By Zhi ‘George’ Zhou, PhD, PE, BCEE and Kayla Heriaud
The Safe Drinking Water Act is a federal law that regulates the United States’ public drinking water. Under the SDWA, US EPA has established National Primary Drinking Water Regulations (NPDWRs) that set legally enforceable levels which a contaminant known to cause human health effects cannot exceed in drinking water in order to protect public health. Additionally, US EPA conducts national monitoring of drinking water every five years to gather occurrence data for contaminants that are not regulated and are suspected to pose a public health risk. This monitoring effort is known as the Unregulated Contaminant Monitoring Rule (UCMR) and helps the US EPA make the determination of whether to regulate additional contaminants under the NPDWRs. The contaminants identified in the UCMR process are often contaminants of emerging concern (CECs; also known as emerging contaminants).
As one of the most widely detected emerging contaminants, per- and poly-fluoroalkyl substances (PFAS) have gained a lot of attention due to their persistence and health risks. US EPA issued a non-enforceable lifetime health advisory limit of 70 ng/L for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) combined. Other contaminants of emerging concern due to their wide detection and health concerns in drinking water are manganese (Mn), uranium (U) and Legionella pneumophila (L. pneumophila). The current non-enforceable guideline for Mn in drinking water is 50 μg/L. The current maximum contaminant level (MCL) for U is 30 μg/L in drinking water. L. pneumophila was considered but not included in the final list of UCMR 4.
Grant recipient determines removal of select emerging contaminants by POU devices
POU treatment systems, which treat water closest to the point of consumption, provide many benefits to remove trace-level contaminants remaining in treated drinking water. Although PFAS, Mn and L. pneumophila frequently occur in drinking water, limited studies have been done to evaluate removal of these emerging contaminants by POU technologies. To address the knowledge gap, the Water Quality Research Foundation (WQRF) funded research conducted by the author at Purdue University. He investigated the removal efficiencies of three PFAS chemicals with different carbon chain lengths (PFOS, PFBS and PFHxS), Mn, U and L. pneumophila by RO and activated carbon (AC) POU technologies. Three unique RO membranes and three unique AC devices were tested in this study.
Both RO membranes and AC filters demonstrated average PFAS removal efficiencies greater than 90 percent for all POU devices tested. Among the three evaluated PFAS with different carbon chain-lengths (PFOS: eight carbons, PFHxS: six carbons, PFBS: four carbons), higher removal efficiencies were observed in long-chain PFAS (carbon chain-lengths >_ 6), while relatively low removal efficiencies were observed for PFBS. These results suggest that the tested POU technologies are generally effective to remove PFAS, but short-chain PFBS may not be consistently removed.
All tested metals were effectively removed by RO membranes with average removal efficiencies greater than 95 percent. AC filters in this study were ineffective at reducing Mn and U with average removal efficiencies below 27 percent. The results showed that L. pneumophila was effectively removed by RO membranes with removal efficiencies being 100 percent, while AC filters did not remove L. pneumophila effectively (efficiencies were all below 31.3 percent). The full research report and executive summary can be accessed at WQRF.org/completed-studies.
Novel finding warrants future research
Three statistically significant correlations were found and four observed positive correlations between PFAS removal efficiency and solubility out of 18 samples. These correlations indicated that PFAS solubility was a more accurate indicator than chain length to describe removal efficiencies by RO membranes in the WQRF-funded study. Further POU mechanistic studies should be conducted to evaluate whether solubility is a better predictor of reduction as compared to carbon chain length for PFAS removal.
Additional WQRF-funded emerging contaminant research
WQRF currently has two additional research efforts focused on emerging contaminants. The first is a national consumer seeking to determine which emerging contaminants are already known by consumers and are of their greatest concern. The study results are anticipated to be released in Q1 of 2022. The results of the consumer study will prioritize the emerging contaminants for the Phase 2 study, which is focused on determining removal efficacies by POU and/or POE devices. The research task force is currently working on developing the request for proposals and anticipates research to begin by Q1 of 2023.
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About the authors
Zhi ‘George’ Zhou, PhD, PE, BCEE is an associate professor of Civil Engineering and Environmental and Ecological Engineering at Purdue University. His research focuses on water quality, wastewater treatment, water reuse and environmental biotechnologies. His recent projects include POU water filtration technologies, antibiotic resistant bacteria, cost-effective biofuels and electrochemical filtration. He is a licensed Professional Engineer (Civil Engineer) in California and a Board-Certified Environmental Engineer (BCEE).
Kayla Heriaud serves as the Research Project Leader for the Water Quality Research Foundation, where she is responsible for reviewing industry needs for research, managing projects from inception to completion and promoting the Foundation’s key achievements. Heriaud holds a Bachelor’s Degree in biology from the University of St. Francis.
The Water Quality Research Foundation (WQRF), formerly the Water Quality Research Council (WQRC), was formed in 1952 to serve on behalf of the Water Quality Association (WQA) as a universally recognized, independent research organization. WQRF’s Vision is water quality improvement through relevant research and mission is advancing knowledge and the science of high quality, sustainable water.