Experience of drinking water disinfection in Saint-Petersburg

Summary

The experience of the SUE «Vodokanal of St. Petersburg» activities in the field of retrofitting the technology of two-stage disinfection of drinking water with sodium hypochlorite and UV-irradiation is presented. The concept of ensuring guaranteed safety of the drinking water supply in and around Saint-Petersburg is described. The upgrade of the water disinfection system was carried out at the operating facilities eliminating any decrease in purification efficiency and waterworks capacity. The water treatment facilities use «A» trademark sodium hypochlorite and low-concentrated sodium hypochlorite (NaOCl) manufactured at the factories at the Southern and Northern Waterworks. The process of sodium hypochlorite production includes: salt storage, preparation of saturated salt solution, preparation of softened water, preparation of 3–4% (mass.) concentration work salt solution, production of 0.8% concentration (mass.) sodium hypochlorite, sodium hypochlorite storage in two tanks. The process of NaOCl production is operated in automatic mode. In order to affect efficiently the entire spectrum of microorganisms including bacteria, viruses and protozoan cysts UV-irradiation is used. The outstanding feature of the UV-disinfection plants at the facilities of SUE «Vodokanal of St. Petersburg» is the fact that the UV-equipment is installed at the point of drinking water supply to the distribution network (the contact time is less than 1 minute). The reliability of water disinfection is ensured by the selected method of UV-irradiation of thin water layer. Beginning from 2017 the equipment operation and irradiation dosage monitoring has been carried out in automatic mode. The analytical equipment installed at the facilities was manufactured in Saint-Petersburg.

Key words

potable water , sodium hypochlorite , ultra-violet irradiation , water supply plant , sanitation-and-epidemiological safety , liquid chlorine