Background The closing of old industrial landfills – particularly those located in East Germany, the Czech Republic and Slovakia – requires substantial amounts of technical material. For example, the two large landfill sites at Leuna and Schkopau, which cover a total surface area of 5 million m², require more than 8 m3 million of natural construction material to obtain the surface profile and sealing, and more than 6 m3 million of top soil for providing the recultivation layer. Alternatives to natural construction material, however, are available. Waste of low organic content can be converted to substitute material while ensuring long-term stability as carbon dioxide (CO2) sink is obtained. Objectives The CONWASTE project aimed to show that the conversion of specific volume of waste material is a practicable method of producing site-specific sealing and cultivation layers without recourse to natural resources. It had already been confirmed on laboratory and small-scale experiments and the demonstration project was set up to prove its viability on a larger scale. A major objective of the project was the conversion of waste known as "diagnetic inertisation" to get an impervious disposal body. The production of the substitute material depends on the location and type of waste of the disposal. At the start of the project, no facility was producing surface sealing layers made of converted waste. Results The project’s CONWASTE surface sealing system of landfills proved efficient in reducing the vertical infiltration of precipitation water. The state-of-the-art sealing system consists of a material mix of mineral waste, industrial ashes and waste from the cement industry. The material mix was processed by a treatment plant, which is located on site at the landfill area. The environmental benefits of the project are: Reuse of waste materials; Avoiding the disposal of the waste material in other waste dumps; No exploitation of natural resources such as for example clay, sand and cultivated soils; Reduction of spreading waste materials in natural surroundings (sewage waste as fertiliser) and thus reduction of the dispersion of pollutants; and Creation of a spatially tight network between waste producers and waste material exploiters and thus significant reduction of the dispersion of pollutants and reduction of transportation.During the final stage of the project – as a result of CONWASTE findings – the beneficiary officially applied for permits to use the sealing and cover system also for the other landfills in the Saxony-Anhalt region of Germany that it owns. Meanwhile the authorities gave the go ahead. It will have repercussions for the closure of other sites. The CONWASTE sealing system is considerably more cost effective than conventional systems and the material mix used for the sealing system can store CO2, which mitigates the negative effect of carbon emissions to global warming. The project also has the added value of enabling the cultivation of layer biomass for renewable energy even though these areas are not suitable for food production. Further information on the project can be found in the project's layman report (see "Read more" section).