Biological Oxygen Demand (BOD) Calculator

BOD is a measure of the amount of oxygen that bacteria consume while decomposing organic matter in water. It's a key indicator of water quality and pollution levels in wastewater treatment and environmental monitoring.

BOD₅ is the oxygen demand measured after 5 days of incubation, while BOD₂₀ is measured after 20 days. BOD₅ is more commonly used as a standard test, typically representing 60-70% of the ultimate BOD.

The rate constant k varies by waste type and temperature. Typical values range from 0.1 to 0.3 day⁻¹ for domestic wastewater. It can be determined experimentally by measuring BOD at multiple time intervals and fitting the data to the BOD equation.

Ultimate BOD (L) is the maximum amount of oxygen that can be consumed by bacteria when all biodegradable organic matter is completely oxidized. It represents the theoretical limit of oxygen demand for a given sample.

Use the exertion formula when you know the ultimate BOD and rate constant to predict BOD at any time. Use the dilution method when performing actual laboratory BOD tests with diluted samples and need to account for dilution factors and blank corrections.

Clean natural water: <3 mg/L, moderately polluted water: 3-5 mg/L, heavily polluted water: >5 mg/L, raw domestic wastewater: 200-400 mg/L, treated wastewater: 20-30 mg/L.

BOD tests are typically conducted at 20°C because bacterial activity is temperature-dependent. Higher temperatures increase bacterial metabolism and oxygen consumption rates, while lower temperatures slow the process.

Higher BOD values indicate more organic pollution and greater oxygen demand. For discharge standards, most regulatory agencies require BOD₅ levels below 30 mg/L for treated wastewater, with some requiring as low as 10 mg/L for sensitive receiving waters.