Wastewater treatment technologies

Wastewater treatment in St. Petersburg comprises of four main stages:

  • mechanical treatment
  • biological treatment
  • chemical treatment
  • disinfection

 The sludge produced in the course of wastewater treatment undergoes:

  • dewatering
  • incineration

The processes charts of the wastewater treatment plants, which receive wastewater from the combined (household/runoff) sewerage system, include the following stages of wastewater and sludge treatment:

  • Mechanical treatment is designed for removing large contaminants and mineral suspended matter from wastewater by means of screens, sand traps, primary sedimentation tanks.
  • Biological treatment is designed for removing suspended matter remained in wastewater after mechanical treatment, as well as dissolved organic contaminants. The treatment is performed by microorganisms in the activated sludge. Wastewater is treated in aeration tanks, secondary sedimentation tanks.
  • Chemical treatment is designed for chemical removal of phosphorus phosphates.
  • Tertiary treatment. Since almost all water bodies in St. Petersburg are attributed to fishery basins, the requirements for the quality of effluent discharged into water bodies in terms of suspended substances is less than 3 mg/l. Therefore, to stabilize the quality of effluent, it is necessary to introduce tertiary treatment (post-treatment) at all WWTPs. For now, the tertiary treatment is introduced only at WWTPs in Repino and Petrodvorets.
  • Disinfection. Disinfection of the effluent is necessary to meet the requirements of the following regulatory documents:

- Article 60 of the Water Code of the Russian Federation; 

- clause 4 of SanPiN "Sanitary and epidemiological requirements for protection of coastal waters of the seas from pollution in places of water use of the population”;

- clause 4 of SanPiN "Hygienic requirements for surface water protection".

Disinfection by means of UV has been implemented at WWTPs in Repino, Sestroretsk, Petrodvorets and at the South-West Wastewater Treatment Plant.

  • Sludge treatment. The main goal at the stage of treatment of sludge produced in the course of wastewater treatment is to:

‐ minimize sludge volumes

- eliminate negative impact on the environment (smell, pathogenic microflora)

The optimal solution for the disposal of sludge generated at wastewater treatment plants is the incineration of the dewatered sludge. Advantages of incineration:

  • Reduction of the amount of generated sludge by 10 times
  • No pathogenic microflora and unpleasant odors in the ash

In order to reach the quality indicators of wastewater treatment in accordance with the recommendations of the Helsinki Commission, SUE “Vodokanal of St. Petersburg” constantly modernizes biological treatment facilities by introducing enhanced nutrients removal. A modern scheme of biological treatment of Cape Town University (UCT) has been introduced at the South-West WWTP and Sestroretsk WWTP. The wastewater treatment process developed by Johansburg University (JHB) has been implemented at Petrodvorets, Repino and Pushkin WWTPs. These technological solutions allow adjusting the biological treatment system, regulating the volume of recycles and oxygen supply for aeration. As a result, in case of any changes in external factors that affect the treatment process, such as wastewater temperature and input concentrations of contaminants, it became possible to choose the optimal mode and ensure the required quality of treatment. Projects for the reconstruction of the municipal wastewater treatment plants provide for the modernization of all biological treatment facilities with the use of effective UCT and JHB technological solutions. The work is already underway to upgrade the aeration tanks at the largest wastewater treatment plants – the Northern WWTP and the Central WWTP. To enhance the removal of phosphorus and stabilize treatment quality parameters, the method of chemical sedimentation of phosphorus has already been implemented at all wastewater treatment facilities in the city. The chemical treatment of wastewater is when, after dosing the chemical agent, the iron forms an insoluble compounds with phosphates, and such compounds are removed from the system together with sludge. After the introduction of chemical treatment at all plants, the treated effluent consistently meets the HELCOM recommendations - no more than 0.5 mg / l of total phosphorus. To improve wastewater treatment technologies at wastewater treatment plants, in 2018, Vodokanal:

  • completed the 1st stage of reconstruction of the largest treatment plant - the Northern WWTP;
  • finalized the reconstruction of no.5 and no.6 aeration tanks at the Central WWTP using the JHB enhanced nutrients removal technology;
  • completed the construction of new wastewater treatment plant in the settlement of Molodezhnoye with the introduction of biomembrane process;
  • finalized repairing of the aeration tank at Pontonny WWTP;
  • continued capital repair of sludge incineration lines of SIPs at the Central WWTP, Northern WWTP and South-West WWTP.

In 2018, the efficiency of wastewater treatment at the plants of SUE “Vodokanal of St. Petersburg” was more than 98% for suspended solids and BOD; 95.0% - total phosphorus and 74% - total nitrogen.