Water treatment technologies

In general, the water treatment process includes the following stages:

  • water ammonation (ammonium sulfate is used),
  • water disinfection (sodium hypochlorite is used),
  • coagulation of pollutants (aluminium sulfate is used),
  • flocculation (cationic flocculant is used),
  • sand filtration in contact clarifiers (one-stage treatment scheme),
  • sedimentation and sand filtration in rapid filters (two-stage treatment scheme),
  • UV disinfection.


  • The new K-6 water treatment block at the Southern Waterworks
  • Ozonation unit at K-6 block


Since 2007, Vodokanal has been applying a unique two-stage process of the integrated water disinfection at St. Petersburg waterworks.

This process is based on a highly effective but safe chemical – sodium hypochlorite (chemical method) and UV water treatment (physical method). Such combination enables us to fully guarantee epidemiological safety of water supply in St. Petersburg, and total compliance of microbiological indicators of water quality with the current norms.

St. Petersburg has become the first big city to treat all potable water with ultraviolet and to use no liquid chlorine for potable water disinfection.

The official ceremony of discarding the last chlorine container was held at the Northern Waterworks on 26 June 2009. Chlorine (a hazardous substance to store and transport) gave place to safe sodium hypochlorite. Two plants for production of low-concentrated sodium hypochlorite are in operation in St. Petersburg – at the Southern Waterworks (since 2006) and at the Northern Waterworks (since 2008).

Another technology used by Vodokanal for over several years is a powdered activated carbon (PAC) dosing system, which ensures removal of odors and oil products.

Since 2011, the Southern Waterworks has been operating a new K-6 treatment block which utilizes the most advanced water technologies capable of coping with any changes of the Neva water quality.    

K-6 water treatment block includes the following major process stages

- pre-ozonation (ozone is extracted from the air on site);

- clarification: coagulation, flocculation, sedimentation in lamellar clarifiers;

- filtration in two-layer (sand and activated carbon) rapid gravity filters;

- disinfection, first step: sodium hypochlorite in combination with ammonia sulfate (sodium hypochlorite is successful in eliminating bacteria);

- disinfection, second step: UV-treatment (eliminates viruses).

Advantages of the new block:

- guaranteed quality of potable water regardless of the Neva water condition;

- reduction of the environmental load on the Neva River (backwash water is not discharged into the river but is treated and used again);

- dewatering of sludge generated in the course of water treatment.

Vodokanal is proud of its unique system of water quality biomonitoring - diagnostics of the functional status of crayfish and fish.

The method developed by the Environmental Safety Research Institute under the Russian Academy of Sciences consists of measuring the local crayfish cardiorythm and analyzing the behavior of fish. If the water from the Neva contains toxic substances, the heart rate of crayfish increases, and the behavior of fish changes significantly. Now, the biomonitoring system is used at all waterworks in the city.

 The "staff" of the Main Waterworks includes 12 crayfish. Their working schedule: two days in the aquarium under supervision, then four days of rest and active eating. Vodokanal employs male crawfish only.