Silvia Silvestri

Monitoring of volatile compound emissions during dry anaerobic digestion of the Organic Fraction of Municipal Solid Waste by Proton Transfer Reaction Time-of-Flight Mass Spectrometry.

Volatile Organic Compounds (VOCs) formed during anaerobic digestion of aerobically pre-treated Organic Fraction of Municipal Solid Waste (OFMSW), have been monitored over a 30 day period by a direct injection mass spectrometric technique: Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS). Most of the tentatively identified compounds exhibited a double-peaked emission pattern which is probably the combined result from the volatilization or oxidation of the biomass-inherited organic compounds and the microbial degradation of organic substrates. Of the sulfur compounds, hydrogen sulfide had the highest accumulative production. Alkylthiols were the predominant sulfur organic compounds, reaching their maximum levels during the last stage of the process. H(2)S formation seems to be influenced by the metabolic reactions that the sulfur organic compounds undergo, such as a methanogenesis induced mechanism i.e. an amino acid degradation/sulfate reduction. Comparison of different batches indicates that PTR-ToF-MS is a suitable tool providing information for rapid in situ bioprocess monitoring.

Biogas from the organic fraction of municipal solid waste: dealing with contaminants for a solid oxide fuel cell energy generator

The present work investigates electricity production using a high efficiency electrochemical generator that employs as fuel a biogas from the dry anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). The as-produced biogas contains several contaminants (sulfur, halogen, organic silicon and aromatic compounds) that can be harmful for the fuel cell: these were monitored via an innovative mass spectrometry technique that enables for in-line and real-time quantification. A cleaning trap with activated carbons for the removal of sulfur and other VOCs contained in the biogas was also tested and monitored by observing the different breakthrough times of studied contaminants. The electrochemical generator was a commercial Ni anode-supported planar Solid Oxide Fuel Cell (SOFC), tested for more than 300 h with a simulated biogas mixture (CH4 60 vol.%, CO2 40 vol.%), directly fed to the anode electrode. Air was added to promote the direct internal conversion of CH4 to H2 and CO via partial oxidation (POx). The initial breakthrough of H2S from the cleaning section was also simulated and tested by adding ∼1 ppm(v) of sulfur in the anode feed; a full recovery of the fuel cell performance after 24h of sulfur exposure (∼1 ppm(v)) was observed upon its removal, indicating the reliable time of anode exposure to sulfur in case of exhausted guard bed.