Watermelons in your Car’s gas tank!

Well… if the recent findings are any indicator, your car could be getting its bioethanol from ‘reject’ watermelons in the near future. The fact is, one in every 5 watermelons is rejected and of no use to the growers as a source of revenue. Scientists have recently found a way to convert these rejects into “biofuel”.

Watermelons consist of simple sugars that allow for more efficient conversion to ethanol, as compared to corn that contain complex sugars, and hence have to be broken down using enzymatic degradation. Further, watermelons consist of nutrients like lycopene and L-citrulline. Processing of watermelons to produce lycopene and L-citrulline, yields a waste stream of watermelon juice. The rationale behind the investigation was based on the fact that watermelon juice contains 7- 10% (weight/volume) directly fermentable sugars, and 15-35 μmol/ml of free amino acids. Thus its potential as feedstock, diluent, and nitrogen supplement was investigated in fermentations to produce bioethanol.

The study showed that whole watermelon juice as well as watermelon, with the lycopene-containing chromoplasts removed, could be fermented to produce significant amount of ethanol. Lycopene containing chloroplast could be easily solubilised after fermentation, suggesting two uses for wasted watermelons. The first was as a biofuel and the second was for harvesting nutrients like Lycopene and L-citrulline. Further, the watermelon juice in the form of waste stream could be used as a as diluent, sugar supplement, and nitrogen supplement in the fermentation of molasses. It also served as nitrogen source for yeast in the fermentation process making it a useful diluent in fermenting other sugars. The results clearly demonstrated multiple uses for the water melon juice, from this study.

Speaking of the economics of the production, the authors say that the current unmarketable watermelons – 8.4 t/ha (tones/hectare), left in the field at harvest, would produce about 220 L/ha (liters/hectare) of ethanol for on-farm use. This could also act as an additional revenue stream for the grower. The authors have also discussed the application and feasibility of this technology on the farms and given an approximate estimate of the production rate of ethanol from the 20% of the watermelon yield.

The article appears in the recent issue of Biotechnology for Biofuels – 2009, 2:18 and is available for free download.

This article was contributed by Dr. Shailaja Divekar, Georgetown University Medical Center, Washington DC