The presence of chromium reducing bacteria is indicative of pollution 

 of water by chromates. This is also true in the case where hexavalent 

 chromium is absent (indicative of decomposition). In this instance it is 

 impossible to analyse for the presence of chromium with a spectrophoto- 

 meter. 



EVALUATION OF THE QUALITY OF WATER BY THE INTENSITY OF BACTERIAL PROCESSES 



Daily Oxygen Consumption for Respiration of Bacteria as an Index of the 

 Water Quality 



All the organisms inhabiting water constantly consume oxygen for their 

 respiration. Only in rare instances will oxygen consumption by algae or 

 zooplankton exceed that of bacteria. In most cases, the role of microor- 

 ganisms in oxygen consumption and, therefore, in destruction of organic 

 matter, is greater than that of all other aquatic organisms taken together. 

 This is demonstrated by the indirect estimations of the number and rate of 

 reproduction of separate groups of organisms. In all cases, bacteria re- 

 produce most rapidly, as a further illustration, in the water passed 

 through a membrane filter where only bacteria remain, the rate of oxygen 

 consumption essentially does not change (Romanenko and Dobrynin, 1973). 



It is well established that respiration is biochemical process in 

 which oxygen is combined with organic substances. In the end, the process 

 may be expressed by the following equation: 



CH 2 + 2 = C0 2 + H 2 



It follows from this that 32 weight parts of molecular oxygen are used 

 per 12 weight parts of carbon of organic matter. Thus, to determine the 

 amount of decomposed organic matter, the number of milligrams of consumed 

 oxygen by is multiplied by 0.375 (i.e., ratio 12:32). This application 

 can be made if the coefficient of respiration is 1, i.e., when carbohy- 

 drates are destroyed in respiration. Occasionally 0.8 or 0.9 is used 

 instead of 1 . In this case, the value of the accepted coefficient should 

 be multiplied by 0.375. It should be noted that the experimental data on 

 respiration coefficients are very few, and often depart from theoretical 

 consideration. 



To determine destruction of organic matter (Vinberg, 1934), 100-150 ml 

 bottles are filled with water straight from the Ruttner sampler. The pro- 

 cedure is performed in such a way so that the water will have as little 

 contact with atmosphere as possible. A rubber tube from the sampler is 

 placed in the bottom of the bottle and approximately 2-3 volumes are 

 passed through it. The bottles are closed with ground glass stoppers. In 

 two bottles, oxygen is measured immediately by the Winkler method (Alekin, 

 1954). The remaining two bottles are placed in a light-proof bag and 

 incubated for a standard time: a day in oligotrophic and mesotrophic 

 waters, 12 hours in more rich waters, 6-12 hours in eutrophic waters in 

 summer. In winter and summer at low temperatures, the time of incubation 

 may be decreased to several days. The time utilized should be the minimum 



65 



