Biological Oxygen Demand, 7 days, BOD7
Biochemical oxygen demand (BOD) is a parameter in the assessment of the purity of water. BOD is the quantity of oxygen (dissolved in water) which is consumed in the biological breakdown of the organic substances in a water sample. Biochemical oxygen demand is indicated in milligrams of oxygen per litre and represents an approximate measure of the presence of organic pollutants and bacteria.
Pure water has a BOD of 0, while wastewater may have values of several hundred milligrams per litre. BOD7 indicates the quantity of oxygen consumed over 7 days.
Water with a high concentration of organic substances may nevertheless have a low BOD if the pollutants include bactericidal chemicals. In such chemically polluted water, an (approximate) measure of the concentration of organic substances can be obtained by measuring the consumption of added oxidants, see chemical oxygen demand.
Source: Nationalencyclopedin 2010 and ÅF Group