Modeling PFAS Removal Using Granular Activated Carbon for Full-Scale System Design.

Per- and polyfluoroalkyl substances (PFAS) are increasingly of interest to drinking water utilities due to state regulations, the release of federal and state health advisories, and public concern. Pilot-scale data were fitted for 16 PFAS species and five commercial-activated carbons using an open-source pore and surface diffusion model that includes an automated parameter-fitting tool. The estimated model parameters are presented, and an uncertainty analysis was evaluated considering the expected temporal variability of influent concentrations. Expected treatment performance differed between two seasons in the pilot phase for the same carbon, which was not captured by modeled uncertainty. However, modeling results can support a utility's decision to choose activated carbon, and make design and operational decisions that can address changing water production rates and treatment goals. For the utility that undertook this pilot study and their desired treatment goals, granular activated carbon (GAC) was found to be an effective treatment technology for PFAS removal.

Investigation of Chloramines, Disinfection Byproducts, and Nitrification in Chloraminated Drinking Water Distribution Systems.

Four chloraminated drinking water distribution systems (CDWDSs) required to maintain numeric versus "detectable" residuals were spatially and temporally sampled for water quality and associated trihalomethane (THM) and haloacetic acid (HAA) formation. Monochloramine decreased from entry point (EP) to maximum residence time (MRT) samples while THMs and HAAs initially increased and then stabilized or slightly decreased. Subsequently, EP and MRT samples were used in laboratory-held studies to further evaluate disinfectant residual stability, chloramine speciation, and nitrification occurrence. MRT water exhibited a faster monochloramine concentration decline compared to EP water, indicating a decreasing disinfectant residual stability from increasing water age through distribution. Using a simple technique based on published inorganic chloramine chemistry, samples were also investigated for nondisinfectant positive interference (NDPI) on total chlorine measurements. NDPI concentrations represented up to 100% of the total chlorine concentration when total chlorine concentrations decreased to 0.05 mg-Cl2/L, indicating little to no effective disinfectant residual remained.

Granular Activated Carbon Adsorption of Carcinogenic Volatile Organic Compounds at Low Influent Concentrations.

The effectiveness of granular activated carbon (GAC) for carcinogenic volatile organic compounds (cVOCs) has not been evaluated in the low- to sub- microgram per liter range. Rapid small scale column tests (RSSCTs) were employed to determine the GAC performance at empty bed contact times (EBCTs) of 7.5 and 15 minutes for 13 cVOCs at a target influent concentration of 5 µg/L in a typical groundwater matrix. Breakthrough was assessed for vinyl chloride, dichloromethane, 1,1-dichloroethane, 1,2-dichloroethane, 1,2-dichloropropane, carbon tetrachloride, 1,3-butadiene, 1,1,1,2-tetrachloroethane, 1,2,3-trichloropropane, trichloroethylene and tetrachloroethylene. The throughput to breakthrough was found to be linearly correlated to capacities calculated with single-solute equilibrium isotherm parameters. Modest decreases, 9 to 13% on average, in throughput to 50% and 75% breakthrough were found when the EBCT was increased from 7.5 to 15 minutes. The carbon use rate (CUR), when scaled to simulate full-scale adsorption, indicated that GAC would be a viable technology for seven of the VOCs evaluated, with a CUR threshold less than 0.2 lbs/1000 gal. It may be possible to use 1,1 DCA and 1,2 DCA as surrogates for assessing chemicals near the feasibility limit.

Evaluation of Monochloramine and Free Chlorine Penetration in a Drinking Water Storage Tank Sediment Using Microelectrodes.

Sediment accumulation in water storage tanks may protect microorganisms from disinfectant exposure, causing the degradation of water quality. However, microbial activity and disinfectant penetration within water storage sediment remain largely uncharacterized. This study evaluated the penetration of monochloramine and free chlorine into a 2 cm (20000 µm) deep drinking water storage tank sediment using microelectrodes. The sediment was successively exposed to monochloramine for 4 months, free chlorine for 2 months, and monochloramine for 2 months. Temporal monochloramine, free chlorine, dissolved oxygen (DO), pH, ammonium, nitrite, and nitrate profiles were acquired using microelectrodes. The results showed that complete monochloramine or free chlorine penetration was not observed. Likewise, DO never fully penetrated the sediment, progressing inward with time to a maximum depth of 10000 µm and indicating microbial activity persisted over the entire 8 months. Decreasing ammonium and increasing nitrate concentrations, with minimal nitrite accumulation, further demonstrated microbial activity and indicated complete sediment nitrification. There were measurable levels of ammonium, nitrite, and nitrate during free chlorine application, and nitrification activity gradually resumed upon a switch back to monochloramine. These findings suggest that the periodic removal of sediment from drinking water storage facilities is desirable to remove potentially protected environments for microorganisms.

Occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in Source Water and Their Treatment in Drinking Water.

Per-and polyfluoroalkyl substances (PFAS) occurrence in drinking water and treatment methods for their removal are reviewed. PFAS are fluorinated substances whose unique properties make them effective surface-active agents with uses ranging from stain repellants to fire-fighting foams. In response to concerns about drinking water contamination and health risks from PFAS exposure, the United States Environmental Protection Agency published Health Advisories (HAs) for perfluorooctanoic acid and perfluorooctane sulfonic acid. The occurrence of six PFAS in drinking water has been reported in the Third Unregulated Contaminant Monitoring Rule (UCMR3), and subsequent analysis of the dataset suggested that four percent of water systems reported at least one detectable PFAS compound and 1.3 percent of water systems reported results above the HAs. Many treatment technologies have been evaluated in the literature, with the most promising and readily applied treatment technologies being activated carbon, anion exchange resins, and high-pressure membrane systems. From these data and literature reports, research and data gaps were identified and suggestions for future research are provided.

Three-Dimensional Free Chlorine and Monochloramine Biofilm Penetration: Correlating Penetration with Biofilm Activity and Viability.

Disinfectant biofilm penetration and its effect on biofilm aerobic activity and viability are still unclear. In this study, free chlorine and monochloramine were applied until full biofilm penetration occurred, and their effects on biofilm aerobic activity and viability were investigated in three dimensions throughout the entire biofilm depth, extending previous work where viability analysis was limited to the upper biofilm (50 µm depth), free chlorine penetration did not reach completion, and only one-dimensional (depth) profiles were obtained. The free chlorine and monochloramine biofilm concentration profiles were correlated spatially and temporally with aerobic microbial activity and cell-membrane integrity based viability using a combination of (1) microelectrode measurements for disinfectant penetration and (2) LIVE/DEAD BacLight staining, cryo-cross-sectioning, and confocal micrographs analysis for viability measurements throughout the entire biofilm depth. Compared to monochloramine, free chlorine penetration (1) was slower, (2) led to a greater decrease in biofilm thickness from sloughing, and (3) corresponded directly with a viability decrease. In addition, biofilm heterogeneity led to minor differences in either disinfectant's biofilm penetration, and prior biofilm exposure to monochloramine provided little impact to subsequent free chlorine biofilm penetration.

Characterizing Ohio River NOM Variability and Reconstituted-Lyophilized NOM as a Source Surrogate.

Natural organic matter (NOM) was collected, concentrated, and lyophilized on a monthly basis for 15 months to create a temporal NOM library and assess seasonal variability of untreated Ohio River water. Using fluorescence spectroscopy with parallel factor analysis, similar spectral components for both the ultrafiltered source water (UF1X) and reconstituted lyophilized NOM were observed in a two-component model throughout the study, with overall average emission and excitation wavelengths of 418 nm and 270 nm, respectively, for component 1 and 482 nm and 370 nm, respectively, for component 2. Fluorescence spectroscopy, high-pressure liquid chromatography-size exclusion chromatography, and elemental analysis indicated that the NOM was humic-like during the study with only small seasonal changes. Data from these analyses also demonstrated similarity between results for UF1X, reverse osmosis-concentrated NOM, and reconstituted- lyophilized NOM, validating the use of the reconstituted- lyophilized NOM as a surrogate for its source.

Method to assess component contribution to toxicity of complex mixtures: Assessment of puberty acquisition in rats exposed to disinfection byproducts.

A method based on regression modeling was developed to discern the contribution of component chemicals to the toxicity of highly complex, environmentally realistic mixtures of disinfection byproducts (DBPs). Chemical disinfection of drinking water forms DBP mixtures. Because of concerns about possible reproductive and developmental toxicity, a whole mixture (WM) of DBPs produced by chlorination of a water concentrate was administered as drinking water to Sprague-Dawley (S-D) rats in a multigenerational study. Age of puberty acquisition, i.e., preputial separation (PPS) and vaginal opening (VO), was examined in male and female offspring, respectively. When compared to controls, a slight, but statistically significant delay in puberty acquisition was observed in females but not in males. WM-induced differences in the age at puberty acquisition were compared to those reported in S-D rats administered either a defined mixture (DM) of nine regulated DBPs or individual DBPs. Regression models were developed using individual animal data on age at PPS or VO from the DM study. Puberty acquisition data reported in the WM and individual DBP studies were then compared with the DM models. The delay in puberty acquisition observed in the WM-treated female rats could not be distinguished from delays predicted by the DM regression model, suggesting that the nine regulated DBPs in the DM might account for much of the delay observed in the WM. This method is applicable to mixtures of other types of chemicals and other endpoints.

Biofilm community dynamics in bench-scale annular reactors simulating arrestment of chloraminated drinking water nitrification.

Annular reactors (ARs) were used to study biofilm community succession and provide ecological insight during nitrification arrestment through simultaneously increasing monochloramine (NH2Cl) and chlorine to nitrogen mass ratios, resulting in four operational periods (I-IV). Analysis of 16S rRNA-encoding gene sequence reads (454-pyrosequencing) examined viable and total biofilm communities and found total samples were representative of the underlying viable community. Bacterial community structure showed dynamic changes corresponding with AR operational parameters. Period I (complete nitrification and no NH2Cl residual) was dominated by Bradyrhizobium (total cumulative distribution: 38%), while environmental Legionella-like phylotypes peaked (19%) during Period II (complete nitrification and minimal NH2Cl residual). Nitrospira moscoviensis (nitrite-oxidizing bacteria) was detected in early periods (2%) but decreased to <0.02% in later periods, corresponding to nitrite accumulation. Methylobacterium (19%) and members of Nitrosomonadaceae (42%) dominated Period III (complete ammonia and partial nitrite oxidation and low NH2Cl residual). An increase in Afipia (haloacetic acid-degrading bacteria) relative abundance (<2% to 42%) occurred during Period IV (minimal nitrification and moderate to high NH2Cl residual). Microbial community and operational data provided no evidence of taxa-time relationship, but rapid community transitions indicated that the system had experienced ecological regime shifts to alternative stable states.

Applying microelectrodes to investigate aged ductile iron and copper coupon reactivity during free chlorine application.

In drinking water distribution systems, including premise plumbing, dissolved oxygen (DO) and free chlorine (FC) are common oxidants and ductile iron (DI) and copper (Cu) are commonly used pipe materials. Microelectrodes as a tool have been applied in previous corrosion research and were used in this study to collect quantifiable data and understand DO and FC reactivity and pH changes at the water-metal interface. Using microelectrodes, pH, DO, and FC profiles from the bulk water to near and at the surface of aged DI (154-190 d) and Cu (2 d and 86-156 d) coupons were investigated during periods of flow and stagnation (30 min). Using the measured microelectrode profiles, oxidant fluxes and apparent surface reaction rate constants were calculated to elucidate differences between DO and FC reactivity with the coupons. Microelectrodes were successfully applied to measure pH, DO, and FC profiles from the bulk water to near aged DI and Cu coupon surfaces; Cu coupons aged quickly and exhibited less reactivity at 2 d with DO and FC than aged DI coupons did after 154-190 d; and for the aged DI coupon experiments, orthophosphate presence stabilized pH profiles where without orthophosphate pH fluctuations of greater than 2 pH units occurred from the bulk water to the DI coupon surface.

Comprehensive assessment of a chlorinated drinking water concentrate in a rat multigenerational reproductive toxicity study.

Some epidemiological studies report associations between drinking water disinfection byproducts (DBPs) and adverse reproductive/developmental effects, e.g., low birth weight, spontaneous abortion, stillbirth, and birth defects. Using a multigenerational rat bioassay, we evaluated an environmentally relevant "whole" mixture of DBPs representative of chlorinated drinking water, including unidentified DBPs as well as realistic proportions of known DBPs at low-toxicity concentrations. Source water from a water utility was concentrated 136-fold, chlorinated, and provided as drinking water to Sprague-Dawley rats. Timed-pregnant females (P0 generation) were exposed during gestation and lactation. Weanlings (F1 generation) continued exposures and were bred to produce an F2 generation. Large sample sizes enhanced statistical power, particularly for pup weight and prenatal loss. No adverse effects were observed for pup weight, prenatal loss, pregnancy rate, gestation length, puberty onset in males, growth, estrous cycles, hormone levels, immunological end points, and most neurobehavioral end points. Significant, albeit slight, effects included delayed puberty for F1 females, reduced caput epidydimal sperm counts in F1 adult males, and increased incidences of thyroid follicular cell hypertrophy in adult females. These results highlight areas for future research, while the largely negative findings, particularly for pup weight and prenatal loss, are notable.

Microelectrode evaluation of in situ oxidant reactivity and pH variability at new ductile iron and copper coupon surfaces.

Thirty-two short term (∼7.5 h) abiotic experiments were conducted with new ductile iron and copper coupons exposed to various water qualities, including pH (7 or 9), dissolved inorganic carbon (DIC, 10 or 50 mg C L-1) and phosphate (0 or 3 mg P L-1) concentrations and 4 mg Cl2 L-1 free chlorine or monochloramine. To quantify oxidant reactivity with the new metal coupons, microelectrodes were used to obtain oxidant (free chlorine or monochloramine and dissolved oxygen (DO)) concentration and pH microprofiles from the bulk water to near the metal coupon surface. From the microprofiles, apparent surface reaction rate constants (k) were determined for each oxidant. An ANOVA analysis evaluated if the five variables (Material, Oxidant, Phosphate, DIC, and pH) significantly affected estimates of k, finding that the Material and Oxidant variables and their interaction were statistically significant (p<0.05), but the effect of variables of Phosphate, DIC, and pH on k values were not significant in this study. In general, both ductile iron and copper coupons showed significant surface reactivity towards free chlorine and monochloramine. For ductile iron, DO consumption was greater than for copper, which showed minimal DO reactivity, and DO was less reactive towards the copper surface than either free chlorine or monochloramine. Furthermore, pH microprofiles provided insight into the complexity that might exist near corroding metal surfaces where the bulk water pH may be substantially different from that measured near metal surfaces which is significant as pH is a controlling variable in terms of scale formation and metal solubility. This study represents an important first step towards using microelectrodes to (1) understand and provide direct measurement of oxidant microprofiles from the bulk water to the metal surface; (2) determine pipe wall reactivity using the directly measured concentrations profiles versus estimated pipe wall reactivity from bulk water measurements, and (3) understand how variables measured by bulk water samples (e.g., pH) may be drastically different from what is occurring at and near the metal surface. Together, these insights will assist in understanding disinfectant residual maintenance, corrosion, and metal release.

Polanyi adsorption potential theory for estimating PFAS treatment with granular activated carbon.

Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals that have gained interest because some PFAS have been shown to have negative health effects and prolonged environmental and biological persistence. Chemicals classified as PFAS have a wide range of chemical moieties that impart widely variable properties, leading to a range of water treatment process efficacies. The Polanyi Potential Adsorption Theory was used to estimate Freundlich isotherm parameters to predict the efficacy of granular activated carbon (GAC) treatment for 428 PFAS chemicals for which the vast majority had no previously published treatment data. This method accounts for the physical/chemical characteristics of the individual PFAS beyond molecular weight or chain length that have previously been employed. From a statistical analysis of available data and model results, many of the 428 PFAS were predicted to be effectively treatable by GAC. Although not directly applicable to full-scale design, the approach demonstrates a systematic method for predicting the effectiveness of GAC where isotherm or column data are not available. This then can be used to prioritize future research.

Role of grinding method on granular activated carbon characteristics.

A coconut shell (AC1230CX) and a bituminous coal based (F400) granular activated carbon (GAC) were ground with mortar and pestle (MP), a blender, and a bench-scale ball milling unit (BMU). Blender was the most time-efficient for particle size reduction. Four size fractions ranging from 20 × 40 to 200 × 325 were characterized along with the bulk GACs. Compared to bulk GACs, F400 blender and BMU 20 × 40 fractions decreased in specific surface area (SSA, -23% and -31%, respectively) while smaller variations (-14% to 5%) occurred randomly for AC1230CX ground fractions. For F400, the blender and BMU size fraction dependencies were attributed to the combination of (i) radial trends in the F400 particle properties and (ii) importance of shear (outer layer removal) versus shock (particle fracturing) size reduction mechanisms. Compared to bulk GACs, surface oxygen content (At%-O1s) increased up to 34% for the F400 blender and BMU 20 × 40 fractions, whereas all AC1230CX ground fractions, except for the blender 100 × 200 and BMU 60 × 100 and 100 × 200 fractions, showed 25-29% consistent increases. The At%-O1s gain was attributed to (i) radial trends in F400 properties and (ii) oxidization during grinding, both of which supported the shear mechanism of mechanical grinding. Relatively small to insignificant changes in point of zero charge (pHPZC) and crystalline structure showed similar trends with the changes in SSA and At%-O1s. The study findings provide guidance for informed selection of grinding methods based on GAC type and target particle sizes to improve the representativeness of adsorption studies conducted with ground GAC, such as rapid small-scale column tests. When GACs have radial trends in their properties and when the target size fraction only includes larger particle sizes, manual grinding is recommended.

Anion Exchange Resin and Inorganic Anion Parameter Determination for Model Validation and Evaluation of Unintended Consequences during PFAS Treatment.

When implementing anion exchange (AEX) for per- and polyfluoroalkyl substances treatment, temporal drinking water quality changes from concurrent inorganic anion (IA) removal can create unintended consequences (e.g., corrosion control impacts). To understand potential effects, four drinking water-relevant IAs (bicarbonate, chloride, sulfate, and nitrate) and three gel-type, strong-base AEX resins were evaluated. Batch binary isotherm experiments provided estimates of IA selectivity with respect to chloride ( K x ∕ C ) for IA/resin combinations where bicarbonate < sulfate ≤ nitrate at studied conditions. A multi-IA batch experiment demonstrated that binary isotherm-determined K x ∕ C values predicted competitive behavior. Subsequent column experiments with and without natural organic matter (NOM) allowed for the validation of a new ion exchange column model (IEX-CM; https://github.com/USEPA/Water_Treatment_Models). IA breakthrough was well-simulated using binary isotherm-determined K x ∕ C values and was minimally impacted by NOM. Initial AEX effluent water quality changes with corrosion implications included increased chloride and decreased sulfate and bicarbonate concentrations, resulting in elevated chloride-to-sulfate mass ratios (CSMRs) and Larson ratios (LRs) and depressed pH until the complete breakthrough of the relevant IA(s). IEX-CM utility was further illustrated by simulating the treatment of low-IA source water and a change in the source water to understand the resulting duration of changes in IAs and water quality parameters.

Strong Base Anion Exchange Selectivity of Nine Perfluoroalkyl Chemicals Relevant to Drinking Water.

Selectivity with respect to chloride (KPFAS∕C) was determined for nine drinking water relevant perfluoroalkyl and polyfluoroalkyl substances (PFAS): perfluoro-2-propoxypropanoic acid (GenX), five perfluoroalkyl carboxylic acids (PFCAs), and three perfluoroalkyl sulfonic acids (PFSAs). Three single-use strong base anion exchange gel resins were investigated, targeting drinking water relevant equilibrium PFAS liquid concentrations (≤500 ng/L). Except for the longest carbon chain PFCA (perfluorodecanoic acid) and PFSA (perfluorooctanesulfonic acid) studied, PFAS followed traditional ion exchange theory (law of mass action), including increasing equilibrium PFAS liquid concentrations with increasing equilibrium chloride liquid concentrations. Overall, KPFAS∕C values were (i) similar among resins for a given PFAS, (ii) 1-5 orders of magnitude greater than the selectivity of inorganic anions (e.g., nitrate) previously studied, (iii) 2 orders of magnitude greater for the same carbon chain length PFSA versus PFCA, (iv) found to proportionally increase with carbon chain length for both PFSAs and PFCAs, and (v) similar for GenX and perfluorohexanoic acid (six-carbon PFCA). A multisolute competition experiment demonstrated binary isotherm-determined KPFAS∕C values could be applied to simulate a multisolute system, extending work previously done with only inorganic anions to PFAS. Ultimately, estimated KPFAS∕C values allow future extension and validation of an open-source anion exchange column model to PFAS.

Developmental toxicity evaluations of whole mixtures of disinfection by-products using concentrated drinking water in rats: gestational and lactational effects of sulfate and sodium.

A developmental toxicity bioassay was used in three experiments to evaluate water concentrates for suitability in multigenerational studies. First, chlorinated water was concentrated 135-fold by reverse osmosis; select lost disinfection by-products were spiked back. Concentrate was provided as drinking water to Sprague-Dawley and F344 rats from gestation day 6 to postnatal day 6. Maternal serum levels of luteinizing hormone on gestation day 10 were unaffected by treatment for both strains. Treated dams had increased water consumption, and increased incidences of polyuria, diarrhea, and (in Sprague-Dawley rats) red perinasal staining. Pup weights were reduced. An increased incidence of eye defects was seen in F344 litters. Chemical analysis of the concentrate revealed high sodium (6.6 g/l) and sulfate (10.4 g/l) levels. To confirm that these chemicals caused polyuria and osmotic diarrhea, respectively, Na2SO4 (5-20 g/l) or NaCl (16.5 g/l) was provided to rats in drinking water. Water consumption was increased at 5- and 10-g Na2SO4/l and with NaCl. Pup weights were reduced at 20-g Na2SO4/l. Dose-related incidences and severity of polyuria and diarrhea occurred in Na2SO4-treated rats; perinasal staining was seen at 20 g/l. NaCl caused polyuria and perinasal staining, but not diarrhea. Subsequently, water was concentrated ∼120-fold and sulfate levels were reduced by barium hydroxide before chlorination, yielding lower sodium (≤1.5 g/l) and sulfate (≤2.1 g/l) levels. Treatment resulted in increased water consumption, but pup weight and survival were unaffected. There were no treatment-related clinical findings, indicating that mixtures produced by the second method are suitable for multigenerational testing.

Validating the use of lyophilized natural organic matter as background material in GAC rapid small-scale column tests.

Utilities often test the effectiveness of different granular activated carbons (GACs) to determine which is most advantageous for their system. For surface water systems, in particular, the seasonal and annual variability of natural organic matter (NOM) in the source water makes it difficult to benchmark the effectiveness of GACs over multiple contract periods. This study produced stable, lyophilized NOM from the filtered water (FW), i.e., the influent to GAC contactors, which was then reconstituted (Recon) and tested against the FW itself in parallel rapid small-scale column tests (RSSCTs). The results demonstrated nearly identical NOM breakthrough profiles. RSSCTs conducted with both FW and Recon were shown to simulate the full-scale contactor performance well, while similar RSSCTs with regenerated GAC yielded a slightly earlier breakthrough, possibly due to the changes in GAC characteristics during regeneration and grinding. RSSCTs evaluating the removal of microcystin-LR (MC-LR) in the presence of background NOM contained in FW and Recon showed slightly different results, possibly due to the difference in chloride concentrations of these two waters. This work validates that reconstituted lyophilized NOM can be used as a source water surrogate for GAC evaluations when the constituent of interest is NOM, and potentially for other constituents depending upon the influence of additional inorganic constituents that were not evaluated as part of this study.

Evaluation of Preformed Monochloramine Reactivity with Processed Natural Organic Matter and Scaling Methodology Development for Concentrated Waters.

To evaluate natural organic matter (NOM) processing impacts on preformed monochloramine (PM) reactivity and as a first step in creating concentrated disinfection byproduct (DBP) mixtures from PM, a rational methodology was developed to proportionally scale PM NOM-related demand in unconcentrated source waters to waters with concentrated NOM. Multiple NOM preparations were evaluated, including a liquid concentrate and reconstituted lyophilized solid material. Published kinetic models were evaluated and used to develop a focused reaction scheme (FRS) that was relatively simple to implement and focused on monochloramine loss, including considerations for inorganic chloramine stability (i.e., autodecomposition) and bromide and iodide impacts. The FRS included critical reaction pathways and accurately simulated (without modification) monochloramine experimental data with and without bromide and iodide present over a range of PM-dosed NOM-free waters. For NOM-containing waters, addition of two NOM reactions in the FRS allowed (i) apportioning monochloramine loss to either inorganic or NOM-related reactions and (ii) selecting experiment conditions to provide an equivalent monochloramine NOM-related demand in unconcentrated and concentrated waters. The methodology provides a framework for future experimentation to evaluate DBP scaling and their speciation in concentrated water matrices when providing an equivalent NOM-related monochloramine demand in unconcentrated and concentrated matrices.

Free chlorine and monochloramine application to nitrifying biofilm: comparison of biofilm penetration, activity, and viability.

Biofilm in drinking water systems is undesirable. Free chlorine and monochloramine are commonly used as secondary drinking water disinfectants, but monochloramine is perceived to penetrate biofilm better than free chlorine. However, this hypothesis remains unconfirmed by direct biofilm monochloramine measurement. This study compared free chlorine and monochloramine biofilm penetration into an undefined mixed-culture nitrifying biofilm by use of microelectrodes and assessed the subsequent effect on biofilm activity and viability by use of dissolved oxygen (DO) microelectrodes and confocal laser scanning microscopy (CLSM) with LIVE/DEAD BacLight. For equivalent chlorine concentrations, monochloramine initially penetrated biofilm 170 times faster than free chlorine, and even after subsequent application to a monochloramine penetrated biofilm, free chlorine penetration was limited. DO profiles paralleled monochloramine profiles, providing evidence that either the biofilm was inactivated with monochloramine's penetration or its persistence reduced available substrate (free ammonia). While this research clearly demonstrated monochloramine's greater penetration, this penetration did not necessarily translate to immediate viability loss. Even though free chlorine's penetration was limited compared to that of monochloramine, it more effectively (on a cell membrane integrity basis) inactivated microorganisms near the biofilm surface. Limited free chlorine penetration has implications when converting to free chlorine in full-scale chloraminated systems in response to nitrification episodes.