Air quality in olive mill wastewater evaporation ponds: Assessment of chemical and microbiological pollutants.

Olive mill wastewater (OMW), a pollutant residue from the olive oil industry, is typically stored as sludge in evaporation ponds. This study examines the long-term emissions of OMW sludge and its impact on local air quality, analysing chemical pollutants like PM, volatile organic compounds (VOCs), and trace elements (TEs), along with microbial communities (bacteria and fungi). The study also considered meteorological conditions and back-trajectories to identify sources of these elements. The ecological risk index (ERI) was found to be over 720 due to high Hg levels in the sludge (19.0 ± 0.9 ng/g) and air (0.28 ± 0.13 ng/m³), indicating a significant ecological threat. VOCs, particularly oxygenated compounds such as aldehydes and phenol, contributed to the area's strong odour. Meteorological conditions and Sahara dust intrusions influenced bioaerosol loads and seasonal bacterial diversity, whose composition is closely associated with VOC concentrations. The results could contribute to a better understanding of the environmental dynamics in the OMW sludge evaporation ponds, and they could also assist in formulating effective management strategies.