Energy recovery alternatives for the sustainable management of olive oil industry waste in Australia: life cycle assessment

Abstract

Over the last two decades, the olive oil industry in Australia has been growing at an annual rate of 9%. Nevertheless, the highly polluting solid waste and wastewater generated by the industry poses significant challenges for the environmental sustainability of the industry. This paper analysed five alternatives for managing this waste stream using life cycle assessment methodology. The options included manufacturing briquettes as solid fuel for home heating; pellets for domestic or industrial water heating; pyrolysis and composting. The functional unit used in this study is the processing of 1 Mg of olive solid waste at the mill. Emissions were categorised into eight impact categories: ozone layer depletion potential (ODP), global warming potential (GWP100), eutrophication potential (EP), acidification potential (AP), human toxicity (HTP), fossil fuel depletion potential (FDP), ionising radiation potential (IRP), and photochemical oxidant formation potential (POFP). The study showed that although composting (current best practices - CBP) can achieve significant environmental benefits, using the olive waste to produce energy products may achieve better results, especially when displacing electricity from the main grid. The production of pellets for use in domestic hot water boilers (PHWH) is the option that is likely to deliver the highest environmental benefits. For example, GWP100 and ODP of the PHWH were estimated to be -1057 kg CO2-Eq, -1.5 נ10-5 kg CFC-11-Eq compared to -12.4 kg-CO2-Eq and 5.3 נ10-8 kg CFC-11-Eq achieved by the CBP, respectively. Future energy scenario and transportation distances were identified as significant parameters affecting the performance of the options. Sensitivity analysis showed that the expected change in the future Australian energy mix to cleaner energy sources is unlikely to have a significant effect on the performance of the alternatives. The results also showed little sensitivity to transportation distances of the energy product to the end user. This paper is the first to evaluate options for energy utilisation of olive solid waste using life cycle assessment and compare it to industry current best practices (composting). Although the paper focuses on the Australian olive oil industry, the results are also relevant to other countries and regions were olive solid waste is generated in relatively moderate quantities but distributed over large geographic area. Keywords LCA; Energy from waste; Waste management; Olive husk; Renewable energy