Wastewater BOD & COD Removal Efficiency Engine

Wastewater Treatment Engineering: BOD5, COD & Organic Mass Loading

Biological treatment processes rely on Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) to evaluate plant capacity and receiving water impact:

• BOD5 vs. COD:

• BOD5 (Biochemical Oxygen Demand): Measures the dissolved oxygen consumed by aerobic microorganisms decomposing organic matter over 5 days at 20°C.

• COD (Chemical Oxygen Demand): Measures the total oxygen required to chemically oxidize all organic compounds (both biodegradable and non-biodegradable).

• The Biodegradability Index:

• >0.5: Readily biodegradable municipal sewage; highly suitable for standard activated sludge.

• 0.2 to 0.4: Industrial wastewater requiring specialized biomass or extended hydraulic retention times.

• <0.2: Refractory toxic waste requiring chemical coagulation, Fenton's reagent, or ozone oxidation.

• The 8.34 Conversion Factor: Density of water links volumetric flow rate in MGD directly to pollutant mass loading in lbs/day.

How to Use This Calculator

Enter your Daily Wastewater Inflow Volume (Q [Million Gallons / Day - MGD]) (e.g. 3.5 (3.5 MGD municipal / industrial flow)), Influent Raw BOD₅ Concentration (mg / L) (e.g. 280 (Raw influent 5-day biological oxygen demand)), Effluent Treated BOD₅ Concentration (mg / L) (e.g. 12 (Discharged treated effluent BOD)), Influent Raw COD Concentration (mg / L) (e.g. 560 (Raw chemical oxygen demand)), Effluent Treated COD Concentration (mg / L) (e.g. 45 (Discharged treated effluent COD)), and EPA NPDES Maximum Allowable BOD Discharge Limit (mg / L) (e.g. 30 (30 mg/L secondary treatment standard)). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Metcalf \& Eddy Environmental Wastewater Engineering equations:

BOD_5 Removal Efficiency (\%) = (BOD_in - BOD_outBOD_in) × 100\%

COD Removal Efficiency (\%) = (COD_in - COD_outCOD_in) × 100\%

Daily Mass Loading (lbs/day) = Flow (MGD) × Concentration (mg/L) × 8.34 lb/gal

Mass Removed (lbs/day) = Mass Loading_in - Mass Loading_out

Biodegradability Ratio = (BOD_5) / (COD)

Worked Example

For example, evaluating a municipal wastewater treatment facility treating 3.5 MGD with influent \ and discharging treated effluent with \ and \ against a BOD removal efficiency is \ and COD removal is 91.96\%. Raw influent organic load is 8,173.2 lbs/day, removing 7,822.9 lbs/day and discharging only 350.3 lbs/day, achieving full regulatory compliance.

Understanding Your Result

Health calculations provide population-average estimates based on validated formulas. Individual variation exists — your actual physiology may differ from the calculated baseline. Compare your result to the relevant clinical reference range (WHO, CDC, NIH, or specialty guidelines). For values outside normal ranges or for clinical decisions, consult a qualified healthcare provider. A single measurement is less meaningful than a trend over time under consistent measurement conditions.