Life cycle assessment of Virginia mallow production with different fertilisation options

Abstract

Abstract Lignocellulosic crops can be a significant source of feedstock for the chemical industry. They can be grown on poorer soils, but fertilisation should be applied to achieve a considerable yield. The aim of the study was to determine the environmental impact of the production of Virginia mallow (Sida hermaphrodita Rusby L.) biomass fertilised with digestate: wet (WD), dried (DD) and torrefied (TD), obtained from an agricultural biogas plant and fertilised with mineral fertilisers (MF) and non-fertilised (C). All the fertilisers were applied at a rate equivalent to 85 and 170 kg ha−1 N. The system boundaries covered the production and use of digestate and mineral fertilisers, preparation of a field, growing Virginia mallow, harvest and transport of biomass from the field to the farm. The life cycle impact assessment of cultivation was done using the ReCiPe Midpoint method. The most beneficial effect on climate change was observed for utilisation of dried and torrefied digestate. The most adverse effect on human toxicity was observed when the TD was applied at both fertilisation rates. Higher particulate matter formation for all the growing options than for C resulted from production of fertilisers and use of machines. The lowest impact on terrestrial acidification was observed in the MF 85 option and the highest was in TD 170, which resulted mainly from high field emission. The use of digestates and mineral fertilisers resulted in an increased effect on freshwater eutrophication (30–56-fold). Torrefaction of digestate had the largest impact on terrestrial ecotoxicity. The greatest impact on fossil depletion was found for MF 170. The impact category with the highest normalized score was freshwater eutrophication. The production of Virginia mallow intended for bioproducts can fulfil the condition of low GHG emission. The application of fertilisation in all forms affected the environment more in the other impact categories than the base scenario. The application of WD 85, WD 170 and DD 85 could be recommended for Virginia mallow instead of mineral fertilisers, whereas DD 170 and TD at both rates had the most adverse environmental effect.