Rail transport has always pretended to be most resource conserving in terms of natural resources consumption per unit of transported goods and ecologically less harmful as for emission and discharge of contaminants. Nevertheless the issue of the quality of purified effluent at the installations of JSC Russian Railways is still urgent and the environmental activities are among the most demanded engineering tasks.

Regardless of almost ultimate renunciation of steam traction, the railways increase water consumption because of the growth of their length and traffic capacity. An important part of the water is consumed irrevocably (in passenger coaches, for reception of steam, fabrication of ice) as the rate of water recycling and reuse is about 30%. The remainder goes to surface water bodies. The most harmful are: cleaning and steaming posts for rolling stock, disinfection posts for cars, locomotive and wagon depots etc. The most common pollutants are oil, petrol, diesel fuels, phenols, dissolved acids. Carbon monoxide, nitrogen oxide, hydrocarbon, phenols are emitted at different stages of operations and so form the priority indices of the level of pollution.

Different tools of purification have their own advantages and disadvantages. The main industrial method of chlorination can’t ensure the totality of hygienic and ecological requirements. The up-andcoming industrial method is decontamination of waters by ultraviolet radiation. The basic principles of decontamination by ultraviolet instruments, together with mode of processing of waters, results’ monitoring tools and indices are described.

Ultraviolet radiation finds also some other applications. The proposed method of control of waters is based on the capacity of most organic matters of different classes to absorb light in the range of 200–280 nanometer. The proposal of the authors consists in measuring ultraviolet rate (A 254) with the wavelength of 254 nanometer in quartz dish with measured solution layer’s thickness of 10 mm, distilled water serving a solution of comparison. A spectrophotometer of any model capable to take measures in ultraviolet spectral region can be used. Ultraviolet rate is a new optical index, which can define demand of chemical oxygen, biochemical consumption of oxygen, contents of residual organic impurities in purified wastewaters. The correlation dependencies «A254– demand of chemical oxygen» and «A254 – biochemical consumption of oxygen» permit to assess the level of quality of purified wastewater. The proposed method can ensure continued real-time monitoring of the quality of water purification.