Navigation Links
Ethanol blends carry hidden risk
Date:12/13/2013

HOUSTON (Dec. 12, 2013) Blending more ethanol into fuel to cut air pollution from vehicles carries a hidden risk that toxic or even explosive gases may find their way into buildings, according to researchers at Rice University.

Those problems would likely occur in buildings with cracked foundations that happen to be in the vicinity of fuel spills. Vapors that rise from contaminated groundwater can be sucked inside, according to Rice environmental engineer Pedro Alvarez. Once there, trapped pools of methane could ignite and toxic hydrocarbons could cause health woes, he said.

The timely warning comes as the United States works to stimulate the production and consumption of ethanol. The Rice study, detailed this week in the American Chemical Society journal Environmental Science and Technology, emerges as the Environmental Protection Agency (EPA) prepares technical guidance for higher ratios of ethanol in fuels.

"The safe distances (between buildings and groundwater) that the EPA are setting up are going to work well 95 percent of the time," said Alvarez, a member of the agency's Science Advisory Board. "But there's the 5 percent where things go wrong, and we need to be prepared for extreme events with low probability."

Computer simulations at Rice determined that fuel with 5 percent or less ethanol content does not rise to the level of concern, because small amounts of ethanol and benzene, a toxic, volatile hydrocarbon present in gasoline, degrade rapidly in the presence of oxygen. Methane produced when ethanol ferments is often degraded by methanotrophic bacteria, which also require oxygen.

But fuel blends of 20 to 95 percent ethanol and gasoline, intended for "flex-fuel" vehicles, could increase the generation of methane. Ethanol and gasoline separate into distinct plumes as they spread underground from the site of a spill. As liquid ethanol degrades into gaseous methane, it expands, driving advective flow and forcing the gas outward and upward. That could overwhelm natural attenuation and should prompt new thinking about how to manage vapor-intrusion risks, Alvarez said.

"We want the bacterial activity to eat these vapors before they reach us," Alvarez said. He said many factors, including shallow groundwater or soil with low permeability that is not easily ventilated, could stand in the way.

"The amount of oxygen allowed to diffuse in would determine the assimilative capacity of the soil and the degradation capability," he said. "The bacteria will be there, but they're not going to do you much good if they run out of oxygen. The problem is bacteria that eat the methane use up all the oxygen, and the ones you want to degrade benzene can't do their job because they don't have any oxygen left."

Benzene is a carcinogen. According to the federal Centers for Disease Control and Prevention, long-term exposure can harm bone marrow and cause a decrease in red blood cells, leading to anemia. It can also cause excessive bleeding and affect the immune system.

Alvarez said studies have assessed the amount of methane generated by spills, but none have directly addressed what happens when the highly flammable vapors rise into confined spaces, where they can accumulate. He said flux chambers have been used to measure methane in such spaces, but they don't account for building effects like typically lower interior pressure that would draw vapors in through cracked foundations.

So the Rice lab led by Alvarez, with the participation of researchers from Chevron, Shell and the University of Houston, programmed a three-dimensional vapor intrusion model to simulate the degradation, migration and intrusion pathways of methane and benzene under various site conditions. The program modeled a small building with a perimeter crack around the foundation, sitting in the center of an open field. The atmospheric pressure was assumed to be slightly less inside than outside.

The simulations determined that when there is no generation of methane from a plume, benzene would not be a problem -- even for sources less than a meter below a foundation. But methane generation near a source significantly increased indoor concentrations of benzene; traces of the gas would be detected even when the source lay as much as 13 meters below a building.

Alvarez said the paper's lead author, Rice graduate student Jie Ma, has done extensive work to characterize bacterial activity at spill sites. "He figured out where the ones eating methane and consuming oxygen are most active. Most of them are concentrated in a very thin layer called the capillary fringe, where capillary forces suck the water up, above the saturated zone.

"It turns out this is a sweet spot where there's enough oxygen and moisture for the microbes to be happy, and it's close to high methane concentrations," Alvarez said. "They were present in several orders of magnitude higher than anywhere else. It's because of this biological filter that we rarely get explosions above the ground.

"That's the positive effect. The negative effect is that they're consuming the oxygen, and while they're saving us from explosions, they're allowing benzene to flow through. It's a trade-off."


'/>"/>

Contact: David Ruth
david@rice.edu
713-348-6327
Rice University
Source:Eurekalert  

Related biology news :

1. Too green to be true? Researchers develop highly effective method for converting CO2 into methanol
2. Researchers say sunlight yields more efficient carbon dioxide to methanol model
3. Powerful enzymes create ethanol from agricultural harvest waste
4. Gut microbes in healthy kids carry antibiotic resistance genes
5. Radio waves carry news of climate change
6. Bees under threat from disease-carrying bumblebee imports, research reveals
7. PARP inhibitor shows activity in pancreatic, prostate cancers among patients carrying BRCA mutations
8. Biological wires carry electricity thanks to special amino acids
9. Achilles heel: Popular drug-carrying nanoparticles get trapped in bloodstream
10. Notre Dame research reveals migrating Great Lakes salmon carry contaminants upstream
11. Western aspen trees commonly carry extra set of chromosomes
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Ethanol blends carry hidden risk
(Date:2/16/2017)... 16, 2017  Genos, a community for personal ... has received Laboratory Accreditation from the College of ... to laboratories that meet stringent requirements around quality, ... processes. "Genos is committed to maintaining ... We,re honored to be receiving CAP accreditation," said ...
(Date:2/10/2017)... Feb 10, 2017 Research and ... "Personalized Medicine - Scientific and Commercial Aspects" to ... ... Diagnosis is integrated with therapy for selection of treatment as ... detection and prevention of disease in modern medicine. Biochip/microarray technologies ...
(Date:2/8/2017)... , Feb. 7, 2017 Report Highlights ... The global ... reach $11.4 billion by 2021, growing at a compound annual ... - An overview of the global markets for synthetic biology. ... estimates for 2016, and projections of compound annual growth rates ...
Breaking Biology News(10 mins):
(Date:2/21/2017)... ... February 21, 2017 , ... ... -Sciences division, Treximo will pair its $200M operational capacity with its strategic ... project management in areas affecting quality and operational management. With office ...
(Date:2/21/2017)... ... 21, 2017 , ... Creation Technologies, a private company and ... manufacturers (OEMs) , today announced it has received the ‘Highest Overall Customer Rating’ ... its category of electronics manufacturing services (EMS) providers with annual revenues over $500 ...
(Date:2/21/2017)... ANGELES , Feb. 21, 2017  Lexus, a returning partner ... role as the official and exclusive automobile partner of the men,s ... spring race. The 2017 Amgen Tour of ... commitment and feature some of the best professional cycling teams in ... , May 14-20. The four-day Amgen Breakaway from Heart Disease ...
(Date:2/21/2017)... February 21, 2017 Scientists From ... Adoption by Plastic Industry  ... STEER, creator of advanced ... in the fields of plastics, pharmaceuticals, food and nutraceuticals, biomaterials ... a leading science & technology company, on creating co-rotating ...
Breaking Biology Technology: