Multi-technique characterization, contamination levels, and ecological risk evaluation in different sludges

ABSTRACT In the present study, three types of sludges were characterized (SR-refinery sludge, SS-municipal wastewater treatment sludge, and SW- drinking water treatment plant sludge) using advanced analytical approaches like XRD, FTIR, SEM, and XRF. Furthermore, the pollution load index (PLI), geo-accumulation index (I geo ), and risk index (RI) were used to determine the ecological risk assessment of ten heavy metals. SR is characterized by low crystallinity and high organic content, limiting its potential for recovery. SW features well-defined silicate and iron-phosphate phases with low organic content and seem suitable for adsorbents and ceramics. While, SS is rich in minerals with phosphate and sulfate phases and definitely worth utilizing for the recovery of phosphorus and fertilization purposes. The use of PLI, I geo , Er, and RI shown collectively implies that none of the investigated sites is at high risk of heavy metal contamination. The finding of this study, therefore, show that the levels of the presence of heavy metals in the sites are at acceptable limits thus minimizing the potential ecological and health-related risks accompanying with heavy metal pollution. Cluster analysis also demonstrates that the integrated characterization makes it possible to distinguish sludges, assess environmental quality, and indicate the main source of pollution, which is a foundation for developing targeted strategies for each sludge type.