FACULTATIVE LAGOONS Typical layout: two to three ponds in series: AREAL LOADING RATE CALCULATIONS: Average winter temperature (coldest month, o C) Total System BOD loading rate (kg/ha /day) Primary cell loading rate (kg/ha /day) > 15 45-90 100 0 - 15 22 - 45 60 < 0 11 - 22 40 PHYSICAL CHARACTERISTICS Location System Detention Time (days) Southern US 6 - 30 Michigan 120 - 180 Colorado 45 plus 1 - 3 day polishing Pond Water Depth (m) Sludge Depth (m) Total Depth (m) Primary 0.6 - 1.8 0.6 1.2 - 2.4 Secondary 2.4 - 3.0 0.3 2.7 - 3.3 Experience with operating lagoons throughout the US indicates that design guidelines will result in removal of ~ 85% of influent BOD. Effluent suspended solids due to algae growth may require polishing in a sand or gravel filter or other solids separation process.