Effect of Thermal Drying and Chemical Treatments with Wastes on Microbiological Contamination Indicators in Sewage Sludge

摘要

This work aims to evaluate the microbiological contamination of sewage sludge (SS) collected in urban wastewater treatment plants (WWTP) from Portugal. Two types of SS were considered: urban mixed (UM) and from anaerobic digestion (AD). The two types of samples were characterized in relation to the main physical and chemical parameters, as well as the microbiological contamination ( and spp). Then, sanitation tests were conducted through thermal drying and chemical treatments. Towards a circular economy, industrial alkaline wastes (green liquor dregs - GLD, lime mud, coal fly ash, eggshell) were tested as alternatives to lime. Only six out of nineteen samples complied with the legal limits for both microorganisms. However, drying at 130 °C sanitized selected samples below the limit, regardless of the initial moisture or contamination. Additionally, CaO (obtained from eggshell) led to the complete elimination of at any dosage studied (0.05–0.15 g/g SS ). GLD evidenced the ability to reduce contamination at room temperature, but not enough to comply with the legal limit. In general, this work highlights the need to sanitize the SS before its application to the soil, and the positive role of some wastes on this goal.