Food waste offers a tantalizing source of renewable biofuel, and orange peels are a perfect example of the potential. According to the American Chemical Society, we are sitting on a veritable gold mine of citrus waste. Global agriculture produces about 15.6 million tons of orange and other citrus waste annually in the form of discarded peels that could be put to use producing biofuels along with bio-based solvents, fragrances, water purifiers and other projects. So… how close are we to this vision of a more citrus-centric planet?
The Exploding Orange Problem
The problem with oranges, and with the citrus industry as a whole, is that approximately half of the harvested product goes to waste in the form of peelings.
This represents a significant environmental liability in terms of disposal. The two main options, burning and landfilling, contribute to directly to greenhouse gas emissions.
As described by Joan Coyle of the American Chemical Society, the current choices for reclaiming orange peels are also not optimal. Large-scale juice manufacturers can process the peels as a source of livestock feed or pectin (a common food additive), but these processes involve additional expenses and increased energy use.
From Orange Peel to Your Gas Tank
To address the problem, an international team of researchers has assembled a partnership rather fancifully named OPEC, for Orange Peel Exploitation Company.
OPEC joins the University of York, the University of Sao Paulo and the University of Cordoba in a “zero waste” biorefinery project that will use high-intensity, low temperature microwaves to extract liquid from the cellulose in citrus peels, rather than depending on mechanical processes or the addition of acids.
Once separated, the cellulose and liquid can yield a number of valuable products aside from bio-ethanol. Allison Jarrell of Inside Science provides a list that includes:
“…limonene, which can be used as a fragrance, in household cleaners and as a solvent holds promise to replace petroleum-derived products; pectin, often used in cosmetics, pharmaceuticals and in foods like jellies; and cellulose, which is used as a thickening agent or can be converted into a solid biofuel.”
According to the British Science Association, the spongy cellulose could also be used as an absorbent filter, and the microwave process can also incorporate other feedstocks including household waste and paper.
As Jarrell notes, aside from yielding direct bottom line benefits the process could provide juice producers with a way to promote themselves as green, zero-waste facilities, without having to pay local farmers to cart away the peels as cattle feed.
OPEC expects to have a biorefinery up and running soon in York. Meanwhile, over here in the States, a researcher at the University of Central Florida has been developing a method for refining ethanol from orange peels with the help of a tobacco enzyme, so the future of orange peel-to-biofuel is looking pretty sunny.
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Tina Casey specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. You can also follow her on Twitter @TinaMCasey and Google+.