Environmentally Sustainable Biogas? The Key Role of Manure Co-Digestion with Energy Crops

Alessandro Agostini,David Baxter,Luisa Marelli,Stefano Amaducci,Vincenzo Tabaglio,Jacopo Giuntoli,Ferdinando Battini,Monica Padella

doi:10.3390/en8065234

Abstract

We analysed the environmental impacts of three biogas systems based on dairy manure, sorghum and maize. The geographical scope of the analysis is the Po valley, in Italy. The anaerobic digestion of manure guarantees high GHG (Green House Gases) savings thanks to the avoided emissions from the traditional storage and management of raw manure as organic fertiliser. GHG emissions for maize and sorghum-based systems, on the other hand, are similar to those of the Italian electricity mix. In crop-based systems, the plants with open-tank storage of digestate emit 50% more GHG than those with gas-tight tanks. In all the environmental impact categories analysed (acidification, particulate matter emissions, and eutrophication), energy crops based systems have much higher impacts than the Italian electricity mix. Maize-based systems cause higher impacts than sorghum, due to more intensive cultivation. Manure-based pathways have always lower impacts than the energy crops based pathways, however, all biogas systems cause much higher impacts than the current Italian electricity mix. We conclude that manure digestion is the most efficient way to reduce GHG emissions; although there are trade-offs with other local environmental impacts. Biogas production from crops; although not providing environmental benefits per se; may be regarded as an option to facilitate the deployment of manure digestion.

Highlights

According to the International Panel on Climate Change (IPCC), human interference with the climate system is occurring, and climate change poses risks for human and natural systems [1].In order to contribute to the global efforts to reduce Green House Gases (GHG) emissions and limit global warming, the European Union set an ambitious GHG reduction target, −20% compared to 1990 levels, to be achieved by the year 2020
In this work we have analysed the environmental impacts of electricity production via anaerobic digestion of three biogas production Our analysis shows that the introduction of biogas production from dairy farm manure, and its conversion to electricity, decreases significantly the GHG emissions of the farm in absolute terms, thanks to the avoided GHG emissions that would otherwise derive from the management of the raw manure
When biogas is produced from digestion of maize or sorghum silage, the resulting GHG emissions are of the same order of magnitude of the Italian electricity mix

Summary

Introduction

According to the International Panel on Climate Change (IPCC), human interference with the climate system is occurring, and climate change poses risks for human and natural systems [1].In order to contribute to the global efforts to reduce Green House Gases (GHG) emissions and limit global warming, the European Union set an ambitious GHG reduction target, −20% compared to 1990 levels, to be achieved by the year 2020. European member states are committed both to increase their share of renewable energy sources and to reduce their GHG emissions. No mandatory sustainability criteria have been formulated at a European level for solid biomass and biogas used for power and heat production. The European Commission (EC) provided recommendations to Member States to develop criteria similar to the ones designed for transport biofuels [2]. A recent document from the EC presented the state of play of bioenergy in the EU [3] and introduced updated typical and default GHG emissions values for a large selection of bioenergy pathways, including several pathways for the production of power by anaerobic digestion of manure, maize and biowastes [4]. This document suggests the application of a GHG emission savings threshold of at least

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