Bioethanol can be produced from the processing industry waste rich in sugar/ starch by the microbial technology that may evolve an alternative to our limited and non-renewable resource of energy. Increasing environmental regulations for controlling waste disposal will further enhance the possibilities of ethanol pro­duction from waste.

9.7.1 Sugar Molasses

A process has been developed for the preparation of power alcohol from molasses on pilot scale with immobilized whole cells. Ethanol production from molasses has also been scaled up with addition of 15% total sugar content using Z. mobilis [39]. A scheme of fuel ethanol production from sugarcane bagasse has been shown in Fig. 9.15. Ethanol production by Z. mobilis can be increased by addition of cal­cium carbonate in high sugar medium and at higher fermentation temperature (43°C) [175].

Batch fermentations of sugarcane blackstrap molasses to ethanol using pressed yeast as inoculum, demonstrated an exponential relationship between the time necessary to complete fermentation and the initial concentrations of sugar and the yeast cells [18]. Fed-batch alcoholic fermentation of sugarcane blackstrap molasses (at 32°C, pH 4.5-5.0) without air and compressed yeast enhanced the average yeast yields and average yeast productivities without affecting the ethanol yield.

Neutral spirits and ethanol are the major fermentation products from citrus molasses [21, 51]. In Florida only, 1 million L of alcohol is produced from citrus molasses annually. The process includes dilution of molasses to 25°B followed by fermentation yeast. The alcohol is recovered by distillation. Enzymatic digestion of citrus peel, solubilizing of 85% total peel solids with 65% hexose sugar [133] made available more sugar for fermentation, thus increasing the yield of alcohol. However, reduced yield of alcohol has been reported from molasses produced by

heat evaporators (30-50°B) where some loss of fermentable sugar during handling and storage might have taken place [21].