The project IRAS ATCZ183 realized by biochemists from our Faculty of Science and Austrian colleagues was awarded as "Best Practice" at an international conference focused on the outputs of the European INTERREG V-A AT-CZ programme. As part of the project, scientists have been looking for suitable ways to use bacteria to tackle the problem of metals that accumulate in fly ash and slag during thermal waste disposal, which then burden the environment.
The researchers believe that with the help of bacteria and appropriate recycling biotechnologies, metals can not only be removed from the end products of waste incineration but even put back into production, thus promoting our raw material self-sufficiency and circular economy. Scientists have focused on the metals found in high concentrations in slag and fly ash, which are produced during waste incineration and then landfilled or used in construction. However, the metals contained in slag and fly ash remain unused and are even harmful to the environment.
Scientists tested the proposed procedure thanks to an international project. They employed the bacteria in the proposed procedure twice. First, they were used to produce sulfuric acid and surfactants in a bioreactor. The sulfuric acid and other metabolites produced in this way were injected into another bioreactor with slag or fly ash, where they were acid-leached. This leaching was further enhanced by acid-forming bacteria, some of which could oxidize iron.
The innovative contribution of the proposed approach is to recover the dissolved metals from the solution so they can be reused. This is where the bacteria come in again, albeit different from the acid-forming ones used in the first phase. These are the fermenting bacteria that are found, for example, in activated sludge in wastewater treatment.
"The metal-containing leachate is injected into a microbial fuel cell, the principle of which is the decomposition of organic matter (preferably organic waste) by bacteria in the anaerobic environment of the anode. This metabolic process produces electrons and protons. The electrons flow towards the cathode to form an electric current, and the protons also pass through the membrane towards the cathode, where they combine with oxygen to form water. Pure metals such as zinc and copper are then produced at the cathode," described Jiří Kučera from the Department of Biochemistry, Faculty of Science, MU.
The Environmental Biotechnology research group headed by Martin Mandl from the Department of Biochemistry, Faculty of Science, MU, collaborated on the IRAS project with the metallurgical center K1-MET GmbH in Linz, the University of Natural Resources and Life Sciences (BOKU) in Tulln and the Energy Agency Vysočina. This successful project with cross-border cooperation is followed this year by OPTIMO (ATCZ 291). The new project aims to increase the efficiency of the production of biogenic sulfuric acid, which can be used for the (biological) leaching of metals from secondary raw materials.
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