Prospect on Renewable Energy and Comparative Analysis of Bioethanol Produced from Orange, Banana and Watermelon by Co-culture of Aspergillus niger and Saccharomyces cerevisiae

Abstract

Excessive dependence on non-renewable energy sources has contributed to global environmental degradation and rising public health concerns, highlighting the urgent need for sustainable alternatives such as bioethanol. Fruit processing wastes like banana, orange, and watermelon peels are often discarded despite their rich carbohydrate content, making them promising substrates for renewable biofuel production. This study aimed to evaluate the potential of banana, orange, and watermelon peels as low-cost substrates for bioethanol production using locally sourced Aspergillus niger and Saccharomyces cerevisiae, and to compare their ethanol yields under co-culture fermentation. A. niger was isolated from humus-rich soil at the Abubakar Tatari Ali Polytechnic botanical garden, while S. cerevisiae was isolated from the indigenous fermented beverage “Burukutu”. Identification was based on cultural, morphological, and biochemical characteristics, followed by screening for enzymatic and fermentative capabilities. Substrates underwent proximate analysis and acid hydrolysis, after which co-culture fermentation (pH 5.5, 8 g substrate, 30°C, 5 days) was conducted. Ethanol levels were monitored across fermentation days. A. niger exhibited strong α-amylase activity with a 47 mm clear zone on starch agar, while S. cerevisiae demonstrated typical budding morphology, thermotolerance up to 40°C, and ethanol tolerance up to 12%. Watermelon peel had the highest carbohydrate content (50.55%), banana peel contained high lipid (24.32%) and fiber (15.30%), and orange peel showed high moisture (42.02%). Ethanol yields peaked on day four at 12.46% (banana), 11.60% (watermelon), and 8.90% (orange), followed by a decline due to substrate depletion and ethanol inhibition. Locally sourced microbial strains and fruit peel wastes are viable resources for bioethanol production, demonstrating strong potential for renewable energy generation and environmentally friendly waste management. This study provides evidence that indigenous microbial strains and readily available fruit wastes can be integrated into sustainable bioethanol production systems. It further establishes the effectiveness of co-culture fermentation and enzymatic hydrolysis in enhancing ethanol yield, supporting circular bioeconomy strategies and low-cost biofuel innovations in developing nations.