Transformation Of Natural Organic Matter Research Articles

Molecular weight fraction-specific transformation of natural organic matter during hydroxyl radical and sulfate radical oxidation

Aquatic natural organic matter (NOM) is one of the main scavengers of reactive species (e.g., •OH and SO4•−) during oxidation processes and undergoes complex transformations. Here, the organic content, optical properties, and redox state in various MW fractions and bulk Suwannee River NOM (SRNOM) were simultaneously evaluated during •OH and SO4•− oxidation processes for the first time. The SRNOM transformation pathways were specific to radical species and MW fractions, which was evidenced by a proportional decrease in electron-donating moieties and chromophores during •OH oxidation but a higher decrease in electron-donating moieties than chromophores during SO4•− oxidation, particularly in lower MW fractions (<3 kDa). The •OH decomposed reactive moieties mainly via aromatic ring opening or depolymerization in all MW fractions. SO4•− oxidation followed a similar pathway in higher MW fractions (>3 kDa) but mainly formed compounds with UV-absorbing properties (e.g., quinones) in lower MW fractions (<3 kDa). With competitive kinetics and depolymerization model, •OH was quantified as approximately 10 times more reactive towards MW fractions than SO4•−. However, the SO4•− concentrations were approximately 10 times those of •OH, resulting in comparable performance to •OH oxidation. SRNOM depolymerization by •OH and SO4•− resulted in formation of more precursors of disinfection byproducts than the parent constituents, especially for •OH. This work improves our understanding of the transformation of specific SRNOM fractions during radical oxidation processes.

High throughput identification of carbonyl compounds in natural organic matter by directional derivatization combined with ultra-high resolution mass spectrometry

Carbonyl compounds are important components of natural organic matter (NOM) with high reactivity, so that play a pivotal role in the dynamic transformation of NOM. However, due to the lack of effective analytical methods, our understanding on the molecular composition of these carbonyl compounds is still limited. Here, we developed a high-throughput screening method to detect carbonyl molecules in complex NOM samples by combining chemical derivatization with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). In six different types of dissolved organic matter (DOM) samples tested in this study, 20–30 % of detected molecules contained at least one carbonyl group, with relative abundance accounted for 45–70 %. These carbonyl molecules displayed lower unsaturation level, lower molecular weight, and higher oxidation degree compared to non-carbonyl molecules. More importantly, the measured abundances of carbonyl molecules were consistent with the results of 13C nuclear magnetic resonance (NMR) analysis. Based on this method, we found that carbonyl molecules can be produced at DOM-ferrihydrite interface, thus playing a role in shaping the molecular diversity of DOM. This method has broad application prospects in screening carbonyl compounds from complex mixtures, and the same strategy can be used to directional identification of molecules with other functional groups as well.

Insights into the transformation of natural organic matter during UV/peroxydisulfate treatment by FT-ICR MS and machine learning: Non-negligible formation of organosulfates

Natural organic matter (NOM) is a major sink of radicals in advanced oxidation processes (AOPs) and understanding the transformation of NOM is important in water treatment. By using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in conjunction with machine learning, we comprehensively investigated the reactivity and transformation of NOM, and the formation of organosulfates during the UV/peroxydisulfate (PDS) process. After 60 min UV/PDS treatment, the CHO formula number and dissolved organic carbon concentration significantly decreased by 83.4 % and 74.8 %, respectively. Concurrently, the CHOS formula number increased substantially from 0.7 % to 20.5 %. Machine learning identifies DBE and AImod as the critical characteristics determining the reactivity of NOM during UV/PDS treatment. Furthermore, linkage analysis suggests that decarboxylation and dealkylation reactions are dominant transformation pathways, while the additions of SO3 and SO4 are also non-negligible. According to SHAP analysis, the m/z, number of oxygens, DBE and O/C of NOM were positively correlated with the formation of organosulfates in UV/PDS process. 92 organosulfates were screened out by precursor ion scan of HPLC-MS/MS and verified by UPLC-Q-TOF-MS, among which, 7 organosufates were quantified by authentic standards with the highest concentrations ranging from 2.1 to 203.0 ng L‒1. In addition, the cytotoxicity of NOM to Chinese Hamster Ovary (CHO) cells increased by 13.8 % after 30 min UV/PDS treatment, likely responsible for the formation of organosulfates. This is the first study to employ FT-ICR MS combined with machine learning to identify the dominant NOM properties affecting its reactivity and confirmed the formation of organosulfates from sulfate radical oxidation of NOM.

Interpretable Machine Learning and Reactomics Assisted Isotopically Labeled FT-ICR-MS for Exploring the Reactivity and Transformation of Natural Organic Matter during Ultraviolet Photolysis.

Isotopically labeled FT-ICR-MS combined with multiple post-analyses, including interpretable machine learning (IML) and a paired mass distance (PMD) network, was employed to unravel the reactivity and transformation of natural organic matter (NOM) during ultraviolet (UV) irradiation. FT-ICR-MS analysis was used to assign formulas, which were classified on the basis of their molecular compositions and structural categories. Isotope (deuterium, D) labeling was utilized to unequivocally determine the photochemical products and examine the development of OD radical-mediated NOM transformation. With regard to the reactive molecular formulas, CHOS formulas exhibited the highest reactivity (86.5% of precursors disappeared) followed by CHON (53.4%) and CHO (24.6%) formulas. With regard to structural categories, the degree of reactivity decreased in the following order: tannins > condensed aromatics > lignin/CRAMs. The IML algorithm demonstrated that the crucial features governing the reactivity of formulas were the molecular weight, DBE-O, NOSC, and the presence of heteroatoms (i.e., N and S), suggesting that the large and unsaturated compounds containing S and N are more prone to photodegradation. The reactomics approach using the PMD network further indicated that 11 specific molecular formulas in the CHOS and CHO class served as hubs, implying a higher photoreactivity and participation in a range of transformations. The isotope labeling analyses also found that, among the reactions observed, hydroxylation (i.e., +OD) is dominant for lignin/CRAMs and condensed aromatics, and formulas containing ≤10 D atoms were developed. Overall, this study, by adopting rigorous and interpretable techniques, could provide in-depth insights into the molecular-level dynamics of NOM under UV irradiation.

Overlooked impacts of natural organic matter conversion in a Fe(II)-induced peroxymonosulfate activation system for river water remediation

The peroxymonosulfate (PMS) process may be hindered severely due to natural organic matter (NOM) conversion in the treatment of emerging pollutants from river water, becoming a critical engineering and technical issue. In this study, a Fe(II)-induced river water (RW)/PMS catalytic system was constructed for investigating molecular transformation of NOM and related influence mechanism to sulfamethoxazole (SMX) degradation. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) analysis indicated that NOM molecules containing no more than one heteroatom in river may be attacked by hydroxyl radicals (OH) and then polymerized, converting into molecules with two or three heteroatoms during PMS oxidation. Based on the correlation analysis, CHONP-NOM, CHOSP-NOM and CHONSP-NOM showed a significant inhibition against SMX degradation, while CHONS-NOM exhibited a moderate inhibitory effect. Besides, more condensed aromatic structures, carbohydrates and tannins were generated via reactive species (OH and sulfate radicals (SO4−)) oxidation, radical addition and polymerization reactions. Notably, condensed aromatic structures, carbohydrates and tannins presented weak, modest and strong inhibition to SMX degradation, respectively. Based on the current results, the inhibition of target pollutants degradation would be mitigated via regulation of NOM molecules in a Fe(II)-induced PMS activation system, providing valuable information to reduce NOM impact. In addition, this study paves the way to achieve efficient removal of emerging pollutants from river water.

Oxygen Limitation Accelerates Regeneration of Active Sites on a MnO2 Surface: Promoting Transformation of Organic Matter and Carbon Preservation.

Birnessite (δ-MnO2) is a layered manganese oxide widely present in the environment and actively participates in the transformation of natural organic matter (NOM) in biogeochemical processes. However, the effect of oxygen on the dynamic interface processes of NOM and δ-MnO2 remains unclear. This study systematically investigated the interactions between δ-MnO2 and fulvic acid (FA) under both aerobic and anaerobic conditions. FA was transformed by δ-MnO2 via direct electron transfer and the generated reactive oxygen species (ROS). During the 32-day reaction, 79.8% of total organic carbon (TOC) in solution was removed under anaerobic conditions, unexpectedly higher than that under aerobic conditions (69.8%), suggesting that oxygen limitation was more conducive to the oxidative transformation of FA by δ-MnO2. The oxygen vacancies (OV) on the surface of δ-MnO2 were more exposed under anaerobic conditions, thus promoting the adsorption and transformation of FA as well as regeneration of the active sites. Additionally, the reaction of FA with δ-MnO2 weakened the strongly bonded lattice oxygen (Olatt), and the released Olatt was an important source of ROS. Interestingly, a part of organic carbon (OC) was preserved by forming MnCO3, which might be a novel mechanism for carbon preservation. These findings contribute to an improved understanding of the dynamic interface processes between MnO2 and NOM and provide new insights into the effects of oxygen limitation on the cycling and preservation of OC.

Characterizing Natural Organic Matter Transformations by Microbial Communities in Terrestrial Subsurface Ecosystems: A Critical Review of Analytical Techniques and Challenges.

Determining the mechanisms, traits, and pathways that regulate microbial transformation of natural organic matter (NOM) is critical to informing our understanding of the microbial impacts on the global carbon cycle. The capillary fringe of subsurface soils is a highly dynamic environment that remains poorly understood. Characterization of organo-mineral chemistry combined with a nuanced understanding of microbial community composition and function is necessary to understand microbial impacts on NOM speciation in the capillary fringe. We present a critical review of the popular analytical and omics techniques used for characterizing complex carbon transformation by microbial communities and focus on how complementary information obtained from the different techniques enable us to connect chemical signatures with microbial genes and pathways. This holistic approach offers a way forward for the comprehensive characterization of the formation, transformation, and mineralization of terrestrial NOM as influenced by microbial communities.

Natural Organic Matter (NOM) Transformations and their Effects on Water Treatment Process: A Contemporary Review

Abstract: One of the several significant concerns related to water treatment plants is the transformation of natural organic matter (NOM) concerning quality and quantity due to the changing climatic conditions. The NOM consists of heterogeneous functionalized groups. Phenolic and carboxyl groups are the dominant groups that are pH-dependent and show a stronger affinity towards the metals. Properties of natural organic matter and trace elements govern the binding kinetics, influencing cations' binding to functionalized groups at lower pH. The water treatment process mechanisms like adsorption, coagulation, membrane filtration, and ion exchange efficiencies are sturdily influenced by the presence of NOM with cations and by the natural organic matter alone. The complexation among the natural organic matter and coagulants enhances the removal of NOM from the coagulation processes. The current review illustrates detailed interactions between natural organic matter and the potential impacts of cations on NOM in the water and wastewater treatment facilities.

The Role of Laccase from Zygomycetous Fungus Mortierella elasson in Humic Acids Degradation

Biochemical stability of soil humus is an important factor affecting soil quality. Fungi are among the most efficient decomposers of humic matter due to presence of oxidative enzymes, including phenoloxidase laccase. Production of laccase by zygomycetes, a group of cellulolytic fungi widespread in soil, is poorly studied. The potential role of laccase from zygomycetes in humus turnover is unknown. Here, we show for the first time that laccase of zygomycetous fungus Mortierella elasson can effectively depolymerize humic acids in vitro. The fungus produced laccase extracellularly in a liquid culture medium. Unlike in case of laccases in ligninolytic basidiomycetes, attempts to increase enzyme activity using inductors, changes in the source of nitrogen and carbon failed to lead to any increase in laccase production. Laccase was purified using ion exchange chromatography and gel filtration. The molecular weight of the laccase was 51.75 kDa. The laccase catalyzed the oxidation of ABTS and K4[Fe(CN)6], phenolic compounds, but not tyrosine. The laccase activity was inhibited by NaN3 and NaF. The pH optimum of the laccase activity was 3.0 for ABTS and 5.0 for 2,6-dimethoxy phenol. The enzyme had moderate thermal stability and was rapidly inactivated at 70 °C. Purified laccase depolymerized humic acids from retisol, compost and peat more effectively than culture liquid containing laccase. The results of the study extend our knowledge of the role of laccases from different producers in the transformation of natural organic matter.

Characterization of the transformation of natural organic matter and disinfection byproducts after chlorination, ultraviolet irradiation and ultraviolet irradiation/chlorination treatment

The ultraviolet (UV)/chlorination process provides an emerging strategy to disinfect and remove trace organic contaminants in drinking water and wastewater treatment plants. Different strategies for UV irradiation, chlorination, and UV/chlorination affect the characteristics of natural organic matter (NOM) and the formation of disinfection by-products (DBPs). The underlying effect remains poorly understood. In this work, Orbitrap-high resolution mass spectrometry, with a high accuracy for mass identification and a low cost, was used to investigate NOM transformation and DBP formation with UV irradiation, chlorination, and UV/chlorination. Of the untreated and treated (UV irradiation, chlorination, and UV/chlorination) NOM sample, most identified compounds were phenolic and highly unsaturated aliphatic compounds. Compared with UV irradiation, chlorination, and UV/chlorination had a stronger effect on the transformation of NOM molecular composition and resulted in more oxidized groups. A comparison of UV/chlorination with chlorination showed that UV/chlorination formed less nitrogen-containing Cl-containing DBPs, and more oxidized and saturated Cl-containing DBPs. After chlorination and UV/chlorination, more than 60% of the identified DBPs could track their precursors on the basis of electrophilic substitution and addition reactions. The UV/chlorination precursors were more saturated than for chlorination. This systematic investigation is expected to guide the future advanced development of water treatment strategies and provide a method to auto-analysis of mass spectra data and visualize the DBP character.

Molecular characterization of transformation and halogenation of natural organic matter during the UV/chlorine AOP using FT-ICR mass spectrometry

UV/chlorine process, as an emerging advanced oxidation process (AOP), was effective for removing micro-pollutants via various reactive radicals, but it also led to the changes of natural organic matter (NOM) and formation of disinfection byproducts (DBPs). By using negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), the transformation of Suwannee River NOM (SRNOM) and the formation of chlorinated DBPs (Cl-DBPs) in the UV/chlorine AOP and subsequent post-chlorination were tracked and compared with dark chlorination. In comparison to dark chlorination, the involvement of ClO•, Cl•, and HO• in the UV/chlorine AOP promoted the transformation of NOM by removing the compounds owning higher aromaticity (AImod) value and DBE (double-bond equivalence)/C ratio and causing the decrease in the proportion of aromatic compounds. Meanwhile, more compounds which contained only C, H, O, N atoms (CHON) were observed after the UV/chlorine AOP compared with dark chlorination via photolysis of organic chloramines or radical reactions. A total of 833 compounds contained C, H, O, Cl atoms (CHOCl) were observed after the UV/chlorine AOP, higher than 789 CHOCl compounds in dark chlorination, and one-chlorine-containing components were the dominant species. The different products from chlorine substitution reactions (SR) and addition reactions (AR) suggested that SR often occurred in the precursors owning higher H/C ratio and AR often occurred in the precursors owning higher aromaticity. Post-chlorination further caused the cleavages of NOM structures into small molecular weight compounds, removed CHON compounds and enhanced the formation of Cl-DBPs. The results provide information about NOM transformation and Cl-DBPs formation at molecular levels in the UV/chlorine AOP.

Monitoring the characteristics and removal of natural organic matter fractions in selected South African water treatment plants

Abstract This study used spectroscopic methods to investigate the fate and dynamics of natural organic matter (NOM) as it traverses the treatment train at three water treatment plants (WTPs) in South Africa. The character, quantity, and removability of NOM at specific treatment stages was investigated by measuring changes in dissolved organic carbon (DOC) concentration, specific ultra-violet absorbance, UV absorbance, various spectroscopic indices, and maximum fluorescence intensity levels. A novel method of identifying and quantifying fluorescent fractions by combining synchronous fluorescence spectroscopy (SFS) and Gaussian peak fitting is presented. The dynamics of NOM removal were modeled using 2D-SFS correlation spectroscopy. Humic and fulvic substances dominated coastal plants and were the most amenable for removal by coagulation as shown by Hermanus WTP (plant H), which had a 42% DOC removal at the coagulation stage. Tyrosine-like, tryptophan-like and microbial humic-like substances were degraded or transformed concurrently at plant Flag Bushiole (FB) whereas, at plant H, fulvic-like matter was transformed first followed by tyrosine-like then humic-like matter. Through 2D-SFS, this study revealed that NOM transformation was varied as a consequence of NOM character, the type and dosage of treatment chemicals used, and WTPs operational parameters.

Investigating the fate of natural organic matter at a drinking water treatment plant in South Africa using optical spectroscopy and chemometric analysis

The removal dynamics of biodegradable dissolved organic carbon (BDOC) and natural organic matter (NOM) polarity fractions at a water treatment plant (WTP) in South Africa was studied using UV-Vis absorbance, fluorescence excitation-emission matrix, and two-dimensional synchronous fluorescence spectroscopy (SFS). This study gave insights into the transformation of NOM due to treatment processes. The objectives of the study were: (i) to use chemometric analysis and two-dimensional SFS correlations to investigate the evolution of NOM arising from treatment processes, and (ii) to access the chemical profile dynamics of polarity and BDOC fractions throughout the treatment train. The UV254 absorbance, which indicates aromaticity, reduced by 45% along the WTP. Gaussian fitting of UV-Vis data showed a decreasing trend in intensity and number of bands along the treatment process. The removal efficiency of NOM components followed the order: humic-like (HL) &gt; tyrosine-like (TYL) &gt; fulvic-like (FL) &gt; tryptophan-like (TPL) &gt; microbial-like (MBL). At the source, the relative distribution of the hydrophobic (HPO), hydrophilic (HPI), and transphilic (TPI) fractions was 45%, 31%, and 24%, respectively. The HPI was recalcitrant to treatment, and the TYL component of the HPI fraction was conjectured to be a disinfection byproduct limiting reagent. The HL and FL components of the BDOC fraction were the major substrates for bacterial growth. According to two-dimensional-SFS correlation, TYL, TPL, and MBL varied concurrently across the treatment stages. Used for the first time in South Africa, the robustness of a multi-dimensional approach of optical methods coupled with chemometric tools for the assessment of the fate of NOM along the treatment processes was revealed by this study.

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).

Comparative Study of Ozone Alone and Catalytic Ozonation for Transformation of Natural Organic Matter in River Water

Ozone alone and catalytic ozonation of natural organic matter had been carried out in semibatch model reactor. The experimental results demonstrated that ozonation alone and catalytic ozonation are equivalent with minimization of natural organic matter(NOM), with the removal rate of TOC, UV254 about 7 % and 50 % respectively. But it is a promising method for changing the molecular weight and specially for enhancement of biodegradation. The AOC in river water was 233 ug L-1, which increase up to 325 ug L-1, 677 ug L-1, 633 ug L-1 in ozonation alone, catalytic ozonation (H2O2) and catalytic ozonation (ZnO) after 30 minutes reaction respectively. Through the research, it can be conclued that catalytic ozonation-BAC may be an promising way for water treatment.

Spatial and seasonal patterns of fluorescent organic matter in Lake Kinneret (Sea of Galilee) and its catchment basin

Lake Kinneret (Sea of Galilee) is one of the major water resources in Israel. The origin and characteristics of natural organic matter (NOM) in the lake and its tributary rivers were studied using fluorescence excitation emission matrices (EEM) and parallel factor analysis. Two humic-like and one proteinous components were sufficient to describe EEM variability among 167 water samples collected between 2/2005 and 9/2006. The two humic-like components showed different relations in lake and riverine samples. Their vertical distribution in the lake was affected by seasonal stratification and distance from water surface, presumably reflecting the release of humic-like matter from sediments, its production via NOM transformation in the bottom layers, and its photodegradation in the upper layers. Vertical distribution of the proteinous component, indicating biological activity at upper water layers, did not correlate with that of the humic-like components. Dissolved organic carbon concentrations did not show any vertical stratification, emphasizing the power of EEM to explore NOM dynamics.

Efficiency of the activated carbon filtration in the natural organic matter removal

The removal and transformation of natural organic matter were monitored in the different stages of the drinking water treatment train. Several methods to measure the quantity and quality of organic matter were used. The full-scale treatment sequence consisted of coagulation, flocculation, clarification by flotation, disinfection with chlorine dioxide, activated carbon filtration and post-chlorination. High-performance size-exclusion chromatography separation was used to determine the changes in the humic substances content during the purification process; in addition, a UV absorbance at wavelength 254 nm and total organic carbon amount were measured. A special aim was to study the performance and the capacity of the activated carbon filtration in the natural organic matter removal. Four of the activated carbon filters were monitored over the period of 1 year. Depending on the regeneration of the activated carbon filters, filtration was effective to a degree but did not significantly remove the smallest molar mass organic matter fraction. Activated carbon filtration was most effective in the removal of intermediate molar mass compounds (range 1000–4000 g/mol). Regeneration of the carbon improved the removal capacity considerably, but efficiency was returned to a normal level after few months.

Modeling the Kinetics of the Reaction of Ozone with Natural Organic Matter in Huron River Water

A mamematical model that describes the transformation of natural organic matter (NOM) in Huron River water was developed. The model was expressed in terms of the concentration of humic and nonhumic fractions of NOM. The kinetic parameters, including stoichiometric coefficients and activation energies were determined. The model accurately described the transformation of humic and nonhumic fractions during ozonation over a wide range of ozone doses, temperatures, and hydraulic retention times. The relative difference between experimental and calculated data did not exceed 10 percent.

The Performance and Microbiology of Ozone‐Enhanced Biological Filtration

Pilot‐scale studies were conducted to determine the effects of preozonation and water column biofilm support media on slow sand filtration. The performance of the enhanced slow sand filters was compared with that of the full‐scale treatment facility at Andover, Mass., which uses preozonation and granular activated carbon to enhance its conventional processes. Preozonation and biofilm support were observed to have a positive influence on filter performance, transformation of natural organic matter, microbiology, and removal of biodegradable dissolved organic carbon (BDOC). The pilot filter with the media of a larger effective size, an ozone dose of 2 mg per mg of nonpurgeable dissolved organic carbon (NPDOC), and biofilm support produced removals of turbidity, NPDOC, UV absorbance, and trihalomethane formation potential comparable to the full‐scale facility. And the enhanced pilot filter produced a lower finished‐water BDOC value than the full‐scale plant. Thus, enhanced slow sand filters hold promise for utilities that must comply with the Surface Water Treatment Rule and future disinfection by‐product rules.

Transformation of NOM by Ozone and its Effect on Iron and Aluminum Solubility

Ozonation may alter the functional group composition, molecular weight (MW), and behavior of natural organic matter (NOM) in reactions of significance for drinking water treatment. In this work, the transformation of NOM by ozone was monitored by acid‐base titrations, ion chromatography, and gel‐permeation chromatography (GPC). The results led to an improved understanding of how ozonation affects NOM and how ozonated NOM affects the solubility of freshly precipitated iron and aluminum hydroxides. Organic acidity increased substantially during ozonation, and most of the newly produced organic acid groups were ionized at pH 4.0. Of 27 simple organic acids assayed in ozonated NOM, oxalic acid was dominant. The concentration of oxalate produced upon ozonation increased with ozone dose, solution pH, and Fe(II) concentration. Ozonation of NOM destroyed compounds of high and low apparent MW as determined by GPC and increased the concentration of compounds with intermediate apparent MW. Within the group of compounds formed with intermediate apparent MW, however, the dominant identifiable compounds were low‐MW organic acids such as oxalic and formic acids. Based on this and other observations, changes in the chromatograms of NOM as a result of ozonation appear to reflect changes in functional group composition and polarity of the molecules more—and true MW changes less—than previously recognized. At relatively high ozone doses and slightly acidic pH values, oxalic acid produced upon ozonation of NOM can complex and solubilize significant concentrations of aluminum. The concentration of soluble metal that formed in the presence of ozonated NOM can be predicted reasonably well by considering oxalate as the only metal‐complexing ligand present in such systems.