Influence Of Natural Organic Matter Research Articles

Oxidation of the Cyanobacterial Hepatotoxin Microcystin-LR by Chlorine Dioxide: Influence of Natural Organic Matter

Cyanobacteria (blue-green algae) are known producers of cytotoxic, hepatotoxic, and neurotoxic compounds with severe acute and chronic effects on vertebrates. Successful removal of these toxins in drinking water treatment is therefore of importance for public health. In the present work the oxidation of the cyanobacterial hepatotoxin microcystin-LR (MC-LR) by chlorine dioxide (ClO2) was studied at natural microcystin concentrations (10 microg L(-1)) and normal ClO2 dosages (1 mg L(-1)) in the absence and presence of natural organic matter (NOM). ClO2 was found to be rapidly consumed by fulvic and humic acids, leaving less residual ClO2 to oxidize MC-LR. Predicted decrease rates in MC-LR concentration correlated highly with experimental data both in pure water and in the presence of NOM. Rate constants determined at high ClO2 and MC-LR concentrations in pure water could be used to predict the oxidation of MC-LR at natural concentrations. Toxicity tests with a protein phosphatase inhibition assay on reaction solutions and high-performance liquid chromatography fractions revealed that PP1 enzyme inhibition emerged only from intact MC-LR, while the oxidation products, dihydroxy isomers of MC-LR, were nontoxic even at unnaturally high concentrations.

Soil remediation time to achieve clean-up goals II: Influence of natural organic matter and water contents

This work reports a relatively rapid procedure for the forecasting of the remediation time (RT) of sandy soils contaminated with cyclohexane using vapour extraction. The RT estimated through the mathematical fitting of experimental results was compared with that of real soils. The main objectives were: (i) to predict the RT of soils with natural organic matter (NOM) and water contents different from those used in experiments; and (ii) to analyse the time and efficiency of remediation, and the distribution of contaminants into the soil matrix after the remediation process, according to the soil contents of: (ii 1) NOM; and (ii 2) water. For sandy soils with negligible clay contents, artificially contaminated with cyclohexane before vapour extraction, it was concluded that: (i) if the NOM and water contents belonged to the range of the prepared soils, the RT of real soils could be predicted with relative differences not higher than 12%; (ii 1) the increase of NOM content from 0% to 7.5% increased the RT (1.8–13 h) and decreased the remediation efficiency (RE) (99–90%) and (ii 2) the increase of soil water content from 0% to 6% increased the RT (1.8–4.9 h) and decreased the RE (99–97%). NOM increases the monolayer capacity leading to a higher sorption into the solid phase. Increasing of soil water content reduces the mass transfer coefficient between phases. Concluding, NOM and water contents influence negatively the remediation process, turning it less efficient and more time consuming, and consequently more expensive.

The Influence of Natural Organic Matter Rigidity on the Sorption, Desorption, and Competitive Displacement Rates of 1,2-Dichlorobenzene

The influence of natural organic matter (NOM) rigidity on the sorption, desorption, and competitive displacement rates of 1,2-Dichlorobenzene (1,2-DCB) was evaluated using batch reactor experiments with two surface soils (Yolo and Forbes) and a shale (Ohio). Previous characterization suggests that the shale NOM is the most reduced and condensed, the Yolo soil is the most oxidized and amorphous, and Forbes soil has an intermediate NOM structure. The rate study for each sorbent was conducted under the same reactor parameters, and 1,2-DCB mass-transfer rates were determined using the distributed first-order mass-transfer rate model based on the gamma probability density function. To measure competitive displacement rates, 1,2,4-trichlorobenzene (1,2,4-TCB) was delivered as a competitor after 34 days pre-equilibration. Higher fractions of contaminant subject to instantaneous mass transfer and much faster rates of approach to apparent sorption equilibrium are found in Yolo soil when compared with Forbes soil and the shale. The size of the instantaneously desorbing fraction thus appears inversely related to the hard carbon fraction. In the NOM compartment where mass transfer is rate-limited, rate coefficient distributions are shifted toward lower rates for desorption and competitive displacement of 1,2-DCB in Ohio shale, followed by Forbes soil. Sorption and desorption rate distributions are almost the same for the shale, while desorption rates are a few times greater than sorption rates in Yolo and Forbes soils. Mass-transfer coefficients for competitive displacement are considerably slower than those for desorption in Forbes soil and the shale. However, the mass-transfer rates for the two processes seem to be similar in Yolo soil, which has a NOM matrix comprising a relatively larger soft organic carbon fraction. The concept of "solute induced softening" is discussed as a mechanistic rationale for the experimental observations.

Combined influence of natural organic matter (NOM) and colloidal particles on nanofiltration membrane fouling

The combined influence of natural organic matter (NOM) and colloidal particles on the fouling of thin-film composite nanofiltration (NF) membranes is systematically investigated. Combined fouling is compared to the individual fouling behaviors (i.e., colloid or NOM alone) with respect to fouling mechanisms and the effect of concentration factor (or recovery). Results demonstrate that (1) “cake-enhanced osmotic pressure” (CEOP) is a key fouling mechanism for individual colloidal fouling, (2) NOM–calcium complexation is the dominant factor governing individual NOM fouling, and (3) combined fouling is affected by both CEOP and NOM–calcium complexation. The extent of flux decline for combined fouling, however, is less than what inferred from additivity of the individual contributions of colloidal and NOM fouling to flux decline. This observation implies that the contributions of the fouling mechanisms appear to be relatively less significant for combined fouling compared to their separate influences on individual colloidal and NOM fouling. An increase in colloidal stability in presence of NOM and the competition between colloids and NOM for calcium are likely explanations for this behavior. It is further shown that NF membrane salt rejection increases noticeably in case of combined fouling compared to individual colloidal fouling due to the formation of an active rejecting layer by the accumulated NOM on the membrane surface. Results from combined fouling runs involving EDTA treatment confirm that both CEOP and NOM–calcium complexation take place simultaneously.

Influence of pH, ionic strength and humic acid on adsorption of Cd(II) and Pb(II) onto vermiculite

Adsorption of Cd(II) and Pb(II) onto a suspension of vermiculite was studied as a function of ionic medium (0.002 or 0.02 mol L −1 KNO 3) and pH (5.0, 6.0 and 7.0). In order to evaluate the influence of natural organic matter on the adsorption properties of vermiculite, the clay mineral was treated with a sedimentary humic acid under the above mentioned conditions of pH and ionic strength, followed by the addition of Cd(II) and Pb(II). Adsorption was studied by the batch approach using a continuous flow-anodic stripping voltammetry technique for determination of the equilibrium concentrations of the metal cations. With this technique, the determination of metal concentrations higher than 2.0 × 10 −8 mol L −1 was possible, a feature that allowed us to perform the adsorption studies using a range of initial concentrations between 2.0 × 10 −7 and 1.0 × 10 −5 mol L −1, which is at least one order of magnitude lower than usually reported in adsorption studies. Adsorption of Cd(II) was strongly pH dependent, with maximum removal occurring at pH 7.0 in ionic medium of 0.002 mol L −1 KNO 3. Adsorption of Pb(II) was much more intense than Cd(II), and less pH dependent, with the maximum removal occurring at pH 5 and ionic strength 0.002. Adsorption of Cd(II) was enhanced onto the humic acid modified vermiculite in medium of 0.020 mol L −1 KNO 3 in the three pH studied, but in 0.002 mol L −1 KNO 3, only at pH 5.0 the presence of humic acid enhanced the adsorption of Cd(II), demonstrating that at this pH the predominant adsorption mechanism is ion exchange. At pH 6.0 and 7.0 a combination of ion exchange and complexation seems to govern adsorption of Cd(II) onto the humic acid modified vermiculite. For Pb(II) a similar behavior was observed at pH 5.0 and 6.0, but at pH 7.0 in 0.002 mol L −1 KNO 3 the presence of humic acid decreased the adsorption as a consequence of the formation of stable complexes in solution, which desorbed the humic acid molecules previously adsorbed on the vermiculite surface.

The influences of solid-phase organic constituents on the partition of aliphatic and aromatic organic contaminants

The influence of natural organic matter (NOM) constituents on contaminant distribution coefficients was evaluated by determining the K oc values of aromatic and aliphatic organic compounds (solutes) with clays modified with both aromatic- and aliphatic-rich organic constituents. The studied compounds consisted of naphthalene, phenanthrene, n-pentane, and 2,3,4-trimethylmethane; the solid samples comprised two clays with little organic content, kaolinite and Ca-montmorillonite. Two aliphatic surfactants and three aromatic dyes, sorbed to the clays, served as reference NOM constituents. For solutes of comparable water solubilities, the organic-carbon normalized distribution coefficients ( K oc ) of the aliphatic solutes between sorbed aliphatic organic matter and aqueous solution slightly exceed those of the aromatic solutes. By contrast, the aromatic solutes exhibited higher K oc values than did the aliphatic compounds with sorbed aromatic-rich organic matter. The difference in K oc values could be attributed to either comparable solubility parameters or the difference in the chemical structure between nonionic organic solutes and specific components of the simulated NOM. The much higher K oc values observed for the aromatic solutes indicate that the NOM composition is a major factor determining the NOC environmental distribution.

Influence of natural organic matter on the morphology of corroding lead surfaces and behavior of lead-containing particles

Influence of natural organic matter (NOM) on the morphology of lead surfaces exposed to drinking water and on the properties of lead-containing colloidal particles was explored based on the data of scanning electron microscopy, sequential filtrations, measurements of particle size distributions and electrophoretic potential. It was demonstrated that NOM prevented the formation of cerussite and hindered the growth of hydrocerussite crystals. Measurements of zeta-potential showed that the surface activity was highest for unaltered NOM, while ozonation and chlorination decreased it. The concentrations of soluble lead and tin increased several fold in the presence of NOM, while large colloidal particles of lead and solder corrosion products tended to break down to form smaller fragments. It is suggested that these phenomena are important for understanding of lead release mechanisms in drinking water.

Influence of natural organic matter and ionic composition on the kinetics and structure of hematite colloid aggregation: implications to iron depletion in estuaries.

The stability and aggregation behavior of iron oxide colloids in natural waters play an important role in controlling the fate, transport, and bioavailability of trace metals. Time-resolved dynamic light scattering experiments were carried out in a study of the aggregation kinetics and aggregate structure of natural organic matter (NOM) coated hematite colloids and bare hematite colloids. The aggregation behavior was examined over a range of solution chemistries, by adjusting the concentration of the supporting electrolyte-NaCl, CaCl2, or simulated seawater. With the solution pH adjusted so that NOM-coated and bare hematite colloids were at the same zeta potential, we observed a significant difference in colloid stability which results from the stability imparted to the colloids by the adsorbed NOM macromolecules. This enhanced stability of NOM-coated hematite colloids was not observed with CaCl2. Aggregate form expressed as fractal dimension was determined for both NOM-coated and bare hematite aggregates in both NaCl and CaCl2. The fractal dimensions of aggregates formed in the diffusion-limited regime indicate slightly more loosely packed aggregates for bare hematite than theory predicts. For NOM-coated hematite, a small decrease in fractal dimension was observed when the solution composition changed from NaCl to CaCl2. For systems in the reaction-limited regime, the measured fractal dimensions agreed with those in the literature. Colloid aggregation was also studied in synthetic seawater, a mixed cation system to simulate estuarine mixing. Those results describe the important phenomena of iron oxide aggregation and sedimentation in estuaries. When compared to field data from the Mullica Estuary, U.S.A., it is shown that collision efficiency is a good predictor of the iron removal in this natural system.

Influence of Natural Organic Matter (NOM) on the Speciation of Aluminum during Water Treatment

Natural organic matter (NOM) is a term collectively used to describe the complex matrix of organic material present in natural waters. The impact of NOM on the speciation of aluminum at Buffalo Pound water treatment plant was evaluated in the present study using fulvic acid. The first stage of the study was to conduct aluminum (Al) speciation experiments (using background dissolved organic carbon levels present in the raw water) at the pilot scale water treatment plant located within the main plant changing the aluminum sulfate (alum) dose from 68 mg L-1 (yearly average dose of the main plant) to 34 mg L-1. The second stage of the study was to conduct jar tests at various alum/DOC ratios. Pilot scale speciation study showed that when the alum/DOC ratio was 5.3, most of the total aluminum in the filtered water was in the form of particulate aluminum. Such an increased particulate aluminum level did not increase the finished water turbidity. Soluble organic aluminum also increased compared to the level in raw water when the alum/DOC ratio was 5.3. Al speciation study conducted during jar testing showed that organically bound aluminum increased from 8 μg L-1 (raw water) to 15 μg L-1 in the finishedwater when the alum/DOC = 1.37. Jar test results also showed that an alum/DOC of at least 7.3 should be maintained in the main plant in order to meet the proposed operating guidelines of 100 μg L-1 of total aluminum by Health Canada given the conditions that finished water soluble aluminum levels may be in the range of 35–40 μg L-1.

Biodegradability of organic by-products after natural organic matter oxidation with ClO 2—case study

Apart from well-known chlorites and chlorates, chlorine dioxide also generates easily biodegradable carbonyl compounds and short chain carboxylic acids during water disinfection. The main goal of the presented study was to examine the influence of natural organic matter (NOM) oxidation with chlorine dioxide, on the quantity as well as the quality of formed biodegradable by-products. In the experiments conducted at the pilot plant the sand filtered water (MWI) and ozonated/biofiltrated water (BAF) were oxidised with ClO 2. The amount of BDOC formed as a result of the oxidation of both waters with ClO 2 was compared. The results showed considerable differences in formation of ClO 2 oxidation by-products between non-ozonated and ozonated/biofiltered waters. The disinfection of ozonated/biofiltrated water with ClO 2 generated comparable amounts of aldehydes and much higher amounts of carboxylic acids than ClO 2 oxidation of sand filtered water. These findings are essential for waterworks with ozonation/biofiltration units and ClO 2 disinfection implemented.

Effect of natural organic compounds on the removal of organic carbon in coagulation and flocculation processes

Natural organic matter (NOM) in water contains organic compounds that are both hydrophobic and hydrophilic with a wide range of molecular weights. It is composed of non-homogeneous organic compounds such as humic substances, amino acids, sugars, aliphatic and aromatic acids, and other chemical synthetic organic matters. NOM in water is a major concern not only because of its contribution to the formation of disinfection by-products (DBPs) and taste and odor, but also its influence on the demand for coagulants and disinfectants, the removal efficiency of water treatment processes, etc. This research aims at identifying the influence of NOM in coagulation and flocculation processes in order to optimize the coagulation and flocculation conditions. In this study, pretreated pond water was used as the source water. It was observed from the experimental results that:The optimum pH for coagulation to remove NOM is around 7.The optimum alum dose at this pH can vary from 125-1,225 mgl-1 when the TOC is increased from 4 to 25 mgl-1.The presence of secondary compounds such as Ca2+, Mg2+ divalent cations had no significant effect on the removal of organic matter.The presence of clay increased the organic removal by 15%.The organic compound with higher molecular weight has higher removal affinity in coagulation process.Floc size and settling velocity of floc and sludge production all increased with the increase in NOM concentration. From the results of Capillary Suction Time (CST) tests, the floc formed with lower TOC readily released the water to make the dewatering process easier.The organic removal efficiency was significantly different for natural water containing non-homogeneous organic compounds compared to the synthetic water containing humic acid only (homogeneous organic matter). For example, the NOM removal efficiency was 80% for the synthetic water containing humic acid with TOC of 7 mgl-1 at pH 7; but the NOM removal for the pretreated pond water was 60%.

Control of Pa/Th ratio by particulate chemical composition in the ocean

Controlled laboratory experiments were carried out using pure sorbents to examine the interactions of 234Th (or 233Pa) with particle surfaces and whether there is a fractionation between 234Th and 233Pa by particulate chemical composition. Our results show that the adsorption of 233Pa and 234Th on particle surfaces is highly selective and compound specific, resulting in a fractionation of 233Pa/234Th ratio, especially on SiO2 (Kd ratio, Kd‐233Pa/Kd‐234Th, = 10) and CaCO3 (Kd ratio, Kd‐233Pa/Kd‐234Th, = 0.01) surfaces. These new results agree well with previously published field observations that showed an increase of 231Pa/230Th ratio (or Kd of 231Pa) with increasing opal abundance and decreasing carbonate content in oceanic particles. In addition, they highlight the complications of using 231Pa/230Th ratio as a proxy and have implications for both oceanography and trace element geochemistry although more studies are needed to further examine the influence of natural organic matter on the fractionation of Th/Pa ratios.

Plumbosolvency Control in Soft Waters

AbstractExperience of plumbosolvency control in the soft waters of north‐west England is presented, and expectations for complying with the new lead standards are indicated. The influence of natural organic matter on the solubility of lead is highlighted ‐ in particular its importance in the setting of target pH values in phosphated waters. An analysis of a large quantity of regulatory lead‐compliance data confirms the benefit of the introduction of phosphate. At a distribution zone level, the impact and benefit of a change in plumbosolvency conditions on regulatory data are demonstrated using a non‐parametric statistical technique. To assist in the operational management of plumbosolvency conditions, a number of performance metrics have been developed; these quantify (in a simple way), the quantity, variability and delivery of phosphate, and pH. The expected benefit from plumbosolvency control has been assessed in several ways, indicating that reasonable compliance against 25 μg/l might be achievable, but against 10 μg/l this is more questionable.

Influence of natural organic matter on the adsorption of metal ions onto clay minerals.

The influence of natural organic matter (NOM) on the adsorption of Al, Fe, Zn, and Pb onto clay minerals was investigated. Adsorption experiments were carried out at pH = 5 and pH = 7 in the presence and absence of NOM. In general, the presence of NOM decreased the adsorption of metal ions onto the clay particles. Al and Fe were strongly influenced by NOM, whereas Zn and Pb adsorption was only slightly altered. The interaction of the metal ions with the minerals and the influence of NOM on this interaction was investigated by coupling SdFFF with an inductively coupled plasma mass spectrometer (ICPMS) or an inductively coupled plasma atomic emission spectrometer (ICPAES). Quantitative atomization of the clay particles in the ICP was confirmed by comparing elemental content determined by direct injection of the clay into the ICPMS with values from acid digestion. Particle sizes of the clays were found to be between 0.1 and 1 microm by sedimentation field-flow fractionation (SdFFF) with UV detection. Aggregation of particles due to metal adsorption was observed using SdFFF-ICPMS measurements. This aggregation was dependent on the specific metal ion and decreased in the presence of NOM and at higher pH value.

Arsenic removal by a charged ultrafiltration membrane — influences of membrane operating conditions and water quality on arsenic rejection

The influences of membrane operating conditions and water quality on the rejection of arsenic by a negatively charged ultrafiltration (UF) membrane were investigated through a series of bench-level experiments. In general, the trends in arsenic rejection measured by these experiments are qualitatively consistent with the Donnan theory. In particular, the presence of co-occurring divalent ions was shown to have a detrimental influence on anionic As(V) rejection. As(V) rejection by the UF membrane was also shown to be sensitive to membrane operating conditions through the phenomena of concentration polarization. The possible influence of natural organic matter (NOM) on As(V) rejection by charged membranes was also explored.

Nitrate and natural organic matter in aqueous solutions irradiated by simulated sunlight

By means of simulated sunlight, the influence of natural organic matter (NOM) on the photochemical degradation of halogenated pesticides in the absence and presence of nitrate as a precursor of the highly reactive OH radicals in aqueous solutions and freshwater was investigated. Solutions of dichlorprop or terbutylazine (a) in phosphate-buffered demineralized water containing nitrate and/or NOM and (b) in natural freshwaters were irradiated by a 1000-W Xe short-arc lamp. The collimated beam was filtered using a combination of optical filters (WG 320 and WG 295) to simulate the solar spectrum under summer midday conditions. In the absence of nitrate and NOM, the pesticides were degraded photolytically by simulated sunlight. The degradation rates depended on the absorption spectrum in the UVB range and the quantum yield of the degradation. The photochemical degradation of the pesticides was faster in the presence of nitrate due to the sunlight-induced formation of OH radicals. In the absence of nitrate, low concentrations of NOM of a brownwater lake accelerated the degradation due to the formation of reactive species by NOM. At higher concentrations of NOM, the inner filter effect of NOM lowered the degradation rates. In the presence of 50 mg l-1 nitrate, NOM decreased the degradation rate significantly. In case the natural water samples were used as a matrix for the experiments (nitrate concentrations between 2 mg l-1 and 15 mg l-1, DOC concentrations below 2.3 mg l-1), NOM acted mainly as a radiation filter and as a scavenger of OH radicals. As a consequence, in most freshwater systems, the accelerating effect of NOM by the formation of reactive species is of minor importance compared to the inner filter effect and to radical scavenging.

Characterization of NOM adsorption to clay minerals by size exclusion chromatography

Mineral-bound humic substances modify the surfaces of clay minerals, changing the nature and number of adsorption sites for contaminants. Due to their effect on the surface charge of colloidal particles they can also change the particles mobility and thus their transport behavior. In this paper the influence of natural organic matter on the zetapotential of kaolinite and montmorillonite is shown. Adsorption experiments with kaolinite and montmorillonite show that due to adsorption the humic substances are fractionated. The equilibrium pH value does not influence the fractionation due to adsorption. Large hydrophobic molecules showed the strongest affinity towards the clay surfaces. Substances with a small apparent molecular size and a high content of carboxylic functional groups made up the non-adsorbing fraction of the NOM. Ca 2+ had no measurable effect on the adsorption. The low influence of the adsorbed NOM on the zetapotential of the clay minerals suggests physical adsorption as the predominant adsorption mechanism.

Role of Natural Organic Matter in Accelerating Bacterial Biodegradation of Sodium Dodecyl Sulfate in Rivers

The influence of natural organic matter (NOM) on the adsorption of sodium dodecyl sulfate (SDS) and bacteria to riverine sediment surfaces and the effects of these interactions on the rates of SDS ...

Influence of natural organic matter on the corrosion of leaded brass in potable water

Natural organic matter (NOM) affects the rate of metal leaching from the surface of leaded brass and the morphology of lead-containing corrosion products. SEM data indicate that lead forms a separate phase on the surface of the alloy. In organic-free water, hexagonal thin plates of hydrocerussite Pb 3(OH) 2(CO 3) 2 accumulate on and near corroding lead islets. NOM inhibits the growth of the crystals of hydrocerussite and promotes the formation of an amorphous hydrated surface film. The galvanic coupling of the surface lead phase with the rest of the alloy accelerates its oxidation. The share of lead in the oxidized metal leached from or accumulated on the surface, substantially exceeds that in the bulk alloy both in organic free-water and in the presence of NOM. NOM increases both short- and long-term lead leaching. Its effects are most noticeable in the range of dissolved carbon concentrations 0–2 mg/l.

Drinking Water Distribution - the Effect of Natural Organic Matter (NOM) on the Corrosion of Iron and Copper

The objective was to study the influence of natural organic matter (NOM) on the corrosion and by-product release of iron and copper. The corrosion was studied using potentiodynamic sweeps, coupon tests and field measurements in different Swedish municipalities. For iron it was found that the corrosion rate decreases in the presence of NOM. The results are explained in terms of surface complexation and a good correlation is found between theoretical calculations and experimental results. In the case of copper it was found that NOM both increases the corrosion rate and the content of copper in the water after one night of stagnation. The results are compared with equilibrium calculations and a good correlation is achieved.