Review of per- and poly-fluoroalkyl treatment in combustion-based thermal waste systems in the United States.

Per- and poly-fluoroalkyl substances (PFAS) are a class of synthetic chemicals known for their widespread presence and environmental persistence. Carbon-fluorine (C-F) bonds are major components among PFAS and among the strongest organic bonds, thus destroying PFAS may present significant challenge. Thermal treatment such as incineration is an effective and approved method for destroying many halogenated organic chemicals. Here, we present the results of existing studies and testing at combustion-based thermal treatment facilities and summarize what is known regarding PFAS destruction and mineralization at such units. Available results suggest the temperature and residence times reached by some thermal treatment systems are generally favorable to the destruction of PFAS, but the possibility for PFAS or fluorinated organic byproducts to escape destruction and adequate mineralization and be released into the air cannot be ruled out. Few studies have been conducted at full-scale operating facilities, and none to date have attempted to characterize possible fluorinated organic products of incomplete combustion (PICs). Further, the ability of existing air pollution control (APC) systems, designed primarily for particulate and acid gas control, to reduce PFAS air emissions has not been determined. These data gaps remain primarily due to the previous lack of available methods to characterize PFAS destruction and PIC concentrations in facility air emissions. However, newly developed stack testing methods offer an improved understanding of the extent to which thermal waste treatment technologies successfully destroy and mineralize PFAS in these waste streams.

Characterization of per- and polyfluoroalkyl substances (PFAS) and other constituents in MSW landfill leachate from Puerto Rico.

Elevated per- and polyfluoroalkyl substance (PFAS) concentrations have been reported in municipal solid waste (MSW) landfill leachate with higher levels in wet and warmer subtropical climates. Information about landfill leachate characteristics is much more limited in tropical climates. In this study, 20 landfill leachate samples were collected from three MSW landfills on the tropical island of Puerto Rico and results were compared against landfills nationally and within Florida, USA. The samples collected in Puerto Rico underwent physical-chemical analysis, as well as a quantitative analysis of 92 PFAS. Samples described in this study include discrete leachate types, such as leachate, gas condensate, and leachate which has undergone on-site treatment (e.g., RO treatment, phytoremediation, lagoons). A total of 51 PFAS were detected above quantitation limits, including perfluorohexylphosphonic acid, a perfluoroalkyl acid (PFAA) which has not been reported previously in landfill leachate. ∑PFAS concentrations in this study (mean: 38,000 ng L-1), as well as concentrations of individual PFAS, are significantly higher than other reported MSW landfill leachate concentrations. The profiles of leachates collected from on-site treatment systems indicate possible transformation of precursor PFAS as a result of treatment processes - oxidizing conditions, for example, may facilitate aerobic transformation, increase the concentrations of PFAAs, and possibly increase the apparent ∑PFAS concentration. Extreme climate events, including rising temperatures and more frequent hurricanes, have placed additional strain on the solid waste management infrastructure on the island - adding complexity to an already challenging PFAS management issue. As concern grows over PFAS contamination in drinking water, these findings should inform solid waste and leachate management decisions in order to minimize PFAS emissions in island environments.

Assessment of Municipal Solid-Waste Landfill Liner Performance.

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 L ha-1 day-1 (40.7 gal. acre-1 day-1) to 22,400 L ha-1 day-1 (2,390 gal. acre-1 day-1) on a sitewide basis, and the average LDS leachate collection rates ranged from 1.8 L ha-1 day-1 (0.2 gal. acre-1 day-1) to 577 L ha-1 day-1 (61.7 gal. acre-1 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.

Leachate indicators of an elevated temperature landfill.

Elevated temperature landfills (ETLFs) are municipal solid waste (MSW) landfills that have been impacted by subsurface exothermic reactions (SERs) and display unusual gas and leachate composition. Leachate quantity and quality data were analyzed to identify indicators of a SER at an ETLF in Ohio, USA. ETLF leachate generation increased from 2.04 to 14.4 m3/hectare-day (218 to 1,539 gallons/acre-day), peaking 16 months after the reaction was first noticed. The leachate generation rate for this ETLF remains about two times greater than the average Ohio MSW landfill. Several general parameters such as pH, electrical conductivity (EC), and total dissolved solids (TDS) remain impacted 5 years later. Similarly, metals such as arsenic, iron, calcium, potassium, and magnesium have increased in concentration. Volatile organic compounds (VOCs) behavior was less consistent as a group of chemicals. Increases of VOCs such as acetone, benzene, and methyl ethyl ketone (MEK) also increased. Importantly, in one year, benzene exceeded its toxicity characteristic threshold meaning the leachate was a hazardous waste, substantially increasing treatment and disposal costs. It is not clear if the VOCs are produced directly by the SER or if they are an indicator that microbial processes -which would otherwise consume them- have been disrupted. ETLFs likely do not all undergo the same exothermic reaction(s) and, unlike the analysis of landfill gas composition, temporal changes in leachate constituents' concentrations may be more important than comparing to absolute values.

A critical review of perfluoroalkyl and polyfluoroalkyl substances (PFAS) landfill disposal in the United States.

Landfills manage materials containing per- and polyfluoroalkyl substances (PFAS) from municipal solid waste (MSW) and other waste streams. This manuscript summarizes state and federal initiatives and critically reviews peer-reviewed literature to define best practices for managing these wastes and identify data gaps to guide future research. The objective is to inform stakeholders about waste-derived PFAS disposed of in landfills, PFAS emissions, and the potential for related environmental impacts. Furthermore, this document highlights data gaps and uncertainties concerning the fate of PFAS during landfill disposal. Most studies on this topic measured PFAS in liquid landfill effluent (leachate); comparatively fewer have attempted to estimate PFAS loading in landfills or other effluent streams such as landfill gas (LFG). In all media, the reported total PFAS heavily depends on waste types and the number of PFAS included in the analytical method. Early studies which only measured a small number of PFAS, predominantly perfluoroalkyl acids (PFAAs), likely report a significant underestimation of total PFAS. Major findings include relationships between PFAS effluent and landfill conditions - biodegradable waste increases PFAS transformation and leaching. Based on the results of multiple studies, it is estimated that 84% of PFAS loading to MSW landfills (7.2 T total) remains in the waste mass, while 5% leaves via LFG and 11% via leachate on an annual basis. The environmental impact of landfill-derived PFAS has been well-documented. Additional research is needed on PFAS in landfilled construction and demolition debris, hazardous, and industrial waste in the US.

Growth Media Efficacy in Biochemical Methane Potential Assays.

The Biochemical Methane Potential (BMP) assay is a vital tool for quantifying the amount of methane that specific biodegradable materials can generate in landfills and similar anaerobic environments. Applications of the protocol are extensive and while simple in design, the BMP assay can use anaerobic seed from many different types of sources to determine the methane potential from most biodegradable substrates. Many researchers use differing protocols for this assay, both including and excluding the use of synthetic growth medias, intended to provide vital nutrients and trace elements that facilitate methanogenesis and leave the substrate being tested as the only limiting factor in methane generation potential. The variety of previous approaches inspired this effort to determine the efficacy of adding synthetic growth media to BMP assays. The presented findings suggest the use of M-1 synthetic growth media, defined in this study, at a volumetric ratio of 10% active sludge: 90% M-1 media yielded optimal results in terms of gas yield and reduced variability.

Assessing moisture contributions from precipitation, waste, and leachate for active municipal solid waste landfills.

Precipitation, evapotranspiration (ET), waste tonnage, landfill gas (LFG), and leachate data were aggregated from public sources to perform a 5-10 year water balance and estimate the contributions of three water sources (precipitation, incoming waste, and leachate recycling) for 36 active municipal solid waste (MSW) landfills in Ohio, USA. Uniquely, the water balance incorporated waste decomposition, using gas collection data to inform mass loss from biodegradation. Moisture contents of 20-30% for incoming waste indicate that entrained water is the largest source of landfill moisture. Infiltration of precipitation into the landfill after ET was the second largest source. Even at facilities where a majority of the leachate generated was recirculated, it did not significantly affect the moisture content in that year. Using the water balance approach, it appears leachate recirculation is unlikely to increase moisture content above 40% by mass, a regulatory threshold in the US, which would impose stricter air pollution control requirements. However, poor stormwater management could easily allow for "bioreactor" conditions to develop. The calculated landfill moisture content was significantly affected by the assumed runoff coefficient (CRO) parameter. CRO values below 20% and above 50% produced unrealistically high or low moisture contents, respectively. This approach can assist operators and regulators in understanding the contribution of different sources to a landfill's moisture profile and avoid future operational problems.

Understanding landfill gas behavior at elevated temperature landfills.

Landfill gas (LFG) wellhead data were compared to understand the range of observations due to unique conditions at five elevated temperature landfills (ETLFs) in the U.S. Correlations of the primary gas ratio, CH4:CO2, show distinct compositional indicators for (1) typical operation, (2) subsurface exothermic reactions (SERs), (3) high moisture content, and (4) air intrusion that can help operators and regulators diagnose conditions across gas extraction wells. ETLFs A, B, D, and E showed similar trends, such as decreasing CH4 and increasing CO2, CO, and H2 that have been previously described. ETLF C uniquely exhibited elevated CH4 and temperatures simultaneously due to carbonation (i.e., CO2 consumption) of a steel slag which was used as alternative daily cover (ADC). At the maximum gas well temperature, T = 82 °C/180 °F, CH4 and CO2 concentrations were 47% and 28%, respectively. At ETLFs A, B, and E, H2 > 50% were regularly observed in affected gas wells for several years. At the five ETLFs, maximum CO concentrations ranged from 1400-16,000 ppmv. Like the analysis of CH4:CO2, it is hypothesized here that H2 (%):CO (ppmv) may infer the types of waste that are thermally degrading. Co-disposal of industrial wastes and MSW and the use of potentially reactive ADCs should remain an important consideration for landfill operators and regulators because of their potential long-term impacts to LFG quality.

Dataset of leachate volumes and surface areas for municipal solid waste (MSW) landfills in Ohio, USA from 1988-2020.

This data brief presents leachate disposal and management data for 43 active or closed municipal solid waste (MSW) landfills and planar surface areas for 40 of those landfills in Ohio, USA. Data were extracted from publicly available Annual Operational Reports from the Ohio Environmental Protection Agency (Ohio EPA) and consolidated into a digital dataset of two delimited text files. A total of 9,985 data points represent monthly leachate disposal totals, arranged by management type and by landfill. Leachate management data for some landfills extend from 1988-2020 but are mostly limited to 2010-2020. Annual planar surface areas were identified from topographic maps in the annual reports. A total of 610 data points were created for the annual surface area dataset. This dataset aggregates and organizes the information, allowing for accessibility and increased application to engineering analysis and research projects.

Relationships between per- and polyfluoroalkyl substances (PFAS) and physical-chemical parameters in aqueous landfill samples.

Variable chemistries of liquids from landfills can potentially impact levels of per- and polyfluoroalkyl substances (PFAS). The objective of the current study was to evaluate relationships between physical-chemical properties (bulk measurements, oxygen demand components, and metals) and PFAS concentrations in different types of aqueous landfill samples. Aqueous landfill samples were collected from 39 landfill facilities in Florida, United States. These samples included leachates from landfills that receive different waste types, such as municipal solid waste incineration ash (MSWA), construction and demolition debris (C&D), and municipal solid waste (MSW). Additional aqueous landfill samples were sourced from treated landfill leachate, gas condensate, stormwater, and groundwater from within and near the landfill boundaries. Results showed significant correlations (p < 0.05) between ∑26PFAS and alkalinity (rs = 0.83), total organic carbon (TOC) (rs = 0.84), and ammonia (rs = 0.79) for all leachate types. Other physical-chemical parameters that were significantly correlated (rs > 0.60, p < 0.05) with PFAS included specific conductivity, chemical oxygen demand (COD), and to a lesser extent, total dissolved solids (TDS) and total solids (TS). For gas condensates, PFAS was significantly correlated with TOC. Stormwater and groundwater, within and near the landfill boundaries, had considerably lower levels of PFAS and had a minimal correlation between PFAS and physical-chemical parameters. Although PFAS concentrations and physical-chemical parameters and their correlations varied between different types of aqueous landfill samples, results suggest that physical-chemical properties can be useful indicators of relative PFAS concentrations within a leachate type. More research is needed to validate the mechanisms that relate physical-chemical parameters to PFAS concentrations in landfill leachates.

Underestimation of Per- and Polyfluoroalkyl Substances in Biosolids: Precursor Transformation During Conventional Treatment.

Wastewater treatment plants generate a solid waste known as biosolids. The most common management option for biosolids is to beneficially reuse them as an agricultural amendment, but because of the risk of pathogen exposure, many regulatory bodies require pathogen reduction before biosolids reuse. Per- and polyfluoroalkyl substances (PFAS) are well documented in biosolids, but limited information is available on how biosolids treatment processes impact PFAS. Furthermore, quantification of PFAS has focused on perfluoroalkyl acids (PFAAs) which are a small fraction of thousands of PFAS known to exist. The objective of this study was to quantify 92 PFAS in biosolids collected from eight biosolids treatment facilities before and after four pathogen treatment applications: composting, heat treatment, lime treatment, and anaerobic digestion. Overall, total PFAS concentrations before and after treatment were dominated by PFAA precursor species, in particular, diPAPs which accounted for a majority of the mass of the Σ92PFAS. This differs from historic data that found PFAAs, primarily PFOS, to dominate total PFAS concentrations. Treatment options such as heat treatment and composting changed the ratio of PFAA precursors to PFAAs indicating a transformation of PFAS during treatment. This study finds that PFAA precursors are likely underrepresented by other studies and make up a larger percentage of the total PFAS concentration in biosolids than previously estimated.

Per- and polyfluoroalkyl substances (PFAS) distribution in landfill gas collection systems: leachate and gas condensate partitioning.

While per- and polyfluoroalkyl substances (PFAS) have been reported extensively in municipal solid waste (MSW) landfill leachate,they have rarely been quantified in landfill gas or in discrete landfill liquids such as landfill gas condensate (LGC), and the potential for PFAS to partition to the condensate has not been reported. LGC and leachate collected from within gas wells known as gas well pump-out (GWP) from three MSW landfills underwent physical-chemical characterization and PFAS analysis to improve understanding of the conditions under which these liquids form and to illuminate PFAS behavior within landfills. LGC was observed to be clear liquid containing ammonia and alkalinity while GWP strongly resembled leachate - dark in color, high in chloride and ammonia. Notably, arsenic and antimony were found in concentrations exceeding regulatory thresholds by over two orders of magnitude in many LGC samples. LGC contained a lower average concentration of ΣPFAS (19,000 ng L) compared to GWP (56,000 ng L); however, LGC contained more diversity of PFAS, with 53 quantified compared to 44 in GWP. LGC contained proportionally more precursor PFAS than GWP, including more semi-volatile PFAS which are rarely measured in water matrices, such as fluorotelomer alcohols and perfluoroalkane sulfonamido ethanols. This study provides the first detailed comparison of these matrices to inform timely leachate management decisions.

Evaluation of per- and polyfluoroalkyl substances (PFAS) in leachate, gas condensate, stormwater and groundwater at landfills.

Per- and polyfluoroalkyl substances (PFAS), found in many consumer products, are commonly disposed of in landfills at the end of their service lives. To identify landfill liquids that should be prioritized for treatment, this study aimed to evaluate PFAS levels in different aqueous samples from landfills and identify relationships between PFAS and landfill characteristics. Twenty-six PFAS including 11 perfluoroalkyl carboxylic acids (PFCAs), 7 perfluoroalkyl sulfonates (PFSAs), and 8 perfluoroalkyl acid precursors (PFAA-precursors) were measured in municipal solid waste (MSW) leachate, construction and demolition debris (CDD) leachate, municipal solid waste incineration (MSWI) ash leachate, gas condensate, stormwater, and groundwater from landfills. Based on the median, results show that PFAS levels in MSW leachate were the highest (10,000 ng L-1), CDD leachate were intermediate (6200 ng L-1), and MSWI ash leachate were the lowest (1300 ng L-1) among the leachates evaluated. PFAS levels in gas condensate (7000 ng L-1) were similar to MSW leachate. PFAS in stormwater and groundwater were low (medians were less than 500 ng L-1). Dominant subgroups included PFCAs and PFAA-precursors in all leachates. PFSAs were also found in CDD leachate, PFAA-precursors in gas condensate, and PFCAs in stormwater and groundwater. Landfill characteristics significantly correlated with ∑26PFAS included waste proportions (percentage of MSWI ash in landfill, |rs| = 0.22), operational status (active or not, |rs| = 0.27) and rainfall (30-d cumulative rainfall, |rs| = 0.39). The results from this study can be used to prioritize which landfills and which reservoir of liquids (and corresponding subgroup of PFAS) to target for PFAS management.

Concentrations of perfluoroalkyl and polyfluoroalkyl substances before and after full-scale landfill leachate treatment.

Many consumer and industrial products, industrial wastes and dewatered sludge from municipal wastewater treatment plants containing per- and polyfluoroalkyl substances (PFAS) are disposed of in landfills at the end of their usage, with PFAS in these products leached into landfill leachates. On-site leachate treatment is one possible method to reduce PFAS in leachates. Many landfills are equipped with on-site leachate treatment systems, but few full-scale facilities have been systematically evaluated for PFAS concentration changes. The objective of this study was to evaluate a cross-section of full-scale on-site landfill treatment systems to measure changes in PFAS concentrations. Leachate samples were collected before and after treatment from 15 facilities and were evaluated for 26 PFAS, including 11 perfluoroalkyl carboxylic acids (PFCAs), 7 perfluoroalkyl sulfonic acids (PFSAs), and 8 perfluoroalkyl acid precursors (PFAA-precursors). Transformation of precursors was evaluated by the total oxidizable precursor (TOP) assay. Results showed no obvious reductions in total measured PFAS (∑26PFAS) for on-site treatment systems including ponds, aeration tanks, powdered activated carbon (PAC), and sand filtration. Among evaluated on-site treatment systems, only systems fitted with reverse osmosis (RO) showed significant reductions (98-99 %) of ∑26PFAS in the permeate. Results from the TOP assay showed that untargeted PFAA-precursors converted into targeted short-chain PFCAs increasing ∑26PFAS in oxidized samples by 30 %, on average. Overall, results of this study confirm the efficacy of RO systems and suggest the presence of additional precursors beyond those measured in this study.

Municipal solid waste incineration (MSWI) ash co-disposal: Influence on per- and polyfluoroalkyl substances (PFAS) concentration in landfill leachate.

Municipal solid waste incineration (MSWI) ash is often managed through co-disposal with unburned wastes in landfills, a practice previously reported to result in enhanced leaching of pollutants (e.g., heavy metals) in landfill leachate. The objective of this study was to evaluate the effect of co-disposed unburned wastes on per- and polyfluoroalkyl substances (PFAS) in MSWI ash landfill leachate. Leachate was collected from four landfills containing MSWI ash, either as a sole waste stream or co-disposed of with sewage sludge and MSW screenings. Samples of ash and unburned materials were collected and assessed separately for leachable PFAS in the laboratory. All samples were analyzed for 26 PFAS. Results showed that greater ash content was associated with lower leachate PFAS concentrations. The pure ash monofill exhibited the lowest PFAS in landfill leachate (290 ng L-1) while the landfill contained a large amount of unburned waste had the highest PFAS (11,000 ng L-1). For laboratory leaching tests, average ∑26PFAS concentration in lab ash leachate (310 ng L-1) was 10 and 24 times lower than observed in lab sewage sludge leachate (3,200 ng L-1) and lab MSW screenings leachate (7,500 ng L-1), respectively. Leachate from the ash-only landfill had ∑26PFAS concentration similar to what was measured in the ash itself. On the contrary, ∑26PFAS concentration in co-disposal landfill leachates were similar to those in PFAS-rich unburned waste itself, regardless of the percentages of landfilled unburned wastes. We hypothesize that leachate generated in co-disposal scenarios preferentially flows through PFAS-rich unburned materials and that biotransformation of precursors enhanced by unburned waste degradation further contributes to higher concentrations of terminal PFAS in ash co-disposal sites. Landfill operators should expect PFAS in leachates to be higher when PFAS-rich unburned wastes are disposed of alongside MSWI ash, even if the unburned fraction is small.

Greenhouse gas reporting data improves understanding of regional climate impact on landfill methane production and collection.

A critical examination of the US Environmental Protection Agency's (US EPA's) Greenhouse Gas Reporting Program (GHGRP) database provided an opportunity for the largest evaluation to date of landfilled waste decomposition kinetics with respect to different US climate regimes. In this paper, 5-8 years of annual methane collection data from 114 closed landfills located in 29 states were used to estimate site-specific waste decay rates (k) and methane collection potentials (Lc). These sites account for approximately 9% of all landfills required to report GHG emissions to the US EPA annually. The mean methane collection potential (Lc) for the sites located in regions with less than 635 mm (25 in) annual rainfall was significantly (p<0.002) lower than the mean methane collection potential of the sites located in regions with more than 635 mm (25 in) annual precipitation (49 and 73 m3 methane Mg-1 waste, respectively). This finding suggests that a fraction of the in-place biodegradable waste may not be decomposing, potentially due to a lack of adequate moisture content of landfills located in arid regions. The results of this evaluation offer insight that challenges assumptions of the traditional landfill methane estimation approach, especially in arid climates, that all methane corresponding to the total methane generation potential of the buried solid waste will be produced. Decay rates showed a significant correlation with annual precipitation, with an average k of 0.043 year-1 for arid regions (< 508 mm (20 in) year-1), 0.074 year-1 for regions with 508-1,016 mm (20-40 in) annual precipitation, and 0.09 year-1 in wet regions (> 1,016 mm (40 in) year-1). The data suggest that waste is decaying faster than the model default values, which in turn suggests that a larger fraction of methane is produced during a landfill's operating life (relative to post-closure).

From Waste Collection Vehicles to Landfills: Indication of Per- and Polyfluoroalkyl Substance (PFAS) Transformation.

Municipal solid waste contain diverse and significant amounts of per- and polyfluoroalkyl substances (PFAS), and these compounds may transform throughout the "landfilling" process from transport through landfill degradation. Fresh vehicle leachates, from commercial and residential waste collection vehicles at a transfer station, were measured for 51 PFAS. Results were compared to PFAS levels obtained from aged landfill leachate at the disposal facility. The landfill leachate was dominated by perfluoroalkyl acids (PFAAs, including perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs); 86% of the total PFAS, by median mass concentration), while the majority of PFAS present in commercial and residential waste vehicle leachate were PFAA-precursors (70% and 56% of the total PFAS, by median mass concentration, respectively), suggesting precursor transformation to PFAAs during the course of landfill disposal. In addition, several PFAS, which are not routinely monitored-perfluoropropane sulfonic acid (PFPrS), 8-chloro-perfluoro-1-octane sulfonic acid (8Cl-PFOS), chlorinated polyfluoroether sulfonic acids (6:2, 8:2 Cl-PFESAs), sodium dodecafluoro-3H-4,8-dioxanonanoate (NaDONA), and perfluoro-4-ethylcyclohexanesulfonate (PFECHS)-were detected. Potential degradation pathways were proposed based on published studies: transformation of polyfluoroalkyl phosphate diester (diPAPs) and fluorotelomer sulfonic acids (FTS) to form PFCAs via formation of intermediate products such as fluorotelomer carboxylic acids (FTCAs).

Removal of Stabilized Silver Nanoparticles from Surface Water by Conventional Treatment Processes.

Engineered nanomaterials are used in many applications, including pollution sensors, photovoltaics, medical imaging, drug delivery and environmental remediation. Due to their numerous applications, silver nanoparticles (Ag NPs) are receiving a large amount of attention. Ag NPs may occur in drinking water sources either during manufacturing, consumption and/or disposal processes. This potentially leads to the presence of Ag NPs in finished drinking water, which could have public health impacts. The objective of this research was to investigate the removal of several types of stabilized Ag NPs by potable water treatment processes. Specifically, this research achieved these objectives through; 1) Synthesis of Citrate-reduced Ag NPs, Polyvinylpyrrolidone stabilized (PVP) Ag NPs and Branched polyethyleneimine stabilized (BPEI) Ag NPs, 2) Characterization of synthesized Ag NPs to determine their aggregation potential, Zeta potential profiles, (pHpzc) and obtain morphological data from SEM images, and 3) An evaluation of the efficacy of conventional water treatment processes (i.e., coagulation, flocculation, sedimentation and sand filtration) in removing stabilized Ag NPs from natural water. The three NPs were found to be stable at the nano size in natural water. Alum coagulation had no impact on the PVP and BPEI Ag NPs. Flocculation and settling were found to be key steps for removal of these NPs. The three Ag NPs were not permanently removed by means of conventional water treatment processes employed in this study.

Nanosilver as a disinfectant in dental unit waterlines: Assessment of the physicochemical transformations of the AgNPs.

Dental unit water lines (DUWL) are susceptible to biofilm development and bacterial growth leading to water contamination, causing health and ecological effects. This study monitors the interactions between a commonly used nanosilver disinfectant (ASAP-AGX-32, an antimicrobial cleaner for dental units, 0.0032% Ag) and biofilm development in DUWL. To simulate the disinfection scenario, an in-house DUWL model was assembled and biofilm accumulation was allowed. Subsequent to biofilm development, the disinfection process was performed according to the manufacturer's instructions. The pristine nanosilver particles in the cleaner measured between 3 and 5 nm in diameter and were surrounded by a stabilizing polymer. However, the polymeric stabilizing agent diminished over the disinfection process, initiating partial AgNPs aggregation. Furthermore, surface speciation of the pristine AgNPs were identified as primarily AgO, and after the disinfection process, transformations to AgCl were observed. The physicochemical characteristics of AgNPs are known to govern their fate, transport and environmental implications. Hence, knowledge of the AgNPs characteristics after the disinfection process (usage scenario) is of significance. This study demonstrates the adsorption of AgNPs onto biofilm surfaces and, therefore, will assist in illustration of the toxicity mechanisms of AgNPs to bacteria and biofilms. This work can be an initial step in better understanding how AgNPs transform depending on the conditions they are exposed to during their lifetime. Until this date, most research has been focused on assessing the impacts of pristine (lab synthesized) nanomaterials on various systems. However, it is our belief that nanoparticles may undergo transformations during usage, which must be taken into consideration. Furthermore, this experiment is unique as it was conducted with a commonly used, commercially available nanosilver suspension leading to more realistic and applicable findings.

Analysis of metallic and metal oxide nanomaterial environmental emissions.

The current study presents evidence on metallic and metal oxide engineered nanomaterial (ENM) emissions into the environment and an analytic perspective of the outcomes of evaluated studies with respect to different individual end points along the lifecycle trajectory. The key findings suggest that 1) the published literature on emissions of metallic ENMs is limited in both the number and information available on the characteristics of emitted ENMs; 2) the studies are classified as experimental and computational studies focused on predicting ENM emissions; 3) the majority of studies investigated ENM emissions during nanomaterial use and waste management, followed by raw material manufacturing, and finally, nano-enabled product manufacturing; 4) the studies primarily reported the concentration/quantity of emitted ENMs, whereas the physical-chemical characteristics of emitted ENMs were rarely measured or reported; and 5) the published literature primarily focused on emissions of silver and titanium dioxide ENMs and lacked similar information on other surging metallic and metal oxide ENMs such as nano-zero valent iron (nZVI), aluminum (Al), and aluminum oxide (Al2O3) ENMs. The evidence suggests that emitted nanoparticles into the air cover a wide range of concentrations below and above the allowable occupational exposure limits. The concentrations of nanoparticles in water systems are considered in the toxic to very toxic range for a variety of biological species. Given the critical gaps in knowledge, one cannot read across different sources of emissions for metallic and metal oxide ENMs hampering efforts with respect to understanding realistic scenarios for transformations in the natural environment and biological media.