Degradation Of Natural Organic Matter Research Articles

A stochastic model for the synthesis and degradation of natural organic matter. Part III: Modeling Cu(II) complexation

An agent-based biogeochemical model has been developed which begins with biochemical precursor molecules and simulates the transformation and degradation of natural organic matter (NOM). This manuscript presents an empirical quantitative structure activity relationship (QSAR) which uses the numbers of ligand groups, charge density and heteroatom density of a molecule to estimate Cu-binding affinity ( K Cu ′ ) at pH 7.0 and ionic strength 0.10 for the molecules in this model. Calibration of this QSAR on a set of 41 model compounds gives a root mean square error of 0.88 log units and r 2 = 0.93. Two simulated NOM assemblages, one beginning with small molecules (tannins, terpenoids, flavonoids) and one with biopolymers (protein, lignin), give markedly different distributions of log K Cu ′ . However, calculations based on these log K Cu ′ distributions agree qualitatively with published experimental Cu(II) titration data from river and lake NOM samples.

Contribution of Metal Species to the Heterogeneous Photocatalytic Degradation of Natural Organic Matter

The role of organic matters which are high molecular weight macromolecules in natural water supplies and their subsequent removal by advanced oxidation technologies has gained importance because they posses a substantial capacity to complex dissolved metal species. The present study was conducted to evaluate the impact of aqueous Cr(VI) and Mn(II) species on the photocatalytic oxidation of humic acids as a major component of natural organic matter in aquatic systems. The photocatalytic decolorization rate of humic acid was followed by pseudo-first-order and Langmuir Hinshelwood kinetic models. The presence of aqueous Cr(VI) and Mn(II) species did not significantly alter the degradation efficiency (≤20%) in terms of first-order kinetic model. Although the impact of manganese species could be considered as insignificant, a substantial adsorption effect could be assessed as reflected by respective Langmuir-Hinshelwood kinetic model parameters.

Ozone-enhanced photocatalytic degradation of natural organic matter in water

Ozone-enhanced photocatalytic degradation of macromolecular natural organic matter (NOM) in drinking water source was investigated. The influences of ozone dosage, retention time and bicarbonate concentration on the NOM degradation rate were studied. The change of molecular weight distribution of NOM caused by ozone-enhanced photocatalysis was analysed, as well as the degradation rate of NOM with different molecular weight (MW). It was shown that ozone-enhanced photocatalysis was much better for NOM degradation than sole ozonation or photocatalysis. Increase of both ozone dosage and retention time could effectively increase the TOC removal rate, while biodegradability could be improved solely by an increase in ozone dosage. The existence of bicarbonate significantly reduced the photocatalytic degradation rate of NOM; however, its impact was effectively offset by the addition of ozone into the photocatalytic process. Macromolecular NOM was transformed into smaller molecules, and the larger NOM was mineralized by ozone-enhanced photocatalysis much faster than the smaller NOM.

Characteristics of Natural Organic Matter Degradation in Water by UV/H2O2 Treatment

This study evaluated the UV/H2O2 system for degradation of natural organic matter in water. The photolysis experiments were conducted in a 10-l batch reactor using a 450-watt high-pressure mercury vapor lamp as the light source. The addition of H2O2 in water greatly improved the rate of humic acid degradation by UV light and 90% of the humic acid was removed within 30 min of photolysis. Kinetic data showed that the first-order reaction could be used to describe the kinetics of both humic acid oxidation and H2O2 decomposition, and the optimum H2O2 dose was 0.01%∼0.05% for humic acid oxidation. It was also observed that the absorption of UVC (UV with wavelength between 200 and 280 nm) is responsible for the dissociation of H2O2 to generate the reactive hydroxyl radicals. Depending on the initial dosages, the H2O2 added to the system can be completely decomposed by UV within 50 to 90 minutes. Upon UV irradiation, the humic intermediates with smaller molecular sizes increase as a result of the degradation of larger humic substances. Photolysis of surface water also shows that the UV/H2O2 was effective in reducing trihalomethanes (THMs) formation in treating surface water with high contents of organic precursors. The distribution of THMs shifted from chlorine-THMs to bromine-THMs after UV/H2O2 treatments when bromide was present in water. However, higher H2O2 dosages would be necessary for the photolysis of surface water containing high concentrations of organic THM precursors. As observed from the Fourier transform infrared (FTIR) spectra, the functional groups of treated humic acids were destructed significantly, including −OH (from −COOH and −COH), aromatic −C=C, and −C=O conjugated with aromatic rings.

A Stochastic Model for the Synthesis and Degradation of Natural Organic Matter. Part I. Data Structures and Reaction Kinetics

Here we present a stochastic biogeochemical model for the formation, transformation and mineralization of natural organic matter (NOM). The model is agent-based, with each software agent representing a single molecule of defined composition. Molecular properties and reactivities are estimated from composition and environmental parameters. Environmental parameters including temperature, pH, light intensity, dissolved O2, moisture and enzyme activities are user controlled. Time is treated in discrete steps, and during each step potential reaction probabilities are evaluated for each molecule based on its structure and the environmental parameters. When reactions occur, the molecular composition is modified accordingly. The model uses small natural products and biopolymers for inputs, and the composition of the molecules produced is constrained only by the inputs and reaction stoichiometries, not by pre-defined structures. Example simulations using the program AlphaStep are presented, in which the breakdown of biopolymers and the condensation of small molecules both lead to molecular assemblages with elemental composition and average properties similar to those of aquatic NOM. This batch-reactor model can be expanded to include spatial information and environmental feedback.

The role of soluble Fe(III) in the cycling of iron and sulfur in coastal marine sediments

In marine sediments, Fe(III) is found predominantly as a solid. Recently, however, soluble species of Fe3+ complexed by natural organic ligands have been detected in coastal marine sediments with voltammetric microelectrodes. The role of soluble Fe3+ complexes in diagenesis is unknown. In anoxic conditions, soluble Fe3+ can effectively oxidize FeS2 and recycle iron and sulfur for use as terminal electron acceptors during natural organic matter (NOM) degradation. Alternatively, soluble Fe3+ complexes can catalyze the formation of FeS and FeS2 through the rapid chemical reduction of Fe3+ by dissolved sulfide. To better understand the role of soluble Fe3+ in the transformation of iron and sulfur in marine sediments, we incubated the first few centimeters of unvegetated salt marsh sediment in plug-flow reactors. Microbial iron reduction seemed to prevail in suboxic conditions, but sulfate reduction outcompeted microbial iron reduction in the presence of reactive organic metabolites. The dominance of sulfate reduction led to the complete removal of reactive iron oxides by precipitation of FeS. Experiments mimicking the enrichment of soluble Fe3+ complexes in reduced sediments show that soluble Fe3+ does not reoxidize FeS and pyrite; rather, it promotes pyrite precipitation by enhancing sulfate reduction via complex bacterial interactions. The rate of pyrite formation in the presence of soluble Fe3+ is much higher than previously reported in the literature, suggesting that soluble Fe3+ might promote alternative pathways for microbial degradation of NOM that ultimately results in the immobilization of Fe and S as reduced iron sulfide minerals.

The effects of combined ozonation and filtration on disinfection by-product formation

The effects of combined ozonation and membrane filtration on the removal of the natural organic matter (NOM) and the formation of disinfection by-products (DBPs) were investigated. Ozonation/filtration resulted in a reduction of up to 50% in the dissolved organic carbon (DOC) concentration. Furthermore, humic substances were converted to non-humic substances, with changes in the humic and non-humic substance concentrations of up to −50% and +20%, respectively. Ozonation/filtration resulted in the formation of partially oxidized compounds from NOM that were less reactive with chlorine, decreasing the concentration of simulated distribution system total trihalomethanes (SDS TTHMs) and simulated distribution system halo acetic acids (SDS HAAs) by up to 80% and 65%, respectively. Reducing the molecular weight cut-off (MWCO) of the membranes resulted in reductions in the concentrations of SDS TTHMs and SDS HAAs. Using a membrane with a 5 kD MWCO, the minimum gaseous ozone concentration required to bring about effective NOM degradation and meet regulatory requirements for chlorinated DBPs was 2.5 g/m 3.

Solar photocatalysis—a possible step in drinking water treatment

Possibility of the use of solar radiation for reduction of Natural Organic Matter (NOM) content in natural lake water, as a source for drinking water preparation, was the topic of this research. Solar radiation alone does not have enough energy for sufficient degradation of NOM, but in combination with heterogeneous photocatalyst-titanium dioxide (TiO 2), with or without other chemicals, the degradation potential could increase. In specific geographical conditions in Republic of Croatia, e.g. Adriatic islands or Dalmatia, solar radiation could be used for photocatalytic degradation of natural organic matter (NOM) in surface waters and therewith lighten the process of preparing them to the potable water. Specific quality of the geographical locality appears in fact that it is a very attractive tourist destination, especially in period June–September. In this period the drinking water demand is the biggest and, fortunately, the intensity of the solar radiation, too. So, there is a proportion between the drinking water demand and solar radiation available for the use in drinking water treatment. A number of tests with lake water exposed to solar radiation in non-concentrating reactors were performed and photodegradation of NOM for various combinations of doses and crystal forms of TiO 2 with H 2O 2 was studied. Irradiation intensity was estimated from global solar radiation measurements. The best performance for the NOM degradation had combination of 1 g/L TiO 2 both anatase and rutile+solar radiation+H 2O 2, but—economically—it was not the best combination. An estimation of the biodegradation potential of dissolved organic matter after the photocatalytic step is given, too.

河川水における溶存化学成分からのヒドロキシルラジカルの光化学的生成に関する研究

The hydroxyl radial, which is one of the most reactive free radicals in the environment, plays an important role in the photochemical degradation of natural organic matter and organic pollutants. The photochemical formation rates of hydroxyl radicals in 41 water samples collected from 6 rivers in Hiroshima Prefecture were determined and the sources of hydroxyl radicals were discussed. The hydroxyl radical photochemical formation rates in the Kurose and Seno rivers were much higher than those in the Ohta and Oze rivers. River water samples containing high nitrite concentrations were found to show high hydroxyl radical formation rates. In the samples which had the higher hydroxyl radical formation rates, nitrite was found to be the most important source of hydroxyl radicals. On the other hand, with decreasing photochemical formation rate of hydroxyl radicals, the percent contribution of unknown sources other than nitrate, nitrite and hydrogen peroxide increased.

Photocatalytic degradation of carbamazepine, clofibric acid and iomeprol with P25 and Hombikat UV100 in the presence of natural organic matter (NOM) and other organic water constituents

The photocatalytic degradation of natural organic matter (NOM) and organic substance mixtures under simulated solar UV light has been investigated with suspended TiO(2). It could be shown by size-exclusion chromatography that photocatalysis of NOM led to a reduction of the average hydrodynamic radii and presumably of the nominal molecular weight, too. The decrease of the UV/Vis absorption of NOM was faster than the NOM mineralization. This study also focuses on the different abilities of photocatalytic materials (P25 and Hombikat UV100) to decrease persistent substances influenced by the presence of NOM and mixtures of pharmaceuticals or diagnostic agents. In general, the presence of NOM and other organic substances retarded the photocatalysis of a specific persistent substance by the combination of radiation attenuation, competition for active sites and surface deactivation of the catalyst by adsorption. The results of this work prove that photocatalysis is a promising technology to reduce persistent substances like NOM, carbamazepine, clofibric acid, iomeprol and iopromide even if they are present in a complex matrix.

Vacuum ultraviolet irradiation for natural organic matter removal

Research Article| June 01 2004 Vacuum ultraviolet irradiation for natural organic matter removal James Thomson; James Thomson 1School of Civil and Chemical Engineering, RMIT University, GPO Box 2476V, Melbourne, Victoria 3001, Australia and Cooperative Research Centre for Water Quality and Treatment, Private Mail Bag 3, Salisbury, South Australia 5108, Australia Search for other works by this author on: This Site PubMed Google Scholar Felicity A. Roddick; Felicity A. Roddick 1School of Civil and Chemical Engineering, RMIT University, GPO Box 2476V, Melbourne, Victoria 3001, Australia and Cooperative Research Centre for Water Quality and Treatment, Private Mail Bag 3, Salisbury, South Australia 5108, Australia Tel: +61 3 9925 2080 Fax: +61 3 9925 3746; E-mail: felicity.roddick@rmit.edu.au Search for other works by this author on: This Site PubMed Google Scholar Mary Drikas Mary Drikas 2Australian Water Quality Centre and Cooperative Research Centre for Water Quality and Treatment, Private Mail Bag 3, Salisbury, South Australia 5108, Australia Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2004) 53 (4): 193–206. https://doi.org/10.2166/aqua.2004.0017 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Twitter LinkedIn Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation James Thomson, Felicity A. Roddick, Mary Drikas; Vacuum ultraviolet irradiation for natural organic matter removal. Journal of Water Supply: Research and Technology-Aqua 1 June 2004; 53 (4): 193–206. doi: https://doi.org/10.2166/aqua.2004.0017 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Low pressure mercury vapour lamps were used alone and in combination with hydrogen peroxide (H2O2) to investigate the removal of natural organic matter (NOM) from highly coloured surface water, high in total organic carbon (TOC). A potential benefit of vacuum ultraviolet (VUV) irradiation is additive-free degradation of NOM by hydroxyl radicals rather than concentration and subsequent disposal problems associated with many conventional techniques. For mineralization and chromophore removal the UV/VUV/H2O2 combination was most effective, followed by UV/VUV. Photooxidation alone was inappropriate because small (but much greater than normal UV disinfection doses) and intermediate doses increased chlorine demand, trihalomethane formation potential, nitrite, hydrogen peroxide and low molecular weight carbonyl compound concentrations. Subsequent biological treatment reduced the chlorine reactivity significantly, by removal of oxidized NOM intermediates. Low molecular weight carbonyl compound concentrations in the water increased significantly on irradiation, and differences in their speciation indicated that different reaction mechanisms were dominant in different treatments. Trihalomethane (THM) distribution shifted to more highly brominated compounds as the NOM concentration decreased with treatment. Results from this preliminary study indicate that NOM can be removed from water by VUV irradiation combined with biological treatment leading to improved drinking water quality. chlorine, hydrogen peroxide (H2O2), low molecular weight carbonyl compounds, natural organic matter (NOM), nitrite (NO−2), vacuum ultraviolet (VUV) irradiation This content is only available as a PDF. © IWA Publishing 2004 You do not currently have access to this content.

Photocatalytic degradation of natural organic matter: Kinetic considerations and light intensity dependence

The current study was conducted to investigate the photocatalytic degradation kinetics of humic acid at different light intensities using commercial TiO2 powders. The pseudo first order kinetic model and Langmuir‐Hinshelwood (L‐H) rate equation in modified forms were used to compare the photocatalytic activities of TiO2 materials as a function of light intensity. Under constant irradiation conditions, the pseudo first order reaction rates as well as L‐H rates were found to be decreasing in the following trend; Degussa P‐25, Millennium PC‐500 and Millennium PC‐100. The pseudo first order rate constants showed the same decreasing trend as the pseudo first order reaction rates while L‐H rate constants exhibited a light intensity related change in the ordering of the photocatalysts. At the lowest light intensity, L‐H rate constants decreased as follows: Millennium PC‐500 > Millennium PC‐100 > Degussa P‐25. However, increasing the light intensity changed the order to; Millennium PC‐100 > Millennium PC‐500 > Degussa P‐25 revealing the significance of the L‐H adsorption constant. Under constant irradiation conditions, ionic strength dependent changes in the structure of humic acid did not alter degradation efficiency trend of the photocatalyst specimens and they were ordered such as; Degussa P‐25 > Millennium PC‐500 > Hombikat UV‐100 > Millennium PC‐100 > Merck. The results presented in this research also confirmed the effectiveness of Degussa P‐25 as a photocatalyst for the degradation of humic acid.

Natural organic matter (NOM) in a limed lake and its tributaries

The chemistry of a limed lake and its main tributaries were studied for 3 years (1992–94) with an emphasis on natural organic matter (NOM). Increased transparency and decreased water colour indicated a general reduction of NOM in the lake. Increased A 254 nm /A 410 nm ratios in the epilimnion during summer and early autumn suggested degradation of higher molecular size organic matter into low molecular size NOM. Increase in ammonium and dissolved inorganic carbon concentrations in the lake was possibly due to the NOM degradation. Using budget calculations and the literature values, photodegradation and microbial activity were estimated to be the main mechanisms of the NOM removal. These mechanisms accounted for about 30–35% and 60–65% of the total loss of organic matter, respectively, in the summer and early autumn period. Low sedimentation rates indicate that co-precipitation of organic matter with calcium, aluminium and/or iron was of minor importance in these seasons.

Analysis of poly(vinyl chloride) and other polymers in sediments and suspended matter of a coastal lagoon by pyrolysis-gas chromatography-mass spectrometry

Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) was used for the analysis of synthetic polymers in core sediments and suspended particulate matter (SPM) of the coastal lagoon Pialassa Baiona (Adriatic Sea). Pyrograms exhibited a multitude of peaks deriving from the thermal degradation of natural organic matter (humic substances, planktonic material), artificial resins and synthetic rubbers. Upon pyrolysis, sediments generated high levels of styrene and benzene and a series of aromatic hydrocarbons (α-methylstyrene, indene, naphthalenes, biphenyl, diphenylpropane) indicative of the presence of vinyl polymers (e.g. poly(vinyl chloride), polystyrene), whereas markers for rubbers (butadiene dimer, styrene-butadiene) were identified in pyrograms of SPM. Concentrations of styrene polymers (expressed as polystyrene, PS) and poly(vinyl chloride) (PVC) were estimated in sediment cores by Py-GC-MS using the evolved benzene and styrene for quantitation, and values greater than 1 mg/g were observed in the most polluted layers. Plastic materials were isolated from sediments by Soxhlet-extraction with dichloromethane followed by precipitation in n-hexane and analysed by Py-GC-MS and spectroscopic techniques ( 1H- and 13C-NMR spectroscopy, FTIR). PVC made up the bulk of the isolated polymers which were found at concentrations up to 55 mg/g. PVC concentrations determined by both methods (direct pyrolysis and polymer extraction), showed maxima in subsurface strata and were strongly correlated with Hg concentrations. This finding suggests that the presence of resins is due to past industrial activity, even though the identification of styrene-plastic rubbers in SPM indicates that polymers are still redistributed and/or discharged into the lagoon.

Isotopic evidence for biological controls on migration of petroleum hydrocarbons

The isotopic compositions of potential metabolic byproducts of petroleum hydrocarbon biodegradation in soil gas and groundwater samples from a shallow plume of aviation gas (AVGAS) were analyzed to assess levels and pathways of intrinsic bioremediation occurring at the site. Gasoline range organic compounds (GROs) in soil gas samples from the original source area were low (<1000 ppm), but GRO levels under an adjacent, asphalt-covered parking lot exceeded 100,000 ppm. Soil gas CH 4 was >20% in the central part of the plume and correlated well with GRO concentrations. The 14C contents of the CH 4, associated soil gas CO 2 and dissolved inorganic carbon compounds (DIC) in the groundwater were all less than 0.1 times modern, indicating they were primarily formed from degradation of AVGAS and not other potential carbon sources such as degradation of natural organic matter or dissolution of carbonate shells. The δD and δ 13C values of the CH 4 indicate that it was produced via acetate fermentation. The δ 13C values of CO 2 and DIC in the central part of the plume were high, suggesting that a large fraction of the CO 2 in that area was also produced by acetate fermentation. At the down-gradient edges of the plume, CH 4 levels dropped to zero and the δ 13C values of CO 2 were much lower (−26‰), indicating that aerobic degradation of the AVGAS was dominant in this area. Beyond the down-gradient edges of the plume, the 14C contents of both groundwater DIC and soil gas CO 2 were significantly below modern levels, implying that most of the carbon there was derived from hydrocarbons and had migrated beyond the edge of the plume. These data show that methanogenic activity in the central part of the plume was slowly degrading the AVGAS, but aerobic activity at the edges of the plume was effectively limiting migration of the hydrocarbons.

Effect of natural organic matter loading on the atrazine adsorption capacity of an aging powdered activated carbon slurry

The effect of natural organic matter loading and calcium carbonate precipitate towards atrazine adsorption capacity of an aging powdered activated carbon slurry was investigated in an hybrid membrane process consisting of an immersed microfiltration membrane system in a completely stirred tank reactor containing powdered activated carbon. The reactor was fed with clarified Seine river water containing natural organic matter (NOM). Samples of the slurry were taken from the reactor and dried at low temperature to avoid the adsorbed NOM degradation. Thermal and CaCO 3 analyses were carried out to characterize each sample. The adsorption capacity of each sample was measured by the classical method of isotherms, a modelling method was applied to predict the adsorption capacity in natural water. Kinetic experiments were carried out and the results were also modelized to determine kinetic parameters ( k f and D s). The isotherms showed a significant decrease of the capacity during the 62 d of aging (from 3.4 to 0.4 mg g −1 for an equilibrium concentration of 0.1 μg L −1 in distilled-deionized water). A linear relationship was found between the Freundlich constant K and the age ( r 2>0.9). The kinetic experiments showed also the decrease of the D s value (from 1.16×10 −15 to 8.3×10 −17 m 2 s −1) while k f remained constant and appeared as a non-limiting parameter. Operating charts based on these results were drawn as tools for operators giving operating conditions (age of PAC slurry and fresh PAC dosage rate) to remove a given concentration of atrazine.