Trihalomethane Precursors Research Articles

Trihalomethanes formation enhanced by manganese chlorination and deposition in plastic drinking water pipes

Residual manganese(II) in finished water undergoes further oxidation and deposition in drinking water distribution systems (DWDS), and Mn deposits can function as sites for accumulating organic and inorganic pollutants. This study aims to explore how Mn transformation and deposition affect the formation of disinfection byproducts (DBPs) in chlorinated DWDS, and trihalomethanes (THMs) was selected as a representative DBP. In a 100 μg/L Mn system, regulated THMs (chlorinated/bromated-THMs) increased by over 20% higher than Mn-free system after 150-day operation; when 50 μg/L iodide (I−) entered pipe systems after 150 days, iodinated THMs (I-THMs) in 100 μg/L Mn system increased by over 30% compared with Mn-free system. These promotions were attributed primarily to the accumulation of biomolecules and organic substances by tight and hard chlorinated Mn deposits. The residence of inactivated cells and the bridging role of surface Mn(III) in Mn deposits increased the quantity of THM precursors in DWDS. Furthermore, the rapid catalytic oxidation of Mn(II) by preformed Mn oxides (MnOx) inhibited the conversion of free iodine (HOI/OI−) to iodate, resulting in the generation of more I-THMs. This study provides new insights into the DBP risks caused by Mn in DWDS.

Variation of carbonaceous disinfectants by-products precursors and their correlation with molecular characteristics of dissolved organic matter and microbial communities in a raw water distribution system

The raw water distribution systems (RWDSs) play key roles in urban water supply systems. The changes of disinfection byproducts (DBPs) precursors of trihalomethanes (THMs), haloacetic acids (HAAs) and halogenated acetaldehydes (HALs) in the RWDS in Taihu Basin were investigated by formation potentials. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) method and 454-pyrosequencing were employed to study the variation of molecular characteristics of low molecular weight-dissolved organic matter (LMW-DOM) and microbial communities of pipeline biofilms respectively, which played crucial roles in the variation of DBPs precursors. The results showed that both DBPs precursors and the molecular characteristics of LMW-DOM in the RWDS had changed. Moreover, the LMW-DOM could be an indicator due to the good positive correlation with precursors of HAAs and HALs. Specifically, the LMW-DOM showed continuous accumulation in the RWDS. The LMW-DOM tended to possess higher m/z and more CH2 or long alkyl chains while pre-chlorination controlled this trend. The LMW-DOM in the pre-chlorinated pipe section also possessed higher saturation. Additionally, lignins served as an important part of DBPs precursors and dominated the LMW-DOM. The microbial diversity decreased in the RWDS, and the abundance and diversity of the microbial community in the pre-chlorinated section were significantly lower than those in the no-chlorinated section. Finally, most DBPs precursors had positive correlation with dominant phylum and genus in RWDS. This study reveals variation of DBPs precursors, LMW-DOM and microbial pipeline biofilms as well, and provide important data for further research on raw water safety and stability in RWDSs.

Parallel factor analysis of fluorescence excitation emissions to identify seasonal and watershed differences in trihalomethane precursors

Concentration and chemical composition of dissolved organic matter (DOM) play a major role in formation and speciation of disinfection by-products, such as trihalomethanes (THMs), in water treatment plants (WTPs) during disinfection. This study characterized DOM across the process trains of WTPs using fluorescence excitation emission matrices (EEMs) together with parallel factor analysis (PARAFAC). The PARAFAC model was developed from 216 EEMs of bimonthly water samples from three WTPs in Khon Kaen, Thailand, from May 2018 to Mar 2019. Three PARAFAC components identified were humic-like DOM of terrestrial, and microbial or agricultural origin, while the one protein-like component was previously defined as tryptophan-like fluorophore. The relationships between water quality parameters, including the maximum fluorescent intensities (Fmax) of PARAFAC components and THM formation potential (THM-FP) were investigated using Spearman's rank correlation. The Fmax of PARAFAC components, UVA254, DOC, and THM-FP were greater in dry season. Chloroform was the primary THM formed at two sites using surface water as their water source, while the site using surface water with saline groundwater intrusion had higher concentration of brominated THMs. Results indicated that Fmax of humic-like components extracted by PARAFAC analysis were the most accurate THM-FP surrogate parameter assessed for the water samples tested and the correlations between Fmax and THM-FP were site specific (ρ = 0.81–0.85). The result demonstrates that fluorescence spectroscopy analysis has yielded insights into relationships between the DOM optical characteristics and their total THM-FP even at sites with different speciation of THMs.

Research about Organic Matter Removal and Biofilms Development of Pilot-Scale UV/H2O2-BAC Process

As a green advanced process for drinking water treatment, the UV/hydrogen peroxide (UV/H2O2) process has been gradually applied in China. To study the effect and mechanism of organic matter removal and the development of microbial communities in the UV/H2O2-biological activated carbon (UV/H2O2-BAC) process, a pilot-scale UV/H2O2-BAC system was built and operated over one year. Low water temperature affects the UV/H2O2 process efficiency, the biofilms in the BAC system were mature and stable after 240 days, and the contribution rate of BAC adsorption to dissolved organic carbon (DOC) removal was approximately 14.2% after one year of operation. The liquid chromatography-organic carbon detection (LC-OCD) analysis shows that UV/H2O2 process can increase the amounts of Low Molecular Weight (LMW) neutrals, and the specific UV absorbance (SUVA254) value is not suitable for predicting Trihalomethanes (THMs) precursor contents in water after UV/H2O2 treatment. High-throughput sequencing results prove that microbial species in the middle section are the most abundant compared to those in the influent and effluent sections, hydrogen peroxide has lower inhibition on the development of microbial community than ozone and the low concentration of hydrogen peroxide (<0.25 mg/L) promotes the development of the microbial communities, hydrogen peroxide can reduce Proteobacteria abundance by inhibiting the growth of anaerobes. Acidobacteria may have a certain contribution to the degradation of soil organic matter (SOM), and the effluent section of BAC with low DOC concentration cannot form the dominant species of Rhodobacter.

Characteristics of trihalomethane and haloacetic acid precursors in filter backwash and sedimentation sludge waters during drinking water treatment

Trihalomethanes (THMs) and haloacetic acids (HAAs) are the most common disinfection byproducts posing human health risks. This study investigated the precursors of THMs and HAAs in filter backwash water (FBW) and sedimentation sludge water (SSW) by the methods of ultrafiltration membranes, synthetic resins and excitation-emission matrix (EEM) spectra. The concentrations of dissolved organic carbon (DOC) in FBW and SSW ranged from 1.7 to 2.7 mg/L and 2.7 to 5.8 mg/L, respectively. After chlorination, THMs and HAAs ranging from 223 to 608 μg/L and 26 to 110 μg/L were generated in FBW and SSW, respectively. There were more THM precursors than HAAs in FBW and SSW, but the formation of HAAs was often affected by water quality in terms of DOC, specific ultraviolet absorbance (SUVA), etc. High concentrations of bromo-trihalomethanes (Br-THMs) were generated in FBW and SSW, while monochloroacetic acid (MCAA) was the dominant species. The effect of bromide concentration on the formation of total THMs was greater than that of HAAs. Fluorescence analysis revealed that aromatic protein-like compounds were the dominant dissolved organic matter (DOM) in FBW and SSW. The concentrations of THMs and HAAs in the MW < 3 kDa fraction accounted for 58–80% and 62–74% of the whole sample, respectively. Hydrophilic (HPI) organic matter with molecular weight (MW) < 3 kDa was the main precursor of THMs and HAAs in FBW and SSW. Both HPI and hydrophobic (HPO) fractions were proven to play a considerable role in the formation of HAAs. Therefore, the corresponding treatment strategies should be considered to remove low-MW, HPI and HPO organics according to the water quality of FBW and SSW before recycling in order to avoid the formation of THMs and HAAs.

Heterogeneous Fenton-like reaction followed by GAC filtration improved removal efficiency of NOM and DBPs without adjusting pH

This paper explores the removal of natural organic matter (NOM) and disinfection by-products (DBPs) in drinking water by heterogeneous Fenton-like oxidation and granular activated carbon (GAC) filtration in a pilot scale test without adjusting pH of the water. pH of the used water in this study was from 7.5 to 8.7. Comparing with conventional water treatment processes, heterogeneous Fenton-like reaction and GAC filtration increased the removal rate of dissolved organic carbon (DOC), NOM with different apparent molecular weight (AMW) (F1-F7) and with different compositions (C1-C5) to 75.11%, 88.65% and 58.73%, respectively. Moreover, heterogeneous Fenton-like reaction and GAC filtration increased the removal rate of DBPs to 88.18%. The multivariate statistical analysis indicated that haloacetic acids (HAAs) and haloketones (HKs) mainly came from fulvic-like and humic-like NOM with AMW lower than 1.5 K Da. These substances with AMW between 1.5 K Da and 3.5 K Da were the main precursors of trihalomethanes (THMs). The main precursors of halonitriles (HANs) were soluble microbial byproduct-like (SMP-like), tyrosine-like and tryptophan-like substance with the AMW between 3.5 K Da and 4.5 K Da. Overall, without adjusting pH of water, heterogeneous Fenton-like reaction and GAC filtration improved the removal efficiency of NOM and DBPs, and controlled the genotoxicity of drinking water.

Disinfection byproduct formation from algal organic matters after ozonation or ozone combined with activated carbon treatment with subsequent chlorination

Algal organic matter (AOM), including extracellular organic matter (EOM) and intracellular organic matter (IOM) from algal blooms, is widely accepted as essential precursors of disinfection byproducts (DBPs). This study evaluated the effect of ozonation or ozone combined with activated carbon (O3-AC) treatment on characteristic alternation and DBP formation with subsequent chlorination of Chlorella sp.. The effects of pH and bromide concentration on DBP formation by ozonation or O3-AC treatment were also investigated. Results showed that the potential formation of DBPs might be attributed to ozonation, but these DBP precursors could be further removed by activated carbon (AC) treatment. Moreover, the formation of target DBPs was controlled at acidic pH by alleviating the reactions between chlorine and AOM. Besides, the bromide substitution factor (BSF) value of trihalomethanes (THMs) from EOM and IOM remained constant after AC treatment. However, THM precursors could be significantly decreased by AC treatment. The above results indicated that O3-AC was a feasible treatment method for algal-impacted water.

Pilot Test on Pre-Swim Hygiene as a Factor Limiting Trihalomethane Precursors in Pool Water by Reducing Organic Matter in an Operational Facility.

Pool water must be constantly disinfected. Chlorine compounds used to disinfect pools react with organic substances such as sweat, urine, and personal care products introduced into pool water by users and results in the formation of disinfection byproducts. Trihalomethanes (THM), including chloroform and dissolved organic carbon (DOC) concentrations, were quantified using a two-stage process: determining initial THM and chloroform levels; then searching for a cheap and easy-to-use method to improve water quality. The method proposed here to limit THM and DOC concentrations in water is controlled showering. At three swimming pool facilities, chloroform concentrations (13.8 ± 0.33 µg/L, 15.5 ± 0.44 µg/L, and 13.9 ± 0.06 µg/L) were below the threshold concentration of 30 μg/L. At a fourth facility, however, the chloroform concentration exceeded that threshold (40.7 ± 9.68 μg/L) when showering was not controlled. Those conditions improved after the introduction of a mandatory shower; concentrations of DOC, THMs, and chloroform all decreased. The chloroform concentration decreased to 29.4 ± 3.8 μg/L, the THM concentration was 31.3 ± 3.9 μg/L, and the DOC concentration was 6.09 ± 0.05 mg/L. Pilot tests were carried out at real facilities to determine whether the control of pre-swim hygiene was possible. The introduction of proper pre-swim hygiene limited the concentration of DOC in water and can lead to a healthier environment for everyone attending the swimming facility.

Trihalomethane precursors: Land use hot spots, persistence during transport, and management options

To meet drinking water regulations, rather than investing in costly treatment plant operations, managers can look for ways to improve source water quality; this requires understanding watershed sources and fates of constituents of concern. Trihalomethanes (THMs) are one of the major classes of regulated disinfection byproducts, formed when a specific fraction of the organic carbon pool—referred to as THM precursors—reacts with chorine and/or bromine during treatment. Understanding the source, fate, timing and duration of the organic compounds that react to form THMs will allow identification of targeted and effective management actions. In this study we evaluated THM precursor contributions from multiple land use categories and hydrologic contexts, including novel data for urban land uses that demonstrate strong potential to release water with high THM formation potential (THMFP; median 618 μg L−1): greater than storm runoff integrated across a mixed-use (1/3 natural, 2/3 agricultural) watershed (median 460 μg L−1), irrigation runoff from agricultural systems (357 μg L−1), or runoff from a natural forested (median 123 μg L−1) and shrubland/grassland (median 259 μg L−1) watersheds. While individual storm events released high THM precursor concentrations over short periods, dry season agricultural irrigation as well as urban landscapes have the potential to release water high in THM precursors for several months. Experimental bioassays and sampling along 333 miles of the California Aqueduct confirmed bioavailability and photooxidation potential of less than 10% for THM precursors, suggesting that rivers with residence times of days to weeks may act as THM precursor conduits, shuttling THM precursors from hundreds of miles away to drinking water intakes with minimal degradation. This finding has considerable implications for water managers, who may therefore consider THM precursor management strategies that target even sources located far upstream.

Two years of post-wildfire impacts on dissolved organic matter, nitrogen, and precursors of disinfection by-products in California stream waters

We investigated the effects of two California wildfires (Rocky and Wragg Fires, 2015) compared to an unburned reference watershed on water quality, dissolved organic matter (DOM), and precursors of disinfection by-products (DBPs) for two years’ post-fire. The two burned watersheds both experienced wildfires but differed in the proportion of burned watershed areas. Burned watersheds showed rapid water quality degradation from elevated levels of turbidity, color, and suspended solids, with greater degradation in the more extensively burned watershed. During the first year’s initial flushes, concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium (NH4+/NH3), and specific ultraviolet absorbance (SUVA254) were significantly higher (67 ± 40%, 418 ± 125%, 192 ± 120%, and 31 ± 17%, respectively) in the more extensively burned watershed compared to the reference watershed. These elevated values gradually declined and finally returned to levels like the reference watershed in the second year. Nitrate concentrations were near detection limits (0.01 mg-N/L) in the first year but showed a large increase in fire-impacted streams during the second rainy season, possibly due to delayed nitrification. Changes in DOM composition, especially during the initial storm events, indicated that fires can attenuate humic-like and soluble microbial by-product-like (SMP) DOM while increasing the proportion of fulvic-like, tryptophan-like, and tyrosine-like compounds. Elevated bromide (Br−) concentrations (up to 8.7 μM]) caused a shift in speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) to brominated species for extended periods (up to 2 years). Wildfire also resulted in elevated concentrations of N-nitrosodimethylamine (NDMA) precursors. Such changes in THM, HAA, and NDMA precursors following wildfires pose a potential treatability challenge for drinking water treatment, but the effects are relatively short-term (≤1 year).

Ozonation of natural organic matter and aquatic humic substances: the effects of ozone on the structural characteristics and subsequent trihalomethane formation potential

Abstract The effect of ozonation on the structural and chemical characteristics of natural organic matter (NOM) and its isolated humic fractions, humic acid (HA) and fulvic acid, were studied using Fourier transform infrared coupled to attenuated total reflectance (FTIR-ATR), ultraviolet/visible (UV/Vis) spectroscopy, and synchronous scanning fluorescence (SSF) spectroscopy. The results were linked to the effect of ozonation on trihalomethane formation potential (THMfp) reduction for water standards with high THM precursors. Results showed that ozonation at a dose of 1 mg ozone/mg dissolved organic carbon (DOC) was capable of reducing DOC, UV absorbance at 254 nm (UV254), and THMfp by up to 42%, 95%, and 89% for the HA water standard, respectively. The study of UV/Vis, FTIR-ATR, and SSF revealed trends showing that ozone can alter the composition of DOC in the water standards, causing a significant reduction in aromaticity. The reduction of UV254 for each ozonated sample also affirms that ozone mainly targets aromatic moieties contained in NOM. FTIR-ATR results showed that the reduction of unsaturated functional groups, including aromatic rings and C = C bonds in the water standards tested, were the main components impacted by ozone application. SSF results also revealed that ozonation decreases the fluorescence intensity of the maximum peak – as well as the whole spectra.

Removal of trihalomethane (THM) precursors from water during coagulation enhanced by ozonation

Removal of trihalomethane (THM) precursors from water during coagulation enhanced by ozonation

Hurricane resulted in releasing more nitrogenous than carbonaceous disinfection byproduct precursors in coastal watersheds

The frequency of Atlantic hurricanes has been predicted to increase significantly by the end of this century. Watershed disturbance initiated by hurricanes can alter dissolved organic matter (DOM) quantity and quality in source water dramatically. DOM is an important disinfection by-product (DBP) precursor, and thus hurricanes can have a significant impact on water treatability and drinking water safety. The interactions between land use and land cover (LULC) of a watershed and DBP formation potential (FP) in source water under hurricane events have rarely been evaluated. Here, we quantified the FPs of two carbonaceous (trihalomethanes [THMs] and haloacetic acids [HAA]) and two nitrogenous (haloacetonitrile [HAN] and N-nitrosodimethylamine [NDMA]) DBPs at eighteen sub-watersheds with varying LULC along the Yadkin-Pee Dee River basin across North and South Carolina during and after the flooding condition caused by the 2016 Hurricane Matthew. Using chlorine as a disinfectant, THM FP was 238% (±117%) higher (p < .001) under the flooding condition than baseflow condition, while HAA FP did not change significantly as a result of the flooding. DOM composition under the flooding condition changed in favor of the formation of THMs rather than HAAs by a decrease of fulvic acid-like compounds and an increase in DOM aromaticity (SUVA). The FPs of studied DBPs under the flooding condition compared with the baseflow, followed the order of HAN (356.5%) > NDMA (246.4%) > THM (115.2%) using chloramine as a disinfectant. Higher HAN FP and NDMA FP compared to THM FP suggested that more nitrogenous than carbonaceous DBPs precursors were released during this hurricane event. LULC analysis revealed that forested wetlands were the major contributor of THM, HAA, and HAN precursors, whereas NDMA precursor was derived from developed areas. This unique study highlights the dynamic interplay between LULC and exports of carbonaceous and nitrogenous DBPs precursors during and after hurricanes.

Removal of THM Precursors by Adsorption, Coagulation and UV Irradation

The general characteristics of humic substances (HS) and their negative effect on water quality and its treatment are described. The paper presents the results from the removal of humic substances from the Hriňová (Slovakia) water reservoir using 1) granular activated carbon (GAC) from two producers (Chemviron, Cabot) at three different pH levels, 2) by coagulation with two coagulants (aluminum sulfate and ferric sulfate), and 3) by an advanced oxidation process using UV radiation with the addition of the oxidizing agent hydrogen peroxide. The effectiveness of the removal of humic substances (expressed by the TOC parameter) from water with adsorption by GAC, depending on the contact time with the water, ranged from 14 % for one hour to 50% for eight hours of contact time. The calculated GAC adsorption capacity of the humic substances ranged from 0.05 mg/g for one hour to 0.19 mg/g for eight hours of contact time. The pH of the water had no significant effect on the level of efficiency. A high level of efficiency (50%) and the lowest value of TOC are obtained at a pH of 6.5. The humic substances remain in the water though the optimal dose of the coagulant was used. The ferric sulfate coagulant is more suitable for removing of humic substances from water as aluminum sulfate. A dose of 16 mg/L of 1% solution Fe2(SO4)3, which is the equivalent of 4.47 mg/L Fe3+, is sufficient for the reduction of humic substances below 1 mg/L. The effectiveness of the removal of humic substances with coagulation using iron sulfate was 83% for a parameter of HS and 50% for TOC or CODMn. The iron sulfate has the influence on a reduction in pH of water, therefore pH of water should be adjusted after coagulation. A laboratory study of removal of humic acids from surface water by UV radiation and addition of hydrogen peroxide in order to increase the oxidation of organics are presented. The results showed that UV radiation and addition of H2O2 during the first few minutes of irradiation increases the concentration of the humic substances, CODMn and TOC in water. After 3 minutes of exposure to UV radiation, these values were reduced to baseline, and in the next irradiation phase the values of the monitored parameters decreased. The highly reactive OH radicals with a high oxidation potential oxidize humic substances to various intermediates (a lower molecular weight substances). After 20 minutes of irradiation, a decrease in the parameters of approx. 39% for TOC, 62% for CODMn and 37% for humic substances was observed.

A novel process of adsorption cum enhanced coagulation-flocculation spiked with magnetic nanoadsorbents for the removal of aromatic and hydrophobic fraction of natural organic matter along with turbidity from drinking water

Abstract The present study developed a novel conjugate process for the removal of aromatic, hydrophobic fraction of natural organic matter and turbidity from drinking water supplies. Magnetic nanoadsorbents were synthesized under laboratory conditions and their surface properties were enhanced by surface modifiers followed by their characterization. The synthesized magnetic nanoadsorbents was then used in combination with conventional aluminum and iron coagulants for the removal of both natural organic matter and turbidity from drinking water. Adsorption cum enhanced coagulation-flocculation study was conducted in two different stages i.e. adsorption of natural organic matter by magnetic nanoadsorbents (stage 1) followed by coagulation-flocculation experiments using conventional coagulants like alum and ferric chloride (stage 2). Study indicated that magnetic nanoadsorbents-alum conjugate process is efficient in removing trihalomethane precursors. Significant removal of dissolved organic matter (98.7%), ultra violet absorbance at 254 nm (99.7%) and trihalomethane formation potential (91%) was achieved. The overall study showed that the developed magnetic nanoadsorbents-alum conjugate process is highly efficient in removing the trihalomethane precursors with a marked reduction in the overall cost for its large scale application.

Ozonation of Coking Wastewater Effluent to Remove Disinfection By-Product Precursors Using an O3 Fluidized Bed Reactor

Various types of dissolved organic matter (DOM) exist in the effluent of coking wastewater treatment plants. These can become precursors for disinfection by-products (DBPs) during chlorination in downstream drinking water treatment plants, representing a significant threat to the water supply. In this study, an O3 fluidized bed reactor (FBR) process is proposed to stabilize and reduce the number of precursors of haloacetonitriles (HANs) and trihalomethanes (THMs) in coking wastewater effluent. It was found that higher O3 concentrations resulted in lower amounts of precursors. Analysis of dissolved organic carbon (DOC) and total organic carbon (TOC), as well as three-dimensional excitation-emission matrix (3D EEM) fluorescence spectroscopy, showed that O3 preferentially decomposed DOM containing unsaturated and aromatic components. Ozonation also changed the species of organic compounds in the effluent. Furthermore, nitrogenous organic compounds such as nitrogen-containing heterocyclic compounds and nitrile were quickly oxidized. Amines were first increased then decreased, while the olefin and phenol, which contain unsaturated functional groups, were also selectively oxidized by ozonation. Organic acids and alkanes were formed during ozonation; however, these intermediate compounds showed relatively low formation potential for HANs and THMs. Therefore, the precursors can be mineralized or converted to organic compounds, which are less likely to form disinfection by-products. These results indicate that the ozonation treatment of coking wastewater effluent can effectively minimize disinfection by-product formation potential (DBPFP), reducing risks to the downstream water supply.

Trihalomethane precursor reactivity changes in drinking water treatment unit processes during a storm event.

Source water quality can significantly impact the efficacy of water treatment unit processes and the formation of chlorinated and brominated trihalomethanes (THMs). Current water treatment plant performance models may not accurately capture how source water quality variations, such as organic matter variability, can impact treatment unit processes. To investigate these impacts, a field study was conducted wherein water samples were collected along the treatment train for 72 hours during a storm event. Systematic sampling and detailed analyses of water quality parameters, including non-purgeable organic carbon (NPOC), UV absorbance, and THM concentrations, as well as chlorine spiking experiments, reveal how the THM formation potential changes in response to treatment unit processes. Results show that the NPOC remaining after treatment has an increased reactivity towards forming THMs, and that brominated THMs form more readily than chlorinated counterparts in a competitive reaction. Thus both the reactivity and quantity of THM precursors must be considered to maintain compliance with drinking water standards, a finding that should be incorporated into the development of model-assisted treatment operation and optimization. Advanced granular activated carbon (GAC) treatment beyond conventional coagulation-flocculation-sedimentation processes may also be necessary to remove the surge loading of THM-formation precursors during a storm event.

Performance of BAC for DBPs precursors’ removal for one year with micro-polluted lake water in East-China

ABSTRACT Effectiveness of biological activated carbon (BAC) filter in removing disinfection byproducts (DBPs) precursors of micro-polluted lake water for one year was conducted. The formation potential (FP) of DBPs (trihalomethanes (THMs), haloacetic acids (HAAs) and Nitrosamines (NAs)), dissolved organic carbon (DOC), molecular weight (MW) distribution and excitation emission matrix fluorescence (EEM) of dissolved organic material (DOM) in the influent and effluent of BAC were determined. The results indicated that the removal efficiency (RE) of DOC ranged from 42.9–28.3%. Neither virgin GAC nor long-term operated BAC could efficiently dispose of THMs and HAAs precursors (RE from 35.2–18.8%, from 42 to 8.4%, respectively), however, BAC still showed good ability in removal of NAs precursors after a year operation, of which RE just dropped from 81.7–69.6%. There was strong correlation between RE of NAs precursors and DOC with small MW (<0.5 kDa). The removal of HAAs precursors showed relatively close relation to aromatic protein-like components and soluble microbial pollutants (SMPs). Weak direct relationship was found between the water quality parameters and THMs precursors.

Importance of correcting for fluorescence quenching in fluorescence-based prediction of trihalomethane formation potential

AbstractFluorescence excitation–emission matrix (EEM) spectroscopy is often used to determine the levels of trihalomethane (THM) precursors in natural organic matter. However, humic substances are known to quench the fluorescence of amino acids and proteins. To date, none of the EEM-based models for predicting THM formation potential (THMFP) have explicitly accounted for these quenching effects. Thus, we investigated the importance of correcting for fluorescence quenching during THMFP prediction. Fluorescence titration experiments revealed that the correction improved the accuracy of THM prediction. EEM-based models using the corrected fluorescence intensity displayed the highest accuracy (R2 &amp;gt; 0.99; mean absolute error 8.1 μg/L and 13.9 μg/L for chloroform and bromoform, respectively) among models using individual parameters of EEM intensity, dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254), specific UV254 (SUVA254) and differential ultraviolet absorbance at 272 nm (ΔUV272). Thus, EEM-based models require both the fluorescence intensity of a humic-like component and the corrected fluorescence intensity of a protein-like component for accurate THMFP prediction, for both chlorination and bromination processes. We also found it to be unnecessary to combine DOC with EEM intensity in terms of prediction accuracy, as long as the fluorescence quenching correction is applied.

Fluorescence spectroscopy for assessing trihalomethane precursors removal by MIEX resin.

This study investigated the applicability of fluorescence excitation-emission matrix spectroscopy (EEMS) to assess total trihalomethane formation potentials (TTHMFPs) and the ability of magnetic ion exchange (MIEX®) resin to reduce TTHMFP. We treated a surface water and secondary wastewater effluent with MIEX mimicking full-scale operation by repeatedly exposing the same resin batch to additional feed water, with batches ranging from 500 to 5,000 resin bed volumes. Results showed that MIEX was more effective at removing or reducing ultraviolet absorbance (UVA254), dissolved organic carbon (DOC), and TTHMFP in surface water than in secondary effluent. The greater UVA254, DOC and TTHMFP removal for surface waters was explained by the stronger affinity of MIEX for terrestrial dissolved organic matter (DOM) compared to microbial DOM. Fluorescence EEMS results showed that the ratio between terrestrial and microbial fluorescent signals of DOM was significantly greater in surface water than in secondary effluent. Fluorescence surrogate parameters were strongly correlated with TTHMFP, namely, fluorescence intensity of humic-like peak C (R2 = 0.98, p < 0.01), protein-like peak T (R2 = 0.96, p < 0.01), and fulvic-like peak A (R2 = 0.87, p < 0.01). Correlations between fluorescence surrogate parameters and TTHMFP were substantially stronger than correlations between DOC and TTHMFP. Overall, the results indicate that fluorescent parameters extracted from EEMS data can be used as quick surrogate parameters to monitor TTHMFP for a diverse group of raw and MIEX-treated waters.