Environmental impact on use of perennial energy crops for biogas

Abstract

Anaerobic digestion of biomass is usually used for treatment of manure or other residues, but harvested crops may also be used as co-substrate which increases the profitability of the system. One of the main crops for biogas production still is maize, but it is expected that this monoculture could be replaced by perennial grasses. Perennial grasses are high yielding, do not require much management, their chemical composition is suitable for biogas production and they may increase the biodiversity as well as improve soil properties. The aim of the study was to analyse the greenhouse gas emissions and CO2 savings in the process biomass – biogas – biomass. The LCA analysis was conducted using the SimaPro software where inputs were based on experimental investigation of perennial grass cocksfoot (Dactylis glomerate) yield and biogas produced at lab scale biogas digester at mesophilic conditions. The results of the experiment present the productivity of cocksfoot varies due to the year of sward use, climate conditions and rate of fertilizers applied. The increase in biomass yield has significant influence on the biogas production boundary. The energy input is mainly influenced by the type of fertilization and biomass yield. When comparing global warming potential, the results found reveal that energy generation through biogas from perennial grass during its 6 years vegetation lead to significant reduction of emissions of CO2 to atmosphere. Application of organic digestate for fertilisation strongly reduces CO2 emissions by avoiding mineral oil-based energy input for mineral nitrogen fertilisers. Even additional digestate transportation to the fields does not overcome mineral fertilisation impact. Perennial grass processing into biogas has positive effect on the environment in terms of the GHG potential and creates sustainable closed cycle.