Using worms and compost to clean up oil spills
When the container ship Cosco Busan struck the Bay Bridge in 2007, spilling 53,000 gallons of fuel into San Francisco Bay, cleanup contractors used giant plastic sponges to soak up most of the oil, then incinerated the waste. It’s a standard practice, but one that Thomas Azwell, a Ph.D. student in environmental science, policy, and management, points out turns an oil spill in the water into a “carbon spill in the air.” Inspired by the Cosco Busan incident, Azwell was determined to find a better way to get rid of industrial oil. His method: composting.
Most oils break down fairly easily, but the bunker fuel of a container ship is problematic; its chemical structure is too complex for existing bioremediation methods — such as using mushrooms as decomposing agents or a humanmade wetland as a biological filter — to be effective. Azwell, however, aimed to intensify the decomposition process by using the high bacterial concentration in compost piles to break down bunker oil’s long carbon chains.
Azwell created a windrow, or compost pile, 50 feet long, 6 feet tall, and 10 feet wide. He mixed nine 55-gallon drums of bunker-C oil in with the organic matter, allowing the bacteria to use the oil as a carbon food source. That process produced 125-degree temperatures within the windrow for two months before the pile began to cool down — signaling that the bacteria had finished breaking down the organic materials. Next came the crucial test: had the bacteria effectively broken down the hydrocarbons? To test the soil’s toxicity, Azwell used earthworms. “Earthworms have an intimate relationship with compost,” he says. “If they can eat the compost, their end product will be deemed safe for dispersal into the environment.”
Trucking in 2,000 pounds of worms, Azwell dumped them in the windrow to complete the work started by the bacteria, crossing his fingers that the hydrocarbons had been broken down and the worms would enjoy this feast. After 90 days, the worms in his vermicompost pile had not only survived, but doubled in population. “The worms loved it,” Azwell says. “They had plenty of food, water, and air.”
The worms not only validated Azwell’s remediation experiment, but added value to the compost by improving soil aeration and water retention properties, providing plant growth hormones, and increasing the concentration of key nutrients. Norman Terry, professor of plant and microbial biology and an expert in bioremediation, says that Azwell’s work has much promise. “Although final results have not yet come in, this low-cost, low-tech solution could be a very effective bioremediation method.”
Azwell works as part of Terry’s lab group to investigate the plant-microbe interactions at work here, and also in the lab of Jeff Romm, professor of society and environment, to look broadly at how his innovations could deliver industrial and social benefits. And he is already working with industry, transforming organic waste from California Costco stores into a soil amendment product called Vermigrow. He hopes that his successes will lead to low-cost, environmentally safe methods of oil waste disposal, as well as to advances in the use of earthworm culture in sustainable agriculture.