Peeling Back Waste: The Onionator

Specifically, onion growers in Oregon’s Malheur County annually produce over two million pounds of plastic irrigation tubing, also known as drip tape. Additionally, landfills are unwilling to accept any drip tape or participate in recycling facilities. Mechanically recycling is not an option, which has ultimately led to the accumulation of drip tape in the county.

The Plastics to Fuel (PTF) project aims to provide a localized solution for such communities, to convert waste plastics into agricultural-grade diesel fuel for their immediate use. In Malheur County, PTF collected drip tape and characterized it using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The analysis found that drip tape is polyethylene and is suitable for conducting pyrolysis.

Pyrolysis is a chemical process where materials are heated in the absence of oxygen. Plastics like polyethylene consist of long carbon chains, which are broken into smaller, fuel-sized molecules. When optimized, it is possible to achieve a net positive energy conversion of 4-6:1 when using PE or PP feed.

The Onionator is a 25-kilogram feedstock, one-step batch pyrolysis reactor, using only heated air in a kiln design to perform pyrolysis. The Onionator was designed by a 2025 OSU Mechanical Capstone Engineering Team. It was engineered as a demonstration system to be placed at the OSU Malheur County Ag Experiment Station to introduce the onion growers to the pyrolysis technology to address their waste drip tape issues. A commercial pyrolysis facility is commonly designed with a catalytic system and gas recovery to ensure efficiency. However, the Onionator demonstration was designed for simplicity, using only heat and a packed-bed of rocks as a reflux system with no gas capture. The main reason for this is that this will be a model system for deployment in low-resource and island communities, where a catalyst might not be available.

PTF analyzed the product using methods such as Gas Chromatography Flame Ionization Detection (GC-FID) and Nuclear Magnetic Resonance (NMR). GC-FID determines the product’s relative carbon distribution while NMR shows chemical groups present. Farm (red) diesel has a typical carbon number distribution of 7- 28 carbon units, with a mean of 19 carbon units. More than a dozen drip tape runs have been conducted in a 1 kg, lab-scale reactor (Helenator) with an average C-Number of 16. Indicating that drip tape-derived diesel could easily be blended with Farm diesel to run tractors, generators, etc. on a typical farm.

Implementation of the Onionator is ongoing with the PTF team at the Malheur Ag Experiment Station. Collaboration with the local community college will train students to operate the system and produce small-scale agricultural diesel, fostering local engagement and vocational education. This partnership will hopefully result in a commercial-scale pyrolysis unit in Malheur County to alleviate the growing waste drip tape issue.