Researchers from the Southern Central Agricultural Research Laboratory of the United States Department of Agriculture Agricultural Research Service (USDA-ARS) have found that "reject" watermelon juice can be used as a direct feedstock, or as a nitrogen supplement for the production of ethanol by fermentation. Certain economic scenarios are said to contribute to the potential of waste watermelon juice as a valuable resource for ethanol production. About 20% of the annual watermelon crop become "rejects" (due to surface blemishes present or the fruit is out of shape). Lycopene and L-citrulline (value-added "nutraceuticals" for health) can be potentially extracted from the "reject" watermelon juice, resulting in the generation of about 500 liters of "cull watermelon wastewater" per ton of "reject" watermelon processed. The wastewater is said to contain 7% to 10% (w/v) of fermentatble sugars and 15 micromole/L to 35 micromole/L of free amino acids. The sugar content makes the wastewater a good saccharine feedstock for ethanol fermentation, and the amino acid content also makes it a good nitrogen supplement for ethanol fermentation. The researchers found that lycopene-free watermelon juice with the residual amino acids were "readily fermentable as the sole feedstock or as diluent, feedstock supplement, and nitrogen supplement to granulated sugar or molasses". "Utilizing watermelon juice as diluent, supplemental feedstock, and nitrogen source for fermentation of processed sugar or molasses allowed complete fermentation of up to 25% (w/v) sugar concentration at pH 3 (0.41 to 0.46 g ethanol per g sugar) or up to 35% (w/v) sugar concentration at pH 5 with a conversion to 0.36 to 0.41 g ethanol per g sugar". The full paper can be accessed in the open access journal website, Biotechnology for Biofuels (URL above)..