The tree nut industry continues to think outside the box to find new uses for its discarded shells and hulls, be they almond, walnut, pecan, or pistachio.

Almond coverings were once used as livestock bedding, but that use is diminishing with reduced dairy demand. Pecan shells get loaded into ovens as fuel to cook potato chips for a snack food producer. Ground up nut shells are being added to recycled plastic dinnerware to increase utensil strength.

Nut hulls high in sugar content are being tested as a possible alternative for high fructose corn syrup or conversely as flavoring agents for beer. Walnut shells are ground up and sold as a polishing material for the burnishing of metals. Nuts with essential oils are ground and pressed into pellets to be used as fuel.

Depending on the kind of nut and the tree stock it came from, there may be numerous uses for the end or waste product. At least that’s the way Eric McAfee of Aemetis Inc. in Cupertino, Calif., views the problem of mounting waste piles of nut shells.

As owner of a renewable fuels company, he told the 2019 Almond Conference his goal was to cease open burning of orchard waste by using technology to produce zero-emission fuels as replacements for petroleum-based products.

True to his mission, he is building the first biomass-to-ethanol plant on a 140-acre former Army munitions production facility near Modesto. He expected to open in late Spring, but plans have slowed down a bit due to the coronavirus, although his lease is signed and in place.

“We’re in the final engineering phase of the project before actual construction gets underway,” he says. “In the meantime, because we currently have the expertise to make alcohol, we’re producing alcohol to be used in hand sanitizer and are starting to use unwanted orchard wood in that project,” he says.

Focus on waste

Tree waste, whatever its form, is the focus here. 

“We hope to be part of the solution of the current waste product issue, a solution that growers currently don’t have. Right now, orchard waste sits in the field and they’re stuck burning that waste on-site which creates air pollution. As this thing gets going, we hope to reduce the cost of removing orchard material, so it could be a cost reduction for farmers.”

Part of his waste plant material fuel stock will utilize more than 2 million tons of ag waste produced annually in the Central Valley, much of it unproductive orchards and other woody waste to produce cellulosic ethanol.

“This is one of the largest air pollution sources in the Central Valley, which is, I believe, the second worst air quality region in the U.S., partly because some 3.2 billion pounds of wood gets burned every year — kind of like a big campfire burning year-round.

“By putting out that campfire, we improve air quality, an environmental benefit, as well as a financial benefit to growers because we’re reducing the cost of removing their orchard, which currently runs something like $500 an acre or something crazy like that. That’s a major cost to farmers who want to replace their orchards and we can help in mitigating that expense.”

With some one and a half million acres of almond and walnut orchards in the state that have some 40,000 almond trees removed annually at the end of their average 20 year production lifespan — along with pistachio shells and hulls — he figures that will support production of hundreds of millions of gallons of cellulosic ethanol per year.

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