Journal of Environmental Engineering

Abstract

Efficient delivery of engineered nanoparticles (NPs) to a non-aqueous-phase liquid (NAPL) target zone located above the water table requires an understanding of their transport and binding characteristics. In this investigation, NPs coated with a tunable amphiphilic copolymer were employed in a series of experiments using a 1.4-m-long lysimeter. A crude oil zone was emplaced in the lysimeter to evaluate NP binding capabilities to a representative NAPL. Experimental observations were supported by a reactive transport model. NPs coated with a polymer concentration that promotes enhanced binding to crude oil were successfully delivered and retained in the NAPL zone at concentrations about three times higher than elsewhere in the lysimeter and consistent with the distribution of total petroleum hydrocarbons. Model simulations were able to reproduce the observed asymmetrical NP breakthrough curves and retention profile. The estimated attachment rate coefficient was two orders of magnitude higher for the NAPL zone than elsewhere, supporting the observed preferential binding to the crude oil. Depth-dependent straining was used in the model to capture the NP retention observed near the top of the lysimeter, presumably due to film straining caused by the increased capillary pressure. In addition to the reversible attachment and straining mechanisms, model simulations also indicated that loss of aqueous NP mass was required deeper in the lysimeter to provide a reasonable fit to the observed NP data. Due to increased contact with sediments, the polymer structure that coats the NPs may be slowly removed, leading to aggregation and reduced mobility because of physical trapping. Findings of this study revealed that despite the demonstrated targeted binding capability of these NPs in unsaturated systems, their delivery to a target NAPL zone distant from an injection location may be a challenge due to possible aggregation over longer travel distances and thus an important design consideration.

Practical Applications

Soil and groundwater contamination by petroleum hydrocarbons is a global issue due to the harm it causes to the environment and human health. Hence, developing novel in situ technologies is necessary due to limitations associated with ex situ remediation. One emerging technology called nanoremediation involves injecting nanosize particles into the impacted area to interact with contaminants effectively due to their small size and large surface area. By modifying their surface, particles can transport through soil and stick to specific contaminants, which is called targeted delivery. To better understand this technology, it should be studied under conditions similar to those in the field. Hence, we investigated targeted delivery of engineered nanoparticles in a large 1.4-m-long column packed with natural soil, representative of the unsaturated zone above a shallow aquifer. Our findings demonstrated preferential nanoparticle attachment to the crude oil–impacted sediment which provides the foundation to advance the use of these nanoparticles as a treatment agent and increases treatment efficiency. However, the noted increase in nanoparticle retention over longer travel distances is suggestive of their stability issues in unsaturated porous media, which may pose a limitation for the delivery of these NPs to a target zone distal from the injection location.

Abstract

Wastewater treatment plants (WWTPs) are critical infrastructures responsible for processing wastewater before discharging effluent to rivers and other potential uses. WWTPs use large, connected deep tunnels for storing sanitary and wet-weather flows for treatment. However, wastewater in those systems cannot exceed safe tunnel levels in order to prevent overflows of untreated wastewater into the environment. Further, WWTPs are among the 16 national lifeline infrastructure sectors in which the utilization of sensor technology has increased, making the sectors vulnerable to all forms of cyber threats. Considering these challenges, the work presented in this manuscript uncovers the role of AI at WWTPs by focusing on two problems: tunnel water-level prediction and detection of security threats. This is done by proposing an AI framework: ${\mathrm{P}}_2\mathrm{O}$ (prediction, protection, and optimization). The prediction module forecasts the tunnel water level using deep-learning models based on the current wastewater flow in the tunnel and other inputs from the sensors and gauges. The protection module focuses on classifying the intentionality of an anomaly, i.e., whether an attack is adversarial in nature or merely an outlier, using recurrent neural network models. Last, the optimization module aims to provide actionable recommendations to pump operators using a genetic algorithm. The experimental results of ${\mathrm{P}}_2\mathrm{O}$ indicate that the prediction module can predict the tunnel water level with 85% accuracy, and the protection module can detect about 97% of intentional attacks on WWTPs. AI models within ${\mathrm{P}}_2\mathrm{O}$ are evaluated; the experimental results are presented and discussed.

Practical Applications

This manuscript presents ${\mathrm{P}}_2\mathrm{O}$, which is a novel AI framework that can predict about 85% of wastewater overflow incidences and about 95% of intentional cyberattacks on a WWTP, as indicated in the experiments. The deployment of ${\mathrm{P}}_2\mathrm{O}$ at a WWTP is essential, especially considering the adverse effects of overflowing wastewater on the environment (i.e., rivers and other water bodies). Moreover, cyberattacks on WWTPs can be subtle, making them challenging to detect; on average, most of them are noticed within one week to one month after the attack. This makes national infrastructure vulnerable to external and internal threats, influencing the well-being of water bodies and overall national security. ${\mathrm{P}}_2\mathrm{O}$ provides a real-time monitoring interface and can recommend optimal actions in different scenarios (i.e., outliers) for pump operators and process engineers at WWTPs.

A permeable reactive barrier (PRB) is an effective groundwater in situ remediation technology, and the design methods used for PRBs are significant in ensuring that they meet remediation goals. Steady-state analytical solutions are an effective tool to provide conservative and simple design methods. A steady-state analytical solution is proposed to describe organic contaminant transport through the PRB and aquifer in a PRB and cut-off wall system. The proposed analytical solution may serve as an effective tool to provide conservative and simple design methods. The shape factor ($S$) is introduced at the PRB-aquifer interface to investigate the effects of a PRB’s layout forms on its performance. The results show that the relative contaminant concentration at the point of compliance for a PRB with $S=8$ is 11 orders of magnitude larger than that without considering the shape factor. Effects of degradation, dispersion, and advection on PRB design are subjected to dimensionless analysis. Dimensionless analysis shows that degradation plays a key role in decreasing contaminant concentration in the PRB. In addition, increasing advection may promote contaminant transport from the source to the aquifer. Simplified solutions to estimate PRB thickness and source remediation time are derived for the practical design and performance evaluation of the PRB system.

Abstract

The efficiency of a hybrid upflow anaerobic sludge blanket reactor (HUASB) where coconut fiber is used as an inert media was investigated under different hydraulic residence times (started with 6 h and then decreased to 2 h) with varied organic loading rates (ranged from 0.5 to $6.0\mathrm{kg}\mathrm{c}\mathrm{h}\mathrm{e}\mathrm{m}\mathrm{i}\mathrm{c}\mathrm{a}\mathrm{l}\mathrm{o}\mathrm{x}\mathrm{y}\mathrm{g}\mathrm{e}\mathrm{n}\mathrm{d}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{n}\mathrm{d}(\mathrm{COD})/{\mathrm{m}}^{-3}{\mathrm{day}}^{-1}$). The 3.5-L lab-scale reactor was used for sewage treatment under mesophilic conditions for 8 months. The COD reduction varied from $74\%\pm 1.7\%$ to $61\%\pm 2.4\%$, the total suspended solids (TSS) reduction was in the range of $72\%\pm 2.2\%$ to $54\%\pm 2.7\%$, and the methane content in the biogas was $65.1\%\pm 0.3\%$. An attempt has been made to understand the performance of the lab-scale reactor for primary population of microorganisms using a microscopic technique. Different groups of anaerobic bacteria and granulation were visualized and quantified using unstained observations, Gram staining, ocular micrometry (granular size determination), Neubauer’s chamber (counting of microorganisms), and scanning electron microscopy. Correlation analysis among the various operational parameters has also been prepared. Overall, the performance of the HUASB reactor using coconut fiber appears to be a cost-efficient sewage treatment alternative in developing nations.

Practical Applications

A HUASB is a high-rate anaerobic treatment process that consists of a suspended and attached growth treatment method. The treatment unit can sustain a high organic loading because it has a high biomass content and good sludge-settling characteristics. The study investigates the effectiveness of a HUASB reactor using coconut fiber as a novel inert media for sewage treatment. Based on the findings, this technology can be applied at a sewage treatment facility. This treatment also has the potential for reduced environmental and economical footprints.

The present investigation demonstrates a batch electrocoagulation (EC) process performance for the abatement of salicylic acid–laden wastewater. The electro-charge loading optimization was assessed using response surface methodology (RSM) with a central composite design (CCD) model. The EC at an optimum electro-charge loading of $20.69{\mathrm{Fm}}^{-3}$ in the presence of NaCl electrolyte with concentration of $1\mathrm{g}{\mathrm{L}}^{-1}$ and a pH of 7.0, resulted in $88.38\%\pm 3.52\%$ reduction of salicylic acid with an initial concentration of ${50\mathrm{mg}\mathrm{L}}^{-1}$. The analysis of variance (ANOVA) and regression equation resulted in a p-value of $<0.05$, F-value of 113.65, and a unit value of desirability for the optimized model, suggesting the model is statistically significant. Moreover, at an optimum surface-to-volume ratio ($\mathrm{S}/\mathrm{V}$) of ${6.8\mathrm{m}}^3{\mathrm{m}}^{-2}$, about $1.23\mathrm{kWh}{\mathrm{m}}^{-3}$ of energy consumption was observed. Further, in the case of chemical coagulation, about $37\%\pm 2.2\%$ removal efficiency of salicylic acid was obtained at an optimum pH and alum dose of 7.0 and $250\mathrm{mg}{\mathrm{L}}^{-1}$, respectively. Also, the EC process demonstrated satisfactory performance during the treatment of real institutional wastewater spiked with $50\mathrm{mg}{\mathrm{L}}^{-1}$ of salicylic acid by achieving $75.2\%\pm 5.7\%$ removal efficacy at optimum operating conditions. Finally, the sludge characterization revealed the presence of metal hydroxide species ${[\mathrm{Al}(\mathrm{OH})}_3]$ flocs, responsible for effectively adsorbing and separating salicylic acid molecules from wastewater.

Lab-based experiments were performed to develop an engineered column system for ultraviolet silica-based granular media (UV/SGM) to degrade per- and polyfluoroalkyl substances (PFAS) in concentrated liquid waste and challenge the laboratory scalability of the system and develop a field-applicable system. UV/SGM is an innovative photocatalyst developed to degrade a variety of PFAS compounds and predominantly designed to treat low-volume highly concentrated waste. Scalability is presented by increased system wattage, volume, or flow rate at the lab scale. The resulting reactor configuration presents a proportional UV wattage to treatment volume and relative flow rate as pilot-scale treatment conditions. Treatment efficiency was established by amending concentrated PFAS waste in both strong acid ($\mathrm{pH}<4$) and strong base (pH 13). UV/SGM takes advantage of the high affinity of silicon and fluorine, which overcomes Coulombic interactions in a high-pH solution for most fluorotelomers and perfluoroalkyl sulfonic acids (PFSAs), whereas increased adsorption/degradation of perfluoroalkyl carboxylic acids (PFCAs) occurs under low pH. Final reactor configurations presented in the study improved the efficiency of UV/SGM to degrade fluorotelomers and PFSAs under basic conditions while taking advantage of photolysis to degrade PFCAs. The system demonstrated $>90\%$ degradation of $\sim 50\mathrm{mg}/\mathrm{L}$ total PFAS in a PFAS-spiked deionized water. Electrical energy per log order reduction (EE/O) calculated by reduction of PFAS ranged from $\sim 75$ to $\sim 410\mathrm{kWh}/{\mathrm{m}}^3$; however, fluoride recovered increased, respectively, with EE/O for systems of equivalent flow rate. Therefore, evaluating EE/O based on complete defluorination, rather than parent PFAS removal, could aid in technology energy comparison.

Significant amounts of energy are consumed in the heating of water in the hospitality and food services sectors. The majority of this energy is still present in the subsequent wastewater, which is sent to the sewer system, representing a significant waste of energy resources. The present research focuses on the recovery of waste heat from commercial kitchen wastewater to fulfill the dual objectives of reducing energy consumption and ${\mathrm{CO}}_2$ emissions, while simultaneously improving fat, oil, and grease (FOG) removal efficiency in grease interceptors or grease traps (GT). A GT was retrofitted with a novel heat exchanger design (termed a hybrid GT) to enable wastewater heat recovery and enhance FOG removal capabilities. Hot wastewater containing FOG was assessed in a full-scale experimental GT. The governing parameters of temperature, mass flow rate, and FOG content were monitored. Results indicated that the hybrid GT improves FOG removal performance by lowering the temperature of GT hot wastewater by 25%. The hybrid GT reduced primary energy consumption through heat recovery at a maximum rate of $0.9\mathrm{kJ}/\mathrm{s}$, and reduced the corresponding cost of conventional fossil fuel use for water heating. It also reduced the carbon footprint by 920 kg ${\mathrm{CO}}_2\mathrm{e}$ per kWh of energy saving. Heat recovery could bring down the cost of food preparation and increase profitability. The hybrid GT also improved FOG retention through lowering wastewater temperatures and encouraging faster solidification of FOG in the GT. Faster solidification of FOG retained greater amounts of FOG in the first chamber of the GT. FOG passing to the second chamber of the GT was reduced enhancing the systems utility. The present research highlights significant potential for further improvements in the process of heat recovery from GTs in commercial kitchens, as well as significant potential for energy, cost, and environmental benefits arising from the adoption of this technology.

Abstract

Production of insensitive munitions (IM) creates wastewater containing 3-nitro-1,2,4-triazol-5-one (NTO). Because NTO is an anion in neutral pH wastewaters, it can be removed via ion exchange (IX), released during IX brine recharge, and may be subsequently degraded by halophiles. IX brine regeneration through halophilic NTO biotransformation was observed over 210 cycles in a sequencing batch reactor (SBR) and averaged $64.8\%\pm 20.2\%$ NTO removal. NTO formed 3-amino-1,2,4-triazol-5-one (ATO) under sulfate- and nitrate-reducing conditions. Variable NTO reductions were observed over four phases including anoxic enrichment ($80.5\%\pm 7.7\%$, Cycles 0 to 41); anoxic followed by aerobic ($42.2\%\pm 23.5\%$, Cycles 42 to 81); anoxic supplemented with nitrate ($64.7\%\pm 21.5\%$, Cycles 82 to 177); and anoxic stress test with nitrate and perchlorate ($91.0\%\pm 9.7\%$, Cycles 178 to 210). Sequencing results showed 69% of the genera to be halophiles and sulfate-reducing bacteria and archaea including Desulfovibrio and Halanaerobium. ATO reduction in each cycle was shown to be correlated with the abundance of genus Alkalibacterium. The presence of the potential cocontaminants in munitions wastewater IX brine, nitrate and perchlorate, were shown to either increase or not interfere with NTO transformation, respectively. The results of these studies demonstrate that NTO biotransformation by halophiles in brine solutions is feasible and could be utilized for IX brine regeneration.

Practical Applications

Explosive production and munitions manufacturing in the US creates wastewater containing explosive contaminants. Treatment of this wastewater to remove the explosives is required before the water can be released to the environment. IX can remove the explosive NTO from munitions manufacturing wastewater, but to be economical, the resins need to be reused many times. Regeneration of the IX resin for reuse generates brine that contains the explosive NTO. To remove NTO from the brine so it can be reused, salt-tolerant bacteria were grown that biodegrade NTO. The bacteria were able to biotransform NTO over for 210 cycles and over 500 days from a synthetic IX brine. After optimization of the treatment system, the bacteria were degrading $91.0\%\pm 9.7\%$ of the NTO in each cycle. This system, IX with brine regeneration, for munitions wastewater treatment is potentially more economical and sustainable than current wastewater treatment methods.

The novel Fe-doped ${\mathrm{MoS}}_2/\mathrm{granulated}$ activated carbon (GAC) particle electrodes (FMG PEs) were controllably synthesized by a hydrothermal method and used in the three-dimensional (3D) electroactivation of peroxydisulfate (E-PDS-FMG) for carbamazepine (CBZ) degradation. The performance, mechanism, and influencing factors of CBZ degradation by the E-PDS-FMG system were systematically discussed. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analyses showed that the E-PDS-FMG system has an excellent conductivity and a high electron transfer rate and exhibited a superior electrocatalytic performance for CBZ degradation. A CBZ removal rate greater than 99% can be achieved within 25 min under the conditions of FMG dosage of $0.4\mathrm{g}{\mathrm{L}}^{-1}$, PDS concentration of 2.0 mM, current density of $1.0\mathrm{mA}{\mathrm{cm}}^{-2}$, and initial pH value of 5. Sulfate radicals (${\mathrm{SO}}_4^{·-}$) and hydroxyl radicals (OH) were recognized as the major active species through quenching experiments and electron paramagnetic resonance (EPR) measurement. In addition, Fe (IV) was also involved in the E-PDS-FMG system according to the transformation of methyl phenyl sulfoxide (PMSO) to methyl phenyl sulfone (${\mathrm{PMSO}}_2$). Furthermore, the possible mechanism of the E-PDS-FMG system was proposed. FMG PEs were applied as the catalyst and particle electrodes for PDS activation, improving the yield of OH, ${\mathrm{SO}}_4^{·-}$, and Fe (IV). The increase of FMG dosage and PDS concentration accelerated the degradation of CBZ, and the E-PDS-FMG system exhibited a high degradation ability on CBZ removal in a wide pH range. The results all indicate that the E-PDS-FMG system is a promising technology for organic pollutant removal from water due to its excellent electrocatalytic performance and remarkable stability.

In this study, magnesium oxide-corncob biochar (MgO-CB) was prepared by ${\mathrm{MgCl}}_2$ modified corncob biomass for the adsorptive removal of phosphate from water. The adsorbents were characterized by scanning electron microscopy (SEM), x-ray diffractometer (XRD), and Fourier transform infrared spectroscopy (FT-IR), and the adsorption mechanism of the adsorbents was studied. Batch adsorption experiments studied the adsorption performance of MgO-CB for phosphate, and the effects of solution pH, adsorbent dosage, and coexisting ions on the adsorption effect were also investigated. The results showed that the theoretical maximum adsorption capacity of MgO-CB could reach $158.98\mathrm{mg}/\mathrm{g}$ when the initial phosphate concentration was $120\mathrm{mg}/\mathrm{L}$. MgO-CB exhibited good adsorption performance in the pH range of 3 to 10, and the coexisting ions ${\mathrm{CO}}_3^{2-}$ and ${\mathrm{SO}}_4^{2-}$ significantly impacted the adsorption. The adsorption process of MgO-CB for phosphate proceeded relatively fast in the first 400 min and basically tended to equilibrium around 600 min. The adsorption process was consistent with the pseudo-second-order kinetic model and the Langmuir isothermal adsorption model, indicating that the adsorption process was dominated by chemisorption. Thermodynamic analysis showed that the change in temperature from 15°C to 45°C had little effect on the adsorption capacity of MgO-CB for phosphate, and the adsorption process was spontaneous, endothermic, and entropy-increasing. The mechanism of phosphate adsorption by MgO-CB involved electrostatic attraction, chemical precipitation, and ligand exchange to form inner-sphere complexation.

In view of the current bottlenecks of low nitrogen and phosphorus removal efficiency and high cathode cost of microbial fuel cells (MFCs), this study constructed single-chamber biocathode MFCs to carry out related research. Single-chamber MFCs with microalgae were fabricated, and nitrogen removal efficiency and greenhouse gas emissions (GHG) were investigated. The results indicated that algae MFCs could significantly reduce GHG (${\mathrm{CH}}_4$, ${\mathrm{CO}}_2$, and ${\mathrm{N}}_2\mathrm{O}$) emissions through the competition of electron donor and sequestrating atmospheric ${\mathrm{CO}}_2$. Compared with the control group, the microalgal MFC significantly promoted the removal of total nitrogen (TN) and total phosphorus (TP). The highest open-circuit voltage (0.33 V) and power density ($49\mathrm{mW}{\mathrm{m}}^{-3}$) were observed in the closed circuit with algae (CC) reactor. Running MFC significantly increased the biomass of algae and produced good quality of biofuel. Quantitative polymerase chain reaction (q-PCR) analysis indicated that $mcr\mathrm{A}$ gene copies in the CC reactor ($3.2\times {10}^3$ copies ${\mathrm{mL}}^{-1}$) were significantly higher than those of the no algae (NA) and CC reactors, while the lowest denitrifying gene copies ($narG$, $nirS$, and $nos\mathrm{Z}$) were observed in the NA reactor. The Chloroflexi (22%) and Proteobacteria (31%) were the predominant bacterial communities in the CC reactor. Geobacter and Desulfobulbus were the main genera of exoelectrogens. This study can provide reference for nutrients (nitrogen, phosphorus) removal and GHG control in MFC wastewater treatment, but its long-term stability needs to be further studied.

Abstract

The leachate collection system (LCS) and leak detection system (LDS) flow rate data from 240 cells (or a combination of cells) at 54 municipal solid-waste landfills (located in seven US states) with double-liner systems were analyzed to assess the performance of the primary liner system. The average LCS leachate collection rates for the study sites ranged from $380\mathrm{L}{\mathrm{ha}}^{-1}{\mathrm{day}}^{-1}$ ($40.7\mathrm{gal.}{\mathrm{acre}}^{-1}{\mathrm{day}}^{-1}$) to $\mathrm{22,400}\mathrm{L}{\mathrm{ha}}^{-1}{\mathrm{day}}^{-1}$ ($\mathrm{2,390}\mathrm{gal.}{\mathrm{acre}}^{-1}{\mathrm{day}}^{-1}$) on a sitewide basis, and the average LDS leachate collection rates ranged from $1.8\mathrm{L}{\mathrm{ha}}^{-1}{\mathrm{day}}^{-1}$ ($0.2\mathrm{gal.}{\mathrm{acre}}^{-1}{\mathrm{day}}^{-1}$) to $577\mathrm{L}{\mathrm{ha}}^{-1}{\mathrm{day}}^{-1}$ ($61.7\mathrm{gal.}{\mathrm{acre}}^{-1}{\mathrm{day}}^{-1}$) on a sitewide basis. Assuming all leachate generated is collected either by the LCS or LDS, the data suggest that the primary liner systems’ aggregated efficiency is over 98%. The collection efficiency at sites that used a composite liner (geomembrane underlain by a geosynthetic clay liner or a compacted clay liner) system was not statistically different from the sites that used only a geomembrane as the primary liner (geomembrane underlain by a permeable layer) (median of 99% for both types). Leakage rates were compared with those estimated from the equations used by the hydrologic evaluation of landfill performance (HELP) model. The comparison suggests that the equations used by the HELP model to estimate leakage through the liner overestimate the leakage rate through geomembrane primary liners but underestimate the leakage rate through composite primary liners based on the HELP-model-default defect size and suggested defect frequency. It is also possible that groundwater intrusion could contribute to a portion of the leachate collected from the LDS because leachate quality data collected from a few sites indicated the LCS leachate had a higher concentration of most constituents than the leachate collected from LDS.

Practical Applications

The findings from this investigation have practical relevance to landfill operators and researchers involved in this field of study. The results suggest that incorporating a geosynthetic clay liner (GCL) or compacted clay liner (CCL) between the LCS and LDS may not significantly impact the leakage rate through the primary liner, possibly because of the poor contact between the geomembrane and GCL due to the presence of wrinkles in the geomembrane. More data from additional sites should be evaluated before concluding that GCL underlying a geomembrane does not offer an additional benefit of minimizing leachate leakage through a geomembrane. Additionally, the inconsistency between the measured and predicted leakage rates from equations used in this field of study indicate that the models used by researchers and consultants to predict liner leakage may need to be revisited and updated to reflect the leachate leakage rates observed at MSW landfills. The authors have identified potential future research areas based on this study’s findings. A more in-depth analysis of the reasons for the inconsistency between the measured and predicted leakage rates and examining alternative equations should be considered for future research. Future research should consider collecting additional LCS, LDS, and groundwater quality data from sites with double-liner systems, which would help determine whether leachate from the LCS is the predominant component of the leachate collected from the LDS or if groundwater or another outside source of water is a larger contributor. Finally, future research should consider assessing the contact quality between the geomembrane and underlying GCL/CCL achieved with current construction practices and its impact on the leakage rate through the primary liner.

Per- and polyfluoroalkyl substances (PFAS) from aqueous film forming foam (AFFF) can be accidentally backflushed into drinking water systems during firefighting operations or at industrial facilities. If this contaminated water enters household plumbing systems, homeowners may need to decontaminate their plumbing. This study examines the persistence of PFAS from AFFF on home plumbing, along with the effects of flushing and stagnation. Two sources of AFFF were investigated, representing older formulations (that contain longer chain PFAS) and newer formulations (that contain shorter chain PFAS). Experiments were conducted in copper, polyvinyl chloride (PVC), and cross-linked polyethylene (PEX) pipes with flushing after contamination followed by intermittent flow and periods of stagnation meant to mimic typical household use. Flushing immediately reduced the PFAS concentration in water leaving the pipe by 99.95% to 99.99%. However, PFAS concentration increased after periods of stagnation, corresponding to slow release of adhered PFAS. Flushing may be a valuable part of the decontamination process, but flushing parameters and duration need to be optimized for local conditions.