Environmental assessment of biorefinery processes for the valorization of lignocellulosic wastes into oligosaccharides

Abstract

The European Commission is adopting strategies in order to “closing the loop” of product life cycles in industrial production systems through better recycling and re-use under the perspective of circular economy. One of the most relevant goals in the application of this approach is to convert low-value side streams into more valuable products. In this sense, the conversion of lignocellulosic biomass into biofuels and chemicals is a major challenge not only from the technological but also from the economic and environmental perspectives. In this study, the production of pectin-derived oligosaccharides (POS) from sugar beet pulp (SBP) was environmentally assessed by means of the Life Cycle Assessment methodology under a cradle-to-gate approach. Two different scenarios at pilot scale were considered: Scenario 1 based on conventional autohydrolysis at high temperature and Scenario 2 based on enzymatic hydrolysis. The outcomes of this environmental study are highly dependent on the production yield of the target compounds (POS) and the valorisation strategy considered. In fact, the POS yield of the autohydrolysis approach is around 20% higher than in the enzymatic one. According to the results, Scenario 1 reports the worst results when a functional unit based on the amount of valorised material (100 kg of oven-dried SBP) is considered. However, the profile entirely changes when a unit based on the economic revenue (1 €) is managed. Therefore, attention should be paid on the selection of the functional unit since decision making strategies should highly depend on it. Without waiting for the opportunity to conduct LCA of already-developed processes of the biorefinery system, the development of new alternatives must be carried out with sustainability in mind. Accordingly, the proposal of valorisation strategies for secondary streams should include the analysis of the environmental impacts associated to each alternative, even at the pilot plant stage.