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The aim of the VUB-ULB project SUBLIMUS is to develop a cheap and green way to harvest gold and silver from the sludge residues of the sewage treatment plants of the Brussels-Capital Region. Most of this sludge is currently incinerated and sent to landfill.

 

Project coordinator Dr Natacha Brion from VUB’s Analytical, Environmental and Geo-Chemistry research group: “In a world where primary raw materials are becoming increasingly scarce, it is crucial to evaluate the recycling potential of existing unused waste streams, such as sludge from sewage treatment plants.”

 

It is estimated that ores from mines, the traditional sources for metals such as lead, tin, zinc, gold and silver, will be exhausted in about 20 years. The reuse of metals will therefore become increasingly important, as will the search for ores in hard-to-reach places.

 

Precious metals such as gold, silver and platinum end up with other heavy metals (copper, zinc, lead etc) in sewage water via various processes: for example, erosion of gold and silver jewellery, use in medicines and disinfectants and emissions from diesel engines catalysts. These metals are contained in the sludge of the sewage treatment plants after the waste water is treated. Sludge has traditionally been used as a fertilizer in agriculture, but because of the high metal concentrations, this practice is now prohibited in Flanders.

 

“Large quantities of sludge from waste water treatment plants show toxic metal concentrations,” says project coordinator Dr Natacha Brion. “So far, there is almost no other solution than to dispose of it after incineration, with the associated costs and environmental risks. Extraction and recycling of metals from sludge is therefore not only a way of meeting the metal scarcity, it also makes it possible to turn a toxic waste product into a fully-fledged source of raw materials.”

 

Environmental benefits

For the SUBLIMUS project, three Brussels research groups are working together: VUB’s Analytical, Environmental and Geo-Chemistry (AMGC), ULB’s Engineering of Molecular NanoSystems (EMNS)  and Meurice R&D of the Haute Ecole Lucia de Brouckère. SUBLIMUS consists of three stages. First, researchers study the amount of precious and heavy metals found in the sludge. For this purpose, VUB researchers are carrying out measurements in sludge samples from the two Brussels treatment plants. In the next stage, they will investigate how these metals can be extracted from the sludge in an environmentally friendly way. Here, Meurice R&D researchers will investigate whether they can use special bacteria to “wash” metals from the sludge. Finally, VUB and ULB scientists are investigating how they can purify and recycle the precious metals from this metal mixture in an environmentally friendly way. An example is the development of specific gold-binding nanomaterials with magnetic properties that can be removed from the mixture with a magnet after bonding.

 

The research programme started in March 2019 and will continue until the end of February 2022. It is financed by Innoviris, the regional institute for research and innovation.