Circular bioeconomy: Life cycle assessment of scaled-up cascading production from orange peel waste under current and future electricity mixes

Orange peel waste (OPW) is present in large quantities both locally and globally, which makes them feasible input into the circular bioeconomy. However, due to their antimicrobial and anti-nutritional activity, they are problematic biomass, and proper waste management is yet to be determined. This life cycle assessment (LCA) quantifies the environmental performance of biorefinery producing limonene, citric acid, and animal feed from OPW generated from juice factories. Only previously assessed sustainable technologies were considered (cold press, microwave extraction, solid-state fermentation). The life cycle inventories were refined by a scale-up procedure to reflect industrial production at i) 0.5 t, ii) 100 t, and iii) 1000 t of OPW weekly. The data were translated per functional unit of 1 tonne OPW. Three electricity mixes and both attributional (average) and consequential (marginal) inventories were compared. Results showed that the environmental performance, in particular for climate change, was essentially dependent upon the electricity input, with 4388 CO2 eq for current electricity mix, 2404 CO2 eq using renewable, and 594 CO2 eq using electricity from wind. Business-as-usual scenarios for OPW (incineration and animal feed) showed better performance in most scenarios, representing -150 CO2 eq (animal feed) and -135 CO2 eq (incineration) in the climate change. Lower impacts are reached due to avoided impacts of fossil fuel use and conventional feed cultivation. Renewable energy had better environmental performance than the current electricity mix, except for eutrophication, due to digestate spreading associated with biogas use, calling for mitigation action. Our results suggest that stopping the biorefinery processes immediately after the recovery of limonene via solvent-free microwave extraction process, with subsequent use of the dried OPW as animal feed, is the most environmentally performant option. This represents a feasible strategy for the circular bioeconomy and is in line with the updated food waste hierarchy.

Automated summary

This study evaluates the environmental performance of producing limonene, citric acid, and animal feed from orange peel waste generated from juice factories, showing that the environmental performance largely depends on electricity input. Stopping the biorefinery processes immediately after recovering limonene and using the dried OPW as animal feed is the most environmentally sound option.