BOD and COD Load Calculator

From concentration to load

A BOD or COD load is measured concentration multiplied by wastewater flow. With flow in m³/day and concentration in mg/L, divide the product by 1000 to obtain kg/day. For example, 100 m³/h at 200 mg/L gives a daily load of 480 kg. This calculator does not convert BOD into COD.

Removal efficiency

Enter inlet and outlet flows separately to calculate the mass load difference rather than concentration reduction alone. An inlet load of 480 and outlet load of 48 kg/day gives 90 percent removal. Negative removal is retained. Check flow records, sample timing and analytical methods when interpreting it. The result does not establish discharge compliance or size a treatment plant.

Check load separately from concentration reduction

Let inlet flow be 40 m³/h at 250 mg/L. Daily flow is 40 × 24 = 960 m³ and inlet load is 960 × 250 / 1000 = 240 kg/day. Additional dilution water raises outlet flow to 50 m³/h. At 100 mg/L, outlet load is 50 × 24 × 100 / 1000 = 120 kg/day. Removed load is 120 kg/day and removal based on load is 50 percent. Concentrations alone would suggest a 60 percent reduction.

This difference shows why flows must also be measured. Dilution can lower concentration without the same proportional mass removal. Check that inlet and outlet samples represent comparable periods. Applying one instantaneous concentration to an entire day with varying flow can be misleading.

BOD and COD are different analyses. Do not use one as the inlet parameter and the other as its outlet value. Both streams need the same parameter and analytical definition. This calculation gives only the load difference across the selected boundary. Storage, transfer to sludge or discharge through another stream means the difference cannot all be interpreted as biological degradation.

Frequently asked questions

How do you calculate BOD load in kg/day?

With an example flow of 100 m³/h and BOD concentration 200 mg/L, multiplying flow by concentration and assuming the flow continues for the whole day gives an incoming BOD load of 480 kg/day. This is a preliminary calculation requiring representative flow and concentration measurements from the same period, and it does not convert BOD to COD or size a treatment plant.

Calculate with these values