Prospective LCA-based optimisation of tomato waste drying for biorefinery purposes

Tomato waste is currently an untapped potential source of different bioactive compounds, including lycopene, polyphenols, polysaccharides, and proteins. Drying is an energy-intensive process with potentially significant environmental impacts. However, drying is a necessary pretreatment for tomato waste before lipid-soluble bioactive compounds can be extracted. This work attempts to optimise tomato waste drying from the point of view of minimising environmental impacts at an early stage of technology development by using prospective LCA as a tool for optimisation. A comprehensive approach is adopted, starting from experimental investigation, followed by modelling of process kinetics and extrapolating differences in resulting residence times into the size of equipment, which in turn influences LCA inventory, i.e., required size of equipment. Modelling showed that the modified Page model achieved the lowest square error when fitting to experimental data. The study determined that environmental impacts decreased with increasing drying temperature, owing to a decreased contribution from capital goods, which in extreme cases (drying at 75°C) could contribute as much as 36.9% of the climate change impact. The climate change impact could be decreased from 0.42 to 0.11 kgCO2eq per functional unit (1 kg of evaporated water) by replacing natural gas with biogas for the generation of heat for drying. However, other impact categories (eutrophication, ecotoxicity) showed a reverse trend, highlighting the need for further improvement in digestate and feedstock management in anaerobic digestion plants supplying biogas for the production of heat for such dryers.