Watermelons: The Newest Renewable Energy Source

Article written: 25 Aug , 2009
Updated: 24 Dec , 2015
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This has nothing to do with space or astronomy, but is perhaps one of the juiciest pieces of new I have ever read. Could we one day be driving cars fueled by watermelons? Researchers say that watermelon juice can be a valuable source of biofuel, as it can be efficiently fermented into ethanol. But have no fear, using watermelons for biofuel wouldn’t cut into the amount of watermelons available for the public to eat. This research evaluated the biofuel potential of juice from ‘cull’ watermelons – those not sold due to cosmetic imperfections, and currently ploughed back into the field. Wayne Fish from the US Department of Agriculture said, “About 20% of each annual watermelon crop is left in the field because of surface blemishes or because they are misshapen. We’ve shown that the juice of these melons is a source of readily fermentable sugars, representing a heretofore untapped feedstock for ethanol biofuel production.”

The researchers conclude that at a “production ratio of ~0.4 g ethanol/g sugar, as measured in this study, approximately 220 L/ha of ethanol would be produced from cull watermelons.”

As well as using the juice for ethanol production, either directly or as a diluent for other biofuel crops, Fish suggests that it can be a source of lycopene and L-citrulline, two ‘nutraeuticals’ for which enough demand currently exists to make extraction economically worthwhile. After these compounds have been removed from the ‘cull’ juice, it can still be fermented into ethanol.

Read the “juicy” paper here.



15 Responses

  1. Savino says

    Nice…

    But, what about the ethanol from the sugarcane?

    You can produce about 6.800 L/Ha with sugarcane. Its a well stabilished techologic, cheap and you can buy a lot from Brazil and other countries…. so… why waste watermelons!

  2. Dave Finton says

    Personally, I’m a little leery of using food crop as a biofuel source. No matter what you use, it’s going to be highly inefficient with regards to land use and net energy production (which right now is in the negative with current technologies).

    A better way to go would be to use more of an industrial solution, such as using algae or something that can be produced on small plots of land instead of using up valuable farming space.

    IMHO =)

  3. Jorge says

    Actually, the worse thing about using food crops as energy source is the price changes that would bring along. It happened with corn biofuel already, and will happen with anything that would be grown both for food and for energy production.

    What I’d really like to see as far as biofuels are concerned is a way to use up what in the old days was collected in the forests for firewood and kindling. We have huge problems with bushfires in mediterranean Europe, in California and in other regions, and part of the problem is the fact that our forests are no longer harvested for firewood. In my country there have been some experiments in forest cleaning, after a particularly destructive (and deadly) fire season a few years ago, and they had a major impact in how large and how strong bushfires were in the next summer, but without an economic stimulus to do that it’s just not viable in the long run. Particularly when the economy tanks and state budgets shrink further. Biofuel could provide that stimulus.

  4. GekkoNZ says

    commenting on the above threads, how is using a food crop like watermelons bad, when you are using watermelons that are plowed back into the field due to their unsuitability as food?

    You are not taking away any of the crop that is sold as food. You therefore are not affecting its price, nor reducing the amount of crop sold as food.

    It is simply another form of energy recovery from waste products, therefore it is not inefficient with regards to land use. It is not “wasting” watermelon, as they are going to waste anyway.

    The only downside I see to it, is the loss of nutrients put back into the field due to the “bad” watermelons being plowed back into it.

    Other than that, i can only see a win-win here.

  5. Hex says

    Studying zymurgy lately. Home brew hard cider from our own trees! Noticed a lot of CO2 is produced in the yeast/fermentation process. Read that equal parts of CO2 and Ethanol are produced in the reaction. Also yeast will at best yield 15% Ethanol which must be distilled with heat or cold to extract 100% from water/waste. When it’s fuel, combustion creates more CO2. How does Ethanol solve ANY CO2 problems?

  6. Torbjorn Larsson OM says

    My immediate reaction was along the lines of Dave Finton. I’m skeptic that crops or crop waste give any net energy at all.

    If it is generating inefficiencies, and I believe I’ve seen results along those lines, it is like the “ecological food” craze. Apparently massive resources are wasted to produce equal (or possibly inferior) products at higher cost. Not to poison the well, but I find it interesting what people are ready to do based on little fact at all, and how counterproductive it can be.

    @ Dave:

    I believe part of what drives Venter’s enterprises is the possibility to grow synthetic bacteria that produce fuel hydrocarbons directly. Almost certainly guaranteed a net energy production, at least if they can tie in photosynthesis.

  7. Torbjorn Larsson OM says

    @ GekkoNZ:

    You have energy (fuel) losses all the way, and you have to sum them all to compare with fossil gas production.

    First you have energy loss from producing the waste in the first place, where fossil gas is produced, transported, and used up on the fields. Less waste, less energy loss.

    Second you have energy losses from collecting the waste (instead of using it in place).

    Third loss is from converting waste energy mass from non-fuel to fuel form.

    Fourth loss is from transporting the fuel from conversion plants to the fuel user. (This loss is also seen with fossil gas production.)

    Fifth, a problem you touched, is that you have to replace the loss of nutrients from not reusing the waste. It is likely most cost (and energy) effective replaced with synthetic PKN, which means more energy loss from production, energy loss from transport to the field, energy loss from distributing it onto the fields, but also energy loss from final crop waste management (likely merely transport to a dump site at this time).

    When you sum all these energy losses, and then compare with the losses from fossil gas production (a production which gives a net energy contribution), it is arguable (and in fact, IIRC, found in some investigations contrary to facts) that this type of waste use gives any benefits.

    It is likely waste waste.

    @ Hex:

    As renewable (i.e. non-fossil) fuels recycles carbon over atmospheric lifetimes instead of over geological lifetimes, it doesn’t matter whether the carbon dioxide results from breakdown in nature, which would happen anyway, or combustion in engines. So it solves AGW from fuel production.

    [If you want to nitpick, not fully though, I think. Some of the produced fuel may result from more efficient use of land, if Venter’s et al ideas come through and we can have a net gain at all. I can’t see how this but will somewhat drive the balance of CO2 up in the air and C down in the earth. Just as more efficiency in food production will increase AGW somewhat by the same mechanism.

    It is first if and when hydrogen fuels are used that we may have “clean” cars, bypassing the need for, and local and global problems with, CO2 and CH emissions in the first place. Modulo the ever present NOX emissions, of course.]

  8. Lawrence B. Crowell says

    We should not expect to hitch the planetary bio-energy system to run our power and transportation systems. Currently about 1% of energy in the United States comes from biofuels, which involves 6% of our agircultural production. So it is not hard to do the math to see how much we can expect.

    Bioenergy as a means of resource recovery and the like is fine. However, I suspect it will always be a niche area. Even ideas of algae based fuels is limited. There is only a peak of 1200watts/m^2 of solar energy and a limited amount of “energy real estate” available.

    cheers LC

  9. Dark Gnat says

    I think Kudzu would be a better choice for producing Ethanol, as it typically isn’t eaten, and it grows everywhere.

    Still, I think using Ethanol is more of a “feel good” practice that actually does more harm than good.

    Too bad there’s no big ball of plasma in the sky that we could harness enrgy from…..

    by golly, there is!

  10. Jorge says

    @GekkoNZ

    The problem is: as fuel from fossil reserves gets further drained, you’ll see a pressure from the consumption to have more biofuel available, which will bring about an increase in prices. At some point, farmers will get more profit by selling their crops directly to biofuel companies than they would if they sold them as food, so they’ll shift… and/or raise food prices accordingly.

    So the problem is not the reuse of waste: it’s the fact that it won’t be restricted to waste reuse for long. The very economy of our overly eager energy sector makes that inevitable.

  11. wjwbudro says

    @ Lawrence B. Crowell:

    “There is only a peak of 1200watts/m^2 of solar energy and a limited amount of “energy real estate” available.”

    Is that based on current technology and is that continuous power at peak sol conditions? I Googled and could not find where exactly technology is now and what is expected in the future. Of course that may be because I don’t know “exactly” where to look. lol
    Hopefully advancements in solar and storage technology will greatly reduce the large footprint and commercial and residential roof installations will be a affordable choice in the near future. Regardless the cost, it may turn out to be a requirement rather than choice to reduce the impact coal fired plants have on the environment both air, water and ground.
    And you’re right GekkoNZ; one way or another we are going to pay the price: To enjoy stable fuel costs, it’s going to cost a whole lot more to feed our livestock as well as ourselves. The corn/ethanol push was more political than economics and look what it got us. 10% ethanol = 15% less mileage and they’re still debating the pollutant reduction benefits. And look at the destruction of our rain forests!
    If we can get solar/wind/geothermal etc. competitive with fossil and bio production we can at least begin to phase in more electric vehicles and maybe get rid of the gas/diesel generators esp. in the developing countries. Over half of the mom and pop factories in rural china and India and elsewhere power their operation with generators.
    This may cause a few chuckles here but, I’ll ask anyway. Is there any scientific work being done with regard to reducing the impact of nuclear waste and how serious is the problem now and in the future as more nuclear plants come on line? Sorry that should be another discussion on another forum.

  12. Hex says

    Fusion is our only real hope. H+H=He.

  13. Jon Hanford says

    I, too, echo Dave Finton, Torbjorn Larsson OM and wjwbudro concerns with using food crop for ethanol production. Cellulosic sources of ethanol production (like algae) seem to be the more sensible solution here. But in the end, were still using fossil-derived fuels (ethanol) to sustain our energy use. Solar, wind, wave, nuclear and other renewable energy sources seems to be the logical next step in our move away from fossil fuels.

  14. wiseguy says

    Watermellons for fuel?Oh brother.0_o

    There is no intelligent life on Earth.XD

    Your parrents have been lying to you your whole life.XD

  15. Entropic Alchemist says

    Making fuels from renewables is not a “single source” thing. Every new thing that we can get biofuels out of we will do so, and it will help to minimise the load on any one resource.

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