Bustling rivers such as the Mississippi and the Ohio are the source of drinking water for millions of Americans. But these rivers are likely to contain hazardous chemicals and pathogens that must be removed or neutralized before the water is safe for drinking.
New research suggests that the soil alongside these channels could help with the cleanup.
Drawing river water through the adjacent earth may strip away some unwanted pollutants, including harmful viruses, protozoa and bacteria, researchers at Hopkins believe.
The idea is called river-bank filtration. Instead of pulling water directly from the river for subsequent treatment and distribution, utilities drill wells nearby. River water drawn from these wells must first pass through hundreds of feet of soil, which serves as a natural filter.
How effective are river banks as a cleansing agent? Scientists at Hopkins have launched a three-year study to find out. The researchers want to determine how well river-bank filtration removes pathogens, such as viruses, protozoa and bacteria. They also want to find out if this process removes other organic matter that reacts during disinfection within a treatment plant to form potentially harmful by-products.
"You can surmise that going through the ground should be a better method; that's your intuition," says Edward J. Bouwer, lead investigator in the study. "But we want to quantify how much better it is."
The work is important because dangerous microbes and cancer-causing chemicals sometimes slip past traditional water treatment. "We're worried about resistant pathogens created by the overuse of antibiotics," says Bouwer, a professor in the Department of Geography and Environmental Engineering. "Some bacteria are becoming more resistant to disinfection. We're also worried about the by-products created during disinfection. Some of them may be carcinogenic."
The Hopkins study, supported by a $300,000 grant from the U.S. Environmental Protection Agency, will focus on water drawn from wells alongside the Wabash, Ohio and Missouri rivers near Terra Haute, Ind.; Louisville, Ky.; and Kansas City, Mo. The wells are all owned by the American Waterworks Service Co., which is providing $256,000 in labor, equipment and other in-kind support for the study.
The company is testing a natural filtration method developed in Europe two decades ago to produce cleaner drinking water from polluted rivers such as the Rhine. "The focus in the 1970s was mainly to get rid of taste and odor problems and to remove hazardous materials like pesticides and hydrocarbons," Bouwer says. "But there has been limited recent work to look at how it affects the pathogens and by-products of disinfection. We will be doing work that is more relevant to today's concerns."
The study will pay particular attention to disinfection by-products, a source of growing alarm. After vegetation decays, tiny bits of surviving plant material make their way into a water source. In its natural state, this organic matter may affect how water tastes or smells, but it poses no health risks. However, when treatment plants add a disinfectant to kill pathogens, the chemical can also react with the harmless organic matter, creating not-so-harmless by-products. For example, chlorine mixed with the plant material can produce chloroform, a suspected carcinogen.
For water utilities, that poses a dilemma. "Viruses and other pathogens in drinking water are a real threat," says Bouwer. "But the trade-off is, if you use disinfectants to kill them, you're going to create these by-products that are harmful themselves."
One solution is to remove more of the harmless plant matter before a disinfectant is added to the water. One way is to "feed" this material to bacteria in the soil before the water reaches the treatment plant.
Bouwer's team--which includes William P. Ball and Charles R. O'Melia, both faculty members in the Department of Geography and Environmental Engineering--wants to find out if river-bank filtration will accomplish this. The researchers will compare water samples taken directly from the rivers with those drawn from nearby wells. They will also replicate the treatment process in labs at Hopkins to determine the quality of drinking water produced from both sources.
First results from the experiments are expected in about 12 to 18 months. When the project is completed, the researchers hope to publish design guidelines to show other utilities how and where to dig the most effective river-bank filtration wells.