Design population served. Used to compute design flow if flow_mgd is not provided. Multiply by flow_per_capita_gpd to get total flow. Only required when flow_mgd is not provided.

Design wastewater flow in million gallons per day. If omitted, calculated from population and flow_per_capita_gpd. Typical small plants: 0.1-5 MGD.

Per capita wastewater flow in gallons per day. US average is ~100 gpd per person. Range: 60-120 gpd depending on water use patterns and infiltration. If omitted, defaults to 100 gpd.

Influent 5-day biochemical oxygen demand in mg/L. Typical domestic wastewater: 150-300 mg/L. Higher for industrial contributions. If omitted, defaults to 200 mg/L.

Influent total suspended solids in mg/L. Typical domestic wastewater: 150-350 mg/L. If omitted, defaults to 220 mg/L.

Required effluent BOD5 in mg/L. NPDES secondary treatment standard is 30 mg/L monthly average; many permits require 10-20 mg/L. If omitted, defaults to 20 mg/L.

Required effluent TSS in mg/L. NPDES secondary treatment standard is 30 mg/L monthly average; many permits require 10-20 mg/L. If omitted, defaults to 20 mg/L.

Wastewater temperature in degrees Celsius. Affects biokinetic rates. Design to the coldest month. Typical range: 10-25 C. If omitted, defaults to 20 C.

Solids retention time (mean cell residence time) in days. Conventional activated sludge: 5-15 days. Extended aeration: 20-30 days. Drives sludge age and nitrification. If omitted, defaults to 10 days.

Mixed liquor suspended solids concentration in mg/L. Conventional: 1500-3500 mg/L. Extended aeration: 3000-6000 mg/L. Higher MLSS allows smaller tanks but requires more oxygen. If omitted, defaults to 3000 mg/L.