Biofuels consist largely of ethanol extracted from a variety of crops, including corn, which is often mixed together with gasoline. Yet, in terms of its fluid properties, biofuels differ significantly from gasoline, leading researchers to question how biofuels with a large ethanol component would spread in an aquatic environment following a large biofuel spill.
Upon further investigation, they discovered that unlike pure gasoline, which tends to float on water, ethanol-based liquid fuels readily mix with water. This characteristic could potentially make them more hazardous to aquatic organisms and wildlife. Consequently, oil spill response guidelines may need to be amended to address issues related to ethanol fuel spills.
The results of this study were presented in a paper titled “Characterization of Mixing Between Water and Biofuels,” at the 65th Annual Meeting of the American Physical Society (APS) Division of Fluid Dynamics, held recently in San Diego, California.
“Ethanol/gasoline blends are often presented as more environmentally benign than pure gasoline, but there is, in fact, little scientific research into the effects these blends could have on the health of surface waters,” says Avery Demond, Director of the Environmental and Water Resources Engineering program at the University of Michigan, and one of the scientists researching this issue. While some reports contain methods that can be used to determine how ethanol will spread in water in line with the principals of passive diffusion/dispersal processes, according to Demond, these methods are not based on sound scientific research of how ethanol would react with water.
In an effort to broaden our understanding of how ethanol and water react, the research team ran a series of controlled experiments in a water tank, which they filled with water. The water was then covered with a plate, onto which mixtures of ethanol were poured. The plate was subsequently removed and the reaction between the two liquids observed and filmed as they mixed. The video footage illustrates flow patterns – referred to as convection cells – that form where the ethanol and water meet. When the water and ethanol started to mix, heat was produced, which altered the density and viscosity of the ethanol, allowing circulation currents to develop. Gasoline on the other hand, is typically insoluble in water and tends to remain floating as a surface film, where it readily vaporizes into the atmosphere.
Mixing Patterns Could Increase the Impact of Biofuel Spills on Aquatic Ecosystems
According to Demond, the mixing patterns observed between ethanol and water are considered quite extraordinary: “I’ve never seen anything quite like it and it certainly is not passive the way that modeling guidelines suggest.”
The research team’s next goal is to assess the volatility of different ethanol-based fuel mixtures in order to get a clearer understanding as to how much ethanol would be vaporized into the atmosphere and how much would disperse into the water column in the event of an aquatic spill.
While ethanol is considered biodegradable, it is toxic to aquatic organisms in high concentrations. The ethanol component of ethanol-gasoline fuel blends may also facilitate the transportation of carcinogens contained in gasoline into the aquatic environment in the event of mixing following a spill.
“We can’t make statements about the environmental impact of ethanol before we’ve more fully investigated its potential effects on surface water quality in the event of a spill,” note the researchers.
The scientists hope that this research will address lingering questions regarding the potential of ethanol fuels to mix with water, and ultimately give both scientists and decision-makers a clearer understanding of possible environmental impacts associated with ethanol-based biofuels. Hopefully this will equip them with the knowledge to prevent environmental devastation that could arise as a consequence of potential biofuel spills in the future.