Assuring the sustainable production of biogas from anaerobic mono-digestion

This study aims to analyse the potential environmental benefits and impacts associated to the anaerobic mono-digestion of two different substrates (pig slurry and maize silage). The Life Cycle Assessment methodology was applied in two full-scale Italian biogas plants (Plant A - pig slurry and Plant B - maize silage) in order to calculate the environmental profile of both systems with the aim of identifying the most suitable alternative from an environmental point of view. The study also includes credits due to avoided processes such as electricity production from the grid and mineral fertilisation as well as the conventional management of pig slurry regarding Plant A. The main outcomes show the importance of the feedstock composition on the environmental performance of these systems. While the assessment of Plant A ended up in environmental benefits in all impact categories as a consequence of credits related to replaced processes, its capacity for bioenergy production was limited. On the contrary, the use of maize silage as substrate provided a larger production capacity but it was also associated to negative environmental impacts. In this system, the cultivation of maize showed up as the largest responsible of the environmental impacts, specifically due to diesel fuel consumption in agricultural activities as well as on-site emissions linked to the application of fertilisers. A sensitivity analysis proved that the environmental profile of these bioenergy systems could be improved through surplus heat use as well as technological improvements such as the replacement of the traditional dehumidification unit by a chiller. © 2014 Elsevier Ltd. All rights reserved.