What is the difference between BOD and COD?

BOD (Biochemical Oxygen Demand) measures oxygen consumed by biological decomposition of organic matter over 5 days, while COD (Chemical Oxygen Demand) measures oxygen required to chemically oxidize all organic matter using a strong oxidizing agent. COD is always higher than BOD as it includes non-biodegradable organics. COD test takes 2-3 hours versus 5 days for BOD. BOD/COD ratio indicates biodegradability of wastewater.