text: 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.