Absence Of Dissolved Organic Matter Research Articles

Effect of dissolved organic matter on bacterial regrowth and response after ultraviolet disinfection

The effect of dissolved organic matter (DOM) on bacterial regrowth in water after disinfection using ultraviolet (UV) light emitting diodes (UVLEDs) is still unclear. Herein, the regrowth and responses of Vibrio parahaemolyticus and Bacillus cereus were investigated after being exposed to UVLEDs at combined wavelengths (265 and 280 nm) in a phosphate-buffered saline consisting of Suwannee River natural organic matter (SRNOM) and Suwannee River fulvic acid (SRFA). Low-molecular-weight (MW) organic compounds, which may form into intermediary photoproducts, and indicate bacterial repair metabolism, were characterized through non-target screening using orbitrap mass spectrometry. This study demonstrates the ability of the UVLEDs-inactivated cells to regrow. After UV exposure, a considerable upregulation of RecA was observed in two strains. With increasing the incubation time, the expression levels of RecA in V. parahaemolyticus increased, which may be attributed to the dark repair mechanism. Coexisting anionic DOM affects both the disinfection and bacterial regrowth processes. The time required for bacterial regrowth after UV exposure reflects the time needed for the individual cells to reactivate, and it differs in the presence or absence of DOM. In the presence of DOM, the cells were less damaged and required less time to grow. The UVLEDs exposure results in the occurrence of low-MW organic compounds, including carnitine or acryl-carnitine with N-acetylmuramic acid, which are associated with bacterial repair metabolism. Overall, the results of this study expand the understanding of the effects of water matrices on bacterial health risks. This can aid in the development of more effective strategies for water disinfection.

Dissolved organic matter promoted hydroxyl radical formation and phenanthrene attenuation during oxygenation of iron-pillared montmorillonites

The oxygenation of Fe(II)-bearing minerals for hydroxyl radicals (HO•) formation and contaminant attenuation receives increasing attentions. However, information on dissolved organic matter (DOM) with different types, concentrations, and molecular weights (MWs) in manipulating HO• formation and contaminant attenuation during mineral oxygenation remain unclear. In this study, four iron-pillared montmorillonites (IPMs) and two DOM samples [e.g., humic acids (HA) and fulvic acids (FA)] were prepared to explore the HO• formation and phenanthrene attenuation during the oxygenation of IPMs in the presence or absence of DOMs. Results showed that iron-pillared and high-temperature calcination procedures extended the interlayer domain of IPMs, which provided favorable conditions for a high HO• production from 1293 to 14537 μmol kg−1. The surface-absorbed/low crystalline Fe(Ⅱ) was the predominant Fe(Ⅱ) fractionations for HO• production, and presence of DOMs significantly enhanced the HO• production and phenanthrene attenuation. Moreover, regardless of the types and concentrations, the low MW (LMW, <1 kDa) fraction within DOM pool contributed highest to HO• production and phenanthrene attenuation, followed by the bulk and high MW (HMW-, 1 kDa∼0.45 μm) fractions, and FA exhibited more efficient effects in promoting HO• production and phenanthrene attenuation than HA. The fluorescent spectral analysis further revealed that phenolic-like fluorophores in LMW-fraction were the main substances responsible for the enhanced HO• production and phenanthrene attenuation. The results deepen our understandings toward the behaviors and fate of aquatic HO• and contaminants, and also provide technical guidance for the remediation of contaminated environments.

Soil organic matter facilitates the transport of microplastic by reducing surface hydrophobicity

Groundwater contamination by microplastic (MP) causes increasing concern about the critical factors that determine MP transport mechanisms in the vadose zone. Strong water repellency of native microplastic surfaces and respective attractive hydrophobic interactions with components of the soil matrix limits its mobility. However, adsorption of dissolved organic matter (DOM) onto microplastic surfaces can potentially make them more hydrophilic, enhancing their mobility. Consequently, the main objective of this study was to systematically determine the effects of DOM on both the surface properties and the mobility of polystyrene microplastic (PSP), and to use the extended DLVO theory (XDLVO) to predict PSP transport behavior with natural DOM for the first time. Breakthrough experiments were conducted in columns filled with quartz sand, through which PSP (1 µm) were percolated at either 0 or 5 mg/L dissolved organic carbon (DOC) derived from beech (Fagus sylvatica) litter at ionic strengths ranging from 0.5 to 2.5 mM CaCl2, since the cation background also affects wettability and mobility. Using sessile drop contact angle and zeta potential measurements, XDLVO interaction energy components including Lewis acid-base energies were approximated. Breakthrough curve analysis confirmed that DOM coming from natural sources strongly enhanced the mobility of PSP in the quartz sand matrix, in particular at higher ionic strength. At 2.5 mM CaCl2, the presence of DOM increased PSP breakthrough from 1 % to 60 %. Consequently, in the absence of DOM, laser microscope images showed much more pronounced formation of microplastic clusters on quartz grain surfaces than at co-percolation of PSP with DOM. This behavior could be clearly predicted with the XLDVO approach, which suggests at 0 mg/L DOC a deep primary energy minimum between individual PSP and between PSP and quartz surfaces. In contrast, repulsive hydrophilic interactions between the surfaces were predicted at 5 mg/L DOC. We conclude that even low concentrations of DOM, as usually found in subsoil, can significantly enhance the mobility of microplastic in soils via rendering the surfaces more hydrophilic. This implies potentially serious repercussions for the spread of this contaminant in the environment.

Investigation of cytotoxic cadmium in aquatic green algae by synchrotron radiation-based Fourier transform infrared spectroscopy: Role of dissolved organic matter

The heavy metal Cd can cause severe toxicity on aquatic algae, but there are few studies on the cytotoxicity of heavy metal on algae based on synchrotron radiation technology. In this study, synchrotron radiation-based Fourier transform infrared spectromicroscopy (SR-FTIR) was used to characterize in vivo the toxic effects of Cd on Cosmarium sp. cells, emphasizing the influence of dissolved organic matter (DOM) on Cd toxicity. Results showed that, in the absence of DOM, obvious growth inhibition, cell volume reduction, and photosynthesis disruption could be observed with increasing Cd concentrations (0–500 μg/L). Based on the SR-FTIR imaging and functional group quantification, it was shown that the biosynthesis of biomolecules such as proteins, lipids, and carbohydrates was inhibited in algal cells. However, the addition of DOM caused significant heterogeneities in biomacromolecule biosynthesis that an increased biosynthesis of carbohydrates and structural lipids but an inhibited biosynthesis of proteins and storage lipids were observed. Furthermore, the correlation analysis and principal component analysis showed a good correlation between v(C-OH)/Amide II and biochemical parameters, indicating that changes of carbohydrates could be used as the biomarker to indicate the cytotoxicity of heavy metals to algal cells. These findings provide insight into the mechanisms of heavy metal cytotoxicity to aquatic algae and systematic cytotoxicity assessment under various aquatic conditions.

Natural organic matter source, concentration, and pH influences the toxicity of zinc to a freshwater microalga

Zinc is a contaminant of concern in aquatic environments and is a known toxicant to many aquatic organisms. Dissolved organic matter (DOM) is a toxicity modifying factor for zinc and is an important water chemistry parameter. This study investigated the influence of DOM concentration, source, and water pH on the chronic toxicity of zinc to a freshwater microalga, Chlorella sp. The influence of DOM on zinc toxicity was dependent on both concentration and source. In the absence of DOM, the 72-h EC50 was 112 μg Zn.L−1. In the presence of a DOM high in fulvic-like components, zinc toxicity was either slightly decreased (<4-fold increase in EC10s across 15 mg C.L−1 range) or unchanged (minimal difference in EC50s). In the presence of a DOM high in humic-like (aromatic and high molecular weight) components, zinc toxicity was slightly decreased at the EC10 level and strongly increased at the EC50 level. The influence of pH on zinc toxicity was dependent on the source of DOM present in the water. In the presence of DOM high in humic-like components pH did not influence toxicity. In the presence of DOM high in fulvic-like components, pH had a significant effect on EC50 values. Labile zinc (measured by diffusive gradients in thin-films) followed linear relationships with dissolved zinc but could not explain the changes in observed toxicity, with similar DGT-labile zinc relationships shown for the two DOMs despite each DOM influencing toxicity differently. This indicates changes in toxicity may be unrelated to changes in zinc lability. The results suggest that increased toxicity of zinc in the presence of DOM may be due to direct uptake of Zn-DOM complexes. This study highlights the importance of considering DOM source and characteristics when incorporating DOM into water quality guidelines through bioavailability models.

Interactions of dissolved organic matter with short-range ordered aluminosilicates by adsorption and co-precipitation

Retention of dissolved organic matter (DOM) by short-range ordered aluminosilicates (SROAS) by adsorption and co-precipitation contributes to carbon accrual in soils and sediments. In this study, we investigated effects of SROAS composition on DOM adsorption, partitioning of carbon moieties by adsorption and co-precipitation, and the mineral structure of co-precipitates. We used four types of sorptive solutions, representing DOM collected in situ from topsoil and subsoil horizons of a Dystric Cambisol, and water-extracted DOM from beech and fir litter. We studied adsorption of soil DOM on three SROAS that structurally resemble proto-imogolites and Si-rich allophanes as a function of contact time (1–168 h) at initial pH 5. Co-precipitation of soil and litter-extracted DOM was quantified as a function of the molar Al:C ratio (0.3–1.4) and at two levels of Si concentration (molar Al:Si = 1 and 2). To resolve the impact of DOM on mineral structure, we first examined time-dependent structural evolution of SROAS within 1 to 72 h and subsequently investigated the effects of DOM interference in crystallization processes. Mineral structure of SROAS and co-precipitates was resolved by infrared, solid-state 27Al- and 29Si-NMR spectroscopy. Chemical composition of DOM prior to reaction with SROAS and in co-precipitates was analysed by solid-state 13C-NMR spectroscopy. Maximal C contents of adsorption complexes were 7.1 mg C g−1 for Al-rich and 20.4 mg C g−1 for Si-rich SROAS. We found selective adsorption of aromatic C and preferential exclusion of polysaccharide and alkyl C for both topsoil and subsoil DOM. Adsorption was larger for a Si-rich SROAS, since it exhibited a greater accessibility of aluminol groups. As a function of aromatic C content in initial DOM, 39.9 to 81% of C was retained by co-precipitation. Composition of co-precipitated organic matter was determined by C speciation in DOM supply, involving marked uptake of polysaccharides. In the absence of DOM, up to 50% of Si was present in imogolite-like configuration after 72 h, evidencing rapid development of short-range order. Complexation of Al by DOM during formation of SROAS caused partial exclusion of Si and slowed structural evolution, consequently enhancing abundance of ill-defied Si species in co-precipitates. Interactions of DOM with SROAS may cause selective accumulation of organic compounds and promote Si mobility in Andosols and Podzols.

Dissolved organic matter modulates the impact of herbicides on a freshwater alga: A laboratory study of a three-way interaction

In freshwater environments, microorganisms such as microalgae are influenced by the concentrations of dissolved chemicals but can modify the fate of these substances by biosorption, accumulation and even metabolization. In this laboratory study, we assessed the growth and physiology of non-axenic cultures of the chlorophyte Sphaerellopsis sp. exposed to environmental concentrations of diuron, irgarol and S-metolachlor (0.5, 0.5 and 5 μg·L−1, respectively) singly and in mixture, in the presence or absence of natural dissolved organic matter (DOM). The growth, photosynthetic efficiency and relative intracellular lipid content of Sphaerellopsis sp., as were measured after 14 days of exposure, as were the concentrations of bacteria in the cultures. DOM absorbance and fluorescence, and concentrations of the herbicides and their metabolites in the culture medium were also recorded. The growth of Sphaerellopsis sp. was very low in the absence of DOM but dramatically enhanced in treatments where DOM was added. As a result, the toxicity of the herbicides observed in treatments without DOM was overcome in those where DOM was added. The chemical characteristics of DOM were modified by the microalgae, and the fate of the herbicides was affected by the interaction between microorganisms (both bacteria and algae) and the DOM. Herbicide concentrations decreased over time, with a simultaneous increase in some of their metabolites, suggesting a biological degradation in the presence of DOM.

Degradation studies of UV filter hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]-benzoate (DHHB) in aqueous solution

High performance liquid chromatography coupled with ultra-violet, diode array detection (HPLC-UV-DAD), was used to study the degradation reactions of ultraviolet (UV) filter hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]-benzoate (DHHB). Degradation by-products were detected and identified by means of liquid chromatography coupled with diode array detection and mass spectrometry (LC-DAD-MS). Environmentally-relevant characteristics, such as water pH, chlorine levels, water temperature and dissolved organic matter (DOM) concentration, were modulated and studied in order to determine their influence on the degradation reactions.Results show that DHHB degrades quite rapidly in typical drinking water disinfection conditions, displaying a kinetic rate constant of kobs = 0.0060 ± 0.0002 s−1 and a half-life period of merely t1/2 = 116 ± 4 s. As far as the non-volatile disinfection by-products (DBPs) are concerned, only the mono and dichlorinated forms of DHHB were detected in the degradation reactions. Regarding influential variables on DHHB degradation, the presence or absence of DOM in solution did not alter the trends that were found (degradation of DHHB is more significant at lower pH values and higher levels of active chlorine in solution). Chlorinated DBPs have also been found to predominate under higher pH values and lower levels of chlorine, whereas they were found to be unstable and further degradable, quite likely into smaller and more volatile compounds, when in lower pH and higher chlorine concentrations. As for the photo-degradation studies, DHHB was found to be extremely photo-stable, with only about 15% degradation rate detected during artificial irradiation periods of 6 h.

Inhibitory Effect of Dissolved Organic Matter on the Transformation of Selected Anilines and Sulfonamide Antibiotics Induced by the Sulfate Radical.

Dissolved organic matter (DOM) has been shown to inhibit the oxidation of aromatic amines initiated by excited triplet states, an effect that was attributed to the reduction of oxidation intermediates back to their parent compounds. The present study focuses on the quantification of an analogous inhibitory effect of DOM on aqueous oxidations induced by the sulfate radical (SO4·-). Second-order rate constants for the SO4·--induced transformation of selected anilines and sulfonamide antibiotics were determined by competition kinetics in the presence and absence of DOM from three different isolates at pH 8. In the presence of 1 mgC L-1 of DOM, a significant reduction in the rate constant was observed for most of the compounds compared to DOM-free solutions, but for two electron-rich anilines, increases in the rate constant were measured. For 4-cyanoaniline and sulfamethoxazole, the DOM concentration dependence of the rate constant consisted of a sharp decrease up to ∼1.0 mgC L-1 of DOM followed by a region of slight changes or even increases for higher DOM concentrations (up to 5 mgC L-1). This behavior was attributed to the occurrence of the aforementioned inhibitory effect and a counteracting accelerated transformation of the contaminants due to reactions with secondary radical oxidants resulting from DOM oxidation by SO4·-. Both effects of inhibition and secondary oxidants should be considered when assessing the abatement of aromatic amines in SO4·--based advanced oxidation processes.

Influence of different redox conditions and dissolved organic matter on pesticide biodegradation in simulated groundwater systems

Insights into the influence of redox conditions, that is the availability of electron acceptors, and dissolved organic matter (DOM) on pesticide biodegradation in groundwater are key to understanding the environmental fate of pesticides in natural groundwater systems. Here, the influence of redox conditions and supplemental DOM addition on biodegradation of pesticides, 2,4-dichlorophenoxyacetic acid (2,4-D), 2,6-dichlorobenzamide (BAM), mecoprop-p (MCPP) and bentazone, was tested in microcosm and subsequent column experiments. Pesticide degradation, functional genes and changes in specific fractions and quantity of DOM were systematically quantified. In aerobic microcosm experiments, the highest 2,4-D degradation rate was obtained with the presence of more assimilable DOM. In column experiments, minimal pesticide degradation (≤33.77%) in any anaerobic redox conditions was observed in the absence of DOM. However, in the presence of DOM, 2,4-D biodegradation was considerably enhanced under nitrate-reducing conditions (from 23.5 ± 10.2% to 82.3 ± 11.6%) and in a column without external electron acceptor amendment (from −6.3 ± 12.6% to 31.1 ± 36.3%). Observed preferential depletion of the fulvic acid fraction of DOM provides indications for specific functional DOM properties. The qPCR results show an increase in microbial biomass and functional genes (tfdA) in liquid phase after DOM addition. The results of this work provide insights into the interplays among DOM, redox geochemistry, and pesticide biodegradation, and show the potential of a novel approach – DOM addition to groundwater systems – for in situ biostimulation technology to remove pesticides from groundwater systems.

Reciprocal influences of dissolved organic matter and nanosized zero-valent iron in aqueous media

We investigated concurrent effects between nano-sized zero-valent iron (NZVI) and dissolved organic matter (DOM). Specific UV absorbance of DOM revealed that aromatic/hydrophobic moieties of DOM were bounded to NZVI surfaces. The DOM fluorescence emission peak shifted toward lower wavelength after NZVI exposure, which indicated removal of aromatic DOM fractions. This blue shift of the emission peak also attributes to the reduction of electron acceptors through NZVI-DOM charge transfer complexes. High molecular weight (103–104 Da) DOM fractions, which are suspected to be both aromatic and hydrophobic, were removed. X-ray absorption spectroscopy (XAS) elucidated that Fe(0) content in the 30-d aged NZVI in the presence of DOM (61.6%) was substantially higher than that in the absence of DOM (25.0%). Corrosion and oxidation of NZVI were mitigated due to interruption of electron transfer by surface bounded DOM and stabilization of Fe(II) by Fe-DOM complexes. The XAS also revealed that the evolution of the iron (oxyhydr)oxide shell of NZVI was significantly altered by complexed aromatic DOM.

The influences of dissolved organic matter and surfactant on the desorption of Cu and Zn from road-deposited sediment

This study showcases the desorption behaviours of copper (Cu) and zinc (Zn) in road-deposited sediment (RDS). Batch tests were conducted to investigate the influences of rainwater, major wastewater constituents of dissolved organic matter (DOM) and surfactant on the metals leaching from RDS. Results show that the rainwater solutions considerably enhanced the total amounts of Cu (319 ± 46% of the total leaching amount by blank solutions) and Zn (617 ± 130%) released from RDS compared with blank solutions. DOM enhanced the leaching of Cu from RDS at a neutral pH. By contrast, DOM had an adverse effect on the mobilization of Zn. In the absence of DOM, a higher concentration of sodium dodecyl sulfonate (SDS) slightly increased the release of Cu from RDS than a lower concentration of SDS. However, the existence of SDS suppressed the release of Zn from RDS.

Transport of organic contaminants in subsoil horizons and effects of dissolved organic matter related to organic waste recycling practices.

Compost amendment on agricultural soil is a current practice to compensate the loss of organic matter. As a consequence, dissolved organic carbon concentration in soil leachates can be increased and potentially modify the transport of other solutes. This study aims to characterize the processes controlling the mobility of dissolved organic matter (DOM) in deep soil layers and their potential impacts on the leaching of organic contaminants (pesticides and pharmaceutical compounds) potentially present in cultivated soils receiving organic waste composts. We sampled undisturbed soil cores in the illuviated horizon (60-90 cm depth) of an Albeluvisol. Percolation experiments were made in presence and absence of DOM with two different pesticides, isoproturon and epoxiconazole, and two pharmaceutical compounds, ibuprofen and sulfamethoxazole. Two types of DOM were extracted from two different soil surface horizons: one sampled in a plot receiving a co-compost of green wastes and sewage sludge applied once every 2 years since 1998 and one sampled in an unamended plot. Results show that DOM behaved as a highly reactive solute, which was continuously generated within the soil columns during flow and increased after flow interruption. DOM significantly increased the mobility of bromide and all pollutants, but the effects differed according the hydrophobic and the ionic character of the molecules. However, no clear effects of the origin of DOM on the mobility of the different contaminants were observed.

Effects of varying estuarine conditions on the sorption of phenanthrene to sediment particles of Yangtze Estuary

The sorption of phenanthrene on the Yangtze Estuary sediment was studied under varying conditions of particle size, sediment organic contents, salinity, and dissolved organic matter (DOM) concentrations. Small sediment particles showed higher trapping capacity for phenanthrene due to the higher organic contents associated. The organic carbon-based partition coefficient of phenanthrene to the Yangtze Estuary sediment was obtained as 7120L/kg, lower than the values for other soils or sediments reported in previous studies. The magnitude and direction of the salt effect were complicated by the specific DOM studied. The sediment sorption capacity was greatly increased in saline water in the absence of DOM but decreased in the presence of DOM. Given the conditions in the Yangtze Estuary, the equilibrium sorption of phenanthrene would be decreased with increasing salinity. Overall, the nature and content of both sediment-bound and dissolved organic matter dominate the sorption of hydrophobic organic contaminants in the estuary.

Adsorption of dissolved organic matter (DOM) onto the synthetic iron pipe corrosion scales (goethite and magnetite): Effect of pH

This study was performed to investigate dissolved organic matter (DOM) adsorption equilibrium using synthetic iron pipe corrosion scales i.e. goethite and magnetite for different pH values ranging from 2.5 to 10.5. The synthesized goethite and magnetite was characterized by XRD, SEM and BET surface area. SEM micrographs for before and after DOM adsorption study revealed a significant change on the morphology of goethite and magnetite surface. Molecular weight distributions of DOM measured by HPSEC revealed that the higher molecular weight fractions adsorbed preferentially onto goethite and magnetite surface, and it was pronouncedly observed at lower pH. The DOM adsorption data illustrated to be fit well by the Langmuir adsorption isotherm indicating monolayer coverage. The standard Gibb’s free energy (ΔGads∘) changes of adsorption process stating the DOM adsorption onto goethite and magnetite surface was spontaneous under the experimental conditions. However, the maximal adsorption capacity for goethite and magnetite were revealed to be 4.75mg-C/g and 3.79mg-C/g respectively at pH 2.5. The DOM adsorption study was observed to be highly pH dependent. Consequently, zeta (ζ) potential measurements revealed that surface charge of goethite and magnetite was modified due to DOM adsorption onto their surfaces, and their pH for point zero charge (pHPZC) was shifted to lower pH compared to that of in absence of DOM. Nevertheless, it has been suggested that ligand exchange between carboxyl/hydroxyl functional groups of DOM and, goethite and magnetite surface was the leading interaction mechanism for DOM adsorption process. FTIR spectroscopy study was in agreement with the conclusion cited above.

Acute waterborne copper toxicity to the euryhaline copepod Acartia tonsa at different salinities: Influence of natural freshwater and marine dissolved organic matter

The influence of natural dissolved organic matter (DOM) on acute waterborne Cu toxicity was evaluated in the euryhaline copepod Acartia tonsa at 3 different water salinities. Three sources of freshwater DOM (extracted by reverse osmosis) and 2 sources of marine DOM (extracted using a solid-phase technique) were used. Artificial salt water was used to prepare the experimental media. Different combinations of Cu concentrations and DOM sources and concentrations were tested at salinities of 5, 15, and 30 ppt. Toxicity data (48-h median lethal concentration [LC50] values) were calculated based on dissolved Cu concentrations. In a broad view, data showed that increasing salinity was protective against the acute waterborne Cu toxicity. In general, Cu toxicity was also lower in the presence than in the absence of DOM. Toxicity (48-h LC50) values from all treatments at the same salinity showed a positive linear relationship with the dissolved organic carbon (DOC). Thus, the protective effect of DOM against the acute Cu toxicity seems to be dependent mainly on the DOM concentration. However, it seems also to be dependent to some extent on the source of DOM used. In summary, findings reported in the present study clearly indicate that both salinity and DOM (source and concentration) should be taken into account in the development of an estuarine version of the biotic ligand model.

Multiple Roles of Extracellular Polymeric Substances on Resistance of Biofilm and Detached Clusters

In this study, multiple roles of biofilm EPS were assessed with respect to the resistance of biofilm and detached biofilm clusters to chlorine disinfection. Strains from an opportunistic pathogen, Pseudomonas aeruginosa (wild type, EPS- and EPS+) with altered extracellular polymeric substances (EPS) secretion capabilities were tested. The impact of biofilm EPS quantity on disinfection was evaluated by monitoring biofilm viability, biofilm structure, removal of dissolved organic matter (DOM), and viability of detached biofilm simultaneously during chlorine disinfection. The obtained results suggested that the presence of EPS increased biofilm and detached biofilm resistance to chlorine in both presence and absence of DOM. The quantity of EPS had an effect on biofilm structure and the structural characteristics were closely related to both overall biofilm viability and the spatial distribution of viable cells within the biofilm. Additionally, the increased amount of EPS influenced selective removal of DOM with polar functional groups. However the DOM removal did not have a significant impact on the viability of biofilm cells during chlorine disinfection. Meanwhile, the viability of detached biofilm clusters, particularly the EPS overproducing strain, was significantly increased in the presence of DOM. The combined results suggested that biofilm EPS played multiple roles toward influencing the resistance of both biofilm and detached biofilm to disinfectant.

Influence of dissolved organic matter on particle-water interactions of Co, Cu and Cd under estuarine conditions

Influence of dissolved organic matter (DOM) on particle-water interactions of trace metals (Co, Cu, and Cd) between particulate (>0.2 μm) and dissolved (≤0.2 μm) phases has been investigated along a salinity gradient using samples from the estuarine area of northern Sagami Bay, Japan. Partitioning experiments were performed by mixing riverine suspended particles with the mixtures of different proportions of river and marine end-members and determining concentrations of Co, Cu and Cd in particulate and dissolved phases. Concentrations and distribution coefficients (Kds) between particulate and dissolved phases of Co and Cu were dependent on the presence of DOM. The Kds of Co and Cu in the mixtures in the presence of DOM were lower than those in mixtures that had been ultraviolet-irradiated (UV-irradiated) (absence of DOM), throughout the salinity gradient. In addition, speciation calculations estimated that a greater fraction of Co and Cu in the dissolved phase was present in organic form throughout the salinity gradient, while the seawater ion concentrations and ligand competition (e.g., competition from Ca and Mg and formation of stable and soluble chloro-, sulphato-, and carbonato complexes) had a small effect on the speciation of Co. These results indicate that DOM may play an important role in controlling the speciation and the particle-water interactions of Co and Cu in the estuarine waters. As for Cd, the effect of DOM on the interactions of this metal was less intense than for Co and Cu. Seawater ions appeared to act as an important variable for controlling the particle-water interactions of Cd in the estuarine waters.

Influence of growth phase on harvesting of Chlorella zofingiensis by dissolved air flotation

The effects of changes in cellular characteristics and dissolved organic matter (DOM) on dissolved air flotation (DAF) harvesting of Chlorella zofingiensis at the different growth phases were studied. Harvesting efficiency increased with Al3+ dosage and reached more than 90%, regardless of growth phases. In the absence of DOM, the ratio of Al3+ dosage to surface functional group concentration determined the harvesting efficiency. DOM in the culture medium competed with algal cell surface functional groups for Al3+, and more Al3+ was required for cultures with DOM than for DOM-free cultures to achieve the same harvesting efficiency. As the culture aged, the increase of Al3+ dosage due to increased DOM was less than the decrease of Al3+ dosage associated with reduced cell surface functional groups, resulting in overall reduced demand for Al3+. The interdependency of Al3+ dosage and harvesting efficiency on concentrations of cell surface functional groups and DOM was successfully modeled.

Removal of inorganic mercury and methylmercury from surface waters following coagulation of dissolved organic matter with metal-based salts

The presence of inorganic mercury (IHg) and methylmercury (MeHg) in surface waters is a health concern worldwide. This study assessed the removal potential use of metal-based coagulants as a means to remove both dissolved IHg and MeHg from natural waters and provides information regarding the importance of Hg associations with the dissolved organic matter (DOM) fraction and metal hydroxides. Previous research indicated coagulants were not effective at removing Hg from solution; however these studies used high concentrations of Hg and did not reflect naturally occurring concentrations of Hg. In this study, water collected from an agricultural drain in the Sacramento–San Joaquin Delta was filtered to isolate the dissolved organic matter (DOM) fraction. The DOM was then treated with a range of coagulant doses to determine the efficacy of removing all forms of Hg from solution. Three industrial-grade coagulants were tested: ferric chloride, ferric sulfate, and polyaluminum chloride. Coagulation removed up to 85% of DOM from solution. In the absence of DOM, all three coagulants released IHg into solution, however in the presence of DOM the coagulants removed up to 97% of IHg and 80% of MeHg. Results suggest that the removal of Hg is mediated by DOM-coagulant interactions. There was a preferential association of IHg with the more aromatic, higher molecular weight fraction of DOM but no such relationship was found for MeHg. This study offers new fundamental insights regarding large-scale removal of Hg at environmentally relevant regarding large-scale removal of Hg at environmentally relevant concentrations.