page_title: Facultative lagoon
section_title: Subsequent polishing ponds
hierarchical_section_title: Facultative lagoon / Fundamentals / Subsequent polishing ponds
caption_attribution_description: English: Photo: A. Schöpe (Jan. 2009)
context_page_description: Facultative lagoons are a type of waste stabilization pond used for biological treatment of industrial and domestic wastewater. Sewage or organic waste from food or fiber processing may be catabolized in a system of constructed ponds where adequate space is available to provide an average waste retention time exceeding a month. A series of ponds prevents mixing of untreated waste with treated wastewater and allows better control of waste residence time for uniform treatment efficiency.
context_section_description: Overflow from the facultative lagoon may be routed through one or more polishing ponds supporting lower populations of anaerobic micro-organisms and a higher proportion of aerobic organisms adapted to survival in lower concentrations of organic material.  Effluent from the final polishing pond may be suitable for discharge to natural receiving waters.
caption: Facultative lagoon (polishing pond) providing tertiary treatment after a constructed wetland in Hamburg-Allermöhe, Germany
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