Solar and open sun drying of untreated and pretreated banana stalk chips biomass: a sustainable processing of biomass using renewable solar energy

The stalk of banana is an abundant biomass that can be sustainably converted into bioenergy, biofuels, biosorbents, animal feeds and fibers. The moisture content of freshly harvested banana stalk is high, so drying is essential before its storage and prior to some of the conversion processes. Hence, solar and open sun drying characteristics of banana stalk chips were investigated. Untreated (5, 10 and 15 mm thick) and pretreated (hot water, salt water and sulphite) banana stalk chips were dehydrated in a solar dryer and directly in sunlight. The data were fitted to twelve drying models. The moisture diffusivities were also evaluated. Banana stalk dried mainly in the falling-rate phase and the rate of drying increased with decreasing chip thickness. However, the chips dried slower in direct sunlight compared to the solar dryer. The pretreatments significantly (P < 0.05) enhanced the rate of dehydration of the chips in the solar dryer. Diffusivities for the solar and direct sunlight drying of banana stalk chips were 1.28 × 10 –9 –5.32 × 10 –9 m 2 s −1 and 1.08 × 10 –9 –3.65 × 10 –9 m 2 s −1 , respectively. The Weibull model aptly described the solar drying of the chips while the Midilli-Kucuk and Weibull models most properly depicted the open sun dehydration of untreated and pretreated chips, respectively. Solar energy may be more efficiently utilized for drying banana stalk chips biomass by using a solar dryer as well as a very thin layer of chips and by pretreating the biomass prior to the drying operation. The effective use of solar energy for drying banana stalk biomass can reduce its processing cost and enhance the sustainability of biomass utilization.