Upscaling Biogas Production using Fruit Waste (Pawpaw, Watermelon and Banana) Co Digested with Cow Dung, and Gutter’s Sludge

Abstract

Nigeria faces a significant challenge of fruit waste due to improper handling and transportation practices, leading to damage and microbial contamination, resulting in environmental pollution. These wastes can be utilized to produce biogas which is environmentally safer and cleaner. This study explores the potential of using fruit waste (Pawpaw, Watermelon, and Banana) as substrates co-digested with cow dung and gutter sludge to upscale biogas production. Physicochemical analyses of the substrates and inoculums was conducted, followed by construction of pilot biogas digesters, and then isolation of methanogenic bacteria. A combination of single and mixed fruit ratio were added into the digesters with the cow dung and gutter sludge as co-digesters. For the up scaling, a 25L digester was constructed and the best mix ratio from the pilot digesters were fed into the digesters. Isolation of methanogens was carried out to access which substrate or inoculum had greater potential in the production of biogas individually or when co-digested by the presence of methanogenic colonies after incubation. The results revealed similar physicochemical parameters among the fruit waste substrates, while cow dung and gutter sludge showed variations, particularly in carbon-nitrogen ratios. The pilot study demonstrated that the mix ratio containing all three fruits, co-digested with cow dung and gutter sludge, produced the highest methane yield (11.2%). In upscaling, a 25L digester produced gas efficiently, albeit with some depletion over time, possibly due to methanotroph activity or exposure to sunlight. Methanogenic colonies were successfully isolated from lower dilutions of gutter sludge. This study highlights the potential of fruit waste as a valuable substrate, particularly when co-digested with cow dung and gutter sludge, which can serve as an effective inoculum due to the presence of methanogens.