Sizing Septic Tank Volume: Vol = (Average Flow Rate per hour)(1 hr) Size of Tile Field: Determined by “perc” test

Clarifier (Sedimentation Tank) Design: Primary: Hydraulic detention time = 2 hrs Overflow rate = 40 m3/m2-day Secondary: Overflow rate = 15 m3/m2-day Depth = 1.3 m

Biological Treatment Principles:

The quantity of new biomass produced is a function of the growth rate of the microbes. Under aerobic conditions “cell yield” varies from about 0.1 to 0.4 g cells per g of BOD5 used. Under anaerobic conditions “cell yield” is much lower – 0.05 g cells per g BOD5

Activated Sludge Design Parameters: F/M = 0.3 kg BOD5/kg MLSS-day Volumetric loading: 0.8 kg BOD5/m3-day Hydraulic residence time = 5 hrs Air supplied = 60 m3/kg BOD5

Trickling Filter Design Parameters: Hydraulic loading: 10 m3/m2-day Depth: 2 m

Anaerobic Digester Design Parameters: Solids loading: 2 kg/m3-day Solids retention time = 20 hrs Note that anaerobic digestion is considered to be a mesophilic process where optimum temperature is 350C ( 90oF)

Gas (methane) production rate in anaerobic digesters: 0.4 m3 per kg biomass digested (biomass digested = waste biomass from aerobic process, i.e., activated sludge, trickling filter) This methane can be used to heat the digester.

Design for RBC’s: 0.6 lbs of BOD5 per 1000 ft2 of media per day Rotational speed = 1.6 rpm Basin depth enough to cover 40% of media surface Media should be less than 12 ft dia. Energy to drive shaft = 2.5 kw/shaft

Constructed Wetland design parameter is hydraulic retention time Constructed Wetland design parameter is hydraulic retention time. Typical number for this parameter is 10 days. Hydraulic retention time = Vol./Flow rate For 1000 gal/day flow and a depth of wetland = 2 ft this would give a surface area of 688 ft2. Typical L/W = 2:1

Soil Type Perc rate (mpi) Sand < 10 Sand loam Porous silt loam 10 - 45 Silty clay loam Clay, compact Silt loams > 45 Silty clay loams