Raw water is purified at water treatment plants and is then transported to drinking water distribution centers, at which point purification stops. Because water pipes run for miles until they reach faucets, the water contained is exposed to microbes that are collected over the span of six weeks, resulting in the formation of a biofilm.  

A biofilm is a thin layer of microorganisms in which the cells stick together and collectively attach themselves to a surface. This affects the quality of drinking water, because biofilms release pathogens into the water flow.

The department of civil and environmental engineering at the University recently studied the mechanical and structural properties of biofilms and how they respond to two common drinking water disinfectants, chlorine and chloramine. This research was conducted at Newmark Laboratory.

Thanh Helen Nguyen, associate professor in the department, along with Ph.D. student Yun Shen, conducted this study, titled “Response of Simulated Drinking Water Biofilm Mechanical and Structural Properties to Long-Term Disinfectant Exposure,” which was published in ACS Publications in January.

The first step in the process was to actually build a simulated drinking water biofilm that best resembled a naturally-occurring biofilm found in water pipes. Shen said this step took an entire year.

The simulated biofilm was then exposed to chlorine and chloramine over a period of three months to test how either affects the growth of the biofilm.

Results showed that the disinfectant could not completely remove the biofilm layer, but it could change the biofilm properties – namely, thickness and stiffness.

The biofilm thickness and stiffness were measured during the three months of disinfectant exposure. In the first month, chlorine and chloramine were most effective in reducing the thickness and increasing the stiffness of the biofilm.

“After longer disinfectant exposure time (two to three months), biofilm volume started to recover again. Some bacteria in the biofilms may adapt themselves to disinfectant,” Shen said. “However, although long-time disinfectant could not reduce the total volume of the biofilm, it could still stiffen the biofilms, thus preventing the detachment of the biofilm.”

The disinfectant strengthened the biofilms, thus preventing detachment of the biofilm when drinking water flows through. Therefore, the release of pathogens into the drinking water would be reduced.

Nguyen emphasized the importance of this research by explaining that the disinfection process at the water treatment plant is well-studied and controlled, but the problem arises when the water is released into the distribution system, because it travels for miles before reaching its destination.

“(We don’t) see a distribution system . . . miles and miles and miles of distribution system connects the water from the water treatment plant to us, so depending how far we live, you might have a different water quality,” Nguyen said. “The research is to contribute to the understanding of the factors that control the disinfection in the distribution system after the water treatment plant.”

Nguyen said this complicated study needed several different tools to be completed successfully.

Stephen A. Boppart and his team at Beckmann Institute helped with the imaging of the biofilm.

“Professor Boppart is very famous for developing imaging technique for biofilm in human ear infections,” Nguyen said. “A lot of his research is done at Carle Hospital, but he’s always curious to try his method to other applications.”

Other University professors also assisted in the research. Rosa Espinosa, material scientist, helped Shen study an advanced surface characterization tool commonly used in material science, called atomic force tomography, to investigate the mechanical properties of biofilms. Wen-Tso Liu, microbiologist, helped Shen understand the microorganism activities and biofilm composition in distribution systems.

Eberhard Morgenroth, professor for process engineering in water management in Switzerland, assisted in analyzing the imaging data.

Nguyen was granted $600,000 by the United States Environmental Protection Agency in order to conduct this research.

The next step is to try to maintain the disinfectant residue because it is easily consumed along the way, Nguyen said.

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