Protecting drinking water from disease transmission by means of zeolite filters
WASHINGTON - Septic tanks, sewage overflow, and landfills can contaminate drinking water supplies with germs responsible for human infections, including hepatitis viruses and E. coli bacteria. The development of an inexpensive means for blocking the transmission of bacteria and viruses to humans could significantly reduce disease outbreaks associated with groundwater and could also alleviate concerns regarding bioterrorist threats to drinking water supplies.
A team of scientists headed by Dirk Schulze-Makuch of the University of Texas at El Paso has experimented with the removal of viruses from drinking water using a filter made of naturally occurring minerals known as zeolites. Their findings are presented in the April 30 issue of Eos, a publication of the American Geophysical Union.
In typical ground water, viruses carry a negative surface charge. Adding a filter that carries a positive charge to wells will cause the viruses to adhere to the filter, rather than being transmitted to humans who drink the water.
Schulze-Makuch and his colleagues suggest, based on their experiments, that zeolites would be effective filter components to block virus migration in ground water. Like clay minerals, zeolites have a large surface area, providing more places for viruses to adhere. Unlike clays, however, zeolites do not swell in water but remain rigid, serving as a filter through which water can pass freely.
Zeolites possess a negative surface charge, which limits their natural ability to attract viruses. In order to reverse this charge, the scientists treated zeolites with a chemical, abbreviated HDTMA (hexadecyltrimethylammonium), which is found in hair conditioner and mouthwash. They then conducted laboratory and field studies to compare the performance of treated zeolite as a suitable virus barrier with that of untreated zeolite and of iron-oxide coated sand.
The researchers found that in both laboratory and field tests, untreated zeolite failed to remove viruses from the water. Iron-oxide coated sand was effective in removing viruses from water in the laboratory, but largely failed to do so in the field. Treated zeolite was an effective barrier in both situations. In the field, treated zeolite removed at least 99 percent of viruses from the water and 100 percent of E. coli.
The scientists believe that the results of their study, along with the relatively low cost of treated zeolite, suggest that a filter pack composed of treated zeolite could be an effective and practical means for controlling the spread of diseases through drinking water wells. They note, however, that additional studies into the effective lifetime of the filter pack and the effect of HDTMA itself on humans are necessary, before determining the feasibility of using treated zeolite as a barrier to viruses and bacteria.
The study was supported by the Environmental Protection Agency.