Published in Scientific Papers. Series E. Land Reclamation, Earth Observation & Surveying, Environmental Engineering, Vol. XIV
Written by Denisa BACALU-RUS, Lucian COPOLOVICI, Dana COPOLOVICI, Ioan BOTH, Maria MIHĂILESCU
Sludge from sewage treatment plants is a byproduct of wastewater treatment processes, consisting of solid particles, microorganisms, and organic and inorganic substances. It is generated during sedimentation and digestion processes to remove contaminants such as organic matter, heavy metals, and chemicals from water. Before storage or disposal, sludge is typically treated to reduce its volume and eliminate pathogens. Standard treatment methods include dehydration, biological stabilization, and incineration. Depending on its composition, treated sludge can be repurposed for agricultural use as fertilizer, provided it meets strict regulatory standards to prevent soil and groundwater contamination. In Romania, sewage sludge is generally classified as waste under European and national legislation. According to the European Union Waste Directive 2008/98/EC, sludge is considered waste if it cannot be safely treated, recovered, or reused. Studies have explored its potential environmental risks, including soil contamination and its suitability as a fertilizer. This article presents a structural sludge analysis, focusing on its physicochemical properties and moisture content. Experiments were conducted to evaluate the behavior of sludge samples under varying temperatures, exposure durations, and drying conditions. Results showed that evaporation rates increased with temperature, with significant differences observed between ventilated and non-ventilated drying environments. At temperatures ranging from 50°C to 100°C, sludge mass consistently decreased, with the lowest masses recorded in ventilated drying processes at 100°C. In non-ventilated conditions, the percentage of evaporation increased progressively with prolonged heat treatment. Additionally, heavy metal concentrations in the sludge were experimentally determined and found to be below the limits imposed by national legislation. These results confirm that the analyzed sludge samples are suitable for agricultural use, aligning with regulatory requirements.
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