A Method for Determination of Hydrocarbon and Nitrogenous Biochemical Oxygen Demands in Natural Waters by Manometric Method

The aim of the work was the simultaneous determination of hydrocarbon biochemical oxygen demand - cBOD and nBOD (nitrogen) in the same water sample without using a nitrification inhibitor by the manometric method. Daily measurements of cBOD are determined by recording the pressure drop resulting from the absorption of carbon dioxide released by the oxidation of hydrocarbon organic matter by microorganisms with KOH (potassium hydroxide). Here, the processes of oxidation of mineral substances in water and especially the developing nitrification processes, which absorb oxygen dissolved in water and cause an additional pressure drop in the vessel, are a disturbing factor, for the measurement of which, in the daily 24-hour cycle of registrations, it is recommended to close the absorption hole of the vial with KOH for 8 hours. The 24-hour nBOD and cBOD results are calculated from the result of the pressure drop in these 8 hours. In the paper, in the form of a table, the detailed form of calculation of the recorded results of BODs at two pH-s of a natural water sample within 1-20 days is given. The possibility of anthropogenic impact assessment using this method is shown on the example of natural water. It is concluded that with the proposed method of measuring BODs records the complete and separate results of cBOD are recorded under conditions of developing nitrification in water. All information from both nitrification and BOD-full is recorded simultaneously, which gives a complete picture of the overall oxygen balance in the water. The proposed method is practically applicable and fully comparable with the results obtained by the standard manometric method.