Treatment processes

Water treatment processes

  1. Surface water is collected to Lake Ülemiste and directed to Water Treatment Plant.
  2. Raw water passes through screens and microfilters, which remove algae and suspended solids from the water.
  3. Water is channelled into reservoirs, where a mixture of ozone and air is injected into the water to oxidize organic substances.
  4. A water treatment chemical coagulant is added to clarify the water.
  5. During the clarification phase suspended solids, chemical flocks and precipitates are removed from the water.
  6. Water passes through filters. In summer, dependent on the quality of raw water coming into the plant, activated carbon may be added in order to remove any remaining particles and to improve the taste of the drinking water.
  7. Chlorine is added to the water for disinfection purposes.
  8. The water is directed to drinking water reservoirs, from where it is pumped to the city water network in accordance with demand.

Wastewater treatment processes

  1. Wastewater collected through the sewerage network is directed into the Main Pumping Station. Storm water is also collected into the combined sewerage system and directed to the Main Pumping Station.
  2. Storm water collected in the areas of separate sewerage network is led to the storm water outlets through a separate storm water network.
  3. The first stage of wastewater treatment is the mechanical treatment stage. In that stage, wastewater is screened to remove larger solids and the grit removal tanks remove grit and sand from the wastewater.
  4. Smaller solid particles are removed in the primary sedimentation basins, formed sludge is removed from the process.
  5. Coagulant is added to the wastewater in order to chemically remove phosphorus.
  6. For biological treatment, wastewater is conducted to the aeration tanks, where the vital activity of various bacteria (activated sludge) helps to remove nitrogen and biologically decomposing substances from wastewater. To ensure a living environment suitable for the bacteria and to make their work more efficient, air and additional carbon in the form of methanol are injected.
  7. Activated sludge that has formed in aeration tanks is settled in the secondary sedimentation basins.
  8. Additional volume of nitrogen and biodegradable pollutants are removed from wastewater in biofilter as a result of the vital processes of the bacteria. Additional carbon in the form of methanol is added to increase the efficiency of the work of the bacteria.
  9. Treated wastewater i.e. effluent is pumped via a deep sea outlet into the sea.
  10. Sludge removed during the different phases of the treatment process is pumped to the sludge treatment unit.
  11. Sludge is digested and stabilized in anaerobic digesters where bacteria make the organic matter decompose.
  12. The biogas created in the course of anaerobic sludge digestion is used for the technological process and heating the plant buildings.
  13. The stabilized sludge is dried and mixed with peat.
  14. The outcome – sludge mixture with high nutrient content - is used in cultivation.