Effect of nickel and cadmium speciation on nitrification inhibition

Heavy metals have been postulated to cause significant nitrification inhibition. Using biomass from a well-controlled continuously operated lab-scale nitrifying bioreactor, the effect of nickel and cadmium on ammonium and nitrite oxidation was quantified. The extent of inhibition was calculated from the kinetics of ammonium oxidation and nitrite oxidation, inferred from maximum specific oxygen uptake rates (SOUR) measured in batch respirometric assays. Nickel and cadmium inhibited ammonium oxidation but not nitrite oxidation up to total analytical concentrations of approximately 1.0 mM. Metal fractions (total and free ion) were correlated with the extent of ammonium oxidation inhibition in the presence of various metal complexing agents (EDTA, NTA, citrate, SO4(2-)). Inhibition was not a function of the total analytical metal concentration but strongly correlated with free cation concentration, [Ni2+] or [Cd2+]. This relationship could be described by either an empirical noncompetitive inhibition model for [Ni2+] or a linear model in the case of [Cd2+]. Furthermore, the free Ni2+ or Cd2+ concentrations could be modulated by the addition of a strong chelating agent (e.g., EDTA), resulting in reduced deleterious effects. However, at elevated doses, EDTA itself impaired nitrification. In sum, predictions and mandatory strategies of nitrification inhibition by heavy metals should be based on free cation concentrations and not on total metal concentrations.     

Facilitating effects of metal cations on phenanthrone sorption in soils

Effects of metal cations (Na+, Ca2+, and Al3+) on phenanthrene sorption were investigated using two soils with contrasting organic carbon (OC) contents. The presence of the polyvalent cations (i.e., Ca2+ or Al3+) at a concentration of 0.01 mol/L significantly increased the capacity and nonlinearity of phenanthrene sorption to soils compared with the monovalent Na+. The effects were governed by the content of soil OC. Rubbery OC (i.e., soft, amorphous OC including dissolved organic carbon (DOC)) tended to become condensed on soil surfaces as evidenced by a decrease in the signals of the 1H NMR spectra of DOC and an increase in the glass transition temperature (Tg) of the soils when the polyvalent cations were present. Increasing Ca2+ concentration led initially to an effect similar to that of the polyvalent cations in the low cation concentration range, and the effect was gradually attenuated as Ca2+ concentration further increased. These findings lead us to propose that the modifications in the physical configuration and chemical characteristics of OC resulting from the presence of metal cations account for the increase in the capacity and nonlinearity of phenanthrene sorption to the soils. This study points to an important role of metal cations in the sorption and fate of phenanthrene in the soil environment.     

Influence of metal ion sorption on colloidal surface forces measured by atomic force microscopy

Atomic force microscopy (AFM) is employed to directly measure colloidal surface forces between a silica particle and a smooth glass plate in an aqueous solution with or without the presence of copper ions. Without the presence of copper ions, results show that the force between these two surfaces is repulsive and that its magnitude decreases with increasing ionic strength and decreasing pH. The surface forces are calculated based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for constant surface charge and are then compared with AFM force measurements. A good agreement between theory and experimental data is reported except at very small separation distances (<3 nm) between the silica particle and the glass plate. This behavior may be attributed to non-DLVO forces, such as the hydration effect that results from the bounded water molecules on the surface of the silica particle, or to surface roughness. When copper ions are present in acidic aqueous solutions, the magnitude of the force is found to be the same as that without the presence of copper ions, which indicates that no sorption of copper ions by the silica particle occurs under these conditions. Near neutral pH, sorption of copper ions causes charge reversal for the silica particle from negative to positive. Therefore, the force between the silica particle and the glass plate changes from repulsive to attractive. The transient zeta-potential of the silica particle during sorption of copper ions is determined by representing the experimental data with the DLVO theory. In alkaline solutions, where removal of copper ions is known to occur mainly by bulk precipitation, the measured force is similar to that without the presence of copper ions, which suggests that sorption does not occur under such conditions.     

Predicting divalent metal sorption to hydrous Al, Fe, and Mn oxides

Intraparticle diffusion in microporous amorphous oxides of aluminum, iron, and manganese affects contaminant mobility and bioavailability in soils and sediments. This sorption is a lengthy process, as such, predictive methods to assess thermodynamic and transport parameters would be useful. Based on enthalpies observed in recent work, adsorption of Zn, Cd, and Sr to amorphous oxides is a physical type of reaction where the metal ions retain their waters of hydration. Consequently the adsorbate-surface interactions are a function of electrostatic forces of attraction. Accordingly, knowing the hydrated radius and the hydration number of a metal cation, a correlation is used to predict enthalpy and hence affinity. Using the resulting enthalpy and the Polanyi relation, the activation energy was evaluated for Ni and Ca. This Polanyi relationship reveals that for a given metal the activation energies with respect to these oxides are comparable. Additionally, metals of the same periodic group appear to form similar sorption complexes with a particular oxide and therefore have an equivalent Polanyi constant, alpha. Assuming a sinusoidal function describes the surface potential along the oxide surface, the surface diffusivity was predicted from the site activation theory. In this work, the predicted sorption parameters proved to be equivalent to experimental ones given the associated errors.     

Impact of de-ashing humic Acid and humin on organic matter structural properties and sorption mechanisms of phenanthrene

Organic matter-mineral interactions greatly affect the fate of hydrophobic organic compounds (HOCs) in the environment. In the present study, the impact of organic matter-mineral interaction on sorption of phenanthrene (PHE) by the original and de-ashed humic acids (HAs) and humin (HM) was examined. After de-ashing treatment, the overall polarity of organic matter in HAs and HM consistently decreased. Differently, the surface polarity of HAs increased but that of HM decreased. No correlation between K(oc) values of PHE by all tested sorbents and their bulk polarity was observed due to inaccessibility of a portion of interior sorption domains. The inaccessibility of interior sorption domains in HAs and HM was partly due to the crystalline structure in organic matter as indicated by differential scanning calorimetric (DSC) and 13C NMR data and the interference from minerals. A good correlation between surface polarity of the original and de-ashed HAs and HMs and their K(oc) values for PHE indicated its importance in HOC sorption. Dissimilar changes in surface polarity of HAs and HM after de-ashing treatment can be ascribed to the distinct interactions between organic matter and minerals. The solid-state 13C NMR, XPS, and elemental composition data of all tested sorbents revealed that a larger fraction of O atoms in HAs were involved in organic matter-mineral interaction as compared to HM. Results of this work highlight the importance of soil organic matter (SOM)-mineral interactions, surface polarity, and microscaled domain arrangement of SOM in HOC sorption.     

Impact of reclaimed water on select organic matter properties of a receiving stream-fluorescence and perylene sorption behavior

Surface water samples obtained from the Bull Run tributary upstream and downstream of the Upper Occoquan Sewage Authority(UOSA) advanced wastewater reclamation facility (WRF) were characterized by fluorescence excitation-emission matrix (EEM) spectroscopy, and sorption coefficients (Kmoc) of macromolecular organic carbon isolates were quantified by fluorescence quenching. The EEM data revealed a signature fluorescence distribution in the downstream samples that was attributed to the presence of proteinlike material. The Kmoc values for upstream samples were consistently and significantly higher than those of corresponding downstream samples. There was a moderate correlation (R2 = 0.67) between log Kmoc and the molar extinction coefficient at 280 nm (E280) and a strong correlation (R2 = 0.96) between Kmoc and the proteinlike fluorescence region for macromolecular isolates with negligible quantum yields. This study demonstrates that organic matter downstream of the UOSA-WRF has unique fluorescence and perylene sorption characteristics compared to those of upstream organic matter during summer baseflow conditions. This implies that wastewater treatment facilities, including those advanced facilities designed to reclaim wastewater for indirect potable reuse, can influence the composition and behavior of organic matter in a receiving stream.     

Heavy metal sorption at the muscovite (001)-fulvic acid interface

The role of fulvic acid (FA) in modifying the adsorption mode and sorption capacity of divalent metal cations on the muscovite (001) surface was evaluated by measuring the uptake of Cu(2+), Zn(2+), and Pb(2+) from 0.01 m solutions at pH 3.7 with FA using in situ resonant anomalous X-ray reflectivity. The molecular-scale distributions of these cations combined with those previously observed for Hg(2+), Sr(2+), and Ba(2+) indicate metal uptake patterns controlled by cation-FA binding strength and cation hydration enthalpy. For weakly hydrated cations the presence of FA increased metal uptake by approximately 60-140%. Greater uptake corresponded with increasing cation-FA affinity (Ba(2+) ≈ Sr(2+) < Pb(2+) < Hg(2+)). This trend is associated with differences in the sorption mechanism: Ba(2+) and Sr(2+) sorbed in the outer portion of the FA film whereas Pb(2+) and Hg(2+) complexed with FA effectively throughout the film. The more strongly hydrated Cu(2+) and Zn(2+) adsorbed as two distinct outer-sphere complexes on the muscovite surface, with minimal change from their distribution without FA, indicating that their strong hydration impedes additional binding to the FA film despite their relatively strong affinity for FA.     

Characterization of sorption sites on Pilayella littoralis and metal binding assessment using 113Cd and 27Al nuclear magnetic resonance

Metal interactions with the cellular structures of the marine alga Pilayella littoralis have been investigated to better understand how biomaterials sorb dissolved metals. Algae metal binding capacity at pH 5.0 was 2000, 850, 430, and 560 micromol g(-1) of dried material for Al(III), Cu(II), Cd(II), and Co(II), respectively. Binding site characterization was assessed by 1H and 13C nuclear magnetic resonance spectroscopy. Also, Fourier Transform Infrared spectroscopy (FTIR) provided some information about the types of functional groups that appear to be present in the algal material. The results suggested the presence of carboxylate, ether, amino, and hydroxyl groups. Investigation of metal competition for the alga binding sites was performed using 27Al and 113Cd NMR spectroscopy, which proved to be a valuable technique for Al and Cd sorption assessment. Aluminum and Cu were efficiently sorbed by the alga sites, and the binding affinity order of these metals was Al(III) > Cu(II) > Cd(II) > Co(II).     

Extracellular polymeric substances from Bacillus subtilis associated with minerals modify the extent and rate of heavy metal sorption

Extracellular polymeric substances (EPS) are an important source of organic matter in soil. Once released by microorganisms, a portion may be sorbed to mineral surfaces, thereby altering the mineral?s ability to immobilize heavy metals. EPS from Bacillus subtilis were reacted with Ca-saturated bentonite and ferrihydrite in 0.01 M KCl at pH 5.0 to follow the preferential uptake of EPS-C, -N, and -P. The sorption kinetics of Pb(2+), Cu(2+), and Zn(2+) to the resulting EPS-mineral composites was studied in single and binary metal batch experiments ([metal](total) = 50 μM, pH 5.0). Bentonite sorbed much more EPS-C (18.5 mg g(-1)) than ferrihydrite (7.9 mg g(-1)). During sorption, EPS were chemically and size fractionated with bentonite favoring the uptake of low-molecular weight components and EPS-N, and ferrihydrite selectively retaining high-molecular weight and P-rich components. Surface area and pore size measurements by N(2) gas adsorption at 77 K indicated that EPS altered the structure of mineral-EPS associations by inducing partial disaggregation of bentonite and aggregation of ferrihydrite. Whereas mineral-bound EPS increased the extent and rate of Pb(2+), Cu(2+), and Zn(2+) sorption for bentonite, either no effect or a decrease in metal uptake was observed for ferrihydrite. The extent of sorption always followed the order Pb(2+) > Cu(2+) > Zn(2+), which also prevailed in binary Pb(2+)/Cu(2+) systems. In consequence, sorption of EPS to different minerals may have contrasting consequences for the immobilization of heavy metals in natural environments by inducing mineral-specific alterations of the pore size distribution and, thus, of available sorption sites.     

In vitro growth inhibition of mastitis causing bacteria by phenolics and metal chelators

Antimicrobial activities of three phenolic compounds and four metal chelators were tested at 0, 250, 500, and 1000 ppm in vitro against four major mastitis-causing bacteria, Streptococcus agalactiae, Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli. Overall, butylated hydroxyanisole and tert-butylhydroquinone showed the greatest antimicrobial activity. These phenolics were bactericidal at 250 to 500 ppm against all four bacteria tested. The butylated hydroxytoluene was bactericidal against the gram-positive bacteria but was ineffective against the coliforms. At 250 ppm, disodium ethylenediaminetetraacetic acid was bactericidal against the gram-positive bacteria but much less effective against the gram-negatives. However, diethylenetriaminepentaacetic acid was more growth inhibitory than ethylenediaminetetraacetic acid against the gram-negative bacteria and especially against Escherichia coli. All other compounds were generally much less effective or ineffective against all four microorganisms. Therefore, butylated hydroxyanisole, butylated hydroxytoluene, tert-butylhydroquinone, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid may have practical implications in the prevention or treatment of bovine mastitis.     

动态水分吸附法研究发酵饼干水分吸附特性

以发酵饼干为研究对象,采用动态水分吸附法研究发酵饼干在25℃的水分吸附等温线与水分吸附动力学特性,同时与饱和盐溶液法得到的水分吸附等温线进行对比,并基于常用的等温吸湿模型对实验数据进行拟合。结果表明:动态水分吸附仪能在更短的时间里采集更多的数据,高频率的实时数据采集能够更准确地获得食品的水分吸附动力学特性;其从水分活度适用范围和拟合精度方面来看,GAB模型拟合饼干的等温吸湿的效果最佳。与饱和盐溶液法结果相比,动态水分吸附法得到的饼干平衡含水率略低。      

Influence of sediment bioreduction and reoxidation on uranium sorption

The influence of sediment bioreduction and reoxidation on U(VI) sorption was studied using Fe(II) oxide-containing saprolite from the U.S. Department of Energy (DOE) Oak Ridge site. Bioreduced sediments were generated by anoxic incubation with a metal-reducing bacterium, Shewanella putrefaciens strain CN32, supplied with lactate as an electron donor. The reduced sediments were subsequently reoxidized by air contact. U(VI) sorption was studied in NaNO3-HCO3 electrolytes that were both closed and open to atmosphere and where pH, U(VI), and carbonate concentration were varied. M?ssbauer spectroscopy and chemical analyses showed that 50% of the Fe(III)-oxides were reduced to Fe(II) that was sorbed to the sediment during incubation with CN32. However, this reduction and subsequent reoxidation of the sorbed Fe(II) had negligible influence on the rate and extent of U sorption or the extractability of sorbed U by 0.2 mol/L NaHCO3. Various results indicated that U(VI) surface complexation was the primary process responsible for uranyl sorption by the bioreduced and reoxidized sediments. A two-site, nonelectrostatic surface complexation model best described U(VI) adsorption under variable pH, carbonate, and U(VI) conditions. A ferrihydrite-based diffuse double layer model provided a better estimation of U(VI) adsorption without parameter adjustment than did a goethite-based model, even though a majority of the Fe(III)-oxides in the sediments were goethite. Our results highlight the complexity of the coupled U-Fe redox system and show that sorbed Fe(II) is not a universal reductant for U(VI) as commonly assumed.     

Competitive sorption of pyrene on wood chars

Sorption isotherms of pyrene on original and heat-treated wood chars were examined to understand its sorption behavior. Pyrene in single-solute systems had nonlinear isotherms. Polanyi-based dual-domain model fit sorption data well, and the model results showed that the adsorption component dominated pyrene sorption by original char at all aqueous concentrations. In contrast, this adsorption component contributed a much lower fraction to the total sorption by the heat-treated char, and dominated only at low solute concentrations; with increasing concentration, partitioning became a predominant contributor to the total sorption. Competitive effect of four cosolutes, phenanthrene (Phen), benzo[a]anthracene (BaA), 2,2-methylene-bis (4-methyl-6-tert-butylphenol) (MMBP), and phenol on pyrene sorption by original and treated chars was examined to understand the underlying mechanism of competition. Hydrophobicity (adsorbability) and molecular size of competitors played an important role in competition with pyrene by both chars, suggesting the direct competition for sorption sites and pore blockage mechanism. Competitive sorption results indicated that the fate and transport of hydrophobic organic chemicals (e.g., pyrene) could be strongly affected in the presence of coexisting organic contaminants with high hydrophobicity and large molecularsize,thereby, enhancing the mobility and leachability of these chemicals.     

Moisture sorption isotherms and isosteric heat of sorption of coffee in different processing levels

The desorption isotherms and thermodynamic properties of coffee from different processing stages were obtained during the drying process of this product. The isotherms were determined by a static gravimetric method for various temperature and humidity conditions. Equilibrium moisture content (M_e) data were correlated by several mathematical models and an artificial neural network (ANN) model. The M_e for coffee fruits, pulped coffee and green coffee increased with an increase in the water activity (a_w) at any particular temperature. At a constant a_w, coffee fruits samples had higher M_e than the remaining coffee samples. Based on statistical parameters, the ANN model, modified Henderson and GAB models were adequate to describe the sorption characteristics of the samples. Isosteric heat of sorption was evaluated by means of the Clausius–Clapeyron equation. It decreased with increasing moisture content. The coffee fruits had higher isosteric heat of sorption than that pulped coffee and green coffee.     

Moisture sorption studies on onion powder

Moisture sorption studies were conducted on three samples of onion powders, i.e. freeze-dried, vacuum shelf-dried and through flow-dried onions. The data obtained for texture (flowability) and per cent moisture were used in determining critical moisture levels. The monolayer moisture contents, corresponding to Brunauer Emmett Teller (BET) theory were taken as the safe minimum moisture levels in onion powder. The moisture content values (moisture-free basis), which correspond to a monomolecular layer of adsorbed water computed by BET equation, were 2.09, 1.96 and 1.94%, for freeze-dried, vacuum shelf-dried and through flow-dried onion powders, respectively. This study on initial and critical moisture levels of dehydrated onion powders helps in the selection of the packaging materials for storage.     

Effect of temperature and salinity on phosphate sorption on marine sediments

Our previous studies on the phosphate sorption on sediments in Florida Bay at 25 °C in salinity 36 seawater revealed that the sorption capacity varies considerably within the bay but can be attributed to the content of sedimentary P and Fe. It is known that both temperature and salinity influence the sorption process and their natural variations are the greatest in estuaries. To provide useful sorption parameters for modeling phosphate cycle in Florida Bay, a systematic study was carried out to quantify the effects of salinity and temperature on phosphate sorption on sediments. For a given sample, the zero equilibrium phosphate concentration and the distribution coefficient were measured over a range of salinity (2-72) and temperature (15-35 °C) conditions. Such a suite of experiments with combinations of different temperature and salinity were performed for 14 selected stations that cover a range of sediment characteristics and geographic locations of the bay. Phosphate sorption was found to increase with increasing temperature or decreasing salinity and their effects depended upon sediment's exchangeable P content. This study provided the first estimate of the phosphate sorption parameters as a function of salinity and temperature in marine sediments. Incorporation of these parameters in water quality models will enable them to predict the effect of increasing freshwater input, as proposed by the Comprehensive Everglades Restoration Plan, on the seasonal cycle of phosphate in Florida Bay.     

Assessing the effect of humic acid redox state on organic pollutant sorption by combined electrochemical reduction and sorption experiments

Natural Organic Matter (NOM) is a major sorbent for organic pollutants in soils and sediments. While sorption under oxic conditions has been well investigated, possible changes in the sorption capacity of a given NOM induced by reduction have not yet been studied. Reduction of quinones to hydroquinones, the major redox active moieties in NOM, increases the number of H-donor moieties and thus may affect sorption. This work compares the sorption of four nonionic organic pollutants of different polarities (naphthalene, acetophenone, quinoline, and 2-naphthol), and of the organocation paraquat to unreduced and electrochemically reduced Leonardite Humic Acid (LHA). The redox states of reduced and unreduced LHA in all sorption experiments were stable, as demonstrated by a spectrophotometric 2,6-dichlorophenol indophenol reduction assay. The sorption isotherms of the nonionic pollutants were highly linear, while paraquat sorption was strongly concentration dependent. LHA reduction did not result in significant changes in the sorption of all tested compounds, not even of the cationic paraquat at pH 7, 9, and 11. This work provides the first evidence that changes in NOM redox state do not largely affect organic pollutant sorption, suggesting that current sorption models are applicable both to unreduced and to reduced soil and sediment NOM.