Graphical Method for Calculating Biochemical Oxygen Demand

A new method for handling the data from a series of biochemical oxygen demand dilutions consists of graphing the dissolved oxygen remaining in each dilution verus the volume of sample added. The demand is then calculated from the best straight line using the equation: Demand = (slope × sample volume) - y intercept + sample dissolved oxygen. No initial dissolved oxygen determinations are required. The oxygen demand of the dilution water and of the seed are automatically compensated for in the calculation. It is no longer necessary to attempt to keep the dilution water blank below 0.2 mg/l. Results from a wastewater treatment plant show that the graphical method is advantageous in practical situations.