Effects of oxidative processes in cover soil of solid waste landfills on volatile organic compounds (VOCs) - Il ruolo dei suoli di copertura in discariche RSU (Rifiuti Solidi Urbani) nei processi ossidativi su composti organici volatili (COV)

The composition of non-methane volatile organic compounds (VOCs) in the cover soil, at depths of 30, 50 and 70 cm, from Case Passerini landfill site (Florence, Italy) was determined by GC-MS. The study was aimed to investigate the VOC behavior as they are released from the landfill body and pass through the cover soil before being dispersed into the atmosphere. A total of 48 different VOCs were identified. The aromatic compounds represent the dominant group (71.5 % of total VOC), followed by alkanes (6.8 %), ketones (5.7 %), organic acids (5.2 %), aldehydes (3.0 %), esters (2.6 %), halogenated compounds (2.1 %) and terpenes (1.3 %). Cyclics, heterocyclics, N- and S-bearing compounds and phenols are ≥ 1 %. The vertical distribution of VOCs within the cover soil shows significant variations: alkanes, aromatics and cyclics decrease at decreasing depth, whereas an inverse trend is displayed by the O-bearing species. Total VOC and CH 4 concentrations at a depth of 30 cm in the soil are comparable, inferring that microbial activity is likely affecting the VOCs at a very minor extent with respect to CH 4. According to these considerations, to assess the impact of biogas as diffuse emissions from solid waste landfills, usually carried out on the sole basis of CO 2 and CH 4 soil flow rates, the physical-chemical behavior of VOCs in the cover soil, regulating the discharge of these highly contaminant compounds in ambient air, has to be taken into account. Furthermore, the soil vertical distribution of these species can be used to better evaluate the efficiency of oxidative capability of intermediate and final covers.