Hot Microbes Cause Groundwater Cleanup Rethink

Schematic showing how biosparging enhances the microbial degradation of contaminants. (Credit: Willem van Aken / Courtesy of CSIRO Australia)

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CSIRO researchers have discovered that micro-organisms that help break down contaminants under the soil can actually get too hot for their own good.

While investigating ways of cleaning up groundwater contamination, scientists examined how microbes break down contaminants under the soil’s surface and found that subsurface temperatures associated with microbial degradation can become too hot for the microbes to grow and consume the groundwater contaminants.

This can slow down the clean up of the groundwater and even continue the spread of contamination.

The new findings mean that researchers now have to rethink the way groundwater remediation systems are designed.

CSIRO Water for a Healthy Country Flagship scientist Mr Colin Johnston, who is based in Perth, Western Australia, said the researchers were investigating how temperatures below the soil’s surface could be used as an indicator of the microbial degradation process associated with biosparging.

Biosparging is a technique that injects air into polluted groundwater to enhance the degradation of contaminants.

The contaminants are ‘food’ to the microbes and the oxygen in the air helps the microbes unlock the energy in the food so that they metabolise and grow, consuming more contaminants and stopping the spread of the contamination.

“Observations of diesel fuel contamination showed that, at 3.5 metres below the ground surface, temperatures reached as high as 47 °C,” Mr Johnston said.

“This is close to the 52 °C maximum temperature tolerated by the community of micro-organisms that naturally live in the soil at this depth and within the range where the growth of the community was suppressed.”

The growth of the soil’s micro-organism community can also be helped by adding nutrients.

However computer modelling confirmed that any attempts to further increase degradation of the contamination through the addition of nutrients had the potential to raise temperatures above the maximum for growth.

“Although increasing the flow of air would reduce temperatures and overcome these limitations a fine balance needs to be struck as the injected air can generate hazardous vapours that overwhelm the micro-organisms leading to unwanted atmospheric emissions at the ground surface,” Mr Johnston said.

“This would be particularly so for highly volatile compounds such as gasoline.

“It appears that prudent manipulation of operating conditions and appropriate timing of nutrient addition may help limit temperature increases.”

Mr Johnston said further research was required to better understand the thermal properties in the subsurface as well as the seasonal effects of rainfall infiltration and surface soil heating.

Story Source:
Adapted from materials provided by CSIRO Australia.

Nanoparticles To Combat Polluted Groundwater

Nanotechnology - Cleaning Up Our Water
Chemical Engineers Call On Nanoparticles To Combat Polluted Groundwater

Chemical engineers created nanoparticles out of gold and palladium to break down pollutants in groundwater. Adding the particles to groundwater converts dangerous contaminants like trichloroethylene into non-toxic compounds.

He's just 37 years old, but he's already making a difference in the world! A young engineer is creating small solutions to big problems.

We've seen it in the movies -- polluted drinking water is a health and environmental concern. In fact, right now, 30 states need to clean up their groundwater. "They've been designated by the EPA as being highly contaminated, and they've got to do something about the contaminated water," Michael Wong, Ph.D., a chemical engineer at Rice University in Houston, told Ivanhoe.

Dr. Wong is one of Smithsonian Magazine's America's Young Innovators … and for good reason. He's trying to come up with a way to use nanoparticles to clean up our water. "Water is not just H2O. Water has all sorts of stuff in it and the stuff we don't want, those are the things that can really hurt you," Dr. Wong explains.

He's using nanoparticles made out of gold and palladium -- a metal related to platinum -- to get rid of chemicals. One of the most common pollutants in United States groundwater is trichloroethylene, or TCE, a solvent used to degrease metals. And it can cause cancer.

"Our idea was, let's go ahead and break it down -- break it down into something that's safer," Dr. Wong says. "Safer chemicals that won't hurt your body and hurt the animals and the fish and what not."

Wong uses nanoparticles -- ten thousand times smaller than a human hair -- and hydrogen to break TCE into something non-toxic. "We are going to pump water through this guy here and the water is being pumped from the bottom up," Dr. Wong explains.

Glass beads will help to hold the nanoparticles in place. "Then clean water comes out," Dr. Wong says. Dr. Wong plans to test it at military sites first -- then move onto industrial sites and dry cleaning businesses. "I'd like to see our reactor do a really good job of getting rid of some of the contaminants," Dr. Wong says. Possibly, making our water and environment cleaner in the future. Dr. Wong says his reactor will be more efficient and cost less than the carbon reactors being used now.

WHAT IS HAZARDOUS WASTE? In the U.S., hazardous waste is defined as any discarded solid or liquid that is highly corrosive, toxic, reactive enough to release toxic fumes, or easily ignited. It can include solvents, pesticides, and spilled chemicals -- including acids, ammonia, chlorine bleach and other industrial cleaning agents -- as well as most heavy metals. Long-term exposure to hazardous waste can lead to chronic respiratory diseases such as asthma, damaged liver and kidneys, or cancer. Poisoning and chemical burns can result from contact with even small amounts of toxic chemical waste. Even brief exposure can cause headaches, dizziness, and nausea.

WHERE THAT GLASS OF WATER COMES FROM: Drinking water can come from either ground water sources, via wells, or surface water sources, such as rivers, lakes and streams. Most U.S. water systems in small and rural areas use a ground water source, while large metropolitan areas tend to rely on surface water. Causes of contamination can range from agricultural runoff to improper use of household chemicals.

SECONDARY STANDARDS: Even if your tap water meets the EPA's basic requirement for safe drinking water, some people still object to the taste, smell or appearance of their water. These are aesthetic concerns, however, and therefore fall under the EPA's voluntary secondary standards. Some tap water is drinkable, but may be temporarily clouded because of air bubbles, or have a chlorine taste. A bleachy taste can be improved by letting the water stand exposed to the air for a while.