Characterization of the chemical contamination of the organic fraction obtained from separate waste collection within the waste recovery value chain

Nowadays, international and national waste directives prioritize not only the recycling of wastes, but also material and energy recovery from wastes themselves. Among the several waste categories, organic wastes (including its fraction deriving from solid urban wastes-FORSU) can be converted into new resources, re-entering into the production cycle through the anaerobic digestion and the composting practices. Such processes promote the recovery both in terms of energy and material, producing biomethane and compost respectively, thus closing the circle of circular economy. However, one aspect that must be considered is the quality of the recovered products so obtained, which is strongly dependent from the quality of the waste feedstock. Indeed, the assessment of contamination by organic and inorganic micropollutants possibly present in FORSU is of mandatory importance to produce a high-quality compost, which is frequently used as a soil improver and that is demonstrated to contribute, together with the application of sustainable agricultural practices, to reduce desertification and soil erosion. Differently from compost, methods to evaluate the contamination from organic micropollutants in FORSU are rarely investigated. Based on the above-mentioned assumptions, the aim of the presented work was to innovatively develop an analytical method for the extraction and quantification of selected organic and inorganic micropollutants in FORSU samples. In detail, this study focused on the determination of 16 polycyclic aromatic hydrocarbons (PAHs), and 14 polychlorinated biphenyls (PCBs, including dioxin-like compounds), as well as toxic metals (Sn, Cd, As, Cr, Ni, Pb, Sb, Se). To what concern organic micropollutants, a microwave assisted extraction (MAE) technique was successfully optimized to extract PAHs and PCBs, through the study the effects of extraction temperature and solvents. Purification of the extracts was obtained by means of a silica-based solidphase extraction cartridge, to promote the elimination of co-extracted interfering polar compounds, followed by a sulfuric acid treatment, to oxidize organic interfering species still present. The analysis was carried out by means of gas chromatography coupled with mass spectrometry (GC-MS). Extraction yields of the optimized method, calculated after fortification of FORSU samples with isotopically marked surrogates, were quantitative for all the analytes, with RSD% below 8.6%, despite the complexity of the matrix. For metal analysis, the sample was mineralized by microwave-assisted procedure with HNO3 and H2O2, and the analysis were performed by inductively coupled plasma mass spectrometry, ICP-MS. Finally, both the methods were applied to the quantification of target analytes in FORSU samples belonging from a local treatment plant (Piedmont, Italy), comparing detected concentration with the only national legislative requirement, i.e. DGRV 235/09 normative.