After years of planning, pandemic-era negotiations, global supply chain disruptions, and intense construction work, the Vilnius Wastewater Treatment Plant (WWTP) reconstruction project – one of the largest and most complex infrastructure initiatives in Lithuania – has been officially completed. Implemented by UAB Arginta, the nearly 50-million-euro reconstruction marks a new chapter in sustainable wastewater treatment for the capital city, improving capacity, efficiency, and environmental impact. Throughout the reconstruction, Arginta demonstrated not only engineering expertise but also flexibility under pressure, successfully delivering a flagship environmental project for Lithuania.
From delays to delivery
However, looking back, the path to modernising the Vilnius WWTP was far from smooth. The initial tender for the project had to be reissued four times, a reflection of both the high expectations and the constrained budget attached to the job. The urgency to replace the ageing infrastructure was driven by stricter EU environmental regulations and the increasing demands of a growing urban population.
Eventually, in August 2020, a breakthrough occurred. Despite ongoing global disruptions caused by the COVID-19 pandemic, UAB Arginta submitted a joint technical and financial proposal and was awarded the contract. Coordination between more than 15 engineers from Lithuania and Italy largely took place remotely, a logistical feat during the lockdown.
The first phase of reconstruction was completed in September 2023 and was primarily funded by the European Union, which covered 80 percent of the costs, easing the financial burden on Vilnius residents. The second phase wrapped up exactly a year later in 2024.
Construction through crisis: a timeline of resilience
While the initial lockdown posed coordination challenges, the subsequent years brought even more pressure. A second COVID wave and the geopolitical fallout from the war in Ukraine caused spikes in material and labour costs, further tightening already thin margins and testing the resilience of project schedules.
Despite these hurdles, the plant was reconstructed within the planned timeframe.
“The ability to complete such a large-scale, high-risk project during some of the most turbulent years in recent history speaks volumes about the capabilities of UAB Arginta,” said a representative from the project team.
Engineering marvel: the aeration tank and beyond
The centrepiece of the reconstruction is undoubtedly the massive aeration tank, comprised of six bioreactors with two compartments each. Spanning 138 metres in length and 216 metres in width, with a depth of 5.7 metres, this tank is the largest structure within the plant.
This component received special structural attention due to a serious accident in 1993 when a partition wall collapsed during testing. In the recent reconstruction, each bioreactor wall and floor was meticulously inspected, reinforced, and where necessary, retrofitted with new steel reinforcement. Consultations with original project engineers ensured both historical continuity and modern safety compliance.
Modernisation under operation: keeping the water flowing
One of the most technically demanding aspects of the reconstruction was maintaining continuous wastewater treatment operations. UAB Arginta developed bespoke bypasses and temporary flow diversions to allow uninterrupted service during construction. Every major subsystem – from sedimentation tanks to the pumping stations – was rebuilt without halting the plant’s critical operations.
“This kind of live-reconstruction is not only complex but risky,” said the lead engineer. “A single mistake could have affected thousands of residents and businesses.”
Key upgrades: a tour of innovation and sustainability
The project featured a comprehensive overhaul of the plant’s infrastructure and technology:
- new flow channels & measurement: Installation of two Venturi flumes (8,500 m³/h each) ensures precise flow tracking.
- preliminary treatment modernisation: A new building houses advanced screening, washing, and dewatering equipment for incoming wastewater.
- primary clarifiers: Three massive clarifiers now operate with Lithuania’s first screw-type sludge removal systems.
- biological treatment overhaul: The aeration tank now includes over 26,000 diffusers and is supported by a new blower station featuring seven high-efficiency turbo blowers.
- tertiary treatment: For the first time in Lithuania, a system is in place to remove microplastics larger than 10 µm using pile cloth filters and drum screens.
- advanced automation: The new SCADA system allows full remote control and energy optimisation, applying the "most open valve" strategy for reduced operational costs.
- air quality control: Biofilters with automatic humidification manage odour emissions, protecting the surrounding neighbourhoods.
Firsts in the Baltics: innovation paves the way
Among the cutting-edge features is the scum removal and treatment system. It collects scum using bridge-mounted screw conveyors and processes it through a Dissolved Air Flotation (DAF) system. The system separates emulsified fats and solids, achieving 95 percent removal efficiency and reducing scum moisture to under 60 percent. This is one of the first such systems in the region.
The tertiary treatment unit is another regional breakthrough. Besides reducing suspended solids to below 3.5 mg/l, it removes microplastics from the backwash water. A two-stage process, involving drum screens and screw presses, ensures 70 percent+ removal of synthetic debris.
The turbo blowers installed represent a leap forward in energy efficiency. With direct-drive turbines operating at around 15,000 RPM and no oil-based gearbox, maintenance costs are reduced and performance is optimised via frequency control.
With its upgraded systems, Vilnius WWTP now stands among the most advanced and environmentally responsible facilities in the Baltic region, an achievement that sets a new benchmark for the future of wastewater management in Eastern Europe.
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