Grantee Research Project Results
Final Report: Decreasing polyfluoroalkyl substances (PFASs) in municipal wastewater effluent and minimizing release from land-applied biosolids
EPA Grant Number: R839640Title: Decreasing polyfluoroalkyl substances (PFASs) in municipal wastewater effluent and minimizing release from land-applied biosolids
Investigators: Lee, Linda S. , Chaplin, Brian , Judy, Jonathan
Institution: Purdue University , University of Florida , University of Illinois at Chicago
EPA Project Officer: Hahn, Intaek
Project Period: August 1, 2019 through July 31, 2022 (Extended to July 31, 2023)
Project Amount: $899,960
RFA: Practical Methods to Analyze and Treat Emerging Contaminants (PFAS) in Solid Waste, Landfills, Wastewater/Leachates, Soils, and Groundwater to Protect Human Health and the Environment (2018) RFA Text | Recipients Lists
Research Category: Human Health , Water , Drinking Water , Water Quality , PFAS Treatment
Objective:
Our overall goal is to reduce PFAS loads in water resource and recovery facilities (WRRFs) and mitigate PFAS release from biosolids such that both the beneficial use of biosolids and water quality are protected. Our objectives are to determine the technical and economic feasibility of treating WWTP centrate using a treatment train approach consisting of nanofiltration followed by electrochemical oxidation of the PFAS present in the nanofiltration retentate solutions (Obj. 1); determine the degree to which these methods are applicable for treating leachate from municipal solid waste and construction and demolition landfills (Obj. 2); quantify and correlate PFAS leaching potential from biosolids as a function of biosolids characteristics including iron, aluminum and organic matter (OM) content, production practices and PFAS properties (Obj. 3); determine the reduction in PFAS leaching from biosolids after amending biosolids with sorbents at different rates, including drinking water treatment residuals (WTRs) and other cost-effectiveness of using amendments (Obj. 4); determine the reduction in PFAS leaching after low temperature oxygen-free pyrolysis of biosolids and subsequent PFAS sorption by pyrolyzed biosolids (Obj. 5); and determine changes in PFAS pre and post typical anaerobic digestion, a commercial Cambi thermal hydrolysis process (THP) and an autothermal aerobic digestion (ATAD) process (Obj. 6). Our associated hypothesis were that targeted separation and subsequent electrochemical treatment of PFASs in WWTP centrate and landfill leachate can reduce PFAS concentrations in WWTP effluent and biosolids (Obj. 1 & 2); PFAS leaching from biosolids will be correlated to quantifiable biosolid characteristics (Obj. 3) amending biosolids with low cost sorbents will reduce PFAS leaching from biosolids (Obj. 4); the biochar produced under low temperature pyrolysis can lead to PFAS entrapment during biosolids carbonization, stabilizing PFAS in the biochar and thereby reducing their availability to leaching and plant uptake (Obj. 5) and the biosolid-derived biochar can serve as a sorptive sink for PFAS released from untreated biosolids (Obj. 4 and 5); and THP and ATAD will lead to conversion of some PFAS precursors to perfluoroalkyl acids (PFAAs) and possibly also reduce total PFAS loads depending on operating conditions (Obj. 6). Obj. 5 and 6 were added post award but before the kick-off meeting with permission of our EPA Project Officer.
Summary/Accomplishments (Outputs/Outcomes):
This study focused on reducing PFAS loads within water resource and recovery facilities (WRRFs) and minimizing PFAS release from biosolids targeted for land application. To reduce the PFAS in the liquid extracted from the wastewater treatment plant biosolids (i.e., centrate), electrochemical oxidation was investigated to destroy PFAS in centrate (Obj. 1) and landfill leachate (Obj. 2). Towards minimizing release of PFAS from land-applied biosolids we investigated PFAS partitioning into water from a representative subset of biosolids as a function of biosolids characteristics (Obj. 3), PFAS concentration in changes in PFAS concentration and class distribution in biosolids under different wastewater treatment processing strategies (Obj. 5 and 6), PFAS concentrations in water treatment residuals (WTRs) towards their potential use as sorbents (Obj 4), and evaluating if WTRs as well as biochar may minimize release of PFAS from biosolids when mixed with biosolids prior to landapplication.
Obj. 1. The centrate is a liquid stream extracted from the WW treatment plant biosolids and an important side stream containing PFAS that is typically just routed back to the front of the WW treatment process. We investigated using electrochemical oxidation to destroy PFAS, thus reducing their reentry into the WW (Obj. 1). The effects of the centrate components on the electrochemical oxidation of PFAS with a Ti4O7 anode were investigated in a variety of electrolyte solutions (Na2HPO4, (NH4)2HPO4, NaCl, NaClO4, and NaHCO3) as well as synthetic centrate at 3.2 V/SHE. PFOA oxidation was inhibited in all electrolytes relative to the inert NaClO4 electrolyte. However, with sodium acetate PFOA oxidation was not inhibited. Xray photoionization spectroscopy (XPS) analysis indicated that electrochemical reactions resulted in the adsorption of both phosphorus and nitrogen species on the electrode surface in the Na2HPO4 and (NH4)2HPO4 electrolytes, which blocked reaction sites for PFAS oxidation. Inhibition of PFOA oxidation in the NaCl electrolyte was attributed to competitive side reactions related to chloride oxidation, and inhibition in the NaHCO3 electrolyte was attributed to hydroxyl radical scavenging and electrode blocking. The centrate was concentrated using nanofiltration by a volume factor of 10 before the electrochemical oxidation at 30 mA/cm2. Total chemical oxygen demand was removed by 87%, and total PFAS removal was 83% after 233 seconds of electrolysis time. However, short-chain PFAS such as perfluorohexanoic acid (PFHxA) was only removed by 38%, and perfluoropentanoic acid (PFPeA) concentration increased by ~4.2-fold. The energy consumption per log PFAS oxidation was 1.02 and 1.84 kWh m-3 for 73% and 83% removal, respectively, indicating that electrochemical oxidation may be a feasible strategy to treat PFAS in domestic wastewater centrate solutions.
Obj. 2. We also began investigating the electrochemical oxidation potential to remove PFAS from a landfill leachate (Obj. 2) based on lessons learned with PFAs in centrate. Coagulation-flocculation was applied to the landfill leachate to remove heavy metals before electrochemical oxidation treatment. PFAS analysis was also performed on samples before and after coagulation experiments to determine their removal. Landfill leachate samples were dosed with 50 mL of FeCl3 (2.5 g/L and 4 g/L) at different solution pH values (4.0, 5.0, 6.0, and 8.1). Samples were shaken at 180 rpm for 1 minute after dosing, shake speed was then reduced to 50 rpm for 20 minutes to allow for flocculation, and samples filtered with 0.45 µm membranes. Coagulation-flocculation successfully removed longer-chain PFAS with the maximum removal being for PFOS (97%). The concentrations of PFBS and PFBA were not significantly different before and after coagulation-flocculation. The 3:3 FTCA was produced in the process of coagulation-flocculation. The final 3:3 FTCA was 20 ± 6 times higher in the pH 6 and 4 g FeCl3/L treatment. However, the reason for this increase was not understood. The pH did not significantly affect PFAS removal.
The electrooxidation of the landfill leachate was conducted in a two-electrode setup at a constant current of 30 mA/cm2 with REM as the anode and stainless-steel mesh as the cathode. Coagulation/flocculation at pH of 8.1 and 4 g/L FeCl3 was used as a pretreatment prior to electrochemical oxidation. The experiment was unsuccessful as the Ti4O7 membrane broke after 5 hours and became unstable after 3 hours. Electrochemical oxidation of landfill leachate is being repeated and results will be available in the near future for a manuscript submission.
Obj. 3. PFAS biosolids-porewater partition coefficients in the context of biosolids production practices and biosolids characteristics were investigated. Characteristics considered included oxalate extractable Fe and Al (assumed to represent Fe and Al-oxides), organic matter (OM) content by loss-on-ignition (LOI), dissolved organic carbon (DOC) and protein content. Major findings of this work included that solids-porewater partition coefficients for shorter-chain PFAS showed positive correlations to protein content while OM content correlated better to partitioning of the longer chain PFAS. We also found both oxalate-extractable Fe and Al content were also positively correlated with some PFAS biosolidsporewater partition coefficients, suggesting that inorganic constituents, as well as organic constituents, may impact PFAS partitioning during waste treatment. This work (Gravesen et al. 2023a) was published in early 2023 in Environ. Pollution.
We characterized several drinking water treatment residuals (DWTRs) including five Al-based, two Ca-based, and one Fe-based DWTRs (Obj. 4). Characteristics examined included total Al, Fe, and Ca by acid digestion, oxalate-extractable Fe and Al, OM by LOI, pH, EC and PFAS concentrations. Furthermore, the degree to which resident PFAS desorb from WTRs was assessed, as was the degree to which amending biosolids-porewater with WTRs affects PFAS desorption, with the latter assessment simulating a beneficial reuse scenario where WTRs have been co-applied with biosolids with the intent to reduce PFAS mobility. Total native PFAS concentrations ranged from < method detection limits to ~34 μg kg-1. The most commonly detected PFAS was PFOS in 6 of the 8 DWTRs, followed by PFHxA, PFOA, and L-PFHxS (each being detected in 2 different DWTRs). The highest concentration measured was in a DWTR derived from an aluminum chlorohydrate (ACH) coagulant and is actually used to treat wastewater (WW) rather than drinking water prior to pumping the treated WW into the aquifer. PFAS concentrations were < LOD in both Ca-DWTRs examined and even in the ACH WWETR, PFAS concentrations were very low compared to those reported in biosolids. Desorption of resident PFAAs from the WTRs was negligible for the carboxylates (PFCAs). Some desorption of the sulfonates (PFSAs) was detected, particularly for PFOS which had the highest concentration among all resident PFAAs. Amending biosolids porewater (~3500 ng L-1 total PFAAs) with ACH WWETR resulted in strong effects on PFAS sorption, especially for long chain PFAS, with > 90% of some PFAS sorbed at the highest WWETR concentration tested. PFAS desorption from the WWETR was minimal, ranging from 0-26%. These finding suggest that WTRs, if introduced into the environment, are unlikely to be a major source of PFAS. This work (Gravesen et al. 2023b) was published in September 2023 in J. of Environmental Quality.
We followed up the Gravesen et al. studies with an investigation on how amending/adding DWTRs to biosolids would affect PFAS retention. WWTPs that recycle DWTRs into WWTP influent can produce biosolids with highly-elevated Al and Fe content (in the case of Al or Fe DWTRs). Furthermore, high Al, Fe and Ca phases are being investigated and used as amendments in various contexts to influence PFAS retention. Considering the high Al, Fe and Ca content of DWTRs, these materials may have value as low-cost, widely-available PFAS sorbents. We completed a series of bench-scale partitioning studies using 13C radiolabeled PFOA to examine how amending biosolids with Al, Fe, and Ca DWTRs affects PFOA partitioning. Biosolids used for this work were collected from MWRD in Chicago and contained relatively high PFAS content. This work was coupled with plant uptake studies in soil amended with the Chicago biosolids treated with the DWTRs. Biosolids were amended at 5% wt/wt with DWTRs. Plant uptake studies were designed to simulate two separate environmental scenarios: one using ryegrass where biosolids were applied to the soil at a rate consistent with mine reclamation (13 % w/w, resulting in 0.65% w/w DWTR in the biosolidsamended soil) and another using tomato with biosolids applied at an agronomically-relevant rate biosolids (0.9 % w/w, resulting in 0.045% w/w DWTR in the biosolids-amended soil). The partitioning work demonstrated that all three DWTR types (Al, Fe and Ca) approximately doubled the amount of 13C radiolabeled PFOA retained (i.e., not desorbed) from the biosolids. Despite the fact that 30 different PFAS were detected in the biosolids, only 3 relatively short-chain carboxylic acids (PFBA, PFPeA and PFHxA) were detected in the ryegrass tissues, with these three PFAS as well as PFOA being detected in the tomato tissues. While amending biosolids with DWTRs doubled 13 C-PFOA partitioning to solids during our bench-scale work, DWTR amendment did not result in significantly reduced PFAS uptake in tomato (data not shown). DWTR amendment also had a relatively small impact on PFAS uptake in ryegrass, although PFBA did accumulate at significantly lower rate as a result of Fe and Ca-DWTR amendment. This work (Broadbent et al., 2023) was published in September 2023 in J. of Environmental Quality.
We hypothesized that the reason we did not see widespread significant differences in
phytoaccumulation was related to the relatively-high Al content of the soil used, the investigation of native (i.e., relatively low) PFAS concentrations and the use of a single (5% wt/wt) DWTR amendment rate that may have been too low. To follow up this work, we investigated PFAS partitioning of 9 PFAS (PFBS, PFHxA, PFHpA, PFHxS, PFOA, PFOS, PFDA, PFBA, PFPeA, added to biosolids at 100 ug kg-1) amended with Al, Ca and Fe DWTRs at rates of either 2.5, 5 and 10% wt/wt. Three different biosolids with differing characteristics were used: 1) High OM, low FeOx;
2) High OM, high FeOx; and 3) Low OM, high AlOx. In general, in all three biosolids and for all three DWTRs, amending biosolids with 10% DWTRs significantly reduced PFAS in the liquid phase, suggesting that amendment rate was a more important variable than variables related to biosolids, DWTR or PFAS characteristics. This work is being prepared for publication, with submission estimated to occur December 2023-March 2024.
Obj. 4. We tested PFAS attenuation by biosolids-based biochar. We had a Class A biosolid from 20062007 containing (875 µg/kg ΣPFAAs) pyrolyzed at 350 °C under 10 mL/min nitrogen at the Illinois Sustainable Technology Center, Illinois Institute of Technology (compliments of Dr. Wei Zheng). PFAA analysis was performed on the ground and unground biochar. PFAA concentrations in ground samples were 10-12% higher than the original biosolids due to volume reduction (volatile organics) during pyrolysis. PFAA recovery from unground samples was < 5% of what was found after grinding highlighting the need to grind biochar prior to extraction for chemical constituents. Release of PFAAs from the biochar into deionized water was assessed at 0.1 g: 40 mL mass to volume ratio with a 6-d end-to-end rotation. The liquid and solid were separated via centrifugation. Solid-phase extraction (SPE) was performed on the supernatant and the solids were freeze-dried and then extracted for PFAS. PFAA release into porewater from 1-2 mm biosolids-based biochar particles was less than 7 ppt for each PFCA and no release of PFSAs above limits of quantitation. PFAA release from the biosolids prior to pyrolysis ranged from 6 to 1200 ppt range for the different PFAAs. Therefore, although lowtemperature pyrolysis did not remove PFAAs, the biochar structure minimized PFAA release into water.
Obj. 4 & 5. The attenuation potential of both the ACH-WTRs and biosolid-based biochar were evaluated using biosolids-amended soil columns operated under transient unsaturated conditions were used. The upper part of the soil columns was packed with a sandy low organic matter soil mixed with 3 wt % biosolids only (control) or amended with 1 wt % ACH WTRs or 1.5 wt% biosolids-based biochar. The control, ACH-WTR and biochar treatments were done in triplicate. Simulated rain events were invoked weekly for four months to date (2.7 pore volume per week, ~75 pore volumes in total). Column leachate was analyzed for PFAS, dissolved organic matter, pH, and electrical conductivity. Data reflects that for most PFAS, PFAS attenuation is occurring in both the ACH-WTR and biochar treatments relative to the control (biosolids only) columns. However, initial leaching (first two events) from the biochar-amended columns resulted in the highest release of the short-chain PFAAs along with DOC. Data synthesis and interpretation is being competed. A manuscript submission is expected in February/March of 2024.
Obj. 6. our primary goal was to provide a deeper understanding of how anaerobic digestion (AD) and incorporation a thermal hydrolysis process (THP) prior to AD process influences PFAS fate at the WRRF. We were presented with an exceptional opportunity at an established WRRF that had been using typical AD processes but would soon be moving to integrating CAMBI® THP prior to AD. Our analysis encompassed both pre-installation and post-installation phases, thereby affording us a comprehensive view of the system's impact on 58 PFAS concentrations within the solids stream. Samples were collected monthly for 5-months for each phase. Each sample from each sampling event was a composite of multiple grab samples mixed onsite at the WRRF. We determined the change in quantifiable PFAS concentrations and relative PFAS distribution in solids before and after AD prior to and after the CAMBI® THP installation as well as changes in the pre- and post-CAMBI® THP step prior to AD. Volatile solids reduction during AD and additions of fat, oil and grease (FOG) and nonpotable water in the treatment train were considered in evaluating treatment effects on PFAS concentrations. Recovery of 58 native PFAS determined in the duplicate matrix spiked for each of the five types of solid samples ranged between 64-123% with native spike recoveries being lowest for the pre-THP samples and highest for the post-AD only samples. Significant differences in PFAS surrogate recoveries were observed across the five sample types. Matrices were visibly the cleanest after the AD step in both treatment systems, which was reflected in the highest recoveries being in post-AD followed by the post-THP+AD samples. The cleaner matrix post-AD also allowed quantitation of the phosphinates, which were < LOD in the pre-AD samples. The lowest surrogate recoveries were observed for the post-THP samples, which was due to the addition of the FOG samples after the preTHP samples were taken but prior to entering the CAMBI® THP. FOG samples were also collected, but have been difficult to analyze even using a modified total oxidizable precursor (TOP) assay.
Even with the complications caused by varying matrix effects, clear trends in changes in PFAS distribution (% relative to total PFAS in the sample) are evident. Precursors and intermediates to the PFAAs made up 86 to 97% of the quantifiable PFAS (∑PFAS) entering the WRRF (pre-AD and preTHP) with most being diPAPs (58-65% of ∑PFAS) consistent with recent literature. The % of PFAA precursors and intermediates relative to ∑PFAS was broader across all sample types (72% - 97% of ∑PFAS) because of the FOG-induced matrix effects, which was observed in the post-THP samples. The next largest contributor to ∑PFAS entering the WRRF were the FTCAs (24-33% of ∑PFAS), known intermediates from precursors to PFAAs. Both higher % contribution from diPAPs and FTCAs entering the WRRF wase observed after the CAMBI® THP and service area increased, but ranges are still within 10% of each other.
Prior to the CAMBI® THP installation, AD resulted in significant decreases in the diPAPs and FTUCAs and subsequent increases in the PFCAs. After incorporation of the CAMBI® THP, % contribution of precursors, PFSAs and PFCAs increased, but assessing this in terms of the actual THP process is difficult given the direct and indirect effects of the FOG addition in terms of additional PFAS and matrix effects, respectfully. However, comparing pre-THP with post-THP+AD, a decrease in precursor contribution is observed. On a total fluorine mass balance (accounting for the number of fluorine atoms in each PFAS), pre and post AD resulted in 13.1% more fluorine, which may be due to the breakdown of some unquantified precursors as well improved sensitivity with a cleaner matrix post-AD. Pre-THP to post-THP, there was a 28% decrease in total fluorine calculated, which is likely due to the matrix effect limited quantitation of PFAS present at lower concentrations. When comparing post-THP to post-THP+AD there is an 84.2% increase in the moles of fluorine, which primarily may be due to the cleaner matrix after AD. If post-THP+AD is compared to pre-THP (prior to the FOG addition and THP process), the increase in total fluorine from quantified PFAS was much less at only 32.4 %. Overall, although there may be changes in the PFAS distribution with and without THP, overall THP does not appear to remove PFAS; therefore, the primary benefit of CAMBI® THP remains the ability to generate biogas for offsetting energy costs. When comparing relative changes in PFAS distribution after digestion, the ATAD process (performed at a completely different plant and state) led to large decreases in the precursors with corresponding increases in PFAAs and some intermediates
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 28 publications | 6 publications in selected types | All 6 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Broadbent E, Gravesen C, Choi YJ, Lee L, Wilson PC, Judy JD. Effects of drinking water treatment residual amendments to biosolids on plant uptake of per‐and polyfluoroalkyl substances. Journal of Environmental Quality 2023. |
R839640 (Final) |
Exit Exit |
|
Gravesen CR, Lee LS, Choi YJ, Silveira ML, Judy JD. PFAS release from wastewater residuals as a function of composition and production practices. Environmental Pollution 2023;322:121167. |
R839640 (Final) |
not available |
|
Gravesen CR, Lee LS, Alukkal CR, Openiyi EO, Judy JD. Per‐and polyfluoroalkyl substances in water treatment residuals:occurrence and desorption. Journal of Environmental Quality 2023. |
R839640 (Final) |
not available |
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.