Recovering residues to save on raw materials
While thermally treating waste, we aim to recover as many materials as possible. We do this by means of a sophisticated ash treatment. Residues from our treatment processes replace valuable raw materials in our processes.
Ash treatment following thermal treatment
Of the total quantity of waste that we treat in the grate incinerators, less than 3% is deposited in landfills as residue fraction of ash treatment. The bottom ashes from our own installations, and possibly from other household treatment plants, are washed and sieved and all impurities removed. The ash-treatment installation in Doel processes the ashes into a useful end-product for the metal or construction industry:
- ferrous and non-ferrous metals are separated by various crushing, sieving and washing units and are sold to the metal industry as a secondary raw material;
- granulates are used for the construction of dykes and in construction, for example in foundation works, for their draining capacity, among other reasons;
- sand fractions are put to good use in construction and stability applications in landfills.
Residues replace valuable raw materials
We want to replace as many valuable and primary raw materials as possible with waste in our processes. The physicochemical units at the Antwerp plant treat industrial liquid and solid inorganic waste. This way, we replace auxiliary materials, such as lime and cement, as much as possible with residues from our processes, thus saving raw materials.
- In Physicochemistry 1, where we process liquid waste from metal treatment, we replace at least 50% of the quicklime (almost 1,000 tonnes), which neutralises the contamination, with residues from our incineration process. In addition, we use acid wastes instead of iron (III) chloride (FeCl3), which saves another approx. 600m³ of raw materials.
- In Physicochemistry 2, where fixed inorganic waste is mixed with cement, lime and chemical substances to catch polluted substances so that the waste can be disposed of, the cement is partially replaced by certain residues.
Useful applications in landfills
Indaver has tested how the ashes from the ash treatment can be used as filters for the landfill gas at the Hooge Maey landfill before it is processed in the engines. In the first phase, the ashes remove sulphur and CO2, after which an active carbon filter takes over. This lengthens the active carbon filter’s lifespan. Tests show that the residues are suitable for this (partial) desulphurisation of landfill gas. This is currently being studied for possible applications.
Another useful application at the landfill is for the final capping. Usually, clay is used for the water-inhibiting support layer. A significant quantity of clay can be saved by using Hydrostab®, a mixture of de-watered water purification sludge, a granular fraction, a filler fraction and water glass that was developed by Geo Milieu.