Abstract
This paper deals with the development of a citrus peel waste (CPW) biorefinery that employs low environmental impact technologies for production of ethanol and methane. Three major yeasts were compared for ethanol production in batch fermentations using CPW pretreated through acid hydrolysis and a combination of acid and enzyme hydrolysis. The most efficient conditions for production of CPW-based hydrolyzates included processing at 116 °C for 10 min. Pichia kudriavzevii KVMP10 achieved the highest ethanol production that reached 30.7 g L−1 in fermentations conducted at elevated temperatures (42 °C). A zero-waste biorefinery was introduced by using solid biorefinery residues in repeated batch anaerobic digestion fermentations achieving methane formation of 342 mL gVS−1 (volatile solids). Methane production applying untreated and dried CPW reached a similar level (339–356 mL gVS−1) to the use of the side stream, demonstrating that the developed bioprocess constitutes an advanced alternative to energy intensive methods for biofuel production.
Highlights
Vegetable and fruit waste account for 20–50% of household waste in various countries, while citrus peel waste (CPW) comprises a principal residue under the specific category [1]
The current biorefinery aimed for CPW valorization through the removal of essential oils and pectin, as well as fermentation of the hydrolyzate formed as fermentation feedstock for bioethanol production
Pectin was extracted from the hydrolyzate generated through precipitation with the addition of ethanol, while the hydrolyzate was subsequently applied to distillation for ethanol removal
Summary
Vegetable and fruit waste account for 20–50% of household waste in various countries, while citrus peel waste (CPW) comprises a principal residue under the specific category [1]. CPW formed during processing of the fruit consists mainly of peels and pressed pulp (seeds and segment membranes), accounting for 50% of the fruit’s weight [3,4]. The thermal dehydration process of CPW to produce animal feeds is energy consuming and not always cost-effective [5], while the final product consists of rather poor animal feed, due to low protein content and high quantity of sugars [6]. The waste includes elevated organic matter (approximately 95% of total solids) and water content (approximately 80–90%), as well as low pH (3–4), making CPW inappropriate for landfilling based on the latest EU Waste Framework
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