Objective:
If grown solely as a feedstock for ethanol production, watermelon would likely have a difficult time competing with several of the current ethanol feedstocks in the U.S. However, utilization of a watermelon juice waste stream as feedstock for ethanol production would provide simple sugars for direct fermentation to ethanol while at the same time eliminating a major portion of the sewage treatment costs for such a waste stream. A similar argument can be made for the watermelon waste products, rind and pulp from the flesh. Like other ethanol feedstocks, these two waste products would first have to be broken down to simple sugars, either chemically or enzymatically, before their fermentation to ethanol. At this point in time, little is known about the industrial fermentation of watermelon juice to ethanol fuel other than anecdotal recipes for making “watermelon wine”. The objectives of this project are (1) to experimentally optimize the conditions for fermentation of watermelon juice to fuel ethanol, and (2) to optimize the process and conditions for conversion of the complex carbohydrates of watermelon pulp and rind to their constituent sugars for subsequent fermentation.

Approach:
Conditions of the watermelon juice fermentation process that must be optimized include: optimizing the temperature of the process, finding the most robust and productive yeast strain, establishing the fermentation time to reach maximal yield, establishing which antifoaming agent is most efficient and at what level, and determining the optimal pH for the process. Our plan is to grow and process watermelons here at the Lane Ag Research Center, Lane, OK to produce lycopene. We will utilize the watermelon juice from this processing as the direct feedstock for ethanol production experiments. Likewise, various chemical and enzyme treatments will be evaluated for breakdown of rind tissue to its constituent sugars for subsequent fermentation. Only under carefully controlled conditions can processes be developed that can be scaled up to industrial levels. A commercial bench-scale fermentor is critical to these experiments in order to be able to reproducibly adjust and control conditions.