The sector of biomethane production is receiving growing consideration in Europe, as an evolution of the conventional exploitation of biogas in combined heat and power (CHP) generators. From the technical point of view, a common need is to have available tools and calculations suitable for analysing the environmental advantages of this approach. The present paper compares the emissions of air pollutants related to three options for biogas valorisation from waste anaerobic digestion (AD) plants equipped with a post-composting stage: (1) CHP generation and electric energy supply to an electricity distribution network, and biomethane production through (2) pressurised water scrubbing and (3) chemical absorption. In the last two cases, biomethane is considered useful for natural-gas buses for the public. The results demonstrate that option (1) produces a lower amount of global pollutants but a higher amount of local contaminants compared to options (2) and (3). Therefore, decision makers should consider what impacts are more important for the specific context in which an AD and post-composting plant will be located. In addition, this paper estimates the benefits in terms of energy balance and surface occupancy when a conventional composting plant is converted into an AD and post-composting process.
anaerobic digestion, biogas, biomethane, composting, emissions
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