Plant Waste

Fuel made from plant waste is made primarily from either waste vegetable oil (WVO) or WVO converted into biodiesel, a diesel fuel made either partially or wholly from biological materials. With a few exceptions, WVO requires modifying existing equipment, while WVO converted into biodiesel can be used in most diesel-burning engines.

Fuel from waste or converted vegetable oil has pros and cons, but both confer many environmental and economic benefits. Used oil contains nearly twice the energy value of coal and more energy than No. 2 fuel oil. Compared to petroleum diesel, biodiesel produces fewer volatile organic compounds (VOCs) and particulates and less CO2, sulfur dioxide, carbon monoxide and mercury. Some studies suggest that biodiesel produces slightly higher levels of nitrogen oxide (NOx) pollution, but researchers are investigating new additives and diesel technology that could significantly lower these emissions.

Mike Collins and Rebecca Nixon of Old Athens Farm in southeastern Vermont decided to switch to straight waste vegetable oil to heat their three greenhouses after using as much as 3,000 gallons of No. 2 oil in one winter. Each greenhouse now has a waste oil burner, generating 350,000 BTU for 3,200 square feet.

Collins and Nixon, who grow organic vegetables and berries for direct markets on two acres, and produce greenhouse tomatoes, cucumbers and eggplants, collect waste oil from nearby restaurants. The restaurants are within normal vegetable delivery routes, saving transport-related time and energy. Collins and Nixon avoid oil with hydrogenated fats as it does not perform well in waste oil burners.

The oil, generally kept in containers ranging from five to 50 gallons, is brought to the farm, filtered through a screen and then stored in large plastic tanks in the greenhouse. Because it solidifies in cold weather, any oil kept outside in the winter must be pre-warmed before use.