Using Bioremediation to Treat Pollutants in the Environment

Katie Huston for TEI

Sarina Ergas knows that small organisms can make a big difference. Ergas, an Associate Professor in the Department of Civil and Environmental Engineering, specializes in bioremediation, a process of using microorganisms to biodegrade toxic compounds to non-toxic substances to reduce pollutant concentrations in the environment.

“We have microorganisms that we find can carry out some particular process that we want them to carry out, and then what we have to do is figure out what their needs are,” she says. “We can’t just make them do our bidding. We have to get on their agenda. Microorganisms don’t do this altruistically. They only want one thing: to grow and create more bacteria.”

Along with Klaus Nüsslein in the Department of Microbiology, she recently received a $300,000 grant from the National Science Foundation to continue their research on reducing perchlorate to chloride. Perchlorate is a fairly common groundwater contaminant, Ergas says, that was used in rockets and missiles, and to manufacture products such as airbags and roadside flares. It has the potential to cause disruption of the thyroid gland, which can cause developmental delays and other problems with growing children. Evidence also exists that it may cause thyroid tumors and hypothyroidism in adults.

Microorganisms such as iron-reducing bacteria and sulfate-reducing bacteria, however, can clean up contaminated water through natural processes. Ergas’ role is to figure out what kinds of environmental conditions allow these microorganisms to thrive and what substrates, or organic compounds, they need to grow. Ergas and Nüsslein are currently looking at a treatment process with a microorganism that uses sulfur as an electron donor for biological perchlorate reduction, trying to establish optimal environmental conditions for it to thrive.

Using microorganisms to treat pollutants has many advantages. “They work cheap. You don’t have to pay them a lot,” Ergas says. “They’re very ubiquitous, they’re all over the place. They have a lot of surface area and contact with the environment, they have very high rates of transformation.”

Biological processes can often speed reaction rates by a factor of 100,000 to 10 billion, and using microorganisms for remediation also eliminates the formation of residual waste products, Ergas says. “You don’t wind up with a residual that needs to be treated further. When you have biological perchlorate reduction, you actually get rid of the perchlorate. You transform it into harmless products,” she says.

Ergas says that she and Nüsslein make a good team. “I work on the engineering side, so I’m interested in the process, substrates, environmental conditions, reactors, how we design this system. He’s really interested in who are the organisms, what are their capabilities, what enzymes are active in the process,” she says. “We’re really interested in trying to use molecular tools to understand the bioreactor process.” The NSF grant will allow them to scale up their work. “We’re going to do some pilot tests on the Massachusetts military reservation, where they have extensive perchlorate contamination, out on Cape Cod,” Ergas says.

Ergas also spent the summer and fall of 2007 on sabbatical as a Fulbright Fellow at the Israel Institute of Technology studying water reuse systems, specifically the use of membranes in biological wastewater treatment processes. Israel was a good place to be according to Ergas, as the country is at the forefront of developing wastewater treatment technology and reuses about 75 percent of its water.

Back on the UMass Amherst campus, she’s collaborating with Todd Emrick, from the Department of Polymer Science and Engineering, who’s developing new membrane materials and coatings. Membranes are polymeric materials, such as polyvinyl chloride or polysulfone, with very small pores in them. Over time, bacteria stick to the surface of the membrane, which causes clogging or “fouling” and reduces water flow through the membrane. “If you want to use membranes in water reuse application, your biggest problem is going to be fouling, that the organisms grow on the surface and they clog up,” Ergas says.

Ergas uses small membrane modules and simulated wastewater with fluorescently tagged microorganisms that produce red protein to test the effectiveness of different membrane surface coatings. In Israel, she used a technology called confocal laser scanning microscopy to evaluate the amount of biomass that stuck to the membranes. “We were able to really characterize not only visually, but really getting some quantitative information about how much biomass was on the surface,” she says. “It’s a lot of fun.”

Ergas found that uncoated membranes foul more easily. “What you see is just layers and layers of bacteria growing one on top of another.” Different coatings showed different levels of effectiveness, and the results allow Emrick to fine-tune the membranes’ chemical composition.

Ergas sees a lot of potential in membranes. “The initial results have been promising,” she says. The “very high quality water” that they can produce “could be reused in all kinds of applications. You could use it for irrigation, you could use it for recharging groundwater aquifers, you could use it for firefighting, toilet flushing. It’s a very good tool for areas where water is scarce, to try to reclaim as much of the wastewater as possible for non-drinking water uses.”

Ergas is also working on denitrification of storm water, heading a project on a dairy farm out in Putnam, Connecticut. On farms, nitrogen finds its way into the water supply through ammonia volatilization, fertilizer and manure. Nitrogen in agricultural runoff is a big source of eutrophication, which happens because of the overgrowth of plants and algae. Oxygen is depleted from water when this organic matter is degraded. Sometimes this even leads to toxic algae blooms, Ergas says. “In certain places like Long Island Sound, there are large regions of the sound that are hypoxic, that there’s no oxygen, leading to major fish kills,” Ergas says.

Bacteria can be used to convert the nitrogen in agricultural runoff into nitrogen gas that is absorbed into the atmosphere, and she wants to fine-tune this process. Denitrification is used regularly in wastewater treatment, but is not often used to control runoff. “We understand how to do this in a wastewater treatment plant, but how do we get this to work in something like a dairy farm, where you really need something that’s passive, that’s robust?” Ergas asks. “The farmer’s interested in milk; he’s not necessarily interested in controlling nitrogen in his runoff. So we try to make this process easy and reliable on the engineering side of things.” She’s using a pipeline to channel detention pond water into bioretention units, again to fine-tune the conditions the microorganisms need to thrive.

Bioremediation is not without its challenges. One downside, Ergas says, is that sometimes her research can progress slowly. “If you’re trying to get a population to adapt to new conditions, it might take many generations before an acclimation occurs,” she says. “Oftentimes my students will run bioreactors for a year, two years, three years even, before they get the results that they’re looking for.”

Ergas has also experienced some resistance from environmental managers to the idea of bioremediation, which she says can be frustrating. “There’s a lot of agreement that bioremediation is a cool process, that it’s cheap and very effective, yet there’s a lot of unknowns,” she says.

However, she is optimistic about bioremediation’s potential, and she enjoys the work she’s doing. “There’s something about it that’s sort of mysterious in working with living organisms. It’s very satisfying,” Ergas says.