Bottom ash is formed by incinerating non-hazardous waste at high temperatures of around 1000 °C and is a solid, porous, stone-like material.
At the end of the waste incineration process, the resulting bottom ash can be safely used for road construction, building foundations, the production of paving blocks, covering waste layers in landfills, landfill closure, and the construction of temporary roads on landfill sites.
Each year, Gren processes non-recyclable waste to generate clean energy for homes and businesses. About 25% of this waste becomes bottom ash, which Gren prepares for reuse instead of disposal. This initiative supports Lithuania’s transition to a circular economy, where nothing goes to waste and every material finds a new purpose.
Between 2021 and 2025, Gren has reused approximately 248,000 tonnes of bottom ash, equivalent to nearly 1 million tonnes of waste processed through circular use. What once would have decomposed in landfills is now the foundation of Lithuania’s roads, bike paths, and industrial sites.
Through research, innovation, and partnership, Gren proves that circular solutions are not just a vision – they are already shaping Lithuania’s infrastructure today. With every kilometre of road and every bike path built, Gren is transforming waste into value and helping create a cleaner, more sustainable future for everyone.
Reusing bottom ash delivers measurable benefits:
Gren’s bottom ash complies with strict environmental criteria: metal content ≤5%, organic carbon ≤3%, ignition loss ≤6%, and controlled leaching values. Before reuse, the material is conditioned for approximately three months to ensure stability and environmental safety.
The use of bottom ash connects daily operations with clear environmental and climate outcomes. By turning a residual stream into a certified secondary raw material, we reduce environmental impact while supporting circular construction and national climate objectives.
Bottom ash quality and reuse indicators are monitored and recorded, demonstrating how ESG commitments translate into real, measurable actions.
Gren’s bottom ash has been successfully used in multiple infrastructure projects, including:
These projects demonstrate how circular materials can safely and effectively replace imported natural aggregates, reducing both environmental impact and material costs.
In 2021, a unique road section was built in the Jurbarkas district where slag generated from waste-to-energy processing of non‑hazardous waste was used. This was the first project of its kind in Lithuania, aimed at conducting a comprehensive study of the road and determining the impact of slag on road performance during operation. In the one‑kilometre-long test section, 9,000 tonnes of slag were used. The slag was produced at the waste‑to‑energy plant of UAB Gren Klaipėda and prepared for use.
In 2025, a bicycle and pedestrian path was constructed on Sausio 15‑osios Street in Klaipėda using slag generated by Gren Klaipėda. During the works, nearly half a kilometre of the section from the intersection with Taikos Avenue to Tilžės Street was renovated. A bicycle path with a red asphalt surface and a pedestrian walkway paved with grey paving stones were installed.
Gren collaborates closely with the VILNIUS TECH Road Research Institute, whose studies have confirmed that bottom ash meets all environmental and engineering requirements for use in unbound road base layers.
This innovation was recognised with the 2024 Baltic Road Award for Scientific Innovation, acknowledging Lithuania’s leadership in applying circular economy principles to road engineering.
The awards are presented during the International Baltic Road Conference, which takes place every four years in one of the Baltic countries.
Explore how Gren transforms waste into energy that supports local communities and reduces landfill.
