Disinfection byproduct relationships and speciation in chlorinated nanofiltered waters

The formation and speciation of disinfection byproducts (DBPs) resulting from chlorination of nanofilter permeates obtained from various source water locations and membrane types are examined. Specific ultraviolet absorbance and bromide utilization are shown to decrease following nanofiltration. Both dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm were found to correlate strongly with trihalomethane (THM), haloacetic acid (HAA), and total organic halide (TOX) concentrations in chlorinated nanofilter permeates, suggesting that they can be employed as surrogates for DBPs in nanofiltered waters. Because smooth curves were obtained for individual THM and HAA species as well as bromine and chlorine incorporation into THMs and HAAs as a function of Br-/DOC molar ratio, it is likely that mole fractions of these DBPs are more strongly influenced by chlorination conditions, Br-, and DOC concentrations than NOM source and membrane type. Mole fractions of mono-, di-, and trihalogenated HAAs were found to be independent of Br-/DOC. Even at a very low Br-/DOC of 2.9microM/mM, the mixed bromochloro- and tribromoacetic acids constituted 20% of total HAAs on a molar basis. This increased to approximately 50% as Br-/DOC increased to approximately 25microM/mM or more, proving that a large fraction of HAAs may not be covered under existing federal regulations. Total THM and HAA9 concentrations decreased in permeate waters with increasing Br-/DOC suggesting that nanofilter permeates are limited with respect to DBP precursors.     

Formation of N-nitrosodimethylamine (NDMA) from humic substances in natural water

N-nitrosodimethylamine (NDMA)formation in chloraminated Iowa River water (IRW) is primarily attributed to reactions with natural organic matter (NOM) generally classified as humic substances. Experiments were conducted to determine the contribution of various NOM humic fractions to the NDMA formation potential (NDMA FP) in this drinking water source. NOM was concentrated by reverse osmosis (RO) and humic fractions were obtained by a series of resin elution procedures. Mass balances showed that nearly 90% of the NDMA formation potential could be recovered in the NOM concentrate and in water reconstituted using additions of the various humic fractions. Generally, the hydrophilic fractions tended to form more NDMA than hydrophobic fractions, and basic fractions tend to form more NDMA than acid fractions when normalized to a carbon basis. Overall, the hydrophobic acid fraction was the dominant source of NDMA when both formation efficiency and water composition were considered. The amount of NDMA formed in a sample was found to correlate linearly with an oxidation-induced decrease in specific UV absorbance (SUVA) value at 272 nm. This is consistent with a mechanism in which precursors are formed as the direct consequence of the oxidation of NOM. The NDMA FP estimated using the slope of this relationship and the initial SUVA value compared closely to the value obtained by measuring the NDMA formed in solutions dosed with excess concentrations of monochloramine that presumably exhaust all potential precursor sources. However, the NOMA FP could not be correlated to the SUVA value of the individual humic fractions indicating that the relationship of the NDMA FP to SUVA value is probably a water-specific parameter dependent on the exact composition of humic fractions. It is hypothesized that either specific NDMA precursors are distributed among the various humic fractions or that the humic material itself represents a "generic" nonspecific precursor source that requires some degree of oxidation to eventually produce NDMA. The nonmonotonic behavior of NOM fluorescence spectra during chloramination and lack of correlation between NOM fluorescence characteristics and NDMA formation limited the usage of fluorescence spectra into probing NDMA formation.     

TiO2 photocatalysis of natural organic matter in surface water: impact on trihalomethane and haloacetic acid formation potential

In this study, changes in the physical and structural properties of natural organic matter (NOM) during titanium dioxide photocatalytic oxidation process were investigated using several complementary analytical techniques. Potential of the treated water to form trihalomethanes (THMs) and haloacetic acids (HAAs) was also studied. High-performance size exclusion chromatography analysis showed that NOM with apparent molecular weights of 1-4 kDa were preferentially degraded, leading to the formation of lower molecular weight organic compounds. Resin fractionation of the treated water demonstrated that the photocatalytic oxidation changed the affinity of the bulk organic character from predominantly hydrophobic to more hydrophilic. Short chain aldehydes and ketones were identified by mass spectroscopy as one of the key degradation products. The addition of hydrogen peroxide to photocatalysis was found to increase the degradation kinetics but did not affect the reaction pathway, thus producing similar degradation end products. The amount of THMs normalized per dissolved organic carbon (specific THM) formed upon chlorination of NOM treated with photocatalytic oxidation was reduced from 56 to 10 microg/mg. In contrast, the specific HAAs formation potential of the treated water remained relatively unchanged from the initial value of 38 microg/mg, which could be due to the presence of hydrophilic precursor compounds that were formed as a result of the photocatalytic oxidation process.     

Comparison of byproduct formation in waters treated with chlorine and iodine: relevance to point-of-use treatment

Due to their efficacy in deactivating a range of microbial pathogens, particularly amoebic cysts, iodine-based disinfectants have been a popular option for point-of-use (POU) drinking water disinfection by campers, the military, and rural consumers in developing countries. Recently, concerns regarding the formation of cytotoxic and genotoxic iodinated disinfection byproducts (I-DBPs) have arisen during chloramine disinfection of iodide-containing waters in the developed world; similar concerns should pertain to iodine-based POU disinfection. Because there are alternative POU disinfection techniques, including chlorine-based disinfectants, this paper compared disinfection byproduct formation from a range of iodine-based disinfectants at their recommended dosages to chlorination and chloramination under overdosing conditions. Just as chloroform was the predominant trihalomethane (THM) forme during chlorination or chloramination, iodoform was the predominant THM formed during iodination. Conditions fostering THM formation were similar between these treatments, except that THM formation during chlorination increased with pH, while it was slightly elevated at circumneutral pH during iodination. Iodoform formation during treatment with iodine tincture was higher than during treatment with iodine tablets. On a molar basis, iodoform formation during treatment with iodine tincture was 20-60% of the formation of chloroform during chlorination, and total organic iodine (TOI) formation was twice that of total organic chlorine (TOCl), despite the 6-fold higher oxidant dose during chlorination. Based upon previous measurements of chronic mammalian cell cytotoxicity for the individual THMs, consumers of two waters treated with iodine tincture would receive the same THM-associated cytotoxic exposure in 4-19 days as a consumer of the same waters treated with a 6-fold higher dose of chlorine over 1 year. Iodoacetic acid, diiodoacetic acid, and other iodo-acids were also formed with iodine tincture treatment, but at levels <11% of iodoform. However, testing of a Lifestraw Personal POU device, which combines an iodinated anion exchange resin with activated carbon post-treatment, indicated minimal formation of I-DBPs and no iodine residual. Although N-nitrosamines have been associated with oxidant contact with anion exchange resins, N-nitrosamine formation rapidly declined to low levels (4 ng/L) using the Lifestraw device after the first few flushes of water.     

Role of aluminum speciation in the removal of disinfection byproduct precursors by a coagulation process

Humic acid (HA) was extracted and separated into different molecular weight (MW) fractions, then coagulated by aluminum chloride and polyaluminum chloride (PACl). The removal of disinfection byproduct (DBP) precursors and the aluminum speciation variation of the coagulants were investigated in detail. In particular, the role of aluminum speciation in the removal of DBP precursors was discussed. During the coagulation process, AlCl3 hydrolyzed into dominating in situ Al13 species at pH 5.5. The in situ Al13 species exhibited better removal ability for haloacetic acid (HAA) precursors than PACl. At pH 7.5, in situ hydrolyzed Al13 species of AlCl3 decomposed into dimeric Al species. In this case, preformed Al13 of PACl had a high removal ability of HAA precursors. Specially, the greatest reduction of HAA precursors with a low MW (<30 kDa) was through charge neutralization at pH 5.5, and that of HAA precursors in high MW (> 30 kDa) fractions was through adsorption at pH 7.5. Different from HAA precursors, the in situ Al13 species did not have a high removal ability of trihalomethane (THM) precursors. Therefore, PACl exhibited a better removal ability of THM precursors than AlCl3 at different pH values. In the different MW fractions, the greatest reduction of THM precursors was through charge neutralization at pH 5.5.     

Bromide oxidation and formation of dihaloacetic acids in chloraminated water

A comprehensive reaction model was developed that incorporates the effect of bromide on monochloramine loss and formation of bromine and chlorine containing dihaloacetic acids (DHAAs) in the presence of natural organic matter (NOM). Reaction pathways accounted for the oxidation of bromide to active bromine (Br(l)) species, catalyzed monochloramine autodecomposition, NOM oxidation, and halogen incorporation into DHAAs. The reaction scheme incorporates a simplified reaction pathway describing the formation and termination of Br(l). In the absence of NOM, the model adequately predicted bromide catalyzed monochloramine autodecomposition. The Br(l) reaction rate coefficients are 4 orders of magnitude greater than HOCl for the same NOM sources under chloramination conditions. Surprisingly, the rate of NOM oxidation by Br(l) was faster than bromide catalyzed monochloramine autodecomposition by Br(l) so that the latter reactions could largely be ignored in the presence of NOM. Incorporation of bromine and chlorine into DHAAs was proportional to the amount of NOM oxidized by each halogen and modeled using simple bromine (alpha(Br)) and chlorine (alpha(Cl)) incorporation coefficients. Both coefficients were found to be independent of each other and alpha(Br) was one-half the value of alpha(Cl). This indicates that chlorine incorporates itself into DHAA precursors more effectivelythan bromine. Model predictions compared well with DHAA measurements in the presence of increasing bromide concentrations and is attributable to the increased rate of NOM oxidation, which is rate limited by the oxidation of bromide ion in chloraminated systems.     

Factors influencing the formation and relative distribution of haloacetic acids and trihalomethanes in drinking water

Various water quality and treatment characteristics were evaluated under controlled chlorination conditions to determine their influences on the formation and distribution of nine haloacetic acids and four trihalomethanes in drinking water. Raw waters were sampled from five water utilities and were coagulated with alum and fractionated with XAD-8 resin. The resulting four fractions--raw and coagulated water and the hydrophobic and hydrophilic extracts--were then chlorinated at pH 6 and 8 and held at 20 degrees C for various contact times. The results show that increasing pH from 6 to 8 increased trihalomethane formation but decreased trihaloacetic acid formation, with little effect on dihaloacetic acid formation. More trihalomethanes were formed than haloacetic acids at pH 8, while the reverse was true at pH 6. Hydrophobic fractions always gave higher haloacetic acid and trihalomethane formation potentials than their corresponding hydrophilic fractions, but hydrophilic carbon also played an important role in disinfection byproduct formation for waters with low humic content. The bromine-containing species comprised a higher molar proportion of the trihalomethanes than of the haloacetic acids. The hydrophilic fractions were more reactive with bromine than their corresponding hydrophobic fractions. Coagulation generally removed more haloacetic acid precursors than trihalomethane precursors. Waters with higher specific ultraviolet absorbance values were more amenable to removal of organic material by coagulation than waters with low specific ultraviolet absorbance values. Experimental evidence suggests that haloacetic acid precursors have a higher aromatic content than trihalomethane precursors.     

Nature and chlorine reactivity of organic constituents from reclaimed water in groundwater, Los Angeles County, California

The nature and chlorine reactivity of organic constituents in reclaimed water (tertiary-treated municipal wastewater) before, during, and after recharge into groundwater at the Montebello Forebay in Los Angeles County, CA, was the focus of this study. Dissolved organic matter (DOM) in reclaimed water from this site is primarily a mixture of aromatic sulfonates from anionic surfactant degradation, N-acetyl amino sugars and proteins from bacterial activity, and natural fulvic acid, whereas DOM from native groundwaters in the aquifer to which reclaimed water was recharged consists of natural fulvic acids. The hydrophilic neutral N-acetyl amino sugars that constitute 40% of the DOM in reclaimed water are removed during the first 3 m of vertical infiltration in the recharge basin. Groundwater age dating with 3H and 3He isotopes, and determinations of organic and inorganic C isotopes, enabled clear differentiation of recent recharged water from older native groundwater. Phenol structures in natural fulvic acids in DOM isolated from groundwater produced significant trihalomethanes (THM) and total organic halogen (TOX) yields upon chlorination, and these structures also were responsible for the enhanced SUVA and specific fluorescence characteristics relative to DOM in reclaimed water. Aromatic sulfonates and fulvic acids in reclaimed water DOM produced minimal THM and TOX yields.     

Degradation of tertiary alkylamines during chlorination/chloramination: implications for formation of aldehydes, nitriles, halonitroalkanes, and nitrosamines

Drinking water utilities are exploring the use of waters impacted by wastewater effluents and agricultural runoff to meet the demands of growing populations. Due to the elevated organic nitrogen concentrations in these waters, the pathways responsible for transformation of organic nitrogen into toxic nitrogenous disinfection byproducts during chlorine and chloramine disinfection are of current concern. Tertiary alkylamines are important functional groups in human waste products and various consumer products that can be released to drinking water supplies via wastewater effluents. We investigated degradation pathways for model tertiary alkylamines during chlorination and chloramination. Our results indicate that tertiary alkylamines degrade nearly instantaneously during chlorination to form aldehydes and secondary alkylamines quantitatively, with no significant regioselectivity. Similar results were observed during chloramination, but the observed degradation rates were much slower, with lower yields of aldehydes. As these major products were fairly stable, these results explain why tertiary amines are significant precursors of secondary nitrosamines during chloramination. Trichloronitromethane formed at very low yields during chlorination, but was not observed during chloramination; monochloronitromethane and dichloronitromethane were never detected. Despite the significant yields of aldehydes during chloramination, our results indicated low nitrile yields bythe reaction between chloramines and aldehydes.     

Fractionation of natural organic matter in drinking water and characterization by 13C cross-polarization magic-angle spinning NMR spectroscopy and size exclusion chromatography

Natural organic matter from drinking water sources was fractionated, and the fractions were characterized by NMR and SEC with the aim of relating NOM structure to treatability. Organic matter was isolated from two Australian surface waters (Horsham, Moorabool) by reverse osmosis and from a groundwater (Wanneroo) by anion exchange. The isolates were fractionated according to polarity and charge by resin adsorption. 13C NMR spectra of the freeze-dried fractions showed the most hydrophobic fraction to be high in aliphatic and aromatic carbon while slightly hydrophobic organics have more carbonyl and alkoxyl carbon. The Horsham and Wanneroo hydrophilic fractions show strong alkoxyl signals attributed to carbohydrate. Moorabool hydrophilics contain aromatic (phenolic) carbon; the apparent absence of carbohydrate appears to be an artifact. Size-exclusion chromatograms were recorded on the original and fractionated organics with both UV and dissolved organic carbon detection. The Horsham and Moorabool organics have similar molecular size distributions while Wanneroo is dominated by strongly absorbing species having large hydrodynamic radii. The hydrophobic and charged hydrophilic fractions also have high apparent MW, while the neutral fraction is higher in low-MW compounds of relatively low specific absorbance, suggestive of carbohydrates.     

Study on transformation of natural organic matter in source water during chlorination and its chlorinated products using ultrahigh resolution mass spectrometry

Natural organic matter (NOM) can affect the performance of water treatment processes, and serves as a main precursor for the formation of disinfection byproduct (DBPs) during chlorination. To minimize such undesirable effects, a better understanding of its structural information and reactivity toward chlorine is necessary. In this study, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) was used to study the molecular composition of NOM in source water. More than four thousand NOM components were resolved in the sample. NOM molecules with a low degree of oxidation (low O/C ratio) were found to be more reactive toward chlorine than those with high O/C ratio. Totally, 659 one-chlorine containing products and 348 two-chlorine containing products were detected in the chlorinated sample at a high confidence level. The chlorinated products can be arranged into series, which indicate they were originated from precursor compounds in series related by the replacement of CH(4) against oxygen. Of the 1007 chlorine-containing products observed in this study, only 7 molecular formulas can be found in previous studies, showing the distinct difference from previous studies. This study explored the reactivity of NOM toward chlorine on a molecular level, which was previously explained on the level of whole mixtures or fractions of NOM, and the identified chlorinated products may contribute to our knowledge of the unknown total organic halide (TOX).     

I-THM formation and speciation: preformed monochloramine versus prechlorination followed by ammonia addition

An increasing number of utilities in the United States have been switching from chlorination to chloramination practices to comply with the more stringent trihalomethane (THM) and haloacetic acid (HAA) regulations. This has important implications for disinfection byproduct (DBP) formation because the reactions of chlorine and monochloramine (NH(2)Cl) with natural organic matter (NOM) are not the same. In this study, iodinated trihalomethane (I-THM) formation from preformed NH(2)Cl and prechlorination (at two chlorine doses and contact times) followed by ammonia addition was compared. A representative bromide/iodide ratio of 10:1 was selected and four bromide/iodide levels (ambient, 50/5 or 100/10, 200/20, and 800/80 [μg/L/μg/L]) were evaluated. The results showed that I-THM formation was generally lower for prechlorination as compared to preformed NH(2)Cl due to the oxidation of iodide to iodate by chlorine. However, while prechlorination minimized iodoform (CHI(3)) formation, prechlorination sometimes formed more I-THMs as compared to preformed NH(2)Cl due to a large increase in the formation of brominated I-THM species, which were formed at much smaller amounts from preformed NH(2)Cl. I-THM concentrations and speciation for the two chloramination scenarios (i.e., preformed NH(2)Cl vs prechlorination followed by ammonia) depended on chlorine dose, contact time, bromide/iodide concentration, and NOM characteristics of the source water (SUVA(254)).     

Characterization of high molecular weight disinfection byproducts from chlorination of humic substances with/without coagulation pretreatment using UF-SEC-ESI-MS/MS

Chlorinated disinfection byproducts (DBPs) generated from the reaction of the disinfectant chlorine with naturally occurring humic substances in raw water have been intensively studied over the past three decades, yet only a fraction of the total organic halogen (TOX) formed during chlorination has been chemically identified or even well characterized. The majority of the unknown portion of the TOX is likely attributable to high molecular weight (MW) DBPs (above 500), which may have potential adverse health effects. In this work, typically dosed chlorinated Suwannee River fulvic acid (SRFA) samples with and without coagulation pretreatment were separated and fractionated by using ultrafiltration (UF) and size exclusion chromatography (SEC) techniques. The SEC fractions corresponding to the high MW region were concentrated with nitrogen sparging and characterized by negative ion electrospray ionization mass spectrometry (ESI-MS) and ESI-MS/MS. The results demonstrate that the ESI-MS/MS precursor ion scan is an effective tool for the selective detection of the electrospray ionizable chlorine-containing compounds in a complex mixture. Many high MW chlorine-containing DBPs were tentatively found in the UF-SEC fractions of the chlorinated SRFA samples with/without coagulation pretreatment. The SEC-UV chromatograms and SEC-ESI-MS spectra show that coagulation could significantly reduce the formation of high MW chlorinated DBPs.     

Haloacetic acid and trihalomethane formation from the chlorination and bromination of aliphatic beta-dicarbonyl acid model compounds

While it is known that resorcinol- and phenol-type aromatic structures within natural organic matter (NOM) react during drinking water chlorination to form trihalomethanes (THMs), limited studies have examined aliphatic-type structures as THM and haloacetic acid (HAA) precursors. A suite of aliphatic acid model compounds were chlorinated and brominated separately in controlled laboratory-scale batch experiments. Four and two beta-dicarbonyl acid compounds were found to be important precursors for the formation of THMs (chloroform and bromoform (71-91% mol/mol)), and dihaloacetic acids (DXAAs) (dichloroacetic acid and dibromoacetic acid (5-68% mol/mol)), respectively, after 24 h at pH 8. Based upon adsorbable organic halide formation, THMs and DXAAs, and to a lesser extent mono and trihaloacetic acids, were the majority (> 80%) of the byproducts produced for most of the aliphatic beta-dicarbonyl acid compounds. Aliphatic beta-diketone-acid-type and beta-keto-acid-type structures could be possible fast- and slow-reacting THM precursors, respectively, and aliphatic beta-keto-acid-type structures are possible slow-reacting DXAA precursors. Aliphatic beta-dicarbonyl acid moieties in natural organic matter, particularly in the hydrophilic fraction, could contribute to the significant formation of THMs and DXAAs observed after chlorination of natural waters.     

Biodegradability, DBP formation, and membrane fouling potential of natural organic matter: characterization and controllability

Various natural organic matter (NOM) constituents were evaluated in terms of their biodegradability, disinfection byproduct (DBP) formation potentials, and membrane fouling. The biodegradability of NOM was evaluated with respect to biodegradable dissolved organic carbon (BDOC) and its inhibition control. NOM was divided into (i) colloidal and noncolloidal NOM, using a dialysis membrane with a molecular weight cutoff of 3500 Da and (ii) hydrophobic, transphilic, and hydrophilic NOM constituents, using XAD-8/4 resins. The colloidal, and noncolloidal hydrophilic, NOM were identified as being more problematic than the other components, exhibiting relatively higher biodegradability and reactivity toward DBP formation potential. A higher biodegradability especially can provide a high risk of membrane biofouling, if a membrane is fouled by highly biodegradable NOM. Colloidal, and noncolloidal hydrophilic, NOM constituents were also shown as major foulants of negatively charged membranes due to their high neutral fractions. Filter adsorber (F/A) types of activated carbons were evaluated in terms of removals of NOM, DBP formation potential, and BDOC and were compared to conventional processes and a nanofiltration membrane. The F/A process exhibited a comparatively good efficiency, especially in DBP and BDOC control, but was not so good at removing NOM. This suggests that F/A could potentially be combined with a membrane process to minimize the DBP formation potential and bio-/organic-fouling (i.e., F/A process as a pretreatment for a membrane process).     

Nitrile, aldehyde, and halonitroalkane formation during chlorination/chloramination of primary amines

The decreasing availability of pristine water supplies is prompting drinking water utilities to exploit waters impacted by wastewater effluents and agricultural runoff. As these waters feature elevated organic nitrogen concentrations, the pathways responsible for transformation of organic nitrogen into toxic nitrogenous disinfection byproducts during chlorine and chloramine disinfection are of current concern. Partially degraded biomolecules likely constitute a significant fraction of organic nitrogen in these waters. As primary amines occur in important biomolecules, we investigated formation pathways for nitrile, aldehyde, and halonitroalkane byproducts during chlorination and chloramination of model primary amines. Chlorine and chloramines transformed primary amines to nitriles and aldehydes in significant yields overtime scales relevant to drinking water distribution systems. Yields of halonitroalkanes were less significant yet may be important because of the high toxicity associated with these compounds. Our results indicate that chloramination should reduce nitrile concentrations compared to chlorination but may increase the formation of aldehydes and halonitroalkanes at high oxidant doses.     

Ultrafiltration of nonionic surfactants and dissolved organic matter

A brownwater sample with a high content of humic substances (HS) was fractionated by multistage ultrafiltration (mst-UF) into five fractions with nominal molecular weights ranging from >30 to <1 kDa. Fractions were characterized with respect to molecular size distribution and structure. Size exclusion chromatography with online DOC detection revealed that mst-UF yielded fractions with decreasing Mp (molecular weight at peak maximum) and polydispersities from nominally large to small mst-UF fractions. 13C MAS NMR analysis showed that the content of carbohydrate structures decreased from the original sample toward smaller molecular weight (MW) fractions, which in turn contained more carboxylic groups and branched aliphatic structures. Specific UV absorbances (SUVA254) were highest in the >30 kDa fraction and decreased with decreasing MW. To evaluate whether separation mechanisms other than size exclusion were of importance during the fractionation, the behavior of low molecular weight model compounds (MC) with a range of polarities was studied. Recoveries decreased with increasing hydrophobicity of the MC. For selected nonylphenol ethoxylates and 4-nonylphenol the recovery correlated well with the hydrophile-lipophile balance value. The presence of dissolved organic matter (DOM) caused an additional loss of hydrophobic MC, possibly because of sorption of the compounds onto DOM fouling layers. The hydrophilic MC caffeine was recovered almost completely (85-86%) regardless of the DOM content of the model solution. It was concluded that size exclusion was the dominant fractionation mechanism for caffeine, whereas hydrophobic interactions played a major role during the mst-UF fractionation of nonpolar contaminants. For a better understanding of the behavior of polyfunctional molecules such as HS, the effect of other physicochemical properties needs to be investigated in further studies.     

Effect of ammonia nitrogen and dissolved organic matter fractions on the genotoxicity of wastewater effluent during chlorine disinfection

Chlorine is a widely used disinfectant which prevents the spread of harmful pathogens when reusing wastewater, but harmful byproducts might be formed and cause adverse ecological and health effects. In this study, the potential effects of chlorination on the genotoxicity of different biologically treated wastewater samples were investigated using the umutest. For the firsttime, ammonia nitrogen (NH3-N) was found to significantly influence genotoxicity during wastewater chlorination. After chlorination, the genotoxicity decreased in wastewater with a low NH3-N concentration (<10-20 mg/L), but it increased notably in wastewater with a high NH3-N concentration (>10-20 mg/L). By fractionating the DOM (dissolved organic matter) in wastewater into different fractions, it was found that the hydrophilic substances (HIS) fraction of DOM was the key fraction involved in decreasing genotoxicity during the chlorination of wastewater with a low NH3-N concentration, while the hydrophobic acids (HOA) fraction of DOM was the key fraction involved in increasing genotoxicity during chlorination of wastewater with a high NH3-N concentration. Furthermore, fluorescence spectroscopy analysis on different fractions indicated that some free or combined aromatic amino acids might produce highly genotoxic byproducts during the chlorination of wastewater with a high NH3-N content, and this was then demonstrated through experiments on the chlorination of free aromatic amino acids.     

Influence of the order of reagent addition on NDMA formation during chloramination

The formation of the potent carcinogen, N-nitrosodimethylamine (NDMA), during chlorine disinfection has caused significant concern among drinking water and wastewater recycling utilities practicing intentional or unintentional chloramination. Previous research modeled NDMA formation as arising from a reaction between monochloramine and organic nitrogen precursors, such as dimethylamine, via an unsymmetrical dimethylhydrazine (UDMH) intermediate. Contrary to the importance of monochloramine indicated by previous studies, hypochlorite formed an order of magnitude more NDMA than monochloramine when applied to a secondary municipal wastewater effluent containing excess ammonia. Experiments involving variation of the order that each reagent (i.e., hypochlorite, ammonium chloride, and dimethylamine) was added to solution suggest two factors that may be more important for NDMA formation than the presence of monochloramine: (i) the chlorination state of organic nitrogen precursors and (ii) the partial formation of dichloramine. Although dichloramine formation was most influenced by the pH conditions under which inorganic chloramine formation was performed, mixing effects related to the order of reagent addition may be important at full-scale plants. Chloramination strategies are suggested that may reduce NDMA formation by nearly an order of magnitude.     

Impact of simulated solar irradiation on disinfection byproduct precursors

The Sacramento-San Joaquin Delta is the major drinking water source for 23 million California residents. Consequently, many studies have examined disinfection byproduct (DBP) formation in relation to Delta dissolved organic carbon (DOC) concentration. However, DOC characteristics within the Delta are not the same as those entering downstream water treatment facilities. As water is transferred to Southern California through the California Aqueduct, a 714.5 km-open channel, it is exposed to sunlight, potentially altering DBP precursors. We collected water from three sites within the Delta and one nearthe California Aqueduct, representing different DOC sources, and irradiated them in a solar simulator at a dose equivalent to that received during four days conveyance in the aqueduct. Photolytic changes in DOC were assessed by measuring CO2 and organic acid production, fluorescence, and ultraviolet absorbance over time. Trihalomethane (THM) and haloacetic acid (HAA) formation potentials, as well as the distribution of hydrophobic, transphilic, and hydrophilic acid fractions were determined at exposures equivalent to one and four days. Solar irradiation significantly decreased ultraviolet absorbance and fluorescence intensity, produced organic acids, and increased the hydrophilic fraction of waters. These changes in DOC caused a shift in bromine incorporation among the THM and HAA species. Our results are the first to demonstrate the importance of sunlight in altering DOC with respect to DBP formation.