Volatile Organic Compounds (VOCs) emitted during the composting phase of different agricultural wastes

Although compost production for agricultural use is becoming one of the best practices for reusing livestock effluents and agricultural waste, little is known about the emission of VOCs from this process. For this reason, a methodology was developed to determine the quantity and type of VOCs emitted by microbial degradation in an aerobic environment of buffalo farm effluents, previously used for biogas production in an anaerobic environment, and olive mill wastes (OMWs). In both cases, composting was carried out in laboratory, by using aerated reactors with and without biochar. VOCs sampling was carried out simultaneously with the production of CO2 and other gases. Data show that composting of both matrices produces a significant amount of VOCs, which is always slightly higher in reactors without biochar. The most abundant components were found to be highly volatile carbonyls, such as formaldehyde and acetone. However, both quantity and composition of VOCs emitted from the composting of the two matrices differed substantially. Composting the buffalo matrix, already partially degraded anaerobically, produced a higher emission of VOCs with a much higher presence of alcohols. In contrast, the composting of the OMWs matrix was characterized by a greater presence of cyclic and aromatic compounds derived from lignin decomposition. In both cases, reduced VOCs (monoterpenes) were identified, albeit at trace levels, as well as compounds (theaspiranes), whose origin could be attributable to additives or components derived from OMWs.