Valorisation of Edible Oil Wastewater Sludge: Bioethanol and Biodiesel Production

Abstract

This study aimed to reuse primary wastewater sludge from the edible oil industry as a novel feedstock for both monounsaturated fats and bioethanol for biodiesel production. Results showed that the fatty acid profile of the oilseed primary wastewater sludge was favourable for biodiesel production; with a maximum 45% (w/w) monounsaturated fats extracted using ethanol at an ethanol to solid ratio of 25:1. The residue after the extraction of fats from the sludge contained sufficient fermentable sugars for bioethanol production. A maximum theoretical yield of bioethanol of 106% was obtained after enzymatic hydrolysis followed by fermentation using the industrial Saccharomyces cerevisiae strain MH-1000 at an optimum density of 2 × 105 CFU/mL. A novel nano-magnetic catalyst synthesised from cupriferous mineral processing wastes was employed. A maximum biodiesel yield of 94% was obtained at an oil to ethanol ratio of 1:9, catalyst loading of 5 wt.%, and reaction time of 180 min at 75 °C. The approach employed in this study has the potential to reduce material costs, energy consumption and water usage associated with conventional biodiesel production technologies. It may also mitigate the impacts of conventional biodiesel production on food and land security, while simultaneously reducing waste.