Optimization of biogas production from banana peels: Effect of particle size on methane yield

Abstract

The cooking banana cultivars (matooke) in Uganda have so long been considered to have weak linkages to upstream processing. However, the work of the Presidential Initiative on Banana Industrial Development (PIBID) has shown that upstream processing into other products is possible. PIBID in full scale processing however, would generate too much matooke associated waste (33% wastes per bunch) requiring a sustainable waste handling mechanism. Anaerobic digestion of this waste for biogas production was sought as a means of coupling products to by-products. Knowledge on the pretreatment of this waste was needed for effective anaerobic digestion. Thus, the need to assess the changes in the physicochemical characteristics of matooke peels under storage in affecting their potential for anaerobic digestion as well as the need to optimize particle size for optimum biogas production. Proximate and ultimate analyses were carried out on five banana peel cultivars after 1 day, 4 days and 7 days of peel storage at ambient conditions. Peels of one cultivar were reduced to 1mm, 5mm and 10mm particle sizes and the other four cultivar peels reduced to 1mm of particle size. Batch digesters of 100ml at 370C for 35 days of methane production with 400mg of samples were used. Peel storage pretreatment for utmost 4 days was found to bring the C/N ratio to the optimal range of 10-32 for anaerobic digestion. C/N ratio was also found to be cultivar dependent as it was significant at α=0.05 between the different banana cultivars. A model of methane content depending on particle size was developed. Plots of mean specific methane yield and methane content against particle size estimated an optimal particle size of 6.73mm for