Energy Recovery from Olive Pomace by Hydrothermal Carbonization on Hypothetical Industrial Scale: a LCA Perspective

This work aimed to analyze and compare the environmental impacts of hydrothermal carbonization (HTC) process performed on olive pomace, aimed at energy recovery. Twelve alternative pathways, considering variable process conditions in terms of temperature (260, 280 and 305 °C), heat recovery layouts and the subsequent combustion of the generated solid product, were analyzed. Results, related only to the processing phases (i.e. without including avoided effects), showed, as expected, that the final environmental performance depends on the HTC process temperature. Moreover, it was noted that the resulting impacts are from 1.4 to 2.0 lower for the layouts with heat recovery, for all the analyzed impact categories, with exception of Freshwater Toxicity. It was also reported that by substituting the fuel in marginal processes of heat production, environmental load reduction potential, regarding all impact categories, can be achieved. The highest benefits were achieved by substituting coal with HTC pellet in the heat production, followed by wood pellets and natural gas. Concerning the contribution analysis, the combustion processes of HTC and wood pellet represent the major contributions to the Climate Change and Acidification impacts, the combustion processes of HTC and wood pellet represent the major contributions, around the 95% and the 75% of the total, respectively, for the cases with the highest HTC temperature and no recovery scheme. For the Eutrophication potential, biomass production contributes significantly to the final effect. Regarding the Freshwater Ecotoxicity, the major part of the impact is coming from the HTC process and the relative liquid phase emissions assumed to be composed by phenols and furfurals released from the process. However, this part of the system needs to be further analyzed in detail. Graphic Abstract