Effects of massive desiccation of olive waste residues on air quality

Abstract

New industries are proliferating in the recovery of agri-food wastes, such as those involved in the revaluation of alperujo, generated in the production of olive oil. Despite the potential environmental benefits, their activity is not exempt from new forms of emissions, aggravated by the massification of waste treatments. This work reports a six-month field campaign carried out in an alperujo desiccation plant which can serve as a proxy for these emerging industries in the Mediterranean countries. The study focused on air quality parameters, covering criteria pollutants, metals and microbiological load of particulate matter and the characterization of volatile organic compounds (VOCs). The results show a slight contribution of the factory to the NOx levels in the surroundings (3.0-12.5 μg/m³). Statistically significant effects were not observed for ozone, CO, SO₂, or PM₁₀. Concerning the levels of metals, concentrations were low and calculated health risk indexes indicated safe conditions in the area. The most abundant elements were Na (6.5 × 10² ng/m³), K (4.0 × 10² ng/m³), Al (2.7 × 10² ng/m³), Zn (2.1 × 10² ng/m³), Ca (2.16 × 10² ng/m³), Fe (3.6 × 10¹ ng/m³) and Mg (3.2 × 10¹ ng/m³). Bacterial counts, with a mean value of 15.9 CFU/m³, showed a seasonal shift, mainly explained by weather (air moisture and temperature) and PM_2.5 concentration. The genomic analysis showed Cutibacterium as the dominant genus during the cold months while Bacillus predominated in the warm season. The VOCs with higher average concentrations were acetic acid (130 μg/m³), nonanoic acid (124 μg/m³), benzoic acid (29.7 μg/m³), octanoic acid (19.9 μg/m³) and nonanal (4.70 μg/m³), with the rest of compounds in concentrations below 4 μg/m³. Odorant pollutants with the greatest contribution to olfactory nuisance were aldehydes (from pentanaldehyde to decanaldehyde), acetic acid and phenol. Although the observable effects of the waste treatments were low, several parameters showed an influence on the environment which should be assessed to foresee and prevent long-term consequences.