‘Green’ Water Cleanup
Stephanie McPherson for TEI
David Reckhow, Civil and Environmental Engineering
David Reckhow, Professor of Civil and Environmental Engineering, works to ensure the safety of drinking water supplies across the country. “I’m involved with a lot of aspects of water treatment […] the purification of what we call raw drinking waters,” Reckhow says. Water contamination comes in many forms and Reckhow’s laboratory work determines the most efficient ways to clean contaminated water.
Organic compounds such as polysaccharides and proteins are harmless products of terrestrial and aquatic plants. But when they interact with disinfecting agents, they are converted to compounds that have deleterious effects. These disinfection byproducts are associated with cancer, particularly of the bladder. Reckhow’s group examines exactly what these harmful compounds are and how to control them. They begin as nontoxic, normal organic materials released from both aquatic and terrestrial plants. As they flow downstream and into water treatment plants, they nteract with bacteria and chlorine to create dangerous arcinogens. “We’re concerned about the nature of the organic material and how it changes from the well water or the lake in its pristine form,” says Reckhow. “[We want] to minimize the risk to people.”
To address the problem Reckhow first collects water samples from water treatment plants around the country and conducts laboratory analyses. With newly-developed analytical instruments such as liquid chromatrographs and mass spectrometers (LC/MS) he can identify the exact compounds present in the water. Next, he determines the optimal methods for removal and mitigation. Most treatment plants around the country use conventional removal methods. Some put coagulants in the water to form particles, which draw contaminants out. Some use media filtration – the process of running water over sand or activated carbon, which sifts out unwanted organics. Some treatment plants also continue to use chlorine disinfection. The town of Amherst is on the cutting edge of water purification treatment, using ozone as a chemical to partially oxidize the contaminant, making it easier to break down and dispose of through other methods. Reckhow is perfecting this method, using beneficial bacteria to rid the water of the oxidized organics leaving only carbon dioxide and water. “That’s the beauty of the synergy,” he says. “If you do that right, then it’s a great one two punch for contaminants.”
Reckhow’s research also focuses on another group of contaminants affecting water supplies - pharmaceuticals and personal care products, also known as PPCPs. Everyday products like pain medication, perfume and shampoo wind up in the water system and, without proper filtration, enter the water system. This problem is particularly prevalent downstream from major cities, and in the Southwest, which is perpetually effected by water shortages. “They absolutely need to reuse the water that someone from an upstream community used already,” says Reckhow.
Through funding from the Water Research Foundation, Reckhow also is testing the effectiveness of 15 city treatment plants around the country. In his lab, PPCP contaminated water runs through pilot scale models of each plant. The water is measured before and after a run using a specialized LC/MS instrument dubbed “Betsy.” With this newly-developed hybrid instrument, his group is able to analyze PPCPs in smaller samples (20 mL) in a fraction of the time required by conventional methods. They compare the results pre- and post-filtration to determine just how much contaminant is removed. If the result is unsatisfactory, Reckhow tests various advanced methods until the outcome is desirable. After the tests are complete, the necessary adjustments to improve treatment are communicated to the water treatment practitioners.
Another project focuses on the Merrimack River, running from New Hampshire through Massachusetts. Towns along the river are concerned about wastewater flowing downstream. Reckhow is collaborating with faculty at the University of New Hampshire and the U.S. Geological Survey to understand the nature of the PPCPs present along the watershed. Once the state of the river is determined, they will begin to install a new pilot-scale system using riverbank filtration – a method successfully carried out in Europe. Instead of pumping the water directly out of the river, the water is pumped from a well approximately 100 feet away from the bank. “It sucks water down out of river through the ground and into the well so the water travels in the subsurface and, in the process, it gets purified by natural bacteria,” Reckhow says. “It’s extremely low tech, but really green.” The team could even apply ozone to the water before it travels through the ground, enhancing biodegradation processes.
This method, while environmentally friendly due to the use of natural bacteria, requires more energy than pumping straight from the river. The water would need to be siphoned up a pipe resting far below the bank’s height. While digging a well also incurs costs, riverbank filtration may be more cost-effective than traditional methods. Some issues still need to be addressed, as the method has not been widely tested in the United States. “Engineers are inherently conservative,” Reckhow says. “You want to build something you know is going to work for a long time, and [with] these you can’t always be sure.” The only way to find out, he says, is to jump right in and try.
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