Sludge is a by-product of municipal sewage treatment plants, which, in addition to other pollutants, contains potentially toxic metals (PTM). It is precisely these that limit its use in agriculture, as they exceed the limit values set by law. The use of remedied sludge in agriculture leads to a sustainable method of sludge management due to the return of organic matter and nutrients, especially phosphorus, to the soil. In the master's thesis, we used an already existing technology of PTM removal from sewage sludge and adapted it for potential use as part of the process at sewage treatment plants. EDTA was used as a chelating agent for PTM binding and removal. In the first part of the experiment, we compared different concentrations of EDTA and found that 35 mM EDTA has the best ratio between PTM removal and affordability. The selected concentration of EDTA was then used to wash the sludge, consisting of anaerobic and aerobic sludge in a ratio of 1:8. In the anaerobic part of the experiment, we observed the effect of EDTA on methane production during the incubation of the samples, and later iron was removed from the sewage sludge, as its presence later hinders the removal of other metals. It was found that EDTA has no effect on methanogenesis, and the addition of citric acid accelerates this process. In the aerobic part of the experiment, the remaining PTM were removed from the mud by washing it three times. Based on measurements of sludge, process solutions and waste, we determined the efficiency of PTM removal from sludge. We found that the removal of metals from the sludge is sufficient for the concentrations to fall below the legal limit values for use in agriculture. The phosphorus content in the sludge before and after remediation does not differ significantly. We also successfully recycled EDTA and process solutions in the experiment, which contributes to the sustainability of the process, as it does not produce waste water.
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