“Vilniaus vandenys” collects and treats wastewater in Vilnius City, Šalčininkai, Švenčionys and Vilnius districts. The company operates 6 wastewater treatment plants: the plant of Švenčionys, Švenčionėliai, Nemenčinė, Šalčininkai, Eišišiškės and the largest wastewater treatment plant in Lithuania – Vilnius City Wastewater Treatment Plant.
More than 1,497 km of sewerage networks and 237 sewage pumping stations are in operation to collect and transport wastewater to sewage treatment plants.
In Vilnius City Centre, in the Old Town, part of Antakalnis and Naujamiestis, there is a mixed wastewater treatment system, which receives both wastewater and rainwater. Other districts have separate sewage and rainwater treatment systems.
All of the wastewater of Vilnius City goes to the Vilnius Wastewater Treatment Plant, where it is treated mechanically and then biologically:
The process of mechanical wastewater treatment:
1. The wastewater flows through large 10 mm mesh grates that trap large debris.
2. The wastewater is fed through finer grates with 6 mm gaps.
3. The wastewater is discharged into sand traps, where the sand is trapped – it is heavy and settles to the bottom.
4. The wastewater is discharged to primary settling tanks. This is where solid, organic and other undissolved particles are deposited. This produces primary sludge, which is directed through underground pipelines to a sludge tank.
Biological wastewater treatment process:
5. The wastewater is directed to aerotanks – activated sludge tanks. Here, wastewater is treated by micro-organisms: bacteria break down and consume the organic pollutants in the wastewater as food, while pumps blow air and mix the water to keep the activated sludge from settling and to provide the micro-organisms with oxygen.
6. The treated wastewater is discharged to secondary settling tanks. These plants separate the treated water from the activated sludge. The treated water is directed to the outlet and the sludge to the sludge tank.
7. The water treated in the water treatment plant is discharged into the River Neris through a canal. The quality of the discharged wastewater is monitored by the wastewater laboratory of “Vilniaus vandenys.”