. Finally, inside the sediments in the bottom layer, there is no oxygen at all. Here, organic matter is removed by digestion undertaken by anaerobic organisms.
caption: A poorly maintained anaerobic treatment pond in Kariba, Zimbabwe (sludge needs to be removed)
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