The innovative idea behind the ‘ECO’ project is the combination of waste water treatment with the separation of CO₂ from industrial flue gases. For this purpose, the formation of gas hydrates is combined with the use of adsorbents made from renewable raw materials in order to remove both pollutants such as heavy metals from industrial wastewater and the greenhouse gas CO₂ from industrial waste gases in a single step.

Gas hydrates are ice-like, crystalline solids formed from gas molecules (such as CO₂) and water molecules, whereby the water molecules form a three-dimensional network of defined cages via hydrogen bonds. The cages are stabilized by the inclusion of gas molecules.  Gas hydrates form under elevated pressures and at low temperatures conditions if sufficient quantities of gas and water are present. If wastewater contaminated with heavy metal and salt ions is used as the aqueous phase for gas hydrate formation, salt and heavy metal ions enrich in the aqueous phase, as only water and gas molecules are primarily involved in the formation of gas hydrates. However, gas hydrates are not just suitable for the treatment of waste water, but also for the purification of gases, as certain gas molecules are preferentially incorporated into the hydrate structure. In a gas mixture containing carbon dioxide (CO₂) in addition to nitrogen, CO₂ enriches in the hydrate structure, while the gas phase is depleted of CO₂.

The use of adsorbents made from renewable raw materials fulfils two functions here:

(1) Firstly, the adsorbent binds a large number of impurities from the concentrated, highly contaminated liquid phase that remains after separation of the gas hydrates, whereby the adsorbent can then be easily separated from the aqueous phase. 

(2) Secondly, we expect that the adsorbent is very likely to promote gas hydrate formation, so that hydrate formation can be carried out at lower pressure or higher temperatures and thus more economically than in current protocols.

The joint project is being carried out at the GFZ (coordinator) and the University of Potsdam.