Environmental life cycle assessment of different biorefinery platforms valorizing olive wastes to biofuel, phosphate salts, natural antioxidant, and an oxygenated fuel additive (triacetin)

Abstract

Olive agro-industry is a chemical- and energy-intensive agricultural activity and given its large scale globally is faced with serious challenges from the sustainability perspective. On the other hand, different by-products and residues generated are not generally used and end up as wastes. Therefore, it is of crucial importance to design and implement innovative platforms based on circular bioeconomy and zero-discharge principles to enhance the sustainability features of the olive supply chain system. In light of that, the present study was aimed at designing and experimentally scrutinizing two olive agro-biorefinery scenarios against the conventional olive oil production system (i.e., olive/olive oil production, including olive cultivation and oil extraction). The first agro-biorefinery system included olive cultivation and oil extraction from fruit and pomace for edible use. Moreover, the remaining pomace post-oil extraction was used as an animal feed. The second agro-biorefinery system included olive cultivation, olive oil extraction, olive pomace oil extraction, and its conversion into biodiesel. In addition, crude biodiesel glycerol was also valorized into two different phosphate salts and an oxygenated fuel additive (namely triacetin), while olive oil leaves were converted into a natural antioxidant for biodiesel. The performance of the natural antioxidant against the most promising synthetic antioxidant used by the biodiesel industry (i.e., propyl gallate) was also investigated. The developed scenarios were environmentally compared using the IMPACT 2002+ method. Overall, both developed agro-biorefineries outperformed the conventional system in terms of all four endpoint damage categories. Compared to the conventional olive oil production system, the production of 1 ton of olive oil in the first and second agro-biorefinery systems was associated with 10.62% and 4.08% saving in climate change damage category, 6.73% and 11.21% saving in primary energy consumption, and 12.01% and 1.55% saving in damage to human health. In addition, the implementation of the circular bioeconomy approach in olive oil production led to 31.28% and 26.38% saving in ecosystem quality damage category for Sc-2 and Sc-3, respectively. Overall, the weighted endpoint damage categories of olive oil production could be saved by 12.27% and 4.49% if respectively, the first and second agro-biorefinery scenarios were used. These findings revealed that through the transition from linear economy-oriented olive agri-food system to a bioeconomy-oriented olive agro-biorefinery, not only a wide spectrum of value-added bioproducts could be achieved, but also the environmental impacts per each ton of olive oil produced could be mitigated.