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Evaluation of Atmospheric Water Generation Technology: Microbial Water Quality
Jahne, M., S. Pfaller, J. Garland, AND C. Impellitteri. Evaluation of Atmospheric Water Generation Technology: Microbial Water Quality. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-18/379, 2018.
Atmospheric water generators (AWGs) produce potable water from ambient air. Recent high-profile natural disasters, such as Hurricane Harvey, and public water infrastructure failures, such as those that occurred in Flint, Michigan, have increased the interest in AWG technology as both emergency and longer-term supply solutions. In August of 2017, EPA’s Office of Research and Development (ORD) announced a Cooperative Research and Development Agreement (CRADA) developed to further advance the science of AWG, and assess its potential as a water production and supply solution for different scenarios. In January 2018, EPA signed a CRADA with Watergen, a corporation developing cutting-edge AWG technology, to evaluate their GEN-350 system (http://water-gen.com/). This report covers the results of an overall assessment of the quality of water produced by the AWG. Results of this work emphasize that atmospheric condensate is not sterile and should be treated adequately prior to potable use. Findings will be of interest to States, public agencies, and other parties interested in utilizing AWG technology.
Atmospheric water generators (AWGs) have the potential to expand the availability of water during shortages, contamination events and interruptions of service. Given the nature of atmospheric water generation (i.e., condensation of atmospheric water vapor), high quality produced water is generally anticipated; however, it may not be safe for human consumption. Concentrating large volumes of air can simultaneously concentrate contaminants, and microbial growth in plumbing and stored water is possible. An initial review of water quality data provided by Watergen USA (hereafter referred as Watergen), a manufacturer of AWG technology, confirmed both the generally high quality of produced water (e.g., no elemental analyses above current EPA primary or secondary drinking water standards), but an elevated level of overall microbial numbers (i.e, heterotrophic bacteria). Indicators of fecal contamination (e.g., fecal coliforms, E. coli) were not detected. The primary microorganisms of human health concern are opportunistic pathogens, such as Legionella spp. and Mycobacterium spp., that are commonly associated with drinking water infrastructure. Detection of these organisms, particularly L. pneumophila serogroup 1 and M. avium, would constitute a potential health concern. The objective of this study was to evaluate the microbial quality of untreated condensate and produced (treated) water from a commercial AWG unit (Watergen GEN-350) during the three-month study. Opportunistic pathogens were not detected in weekly samples collected; however, high levels of heterotrophic bacteria, detected using heterotrophic plate counts (HPC) of treated water, indicate inadequate disinfection and/or microbial regrowth following treatment. The presence of heterotrophic bacteria do not represent a human health risk, but suggest microbial instability and conditions favorable for microbial growth. It is therefore recommended that chlorination or ozonation be included as an additional unit process in the GEN-350 treatment train. While not directly transferrable to other AWG systems, results of this work emphasize that atmospheric condensate is not sterile and should be treated adequately prior to potable use.