Chemical Oxygen Demand Chemical oxygen demand (COD) is one of the most important parameters in effluent monitoring and treatment. The COD test is used to predict the requirement an effluent will have for oxygen and hence the effluent's likely impact on the aquatic life of the receiving water course. COD can be measured in three ranges. LR (0-150 mg/l) is applicable for final effluents and treated waste water. MR (0-1500 mg/l) is suitable for measuring crude sewages, untreated and partially treated waste water. HR (0-15000) is suitable for monitoring trade effluents.