Economic Exploitation of Rejected Watermelon Fruits as a Potential Source of Renewable Energy

Watermelon is one of the most important crops in Egypt relating to both fruits and vegetables. There is a variety of foliar diseases that affect watermelon plants which include fungal, bacterial and viral diseases. Viral diseases are a major problem in watermelon planting especially watermelon mosaic virus-2 (WMV-2) which causes economic damage reflected mostly as reduced plant growth, yield losses of more than 38%, decrease in fruit quality and consumers refuse it as misshapen and deformated fruit. The present investigation was planned to examine a suitable fermentation process for recycling the refused watermelon fruits for production of bioethanol. Four strains of Zymomonas mobilis; Zymomonas mobilis ATCC 31821, ATCC 31822, ATCC 31823 and ATCC 10988 were examined for ethanol production using different meida. Such media were prepared from different parts of infected watermelon fruits as red flesh, white tissues, lycopene and lycopene – free juice. Also, Bawa and yoshiyuki medium and molasses were used for the comparison. The watermelon juice was a superior medium for ethanol production applying all Z. mobilis strains. Z. mobilis ATCC 10988 was the most active ethanol producer giving the largest amount of ethanol with highest efficiency production of 4.26g/100 ml and 97.85%, respectively. The watermelon juice supplemented with salts of Bawa and yoshiyuki medium was tested for bioethanol production. The results showed that addition of minerals decreased ethanol production from 4.26 to 3.86 g/100 ml and reduced efficiency from 97.85% to 93.26% by using Z. mobilis ATCC 10988. Comparison between watermelon juice and molasses for ethanol production using Z. mobilis ATCC 10988 proved that watermelon juice is more effective than molasses giving ethanol content of up to 4.26 g/100 ml and 2.65 g/100 ml and production efficiency of 97.85% and 60%, respectively.