Quantification, characterization and improvement of biomethane production from banana wastes by fungal pre-treatment

Bananas represent an important staple food and cash crop in Tanzania. However, it’s processing into food and finished products results in generation of enormous quantities of wastes that are underutilized and disposed off into the environment leading to pollution problems. Despite being a menace to the environment, banana wastes have a big potential for biogas production. Nevertheless, the difficulty inherent in utilizing particulate banana waste for biogas production lies in its lignocellulosic components which are difficult to biodegrade. Additionally, the composition of the waste and quantities generated in Tanzania are not established. This study established quantities and characteristics of banana waste fractions from common banana cultivars used for food and desserts at Horticulture Research and Training Institute, Tengeru, Arusha, Tanzania, as a case study. The study further attempted to improve on biomethane production from the waste by fungal pre-treatment for lignocellulose degradation. For the four cultivars that were studied being Mshare-Kahuti, Mbwailuma (matoke), Kisukari-Mshare and Kimalindi, the average wet weight comprised about 11% leaves, 1% male bud, 10% peels, 3% peduncle, 21% corm and 53% pseudostem. The corresponding waste quantities generated annually from one hectare was estimated to be 57; 99; 64 and 125 tonnes/year for Mshare-Kahuti, Mbwailuma (matoke),Kisukari-Mshare and Kimalindi, respectively. Methane yield of various fresh fractions of Mshare (used for food) and Kisukari (used for desserts) banana wastes were investigated in batch anaerobic bioreactors. The yields for Mshare ranged between 0.146 and 0.273 CH4 m3/kg of volatile solids (VS) added whereby the highest yield was obtained from corm and peels. On the other hand, the yields for Kisukari ranged between 0.068 and 0.256 CH4 m3/kg of VS added. The male bud and corm fractions gave the highest yield. The effect of solid state-fermentation pre-treatment with Pleurotus sapidus (P 969) at 10% (wet wt bases) for 7, 14 and 21 days on the extent of methane yield was investigated at an ambient temperature of 29±1°C. Methane yields increased by 8-90% where maximum methane yield for Mshare-Kahuti was 0.310 CH4 m3/kg VS added and for Kisukari-Mshare 0.330 CH4 m3/kg VS added which were recorded for 21days incubation period. This represented an 82-90 % yield increment for Kisukari and Mshare, respectively as compared to untreated waste. The results confirmed the potential of Pleurotus sapidus (P 969) fungus as a pre-treatment strategy prior to anaerobic digestion to achieve significant improvements in biogas production using banana wastes. The study also established the best possible time for pre-treatment of banana wastes be 21 days.