What is BOD5?
BOD stands for Biochemical Oxygen Demand. ‘5’ stands for a test that takes 5 days to carry out.The test is essentially a measure of the ‘Organic’ or ‘Polluting’ strength of an effluent. A measured sample is prepared for incubation and the oxygen level is determined.The sample is than incubated for 5 days at 20°C and the oxygen level is measured again. The difference in oxygen levels is used to calculate the BOD5. This represents the level of activity by micro-organisms naturally present in the effluent. The level of activity is proportional to the ‘Organic’ or ‘Polluting’ strength.If an effluent is too strong for a receiving aquatic environment then oxygen will be naturally depleted in the same process. Mg/l stands for Milligrams per litre. One Mg/l is the same as one part per million. Untreated sewage typically has a BOD5 of 400-500 mg/l. The Biodigester reduces this to less than 20mg/l.
