Apparent Reactivity of Bromine in Bromochloramine Depends on Synthesis Method: Implicating Bromine Chloride and Molecular Bromine as Important Bromine Species.

The chloramination of bromide containing waters results in the formation of bromine containing haloamines: monobromamine (NH2Br), dibromamine (NHBr2), and bromochloramine (NHBrCl). Many studies have directly shown that bromamines are more reactive than chloramines in oxidation and substitution reactions with organic water constituents because the bromine atom in oxidants is more labile than the chlorine atom. However, similar studies have not been performed with NHBrCl. It has been assumed that NHBrCl has similar reactivity as bromamines with organic constituents in both oxidation and substitution reactions because NHBrCl, like bromamines, rapidly oxidizes N,N-diethyl-p-phenylenediamine. In this study, we examined the reactivity of NHBrCl with phenol red to determine if NHBrCl reacts as readily as bromamines in an isolated substitution reaction. NHBrCl was synthesized two ways to assess whether NHBrCl or the highly reactive intermediates, bromine chloride (BrCl) and molecular bromine (Br2), were responsible for bromine substitution of phenol red. NHBrCl was found to be much less reactive than bromamines with phenol red and that BrCl and Br2 appeared to be the true brominating agents in solutions where NHBrCl is formed. This work highlights the need to reexamine what the true brominating agents are in chloraminated waters containing bromide.

Role of Carbonate Species on General Acid Catalysis of Bromide Oxidation by Hypochlorous Acid (HOCl) and Oxidation by Molecular Chlorine (Cl2).

Kinetic models for disinfectant decay and disinfection byproduct (DBP) formation are necessary for predicting water quality from the treatment plant to the tap. A kinetic model for conditions relevant to chloramine disinfection of drinking water (pH 6-9 and carbonate-buffered) was developed to simulate incomplete bromide (Br-) oxidation during short prechlorination periods because it is the first step in a complex system of reactions that leads to disinfectant loss and DBP formation. Hypochlorous acid (HOCl+Br-→kHOClHOBr+Cl-) and molecular chlorine (Cl2+Br-+H2O→kCl2HOBr+2Cl-+H+) were the free chlorine species relevant to Br- oxidation, and Cl2 hydrolysis and formation reactions (Cl2+H2O+A-⇌k-4k4HOCl+HA+Cl-) were necessary to accurately simulate Cl2 concentrations instead of assuming equilibrium. Previous work has shown that Br- oxidation by HOCl and Cl2 formation are acid-catalyzed and Cl2 hydrolysis is base-catalyzed, but the impact of carbonate species had not been studied. This work showed that the carbonate species have an enhanced catalytic impact with rate constants up to 1000 times larger than would be estimated by the Brønsted relationship for similar acids, which causes the oxidation by HOCl rate constant (kHOCl) to nearly double and oxidation by Cl2 to occur above pH 7 in high-alkalinity waters.

Bromamine Decomposition Revisited: A Holistic Approach for Analyzing Acid and Base Catalysis Kinetics.

Chloramine chemistry is complex, with a variety of reactions occurring in series and parallel and many that are acid or base catalyzed, resulting in numerous rate constants. Bromide presence increases system complexity even further with possible bromamine and bromochloramine formation. Therefore, techniques for parameter estimation must address this complexity through thoughtful experimental design and robust data analysis approaches. The current research outlines a rational basis for constrained data fitting using Brønsted theory, application of the microscopic reversibility principle to reversible acid or base catalyzed reactions, and characterization of the relative significance of parallel reactions using fictive product tracking. This holistic approach was used on a comprehensive and well-documented data set for bromamine decomposition, allowing new interpretations of existing data by revealing that a previously published reaction scheme was not robust; it was not able to describe monobromamine or dibromamine decay outside of the conditions for which it was calibrated. The current research's simplified model (3 reactions, 17 constants) represented the experimental data better than the previously published model (4 reactions, 28 constants). A final model evaluation was conducted based on representative drinking water conditions to determine a minimal model (3 reactions, 8 constants) applicable for drinking water conditions.

Monochloramine Cometabolism by Mixed-Culture Nitrifiers under Drinking Water Conditions.

Chloramines are the second most used secondary disinfectant by United States water utilities. However, chloramination may promote nitrifying bacteria. Recently, monochloramine cometabolism by the pure culture ammonia-oxidizing bacteria, Nitrosomonas europaea, was shown to increase monochloramine demand. The current research investigated monochloramine cometabolism by nitrifying mixed cultures grown under more relevant drinking water conditions and harvested from sand-packed reactors before conducting suspended growth batch kinetic experiments. Four types of batch kinetic experiments were conducted: (1) positive controls to estimate ammonia kinetic parameters, (2) negative controls to account for biomass reactivity, (3) utilization associated product (UAP) controls to account for UAP reactivity, and (4) cometabolism experiments to estimate cometabolism kinetic parameters. Kinetic parameters were estimated in AQUASIM with a simultaneous fit to the experimental data. Cometabolism kinetics were best described by a first-order model. Monochloramine cometabolism kinetics were similar to those of ammonia metabolism, and monochloramine cometabolism accounted for 30% of the observed monochloramine loss. These results demonstrated that monochloramine cometabolism occurred in mixed cultures similar to those found in drinking water distribution systems; therefore, monochloramine cometabolism may be a significant contribution to monochloramine loss during nitrification episodes in drinking water distribution systems.

Simultaneous time-resolved inorganic haloamine measurements enable analysis of disinfectant degradation kinetics and by-product formation.

We demonstrate the application of proton transfer time-of-flight mass spectrometry (PTR-TOF-MS) in monitoring the kinetics of disinfectant decay in water with a sensitivity one to three orders of magnitude greater than other analytical methods. Chemical disinfection inactivates pathogens during water treatment and prevents regrowth as water is conveyed in distribution system pipes, but it also causes formation of toxic disinfection by-products. Analytical limits have hindered kinetic models, which aid in ensuring water quality and protecting public health by predicting disinfection by-products formation. PTR-TOF-MS, designed for measuring gas phase concentrations of organic compounds, was able to simultaneously monitor aqueous concentrations of five inorganic haloamines relevant to chloramine disinfection under drinking water relevant concentrations. This novel application to aqueous analytes opens a new range of applications for PTR-TOF-MS.

Relative importance of nitrite oxidation by hypochlorous acid under chloramination conditions.

Nitrification can occur in water distribution systems where chloramines are used as the disinfectant. The resulting product, nitrite, can be oxidized by monochloramine and hypochlorous acid (HOCl), potentially leading to rapid monochloramine loss. This research characterizes the importance of the HOCl reaction, which has typically been ignored because of HOCl's low concentration. Also, the general acid-assisted rate constants for carbonic acid and bicarbonate ion were estimated for the monochloramine reaction. The nitrite oxidation reactions were incorporated into a widely accepted chloramine autodecomposition model, providing a comprehensive model that was implemented in AQUASIM. Batch kinetic experiments were conducted to evaluate the significance of the HOCl reaction and to estimate carbonate buffer rate constants for the monochloramine reaction. The experimental data and model simulations indicated that HOCl may be responsible for up to 60% of the nitrite oxidation, and that the relative importance of the HOCl reaction for typical chloramination conditions peaks between pH 7.5 and 8.5, generally increasing with (1) decreasing nitrite concentration, (2) increasing chlorine to nitrogen mass ratio, and (3) decreasing monochloramine concentration. Therefore, nitrite's reaction with HOCl may be important during chloramination and should be included in water quality models to simulate nitrite and monochloramine's fate.

Ammonia-oxidizing bacteria in biofilters removing trihalomethanes are related to Nitrosomonas oligotropha.

Ammonia-oxidizing bacteria (AOB) in nitrifying biofilters degrading four regulated trihalomethanes-trichloromethane, bromodichloromethane, dibromochloromethane, and tribromomethane-were related to Nitrosomonas oligotropha. N. oligotropha is associated with chloraminated drinking water systems, and its presence in the biofilters might indicate that trihalomethane tolerance is another reason that this bacterium is dominant in chloraminated systems.

Gas-phase formaldehyde adsorption isotherm studies on activated carbon: correlations of adsorption capacity to surface functional group density.

Formaldehyde (HCHO) adsorption isotherms were developed for the first time on three activated carbons representing one activated carbon fiber (ACF) cloth, one all-purpose granular activated carbon (GAC), and one GAC commercially promoted for gas-phase HCHO removal. The three activated carbons were evaluated for HCHO removal in the low-ppm(v) range and for water vapor adsorption from relative pressures of 0.1-0.9 at 26 °C where, according to the IUPAC isotherm classification system, the adsorption isotherms observed exhibited Type V behavior. A Type V adsorption isotherm model recently proposed by Qi and LeVan (Q-L) was selected to model the observed adsorption behavior because it reduces to a finite, nonzero limit at low partial pressures and it describes the entire range of adsorption considered in this study. The Q-L model was applied to a polar organic adsorbate to fit HCHO adsorption isotherms for the three activated carbons. The physical and chemical characteristics of the activated carbon surfaces were characterized using nitrogen adsorption isotherms, X-ray photoelectron spectroscopy (XPS), and Boehm titrations. At low concentrations, HCHO adsorption capacity was most strongly related to the density of basic surface functional groups (SFGs), while water vapor adsorption was most strongly influenced by the density of acidic SFGs.

Modeling of trihalomethane cometabolism in nitrifying biofilters.

The computer program AQUASIM was used to model biofilter experiments seeded with Lake Austin, Texas mixed-culture nitrifiers. These biofilters degraded four trihalomethanes (THMs) (trichloromethane (TCM) or chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM) or bromoform) commonly found in treated drinking water. Apparent steady-state data from the biofilter experiments and supporting batch experiments were used to estimate kinetic parameters for TCM, DBCM and ammonia degradation. Subsequently, the model was verified against other experimental biofilter data. To allow for full-scale simulations, BDCM and TBM rate constants were estimated using data from batch kinetic studies. Finally, the model was used to simulate full-scale filter performance under different filter surface loading rates and THM speciation seen in practice. Overall, total THM removals ranged from 16% to 54% in these simulations with influent total THM concentrations of 75-82microg/L, which illustrates the potential of THM cometabolism to have a significant impact on treated water quality.

Cometabolism of trihalomethanes by mixed culture nitrifiers.

Three mixed-culture nitrifier sources degraded low concentrations (25-450 microg/L) of four trihalomethanes (THMs) (trichloromethane (TCM) or chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM) or bromoform) commonly found in treated drinking water. Individual THM rate constants (k1THM) increased with increasing THM bromine-substitution with TBM>DBCM>BDCM>TCM and were comparable to previous studies with the pure culture nitrifier, Nitrosomonas europaea. A decrease in temperature resulted in a decrease in both ammonia and THM degradation rates with ammonia rates affected to a greater extent than THM degradation rates. The significant effect of temperature indicates that seasonal variations in water temperature should be a consideration for technology implementation. Product toxicity, measured by transformation capacity (T(c)), was similar to that observed with N. europaea. Because both rate constants and product toxicities increase with increasing THM bromine-substitution, a water's THM speciation is an important consideration for process implementation during drinking water treatment. Even though a given water is kinetically favored, the resulting THM product toxicity may not allow stable treatment process performance.

Dissolution kinetics of high explosives particles in a saturated sandy soil.

Solid phase high explosive (HE) residues from munitions detonation may be a persistent source of soil and groundwater contamination at military training ranges. Saturated soil column tests were conducted to observe the dissolution behavior of individual components (RDX, HMX, and TNT) from two HE formulations (Comp B and C4). HE particles dissolved readily, with higher velocities yielding higher dissolution rates, higher mass transfer coefficients, and lower effluent concentrations. Effluent concentrations were below solubility limits for all components at superficial velocities of 10-50 cm day(-1). Under continuous flow at 50 cm day(-1), RDX dissolution rates from Comp B and C4 were 34.6 and 97.6 microg h(-1) cm(-2) (based on initial RDX surface area), respectively, significantly lower than previously reported dissolution rates. Cycling between flow and no-flow conditions had a small effect on the dissolution rates and effluent concentrations; however, TNT dissolution from Comp B was enhanced under intermittent-flow conditions. A model that includes advection, dispersion, and film transfer resistance was developed to estimate the steady-state effluent concentrations.

Enhanced desorption of RDX from granular activated carbon.

Several methods (cosolvents, surfactants, and cyclodextrins) were compared for improving desorption of a high explosive, RDX, from granular activated carbon (GAC). In batch desorption tests, 3% of the adsorbed RDX (initially 71.1 mg RDX/g GAC) was desorbed by water over 11 days, compared to 92.6% desorption by 100% ethanol. Solutions of ethanol or methanol in water also effectively desorbed RDX, although methanol was somewhat less effective than ethanol. Sodium dodecyl sulfate desorbed as much as 70% of the adsorbed RDX, while the non-ionic surfactants Tween 80, Triton X-100, and Brij 30 desorbed as much as 42 to 51% of the RDX. In continuous flow column tests, GAC was partially regenerated. One-half of the adsorbed RDX was desorbed by 2100 bed volumes (BV) of 10% ethanol, compared to the 22 500 BV of buffered water. Column modeling indicated that competitive adsorption and altered equilibrium conditions combined to enhance RDX desorption.

Scale-up considerations for a hollow-fiber-membrane bioreactor treating trichloroethylene-contaminated water.

Scale-up of a hollow-fiber-membrane (HFM) bioreactor treating trichloroethylene- (TCE-) contaminated water via co-metabolism with the methanotroph Methylosinus trichosporium OB3b PP358 was investigated through cost comparisons, bioreactor experiments, and mathematical modeling. Cost comparisons, based on a hypothetical treatment scenario of 568-L/min (150-gpm) flowrate with an influent TCE concentration of 100 microg/L, resulted in a configuration of treatment trains with two HFM modules in series and an overall annual cost of US dollar 0.36/m3 treated. Biological experiments were conducted with short lumen and shell residence times, 0.16 and 0.40 min, respectively, as a result of the cost comparisons. A new variable, specific transformation, was defined for characterizing the cometabolic transformation in continuous-flow systems, and values as large as 38.5 microg TCE/mg total suspended solids were sustainable for TCE treatment. Using mathematical modeling, HFM bioreactor system design was investigated, resulting in a five-step system design strategy to facilitate sizing of the unit processes.

Hydroxylamine addition impact to Nitrosomonas europaea activity in the presence of monochloramine.

In drinking water, monochloramine may promote ammonia­oxidizing bacteria (AOB) growth because of concurrent ammonia presence. AOB use (i) ammonia monooxygenase for biological ammonia oxidation to hydroxylamine and (ii) hydroxylamine oxidoreductase for biological hydroxylamine oxidation to nitrite. In addition, monochloramine and hydroxylamine abiotically react, providing AOB a potential benefit by removing the disinfectant (monochloramine) and releasing growth substrate (ammonia). Alternatively and because biological hydroxylamine oxidation supplies the electrons (reductant) required for biological ammonia oxidation, the monochloramine/hydroxylamine abiotic reaction represents a possible inactivation mechanism by consuming hydroxylamine and inhibiting reductant generation. To investigate the abiotic monochloramine and hydroxylamine reaction's impact on AOB activity, the current study used batch experiments with Nitrosomonas europaea (AOB pure culture), ammonia, monochloramine, and hydroxylamine addition. To decipher whether hydroxylamine addition benefitted N. europaea activity by (i) removing monochloramine and releasing free ammonia or (ii) providing an additional effect (possibly the aforementioned reductant source), a previously developed cometabolism model was coupled with an abiotic monochloramine and hydroxylamine model for data interpretation. N. europaea maintained ammonia oxidizing activity when hydroxylamine was added before complete ammonia oxidation cessation. The impact could not be accounted for by monochloramine removal and free ammonia release alone and was concentration dependent for both monochloramine and hydroxylamine. In addition, a preferential negative impact occurred for ammonia versus hydroxylamine oxidation. These results suggest an additional benefit of exogenous hydroxylamine addition beyond monochloramine removal and free ammonia release, possibly providing reductant generation.

Fate of biodegradable dissolved organic carbon produced by ozonation on biological activated carbon.

The adsorption and desorption characteristics of BDOC produced by ozonation and the replacement of BDOC by non-BDOC on BAC was studied. The fate of BDOC produced by ozonation in the BAC column was also evaluated by comparative experiment between the BAC supplied with the mixture of BDOC and non-BDOC and the BAC supplied only with non-BDOC. Fulvic acids extracted from two river sediments and one forest soil were used. BDOC produced by ozonation showed the same or lower adsorption capacity than non-BDOC after biodegradation. The adsorption rate of BDOC on GAC was lower than that of non-BDOC. BDOC produced by ozonation had low desorbability and majority of BDOC produced were not replaced by non-BDOC. BDOC in the ozonated fulvic acid did not affect the breakthrough of the ozonated fulvic acid on GAC in the early stage of adsorption, suggesting that most of BDOC were biodegraded on the surface of GAC before adsorption. Therefore, the production of BDOC by ozonation before the GAC treatment is very effective for the extension of GAC service life and the reduction of DOC loading to GAC.

A proposed abiotic reaction scheme for hydroxylamine and monochloramine under chloramination relevant drinking water conditions.

Drinking water monochloramine (NH2Cl) use may promote ammonia-oxidizing bacteria (AOB). AOB use (i) ammonia monooxygenase for biological ammonia (NH3) oxidation to hydroxylamine (NH2OH) and (ii) hydroxylamine oxidoreductase for NH2OH oxidation to nitrite. NH2Cl and NH2OH may react, providing AOB potential benefits and detriments. The NH2Cl/NH2OH reaction would benefit AOB by removing the disinfectant (NH2Cl) and releasing their growth substrate (NH3), but the NH2Cl/NH2OH reaction would also provide a possible additional inactivation mechanism besides direct NH2Cl reaction with cells. Because biological NH2OH oxidation supplies the electrons required for biological NH3 oxidation, the NH2Cl/NH2OH reaction provides a direct mechanism for NH2Cl to inhibit NH3 oxidation, starving the cell of reductant by preventing biological NH2OH oxidation. To investigate possible NH2Cl/NH2OH reaction implications on AOB, an understanding of the underlying abiotic reaction is first required. The present study conducted a detailed literature review and proposed an abiotic NH2Cl/NH2OH reaction scheme (RS) for chloramination relevant drinking water conditions (µM concentrations, air saturation, and pH 7-9). Next, RS literature based kinetics and end-products were evaluated experimentally between pHs 7.7 and 8.3, representing (i) the pH range for future experiments with AOB and (ii) mid-range pHs typically found in chloraminated drinking water. In addition, a (15)N stable isotope experiment was conducted to verify nitrous oxide and nitrogen gas production and their nitrogen source. Finally, the RS was slightly refined using the experimental data and an AQUASIM implemented kinetic model. A chloraminated drinking water relevant RS is proposed and provides the abiotic reaction foundation for future AOB biotic experiments.

A coupled sensor-spectrophotometric device for continuous measurement of formaldehyde in indoor environments.

Despite long-standing awareness of adverse health effects associated with chronic human exposure to formaldehyde, this hazardous air pollutant remains a challenge to measure in indoor environments. Traditional analytical techniques evaluate formaldehyde concentrations over several hours to several days in a single location in a residence, making it difficult to characterize daily temporal and spatial variation in human exposure to formaldehyde. There is a need for portable, easy-to-use devices that are specific and sensitive to gas-phase formaldehyde over short sampling periods so that dynamic processes governing formaldehyde fate, transport, and potential remediation in indoor environments may be studied more effectively. A recently developed device couples a chemical sensor element with spectrophotometric analysis for detection and quantification of part per billion (ppbv) gas-phase formaldehyde concentrations. This study established the ability of the coupled sensor-spectrophotometric device (CSSD) to report formaldehyde concentrations accurately and continuously on a 30-min sampling cycle at low ppbv concentrations previously untested for this device in a laboratory setting. Determination of the method detection limit (MDL), based on 40 samples each at test concentrations of 5 and 10 ppbv, was found to be 1.9 and 2.0 ppbv, respectively. Performance of the CSSD was compared with the dinitrophenylhydrazine (DNPH) derivatization method for formaldehyde concentrations ranging from 5-50 ppbv, and a linear relationship with a coefficient of determination of 0.983 was found between these two analytical techniques. The CSSD was also used to monitor indoor formaldehyde concentrations in two manufactured homes. During this time, formaldehyde concentrations varied from below detection limit to 65 ppbv and were above the US National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) of 16 ppbv, which is also the exposure limit value now adopted by the US Federal Emergency Management Agency (FEMA) to procure manufactured housing, 80% and 100% of the time, respectively.

Monochloramine cometabolism by Nitrosomonas europaea under drinking water conditions.

Chloramine is widely used in United States drinking water systems as a secondary disinfectant, which may promote the growth of nitrifying bacteria because ammonia is present. At the onset of nitrification, both nitrifying bacteria and their products exert a monochloramine demand, decreasing the residual disinfectant concentration in water distribution systems. This work investigated another potentially significant mechanism for residual disinfectant loss: monochloramine cometabolism by ammonia-oxidizing bacteria (AOB). Monochloramine cometabolism was studied with the pure culture AOB Nitrosomonas europaea (ATCC 19718) in batch kinetic experiments under drinking water conditions. Three batch reactors were used in each experiment: a positive control to estimate the ammonia kinetic parameters, a negative control to account for abiotic reactions, and a cometabolism reactor to estimate the cometabolism kinetic constants. Kinetic parameters were estimated in AQUASIM with a simultaneous fit to all experimental data. The cometabolism reactors showed a more rapid monochloramine decay than in the negative controls, demonstrating that cometabolism occurs. Cometabolism kinetics were best described by a pseudo first order model with a reductant term to account for ammonia availability. Monochloramine cometabolism kinetics were similar to those of ammonia metabolism, and monochloramine cometabolism was a significant loss mechanism (30-60% of the observed monochloramine decay). These results suggest that monochloramine cometabolism should occur in practice and may be a significant contribution to monochloramine decay during nitrification episodes in drinking water distribution systems.

Performance and biofilm activity of nitrifying biofilters removing trihalomethanes.

Nitrifying biofilters seeded with three different mixed-culture sources removed trichloromethane (TCM) and dibromochloromethane (DBCM) with removals reaching 18% for TCM and 75% for DBCM. In addition, resuspended biofilm removed TCM, bromodichloromethane (BDCM), DBCM, and tribromomethane (TBM) in backwash batch kinetic tests, demonstrating that the biofilters contained organisms capable of biotransforming the four regulated trihalomethanes (THMs) commonly found in treated drinking water. Upon the initial and subsequent increased TCM addition, total ammonia nitrogen (TOTNH(3)) removal decreased and then reestablished, indicating an adjustment by the biofilm bacteria. In addition, changes in DBCM removal indicated a change in activity related to DBCM. The backwash batch kinetic tests provided a useful tool to evaluate the biofilm's bacteria. Based on these experiments, the biofilters contained bacteria with similar THM removal kinetics to those seen in previous batch kinetic experiments. Overall, performance or selection does not seem based specifically on nutrients, source water, or source cultures and most likely results from THM product toxicity, and the use of GAC media appeared to offer benefits over anthracite for biofilter stability and long-term performance, although the reasons for this advantage are not apparent based on research to date.

Autohydrogenotrophic perchlorate reduction kinetics of a microbial consortium in the presence and absence of nitrate.

This is the first study to model the effects of nitrate on autohydrogenotrophic perchlorate biokinetics. Batch experiments demonstrated that the presence of nitrate significantly inhibited perchlorate degradation by a hydrogen-oxidizing, perchlorate-reducing microbial consortium. However, the consortium was capable of significant perchlorate reduction while the bulk of the nitrate was still present. Results showed that a modified competitive inhibition model successfully predicted autohydrogenotrophic perchlorate degradation in the presence of nitrate (initial concentrations of ∼230 µg ClO(4)(-)/L and 2.2-4.6 mg NO(3)(-)-N/L). The model describes perchlorate degradation as a function of the biomass, perchlorate, hydrogen, and nitrate concentrations, as well as the single-component perchlorate (28 µg/L), hydrogen (2.3 × 10(-6) M (aq)), and nitrate (0.15 mg/L as N) half-saturation coefficients (K(s)) and perchlorate maximum substrate utilization rate (k) (1.8 µg ClO(4)(-)/mg TSS-hr). Single-component parameters were obtained through a series of batch experiments performed under perchlorate-, nitrate-, and hydrogen-limiting conditions with initial concentrations of 80-340 µg ClO(4)(-)/L, 2.7-3.6 mg NO(3)(-)-N/L, and 1%-3% H(2) (g) by volume.