Microwave and Steam Mediated Alkaline Pretreatments of Sweet Sorghum Bagasse: Study of the Energy Efficiency

The effects of microwave and steam mediated pretreatments were evaluated and compared relative to the hydrolysis of sweet sorghum bagasse (SSB) in the presence of sodium hydroxide. The results established the optimum parameters for energy consumption and sugar production after hydrolysis of the pretreated SSB. The energy balance was better in microwave treatment compared with the steam treatment. The results recommended pretreatment at 300 watts power setting in the microwave oven up to 10 min. At higher wattage setting and longer exposure time, increased sugar yields were obtained, although the efficiency of the process decreased when the energy balance was calculated. The energy balance was calculated as the proportion of energy consumed during the pretreatments to the energy that can be produced by fermenting released glucose to ethanol. In this study, the energy consumed during the different pretreatments varied from 1/33 to 1/200 of the energy obtainable by fermenting released glucose to ethanol. Overall, the pretreatment of SSB to produce fermentable sugars was effective, and the energy balance was positive both in microwave and steam pretreatments of alkaline suspension of SSB. In microwave treatment the energy applied can be more accurately dosed, and consequently the energy balance was improved compared to steam treatment.