Environmental life cycle assessment of different biorefinery platforms valorizing municipal solid waste to bioenergy, microbial protein, lactic and succinic acid

The progressive exhaustion of fossil energy resources and the environmental problems provoked by the excessive use of these resources have driven us to transit from a fossil fuel dependent economy to a more bio-based economy. In this regard, exploiting the organic fraction of municipal solid waste (OFMSW) for producing high value bioproducts and bioenergy under a biorefinery approach has attracted great interest. This paper presents the state of the art of urban biowaste biorefinery concepts. Accordingly, different novel valorization pathways, namely single cell protein, biosuccinic acid, and lactic acid, as well as bioenergy production were consolidated into some scenarios. Moreover, successfully tested hydrogen-assisted biological biogas upgrading was also incorporated into some scenarios as energy source for methanotrophs to upcycle nitrogen rich digestate into single cell protein. Upon the successful lab-scale experiments, different biorefinery platforms were developed and their sustainability was environmentally scrutinized using consequential life cycle assessment. The results obtained herein demonstrated that despite having different net environmental benefits, all the developed scenarios were eco-friendly solutions for valorizing biowaste into bioproducts and bioenergy. Scenarios including microbial protein production led to a saving of -58 to -147 kg CO2,eq/t biopulp in Climate change category, depending on the biorefining pathway. The net saving in Climate change category achieved for Succinic acid- and Lactic acid-based biorefinery was estimated at -73 and -173 kg CO2,eq/t biopulp, respectively. Biological biogas upgrading, if implemented, could increase energy payback by 9724 MJ/t biopulp and contribute more to the sustainability of other developed scenarios. Although scenarios with the main focus on bioenergy production outperformed others in terms of environmental sustainability, some complementary factors such as policy decisions, energy directives, economic issues, and carbon trade schemes must be taken into account in order to introduce the best valorization pathway.