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Removal of potentially toxic metals from sewage sludge using EDTA

Abstract:

Sewage sludge has the potential to be used as a fertilizer in agriculture because of its high nutritional value, but it is often contaminated with toxic metals (TM). This study investigated whether ReSoil® technology, based on the use of EDTA (50, 70, and 100 mmol l-1), efficiently removes TM from sewage sludge collected after aerobic (blato1) and anaerobic (blato2) treatment. The highest removal efficiency of Pb was achieved in blato1 (up to 60 %) and of Zn and Cu in blato2 (up to 55 and 29 %, respectively). The content of nutrients did not change significantly after remediation, only available phosphorus decreased up to 1.7-times in blato2, but its content remained high (489-510 mg 100-1g-1). After remediation, the concentration of all metals, except Zn, in the leachates was below the limit for non-hazardous substances. To demonstrate the possibility of recycling process solutions and EDTA, blato2 was washed in 5 consecutive batches with 50 mmol l-1washing solution, removing on average 28 % Pb, 48 % Zn, 35 % Cu, 30 % Mn, and 10 % Fe. ReSoil® technology removes metals from sludge and preserves its nutritional value. However, the efficiency of the technology depends on the treatment process used in the wastewater treatment plant.