Date of Award
Senior Honors Thesis
College or School
Civil and Environmental Engineering
Program or Major
Bachelor of Science
Perfluoroalkyl substances, or PFAS, are an emerging contaminant of concern in environmental engineering. This group of chemicals has been used by manufacturers since the 1940s due to their desirable waterproofing qualities. They also have a high chemical stability at high temperatures, which makes treatment difficult. A large variety of manufactured items contain PFAS, such as fabrics and apparel, non-stick items, and food wrappers. Recently, these compounds have come under question due to studies supporting harmful health effects, such as low birthweight, cancer, thyroid hormone disruption, and a weakened immune system. Due to their chemical structure, PFAS compounds are difficult to treat for, but some methods are available. Current treatment and transformation processes for PFAS include activated carbon sorption, oxidation, reduction with aqueous iodide or dithionate and sulfate, thermal destruction or degradation, microbial treatment, and others such as ozonation (Merino et al., 2016). Microbial treatment can occur during biological treatment in wastewater treatment plants and can vary depending on the processes used. PFAS compounds can enter the wastewater system from a variety of sources and undergo biodegradation before being distributed between effluent and sludge. This study will aim to examine how different biological treatment processes impact PFAS removal and effluent concentrations.
1.2. Background: PFAS compounds enter the wastewater system from industries, household products and clothing, and from the environment through runoff and groundwater. Another source is landfill leachate, which contains large concentrations of PFAS due to the many products that contain or used to contain them being discarded. Not all wastewater treatment plants accept landfill leachate, so the previous statement only applies to those that do. In many past studies, such as the following one, it has been shown that PFOA and PFOS concentrations increase between influent and effluent due to the degradation compounds during treatment processes. In biological treatment, microbes break down polyfluoroalkyl substances into perfluoroalkyl ones, which explains the concentration increase between influent and effluent (Merino et al., 2016).
A 2005 study by Wang et al. observed the effects of biotransformation on 8:2 FTOH in a series of bottles with bacterial cultures mixed with activated sludge in aerobic and anaerobic environments (Sáez et al., 2008). Results supported that the 8:2 FTOH was ultimately being biodegraded into PFOA using the byproduct 7:3 FTCA as a substrate for beta oxidation (Butt et al., 2014). PFOA can then further degrade into short-chain compounds, such as HFBA, PFPeA, PFHxA, and PFHpA. PFOS can degrade into PFBS and HFBA (Huang and Jaffé, 2019). These results support the previously proposed statement that activated sludge systems biodegrade polyfluoroalkyl substances to perfluoroalkyl ones. An analysis done on 19 Australian WWTPs found that there was an increase in PFPeA, PFHxA, PFHpA, PFOA, PFNA, and PFDA from influent to effluent (Coggan et al., 2019). This statement supports the biodegradation pathway of PFOA as a determinant of PFAS compounds present in wastewater effluent. Most of the plants studied were activated sludge, with 6 being lagoon systems. After the treatment process, the remaining PFAS compounds are separated into sludge and effluent. This separation is due to the hydrophobicity and hydrophilicity of various species of PFAS. The hydrophobic long-chain PFAS compounds are attracted to sludge as they are repelled by water, while the hydrophilic short-chain PFAS compounds are attracted to water and remain in the effluent.
This study will aim to analyze the WWTP influent and effluent PFAS concentration data for the state of New Hampshire taken in 2017 for how different biological treatment methods impact removal of seventeen PFAS compounds. The data will also be compared to the Great Bay dataset collected by Ellie Tavasoli to determine whether the data patterns agree. There is no overlap in treatment plants observed between the two data sets.
1. Do the New Hampshire WWTPs show a pattern of increasing PFAS concentrations from influent to effluent? Are there any noticeable patterns/trends in the data?
2. How does removal for different PFAS species differ based on the biological treatment method used? How do variations effect the removal (leachate, seasons, etc.)?
3. How do the trends in the New Hampshire data compare to the Great Bay data collected by Ellie Tavasoli? Do they agree?
1.4. Approach: Information will be collected from each of the state surveyed plants to determine the biological treatment process used at each plant to be used in the analysis. Once compiled, the data will be analyzed and compared to assess whether certain treatment processes may influence the PFAS removal between sites and how that will impact the effluent PFAS concentrations. The operators of each of the state WWTPs will need to be contacted in order to learn what biological process each plant is using. Once the treatment processes are known, the state dataset will be able to be grouped and analyzed for PFAS removal by treatment process and PFAS species.
1.5. Expected Outcome: It is expected that there will be noticeable patterns in the state dataset, such as an increase in PFAS concentrations from influent to effluent, and that they will be similar to those seen in the Great Bay. It is also expected that different processes will impact different PFAS compounds, and that that process will be affected based on factors like leachate acceptation and time of year sampled.
Harvell, Zachary P., "PFAS Removals and Increases in the Effluent of Thirteen New Hampshire Wastewater Treatment Facilities Due to the Effects of Biological Treatment Processes" (2020). Honors Theses and Capstones. 544.