The Waste Water Treatment Plant in Biržai is built in the area located 3 km east of the existing treatment plant. The designed flow of waste water to be treated: maximal – 3300 m3/day; average – 2800 m3/day. There is a possibility for capacity expansion during the second stage. Waste water is treated using the following processes: primary mechanical treatment, removal of organic substances, nitrification and denitrification; phosphor removal; sludge treatment; sludge consolidation tank, sludge drying. The erected equipment includes a receiving tank, a channel with bar screens, distribution chambers, two aerated circular flow grit chambers, grit drying site, soil dumping site. There are two process lines installed for biological treatment including two radial secondary settling tanks. Next to the aeration unit, technical rooms, a pump house for active sludge, an air blower unit, a sludge drying plant and an office building with auxiliary rooms were built. Installation of utility networks was also carried out. The Waste Water Treatment Plant is equipped with advanced and state-of-the-art process equipment built abroad – stirrers and pumps by FLYGT (Sweden), an aeration system by NOPOL (Finland), air blowers by AERZEN (Germany), a sanitary sewage receiving station by POMILTEK (Finland), secondary settling tanks by MULEBY (Denmark) – and in Lithuania (sludge scrapers-bridges, etc. by EKRA AB). There is a computerised central system for treatment process control. The central control system of the Waste Water Treatment Plant automatically takes records and sets such parameters as temperature, pH, amount of treated waste water, the amount of oxygen in an aeration tank, amount of circulating sludge, amount of circulating sludge, amount of surplus sludge, outdoor temperature, sludge level in the intermediate chamber, soil level in sanitary sewage in the discharge tank and waste water level in the pump house. Furthermore, there is a possibility to present other parameters.