Measurements were done
in a 5-cm3 cuvette. A sodium–potassium phosphate buffer solution (pH 6.8) was used; the total concentration of the salts, 20 mM.
The solution was mixed by a magnetic mixer (200 rpm). A mixture of glucose and glutamic acid (GGA) at a mass ratio of 1:1,
applied as the BOD5 determination standard in the Russian Federation and in international practice [2], was used as a model
mixture. In accordance with the regulatory documents, a value
of BOD5 equal to 205 mg/dm3 was taken to correspond to a solution containing 150 mg/dm3 glucose and 150 mg/dm3 glutamic acid
(BOD5 = 0.68 × CGGA).