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Environmental Assessment of a Bio-Refinery Concept Comprising Biogas Production, Lactic Acid Extraction and Plant Nutrient Recovery

The process of nutrient recovery from biogas digestate and the extraction of lactic acid from silages is technically feasible, but so far no investigations are available on the environmental sustainability of these technologies in the context of the biogas production chain. The aim of the present study is to show whether the recovery of nutrients from digestate (NR) and the extraction of lactic acid from silages (LA) can be integrated in the biogas production process system in an environmentally sustainable way. The modelling in the present study is based on the standards DIN ISO 14040 and DIN ISO 14044 and the results are evaluated with respect to the 100-year global warming potential, the primary energy demand and the eutrophication potential. Results show that the recovery of nutrients from digestate can be a sustainable solution to the problem of surplus nutrients in biogas regions. Furthermore, lactic acid, which is extracted from silages can provide an environmentally sustainable source of income for biogas plant operators. The urgency of the nutrient surplus problem in these regions calls for increased research and the support of policy makers to foster development activities.