Sources of per- and polyfluoroalkyl substances in an arid, urban, wastewater-dominated watershed.

Per- and polyfluoroalkyl substances (PFAS) enter surface waters from various sources such as wastewater treatment plants, fire-fighting sites, and PFAS-producing and PFAS-using industries. The Las Vegas Wash in Southern Nevada of the United States (U.S.) conveys wastewater effluent from the Las Vegas metropolitan area to Lake Mead, a drinking water source for millions of people in the U.S. Southwest. PFAS have previously been detected in the Las Vegas Wash, but PFAS sources were not identified. In this study, upstream wash tributaries, wastewater treatment effluents, and shallow groundwater wells were sampled in multiple campaigns during dry-weather conditions to investigate possible PFAS sources. Out of 19 PFAS, two short-chain PFAS-perfluoropentanoic acid (48 % of the total molar concentration) and perfluorohexanoic acid (32 %)-comprised the majority of PFAS loading measured in the Las Vegas Wash, followed by perfluorooctanoic acid (9 %). On a mass loading basis, the majority of total measured PFAS (approximately 90 %) and at least 48 % of each specific PFAS in the Las Vegas Wash likely entered via municipal wastewater effluents, of which the main source was likely residential wastewater. One of the drainage areas with a major civilian airport was identified as a potential source of relatively enriched perfluorosulfonic acids to a small wash tributary and shallow groundwater samples. Nonetheless, that tributary contributed at most 15 % of any specific PFAS to the mainstem of the Las Vegas Wash. Total PFAS concentrations were relatively low for the small tributary associated with an urban smaller airport and the lack of flow in the tributary channel immediately downgradient of an Air Force base indicates the smaller airport and base were unlikely significant PFAS sources to the Las Vegas Wash. Overall, this study demonstrated effective PFAS source investigation methodology and the importance of wastewater effluent as a PFAS environmental pathway.

Per- and polyfluoroalkyl substances and organofluorine in lakes and waterways of the northwestern Great Basin and Sierra Nevada.

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic chemicals that occur ubiquitously in the environment and have been linked to numerous adverse health effects in humans and aquatic organisms. Although numerous environmental monitoring studies have been conducted, only one has evaluated PFAS in surface waters of the northwestern Great Basin, which features unique topography that results in dozens of endorheic basins and terminal lakes with no natural outlet, where PFAS may accumulate. To close this knowledge gap, we evaluated the occurrence of PFAS in grab samples from 15 lakes (headwater and terminal lakes) and 10 rivers in the Great Basin located in Nevada and California of the United States. PFAS and organofluorine were quantified by liquid chromatography tandem mass spectroscopy (LC-MS/MS) and combustion ion chromatography, respectively. The highest concentrations of PFAS occurred in samples taken near sites with known or suspected prior aqueous film forming foam (AFFF) application (~20 to 4754 ng/L). Samples near wastewater treatment plants and in urban areas also tended to have PFAS concentrations greater than those measured in remote, less anthropogenically influenced areas (~2 to 15 ng/L, <3 ng/L respectively). In limited snapshot sampling events PFAS appeared to accumulate in terminal lakes to some extent; in-lake concentrations were two to five times greater than those of their inflows. Fluorotelomer sulfonates were present downstream of a known AFFF application area likely to have had fluorotelomer-based foams applied to it, and the concentrations decayed in a predictable manner, suggesting they may be used as an indicator of PFAS transport away from an AFFF source. In all but two samples, organofluorine concentrations were greater than the sum of targeted PFAS (on a F basis) (median of 0.6 % of organofluorine identified via LC-MS/MS), although there was considerable variability in organofluorine measured in replicate samples.

Critical Review on Bromate Formation during Ozonation and Control Options for Its Minimization.

Ozone is a commonly applied disinfectant and oxidant in drinking water and has more recently been implemented for enhanced municipal wastewater treatment for potable reuse and ecosystem protection. One drawback is the potential formation of bromate, a possible human carcinogen with a strict drinking water standard of 10 µg/L. The formation of bromate from bromide during ozonation is complex and involves reactions with both ozone and secondary oxidants formed from ozone decomposition, i.e., hydroxyl radical. The underlying mechanism has been elucidated over the past several decades, and the extent of many parallel reactions occurring with either ozone or hydroxyl radicals depends strongly on the concentration, type of dissolved organic matter (DOM), and carbonate. On the basis of mechanistic considerations, several approaches minimizing bromate formation during ozonation can be applied. Removal of bromate after ozonation is less feasible. We recommend that bromate control strategies be prioritized in the following order: (1) control bromide discharge at the source and ensure optimal ozone mass-transfer design to minimize bromate formation, (2) minimize bromate formation during ozonation by chemical control strategies, such as ammonium with or without chlorine addition or hydrogen peroxide addition, which interfere with specific bromate formation steps and/or mask bromide, (3) implement a pretreatment strategy to reduce bromide and/or DOM prior to ozonation, and (4) assess the suitability of ozonation altogether or utilize a downstream treatment process that may already be in place, such as reverse osmosis, for post-ozone bromate abatement. A one-size-fits-all approach to bromate control does not exist, and treatment objectives, such as disinfection and micropollutant abatement, must also be considered.

Occurrence of quantifiable and semi-quantifiable poly- and perfluoroalkyl substances in united states wastewater treatment plants.

Both quantifiable and semi-quantifiable poly- and perfluoroalkyl substances (PFAS) were evaluated in the influent, effluent, and biosolids of 38 wastewater treatment plants. PFAS were detected in all streams at all facilities. For the means of the sums of detected, quantifiable PFAS concentrations were 98 ± 28 ng/L, 80 ± 24 ng/L, and 160,000 ± 46,000 ng/kg (dry weight basis) in the influent, effluent, and biosolids (respectively). In the aqueous influent and effluent streams this quantifiable PFAS mass was typically associated with perfluoroalkyl acids (PFAAs). In contrast, quantifiable PFAS in the biosolids were primarily polyfluoroalkyl substances that potentially serve as precursors to the more recalcitrant PFAAs. Results of the total oxidizable precursor (TOP) assay on select influent and effluent samples showed that semi-quantified (or, unidentified) precursors accounted for a substantial portion (21 to 88%) of the fluorine mass compared to that associated with quantified PFAS, and that this fluorine precursor mass was not appreciably transformed to perfluoroalkyl acids within the WWTPs, as influent and effluent precursor concentrations via the TOP assay were statistically identical. Evaluation of semi-quantified PFAS, consistent with results of the TOP assay, showed the presence of several classes of precursors in the influent, effluent, and biosolids; perfluorophosphonic acids (PFPAs) and fluorotelomer phosphate diesters (di-PAPs) occurred in 100 and 92% of biosolid samples, respectively. Analysis of mass flows showed that, for both quantified (on a fluorine mass basis) and semi-quantified PFAS, the majority of PFAS exited WWTPs through the aqueous effluent compared to the biosolids stream. Overall, these results highlight the importance of semi-quantified PFAS precursors in WWTPs, and the need to further understand the impacts of their ultimate fate in the environment.

Characterizing the chemical and microbial fingerprint of unsheltered homelessness in an urban watershed.

Unsheltered homelessness is rapidly becoming a critical issue in many cities worldwide. The worsening situation not only highlights the socioeconomic plight, but it also raises awareness of ancillary issues such as the potential implications for urban water quality. The objective of this study was to simultaneously leverage diverse source tracking tools to develop a chemical and microbial fingerprint describing the relative contribution of direct human inputs into Las Vegas' tributary washes. By evaluating a wide range of urban water matrices using general water quality parameters, fecal indicator bacteria (FIB), human-associated microbial markers [e.g., HF183, crAssphage, and pepper mild mottle virus (PMMoV)], 16S rRNA gene sequencing data, and concentrations of 52 anthropogenic trace organic compounds (TOrCs), this study was able to differentiate principal sources of these constituents, including contributions from unsheltered homelessness. For example, HF183 (31% vs. 0%), crAssphage (61% vs. 5%), and PMMoV (72% vs. 55%) were more frequently detected in tributary washes with higher homeless census counts vs. 'control' tributary washes. Illicit drugs or their metabolites (e.g., heroin, acetylmorphine, amphetamine, and cocaine) and select TOrCs (e.g., acetaminophen, caffeine, ibuprofen, and naproxen) were also detected more frequently and at higher concentrations in the more anthropogenically-impacted washes. These data can be used to raise awareness of the shared interests between the broader community and those who are experiencing homelessness, notably the importance of protecting environmental health and water quality. Ultimately, this may lead to more rapid adoption of proven strategies for achieving functional zero homelessness, or at least additional resources for unsheltered individuals.

Pretreatment strategies for ion exchange to control brominated disinfection byproducts in potable reuse.

The application of ion exchange (IX) resins to remove disinfection byproduct (DBP) precursors in wastewater effluents is challenging due to relatively high concentrations of competing anions. This study examined various pretreatment strategies to target competing ions to improve IX removal of DBP precursors, bromide and dissolved organic matter (DOM), measured as trihalomethane and haloacetic acid formation potentials (THMFP and HAAFP). IX batch experiments were performed with four commercial anion exchange (AIX) resins selective for bromide (BrP), DOM (A860), sulfate (MTA) and PFOA/PFOS (PFA), and one cation exchange (CIX) resin selective for iodide (CT). For single AIX treatments the bromide removal ranking was the following: PFA (58%) > MTA (51%) > BrP (43%) > A860 (16%), which corresponded with decreasing brominated THMFP removals and increasing bromine incorporation factors. For dual AIX combinations (PFA and BrP, MTA and BrP), either simultaneous or sequential treatments had the highest bromide (PFA + BrP [69%], MTA + BrP [67%], (PFA→BrP [77%], MTA→BrP [74%]) and Br-THMFP (THMFP [∼80%]) and Br-HAAFP (HAAFP [∼77%]) removals, and therefore the lowest fractions of brominated DBPs (Br-DBPs). Despite ozone (O3), biological active carbon (BAC), and granular activated carbon (GAC) pretreatments reducing the overall DOM concentration (33%), these pretreatment steps did not improve the bromide removals of the resins, although it did increase the Br-THMFP and Br-HAAFP removals by 2-38% and 13-20%, respectively. Nanofiltration (NF) pretreatment significantly removed sulfate (97%) resulting in an increased bromide removal of 19% by the AIX resins, which led to increased removal of Br-THMFP and Br-HAAFP by 93% and 96%, respectively. Among all the IX resins the CT resin had the highest bromide removal (83%) and lowest fraction of Br-DBPs. The results reveal pretreatment with existing technologies including AIX, O3/BAC/GAC, or NF can potentially enhance the removal of brominated DBP precursors by IX resins during potable reuse applications.

Using machine learning classification to detect simulated increases of de facto reuse and urban stormwater surges in surface water.

Water quality events such as increases in stormwater or wastewater effluent in drinking water sources pose hazards to drinking water consumers. Stormwater and wastewater effluent enter Lake Mead-an important drinking water source in the southwest USA-via the Las Vegas Wash. Previous studies have applied machine learning and online instruments to detect contamination in water distribution systems. However, alert systems at drinking water intakes would provide more time for corrective action. An array of online instruments measuring pH, conductivity, redox potential, turbidity, temperature, tryptophan-like fluorescence, UV absorbance (UVA254), TOC, and chlorophyll-a was fed raw water directly from Lake Mead. Wastewater effluent, dry weather Las Vegas Wash, and storm-impacted Las Vegas Wash samples were blended into the instrument inlets at known ratios to simulate three types of adverse water quality events. Data preprocessing was conducted to correct for diurnal patterns or instrument drift. Supervised machine learning was conducted using previously published models in R. Ninety-nine models were screened on the raw data. Eight high-performing models were evaluated in-depth and optimized. Weighted k-Nearest Neighbors, Single C5.0 Ruleset, Mixture Discriminant Analysis, and an ensemble of these three models had accuracy over 97% when assigning test set data among three classes (Normal, Event, or Maintenance). The ensemble detected all event types at the earliest timepoint and had one false positive that was not a lag error (i.e., consecutively following a true positive). Omitting Maintenance, the Adaboost model had over 99% test set accuracy and zero false positives that were not lag errors. Data preprocessing was beneficial, but the optimal methods were model-specific. All nine water quality variables were useful for most models, but UVA254 and turbidity were most important.

Biochar Water Treatment for Control of Organic Micropollutants with UVA Surrogate Monitoring.

Biochar adsorbent can be produced in low-resource settings using local materials and simple pyrolysis technology, and it has shown promise for uptake of micropollutants (MPs) such as pesticides, pharmaceuticals, industrial compounds, and chemicals released from consumer goods present in water at ng/L to µg/L levels. Accordingly, the use of biochar in water treatment applications where granular activated carbon (GAC) is economically or logistically infeasible is gaining interest. Monitoring treatment systems for individual MPs require laboratory analytical techniques that are typically cost-prohibitive and impractical for low-resource settings. Therefore, identification of surrogate parameters(s) for adsorbent bed life that can be measured inexpensively and in the field is a high priority. Background dissolved organic matter (DOM) is ubiquitous in natural and anthropogenic waters at concentrations typically 1,000 to 100,000 that of MPs. Some constituents of DOM foul the adsorbent and reduce bed life for removal of target contaminants. Aromatic DOM foulants absorb ultraviolet light at a wavelength of 254 nm (UVA254). Because DOM fouling directly affects MP adsorption capacity and DOM is a bulk water parameter that can be quantified using relatively inexpensive and portable instruments, it could be exploited as a surrogate for monitoring biochar adsorber bed life under field conditions. The objective of this study was to quantify removal of MPs from waters containing different types and concentrations of background DOM (surface water, wastewater, dump leachate) and thus exhibiting different UVA254 breakthrough profiles in bench-scale column experiments. Breakthrough profiles of weakly to moderately adsorbing MPs, including herbicides, pharmaceuticals and personal care products, and perfluoroalkyl acids, were collected using biochars generated under different pyrolysis conditions and a commercial GAC as a performance benchmark. Optimal conditions for biochar water treatment include using biochar produced from wood at ≥850°C under slightly aerobic conditions, empty bed contact times of ≥30 min, and upstream treatment processes to reduce DOM. Relative UVA254 breakthrough (C/C 0) up to 0.6-0.9 corresponded to ≥90% MP removal for most MP-water combinations studied.

Assessment of PFAS fate, transport, and treatment inhibition associated with a simulated AFFF release within a WASTEWATER treatment plant.

Sequencing batch reactors (SBRs) were operated for 36 days to simulate the potential wastewater treatment impacts as well as fate and transport of per- and polyfluoroalkyl substances (PFAS) that could be associated with a release of alcohol resistant aqueous film forming foam (AR-AFFF) from on-site methanol fire suppression systems. The results of this study indicate that two days of exposure to AFFF were associated with small reductions in mixed liquor solids content and nitrification rates. No impacts on denitrification or biological phosphorus removal were observed. The addition of AFFF was associated with increases in 6:2 fluorotelomer sulfonate (6:2 FTS) in influent, effluent, and solids samples in the SBR. The following biotransformation pathway is proposed: an unidentified fluorotelomer precursor quickly degraded to 6:2 FTS, which then slowly degraded to several identified degradation intermediates and terminal, short-chain perfluorocarboxylic acid products. Data for 6:2 FTS, which was used as a proxy for AFFF-associated PFAS, were extrapolated to estimate that a removal of approximately 70% of AFFF via effluent and solids wasting would occur after 4 days at a full-scale treatment plant. This information can be used to better understand potential impacts on downstream processes, including potable reuse and biosolids production.

Controlling disinfection byproducts from treated wastewater using adsorption with granular activated carbon: Impact of pre-ozonation and pre-chlorination.

This study measured chlorine- and chloramine-reactive precursors using formation potential (FP) tests of nine U.S. Environmental Protection Agency (EPA) regulated and 57 unregulated disinfection byproducts (DBPs) in tertiary-filtered wastewater before and after pilot-scale granular activated carbon (GAC) adsorption. Using breakthrough of precursor concentration and of concentration associated calculated cytotoxicity and genotoxicity (by correlating known lethal concentrations reported elsewhere), the performance of three parallel GAC treatment trains were compared against tertiary-filtered wastewater: ozone/GAC, chlorine/GAC, and GAC alone. Results show GAC alone was the primary process, versus ozone or chlorine alone, to remove the largest fraction of total chlorine- and chloramine-reactive DBP precursors and calculated cytotoxicity and genotoxicity potencies. GAC with pre-ozonation removed the most chlorine- and chloramine-reactive DBP precursors followed by GAC with pre-chlorination and lastly GAC without pre-treatment. GAC with pre-ozonation produced an effluent with cytotoxicity and genotoxicity of DBPs from FP that generally matched that of GAC without pre-oxidation; meanwhile removal of toxicity was greater by GAC with pre-chlorination. The cytotoxicity and genotoxicity of DBPs from FP tests did not scale with DBP concentration; for example, more than 90% of the calculated cytotoxicity resulted from 20% of the DBPs, principally from haloacetaldehydes, haloacetamides, and haloacetonitriles. The calculated cytotoxicity and genotoxicity from DBPs associated with FP-chloramination were at times higher than with FP-chlorination though the concentration of DBPs was five times higher with FP-chlorination. The removal of DBP precursors using GAC based treatment was at least as effective as removal of DOC (except for halonitromethanes for GAC without pre-oxidation and with pre-chlorination), indicating DOC can be used as an indicator for DBP precursor adsorption efficacy. However, the DOC was not a good surrogate for total cytotoxicity and genotoxicity breakthrough behavior, therefore, unregulated DBPs could have negative health implications that are disconnected from general water quality parameters, such as DOC, and regulated classes of DBPs. Instead, cytotoxicity and genotoxicity correlate with the concentration of specific classes of unregulated DBPs.

GAC to BAC: Does it make chloraminated drinking water safer?

Biological activated carbon (BAC) is widely used as a polishing step at full-scale drinking water plants to remove taste and odor compounds and assimilable organic carbon. BAC, especially with pre-ozonation, has been previously studied to control regulated disinfection by-products (DBPs) and DBP precursors. However, most previous studies only include regulated or a limited number of unregulated DBPs. This study explored two full-scale drinking water plants that use pre-chloramination followed by BAC and chloramine as the final disinfectant. While chloramine generally produces lower concentrations of regulated DBPs, it may form increased levels of unregulated nitrogenous and iodinated DBPs. We evaluated 71 DBPs from ten DBP classes including haloacetonitriles, haloacetamides, halonitromethanes, haloacetaldehydes, haloketones, iodinated acetic acids, iodinated trihalomethanes, nitrosamines, trihalomethanes, and haloacetic acids, along with speciated total organic halogen (total organic chlorine, bromine and iodine) across six different BAC filters of increasing age. Most preformed DBPs were well removed by BAC with different ages (i.e., operation times). However, some preformed DBPs were poorly removed or increased following treatment with BAC, including chloroacetaldehyde, dichloronitromethane, bromodichloronitromethane, N-nitrosodimethylamine, dibromochloromethane, tribromomethane, dibromochloroacetic acid, and tribromoacetic acid. Some compounds, including dibromoacetaldehyde, bromochloroacetamide, and dibromoacetamide, were formed only after treatment with BAC. Total organic halogen removal was variable in both plants and increases in TOCl or TOI were observable on one occasion at each plant. While calculated genotoxicity decreased in all filters, decreases in overall DBP formation did not correlate with decreases in calculated cytotoxicity. In three of the six filters, calculated toxicity increased by 4-27%. These results highlight that DBP concentration alone may not always provide an adequate basis for risk assessment.

Simultaneous ozone and granular activated carbon for advanced treatment of micropollutants in municipal wastewater effluent.

The main objective of this study was to compare the efficacy of ozone (O3) and O3 with granular activated carbon (GAC) (O3/GAC) at pilot-scale for the enhanced removal of micropollutants (MPs) from wastewater effluent. The results revealed enhanced removal of tris (2-carboxylethyl) phosphine (TCEP), sucralose, and meprobamate during the O3/GAC treatment experiments compared to the sum of their removal during isolated ozonation and GAC adsorption experiments. The long-term O3/GAC experiment showed the promotive effect of GAC substantially decreased after 20 h of O3 exposure. This decreased performance correlates with changes to GAC surface properties caused by O3. After 6 h of operation, O3 initially led to an increase in Brunauer-Emmett-Teller (BET) surface area on the GAC improving the elimination level of investigated MPs (except N-nitrosomorpholine (NMOR)). However, after 20 h of exposure, O3 ultimately caused structural damages to the GAC surface, decreased the BET surface area in the final stages of the experiment, and a 4-fold increase in O1s:C1s ratio on the GAC surface was observed due to an increase in surface acidic functional groups caused by O3 treatment.

N-nitrosomorpholine in potable reuse.

As potable reuse guidelines and regulations continue to develop, the presence of N-nitrosamines is a primary concern because of their associated health concerns. In this study, bench-, pilot-, and full-scale tests were conducted to focus on the occurrence and treatment of N-nitrosomorpholine (NMOR) in United States (U.S.) potable reuse systems. Out of twelve U.S. wastewater effluents collected, ambient NMOR was detected in eleven (average = 20 ±â€¯18 ng/L); in contrast, only two of the thirteen surface water and stormwater samples had NMOR. Across all of these samples maximum formation potential by chloramination produced an average increase of 3.6 ±â€¯1.8 ng/L. This result underscores the need to understand the sources of NMOR as it is not likely a disinfection byproduct and it is not known to be commercially produced within the U.S. At the pilot-scale, three potable reuse systems were evaluated for ambient NMOR with oxidation (i.e., chlorination and ozonation), biofiltration, and granular activated carbon (GAC). Both pre-oxidation and biofiltration were ineffective at mitigating NMOR during long-term pilot plant operation (at least eight-months). GAC adsorbers were the only pilot-scale treatment to remove NMOR; however, complete breakthrough occurred rapidly from <2000 to 10,000 bed volumes. For comparison, a full-scale reverse osmosis (RO) potable reuse system was monitored for a year and confirmed that RO effectively removes NMOR. Systematic bench-scale UV-advanced oxidation experiments were undertaken to assess the mitigation potential for NMOR. At a fluence dose of 325 ±â€¯10 mJ/cm2, UV alone degraded 90% of the NMOR present. The addition of 5 mg/L hydrogen peroxide did not significantly decrease the UV dose required for one-log removal. These data illustrate that efficient NMOR removal from potable reuse systems is limited to RO or UV treatment.

Impact of blending for direct potable reuse on premise plumbing microbial ecology and regrowth of opportunistic pathogens and antibiotic resistant bacteria.

Little is known about how introducing recycled water intended for direct potable reuse (DPR) into distribution systems and premise plumbing will affect water quality at the point of use, particularly with respect to effects on microbial communities and regrowth. The examination of potential growth of opportunistic pathogens (OPs) and spread of antibiotic resistance genes (ARGs), each representing serious and growing public health concerns, by introducing DPR water has not previously been evaluated. In this study, the impact of blending purified DPR water with traditional drinking water sources was investigated with respect to treatment techniques, blending location, and blending ratio. Water from four U.S. utility partners was treated in bench- and pilot-scale treatment trains to simulate DPR with blending. Water was incubated in simulated premise plumbing rigs made of PVC pipe containing brass coupons to measure regrowth of total bacteria (16S rRNA genes, heterotrophic plate count), OPs (Legionella spp., Mycobacterium spp., Pseudomonas aeruginosa), ARGs (qnrA, vanA), and an indicator of horizontal gene transfer and multi-drug resistance (intI1). The microbial community composition was profiled and the resistome (i.e., all ARGs present) was characterized in select samples using next generation sequencing. While regrowth of total bacteria (16S rRNA genes) from the start of the incubation through week eight consistently occurred across tested scenarios (Wilcoxon, p ≤ 0.0001), total bacteria were not more abundant in the water or biofilm of any DPR scenario than in the corresponding conventional potable condition (p ≥ 0.0748). Regrowth of OP marker genes, qnrA, vanA, and intI1 were not significantly greater in water or biofilm for any DPR blends treated with advanced oxidation compared to corresponding potable water (p ≥ 0.1047). This study of initial bacteria colonizing pipes after introduction of blended DPR water revealed little evidence (i.e., one target in one water type) of exacerbated regrowth of total bacteria, OPs, or ARGs in premise plumbing.

Removal of perfluoroalkyl and polyfluoroalkyl substances in potable reuse systems.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a group of persistent contaminants that have been identified throughout the aquatic environment. In this study, ten targeted perfluoroalkyl acids (PFAAs), three targeted PFAA precursors, and non-targeted PFAA precursors were monitored in four full- and pilot-scale potable reuse plants at each stage of advanced treatment. Non-targeted PFAA precursors were quantified by applying a total oxidizable precursor assay in which PFAA precursors are oxidized by hydroxyl radicals to targeted PFAAs. Two of the potable reuse systems had membrane-based treatments with reverse osmosis and UV-advanced oxidation (RO-UV/AOP) and two used ozone, biological activated carbon filtration and granular activated carbon adsorption (O3-BAC-GAC). The total targeted PFAAs in the four tertiary effluents, the influent sources for the potable reuse systems, ranged from 52 to 227 ng/L with non-targeted PFAA precursors accounting for 30-67% of total PFASs on a molar basis. The RO-UV/AOP treatment trains reduced PFAAs and PFAA precursors to below their method reporting limits through the barrier provided by RO. The O3-BAC-GAC based treatment trains reduced, but did not completely remove PFAAs or PFAA precursors and the PFASs present in the product water were primarily shorter-chain PFAAs, some of which lack human health guidance values for drinking water. The relative fraction of targeted shorter-chain PFAAs increased after each treatment step indicating that there was preferential removal of the PFAA precursors and longer-chain PFAAs. This study provides new insight on the concentrations and treatment of PFAA precursors through potable reuse treatment systems.

Biotransformation and sorption of trace organic compounds in biological nutrient removal treatment systems.

This study determined biotransformation rates (kbio) and sorption-distribution coefficients (Kd) for a select group of trace organic compounds (TOrCs) in anaerobic, anoxic, and aerobic activated sludge collected from two different biological nutrient removal (BNR) treatment systems located in Nevada (NV) and Ohio (OH) in the United States (US). The NV and OH facilities operated at solids retention times (SRTs) of 8 and 23 days, respectively. Using microwave-assisted extraction, the biotransformation rates of the chosen TOrCs were measured in the total mixed liquor. Sulfamethoxazole, trimethoprim, and atenolol biotransformed in all three redox regimes irrespective of the activated sludge source. The biotransformation of N, N-diethyl-3-methylbenzamide (DEET), triclosan, and benzotriazole was observed in aerobic activated sludge from both treatment plants; however, anoxic biotransformation of these three compounds was seen only in anoxic activated sludge from NV. Carbamazepine was recalcitrant in all three redox regimes and both sources of activated sludge. Atenolol and DEET had greater biotransformation rates in activated sludge with a higher SRT (23 days), while trimethoprim had a higher biotransformation rate in activated sludge with a lower SRT (8 days). The remaining compounds did not show any dependence on SRT. Lyophilized, heat inactivated sludge solids were used to determine the sorption-distribution coefficients. Triclosan was the most sorptive compound followed by carbamazepine, sulfamethoxazole, DEET, and benzotriazole. The sorption-distribution coefficients were similar across redox conditions and sludge sources. The biotransformation rates and sorption-distribution coefficients determined in this study can be used to improve fate prediction of the target TOrCs in BNR treatment systems.

Investigation of biotransformation, sorption, and desorption of multiple chemical contaminants in pilot-scale drinking water biofilters.

The evolving demands of drinking water treatment necessitate processes capable of removing a diverse suite of contaminants. Biofiltration can employ biotransformation and sorption to remove various classes of chemicals from water. Here, pilot-scale virgin anthracite-sand and previously used biological activated carbon (BAC)-sand dual media filters were operated for ∼250 days to assess removals of 0.4 mg/L ammonia as nitrogen, 50-140 µg/L manganese, and ∼100 ng/L each of trace organic compounds (TOrCs) spiked into pre-ozonated Colorado River water. Anthracite achieved complete nitrification within 200 days and started removing ibuprofen at 85 days. Limited manganese (10%) removal occurred. In contrast, BAC completely nitrified ammonia within 113 days, removed all manganese at 43 days, and exhibited steady state removal of most TOrCs by 140 days. However, during the first 140 days, removal of caffeine, DEET, gemfibrozil, naproxen, and trimethoprim decreased, suggesting a shift from sorption to biotransformation. Acetaminophen and sulfamethoxazole were removed at consistent levels, with complete removal of acetaminophen achieved throughout the study; ibuprofen removal increased with time. When subjected to elevated (1 µg/L) concentrations of TOrCs, BAC removed larger masses of chemicals; with a subsequent decrease and ultimate cease in the TOrCs spike, caffeine, DEET, gemfibrozil, and trimethoprim notably desorbed. By the end of operation, anthracite and BAC exhibited equivalent quantities of biomass measured as adenosine triphosphate, but BAC harbored greater microbial diversity (examined with 16S rRNA sequencing). Improved insight was gained regarding concurrent biotransformation, sorption, and desorption of multiple organic and inorganic contaminants in pilot-scale drinking water biofilters.

Use of ozone-biofiltration for bulk organic removal and disinfection byproduct mitigation in potable reuse applications.

The purpose of this research was to investigate the impacts of ozone dose and empty bed contact time (EBCT) in ozone-biofiltration systems on disinfection byproduct (DBP) formation potential. The data were used to evaluate the possibility of using DBP formation potential as an alternative guideline for total organic carbon (TOC) removal in potable reuse applications. A pilot-scale ozone-biofiltration system was operated with O3/TOC ratios ranging from 0.1 to 2.25 and EBCTs ranging from 2 to 20 min. The biofiltration columns contained anthracite or biological activated carbon (BAC). Bench-scale chlorination was performed using the uniform formation conditions (UFC) approach, and quenched samples were analyzed for total trihalomethanes (TTHMs) and regulated haloacetic acids (HAA5s). The data demonstrated that ozone-biofiltration achieved TOC removals ranging from ∼10 to 30%, depending on operational conditions, but biofiltration without ozone generally achieved <10% TOC removal. UFC testing demonstrated that ozone alone was efficient in transforming bulk organic matter and reducing DBP formation potential by 10-30%. The synergistic combination of ozone and biofiltration achieved average overall reductions in TTHM and HAA5 formation potential of 26% and 51%, respectively. Finally, a maximum TOC concentration of 2.0 mg/L was identified as a recommended treatment target for reliable compliance with TTHM and HAA5 regulations for potable reuse systems in the United States.

Microbial community characterization of ozone-biofiltration systems in drinking water and potable reuse applications.

Microbial community structure in the ozone-biofiltration systems of two drinking water and two wastewater treatment facilities was characterized using 16S rRNA gene sequencing. Collectively, these datasets enabled comparisons by facility, water type (drinking water, wastewater), pre-oxidation (ozonation, chlorination), media type (anthracite, activated carbon), media depth, and backwash dynamics. Proteobacteria was the most abundant phylum in drinking water filters, whereas Bacteroidetes, Chloroflexi, Firmicutes, and Planctomycetes were differentially abundant in wastewater filters. A positive correlation was observed between media depth and relative abundance of Cyanobacteria in drinking water filters, but there was only a slight increase in one alpha diversity metric with depth in the wastewater filters. Media type had a significant effect on beta but not alpha diversity in drinking water and wastewater filters. Pre-ozonation caused a significant decrease in alpha diversity in the wastewater filters, but the effect on beta diversity was not statistically significant. An evaluation of backwash dynamics resulted in two notable observations: (1) endosymbionts such as Neochlamydia and Legionella increased in relative abundance following backwashing and (2) nitrogen-fixing Bradyrhizobium dominated the microbial community in wastewater filters operated with infrequent backwashing. Bradyrhizobium is known to generate extracellular polymeric substances (EPS), which may adversely impact biofilter performance and effluent water quality. These findings have important implications for public health and the operation and resiliency of biofiltration systems.

The use of carbon adsorbents for the removal of perfluoroalkyl acids from potable reuse systems.

Bench- and pilot-scale sorption tests were used to probe the performance of several biochars at removing perfluoroalkyl acids (PFAA) from field waters, compared to granular activated carbon (GAC). Screening tests using organic matter-free water resulted in hardwood (HWC) (Kd = 41 L g-1) and pinewood (PWC) (Kd = 49 L g-1) biochars having the highest perfluorooctanoic acid (PFOA) removal performance that was comparable to bituminous coal GAC (Kd = 41 L g-1). PWC and HWC had a stronger affinity for PFOA sorbed in Lake Mead surface water (KF = 11 mg(1-n) Ln g-1) containing a lower (2 mg L-1) dissolved organic carbon (DOC) concentration than in a tertiary-filtered wastewater (KF = 8 mg(1-n) Ln g-1) with DOC of 4.9 mg L-1. A pilot-scale study was performed using three parallel adsorbers (GAC, anthracite, and HWC biochar) treating the same tertiary-filtered wastewater. Compared to HWC, and anthracite, GAC was the most effective in mitigating perfluoropentanoic acid (PFPnA), perfluorohexanoic acid (PHxA), PFOA, perfluorooctane sulfonic acid (PFOS), and DOC (45-67% removed at 4354 bed volumes) followed by HWC, and then anthracite. Based on bench- and pilot-scale results, shorter-chain PFAA [perfluorobutanoic acid (PFBA), PFPnA, or PFHxA] were more difficult to remove with both biochar and GAC than the longer-chain, PFOS and PFOA.